key: cord-0036802-ey4hidcr
authors: Thiriet, Marc
title: Growth Factors
date: 2011-10-13
journal: Control of Cell Fate in the Circulatory and Ventilatory Systems
DOI: 10.1007/978-1-4614-0329-6_3
sha: 8356b1887a05eb848d35a660cd3304901b51b1f4
doc_id: 36802
cord_uid: ey4hidcr

Any cell needs extracellular signals for its growth, proliferation, and survival, among other events. Chemical, mechanical, electrical, and other physical interactions of cells with the extracellular matrix yield functional and structural signals for normal cellular activity as well as formation and maintenance of three-dimensional tissues. Environmental chemical signals are transmitted by hormones (Sect. 1.4) and growth factors (Table 3.1), in addition to nervous cues (Sect. 1.1).

particular, cell growth is controlled by a balance between growth-promoting and -inhibiting factors. Growth factors promote not only cell division, maturation, and functioning, but also tissue growth and remodeling. Growth factors act on [307]:

(1) growth factor-producing cells (intra-and autocrine effects), 1 (2) neigh- Table 3 .2. Members of the CCN family (Source: [309] ; CEF: chicken embryo fibroblast; CTGF: connective tissue growth factor; CTGFL: connective tissue growth factor-like protein; CyR: cysteine-rich protein; ELM: expressed low in metastasis; FISP: fibroblast-inducible secreted protein; HCS: hypertrophic chondrocyte-specific gene product; HICP: heparin-inducible CCN-like protein; IGFBP: insulin-like growth factor-binding protein; IGFBPRP: IGFBP-related protein; NOv: nephroblastoma overexpressed protein: WISP: Wnt-inducible signaling pathway protein). CCN placentation, embryo-and fetogenesis, as well as wound healing and fibrosis. They bind to and activate integrins. At least in fibroblasts or endothelial cells, CCN family members CCN1 to CCN3 activate focal adhesion kinase and mitogen-activated protein kinase [308] . Both estrogen-inducible CCN1 and CCN2 regulate endothelial cell proliferation and angiogenesis [308] . The CTGF transcript is detected in fibroblasts, epi-and endothelial cells, vascular smooth muscle cells, and chondrocytes. Transforming growth factorβ, bone morphogenic protein-2, platelet-derived (PDGF), epidermal (EGF), and fibroblast (FGF) growth factor stimulate CTGF synthesis [310] . In addition, CTGF interacts synergistically with EGF, PDGF, IGF1, and FGF2.

Connective tissue growth factor promotes fibroblast proliferation, adhesion, and migration, as well as extracellular matrix formation. It intervenes in extracellular matrix remodeling during embryo-and fetogenesis, wound healing, etc. It is involved in diverse auto-and paracrine actions in several cell types, such as vascular endothelial and smooth muscle cells, as well as epithelial and neuronal cells and cells of supportive skeletal tissues [311] . In some circumstances, CTGF has antimitotic and apoptotic effects.

Connective tissue growth factor not only regulates cell proliferation and apoptosis, as well as angiogenesis and tissue fibrosis, but also tumor growth and metastasis. Sphingosine 1-phosphate isoform S1P2 (Sect. 3.17), but not S1P1, upregulates CTGF in a concentration-and time-dependent manner via small GTPase RhoA and kinases RoCK and Jun N-terminal kinase [312] .

Connective tissue growth factor binds to transforming growth factor-β. It is able to suppress transcription of related SMAD7 factor (Sect. 3.8).

Epidermal growth factor (EGF) binds to the HER family of receptors (Vol. . Receptor Kinases) of responsive cells and primes phosphorylation of EGF receptor and other proteins. The kinase domain of EGF receptor is auto-inhibited at rest. Activation of EGFR needs formation of an asymmetrical dimer [313] . Epidermal growth factor promotes receptor dimerization and activates the intracellular Tyr kinase domain. Activated receptors phosphorylate each other on various interaction sites and liberate recruitment motifs for enzymes or adaptors. Epidermal growth factor fosters proliferation of cells, especially fibroblasts. Mutations of the Egfr gene can thus lead to cancer.

Epidermal growth factor generates an initial rapid (20-mn) wave of transcription of a small number of immediate-early genes (IEG), such as components of Activator protein-1, Fos and Jun, that encode transcription factors for signaling responses. Certain proteins, such as bimodal regulator of receptor Tyr kinase Sprouty2 and ErbB (HER) receptor feedback inhibitor ErRFI1 8 with a peak expression 60 to 120 mn after stimulated EGF receptor degradation, generate a refractory period by inhibiting EGF receptors to avoid repetitive stimulation. In addition to transcription factors encoded by immediate early genes, epidermal growth factor initiates a coordinated transcriptional program of microRNAs that are attenuators of growth factor signaling [314] .

The coordinate expression of delayed-early genes (DEG) impedes the action of immediate early genes ( Fig. 3 .2). The delayed-early genes have a peak expression 40 to 240 mn after growth factor stimulation. Epidermal growth factor signaling encompasses genes that are coexpressed in feedbacks for signaling attenuation at specific nodes of the chemical reaction cascade. A node of the mitogen-activated protein kinase module of the EGF pathway is inhibited by dual-specificity MAPK phosphatases [315] . Other inhibitors also determine the activation duration. These inhibitory feedback loops are triggered by the signaling pathway itself to limit its activity duration. These inhibitors comprise transcription regulators and RNA-binding attenuators. 9

Epidermal growth factor (or β-urogastrone) is the founding member of the EGF superfamily. Members of this superfamily share similar structural and functional characteristics. The EGF superfamily also includes: heparinbinding EGF-like growth factor, transforming growth factor-α, amphiregulin, epiregulin, epigen, βcellulin, and neuregulin-1 to -4.

Heparin-binding EGF-like growth factor (HBEGF) intervenes in cardiogenesis and functioning, cardiac hypertrophy and wound healing. Heparin-binding EGF-like growth factor is synthesized as a membrane-anchored precursor (proHBEGF) that is cleaved to release a soluble HBEGF by specific metallopeptidases. In fact, proteolytic cleavage of proHBEGF yields N-and Cterminal fragments (HBEGF and HBEGFc) that both function as signaling molecules [316] .

Transforming growth factor-α (TGFα) is produced in macrophages, brain cells, and keratinocytes. It promotes epithelial development.

Amphiregulin (AReg) is an autocrine growth factor as well as a mitogen for astrocytes, Schwann cells, and fibroblasts.

Epiregulin (EReg) is another autocrine growth factor for human keratinocytes. Table 3.3 . Examples of signaling pathways of epidermal growth factor (EGF) that suppress cell apoptosis and foster cell mobility. Neuraminidase-3 (Neu3), or membrane sialidase-3 (Sial3) that, in particular, localizes to the extracellular leaflet of the plasma membrane removes sialic acid from sialoglycoproteins and -lipids (with high specificity for gangliosides, i.e., sialoglycosphingolipid [composed of ceramide, oligosaccharide, and sialic acids]). It can intervene in EGF signaling, as it enhances Tyr phosphorylation of epidermal growth factor receptor (EGFR) in response to EGF.

Pathway Effect EGF-EGFR-Ras-ERK Cell motility EGF-EGFR-Ras-PI3K-PKB Cell survival

Epigen (Epgn) 10 is a widely expressed transmembrane glycoprotein that undergoes cleavage to release a soluble EGF-like domain-containing fragment. It can promote the proliferation of epithelial cells, hence favoring wound healing.

βCellulin (BtC) primes the phosphorylation of all the 3 EGFRs on endothelial cells (HER2-HER4) [317] . It provokes the phosphorylation of components of mitogen-activated protein kinase (MAPK) modules, such as extracellular signal-regulated kinases ERK1 and ERK2 and P38MAPK, and triggers the PI3K-PKB (phosphatidylinositol 3-kinase-protein inase-B) pathway (Table 3 .3).

Neuregulins (NRg1-NRg4) are encoded by 4 genes. Neuregulins are characterized by numerous alternatively spliced variants that explain structural and functional diversity. Neuregulins mediate intercellular interactions in the nervous system, heart, breast, and other organ systems. They contribute to the regulation of cell growth, proliferation, adhesion, migration, differentiation, and apoptosis. Neuregulin signaling between apposed cells is bidirectional. Forward signaling from a NRg-producing cell to a NRg-responsive cell relies on receptor Tyr kinases of the HER family. Reverse signaling (backward or back signaling) occurs from HER-expressing cells to NRg-producing cells. Neuregulin then serves as receptor and HER as agonist. This bidirectional communication is illustrated by motor neurons that produce NRgs and inform HER-synthesizing Schwann cells and skeletal myocytes. Neuregulins are ligands for HER3 and HER4 receptors. The HER2 receptor 11 is activated on neuregulin binding to HER3 and HER4 receptors. The HER2 receptor is required for neuregulin signaling [318] . Therefore, neuregulins bind to HER3, HER4, or both HER3 and HER4 that then form homoor heterodimers often including HER2 (e.g., HER2-HER4 and HER3-HER4), with which neuregulins interact only after linking to HER3 or HER4 [319].

Neuregulin-1 operates in the development of the nervous system and heart (Table 3 .4). Like EGF, TGFα, and other ligands of receptors of the HER family, NRg1 is synthesized as proprotein. Neuregulin-1 acts in both juxtaand paracrine signaling. Most NRg1s are produced as transmembrane proteins. Nevertheless, after proteolytic cleavage and shedding or secretion (e.g., NRg1-2β3 isoform), NRg1s serve as diffusible messengers for short-distance intercellular communication. Adamlysins ADAM17 12 and ADAM19 13 can cleave plasmalemmal NRgs [319] . Soluble NRg1 fragment produced by shedding allows communication between endocardium and myocardium. As a paracrine factor released by microvascular endothelial cells, NRg1 ensures cardioprotection. Shedding of NRg1 can also produce an autocrine signal. Plasmatic NRg1β can serve as a biomarker in patients with heart failure, especially ischemic cardiomyopathy [320] .

Neuregulin-1 is encoded by a single gene. However, 15 known isoforms arise due to differential splicing (NRg1-1-NRg1-6). Type-1, -2-, and -3 NRg1 splice variants are further subdivided in α and β subtypes. Type-1 and -2 NRg1s are sometimes referred to as immunoglobulin-like domain-containing NRgs (IgNRg) and type-3 NRg1 as cysteine-rich domain-containing NRgs (CrdNRg) .

Heregulin (HRg) is the type-1 NRg1; 14 glial growth factor (GGF) type-2 NRg1; and sensory and motor neuron-derived factor (SMDF) type-3 NRg1. The major NRg1 isoforms that act as glial growth factors are type-3 NRg1s (GGF1-GGF2), not type-2 NRg1, originally called glial growth factor [319] . Isoforms of NRg1 that differ in their N-terminus or EGF-like domain have distinct functions. Heregulins participate in synapse development.

Some NRg1 splice forms are produced as transmembrane precursors that are processed and released, whereas others are soluble. The sequences of NRg1-1β1a and NRg1-3β1a differ only in their N-terminus. Nonetheless, NRg1-1β1a is a transmembrane protein that can be liberated once cleaved, whereas cleavage of NRg1-3β1a creates a transmembrane N-terminal fragment [319] . Unlike NRg1-1β3, transmembrane type-1 NRgs (i.e., NRg1-1β1a, NRg1-1β2a, and NRg1-1β4a) are released.

Type-1 and -2 NRgs serve as paracrine factors, type-3 NRgs as juxtacrine messengers [319] . The retention of type-3 NRg1s in the plasma membrane confines the range of signaling. In addition, type-1 and -2 NRgs bind to heparin and other glycosaminoglycans (carbohydrate side chains of proteoglycans) in the extracellular matrix and on cell surfaces, but not type-3 NRg1s.

Paracrine signals transmitted by NRg1s from endocardium contribute to myocardial differentiation. During cardiogenesis, type-1 and low concentrations of type-3 NRgs are produced by the endocardium. On the other hand, type-2 NRgs are not expressed by the embryonic myocardium [319] . Neuregulin-1 functions in the heart beyond embryo-and fetogenesis. In adults, the endothelium of the cardiac microvasculature may be a source of paracrine NRg1 signals.

Intracellular or membrane processing of tissue-specific proheregulin isoforms (e.g., αand βHRg) generate corresponding soluble forms. γ-Heregulin that also targets HER3 and HER4 receptors can function as an autocrine growth factor [318] .

NRg1β-induced migration relies on ERK1 and ERK2, JNK, PI3K, PKB, SRC family kinases, and RoCK1 and RoCK2 [321] . On the other hand, NRg1α does not exert any effect on the migration of certain types of malignant peripheral nerve sheath tumor cells, but can inhibited the migration of other cell lines.

Neuregulin-2 elicits growth and differentiation of epithelial, neuronal, and glial cells, among others. At the neuromuscular junction, NRg1 and NRg2 cause acetylcholine receptor transcription [322] . Like neuregulin-1, NRg2 as well as HER2 and HER4 receptors are required for cardiogenesis.

Neuregulin-2 activation of HER4 homodimers can elicit different patterns of receptor phosphorylation and signaling than those resulting from activation of HER4 homodimers in the same cell type by NRg1 [319] . Like NRg1, alternative transcripts encode distinct isoforms (NRg2α-NRg2β).

Neuregulin-1, -2, and -3 are expressed in the mammalian nervous system. Neuregulin-3 binds to and activates HER4, but not HER2 and HER3 receptors. It acts in epidermal morphogenesis. An NRg3 isoform (human fetal brain neuregulin ) is specific to human embryonic central nervous system. This type-1 glycosylated plasmalemmal protein is shed into the extracellular space, from which it activates HER4 [323] .

Neuregulin-4 activates HER1 receptor (EGFR). Various NRg4 splice variants exist (NRg4a1-NRg4a2, NRg4b1-NRg4b3). Type-A variant (NRg4a1) localizes to the membrane, whereas type-B variant (NRg4b1) lacks the transmembrane domain and resides in the cytosol [324] . NRg4 is involved in the differentiation of the somatostatin-expressing δ cells of pancreatic islets [319].

Fibroblast growth factors (FGF) that are also characterized by Tyr kinase activity are particularly involved in embryo-and angiogenesis as well as wound healing. There are several kinds of fibroblast growth factors. 15 Twenty-two fibroblast growth factors encoded by 22 genes (FGF1-FGF14 and FGF16-FGF23, as FGF19 is a human ortholog of mouse FGF15) have been identified in humans. Many of the Fgf gene products also exist in multiple isoforms generated by alternative splicing of messenger RNA.

Fibroblast growth factors signal via their cognate receptor Tyr kinases encoded by 4 Fgfr genes (FGFR1-FGFR4; Vol. . Except FGF11 to FGF15, FGF19, FGF21, and FGF23, all canonical FGFs activate FGFRs with different degrees of specificity [325] . Once secreted, canonical FGFs bind to FGFRs and induce their dimerization and phosphorylation of specific cytoplasmic Tyr residues.

Two factors -FGF1 and FGF2 -were originally isolated as growth factors for fibroblasts. Fibroblast growth factor FGF1 16 binds to FGFR1 to FGFR4 receptors. Fibroblast growth factor FGF2 17 promotes endothelial cell proliferation and formation of tubular, endothelial structures. It binds to the receptor FGFR1 as well as some heparan sulfate proteoglycans, such as glypicans Gpc3 and Gpc4 and syndecans Sdc2 to Sdc4 [326] .

The EGF superfamily encompasses other proteins that are similar to FGF1 or -2, such as heparin-binding EGF-like growth factor (HBEGF). The latter is a member of the EGF superfamily that is synthesized as a membraneanchored precursor (proHBEGF) . It is cleaved to by specific metallopeptidases that thus release a soluble HBEGF protein (N-terminal region [HBEGF N ]) and a C-terminal fragment (HBEGF C ). Both fragments function as signaling molecules.

The mammalian FGF superfamily can be decomposed into 7 families [325] ( Table 3 .5): (1) canonical FGF families (cFGF) that encompass the FGF1 (with FGF1, -2, and -5), FGF3 (with FGF3, , FGF7 (with FGF7, 18 FGF8 (with FGF8, and FGF9 (with FGF9, subfamilies; (2) intracellular FGF11 family (iFGF; with FGF11, ; 19 and (3) hormone-like FGF19 family (hFGF; with FGF19, -21, and -23). 20

Seven FGFR isoforms (FGFR1b, FGFR1c, FGFR2b, FGFR2c, FGFR3b, FGFR3c, and FGFR4) result from 4 Fgfr genes. The isoforms transcribed from the genes Fgfr1, Fgfr2, and Fgfr3 derive from alternative mRNA splicing that specifies the C-terminus structure, as it utilizes one of 2 unique exons in 2 different versions (FGFRib and FGFRic, i = 1, 2, 3) of Ig-like domain III. The FGFRia splice form encodes a secreted (extracellular) FGFR form (sFGFR) without known signaling capability. Yet, sFGFR1 oligomerizes upon ligand binding. Secreted sFGFR1 preferentially binds FGF2 over FGF1 [328] .

The FGFRib and FGFRic splice forms are used according to cell lineage. The b isoform is restricted to epithelial lineages and c isoform is preferentially expressed in mesenchymal lineages [329] . The FGF7 subfamily is expressed in mesenchymal tissues (connective tissue, bone, cartilage, and lymphatic and blood circulatory networks). Its members have the greatest affinity for 17 A.k.a. basic fibroblast growth factor (bFGF), FGFβ, and HBGF2. 18 FGF7 and FGF10 are also called keratinocyte growth factors KGF1 and KGF2. 19 Originally the family of FGF homologous factors (FHF1-FHF4). 20 Another decomposition of the FGF superfamily exists at least in mice [327] as well as Fig.1 concentrations high enough (concentration 3-800 nm, heparin concentration >10 μg/ml), they target FGFR1c, -2c, -3c, and -4 (but not FGFR1b, -2b, and -3b) [329] . Extracellular FGF monomers have a reduced heparin-binding affinity. Homodimerization of FGF regulates receptor binding, at least for members of the FGF9 subfamily (FGF9 and FGF20), and concentration gradients in the extracellular matrix due to heparan sulfate-dependent diffusion [330] . Dimerization of FGF thus operates as an autoregulatory mechanism for growth factor activity. Intracellular FGFs interact with intracellular domains of voltage-gated sodium channels and mitogen-activated protein kinase scaffold, the MAPK8interacting protein MAPK8IP2 [325] . 22 Members of the canonical and hormone-like families are released from cells. FGF3 to FGF8, FGF10, FGF17 to FGF19, and FGF21 to FGF23 are secreted proteins with cleavable N-terminal signal peptides. On the other hand, FGF9, FGF16, and FGF20 contain uncleavable bipartite signal sequences [325] . Isoforms FGF1 and FGF2 might be released by exocytosis.

All canonical FGFs possess binding sites for acidic glycosaminoglycans, such as heparin and heparan sulfate. In the presence of heparan sulfate, FGF binding to FGFR is stabilized, once (2:2:2) FGF-FGFR-heparan sulfate hexamer is formed [331] . Acidic glycosaminoglycans in the form of heparan sulfate proteoglycans retain secreted FGFs in the vicinity of FGF-producing cells. They can then act as paracrine regulators. On the other hand, hFGFs have low affinity for heparin and operate as endocrine regulators.

The fibroblast growth factor-19 family that encompasses FGF19 (human ortholog of murine FGF15 isotype), FGF21, and FGF23 regulates glucose metabolism, bile acid synthesis, mineral ion homeostasis, and phosphate and vitamin-D metabolisms.

Factors FGF19 and FGF21 act as endocrine hormones. Whereas FGF19 has both metabolic and proliferative effects, FGF21 has only metabolic effects because of structural differences that determine distinct receptor interactions [332] . The FGF19 factor reduces the plasma glucose concentration and heightens insulin sensitivity. The FGF21 factor is predominantly synthesized in liver, where it promotes the production of GluT1 glucose transporter. Factors FGF19 and FGF23 are secreted from ileal enterocytes and bone cells, respectively, to circulate in the blood stream.

Fibroblast growth factor-21 acts as a liver-derived endocrine factor that stimulates glucose uptake in adipocytes after binding the complex formed by FGF receptors and β-Klotho 23 and activating the mitogen-activated protein kinase cascade [333] . Klotho confers tissue-specific activity to FGF factor. In addition, FGF21 adapts cells to starvation, as it stimulates fatty acid release from adipocytes and promotes their conversion in hepatocytes to ketones that can be used as an energy source when glucids are scarce. However, unlike in vitro observations, β-Klotho is not essential for FGF21 signaling in adipocytes in vivo, because FGF21 cues are transduced in the absence of β-Klotho, but relies on a cofactor [334] .

On the other hand, the mineral homeostasis is regulated by FGF23 and the feedback control of α-Klotho and calcitriol 24 Similarly, the bile acidcholesterol metabolism depends on FGF19 and feedback from β-Klotho and bile acids [334] . Tissue-specific signaling from FGF19 family members relies on interactions between FGF19, FGF21, and FGF23 with β-Klotho cofactor and α-Klotho, respectively. 25 

Fibroblast growth factors FGF7 and FGF22 are expressed by CA3 pyramidal neurons in the hippocampus. Factors FGF22 and FGF7 promote the formation of glutamate-mediated excitatory and GABA-mediated inhibitory synapses on dendrites of CA3 pyramidal neurons via FGFR1 and FGFR2 receptor, respectively [335] . These postsynaptic neuron-derived presynaptic organizers participate in the local differentiation of axons into functional presynaptic terminals. This presynaptic differentiation includes the clustering of synaptic vesicles, formation of active zones, cytoskeletal restructuring and assembly of vesicle recycling machinery. Hence, fibroblast growth factors FGF7 and FGF22 work in synergy with other synaptogenic molecules such as neuroligins, ephrins, brain-derived neurotrophic factor, Wnts, cell adhesion molecule-1 (CAdM1), 26 netrin-G ligands, thrombospondins, signal regulatory proteins (SiRP), 27 leucine-rich repeat transmembrane neuronal proteins LRRTM1, and neuronal PAS domain protein NPAS4 28 as well as glial cells to coordinate the formation of appropriate synapses.

Hepatocyte growth factor (HGF) 29 contributes to tissue morphogenesis, angiogenesis, wound repair, and tissue regeneration. It belongs to the family of "serine peptidase" growth factors, but does not have peptidase activity as key catalytic residues are missing. It is secreted by mesenchymal cells. It targets primarily epithelial and endothelial cells, but also acts on hematopoietic progenitor cells. 26 A.k.a. synaptic cell adhesion molecule SynCAM1, nectin-like protein NecL2, and immunoglobulin superfamily member IGSF4. 27 The family of signal regulatory proteins comprises at least 15 members [336] .

Signal regulatory protein-α is also called Tyr-protein phosphatase non-receptor type substrate PTPNS1. The transmembrane polypeptide SiRPα1 is a substrate of activated RTKs that represses cell responses caused by growth factors and insulin [336] . 28 A.k.a. PAS domain-containing protein PASD10. It is selectively expressed in the nervous system. It activates the production of the dendritic-cytoskeleton modulator at synapses: developmentally regulated brain protein (drebrin). 29 A.k.a. hepapoietin-A and scattering factor.

Protein HGF possesses an α chain that contains its N-terminus and 4 kringle domains and a β chain with a serine peptidase domain [338] . It is synthesized as a single inactive polypeptide proHGF, although this precursor can bind hepatocyte growth factor receptor (HGFR). ProHGF cleavage (Arg494) by serine peptidases into a 69-kDa α chain and 34-kDa β chain leads to its active form. A disulfide bond between the α and β chains produces the active heterodimer. Mastocyte chymase, neutrophil elastase, and plasma kallikrein also cleave HGF (Cys487) and generate a free α chain, a competitive inhibitor of HGF.

It has 2 natural splice variants -NK1 and NK2 -that contain the Nterminus and the first kringle (K1) or the first 2 kringle domains of HGF [338] . The splice variant NK1, an agonist of HGFR, forms an NK1 homodimer. Heparan sulfate is necessary for its full activity. On the other hand, NK2, a monomer and HGFR antagonist that possesses the N-terminus and first 2 kringle domains, impedes HGF activity.

The HGFR receptor 30 dimerizes upon HGF binding and transmits signals via the MAPK modules and PI3K-PKB pathways to prime cell survival, proliferation, and motility.

Lymphatic endothelial cells express higher levels of hepatocyte growth factor receptor than blood vascular endothelial cells [339] . The HGF factor promotes the proliferation of lymphatic endothelial cells, their migration (which is partially mediated via α 9 integrin), and the formation of lymphatic vessels.

Insulin is a major anabolic hormone. Pancreatic β cells secrete insulin in response to elevated glucose level in the plasma. Insulin promotes glucose uptake by all cell types, particularly adipocytes and myocytes, and prevents glycogenolysis and gluconeogenesis in the liver (Table 3 .7). Insulin regulates glucose homeostasis by activating phosphoinositide 3-kinase and increasing glucose uptake rate, especially into myocytes and adipocytes, using the GluT4 transporter. Insulin also stimulates the CAP-CBL axis via the initiator SH2B2 that recruits both CBL and CBL-associated protein (CAP) to the insulin receptor (IR). Subsequent CBL phosphorylation dissociates the CAP-CBL complex from IR. This complex then migrates to flotillin. 31 The resulting recruitment of the CRK-RapGEF1 complex leads to the activation of the small GTPase RhoQ. Activated RhoQ causes actin remodeling and enables GluT4 to dock to the plasma membrane. Conversely, a low glucose concentration leads to a low insulin level combined with an elevated level in antagonist hormones 30 A.k.a. mesenchymal-epithelial transition factor (MET or cMET; Vol. . 31 Flotillins are membrane nanodomain (raft and caveolae)-associated, integral membrane proteins. 

(glucagon, adrenaline, and corticosteroids) and favors glucose production in the liver.

The pancreas has pancreatic islets that release glucagon and insulin. Insulin and glucagon produced by the pancreatic α cells and secreted in response to low glycemia have opposite effects on hepatic control (glucose storage and delivery) of glycemia. Insulin increases the synthesis of glycogen and fatty acids, as well as amino acid and potassium uptake, and decreases proteinolysis, lipolysis, and gluconeogenesis. Glucagon GPCR transmits signal destined for carbohydrate metabolism in the liver and insulin release from the pancreatic β cells.

Insulin receptor (Vol. . Receptor Kinases) is composed of 2 extracellular insulin-binding α and 2 transmembrane β subunits. β Subunits have cytoplasmic ATP-binding and Tyr kinase domains. Insulin binding induces autophosphorylation of β subunits, activating the receptor catalytic activity.

Insulin signaling targets many mediators, such as glucose transporter-4 (Vol. . Membrane Compound Carriers), insulin-receptor substrate proteins, CCAAT-enhancer-binding protein-α, and peroxisome proliferatoractivated receptor-γ (NR1c3; Vol. 3 -Chap. 6. Receptors), as well as longchain fatty acid acylCoA synthase.

In adipocytes, insulin is the main regulator of hormone-sensitive lipase that is the rate-controlling enzyme for triglyceride hydrolysis. In response to insulin, adipocytes also secrete several small soluble proteins, such as adiponectin, adipsin, and leptin.

In any cell, binding of insulin to receptors causes fusion of cytoplasmic vesicles that sequester glucose transporters GluT4 with the plasma membrane and insertion of glucose transporters into the membrane. In the absence of insulin, glucose transporters are internalized. Certain substances can alter conformation of the cytoplasmic kinase domain or bind to modulator-binding sites of the insulin receptor.

Insulin binds to and stimulates insulin receptor Tyr kinase that activates phosphatidylinositol 3-kinase and protein kinase-B to mediate most effects. Upon stimulation by insulin, insulin receptor recruits and phosphorylates insulin-receptor substrate proteins that excite the PI3K-PKB pathway. Activated PKB phosphorylates effector kinases and transcription factors.

A second, PI3K-independent insulin pathway exists that involves a complex made of insulin receptor, scaffold protein β-arrestin-2 (Vol. 1 -Chap. 9. Intracellular Transport), 32 Src kinase, and protein kinase-B [342] . Insulin favors interaction between β-arrestin-2, protein kinase-B, and Src kinase with activated insulin receptor. The absence of β-arrestin-2 indeed attenuates glucose metabolism and insulin sensitivity on the one hand and augments hepatic glucose production, although PI3K-dependent insulin signaling remains efficient. β-Arrestin-2 loss reduces insulin-stimulated Src binding and Tyr phosphorylation of protein kinase-B.

Type-1 diabetes is caused by loss in insulin-producing β cells of the pancreas by autoimmune destruction. Chronic hyperglycemia causes endothelial dysfunction and vascular damages. On the other hand, insulin resistance (Vol. 6 -Chap. 7. Vascular Diseases) that precedes the onset of and characterizes type-2 diabetes is a defect of insulin stimulation of its receptor. Insulin signaling is disturbed because of protein modifications such as phosphorylation of insulin-receptor substrate proteins. tumor-necrosis factor-α, interleukin-6, and free fatty acids that are secreted at high quantities by enlarged adipocytes intervene in the development of insulin resistance. These substance cause Ser phosphorylation of insulin-receptor substrate-1 and -2, which reduces their capacity to be phosphorylated by insulin receptor.

Moreover, in obesity, activated Jun N-terminal kinases (Vol. 4 -Chap. 5. Mitogen-Activated Protein Kinase Modules) mediate Ser phosphorylation of insulin-receptor substrate protein IRS1. β-Arrestin-2 level is reduced in a mouse model of type-2 diabetes [342] .

Caveolin-1 stabilizes the insulin receptor. MicroRNA-103 and -107 target the CAV1 gene and contribute to insulin resistance [343] . 33

Insulin-like growth factor-1 34 (IGF1) can be produced in response to growth hormone. It acts as a growth and differentiation factor. The cellular response to IGF1 depends on the differentiation state, plasmalemmal receptor density, and cell environment. Insulin-like growth factor-1 is synthesized in numerous cell types. Its production varies according to the cell type.

The cardiac synthesis of IGF1 is higher in athletes than sedentary control subjects, whereas the production of endothelin-1 and angiotensin-2 does not change [344] . Heterotetramer IGFR1 is a receptor Tyr kinase. Insulin-like growth factor-1 acts exclusively via this class-2 receptor Tyr kinase (Vol. .

On the other hand, IGF2 is almost exclusively expressed in embryonic and neonatal tissues. Whereas IGF1 operates during both pre-and postnatal development, IGF2 intervenes only during embryo/fetogenesis [345] . The expression of components of the insulin-like growth factor signaling (IGF1 and IGF2, IGF1R and IGF2R receptors, and soluble IGF-binding proteins [IGFBP1-IGFBP7] and IGF-binding protein-like molecule IGFBPL1) is ubiquitous 33 MicroRNA-103 and -107 are upregulated in obese mice. Repression of miR103 and miR107 improves insulin-stimulated glucose uptake. Conversely, upregulation of miR103 and miR107 impairs glucose homeostasis. 34 A.k.a. somatomedin-C. during intra-uterine and postnatal development. 35 Insulin-like growth factor-2 at relatively low concentrations mainly binds to type-2 IGF receptor [346] . Type-2 IGFR is coupled to calcium gating. However, IGF2 can also operate via type-1 IGF receptor.

Mitogenic IGF2 targets somatic cells in various tissues. In the brain, it is highly expressed in the hippocampus. Memory consolidation involves synthesis of proteins, especially the transcription factors of the families of cAMP response element-binding proteins and CCAAT enhancer-binding proteins. 36 In rats, IGF2 enhances memory during a specific time window after learning (sensitive period of memory consolidation) [347] . 37 Insulin-like growth factor-binding proteins (IGFBP) bind to and modulate the activity of insulin-like growth factors. Insulin-like growth factor binders include 6 members (IGFBP1-IGFBP6; Table 3 .8).). In addition, IGFBPs also have IGF-independent activities. Proteins IGFBP1, IGFBP2, and IGFBP6 are modest Wnt inhibitors, but IGFBP4 is the most potent repressor of the canonical Wnt pathway (Vol. 3 -Chap. 10. Morphogen Receptors). Proteins IGFBP3 and IGFBP5 do not intervene in Wnt-β-catenin signaling. Protein IGFBP4 binds and inhibits components of the canonical Wnt signaling pathway to promote cardiomyocyte differentiation, independently of IGF1 and IGF2. 38 35 Insulin-like growth factor receptor IGFR2 is also called mannose 6-phosphate receptor (M6PR). It binds with high affinity to IGF2, but not IGF1. It lacks the major intracellular domains used in signal transduction. Its primary function is the inhibition of the action of IGF2 in utero. It controls the interstitial IGF2 concentration, as it fosters its endocytosis and lysosomal degradation [345] . 36 The transcription factor C/EBPβ is upregulated for more than 28 h after training [347] . 37 The concentrations of IGF2 messenger RNA and protein increase between 20 and 36 h after training, but neither immediately, nor 3 d after training. Enhancement of IGF2-dependent memory requires cytoskeletal-associated proteins and glycogen-synthase kinase GSK3 [347] . Moreover, IGF2 increases the expression of the α-amino 3-hydroxy 5-methyl 4-isoxasolepropionic acid (AMPA)-type ionotropic glutamate receptor GluR1 subunit. In the hippocampus, IGF2 promotes a long-term potentiation after weak synaptic stimulation. The effect of the memory enhancer IGF2 is selectively mediated by IGF2R (mannose 6-phosphate receptor), but not IGFR1 receptor. 38 Protein IGFBP4 binds to the extracellular domain of Wnt receptor Frizzled Fz8 and coreceptor low-density lipoprotein receptor-related protein LRP6 [348] . It is expressed in cells adjacent to cardiomyocyte progenitors (paracrine regulation). It competes with Wnt3a to bind to Frizzled-8 and impedes the Fz8-LRP6-Wnt3a-β-catenin signaling. Proteins IGFBP1, -2, and -6 are also able to bind LRP6 and Frizzled-8, but they are only slightly expressed in heart. 

The family of platelet-derived growth factors (PDGF) comprises 4 protomers (PDGFa-PDGFd) that homo-(mainly) and heterodimerize (Table 3 .9). Platelet-derived growth factors are potent activators of the PI3K pathway. They bind to 2 plasmalemmal receptor Tyr kinases, PDGFRα and PDGFRβ receptors that also homo-and heterodimerize upon PDGF binding.

Platelet-derived growth factor consists of different combinations of 2 subunits among 4 protomers (encoded by the PDGFA to PDGFD genes) to form homodimers (PDGFaa, PDGFbb, PDGFcc, and PDGFdd) as well as a single heterodimer (PDGFab). The PDGFaa factor specifically interacts with PDGFRαα homodimer, whereas PDGFbb links to both homo-and heterodimers formed by PDGFRα and PDGFRβ. The isoform PDGFcc associates to PDGFRαα and PDGFRαβ, whereas PDGFdd activates PDGFRαβ and PDGFRββ. Subunits PDGFRα and PDGFRβ are predominantly expressed on vascular endothelial and smooth muscle cells, respectively. 39 Binding of PDGF to its cognate receptors primes signaling cascades that initiate proliferation, migration, and differentiation of various cell types, such as fibroblasts and smooth muscle cells.

A combination of FGF2 and vascular stabilizer PDGFbb that target mainly endothelial cells and vascular mural cells (pericytes and smooth muscle cells), respectively, promotes collateral growth and stabilization [349] . 40 Both PDGFaa and PDGFbb are able to synergistically stimulate angiogenesis with FGF2, but only PDGFbb can stabilize in the presence of FGF2. The PDGFbb receptor actually needs to cooperatively work with FGF2 for vessel stability. PDGFRα is mainly involved in angiogenesis, whereas PDGFRβ mediates vessel stability.

Angiogenesis requires both migration and proliferation of endothelial cells and coverage of vascular sprouts by vascular smooth muscle cells or pericytes for vessel stabilization via vascular endothelial and platelet-derived growth factors, respectively. Growth factor PDGF also induces neovascularization by stimulating vascular smooth muscle cells and pericytes to release proangiogenic mediators.

Transforming growth factors comprise 2 classes of polypeptidic growth factors, TGFα and TGFβ, that act via different receptors. The former induces epithelial development, whereas the latter operates in cell growth and differentiation, embryogenesis, tissue regeneration, and regulation of the immune system.

Transforming growth factor-α (TGFα), secreted by activated macrophages and platelets, as well as brain cells and keratinocytes, binds to EGF receptor (EGFR) and its own receptor.

In addition to TGFβ isotypes, the TGFβ superfamily includes (Tables 3.10 and 3.11): (1) dimeric activins, (2) dimeric inhibins, (3) Nodal, (4) anti-39 PDGFRβ and -α are also expressed in endothelial cells and smooth muscle cells, respectively. 40 Combination of PDGFbb and FGF2, but not PDGFbb and VEGF or FGF2 and VEGF, is able to induce angiogenesis and arteriogenesis. Activin Activin-A (βA-βA dimer) Activin-AB (βA-βB dimer) Activin-AC (βA-βC dimer) Activin-B (βB-βB dimer) Activin-BC (βB-βC dimer) Activin-C (βC-βC dimer)

Nodal Nodal, Nodal-BMP4, and Nodal-BMP7 dimers Müllerian hormone (AMH), 41 (5) members of the family of bone morphogenetic proteins (BMP), 42 and (6) components of the family of growth and differentiation factors (GDF). The transforming growth factor-β superfamily comprises: (1) 3 TGFβ isoforms (TGFβ1-TGFβ3); (2) 4 activin β chains (β A -β C and β E ; activin-β A and -β B are identical to the 2 β subunits of inhibins), that form 2 inhibins (inhibin-A and -B, i.e., α-β A and α-β B dimers, respectively) and 7 activins (activin-A, -AB, -AC, -B, -BC, -C, and -E, i.e.,

(3) 10 bone morphogenetic proteins (BMP2-BMP7, BMP8a and -8b, BMP10, and BMP15); and (4) 11 growth and differentiation factors (GDF1-GDF3, GDF5-GDF11, and GDF15). These 41 A.k.a. Müllerian-inhibiting factor (MIF), hormone (MIH), and substance (MIS). 42 Metallopeptidase BMP1 that acts on procollagen-1, -2, and -3, does not belong to the TGFβ superfamily. Bone morphogenetic proteins with several other signals, such as Wnt and FGF, are involved in heart development. Noggin, a bone morphogenetic protein antagonist, is transiently and strongly expressed in the heart-forming region during gastrulation [350] . Cardiomyocytes can be obtained from mouse embryonic stem cells by inhibition of BMP signaling. Table 3 .11. Common members of the bone morphogenetic protein (BMP) and growth differentiation factor (GDF) families. Factor GDF2 is one of the most potent BMPs in bone formation. Factor GDF5 (a.k.a. cartilage-derived morphogenetic protein CDMP1) participates in development of the central nervous system as well as skeleton and joints. It also promotes survival of dopamine-sensitive neurons. It targets AcvR2a and AcvR2b associated with AcvR1 receptors. Factor GDF6 contributes to the control of eye development. It binds to BMPR2 linked to BMPR1a or BMPR1b receptors. Factor GDF7 induces the formation of sensory neurons in the dorsal spinal cord. Agents GDF10 and BMP3 are considered as a separate subgroup within the TGFβ superfamily. Factor GDF11 controls anterior-posterior patterning.

BMP Member Corresponding GDF member

molecules generally form homodimers, but heterodimers exist, such as Nodal-BMP4 and Nodal-BMP7 complexes, in addition to inhibins and activin-AB, -AC, and -BC.

Transforming growth factor-β isoforms as well as other TGFβ superfamily members are synthesized as dimeric preproproteins. A large N-terminal prodomain is required for the proper folding and dimerization of the Cterminal growth-factor domain. 43 It also confers latency, at least, on some superfamily members and enables storage in the extracellular matrix, once complexed particularly with latent TGF-binding proteins (LTBP) or fibrillins. 44 Precursors of the TGFβ superfamily members are processed and secreted by cells in an inactive form. In particular, transforming growth factor-β is stored in the extracellular matrix as a latent TGFβ. Activation of members of the TGFβ superfamily thus follows their liberation from latency. 43 The prodomain of Nodal, which links to Cripto, is cleaved by peptidases secreted by neighboring cells [351] . Anti-Müllerian hormone is secreted mostly uncleaved; its prodomain potentiates its activity. Protein Lefty is cleaved to enable access of the growth-factor domain to its receptors. 44 Many members of the TGFβ superfamily remain associated with their prodomains after secretion, such as BMP4, BMP7, BMP10, GDF2, GDF5 and GDF8. Many of these prodomains bind to fibrillin-1 and -2. Binding to LTBPs or fibrillins strengthens the latent prodomain-growth factor complex [351] .

Precursors of TGFβ are cleaved by peptidases of the subtilisin-like proprotein convertase family such as furin. 45 Mature dimeric growth factors can also be secreted. TGFβ isoforms, GDF8, 46 and GDF11 are secreted as propeptides. They undergo an additional cleavage by specific enzymes of the bone morphogenetic protein-1-Tolloid-related family of metallopeptidases to release the active form, like endorepellin (angiostatic C-terminal fragment of perlecan). However, Nodal precursor binds to receptors and activates signaling without being processed [353] .

Components of the extracellular matrix, such as fibrillins, emilin, and auxiliary receptor endoglin, control the availability of active extracellular TGFβ (extracellular regulation of TGFβ signaling) [354] . Fibrillins have a dual role, because they concentrate TGFβ at sites of function (positive activity), but sequester TGFβ and inhibit its activation (negative activity).

Emilin-1 protects TGFβ from proteolysis by furin convertase, and then inhibits TGFβ signaling. Emilin-1 particularly impedes excessive TGFβ signaling characterized by a reduction in arterial lumen with a resultant increase in vascular resistance and hypertension.

Sequestered TGFβ can be rapidly released by peptidases (plasmin, mastocyte chymase, thrombin, and matrix metallopeptidases MMP2 and MMP9). Activated TGFβ can then act on neighboring cells. Factor TGFβ can also be activated by thrombospondin-1 as well as β 6 and β 8 integrins.

All of the 33 members of the TGFβ superfamily (nodal, activins, inhibins, bone morphogenetic proteins, and growth differentiation factors) undergo a folding of their prodomain that shields the growth factor from recognition by receptors [351] . Activation of TGFβ requires the binding of α V β 6 integrin to an RGD sequence in the N-terminal prodomain and exertion of force on this domain by latent TGFβ-binding proteins in the extracellular matrix.

Among the 3 structurally and functionally distinct TGFβ isoforms, TGFβ1 is the prevalent isoform, whereas TGFβ2 and TGFβ3 are expressed in a limited number of tissues. Isotype TGFβ1 is particularly synthesized by endothelial cells, vascular smooth muscle cells, myofibroblasts, macrophages, lymphocytes, and hematopoietic cells, and TGFβ2 by keratinocytes among others. 45 Furin is a portmanteau for Fes upstream region protein. It is also called paired basic amino acid cleaving enzyme (PACE). In addition to transforming growth factor-β precursor, its substrates include proparathyroid hormone, proalbumin, proβsecretase, membrane type-1 matrix metallopeptidase, β subunit of pro-nerve growth factor, and von Willebrand factor. Furin and furin-like proprotein convertases target the iron regulator hemojuvelin (or repulsive guidance molecule RGMc), a glycosyl-phosphatidylinositol-anchored protein and soluble glycoprotein of the liver and striated muscles [352] . 46 A.k.a. myostatin (Mstn). It interacts with secreted glycoproteic inhibitor follistatin-like FSTL3 and AcvR2b receptor.

Factor TGFβ is a growth inhibitor for endothelial cells, fibroblasts, and other cell types. Several factors regulate TGFβ synthesis. In vascular smooth muscle cells, angiotensin-2 stimulates TGFβ expression and promotes its conversion to active form. Matrix metallopeptidase MMP2 enhances active TGFβ1 in vascular smooth muscle cells. In addition, angiotensin-2 and endothelin-1 stimulate thrombospondin-1 that increases separation of active TGFβ from inactive latent complex.

The 3 TGFβ isoforms act as auto-, para-, and sometimes endocrine factors. They regulate via their cognate receptor Ser/Thr kinases and SMAD effectors (homologs of Caenorhabditis elegans SMA and Drosophila MAD; Vol. 3 -Chap. 8. Receptor Kinases) the fate (cell growth, adhesion, migration, differentiation, and apoptosis) of many cell types, especially endothelial and vascular smooth muscle cells, both during embryogenesis and after birth, during childhood as well as in adults. Effectors SMADs transmit the signal down to DNA. Signaling magnitude and duration determine cell response features in a given cell type and signaling context [353] . Endocytosis kinetics of TGFβ receptors could regulate the duration and magnitude of signaling. The SMAD signaling is generally slow and sustained.

Transforming growth factor-β initiates a signaling cascade not only by binding and then activating its cognate receptors, but also by triggering the assembly of an active heterotetrameric receptor. TGFβ receptor-1 (TβR1) acts downstream from high-affinity TGFβ receptor-2 (TβR2) 47 and determines the signaling specificity.

Members of the TGFβ superfamily target 2 main classes of receptors: the TGFβ receptor-1 (TGFBR1 class) and -2 (TGFBR2 class) sets (Tables 3.12,  3 .13, and 3.14). The TGFBR1 class is composed of 2 subsets: (1) TGFBR1class subset 1 with activin receptor-like kinases ALK4, ALK5, and ALK7 and (2) TGFBR1-class subset 2 with ALK1, ALK2, ALK3, and ALK6. The TGFBR2 class includes TβR2, activin receptor-2 (AcvR2), BMP receptor-2 (BMPR2), and anti-Müllerian hormone receptor-2 (AMHR2). Each TβR2 associates with a TβR1 of a given subset. For example, bone morphogenetic proteins signal via BMPR2 and a receptor of the TβR1 subset 2.

Two main sets of proteins control ligand-receptor interactions. (1) Accessory TGFβ receptors (TGFβ receptor-3) comprise βglycan, endoglin, and Cryptic family members. The expression of plasmalemmal coreceptors is needed for receptor activation by given cell types, thus allowing these cells Table 3 .12. Signaling by members of the TGFβ superfamily (Sources: [353, 354] ). The TGFβ superfamily comprises: (1) 3 TGFβ isoforms (TGFβ1-TGFβ3);

(2) 4 activin-βs (activin-βA-activin-βC and activin-βE) that build 2 inhibins (inhibin-A and -B) as well as 7 activins (activin-A, -AB, -AC, -B, -BC, -C, and -E); (3) Nodal; (4) 10 bone morphogenetic proteins (BMP2-BMP7, BMP8A-8B, BMP10, BMP15), (5) 11 growth and differentiation factors (GDF1-GDF3, GDF5-GDF11, GDF15), and (6) anti-Müllerian hormone (AMH). members of the TGFβ superfamily have 2 types of receptors: TβR1 and TβR2 receptor Ser/Thr protein kinases that are encoded by the genes TGFBR1 (transforming growth factor-β receptor-1; a.k.a. 53-kDa activin-A receptor type 2-like kinase [ALK2]) and TGFBR2 ([70-80-kDa] TGFβ receptor-2). Transforming growth factor-β receptor-3 (> 300-kDa) encoded by the TGFBR3 gene is a cell-surface chondroitin sulfate-heparan sulfate proteoglycan. Signaling by members of the TGFβ superfamily uses a limited number of receptors of both types, but multiple kinds of interactions occur (1) between ligands and receptors on the one hand and (2) between receptor types on the other. Receptor AcvR2b binds various TβR1: ALK4 in response to activin, ALK4 or ALK7 to Nodal, ALK3 to BMP2, ALK2 to BMP7, ALK4 or ALK5 to GDF8, and ALK4, ALK5 or ALK7 to GDF11. Coreceptors modulate ligand binding to receptors.

Effector class ligands

TβR1 subset 1 BMP, GDF, AMH TβR1 subset 2 TGFBR3 β-Glycan, endoglin, Cryptic Coreceptor to respond to corresponding ligands. Elevated levels of endoglin in endothelial cells of developing blood vessels cause endothelial dysfunction, reducing the activity of nitric oxide synthase NOS3 [354].

(2) Extracellular ligandsequestering proteins include chordin, noggin, and Twisted gastrulation; members of the Cerberus family; and sclerostin. These diffusible inhibitors modulate the signaling amplitude and duration.

Natural TGFβ antagonists include numerous binding partners of members of the TGFβ superfamily (Table 3 .15). Latent TGFβ-binding proteins (LTBP1-LTBP4) control TGFβ availability. Regulator TGFβ is synthesized as a large, homodimeric, inactive precursor (preproTGFβ). The dimeric precursor is cleaved intracellularly to produce the small latent TGFβ complex (SLTC), formed by the C-terminal region that will generate the mature TGFβ and latency-associated peptide (LAP or Table 3 .13. Receptors of the TGFβ superfamily (ALK: activin receptor-like kinase).

BMPR1b ALK6 ALK class 1: ALK4, ALK5, and ALK7 ALK class 2: ALK1, ALK2, ALK3, and ALK6

Class-2 receptors TβR2 AcvR2 BMPR2 AMHR2 Table 3 .14. Signaling from TGFβ superfamily members (ALKC1[2]: class-1[2] activin receptor-like kinase). Latent TGFβ-binding proteins (LTBP1-LTBP4) control TGFβ availability. Once liberated from the small and large latent complexes, TGFβ family members can be intercepted by diffusible proteins that bind these ligands and inhibit their access to cognate receptors.

Agonists Type-2 receptor Type-1 receptor Inhibitors

The dimer SLTC is then secreted, but cannot bind to the TGFβ receptors. It binds to latent TGFβ-binding protein (LTBP1-LTBP4). In fact, the SLTC dimer usually binds to LTBP to form a trimer, the large latent TGFβ complex (LLTC). The latter binds (via LTBP) to collagen, fibronectin, and fibrillin-1, hence it is anchored to the extracellular matrix.

Activation of TGFβ then requires dissociation from the latent TGFβ complex. Once liberated from these latent aggregates, TGFβ superfamily members can be intercepted by diffusible proteins that bind these ligands and inhibit their access to cognate receptors.

Receptors that activate LAP such as the scavenger receptor ScaRb3, 49 thrombospondin Tsp1, and α V β 6 integrin, are expressed on monocytes, endothelial cells, and dendritic cells, but not on T lymphocytes. Regulatory T lymphocytes that are activated by TGFβ then required their interaction with antigen-presenting cells.

The DAN family of TGFβ endogenous, glycoproteic antagonists comprises multiple members that restrict the activity of bone morphogenetic proteins and/or Wnt morphogens. The founding member of this family, Differential screening-selected gene aberrative in neuroblastoma (DAN), 50 localizes to axons. Seven BMP antagonists of the DAN family have been identified in rodents, such as tumor suppressor DAN, head-inducing factor Cerberus-related protein Cer1, gremlin, protein related to DAN and Cerberus (PRDC). Some members of the Cerberus-DAN family are implicated in left-right patterning owing to their asymmetrical distribution. Unlike Lefty proteins, DAN family members bind directly to extracellular Nodal and prevent signaling. Cerberus-related protein Cer1 51 antagonizes GDF5, GDF6, and GDF7 factors (Table 3 .15).

Chordin is involved in the body's patterning during embryogenesis. Chordin-like protein-1 (ChrdL1) 52 is upregulated by hypoxia, especially in retinal pericytes [355] . Chordin-like protein-2 (ChrdL2) 53 is expressed preferentially in chondrocytes of developing cartilage and degenerated (osteoarthritic) joint cartilage [356] . It precludes generation, maturation, and regeneration of articular chondrocytes.

Decorin is a proteoglycan that interacts with fibronectin, thrombospondin, and TGFβ, among others. It regulates TGFβ activity. Follistatin is a folliclestimulating hormone (FSH)-suppressing, activin-binding protein. This ubiquitous glycoprotein is an autocrine regulator that serves as a safeguard against uncontrolled cellular proliferation. 49 A.k.a. CD36, thrombospondin receptor, platelet collagen receptor, fatty acid translocase, and glycoproteins GP3a and GP4. 50 A.k.a. DAN domain family member-1 (DAND1), neuroblastoma candidate region, suppression of tumorigenicity-1 (NBL1) and NO3. 51 A.k.a. DAN domain-containing protein DAND4. 52 A.k.a. neuralin-1 (Nrln1), neurogenesin-1, and ventroptin (Vopt). 53 A.k.a. breast tumor novel factor BNF11. Table 3 .15. Inhibitors of the signal transduction triggered by members of the TGFβ superfamily (DAN: differential screening-selected gene aberrative in neuroblastoma; FLRG: follistatin-like related gene product; FSRP: follistatin-related protein; GASP: GDF-associated serum protein).

Binding partners 

Factor TGFβ binds to connective tissue growth factor for intense, prolonged TGFβ activity. TGFβ also causes CTGF synthesis that leads to SMAD7 transcriptional suppression, as it primes transcription factor TGFβ-inducible early gene product TIEG1, thereby relieving SMAD7-mediated negative feedback loop. In vascular smooth muscle cells, CTGF is a signaling mediator of angiotensin-2 and TGFβ via SMAD and the RhoA-RoCK-NADPH oxidase-ROS-MAPK pathway (Vol. 3 -Chap. 7. G-Protein-Coupled Receptors).

Angiotensin-2 regulates TGFβ expression as well as its activation and secretion. Angiotensin-2 can activate the SMAD pathway independently of TGFβ via AT 1 receptors [359] . In vascular smooth muscle cells, angiotensin-2 provokes rapid SMAD2 phosphorylation via P38MAPK mitogen-activated protein kinase and nuclear translocation of phosphorylated SMAD2 as well as SMAD4.

Ubiquitin ligase Arkadia 57 is a potentiator of transforming growth factor-β, as it provokes ubiquitin-dependent degradation of several inhibitors of TGFβ, such as inhibitory SMAD7 as well as members of the SKI family of corepressors of TGFβ signaling such as v-Ski sarcoma viral oncogene homolog (Ski) and Ski-like protein SkiL that interact with SMAD proteins [360] . In particular, Arkadia interacts with Axin that sequesters SMAD7 in the cytoplasm and forms a complex with Axin and SMAD7 to support SMAD7 polyubiquitination and degradation. In addition, Arkadia ubiquitinates μ2 subunit of the clathrin adaptor complex AP2, hence limiting EGFR endocytosis by AP2 complex [361] . 58 folding and stabilization. On the other hand, HSP90 ADP associates with different cochaperones such as HSP70 for ubiquitin-mediated degradation mediated by Cterminus heat shock cognate-70-interacting protein (CHIP) of target proteins, such as HER2 plasmalemmal receptor and protein kinase-B. 57 A.k.a. RING finger protein RNF111. 58 Heterotetramer AP2 consists of large adaptins α and β2, a medium subunit μ2, and small τ2 component. Adaptin α recruits endocytotic accessory proteins Epsin, Eps15, and clathrin coat-associated protein AP180 (91-kDa synaptosomal-associated protein SNAP91). Adaptin β2 triggers clathrin assembly.

Distinct modes of graded and switch-like assembly of receptor Ser/Thr kinases exist for signal transduction [362] . Dimers TβR3 form cooperative heterohexamers with pairs of TβR1 and TβR2. Bone morphogenetic proteins form distinct heterotetramers of receptor pairs. Factor TGFβ causes a rapid activation of the mitogen-activated protein kinase modules that are involved in the Ras-ERK, MAP3K7-MAP2K4-JNK, MAP3K7-MAP2K3/6-P38MAPK, Rho/Rac/CDC42-MAPK, and PI3K-PKB pathways.

Following ligand binding, TGFβ receptor-2 transphosphorylates TGFβR1, which stimulates additional trans-and autophosphorylation before phosphorylating receptor-associated SMADs (rSMAD), thereby promoting their nuclear translocation and gene regulation. In addition, SMAD-independent pathways exist.

Moreover, active TGFβR1 is sumoylated to enhance SMAD3 recruitment, binding, and phosphorylation [363] . Sumoylation requires kinase activities of both TβR1 and TβR2. The TβR1-TβR2 complex afterward undergoes ubiquitination and degradation.

Canonical signaling triggered by TGFβ superfamily members includes 2 main intracellular pathways according to SMAD mediators. Receptor TβR2 phosphorylates (activates) TβR1 that is then able to recruit receptor-regulated SMADs. Receptors of the TGFBR1 subset activate only a subset of rS-MADs: (1) receptors of ALK class 1 that specifically phosphorylate SMAD2 and SMAD3 and (2) receptors of ALK class 2 that are specific for SMAD1, SMAD5, and SMAD8 (or SMAD9).

Consequently, SMAD2 and SMAD3 are phosphorylated by TGFβ, activins, and Nodal, whereas SMAD1, SMAD5, and SMAD8 are activated by bone morphogenetic proteins, growth and differentiation factors, and anti-Müllerian hormone. However, in endothelial cells, TGFβ can recruit both ALK5 (TGFBR1 subset 1) and ALK1 (TGFBR1 subset 2) to form a single receptor complex, and thus activate both pathways [353] .

In addition, the Nodal-SMAD2 and Nodal-SMAD3 pathways recruit lysine (K)-specific demethylase KDM6b to counteract repression by Polycombgroup proteins on Nodal target genes [364] . Polycomb-group proteins remodel chromatin that is composed of DNA wrapped around histones, hence reducing DNA accessibility and causing epigenetic silencing of genes. 59 Therefore, intercellular signaling via Nodal balances epigenetic regulation mediated by Polycomb-group proteins, especially during the embryogenesis. 59 Histones undergo numerous post-translational modifications, such as acetylation and methylation. The Polycomb repressive complex PRC2 trimethylates histone-H3 (Lys47) to yield a binding site for the Polycomb repressive complex PRC1 that represses gene expression [364] . This process is reversible, as histone demethylases target methylated histone-H3 M .

Once TβR1 has phosphorylated specific intracellular SMAD effectors, the latter form homomers that link common mediator SMAD4. The SMAD complexes impart the signal into the nucleus and regulate -positively or negatively -target gene transcription.

Signaling from TGFβ is modulated by other signaling pathways and posttranslational modifications, as SMADs are controlled by phosphorylation, acetylation, ubiquitination, and sumoylation (Vol. 1 -Chap. 5. Protein Synthesis).

Phosphorylated receptor-regulated SMADs (rSMAD P ) form heteromers with their partner SMAD4 that translocate and accumulate in the nucleus and bind to DNA. The DNA-binding domain can be phosphorylated by kinases, such as mitogen-activated protein kinases, glycogen synthase kinase-3β, and cyclin-dependent kinases. Mediators SMADs can hence interact with other signaling pathways. Another binding domain is involved in SMAD interactions with receptors, other SMADs, transcription factors, coactivators, and corepressors.

Nuclear accumulation of active SMAD complexes is correlated to the degree of receptor activation. The SMAD complexes preferentially reside in the nucleus, whereas rSMAD monomers localize to the cytoplasm. Both rSMAD phosphorylation and SMAD nuclear accumulation are maintained when receptors are active. Nuclear phosphatases dephosphorylate SMADs that then return to the cytosol. Nuclear accumulation of SMADs during active signaling then overcomes SMAD dephosphorylation. In the absence of signal, SMADs travel continuously between the cytoplasm and the nucleus. However, SMADs are exported from the nucleus faster than they are imported.

Inhibitory SMADs (iSMAD) are activated by TGFβ superfamily members. They prevent TβR1 activation and dephosphorylate (inactivate) or degrade active receptors. Isoform SMAD7 can bind to SMAD-responsive elements and inhibit SMAD-dependent promoter activation. In particular, the pathways activated by TβR2 linked with ALK5 and coreceptor β-glycan on the one hand, and BMPR2 associated with a member of TGFBR1 subset 2 (ALK1-ALK3 and ALK6) and endoglin on the other hand, with their corresponding rSMAD effector, SMAD2 and -3 as well as SMAD1, -5, and -8, are inhibited by SMAD7 and SMAD6, respectively [354] .

Receptors of TGFβ can relay cues via non-SMAD pathways. The receptor TβR2 phosphorylates the polarity protein Par6 and TβR1 scaffold protein SH2 domain-containing transforming protein SHC1 [353] . In addition, TGFβ stimulates G-protein-coupled receptor kinase-2 (GRK2) that desensitizes G-protein-coupled receptors and inhibits TGFβ signaling (negative feedback loop) [365] .

Factor TGFβ also activates MAP3K7 mitogen-activated protein kinase. Enzyme MAP3K7, or TGFβ-activated kinase TAK1, phosphorylates (activates) P38MAPK and Jun N-terminal kinases, which leads to apoptosis. Factor TGFβ causes autoubiquitination and activation of tumor-necrosis factor receptor-associated factor TRAF6 that binds to TGFβR1 [366] . Ubiquitin ligase TRAF6 then ubiquitinates (activates) MAP3K7 kinase.

Factor TGFβ promotes production and association of transcription factor human immunodeficiency virus type-1 enhancer binding protein HIVEP2 (Schnurri-2 homolog) and chloride intracellular channel ClIC4, as well as their nuclear accumulation. 60 In the nucleus, ClIC4 mediates TGFβ transcriptional response by binding to SMAD2 P and SMAD3 P , hence precluding their dephosphorylation by magnesium-dependent PPM1a protein phosphatase [367] .

Growth factor TGFβ activates protein kinase-B 61 in glomerular mesangial cells via the microRNAs miR216a and miR217 that target phosphatase and tensin homolog, an inhibitor of PKB activation [368] . It intervenes in hypertrophy and survival of glomerular mesangial cells.

Signaling from TGFβ is attenuated and terminated by the activation of the TMEPAI gene, as its product transmembrane prostate androgen-induced protein (TMePAI) 62 impedes TGFβ signaling. Protein TMePAI reduces TβR1mediated phosphorylation of SMAD2 and SMAD3 effectors, as it competes with and sequesters adaptor SMAD anchor for receptor activation (SARA) 63 away from TβR1 [369] . 64 Therefore, TGFβ-induced TMePAI reduces the production of proteins from TGFβ-activated genes, such as JunB, Myc, plasminogen activator inhibitor PAI1 (or Serpin-E1), and cyclin-dependent kinase inhibitor CDKI1a.

Among the 3 isoforms, TGFβ1 is predominantly expressed in immunocytes. Transforming growth factor-β possesses both positive and negative roles in inflammation (Tables 3.16 and 3.17) . 65 In the presence of interleukin-2, immunoregulator TGFβ stimulates FoxP3+ regulatory T cells [370] . In the presence of interleukin-6, it activates T H17 cells. 66 In addition, pleiotropic cytokines TGFβ and interleukin-10 suppress the immune response.

Transforming growth factor-β [370]: (1) suppresses pro-inflammatory effector T H cell differentation (Table 3 .18); (2) converts naive T cells into 60 Cellular stress such as DNA damage causes ClIC4 nuclear translocation. Transcription factor HIVEP2 also acts in bone morphogenetic protein signaling. 61 Protein kinase-B is particularly activated by transforming growth factor-β1 in diabetic kidneys. 62 A.k.a. prostate transmembrane protein, androgen-induced PMePA1. 63 A.k.a. mother against decapentaplegic homolog-interacting protein (MADHIP), SMADIP, and zinc finger, FYVE domain-containing protein ZFYVE9. 64 Protein SARA presents inactive SMADs to the TβR1-TβR2 complex to facilitate SMAD phosphorylation and transduce the TGFβ signal. 65 Among immunocytes, T helper cells are major regulators of immune responses.

After activation by antigenic stimulation, naive TH cells differentiate into effector or regulatory T cells that are responsible for positive and negative regulation of (3) hinders the proliferation of T and B lymphocytes; (4) prevents effector cytokine production, such as interleukin-2 immunity, respectively. Autoimmune and inflammatory diseases can be caused by excess immune reactions and decreased immune suppression. 66 Interleukin-6 may suppress FoxP3 activity to strenghten the differentiation into TH17 cell with respect to induced regulatory T cells. Interleukin-6 also maintains high levels of NR1f3-2 (a.k.a. RORγ2), as the transcription factor FoxP3 hampers the transcriptional activity of NR1f3-2. Factor NR1f3-2 is activated by TGFβ and interleukin-6 to promote TH17-cell differentiation. Signal transducer and activator of transduction STAT3, which is also involved in TH17-cell differentiation, also represses FoxP3 function. In addition, interferon regulatory factor IRF4 and transcription factor MAF (V-Maf musculoaponeurotic fibrosarcoma oncogene homolog) that are upregulated by STAT3 support NR1f3-2 expression [370] . 67 After emigrating from the bone marrow, thymocyte progenitors enter the thymus. After positive selection, CD4+ or CD8+ single-positive cells migrate as naive T cells. Naturally occurring CD4+, CD25+, FoxP3+ regulatory T cells (nTReg) also develop in the thymus from immature CD4+ T cells. Dendritic cells in the presence of TGFβ and CD8+, CD205+ dendritic cells promote expansion of nTRegs and selectively repress that of effector T cells. Naive T cells are activated by antigen-presenting cells and differentiate into effector or memory T cells. IL1RA, IL1R2  IL1, IL5, IL6,  IL4, IL6  IL12, IL17, IL22, IL23 IL10, IL13, IL32, IL35 CNTF, CT1, LIF, OSM Interferons and -4 and interferon-γ; 68 and (5) inhibits macrophages, granulocytes, antigenpresenting dendritic and natural killer cells, and mastocytes.

Transforming growth factor-β and bone morphogenetic proteins are involved in lung formation and cardiomyo-and vasculogenesis as well as embryonic and adult angiogenesis in normal conditions and diseases. Bone morphogenetic protein BMP4 provokes capillary sprouting of endothelial cells. In 68 Transforming growth factor-β prevents TBx21 activity, hence Ifnγ production, on the one hand, and STAT6 function, thus IL4, on the other. In addition, upon TGFβ stimulus, the SMAD2-SMAD3-SMAD4 complex excites protein inhibitor of activated STAT1 (PIAS1) that then hinders Ifnγ transcriptional effect. Conversely, Ifnγ receptor (IfnGR1) activates STAT1. The STAT1 target genes such as SMAD7 preclude TGFβ signaling. Moreover, Ifnγ hampers TGFβ1 responses via sequestration of the nuclear coactivator P300 by STAT1, hence preventing SMAD-P300 linkage and SMAD transcriptional activity. addition, BMP2 and BMP4 exert pro-inflammatory effects on the endothelium.

Both TGFβ and BMP stimulate several microRNAs such as miR21 that favors expression of SMC contractile genes, such as smooth-muscle α-actin, calponin-1, and transgelin (or 22-kDa actin-binding smooth muscle protein SM22α) [371] .

The BMP pathway also activates the transcription of SMC-specific contractile genes, as it promotes the nuclear translocation of 2 transcription activators myocardin-related transcription factor MRTFa 69 and MRTFb (or MKL2) that interact with the transcription factor myocardin.

The activity of bone morphogenetic proteins is regulated by: (1) extracellular modulators, (2) cell-surface receptors, and (3) intracellular mediators. Extracellular BMP-binding chordin that is encoded by the gene CHRD assists in transporting BMPs. It actually protects BMPs from degradation. However, chordin is a BMP antagonist, as it interferes with interactions between BMPs and their receptors.

Several BMP inhibitors exist in addition to chordin, such as the ubiquitous, activin-binding, glycoproteic, autocrine regulator follistatin 70 (encoded by the FST gene), noggin (encoded by the gene NOG), and sclerostin (produced by osteoclasts from the SOST gene).

BMP endothelial cell precursor-derived regulator (BMPER) is an extracellular BMP modulator that controls BMP4 activity in endothelial cells, such as sprouting and migration. Regulator BMPER is not strongly diffusible, thereby accumulating BMP activity where it localizes. Synthesis of BMPER is activated by the transcription factor Krüppel-like factor KLF15 [372]. Endothelin-1 that operates via its receptor ET B is a potent inhibitor of KLF15 and, hence, BMPER production in endothelial cells.

In response to vascular injury, vascular smooth muscle cell experiences a phenotype change from a quiescent contractile to a proliferative phenotype. Both bone morphogenetic proteins and transforming growth factor-β promote the contractile phenotype, whereas platelet-derived growth factor-BB favors a switch to the proliferative phenotype. Factor PDGFbb stimulates miR24 that impedes activity of Tribbles-like protein Trb3 that is associated with reduced BMP and TGFβ signaling to prevent resulting inhibition of proliferation and migration of vascular smooth muscle cells [371] . In addition, PDGFbb suppresses the activity of myocardin, a smooth muscle and myocardium-specific transcriptional coactivator of serum response factor. Furthermore, PDGFbb induces the expression of miR221 that impedes those of SCFR receptor and cyclin-dependent kinase inhibitor CKI1b. Downregulation of SCFR lowers myocardin activity, whereas that of cyclin-dependent kinase inhibitor CKI1b promotes proliferation. 70 A.k.a. follicle-stimulating hormone-suppressing protein. 

Vascular endothelial growth factor (VEGF) 71 regulates the development of vascular endothelia and endocardium. It increases nitric oxide activity that stimulates endothelial proliferation via the protein kinase-G pathway. It permanently acts on endothelial cells to maintain the vasculature in a suitable state. Inhibition of vascular endothelial growth factor indeed causes capillary regression associated with endothelial fenestrations [373] . The VEGF family consists of 5 members ( Table 3 .19) that include VEGF isoforms (VEGFa-VEGFd encoded by the genes VegfA-VegfD) 72 and placental growth factor (PlGF). Vascular endothelial growth factor VEGFa (or VEGF) is considered as the master regulator of angiogenesis and vascular permeability. Isoform VEGFa is a mitogen for endothelial cells involved in vasculo-and angiogenesis, whereas other VEGF isoforms contribute to lymphangiogenesis.

The balance between different alternatively spliced VEGFa variants regulates vessel growth and patterning. In humans, the alternative splicing of a single precursor mRNA gives rise to 4 VEGFa products: VEGF 121 and 71 A.k.a. vascular permeability factor. Vessel wall fenestrations induced by VEGFa (distinguished from other isoforms [VEGFb-VEGFd]) allow leakage of small molecules. Large substances are transported via caveolae, vesiculovacuolar organelles, and transendothelial pores. Permeability created by VEGFa depends on nitric oxide. 72 The gene VegfD is also termed Fos-induced growth factor gene (Figf). Proteins related to VEGFs comprise those encoded by viruses (VEGFe) and those found in the venom of some snakes (VEGFf).

VEGF 165 isoforms are secreted as homodimeric glycoproteins; VEGF 189 and VEGF 206 isoforms are bound to extracellular matrix constituents. The concentration of vascular endothelial growth factor VEGFa evolves in a limited range during development. 73 The transcriptional coactivator and histone acetyltransferase P300 stimulates the production of VEGFa.

Concentrations of circulating vascular endothelial growth factor-A and hepatocyte growth factor are higher in women and smokers [374] . They are also correlated with mean flow velocity in brachial artery and body mass index. On the other hand, plasmatic level of soluble receptor VEGFR1 is lower in women and smokers.

Isoform VEGFa interacts with the Notch pathway (Vol. 3 -Chap. 10. Morphogen Receptors). Delta-like (Notch) ligand DLL4 is expressed in response to VEGFa. On the other hand, Notch activated by DLL4 suppresses the expression of VEGFR2 [375] . Ligand DLL4 is thus expressed in VEGFactivated endothelial cells that are selected for sprouting, whereas neighboring Notch-activated cells remain quiescent.

Furthermore, VEGFa reduces DNA methylation in the promoter regions of the genes of octamer-binding transcription factor Oct4 74 and Reduced expression protein REx1 75 in endothelial progenitor cells [376] . In addition, VEGF hinders the production of miR101, thereby counteracting the repression by miR101 of the histone methyltransferase enhancer of zeste homolog EZH2 of the Polycomb group family. 76

Vascular endothelial growth factor VEGFb is expressed in the heart, skeletal muscle, and adipose tissue, as well as smooth muscle cells in adults. Two different VEGFb subtypes exist: heparin-binding VEGFb 167 and diffusible VEGFb 186 .

Unlike other VEGF family members, in most conditions, vascular endothelial growth factor-B does not markedly influence angiogenesis and blood vessel permeability. It can even be anti-angiogenic. Isoform VEGFb is rather involved in the maintenance of newly formed blood vessels. Although VEGFb is dispensable for growth of blood vessels, it is critical for their survival [377] . Moreover, survival effect of VEGFb is exerted not only on vascular endothelial cells, but also on pericytes, smooth muscle cells, and vascular stem and progenitor cells. Therefore, VEGFb targets vascular cells of the blood-wall interface as well as coverage cells of blood vessels of various bore (pericytes and smooth muscle cells).

73 A single VEGFa allele as well as a 2-fold increase impede a normal development. 74 A.k.a. Oct3 and POU domain, class-5, transcription factor POU5F1. 75 A.k.a. zinc finger protein ZFP42. 76 A.k.a. lysine N-methyltransferase KMT6.

Factor VEGFb, indeed, regulates the expression of many vascular prosurvival genes via both receptors VEGFR1 and neuropilin Nrp1, a receptor for semaphorins (or collapsins). 77 Isoform VEGFb is poorly angiogenic in most tissues. On the other hand, dietary lipids in the blood circulation must be transported through the vascular endothelium to be metabolized by cells. Isotype VEGFb abounds particularly in tissues enriched in mitochondria that use fatty acids as a chemical energy source, such as the heart, skeletal muscles, and brown adipose tissue [378] . In endothelial cells, VEGFb regulates the fatty acid transport. It indeed augments the abundance of fatty acid transport proteins (FATP) via VEGFR1 and neuropilin-1 [378]. Overexpression of FATP3 or FATP4 raises uptake of long-chain fatty acids.

Vascular endothelial growth factor-C participates in angio-and lymphangiogenesis. It also contributes to endothelial cell growth and survival. Moreover, it can influence the permeability of blood vessels. Secreted VEGFc undergoes a proteolytic maturation and generates multiple processed forms which bind and activate VEGFR3 receptors. Only the fully processed form can bind and activate VEGFR2 receptors.

The 2 isoforms VEGFc and VEGFd constitute a subfamily of VEGF proteins. Both VEGFc and VEGFd are secreted as propeptides. The Ser peptidase plasmin cleaves both propeptides [379] . Enzymatic cleavage gives rise to their mature forms. Dimers of the central VEGF homology domain (VHD that spans about one-third of the VEGFc precursor) bind receptors with much greater affinity than the full-length forms. They can signal via VEGFR2 and VEGFR3 receptors that launch programs for angio-and lymphangiogenesis, respectively.

Lymphangiogenic factors VEGFc and VEGFd are synthesized by activated tumor-associated macrophages to promote peritumoral lymphangiogenesis [380] . These cells also produce VEGFc-and VEGFd-specific VEGFR3 receptor. These cells derive from circulating monocytes that do not express VEGFc and VEGFd isoforms. Once stimulated by various factors, such as tumor-necrosis factor-α and VEGFd, these monocytes start to synthesize VEGFc.

Vascular endothelial growth factor-D is secreted and undergoes a proteolytic maturation. The primary gene product has long N-and C-termini. 77 Semaphorins constitute a large family of secreted, transmembrane, and membrane-associated glycosyl-phosphatidylinositol (GPI)-anchored proteins that convey information in the immune system and during organogenesis, particularly neuro-, vasculo-, and angiogenesis.

Proteolytic processing releases the central VEGF homology domain (VHD) that binds and activates VEGFRs. In fact, multiple resulting forms bind and activate VEGFR2 and VEGFR3 receptors. In adult humans, VEGFd reaches its highest levels in heart, lung, skeletal muscle, and intestinal tract. It serves as a mitogen for endothelial cells.

Lymphangiogenic factors VEGFc and VEGFd cause the migration of microvascular endothelial cells that produce α 9 β 1 integrins and VEGFR3 [381].

Placental growth factor was initially described in placenta, but it is produced in other organs, such as lungs and heart. 78 In humans, the PLGF gene leads to 4 isoforms (PlGF1-PlGF4) by alternative splicing. These PlGF isoforms differ in binding affinities and secretion modalities [382] . Factor PlGF can form heterodimers with VEGF, hence increasing VEGF-induced chemotaxis of endothelial cells. It is a pleiotropic cytokine with pro-inflammatory and -angiogenic activities. It promotes infiltration of macrophages and T lymphocytes in tissues.

Factor PlGF binds to VEGF receptor-1 (VEGFR1) and to one of its semaphorin-related coreceptor neuropilins Nrp1, besides Nrp2 and heparan sulfate proteoglycans that can favor retention of lipoproteins [382] . Isoform PlGF2 augments the expression of vascular cell adhesion molecule VCAM1 at the luminal side of endothelial cells to promote monocyte adhesion and rolling [383].

Receptor Tyr kinases of VEGF (Vol. 3 -Chap. 8. Receptor Kinases) are encoded by the Fms-like Tyr kinase (Flt) gene family. 79 The Flt1 gene encodes vascular endothelial growth factor receptor-1 (VEGFR1). 80 The Flt4 gene encodes VEGFR3 for VEGFc and VEGFd that are involved in lymphangiogenesis and maintenance of the lymphatic endothelium. Vascular endothelial growth factor receptor-2 81 is encoded by the Kdr gene. Subtype VEGFa is a ligand for both VEGFR1 and VEGFR2; VEGFb for VEGFR1 and neuropilin-1. 82 As VEGFa binds to both VEGFR1 and VEGFR2, it stimulates endothelial cell proliferation, migration, and survival for angiogenesis as well as vascular permeability.

Receptors VEGFRs have distinct functions in the growth regulation of blood and lymph vessels. Some VEGF receptor subtypes that are mainly observed on lymphatic endothelial cells are activated neither by VEGFa nor VEGFb, but VEGFc [384] . Isoform VEGFc provokes the proliferation of the lymphatic vessels, but not blood vessels. Subtype VEGFd is also able to trigger growth of lymphatic vessels [385] .

Protein VEGF leads to phosphorylation of protein kinase-B and endothelial nitric oxide synthase (NOS3) in arterioles. Phosphorylation by VEGF of PKB, but not NOS3, is significantly reduced in coronary arterioles of old rats with respect to that of young rats. Decay in flow-induced vasodilation in coronary arterioles with aging involves the VEGFR2-phosphatidylinositol 3-kinase-PKB pathway [386] .

Vascular endothelial cells continuously perceive mechanical and chemical stimuli and coordinate the activity of the corresponding signaling pathways. Once stimulated by chemicals, VEGF quickly binds VEGFR2, recruiting in particular adaptor NCKβ to trigger the mitogen-activated protein kinase (MAPK; Vol. 3 -Chap. 5. Mitogen-Activated Protein Kinase Modules) pathway. 83 Mechanical stimuli, such as wall shear stress, activate similar plasmalemmal targets (e.g., integrins and VEGFR2) and effectors (e.g., extracellular signal-regulated protein kinases and Jun N-terminal kinases). These convergent modules of the pathway triggered by mechanical and chemical stimuli then require insulation by different molecular complexes to keep their specificity, i.e., to possess divergent modules responsible for the specific response to different stimuli. VEGF, but not shear stress, induces the formation of a VEGFR2-NCKβ complex (Fig. 3.3) [387]. The wall shear stress activates extracellular signal-regulated protein kinase via VEGFR2 and recruitment of CBL adaptor, but not NCKβ. 84 It bypasses VEGFR2 phosphorylation for JNK activation, but uses small GTPases Rho, and Src, PI3K, and RoCK kinases. Angiogenesis is achieved by the concerted migration and proliferation of endothelial and mural cells (pericytes and vascular smooth muscle cells). Endothelial cells form new vessels, whereas mural cells support and stabilize nascent vessels. However, upon stimulation of mural cells by PDGF to initiate angiogenesis by releasing pro-angiogenic mediators, in the presence of synergistic stimulation of VEGF and PDGF, VEGF is able to impede neovessel maturation, as it can ablate pericyte coverage of nascent vascular sprouts and hence destabilize these nascent vessels [388] . During PDGF-VEGF costimulation, VEGF activates VEGFR2 that suppresses PDGFRβ signaling in vascular smooth muscle cells, as VEGF induces the formation of VEGFR2-PDGFRβ complex. Dual expression of PDGFRβ and VEGFR2 is limited to α-smooth muscle actin+ perivascular cells. Inhibition of VEGFR2 prevents assembly of this receptor complex. In the case of joint exposure to both VEGF and PDGF, an antagonistic competition occurs between these 2 factors, as they both combine with FGF2. Tumors express high VEGF levels and develop tortuous, leaky, immature blood vessels with minimal pericyte coverage due to coexpression of VEGFR2 and PDGFRβ on perivascular cells. Anti-VEGF therapy normalizes tumor vasculature, hence accelerating tumor growth, but allows efficient delivery of cytotoxic agents.

Certain organs such as kidneys (especially glomerular endothelial cells) constitutively express VEGF in adulthood. Glomerular VEGF is increased in response to hypertension and activation of the renin-angiotensin system [389] . VEGF upregulation can correspond to adaptation to hypertension, as VEGF increases expression of endothelial nitric oxide synthase. Table 3 .20. VEGF signaling in cardiomyocytes (Source: [391] ). Copper heigthens the VEGFR1-to-VEGFR2 ratio (DAG: diacylglycerol; ERK: extracellular-regulated kinase; GRB: growth factor receptor-bound protein; IP3: inositol trisphosphate; MAP2K: mitogen-activated protein kinase kinase; PKC: protein kinase-C; PKG: cGMP-dependent protein kinase; PLC: phospholipase-C; SOS: Son of sevenless; SHC: Src homology and collagen-like protein).

Proliferation VEGFR2-SHC-GRB2-SOS-Ras-Raf-MAP2K1/2-ERK1/2 CMC growth VEGFR2-PLCγ-DAG/IP3-PKC-ERK1/2 Regression of VEGFR1-PKG1 hypertrophy

Endothelial growth factor receptors are differentially expressed in distinct types of vessels in the human heart. Endothelial receptor Tyr kinases include 3 members of the vascular endothelial growth factor receptor family and 2 members of the angiopoietin receptor (TIE) family. In addition, VEGF 165 isoform binds to semaphorin receptor neuropilin-1. In human fetal hearts, the endocardium contains VEGFR1, VEGFR2, Nrp1, TIE1, and TIE2, but not VEGFR3 [390] . Superficial coronary vessels possess VEGFR1, Nrp1, Tie1, and Tie2, but neither VEGFR2 nor VEGFR3. Myocardial capillaries and epicardial blood vessels possess VEGFR1, VEGFR2, Nrp1, and Tie1 (weakly Tie2). Epicardial lymphatic vessels are labeled by VEGFR2 and VEGFR3 (weakly Tie1 and Tie2), but neither VEGFR1 nor Nrp1 receptor. Besides, endothelial and smooth muscle cells as well as cardiomyocytes develop from a common VEGFR2+ cardiovascular progenitor. Vascular endothelial growth factor binds to its receptors to participate in cardiovascular development, as it favors stem cell differentiation into cardiomyocytes as well as stem cell migration and survival [391] . In adults, because it activates mitogen-activated protein kinases, it can elicit re-entry of cardiomyocytes into the cell division cycle, thereby promoting cardiac adaptive (due to repeated exercises) and maladaptive (in response to pressure overload) hypertrophy.

In mouse myocardium, VEGFR1-specific ligand VEGFb 186 and VEGFR2specific agonist VEGFe are equally potent in inducing angiogenesis, but less efficient than VEGFa 165 that stimulates both VEGFR1 and VEGFR2 [392] .

In cardiomyocytes, VEGF causes cardiac hypertrophy or regression according to the prevalent binding to VEGFR2 or VEGFR1, respectively [391] . Copper increases the ratio of VEGFR1 to VEGFR2, hence switching VEGF signaling from cell growth to reversal of cardiomyocyte hypertrophy via cGMP-dependent protein kinase PKG1 [391] (Table 3 .20).

Midkine (mid-gestation and kidney protein [MdK]), or neurite growth-promoting factor-2 (NeGF2), 85 and pleiotrophin (Ptn or NeGF1) 86 constitute the NEGF family. Midkine is strongly produced during mid-gestation. Midkine and pleiotrophin expression is restricted in adults.

Midkine and pleiotrophin are pleiotropic, as they act in cell proliferation, survival, and migration, especially during angiogenesis and neurogenesis, as well as inflammation and fibrinolysis in vascular endothelia [393] . They also operate in epithelial-mesenchymal interactions during organogenesis.

Both midkine and pleiotrophin bind to transmembrane receptor Tyr kinase anaplastic lymphoma kinase [394] (ALK; Vol. 3 -Chap. 8. Receptor Kinases). Midkine targets a complex formed by chondroitin sulfate proteoglycan, receptor protein Tyr phosphatase PTPRb (PTPζ), low-density lipoprotein receptor-related protein (LRP), anaplastic leukemia kinase, and syndecans [393] . Signaling mediators of both midkine and pleiotrophin include phosphatidylinositol 3-kinase and mitogen-activated protein kinase.

In endothelial cells associated with smooth muscle cells, midkine not only increases their proliferation rate, but also synthesis of glycosaminoglycan [395] . Interaction between endothelial and smooth muscle cells is required.

Upon exposure to midkine, synthesis of interleukin-8 by smooth muscle cells rises. Once secreted, IL8 can act on endothelial cells (paracrine regulation). In addition, midkine and pleiotrophin are upregulated during ischemia. Midkine is also involved in intimal hyperplasia.

Semaphorins form a family of membrane-bound and secreted proteins that are short-range repulsive cues for endothelial cells during angiogenesis and for neurons during neurogenesis. They prevent axons to develop toward inappropriate regions. In particular, semaphorin-3 controls both axon guidance and angiogenesis. Semaphorins also intervene in immune defense, cardiogenesis, and osteogenesis.

There are 8 classes of semaphorins. Class-1 and -2 semaphorins exist in invertebrates only, class-5 semaphorins are specific to virus and observed in both vertebrates and invertebrates, and class-3, -4, -6, and -7 semaphorins in vertebrates only. In humans, they are encoded by the genes SEMA3A to SEMA3G, 85 A.k.a. retinoic acid-inducible heparin-binding protein (RIHB) and amphiregulinassociated protein (ARAP). This alias is also used for ArfGAP with RhoGAP, ankyrin repeat, PH domains. 86 A.k.a. heparin-binding brain mitogen [HBBM], heparin-binding growthassociated molecule [HBGAM], heparin-binding growth factor HBGF8, and osteoblast-specific factor OSF1.

SEMA4A to SEMA4G, SEMA5A and SEMA5B, SEMA6A to SEMA6D, and SEMA7A. Semaphorins signal via the plasmalemmal receptors plexins and neuropilins. In fact, many semaphorins interact with receptor complexes that are formed by neuropilins and plexins. However, semaphorin-3E can signal independently of neuropilin via plexin-D1 that is expressed in endothelial cells. Loss of plexin-D1 causes aberrant sprouting. Plexin-A1 is the principal receptor component for class-3 and -4 semaphorins. Independently of neuropilin, plexin-A1 operates in neurogenesis and cardiogenesis as a receptor for class-6 semaphorins (Sema6c and Sema6d).

Neuropilin-1 (Nrp1) is a coreceptor for semaphorin-3A and vascular endothelial growth factor-A that acts with VEGFR2, both in vascular endothelial and smooth muscle cells. 87 Neuropilin-1 increases VEGF binding in both vascular endothelial and smooth muscle cells, in which it regulates VEGFR2 expression. Neuropilin-1 enhances VEGF signaling in endothelial cells, whereas it hinders VEGF activity in smooth muscle cells. Neuropilin-1 is also targeted by heparan sulfate or chondroitin sulfate [396] .

Several semaphorins are costimulators that favor the activation of B and T lymphocytes, macrophages, and dendritic cells. In the immune system, plexin-A1 is expressed specifically in dendritic cells. Dendritic cells are antigenpresenting cells that reside in tissues as sentinels and move to ensure their immune role at the right site at the appropriate instant. After antigen exposure, they enter into lymphatics and migrate to lymphoid organs, where they activate T lymphocytes. Plexin-A1 is required for the entry of dendritic cells into lymphatics [397] . Semaphorin-3A produced by lymphatic cells, but neither Sema6c nor Sema6d, is involved in the transmigration of dendritic cells through the lymphatic endothelium. Semaphorin-3A promotes phosphorylation of the myosin light chain, hence actomyosin contraction at the trailing edge of migrating dendritic cells.

Angioneurins constitute a group of substances that influence both neural and vascular cell fate, especially survival and growth, as they are both neurotrophic and angiogenic factors [398] . Neurovascular crosstalk uses common signaling pathways, such as Notch cues. Angioneurins are secreted by endothelial cells, neural stem cells, and astrocytes.

Angioneurins not only support neuroregeneration, but also prevent neurodegeneration. 88 Angioneurins protect neurons from ischemia and control 87 The composition of Nrp1 glycosaminoglycan chains differs between endothelial cells and smooth muscle cells. These cell types then differentially respond to VEGF and neuropilin. 88 Several neurodegenerative disorders (Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, etc.) are characterized by vascular defects. Neurotrophic and Nerve growth factor, brain-derived neurotrophic factor, axon-guidance neurotrophin NT3 and NT4, factors semaphorins and neuropilin receptors, netrins, slits, ephrins

Angiogenic factors Vascular endothelial growth factor-A, -B, and -C, fibroblast growth factor-2, platelet-derived growth factor, transforming growth factor-β1, insulin-like growth factor-1, hepatocyte growth factor, epidermal growth factor, angiogenins, angiopoietin-1, progranulin the blood-brain barrier integrity. They also promote neurogenesis, because they influence synaptic transmission, stimulate axon sprouting, neurite extension and branching, and elicit myelination or remyelination via migration and proliferation of Schwann cells.

Many molecules act on the development of both the nervous and vascular systems. Neurogenic and angiogenic factors guide blood vessels and nerves along predestined tracks to their final destination during genesis. Vascular endothelial growth factor-A controls both angiogenesis and neurogenesis. The VEGFa isoform enhances vascular perfusion and promotes the survival of multiple types of neurons, as well as astrocytes and microglial cells. Brainderived neurotrophic factor (BDNF) acting via its receptor NTRK2 on endothelial cells stimulates angiogenesis in the heart, skeletal muscle, and skin, and maintains the stability of cardiac vessel walls during development. Neurotrophin NT4 binds to NTRK2 and has similar functions. Neurotrophin NT3 that binds to NTRK3 and leukemia-inhibitory factor (LIF) of the interleukin-6 family to inhibit the growth of some endothelial cells. Nerve growth factor (NGF) increases VEGF expression and enhances vascular cell growth. Ciliary neurotrophic factor (CNF) and glial-cell-line-derived neurotrophic factor (GDNF) do not act on angiogenesis.

Fibroblast growth factor FGF2, transforming growth factor TGFβ1, and hepatocyte growth factor ensure the integrity of the blood-brain barrier. FGF2 acts on astrocyte architecture and HGF and FGF2 upregulate tightjunction proteins. Angiopoietin-1, stromal-derived factor-1α, and vascular endothelial growth factor are synthesized by endothelial cells to release neurogenic factors, such as neurotrophins and BDNF. Astrocytes secrete FGF2, IGF1, and VEGF that target neural stem cells. Erythropoietin is also involved.

Adrenomedullin is a peptide discovered in 1993 in pheochromocytoma in adrenal medulla [399] . Mature active adrenomedullin shares moderate structural similarity to the calcitonin family of regulatory peptides (amylin, calcitonin, and calcitonin gene-related protein).

The main sources of plasma adrenomedullin are vascular endothelial and smooth muscle cells. Adrenomedullin is also expressed in adventitial fibroblasts. Adrenomedullin circulates in blood in high concentrations. Circulating adrenomedullin (plasma half-life 22 mn) includes mature, amidated and predominant, inactive, glycated form.

Adrenal cells secrete adrenomedullin as well as proadrenomedullin peptide (PAMP). The PAMP peptide causes a dose-dependent elevated release of all steroids (aldosterone, cortisol, and dehydroepiandrosterone). On the other hand, adrenomedullin only increases aldosterone and cortisol secretion, but not that of dehydroepiandrosterone [400] .

Both adrenomedullin and PAMP can act as auto-and paracrine regulators of adrenal steroid secretion. Moreover, PAMP, but not adrenomedullin, is an inhibitor of adrenal catecholamine release in vivo [401] .

The human adrenomedullin gene (AM) 89 encodes a 185-amino acid precursor peptide that can be differentially cleaved to form 52-amino acid adrenomedullin and various peptides: adrenomedullin fragments AM 22−−52 and AM 95−−146 and adrenotensin.

Oxidative stress increases adrenomedullin production. The blood concentration of adrenomedullin increases in cardiovascular diseases, such as atheroma, heart failure, hypertension, and septic shock [402] . Adrenomedullin protects against progression of vascular damage and maladaptive remodeling.

Adrenomedullin binds to heterodimers formed by calitonin receptor-like receptor (CalcLR) and receptor activity-modifying protein (RAMP), 90 as well as calcitonin gene-related protein receptors (Vol. 3 -Chap. 7. G-Protein-Coupled Receptors).

Adrenomedullin stimulation produces cyclic adenosine monophosphate and nitric oxide. It indeed activates adenylyl cyclase and nitric oxide synthase [403] . In fact, adrenomedullin stimulates inducible nitric oxide synthase NOS2 in interleukin-1β-stimulated vascular smooth muscle cells via, at least partly, a cAMP-dependent pathway.

Ventriculomyocytes and fibroblasts also produce adrenomedullin [404] . Cytokines, such as IL1β and TNFα, regulate its synthesis and secretion in the cardiac ventricles.

Adrenomedullin is a potent and long-lasting vasodilator that is able to initiate hypotension, as it reduces peripheral resistances. Reduction in arterial 89 The AM gene is located on chromosome 11 with 4 exons and 3 introns. It is expressed in most organs. 90 Receptor activity-modifying protein RAMP2 has a higher affinity than RAMP3 protein.

pressure is associated with a rise in cardiac output, as adrenomedullin has positive inotropic effect. Adrenomedullin attenuates the effect of angiotensin-2, but not that of noradrenaline. In addition, it increases plasma renin activity, but impedes an angiotensin-2-induced rise in plasma aldosterone level [405] .

Adrenomedullin lowers oxidative stress and prevents endothelial cell apoptosis. It also regulates endothelial permeability and stabilizes the endothelial barrier [406] . It diminishes thrombin-and H 2 O 2 -induced myosin light-chain phosphorylation as well as stress fiber formation and gap formation in cultured human umbilical vein endothelial cells.

Adrenomedullin contributes to the differentiation of bone marrow-derived mononuclear cells into endothelial progenitors [407] . It favors survival, adhesion, and differentiation of transplanted mononuclear cells.

Adrenomedullin hinders the expression of hepatocyte growth factor and cyclooxygenase-2 in gastric mucosa via CGRP receptors [408] .

Adrenomedullin works via CalcLR-RAMP2 complex, cAMP, and phosphorylated extracellular signal-regulated kinases during vasculogenesis and lymphangiogenesis (Vol. 5 -Chap. 10. Vasculature Growth). This lymphatic growth factor promotes also lymphangiogenesis after injury [409] .

Prospero-related homeobox transcription factor Prox1 that is specific to venous and lymphatic endothelial cells upregulates CalcRL receptor. In venous endothelium, Prox1 controls the transition from venous to lymphatic endothelial cells and lymphatic sprouting from veins. Adrenomedullin elicits proliferation, migration, and lymph vessel formation of cultured human lymphatic endothelial cells. In injury sites, adrenomedullin increases the number of both lymphatic and blood vessels, at least partly, via the cAMP-ERK pathway.

Progranulin (PGrn) 91 is a pleiotropic, cysteine-rich growth factor 92 that is glycosylated In the central nervous system, this neurotrophic factor is synthesized by microglial cells and neurons. 95 It is also produced by epithelial cells, especially those of rapidly cycling epithelia (skin and gastrointestinal and reproductive tracts), and much less strongly in weakly proliferating epithelia (lung alveoli and nephron) [413] . It is expressed by mesenchymal cells such as fibroblasts 96 and chondrocytes, as well as leukocytes, particularly immunocytes [413] . 97 This multifunctional, secreted protein mediates cell cycle progression and cell motility. It is indeed manufactured during tissue development and remodeling. In particular, this autocrine growth factor is a potent mitogen for fibroblasts. It increases the expression of cyclin-D and -B. Progranulin binds the matrix proteins perlecan and chondrocyte oligomeric matrix protein (COMP) [414] . Perlecan decreases the proliferative activity of progranulin, whereas COMP fosters it.

Progranulin is implicated not only in embryo-and fetogenesis, but also in tissue repair and inflammation. Overproduction provokes tumorigenesis. Progranulin is involved in inflammation with secretory leukocyte peptidase inhibitor (SLPI) 98 produced by macrophages and neutrophils that binds to and protects it from proteolysis [411] . It interacts also with elastase released in large quantities by neutrophils that cleaves it into smaller peptides. Agent SLPI indeed binds directly to both progranulin and elastase. Hence, anti-inflammatory effect of progranulin is protected by its binding partners, not only secretory leukocyte peptidase inhibitor, but also apolipoprotein-A1. Yet, during inflammation, neutrophils and macrophages release peptidases that digest progranulin into granulins. Granulins can neutralize the antiinflammatory effects of progranulin.

Progranulin is a potent inhibitor of the inflammatory cytokine tumornecrosis factor-α. It actually binds directly to the tumor-necrosis factor receptor and antagonizes the TNFα-TNFR interaction, thereby preventing TNFαinitiated signaling [410] . 95 Progranulin is highly expressed in specific subsets of neurons, such as cortical neurons, Purkinje cells of the cerebellum, and granule cells of the hippocampus [413] . Mutations in the PGRN gene cause frontotemporal lobar degeneration [411]. 96 Progranulin is not or weakly detected in most mesenchymal tissues, such as connective and adipose tissues, cardiac, skeletal, and smooth muscle, and vascular conduits [413] . 97 Progranulin is highly expressed in lymphoid tissues of the lung, gut, and spleen.

In the spleen, the progranulin transcript is confined mainly to marginal cells of the periarteriolar lymphoid sheath (PALS). 98 A.k.a. antileukoproteinase (ALP), mucus peptidase inhibitor (MPI), seminal peptidase inhibitor, and WAP four-disulfide core domain-containing protein WAP4 and WFDC4.

Progranulin contributes to wound healing, during which it promotes angiogenesis [412] . This paracrine factor stimulates proliferation and migration of fibroblasts and endothelial cells. 99 Progranulin activates the extracellular-regulated kinase modules and the PI3K-PKB and PI3K-S6K cascades [414] . It promotes phosphorylation of focal adhesion kinase, hence cell motility.

Prokineticins are small, secreted chemokine-like peptides that constitute a family of 2 known members: prokineticin-1 and -2. They signal via 2 ubiquitous Gq-coupled prokineticin receptors PKR1 (PK 1 ) and PKR2 (PK 2 ) [415]. Prokineticin-1 and -2 as well as PKR1 are synthesized in the human myocardium by endothelial cells and cardiomyocytes [416] .

Prokineticins and their receptors are also highly expressed in bone marrow cells, circulating leukocytes, and peripheral immunocytes. They act as cytokines [417] . Prokineticin-2 is a more potent ligand at both PKR1 and PKR2 than prokineticin-1.

Prokineticins promote proliferation and differentiation of granulocytic and monocytic cell lineages in bone marrow. They also stimulate gut smooth muscle contraction, especially in myenteric and submucosal enteric plexuses of proximal colon.

Prokineticin-1 elicits angiogenesis in various endocrine glands [418] . 100 Signaling via Gq and G13 indeed contributes to vessel formation.

The receptor PKR1 favors cardiomyocyte survival and reduces hypoxiainduced apoptosis. Signaling via Gα q/11 regulates the cardiac development and hypertrophy. Other Gq-coupled receptors are involved in cardiomyocyte protection.

Overexpression of PKR1 by cardiomyocytes upregulates prokineticin-2 that has paracrine activity and provokes the proliferation and differentiation of epicardial-derived progenitor cells [419] . The receptor PKR1 also enhances the proliferation of endothelial cells in the myocardium. Moreover, PKR1 in coronary endothelial cells favors the postnatal coronary angiogenesis.

On the other hand, PKR2 overexpression by cardiomyocytes causes: (1) cardiac hypertrophy with increased sarcomere numbers and without dysfunction (autocrine activity) and (2) abnormal endothelial cell shape with altered distribution of tight junction protein zona occludens-1 (Vol. 1 -Chap. 7. Plasma Membrane) that leads to endothelial fenestrations and vascular leakage (paracrine activity) without angiogenesis [420] . 99 Although quiescent fibroblasts and endothelial cells synthesize low amounts of progranulin, these cells can rapidly raise their production when they deploy a tissue remodeling program with elevated cell proliferation and migration. 100 Hence its original name endocrine gland-derived vascular endothelial growth factor (egVEGF).

Prokineticin-2 expression depends on light entrainment in the suprachiasmatic nucleus of hypothalamus. The gene PK2 is controlled by the circadian clock (Chap. 5) and its transcription is modulated by light [421] . It transmits circadian rhythm with a positive feeback on its expression and operates as an output for the circadian locomotor rhythm. In the central nervous system, prokineticin-2 is also involved in olfactory bulb morphogenesis that persists in adult brain [422].

Melatonin is synthesized and released into the circulation by the epiphysis (epiphysis cerebri), or pineal gland, under the control of the circadian clock. Exogenous melatonin does not modify the cardiac frequency and mean arterial pressure, as well as the cerebral blood flow. However, it influences the blood flow distribution. The blood flow renal blood flow velocity lowers after the ingestion of melatonin with respect to administration of sucrose (40.5 ± 2.9 vs. 45.4 ± 1.5 cm/s) [423] . On the other hand, the forearm blood flow rises upon melatonin stimulation (2.4 ± 0.2 vs. 1.9 ± 0.1 ml×100 ml/mn). Renal vasoconstriction results from a melatonin-mediated increase of the sympathetic input to the renal arterial bed.

Sphingosine 1-phosphate (S1P) is an active metabolite of sphingolipids at the plasma membrane that acts as a lipid growth factor. Sphingosine 1-phosphate has a short life, as it is degraded by plasmalemmal S1P lyase or dephosphorylated by plasmalemmal S1P phosphatase.

Sphingolipids in cholesterol-enriched membrane rafts are rapidly metabolized upon stimulation of plasmalemmal receptors that convert sphingomyelin and glycosphingolipids to ceramide by sphingomyelinases and subsequently to sphingosine (Sph) by ceramidases. Sphingosine kinases SphK1 and SphK2 phosphorylate sphingosine to generate lysosphingolipid.

Sphingosine 1-phosphate has a cell-intrinsic (e.g., acts on calcium flux) and -extrinsic activity via cognate G-protein-coupled receptors (S1PR1-S1PR5 or S1P 1 -S1P 5 ; Vol. 3 -Chap. 7. G-Protein-Coupled Receptors). It is exported from producing cells by ATP-binding cassette or other transporters.

Among its intrinsic effects, sphingosine 1-phosphate participates in TNFα signaling and NFκB activation in anti-apoptotic, inflammatory, and immune processes. Ubiquitin ligase tumor-necrosis factor receptor-associated factor TRAF2 is involved in polyubiquitination of TNFRSF receptor-interacting kinase RIPK1 that then recruits and stimulates IκB kinase to activate the transcription factor NFκB. It binds to sphingosine kinase-1 as well as sphingosine 1-phosphate [424] . The latter, which stimulates the ligase activity of TRAF2, is required for Lys63-linked polyubiquitination of RIPK1, thereby preventing RIPK1 switching from a prosurvival to pro-apoptotic adaptor.

Blood concentration of S1P (in the low-micromolar range) is mainly determined by the secretion from erythocytes and endothelial cells. Free and albumin-bound S1P are more easily degraded than high-density lipoproteinbound S1P.

Tissular concentration of S1P is low compared with that in lymph (in the hundred-nanomolar range) and blood. Sphingosine 1-phosphate is also secreted by platelets and mastocytes activated by thrombin or IgE-bound antigen, respectively.

Sphingosine 1-phosphate produced from phosphorylation of sphingosine of platelet membrane by sphingosine kinase, activates endothelial cells by phospholipase-D, independently of protein kinase-C and Ca ++ [425] . S1P is produced and is then secreted [426] . 101 In addition, S1P in synergy with thrombin causes tissue factor release from endothelial cells to promote blood coagulation. Secretion of S1P by platelets increases adhesion of leukocytes on the endothelium.

Endothelial cells have an intracellular reserve of functional S1P 1 receptors in caveolae. Sphingosine 1-phosphate is a ligand for some types of the family of G-protein-coupled lysosphingolipid receptors. 102 Sphingosine 1-phosphate mediates endothelial cell maturation, migration, and angiogenesis ( Fig. 3.4) . It controls vascular permeability (barrierenhancing effect), as it regulates Rho GTPases and cortical actin polymerization. 103 Moreover, S1P enhances assembling of adherens junctions and focal adhesions [429, 430] , using the Rho and Rac pathways. The S1P-S1P 1 complex also tightens adherens junctions between endothelial cells. Lipid S1P stimulates the translocation of actin-binding proteins, such as cortactin that enhances actin polymerization (whereas actin-severing proteins such as cofilin are inactivated) and myosin light-chain kinase for adhesion stabilization. It redistributes cadherin and catenin to the cell cortex, as these molecules are involved in adherens junctions.

Receptor S1P 1 is expressed by most immunocytes, whereas other receptors have a more limited distribution in the immune system. Receptors S1P 1 and S1P 4 are synthesized by T lymphocytes; S1P 1 and S1P 2 by mastocytes and macrophages; S1P 5 by dendritic and natural killer cells.

Receptor expression depends on cell differentiation stage and cell activation. Immature and mature dendritic cells mainly express S1PR4 and S1PR3, respectively. Changes in local S1P concentration could induce a switch from pro-inflammatory M1 to anti-inflammatory M2 macrophage subtypes. Signaling from S1PR1 regulates proliferation and maturation of T lymphocytes, as well as cytokine synthesis.

The development of the immune system relies, in particular, on egress of developing T lymphocytes, or thymocytes, from the thymus to organs, where they can defend against microorganisms.

Sphingosine 1-phosphate operates in immunocyte function and migration to ensure the body's immunity [431] . Receptor S1PR1 intervenes in B-and T-lymphocyte exit from lymph nodes as well as mature thymocyte egress from thymus, IgG-secreting plasmocyte from spleen, and IgA-producing B lymphocyte from Peyers patches.

The thymus is used for T-cell development and tolerance induction. Double-negative (CD4− and CD8−) precursors develop into double-positive thymocytes in the thymic cortex. Cells selected for weak recognition of major histocompatibility complexes give rise to semi-mature, single-positive (CD4+ or CD8+) thymocytes that localize to the medulla. On the other hand, strongly self-reactive, semimature, single-positive thymocytes are rejected. Cells that pass through the tolerance checkpoint undergo further maturation in the medulla.

In single-positive thymocytes, the transcription factor Krüppel-like factor KLF2 is upregulated. Therefore, KLF2 target genes are activated, such as those that encode S1P 1 and L-selectin (or CD62L). Perivascular channels that contain thymocytes in the thymus may serve as a thymocyte reservoir, in which pericyte-and vessel-derived S1P is protected from rapid degradation. Mature single-positive lymphocytes then exit the thymus.

Thymocyte exit from the thymus at corticomedullary junctions via blood vessels, rather than lymphatics (at least in mice), requires S1P detection by thymocytes [432] . Postcapillary thin-walled venules at the corticomedullary junction have relatively large caliber (10-50 μm). They possess a single layer of ensheathing α-smooth muscle actin-positive pericytes. Unlike most vascular beds, thymic blood vessels are ensheathed by neural crest-derived pericytes. These neural crest-derived pericytes release S1P for exiting thymocytes. These specialized pericytes hence promote reverse transmigration of cells across the vascular endothelium. Endothelial cells that also produce S1P can work in synergy with pericytes to elicit thymocyte egress. Lymphatics can also contribute to lymphocyte egress from the thymus.

Chemotaxis mediated by S1P depends on S1P concentration and receptor type. 104 The S1P lipid increases inflammation, as it stimulates the production of inflammatory mediators, such as interleukin-1β and tissue factor.

Sphingosine 1-phosphate activates S1PR3 on dendritic cells and S1PR2 in mastocytes, hence priming degranulation. Elevated circulating S1P concentration often raises helper-2 T-cell responses (without changing or possibly dampening T H1 cell response). 105 Differentiating dendritic cell precursors as well as activated hematopoietic stem cells and mastocytes upregulate S1P receptors. The S1PR1 receptor regulates immunocyte migration (Table 3 .22). Receptors S1PR3 and S1PR5 also regulate circulation and localization of dendritic cells and natural killer cells, respectively.

Ligands of S1PR1 sequester lymphocytes in secondary lymphoid organs. They hinder T-cell motility between medullary cords and lymphatic sinuses, mainly the migration through the endothelium of lymph nodes [433] . Expression of S1PR1 by lymphocytes is regulated via Krüppel-like factor-2, downregulated by high S1P levels and C-type lectin CLec2c (or CD69; a receptor in lymphocytes, natural killer cells, and platelets) upon lymphocyte activation.

Adipose tissue operates as an endocrine organ, as adipocytes secrete adipokines. Adipokines indeed function as hormones and cytokines. They are secreted not only by adipocytes, but also other cell types.

Adipocytes secrete numerous proteins that influence the activity of insulin receptor by auto-, para-, and endocrine mechanisms. Several adipocytederived hormones and cytokines, such as leptin, resistin, retinol-binding protein-4, tumor-necrosis factor-α and its soluble receptors sTNFR1 and sTNFR2, interleukin-1 and -6, plasminogen activator inhibitor-1, and lipocain-1 hamper insulin signaling.

On the other hand, apelin, adiponectin, chemerin, omentin, vaspin, and visfatin enhance signal transmission from insulin receptor. Elevated plasma level of leptin and resistin as well as lowered plasma concentration of adiponectin are correlated with risks of cardiovascular diseases (Table 3 .23). Table 3 .22. Sphingosine 1-phosphate receptors (S1PRi or S1Pi) in immunocytes (Source: [431] ). Receptor S1PR1 increases the chemotaxis of immunocytes, as well as S1PR5 in natural killer (NK) cells and S1PR2 in macrophages, although the latter reduces mastocyte migration.

Innate immunocytes Dendritic cell S1PR1-S1PR5 Eosinophil S1PR2-S1PR3 Macrophage S1PR1/2 Mastocyte S1PR1/2 NK cell S1PR5

Adaptive immunocytes B lymphocyte S1PR1/3 NKT cell S1PR2/4 T lymphocyte S1PR1/4 

Adiponectin 106 is synthesized mainly by adipocytes. 107 It forms homomultimers. Adiponectins exist as low-molecular-weight, full-length trimers, and 106 Necto: to bind. 107 The adiponectin gene ADIPOQ localizes to chromosomal band 3q27, a susceptibility locus for diabetes and cardiovascular disease [444] . It is also named C1q and collagen domain-containing protein, adipose most abundant gene transcript-1 (APM1), adipocyte complement-related 30-kDa protein (ACRP30), adiponec-globular cleavage fragments. The trimer can dimerize to form a mid-molecularweight hexamer. The latter can oligomerize to give rise to high-molecularweight polymers, such as 12-and 18-mers. Full-length adiponectin requires post-translational modifications (e.g., hydroxylation and glycosylation) to be active. Low-, mid-, and high-molecular-weight adiponectin complexes bind to heparin-binding EGF-like growth factor (HBEGF); hexa-and polymers to platelet-derived growth factor PDGFb; and polymers to FGF2 fibroblast growth factor. It is similar to collagen-8 and -10 as well as C1q complement factor (Sect. 3.21). Adiponectin specifically binds to collagen-1, -3, and -5 in intima of catheter-injured vessel wall [435] . Adiponectin is also produced in skeletal myocytes, hepatocytes, cardiomyocytes, and endothelial cells. Adiponectin circulates in blood at high concentrations (5-10 mg/ml). Men have lower plasma adiponectin levels than women.

Adiponectin is involved in the control of fat metabolism and insulin sensitivity, with anti-inflammatory, antidiabetic, and anti-atherogenic activities. In liver and other tissues, adiponectin raises fatty acid oxidation and reduces glucose synthesis. In myocytes, adiponectin-induced activation of cell energy sensor adenosine monophosphate-activated protein kinase stimulates phosphorylation of acetyl coenzyme-A carboxylase, glucose uptake, and fatty acid oxidation. In hepatocytes, full-length and globular adiponectin stimulates AMP-activated protein kinase phosphorylation (activation). Globular adiponectin yields this effect in skeletal myocytes, cardiomyocytes, and hepatocytes. Low-molecular-weight adiponectin, but not high-molecular-weight adiponectin, reduces lipopolysaccharide-mediated interleukin-6 release in human monocytes and represses nuclear factor-κB activation [436] . Adiponectin synthesis by adipocytes is reduced in obesity, insulin resistance, and type-2 diabetes (metabolic syndrome; Vol. 6 -Chap. 7. Vascular Diseases).

Adiponectin possesses an adaptor, phosphotyrosine interaction, PH domain, and leucine zipper containing-protein APPL1, 108 as well as 2 G-proteincoupled receptors, AdipoR1 and AdipoR2 (Vol. , that are mainly synthesized in skeletal muscle and liver, respectively. In addition, T-cadherin may contribute to adiponectin signaling. Activation of AdipoR1 and AdipoR2 by adiponectin leads to phosphorylation of AMP-activated protein kinase and its downstream target acetylCoA carboxylase.

Adiponectin promotes endothelial expression of vascular cell adhesion molecule VCAM1, intercellular adhesion molecule ICAM1, and pentraxin-3 tin serum level quantitative trait locus 1 (AdipQTL1), gelatin-binding protein-28 (GBP28), and ACDC. 108 A.k.a. Deleted in colorectal cancer (DCC)-interacting protein-13α. It is involved in crosstalk between adiponectin and insulin signaling. It binds to many proteins, such as small GTPase Rab5a, transmembrane dependence (i.e., active upon ligand binding as well as unbound) receptor DCC, and PKB2 kinase and phosphoinositide 3-kinase catalytic subunit PI3KC1Cα (encoded by the PIK3CA gene). [444]. 109 Adiponectin acts as an anti-oxidant, as it decreases reactive oxygen species. It also augments endothelial production of nitric oxide.

Adiponectin stimulates a ceramidase activity associated with its receptors AdipoR1 and AdipoR2 in cells that express both receptors to promote insulin sensitivity and cell survival and decrease inflammation [437] . It enhances ceramide catabolism and formation of anti-apoptotic sphingosine 1-phosphate. This effector explains the entire set of beneficial effects exerted by adiponectin.

Adiponectin affects gluconeogenesis and lipid catabolism. Adiponectin hinders atherosclerosis. Adiponectin favors insulin activity in the muscles and liver via activated AMPK (Table 3 .24). Nuclear receptor NR1c3, or transcription factor PPARγ, upregulates adiponectin expression and reduces the plasma concentration of TNFα. Tumor-necrosis factor-α produced in adipose tissues, prevents adiponectin synthesis. It phosphorylates insulin receptors, and hence desensitizes insulin signaling.

Epicardial adipose tissue as well as cardiomyocytes synthesize adiponectin. In cardiomyocytes, adiponectin causes glucose and fatty acid uptake and AMPK phosphorylation. Adiponectin expression is correlated with coronary function. Plasma adiponectin level in the great cardiac vein is significantly higher than that in the left coronary artery [438] . Therefore, adiponectin is locally produced in the coronary circulation and participates in the modulation of coronary blood flow in different regions of the myocardium.

Full-length adiponectin promotes cardiomyocyte survival via the AMPK pathway. It also protects from ischemia-reperfusion injury (Vol. 6 -Chap. 6. Heart Pathologies) via suppression of tumor-necrosis factor signaling owing to cyclooxygenase-2 [436] . Adiponectin stimulates production of nitric oxide via AMPK-mediated phosphorylation of NOS3 nitric oxide synthase. However, adiponectin inhibits expression of inducible nitric oxide synthase NOS2 and NADPH oxidase. It then blocks peroxynitrite formation and represses oxidative and nitrative stresses.

Adiponectin suppresses endothelial cell apoptosis [439] . Adiponectin is involved in angiogenesis. It stimulates formation of capillary-like structures in vitro by umbilical vein endothelial cells via the AMPK-NOS3 axis [440] . Adiponectin promotes phosphorylation of AMP-activated protein kinase, stimulates the phosphatidylinositol 3-kinase-protein kinase-B pathway, and activates endothelial nitric oxide synthase NOS3 [436] .

On the other hand, adiponectin impedes endothelial cell proliferation and superoxide production induced by oxidized low-density lipoproteins via NADPH oxidase [441] . Globular adiponectin also enhances NOS3 activity that is repressed by oxidized low-density lipoproteins. Globular adiponectin attenuates or suppresses proliferation and migration of coronary artery endothelial cells induced by vascular endothelial growth factor as well as related signaling effects, such as generation of reactive oxygen species, activation of protein kinase-B, kinases ERK1 and ERK2, and GTPase RhoA in vitro [442] .

Adiponectin protects the cardiovascular system owing to its insulin-sensitizing and anti-inflammatory properties via AMP-activated protein kinases and the cAMP-PKA pathway. In endothelial cells, both globular and full-length adiponectins enhance the production of nitric oxide and limit synthesis by mitochondria and NADPH oxidases of reactive oxygen species induced by elevated glucose levels.

In addition, the cAMP-PKA pathway mediates adiponectin effects in endothelial cells against activity of tumor-necrosis factor and high glucose levels. Adiponectin then impedes expression of cell adhesion molecules (e.g., Eselectin and vascular cell adhesion molecule-1 [443]) induced by TNFα, hence leukocyte extravasation.

In human aortic endothelial cells, adiponectin suppresses TNFα-induced IκBα phosphorylation and subsequent NFκB activation. As it leads to cAMP accumulation, it allows crosstalk between cAMP-PKA and NFκB pathways. Globular and full-length adiponectin also protect against an increase in endothelial permeability induced by angiotensin-2 or tumor-necrosis factor [436].

Adiponectin has dominant anti-inflammatory features, thus anti-atherogenic and antidiabetic effects (Table 3 .25). Adiponectin regulates the expression Table 3 .25. Adipocytokines and their activity in inflammation and immunity (Sources: [444, 445] ). Adiponectin antagonizes tumor-necrosis factor-α (TNFα), as it impedes its production in various cells, such as hepatocytes and macrophages, and counteracts its effects. It also inhibits endothelial nuclear factor-κB (NFκB) signaling via a cAMP-dependent pathway. Adiponectin may play a role in cell growth, angiogenesis, and tissue remodeling by binding and sequestering various growth factors with distinct binding affinities according to its complex type (tri-, hexa-, or polymer).

Inflammatory and of both pro-and anti-inflammatory cytokines. It suppresses the synthesis of tumor-necrosis factor-α, interleukins IL6 and IL8, and interferon-γ and favors the production of anti-inflammatory cytokines, such as interleukins IL10 and IL1-receptor antagonist (IL1RA) by monocytes, macrophages, and dendritic cells. Adiponectin increases the synthesis of tissue inhibitor of metallopeptidases in macrophages via IL10 [446] . Adiponectin inhibits the expression of adhesion molecules via inhibition of TNF and NFκB. Globular adiponectin suppresses TNF-induced activation of NFκB, prevents activation of IκB kinase, and leads to cAMP accumulation in endothelial cells [445] . This effect is blocked by inhibitors of adenylyl cyclase or protein kinase-A. Adiponectin also hampers foam cell formation. Adiponectin reduces vascular smooth muscle cell proliferation, migration, and apoptosis by attenuating synthesis of platelet-derived and fibroblast growth factors. Table 3 .26. Apelin effects on blood circulation (Source: [447] ; EC: endothelial cell; SMC: smooth muscle cell). Its effectors comprise: (1) inhibitory G protein (Gi) that inhibits adenylyl cyclase; (2) Ca ++ ; and (3) ERK and S6K kinases and the PI3K-PKB axis. Neurons of the supraoptic and paraventricular nuclei of the hypothalamus synthesize apelin, apelin receptor, and vasopressin (or antidiuretic hormone). Water deprivation enhances production of apelin receptor and vasopressin in the supraoptic nucleus. Apelin and its receptor are also expressed in peripheral tissues with highest levels in heart, kidney, and lung.

Vasoconstriction ApJ receptor (SMC) Vasodilation Nitric oxide (ApJ receptor on EC) Positive inotropy Na + -H + exchanger Blood volume Vasopressin

Apelin is synthesized from a single gene in adipocytes, vascular and cardiac cells, some cells of the endocrine pancreas, gastric enterochromaffin-like cells, and colonic epithelial cells. Its production increases with elevated insulin level. On the other hand, the concentration of cardiac apelin is lowered by angiotensin-2. Apelin circulates in blood and can then act as a hormone. Apelin regulates the cardiovascular function and fluid homeostasis (Table 3 .26).

Apelin activates the G-protein-coupled receptor ApJ 110 that signals via inhibitory G protein (Gi; Vol. 4 -Chap. 8. Guanosine Triphosphatases). Consequently, it inhibits adenylyl cyclase. 111 On the other hand, activated ApJ stimulates extracellular-regulated kinases (Vol. 4 -Chap. 5. Mitogen-Activated Protein Kinase Modules) via protein kinase-C. In addition, apelin can activate S6K kinase . Cytosolic Protein Ser/Thr Kinases).

Apelin derives from a 77-amino acid preproapelin with a conserved 23-amino acid C-terminus (amino acids 55-77). Paired basic amino acid residues (Arg-Arg and Arg-Lys) are cleaving sites for endopeptidases. Many possible isoforms result from the maturation of a prepropeptide (preproapelin) into apelin peptides: apelin 36 (or apelin (42−−77) ), the long form of apelin and shorter isoforms that correspond to a shorter C-terminus (Table 3 .27). In addition, apelin 13 gives rise to a pyroglutaminated form ( pGlu apelin 13 ). These Table 3 .27. Apelin isoforms. For example, apelin36, the long form of apelin, and apelin15 contain the C-terminal 36 and 15 residues of preproapelin, respectively. The 12 C-terminal residues (66-77) are the minimal structural core required for apelin activity. Isoform Other type of notation Apelin11 Apelin (67−−77) ) Apelin12 Apelin (66−−77) ) Apelin13 Apelin (65−−77) ) Apelin15 Apelin (63−−77) ) Apelin16 Apelin (62−−77) ) Apelin17 Apelin (61−−77) ) Apelin19 Apelin (59−−77) ) isoforms differ by their tissue distribution and activity potency. Yet, these numerous apelin isoforms interact with a single receptor.

Apelin is a substrate of angiotensin-converting enzyme-related carboxypeptidase ACE2, another enzyme of the renin-angiotensin-aldosterone system, in addition to angiotensin-converting enzyme ACE1 [448] . 112 The carboxypeptidase ACE2 cleaves (inactivates) apelin-36 and hydrolyzes apelin-13 [447] .

Apelins were initially discovered as inducers of extracellular acidification. Apelin 13 and pGlu apelin 13 have similar activities. Apelin 17 and apelin 36 are 8-and 60-fold less efficient, respectively [447] . However, elevation in extracellular acidification generated by pGlu apelin 13 is transient, whereas that by apelin 36 is sustained. Repression of adenylyl cyclase is stronger by apelin 13 and pGlu apelin 13 that have similar affinity for their substrate than by apelin 17 (slightly lower affinity) and apelin 36 (3 times lower affinity). In addition, apelin 36 , apelin 17 , and apelin 13 cause a sharp elevation in intracellular calcium concentration with little dose-response difference.

Apelin receptor is expressed on activated T lymphocytes. Apelin 36 is more effective in the inhibition of human immunodeficiency virus infection, as it blocks apelin receptor that serves as a HIV coreceptor [448] . 113 Apelin 13 and, to a much lesser extent, apelin 36 , stimulate proliferation of gastric epithelial cells in vitro [447] . Apelin also acts as a mitogenic peptide for endothelial cells. Apelin 13 , and to a lesser extent, apelin 36 operate as chemoattractants, especially during retinal angiogenesis. Apelin can also modulate cytokine production.

Apelin has potent positive inotropic and vasorelaxant activity as well as antiatherogenic and anti-aneurysmal properties. It can reduce expression and activation of inflammatory cytokines and chemokines, although it neither markedly changes intimal adhesion molecule expression nor medial and adventitial cell cytokine production [449] .

Apelin acts as a potent endothelium-independent vasoconstrictor and endothelium-dependent vasodilator by targeting its receptors on vascular smooth muscle and endothelial cells, respectively. Apelin 12 is more potent for reducing blood pressure than apelin 13 , a strong regulator of the cardiovascular function, whereas apelin 11 remains inactive.

Apelin receptor is produced in vascular endothelial cells that line small intramyocardial, endocardial, renal, pulmonary, and adrenal vessels as well as large vessels, such as coronary arteries and saphenous veins [448] . Although both the receptor and its ligand can be expressed by endothelial cells, subsets of endothelial cell population can produce either apelin or its receptor for paracrine signaling (but not autocrine regulation) [447] .

Apelin receptor expression increases during formation of retinal vessels and diminishes after vessel stabilization. Lower ApJ levels are also observed in vascular smooth muscle cells as well as cardiomyocytes.

Apelin and its receptor are highly expressed in the heart of various species, but more abundantly in the right atrium than in the left ventricle. Apelin is a positive inotropic agent, as it promotes activity of Na + -H + exchangers. Cardiac apelin level is downregulated by angiotensin-2. In humans, apelin plasma level is significantly elevated by insulin as well as in obesity. During hypoxia such as in ischemic cardiomyopathy, apelin level is heightened, whereas it decays in atrial fibrillation and chronic heart failure [444] . In addition, apelin expression is significantly attenuated in ventriculomyocytes of experimental models of chronic pressure overload [447] . In humans with idiopathic dilated cardiomyopathy, apelin level decays, but atrial and ventricular apelin receptor level rises. Apelin plasma level in the early stage of heart failure can also rise and then fall.

Messenger RNAs that encode apelin and its receptor abound in the central nervous system. In humans, apelin is expressed in the caudate nucleus, hippocampus, thalamus, hypothalamus, basal forebrain, frontal cortex, corpus callosum, amygdala, substantia nigra, and pituitary, as well as spinal cord [448] .

Apelin and its receptor are coexpressed in neurons of the supraoptic and paraventricular nuclei of the hypothalamus that synthesize vasopressin. It hence participates in the regulation of fluid homeostasis. 114 At least in the hypothalamus, apelin released by a neuron can activate presynaptic apelin receptors on the same neuron as well as those on nearby neurons, i.e., for both auto-and paracrine regulations [447] . In addition, acute stress increases apelin receptor production in the paraventricular nucleus. Repeated stresses cause a sustained upregulation of apelin receptors.

Leptin (λ πτoς: thin) is encoded by the human LEP gene (murine obese gene [OB] ). The expression of the leptin gene is regulated by food intake and energy status, as well as several hormones and inflammatory mediators (e.g., tumor-necrosis factor, interleukin-1, and leukemia inhibitory factor). This non-glycosylated peptide is mainly produced by adipocytes in response to high lipid levels. Yet, leptin can be produced by various tissues, especially those of the cardiovascular system, such as blood vessel wall cells and cardiomyocytes that also synthesize leptin receptors (Vol. 3 -Chap. 6. Receptors).

Leptin modulates via the hypothalamus satiety and fat storage. In the hypothalamus, leptin also contributes to the control of the concentration of growth hormone, thyroxin, and sex steroids [444] . Leptin participates in the regulation of pancreatic islet cell activity, hematopoiesis, angiogenesis, wound healing, osteogenesis, and gastrointestinal function.

Leptin interacts with 6 types of cognate receptors (LepRa-LepRf) that belong to the class-1 cytokine receptors. Signal transduction involves the JaK-STAT pathways (Vol. 4 -Chap. 3. Cytosolic Protein Tyrosine Kinases) and AMP-activated protein kinase (Vol. 1 -Chap. 4. Cell Structure and Function).

Leptin circulates in the blood (at a concentration of a few ng/ml) and in the cerebrospinal fluid, crossing the blood-brain barrier in order to regulate food intake by the hypothalamus. Leptin concentration is proportional to insulin concentration and inversely proportional to glucocorticoid level [444] .

Testicular and ovarian steroids decrease and increase leptin concentration, respectively [444] . Angiotensin-2 stimulates leptin production in adipose tissue by activating angiotensin-2 type-1 receptor and extracellular signal-regulated kinases ERK1 and ERK2 [73] (Vol. 4 -Chap. 5. Mitogen-Activated Protein Kinase Modules).

Obese humans develop leptin and insulin resistance characterized by endoplasmic reticulum stress during which un-and misfolded proteins accumulate in the endoplasmic reticulum. 115 Endoplasmic reticulum stress blocks leptin ability to activate its signaling pathways [450] . Reduced endoplasmic reticulum stress sensitizes cells to leptin.

Elevated leptin level is able to induce leptin resistance via an increase in concentration of suppressor of cytokine signaling SOCS3 that blocks leptin receptors. Increased serum leptin concentration is often associated with insulin resistance, hypertension, endothelial dysfunction, and inflammation, as well as myocardial infarction and stroke. Conversely, administration of leptin stimulates the sympathetic nervous system, natriuresis, and nitric oxide-dependent vasodilation.

In the brain, leptin influences the cortex, hippocampus, and hypothalamus activity. Leptin acts on hypothalamic neurons to repress food intake and promote energy consumption. 116 Leptin favors energy expenditure especially for the body's growth, reproduction, and immunity. In the hypothalamus, leptin controls not only appetite, but also level of sex steroids, thyroxin, and growth hormone. Leptin can be coexpressed with growth hormone in somatotrope neurons of the anterior pituitary. 117

Leptin receptor LepRb is found in the hypothalamus, especially in the satiety center. 118 Leptin hampers the activity of neurons in the arcuate nucleus expressing neuropeptide-Y and agouti-related peptide (AgRP). It favors the activity of neurons expressing α-melanocyte-stimulating hormone 115 RNA-dependent protein kinase-like endoplasmic reticulum-bound eIF2α kinase (PERK) that is a resident endoplasmic reticulum-stress inducible kinase and inositol-requiring kinase IRE1 are major participants of the unfolded protein response. Their activity rises during development of obesity. Conversely, transcription factors X-box binding protein XBP1 and Activating transcription factor ATF6 favor endoplasmic reticulum adaptive capacity. 116 Adipose tissues aim at storing energy. Adipocytes saturated with lipids can lead to lipid accumulation in other tissues, reducing their functioning. Increased leptin activity in the arcuate nucleus in the hypothalamus inhibits the production of neuropeptide-Y in the paraventricular nucleus, thereby reducing feeding. 117 Somatotrope neurons have leptin receptors. Leptin can thus be an autocrine or paracrine regulator. 118 Leptin receptor is expressed at low levels in manifold tissues, but at high levels in the mediobasal hypothalamus, particularly in the arcuate, ventromedial, dorsomedial, and ventral premamillary hypothalamic nuclei [451] . Expression of LepRb is moderate in the periventricular region and posterior hypothala-derived from pro-opiomelanocortin and cocaine-and amphetamine-regulated transcript in the lateral arcuate nucleus. Melanin-concentrating hormone and orexins expressed in lateral hypothalamic area are inhibited indirectly by leptin. In addition, leptin increases catecholamine (adrenaline and noradrenaline) secretion by acting on the ventromedial hypothalamus, but not on hypothalamic arcuate, paraventricular, and dorsomedial nuclei, to prime a sympathetic activation [453] . Leptin controls cell metabolism via its actions in the hypothalamus and peripheral organs. Leptin regulates energy balance between intake and expenditure and glucose metabolism by activation of long-form leptin receptor LepRb in hypothalamic leptin-responsive neurons via mechanisms that depend or not on LepRb Tyr phosphorylation [454] . Leptin-bound phosphorylated LepRb (Tyr1138) activates Janus kinase JaK2 and recruits STAT3 signal transducer and activator of transcription. Phosphorylated LepRb (Tyr985) mediates cellular events that involve cytosolic phosphatase PTPn11, extracellular signal-regulated kinase, and SOCS3 suppressor of cytokine signaling. Additional mechanisms independent on LepRb Tyr phosphorylation control food intake, physical activity, adaptive thermogenesis, and glucose metabolism.

Leptin influences synaptic adaptivity (plasticity). It stimulates the presence of ionotropic glutamate receptor-1 (GluR1 [AMPAR]; Vol. 3 -Chap. 2. Membrane Ion Carriers) at hippocampal synapses and increases synaptic strength, as it inhibits the phosphatase PTen [455]. Phosphatidylinositol (3, 4, 5) -trisphosphate, the level of which then rises, actually enables GluR1 exocytosis. Leptin enhances the amplitude of excitatory postsynaptic currents in the hippocampus.

In the heart, leptin regulates the contractility, metabolism, production of extracellular matrix components by cardiomyocytes, and contributes to the cardiomyocyte size [434] .

Leptin receptors are widely distributed on endothelial cells and vascular smooth muscle cells. Leptin stimulates mitogen-activated protein kinases and mic nucleus and low in the paraventricular nucleus and lateral hypothalamic area. Receptor LepRb also localizes to the nucleus tractus solitarius, lateral parabrachial nucleus, as well as motor and sensory nuclei and brainstem areas that are not associated with energy balance. Activation of leptin receptors in the hypothalamus: (1) represses orexigenic pathways that involve neuropeptide-Y and agouti-related peptide and (2) stimulates anorexigenic pathways that are linked to pro-opiomelanocortin and cocaine-and amphetamine-regulated transcript [452] . phosphatidylinositol 3-kinase. Leptin induces smooth muscle cell proliferation and migration [456] . Leptin also favors platelet aggregation. It promotes angiogenesis [457] (Vol. 5 -Chap. 10. Vasculature Growth). In addition, leptin intervenes in hematopoiesis.

Leptin upregulates the expression of vascular endothelial growth factor via activation of NFκB and PI3K [452] . Leptin also supports the production of nitric oxide synthase NOS2, thereby that of reactive oxygen species.

Plasma leptin action on arterial blood pressure regulation depends on soluble leptin receptor, nitric oxide metabolism, and blood flow behavior, as well as leptin-mediated hypothalamic activation centers of sympathetic neuronal regulation [458] . Effects of sympathetic neuronal activation differ according to organs. Kidneys belong to main targets of the sympathetic nervous system. Leptin's excitation modifies glomerular perfusion and sodium excretion. Impaired leptin function in vascular cells can facilitate onset of hypertension. In vitro, leptin stimulates the proliferation and hypertrophy of vascular smooth muscle cells and their production of matrix metallopeptidase MMP2. It can then alter arterial wall remodeling. Leptin also stimulates the production of cytokines, such as tumor-necrosis factor-α and interleukin-6, that can alter blood vessel wall functioning. It also promotes the secretion of pro-atherogenic lipoprotein lipase by cultured macrophages [434] . In aortic endothelial cells, leptin causes superoxide and CCL2 production, hence favoring monocyte recruitment.

By its short-and long-term effect in the kidney, leptin influences blood pressure by 2 opposing processes: (1) via renal sympathetic activation and (2) via nitric oxide synthesis. Kidneys express high amounts of leptin receptors. In addition to its direct effect on the renal functioning via leptin receptors, leptin has indirect activity via nitric oxide in renal tubules.

Leptin stimulates overall sympathetic nerve activity, especially in kidneys, adrenal glands, and brown adipose tissue [459] . However, leptin does not increase arterial pressure and heart rate. In the renal medulla, leptin inhibits Na + -K + ATPase that is responsible for tubular sodium reabsorption, hence augmenting natriuresis [460] . On the other hand, leptin does not influence cortical Na + -K + ATPase. Leptin-induced nitric oxide impedes renal sodium reabsorption, as it attenuates the activity of both apical transporters and basolateral Na + -K + ATPases [461]. In particular, quantity of Na + -Cl − cotransporters is related to nitric oxide production.

Leptin stimulates nitric oxide production and release in vascular endothelial cells by activating a PI3K-independent PKB-NOS3 pathway, thus inducing vasorelaxation [462] . Nitric oxide synthesis in the renal medulla enhances medullary blood flow, hence preventing sodium retention and blood pressure elevation [463] . Leptin-induced nitric oxide activity hence opposes pressor and antinatriuretic effect of leptin-primed sympathetic activation.

Lung genesis depends on endodermal sonic Hedgehog signaling to mesodermal Wnt-β-catenin pathway (Vol. 3 -Chap. 10. Morphogen Receptors), followed by parathyroid hormone-related protein (PTHrP) action from endoderm to mesoderm [464] . Intra-uterine lung development is driven by fluid-caused distension. Distension (maturation) of fetal rat lung explants upregulates PTHrP signaling, as well as fibroblast-specific adipocyte differentiation-related protein (ADRP) and peroxisome proliferator-activated receptor-γ, but downregulates sonic Hedgehog and Wnt-β-catenin signaling. Parathyroid hormone-related protein and cAMP repress sonic Hedgehog and Wnt-β-catenin axes. Lung genesis indeed culminates with pulmonary surfactant production by epithelial type-2 cells. Differentiation of alveolar epithelial and mesenchymal cells is promoted by parathyroid hormone-related protein that is a stretch-sensitive molecule produced by alveolar type-2 pneumocytes.

Developing lung lipofibroblasts express leptin [465] . Leptin and its receptor are mutually expressed exclusively by fetal lung fibroblasts and type-2 pneumocytes that can therefore interact in a paracrine manner. Leptin thus participates in the parathyroid hormone-related protein paracrine stimulation of fetal lung maturation. In fetal lung acini, leptin is produced in alveolar interstitial fibroblasts that are subjected to parathyroid hormone-related protein secreted by formative alveolar epithelium under moderate stretch [466] . Leptin then acts back on leptin receptors of alveolar type-2 pneumocytes to prime surfactant synthesis.

Leptin also stimulates synthesis of surfactant phospholipids and proteins in adult human airway epithelial cells. When alveolar lipofibroblasts and epithelial type-2 cells are simultaneously stretched in vitro, surfactant synthesis increases (5-fold) [466] . Lipofibroblast stretching upregulates adipose differentiation-related protein expression and enhances parathyroid hormonerelated protein binding (2.5-fold) and triglyceride uptake (15-25%). Alveolar type-2 pneumocyte stretching augments leptin stimulation of surfactant synthesis (3-fold) . Paracrine leptin control hence is also stretch sensitive.

Leptin-bound receptors in neurons attenuate bone formation and accrue osteoclast differentiation, whereas in osteoblasts they do not influence bone remodeling [467] . However, leptin via mediator cocaine-and amphetamineregulated transcript (CART) inhibits bone resorption. Leptin regulates bone mass via sympathetic activity independently of its effect on energy metabolism. Leptin activation of the sympathetic tone could occur after binding to its receptor on hypothalamic neurons.

Leptin stimulates AMP-activated protein kinase that decreases ATP-consuming anabolism and increases ATP-manufacturing catabolism. Leptin decreases insulin levels by inhibition of proinsulin synthesis and reduction of secretion.

In myocytes, leptin improves insulin sensitivity and reduces intracellular lipid levels by direct activation of AMP-activated protein kinase combined with indirect inputs to the central nervous system. In hepatocytes, leptin also enhances insulin sensitivity.

Leptin has dominant pro-inflammatory effects (Table 3 .25). It heightens immune responsiveness by directly acting on immune cells. Leptin binds to its receptor LepRb and activates: (1) the mitogen-activated protein kinase pathway (P38MAPK and ERK) and (2) signal transducer and activator of transcription STAT3, thus producing pro-inflammatory cytokines TNFα and interleukin-6 and -12 in monocytes and macrophages.

Leptin favors activities of monocytes, macrophages, and natural killer cells [445] . Leptin stimulates the chemotaxis of neutrophils and the production by neutrophils of reactive oxygen species. It also stimulates the production of IgG2a by B lymphocytes. Moreover, it increases secretion by T lymphocytes.

Resistin 119 (Retn) causes resitance of tissues to insulin (hence its name "resist + in") is synthesized by adipocytes and other cells of adipose tissues, as well as by myocytes, pancreatic cells, and macrophages. Primary resistin sources can differ between mammals: adipocytes in rodents and stromal vascular cells in human adipose tissue. Resistin prepeptide size also varies between mammals (slightly shorter in humans than in rodents). Resistin circulates mostly as high-molecular-weight hexamers and also more active low-molecular weight complexes [445] .

Resistin synthesis is influenced by insulin, endothelin-1, and adrenaline, as well as pituitary, thyroid, and steroid hormones. Resistin can functionally interact with other adipokines, such as adiponectin and leptin.

Resistin activates phosphatidylinositol 3-kinase and members of the mitogen-activated protein kinase modules: extracellular signal-regulated protein kinase, P38MAPK, and Jun N-terminal kinase.

Resistin can reduce glucose uptake by muscles, adipose tissues, and liver, hence affecting insulin sensitivity. Therefore, in cardiomyocytes, resistin can impair glucose metabolism. Resistin has dominant pro-inflammatory features. Resistin increases the production of tumor-necrosis factor and interleukins IL1β, IL6, and IL12 by various cell types via NFκB [444] . These cytokines upregulate the resistin expression. In human vascular endothelial cells, resistin increases the synthesis of pro-inflammatory agents and provokes the release of endothelin-1 and production of adhesion molecules and chemokine ligands. Resistin actually heightens the production of intercellular (ICAM1) and vascular cell (VCAM1) adhesion molecule-1, as well as chemokine ligand CCL2 by endothelial cells [444] .

High plasma level of resistin correlates with pro-atherogenic inflammatory markers, metabolic syndrome, endothelial dysfunction, and elevated cardiovascular risk. In human coronary artery endothelial cells, clinically relevant concentrations of resistin (40 or 80 ng/ml) administered during 24 h reduce the production of endothelial nitric oxide synthase (NOS3) and elevate the cellular levels of reactive oxygen species via P38MAPK and JNK [468].

Visfatin, or nicotinamide phosphoribosyltransferase (NAmPT or NAmPRTase) 120 is produced by adipocytes and lymphocytes. Therefore, this protein acts as both an enzyme and adipokine that can circulate in the blood stream.

Plasma level of visfatin is negatively correlated to endothelial function. Visfatin is able to upregulate the activity of interleukin-6 and tumor-necrosis factor-α [434] . It also favors production of transforming growth factor-β1, plasminogen activator inhibitor-1, and collagen-1. In addition, visfatin fosters the maturation of vascular smooth muscle cells and inhibits neutrophil apoptosis [444] .

Visfatin has an insulin-like activity because it binds to and activates insulin receptor at a binding site different from that of insulin [469] . It thus favors glucose uptake, as it enhances synthesis and membrane incorporation of glucose transporter GluT1.

Vasodilator visfatin initiates [470]: (1) phosphorylation (Ser1177) and dephosphorylation (Thr495) of nitric oxide synthase NOS3; (2) phosphorylation (Ser473) of protein kinase-B; and (3) phosphorylation of vasodilatorstimulated phosphoprotein (Ser239). Furthermore, visfatin has angiogenic activity via extracellular signal-regulated protein kinase-1 and -2 and fibroblast growth factor-2 [471]. Moreover, it acts on endothelial cells by an auto-and/or paracrine mechanism. It indeed upregulates the expression of chemokine CCL2 and its receptor CCR2 via phosphatidylinositol 3-kinase and nuclear factor-κB [472] .

Visfatin released by perivascular adipose tissue not only inhibits vascular smooth muscle cell contraction, but also stimulates proliferation of these cells [473] . This effect relies on the nicotinamide phosphoribosyltransferase activity that produces nicotinamide mononucleotide needed for mitogenactivated protein kinases P38MAPK and extracellular signal-regulated kinases ERK1 and ERK2.

Leptin increases visfatin production in adipose tissue via phosphatidylinositol 3-kinase and mitogen-activated protein kinase [474] . High-glucose level also elevates visfatin synthesis in mesangial cells that reside around renal blood vessels [475] .

On the other hand, angiotensin-2 binds to the nuclear receptor NR1c3 (or peroxisome proliferator-activated receptor-γ) in adipocytes, skeletal myocytes, and endothelial cells. It then prevents the release of visfatin [476].

Adipsin 121 is mainly synthesized in monocytes and resident macrophages in adipose tissue. It intervenes in the rate-limiting step in the complement activation alternative pathway. It could also generate an acylation-stimulating protein that increases adipocyte triglyceride production [444].

Angiopoietin-like peptide-4 (AngptL4), 122 induced by peroxisome proliferatoractivated receptors (nuclear receptors NR1c) especially in the liver and adipose tissue, increases the triglyceride level [444] . Its concentration correlates with those of lipoproteins. It inhibits lipoprotein lipase as well as blood triglyceride clearance.

This glycosylated, secreted protein is, in particular, produced under hypoxia by endothelial cells [479] . During hypoxia, full-length AngptL4 accumulates in the subendothelial extracellular matrix via heparan sulfate proteoglycan. Therefore, in the extracellular matrix, AngptL4 exists either as a matrix-bound, immobilized, full-length protein or soluble form. This survival factor for vascular endothelial cells is involved not only in lipid metabolism, but also the regulation of glucose homeostasis and angiogenesis. 123

Chemerin, or retinoic acid receptor responder RARRes2, 124 is a chemoattractant. Chemerin is an adipokine that serves as a regulator in adipogenesis or adipocyte function. 125 It operates in auto-and paracrine signaling for adipocyte differentiation.

Chemerin is secreted as an inactive prochemerin that undergoes extracellular serine peptidase cleavage of its C-terminus to generate an active chemerin that can circulate in blood (estimated concentration 3.0-4.4 nM in humans). Chemerin concentration increases when body mass, blood pressure, and triglyceride level rise [444] .

Chemerin targets the G-protein-coupled receptor CmkLR1 chemokine-like receptor. Chemerin receptor defects impair cell differentiation into adipocytes and decrease adiponectin and leptin expression [444].

Hepcidin is mainly synthesized in the liver as a hepcidin preprohormone and then prohormone, before being secreted. It was first described as a urinary antimicrobial peptide.

This hormone regulates iron metabolism, as it prevents iron efflux from enterocytes and macrophages. This peptide actually inhibits ferroportin involved in iron export as well as iron absorption and secretion by enterocytes and transport across the placenta [444] . Iron release from macrophages is also prevented by ferroportin inhibition.

Hepcidine concentration correlates with levels of C-reactive protein and interleukin-6 [444]. Interleukin-6 that is synthesized by white adipose tissue is a potent stimulator of hepcidin production and secretion by the liver. It is also produced in adipose tissue, particularly in obese subjects. Its expression rises during iron overload and inflammation. During adipocyte hypoxia, hepcidin concentration can either decay or heighten [477] .

Acute inflammation, especially during cardiac surgery, can affect the regulation of hepcidin expression in subcutaneous adipose tissue, but not in epicardial adipose tissue, thereby contributing to inflammation-induced systemic changes of iron metabolism [478] . 126 124 A.k.a. tazarotene-induced gene product TIG2. 125 Retinoids inhibit cell differentiation. They are then used in the treatment of hyperproliferative dermatological diseases. 126 When iron metabolism is dysregulated, iron is sequestered in the reticuloendothelial system. A subsequent hypoferremia oocurs, i.e., a limited availability for erythropoiesis, that causes anemia observed in chronic inflammatory diseases.

Omentin 127 is a galactofuranose binding-lectin. It indeed acts as a receptor for lactoferrin as well as bacterial arabinogalactans. In addition, it is an insulin sensitizer made by vascular stromal cells within fat pads that enhances glucose uptake [452] . It is encoded by 2 genes that are selectively expressed in visceral adipose tissue. Omentin concentration decays in obesity and insulin resistance [444] . On the other hand, omentin concentration rises when high-density lipoprotein and adiponectin concentration heightens.

3.18.6.6 Retinol-Binding Protein-4

Retinol-binding protein-4 (RBP4) of the lipocalin family is devoted to the delivery of retinol, a form of vitamin A. It is actually the specific blood carrier of retinol. It delivers retinol from the liver store to tissues. It is also secreted by adipocytes. In plasma, the RBP-retinol complex interacts with transthyretin that prevents its filtration through the renal glomerulus.

This adipokine impairs insulin action on the liver and muscles [452] . Retinol-binding protein-4 contributes to insulin resistance.

Visceral adipose tissue-derived serine peptidase inhibitor (serpin) yields the portmanteau vaspin (the noun serpin is also a portmanteau). Vaspin or Serpin-A12 suppresses the production of tumor-necrosis factor, leptin, and resistin [445] . However, this extracellular adipokine improves insulin sensitivity.

The concentration of insulin-sensitizing vaspin decays in physically fit subjects and rises in obese humans, especially those with impaired glucose tolerance [444].

Transient increases in non-esterified fatty acid levels, such as acute changes after a meal, enhance insulin secretion, whereas chronic elevations associated with insulin resistance reduce insulin secretion by the pancreas. Insulin resistance is actually linked to lipolysis and release of non-esterified fatty acids into the circulation [452] . Circulating non-esterified fatty acids reduce glucose uptake by adipocytes and myocytes, and promote glucose release by hepatocytes.

127 A.k.a. endothelial lectin, intelectin-1 (Itln1), and intestinal lactoferrin receptor (IntL).

Colony-stimulating factors (CSF) are devoted to hematopoietic (blood) cells.

They are able to generate mature myeloid cells from bone marrow precursors. They can also act on mature myeloid cells, especially during immune responses. Colony-stimulating factors include granulocyte colony-stimulating factor (gCSF), or colony-stimulating factor CSF3, granulocyte-macrophage colony-stimulating factor (gmCSF), or CSF2, and macrophage colony-stimulating factor (mCSF), or CSF1. Colony-stimulating factors intervene in wound healing, as well as placental and fetal development. Smooth muscle, endothelial and epithelial cells, neurons, and keratinocytes express receptors for gmCSF and mCSF [480] .

Colony-stimulating factors act as pro-inflammatory cytokines that are associated with tumor-necrosis factor and some interleukins, such as IL1, IL17, and IL23 [480] . In vitro, gmCSF favors production of pro-inflammatory cytokines, such as tumor-necrosis factor and interleukins IL6, IL12, and IL23. Cultured cells stimulated by mCSF tend to manufacture interleukin-10 and CCL2 chemokine ligand.

Granulocyte-macrophage colony-stimulating factor (gmCSF or CSF2) is synthesized upon stimulation, especially by interleukin-1, tumor-necrosis factor, and lipopolysaccharides. Secreted gmCSF is a single glycosylated polypeptide chain. In vitro, gmCSF promotes survival and activation of macrophages, neutrophils, and eosinophils, as well as maturation of dendritic cells. Moreover, gmCSF is required for maturation of alveolar macrophages and invariant natural killer T cells [480] .

The gmCSF receptor (CSF2R) is a heterodimer composed of a specific ligand-binding CSF2Rα and a signal-transduction CSF2Rβ subunit. The latter is also a component of interleukin IL3R and IL5R receptors. Activated gmCSF receptor stimulates 3 known pathways: (1) the Janus kinase-signal transducer and activator of transcription (JaK-STAT); (2) mitogen-activated protein kinase (MAPK); and (3) phosphoinositide 3-kinase (PI3K) axis.

In vitro, gmCSF and mCSF preferentially target cells with antigenpresenting and phagocytic features, respectively. Stimulation of immature cells of the macrophage lineage with gmCSF alone promotes dendritic cell-like phenotype, whereas stimulation with both mCSF and gmCSF leads to a stronger macrophage phenotype. A costimulus such as that caused by lipopolysaccharides and gmCSF or mCSF is usually required to activate monocytes and macrophages.

Macrophage colony-stimulating factor (mCSF or CSF1) is constitutively produced by several cell types, such as endothelial and smooth muscle cells, fibroblasts, stromal cells, macrophages, and osteoblasts. Several mCSF types exist: cell-surface protein, secreted glycoprotein, and proteoglycan. The glycoprotein and proteoglycan isoforms circulate throughout the body.

The mCSF receptor (CSF1R) is a homodimeric type-3 receptor Tyr kinase. It elicits survival, proliferation, differentiation, and possibly activation of cells of the monocyte-macrophage lineage. Furthermore, mCSF is crucial for maintenance of several macrophage-lineage populations associated with tissue integrity.

The blood concentration of granulocyte colony-stimulating factor (gCSF or CSF3) rises under stress such as infection. The gCSF receptor belongs to the type-1 cytokine receptors. The colony-stimulating factor-3 receptor (CSF3R) reaches its highest expression on neutrophils. Activation of CSF3R triggers numerous signaling cascades using cytosolic kinases.

Tumor-necrosis factors (TNF) belong to the class of cytokines that includes chemokines, interleukins, interferons, and others molecules (monokines, lymphokines, stem cell factor, colony-stimulating factor, glucose phosphate isomerase [GPI], 128 osteopontin, etc.).

Tumor-necrosis factors act via TNF receptors, TNFR1 and TNFR2, that are also called tumor-necrosis factor receptor superfamily member-1A (TN-FRSF1a) and -1B (TNFRSF1b).

Tumor-necrosis factor irreversibly triggers the caspase cascade, hence apoptosis. The TNFR receptors actually associate with procaspases via adaptors to cleave other inactive procaspases (Chap. 4). Tumor-necrosis factors also launch a pro-inflammatory program in immune cells.

Tumor-necrosis factors are able to interact with receptors on endothelial cells to increase vascular permeability, thereby favoring leukocyte extravasation to reach the site of infection.

The tumor-necrosis factor superfamily (TNFSF) comprises numerous members, the so-called TNF ligands, among which tumor-necrosis factor, more precisely TNFα, or tumor-necrosis factor superfamily member-2 (TNFSF2) 129 and tumor-necrosis factor-β, or TNFSF1. 130

Tumor-necrosis factor-α acts synergistically with EGF and PDGF growth factors. Agent TNFSF2 induces expression of several interleukins. Tumornecrosis factor-β is able to kill different cell types and induce terminal differentiation in others. Protein TNFSF1 inhibits lipoprotein lipase in endothelial cells. It is mainly synthesized by T lymphocytes, in particular CD8+ cytotoxic T lymphocytes.

Ligands of the TNFSF superfamily are detected on B lymphocytes, dendritic cells, macrophages, CD4+ and CD8+ T lymphocytes, NK and NKT cells, mastocytes, and smooth muscle and endothelial cells during inflammation. They include homotrimers TNFSF4 and TNFSF15 as well as TNFSF7 and TNFSF9 [481] (Tables 3.28, 3.29, and 3.30) .

The superfamily of TNF ligands also contains numerous other members, such as TNFSF6 that is synthesized by monocytes, dendritic cells, and bone marrow stromal cells, TNFSF10, TNFSF11 that is expressed by helper T cells, and TNFSF13b. Member TNFSF12-TNFSF13 is a hybrid protein composed of the cytoplasmic and transmembrane domains of TNFSF12 fused to the C-terminus of TNFSF13.

The tumor-necrosis factor receptor superfamily (TNFRSF) is constituted by: TNFRSF1a/b, TNFRSF3-6, TNFRSF6b, TNFRSF7-9, TNFRSF10a-10d, TNFRSF11a/b, TNFRSF12a, TNFRSF13b/c, TNFRSF14, TNFRSF16-19, TNFRSF21, TNFRSF25, and TNFRSF27 (Table 3 .31). In particular, TN-FRSF4, TNFRSF7, TNFRSF9, and TNFRSF25 associate with TNF ligands TNFSF4, TNFSF7, TNFSF9, and TNFSF15, respectively.

Members of the TNFRSF superfamily also link to adaptors TNFR-associated factors (TRAF) that can bind to and prevent activity of inhibitors of nuclear factor-κB (Vol. 4 -Chap. 9. Other Major Signaling Mediators). In CD4+ and CD8+ T lymphocytes, TNFRSF4, -7, and -9 increase the expression of anti-apoptotic molecules [481] . Receptors TNFRSF4, -7, -9, and -25 are rapidly expressed on human natural and inducible CD4+, CD25+, FoxP3+ regulatory T cells. Interactions between TNFSF and TNFRSF can then modulate development and function of these regulatory T cells.

Upon immunocyte activation, certain interactions between ligands and receptors 131 mediate crosstalk between T lymphocytes and other cell types to modulate immune response. Expression of TNF ligands and receptors is 2 lymphotoxin-β or 2 lymphotoxin-α and 1 lymphotoxin-β) to anchor it to the plasma membrane. 131 Interactions between TNFSF4 and TNFRSF4, TNFSF7 and TNFRSF7, and TNFSF15 and TNFRSF25 can: (1) stimulate conventional T lymphocytes and antigen-presenting cells;

(2) mediate communication between CD4+ and CD8+ T lymphocytes, NK and T cells, NKT and antigenpresenting cells, and T lymphocytes and other types of immune or tissue cells; TNFα  TNFSF2  TNFβ  LTα  TNFSF3  LTβ  TNFSF4  OX40L  CD134L, CD252  TNFSF5  CD40L  CD154  TNFSF6  FasL  CD95L  TNFSF7  CD27L  CD70  TNFSF8  CD30L  CD153  TNFSF9  4-1BBL  CD137L  TNFSF10 TRAIL  CD253, Apo2L, TL2  TNFSF11 RANKL  CD254, ODF, OPgL, TRANCE  TNFSF12 TWeak  Apo3L  TNFSF13 APrIL  TALL2, TRDL1  TNFSF13b TNFSF20, TALL1 CD257, BAFF, BLyS, DTL, THANK  TNFSF14 Light  CD258, HVEML  TNFSF15 VEGI  TL1a  TNFSF18 GITRL  TL6, AITRL enhanced by T lymphocytes, and antigen-presenting, natural killer (NK), NKT, and activated endothelial cells, as well as other cell types.

Receptors TNFRSF4, -7, -9, and -25 can cooperate with T-cell receptors to promote T-cell division [481] . Members of the TNFSF and TNFRSF superfamilies enable interactions between antigen-presenting cells (dendritic cells, B lymphocytes, and macrophages) and CD4+, CD8+ T lymphocytes, respectively. These interactions are elicited by activating signals from TNFRSF5-TNFSF5 pairs and Toll-like and T-cell receptors (Vol. . Receptors of the Immune System), or cytokine receptors bound to their specific cytokines (TNF, interleukins, and thymic stromal lymphopoietin) [481] . These interactions initiate intracellular signaling in TNFR-loaded cells that stimulates nuclear factor-κB1 and -κB2, 132 as well as other mediators, such as kinases (phosphoinositide 3-kinase, protein kinase-B, and extracellular-signalregulated and Jun N-terminal kinase), and transcription factors (e.g., nuclear factor of activated T cells). These interactions also prime intracellular signaling in TNF ligand-loaded cells that generates secretion of pro-inflammatory cytokines by antigen-presenting cells (TNF and interleukins IL1, IL6, and IL12) and favors cell proliferation.

132 Activated nuclear factor-κB1 causes cell division and enhances cell survival. Nuclear factor-κB1 indeed promotes cell proliferation via survivin, aurora-B kinase, cyclin-cyclin-dependent kinase complexes, as well as survival via anti-apoptotic proteins (B-cell lymphoma BCL2, BCL2-related protein-A1, and BCLxL) and/or inhibition of pro-apoptotic proteins (e.g., BCL2-interacting mediator of cell death). It can also contribute to the production of cytokines (interleukins IL2, IL4, and IL5, as well as interferon-γ. Stimulation of cell growth, angiogenesis, apoptosis, induction of inflammatory cytokines TNFSF13 TNFRSF17 B/T-cell proliferation, T-cell survival, T-cell-independent type-2 antigen response TNFSF13b TNFRSF13c, B-cell development TNFRSF17

(survival and maturation factor) TNFSF14 TNFRSF3

Initiation of T-cell costimulation  TNFRSF6b  TNFSF15 TNFRSF25  Inhibition of endothelial cell proliferation,  angiogenesis, apoptosis  TNFSF18 TNFRSF18 T-cell regulation, EDA1/2 hair follicle and sweat gland development

Complement C1q molecule is composed of 18 polypeptidic chains (6 A, 6 B, and 6 C chains). Agent C1q is a component of the classical pathway of TNFRSF12a CD266, TWEAKR  TNFRSF13b CD267, TNFRSF14b  TNFRSF13c CD268, BAFFR, BR3  TNFRSF14 CD258, TR2, ATAR, HVEM, LIGHTR  TNFRSF16 NGFR  TNFRSF17 CD269, BCMA  TNFRSF18 AITR, GITR  TNFRSF19 TAJ, TRADE, TRoy  TNFRSF21 DR6  TNFRSF25 TNFRSF12, DR3, DDR3, TR3, Apo3, LARD, TRAMP,  WSL1, WSL-LR  TNFRSF27 EdA2R, XEDAR, TR14 complement activation for antimicrobial defense. It connects classical pathwaydriven innate immunity to IgG-or IgM-mediated acquired immunity. 133 Molecule C1q possesses many partners (Table 3 .32), hence operating in several processes ( This globular domain pertains also to various proteins, such as adiponectin, collagen-8 and -10, multimerin, precerebellin, and elastin microfibril interfacelocated protein (emilin).

β-Amyloid C-reactive protein (CRP) Decorin IgG, IgM Lipopolysaccharides Pentraxins (Ptx) Phospholipids (e.g., cardiolipin) Serum amyloid protein (SAP) Viral proteins P38MAPK and NFκB and stimulates the production of pro-inflammatory cytokines and chemokines in macrophages.

On the other hand, members of the TNF superfamily are involved in inflammation, adaptive immunity, apoptosis, energy homeostasis, and tissue regeneration. Both C1q and TNFα are most often inducers of pro-inflammatory activators. 136 Members of the C1q and TNF superfamily are active as selfassembling trimers.

Among cytokines, interleukins (IL) can be grouped into several families (Table 3.34; Vol. . Receptors of the Immune System). Interleukins are involved in immunity and hematopoiesis (Table 3 .35; Vol. 5 -Chap. 2. Hematopoiesis). Interleukins bind to their cognate receptors (Table 3 .36). Interleukin-8 is the CXCL8 chemokine; the interleukin-8 G-protein-coupled receptors IL8Rα and IL8Rβ that are encoded by the IL8RA and IL8RB genes correspond to the CXCR1 and CXCR2 chemokine receptors.

The interleukin-1 family (IL1F) comprises 11 members: IL1α, IL1β, IL1 receptor antagonist (IL1RA), IL18 (or IL1F4), 137 IL33 (or IL1F11), and IL1F5 136 Agent C1q can suppress lipopolysaccharide-induced production of interleukin-12β subunit and TNFα in bone marrow-derived dendritic cells. It precludes the LPS-induced MyD88-dependent pathway, thereby reducing NFκB activity and delaying MAPK phosphorylation [482] . Adiponectin can also suppress mature macrophage function. 137 A.k.a. interferon-γ-inducing factor (IGIF). Table 3 .33. Proteins that contain globular, trimeric C1q (gC1q), their cellular sources and functions (Source: [482] CORS26: 26-kDa collagenous repeat-containing sequence protein; CTRP5: C1q-and tumor-necrosis factor-related protein-5; emilin: elastin microfibril interface-located protein). Except in precerebellin and multimerin, the gC1q domain is always located at the C-terminus of a collagen-like sequence. The gC1q structure is homo-(adiponectin, collagen-8 and -10, and multimerin) or heterotrimeric (C1q).

Source Function Interleukin-1 family members are synthesized by and act on innate immune cells, such as basophils, eosinophils, neutrophils, mastocytes, and natural killer cells, to contribute to their survival and activity. Natural killer cells promote immune response from type-1 helper T cells by secreting interferonγ. In addition, IL1 family members target lymphocytes to reinforce certain adaptive immune responses: IL18 and IL33 mainly activate T H1 and T H2 cells, IL1α, IL1β, IL1RA, IL18 (IL1F4), IL33 (IL1F11),  IL1F5-IL1F10   IL2F  IL2, IL3, IL4, IL7, IL9, IL13, IL15, IL21   IL6F  IL6, IL11, IL27, IL30, IL31 Interleukin-1 139 increases B-cell proliferation caused by mitogens. Therefore, IL1 family members promote innate and adaptive immune responses, as they enhance activities of B lymphocytes and helper T cells.

Interleukin-1 is secreted by macrophages, neutrophils, endothelial and smooth muscle cells, B and T lymphocytes, and fibroblasts in particular. Interleukin-1α and -β rapidly increase expression of hundreds of genes in multiple cell types. Positive and negative feedbacks amplify and terminate IL1 signaling.

Interleukin-1β is secreted and circulates, whereas IL1α is generally connected to the plasma membrane of the producing cell and acts locally [483] . Interleukin-1β is mainly produced by monocytes and macrophages, whereas IL1α is more widely expressed. The latter is, in particular, synthesized by endothelial cells. Interleukins IL1α and IL1β are agonists, whereas IL1RA is a specific antagonist.

Interleukin-1 controls the expression of numerous genes. Interleukin-1 increases the synthesis of [484]: (1) several cytokines, including IL1RA and itself;

(2) enzymes, such as cyclooxygenase and nitric oxide synthase; (3) growth factors (fibroblast, keratinocyte, hepatocyte, nerve, and insulin-like growth factor); (4) clotting factors; (5) neuropeptides, (6) extracellular matrix molecules, 138 Receptor IL18R is uniquely produced by TH1 cells in response to IL12 stimulation [483] . Interleukin-18 amplifies proliferation and Ifn-γ production in TH1 cells. Interleukin-33 enhances the cytokine production by TH2 cells that express IL1RL1 receptor. 139 A.k.a. leukocyte endogenous mediator, hematopoietin-1, endogenous pyrogen, catabolin, and osteoclast-activating factor. etc.; as well as density of plasmalemmal receptors for IL2, IL3, IL5, and gm-CSF in particular. Interleukin-1 increases the production of colony-stimulating factors and stem cell factors. It enhances the activation of T lymphocytes in response to antigens. This activation leads to increased T-cell production of IL2 that raises T-cell activation (autocrine loop). It also induces expression of interferon-γ by T lymphocytes. This T-cell activation by IL1 is mimicked by tumor-necrosis factor-α secreted by activated macrophages. Liganded IL1 receptor primes a sequence of phosphorylation and ubiquitination that activates NFκB and JNK and P38MAPK pathways. These pathways cooperate to stimulate the expression of canonical IL1 target genes, such as those that encode cytokines IL6 and IL8, chemokine CCL2, enzymes cyclooxygenase COx2, MAPK phosphatase DUSP1, inhibitor of NFκB-α, and IL1α and -β [485]. promote cellular immune response and type-2 cytokines (IL4, IL5, IL6, IL9, IL10 , and IL13) that favor humoral immune (antibody) response. Type-1 and -2 cytokines then refer to cytokines produced by CD4+ type-1 (TH1) and -2 (TH2) helper T cells, respectively. Some of these type-1 and -2 cytokines are cross-regulators: interferon-γ and interleukin-12 decrease the concentrations of type-2 cytokines, whereas IL4 and IL10 reduce the levels of type-1 cytokines. Naive CD8+ T cells can polarize into CD8+ and CD4+ type-1 or -2 effectors that produce type-1 or -2 cytokines, such as CD8+ cytotoxic TC1 and TC2 cells.

Class-1 cytokines T lymphocytes, NK cells, and macrophages are targeted by IL18, which promotes the production of interferon-γ and tumor-necrosis factor [486] .

Both IL1 and IL18 enhance the secretion by mastocytes of IL3, IL5, IL6, IL13, and tumor-necrosis factor, but only in the presence of IgE or IL3. Interleukin-18 promotes the production of IL4 to IL6 and IL13 by basophils when combined with another stimulus, particularly IL3, hence T H2 immune response [483] . Interleukin-18 as well as IL1 and IL33 cooperate with IgE to improve histamine release by basophils. Interleukin-18 excites natural killer cells for Ifnγ production and enhances their cytolytic action, as it raises the production of perforin and TNFSF6 [483] . Both IL18 and IL33 influence activity of natural killer T cells. They enhance production by NKT cells of IL4, IL5, IL13, gmCSF, and TNF upon T-cell receptor stimulation.

Interleukin-33 abounds in many tissues. It particularly acts on eosinophils to enhance their survival and adhesion, as well as their production of superoxide (O − 2 ) and CXC-chemokine ligand CXCL8. Moreover, it amplifies eosinophilmediated immune responses, as it operates synergistically with 3 important eosinophil-targeting cytokines IL3, IL5, and granulocyte-macrophage colonystimulating factor.

In addition, IL33 stimulates cytokine production by mastocytes in the absence of additional signals (unlike IL18). It also increases mastocyte maturation and survival. Moreover, it enhances the effects of other stimuli of mastocyte activation, such as thymic stromal lymphopoietin or IgE [483] . Once stimulated by IL12, IL33 promotes Ifnγ production by natural killer cells.

Interleukins IL36α, IL36β, and IL36γ, also called IL1 family members IL1F6, IL1F8, and IL1F9, respectively, are encoded by distinct genes. They target the same receptor complex composed of interleukin-1 receptor-like protein IL1RL2 141 and IL1R accessory protein (IL1RAcP). These pro-inflammatory cytokines prime similar signaling axes.

IL36 Receptor antagonist (IL36RA) corresponds to IL1 Family member IL1F5. It binds to IL1RL2 and antagonizes cytokine ligands similarly to IL1RA that counteracts IL1α and IL1β.

Interleukin-37, or IL1F7, produces anti-inflammatory effects in macrophages and epithelial cells, as it prevents the production of inflammatory cytokines induced by Toll-like receptor agonists as well as that of IL1 and tumor-necrosis factor. progenitors, which lead to B and naive T cells. In particular, IL7R plays a role on the common lymphoid progenitor, the source of all lymphoid lineages [488] . IL7 is compulsory for T-cell but not B-cell development. IL7 also stimulates the proliferation of mature T cells.

Interleukin-9 acts on erythroid progenitors, in the presence of Epo, and T and B cells [489] . It is also involved in immunity against helminths. It recruits mastocytes to the infection site. Transforming growth factor-β is required for IL9-producing T-cell differentiation from type-2 helper T cells [490] . Among committed T lymphocytes, interleukin-9 is synthesized in T H2 , T H9 , T H17 , and regulatory T cells (Table 3 .37). The transcription factor PU1 of the ETS family 142 is required for the development of IL9-secreting subsets of CD4+ helper T cells [491] . Interleukin-9 receptor (IL9R) that is composed of the cytokine-specific IL9R α and γ chain promotes the cross-phosphorylation of JaK1 and JaK3 Janus kinases. This cross-phosphorylation enables activation of signal transducer and activator of transcription complexes, specifically STAT1 homodimers, STAT5 homodimers, and STAT1-STAT3 heterodimers [492] . Target cells of IL9 include mast, regulatory T, T helper-17, and antigen-presenting cells (Table 3 .38). 

Mastocyte Mastocyte proliferation, synthesis of IL1β/5/6/9/10/13 (IL5 and IL13 elicit eosinophilia and airway mucus production)

Autocrine growth factor (cell proliferation) TReg Enhancement of cell regulation APCs

Interleukin-15 is expressed in heart, skeletal muscle, lungs, liver, and kidneys, as well as in activated monocytes, macrophages, endothelial cells, fibroblasts, etc. It triggers the proliferation of activated B lymphocytes and their immunoglobulin production, as well as the proliferation of NK cells and activated CD4+CD8+ T cells. IL16 synthesized by CD4+CD8+ T cells, eosinophils, and mastocytes is a chemokine for CD4+ cells, monocytes, and eosinophils.

Thymic stromal lymphopoietin (TSLP) is a type-1 cytokine that promotes the activation of B and dendritic cells (Table 3 .39). It binds to specific receptors on CD11c+ (α X integrin) dendritic cells. It activates dendritic cells to produce IL4, IL5, IL13, and TNFα. In addition, TSLP promotes T H2 cell responses [493] . Signal TSLP on dendritic cells improves cell survival, upregulates major histocompatibility complex class-2 molecules, costimulators CTLA4 counterreceptor CD86 and TNFRSF5, various chemokines, notably CCL17 and CCL22 that target CCR4 [493] . The TSLP receptor contains TSLPR and IL7Rα. 143 Receptor engagement can activate STAT5 transcription factor.

Fibroblasts, endothelial cells, activated B cells, monocytes, and helper T cells produce IL6. The latter promotes development and functioning of both B and T lymphocytes and megakaryocyte maturation [494] . Interleukin-6 acts in synergy with IL1 and tumor-necrosis factor. It enhances the production of immunoglobulin and glucocorticoid synthesis. Skeletal myocytes also produce IL6 during exercise. Interleukin-6 acts as an autocrine factor that upregulates its mRNA levels via Ca ++ -calmodulindependent kinase kinase (Vol. 1 -Chap. 4. Cell Structure and Function), thereby supporting AMPK activation during exercise. It is rapidly released into the circulation following exercise. It increases fatty acid oxidation, basal and insulin-stimulated glucose uptake, and translocation of GluT4 to the plasma membrane. Interleukin-6 and other myokines may defend against type-2 diabetes 144 with insulin-sensitizing effect. Interleukin-6 increases lipolysis 144 Diabetes mellitus, or simply diabetes, is characterized by altered metabolism with hyperglycemia caused by low production of insulin by β cells of the pancreas with or without resistance to insulin. The classical triad of diabetes symptoms is polyuria (frequent urination), polydipsia (increased thirst and fluid intake), and polyphagia (increased appetite). Type-1, -2, and gestational diabetes have different causes. Type-1 diabetes is usually due to autoimmune destruction of the pancreatic β cells. Type-2 diabetes results from insulin resistance in target tissues. Gestational diabetes occurs when pregnancy hormones are responsible for insulin resistance in genetically predisposed women.

Specific OsM activity is mediated by type-2 receptor, whereas common functions of LIF and OsM depend on type-1 receptor. Receptors LIFR or OsMR can homodimerize in embryonic stem and tumor cells. Interleukin-10, an anti-inflammatory cytokine, limits the immune response to pathogens, thereby preventing damage to the body's cells. In humans, IL10 is a homodimer. Interleukin-10 is expressed by many immune cells, CD4+ T cells (T H0 , T H1 , T H2 , and T H17 clones), regulatory T lymphocytes, CD8+ T cells, monocytes, and macrophages [484] , as well as B cells, eosinophils, and mastocytes [500] , and dendritic and natural killer cells, eosinophils, and neutrophils [501] (Table 3 .40).

The synthesis of interleukin-10 is regulated by chromatin structure (epigenetic control), in addition to the transcription control and post-transcriptional regulation [501] . 146 Production of IL10 is often triggered by pro-inflammatory cytokines. Extracellular signal-regulated kinases ERK1 and ERK2 contribute in many cell types to IL10 synthesis. In macrophages, positive and negative feedback loops regulate IL10 production [501] . 147 Interleukin-10 hinders the synthesis of T H1 -derived (IL2, Ifnγ, and gm-CSF) and monocyte-derived (IL1α and -β, IL6, IL8, TNFα, gmCSF, and gCSF) cytokines, but induces IL1Ra production by macrophages. Interleukin-10 can prevent monocyte differentiation into type-1 dendritic cells, the most important antigen-presenting cells. In the presence of monocytes and/or macrophages, IL10 precludes the proliferation of resting T cells, the reduced proliferation being only partially due to decreased IL2 production. Interleukin-10 146 Transcription factors Specific protein SP1, Activating transcription factor ATF1, CCAAT-enhancer binding protein C/EBPβ, cAMP-responsive-element-binding protein (CREB), Ifn-regulatory factor IRF1, nuclear factor-κB, and signal transducer and activator of transcription STAT3 transactivate the Il10 gene in macrophages and T-cell lines [501] . In addition, 2 cofactors of the homeobox (HOX) family, pre-B-cell leukemia transcription factor PBx1 and PBX-regulating protein PReP1, cause IL10 expression in mouse macrophages. In TH1 cells, mothers against decapentaplegic homolog SMAD4 and musculoaponeurotic fibrosarcoma proto-oncogene homolog (MAF) promote IL10 synthesis. In TH2 cells, MAF, Jun and GATA-binding protein GATA3 elicits IL10 expression. 147 Signaling pathways based on kinases P38MAPK and ERKs that provoke IL10 production are controlled by interferon-γ and IL10 itself. The latter stimulates dual-specificity protein phosphatase DUSP1 that impedes P38MAPK action. On the other hand, IL10 upregulates mitogen-activated protein kinase kinase kinase MAP3K8 to amplify its own production. In addition, Ifnγ can also block the PI3K-PKB pathway, thereby relieving the inhibtion on glycogen synthase kinase GSK3. The latter suppresses IL10 expression via cAMP response elementbinding protein (CREB) and Activator protein-1. 

In humans, 5 molecules are structurally related to IL10: IL19, IL20, IL22, IL24, and IL26 (Table 3 .42). Interleukin-22 is a member of the IL10 family that is involved in inflammation and wound healing. It is mainly produced by T H17 and T H22 cells.

Interleukin-12 is produced by macrophages, activated monocytes, and neutrophils. A positive feedback exists between IL12 and Ifnγ, this loop being controlled by IL10, TGFβ, IL4, and IL13, which downregulate IL12 production and the ability of T and NK cells to respond to IL12 [484] . Interleukin-12 activates NK cells and enhances via Ifnγ the phagocytic activity. It favors T H1 cell differentiation and functioning and inhibits T H2 cell differentiation. It synergizes with other hematopoietic factors to promote proliferation of early multipotent hematopoietic progenitors and lineage-committed precursors [503].

Most of interleukin-17 released during inflammation is produced by innate immune cells (Table 3 .43) rather than T H17 cells and CD4+ memory T cells. Innate immune, IL23-dependent, IL17-producing cells include macrophages ). Interleukin-10 has potent effects on numerous cell populations, in particular circulating and resident immune cells as well as epithelial cells. It is immunoregulatory rather than simply immunosuppressive and anti-inflammatory. It indeed stimulates some functions of innate immunity, such as NK cell activity, non-inflammatory removal of particles, cells, and microbes by stimulating phagocytosis, and TH2-related immunity, but suppresses directly and indirectly TH response and pro-inflammatory cytokine secretion by macrophages. It acts on dendritic cells and macrophages (autocrine inhibition) to prevent the development of TH1 responses. It can suppress TH2 and allergic responses. On the other hand, IL10 enhances the differentiation of IL10-secreting TReg cells. In some circumstances, IL10 activates mastocytes and improves the activity of CD8+ T, NK, and B cells. ; βG: β-glucan; AHR, aryl hydrocarbon receptor; BP: bacterial product; CLec7a: C-type lectin domain family-7 member-A, or dectin-1; GL: glycolipid; ID2: inhibitor of DNA-binding-2; IL: interleukin; IRF4:interferon regulatory factor; Ly6g: lymphocyte antigen 6 complex, locus G; MICA: MHC class-1 polypeptide-related sequence-A; NCR: natural cytotoxicity triggering receptor [NCR1 a.k.a. natural killer cell P46-related protein (NKp46)]; NKG2d: natural killer group-2 member-D; NOD2: nucleotide-binding oligomerization domain protein-2; RAE1: retinoic acid early transcript-1; ROR: retinoic acid receptor-related orphan receptor; Runx: Runt-related transcription factor; SCA: stem cell antigen; STAT: signal transducer and activator of transcription; TLR: Toll-like receptor; TNF: tumor-necrosis factor). Interleukin-17A is synthesized at its highest levels in thymus-dependent lymphocytes, such as adaptive αβ Tand innate γδ T cells, as well as invariant natural killer T (iNKT) and lymphoidtissue inducer-like (LTi) cells. Cluster of differentiation CD90, or Thy1, is a glycosylphosphatidylinositol (GPI)-anchored cell surface antigen originally discovered as a thymocyte antigen. and dendritic cells that predominantly reside in the skin and mucosae, where they serve as sentinels of the immune system [504] . They possess IL23R to amplify the inflammatory response. 

Type-1 (interferon-I), -2 (interferon-II), and -3 (interferon-III) interferons (Table 3 .45) have antiviral, antiproliferative, and immunomodulatory effects. They activate the Janus kinase-signal transducer and activator of transcription signaling, mitogen-activated protein kinase P38MAPK, and phosphatidylinositol 3-kinase cascades [510] . Interferons induce the expression of multiple genes. Certain genes are regulated by Ifn I and -II, whereas others are selectively regulated by distinct Ifns. Type-1 interferons (Ifnα, Ifnβ, Ifnδ, Ifn , Ifnζ, Ifnκ, Ifnω, and Ifnτ), 151 produced by many cell types, such as T and B cells, bind to a specific receptor (interferon-α and -β receptors [IfnAR]) to yield antiviral activities. They stimulate both macrophages and natural killer cells. Interferon-ω is released by leukocytes at the site of viral infections or tumors.

Type-2 interferon, or interferon-γ, is secreted by CD8+ T cells. Interferonγ is involved in the regulation of the immune and inflammatory responses. It potentiates the effects of Ifnα and Ifnβ. It promotes the presentation of antigen to CD4+ helper T cells. It also stimulates macrophages.

Type-3 interferons, i.e., members of the interferon-λ class, include interleukin-28a (Ifnλ2), -28b (Ifnλ3), and -29 (Ifnλ1). They pertain to the class-2 150 During extravasation, leukocytes migrate stimulated by IL8 concentration gradient and accumulate at locations of high concentration. 151 Type-1, class-α interferons are produced by leukocytes against viral infection. They include 13 subtypes (Ifnα1-Ifnα2, Ifnα4-Ifnα8, Ifnα10, IfnαFNA13-Ifnα14, Ifnα16-Ifnα17, and Ifnα21, in addition to Ifnα pseudogene IfnαP22). Type-1, class-β interferons that are synthesized by fibroblasts have also an antiviral activity. Two Ifnβ subtypes exist (Ifnβ1 and Ifnβ3; Ifnβ2 corresponds to interleukin-6). In humans, another isoform exists: Ifnκ (but not Ifnδ, Ifn , Ifnζ, and Ifnτ). In humans, interferon-ω released by leukocytes comprises a single functional form (Ifnω1) and several pseudogenes (IfnωP2, -P4, -P5, -P9, -P15, -P18, and -P19).

family Interleukin-1α, -1β, -18, -33 Interleukin-1 receptors IL1R1 and IL1R2 IL1 receptor-related proteins IL1RL1 and IL1RL2 IL1 receptor accessory protein (IL1RAcP) IL2 receptor family Interleukin-2

Granulocyte-macrophage colony-stimulating factor IL6 receptor family Interleukin-6, -11, -12A/B, -23 Oncostatin-M, leukemia inhibitory factor, ciliary neurotrophic factor, cardiotrophin-1, B-cell-stimulating factor-3, leptin, granulocyte colony-stimulating factor (CSF3)

Single-chain family Erythropoietin, growth hormone, prolactin Class-2 cytokines IL10 receptor family Interleukin-10

Type-I interferons Interferon-α, -β, -κ, -ω (IfnαR1-IfnαR2)

Type-II interferons Interferon-γ (IfnγR1-IfnγR2)

Type-III interferons Interferon-λ (interleukin-28 and -29)

Interleukin-18 is expressed by macrophages and dendritic cells as well as epithelial cells. 140 Molecule ProIL18 is constitutively produced, but needs to be processed by caspase-1 to be activated

Plasmalemmal receptor IL1RL1 is a marker of type-2 helper T lymphocytes. Receptor IL1RL1 (IL1RL1b or ST2) can be secreted (soluble IL1RL1 form [IL1RL1a]). Activity of IL1 is controlled by both the receptor antagonist IL1RA and IL1R2 decoy receptor. Interleukins IL18 and IL33 are inhibited by the binding partner IL18BP and soluble IL1RL1a

Therefore, some IL1 family members are counteracted by a corresponding receptor antagonist and others by a soluble receptor or binding protein. Expression of IL1 receptor member IL1RL1b can be primed by mechanical stimulus in cardiomyocytes

The IL2 family of cytokines include IL2, IL4, IL7, IL9, IL13, IL15, IL21, and thymic stromal lymphopoietin (TSLP)

It also acts on macrophages as well as B-, NK-, and lymphokine-activated killer cells [484]. Natural killer cells secrete TNFα, Ifnγ, and gmCSF in response to IL2 that activates macrophages

IL3 acts on hematopoietic progenitors, in combination with other cytokines. Activated CD4+, CD8+ T cells, basophils, and mastocytes produce IL4 and IL13. IL4 is a T-cell growth factor and promotes the differentiation of T

Interleukin-3 elicits many actions of IL4. Interleukin-5, manufactured by activated CD4+, CD8+ T cells and mastocytes, influences eosinophil and basophil production and functioning. It enhances IL2-dependent differentiation and proliferation of T cells

Interleukin-7 is the major thymopoietic cytokine that is produced by bone marrow and thymic stromal cells. IL7 stimulates stem cells to form lymphoid and fatty acid oxidation in patients with type-2 diabetes independently of growth hormone and/or cortisol

Interleukin-6 stimulates the production of anti-inflammatory cytokines, such as IL1 receptor antagonist and IL10. Interleukin-10 impedes the production of IL1a, IL1b, IL8, and TNFα. Long-term effect of exercise can hinder chronic diseases associated with inflammation, such as type-2 diabetes. However, IL6 activates suppressor of cytokine signaling (SOCS) in the liver

Interleukin-6 increases SOCS3 expression 2-fold in muscle and concomitantly glucose uptake. Negative effects of IL6 on SOCS3 can be overridden by the positive effects on AMPK

IL11 stimulates the proliferation of primitive stem cells as well as commitment and differentiation of multi-lineage progenitors [498]. IL11 acts synergistically to stimulate: (1) megakaryocytopoiesis and thrombopoiesis with IL3, Tpo, or SCF; (2) erythropoiesis with IL3, SCF, or Epo; and (3) myeloid colony formation with stem cell factor

Cytokines of the IL6 family include cardiotrophin-1 (CT1), ciliary neurotrophic factor (CNTF), leukemia inhibitory factor (LIF), and oncostatin-M (OsM). All IL6s that homo-or heterodimerize protein GP130 (i.e., complexes GP130-GP130, GP130-LIFR, and GP130-OsMR) activate kinases JaK1, JaK2, and, to a lesser extent Tyk2

Cardiotrophin-1 is produced by cardiomyocytes and cardiac fibroblasts subjected to mechanical stress overload and/or exposed to an excessive amount of angiotensin-2

Secreted CT1 interacts with heterodimeric receptor formed by GP130 and leukemia inhibitory factor receptor (LIFR) to initiate exaggerated cardiomyocyte growth, reduce calsequestrin expression, and impede formation of longitudinal bundles of cardiomyocytes

Upon homodimerization, GP130 phosphorylates (activates) both STAT1 and STAT3. Protein GP130 preferentially activates STAT3

Interleukin-17 (IL17 or IL17a) is secreted by CD4+, CD45RA+, CD45RO+ activated memory T cells

Interleukin-17 stimulates T and endothelial cells as well as fibroblasts and macrophages to express various cell-specific cytokines [506]. It also exhibits indirect hematopoietic activity by enhancing the capacity of fibroblasts to sustain the proliferation of CD34+ hematopoietic progenitors and their differentiation into neutrophils

Interleukin-17a 149 is both an innate and adaptive cytokine

Interleukin-34 is expressed in various tissues (heart, brain, lung, liver, kidney, thymus, testis, ovary, small intestine, prostate, and colon), especially in the spleen, in particular by sinusoidal endothelium in its red pulp. It regulates myeloid cell growth and differentiation. Interleukin-34 binds to macrophage colony-stimulating factor receptor (or colony-stimulating factor receptor CSF1R)

Stimulated monocytes, neutrophils, T and NK cells, fibroblasts, and endothelial cells secrete interleukin-8

IL8-related chemotactic cytokine growth-regulated oncogene GROα. 149 Initially termed cytotoxic T-lymphocyte antigen CTLA8

Cytosolic Protein Tyrosine Kinases) associate with IfnAR1 and IfnAR2c subunits, respectively. Interferon-II (interferon-γ) receptor is also a heterodimer with IfnγR1 and IfnγR2 subunits encoded by the IFNGR1 and IFNGR2 genes. Members of the interferon-λ class target the receptor dimer made of IL28Rα