key: cord-0742882-8cpe2ddi authors: Lee, Ji Yong; Kim, Han-Soo title: Extracellular Vesicles in Regenerative Medicine: Potentials and Challenges date: 2021-07-23 journal: Tissue Eng Regen Med DOI: 10.1007/s13770-021-00365-w sha: 1715b8034c718dba46a3a69d5ee301b0bbef0d95 doc_id: 742882 cord_uid: 8cpe2ddi The ultimate goal of regenerative medicine is to regain or restore the damaged or lost function of tissues and organs. Several therapeutic strategies are currently being explored to achieve this goal. From the point of view of regenerative medicine, extracellular vesicles (EVs) are exceptionally attractive due to the fact that they can overcome the limitations faced by many cell therapies and can be engineered according to their purpose through various technical modifications. EVs are biological nanoscale vesicles naturally secreted by all forms of living organisms, including prokaryotes and eukaryotes, and act as vehicles of communication between cells and their surrounding environment. Over the past decade, EVs have emerged as a new therapeutic agent for various diseases and conditions owing to their multifaceted biological functions. This is reflected by the number of publications on this subject found in the Web of Science database, which currently exceeds 12,300, over 85% of which were published within the last decade, demonstrating the increasing global trends of this innovative field. The reviews collected in this special issue provide an overview of the different approaches being explored in the use of EVs for regenerative medicine. composition of these subcellular particles includes growth factor receptors, ligands, adhesion proteins, mRNAs, microRNAs (miRNAs), long non-coding RNAs (lncRNAs), second messengers, metabolites, and lipids that reflect their cellular origin. The decorating proteins on the surface of EVs may serve as a type of postal code that delivers membrane-enclosed messages. In general, EVs are commonly divided into two major subgroups according to their size and biogenesis: microvesicles (MVs) and exosomes. MVs are 100-500 nm in diameter, are generated by budding off from the plasma membrane, and represent a subgroup of larger vesicles. Exosomes, which are much smaller vesicles with a diameter of approximately 40-150 nm, are formed by the reverse budding of endosomal multivesicular bodies and are secreted from cells upon the fusion of these bodies with the plasma membrane. It is difficult to obtain pure vesicle fractions of microvesicles and exosomes because of the size, density, and protein marker overlaps between microvesicles and exosomes. Due to the methodological difficulties associated with distinguishing these sub-groups, it has also been proposed to substitute the term ''extracellular vesicles (EVs)'' in accordance with ISEV 2018 guidelines [3] . Mesenchymal stem cells (MSCs) can be applied in regeneration, and have a long history of extensive basic research and beneficial results in clinical trials. Many preclinical studies have reported paracrine factors as key therapeutic agents for MSC-based cell therapies [4] . Among these paracrine factors, the therapeutic roles of EVs in regenerative medicine have been elucidated by studies utilizing animal disease models of kidney, musculoskeletal, cardiovascular, hepatic, neurological diseases and hair loss [5] [6] [7] [8] [9] [10] . A recent study showed that MSCs-EVs ameliorated LPS-induced acute respiratory distress syndrome (ARDS) in a mouse model, indicating their utility in the control of the inflammatory response and fibrotic events following Covid-19 infection [11] . In addition to MSCs, embryonic stem cells, induced pluripotent stem cells, tissue-specific stem cells, progenitor cells derived from stem cells, and even terminally differentiated cells may also be successfully used in tissue regeneration as EV producers [12] [13] [14] . Accumulating evidence of preclinical therapeutic efficacy and their versatility in tissue repair and regeneration has brought attention to EVs as a potential regenerative substance. Although recent studies have shown that the regulation of apoptosis, cell proliferation, differentiation, migration, angiogenesis, oxidative stress, aging, and inflammation are mainly attributed to the action of EVs [15] , the molecular biological mechanisms involved in EVmediated tissue repair and regeneration have not been fully elucidated. Studies have suggested that three molecular entities in the EV composition play key roles in EV-mediated tissue repair and regeneration processes: miRNAs, mRNAs, and proteins. To date, several specialized signaling pathways related to regenerative processes, such as mitogen-activated protein kinase, Wnt/b-catenin, PI3K/ Akt, Notch, TGF-b/Smad, STAT and Hedgehog signaling, CaMKII, and Efna3 signaling, have been identified upon EV stimulation [16] [17] [18] [19] . EVs can deliver key proteins directly or control their upstream or downstream components by regulating gene expression with mRNAs or miRNAs [20] , a subtype of small (19-24 nucleotides), noncoding RNA molecules that target mainly mRNA molecules to regulate gene expression at the post-transcriptional level. Many studies have evaluated the miRNA cargo of EVs and proposed their regulatory roles in cell proliferation, differentiation, and apoptosis during tissue regeneration. Several miRNAs act as potential contenders for tissues and organ-specific tissue regeneration. For example, miR-124 and miR-9/9* induce the direct conversion of fibroblasts into neuron-like cells by modulating chromatin remodeling complex [21] , and miR-1 and miR-133a protects the myocardium against apoptosis, oxidative stress, and fibrosis and promotes cardiac regeneration [22] . Furthermore, the immunomodulatory role of EVs has been demonstrated by miR-146a in BM-MSC-derived MVs in allogenic kidney transplantation [23] . mRNAs are another prime messenger in EVs in tissue regeneration. In particular, the horizontal transfer of mRNAs from donor cells to recipient cells is evident in studies utilizing MSC-derived EVs [18] . The therapeutic action of MSC-EV-delivered mRNAs related to Gene Ontology terms of immune regulation and damage repair to recipient cells have already been documented in several studies [24] . For example, Choi et al. [25] found that MSC-EVs containing mRNA of vascular endothelial growth factor (VEGF-A), basic fibroblast growth factor (bFGF), and insulin-like growth factor 1 (IGF-1) induced the proliferation of peritubular capillary endothelial cells in acute renal ischemic mice. Additionally, the horizontal transfer of neuregulin 1 mRNA in adipose stem cell (ASC)-derived EVs diminished muscle damage and inflammation in a mouse model of hind limb ischemia [26] . However, it should be noted that the regenerative effect observed in this study is not solely manifested by the horizontal transfer of mRNA species by EVs. Proteins in EVs are known to modulate the intracellular and extracellular microenvironment of recipient cells. Proteome studies of MSC-EVs have identified proteins associated with tissue repair and regeneration via angiogenesis, coagulation, apoptosis, inflammation, and extracellular matrix remodeling [27, 28] . The accumulation of knowledge regarding EVs using disease models has provided potential opportunities for their clinical applications in a variety of diseases [29, 30] . Based on their compact size, collection efficiency, biocompatibility, and engineered production, EVs have many advantages as a therapeutic delivery tool for regenerative medicine. However, several regulatory hurdles and technical challenges must be addressed for the successful clinical translation of these remarkable biological particles. These include defining therapeutically active sub-populations of EVs among heterogeneous vesicles, the optimization of the purification step, scale-up production, dosage, route of administration, safety of EVs (toxicity, immune response, and pharmacodynamics), regulation of complications, and quality management [31, 32] . Although several clinical trials of EVs are in progress, majority are focused on biomarkers, pathological mechanisms, and cancer treatment, and only a few studies have focused on Tissue Eng Regen Med tissue repair and regeneration. The EV clinical studies in the field of regenerative medicine that are ongoing are summarized in Table 1 . In just a few years, several biotech companies have developed EV-based therapeutic agents from different cell sources, and have attempted to enhance the therapeutic potential of EVs using various strategies, including technology related to enhanced isolation efficiency, characterization, large-scale production, and loading cargo with a combination of other biomaterials. Commercial EV-based products for tissue repair and regeneration of other organs in human clinical settings have already been developed and registered ( Table 2) . Although EVs have shown potential as a new biological therapeutic agent in the field of regenerative medicine, and their effectiveness has been verified through in vivo and in vitro studies, the mechanisms by which the biological components of EVs promote tissue repair and regeneration remain unknown. However, once the relative contributions of specific molecules become clear, researchers will be able to enhance the therapeutic potential of EVs via biochemical or genetic engineering for disease-and organ-specific repair and regeneration. The special issue ''Current progress in extracellular vesicles in stem cells and tissue regeneration'' was enthusiastically released by the Editorial Board of Tissue Engineering and Regenerative Medicine to identify unresolved issues and report on cutting-edge developments in tissue engineering and regenerative medicine. As reviewed in this special issue, advances in the isolation and characterization of EVs, along with their intrinsic capacity, clearly opens new avenues for tissue repair and regeneration in humans. We would like to thank all of the contributing authors of the papers collected in this special issue and hope that the readers will both enjoy and be inspired by this emerging and state-of-the-art research topic. Exosomes: from garbage bins to promising therapeutic targets The exosome journey: from biogenesis to uptake and intracellular signalling Extracellular vesicles or exosomes? On primacy, precision, and popularity influencing a choice of nomenclature Mesenchymal stem/stromal cell-based therapy: mechanism, systemic safety and biodistribution for precision clinical applications Microvesicles from brain-extract-treated mesenchymal stem cells improve neurological functions in a rat model of ischemic stroke Mesenchymal stem cell-derived extracellular vesicle therapy for stroke: challenges and progress Mesenchymal stromal cell uses for acute kidney injury-current available data and future perspectives: a mini-review Native and bioengineered extracellular vesicles for cardiovascular therapeutics Extracellular vesicles isolated from mesenchymal stromal cells primed with neurotrophic factors and signaling modifiers as potential therapeutics for neurodegenerative diseases Human hair outer root sheath cells and platelet-lysis exosomes promote hair inductivity of dermal papilla cell MSC-NTF (NurOwnÒ) exosomes: a novel therapeutic modality in the mouse LPS-induced ARDS model Extracellular vesicles derived from preosteoblasts influence embryonic stem cell differentiation Acellular therapeutic approach for heart failure: in vitro production of extracellular vesicles from human cardiovascular progenitors Extracellular vesicle-induced differentiation of neural stem progenitor cells Attenuation of tumor necrosis factor-a induced inflammation by umbilical cord-mesenchymal stem cell derived exosome-mimetic nanovesicles in endothelial cells IL-3R-alpha blockade inhibits tumor endothelial cellderived extracellular vesicle (EV)-mediated vessel formation by targeting the b-catenin pathway Extracellular vesicles mediate mesenchymal stromal celldependent regulation of B cell PI3K-AKT signaling pathway and atin cytoskeleton Signal exchange through extracellular vesicles in neuromuscular junction establishment and maintenance. From physiology to pathology Neuroprotective effect of mesenchymal stromal cell-derived extracellular vesicles against cerebral ischemia-reperfusion-induced neural functional injury: a pivotal role for AMPK and JAK2/STAT3/NF-jB signaling pathway modulation MicroRNAs (miRNAs) and long non-coding RNAs (lncRNAs) as new tools for cancer therapy: first steps from bench to bedside MicroRNA-mediated conversion of human fibroblasts to neurons miR-133a enhances the protective capacity of cardiac progenitors cells after myocardial infarction Biological properties of extracellular vesicles and their physiological functions Exosome mediated transfer of mRNAs and microRNAs is a novel mechanism of genetic exchange between cells Microparticles from kidney-derived mesenchymal stem cells act as carriers of proangiogenic signals and contribute to recovery from acute kidney injury Extracellular vesicles from adipose stem cells prevent muscle damage and inflammation in a mouse model of hind limb ischemia: role of neuregulin-1 Proteomic analysis of microvesicles derived from human mesenchymal stem cells Functional proteins of mesenchymal stem cell-derived extracellular vesicles Applying extracellular vesicles based therapeutics in clinical trials: an ISEV position paper Exosomes as therapeutic vehicles for cancer Three-dimensional spheroid culture increases exosome secretion from mesenchymal stem cells Advances in therapeutic applications of extracellular vesicles Ethical statement Ethical approval and consent to participate is not applicable to this article as no data were generated or analyzed during the current study.