key: cord-0727571-jp0s64gq authors: Dotan, Arad; Kanduc, Darja; Muller, Sylviane; Makatsariya, Alexander; Shoenfeld, Yehuda title: Molecular mimicry between SARS‐CoV‐2 and the female reproductive system date: 2021-08-18 journal: Am J Reprod Immunol DOI: 10.1111/aji.13494 sha: 4f192074753bf3ca404e98fe38db242c86dbe061 doc_id: 727571 cord_uid: jp0s64gq Oogenesis, the process of egg production by the ovary, involves a complex differentiation program leading to the production of functional oocytes. This process comprises a sequential pathway of steps that are finely regulated. Genetic predisposition and abnormal immune responses are some of the numerous possible causes of female infertility. The question related to SARS‐CoV‐2 infection and fertility has been evoked for several reasons, including the high expression of ACE2 in the female reproductive tissues, the entry receptor for SARS‐CoV‐2, and the potential damage to germline (oocytes) due to the dysfunction of autophagy in COVID‐19. In addition, molecular mimicry may contribute to female infertility by leading to the generation of deleterious autoantibodies, which could also participate to the onset of an autoimmune disease in infected patients. We carried out a systematic study to improve our understanding of the possible effects of SARS‐CoV‐2 infection on female fertility using the angle of molecular mimicry as a starting point. Results show a number of rather long linear sequences shared by the SARS‐CoV‐2 proteins and oogenesis‐related proteins that might play a role in the production of possibly pathogenic crossreactive autoantibodies. SARS‐CoV‐2 spike glycoprotein was found to share 41 minimal immune determinants, i.e., pentapeptides, with 27 human proteins that relate to oogenesis, uterine receptivity, decidualization, and placentation. All the shared pentapeptides that we identified, with the exception of four, are also present in SARS‐CoV‐2 spike glycoprotein–derived epitopes that have been experimentally validated as immunoreactive. This article is protected by copyright. All rights reserved Oogenesis, the process of egg production by the ovary, involves a complex differentiation program leading to the production of functional oocytes. The ovaries (or female gonads) are filled with follicles in which the oocyte grows to maturity. It is well documented that females do not make new eggs and that the pool of eggs presents in the ovary at birth represent the total numbers of oocytes that will continuously decline over the female's life. At the time of menopause, virtually no eggs remain. The large supplies of eggs within ovary are immature. They undergo growth and maturation each month. The maturation program of oocytes comprises a sequential pathway of steps that are finely regulated (1, 2) . There are numerous possible causes of female infertility. Genetic and abnormal immune responses are often presented as factors that may lead to infertility (3) . Infertility resulting from the effect of autoantibodies (autoAbs) has been a matter of many debates (4) (5) (6) . Certain autoAbs such as anti-phospholipid, anti-thyroid (anti-thyroperoxidase and/or anti-thyroglobulin), anti-nuclear, anti-annexin V, anti-prothrombin, anti-laminin, anti-follicle stimulating hormone Abs have been associated with infertility, especially due to premature ovarian insufficiency, in addition to pregnancy loss (5, 6) . Anti-sperm Abs also seem to be more frequent in the population of infertile women. The direct pathological role of these autoAbs is generally unknown. The question related to SARS-CoV-2 infection and fertility (in females and males) has been evoked for several reasons. First, it is well documented nowadays, that the angiotensin converting enzyme II (ACE2) is an entry receptor for SARS-CoV-2, the virus responsible for coronavirus disease 19 (COVID-19) (7, 8) . ACE2 is a type I-transmembrane metallocarboxypeptidase with homology to ACE, a key player enzyme in the renin-angiotensin system, and a target for the treatment of hypertension. It is highly expressed in the small intestine, kidneys, heart, thyroid, adipose tissue, and especially in testis, ovaries, uterus, vagina and placenta (2, 9, 10 ). Although at a lower level, ACE2 is also present in other organs and tissues. It has therefore been postulated that via ACE2, SARS-CoV-2 might cause direct injury in these tissues (2,10, Table 1, supplementary Table S1 ). ACE2 regulates follicular development and ovulation, modulates luteal angiogenesis and degeneration, and affects the regular changes of endometrial tissue and embryo development (10) . The question has thus been raised to know whether COVID-19 might have an effet on female fertility (2,10). Second, as said above, over years, there is a decline in female fertility linked to a reduction in both the quantity and quality of the germline (oocytes). Recent advances have revealed that autophagy, in relation with oxidative stress, influences oocyte longevity (11, 12) . It turns out that autophagy is especially involved in SARS-CoV-2 infection (13, 14) . Any dysfunction of autophagy, in the case of COVID-19, might therefore have important consequences in oocyte maturation that de facto could influence ovulation and fertility. Third, as shown in the case of numerous other infections, Abs generated against viral proteins could cross-react with common sequences shared by pathogens and self-components. This mechanism of molecular mimicry may lead to the generation of deleterious Abs, which could participate to the onset of an autoimmune disease in infected patients (15) (16) (17) . With this aim in mind, we carried out a systematic study to improve our understanding of the possible effects of SARS-CoV-2 infection on female fertility using the angle of molecular mimicry as a starting point. We identified a number of rather long linear sequences shared by the SARS-CoV-2 proteins and oogenesis-related proteins that might play a role in the production of possibly pathogenic crossreactive Abs. Peptide sharing between oogenesis-related human proteins and spike glycoprotein (NCBI, GenBank Protein Accession Id=QHD43416.1) from SARS-CoV-2 (NCBI:txid2697049) was analyzed using pentapeptides as sequence probes since a peptide grouping formed by five amino acid (aa) residues defines a minimal immune determinant that can 1) induce highly specific Abs, and 2) determine antigen-Ab specific interaction (18, 19) . A library of 82 human proteins linked to oogenesis was assembled at random from UniProtKB database (www.uniprot.org/) (20) using oogenesis, uterine receptivity, decidualization, and placentation as a key words. The 82 human proteins are listed in Supplementary Table S1 . For the analyses, an artificial polyprotein was built by joining the 82 aa sequences of the oogenesis-associated proteins. The spike glycoprotein primary sequence was dissected into pentapeptides offset by one residue (that is: MFVFL, FVFLV, VFLVL, FLVLL and so forth) and the resulting viral pentapeptides were analyzed for occurrences within the polyprotein. Occurrences and the corresponding proteins were annotated. The immunological potential of the peptides shared between SARS-CoV-2 spike glycoprotein and oogenesis-related proteins was analyzed by searching the Immune Epitope DataBase (IEDB, www.iedb.org/) (21) for immunoreactive SARS-CoV-2 spike glycoprotein epitopes hosting the shared pentaptides. Quantitatively, SARS-CoV-2 spike glycoprotein was found to share 41 minimal immune determinants, i.e., pentapeptides, with 27 human proteins that relate to oogenesis, placentation and/or decidualization. The shared pentapeptides are the oogenesis related proteins are described in Table 1 . Exploration of the Immune Epitope DataBase (IEDB, www.iedb.org/) (21) revealed that all the shared pentapeptides described in Table 1 , with the exception of two (namely, VLGQS, QVAVL, ALGKL and SNLLL), are also present in SARS-CoV-2 spike glycoprotein-derived epitopes that have been experimentally validated as immunoreactive (see IEDB, www.iedb.org/ for immunoassays and references) (21) . Since its appearance, SARS-CoV-2 has rightly attracted the scientific-clinical attention on organs and functions that are object of the viral attack and contribute to the acute pathology associated with this disease, that is respiratory failure and dysfunctional immune system (70, 71) . However and of relevant importance, it also emerged the possibility that the virus can affect multiple functions and, among them, human fertility (72, 73) . Evidences indicate that the virus can target human reproductive organs that express its main receptor ACE2, although it is as yet unclear if this has any implications for human fertility (74) . This article is protected by copyright. All rights reserved. Here, a mechanism, i.e., cross-reactivity, and a molecular platform, i.e., peptide sequences derived from infertility-related proteins and also present in SARS-CoV-2, are proposed as possible links between infertility occurrence and SARS-CoV-2 infection. Actually, already in 1998 [75] , it was shown that the sharing of a short peptide between murine myelin basic protein and hepatitis B virus (HBV) could lead to pathogenic autoimmune cross-reactivity in animal models, so explaining the high incidence of demyelinating diseases that was observed following HBV infection. These studies and some others in the same line were guided by the idea that amino acid sequence similarities between the pathogens and the human host may lead to autoimmune pathologies through cross-reactivity phenomena occurring after pathogen infection. Taken Citing only a few, we can list here the loss of germ cells, severe reduction in testis and ovary size, alteration in male sex determination, sex reversal, alteration of folliculogenesis, alteration of the balance of the sexually dimorphic gene expression, reduced fertility, alterations of puberty with precocious puberty, absence of or incomplete sexual maturation, dysfunction of reproductive function, non-obstructive azoospermia and premature ovarian insufficiency [see Table 1 Plays a key role in the male and female germline by promoting transition from mitotic to meiotic divisions in stem cells 69 1 Hexapeptides derived from overlapping pentapeptides given bold 2 Human proteins given by Uniprot accession and name in italics. 3 Functions and/or associated pathologies: data from from Uniprot, Pubmed, and OMIM public databases Table 2 . 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