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Viruses 2014, 6(11), 4609-4627; doi:10.3390/v6114609

Implication of Human Endogenous Retrovirus Envelope Proteins in Placental Functions

Département des Sciences Biologiques and Centre de recherche BioMed, Université du Québec à Montréal, 2080 Saint-Urbain, Montréal, PQ H2X 3X8, Canada
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Received: 11 October 2014 / Revised: 2 November 2014 / Accepted: 7 November 2014 / Published: 24 November 2014
(This article belongs to the Special Issue Endogenous Viruses)
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Abstract

Human endogenous retroviruses (ERVs) represent 8% of the total human genome. Although the majority of these ancient proviral sequences have only retained non-coding long terminal repeats (LTRs), a number of “endogenized” retroviral genes encode functional proteins. Previous studies have underlined the implication of these ERV-derived proteins in the development and the function of the placenta. In this review, we summarize recent findings showing that two ERV genes, termed Syncytin-1 and Syncytin-2, which encode former envelope (Env) proteins, trigger fusion events between villous cytotrophoblasts and the peripheral multinucleated syncytiotrophoblast layer. Such fusion events maintain the stability of this latter cell structure, which plays an important role in fetal development by the active secretion of various soluble factors, gas exchange and regulation of fetomaternal immunotolerance. We also highlight new studies showing that these ERV proteins, in addition to their localization at the cell surface of cytotrophoblasts, are also incorporated on the surface of various extracellular microvesicles, including exosomes. Such exosome-associated proteins could be involved in the various functions attributed to these vesicles and could provide a form of tropism. Additionally, through their immunosuppressive domains, these ERV proteins could also contribute to fetomaternal immunotolerance in a local and more distal manner. These various aspects of the implication of Syncytin-1 and -2 in placental function are also addressed in the context of the placenta-related disorder, preeclampsia. View Full-Text
Keywords: human endogenous retrovirus; Syncytin-1 and -2; placenta; syncytiotrophoblast; immunotolerance; exosomes; pre-eclampsia human endogenous retrovirus; Syncytin-1 and -2; placenta; syncytiotrophoblast; immunotolerance; exosomes; pre-eclampsia
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Lokossou, A.G.; Toudic, C.; Barbeau, B. Implication of Human Endogenous Retrovirus Envelope Proteins in Placental Functions. Viruses 2014, 6, 4609-4627.

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