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The Relationship of the Mechanisms of the Pathogenesis of Multiple Sclerosis and the Expression of Endogenous Retroviruses - PubMed

  • ️Wed Jan 01 2020

Review

The Relationship of the Mechanisms of the Pathogenesis of Multiple Sclerosis and the Expression of Endogenous Retroviruses

Vera R Lezhnyova et al. Biology (Basel). 2020.

Abstract

Two human endogenous retroviruses of the HERV-W family can act as cofactors triggering multiple sclerosis (MS): MS-associated retrovirus (MSRV) and ERVWE1. Endogenous retroviral elements are believed to have integrated in our ancestors' DNA millions of years ago. Their involvement in the pathogenesis of various diseases, including neurodegenerative pathologies, has been demonstrated. Numerous studies have shown a correlation between the deterioration of patients' health and increased expression of endogenous retroviruses. The exact causes and mechanisms of endogenous retroviruses activation remains unknown, which hampers development of therapeutics. In this review, we will summarize the main characteristics of human endogenous W retroviruses and describe the putative mechanisms of activation, including epigenetic mechanisms, humoral factors as well as the role of the exogenous viral infections.

Keywords: CpG methylation; ERVWE1; HERV-W; MSRV; citrullination; multiple sclerosis.

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Conflict of interest statement

The authors declare that they have no conflict of interests.

Figures

Figure 1
Figure 1

The structure of the HERV-W family and the ERVWE1 gene. (A) The HERV-W family includes four genes, with an up and down stream LTRs. These LTRs consist of U3, R and U5 region. The U3 region of 5′-LTR consist of tRNATrp-binding PBS, CAAT and TATA box sites. The gag gene encodes elements of the matrix, capsid and nucleocapsid, while pro gene encodes for protease. Viral pol gene encodes for reverse transcriptase and integrase. Finally, the envelop protein is coded by the env gene. (B) The ERVWE1 gene is “domesticated” and retains the ability to express genes of the HERV-W family. It consists of the env gene, called Syncitin-1, with an ORF and is also surrounded by two LTR from 5′ and 3′ ends. Trophoblast-specific enhancer (TSE) containing AP-2, Sp-1 and GCMa binding sites is located upstream of the 5′-LTR. The U3 region of 5′-LTR contains PPAR-γ, Oct-1, GATA, AP-2, Sp-1, CREB, CAAT and TATA box binding sites. R region contains a CAP transcription initiation site at the 5′ end and a polyadenylation site at the 3′ end. The R region of the 3′-LTR includes a polyadenylation site. The whole ERVWE1 gene is flanked by the MaLR retrotransposon.

Figure 2
Figure 2

The mechanism of RNA interference. The Dicer enzyme cleaves specific to HERV-W double-stranded miRNA and promotes the loading of each strand into the RISC complex. Dicer binds to the transactivating response RNA-binding protein (TRBP) to facilitate the transfer of dsRNA fragments to Argonaute 2 (Ago2). The least stable 5′ end RNA strand is integrated with the Ago2 protein in RISC, and the second passenger strand is degraded. The RISC complex with guide strand miRNA complementary binds to the 3′-LTR of the mRNA HERV-W and silences it.

Figure 3
Figure 3

The mechanism of regulation of HERV-W transcription by histone citrullination. (A) Repression of HERV-W transcription upon the interaction of HP1α with histone H3K9 in LTR. (B) Enhanced expression of HERV-W due to the formation of citrullinated H3K9 histone by PADI4.

Figure 4
Figure 4

Regulation of HERV-W transcription by methylation of CpG sites in the promoter region.

Figure 5
Figure 5

ERVWE1 expression mechanism due to activation of cAMP/PKA signaling pathway by CD9.

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