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. 2012;7(9):e44991.
doi: 10.1371/journal.pone.0044991. Epub 2012 Sep 27.

Expression and activation by Epstein Barr virus of human endogenous retroviruses-W in blood cells and astrocytes: inference for multiple sclerosis

Giuseppe Mameli  1 , Luciana Poddighe, Alessandra Mei, Elena Uleri, Stefano Sotgiu, Caterina Serra, Roberto Manetti, Antonina Dolei
Affiliations

Expression and activation by Epstein Barr virus of human endogenous retroviruses-W in blood cells and astrocytes: inference for multiple sclerosis

Giuseppe Mameli et al. PLoS One. 2012.

Abstract

Background: Proposed co-factors triggering the pathogenesis of multiple sclerosis (MS) are the Epstein Barr virus (EBV), and the potentially neuropathogenic MSRV (MS-associated retrovirus) and syncytin-1, of the W family of human endogenous retroviruses.

Methodology/principal findings: In search of links, the expression of HERV-W/MSRV/syncytin-1, with/without exposure to EBV or to EBV glycoprotein350 (EBVgp350), was studied on peripheral blood mononuclear cells (PBMC) from healthy volunteers and MS patients, and on astrocytes, by discriminatory env-specific RT-PCR assays, and by flow cytometry. Basal expression of HERV-W/MSRV/syncytin-1 occurs in astrocytes and in monocytes, NK, and B, but not in T cells. This uneven expression is amplified in untreated MS patients, and dramatically reduced during therapy. In astrocytes, EBVgp350 stimulates the expression of HERV-W/MSRV/syncytin-1, with requirement of the NF-κB pathway. In EBVgp350-treated PBMC, MSRVenv and syncytin-1 transcription is activated in B cells and monocytes, but not in T cells, nor in the highly expressing NK cells. The latter cells, but not the T cells, are activated by proinflammatory cytokines.

Conclusions/significance: In vitro EBV activates the potentially immunopathogenic and neuropathogenic HERV-W/MSRV/syncytin-1, in cells deriving from blood and brain. In vivo, pathogenic outcomes would depend on abnormal situations, as in late EBV primary infection, that is often symptomatic, or/and in the presence of particular host genetic backgrounds. In the blood, HERV-Wenv activation might induce immunopathogenic phenomena linked to its superantigenic properties. In the brain, toxic mechanisms against oligodendrocytes could be established, inducing inflammation, demyelination and axonal damage. Local stimulation by proinflammatory cytokines and other factors might activate further HERV-Ws, contributing to the neuropathogenity. In MS pathogenesis, a possible model could include EBV as initial trigger of future MS, years later, and HERV-W/MSRV/syncytin-1 as actual contributor to MS pathogenicity, in striking parallelism with disease behaviour.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Chromosomal representation of multiple sites of integration in human DNA of HERV-Wenv loci covering ≥80% of the HERV-Wenv gene.
The in silico analysis of the current version of the human genome was performed by NCBI Basic Local Alignment Search Tool (BLAST) program, using as queries the MSRVenv and syncytin-1 sequences (PV14 MSRV clone, GenBank accession number AF331500, and ERVW-1env coding sequence NM_014590.3, respectively). From the initial BLAST-identified regions, only the sequences covering ≥80% of the HERV-Wenv gene were selected as target and are reported. Red dashes: target:score ≥200; mauves dashes: target:score 80–200. Hits: number of loci; Hit GIs: Locus number all matches; MT: mitochondrial chromosome.
Figure 2
Figure 2. Basal expression of MSRVenv/ syncytin-1/HERV-Wenv in U87-MG astrocytes and PBMC subsets. A.
Detection of MSRVenv and syncytin-1 mRNAs of U87-MG cells, by real time RT-PCR (means of three experiments run in duplicate, calculated by the 2−ΔCt method; bars indicate standard deviation. B. Flow cytometry evaluation of the HERV-Wenv protein on U87-MG plasma membrane. Shaded histograms: HERV-Wenv-specific staining; open histograms: isotype control. C. MSRVenv and Syncytin-1 mRNA expression on PBMC from MSRV(+) donors as such, and after immunobeads separation in CD3+T, CD19+ B, CD56+/CD19−/CD3− NK and CD19−/CD3–/CD56− monocyte subsets, and subsequent monocyte differentiation into MDM (bars indicate standard deviation). D. Flow cytometry evaluation of the HERV-Wenv protein on the membrane of PBMC from a representative MSRV(+) donor in toto and after sorting of the CD3+T, CD19+ B, CD56+/CD19−/CD3− NK and CD19−/CD3−/CD56− monocyte subsets. Shaded histograms: HERV-Wenv-specific staining; open histograms: isotype control. E. Cell populations distribution of PBMC from a representative MSRV(+) donor before, and after capture by magnetic beads charged with anti-HERV-Wenv or with an unrelated isotype antibody. The unprocessed PBMC and the cells retained by the immunobeads were sorted for T, B, NK and monocyte markers. The unretained cells were also analysed (not shown). F. Presence of surface HERV-Wenv protein in blood cells from five MSRV(+) HD, five untreated MS patients and three MS patients under effective therapy, evaluated by flow cytometry in PBMC in toto and after sorting of the CD3+T, CD19+ B, CD56+/CD19−/CD3− NK and CD19−/CD3−/CD56− monocyte subsets. Each dot represents an individual; horizontal bars represent the means. HERV-Wenv positivity of CD3+T cells was <2% for all samples (not shown).
Figure 3
Figure 3. MSRVenv and syncytin-1 stimulation by EBV and EBVgp350 in U87-MG astrocytes.
The levels of MSRVenv and syncytin-1 mRNAs were evaluated by real time RT-PCR as in Figure 2A, and are expressed as mean fold increases over controls (2−ΔΔCt method). A. Expression of MSRVenv and syncytin-1 in astrocytes cultured alone or co-cultured with the EBV-producer B95-8 cells for 24–48 h. B. Effects of 10 (•) or 100 (♦) ng/ml of EBVgp350 on MSRVenv and syncytin-1 mRNA accumulation during time. C. Suppression of EBVgp350 effects by its pre-incubation with anti-EBVgp350 neutralizing antibody. D. Requirement of NF-κB. Expression of MSRVenv and syncytin-1 by U-87MG cells transfected or not with siRNA against the NF-κB p65 subunit and left overnight with/without 10 ng/ml of EBVgp350. E. Western blot assay of protein extracts from aliquots of the same cultures of Figure 3D. The relevant band was recognized by antibody against the NF-κB p65 subunit; the anti-Grb2 antibody was used to control the loading of equal amounts of proteins.
Figure 4
Figure 4. Expression of MSRVenv and syncytin-1 by PBMC subsets exposed to EBVgp350 or proinflammatory cytokines.
A. Levels of MSRVenv and syncytin-1 mRNAs of PBMC from MSRV(+) HD treated overnight with 1–100 ng/ml of EBVgp350, either as such or separated in T, B, NK and monocyte subsets. B. Comparison of the MSRVenv and syncytin-1 mRNA levels of monocytes and MDM after overnight EBVgp350 treatment. A and B: Data are the means of three experiments run in duplicate, calculated by the 2−ΔΔCt method; C. Expression of the HERV-Wenv protein on the plasma membrane, evaluated by flow cytometry as present env-specific positivity of PBMC treated for 24 h with TNFα (1 ng/ml), IFNγ (1000 IU/ml), or PMA (50 NM); the bars indicate standard deviations.
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This work was supported in part by grants from Fondazione Italiana Sclerosi Multipla Onlus (FISM) (grant N° 2010/R/16, AD), and from Regione Autonoma Sardegna (grant 2010, AD). AM was supported by a research fellowship of Regione Sardegna, POR Sardegna, FSE 2007–2013, L.R.7/2007. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.