Human Endogenous Retrovirus and Neuroinflammation in Chronic Inflammatory Demyelinating Polyradiculoneuropathy

Abstract

Background: Human endogenous retroviruses HERV-W encode a pro-inflammatory protein, named MSRV-Env from its original identification in Multiple Sclerosis. Though not detected in various neurological controls, MSRV-Env was found in patients with chronic inflammatory demyelinating polyradiculoneuropathies (CIDPs). This study investigated the expression of MSRV in CIDP and evaluated relevant MSRV-Env pathogenic effects.

Methods: 50 CIDP patients, 19 other neurological controls (ONDs) and 65 healthy blood donors (HBDs) were recruited from two different countries. MSRV-env and -pol transcripts, IL6 and CXCL10 levels were quantified from blood samples. MSRV-Env immunohistology was performed in distal sensory nerves from CIDP and neurological controls biopsies. MSRV-Env pathogenic effects and mode of action were assayed in cultured primary human Schwann cells (HSCs).

Findings: In both cohorts, MSRV-env and -pol transcripts, IL6 positivity prevalence and CXCL10 levels were significantly elevated in CIDP patients when compared to HBDs and ONDs (statistically significant in all comparisons). MSRV-Env protein was detected in Schwann cells in 5/7 CIDP biopsies. HSC exposed to or transfected with MSRV-env presented a strong increase of IL6 and CXCL10 transcripts and protein secretion. These pathogenic effects on HSC were inhibited by GNbAC1, a highly specific and neutralizing humanized monoclonal antibody targeting MSRV-Env.

Interpretation: The present study showed that MSRV-Env may trigger the release of critical immune mediators proposed as instrumental factors involved in the pathophysiology of CIDP. Significant MSRV-Env expression was detected in a significant proportion of patients with CIDP, in which it may play a role according to its presently observed effects on Schwann cells along with previously known effects on immune cells. Experimental results also suggest that a biomarker-driven therapeutic strategy targeting this protein with a neutralizing antibody such as GNbAC1 may offer new perspectives for treating CIDP patients with positive detection of MSRV-Env expression.

Funding: Geneuro-Innovation, France.

Keywords: CIDP; Endogenous retrovirus; GNbAC1; HERV; HERV-W; MSRV; Peripheral neuropathies; Schwann cell.

Fig. 1

MSRV-Env and MSRV-Pol transcripts levels are increased in peripheral blood mononuclear cells of CIDP patients in two independent studies. MSRV-Env (Study 1: A; Study 2: D) and MSRV-Pol (Study 1: B; Study 2: E) RNA levels were quantified by qRT-PCR in PBMC from healthy blood donors (HBDS), CIDP patients (CIDP), and other neurological diseases controls (ONDs). MSRV-Env and MSRV-Pol expressions are strongly correlated in HBDS (black dots), OND (green dots) and CIDP (red dots) in Studies 1 and 2 (respectively C and F). Data are expressed as relative expression of the targeted transcript to GUS B reference transcript, and plots represent individual values. *P < 0.05, ***P < 0.001 versus HBDS.

Fig. 2

MSRV-Env is expressed in peripheral nerves biopsies from CIDP patients. Representative immunohistological analysis showing that MSRV-Env immunoreactivity (brown) is found in the cytoplasm of Schwann cells (low magnification: A; high magnification: B). No staining is observed in the corresponding serial section of the same biopsy incubated with a non-relevant isotype antibody (C) or in a biopsy from a control neuropathy (D). Scale bar: 0.5 μm.

Fig. 3

Characterization of human Schwann cells in primary culture. Morphology of HSC in light microscopy (A). Immunocytofluorescence analyses show that HSC in primary culture strongly express TLR4 (B), S100β (C), P0 myelin protein (D), and P75/NGF receptor (E). No staining is observed when the secondary antibody coupled to FITC is used alone (F). Cell nuclei are labelled with DAPI (blue), scale bar: 5 μm.

Fig. 4

Human Schwann cells expressing MSRV-Env produce and release IL6 and CXCL10. HSCs were transfected with a plasmid encoding the full length MSRV-Env (Env-T) or a fraction of the extracellular domain of MSRV-Env (Env-SU), or the corresponding empty plasmid (control). Culture media and HSC transcripts were isolated 48 h after transfection. IL6 (A; F) and CXCL10 (B; F) transcripts levels were quantified by qRT-PCR. IL6 (C), CXCL10 (D) and MSRV-Env-SU (E) proteins levels in the culture media were quantified by ELISA. HSCs were incubated without (Env-SU) or with GNbAC1 (+ GNbAC1) at 200 nM for 48 h after transfection with MSRV-Env-SU (F). Data are expressed in pg/mL (A; B), ng/mL (E), or as relative expression of the targeted transcript to GUS B reference transcript (C; D; F) and represent Mean ± SEM of 6 to 9 experiments. *P < 0.05, **P < 0.01, ***P < 0.001 versus control (A–E) or MSRV-Env-SU (F).

Fig. 5

GNbAC1 inhibits IL6 and CXCL10 expressions induced by MSRV-Env in human Schwann cells. HSCs were stimulated 1 h (IL6) or 4 h (CXCL10) with recombinant full length MSRV-Env (3 nM) alone or together with GNbAC1 (200 nM) or LPS-RS (300 ng mL^− 1) before RNA isolation. IL6 (A; C) and CXCL10 (B; C) transcripts levels were quantified by qRT-PCR. Data are expressed as relative expression of the targeted transcript to GUS B reference transcript (A; B) or as % of control response to MSRV-Env (in the absence of GNbAC1 or LPS-RS) and represent Mean ± SEM of 6 to 8 experiments. *P < 0.05, **P < 0.01, ***P < 0.001 versus control (A; B) or MSRV-Env (C).