Abstract The human endogenous retrovirus type W (HERV-W) has been identified as a human-specific neuropathological factor that preferentially affects glial cell types in multiple sclerosis (MS). Recent work using transgenic mice with expression of the HERV-W envelope (ENV) protein unveiled that this endogenous retroviral element disrupts myelin repair and polarizes microglial and astroglial cells towards axon-damaging neurotoxic phenotypes. Moreover, initial clinical trials using Temelimab, a neutralizing antibody targeting the HERV-W ENV protein, have provided circumstantial evidence that ENV exerts anti-regenerative and neurodegenerative effects in MS patients. Aligning these observations, it was therefore concluded that HERV-W represents an important factor contributing to disease progression independent of relapse activity (PIRA). Building on these findings, we here applied a neutralizing anti-ENV antibody in a non-inflammatory demyelination mouse model to directly evaluate its potential to mitigate neurodegeneration and ameliorate remyelination. In transgenic mice with human-specific expression of the HERV-W ENV protein, repetitive intraperitoneal anti-ENV antibody injections resulted in accelerated oligodendroglial differentiation, enhanced remyelination, axonal protection, and reduced neurofilament light chain leakage in the serum. Neurotoxic microglial traits were also reduced, while homeostatic parameters were stabilized. As astroglial cells underwent a similar shift, inducing regenerative traits at the expense of toxic parameters, anti-ENV application overall generated a less hostile cellular environment. This study provides direct evidence of the capacity of HERV-W neutralizing antibodies to access the central nervous system and to ameliorate damage conferred by this viral entity previously associated with smouldering disease processes. Significance Statement Although neurodegeneration is a hallmark of multiple sclerosis (MS), its underlying mechanisms are poorly understood. Clinically, it manifests as smouldering MS or progression without relapse activity (PIRA). This is the primary factor leading to the accumulation of clinical disability and is currently untreatable. This study provides the first direct evidence that antibodies directed against the HERV-W ENV protein can attenuate the activity of neurodegeneration-promoting glial cells in vivo . Our data validates neutralization of this endogenous retroviral element as a promising therapeutic approach particularly relevant to the chronic form of MS.

Multiple Sclerosis (MS), an autoimmune disorder, is characterized by severe neuroinflammation, leading to demyelination and neuronal damage in the CNS, resulting in significant clinical impairment. MS progression involves complex pathological processes like immune cell invasion and cytokine-mediated recruitment to the CNS. Experimental autoimmune encephalomyelitis (EAE), widely used as a model for MS, despite its translational limitations, has been crucial for identifying effective treatments. Recent studies have shown that sodium channel (NaV) blockers and monoamine oxidase- (MAO) B inhibitors can alleviate symptoms of EAE and optic neuritis (ON), but their mode of action remains partially unclear. To evaluate the effects and understand the action mechanism of NaV blockers and MAO-B inhibitors (rasagiline, safinamide, flecainide and phenytoin) in neurological conditions, various techniques were used, including optical coherence tomography (OCT), optomotor response measurement (OMR), flow cytometry, histological evaluations, Evans blue assay, blood-brain barrier (BBB) permeability assay, western blot, proliferations assay, and gene expression analyses. The study found that the primary therapeutic effect comes from inhibiting the NaV 1.5 sodium channel, not MAO-B inhibition. Flecainide, a NaV 1.5 channel blocker, significantly reduced EAE disability scores, mitigated neurodegeneration, preserved visual function, and restricted immune cell migration into the CNS. Importantly, blocking the NaV 1.5 channel had an effect on the BBB, limiting lymphocyte entry into the CNS. This research highlights sodium channel blockers' potential in treating EAE. The findings demonstrate induced neuroprotection and reduced disease progression, suggesting a novel therapeutic approach. Crucially, it reveals for the first time that NaV 1.5 channel blockade leads to neuroprotection primarily by affecting the BBB, a key factor in controlling immune cell migration, thus addressing a critical aspect of neuroinflammation.

Human endogenous retroviruses (HERVs) are inherited genetic elements derived from exogenous retroviral infections occurring throughout evolution. Accumulating evidence implicates increased expression of HERV type W envelope (HERV-W ENV) in psychiatric and neurodevelopmental disorders. To gain more mechanistic insights into the neurobiological disease pathways affected by HERV-W ENV expression, we took advantage of a mouse model that recapitulates the expression of the human-specific HERV-W ENV protein. Behavioral and cognitive phenotyping of transgenic (TG) mice expressing HERV-W ENV and wild-type (WT) controls showed that expression of this retroviral envelope caused deficits in numerous functional domains, including repetitive behavior, social and object recognition memory, and sensorimotor gating. Genome-wide RNA sequencing of hippocampal tissue demonstrated that transgenic expression of HERV-W ENV led to transcriptomic alterations that are highly relevant for psychiatric and neurodevelopmental disorders, cognitive functions, and synaptic development. Differential gene expression in TG mice encompassed a downregulation of several genes associated with schizophrenia and autism spectrum disorder, including Setd1a, Cacna1g, Ank3, and Shank3, as well as a downregulation of histone methyltransferase genes that belong to the Set1-like histone H3 lysine 4 (H3K4) methyltransferase family (Kmt2a, Kmt2b and Kmt2d). Concomitant to the latter, HERV-W ENV mice displayed increased enzymatic activity of lysine-specific demethylase-1 (LSD1), increased H3K4 mono-methylation, and decreased H3K4 di- and tri-methylation in the hippocampus. Importantly, pharmacological inhibition of LSD1 through oral ORY-1001 treatment normalized abnormal H3K4 methylation and rescued the behavioral and cognitive deficits in HERV-W ENV mice. In conclusion, our study suggests that the expression of HERV-W ENV has the capacity to disrupt various behavioral and cognitive functions and to alter the brain transcriptome in a manner that is highly relevant to neurodevelopmental and psychiatric disorders. Moreover, our study identified epigenetic pathways that may offer avenues for pharmacological interventions against behavioral and cognitive deficits induced by increased HERW-W expression.

The endogenous retrovirus type W (HERV-W) is a human-specific entity, which was initially discovered in multiple sclerosis (MS) patient derived cells. We initially found that the HERV-W envelope (ENV) protein negatively affects oligodendrogenesis and controls microglial cell polarization towards a myelinated axon associated and damaging phenotype. Such first functional assessments were conducted ex vivo, given the human-specific origin of HERV-W. Recent experimental evidence gathered on a novel transgenic mouse model, mimicking activation and expression of the HERV-W ENV protein, revealed that all glial cell types are impacted and that cellular fates, differentiation, and functions were changed. In order to identify HERV-W-specific signatures in glial cells, the current study analyzed the transcriptome of ENV protein stimulated microglial- and astroglial cells and compared the transcriptomic signatures to lipopolysaccharide (LPS) stimulated cells, owing to the fact that both ligands can activate toll-like receptor-4 (TLR-4). Additionally, a comparison between published disease associated glial signatures and the transcriptome of HERV-W ENV stimulated glial cells was conducted. We, therefore, provide here for the first time a detailed molecular description of specific HERV-W ENV evoked effects on those glial cell populations that are involved in smoldering neuroinflammatory processes relevant for progression of neurodegenerative diseases. (c) 2024 The Author(s). Published by Elsevier Masson SAS on behalf of Institut Pasteur. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

IntroductionMultiple Sclerosis (MS), a debilitating central nervous system (CNS) disorder, is characterized by inflammation, demyelination, and neuronal degeneration. Despite advancements in immunomodulatory treatments, neuroprotective or restorative strategies remain inadequate. Our research is focusing on the potential of the positive allosteric modulator of AMPA receptors (AMPA-PAM), PF4778574, in addressing MS symptoms.MethodsWe utilized the MOG35-55 induced experimental autoimmune encephalomyelitis (EAE) model in C57BL6J mice to examine PF4778574’s therapeutic and prophylactic efficacy. Our comprehensive approach included clinical scoring, optical coherence tomography (OCT), optomotor response (OMR) and histological assessments. Additionally, we explored the effects of PF4778574 in comparison and in combination with the immunomodulatory agent fingolimod, and investigated the impact on Cuprizone induced toxic demyelination.ResultsProphylactic administration of PF4778574 showed notable improvement in clinical EAE indices and reduction in neuronal loss. While it did not diminish microglial activity, it reduced demyelinated areas in optic nerves and in the corpus callosum. Both PF4778574 and fingolimod significantly enhanced clinical EAE scores and decreased demyelination. However, their combination did not yield additional benefits. In the cuprizone model, PF4778574 increased oligodendrocyte precursor and mature myelin-forming cells, suggesting a pro-remyelinating effect.DiscussionPF4778574 demonstrates promise in mitigating EAE effects, especially in terms of clinical disability and demyelination. These results suggest AMPA-PAMs as potential targets of interest for MS treatment beyond immunomodulatory approaches.

Astrocytes that reside in superficial (SL) and deep cortical layers have distinct molecular profiles and morphologies, which may underlie specific functions. Here, we demonstrate that the production of SL and deep layer (DL) astrocyte populations from neural progenitor cells in the mouse is temporally regulated. Lineage tracking following in utero and postnatal electroporation with PiggyBac (PB) EGFP and birth dating with EdU and FlashTag, showed that apical progenitors produce astrocytes during late embryogenesis (E16.5) that are biased to the SL, while postnatally labeled (P0) astrocytes are biased to the DL. In contrast, astrocytes born during the predominantly neurogenic window (E14.5) showed a random distribution in the SL and DL. Of interest, E13.5 astrocytes birth dated at E13.5 with EdU showed a lower layer bias, while FT labeling of apical progenitors showed no bias. Finally, examination of the morphologies of "biased" E16.5- and P0-labeled astrocytes demonstrated that E16.5-labeled astrocytes exhibit different morphologies in different layers, while P0-labeled astrocytes do not. Differences based on time of birth are also observed in the molecular profiles of E16.5 versus P0-labeled astrocytes. Altogether, these results suggest that the morphological, molecular, and positional diversity of cortical astrocytes is related to their time of birth from ventricular/subventricular zone progenitors.

Gliomas are the most common parenchymal tumors of the central nervous system (CNS). With regard to their still unclear etiology, several recent studies have provided evidence of a new category of pathogenic elements called human endogenous retroviruses (HERVs) which seem to contribute to the evolution and progression of many neurological diseases such as amyotrophic lateral sclerosis (ALS), schizophrenia, chronic inflammatory polyneuropathy (CIDP) and, particularly, multiple sclerosis (MS). In these diseases, HERVs exert effects on cellular processes such as inflammation, proliferation, and migration. In previous studies, we demonstrated that in MS, the human endogenous retrovirus type-W envelope protein (HERV-W ENV) interferes with lesion repair through the activation of microglia (MG), the innate myeloid immune cells of the CNS. Here, we now show that HERV-W ENV is also present in the microglial cells (MG) of the tumor microenvironment (TME) in gliomas. It modulates the behavior of glioblastoma (GBM) cell lines in GBM/MG cocultures by altering their gene expression, secreted cytokines, morphology, proliferation, and migration properties and could thereby contribute to key tumor properties.

>Introduction to human endogenous retrovirus type-W(HERV-W): Genomic inheritance from the past includes retroviral sequences that have been stably incorporated into our genomes and account for up to 8% of human DNA.

Introduction Multiple Sclerosis (MS), an autoimmune disorder, is characterized by severe neuroinflammation, leading to demyelination and neuronal damage in the CNS, resulting in significant clinical impairment. MS progression involves complex pathological processes like immune cell invasion and cytokine-mediated recruitment to the CNS. Experimental autoimmune encephalomyelitis (EAE), a model for MS, has been crucial for identifying effective treatments. Recent studies have shown that sodium channel (Nav) blockers and monoamine oxidase- (MAO) B inhibitors can alleviate symptoms of EAE and optic neuritis (ON), but their mode of action remains partially unclear. Methods To evaluate the effects and understand the action mechanism of Nav blockers and MAO-B inhibitors (rasagiline ,safinamide, flecainide and phenytoin) in neurological conditions, various techniques were used, including optical coherence tomography (OCT), optomotor response measurement (OMR), flow cytometry, histological evaluations, Evans blue assay, blood-brain barrier (BBB) permeability assay and gene expression analyses. Results The study found that the primary therapeutic effect comes from inhibiting the Nav 1.5 sodium channel, not MAO-B inhibition. Flecainide, a Nav 1.5 channel blocker, significantly reduced EAE disability scores, mitigated neurodegeneration, preserved visual function, and restricted immune cell migration into the CNS. Importantly, blocking the Nav 1.5 channel had an effect on the BBB, limiting lymphocyte entry into the CNS. Discussion/Conclusion This research highlights sodium channel blockers' potential in treating neuroinflammatory diseases like MS. The findings demonstrate reduced disease progression and neuroprotection, suggesting a novel therapeutic approach. Crucially, it reveals for the first time that Nav 1.5 channel blockade leads to neuroprotection primarily by affecting the BBB, a key factor in controlling immune cell migration, thus addressing a critical aspect of MS pathology.

Astrocytes are indispensable for central nervous system development and homeostasis. In response to injury and disease, astrocytes are integral to the immunological- and the, albeit limited, repair response. In this review, we will examine some of the functions reactive astrocytes play in the context of multiple sclerosis and related animal models. We will consider the heterogeneity or plasticity of astrocytes and the mechanisms by which they promote or mitigate demyelination. Finally, we will discuss a set of biomedical strategies that can stimulate astrocytes in their promyelinating response.

BACKGROUND:Promotion of myelin repair in the context of demyelinating diseases such as multiple sclerosis (MS) still represents a clinical unmet need, given that this disease is not only characterized by autoimmune activities but also by impaired regeneration processes. Hence, this relates to replacement of lost oligodendrocytes and myelin sheaths-the primary targets of autoimmune attacks. Endogenous remyelination is mainly mediated via activation and differentiation of resident oligodendroglial precursor cells (OPCs), whereas its efficiency remains limited and declines with disease progression and aging. Teriflunomide has been approved as a first-line treatment for relapsing remitting MS. Beyond its role in acting via inhibition of de novo pyrimidine synthesis leading to a cytostatic effect on proliferating lymphocyte subsets, this study aims to uncover its potential to foster myelin repair.METHODS:Within the cuprizone mediated de-/remyelination model teriflunomide dependent effects on oligodendroglial homeostasis and maturation, related to cellular processes important for myelin repair were analyzed in vivo. Teriflunomide administration was performed either as pulse or continuously and markers specific for oligodendroglial maturation and mitochondrial integrity were examined by means of gene expression and immunohistochemical analyses. In addition, axon myelination was determined using electron microscopy.RESULTS:Both pulse and constant teriflunomide treatment efficiently boosted myelin repair activities in this model, leading to accelerated generation of oligodendrocytes and restoration of myelin sheaths. Moreover, teriflunomide restored mitochondrial integrity within oligodendroglial cells.CONCLUSIONS:The link between de novo pyrimidine synthesis inhibition, oligodendroglial rescue, and maintenance of mitochondrial homeostasis appears as a key for successful myelin repair and hence for protection of axons from degeneration.

Aims Aims: To describe endoscopic changes in small bowel mucosa secondary to severe SARS-CoV-2 infection in patients with and without gastrointestinal symptoms during acute infection and 3 months follow-up, and its association with inflammatory serum markers.

Patients with COVID-19 may develop abnormal inflammatory response, followed in some cases by severe disease and long-lasting syndromes. We show here that in vitro exposure to SARS-CoV-2 activates the expression of the human endoge-nous retrovirus (HERV) HERV-W proinflammatory envelope protein (ENV) in peripheral blood mononuclear cells from a subset of healthy donors, in ACE2 receptor and infection-independent manner. Plasma and/or sera of 221 COVID-19 patients from different cohorts, infected with successive SARS-CoV-2 variants including the Omicron, had detectable HERV-W ENV, which correlated with ENV expression in T lymphocytes and peaked with the disease severity. HERV-W ENV was also found in postmortem tissues of lungs, heart, gastrointestinal tract, brain olfactory bulb, and nasal mucosa from COVID-19 patients. Altogether, these results demonstrate that SARS-CoV-2 could induce HERV-W envelope protein expression and suggest its involvement in the immunopathogenesis of certain COVID-19-associated syndromes and thereby its relevance in the development of personalized treatment of patients.

BACKGROUND:The envelope protein of human endogenous retrovirus W (HERV-W-Env) is expressed by macrophages and microglia, mediating axonal damage in chronic active MS lesions.OBJECTIVE AND METHODS:This phase 2, double-blind, 48-week trial in relapsing-remitting MS with 48-week extension phase assessed the efficacy and safety of temelimab; a monoclonal antibody neutralizing HERV-W-Env. The primary endpoint was the reduction of cumulative gadolinium-enhancing T1-lesions in brain magnetic resonance imaging (MRI) scans at week 24. Additional endpoints included numbers of T2 and T1-hypointense lesions, magnetization transfer ratio, and brain atrophy. In total, 270 participants were randomized to receive monthly intravenous temelimab (6, 12, or 18 mg/kg) or placebo for 24 weeks; at week 24 placebo-treated participants were re-randomized to treatment groups.RESULTS:The primary endpoint was not met. At week 48, participants treated with 18 mg/kg temelimab had fewer new T1-hypointense lesions (p = 0.014) and showed consistent, however statistically non-significant, reductions in brain atrophy and magnetization transfer ratio decrease, as compared with the placebo/comparator group. These latter two trends were sustained over 96 weeks. No safety issues emerged.CONCLUSION:Temelimab failed to show an effect on features of acute inflammation but demonstrated preliminary radiological signs of possible anti-neurodegenerative effects. Current data support the development of temelimab for progressive MS.TRIAL REGISTRATION:CHANGE-MS: ClinicalTrials.gov: NCT02782858, EudraCT: 2015-004059-29; ANGEL-MS: ClinicalTrials.gov: NCT03239860, EudraCT: 2016-004935-18.

Background Cladribine is a synthetic purine analogue that interferes with DNA synthesis and repair next to disrupting cellular proliferation in actively dividing lymphocytes. The compound is approved for the treatment of multiple sclerosis (MS). Cladribine can cross the blood-brain barrier, suggesting a potential effect on central nervous system (CNS) resident cells. Here, we explored compartment-specific immunosuppressive as well as potential direct neuroprotective effects of oral cladribine treatment in experimental autoimmune encephalomyelitis (EAE) mice. Methods In the current study, we compare immune cell frequencies and phenotypes in the periphery and CNS of EAE mice with distinct grey and white matter lesions (combined active and focal EAE) either orally treated with cladribine or vehicle, using flow cytometry. To evaluate potential direct neuroprotective effects, we assessed the integrity of the primary auditory cortex neuronal network by studying neuronal activity and spontaneous synaptic activity with electrophysiological techniques ex vivo. Results Oral cladribine treatment significantly attenuated clinical deficits in EAE mice. Ex vivo flow cytometry showed that cladribine administration led to peripheral immune cell depletion in a compartment-specific manner and reduced immune cell infiltration into the CNS. Histological evaluations revealed no significant differences for inflammatory lesion load following cladribine treatment compared to vehicle control. Single cell electrophysiology in acute brain slices was performed and showed an impact of cladribine treatment on intrinsic cellular firing patterns and spontaneous synaptic transmission in neurons of the primary auditory cortex. Here, cladribine administration in vivo partially restored cortical neuronal network function, reducing action potential firing. Both, the effect on immune cells and neuronal activity were transient. Conclusions Our results indicate that cladribine exerts a neuroprotective effect after crossing the blood-brain barrier independently of its peripheral immunosuppressant action.

BACKGROUND & AIMS: The 2-pore potassium channel subfamily K member 9 (KCNK9) regulates intracellular calcium concentration and thus modulates cell survival and inflammatory signaling pathways. It also was recognized as a risk allele for inflammatory bowel disease. However, it remains unclear whether KCNK9 modulates inflammatory bowel disease via its impact on immune cell function or whether its influence on calcium homeostasis also is relevant in intestinal epithelial cells. METHODS: Kcnk9(-/- )mice were challenged with 3% dextran sulfate sodium (DSS) to induce experimental acute colitis. Primary cultures of intestinal epithelial cells were generated, and expression of potassium channels as well as cytosolic calcium levels and susceptibility to apoptosis were evaluated. Furthermore, we evaluated whether KCNK9 deficiency was compensated by the closely related 2-pore potassium channel KCNK3 in vivo or in vitro. RESULTS: Compared with controls, KCNK9 deficiency or its pharmacologic blockade were associated with aggravated DSS-induced colitis compared with wild-type animals. In the absence of KCNK9, intestinal epithelial cells showed increased intracellular calcium levels and were more prone to mitochondrial damage and caspase-9-dependent apoptosis. We found that expression of KCNK3 was increased in Kcnk(-9-) mice but did not prevent apoptosis after DSS exposure. Conversely, increased levels of KCNK9 in Kcnk3(-/- )mice were associated with an ameliorated course of DSS-induced colitis. CONCLUSIONS: KCNK9 enhances mitochondria' stability, reduces apoptosis, and thus supports epithelial cell survival after DSS exposure in vivo and in vitro. Conversely, its increased expression in Kcnk3(-/-) resulted in less mitochondria' damage and apoptosis and was associated with beneficial outcomes in DSS-induced colitis.

Patients with COVID-19 may develop abnormal inflammatory response and lymphopenia, followed in some cases by delayed-onset syndromes, often long-lasting after the initial SARS-CoV-2 infection. As viral infections may activate human endogenous retroviral elements (HERV), we studied the effect of SARS-CoV-2 on HERV-W and HERV-K envelope (ENV) expression, known to be involved in immunological and neurological pathogenesis of human diseases. Our results have showed that the exposure to SARS-CoV-2 virus activates early HERV-W and K transcription but only HERV-W ENV protein expression, in an infection- and ACE2-independent way within peripheral blood mononuclear cell cultures from one-third of healthy donors. Moreover, HERV-W ENV protein was significantly increased in serum and plasma of COVID-19 patients, correlating with its expression in CD3+ lymphocytes and with disease severity. Finally, HERV-W ENV was found expressed in post-mortem tissues of lungs, heart, brain olfactory bulb and nasal mucosa from acute COVID-19 patients in cell-types relevant for COVID-19-associated pathogenesis within affected organs, but different from those expressing of SARS-CoV-2 antigens. Altogether, the present study revealed that SARS-CoV-2 can induce HERV-W ENV expression in cells from individuals with symptomatic and severe COVID-19. Our data suggest that HERV-W ENV is likely to be involved in pathogenic features underlying symptoms of acute and post-acute COVID. It highlights the importance to further understand patients genetic susceptibility to HERV-W activation and the relevance of this pathogenic element as a prognostic marker and a therapeutic target in COVID-19 associated syndromes.