pHERV-W envelope protein fuels microglial cell-dependent damage of myelinated axons in multiple sclerosis.

Axonal degeneration is central to clinical disability and disease progression in multiple sclerosis (MS). Myeloid cells such as brain-resident microglia and blood-borne monocytes are thought to be critically involved in this degenerative process. However, the exact underlying mechanisms have still not been clarified. We have previously demonstrated that human endogenous retrovirus type W (HERV-W) negatively affects oligodendroglial precursor cell (OPC) differentiation and remyelination via its envelope protein pathogenic HERV-W (pHERV-W) ENV (formerly MS-associated retrovirus [MSRV]-ENV). In this current study, we investigated whether pHERV-W ENV also plays a role in axonal injury in MS. We found that in MS lesions, pHERV-W ENV is present in myeloid cells associated with axons. Focusing on progressive disease stages, we could then demonstrate that pHERV-W ENV induces a degenerative phenotype in microglial cells, driving them toward a close spatial association with myelinated axons. Moreover, in pHERV-W ENV-stimulated myelinated cocultures, microglia were found to structurally damage myelinated axons. Taken together, our data suggest that pHERV-W ENV-mediated microglial polarization contributes to neurodegeneration in MS. Thus, this analysis provides a neurobiological rationale for a recently completed clinical study in MS patients showing that antibody-mediated neutralization of pHERV-W ENV exerts neuroprotective effects.

Case Report: Acute Transverse Myelitis after Zika Virus Infection.

We report here one case of Zika virus (ZIKV) infection associated with auto-immunity directed against the central nervous system in a Brazilian woman who developed acute transverse myelitis 9 days after recovery from an acute episode of fever with generalized erythema. Imaging of the spinal cord showed an elongated area on the T1-T10 level with gadolinium uptake. The diagnostic of the ZIKV infection was confirmed by cerebrospinal fluid and serum analysis. This patient had serum positivity for autoantibodies against myelin oligodendrocyte glycoprotein (MOG), a specific antibody against the myelin sheath. We propose that a direct central nervous system infection by ZIKV could lead to a specific auto-immunity against MOG protein.

Complex interaction between mutant HNRNPA1 and gE of varicella zoster virus in pathogenesis of multiple sclerosis.

Multiple sclerosis (MS) is a demyelinating disease of the central nervous system causing axonal injury, neuronal loss, and atrophy of the central nervous system leading to permanent neurological and clinical disability. Presence of mutations in M9 domain of HNRNPA1 and detection of autoantibodies against this domain in HNRNPA1 qualifies it as a strong candidate for causing MS. These two aspects indicate the presence of a facilitator in associating them. Varicella zoster virus (VZV), known to cause chicken pox infection in humans, is a significant contender in sensitizing the infected people towards MS. Reactivation of latent herpes viruses by other infectious agents and cross-recognition of common viral antigens with antigens found in the myelin sheath induces molecular mimicry or superantigens. Mutations in HNRNPA1 cause mislocalization to the cytoplasm, and co-localize with stress granules (SG) causing cellular apoptosis, this creates the first step toward MS pathogenesis. Mutant HNRNPA1 accumulates in SG allowing the cells to display peptides of HNRNPA1 on surfaces of major histocompatibility complex (MHC) I triggering a cascade of immune reactions. Since glycoprotein E (gE) of VZV shares >62% amino acids sequence similarity with Prion-like domain (PrLD) of HNRNPA1, signifying the reason behind autoantibodies against M9 and PrLD of HNRNPA1. This review attempts to delineate the interactions of VZV, gE of VZV, with M9 domain and PrLD of HNRNPA1 in a step-by-step process. This supports the tripartite model that an environmental trigger in genetically susceptible individuals causes an autoimmune response to self-CNS antigens that result in the pathology observed in the brain and spinal cord of MS patients.

Zika virus tropism and interactions in myelinating neural cell cultures: CNS cells and myelin are preferentially affected.

The recent global outbreak of Zika virus (ZIKV) infection has been linked to severe neurological disorders affecting the peripheral and central nervous systems (PNS and CNS, respectively). The pathobiology underlying these diverse clinical phenotypes are the subject of intense research; however, even the principal neural cell types vulnerable to productive Zika infection remain poorly characterised. Here we used CNS and PNS myelinating cultures from wild type and Ifnar1 knockout mice to examine neuronal and glial tropism and short-term consequences of direct infection with a Brazilian variant of ZIKV. Cell cultures were infected pre- or post-myelination for various intervals, then stained with cell-type and ZIKV-specific antibodies. In bypassing systemic immunity using ex vivo culture, and the type I interferon response in Ifnar1 deficient cells, we were able to evaluate the intrinsic infectivity of neural cells. Through systematic quantification of ZIKV infected cells in myelinating cultures, we found that ZIKV infection is enhanced in the absence of the type I interferon responses and that CNS cells are considerably more susceptible to infection than PNS cells. In particular, we demonstrate that CNS axons and myelinating oligodendrocytes are especially vulnerable to injury. These results have implications for understanding the pathobiology of neurological symptoms associated with ZIKV infection. Furthermore, we provide a quantifiable ex vivo infection model that can be used for fundamental and therapeutic studies on viral neuroinvasion and its consequences.

Rabies virus-mediated oligodendrocyte labeling reveals a single oligodendrocyte myelinates axons from distinct brain regions.

Oligodendrocytes myelinate neuronal axons during development and increase conduction velocity of neuronal impulses in the central nervous system. Neuronal axons extend from multiple brain regions and pass through the white matter; however, whether oligodendrocytes ensheath a particular set of axons or do so randomly within the mammalian brain remains unclear. We developed a novel method to visualize individual oligodendrocytes and axon derived from a particular brain region in mouse white matter using a combinational injection of attenuated rabies virus and adeno-associated virus. Using this method, we found that some populations of oligodendrocytes in the corpus callosum predominantly ensheathed axons derived from motor cortex or sensory cortex, while others ensheathed axons from both brain regions, suggesting heterogeneity in preference of myelination toward a particular subtype of neurons. Moreover, our newly established method is a versatile tool for analyzing precise morphology of each oligodendrocyte in animal models for demyelinating disorders and addressing the role of oligodendrocyte in higher brain functions. GLIA 2016. GLIA 2017;65:93-105.

JC Polyomavirus Abundance and Distribution in Progressive Multifocal Leukoencephalopathy (PML) Brain Tissue Implicates Myelin Sheath in Intracerebral Dissemination of Infection.

Over half of adults are seropositive for JC polyomavirus (JCV), but rare individuals develop progressive multifocal leukoencephalopathy (PML), a demyelinating JCV infection of the central nervous system. Previously, PML was primarily seen in immunosuppressed patients with AIDS or certain cancers, but it has recently emerged as a drug safety issue through its association with diverse immunomodulatory therapies. To better understand the relationship between the JCV life cycle and PML pathology, we studied autopsy brain tissue from a 70-year-old psoriasis patient on the integrin alpha-L inhibitor efalizumab following a ~2 month clinical course of PML. Sequence analysis of lesional brain tissue identified PML-associated viral mutations in regulatory (non-coding control region) DNA, capsid protein VP1, and the regulatory agnoprotein, as well as 9 novel mutations in capsid protein VP2, indicating rampant viral evolution. Nine samples, including three gross PML lesions and normal-appearing adjacent tissues, were characterized by histopathology and subject to quantitative genomic, proteomic, and molecular localization analyses. We observed a striking correlation between the spatial extent of demyelination, axonal destruction, and dispersion of JCV along white matter myelin sheath. Our observations in this case, as well as in a case of PML-like disease in an immunocompromised rhesus macaque, suggest that long-range spread of polyomavirus and axonal destruction in PML might involve extracellular association between virus and the white matter myelin sheath.

Altered Oligodendrocyte Maturation and Myelin Maintenance: The Role of Antiretrovirals in HIV-Associated Neurocognitive Disorders.

Despite effective viral suppression through combined antiretroviral therapy (cART), approximately half of HIV-positive individuals have HIV-associated neurocognitive disorders (HAND). Studies of antiretroviral-treated patients have revealed persistent white matter abnormalities including diffuse myelin pallor, diminished white matter tracts, and decreased myelin protein mRNAs. Loss of myelin can contribute to neurocognitive dysfunction because the myelin membrane generated by oligodendrocytes is essential for rapid signal transduction and axonal maintenance. We hypothesized that myelin changes in HAND are partly due to effects of antiretroviral drugs on oligodendrocyte survival and/or maturation. We showed that primary mouse oligodendrocyte precursor cell cultures treated with therapeutic concentrations of HIV protease inhibitors ritonavir or lopinavir displayed dose-dependent decreases in oligodendrocyte maturation; however, this effect was rapidly reversed after drug removal. Conversely, nucleoside reverse transcriptase inhibitor zidovudine had no effect. Furthermore, in vivo ritonavir administration to adult mice reduced frontal cortex myelin protein levels. Finally, prefrontal cortex tissue from HIV-positive individuals with HAND on cART showed a significant decrease in myelin basic protein compared with untreated HIV-positive individuals with HAND or HIV-negative controls. These findings demonstrate that antiretrovirals can impact myelin integrity and have implications for myelination in juvenile HIV patients and myelin maintenance in adults on lifelong therapy.

New aspects of the pathogenesis of canine distemper leukoencephalitis.

Canine distemper virus (CDV) is a member of the genus morbillivirus, which is known to cause a variety of disorders in dogs including demyelinating leukoencephalitis (CDV-DL). In recent years, substantial progress in understanding the pathogenetic mechanisms of CDV-DL has been made. In vivo and in vitro investigations provided new insights into its pathogenesis with special emphasis on axon-myelin-glia interaction, potential endogenous mechanisms of regeneration, and astroglial plasticity. CDV-DL is characterized by lesions with a variable degree of demyelination and mononuclear inflammation accompanied by a dysregulated orchestration of cytokines as well as matrix metalloproteinases and their inhibitors. Despite decades of research, several new aspects of the neuropathogenesis of CDV-DL have been described only recently. Early axonal damage seems to represent an initial and progressive lesion in CDV-DL, which interestingly precedes demyelination. Axonopathy may, thus, function as a potential trigger for subsequent disturbed axon-myelin-glia interactions. In particular, the detection of early axonal damage suggests that demyelination is at least in part a secondary event in CDV-DL, thus challenging the dogma of CDV as a purely primary demyelinating disease. Another unexpected finding refers to the appearance of p75 neurotrophin (NTR)-positive bipolar cells during CDV-DL. As p75NTR is a prototype marker for immature Schwann cells, this finding suggests that Schwann cell remyelination might represent a so far underestimated endogenous mechanism of regeneration, though this hypothesis still remains to be proven. Although it is well known that astrocytes represent the major target of CDV infection in CDV-DL, the detection of infected vimentin-positive astrocytes in chronic lesions indicates a crucial role of this cell population in nervous distemper. While glial fibrillary acidic protein represents the characteristic intermediate filament of mature astrocytes, expression of vimentin is generally restricted to immature or reactive astrocytes. Thus, vimentin-positive astrocytes might constitute an important cell population for CDV persistence and spread, as well as lesion progression. In vitro models, such as dissociated glial cell cultures, as well as organotypic brain slice cultures have contributed to a better insight into mechanisms of infection and certain morphological and molecular aspects of CDV-DL. Summarized, recent in vivo and in vitro studies revealed remarkable new aspects of nervous distemper. These new perceptions substantially improved our understanding of the pathogenesis of CDV-DL and might represent new starting points to develop novel treatment strategies.

Effect of microtubule disruption on neuronal spread and replication of demyelinating and nondemyelinating strains of mouse hepatitis virus in vitro.

The isogenic host attachment spike protein recombinant demyelinating strain of mouse hepatitis virus (MHV) (RSA59) and the nondemyelinating strain (RSMHV2) differ in their abilities to infect distinct types of neural cells, spread from cell to cell, and induce subsequent demyelination and axonal loss. The differential demyelination properties of RSA59 and RSMHV2 may be a function of spike protein-mediated neuronal transport. Disruption of microtubules with colchicine and vinblastine significantly blocks neuronal transport and reduces the replication of RSA59, whereas RSMHV2 remains unaffected.

Microglia play a major role in direct viral-induced demyelination.

Microglia are the resident macrophage-like populations in the central nervous system (CNS). Microglia remain quiescent, unable to perform effector and antigen presentation (APC) functions until activated by injury or infection, and have been suggested to represent the first line of defence for the CNS. Previous studies demonstrated that microglia can be persistently infected by neurotropic mouse hepatitis virus (MHV) which causes meningoencephalitis, myelitis with subsequent axonal loss, and demyelination and serve as a virus-induced model of human neurological disease multiple sclerosis (MS). Current studies revealed that MHV infection is associated with the pronounced activation of microglia during acute inflammation, as evidenced by characteristic changes in cellular morphology and increased expression of microglia-specific proteins, Iba1 (ionized calcium-binding adaptor molecule 1), which is a macrophage/microglia-specific novel calcium-binding protein and involved in membrane ruffling and phagocytosis. During chronic inflammation (day 30 postinfection), microglia were still present within areas of demyelination. Experiments performed in ex vivo spinal cord slice culture and in vitro neonatal microglial culture confirmed direct microglial infection. Our results suggest that MHV can directly infect and activate microglia during acute inflammation, which in turn during chronic inflammation stage causes phagocytosis of myelin sheath leading to chronic inflammatory demyelination.

CXCR4 signaling regulates remyelination by endogenous oligodendrocyte progenitor cells in a viral model of demyelination.

Following intracranial infection with the neurotropic JHM strain of mouse hepatitis virus (JHMV), susceptible mice will develop widespread myelin destruction that results in pathological and clinical outcomes similar to those seen in humans with the demyelinating disease Multiple Sclerosis (MS). Partial remyelination and clinical recovery occurs during the chronic phase following control of viral replication yet the signaling mechanisms regulating these events remain enigmatic. Here we report the kinetics of proliferation and maturation of oligodendrocyte progenitor cells (OPCs) within the spinal cord following JHMV-induced demyelination and that CXCR4 signaling contributes to the maturation state of OPCs. Following treatment with AMD3100, a specific inhibitor of CXCR4, mice recovering from widespread demyelination exhibit a significant (P < 0.01) increase in the number of OPCs and fewer (P < 0.05) mature oligodendrocytes compared with HBSS-treated animals. These results suggest that CXCR4 signaling is required for OPCs to mature and contribute to remyelination in response to JHMV-induced demyelination. To assess if this effect is reversible and has potential therapeutic benefit, we pulsed mice with AMD3100 and then allowed them to recover. This treatment strategy resulted in increased numbers of mature oligodendrocytes, enhanced remyelination, and improved clinical outcome. These findings highlight the possibility to manipulate OPCs in order to increase the pool of remyelination-competent cells that can participate in recovery.

Mechanisms of primary axonal damage in a viral model of multiple sclerosis.

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the CNS. Recent studies have demonstrated that significant axonal injury also occurs in MS patients and correlates with neurological dysfunction, but it is not known whether this neuronal damage is a primary disease process, or occurs only secondary to demyelination. In the current studies, neurotropic strains of mouse hepatitis virus (MHV) that induce meningitis, encephalitis, and demyelination in the CNS, an animal model of MS, were used to evaluate mechanisms of axonal injury. The pathogenic properties of genetically engineered isogenic spike protein recombinant demyelinating and nondemyelinating strains of MHV were compared. Studies demonstrate that a demyelinating strain of MHV causes concomitant axonal loss and macrophage-mediated demyelination. The mechanism of axonal loss and demyelination in MHV infection is dependent on successful transport of virus from gray matter to white matter using the MHV host attachment spike glycoprotein. Our data show that axonal loss and demyelination can be independent direct viral cytopathic events, and suggest that similar direct axonal damage may occur in MS. These results have important implications for the design of neuroprotective strategies for CNS demyelinating disease, and our model identifies the spike protein as a therapeutic target to prevent axonal transport of neurotropic viruses.

HIV-1 Tat and morphine have interactive effects on oligodendrocyte survival and morphology.

Human immunodeficiency virus (HIV)-infected individuals who abuse opiates show faster progression to AIDS, and enhanced incidence of HIV-1 encephalitis. Most opiates with abuse liability are preferential agonists for mu-opioid receptors (MORs), and MORs are expressed on both neurons and glia, including oligodendrocytes (OLs). Tat, gp120, and other viral toxins, cause neurotoxicity in vitro and/or when injected into brain, and co-exposure to opiates can augment HIV-1 protein-induced insults to both glial and neuronal populations. We examined the effects of HIV-1 Tat +/- opiate exposure on OL survival and differentiation. In vivo studies utilized transgenic mice expressing Tat(1-86) regulated by an inducible glial fibrillary acidic protein promoter. Although MBP levels were unchanged on immunoblots, certain structural and apoptotic indices were abnormal. After only 2 days of Tat induction, OLs showed an upregulation of active caspase-3 that was enhanced by morphine exposure. Tat also upregulated TUNEL staining, but only in the presence of morphine. Tat significantly reduced the length of processes in Golgi-Kopsch impregnated OLs. A greater proportion of cells exhibited diminished or aberrant cytoplasmic processes, especially when mice expressing Tat were co-exposed to morphine. Collectively, our data show that OLs in situ are extremely sensitive to effects of Tat +/- morphine, although it is not clear if immature OLs as well as differentiated OLs are targeted equally. Significant elevations in caspase-3 activity and TUNEL labeling, and evidence of increased degeneration/regeneration of OLs exposed to Tat +/- morphine suggest that toxicity toward OLs may be accompanied by heightened OL turnover.

Myelin sheaths and autoimmune response induced by myelin proteins and alphaviruses. I. Physicochemical background.

Myelin proteins of the central and peripheral nervous system range from very hydrophilic to extremely hydrophobic proteins. Their biological function and involvement in various clinically defined neurological diseases are well documented. In this review the myelin proteins will be compared with proteins of alphaviruses with emphasis on Semliki Forest Virus (strain pSP6-SFV4), to elucidate better the multiple function and the potential role in several neurological diseases. The main purpose of this review is to assist neuroscientists, neurochemists, neurologists, and other interested scientists in developing a better understanding on the information relating to myelin proteins referred in autoimmune diseases. Therefore, this review is focused on simple physiochemical background of proteins and structural aspect, which may be involved in autoimmunity. It is very unusual that few different a.a. sequences (epitops) induce indeed the same autoimmune reaction.

Genetically dominant spinal cord repair in a murine model of chronic progressive multiple sclerosis.

For reasons that are not well understood, central nervous system repair in multiple sclerosis is often minimal. We present evidence, in a murine model of chronic progressive multiple sclerosis, that genetic factors can substantially influence remyelination, axonal integrity, and neurologic function. Four inbred mouse strains, SJL, B10.D1-H2(q), FVB, and SWR, developed extensive inflammatory demyelination by 3 months after infection with Theiler's murine encephalomyelitis virus. Demyelination continued lifelong in SJL and B10.D1-H2(q) mice, accompanied by axonal injury, minimal remyelination, and progressive motor dysfunction. In contrast, FVB and SWR mice showed less axonal injury, progressive remyelination, and stabilization of motor function. Genetic dominance of the reparative traits was demonstrated by crossing remyelinating strains (FVB and SWR) with nonremyelinating strains (SJL and B10.D1-H2(q)). All F1 mice developed a phenotype identical to FVB and SWR, showing extensive remyelination, partial preservation of axons, and preserved motor function. Analyses of viral RNA and antigen, immune cell infiltration, and antiviral antibody titers did not predict the phenotypic differences between strains. These results highlight the significant extent to which hereditary factors can control disease course and demonstrate that the switch from a pathogenic to a reparative phenotype can occur even after prolonged inflammatory demyelination.

Canine distemper, a re-emerging morbillivirus with complex neuropathogenic mechanisms.

Paramyxoviruses are responsible for a wide variety of diseases both in humans and in animals. Common to many paramyxoviruses is the fact that they can cause neurological symptoms in their final host. Newly discovered paramyxoviruses, such as the Hendra and Nipah viruses, show the same pattern of pathogenesis as that of the paramyxoviruses already known. Canine distemper virus (CDV) is a well-studied member of the genus Morbillivirus. Study of the neuropathogenesis of CDV might give insight into disease mechanisms and suggest approaches for the prevention of other recently discovered paramyxovirus infections.

Antibodies directed against rubella virus induce demyelination in aggregating rat brain cell cultures.

To link the presence of intrathecal virus-specific oligoclonal immunoglobulin G (IgG) in multiple sclerosis patients to a demyelinating activity, aggregating rat brain cell cultures were treated with antibodies directed against two viruses, namely, rubella (RV) and hepatitis B (HB). Anti-RV antibodies in the presence of complement decreased myelin basic protein concentrations in a dose-dependent manner, whereas anti-HB antibodies had no effect. A similar but less pronounced effect was observed on the enzymatic activity of 2',3'-cyclic nucleotide 3'-phosphohydrolase, which is enriched in noncompact membranes of oligodendrocytes. These effects were comparable to those in cultures treated with antibodies directed against myelin oligodendrocyte glycoprotein (MOG), previously found to be myelinotoxic both in vitro and in vivo. Sequence homologies were found between structural glycoprotein E(2) of RV and MOG, suggesting that demyelination was due to molecular mimicry. To support the hypothesis that demyelination was caused by anti-RV IgG that recognized an MOG epitope, we found that anti-RV antibodies depleted MOG in a dose-dependent manner. Further evidence came from the demonstration that anti-RV and anti-MOG IgG colocalized on oligodendrocyte processes and that both revealed by Western blot a 28 kDa protein in CNS myelin, a molecular weight corresponding to MOG. These findings suggest that a virus such as RV exhibiting molecular mimicry with MOG can trigger an autoimmune demyelination.