Myelin-oligodendrocyte glycoprotein (MOG) is a surface marker of oligodendrocyte maturation

Myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD): Insights into pathogenesis and biomarkers of prognosis

MOG antibody-associated disease (MOGAD), an inflammatory demyelinating pathology, is typically associated with the clinical phenotypes acute disseminated encephalomyelitis (ADEM), optic neuritis (ON), or transverse myelitis (TM). The mainstay of diagnosis is detection of antibodies targeting oligodendrocyte-expressed MOG (MOG-IgG). MOG-IgG-mediated demyelination occurs via complement-dependent cytotoxicity (CDC), antibody-dependent cellular cytotoxicity (ADCC), enhanced cognate T-cell CNS infiltration and activation, and oligodendrocyte cytoskeleton disruption, but the exact role of the immune system in MOGAD is still poorly understood. The disease course is either monophasic or relapsing, with relapsing course affecting approximately two-thirds of individuals. Neurological disability accumulates with relapse and may manifest as visual, motor, sensory, and cognitive deficits. Thus, accurate disease course prediction is of paramount importance. Prognostic biomarkers, implemented at a global scale, have the potential to guide timely therapeutic decisions to limit relapse-associated disability accrual while simultaneously avoiding unnecessary immunosuppression in monophasic individuals. This review explores recent insights in the understanding of MOGAD pathogenesis as well as advances in prognostic biomarkers of relapsing course and disease activity.

MCL-1 regulates cellular transitions during oligodendrocyte development

Oligodendrocytes are the myelinating cells of the central nervous system. Regulation of the early stages of oligodendrocyte development is critical to the function of the cell. Specifically, myelin sheath formation is an energetically demanding event that requires precision, as alterations may lead to dysmyelination. Recent work has established that fatty acid β-oxidation is required for the function of oligodendrocytes. We have shown that MCL-1, a well-characterized anti-apoptotic protein, is required for the development of oligodendrocytes in vivo. Further, it was recently uncovered that MCL-1 regulates long-chain fatty acid β-oxidation through its interaction with acyl-CoA synthetase long-chain family member 1 (ACSL1), an enzyme responsible for the conversion of long-chain fatty acids into acyl-CoA. Here, we introduce an in vitro system to isolate human stem cell-derived oligodendrocyte progenitor cells and investigate the involvement of MCL-1 during human oligodendrocyte development. Using this system, we pharmacologically inhibited MCL-1 in oligodendrocyte progenitor cells (OPCs) to elucidate the non-apoptotic function of the protein at this developmental stage. Additionally, we used a motor neuron co-culture system to investigate the downstream effects that MCL-1 inhibition has at later developmental stages when oligodendrocytes begin to contact axons and generate myelin basic protein. We demonstrate that the mitochondrial network changes in human oligodendrocyte development resemble those reported in vivo. Our findings point to MCL-1 as a critical factor essential at the OPC stage for proper oligodendrocyte morphogenesis.

Antagonistic actions of PAK1 and NF2/Merlin drive myelin membrane expansion in oligodendrocytes

In the central nervous system, the formation of myelin by oligodendrocytes (OLs) relies on the switch from the polymerization of the actin cytoskeleton to its depolymerization. The molecular mechanisms that trigger this switch have yet to be elucidated. Here, we identified P21-activated kinase 1 (PAK1) as a major regulator of actin depolymerization in OLs. Our results demonstrate that PAK1 accumulates in OLs in a kinase-inhibited form, triggering actin disassembly and, consequently, myelin membrane expansion. Remarkably, proteomic analysis of PAK1 binding partners enabled the identification of NF2/Merlin as its endogenous inhibitor. Our findings indicate that Nf2 knockdown in OLs results in PAK1 activation, actin polymerization, and a reduction in OL myelin membrane expansion. This effect is rescued by treatment with a PAK1 inhibitor. We also provide evidence that the specific Pak1 loss-of-function in oligodendroglia stimulates the thickening of myelin sheaths in vivo. Overall, our data indicate that the antagonistic actions of PAK1 and NF2/Merlin on the actin cytoskeleton of the OLs are critical for proper myelin formation. These findings have broad mechanistic and therapeutic implications in demyelinating diseases and neurodevelopmental disorders.

Evolution of glial cells: a non-bilaterian perspective

Nervous systems of bilaterian animals generally consist of two cell types: neurons and glial cells. Despite accumulating data about the many important functions glial cells serve in bilaterian nervous systems, the evolutionary origin of this abundant cell type remains unclear. Current hypotheses regarding glial evolution are mostly based on data from model bilaterians. Non-bilaterian animals have been largely overlooked in glial studies and have been subjected only to morphological analysis. Here, we provide a comprehensive overview of conservation of the bilateral gliogenic genetic repertoire of non-bilaterian phyla (Cnidaria, Placozoa, Ctenophora, and Porifera). We overview molecular and functional features of bilaterian glial cell types and discuss their possible evolutionary history. We then examine which glial features are present in non-bilaterians. Of these, cnidarians show the highest degree of gliogenic program conservation and may therefore be crucial to answer questions about glial evolution.

Extracellular Vesicles in Multiple Sclerosis: Their Significance in the Development and Possible Applications as Therapeutic Agents and Biomarkers

Extracellular vesicles (EVs) are "micro-shuttles" that play a role as mediators of intercellular communication. Cells release EVs into the extracellular environment in both physiological and pathological conditions and are involved in intercellular communication, due to their ability to transfer proteins, lipids, and nucleic acids, and in the modulation of the immune system and neuroinflammation. Because EVs can penetrate the blood-brain barrier and move from the central nervous system to the peripheral circulation, and vice versa, recent studies have shown a substantial role for EVs in several neurological diseases, including multiple sclerosis (MS). MS is a demyelinating disease where the main event is caused by T and B cells triggering an autoimmune reaction against myelin constituents. Recent research has elucidate the potential involvement of extracellular vesicles (EVs) in the pathophysiology of MS, although, to date, their potential role both as agents and therapeutic targets in MS is not fully defined. We present in this review a summary and comprehensive examination of EVs' involvement in the pathophysiology of multiple sclerosis, exploring their potential applications as biomarkers and indicators of therapy response.

Gliomas: a reflection of temporal gliogenic principles

The hijacking of early developmental programs is a canonical feature of gliomas where neoplastic cells resemble neurodevelopmental lineages and possess mechanisms of stem cell resilience. Given these parallels, uncovering how and when in developmental time gliomagenesis intersects with normal trajectories can greatly inform our understanding of tumor biology. Here, we review how elapsing time impacts the developmental principles of astrocyte (AS) and oligodendrocyte (OL) lineages, and how these same temporal programs are replicated, distorted, or circumvented in pathological settings such as gliomas. Additionally, we discuss how normal gliogenic processes can inform our understanding of the temporal progression of gliomagenesis, including when in developmental time gliomas originate, thrive, and can be pushed towards upon therapeutic coercion.

Consequences of oxygen deprivation on myelination and sex-dependent alterations

Oxygen deprivation is one of the main causes of morbidity and mortality in newborns, occurring with a higher prevalence in preterm infants, reaching 20 % to 50 % mortality in newborns in the perinatal period. When they survive, 25 % exhibit neuropsychological pathologies, such as learning difficulties, epilepsy, and cerebral palsy. White matter injury is one of the main features found in oxygen deprivation injury, which can lead to long-term functional impairments, including cognitive delay and motor deficits. The myelin sheath accounts for much of the white matter in the brain by surrounding axons and enabling the efficient conduction of action potentials. Mature oligodendrocytes, which synthesize and maintain myelination, also comprise a significant proportion of the brain's white matter. In recent years, oligodendrocytes and the myelination process have become potential therapeutic targets to minimize the effects of oxygen deprivation on the central nervous system. Moreover, evidence indicate that neuroinflammation and apoptotic pathways activated during oxygen deprivation may be influenced by sexual dimorphism. To summarize the most recent research about the impact of sexual dimorphism on the neuroinflammatory state and white matter injury after oxygen deprivation, this review presents an overview of the oligodendrocyte lineage development and myelination, the impact of oxygen deprivation and neuroinflammation on oligodendrocytes in neurodevelopmental disorders, and recent reports about sexual dimorphism regarding the neuroinflammation and white matter injury after neonatal oxygen deprivation.

The role and therapeutic applications of exosomes in multiple sclerosis disease

A range of the central nervous system (CNS) and immune cells are affected by multiple sclerosis (MS), a complex autoimmune disease of the CNS. Chronic neuroinflammation, demyelination, and neuronal death are all features of MS, but the disease's molecular mechanisms are unknown. Exosomes are small, membrane-bound extracellular vesicles with a crucial role in cell communication. They are stable in biological fluids and emerge from the cell membrane during endocytic internalization. It might be possible to recognize better the mechanisms involved in the development and progress of illnesses by understanding the variety of exosomal contents and their associated targets, like neurologic disorders. In this review, we sought to bring together important data on the biology of exosomes in MS and highlight discoveries on these nanoparticles' prognostic, diagnostic and therapeutic potential.

Laminin regulates oligodendrocyte development and myelination

Oligodendrocytes are the cells that myelinate axons and provide trophic support to neurons in the CNS. Their dysfunction has been associated with a group of disorders known as demyelinating diseases, such as multiple sclerosis. Oligodendrocytes are derived from oligodendrocyte precursor cells, which differentiate into premyelinating oligodendrocytes and eventually mature oligodendrocytes. The development and function of oligodendrocytes are tightly regulated by a variety of molecules, including laminin, a major protein of the extracellular matrix. Accumulating evidence suggests that laminin actively regulates every aspect of oligodendrocyte biology, including survival, migration, proliferation, differentiation, and myelination. How can laminin exert such diverse functions in oligodendrocytes? It is speculated that the distinct laminin isoforms, laminin receptors, and/or key signaling molecules expressed in oligodendrocytes at different developmental stages are the reasons. Understanding molecular targets and signaling pathways unique to each aspect of oligodendrocyte biology will enable more accurate manipulation of oligodendrocyte development and function, which may have implications in the therapies of demyelinating diseases. Here in this review, we first introduce oligodendrocyte biology, followed by the expression of laminin and laminin receptors in oligodendrocytes and other CNS cells. Next, the functions of laminin in oligodendrocyte biology, including survival, migration, proliferation, differentiation, and myelination, are discussed in detail. Last, key questions and challenges in the field are discussed. By providing a comprehensive review on laminin's roles in OL lineage cells, we hope to stimulate novel hypotheses and encourage new research in the field.

Teriflunomide Promotes Oligodendroglial 8,9-Unsaturated Sterol Accumulation and CNS Remyelination

Background and Objectives

To test whether low concentrations of teriflunomide (TF) could promote remyelination, we investigate the effect of TF on oligodendrocyte in culture and on remyelination in vivo in 2 demyelinating models.

Methods

The effect of TF on oligodendrocyte precursor cell (OPC) proliferation and differentiation was assessed in vitro in glial cultures derived from neonatal mice and confirmed on fluorescence-activated cell sorting–sorted adult OPCs. The levels of the 8,9-unsaturated sterols lanosterol and zymosterol were quantified in TF- and sham-treated cultures. In vivo, TF was administered orally, and remyelination was assessed both in myelin basic protein–GFP-nitroreductase (Mbp:GFP-NTR) transgenic Xenopus laevis demyelinated by metronidazole and in adult mice demyelinated by lysolecithin.

Results

In cultures, low concentrations of TF down to 10 nM decreased OPC proliferation and increased their differentiation, an effect that was also detected on adult OPCs. Oligodendrocyte differentiation induced by TF was abrogated by the oxidosqualene cyclase inhibitor Ro 48-8071 and was mediated by the accumulation of zymosterol. In the demyelinated tadpole, TF enhanced the regeneration of mature oligodendrocytes up to 2.5-fold. In the mouse demyelinated spinal cord, TF promoted the differentiation of newly generated oligodendrocytes by a factor of 1.7-fold and significantly increased remyelination.

Discussion

TF enhances zymosterol accumulation in oligodendrocytes and CNS myelin repair, a beneficial off-target effect that should be investigated in patients with multiple sclerosis.

Use of CRISPR/Cas9-mediated disruption of CNS cell type genes to profile transduction of AAV by neonatal intracerebroventricular delivery in mice

Adeno-associated virus (AAV) transduction efficiency and tropism are conventionally determined by high expression of a fluorescent reporter gene. Emerging data has suggested that such conventional methods may underestimate AAV transduction for cells in which reporter expression from AAV vectors is undetectable. To explore an alternative method that captures AAV transduction in cells in which low expression of a cargo is sufficient for the intended activity, we sought after CRISPR/Cas9-mediated gene disruption. In this study, we use AAV to deliver CRISPR/guide RNA designed to abolish the genes NeuN, GFAP, or MOG expressed specifically in neurons, astrocytes, or oligodendrocytes respectively in the central nervous system (CNS) of mice. Abrogated expression of these cell-type-specific genes can be measured biochemically in CNS subregions and provides quantitative assessment of AAV transduction in these CNS cell types. By using this method, we compared CNS transduction of AAV9, AAV-PHP.B, and AAV-PHP.eB delivered via intracerebroventricular injection (ICV) in neonatal mice. We found both AAV-PHP.B and AAV-PHP.eB resulted in marked disruption of the NeuN gene by CRISPR/Cas9, significantly greater than AAV9 in several brain regions and spinal cord. In contrast, only modest disruption of the GFAP gene and the MOG gene was observed by all three AAV variants. Since the procedure of ICV circumvents the blood-brain barrier, our data suggests that, independent of their ability to cross the blood-brain barrier, AAV-PHP.B variants also exhibit remarkably improved neuronal transduction in the CNS. We anticipate this approach will facilitate profiling of AAV cellular tropism in murine CNS.

Extracellular Vesicles in Multiple Sclerosis: Role in the Pathogenesis and Potential Usefulness as Biomarkers and Therapeutic Tools

Although extracellular vesicles (EVs) were initially relegated to a waste disposal role, nowadays, they have gained multiple fundamental functions working as messengers in intercellular communication as well as exerting active roles in physiological and pathological processes. Accumulating evidence proves the involvement of EVs in many diseases, including those of the central nervous system (CNS), such as multiple sclerosis (MS). Indeed, these membrane-bound particles, produced in any type of cell, carry and release a vast range of bioactive molecules (nucleic acids, proteins, and lipids), conferring genotypic and phenotypic changes to the recipient cell. This means that not only EVs per se but their content, especially, could reveal new candidate disease biomarkers and/or therapeutic agents. This review is intended to provide an overview regarding current knowledge about EVs’ involvement in MS, analyzing the potential versatility of EVs as a new therapeutic tool and source of biomarkers.

Shenzhiling oral solution promotes myelin repair through PI3K/Akt-mTOR pathway in STZ-induced SAD mice

Most forms of Alzheimer's disease are sporadic. A model of sporadic Alzheimer's disease induced with bilateral intraventricular injection of streptozotocin leads to insulin resistance in the brain accompanied by memory decline, synaptic dysfunction, amyloid plaque deposition, oxidative stress, and neuronal apoptosis, all of which mimic the pathologies associated with sporadic Alzheimer's disease. Myelin injury is an essential component of Alzheimer's disease, playing a key role in early cognitive impairment. Our previously research found that sporadic Alzheimer's disease model showed myelin injury and that Shenzheling oral solution improved mild-to-moderate Alzheimer's disease; therefore, the protective effect of Shenzheling oral solution on myelin injury in early cognitive impairment is worth attention. In this study, the Morris water maze test results showed impairments in the learning and memory functions of mice in the model group, whereas the learning and memory function significantly improved after drug intervention. Immunohistochemistry showed increased β-amyloid plaques in the model group and decreased amounts in the drug group. Moreover, results of electron microscopy, western blot, and polymerase chain reaction showed that Shenzhiling oral solution improved early cognitive impairment and repaired myelin sheath damage; the potential mechanism of these effects may relate to the PI3K/Akt-mTOR signaling pathway. These findings support the application and promotion of Shenzhiling oral solution to treat sporadic Alzheimer's disease.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02900-x.

Animal Models of Multiple Sclerosis

Animal models with high translational validity are essential tools in understanding disease pathogenesis and in the development of therapeutic strategies. Multiple sclerosis (MS) is an autoimmune demyelinating disease of the central nervous system characterized by progressive neurological deficits and socioeconomic burden. Experimental autoimmune encephalomyelitis (EAE) is the most extensively utilized animal model of MS, with well-characterized rodent and non-human primate variants. The EAE model is typically induced by either active immunization with myelin-derived proteins or peptides in adjuvant or by passive transfer of activated myelin-specific CD4⁺ T lymphocytes. To date, the EAE model has been an essential tool in the development of at least seven U.S. Food and Drug Administration (FDA)-approved immunomodulatory drugs for the treatment of MS, including glatiramer acetate, fingolimod, and natalizumab. However, the translational validity of the EAE model is frequently compromised due to poor study design, inconsistent clinical scoring endpoints, and inappropriate statistical calculations. No single animal model accurately reflects the complexity of human MS pathogenesis. Beyond EAE, multiple additional animal models are described, including Theiler's murine encephalomyelitis virus and cuprizone-induced demyelination, which facilitate the study of pathogen-induced CNS autoimmunity and remyelination, respectively. This overview summarizes several of the most frequently used animal models of MS and highlights key factors that significantly influence the experimental outcome and affect translational validity. © 2021 Wiley Periodicals LLC.

A2 B Adenosine Receptors and Sphingosine 1-Phosphate Signaling Cross-Talk in Oligodendrogliogenesis

Oligodendrocyte-formed myelin sheaths allow fast synaptic transmission in the brain. Impairments in the process of myelination, or demyelinating insults, might cause chronic diseases such as multiple sclerosis (MS). Under physiological conditions, remyelination is an ongoing process throughout adult life consisting in the differentiation of oligodendrocyte progenitor cells (OPCs) into mature oligodendrocytes (OLs). During pathological events, this process fails due to unfavorable environment. Adenosine and sphingosine kinase/sphingosine 1-phosphate signaling axes (SphK/S1P) play important roles in remyelination processes. Remarkably, fingolimod (FTY720), a sphingosine analog recently approved for MS treatment, plays important roles in OPC maturation. We recently demonstrated that the selective stimulation of A_{2 B} adenosine receptors (A_{2 B} Rs) inhibit OPC differentiation in vitro and reduce voltage-dependent outward K⁺ currents (I _K ) necessary to OPC maturation, whereas specific SphK1 or SphK2 inhibition exerts the opposite effect. During OPC differentiation A_{2 B} R expression increases, this effect being prevented by SphK1/2 blockade. Furthermore, selective silencing of A_{2 B} R in OPC cultures prompts maturation and, intriguingly, enhances the expression of S1P lyase, the enzyme responsible for irreversible S1P catabolism. Finally, the existence of an interplay between SphK1/S1P pathway and A_{2 B} Rs in OPCs was confirmed since acute stimulation of A_{2 B} Rs activates SphK1 by increasing its phosphorylation. Here the role of A_{2 B} R and SphK/S1P signaling during oligodendrogenesis is reviewed in detail, with the purpose to shed new light on the interaction between A_{2 B} Rs and S1P signaling, as eventual innovative targets for the treatment of demyelinating disorders.

Multimodal single-cell analysis reveals distinct radioresistant stem-like and progenitor cell populations in murine glioma

Radiation therapy is part of the standard of care for gliomas and kills a subset of tumor cells, while also altering the tumor microenvironment. Tumor cells with stem-like properties preferentially survive radiation and give rise to glioma recurrence. Various techniques for enriching and quantifying cells with stem-like properties have been used, including the fluorescence activated cell sorting (FACS)-based side population (SP) assay, which is a functional assay that enriches for stem-like tumor cells. In these analyses, mouse models of glioma have been used to understand the biology of this disease and therapeutic responses, including the radiation response. We present combined SP analysis and single-cell RNA sequencing of genetically-engineered mouse models of glioma to show a time course of cellular response to radiation. We identify and characterize two distinct tumor cell populations that are inherently radioresistant and also distinct effects of radiation on immune cell populations within the tumor microenvironment.

Detection of MOG-IgG by cell-based assay: moving from discovery to clinical practice

Myelin oligodendrocyte glycoprotein (MOG) is a unique CNS-specific mammalian protein that is expressed on the surface of compact myelin and oligodendrocyte cell bodies. MOG is an accessible target for autoantibodies, associated with immune-mediated demyelination in the central nervous system. The identification of MOG reactive immunoglobulin G antibodies (MOG-IgG) helps to distinguish a subgroup of patients from multiple sclerosis and other CNS disorders, reducing the risk of clinical misdiagnosis. The development of the cell-based assays (CBA) improved the detection of clinically meaningful MOG-IgG binding to conformational MOG expressed in the cell membrane surface. In this review, we describe factors that impact on the results of CBA, such as MOG conformation, protein glycosylation, addition of fluorescent tags, serum dilution, secondary antibodies, and data interpretation.

Sphingosine-1-Phosphate Receptor Modulators and Oligodendroglial Cells: Beyond Immunomodulation

Multiple sclerosis (MS) is an autoimmune inflammatory disease characterized by demyelination, axonal loss, and synaptic impairment in the central nervous system (CNS). The available therapies aim to reduce the severity of the pathology during the early inflammatory stages, but they are not effective in the chronic stage of the disease. In this phase, failure in endogenous remyelination is associated with the impairment of oligodendrocytes progenitor cells (OPCs) to migrate and differentiate into mature myelinating oligodendrocytes. Therefore, stimulating differentiation of OPCs into myelinating oligodendrocytes has become one of the main goals of new therapeutic approaches for MS. Different disease-modifying therapies targeting sphingosine-1-phosphate receptors (S1PRs) have been approved or are being developed to treat MS. Besides their immunomodulatory effects, growing evidence suggests that targeting S1PRs modulates mechanisms beyond immunomodulation, such as remyelination. In this context, this review focuses on the current understanding of S1PR modulators and their direct effect on OPCs and oligodendrocytes.

Novel Treatment Strategies Targeting Myelin and Oligodendrocyte Dysfunction in Schizophrenia

Oligodendrocytes are the glial cells responsible for the formation of the myelin sheath around axons. During neurodevelopment, oligodendrocytes undergo maturation and differentiation, and later remyelination in adulthood. Abnormalities in these processes have been associated with behavioral and cognitive dysfunctions and the development of various mental illnesses like schizophrenia. Several studies have implicated oligodendrocyte dysfunction and myelin abnormalities in the disorder, together with altered expression of myelin-related genes such as Olig2, CNP, and NRG1. However, the molecular mechanisms subjacent of these alterations remain elusive. Schizophrenia is a severe, chronic psychiatric disorder affecting more than 23 million individuals worldwide and its symptoms usually appear at the beginning of adulthood. Currently, the major therapeutic strategy for schizophrenia relies on the use of antipsychotics. Despite their widespread use, the effects of antipsychotics on glial cells, especially oligodendrocytes, remain unclear. Thus, in this review we highlight the current knowledge regarding oligodendrocyte dysfunction in schizophrenia, compiling data from (epi)genetic studies and up-to-date models to investigate the role of oligodendrocytes in the disorder. In addition, we examined potential targets currently investigated for the improvement of schizophrenia symptoms. Research in this area has been investigating potential beneficial compounds, including the D-amino acids D-aspartate and D-serine, that act as NMDA receptor agonists, modulating the glutamatergic signaling; the antioxidant N-acetylcysteine, a precursor in the synthesis of glutathione, protecting against the redox imbalance; as well as lithium, an inhibitor of glycogen synthase kinase 3β (GSK3β) signaling, contributing to oligodendrocyte survival and functioning. In conclusion, there is strong evidence linking oligodendrocyte dysfunction to the development of schizophrenia. Hence, a better understanding of oligodendrocyte differentiation, as well as the effects of antipsychotic medication in these cells, could have potential implications for understanding the development of schizophrenia and finding new targets for drug development.

Tissue-selective regulation of protein homeostasis and unfolded protein response signalling in sporadic ALS

Amyotrophic lateral sclerosis (ALS) is a disorder that affects motor neurons in motor cortex and spinal cord, and the degeneration of both neuronal populations is a critical feature of the disease. Abnormalities in protein homeostasis (proteostasis) are well established in ALS. However, they have been investigated mostly in spinal cord but less so in motor cortex. Herein, we monitored the unfolded protein (UPR) and heat shock response (HSR), two major proteostasis regulatory pathways, in human post‐mortem tissue derived from the motor cortex of sporadic ALS (SALS) and compared them to those occurring in spinal cord. Although the UPR was activated in both tissues, specific expression of select UPR target genes, such as PDIs, was observed in motor cortex of SALS cases strongly correlating with oligodendrocyte markers. Moreover, we found that endoplasmic reticulum‐associated degradation (ERAD) and HSR genes, which were activated predominately in spinal cord, correlated with the expression of neuronal markers. Our results indicate that proteostasis is strongly and selectively activated in SALS motor cortex and spinal cord where subsets of these genes are associated with specific cell type. This study expands our understanding of convergent molecular mechanisms occurring in motor cortex and spinal cord and highlights cell type–specific contributions.

KIR2DL4-HLAG interaction at human NK cell-oligodendrocyte interfaces regulates IFN-γ-mediated effects

Interactions between germline-encoded natural killer (NK) cell receptors and their respective ligands on tumorigenic or virus-infected cells determine NK cell cytotoxic activity and/or cytokine secretion. NK cell cytokine responses can be augmented in and can potentially contribute to multiple sclerosis (MS), an inflammatory disease of the central nervous system focused upon the oligodendrocytes (OLs). To investigate mechanisms by which NK cells may contribute to MS pathogenesis, we developed an in vitro human model of OL-NK cell interaction. We found that activated, but not resting human NK cells form conjugates with, and mediate cytotoxicity against, human oligodendrocytes. NK cells, when in conjugate with OLs, rapidly synthesize and polarize IFN-γ toward the OLs. IFN-γ  is capable of reducing myelin oligodendrocyte and myelin associated glycoproteins (MOG and MAG) content. This activity is independent of MHC class-I mediated inhibition via KIR2DL1, but dependent upon the interaction between NK cell-expressed KIR2DL4 and its oligodendrocyte-expressed ligand, HLA-G. NK cells from patients with MS express higher levels of IFN-γ following conjugation to OLs, more actively promote in vitro reduction of MOG and MAG and have higher frequencies of the KIR2DL4 positive population. These data collectively suggest a mechanism by which NK cells can promote pathogenic effects upon OLs.

The effects of Centella asiatica (L.) Urban on neural differentiation of human mesenchymal stem cells in vitro

Background

Centella asiatica (L.) Urban, known as Indian Pennywort, is a tropical medicinal plant from Apiaceae family native to Southeast Asian countries. It has been widely used as a nerve tonic in Ayuverdic medicine since ancient times. However, whether it can substitute for neurotrophic factors to induce human mesenchymal stem cell (hMSCs) differentiation into the neural lineage remains unknown. This study aimed to investigate the effect of a raw extract of C. asiatica (L.) (RECA) on the neural differentiation of hMSCs in vitro.

Methods

The hMSCs derived from human Wharton’s jelly umbilical cord (hWJMSCs; n = 6) were treated with RECA at different concentrations; 400, 800, 1200, 1600, 2000 and 2400 μg/ml. The cytotoxicity of RECA was evaluated via the MTT (3-(4, 5-dimethylthiazolyl-2)-2, 5-diphenyltetrazolium bromide) and cell proliferation assays. The hWJMSCs were then induced to neural lineage for 9 days either with RECA alone or RECA in combination with neurotrophic factors (NF). Cell morphological changes were observed under an inverted microscope, while the expression of the neural markers S100β, p75 NGFR, MBP, GFAP and MOG was analyzed by quantitative polymerase chain reaction and immunocytochemistry. The cell cycle profile of differentiated and undifferentiated hWJMSCs was investigated through cell cycle analysis.

Results

RECA exerted effects on both proliferation and neural differentiation of hWJMSCs in a dose-dependent manner. RECA reduced the proliferation of hWJMSCs and was cytotoxic to cells above 1600 μg/ml, with IC₅₀ value, 1875 ± 55.67 μg/ml. In parallel with the reduction in cell viability, cell enlargement was also observed at the end of the induction. Cells treated with RECA alone had more obvious protein expression of the neural markers compared to the other groups. Meanwhile, gene expression of the aforementioned markers was detected at low levels across the experimental groups. The supplementation of hWJMSCs with RECA did not change the normal life cycle of the cells.

Conclusions

Although RECA reduced the proliferation of hWJMSCs, a low dose of RECA (400 μg/ml), alone or in combination of neurotrophic factors (NF + RECA 400 μg/ml), has the potential to differentiate hWJMSCs into Schwann cells and other neural lineage cells.

Electronic supplementary material

The online version of this article (10.1186/s12906-019-2581-x) contains supplementary material, which is available to authorized users.

Downregulation of aspartoacylase during the progression of myelin breakdown in the dmy mutant rat with mitochondrial magnesium channel MRS2 defect

OBJECTIVE

The dmy rat is an autosomal recessive mutant that exhibits severe rapid myelin breakdown throughout the central nervous system at 7-8 weeks of age. The dmy rat has a point mutation in Mrs2 gene, which encodes an essential component of the major electrophoretic Mg²⁺ influx system in the mitochondria. However, it remains unknown how mitochondrial dysfunction leads to the myelin breakdown.

METHODS

We focused on the aspartoacylase (ASPA) and mitochondrion-related metabolites to clarify the mechanism of myelin pathology in dmy rats. Aspa mRNA was significantly decreased in both the gray matter and the ventral white matter of spinal cord in the dmy rats from 4 to 8 weeks of age. Very faint immunohistochemical expression for ASPA was noted in the gray and white matter of the affected dmy rats at 8 weeks. Liquid chromatography mass spectrometry revealed no different amount of N-acetylaspartate (NAA), which is synthesized from aspartate and acetyl-coenzyme A (CoA) in neurons, in the brain and spinal cord between the dmy and control rats.

CONCLUSION

Our results indicated that the pyruvate dehydrogenase activity might be reduced due to the loss of Mg²⁺ transport activity in the mitochondria of the dmy rats, suggesting acetyl CoA production might be reduced. The number of oligodendrocytes was well preserved until 7 weeks. It is intriguing that prior to the myelin destruction at 7-8 weeks, disrupted expression of Aspa mRNA and ASPA protein undergoes from early stage of myelinogenesis. These data indicate that ASPA expression would be a useful index to evaluate a function of oligodendrocyte in the dmy rat.

Function of Lymphocytes in Oligodendrocyte Development

Oligodendrocytes generate myelin sheaths to promote rapid neurotransmission in the central nervous system (CNS). During brain development, oligodendrocyte precursor cells (OPCs) are generated in the medial ganglionic eminence, lateral ganglionic eminence, and dorsal pallium. OPCs proliferate and migrate throughout the CNS at the embryonic stage. After birth, OPCs differentiate into mature oligodendrocytes, which then insulate axons. Oligodendrocyte development is regulated by the extrinsic environment including neurons, astrocytes, and immune cells. During brain development, B lymphocytes are present in the meningeal space, and are involved in oligodendrocyte development by promoting OPC proliferation. T lymphocytes mediate oligodendrocyte development during the remyelination process. Moreover, a subset of microglia contributes to oligodendrocyte development during the neonatal periods. Therefore, the immune system, especially lymphocytes and microglia, contribute to oligodendrocyte development during brain development and remyelination.

Inhibition of MAPK/ERK pathway promotes oligodendrocytes generation and recovery of demyelinating diseases

Oligodendrocytes (OLs) are the myelinating glia of the central nervous system. Injury to OLs causes myelin loss. In demyelinating diseases, such as multiple sclerosis, the remyelination is hindered principally due to a failure of the oligodendrocyte precursor cells (OPCs) to differentiate into mature OLs. To identify inducers of OPC to OL differentiation, a high‐throughput screening based on myelin basic protein expression using neural progenitor cells‐derived OPCs has been performed and, PD0325901—an MEK (MAPK kinase) inhibitor—is found to significantly enhance OPC to OL differentiation in a dose‐ and time‐dependent manner. Other MEK inhibitors also display similar effect, indicating blockade of MAPK–ERK signaling is sufficient to induce OPC differentiation into OLs. PD0325901 facilitates the formation of myelin sheaths in OPC–neuron co‐culture in vitro. And in experimental autoimmune encephalomyelitis model and cuprizone‐induced demyelination model, PD0325901 displays significant therapeutic effect by promoting myelin regeneration. Our results suggest that targeting the MAPK–ERK pathway might be an intriguing way to develop new therapies for demyelinating diseases.

New Insights Into Immune Cell-Derived Extracellular Vesicles in Multiple Sclerosis

Extracellular vesicles (EVs) are small vesicles including microvesicles and exosomes which differ in their distinct size, density, biogenesis, and content. Until recently, EVs were considered as simply scrap products. Nowadays, they are engendering huge interest and their shedding plays a well-recognized role in intercellular communication, not only participating in many physiological processes, but also suspected of being involved in the pathogenesis of many diseases. The present review aims to summarize the latest updates on immune cell-derived EVs, focusing on the current status of knowledge in Multiple Sclerosis. Significant progress has been made on their physical and biological characterization even though many aspects remain unclear and need to be addressed. However, it is worth further investigating in order to deepen the knowledge of this unexplored and fascinating field that could lead to intriguing findings in the evaluation of EVs as biomarkers in monitoring the course of diseases and the response to treatments.

Rapid and Specific Immunomagnetic Isolation of Mouse Primary Oligodendrocytes

The efficient and robust isolation and culture of primary oligodendrocytes (OLs) is a valuable tool for the in vitro study of the development of oligodendroglia as well as the biology of demyelinating diseases such as multiple sclerosis and Pelizaeus-Merzbacher-like disease (PMLD). Here, we present a simple and efficient selection method for the immunomagnetic isolation of stage three O4⁺ preoligodendrocytes cells from neonatal mice pups. Since immature OL constitute more than 80% of the rodent-brain white matter at postnatal day 7 (P7) this isolation method not only ensures high cellular yield, but also the specific isolation of OLs already committed to the oligodendroglial lineage, decreasing the possibility of isolating contaminating cells such as astrocytes and other cells from the mouse brain. This method is a modification of the techniques reported previously, and provides oligodendrocyte preparation purity above 80% in about 4 h.

Microvesicles in the brain: Biomarker, messenger or mediator?

Microvesicles (MVs) are cell-derived vesicles produced after membrane remodeling of eukaryotic cells during activation or apoptosis. MVs are considered a novel biomarker/messenger for many diseases. Neurons, astrocytes, microglia, as well as neural stem cells, have been described to release MVs, many studies have demonstrated the involvement of platelets and endothelial MVs in some central nervous diseases. This review is focused on understanding the role of MVs in the brain; new findings demonstrated that MVs can contribute to the onset and progression of some neurodegenerative and neuroinflammatory diseases, as well as to the development and regeneration of the nervous system.

Role of adenosine in oligodendrocyte precursor maturation

Differentiation and maturation of oligodendroglial cells are postnatal processes that involve specific morphological changes correlated with the expression of stage-specific surface antigens and functional voltage-gated ion channels. A small fraction of oligodendrocyte progenitor cells (OPCs) generated during development are maintained in an immature and slowly proliferative or quiescent state in the adult central nervous system (CNS) representing an endogenous reservoir of immature cells. Adenosine receptors are expressed by OPCs and a key role of adenosine in oligodendrocyte maturation has been recently recognized. As evaluated on OPC cultures, adenosine, by stimulating A₁ receptors, promotes oligodendrocyte maturation and inhibits their proliferation; on the contrary, by stimulating A_2A receptors, it inhibits oligodendrocyte maturation. A₁ and A_2A receptor-mediated effects are related to opposite modifications of outward delayed rectifying membrane K⁺ currents (I_K) that are involved in the regulation of oligodendrocyte differentiation. Brain A₁ and A_2A receptors might represent new molecular targets for drugs useful in demyelinating pathologies, such as multiple sclerosis (MS), stroke and brain trauma.

Modelling MS: Chronic-Relapsing EAE in the NOD/Lt Mouse Strain

Modelling complex disorders presents considerable challenges, and multiple sclerosis (MS) is no exception to this rule. The aetiology of MS is unknown, and its pathophysiology is poorly understood. Moreover, the last two decades have witnessed a dramatic revision of the long-held view of MS as an inflammatory demyelinating white matter disease. Instead, it is now regarded as a global central nervous system (CNS) disorder with a neurodegenerative component. Currently, there is no animal model recapitulating MS immunopathogenesis. Available models are based on autoimmune-mediated demyelination, denoted experimental autoimmune encephalomyelitis (EAE) or virally or chemically induced demyelination. Of these, the EAE model has been the most commonly used. It has been extensively improved since its first description and now exists as a number of variants, including genetically modified and humanized versions. Nonetheless, EAE is a distinct disease, and each variant models only certain facets of MS. Whilst the search for more refined MS models must continue, it is important to further explore where mechanisms underlying EAE provide proof-of-principle for those driving MS pathogenesis. EAE variants generated with the myelin component myelin oligodendrocyte glycoprotein (MOG) have emerged as the preferred ones, because in this particular variant disease is associated with both T- and B-cell effector mechanisms, together with demyelination. MOG-induced EAE in the non-obese diabetic (NOD) mouse strain exhibits a chronic-relapsing EAE clinical profile and high disease incidence. We describe the generation of this variant, its contribution to the understanding of MS immune and pathogenetic mechanisms and potential for evaluation of candidate therapies.

Temporal oligodendrocyte lineage progression: in vitro models of proliferation, differentiation and myelination

Oligodendrocytes are neuroglial cells responsible, within the central nervous system, for myelin sheath formation that provides an electric insulation of axons and accelerate the transmission of electrical signals. In order to be able to produce myelin, oligodendrocytes progress through a series of differentiation steps from oligodendrocyte precursor cells to mature oligodendrocytes (migration, increase in morphologic complexity and expression pattern of specific markers), which are modulated by cross talk with other nerve cells. If during the developmental stage any of these mechanisms is affected by toxic or external stimuli it may result into impaired myelination leading to neurological deficits. Such being the case, several approaches have been developed to evaluate how oligodendrocyte development and myelination may be impaired. The present review aims to summarize changes that oligodendrocytes suffer from precursor cells to mature ones, and to describe and discuss the different in vitro models used to evaluate not only oligodendrocyte development (proliferation, migration, differentiation and ability to myelinate), but also their interaction with neurons and other glial cells. First we discuss the temporal oligodendrocyte lineage progression, highlighting the differences between human and rodent, usually used as tissue supply for in vitro cultures. Second we describe how to perform and characterize the different in vitro cultures, as well as the methodologies to evaluate oligodendrocyte functionality in each culture system, discussing their advantages and disadvantages. Finally, we briefly discuss the current status of in vivo models for oligodendrocyte development and myelination.

Connexins-mediated glia networking impacts myelination and remyelination in the central nervous system

In the central nervous system (CNS), the glial gap junctions are established among astrocytes (ASTs), oligodendrocytes (OLs), and/or between ASTs and OLs due to the expression of membrane proteins called connexins (Cxs). Together, the glial cells form a network of communicating cells that is important for the homeostasis of brain function for its involvement in the intercellular calcium wave propagation, exchange of metabolic substrates, cell proliferation, migration, and differentiation. Alternatively, Cxs are also involved in hemichannel function and thus participate in gliotransmission. In recent years, pathologic changes of oligodendroglia or demyelination found in transgenic mice with different subsets of Cxs or pharmacological insults suggest that glial Cxs may participate in the regulation of the myelination or remyelination processes. However, little is known about the underlying mechanisms. In this review, we will mainly focus on the functions of Cx-mediated gap junction channels, as well as hemichannels, in brain glial cells and discuss the way by which they impact myelination and remyelination. These aspects will be considered at the light of recent genetic and non-genetic studies related to demyelination and remyelination.

Neural differentiation on synthetic scaffold materials

The potential of stem cells to differentiate into a variety of subgroups of neural cells makes stem cell differentiation and transplantation a promising candidate for neurodegenerative disorder therapies. However, selective differentiation of stem cells to neurons while preventing glial scar formation is a complex process. Mimicking the natural environment of neural tissue is pivotal, thus various synthetic materials have been developed for this purpose. The synthetic scaffolds can direct stem cells into a neural lineage by including extracellular factors that act on cell fate, which are mainly soluble signals, extracellular matrix proteins and physical factors (e.g. elasticity and topography). This article reviews synthetic materials developed for neural regeneration in terms of their extracellular matrix mimicking properties. Functionalization of synthetic materials by addition of bioactive chemical groups and adjustment of physical properties such as topography, electroactivity and elasticity are discussed.

Evoked potential and behavioral outcomes for experimental autoimmune encephalomyelitis in Lewis rats

A reliable outcome measurement is needed to assess the effects of experimental lesions in the rat spinal cord as well as to assess the benefits of therapies designed to modulate them. The Basso, Beattie, and Bresnahan (BBB) behavioral scores can be indicative of the functionality in motor pathways. However, since lesions are often induced in the more accessible dorsal parts associated with the sensory pathways, the BBB scores may not be ideal measure of the disability. We propose somatosensory evoked potential (SEP) as a complementary measure to assess the integrity of sensory pathways. We used the focal experimental autoimmune encephalomyelitis (EAE) model, in which focal demyelinating lesions were induced by injecting cytokine-ethidium bromide into dorsal white matter after MOG-IFA immunization. Both the SEP and BBB measures reflected injury; however, the SEP was uniformly and consistently altered after the injury whereas the BBB varied widely. The results suggest that the SEP measures are more sensitive and reliable markers of focal spinal cord demyelination compared to the behavioral measures like the BBB score.

Effect of MOG sensitization on somatosensory evoked potential in Lewis rats

Myelin oligodendrocyte glycoprotein (MOG) is commonly used as an immunogen to induce an immune response against endogenous myelin, thereby modeling multiple sclerosis in rodents. When MOG is combined with complete Freund's adjuvant (CFA), multifocal, multiphasic disease ensues; whereas when MOG is combined with incomplete Freund's adjuvant (IFA), clinical disease is usually absent. MOG-IFA immunized animals can be induced to have neurological disease after intraspinal injections of cytokines and ethidium bromide (EtBr). In this study, we investigated whether MOG-IFA immunized rats exhibited subclinical injury as defined by somatosensory evoked potential (SEP) recordings. The titration of anti-MOG-125 antibodies showed robust peripheral mounting of immune response against myelin in MOG-immunized rats. However the SEP measures showed no significant change over time. Upon injecting cytokine-EtBr in the spinal cord after MOG sensitization, the SEP recordings showed reduced amplitude and prolonged latency, suggestive of axonal injury and demyelination in the dorsal column, respectively. These findings were later confirmed using T2-weighted MRI and histological hematoxylin-eosin stain of the spinal cord. This report establishes that MOG-IFA immunization alone does not alter neuronal conduction in SEP-related neural-pathways and that longitudinal in-vivo SEP recordings provide a sensitive read-out for focal myelitis (MOG-IFA and intraspinal cytokine-EtBr) in rats.

Distinct mechanisms of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyrimidine resistance revealed by transcriptome mapping in mouse striatum

The etiology of idiopathic Parkinson's disease is thought to involve interplay between environmental factors and predisposing genetic traits, although the identification of genetic risk factors remain elusive. The neurotoxicant, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyrimidine (MPTP) produces parkinsonian-like symptoms and pathology in mice and humans. As sensitivity to MPTP is genetically determined in mice this provides an opportunity to identify genes and biological mechanisms that modify the response to an exogenous agent that produces a Parkinson's disease-like condition. MPTP primarily targets dopaminergic nerve terminals in the striatum and elicits changes in striatal gene expression. Therefore, we used Affymetrix and qRT-PCR technology to characterize temporal mRNA changes in striatum in response to MPTP in genetically MPTP-sensitive, C57BL/6J, and MPTP-resistant Swiss Webster and BCL2-associated X protein (Bax)-/- mice. We identified three phases of mRNA expression changes composed of largely distinct gene sets. An early response (5 h) occurred in all strains of mice and multiple brain regions. In contrast, intermediate (24 h) and late (72 h) phases were striatum specific and much reduced in Swiss Webster, indicating these genes contribute and/or are responsive to MPTP-induced pathology. However, Bax-/- mice have robust intermediate responses. We propose a model in which the acute entry of MPP+ into dopaminergic nerve terminals damages them but is insufficient per se to kill the neurons. Rather, we suggest that the compromised nerve terminals elicit longer lasting transcriptional responses in surrounding cells involving production of molecules that feedback on the terminals to cause additional damage that results in cell death. In Swiss Webster, resistance lies upstream in the cascade of events triggered by MPTP and uncouples the acute events elicited by MPTP from the damaging secondary responses. In contrast, in Bax-/- mice resistance lies downstream in the cascade and suggests enhanced tolerance to the secondary insult rather than its attenuation.

Splice variation in the cytoplasmic domains of myelin oligodendrocyte glycoprotein affects its cellular localisation and transport

Although myelin oligodendrocyte glycoprotein is a candidate autoantigen in multiple sclerosis, its function remains unknown. In humans, mRNA expressed by the myelin oligodendrocyte glycoprotein gene is alternatively spliced resulting in at least nine unique protein isoforms. In this study, we investigated the sub-cellular localisation and membrane trafficking of six isoforms by cloning them into mammalian expression vectors. Confocal microscopy revealed that these protein products are expressed in different cellular compartments. While two full-length isoforms (25.6 and 25.1) are expressed at the cell surface, three alternatively spliced forms (22.7, 21.0 and 20.5) have a more intracellular distribution, localising to the endoplasmic reticulum and/or endosomes. Isoform 16.3, which lacks a transmembrane domain, is secreted. A switch in the sub-cellular localisation of myelin oligodendrocyte glycoprotein may have profound effects on receptor:ligand interactions and consequently the function of the protein. The structural features of the alternative isoforms and their differential, sub-cellular expression patterns could dictate the exposure of major immunogenic determinants within the central nervous system. Our findings highlight myelin oligodendrocyte glycoprotein splicing as a factor that could be critical to the phenotypic expression of multiple sclerosis.

Alternative isoforms of myelin/oligodendrocyte glycoprotein with variable cytoplasmic domains are expressed in human brain

The human myelin/oligodendrocyte glycoprotein (MOG) gene is encoded by 10 exons that exhibit a complex pattern of alternative splicing. This report demonstrates that several MOG-specific alternative splice variants are indeed expressed in human oligodendrocytes (OLs) and myelin during perinatal development and are retained through adulthood. While all forms possess the common extracellular Ig-like domain, these alternative MOG structures differ significantly in their respective cytoplasmic domains. Peptide-specific antibodies were generated to facilitate detection of these different MOG moieties. The fidelity of these antibodies is shown using N20 OLs expressing individual MOG variants. These antibodies also only co-localize with another well-characterized marker of OLs and myelin--PLP/DM20 proteins. Among the human tissue samples tested, very limited expression occurred by 36 weeks gestation for 2-3 MOG variants, and the remaining MOG isoforms were not evident until shortly after birth. This study represents the first evidence of alternative translation products from the MOG gene. To date, it is believed that alternative splicing of MOG is limited to primates. Recent completion of various genome projects has revealed that alternative splicing is much more prevalent than originally estimated, and species-specific alternative splicing is now being shown to be highly relevant to expanding proteomic diversity.

The innate immune facet of brain: human neurons express TLR-3 and sense viral dsRNA

Inflammation is an important factor in the pathogenesis of neurodegenerative diseases, such as Alzheimer's disease or multiple sclerosis, and during microbial infections of the nervous system. Glial cells were thought to be the main contributor for cytokine and chemokine production and Toll-like receptor (TLR) expression in the brain. Here, we report that human neurons express TLR-3, a major receptor in virus-mediated innate immune response. We established that these cells can mount a strong inflammatory response characterized by the expression of inflammatory cytokines (TNF-alpha, IL-6), chemokines (CCL-5 and CXCL-10), and antiviral molecules (2'5'OAS and IFN-beta) after treatment with dsRNA - a by-product of viral infection and ligand of TLR-3. This work firmly establishes that human neurons, in absence of glia, have the intrinsic machinery to trigger robust inflammatory, chemoattractive, and antiviral responses.

Clinical relevance of antibodies against myelin oligodendrocyte glycoprotein in different clinical types of multiple sclerosis

OBJECTIVE

Myelin oligodendrocyte glycoprotein (MOG) is a highly immunogenic minor component on the outside surface of CNS myelin which is believed to be one of the autoantigens in multiple sclerosis. The aim of this study was to evaluate the diagnostic potential of anti-MOG IgG antibody levels in cerebrospinal fluid (CSF) and serum of patients with relapsing-remitting multiple sclerosis (RRMS), primary progressive multiple sclerosis (PPMS) and non-inflammatory neurological diseases (NIND) as markers for the different clinical types of multiple sclerosis.

PATIENTS AND METHODS

Consecutive serum and cerebrospinal fluid samples were taken from 21 patients with RRMS, 7 patients with PPMS and 19 patients with NIND. The antibody responses to MOG were determined in paired samples of these different clinical groups by enzyme-linked immunoassay using a recombinant human MOG protein.

RESULTS

The performed analysis indicated that the differences in levels of anti-MOG IgG antibody in serum and cerebrospinal fluid from the patients with RRMS, PPMS or NIND were not statistically significant.

CONCLUSION

The assay is not sensitive or specific enough to be used as a differential diagnostic tool for the clinical types of MS, nor for MS itself.

Astrocytes promote myelination in response to electrical impulses

Myelin, the insulating layers of membrane wrapped around axons by oligodendrocytes, is essential for normal impulse conduction. It forms during late stages of fetal development but continues into early adult life. Myelination correlates with cognitive development and can be regulated by impulse activity through unknown molecular mechanisms. Astrocytes do not form myelin, but these nonneuronal cells can promote myelination in ways that are not understood. Here, we identify a link between myelination, astrocytes, and electrical impulse activity in axons that is mediated by the cytokine leukemia inhibitory factor (LIF). These findings show that LIF is released by astrocytes in response to ATP liberated from axons firing action potentials, and LIF promotes myelination by mature oligodendrocytes. This activity-dependent mechanism promoting myelination could regulate myelination according to functional activity or environmental experience and may offer new approaches to treating demyelinating diseases.

Oligodendrocyte progenitor cells in the adult rat CNS express myelin oligodendrocyte glycoprotein (MOG)

While the effects of high dose X-irradiation on mitotically active progenitor cells and remyelination are well-documented, its effects on myelinating oligodendrocytes are less clear, due in part to divergent views on their mitotic capacity. To examine the effect of X-irradiation on oligodendrocytes, the spinal cord of rats was exposed to 40 Gy of X-irradiation and the number of oligodendrocytes and oligodendrocyte progenitors in the dorsal funiculi at T12 and L1 was determined by in situ hybridization using cRNA-probes for platelet derived growth factor alpha receptor (PDGFRalpha) (to identify oligodendrocyte progenitors), exon 3b of proteolipid protein (PLP) (to identify mature oligodendrocytes) and myelin oligodendrocyte glycoprotein (MOG). X-irradiation resulted in no change in the number of PLP positive cells and no loss of myelin internodes, but caused an almost complete loss of PDGFRalpha-expressing cells, and a reduction in the number of MOG positive cells to a number similar to that found using the PLP exon 3b probe. Importantly, the number of radiation-sensitive MOG-expressing cells was similar to the number of PDGFRalpha positive cells. To determine if the radiation-sensitive MOG positive cells were the same population as the radiation sensitive PDGFRalpha-expressing cells, MOG and PDGFRalpha-expressing cells were isolated from the adult CNS using antibody coated magnetic beads. Twelve to thirteen percent of MOG positive cells were PDGFRalpha positive and nearly all the PDGFRa isolated cells were MOG and galactocerebroside positive. Double immunofluorescence revealed colocalization of NG2 and MOG on cells in the normal adult rat spinal cord. These results show that in situ in the adult rat spinal cord white matter oligodendrocyte progenitors are MOG positive and indicates that expression of MOG cannot be regarded a marker that only identifies mature myelin-supporting oligodendrocytes in tissue.

Immunohistochemical and morphometrical studies on myelin breakdown in the demyelination (dmy) mutant rat

The demyelination (dmy) rat is a unique mutant exhibiting severe myelin breakdown in the central nervous system (CNS). In this study, we conducted immunohistochemical and morphometrical investigations in the dmy rat. From around 6 weeks of age, the affected rats developed ataxia especially in the hindlimbs. Afterwards, ataxia worsened rapidly, resulting in complete paralysis of the hindlimbs and recumbency. Histopathology at 7 to 10 weeks of age revealed myelin destruction throughout the white matter of the CNS in the dmy rats. The most severely affected lesions were distributed in the corpus callosum, capsula interna, striatum, subcortical white matter, cerebellar peduncle, and ventral and lateral parts of the spinal cord. Immunohistochemistry demonstrated prominent astrogliosis and many ED-1 positive macrophages in the myelin-destructed areas. Until the 4th week, no significant differences in myelin thickness and fiber diameter were found between dmy and control rats. However, from 5 weeks of age, myelin thickness of residual myelinated fibers in dmy rats became significantly less than that in controls. These data indicated that the dmy phenotype shows a prolonged period of myelin destruction, suggesting that dmy mutation affects the adequate maintenance of myelin.

Identification and functional characterization of mouse TPO1 as a myelin membrane protein

TPO1 is a member of the AIGP family, a unique group of proteins that contains 11 putative transmembrane domains. Expression of the rat TPO1 gene is upregulated in cultured oligodendrocytes (OLs) during development from pro-oligodendroblasts to postmitotic OLs. However, the distribution of native TPO1 protein in cultured OLs and in the brain has not been elucidated. We investigated the distribution and cellular function of TPO1 in myelinating cells of the nervous system. In mice, TPO1 gene expression was detected in the central (CNS) and peripheral (PNS) nervous systems and was markedly upregulated at postnatal days 10-20, an early phase of myelination in the mouse brain. To investigate TPO1 localization, we generated affinity-purified antibodies to synthetic peptides derived from mouse TPO1. Immunohistochemical analysis showed that TPO1 was expressed in OLs and Schwann cells but not in neurons and astrocytes. Schwann cells from trembler mice, which lack PNS myelin, had significantly decreased TPO1 expression and an altered localization pattern, suggesting that TPO1 is a functional myelin membrane protein. In OL lineage cell cultures, TPO1 was detected in A2B5+ bipolar early progenitors, A2B5+ multipolar Pro-OLs, GalC+ immature OLs and MBP+ mature OLs. The subcellular localization of TPO1 in OL lineage cells was mapped to the GM130+ Golgi in cell bodies and Fyn+ cell processes and myelin-like sheets. Furthermore, TPO1 selectively colocalized with non-phosphorylated Fyn and promoted Fyn autophosphorylation in COS7 cells, suggesting that TPO1 may play a role in myelin formation via Fyn kinase activation in the PNS and CNS.

Virus infection switches TLR-3-positive human neurons to become strong producers of beta interferon

To study the capacity of human neurons to mount innate immunity responses to viral infections, we infected cells of a human postmitotic neuron-derivative cell line, NT2-N, with rabies virus (RABV) and herpes simplex type 1 (HSV-1). Changes in neuronal gene expression were analyzed by use of Affymetrix microarrays. Applying a twofold cutoff, RABV increased the transcription of 228 genes, and HSV-1 increased the transcription of 263 genes. The most striking difference between the two infections concerns genes involved in immunity. These genes represent 24% of the RABV-upregulated genes and only 4.9% of the HSV-1-upregulated genes. Following RABV infection, the most upregulated genes belong to the immunity cluster and included almost exclusively genes for beta interferon (IFN-beta) primary and secondary responses as well as genes for chemokines (CCL-5, CXCL-10) and inflammatory cytokines (interleukin 6 [IL-6], tumor necrosis factor alpha, interleukin 1 alpha). In contrast, HSV-1 infection did not increase IFN-beta gene transcripts and triggered the production of only IL-6 and interferon regulatory factor 1 mRNAs. The microarray results were confirmed by real-time PCR, immunocytochemistry, and enzyme-linked immunosorbent assay. Human neurons were found to express Toll-like receptor 3. They produced IFN-beta after treatment with poly(I:C) but not with lipopolysaccharide. Thus, human neurons can mount an innate immunity response to double-stranded RNA. These observations firmly establish that human neurons, in absence of glia, have the intrinsic machinery to sense virus infection.

ES cell-derived glial precursors contribute to remyelination in acutely demyelinated spinal cord lesions

Pluripotent embryonic stem (ES) cells have emerged as a powerful tool for disease modeling and neural regeneration. Transplantation studies in rodents indicate that ES cell-derived glial precursors (ESGPs) efficiently restore myelin in dysmyelinating mutants and chemically induced foci of myelin loss. Here we explore the myelination potential of ESGPs in an antibody/complement-induced demyelination model. Microinjection of an antibody to myelin oligodendrocyte glycoprotein (MOG) and complement was employed to generate circumscribed areas of demyelination in the adult rat spinal cord. ESGPs transplanted into 2-day-old lesions were found to survive and differentiate into both oligodendrocytes and astrocytes. The engrafted cells remained largely confined to the lesion site and showed no evidence of tumor formation up until 4 weeks after transplantation. Within areas of pronounced microglial activation and macrophage extravasation, engrafted ES cell-derived oligodendrocytes contacted and enwrapped host axons and alongside endogenous glia, contributed to the formation of new myelin sheaths. These findings demonstrate that ESGPs transplanted into acutely demyelinated lesions can contribute to myelin repair.

Virus infection switches TLR-3-positive human neurons to become strong producers of beta interferon

To study the capacity of human neurons to mount innate immunity responses to viral infections, we infected cells of a human postmitotic neuron-derivative cell line, NT2-N, with rabies virus (RABV) and herpes simplex type 1 (HSV-1). Changes in neuronal gene expression were analyzed by use of Affymetrix microarrays. Applying a twofold cutoff, RABV increased the transcription of 228 genes, and HSV-1 increased the transcription of 263 genes. The most striking difference between the two infections concerns genes involved in immunity. These genes represent 24% of the RABV-upregulated genes and only 4.9% of the HSV-1-upregulated genes. Following RABV infection, the most upregulated genes belong to the immunity cluster and included almost exclusively genes for beta interferon (IFN-beta) primary and secondary responses as well as genes for chemokines (CCL-5, CXCL-10) and inflammatory cytokines (interleukin 6 [IL-6], tumor necrosis factor alpha, interleukin 1 alpha). In contrast, HSV-1 infection did not increase IFN-beta gene transcripts and triggered the production of only IL-6 and interferon regulatory factor 1 mRNAs. The microarray results were confirmed by real-time PCR, immunocytochemistry, and enzyme-linked immunosorbent assay. Human neurons were found to express Toll-like receptor 3. They produced IFN-beta after treatment with poly(I:C) but not with lipopolysaccharide. Thus, human neurons can mount an innate immunity response to double-stranded RNA. These observations firmly establish that human neurons, in absence of glia, have the intrinsic machinery to sense virus infection.