Age-dependent effects of metformin on human oligodendrocyte lineage cell ensheathment capacity.

Metformin restores the myelination potential of aged rat A2B5+ oligodendrocyte progenitor cells and may enhance recovery in children with post-radiation brain injury. Human late progenitor cells (O4+A2B5+) have a superior capacity to ensheath nanofibres compared to mature oligodendrocytes, with cells from paediatric sources exceeding adults. In this study, we assessed the effects of metformin on ensheathment capacity of human adult and paediatric progenitors and mature oligodendrocytes and related differences to transcriptional changes. A2B5+ progenitors and mature cells, derived from surgical tissues by immune-magnetic separation, were assessed for ensheathment capacity in nanofibre plates over 2 weeks. Metformin (10 µM every other day) was added to selected cultures. RNA was extracted from treated and control cultures after 2 days. For all ages, ensheathment by progenitors exceeded mature oligodendrocytes. Metformin enhanced ensheathment by adult donor cells but reduced ensheathment by paediatric cells. Metformin marginally increased cell death in paediatric progenitors. Metformin-induced changes in gene expression are distinct for each cell type. Adult progenitors showed up-regulation of pathways involved in the process of outgrowth and promoting lipid biosynthesis. Paediatric progenitors showed a relatively greater proportion of down- versus up-regulated pathways, these involved cell morphology, development and synaptic transmission. Metformin-induced AMP-activated protein kinase activation in all cell types; AMP-activated protein kinase inhibitor BML-275 reduced functional metformin effects only with adult cells. Our results indicate age and differentiation stage-related differences in human oligodendroglia lineage cells in response to metformin. Clinical trials for demyelinating conditions will indicate how these differences translate in vivo.

Regulation of stress granule formation in human oligodendrocytes.

Oligodendrocyte (OL) injury and subsequent loss is a pathologic hallmark of multiple sclerosis (MS). Stress granules (SGs) are membrane-less organelles containing mRNAs stalled in translation and considered as participants of the cellular response to stress. Here we show SGs in OLs in active and inactive areas of MS lesions as well as in normal-appearing white matter. In cultures of primary human adult brain derived OLs, metabolic stress conditions induce transient SG formation in these cells. Combining pro-inflammatory cytokines, which alone do not induce SG formation, with metabolic stress results in persistence of SGs. Unlike sodium arsenite, metabolic stress induced SG formation is not blocked by the integrated stress response inhibitor. Glycolytic inhibition also induces persistent SGs indicating the dependence of SG formation and disassembly on the energetic glycolytic properties of human OLs. We conclude that SG persistence in OLs in MS reflects their response to a combination of metabolic stress and pro-inflammatory conditions.

ALCAM on human oligodendrocytes mediates CD4 T cell adhesion.

Multiple sclerosis is a chronic neuroinflammatory disorder characterized by demyelination, oligodendrocyte damage/loss and neuroaxonal injury in the context of immune cell infiltration in the CNS. No neuroprotective therapy is available to promote the survival of oligodendrocytes and protect their myelin processes in immune-mediated demyelinating diseases. Pro-inflammatory CD4 Th17 cells can interact with oligodendrocytes in multiple sclerosis and its animal model, causing injury to myelinating processes and cell death through direct contact. However, the molecular mechanisms underlying the close contact and subsequent detrimental interaction of Th17 cells with oligodendrocytes remain unclear. In this study we used single cell RNA sequencing, flow cytometry and immunofluorescence studies on CNS tissue from multiple sclerosis subjects, its animal model and controls to characterize the expression of cell adhesion molecules by mature oligodendrocytes. We found that a significant proportion of human and murine mature oligodendrocytes express melanoma cell adhesion molecule (MCAM) and activated leukocyte cell adhesion molecule (ALCAM) in multiple sclerosis, in experimental autoimmune encephalomyelitis and in controls, although their regulation differs between human and mouse. We observed that exposure to pro-inflammatory cytokines or to human activated T cells are associated with a marked downregulation of the expression of MCAM but not of ALCAM at the surface of human primary oligodendrocytes. Furthermore, we used in vitro live imaging, immunofluorescence and flow cytometry to determine the contribution of these molecules to Th17-polarized cell adhesion and cytotoxicity towards human oligodendrocytes. Silencing and blocking ALCAM but not MCAM limited prolonged interactions between human primary oligodendrocytes and Th17-polarized cells, resulting in decreased adhesion of Th17-polarized cells to oligodendrocytes and conferring significant protection of oligodendrocytic processes. In conclusion, we showed that human oligodendrocytes express MCAM and ALCAM, which are differently modulated by inflammation and T cell contact. We found that ALCAM is a ligand for Th17-polarized cells, contributing to their capacity to adhere and induce damage to human oligodendrocytes, and therefore could represent a relevant target for neuroprotection in multiple sclerosis.

Mechanisms of metabolic stress induced cell death of human oligodendrocytes: relevance for progressive multiple sclerosis.

Oligodendrocyte (OL) injury and loss are central features of evolving lesions in multiple sclerosis. Potential causative mechanisms of OL loss include metabolic stress within the lesion microenvironment. Here we use the injury response of primary human OLs (hOLs) to metabolic stress (reduced glucose/nutrients) in vitro to help define the basis for the in situ features of OLs in cases of MS. Under metabolic stress in vitro, we detected reduction in ATP levels per cell that precede changes in survival. Autophagy was initially activated, although ATP levels were not altered by inhibitors (chloroquine) or activators (Torin-1). Prolonged stress resulted in autophagy failure, documented by non-fusion of autophagosomes and lysosomes. Consistent with our in vitro results, we detected higher expression of LC3, a marker of autophagosomes in OLs, in MS lesions compared to controls. Both in vitro and in situ, we observe a reduction in nuclear size of remaining OLs. Prolonged stress resulted in increased ROS and cleavage of spectrin, a target of Ca2+-dependent proteases. Cell death was however not prevented by inhibitors of ferroptosis or MPT-driven necrosis, the regulated cell death (RCD) pathways most likely to be activated by metabolic stress. hOLs have decreased expression of VDAC1, VDAC2, and of genes regulating iron accumulation and cyclophilin. RNA sequencing analyses did not identify activation of these RCD pathways in vitro or in MS cases. We conclude that this distinct response of hOLs, including resistance to RCD, reflects the combined impact of autophagy failure, increased ROS, and calcium influx, resulting in metabolic collapse and degeneration of cellular structural integrity. Defining the basis of OL injury and death provides guidance for development of neuro-protective strategies.

Analysis of the microglia transcriptome across the human lifespan using single cell RNA sequencing.

BACKGROUND: Microglia are tissue resident macrophages with a wide range of critically important functions in central nervous system development and homeostasis. METHOD: In this study, we aimed to characterize the transcriptional landscape of ex vivo human microglia across different developmental ages using cells derived from pre-natal, pediatric, adolescent, and adult brain samples. We further confirmed our transcriptional observations using ELISA and RNAscope. RESULTS: We showed that pre-natal microglia have a distinct transcriptional and regulatory signature relative to their post-natal counterparts that includes an upregulation of phagocytic pathways. We confirmed upregulation of CD36, a positive regulator of phagocytosis, in pre-natal samples compared to adult samples in situ. Moreover, we showed adult microglia have more pro-inflammatory signature compared to microglia from other developmental ages. We indicated that adult microglia are more immune responsive by secreting increased levels of pro-inflammatory cytokines in response to LPS treatment compared to the pre-natal microglia. We further validated in situ up-regulation of IL18 and CXCR4 in human adult brain section compared to the pre-natal brain section. Finally, trajectory analysis indicated that the transcriptional signatures adopted by microglia throughout development are in response to a changing brain microenvironment and do not reflect predetermined developmental states. CONCLUSION: In all, this study provides unique insight into the development of human microglia and a useful reference for understanding microglial contribution to developmental and age-related human disease.

Regional and age-related diversity of human mature oligodendrocytes.

Morphological and emerging molecular studies have provided evidence for heterogeneity within the oligodendrocyte population. To address the regional and age-related heterogeneity of human mature oligodendrocytes (MOLs) we applied single-cell RNA sequencing to cells isolated from cortical/subcortical, subventricular zone brain tissue samples, and thoracolumbar spinal cord samples. Unsupervised clustering of cells identified transcriptionally distinct MOL subpopulations across regions. Spinal cord MOLs, but not microglia, exhibited cell-type-specific upregulation of immune-related markers compared to the other adult regions. SVZ MOLs showed an upregulation of select number of development-linked transcription factors compared to other regions; however, pseudotime trajectory analyses did not identify a global developmental difference. Age-related analysis of cortical/subcortical samples indicated that pediatric MOLs, especially from under age 5, retain higher expression of genes linked to development and to immune activity with pseudotime analysis favoring a distinct developmental stage. Our regional and age-related studies indicate heterogeneity of MOL populations in the human CNS that may reflect developmental and environmental influences.

Contact-Dependent Granzyme B-Mediated Cytotoxicity of Th17-Polarized Cells Toward Human Oligodendrocytes.

Multiple sclerosis (MS) is characterized by the loss of myelin and of myelin-producing oligodendrocytes (OLs) in the central nervous system (CNS). Pro-inflammatory CD4+ Th17 cells are considered pathogenic in MS and are harmful to OLs. We investigated the mechanisms driving human CD4+ T cell-mediated OL cell death. Using fluorescent and brightfield in vitro live imaging, we found that compared to Th2-polarized cells, Th17-polarized cells show greater interactions with primary human OLs and human oligodendrocytic cell line MO3.13, displaying longer duration of contact, lower mean speed, and higher rate of vesicle-like structure formation at the sites of contact. Using single-cell RNA sequencing, we assessed the transcriptomic profile of primary human OLs and Th17-polarized cells in direct contact or separated by an insert. We showed that upon close interaction, OLs upregulate the expression of mRNA coding for chemokines and antioxidant/anti-apoptotic molecules, while Th17-polarized cells upregulate the expression of mRNA coding for chemokines and pro-inflammatory cytokines such as IL-17A, IFN-γ, and granzyme B. We found that secretion of CCL3, CXCL10, IFN-γ, TNFα, and granzyme B is induced upon direct contact in cocultures of human Th17-polarized cells with human OLs. In addition, we validated by flow cytometry and immunofluorescence that granzyme B levels are upregulated in Th17-polarized compared to Th2-polarized cells and are even higher in Th17-polarized cells upon direct contact with OLs or MO3.13 cells compared to Th17-polarized cells separated from OLs by an insert. Moreover, granzyme B is detected in OLs and MO3.13 cells following direct contact with Th17-polarized cells, suggesting the release of granzyme B from Th17-polarized cells into OLs/MO3.13 cells. To confirm granzyme B-mediated cytotoxicity toward OLs, we showed that recombinant human granzyme B can induce OLs and MO3.13 cell death. Furthermore, pretreatment of Th17-polarized cells with a reversible granzyme B blocker (Ac-IEPD-CHO) or a natural granzyme B blocker (serpina3N) improved survival of MO3.13 cells upon coculture with Th17 cells. In conclusion, we showed that human Th17-polarized cells form biologically significant contacts with human OLs and exert direct toxicity by releasing granzyme B.

Diverse injury responses of human oligodendrocyte to mediators implicated in multiple sclerosis.

Early multiple sclerosis lesions feature relative preservation of oligodendrocyte cell bodies with dying back retraction of their myelinating processes. Cell loss occurs with disease progression. Putative injury mediators include metabolic stress (low glucose/nutrient), pro-inflammatory mediators (interferon γ and tumour necrosis factor α), and excitotoxins (glutamate). Our objective was to compare the impact of these disease relevant mediators on the injury responses of human mature oligodendrocytes. In the current study, we determined the effects of these mediators on process extension and survival of human brain derived mature oligodendrocytes in vitro and used bulk RNA sequencing to identify distinct effector mechanisms that underlie the responses. All mediators induced significant process retraction of the oligodendrocytes in dissociated cell culture. Only metabolic stress (low glucose/nutrient) conditions resulted in delayed (4-6 days) non-apoptotic cell death. Metabolic effects were associated with induction of the integrated stress response, which can be protective or contribute to cell injury dependent on its level and duration of activation. Addition of Sephin1, an agonist of the integrated stress response induced process retraction under control conditions and further enhanced retraction under metabolic stress conditions. The antagonist ISRIB restored process outgrowth under stress conditions, and if added to already stressed cells, reduced delayed cell death and prolonged the period in which recovery could occur. Inflammatory cytokine functional effects were associated with activation of multiple signalling pathways (including Jak/Stat-1) that regulate process outgrowth, without integrated stress response induction. Glutamate application produced limited transcriptional changes suggesting a contribution of effects directly on cell processes. Our comparative studies indicate the need to consider both the specific injury mediators and the distinct cellular mechanisms of responses to them by human oligodendrocytes to identify effective neuroprotective therapies for multiple sclerosis.

Human Oligodendrocyte Myelination Potential; Relation to Age and Differentiation.

OBJECTIVE: Myelin regeneration in the human central nervous system relies on progenitor cells within the tissue parenchyma, with possible contribution from previously myelinating oligodendrocytes (OLs). In multiple sclerosis, a demyelinating disorder, variables affecting remyelination efficiency include age, severity of initial injury, and progenitor cell properties. Our aim was to investigate the effects of age and differentiation on the myelination potential of human OL lineage cells. METHODS: We derived viable primary OL lineage cells from surgical resections of pediatric and adult brain tissue. Ensheathment capacity using nanofiber assays and transcriptomic profiles from RNA sequencing were compared between A2B5+ antibody-selected progenitors and mature OLs (non-selected cells). RESULTS: We demonstrate that pediatric progenitor and mature cells ensheathed nanofibers more robustly than did adult progenitor and mature cells, respectively. Within both age groups, the percentage of fibers ensheathed and ensheathment length per fiber were greater for A2B5+ progenitors. Gene expression of OL progenitor markers PDGFRA and PTPRZ1 were higher in A2B5+ versus A2B5- cells and in pediatric A2B5+ versus adult A2B5+ cells. The p38 MAP kinases and actin cytoskeleton-associated pathways were upregulated in pediatric cells; both have been shown to regulate OL process outgrowth. Significant upregulation of "cell senescence" genes was detected in pediatric samples; this could reflect their role in development and the increased susceptibility of pediatric OLs to activating cell death responses to stress. INTERPRETATION: Our findings identify specific biological pathways relevant to myelination that are differentially enriched in human pediatric and adult OL lineage cells and suggest potential targets for remyelination enhancing therapies. ANN NEUROL 2022;91:178-191.

Pro-inflammatory T helper 17 directly harms oligodendrocytes in neuroinflammation.

T helper (Th)17 cells are considered to contribute to inflammatory mechanisms in diseases such as multiple sclerosis (MS). However, the discussion persists regarding their true role in patients. Here, we visualized central nervous system (CNS) inflammatory processes in models of MS live in vivo and in MS brains and discovered that CNS-infiltrating Th17 cells form prolonged stable contact with oligodendrocytes. Strikingly, compared to Th2 cells, direct contact with Th17 worsened experimental demyelination, caused damage to human oligodendrocyte processes, and increased cell death. Importantly, we found that in comparison to Th2 cells, both human and murine Th17 cells express higher levels of the integrin CD29, which is linked to glutamate release pathways. Of note, contact of human Th17 cells with oligodendrocytes triggered release of glutamate, which induced cell stress and changes in biosynthesis of cholesterol and lipids, as revealed by single-cell RNA-sequencing analysis. Finally, exposure to glutamate decreased myelination, whereas blockade of CD29 preserved oligodendrocyte processes from Th17-mediated injury. Our data provide evidence for the direct and deleterious attack of Th17 cells on the myelin compartment and show the potential for therapeutic opportunities in MS.

One-step Reprogramming of Human Fibroblasts into Oligodendrocyte-like Cells by SOX10, OLIG2, and NKX6.2.

Limited access to human oligodendrocytes impairs better understanding of oligodendrocyte pathology in myelin diseases. Here, we describe a method to robustly convert human fibroblasts directly into oligodendrocyte-like cells (dc-hiOLs), which allows evaluation of remyelination-promoting compounds and disease modeling. Ectopic expression of SOX10, OLIG2, and NKX6.2 in human fibroblasts results in rapid generation of O4+ cells, which further differentiate into MBP+ mature oligodendrocyte-like cells within 16 days. dc-hiOLs undergo chromatin remodeling to express oligodendrocyte markers, ensheath axons, and nanofibers in vitro, respond to promyelination compound treatment, and recapitulate in vitro oligodendroglial pathologies associated with Pelizaeus-Merzbacher leukodystrophy related to PLP1 mutations. Furthermore, DNA methylome analysis provides evidence that the CpG methylation pattern significantly differs between dc-hiOLs derived from fibroblasts of young and old donors, indicating the maintenance of the source cells' "age." In summary, dc-hiOLs represent a reproducible technology that could contribute to personalized medicine in the field of myelin diseases.

Identification of novel myelin repair drugs by modulation of oligodendroglial differentiation competence.

BACKGROUND: In multiple sclerosis loss of myelin and oligodendrocytes impairs saltatory signal transduction and leads to neuronal loss and functional deficits. Limited capacity of oligodendroglial precursor cells to differentiate into mature cells is the main reason for inefficient myelin repair in the central nervous system. Drug repurposing constitutes a powerful approach for identification of pharmacological compounds promoting this process. METHODS: A phenotypic compound screening using the subcellular distribution of a potent inhibitor of oligodendroglial cell differentiation, namely p57kip2, as differentiation competence marker was conducted. Hit compounds were validated in terms of their impact on developmental cell differentiation and myelination using both rat and human primary cell cultures and organotypic cerebellar slice cultures, respectively. Their effect on spontaneous remyelination was then investigated following cuprizone-mediated demyelination of the corpus callosum. FINDINGS: A number of novel small molecules able to promote oligodendroglial cell differentiation were identified and a subset was found to foster human oligodendrogenesis as well as myelination ex vivo. Among them the steroid danazol and the anthelminthic parbendazole were found to increase myelin repair. INTERPRETATION: We provide evidence that early cellular processes involved in differentiation decisions are applicable for the identification of regeneration promoting drugs and we suggest danazol and parbendazole as potent therapeutic candidates for demyelinating diseases. FUNDING: This work was supported by the Jürgen Manchot Foundation, Düsseldorf; Research Commission of the Medical Faculty of Heinrich-Heine-University Düsseldorf; Christiane and Claudia Hempel Foundation; Stifterverband/Novartisstiftung; James and Elisabeth Cloppenburg, Peek and Cloppenburg Düsseldorf Stiftung and International Progressive MS Alliance (BRAVEinMS).

Age-related injury responses of human oligodendrocytes to metabolic insults: link to BCL-2 and autophagy pathways.

Myelin destruction and oligodendrocyte (OL) death consequent to metabolic stress is a feature of CNS disorders across the age spectrum. Using cells derived from surgically resected tissue, we demonstrate that young (

Effects of Biotin on survival, ensheathment, and ATP production by oligodendrocyte lineage cells in vitro.

Mechanisms implicated in disease progression in multiple sclerosis include continued oligodendrocyte (OL)/myelin injury and failure of myelin repair. Underlying causes include metabolic stress with resultant energy deficiency. Biotin is a cofactor for carboxylases involved in ATP production that impact myelin production by promoting fatty acid synthesis. Here, we investigate the effects of high dose Biotin (MD1003) on the functional properties of post-natal rat derived oligodendrocyte progenitor cells (OPCs). A2B5 positive OPCs were assessed using an in vitro injury assay, culturing cells in either DFM (DMEM/F12+N1) or "stress media" (no glucose (NG)-DMEM), with Biotin added over a range from 2.5 to 250 µg/ml, and cell viability determined after 24 hrs. Biotin reduced the increase in OPC cell death in the NG condition. In nanofiber myelination assays, biotin increased the percentage of ensheathing cells, the number of ensheathed segments per cell, and length of ensheathed segments. In dispersed cell culture, Biotin also significantly increased ATP production, assessed using a Seahorse bio-analyzer. For most assays, the positive effects of Biotin were observed at the higher end of the dose-response analysis. We conclude that Biotin, in vitro, protects OL lineage cells from metabolic injury, enhances myelin-like ensheathment, and is associated with increased ATP production.

RNA-binding protein altered expression and mislocalization in MS.

OBJECTIVE: To determine whether there are nuclear depletion and cellular mislocalization of RNA-binding proteins (RBPs) transactivation response DNA-binding protein of 43 kDa (TDP-43), fused in sarcoma (FUS), and polypyrimidine tract-binding protein (PTB) in MS, as is the case in amyotrophic lateral sclerosis (ALS) and oligodendrocytes infected with Theiler murine encephalomyelitis virus (TMEV), we examined MS lesions and in vitro cultured primary human brain-derived oligodendrocytes. METHODS: Nuclear depletion and mislocalization of TDP-43, FUS, and PTB are thought to contribute to the pathogenesis of ALS and TMEV demyelination. The latter findings prompted us to investigate these RBPs in the demyelinated lesions of MS and in in vitro cultured human brain-derived oligodendrocytes under metabolic stress conditions. RESULTS: We found (1) mislocalized TDP-43 in oligodendrocytes in active lesions in some patients with MS; (2) decreased PTB1 expression in oligodendrocytes in mixed active/inactive demyelinating lesions; (3) decreased nuclear expression of PTB2 in neurons in cortical demyelinating lesions; and (4) nuclear depletion of TDP-43 in oligodendrocytes under metabolic stress induced by low glucose/low nutrient conditions compared with optimal culture conditions. CONCLUSION: TDP-43 has been found to have a key role in oligodendrocyte function and viability, whereas PTB is important in neuronal differentiation, suggesting that altered expression and mislocalization of these RBPs in MS lesions may contribute to the pathogenesis of demyelination and neurodegeneration. Our findings also identify nucleocytoplasmic transport as a target for treatment.

Developmental trajectory of oligodendrocyte progenitor cells in the human brain revealed by single cell RNA sequencing.

Characterizing the developmental trajectory of oligodendrocyte progenitor cells (OPC) is of great interest given the importance of these cells in the remyelination process. However, studies of human OPC development remain limited by the availability of whole cell samples and material that encompasses a wide age range, including time of peak myelination. In this study, we apply single cell RNA sequencing to viable whole cells across the age span and link transcriptomic signatures of oligodendrocyte-lineage cells with stage-specific functional properties. Cells were isolated from surgical tissue samples of second-trimester fetal, 2-year-old pediatric, 13-year-old adolescent, and adult donors by mechanical and enzymatic digestion, followed by percoll gradient centrifugation. Gene expression was analyzed using droplet-based RNA sequencing (10X Chromium). Louvain clustering analysis identified three distinct cellular subpopulations based on 5,613 genes, comprised of an early OPC (e-OPC) group, a late OPC group (l-OPC), and a mature OL (MOL) group. Gene ontology terms enriched for e-OPCs included cell cycle and development, for l-OPCs included extracellular matrix and cell adhesion, and for MOLs included myelination and cytoskeleton. The e-OPCs were mostly confined to the premyelinating fetal group, and the l-OPCs were most highly represented in the pediatric age group, corresponding to the peak age of myelination. Cells expressing a signature characteristic of l-OPCs were identified in the adult brain in situ using RNAScope. These findings highlight the transcriptomic variability in OL-lineage cells before, during, and after peak myelination and contribute to identifying novel pathways required to achieve remyelination.

Distinct Function-Related Molecular Profile of Adult Human A2B5-Positive Pre-Oligodendrocytes Versus Mature Oligodendrocytes.

Remyelination in the human CNS is ascribed to progenitor cells rather than previously myelinating oligodendrocytes (OLs). The ganglioside-recognizing antibody A2B5 has been used to isolate putative progenitor cells, whose in vitro features resemble cells labeled as "pre-oligodendrocytes." Here, we compare the transcriptional profiles of adult human brain-derived A2B5 antibody-selected cells (A+) after initial isolation (day in vitro (DIV1)) and after DIV6, with nonselected (A-) cells (mature OLs), with regard to their differentiation state and functional properties. While a number of previously recognized progenitor associated genes, specifically PTPRZ1 and PDGFRα, were upregulated in the A2B5+ population, a number of such genes were comparably expressed in the mature OLs, as were mature myelin genes. Additional progenitor-related genes were upregulated in the A+ population. We show that A2B5+ cells have greater capacity to ensheath nanofibers, a model of myelination potential; consistent with this, ingenuity pathway analysis indicated that A+ cells had upregulated expression of genes within cell growth and cell signaling pathways. Differential expression of cell death/survival pathways complements previous functional studies showing their increased susceptibility to metabolic stress. At DIV6, we observed significantly fewer differentially expressed genes; suggestive of cell maturation occurring in vitro, indicating the complexity in comparing in vitro and in situ cell properties.

Deep learning for high-throughput quantification of oligodendrocyte ensheathment at single-cell resolution.

High-throughput quantification of oligodendrocyte myelination is a challenge that, if addressed, would facilitate the development of therapeutics to promote myelin protection and repair. Here, we established a high-throughput method to assess oligodendrocyte ensheathment in-vitro, combining nanofiber culture devices and automated imaging with a heuristic approach that informed the development of a deep learning analytic algorithm. The heuristic approach was developed by modeling general characteristics of oligodendrocyte ensheathments, while the deep learning neural network employed a UNet architecture and a single-cell training method to associate ensheathed segments with individual oligodendrocytes. Reliable extraction of multiple morphological parameters from individual cells, without heuristic approximations, allowed the UNet to match the accuracy of expert-human measurements. The capacity of this technology to perform multi-parametric analyses at the level of individual cells, while reducing manual labor and eliminating human variability, permits the detection of nuanced cellular differences to accelerate the discovery of new insights into oligodendrocyte physiology.

Immunology of oligodendrocyte precursor cells in vivo and in vitro.

Remyelination following myelin/oligodendrocyte injury in the central nervous system (CNS) is dependent on oligodendrocyte progenitor cells (OPCs) migrating into lesion sites, differentiating into myelinating oligodendrocytes (OLs), and ensheathing axons. Experimental models indicate that robust OPC-dependent remyelination can occur in the CNS; in contrast, histologic and imaging studies of lesions in the human disease multiple sclerosis (MS) indicate the variable extent of this response, which is particularly limited in more chronic MS lesions. Immune-mediated mechanisms can contribute either positively or negatively to the presence and functional responses of OPCs. This review addresses i) the molecular signature and functional properties of OPCs in the adult human brain; ii) the status (presence and function) of OPCs in MS lesions; iii) experimental models and in vitro data highlighting the contribution of adaptive and innate immune constituents to OPC injury and remyelination; and iv) effects of MS-directed immunotherapies on OPCs, either directly or indirectly via effects on specific immune constituents.

Helper CD4 T cells expressing granzyme B cause glial fibrillary acidic protein fragmentation in astrocytes in an MHCII-independent manner.

During inflammatory processes of the central nervous system, helper T cells have the capacity to cross the blood-brain barrier and injure or kill neural cells through cytotoxic mechanisms. Glial fibrillary acidic protein (GFAP) is an intermediate filament protein that is part of the astrocyte cytoskeleton that can become fragmented in neuroinflammatory conditions. The mechanism of action by which helper T cells with cytotoxic properties injure astrocytes is not completely understood. Primary human astrocytes were obtained from fetal brain tissue. Human helper (CD4+ ) T cells were isolated from peripheral blood mononuclear cells and activated with the superantigen staphylococcal enterotoxin E (SEE). Granzyme B was detected by enzyme linked immunosorbent assay and intracellular flow cytometry. GFAP fragmentation was monitored by western blotting. Cell death was monitored by lactic acid dehydrogenase release and terminal biotin-dUTP nick labeling (TUNEL). Astrocyte migration was monitored by scratch assay. Adult human oligodendrocytes were cultured with sublethally injured astrocytes to determine support function. Helper T cells activated with SEE expressed granzyme B but not perforin. Helper T cells released granzyme B upon contact with astrocytes and caused GFAP fragmentation in a caspase-dependent, MHCII-independent manner. Sublethally injured astrocytes were not apoptotic; however, their processes were thin and elongated, their migration was attenuated, and their ability to support oligodendrocytes was reduced in vitro. Helper T cells can release granzyme B causing sublethal injury to astrocytes, which compromises the supportive functions of astrocytes. Blocking these pathways may lead to improved resolution of neuroinflammatory lesions.