Oligodendrocyte Development and Plasticity

Piezo1 in microglial cells: Implications for neuroinflammation and tumorigenesis

Microglia, the central nervous system (CNS) resident immune cells, are pivotal in regulating neurodevelopment, maintaining neural homeostasis, and mediating neuroinflammatory responses. Recent research has highlighted the importance of mechanotransduction, the process by which cells convert mechanical stimuli into biochemical signals, in regulating microglial activity. Among the various mechanosensitive channels, Piezo1 has emerged as a key player in microglia, influencing their behavior under both physiological and pathological conditions. This review focuses on the expression and role of Piezo1 in microglial cells, particularly in the context of neuroinflammation and tumorigenesis. We explore how Piezo1 mediates microglial responses to mechanical changes within the CNS, such as alterations in tissue stiffness and fluid shear stress, which are common in conditions like multiple sclerosis, Alzheimer's disease, cerebral ischemia, and gliomas. The review also discusses the potential of targeting Piezo1 for therapeutic intervention, given its involvement in the modulation of microglial activity and its impact on disease progression. This review integrates findings from recent studies to provide a comprehensive overview of Piezo1's mechanistic pathways in microglial function. These insights illuminate new possibilities for developing targeted therapies addressing CNS disorders with neuroinflammation and pathological tissue mechanics.

Transforming growth factor-β receptor I kinase plays a crucial role in oligodendrocyte regeneration after demyelination

Multiple sclerosis (MS) is an autoimmune disease characterized by the loss of oligodendrocytes (OLs) and axon demyelination in the central nervous system. Most therapeutic agents focus on regulating the immune response by suppressing autoimmune reactions. Therefore, developing therapeutic agents that promote remyelination by OLs at disease sites that have already undergone demyelination is necessary. In this study, we generated a new transgenic zebrafish with high efficiency for OL ablation and established a high-throughput screening (HTS)-based platform to identify therapeutic candidates that promote remyelination. Next, we screened a library of kinase inhibitors and identified one candidate, a transforming growth factor-β receptor I (TGF-βRI) kinase inhibitor. Treatment with this kinase inhibitor rapidly recruited microglia to induce clearance of myelin debris, early after OL removal. It also increased the proliferation of OL progenitor cells in demyelinating zebrafish larvae, resulting in restored OL numbers and reduced locomotor activity. Based on these results, we expect our HTS-based platform, along with our newly developed zebrafish model, to be very useful for identifying therapeutic agents that promote remyelination. Furthermore, since the candidate TGF-βRI kinase inhibitor identified in this study restored the phenotype following demyelination, we suggest that TGF-βRI kinase may potentially be a therapeutic target for the treatment of demyelinating diseases.

Revisiting the Pathogenesis of X-Linked Adrenoleukodystrophy

BACKGROUND

X-ALD is a white matter (WM) disease caused by mutations in the ABCD1 gene encoding the transporter of very-long-chain fatty acids (VLCFAs) into peroxisomes. Strikingly, the same ABCD1 mutation causes either devastating brain inflammatory demyelination during childhood or, more often, progressive spinal cord axonopathy starting in middle-aged adults. The accumulation of undegraded VLCFA in glial cell membranes and myelin has long been thought to be the central mechanism of X-ALD.

METHODS

This review discusses studies in mouse and drosophila models that have modified our views of X-ALD pathogenesis.

RESULTS

In the Abcd1 knockout (KO) mouse that mimics the spinal cord disease, the late manifestations of axonopathy are rapidly reversed by ABCD1 gene transfer into spinal cord oligodendrocytes (OLs). In a peroxin-5 KO mouse model, the selective impairment of peroxisomal biogenesis in OLs achieves an almost perfect phenocopy of cerebral ALD. A drosophila knockout model revealed that VLCFA accumulation in glial myelinating cells causes the production of a toxic lipid able to poison axons and activate inflammatory cells. Other mouse models showed the critical role of OLs in providing energy substrates to axons. In addition, studies on microglial changing substates have improved our understanding of neuroinflammation.

CONCLUSIONS

Animal models supporting a primary role of OLs and axonal pathology and a secondary role of microglia allow us to revisit of X-ALD mechanisms. Beyond ABCD1 mutations, pathogenesis depends on unidentified contributors, such as genetic background, cell-specific epigenomics, potential environmental triggers, and stochasticity of crosstalk between multiple cell types among billions of glial cells and neurons.

Canonical and non-canonical roles of oligodendrocyte precursor cells in mental disorders

Psychiatric research has shifted from a neuroncentric view to understanding mental disorders as disturbances of heterogeneous brain networks. Oligodendrocyte precursor cells (OPCs)- actively involved in the modulation of neuronal functions - are altered in psychiatric patients, but the extent and related consequences are unclear. This review explores canonical and non-canonical OPC-related pathways in schizophrenia, bipolar disorder, post-traumatic stress disorder, and depression in humans, highlighting potential mechanisms shared across diagnostic entities.

Spatiotemporal calcium dynamics orchestrate oligodendrocyte development and myelination

Oligodendrocyte lineage cells (OLCs), comprising oligodendrocyte precursor cells (OPCs) and oligodendrocytes, are pivotal in sculpting central nervous system (CNS) architecture and function. OPCs mature into oligodendrocytes, which enwrap axons with myelin sheaths that are critical for enhancing neural transmission. Notably, OLCs actively respond to neuronal activity, modulating neural circuit functions. Understanding neuron-OLC interactions is key to unraveling how OLCs contribute to CNS health and pathology. This review highlights insights from zebrafish and mouse models, revealing how synaptic and extrasynaptic pathways converge to shape spatiotemporal calcium (Ca2+) dynamics within OLCs. We explore how Ca2+ signal integration across spatial and temporal scales acts as a master regulator of OLC fate determination and myelin plasticity.

Low-Intensity Pulsed Ultrasound Promotes Oligodendrocyte Maturation and Remyelination by Down-regulating the Interleukin-17A/Notch1 Signaling Pathway in Mice with Ischemic Stroke

Increasing evidence indicates that oligodendrocyte (OL) numbers and myelin as a dynamic cellular compartment perform a key role in the maintenance of neuronal function. Inhibiting white matter (WM) demyelination or promoting remyelination has garnered interest for its potential therapeutic strategy against ischemic stroke. Our previous work has shown that low-intensity pulsed ultrasound (LIPUS) could improve stroke recovery. However, it is unclear whether LIPUS can maintain WM integrity early after stroke or promote late WM repair. This study evaluated the efficacy of LIPUS on WM repair and long-term neurologic recovery after stroke. Male adult C57BL/6 mice underwent a focal cerebral ischemia model and were randomized to receive ultrasound stimulation (30 min once daily for 14 days). The effect of LIPUS on sensorimotor function was assessed by modified neurological severity score, rotarod test, grip strength test, and gait analysis up to 28 days after stroke. We found that ischemic stroke-induced WM damage was severe on day 7 and partially recovered on day 28. LIPUS prevented neuronal and oligodendrocyte progenitor cell (OPC) death during the acute phase of stroke (d7), protected WM integrity, and reduced brain atrophy and tissue damage during the recovery phase (d28). To further confirm the effect of LIPUS on remyelination, we assessed the proliferation and differentiation of OPCs. We found that LIPUS did not increase the number of OPCs (PDGFRα+ or NG2+), but markedly increased the number of newly produced mature OLs (APC+) and myelin protein levels. Mechanistically, LIPUS may promote OL maturation and remyelination by down-regulating the interleukin-17A/Notch1 signaling pathway. In summary, LIPUS can protect OLs and neurons early after stroke and promote long-term WM repair and functional recovery. LIPUS will be a viable strategy for the treatment of ischemic stroke in the future.

Single cell RNAseq to identify subpopulations of glial progenitors in iPSC-derived oligodendroglial lineage cultures

Cellular heterogeneity is a common issue in differentiation protocols of oligodendrocytes (OLs) from human induced pluripotent stem cells. Our previous work described a novel method to generate OLs and highlighted the presence of glial progenitors. Here, we unravel the glial heterogeneity and characterize the response of isolated subpopulations to differentiation. This study provides a novel tool for studying the dynamics of glial development in vitro and on a transcriptomic level.

Effect of Cytoskeletal Linker Protein GAS2L1 on Oligodendrocyte and Myelin Development

Oligodendrocytes (OLs), the myelin-forming cells of the central nervous system (CNS), develop from OL precursor cells (OPCs) through a complex process involving significant morphological changes that are critically dependent on the dynamic interactions between cytoskeletal networks. Growth arrest-specific 2-like protein 1 (GAS2L1) is a cytoskeletal linker protein that mediates the cross-talk between actin filaments and microtubules. However, its role in OL and myelin development remains unknown. Here, we report that GAS2L1 is expressed in both OPCs and mature OLs, and that overexpression or knockdown of Gas2l1 in cultured OPCs in vitro impaired or enhanced their differentiation, respectively, while both inhibited their proliferation. We generated a Gas2l1 fl/fl mouse line and found that mice with conditional knockout of Gas2l1 in OL lineage cells (Olig1-Cre;Gas2l1 fl/fl , cKO) showed an increased number of mature OLs and enhanced myelination, as well as a reduction in the branching complexity of OPCs. In addition, an alternative mouse line with postnatally induced Gas2l1 ablation specifically in OPCs (Pdfgra-CreER T2 ;Gas2l1 fl/fl , iKO) recapitulated the acceleration of OL and myelin development as well as the inhibition of OPC process branching. Furthermore, EdU tracking in Gas2l1 iKO mice in vivo and in their OPC cultures in vitro showed both a reduction in OPC proliferation and an increase in OL maturation. Finally, cultured OPCs from iKO mice showed an increase in filopodia extension. Taken together, our results demonstrate an effect of GAS2L1 on the regulation of OL/myelin development and may provide a novel potential therapeutic target for various diseases involving OL/myelin pathology.

Oligodendrocyte precursor cells establish regulatory contacts with the soma of active neurons

Oligodendrocyte precursor cells (OPCs) can generate myelinating oligodendrocytes life-long, a process that is dependent on neuronal activity. However, it is possible that OPCs have additional functions, influencing neuronal functions directly. We have used a mouse genetic model of juvenile seizures and chemical induction of neuronal activity to examine the morphological and molecular changes in OPCs around activated principal neurons. We found an increase in process extension of OPCs specifically toward the soma of activated neurons. Moreover, we found that the close proximity of OPC processes around neurons expressing the immediate early gene c-Fos decreased the calcium transients in these neurons, indicating a regulative function of OPCs. Analyses of transcriptome and chromatin accessibility revealed significant changes in genes involved in transforming growth factor beta (TGFβ) signaling. Extracellular matrix genes, particularly those encoding type VI collagen, an established binding partner for the OPC surface protein NG2, was increased around active neurons. Our findings indicate that OPCs are an integral part of the neural network and may help to decrease the activity of neurons that have previously been over-excited, in order to protect these neurons.

Microglial Lcn2 knockout enhances chronic intracerebral hemorrhage recovery by restoring myelin and reducing inflammation

Rationale: Damage to white matter and myelin poses a significant challenge to neurological recovery in the chronic phase of intracerebral hemorrhage (ICH). The repair of myelin damage post-ICH largely depends on the activation and differentiation of oligodendrocyte precursor cells (OPCs) into oligodendrocytes, a process that is significantly influenced by the inflammatory microenvironment. Lipocalin-2 (Lcn2) regulate phenotypic transformation of microglia and thus modulates inflammation. However, the exact role of Lcn2 in facilitating myelin recovery during the chronic phase of ICH remains to be fully understood. Methods: To create the ICH model, autologous blood from male C57BL/6 and Lcn2fl/flCx3cr1Cre mice was utilized. Behavioral tests were conducted to evaluate neurological recovery. The differentiation of OPCs and extent of myelin recovery were assessed using OPC and myelin markers. A multi-factor inflammatory chip was employed to investigate potential molecular regulatory mechanisms. Additionally, the Lcn2 inhibitor ZINC-94/89 was administered to explore its potential in targeting Lcn2 for enhancing myelin recovery during the chronic phase of ICH. Results: Knocking out Lcn2 in microglia significantly improved behavioral performance in chronic ICH mice, reduced inflammatory response, and enhanced myelin recovery. Both in vivo and in vitro experiments confirmed that Lcn2 knockout promoted microglia transformation to the M2 phenotype and enhanced OPCs differentiation. Mechanistically, Lcn2 knockout might affect Gdf-1 secretion in BV2 cells by modulating the JAK/STAT signaling pathway. Treatment with JAK inhibitors decreased Gdf-1 expression in BV2 cells, inhibiting OPCs migration and differentiation. Additionally, phosphorylation of Stat3 at Thr705 plays a critical role in enhancing Gdf-1 transcription and translation. Administration of the Lcn2 inhibitor ZINC-94/89 significantly improved behavioral performance, reduced inflammatory response, and promoted myelin recovery in chronic ICH mice. Conclusions: Lcn2 is crucial for myelin recovery in the chronic phase of ICH by modulating microglial phenotypes, thereby enhancing the migration and differentiation of OPCs. Administering an Lcn2 inhibitor early on could serve as a novel and effective strategy to boost recovery during this phase.

Transient Upregulation of Procaspase-3 during Oligodendrocyte Fate Decisions

Oligodendrocytes are generated throughout life and in neurodegenerative conditions from brain resident oligodendrocyte precursor cells (OPCs). The transition from OPC to oligodendrocyte involves a complex cascade of molecular and morphological states that position the cell to make a fate decision to integrate as a myelinating oligodendrocyte or die through apoptosis. Oligodendrocyte maturation impacts the cell death mechanisms that occur in degenerative conditions, but it is unclear if and how the cell death machinery changes as OPCs transition into oligodendrocytes. Here, we discovered that differentiating oligodendrocytes transiently upregulate the zymogen procaspase-3 in both female and male mice, equipping these cells to make a survival decision during differentiation. Pharmacological inhibition of caspase-3 decreases oligodendrocyte density, indicating that procaspase-3 upregulation is linked to successful oligodendrocyte generation. Moreover, using procaspase-3 as a marker, we show that oligodendrocyte differentiation continues in the aging cortex and white matter. Taken together, our data establish procaspase-3 as a differentiating oligodendrocyte marker and provide insight into the underlying mechanisms occurring during the decision to integrate or die.

Glioblastoma Tumor Microenvironment and Purinergic Signaling: Implications for Novel Therapies

Glial-origin brain tumors, particularly glioblastomas (GBMs), are known for their devastating prognosis and are characterized by rapid progression and fatal outcomes. Despite advances in surgical resection, complete removal of the tumor remains unattainable, with residual cells driving recurrence that is resistant to conventional therapies. The GBM tumor microenviroment (TME) significantly impacts tumor progression and treatment response. In this review, we explore the emerging role of purinergic signaling, especially the P2X7 receptor (P2X7R). Due to its unique characteristics, it plays a key role in tumor progression and offers a potential therapeutic strategy for GBM through TME modulation. We discuss also the emerging role of the P2X4 receptor (P2X4R) as a promising therapeutic target. Overall, targeting purinergic signaling offers a potential approach to overcoming current GBM treatment limitations.

Multiple Sclerosis: Glial Cell Diversity in Time and Space

Multiple sclerosis (MS) is the most prevalent human inflammatory disease of the central nervous system with demyelination and glial scar formation as pathological hallmarks. Glial cells are key drivers of lesion progression in MS with roles in both tissue damage and repair depending on the surrounding microenvironment and the functional state of the individual glial subtype. In this review, we describe recent developments in the context of glial cell diversity in MS summarizing key findings with respect to pathological and maladaptive functions related to disease-associated glial subtypes. A particular focus is on the spatial and temporal dynamics of glial cells including subtypes of microglia, oligodendrocytes, and astrocytes. We contextualize recent high-dimensional findings suggesting that glial cells dynamically change with respect to epigenomic, transcriptomic, and metabolic features across the inflamed rim and during the progression of MS lesions. In summary, detailed knowledge of spatially restricted glial subtype functions is critical for a better understanding of MS pathology and its pathogenesis as well as the development of novel MS therapies targeting specific glial cell types.

A dual role for pleiotrophin in modulating inflammation and myelination in the presence of chondroitin sulfate proteoglycans after nervous system injury

Chondroitin sulfate proteoglycans (CSPGs), key components of the extracellular matrix and the glial scar that forms around central nervous system (CNS) injuries, are recognized for hindering neuronal regeneration. We previously demonstrated the potential of pleiotrophin (PTN) to induce neurite outgrowth even in the presence of inhibitory CSPGs. The effects of PTN on microglia and oligodendrocytes are not well described. Here, we examined how PTN administration alters the differentiation of oligodendrocyte precursor cells (OPCs) into mature oligodendrocytes in the presence of CSPGs using in vitro cell culture model. Moreover, we explored the effects of PTN on the inflammatory activity of microglia with and without inflammatory stimulation (IFN-γ) in a CSPG-rich environment. The data showed that the CSPG matrix inhibited the differentiation of OPCs into mature oligodendrocytes. PTN induced dose-dependent differentiation of OPCs into mature oligodendrocytes, with an optimal effect at 10 nM PTN. Moreover, PTN modified the immunological response of microglia in the presence of CSPGs, with reduced proinflammatory activity that was further reduced by PTN administration, in contrast to the increased release of matrix metalloproteinases (MMP 9). However, when IFN-γ-activated microglia were treated with PTN, proinflammatory signaling was stimulated at higher PTN concentrations (10 nM and 100 nM). Overall, our results indicate that PTN can overcome the inhibitory effect of CSPGs on the differentiation of OPCs into oligodendrocytes and can modulate inflammation mediated by CSPGs from microglia. Collectively, these findings demonstrate that PTN can effectively counteract the inhibitory effects of CSPGs on the differentiation of OPCs into mature oligodendrocytes while also modulating microglial responses to reduce proinflammatory activity and increase MMP-9 release. Thus, PTN has great potential to improve remyelination and neuroprotective strategies in the treatment of demyelinating diseases or any injury.

Glia-glia crosstalk via semaphorins: Emerging implications in neurodegeneration

The central nervous system (CNS) is wired by a complex network of integrated glial and neuronal signals, which is critical for its development and homeostasis. In this context, glia-glia communication is a complex and dynamic process that is essential for ensuring optimal CNS function. Semaphorins, which include secreted and transmembrane molecules, and their receptors, mainly found in the plexin and neuropilin families, are expressed in a wide range of cell types, including glia. In the CNS, semaphorin signalling is involved in a spectrum of processes, including neurogenesis, neuronal migration and wiring, and glial cell recruitment. Recently, semaphorins and plexins have attracted intense research aimed at elucidating their roles in instructing glial cell behavior during development or in response to inflammatory stimuli. In this review, we provide an overview of the multifaceted role of semaphorins in glia-glia communication, highlighting recent discoveries about semaphoring-dependent regulation of glia functions in healthy conditions. We also discuss the mechanisms of gliaglia crosstalk mediated by semaphorins under pathological conditions, and how these interactions may provide potential avenues for therapeutic intervention in neuroinflammation-mediated neurodegeneration.

The Role of Glial Cells in the Pathophysiology of Epilepsy

Epilepsy is a chronic neurological disorder marked by recurrent seizures, significantly impacting individuals worldwide. Current treatments are often ineffective for a third of patients and can cause severe side effects, necessitating new therapeutic approaches. Glial cells, particularly astrocytes, microglia, and oligodendrocytes, are emerging as crucial targets in epilepsy management. Astrocytes regulate neuronal homeostasis, excitability, and synaptic plasticity, playing key roles in maintaining the blood-brain barrier (BBB) and mediating neuroinflammatory responses. Dysregulated astrocyte functions, such as reactive astrogliosis, can lead to abnormal neuronal activity and seizure generation. They release gliotransmitters, cytokines, and chemokines that may exacerbate or mitigate seizures. Microglia, the innate immune cells of the CNS, contribute to neuroinflammation, glutamate excitotoxicity, and the balance between excitatory and inhibitory neurotransmission, underscoring their dual role in seizure promotion and protection. Meanwhile, oligodendrocytes, primarily involved in myelination, also modulate axonal excitability and contribute to the neuron-glia network underlying seizure pathogenesis. Understanding the dynamic interactions of glial cells with neurons provides promising avenues for novel epilepsy therapies. Targeting these cells may lead to improved seizure control and better clinical outcomes, offering hope for patients with refractory epilepsy.

Identification of a Subpopulation of Astrocyte Progenitor Cells in the Neonatal Subventricular Zone: Evidence that Migration is Regulated by Glutamate Signaling

In mice engineered to express enhanced green fluorescent protein (eGFP) under the control of the entire glutamate transporter 1 (GLT1) gene, eGFP is found in all 'adult' cortical astrocytes. However, when 8.3 kilobases of the human GLT1/EAAT2 promoter is used to control expression of tdTomato (tdT), tdT is only found in a subpopulation of these eGFP-expressing astrocytes. The eGFP mice have been used to define mechanisms of transcriptional regulation using astrocytes cultured from cortex of 1-3 day old mice. Using the same cultures, we were never able to induce tdT+ expression. We hypothesized that these cells might not have migrated into the cortex by this age. In this study, we characterized the ontogeny of tdT+ cells, performed single-cell RNA sequencing (scRNA-seq), and tracked their migration in organotypic slice cultures. At postnatal day (PND) 1, tdT+ cells were observed in the subventricular zone and striatum but not in the cortex, and they did not express eGFP. At PND7, tdT+ cells begin to appear in the cortex with their numbers increasing with age. At PND1, scRNA-seq demonstrates that the tdT+ cells are molecularly heterogeneous, with a subpopulation expressing astrocytic markers, subsequently validated with immunofluorescence. In organotypic slices, tdT+ cells migrate into the cortex, and after 7 days they express GLT1, NF1A, and eGFP. An ionotropic glutamate receptor (iGluR) antagonist reduced by 50% the distance tdT+ cells migrate from the subventricular zone into the cortex. The pan-glutamate transport inhibitor, TFB-TBOA, increased, by sixfold, the number of tdT+ cells in the cortex. In conclusion, although tdT is expressed by non-glial cells at PND1, it is also expressed by glial progenitors that migrate into the cortex postnatally. Using this fluorescent labeling, we provide novel evidence that glutamate signaling contributes to the control of glial precursor migration.

Adolescent seizure impacts oligodendrocyte maturation, neuronal-glial circuit Formation, and myelination in the mammalian forebrain

Oligodendrocyte progenitor cells differentiate into oligodendrocytes, which myelinate axons during development and following demyelinating injury. However, the mechanisms that drive the timing and specificity of developmental myelination are not well understood. We hypothesized that oligodendrocyte progenitor cell proliferation and differentiation would be affected by pathological neuronal activity during adolescent development when developmental myelination is occurring and that this would also impact neuron-to-oligodendrocyte progenitor cell connectivity and myelination. We used kainic acid to induce a seizure in mice, treating equal numbers of males and females, in sample sizes of at least five animals. We found that the seizures led to increased cell death overall, specifically in the oligodendrocyte-lineage cells. We found that both oligodendrocyte progenitor cell proliferation and overall numbers increased, and the number of mature oligodendrocytes decreased. We found a decrease in myelin in the cerebral cortex, corpus callosum, and hippocampus after a seizure. We observed an increase in demyelinating lesions, but no change in neuronal process length, in brains after seizure, suggesting that the demyelination was due primarily to the loss of both oligodendrocyte-lineage cells. We found that Kir4.1 potassium channel expression on oligodendrocyte progenitor cells decreased after seizure, but not mature oligodendrocytes. Finally, we found a decrease in neuron-to-oligodendrocyte progenitor cell connections in seizure mice compared to controls. These findings provide insight into the response of the adolescent brain to seizure activity, as well as how seizures affect oligodendrocyte development, neuronal-glial connections, and myelin formation.

Deciphering the physiopathology of neurodevelopmental disorders using brain organoids

Neurodevelopmental disorders (NDD) encompass a range of conditions marked by abnormal brain development in conjunction with impaired cognitive, emotional and behavioural functions. Transgenic animal models, mainly rodents, traditionally served as key tools for deciphering the molecular mechanisms driving NDD physiopathology and significantly contributed to the development of pharmacological interventions aimed at treating these disorders. However, the efficacy of these treatments in humans has proven to be limited, due in part to the intrinsic constraint of animal models to recapitulate the complex development and structure of the human brain but also to the phenotypic heterogeneity found between affected individuals. Significant advancements in the field of induced pluripotent stem cells (iPSCs) offer a promising avenue for overcoming these challenges. Indeed, the development of advanced differentiation protocols for generating iPSC-derived brain organoids gives an unprecedented opportunity to explore human neurodevelopment. This review provides an overview of how 3D brain organoids have been used to investigate various NDD (i.e. Fragile X syndrome, Rett syndrome, Angelman syndrome, microlissencephaly, Prader-Willi syndrome, Timothy syndrome, tuberous sclerosis syndrome) and elucidate their pathophysiology. We also discuss the benefits and limitations of employing such innovative 3D models compared to animal models and 2D cell culture systems in the realm of personalized medicine.

Are oligodendrocytes bystanders or drivers of Parkinson's disease pathology?

The major pathological feature of Parkinson 's disease (PD), the second most common neurodegenerative disease and most common movement disorder, is the predominant degeneration of dopaminergic neurons in the substantia nigra, a part of the midbrain. Despite decades of research, the molecular mechanisms of the origin of the disease remain unknown. While the disease was initially viewed as a purely neuronal disorder, results from single-cell transcriptomics have suggested that oligodendrocytes may play an important role in the early stages of Parkinson's. Although these findings are of high relevance, particularly to the search for effective disease-modifying therapies, the actual functional role of oligodendrocytes in Parkinson's disease remains highly speculative and requires a concerted scientific effort to be better understood. This Unsolved Mystery discusses the limited understanding of oligodendrocytes in PD, highlighting unresolved questions regarding functional changes in oligodendroglia, the role of myelin in nigral dopaminergic neurons, the impact of the toxic environment, and the aggregation of alpha-synuclein within oligodendrocytes.

In vitro models for human neuroglia

Neuroglia are a heterogenous population of cells in the nervous system. In the central nervous system, this group is classified into astrocytes, oligodendrocytes, and microglia. Neuroglia in the peripheral nervous system are divided into Schwann cells and enteric glia. These groups of cells display considerable differences in their developmental origin, morphology, function, and regional abundance. Compared to animal models, human neuroglia differ in their transcriptomic profile, morphology, and function. Investigating the physiology of healthy or diseased human neuroglia in vivo is challenging due to the inaccessibility of the tissue. Therefore, researchers have developed numerous in vitro models attempting to replicate the natural tissue environment. Earlier models made use of postmortem, postsurgical, or fetal tissue to establish human neuroglial cells in vitro, either as a pure population of the desired cell type or as organotypic slice cultures. Advancements in human stem cell differentiation techniques have greatly enhanced the possibilities for creating in vitro models of human neuroglia. This chapter provides an overview of the current models used to study the functioning and development of human neuroglia in vitro, both in health and disease.

Prenatal influences on postnatal neuroplasticity: Integrating DOHaD and sensitive/critical period frameworks to understand biological embedding in early development

Early environments can have significant and lasting effects on brain, body, and behavior across the lifecourse. Here, we address current research efforts to understand how experiences impact neurodevelopment with a new perspective integrating two well-known conceptual frameworks - the Developmental Origins of Health and Disease (DOHaD) and sensitive/critical period frameworks. Specifically, we consider how prenatal experiences characterized in the DOHaD model impact two key neurobiological mechanisms of sensitive/critical periods for adapting to and learning from the postnatal environment. We draw from both animal and human research to summarize the current state of knowledge on how particular prenatal substance exposures (psychoactive substances and heavy metals) and nutritional profiles (protein-energy malnutrition and iron deficiency) each differentially impact brain circuits' excitation/GABAergic inhibition balance and myelination. Finally, we highlight new research directions that emerge from this integrated framework, including testing how prenatal environments alter sensitive/critical period timing and learning and identifying potential promotional/buffering prenatal exposures to impact postnatal sensitive/critical periods. We hope this integrative framework considering prenatal influences on postnatal neuroplasticity will stimulate new research to understand how early environments have lasting consequences on our brains, behavior, and health.

Targeting Oligodendrocyte Dynamics and Remyelination: Emerging Therapies and Personalized Approaches in Multiple Sclerosis Management

Multiple sclerosis (MS) is a progressive autoimmune condition that primarily affects young people and is characterized by demyelination and neurodegeneration of the central nervous system (CNS). This in-depth review explores the complex involvement of oligodendrocytes, the primary myelin- producing cells in the CNS, in the pathophysiology of MS. It discusses the biochemical processes and signalling pathways required for oligodendrocytes to function and remain alive, as well as how they might fail and cause demyelination to occur. We investigate developing therapeutic options that target remyelination, a fundamental component of MS treatment. Remyelination approaches promote the survival and differentiation of oligodendrocyte precursor cells (OPCs), restoring myelin sheaths. This improves nerve fibre function and may prevent MS from worsening. We examine crucial parameters influencing remyelination success, such as OPC density, ageing, and signalling pathway regulation (e.g., Retinoid X receptor, LINGO-1, Notch). The review also examines existing neuroprotective and antiinflammatory medications being studied to see if they can assist oligodendrocytes in surviving and reducing the severity of MS symptoms. The review focuses on medicines that target the myelin metabolism in oligodendrocytes. Altering oligodendrocyte metabolism has been linked to reversing demyelination and improving MS patient outcomes through various mechanisms. We also explore potential breakthroughs, including innovative antisense technologies, deep brain stimulation, and the impact of gut health and exercise on MS development. The article discusses the possibility of personalized medicine in MS therapy, emphasizing the importance of specific medicines based on individual molecular profiles. The study emphasizes the need for reliable biomarkers and improved imaging tools for monitoring disease progression and therapy response. Finally, this review focuses on the importance of oligodendrocytes in MS and the potential for remyelination therapy. It also underlines the importance of continued research to develop more effective treatment regimens, taking into account the complexities of MS pathology and the different factors that influence disease progression and treatment.

Nzf2 promotes oligodendrocyte differentiation and regeneration via repressing HDAC1-mediated histone deacetylation

Proper axonal myelination and function of the vertebrate central nervous system rely largely on the timely differentiation of oligodendrocytes (OLs), yet key regulatory factors remain enigmatic. Our study reveals neural zinc finger (Nzf2) as a crucial orchestrator that controls the timing of OL differentiation both during development and myelin repair, contrasting with its previously suggested role in direct myelin gene regulation. Nzf2 ablation delays the onset of OL differentiation, while hyperactivation stimulates OL differentiation both during development and remyelination. Using RNA-seq and ChIP-seq, we pinpoint Nkx2.2 as a critical downstream target of Nzf2. Specific binding of Nzf2 in the Nkx2.2 gene locus inhibits histone deacetylation by disrupting the HDAC1 repressor complex and reducing deacetylase activity. Furthermore, Nzf2 overrides the inhibitory Notch signaling to initiate OL differentiation. Thus, we propose that the Notch-Nzf2-Nkx2.2 axis is a vital component of OL differentiation timing mechanism, suggesting Nzf2 as a potential therapeutic target for stimulating OL differentiation and boosting myelin repair in demyelinating diseases.

Oligodendrocytes in Huntington's Disease: A Review of Oligodendrocyte Pathology and Current Cell Reprogramming Approaches for Oligodendrocyte Modelling of Huntington's Disease

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder traditionally characterized by the selective loss of medium spiny neurons in the basal ganglia. However, it has become apparent that white matter injury and oligodendrocyte dysfunction precede the degeneration of medium spiny neurons, garnering interest as a key pathogenic mechanism of HD. Oligodendrocytes are glial cells found within the central nervous system involved in the production of myelin and the myelination of axons. Myelin is a lipid-rich sheath that wraps around axons, facilitating signal conduction and neuronal viability. The degeneration of myelin hinders effective communication and leaves neurons vulnerable to external damage and subsequent degeneration. Abnormalities in oligodendrocyte maturation have been established in the HD human brain, however, investigations into the underlying dysfunction of human oligodendrocytes in HD are limited. This review will detail the involvement of oligodendrocytes and white matter damage in HD. Recent developments in modeling human-specific oligodendrocyte pathology in HD will be discussed, with a particular focus on emerging somatic cell reprogramming approaches.

Trametinib, an anti-tumor drug, promotes oligodendrocytes generation and myelin formation

Oligodendrocytes (OLs) are differentiated from oligodendrocyte precursor cells (OPCs) in the central nervous system (CNS). Demyelination is a common feature of many neurological diseases such as multiple sclerosis (MS) and leukodystrophies. Although spontaneous remyelination can happen after myelin injury, nevertheless, it is often insufficient and may lead to aggravated neurodegeneration and neurological disabilities. Our previous study has discovered that MEK/ERK pathway negatively regulates OPC-to-OL differentiation and remyelination in mouse models. To facilitate possible clinical evaluation, here we investigate several MEK inhibitors which have been approved by FDA for cancer therapies in both mouse and human OPC-to-OL differentiation systems. Trametinib, the first FDA approved MEK inhibitor, displays the best effect in stimulating OL generation in vitro among the four MEK inhibitors examined. Trametinib also significantly enhances remyelination in both MOG-induced EAE model and LPC-induced focal demyelination model. More exciting, trametinib facilitates the generation of MBP+ OLs from human embryonic stem cells (ESCs)-derived OPCs. Mechanism study indicates that trametinib promotes OL generation by reducing E2F1 nuclear translocation and subsequent transcriptional activity. In summary, our studies indicate a similar inhibitory role of MEK/ERK in human and mouse OL generation. Targeting the MEK/ERK pathway might help to develop new therapies or repurpose existing drugs for demyelinating diseases.

Neonatal Brain Injury Triggers Niche-Specific Changes to Cellular Biogeography

Preterm infants are at risk for brain injury and neurodevelopmental impairment due, in part, to white matter injury following chronic hypoxia exposure. However, the precise molecular mechanisms by which neonatal hypoxia disrupts early neurodevelopment are poorly understood. Here, we constructed a brain-wide map of the regenerative response to newborn brain injury using high-resolution imaging-based spatial transcriptomics to analyze over 800,000 cells in a mouse model of chronic neonatal hypoxia. Additionally, we developed a new method for inferring condition-associated differences in cell type spatial proximity, enabling the identification of niche-specific changes in cellular architecture. We observed hypoxia-associated changes in region-specific cell states, cell type composition, and spatial organization. Importantly, our analysis revealed mechanisms underlying reparative neurogenesis and gliogenesis, while also nominating pathways that may impede circuit rewiring following neonatal hypoxia. Altogether, our work provides a comprehensive description of the molecular response to newborn brain injury.

Spontaneous running wheel exercise during pregnancy prevents later neonatal-anoxia-induced somatic and neurodevelopmental alterations

Introduction

About 15-20 % of babies that suffer perinatal asphyxia die and around 25 % of the survivors exhibit permanent neural outcomes. Minimization of this global health problem has been warranted. This study investigated if the offspring of pregnant female rats allowed to spontaneously exercise on running wheels along a 11-day pregnancy period were protected for somatic and neurodevelopmental disturbs that usually follow neonatal anoxia.

Methods

spontaneous exercise was applied to female rats which were housed in cages allowing free access to running wheels along a 11-day pregnancy period. Their offspring were submitted to anoxia 24-36 h after birth. Somatic and sensory-motor development of the pups were recorded until postnatal day 21 (P21). Myelin basic protein (MBP)-stained areas of sensory and motor cortices were measured at P21. Neuronal nuclei (NeuN)-immunopositive cells and synapsin-I levels in hippocampal formation were estimated at P21 and P75.

Results

gestational exercise and / or neonatal anoxia increased the weight and the size of the pups. In addition, gestational exercise accelerated somatic and sensory-motor development of the pups and protected them against neonatal-anoxia-induced delay in development. Further, neonatal anoxia reduced MBP stained area in the secondary motor cortex and decreased hippocampal neuronal estimates and synapsin-I levels at P21; gestational exercise prevented these effects. Therefore, spontaneous exercise along pregnancy is a valuable strategy to prevent neonatal-anoxia-induced disturbs in the offspring.

Conclusion

spontaneous gestational running wheel exercise protects against neonatal anoxia-induced disturbs in the offspring, including (1) physical and neurobehavioral developmental impairments, and (2) hippocampal and cortical changes. Thus, spontaneous exercise during pregnancy may represent a valuable strategy to prevent disturbs which usually follow neonatal anoxia.

Oligodendrocytes, the Forgotten Target of Gene Therapy

If the billions of oligodendrocytes (OLs) populating the central nervous system (CNS) of patients could express their feelings, they would undoubtedly tell gene therapists about their frustration with the other neural cell populations, neurons, microglia, or astrocytes, which have been the favorite targets of gene transfer experiments. This review questions why OLs have been left out of most gene therapy attempts. The first explanation is that the pathogenic role of OLs is still discussed in most CNS diseases. Another reason is that the so-called ubiquitous CAG, CBA, CBh, or CMV promoters-widely used in gene therapy studies-are unable or poorly able to activate the transcription of episomal transgene copies brought by adeno-associated virus (AAV) vectors in OLs. Accordingly, transgene expression in OLs has either not been found or not been evaluated in most gene therapy studies in rodents or non-human primates. The aims of the current review are to give OLs their rightful place among the neural cells that future gene therapy could target and to encourage researchers to test the effect of OL transduction in various CNS diseases.

Should We Consider Neurodegeneration by Itself or in a Triangulation with Neuroinflammation and Demyelination? The Example of Multiple Sclerosis and Beyond

Neurodegeneration is preeminent in many neurological diseases, and still a major burden we fail to manage in patient's care. Its pathogenesis is complicated, intricate, and far from being completely understood. Taking multiple sclerosis as an example, we propose that neurodegeneration is neither a cause nor a consequence by itself. Mitochondrial dysfunction, leading to energy deficiency and ion imbalance, plays a key role in neurodegeneration, and is partly caused by the oxidative stress generated by microglia and astrocytes. Nodal and paranodal disruption, with or without myelin alteration, is further involved. Myelin loss exposes the axons directly to the inflammatory and oxidative environment. Moreover, oligodendrocytes provide a singular metabolic and trophic support to axons, but do not emerge unscathed from the pathological events, by primary myelin defects and cell apoptosis or secondary to neuroinflammation or axonal damage. Hereby, trophic failure might be an overlooked contributor to neurodegeneration. Thus, a complex interplay between neuroinflammation, demyelination, and neurodegeneration, wherein each is primarily and secondarily involved, might offer a more comprehensive understanding of the pathogenesis and help establishing novel therapeutic strategies for many neurological diseases and beyond.

Transient upregulation of procaspase-3 during oligodendrocyte fate decisions

Oligodendrocytes are generated throughout life and in neurodegenerative conditions from brain resident oligodendrocyte precursor cells (OPCs). The transition from OPC to oligodendrocyte involves a complex cascade of molecular and morphological states that position the cell to make a fate decision to integrate as a myelinating oligodendrocyte or die through apoptosis. Oligodendrocyte maturation impacts the cell death mechanisms that occur in degenerative conditions, but it is unclear if and how the cell death machinery changes as OPCs transition into oligodendrocytes. Here, we discovered that differentiating oligodendrocytes transiently upregulate the zymogen procaspase-3, equipping these cells to make a survival decision during differentiation. Pharmacological inhibition of caspase-3 decreases oligodendrocyte density, indicating that procaspase-3 upregulation promotes differentiation. Moreover, using procaspase-3 as a marker, we show that oligodendrocyte differentiation continues in the aging cortex and white matter. Taken together, our data establish procaspase-3 as a differentiating oligodendrocyte marker and provide insight into the underlying mechanisms occurring during the decision to integrate or die.

White Matter Lesion Volumes on 3-T MRI in People With MS Who Had Followed a Diet and Lifestyle Program for More Than 10 Years

Background: Cerebral white matter lesion (WML) formation in people with multiple sclerosis (pwMS) is linked to the death of myelin-producing oligodendrocytes. Current MS treatment strategies focus on limiting WML accumulation and disability. Using a pathology-supported genetic testing (PSGT) program, we identified specific risk factors for MS, categorized as deficiencies and aggravators. We developed a novel clinical methodology to mitigate these risk factors, including personalized lifestyle interventions and optimization of cerebral nutrients to prevent oligodendrocyte demise and promote remyelination. Objective: To conduct a pilot case-control study over a 10-year period to ascertain whether the PSGT Program can reduce or prevent WML formation in pwMS. Methods: MRI was performed at baseline as well as after an interval period of at least 10 years or longer in 22 pwMS. WML volumes were determined using Sequence Adaptive Multimodal SEGmentation (SAMSEG) software, part of FreeSurfer 7.2. Other variables included age at MRI, disease duration, disability status, and medication. Results: PwMS (n = 13) who had followed the PSGT program for more than 10 years, had significantly smaller lesion volumes (mm3) compared to pwMS who did not adhere to the program (n = 9) (4950 ± 5303 vs. 17934 ± 11139; p = 0.002). WML volumes were significantly associated (p = 0.02) with disability (EDSS) but not with age (p = 0.350), disease duration (p = 0.709), or Interferon-β treatment (p = 0.70). Conclusion: Dietary and lifestyle changes may lower the risk of developing cerebral WMLs in pwMS and potentially slow disease progression. Larger studies are required to confirm the effectiveness of such interventions in pwMS.

DOR activation in mature oligodendrocytes regulates α-ketoglutarate metabolism leading to enhanced remyelination in aged mice

The decreased ability of mature oligodendrocytes to produce myelin negatively affects remyelination in demyelinating diseases and aging, but the underlying mechanisms are incompletely understood. In the present study, we identify a mature oligodendrocyte-enriched transcriptional coregulator diabetes- and obesity-related gene (DOR)/tumor protein p53-inducible nuclear protein 2 (TP53INP2), downregulated in demyelinated lesions of donors with multiple sclerosis and in aged oligodendrocyte-lineage cells. Dor ablation in mice of both sexes results in defective myelinogenesis and remyelination. Genomic occupancy in oligodendrocytes and transcriptome profiling of the optic nerves of wild-type and Dor conditional knockout mice reveal that DOR and SOX10 co-occupy enhancers of critical myelinogenesis-associated genes including Prr18, encoding an oligodendrocyte-enriched, proline-rich factor. We show that DOR targets regulatory elements of genes responsible for α-ketoglutarate biosynthesis in mature oligodendrocytes and is essential for α-ketoglutarate production and lipid biosynthesis. Supplementation with α-ketoglutarate restores oligodendrocyte-maturation defects in Dor-deficient adult mice and improves remyelination after lysolecithin-induced demyelination and cognitive function in 17-month-old wild-type mice. Our data suggest that activation of α-ketoglutarate metabolism in mature oligodendrocytes can promote myelin production during demyelination and aging.

Demyelination and impaired oligodendrogenesis in the corpus callosum following lead exposure

The corpus callosum is an oligodendrocyte-enriched brain region, replenished by newborn oligodendrocytes from oligodendrocyte progenitor cells (OPCs) in subventricular zone (SVZ). Lead (Pb) exposure has been associated with multiple sclerosis, a disease characterized by the loss of oligodendrocytes. This study aimed to investigate the effects of Pb exposure on oligodendrogenesis in SVZ and myelination in the corpus callosum. Adult female mice were used for a disproportionately higher prevalence of multiple sclerosis in females. Acute Pb exposure (one ip-injection of 27 mg Pb/kg as PbAc2 24 hr before sampling) caused mild Pb accumulation in the corpus callosum. Ex vivo assay using isolated SVZ tissues collected from acute Pb-exposed brains showed a diminished oligodendrogenesis in SVZ-derived neurospheres compared with controls. In vivo subchronic Pb exposure (13.5 mg Pb/kg by daily oral gavage 4 wk) revealed significantly decreased newborn BrdU+/MBP+ oligodendrocytes in the corpus callosum, suggesting demyelination. Mechanistic investigations indicated decreased Rictor in SVZ OPCs, defective self-defense pathways, and reactive gliosis in the corpus callosum. Given the interwined pathologies between multiple sclerosis and Alzheimer's disease, the effect of Pb on myelination was evaluated in AD-modeled APP/PS1 mice. Myelin MRI on mice following chronic exposure (1,000 ppm Pb in drinking water as PbAc2 for 20 wk) revealed a profound demyelination in the corpus callosum compared with controls. Immunostaining of the choroid plexus showed diminished signaling molecule (Klotho, OTX2) expressions in Pb-treated animals. These observations suggest that Pb caused demyelination in the corpus callosum, likely by disrupting oligodendrogenesis from SVZ OPCs. Pb-induced demyelination represents a crucial pathogenic pathway in Pb neurotoxicity, including multiple sclerosis.

Cspg4 sculpts oligodendrocyte precursor cell morphology

The extracellular matrix (ECM) provides critical biochemical and structural cues that regulate neural development. Chondroitin sulfate proteoglycans (CSPGs), a major ECM component, have been implicated in modulating oligodendrocyte precursor cell (OPC) proliferation, migration, and maturation, but their specific roles in oligodendrocyte lineage cell (OLC) development and myelination in vivo remain poorly understood. Here, we use zebrafish as a model system to investigate the spatiotemporal dynamics of ECM deposition and CSPG localization during central nervous system (CNS) development, with a focus on their relationship to OLCs. We demonstrate that ECM components, including CSPGs, are dynamically expressed in distinct spatiotemporal patterns coinciding with OLC development and myelination. We found that zebrafish lacking cspg4 function produced normal numbers of OLCs, which appeared to undergo proper differentiation. However, OPC morphology in mutant larvae was aberrant. Nevertheless, the number and length of myelin sheaths produced by mature oligodendrocytes were unaffected. These data indicate that Cspg4 regulates OPC morphogenesis in vivo, supporting the role of the ECM in neural development.

Glial cell derived pathway directs regenerating optic nerve axons toward the CNS midline

Several RGC intrinsic signaling pathways have been shown to enhance RGC survival and RGC axonal growth after optic nerve injury. Yet an unresolved challenge for regenerating RGC axons is to properly navigate the optic chiasm located at the Central Nervous System midline. Here, we use live-cell imaging in larval zebrafish to show that regrowing RGC axons initiate growth toward the midline and extend along a trajectory similar to their original projection. From a candidate genetic screen, we identify the glycosyltransferase Lh3 to be required during the process of regeneration to direct regrowing RGC axons toward the midline. Moreover, we find that mutants in collagen 18a1 (col18a1), a putative Lh3 substrate, display RGC axonal misguidance phenotypes similar to those we observe in lh3 mutants, suggesting that lh3 may act through col18a1 during regeneration. Finally, we show that transgenic lh3 expression in sox10+ presumptive olig2+ oligodendrocytes located near the optic chiasm restores directed axonal growth. Combined these data identify lh3 and col18a1 as part of a glial derived molecular pathway critical for guiding in vivo regenerating RGC axons towards and across the optic chiasm.

The Hidden Hand in White Matter: Pericytes and the Puzzle of Demyelination

Disruption of myelin, the fatty sheath-insulating nerve fibers in the white matter, blocks or slows the rapid transmission of electrical signals along nerve cells and contributes to several neurodegenerative diseases such as multiple sclerosis. Traditionally, research has focused on neuronal dysfunction as the primary factor, including autoimmunity, infections, inflammation, and genetic disorders causing demyelination. However, recent insights emphasize the critical role of pericytes, non-neuronal cells that regulate blood flow and maintain the health of blood vessels within white matter. This Perspective explores the principal mechanisms through which pericyte dysfunction contributes to damage and demyelination, including impaired communication with neurons (neurovascular uncoupling), excessive formation of scar tissue (fibrosis), and the infiltration of detrimental substances from the bloodstream. Understanding these mechanisms of pericyte-driven demyelination may lead to the creation of new therapeutic strategies for tackling a range of neurodegenerative conditions.

Progesterone alleviates esketamine-induced hypomyelination via PI3K/Akt signaling pathway in the developing rat brain

The neurodevelopmental toxicity of anesthetics has been confirmed repeatedly, and esketamine is now widely used in pediatric surgeries. Oligodendrocyte precursor cells (OPCs) evolved into mature oligodendrocytes (OLs) and formed myeline sheath during the early brain development. In this study, we investigated whether esketamine exposure interrupted development of OPCs and induced hypomyelination in rats. Further we explored the roles of PI3K/Akt phosphorylation in OPCs development and myelination. Sprague Dawley rats with different ages (postnatal day (P) 1, 3, 7 and 12) were exposed to 40mg/kg esketamine. Progesterone treatment was given (16 mg/kg per day for 3 days) 24 h after esketamine exposure via the intraperitoneal route. Corpus callosum tissues were collected at P8 or P14 for western blot and immunofluorescence analyses. Esketamine exposure at P7 and P12 significantly reduced myelin basic protein (MBP) expression and CC1+ OLs number in corpus callosum. Esketamine exposure at P7 not only aggravated the mature OLs apoptosis, also decreased the OPCs proliferation and differentiation, which was related with dephosphorylation of PI3K/Akt. Progesterone was able to promote OPCs differentiation and ameliorate esketamine-induced hypomyelination by enhancing PI3K/Akt phosphorylation. Stage-dependent abnormality of OPCs/OLs after esketamine leads to the esketamine-induced hypomyelination. Esketamine interrupted OPCs evolution via PI3K/Akt signaling pathway, which can be ameliorated by progesterone.

Timed fetal inflammation and postnatal hypoxia cause cortical white matter injury, interneuron imbalances, and behavioral deficits in a double-hit rat model of encephalopathy of prematurity

Extreme preterm birth-associated adversities are a major risk factor for aberrant brain development, known as encephalopathy of prematurity (EoP), which can lead to long-term neurodevelopmental impairments. Although progress in clinical care for preterm infants has markedly improved perinatal outcomes, there are currently no curative treatment options available to combat EoP. EoP has a multifactorial etiology, including but not limited to pre- or postnatal immune activation and oxygen fluctuations. Elucidating the underlying mechanisms of EoP and determining the efficacy of potential therapies relies on valid, clinically translatable experimental models that reflect the neurodevelopmental and pathophysiological hallmarks of EoP. Here, we expand on our double-hit rat model that can be used to study EoP disease mechanisms and therapeutic options in a preclinical setting. Pregnant Wistar dams were intraperitoneally injected with 10 μg/kg LPS on embryonic day (E)20 and offspring was subjected to hypoxia (140 min, 8% O2) at postnatal day 4. Rats exposed to fetal inflammation and postnatal hypoxia (FIPH) showed neurodevelopmental impairments, such as reduced nest-seeking ability, ultrasonic vocalizations, social engagement, and working memory, and increased anxiety and sensitivity. Impairments in myelination, oligodendrocyte maturation and interneuron development were examined as hallmarks for EoP, in different layers and coordinates of the cortex using histological and molecular techniques. Myelin density and complexity was decreased in the cortex, which partially coincided with a decrease in mature oligodendrocytes. Furthermore, interneuron populations (GAD67+ and PVALB+) were affected. To determine if the timing of inducing fetal inflammation affected the severity of EoP hallmarks in the cortex, multiple timepoints of fetal inflammation were compared. Inflammation at E20 combined with postnatal hypoxia gave the most severe EoP phenotype in the cortex. In conclusion, we present a double-hit rat model which displays various behavioral, anatomical and molecular hallmarks of EoP, including diffuse white matter injury. This double-hit model can be used to investigate pathophysiological mechanisms and potential therapies for EoP.

A New Acquaintance of Oligodendrocyte Precursor Cells in the Central Nervous System

Oligodendrocyte precursor cells (OPCs) are a heterogeneous multipotent population in the central nervous system (CNS) that appear during embryogenesis and persist as resident cells in the adult brain parenchyma. OPCs could generate oligodendrocytes to participate in myelination. Recent advances have renewed our knowledge of OPC biology by discovering novel markers of oligodendroglial cells, the myelin-independent roles of OPCs, and the regulatory mechanism of OPC development. In this review, we will explore the updated knowledge on OPC identity, their multifaceted roles in the CNS in health and diseases, as well as the regulatory mechanisms that are involved in their developmental stages, which hopefully would contribute to a further understanding of OPCs and attract attention in the field of OPC biology.

Ablation of oligodendrogenesis in adult mice alters brain microstructure and activity independently of behavioral deficits

Oligodendrocytes continue to differentiate from their precursor cells even in adulthood, a process that can be modulated by neuronal activity and experience. Previous work has indicated that conditional ablation of oligodendrogenesis in adult mice leads to learning and memory deficits in a range of behavioral tasks. The current study replicated and re-evaluated evidence for a role of oligodendrogenesis in motor learning, using a complex running wheel task. Further, we found that ablating oligodendrogenesis alters brain microstructure (ex vivo MRI) and brain activity (in vivo EEG) independent of experience with the task. This suggests a role for adult oligodendrocyte formation in the maintenance of brain function and indicates that task-independent changes due to oligodendrogenesis ablation need to be considered when interpreting learning and memory deficits in this model.

Myelin basic protein mRNA levels affect myelin sheath dimensions, architecture, plasticity, and density of resident glial cells

Myelin Basic Protein (MBP) is essential for both elaboration and maintenance of CNS myelin, and its reduced accumulation results in hypomyelination. How different Mbp mRNA levels affect myelin dimensions across the lifespan and how resident glial cells may respond to such changes are unknown. Here, to investigate these questions, we used enhancer-edited mouse lines that accumulate Mbp mRNA levels ranging from 8% to 160% of wild type. In young mice, reduced Mbp mRNA levels resulted in corresponding decreases in Mbp protein accumulation and myelin sheath thickness, confirming the previously demonstrated rate-limiting role of Mbp transcription in the control of initial myelin synthesis. However, despite maintaining lower line specific Mbp mRNA levels into old age, both MBP protein levels and myelin thickness improved or fully normalized at rates defined by the relative Mbp mRNA level. Sheath length, in contrast, was affected only when mRNA levels were very low, demonstrating that sheath thickness and length are not equally coupled to Mbp mRNA level. Striking abnormalities in sheath structure also emerged with reduced mRNA levels. Unexpectedly, an increase in the density of all glial cell types arose in response to reduced Mbp mRNA levels. This investigation extends understanding of the role MBP plays in myelin sheath elaboration, architecture, and plasticity across the mouse lifespan and illuminates a novel axis of glial cell crosstalk.

Axonal neurotransmitter release in the regulation of myelination

Myelination of axons is a key determinant of fast action potential propagation, axonal health and circuit function. Previously considered a static structure, it is now clear that myelin is dynamically regulated in response to neuronal activity in the central nervous system (CNS). However, how activity-dependent signals are conveyed to oligodendrocytes remains unclear. Here, we review the potential mechanisms by which neurons could communicate changing activity levels to myelin, with a focus on the accumulating body of evidence to support activity-dependent vesicular signalling directly onto myelin sheaths. We discuss recent in vivo findings of activity-dependent fusion of neurotransmitter vesicles from non-synaptic axonal sites, and how modulation of this vesicular fusion regulates the stability and growth of myelin sheaths. We also consider the potential mechanisms by which myelin could sense and respond to axon-derived signals to initiate remodelling, and the relevance of these adaptations for circuit function. We propose that axonal vesicular signalling represents an important and underappreciated mode of communication by which neurons can transmit activity-regulated signals to myelinating oligodendrocytes and, potentially, more broadly to other cell types in the CNS.

Lateral/caudal ganglionic eminence makes limited contribution to cortical oligodendrocytes

The emergence of myelinating oligodendrocytes represents a pivotal developmental milestone in vertebrates, given their capacity to ensheath axons and facilitate the swift conduction of action potentials. It is widely accepted that cortical oligodendrocyte progenitor cells (OPCs) arise from medial ganglionic eminence (MGE), lateral/caudal ganglionic eminence (LGE/CGE), and cortical radial glial cells (RGCs). Here, we used two different fate mapping strategies to challenge the established notion that the LGE generates cortical OPCs. Furthermore, we used a Cre/loxP-dependent exclusion strategy to reveal that the LGE/CGE does not give rise to cortical OPCs. Additionally, we showed that specifically eliminating MGE-derived OPCs leads to a significant reduction of cortical OPCs. Together, our findings indicate that the LGE does not generate cortical OPCs, contrary to previous beliefs. These findings provide a new view of the developmental origins of cortical OPCs and a valuable foundation for future research on both normal development and oligodendrocyte-related disease.

Stimulating myelin restoration with BDNF: a promising therapeutic approach for Alzheimer's disease

Alzheimer's Disease (AD) is a chronic neurodegenerative disorder constituting the most common form of dementia (60%-70% of cases). Although AD presents majorly a neurodegenerative pathology, recent clinical evidence highlights myelin impairment as a key factor in disease pathogenesis. The lack of preventive or restorative treatment is emphasizing the need to develop novel therapeutic approaches targeting to the causes of the disease. Recent studies in animals and patients have highlighted the loss of myelination of the neuronal axons as an extremely aggravating factor in AD, in addition to the formation of amyloid plaques and neurofibrillary tangles that are to date the main pathological hallmarks of the disease. Myelin breakdown represents an early stage event in AD. However, it is still unclear whether myelin loss is attributed only to exogenous factors like inflammatory processes of the tissue or to impaired oligodendrogenesis as well. Neurotrophic factors are well established protective molecules under many pathological conditions of the neural tissue, contributing also to proper myelination. Due to their inability to be used as drugs, many research efforts are focused on substituting neurotrophic activity with small molecules. Our research team has recently developed novel micromolecular synthetic neurotrophin mimetics (MNTs), selectively acting on neurotrophin receptors, and thus offering a unique opportunity for innovative therapies against neurodegenerative diseases. These small sized, lipophilic molecules address the underlying biological effect of these diseases (neuroprotective action), but also they exert significant neurogenic actions inducing neuronal replacement of the disease areas. One of the significant neurotrophin molecules in the Central Nervous System is Brain-Derived-Neurotrophin-Factor (BDNF). BDNF is a neurotrophin that not only supports neuroprotection and adult neurogenesis, but also mediates pro-myelinating effects in the CNS. BDNF binds with high-affinity on the TrkB neurotrophin receptor and enhances myelination by increasing the density of oligodendrocyte progenitor cells (OPCs) and playing an important role in CNS myelination. Conclusively, in the present review, we discuss the myelin pathophysiology in Alzheimer's Diseases, as well as the role of neurotrophins, and specifically BDNF, in myelin maintenance and restoration, revealing its valuable therapeutic potential against AD.

Build muscles and protect myelin

Multiple sclerosis (MS) is a chronic and debilitating autoimmune disease of the central nervous system (CNS) in which a CNS-driven immune response destroys myelin, leading to wide range of symptoms including numbness and tingling, vision problems, mobility impairment, etc. Oligodendrocytes are the myelinating cells in the CNS, which are generated from oligodendroglial progenitor cells (OPCs) via differentiation. However, for multiple reasons, OPCs fail to differentiate to oligodendrocytes in MS and as a result, stimulating the differentiation of OPCs to oligodendrocytes is considered beneficial for MS. The β-hydroxy β-methylbutyrate (HMB) is a widely-used muscle-building supplement in human and recently it has been shown that low-dose HMB is capable of stimulating the differentiation of cultured OPCs to oligodendrocytes for remyelination. Moreover, other causes of autoimmune demyelination are the decrease and/or suppression of Foxp3-expressing anti-autoimmune regulatory T cells (Tregs) and upregulation of autoimmune T-helper 1(Th1) and Th17 cells. Experimental autoimmune encephalomyelitis (EAE) is an animal model of MS in which the autoimmune demyelination is nicely visible. It has been reported that in EAE mice, oral HMB upregulates Tregs and decreases Th1 and Th17 responses, leading to remyelination in the CNS. Here, we analyze these newly-described features of HMB, highlighting the putative promyelinating nature of this supplement.

Cspg4 sculpts oligodendrocyte precursor cell morphology

The extracellular matrix (ECM) provides critical biochemical and structural cues that regulate neural development. Chondroitin sulfate proteoglycans (CSPGs), a major ECM component, have been implicated in modulating oligodendrocyte precursor cell (OPC) proliferation, migration, and maturation, but their specific roles in oligodendrocyte lineage cell (OLC) development and myelination in vivo remain poorly understood. Here, we use zebrafish as a model system to investigate the spatiotemporal dynamics of ECM deposition and CSPG localization during central nervous system (CNS) development, with a focus on their relationship to OLCs. We demonstrate that ECM components, including CSPGs, are dynamically expressed in distinct spatiotemporal patterns coinciding with OLC development and myelination. We found that zebrafish lacking cspg4 function produced normal numbers of OLCs, which appeared to undergo proper differentiation. However, OPC morphology in mutant larvae was aberrant. Nevertheless, the number and length of myelin sheaths produced by mature oligodendrocytes were unaffected. These data indicate that Cspg4 regulates OPC morphogenesis in vivo, supporting the role of the ECM in neural development.

Oligodendroglia-to-pericyte conversion after lipopolysaccharide exposure is gender-dependent

To investigate the sex-dependent differentiation of Sox10 cells and their response to pathological conditions such as lipopolysaccharide (LPS) exposure or ischemia, we utilized Sox10 Cre-ERT2, tdTomato mice. Tamoxifen administration induced the expression of red fluorescent protein (RFP) in these cells, facilitating their subsequent tracking and analysis after LPS injection and ischemia via immunofluorescence staining. Propidium iodide (PI) was injected to label necrotic cells following LPS administration. We found that the conversion of Sox10 cells to pericytes in female mice was significantly higher than in male mice, especially in those exposed to LPS. After LPS injection, the number of PI+ necrotic cells were significantly greater in females than in males. Moreover, RFP+ cells did not co-localize with glial fibrillary acidic protein (GFAP) or cluster of differentiation 11b (CD11b). Similarly, after brain ischemia, RFP+ cells did not express cluster of differentiation 13 (CD13), neuronal nuclei (NeuN), GFAP, or ionised calcium binding adaptor molecule 1 (Iba-1). These findings indicate that the conversion of Sox10 cells to pericytes following LPS exposure is sex-dependent, with neither male nor female groups showing differentiation into other cell types after LPS exposure or under ischemic conditions. The differences in LPS-induced necrosis of pericytes between sexes may explain the variations in the conversion of Sox10 cells to pericytes in both sexes.

Deleterious effect of sustained neuroinflammation in pediatric traumatic brain injury

INTRODUCTION

Despite improved management of traumatic brain injury (TBI), it still leads to lifelong sequelae and disability, particularly in children. Chronic neuroinflammation (the so-called tertiary phase), in particular, microglia/macrophage and astrocyte reactivity, is among the main mechanisms suspected of playing a role in the generation of lesions associated with TBI. The role of acute neuroinflammation is now well understood, but its persistent effect and impact on the brain, particularly during development, are not. Here, we investigated the long-term effects of pediatric TBI on the brain in a mouse model.

METHODS

Pediatric TBI was induced in mice on postnatal day (P) 7 by weight-drop trauma. The time course of neuroinflammation and myelination was examined in the TBI mice. They were also assessed by magnetic resonance, functional ultrasound, and behavioral tests at P45.

RESULTS

TBI induced robust neuroinflammation, characterized by acute microglia/macrophage and astrocyte reactivity. The long-term consequences of pediatric TBI studied on P45 involved localized scarring astrogliosis, persistent microgliosis associated with a specific transcriptomic signature, and a long-lasting myelination defect consisting of the loss of myelinated axons, a decreased level of myelin binding protein, and severe thinning of the corpus callosum. These results were confirmed by reduced fractional anisotropy, measured by diffusion tensor imaging, and altered inter- and intra-hemispheric connectivity, measured by functional ultrasound imaging. In addition, adolescent mice with pediatric TBI showed persistent social interaction deficits and signs of anxiety and depressive behaviors.

CONCLUSIONS

We show that pediatric TBI induces tertiary neuroinflammatory processes associated with white matter lesions and altered behavior. These results support our model as a model for preclinical studies for tertiary lesions following TBI.