Regenerating CNS myelin - from mechanisms to experimental medicines

Heterogeneity of mature oligodendrocytes in the central nervous system

Mature oligodendrocytes form myelin sheaths that are crucial for the insulation of axons and efficient signal transmission in the central nervous system. Recent evidence has challenged the classical view of the functionally static mature oligodendrocyte and revealed a gamut of dynamic functions such as the ability to modulate neuronal circuitry and provide metabolic support to axons. Despite the recognition of potential heterogeneity in mature oligodendrocyte function, a comprehensive summary of mature oligodendrocyte diversity is lacking. We delve into early 20 th -century studies by Robertson and Río-Hortega that laid the foundation for the modern identification of regional and morphological heterogeneity in mature oligodendrocytes. Indeed, recent morphologic and functional studies call into question the long-assumed homogeneity of mature oligodendrocyte function through the identification of distinct subtypes with varying myelination preferences. Furthermore, modern molecular investigations, employing techniques such as single cell/nucleus RNA sequencing, consistently unveil at least six mature oligodendrocyte subpopulations in the human central nervous system that are highly transcriptomically diverse and vary with central nervous system region. Age and disease related mature oligodendrocyte variation denotes the impact of pathological conditions such as multiple sclerosis, Alzheimer's disease, and psychiatric disorders. Nevertheless, caution is warranted when subclassifying mature oligodendrocytes because of the simplification needed to make conclusions about cell identity from temporally confined investigations. Future studies leveraging advanced techniques like spatial transcriptomics and single-cell proteomics promise a more nuanced understanding of mature oligodendrocyte heterogeneity. Such research avenues that precisely evaluate mature oligodendrocyte heterogeneity with care to understand the mitigating influence of species, sex, central nervous system region, age, and disease, hold promise for the development of therapeutic interventions targeting varied central nervous system pathology.

Repeated intermittent administration of 3,4-methylenedioxymethamphetamine mitigates demyelination in the brain from cuprizone-treated mice

3,4-Methylenedioxymethamphetamine (MDMA), commonly known as a recreational drug, may also offer therapeutic benefits for mental health. Population-based studies suggest that MDMA users have a lower risk of demyelinating diseases, such as depression. Given the role of the gut microbiota in mediating MDMA's effects, we hypothesized that MDMA might confer mental health benefits via the gut-brain axis. Cuprizone (CPZ) induces demyelination by chelating copper, which leads to oligodendrocyte death and subsequent myelin loss. This study investigated the impact of MDMA on brain demyelination in CPZ-treated mice, focusing on the gut-brain axis. Repeated intermittent MDMA administration (10 mg/kg, three times weekly for 6 weeks) significantly reduced demyelination in the corpus callosum (CC) of CPZ-treated mice. Gut microbiota and non-targeted metabolomics analyses revealed notable differences in specific gut bacteria and plasma (β-D-allose and L-sorbose) or fecal metabolite (carnitine) levels between MDMA-treated and vehicle-treated CPZ-exposed mice. Negative correlations were found between the levels of metabolites (β-D-allose, L-sorbose, and carnitine) and the relative abundance of Romboutsia and Romboutsia timonensis. These findings suggest that intermittent MDMA administration may alleviate demyelination in the CC of CPZ-treated mice via the gut-brain axis. Further research is needed to elucidate the roles of gut microbiota and metabolites in MDMA's effects on brain demyelination and to investigate other demyelination models.

Meningeal lymphatic vessel crosstalk with central nervous system immune cells in aging and neurodegenerative diseases

Meningeal lymphatic vessels form a relationship between the nervous system and periphery, which is relevant in both health and disease. Meningeal lymphatic vessels not only play a key role in the drainage of brain metabolites but also contribute to antigen delivery and immune cell activation. The advent of novel genomic technologies has enabled rapid progress in the characterization of myeloid and lymphoid cells and their interactions with meningeal lymphatic vessels within the central nervous system. In this review, we provide an overview of the multifaceted roles of meningeal lymphatic vessels within the context of the central nervous system immune network, highlighting recent discoveries on the immunological niche provided by meningeal lymphatic vessels. Furthermore, we delve into the mechanisms of crosstalk between meningeal lymphatic vessels and immune cells in the central nervous system under both homeostatic conditions and neurodegenerative diseases, discussing how these interactions shape the pathological outcomes. Regulation of meningeal lymphatic vessel function and structure can influence lymphatic drainage, cerebrospinal fluid-borne immune modulators, and immune cell populations in aging and neurodegenerative disorders, thereby playing a key role in shaping meningeal and brain parenchyma immunity.

An In Silico Study on Withania somnifera Bioactives and Curcumin Analogs as Potential Inducers of Smoothened (Smo) Receptor of Sonic Hedgehog (SHH) Pathway to Promote Oligodendrogenesis

Demyelinating disorder is a subset of neurodegenerative conditions wherein factors such as aging and/or auto-immune attack cause damage and degradation of myelin sheath which enwraps the neuronal axons. Lowered axonal integrity and sub-par conduction of nerve impulses due to impaired action potentials make neurodegeneration imminent as the neurons do not have mitotic ability to replenish their numbers. Oligodendrocytes (OLs) myelinate the axonal segments of neurons and perform neuronal maintenance. Neuroregenerative stem cell therapy exploits this property for remyelination by targeting OL replenishment using in vitro stem cell differentiation protocols for inducing OL lineage cells. But some shortcomings of such protocols are over-reliance on synthetic inducers, lengthy differentiation process, low differentiation efficiency besides being financially expensive. This in silico study sought to identify herbal substitutes of currently available OL-lineage-specific synthetic inducers from a virtual library of curcumin analogs and Withania somnifera bioactives. Smoothened (Smo) receptor belonging to the canonical sonic hedgehog (SHH) signaling pathway promotes in vivo differentiation of OLs as well as their subsequent lineage progression to myelinating OLs. Therefore, we performed pharmacokinetics prediction for the bioactives followed by their molecular docking and molecular dynamics simulation with Smo. From a pool of 1289 curcumin analogs and 80 Withania somnifera-derived bioactives, the best docked ligands were identified as the compounds with PubChem IDs 68815167 and 25880, respectively. Molecular dynamics simulation of these ligands further concluded the Withania somnifera bioactive 25880 to have the best activity with Smo. This compound may be deemed as a potential lead molecule for an agonistic interaction with and activation of Smo to initialize its downstream signaling cascade for enriching OL differentiation.

Gastrodin promotes CNS myelinogenesis and alleviates demyelinating injury by activating the PI3K/AKT/mTOR signaling

Demyelination is a common feature of numerous neurological disorders including multiple sclerosis and leukodystrophies. Although myelin can be regenerated spontaneously following injury, this process is often inadequate, potentially resulting in neurodegeneration and exacerbating neurological dysfunction. Several drugs aimed at promoting the differentiation of oligodendrocyte precursor cells (OPCs) have yielded unsatisfactory clinical effects. A recent study has shifted the strategy of pro-OPC differentiation towards enhancing myelinogenesis. In this study we identified the pro-myelinating drug using a zebrafish model. Five traditional Chinese medicine monomers including gastrodin, paeoniflorin, puerarin, salidroside and scutellarin were assessed by bath-application in Tg (MBP:eGFP-CAAX) transgenic line at 1-5 dpf. Among the 5 monomers, only gastrodin exhibited significant pro-myelination activity. We showed that gastrodin (10 µM) enhanced myelin sheath formation and oligodendrocyte (OL) maturation without affecting the number of OLs. Gastrodin markedly increased the phosphorylation levels of PI3K, AKT, and mTOR in primary cultured OLs via direct interaction with PI3K. Co-treatment with the PI3K inhibitor LY294002 (5 µM) mitigated gastrodin-induced OL maturation. Furthermore, injection of gastrodin (100 mg·kg-1·d-1, i.p.) effectively facilitated remyelination in a lysophosphatidylcholine-induced demyelinating mouse model and alleviated demyelination in the experimental autoimmune encephalomyelitis mice. These results identify gastrodin as a promising therapeutic agent for demyelinating diseases and highlight the potential of the zebrafish model for screening pro-myelinogenic pharmacotherapy.

Recent advances in mesenchymal stem cell therapy for multiple sclerosis: clinical applications and challenges

Multiple sclerosis (MS), a chronic autoimmune disorder of the central nervous system (CNS), is characterized by inflammation, demyelination, and neurodegeneration, leading to diverse clinical manifestations such as fatigue, sensory impairment, and cognitive dysfunction. Current pharmacological treatments primarily target immune modulation but fail to arrest disease progression or entirely reverse CNS damage. Mesenchymal stem cell (MSC) therapy offers a promising alternative, leveraging its immunomodulatory, neuroprotective, and regenerative capabilities. This review provides an in-depth analysis of MSC mechanisms of action, including immune system regulation, promotion of remyelination, and neuroregeneration. It examines preclinical studies and clinical trials evaluating the efficacy, safety, and limitations of MSC therapy in various MS phenotypes. Special attention is given to challenges such as delivery routes, dosing regimens, and integrating MSCs with conventional therapies. By highlighting advancements and ongoing challenges, this review underscores the potential of MSCs to revolutionize MS treatment, paving the way for personalized and combinatory therapeutic approaches.

RhoA regulates oligodendrocyte differentiation and myelination by orchestrating cortical and membrane tension

Timely differentiation and myelin formation by oligodendrocytes are essential for the physiological functioning of the central nervous system (CNS). While the Rho GTPase RhoA has been hinted as a negative regulator of myelin sheath formation, the precise in vivo mechanisms have remained elusive. Here we show that RhoA controls the timing and progression of myelination by oligodendrocytes through a fine-tuned balance between cortical tension, membrane tension and cell shape. Using a conditional mouse model, we observe that Rhoa ablation results in the acceleration of myelination driven by hastened differentiation and facilitated through membrane expansion induced by changes in MLCII activity and in F-actin redistribution and turnover within the cell. These findings reveal RhoA as a central molecular integrator of alterations in actin cytoskeleton, actomyosin contractility and membrane tension underlying precise morphogenesis of oligodendrocytes and normal myelination of the CNS.

Microbiome depletion by broad-spectrum antibiotics does not influence demyelination and remyelination in cuprizone-treated mice

Demyelination in the central nervous system (CNS) is a feature of various psychiatric and neurological disorders. Emerging evidence suggests that the gut-brain axis may play a crucial role in CNS demyelination. The cuprizone (CPZ) model, which involves the administration of CPZ-containing food pellets, is commonly used to study the effects of different compounds on CNS demyelination and subsequent remyelination. This study aimed to evaluate the impact of microbiome depletion, induced by an antibiotic cocktail (ABX), on demyelination in CPZ-treated mice and the subsequent remyelination following CPZ withdrawal. Our findings indicate that a chronic 4-week oral ABX regimen, administered both during and after a 6-week CPZ exposure, does not affect demyelination or remyelination in the brains of CPZ-treated mice. Specifically, ABX treatment for 2 weeks before and 2 weeks after CPZ exposure, in the final 4 weeks before sacrifice, and for 4 weeks post-CPZ withdrawal, did not significantly alter these processes compared to control mice receiving water instead of ABX. These results indicate that despite effective microbiome depletion, a 4-week oral ABX regimen does not influence demyelination or remyelination in the CPZ model. Thus, it is unlikely that gut microbiota depletion by ABX plays a significant role in these processes. However, further research is needed to fully understand the role of the host microbiome on CPZ-induced demyelination.

Therapeutic potential of Pranlukast against cuprizone-induced inflammatory demyelination and sensory impairment in mice: comparison with Fingolimod

Inflammatory demyelination is present in debilitating diseases such as Multiple Sclerosis (MS). Several drugs are available for MS treatment, with fingolimod as a first-line oral option in the United States. However, a cure has yet to be established, and therapeutic failures are common, highlighting the need for continued research into new pharmacological targets. Pranlukast has shown positive effects on myelination in cell cultures and after LPC-induced demyelination in mice, but it is not yet part of the therapeutic arsenal for this disease. This study investigates pranlukast's effect on demyelination protection in an MS animal model, compared to fingolimod. For this purpose, young adult Swiss mice were treated for five weeks with a 0.2% cuprizone diet and received daily intraperitoneal injections of pranlukast (0.1mg/kg), fingolimod (1mg/kg), or vehicle. Pranlukast treatment, like fingolimod, partially preserved sensory function in the tactile sensitivity test. Both treatments partially preserved myelin basic protein (MBP) levels, but only fingolimod preserved lipids and myelinated fibers in the corpus callosum (CC) at all g-ratio ranges. Cuprizone and Pranlukast groups presented more microglia/macrophages in the CC, but fewer presenting reactive microglia/macrophages and less NOS2 staining in pranlukast-treated when compared to the cuprizone group, while fingolimod treatment prevented the increase in Iba1 in the CC. In summary, this study demonstrated that pranlukast is a good candidate as a novel drug for use in conditions of inflammatory demyelination, such as MS, by restoring function through modulation of the inflammatory environment.

Myelin ensheathment and drug responses of oligodendrocytes are modulated by stiffness of artificial axons

Myelination is a key biological process wherein glial cells such as oligodendrocytes wrap myelin around neuronal axons, forming an insulative sheath that accelerates signal propagation down the axon. A major obstacle to understanding myelination is the challenge of visualizing and reproducibly quantifying this inherently three-dimensional process in vitro. To this end, we previously developed artificial axons (AAs), a biocompatible platform consisting of 3D-printed hydrogel-based axon mimics designed to more closely recapitulate the micrometer-scale diameter and sub-kilopascal mechanical stiffness of biological axons. First, we present our platform for fabricating AAs with tunable axon diameter, stiffness, and inter-axonal spacing. Second, we demonstrate that increasing the Young's modulus E or stiffness of polymer comprising the AAs increases the extent of myelin ensheathment by rat oligodendrocytes. Third, we demonstrate that the responses of oligodendrocytes to pro-myelinating compounds are also dependent on axon stiffness, which can affect compounds efficacy and the relative ranking. These results reinforce the importance of studying myelination in mechanically representative environments, and highlight the importance of considering biophysical cues when conducting drug screening studies.

Traumatic Brain Injury Promotes Neurogenesis and Oligodendrogenesis in Subcortical Brain Regions of Mice

Traumatic brain injury (TBI) is one of the major causes of severe neurological disorders and long-term dysfunction in the nervous system. Besides inducing neurodegeneration, TBI alters stem cell activity and neurogenesis within primary neurogenic niches. However, the fate of dividing cells in other brain regions remains unclear despite offering potential targets for therapeutic intervention. Here, we investigated cell division and differentiation in non-neurogenic brain regions during the acute and delayed phases of TBI-induced neurodegeneration. We subjected mice to lateral fluid percussion injury (LFPI) to model TBI and analyzed them 1 or 7 weeks later. To assess cellular proliferation and differentiation, we administered 5-ethinyl-2'-deoxyuridine (EdU) and determined the number and identity of dividing cells 2 h later using markers of neuronal precursors and astro-, micro-, and oligodendroglia. Our results demonstrated a significant proliferative response in several brain regions at one week post-injury that notably diminished by seven weeks, except in the optic tract. In addition to active astro- and microgliosis, we detected oligodendrogenesis in the striatum and optic tract. Furthermore, we observed trauma-induced neurogenesis in the striatum. These findings suggest that subcortical structures, particularly the striatum and optic tract, may possess a potential for self-repair through neuronal regeneration and axon remyelination.

Nuclear receptor PPARγ targets GPNMB to promote oligodendrocyte development and remyelination

Myelin injury occurs in brain ageing and in several neurological diseases. Failure of spontaneous remyelination is attributable to insufficient differentiation of oligodendrocyte precursor cells (OPCs) into mature myelin-forming oligodendrocytes in CNS demyelinated lesions. Emerging evidence suggests that peroxisome proliferator-activated receptor γ (PPARγ) is the master gatekeeper of CNS injury and repair and plays an important regulatory role in various neurodegenerative diseases. Although studies demonstrate positive effects of PPARγ in oligodendrocyte ontogeny in vitro, the cell-intrinsic role of PPARγ and the molecular mechanisms involved in the processes of OPC development and CNS remyelination in vivo are poorly understood. Here, we identify PPARγ as an enriched transcription factor in the dysfunctional OPCs accumulated in CNS demyelinated lesions. Its expression increases during OPC differentiation and myelination and is closely related to the process of CNS demyelination/remyelination. Administration of pharmacological agonists of PPARγ not only promotes OPC differentiation and CNS myelination, but also causes a significant increase in remyelination in both cuprizone- and lysophosphatidylcholine-induced demyelination models. In contrast, the attenuation of PPARγ function, either through the specific knockout of PPARγ in oligodendrocytes in vivo or through its inhibition in vitro, leads to decreased OPC maturation, hindered myelin generation and reduced therapeutic efficacy of PPARγ agonists. At a mechanistic level, PPARγ induces myelin repair by directly targeting glycoprotein non-metastatic melanoma protein B (GPNMB), a novel regulator that drives OPCs to differentiate into oligodendrocytes, promotes myelinogenesis in the developing CNS of postnatal mice and enhances remyelination in mice with lysophosphatidylcholine-induced demyelination. In conclusion, our evidence reveals that PPARγ is a positive regulator of endogenous OPC differentiation and CNS myelination/remyelination and suggests that PPARγ and/or its downstream sensor (GPNMB) might be a candidate pharmacological target for regenerative therapy in the CNS.

The Role of Oligodendrocyte Lineage Cells in the Pathogenesis of Alzheimer's Disease

Alzheimer's disease (AD) is a central nervous system degenerative disease with a stealthy onset and a progressive course characterized by memory loss, cognitive dysfunction, and abnormal psychological and behavioral symptoms. However, the pathogenesis of AD remains elusive. An increasing number of studies have shown that oligodendrocyte progenitor cells (OPCs) and oligodendroglial lineage cells (OLGs), especially OPCs and mature oligodendrocytes (OLGs), which are derived from OPCs, play important roles in the pathogenesis of AD. OLGs function mainly by myelinating axons, transmitting electrical signals, and regulating neural development. In addition to myelin, OPCs and OLGs can also participate in AD pathogenesis in other ways. This review summarizes the mechanisms by which OPCs and OLGs affect myelin formation, oxidative stress, neuroinflammation, the blood-brain barrier, synaptic function, and amyloid-beta protein and further elucidates the mechanisms by which oligodendrocyte lineage cells participate in AD pathogenesis and treatment, which is highly important for clarifying the pathogenesis of AD, clinical treatment, and prevention.

The isoflavone puerarin promotes generation of human iPSC-derived pre-oligodendrocytes and enhances endogenous remyelination in rodent models

Puerarin, a natural isoflavone, is commonly used as a Chinese herbal medicine for the treatment of various cardiovascular and neurological disorders. It has been found to be neuroprotective via TrK-PI3K/Akt pathway, which is associated with anti-inflammatory and antioxidant effects. Myelin damage in diseases such as multiple sclerosis (MS) and ischemia induces activation of endogenous oligodendrocyte progenitor cells (OPC) and subsequent remyelination by newly formed oligodendrocytes. It has been shown that human-induced pluripotent stem cells (hiPSC)-derived OPCs promote remyelination when transplanted to the brains of disease models. Here, we ask whether and how puerarin is beneficial to the generation of hiPSC-derived OPCs and oligodendrocytes, and to the endogenous remyelination in mouse demyelination model. Our results show that puerarin increases the proportion of O4+ pre-oligodendrocytes differentiated from iPSC-derived neural stem cells. In vitro, puerarin increases proliferation of rat OPCs and enhances mitochondrial activity. Treatment of puerarin at progenitor stage increases the yielding of differentiated oligodendrocytes. In rat organotypic brain slice culture, puerarin promotes both myelination and remyelination. In vivo, puerarin increases oligodendrocyte repopulation during remyelination in mouse spinal cord following lysolethicin-induced demyelination. Our findings suggest that puerarin promotes oligodendrocyte lineage progression and myelin repair, with a potential to be developed into therapeutic agent for neurological diseases associated with myelin damage.

(Re)building the nervous system: A review of neuron-glia interactions from development to disease

Neuron-glia interactions are fundamental to the development and function of the nervous system. During development, glia, including astrocytes, microglia, and oligodendrocytes, influence neuronal differentiation and migration, synapse formation and refinement, and myelination. In the mature brain, glia are crucial for maintaining neural homeostasis, modulating synaptic activity, and supporting metabolic functions. Neurons, inherently vulnerable to various stressors, rely on glia for protection and repair. However, glia, in their reactive state, can also promote neuronal damage, which contributes to neurodegenerative and neuropsychiatric diseases. Understanding the dual role of glia-as both protectors and potential aggressors-sheds light on their complex contributions to disease etiology and pathology. By appropriately modulating glial activity, it may be possible to mitigate neurodegeneration and restore neuronal function. In this review, which originated from the International Society for Neurochemistry (ISN) Advanced School in 2019 held in Montreal, Canada, we first describe the critical importance of glia in the development and maintenance of a healthy nervous system as well as their contributions to neuronal damage and neurological disorders. We then discuss potential strategies to modulate glial activity during disease to protect and promote a properly functioning nervous system. We propose that targeting glial cells presents a promising therapeutic avenue for rebuilding the nervous system.

Unraveling the role of oligodendrocytes and myelin in pain

Oligodendrocytes, the myelin-producing cells in the central nervous system (CNS), are crucial for rapid action potential conduction and neuronal communication. While extensively studied for their roles in neuronal support and axonal insulation, their involvement in pain modulation is an emerging research area. This review explores the interplay between oligodendrocytes, myelination, and pain, focusing on neuropathic pain following peripheral nerve injury, spinal cord injury (SCI), chemotherapy, and HIV infection. Studies indicate that a decrease in oligodendrocytes and increased cytokine production by oligodendroglia in response to injury can induce or exacerbate pain. An increase in endogenous oligodendrocyte precursor cells (OPCs) may be a compensatory response to repair damaged oligodendrocytes. Exogenous OPC transplantation shows promise in alleviating SCI-induced neuropathic pain and enhancing remyelination. Additionally, oligodendrocyte apoptosis in brain regions such as the medial prefrontal cortex is linked to opioid-induced hyperalgesia, highlighting their role in central pain mechanisms. Chemotherapeutic agents disrupt oligodendrocyte differentiation, leading to persistent pain, while HIV-associated neuropathy involves up-regulation of oligodendrocyte lineage cell markers. These findings underscore the multifaceted roles of oligodendrocytes in pain pathways, suggesting that targeting myelination processes could offer new therapeutic strategies for chronic pain management. Further research should elucidate the underlying molecular mechanisms to develop effective pain treatments.

Deferiprone promoted remyelination and functional recovery through enhancement of oligodendrogenesis in experimental demyelination animal model

Remyelination refers to myelin regeneration, which reestablishes metabolic supports to axons. However, remyelination often fails in multiple sclerosis (MS), leading to chronic demyelination and axonal degeneration. Therefore, pharmacological approaches toward enhanced remyelination are highly demanded. Recently, deferiprone (DFP) was reported to exert neuroprotective effects, besides its iron-chelating ability. Since DFP exerts protective effects through various mechanisms, which share several factors with myelin formation process, we aimed to investigate the effects of DFP treatment on remyelination. Focal demyelination was induced by injection of lysolecithin, into the optic nerve of male C57BL/6J mice. The animals were treated with DFP/vehicle, starting from day 7 and continued during the myelin repair period. Histopathological, electrophysiological, and behavioral studies were used to evaluate the outcomes. Results showed that DFP treatment enhanced remyelination, decreased g-ratio and increased myelin thickness. At the mechanistic level, DFP enhanced oligodendrogenesis and ameliorated gliosis during the remyelination period. Furthermore, our results indicated that enhanced remyelination led to functional recovery as evaluated by the electrophysiological and behavioral tests. Even though the exact molecular mechanisms by which DFP-enhanced myelin repair remain to be elucidated, these results raise the possibility of using deferiprone as a therapeutic agent for remyelination therapy in MS.

The phytohormone abscisic acid enhances remyelination in mouse models of multiple sclerosis

Introduction

Over the past few decades, there has been a sudden rise in the incidence of Multiple Sclerosis (MS) in Western countries. However, current treatments often show limited efficacy in certain patients and are associated with adverse effects, which highlights the need for safer and more effective therapeutic approaches. Environmental factors, particularly dietary habits, have been observed to play a substantial role in the development of MS. In this study, we are the first to investigate the potential protective effect of the phytohormone abscisic acid (ABA) in MS. ABA, which is abundant in fruits such as figs, apricots and bilberries, is known to cross the blood-brain barrier and has demonstrated neuroprotective effects in conditions like depression and Alzheimer's disease.

Methods

In this study, we investigated whether ABA supplementation enhances remyelination in both ex vivo and in vivo mouse models.

Results

Our results indicated that ABA enhanced remyelination and that this enhanced remyelination is associated with increased lipid droplet load, reduced levels of degraded myelin, and a higher abundance of F4/80+ cells in the demyelinated brain of mice treated with ABA. In in vitro models, we further demonstrated that ABA treatment elevates lipid droplet formation by enhancing the phagocytic capacity of macrophages. Additionally, in a mouse model of microglial activation, we showed that ABA-treated mice maintain a less inflammatory microglial phenotype.

Conclusion

Our findings highlight a crucial role for macrophages and microglia in enabling ABA to enhance the remyelination process. Furthermore, ABA's ability to improve remyelination together with its ability to reduce microglial activation, make ABA a promising candidate for modulating macrophage phenotype and reducing neuroinflammation in MS.

Transforming growth factor-β1 mediates the beneficial effects of arketamine on demyelination and remyelination in the brains of cuprizone-treated mice

The novel antidepressant arketamine, the (R)-enantiomer of ketamine, has been shown to ameliorate demyelination and facilitate remyelination in the brains of cuprizone (CPZ)-treated mice. However, the mechanisms behind its effects remain unclear. Given the role of transforming growth factor β1 (TGF-β1) in arketamine's antidepressant-like effects, we examined whether TGF-β1 also plays a role in arketamine's effects on demyelination and remyelination in CPZ-treated mice. Additionally, we investigated the effects of intranasal TGF-β1 on demyelination and remyelination in these mice. Repeated intermittent administration of arketamine (10 mg/kg/day, twice weekly for the last 2-weeks) attenuated demyelination in the corpus callosum (CC) of CPZ (6 weeks)-treated mice. Furthermore, pretreatment with RepSox (10 mg/kg/day), an inhibitor of the TGF-β receptor 1, significantly blocked the beneficial effects of arketamine on the demyelination in the CC of CPZ-treated mice. Additionally, repeated intermittent administration of TGF-β1 (3.0 μg/kg/day, twice weekly for 2 weeks) significantly ameliorated demyelination and facilitated remyelination in the CC of CPZ-treated mice. These data suggest that arketamine can mitigate demyelination and facilitates remyelination in the brains of CPZ-treated mice through a TGF-β1-dependent mechanism.

Genetic Downregulation of GABAB Receptors from Oligodendrocyte Precursor Cells Protects Against Demyelination in the Mouse Spinal Cord

GABAergic signaling and GABAB receptors play crucial roles in regulating the physiology of oligodendrocyte-lineage cells, including their proliferation, differentiation, and myelination. Therefore, they are promising targets for studying how spinal oligodendrocyte precursor cells (OPCs) respond to injuries and neurodegenerative diseases like multiple sclerosis. Taking advantage of the temporally controlled and cell-specific genetic downregulation of GABAB receptors from OPCs, our investigation addresses their specific influence on OPC behavior in the gray and white matter of the mouse spinal cord. Our results show that, while GABAB receptors do not significantly alter spinal cord myelination under physiological conditions, they distinctly regulate the OPC differentiation and Ca2+ signaling. In addition, we investigate the impact of OPC-GABAB receptors in two models of toxic demyelination, namely, the cuprizone and the lysolecithin models. The genetic downregulation of OPC-GABAB receptors protects against demyelination and oligodendrocyte loss. Additionally, we observe the enhanced resilience to cuprizone-induced pathological alterations in OPC Ca2+ signaling. Our results provide valuable insights into the potential therapeutic implications of manipulating GABAB receptors in spinal cord OPCs and deepen our understanding of the interplay between GABAergic signaling and spinal cord OPCs, providing a basis for future research.

Spatially resolved gene signatures of white matter lesion progression in multiple sclerosis

Multiple sclerosis (MS) is an inflammatory disease of the central nervous system characterized by myelin loss and progressive neurodegeneration. To understand MS lesion initiation and progression, we generate spatial gene expression maps of white matter (WM) and grey matter (GM) MS lesions. In different MS lesion types, we detect domains characterized by a distinct gene signature, including an identifiable rim around active WM lesions. Expression changes in astrocyte-specific, oligodendrocyte-specific and microglia-specific gene sets characterize the active lesion rims. Furthermore, we identify three WM lesion progression trajectories, predicting how normal-appearing WM can develop into WM active or mixed active-inactive lesions. Our data shed light on the dynamic progression of MS lesions.

Agomelatine promotes differentiation of oligodendrocyte precursor cells and preserves white matter integrity after cerebral ischemic stroke

White matter injury contributes to neurological disorders after acute ischemic stroke (AIS). The repair of white matter injury is dependent on the re-myelination by oligodendrocytes. Both melatonin and serotonin antagonist have been proved to protect against post-stroke white matter injury. Agomelatine (AGM) is a multi-functional treatment which is both a melatonin receptor agonist and selective serotonin receptor antagonist. Whether AGM protects against white matter injury after stroke and the underlying mechanisms remain elusive. Here, using the transient middle cerebral artery occlusion (tMCAO) model, we evaluated the therapeutic effects of AGM in stroke mice. Sensorimotor and cognitive functions, white matter integrity, oligodendroglial regeneration and re-myelination in stroke hemisphere after AGM treatment were analyzed. We found that AGM efficiently preserved white matter integrity, reduced brain tissue loss, attenuated long-term sensorimotor and cognitive deficits in tMCAO models. AGM treatment promoted OPC differentiation and enhanced re-myelination both in vitro, ex vivo and in vivo, although OPC proliferation was unaffected. Mechanistically, AGM activated low density lipoprotein receptor related protein 1 (LRP1), peroxisome proliferator-activated receptor γ (PPARγ) signaling thus promoted OPC differentiation and re-myelination after stroke. Inhibition of PPARγ or knock-down of LRP1 in OPCs reversed the beneficial effects of AGM. Altogether, our data indicate that AGM represents a novel therapy against white matter injury after cerebral ischemia.

Thyroid hormone T4 mitigates traumatic brain injury in mice by dynamically remodeling cell type specific genes, pathways, and networks in hippocampus and frontal cortex

The complex pathology of mild traumatic brain injury (mTBI) is a main contributor to the difficulties in achieving a successful therapeutic regimen. Thyroxine (T4) administration has been shown to prevent the cognitive impairments induced by mTBI in mice but the mechanism is poorly understood. To understand the underlying mechanism, we carried out a single cell transcriptomic study to investigate the spatiotemporal effects of T4 on individual cell types in the hippocampus and frontal cortex at three post-injury stages in a mouse model of mTBI. We found that T4 treatment altered the proportions and transcriptomes of numerous cell types across tissues and timepoints, particularly oligodendrocytes, astrocytes, and microglia, which are crucial for injury repair. T4 also reversed the expression of mTBI-affected genes such as Ttr, mt-Rnr2, Ggn12, Malat1, Gnaq, and Myo3a, as well as numerous pathways such as cell/energy/iron metabolism, immune response, nervous system, and cytoskeleton-related pathways. Cell-type specific network modeling revealed that T4 mitigated select mTBI-perturbed dynamic shifts in subnetworks related to cell cycle, stress response, and RNA processing in oligodendrocytes. Cross cell-type ligand-receptor networks revealed the roles of App, Hmgb1, Fn1, and Tnf in mTBI, with the latter two ligands having been previously identified as TBI network hubs. mTBI and/or T4 signature genes were enriched for human genome-wide association study (GWAS) candidate genes for cognitive, psychiatric and neurodegenerative disorders related to mTBI. Our systems-level single cell analysis elucidated the temporal and spatial dynamic reprogramming of cell-type specific genes, pathways, and networks, as well as cell-cell communications as the mechanisms through which T4 mitigates cognitive dysfunction induced by mTBI.

Microglia regulate cortical remyelination via TNFR1-dependent phenotypic polarization

Microglia are strongly implicated in demyelinating neurodegenerative diseases with increasing evidence for roles in protection and healing, but the mechanisms that control CNS remyelination are poorly understood. Here, we show that microglia-specific deletion of tumor necrosis factor receptor 1 (TNFR1) and pharmacological inhibition of soluble TNF (solTNF) or downstream interleukin-1 receptor (IL-1R) allow maturation of highly activated disease-associated microglia with increased size and myelin phagocytosis capacity that accelerate cortical remyelination and motor recovery. Single-cell transcriptomic analysis of cortex at disease onset reveals that solTNF inhibition enhances reparative IL-10-responsive while preventing damaging IL-1-related signatures of disease-associated microglia. Longitudinal brain transcriptome analysis through disease reveals earlier recovery upon therapeutic loss of microglia TNFR1. The functional relevance of microglia inflammatory polarization pathways for disease is validated in vivo. Furthermore, disease-state microglia producing downstream IL-1/IL-18/caspase-11 targets are identified in human demyelinating lesions. Overall, redirecting disease microglia polarization by targeting cytokines is a potential approach for improving CNS repair in demyelinating disorders.

Preventing production of new oligodendrocytes impairs remyelination and sustains behavioural deficits after demyelination

Damage to oligodendrocytes (OLs) and myelin sheaths (demyelination) has been shown to be associated with numerous neurological and psychiatric disorders. Remyelination is a rare and reliable regenerative response that occurs in the central nervous system (CNS). It is generally believed that OL progenitor cells (OPCs) are the cell source to generate new OLs to remyelinate the demyelinated axons. However, several recent studies have argued that pre-existing mature OLs that survive within the demyelinated area are responsible for remyelination. Here, by conditional knock-out (KO) of a transcription factor gene that is essential for OPC differentiation, namely myelin regulatory factor (Myrf), to block the production of adult new OLs and examined its effect on remyelination after cuprizone (CPZ)-induced demyelination. We found that OPCs specific Myrf cKO mice show dramatic impairment in remyelination after 4 weeks of recovery from 5 weeks of CPZ diet and they leave over significant behavioral deficits such as anxiety-like behavior, decreased motor skills, and impaired memory compared to control mice that have recovered for the same time. Our data support the idea that OPCs are the major cell sources for myelin regeneration, suggesting that targeting the activation of OPCs and promoting their differentiation to boost new OLs production is critical for therapeutic intervention for demyelinating diseases such as multiple sclerosis (MS).

The physiological role of the unfolded protein response in the nervous system

The unfolded protein response (UPR) is a cellular stress response pathway activated when the endoplasmic reticulum, a crucial organelle for protein folding and modification, encounters an accumulation of unfolded or misfolded proteins. The UPR aims to restore endoplasmic reticulum homeostasis by enhancing protein folding capacity, reducing protein biosynthesis, and promoting protein degradation. It also plays a pivotal role in coordinating signaling cascades to determine cell fate and function in response to endoplasmic reticulum stress. Recent research has highlighted the significance of the UPR not only in maintaining endoplasmic reticulum homeostasis but also in influencing various physiological processes in the nervous system. Here, we provide an overview of recent findings that underscore the UPR's involvement in preserving the function and viability of neuronal and myelinating cells under physiological conditions, and highlight the critical role of the UPR in brain development, memory storage, retinal cone development, myelination, and maintenance of myelin thickness.

Glial Cell Development and Function in the Zebrafish Central Nervous System

Over the past decades the zebrafish has emerged as an excellent model organism with which to study the biology of all glial cell types in nervous system development, plasticity, and regeneration. In this review, which builds on the earlier work by Lyons and Talbot in 2015, we will summarize how the relative ease to manipulate the zebrafish genome and its suitability for intravital imaging have helped understand principles of glial cell biology with a focus on oligodendrocytes, microglia, and astrocytes. We will highlight recent findings on the diverse properties and functions of these glial cell types in the central nervous system and discuss open questions and future directions of the field.

CRISPR-edited human ES-derived oligodendrocyte progenitor cells improve remyelination in rodents

In Multiple Sclerosis (MS), inflammatory demyelinated lesions in the brain and spinal cord lead to neurodegeneration and progressive disability. Remyelination can restore fast saltatory conduction and neuroprotection but is inefficient in MS especially with increasing age, and is not yet treatable with therapies. Intrinsic and extrinsic inhibition of oligodendrocyte progenitor cell (OPC) function contributes to remyelination failure, and we hypothesised that the transplantation of 'improved' OPCs, genetically edited to overcome these obstacles, could improve remyelination. Here, we edit human(h) embryonic stem cell-derived OPCs to be unresponsive to a chemorepellent released from chronic MS lesions, and transplant them into rodent models of chronic lesions. Edited hOPCs display enhanced migration and remyelination compared to controls, regardless of the host age and length of time post-transplant. We show that genetic manipulation and transplantation of hOPCs overcomes the negative environment inhibiting remyelination, with translational implications for therapeutic strategies for people with progressive MS.

Anti-inflammatory and remyelinating effects of fexagratinib in experimental multiple sclerosis

BACKGROUND AND PURPOSE

FGF, VEGFR-2 and CSF1R signalling pathways play a key role in the pathogenesis of multiple sclerosis (MS). Selective inhibition of FGFR by infigratinib in MOG35-55-induced experimental autoimmune encephalomyelitis (EAE) prevented severe first clinical episodes by 40%; inflammation and neurodegeneration were reduced, and remyelination was enhanced. Multi-kinase inhibition of FGFR1-3, CSFR and VEGFR-2 by fexagratinib (formerly known as AZD4547) may be more efficient in reducing inflammation, neurodegeneration and regeneration in the disease model.

EXPERIMENTAL APPROACH

Female C57BL/6J mice were treated with fexagratinib (6.25 or 12.5 mg·kg-1) orally or placebo over 10 days either from time of EAE induction (prevention experiment) or onset of symptoms (suppression experiment). Effects on inflammation, neurodegeneration and remyelination were assessed at the peak of the disease (Day 18/20 post immunization) and the chronic phase of EAE (Day 41/42).

KEY RESULTS

In the prevention experiment, treatment with 6.25 or 12.5 mg·kg-1 fexagratinib prevented severe first clinical episodes by 66.7% or 84.6% respectively. Mice treated with 12.5 mg·kg-1 fexagratinib hardly showed any symptoms in the chronic phase of EAE. In the suppression experiment, fexagratinib resulted in a long-lasting reduction of severe symptoms by 91 or 100%. Inflammation and demyelination were reduced, and axonal density, numbers of oligodendrocytes and their precursor cells, and remyelinated axons were increased by both experimental approaches.

CONCLUSION AND IMPLICATIONS

Multi-kinase inhibition by fexagratinib in a well-tolerated dose of 1 mg·kg-1 in humans may be a promising approach to reduce inflammation and neurodegeneration, to slow down disease progression and support remyelination in patients.

The gut microbiota-oligodendrocyte axis: A promising pathway for modulating oligodendrocyte homeostasis and demyelination-associated disorders

The bidirectional regulation between the gut microbiota and brain, known as gut-brain axis, has received significant attention. The myelin sheath, produced by oligodendrocytes or Schwann cells, is essential for efficient nervous signal transmission and the maintenance of brain function. Growing evidence shows that both oligodendrogenesis and myelination are modulated by gut microbiota and its metabolites, and when dysbiosis occurs, changes in the microbiota composition and/or associated metabolites may impact developmental myelination and the occurrence of neurodevelopmental disabilities. Although the link between the microbiota and demyelinating disease such as multiple sclerosis has been extensively studied, our knowledge about the role of the microbiota in other myelin-related disorders, such as neurodegenerative diseases, is limited. Mechanistically, the microbiota-oligodendrocyte axis is primarily mediated by factors such as inflammation, the vagus nerve, endocrine hormones, and microbiota metabolites as evidenced by metagenomics, metabolomics, vagotomy, and morphological and molecular approaches. Treatments targeting this axis include probiotics, prebiotics, microbial metabolites, herbal bioactive compounds, and specific dietary management. In addition to the commonly used approaches, viral vector-mediated tracing and gene manipulation, integrated multiomics and multicenter clinical trials will greatly promote the mechanistic and interventional studies and ultimately, the development of new preventive and therapeutic strategies against gut-oligodendrocyte axis-mediated brain impairments. Interestingly, recent findings showed that microbiota dysbiosis can be induced by hippocampal myelin damage and is reversible by myelin-targeted drugs, which provides new insights into understanding how hippocampus-based functional impairment (such as in neurodegenerative Alzheimer's disease) regulates the peripheral homeostasis of microbiota and associated systemic disorders.

CNS macrophage contributions to myelin health

Myelin is the membrane surrounding neuronal axons in the central nervous system (CNS), produced by oligodendrocytes to provide insulation for electrical impulse conduction and trophic/metabolic support. CNS dysfunction occurs following poor development of myelin in infancy, myelin damage in neurological diseases, and impaired regeneration of myelin with disease progression in aging. The lack of approved therapies aimed at supporting myelin health highlights the critical need to identify the cellular and molecular influences on oligodendrocytes. CNS macrophages have been shown to influence the development, maintenance, damage and regeneration of myelin, revealing critical interactions with oligodendrocyte lineage cells. CNS macrophages are comprised of distinct populations, including CNS-resident microglia and cells associated with CNS border regions (the meninges, vasculature, and choroid plexus), in addition to macrophages derived from monocytes infiltrating from the blood. Importantly, the distinct contribution of these macrophage populations to oligodendrocyte lineage responses and myelin health are only just beginning to be uncovered, with the advent of new tools to specifically identify, track, and target macrophage subsets. Here, we summarize the current state of knowledge on the roles of CNS macrophages in myelin health, and recent developments in distinguishing the roles of macrophage populations in development, homeostasis, and disease.

Zinc-Finger Protein ZFP488 Regulates the Timing of Oligodendrocyte Myelination and Remyelination

Oligodendrocyte myelination and remyelination after injury are intricately regulated by various intrinsic and extrinsic factors, including transcriptional regulators. Among these, the zinc-finger protein ZFP488 is an oligodendrocyte-enriched transcriptional regulator that promotes oligodendrocyte differentiation in the developing neural tube and in oligodendroglial cell lines. However, the specific in vivo genetic requirements for ZFP488 during oligodendrocyte development and remyelination have not been defined. To address this gap, we generated a lineage-traceable ZFP488 knock-out mouse line, wherein an H2b-GFP reporter replaces the ZFP488-coding region. Using these mice of either sex, we examined the dynamics of ZFP488 expression from the endogenous promoter in the developing central nervous system (CNS). We observed a unique expression pattern in the oligodendrocyte lineage, with ZFP488 expression particularly enriched in differentiated oligodendrocytes. ZFP488 loss resulted in delayed myelination in the developing CNS and impaired remyelination after demyelinating injury in the brain. Integrated transcriptomic and genomic profiling further revealed that ZFP488 loss decreased the expression of myelination-associated genes but not oligodendrocyte progenitor-associated genes, suggesting that ZFP488 serves as a positive regulator of myelination by regulating maturation programs. Thus, our genetic loss-of-function study revealed that ZFP488 regulates a stage-dependent differentiation program that controls the timing of CNS myelination and remyelination.

Trem2-deficiency aggravates and accelerates age-related myelin degeneration

Aging is the greatest known risk factor for most neurodegenerative diseases. Myelin degeneration is an early pathological indicator of these diseases and a normal part of aging; albeit, to a lesser extent. Despite this, little is known about the contribution of age-related myelin degeneration on neurodegenerative disease. Microglia participate in modulating white matter events from demyelination to remyelination, including regulation of (de)myelination by the microglial innate immune receptor triggering receptor expressed on myeloid cells 2 (TREM2). Here, we demonstrate Trem2-deficiency aggravates and accelerates age-related myelin degeneration in the striatum. We show TREM2 is necessary for remyelination by recruiting reparative glia and mediating signaling that promotes OPC differentiation/maturation. In response to demyelination, TREM2 is required for phagocytosis of large volumes of myelin debris. In addition to lysosomal regulation, we show TREM2 can modify the ER stress response, even prior to overt myelin debris, that prevents lipid accumulation and microglial dysfunction. These data support a role for Trem2-dependent interactions in age-related myelin degeneration and suggest a basis for how early dysfunctional microglia could contribute to disease pathology through insufficent repair, defective phagocytosis, and the ER stress response.

Innate immune training restores pro-reparative myeloid functions to promote remyelination in the aged central nervous system

The reduced ability of the central nervous system to regenerate with increasing age limits functional recovery following demyelinating injury. Previous work has shown that myelin debris can overwhelm the metabolic capacity of microglia, thereby impeding tissue regeneration in aging, but the underlying mechanisms are unknown. In a model of demyelination, we found that a substantial number of genes that were not effectively activated in aged myeloid cells displayed epigenetic modifications associated with restricted chromatin accessibility. Ablation of two class I histone deacetylases in microglia was sufficient to restore the capacity of aged mice to remyelinate lesioned tissue. We used Bacillus Calmette-Guerin (BCG), a live-attenuated vaccine, to train the innate immune system and detected epigenetic reprogramming of brain-resident myeloid cells and functional restoration of myelin debris clearance and lesion recovery. Our results provide insight into aging-associated decline in myeloid function and how this decay can be prevented by innate immune reprogramming.

Astrocyte-derived clusterin disrupts glial physiology to obstruct remyelination in mouse models of demyelinating diseases

Multiple sclerosis (MS) is a debilitating demyelinating disease characterized by remyelination failure attributed to inadequate oligodendrocyte precursor cells (OPCs) differentiation and aberrant astrogliosis. A comprehensive cell atlas reanalysis of clinical specimens brings to light heightened clusterin (CLU) expression in a specific astrocyte subtype links to active lesions in MS patients. Our investigation reveals elevated astrocytic CLU levels in both active lesions of patient tissues and female murine MS models. CLU administration stimulates primary astrocyte proliferation while concurrently impeding astrocyte-mediated clearance of myelin debris. Intriguingly, CLU overload directly impedes OPC differentiation and induces OPCs and OLs apoptosis. Mechanistically, CLU suppresses PI3K-AKT signaling in primary OPCs via very low-density lipoprotein receptor. Pharmacological activation of AKT rescues the damage inflicted by excess CLU on OPCs and ameliorates demyelination in the corpus callosum. Furthermore, conditional knockout of CLU emerges as a promising intervention, showcasing improved remyelination processes and reduced severity in murine MS models.

The refined Pathways to Cures Research Roadmap for multiple sclerosis cures

BACKGROUND

Multiple sclerosis is a chronic immune-mediated disease of the central nervous system affecting nearly 3 million people worldwide. Although much progress has been made in the understanding and treatment of MS, cures remain elusive.

OBJECTIVES

To accelerate the development of cures for MS by updating the Pathways to Cures Research Roadmap based on a contemporary understanding of disease. The refined Roadmap will help to promote research in scientific areas with great potential to reveal insights leading to cures and inspire greater coordination of global resources.

METHODS

Refinements to the Roadmap were achieved during a Global Summit that included close to 200 academic and industry scientists, health care providers, policy makers, funders, and people with MS from 15 countries.

RESULTS

The refined Roadmap describes three pathways that target opportunities for generating scientific insights leading to cures. Recommendations for accelerating research progress include, lowering barriers for global data sharing, enhancing collaboration and coordination among research supporters, committing to sustained funding, considering implications for implementation, engaging PwMS and committing to diversity, equity, and inclusion in the global MS movement.

CONCLUSION

The refined roadmap provides a strategic framework for tackling the complexities of MS and advancing prevention strategies, effective treatments, and cures.

ApTOLL: A new therapeutic aptamer for cytoprotection and (re)myelination after multiple sclerosis

BACKGROUND AND PURPOSE

ApTOLL is an aptamer selected to antagonize toll-like receptor 4 (TLR4), a relevant actor for innate immunity involved in inflammatory responses in multiple sclerosis (MS) and other diseases. The currently available therapeutic arsenal to treat MS is composed of immunomodulators but, to date, there are no (re)myelinating drugs available in clinics. In our present study, we studied the effect of ApTOLL on different animal models of MS.

EXPERIMENTAL APPROACH

The experimental autoimmune encephalomyelitis (EAE) model was used to evaluate the effect of ApTOLL on reducing the inflammatory component. A more direct effect on oligodendroglia was studied with the cuprizone model and purified primary cultures of murine and human oligodendrocyte precursor cells (OPCs) isolated through magnetic-activated cell sorting (MACS) from samples of brain cortex. Also, we tested these effects in an ex vivo model of organotypic cultures demyelinated with lysolecithin (LPC).

KEY RESULTS

ApTOLL treatment positively impacted the clinical symptomatology of mice in the EAE and cuprizone models, which was associated with better preservation plus restoration of myelin and oligodendrocytes in the demyelinated lesions of animals. Restoration was corroborated on purified cultures of rodent and human OPCs.

CONCLUSION AND IMPLICATIONS

Our findings reveal a new therapeutic approach for the treatment of inflammatory and demyelinating diseases such as MS. The molecular nature of the aptamer exerts not only an anti-inflammatory effect but also neuroprotective and remyelinating effects. The excellent safety profile demonstrated by ApTOLL in animals and humans opens the door to future clinical trials in MS patients.

Macrophage GIT1 promotes oligodendrocyte precursor cell differentiation and remyelination after spinal cord injury

Spinal cord injury (SCI) can result in severe motor and sensory deficits, for which currently no effective cure exists. The pathological process underlying this injury is extremely complex and involves many cell types in the central nervous system. In this study, we have uncovered a novel function for macrophage G protein-coupled receptor kinase-interactor 1 (GIT1) in promoting remyelination and functional repair after SCI. Using GIT1flox/flox Lyz2-Cre (GIT1 CKO) mice, we identified that GIT1 deficiency in macrophages led to an increased generation of tumor necrosis factor-alpha (TNFα), reduced proportion of mature oligodendrocytes (mOLs), impaired remyelination, and compromised functional recovery in vivo. These effects in GIT1 CKO mice were reversed with the administration of soluble TNF inhibitor. Moreover, bone marrow transplantation from GIT1 CWT mice reversed adverse outcomes in GIT1 CKO mice, further indicating the role of macrophage GIT1 in modulating spinal cord injury repair. Our in vitro experiments showed that macrophage GIT1 plays a critical role in secreting TNFα and influences the differentiation of oligodendrocyte precursor cells (OPCs) after stimulation with myelin debris. Collectively, our data uncovered a new role of macrophage GIT1 in regulating the transformation of OPCs into mOLs, essential for functional remyelination after SCI, suggesting that macrophage GIT1 could be a promising treatment target of SCI.

Clinical concentration of sevoflurane had no short-term effect on the myelin sheath in prefrontal cortex of aged marmosets

Introduction

The fragile brain includes both the developing brain in childhood and the deteriorating brain in elderly. While the effects of general anesthesia on the myelin sheath of developing brain have been well-documented, limited research has explored its impact on degenerating brain in elderly individuals.

Methods

In our study, aged marmosets in control group were only anesthetized with 6-8% sevoflurane and 100% oxygen (2 L/min) for 1-2 min for anesthesia induction. In addition to anesthesia induction, the anesthesia group was exposed to a clinical concentration of sevoflurane (1.5-2%) for 6 h to maintain anesthesia. After anesthesia, scanning electron microscopy (SEM) and artificial intelligence-assisted image analysis were utilized to observe the effects of general anesthesia on the myelin sheath in prefrontal cortex (PFC) of aged marmosets.

Results

Compared with the control group, our findings revealed no evidence that 6 h of sevoflurane general anesthesia altered the thickness of myelin sheath, the diameter of myelinated axons, and the g-ratio in prefrontal cortex of aged marmosets.

Conclusion

Clinical concentration of sevoflurane may have no short-term effect on the myelin sheath in prefrontal cortex of aged marmosets.

Remyelinating Drugs at a Crossroad: How to Improve Clinical Efficacy and Drug Screenings

Axons wrapped around the myelin sheath enable fast transmission of neuronal signals in the Central Nervous System (CNS). Unfortunately, myelin can be damaged by injury, viral infection, and inflammatory and neurodegenerative diseases. Remyelination is a spontaneous process that can restore nerve conductivity and thus movement and cognition after a demyelination event. Cumulative evidence indicates that remyelination can be pharmacologically stimulated, either by targeting natural inhibitors of Oligodendrocyte Precursor Cells (OPCs) differentiation or by reactivating quiescent Neural Stem Cells (qNSCs) proliferation and differentiation in myelinating Oligodendrocytes (OLs). Although promising results were obtained in animal models for demyelination diseases, none of the compounds identified have passed all the clinical stages. The significant number of patients who could benefit from remyelination therapies reinforces the urgent need to reassess drug selection approaches and develop strategies that effectively promote remyelination. Integrating Artificial Intelligence (AI)-driven technologies with patient-derived cell-based assays and organoid models is expected to lead to novel strategies and drug screening pipelines to achieve this goal. In this review, we explore the current literature on these technologies and their potential to enhance the identification of more effective drugs for clinical use in CNS remyelination therapies.

Evidence for TGF-β1/Nrf2 Signaling Crosstalk in a Cuprizone Model of Multiple Sclerosis

Multiple sclerosis (MS) is a chronic and degenerative disease that impacts central nervous system (CNS) function. One of the major characteristics of the disease is the presence of regions lacking myelin and an oxidative and inflammatory environment. TGF-β1 and Nrf2 proteins play a fundamental role in different oxidative/inflammatory processes linked to neurodegenerative diseases such as MS. The evidence from different experimental settings has demonstrated a TGF-β1-Nrf2 signaling crosstalk under pathological conditions. However, this possibility has not been explored in experimental models of MS. Here, by using the cuprizone-induced demyelination model of MS, we report that the in vivo pharmacological blockage of the TGF-β1 receptor reduced Nrf2, catalase, and TGFβ-1 protein levels in the demyelination phase of cuprizone administration. In addition, ATP production, locomotor function and cognitive performance were diminished by the treatment. Altogether, our results provide evidence for a crosstalk between TGF-β1 and Nrf2 signaling pathways under CNS demyelination, highlighting the importance of the antioxidant cellular response of neurodegenerative diseases such as MS.

Spatial dynamics of mammalian brain development and neuroinflammation by multimodal tri-omics mapping

The ability to spatially map multiple layers of the omics information over different time points allows for exploring the mechanisms driving brain development, differentiation, arealization, and alterations in disease. Herein we developed and applied spatial tri-omic sequencing technologies, DBiT ARP-seq (spatial ATAC-RNA-Protein-seq) and DBiT CTRP-seq (spatial CUT&Tag-RNA-Protein-seq) together with multiplexed immunofluorescence imaging (CODEX) to map spatial dynamic remodeling in brain development and neuroinflammation. A spatiotemporal tri-omic atlas of the mouse brain was obtained at different stages from postnatal day P0 to P21, and compared to the regions of interest in the human developing brains. Specifically, in the cortical area, we discovered temporal persistence and spatial spreading of chromatin accessibility for the layer-defining transcription factors. In corpus callosum, we observed dynamic chromatin priming of myelin genes across the subregions. Together, it suggests a role for layer specific projection neurons to coordinate axonogenesis and myelination. We further mapped the brain of a lysolecithin (LPC) neuroinflammation mouse model and observed common molecular programs in development and neuroinflammation. Microglia, exhibiting both conserved and distinct programs for inflammation and resolution, are transiently activated not only at the core of the LPC lesion, but also at distal locations presumably through neuronal circuitry. Thus, this work unveiled common and differential mechanisms in brain development and neuroinflammation, resulting in a valuable data resource to investigate brain development, function and disease.

A preclinical mice model of multiple sclerosis based on the toxin-induced double-site demyelination of callosal and cerebellar fibers

BACKGROUND

Multiple sclerosis (MS) is an irreversible progressive CNS pathology characterized by the loss of myelin (i.e. demyelination). The lack of myelin is followed by a progressive neurodegeneration triggering symptoms as diverse as fatigue, motor, locomotor and sensory impairments and/or bladder, cardiac and respiratory dysfunction. Even though there are more than fourteen approved treatments for reducing MS progression, there are still no cure for the disease. Thus, MS research is a very active field and therefore we count with different experimental animal models for studying mechanisms of demyelination and myelin repair, however, we still lack a preclinical MS model assembling demyelination mechanisms with relevant clinical-like signs.

RESULTS

Here, by inducing the simultaneous demyelination of both callosal and cerebellar white matter fibers by the double-site injection of lysolecithin (LPC), we were able to reproduce CNS demyelination, astrocyte recruitment and increases levels of proinflammatory cytokines levels along with motor, locomotor and urinary impairment, as well as cardiac and respiratory dysfunction, in the same animal model. Single site LPC-injections either in corpus callosum or cerebellum only, fails in to reproduce such a complete range of MS-like signs.

CONCLUSION

We here report that the double-site LPC injections treatment evoke a complex MS-like mice model. We hope that this experimental approach will help to deepen our knowledge about the mechanisms of demyelinated diseases such as MS.

Early depletion of gut microbiota shape oligodendrocyte response after traumatic brain injury

White matter injury (WMI) is thought to be a major contributor to long-term cognitive dysfunctions after traumatic brain injury (TBI). This damage occurs partly due to apoptotic death of oligodendrocyte lineage cells (OLCs) after the injury, triggered directly by the trauma or in response to degenerating axons. Recent research suggests that the gut microbiota modulates the inflammatory response through the regulation of peripheral immune cell infiltration after TBI. Additionally, T-cells directly impact OLCs differentiation and proliferation. Therefore, we hypothesized that the gut microbiota plays a critical role in regulating the OLC response to WMI influencing T-cells differentiation and activation. Gut microbial depletion early after TBI chronically reduced re-myelination, acutely decreased OLCs proliferation, and was associated with increased myelin debris accumulation. Surprisingly, the absence of T-cells in gut microbiota depleted mice restored OLC proliferation and remyelination after TBI. OLCs co-cultured with T-cells derived from gut microbiota depleted mice resulted in impaired proliferation and increased expression of MHC-II compared with T cells from control-injured mice. Furthermore, MHC-II expression in OLCs appears to be linked to impaired proliferation under gut microbiota depletion and TBI conditions. Collectively our data indicates that depletion of the gut microbiota after TBI impaired remyelination, reduced OLCs proliferation with concomitantly increased OLC MHCII expression, and required the presence of T cells. This data suggests that T cells are an important mechanistic link by which the gut microbiota modulate the oligodendrocyte response and white matter recovery after TBI.

The interplay of inflammation and remyelination: rethinking MS treatment with a focus on oligodendrocyte progenitor cells

BACKGROUND

Multiple sclerosis (MS) therapeutic goals have traditionally been dichotomized into two distinct avenues: immune-modulatory-centric interventions and pro-regenerative strategies. Oligodendrocyte progenitor cells (OPCs) were regarded for many years solely in concern to their potential to generate oligodendrocytes and myelin in the central nervous system (CNS). However, accumulating data elucidate the multifaceted roles of OPCs, including their immunomodulatory functions, positioning them as cardinal constituents of the CNS's immune landscape.

MAIN BODY

In this review, we will discuss how the two therapeutic approaches converge. We present a model by which (1) an inflammation is required for the appropriate pro-myelinating immune function of OPCs in the chronically inflamed CNS, and (2) the immune function of OPCs is crucial for their ability to differentiate and promote remyelination. This model highlights the reciprocal interactions between OPCs' pro-myelinating and immune-modulating functions. Additionally, we review the specific effects of anti- and pro-inflammatory interventions on OPCs, suggesting that immunosuppression adversely affects OPCs' differentiation and immune functions.

CONCLUSION

We suggest a multi-systemic therapeutic approach, which necessitates not a unidimensional focus but a harmonious balance between OPCs' pro-myelinating and immune-modulatory functions.

Dysregulated Cholinergic Signaling Inhibits Oligodendrocyte Maturation Following Demyelination

Dysregulation of oligodendrocyte progenitor cell (OPC) recruitment and oligodendrocyte differentiation contribute to failure of remyelination in human demyelinating diseases such as multiple sclerosis (MS). Deletion of muscarinic receptor enhances OPC differentiation and remyelination. However, the role of ligand-dependent signaling versus constitutive receptor activation is unknown. We hypothesized that dysregulated acetylcholine (ACh) release upon demyelination contributes to ligand-mediated activation hindering myelin repair. Following chronic cuprizone (CPZ)-induced demyelination (male and female mice), we observed a 2.5-fold increase in ACh concentration. This increase in ACh concentration could be attributed to increased ACh synthesis or decreased acetylcholinesterase-/butyrylcholinesterase (BChE)-mediated degradation. Using choline acetyltransferase (ChAT) reporter mice, we identified increased ChAT-GFP expression following both lysolecithin and CPZ demyelination. ChAT-GFP expression was upregulated in a subset of injured and uninjured axons following intraspinal lysolecithin-induced demyelination. In CPZ-demyelinated corpus callosum, ChAT-GFP was observed in Gfap+ astrocytes and axons indicating the potential for neuronal and astrocytic ACh release. BChE expression was significantly decreased in the corpus callosum following CPZ demyelination. This decrease was due to the loss of myelinating oligodendrocytes which were the primary source of BChE. To determine the role of ligand-mediated muscarinic signaling following lysolecithin injection, we administered neostigmine, a cholinesterase inhibitor, to artificially raise ACh. We identified a dose-dependent decrease in mature oligodendrocyte density with no effect on OPC recruitment. Together, these results support a functional role of ligand-mediated activation of muscarinic receptors following demyelination and suggest that dysregulation of ACh homeostasis directly contributes to failure of remyelination in MS.

Buyang huanwu decoction promotes remyelination via miR-760-3p/GPR17 axis after intracerebral hemorrhage

ETHNOPHARMACOLOGICAL RELEVANCE

The repairment of myelin sheaths is crucial for mitigating neurological impairments of intracerebral hemorrhage (ICH). However, the current research on remyelination processes in ICH remains limited. A representative traditional Chinese medicine, Buyang Huanwu decoction (BYHWD), shows a promising therapeutic strategy for ICH treatment.

AIM OF THE STUDY

To investigate the pro-remyelination effects of BYHWD on ICH and explore the underlying mechanisms.

MATERIALS AND METHODS

The collagenase-induced mice ICH model was created for investigation. BYHWD's protective effects were assessed by behavioral tests and histological staining. Transmission electron microscopy was used for displaying the structure of myelin sheaths. The remyelination and oligodendrocyte differentiation were evaluated by the expressions of myelin proteolipid protein (PLP), myelin basic protein (MBP), MBP/TAU, Olig2/CC1, and PDGFRα/proliferating cell nuclear antigen (PCNA) through RT-qPCR and immunofluorescence. Transcriptomics integrated with disease database analysis and experiments in vivo and in vitro revealed the microRNA-related underlying mechanisms.

RESULTS

Here, we reported that BYHWD promoted the neurological function of ICH mice and improved remyelination by increasing PLP, MBP, and TAU, as well as restoring myelin structure. Besides, we showed that BYHWD promoted remyelination by boosting the differentiation of PDGFRα+ oligodendrocyte precursor cells into olig2+/CC1+ oligodendrocytes. Additionally, we demonstrated that the remyelination effects of BYHWD worked by inhibiting G protein-coupled receptor 17 (GPR17). miRNA sequencing integrated with miRNA database prediction screened potential miRNAs targeting GPR17. By applying immunofluorescence, RNA in situ hybridization and dual luciferase reporter gene assay, we confirmed that BYHWD suppressed GPR17 and improved remyelination by increasing miR-760-3p.

CONCLUSIONS

BYHWD improves remyelination and neurological function in ICH mice by targeting miR-760-3p to inhibit GPR17. This study may shed light on the orchestration of remyelination mechanisms after ICH, thus providing novel insights for developing innovative prescriptions with brain-protective properties.

The combined administration of LNC-encapsulated retinoic acid and calcitriol stimulates oligodendrocyte progenitor cell differentiation in vitro and in vivo after intranasal administration

Intranasal administration is an efficient strategy for bypassing the BBB, favoring drug accumulation in the brain, and improving its efficiency. Lipid nanocapsules (LNC) are suitable nanocarriers for the delivery of lipophilic drugs via this route and can be used to encapsulate lipophilic molecules such as retinoic acid (RA) and calcitriol (Cal). As the hallmarks of multiple sclerosis (MS) are neuroinflammation and oligodendrocyte loss, our hypothesis was that by combining two molecules known for their pro-differentiating properties, encapsulated in LNC, and delivered by intranasal administration, we would stimulate oligodendrocyte progenitor cells (OPC) differentiation into oligodendrocytes and provide a new pro-remyelinating therapy. LNC loaded with RA (LNC-RA) and Cal (LNC-Cal) were stable for at least 8 weeks. The combination of RA and Cal was more efficient than the molecules alone, encapsulated or not, on OPC differentiation in vitro and decreased microglia cell activation in a dose-dependent manner. After the combined intranasal administration of LNC-RA and LNC-Cal in a mouse cuprizone model of demyelination, increased MBP staining was observed in the corpus callosum. In conclusion, intranasal delivery of lipophilic drugs encapsulated in LNC is a promising strategy for myelinating therapies.

Antidepressant potential of total flavonoids from Astragalus in a chronic stress mouse model: Implications for myelination and Wnt/β-catenin/Olig2/Sox10 signaling axis modulation

ETHNOPHARMACOLOGICAL RELEVANCE

Radix Astragali, a versatile traditional Chinese medicinal herb, has a rich history dating back to "Sheng Nong's herbal classic". It has been employed in clinical practice to address various ailments, including depression. One of its primary active components, total flavonoids from Astragalus (TFA), remains unexplored in terms of its potential antidepressant properties. This study delves into the antidepressant effects of TFA using a mouse model subjected to chronic unpredictable mild stress (CUMS).

AIMS OF THE STUDY

The study aimed to scrutinize how TFA influenced depressive behaviors, corticosterone and glutamate levels in the hippocampus, as well as myelin-related protein expression in CUMS mice. Additionally, it sought to explore the involvement of the Wnt/β-catenin/Olig2/Sox10 signaling axis as a potential antidepressant mechanism of TFA.

MATERIALS AND METHODS

Male C57BL/6 mice were subjected to CUMS to induce depressive behaviors. TFA were orally administered at two different doses (50 mg/kg and 100 mg/kg). A battery of behavioral tests, biochemical analyses, immunohistochemistry, UPLC-MS/MS, real-time PCR, and Western blotting were employed to evaluate the antidepressant potential of TFA. The role of the Wnt/β-catenin/Olig2/Sox10 signaling axis in the antidepressant mechanism of TFA was validated through MO3.13 cells.

RESULTS

TFA administration significantly alleviated depressive behaviors in CUMS mice, as evidenced by improved sucrose preference, reduced immobility in tail suspension and forced swimming tests, and increased locomotor activity in the open field test. Moreover, TFA effectively reduced hippocampal corticosterone and glutamate levels and promoted myelin formation in the hippocampus of CUMS mice. Then, TFA increased Olig2 and Sox10 expression while inhibiting the Wnt/β-catenin pathway in the hippocampus of CUMS mice. Finally, we further confirmed the role of TFA in promoting myelin regeneration through the Wnt/β-catenin/Olig2/Sox10 signaling axis in MO3.13 cells.

CONCLUSIONS

TFA exhibited promising antidepressant effects in the CUMS mouse model, facilitated by the restoration of myelin sheaths and regulation of corticosterone, glutamate, Olig2, Sox10, and the Wnt/β-catenin pathway. This research provides valuable insights into the potential therapeutic application of TFA in treating depression, although further investigations are required to fully elucidate the underlying molecular mechanisms and clinical relevance.