Myelin-mediated inhibition of oligodendrocyte precursor differentiation can be overcome by pharmacological modulation of Fyn-RhoA and protein kinase C signalling

Myelin debris phagocytosis in demyelinating disease

Demyelinating diseases are often caused by a variety of triggers, including immune responses, viral infections, malnutrition, hypoxia, or genetic factors, all of which result in the loss of myelin in the nervous system. The accumulation of myelin debris at the lesion site leads to neuroinflammation and inhibits remyelination; therefore, it is crucial to promptly remove the myelin debris. Initially, Fc and complement receptors on cellular surfaces were the primary clearance receptors responsible for removing myelin debris. However, subsequent studies have unveiled the involvement of additional receptors, including Mac-2, TAM receptors, and the low-density lipoprotein receptor-related protein 1, in facilitating the removal process. In addition to microglia and macrophages, which serve as the primary effector cells in the disease phase, a variety of other cell types such as astrocytes, Schwann cells, and vascular endothelial cells have been demonstrated to engage in the phagocytosis of myelin debris. Furthermore, we have concluded that oligodendrocyte precursor cells, as myelination precursor cells, also exhibit this phagocytic capability. Moreover, our research group has innovatively identified the low-density lipoprotein receptor as a potential phagocytic receptor for myelin debris. In this article, we discuss the functional processes of various phagocytes in demyelinating diseases. We also highlight the alterations in signaling pathways triggered by phagocytosis, and provide a comprehensive overview of the various phagocytic receptors involved. Such insights are invaluable for pinpointing potential therapeutic strategies for the treatment of demyelinating diseases by targeting phagocytosis.

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.

Fyn Kinase in Alzheimer's Disease: Unraveling Molecular Mechanisms and Therapeutic Implications

Alzheimer's disease, characterized by the accumulation of abnormal protein aggregates and neuronal damage in the brain, leads to a gradual decline in cognitive function and memory. As a complex neurodegenerative disorder, it involves disruptions in various biochemical pathways and neurotransmitter systems, contributing to the progressive loss of neurons and synaptic connections. The complexity of Alzheimer's signaling pathways complicates treatment, presenting a formidable challenge in the quest for effective therapeutic interventions. A member of the Src family of kinases (SFKs), Fyn, is a type of non-receptor tyrosine kinase that has been linked to multiple essential CNS processes, such as myelination and synaptic transmission. Fyn is an appealing target for AD treatments because it is uniquely linked to the two major pathologies in AD by its interaction with tau, in addition to being activated by amyloid-beta (Aβ) through PrPC. Fyn mediates neurotoxicity and synaptic impairments caused by Aβ and is involved in regulating the process of Aβ synthesis.Additionally, the tau protein's tyrosine phosphorylation is induced by Fyn. Fyn is also a challenging target because of its widespread body expression and strong homology with other kinases of the Src family, which could cause unintentional off-target effects. This review emphasizes signaling pathways mediated by Fyn that govern neuronal development and plasticity while also summarizing the most noteworthy recent research relevant to Fyn kinase's function in the brain. Additionally, the therapeutic inhibition of Fyn kinase has been discussed, with a focus on the Fyn kinase inhibitors that are in clinical trials, which presents a fascinating opportunity for targeting Fyn kinase in the creation of possible therapeutic approaches for the management of Alzheimer's disease.

Constraint-Induced Movement Therapy Promotes Myelin Remodeling and Motor Function by Mediating Sox2/Fyn Signals in Rats With Hemiplegic Cerebral Palsy

OBJECTIVE

Hypoxic-ischemic brain injury in infants often leads to hemiplegic motor dysfunction. The mechanism of their motor dysfunction has been attributed to deficiencies of the transcription factor sex-determining region (SRY) box 2 (Sox2) or the non-receptor-type tyrosine kinase Fyn (involved in neuronal signal transduction), which causes a defect in myelin formation. Constraint-induced movement therapy (CIMT) following cerebral hypoxia-ischemia may stimulate myelin growth by regulating Sox2/Fyn, Ras homolog protein family A (RhoA), and rho-associated kinase 2 (ROCK2) expression levels. This study investigated how Sox2/Fyn regulates myelin remodeling following CIMT to improve motor function in rats with hemiplegic cerebral palsy (HCP).

METHODS

To investigate the mechanism of Sox2 involvement in myelin growth and neural function in rats with HCP, Lentivirus (Lenti)-Sox2 adeno-associated virus and negative control-Lenti-Sox2 (LS) adeno-associated virus were injected into the lateral ventricle. The rats were divided into a control group and an HCP group with different interventions (CIMT, LS, or negative control-LS [NS] treatment), yielding the HCP, HCP plus CIMT (HCP + CIMT), HCP + LS, HCP + LS + CIMT, HCP + NS, and HCP + NS + CIMT groups. Front-limb suspension and RotaRod tests, Golgi-Cox staining, transmission electron microscopy, immunofluorescence staining, western blotting, and quantitative polymerase chain reaction experiments were used to analyze the motor function, dendrite/axon area, myelin ultrastructure, and levels of expression of oligodendrocytes and Sox2/Fyn/RhoA/ROCK2 in the motor cortex.

RESULTS

The rats in the HCP + LS + CIMT group had better values for motor function, dendrite/axon area, myelin ultrastructure, oligodendrocytes, and Sox2/Fyn/RhoA/ROCK2 expression in the motor cortex than rats in the HCP and HCP + NS groups. The improvement of motor function and myelin remodeling, the expression of oligodendrocytes, and the expression of Sox2/Fyn/RhoA/ROCK2 in the HCP + LS group were similar to those in the HCP + CIMT group.

CONCLUSION

CIMT might overcome RhoA/ROCK2 signaling by upregulating the transcription of Sox2 to Fyn in the brain to induce the maturation and differentiation of oligodendrocytes, thereby promoting myelin remodeling and improving motor function in rats with HCP.

IMPACT

The pathway mediated by Sox2/Fyn could be a promising therapeutic target for HCP.

Oligodendrocyte progenitor cells' fate after neonatal asphyxia-Puzzling implications for the development of hypoxic-ischemic encephalopathy

Premature birth or complications during labor can cause temporary disruption of cerebral blood flow, often followed by long-term disturbances in brain development called hypoxic-ischemic (HI) encephalopathy. Diffuse damage to the white matter is the most frequently detected pathology in this condition. We hypothesized that oligodendrocyte progenitor cell (OPC) differentiation disturbed by mild neonatal asphyxia may affect the viability, maturation, and physiological functioning of oligodendrocytes. To address this issue, we studied the effect of temporal HI in the in vivo model in P7 rats with magnetic resonance imaging (MRI), microscopy techniques and biochemical analyses. Moreover, we recreated the injury in vitro performing the procedure of oxygen-glucose deprivation on rat neonatal OPCs to determine its effect on cell viability, proliferation, and differentiation. In the in vivo model, MRI evaluation revealed changes in the volume of different brain regions, as well as changes in the directional diffusivity of water in brain tissue that may suggest pathological changes to myelinated neuronal fibers. Hypomyelination was observed in the cortex, striatum, and CA3 region of the hippocampus. Severe changes to myelin ultrastructure were observed, including delamination of myelin sheets. Interestingly, shortly after the injury, an increase in oligodendrocyte proliferation was observed, followed by an overproduction of myelin proteins 4 weeks after HI. Results verified with the in vitro model indicate, that in the first days after damage, OPCs do not show reduced viability, intensively proliferate, and overexpress myelin proteins and oligodendrocyte-specific transcription factors. In conclusion, despite the increase in oligodendrocyte proliferation and myelin protein expression after HI, the production of functional myelin sheaths in brain tissue is impaired. Presented study provides a detailed description of oligodendrocyte pathophysiology developed in an effect of HI injury, resulting in an altered CNS myelination. The described models may serve as useful tools for searching and testing effective of effective myelination-supporting therapies for HI injuries.

The role of foam cells in spinal cord injury: challenges and opportunities for intervention

Spinal cord injury (SCI) results in a large amount of tissue cell debris in the lesion site, which interacts with various cytokines, including inflammatory factors, and the intrinsic glial environment of the central nervous system (CNS) to form an inhibitory microenvironment that impedes nerve regeneration. The efficient clearance of tissue debris is crucial for the resolution of the inhibitory microenvironment after SCI. Macrophages are the main cells responsible for tissue debris removal after SCI. However, the high lipid content in tissue debris and the dysregulation of lipid metabolism within macrophages lead to their transformation into foamy macrophages during the phagocytic process. This phenotypic shift is associated with a further pro-inflammatory polarization that may aggravate neurological deterioration and hamper nerve repair. In this review, we summarize the phenotype and metabolism of macrophages under inflammatory conditions, as well as the mechanisms and consequences of foam cell formation after SCI. Moreover, we discuss two strategies for foam cell modulation and several potential therapeutic targets that may enhance the treatment of SCI.

Local delivery of AdipoRon from self-assembled microparticles to inhibit myelin lipid uptake and to promote lipid efflux from rat macrophages

Objective.Abundant lipid-laden macrophages are found at the injury site after spinal cord injury (SCI). These cells have been suggested to be pro-inflammatory and neurotoxic. AdipoRon, an adiponectin receptor agonist, has been shown to promote myelin lipid efflux from mouse macrophage foam cells. While it is an attractive therapeutic strategy, systemic administration of AdipoRon is likely to exert off-target effects. In addition, the pathophysiology after SCI in mice is different from that in humans, whereas rat and human SCI share similar functional and histological outcomes. In this study, we evaluated the effects of AdipoRon on rat macrophage foam cells and developed a drug delivery system capable of providing sustained local release of AdipoRon to the injured spinal cord.Approach.Rat macrophages were treated with myelin debris to generate anin vitromodel of SCI foam cells, and the effects of AdipoRon treatment on myelin uptake and efflux were studied. AdipoRon was then loaded into and released from microparticles made from dextran sulfate and fibrinogen for sustained release.Main results.AdipoRon treatment not only significantly promotes efflux of metabolized myelin lipids, but also inhibits uptake of myelin debris. Myelin debris alone does not appear to be inflammatory, but myelin debris treatment potentiates inflammation when administered along with pro-inflammatory lipopolysaccharide (LPS) and interferon-γ. AdipoRon significantly attenuated myelin lipid-induced potentiation of inflammation. Bioactive AdipoRon can be released in therapeutic doses from microparticles.Significance.These data suggest that AdipoRon is a promising therapeutic capable of reducing lipid accumulation via targeting both myelin lipid uptake and efflux, which potentially addresses chronic inflammation following SCI. Furthermore, we developed microparticle-based drug delivery systems for local delivery of AdipoRon to avoid deleterious side effects. This is the first study to release AdipoRon from drug delivery systems designed to reduce lipid accumulation and inflammation in reactive macrophages after SCI.

Growth arrest specific protein 6 alleviated white matter injury after experimental ischemic stroke

Ischemic white matter injury leads to long-term neurological deficits and lacks effective medication. Growth arrest specific protein 6 (Gas6) clears myelin debris, which is hypothesized to promote white matter integrity in experimental stroke models. By the middle cerebral artery occlusion (MCAO) stroke model, we observed that Gas6 reduced infarcted volume and behavior deficits 4 weeks after MCAO. Compared with control mice, Gas6-treatment mice represented higher FA values in the ipsilateral external capsules by MRI DTI scan. The SMI32/MBP ratio of the ipsilateral cortex and striatum was profoundly alleviated by Gas6 administration. Gas6-treatment group manifested thicker myelin sheaths than the control group by electron microscopy. We observed that Gas6 mainly promoted OPC maturation, which was closely related to microglia. Mechanically, Gas6 accelerated microglia-mediated myelin debris clearance and cholesterol transport protein expression (abca1, abcg1, apoc1, apoe) in vivo and in vitro, accordingly less myelin debris and lipid deposited in Gas6 treated stroke mice. HX531 (RXR inhibitor) administration mitigated the functions of Gas6 in speeding up debris clearance and cholesterol transport protein expression. Generally, we concluded that Gas6 cleared myelin debris and promoted cholesterol transportation protein expression through activating RXR, which could be one critical mechanism contributing to white matter repair after stroke.

Microglia promote remyelination independent of their role in clearing myelin debris

Multiple sclerosis (MS) is an inflammatory disease characterized by myelin loss. While therapies exist to slow MS progression, no treatment currently exists for remyelination. Remyelination, linked to reduced disability in MS, relies on microglia and monocyte-derived macrophages (MDMs). This study aims to understand the role of microglia during remyelination by lineage tracing and depleting them. Microglial lineage tracing reveals that both microglia and MDMs initially accumulate, but microglia later dominate the lesion. Microglia and MDMs engulf equal amounts of inhibitory myelin debris, but after microglial depletion, MDMs compensate by engulfing more myelin debris. Microglial depletion does, however, reduce the recruitment and proliferation of oligodendrocyte progenitor cells (OPCs) and impairs their subsequent differentiation and remyelination. These findings underscore the essential role of microglia during remyelination and offer insights for enhancing this process by understanding microglial regulation of remyelination.

Oligodendrocyte progenitor cells differentiation induction with MAPK/ERK inhibitor fails to support repair processes in the chronically demyelinated CNS

Remyelination failure is considered a major obstacle in treating chronic-progressive multiple sclerosis (MS). Studies have shown blockage in the differentiation of resident oligodendrocyte progenitor cells (OPC) into myelin-forming cells, suggesting that pushing OPC into a differentiation program might be sufficient to overcome remyelination failure. Others stressed the need for a permissive environment to allow proper activation, migration, and differentiation of OPC. PD0325901, a MAPK/ERK inhibitor, was previously shown to induce OPC differentiation, non-specific immunosuppression, and a significant therapeutic effect in acute demyelinating MS models. We examined PD0325901 effects in the chronically inflamed central nervous system. Treatment with PD0325901 induced OPC differentiation into mature oligodendrocytes with high morphological complexity. However, treatment of Biozzi mice with chronic-progressive experimental autoimmune encephalomyelitis with PD0325901 showed no clinical improvement in comparison to the control group, no reduction in demyelination, nor induction of OPC migration into foci of demyelination. PD0325901 induced a direct general immunosuppressive effect on various cell populations, leading to a diminished phagocytic capability of microglia and less activation of lymph-node cells. It also significantly impaired the immune-modulatory functions of OPC. Our findings suggest OPC regenerative function depends on a permissive environment, which may include pro-regenerative inflammatory elements. Furthermore, they indicate that maintaining a delicate balance between the pro-myelinating and immune functions of OPC is of importance. Thus, the highly complex mission of creating a pro-regenerative environment depends upon an appropriate immune response controlled in time, place, and intensity. We suggest the need to employ a multi-systematic therapeutic approach, which cannot be achieved through a single molecule-based therapy.

How does Nogo receptor influence demyelination and remyelination in the context of multiple sclerosis?

Multiple sclerosis (MS) can progress with neurodegeneration as a consequence of chronic inflammatory mechanisms that drive neural cell loss and/or neuroaxonal dystrophy in the central nervous system. Immune-mediated mechanisms can accumulate myelin debris in the disease extracellular milieu during chronic-active demyelination that can limit neurorepair/plasticity and experimental evidence suggests that potentiated removal of myelin debris can promote neurorepair in models of MS. The myelin-associated inhibitory factors (MAIFs) are integral contributors to neurodegenerative processes in models of trauma and experimental MS-like disease that can be targeted to promote neurorepair. This review highlights the molecular and cellular mechanisms that drive neurodegeneration as a consequence of chronic-active inflammation and outlines plausible therapeutic approaches to antagonize the MAIFs during the evolution of neuroinflammatory lesions. Moreover, investigative lines for translation of targeted therapies against these myelin inhibitors are defined with an emphasis on the chief MAIF, Nogo-A, that may demonstrate clinical efficacy of neurorepair during progressive MS.

Promoting the Differentiation of Neural Progenitor Cells into Oligodendrocytes through the Induction of Olig2 Expression: A Transcriptomic Study Using RNA-seq Analysis

Oligodendrocytes are the myelinating cells of the central nervous system that facilitate efficient signal transduction. The loss of these cells and the associated myelin sheath can lead to profound functional deficits. Moreover, oligodendrocytes also play key roles in mediating glial-neuronal interactions, which further speaks to their importance in health and disease. Neural progenitor cells (NPCs) are a promising source of cells for the treatment of oligodendrocyte-related neurological diseases due to their ability to differentiate into a variety of cell types, including oligodendrocytes. However, the efficiency of oligodendrocyte differentiation is often low. In this study, we induced the expression of the Olig2 transcription factor in tripotent NPCs using a doxycycline-inducible promoter, such that the extent of oligodendrocyte differentiation could be carefully regulated. We characterized the differentiation profile and the transcriptome of these inducible oligodendrogenic NPCs (ioNPCs) using a combination of qRT-PCR, immunocytochemistry and RNA sequencing with gene ontology (GO) and gene set enrichment analysis (GSEA). Our results show that the ioNPCs differentiated into a significantly greater proportion of oligodendrocytes than the NPCs. The induction of Olig2 expression was also associated with the upregulation of genes involved in oligodendrocyte development and function, as well as the downregulation of genes involved in other cell lineages. The GO and GSEA analyses further corroborated the oligodendrocyte specification of the ioNPCs.

Myelin sheath injury and repairment after subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) can lead to damage to the myelin sheath in white matter. Through classification and analysis of relevant research results, the discussion in this paper provides a deeper understanding of the spatiotemporal change characteristics, pathophysiological mechanisms and treatment strategies of myelin sheath injury after SAH. The research progress for this condition was also systematically reviewed and compared related to myelin sheath in other fields. Serious deficiencies were identified in the research on myelin sheath injury and treatment after SAH. It is necessary to focus on the overall situation and actively explore different treatment methods based on the spatiotemporal changes in the characteristics of the myelin sheath, as well as the initiation, intersection and common action point of the pathophysiological mechanism, to finally achieve accurate treatment. We hope that this article can help researchers in this field to further clarify the challenges and opportunities in the current research on myelin sheath injury and treatment after SAH.

Title: Immunotherapy; a ground-breaking remedy for spinal cord injury with stumbling blocks: An overview

Spinal cord injury (SCI) is a debilitating disorder with no known standard and effective treatment. Despite its ability to exacerbate SCI sequel by accelerating auto-reactive immune cells, an immune response is also considered essential to the healing process. Therefore, immunotherapeutic strategies targeting spinal cord injuries may benefit from the dual nature of immune responses. An increasing body of research suggests that immunization against myelin inhibitors can promote axon remyelination after SCI. However, despite advancements in our understanding of neuroimmune responses, immunoregulation-based therapeutic strategies have yet to receive widespread acceptance. Therefore, it is a prerequisite to enhance the understanding of immune regulation to ensure the safety and efficacy of immunotherapeutic treatments. The objective of the present study was to provide an overview of previous studies regarding the advantages and limitations of immunotherapeutic strategies for functional recovery after spinal cord injury, especially in light of limiting factors related to DNA and cell-based vaccination strategies by providing a novel prospect to lay the foundation for future studies that will help devise a safe and effective treatment for spinal cord injury.

mTORC2 Loss in Oligodendrocyte Progenitor Cells Results in Regional Hypomyelination in the Central Nervous System

In the CNS, oligodendrocyte progenitor cells (OPCs) differentiate into mature oligodendrocytes to generate myelin, an essential component for normal nervous system function. OPC differentiation is driven by signaling pathways, such as mTOR, which functions in two distinct complexes: mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2), containing Raptor or Rictor, respectively. In the current studies, mTORC2 signaling was selectively deleted from OPCs in PDGFRα-Cre X Rictor^fl/fl mice. This study examined developmental myelination in male and female mice, comparing the impact of mTORC2 deletion in the corpus callosum and spinal cord. In both regions, Rictor loss in OPCs resulted in early reduction in myelin RNAs and proteins. However, these deficits rapidly recovered in spinal cord, where normal myelin was noted at P21 and P45. By contrast, the losses in corpus callosum resulted in severe hypomyelination and increased unmyelinated axons. The hypomyelination may result from decreased oligodendrocytes in the corpus callosum, which persisted in animals as old as postnatal day 350. The current studies focus on uniquely altered signaling pathways following mTORC2 loss in developing oligodendrocytes. A major mTORC2 substrate is phospho-Akt-S473, which was significantly reduced throughout development in both corpus callosum and spinal cord at all ages measured, yet this had little impact in spinal cord. Loss of mTORC2 signaling resulted in decreased expression of actin regulators, such as gelsolin in corpus callosum, but only minimal loss in spinal cord. The current study establishes a regionally specific role for mTORC2 signaling in OPCs, particularly in the corpus callosum.SIGNIFICANCE STATEMENT mTORC1 and mTORC2 signaling has differential impact on myelination in the CNS. Numerous studies identify a role for mTORC1, but deletion of Rictor (mTORC2 signaling) in late-stage oligodendrocytes had little impact on myelination in the CNS. However, the current studies establish that deletion of mTORC2 signaling from oligodendrocyte progenitor cells results in reduced myelination of brain axons. These studies also establish a regional impact of mTORC2, with little change in spinal cord in these conditional Rictor deletion mice. Importantly, in both brain and spinal cord, mTORC2 downstream signaling targets were impacted by Rictor deletion. Yet, these signaling changes had little impact on myelination in spinal cord, while they resulted in long-term alterations in myelination in brain.

Enhancing axonal myelination in seniors: A review exploring the potential impact cannabis has on myelination in the aged brain

Consumption of cannabis is on the rise as public opinion trends toward acceptance and its consequent legalization. Specifically, the senior population is one of the demographics increasing their use of cannabis the fastest, but research aimed at understanding cannabis' impact on the aged brain is still scarce. Aging is characterized by many brain changes that slowly alter cognitive ability. One process that is greatly impacted during aging is axonal myelination. The slow degradation and loss of myelin (i.e., demyelination) in the brain with age has been shown to associate with cognitive decline and, furthermore, is a common characteristic of numerous neurological diseases experienced in aging. It is currently not known what causes this age-dependent degradation, but it is likely due to numerous confounding factors (i.e., heightened inflammation, reduced blood flow, cellular senescence) that impact the many cells responsible for maintaining overall homeostasis and myelin integrity. Importantly, animal studies using non-human primates and rodents have also revealed demyelination with age, providing a reliable model for researchers to try and understand the cellular mechanisms at play. In rodents, cannabis was recently shown to modulate the myelination process. Furthermore, studies looking at the direct modulatory impact cannabis has on microglia, astrocytes and oligodendrocyte lineage cells hint at potential mechanisms to prevent some of the more damaging activities performed by these cells that contribute to demyelination in aging. However, research focusing on how cannabis impacts myelination in the aged brain is lacking. Therefore, this review will explore the evidence thus far accumulated to show how cannabis impacts myelination and will extrapolate what this knowledge may mean for the aged brain.

Neurodegeneration in multiple sclerosis

Axonal loss in multiple sclerosis (MS) is a key component of disease progression and permanent neurologic disability. MS is a heterogeneous demyelinating and neurodegenerative disease of the central nervous system (CNS) with varying presentation, disease courses, and prognosis. Immunomodulatory therapies reduce the frequency and severity of inflammatory demyelinating events that are a hallmark of MS, but there is minimal therapy to treat progressive disease and there is no cure. Data from patients with MS, post-mortem histological analysis, and animal models of demyelinating disease have elucidated patterns of MS pathogenesis and underlying mechanisms of neurodegeneration. MRI and molecular biomarkers have been proposed to identify predictors of neurodegeneration and risk factors for disease progression. Early signs of axonal dysfunction have come to light including impaired mitochondrial trafficking, structural axonal changes, and synaptic alterations. With sustained inflammation as well as impaired remyelination, axons succumb to degeneration contributing to CNS atrophy and worsening of disease. These studies highlight the role of chronic demyelination in the CNS in perpetuating axonal loss, and the difficulty in promoting remyelination and repair amidst persistent inflammatory insult. Regenerative and neuroprotective strategies are essential to overcome this barrier, with early intervention being critical to rescue axonal integrity and function. The clinical and basic research studies discussed in this review have set the stage for identifying key propagators of neurodegeneration in MS, leading the way for neuroprotective therapeutic development. This article is categorized under: Immune System Diseases > Molecular and Cellular Physiology Neurological Diseases > Molecular and Cellular Physiology.

Forced Remyelination Promotes Axon Regeneration in a Rat Model of Spinal Cord Injury

Spinal cord injuries result in the loss of motor and sensory functions controlled by neurons located at the site of the lesion and below. We hypothesized that experimentally enhanced remyelination supports axon preservation and/or growth in the total spinal cord transection in rats. Multifocal demyelination was induced by injection of ethidium bromide (EB), either at the time of transection or twice during transection and at 5 days post-injury. We demonstrated that the number of oligodendrocyte progenitor cells (OPCs) significantly increased 14 days after demyelination. Most OPCs differentiated into mature oligodendrocytes by 60-90 dpi in double-EB-injected rats; however, most axons were remyelinated by Schwann cells. A significant number of axons passed the injury epicenter and entered the distant segments of the spinal cord in the double-EB-injected rats. Moreover, some serotoninergic fibers, not detected in control animals, grew caudally through the injury site. Behavioral tests performed at 60-90 dpi revealed significant improvement in locomotor function recovery in double-EB-injected rats, which was impaired by the blockade of serotonin receptors, confirming the important role of restored serotonergic fibers in functional recovery. Our findings indicate that enhanced remyelination per se, without substantial inhibition of glial scar formation, is an important component of spinal cord injury regeneration.

Huntington disease oligodendrocyte maturation deficits revealed by single-nucleus RNAseq are rescued by thiamine-biotin supplementation

The complexity of affected brain regions and cell types is a challenge for Huntington's disease (HD) treatment. Here we use single nucleus RNA sequencing to investigate molecular pathology in the cortex and striatum from R6/2 mice and human HD post-mortem tissue. We identify cell type-specific and -agnostic signatures suggesting oligodendrocytes (OLs) and oligodendrocyte precursors (OPCs) are arrested in intermediate maturation states. OL-lineage regulators OLIG1 and OLIG2 are negatively correlated with CAG length in human OPCs, and ATACseq analysis of HD mouse NeuN-negative cells shows decreased accessibility regulated by OL maturation genes. The data implicates glucose and lipid metabolism in abnormal cell maturation and identify PRKCE and Thiamine Pyrophosphokinase 1 (TPK1) as central genes. Thiamine/biotin treatment of R6/1 HD mice to compensate for TPK1 dysregulation restores OL maturation and rescues neuronal pathology. Our insights into HD OL pathology spans multiple brain regions and link OL maturation deficits to abnormal thiamine metabolism.

Cannabinoid CB1 receptor gene inactivation in oligodendrocyte precursors disrupts oligodendrogenesis and myelination in mice

Cannabinoids are known to modulate oligodendrogenesis and developmental CNS myelination. However, the cell-autonomous action of these compounds on oligodendroglial cells in vivo, and the molecular mechanisms underlying these effects have not yet been studied. Here, by using oligodendroglial precursor cell (OPC)-targeted genetic mouse models, we show that cannabinoid CB₁ receptors exert an essential role in modulating OPC differentiation at the critical periods of postnatal myelination. We found that selective genetic inactivation of CB₁ receptors in OPCs in vivo perturbs oligodendrogenesis and postnatal myelination by altering the RhoA/ROCK signaling pathway, leading to hypomyelination, and motor and cognitive alterations in young adult mice. Conversely, pharmacological CB₁ receptor activation, by inducing E3 ubiquitin ligase-dependent RhoA proteasomal degradation, promotes oligodendrocyte development and CNS myelination in OPCs, an effect that was not evident in OPC-specific CB₁ receptor-deficient mice. Moreover, pharmacological inactivation of ROCK in vivo overcomes the defects in oligodendrogenesis and CNS myelination, and behavioral alterations found in OPC-specific CB₁ receptor-deficient mice. Overall, this study supports a cell-autonomous role for CB₁ receptors in modulating oligodendrogenesis in vivo, which may have a profound impact on the scientific knowledge and therapeutic manipulation of CNS myelination by cannabinoids.

Differential Gene Expression Associated with Soybean Oil Level in the Diet of Pigs

Simple Summary

Findings from the analysis of the pig transcriptome may help to better understand the biological mechanisms that can be modulated by the diet. Thus, the aim of this study was to identify the differentially expressed genes from the skeletal muscle and liver samples of pigs fed diets with two different levels of soybean oil (1.5 or 3%). The FA profile in the tissues was modified by the diet mainly related to monounsaturated (MUFA) and polyunsaturated (PUFA). This nutrigenomics study verified the effect of different levels of soybean oil in the pig diet on the transcriptome profile of skeletal muscle and liver, where the higher level of soybean oil added to the diet led to a higher expression of genes targeting biological processes related to lipid oxidation and consequently to metabolic diseases and inflammation.

Abstract

The aim of this study was to identify the differentially expressed genes (DEG) from the skeletal muscle and liver samples of animal models for metabolic diseases in humans. To perform the study, the fatty acid (FA) profile and RNA sequencing (RNA-Seq) data of 35 samples of liver tissue (SOY1.5, n = 17 and SOY3.0, n = 18) and 36 samples of skeletal muscle (SOY1.5, n = 18 and SOY3.0, n = 18) of Large White pigs were analyzed. The FA profile of the tissues was modified by the diet, mainly those related to monounsaturated (MUFA) and polyunsaturated (PUFA) FA. The skeletal muscle transcriptome analysis revealed 45 DEG (FDR 10%), and the functional enrichment analysis identified network maps related to inflammation, immune processes, and pathways associated with oxidative stress, type 2 diabetes, and metabolic dysfunction. For the liver tissue, the transcriptome profile analysis revealed 281 DEG, which participate in network maps related to neurodegenerative diseases. With this nutrigenomics study, we verified that different levels of soybean oil in the pig diet, an animal model for metabolic diseases in humans, affected the transcriptome profile of skeletal muscle and liver tissue. These findings may help to better understand the biological mechanisms that can be modulated by the diet.

Laminin-511 activates the human induced pluripotent stem cell survival via α6β1 integrin-Fyn-RhoA-ROCK signaling

In human induced pluripotent stem cells (hiPSCs), laminin-511/α6β1 integrin interacts with E-cadherin, an intercellular adhesion molecule, to induce the activation of the PI3K-dependent signaling pathway. The interaction between laminin-511/α6β1 integrin and E-cadherin, an intercellular adhesion molecule, results in protection against apoptosis via the proto-oncogene tyrosine-protein kinase Fyn(Fyn)-RhoA-ROCK signaling pathway and the Ras homolog gene family member A (RhoA)/Rho kinase (ROCK) signaling pathway (the major pathway for cell death). In this paper, the impact of laminin-511 on hiPSC on α6β1 integrin-Fyn-RhoA-ROCK signaling is discussed and explored along with validation experiments. PIK3CA mRNA (mean [standard deviation {SD}]: iMatrix-511, 1.00 [0. 61]; collagen+MFGE8, 0.023 [0.02]; **P<0.01; n=6) and PIK3R1 mRNA (mean [SD]: iMatrix-511, 1.00 [0. 79]; collagen+MFGE8, 0.040 [0.06]; *P<0.05; n=6) were upregulated by iMatrix-511 resulting from an increased expression of Integrin α6 mRNA (mean [SD]: iMatrix-511, 1.00 [0. 42]; collagen+MFGE8, 0.23 [0.05]; **P<0.01; n=6). iMatrix-511 increased the expression of p120-Catenin mRNA (mean [SD]: iMatrix-511, 1.00 [0. 71]; collagen+MFGE8, 0.025 [0.03]; **P<0.01; n=6) and RAC1 mRNA (mean [SD]: iMatrix-511, 1.00 [0. 28]; collagen+MFGE8, 0.39 [0.15]; **P<0.01; n=6) by increasing the expression of E-cadherin mRNA (mean [SD]: iMatrix-511, 1.00 [0. 38]; collagen+MFGE8, 0.16 [0.11]; **P<0.01; n=6). As a result, iMatrix-511 increased the expression of P190 RhoGAP (GTPase-activating proteins) mRNA, such as ARHGAP1 mRNA (mean [SD]: iMatrix-511, 1.00 [0. 57]; collagen+MFGE8, 0.032 [0.03]; **P<0.01; n=6), ARHGAP4 mRNA (mean [SD]: iMatrix-511, 1.00 [0. 56]; collagen+MFGE8, 0.039 [0.049]; **P<0.01; n=6), and ARHGAP5 mRNA (mean [SD]: iMatrix-511, 1.00 [0. 39]; collagen+MFGE8, 0.063 [0.043]; **P<0.01; n=6). Western blotting showed that phospho-Rac1 remained in the cytoplasm and phospho-Fyn showed nuclear transition in iPSCs cultured on iMatrix-511. Proteome analysis showed that PI3K signaling was enhanced and cytoskeletal actin was activated in iPSCs cultured on iMatrix-511. In conclusion, laminin-511 strongly activated the cell survival by promoting α6β1 integrin-Fyn-RhoA-ROCK signaling in hiPSCs.

Rho-Kinase Inhibition Improves the Outcome of Focal Subcortical White Matter Lesions

BACKGROUND

Subcortical white matter lesions are exceedingly common in cerebral small vessel disease and lead to significant cumulative disability without an available treatment. Here, we tested a rho-kinase inhibitor on functional recovery after focal white matter injury.

METHODS

A focal corpus callosum lesion was induced by stereotactic injection of N⁵-(1-iminoethyl)-L-ornithine in mice. Fasudil (10 mg/kg) or vehicle was administered daily for 2 weeks, starting one day after lesion induction. Resting-state functional connectivity and grid walk performance were studied longitudinally, and lesion volumes were determined at one month.

RESULTS

Resting-state interhemispheric functional connectivity significantly recovered between days 1 and 14 in the fasudil group (P<0.001), despite worse initial connectivity loss than vehicle before treatment onset. Grid walk test revealed an increased number of foot faults in the vehicle group compared with baseline, which persisted for at least 4 weeks. In contrast, the fasudil arm did not show an increase in foot faults and had smaller lesions at 4 weeks. Immunohistochemical examination of reactive astrocytosis, synaptic density, and mature oligodendrocytes did not reveal a significant difference between treatment arms.

CONCLUSIONS

These data show that delayed fasudil posttreatment improves functional outcomes after a focal subcortical white matter lesion in mice. Future work will aim to elucidate the mechanisms.

Oligodendrocyte death and myelin loss in the cuprizone model: an updated overview of the intrinsic and extrinsic causes of cuprizone demyelination

The dietary consumption of cuprizone – a copper chelator – has long been known to induce demyelination of specific brain structures and is widely used as model of multiple sclerosis. Despite the extensive use of cuprizone, the mechanism by which it induces demyelination are still unknown. With this review we provide an updated understanding of this model, by showcasing two distinct yet overlapping modes of action for cuprizone-induced demyelination; 1) damage originating from within the oligodendrocyte, caused by mitochondrial dysfunction or reduced myelin protein synthesis. We term this mode of action ‘intrinsic cell damage’. And 2) damage to the oligodendrocyte exerted by inflammatory molecules, brain resident cells, such as oligodendrocytes, astrocytes, and microglia or peripheral immune cells – neutrophils or T-cells. We term this mode of action ‘extrinsic cellular damage’. Lastly, we summarize recent developments in research on different forms of cell death induced by cuprizone, which could add valuable insights into the mechanisms of cuprizone toxicity. With this review we hope to provide a modern understanding of cuprizone-induced demyelination to understand the causes behind the demyelination in MS.

Cerebrospinal fluid of progressive multiple sclerosis patients reduces differentiation and immune functions of oligodendrocyte progenitor cells

Oligodendrocyte progenitor cells (OPCs) are responsible for remyelination in the central nervous system (CNS) in health and disease. For patients with multiple sclerosis (MS), remyelination is not always successful, and the mechanisms differentiating successful from failed remyelination are not well‐known. Growing evidence suggests an immune role for OPCs, in addition to their regenerative role; however, it is not clear if this helps or hinders the regenerative process. We studied the effect of cerebrospinal fluid (CSF) from relapsing MS (rMS) and progressive MS (pMS) patients on primary OPC differentiation and immune gene expression and function. We observed that CSF from either rMS or pMS patients has a differential effect on the ability of mice OPCs to differentiate into mature oligodendrocytes and to express immune functions. CSF of pMS patients impaired differentiation into mature oligodendrocytes. In addition, it led to decreased major histocompatibility complex class (MHC)‐II expression, tumor necrosis factor (TNF)‐α secretion, nuclear factor kappa‐B (NFκB) activation, and less activation and proliferation of T cells. Our findings suggest that OPCs are not only responsible for remyelination, but they may also play an active role as innate immune cells in the CNS.

The roles of microglia and astrocytes in phagocytosis and myelination: Insights from the cuprizone model of multiple sclerosis

In human demyelinating diseases such as multiple sclerosis (MS), an imbalance between demyelination and remyelination can trigger progressive degenerative processes. The clearance of myelin debris (phagocytosis) from the site of demyelination by microglia is critically important to achieve adequate remyelination and to slow the progression of the disease. However, how microglia phagocytose the myelin debris, and why clearance is impaired in MS, is not fully known; likewise, the role of the microglia in remyelination remains unclear. Recent studies using cuprizone (CPZ) as an animal model of central nervous system demyelination revealed that the up‐regulation of signaling proteins in microglia facilitates effective phagocytosis of myelin debris. Moreover, during demyelination, protective mediators are released from activated microglia, resulting in the acceleration of remyelination in the CPZ model. In contrast, inadequate microglial activation or recruitment to the site of demyelination, and the production of toxic mediators, impairs remyelination resulting in progressive demyelination. In addition to the microglia‐mediated phagocytosis, astrocytes play an important role in the phagocytic process by recruiting microglia to the site of demyelination and producing regenerative mediators. The current review is an update of these emerging findings from the CPZ animal model, discussing the roles of microglia and astrocytes in phagocytosis and myelination.

Role of Fyn Kinase Inhibitors in Switching Neuroinflammatory Pathways

Fyn kinase is a member of the Src non-receptor tyrosine kinase family. Fyn is involved in multiple signaling pathways extending from cell proliferation and differentiation to cell adhesion and cell motility, and it has been found to be overexpressed in various types of cancers. In the central nervous system, Fyn exerts several different functions such as axon-glial signal transduction, oligodendrocyte maturation and myelination, and it is implicated in neuroinflammatory processes. Based on these premises, Fyn emerges as an attractive target in cancer and neurodegenerative disease therapy, particularly Alzheimer disease (AD), based on its activation by Aβ via cellular prion protein and its interaction with tau protein. However, Fyn is also a challenging target since the Fyn inhibitors discovered so far, due to the relevant homology of Fyn with other kinases, suffer from off-target effects. This review covers the efforts performed in the last decade to identify and optimize small molecules that effectively inhibit Fyn, both in enzymatic and in cell assays, including drug repositioning practices, as an opportunity of therapeutic intervention in neurodegeneration.

Remyelination in PNS and CNS: current and upcoming cellular and molecular strategies to treat disabling neuropathies

Myelin is a lipid-rich nerve cover that consists of glial cell's plasmalemma layers and accelerates signal conduction. Axon-myelin contact is a source for many developmental and regenerative signals of myelination. Intra- or extracellular factors including both enhancers and inhibitors are other factors affecting the myelination process. Myelin damages are observed in several congenital and hereditary diseases, physicochemical conditions, infections, or traumatic insults, and remyelination is known as an intrinsic response to injuries. Here we discuss some molecular events and conditions involved in de- and remyelination and compare the phenomena of remyelination in CNS and PNS. We have explained applying some of these molecular events in myelin restoration. Finally, the current and upcoming treatment strategies for myelin restoration are explained in three groups of immunotherapy, endogenous regeneration enhancement, and cell therapy to give a better insight for finding the more effective rehabilitation strategies considering the underlying molecular events of a lesion formation and its current condition.

Rnd3 is necessary for the correct oligodendrocyte differentiation and myelination in the central nervous system

Rho small GTPases are proteins with key roles in the development of the central nervous system. Rnd proteins are a subfamily of Rho GTPases, characterized by their constitutive activity. Rnd3/RhoE is a member of this subfamily ubiquitously expressed in the CNS, whose specific functions during brain development are still not well defined. Since other Rho proteins have been linked to the myelination process, we study here the expression and function of Rnd3 in oligodendrocyte development. We have found that Rnd3 is expressed in a subset of oligodendrocyte precursor cells and of mature oligodendrocytes both in vivo and in vitro. We have analyzed the role of Rnd3 in myelination using mice lacking Rnd3 expression (Rnd3^gt/gt mice), showing that these mice exhibit hypomyelination in the brain and a reduction in the number of mature and total oligodendrocytes in the corpus callosum and striatum. The mutants display a decreased expression of several myelin proteins and a reduction in the number of myelinated axons. In addition, myelinated axons exhibit thinner myelin sheaths. In vitro experiments using Rnd3^gt/gt mutant mice showed that the differentiation of the precursor cells is altered in the absence of Rnd3 expression, suggesting that Rnd3 is directly required for the differentiation of oligodendrocytes and, in consequence, for the correct myelination of the CNS. This work shows Rnd3 as a new protein involved in oligodendrocyte maturation, opening new avenues to further study the function of Rnd3 in the development of the central nervous system and its possible involvement in demyelinating diseases.

Traumatic Brain Injury: An Age-Dependent View of Post-Traumatic Neuroinflammation and Its Treatment

Traumatic brain injury (TBI) is a leading cause of death and disability all over the world. TBI leads to (1) an inflammatory response, (2) white matter injuries and (3) neurodegenerative pathologies in the long term. In humans, TBI occurs most often in children and adolescents or in the elderly, and it is well known that immune responses and the neuroregenerative capacities of the brain, among other factors, vary over a lifetime. Thus, age-at-injury can influence the consequences of TBI. Furthermore, age-at-injury also influences the pharmacological effects of drugs. However, the post-TBI inflammatory, neuronal and functional consequences have been mostly studied in experimental young adult animal models. The specificity and the mechanisms underlying the consequences of TBI and pharmacological responses are poorly understood in extreme ages. In this review, we detail the variations of these age-dependent inflammatory responses and consequences after TBI, from an experimental point of view. We investigate the evolution of microglial, astrocyte and other immune cells responses, and the consequences in terms of neuronal death and functional deficits in neonates, juvenile, adolescent and aged male animals, following a single TBI. We also describe the pharmacological responses to anti-inflammatory or neuroprotective agents, highlighting the need for an age-specific approach to the development of therapies of TBI.

Targeting Nuclear Receptors in Neurodegeneration and Neuroinflammation

Nuclear receptors, also known as ligand-activated transcription factors, regulate gene expression upon ligand signals and present as attractive therapeutic targets especially in chronic diseases. Despite the therapeutic relevance of some nuclear receptors in various pathologies, their potential in neurodegeneration and neuroinflammation is insufficiently established. This perspective gathers preclinical and clinical data for a potential role of individual nuclear receptors as future targets in Alzheimer's disease, Parkinson's disease, and multiple sclerosis, and concomitantly evaluates the level of medicinal chemistry targeting these proteins. Considerable evidence suggests the high promise of ligand-activated transcription factors to counteract neurodegenerative diseases with a particularly high potential of several orphan nuclear receptors. However, potent tools are lacking for orphan receptors, and limited central nervous system exposure or insufficient selectivity also compromises the suitability of well-studied nuclear receptor ligands for functional studies. Medicinal chemistry efforts are needed to develop dedicated high-quality tool compounds for the therapeutic validation of nuclear receptors in neurodegenerative pathologies.

Macrophage phagocytosis after spinal cord injury: when friends become foes

After spinal cord injury (SCI), macrophages can exert either beneficial or detrimental effects depending on their phenotype. Aside from their critical role in inflammatory responses, macrophages are also specialized in the recognition, engulfment, and degradation of pathogens, apoptotic cells, and tissue debris. They promote remyelination and axonal regeneration by removing inhibitory myelin components and cellular debris. However, excessive intracellular presence of lipids and dysregulated intracellular lipid homeostasis result in the formation of foamy macrophages. These develop a pro-inflammatory phenotype that may contribute to further neurological decline. Additionally, myelin-activated macrophages play a crucial role in axonal dieback and retraction. Here, we review the opposing functional consequences of phagocytosis by macrophages in SCI, including remyelination and regeneration versus demyelination, degeneration, and axonal dieback. Furthermore, we discuss how targeting the phagocytic ability of macrophages may have therapeutic potential for the treatment of SCI.

Failed, Interrupted, or Inconclusive Trials on Neuroprotective and Neuroregenerative Treatment Strategies in Multiple Sclerosis: Update 2015-2020

In the recent past, a plethora of drugs have been approved for the treatment of multiple sclerosis (MS). These therapeutics are mainly confined to immunomodulatory or immunosuppressive strategies but do not sufficiently address remyelination and neuroprotection. However, several neuroregenerative agents have shown potential in pre-clinical research and entered Phase I to III clinical trials. Although none of these compounds have yet proceeded to approval, understanding the causes of failure can broaden our knowledge about neuroprotection and neuroregeneration in MS. Moreover, most of the investigated approaches are characterised by consistent mechanisms of action and proved convincing efficacy in animal studies. Therefore, learning from their failure will help us to enforce the translation of findings acquired in pre-clinical studies into clinical application. Here, we summarise trials on MS treatment published since 2015 that have either failed or were interrupted due to a lack of efficacy, adverse events, or for other reasons. We further outline the rationale underlying these drugs and analyse the background of failure to gather new insights into MS pathophysiology and optimise future study designs. For conciseness, this review focuses on agents promoting remyelination and medications with primarily neuroprotective properties or unconventional approaches. Failed clinical trials that pursue immunomodulation are presented in a separate article.

Extracellular vesicles and intercellular communication in the central nervous system

Neurons and glial cells of the central nervous system (CNS) release extracellular vesicles (EVs) to the interstitial fluid of the brain and spinal cord parenchyma. EVs contain proteins, nucleic acids and lipids that can be taken up by, and modulate the behaviour of, neighbouring recipient cells. The functions of EVs have been extensively studied in the context of neurodegenerative diseases. However, mechanisms involved in EV-mediated neuron-glial communication under physiological conditions or healthy ageing remain unclear. A better understanding of the myriad roles of EVs in CNS homeostasis is essential for the development of novel therapeutics to alleviate and reverse neurological disturbances of ageing. Proteomic studies are beginning to reveal cell type-specific EV cargo signatures that may one day allow us to target specific neuronal or glial cell populations in the treatment of debilitating neurological disorders. This review aims to synthesise the current literature regarding EV-mediated cell-cell communication in the brain, predominantly under physiological conditions.

B-cells expressing NgR1 and NgR3 are localized to EAE-induced inflammatory infiltrates and are stimulated by BAFF

We have previously reported evidence that Nogo-A activation of Nogo-receptor 1 (NgR1) can drive axonal dystrophy during the neurological progression of experimental autoimmune encephalomyelitis (EAE). However, the B-cell activating factor (BAFF/BlyS) may also be an important ligand of NgR during neuroinflammation. In the current study we define that NgR1 and its homologs may contribute to immune cell signaling during EAE. Meningeal B-cells expressing NgR1 and NgR3 were identified within the lumbosacral spinal cords of ngr1^+/+ EAE-induced mice at clinical score 1. Furthermore, increased secretion of immunoglobulins that bound to central nervous system myelin were shown to be generated from isolated NgR1- and NgR3-expressing B-cells of ngr1^+/+ EAE-induced mice. In vitro BAFF stimulation of NgR1- and NgR3-expressing B cells, directed them into the cell cycle DNA synthesis phase. However, when we antagonized BAFF signaling by co-incubation with recombinant BAFF-R, NgR1-Fc, or NgR3 peptides, the B cells remained in the G0/G1 phase. The data suggest that B cells express NgR1 and NgR3 during EAE, being localized to infiltrates of the meninges and that their regulation is governed by BAFF signaling.

Myelin plasticity modulates neural circuitry required for learning and behavior

Oligodendrocytes, which form the myelin sheaths that insulate axons, regulate conduction velocity. Myelinated axons make up the brain's white matter and contribute to the efficiency of information processing by regulating the timing of neural activity. Traditionally, it has been thought that myelin is a static, inactive insulator around the axon. However, recent studies in humans using magnetic resonance imaging have shown that structural changes in the white matter occur during learning and training, suggesting that 1) white matter change depends on neural activity and 2) activity-dependent changes in white matter are essential for learning and behavior. Furthermore, suppression of oligodendrocytes and their progenitor cells leads to deficits in motor learning and remote fear memory consolidation, suggesting a causal relationship between glial function and the learning process. However, for technical reasons, it remains unclear how myelin-generating glia modulate neural circuitry and what underlying mechanisms they employ to affect learning and behavior. Recent advances in optical and genetic techniques have helped elucidate this mechanism. In this review, we highlight evidence that neural activities regulated by myelin plasticity play a pivotal role in learning and behavior and provide further insight into possible therapeutic targets for treating diseases accompanied by myelin impairment.

Integrative genomics approach identifies conserved transcriptomic networks in Alzheimer's disease

Alzheimer's disease (AD) is a devastating neurological disorder characterized by changes in cell-type proportions and consequently marked alterations of the transcriptome. Here we use a data-driven systems biology meta-analytical approach across three human AD cohorts, encompassing six cortical brain regions, and integrate with multi-scale datasets comprising of DNA methylation, histone acetylation, transcriptome- and genome-wide association studies and quantitative trait loci to further characterize the genetic architecture of AD. We perform co-expression network analysis across more than 1200 human brain samples, identifying robust AD-associated dysregulation of the transcriptome, unaltered in normal human aging. We assess the cell-type specificity of AD gene co-expression changes and estimate cell-type proportion changes in human AD by integrating co-expression modules with single-cell transcriptome data generated from 27 321 nuclei from human postmortem prefrontal cortical tissue. We also show that genetic variants of AD are enriched in a microglial AD-associated module and identify key transcription factors regulating co-expressed modules. Additionally, we validate our results in multiple published human AD gene expression datasets, which can be easily accessed using our online resource (https://swaruplab.bio.uci.edu/consensusAD).

GPR56: An adhesion GPCR involved in brain development, neurological disorders and cancer

GPR56/ADGRG1 is a member of the adhesion G-protein coupled receptor (aGPCR) family and one of the important players in the normal development of the brain. It plays a pivotal role in the diverse neurobiological processes, including cortical formation, oligodendrocyte development, and myelination. Mutations in GPR56 are known to cause brain malformation, myelination defects and are also implied in many cancers, including brain tumors. Since its identification almost two decades ago, GPR56 has emerged from an orphaned and uncharacterized GPCR to an increasingly well studied receptor. Yet, much needs to be understood about GPR56, both in terms of its molecular interactions and biological functions that may be relevant in normal health and disease. The review is focussed on the recent available knowledge of GPR56, which would give useful insights into its known and potential roles in the human brain, neurological disorders, and brain tumors like glioblastoma.

Establishment of a simple one-step method for oligodendrocyte progenitor cell preparation from rodent brains

BACKGROUND

Oligodendrocytes, which form myelin, enable rapid and efficient nerve conduction. Destruction of myelin causes demyelinating diseases such as multiple sclerosis. Primary oligodendrocyte progenitor cells (OPCs) from postnatal rodents have been utilized to elucidate the developmental mechanism of oligodendrocytes in vitro. However, this process is complicated and takes up to several weeks.

NEW METHOD

We established a method to culture OPCs from neonatal rat brain in DMEM/F-12 with Stem-Pro, bFGF (10 ng/mL), and rhPDGF (30 ng/mL). The culture, without shaking or immunopanning, became OPC-enriched rather than a mixed glial culture.

RESULTS

Immunofluorescent analysis using cell lineage markers suggested that these cells were initially glial progenitors, which gradually changed to OPCs with a few cells further differentiating into oligodendrocytes. Using compounds that promote OPC differentiation, we confirmed that these cells were compatible for high-throughput screening in a 96-well plate format. In co-culture with dorsal root ganglion neuron, OPCs showed myelin sheath-like morphologies. This method was also applicable to mouse OPCs.

COMPARISON WITH EXISTING METHODS

Although the purity of the OPCs was not comparable to that after immunopanning, most cells were of the oligodendrocyte lineage at 8 DIV, while less than 10% were astrocytes. This method requires mediums with only two growth factors without any specific equipment like antibodies or magnet and takes simple procedures.

CONCLUSIONS

The simplicity and high yield of our method make it a good choice when working with oligodendrocytes/OPCs. We believe that this method is an affordable protocol for various biological applications without any special techniques or equipment.

Histone Deacetylase SIRT1 Mediates C5b-9-Induced Cell Cycle in Oligodendrocytes

Sublytic levels of C5b-9 increase the survival of oligodendrocytes (OLGs) and induce the cell cycle. We have previously observed that SIRT1 co-localizes with surviving OLGs in multiple sclerosis (MS) plaques, but it is not yet known whether SIRT1 is involved in OLGs survival after exposure to sublytic C5b-9. We have now investigated the role of SIRT1 in OLGs differentiation and the effect of sublytic levels of C5b-9 on SIRT1 and phosphorylated-SIRT1 (Ser27) expression. We also examined the downstream effects of SIRT1 by measuring histone H3 lysine 9 trimethylation (H3K9me3) and the expression of cyclin D1 as a marker of cell cycle activation. OLG progenitor cells (OPCs) purified from the brain of rat pups were differentiated in vitro and treated with sublytic C5b-9 or C5b6. To investigate the signaling pathway activated by C5b-9 and required for SIRT1 expression, we pretreated OLGs with a c-jun antisense oligonucleotide, a phosphoinositide 3-kinase (PI3K) inhibitor (LY294002), and a protein kinase C (PKC) inhibitor (H7). Our data show a significant reduction in phospho-SIRT1 and SIRT1 expression during OPCs differentiation, associated with a decrease in H3K9me3 and a peak of cyclin D1 expression in the first 24 h. Stimulation of OLGs with sublytic C5b-9 resulted in an increase in the expression of SIRT1 and phospho-SIRT1, H3K9me3, cyclin D1 and decreased expression of myelin-specific genes. C5b-9-stimulated SIRT1 expression was significantly reduced after pretreatment with c-jun antisense oligonucleotide, H7 or LY294002. Inhibition of SIRT1 with sirtinol also abolished C5b-9-induced DNA synthesis. Taken together, these data show that induction of SIRT1 expression by C5b-9 is required for cell cycle activation and is mediated through multiple signaling pathways.

The Role of Vesicle Trafficking and Release in Oligodendrocyte Biology

Oligodendrocytes are a subtype of glial cells found within the central nervous system (CNS), responsible for the formation and maintenance of specialized myelin membranes which wrap neuronal axons. The development of myelin requires tight coordination for the cell to deliver lipid and protein building blocks to specific myelin segments at the right time. Both internal and external cues control myelination, thus the reception of these signals also requires precise regulation. In late years, a growing body of evidence indicates that oligodendrocytes, like many other cell types, may use extracellular vesicles (EVs) as a medium for transferring information. The field of EV research has expanded rapidly over the past decade, with new contributions that suggest EVs might have direct involvement in communications with neurons and other glial cells to fine tune oligodendroglial function. This functional role of EVs might also be maladaptive, as it has likewise been implicated in the spreading of toxic molecules within the brain during disease. In this review we will discuss the field's current understanding of extracellular vesicle biology within oligodendrocytes, and their contribution to physiologic and pathologic conditions.

Prognostic Factors for Recovery of Vision in Canine Optic Neuritis of Unknown Etiology: 26 Dogs (2003-2018)

Optic neuritis (ON) is a recognized condition, yet factors influencing recovery of vision are currently unknown. The purpose of this study was to identify prognostic factors for recovery of vision in canine ON of unknown etiology. Clinical databases of three referral hospitals were searched for dogs with presumptive ON based on clinicopathologic, MRI/CT, and fundoscopic findings. Twenty-six dogs diagnosed with presumptive ON of unknown etiology, isolated (I-ON) and MUE-associated (MUE-ON), were included in the study. Their medical records were reviewed retrospectively, and the association of complete recovery of vision with signalment, clinicopathologic findings, and treatment was investigated. Datasets were tested for normality using the D'Agostino and Shapiro-Wilk tests. Individual datasets were compared using the Chi-squared test, Fisher's exact test, and the Mann-Whitney U-test. For multiple comparisons with parametric datasets, the one-way analysis of variance (ANOVA) was performed, and for non-parametric datasets, the Kruskal-Wallis test was performed to test for independence. For all data, averages are expressed as median with interquartile range and significance set at p < 0.05. Twenty-six dogs met the inclusion criteria. Median follow-up was 230 days (range 21–1901 days, mean 496 days). Six dogs (23%) achieved complete recovery and 20 dogs (77%) incomplete or no recovery of vision. The presence of a reactive pupillary light reflex (p = 0.013), the absence of fundoscopic lesions (p = 0.0006), a younger age (p = 0.038), and a lower cerebrospinal fluid (CSF) total nucleated cell count (TNCC) (p = 0.022) were statistically associated with complete recovery of vision. Dogs with I-ON were significantly younger (p = 0.046) and had lower CSF TNCC (p = 0.030) compared to the MUE-ON group. This study identified prognostic factors that may influence complete recovery of vision in dogs with ON. A larger cohort of dogs is required to determine whether these findings are robust and whether additional parameters aid accurate prognosis for recovery of vision in canine ON.

Retrogeniculate Lesion of the Visual Pathways: Retinal Optical Coherence Tomography Angiography Shows Evidence of Transsynaptic Retrograde Degeneration

Transsynaptic retrograde degeneration (TSRD) of the visual pathways is the loss of retinal ganglion cells occurring upstream from a posterior visual pathway lesion. We present a case of a 54-year-old woman with an epidermoid cyst at the right temporo-occipital junction, in whom retinal optical coherence tomography angiography showed a reduction of the superficial retinal capillary density consistent with TSRD. While this reduction has been described in chronic optic neuropathies and pregeniculate lesions, to our knowledge, this is the first case report showing how a reduction in the superficial retinal capillary density occurs also for a postgeniculate lesion.

Ganglion Cell Topography Indicates Pre- or Postnatal Damage to the Retro-Geniculate Visual System, Predicts Visual Field Function and May Identify Cerebral Visual Impairment in Children - A Multiple Case Study

In this paper, we quantify the degree of ganglion cell layer thinning due to retrograde trans-synaptic degeneration (RTSD) from retro-geniculate damage in six cases who had homonymous visual field defects known since childhood. Three had prenatal injuries, occurring close to mid-gestation and in the first parts of the early and late third trimester, respectively, and representing injuries at different early developmental stages. Three had later acquired injuries, at age 1.5, 4 and 13 years. The impact of the injury to the optic radiations was revealed by fibre tractography. The ganglion cell thinning corresponded with the visual field defects and the extent and location of the primary brain damage. The most important sign of RTSD was asymmetry of the ganglion cell topography within the macular area.

The endocannabinoid 2-AG enhances spontaneous remyelination by targeting microglia

Remyelination is an endogenous process by which functional recovery of damaged neurons is achieved by reinstating the myelin sheath around axons. Remyelination has been documented in multiple sclerosis (MS) lesions and experimental models, although it is often incomplete or fails to affect the integrity of the axon, thereby leading to progressive disability. Microglia play a crucial role in the clearance of the myelin debris produced by demyelination and in inflammation-dependent OPC activation, two processes necessary for remyelination to occur. We show here that following corpus callosum demyelination in the TMEV-IDD viral murine model of MS, there is spontaneous and partial remyelination that involves a temporal discordance between OPC mobilization and microglia activation. Pharmacological treatment with the endocannabinoid 2-AG enhances the clearance of myelin debris by microglia and OPC differentiation, resulting in complete remyelination and a thickening of the myelin sheath. These results highlight the importance of targeting microglia during the repair processes in order to enhance remyelination.

Myelin: Methods for Purification and Proteome Analysis

Molecular characterization of myelin is a prerequisite for understanding the normal structure of the axon/myelin-unit in the healthy nervous system and abnormalities in myelin-related disorders. However, reliable molecular profiles necessitate very pure myelin membranes, in particular when considering the power of highly sensitive "omics"-data acquisition methods. Here, we recapitulate the history and recent applications of myelin purification. We then provide our laboratory protocols for the biochemical isolation of a highly pure myelin-enriched fraction from mouse brains and for its proteomic analysis. We also supply methodological modifications when investigating posttranslational modifications, RNA, or myelin from peripheral nerves. Notably, technical advancements in solubilizing myelin are beneficial for gel-based and gel-free myelin proteome analyses. We conclude this article by exemplifying the exceptional power of label-free proteomics in the mass-spectrometric quantification of myelin proteins.

Evaluation of Pupil Fields Using a Newly Developed Perimeter in Glaucoma Patients

PURPOSE

To evaluate objective pupil fields using a newly developed perimeter for the detection of glaucomatous damage.

MATERIALS AND METHODS

Forty-three eyes of 32 glaucoma patients (42-69 years) were examined. Glaucomatous eyes were classified into three stages using the Hodapp-Anderson-Parrish grading scale (early, 16; moderate, 14; and severe, 13 eyes). The head-mounted perimeter "imo" was used to measure the percentage pupil constriction (PPC) of the pupil fields at 36 test points. A stimulus target size of Goldmann V with 0 decibels (dB) light under 31.4 apostilbs (asb) background was presented. Visual fields were measured with the Humphrey Field Analyzer 10-2 program. Using the 3D OCT-2000, 10 × 10 grid of the macular thickness were also obtained. Median correlation coefficients (r) of each examined eye were analyzed between the PPC and visual field sensitivity (dB), and the thickness of the retinal nerve fiber layer (RNFL), ganglion cell layer (GCL)⁺ (GCL + inner plexiform layer [IPL]), and GCL⁺⁺ (RNFL + GCL + IPL), respectively.

RESULTS

Moderate correlations between the PPC and dB (r = 0.44-0.55), and GCL⁺⁺ (r = 0.43-0.45) were obtained in the correspondence analysis of 12 test points. There were no significant differences in glaucoma severity (P = 0.924-1.000). However, some patients with extremely early stage glaucoma (visual field index ≥90%) tended to have poor correlation.

CONCLUSIONS

Pupil fields of the imo generally corresponded to the visual fields and the RNFL + GCL + IPL thickness, even in early glaucoma; however, the examiner must clearly understand the criteria of patient selection.

Can We Design a Nogo Receptor-Dependent Cellular Therapy to Target MS?

The current landscape of therapeutics designed to treat multiple sclerosis (MS) and its pathological sequelae is saturated with drugs that modify disease course and limit relapse rates. While these small molecules and biologicals are producing profound benefits to patients with reductions in annualized relapse rates, the repair or reversal of demyelinated lesions with or without axonal damage, remains the principle unmet need for progressive forms of the disease. Targeting the extracellular pathological milieu and the signaling mechanisms that drive neurodegeneration are potential means to achieve neuroprotection and/or repair in the central nervous system of progressive MS patients. The Nogo-A receptor-dependent signaling mechanism has raised considerable interest in neurological disease paradigms since it can promulgate axonal transport deficits, further demyelination, and extant axonal dystrophy, thereby limiting remyelination. If specific therapeutic regimes could be devised to directly clear the Nogo-A-enriched myelin debris in an expedited manner, it may provide the necessary CNS environment for neurorepair to become a clinical reality. The current review outlines novel means to achieve neurorepair with biologicals that may be directed to sites of active demyelination.