Myelin Formation Research Articles

Polypyrrole-coated poly(l-lactic acid-co-ε-caprolactone)/silk fibroin nanofibrous nerve guidance conduit induced nerve regeneration in rat

According to our previous study, polypyrrole (Ppy) possessed good conductivity and non-cytotoxicity. In this study, the surface of electrospun poly(l-lactic acid-co-ε-caprolactone)/silk fibroin (PLCL/SF) was coated with Ppy to fabricate Ppy-coated nerve guidance conduit (NGC). Firstly, the presence of Ppy on the prepared NGC was characterized and confirmed by scanning electron microscopy (SEM), X-ray photoelectron spectroscopic spectra (XPS) and Fourier transforms infrared spectroscopy (FTIR). Subsequently, Ppy-coated NGC was used to repair a 10 mm sciatic nerve gap in vivo. 4 and 12 weeks after implantation, the regenerated nerve tissues on defect sites were removed and sectioned for further evaluation. Histological analysis with hematoxylin-eosin (HE), toluidine blue (TB), and luxol fast blue (LFB) staining indicated that the coated Ppy could promote SCs proliferation in early post-surgery, and enhance myelin formation in later post-surgery. In consideration of immunofluorescence and morphology observation with SEM and TEM, it showed that the nerve regeneration of Ppy-coated NGC group was close to autograft group, which was better than PLCL/SF NGC. In addition, walking track analysis indicated that Ppy-coated NGC group showed a similar performance compared with the autograft group, and significantly better than PLCL/SF NGC group. These promising results showed the potential of Ppy-coated NGC in peripheral nerve regeneration.

The Effects of Placental Transfusion on 12‐Month Brain Myelin Content in Term Infants: A Randomized Controlled Trial

IntroductionImmediate cord clamping (ICC) continues to be the standard practice in the United States. This results in leaving about 30% of the fetal‐placental iron‐rich blood behind in the placenta and puts an infant at risk for lower iron stores. Evidence (animal and human) suggests iron is critical to early brain white matter development as it plays a significant role in myelin formation. The purpose of this study was to determine, at 12 months of age, if infants who received a full placental transfusion at birth differ in myelin content and developmental outcomes compared to infants who received no placental transfusion. The hypothesis was that healthy, term infants who received a full placental transfusion via delayed cord clamping (DCC) will have greater brain myelin content and better neurodevelopmental outcomes compared to infants who received no placental transfusion (ICC) at 12 months of age.MethodsSeventy‐three term pregnant women with singleton fetuses were enrolled in a prospective randomized controlled trial and randomized to either ICC (< 20 s) or DCC (≥ 5 min). At 4 and 12 months, the infants’ hemoglobin and ferritin levels were measured, and the infants underwent a non‐sedated MRI and neurodevelopmental testing.ResultsMaternal and infant demographics were not different between groups. Mean (SD) cord clamping time was 318 (158) seconds in the DCC group versus 10 (5) seconds in the ICC group (P < .0001). At 4 months, infants who received DCC had higher ferritin levels (91 [57] vs 61 [30] ng/mL, P < .04). At 12 months, infants randomized to DCC had significantly greater brain myelin content in the following brain regions: left and right (R) internal capsule, R parietal, R occipital, R frontal, and R orbital areas. The DCC group had a slightly higher social‐emotional performance than the ICC group using the BITSEA Competence score (17 [3] vs 15 [3], P = .08). No differences were seen in ferritin or hemoglobin levels between groups at 12 months.DiscussionAt 12 months, placental transfusion at birth appears to increase brain myelin content in regions involving motor and visual/spatial pathways and sensory processing. Neurodevelopmental testing suggests a trend of better social‐emotional outcomes associated with DCC. In conclusion, the endowment of iron‐rich blood obtained through DCC may offer a longitudinal advantage for early white matter development in the brain.

Developmental defects and aberrant accumulation of endogenous psychosine in oligodendrocytes in a murine model of Krabbe disease

Krabbe disease (KD), or globoid cell leukodystrophy, is an inherited lysosomal storage disease with leukodystrophy caused by a mutation in the galactosylceramidase (GALC) gene. The majority of patients show the early onset form of KD dominated by cerebral demyelination with apoptotic oligodendrocyte (OL) death. However, the initial pathophysiological changes in developing OLs remain poorly understood. Here, we show that OLs of twitcher mice, an authentic mouse model of KD, exhibited developmental defects and impaired myelin formation in vivo and in vitro. In twitcher mouse brain, abnormal myelination and reduced expression of myelin genes during the period of most active OL differentiation and myelination preceded subsequent progressive OL death and demyelination. Importantly, twitcher mouse OL precursor cells proliferated normally, but their differentiation and survival were intrinsically defective. These defects were associated with aberrant accumulation of endogenous psychosine (galactosylsphingosine) and reduced activation of the Erk1/2 and Akt/mTOR pathways before apoptotic cell death. Collectively, our results demonstrate that GALC deficiency in developing KD OLs profoundly affects their differentiation and maturation, indicating the critical contribution of OL dysfunction to KD pathogenesis.

Lactosylceramide synthases encoded by B4galt5 and 6 genes are pivotal for neuronal generation and myelin formation in mice.

It is uncertain which β4-galactosyltransferase (β4GalT; gene name, B4galt), β4GalT-5 and/or β4GalT-6, is responsible for the production of lactosylceramide (LacCer) synthase, which functions in the initial step of ganglioside biosynthesis. Here, we generated conditional B4galt5 knockout (B4galt5 cKO) mice, using Nestin-Cre mice, and crossed these with B4galt6 KO mice to generate B4galt5 and 6 double KO (DKO) mice in the central nervous system (CNS). LacCer synthase activity and major brain gangliosides were completely absent in brain homogenates from the DKO mice, although LacCer synthase activity was about half its normal level in B4galt5 cKO mice and B4galt6 KO mice. The DKO mice were born normally but they showed growth retardation and motor deficits at 2 weeks and died by 4 weeks of age. Histological analyses showed that myelin-associated proteins were rarely found localized in axons in the cerebral cortex, and axonal and myelin formation were remarkably impaired in the spinal cords of the DKO mice. Neuronal cells, differentiated from neurospheres that were prepared from the DKO mice, showed impairments in neurite outgrowth and branch formation, which can be explained by the fact that neurospheres from DKO mice could weakly interact with laminin due to lack of gangliosides, such as GM1a. Furthermore, the neurons were immature and perineuronal nets (PNNs) were poorly formed in DKO cerebral cortices. Our results indicate that LacCer synthase is encoded by B4galt5 and 6 genes in the CNS, and that gangliosides are indispensable for neuronal maturation, PNN formation, and axonal and myelin formation.

Phenelzine, a small organic compound mimicking the functions of cell adhesion molecule L1, promotes functional recovery after mouse spinal cord injury.

Neural cell adhesion molecule L1 contributes to nervous system development and maintenance by promoting neuronal survival, neuritogenesis, axonal regrowth/sprouting, myelination, and synapse formation and plasticity. L1 also enhances recovery after spinal cord injury and ameliorates neurodegenerative processes in experimental rodent models. Aiming for clinical translation of L1 into therapy we screened for and functionally characterized in vitro the small organic molecule phenelzine, which mimics characteristic L1 functions. The present study was designed to evaluate the potential of this compound in vivo in a mouse model of spinal cord injury. In mice, intraperitoneal injection of phenelzine immediately after severe thoracic compression, and thereafter once daily for 6 weeks, improved hind limb function, reduced astrogliosis and promoted axonal regrowth/sprouting at 4 and 5 weeks after spinal cord injury compared to vehicle control-treated mice. Phenelzine application upregulated L1 expression in the spinal cord and stimulated the cognate L1-mediated intracellular signaling cascades in the spinal cord tissue. Phenelzine-treated mice showed decreased levels of pro-inflammatory cytokines, such as interleukin-1β, interleukin-6, and tumor necrosis factor-α in the injured spinal cord during the acute phase of inflammation. This study provides new insights into the role of phenelzine in L1-mediated neural functions and modulation of inflammation. The combined results raise hopes that phenelzine may develop into a therapeutic agent for nervous system injuries.

Inherited disorders of cobalamin metabolism disrupt nucleocytoplasmic transport of mRNA through impaired methylation/phosphorylation of ELAVL1/HuR.

The molecular mechanisms that underlie the neurological manifestations of patients with inherited diseases of vitamin B12 (cobalamin) metabolism remain to date obscure. We observed transcriptomic changes of genes involved in RNA metabolism and endoplasmic reticulum stress in a neuronal cell model with impaired cobalamin metabolism. These changes were related to the subcellular mislocalization of several RNA binding proteins, including the ELAVL1/HuR protein implicated in neuronal stress, in this cell model and in patient fibroblasts with inborn errors of cobalamin metabolism and Cd320 knockout mice. The decreased interaction of ELAVL1/HuR with the CRM1/exportin protein of the nuclear pore complex and its subsequent mislocalization resulted from hypomethylation at R-217 produced by decreased S-adenosylmethionine and protein methyl transferase CARM1 and dephosphorylation at S221 by increased protein phosphatase PP2A. The mislocalization of ELAVL1/HuR triggered the decreased expression of SIRT1 deacetylase and genes involved in brain development, neuroplasticity, myelin formation, and brain aging. The mislocalization was reversible upon treatment with siPpp2ca, cobalamin, S-adenosylmethionine, or PP2A inhibitor okadaic acid. In conclusion, our data highlight the key role of the disruption of ELAVL1/HuR nuclear export, with genomic changes consistent with the effects of inborn errors of Cbl metabolisms on brain development, neuroplasticity and myelin formation.

To Be or Not to Be: Environmental Factors that Drive Myelin Formation during Development and after CNS Trauma

Oligodendrocytes are specialized glial cells that myelinate central nervous system (CNS) axons. Historically, it was believed that the primary role of myelin was to compactly ensheath axons, providing the insulation necessary for rapid signal conduction. However, mounting evidence demonstrates the dynamic importance of myelin and oligodendrocytes, including providing metabolic support to neurons and regulating axon protein distribution. As such, the development and maintenance of oligodendrocytes and myelin are integral to preserving CNS homeostasis and supporting proper functioning of widespread neural networks. Environmental signals are critical for proper oligodendrocyte lineage cell progression and their capacity to form functional compact myelin; these signals are markedly disturbed by injury to the CNS, which may compromise endogenous myelin repair capabilities. This review outlines some key environmental factors that drive myelin formation during development and compares that to the primary factors that define a CNS injury milieu. We aim to identify developmental factors disrupted after CNS trauma as well as pathogenic factors that negatively impact oligodendrocyte lineage cells, as these are potential therapeutic targets to promote myelin repair after injury or disease.

Schwann-Cell-Specific Deletion of Phosphatidylinositol 4-Kinase Alpha Causes Aberrant Myelination

Active membrane remodeling during myelination relies on phospholipid synthesis and membrane polarization, both of which are known to depend on inositol phospholipids. Here, we show that sciatic nerves of mice lacking phosphatidylinositol 4-kinase alpha (PI4KA) in Schwann cells (SCs) show substantially reduced myelin thickness with grave consequences on nerve conductivity and motor functions. Surprisingly, prolonged inhibition of PI4KA in immortalized mouse SCs failed to decrease plasma membrane phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) levels or PI 3-kinase (PI3K) activation, in spite of large reductions in plasma membrane PI4P levels. Instead, it caused rearrangements of the actin cytoskeleton, which was also observed in sciatic nerves of knockout animals. PI4KA inactivation disproportionally reduced phosphatidylserine, phosphatidylethanolamine, and sphingomyelin content in mutant nerves, with similar changes observed in SCs treated with a PI4KA inhibitor. These studies define a role for PI4KA in myelin formation primarily affecting metabolism of key phospholipids and the actin cytoskeleton.

Microglial transglutaminase-2 drives myelination and myelin repair via GPR56/ADGRG1 in oligodendrocyte precursor cells.

In the central nervous system (CNS), myelin formation and repair are regulated by oligodendrocyte (OL) lineage cells, which sense and integrate signals from their environment, including from other glial cells and the extracellular matrix (ECM). The signaling pathways that coordinate this complex communication, however, remain poorly understood. The adhesion G protein-coupled receptor ADGRG1 (also known as GPR56) is an evolutionarily conserved regulator of OL development in humans, mice, and zebrafish, although its activating ligand for OL lineage cells is unknown. Here, we report that microglia-derived transglutaminase-2 (TG2) signals to ADGRG1 on OL precursor cells (OPCs) in the presence of the ECM protein laminin and that TG2/laminin-dependent activation of ADGRG1 promotes OPC proliferation. Signaling by TG2/laminin to ADGRG1 on OPCs additionally improves remyelination in two murine models of demyelination. These findings identify a novel glia-to-glia signaling pathway that promotes myelin formation and repair, and suggest new strategies to enhance remyelination.

Uncovering the Role of Sox2 in Oligodendroglia.

In the CNS, oligodendrocytes are responsible for the formation of myelin. To build these insulating sheaths surrounding axons, cells of the oligodendrocyte lineage must go through an intricate and temporally matched sequence of proliferation, migration, differentiation, and myelination ([Michalski

Auditory function in Pelizaeus-Merzbacher disease.

Pelizaeus-Merzbacher disease (PMD; MIM 312080), an inherited defect of central nervous system myelin formation, affects individuals in many ways, including their hearing and language abilities. The aim of this study was to assess the auditory abilities in 18 patients with PMD by examining the functional processes along the central auditory pathways using auditory brainstem responses (ABR) and cortical auditory evoked potentials (CAEP) in response to speech sounds. The significant ABR anomalies confirm the existence of dyssynchrony previously described at the level of the brainstem in patients with PMD. Despite the significant auditory dyssynchrony observed at the level of the brainstem, CAEPs were present in most patients, albeit somehow abnormal in terms of morphology and latency, resembling a type of auditory neuropathy spectrum disorder.

10.2 REDOX DYSREGULATION, OLIGODENDROCYTES AND WHITE MATTER ALTERATIONS IN SCHIZOPHRENIA

BackgroundWidespread (Klauser et al., 2016) and progressive (Cropley et al., 2017) cerebral anomalies of white matter diffusion properties (i.e. fractional anisotropy, FA) have been observed in the Australian Schizophrenia Research Bank (ASRB), one of the largest samples of patients with schizophrenia. From a topological perspective, widespread alterations of white matter tend to concentrate into hub regions that interconnect brain areas over long-distances in a so-called “rich-club” (van den Heuvel et al., 2013; Klauser et al., 2016) in which the metabolic demand is high and thus are most likely to suffer from oxidative stress. Evidence from human and animal models suggests that redox dysregulation leading to oxidative stress during neurodevelopment is implicated in schizophrenia pathogenesis (Steullet et al., 2017). At the cellular level, the triad composed of NMDAR hypofunction, neuroinflammation and dopamine dysregulation interacts with redox imbalance and leads to oxidative stress, affecting oligodendrocytes precursor cells (OPC) and parvalbumine interneurons (Steullet et al., 2016). However, the links between redox imbalance, oligodendrocytes and gross alterations of white matter integrity are largely unexplored. Under oxidative stress induced in vitro by impairing the synthesis of glutathione (GSH), the key player in antioxidant defense, OPC showed a decreased proliferation mediated by an upregulation of Fyn kinase activity. In the prefrontal cortex of a mouse model with impaired GSH synthesis, mature oligodendrocyte numbers as well as myelin markers were decreased at peripuberty (Monin et al., 2014). FA was also reduced in fornix-fimbria and anterior commissure, a change accompanied by a reduced conduction velocity (Corcoba et al., 2015).Methods49 patients with psychosis and 64 healthy controls were scanned with the same 3-Tesla scanner. The diffusion spectrum imaging (DSI) sequence included 128 diffusion-weighted images with a maximum b-value of 8000 s mm−2. White matter diffusion properties were estimated using generalized fractional anisotropy (gFA). Total blood cysteine (Cys, protein-bound form, free reduced and free oxidized form), the rate-limiting precursor of GSH, was measured by high performance liquid chromatography from plasma samples collected at the same time-point as MRI brain scans. Whole brain voxel-based analyses were performed using cluster-based non-parametric permutation testing on gFA maps. Cerebral levels of GSH were assessed by localized 1H-MRS measurements from a volume of interest in medial prefrontal cortex.ResultsAs previously described in ASRB, we observed widespread abnormalities of white matter in patients. Interestingly, the degree of white matter alterations (i.e. decreased gFA) patients could be predicted by the levels of blood cysteine, a precursor of GSH, strongly suggesting the important role played by oxidative stress in the pathophysiological mechanism. Also, we found that white matter alterations could be reversed by 6 months of add-on treatment with the antioxidant and GSH precursor N-acetyl-cysteine (NAC). Most importantly, this improvement was positively correlated with an increase in prefrontal GSH levels.DiscussionWe propose that developmental redox imbalance inducing oxidative stress may lead to impairments of oligodendrocytes, myelin formation and eventually to the disruption of fibers integrity and conductivity, especially in brain regions having high metabolic demand. In patients, alterations of white matter are inversely correlated with blood levels of GSH precursor cysteine and could be prevented by the early administration of the antioxidant NAC.

10. THE MOLECULAR MECHANISMS OF SCHIZOPHRENIA FROM GLIAL CELLS PERSPECTIVE

Overall : In the past decade, rapid advances in the field of neuroscience resulted in a dramatic paradigm shift in the way we understand the role of glia in normal brain functions and brain disorder pathology. A growing body of evidence shows that diversified populations of astrocytes, microglia, oligodendrocyte precursors and mature oligodendrocytes play a critical role in the regulation of synaptic functions, blood-brain barrier, immune response regulation, myelination and axonal conduction, and in the synthesis of the extracellular matrix, a key regulator of neural plasticity. Building on this evidence, exciting new findings are beginning to emerge, shedding light on glia abnormalities in schizophrenia and their impact these functions. This symposium aims to discuss and integrate the current state of knowledge on direct evidence for glial abnormalities in schizophrenia and their underlying mechanisms.Dr. Juliana Nascimiento will present novel findings on the effects of NMDAr antagonists and antipsychotics influence glial cell lines and 3D cultures as neurospheres and cerebral organoids. Results from these studies point to the central role of glycolysis, EIF2 signaling and translational machinery in oligodendrocytes and astrocytes. Dr. Paul Klauser will report on elegant investigations on the implication of developmental redox imbalance inducing oxidative stress leading to impairments of oligodendrocytes, myelin formation and eventually to the disruption of white fibers integrity and conductivity, especially in brain regions where the metabolic demand is high. In patients, alterations of white matter were found to be inversely correlated with blood levels of GSH precursor cysteine and could be prevented by the early administration of the antioxidant N-acetyl cysteine. Dr. Sabina Berretta will discuss recent findings on novel modalities of interaction between glial cells, extracellular matrix and neurons, postulated to affect synaptic structural plasticity and axonal conductance. A growing body of evidence from her group shows disruption of such interactions in schizophrenia, potentially contributing to synaptic pathology and impacting neural connectivity. Dr. Dost Ongur will build on previous work showing abnormal diffusion of neuron-specific metabolite NAA in frontal white matter in patients with chronic schizophrenia in the absence of abnormalities in the diffusion of non-specific metabolites Cr and Cho. State-of-the-art recent studies on first episode psychosis patients and matched healthy controls show that NAA diffusion is normal in first episode patients but Cr and Cho diffusion is abnormal, suggesting that white matter abnormalities in non-neuronal elements in early phases of schizophrenia which are followed by neuronal damage in chronic disease.

Molecular Neuropathology of Astrocytes and Oligodendrocytes in Alcohol Use Disorders.

Postmortem studies reveal structural and molecular alterations of astrocytes and oligodendrocytes in both the gray and white matter (GM and WM) of the prefrontal cortex (PFC) in human subjects with chronic alcohol abuse or dependence. These glial cellular changes appear to parallel and may largely explain structural and functional alterations detected using neuroimaging techniques in subjects with alcohol use disorders (AUDs). Moreover, due to the crucial roles of astrocytes and oligodendrocytes in neurotransmission and signal conduction, these cells are very likely major players in the molecular mechanisms underpinning alcoholism-related connectivity disturbances between the PFC and relevant interconnecting brain regions. The glia-mediated etiology of alcohol-related brain damage is likely multifactorial since metabolic, hormonal, hepatic and hemodynamic factors as well as direct actions of ethanol or its metabolites have the potential to disrupt distinct aspects of glial neurobiology. Studies in animal models of alcoholism and postmortem human brains have identified astrocyte markers altered in response to significant exposures to ethanol or during alcohol withdrawal, such as gap-junction proteins, glutamate transporters or enzymes related to glutamate and gamma-aminobutyric acid (GABA) metabolism. Changes in these proteins and their regulatory pathways would not only cause GM neuronal dysfunction, but also disturbances in the ability of WM axons to convey impulses. In addition, alcoholism alters the expression of astrocyte and myelin proteins and of oligodendrocyte transcription factors important for the maintenance and plasticity of myelin sheaths in WM and GM. These changes are concomitant with epigenetic DNA and histone modifications as well as alterations in regulatory microRNAs (miRNAs) that likely cause profound disturbances of gene expression and protein translation. Knowledge is also available about interactions between astrocytes and oligodendrocytes not only at the Nodes of Ranvier (NR), but also in gap junction-based astrocyte-oligodendrocyte contacts and other forms of cell-to-cell communication now understood to be critical for the maintenance and formation of myelin. Close interactions between astrocytes and oligodendrocytes also suggest that therapies for alcoholism based on a specific glial cell type pathology will require a better understanding of molecular interactions between different cell types, as well as considering the possibility of using combined molecular approaches for more effective therapies.

Pericytes modulate myelination in the central nervous system.

Multiple sclerosis is a highly prevalent chronic demyelinating disease of the central nervous system. Remyelination is the major therapeutic goal for this disorder. The lack of detailed knowledge about the cellular and molecular mechanisms involved in myelination restricts the design of effective treatments. A recent study by using [De La Fuente et al. (2017) Cell Reports, 20(8): 1755-1764] by using state-of-the-art techniques, including pericyte-deficient mice in combination with induced demyelination, reveal that pericytes participate in central nervous system regeneration. Strikingly, pericytes presence is essential for oligodendrocyte progenitors differentiation and myelin formation during remyelination in the brain. The emerging knowledge from this research will be important for the treatment of multiple sclerosis.

IGFBP-7 inhibits the differentiation of oligodendrocyte precursor cells via regulation of Wnt/β-Catenin signaling.

Oligodendrocytes (OLs) are glial cells that form myelin sheaths in the central nervous system. Myelin sheath plays important role in nervous system and loss of it in neurodegenerative diseases can lead to impairment of movement. Understanding the signals and factors that regulate OL differentiation can help to address novel strategies for improving myelin repair in neurodegenerative diseases. The aim of this study was to investigate the role of insulin-like growth factor-binding proteins 7 (IGFBP-7) in differentiating OL precursor cells (OPCs). It was found that oligodendrocyte precursors undergoing differentiation were accompanied by selective expression of IGFBP-7. In addition, knockdown of IGFBP-7 promoted differentiation of oligodendrocytes and increased formation of myelin in cultured cells. In contrast, excessive expression of IGFBP-7 inhibited differentiation of oligodendrocytes. Furthermore, overexpression of IGFBP-7 in oligodendrocyte precursor cells increased transcription of Wnt target genes and promoted β-Catenin nuclear translocation. These findings suggest that IGFBP-7 negatively regulates differentiation of oligodendrocyte precursor cells via regulation of Wnt/β-Catenin signaling.

Activin receptors regulate the oligodendrocyte lineage in health and disease

The most prevalent neurological disorders of myelin include perinatal brain injury leading to cerebral palsy in infants and multiple sclerosis in adults. Although these disorders have distinct etiologies, they share a common neuropathological feature of failed progenitor differentiation into myelin-producing oligodendrocytes and lack of myelin, for which there is an unmet clinical need. Here, we reveal that a molecular pathology common to both disorders is dysregulation of activin receptors and that activin receptor signaling is required for the majority of myelin generation in development and following injury. Using a constitutive conditional knockout of all activin receptor signaling in oligodendrocyte lineage cells, we discovered this signaling to be required for myelination via regulation of oligodendrocyte differentiation and myelin compaction. These processes were found to be dependent on the activin receptor subtype Acvr2a, which is expressed during oligodendrocyte differentiation and axonal ensheathment in development and following myelin injury. During efficient myelin regeneration, Acvr2a upregulation was seen to coincide with downregulation of Acvr2b, a receptor subtype with relatively higher ligand affinity; Acvr2b was shown to be dispensable for activin receptor-driven oligodendrocyte differentiation and its overexpression was sufficient to impair the abovementioned ligand-driven responses. In actively myelinating or remyelinating areas of human perinatal brain injury and multiple sclerosis tissue, respectively, oligodendrocyte lineage cells expressing Acvr2a outnumbered those expressing Acvr2b, whereas in non-repairing lesions Acvr2b+ cells were increased. Thus, we propose that following human white matter injury, this increase in Acvr2b expression would sequester ligand and consequently impair Acvr2a-driven oligodendrocyte differentiation and myelin formation. Our results demonstrate dysregulated activin receptor signaling in common myelin disorders and reveal Acvr2a as a novel therapeutic target for myelin generation following injury across the lifespan.

Iron released from reactive microglia by noggin improves myelin repair in the ischemic brain

We previously reported that the bone morphogenetic protein (BMP) antagonist, noggin, improved the repair process with an increase in the reactive microglia/macrophage population in the ischemic brain. Since BMP plays a role in intracellular iron homeostasis via the hepcidin/ferroportin axis, and iron is required for myelination, this study was aimed to determine whether noggin affected iron status and remyelination in the brain following ischemic stroke. We further examined the effect of blocking the BMP/hepcidin pathway on reactive microglia (BV2) and myelination of oligodendroglial cells (MO3.13) to define the link between microglial iron status and myelin formation. Following the noggin infusion into the ischemic brain of mice, the induction of hepcidin and ferritin protein levels decreased, and the number of myelinated axons and myelin thickness increased at 8 weeks after ischemic stroke. Noggin repressed the increase in hepcidin and ferritin levels in BV2 exposed to lipopolysaccharide (LPS) and oxygen/glucose deprivation and reperfusion (OGD/R). When MO3.13 were exposed to the conditioned media from noggin-treated BV2 (noggin CM) during reperfusion, OGD/R-induced MO3.13 cell death was reduced. Under normal conditions, noggin CM induced myelin production with an increase in ferritin levels in MO3.13, which was reversed by the iron chelator, deferoxamine. These results indicated that noggin altered the iron status in reactive microglia from the iron-storing to the iron-releasing phenotype, which contributed to myelin synthesis by providing iron. We suggest that the BMP/hepcidin pathway can be a target for the regulation of the iron status in microglia to enhance remyelination in the ischemic brain.

CLC-2 is a positive modulator of oligodendrocyte precursor cell differentiation and myelination.

Oligodendrocytes (OLs) are myelin-forming cells that are present within the central nervous system. Impaired oligodendrocyte precursor cell (OPC) differentiation into mature OLs is a major cause of demyelination diseases. Therefore, identifying the underlying molecular mechanisms of OPC differentiation is crucial to understand the processes of myelination and demyelination. It has been acknowledged that various extrinsic and intrinsic factors are involved in the control of OPC differentiation; however, the function of ion channels, particularly the voltage-gated chloride channel (CLC), in OPC differentiation and myelination are not fully understood. The present study demonstrated that CLC-2 may be a positive modulator of OPC differentiation and myelination. Western blotting results revealed that CLC-2 was expressed in both OPCs and OLs. Furthermore, CLC-2 currents (ICLC-2) were recorded in both types of cells. The inhibition of ICLC-2 by GaTx2, a blocker of CLC-2, was demonstrated to be higher in OPCs compared with OLs, indicating that CLC-2 may serve a role in OL differentiation. The results of western blotting and immunofluorescence staining also demonstrated that the expression levels of myelin basic protein were reduced following GaTx2 treatment, indicating that the differentiation of OPCs into OLs was inhibited following CLC-2 inhibition. In addition, following western blot analysis, it was also demonstrated that the protein expression of the myelin proteins yin yang 1, myelin regulatory factor, Smad-interacting protein 1 and sex-determining region Y-box 10 were regulated by CLC-2 inhibition. Taken together, the results of the present study indicate that CLC-2 may be a positive regulator of OPC differentiation and able to contribute to myelin formation and repair in myelin-associated diseases by controlling the number and open state of CLC-2 channels.

Sox2 Is Essential for Oligodendroglial Proliferation and Differentiation during Postnatal Brain Myelination and CNS Remyelination.

In the CNS, myelination and remyelination depend on the successful progression and maturation of oligodendroglial lineage cells, including proliferation and differentiation of oligodendroglial progenitor cells (OPCs). Previous studies have reported that Sox2 transiently regulates oligodendrocyte (OL) differentiation in the embryonic and perinatal spinal cord and appears dispensable for myelination in the postnatal spinal cord. However, the role of Sox2 in OL development in the brain has yet to be defined. We now report that Sox2 is an essential positive regulator of developmental myelination in the postnatal murine brain of both sexes. Stage-specific paradigms of genetic disruption demonstrated that Sox2 regulated brain myelination by coordinating upstream OPC population supply and downstream OL differentiation. Transcriptomic analyses further supported a crucial role of Sox2 in brain developmental myelination. Consistently, oligodendroglial Sox2-deficient mice developed severe tremors and ataxia, typical phenotypes indicative of hypomyelination, and displayed severe impairment of motor function and prominent deficits of brain OL differentiation and myelination persisting into the later CNS developmental stages. We also found that Sox2 was required for efficient OPC proliferation and expansion and OL regeneration during remyelination in the adult brain and spinal cord. Together, our genetic evidence reveals an essential role of Sox2 in brain myelination and CNS remyelination, and suggests that manipulation of Sox2 and/or Sox2-mediated downstream pathways may be therapeutic in promoting CNS myelin repair.SIGNIFICANCE STATEMENT Promoting myelin formation and repair has translational significance in treating myelin-related neurological disorders, such as periventricular leukomalacia and multiple sclerosis in which brain developmental myelin formation and myelin repair are severely affected, respectively. In this report, analyses of a series of genetic conditional knock-out systems targeting different oligodendrocyte stages reveal a previously unappreciated role of Sox2 in coordinating upstream proliferation and downstream differentiation of oligodendroglial lineage cells in the mouse brain during developmental myelination and CNS remyelination. Our study points to the potential of manipulating Sox2 and its downstream pathways to promote oligodendrocyte regeneration and CNS myelin repair.