Nfat/calcineurin signaling promotes oligodendrocyte differentiation and myelination by transcription factor network tuning

The myelination-associated G protein-coupled receptor 37 is regulated by Zfp488, Nkx2.2, and Sox10 during oligodendrocyte differentiation

Oligodendrocyte differentiation and myelination in the central nervous system are controlled and coordinated by a complex gene regulatory network that contains several transcription factors, including Zfp488 and Nkx2.2. Despite the proven role in oligodendrocyte differentiation little is known about the exact mode of Zfp488 and Nkx2.2 action, including their target genes. Here, we used overexpression of Zfp488 and Nkx2.2 in differentiating CG4 cells to identify aspects of the oligodendroglial expression profile that depend on these transcription factors. Although both transcription factors are primarily described as repressors, the detected changes argue for an additional function as activators. Among the genes activated by both Zfp488 and Nkx2.2 was the G protein-coupled receptor Gpr37 that is important during myelination. In agreement with a positive effect on Gpr37 expression, downregulation of the G protein-coupled receptor was observed in Zfp488- and in Nkx2.2-deficient oligodendrocytes in the mouse. We also identified several potential regulatory regions of the Gpr37 gene. Although Zfp488 and Nkx2.2 both bind to one of the regulatory regions downstream of the Gpr37 gene in vivo, none of the regulatory regions was activated by either transcription factor alone. Increased activation by Zfp488 or Nkx2.2 was only observed in the presence of Sox10, a transcription factor continuously present in oligodendroglial cells. Our results argue that both Zfp488 and Nkx2.2 also act as transcriptional activators during oligodendrocyte differentiation and cooperate with Sox10 to allow the expression of Gpr37 as a modulator of the myelination process.

Sox10 Activity and the Timing of Schwann Cell Differentiation Are Controlled by a Tle4-Dependent Negative Feedback Loop

The HMG-domain containing transcription factor Sox10 plays a crucial role in regulating Schwann cell survival and differentiation and is expressed throughout the entire Schwann cell lineage. While its importance in peripheral myelination is well established, little is known about its role in the early stages of Schwann cell development. In a search for direct target genes of Sox10 in Schwann cell precursors, the transcriptional co-repressor Tle4 was identified. At least two regions upstream of the Tle4 gene appear involved in mediating the Sox10-dependent activation. Once induced, Tle4 works in tandem with the bHLH transcriptional repressor Hes1 and exerts a dual inhibitory effect on Sox10 by preventing the Sox10 protein from transcriptionally activating maturation genes and by suppressing Sox10 expression through known enhancers of the gene. This mechanism establishes a regulatory barrier that prevents premature activation of factors involved in differentiation and myelin formation by Sox10 in immature Schwann cells. The identification of Tle4 as a critical downstream target of Sox10 sheds light on the gene regulatory network in the early phases of Schwann cell development. It unravels an elaborate regulatory circuitry that fine-tunes the timing and extent of Schwann cell differentiation and myelin gene expression.

Transcription factor Olig2 is a major downstream effector of histone demethylase Phf8 during oligodendroglial development

The plant homeodomain finger protein Phf8 is a histone demethylase implicated by mutation in mice and humans in neural crest defects and neurodevelopmental disturbances. Considering its widespread expression in cell types of the central nervous system, we set out to determine the role of Phf8 in oligodendroglial cells to clarify whether oligodendroglial defects are a possible contributing factor to Phf8-dependent neurodevelopmental disorders. Using loss- and gain-of-function approaches in oligodendroglial cell lines and primary cell cultures, we show that Phf8 promotes the proliferation of rodent oligodendrocyte progenitor cells and impairs their differentiation to oligodendrocytes. Intriguingly, Phf8 has a strong positive impact on Olig2 expression by acting on several regulatory regions of the gene and changing their histone modification profile. Taking the influence of Olig2 levels on oligodendroglial proliferation and differentiation into account, Olig2 likely acts as an important downstream effector of Phf8 in these cells. In line with such an effector function, ectopic Olig2 expression in Phf8-deficient cells rescues the proliferation defect. Additionally, generation of human oligodendrocytes from induced pluripotent stem cells did not require PHF8 in a system that relies on forced expression of Olig2 during oligodendroglial induction. We conclude that Phf8 may impact nervous system development at least in part through its action in oligodendroglial cells.

Exosome-specific loading Sox10 for the treatment of Cuprizone-induced demyelinating model

Demyelination is a pathological feature commonly observed in various central nervous system diseases. It is characterized by the aggregation of oligodendrocyte progenitor cells (OPCs) in the lesion area, which face difficulties in differentiating into mature oligodendrocytes (OLGs). The differentiation of OPCs requires the presence of Sox10, but its expression decreases under pathological conditions. Therefore, we propose a therapeutic strategy to regulate OPCs differentiation and achieve myelin repair by endogenously loading Sox10 into exosomes. To accomplish this, we generated a lentivirus-armed Sox10 that could anchor to the inner surface of the exosome membrane. We then infected HEK293 cells to obtain exosomes with high expression of Sox10 (exosomes-Sox10, ExoSs). In vitro, experiments confirmed that both Exos and ExoSs can be uptaken by OPCs, but only ExoSs exhibit a pro-differentiation effect on OPCs. In vivo, we administered PBS, Exos, and ExoSs to cuprizone-induced demyelinating mice. The results demonstrated that ExoSs can regulate the differentiation of PDGFRα+ OPCs into APC+ OLGs and reduce myelin damage in the corpus callosum region of the mouse brain compared to other groups. Further testing suggests that Sox10 may have a reparative effect on the myelin sheath by enhancing the expression of MBP, possibly facilitated by the exosome delivery of the protein into the lesion. This endogenously loaded technology holds promise as a strategy for protein-based drugs in the treatment of demyelinating diseases.

Molecular mechanism of lncRNAs in pathogenesis and diagnosis of auto-immune diseases, with a special focus on lncRNA-based therapeutic approaches

Autoimmune diseases are a diverse set of conditions defined by organ damage due to abnormal innate and acquired immune system responses. The pathophysiology of autoimmune disorders is exceedingly intricate and has yet to be fully understood. The study of long non-coding RNAs (lncRNAs), non-protein-coding RNAs with at least 200 nucleotides in length, has gained significant attention due to the completion of the human genome project and the advancement of high-throughput genomic approaches. Recent research has demonstrated how lncRNA alters disease development to different degrees. Although lncRNA research has made significant progress in cancer and generative disorders, autoimmune illnesses are a relatively new research area. Moreover, lncRNAs play crucial functions in differentiating various immune cells, and their potential relationships with autoimmune diseases have received growing attention. Because of the importance of Th17/Treg axis in auto-immune disease development, in this review, we discuss various molecular mechanisms by which lncRNAs regulate the differentiation of Th17/Treg cells. Also, we reviewed recent findings regarding the several approaches in the application of lncRNAs in the diagnosis and treatment of human autoimmune diseases, as well as current challenges in lncRNA-based therapeutic approaches to auto-immune diseases.

Erythropoietin regulates developmental myelination in the brain stimulating postnatal oligodendrocyte maturation

Myelination is a process tightly regulated by a variety of neurotrophic factors. Here, we show-by analyzing two transgenic mouse lines, one overexpressing EPO selectively in the brain Tg21(PDGFB-rhEPO) and another with targeted removal of EPO receptors (EPORs) from oligodendrocyte progenitor cells (OPC)s (Sox10-cre;EpoRfx/fx mice)-a key function for EPO in regulating developmental brain myelination. Overexpression of EPO resulted in faster postnatal brain growth and myelination, an increased number of myelinating oligodendrocytes, faster axonal myelin ensheathment, and improved motor coordination. Conversely, targeted ablation of EPORs from OPCs reduced the number of mature oligodendrocytes and impaired motor coordination during the second postnatal week. Furthermore, we found that EPORs are transiently expressed in the subventricular zone (SVZ) during the second postnatal week and EPO increases the postnatal expression of essential oligodendrocyte pro-differentiation and pro-maturation (Nkx6.2 and Myrf) transcripts, and the Nfatc2/calcineurin pathway. In contrast, ablation of EPORs from OPCs inactivated the Erk1/2 pathway and reduced the postnatal expression of the transcripts. Our results reveal developmental time windows in which EPO therapies could be highly effective for stimulating oligodendrocyte maturation and myelination.

Exploring the heterogeneous transcriptional response of the CNS to systemic LPS and Poly(I:C)

Peripheral contact to pathogen-associated molecular patterns (PAMPs) evokes a systemic innate immune response which is rapidly relayed to the central nervous system (CNS). The remarkable cellular heterogeneity of the CNS poses a significant challenge to the study of cell type and stimulus dependent responses of neural cells during acute inflammation. Here we utilized single nuclei RNA sequencing (snRNAseq), serum proteome profiling and primary cell culture methods to systematically compare the acute response of the mammalian brain to the bacterial PAMP lipopolysaccharide (LPS) and the viral PAMP polyinosinic:polycytidylic acid (Poly(I:C)), at single cell resolution. Our study unveiled convergent transcriptional cytokine and cellular stress responses in brain vascular and ependymal cells and a downregulation of several key mediators of directed blood brain barrier (BBB) transport. In contrast the neuronal response to PAMPs was limited in acute neuroinflammation. Moreover, our study highlighted the dominant role of IFN signalling upon Poly(I:C) challenge, particularly in cells of the oligodendrocyte lineage. Collectively our study unveils heterogeneous, shared and distinct cell type and stimulus dependent acute responses of the CNS to bacterial and viral PAMP challenges. Our findings highlight inflammation induced dysregulations of BBB-transporter gene expression, suggesting potential translational implications on drug pharmacokinetics variability during acute neuroinflammation. The pronounced dependency of oligodendrocytes on IFN stimulation during viral PAMP challenges, emphasizes their limited molecular viral response repertoire.

Oligodendrocyte pathology in Huntington's disease: from mechanisms to therapeutics

Oligodendrocytes (OLGs), highly specialized glial cells that wrap axons with myelin sheaths, are critical for brain development and function. There is new recognition of the role of OLGs in the pathogenesis of neurodegenerative diseases (NDDs), including Huntington's disease (HD), a prototypic NDD caused by a polyglutamine tract expansion in huntingtin (HTT), which results in gain- and loss-of-function effects. Clinically, HD is characterized by a constellation of motor, cognitive, and psychiatric disturbances. White matter (WM) structures, representing myelin-rich regions of the brain, are profoundly affected in HD, and recent findings reveal oligodendroglia dysfunction as an early pathological event. Here, we focus on mechanisms that underlie oligodendroglial deficits and dysmyelination in the progression of the disease, highlighting the pathogenic contributions of mutant HTT (mHTT). We also discuss potential therapeutic implications involving these molecular pathways.

NFAT signaling dysregulation in cancer: Emerging roles in cancer stem cells

The nuclear factor of activated T cells (NFAT) was first identified as a transcriptional regulator of activated T cells. The NFAT family is involved in the development of tumors. Furthermore, recent evidence reveals that NFAT proteins regulate the development of inflammatory and immune responses. New discoveries have also been made about the mechanisms by which NFAT regulates cancer progression through cancer stem cells (CSC). Here, we discuss the role of the NFAT family in the immune system and various cancer types.

Identification of Myelin Basic Protein Proximity Interactome Using TurboID Labeling Proteomics

Myelin basic protein (MBP) is one of the key structural elements of the myelin sheath and has autoantigenic properties in multiple sclerosis (MS). Its intracellular interaction network is still partially deconvoluted due to the unfolded structure, abnormally basic charge, and specific cellular localization. Here we used the fusion protein of MBP with TurboID, an engineered biotin ligase that uses ATP to convert biotin to reactive biotin-AMP that covalently attaches to nearby proteins, to determine MBP interactome. Despite evident benefits, the proximity labeling proteomics technique generates high background noise, especially in the case of proteins tending to semi-specific interactions. In order to recognize unique MBP partners, we additionally mapped protein interaction networks for deaminated MBP variant and cyclin-dependent kinase inhibitor 1 (p21), mimicking MBP in terms of natively unfolded state, size and basic amino acid clusters. We found that in the plasma membrane region, MBP is colocalized with adhesion proteins occludin and myelin protein zero-like protein 1, solute carrier family transporters ZIP6 and SNAT1, Eph receptors ligand Ephrin-B1, and structural components of the vesicle transport machinery-synaptosomal-associated protein 23 (SNAP23), vesicle-associated membrane protein 3 (VAMP3), protein transport protein hSec23B and cytoplasmic dynein 1 heavy chain 1. We also detected that MBP potentially interacts with proteins involved in Fe²⁺ and lipid metabolism, namely, ganglioside GM2 activator protein, long-chain-fatty-acid-CoA ligase 4 (ACSL4), NADH-cytochrome b5 reductase 1 (CYB5R1) and metalloreductase STEAP3. Assuming the emerging role of ferroptosis and vesicle cargo docking in the development of autoimmune neurodegeneration, MBP may recruit and regulate the activity of these processes, thus, having a more inclusive role in the integrity of the myelin sheath.

Myelinated axon as a plastic cable regulating brain functions

Each oligodendrocyte (OC) forms myelin approximately in around 10 different axons to coordinate information transfer by regulating conduction velocity in the central nervous system (CNS). In the classical view, myelin has been considered a static structure that rarely turns over under healthy conditions because myelin tightly holds axons by their laminar complex structure. However, in recent decades, the classical views of static myelin have been renewed with pioneering studies that showed plastic changes in myelin throughout life with new experiences, such as the acquisition of new motor skills and the formation of memory. These changes in myelin regulate conduction velocity to optimize the temporal pattern of neuronal circuit activity among distinct brain regions associated with skill learning and memory. Here, we introduce pioneering studies and discuss the implications of plastic myelin on neural circuits and brain function.

Inhibition of CXCR2 enhances CNS remyelination via modulating PDE10A/cAMP signaling pathway

CXC chemokine receptor 2 (CXCR2) plays an important role in demyelinating diseases, but the detailed mechanisms were not yet clarified. In the present study, we mainly investigated the critical function and the potential molecular mechanisms of CXCR2 on oligodendrocyte precursor cell (OPC) differentiation and remyelination. The present study demonstrated that inhibiting CXCR2 significantly enhanced OPC differentiation and remyelination in primary cultured OPCs and ethidium bromide (EB)-intoxicated rats by facilitating the formation of myelin proteins, including PDGFRα, MBP, MAG, MOG, and Caspr. Further investigation identified phosphodiesterase 10A (PDE10A) as a main downstream protein of CXCR2, interacting with the receptor to regulate OPC differentiation, in that inhibition of CXCR2 reduced PDE10A expression while suppression of PDE10A did not affect CXCR2. Furthermore, inhibition of PDE10A promoted OPC differentiation, whereas overexpression of PDE10A down-regulated OPC differentiation. Our data also revealed that inhibition of CXCR2/PDE10A activated the cAMP/ERK1/2 signaling pathway, and up-regulated the expression of key transcription factors, including SOX10, OLIG2, MYRF, and ZFP24, that ultimately promoted remyelination and myelin protein biosynthesis. In conclusion, our findings suggested that inhibition of CXCR2 promoted OPC differentiation and enhanced remyelination by regulating PDE10A/cAMP/ERK1/2 signaling pathway. The present data also highlighted that CXCR2 may serve as a potential target for the treatment of demyelination diseases.

Presentation and integration of multiple signals that modulate oligodendrocyte lineage progression and myelination

Myelination is critical for fast saltatory conduction of action potentials. Recent studies have revealed that myelin is not a static structure as previously considered but continues to be made and remodeled throughout adulthood in tune with the network requirement. Synthesis of new myelin requires turning on the switch in oligodendrocytes (OL) to initiate the myelination program that includes synthesis and transport of macromolecules needed for myelin production as well as the metabolic and other cellular functions needed to support this process. A significant amount of information is available regarding the individual intrinsic and extrinsic signals that promote OL commitment, expansion, terminal differentiation, and myelination. However, it is less clear how these signals are made available to OL lineage cells when needed, and how multiple signals are integrated to generate the correct amount of myelin that is needed in a given neural network state. Here we review the pleiotropic effects of some of the extracellular signals that affect myelination and discuss the cellular processes used by the source cells that contribute to the variation in the temporal and spatial availability of the signals, and how the recipient OL lineage cells might integrate the multiple signals presented to them in a manner dialed to the strength of the input.

KLF9 and KLF13 transcription factors boost myelin gene expression in oligodendrocytes as partners of SOX10 and MYRF

Differentiated oligodendrocytes produce myelin and thereby ensure rapid nerve impulse conduction and efficient information processing in the vertebrate central nervous system. The Krüppel-like transcription factor KLF9 enhances oligodendrocyte differentiation in culture, but appears dispensable in vivo. Its mode of action and role within the oligodendroglial gene regulatory network are unclear. Here we show that KLF9 shares its expression in differentiating oligodendrocytes with the closely related KLF13 protein. Both KLF9 and KLF13 bind to regulatory regions of genes that are important for oligodendrocyte differentiation and equally recognized by the central differentiation promoting transcription factors SOX10 and MYRF. KLF9 and KLF13 physically interact and synergistically activate oligodendrocyte-specific regulatory regions with SOX10 and MYRF. Similar to KLF9, KLF13 promotes differentiation and myelination in primary oligodendroglial cultures. Oligodendrocyte differentiation is also altered in KLF13-deficient mice as demonstrated by a transiently reduced myelin gene expression during the first postnatal week. Considering mouse phenotypes, the similarities in expression pattern and genomic binding and the behaviour in functional assays, KLF9 and KLF13 are important and largely redundant components of the gene regulatory network in charge of oligodendrocyte differentiation and myelination.

Schwann cell precursors represent a neural crest-like state with biased multipotency

Schwann cell precursors (SCPs) are nerve-associated progenitors that can generate myelinating and non-myelinating Schwann cells but also are multipotent like the neural crest cells from which they originate. SCPs are omnipresent along outgrowing peripheral nerves throughout the body of vertebrate embryos. By using single-cell transcriptomics to generate a gene expression atlas of the entire neural crest lineage, we show that early SCPs and late migratory crest cells have similar transcriptional profiles characterised by a multipotent "hub" state containing cells biased towards traditional neural crest fates. SCPs keep diverging from the neural crest after being primed towards terminal Schwann cells and other fates, with different subtypes residing in distinct anatomical locations. Functional experiments using CRISPR-Cas9 loss-of-function further show that knockout of the common "hub" gene Sox8 causes defects in neural crest-derived cells along peripheral nerves by facilitating differentiation of SCPs towards sympathoadrenal fates. Finally, specific tumour populations found in melanoma, neurofibroma and neuroblastoma map to different stages of SCP/Schwann cell development. Overall, SCPs resemble migrating neural crest cells that maintain multipotency and become transcriptionally primed towards distinct lineages.

Recent advances in the regulation mechanism of SOX10

Neural crest (NC) is the primitive neural structure in embryonic stage, which develops from ectodermal neural plate cells and epithelial cells. When the neural fold forms into neural tube, neural crest also forms a cord like structure above the neural tube and below the ectoderm. Neural crest cells (NCC) have strong migration and proliferation abilities. A number of tissue cells differentiate from neural crest cells, such as melanocytes, central and peripheral neurons, glial cells, craniofacial cells, osteoblasts, chondrocytes and smooth muscle cells. The migration and differentiation of neural crest cells are regulated by a gene network where a variety of genes, transcriptional factors, signal pathways and growth factors are involved.

Central nervous system regeneration: the roles of glial cells in the potential molecular mechanism underlying remyelination

Glial cells play crucial roles in brain homeostasis and pathogenesis of central nervous system (CNS) injuries and diseases. However, the roles of these cells and the molecular mechanisms toward regeneration in the CNS have not been fully understood, especially the capacity of them toward demyelinating diseases. Therefore, there are still very limited therapeutic strategies to restore the function of adult CNS in diseases such as multiple sclerosis (MS). Remyelination, a spontaneous regeneration process in the CNS, requires the involvement of multiple cellular and extracellular components. Promoting remyelination by therapeutic interventions is a promising novel approach to restore the CNS function. Herein, we review the role of glial cells in CNS diseases and injuries. Particularly, we discuss the roles of glia and their functional interactions and regulatory mechanisms in remyelination, as well as the current therapeutic strategies for MS.

OUP accepted manuscript

In oligodendrocytes of the vertebrate central nervous system a complex network of transcriptional regulators is required to ensure correct and timely myelination of neuronal axons. Here we identify Zfp276, the only mammalian ZAD-domain containing zinc finger protein, as a transcriptional regulator of oligodendrocyte differentiation and central myelination downstream of Sox10. In the central nervous system, Zfp276 is exclusively expressed in mature oligodendrocytes. Oligodendroglial deletion of Zfp276 led to strongly reduced expression of myelin genes in the early postnatal mouse spinal cord. Retroviral overexpression of Zfp276 in cultured oligodendrocyte precursor cells induced precocious expression of maturation markers and myelin genes, further supporting its role in oligodendroglial differentiation. On the molecular level, Zfp276 directly binds to and represses Sox10-dependent gene regulatory regions of immaturity factors and functionally interacts with the transcriptional repressor Zeb2 to enable fast transition of oligodendrocytes to the myelinating stage.

Evolutionary Origins of the Oligodendrocyte Cell Type and Adaptive Myelination

Oligodendrocytes are multifunctional central nervous system (CNS) glia that are essential for neural function in gnathostomes. The evolutionary origins and specializations of the oligodendrocyte cell type are among the many remaining mysteries in glial biology and neuroscience. The role of oligodendrocytes as CNS myelinating glia is well established, but recent studies demonstrate that oligodendrocytes also participate in several myelin-independent aspects of CNS development, function, and maintenance. Furthermore, many recent studies have collectively advanced our understanding of myelin plasticity, and it is now clear that experience-dependent adaptations to myelination are an additional form of neural plasticity. These observations beg the questions of when and for which functions the ancestral oligodendrocyte cell type emerged, when primitive oligodendrocytes evolved new functionalities, and the genetic changes responsible for these evolutionary innovations. Here, I review recent findings and propose working models addressing the origins and evolution of the oligodendrocyte cell type and adaptive myelination. The core gene regulatory network (GRN) specifying the oligodendrocyte cell type is also reviewed as a means to probe the existence of oligodendrocytes in basal vertebrates and chordate invertebrates.

Ethanol effects on cerebellar myelination in a postnatal mouse model of fetal alcohol spectrum disorders

Fetal alcohol spectrum disorders (FASD) are alarmingly common, result in significant personal and societal loss, and there are no effective treatments for these disorders. Cerebellar neuropathology is common in FASD and can cause impaired cognitive and motor function. The current study evaluates the effects of ethanol on oligodendrocyte-lineage cells, as well as molecules that modulate oligodendrocyte differentiation and function in the cerebellum in a postnatal mouse model of FASD. Neonatal mice were treated with ethanol from P4-P9 (postnatal day), the cerebellum was isolated at P10, and mRNAs encoding oligodendrocyte-associated molecules were quantitated by qRT-PCR. Our studies demonstrated that ethanol significantly reduced the expression of markers for multiple stages of oligodendrocyte maturation, including oligodendrocyte precursor cells, pre-myelinating oligodendrocytes, and mature myelinating oligodendrocytes. Additionally, we determined that ethanol significantly decreased the expression of molecules that play critical roles in oligodendrocyte differentiation. Interestingly, we also observed that ethanol significantly reduced the expression of myelin-associated inhibitors, which may act as a compensatory mechanism to ethanol toxicity. Furthermore, we demonstrate that ethanol alters the expression of a variety of molecules important in oligodendrocyte function and myelination. Collectively, our studies increase our understanding of specific mechanisms by which ethanol modulates myelination in the developing cerebellum, and potentially identify novel targets for FASD therapy.

Expression and clinical significance of IL7R, NFATc2, and RNF213 in familial and sporadic multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory and autoimmune disorder of the central nervous system characterized by myelin loss and axonal dysfunction. Increased production of inflammatory factors such as cytokines has been implicated in axon destruction. In the present study, we compared the expression level of IL7R, NFATc2, and RNF213 genes in the peripheral blood of 72 MS patients (37 familial MS, 35 sporadic MS) and 74 healthy controls (34 individuals with a family history of the disease, 40 healthy controls without a family history) via Real-time PCR. Our results showed that the expression level of IL7R was decreased in the sporadic patients in comparison with other groups. Additionally, there was an increased NFATc2 expression level in MS patients versus healthy controls. Increased expression of NFATc2 in sporadic and familial groups compared to the controls, and familial group versus FDR was also seen. Our results also represented an increased expression level of RNF213 in familial patients as compared to the control group. The similar RNF213 expression between sporadic and control group, as well as FDR and familial group was also seen. Diagnostic evaluation was performed by receiver operating characteristic (ROC) curve analysis and area under the curve (AUC) calculation. The correlation of clinical parameters including onset age and Expanded Disability Status Scale (EDSS) with our gene expression levels were also assessed. Overall, decreased expression level of IL7R in the sporadic cases and increased expression level of NFATc2 may be associated with the pathogenesis of MS disease. Confirmation of the effects of differential expression of RNF213 gene requires further studies in the wider statistical populations.

Using the lineage determinants Olig2 and Sox10 to explore transcriptional regulation of oligodendrocyte development

The transcription factors Olig2 and Sox10 jointly define oligodendroglial identity. Because of their continuous presence during development and in the differentiated state they shape the oligodendroglial regulatory network at all times. In this review, we exploit their eminent role and omnipresence to elaborate the central principles that organize the gene regulatory network in oligodendrocytes in such a way that it preserves its identity, but at the same time allows defined and stimulus-dependent changes that result in an ordered lineage progression, differentiation, and myelination. For this purpose, we outline the multiple functional and physical interactions and intricate cross-regulatory relationships with other transcription factors, such as Hes5, Id, and SoxD proteins, in oligodendrocyte precursors and Tcf7l2, Sip1, Nkx2.2, Zfp24, and Myrf during differentiation and myelination, and interpret them in the context of the regulatory network.

Transcription Factor-Based Strategies to Generate Neural Cell Types from Human Pluripotent Stem Cells

In the last years, the use of pluripotent stem cells in studies of human biology has grown exponentially. These cells represent an infinite source for differentiation into several human cell types facilitating the investigation on biological processes, functionality of cells, or diseases mechanisms in relevant human models. In the neurobiology field, pluripotent stem cells have been extensively used to generate the main neuronal and glial cells of the brain. Traditionally, protocols following developmental cues have been applied to pluripotent stem cells to drive differentiation toward different cell lineages; however, these protocols give rise to populations with mixed identities. Interestingly, new protocols applying overexpression of lineage-specific transcription factors (TFs) have emerged and facilitated the generation of highly pure populations of specific subtypes of neurons and glial cells in an easy, reproducible, and rapid manner. In this study, we review protocols based on this strategy to generate excitatory, inhibitory, dopaminergic, and motor neurons as well as astrocytes, oligodendrocytes, and microglia. In addition, we will discuss the main applications for cells generated with these protocols, including disease modeling, drug screening, and mechanistic studies. Finally, we will discuss the advantages and disadvantages of TF-based protocols and present our view of the future in this field.

Q134R: Small chemical compound with NFAT inhibitory properties improves behavioral performance and synapse function in mouse models of amyloid pathology

Inhibition of the protein phosphatase calcineurin (CN) ameliorates pathophysiologic and cognitive changes in aging rodents and mice with aging-related Alzheimer's disease (AD)-like pathology. However, concerns over adverse effects have slowed the transition of common CN-inhibiting drugs to the clinic for the treatment of AD and AD-related disorders. Targeting substrates of CN, like the nuclear factor of activated T cells (NFATs), has been suggested as an alternative, safer approach to CN inhibitors. However, small chemical inhibitors of NFATs have only rarely been described. Here, we investigate a newly developed neuroprotective hydroxyquinoline derivative (Q134R) that suppresses NFAT signaling, without inhibiting CN activity. Q134R partially inhibited NFAT activity in primary rat astrocytes, but did not prevent CN-mediated dephosphorylation of a non-NFAT target, either in vivo, or in vitro. Acute (≤1 week) oral delivery of Q134R to APP/PS1 (12 months old) or wild-type mice (3-4 months old) infused with oligomeric Aβ peptides led to improved Y maze performance. Chronic (≥3 months) oral delivery of Q134R appeared to be safe, and, in fact, promoted survival in wild-type (WT) mice when given for many months beyond middle age. Finally, chronic delivery of Q134R to APP/PS1 mice during the early stages of amyloid pathology (i.e., between 6 and 9 months) tended to reduce signs of glial reactivity, prevented the upregulation of astrocytic NFAT4, and ameliorated deficits in synaptic strength and plasticity, without noticeably altering parenchymal Aβ plaque pathology. The results suggest that Q134R is a promising drug for treating AD and aging-related disorders.

Serine/Threonine Phosphatases in LTP: Two B or Not to Be the Protein Synthesis Blocker-Induced Impairment of Early Phase

Dephosphorylation of target proteins at serine/threonine residues is one of the most crucial mechanisms regulating their activity and, consequently, the cellular functions. The role of phosphatases in synaptic plasticity, especially in long-term depression or depotentiation, has been reported. We studied serine/threonine phosphatase activity during the protein synthesis blocker (PSB)-induced impairment of long-term potentiation (LTP). Established protein phosphatase 2B (PP2B, calcineurin) inhibitor cyclosporin A prevented the LTP early phase (E-LTP) decline produced by pretreatment of hippocampal slices with cycloheximide or anisomycin. For the first time, we directly measured serine/threonine phosphatase activity during E-LTP, and its significant increase in PSB-treated slices was demonstrated. Nitric oxide (NO) donor SNAP also heightened phosphatase activity in the same manner as PSB, and simultaneous application of anisomycin + SNAP had no synergistic effect. Direct measurement of the NO production in hippocampal slices by the NO-specific fluorescent probe DAF-FM revealed that PSBs strongly stimulate the NO concentration in all studied brain areas: CA1, CA3, and dentate gyrus (DG). Cyclosporin A fully abolished the PSB-induced NO production in the hippocampus, suggesting a close relationship between nNOS and PP2B activity. Surprisingly, cyclosporin A alone impaired short-term plasticity in CA1 by decreasing paired-pulse facilitation, which suggests bi-directionality of the influences of PP2B in the hippocampus. In conclusion, we proposed a minimal model of signaling events that occur during LTP induction in normal conditions and the PSB-treated slices.

Can Enhancing Neuronal Activity Improve Myelin Repair in Multiple Sclerosis?

Enhanced neuronal activity in the healthy brain can induce de novo myelination and behavioral changes. As neuronal activity can be achieved using non-invasive measures, it may be of interest to utilize the innate ability of neuronal activity to instruct myelination as a novel strategy for myelin repair in demyelinating disorders such as multiple sclerosis (MS). Preclinical studies indicate that stimulation of neuronal activity in demyelinated lesions indeed has the potential to improve remyelination and that the stimulation paradigm is an important determinant of success. However, future studies will need to reveal the most efficient stimulation protocols as well as the biological mechanisms implicated. Nonetheless, clinical studies have already explored non-invasive brain stimulation as an attractive therapeutic approach that ameliorates MS symptomatology. However, whether symptom improvement is due to improved myelin repair remains unclear. In this mini-review, we discuss the neurobiological basis and potential of enhancing neuronal activity as a novel therapeutic approach in MS.

Formation of the node of Ranvier by Schwann cells is under control of transcription factor Sox10

The transcription factor Sox10 is an essential regulator of genes that code for structural components of the myelin sheath and for lipid metabolic enzymes in both types of myelinating glia in the central and peripheral nervous systems. In an attempt to characterize additional Sox10 target genes in Schwann cells, we identified in this study a strong influence of Sox10 on the expression of genes associated with adhesion in the MSC80 Schwann cell line. These included the genes for Gliomedin, Neuronal cell adhesion molecule and Neurofascin that together constitute essential Schwann cell contributions to paranode and node of Ranvier. Using bioinformatics and molecular biology techniques we provide evidence that Sox10 directly activates these genes by binding to conserved regulatory regions. For activation, Sox10 cooperates with Krox20, a transcription factor previously identified as the central regulator of Schwann cell myelination. Both the activating function of Sox10 as well as its cooperation with Krox20 were confirmed in vivo. We conclude that the employment of Sox10 and Krox20 as regulators of structural myelin sheath components and genes associated with the node of Ranvier is one way of ensuring a biologically meaningful coordinated formation of both structures during peripheral myelination.

Genome-Wide Association Analysis of Neonatal White Matter Microstructure

A better understanding of genetic influences on early white matter development could significantly advance our understanding of neurological and psychiatric conditions characterized by altered integrity of axonal pathways. We conducted a genome-wide association study (GWAS) of diffusion tensor imaging (DTI) phenotypes in 471 neonates. We used a hierarchical functional principal regression model (HFPRM) to perform joint analysis of 44 fiber bundles. HFPRM revealed a latent measure of white matter microstructure that explained approximately 50% of variation in our tractography-based measures and accounted for a large proportion of heritable variation in each individual bundle. An intronic SNP in PSMF1 on chromosome 20 exceeded the conventional GWAS threshold of 5 x 10-8 (p = 4.61 x 10-8). Additional loci nearing genome-wide significance were located near genes with known roles in axon growth and guidance, fasciculation, and myelination.

Oligodendrocyte myelin glycoprotein as a novel target for pathogenic autoimmunity in the CNS

Autoimmune disorders of the central nervous system (CNS) comprise a broad spectrum of clinical entities. The stratification of patients based on the recognized autoantigen is of great importance for therapy optimization and for concepts of pathogenicity, but for most of these patients, the actual target of their autoimmune response is unknown. Here we investigated oligodendrocyte myelin glycoprotein (OMGP) as autoimmune target, because OMGP is expressed specifically in the CNS and there on oligodendrocytes and neurons. Using a stringent cell-based assay, we detected autoantibodies to OMGP in serum of 8/352 patients with multiple sclerosis, 1/28 children with acute disseminated encephalomyelitis and unexpectedly, also in one patient with psychosis, but in none of 114 healthy controls. Since OMGP is GPI-anchored, we validated its recognition also in GPI-anchored form. The autoantibodies to OMGP were largely IgG1 with a contribution of IgG4, indicating cognate T cell help. We found high levels of soluble OMGP in human spinal fluid, presumably due to shedding of the GPI-linked OMGP. Analyzing the pathogenic relevance of autoimmunity to OMGP in an animal model, we found that OMGP-specific T cells induce a novel type of experimental autoimmune encephalomyelitis dominated by meningitis above the cortical convexities. This unusual localization may be directed by intrathecal uptake and presentation of OMGP by meningeal phagocytes. Together, OMGP-directed autoimmunity provides a new element of heterogeneity, helping to improve the stratification of patients for diagnostic and therapeutic purposes.

Extrinsic immune cell-derived, but not intrinsic oligodendroglial factors contribute to oligodendroglial differentiation block in multiple sclerosis

Multiple sclerosis (MS) is the most frequent demyelinating disease in young adults and despite significant advances in immunotherapy, disease progression still cannot be prevented. Promotion of remyelination, an endogenous repair mechanism resulting in the formation of new myelin sheaths around demyelinated axons, represents a promising new treatment approach. However, remyelination frequently fails in MS lesions, which can in part be attributed to impaired differentiation of oligodendroglial progenitor cells into mature, myelinating oligodendrocytes. The reasons for impaired oligodendroglial differentiation and defective remyelination in MS are currently unknown. To determine whether intrinsic oligodendroglial factors contribute to impaired remyelination in relapsing–remitting MS (RRMS), we compared induced pluripotent stem cell-derived oligodendrocytes (hiOL) from RRMS patients and controls, among them two monozygous twin pairs discordant for MS. We found that hiOL from RRMS patients and controls were virtually indistinguishable with respect to remyelination-associated functions and proteomic composition. However, while analyzing the effect of extrinsic factors we discovered that supernatants of activated peripheral blood mononuclear cells (PBMCs) significantly inhibit oligodendroglial differentiation. In particular, we identified CD4⁺ T cells as mediators of impaired oligodendroglial differentiation; at least partly due to interferon-gamma secretion. Additionally, we observed that blocked oligodendroglial differentiation induced by PBMC supernatants could not be restored by application of oligodendroglial differentiation promoting drugs, whereas treatment of PBMCs with the immunomodulatory drug teriflunomide prior to supernatant collection partly rescued oligodendroglial differentiation. In summary, these data indicate that the oligodendroglial differentiation block is not due to intrinsic oligodendroglial factors but rather caused by the inflammatory environment in RRMS lesions which underlines the need for drug screening approaches taking the inflammatory environment into account. Combined, these findings may contribute to the development of new remyelination promoting strategies.

Egr2-guided histone H2B monoubiquitination is required for peripheral nervous system myelination

Schwann cells are the nerve ensheathing cells of the peripheral nervous system. Absence, loss and malfunction of Schwann cells or their myelin sheaths lead to peripheral neuropathies such as Charcot-Marie-Tooth disease in humans. During Schwann cell development and myelination chromatin is dramatically modified. However, impact and functional relevance of these modifications are poorly understood. Here, we analyzed histone H2B monoubiquitination as one such chromatin modification by conditionally deleting the Rnf40 subunit of the responsible E3 ligase in mice. Rnf40-deficient Schwann cells were arrested immediately before myelination or generated abnormally thin, unstable myelin, resulting in a peripheral neuropathy characterized by hypomyelination and progressive axonal degeneration. By combining sequencing techniques with functional studies we show that H2B monoubiquitination does not influence global gene expression patterns, but instead ensures selective high expression of myelin and lipid biosynthesis genes and proper repression of immaturity genes. This requires the specific recruitment of the Rnf40-containing E3 ligase by Egr2, the central transcriptional regulator of peripheral myelination, to its target genes. Our study identifies histone ubiquitination as essential for Schwann cell myelination and unravels new disease-relevant links between chromatin modifications and transcription factors in the underlying regulatory network.

Lipid Pathology of the Corpus Callosum in Schizophrenia and the Potential Role of Abnormal Gene Regulatory Networks with Reduced Microglial Marker Expression

Structural changes in the corpus callosum have been reported in schizophrenia; however, the underlying molecular mechanism remains unclear. As the corpus callosum is high in lipid content, we analyzed the lipid contents of the corpora callosa from 15 patients with schizophrenia and 15 age- and sex-matched controls using liquid chromatography coupled to tandem mass spectrometry and identified lipid combinations associated with schizophrenia. Real-time quantitative polymerase chain reaction analyses using extended samples (schizophrenia, n = 95; control, n = 91) showed low expression levels of lipid metabolism-related genes and their potential upstream transcription factors in schizophrenia. Subsequent pathway analysis identified a gene regulatory network where nuclear factor of activated T cells 2 (NFATC2) is placed most upstream. We also observed low gene expression levels of microglial markers, inflammatory cytokines, and colony-stimulating factor 1 receptor (CSF1R), which is known to regulate the density of microglia, in the corpus callosum in schizophrenia. The interactions between CSF1R and several genes in the presently identified gene network originating from NFATC2 have been reported. Collectively, this study provides evidence regarding lipid abnormalities in the corpora callosa of patients with schizophrenia and proposes the potential role of impaired “NFATC2-relevant gene network-microglial axis” as its underlying mechanism.

Transcription factor Tcf4 is the preferred heterodimerization partner for Olig2 in oligodendrocytes and required for differentiation

Development of oligodendrocytes and myelin formation in the vertebrate central nervous system is under control of several basic helix-loop-helix transcription factors such as Olig2, Ascl1, Hes5 and the Id proteins. The class I basic helix-loop-helix proteins Tcf3, Tcf4 and Tcf12 represent potential heterodimerization partners and functional modulators for all, but have not been investigated in oligodendrocytes so far. Using mouse mutants, organotypic slice and primary cell cultures we here show that Tcf4 is required in a cell-autonomous manner for proper terminal differentiation and myelination in vivo and ex vivo. Partial compensation is provided by the paralogous Tcf3, but not Tcf12. On the mechanistic level Tcf4 was identified as the preferred heterodimerization partner of the central regulator of oligodendrocyte development Olig2. Both genetic studies in the mouse as well as functional studies on enhancer regions of myelin genes confirmed the relevance of this physical interaction for oligodendrocyte differentiation. Considering that alterations in TCF4 are associated with syndromic and non-syndromic forms of intellectual disability, schizophrenia and autism in humans, our findings point to the possibility of an oligodendroglial contribution to these disorders.

Lesion stage-dependent causes for impaired remyelination in MS

Multiple sclerosis (MS) is the most frequent demyelinating disease and a leading cause for disability in young adults. Despite significant advances in immunotherapies in recent years, disease progression still cannot be prevented. Remyelination, meaning the formation of new myelin sheaths after a demyelinating event, can fail in MS lesions. Impaired differentiation of progenitor cells into myelinating oligodendrocytes may contribute to remyelination failure and, therefore, the development of pharmacological approaches which promote oligodendroglial differentiation and by that remyelination, represents a promising new treatment approach. However, this generally accepted concept has been challenged recently. To further understand mechanisms contributing to remyelination failure in MS, we combined detailed histological analyses assessing oligodendroglial cell numbers, presence of remyelination as well as the inflammatory environment in different MS lesion types in white matter with in vitro experiments using induced-pluripotent stem cell (iPSC)-derived oligodendrocytes (hiOL) and supernatants from polarized human microglia. Our findings suggest that there are multiple reasons for remyelination failure in MS which are dependent on lesion stage. These include lack of myelin sheath formation despite the presence of mature oligodendrocytes in a subset of active lesions as well as oligodendroglial loss and a hostile tissue environment in mixed active/inactive lesions. Therefore, we conclude that better in vivo and in vitro models which mimic the pathological hallmarks of the different MS lesion types are required for the successful development of remyelination promoting drugs.

Experimentally Induced Sepsis Causes Extensive Hypomyelination in the Prefrontal Cortex and Hippocampus in Neonatal Rats

Neonatal sepsis is associated with cognitive deficit in the later life. Axonal myelination plays a pivotal role in neurotransmission and formation of learning and memory. This study aimed to explore if systemic lipopolysaccharide (LPS) injection would induce hypomyelination in the prefrontal cortex and hippocampus in developing septic neonatal rats. Sprague-Dawley rats (1-day old) were injected with LPS (1 mg/kg) intraperitoneally. By electron microscopy, axonal hypomyelination was evident in the subcortical white matter and hippocampus. The expression of myelin proteins including CNPase, MBP, PLP and MAG was downregulated in both areas of the brain at 7, 14 and 28 days after LPS injection. The frequency of MBP and PLP-positive oligodendrocyte was significantly reduced using in situ hybridization in the cerebral cortex and hippocampus at the corresponding time points after LPS injection, whereas the expression of NG2 and PDGFRα was noticeably increased. In tandem with this was reduction of Olig1 and Olig2 expressions which are involved in differentiation/maturation of OPCs. Expression of NFL, NFM, and NFH was significantly downregulated, indicating that axon development was disrupted after LPS injection. Morris Water Maze behavioral test, Open field test, Rotarod test, and Pole test were used to evaluate neurological behaviors of 28 days rats. The rats in the LPS group showed the impairment of motor coordination, balance, memory, and learning ability and represented bradykinesia and anxiety-like behavior. The present results suggest that following systemic LPS injection, differentiation/maturation of OPCs was affected which may be attributed to the inhibition of transcription factors Olig1 and Olig2 expression resulting in impairment to axonal development. It is suggested that this would ultimately lead to axonal hypomyelination in the prefrontal cortex and hippocampus, which may be associated with neurological deficits in later life.

Protective effects of 4-aminopyridine in experimental optic neuritis and multiple sclerosis

Chronic disability in multiple sclerosis is linked to neuroaxonal degeneration. 4-aminopyridine (4-AP) is used and licensed as a symptomatic treatment to ameliorate ambulatory disability in multiple sclerosis. The presumed mode of action is via blockade of axonal voltage gated potassium channels, thereby enhancing conduction in demyelinated axons. In this study, we provide evidence that in addition to those symptomatic effects, 4-AP can prevent neuroaxonal loss in the CNS. Using in vivo optical coherence tomography imaging, visual function testing and histologic assessment, we observed a reduction in retinal neurodegeneration with 4-AP in models of experimental optic neuritis and optic nerve crush. These effects were not related to an anti-inflammatory mode of action or a direct impact on retinal ganglion cells. Rather, histology and in vitro experiments indicated 4-AP stabilization of myelin and oligodendrocyte precursor cells associated with increased nuclear translocation of the nuclear factor of activated T cells. In experimental optic neuritis, 4-AP potentiated the effects of immunomodulatory treatment with fingolimod. As extended release 4-AP is already licensed for symptomatic multiple sclerosis treatment, we performed a retrospective, multicentre optical coherence tomography study to longitudinally compare retinal neurodegeneration between 52 patients on continuous 4-AP therapy and 51 matched controls. In line with the experimental data, during concurrent 4-AP therapy, degeneration of the macular retinal nerve fibre layer was reduced over 2 years. These results indicate disease-modifying effects of 4-AP beyond symptomatic therapy and provide support for the design of a prospective clinical study using visual function and retinal structure as outcome parameters.

Bu-Shen-Yi-Sui Capsule, an Herbal Medicine Formula, Promotes Remyelination by Modulating the Molecular Signals via Exosomes in Mice with Experimental Autoimmune Encephalomyelitis

Multiple sclerosis (MS) is a common inflammatory demyelinating disorder of the central nervous system. Bu-shen-yi-sui capsule (BSYSC) could significantly reduce the relapse rate, prevent the progression of MS, and enhance remyelination following neurological injury in experimental autoimmune encephalomyelitis (EAE), an established model of MS; however, the mechanism underlying the effect of BSYSC on remyelination has not been well elucidated. This study showed that exosomes carrying biological information are involved in the pathological process of MS and that modified exosomes can promote remyelination by modulating related proteins and microRNAs (miRs). Here, the mechanism by which BSYSC promoted remyelination via exosome-mediated molecular signals was investigated in EAE mice and oligodendrocyte progenitor cells (OPCs) in vitro. The results showed that BSYSC treatment significantly improved the body weight and clinical scores of EAE mice, alleviated inflammatory infiltration and nerve fiber injury, protected the ultrastructural integrity of the myelin sheath, and significantly increased the expression of myelin basic protein (MBP) in EAE mice. In an in vitro OPC study, BSYSC-containing serum, especially 20% BSYSC, promoted the proliferation and migration of OPCs and induced OPCs to differentiate into mature oligodendrocytes that expressed MBP. Furthermore, BSYSC treatment regulated the expression of neuropilin- (NRP-) 1 and GTX, downregulated the expression of miR-16, let-7, miR-15, miR-98, miR-486, and miR-182, and upregulated the level of miR-146 in serum exosomes of EAE mice. In conclusion, these results suggested that BSYSC has a neuroprotective effect and facilitates remyelination and that the mechanism underlying the effect of BSYSC on remyelination probably involves regulation of the NRP-1 and GTX proteins and miRs in serum exosomes, which drive promyelination.

Long Noncoding RNAs and Circular RNAs in Autoimmune Diseases

Immune responses are essential for the clearance of pathogens and the repair of injured tissues; however, if these responses are not properly controlled, autoimmune diseases can occur. Autoimmune diseases (ADs) are a family of disorders characterized by the body's immune response being directed against its own tissues, with consequent chronic inflammation and tissue damage. Despite enormous efforts to identify new drug targets and develop new therapies to prevent and ameliorate AD symptoms, no definitive solutions are available today. Additionally, while substantial progress has been made in drug development for some ADs, most treatments only ameliorate symptoms and, in general, ADs are still incurable. Hundreds of genetic loci have been identified and associated with ADs by genome-wide association studies. However, the whole list of molecular factors that contribute to AD pathogenesis is still unknown. Noncoding (nc)RNAs, such as microRNAs, circular (circ)RNAs, and long noncoding (lnc)RNAs, regulate gene expression at different levels in various diseases, including ADs, and serve as potential drug targets as well as biomarkers for disease progression and response to therapy. In this review, we will focus on the potential roles and genetic regulation of ncRNA in four autoimmune diseases-systemic lupus erythematosus, rheumatoid arthritis, multiple sclerosis, and type 1 diabetes mellitus.

yippee like 3 (ypel3) is a novel gene required for myelinating and perineurial glia development

Hypomyelination, a neurological condition characterized by decreased production of myelin sheets by glial cells, often has no known etiology. Elucidating the genetic causes of hypomyelination provides a better understanding of myelination, as well as means to diagnose, council, and treat patients. Here, we present evidence that YIPPEE LIKE 3 (YPEL3), a gene whose developmental role was previously unknown, is required for central and peripheral glial cell development. We identified a child with a constellation of clinical features including cerebral hypomyelination, abnormal peripheral nerve conduction, hypotonia, areflexia, and hypertrophic peripheral nerves. Exome and genome sequencing revealed a de novo mutation that creates a frameshift in the open reading frame of YPEL3, leading to an early stop codon. We used zebrafish as a model system to validate that YPEL3 mutations are causative of neuropathy. We found that ypel3 is expressed in the zebrafish central and peripheral nervous system. Using CRISPR/Cas9 technology, we created zebrafish mutants carrying a genomic lesion similar to that of the patient. Our analysis revealed that Ypel3 is required for development of oligodendrocyte precursor cells, timely exit of the perineurial glial precursors from the central nervous system (CNS), formation of the perineurium, and Schwann cell maturation. Consistent with these observations, zebrafish ypel3 mutants have metabolomic signatures characteristic of oligodendrocyte and Schwann cell differentiation defects, show decreased levels of Myelin basic protein in the central and peripheral nervous system, and develop defasciculated peripheral nerves. Locomotion defects were observed in adult zebrafish ypel3 mutants. These studies demonstrate that Ypel3 is a novel gene required for perineurial cell development and glial myelination.

Neuron-oligodendroglia interactions: Activity-dependent regulation of cellular signaling

Oligodendrocyte lineage cells (oligodendroglia) and neurons engage in bidirectional communication throughout life to support healthy brain function. Recent work shows that changes in neuronal activity can modulate proliferation, differentiation, and myelination to support the formation and function of neural circuits. While oligodendroglia express a diverse collection of receptors for growth factors, signaling molecules, neurotransmitters and neuromodulators, our knowledge of the intracellular signaling pathways that are regulated by neuronal activity remains largely incomplete. Many of the pathways that modulate oligodendroglia behavior are driven by changes in intracellular calcium signaling, which may differentially affect cytoskeletal dynamics, gene expression, maturation, integration, and axonal support. Additionally, activity-dependent neuron-oligodendroglia communication plays an integral role in the recovery from demyelinating injuries. In this review, we summarize the modalities of communication between neurons and oligodendroglia and explore possible roles of activity-dependent calcium signaling in mediating cellular behavior and myelination.

Calcium Signaling in the Oligodendrocyte Lineage: Regulators and Consequences

Cells of the oligodendrocyte lineage express a wide range of Ca²⁺ channels and receptors that regulate oligodendrocyte progenitor cell (OPC) and oligodendrocyte formation and function. Here we define those key channels and receptors that regulate Ca²⁺ signaling and OPC development and myelination. We then discuss how the regulation of intracellular Ca²⁺ in turn affects OPC and oligodendrocyte biology in the healthy nervous system and under pathological conditions. Activation of Ca²⁺ channels and receptors in OPCs and oligodendrocytes by neurotransmitters converges on regulating intracellular Ca²⁺, making Ca²⁺ signaling a central candidate mediator of activity-driven myelination. Indeed, recent evidence indicates that localized changes in Ca²⁺ in oligodendrocytes can regulate the formation and remodeling of myelin sheaths and perhaps additional functions of oligodendrocytes and OPCs. Thus, decoding how OPCs and myelinating oligodendrocytes integrate and process Ca²⁺ signals will be important to fully understand central nervous system formation, health, and function.

Aberrant Oligodendrogenesis in Down Syndrome: Shift in Gliogenesis?

Down syndrome (DS), or trisomy 21, is the most prevalent chromosomal anomaly accounting for cognitive impairment and intellectual disability (ID). Neuropathological changes of DS brains are characterized by a reduction in the number of neurons and oligodendrocytes, accompanied by hypomyelination and astrogliosis. Recent studies mainly focused on neuronal development in DS, but underestimated the role of glial cells as pathogenic players. Aberrant or impaired differentiation within the oligodendroglial lineage and altered white matter functionality are thought to contribute to central nervous system (CNS) malformations. Given that white matter, comprised of oligodendrocytes and their myelin sheaths, is vital for higher brain function, gathering knowledge about pathways and modulators challenging oligodendrogenesis and cell lineages within DS is essential. This review article discusses to what degree DS-related effects on oligodendroglial cells have been described and presents collected evidence regarding induced cell-fate switches, thereby resulting in an enhanced generation of astrocytes. Moreover, alterations in white matter formation observed in mouse and human post-mortem brains are described. Finally, the rationale for a better understanding of pathways and modulators responsible for the glial cell imbalance as a possible source for future therapeutic interventions is given based on current experience on pro-oligodendroglial treatment approaches developed for demyelinating diseases, such as multiple sclerosis.

Sox9 overexpression exerts multiple stage-dependent effects on mouse spinal cord development

The high-mobility-group (HMG)-domain protein Sox9 is one of few transcription factors implicated in gliogenesis in the vertebrate central nervous system. To further study the role of Sox9 in early spinal cord development, we generated a mouse that allows expression of Sox9 in a temporally and spatially controlled manner. Using this mouse, we show that premature Sox9 expression in neural precursor cells disrupted the neuroepithelium of the ventricular zone. Sox9 also compromised development and survival of neuronal precursors and neurons. Additionally, we observed in these mice substantial increases in oligodendroglial and astroglial cells. Reversing the normal order of appearance of essential transcriptional regulators during oligodendrogenesis, Sox10 preceded Olig2. Our study reinforces the notion that Sox9 has a strong gliogenic activity. It also argues that Sox9 expression has to be tightly controlled to prevent negative effects on early spinal cord structure and neuronal development.

Stage-specific regulation of oligodendrocyte development by Hedgehog signaling in the spinal cord

Elucidation of signaling pathways that control oligodendrocyte (OL) development is a prerequisite for developing novel strategies for myelin repair in neurological diseases. Despite the extensive work outlining the importance of Hedgehog (Hh) signaling in the commitment and generation of OL progenitor cells (OPCs), there are conflicting reports on the role of Hh signaling in regulating OL differentiation and maturation. In the present study, we systematically investigated OPC specification and differentiation in genetically modified mouse models of Smoothened (Smo), an essential component of the Hh signaling pathway in vertebrates. Through conditional gain-of-function strategy, we demonstrated that hyperactivation of Smo in neural progenitors induced transient ectopic OPC generation and precocious OL differentiation accompanied by the co-induction of Olig2 and Nkx2.2. After the commitment of OL lineage, Smo activity is not required for OL differentiation, and sustained expression of Smo in OPCs stimulated cell proliferation but inhibited terminal differentiation. These findings have uncovered the stage-specific regulation of OL development by Smo-mediated Hh signaling, providing novel insights into the molecular regulation of OL differentiation and myelin repair.

A principled strategy for mapping enhancers to genes

Mapping enhancers to genes is a fundamental goal of modern biology. We have developed an innovative strategy that maps enhancers to genes in a principled manner. We illustrate its power by applying it to Myrf. Despite being a master regulator of oligodendrocytes, oligodendrocyte enhancers governing Myrf expression remain elusive. Since chromatin conformation capture studies have shown that a gene and its enhancer tend to be found in the same topologically associating domain (TAD), we started with the delineation of the Myrf TAD. A genome-wide map of putative oligodendrocyte enhancers uncovered 6 putative oligodendrocyte enhancers in the Myrf TAD, narrowing down the search space for Myrf enhancers from the entire genome to 6 loci in a principled manner. Epigenome editing experiments revealed that two of them govern Myrf expression for oligodendrocyte development. Our new method is simple, principled, and powerful, providing a systematic way to find enhancers that regulate the expression of a gene of interest. Since it can be applied to most cell types, it would greatly facilitate our effort to unravel transcriptional regulatory networks of diverse cell types.

[Simvastatin promotes murine osteoclasts apoptosis in vitro through NFATc1 pathway]

OBJECTIVE

To explore the mechanism by which simvastatin (SIM) regulates osteoclast apoptosis.

METHODS

Murine macrophage RAW264.7 cells were divided into 5 groups, namely group A (control group), group B (sRANKL+ M-CSF), group C (SIM+sRANKL+M-CSF), group D (VIVIT peptide+sRANKL+ M-CSF), and group E (SIM+VIVIT peptide+sRANKL+M-CSF). WST-1 assay was used to assess the effects of simvastatin on the proliferation activity of the osteoclasts, and flow cytometry was performed to analyze the effects of SIM and VIVIVIT peptide (a NFATc1 pathway inhibitor) on apoptosis of the osteoclasts. The translocation of NFATc1 into the nucleus was investigated using immunofluorescence assay, and Western blotting was employed to assess the effect of SIM on the phosphorylation of NFATc1 in the nucleus.

RESULTS

WST-1 assay showed that SIM (1×10^-6 mol/L) treatment for 24 and 48 h significantly inhibited the proliferation of the osteoclasts (P=0.039 and 0.022, respectively). Compared with the control group, the SIM-treated osteoclasts exhibited significantly reduced cell percentage in G0/G1 phase (P=0.041) and increased cells in sub-G1 phase (P=0.028) with obvious cell apoptosis. DAPI staining and flow cytometry showed that both SIM and VIVIVIT peptide alone significantly promoted osteoclast apoptosis (P=0.002 and 0.015, respectively), and their combination produced a similar pro-apoptosis effect (P=0.08). Immunofluorescence and Western blotting showed that SIM significantly inhibited the intranuclear translocation of NFATc1 and the phosphorylation of NFATc1 pathway protein (P=0.013).

CONCLUSIONS

SIM promotes osteoclast apoptosis through NFATc1 signaling pathway.

Ca2+ Signaling in Oligodendrocyte Development

Calcium signaling has essential roles in the development of the nervous system, from neural induction to the proliferation, migration, and differentiation of both neuronal and glia cells. The temporal and spatial dynamics of Ca²⁺ signals control the highly diverse yet specific transcriptional programs that establish the complex structures of the nervous system. Ca²⁺-signaling pathways are shaped by interactions among metabotropic signaling cascades, ion channels, intracellular Ca²⁺ stores, and a multitude of downstream effector proteins that activate specific genetic programs. Progress in the last decade has led to significant advances in our understanding of the functional architecture of Ca²⁺ signaling networks involved in oligodendrocyte development. In this review, we summarize the molecular and functional organizations of Ca²⁺-signaling networks during the differentiation of oligodendrocyte, especially its impact on myelin gene expression, proliferation, migration, and myelination. Importantly, the existence of multiple routes of Ca²⁺ influx opens the possibility that the activity of calcium channels can be manipulated pharmacologically to encourage oligodendrocyte maturation and remyelination after demyelinating episodes in the brain.