NG2 regulates directional migration of oligodendrocyte precursor cells via Rho GTPases and polarity complex proteins

Diffuse midline glioma invasion and metastasis rely on cell-autonomous signaling

BACKGROUND

Diffuse midline gliomas (DMG) are pediatric tumors with negligible 2-year survival after diagnosis characterized by their ability to infiltrate the central nervous system. In the hope of controlling the local growth and slowing the disease, all patients receive radiotherapy. However, distant progression occurs frequently in DMG patients. Current clues as to what causes tumor infiltration circle mainly around the tumor microenvironment, but there are currently no known determinants to predict the degree of invasiveness.

METHODS

In this study, we use patient-derived glioma stem cells (GSCs) to create patient-specific 3D avatars to model interindividual invasion and elucidate the cellular supporting mechanisms.

RESULTS

We show that GSC models in 3D mirror the invasive behavior of the parental tumors, thus proving the ability of DMG to infiltrate as an autonomous characteristic of tumor cells. Furthermore, we distinguished 2 modes of migration, mesenchymal and ameboid-like, and associated the ameboid-like modality with GSCs derived from the most invasive tumors. Using transcriptomics of both organoids and primary tumors, we further characterized the invasive ameboid-like tumors as oligodendrocyte progenitor-like, with highly contractile cytoskeleton and reduced adhesion ability driven by crucial over-expression of bone morphogenetic pathway 7 (BMP7). Finally, we deciphered MEK, ERK, and Rho/ROCK kinases activated downstream of the BMP7 stimulation as actionable targets controlling tumor cell motility.

CONCLUSIONS

Our findings identify 2 new therapeutic avenues. First, patient-derived GSCs represent a predictive tool for patient stratification in order to adapt irradiation strategies. Second, autocrine and short-range BMP7-related signaling becomes a druggable target to prevent DMG spread and metastasis.

ANKS1B encoded AIDA-1 regulates social behaviors by controlling oligodendrocyte function

Heterozygous deletions in the ANKS1B gene cause ANKS1B neurodevelopmental syndrome (ANDS), a rare genetic disease characterized by autism spectrum disorder (ASD), attention deficit/hyperactivity disorder, and speech and motor deficits. The ANKS1B gene encodes for AIDA-1, a protein that is enriched at neuronal synapses and regulates synaptic plasticity. Here we report an unexpected role for oligodendroglial deficits in ANDS pathophysiology. We show that Anks1b-deficient mouse models display deficits in oligodendrocyte maturation, myelination, and Rac1 function, and recapitulate white matter abnormalities observed in ANDS patients. Selective loss of Anks1b from the oligodendrocyte lineage, but not from neuronal populations, leads to deficits in social preference and sensory reactivity previously observed in a brain-wide Anks1b haploinsufficiency model. Furthermore, we find that clemastine, an antihistamine shown to increase oligodendrocyte precursor cell maturation and central nervous system myelination, rescues deficits in social preference in 7-month-old Anks1b-deficient mice. Our work shows that deficits in social behaviors present in ANDS may originate from abnormal Rac1 activity within oligodendrocytes.

Schwann Cell-Derived Exosomal Vesicles: A Promising Therapy for the Injured Spinal Cord

Exosomes are nanoscale-sized membrane vesicles released by cells into their extracellular milieu. Within these nanovesicles reside a multitude of bioactive molecules, which orchestrate essential biological processes, including cell differentiation, proliferation, and survival, in the recipient cells. These bioactive properties of exosomes render them a promising choice for therapeutic use in the realm of tissue regeneration and repair. Exosomes possess notable positive attributes, including a high bioavailability, inherent safety, and stability, as well as the capacity to be functionalized so that drugs or biological agents can be encapsulated within them or to have their surface modified with ligands and receptors to imbue them with selective cell or tissue targeting. Remarkably, their small size and capacity for receptor-mediated transcytosis enable exosomes to cross the blood-brain barrier (BBB) and access the central nervous system (CNS). Unlike cell-based therapies, exosomes present fewer ethical constraints in their collection and direct use as a therapeutic approach in the human body. These advantageous qualities underscore the vast potential of exosomes as a treatment option for neurological injuries and diseases, setting them apart from other cell-based biological agents. Considering the therapeutic potential of exosomes, the current review seeks to specifically examine an area of investigation that encompasses the development of Schwann cell (SC)-derived exosomal vesicles (SCEVs) as an approach to spinal cord injury (SCI) protection and repair. SCs, the myelinating glia of the peripheral nervous system, have a long history of demonstrated benefit in repair of the injured spinal cord and peripheral nerves when transplanted, including their recent advancement to clinical investigations for feasibility and safety in humans. This review delves into the potential of utilizing SCEVs as a therapy for SCI, explores promising engineering strategies to customize SCEVs for specific actions, and examines how SCEVs may offer unique clinical advantages over SC transplantation for repair of the injured spinal cord.

APPlications of amyloid-β precursor protein metabolites in macrocephaly and autism spectrum disorder

Metabolites of the Amyloid-β precursor protein (APP) proteolysis may underlie brain overgrowth in Autism Spectrum Disorder (ASD). We have found elevated APP metabolites (total APP, secreted (s) APPα, and α-secretase adamalysins in the plasma and brain tissue of children with ASD). In this review, we highlight several lines of evidence supporting APP metabolites' potential contribution to macrocephaly in ASD. First, APP appears early in corticogenesis, placing APP in a prime position to accelerate growth in neurons and glia. APP metabolites are upregulated in neuroinflammation, another potential contributor to excessive brain growth in ASD. APP metabolites appear to directly affect translational signaling pathways, which have been linked to single gene forms of syndromic ASD (Fragile X Syndrome, PTEN, Tuberous Sclerosis Complex). Finally, APP metabolites, and microRNA, which regulates APP expression, may contribute to ASD brain overgrowth, particularly increased white matter, through ERK receptor activation on the PI3K/Akt/mTOR/Rho GTPase pathway, favoring myelination.

The cortical NG2-glia response to traumatic brain injury

Traumatic brain injury (TBI) is a significant worldwide cause of morbidity and mortality. A chronic neurologic disease bearing the moniker of "the silent epidemic," TBI currently has no targeted therapies to ameliorate cellular loss or enhance functional recovery. Compared with those of astrocytes, microglia, and peripheral immune cells, the functions and mechanisms of NG2-glia following TBI are far less understood, despite NG2-glia comprising the largest population of regenerative cells in the mature cortex. Here, we synthesize the results from multiple rodent models of TBI, with a focus on cortical NG2-glia proliferation and lineage potential, and propose future avenues for glia researchers to address this unique cell type in TBI. As the molecular mechanisms that regulate NG2-glia regenerative potential are uncovered, we posit that future therapeutic strategies may exploit cortical NG2-glia to augment local cellular recovery following TBI.

Glial progenitor cells of the adult human white and grey matter are contextually distinct

Genomic analyses have revealed heterogeneity among glial progenitor cells (GPCs), but the compartment selectivity of human GPCs (hGPCs) is unclear. Here, we asked if GPCs of human grey and white brain matter are distinct in their architecture and associated gene expression. RNA profiling of NG2-defined hGPCs derived from adult human neocortex and white matter differed in their expression of genes involved in Wnt, NOTCH, BMP and TGFβ signaling, suggesting compartment-selective biases in fate and self-renewal. White matter hGPCs over-expressed the BMP antagonists BAMBI and CHRDL1, suggesting their tonic suppression of astrocytic fate relative to cortical hGPCs, whose relative enrichment of cytoskeletal genes presaged their greater morphological complexity. In human glial chimeric mice, cortical hGPCs assumed larger and more complex morphologies than white matter hGPCs, and both were more complex than their mouse counterparts. These findings suggest that human grey and white matter GPCs comprise context-specific pools with distinct functional biases.

Catalpol Regulates Oligodendrocyte Regeneration and Remyelination by Activating the GEF-Cdc42/Rac1 Signaling Pathway in EAE Mice

The main obstacle to remyelination in demyelinating diseases, such as multiple sclerosis, is the inability of oligodendrocyte precursor cells (OPCs) to differentiate into mature oligodendrocytes (OLs) in the demyelinating region. Consequently, promoting OL differentiation and myelin remodeling is a key goal in the search for treatments. Rho GTPases play diverse and important roles throughout the development of neuronal axons and the formation of the myelin sheath. The current study aimed to investigate the direct protective effects of catalpol on demyelination damage induced by myelin oligodendrocyte glycoprotein (MOG) immunization and to explore whether the GEF-Cdc42/Rac1 signaling pathway contributes to the regeneration effect induced by catalpol. In the MOG-induced experimental autoimmune encephalomyelitis (EAE) mouse model of demyelination, we observed that catalpol significantly promoted OL development by enhancing the expression of glutathione S-transferase pi (GST-pi) in the affected brain. By Luxol fast blue staining and myelin basic protein (MBP) expression assessment, catalpol was found to increase MBP expression and promote myelin repair. Furthermore, catalpol promoted OL differentiation associated with the upregulation of Cdc42/Rac1 expression and activation in vivo. In addition, PAK1/MRCKα, proteins downstream of Cdc42/Rac1, was positively regulated by catalpol. We also found that catalpol alleviated clinical neurological dysfunction, inhibited inflammatory infiltration, increased the proportion of Treg cells, and suppressed demyelination. Overall, our study is the first to reveal that catalpol can promote OL generation and myelination and contributes to the crucial regulatory process of GEF-Cdc42/Rac1 signaling expression and activation. Therefore, catalpol is a promising drug candidate for the potential treatment of demyelinating diseases.

Developmental Cues and Molecular Drivers in Myelinogenesis: Revisiting Early Life to Re-Evaluate the Integrity of CNS Myelin

The mammalian central nervous system (CNS) coordinates its communication through saltatory conduction, facilitated by myelin-forming oligodendrocytes (OLs). Despite the fact that neurogenesis from stem cell niches has caught the majority of attention in recent years, oligodendrogenesis and, more specifically, the molecular underpinnings behind OL-dependent myelinogenesis, remain largely unknown. In this comprehensive review, we determine the developmental cues and molecular drivers which regulate normal myelination both at the prenatal and postnatal periods. We have indexed the individual stages of myelinogenesis sequentially; from the initiation of oligodendrocyte precursor cells, including migration and proliferation, to first contact with the axon that enlists positive and negative regulators for myelination, until the ultimate maintenance of the axon ensheathment and myelin growth. Here, we highlight multiple developmental pathways that are key to successful myelin formation and define the molecular pathways that can potentially be targets for pharmacological interventions in a variety of neurological disorders that exhibit demyelination.

Glial Patchwork: Oligodendrocyte Progenitor Cells and Astrocytes Blanket the Central Nervous System

Tiling is a developmental process where cell populations become evenly distributed throughout a tissue. In this review, we discuss the developmental cellular tiling behaviors of the two major glial populations in the central nervous system (CNS)—oligodendrocyte progenitor cells (OPCs) and astrocytes. First, we discuss OPC tiling in the spinal cord, which is comprised of the three cellular behaviors of migration, proliferation, and contact-mediated repulsion (CMR). These cellular behaviors occur simultaneously during OPC development and converge to produce the emergent behavior of tiling which results in OPCs being evenly dispersed and occupying non-overlapping domains throughout the CNS. We next discuss astrocyte tiling in the cortex and hippocampus, where astrocytes migrate, proliferate, then ultimately determine their exclusive domains by gradual removal of overlap rather than sustained CMR. This results in domains that slightly overlap, allowing for both exclusive control of “synaptic islands” and astrocyte-astrocyte communication. We finally discuss the similarities and differences in the tiling behaviors of these glial populations and what remains unknown regarding glial tiling and how perturbations to this process may impact injury and disease.

The emerging role of the chondroitin sulfate proteoglycan family in neurodegenerative diseases

Chondroitin sulfate (CS) is a kind of linear polysaccharide that is covalently linked to proteins to form proteoglycans. Chondroitin sulfate proteoglycans (CSPGs) consist of a core protein, with one or more CS chains covalently attached. CSPGs are precisely regulated and they exert a variety of physiological functions by binding to adhesion molecules and growth factors. Widely distributed in the nervous system in human body, CSPGs contribute to the major component of extracellular matrix (ECM), where they play an important role in the development and maturation of the nervous system, as well as in the pathophysiological response to damage to the central nervous system (CNS). While there are more than 30 types of CSPGs, this review covers the roles of the most important ones, including versican, aggrecan, neurocan and NG2 in the pathogenesis of neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis and multiple sclerosis. The updated reports of the treatment of neurodegenerative diseases are involving CSPGs.

Mechanisms of oligodendrocyte progenitor developmental migration

Oligodendrocytes, the myelinating cells of the central nervous system (CNS), develop from oligodendrocyte progenitor cells (OPCs) that must first migrate extensively throughout the developing brain and spinal cord. Specified at particular times from discrete regions in the developing CNS, OPCs are one of the most migratory of cell types and disperse rapidly. A variety of factors act on OPCs to trigger intracellular changes that regulate their migration. We will discuss factors that act as long-range guidance cues, those that act to regulate cellular motility, and those that are critical in determining the final positioning of OPCs. In addition, recent evidence has identified the vasculature as the physical substrate used by OPCs for their migration. Several new findings relating to this oligodendroglial-vascular signaling axis reveal new insight on the relationship between OPCs and blood vessels in the developing and adult brain.

The effect of antiepileptic drugs on re-myelinization of axons: Phenytoin, levetiracetam, carbamazepine, and valproic acid, used following traumatic brain injury

OBJECTIVE

Traumatic brain injury is a major health and socioeconomic problem and the first cause of young death worldwide. For this reason, the prevention of post-traumatic brain injury and the research of new methods for it are important today. In this study, we aimed to determine whether the use of antiepileptic drugs contributed to axonal healing after traumatic brain injury.

METHODS

Thirty-six Long-Evans rats, each weighing 300-350 g, were used in this study. A total of 6 groups, including the sham, control, and 4 study groups, were determined. A 1.5 mm-sized trauma was created in the biparietal area with a blunt-tipped dissector. Carbamazepine phenytoin valproic acid and levetiracetam (phenytoin: 30 mg/kg, valproic acid: 60 mg/kg, levetiracetam: 80 mg/kg, and carbamazepine: 36 mg/kg) were intraperitoneally administered to the study groups, and the control group intraperitoneally received a physiological saline solution (15 ml/kg) twice daily for 3 days. After 72 h, hemispheres of the sacrificed subjects were taken for examination in biochemistry and histology. Glutathione, malondialdehyde, and NG2 levels in the samples were determined.

RESULTS

No significant difference was found in biochemical measurements. Histopathological examination revealed that the NG2 expression was more intense in the group treated with phenytoin and levetiracetam (phenytoin was partly higher) and the amount of edema decreased. The NG2 expression increased and the edema decreased, though lower in the group treated with carbamazepine and valproic acid, compared with phenytoin and levetiracetam. An increase in the NG2 expression and edema intensity were determined in the control and sham groups.

CONCLUSION

Antiepileptic drug selection after traumatic brain injury is an important medical matter. Although the patient-oriented selection is essential, the study suggests that the choice of phenytoin, levetiracetam carbamazepine, and valproic acid will, respectively, have an accelerating effect for axonal healing.

Diversity of Adult Neural Stem and Progenitor Cells in Physiology and Disease

Adult neural stem and progenitor cells (NSPCs) contribute to learning, memory, maintenance of homeostasis, energy metabolism and many other essential processes. They are highly heterogeneous populations that require input from a regionally distinct microenvironment including a mix of neurons, oligodendrocytes, astrocytes, ependymal cells, NG2+ glia, vasculature, cerebrospinal fluid (CSF), and others. The diversity of NSPCs is present in all three major parts of the CNS, i.e., the brain, spinal cord, and retina. Intrinsic and extrinsic signals, e.g., neurotrophic and growth factors, master transcription factors, and mechanical properties of the extracellular matrix (ECM), collectively regulate activities and characteristics of NSPCs: quiescence/survival, proliferation, migration, differentiation, and integration. This review discusses the heterogeneous NSPC populations in the normal physiology and highlights their potentials and roles in injured/diseased states for regenerative medicine.

Manipulating oligodendrocyte intrinsic regeneration mechanism to promote remyelination

In demyelinated lesions, astrocytes, activated microglia and infiltrating macrophages secrete several factors regulating oligodendrocyte precursor cells' behaviour. What appears to be the initiation of an intrinsic mechanism of myelin repair is only leading to partial recovery and inefficient remyelination, a process worsening over the course of the disease. This failure is largely due to the concomitant accumulation of inhibitory cues in and around the lesion sites opposing to growth promoting factors. Here starts a complex game of interactions between the signalling pathways controlling oligodendrocytes migration or differentiation. Receptors of positive or negative cues are modulating Ras, PI3K or RhoGTPases pathways acting on oligodendrocyte cytoskeleton remodelling. From the description of this intricate signalling network, this review addresses the extent to which the modulation of the global response to inhibitory cues may pave the route towards novel therapeutic approaches for myelin repair.

NG2-Glia Transiently Overcome Their Homeostatic Network and Contribute to Wound Closure After Brain Injury

In the adult brain, NG2-glia represent a cell population that responds to injury. To further investigate if, how and why NG2-glia are recruited to the injury site, we analyzed in detail the long-term reaction of NG2-glia after a lesion by time-lapse two-photon in vivo microscopy. Live imaging over several weeks of GFP-labeled NG2-glia in the stab wounded cerebral cortex revealed their fast and heterogeneous reaction, including proliferation, migration, polarization, hypertrophy, or a mixed response, while a small subset of cells remained unresponsive. At the peak of the reaction, 2-4 days after the injury, NG2-glia accumulated around and within the lesion core, overcoming the homeostatic control of their density, which normalized back to physiological conditions only 4 weeks after the insult. Genetic ablation of proliferating NG2-glia demonstrated that this accumulation contributed beneficially to wound closure. Thus, NG2-glia show a fast response to traumatic brain injury (TBI) and participate in tissue repair.

The Distribution of GPR17-Expressing Cells Correlates with White Matter Inflammation Status in Brain Tissues of Multiple Sclerosis Patients

In multiple sclerosis (MS), oligodendrocyte precursor cells (OPCs) are recruited to the site of injury to remyelinate damaged axons; however, in patients this process is often ineffective due to defects in OPC maturation. The membrane receptor GPR17 timely regulates the early stages of OPC differentiation; however, after reaching its highest levels in immature oligodendrocytes, it has to be downregulated to allow terminal maturation. Since, in several animal models of disease GPR17 is upregulated, the aim of this work was to characterize GPR17 alterations in MS patients. We developed immunohistochemistry and immunofluorescence procedures for the detection of GPR17 in human tissues and stained post-mortem MS brain lesions from patients with secondary progressive MS and control subjects. The inflammatory activity in each lesion was evaluated by immunohistochemistry for the myelin protein MOG and the HLA antigen to classify them as active, chronic inactive or chronic active. Hence, we assessed the distribution of GPR17-positive cells in these lesions compared to normal appearing white matter (NAWM) and white matter (WM) of control subjects. Our data have shown a marked increase of GPR17-expressing oligodendroglial cells accumulating at NAWM, in which moderate inflammation was also found. Furthermore, we identified two distinct subpopulations of GPR17-expressing oligodendroglial cells, characterized by either ramified or rounded morphology, that differently populate the WM of healthy controls and MS patients. We concluded that the coordinated presence of GPR17 in OPCs at the lesion sites and inflamed NAWM areas suggests that GPR17 could be exploited to support endogenous remyelination through advanced pharmacological approaches.

Microglial Cell Morphology and Phagocytic Activity Are Critically Regulated by the Neurosteroid Allopregnanolone: A Possible Role in Neuroprotection

Microglial cells are key players in neural pathogenesis and microglial function regulation appears to be pivotal in controlling neuroinflammatory/neurological diseases. Here, we investigated the effects and mechanism of action of neurosteroid allopregnanolone (ALLO) on murine microglial BV-2 cells and primary microglia in order to determine ALLO-induced immunomodulatory potential and to provide new insights for the development of both natural and safe neuroprotective strategies targeting microglia. Indeed, ALLO-treatment is increasingly suggested as beneficial in various models of neurological disorders but the underlying mechanisms have not been elucidated. Therefore, the microglial cells were cultured with various serum concentrations to mimic the blood-brain-barrier rupture and to induce their activation. Proliferation, viability, RT-qPCR, phagocytosis, and morphology analyzes, as well as migration with time-lapse imaging and quantitative morphodynamic methods, were combined to investigate ALLO actions on microglia. BV-2 cells express subunits of GABA-A receptor that mediates ALLO activity. ALLO (10µM) induced microglial cell process extension and decreased migratory capacity. Interestingly, ALLO modulated the phagocytic activity of BV-2 cells and primary microglia. Our results, which show a direct effect of ALLO on microglial morphology and phagocytic function, suggest that the natural neurosteroid-based approach may contribute to developing effective strategies against neurological disorders that are evoked by microglia-related abnormalities.

Neural crest cell-derived pericytes act as pro-angiogenic cells in human neocortex development and gliomas

Central nervous system diseases involving the parenchymal microvessels are frequently associated with a ‘microvasculopathy’, which includes different levels of neurovascular unit (NVU) dysfunction, including blood–brain barrier alterations. To contribute to the understanding of NVU responses to pathological noxae, we have focused on one of its cellular components, the microvascular pericytes, highlighting unique features of brain pericytes with the aid of the analyses carried out during vascularization of human developing neocortex and in human gliomas. Thanks to their position, centred within the endothelial/glial partition of the vessel basal lamina and therefore inserted between endothelial cells and the perivascular and vessel-associated components (astrocytes, oligodendrocyte precursor cells (OPCs)/NG2-glia, microglia, macrophages, nerve terminals), pericytes fulfil a central role within the microvessel NVU. Indeed, at this critical site, pericytes have a number of direct and extracellular matrix molecule- and soluble factor-mediated functions, displaying marked phenotypical and functional heterogeneity and carrying out multitasking services. This pericytes heterogeneity is primarily linked to their position in specific tissue and organ microenvironments and, most importantly, to their ontogeny. During ontogenesis, pericyte subtypes belong to two main embryonic germ layers, mesoderm and (neuro)ectoderm, and are therefore expected to be found in organs ontogenetically different, nonetheless, pericytes of different origin may converge and colonize neighbouring areas of the same organ/apparatus. Here, we provide a brief overview of the unusual roles played by forebrain pericytes in the processes of angiogenesis and barriergenesis by virtue of their origin from midbrain neural crest stem cells. A better knowledge of the ontogenetic subpopulations may support the understanding of specific interactions and mechanisms involved in pericyte function/dysfunction, including normal and pathological angiogenesis, thereby offering an alternative perspective on cell subtype-specific therapeutic approaches.

Neural crest cell-derived pericytes act as pro-angiogenic cells in human neocortex development and gliomas

Central nervous system diseases involving the parenchymal microvessels are frequently associated with a ‘microvasculopathy’, which includes different levels of neurovascular unit (NVU) dysfunction, including blood–brain barrier alterations. To contribute to the understanding of NVU responses to pathological noxae, we have focused on one of its cellular components, the microvascular pericytes, highlighting unique features of brain pericytes with the aid of the analyses carried out during vascularization of human developing neocortex and in human gliomas. Thanks to their position, centred within the endothelial/glial partition of the vessel basal lamina and therefore inserted between endothelial cells and the perivascular and vessel-associated components (astrocytes, oligodendrocyte precursor cells (OPCs)/NG2-glia, microglia, macrophages, nerve terminals), pericytes fulfil a central role within the microvessel NVU. Indeed, at this critical site, pericytes have a number of direct and extracellular matrix molecule- and soluble factor-mediated functions, displaying marked phenotypical and functional heterogeneity and carrying out multitasking services. This pericytes heterogeneity is primarily linked to their position in specific tissue and organ microenvironments and, most importantly, to their ontogeny. During ontogenesis, pericyte subtypes belong to two main embryonic germ layers, mesoderm and (neuro)ectoderm, and are therefore expected to be found in organs ontogenetically different, nonetheless, pericytes of different origin may converge and colonize neighbouring areas of the same organ/apparatus. Here, we provide a brief overview of the unusual roles played by forebrain pericytes in the processes of angiogenesis and barriergenesis by virtue of their origin from midbrain neural crest stem cells. A better knowledge of the ontogenetic subpopulations may support the understanding of specific interactions and mechanisms involved in pericyte function/dysfunction, including normal and pathological angiogenesis, thereby offering an alternative perspective on cell subtype-specific therapeutic approaches.

Myelin Debris Stimulates NG2/CSPG4 Expression in Bone Marrow-Derived Macrophages in the Injured Spinal Cord

Although the increased expression of members of the chondroitin sulfate proteoglycan family, such as neuron-glial antigen 2 (NG2), have been well documented after an injury to the spinal cord, a complete picture as to the cellular origins and function of this NG2 expression has yet to be made. Using a spinal cord injury (SCI) mouse model, we describe that some infiltrated bone marrow-derived macrophages (BMDMΦ) are early contributors to NG2/CSPG4 expression and secretion after SCI. We demonstrate for the first time that a lesion-related form of cellular debris generated from damaged myelin sheaths can increase NG2/CSPG4 expression in BMDMΦ, which then exhibit enhanced proliferation and decreased phagocytic capacity. These results suggest that BMDMΦ may play a much more nuanced role in secondary spinal cord injury than previously thought, including acting as early contributors to the NG2 component of the glial scar.

Oligodendroglial Energy Metabolism and (re)Myelination

Central nervous system (CNS) myelin has a crucial role in accelerating the propagation of action potentials and providing trophic support to the axons. Defective myelination and lack of myelin regeneration following demyelination can both lead to axonal pathology and neurodegeneration. Energy deficit has been evoked as an important contributor to various CNS disorders, including multiple sclerosis (MS). Thus, dysregulation of energy homeostasis in oligodendroglia may be an important contributor to myelin dysfunction and lack of repair observed in the disease. This article will focus on energy metabolism pathways in oligodendroglial cells and highlight differences dependent on the maturation stage of the cell. In addition, it will emphasize that the use of alternative energy sources by oligodendroglia may be required to save glucose for functions that cannot be fulfilled by other metabolites, thus ensuring sufficient energy input for both myelin synthesis and trophic support to the axons. Finally, it will point out that neuropathological findings in a subtype of MS lesions likely reflect defective oligodendroglial energy homeostasis in the disease.

Regenerative neurogenic response from glia requires insulin-driven neuron-glia communication

Understanding how injury to the central nervous system induces de novo neurogenesis in animals would help promote regeneration in humans. Regenerative neurogenesis could originate from glia and glial neuron-glia antigen-2 (NG2) may sense injury-induced neuronal signals, but these are unknown. Here, we used Drosophila to search for genes functionally related to the NG2 homologue kon-tiki (kon), and identified Islet Antigen-2 (Ia-2), required in neurons for insulin secretion. Both loss and over-expression of ia-2 induced neural stem cell gene expression, injury increased ia-2 expression and induced ectopic neural stem cells. Using genetic analysis and lineage tracing, we demonstrate that Ia-2 and Kon regulate Drosophila insulin-like peptide 6 (Dilp-6) to induce glial proliferation and neural stem cells from glia. Ectopic neural stem cells can divide, and limited de novo neurogenesis could be traced back to glial cells. Altogether, Ia-2 and Dilp-6 drive a neuron-glia relay that restores glia and reprogrammes glia into neural stem cells for regeneration.

Sphingosine-1-Phosphate Receptor Modulators and Oligodendroglial Cells: Beyond Immunomodulation

Multiple sclerosis (MS) is an autoimmune inflammatory disease characterized by demyelination, axonal loss, and synaptic impairment in the central nervous system (CNS). The available therapies aim to reduce the severity of the pathology during the early inflammatory stages, but they are not effective in the chronic stage of the disease. In this phase, failure in endogenous remyelination is associated with the impairment of oligodendrocytes progenitor cells (OPCs) to migrate and differentiate into mature myelinating oligodendrocytes. Therefore, stimulating differentiation of OPCs into myelinating oligodendrocytes has become one of the main goals of new therapeutic approaches for MS. Different disease-modifying therapies targeting sphingosine-1-phosphate receptors (S1PRs) have been approved or are being developed to treat MS. Besides their immunomodulatory effects, growing evidence suggests that targeting S1PRs modulates mechanisms beyond immunomodulation, such as remyelination. In this context, this review focuses on the current understanding of S1PR modulators and their direct effect on OPCs and oligodendrocytes.

iPS-Derived Early Oligodendrocyte Progenitor Cells from SPMS Patients Reveal Deficient In Vitro Cell Migration Stimulation

The most challenging aspect of secondary progressive multiple sclerosis (SPMS) is the lack of efficient regenerative response for remyelination, which is carried out by the endogenous population of adult oligoprogenitor cells (OPCs) after proper activation. OPCs must proliferate and migrate to the lesion and then differentiate into mature oligodendrocytes. To investigate the OPC cellular component in SPMS, we developed induced pluripotent stem cells (iPSCs) from SPMS-affected donors and age-matched controls (CT). We confirmed their efficient and similar OPC differentiation capacity, although we reported SPMS-OPCs were transcriptionally distinguishable from their CT counterparts. Analysis of OPC-generated conditioned media (CM) also evinced differences in protein secretion. We further confirmed SPMS-OPC CM presented a deficient capacity to stimulate OPC in vitro migration that can be compensated by exogenous addition of specific components. Our results provide an SPMS-OPC cellular model and encouraging venues to study potential cell communication deficiencies in the progressive form of multiple sclerosis (MS) for future treatment strategies.

Induction of immunological tolerance to myelinogenic glial-restricted progenitor allografts

The immunological barrier currently precludes the clinical utilization of allogeneic stem cells. Although glial-restricted progenitors have become attractive candidates to treat a wide variety of neurological diseases, their survival in immunocompetent recipients is limited. In this study, we adopted a short-term, systemically applicable co-stimulation blockade-based strategy using CTLA4-Ig and anti-CD154 antibodies to modulate T-cell activation in the context of allogeneic glial-restricted progenitor transplantation. We found that co-stimulation blockade successfully prevented rejection of allogeneic glial-restricted progenitors from immunocompetent mouse brains. The long-term engrafted glial-restricted progenitors myelinated dysmyelinated adult mouse brains within one month. Furthermore, we identified a set of plasma miRNAs whose levels specifically correlated to the dynamic changes of immunoreactivity and as such could serve as biomarkers for graft rejection or tolerance. We put forward a successful strategy to induce alloantigen-specific hyporesponsiveness towards stem cells in the CNS, which will foster effective therapeutic application of allogeneic stem cells.

Matrix metalloproteinases shape the oligodendrocyte (niche) during development and upon demyelination

The oligodendrocyte lineage cell is crucial to proper brain function. During central nervous system development, oligodendrocyte progenitor cells (OPCs) migrate and proliferate to populate the entire brain and spinal cord, and subsequently differentiate into mature oligodendrocytes that wrap neuronal axons in an insulating myelin layer. When damage occurs to the myelin sheath, OPCs are activated and recruited to the demyelinated site, where they differentiate into oligodendrocytes that remyelinate the denuded axons. The process of OPC attraction and differentiation is influenced by a multitude of factors from the cell's niche. Matrix metalloproteinases (MMPs) are powerful and versatile enzymes that do not only degrade extracellular matrix proteins, but also cleave cell surface receptors, growth factors, signaling molecules, proteases and other precursor proteins, leading to their activation or degradation. MMPs are markedly upregulated during brain development and upon demyelinating injury, where their broad functions influence the behavior of neural progenitor cells (NPCs), OPCs and oligodendrocytes. In this review, we focus on the role of MMPs in (re)myelination. We will start out in the developing brain with describing the effects of MMPs on NPCs, OPCs and eventually oligodendrocytes. Then, we will outline their functions in oligodendrocyte process extension and developmental myelination. Finally, we will review their potential role in demyelination, describe their significance in remyelination and discuss the evidence for a role of MMPs in remyelination failure, focusing on multiple sclerosis. In conclusion, MMPs shape the oligodendrocyte (niche) both during development and upon demyelination, and thus are important players in directing the fate and behavior of oligodendrocyte lineage cells throughout their life cycle.

Glial Cell AMPA Receptors in Nervous System Health, Injury and Disease

Glia form a central component of the nervous system whose varied activities sustain an environment that is optimised for healthy development and neuronal function. Alpha-amino-3-hydroxy-5-methyl-4-isoxazole (AMPA)-type glutamate receptors (AMPAR) are a central mediator of glutamatergic excitatory synaptic transmission, yet they are also expressed in a wide range of glial cells where they influence a variety of important cellular functions. AMPAR enable glial cells to sense the activity of neighbouring axons and synapses, and as such many aspects of glial cell development and function are influenced by the activity of neural circuits. However, these AMPAR also render glia sensitive to elevations of the extracellular concentration of glutamate, which are associated with a broad range of pathological conditions. Excessive activation of AMPAR under these conditions may induce excitotoxic injury in glial cells, and trigger pathophysiological responses threatening other neural cells and amplifying ongoing disease processes. The aim of this review is to gather information on AMPAR function from across the broad diversity of glial cells, identify their contribution to pathophysiological processes, and highlight new areas of research whose progress may increase our understanding of nervous system dysfunction and disease.

Novel Contribution of Secreted Amyloid-β Precursor Protein to White Matter Brain Enlargement in Autism Spectrum Disorder

The most replicated neuroanatomical finding in autism is the tendency toward brain overgrowth, especially in younger children. Research shows that both gray and white matter are enlarged. Proposed mechanisms underlying brain enlargement include abnormal inflammatory and neurotrophic signals that lead to excessive, aberrant dendritic connectivity via disrupted pruning and cell adhesion, and enlargement of white matter due to excessive gliogenesis and increased myelination. Amyloid-β protein precursor (βAPP) and its metabolites, more commonly associated with Alzheimer's disease (AD), are also dysregulated in autism plasma and brain tissue samples. This review highlights findings that demonstrate how one βAPP metabolite, secreted APPα, and the ADAM family α-secretases, may lead to increased brain matter, with emphasis on increased white matter as seen in autism. sAPPα and the ADAM family α-secretases contribute to the anabolic, non-amyloidogenic pathway, which is in contrast to the amyloid (catabolic) pathway known to contribute to Alzheimer disease. The non-amyloidogenic pathway could produce brain enlargement via genetic mechanisms affecting mRNA translation and polygenic factors that converge on molecular pathways (mitogen-activated protein kinase/MAPK and mechanistic target of rapamycin/mTOR), promoting neuroinflammation. A novel mechanism linking the non-amyloidogenic pathway to white matter enlargement is proposed: α-secretase and/or sAPPα, activated by ERK receptor signaling activates P13K/AKt/mTOR and then Rho GTPases favoring myelination via oligodendrocyte progenitor cell (OPC) activation of cofilin. Applying known pathways in AD to autism should allow further understanding and provide options for new drug targets.

Spatiotemporal expression patterns of chondroitin sulfate proteoglycan mRNAs in the developing rat brain

Chondroitin sulfate proteoglycans (CSPGs) are pluripotent components of the extracellular matrix in the brain. Although previous studies have examined the developmental change in certain CSPGs in the whole brain, no known systematic studies have been carried out on the temporal or spatial expression of CSPGs. Here, we used quantitative real-time PCR to examine the CSPG mRNAs expression in the postnatal developing rat brain starting from postnatal day 5-42, mainly focusing on the parietal cortex, hippocampus, and corpus callosum. Results were further verified by immunohistochemistry. Our results showed that aggrecan, brevican, phosphacan, and NG2 generally showed upregulation across developmental stages in all three regions. Neurocan showed a rapid increase until postnatal day 10 in all three regions. Versican, however, showed a sharp decrease until postnatal day 10. Cross-region analysis showed higher expression of most CSPG members in the corpus callosum during later stages of development. Further immunohistochemistry staining confirmed our results by showing prominent CSPGs protein expression in the corpus callosum. In summary, our study reported specific temporal-expression and spatial-expression patterns of the CSPGs species. These results are consistent with the known roles of these members in neurodevelopment. The current study provided clues for the development of CSPGs as potential treatment targets in neurodevelopmental disorders.

Microglial Depletion with Clodronate Liposomes Increases Proinflammatory Cytokine Levels, Induces Astrocyte Activation, and Damages Blood Vessel Integrity

Investigators are increasingly interested in using microglial depletion to study the role of microglia under pathologic conditions. Liposome-encapsulated clodronate is commonly used to eliminate macrophage populations because it causes functionally irreversible inhibition and apoptosis once phagocytized by macrophages. Recent studies have shown that microglia can be depleted in disease models by injecting clodronate liposomes into the brain parenchyma. However, it is unclear whether intracerebral administration of clodronate liposomes is a practical method of eliminating microglia under physiologic conditions or whether microglial depletion induces damage to other brain cells. In this study, injecting 1 μL of clodronate liposomes (7 μg/μL) into the striatum of mice caused ablation of microglia at 1 day that persisted for 3 days. Microglia reappeared in the boundary regions of microglia elimination after 5 days. Importantly, we observed an increase in proinflammatory cytokine levels and an increase in neural/glial antigen 2 and glial fibrillary acidic protein expression in the perilesional region. In contrast, expression levels of myelin basic protein, microtubule-associated protein 2, and postsynaptic protein-95 decreased in the periphery of regions where microglia were depleted. Moreover, clodronate liposome administration decreased the density and integrity of blood vessels in the perilesional regions. In cultured primary neurons, clodronate liposome exposure also attenuated ATP synthesis. Together, these findings suggest that intracerebral administration of clodronate liposomes into brain parenchyma can deplete microglia, but can also damage other brain cells and blood vessel integrity.

Structural deciphering of the NG2/CSPG4 proteoglycan multifunctionality

The chondroitin sulfate proteoglycan 4 ( CSPG4) gene encodes a transmembrane proteoglycan (PG) constituting the largest and most structurally complex macromolecule of the human surfaceome. Its transcript shows an extensive evolutionary conservation and, due to the elaborated intracellular processing of the translated protein, it generates an array of glycoforms with the potential to exert variant-specific functions. CSPG4-mediated molecular events are articulated through the interaction with more than 40 putative ligands and the concurrent involvement of the ectodomain and cytoplasmic tail. Alternating inside-out and outside-in signal transductions may thereby be elicited through a tight functional connection of the PG with the cytoskeleton and its regulators. The potential of CSPG4 to influence both types of signaling mechanisms is also asserted by its lateral mobility along the plasma membrane and its intersection with microdomain-restricted internalization and endocytic trafficking. Owing to the multitude of molecular interplays that CSPG4 may engage, and thanks to a differential phosphorylation of its intracellular domain accounted by crosstalking signaling pathways, the PG stands out for its unique capability to affect numerous cellular phenomena, including those purporting pathologic conditions. We discuss here the progresses made in advancing our understanding about the structural-functional bases for the ability of CSPG4 to widely impact on cell behavior, such as to highlight how its multivalency may be exploited to interfere with disease progression.-Tamburini, E., Dallatomasina, A., Quartararo, J., Cortelazzi, B., Mangieri, D., Lazzaretti, M., Perris, R. Structural deciphering of the NG2/CSPG4 proteoglycan multifunctionality.

Cognitive deficits in mice lacking Nsun5, a cytosine-5 RNA methyltransferase, with impairment of oligodendrocyte precursor cells

Williams-Beuren syndrome (WBS) is a microdeletion disorder with cognitive phenotype. NSUN5 gene, which encodes a cytosine-5 RNA methyltransferase, is located in WBS deletion locus. To investigate the influence of NSUN5 deletion on cognitive behaviors, we produced single-gene Nsun5 knockout (Nsun5-KO) mice. Here, we report that adult Nsun5-KO mice showed spatial cognitive deficits. Size of the brain and hippocampal structures and the number of CA1 or CA3 pyramidal cells in Nsun5-KO mice did not differ from WT mice. Basal properties of Schaffer collateral-CA1 synaptic transmission in Nsun5-KO mice were unchanged, but NMDA receptor (NMDAr)-dependent long-term potentiation (LTP) was not induced. The NMDA-evoked current in CA1 pyramidal cells was reduced in Nsun5-KO mice without the changes in expression and phosphorylation of NMDAr subunits NR2A and NR2B. Although the protein level of AMPA receptor subunit GluR2 was attenuated in Nsun5-KO mice, the AMPA-evoked current was not altered. Hippocampal immuno-staining showed the selective expression of Nsun5 in NG2 or PDGFRα labeled oligodendrocyte precursor cells (OPCs), but not in pyramidal cells or astrocytes. Analysis of RT-PCR determined the Nsun5 expression in purified populations of OPCs rather than neurons or astrocytes. The Nsun5 deficiency led to decreases in the number and neurite outgrowth of OPCs in the hippocampal CA1 and DG, with the decline in NG2 expression and OPCs proliferation. These findings indicate that the Nsun5 deletion suppresses NMDAr activity in neuronal cells probably through the disrupted development and function of OPCs, leading to deficits in NMDAr-dependent LTP and spatial cognitive abilities.

The Intracellular Cleavage Product of the NG2 Proteoglycan Modulates Translation and Cell-Cycle Kinetics via Effects on mTORC1/FMRP Signaling

The NG2 proteoglycan is expressed by oligodendrocyte precursor cells (OPCs) and is abundantly expressed by tumors such as melanoma and glioblastoma. Functions of NG2 include an influence on proliferation, migration and neuromodulation. Similar to other type-1 membrane proteins, NG2 undergoes proteolysis, generating a large ectodomain, a C-terminal fragment (CTF) and an intracellular domain (ICD) via sequential action of α- and γ-secretases which is enhanced by neuronal activity. Functional roles of NG2 have so far been shown for the full-length protein, the released ectodomain and CTF, but not for the ICD. In this study, we characterized the role of the NG2 ICD in OPC and Human Embryonic Kidney (HEK) cells. Overexpressed ICD is predominantly localized in the cell cytosol, including the distal processes of OPCs. Nuclear localisation of a fraction of the ICD is dependent on Nuclear Localisation Signals. Immunoprecipitation and Mass Spectrometry followed by functional analysis indicated that the NG2 ICD modulates mRNA translation and cell-cycle kinetics. In OPCs and HEK cells, ICD overexpression results in an mTORC1-dependent upregulation of translation, as well as a shift of the cell population toward S-phase. NG2 ICD increases the active (phosphorylated) form of mTOR and modulates downstream signaling cascades, including increased phosphorylation of p70S6K1 and increased expression of eEF2. Strikingly, levels of FMRP, an RNA-binding protein that is regulated by mTOR/p70S6K1/eEF2 were decreased. In neurons, FMRP acts as a translational repressor under activity-dependent control and is mutated in Fragile X Syndrome (FXS). Knock-down of endogenous NG2 in primary OPC reduced translation and mTOR/p70S6K1 phosphorylation in Oli-neu. Here, we identify the NG2 ICD as a regulator of translation in OPCs via modulation of the well-established mTORC1 pathway. We show that FXS-related FMRP signaling is not exclusive to neurons but plays a role in OPCs. This provides a signal cascade in OPC which can be influenced by the neuronal network, since the NG2 ICD has been shown to be generated by constitutive as well as activity-dependent cleavage. Our results also elucidate a possible role of NG2 in tumors exhibiting enhanced rates of translation and rapid cell cycle kinetics.

Therapeutic Strategies for Leukodystrophic Disorders Resulting from Perinatal Asphyxia: Focus on Myelinating Oligodendrocytes

Perinatal asphyxia results from the action of different risk factors like complications during pregnancy, preterm delivery, or long and difficult labor. Nowadays, it is still the leading cause of neonatal brain injury known as hypoxic-ischemic encephalopathy (HIE) and resulting neurological disorders. A temporal limitation of oxygen, glucose, and trophic factors supply results in alteration of neural cell differentiation and functioning and/or leads to their death. Among the affected cells are oligodendrocytes, responsible for myelinating the central nervous system (CNS) and formation of white matter. Therefore, one of the major consequences of the experienced HIE is leukodystrophic diseases resulting from oligodendrocyte deficiency or malfunctioning. The therapeutic strategies applied after perinatal asphyxia are aimed at reducing brain damage and promoting the endogenous neuroreparative mechanisms. In this review, we focus on the biology of oligodendrocytes and discuss present clinical treatments in the context of their efficiency in preserving white matter structure and preventing cognitive and behavioral deficits after perinatal asphyxia.

Neurofibromatosis type 2 tumor suppressor protein is expressed in oligodendrocytes and regulates cell proliferation and process formation

The neurofibromatosis type 2 (NF2) tumor suppressor protein Merlin functions as a negative regulator of cell growth and actin dynamics in different cell types amongst which Schwann cells have been extensively studied. In contrast, the presence and the role of Merlin in oligodendrocytes, the myelin forming cells within the CNS, have not been elucidated. In this work, we demonstrate that Merlin immunoreactivity was broadly distributed in the white matter throughout the central nervous system. Following Merlin expression during development in the cerebellum, Merlin could be detected in the cerebellar white matter tract at early postnatal stages as shown by its co-localization with Olig2-positive cells as well as in adult brain sections where it was aligned with myelin basic protein containing fibers. This suggests that Merlin is expressed in immature and mature oligodendrocytes. Expression levels of Merlin were low in oligodendrocytes as compared to astrocytes and neurons throughout development. Expression of Merlin in oligodendroglia was further supported by its identification in either immortalized cell lines of oligodendroglial origin or in primary oligodendrocyte cultures. In these cultures, the two main splice variants of Nf2 could be detected. Merlin was localized in clusters within the nuclei and in the cytoplasm. Overexpressing Merlin in oligodendrocyte cell lines strengthened reduced impedance in XCELLigence measurements and Ki67 stainings in cultures over time. In addition, the initiation and elongation of cellular projections were reduced by Merlin overexpression. Consistently, cell migration was retarded in scratch assays done on Nf2-transfected oligodendrocyte cell lines. These data suggest that Merlin actively modulates process outgrowth and migration in oligodendrocytes.

In vivo spatiotemporal dynamics of NG2 glia activity caused by neural electrode implantation

Neural interface technology provides direct sampling and analysis of electrical and chemical events in the brain in order to better understand neuronal function and treat neurodegenerative disease. However, intracortical electrodes experience inflammatory reactions that reduce long-term stability and functionality and are understood to be facilitated by activated microglia and astrocytes. Emerging studies have identified another cell type that participates in the formation of a high-impedance glial scar following brain injury; the oligodendrocyte precursor cell (OPC). These cells maintain functional synapses with neurons and are a crucial source of neurotrophic support. Following injury, OPCs migrate toward areas of tissue injury over the course of days, similar to activated microglia. The delayed time course implicates these OPCs as key components in the formation of the outer layers of the glial scar around the implant. In vivo two-photon laser scanning microscopy (TPLSM) was employed to observe fluorescently-labeled OPC and microglia reactivity up to 72 h following probe insertion. OPCs initiated extension of cellular processes (2.5 ± 0.4 μm h-1) and cell body migration (1.6 ± 0.3 μm h-1) toward the probe beginning 12 h after insertion. By 72 h, OPCs became activated at a radius of about 190.3 μm away from the probe surface. This study characterized the early spatiotemporal dynamics of OPCs involved in the inflammatory response induced by microelectrode insertion. OPCs are key mediators of tissue health and are understood to have multiple fate potentials. Detailed spatiotemporal characterization of glial behavior under pathological conditions may allow identification of alternative intervention targets for mitigating the formation of a glial scar and subsequent neurodegeneration that debilitates chronic neural interfaces.

ASCL1 regulates proliferation of NG2-glia in the embryonic and adult spinal cord

NG2‐glia are highly proliferative oligodendrocyte precursor cells (OPCs) that are widely distributed throughout the central nervous system (CNS). During development, NG2‐glia predominantly differentiate into oligodendrocytes (OLs) to myelinate axon fibers, but they can also remain as OPCs persisting into the mature CNS. Interestingly, NG2‐glia in the gray matter (GM) are intrinsically different from those in the white matter (WM) in terms of proliferation, differentiation, gene expression, and electrophysiological properties. Here we investigate the role of the transcriptional regulator, ASCL1, in controlling NG2‐glia distribution and development in the GM and WM. In the spinal cord, ASCL1 levels are higher in WM NG2‐glia than those in the GM. This differential level of ASCL1 in WM and GM NG2‐glia is maintained into adult stages. Long‐term clonal lineage analysis reveals that the progeny of single ASCL1+ oligodendrocyte progenitors (OLPs) and NG2‐glia are primarily restricted to the GM or WM, even though they undergo extensive proliferation to give rise to large clusters of OLs in the postnatal spinal cord. Conditional deletion of Ascl1 specifically in NG2‐glia in the embryonic or adult spinal cord resulted in a significant reduction in the proliferation but not differentiation of these cells. These findings illustrate that ASCL1 is an intrinsic regulator of the proliferative property of NG2‐glia in the CNS.

Cell Replacement to Reverse Brain Aging: Challenges, Pitfalls, and Opportunities

Current antiaging strategies focusing on druggable targets have met with relatively limited success to date. Replacement of cells, tissues, and organs could provide an alternative means for targeting age-induced damage and potentially eliminating some of it. However, before this is a viable option, numerous challenges need to be addressed. Most notably, whether the brain, which defines our self-identity, is amenable to replacement therapies is unclear. Here, we consider whether progressive cell replacement is a potential approach to reverse brain aging without grossly altering function. We focus mainly on the neocortex, seat of our highest cognitive functions, because of abundant knowledge on neocortical development, plasticity, and how the neocortex can functionally incorporate new neurons. We outline the primary challenges for brain cell replacement, and key areas that require further investigation.

Loss of Mpdz impairs ependymal cell integrity leading to perinatal-onset hydrocephalus in mice

Hydrocephalus is a common congenital anomaly. LCAM1 and MPDZ (MUPP1) are the only known human gene loci associated with non‐syndromic hydrocephalus. To investigate functions of the tight junction‐associated protein Mpdz, we generated mouse models. Global Mpdz gene deletion or conditional inactivation in Nestin‐positive cells led to formation of supratentorial hydrocephalus in the early postnatal period. Blood vessels, epithelial cells of the choroid plexus, and cilia on ependymal cells, which line the ventricular system, remained morphologically intact in Mpdz‐deficient brains. However, flow of cerebrospinal fluid through the cerebral aqueduct was blocked from postnatal day 3 onward. Silencing of Mpdz expression in cultured epithelial cells impaired barrier integrity, and loss of Mpdz in astrocytes increased RhoA activity. In Mpdz‐deficient mice, ependymal cells had morphologically normal tight junctions, but expression of the interacting planar cell polarity protein Pals1 was diminished and barrier integrity got progressively lost. Ependymal denudation was accompanied by reactive astrogliosis leading to aqueductal stenosis. This work provides a relevant hydrocephalus mouse model and demonstrates that Mpdz is essential to maintain integrity of the ependyma.

NG2 and GFAP co-expression after differentiation in cells transfected with mutant GFAP and in undifferentiated glioma cells

INTRODUCTION

Alexander disease is a rare disorder caused by mutations in the gene coding for glial fibrillary acidic protein (GFAP). In a previous study, differentiation of neurospheres transfected with these mutations resulted in a cell type that expresses both GFAP and NG2.

OBJECTIVE

To determine the effect of molecular marker mutations in comparison to undifferentiated glioma cells simultaneously expressing GFAP and NG2.

METHODS

We used samples of human glioblastoma (GBM) and rat neurospheres transfected with GFAP mutations to analyse GFAP and NG2 expression after differentiation. We also performed an immunocytochemical analysis of neuronal differentiation for both cell types and detection of GFAP, NG2, vimentin, Olig2, and caspase-3 at 3 and 7 days from differentiation.

RESULTS

Both the cells transfected with GFAP mutations and GBM cells showed increased NG2 and GFAP expression. However, expression of caspase-3-positive cells was found to be considerably higher in transfected cells than in GBM cells.

CONCLUSIONS

Our results suggest that GFAP expression is not the only factor associated with cell death in Alexander disease. Caspase-3 expression and the potential role of NG2 in increasing resistance to apoptosis in cells co-expressing GFAP and NG2 should be considered in the search for new therapeutic strategies for the disease.

The Effect of Traditional Chinese Medicine on Neural Stem Cell Proliferation and Differentiation

Neural stem cells (NSCs) are special types of cells with the potential for self-renewal and multi-directional differentiation. NSCs are regulated by multiple pathways and pathway related transcription factors during the process of proliferation and differentiation. Numerous studies have shown that the compound medicinal preparations, single herbs, and herb extracts in traditional Chinese medicine (TCM) have specific roles in regulating the proliferation and differentiation of NSCs. In this study, we investigate the markers of NSCs in various stages of differentiation, the related pathways regulating the proliferation and differentiation, and the corresponding transcription factors in the pathways. We also review the influence of TCM on NSC proliferation and differentiation, to facilitate the development of TCM in neural regeneration and neurodegenerative diseases.

The role of oligodendrocyte precursor cells expressing the GPR17 receptor in brain remodeling after stroke

Following stroke-induced neuronal damage, quiescent oligodendrocyte precursors (OPCs) are activated to proliferate and later to differentiate to myelin-producing cells. GPR17, a receptor transiently expressed on early OPCs, has emerged as a target to implement stroke repair through stimulation of OPC maturation. However, being GPR17 completely downregulated in myelin-producing oligodendrocytes, its actual role in determining the final fate of OPCs after cerebral ischemia is still uncertain. Here, to univocally define the spatiotemporal changes and final fate of GPR17-expressing OPCs, we induced ischemia by middle cerebral artery occlusion (MCAo) in reporter GPR17iCreERT2:CAG-eGreen florescent protein (GFP) mice, in which, upon tamoxifen treatment, cells expressing GPR17 become green and traceable for their entire life. Starting from 3 days and up to 2 weeks after MCAo, GFP+ cells markedly accumulated in regions surrounding the ischemic lesion; several of them proliferated, as shown by co-labeling of the DNA synthesis marker 5-Bromo-2'-deoxyuridine (BrdU). Almost all GFP+/BrdU+ cells expressed the OPC early marker neural/glial antigen 2 (NG2), indicating that they were still precursors. Accumulation of GFP+ cells was also because of OPC recruitment from surrounding areas, as suggested in vivo by acquisition of typical features of migrating OPCs, shown in vitro in presence of the chemoattractant PDGF-AA and confirmed by transplantation of GFP+-OPCs in wild-type MCAo mice. Eight weeks after MCAo, only some of these precociously recruited cells had undergone maturation as shown by NG2 loss and acquisition of mature myelinating markers like GSTpi. A pool of recruited GFP+-OPCs was kept at a precursor stage to likely make it available for further insults. Thus, very early after ischemia, GFP+-OPCs proliferate and migrate toward the lesion; however, most of these cells remain undifferentiated, suggesting functional roles other than myelination.

Neuro-psychopharmacological perspective of Orphan receptors of Rhodopsin (class A) family of G protein-coupled receptors

BACKGROUND

In the central nervous system (CNS), G protein-coupled receptors (GPCRs) are the most fruitful targets for neuropsychopharmacological drug development. Rhodopsin (class A) is the most studied class of GPCR and includes orphan receptors for which the endogenous ligand is not known or is unclear. Characterization of orphan GPCRs has proven to be challenging, and the production pace of GPCR-based drugs has been incredibly slow.

OBJECTIVE

Determination of the functions of these receptors may provide unexpected insight into physiological and neuropathological processes. Advances in various methods and techniques to investigate orphan receptors including in situ hybridization and knockdown/knockout (KD/KO) showed extensive expression of these receptors in the mammalian brain and unmasked their physiological and neuropathological roles. Due to these rapid progress and development, orphan GPCRs are rising as a new and promising class of drug targets for neurodegenerative diseases and psychiatric disorders.

CONCLUSION

This review presents a neuropsychopharmacological perspective of 26 orphan receptors of rhodopsin (class A) family, namely GPR3, GPR6, GPR12, GPR17, GPR26, GPR35, GPR39, GPR48, GPR49, GPR50, GPR52, GPR55, GPR61, GPR62, GPR63, GPR68, GPR75, GPR78, GPR83, GPR84, GPR85, GPR88, GPR153, GPR162, GPR171, and TAAR6. We discussed the expression of these receptors in mammalian brain and their physiological roles. Furthermore, we have briefly highlighted their roles in neurodegenerative diseases and psychiatric disorders including Alzheimer's disease, Parkinson's disease, neuroinflammation, inflammatory pain, bipolar and schizophrenic disorders, epilepsy, anxiety, and depression.

Role of Oligodendrocyte Dysfunction in Demyelination, Remyelination and Neurodegeneration in Multiple Sclerosis

Oligodendrocytes (OLs) are the myelinating cells of the central nervous system (CNS) during development and throughout adulthood. They result from a complex and well controlled process of activation, proliferation, migration and differentiation of oligodendrocyte progenitor cells (OPCs) from the germinative niches of the CNS. In multiple sclerosis (MS), the complex pathological process produces dysfunction and apoptosis of OLs leading to demyelination and neurodegeneration. This review attempts to describe the patterns of demyelination in MS, the steps involved in oligodendrogenesis and myelination in healthy CNS, the different pathways leading to OLs and myelin loss in MS, as well as principles involved in restoration of myelin sheaths. Environmental factors and their impact on OLs and pathological mechanisms of MS are also discussed. Finally, we will present evidence about the potential therapeutic targets in re-myelination processes that can be accessed in order to develop regenerative therapies for MS.

The G Protein-Coupled Receptor GPR17: Overview and Update

The GPR17 receptor is a G protein-coupled receptor (GPCR) that seems to respond to two unrelated families of endogenous ligands: nucleotide sugars (UDP, UDP-galactose, and UDP-glucose) and cysteinyl leukotrienes (LTD₄ , LTC₄ , and LTE₄ ), with significant affinity at micromolar and nanomolar concentrations, respectively. This receptor has a broad distribution at the level of the central nervous system (CNS) and is found in neurons and in a subset of oligodendrocyte precursor cells (OPCs). Unfortunately, disparate results emerging from different laboratories have resulted in a lack of clarity with regard to the role of GPR17-targeting ligands in OPC differentiation and in myelination. GPR17 is also highly expressed in organs typically undergoing ischemic damage and has various roles in specific phases of adaptations that follow a stroke. Under such conditions, GPR17 plays a crucial role; in fact, its inhibition decreases the progression of ischemic damage. This review summarizes some important features of this receptor that could be a novel therapeutic target for the treatment of demyelinating diseases and for repairing traumatic injury.

Roles of chondroitin sulfate proteoglycan 4 in fibrogenic/adipogenic differentiation in skeletal muscle tissues

Intramuscular adipose tissue and fibrous tissue are observed in some skeletal muscle pathologies such as Duchenne muscular dystrophy and sarcopenia, and affect muscle strength and myogenesis. They originate from common fibrogenic/adipogenic cells in the skeletal muscle. Thus, elucidating the regulatory mechanisms underlying fibrogenic/adipogenic cell differentiation is an important step toward the mediation of these disorders. Previously, we established a highly adipogenic progenitor clone, 2G11, from rat skeletal muscle and showed that basic fibroblast growth factor (bFGF) is pro-adipogenic in these cells. Here, we demonstrated that 2G11 cells give rise to fibroblasts upon transforming growth factor (TGF)-β1 stimulation, indicating that they possess mesenchymal progenitor cells (MPC)-like characteristics. The previously reported MPC marker PDGFRα is expressed in other cell populations. Accordingly, we produced monoclonal antibodies that specifically bind to 2G11 cell surface antigens and identified chondroitin sulfate proteoglycan 4 (CSPG4) as a potential MPC marker. Based on an RNA interference analysis, we found that CSPG4 is involved in both the pro-adipogenic effect of bFGF and in TGF-β-induced alpha smooth muscle actin expression and stress fiber formation. By establishing an additional marker for MPC detection and characterizing its role in fibrogenic/adipogenic differentiation, these results will facilitate the development of effective treatments for skeletal muscle pathologies.