Myelination generates aberrant ultrastructure that is resolved by microglia.

To enable rapid propagation of action potentials, axons are ensheathed by myelin, a multilayered insulating membrane formed by oligodendrocytes. Most of the myelin is generated early in development, resulting in the generation of long-lasting stable membrane structures. Here, we explored structural and dynamic changes in central nervous system myelin during development. To achieve this, we performed an ultrastructural analysis of mouse optic nerves by serial block face scanning electron microscopy (SBF-SEM) and confocal time-lapse imaging in the zebrafish spinal cord. We found that myelin undergoes extensive ultrastructural changes during early postnatal development. Myelin degeneration profiles were engulfed and phagocytosed by microglia using exposed phosphatidylserine as one "eat me" signal. In contrast, retractions of entire myelin sheaths occurred independently of microglia and involved uptake of myelin by the oligodendrocyte itself. Our findings show that the generation of myelin early in development is an inaccurate process associated with aberrant ultrastructural features that require substantial refinement.

[Specific interactions between microglia and oligodendrocytes in white matter in continuous schizophrenia]. / Osobennosti vzaimodeistviya mikroglii i oligodendrotsitov v belom veshchestve pri nepreryvnotekushchei shizofrenii.

OBJECTIVE: To study the ultrastructure of microglia adjacent to oligodendrocytes in white matter of the prefrontal cortex in continuous schizophrenia (CSch) as compared to controls and attack-like schizophrenia (ASch) and to perform correlation analysis between the parameters of microglia and adjacent oligodendrocytes previously detected in both clinical types of schizophrenia. MATERIAL AND METHODS: Electron microscopic morphometric study of microglia adjacent to oligodendrocytes was performed in postmortem white matter of the prefrontal cortex (BA10) in 9 cases of CSch, 8 cases of ASch and 20 healthy controls. Group comparisons were made by ANCOVA and Pearson correlation analyses. RESULTS: The reduction of volume fraction (Vv) and the number of mitochondria in microglia was found in elderly subjects (>50 y.o.) as compared to young controls (60%, p<0.05), and the increase in these parameters of lipofuscin granules were detected in elderly subjects as compared to elderly controls in CSch (470%, 606%, p<0.001). Vv and the number of mitochondria in microglia correlated negatively with area of heterochromatin in microglia (r≥-0.7, p<0.05), and area of lipofuscin correlated positively with area of heterochromatin in microglia (r=0.76, p<0.05) and with illness duration (r=0.7, p<0.05) only in the CSch group. The numerical density of microglia was not changed in both schizophrenia groups. Area of heterochromatin was increased in both groups as compared to controls (p<0.05) and correlated negatively with the numerical density of microglia in the CSch group. The number of mitochondria in oligodendrocytes (reduced in CSch) correlated positively with the number of mitochondria in microglia and negatively with Vv of lipofuscin granules in microglia and with area of microglial nucleus only in the CSch group. CONCLUSION: Specific features of CSch as compared to ASch might be associated with the disturbances of mitochondrial and lipid metabolism in microglia, dysfunction of nucleus and accelerated aging of microglia that might lead to alterations of mitochondrial metabolism in oligodendrocytes.

Nutritional regulation of oligodendrocyte differentiation regulates perineuronal net remodeling in the median eminence.

The mediobasal hypothalamus (MBH; arcuate nucleus of the hypothalamus [ARH] and median eminence [ME]) is a key nutrient sensing site for the production of the complex homeostatic feedback responses required for the maintenance of energy balance. Here, we show that refeeding after an overnight fast rapidly triggers proliferation and differentiation of oligodendrocyte progenitors, leading to the production of new oligodendrocytes in the ME specifically. During this nutritional paradigm, ME perineuronal nets (PNNs), emerging regulators of ARH metabolic functions, are rapidly remodeled, and this process requires myelin regulatory factor (Myrf) in oligodendrocyte progenitors. In genetically obese ob/ob mice, nutritional regulations of ME oligodendrocyte differentiation and PNN remodeling are blunted, and enzymatic digestion of local PNN increases food intake and weight gain. We conclude that MBH PNNs are required for the maintenance of energy balance in lean mice and are remodeled in the adult ME by the nutritional control of oligodendrocyte differentiation.

Spatiotemporal dynamic changes, proliferation, and differentiation characteristics of Sox9-positive cells after severe complete transection spinal cord injury.

Studying the spatiotemporal dynamic changes of various cells following spinal cord injury (SCI) is of great significance for understanding the pathological processes of SCI. Changes in the characteristics of Sox9-positive cells, which are widely present in the spinal cord, have rarely been studied following SCI. We found that Sox9-positive cells were widely distributed in the central canal and parenchyma of the uninjured adult spinal cord, with the greatest distribution in the central spinal cord and relatively few cells in the dorsal and ventral sides. Ranging between 14.20% ± 1.61% and 15.60% ± 0.36% of total cells in the spinal cord, almost all Sox9-positive cells were in a quiescent state. However, Sox9-positive cells activated following SCI exhibited different characteristics according to their distance from the lesion area. In the reactive region, Sox9-positive cells highly expressed nestin and exhibited a single-branching structure, whereas in the non-reactive region, cells showed low nestin expression and a multi-branching structure. In response to SCI, a large number of Sox9-positive cells in the spinal cord parenchyma proliferated to participate in the formation of glial scars, whereas Sox9-positive cells in the central canal located near the lesion site accumulated at its broken ends through proliferation. Finally, we found that approximately 6.30% ± 0.35% of Sox9-positive cells differentiated into oligodendrocytes within two weeks after SCI. By examining the spatiotemporal dynamic changes, proliferation and differentiation characteristics of Sox9-positive cells after SCI, our findings provide a theoretical basis for understanding the pathological process of SCI.

Altered oligodendrocytes in spinal enlargements of streptozotocin diabetic rats / Oligodendrocitos alterados en la intumescencia espinal de ratas diabéticas con estreptozotocina

SUMMARY: Disturbances of sensory and motor nerve conduction velocity in the spinal cord as well as degenerated myelin sheaths are observed in diabetic patients and animal models. Indeed, oligodendrocytes (OLs), which are important neuroglial cells, generate myelin in the central nervous system. Spinal enlargement, including cervical and lumbar enlargements, innervates all limbs. Thus, the purposes of this study were to examine and compare the ultrastructural alterations of OLs in spinal enlargements of streptozotocin (STZ)- induced diabetic rats and controls. Thirteen male Sprague-Dawley rats were induced with STZ in citrate buffer and six control rats were injected with the same buffer solution. All rats were sacrificed after inductions at four (short-term DM) and twenty-four weeks (long-term DM). The selected spinal enlargements were processed for transmission electron microscopy. The OL alterations in both the cervical and lumbar enlargements were apparently the same. In short-term DM, the nuclei of OLs became swelled with chromatin clumping. Cytoplasmic organelles were moderately damaged. In long-term DM, OLs contained shrinkage nuclei with thick heterochromatin clumping. Severely degenerated mitochondria with disrupted cristae and broken membranes were observed. Moreover, distended and fragmented rough endoplasmic reticulum were observed, and large clear areas were present in the cytoplasm. Additionally, the loosening, splitting, and destruction of myelin lamellae were found. This study can provide important preliminary information about the alteration of OLs in the spinal cords of diabetic patients, which might be involve in the impairments of sensory and motor conduction velocities in these individuals.

RESUMEN: En pacientes diabéticos y modelos animales se observan alteraciones de la velocidad de conducción nerviosa sensorial y motora en la médula espinal, así como vainas de mielina degeneradas. De hecho, los oligodendrocitos (OL), que son importantes células neurogliales, generan mielina en el sistema nervioso central. La intumescencia espinal, a nivel cervical y lumbar, inerva los miembros. Por lo tanto, los propósitos de este estudio fueron examinar y comparar las alteraciones ultraestructurales de los OL en la intumescencia espinal de ratas diabéticas inducidas por estreptozotocina (STZ) y controles. Se indujeron trece ratas macho Sprague-Dawley con STZ en tampón citrato y se inyectaron seis ratas de control con la misma solución tampón. Todas las ratas se sacrificaron después de la inducción a las cuatro (DM a corto plazo) y a las veinticuatro semanas (DM a largo plazo). Las ampliaciones de la columna seleccionadas se procesaron para microscopía electrónica de transmisión. Las alteraciones de OL en las intumescencias cervical y lumbar eran aparentemente las mismas. En la DM a corto plazo, los núcleos de los OL se hincharon con la acumulación de cromatina. Los orgánulos citoplasmáticos sufrieron daños moderados. En la DM a largo plazo, los OL contenían núcleos de contracción con aglutinación de heterocromatina gruesa. Se observaron mitocondrias severamente degeneradas con crestas y membranas rotas. Además, se observó un retículo endoplásmico rugoso distendido y fragmentado, y estaban presentes grandes áreas claras en el citoplasma. Además, se encontraron el aflojamiento, la división y la destrucción de las laminillas de mielina. Este estudio puede proporcionar información preliminar importante sobre la alteración de los OL en la médula espinal de los pacientes diabéticos, que podría estar involucrada en las alteraciones de las velocidades de conducción sensorial y motora en estos individuos.

Ultrastructural and diffusion tensor imaging studies reveal axon abnormalities in Pompe disease mice.

Pompe disease (PD) is caused by lysosomal glycogen accumulation in tissues, including muscles and the central nervous system (CNS). The intravenous infusion of recombinant human acid alpha-glucosidase (rhGAA) rescues the muscle pathologies in PD but does not treat the CNS because rhGAA does not cross the blood-brain barrier (BBB). To understand the CNS pathologies in PD, control and PD mice were followed and analyzed at 9 and 18 months with brain structural and ultrastructural studies. T2-weighted brain magnetic resonance imaging studies revealed the progressive dilatation of the lateral ventricles and thinning of the corpus callosum in PD mice. Electron microscopy (EM) studies at the genu of the corpus callosum revealed glycogen accumulation, an increase in nerve fiber size variation, a decrease in the g-ratio (axon diameter/total fiber diameter), and myelin sheath decompaction. The morphology of oligodendrocytes was normal. Diffusion tensor imaging (DTI) studies at the corpus callosum revealed an increase in axial diffusivity (AD) and mean diffusivity (MD) more significantly in 9-month-old PD mice. The current study suggests that axon degeneration and axon loss occur in aged PD mice and are probably caused by glycogen accumulation in neurons. A drug crossing the BBB or a treatment for directly targeting the brain might be necessary in PD.

NOGO-A immunolabeling is present in glial cells and some neurons of the recovering lumbar spinal cord in lizards.

The transected lumbar spinal cord of lizards was studied for its ability to recover after paralysis. At 34 days post-lesion about 50% of lizards were capable of walking with a limited coordination, likely due to the regeneration of few connecting axons crossing the transection site of the spinal cord. This region, indicated as "bridge", contains glial cells among which oligodendrocytes and their elongation that are immunolabeled for NOGO-A. A main reactive protein band occurs at 100-110 kDa but a weaker band is also observed around 240 kDa, suggesting fragmentation of the native protein due to extraction or to physiological processing of the original protein. Most of the cytoplasmic immunolabeling observed in oligodendrocytes is associated with vesicles of the endoplasmic reticulum. Also, the nucleus is labeled in some oligodendrocytes that are myelinating sparse axons observed within the bridge at 22-34 days post-transection. This suggests that axonal regeneration is present within the bridge region. Immunolabeling for NOGO-A shows that the protein is also present in numerous reactive neurons, in particular motor-neurons localized in the proximal stump of the transected spinal cord. Ultrastructural immunolocalization suggests that NOGO is synthesized in the ribosomes of these neurons and becomes associated with the cisternae of the endoplasmic reticulum, probably following a secretory pathway addressed toward the axon. The present observations suggest that, like for the regenerating spinal cord of fish and amphibians, also in lizard NOGO-A is present in reactive neurons and appears associated to axonal regeneration and myelination.

Mechanistic Target of Rapamycin Regulates the Oligodendrocyte Cytoskeleton during Myelination.

During differentiation, oligodendrocyte precursor cells (OPCs) extend a network of processes that make contact with axons and initiate myelination. Recent studies revealed that actin polymerization is required for initiation of myelination whereas actin depolymerization promotes myelin wrapping. Here, we used primary OPCs in culture isolated from neonatal rat cortices of both sexes and young male and female mice with oligodendrocyte-specific deletion of mechanistic target of rapamycin (mTOR) to demonstrate that mTOR regulates expression of specific cytoskeletal targets and actin reorganization in oligodendrocytes during developmental myelination. Loss or inhibition of mTOR reduced expression of profilin2 and ARPC3, actin polymerizing factors, and elevated levels of active cofilin, which mediates actin depolymerization. The deficits in actin polymerization were revealed in reduced phalloidin and deficits in oligodendrocyte cellular branching complexity at the peak of morphologic differentiation and a delay in initiation of myelination. We further show a critical role for mTOR in expression and localization of myelin basic protein (Mbp) mRNA and MBP protein to the cellular processes where it is necessary at the myelin membrane for axon wrapping. Mbp mRNA transport deficits were confirmed by single molecule RNA FISH. Moreover, expression of the kinesin family member 1B, an Mbp mRNA transport protein, was reduced in CC1+ cells in the mTOR cKO and in mTOR inhibited oligodendrocytes undergoing differentiation in vitro These data support the conclusion that mTOR regulates both initiation of myelination and axon wrapping by targeting cytoskeletal reorganization and MBP localization to oligodendrocyte processes.SIGNIFICANCE STATEMENT Myelination is essential for normal CNS development and adult axon preservation and function. The mechanistic target of rapamycin (mTOR) signaling pathway has been implicated in promoting CNS myelination; however, there is a gap in our understanding of the mechanisms by which mTOR promotes developmental myelination through regulating specific downstream targets. Here, we present evidence that mTOR promotes the initiation of myelination through regulating specific cytoskeletal targets and cellular process expansion by oligodendrocyte precursor cells as well as expression and cellular localization of myelin basic protein.

Silicon Nanowires for Intracellular Optical Interrogation with Subcellular Resolution.

Current techniques for intracellular electrical interrogation are limited by substrate-bound devices, technically demanding methods, or insufficient spatial resolution. In this work, we use freestanding silicon nanowires to achieve photoelectric stimulation in myofibroblasts with subcellular resolution. We demonstrate that myofibroblasts spontaneously internalize silicon nanowires and subsequently remain viable and capable of mitosis. We then show that stimulation of silicon nanowires at separate intracellular locations results in local calcium fluxes in subcellular regions. Moreover, nanowire-myofibroblast hybrids electrically couple with cardiomyocytes in coculture, and photostimulation of the nanowires increases the spontaneous activation rate in coupled cardiomyocytes. Finally, we demonstrate that this methodology can be extended to the interrogation of signaling in neuron-glia interactions using nanowire-containing oligodendrocytes.

Proteostasis network alteration in lysosomal storage disorders: Insights from the mouse model of Krabbe disease.

In Krabbe disease, a mutation in GALC gene causes widespread demyelination determining cell death by apoptosis, mainly in oligodendrocytes and Schwann cells. Less is known on the molecular mechanisms induced by this deficiency. Here, we report an impairment in protein synthesis and degradation and in proteasomal clearance with a potential accumulation of the misfolded proteins and induction of the endoplasmic reticulum stress in the brain of 6-day-old twitcher mice (TM) (model of Krabbe disease). In particular, an imbalance of the immunoproteasome function was highlighted, useful for shaping adaptive immune response by neurological cells. Moreover, our data show an involvement of cytoskeleton remodeling in Krabbe pathogenesis, with a lamin meshwork disaggregation in twitcher oligodendrocytes in 6-day-old TM. This study provides interesting protein targets and mechanistic insight on the early onset of Krabbe disease that may be promising options to be tested in combination with currently available therapies to rescue Krabbe phenotype.

Quantitative Imaging of White and Gray Matter Remyelination in the Cuprizone Demyelination Model Using the Macromolecular Proton Fraction.

Macromolecular proton fraction (MPF) has been established as a quantitative clinically-targeted MRI myelin biomarker based on recent demyelination studies. This study aimed to assess the capability of MPF to quantify remyelination using the murine cuprizone-induced reversible demyelination model. MPF was measured in vivo using the fast single-point method in three animal groups (control, cuprizone-induced demyelination, and remyelination after cuprizone withdrawal) and compared to quantitative immunohistochemistry for myelin basic protein (MBP), myelinating oligodendrocytes (CNP-positive cells), and oligodendrocyte precursor cells (OPC, NG2-positive cells) in the corpus callosum, caudate putamen, hippocampus, and cortex. In the demyelination group, MPF, MBP-stained area, and oligodendrocyte count were significantly reduced, while OPC count was significantly increased as compared to both control and remyelination groups in all anatomic structures (p < 0.05). All variables were similar in the control and remyelination groups. MPF and MBP-stained area strongly correlated in each anatomic structure (Pearson's correlation coefficients, r = 0.80-0.90, p < 0.001). MPF and MBP correlated positively with oligodendrocyte count (r = 0.70-0.84, p < 0.01 for MPF; r = 0.81-0.92, p < 0.001 for MBP) and negatively with OPC count (r = -0.69--0.77, p < 0.01 for MPF; r = -0.72--0.89, p < 0.01 for MBP). This study provides immunohistological validation of fast MPF mapping as a non-invasive tool for quantitative assessment of de- and remyelination in white and gray matter and indicates the feasibility of using MPF as a surrogate marker of reparative processes in demyelinating diseases.

Parvalbumin expression in oligodendrocyte-like CG4 cells causes a reduction in mitochondrial volume, attenuation in reactive oxygen species production and a decrease in cell processes' length and branching.

Forebrain glial cells - ependymal cells and astrocytes -acquire upon injury- a "reactive" phenotype associated with parvalbumin (PV) upregulation. Since free radicals, e.g. reactive oxygen species (ROS) play a role in the pathogenesis of multiple sclerosis, and that PV-upregulation in glial cells is inversely correlated with the level of oxidative stress, we hypothesized that PV-upregulation might also protect oligodendrocytes by decreasing ROS production. Lentiviral transduction techniques allowed for PV overexpression in CG4 oligodendrocyte progenitor cells (OPCs). Depending on the growth medium CG4 cells can be maintained in an OPC-like state, or induced to differentiate into an oligodendrocyte (OLG)-like phenotype. While increased levels of PV had no effect on cell proliferation and invasiveness in vitro, PV decreased the mitochondria volume in CG4 cell bodies, as well as the mitochondrial density in CG4 processes in both OPC-like and OLG-like states. In line with the PV-induced global decrease in mitochondrial volume, elevated PV levels reduced transcript levels of mitochondrial transcription factors involved in mitochondria biogenesis. In differentiated PV-overexpressing CG4 cells with a decreased mitochondrial volume, UV-induced ROS production was lower than in control CG4 cells hinting towards a possible role of PV in counteracting oxidative stress. Unexpectedly, PV also decreased the length of processes in undifferentiated CG4 cells and moreover diminished branching of differentiated CG4 cell processes, strongly correlated with the decreased density of mitochondria in CG4 cell processes. Thus besides conferring a protective role against oxidative stress, PV in a cell autonomous fashion additionally affects process' growth and branching in CG4 cells.

Mouse Nr2f1 haploinsufficiency unveils new pathological mechanisms of a human optic atrophy syndrome.

Optic nerve atrophy represents the most common form of hereditary optic neuropathies leading to vision impairment. The recently described Bosch-Boonstra-Schaaf optic atrophy (BBSOA) syndrome denotes an autosomal dominant genetic form of neuropathy caused by mutations or deletions in the NR2F1 gene. Herein, we describe a mouse model recapitulating key features of BBSOA patients-optic nerve atrophy, optic disc anomalies, and visual deficits-thus representing the only available mouse model for this syndrome. Notably, Nr2f1-deficient optic nerves develop an imbalance between oligodendrocytes and astrocytes leading to postnatal hypomyelination and astrogliosis. Adult heterozygous mice display a slower optic axonal conduction velocity from the retina to high-order visual centers together with associative visual learning deficits. Importantly, some of these clinical features, such the optic nerve hypomyelination, could be rescued by chemical drug treatment in early postnatal life. Overall, our data shed new insights into the cellular mechanisms of optic nerve atrophy in BBSOA patients and open a promising avenue for future therapeutic approaches.

Individual Oligodendrocytes Show Bias for Inhibitory Axons in the Neocortex.

Reciprocal communication between neurons and oligodendrocytes is essential for the generation and localization of myelin, a critical feature of the CNS. In the neocortex, individual oligodendrocytes can myelinate multiple axons; however, the neuronal origin of the myelinated axons has remained undefined and, while largely assumed to be from excitatory pyramidal neurons, it also includes inhibitory interneurons. This raises the question of whether individual oligodendrocytes display bias for the class of neurons that they myelinate. Here, we find that different classes of cortical interneurons show distinct patterns of myelin distribution starting from the onset of myelination, suggesting that oligodendrocytes can recognize the class identity of individual types of interneurons that they target. Notably, we show that some oligodendrocytes disproportionately myelinate the axons of inhibitory interneurons, whereas others primarily target excitatory axons or show no bias. These results point toward very specific interactions between oligodendrocytes and neurons and raise the interesting question of why myelination is differentially directed toward different neuron types.

Ultrastructural Analysis of Thalamus Damages in a Mouse Model of Osmotic-Induced Demyelination.

A murine model used to investigate the osmotic demyelination syndrome (ODS) demonstrated ultrastructural damages in thalamus nuclei. Following chronic hyponatremia, significant myelinolysis was merely detected 48 h after the rapid reinstatement of normonatremia (ODS 48 h). In ODS samples, oligodendrocytes and astrocytes revealed injurious changes associated with a few cell deaths while both cell types seemed to endure a sort of survival strategy: (a) ODS 12 h oligodendrocytes displayed nucleoplasm with huge heterochromatic compaction, mitochondria hypertrophy, and most reclaimed an active NN cell aspect at ODS 48 h. (b) Astrocytes responded to the osmotic stress by overall cell shrinkage with clasmatodendrosis, these changes accompanied nucleus wrinkling, compacted and segregated nucleolus, destabilization of astrocyte-oligodendrocyte junctions, loss of typical GFAP filaments, and detection of round to oblong woolly, proteinaceous aggregates. ODS 48 h astrocytes regained an active nucleus aspect, without restituting GFAP filaments and still contained cytoplasmic proteinaceous deposits. (c) Sustaining minor shrinking defects at ODS 12 h, neurons showed slight axonal injury. At ODS 48 h, neuron cell bodies emerged again with deeply indented nucleus and, owing nucleolus translational activation, huge amounts of polysomes along with secretory-like activities. (d) In ODS, activated microglial cells got stuffed with huge lysosome bodies out of captures cell damages, leaving voids in interfascicular and sub-vascular neuropil. Following chronic hyponatremia, the murine thalamus restoration showed macroglial cells acutely turned off transcriptional and translational activities during ODS and progressively recovered activities, unless severely damaged cells underwent cell death, leading to neuropil disruption and demyelination.

Transmission Electron Microscopy of Oligodendrocytes and Myelin.

In this chapter, we describe protocols to study different aspects of oligodendrocytes and myelin using electron microscopy. First, we describe in detail how to prepare central nervous system tissue routinely by perfusion fixation of the animal and conventional embedding in Epon resin. Then, we explain how, with some modifications, chemically fixed tissue can be used for immunoelectron microscopy on cryosections. Chemical fixation and Epon embedding can also be applied to purified myelin to assess the quality of the preparation. Furthermore, we describe how cryopreparation by high-pressure freezing can be used to study the fine structure of myelin in nerve, brain, and spinal cord tissue. The differences in the structural appearance of oligodendrocytes and myelin between cryopreserved and conventionally processed samples are compared using representative images. Since primary cultured oligodendrocytes are used to study structure and function in vitro, we provide protocols for chemical fixation and Epon embedding of these cultures. Finally, we explain how the cytoskeleton of cultured oligodendrocytes can be visualized by using transmission electron microscopy on platinum-carbon replicas. In this chapter, we provide a wide range of protocols that can be applied to shed light on the different biological aspects of myelin and oligodendrocytes.

The K2P -channel TASK1 affects Oligodendroglial differentiation but not myelin restoration.

In multiple sclerosis, demyelination occurs as a consequence of chronic autoimmunity in the central nervous system causing progressive neurological impairment in patients. After a demyelinating event, new myelin sheaths are formed by adult oligodendroglial progenitor cells; a process called remyelination. However, remyelination often fails in multiple sclerosis due to insufficient recruitment and differentiation of oligodendroglial precursor cells. A pivotal role for the two-pore-domain potassium (K2P ) channel, TASK1, has already been proven for an animal model of multiple sclerosis. However, the mechanisms underlying the TASK1-mediated effects are still elusive. Here, we tested the role of TASK1 channels in oligodendroglial differentiation and remyelination after cuprizone-induced demyelination in male mice. We found TASK1 channels to be functionally expressed on primary murine and human, pluripotent stem cell-derived oligodendrocytes. Lack of TASK1 channels resulted in an increase of mature oligodendrocytes in vitro as well as a higher number of mature oligodendrocytes and accelerated developmental myelination in vivo. Mechanistically, Task1-deficient cells revealed a higher amount of phosphorylated WNK1, a kinase known to be involved in the downstream signaling of the myelination regulator LINGO-1. Furthermore, we analyzed the effect of genetic TASK1 ablation or pharmacological TASK1 inhibition on disease-related remyelination. Neither channel inhibition nor lack of TASK1 channels promoted remyelination after pathological demyelination. In summary, we conclude that functional TASK1 channels participate in the modulation of differentiating oligodendroglial cells in a previously unknown manner. However, while being involved in developmental myelination our data suggest that TASK1 channels have no major effect on remyelination.

Cuprizone-induced graded oligodendrocyte vulnerability is regulated by the transcription factor DNA damage-inducible transcript 3.

Oligodendrocytes are integral to efficient neuronal signaling. Loss of myelinating oligodendrocytes is a central feature of many neurological diseases, including multiple sclerosis (MS). The results of neuropathological studies suggest that oligodendrocytes react with differing sensitivity to toxic insults, with some cells dying early during lesion development and some cells being resistant for weeks. This proposed graded vulnerability has never been demonstrated but provides an attractive window for therapeutic interventions. Furthermore, the biochemical pathways associated with graded oligodendrocyte vulnerability have not been well explored. We used immunohistochemistry and serial block-face scanning electron microscopy (3D-SEM) to show that cuprizone-induced metabolic stress results in an "out of phase" degeneration of oligodendrocytes. Although expression induction of stress response transcription factors in oligodendrocytes occurs within days, subsequent oligodendrocyte apoptosis continues for weeks. In line with the idea of an out of phase degeneration of oligodendrocytes, detailed ultrastructural reconstructions of the axon-myelin unit demonstrate demyelination of single internodes. In parallel, genome wide array analyses revealed an active unfolded protein response early after initiation of the cuprizone intoxication. In addition to the cytoprotective pathways, the pro-apoptotic transcription factor DNA damage-inducible transcript 3 (DDIT3) was induced early in oligodendrocytes. In advanced lesions, DDIT3 was as well expressed by activated astrocytes. Toxin-induced oligodendrocyte apoptosis, demyelination, microgliosis, astrocytosis, and acute axonal damage were less intense in the Ddit3-null mutants. This study identifies DDIT3 as an important regulator of graded oligodendrocyte vulnerability in a MS animal model. Interference with this stress cascade might offer a promising therapeutic approach for demyelinating disorders.

Carbofuran hampers oligodendrocytes development leading to impaired myelination in the hippocampus of rat brain.

During the mammalian brain development, oligodendrocyte progenitor cells (OPCs) are generated from neuroepithelium and migrate throughout the brain. Myelination is a tightly regulated process which involves time framed sequential events of OPCs proliferation, migration, differentiation and interaction with axons for functional insulated sheath formation. Myelin is essential for efficient and rapid conduction of electric impulses and its loss in the hippocampus of the brain may result in impaired memory and long-term neurological deficits. Carbofuran, a carbamate pesticide is known to cause inhibition of hippocampal neurogenesis and memory dysfunctions in rats. Nonetheless, the effects of carbofuran on OPCs proliferation, fate determination, maturation/differentiation and myelination potential in the hippocampus of the rat brain are still completely elusive. Herein, we investigated the effects of sub-chronic exposure of carbofuran during two different time periods including prenatal and adult brain development in rats. We observed carbofuran hampers OPCs proliferation (BrdU incorporation) and oligodendroglial differentiation in vitro. Similar effects of carbofuran were also observed in the hippocampus region of the brain at both the time points. Carbofuran exposure resulted in reduced expression of key genes and proteins involved in the regulation of oligodendrocyte development and functional myelination. It also affects the survival of oligodendrocytes by inducing apoptotic cell death. The ultrastructural analysis of myelin architecture clearly depicted carbofuran-mediated negative effects on myelin compaction and g-ratio alteration. Conclusively, our study demonstrated that carbofuran alters myelination potential in the hippocampus, which leads to cognitive deficits in rats.

Enhanced oligodendrocyte maturation and myelination in a mouse model of Timothy syndrome.

To study the role of L-type voltage-gated Ca++ channels in oligodendrocyte development, we used a mouse model of Timothy syndrome (TS) in which a gain-of-function mutation in the α1 subunit of the L-type Ca++ channel Cav1.2 gives rise to an autism spectrum disorder (ASD). Oligodendrocyte progenitor cells (OPCs) isolated from the cortex of TS mice showed greater L-type Ca++ influx and displayed characteristics suggestive of advanced maturation compared to control OPCs, including a more complex morphology and higher levels of myelin protein expression. Consistent with this, expression of Cav1.2 channels bearing the TS mutation in wild-type OPCs triggered process formation and promoted oligodendrocyte-neuron interaction via the activation of Ca++ /calmodulin-dependent protein kinase II. To ascertain whether accelerated OPC maturation correlated with functional enhancements, we examined myelination in the TS brain at different postnatal time points. The expression of myelin proteins was significantly higher in the corpus callosum, cortex and striatum of TS animals, and immunohistochemical analysis for oligodendrocyte stage-specific markers revealed an increase in the density of myelinating oligodendrocytes in several areas of the TS brain. Along the same line, electron microscopy studies in the corpus callosum of TS animals showed significant increases both in the percentage of myelinated axons and in the thickness of myelin sheaths. In summary, these data indicate that OPC development and oligodendrocyte myelination is enhanced in the brain of TS mice, and suggest that this mouse model of a syndromic ASD is a useful tool to explore the role of L-type Ca++ channels in myelination.