Electrical stimulation promotes the survival of oligodendrocytes in mixed cortical cultures

Oligodendrocyte (OLG) death plays a major role in white matter dysfunction and demyelination following injury to the CNS. Axonal contact, communication, and neuronal activity appear to promote OLG survival and function in cell culture and during development. The application of electrical stimulation to mixed neural cultures has been shown to promote OLG differentiation and the formation of myelin in vitro. Here we show that OLG viability can be significantly enhanced in mixed cortical cultures by applying biphasic pulses of electrical stimulation (ESTIM). Enhanced survival via ESTIM requires the presence of neurons and is suppressed by inhibition of voltage-gated sodium channels. Additionally, contact between the axon and OLG is necessary for ESTIM to promote OLG survival. This report suggests that patterned neuronal activity could repress delayed progression of white matter injury and promote CNS repair in neurological conditions that involve white matter damage.     

Developmental changes of glial fibrillary acidic protein and myelin basic protein in perinatal leukomalacia: relationship to a predisposing factor

Focal white matter necrosis is frequently seen in the brains of infants with perinatal cerebral hypoperfusion. Periventricular leukomalacia (PL) occurs in the deep white matter of premature and term neonates and subcortical leukomalacia (SL) in the subcortical white matter of young infants. Using immunoperoxidase methods in normal infants, glia positive for glial fibrillary acidic protein (GFAP) were found first in the deep zones of white matter and with increasing age they became more prominent in the subcortical zone. They increased diffusely in the deep or subcortical zones of the cases of PL or SL, respectively. The number of myelin basic protein-positive glia is much larger than that of GFAP-positive glia in the cases of old PL. These findings suggest that an increased number of positive glia may be a reaction to hypoxic, ischemic, or toxic insults, or this shifting, transient increase of positive glia in cerebral white matter may be one of several predisposing factors leading to perinatal leukomalacia. Furthermore, positive staining of GFAP and MBP for reactive astrocytes in old PL suggests that at a certain stage of gliogenesis both GFAP and myelin basic protein may be present within the same cell.     

Insulin-like growth factor-1 reduces postischemic white matter injury in fetal sheep.

Insulin-like growth factor-1 (IGF-1) is known to be important for oligodendrocyte survival and myelination. In the current study, the authors examined the hypothesis that exogenous IGF-1 could reduce postischemic white matter injury. Bilateral brain injury was induced in near-term fetal sheep by 30 minutes of reversible carotid artery occlusion. Ninety minutes after ischemia, either vehicle (n = 8) or a single dose of 3 microg IGF-1 (n = 9) was infused intracerebroventricularly over 1 hour. White matter changes were assessed after 4 days recovery in the parasagittal intragyral white matter and underlying corona radiata. Proteolipid protein (PLP) mRNA staining was used to identify bioactive oligodendrocytes. Glial fibrillary acidic protein (GFAP) and isolectin B-4 immunoreactivity were used to label astrocytes and microglia, respectively. Myelin basic protein (MBP) density and the area of the intragyral white matter tracts were determined by image analysis. Insulin-like growth factor-1 treatment was associated with significantly reduced loss of oligodendrocytes in the intragyral white matter (P < 0.05), with improved MBP density (P < 0.05), reduced tissue swelling, and increased numbers of GFAP and isolectin B-4 positive cells compared with vehicle treatment. After ischemia there was a close association of PLP mRNA labeled cells with reactive astrocytes and macrophages/microglia. In conclusion, IGF-1 can prevent delayed, postischemic oligodendrocyte cell loss and associated demyelination.     

Myelin basic protein induces inflammatory mediators from primary human endothelial cells and blood–brain barrier disruption: implications for the pathogenesis of multiple sclerosis

T. G. D'Aversa, E. A. Eugenin, L. Lopez and J. W. Berman (2013) Neuropathology and Applied Neurobiology 39, 270–283 Myelin basic protein induces inflammatory mediators from primary human endothelial cells and blood–brain barrier disruption: implications for the pathogenesis of multiple sclerosis Aim: Multiple sclerosis (MS) is an autoimmune disease of the central nervous system, characterized by demyelination of white matter, loss of myelin forming oligodendrocytes, changes in the blood–brain barrier (BBB) and leucocyte infiltration. Myelin basic protein (MBP) is a component of the myelin sheath. Degradation of myelin is believed to be an important step that leads to MS pathology. Transmigration of leucocytes across the vasculature, and a compromised BBB participate in the neuroinflammation of MS. We examined the expression and regulation of the chemokine (C–C motif) ligand 2 (CCL2) and the cytokine interleukin‐6 (IL‐6) in human endothelial cells (EC), a component of the BBB, after treatment with MBP. Methods: EC were treated with full‐length MBP. CCL2 and IL‐6 protein were determined by ELISA. Western blot analysis was used to determine signalling pathways. A BBB model was treated with MBP and permeability was assayed using albumin conjugated to Evan's blue dye. The levels of the tight junction proteins occludin and claudin‐1, and matrix metalloprotease (MMP)‐2 were assayed by Western blot. Results: MBP significantly induced CCL2 and IL‐6 protein from EC. This induction was partially mediated by the p38 MAPK pathway as there was phosphorylation after MBP treatment. MBP treatment of a BBB model caused an increase in permeability that correlated with a decrease in occludin and claudin‐1, and an induction of MMP2. Conclusion: These data demonstrate that MBP induces chemotactic and inflammatory mediators. MBP also alters BBB permeability and tight junction expression, indicating additional factors that may contribute to the BBB breakdown characteristic of MS.     

XAV939, a small molecular inhibitor,provides neuroprotective effects on oligodentrocytes

White matter tracts are composed of axons and myelinating oligodendrocytes. Oligodendrocytes are the myelinating cells in the central nervous system that allow formation of myelin and saltatory nerve conduction. Cerebral white matter is highly vulnerable to ischemic injury in adults and neonates. White matter injury in newborn brains results in cerebral palsy and cognitive disability. In this study, we found that XAV939, a small‐molecular inhibitor that stimulated β‐catenin degradation by stabilizing axin, protected against serum and glucose deprivation (SGD)‐induced cell death in oligodentrocyte cell line OLN‐93 cells in a concentration‐dependent manner. We further showed that XAV939 reduced caspase‐3 and caspase‐8 levels and increased the expression of phosphorylated Akt in SGD‐induced OLN‐93 cells. Our data demonstrate that XAV939 protects against neonatal hypoxic/ischemic injury. In summary, our results demonstrate that XAV939 confers neuroprotection against SGD‐induced injury in OLN‐93 cells via its antiapoptotic activity and the loss of oligodendrocytes and neurons in neonatal hypoxic/ischemic injury. © 2014 Wiley Periodicals, Inc.     

Experimental cerebral hypoperfusion induces white matter injury and microglial activation in the rat brain

Though cerebral white matter injury is a frequently described phenomenon in aging and dementia, the cause of white matter lesions has not been conclusively determined. Since the lesions are often associated with cerebrovascular risk factors, ischemia emerges as a potential condition for the development of white matter injury. In the present study, we induced experimental cerebral hypoperfusion by permanent, bilateral occlusion of the common carotid arteries of rats (n=6). A sham-operated group served as control (n=6). Thirteen weeks after the onset of occlusion, markers for astrocytes, microglia, and myelin were found to be labeled by means of immunocytochemistry in the corpus callosum, the internal capsule, and the optic tract. The ultrastructural integrity and oligodendrocyte density in the optic tract were investigated by electron microscopy. Quantitative analysis revealed that chronic cerebral hypoperfusion caused mild astrogliosis in the corpus callosum and the internal capsule, while astrocytic disintegration in the optic tract increased by 50%. Further, a ten-fold increase in microglial activation and a nearly doubled oligodendrocyte density were measured in the optic tract of the hypoperfused rats as compared with the controls. Finally, vacuolization and irregular myelin sheaths were observed at the ultrastructural level in the optic tract. In summary, the rat optic tract appears to be particularly vulnerable to ischemia, probably because of the rat brains angioarchitecture. Since the detected glial changes correspond with those reported in vascular and Alzheimer dementia, this model of cerebral hypoperfusion may serve to characterize the causal relationship between ischemia and white matter damage.     

Minocycline attenuates white matter damage in a rat model of chronic cerebral hypoperfusion

White matter lesions are thought to result from chronic cerebral ischemia and constitute a core pathology of subcortical vascular dementia. This rarefaction has been known to be associated with microglial activation. We investigated whether minocycline, a microglial inhibitor, attenuates the white matter damage induced by chronic cerebral hypoperfusion that is used as a model of vascular dementia. Male Wistar rats were subjected to bilateral, permanent occlusion of the common carotid arteries (BCCAO) to induce chronic cerebral hypoperfusion. Minocycline or saline was injected daily for 2 weeks after BCCAO. In the corpus callosum and the optic tract, white matter damage observed with Klüver-Barrera staining was significantly attenuated in the minocycline-treated group compared to saline-treated controls. In control rats, immunoreactivities of major basic protein (MBP), Ox-42 as a microglial marker, and matrix metalloproteinase (MMP)-2 were increased in the corpus callosum. Minocycline significantly reduced these changes. Co-expression of Ox-42 and MMP-2 was confirmed by double immunofluorescence histochemistry. Our results suggest that chronic treatment with minocycline could be protective against at least some ischemic white matter damage, and its mechanism may be related to suppressing microglial activation.     

Astrocyte‐derived lipocalin‐2 mediates hippocampal damage and cognitive deficits in experimental models of vascular dementia

Lipocalin‐2 (LCN2) has diverse functions in multiple pathophysiological conditions; however, its pathogenic role in vascular dementia (VaD) is unknown. Here, we investigated the role of LCN2 in VaD using rodent models of global cerebral ischemia and hypoperfusion with cognitive impairment and neuroinflammation. Mice subjected to transient bilateral common carotid artery occlusion (tBCCAo) for 50 min showed neuronal death and gliosis in the hippocampus at 7 days post‐tBCCAo. LCN2 expression was observed predominantly in the hippocampal astrocytes, whereas its receptor was mainly detected in neurons, microglia, and astrocytes. Furthermore, Lcn2‐deficient mice, compared with wild‐type animals, showed significantly weaker CA1 neuronal loss, cognitive decline, white matter damage, blood–brain barrier permeability, glial activation, and proinflammatory cytokine production in the hippocampus after tBCCAo. Lcn2 deficiency also attenuated hippocampal neuronal death and cognitive decline at 30 days after unilateral common carotid artery occlusion (UCCAo). Furthermore, intracerebroventricular (i.c.v) injection of recombinant LCN2 protein elicited CA1‐neuronal death and a cognitive deficit. Our studies using cultured glia and hippocampal neurons supported the decisive role of LCN2 in hippocampal neurotoxicity and microglial activation, and the role of the HIF‐1α–LCN2–VEGFA axis of astrocytes in vascular injury. Additionally, plasma levels of LCN2 were significantly higher in patients with VaD than in the healthy control subjects. These results indicate that hippocampal damage and cognitive impairment are mediated by LCN2 secreted from reactive astrocytes in VaD.     

Juvenile striatal white matter is resistant to ischemia‐induced damage

White matter injury following ischemic stroke is a major cause of functional disability. Injury to both myelinated axons and oligodendrocytes, the myelin producing cells in the central nervous system, occurs in experimental models of ischemic stroke. Age‐related changes in white matter vulnerability to ischemia have been extensively studied and suggest that both the perinatal and the aged periods are times of increased white matter vulnerability. However, sensitivity of white matter following stroke in the juvenile brain has not been evaluated. Interestingly, the late pediatric period is an important developmental stage, as it is the time of maximal myelination. The current study demonstrates that neurons in late pediatric/juvenile striatum are vulnerable to ischemic damage, with neuronal injury being comparable in juvenile and adult mice following ischemia. By contrast, actively myelinating striatal oligodendrocytes in the juvenile brain are resistant to ischemia, whereas adult oligodendrocytes are quite sensitive. As a result, myelin sheaths are remarkably intact and axons survive well in the injured striatum of juvenile mice. In addition to relative resistance of juvenile white matter, other glial responses were very different in juvenile and adult mice following cerebral ischemia, including differences in astrogliosis, fibrosis, NG2‐cell reactivity, and vascular integrity. Together, these responses lead to long‐term preservation of brain parenchyma in juvenile mice, compared to severe tissue loss and scarring in adult mice. Overall, the current study suggests that equivalent ischemic insults may result in less functional deficit in children compared to adults and an environment more conducive to long‐term recovery. GLIA 2016;64:1972–1986     

Window of opportunity of cerebral hypothermia for postischemic white matter injury in the near-term fetal sheep.

Postresuscitation cerebral hypothermia is consistently neuroprotective in experimental preparations; however, its effects on white matter injury are poorly understood. Using a model of reversible cerebral ischemia in unanesthetized near-term fetal sheep, we examined the effects of cerebral hypothermia (fetal extradural temperature reduced from 39.4 +/- 0.1 degrees C to between 30 and 33 degrees C), induced at different times after reperfusion and continued for 72 hours after ischemia, on injury in the parasagittal white matter 5 days after ischemia. Cooling started within 90 minutes of reperfusion was associated with a significant increase in bioactive oligodendrocytes in the intragyral white matter compared with sham cooling (41 +/- 20 vs 18 +/- 11 per field, P < 0.05), increased myelin basic protein density and reduced expression of activated caspase-3 (14 +/- 12 vs 91 +/- 51, P < 0.05). Reactive microglia were profoundly suppressed compared with sham cooling (4 +/- 6 vs 38 +/- 18 per field, P < 0.05) with no effect on numbers of astrocytes. When cooling was delayed until 5.5 hours after reperfusion there was no significant effect on loss of oligodendrocytes (24 +/- 12 per field). In conclusion, hypothermia can effectively protect white matter after ischemia, but only if initiated early after the insult. Protection was closely associated with reduced expression of both activated caspase-3 and of reactive microglia.     

Peptidyl argininedeiminase 2 CpG island in multiple sclerosis white matter is hypomethylated

In previous studies, we documented increased citrullinated myelin basic protein (MBP) was present in MBP isolated from multiple sclerosis (MS) normal appearing white matter (NAWM). This increase was due to the myelin enzyme peptidyl argininedeiminase 2 (PAD2). In this study, we show that methylation of cytosine of the PAD2 promoter in DNA from MS NAWM was decreased to one-third of the level of that in DNA from normal white matter. The PAD2 promoter in DNA from thymus obtained from the same MS patients and white matter DNA from Alzheimer's, Huntington's, and Parkinson's was not hypomethylated. DNA demethylase activity in supernatants prepared from NAWM of MS patients was 2-fold higher than the DNA demethylase from normal, Alzheimer's, Huntington's and Parkinson's disease white matter. The amount of PAD2 enzyme and citrullinated MBP was increased in MS NAWM. The decreased methylation of cytosines in the PAD2 promoter may explain the increased synthesis of PAD2 protein that is responsible for the increased amount of citrullinated MBP, which in turn results in loss of myelin stability in MS brain.     

Critical role for PAR1 in kallikrein 6‐mediated oligodendrogliopathy

Kallikrein 6 (KLK6) is a secreted serine protease preferentially expressed by oligodendroglia in CNS white matter. Elevated levels of KLK6 occur in actively demyelinating multiple sclerosis (MS) lesions and in cases of spinal cord injury (SCI), stroke, and glioblastoma. Taken with recent evidence establishing KLK6 as a CNS‐endogenous activator of protease‐activated receptors (PARs), we hypothesized that KLK6 activates a subset of PARs to regulate oligodendrocyte physiology and potentially pathophysiology. Here, primary oligodendrocyte cultures derived from wild type or PAR1‐deficient mice and the murine oligodendrocyte cell line, Oli‐neu, were used to demonstrate that Klk6 (rodent form) mediates loss of oligodendrocyte processes and impedes morphological differentiation of oligodendrocyte progenitor cells (OPCs) in a PAR1‐dependent fashion. Comparable gliopathy was also elicited by the canonical PAR1 agonist, thrombin, as well as PAR1‐activating peptides (PAR1‐APs). Klk6 also exacerbated ATP‐mediated oligodendrogliopathy in vitro, pointing to a potential role in augmenting excitotoxicity. In addition, Klk6 suppressed the expression of proteolipid protein (PLP) RNA in cultured oligodendrocytes by a mechanism involving PAR1‐mediated Erk1/2 signaling. Microinjection of PAR1 agonists, including Klk6 or PAR1‐APs, into the dorsal column white matter of PAR1^+/+ but not PAR1^?/? mice promoted vacuolating myelopathy and a loss of immunoreactivity for myelin basic protein (MBP) and CC‐1⁺ oligodendrocytes. These results demonstrate a functional role for Klk6‐PAR1 signaling in oligodendroglial pathophysiology and suggest that antagonists of PAR1 or its protease agonists may represent new modalities to moderate demyelination and to promote myelin regeneration in cases of CNS white matter injury or disease.     

Cuprizone‐induced demyelination in CNP::GFP transgenic mice

Cuprizone (bis‐cyclohexanone oxaldihydrazone) was previously shown to induce demyelination in white matter enriched brain structures. In the present study we used the cuprizone demyelination model in transgenic mice expressing the enhanced green fluorescent protein (GFP) under the 2′‐3′‐cyclic nucleotide 3′‐phosphodiesterase (CNPase) promoter. The use of these particular transgenic mice allows easy detection of cells belonging to the entire oligodendroglial (OLG) lineage, ranging from OLG precursors to mature myelinating OLGs. We were able to evaluate the precise extent of oligodendroglial cell damage and recovery within the murine adult central nervous system (CNS) after inducing demyelination by acute cuprizone intoxication. A generalized loss of GFP+ cells was observed after cuprizone exposure and correlated with a decline in myelin basic protein (MBP) expression. OLGs were depleted in many brain areas that were previously thought to be unaffected by cuprizone treatment. Thus, in addition to the well‐known cuprizone effects on the medial corpus callosum, we also found a loss of GFP+ cells in most brain structures, particularly in the caudatus putamen, cortex, anterior commissure, olfactory bulb, hippocampus, optic chiasm, brainstem, and cingulum. Loss of GFP+ cells was accompanied by extensive astrogliosis and microglial activation, although neurons were not affected. Interestingly, cuprizone‐treated animals showed both activation of GFAP expression and a higher proliferation rate in subventricular zone cells. A week after cuprizone removal from the diet, GFP+ oligodendroglial cells began repopulating the damaged structures. GFP expression precedes that of MBP and allows OLG detection before myelin restoration. J. Comp. Neurol. 518:2261–2283, 2010. © 2010 Wiley‐Liss, Inc.     

New oligodendrocytes are generated after neonatal hypoxic-ischemic brain injury in rodents

Neonatal hypoxic-ischemic (HI) white matter injury is a major contributor to chronic neurological dysfunction. Immature oligodendrocytes (OLGs) are highly vulnerable to HI injury. As little is known about in vivo OLG repair mechanisms in neonates, we studied whether new OLGs are generated after HI injury in P7 rats. Rats received daily BrdU injections at P12-14 or P21-22 and sacrificed at P14 to study the level of cell proliferation or at P35 to permit dividing OLG precursors to differentiate. In P14 HI-injured animals, the number of BrdU+ cells in the injured hemisphere is consistently greater than controls. At P35, sections were double-labeled for BrdU and markers for OLGs, astrocytes, and microglia. Double-labeled BrdU+/myelin basic protein+ and BrdU+/carbonic anhydrase+ OLGs are abundant in the injured striatum, corpus callosum, and the infarct core. Quantitative studies show four times as many OLGs are generated from P21-35 in HI corpora callosa than controls. Surprisingly, the infarct core contains many newly generated OLGs in addition to hypertrophied astrocytes and activated microglia. These glia and non-CNS cells may stimulate OLG progenitor proliferation or induce their migration. At P35, astrogliosis and microgliosis are dramatic ipsilaterally but only a few microglia and some astrocytes are BrdU+. This finding indicates microglial and astrocytic hyperplasia occurs shortly after HI but before the P21 BrdU injections. Although the neonatal brain undergoes massive cell death and atrophy the first week after injury, it retains the potential to generate new OLGs up to 4 weeks after injury within and surrounding the infarct.     

Myelin basic protein stimulates the proliferation of astrocytes: possible explanation for multiple sclerosis plaque formation

In dissociated mouse brain cell cultures we frequently observed an association between myelin basic protein (MBP) positive oligo-dendrocytes and proliferating astrocytes. When MBP was added in a purified form to the culture medium, it greatly stimulated the proliferation of astrocytes, while other proteins tested did not. This finding allows us to speculate that the gliosis observed in demyelinating diseases or/and in central nervous system (CNS) injury would be due to the mitogenic effect exerted by MBP or its fragments when there is myelin breakdown.     

Blood-brain barrier breakdown in acute and chronic cerebrovascular disease

Disruptions of the blood-brain barrier (BBB) and edema formation both play key roles in the development of neurological dysfunction in acute and chronic cerebral ischemia. Animal studies have revealed the molecular cascades that are initiated with hypoxia/ischemia in the cells forming the neurovascular unit and that contribute to cell death. Matrix metalloproteinases cause reversible degradation of tight junction proteins early after the onset of ischemia, and a delayed secondary opening during a neuroinflammatory response occurring from 24 to 72 hours after. Cyclooxygenases are important in the delayed opening as the neuroinflammatory response progresses. An early opening of the BBB within the 3-hour therapeutic window for tissue-type plasminogen activator can allow it to enter the brain and increase the risk of hemorrhage. Chronic hypoxic hypoperfusion opens the BBB, which contributes to the cognitive changes seen with lacunar strokes and white matter injury in subcortical ischemic vascular disease. This review will describe the molecular and cellular events associated with BBB disruption and potential therapies directed toward restoring the integrity of the neurovascular unit.     

Assessment of white matter injury following prolonged focal cerebral ischaemia in the rat

The ability of putative neuroprotective compounds to protect against white matter injury remains poorly investigated due to the lack of suitable methods for assessing white matter injury. This study was therefore designed to investigate the utility of Tau 1 (oligodendrocytes/axons), myelin basic protein (MBP; myelin) and amyloid precursor protein (APP; axons) immunohistochemistry in assessing white matter injury at various times following middle cerebral artery occlusion (MCAO) in the rat. Focal cerebral, ischaemia was induced in halothane-anaesthetised rats using an intraluminal thread model. At 24 h, 1 and 2 weeks following MCAO, white matter injury was assessed using Tau 1, APP, MBP and Luxol-fast blue staining and neuronal injury with cresyl fast violet (CFV). In histologically normal tissue MBP immunoreactivity was detected in myelinated fibre tracts, while Tau 1 and APP were axonally located. At 24 h following permanent MCAO, MBP, and Tau 1 staining remained relatively unchanged within the myelin and axonal compartments of the ischaemic region. In contrast, increased Tau 1 staining was apparent in oligodendrocytes within ischaemic tissue, while APP accumulated in axons surrounding the lesion. At 1 and 2 weeks following transient MCAO, Tau 1 and APP staining was markedly decreased within ischaemic tissue. Marked reduction in MBP levels within ischaemic tissue were not detected until 2 weeks following MCAO. The area of axonal injury as assessed by reduced Tau 1 or APP staining correlated with the area of neuronal damage as assessed by CFV staining. This study shows that MBP, Tau 1 and APP immunohistochemistry can be utilised to assess myelin and axonal integrity following sustained ischaemia using standard image analysis techniques.     

Intranasal administration of aTf protects and repairs the neonatal white matter after a cerebral hypoxic-ischemic event

Our previous studies showed that the intracerebral injection of apotransferrin (aTf) attenuates white matter damage and accelerates the remyelination process in a neonatal rat model of cerebral hypoxia‐ischemia (HI) injury. However, the intracerebral injection of aTf might not be practical for clinical treatments. Therefore, the development of less invasive techniques capable of delivering aTf to the central nervous system would clearly aid in its effective clinical use. In this work, we have determined whether intranasal (iN) administration of human aTf provides neuroprotection to the neonatal mouse brain following a cerebral hypoxic–ischemic event. Apotransferrin was infused into the naris of neonatal mice and the HI insult was induced by right common carotid artery ligation followed by exposure to low oxygen concentration. Our results showed that aTf was successfully delivered into the neonatal HI brain and detected in the olfactory bulb, forebrain and posterior brain 30 min after inhalation. This treatment successfully reduced white matter damage, neuronal loss and astrogliosis in different brain regions and enhanced the proliferation and survival of oligodendroglial progenitor cells (OPCs) in the subventricular zone and corpus callosum (CC). Additionally, using an in vitro hypoxic model, we demonstrated that aTf prevents oligodendrocyte progenitor cell death by promoting their differentiation. In summary, these data suggest that iN administration of aTf has the potential to be used for clinical treatment to protect myelin and to induce remyelination in demyelinating hypoxic–ischemic events in the neonatal brain. © 2012 Wiley Periodicals, Inc.     

S1P1 deletion in oligodendroglial lineage cells: Effect on differentiation and myelination

Sphingosine 1‐phosphate (S1P) receptors are G protein‐coupled receptors expressed by many cell types, including cells of oligodendrocyte (OLG) lineage. We had previously shown that targeted deletion of S1P₁ in OLG lineage cells did not result in obvious clinical phenotype or altered number of OLGs at 3 months, but there were subtle abnormalities in myelin. In this study, we examined the role of S1P₁ in developmental myelination and cell survival, focusing on age 3 weeks. We found that S1P₁ deficiency led to delayed differentiation of OLG progenitors (OPCs) into OLGs that is independent of p38 phosphorylation. This was accompanied by decreased levels of myelin basic protein (MBP) but not of myelin‐OLG glycoprotein (MOG), and slight decrease in myelin thickness in the corpus callosum of S1P₁ conditional knockout (CKO) mice. S1P₁‐deficient OLGs exhibited slower process extension, which was associated with attenuated phosphorylation of extracellular signal regulated kinases (ERKs) and p21‐activated kinases (PAKs), and with upregulation of tropomodulin1. Basal levels of pAkt were not affected, though expectedly, no response to a selective S1P₁ agonist SEW2871 was observed. S1P₁‐deficient OLGs did not exhibit increased cell death in response to cuprizone, tumor necrosis factor‐α, or deprivation of nutrients and growth factors. We conclude that S1P₁ signaling regulates OLG development, morphological maturation and early myelination. GLIA 2016;64:570–582