Number Of Oligodendrocyte Progenitor Cells Research Articles

Adrenomedullin deficiency and aging exacerbate ischemic white matter injury after prolonged cerebral hypoperfusion in mice.

Adrenomedullin was originally isolated from pheochromocytoma cells and reduces insulin resistance by decreasing oxidative stress. White matter lesions induced by aging and hyperglycemia play a crucial role in cognitive impairment in poststroke patients. Here, we examine whether adrenomedullin deficiency and aging exacerbate ischemic white matter injury after prolonged cerebral hypoperfusion. Adrenomedullin heterozygous, wild-type young/aged mice were subjected to prolonged hypoperfusion. Prolonged cerebral hypoperfusion followed by immunohistochemical analysis was used to evaluate white matter injury. After prolonged hypoperfusion, white matter damage progressed in a time-dependent manner in AM+/− group compared with the wild-type group. The number of oligodendrocyte progenitor cells gradually increased after prolonged hypoperfusion, whereas oligodendrocytes decreased following a transient increase, but the ratio of increase was mild in the AM+/− group (P < 0.05). Oxidative stress was detected in oligodendrocytes, with a larger increase in the AM+/− group (P < 0.05). Aged mice showed the same tendency, but white matter damage was worse, especially in the aged AM+/− group. Our results demonstrated that white matter injury was increased in adrenomedullin deficiency, which induced oxidative stress. White matter injury was more exacerbated because of hyperglycemia in aged AM+/− group. Adrenomedullin may be an important target in the control of ischemic white matter injury.

Oligodendrocyte Progenitor Cell Susceptibility to Injury in Multiple Sclerosis

Remyelination in multiple sclerosis (MS) is often incomplete. In experimental models, oligodendrocyte progenitor cells (OPCs) rather than previously myelinating oligodendrocytes (OLs) are responsible for remyelination. This study compares the relative susceptibility of adult human OPCs and mature OLs to injury in actively demyelinating MS lesions and under invitro stress conditions. In all lesions (n = 20), the number of OLs (Olig2 weak/NogoA positive) was reduced compared to control white matter (mean 38± 4% of control value). In 11 cases, OPC numbers (Olig2 strong; NogoA negative) were also decreased; in eight of these, the reduction was greater for OPCs than for OLs. In the other nine samples, OPC numbers were greater than control white matter, indicating ongoing OPC migration and/or proliferation. Analysis of co-cultures with rat dorsal root ganglia neurons confirmed that OPCs were more capable of contacting and ensheathing axons than OLs. In isolated culture under stress conditions (withdrawal of serum/glucose and/or antioxidants), OPCs showed increased cell death and reduced process extension compared to OLs. Under all culture conditions, OPCs up-regulated expression of genes in the extrinsic proapoptotic pathway, and had increased susceptibility to tumor necrosis factor-induced cell death as compared to OLs. Our data suggest that susceptibility of OPCs to injury within the MS lesion environment contributes to the limited remyelination in MS.

Investigation of Sequential Growth Factor Delivery during Cuprizone Challenge in Mice Aimed to Enhance Oligodendrogliogenesis and Myelin Repair

Repair in multiple sclerosis involves remyelination, a process in which axons are provided with a new myelin sheath by new oligodendrocytes. Bone morphogenic proteins (BMPs) are a family of growth factors that have been shown to influence the response of oligodendrocyte progenitor cells (OPCs) in vivo during demyelination and remyelination in the adult brain. We have previously shown that BMP4 infusion increases numbers of OPCs during cuprizone-induced demyelination, while infusion of Noggin, an endogenenous antagonist of BMP4 increases numbers of mature oligodendrocytes and remyelinated axons following recovery. Additional studies have shown that insulin-like growth factor-1 (IGF-1) promotes the survival of OPCs during cuprizone-induced demyelination. Based on these data, we investigated whether myelin repair could be further enhanced by sequential infusion of these agents firstly, BMP4 to increase OPC numbers, followed by either Noggin or IGF-1 to increase the differentiation and survival of the newly generated OPCs. We identified that sequential delivery of BMP4 and IGF-1 during cuprizone challenge increased the number of mature oligodendrocytes and decreased astrocyte numbers following recovery compared with vehicle infused mice, but did not alter remyelination. However, sequential delivery of BMP4 and Noggin during cuprizone challenge did not alter numbers of oligodendrocytes or astrocytes in the corpus callosum compared with vehicle infused mice. Furthermore, electron microscopy analysis revealed no change in average myelin thickness in the corpus callosum between vehicle infused and BMP4-Noggin infused mice. Our results suggest that while single delivery of Noggin or IGF-1 increased the production of mature oligodendrocytes in vivo in the context of demyelination, only Noggin infusion promoted remyelination. Thus, sequential delivery of BMP4 and Noggin or IGF-1 does not further enhance myelin repair above what occurs with delivery of Noggin alone.

Unconjugated Bilirubin Restricts Oligodendrocyte Differentiation and Axonal Myelination

High levels of serum unconjugated bilirubin (UCB) in newborns are associated with axonal damage and glial reactivity that may contribute to subsequent neurologic injury and encephalopathy (kernicterus). Impairments in myelination and white matter damage were observed at autopsy in kernicteric infants. We have recently reported that UCB reduces oligodendrocyte progenitor cell (OPC) survival in a pure OPC in vitro proliferative culture. Here, we hypothesized that neonatal hyperbilirubinemia may also impair oligodendrocyte (OL) maturation and myelination. We used an experimental model of hyperbilirubinemia that has been shown to mimic the pathophysiological conditions leading to brain dysfunction by unbound (free) UCB. Using primary cultures of OL, we demonstrated that UCB delays cell differentiation by increasing the OPC number and reducing the number of mature OL. This finding was combined with a downregulation of Olig1 mRNA levels and upregulation of Olig2 mRNA levels. Addition of UCB, prior to or during differentiation, impaired OL morphological maturation, extension of processes and cell diameter. Both conditions reduced active guanosine triphosphate (GTP)-bound Rac1 fraction. In myelinating co-cultures of dorsal root ganglia neurons and OL, UCB treatment prior to the onset of myelination decreased oligodendroglial differentiation and the number of myelinating OL, also observed when UCB was added after the onset of myelination. In both circumstances, UCB decreased the number of myelin internodes per OL, as well as the myelin internode length. Our studies demonstrate that increased concentrations of UCB compromise myelinogenesis, thereby elucidating a potential deleterious consequence of elevated UCB.

Subventricular Zone‐Derived Oligodendrogenesis in Injured Neonatal White Matter in Mice Enhanced by a Nonerythropoietic Erythropoietin Derivative

Perinatal hypoxia-ischemia (HI) frequently causes white-matter injury, leading to severe neurological deficits and mortality, and only limited therapeutic options exist. The white matter of animal models and human patients with HI-induced brain injury contains increased numbers of oligodendrocyte progenitor cells (OPCs). However, the origin and fates of these OPCs and their potential to repair injured white matter remain unclear. Here, using cell-type- and region-specific genetic labeling methods in a mouse HI model, we characterized the Olig2-expressing OPCs. We found that after HI, Olig2+ cells increased in the posterior part of the subventricular zone (pSVZ) and migrated into the injured white matter. However, their oligodendrocytic differentiation efficiency was severely compromised compared with the OPCs in normal tissue, indicating the need for an intervention to promote their differentiation. Erythropoietin (EPO) treatment is a promising candidate, but it has detrimental effects that preclude its clinical use for brain injury. We found that long-term postinjury treatment with a nonerythropoietic derivative of EPO, asialo-erythropoietin, promoted the maturation of pSVZ-derived OPCs and the recovery of neurological function, without affecting hematopoiesis. These results demonstrate the limitation and potential of endogenous OPCs in the pSVZ as a therapeutic target for treating neonatal white-matter injury.

Fbxw7 regulates Notch to control specification of neural precursors for oligodendrocyte fate

BackgroundIn the developing vertebrate nervous system elevated levels of Notch signaling activity can block neurogenesis and promote formation of glial cells. The mechanisms that limit Notch activity to balance formation of neurons and glia from neural precursors are poorly understood.ResultsBy screening for mutations that disrupt oligodendrocyte development in zebrafish we found one allele, called vu56, that produced excess oligodendrocyte progenitor cells (OPCs). Positional cloning revealed that the vu56 allele is a mutation of fbxw7, which encodes the substrate recognition component of a ubiquitin ligase that targets Notch and other proteins for degradation. To investigate the basis of the mutant phenotype we performed in vivo, time-lapse imaging, which revealed that the increase in OPC number resulted from production of extra OPCs by ventral spinal cord precursors and not from changes in OPC proliferation or death. Notch signaling activity was elevated in spinal cord precursors of fbxw7 mutant zebrafish and inhibition of Notch signaling suppressed formation of excess OPCs.ConclusionNotch signaling promotes glia cell formation from neural precursors in vertebrate embryos. Our data indicate that Fbxw7 helps attenuate Notch signaling during zebrafish neural development thereby limiting the number of OPCs.

Diosgenin promotes oligodendrocyte progenitor cell differentiation through estrogen receptor‐mediated ERK1/2 activation to accelerate remyelination

Differentiation of oligodendrocyte progenitor cells (OPCs) into mature oligodendrocytes is a prerequisite for remyelination after demyelination, and impairment of this process is suggested to be a major reason for remyelination failure. Diosgenin, a plant-derived steroid, has been implicated for therapeutic use in many diseases, but little is known about its effect on the central nervous system. In this study, using a purified rat OPC culture model, we show that diosgenin significantly and specifically promotes OPC differentiation without affecting the viability, proliferation, or migration of OPC. Interestingly, the effect of diosgenin can be blocked by estrogen receptor (ER) antagonist ICI 182780 but not by glucocorticoid and progesterone receptor antagonist RU38486, nor by mineralocorticoid receptor antagonist spirolactone. Moreover, it is revealed that both ER-alpha and ER-beta are expressed in OPC, and diosgenin can activate the extracellular signal-regulated kinase 1/2 (ERK1/2) in OPC via ER. The pro-differentiation effect of diosgenin can also be obstructed by the ERK inhibitor PD98059. Furthermore, in the cuprizone-induced demyelination model, it is demonstrated that diosgenin administration significantly accelerates/enhances remyelination as detected by Luxol fast blue stain, MBP immunohistochemistry and real time RT-PCR. Diosgenin also increases the number of mature oligodendrocytes in the corpus callosum while it does not affect the number of OPCs. Taking together, our results suggest that diosgenin promotes the differentiation of OPC into mature oligodendrocyte through an ER-mediated ERK1/2 activation pathway to accelerate remyelination, which implicates a novel therapeutic usage of this steroidal natural product in demyelinating diseases such as multiple sclerosis (MS).

Mutation of pescadillo Disrupts Oligodendrocyte Formation in Zebrafish

BackgroundIn vertebrates, the myelin sheath is essential for efficient propagation of action potentials along the axon shaft. Oligodendrocytes are the cells of the central nervous system that create myelin sheaths. During embryogenesis, ventral neural tube precursors give rise to oligodendrocyte progenitor cells, which divide and migrate throughout the central nervous system. This study aimed to investigate mechanisms that regulate oligodendrocyte progenitor cell formation.Methodology/Principal FindingsBy conducting a mutagenesis screen in transgenic zebrafish, we identified a mutation, designated vu166, by an apparent reduction in the number of oligodendrocyte progenitor cells in the dorsal spinal cord. We subsequently determined that vu166 is an allele of pescadillo, a gene known to play a role in ribosome biogenesis and cell proliferation. We found that pescadillo function is required for both the proper number of oligodendrocyte progenitors to form, by regulating cell cycle progression, and for normal levels of myelin gene expression.Conclusions/SignificanceOur data provide evidence that neural precursors require pes function to progress through the cell cycle and produce oligodendrocyte progenitor cells and for oligodendrocyte differentiation.

Abstract 2671: Thymosin Beta 4 Induced Oligodendrogenesis Is Associated With Upregulation Of Serum Response Factor

Background: Thymosin beta 4 (Tβ4) is a G-actin sequestering peptide that improves neurological functional outcome when administered 24 hours after onset of stroke to a rat model of embolic stroke. Tβ4 increases the number of oligodendrocyte progenitor cells (OPCs) as well as mature oligodendrocytes (OLs). Mechanisms of Tβ4 induced oligodendrogenesis (OLG) remain unclear. Serum response growth factor (SRF) is a transcriptional factor which binds with ternary complex co-factors to primarily convey an immediate early gene response to influence and orchestrate neuronal migration and differentiation. Hypothesis: We tested the hypothesis that Tβ4 upregulates SRF with subsequent increase in the markers of OL differentiation. Results: We employed a mouse OPC line (N20.1) to investigate the mechanisms of Tβ4-induced OLG. The cells were plated at a density of 100,000 cells/ml and grown in the presence of 0, 12.5, 25 and 50 ng/ml of Tβ4 (RegeneRx Biopharmaceuticals, Inc.) for 14 days (n=3). Western blot analysis revealed that SRF was dose-dependently upregulated by a factor of 4. Quantitative real time PCR and Western blot analysis showed that Tβ4 treatment induced myelin basic protein (MBP) and 2’, 3’-cyclic nucleotide, 3’-phosphodiesterase (CNPase) expression in a dose-dependent manner by ∼2 fold, indicating the stimulation of OLG. In order to independently demonstrate that SRF promotes the differentiation of progenitor cells into mature oligodendrocytes, SRF was over expressed in the N20.1 cells using a plasmid encoding the SRF gene. After six days SRF over expressed N20.1 cells (n=3) demonstrated an increase of expression of MBP (26 ± 3%) and CNPase (23 ± 3%) when compared to cells transfected with an empty expression plasmid (n=3, MBP, 14 ± 3% and CNPase, 10 ± 4%, p&lt;0.05). Conclusions: In this mouse model of OPCs, SRF was upregulated by Tβ4 and may be involved in Tβ4 induced OLG. Further in vivo investigation of SRF is warranted in our rat model of embolic stroke.

Human Fetal Oligodendrocyte Progenitor Cells from Different Gestational Stages Exhibit Substantially Different Potential to Myelinate

To investigate age-related intrinsic regulation of the capacity of human fetal oligodendrocyte progenitor cells (OPCs) to myelinate, potential OPCs were selected from 15- to 23-gestational-week (gw) human fetal brain tissue based on the expression of gangliosides--recognized with the monoclonal antibody A2B5, which detects multipotent cells including OPCs--or platelet-derived growth factor receptor α (PDGFRα), an early marker of the oligodendroglial lineage. Cells were either cultured alone or cocultured with rat dorsal root ganglia neurons (DRGNs). When cultured alone, both the A2B5- and PDGFRα-selected cells exhibited age-dependent increases in early to mid-stage lineage markers, including sulfatides (O4 antibody) and the transcription factor Olig2, while the cell death rate correlated negatively with age. In coculture with neurons, cells also expressed the myelin components galactocerebroside (GC) and myelin basic protein (MBP), and ensheathed axons. In DRGN cocultures, A2B5+ cells derived from >19 gw produced more GC+/MBP+ cells compared with the 15-17-week cells. The number of GC+ cells making axonal contacts, and ensheathing axonal segments per cell increased proportionally to gestational age. This age-dependent difference in GC/MBP cell number and capacity to ensheath axons persisted when PDGFRα selection was used to enrich for the number of OPCs in cultures derived from younger ages. Addition of the growth factors brain-derived neurotrophic factor (BDNF) and insulin-like growth factor 1 (IGF-1) enhanced OPC differentiation under all conditions. These findings indicate that intrinsic regulatory mechanisms associated with the chronological age of the donor cells are key variables to assess when considering the myelination capacity of OPCs for cellular replacement therapy.

White Matter Protection in Congenital Heart Surgery

Neurodevelopmental delays in motor skills and white matter (WM) injury have been documented in congenital heart disease and after pediatric cardiac surgery. The lack of a suitable animal model has hampered our understanding of the cellular mechanisms underlying WM injury in these patients. Our aim is to identify an optimal surgical strategy for WM protection to reduce neurological injury in congenital heart disease patients. We developed a porcine cardiopulmonary bypass model that displays area-dependent WM maturation. In this model, WM injury was identified after cardiopulmonary bypass-induced ischemia-reperfusion injury. The degree of injury was inversely correlated with the maturation stage, which indicates maturation-dependent vulnerability of WM. Within different oligodendrocyte developmental stages, we show selective vulnerability of O4+ preoligodendrocytes, whereas oligodendrocyte progenitor cells were resistant to insults. This indicates that immature WM is vulnerable to cardiopulmonary bypass-induced injury but has an intrinsic potential for recovery mediated by endogenous oligodendrocyte progenitor cells. Oligodendrocyte progenitor cell number decreased with age, which suggests that earlier repair allows successful WM development. Oligodendrocyte progenitor cell proliferation was observed within a few days after cardiopulmonary bypass-induced ischemia-reperfusion injury; however, by 4 weeks, arrested oligodendrocyte maturation and delayed myelination were detected. Logistic model confirmed that maintenance of higher oxygenation and reduction of inflammation were effective in minimizing the risk of injury at immature stages of WM development. Primary repair in neonates and young infants potentially provides successful WM development in congenital heart disease patients. Cardiac surgery during this susceptible period should avoid ischemia-reperfusion injury and minimize inflammation to prevent long-term WM-related neurological impairment.

虚血性白質障害の分子機構と新たな防御戦略

Brain white matter lesions (WMLs), which are often observed in patients with ischemic cerebrovascular diseases, contribute to cognitive decline. We analyzed the pathologic and regenerative processes in brain white matter lesions of patients diagnosed with vascular dementia. There was a significant increase in the number of oligodendrocyte progenitor cells (OPCs) in the brains of patients with vascular dementia as well as in rats with cerebral hypoperfusion. WMLs can be induced experimentally by bilateral common carotid artery ligation (BCCAL) of rats to cause chronic cerebral ischemia. After chronic cerebral hypoperfusion injury, oxygen free radicals and activated microglia acting as inflammatory elements contribute to chronic cerebral hypoperfusion-induced WMLs. The cell death of oligodendrocytes (OLGs) contributes directly to WMLs. The activation for intracellular signaling pathway of cAMP responsive element binding protein (CREB) phosphorylation in the white matter was suppressed after BCCAL. Type III phosphodiesterase inhibitor (PDE3-I) has potential therapeutic and brain-protective effects based on multitarget mechanism through cell signaling pathway of CREB phosphorylation. The OPCs subsequently underwent cell death and the number of OLGs decreased. In the rat model, PDE3-I prevented cell death, markedly increased the mature OLGs, and promoted restoration of white matter and recovery of cognitive decline.

Sema4D as an inhibitory regulator in oligodendrocyte development

The specific functions of intrinsic regulators of OL differentiation are poorly understood. Sema4D, originally found as a negative regulator of axon guidance, is mainly expressed by oligodendrocytes in the postnatal brain, and our previous study revealed that the lack of Sema4D induced an increase in the number of oligodendrocytes in the cerebral cortex, suggesting that Sema4D may function as an intrinsic regulator of oligodendrocyte development. In this study, we assessed the effects of Sema4D deficiency and of the exogenous addition of Sema4D on oligodendrocyte differentiation. Sema4D deficiency induced an increase in the number of oligodendrocytes in the cerebral cortex at postnatal day 14 and later, without increase in the number of oligodendrocyte progenitor cells. This increase was also observed in cultured oligodendrocytes obtained from Sema4D-deficient mice. Then we investigated whether Sema4D deficiency can increase the proliferation of the progenitor cells or influence the apoptosis. Apoptotic oligodendrocytes were markedly reduced in number in the developing cerebral cortex and in cultured oligodendrocytes obtained from Sema4D-deficient mice, although no significant change was found in proliferation of oligodendrocyte progenitor cells. Exogenous addition of Sema4D prevented the oligodendrocytes from this reduction of apoptosis, and further enhanced apoptosis in oligodendrocytes. Thus, Sema4D may act as an intrinsic inhibitory regulator of oligodendrocyte differentiation by promoting apoptosis.

CXCR4 signaling regulates remyelination by endogenous oligodendrocyte progenitor cells in a viral model of demyelination

Following intracranial infection with the neurotropic JHM strain of mouse hepatitis virus (JHMV), susceptible mice will develop widespread myelin destruction that results in pathological and clinical outcomes similar to those seen in humans with the demyelinating disease Multiple Sclerosis (MS). Partial remyelination and clinical recovery occurs during the chronic phase following control of viral replication yet the signaling mechanisms regulating these events remain enigmatic. Here we report the kinetics of proliferation and maturation of oligodendrocyte progenitor cells (OPCs) within the spinal cord following JHMV-induced demyelination and that CXCR4 signaling contributes to the maturation state of OPCs. Following treatment with AMD3100, a specific inhibitor of CXCR4, mice recovering from widespread demyelination exhibit a significant (P < 0.01) increase in the number of OPCs and fewer (P < 0.05) mature oligodendrocytes compared with HBSS-treated animals. These results suggest that CXCR4 signaling is required for OPCs to mature and contribute to remyelination in response to JHMV-induced demyelination. To assess if this effect is reversible and has potential therapeutic benefit, we pulsed mice with AMD3100 and then allowed them to recover. This treatment strategy resulted in increased numbers of mature oligodendrocytes, enhanced remyelination, and improved clinical outcome. These findings highlight the possibility to manipulate OPCs in order to increase the pool of remyelination-competent cells that can participate in recovery.

Olanzapine stimulates proliferation but inhibits differentiation in rat oligodendrocyte precursor cell cultures

In the developing brain, oligodendrocyte progenitor cells (OPCs) proliferate, migrate, and differentiate into mature oligodendrocytes (OLs) capable of myelinating axons. Recently, OPCs have been identified as an abundant and widespread population in the adult as well as in the developing animal. Current research indicates that these OPCs in the adult brain can proliferate and differentiate into myelinating OLs, albeit with different potentialities from those in developing animals. Multiple lines of evidence, from neuroimaging, postmortem, and genetic association studies, have implicated OL and myelin dysfunction in the pathogenesis of schizophrenia. If altered OL function is involved in pathogenesis, OPCs may thus respond to antipsychotic drugs during the recovery process. In the present study, we used primary OPC cultures from optic nerve of newborn Wistar rat pups to investigate the direct effects of haloperidol (HPD; a typical antipsychotic) and olanzapine (OLZ; an atypical antipsychotic) on the proliferation and differentiation of OPCs. Our results showed that 1) OLZ treatment significantly increased the number of viable OPCs when compared to HPD treatment at relatively high concentrations, 2) OLZ treatment suppressed the expression of myelin basic protein (MBP), and to a greater extent than HPD treatment, and 3) these pharmacological effects may be mediated via the ERK signaling pathway. Our findings suggest a glial mechanism for the antipsychotic action of OLZ, and a role for oligodendrocyte-lineage cells in the pathogenesis and treatment of schizophrenia.

Reactive Astrocytes Inhibit the Survival and Differentiation of Oligodendrocyte Precursor Cells by Secreted TNF-α

Axonal demyelination is a consistent pathological characteristic of spinal cord injury (SCI). Although an increased number of oligodendrocyte progenitor cells (OPCs) is observed in the injured spinal cord, they fail to convert into mature oligodendrocytes. However, little is known about the underlying mechanism. In our study, we identified a link between inhibition of OPC survival and differentiation and reactive astrocytes in glial scar that was mediated by tumor necrosis factor-α (TNF-α). Initially, both glial scar tissue and reactive astrocyte-conditioned medium were shown to inhibit OPC differentiation. Reverse transcriptase polymerase chain reaction (RT-PCR) and immunochemistry revealed that OPCs expressed type 1 TNF-α receptor (TNF-R1). When TNF-α or TNF-R1 was neutralized with antibody, the effect of reactive astrocyte-conditioned medium or recombinant TNF-α protein on OPC differentiation was markedly attenuated. In addition, reactive astrocyte-conditioned medium was also shown to induce OPC apoptosis. All these findings provide the first evidence that reactive astrocytes release TNF-α to inhibit OPC survival and prevent them from differentiating into mature oligodendrocytes, suggesting a mechanism for the failure of remyelination after SCI.

Chondroitinase treatment following spinal contusion injury increases migration of oligodendrocyte progenitor cells

Following spinal cord injury (SCI), the demyelination of spared intact axons near the lesion site likely contributes to the loss of motor function. This demyelination occurs when oligodendrocytes, the myelinating cells of the central nervous system (CNS), are either destroyed during the initial trauma or die as a result of secondary pathology. In an attempt to remyelinate the affected axons, endogenous oligodendrocyte progenitor cells (OPCs) begin to accumulate at the border of demyelination. However, the differentiation of OPCs into fully myelinating cells is limited. While the reasons for this are unknown, it is well known that the injured spinal cord is rich in inhibitory molecules that block repair. One such family of molecules is the chondroitin sulfate proteoglycans (CSPGs), which are known to be highly inhibitory to the process of axonal elongation. Recent in vitro findings have demonstrated that CSPGs are also highly inhibitory to OPCs, affecting both their migration and differentiation. Treatment with the enzyme chondroitinase ABC (cABC), which removes the glycosaminoglycan side chains of CSPGs, reverses the inhibitory effects of CSPGs on these cells. In the present study, we examined the effects of cABC on the migratory behavior of endogenous OPCs in vivo following a moderate spinal contusion injury. The total number of OPCs surrounding the lesion site was significantly increased after cABC treatment as compared to controls. cABC treatment also enhanced axonal sprouting, but OPC migration occurs along a different time course and appears independent of new process outgrowth. These data suggest that CSPGs in the post-injury environment inhibit the migration of OPCs, as well as axonal regeneration. Therefore, cABC treatment may not only enhance regenerative axonal sprouting, but may also enhance remyelination after SCI.

Oligogenesis and Oligodendrocyte Progenitor Maturation Vary in Different Brain Regions and Partially Correlate with Local Angiogenesis after Ischemic Stroke

Oligogenesis plays an important role in functional recovery after ischemic stroke. We tested the hypothesis that oligogenesis and the maturation of oligodendrocyte progenitor cells (OPCs) vary in different brain regions using a rat transient middle cerebral artery occlusion (tMCAO) model. Compared to Day 1, olig2(+) OPCs and oligodendrocytes (OLGs) increased in the peri-infarct basal ganglia (BG) 7 (44%) and 14 (61%) days after 2 hours of MCAO; OPCs (PDGFRα(+)) and OLGs (CC1(+)) increased in this region 14 days after tMCAO by 139% and 126%, respectively. Although the olig2(+) cells and OLGs did not increase significantly in the peri-infarct cortex (CTX), the OPCs increased in this region by 95% at Day 14 vs. Day 1 after tMCAO. The numbers of OPCs and OLGs remained low after an initial reduction at Day 1 in the peri-infarct corpus callosum (CC). Correlation analyses showed that the numbers of olig2(+) cells (r=0.73, P=0.03) and OLGs (r=0.74, P=0.02) correlated with local vessel density; however, the number of OPCs did not correlate with vessel density (r=0.43, P=0.24). Our data show that oligogenesis and the maturation of OPCs differ in various brain regions and the difference in regional angiogenic response is one of the potential reasons.

The ERK2 Mitogen-Activated Protein Kinase Regulates the Timing of Oligodendrocyte Differentiation

Oligodendrocyte development is tightly controlled by a variety of extracellular growth and differentiation factors. The mitogen-activated protein kinases (MAPKs), ERK1 and ERK2, are critical intracellular signaling molecules important for transducing these extracellular signals. The extracellular signal-regulated kinases (ERKs) are ubiquitously expressed, coordinately regulated, and highly similar, but Erk2 deletion in mice is embryonic lethal whereas Erk1 deletion is not. Several studies have suggested that MAPK signaling is important for oligodendrocyte differentiation, although specific roles for the two ERK isoforms have not been investigated. In this study, we deleted Erk2 in the developing mouse cortex from GFAP-expressing radial glia that generate neurons and oligodendrocytes. In vitro analysis revealed that loss of ERK2 resulted in fewer galactocerebroside-expressing mature oligodendrocytes in cortical cultures. In vivo, a delay in the expression of the myelin protein MBP was observed in the corpus callosum at postnatal day 10 (P10). In contrast, Erk1 deletion did not affect oligodendrocyte differentiation. By P21, MBP expression was restored to wild-type levels, demonstrating that the loss of ERK2 results in a delay but not a complete arrest in the appearance of differentiated oligodendrocytes in vivo. Importantly, both the proliferation and total number of oligodendrocyte progenitor cells (OPCs) appeared normal in the Erk2 conditional knock-out cortex, demonstrating that ERK2 plays a specific role in the timing of forebrain myelination but is not critical for the proliferation or survival of OPCs. Oligodendrocyte-specific deletion of Erk2 also resulted in decreased levels of MBP, indicating a cell-autonomous effect of ERK2 in the oligodendrocyte lineage.

Oligodendrocyte progenitor cell numbers and migration are regulated by the zebrafish orthologs of the NF1 tumor suppressor gene

Neurofibromatosis type 1 is the most commonly inherited human cancer predisposition syndrome. Neurofibromin (NF1) gene mutations lead to increased risk of neurofibromas, schwannomas, low grade, pilocytic optic pathway gliomas, as well as malignant peripheral nerve sheath tumors and glioblastomas. Despite the evidence for NF1 tumor suppressor function in glial cell tumors, the mechanisms underlying transformation remain poorly understood. In this report, we used morpholinos to knockdown the two nf1 orthologs in zebrafish and show that oligodendrocyte progenitor cell (OPC) numbers are increased in the developing spinal cord, whereas neurons are unaffected. The increased OPC numbers in nf1 morphants resulted from increased proliferation, as detected by increased BrdU labeling, whereas TUNEL staining for apoptotic cells was unaffected. This phenotype could be rescued by the forced expression of the GTPase-activating protein (GAP)-related domain of human NF1. In addition, the in vivo analysis of OPC migration following nf1 loss using time-lapse microscopy demonstrated that olig2-EGFP(+) OPCs exhibit enhanced cell migration within the developing spinal cord. OPCs pause intermittently as they migrate, and in nf1 knockdown animals, they covered greater distances due to a decrease in average pause duration, rather than an increase in velocity while in motion. Interestingly, nf1 knockdown also leads to an increase in ERK signaling, principally in the neurons of the spinal cord. Together, these results show that negative regulation of the Ras pathway through the GAP activity of NF1 limits OPC proliferation and motility during development, providing insight into the oncogenic mechanisms through which NF1 loss contributes to human glial tumors.