Migration Of Oligodendrocyte Progenitor Cells Research Articles

Myelin Proteolipid Protein Complexes with αv Integrin and AMPA Receptors In Vivo and Regulates AMPA-Dependent Oligodendrocyte Progenitor Cell Migration through the Modulation of Cell-Surface GluR2 Expression.

After demyelination, such as occurs in multiple sclerosis, remyelination of axons is often incomplete, leading to loss of neuronal function and clinical disability. Remyelination may fail because oligodendrocyte precursor cells (OPCs) do not completely migrate into demyelinated areas or OPCs in lesions may not mature into myelinating oligodendrocytes. We have found that the myelin proteolipid protein is critical to regulating OPC migratory responses to the neurotransmitter glutamate through modulation of cell-surface expression of the calcium-impermeable GluR2 subunit of the AMPA glutamate receptor and increased intercellular Ca(2+) signaling. Altered glutamate homeostasis has been reported in demyelinated lesions. Therefore, understanding how OPCs respond to glutamate has important implications for treatment after white matter injury and disease.

CXCL12 Gene Therapy Ameliorates Ischemia-Induced White Matter Injury in Mouse Brain.

Remyelination is an important repair process after ischemic stroke-induced white matter injury. It often fails because of the insufficient recruitment of oligodendrocyte progenitor cells (OPCs) to the demyelinated site or the inefficient differentiation of OPCs to oligodendrocytes. We investigated whether CXCL12 gene therapy promoted remyelination after middle cerebral artery occlusion in adult mice. The results showed that CXCL12 gene therapy at 1 week after ischemia could protect myelin sheath integrity in the perifocal region, increase the number of platelet-derived growth factor receptor-α (PDGFRα)-positive and PDGFRα/bromodeoxyuridine-double positive OPCs in the subventricular zone, and further enhance their migration to the ischemic lesion area. Coadministration of AMD3100, the antagonist for CXCL12 receptor CXCR4, eliminated the beneficial effect of CXCL12 on myelin sheath integrity and negatively influenced OPC proliferation and migration. At 5 weeks after ischemia, CXCR4 was found on the PDGFRα- and/or neuron/glia type 2 (NG2)-positive OPCs but not on the myelin basic protein-positive mature myelin sheaths, and CXCR7 was only expressed on the mature myelin sheath in the ischemic mouse brain. Our data indicated that CXCL12 gene therapy effectively protected white matter and promoted its repair after ischemic injury. The treatment at 1 week after ischemia is effective, suggesting that this strategy has a longer therapeutic time window than the treatments currently available. This study has demonstrated for the first time that CXCL12 gene therapy significantly ameliorates brain ischemia-induced white matter injury and promotes oligodendrocyte progenitor cell proliferation in the subventricular zone and migration to the perifocal area in the ischemic mouse brain. Additional data showed that CXCR4 receptor plays an important role during the proliferation and migration of oligodendrocyte progenitor cells, and CXCR7 might play a role during maturation. In contrast to many experimental studies that provide treatment before ischemic insult, CXCL12 gene therapy was performed 1 week after brain ischemia, which significantly prolonged the therapeutic time window of brain ischemia.

P2X7 receptors and Fyn kinase mediate ATP-induced oligodendrocyte progenitor cell migration.

Recruitment of oligodendrocyte precursor cells (OPCs) to the lesions is the most important event for remyelination after central nervous system (CNS) injury or in demyelinating diseases. However, the underlying molecular mechanism is not fully understood. In the present study, we found high concentrations of ATP could increase the number of migrating OPCs in vitro, while after pretreatment with oxidized ATP (a P2X7 receptor antagonist), the promotive effect was attenuated. The promotive effect of 2'(3')-O-(4-benzoylbenzoyl) adenosine 5'-triphosphate (BzATP) (a P2X7 receptor agonist) was more potent than ATP. After incubation with BzATP, the activity of Fyn, one member of the Src family of kinases, was enhanced. Moreover, the interaction between P2X7 and Fyn was identified by co-immunoprecipitation. After blocking the activity of Fyn or down-regulating the expression of Fyn, the migration of OPCs induced by BzATP was inhibited. These data indicate that P2X7 receptors/Fyn may mediate ATP-induced OPC migration under pathological conditions.

Migration of oligodendrocyte progenitor cells is controlled by transforming growth factor β family proteins during corticogenesis.

During embryonic development oligodendrocyte precursor cells (OPCs) are generated first in the ventral forebrain and migrate dorsally to occupy the cortex. The molecular cues that guide this migratory route are currently completely unknown. Here, we show that bone morphogenetic protein-4 (Bmp4), Bmp7, and Tgfβ1 produced by the meninges and pericytes repelled ventral OPCs into the cortex at mouse embryonic stages. Ectopic activation of Bmp or Tgfβ1 signaling before the entrance of OPCs into the cortex hindered OPC migration into the cortical areas. OPCs without Smad4 signaling molecules also failed to migrate into the cortex efficiently and formed heterotopia in ventral areas. OPC migration into the cortex was also dramatically reduced by conditional inhibition of Tgfβ1 or Bmp expression from mesenchymal cells. The data suggest that mesenchymal Tgfβ family proteins promote migration of ventral OPCs into the cortex during corticogenesis.

The EIIIA domain from astrocyte-derived fibronectin mediates proliferation of oligodendrocyte progenitor cells following CNS demyelination.

Central nervous system remyelination by oligodendrocyte progenitor cells (OPCs) ultimately fails in the majority of multiple sclerosis (MS) lesions. Remyelination benefits from transient expression of factors that promote migration and proliferation of OPCs, which may include fibronectin (Fn). Fn is present in demyelinated lesions in two major forms; plasma Fn (pFn), deposited following blood‐brain barrier disruption, and cellular Fn, synthesized by resident glial cells and containing alternatively spliced domains EIIIA and EIIIB. Here, we investigated the distinctive roles that astrocyte‐derived Fn (aFn) and pFn play in remyelination. We used an inducible Cre‐lox recombination strategy to selectively remove pFn, aFn or both from mice, and examined the impact on remyelination of toxin‐induced demyelinated lesions of spinal cord white matter. This approach revealed that astrocytes are a major source of Fn in demyelinated lesions. Furthermore, following aFn conditional knockout, the number of OPCs recruited to the demyelinated lesion decreased significantly, whereas OPC numbers were unaltered following pFn conditional knockout. However, remyelination completed normally following conditional knockout of aFn and pFn. Both the EIIIA and EIIIB domains of aFn were expressed following demyelination, and in vitro assays demonstrated that the EIIIA domain of aFn mediates proliferation of OPCs, but not migration. Therefore, although the EIIIA domain from aFn mediates OPC proliferation, aFn is not essential for successful remyelination. Since previous findings indicated that astrocyte‐derived Fn aggregates in chronic MS lesions inhibit remyelination, aFn removal may benefit therapeutic strategies to promote remyelination in MS. GLIA 2015;63:242–256

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.

Migrating oligodendrocyte progenitor cells swell prior to soma dislocation.

The migration of oligodendrocyte progenitor cells (OPCs) to the white matter is an indispensable requirement for an intact brain function. The mechanism of cell migration in general is not yet completely understood. Nevertheless, evidence is accumulating that besides the coordinated rearrangement of the cytoskeleton, a finetuned interplay of ion and water fluxes across the cell membrane is essential for cell migration. One part of a general hypothesis is that a local volume increase towards the direction of movement triggers a mechano-activated calcium influx that regulates various procedures at the rear end of a migrating cell. Here, we investigated cell volume changes of migrating OPCs using scanning ion conductance microscopy. We found that during accelerated migration OPCs undergo an increase in the frontal cell body volume. These findings are supplemented with time lapse calcium imaging data that hint an increase in calcium content the frontal part of the cell soma.

UDP‐glucose enhances outward K+ currents necessary for cell differentiation and stimulates cell migration by activating the GPR17 receptor in oligodendrocyte precursors

In the developing and mature central nervous system, NG2 expressing cells comprise a population of cycling oligodendrocyte progenitor cells (OPCs) that differentiate into mature, myelinating oligodendrocytes (OLGs). OPCs are also characterized by high motility and respond to injury by migrating into the lesioned area to support remyelination. K(+) currents in OPCs are developmentally regulated during differentiation. However, the mechanisms regulating these currents at different stages of oligodendrocyte lineage are poorly understood. Here we show that, in cultured primary OPCs, the purinergic G-protein coupled receptor GPR17, that has recently emerged as a key player in oligodendrogliogenesis, crucially regulates K(+) currents. Specifically, receptor stimulation by its agonist UDP-glucose enhances delayed rectifier K(+) currents without affecting transient K(+) conductances. This effect was observed in a subpopulation of OPCs and immature pre-OLGs whereas it was absent in mature OLGs, in line with GPR17 expression, that peaks at intermediate phases of oligodendrocyte differentiation and is thereafter downregulated to allow terminal maturation. The effect of UDP-glucose on K(+) currents is concentration-dependent, blocked by the GPR17 antagonists MRS2179 and cangrelor, and sensitive to the K(+) channel blocker tetraethyl-ammonium, which also inhibits oligodendrocyte maturation. We propose that stimulation of K(+) currents is responsible for GPR17-induced oligodendrocyte differentiation. Moreover, we demonstrate, for the first time, that GPR17 activation stimulates OPC migration, suggesting an important role for this receptor after brain injury. Our data indicate that modulation of GPR17 may represent a strategy to potentiate the post-traumatic response of OPCs under demyelinating conditions, such as multiple sclerosis, stroke, and brain trauma.

CD44 is required for the migration of transplanted oligodendrocyte progenitor cells to focal inflammatory demyelinating lesions in the spinal cord

Remyelination of chronically demyelinated axons in multiple sclerosis (MS) requires the recruitment of endogenous cells or their replacement by transplanted, exogenous oligodendrocyte progenitor cells (OPCs). We have previously shown that an OPC line, CG4, preferentially migrates after transplantation toward focal areas of inflammatory demyelination and axon loss created by injection of zymosan in the rat spinal cord. Here we show that many transplanted CG4 cells had already migrated into the inflammatory lesion after 1 day. We demonstrate that a large number of CG4 cells that had migrated, expressed the adhesion protein, CD44, and that CD44's main ligand, hyaluronic acid (HA) was robustly expressed in the inflammatory lesion. In an in vitro migration assay, migration declined significantly following blocking of CD44 expression on CG4 cells. Likewise, migration of CG4 cells toward a zymosan lesion in vivo was inhibited when transplanted cells were exposed to a CD44 blocking antibody prior to transplantation. These findings suggest that CD44 is a key molecule in the migration of OPCs toward the focal inflammatory demyelinated lesion induced by zymosan, and may be an important in OPC repair in MS.

Astrocyte TNFR2 is required for CXCL12-mediated regulation of oligodendrocyte progenitor proliferation and differentiation within the adult CNS

Multiple sclerosis (MS) is characterized by episodes of inflammatory demyelination with progressive failure of remyelination. Prior studies using murine models of MS indicate that remyelination within the adult central nervous system (CNS) requires the expression and activity of TNFR2 and CXCR4 by oligodendrocyte progenitor cells (OPCs), promoting their proliferation and differentiation into mature oligodendrocytes. Here, we extend these studies by examining the role of TNFR2 in the expression of the CXCR4 ligand, CXCL12, within the corpus callosum (CC) during cuprizone (CPZ) intoxication and by demonstrating that lentiviral-mediated gene delivery of CXCL12 to the demyelinated CC improves OPC proliferation and myelin expression during remyelination. Activated astrocytes and microglia express both TNFR1 and TNFR2 within the demyelinated CC. However, CPZ intoxicated TNFR2−/− mice exhibit loss of up-regulation of CXCL12 in astrocytes with concomitant decreases in numbers of CXCR4+ NG2+ OPCs within the CC. While CXCR4 antagonism does not affect OPC migration from subventricular zones into the CC, it decreases their proliferation and differentiation within the CC. Stereotactic delivery of lentivirus expressing CXCL12 protein into the CC of acutely demyelinated TNFR2−/− mice increases OPC proliferation and expression of myelin. In contrast, chronically demyelinated wild-type mice, which exhibit significant loss of astrocytes and OPCs, are unable to be rescued via CXCL12 lentivirus alone but instead required engraftment of CXCL12-expressing astrocytes for increased myelin expression. Our results show that TNFR2 activation induces CXCL12 expression in the demyelinated CC via autocrine signaling specifically within astrocytes, which promotes OPC proliferation and differentiation. In addition, gene delivery of critical pro-myelinating proteins might be a feasible approach for the treatment of remyelination failure in MS.Electronic supplementary materialThe online version of this article (doi:10.1007/s00401-012-1034-0) contains supplementary material, which is available to authorized users.

CXCL1 regulation of oligodendrocyte progenitor cell migration is independent of calcium signaling

Cell migration is an indispensable aspect of tissue patterning during embryonic development. Oligodendrocytes, the myelinating cells of the central nervous system, migrate significantly during development of the brain. Several growth factors have been identified as being critical regulators of oligodendrocyte progenitor migration, including platelet derived growth factor-A (PDGFA), and fibroblast growth factor-2 (FGF2). Further, the chemokine CXCL1 has been shown to play a critical role in regulating the dispersal of oligodendrocyte progenitors during development, although the mechanisms underlying this regulation are unknown. Previous studies have also shown that calcium flux is required for oligodendrocyte progenitor migration. CXCL1 induces calcium flux in cells; therefore, we hypothesized that CXCL1 inhibition of oligodendrocyte progenitor migration is regulated via changes in intracellular calcium flux. The current study shows that CXCL1 inhibition of oligodendrocyte progenitor migration is independent of calcium signaling. Further, we show that CXCL1 inhibition of oligodendrocyte progenitor migration is specific to PDGFA induced migration. Finally, we show that CXCL1 inhibition of oligodendrocyte progenitor migration is independent of activation of the cell cycle. Our results provide intriguing results relevant to specific aspects of patterning of white matter tracts in the central nervous system, and may further the understanding of tissue remodeling seen during disease-related processes.

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).

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.

Mesenchymal Stem Cells Enhance the Engraftment and Myelinating Ability of Allogeneic Oligodendrocyte Progenitors in Dysmyelinated Mice

Multiple sclerosis is an autoimmune disease characterized by demyelination and axonal loss throughout the central nervous system. No regenerative treatment exists for patients who fail to respond to conventional immunosuppressive and immunomodulating drugs. In this scenario, stem cell therapy poses as a rational approach for neurological regeneration. Transplantation of embryonic-derived oligodendrocyte progenitor cells (OPCs) has been shown to promote remyelination and ameliorate animal models of neurodegenerative diseases. However, its therapeutic application is limited due to potential transplant rejection. In multiple sclerosis, an added concern is that transplant rejection would be most pronounced at sites of previous lesions, exacerbating a hyperactive immune response which could prevent remyelination and precipitate additional demyelination. Routine systemic immunosuppression may not be sufficient to prevent transplant rejection-associated immune reactions in the cerebral microenvironment. Mesenchymal stem cells (MSCs), due to their homing properties and inherent immunosuppressive nature, are a promising tool for clinical application targeted toward immunosuppression at sites of injury. In this study, we used a co-transplantation strategy to investigate the effect of syngeneic MSCs on the survival and remyelination abilities of allogeneic OPCs in adult nonimmunosuppressed shiverer mice. At all time points examined, cotransplantation with MSCs increased OPC engraftment, migration, and maturation in myelinating oligodendrocytes, which produced widespread myelination in the host corpus callosum. In addition, MSCs reduced microglia activation and astrocytosis in the brain of transplanted animals as well as T-cell proliferation in vitro. These data suggest that combining the immunomodulatory and trophic properties of MSCs with the myelinating ability of OPCs might be a suitable strategy for promoting neurological regeneration in demyelinating diseases.

Modulation of canonical transient receptor potential channel 1 in the proliferation of oligodendrocyte precursor cells by the golli products of the myelin basic protein gene.

Golli proteins, products of the myelin basic protein gene, function as a new type of modulator of intracellular Ca(2+) levels in oligodendrocyte progenitor cells (OPCs). Because of this, they affect a number of Ca(2+)-dependent functions, such as OPC migration and process extension. To examine further the Ca(2+) channels regulated by golli, we studied the store-operated Ca(2+) channels (SOCCs) in OPCs and acute brain slice preparations from golli knock-out and golli-overexpressing mice. Our results showed that pharmacologically induced Ca(2+) release from intracellular stores evoked a significant extracellular Ca(2+) entry after store depletion in OPCs. They also indicated that, under these pharmacological conditions, golli promoted activation of Ca(2+) influx by SOCCs in cultured OPCs as well as in tissue slices. The canonical transient receptor potential family of Ca(2+) channels (TRPCs) has been postulated to be SOCC subunits in oligodendrocytes. Using a small interfering RNA knockdown approach, we provided direct evidence that TRPC1 is involved in store-operated Ca(2+) influx in OPCs and that it is modulated by golli. Furthermore, our data indicated that golli is probably associated with TRPC1 at OPC processes. Additionally, we found that TRPC1 expression is essential for the effects of golli on OPC proliferation. In summary, our data indicate a key role for golli proteins in the regulation of TRPC-mediated Ca(2+) influx, a finding that has profound consequences for the regulation of multiple biological processes in OPCs. More important, we have shown that extracellular Ca(2+) uptake through TRPC1 is an essential component in the mechanism of OPC proliferation.

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.

Multiple Kinase Pathways Regulate Voltage-Dependent Ca2+Influx and Migration in Oligodendrocyte Precursor Cells

It is becoming increasingly clear that voltage-operated Ca(2+) channels (VOCCs) play a fundamental role in the development of oligodendrocyte progenitor cells (OPCs). Because direct phosphorylation by different kinases is one of the most important mechanisms involved in VOCC modulation, the aim of this study was to evaluate the participation of serine-threonine kinases and tyrosine kinases (TKs) on Ca(2+) influx mediated by VOCCs in OPCs. Calcium imaging revealed that OPCs exhibited Ca(2+) influx after plasma membrane depolarization via L-type VOCCs. Furthermore, VOCC-mediated Ca(2+) influx declined with OPC differentiation, indicating that VOCCs are developmentally regulated in OPCs. PKC activation significantly increased VOCC activity in OPCs, whereas PKA activation produced the opposite effect. The results also indicated that OPC morphological changes induced by PKC activation were partially mediated by VOCCs. Our data clearly suggest that TKs exert an activating influence on VOCC function in OPCs. Furthermore, using the PDGF response as a model to probe the role of TK receptors (TKr) on OPC Ca(2+) uptake, we found that TKr activation potentiated Ca(2+) influx after membrane depolarization. Interestingly, this TKr modulation of VOCCs appeared to be essential for the PDGF enhancement of OPC migration rate, because cell motility was completely blocked by TKr antagonists, as well as VOCC inhibitors, in migration assays. The present study strongly demonstrates that PKC and TKrs enhance Ca(2+) influx induced by depolarization in OPCs, whereas PKA has an inhibitory effect. These kinases modulate voltage-operated Ca(2+) uptake in OPCs and participate in the modulation of process extension and migration.

Endothelin-1 Regulates Oligodendrocyte Development

In the postnatal brain, oligodendrocyte progenitor cells (OPCs) arise from the subventricular zone (SVZ) and migrate into the developing white matter, where they differentiate into oligodendrocytes and myelinate axons. The mechanisms regulating OPC migration and differentiation are not fully defined. The present study demonstrates that endothelin-1 (ET-1) is an astrocyte-derived signal that regulates OPC migration and differentiation. OPCs in vivo and in culture express functional ET(A) and ET(B) receptors, which mediate ET-1-induced ERK (extracellular signal-regulated kinase) and CREB (cAMP response element-binding protein) phosphorylation. ET-1 exerts both chemotactic and chemokinetic effects on OPCs to enhance cell migration; it also prevents lineage progression from the O4(+) to the O1(+) stage without affecting cell proliferation. Astrocyte-conditioned medium stimulates OPC migration in culture through ET receptor activation, whereas multiphoton time-lapse imaging shows that selective ET receptor antagonists or anti-ET-1 antibodies inhibit OPC migration from the SVZ. Inhibition of ET receptor activity also derepresses OPC differentiation in the corpus callosum in slice cultures. Our findings indicate that ET-1 is a soluble astrocyte-derived signal that regulates OPC migration and differentiation during development.

Effects of extracellular matrix molecules on the growth properties of oligodendrocyte progenitor cells in vitro

The extracellular matrix (ECM) is a component of neural cell niches and regulates multiple functions of diverse cell types. To date, limited information is available concerning its biological effects on the growth properties of oligodendrocyte progenitor cells (OPCs). In the present study, we examined effects of several ECM components, i.e., fibronectin, laminin, and Matrigel, on the survival, proliferation, migration, process extension, and purity of OPCs isolated from embryonic day 15 rat spinal cords. All three ECM components enhanced these biological properties of the OPCs compared with a non-ECM substrate, poly-D-lysine. However, the extents of their effects were somewhat different. Among these ECMs, fibronectin showed the strongest effect on almost all aspects of the growth properties of OPCs, implying that this molecule is a better substrate for the growth of OPCs in vitro. Because of its survival- and growth-promoting effects on OPCs, fibronectin may be considered as a candidate substrate for enhancing OPC-mediated repair under conditions when exogenous delivery or endogenous stimulation of OPCs is applied.

Golli Myelin Basic Proteins Regulate Oligodendroglial Progenitor Cell Migration through Voltage-Gated Ca2+Influx

Migration of oligodendrocyte progenitor cells (OPCs) from proliferative zones to their final location in the brain is an essential step in nervous system development. Golli proteins, products of the myelin basic protein gene, can modulate voltage-gated Ca(2+) uptake in OPCs during process extension and retraction. Given the importance of process extension/retraction on movement, the consequences of golli expression on OPC migration were examined in vivo and in vitro using time-lapse imaging of isolated OPCs and acute brain slice preparations from golli KO and golli J37 overexpressing mice (JOE). The results indicated that golli stimulated migration, and this enhanced motility was associated with increases in the activity of voltage operated Ca(2+) channels (VOCCs). Activation of VOCCs by high K(+) resulted in a significant increase in the migration speed of JOE OPCs versus control cells and golli-mediated modulation of OPC migration disappeared in the presence of VOCC antagonists. During migration, OPCs generated Ca(2+) oscillations that were dependent on voltage-calcium influx and both the amplitude and frequency of these Ca(2+) transients correlated positively with the rate of cell movement under a variety of pharmacological treatments. The Ca(2+) transient amplitude and the rate of cell movement were significantly lower in KO cells and significantly higher in JOE cells suggesting that the presence of golli promotes OPC migration by increasing the size of voltage-mediated Ca(2+) oscillations. These data define a new molecule that regulates Ca(2+) homeostasis in OPCs, and are the first to demonstrate that voltage-gated Ca(2+) channels can regulate an OPC function, such as migration.