Oligodendroglial Progenitor Cells Research Articles

Functional metabotropic glutamate receptors are expressed in oligodendrocyte progenitor cells.

We investigated the expression of metabotropic glutamate receptor (mGluR) isoforms in CG-4 rodent oligodendroglial progenitor cells (OPC) and rat brain oligodendrocytes. Our RT-PCR analysis detected mRNAs for mGluR3 and mGluR5 isoforms in OPCs. Although neurons express both mGluR5a and mGluR5b splice variants, only mGluR5a was identified in OPCs. Antibodies to mGluR2/3 and mGluR5 detected the corresponding receptor proteins in immunoblots of OPC membrane fractions. Furthermore, immunocytochemical analysis identified mGluR5 in oligodendrocyte marker O4-positive OPCs. The expression of mGluR5 was also demonstrated in oligodendrocyte marker (O4 and O1) positive cells in white matter of postnatal 4- and 7-day-old rat brain sections using immunofluorescent double labelling and confocal microscopy. The mGluR5 receptor function was assessed in CG-4 OPCs with fura-2 microfluorometry. Application of the mGluR1/5 specific agonist (S)-3,5-dihydroxyphenylglycine (DHPG) induced calcium oscillations, which were inhibited by the selective mGluR5 antagonist 2-methyl-6-(phenylethynyl) pyridine hydrochloride (MPEP). The DHPG induced calcium oscillations required Ca2+ release from intracellular stores. In OPCs the group II mGluR agonist (2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine (DCG-IV) decreased forskolin-stimulated cAMP synthesis, indicating the presence of functional mGluR3. The newly identified mGluR3 and mGluR5a may be involved in the differentiation of oligodendrocytes, myelination and the development of white matter damage.

Apotransferrin Decreases Migration and Enhances Differentiation of Oligodendroglial Progenitor Cells in an in vitro System

We have previously shown that a single intracranial injection of apotransferrin (aTf) in neonatal rats produces an accelerated mylinogenesis and increases the expression of certain myelin proteins such as myelin basic protein (MBP). In the present work, we studied the effects of aTf upon oligodendrocyte progenitor cell (Opc) cultures. In the presence of aTf, cells developed a multipolar morphology and showed an increased expression of O₄, MBP, O₁ and myelin-associated glycoprotein compared to controls. Migration studies using the agarose drop assay showed that aTf strongly inhibited OPc migration. This effect was not observed when an antibody against the transferrin receptor was added. The expression of two cell adhesion molecules, neural cell adhesion molecule (NCAM), N-cadherin and of polysialylated NCAM (PSA-NCAM) was evaluated by immunocytochemistry and by Western blot. Although NCAM expression did not change, there was a significant increase in N-cadherin expression and a decrease in PSA-NCAM in the aTf-treated cells. Time lapse studies of the expression of PSA-NCAM as an indicator of migration and of MBP as a marker of differentiation showed that in the cultures treated with aTf there is first a decrease in the percentage of cells expressing the former molecule which is followed by an increase in the percentage of cells expressing MBP. These results suggest that aTf added in vitro to cultured OPcs inhibits first their migration and then enhances their differentiation.

Protein kinase C activation is required for the lead-induced inhibition of proliferation and differentiation of cultured oligodendroglial progenitor cells

Lead (Pb) is a common neurotoxicant of major public health concern. Previous studies revealed that cultured oligodendrocyte progenitor cells (OPCs) are highly vulnerable to Pb toxicity. The present study examines the effect of Pb on the survival, proliferation and differentiation of OPCs in vitro. Dose–response studies showed that ≥5–10 μM Pb is cytotoxic to OPCs within 24 h. However, 1 μM of Pb was found to inhibit the proliferation and differentiation of OPCs without affecting cell viability. Pb markedly decreased the proliferative capability of OPCs and inhibited cell-intrinsic lineage progression of OPCs at a late progenitor stage. The Pb-induced decrease of proliferation and differentiation was abolished by inhibition of protein kinase C (PKC) with bisindolylmaleimide I, while the effect of the PKC-activating agent phorbol-12,13-didecanoate was potentiated by Pb. Furthermore, Pb exposure of OPCs caused the translocation of PKC from the cytoplasm to membrane without an increase in total cellular PKC enzymic activity. These results indicate that Pb inhibits the proliferation and differentiation of oligodendrocyte lineage cells in vitro through a mechanism requiring PKC activation.

AN2/NG2 protein-expressing glial progenitor cells in the murine CNS: isolation, differentiation, and association with radial glia.

During early neural development, the lineage specification of initially pluripotent progenitor cells is associated with proliferation, differentiation, and migration. Oligodendroglial progenitor cells migrate from their sites of origin to reach the axons that they will myelinate. We have described a cell-surface protein, AN2, expressed by oligodendroglial progenitor cells in vitro and showed that antibodies against AN2 inhibited the migration of cultured primary oligodendroglial progenitor cells, suggesting that the AN2 antigen plays a role in their migration. Recently, results from MALDI mass spectroscopy showed that AN2 is the mouse homologue of the rat NG2 protein. In this study, we have analyzed cells staining with AN2 antibodies during development and in the adult murine central nervous system (CNS), carried out double stainings with antibodies against NG2, and investigated the differentiation potential of cells in vitro after isolation from early postnatal brain using AN2 antibodies. AN2 and NG2 antibodies stained totally overlapping populations of cells in the CNS. AN2/NG2 expressing cells in embryonic and postnatal brain expressed the PDGF-alpha-receptor and in postnatal brain exhibited electrophysiological properties typical of glial progenitor cells. Cells isolated from early postnatal brain using AN2 monoclonal antibody developed into oligodendrocytes in low serum medium or into astrocytes in the presence of fetal calf serum. In the embryonic spinal cord, cells staining with AN2 antibodies were found closely apposed to radial glial cells, suggesting that glial precursors, like neurons, may use radial glia as scaffolds for migration.

Lead Exposure Affects Levels of Galactolipid Metabolic Enzymes in the Developing Rat Brain

Lead poisoning is known to cause myelin defects. Galactolipids are the major lipid components of myelin and myelin-competent oligodendrocytes. The present study examines the cellular activity of enzymes involved in the galactolipid pathway, tissue concentrations of galactolipids, and the cellular activity of 2′,3′-cyclic nucleotide 3′-phosphohydrolase (CNPase) in rat pups exposed to lead in utero and subsequently through maternal milk from exposed mothers and in drinking water following weaning. Pups from control and lead-treated groups (500 or 2000 ppm lead in the drinking water) were euthanized by decapitation on postnatal day 7, 14, 21, 35, or 56. Lead decreased levels of galactolipids and the oligodendrocyte marker CNPase in the brain to a similar degree. The ratios of galactocerebrosides/sulfatides and nonhydroxy fatty acid/hydroxy fatty acid forms of the galactolipids were not altered by lead treatment. In contrast, the activities of the galactolipid metabolic enzymes were reduced to a degree significantly greater than that of CNPase or galactolipids. These results are consistent with previously obtained data indicating that in vitro cultured oligodendroglial progenitor cells are a target for Pb toxicity. Chronic Pb exposure may impact on brain development by impairing timely myelin production due to perturbation of the early developmental commitment of oligodendroglial progenitors. It is further suggested that perturbation of the galactolipid pathway during the developmental maturation of oligodendrocytes may represent a contributing mechanism for Pb-induced neurotoxicity.

The neurotoxicant, cuprizone, as a model to study demyelination and remyelination in the central nervous system.

Myelin of the adult CNS is vulnerable to a variety of metabolic, toxic, and autoimmune insults. That remyelination can ensue, following demyelinating insult, has been well demonstrated. Details of the process of remyelination are, however difficult to ascertain since in most experimental models of demyelination/remyelination the severity, localization of lesion site, or time course of the pathophysiology is variable from animal to animal. In contrast, an experimental model in which massive demyelination can be reproducibly induced in large areas of mouse brain is exposure to the copper chelator, cuprizone, in the diet. We review work from several laboratories over the past 3 decades, with emphasis on our own recent studies, which suggest an overall picture of cellular events involved in demyelination/remyelination. When 8 week old C57BL/6 mice are fed 0.2% cuprizone in the diet, mature olidgodendroglia are specifically insulted (cannot fulfill the metabolic demand of support of vast amounts of myelin) and go through apoptosis. This is closely followed by recruitment of microglia and phagoctytosis of myelin. Studies of myelin gene expression, coordinated with morphological studies, indicate that even in the face of continued metabolic challenge, oligodendroglial progenitor cells proliferate and invade demyelinated areas. If the cuprizone challenge is terminated, an almost complete remyelination takes place in a matter of weeks. Communication between different cell types by soluble factors may be inferred. This material is presented in the context of a model compatible with present data -- and which can be tested more rigorously with the cuprizone model. The reproducibility of the model indicates that it may allow for testing of manipulations (e.g. available knockouts or transgenics on the common genetic background, or pharmacological treatments) which may accelerate or repress the process of demyelination and or remyelination.

Altered expression of the glutamate transporter EAAC1 in neurons and immature oligodendrocytes after transient forebrain ischemia.

Glutamate uptake is reduced during ischemia because of perturbations of ionic gradients across neuronal and glial membranes. Using immunohistochemical and Western blot analyses, the authors examined the expression of the glutamate transporters EAAC1, GLAST, and GLT-1 in the rat hippocampus and cerebral cortex 8 hours and 1 to 28 days after transient forebrain ischemia. Densitometric analysis of immunoblots of CA1 homogenates showed a moderate increase in EAAC1 protein levels early after the insult. Consistently, it was observed that EAAC1 immunostaining in CA1 pyramidal neurons was more intense after 8 hours and 1 day of reperfusion and reduced at later postischemia stages. A similar transient increase of EAAC1 immunolabeling was detected in layer V pyramidal neurons of the cerebral cortex. In addition, the authors observed that EAAC1 also was located in oligodendroglial progenitor cells in subcortical white matter. The number of EAAC1-labeled cells in this region was increased after 3 and 28 days of reperfusion. Finally, changes in GLAST and GLT-1 expression were not observed in the CA1 region after ischemia using immunohistochemical study or immunoblotting. Enhanced expression of EAAC1 may be an adaptive response to increased levels of extracellular glutamate during ischemia.

Generation of oligodendroglial progenitors in acute inflammatory demyelinating lesions of the rat brain stem is associated with demyelination rather than inflammation.

Remyelination is an extremely efficient process in the adult rodent central nervous system yet the source of new oligodendroglia that appear following primary demyelination is still subject to much debate. Using a reliable marker for oligodendroglial progenitor cells in vivo, the NG2 chondroitin sulphate proteoglycan, we have evaluated the response of endogenous NG2(+) cells in the adult rat brain stem and cerebellum to inflammatory demyelinating lesions in an experimentally induced animal model of multiple sclerosis (MS), antibody augmented experimental allergic encephalomyelitis (ADEAE). We have manipulated T-cell mediated EAE in Lewis rats by injecting in addition, either anti-myelin/oligodendroglial glycoprotein (MOG) antibodies to induce inflammatory demyelination, or non-specific mouse immunoglobulins to induce an inflammatory response without demyelination. We have examined the relationship of NG2(+) progenitor cells to microglia (OX-42(+)), astrocytes (GFAP(+)) and mature oligodendroglia (CNP(+)), in the normal and demyelinated CNS. In the normal CNS NG2-expressing cells are closely intermingled with other glia but represent a distinct cell population. A prominent inflammatory response, identified by the presence of large perivascular and periventricular accumulations of reactive OX42(+) macrophages/microglia, occurred in animals with ADEAE at 7-9 days post injection (DPI), coinciding with severe clinical symptoms. In animals injected with anti-MOG antibodies inflammation was followed by the appearance of large areas of demyelination at 11-14 DPI, at which point the animals had recovered clinically. The response of NG2(+) cells was different depending on whether the inflammation was accompanied by demyelination. In the presence of inflammation, NG2(+) cells responded by an increase in immunoreactivity and an alteration in their morphology, exhibiting enlarged cell bodies and an increased number of intensely stained processes. In areas of demyelination NG2(+) cells had fewer intensely stained processes reminiscent of progenitor cells seen during development. Quantitative analysis revealed a 3-fold increase in the number of NG2(+) cells in demyelinated lesions at 11 DPI, whereas no change was observed in areas of inflammation in the absence of demyelination. Mitotic figures were only seen in NG2(+) cells in areas of demyelination. NG2(+) cell numbers appeared to return to control levels following remyelination. These results suggest that endogenous oligodendroglial progenitors divide and/or migrate, in response to signals triggered by demyelinating rather than inflammatory events, to generate a large progenitor population sufficient to promote the rapid and successful remyelination observed in this model.

NT-3-mediated TrkC receptor activation promotes proliferation and cell survival of rodent progenitor oligodendrocyte cells in vitro and in vivo.

We have previously described the expression of a functional full-length trkC transcript for neurotrophin-3 (NT-3) receptor in oligodendroglia (OL) cells (Kumar and de Vellis, 1996). To date, the role of NT-3 and its signal transduction cascade in OL remains poorly defined. We report that the NT-3 responsive population of cells in the OL lineage are the progenitor cells and that the addition of NT-3 results in the autophosphorylation of p145TrkC. Furthermore, NT-3-mediated activation of p21ras and mitogen-activated protein kinase (MAPK), extracellular signal-regulated protein kinase2 (ERK2), were also observed in the progenitor OL cells. These protein tyrosine kinase (PTK)-induced responses were sensitive to the presence of K252a, an inhibitor for tyrosine kinase. We have determined that NT-3 promotes progenitor OL cell commitment to enter into S-phase of cell cycle to initiate DNA synthesis, in a manner similar to platelet-derived growth factor-AA (PDGF-AA). NT-3 thus plays a role in cell proliferation when present alone, while augmenting the proliferation capacity of PDGF-AA as indicated by the nuclear binding activity of the transcription factor, E2F-1. Both the initiation and progression of mitotic events were confirmed by the expression of c-myc and cdc2 in the presence of NT-3, PDGF-AA or NT-3 plus PDGF-AA. A cell survival assay examining interleukin 1-beta-converting enzyme (ICE)-like protease-mediated cleavage of poly (ADP-ribose) polymerase (PARP) revealed an increase in OL progenitor cell death in the absence of NT-3 or PDGF-AA. In corroboration with our in vitro studies, in vivo results show an increased expression of the progenitor OL cell marker, glycerol phosphate dehydrogenase (GPDH) within 48 hr following an intracranial injection of NT-3, PDGF-AA, or NT-3 plus PDGF-AA in PN4-5 rats. These novel findings suggest that PDGF-AA potentiates the OL progenitor cell's ability to enter into the S-phase of the cell cycle and that NT-3 can augment this activity. Furthermore, PDGF-AA and NT-3 can block ICE-like protease-mediated PARP fragmentation in progenitor OL cells. These results provide important information which further delineates the signal transduction cascades and the role of NT-3 and PDGF-AA on OL progenitor cells.

Isolation and Developmental Characterization of Cerebral Cortical Multipotent Progenitors

Multipotent neural progenitor species present within developing and adult periventricular generative zones can give rise to all of the major cellular elements of the brain. Although lineage specification during development has been thought to be restricted to these generative zones, we have utilized quantitative immunoselection techniques to isolate an enriched population of multipotent neural progenitor cells that express polysialylated neural cell adhesion molecule (PSA-NCAM) from postnatal day 2 cerebral cortex independent of generative zones. This population of cerebral cortical progenitor cells exhibited robust proliferation in response to epidermal growth factor and subsequently gave rise to clonally derived neurons, astrocytes, and oligodendrocytes. Quantitative regional analysis further demonstrated that while the multipotent cells derived from the cerebral cortex uniformly expressed PSA-NCAM, multipotent cells derived from generative zones contained equal proportions of PSA-NCAM-positive and -negative multipotent progenitor cells. The generation of individual cellular lineages from cortical multipotent progenitors could be enhanced by specific cytokines that are expressed within the cerebral cortex. Further, while oligodendroglial progenitor cells derived from cortical multipotent progenitors exhibited responsiveness to platelet-derived growth factor (PDGF) and neurotrophin-3 (NT-3), primary cultures of cortical oligodendroglial progenitors were responsive to PDGF but not to NT-3. These observations suggest that in addition to glial progenitors that commit to a specific lineage prior to migration from generative zones, there is within the cerebral cortex a separate pool of multipotent cells that are capable of generating mature glial progeny in response to specific environmental cues. Therapeutic interventions aimed at differentiation of endogenous cerebral pools of multipotent progenitors may provide a novel strategy for amelioration of the sequelae of environmental and genetic insults to the postnatal cerebrum.

Normal and reactive NG2+ glial cells are distinct from resting and activated microglia.

We have previously used antibodies to the NG2 proteoglycan and the alpha receptor for platelet-derived growth factor (PDGF alpha receptor) to identify oligodendroglial progenitor cells in vivo and in vitro. It has recently become evident that the GD3 antigen, which has been widely used as a marker for oligodendrocyte progenitor cells, is also expressed by microglial cells. In this study we have examined the relationship between the NG2+/PDGF alpha receptor+ glial progenitor cells and microglial cells in normal developing and mature rat brain and in inflammatory lesions in mice with experimental autoimmune encephalomyelitis (EAE). Double-labeling of sections from normal rat brain using anti-NG2 antibodies and lectin from Griffonia simplicifolia (GSA I-B4) or monoclonal antibody 4H1 indicated that there is no overlap between NG2+ glial progenitor cells and microglia in the parenchyma of the central nervous system. In EAE lesions, both NG2+ cells and microglia, identified by antibodies to F4/80 and CD45, displayed reactive changes characterized by increased cell number and staining intensity and shortening and thickening of cell processes. Both cell types were found surrounding perivascular infiltrates of lymphocytes. Double-labeling EAE sections for NG2 and F4/80 or CD45 failed to reveal cells that co-expressed both antigens, suggesting that reactive NG2+ cells are distinct from activated microglia. However, a close spatial relationship between NG2+ cells and microglia was observed in the normal brain and to a greater extent in EAE, where processes of an activated microglial cell were sometimes seen to encircle an NG2+ cell. These observations are indicative of a functional interaction between microglia and the NG2+ glial cells.

Cellular distribution of branched-chain amino acid aminotransferase isoenzymes among rat brain glial cells in culture.

The first step in the catabolism of branched-chain amino acids (BCAA), reversible transamination, is catalyzed by one of the two isoforms of branched-chain amino acid aminotransferase (BCAT). The mitochondrial isoenzyme (BCATm) is widely distributed among tissues, whereas the cytosolic isoenzyme (BCATc) is restricted to only a few organs. Remarkably, BCATc is the prominent isoenzyme found in brain. The physiological significance of the subcellular compartmentation of BCAT is still not understood. To contribute to the elucidation of the cellular distribution of the two isoenzymes in brain, we used cultured rat glial cells in an immunocytochemical study to determine the pattern of BCAT isoenzyme expression by glial cells. Antiserum against BCATm generated a punctate staining pattern of astroglial cells, confirming the mitochondrial location of this isoenzyme. In contrast, the cytosol of galactocerebroside-expressing oligodendroglial cells and O2A progenitor cells displayed intense staining only for BCATc. In addition, subpopulations of astroglial cells exhibited BCATc immunoreactivity. The presence of BCATm in astrocytes is consistent with the known ability of these cells to oxidize BCAA. Furthermore, our results on BCATc provide support for the hypothesis that BCATs are also involved in nitrogen transfer from astrocytes to neurons.

Ciliary neurotrophic factor activates JAK/Stat signal transduction cascade and induces transcriptional expression of glial fibrillary acidic protein in glial cells.

In recent reports, ciliary neurotrophic factor (CNTF) has been implicated as an injury factor involved in regulating astrogliosis in the CNS. In this study, we used a rat oligodendroglial progenitor cell line that is highly responsive to CNTF to examine CNTF-induced alterations that may play a role in activation of the glial fibrillary acidic protein (GFAP) gene. We determined that CNTF induces the transient translocation of Stat1 alpha/p91 to the nucleus. This nuclear translocation was followed by GFAP promoter activation and an up-regulation of GFAP mRNA and protein. Level of CNTF-alpha receptor mRNA, however, were unaffected by addition of the ligand. Transfection studies using an upstream 5'-flanking, 1.9-kb rat GFAP promoter linked to a luciferase reporter gene revealed CNTF-induced transcriptional activation within 1 h of ligand exposure. Moreover, serial-deleted constructs identified a distal (-1,857 to -1,546 bp) and a proximal (-384 to -106 bp) region as being important for CNTF-induced GFAP promoter activation. These two regions showed a strong degree of overlap for CNTF- and serum-induced activation of the GFAP gene. Analysis of the two regions revealed several cis-elements that are thought to be involved in GFAP regulation and/or the regulation of other genes by members of the interleukin-6 family of cytokines. Moreover, we are the first to report the presence of several putative CNTF-responsive elements within our identified distal and proximal regions in the GFAP gene promoter.

Partial purification of a novel mitogen for oligodendroglia

A protein with a MWapp of 50-70 kDa isolated from the salt extract of crude membranes from neonatal rat brain increases the numbers of oligodendroglia in mixed glial cultures prepared from neonatal rat cerebral white matter. After partial purification by ion exchange and gel exclusion chromatography, and elution from an SDS-polyacrylamide gel, this protein ("oligodendroglial trophic factor," OTF) elicited half-maximal oligodendroglial recruitment at a concentration of 5 ng/mL. OTF is a mitogen for oligodendroglia, and to a lesser extent, for oligodendroglial progenitor (O2A) cells, but does not stimulate proliferation of astroglia, Schwann cells, or endoneurial fibroblasts. OTF, unlike platelet-derived growth factor (PDGF), is not an oligodendroglial survival factor. Antibodies against PDGF and basic fibroblast growth factor (bFGF) do not interfere with the accumulation of oligodendroglia induced by OTF. When OTF is given simultaneously with either PDGF or bFGF, there is an additive increase in the numbers of cells of the oligodendroglial lineage.

Oligodendrocyte differentiation and progenitor cell proliferation are independently regulated by cyclic AMP.

Oligodendrocytes, the glial cells specialized to synthesize myelin in the central nervous system, differentiate in primary rat brain cell cultures on a schedule similar to that observed in vivo. The schedule of oligodendrocyte differentiation and the rate of oligodendroglial progenitor cell proliferation in vitro are both modulated by 3',5'-cyclic AMP (cAMP). A 24-hour exposure to 1 mM N6,2'O-dibutyryladenosine 3',5'-cyclic monophosphate (dbcAMP) induced a wave of oligodendrocyte differentiation but inhibited proliferation of oligodendroglial progenitors, and reduced by 30-fold the proliferation of progenitors in response to platelet-derived growth factor (PDGF). When cells were grown in the presence of maximally stimulating concentrations of PDGF, the inhibitory effect of cAMP on progenitor cell proliferation was abolished while the stimulatory effect of cAMP on oligodendrocyte differentiation remained, demonstrating that these two cAMP-regulated events are independent.

Cell proliferation and protooncogene induction in oligodendroglial progenitors.

Cell proliferation and the expression of the protooncogenes c-fos and c-jun have been examined in the primary cultures of oligodendroglial (OL) progenitor cells in response to phorbol 12-myristate 13-acetate (PMA), serum, insulin, insulin-like growth factor-I (IGF-I), platelet-derived growth factor (PDGF), and fibroblast growth factor (FGF). Combined [3H]thymidine autoradiography and immunocytochemistry was used to assess the mitogenic response of O4 (an oligodendrocyte-specific marker)-positive OL progenitors. In addition, the rate of DNA synthesis was measured by the incorporation of [3H]thymidine into acid-precipitable material. It was found that all of the agents tested stimulated DNA synthesis in OL progenitors and induced a rapid increase in c-fos and c-jun protooncogene expression. The induction of c-fos gene expression and DNA synthesis in response to PMA was completely blocked by 1-(5-isoquinolinyl-sulfonyl)-2-methylpiperazine (H-7), a potent inhibitor of protein kinase C (PKC), thereby suggesting a role for PKC in the control of c-fos expression and cell proliferation in OL progenitors.

Oligodendroglial progenitor cells but not oligodendroglia divide during normal development of the rat cerebellum

To identify the stage in the life cycle of oligodendroglia at which they are mitotic during normal in vivo development [3H]thymidine autoradiography has been combined with immunocytochemistry on frozen sections of rat cerebellum. A panel of antibodies have been used that recognize antigens expressed by oligodendroglia at different stages of differentiation from progenitor to mature cell. It has been demonstrated that of the cells of the oligodendroglial lineage only the progenitors, identified by their expression of the ganglioside GD3, were seen to incorporate [3H]thymidine at all the developmental stages tested. Only few dividing GD3-positive cells were observed in the subventricular zones of the fourth-ventricle. The greatest number of dividing GD3-positive progenitors in the rat cerebellum was observed in the folia at postnatal day 7. Silver grains were never observed over cells that could be distinguished as oligodendroglia by their expression of galactocerebroside, 2'3'-cyclic nucleotide 3'-phosphohydrolase, or myelin basic protein. Mitotic astroglia were observed at all stages and could be clearly distinguished by their expression of glial fibrillary acidic protein and glutamine synthetase. When animals were injected with [3H]thymidine at postnatal day 7 and killed at 1-day intervals radiolabel was first observed in galactocerebroside-positive and 2'3'-cyclic nucleotide 3'-phosphohydrolase-positive oligodendroglia at day 9 and in myelin basic protein-positive cells at day 10-11, 3 days after the last cell division. Thus, we have demonstrated for the first time using in situ immunocytochemical techniques, a mitotic glial progenitor cell that is known to give rise to oligodendroglia both in vivo and in vitro.

Oligodendrocyte development and the natural history of multiple sclerosis. A new hypothesis for the pathogenesis of the disease.

The cause of multiple sclerosis (MS) is not known. This article presents a review of recent studies concerned with the development of oligodendrocytes and suggests that the primary lesion in MS could be related to damage to oligodendroglial progenitor cells. Loss of the capacity to generate oligodendrocytes could alter the course of normal development such that insufficient cells are produced to support growth and replace cells lost through attrition, and as a result, regions of demyelination appear. The site and extent of the primary loss of oligodendroglial precursors would then predetermine the time of onset, site, and severity of the neurologic manifestations of MS. It is suggested that MS is a single, continuous process and that clinical, pathologic, and immunologic findings may be understood as the consequences of the acquired inability to generate sufficient oligodendrocytes to maintain myelin.

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Promoting oligodendrocyte (OL) differentiation represents a promising option for remyelination therapy for treating the demyelinating disease multiple sclerosis (MS). The Wnt effector transcription factor 7-like 2 (TCF7l2) was upregulated in MS lesions and had been proposed to inhibit OL differentiation. Recent data suggest the opposite yet underlying mechanisms remain elusive. Here, we unravel a previously unappreciated function of TCF7l2 in controlling autocrine bone morphogenetic protein (BMP)4-mediated signaling. Disrupting TCF7l2 in mice of both sexes results in oligodendroglial-specific BMP4 upregulation and canonical BMP4 signaling activation <i>in vivo</i>. Mechanistically, TCF7l2 binds to <i>Bmp4</i> gene regulatory element and directly represses its transcriptional activity. Functionally, enforced TCF7l2 expression promotes OL differentiation by reducing autocrine BMP4 secretion and dampening BMP4 signaling. Importantly, compound genetic disruption demonstrates that oligodendroglial-specific BMP4 deletion rescues arrested OL differentiation elicited by TCF7l2 disruption <i>in vivo</i>. Collectively, our study reveals a novel connection between TCF7l2 and BMP4 in oligodendroglial lineage and provides new insights into augmenting TCF7l2 for promoting remyelination in demyelinating disorders such as MS. <b>SIGNIFICANCE STATEMENT</b> Incomplete or failed myelin repairs, primarily resulting from the arrested differentiation of myelin-forming oligodendrocytes (OLs) from oligodendroglial progenitor cells, is one of the major reasons for neurologic progression in people affected by multiple sclerosis (MS). Using <i>in vitro</i> culture systems and <i>in vivo</i> animal models, this study unraveled a previously unrecognized autocrine regulation of bone morphogenetic protein (BMP)4-mediated signaling by the Wnt effector transcription factor 7-like 2 (TCF7l2). We showed for the first time that TCF7l2 promotes oligodendroglial differentiation by repressing BMP4-mediated activity, which is dysregulated in MS lesions. Our study suggests that elevating TCF7l2 expression may be possible in overcoming arrested oligodendroglial differentiation as observed in MS patients.