Transplantation of CG4 oligodendrocyte progenitor cells in the myelin-deficient rat brain results in myelination of axons and enhanced oligodendroglial markers

Transplantation of oligodendrocyte (Ol) progenitor cells into the central nervous system is a promising approach for the treatment of myelin disorders. This approach requires providing adequate numbers of healthy cells with myelinating potential. We recently showed the successful transplantation of Ol progenitors into the myelin-deficient (md) rat brain. In the present work, CG4 cells, a cell line with properties of Ol progenitors, were labeled with fast blue and grafted into P3-P5 pups born to carrier mothers. Examination of host brains 2 weeks posttransplant indicated that CG4 cells display a much more extensive migration capacity than their wild-type counterparts. These cells synthesized myelin components. In addition, ultrastructural analysis showed myelin formation along axons of md hosts in various brain regions, including corpus callosum, cerebellum, and brainstem. Furthermore, in situ hybridization studies performed on sagittal sections revealed extensive expression of transferrin-mRNA within the md host parenchyma. The high survival and functional features displayed by CG4 cells after transplantation, together with their striking wide distribution within the host parenchyma, as assessed by the presence of myelinated fibers in mutant hosts, emphasizes the importance of using highly motile and proliferative Ol progenitor cells. Strategies to improve the condition and life span of md rat pups are currently under investigation.

A neural-specific hypomethylated domain in the 5' flanking region of the glial fibrillary acidic protein gene

In the present study we examined the methylation status of the glial fibrillary acidic protein (GFAP) gene promoter, analyzing various CG sites in both the human and rat gene in GFAP-expressing and nonexpressing tissues. Moreover, we studied the methylation of specific CG sites in different rat brain areas during postnatal development, in cell cultures highly enriched in specific neural- or non-neural-cell types (fibroblasts), and in human gliomas. The obtained results do not support a simple correlation between demethylation and expression of the GFAP gene but help to identify a cluster of CG sites in the 5'flanking region (from -1176 to -1471 in the rat) that are hypomethylated in neural cell types and localized in a region highly conserved between rat, mouse and human GFAP promoters. Neural-specific hypomethylation of this conserved zone can be observed also in the human GFAP gene both in normal brain tissue and neoplastic glial cells. A higher demethylation of the -1176 site at early stage of postnatal life was observed in specific rat brain areas, such as hippocampus and cerebellum. The most dramatic differences were observed in the cerebellum where a peak of demethylation of the -1176 site was detected at 15 days of postnatal life, followed by an intense remethylation of this site. Results of experiments in the CG4 glial progenitor cell line showed that demethylation of the -1176 site is already established before transcriptional activation of the GFAP gene. Moreover, results of experiments in primary cell cultures show that in neuronal cell types, such as cerebellar granule cells and embryonic cerebral hemisphere neurons, the level of demethylation of the -1176 site is comparable to that observed in cultured astrocytes. In contrast a high level of methylation can be observed in cultured non-neural cell types (fibroblasts). Such neural-specific hypomethylation could be established in a very early stage in the progression along the neural cell lineage and could play a role in maintaining a local open chromatin conformation which is then necessary to allow the interaction with specific regulatory factors present in astroglial cells.

Transferrin is an early marker of hepatic differentiation, and its expression correlates with the postnatal development of oligodendrocytes in mice

Transferrin (Tf), the iron transport protein, is essential for the growth and differentiation of cells. Therefore, it provides an excellent model to analyze the regulatory mechanisms controlling the expression of a eukaryotic gene in different cell types and during fetal and adult life. In this study, the tissue-specific and developmental regulation of the Tf gene in vivo were analyzed. Human Tf mRNA was detected mainly in fetal and adult liver. A weaker expression was observed in adult and fetal brain and in fetal spleen. By in situ hybridization the presence of mouse Tf mRNA was detected in the hepatic primordia. This is the first observation pointing out Tf as an early marker of hepatic differentiation, prior to the formation of the liver. Thus, TF may be an important tool to follow the hepatic specification of the gut endoderm. Mouse Tf mRNA was also detected in the liver bud and subsequently in the liver throughout fetal life, and in newborn and adult animals. No expression of the Tf gene was observed in the mouse fetal central nervous system (CNS). In contrast, Tf mRNA was detected from the 5th day after birth in the derivatives of the caudal part of the neural tube and subsequently in the derivatives of the rhomboencephalon and that of the prosencephalon. These results indicate that Tf gene expression correlates with the postnatal development of oligodendrocytes in the mouse CNS. To test whether the control elements of the human gene previously found in ex vivo experiments were also active in vivo during fetal and adult life, we fused the -4000/+395' flanking region of the human gene to the coding region of the lacZ gene and generated transgenic mice. The expression of the reporter gene during development was analyzed.

Glial- and fat-specific expression of the rat glycerol phosphate dehydrogenase-luciferase fusion gene in transgenic mice

Glycerol phosphate dehydrogenase (GPDH) is a metabolic enzyme that catalyzes the conversion of dihydroxyacetone phosphate to glycerol-3-phosphate. It provides phospholipid precursors for lipid biosynthesis and energy metabolism. In the brain, GPDH enzymatic activity, protein, mRNA are exclusively associated with oligodendroglial and Bergmann glial cells. Expression of GPDH in the brain increases dramatically during the active period of myelination, and is regulated by extracellular signals. In an effort to understand the mechanism that confers glial-specific expression of GPDH, we have examined the role of the 5' flanking sequence of the rat GPDH gene in conferring cell-specific expression of reporter gene in transgenic mice. Luciferase reporter constructs containing either the full-length GPDH 5' flanking region (p4.3), or a distally truncated version (p2.6), were injected into mouse zygotes. Three independent lines of transgenic mice containing the p4.3, and seven lines of mice containing the p2.6 constructs, were analyzed. Luciferase enzyme activity was detectable only in brain and fat, not in other GPDH-positive organs such as liver, muscle, and kidney. Both the full-length and the distally deleted transgenes were expressed similarly in these two organs, indicating that the distal portion of the 5' flanking region was not required for brain- and fat-specific expression. Immunocytochemical analyses revealed that luciferase immunoreactivity colocalized with glial fibrillary acidic protein (GFAP)-positive Bergmann glia in the cerebellum, and myelin basic protein (MBP)-positive oligodendroglia in the cerebral cortex and the brainstem. Results here suggest that the rat GPDH 5' flanking region directs glial-specific expression of GPDH transcription in the brain, and provide a good model for analyses of changes in glial metabolism in response to extracellular perturbations in vivo.

Expression and functional role of the Id HLH family in cultured astrocytes

The Id family of helix-loop-helix factors (Id1, Id2, and Id3) expressed in many types of cells has been reported to negatively regulate myoblast differentiation and is required for G1/S progression of arrested fibroblasts. Our previous studies have indicated that Id1, Id2, and Id3 mRNA expression appear in the subventricular zone of 1-day-old rat brains. At later ages, Id3 mRNA was only expressed in astrocytes. We now report that Id1 and Id3 mRNA expression increased in astrocytes during the first hour of serum stimulation. Subsequently, the Id1 and Id3 mRNA levels gradually declined to basal level as observed in cultures without serum stimulation. However, there was no significant difference in Id2 mRNA expression between serum-treated and control astrocyte cultures within 1 h of serum induction. In addition, a strong nuclear immunostaining for Id2 and Id3 proteins was observed 24 h after serum stimulation. This observation is consistent with our results that show an increase in Id2 and Id3 protein levels following 24 h serum induction. Furthermore, DNA synthesis in FCS-stimulated astrocytes was blocked by antisense oligonucleotides against Id3 mRNA. The addition of Id3 antisense oligonucleotides caused approximately 50% reduction in Id3 mRNA and protein levels when compared to that in sense-treated cultures. The results indicate that the inhibition of DNA synthesis in FCS-stimulated astrocytes is due to a decrease in Id3 levels by the antisense. These observations suggest that Id3 may play an important role in the regulation of astrocyte proliferation.

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.

CNTF induces GFAP in a S-100 alpha brain cell population: the pattern of CNTF-alpha R suggests an indirect mode of action

In a recent report, we demonstrated that intracerebral injections of the pleiotropic cytokine, ciliary neurotrophic factor (CNTF), into developing postnatal rats evoked a severe inflammatory response as determined by the appearance of reactive astrocytes and activated microglia. Considering the likely involvement of CNTF in the injury response, we felt it was important to further understand the role of CNTF in the developing rat CNS. In this study, we examined the responsiveness of other cell populations to intracerebral injections of CNTF. We report that CNTF increases glial fibrillary acidic protein (GFAP), while having no appreciable effect on the levels of other intermediate filaments including vimentin and neurofilament. Moreover, CNTF did not affect the expression of the mature oligodendrocyte gene, myelin basic protein. These results suggest that CNTF is highly specific in its regulation of GFAP. In our previous study, we showed CNTF to increase GFAP in a cell population that already exists in the CNS parenchyma. To determine the origin of the CNTF-induced reactive astrocytes, therefore, we have utilized a technique of combined in situ hybridization and immunocytochemistry. To examine the possibility that CNTF acts on oligodendrocyte precursors to give rise to reactive astrocytes, the platelet-derived growth factor alpha receptor (PDGF-alpha R) was utilized as a riboprobe in conjunction with an antibody to GFAP. Examination of CNTF-induced GFAP+ astrocytes revealed no colocalization with PDGF-alpha R mRNA. In contrast, when we utilized an S100 alpha antibody recognizing a calcium binding protein in immature astrocytes, we found colocalization of S100 alpha and GFAP mRNA. These data suggest that CNTF induces an upregulation of GFAP in immature S100 alpha + astrocytes. Examination of the CNTF-alpha receptor mRNA revealed no change in expression following CNTF treatment. Unexpectedly, however, the CNTF-induced astrogliotic response appears to be indirect since the CNTF-alpha receptor was solely expressed by neurons in the cytokine-treated animals.

Hippocampal responses to corticosterone and stress, one of which is the 35,000 M(r) protein, glycerol phosphate dehydrogenase

Previously, the synthesis of a hippocampal 35,000 M(r) protein increased in response to glucocorticoid treatment and a variety of stressors. We now show by immunoprecipitation that this cytosolic protein is glycerol 3-phosphate dehydrogenase (E.C.1.1.1.8; GPDH). In addition, four polypeptides encoded by glucocorticoid-induced mRNAs co-migrated with hippocampal protein synthetic products on two-dimensional polyacrylamide gels, including 35,000 M(r) protein of approximately pl 6.3, that had previously been identified as GPDH by hybrid-selection with a GPDH cDNA clone. The 35,000 M(r) in vitro translation product was also immunoprecipitated with the GPDH antibody. Using radiolabeled hippocampal slices and two-dimensional gel analysis, a 35,000 M(r) polypeptide of approximately pl 6.4 increased five-fold after 30 min of intermittent tail-shock. This protein was found predominantly in the 20,000 x g pellet and did not immunoprecipitate with the GPDH antibody. However, a 35,000 M(r) polypeptide was also found in the cytosol as a minor component after stress, which did immunoprecipitate with the GPDH antibody. Therefore, there are at least two shock-induced 35,000 M(r) proteins, one of which is GPDH. These results establish that increases in GPDH mRNA prevalence and protein synthesis occur in response to both glucocorticoids and stress in the adult rat hippocampus. Based on the increased enzyme activity seen in the nervous system in response to glucocorticoids, dietary restriction, and nerve injury, the induction of GPDH may have functional consequences in cellular adaptation to stress.

Evidence for neuronal regulation of oligodendrocyte development: cellular localization of platelet-derived growth factor alpha receptor and A-chain mRNA during cerebral cortex development in the rat

Oligodendrocyte responses in vitro to platelet-derived growth factor (PDGF) include proliferation, survival, migration, and changes in cell morphology and molecular expression. Studies of mixed glial cultures established that astrocytes secrete PDGF; thus astrocytes are considered to be key regulators of oligodendrocyte development in vitro. We previously demonstrated PDGF alpha receptor mRNA expression by oligodendrocyte progenitors and preoligodendrocytes during postnatal development of rat cerebral cortex. In the present study, we have mapped the spatial and temporal expression of PDGF A-chain ligand mRNA and alpha receptor mRNA to determine if the cell-cell interactions that form the basis for PDGF regulation of oligodendrocyte development in vitro are also present in vivo. By in situ hybridization (ISH) we demonstrate that at embryonic day 17 (E17) cells expressing receptor mRNA (PDGFR alpha +) are initially in the subventricular zone, at a distance from cells expressing ligand mRNA (PDGF+) in the cortical plate. By E20 PDGFR alpha + cells are found throughout the corpus callosum and cortical gray matter. PDGF+ cells are restricted to the cortical plate prenatally and only appeared in the corpus callosum postnatally. Combined immunocytochemistry and ISH demonstrated the PDGF+ cells colocalized with neurofilament, but not with GFAP. These data establish that PDGF is expressed by neurons during PDGFR alpha + oligodendrocyte progenitor migration from the subventricular zone to the corpus callosum and gray matter. Furthermore, neurons continue to express PDGF during the generation and differentiation of appropriate numbers of oligodendrocytes needed to myelinate axons as the nervous system matures.

Neurotrophin activates signal transduction in oligodendroglial cells: expression of functional TrkC receptor isoforms

The role of the NT-3 has been implicated in the survival of progenitor oligodendrocytes in culture. The object of this study was to investigate the expression of the TrkC receptor and its responsiveness in glial cells. We report the expression of two TrkC receptor isoforms in rat primary oligodendrocyte cultures, a glial progenitor cell line, CG-4, and in C6 glioma cells. The reverse transcription-polymerase chain reaction-aided amplification of glial trkC with specific primers from the kinase domain, followed by its cloning and sequencing, shows the presence of two trkC transcripts. The sequence of one of the transcripts is homologous to a previously identified trkC isoform which encodes a functional receptor. The other transcript contains a 42-bp insert in the kinase domain. A Western blot of CG-4 and C6 probed with antibody to a TrkC revealed the presence of gp145-kDa protein band. The investigations revealed a rapid autophosphorylation of gp145TrkC in CG-4 and C6 cells in the presence of its specific ligand, NT-3. Furthermore, K252a, a neurotrophin-specific inhibitor, abolishes the NT-3-mediated receptor autophosphorylation. We also examined other NT-3-dependent phosphorylation of cellular substrates in oligodendroglial cells. Interestingly, we observed phosphorylation of phospholipase C gamma-1 in CG-4 and C6 cells, and phosphorylation of phosphatidylinositol 3-kinase in C6 cells in the presence of NT-3. Both the NT-mediated phosphorylation of phospholipase C gamma-1 and phosphorylation of phosphatidylinositol 3-kinase are blocked in the presence of K252a. The detection of the NT-3-mediated early signal transduction events demonstrates that TrkC receptor exhibits NT-3-mediated intracellular response in oligodendroglial cells.

CNTF regulation of astrogliosis and the activation of microglia in the developing rat central nervous system

In response to physical or chemical brain injury, the mammalian central nervous system (CNS) often reacts by evoking astrogliosis. The most prominent feature describing this state is an upregulation of glial fibrillary acidic protein (GFAP). The agent(s) responsible for inducing astrogliosis remains unclear; however, recent observations have shown cytokines may play a pivotal role. During CNS trauma, macrophages and lymphocytes infiltrate the CNS where they are thought to synthesize and secrete cytokines; moreover, activated microglia and reactive astrocytes are known to be capable of cytokine production. We are the first to report that an intracerebral injection of the pleiotropic cytokine, ciliary neurotrophic factor (CNTF), increases astrogliosis and the appearance of activated microglia in the neonatal rat. This response to CNTF was comparable to the response observed in animals receiving a well known pro-inflammatory cytokine, tumor necrosis factor-alpha (TNF-alpha). Only a moderate increase was observed in the proliferative index of cytokine-injected animals; therefore, we conclude that GFAP is largely upregulated in a pre-existing GFAP negative cell population. Interestingly, coinjections of CNTF and TNF-alpha appeared to act synergistically. Coinjected animals displayed a wave of hypertrophied astrocytes reaching far into the contralateral hemisphere. No contralateral spreading of microglia was observed. This article clearly provides interesting information regarding the regulatory mechanisms that govern astrogliosis and discusses the probable relationship of reactive astrocytes to microglia.

Amoeboid microglia expressing GD3 ganglioside are concentrated in regions of oligodendrogenesis during development of the rat corpus callosum

In recent study we demonstrated expression of the platelet-derived growth factor alpha receptor (PDGFR alpha) in cells of the early oligodendrocyte lineage that were identified as either GD3 ganglioside + oligodendrocyte progenitors or O4 sulfatide+ preoligodendrocytes. We also identified a subpopulation of GD3 immunoreactive cells that did not express mRNA for the PDGF receptor. The distinct large amoeboid morphology of these cells was characteristic of cells in the macrophage lineage rather than in the oligodendrocyte lineage. To determine if the GD3-positive but PDGFR alpha mRNA-negative cells were in the macrophage lineage, we compared the spatial and temporal expression patterns of GD3 ganglioside and ED1, a macrophage-specific antigen. Analysis prenatally indicated that at embryonic day 15, ED1+ and GD3+ cell populations resided in the subpial connective tissue. At embryonic day 21, these two populations were seen in a region extending from the lateral ventricle through the subventricular and intermediate zones. In this study we report that these large, round, GD3 immunoreactive cells have the same cell morphology and anatomical distribution as the ED1 immunoreactive cells. Both cell populations contained pyknotic nuclei within their cytoplasm. Furthermore, the GD3+/PDGFR alpha- cells appear to be involved in clearing cellular debris in regions of gliogenesis. These data suggest that this subpopulation of GD3 immunoreactive cells belongs to the microglia/macrophage lineage.

Tissue-specific DNA methylation patterns of the rat glial fibrillary acidic protein gene

The glial fibrillary acidic protein (GFAP) is an intermediate filament protein, specific of the cytoskeleton of astrocytes in the central nervous system. In the present work, as a preliminary step to the study of glial-specific gene expression, we cloned the rat GFAP gene, and we report the sequence of 1.9 kb of the 5' flanking region, exon 1, and the majority of the first intron. By digestion with methylation-sensitive restriction enzymes followed by Southern blot analysis, the methylation status of various CpG sites was examined in this genomic segment. We tested whether structural modification of the GFAP gene, such as DNA methylation, could be related to its tissue-specific transcriptional activity. Therefore, we compared a GFAP-expressing cell population (primary culture of astroglial cells), a mixed population of GFAP-expressing and -nonexpressing cells (adult rat cerebral hemispheres), and a GFAP-nonexpressing tissue (liver). In the 5' flanking region we identified a CpG site at position -1176 whose level of methylation is inversely correlated to GFAP expression. In primary cultured astrocytes, 75% of the GFAP gene alleles were demethylated at this site, while the corresponding value obtained for the cerebral hemispheres was 45%, and for liver only 9%. On the basis of the sequence data, a CpG-rich region (putative CpG island) was identified extending from -38 to +347 and overlapping 80% of the first exon. HhaI and HpaII sites located in the putative CpG island showed a relatively high level of methylation in all the cell populations examined, and did not show any clear correlation with the level of GFAP gene expression or with the methylation status of the -1176 site. Further in vivo developmental studies and in vitro differentiation studies are necessary to better understand the functional differences of the various methylatable CpG sites in the 5' end of the GFAP gene.

Brain-specific expression of the human transferrin gene. Similar elements govern transcription in oligodendrocytes and in a neuronal cell line

We have identified the regulatory sequences that govern the expression of the human transferrin gene in cultured brain cells and compared them with the data obtained with the neuronal cell line B103. Oligodendrocytes and epithelial choroid plexus cells from rat brain were cultured and used for transient expression experiments. Deletion analysis of 1.8 kilobase pairs of the 5' regulatory sequences revealed a -1530/-1140 positive-acting region in oligodendrocytes. The -164/+1 promoter region was sufficient to confer cell type-specific transcription in oligodendrocytes, epithelial choroid plexus cells, and B103 cells. DNase I footprinting experiments revealed three protected sequences, the proximal regions I and II, and the central region I. Gel retardation and antibody reactivity data allowed us to identify most of the nuclear factors present in oligodendrocytes interacting with the promoter sequences. Chicken ovalbumin upstream promoter transcription factor, a CAAT/enhancer-binding protein, and a cAMP response element-binding protein called CRI-BP interact with the proximal regions I and II and central region I sites, respectively. These data confirm the results obtained with the neuronal cell line and emphasize the importance of the three promoter elements for the transferrin gene-specific expression in the central nervous system compared with only two elements required for liver- and testis-specific expression.

Gene expression in astrocytes is affected by subculture

We have investigated the effects of cell passaging and time in culture on astrocyte morphology, transferrin expression and the expression of two main astrocyte markers, glial fibrillary acidic protein (GFAP) and glutamine synthetase (GS: EC 6.3.1.2). When primary astrocytes were subcultured, giving rise to secondary and tertiary cultures, their morphology changed, regardless of the split ratio used to passage the cells. Correlating with this morphological change, a dramatic increase in the accumulation of GFAP and GS mRNAs was observed after cells had been passaged. This effect was in marked contrast to the moderate increase in the levels of GFAP and GS mRNAs observed over several weeks in primary culture. Hydrocortisone induction of GS gene expression was not affected by cell passage. Transferrin mRNA, which is not normally found in astrocytes in vivo, was expressed at a high level in primary cultures of astrocytes. However, transferring mRNA almost completely disappeared after the second passage. Astrocyte-conditioned media, or co-cultures with oligodendrocytes, modified transferrin gene expression. Taken together, these results show that subculturing of primary rat astrocytes leads to a dramatic change in the genetic expression of several proteins and provides a new approach to modify astrocyte differentiation in vitro.

Platelet-derived growth factor receptor is expressed by cells in the early oligodendrocyte lineage

We report the localization of PDGFR alpha mRNA (PDGFR alpha) in phenotypically defined cells during the first postnatal week of rat forebrain development. Using a method of combined immunocytochemistry and in situ hybridization we have demonstrated the cellular colocalization of PDGFR alpha mRNA with GD3 ganglioside or O4 sulfatide, phenotypic markers of oligodendrocytes, in the gray and white matter of the dorsal cerebral cortex at all ages studied. Population analysis of the PDGFR alpha +/GD3+ and PDGFR alpha+/O4+ cells revealed that three populations express PDGFR alpha: GD3+, GD3+/O4+, and O4+, corresponding to two lineage stages, progenitor and preoligodendrocyte, in oligodendrocyte development. Immature oligodendrocytes, identified by galactocerebroside immunoreactivity, did not express detectable levels of PDGFR alpha mRNA. Post-mitotic neurons, identified by immunoperoxidase localization of the 68 kD neurofilament, and astrocytes identified by S-100 or GFAP immunoreactivity were also negative for PDGFR alpha mRNA. The spatial and temporal expression of PDGFR alpha mRNA occurred in oligodendrocyte cell populations which are post-migratory and proliferative, but which do not express myelin proteins characteristic of post-mitotic oligodendrocytes.

Grafting of fast blue labeled glial cells into neonatal rat brain: differential survival and migration among cell types

Cultures of oligodendrocyte progenitor cells, ERD 1.1 cells, a nontransformed immortalized cell line of oligodendrocyte progenitors and C6 glioma cells were labeled with the fluorescent dye Fast Blue and transplanted into brains of 4 day postnatal Wistar rat pups. The localization of fluorescent cells within host brain was examined at various times post-transplantation to determine patterns of cell migration as well as survival and integration among the host tissue. Oligodendrocyte progenitors migrated mainly along white matter tracks, integrating successfully into the host parenchyma. High survival rates were found between 5 and 27 days post grafting. ERD 1.1 cells survived and migrated between 1 and 5 days after transplantation. However, by 27 days survival had dropped from 60 to 20% of the initial cell population. The surviving cells were mainly localized to subventricular and subependymal regions at 27 days. C6 cells migrated extensively rostrally and caudally from the site of injection in the hippocampus and were tumorogenic. This finding confirmed previous reports on the survival and migration patterns of oligodendrocyte progenitors grafted into neonatal brain. However, they show that two cell lines that share phenotypic properties of oligodendrocyte progenitors markedly differ from these cells with respect to migration patterns and integration within host parenchyma. Fast Blue dye was still detectable after repeated cell division in grafted C6 cells, enabling us to track single cells as well as tumor formation. This dye should be useful not only to address issues of development, but also of tumor biology and therapeutic treatment.

CNS glial cells express neurotrophin receptors whose levels are regulated by NGF

Normal CNS glial cells manufacture neurotrophin receptors and are competent to respond to NGF. Neurotrophins bind a common receptor (LNGFR) and ligand-specific, tyrosine kinase-containing subunits (TrkA, TrkB, or TrkC). Northern blots and transcription assays reveal complex transcriptional regulation of LNGFR in astrocytes; from undetectable basal levels, NGF dramatically induces LNGFR within 4-6 h. Oligodendrocytes' relatively high basal levels are unaffected by NGF. TrkA mRNA was undetectable, however, TrkB was present and upregulated by NGF in astrocytes but not oligodendrocytes. The results are consistent with receptor autoregulation by its ligand and suggest that NGF plays a role in normal glial functions.

Rat brain creatine kinase messenger RNA levels are high in primary cultures of brain astrocytes and oligodendrocytes and low in neurons

Rat brain creatine kinase (CKB) gene expression is highest in the brain but is also detectable at lower levels in some other tissues. In the brain, the CKB enzyme is thought to be involved in the regeneration of ATP necessary for transport of ions and neurotransmitters. To understand the molecular events that lead to high CKB expression in the brain, we have determined the steady-state levels of CKB mRNA in homogeneous cultures of primary rat brain astrocytes, oligodendrocytes, and neurons. Northern blot analysis showed that whereas the 1.4-kb CKB mRNA was detectable in neurons, the level was about 17-fold higher in oligodendrocytes and 15-fold higher in astrocytes. The blots were hybridized with a CKB-specific 32P-antisense RNA probe, complementary to the 3' untranslated sequence of CKB, which hybridizes to CKB mRNA but not CKM mRNA. Also, the 5' and 3' ends of CKB mRNA from the glial cells were mapped, using exon-specific antisense probes in the RNase-protection assay, and were found to be the same in astrocytes and oligodendrocytes. This indicated that (a) the site of in vivo transcription initiation in astrocytes and oligodendrocytes was directed exclusively by the downstream, nonconcensus TTAA sequence at -25 bp in the CKB promoter that is also utilized by all other cell types that express CKB and (b) the 3' end of mature CKB mRNA was the same in astrocytes and oligodendrocytes. In addition, there was no detectable alternate splicing in exon 1, 2, or 8 of CKB mRNA in rat astrocytes and oligodendrocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Ontogeny of glycerol phosphate dehydrogenase-positive oligodendrocytes in rat brain. Impaired differentiation of oligodendrocytes in the myelin deficient mutant rat

The ontogeny of oligodendrocytes in the myelin deficient (md) rat mutant and in control rats was explored immunohistochemically using an antiserum against the oligodendrocyte specific enzyme, glycerol phosphate dehydrogenase (GPDH), and the avidin-biotin complex technique. In control rats, GPDH was demonstrated to be expressed relatively early in oligodendrocyte differentiation, prior to either myelin basic protein or proteolipid protein expression. With development, oligodendrocytes containing GPDH increased in number, apparent staining intensity, cell soma area and process elaboration. Fewer GPDH+oligodendrocytes were observed in the brain of mutant rats than in unaffected littermates at all developmental ages, and major developmental increases in oligodendrocyte density were delayed. The density of GPDH+oligodendrocytes was reduced by about 40% in both the corpus callosum and in the cingulate cortex of P22-25 and mutants compared with control rats. The oligodendrocyte cell soma area was not influenced by the md condition, and increased 2-fold with development in rats of both genotypes. The area of coronal sections occupied by the corpus callosum increased about 2.5-fold with development, and was 30% smaller in mutant rats late in their lifespan than in unaffected littermates. The reductions in oligodendrocyte density reported here are of insufficient magnitude to fully account for biochemically measured reductions in oligodendrocyte gene expression accompanying the md trait, indicating that gene expression per oligodendrocyte is also impaired. Cell counts in control rats also revealed that oligodendrocytes are overproduced during development. Cell density and the total number of corpus callosum GPDH+oligodendrocytes per section were maximal at P22-25 and then decreased to adult values. These results suggest that glial cells, like neurons, may be generated in excessive numbers, and some subsequently die, as a normal concomitant of development.

Differentiation of myoblasts and CNS cells grown either separately or as co-cultures on microcarriers

Dispersed neuronal and muscular elements from fetal or neonatal origin, can organize and mature in culture when grown on positively charged cylindrical microcarriers (MCS), to a stage which simulate in vivo maturation. Cells arrange themselves on the MCS to form aggregates which remain floating in the nutrient medium. In such a tridimensional organization, the neuronal tissue is capable of regenerating a network of nerve fibers which establish synapse interconnections and undergo myelination. Oligodendrocytes organize on MCS in a tridimensional pattern and produce extensive myelin-like membranes. Myoblasts in MC-cultures fuse into polynucleated myotubes which become striated and contract spontaneously. Creatine kinase and acetylcholine receptor (AChR) are formed during myogenesis in similar quantities in MC-cultures and in monolayers. When both neuronal and muscle tissues are prepared from the same fetus (autologous nerve-muscle co-cultures) and are cultured on MCS, they interconnect to form neuro-muscular junctions. Cells from both tissues, exhibit better differentiation, for longer periods in MC-cultures than they do in monolayers. The floating functional entities are easy to sample and can be harvested for ultrastructural, immunocytochemical and biochemical analysis. In addition, MC-cultures can be used as a good tool for the study of acute and chronic exposures to toxicological agents, as well as for implantation into demyelinated, injured or dystrophic tissues. In this case the MCS in the implanted entities will serve as identifiable markers.

Transplantation of cultured premyelinating oligodendrocytes into normal and myelin-deficient rat brain

Cultures of oligodendroglial cells at various stages of maturation, from progenitors to maturing oligodendrocytes, were prepared from neonatal rat brain primary cultures and then were prelabeled in the culture dish with the fluorescent dye, fast blue (FB). Single cell suspensions were grafted into normal or myelin-deficient rat brains. The normal as well as the myelin-deficient in vivo environment allowed cell survival, migration, and differentiation. The FB+ cells expressed the oligodendroglial markers, glycerol phosphate dehydrogenase, galactocerebroside, and myelin basic protein. In the normal rat transplanted cells were identifiable at all times studied up to 24 weeks. Extensive migration of FB+ cells was observed in whole-brain sagittal sections. Our results show that the plasticity of oligodendroglia differentiation, extensively studied in vitro, can now be investigated in the normal and myelin-deficient in vivo environment.

Characterization of the major 68 kDa heat shock protein in a rat transformed astroglial cell line

The heat shock response in a transformed astrocyte line was compared with nontransformed astrocytes. The synthesis of HSP 68, the major inducible heat shock protein (HSP 68) was induced by a non-lethal 45 degrees C, 10 min heat shock. Although the incorporation of [35S]methionine into HSP 68 suggested that similar amounts of protein were being synthesized after heat shock, Western immunoblotting demonstrated striking differences in the HSP immunostaining between the two cell types. By one- and 'two-dimensional gel electrophoresis the major 68 kDa heat shock protein (HSP 68) was similar in both cell types. However, HSP 68 from heat shocked, transformed astrocytes did not immunostain with the monoclonal antibody, C-92, which is specific for the major inducible heat shock protein of HeLa cells. In contrast HSP 68 from heat shocked, nontransformed astrocytes immunostained quite well. A polyclonal antibody raised against the inducible 72 kDa heat shock protein of HeLa cells immunostained the HSP 68 from both astrocytes and transformed astrocytes. Analysis of the mRNA from the two cell types after heat shock revealed two bands of approximately 2.5 and 2.8 kb in astrocytes but only a single 2.5 kb band in the heat shocked transformed astroglia. These results suggest that structural differences in the HSP 68 may be present in the transformed astrocytes compared to the normal astrocytes.