Apoptosis occurs in the oligodendroglial lineage, and is prevented by basic fibroblast growth factor

Basic FGF and FGF receptor 1 are expressed in microglia during experimental autoimmune encephalomyelitis: temporally distinct expression of midkine and pleiotrophin

Heparin-binding growth factors have been implicated in central nervous system development, regeneration and pathology. To assess the expression pattern and possible function in multiple sclerosis, the heparin-binding growth factors pleiotrophin (PTN), midkine (MK), basic fibroblast growth factor (FGF-2) and one of its receptors (FGFR1/flg) mRNA and protein levels were examined in an experimental autoimmune encephalomyelitis (EAE) model in the Lewis rat. We assessed the time course of expression of PTN, MK and FGF-2 during EAE and determined the cellular origin of FGF-2 and FGFR1 in normal spinal cord and during inflammatory demyelination. Basal expression of PTN and MK mRNAs in normal spinal cords was significantly upregulated after induction of EAE. MK expression was upregulated two to threefold correlating with disease progression, whereas PTN expression reached peak levels threefold above basal levels during the clinical recovery period. FGF-2 mRNA expression was low in normal spinal cord and dramatically increased in correlation with progressive demyelination. FGF-2 was confined to neurons in normal tissue and shifted dramatically to microglia, paralleling their activation during EAE. Double immunohistochemistry revealed colocalization of FGF-2 to activated microglia/macrophages with strongest expression in the macrophage-rich perivascular core area and microglial expression at the edges of white and gray matter perivascular regions. FGFR1, like its ligand, was induced in activated macrophages/microglia. Growth factor expression in demyelinating diseases could serve several functions, e.g., to modulate the activity of microglia/macrophage in an autocrine fashion, to induce the expression of other factors like insulin-like growth factor 1 or plasminogen activator, which can effect regeneration or degeneration, respectively, and finally to stimulate directly localized proliferation and/or regeneration of oligodendrocytes within the lesion area.

Maturation-dependent apoptotic cell death of oligodendrocytes in myelin-deficient rats

Mutations in the proteolipid protein gene (PLP/plp), which encodes the major intrinsic membrane protein in central nervous system (CNS) myelin, cause inherited dysmyelination in mammals. One of these mutants, the myelin-deficient (md) rat, has severe dysmyelination that is associated with oligodendrocyte cell death. Using the terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end-labeling (TUNEL) assay, which labels apoptotic cells, we find that cell death is increased in multiple white matter tracts of md rats. The tracts that myelinate the earliest show the earliest increase in cell death, and cell death persists for at least 22 days, the lifespan of these mutant animals. In all tracts, and at all developmental ages examined, apoptotic cells expressed the markers of mature oligodendrocytes, such as myelin basic protein, myelin-associated glycoprotein, and the Rip antigen, but not chondroitin sulfate proteoglycan, a marker of oligodendrocyte precursors. Mature oligodendrocytes fail to accumulate in md brain because they die before they fully mature.

Schwann cell undergoes apoptosis during experimental allergic neuritis (EAN)

Schwann cell apoptosis is not detectable in the normal mature mammalian peripheral nervous system (PNS). However, during PNS cell-mediated demyelination, apoptosis contributes to the elimination of endoneurial T-lymphocytes. We report here that approximately 10% of Schwann cells die by apoptosis during the early phases of recovery from experimental autoimmune neuritis (EAN) in the adult rat, a model for the Guillain-Barrè syndrome. Schwann cell apoptosis, follows endoneurial T-cell clearance, and is prominent in the nerve roots, the site of most severe segmental demyelination, but is rare in the more distal regions of the PNS, where Wallerian degeneration predominates. Further immunological analysis showed that the p75 neurotrophin receptor (p75NTR) is expressed in 2% of both apoptotic and non apoptotic Schwann cells, while Ki-67, a marker of cell proliferation, is expressed in 20% of apoptotic and in 1% of non apoptotic Schwann cells. Our new observations indicate that apoptosis during cell-mediated demyelination can be a phenomenon related either to the development or the recovery of autoimmune cell mediated inflammation.

Caffeine and staurosporine enhance the cytotoxicity of cisplatin and camptothecin in human brain tumor cell lines

Caffeine and staurosporine have been shown to attenuate G2 delay produced by DNA-damaging agents and to augment the cytotoxicity of these agents in a number of cell lines in vitro. Studies in rodent brain tumor cell lines suggest that modulation of the G2/M transition may not contribute to the enhanced cytotoxicity produced by caffeine in brain tumor cells. To evaluate the impact of agents that decrease G2 delay on the cytotoxicity of chemotherapy in human brain tumor cells, we examined the ability of caffeine and staurosporine to modulate the G2 delay and cytotoxicity produced by cisplatin (CDDP) and camptothecin (CPT) in U251 glioma and DAOY medulloblastoma cells. Synchronized U251 were incubated with 20 microM CDDP in the presence or absence of 2 mM caffeine. DAOY cells were incubated with 100 nM CPT in the presence or absence of 2 nM staurosporine. Caffeine and staurosporine attenuated G2 delay produced by CDDP and CPT, respectively. Clonogenic assays indicated that continuous exposure to 2 mM caffeine substantially lowered the ID50 and ID90 of CDDP in U251 cells without significantly altering plating efficiency. Twenty-four-hour exposure to 2 nM staurosporine lowered the ID50 and ID90 of CPT in DAOY cells without significantly altering plating efficiency. Evaluation of programmed cell death using terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling assay indicated that one mechanism for synergistic cytotoxicty of caffeine with CDDP and staurosporine with CPT in U251 and DAOY cells, respectively, is to promote apoptosis. These results underscore the importance of understanding regulation of G2/M transition in brain tumor cells. Such an understanding may lead to novel therapies that target G2 check points to augment the efficacy of currently available treatments for brain tumors.

Understanding glial abnormalities associated with myelin deficiency in the jimpy mutant mouse

Jimpy is a shortened life-span murine mutant showing recessive sex-linked inheritance. The genetic defect consists of a point mutation in the PLP gene and produces a severe CNS myelin deficiency that is associated with a variety of complex abnormalities affecting all glial populations. The myelin deficiency is primarily due to a failure to produce the normal amount of myelin during development. However, myelin destruction and oligodendrocyte death also account for the drastic myelin deficit observed in jimpy. The oligodendroglial cell line shows complex abnormalities in its differentiation pattern, including the degeneration of oligodendrocytes through an apoptotic mechanism. Oligodendrocytes seem to be the most likely candidate to be primarily altered in a disorder affecting myelination, but disturbances affecting astrocytes and microglia are also remarkable and may have a crucial significance in the development of the jimpy disorder. In fact, the jimpy phenotype may not be attributed to a defect in a single cell but rather to a deficiency in the normal relations between glial cells. Evidences from a variety of sources indicate that the jimpy mutant could be a model for disturbed glial development in the CNS. The accurate knowledge of the significance of PLP and its regulation during development must be of vital importance in order to understand glial abnormalities in jimpy.

Basic fibroblast growth factor downregulates Bcl-2 and promotes apoptosis in MCF-7 human breast cancer cells

Basic fibroblast growth factor (bFGF) is a mitogen and a survival factor in fibroblasts and endothelial cells. It acts as an angiogenesis factor in breast cancer, but paradoxically inhibits proliferation in several breast cancer cell lines. In this study, we investigated the effects of bFGF on the survival of MCF-7 human breast cancer cells in order to determine if these effects were also opposite to those in fibroblasts. Incubation of NIH 3T3 cells with bFGF for 24 h caused an approximately 30% increase in day 12 +/- 2 adherent colonies while causing an approximately 50% decrease in MCF-7 colony formation. Incubation of NIH 3T3 cells with bFGF prior to etoposide or 5-fluorouracil treatment caused a proportionally smaller decrease in colony forming efficiency as a result of drug treatment, while preincubation of MCF-7 cells with bFGF caused a similar but opposite additive increase in drug-induced diminution of colony forming efficiency. These effects on MCF-7 cells were observed at variable times of incubation and doses of etoposide to 1 microM and 5-fluorouracil to 200 microM and at variable times of incubation and concentrations of bFGF to 1 ng/ml. Incubating with bFGF after drug exposure had similar effects on the reduction of cloning efficiency. The effects of bFGF were similar on programmed cell death, as determined by morphologic characteristics of apoptosis on 400 cell counts and FITC-dUTP 3'-OH DNA end labeling. Basic FGF promoted apoptosis and increased the rate of drug-induced cell death with both etoposide and 5-fluorouracil. While recombinant bFGF affected Bcl-2 protein and mRNA levels in NIH 3T3 cells only marginally and variably and had no discernible effects on Bax protein levels, it markedly downregulated Bcl-2 mRNA and protein levels in MCF-7 cells and caused an increase in Bax protein levels. These changes resulted in a decreased association of Bcl-2 with immunoprecipitable Bax and an increased association of Bax with immunoprecipitable Bcl-2 in MCF-7 cells treated with bFGF. These data suggest that bFGF may cause different phenotypic responses in breast cancer cells from those in surrounding cells and offer one possible mechanism through opposite regulation of Bcl-2 and Bax. Inhibition of colony formation by bFGF was observed in several breast cancer cells lines, demonstrating that this effect demonstrated in MCF-7 cells was more universal.

Fibroblast growth factor receptor (FGFR)-1 and -2 in the ovine corpus luteum throughout the estrous cycle

Fibroblast growth factors (FGFs) probably play an important role in development and maintenance of the vasculature of the corpus luteum (CL). The objective of the present study was to evaluate the distribution and levels of fibroblast growth factor receptors (FGFRs) in the ovine CL from the early, mid- and late stages of the estrous cycle. Presence of FGFR-1 and -2 receptors was evaluated in CL by using Western analysis, immunohistochemistry and topical autoradiography. Western analysis demonstrated that the levels of FGFR-1 and -2 were similar in the early and mid-cycle CL but increased (p < 0.05) in the late stage of the estrous cycle. Immunohistochemistry and topical autoradiography demonstrate that both parenchymal (steroidogenic) and nonparenchymal (e.g. endothelial, fibroblastic) cells express FGFR-1 and -2. FGFR-1 was localized to the luteal vasculature throughout the estrous cycle; in the parenchymal cells, it was present during mid-cycle but was barely detectable in the late stage. Conversely, FGFR-2 was present in the parenchymal cells at all stages of the estrous cycle but localized to the larger microvessels only at the late stage. These data demonstrate that FGF receptors are present in the parenchyma as well as the vasculature of the CL which suggests that FGF is involved in the regulation of luteal parenchymal and vascular function.

Transplanted oligodendrocyte progenitor cells expressing a dominant-negative FGF receptor transgene fail to migrate in vivo

The proliferation, migration, survival, and differentiation of oligodendrocyte progenitor cells, precursors to myelin-forming oligodendrocytes in the CNS, are controlled by a number of polypeptide growth factors in vitro. The requirement and roles for individual factors in vivo, however, are primarily unknown. We have used a cell transplantation approach to examine the role of fibroblast growth factor (FGF) in oligodendrocyte development in vivo. A dominant-negative version of the FGF receptor-1 transgene was introduced into oligodendrocyte progenitors in vitro, generating cells that were nonresponsive to FGF but responsive to other mitogens. When transplanted into the brains of neonatal rats, mutant cells were unable to migrate and remained within the ventricles. These results suggest a role for FGF signaling in establishing a motile phenotype for oligodendrocyte progenitor cell migration in vivo and illustrate the utility of a somatic cell mutagenesis approach for the study of gene function during CNS development in vivo.

Induction of intracellular ceramide by interleukin-1 beta in oligodendrocytes

The sphingomyelin pathway has been implicated in mediating the effect of several extracellular agents leading to important biochemical and cellular changes. The aim of this investigation is to study interleukin-1 beta (IL-1 beta) signaling in oligodendrocytes. For this purpose, the CG4 oligodendrocyte cells were differentiated and incubated with IL-1 beta. This treatment induced a time- and dose-dependent increase of the endocellular ceramide. To mimic the effect of the elevation of endogenous ceramide, the CG4 cells were treated with the ceramide analogue C2-ceramide. Cell survival, measured with the MTT assay, showed that, by increasing the concentration of ceramide, up to 40% of CG4 cells were dying within 6 h, similar data were obtained with the primary differentiated oligodendrocytes. Condensation of chromatin, nuclear fragmentation, and formation of apoptotic bodies indicated that apoptosis was the cause of death. Surprisingly, long-term exposure (72 h) to increasing concentrations of IL-1 beta, which increases intracellular ceramide, did not induce oligodendroglial cell death. These results show that an increase of intracellular ceramide is not sufficient to induce apoptosis in oligodendrocytes and that IL-1 beta signaling through the ceramide pathway in these cells can mediate functions other than programmed cell death.

Immunoreactivity of cyclin D1/cdk4 in neurons and oligodendrocytes after focal cerebral ischemia in rat

We investigated the expression of cyclin D1 and its kinase, cdk4, after induction of focal cerebral ischemia in the rat. Brain from rats (n = 6) subjected to 2 hours of transient middle cerebral artery occlusion and 46 hours of reperfusion, and control sham-operated (n = 3) and normal (n = 2) rats were processed for dual label immunohistochemical study for cellular identification of the expression of these cell cycle proteins. Antibodies raised against microtubule-associated protein 2 and neuronal specific enolase for neurons, glial fibrillary acidic protein for astrocytes, myelin basic protein for oligodendrocytes and lectin histochemical study with the B4-isolectin for microglia were used for cell type identification. Double staining for DNA fragmentation detection (TUNEL) and expression of cyclin D1 and cdk4 also was performed. Cyclin D1 and cdk4 were selectively expressed in morphologically intact or altered neurons and oligodendrocytes localized to the ischemic tissue. Apoptotic cells were not immunoreactive to cyclin D1 and cdk4 at 46 hours after 2 hours of middle cerebral artery occlusion. The selective expression of cell cycle proteins observed in nonapoptotic ischemic postmitotic neurons and oligodendrocytes suggests a role for these proteins in cell survival after transient focal cerebral ischemia.

Growth factors and myelin regeneration in multiple sclerosis

Insulin-like growth factor-I (IGF-I), platelet-derived growth factor (PDGF), fibroblast growth factor (FGF) and ciliary neurotrophic factor (CNTF) are multifunctional growth factors which are found in the CNS. Oligodendroglia are the cells that form and maintain myelin sheaths and many in vitro experiments have shown that these growth factors promote the proliferation, differentiation and survival of cells in the oligodendroglial lineage. Since myelin breakdown is often severe in multiple sclerosis (MS), the possibility of growth factor use in the treatment of MS has been considered and recently, IGF-I treatment has been shown to reduce lesion severity and promote myelin regeneration in experimental autoimmune encephalomyelitis (EAE), an animal model of MS. This review briefly summarizes the structural characteristics of these growth factors and the actions which might help reduce oligodendrocyte-myelin sheath injury in MS and promote myelin regeneration.

Glial lineages and myelination in the central nervous system

Oligodendrocytes, derived from stem cell precursors which arise in subventricular zones of the developing central nervous system, have as their specialist role the synthesis and maintenance of myelin. Astrocytes contribute to the cellular architecture of the central nervous system and act as a source of growth factors and cytokines; microglia are bone-marrow derived macrophages which function as primary immunocompetent cells in the central nervous system. Myelination depends on the establishment of stable relationships between each differentiated oligodendrocyte and short segments of several neighbouring axons. There is growing evidence, especially from studies of glial cell implantation, that oligodendrocyte precursors persist in the adult nervous system and provide a limited capacity for the restoration of structure and function in myelinated pathways damaged by injury or disease.

Cellular proliferation and fibroblast growth factors in the corpus luteum during early pregnancy in ewes

To determine the relationship between cellular proliferation and the presence of FGF-1 and FGF-2 in the ovine corpus luteum (CL) during early pregnancy, ewes received an intravenous injection of bromodeoxyuridine (BrdU) 1 h before slaughter (n = 3/day) on day 12 after estrus (nonpregnant) or on days 12, 18, 24 or 30 after mating (pregnant). The labeling index (LI; number of BrdU-labeled nuclei expressed as a percentage of total nuclei) of each CL was determined by immunohistochemistry and subsequent image analysis. FGF-1 and FGF-2 were immunolocalized by using specific antibodies, and indirect immunoperoxidase detection. Moreover, FGF-2 was immunolocalized by using a primary antibody and fluorescein isothiocyanate (FITC)-labeled secondary antibody, and immunofluorescence was quantified by using an interactive laser cytometer and image analysis. Results demonstrated that the LI was similar for CL of nonpregnant and pregnant ewes on day 12 (4.27 +/- 0.23 vs 5.10 +/- 0.14%) and decreased (P < 0.05) from days 12-30 of pregnancy (2.73 +/- 0.08, 2.02 +/- 0.09 and 1.70 +/- 0.04% on days 18, 24 and 30, respectively). FGF-1 was present in the cytoplasm of large and a few small parenchymal luteal cells, and the distribution and intensity of staining was similar for nonpregnant and pregnant ewes on day 12 as well as across days of pregnancy. In contrast, FGF-2 immunoreactivity was present only in luteal nonparenchymal cells and interstitial areas and was greater (P < 0.05) for pregnant than nonpregnant CL on day 12 (2.34 +/- 0.12 vs 0.14 +/- 0.01%). Although FGF-2 immunoreactivity decreased (P < 0.01) from days 12-30 of pregnancy (0.70 +/- 0.04, 0.22 +/- 0.01 and 0.06 +/- 0.02% on days 18, 24, and 30, respectively), it was highly correlated (r = 0.99, P < 0.01) with luteal LI. We therefore suggest that FGF, and especially FGF-2, play a role in luteal cell proliferation or turnover during early pregnancy, and may thereby contribute to the maintenance of luteal function, which is critical for the successful establishment of pregnancy.

Pathophysiology of oligodendroglial excitotoxicity

Oligodendrocyte-like cells (OLD) derived from the rat oligodendroglial precursor line, CG-4, express Ca(2+)-permeable non-methyl-D-aspartate glutamate receptor channels (GluR). Exposure to kainate, an L-glutamate analogue, markedly elevates OLC Ca2+ influx and cytosolic [Ca2+], and results in damage to both OLC plasma membrane and OLC nuclear DNA. Two observations indicate that kainate-induced OLC internucleosomal DNA nicking is not simply a delayed consequence of cell necrosis: 1) there is no temporal lag between onset of plasma membrane injury and of DNA nicking; and 2) aurintricarboxylic acid, an endonuclease inhibitor, blocks kainate-induced damage to the plasma membrane. N-acetyl-L-cysteine also inhibits OLC kainate injury, suggesting that reactive oxygen species participate in OLC excitotoxicity. Kainate-induced OLC Ca2+ influx and excitotoxicity are blocked by alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA), indicating that these kainate effects are mediated by AMPA-GluR. AMPA and L-glutamate fail to elicit OLC damage unless cyclothiazide, an AMPA-GluR desensitization blocker, is present. OLC express both the "flip" and "flop" forms of GluR2, GluR3, and GluR4 mRNAs, but neither flip nor flop GluR1 mRNA. These data, together with the restriction of the desensitization-blocking activity of cyclothiazide to GluR containing flip-encoded GluR subunits, and the sharply diminished Ca2+ permeability of GluR containing edited GluR2, suggest OLC excitotoxicity is mediated by AMPA-GluR that contain flip GluR3 and/or flip GluR4 protein subunits, but neither flip nor flop GluR2 protein subunits. Rapid desensitization of these GluR is likely to be important in protecting cells of the oligodendroglial lineage from excitotoxicity.

Re-entry into the cell cycle is required for bFGF-induced oligodendroglial dedifferentiation and survival

Remyelination in the CNS following demyelinating disease may be accomplished by surviving mature oligodendrocytes that dedifferentiate, proliferate, migrate, and finally regenerate myelin. We previously reported that basic fibroblast growth factor (bFGF) induces oligodendrocytes in primary mixed glial cultures to dedifferentiate and synthesize DNA (Grinspan et al.: J Neurosci Res 36:672-680, 1993). We now show that this effect is direct and not mediated through the effects of bFGF on other cell types, because we were able to demonstrate similar changes in oligodendrocyte phenotype in enriched oligodendrocyte cultures prepared by immunopanning. The bFGF-induced reversion to the precursor stage of the oligodendroglial lineage can be blocked by agents that inhibit entry to the cell cycle; thus oligodendroglial dedifferentiation is dependent on proliferation. We also report that 2 days of bFGF treatment inhibits oligodendroglial apoptosis. However, when oligodendroglia are prevented from entering the cell cycle in the presence of bFGF, apoptotic cell death is increased. Thus, bFGF induces oligodendroglial dedifferentiation if oligodendroglial DNA synthesis can occur but causes oligodendroglial apoptosis when oligodendroglial DNA synthesis is prevented.

In vitro oligodendrogliotrophic properties of cell adhesion molecules in the immunoglobulin superfamily: myelin-associated glycoprotein and N-CAM

To determine if cell recognition molecules interact trophically with oligodendrocytes (OCs), their effect as growth substrates for differentiating oligodendroblasts was studied in primary culture. Oligodendroblasts purified from postnatal rat cerebrum by immunopanning were plated on substratum-bound cell adhesion molecules or extracellular matrix glycoproteins in chemically defined medium in which OCs terminally differentiate but survive poorly. Growth on myelin-associated glycoprotein (MAG) and neural cell adhesion molecule (N-CAM) selectively increased the number of viable cells per culture 2 weeks after plating as much as tenfold and sixfold, respectively, over background survival on an albumin substrate, whereas L1, tenascin-R, tenascin-C, fibronectin, and laminin were ineffective. Neither MAG nor N-CAM stimulated bromodeoxyuridine incorporation into cultures, indicating that enhanced proliferation did not contribute to better survival. Compared to growth on polyornithine alone, oligodendroblast differentiation in the added presence of MAG or N-CAM was qualitatively unchanged; > 90% of surviving cells developed into OCs that matured further by immunocytochemical and morphological criteria. A striking difference, however, was the quantitative effect of MAG and N-CAM substrates on oligodendrite outgrowth, increasing myelin-like membrane formation two- to threefold (> 8 x 10(3) microns2/cell). These findings support the concept that autotypic or heterotypic cell contact-mediated signaling by recognition molecules at the OC surface contributes trophic support of myelinogenesis.

Oligodendrocytes and their precursors require phosphatidylinositol 3-kinase signaling for survival

Signal transduction in response to several growth factors that regulate oligodendrocyte development and survival involves the activation of phosphatidylinositol 3-kinase, which we detect in oligodendrocytes and their precursors. To investigate the role of this enzyme activity, we analyzed cell survival in cultures of oligodendrocytes treated with wortmannin or LY294002, two potent inhibitors of phosphatidylinositol 3-kinase. Cell survival was inhibited by 60–70% in these cultures within 24 hours, as quantitated by a tetrazolium staining assay for viable cells and by measurement of DNA content. Similar results were obtained with oligodendrocyte precursor cells. Nuclei of the dying cells contained fragmented DNA, as revealed by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling assays, indicating that the cells were dying by apoptosis. Moreover, a significant increase in the number of cells with fragmented nuclear DNA was detected as early as 4 hours, well before any significant differences could be detected in glucose transport or cell viability. Exogenous addition of insulin-like growth factor-I, neurotrophin-3, platelet-derived growth factor, basic fibroblast growth factor, ciliary neurotrophic factor, N-acetyl cysteine, vitamin C, vitamin E, progesterone or serum did not prevent cell death in the presence of wortmannin or LY294002. These findings indicate that survival of oligodendrocytes and their precursors depends on a phosphatidylinositol 3-kinase mediated signaling pathway. Inhibition of this critical enzyme activity induces apoptotic cell death, even in the presence of exogenous growth factors or serum.

Induction of apoptosis by La Crosse virus infection and role of neuronal differentiation and human bcl-2 expression in its prevention

La Crosse virus causes a highly cytopathic infection in cultured cells and in the murine central nervous system (CNS), with widespread neuronal destruction. In some viral infections of the CNS, apoptosis, or programmed cell death, has been proposed as a mechanism for cytopathology (Y. Shen and T. E. Shenk, Curr. Opin. Genet. Dev. 5:105-111, 1995). To determine whether apoptosis plays a role in La Crosse virus-induced cell death, we performed experiments with newborn mice and two neural tissue culture models. Newborn mice infected with La Crosse virus showed evidence of apoptosis with the terminal deoxynucleotidyl transferase-mediated nicked-end labeling (TUNEL) assay and, concomitantly, histopathological suggestion of neuronal dropout. Infection of tissue culture cells also resulted in DNA fragmentation, TUNEL reactivity, and morphological changes in the nuclei characteristic of apoptotic cells. As in one other system (S. Ubol, P. C. Tucker, D. E. Griffin, and J. M. Hardwick, Proc. Natl. Acad. Sci. USA 91:5202-5206, 1994), expression of the human proto-oncogene bcl-2 was able to protect one neuronal cell line, N18-RE-105, from undergoing apoptosis after La Crosse virus infection and prolonged the survival of infected cells. Nevertheless, expression of bcl-2 did not prevent eventual cytopathicity. However, a human neuronal cell line, NT2N, was resistant to both apoptosis and other types of cytopathicity after infection with La Crosse virus, reaffirming the complexity of cell death. Our results show that apoptosis is an important consequence of La Crosse virus infection in vivo and in vitro.

GGF/neuregulin is a neuronal signal that promotes the proliferation and survival and inhibits the differentiation of oligodendrocyte progenitors

We show that GGF/neuregulin is a mitogen for prooligodendrocytes (O4+/O1- cells), oligodendrocytes (O4+/O1+ cells), and type-2 astrocytes. Heregulin beta 1, another neuregulin isoform, is also mitogenic. The proliferative effect of glial growth factor (GGF) does not require, but is greatly potentiated by, serum factors. GGF also promotes the survival of pro-oligodendrocytes under serum-free conditions. High levels of GGF reversibly inhibit the differentiation and lineage commitment of oligodendrocyte progenitors and, in differentiated cultures, result in loss of O1 and myelin basic protein expression. All three erbB receptors are expressed by progenitors and are activated by GGF; the relative abundance of these receptors changes during differentiation. Finally, cortical neurons release a soluble mitogen for pro-oligodendrocytes that is specifically blocked by antibodies to GGF. These results implicate the neuregulins in the neuronal regulation of oligodendrocyte progenitor proliferation, survival, and differentiation.

Astrocytes promote process outgrowth by adult human oligodendrocytes in vitro through interaction between bFGF and astrocyte extracellular matrix

Cell-cell interactions regulate many important functions within the central nervous system. In this report, we demonstrate that process outgrowth by adult human oligodendrocytes (OLs) in vitro, an early event of myelinogenesis in vivo, is promoted by astrocytes. To elucidate the mechanisms by which astrocytes might exert this effect, we tested several growth factors known to be produced by astrocytes and found that only basic fibroblast growth factor (bFGF) could enhance process extension by the OL. In correspondence, the treatment of astrocytes with a neutralizing antibody to bFGF decreased their effects in promoting oligodendroglial process outgrowth. The potency of bFGF, however, was only one-third that of astrocytes, and since bFGF did not synergize with other soluble growth factors, we investigated the potential facilitatory role of the extracellular matrix (ECM) deposited by astrocytes. The astrocyte ECM was found to be a promoter of oligodendroglial process extension, and significantly, bFGF synergized with astrocyte ECM to match the potency of live astrocytes. The astrocyte ECM was found in Western blot analyses to contain fibronectin, vitronectin, and laminin. These purified ECM components, as well as heparan sulfate proteoglycan, did not promote oligodendroglial process extension by themselves, although laminin and fibronectin potentiated the effects of bFGF. We conclude that process outgrowth by OLs is guided by astrocytes; the mechanism of the astrocyte effect appears to be due to the combination of bFGF and an unidentified ECM component.

Regulation of oligodendrocyte development and CNS myelination by growth factors: prospects for therapy of demyelinating disease

Multiple sclerosis (MS), the most common neurological disorder diagnosed in young adults, is characterized by autoimmune demyelination in the central nervous system (CNS). Promotion of remyelination in the brain and spinal cord is a potential strategy for therapeutic intervention in MS and other demyelinating diseases. Recent studies have shown that the development of oligodendrocytes, the myelin-forming cells of the CNS, is extensively controlled by growth factors. These factors regulate the proliferation, migration, differentiation, survival and regeneration of oligodendroglial cells and the synthesis of myelin, and often interact in a complex manner. Moreover, insulin-like growth factor I (IGF-I) has proven effective for therapy of experimental autoimmune encephalomyelitis (EAE), an animal model of autoimmune demyelination. In this review we summarize recent findings on the regulation of oligodendrocyte development and CNS myelination by growth factors, and discuss these findings in the context of possible clinical application for the therapy of neurological disease in humans.

Basic fibroblast growth factor (FGF-2) protects rat cochlear hair cells in organotypical culture from aminoglycoside injury

Given the evidence that basic fibroblast growth factor (FGF-2) can protect neural and retinal cells from degeneration, we evaluated the potential of this growth factor to protect sensory cells in the inner ear. When sensory cells of the organ of Corti are exposed to aminoglycoside antibiotics such as neomycin either in vivo or in vitro, significant ototoxicity is observed. The in vitro cytotoxic effects of neomycin are dose and time dependent. In neonatal rat organ of Corti cultures, complete inner and outer hair cell destruction is observed at high (mM) concentrations of neomycin while inner hair cell survival and severely damaged outer hair cells are noted at moderate (microM) concentrations, with a maximal effect observed after 2 days of culture. Approximately 50% of cochlear outer hair cells are lost at a dose of 35 microM neomycin, and most surviving cells show disorganized stereocilia. Inner hair cells show primarily disorganization of their stereocilia. A significant protective effect is observed when the organ of Corti is pre-treated with FGF-2 (500 ng/ml) for 48 hours, and then FGF-2 is included with neomycin in the culture medium. A greater extent of outer hair cell survival and a significant decrease in stereociliary damage are noted with FGF-2. However, disorganization of inner hair cell stereocilia is unaffected by FGF-2. The protective effect of FGF-2 is specific, since interleukin-1B, nerve growth factor, tumor necrosis factor, and epidermal growth factor are ineffective, while retinoic acid and transforming growth factor alpha show only a moderate protective effect. These results confirm the potential of molecules like FGF-2 for preventing cell death due to a variety of causes.

Antisense inhibition of basic fibroblast growth factor induces apoptosis in vascular smooth muscle cells

Basic fibroblast growth factor (bFGF), a potent mitogen for many cell types, is expressed by vascular smooth muscle cells and plays a prominent role in the proliferative response to vascular injury. Basic FGF has also been implicated as a survival factor for a variety of quiescent or terminally differentiated cells. Autocrine mechanisms could potentially mediate both proliferation and cell survival. To probe such autocrine pathways, endogenous bFGF production was inhibited in cultured rat vascular smooth muscle cells by the expression of antisense bFGF RNA. Inhibition of endogenous bFGF production induced apoptosis in these cells independent of proliferation, and apoptosis could be prevented by exogenous bFGF but not serum or epidermal growth factor. The induction of apoptosis was associated with an inappropriate entry into S phase. These data demonstrate that interruption of autocrine bFGF signaling results in apoptosis of vascular smooth muscle cells, and that the mechanism involves disruption of normal cell cycle regulation.

Platelet-derived growth factor partly prevents chemically induced oligodendrocyte death and improves myelin-like membranes repair in vitro

We have previously shown that pure oligodendrocyte (OL) secondary cultures derived from newborn rat brain, in which cells form myelin-like membranes, can be used as a model to investigate the putative role of growth factors in myelin repair. After disruption of these membranes by lysophosphatidylcholine (LPC), a 3 day treatment with 10 ng/ml basic fibroblast growth factor (bFGF) induced reconstruction of myelin figures, albeit less compacted than in untreated controls. Here we show that in LPC treated cultures: 1) bFGF can not prevent OL from LPC-induced cell death; 2) platelet-derived growth factor (PDGF) pretreatment although preventing some cell death does not improve recovery compared to delayed treatment; 3) PDGF is as potent as bFGF in terms of O-2A progenitor proliferation; 4) PDGF is far more effective than bFGF, inducing the reappearance of more myelin-like structures with a better compaction; 5) there is no potentiation between these growth factors; and 6) after withdrawal of bFGF the compaction of myelin figures partly increases. These results indicate that PDGF, probably by inducing O-2A progenitors to proliferate and then allowing them to differentiate into mature myelinating OL, is a better candidate than bFGF to participate in myelin repair mechanisms in the central nervous system.

Glial transplants: an in vivo analysis of extrinsic and intrinsic determinants of dysmyelination in genetic variants

Myelination in the CNS depends on the ability of oligodendrocytes (Ols) to efficiently colonize the brain, differentiate, and express a precise balance of specific genes necessary for myelin synthesis. Mutations in these genes produce different types of dysmyelination in animal as in human. Defects in the synthesis of myelin constituents usually lead to mild dysmyelinations. IN contrast, mutations affecting the gene encoding the proteolipid, another major protein of myelin, produce various perturbations of Ols biology suggesting a pleiotropic effect of the gene in the development of the CNS. Studies on expansion of cell population and survival have provided contradictory information on the extrinsic and intrinsic action of the gene on Ols biology. On one hand, in vitro studies using conditioned media as in vivo studies on heterozygotes, and transplantations experiments suggest that excess of programmed cell death in these mutants is ruled out by intrinsic factors which could act during embryonic life. On the other hand, attempts to compensate the gene defect by transgenic correction demonstrate a dominant negative effect of the jp mutation on both survival and functional potential of Ols. Finally, total suppression of PLP gene expression has a restricted effect on myelin structure without excess of cell death. These contradictory results are discussed in the perspective of regulation of cell death by competition for growth factors in limiting amount. The proposed model suggests that this contradiction is only apparent, and that excess of cell death in PLP/DM20 mutant is intrinsically determined by diminished competitivity of the mutant Ols for limited amounts of environmental factors.

Programmed cell death in the dysmyelinating mutants

A large number of genetic mutants that are missing a particular myelin protein or that have an aberrant myelin protein composition have been described. These mutations usually cause dysmyelination in the PNS or CNS. Similarly, the nervous system of animals experimentally altered to block synthesis of myelin proteins have recently been generated that show aberrations in the myelin sheath. For both groups of animals, the numbers of myelinating cells remain relatively stable and glial cell death is minimal. The exception is animals with mutations in the proteolipid protein (PLP) gene which exhibit extensive death of oligodendrocytes (OLs). The degree of OL death in the PLP mutants generally correlates with the amount of dysmyelination. Dying OLs in the PLP mutants exhibit the classical features of apoptotic cells. Programmed cell death (PCD) is often, but not necessarily, manifested by cleavage of DNA into abundant oligonucleosomal fragments. Detection of these abundant DNA fragments was examined in normal and jimpy (jp) mice using the TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labeling) method. In normal spinal cord and brain, at least twice as many cells exhibited DNA fragmentation when compared to numbers of pyknotic glia observed microscopically. In jp spinal cord and brain, roughly one-half of cells exhibited DNA fragmentation when compared to numbers of pyknotic glia observed microscopically. PCD of cells in normal development involving DNA fragmentation has been previously described and our results support that conclusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Platelet-derived growth factor is a survival factor for PSA-NCAM+ oligodendrocyte pre-progenitor cells

Mature oligodendroglia, which synthesize and express lipids and proteins characteristic of myelin, are generated from precursor cells which are formed in germinal matrix, then migrate widely through the neuraxis. We now demonstrate that these precursor cells can be recognized at a very early stage by their surface expression of polysialylated neural cell adhesion molecules (PSA-NCAM), and only later bind anti-ganglioside antibodies that had previously been used to recognize "O-2A" oligodendroglial precursor cells. PSA-NCAM expression by these cells is likely to be of functional significance, since a recent study demonstrated that O-2A cells become immobile when stripped of PSA-NCAM. Platelet-derived growth factor (PDGF) proved to be a survival factor for these PSA-NCAM+cells, and in a defined medium, PDGF was sufficient to ensure maturation of immunopurified PSA-NCAM+cells to oligodendroglia.