Tumor Necrosis Factor-α and Basic Fibroblast Growth Factor Decrease Glial Fibrillary Acidic Protein and Its Encoding mRNA in Astrocyte Cultures and Glioblastoma Cells

Abstract: Tumor necrosis factor-α is a pluripotent cytokine that is reportedly mitogenic to astrocytes. We examined expression of the astrocyte intermediate filament component glial fibrillary acidic protein in astrocyte cultures and the U373 glioblastoma cell line after treatment with tumor necrosis factor-α. Treatment with tumor necrosis factor-α for 72 h resulted in a decrease in content of glial fibrillary acidic protein and its encoding mRNA. At the same time, tumor necrosis factor-α treatment increased the expression of the cytokine interleukin-6 by astrocytes. The decrease in glial fibrillary acidic protein expression was greater when cells were subconfluent than when they were confluent. Thymidine uptake studies demonstrated that U373 cells proliferated in response to tumor necrosis factor-α, but primary neonatal astrocytes did not. However, in both U373 cells and primary astrocytes tumor necrosis factor-α induced an increase in total cellular protein content. Treatment of astrocytes and U373 cells for 72 h with the mitogenic cytokine basic fibroblast growth factor also induced a decrease in glial fibrillary acidic protein content and an increase in total protein level, demonstrating that this effect is not specific for tumor necrosis factor-α. The decrease in content of glial fibrillary acidic protein detected after tumor necrosis factor-α treatment is most likely due to dilution by other proteins that are synthesized rapidly in response to cytokine stimulation.     

Immunohistochemical co-localization of glycogen phosphorylase with the astroglial markers glial fibrillary acidic protein and S-100 protein in rat brain sections.

Immunofluorescence double-labelling and immunoenzyme double-staining methods were used to examine the location of glycogen phosphorylase brain isozyme with the astrocyte markers glial fibrillary acidic protein (GFAP) and S-100 protein in formaldehyde-fixed, paraffin-embedded slices from adult rat brain. Astrocytes in the cerebellum and the hippocampus, which express GFAP or S-100 protein immunoreactivity, show glycogen phosphorylase immunoreactivity. Regional intensity and intracellular distribution of the three antigens vary characteristically. In ependymal cells, glycogen phosphorylase immunoreactivity is co-localized with S-100 protein immunoreactivity, but not with GFAP immunoreactivity. These findings confirm that glycogen phosphorylase in the rat brain is exclusively localized in astrocytes and ependymal cells. All astrocytes, as far as they express GFAP or S-100 protein, do contain glycogen phosphorylase.     

Immunohistochemical co-localization of glycogen phosphorylase with the astroglial markers glial fibrillary acidic protein and S-100 protein in rat brain sections

Summary Immunofluorescence double-labelling and immunoenzyme double-staining methods were used to examine the location of glycogen phosphorylase brain isozyme with the astrocyte markers glial fibrillary acidic protein (GFAP) and S-100 protein in formaldehydefixed, paraffin-embedded slices from adult rat brain. Astrocytes in the cerebellum and the hippocampus, which express GFAP or S-100 protein immunoreactivity, show glycogen phosphorylase immunoreactivity. Regional intensity and intracellular distribution of the three antigens vary characteristically. In ependymal cells, glycogen phosphorylase immunoreactivity is co-localized with S-100 protein immunoreactivity, but not with GFAP immunoreactivity. These findings confirm that glycogen phosphorylase in the rat brain is exclusively localized in astrocytes and ependymal cells. All astrocytes, as far as they express GFAP or S-100 protein, do contain glycogen phosphorylase.     

A novel human astrocyte cell line (A735) with astrocyte-specific neurotransmitter function

Summary Studies of brain cell function and physiology are hampered by the limited availability of imortal human brain-derived cell lines, as a result of the technical difficulties encountered in establishing immortal human cells in culture. In this study, we demonstrate the application of recombinant DNA vectors expressing SV40 T antigen for the development of immortal human cell cultures, with morphological, growth, and functional properties of astrocytes. Primary human astrocytes were transfected with the SV40 T antigen expression vectors, pSV3neo or p735.6, and cultures were established with an extended lifespan. One of these cultures gave rise to an immortal cell line, designated A735. All the human SV40-derived lines retained morphological features and growth properties of type 1 astrocytes. Immunohistochemical studies and Western blot analysis of the intermediate filament proteins and glutamine synthetase demonstrated a differentiated but immature astrocyte phenotype. Transport of γ-amino butyric acid and glutamate were examined and found to be by a glial-specific mechanism, consistent with the cell lines’ retaining aspects of normal glial function. We conclude that methods based on the use of SV40 T antigen can successfully immortalize human astrocytes, retaining key astrocyte functions, but T antigen-induced proliferation appeared to interfere with expression of glial fibrillary acidic protein. We believe A735 is the first documented nontumor-derived human glial cell line which is immortal.     

树鼩脑星形胶质细胞的体外培养及纯化

本文旨在建立低等灵长类动物树鼩(Tupaia belangeri)脑星形胶质细胞(astrocyte,AS)原代培养及纯化的技术,为利用新型实验动物树鼩进行研究工作而建立体外模型。将新生树鼩大脑皮质机械分离,置于4°C冰箱20min以损伤神经元,皮质组织块用胰蛋白酶消化后制成细胞悬液,分次贴壁去除成纤维细胞,培养的混合细胞在每次换液时用0.005%胰蛋白酶轻柔漂洗去除神经元。细胞长满培养瓶底面积约70%时,用0.025%胰酶溶液静置消化,至肉眼可见一层白色薄膜从瓶底脱落时终止消化,此白色薄膜即为AS层。AS传至第三代时,用抗胶质纤维酸性蛋白(glial fibrillary acidic protein,GFAP)抗体进行免疫组织化学染色和免疫荧光染色鉴定。结果显示,本方法所得的树鼩脑AS的纯度可达98%以上。该结果提示,这种通过分次贴壁法结合差异消化的培养及纯化技术可获得高纯度的树鼩脑AS,为建立神经系统疾病新的体外细胞培养模型打下了基础。     

The Cytoskeleton of Primary Astrocytes in Culture Contains Actin, Glial Fibrillary Acidic Protein, and the Fibroblast-Type Filament Protein, Vimentin

Abstract: Primary astrocytes were cultured from the forebrains of 1-day-old rats. Immunofluorescence microscopy showed that approximately 80% of the cells were positive for glial fibrillary acidic protein (GFAP) and >80% were stained with an antiserum to the molecular weight 58,000 fibroblast intermediate filament protein (vimentin). Gel electrophoresis of Triton-insoluble cytoskeleton preparations from these cultures revealed three major bands having molecular weights of 58,000, 51,000, and 42,000, together with some prominent lower-molecular-weight species. The protein of molecular weight 51,000 was not present in preparations from fibroblasts. Each of the three major astrocyte proteins was subjected to limited proteolysis, while two of the proteins were cleaved by cyanogen bromide. The electrophoretic peptide patterns of the 58,000 protein were similar to those of vimentin isolated from NIL-8 fibroblasts, and the patterns of the 51,000 protein were similar to those of GFAP isolated from rat spinal cord. The patterns of the protein of molecular weight 42,000 resembled those of muscle actin. Rocket immunoelectrophoresis showed that the 51,000 astrocyte protein reacted with an antiserum to bovine GFAP, but the 58,000 and 42,000 proteins failed to react. We conclude that the major proteins of cytoskeleton preparations from cultured primary astrocytes are vimentin (58,000), GFAP (51,000), and actin (42,000), and that our data show no obvious structural relationship among them.     

Immunocytochemical localization of cytochrome P-450scc in cultured rat oligodendrocytes

Primary cultures of glial cells from newborn rat forebrain were tested after 3 to 4 weeks. Oligodendrocytes and astrocytes were characterized by immunofluorescence with monoclonal antibodies to galactocerebroside and glial fibrillary acidic protein, respectively. The cytoplasm of oligodendrocytes was specifically and intensely immunostained with monospecific polyclonal antibodies to the cytochrome P-450scc involved in the synthesis of pregnenolone from cholesterol. This observation brings additional support to the concept of "neurosteroids".     

Gliogenesis in rat optic nerve: astrocytes are generated in a single wave before oligodendrocytes

The time of origin for astrocytes in the rat optic nerve was investigated to determine whether this cell type is generated in two waves, a first wave which occurs before the formation of oligodendrocytes and a second wave which occurs after the peak period of oligodendrocyte formation. To answer this question, multiple injections of radioactive thymidine were administered to rats after the peak period of oligodendrocyte production in the optic nerve and the animals were sacrificed several weeks after the first injection. Thymidine-labeled cells in the optic nerve were identified with the electron microscope. Of the labeled cells, greater than 80% are oligodendrocytes, 4% are microglia, 2% are astrocytes, and the remainder are unclassifiable. The thymidine-labeled cells in the nerve were not immunostained for glial fibrillary acidic protein (GFAP), a marker characteristic of astrocytes. The number of thymidine-labeled glia generated after the second postnatal week is a small fraction of the total number of glia generated neonatally. No evidence exists for a second wave of astrocyte formation in the rat optic nerve as has been suggested in a study by Miller et al. (1985, Dev. Biol. 111, 35-41); rather, the vast majority of astrocytes are generated during the first 2 postnatal weeks and these data are in keeping with classical studies of gliogenesis. The question of whether astrocytes in the rat optic nerve arise directly from division of an undifferentiated, common progenitor cell or from a cell committed to the astrocyte lineage was addressed by combining thymidine autoradiography with GFAP immunocytochemistry. Rats were sacrificed 1 hr after an injection of thymidine and their nerves were processed for GFAP immunocytochemistry and autoradiography. During the first postnatal week, many thymidine-labeled cells are immunostained for GFAP. These observations demonstrate that cells committed to the astrocyte lineage divide neonatally and give rise to additional astrocytes.     

Low temperature induced de-differentiation of astrocytes

Radial glial cells are astrocyte precursors, which are transiently present in the developing central nervous system and transform eventually into astrocytes in the cerebral cortex and into Bergmann glia in the cerebellum. Previous reports indicate that the transformation from radial glia to astrocytes can be reversed by diffusible chemical signals derived from embryonic forebrain in vitro and by freezing injury in vivo. But there is no direct evidence proving that mature astrocytes can de-differentiate into radial glial cells. Here we show that purified astrocytes could de-differentiate into radial glial-like cells (RGLCs) in vitro with freeze-thaw stimulation. RGLCs had the expression of markers for radial glia including Nestin and Pax6, and astrocyte markers, the glial fibrillary acidic protein and Vimentin. Cortical neurons, when co-cultured with RGLCs, migrated along the processes of RGLCs at an average speed of 26.26 +/- 3.36 microm/h. Moreover, the proliferation of RGLCs was significantly promoted by epidermal growth factor (EGF) at the concentration of 10-30 ng/ml. These results reveal that low temperature induces astrocytes to de-differentiate into immature RGLCs, which provides an in vitro model to investigate mechanisms of astroglial cells de-differentiation.     

A Modified In vitro Method to Obtain Pure Astrocyte Cultures Induced from Mouse Hippocampal Neural Stem Cells Using Clonal Expansion

The aim of the present study was to produce astrocyte cultures of high purity from mouse hippocampal neural stem cells and to compare their in vitro properties with those isolated from enriched mixed glial cultures prepared from mouse hippocampus, which are commonly contaminated by microglia. We produced primary cultures of newborn mouse hippocampal neural stem cells, which have the potential to differentiate into astrocytes, neurons, and oligodendrocytes. We produced monoclonal neural stem cell colonies by limiting dilution. We induced astrocyte differentiation by plating the colonies on poly-l-lysine and culturing them in induction medium consisting of minimum essential medium/F12 supplemented with 10% fetal bovine serum and 100 ng/ml ciliary neurotrophic factor. We then further purified the cells by differential adherence and shaking at a constant temperature, followed by a second round of limiting dilution. Immunocytochemistry for glial fibrillary acidic protein showed that our method yielded 99.4 ± 0.5% pure astrocytes, whereas traditionally enriched mixed glial cultures yielded 94.2 ± 2% pure astrocytes. Induced cells resembled primary astrocyte cultures in functional properties such as cell proliferation rates and lack of tumorigenicity and p53, and expression of epidermal growth factor receptor, bystin, and nitric oxygen synthase. Our novel method of culture and purification of neural stem cells can therefore be used routinely for the primary culture of highly purified astrocytes from mouse hippocampus.     

Subpopulation of nestin positive glial precursor cells occur in primary adult human brain cultures

Glial fibrillary acidic protein (GFAP) is an intermediate filament protein considered to be the best astroglial marker. However, the predominant cell population in adult human brain tissue cultures does not express GFAP; these cells have been termed “glia-like” cells. The basic question about histological origin of adult human brain cultures remains unanswered. Some authors showed that “glia-like” cells in adult human brain cultures might be of non-glial origin. We examined primary explant tissue cultures derived from 70 adult human brain biopsies. Within first 5–10 days approximately 5–10% of the small explants became attached. Outgrowing cells were mostly flat cells. These cells formed confluent layer over 3–6 weeks in culture. At confluence the cultures contained 2–5% of microglial cells, 0.1% GFAP-positive astrocytes, less than 0.01% oligodendrocytes and 95–98% GFAP-negative “glia-like” cells. This population of flat “glia-like” cells was positively stained for vimentin, fibronectin, and 20–30% of these cells stained for nestin. Our findings revealed that 1 mM dibutyryl-cAMP addition, in serum free conditions, induced a reversible stellation in 5-10% of the flat “glia-like” cells but did not induce the expression of GFAP or nestin in morphologically changed stellate cells. These results demonstrate that “glia-like” cells in primary adult human brain cultures constitute heterogeneous cell populations albeit with similar morphological features. Two distinct subpopulations have been shown: (i) the one immunostained for nestin; and (ii) the other reactive for dibutyryl-cAMP treatment.     

A new astrocytic cell line which is able to induce a blood-brain barrier property in cultured brain capillary endothelial cells

Astrocytes, a member of the glial cell family in the central nervous system, are assumed to play a crucial role in the formation of the blood-brain barrier (BBB) in vertebrates. It was shown that astrocytes induce BBB-properties in brain capillary endothelial cells (BCEC) in vitro. We now established an astroglial cell line of non-tumoral origin. The cloned cell line (A7) shows a highly increased proliferation rate and expresses the astrocytic marker glial fibrillary acidic protein. Furthermore, the clone A7 expresses S-100-protein and vimentin, which are also expressed by primary cultured astrocytes. This cell line therefore shows general astrocytic features. In addition, we were able to show that A7 cells re-induce the BBB-related marker enzyme alkaline phosphatase in BCEC, when these two cell types are co-cultured. Thus we have a cell line which can be readily cultured in large quantities, shows common astrocyte properties and is able to influence BCEC with respect to a BBB-related feature. This revised version was published online in July 2006 with corrections to the Cover Date.     

Differential inducibilities of GFAP expression, cytostasis and apoptosis in primary cultures of human astrocytic tumours

Glial fibrillary acidic protein (GFAP) is an astrocytic lineage-specific intermediate filament protein, and its expression or non-expression is inversely correlated with the tumourigenecity of astrocytoma cells. To estimate the GFAP levels of astrocytes in intracranial tumour tissues, we established primary cultures from six astrocytic tumour specimens and used a double-staining flow cytometric method to detect the different levels of GFAP among these primary cultures. Although these primary cultures exhibited the same Matrigel invasiveness, their GFAP expression is inversely related to the rate of cell growth and the histologic grade of the original tumour. Phenylacetate, 12-O-tetradecanoylphorbol-13-acetate (TPA) and sodium butyrate, which are potent inducers of differentiation in various cancer cells, have been examined for their effects on these primary cultures. Cytostasis was more or less caused by these compounds in all six primary cultures, but induction of GFAP was observed only in the primary culture derived from a less malignant astrocytoma specimen having the highest intrinsic GFAP level. Interestingly, this primary culture, but not others, also exhibited increased HRG-α expression after phenylacetate or sodium butyrate treatment. Loss of the inducibility of differentiation-related gene expression could be one of the events involved in the malignant progression of astrocytomas. In addition, the chemotherapeutic agent BiCNU has a killing effect on all six primary culture cells, with LD50 less than 60nM. The underlying mechanism was through the induction of apoptosis in these primary culture cells regardless of their varying malignancies of original tumours. However, unlike colon cancer and leukaemia cells, sodium butyrate could not induce apoptosis within 4 days in these astrocytic tumour cells, indicating that the cell context of different cell types indeed determined the ability of sodium butyrate to induce apoptosis. This revised version was published online in June 2006 with corrections to the Cover Date.     

Absence of ganglioside GM1 in astroglial cells from newborn rat brain

An immunohistochemical method utilizing anti-ganglioside GM1 antiserum combined with the peroxidase-antiperoxidase technique was applied to a mixed cell population in primary cultures of newborn rat brain. Ganglioside GM1 was demonstrated to be present in neurons and oligodendroglia, but was absent in astroglia. This demonstration was confirmed using a newly developed biotinylated choleragen-avidin-peroxidase procedure. Primary cultures from newborn rat brain cells that had been subjected to a single treatment with trypsin (first passage) and then cultured for 14 days were predominately (95%) composed of astrocytes that stained positively for glial fibrillary acidic protein but were negative for GM1 ganglioside. This preparation contained only 0.34 nmol ganglioside NeuNAc per mg protein compared to 23.9 nmol gangliosidic NeuNAc/mg protein for a five day culture of newborn rat brain mixed cell culture that had not been subjected to passage. Prolongation of culture time from 5 to 21 days in the latter preparation reduced the ganglioside NeuNAc content to 4.9 nmol gangliosidic NeuNAc/mg protein as the proportion of astrocytes in the culture increased. Ganglioside GM1 could not be detected by TLC analysis of the lipid extract obtained from the “pure” astrocyte culture, although small amounts of GM3 and some polysialogangliosides were detected. About half of the label incorporated upon 24 h incubation of astrocytes in the presence of $\text{N-[}{}^3\text{H]acetylmannosammine}$ appeared in ganglioside GM3. It is concluded that astrocytes in mixed cell primary cultures from newborn rat brain, as well as astrocytes in astroglial preparations derived from such cultures, do not contain ganglioside GM1.     

Regulation of fructose-1,6-bisphosphatase activity in primary cultured astrocytes

In the gluconeogenic pathway, fructose-1,6-bisphosphatase (EC 3.1.3.11) is the last key-enzyme before the synthesis of glucose-6-phosphate. The extreme diversity of cells present in the whole brain does not facilitate in vivo study of this enzyme and makes it difficult to understand the regulatory mechanisms of the related carbohydrate metabolism. It is for instance difficult to grasp the actual effect of ions like potassium, magnesium and manganese on the metabolic process just as it is difficult to grasp the effect of different pH values and the influence of glycogenic compounds such as methionine sulfoximine. The present investigation attempts to study the expression and regulation of fructose-1,6-bisphosphatase in cultured astrocytes. Cerebral cortex of new-born rats was dissociated into single cells that were then plated. The cultured cells were flat and roughly polygonal and were positively immunostained by anti-glial fibrillary acidic protein antibodies. Cultured astrocytes are able to display the activity of fructose-1,6-bisphosphatase. This activity was much higher than that in brain tissue in vivo. Fructose-1,6-bisphosphatase in cultured astrocytes did not require magnesium ions for its activity. The initial velocity observed when the activity was measured in standard conditions was largely increased when the enzyme was incubated with Mn²⁺. This increase was however followed by a decrease in absorbance resulting in the induction, by the manganese ions, of a singular kinetics in the enzyme activity. Potassium ions also stimulated fructose-1,6-bisphosphatase activity. When the enzyme was exposed to different pH values ranging from 6 to 9 units, the highest activity was observed at pH 6. When the cultured astrocytes were incubated with methionine sulfoximine, the fructose-1,6-bisphosphatase activity increased. This increase was quick and depended on the dose of methionine sulfoximine. These results show that cultured astrocytes are able to maintain fructose-1,6-bisphosphatase activity. With the exception of the higher level activity associated acidic pH ranges, the properties of the enzyme resemble those of the in vivo enzyme. Methionine sulfoximine has a direct effect on astrocytes in its activation of fructose-1,6-bisphosphatase. It is concluded that the expression and the regulation of fructose-1,6-bisphosphatase activity in cultured astrocytes look like those in the brain. Astrocytes are probably the principal cells that express this activity in the brain in vivo.     

Glial uptake of monoamines in primary cultures of rat median raphe nucleus and cerebellum

Summary Glial uptake of serotonin and dopamine was studied in primary cultures of the median raphe nucleus and cerebellum by using consecutive demonstration of monoamine fluorescence and glial fibrillary acidic protein immunofluorescence. Most of the glial cells taking up monoamines were glial fibrillary acidic protein positive. Astrocytes with a strong immunoreactivity exhibited monoamine fluorescence only occasionally, although such cells did take up L-dopa readily. Glial fibrillary acidic protein negative cells — morphologically identified as astrocytes — were seen to exhibit monoamine fluorescence after exposure. Glial uptake of serotonin at a concentration of 10^–4 M was detected in cerebellar cultures but not in cultures from the median raphe nucleus. When the concentration was 10^–3 M uptake of serotonin took place in both the areas but was weaker in cultures from the median raphe nucleus. At concentrations greater than 10^–5 M glial uptake of dopamine was detected in cultures from both the regions studied. No region dependent differences in glial uptake of dopamine was demonstrated, however. Based on these observations astrocytes and astrocyte-like glial cells take up dopamine and serotonin. Also glial cells with a remarkably high content of the glial fibrillary acidic protein are more resistant to monoamine uptake than cells exhibiting less intense or no glial fibrillary acidic protein immunofluorescence. The existence of regional differences in uptake of serotonin between the median raphe nucleus and cerebellum suggests that glial uptake of monoamines is not an entirely passive mechanism but may be actively controlled by glial cells in a region dependent manner.     

Demonstration of astrocytes in cultured amniotic fluid cells of three cases with neural-tube defect

Summary We have investigated the origin of rapidly adhering (RA) cells in three cases of neural tube defects (two anencephali, one encephalocele). We were able to demonstrate the presence of glial fibrillary acidic (GFA) protein in variable percentages (4–80%) of RA cells cultured for 4–6 days by use of indirect immunofluorescence with GFA antiserum. Cells cultured from amniotic fluids of normal pregnancies and fetal fibroblasts were completely GFA protein negative. GFA protein is well established as a highly specific marker for astrocytes. Demonstration of astrocytes may prove to be a criterion of high diagnostic value for neural tube defects. The percentage of astrocytes decreased with increasing culture time, while the percentage of fibronectin positive cells increased both in amniotic fluid cell cultures from neural tube defects and normal pregnancies.     

Antigenic and functional characterization of a rat central nervous system-derived cell line immortalized by a retroviral vector

We have immortalized rat central nervous system (CNS) cells of primary cultures of rat optic nerve with murine leukemia virus psi-2,SV-40-6, which is defective in assembly and contains the SV-40 large T antigen and neomycin resistance genes, to produce a cell line that we named A7. After drug selection, greater than 90% of the growing cells expressed nuclear SV-40 large T cells and a fraction of these contained the astrocyte-specific marker, glial fibrillary acidic protein. The majority of these cells also expressed surface marker A4 (specific for neural tube derivatives), Ran 2, p185 (the 185-kD phosphoprotein product of the neu oncogene), and fibronectin, but did not express the astrocyte enzymes glutamine synthetase and monoamine oxidase B. Surface markers characteristic of glial progenitors (A2B5) and oligodendrocytes (galactocerebroside) were not detected. After two rounds of cell cloning, subclone A7.6-3 expressed Ran 2, fibronectin, and the neural cell adhesion molecule (N-CAM) but not glial fibrillary acidic protein and A4. The A7 cell line and subclones also displayed certain functions of type 1 astrocytes: the conditioned medium of these cells had a potent mitogenic activity for glial progenitor cells which could be neutralized by anti-platelet-derived growth factor antibodies and monolayers of these cells supported the growth of embryonic hypothalamic neurons. We conclude that a retrovirus containing SV-40 large T antigen can immortalize rat CNS cells and that such immortalized glial cells retain at least two important functions of type 1 astrocytes: the ability to secrete platelet-derived growth factor and to support the growth of embryonic CNS neurons. Moreover, such stable immortalized clonal cell lines can be used to study gene regulation in glial cells.