Expression of mRNAs of multiple growth factors and receptors by astrocytes and glioma cells: detection with reverse transcription-polymerase chain reaction

Astrocytes and brain-derived neurotrophic factor (BDNF)

Astrocytes are emerging in the neuroscience field as crucial modulators of brain functions, from the molecular control of synaptic plasticity to orchestrating brain-wide circuit activity for cognitive processes. The cellular pathways through which astrocytes modulate neuronal activity and plasticity are quite diverse. In this review, we focus on neurotrophic pathways, mostly those mediated by brain-derived neurotrophic factor (BDNF). Neurotrophins are a well-known family of trophic factors with pleiotropic functions in neuronal survival, maturation and activity. Within the brain, BDNF is the most abundantly expressed and most studied of all neurotrophins. While we have detailed knowledge of the effect of BDNF on neurons, much less is known about its physiology on astroglia. However, over the last years new findings emerged demonstrating that astrocytes take an active part into BDNF physiology. In this work, we discuss the state-of-the-art knowledge about astrocytes and BDNF. Indeed, astrocytes sense extracellular BDNF through its specific TrkB receptors and activate intracellular responses that greatly vary depending on the brain area, stage of development and receptors expressed. Astrocytes also uptake and recycle BDNF / proBDNF at synapses contributing to synaptic plasticity. Finally, experimental evidence is now available describing deficits in astrocytic BDNF in several neuropathologies, suggesting that astrocytic BDNF may represent a promising target for clinical translation.

Role of transcription factor yin yang 1 in manganese-induced reduction of astrocytic glutamate transporters: Putative mechanism for manganese-induced neurotoxicity

Astrocytes are the most abundant non-neuronal glial cells in the brain. Once relegated to a mere supportive role for neurons, contemporary dogmas ascribe multiple active roles for these cells in central nervous system (CNS) function, including maintenance of optimal glutamate levels in synapses. Regulation of glutamate levels in the synaptic cleft is crucial for preventing excitotoxic neuronal injury. Glutamate levels are regulated predominantly by two astrocytic glutamate transporters, glutamate transporter 1 (GLT-1) and glutamate aspartate transporter (GLAST). Indeed, the dysregulation of these transporters has been linked to several neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD) and Parkinson's disease (PD), as well as manganism, which is caused by overexposure to the trace metal, manganese (Mn). Although Mn is an essential trace element, its excessive accumulation in the brain as a result of chronic occupational or environmental exposures induces a neurological disorder referred to as manganism, which shares common pathological features with Parkinsonism. Mn decreases the expression and function of both GLAST and GLT-1. Astrocytes are commonly targeted by Mn, and thus reduction in astrocytic glutamate transporter function represents a critical mechanism of Mn-induced neurotoxicity. In this review, we will discuss the role of astrocytic glutamate transporters in neurodegenerative diseases and Mn-induced neurotoxicity.

Astrocytes and glutamate homoeostasis in Alzheimer's disease: a decrease in glutamine synthetase, but not in glutamate transporter-1, in the prefrontal cortex

Astrocytes control tissue equilibrium and hence define the homoeostasis and function of the CNS (central nervous system). Being principal homoeostatic cells, astroglia are fundamental for various forms of neuropathology, including AD (Alzheimer's disease). AD is a progressive neurodegenerative disorder characterized by the loss of cognitive functions due to specific lesions in mnesic-associated regions, including the mPFC (medial prefrontal cortex). Here, we analyzed the expression of GS (glutamine synthetase) and GLT-1 (glutamate transporter-1) in astrocytes in the mPFC during the progression of AD in a triple-transgenic mouse model (3xTg-AD). GS is an astrocyte-specific enzyme, responsible for the intracellular conversion of glutamate into glutamine, whereas the removal of glutamate from the extracellular space is accomplished mainly by astroglia-specific GLT-1. We found a significant decrease in the numerical density (Nv, cells/mm³) of GS-positive astrocytes from early to middle ages (1–9 months; at the age of 1 month by 17%, 6 months by 27% and 9 months by 27% when compared with control animals) in parallel with a reduced expression of GS (determined by Western blots), which started at the age of 6 months and was sustained up to 12 months of age. We did not, however, find any changes in the expression of GLT-1, which implies an intact glutamate uptake mechanism. Our results indicate that the decrease in GS expression may underlie a gradual decline in the vital astrocyte-dependent glutamate–glutamine conversion pathway, which in turn may compromise glutamate homoeostasis, leading towards failures in synaptic connectivity with deficient cognition and memory.

ASTROCYTES: EMERGING STARS IN LEUKODYSTROPHY PATHOGENESIS

Astrocytes are the predominant glial cell population in the central nervous system (CNS). Once considered only passive scaffolding elements, astrocytes are now recognised as cells playing essential roles in CNS development and function. They control extracellular water and ion homeostasis, provide substrates for energy metabolism, and regulate neurogenesis, myelination and synaptic transmission. Due to these multiple activities astrocytes have been implicated in almost all brain pathologies, contributing to various aspects of disease initiation, progression and resolution. Evidence is emerging that astrocyte dysfunction can be the direct cause of neurodegeneration, as shown in Alexander's disease where myelin degeneration is caused by mutations in the gene encoding the astrocyte-specific cytoskeleton protein glial fibrillary acidic protein. Recent studies point to a primary role for astrocytes in the pathogenesis of other genetic leukodystrophies such as megalencephalic leukoencephalopathy with subcortical cysts and vanishing white matter disease. The aim of this review is to summarize current knowledge of the pathophysiological role of astrocytes focusing on their contribution to the development of the above mentioned leukodystrophies and on new perspectives for the treatment of neurological disorders.

Enhanced expression of glia maturation factor correlates with glial activation in the brain of triple transgenic Alzheimer's disease mice

We previously demonstrated that glia maturation factor (GMF), a brain specific protein, isolated, sequenced and cloned in our laboratory, induce expression of proinflammatory cytokines and chemokines in the central nervous system. We also reported that the up-regulation of GMF in astrocytes leads to the destruction of neurons suggesting a novel pathway of GMF-mediated cytotoxicity of brain cells, and implicated its involvement in the pathogenesis of inflammatory neurodegenerative diseases. In the present study, we examined the expressions of GMF in triple-transgenic Alzheimer's disease (3xTg-AD) mice. Our results show a 13-fold up-regulation of GMF and 8-12-fold up-regulation of proinflammatory cytokines tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), IL-1β, interferon gamma (IFN-γ), and chemokine (C-C motif) ligand 2 (CCL2) and C-X-C motif chemokine 10 (CXCL10/IP-10) mRNA as determined by quantitative real-time RT-PCR in the brain of 3xTg-AD mice as compared to non-transgenic (Non-Tg) mice. In conclusion, the increase in GMF and cytokine/chemokine expression was correlated with reactive glial fibrillary acidic protein positive astrocytes and ionized calcium binding adaptor molecule 1 (Iba-1)-positive microglia in 3xTg-AD mice.

Clinical course of myelin oligodendrocyte glycoprotein 35-55 induced experimental autoimmune encephalomyelitis is aggravated by glia maturation factor

The role of glia maturation factor (GMF) in myelin oligodendrocyte glycoprotein (MOG) 35-55 peptide-induced experimental autoimmune encephalomyelitis (EAE) was investigated using GMF-deficient (GMF-KO) mice. We demonstrate that GMF-KO mice were resistant to the MOG 35-55 peptide-induced EAE as compared to wild type (Wt) mice (two in eight versus 10 in 10). Next, we examined the effect of administration of recombinant human GMF (rGMF) on MOG 35-55 peptide-induced EAE in mice. Daily administration of rGMF, staring days 1-14, resulted in significant exacerbation of clinical symptoms. Following rGMF injections, both GMF-KO (six in eight) and Wt mice (eight in eight) developed severe EAE (maximal clinical score of 3.5-4.0) with high frequency. The histological examination revealed severe infiltration of inflammatory cells in the spinal cord of MOG-immunized Wt mice while the resistance to EAE in GMF-KO mice was characterized by the absence of inflammatory cells. Administration of rGMF in Wt mice and GMF-KO mice resulted in a significant increase in infiltrating cells in the spinal cord following MOG-immunizations. We also evaluated cytokines and chemokines production as parameters of severity of inflammation in the spinal cord of Wt versus GMF-KO mice with and without GMF-reconstitution following MOG-immunizations. Cytokines (TNF-α, IFN-γ, IL-1β, IL-6) and chemokines (CCL2, CCL3, CXCL10, GM-CSF) production were significantly greater in Wt mice than in GMF-KO mice following MOG-immunization. Furthermore, the reconstitution experiment with rGMF showed that the administration of rGMF in both, Wt mice and GMF-KO mice produced significant increase in the GMF-mediated cytokine/chemokine production.

Augmented expression of glia maturation factor in Alzheimer's disease

We have previously demonstrated that glia maturation factor (GMF), a brain-specific protein, isolated, sequenced, and cloned in our laboratory, is a prominent mediator of inflammation in the CNS leading to the death of neurons. In the present study, we demonstrate, for the first time, a significant upregulation of the GMF protein in various regions of Alzheimer's disease (AD) brains compared with age-matched non-demented (ND) control brains. We analyzed AD and ND brain samples by quantitative enzyme-linked immunosorbent assay (ELISA) using a combination of highly specific monoclonal and polyclonal anti-GMF antibodies developed and characterized in our laboratory. For the comparison between ND controls and AD cases, we examined brain tissue from 12 ad cases (ages ranging from 78-92 years) and eight age-matched ND controls (ages ranging from 76-88 years). We observed a significant increase in GMF concentration in entorhinal cortex, parietal cortex, frontal cortex, occipital cortex, perirhinal cortex, and temporal cortex of AD patients. Our results clearly demonstrate that the GMF protein levels are significantly higher in all AD-affected brain regions than in ND controls. The immunohistochemistry analysis revealed co-localization of GMF with amyloid plaques (AP) and neurofibrillary tangles (NFTs) in AD brains. Our results imply that under conditions of neurodegeneration the expression of GMF is significantly upregulated.

Overexpression of glia maturation factor reinstates susceptibility to myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis in glia maturation factor deficient mice

Glia maturation factor (GMF), a primarily CNS localized protein was discovered and characterized in our laboratory. We previously demonstrated that GMF is the upstream regulator for excessive production and release of proinflammatory cytokines/chemokines in brain cells leading to the destruction of oligodendrocytes, the myelin forming cells, and neurons. We also reported that mice lacking endogenous GMF (GMF-deficient, GMF-KO) were resistant to myelin oligodendrocyte glycoprotein peptide 35-55 (MOG(35-55)) induced EAE, since immunization induced only delayed EAE with diminished severity. In the present study we show that a replication-defective adenovirus-GMF construct caused expression of GMF in CNS of GMF-KO mice and reinstated MOG(35-55) induced early and severe EAE. Our results show that MOG(35-55) immunization caused only a muted EAE and inflammation/demyelination in mice lacking endogenous GMF. The diminished incidence of EAE in GMF-KO mice was consistent with the significantly reduced expressions of cytokines/chemokines. The muted severity of EAE in GMF-KO mice was restored to full blown levels upon reintroduction of GMF using an adeno-GMF-virus (Adv-GMF) vector. Consistent with the clinical findings, histological examination of the CNS of mice with EAE revealed profound differences between wild type (Wt), GMF-KO, and GMF-KO mice with re-introduced GMF (GMF-KO+Adv-GMF). Spinal cord sections from mice with EAE were analyzed for the infiltration of mononuclear cells (inflammation) and myelin loss (demyelination). In Wt mice, 40% of spinal cord quadrants were positive for demyelination and 45% of spinal cord quadrants were positive for inflammation at the peak of EAE. Drastically reduced infiltrates (15%) and demyelination (10%) were found in GMF-KO mice that developed reduced severity of EAE. Upon GMF reintroduction in GMF-KO mice, MOG(35-55) immunization caused extensive monocytes infiltration (48%) and demyelination (46%), similar to that observed in the immunized Wt mice. The levels of cytokine/chemokine in the spinal cords of mice at three time points, corresponding to the onset, peak severity and recovery period of EAE, show a distinct pattern of very large increases in IFN-γ, TNF-α, GM-CSF and MCP-1 in Wt and GMF-KO+Adv-GMF mice compared to GMF-KO and GMF-KO+Adv-LacZ mice.

Derivation of neural stem cells from mesenchymal stemcells: evidence for a bipotential stem cell population

Neural stem cell (NSC) transplantation has been proposed as a future therapy for neurodegenerative disorders. However, NSC transplantation will be hampered by the limited number of brain donors and the toxicity of immunosuppressive regimens that might be needed with allogeneic transplantation. These limitations may be avoided if NSCs can be generated from clinically accessible sources, such as bone marrow (BM) and peripheral blood samples, that are suitable for autologous transplantation. We report here that NSCs can be generated from human BM-derived mesenchymal stem cells (MSCs). When cultured in NSC culture conditions, 8% of MSCs were able to generate neurospheres. These MSC-derived neurospheres expressed characteristic NSC antigens, such as nestin and musashi-1, and were capable of self-renewal and multilineage differentiation into neurons, astrocytes, and oligodendrocytes. Furthermore, when these MSC-derived neurospheres were cocultured with primary astrocytes, they differentiate into neurons that possess both dendritic and axonal processes, form synapses, and are able to fire tetrodotoxin-sensitive action potentials. When these MSC-derived NSCs were switched back to MSC culture conditions, a small fraction of NSCs (averaging 4-5%) adhered to the culture flasks, proliferated, and displayed the morphology of MSCs. Those adherent cells expressed the characteristic MSC antigens and regained the ability to differentiate into multiple mesodermal lineages. Data presented in this study suggest that MSCs contain a small fraction (averaging 4-5%) of a bipotential stem cell population that is able to generate either MSCs or NSCs depending on the culture conditions.

Glia maturation factor modulates beta-amyloid-induced glial activation, inflammatory cytokine/chemokine production and neuronal damage

Glia maturation factor (GMF), discovered and characterized in our laboratory, is a highly conserved protein primarily localized in mammalian central nervous system. Previously we demonstrated that GMF is required in the induced production of proinflammatory cytokines and chemokines in brain cells. We now report that ventricular infusion of human amyloid beta peptide1-42 (Abeta1-42) in mouse brain caused glial activation and large increases in the levels of GMF as well as induction of inflammatory cytokine/chemokine known for launching the neuro inflammatory cascade in Alzheimer's disease (AD). To test the hypothesis that GMF is involved in the pathogenesis of AD, we infused Abeta1-42 in the brain of GMF-deficient (GMF-KO) mice, recently prepared in our laboratory. GMF-deficient mice showed reduced glial activation and significantly suppressed proinflammatory cytokine/chemokine production following Abeta infusion compared to wild type (Wt) mice. The decrease in glial activation in the GMF-KO mice is also associated with significant reduction in Abeta induced loss of pre-synaptic marker, synaptophysin, and post-synaptic density protein-95 (PSD 95). We also examined the potential relationship between GMF or lack of it with learning and memory using the T-maze, Y-maze, and water maze, hippocampal-dependent spatial memory tasks. Our results show that memory retention was improved in GMF-KO mice compared to Wt controls following Abeta infusion. Diminution of these Abeta1-42 effects in primary cultures of GMF-KO astrocyte and microglia were reversed by reconstituted expression of GMF. Taken together, our results indicate a novel mediatory role of GMF in the neuro-inflammatory pathway of Abeta and its pro-inflammatory functions.

Dephosphorylation of Akt in C6 cells grown in serum-free conditions corresponds with redistribution of p85/PI3K to the nucleus

Withdrawal of serum from cell cultures constitutes a useful model for the study of mechanisms involved in the regulation of Akt function in vitro. However, there have been several reports of changes in Akt activity that are not fully explained by the current model of phosphatidylinositol 3'-kinase (PI3K)/Akt signaling. We demonstrate the expected loss of Akt phosphorylation in C6 glioma cells cultured in serum-free conditions, yet we also observed a paradoxical increase in PI3K-lipid kinase activity in the same cultures. These events corresponded with relocalization of p85, the regulatory subunit of PI3K, to the perinuclear region and a local increase in PI3K-lipid kinase products. Treatment with platelet-derived growth factor (PDGF) maintained the association between p85 and the PDGF receptor during serum withdrawal and restored PI3K-lipid production at the plasma membrane. Although this protected Akt from dephosphorylation, it only slightly reversed cell-cycle arrest. These effects were not sensitive to treatment with epidermal growth factor, thus precluding a generalized role for growth factors. Our data suggest that loss of growth factor signaling, including PDGF signaling, may disrupt recruitment and/or anchoring of an active p85(PI3K) complex at the plasma membrane during serum withdrawal, which could account for the concurrent loss of Akt function.

Glia maturation factor overexpression in neuroblastoma cells activates glycogen synthase kinase-3beta and caspase-3

In the present study we report that a replication-defective adenovirus construct of GMF cDNA (GMF-V) induced overexpression of GMF protein in neuroblastoma (N18) cells caused cytotoxicity and loss of cell viability. A significant increase in activation of GSK-3beta occurred after infection with GMF-V when compared with mock and lacZ controls. Overexpression of GMF also increased caspase-3 activity, an early marker of apoptosis. Depletion of GMF gene by introducing GMF-specific siRNA (GsiRNA) completely blocked both activation of GSK-3beta and caspase-3 activation whereas a control scrambled siRNA (CsiRNA) had no effect. A cell-permeable peptide inhibitor of GSK-3beta, and lithium completely prevented GMF-dependent activation of caspase-3. These results demonstrate that GSK-3 mediates activation of the death domain caspase by GMF overexpression. We also show that the phosphorylation of GSK-3-dependent site of Tau was a consequence of GMF-overexpression in N18 cells. Taken together our results imply that GMF is involved in the signaling leading to the activation of GSK-3beta and caspase-3 in N18 cells and strongly suggest its involvement in neurodegeneration since GSK-3beta is known to hyperphosphorylate tau which is associated with the neurotoxicity of neurofibrillary tangles in Alzheimer's disease.

Glia Maturation Factor Regulation of STAT Expression: A Novel Mechanism in Experimental Autoimmune Encephalomyelitis

Inflammatory cytokines are implemented in the pathogenesis of experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis. We previously demonstrated that glia maturation factor (GMF), a brain protein, isolated, sequenced and cloned in our laboratory, induce expression of proinflammatory cytokine/chemokine in the central nervous system (CNS). We found GMF-deficient (knockout) mice relatively resistant to EAE development after immunization with encephalitogenic MOG peptide 35-55. Consistent with these findings, the expression of proinflammatory cytokines in CNS of mice with EAE differed profoundly between wild type and GMF-knockout mice. In the present study we examined the expressions of six murine signal transducers and activators of transcription (STATs) genes, which are known to regulate the cytokine-dependent signal transduction pathways in autoimmune inflammation. The expressions of STATs genes were evaluated in the brains and spinal cords of wild type and GMF-knockout mice at the peak of EAE by quantitative real-time RT-PCR. Compared to GMF-knockout mice, the expressions of STAT1, STAT2, STAT3, STAT4, STAT5, and STAT6 genes were significantly (P < 0.001) upregulated in the wild type mice exhibiting EAE symptoms. The results are consistent with the diminished development of EAE in the GMF-knockout mice. A significant suppression of STATs expression in GMF-knockout mice suggests GMF as an upstream effector of JAK/STAT signaling.

Diminished degradation of myelin basic protein by anti-sulfatide antibody and interferon-gamma in myelin from glia maturation factor-deficient mice

In this study we show the effect of anti-sulfatide (RmAb) antibodies and inflammatory cytokines, TNF-alpha and IFN-gamma in inducing myelin basic protein (MBP) degradation in myelin isolated from control wild type (WT) and glia maturation factor (GMF)-deficient (GMF-KO) mice. GMF was not detected in isolated myelin from WT and GMF-KO mice although it is present in brains of WT mice. Our results show that calcium-dependent neutral protease activity caused significantly elevated degradation of 18.5 and/or 17.5kDa isoforms of MBP in WT myelin treated with RmAb or IFN-gamma. In contrast, MBP degradation in isolated myelin from GMF-KO mice remained unaffected following treatment with RmAb, IFN-gamma, or GM-CSF. Neither the 14kDa isoform of MBP nor proteolipid protein (PLP) showed an elevated degradation compared to controls. A virtual absence of GM-CSF, TNF-alpha and IFN-gamma in GMF-KO brain compared to WT was also evident when the animals were challenged with MOG 35-55. Additionally, the myelin from GMF-KO mice showed difference in distribution of myelin oligodendrocyte glycoprotein (MOG) and beta-tubulin in a sucrose density gradient myelin-axolemmal fractions compared to WT. Taken together, our data suggests a role for GMF in the biochemical organization of myelin and thereby its effect on MBP degradation induced by RmAb and IFN-gamma.

A novel role of glia maturation factor: induction of granulocyte-macrophage colony-stimulating factor and pro-inflammatory cytokines

The glia maturation factor (GMF), which was discovered in our laboratory, is a highly conserved protein predominantly localized in astrocytes. GMF is an intracellular regulator of stress-related signal transduction. We now report that the overexpression of GMF in astrocytes leads to the destruction of primary oligodendrocytes by interactions between highly purified cultures of astrocytes, microglia, and oligodendrocytes. We infected astrocytes with a replication-defective adenovirus carrying the GMF cDNA. The overexpression of GMF caused the activation of p38 MAP kinase and transcription factor NF-kappaB, as well as the induction of granulocyte-macrophage colony-stimulating factor (GM-CSF) mRNA and protein in astrocytes. Small interfering RNA-mediated GMF knockdown completely blocked the GMF-dependent activation of p38 mitogen-activated protein kinase (MAPK), NF-kappaB, and enhanced expression of GM-CSF by astrocytes. Inhibition of p38 MAPK or NF-kappaB by specific inhibitors prevented GM-CSF production. The cell-free conditioned medium from overexpressing GMF astrocytes contained 320 +/- 33 pg/mL of GM-CSF, which was responsible for enhanced production and secretion of TNF-alpha, IL-1beta, IL-6, and IP-10 by microglia. Presence of these inflammatory cytokines in the conditioned medium from microglia efficiently destroyed oligodendrocytes in culture. These results suggest that GMF-induced production of GM-CSF in astrocytes is depending on p38 MAPK and NF-kappaB activation. The GM-CSF-dependent expression and secretion of inflammatory cytokine/chemokine, TNF-alpha, IL-1beta, IL-6, and IP-10, is cytotoxic to oligodendrocytes, the myelin-forming cells in the central nervous system, and as well as neurons. Our results suggest a novel pathway of GMF-initiated cytotoxicity of brain cells, and implicate its involvement in inflammatory diseases such as multiple sclerosis.

Diminished cytokine and chemokine expression in the central nervous system of GMF-deficient mice with experimental autoimmune encephalomyelitis

Pro-inflammatory cytokines/chemokines are implemented in the pathogenesis of experimental autoimmune encephalomyelitis (EAE), an animal model with clinical and pathological similarities to multiple sclerosis. We have previously shown that over-expression of glia maturation factor (GMF) in glial cells cause excessive production and secretion of pro-inflammatory cytokines/chemokines sufficient to destroy the myelin-forming oligodendroglial cell in vitro. In this present investigation, we evaluate the expression of pro-inflammatory mediators in the central nervous system (CNS) of GMF+/+ (wild type) mice and GMF-/- (GMF-knockout) mice at the peak of EAE induced by immunization with MOG 35-55 peptide. GMF+/+ (Wt) mice developed severe EAE with a maximal mean clinical score of 3.6+/-0.5 by day 16 post-immunization, whereas GMF-KO mice showed significantly delayed EAE with an average onset on day 26 pi with reduced mean clinical score of 1.3+/-0.3. Three of fifteen Wt mice as compared to none of GMF-KO mice died of EAE. Encephalitogenic cells from Wt mice transferred to recipient GMF-KO mice caused very mild and with low incidence of EAE. We determined the differences in the expression of cytokines, IFN-gamma, TNF-alpha, IL-1 beta, IL-6, IL-4, IL-10, and chemokines, MIP-1, MIP-2, IP-10, MCP-1, GM-CSF mRNA by quantitative real-time RT-PCR in brain and spinal cord. Our results demonstrate significantly low levels of pro-inflammatory cytokines/chemokines in the CNS of GMF-KO mice and increased expression in Wt mice with EAE. Our data suggest that GMF play a critical role in CNS inflammation.

Reduced severity of experimental autoimmune encephalomyelitis in GMF-deficient mice

Glia maturation factor (GMF), a highly conserved brain-specific protein, isolated, sequenced and cloned in our laboratory. Overexpression of GMF in astrocytes induces the production and secretion of granulocyte-macrophage-colony stimulating factor (GM-CSF), and subsequent immune activation of microglia, expression of several proinflammatory genes including major histocompatibility complex proteins, IL-1beta, and MIP-1beta, all associated with the development of experimental autoimmune encephalomyelitis (EAE), the animal model for multiple sclerosis. Based on GMF's ability to activate microglia and induce well-established proinflammatory mediators, including GM-CSF, we hypothesize that GMF is involved in the pathogenesis of inflammatory disease EAE. In this present investigation, using GMF-deficient mice, we study the role of GMF and how the lack of GMF affects the EAE disease. Our results show a significant decrease in incidence, delay in onset, and reduced severity of EAE in GMF-deficient mice, and support the hypothesis that GMF plays a major role in the pathogenesis of disease.

Markers for OLN-93 oligodendroglia differentiation

Oligodendrocytes are target cells in the pathogenesis of multiple sclerosis (MS), a chronic demyelinating disease of the central nervous system (CNS). During the course of the disease, inflammatory mediators may damage oligodendrocytes and their myelin sheaths. Differentiation of oligodendrocyte progenitors is an important step in the process of remyelination. In the present study, OLN-93 differentiation was studied in co-culture with C6 astrocytes as a natural source of growth and differentiation factors as well as after exposure to insulin-like growth factor-I (IGF-I). Morphological evaluation showed an increased degree of differentiation of OLN-93 cells after IGF-I administration, but not after co-culture with astrocytes. During early differentiation, 2', 3'-cyclic nucleotide 3'-phosphohydrolase (CNP) and zonula occludens-1 (ZO-1) tight junction protein expression were significantly increased. However, neither astrocyte co-culture nor exposure to IGF-I further increased the expression of these markers. Although reverse transcriptase-polymerase chain reaction revealed myelin basic protein (MBP) mRNA expression not to be affected during differentiation, we did find increased MBP protein expression by Western blotting. ZO-1 protein and DM20 mRNA levels were increased during the course of differentiation and after IGF-I administration. The present findings suggest that ZO-1 may be used as a marker for OLN-93 oligodendroglia differentiation.

Increase by FK960, a novel cognitive enhancer, in glial cell line-derived neurotrophic factor production in cultured rat astrocytes

We examined the effect of N-(4-acetyl-1-piperazinyl)-p-fluorobenzamide monohydrate (FK960), a novel anti-dementia drug, on neurotrophic factor production in cultured rat astrocytes. FK960 (100nM) increased mRNA and protein levels of glial cell line-derived neurotrophic factor (GDNF). FK960 did not affect mRNA levels of neurotrophic factors other than GDNF. The effect of FK960 was not affected by antagonists of dopamine and alpha7-nicotinic acetylcholine receptors. FK960 stimulated phosphorylation of mitogen-activated protein/extracellular signal-regulated kinase (ERK) without any effect on phosphoryolation of p38 and c-Jun N-terminal kinase. FK960 increased the levels of c-Fos and phosphorylation of cAMP responsive element binding protein (CREB). The effect of FK960 on c-Fos was inhibited by PD98059 (10microM), an ERK kinase inhibitor, and cycloheximide (1microg/ml), a transcription inhibitor, and the effect of FK960 on CREB phosphorylation was blocked by PD98059. The effect of FK960 on GDNF mRNA expression was attenuated by PD98059, curcumin (10microM), an activator protein-1 inhibitor, cycloheximide and actinomycin D (10microg/ml). These results suggest that FK960 stimulates GDNF production in c-Fos- and CREB-dependent mechanisms in cultured astrocytes and that ERK signal is responsible for both c-Fos expression and CREB phosphorylation in the cascades.

Elevated glial brain-derived neurotrophic factor in Parkinson's diseased nigra

We show the cellular distribution of immunoreactivity (IR) for brain-derived-neurotrophic-factor (BDNF), neurotrophin-3 (NT-3) and tyrosine kinase receptors TRKB and TRKC in idiopathic Parkinson's disease (IPD) and controls at post-mortem. In both groups, nigral neurons, astrocytes, ramified and amoeboid microglia expressed all antigens. Caudate-putamen neurons expressed all antigens except BDNF with similar distribution between groups. In IPD nigra, increased numbers of BDNF-IR and, less frequently, NT-3-IR ramified glia surrounded fragmented neurons, accompanied by BDNF-IR in surrounding neuropil. Amoeboid microglia were abundant only in IPD nigral scars. In IPD, glia might up-regulate neurotrophins in response to signals released from failing nigral neurons.

Intracerebroventricular administration of an endothelin ETB receptor agonist increases expressions of GDNF and BDNF in rat brain

Endothelins (ETs) are suggested to be involved in functional alterations of astrocytes after brain injury, including proliferation, hypertrophy and production of neurotrophic factors. In this study, effects of Ala1,3,11,15-endothelin-1 (Ala1,3,11,15-ET-1), an ETB receptor selective agonist, on neurotrophic factor production were examined in rat brain. A continuous intracerebroventricular administration of Ala1,3,11,15-ET-1 (500 pmol/day for 7 days) increased the numbers of GFAP- and vimentin-positive astrocytes in the hippocampus, caudate putamen and cerebrum. Ala1,3,11,15-ET-1 did not induce neuronal degeneration and activation of microglia/macrophage in these brain regions. The intracerebroventricular administration of Ala1,3,11,15-ET-1 for 7 days caused two- to three-fold increases in glial cell line-derived neurotrophic factors (GDNF) mRNA in the hippocampus and cerebrum. The mRNA levels of brain-derived neurotrophic factors (BDNF) in caudate putamen were increased by Ala1,3,11,15-ET-1. Expressions of nerve growth factor (NGF) and basic fibroblast growth factor (bFGF) mRNA in these regions were not largely affected by Ala1,3,11,15-ET-1, except cerebral NGF mRNA level was increased. The Ala1,3,11,15-ET-1-induced increases in GDNF and BDNF mRNA levels were accompanied by increases in immunoreactive GDNF and BDNF. Immunohistochemical observations showed that GFAP-positive astrocytes expressed GDNF and BDNF in the brain regions of Ala1,3,11,15-ET-1-infused rats. In cultured rat astrocytes, Ala1,3,11,15-ET-1 (100 nm) increased mRNA levels of GDNF and BDNF. These results suggest that activation of brain ETB receptors induced GDNF and BDNF expression in astrocytes.

Neural stem cells from adult hippocampus develop essential properties of functional CNS neurons

Neural stem cells are present both in the developing nervous system and in the adult nervous system of all mammals, including humans. Little is known, however, about the extent to which stem cells in adults can give rise to new neurons. We used immunocytochemistry, electron microscopy, fluorescence microscopy (FM imaging) and electrophysiology to demonstrate that progeny of adult rat neural stem cells, when co-cultured with primary neurons and astrocytes from neonatal hippocampus, develop into electrically active neurons and integrate into neuronal networks with functional synaptic transmission. We also found that functional neurogenesis from adult stem cells is possible in co-culture with astrocytes from neonatal and adult hippocampus. These studies show that neural stem cells derived from adult tissues, like those derived from embryonic tissues, retain the potential to differentiate into functional neurons with essential properties of mature CNS neurons.

Effects of glia maturation factor overexpression in primary astrocytes on MAP kinase activation, transcription factor activation, and neurotrophin secretion

Using the replication-defective adenovirus vector, we overexpressed rat glia maturation factor (GMF) in primary astrocyte cultures derived from embryonic rat brains. Among the three isoforms of MAP kinase, there was a big increase in the phosphorylation of p38, as detected with Western blotting using the phosphospecific antibody. Likewise, there was a substantial increase in the phosphorylation of the transcription factor CREB. Using the electrophoretic mobility shift assay (EMSA), we found a stimulation in the transcription factor NF-kappaB. The activations of CREB and NF-kappaB were blocked by inhibitors of either p38 (SB-203580) or MEK (PD-098059), suggesting that they were events downstream of MAK kinase. There was an increased secretion of BDNF and NGF into the conditioned medium, along with an increase in their messenger RNA. The inductions of BDNF and NGF were also blocked by inhibitors of p38 and MEK, as well as by the inhibition of NF-kappaB with a decoy DNA sequence. Taken together, the results suggest that GMF functions intracellularly in astrocytes as a modulator of MAP kinase signal transduction, leading to a series of downstream events including CREB and NF-kappaB activation, resulting in the induction and secretion of the neurotrophins.

Hepatocyte growth factor is secreted by osteoblasts and cooperatively permits the survival of haematopoietic progenitors

Human osteoblasts (HOBs) support the growth of human haematopoietic progenitor cells, and support the survival and limited expansion of long-term culture-initiating cells. Using human CD34+ cells and the murine myelomonocytic cell line NFS-60 as targets, we previously found that one component of HOB-derived haematopoietic activity is cell-associated granulocyte colony-stimulating factor (G-CSF). However, antibody failed to neutralize all the activity, suggesting that more than one factor supports haematopoietic cells. In the present investigations, we asked whether the HOB-derived, non-G-CSF secreted activity was as a result of other known growth factors. We found that, among the cytokines expressed by HOBs, only hepatocyte growth factor (HGF) and G-CSF stimulated NFS-60 cell proliferation. HOB cells and osteosarcoma cells secreted biologically active HGF, although the levels varied considerably. Moreover, addition of neutralizing HGF antibody to CD34+ cell/HOB co-cultures resulted in a significant reduction ( approximately 50%) in the ability of the HOBs to support haematopoietic progenitor cells. These results suggest that a major component of osteoblast-derived haematopoietic activity is HGF. Secretion of HGF, in concert with cell-associated cytokines such as G-CSF, may account for the stem cell-stimulating activities of osteogenic cells and, thereby, the unique stem cell-supporting role of the osteoblasts within the bone marrow microenvironment.

Cytokine responses to LTP induction in the rat hippocampus: a comparison of in vitro and in vivo techniques

Because exogenous application of a number of cytokines and growth factors can alter synaptic properties, we sought to determine if endogenous cytokine expression is affected by neuronal activity. In addition, we examined whether cytokine expression is altered by the techniques used to stimulate and record from hippocampal neurons. Using semi-quantitative RNase protection and RT-PCR assays, we studied the expression of 18 cytokine, growth factor, and receptor genes in the hippocampus following the induction of Schaffer collateral-CA1 long-term potentiation (LTP). We found that various cytokines are dramatically induced following preparation of slices for in vitro recording and as a result of injury following acute electrode placement in vivo. These increases can be overcome in vivo, however, using permanent electrodes implanted three weeks prior to testing. Using this chronic preparation, we found that interleukin-6 (IL-6) mRNA was upregulated nearly 20-fold by LTP induction in vivo, marking the first demonstration of endogenous regulation of this cytokine in response to LTP. In situ hybridization for IL-6 revealed that upregulation is tightly localized near the site of stimulation and is detected only in non-neuronal cells, identified as GFAP+ astrocytes and GFAP- cells within proximal blood vessels. Coupled with previous results showing that exogenously applied IL-6 can prevent the induction of LTP, this finding suggests a mechanism by which the local release of a cytokine could regulate LTP at nearby sites.

Activation of the Jak-Stat- and MAPK-pathways by oncostatin M is not sufficient to cause growth inhibition of human glioma cells

We have recently described that oncostatin M (OSM), a member of the IL-6 family of cytokines, induces the differentiation of human glioma cells in culture. In order to extend this studies, we analyzed the effect of OSM on other human glioma cell lines including A172, U343-MG and T98G. All of these cell lines express the receptor components of OSM and leukemia inhibitory factor (LIF) gp130, LIFR and the OSM specific OSMRbeta. Therefore, we expected these cell lines to respond to OSM and LIF. Using specific antibodies recognizing proteins of the janus kinase (Jak-)/signal transducers and activator of transcription (Stat-) signaling cascade that has been shown to transduce the signals of the IL-6 cytokines to the nucleus, we could show that Jak1, Jak2 and Tyk2, as well as the Stat proteins Stat1, Stat3 and Stat5b were phosphorylated in all three cell lines by OSM and, at least in part, by LIF. Activation of the Stat proteins was also detected by EMSA which revealed complex formation on the Stat3 DNA-binding element and on a Stat5 binding site. Consistent with our recent findings, OSM treatment also induced the activation of the MAPK erk2 and the tyrosine phosphatase SHP-2 in cells of the A172, T98G and U343-MG cell lines. Although this activation pattern was very close to what we had observed in the GOS3 glioma cells, only T98G showed a growth inhibition in response to OSM while the A172 and the U343-MG cell lines did not respond to OSM treatment in terms of growth inhibition.

Oncostatin M-mediated growth inhibition of human glioblastoma cells does not depend on stat3 or on mitogen-activated protein kinase activation

Oncostatin M (OSM) and other members of the interleukin-6 cytokines, like ciliary neurotrophic factor and leukemia inhibitory factor, can induce differentiation of glial cells. We have recently described that OSM inhibited the growth of human glioma cells in vitro and induced a cell morphology resembling that of mature astrocytes. Using the glioblastoma cell line 86HG39, we demonstrated that treatment of the glioma cells with OSM also leads to a differentiation of the malignant glioma cells as judged by a strong increase in glial fibrillary acidic protein expression. The differentiation and the growth inhibition were not significantly blocked by expression of a dominant-negative (dn) signal transducer and activator of transcription (Stat) 3 protein. OSM exerted a reduction in DNA synthesis even in the presence of a high expression level of dnStat3. Moreover, inhibition of the ras-raf-mitogen-activated protein kinase (MAPK) pathway by the MAPK kinase 1 inhibitor PD98059 resulted in a synergistic enhancement of the OSM effect, indicating that the activation of this pathway counteracts the activity of the cytokine.

Transfection of C6 glioma cells with glia maturation factor upregulates brain-derived neurotrophic factor and nerve growth factor: trophic effects and protection against ethanol toxicity in cerebellar granule cells

Glial cells play active roles in neuronal survival, as well as neuroprotection against toxic insult. Recent studies suggest that the brain protein glia maturation factor (GMF) is involved in intracellular signaling in glia. This study investigated whether or not GMF plays a role in the survival-promoting and neuroprotective functions of glia. C6 glioma cells were transfected in vitro with GMF utilizing an adenovirus vector. The transfected cells overexpressed GMF intracellularly, but did not secrete the protein. The conditioned medium (CM) was obtained from the GMF-transfected cells (CM-GMF) and tested on primary neuronal cultures, consisting of cerebellar granule cells (CGC). The CGC cultures were utilized because these cultures have a background level of cell death, and the survival-promoting, i.e. neurotrophic effect, of the CM could be tested. In addition, since CGC cultures are ethanol-sensitive (ethanol enhances neuronal death), the neuroprotective effect of the CM against ethanol-induced cell death was tested also. We demonstrated that the CM-GMF had an enhanced neurotrophic effect as well as an increased neuroprotective effect against ethanol-induced cell death compared to control CM obtained from untransfected C6 cells (CM-Mock) or CM obtained from cells transfected with an unrelated gene (CM-LacZ). Because neurotrophins have trophic and protective effects, we investigated whether GMF-transfection upregulated the expression of neurotrophins in C6 cells. RT-PCR verified that GMF-transfected C6 cells had increased mRNA levels for BDNF and NGF. Immunoblotting corroborated the RT-PCR results and indicated that CM-GMF contained greater concentrations of BDNF and NGF protein compared to CM-Mock and CM-LacZ. A soluble TrkB-IgG fusion protein, which selectively binds BDNF and prevents its binding to the neuronal TrkB receptor, eliminated the neurotrophic effect of CM-GMF; whereas anti-NGF antibody was ineffective in preventing this effect, suggesting that the neurotrophic effect was due to BDNF. On the other hand, both the TrkB-IgG fusion protein and anti-NGF reduced neuroprotection, suggesting that BDNF and NGF both contribute to the neuroprotective effect of CM-GMF. In conclusion, GMF upregulates the expression of BDNF and NGF in C6 cells, and these factors exert neurotrophic and neuroprotective functions on primary neurons.

Expression pattern of galectin-3 in neural tumor cell lines

Galectin-3 is a member of the galectin family of beta-galactoside-specific animal lectins. Here we show that galectin-3 is constitutively expressed in 15 out of 16 glioma cell lines tested, but not by normal or reactive astrocytes, oligodendrocytes, glial O-2A progenitor cells and the oligodendrocyte precursor cell line Oli-neu. Galectin-3 is also expressed by one oligodendroglioma cell line, but not by primitive neuroectodermal tumor and 4 neuroblastoma cell lines tested so far. In all galectin-3 expressing cell lines, the lectin is predominantly, if not exclusively, localized intracellularly and carries an active carbohydrate recognition domain (shown for C6 rat glioma cells). Moreover, in contrast to primary astrocytes, glioma cells do not or only weakly adhere to substratum-bound galectin-3, probably reflecting an unusual glycosylation pattern. Our findings indicate that the expression of galectin-3 selectively correlates with glial cell transformation in the central nervous system and could thus serve as a marker for glial tumor cell lines and glial tumors.

Acutely isolated astrocytes as models to probe astrocyte functions

Neuroscientists have become increasingly aware and accepting of the concept that astrocytes likely have many important functions in the CNS. One limitation in establishing these functions is the usual problem of what constitutes suitable experimental approaches. A major experimental step for functional studies of astrocytes has been the widespread use of primary astrocyte cultures, an approach that Leif Hertz pioneered. However, it is now becoming clear that, building on this work, an experimental paradigm shift is now needed. Namely, to increasingly study preparations corresponding to in situ conditions, such as slices. An alternative experimental system where the cells have some of the technical advantages of primary astrocyte cultures is freshly isolated astrocytes. Recent experiments from our laboratory have shown metabotropic glutamate receptor expression by such cells. Examples are given of how functional receptor studies and channel activity measured by patch clamp electrophysiology can be combined with single cell RT-PCR to define further the receptor or channel type are described to illustrate the uses of such preparations.

Myocytes respond to both interleukin-4 and interferon-gamma: cytokine responsiveness with the potential to influence the severity and course of experimental myasthenia gravis

Messenger RNA that encodes for interleukin-15 (IL-15) has been reported to be constitutively expressed in skeletal muscle, although the protein product is not generally observed. Furthermore, interferon-gamma (IFN-gamma) has been reported to exacerbate symptoms of experimental myasthenia gravis (EAMG). Therefore, since IL-15 is an activator of IFN-gamma-producing cells, the hypothesis that drove the study reported below proposes that muscle is not a passive participant in the development of disease symptoms in EAMG and, in fact, plays a very important active role by producing immunomodulating factors that can influence the eventual immunopathological impact of the immune system on muscle. Tests of this hypothesis, made using a monoclonal skeletal myocyte line from the Lewis rat, have indicated that myocytes produce IL-15 protein following exposure to interleukin-4 (IL-4), an interesting paradox in light of the usual anti-inflammatory role played by IL-4. Furthermore, the level of IL-15 also can be regulated by IFN-gamma itself. Although yet to be confirmed in vivo, IFN-gamma has been shown to be capable of activating cultured myocytes in a variety of ways that could influence the ongoing autoimmune response associated with EAMG.

Activation of nuclear factor-kappaB in C6 rat glioma cells after transfection with glia maturation factor

The 17-kDa endogenous brain protein glia maturation factor (GMF) was transfected into C6 rat glioma cells using a replication-defective human adenovirus vector. The cells overexpressed GMF but did not secrete the protein into the medium. Transfection with GMF led to the activation of the transcription factor nuclear factor-kappaB (NF-kappaB), as evidenced by electrophoretic mobility shift assay of the nuclear extract, using a double-stranded oligonucleotide probe containing the consensus binding sequence for NF-kappaB. The specificity of binding was demonstrated by competition with unlabeled probe and by the nonbinding of the mutant probe. Binding was detectable as early as 3 h after transfection, peaked at 6 and 12 h, and gradually declined thereafter. The observed NF-kappaB activation was reduced by cotransfection with catalase and by the presence of high concentrations of pyruvate in the medium, suggesting the involvement of H2O2. The p38 mitogen-activated protein kinase inhibitor SB-203580 also suppressed the GMF-activated NF-kappaB, suggesting the involvement of the p38 signal transduction cascade. On the other hand, the phorbol ester phorbol 12-myristate 13-acetate activated NF-kappaB whether or not GMF was overexpressed. Along with NF-kappaB activation was an enhanced expression of superoxide dismutase (SOD), which was suppressed if NF-kappaB nuclear translocation was blocked by its specific decoy DNA, implicating NF-kappaB as an upstream mediator of this antioxidant enzyme. The p38 inhibitor SB-203580 also blocked the GMF-activated SOD. As NF-kappaB and SOD are both pro-survival signals, the results suggest a cytoprotective role for endogenous GMF in glial cells.

Interaction between astrocytes and adult subventricular zone precursors stimulates neurogenesis

Neurogenesis continues in the mammalian subventricular zone (SVZ) throughout life. However, the signaling and cell-cell interactions required for adult SVZ neurogenesis are not known. In vivo, migratory neuroblasts (type A cells) and putative precursors (type C cells) are in intimate contact with astrocytes (type B cells). Type B cells also contact each other. We reconstituted SVZ cell-cell interactions in a culture system free of serum or exogenous growth factors. Culturing dissociated postnatal or adult SVZ cells on astrocyte monolayers-but not other substrates-supported extensive neurogenesis similar to that observed in vivo. SVZ precursors proliferated rapidly on astrocytes to form colonies containing up to 100 type A neuroblasts. By fractionating the SVZ cell dissociates with differential adhesion to immobilized polylysine, we show that neuronal colony-forming precursors were concentrated in a fraction enriched for type B and C cells. Pure type A cells could migrate in chains but did not give rise to neuronal colonies. Because astrocyte-conditioned medium alone was not sufficient to support SVZ neurogenesis, direct cell-cell contact between astrocytes and SVZ neuronal precursors may be necessary for the production of type A cells.

Enhanced expression of neurotrophic factors by C6 rat glioma cells after transfection with glia maturation factor

Glia maturation factor (GMF) is a 17-kDa protein unique to the nervous system. Although GMF was initially characterized as a growth/differentiation factor, the absence of a leader sequence and its intracellular localization in normal brain suggest an intracellularfunction as well. In this paper we transfected the C6 glioma cells with GMF cDNA by infecting the cells with a GMF/adenovirus construct. The transfected cells overexpressed GMF but did not secret the protein into the culture medium. However, the transfected cells showed an increased expression of the neurotrophic factors including nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF). The increase in neurotrophic activity of the C6 cell conditioned medium was demonstrable by its ability to promote neurite outgrowth in PC12 cells.

Inhibition of phospholipase C-gamma1 activation blocks glioma cell motility and invasion of fetal rat brain aggregates

OBJECTIVE

Phospholipase C (PLC)-gamma is a cytosolic enzyme activated by several growth factor (GF) receptors (epidermal GF receptor [EGFR], platelet-derived GF receptor, and insulin-like GF 1 receptor), and its activation is associated with increased cell motility (but not cell proliferation) in nonglioma cell lines. Because up-regulated activation of EGFR has been consistently linked to poor patient survival in patients with glioblastoma multiforme (GBM) and because inhibition of EGFR activation by tyrosine kinase inhibitors prevents glioma infiltration in vitro, we hypothesized that inhibition of PLC-gamma activation would inhibit glioma cell invasiveness.

METHODS

Our experimental model assesses tumor spheroid invasion of fetal rat brain spheroids by confocal microscopy. We treated U87 GBM spheroids, and those derived from a single patient, with the PLC inhibitor U73122. We also transfected rat C6 glioma cells with the PLCz complementary deoxyribonucleic acid coding for a dominant negative PLC-gamma1 src-homology-2/src-homology-3 peptide fragment, which blocks binding and activation of PLC-gamma1 by GF receptors. Two clones (C6F and C6E) were grown into spheroids and were tested for invasiveness in the spheroid model and for responsiveness to GFs in a standard in vitro motility assay.

RESULTS

The infiltration rate of the patient GBM cell line overexpressing wild-type EGFR was reduced by 2 micromol/L U73122 from a slope (percent invasion/h) of 0.74+/-0.08 (with the inactive congener U73343) to 0.04+/-0.053 (P = 8 x 10(-7) by two-tailed t test, 92% reduction); the integral rate, another measure of invasion, was reduced from 49.7+/-13 percent-hours per hour to 13.6+/-12 (P = 0.002, 72% reduction). The U87 spheroid invasion rate was reduced by 0.5 micromol/L U73122 from 46.7+/-8.5 percent-hours per hour to 11.2+/-4.6 (P = 3 x 10(-5)); the slope decreased from 1.7+/-0.41 percent per hour to 0.35+/-0.14 (P = 0.0001). The C6F and C6E clones demonstrated attachment to and "surrounding" of the fetal rat brain aggregate but no true invasion by confocal or light microscopy. PLCz blocked the motility response to epidermal GF, platelet-derived GF, and insulin-like GF. There was a significant decrease in PLC-gamma1-associated tyrosine phosphorylation.

CONCLUSION

These results support a key role for PLC-gamma activation as a common postreceptor pathway for GF-induced tumor infiltration and further identify PLC-gamma1 as a possible target for anti-invasive therapy for GBMs.

Growth inhibition of newly established human glioma cell lines by leukemia inhibitory factor

We have established three new cell lines deriving from malignant human gliomas. The cell lines were described in terms of both morphology and growth characteristics. Most cells in all three cell lines expressed the neuroepithelial marker protein GFAP. In terms of growth characteristics, the cells showed only slight differences. The cell lines showed no expression of the neural form of the c-src gene, pp60c-srcN, but did express the ubiquitous form, pp60c-src. The established glioma cell lines were also examined for expression of members of the neuropoietic cytokine family, CNTF and LIF, and their respective receptor components CNTFRalpha, LIFRbeta and gp130. With the exception of CNTFRalpha both the ligands and their receptor components were expressed in similar amounts in all three cell lines. The presence of ligand and receptor prompted us to study the effects of exogenously supplied factors on the growth of the glioma cell lines. Whereas LIF induced a high c-fos expression, only low c-fos induction was observed upon CNTF treatment. Accordingly, CNTF did not have any noticeable effects on glioma cell growth in culture, while LIF mediated an inhibiting effect on the growth of the three glioma cell lines in culture.

Expression of full-length trkB receptors by reactive astrocytes after chronic CNS injury

Growth factors, including members of the neurotrophin family, are expressed by neuronal and glial elements following injury to the CNS. In order to assess the capacity for glial cells to respond to neurotrophins at sites of chronic injury, full-length trkB receptors were localized following implantation of a nitrocellulose filter into the cerebral cortex for 30 days. Northern analysis demonstrated that filter implants contained cells expressing transcripts for full-length and truncated trkB receptors, in contrast to the predominant expression of truncated trkB receptors by cultured astrocytes. In situ hybridization and immunohistochemistry using probes to the trkB kinase domain colocalized full-length receptors with GFAP-immunopositive reactive astrocytes adjacent to and within the filter implant. In contrast, OX-42-immunopositive microglia/macrophages were not stained for full-length trkB. These data indicate that reactive astrocytes can express functional trkB receptors following a chronic insult to the cerebral cortex and support the hypothesis that neurotrophins may regulate astrocytic responses to injury.

Growth factor profiles of human gliomas. Do non-tumour cells contribute to tumour growth in glioma?

BACKGROUND

Growth factors play a role in proliferation and motility of malignant glial cells, through autocrine and paracrine mechanisms. Also, proliferation of non-tumour cells, e.g., endothelial cells, is likely to be controlled by growth factors. Several growth factors with their appropriate receptors can be involved, but studies on tissue specimens evaluating this in glioma are rare.

MATERIALS AND METHODS

We evaluated the potential role of Transforming growth factor-alpha (TGF-alpha) and Epidermal growth factor receptor (EGF-R), the Platelet-derived growth factor A- and B-chain (PDGF-A and PDGF-B) and its receptors (PDGFR alpha and PDGFR beta, and basic fibroblast growth factor (bFGF) in gliomas by analysing 86 of these tumours on the single cell level for the presence of immunoreactive growth factors and receptors. In a few cases double-staining experiments were done to directly visualize co-expression of factor and receptor.

RESULTS

Multiple growth factors and their receptors are present in astrocytic tumours; the higher the grade, the more growth factors and the more positive cells are found. Oligodendroglial tumours and pilocytic astrocytomas showed little expression. Autocrine and paracrine mechanisms were frequently possible in the astrocytic tumours, often more than one loop could be involved. Interestingly, it was also frequently possible that non-tumour cells produced a growth factor for which the tumour cells expressed the receptor.

CONCLUSIONS

Multiple growth factors appear to be involved in astrocytic tumours, with frequent autocrine and paracrine loops. Expression of these molecules seems to increase with increasing grade. The results argue for a contribution of non-tumour cells to the growth of a tumour.

Interrelationships between astrocyte function, oxidative stress and antioxidant status within the central nervous system

Astrocytes have, until recently, been thought of as the passive supporting elements of the central nervous system. However, recent developments suggest that these cells actually play a crucial and vital role in the overall physiology of the brain. Astrocytes selectively express a host of cell membrane and nuclear receptors that are responsive to various neuroactive compounds. In addition, the cell membrane has a number of important transporters for these compounds. Direct evidence for the selective co-expression of neurotransmitters, transporters on both neurons and astrocytes, provides additional evidence for metabolic compartmentation within the central nervous system. Oxidative stress as defined by the excessive production of free radicals can alter dramatically the function of the cell. The free radical nitric oxide has attracted a considerable amount of attention recently, due to its role as a physiological second messenger but also because of its neurotoxic potential when produced in excess. We provide, therefore, an in-depth discussion on how this free radical and its metabolites affect the intra and intercellular physiology of the astrocyte(s) and surrounding neurons. Finally, we look at the ways in which astrocytes can counteract the production of free radicals in general by using their antioxidant pathways. The glutathione antioxidant system will be the focus of attention, since astrocytes have an enormous capacity for, and efficiency built into this particular system.

Localization, differential expression and retrograde axonal transport suggest physiological role of FGF-2 in spinal autonomic neurons of the rat

Fibroblast growth factor-2 (FGF-2) has marked pharmacological neurotrophic effects on lesioned spinal autonomic neurons following target removal of the adrenal medulla, yet expression and axonal transport in autonomic neurons remain to be shown. We show here FGF-2 and FGF receptor type 1 (FGFR1) protein and mRNA expression in preganglionic intermediolateral neurons of the rat thoracic spinal cord. While immunoreactivity of both FGF-2 and FGFR1 co-localize to intermediolateral neurons, mRNA transcripts of FGFR1, but not of FGF-2, are detectable in intermediolateral preparations by RNase protection analysis, suggesting protein translocation in vivo. Unilateral microinjection of 125iodinated FGF-2 into the adrenal medulla (a major target of intermediolateral neurons) results in significant accumulation of specific radioactivity in thoracic spinal cord tissue, including the intermediolateral neurons, and the ipsilateral splanchnic nerve. Emulsion autoradiography demonstrated labelling over ipsilateral intermediolateral neurons only. Neuronal co-localization of FGF-2/FGFR1 protein, differential mRNA expression, specific retrograde axonal transport and the known neurotrophic actions in vivo, strongly suggest unique physiological roles of FGF-2 in the autonomic nervous system.

Expression of mRNAs of multiple growth factors and receptors by neuronal cell lines: detection with RT-PCR

Neurons and glia are capable of both secreting and responding to a large variety of growth factors. However, information on multiple expression of growth factors and their receptors was usually obtained from uncorrelated observations, using cells from various animals of origin, developmental stages, growth phases, culture ages and culture conditions. Because of its specificity and extreme sensitivity, reverse transcription-polymerase chain reaction (RT-PCR) is uniquely suitable to study a large panel of growth factors and their receptors from a limited cell sample, free of these intervening variables. In this paper we evaluate the expression of mRNA of a total of 35 growth factor-related proteins by conducting RT-PCR on three neuronal cell lines: the PC12 rat pheochromocytoma line, the MAH rat sympathoadrenal progenitor line, and the N18 mouse neuroblastoma line. Three types of results are presented. The first confirms the existing knowledge such as the presence of Trk-A (NFG receptor) in PC12. The second consists of new information that expands and extends earlier observations, such as the presence of CNTF receptor complex in PC12, which explains our previous report that CNTF enhances the biological effects of NGF on these cells. The third consists of novel information that leads the way to further experimentation by the more conventional methods. These include the strong expression of Trk-B by MAH, predicting the biological responsiveness of MAH to BDNF and NT-4, and the expression of CNTF receptor in N18. Our results also suggest that CNTF is an autocrine factor for PC12 and MAH, since both lines express the growth factor as well as the receptor. Thus, RT-PCR is a valuable tool in growth factor research that can be used in complement to, and interactively with, other approaches such as bioassay, receptor binding, and immunochemical determination. It will be particularly useful for screening a large number of growth factors in minute areas of the brain in patients suffering from neurodegenerative diseases such as Parkinson's and Alzheimer's.