Molecular profile of reactive astrocytes--implications for their role in neurologic disease

Astrocytes in the aged rat spinal cord fail to increase GFAP mRNA following sciatic nerve axotomy

Aging in the brain is associated with specific changes in the astrocyte population. The present study establishes that similar changes occur in the aging spinal cord. The levels of glial fibrillary acidic protein (GFAP) mRNA were significantly increased 0.4-fold in aged 8- to 17-month-old rats compared to young 2-month-old rats. The ability of astrocytes in the aging spinal cord to respond to a non-invasive CNS injury was compared to young rats 4 days following sciatic nerve axotomy. The level of GFAP mRNA was significantly increased 0.5-fold in the young rats in response to axotomy. In contrast, the level of GFAP mRNA in aged rats did not increase following injury above that present in non-axotomized rats of the same age.

Astrogliosis in the neonatal and adult murine brain post-trauma: elevation of inflammatory cytokines and the lack of requirement for endogenous interferon-gamma

The relevance of astrogliosis remains controversial, especially with respect to the beneficial or detrimental influence of reactive astrocytes on CNS recovery. This dichotomy can be resolved if the mediators of astrogliosis are identified. We have measured the levels of transcripts encoding inflammatory cytokines in injury systems in which the presence or absence of astrogliosis could be produced selectively. A stab injury to the adult mouse brain using a piece of nitrocellulose (NC) membrane elicited a prompt and marked increase in levels of transcripts for interleukin (IL)-1alpha, IL-1beta, and tumor necrosis factor (TNF)-alpha, which are considered to be microglia/macrophage cytokines. The elevations preceded, or occurred concomitantly with, the rise in glial fibrillary acidic protein mRNA, an early manifestation of astrogliosis. In neonatal mice, IL-1 and TNF-alpha mRNA were elevated to a greater extent by an NC-implant injury, which produced astrogliosis, than after an NC-stab, with minimal astrogliosis. We determined whether endogenous interferon (IFN)-gamma could be responsible for the observed increases in IL-1 and TNF-alpha, because IFN-gamma is a potent microglia/macrophage activator, and because its exogenous administration to rodents enhanced astrogliosis after adult or neonatal insults. A lack of requirement for endogenous IFN-gamma was demonstrated by three lines of evidence. First, no increase in IFN-gamma transcripts could be found at injury. Second, the administration of a neutralizing antibody to IFN-gamma did not attenuate astrogliosis. Third, in IFN-gamma knockout adult mice, astrogliosis and increases in levels of IL-1alpha and TNF-alpha were induced rapidly by injury. The marked elevation of inflammatory cytokines is discussed in the context of astrogliosis and general CNS recovery.

The status and organization of astrocytes, oligodendroglia and microglia in grafts of fetal rat cerebral cortex

Immunohistochemical methods were used to study the status and organization of astrocytes, oligodendroglia and microglia in fetal cerebral cortical tissue grafted on to the dorsal surface of the midbrain in newborn host rats. Grafts were examined 1-6 months posttransplantation. All grafts contained large numbers of hypertrophied, intensely glial fibrillary acidic protein-positive astrocytes. Microglia were also activated, displaying slightly increased levels of OX-42 immunoreactivity. The grafts consisted of lobules of gray matter which were separated by bands of myelinated fibres associated with large numbers of Rip-positive oligodendroglia. These glial cells had a relatively normal morphology. The density of astrocytes and microglia was reduced in these white matter-like regions. In association with chronic changes in glial reactivity, transplants also expressed increased levels of chondroitin sulphate proteoglycans (CS-56 antibody). The observed changes in glial cell phenotype and extracellular matrix in cortical transplants are likely to affect neuronal physiology and connectivity in a number of ways, and highlight the importance of studying both glia and neurons in order to gain a more comprehensive picture of the long-term functional potential of fetal brain grafts.

Astrogliosis in the neonatal and adult murine brain post-trauma: elevation of inflammatory cytokines and the lack of requirement for endogenous interferon-gamma

The relevance of astrogliosis remains controversial, especially with respect to the beneficial or detrimental influence of reactive astrocytes on CNS recovery. This dichotomy can be resolved if the mediators of astrogliosis are identified. We have measured the levels of transcripts encoding inflammatory cytokines in injury systems in which the presence or absence of astrogliosis could be produced selectively. A stab injury to the adult mouse brain using a piece of nitrocellulose (NC) membrane elicited a prompt and marked increase in levels of transcripts for interleukin (IL)-1alpha, IL-1beta, and tumor necrosis factor (TNF)-alpha, which are considered to be microglia/macrophage cytokines. The elevations preceded, or occurred concomitantly with, the rise in glial fibrillary acidic protein mRNA, an early manifestation of astrogliosis. In neonatal mice, IL-1 and TNF-alpha mRNA were elevated to a greater extent by an NC-implant injury, which produced astrogliosis, than after an NC-stab, with minimal astrogliosis. We determined whether endogenous interferon (IFN)-gamma could be responsible for the observed increases in IL-1 and TNF-alpha, because IFN-gamma is a potent microglia/macrophage activator, and because its exogenous administration to rodents enhanced astrogliosis after adult or neonatal insults. A lack of requirement for endogenous IFN-gamma was demonstrated by three lines of evidence. First, no increase in IFN-gamma transcripts could be found at injury. Second, the administration of a neutralizing antibody to IFN-gamma did not attenuate astrogliosis. Third, in IFN-gamma knockout adult mice, astrogliosis and increases in levels of IL-1alpha and TNF-alpha were induced rapidly by injury. The marked elevation of inflammatory cytokines is discussed in the context of astrogliosis and general CNS recovery.

Lymphocyte recruitment following spinal cord injury in mice is altered by prior viral exposure

The inflammatory response induced by mechanical lesion of the spinal cord is known to include the recruitment of neutrophils and macrophages, while the involvement of lymphocytes has been largely ignored. We have studied the pattern of lymphocyte recruitment following partial transection of the mouse spinal cord. Using immunohistochemical techniques, all three types of lymphocytes (CD4-positive T-cells, CD8-positive T-cells and B-cells) were found in the vicinity of the lesion site within hours and persisted for up to 7 days. There was a predominance of B-lymphocytes during the first 3 days. A second, late phase of cell infiltration, dominated by CD8-positive T-lymphocytes, occurred in mice that had been raised in a conventional breeding unit and had acquired antibody titres to a common murine virus (mouse hepatitis virus). In contrast, mice kept in specific pathogen-free facilities did not show this late-phase response. These findings suggest a possible role for lymphocytes in secondary tissue loss, local demyelination, scar formation, cytokine-mediated inflammatory responses or trophic processes. They also provide evidence that a virus infection can significantly enhance the reaction of T-cells to a spinal cord lesion.

Immunologically induced electrophysiological dysfunction: implications for inflammatory diseases of the CNS and PNS

During inflammation of the central or peripheral nervous system, a high number of immunologically active molecules, including bacterial or viral products as well as host-derived cytokines, are released. Patients suffering from inflammatory CNS or PNS diseases often develop transient symptoms with a rapid recovery, which obviously cannot be accounted for by immunologically induced tissue damage. These observations led to the hypothesis that immunologically active molecules can affect directly the electrophysiological functions of neurons and glial cells. Evidence for this hypothesis came from in vitro studies showing that cytokines, such as interleukins or tumor necrosis factors, arachidonic acid and its metabolites, interfere with electrophysiological properties of neurons or glial cells. These molecules affect ion currents, intracellular Ca2+ homeostasis, membrane potentials, and suppress or enhance the induction and maintenance of long-term potentiation. Similarly, virus proteins from human immunodeficiency virus type I were found to alter intracellular Ca2+ concentrations of neurons and astrocytes by modulating either transmitter receptors and channels or membrane transporters. Cerebrospinal fluid from MS patients contains factors which increase Na+ current inactivation and thereby reduce neuronal excitability. Immunoglobulins in sera of patients suffering from multifocal motor neuropathy and from acquired neuromyotonia interfere with nerve fibers, inducing alterations of conduction. Increased knowledge of these mechanisms will help to explain the pathogenesis of neurological symptoms and may provide a rationale for new therapeutic strategies.

Endothelins promote the activation of astrocytes in rat neostriatum through ET(B) receptors

The effects of endothelin (ET)-3 and an ET(B) receptor agonist on astrocytic activation in rat caudate putamen were examined by an immunohistochemical staining of glial fibrillary acidic protein (GFAP), a marker of reactive astrocytes. A single injection of 40 pmol ET-3 into rat caudate putamen increased the number of GFAP positive cells compared to that in the contralateral saline-injected side. Ala(1,3,11,15)-ET-1 (40 pmol), an ET(B) receptor agonist, also increased the number of striatal GFAP positive cells. The increases in GFAP positive cells were maximum (about 150% of the control side) in 1-2 weeks after injections of the ETs, and then reduced in 4 weeks. A continuous infusion of BQ788, an ET(B) receptor antagonist (23 nmol/day), into the lateral ventricle of the cerebrum antagonized the effect of Ala(1,3,11,15)-ET-1, while BQ788 also reduced the number of GFAP positive cells in saline-injected caudate putamen. Intrastriatal injection of 40 pmol Ala(1,3,11,15)-ET-1 did not affect the number of cells stained by B4 isolectin from Griffonia simplicifolia, which labels activated microglia/macrophages. Intraperitoneal administration of 5 mg/kg per day chloroquine and 0.2 mg/kg per day colchicine did not affect the action of Ala(1,3,11,15)-ET-1. These results suggest that activation of ET(B) receptors is involved in the induction of reactive astrocytes.

Gradation of kainic acid-induced rat limbic seizures and expression of hippocampal heat shock protein-70

Systemic injection of kainic acid (KA) induces limbic seizures in rats, which resemble human temporal lobe epilepsy, the most common form of adult human epilepsy. In this study, we have investigated KA-elicited limbic seizures in the rats by correlating the severity of the seizure attacks with the expression of hippocampal heat shock protein-70 (HSP70) which has been suggested to be a marker for neuronal injury/death in this model of seizures. After a systemic injection of KA, six stages of limbic seizures have been classified, namely, staring (stage 1), wet dog shake (stage 2), hyperactivity (stage 3), rearing (stage 4), rearing and falling (stage 5), and jumping (stage 6). Stages 4, 5 and 6 were further divided into mild and severe sub-stages. HSP70 expression was not detected in animals with stages 1 and 2 seizures. At stage 3 a small amount of HSP70 immunoreactive neurons was detected in the CA3 field and the dentate hilus. From stage 4 to stage 5 the degree of HSP70 immunoreactivity increased in the CA1 field from a few positive cells in stage 4 mild to large numbers of immunoreactive neurons in stage 5 severe. HSP70 became detectable in pyramidal cells in the CA2 field from stage 5 severe and higher. In animals with stage 6 seizures, the majority of HSP70 expression became located in glial cells throughout the whole hippocampus. We concluded that HSP70 expression in the hippocampus positively correlates with the severity of KA-elicited limbic seizures.

Synaptic remodeling and free radical formation after brain contusion injury in the rat

The purpose of this study was to explore whether bilateral frontal cortex contusion in rats would demonstrate changes relevant for understanding the pathology of frontal lobe injury in humans. Rats were allowed to survive for 3, 7, or 18 days postinjury (dpi). In the contused rats, albumin was trapped in frontal cortices, as well as in other brain areas, showing that neurons were exposed to plasma components. In the sham-operated rats, which had only craniotomy but no penetration of dura, the level of trapped albumin was also increased compared to intact controls, suggesting a partial lesion-like condition. Choline acetyltransferase activity was severely decreased in the frontal cortices of contused rats, compared to the sham-operated controls. The decrease was most pronounced at 3 dpi and less pronounced 18 dpi, suggesting that after the initial damage, regeneration of the cholinergic terminals occurred. The concentration of the mature presynaptic membrane protein D3(SNAP-25) was also decreased in the frontal cortices of contused rats at 3 and 7 dpi, whereas it was normalized at 18 dpi. Previously, we have evaluated changes in the rate of synaptic remodeling in brain injury by calculating the ratio of the neural cell adhesion molecule (NCAM) to D3(SNAP-25). The NCAM/D3(SNAP-25) ratio at 3 dpi was elevated by more than 60% in the frontal cortices of contused rats, suggesting a high initial rate of synaptic remodeling. The ratios were smaller at 7 and 18 dpi, suggesting that after the initial burst, the rate of remodeling leveled off. In contrast, astrocyte activation was less pronounced at 3 dpi than at 7 and 18 dpi, as measured by the levels of glial fibrillary acidic protein and glutamine synthetase immunoactivities. The immunoreactivity of glutamine synthetase more than doubled in the contused brains but its enzymatic activity increased less than 50%, suggesting that many enzymatic centers had been inactivated by free radicals. Calculated as the difference between the relative immunoreactivity and the relative enzymatic activity the "lost glutamine synthetase activity" increased continuously in frontal cortex and striatum from 3 to 18 dpi, indicating the production of free radicals long after the initial contusion event. In conclusion, following frontal cortical contusions the early synaptic damage was partly compensated by synaptic remodeling. We suggest that the continuous production of free radicals may have contributed to the declining remodeling rate and impair functional recovery.

Murine models of brain aging and age-related neurodegenerative diseases

In the past, structural changes in the brain with aging have been studied using a variety of animal models, with rats and nonhuman primates being the most popular. With the rapid evolution of mouse genetics, murine models have gained increased attention in the neurobiology of aging. The genetic contribution of age-related traits as well as specific mechanistic hypotheses underlying brain aging and age-related neurodegenerative diseases can now be assessed by using genetically-selected and genetically-manipulated mice. Against this background of increased demand for aging research in mouse models, relatively few studies have examined structural alterations with aging in the normal mouse brain, and the data available are almost exclusively restricted to the C57BL/6 strain. Moreover, many older studies have used quantitative techniques which today can be questioned regarding their accuracy. Here we review the state of knowledge about structural changes with aging in outbred, inbred, genetically-selected, and genetically-engineered murine models. Moreover, we suggest several new opportunities that are emerging to study brain aging and age-related neurodegenerative diseases using genetically-defined mouse models. By reviewing the literature, it has become clear to us that in light of the rapid progress in genetically-engineered and selected mouse models for brain aging and age-related neurodegenerative diseases, there is a great and urgent need to study and define morphological changes in the aging brain of normal inbred mice and to analyze the structural changes in genetically-engineered mice more carefully and completely than accomplished to date. Such investigations will broaden knowledge in the neurobiology of aging, particularly regarding the genetics of aging, and possibly identify the most useful murine models.

Okadaic acid stimulates nerve growth factor production via an induction of interleukin-1 in primary cultures of cortical astroglial cells

Neonatal rat cortical astroglial cells in primary culture synthesize and secrete interleukin-1 beta (IL-1) and nerve growth factor (NGF). Treatment of astrocytes with okadaic acid (OA), an inhibitor of phosphoprotein phosphatases, dramatically increased both IL-1 and NGF mRNA content (about 50-fold) with maximal induction seen at 20-30 nM OA. The induction of IL-1 mRNA preceded that of NGF mRNA and was maximal after 9 h of treatment. OA increased IL-1 mRNA half-life by about 10-fold similar to the reported stabilization of the NGF mRNA. Addition of an IL-1 receptor antagonist dose-dependently inhibited the secretion of NGF stimulated by OA and IL-1. The results indicate that OA profoundly stimulates IL-1 expression in glial cells by enhancing IL-1 mRNA stability and that glial cell-derived IL-1 acts in a paracrine/autocrine manner to stimulate NGF production.

Cytokine-mediated neuronal apoptosis

Cytokines have been reported to induce neuronal injury via the free radical nitric oxide (NO); however, the precise mechanism underlying cytokine-mediated neurotoxicity is unclear. We investigated the hypothesis that cytokine-mediated neurotoxicity in primary cultures of human fetal neurons occurs via an apoptotic mechanism triggered by NO. Treatment of mixed neuronal/glial cell cultures with interferon (IFN)-gamma plus interleukin (IL)-1 beta for 13 days induced a high output of NO accompanied by marked neuronal loss. The NO synthase inhibitor N-monomethyl-L-arginine (NMMA) significantly attenuated cytokine-induced neuronal loss, confirming the involvement of NO. Cytokine-mediated neuronal injury was accompanied by morphologic changes and a DNA fragmentation pattern consistent with apoptosis. Treatment of neuronal cell cultures with NMMA protected against cytokine-mediated apoptotic death. These findings, using primary human neuronal cell cultures, support the hypothesis that cytokine-mediated neurotoxicity involving NO proceeds via an apoptotic mechanism. These findings could lead to the development of new therapies for neurodegenerative diseases involving glia, cytokines, and NO.

Differential regulation of ciliary neurotrophic factor (CNTF) and CNTF receptor alpha expression in astrocytes and neurons of the fascia dentata after entorhinal cortex lesion

Neurotrophic factors have been implicated in reactive processes occurring in response to CNS lesions. Ciliary neurotrophic factor (CNTF), in particular, has been shown to ameliorate axotomy-induced degeneration of CNS neurons and to be upregulated at wound sites in the brain. To investigate a potential role of CNTF in lesion-induced degeneration and reorganization, we have analyzed the expression of CNTF protein and CNTF receptor alpha (CNTFR alpha) mRNA in the rat dentate gyrus after unilateral entorhinal cortex lesions (ECLs), using immunocytochemistry and nonradioactive in situ hybridization, respectively. In sham-operated as in normal animals, CNTF protein was not detectable by immunocytochemistry. Starting at 3 d after ECL, upregulation of CNTF expression was observed in the ipsilateral outer molecular layer (OML). Expression was maximal at around day 7, and at this stage immunoreactivity could be specifically localized to astrocytes in the ipsilateral OML. By day 14 postlesion, CNTF immunoreactivity had returned to control levels. CNTFR alpha mRNA was restricted to neurons of the granule cell layer in controls. Three days postlesion, prominent CNTFR alpha expression was observed in the deafferented OML. A similar but less prominent response was noticed in the contralateral OML. After 10 d, CNTFR alpha expression had returned to control levels. Double labeling for CNTFR alpha mRNA and glial fibrillary acidic protein (GFAP) showed that upregulation of CNTFR alpha occurred in reactive, GFAP-immunopositive astrocytes of the OML. A substantial reduction of CNTFR alpha expression in the deafferented granule cells was transiently observed at 7 and 10 d postlesion. Our results suggest a paracrine or autocrine function of CNTF in the regulation of astrocytic and neuronal responses after brain injury.

Selenium is required for normal upregulation of myelin genes in differentiating oligodendrocytes

The purpose of this study was to characterize the selenium requirement for the normal differentiation of oligodendrocyte lineage cells. In primary mixed glial cultures prepared from newborn rat brains, the overall growth of cultures, as seen from the total RNA yield, was not significantly affected by selenium. However, 30 nM selenium was required for the normal upregulation the proteolipid protein, basic protein, and myelin-associated glycoprotein gene expression assessed by Northern blot analysis. Selenium deprivation during initial, rapid phase of the gene upregulation irreversibly suppressed the genes, indicating the existence of a critical period in oligodendrocyte differentiation. In purified oligodendrocyte cultures prepared by mechanical dislodging of progenitor (O-2A) cells from mixed glial cultures, total cell number and total RNA yield were virtually unaffected by selenium deprivation; however, the developmental upregulation of the myelin genes was profoundly attenuated. Immunocytochemical analysis confirmed the suppressive effect of selenium deficiency on the differentiation of oligodendrocyte lineage cells, as seen from a significant decrease in the population of GalC+ and O4+ cells. Because the number of GC+ cells was more reduced than the number of O4+ cells, the results indicate that selenium deficiency may specifically inhibit the progression from immature to mature oligodendrocytes.

Expression of ionotropic glutamate receptor subunits in glial cells of the hippocampal CA1 area following transient forebrain ischemia

We examined by immunohistochemistry the expression of ionotropic glutamate receptor subunits (GluRs) in glial cells of the rat dorsal hippocampus 3 to 28 days after transient forebrain ischemia. In general, the expression of GluRs at all time points studied underwent a drastic reduction that was primarily restricted to the CA1 region. In addition to the disappearance of GluRs as a result of neuronal cell death, we observed their expression in reactive glial cells. The time course of expression and the subunits involved were different for astrocytes and microglia. Reactive astrocytes exhibited kainate, GluR5-7, and N-methyl-D-aspartate (NMDA), NR2A/B, receptor subunits, both of which were maximally expressed approximately 4 weeks after ischemia. In contrast, reactive microglia expressed GluR4 and NR1 subunits, alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA), and NMDA receptor subtypes, respectively, with maximal expression observed between 3 and 7 days after ischemia. These results demonstrate that specific types of GluRs are expressed in reactive glial cells after ischemia and that, overall, their expression levels peak around or after the periods of maximal astrogliosis and microgliosis. Thus, modulation of GluR expression may be one of the molecular components accompanying the gliotic process.

Impaired neuroglial activation in interleukin-6 deficient mice

Astrocyte activation is a ubiquitous hallmark of the damaged brain and has been suggested to play an important regulatory role in the activation, survival, and regeneration of adjacent neurons, microglia, and oligodendrocytes. Little is known, however, about the endogenous signals that lead to this activation of astrocytes. Here we examined the regulation of interleukin 6 (IL6), a proinflammatory cytokine, its receptors, and the effects of IL6-deficiency in a model of traumatic central nervous system injury in the axotomized mouse facial motor nucleus. Facial nerve transection led to a massive but transient upregulation of IL6 mRNA in the disconnected motor nucleus, while IL6-receptor subunits were constitutively expressed on motoneurons and astrocytes. Absence of IL6 in genetically IL6-deficient mice led to massive reduction in the number of activated GFAP-positive astrocytes, a more moderate decrease in microglial activation and proliferation, and an increase in the late neuronal response to axotomy. These results emphasize the role of IL6 in the global regulation of neurons, astrocytes, and microglia and their activation in the injured nervous system.

Different pathways of apoptosis revealed by 2-chloro-adenosine and deoxy-D-ribose in mammalian astroglial cells

Both the adenosine analogue 2-chloro-adenosine (2-CA) and the reducing sugar deoxy-D-ribose (dRib) induce apoptosis of astroglial cells in rat brain primary cultures (Abbracchio et al.: Biochem Biophys Res Commun 213:908-915, 1995). The present study was undertaken to elucidate by both morphological and cytofluorimetric analyses the intracellular mechanism(s) involved in induction of apoptosis by these two agents. The poly(ADP-ribose)polymerase (PARP) inhibitor 3-aminobenzamide did not prevent either 2-CA- or dRib-induced cell death, suggesting that activation of PARP is not critically important for induction of apoptosis in astrocytes. The radical scavenger N-acetyl-cysteine (NAC) strongly inhibited dRib- but not 2-CA-induced cell death, suggesting a differential role for radical formation in apoptosis by these two agents. A time-dependent increase of cells with depolarized mitochondria was observed in dRib-, and to a lesser extent, in 2-CA-treated cultures. NAC also prevented dRib- but not 2-CA-induced mitochondrial changes. We conclude that, in mammalian astrocytes, apoptosis can proceed through diverse and multiple pathways, depending upon the apoptotic stimulus. For dRib, apoptosis likely proceeds through generation of radicals and mitochondrial involvement. An adenosine extracellular receptor linked to an as yet unidentified signaling pathway may instead mediate 2-CA-induced cell death, which may have intriguing implications for both nervous system development and brain response to trauma and ischemia.

Chondroitin sulfate proteoglycan and tenascin in the wounded adult mouse neostriatum in vitro: dopamine neuron attachment and process outgrowth

Extracellular matrix (ECM) molecules, including chondroitin-4 or chondroitin-6 sulfate proteoglycans (CSPGs) and tenascin, are upregulated in and around wounds and transplants to the adult CNS. In the present study, striatal wounds from adult mice were used in a novel in vitro paradigm to assess the effects of these wound-associated molecules on embryonic dopamine cell attachment and neurite outgrowth. Light and electron microscopic immunocytochemistry studies have shown that astroglial scar constituents persist in cultured explants for at least 1 week in vitro, and despite the loss of neurons from adult striatal explants, there is a retention of certain structural features suggesting that the wound explant-neuron coplant is a viable model for analysis of graft-scar interactions. Explants from the wounded striatum taken at different times after a penetrating injury in vivo were used as substrates for embryonic ventral mesencephalon neurons that were plated on their surfaces. Dopamine cell attachment is increased significantly in relation to the expression of both CSPG and tenascin. The increase in neuronal attachment in this paradigm, however, is accompanied by a postlesion survival time-dependent significant decrease in neuritic growth from these cells. In vitro ECM antibody treatment suggests that CSPG may be responsible for heightened dopamine cell attachment and that tenascin simultaneously may support cell attachment while inhibiting neurite growth. The present study offers a new approach for the in vitro analysis of cell and molecular interactions after brain injury and brain grafting, in essence acting as a nigrostriatal transplant-in-a-dish.

Cellular signaling roles of TGF beta, TNF alpha and beta APP in brain injury responses and Alzheimer's disease

beta-Amyloid precursor protein (beta APP), transforming growth factor beta (TGF beta), and tumor necrosis factor-alpha (TNF alpha) are remarkably pleiotropic neural cytokines/neurotrophic factors that orchestrate intricate injury-related cellular and molecular interactions. The links between these three factors include: their responses to injury; their interactive effects on astrocytes, microglia and neurons; their ability to induce cytoprotective responses in neurons; and their association with cytopathological alterations in Alzheimer's disease. Astrocytes and microglia each produce and respond to TGF beta and TNF alpha in characteristic ways when the brain is injured. TGF beta, TNF alpha and secreted forms of beta APP (sAPP) can protect neurons against excitotoxic, metabolic and oxidative insults and may thereby serve neuroprotective roles. On the other hand, under certain conditions TNF alpha and the fibrillogenic amyloid beta-peptide (A beta) derivative of beta APP can promote damage of neuronal and glial cells, and may play roles in neurodegenerative disorders. Studies of genetically manipulated mice in which TGF beta, TNF alpha or beta APP ligand or receptor levels are altered suggest important roles for each factor in cellular responses to brain injury and indicate that mediators of neural injury responses also have the potential to enhance amyloidogenesis and/or to interfere with neuroregeneration if expressed at abnormal levels or modified by strategic point mutations. Recent studies have elucidated signal transduction pathways of TGF beta (serine/threonine kinase cascades), TNF alpha (p55 receptor linked to a sphingomyelin-ceramide-NF kappa B pathway), and secreted forms of beta APP (sAPP; receptor guanylate cyclase-cGMP-cGMP-dependent kinase-K+ channel activation). Knowledge of these signaling pathways is revealing novel molecular targets on which to focus neuroprotective therapeutic strategies in disorders ranging from stroke to Alzheimer's disease.

Stimulation of glutamate uptake and Na,K-ATPase activity in rat astrocytes exposed to ischemia-like insults

The postsynaptic actions of glutamate are rapidly terminated by high affinity glutamate uptake into glial cells. In this study we demonstrate the stimulation of both glutamate uptake and Na,K-ATPase activity in rat astrocyte cultures in response to sublethal ischemia-like insults. Primary cultures of neonatal rat cortical astrocytes were subjected to hypoxia, or to serum- and glucose-free medium, or to both conditions (ischemia). Cell death was assessed by propidium iodide staining of cell nuclei. To measure sodium pump activity and glutamate uptake, 3H-glutamate and 86Rb were both simultaneously added to the cell culture in the presence or absence of 2 mM ouabain. Na,K-ATPase activity was defined as ouabain-sensitive 86Rb uptake. Concomitant transient increases (2-3 times above control levels) of both Na,K-ATPase and glutamate transporter activities were observed in astrocytes after 4-24 h of hypoxia, 4 h of glucose deprivation, and 2-4 h of ischemia. A 24 h ischemia caused a profound loss of both activities in parallel with significant cell death. The addition of 5 mM glucose to the cells after 4 h ischemia prevented the loss of both sodium pump activity and glutamate uptake and rescued astrocytes from death observed at the end of 24 h ischemia. Reoxygenation after the 4 h ischemic event caused the selective inhibition of Na,K-ATPase activity. The observed increases in Na,K-ATPase activity and glutamate uptake in cultured astrocytes subjected to sublethal ischemia-like insults may model an important functional response of astrocytes in vivo by which they attempt to maintain ion and glutamate homeostasis under restricted energy and oxygen supply.

Glial lineages and myelination in the central nervous system

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

Differential regulation of ciliary neurotrophic factor (CNTF) and CNTF receptor alpha expression in astrocytes and neurons of the fascia dentata after entorhinal cortex lesion

Neurotrophic factors have been implicated in reactive processes occurring in response to CNS lesions. Ciliary neurotrophic factor (CNTF), in particular, has been shown to ameliorate axotomy-induced degeneration of CNS neurons and to be upregulated at wound sites in the brain. To investigate a potential role of CNTF in lesion-induced degeneration and reorganization, we have analyzed the expression of CNTF protein and CNTF receptor alpha (CNTFR alpha) mRNA in the rat dentate gyrus after unilateral entorhinal cortex lesions (ECLs), using immunocytochemistry and nonradioactive in situ hybridization, respectively. In sham-operated as in normal animals, CNTF protein was not detectable by immunocytochemistry. Starting at 3 d after ECL, upregulation of CNTF expression was observed in the ipsilateral outer molecular layer (OML). Expression was maximal at around day 7, and at this stage immunoreactivity could be specifically localized to astrocytes in the ipsilateral OML. By day 14 postlesion, CNTF immunoreactivity had returned to control levels. CNTFR alpha mRNA was restricted to neurons of the granule cell layer in controls. Three days postlesion, prominent CNTFR alpha expression was observed in the deafferented OML. A similar but less prominent response was noticed in the contralateral OML. After 10 d, CNTFR alpha expression had returned to control levels. Double labeling for CNTFR alpha mRNA and glial fibrillary acidic protein (GFAP) showed that upregulation of CNTFR alpha occurred in reactive, GFAP-immunopositive astrocytes of the OML. A substantial reduction of CNTFR alpha expression in the deafferented granule cells was transiently observed at 7 and 10 d postlesion. Our results suggest a paracrine or autocrine function of CNTF in the regulation of astrocytic and neuronal responses after brain injury.

Effect of experimental hyperphenylalaninemia on the postnatal rat brain

The molecular mechanism of the disturbance of brain development caused by phenylketonuria remains mostly unknown. We have studied three molecular markers that reflect the development of neurons, glia and the extracellular matrix of the postnatal rat brain in an animal model of hyperphenylalaninemia, in order to elucidate the possible mechanism by which increased phenylalanine influences brain development. The content of NCAM, GFAP and hyaluronate-binding activity were compared in cerebellum and telencephalon of normal rats and those subjected to high phenylalanine. No statistically significant changes were found in telencephalon when experimental animals were compared to controls. In the hyperphenylalaninemic cerebellum, the developmental dynamic of NCAM content (represented by two peaks at about postnatal days 5 and 22 during normal development) is dramatically altered. The GFAP content in the cerebellum of treated rats exceeded those in controls significantly during late developmental stages (postnatal days 28-35). Hyaluronate-binding activity in the extracellular protein fraction from treated rat cerebellum was increased compared to normal rat at the early stages of development only (postnatal day 7). These results suggest that high serum phenylalanine may lead to permanent brain dysfunction through a disturbance of a wide range of developmental events.

Cellular inflammatory response after spinal cord injury in Sprague-Dawley and Lewis rats

The distribution of microglia, macrophages, T-lymphocytes, and astrocytes was characterized throughout a spinal contusion lesion in Sprague-Dawley and Lewis rats by using immunohistochemistry. The morphology, spatial localization, and activation state of these inflammatory cells were described both qualitatively and quantitatively at 12 hours, 3, 7, 14, and 28 days after injury. By use of OX42 and ED1 antibodies, peak microglial activation was observed within the lesion epicenter of both rat strains between three and seven days post-injury preceding the bulk of monocyte influx and macrophage activation (seven days). Rostral and caudal to the injury site, microglial activation plateaued between two and four weeks post-injury in the dorsal and lateral funiculi as indicated by morphological transformation and the de-novo expression of major histocompatibility class II (MHC II) molecules. Similar to the timing of microglial reactions, T-lymphocytes maximally infiltrated the lesion epicenter between three and seven days post-injury. Reactive astrocytes, while present in the acute lesion, were more prominent at later survival times (7-28 days). These cells were interspersed with activated microglia but appeared to surround and enclose tissue sites occupied by reactive microglia and phagocytic macrophages. Thus, trauma-induced central nervous system (CNS) inflammation, regardless of strain, occurs rapidly at the site of injury and involves the activation of resident and recruited immune cells. In regions rostral or caudal to the epicenter, prolonged activation of inflammatory cells occurs preferentially in white matter and primarily consists of activated microglia and astrocytes. Differences were observed in the magnitude and duration of macrophage activation between Sprague-Dawley (SD) and Lewis (LEW) rats throughout the lesion. Increased expression of complement type 3 receptors (OX42) and macrophage-activation antigens (ED1) persisted for longer times in LEW rats while expression of MHC class II molecules was attenuated in LEW compared to SD rats at all times examined. Variations in the onset and duration of T-lymphocyte infiltration also were observed between strains with twice as many T-cells present in the lesion epicenter of Lewis rats by 3 days post-injury. These strain-specific findings potentially represent differences in corticosteroid regulation of immunity and may help predict a range of functional neurologic consequences affected by neuroimmune interactions.

The mitogen-activated protein kinase and JAK-STAT signaling pathways are required for an oncostatin M-responsive element-mediated activation of matrix metalloproteinase 1 gene expression

Both astrocytes in the central nervous system and fibroblasts in somatic tissues are not only the major sources of extracellular matrix components but also of matrix metalloproteinases (MMPs), a family of enzymes directly involved in extracellular matrix breakdown. We have analyzed the regulation of the expression of MMPs and TIMPs (tissue inhibitors of metalloproteinases) in human primary astrocytes stimulated with oncostatin M (OSM) and other extracellular mediators in comparison with normal human dermal fibroblasts. It was found that OSM induced/enhanced transcription of MMP-1 (interstitial collagenase) and MMP-3 (stromelysin 1) in astrocytes, and MMP-1, MMP-9 (gelatinase B), and TIMP-1 in fibroblasts. Analysis of the signal transduction leading to activation of the MMP-1 gene revealed the presence of an OSM-responsive element (OMRE) encompassing the AP-1 binding site and the signal transducer and activator of transcription (STAT) binding element, which mediate activation by OSM. OMRE is also present in the TIMP-1 gene promoter and, although there are some differences in these two motifs, both appear to be targets for the simultaneous action of OSM-induced nuclear effectors. The induced enhancement of transcription by synergistically acting AP-1 and STAT binding elements in response to OSM is Raf-dependent. Cross-talk between the mitogen-activated protein kinase and JAK-STAT pathways is required to achieve maximal induction of the OMRE-driven transcription by OSM.

Trypanosomiasis

African (sleeping sickness) and American (Chagas' disease) trypanosomiasis, caused by protozoa of the family Trypanosomatidae, are diseases that are endemic in parts of Africa and Latin America, respectively. Physicians in developed countries may occasionally see cases because of extensive travel and immigration from endemic countries. Although neurological involvement is common in both, its incidence and clinical presentation differ considerably. African trypanosomiasis, caused by subspecies of Trypanosoma brucei (T b rhodesiense, T b gambiense), is transmitted by the tsetse fly and causes meningoencephalitis, in which somnolence is a prominent feature. Parasites may reach the brain parenchyma through the choroid plexus or the Virchow Robin spaces. American trypanosomiasis, caused by Trypanosoma cruzi is transmitted by reduviid bugs. While lesions in the central nervous system are not prominent, except in the reactivated forms which occur in immunodeficient patients, the peripheral nerve, mainly the autonomic nervous system, is frequently involved, leading to the cardiomegaly and the digestive megaviscera. Congenital infections may also occur. In this paper we give an account of the epidemiology, clinical presentation and pathological features of these two protozoal infections based on human and experimental studies of both the central and peripheral nervous system.

Borna disease virus and the brain

Viruses with the ability to establish persistent infection in the central nervous system (CNS) can induce progressive neurologic disorders associated with diverse pathological manifestations. Clinical, epidemiological, and virological evidence supports the hypothesis that viruses contribute to human mental diseases whose etiology remains elusive. Therefore, the investigation of the mechanisms whereby viruses persist in the CNS and disturb normal brain function represents an area of research relevant to clinical and basic neurosciences. Borna disease virus (BDV) causes CNS disease in several vertebrate species characterized by behavioral abnormalities. Based on its unique features, BDV represents the prototype of a new virus family. BDV provides an important model for the investigation of the mechanisms and consequences of viral persistence in the CNS. The BDV paradigm is amenable to study virus-cell interactions in the CNS that can lead to neurodevelopmental abnormalities, immune-mediated damage, as well as alterations in cell differentiated functions that affect brain homeostasis. Moreover, seroepidemiological data and recent molecular studies indicate that BDV is associated with certain neuropsychiatric diseases. The potential role of BDV and of other yet to be uncovered BDV-related viruses in human mental health provides additional impetus for the investigation of this novel neurotropic infectious agent.

Physiological factors predisposing to neurotoxicity

Many factors determine individual susceptibility to toxic agents in addition to their primary interaction with the target site. Absorption, delivery to target tissues, bio-activation, bio-inactivation, elimination, and adaptive or protective responses all play important parts in determining the overall response of the individual. In addition changes in the physiological significance of the function which is disrupted may be crucially important. Pulmonary absorption can be limited by ventilation or perfusion, both of which increase with work rate. Tissue uptake can be limited by local blood flow, which is strongly influenced by local functional activity. In areas with a blood-tissue barrier, such as brain and testis, tissue uptake can be strongly influenced by developmental state, protein binding or vascular damage. Metabolic transformation can show marked inter-individual variations at both hepatic and extra-hepatic sites, due to genetic or nutritional influences. The capacity for adaptation to toxicological insult can also vary markedly, depending on functional reserve capacity as well as on inherent plasticity. Examples used to illustrate these factors include: the influence of motor activity on the toxicity of carbon monoxide; of noise on the ototoxicity of aminoglycoside antibiotics; of brain activity on the neurotoxicity of dinitrobenzene; of acid-base balance on the toxicity of nicotine; and of developmental stage on the neurotoxicity of haloperidol. In addition disease states can influence sensitivity. Thus anaemia sensitises to manganese; calcium deficiency to lead; nerve trauma to hexane; and Wilson's disease to copper overload.

Leptomeningeal cells modulate the neurite growth promoting properties of astrocytes in vitro

Leptomeningeal cells migrate into the lesion cavity after stab wounds to the adult mammalian central nervous system (CNS) and interact with astrocytes that form a new glia limitans. However, it is not known if leptomeningeal cells alter the ability of astrocytes near the lesion to support axon growth. In this study, we have used an in vitro approach to assess leptomeningeal cell-astrocyte interactions in a model that resembles the interactions of these cells in vivo. We cultured rat cortical astrocytes on top of monolayers of leptomeningeal cells or astrocytes. Differences in the morphology, neurite growth promoting properties, and expression of various extracellular matrix molecules and beta 1-integrin were assessed. Astrocytes acquired a long slender morphology when plated on leptomeningeal cells. Functionally, astrocytes cultured on top of leptomeningeal monolayers supported less neurite growth. Similar results were also obtained when astrocyte monolayers were treated with leptomeningeal cell-conditioned medium. Quantitative immunofluorescence labeling showed a reduction in cell surface bound laminin on astrocytes plated on leptomeningeal monolayers. Qualitative assessment of the immunofluorescence labeling showed an increase in matrix-like deposits of tenascin-C and chondroitin sulfate proteoglycan under similar culture conditions. This study provides the first direct evidence that leptomeningeal cells reduce the neurite growth promoting properties of astrocytes. These results suggest that interactions with leptomeningeal cells may 1) induce the formation of the slender astrocyte processes that form parallel to the lesion wall after penetrating injuries to the CNS; and 2) contribute along with other factors to alter astrocytes near the site of injury to a state that is less permissive for axon growth and regeneration.

Effect of substance P on cytokine production by human astrocytic cells and blood mononuclear cells: characterization of novel tachykinin receptor antagonists

Substance P (SP) has been reported to induce inflammatory cytokine production in human neuroglial cells and peripheral lymphoid cells as well. In order to evaluate the potency of novel non-peptide antagonists of the tachykinin receptors as inhibitors of SP-induced cytokines, we used the astrocytoma cell line U373MG and blood mononuclear cells as models of central and peripheral SP-target cells, respectively. In the first part of this study, we showed that SR 140333, an NK1 tachykinin receptor antagonist, was able to inhibit strongly the SP-induced production of interleukin (IL)-6 and IL-8 in the astrocytoma cell line. The antagonistic activity of SR 140333 toward SP-induced cytokine production was specific and could not be attributed to a general anti-cytokine effect, since cytokine release induced by another inflammatory protein such as IL-1beta was not blocked by this compound. In addition, NK2 and NK3 agonist neuropeptides were at least 1000-fold less effective than SP, while SR 48968 and SR 142801 which are selective NK2 and NK3 receptor antagonists, respectively, displayed a 2.5-3 orders of magnitude lower inhibitory potency than SR 140333. All these data indicated that SR 140333 blocked SP-induced cytokine production in U373MG astrocytic cells via a specific NK1 receptor-mediated process. Since SP has also been described to trigger peripheral blood mononuclear cells (PBMNC) or monocytes to release inflammatory cytokines, we attempted, in the second part of this study, to evaluate the potential antagonistic effect of our compounds on these cells. Experiments on human PBMNC from different donors were carried out to determine first their pattern of cytokine production upon SP stimulation. Surprisingly, we noticed that SP at concentrations ranging from 0.1 to 1000 nM was unable to stimulate the release of any inflammatory cytokine tested. This raises the question of the specificity of the reported in vitro effects of SP on cytokine production by human peripheral immune cells.

Chondroitin sulfate proteoglycan and tenascin in the wounded adult mouse neostriatum in vitro: dopamine neuron attachment and process outgrowth

Extracellular matrix (ECM) molecules, including chondroitin-4 or chondroitin-6 sulfate proteoglycans (CSPGs) and tenascin, are upregulated in and around wounds and transplants to the adult CNS. In the present study, striatal wounds from adult mice were used in a novel in vitro paradigm to assess the effects of these wound-associated molecules on embryonic dopamine cell attachment and neurite outgrowth. Light and electron microscopic immunocytochemistry studies have shown that astroglial scar constituents persist in cultured explants for at least 1 week in vitro, and despite the loss of neurons from adult striatal explants, there is a retention of certain structural features suggesting that the wound explant-neuron coplant is a viable model for analysis of graft-scar interactions. Explants from the wounded striatum taken at different times after a penetrating injury in vivo were used as substrates for embryonic ventral mesencephalon neurons that were plated on their surfaces. Dopamine cell attachment is increased significantly in relation to the expression of both CSPG and tenascin. The increase in neuronal attachment in this paradigm, however, is accompanied by a postlesion survival time-dependent significant decrease in neuritic growth from these cells. In vitro ECM antibody treatment suggests that CSPG may be responsible for heightened dopamine cell attachment and that tenascin simultaneously may support cell attachment while inhibiting neurite growth. The present study offers a new approach for the in vitro analysis of cell and molecular interactions after brain injury and brain grafting, in essence acting as a nigrostriatal transplant-in-a-dish.

Chemokine expression in rat stab wound brain injury

A traumatic injury to the adult mammalian central nervous system (CNS) results in reactive astrogliosis and the migration of hematogenous cells into the damaged neural tissue. Chemokines, a novel class of chemoattractant cytokines, are now being recognized as mediators of the inflammatory changes that occur following injury. The expression of MCP-1 (macrophage chemotactic peptide-1), a member of the beta family of chemokines, has recently been demonstrated in trauma in the rat brain (Berman et al.: J Immunol 156:3017-3023, 1996). Using a stab wound model for mechanical injury, we studied the expression of two other beta chemokines: RANTES (Regulated on Activation, Normal T cell Expressed and Secreted) and MIP-1 beta (macrophage inflammatory protein-1 beta) in the rat brain. The stab wound injury was characterized by widespread gliosis and infiltration of hematogenous cells. Immunohistochemical staining revealed the presence of RANTES and MIP-1 beta in the injured brain. RANTES and MIP-1 beta were both diffusely expressed in the necrotic tissue and were detected as early as 1 day post-injury (dpi). Double-labeling studies showed that MIP-1 beta, but not RANTES, was expressed by reactive astrocytes near the lesion site. In addition, MIP-1 beta staining was also detected on macrophages at the site of injury. The initial expression of the chemokines closely correlated with the appearance of inflammatory cells in the injured CNS, suggesting that RANTES and MIP-1 beta may play a role in the inflammatory events of traumatic brain injury. This study also demonstrates for the first time MIP-1 beta expression in reactive astrocytes following trauma to the rat CNS.

Beta-secretase processing of the beta-amyloid precursor protein in transgenic mice is efficient in neurons but inefficient in astrocytes

Alzheimer's disease is characterized by the extracellular deposition of beta-amyloid peptide (Abeta) in cerebral plaques and evidence is accumulating that amyloid is neurotoxic. Abeta is derived from the beta-amyloid precursor protein (APP). Proteolytic processing of APP by the enzyme, beta-secretase, produces the N terminus of Abeta, and releases a secreted ectodomain of APP (beta-s-APP). To develop animal models for measuring beta-secretase activity in specific brain cells in vivo, we have targeted the expression of the full-length human APP to either neurons or astrocytes in transgenic mice using the neuron- specific enolase (NSE) promoter or a modified glial fibrillary acidic protein (GFAP) gene, respectively. The APP cDNAs expressed were mutated (KM to NL at 670/671) to encode amino acid substitutions that enhance amyloidogenic processing in vitro. Western analyses revealed abundant production of beta-s-APP in the brains of NSE-APP mice and enzyme-linked immunosorbent assay analyses showed production of Abeta in fetal primary mixed brain cultures and brain homogenates from these transgenic animals. Because the NSE promoter drives expression primarily in neurons, this provides in vivo evidence that the beta-secretase cleavage necessary for generation of beta-s-APP and Abeta is efficiently performed in neurons. In contrast, only little beta-s-APP was detected in brain homogenates of GFAP-APP mice, indicating that astrocytes show very little beta-secretase activity in vivo. This provides strong in vivo evidence that the major source of Abeta in brain is from neurons and not from astrocytes.

Gliosis in the LP-BM5 murine leukemia virus-infected mouse: an animal model of retrovirus-induced dementia

Mice infected with the LP-BM5 murine leukemia virus (MuLV) mixture develop severe immunosuppression, neurotransmitter abnormalities and cognitive impairments in the absence of significant viral or macrophage invasion of the CNS. The time-course of the changes in glial activation have been characterized in an effort to understand the cellular basis of the neurobehavioral abnormalities observed in these mice. Glial activation was determined by measuring the relative changes in F4/80 protein and GFAP immunoreactivity using immunoblots. Augmented F4/80 expression preceded that of GFAP, with global elevations of 4-6-fold at 3 weeks, sustained for up to 12 weeks after inoculation. GFAP immunoreactivity increased 2-fold only in the cerebral cortex and striatum 5 weeks postinfection, declining to control levels by 12 weeks. Immunohistochemistry revealed significant increases in microglial size and staining intensity in the cortex, corpus callosum and striatum, with the development of a unique population of highly ramified, intensely stained microglia and microglial nodules in the corpus callosum and striatum. No evidence of ameboid microglia was found. Astrocyte size and degree of ramification was increased in the hippocampus, cortex, striatum and corpus callosum. Thus, microgliosis is an early event in LP-BM5 infection, preceding astrocytosis, neurotransmitter loss, and development of cognitive deficits. Activated microglia may secrete neurotoxins leading to the neurochemical alterations and cognitive deficits observed in these mice. Because gliosis and microglial nodule formation are hallmarks of HIV-1 encephalopathy, LP-BM5 MuLV-infected C57/B16 mice may afford insights into the mechanisms contributing to the early stages of this syndrome.

Astrocytes in kindling: relevance to epileptogenesis

Astrogliosis is a prominent feature of epileptic foci, and may play a causal role in the development of seizures and the persistance of seizure disorders. We have studied morphological changes in astrocytes with respect to the evolution of seizures using the kindling model of epilepsy. Kindling-induced seizures result in a prominent hypertrophy of astrocytes that is accompanied by a reorganization of astrocytic cytoskeleton. The change in the morphology of astrocytes appears to be seizure-intensity dependent, occurs early in the kindling process, and persists for weeks following the last seizure. In addition to hypertrophy, we have observed an increase in proliferation of astrocytes in hippocampus, amygdala and piriform cortex, but no change in the expression of connexin-43 following kindling. Significantly, induction of a localized astrocyte hypertrophy prior to initiation of kindling does not result in seizures and does not facilitate kindling. Altogether these data suggest that 'gliosis' is an adaptive response to seizures.

Amphiphilic helix is essential for the activity of brain injury-derived neurotrophic peptide (BINP)

To study the structure-activity relationships of brain injury-derived neurotrophic peptide (BINP), 12 analogs were synthesized by replacing each amino acid residue with Gly. BINP showed CD spectra typical of an alpha-helical conformation in TFE solution which mimics the membrane environment. In the alpha-helical conformation, BINP showed an amphiphilic profile. Neurotrophic activities of BINP and its analogs were estimated from the effects on supporting septal cholinergic neurons and on rescuing hippocampal neurons from injury caused by glutamate. Both assays showed that the residues on the hydrophobic side of the amphiphilic helix were essential for the neurotrophic activity.

Reduction of the microglial cell number in rat primary glial cell cultures by exogenous addition of dibutyryl cyclic adenosine monophosphate

The present work examined the effects induced by dibutyryl cyclic adenosine monophosphate (dB-cAMP) on microglial cells in primary glial cell cultures from newborn rats. Microglial cells were identified by OX42 immunohistochemistry and nucleoside diphosphatase histochemistry. Double staining for astrocytes was carried out by combination with glial fibrillary acidic protein immunolabeling. Addition of 0.25 mM dB-cAMP to the cultures decreased the microglial cell number about sixfold. The findings suggest that the effect of dB-cAMP on the microglial cells might be either a direct action of dB-cAMP on the microglial cells or an indirect effect mediated by the astroglial cells.

Expression of glial antigens in mouse astrocytes: species differences and regulation in vitro

Expression of developmentally regulated antigens was used to characterize glial cells in cultures from embryonic mouse cerebral cortex. Over 90% of the cells had a flat morphology, and about 50% of these flat cells also expressed the ganglioside GD3. Up to 40% of all the GD3 expressing cells also expressed A2B5 antigen. Flat cells expressing either glial fibrillary acidic protein (GFAP), or GD3 or both were present at all times in vitro. These three populations of flat cells could not be further distinguished on the basis of NG2 or fibronectin expression, or with respect to their responses to the mitogens FGF-2, PDGF, or EGF. The glial cultures also contain a small number (approximately 5%) of process bearing cells with the morphological and immunocytochemical characteristics of oligodendrocyte precursors. The expression of GD3 by flat cells changed with time in culture as the fraction of flat cells expressing only GD3 declined and the fraction of cells expressing GFAP (with or without GD3) increased. The data are consistent with those flat cells expressing only GD3 being astrocyte precursors. Furthermore, between 1 and 3 weeks in vitro GD3/GFAP cells lose GD3 while retaining GFAP. Cells expressing only GFAP could be induced to express GD3 and A2B5 by treatment with FGF-2. The widespread and regulated expression of GD3 and A2B5 by murine glia is different from the restricted pattern of expression previously reported for these antigens in rat brain cell cultures. These results demonstrate that expression of GD3 and A2B5 by murine astrocytes depends on both culture age and extracellular signals and that these gangliosides are not markers for cell lineage in the mouse.

Differential expression of M-CSF, LIF, and TNF-alpha genes in normal and malignant rat glial cells: regulation by lipopolysaccharide and vitamin D

The effect of 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) on the expression of macrophage colony-stimulating factor (M-CSF), leukemia inhibitory factor (LIF), and tumor necrosis factor-alpha (TNF-alpha) genes in primary rat astrocytes and C6 glioma cells was examined. The results show that the hormone differentially regulates the cytokine mRNA in the two cell types. 1,25-(OH)2D3 augments M-CSF and LIF mRNA in C6 glioma cells, while lipopolysaccharide (LPS) has minimal effects. When LPS and 1,25-(OH)2D3 are used in combination, a strong synergistic effect upon the induction of M-CSF and LIF genes is observed. No TNF-alpha transcript has been detected in C6 glioma cells under any stimulus conditions used. In contrast, 1,25-(OH)2D3 has no pronounced effect on M-CSF, LIF, and TNF-alpha transcripts in primary astrocytes when used as a sole stimulus, while treatment with LPS strongly enhances the levels of the three cytokines. However, when 1,25-(OH)2D3 is used in combination with LPS, a partial reduction in LPS-induced levels of M-CSF and TNF-alpha mRNA is observed. The overall results indicate that genes coding for some inflammatory cytokines obey distinct regulatory mechanisms in C6 cells and in primary astrocytes. They also suggest that 1,25-(OH)2D3, by altering the response of astrocytes to an inflammatory stimulus, could participate in the regulation of the CNS immune response.

Alanine substitution for Thr268 and Asp269 of soluble ciliary neurotrophic factor (CNTF) receptor alpha component defines a specific antagonist for the CNTF response

Ciliary neurotrophic factor (CNTF) associates with an alpha subunit (CNTFRalpha) of the receptor complex to initiate signal transduction by facilitating heterodimerization of the gp130 transducing protein and the leukemia inhibitory factor receptor (LIFR) beta. CNTFRalpha is anchored to the membrane by a glycosylphosphatidylinositol linkage; however, a soluble form of the alpha subunit can still bind CNTF to recruit the signal transducing components of the receptor complex. In the present study we show that alanine substitution for residues Thr268 and Asp269 of the CNTFRalpha subunit results in a mutated receptor subunit (R3), which can bind CNTF with an affinity similar to that of the wild type CNTFRalpha but, when expressed as a soluble receptor subunit, lowers the binding of CNTF to its tripartite receptor. In addition, CNTFR3alpha inhibits the proliferation of the TF1 hematopoietic cell line triggered by CNTF plus soluble wild type CNTFRalpha but not by IL-6 or oncostatin M. Similarly, CNTFR3alpha specifically antagonizes the induction of gp130 and LIFRbeta tyrosine phosphorylation observed in response to CNTF and wild type soluble CNTFRalpha in the HepG2 hepatoma cell line, as well as the subsequent events leading to haptoglobin synthesis. Positions 268 and 269 of CNTFRalpha appear to be critical for its interaction with gp130 and LIFRbeta, whereby alanine substitution of the residues at these positions results in antagonism of the CNTF-induced response.

S100 beta induces apoptotic cell death in cultured astrocytes via a nitric oxide-dependent pathway

S100 beta is a calcium binding protein expressed primarily by astrocytes in the brain. In initiating studies of the toxic signalling pathways activated by high concentrations of S100 beta, we previously demonstrated that treatment of astrocytes with microM S100 beta results in a potent stimulation of the mRNA level and enzyme activity of inducible nitric oxide (NO) synthase, an enzyme previously implicated in glial pathology. We provide evidence here that NO formation stimulated by S100 beta can lead to cell death in astrocytes, with characteristics defined for apoptosis. Incubation of astrocytes with S100 beta for 48 h results in an increased percentage of astrocytes undergoing apoptotic cell death, as determined with the TUNEL technique, assays of DNA fragmentation and lactate dehydrogenase release. The cell death induced in responses to S100 beta addition correlates with the levels of NO formation, and an inhibitor of nitric oxide synthase attenuates the NO formation elicited by S100 beta, as well as the cell death. Therefore, we propose that S100 beta has the potential to be trophic or toxic. Although S100 beta may be involved in development, homeostasis and repair, chronic overexpression of the protein may mediate toxic responses or even cell death.

Monitoring the temporal and spatial activation pattern of astrocytes in focal cerebral ischemia using in situ hybridization to GFAP mRNA: comparison with sgp-2 and hsp70 mRNA and the effect of glutamate receptor antagonists

We investigated the temporo-spatial expression of astrocyte glial fibrillary acidic protein (gfap) and sulfated glycoprotein 2 (sgp-2) mRNAs in comparison to 70-kDa heat shock protein (hsp70) mRNA by in situ hybridisation in rats subjected to permanent occlusion of the middle cerebral artery (MCA). Gfap mRNA started to increase in the cingulate cortex of the lesioned hemisphere 6 h after MCA occlusion and gradually spread over the lateral part of the ipsilateral cortex and the striatum from 12 h to 3 days, peaking at 3 days after MCA occlusion. Gfap mRNA also increased in the contralateral cingulate cortex and corpus callosum at 12 and 24 h. Hsp70 mRNA increased markedly in the ipsilateral cortex adjacent to the ischemic lesion, and slightly within the lesion area from 3 to 24 h and disappeared after 3 days. By 7 days, gfap and sgp-2 mRNAs were increased markedly in the peri-infarct area, and in the ipsilateral thalamus parallel with the delayed neuronal damage, whereas the widespread increase of gfap mRNA in the ipsilateral hemisphere declined. Post-occlusion treatment with the glutamate receptor antagonists MK-801 and NBQX slightly attenuate the induction of gfap but did not qualitatively affect the topical expression pattern. Within the cingulate cortex MK-801 treatment resulted in a significant decrease of the signal intensity at all survival times, reflecting most likely an attenuation of lesion-induced spreading depression like depolarization waves by MK-801. The area of hsp70 expression was reduced by both MK-801 and NBQX, most likely reflecting the decrease of the lesion area by both treatment regimens. Our study thus revealed an early and widespread increase of gfap mRNA in the non-ischemic area including the contralateral hemisphere starting between 3 and 6 h, and a delayed circumscribed expression in the peri-infarct border zone after 1 week. Comparison with the expression of hsp70 mRNA suggests that the absence of an early gfap mRNA induction in the peri-lesion zone reflects an impairment of astrocytic function which may be of importance for infarct growth during the early evolution of the pathological process.

Neurotoxicity induced by interleukin-2: involvement of infiltrating immune cells

Interleukin-2 (IL-2), a key regulator of immune functions, also has potent effects on neurons and glia. IL-2 modulates neural cell growth and survival and transmitter and hormone releases and is thought to mediate neuroimmune interactions. Investigating the neuroendocrine consequences of chronically elevated central nervous system (CNS) levels of IL-2, we recently observed marked neurotoxicity [Hanisch et al. (1994) Endocrinology 135:2465-2472]. In the present study, we characterize in detail the modifications in brain tissue architecture as they result in Sprague-Dawley rats from intracerebroventricular (i.c.v.) administration of low amounts of IL-2 (5 and 15 U/h, respectively, delivered by means of osmotic minipumps for up to 14 days). Histological inspection of the brains revealed massive cellular infiltrates in the ipsilateral hemisphere. The infiltrates were associated with pronounced angiogenesis and changes in the composition of the extracellular matrix. These anatomical changes apparently developed between day 7 and 14. They were specific for IL-2 and were not seen in animals treated, for example, with heat-inactivated IL-2 (controls). We further show that chronic central administration of IL-2 let to T and B lymphocyte invasion of the brain and an intracranial agglomeration of large numbers of MHC class II-positive cells. Immunocytochemistry revealed a widespread inundation of CNS tissue and a decoration of glial cells and neurons by endogenous antibodies. Tissue regions around the IL-2-induced infiltrates showed myelin destruction and neuronal cell loss. Chronically elevated CNS levels of IL-2 may, thus, not only interfere with neurotransmission and endocrine functions but also severely disturb tissue homeostasis. Therefore, the present findings could be relevant to brain injuries, CNS disorders, and clinical treatments associated with increased IL-2 levels or involving an immune component.