Astrogliosis in culture: III. Effect of recombinant retrovirus expressing antisense glial fibrillary acidic protein RNA

GFAP at 50

Fifty years have passed since the discovery of glial fibrillary acidic protein (GFAP) by Lawrence Eng and colleagues. Now recognized as a member of the intermediate filament family of proteins, it has become a subject for study in fields as diverse as structural biology, cell biology, gene expression, basic neuroscience, clinical genetics and gene therapy. This review covers each of these areas, presenting an overview of current understanding and controversies regarding GFAP with the goal of stimulating continued study of this fascinating protein.

Toll-Like Receptor 4 Knockdown Attenuates Brain Damage and Neuroinflammation After Traumatic Brain Injury via Inhibiting Neuronal Autophagy and Astrocyte Activation

Toll-like receptor 4 (TLR4) has been linked to various pathophysiological conditions, such as traumatic brain injury (TBI). It is reported that posttraumatic neuroinflammation is an essential event in the progression of brain injury after TBI. Recent evidences indicate that TLR4 mediates glial phagocytic activity and inflammatory cytokines production. Thus, TLR4 may be an important therapeutic target for neuroinflammatory injury post-TBI. This study was designed to explore potential effects and underlying mechanisms of TLR4 in rats suffered from TBI. TBI model was induced using a controlled cortical impact in rats, and application of TLR4 shRNA silenced TLR4 expression in brain prior to TBI induction. Elevated TLR4 was specifically observed in the hippocampal astrocytes and neurons posttrauma. Interestingly, TLR4 shRNA decreased the concentrations of interleukin (IL)-1β, IL-6, and tissue necrosis factor-α; alleviated hippocampal neuronal damage; reduced brain edema formation; and improved neurological deficits after TBI. Meanwhile, to further explore underlying molecular mechanisms of this neuroprotective effects of TLR4 knockdown, our results showed that TLR4 knockdown significantly inhibited the upregulation of autophagy-associated proteins caused by TBI. More importantly, an autophagy inducer, rapamycin pretreated, could partially abolish neuroprotective effects of TLR4 knockdown on TBI rats. Furthermore, TLR4 silencing markedly suppressed GFAP upregulation and improved cell hypertrophy to attenuate TBI-induced astrocyte activation. Taken together, these findings suggested that TLR4 knockdown ameliorated neuroinflammatory response and brain injury after TBI through suppressing autophagy induction and astrocyte activation.

Interactions between Sirt1 and MAPKs regulate astrocyte activation induced by brain injury in vitro and in vivo

Background

Astrocyte activation is a hallmark of traumatic brain injury resulting in neurological dysfunction or death for an overproduction of inflammatory cytokines and glial scar formation. Both the silent mating type information (Sirt1) expression and mitogen-activated protein kinase (MAPK) signal pathway activation represent a promising therapeutic target for several models of neurodegenerative diseases. We investigated the potential effects of Sirt1 upregulation and MAPK pathway pharmacological inhibition on astrocyte activation in vitro and in vivo. Moreover, we attempted to confirm the underlying interactions between Sirt1 and MAPK pathways in astrocyte activation after brain injury.

Methods

The present study employs an interleukin-1β (IL-1β) stimulated primary cortical astrocyte model in vitro and a nigrostriatal pathway injury model in vivo to mimic the astrocyte activation induced by traumatic brain injury. The activation of GFAP, Sirt1, and MAPK pathways were detected by Western blot; astrocyte morphological hypertrophy was assessed using immunofluorescence staining; in order to explore the neuroprotective effect of regulation Sirt1 expression and MAPK pathway activation, the motor and neurological function tests were assessed after injury.

Results

GFAP level and morphological hypertrophy of astrocytes are elevated after injury in vitro or in vivo. Furthermore, the expressions of phosphorylated extracellular regulated protein kinases (p-ERK), phosphorylated c-Jun N-terminal kinase (p-JNK), and phosphorylated p38 activation (p-p38) are upregulated, but the Sirt1 expression is downregulated. Overexpression of Sirt1 significantly increases the p-ERK expression and reduces the p-JNK and p-p38 expressions. Inhibition of ERK, JNK, or p38 activation respectively with their inhibitors significantly elevated the Sirt1 expression and attenuated the astrocyte activation. Both the overproduction of Sirt1 and inhibition of ERK, JNK, or p38 activation can alleviate the astrocyte activation, thereby improving the neurobehavioral function according to the modified neurological severity scores (mNSS) and balance latency test.

Conclusions

Thus, Sirt1 plays a protective role against astrocyte activation, which may be associated with the regulation of the MAPK pathway activation induced by brain injury in vitro and in vivo.

Traumatic scratch injury in astrocytes triggers calcium influx to activate the JNK/c-Jun/AP-1 pathway and switch on GFAP expression

Astrocyte activation is a hallmark of central nervous system injuries resulting in glial scar formation (astrogliosis). The activation of astrocytes involves metabolic and morphological changes with complex underlying mechanisms, which should be defined to provide targets for astrogliosis intervention. Astrogliosis is usually accompanied by an upregulation of glial fibrillary acidic protein (GFAP). Using an in vitro scratch injury model, we scratched primary cultures of cerebral cortical astrocytes and observed an influx of calcium in the form of waves spreading away from the wound through gap junctions. Using the calcium blocker BAPTA-AM and the JNK inhibitor SP600125, we demonstrated that the calcium wave triggered the activation of JNK, which then phosphorylated the transcription factor c-Jun to facilitate the binding of AP-1 to the GFAP gene promoter to switch on GFAP upregulation. Blocking calcium mobilization with BAPTA-AM in an in vivo stab wound model reduced GFAP expression and glial scar formation, showing that the calcium signal, and the subsequent regulation of downstream signaling molecules, plays an essential role in brain injury response. Our findings demonstrated that traumatic scratch injury to astrocytes triggered a calcium influx from the extracellular compartment and activated the JNK/c-Jun/AP-1 pathway to switch on GFAP expression, identifying a previously unreported signaling cascade that is important in astrogliosis and the physiological response following brain injury.

S-nitrosoglutathione induces ciliary neurotrophic factor expression in astrocytes, which has implications to protect the central nervous system under pathological conditions

Accumulating evidence suggests that reactive astrogliosis has beneficial and detrimental outcomes in various CNS disorders, but the mechanism behind this dichotomy is unclear. Recent advances in this direction suggested that NO signaling is critical to regulate the outcomes of reactive astrogliosis in vivo. Using biochemical and genetic approaches, we here investigated the effect of S-nitrosoglutathione (GSNO; a physiological NO donor) in astrocytes in vitro settings. GSNO enhanced the expressions of glial fibrillary acidic protein and neurotrophic factors including ciliary neurotrophic factor (CNTF) in astrocytes in a dose-dependent manner. The enhanced CNTF expression in GSNO-treated astrocytes was ascribed to NO-mediated sGC/cGMP/PKG signaling. It was associated with p38 MAPK-dependent increased peroxisome proliferator-activated receptor-γ transactivation. In addition, the chromatin accessibility of peroxisome proliferator-activated receptor-γ accompanied with ATF2 and CREB (cAMP-response element-binding protein) was enhanced across the CNTF gene promoter in GSNO treated astrocytes. Interestingly, secreted CNTF was responsible for increased expression of glial fibrillary acidic protein in GSNO-treated astrocytes in an autocrine manner via a JAK2- and STAT3-dependent mechanism. In addition, CNTF secreted by GSNO-treated astrocytes enhanced the differentiation of immature oligodendrocytes in vitro. These effects of GSNO were consistent with an endogenously produced NO in astrocytes stimulated with proinflammatory cytokines in vitro. We conclude that NO signaling induces CNTF expression in astrocytes that favors the beneficial outcomes of reactive astrogliosis in vivo. Our data suggest that the endogenously produced NO or its exogenous source has potential to modulate the outcomes of reactive astrogliosis to protect CNS under pathological conditions.

Primary cultures of astrocytes: their value in understanding astrocytes in health and disease

During the past few decades of astrocyte research it has become increasingly clear that astrocytes have taken a central position in all central nervous system activities. Much of our new understanding of astrocytes has been derived from studies conducted with primary cultures of astrocytes. Such cultures have been an invaluable tool for studying roles of astrocytes in physiological and pathological states. Many central astrocytic functions in metabolism, amino acid neurotransmission and calcium signaling were discovered using this tissue culture preparation and most of these observations were subsequently found in vivo. Nevertheless, primary cultures of astrocytes are an in vitro model that does not fully mimic the complex events occurring in vivo. Here we present an overview of the numerous contributions generated by the use of primary astrocyte cultures to uncover the diverse functions of astrocytes. Many of these discoveries would not have been possible to achieve without the use of astrocyte cultures. Additionally, we address and discuss the concerns that have been raised regarding the use of primary cultures of astrocytes as an experimental model system.

Attenuation of astrocyte activation by TAT-mediated delivery of a peptide JNK inhibitor

Astrocyte activation contributes to the brain's response to disease and injury. Activated astrocytes generate harmful radicals that exacerbate brain damage including nitric oxide, peroxides and superoxides. Furthermore, reactive astrocytes hinder regeneration of damaged neural circuits by secreting neuro-developmental inhibitors and glycosaminoglycans (GAGs), which physically block growth cone extension. Therefore, targeted therapeutic strategies to limit astrocyte activation may enhance recovery from many neurodegenerative states. Previously, we demonstrated that the HIV-1 TAT cell-penetrating peptide, a short non-toxic peptide from the full-length TAT protein, delivered a protein cargo to astrocytes in a process dependent on cell-surface GAG. Since activated astrocytes produce GAG, in this study we tested whether TAT could transduce activated astrocytes, deliver a biologically active cargo, and produce a physiological effect. Astrocyte activation was induced by IL-1β, lipopolysaccharide (LPS), or mechanical stretch injury, and quantified by increased GAG and nitrite content. TAT-mediated delivery of a mock therapeutic protein, GFP, increased significantly after activation. Nitrite production, GAG expression, and GFP-TAT transduction were significantly attenuated by inhibitors of JNK, p38, or ERK. TAT fused to a peptide JNK inhibitor delivered the peptide inhibitor to activated astrocytes and significantly reduced activation. Our study is the first to report significant and direct modulation of astrocyte activation with a peptide JNK inhibitor. Our promising in vitro results warrant in vivo follow-up, as TAT-mediated protein delivery may have broad therapeutic potential for preventing astrocyte activation with the possibility of limiting off-target, negative side effects.

A novel and efficient gene transfer strategy reduces glial reactivity and improves neuronal survival and axonal growth in vitro

Background

The lack of axonal regeneration in the central nervous system is attributed among other factors to the formation of a glial scar. This cellular structure is mainly composed of reactive astrocytes that overexpress two intermediate filament proteins, the glial fibrillary acidic protein (GFAP) and vimentin. Indeed, in vitro, astrocytes lacking GFAP or both GFAP and vimentin were shown to be the substrate for increased neuronal plasticity. Moreover, double knockout mice lacking both GFAP and vimentin presented lower levels of glial reactivity in vivo, significant axonal regrowth and improved functional recovery in comparison with wild-type mice after spinal cord hemisection. From these results, our objective was to develop a novel therapeutic strategy for axonal regeneration, based on the targeted suppression of astroglial reactivity and scarring by lentiviral-mediated RNA-interference (RNAi).

Methods and Findings

In this study, we constructed two lentiviral vectors, Lv-shGFAP and Lv-shVIM, which allow efficient and stable RNAi-mediated silencing of endogenous GFAP or vimentin in vitro. In cultured cortical and spinal reactive astrocytes, the use of these vectors resulted in a specific, stable and highly significant decrease in the corresponding protein levels. In a second model — scratched primary cultured astrocytes — Lv-shGFAP, alone or associated with Lv-shVIM, decreased astrocytic reactivity and glial scarring. Finally, in a heterotopic coculture model, cortical neurons displayed higher survival rates and increased neurite growth when cultured with astrocytes in which GFAP and vimentin had been invalidated by lentiviral-mediated RNAi.

Conclusions

Lentiviral-mediated knockdown of GFAP and vimentin in astrocytes show that GFAP is a key target for modulating reactive gliosis and monitoring neuron/glia interactions. Thus, manipulation of reactive astrocytes with the Lv-shGFAP vector constitutes a promising therapeutic strategy for increasing glial permissiveness and permitting axonal regeneration after central nervous system lesions.

Chronic psychotropic drug treatment causes differential expression of connexin 43 and GFAP in frontal cortex of rats

Astrocytic markers glial fibrillary acidic protein (GFAP) and connexin 43 (CX43) are known to have altered expression in brains of subjects with psychiatric disorders including autism and major depression. The current study investigated whether GFAP and CX43 expressions are affected by several commonly used psychotropic medications (clozapine, fluoxetine, haloperidol, lithium, olanzapine, and valproic acid). Using SDS-PAGE and western blotting technique, we observed that CX43 protein expression in prefrontal cortex was significantly increased following chronic treatment with fluoxetine and clozapine, while it was significantly decreased by haloperidol and lithium. GFAP protein expression was significantly decreased following chronic treatment with clozapine and valproic acid. These results suggest that astroglial markers GFAP and CX43 could be potential targets for therapeutic intervention.

Astroglial injury in an ex vivo model: contributions to its analysis in enriched cell cultures

In vitro cell culture models have been proposed to analyze some of the complex structural and functional characteristics involved in astroglial changes after neural injury in vivo. This report contributes to analyze the proposed hypothesis that an experimentally induced discontinuity of a confluent cellular culture could represent a useful model for the analysis of the processes involved in a neural lesion. For this purpose, it was decided to characterize astroglial proliferation and dye coupling state after a "scratch wound" applied to confluent, astrocyte-enriched cell cultures, obtained from several rat brain regions. Proliferation was assessed in terms of bromodeoxyuridine nuclear incorporation as a function of lesion width, serum deprivation, time after confluence, brain region origin, postlesional culture medium changes and agitation, and after application of a gap-junction uncoupling agent. The proliferative reaction after injury was neither cell type-specific nor brain region specific, nor was significantly affected by neither of the above-mentioned variables. Furthermore, injury failed to significantly affect the astroglial dye coupling state. Results suggest that the proliferative response observed under present conditions would depend on the disruption of contact inhibition rather than on astroglial mitogenic signals released from the wound and operating by either extracellular or cell coupling mechanisms. Present results question the validity of astrocyte-enriched cell cultures as an experimental model of neural tissue injury in vivo, as they do not appear to reproduce fundamental characteristics expressed in situ.

New therapeutic targets in atrophic age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of blindness in developed countries. There is no effective treatment for the most prevalent atrophic (dry) form of AMD. Atrophic AMD is triggered by abnormalities in the retinal pigment epithelium (RPE) that lies beneath the photoreceptor cells and normally provides critical metabolic support to these light-sensing cells. Secondary to RPE dysfunction, macular rods and cones degenerate leading to the irreversible loss of vision. Oxidative stress, formation of drusen, accumulation of lipofuscin, local inflammation and reactive gliosis represent the pathologic processes implicated in pathogenesis of atrophic AMD. This review discusses potential target areas for small-molecule and biologic intervention, which may lead to development of new therapeutic treatments for atrophic AMD.

Inhibiting cell cycle progression reduces reactive astrogliosis initiated by scratch injury in vitro and by cerebral ischemia in vivo

Astrogliosis occurs in a variety of neuropathological disorders and injuries, and excessive astrogliosis can be devastating to the recovery of neuronal function. In this study, we asked whether reactive astrogliosis can be suppressed in the lesion area by cell cycle inhibition and thus have therapeutic benefits. Reactive astrogliosis induced in either cultured astrocytes by hypoxia or scratch injury, or in a middle cerebral artery occlusion (MCAO) ischemia model were combined to address this issue. In the cultured astrocytes, hypoxia induced a cell cycle activation that was associated with upregulation of the proliferating cell nuclear marker (PCNA). Significantly, the cell cycle inhibitor, olomoucine, inhibited hypoxia-induced cell cycle activation by arresting the cells at G1/S and G2/M in a dose-dependent manner and also reversed hypoxia-induced upregulation of PCNA. Also in the cultured astrocytes, scratch injury induced reactive astrogliosis, such as hypertrophy and an increase in BrdU(+) astrocytes, both of which were ameliorated by olomoucine. In the MCAO ischemia mouse model, dense reactive glial fibrillary acidic protein and PCNA immunoreactivity were evident at the boundary zone of focal cerebral ischemia at days 7 and 30 after MCAO. We found that intraperitoneal olomoucine administration significantly inhibited these astrogliosis-associated changes. To demonstrate further that cell cycle regulation impacts on astrogliosis, cyclin D1 gene knockout mice (cyclin D1(-/-)) were subjected to ischemia, and we found that the percentage of Ki67-positive astrocytes in these mice was markedly reduced in the boundary zone. The number of apoptotic neurons and the lesion volume in cyclin D1(-/-) mice also decreased as compared to cyclin D1(+/+) and cyclin D1(+/-) mice at days 3, 7, and 30 after local cerebral ischemia. Together, these in vitro and in vivo results strongly suggest that astrogliosis can be significantly affected by cell cycle inhibition, which therefore emerges as a promising intervention to attenuate reactive glia-related damage to neuronal function in brain pathology.

Autoantibodies against Glial Fibrillary Acidic Protein (GFAP) in Cerebrospinal Fluids from Pug Dogs with Necrotizing Meningoencephalitis

Cerebrospinal fluids (CSFs) from 9 Pug dogs with necrotizing meningoencephalitis (NME: Pug dog encephalitis) were examined to identify the antigens for anti-astrocyte autoantibodies. Each CSF exhibited a positive reaction to the cytoplasm of cultured canine astrocytes by an indirect fluorescent antibody test. In an immunoblotting analysis on normal canine brain proteins, eight of 9 CSFs showed a common band of 52 kDa, corresponding to glial fibrillary acidic protein (GFAP), and all of 9 CSFs reacted with purified bovine GFAP. From these results, GFAP is one of the common autoantigens in Pug dogs with NME. On the other hand, the reactivity of CSFs to chymotrypsin-digested bovine GFAP fragments were variable among dogs, indicating that the antibodies in the CSFs recognized different epitopes on GFAP.

Neurite outgrowth is impaired on HSP70-positive astrocytes through a mechanism that requires NF-kappaB activation

In the adult central nervous system (CNS), prominent reactive astrocytosis is seen in acute traumatic brain injury, neurodegenerative diseases and a variety of viral infections. Reactive astrocytes synthesize a number of factors that could play different roles in neuronal regeneration. In this study, the effects of thermal stress were evaluated on nuclear factor-kappaB (NF-kappaB) activation and proinflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) secretion in primary astrocytic cultures. The ability of HSP70-positive astrocytes to support or inhibit neurite outgrowth was investigated in neuron-astrocyte cocultures. Cultured astrocytes from cerebral cortex of rats were exposed to transient hyperthermia (42 degrees C/30 min) and incubated at 37 degrees C for different periods of recovery. During HSP70 accumulation, astrocytes extended large and thick processes associated to rearrangement of glial fibrillary acidic protein (GFAP) filaments and an increase in protein synthesis and GFAP, suggesting an astrogliosis event. A delay of NF-kappaB activation appeared closely related to TNF-alpha secretion by HSP70-positive astrocytes. These cells demonstrated a functional shift from neurite growth-promoting to non-permissive substrate. We also found that gliotoxin, a specific NF-kappaB inhibitor, partially abrogated the inhibitory ability of reactive astrocytes. These findings may suggest a involvement of NF-kappaB and TNF-alpha in modulating the failure of HSP70-positive astrocytes to provide functional support to neuritic outgrowth.

Inactivation of the glial fibrillary acidic protein gene, but not that of vimentin, improves neuronal survival and neurite growth by modifying adhesion molecule expression

Intermediate filaments (IFs) are a major component of the cytoskeleton in astrocytes. Their role is far from being completely understood. Immature astrocytes play a major role in neuronal migration and neuritogenesis, and their IFs are mainly composed of vimentin. In mature differentiated astrocytes, vimentin is replaced by the IF protein glial fibrillary acidic protein (GFAP). In response to injury of the CNS in the adult, astrocytes become reactive, upregulate the expression of GFAP, and reexpress vimentin. These modifications contribute to the formation of a glial scar that is obstructive to axonal regeneration. Nevertheless, astrocytes in vitro are considered to be the ideal substratum for the growth of embryonic CNS axons. In the present study, we have examined the potential role of these two major IF proteins in both neuronal survival and neurite growth. For this purpose, we cocultured wild-type neurons on astrocytes from three types of knock-out (KO) mice for GFAP or/and vimentin in a neuron-astrocyte coculture model. We show that the double KO astrocytes present many features of immaturity and greatly improve survival and neurite growth of cocultured neurons by increasing cell-cell contact and secreting diffusible factors. Moreover, our data suggest that the absence of vimentin is not a key element in the permissivity of the mutant astrocytes. Finally, we show that only the absence of GFAP is associated with an increased expression of some extracellular matrix and adhesion molecules. To conclude, our results suggest that GFAP expression is able to modulate key biochemical properties of astrocytes that are implicated in their permissivity.

Astrocytes produce and release interleukin-1, interleukin-6, tumor necrosis factor alpha and interferon-gamma following traumatic and metabolic injury

The brain is no longer considered immune-privileged due to its capability of producing cytokines in response to neurotrauma; however, the cellular sources of cytokines have not been defined. This study focused on the production of four inflammatory cytokines, interleukin-1 (IL-1alpha), interleukin-6 (IL-6), tumor necrosis factor alpha (TNFalpha), and interferon gamma (IFN-gamma) in primary culture of astrocytes under two different injury models which simulated in vivo mechanical trauma (scratch injury) and ischemia. Results demonstrated that astrocytes after scratch injury were positively immunostained with IL-1alpha, IL-6, and TNFalpha. A slot-blot study of culture media showed that the release of IL-1alpha, IL-6, TNFalpha, and IFN-gamma by astrocytes subsequent to scratch and ischemic injury reached approximately twice the control values. The temporal expression of these cytokines was different for the two models. All four cytokines began to increase 1 h postscratch and remained at high levels throughout the experiment. In the ischemic model, however, the increase of cytokine expression was delayed until 4-8 h of ischemia, when sharp increases were seen in all four cytokines. In this culture system, the exogenous influence of blood-borne factors and leukocytes, which occur with in vivo trauma and ischemia, was eliminated. Accordingly, the cytokines detected in the culture media were derived from astrocytes. This study provides the first evidence that astrocytes, without the influence from other cell types, can produce and release cytokines following mechanical and ischemic injury.

Quercetin inhibits c-fos, heat shock protein, and glial fibrillary acidic protein expression in injured astrocytes

Quercetin, a bioflavonoid, is found widely in many kinds of fruits and vegetables. It is known to engage in many bioactivities, such as interfering with of the progress of stress responses to injury. In the present study, we investigated the effects of quercetin on some injury responses in primary cultures of astrocytes. These injury responses included the elevation of c-fos protein, heat shock protein (HSP70), and glial fibrillary acidic protein (GFAP). After heat shock insult, the levels of c-fos protein and HSP70 in astrocytes increased. With quercetin treatment, these proteins were significantly reduced. The inhibition of these injury responses by quercetin in astrocytes indicated a dose dependency, with the highest effect at 100 microM. We have previously established a scratch injury model in a primary culture of astrocytes. In that model, astrocytes responded to the scratch injury by an elevation in their GFAP level and formation of hypertrophic cell processes, which extend into the scratch areas. Quercetin treatment reduced the number of hypertrophic cell processes being extended into the scratch areas. With 100 microM of quercetin, there was a complete inhibition of the formation of the hypertrophic cell process. Western blot analysis for GFAP indicated that quercetin significantly reduced the induction of GFAP in the scratch model. At 100 microM, the total GFAP content in the injured cultures was reduced to a level lower than that of the control. This implied that quercetin might possess an antigliotic property.

Expression of vascular endothelial growth factor by reactive astrocytes and associated neoangiogenesis

Injury to the central nervous system (CNS) invokes a reparative response known as astrogliosis, characterized largely by hypertrophy, proliferation and increased expression of glial fibrillary acidic protein (GFAP), resulting in reactive astrocytosis. Based on our prior observation that peritumoral reactive astrocytes express Vascular Endothelial Growth Factor (VEGF), a highly potent and specific angiogenic growth factor, we have hypothesized that reactive astrocytosis also contributes to the neovascularization associated with astrogliosis. To evaluate this hypothesis we evaluated human surgical/autopsy specimens from a variety of CNS disorders that induce astrogliosis and an experimental CNS needle injury model in wild type and GFAP:Green Fluorescent Protein (GFP) transgenic mice. Using computer image semi-quantitative analysis we evaluated the number of GFAP-positive reactive astrocytes, degree of VEGF expression by these astrocytes, associated Factor VIII-positive microvascular density (MVD) and Ki-67 proliferating endothelial cells. The degree of reactive astrocytosis correlated to levels of VEGF immunoreactivity and MVD in the neuropathological specimens. The mouse-needle-stick brain injury model demonstrated this correlation was temporally and spatially related and maximal after 1 week. These results, involving both human pathology specimens augmented by experimental animal data, supports our hypothesis that the neoangiogenesis associated with reactive astrogliosis is correlated to increased reactive astrocytosis and associated VEGF expression.

Transient coexpression of nestin, GFAP, and vascular endothelial growth factor in mature reactive astroglia following neural grafting or brain wounds

The spatial and temporal immunoexpression of the intermediate filament (IF) protein nestin and its relationship to glial fibrillary acidic protein (GFAP), vascular endothelial growth factor (VEGF), and its receptor flt-1 (VEGF-R1) in reactive astroglia was examined following stab wounds or transplants of fetal CNS tissue into the adult brain. Since developmentally regulated proteins and gene transcripts can be reexpressed in reactive astroglia following certain brain injuries, we analyzed the nestin profile in these experimental paradigms in order to more fully understand the nature of the gliotic "scar." Nestin expression was transiently up-regulated in some but not all astrocytes which often had a different morphology than the typical stout, stellate GFAP (+) cells; the processes of the nestin (+) cells tended to be slender and elongated. In reactive astroglia from the mature brain, nestin expression was robust but generally localized to the wound or graft site, peaked at 7-10 days postoperative, and was absent by 28 days, whereas GFAP (+) astrocytes were far more widespread and persisted for many months. Only nestin was strongly expressed immediately adjacent to early stab wounds, whereas GFAP (+) cells were located further from the wound sites. In contrast, there was marked nestin/GFAP colocalization at the graft/host interface. Semiquantitative analysis combined with confocal microscopy revealed a unique compartmentalization of protein expression; processes from single astrocytes could be entirely nestin (+), GFAP (+), or could show coexpression. At 4, 7, and 14 days postoperative, 41, 58, and 32% of the immunoexpression, respectively, was accounted for by nestin at the graft/host interface, and it was essentially undetectable at 28 days postoperative. In situ hybridization studies showed nestin transcripts within GFAP (+) cells primarily between 4 and 10 days postoperative and absent by 28 days. Many nestin (+) astrocytes, as shown by electron microscopy, were closely related to the vasculature. Therefore we further examined the expression of vascular endothelial growth factor (VEGF), an endothelial cell mitogen associated with angiogenesis. Nestin colocalized with VEGF in some astrocytes (7%) but far more prominently with the VEGF flt-1 receptor (25%). Early astroglial activation may involve several different IF components and possibly a distinct astrocytic population that shows a rapid, transient nestin expression adjacent to injury sites. Expression of the nestin IF phenotype within affected astrocytes in the surgical vicinity may be indicative of a reversion to an immature phenotype that might be less susceptible to attendant hypoxia after injury. Since injured astrocytes are well known to express many bioactive compounds, such transient reexpression of early, developmentally regulated proteins may be a hallmark for the elaboration of growth factors such as VEGF.

Glial fibrillary acidic protein is necessary for mature astrocytes to react to beta-amyloid

Upregulation of the glial fibrillary acidic protein (GFAP) in astrocytes is a hallmark of the phenomenon known as reactive gliosis and, yet, the function of GFAP in this process is largely unknown. Our previous studies have shown that mature astrocytes react vigorously to substrate bound beta-amyloid protein (BAP) in a variety of ways (i.e., increased GFAP, enhanced motility, unusual aggregation patterns, inhibitory ECM production). In order to uncover which, if any, of these phenomena are causally related to the function of GFAP, primary cortical astrocytes from transgenic mice lacking GFAP were cultured on BAP substrates at low or high density and at various lengths of time following in vitro maturation. Differences between mutant and control cells became progressively more obvious when cells were matured in vitro for two weeks or longer and especially in cultures that were at high density. Mature control astrocytes show a dramatic response to BAP by aggregating into a meshwork of rope-like structures that completely bridge over the peptide surface. In marked contrast, mature GFAP-null astrocytes initiate the response much more slowly and had a much reduced ability to aggregate tightly. Furthermore, we prepared hippocampal slice cultures from GFAP-/- and GFAP+/+ mice and compared their astrocytic responses to injected BAP. GFAP-/- astrocytes of hippocampal slice cultures failed to form a barrier-like structure around the edge of the BAP deposit as did GFAP+/+ astrocytes. Our data suggest that GFAP may be essential for mature astrocytes to constrain certain types of highly inflammatory lesions in the brain.

Adenovirus-mediated suicide gene therapy in an in vitro model of reactive gliosis

Adenovirus-mediated herpes simplex thymidine kinase/ganciclovir (HSV-tk/GCV) system has been demonstrated to be efficient for the treatment of experimental brain tumors. However, no study has been directed to the elimination of proliferating cellular populations in other pathological conditions. In this study we used this suicide gene approach in a primary culture of astrocytes, as a model of reactive gliosis, in order to evaluate its efficiency as a therapeutic strategy for post-traumatic astrogliosis in vivo. First, we evaluated the peak of astrocytic proliferation to characterize our model. Second, the efficiency of adenovirus-mediated lacZ gene transfer is shown to be dependent on vector multiplicity of infection (MOI). As expected, the cells transfected with the HSV-tk gene showed an increase in sensibility to GCV compared with cells transfected with lacZ gene. Finally, an unexpected interaction between the adenoviral vector and bromodeoxyuridine (BrdU) or [3H]-Thymidine ([3H]-Thy) was evidenced in transfected cultures, whose interpretation is discussed. The present study demonstrates that a recombinant adenoviral vector carrying the tk gene confers to in vitro cultured astrocytes a cytotoxic sensibility to GCV, and that this system constitutes a potentially efficient tool to eliminate the hyperplasia of astrocytes following injury to the central nervous system in vivo.

Differential regulation of astrocytic mRNAs in the rat striatum after lesions of the cortex or substantia nigra

This study evaluates the time course of expression of three astrocytic mRNAs, glial fibrillary acidic protein (GFAP), apolipoprotein E (ApoE), and clusterin, in the rat striatum (ST) following a unilateral lesion of either the cortex (CX) or the substantia nigra (SN), using Northern blot and in situ hybridization analyses. We found that while there was a time-dependent increase in astrocytic GFAP mRNA in the deafferented ST following both the CX and the SN lesions, the time course of the response was different between the two lesion paradigms. Specifically, the increase in GFAP mRNA in striatal astrocytes after the SN lesion was rapid and transient returning to control levels by 10 days postlesion, while the response was long lasting and remained increased until at least 27 days after the CX lesion. In addition, the mRNA response for both ApoE and clusterin was differentially regulated in response to the two lesions. Specifically, both clusterin and ApoE mRNAs were rapidly increased in the ST following the CX lesion while both mRNAs remained unchanged following the SN lesion. Data from this study extend information derived from previous investigations on the multifunctional role of astrocytes in the response to brain injury. Specifically, our data support the notion that while the time course of the GFAP response in striatal astrocytes may vary between lesion paradigms, the upregulation of GFAP is part of a generalized response of reactive astrocytes to diverse brain injuries. By comparison, upregulation of the mRNAs for the lipoproteins clusterin and ApoE are lesion specific and may play a role in the transport of recycled myelin lipids from dying axons to actively growing axons and dendrites in reactive synaptogenesis.

Neuritic outgrowth associated with astroglial phenotypic changes induced by antisense glial fibrillary acidic protein (GFAP) mRNA in injured neuron-astrocyte cocultures

In the adult CNS, axons fail to regenerate after injury. Among the cell interactions that lead to this failure are those developed with astrocytes. In an effort to elucidate the mechanisms underlying these negative interactions, we have used astrocytes treated with antisense glial fibrillary acidic protein (GFAP) mRNA to inhibit the formation of gliofilaments, indispensable for the astroglial morphological response to injury, and have studied their permissivity for neuritic outgrowth. In a neuron-astrocyte coculture, a mechanical lesion led to hypertrophy of astrocytes neighboring the lesion. Neuronal cell bodies and neurites were absent both from the area of lesion and from its surroundings. Reactive astrocytes appeared, therefore, to be a nonpermissive substrate. Transfection that used antisense GFAP mRNA blocked astroglial morphological changes and was characterized by both a persistence of neuronal cell bodies in the vicinity of the lesion site and a growth of neurites into the same region. These morphological differences were associated with a 46% decrease in the GFAP translation capacity and a 50% increase in the concentration of GAP-43 in the treated cultures. Neurons were associated mainly with an extracellular laminin network, which was predominant at the lesion site in treated cocultures. In contrast, those astrocytes highly laminin-immunoreactive appeared to be a nonpermissive substrate for neurons. These results show that inhibition in GFAP synthesis, leading to a reduction of astroglial hypertrophy, relieves the blockade of neuritic outgrowth that normally is observed after a lesion. The mechanisms may involve changes in the secretion of extracellular matrix molecules by astrocytes.

Astrocytoma and Schwann cells in coculture

Glial fibrillary acidic protein (GFAP) is the principal intermediate filament protein found in mature astrocytes. Although the exact function of GFAP is poorly understood, it is presumed to stabilize the astrocyte's cytoskeleton and help in maintaining cell shape. Previous studies from our laboratory have shown that when astrocytes were cocultured with primary Schwann cells (pSCs), astrocytes became hypertrophied and fibrous with intensely positive GFAP staining and segregated Schwann cells (SCs) into pockets. In order to understand the functional role of GFAP in this already established astrocyte-SC coculture model, we generated GFAP-negative cell lines from a GFAP-positive astrocytoma cell line and cocultured both the cell lines with pSCs. Our studies demonstrate that the GFAP-positive cell line put out processes toward the SCs, whereas the GFAP-negative cells did not form processes and the majority of the cells remained round. The most significant and interesting finding of this study, however, is the formation of elaborate processes by SCs when grown in coculture with the astrocytoma cells, unlike SCs cultured alone, which showed their typical bipolar spindle-shaped morphology. The extent of processes did not seem to be dependent of GFAP, since SCs cultured with both the cell lines formed similar processes. This coculture model may be useful in elucidating the factor(s) responsible for the formation of processes by SCs and can be further help in our understanding of the mechanism of morphological transformation of SCs.

Astrocyte-astrocytoma cell line interactions in culture

Astrocytomas are the most common brain tumors arising in the CNS and account for 65% of all primary brain tumors. Astrocytes have been shown to have the highest predisposition to malignant transformation compared to any other CNS cell type. The majority of astrocytomas are histologically malignant neoplasm. Previous studies have shown that resident astrocytes are the first cell type to react to tumors and surround them. However, the role of these astrocytes in tumor formation and progression has not been determined. In the present study, we have co-cultured astrocytes with a permanent cell line S635c15 (derived from anaplastic astrocytoma) in order to understand the cellular interactions between astrocytes and astrocytoma cells. Our studies demonstrate that astrocytes in contact with the tumor cells become reactive and fibrous with an increase in glial fibrillary acidic protein (GFAP) immunoreactivity as early as 4 days in culture. By 8 days, astrocytes formed glial boundaries around the tumor cells which grew as round colonies. The astrocytic processes surrounding the tumor cells were also intensely GFAP positive. Since the behavior of these cells observed in culture is very similar to their interaction seen in vivo, this co-culture system may serve as an in vitro model for astrocyte and astrocytoma cell line interaction and aid in our understanding of the molecular and cellular mechanisms during early stages of tumor formation and cell interactions.

Inflammation in EAE: role of chemokine/cytokine expression by resident and infiltrating cells

Experimental allergic encephalomyelitis (EAE) is an inflammatory demyelinating disease of the central nervous system (CNS) which has many clinical and pathological features in common with multiple sclerosis (MS). Comparison of the histopathology of EAE and MS reveals a close similarity suggesting that these two diseases share common pathogenetic mechanisms. Immunologic processes are widely accepted to contribute to the initiation and continuation of the diseases and recent studies have indicated that microglia, astrocytes and the infiltrating immune cells have separate roles in the pathogenesis of the MS lesion. The role of cytokines as important regulatory elements in these immune processes has been well established in EAE and the presence of cytokines in cells at the edge of MS lesions has also been observed. However, the role of chemokines in the initial inflammatory process as well as in the unique demyelinating event associated with MS and EAE has only recently been examined. A few studies have detected the transient presence of selected chemokines at the earliest sign of leukocyte infiltration of CNS tissue and have suggested astrocytes as their cellular source. Based on these studies, chemokines have been postulated as a promising target for future therapy of CNS inflammation. This review summarized the events that occur during the inflammatory process in EAE and discusses the roles of cytokine and chemokine expression by the resident and infiltrating cells participating in the process.

Microglial responses to focal lesions of the rabbit retina: correlation with neural and macroglial reactions

There is a very wide spread Müller glial response to focal laser photocoagulation lesions in the rabbit retina. In this study we have described the microglial response to similar lesions and compared this with the Müller and retinal ganglion cell responses. Microglia were labelled using nucleoside di-phosphatase histochemistry in adult rabbit retinal wholemounts and compared with axonal and Müller cell responses as shown respectively by neurofilament and GFAP immunohistochemistry. In the normal retina, microglia were located in the nerve fibre layer (NFL), inner plexiform layer (IPL), and sparsely in the outer plexiform layer (OPL). Following laser photocoagulation each layer reacted differently. The NFL reaction was exclusively associated with axonal degeneration, as shown by abnormal neurofilament label, and therefore only started several days after injury. In the IPL, neighbouring microglial cells directed their processes towards the lesion by 2 h and had migrated into the lesion by 6 h, but the reaction did not extend more than 2-3 cell diameters from the lesion and was over by 7 days. In the OPL the cell density increased by 1-2 days over a few millimeters from the lesion. The Müller cells expressed GFAP for several millimeters from the lesion starting at 24 h and persisting for over one month and therefore the correlation with the microglial reaction was poor. The different reaction in each retinal layer is evidence that microglial responses are modulated by local factors, probably mainly by contact with injured retinal elements as well as diffusable factors.

Increased cerebrospinal fluid levels of glial fibrillary acidic protein (GFAp) in Lyme neuroborreliosis

Glial fibrillary acidic protein (GFAp), the main protein constituent of the intermediate filaments of astrocytes, was analysed in the cerebrospinal fluid (CSF) of 20 patients with Lyme neuroborreliosis as a marker of the astroglial reaction. The mean GFAp level before antibiotic treatment in the study group was significantly elevated (592 pg/ml +/- 596 [SD]) compared to that in 24 healthy controls (121 +/- 87 [SD]) (p < 0.01). The highest CSF-GFAp levels were seen in the patients with the most severe disease, but the levels were also increased in patients with peripheral paresis, such as facial palsy with no or only minor encephalitic symptoms. This implies that the infection was not limited to radix dorsalis or the meningeal tissues, but affected the central nervous system as well. Furthermore, the astroglial reaction seemed to occur early in Lyme neuroborreliosis since CSF-GFAp levels were elevated also in patients with recent (< 3 weeks) onset of disease. After antibiotic treatment, the GFAp levels decreased. It is suggested the CSF-GFAp concentrations might be useful for monitoring CNS involvement in Lyme neuroborreliosis.

Liposomal delivery of oligodeoxynucleotides

We have previously demonstrated that liposome-incorporated methylphosphonate antisense oligodeoxynucleotides (oligos) specific for BCR-ABL can selectively inhibit the expression of p210Bcr-Abl protein and the proliferation of chronic myelogenous leukemia cells in vitro. Here, we show that liposome-entrapment of phosphodiester and phosphorothioate oligos specific for BCR-ABL can also selectively inhibit the proliferation of chronic myelogenous leukemia cells. We have studied the intracellular localization of liposomes by fluorescent microscopy and found that liposomes are readily taken up by leukemic cells and are localized in the cytoplasm, allowing increased access of oligos to target cells intracellularly. Liposomal oligos are not toxic to peripheral blood mononuclear cells nor to bone marrow progenitors isolated from normal hematological donors. These studies strongly suggest that liposomal delivery of oligos may indeed circumvent the major limitations that preclude the clinical development of antisense oligos.

The principles of gene therapy for the nervous system

Research pertaining to gene transfer into cells of the nervous system is one of the fastest growing fields in neuroscience. An important application of gene transfer is gene therapy, which is based on introducing therapeutic genes into cells of the nervous system by ex vivo or in vivo techniques. With the eventual development of efficient and safe vectors, therapeutic genes, under the control of a suitable promoter, can be targeted to the appropriate neurons or glial cells. Gene therapy is not only applicable to the treatment of genetic diseases of the nervous system and the control of malignant neoplasia, but it also has therapeutic potential for acquired degenerative encephalopathies (Alzheimer's disease, Parkinson's disease), as well as for promoting neuronal survival and regeneration in various pathological states.

Molecular biology of CNS injury

Traumatic or ischemic injuries to the central nervous system (CNS) initiate reactive biochemical changes, some of which are autodestructive and others neuroprotective. Identification of these endogenous factors and their regulation will help to clarify mechanisms of secondary tissue damage and may lead to novel therapies. Recently developed molecular approaches offer opportunities for identifying genes involved in these reactive processes. Three types of molecular strategies are reviewed and examples are provided to demonstrate how each may be applied to elucidate basic mechanisms underlying posttraumatic or postischemic death.

Decrease of NCAM expression and astrocyte-neurone interaction in long-term cultured astrocytes

In order to assess the characteristics of the older astrocyte, we obtained long-term cultured rat astrocytes (20 months) and examined the features of protein expression in relation to neuronal interaction. In short-term cultured astrocytes, NCAM expressed strongly in contrast to weak expression of laminin by both immunocytochemical and ELISA assay. On the contrary, in long-term cultured astrocytes, a marked decrease of NCAM expression was observed along with increased laminin expression compared with short-term cultured astrocytes. The long-term cultured astrocytes remained positive to anti-GFAP antibody and showed a much lower ability to interact with neurones than the short-term cultured astrocytes. NCAM may be one of the responsible molecules related to the astrocyte-neurone interaction in the developing and ageing nervous system.

Astrocyte-Schwann cell interactions in culture

After injury, either as a result of trauma or degenerating/demyelinating diseases, axons of the central nervous system (CNS) normally fail to regenerate. Transplantation of glial cells, particularly Schwann cells, into areas of injury or demyelination has been considered a promising approach to promote recovery. However, the extent of Schwann cell interaction with CNS axons is greatly influenced by the presence of astrocytes which redefine the CNS-PNS (peripheral nervous system) boundary in a lesioned CNS, thereby preventing invasion of Schwann cells. The molecular basis for this restrictive effect of astrocytes on Schwann cells is not known. In the present study, we have cocultured astrocytes and Schwann cells to develop an in vitro model to characterize this interaction. Astrocytes in contact with Schwann cells appeared hypertrophied and showed increased staining for glial fibrillary acidic protein (GFAP). In cocultures maintained for 2-3 weeks, segregation of the two cell types was observed, Schwann cells appeared in groups, and each group was surrounded and separated from one another by astrocytic processes. Since the behavior of these two cell types observed in culture is very similar to their interaction seen in vivo, this coculture model may be useful in further studying the relationship between astrocytes and Schwann cells.

GFAP and astrogliosis

One of the most remarkable characteristics of astrocytes is their vigorous response to diverse neurologic insults, a feature that is well conserved across a variety of different species. The astroglial response occurs rapidly and can be detected within one hour of a focal mechanical trauma (Mucke et al., 1991). Prominent reactive astrogliosis is seen; in AIDS dementia; a variety of other viral infections; prion associated spongiform encephalopathies; inflammatory demyelinating diseases; acute traumatic brain injury; neurodegenerative diseases such as Alzheimer's disease. The prominence of astroglial reactions in various diseases, the rapidity of the astroglial response and the evolutionary conservation of reactive astrogliosis indicate that reactive astrocytes fulfill important functions of the central nervous system (CNS). Yet, the exact role reactive astrocytes play in the injured CNS has so far remained elusive. This chapter summaries the various experimental models and diseases that exhibit astrogliosis and increase in glial fibrillary acidic protein (GFAP). Recent in vitro studies to inhibit GFAP synthesis are also presented.