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

Proteomics-determined differences in the concanavalin-A-fractionated proteome of hippocampus and inferior parietal lobule in subjects with Alzheimer's disease and mild cognitive impairment: implications for progression of AD

Alzheimer's disease (AD) is the most common type of dementia, comprising 60-80% of all reported cases, and currently affects 5.2 million Americans. AD is characterized pathologically by the accumulation of senile plaques (SPs), neurofibrillary tangles (NFTs), and synapse loss. The early stages of memory loss associated with AD have been studied in a condition known as amnestic mild cognitive impairment (MCI), arguably the earliest form of AD. In spite of extensive research across a variety of disciplines, the cause of AD remains elusive. Proteomics techniques have helped to advance knowledge about AD by identifying irregularities in protein expression and post-translational modifications (PTMs) in AD brain. Glycosylation is a less studied PTM with regards to AD and MCI. This PTM is important to study because glycosylation is involved in proper protein folding, protein anchoring to cell membranes, and the delivery of proteins to organelles, and these processes are impaired in AD. Concanavalin-A (Con-A) binds to N-linked glycoproteins, but hydrophobic sites on nonglycoproteins are also known to bind Con-A. To our knowledge, the present study is the first to examine Con-A-associated brain proteins in MCI and AD with focus on the hippocampus and inferior parietal lobule (IPL) brain regions. Proteins found in AD hippocampus with altered levels are glutamate dehydrogenase (GDH), glial fibrillary acidic protein (GFAP), tropomyosin 3 (TPM3), Rab GDP-dissociation inhibitor XAP-4 (XAP4), and heat shock protein 90 (HSP90). Proteins found with altered levels in AD IPL are alpha-enolase, gamma-enolase, and XAP-4. MCI hippocampal proteins with altered levels are dihydropyrimidase-2 (DRP2), glucose-regulated protein 78 (GRP-78), protein phosphatase related protein Sds-22 (Sds22), and GFAP and the only protein found with altered levels in MCI IPL was beta-synuclein. These results are discussed with reference to biochemical and pathological alterations in and progression of AD.

Involvement of brain-derived neurotrophic factor in time-dependent neurodegeneration in the murine superior colliculus after intravitreal injection of N-methyl-D-aspartate

PURPOSE

To clarify the effects on the visual pathway that occur following retinal damage, we examined the morphological alterations present in the superior colliculus (SC) after N-methyl-D-aspartate (NMDA)-induced retinal damage in mice.

METHODS

NMDA was injected into the vitreous body of the left eye in mice to induce retinal damage. The time-dependent neuronal degeneration in the SC was assessed using immunohistochemistry.

RESULTS

The number of neuronal nuclear specific protein (NeuN)-immunostained neurons showed a significant decrease in the contralateral SC at both 90 and 180 days after intravitreal NMDA injection. In contrast, the ipsilateral SC displayed no significant change in the number of NeuN-positive cells. An increase in glial fibrillary acid protein (GFAP) immunoreactivity was observed in the contralateral SC at 7, 30, and 90 days after NMDA injection and in the ipsilateral SC at 7 days, while brain-derived neurotrophic factor (BDNF) expression was increased in the contralateral SC at 30 and 90 days. In the contralateral SC, some GFAP-positive astroglial cells also exhibited BDNF at 30 days after NMDA injection.

CONCLUSIONS

Evidence of time-dependent morphological neuronal degeneration along the retinocollicular pathway from the retina to the SC was detected at 90 and 180 days, but not at 30 days, after NMDA-induced retinal damage. This neurodegeneration was preceded by an increase in BDNF expression in the SC, specifically at 30 and 90 days after NMDA injection. Hence, these findings may provide useful information concerning the pathological mechanisms of several disorders accompanied by retinal degeneration.

Interleukin-4 as a neuromodulatory cytokine: roles and signaling in the nervous system

Although interleukin (IL)-4 is described as a prototypical anti-inflammatory cytokine, in recent years its role as a neuromodulatory cytokine has been extensively discussed. This review highlights the pivotal contributions of IL-4 during the development and normal physiology of neural cells as well as IL-4 connections with the pathophysiology of degenerative or inflammatory processes observed in the central and peripheral nervous system.

Ceramide and neurodegeneration: susceptibility of neurons and oligodendrocytes to cell damage and death

Neurodegenerative disorders are marked by extensive neuronal apoptosis and gliosis. Although several apoptosis-inducing agents have been described, understanding of the regulatory mechanisms underlying modes of cell death is incomplete. A major breakthrough in delineation of the mechanism of cell death came from elucidation of the sphingomyelin (SM)-ceramide pathway that has received worldwide attention in recent years. The SM pathway induces apoptosis, differentiation, proliferation, and growth arrest depending upon cell and receptor types, and on downstream targets. Sphingomyelin, a plasma membrane constituent, is abundant in mammalian nervous system, and ceramide, its primary catabolic product released by activation of either neutral or acidic sphingomyelinase, serves as a potential lipid second messenger or mediator molecule modulating diverse cellular signaling pathways. Neutral sphingomyelinase (NSMase) is a key enzyme in the regulated activation of the SM cycle and is particularly sensitive to oxidative stress. In a context of increasing clarification of the mechanisms of neurodegeneration, we thought that it would be useful to review details of recent findings that we and others have made concerning different pro-apoptotic neurotoxins including proinflammatory cytokines, hypoxia-induced SM hydrolysis and ceramide production that induce cell death in human primary neurons and primary oligodendrocytes: redox sensitive events. What has and is emerging is a vista of therapeutically important ceramide regulation affecting a variety of different neurodegenerative and neuroinflammatory disorders.

Strategies for retinal repair: cell replacement and regeneration

The retina, like most other regions of the central nervous system, is subject to degeneration from both genetic and acquired causes. Once the photoreceptors or inner retinal neurons have degenerated, they are not spontaneously replaced in mammals. In this review, we provide an overview of retinal development and regeneration with emphasis on endogenous repair and replacement seen in lower vertebrates and recent work on induced mammalian retinal regeneration from Müller glia. Additionally, recent studies demonstrating the potential for cellular replacement using postmitotic photoreceptors and embryonic stem cells are also reviewed.

Effects of P2Y1 receptor on glial fibrillary acidic protein and glial cell line-derived neurotrophic factor production of astrocytes under ischemic condition and the related signaling pathways

OBJECTIVE

The present study aimed to explore the role of P2Y(1) receptor in glial fibrillary acidic protein (GFAP) production and glial cell line-derived neurotrophic factor (GDNF) secretion of astrocytes under ischemic insult and the related signaling pathways.

METHODS

Using transient right middle cerebral artery occlusion (tMCAO) and oxygen-glucose-serum deprivation for 2 h as the model of ischemic injury in vivo and in vitro, immunofluorescence, quantitative real-time reverse transcription-polymerase chain reaction (RT-PCR), Western blotting, enzyme linked immunosorbent assay (ELISA) were used to investigate location of P2Y(1) receptor and GDNF, the expression of GFAP and GDNF, and the changes of signaling molecules.

RESULTS

Blockage of P2Y(1) receptor with the selective antagonist N(6)-methyl-2'-deoxyadenosine 3',5'-bisphosphate diammonium (MRS2179) reduced GFAP production and increased GDNF production in the antagonist group as compared with simple ischemic group both in vivo and in vitro. Oxygen-glucose-serum deprivation and blockage of P2Y(1) receptor caused elevation of phosphorylated Akt and cAMP response element binding protein (CREB), and reduction of phosphorylated Janus kinase2 (JAK2) and signal transducer and activator of transcription3 (STAT3, Ser727). After blockage of P2Y(1) receptor and deprivation of oxygen-glucose-serum, AG490 (inhibitor of JAK2) reduced phosphorylation of STAT3 (Ser727) as well as expression of GFAP; LY294002, an inhibitor of phosphatidylinositol 3-kinase (PI3-K), decreased phosphorylation of Akt and CREB; the inhibitor of mitogen-activated protein kinase kinase1/2 (MEK1/2) U0126, an important molecule of Ras/extracellular signal-regulated kinase (ERK) signaling pathway, decreased the phosphorylation of JAK2, STAT3 (Ser727), Akt and CREB.

CONCLUSION

These results suggest that P2Y(1) receptor plays a role in the production of GFAP and GDNF in astrocytes under transient ischemic condition and the related signaling pathways may be JAK2/STAT3 and PI3-K/Akt/CREB, respectively, and that crosstalk probably exists between them.

LAU-0901, a novel platelet-activating factor receptor antagonist, confers enduring neuroprotection in experimental focal cerebral ischemia in the rat

LAU-0901, a novel platelet-activating factor (PAF) receptor antagonist, is highly neuroprotective in a rodent model of cerebral ischemia. This study was conducted to establish whether the neuroprotection induced by LAU-0901 persists with chronic survival. Male Sprague-Dawley rats were anesthetized with isoflurane and subjected to 2 h of temporary middle cerebral artery occlusion (MCAo) induced by means of a poly-L-lisine-coated intraluminal nylon suture. Animals were treated with either LAU-0901 (60 mg/kg) or vehicle (45% cyclodextran) administered i.p. at 2 h from onset of MCAo. They received neurobehavioral examinations during MCAo (60 min) and then at 1, 2, 3, 7, 14, 21 and 28 days followed by histopathology at 30 days. LAU-0901 significantly improved the behavior compared to the vehicle group, beginning on day 1 (by 29%, p=0.00007) and persisting throughout a 30-day survival period (42%, p=0.0001). Compared with vehicle treatment, LAU-0901 treatment significantly increased volume of non-infarcted brain tissue loss relative to the unlesioned hemisphere (16.3 +/- 4.6% vs. 46.0 +/- 10.3%, respectively). These results establish that LAU-0901 confers enduring ischemic neuroprotection.

Activated microglia modulate astroglial enzymes involved in oxidative and inflammatory stress and increase the resistance of astrocytes to oxidative stress in vitro

Neuropathological processes in the central nervous system are commonly accompanied by an activation of microglia and astrocytes. The involvement of both cell populations in the onset and progress of neurological disorders has been widely documented, implicating both beneficial and detrimental influences on the neural tissue. Nevertheless, little is known about the interplay of these glial cell populations, especially under diseased conditions. To examine the effects of activated microglia on astrocytes purified rat astroglial cell cultures were treated with medium conditioned by purified quiescent (MCM[-]) or lipopolysaccharide (LPS)-activated rat microglia (MCM[+]) and subjected to a comparative proteome analysis based on two-dimensional gel electrophoresis. No significant down regulation of proteins was observed. The majority of the 19 proteins identified by means of nano HPLC/ESI-MS/MS in the 12 most prominent protein spots significantly overexpressed (> or =2-fold) in MCM[+] treated astrocytes are involved in inflammatory processes and oxidative stress response: superoxide dismutases (Sod), peroxiredoxins, glutathione S-transferases (Gst), nucleoside diphosphate kinase B, argininosuccinate synthase (Ass), and cellular retinol-binding protein I (Rbp1). Sod2, Rbp1, Gstp1, and Ass were also significantly increased on the mRNA level determined by quantitative RT-PCR. The upregulation of antioxidative enzymes in astrocytes was accompanied by a higher resistance to oxidative stress induced by H2O2. These results show that activated microglia change the expression of antioxidative proteins in astrocytes and protect them against oxidative stress, which might be an effective way to increase the neuroprotective potential of astrocytes under pathological conditions associated with oxidative stress and inflammation.

Further preliminary assessment of three human glioma cell lines as models of human astrocytic toxicity in vitro

Three human astroglioma lines U251-MG, U373-MG and CCF-STTG1 have been evaluated further as possible models for astrocytotoxicity (GFAP and IL-6 release). The effects of bacterial lipopolysaccharide, chloroquine diphosphate and acrylamide were studied on GFAP expression and LPS, chloroquine diphosphate, ethanol, trimethyltin chloride (TMTC) and acrylamide were examined on interleukin-6 (IL-6) release in the U373-MG line only. At 4-h LPS elevated GFAP (17.0±5.0% P<0.05) above control in the U251-MG cell line only. Chloroquine diphosphate over 4h in the U251-MG line resulted in an increase in GFAP-IR to 20.3±4.2% and 21.1±4.1% above control levels 0.1μM (P<0.05) and 1μM (P<0.05) respectively. CQD was associated with decreases in MTT turnover, particularly after 24h incubation. With the U373-MG line, LPS (0.5μg/ml) increased IL-6 expression 640% above control (P<0.001), whilst chloroquine diphosphate (100μM), ethanol (10mM) and TMTC chloride (1μM) also increased IL-6. It is possible that batteries of astrocytic human glioma cell lines may be applicable to the sensitive evaluation of toxicants on astrogliotic expression markers such as GFAP and IL-6.

Targeted activation of astrocytes: a potential neuroprotective strategy

Astrocytes are involved in many key physiological processes in the brain, including glutamatergic transmission, energy metabolism, and blood flow control. They become reactive in response to pathological situations, a response that involves well-described morphological alterations and less characterized functional changes. The functional consequences of astrocyte reactivity seem to depend on the molecular pathway involved and may result in the enhancement of several neuroprotective and neurotrophic functions. We propose that a selective and controlled activation of astrocytes may switch these highly pleiotropic cells into therapeutic agents to promote neuron survival and recovery. This may represent a potent therapeutic strategy for many brain diseases in which neurons would benefit from an increased support from activated astrocytes.

Bioinformatic and statistical analysis of the optic nerve head in a primate model of ocular hypertension

BACKGROUND

The nonhuman primate model of glaucomatous optic neuropathy most faithfully reproduces the human disease. We used high-density oligonucleotide arrays to investigate whole genome transcriptional changes occurring at the optic nerve head during primate experimental glaucoma.

RESULTS

Laser scarification of the trabecular meshwork of cynomolgus macaques produced elevated intraocular pressure that was monitored over time and led to varying degrees of damage in different samples. The macaques were examined clinically before enucleation and the myelinated optic nerves were processed post-mortem to determine the degree of neuronal loss. Global gene expression was examined in dissected optic nerve heads with Affymetrix GeneChip microarrays. We validated a subset of differentially expressed genes using qRT-PCR, immunohistochemistry, and immuno-enriched astrocytes from healthy and glaucomatous human donors. These genes have previously defined roles in axonal outgrowth, immune response, cell motility, neuroprotection, and extracellular matrix remodeling.

CONCLUSION

Our findings show that glaucoma is associated with increased expression of genes that mediate axonal outgrowth, immune response, cell motility, neuroprotection, and ECM remodeling. These studies also reveal that, as glaucoma progresses, retinal ganglion cell axons may make a regenerative attempt to restore lost nerve cell contact.

Interleukin-1beta-dependent signaling between astrocytes and neurons depends critically on astrocytic calcineurin/NFAT activity

Interleukin-1beta (IL-1beta) and the Ca(2+)/calmodulin-dependent protein phosphatase, calcineurin, have each been shown to play an important role in neuroinflammation. However, whether these signaling molecules interact to coordinate immune/inflammatory processes and neurodegeneration has not been investigated. Here, we show that exogenous application of IL-1beta (10 ng/ml) recruited calcineurin/NFAT (nuclear factor of activated T cells) activation in primary astrocyte-enriched cultures within minutes, through a pathway involving IL-1 receptors and L-type Ca(2+) channels. Adenovirus-mediated delivery of the NFAT inhibitor, VIVIT, suppressed the IL-1beta-dependent induction of several inflammatory mediators and/or markers of astrocyte activation, including tumor necrosis factor alpha, granulocyte/macrophage colony-stimulating factor, and vimentin. Expression of an activated form of calcineurin in one set of astrocyte cultures also triggered the release of factors that, in turn, stimulated NFAT activity in a second set of "naive" astrocytes. This effect was prevented when calcineurin-expressing cultures co-expressed VIVIT, suggesting that the calcineurin/NFAT pathway coordinates positive feedback signaling between astrocytes. In the presence of astrocytes and neurons, 48-h delivery of IL-1beta was associated with several excitotoxic effects, including NMDA receptor-dependent neuronal death, elevated extracellular glutamate, and hyperexcitable synaptic activity. Each of these effects were reversed or ameliorated by targeted delivery of VIVIT to astrocytes. IL-1beta also caused an NFAT-dependent reduction in excitatory amino acid transporter levels, indicating a possible mechanism for IL-1beta-mediated excitotoxicity. Taken together, the results have potentially important implications for the propagation and maintenance of neuroinflammatory signaling processes associated with many neurodegenerative conditions and diseases.

Astrocytic and microglial response and histopathological changes in the brain of horses with experimental chronic Trypanosoma evansi infection

This study aimed to characterize astrocytic and microglial response in the central nervous system (CNS) of equines experimentally infected with T. evansi. The experimental group comprised males and females with various degrees of crossbreeding, ages between four and seven years. The animals were inoculated intravenously with 10(6) trypomastigotes of T. evansi originally isolated from a naturally infected dog. All equines inoculated with T. evansi were observed until they presented symptoms of CNS disturbance, characterized by motor incoordination of the pelvic limbs, which occurred 67 days after inoculation (DAI) and 124 DAI. The animals in the control group did not present any clinical symptom and were observed up to the 125th DAI. For this purpose the HE histochemical stain and the avidin biotin peroxidase method was used. Lesions in the CNS of experimentally infected horses were those of a wide spread non suppurative meningoencephalomyelitis.The severity of lesions varied in different parts of the nervous system, reflecting an irregular distribution of inflammatory vascular changes. The infiltration of mononuclear cells was associated with anisomorphic gliosis and reactive microglia was identified. The intensity of the astrocytic response in the CNS of the equines infected by T. evansi characterizes the importance of the performance of these cells in this trypanosomiasis. The characteristic gliosis observed in the animals in this experiment suggests the ability of these cells as mediators of immune response. The parasite, T. evansi, was not identified in the nervous tissues.

Isoflurane preconditioning reduces mouse microglial activation and injury induced by lipopolysaccharide and interferon-gamma

Activation and injury of microglial cells are involved in a broad range of brain diseases including stroke, brain infection and neurodegenerative diseases. However, there is very little information regarding how to reduce microglial reaction and preserve these cells to provide neuroprotection. Here, we showed that the incubation of C8-B4 mouse microglial cells with lipopolysaccharide (LPS) plus interferon-gamma (IFNgamma) for 24 h decreased the viability of these cells. Pretreatment of these cells with 1%, 2% or 3% isoflurane, a commonly used volatile anesthetic, for 1 h at 30 min before the exposure to LPS plus IFNgamma attenuated the reduction of cell viability (preconditioning effect). LPS plus IFNgamma also activated these microglial cells to express inducible nitric oxide synthase (iNOS) and to induce accumulation of nitrite, a stable oxidation product of nitric oxide, in the incubation medium. Isoflurane preconditioning attenuated these LPS plus IFNgamma effects on the iNOS expression and nitrite accumulation. Aminoguanidine, an iNOS inhibitor, attenuated the LPS plus IFNgamma-induced glutamate release and decrease of microglial viability. Isoflurane preconditioning also reduced LPS plus IFNgamma-induced glutamate release. Exogenous glutamate decreased microglial viability. Finally, the isoflurane preconditioning-induced protection was abolished by chelerythrine, a protein kinase C inhibitor. These results suggest that LPS plus IFNgamma activates the iNOS-nitric oxide-glutamate pathway to induce microglial injury and that this activation is attenuated by isoflurane preconditioning. Protein kinase C may be involved in the isoflurane preconditioning effects.

Increased expression of the gamma-secretase components presenilin-1 and nicastrin in activated astrocytes and microglia following traumatic brain injury

Gamma-secretase is an aspartyl protease composed of four proteins: presenilin (PS), nicastrin (Nct), APH1, and PEN2. These proteins assemble into a membrane complex that cleaves a variety of substrates within the transmembrane domain. The gamma-secretase cleavage products play an important role in various biological processes such as embryonic development and Alzheimer's disease (AD). The major role of gamma-secretase in brain pathology has been linked to AD and to the production of the amyloid beta-peptide. However, little is known about the possible role of gamma-secretase following acute brain insult. Here we examined by immunostaining the expression patterns of two gamma-secretase components, PS1 and Nct, in three paradigms of brain insult in mice: closed head injury, intracerebroventricular injection of LPS, and brain stabbing. Our results show that in naïve and sham-injured brains expression of PS1 and Nct is restricted mainly to neurons. However, following insult, the expression of both proteins is also observed in nonneuronal cells, consisting of activated astrocytes and microglia. Furthermore, the proteins are coexpressed within the same astrocytes and microglia, implying that these cells exhibit an enhanced gamma-secretase activity following brain damage. In view of the important role played by astrocytes and microglia in brain disorders, our findings suggest that gamma-secretase may participate in brain damage and repair processes by regulating astrocyte and microglia activation and/or function.

The postoperative brain tumour stem cell (BTSC) niche and cancer recurrence

Currently, surgical resection is one of only a few options for treating brain cancer. Unfortunately, postoperative tumour recurrence remains almost inevitable despite additional radiation or chemotherapy treatment following resection. Clinical observations and a growing body of experimental evidence have led to speculation that there is a population of persistent brain tumour stem cells (BTSCs)--or brain tumour initiating cells--that are difficult to completely remove surgically. Furthermore, residual BTSCs following surgery may actually be more resistant to subsequent radiation and/or chemotherapies. It remains to be determined if brain surgeries render the postoperative tissue microenvironment more favourable for the survival and growth of BTSCs, and therefore the recurrence of brain tumours.We hypothesise that BTSC-based tumour recurrence may develop within a specific niche of the aberrant tumour microenvironment. Even when the gross appearance of the primary tumour seems confined, BTSCs (albeit accounting only for a small population of tumour cells) may microscopically enter the stroma, hampering curative surgeries. This article discusses the theory that surgical resection of brain tumours generates niches recruiting BTSCs to the surgical wounds, stimulating the proliferation and invasiveness of BTSCs, and leading to tumour recurrence. Postoperative brains are marked with active wound repair in peritumoural margins, which is likely to be accompanied by increased inflammatory paracrine production, angiogenesis and reactive astrogliosis. The postoperative BTSC niche concept is consistent with the observation that brain tumour recurrence usually occurs in tissues that are proximal to the resection margin. In this article, we intend to reflect recent advances that may lead to novel strategies to eliminate postoperative brain tumour recurrence.

Spatiotemporal expression of Dexras1 after spinal cord transection in rats

Dexras1, a brain-enriched member of the Ras subfamily of GTPases, as a novel physiologic nitric oxide (NO) effector, anchor neuronal nitric oxide synthase (nNOS) that increased after spinal cord injury (SCI), to specific targets to enhance NO signaling, and is strongly and rapidly induced during treatment with dexamethasone. It is unknown how the central nervous system (CNS) trauma affects the expression of Dexras1. Here we used spinal cord transection (SCT) model to detect expression of Dexras1 at mRNA and protein level in spinal cord homogenates by real-time PCR and Western blot analysis. The results showed that Dexras1 mRNA upregulated at 3 day, 5 day, and 7 day significantly (P < 0.05) that was consistent with the protein level except at 7 day. Immunofluorescence revealed that both neurons and glial cells showed Dexras1 immunoreactivivty (IR) around SCT site, but the proportion is different. Importantly, injury-induced expression of Dexras1 was co-labeled by caspase-3 (apoptotic marker) and Tau-1 (marker for pathological oligodendrocyte). Furthermore, colocalization of Dexras1, carboxy-terminal PSD95/DLG/ZO-1 (PDZ) ligand of nNOS (CAPON) and nNOS was observed in neurons and glial cells, supporting the existence of ternary complexes in this model. Thus, the results that the transient high expression of Dexras1 which localized in apoptotic neurons and pathological oligodendrocytes might provide new insight into the secondary response after SCT.

Endothelins stimulate the production of stromelysin-1 in cultured rat astrocytes

The effects of endothelins (ETs) on the production of stromelysins, a sub-family of matrix metalloproteinases, were examined in cultured astrocytes. The treatment of cultured rat astrocytes with ET-1 increased stromelysin-1 mRNA levels, while stromelysin-2 and -3 mRNAs were not affected. Immunocytochemical observations showed that cultured astrocytes produced stromelysin-1 protein. ET-1 and Ala(1,3,11,15)-ET-1, an ET(B) receptor selective agonist, stimulated the release of stromelysin-1 from cultured astrocytes. Accompanying the increase in protein release, the peptidase activity of stromelysin-1 in the medium was also increased by ET-1. The effects of ET-1 on astrocytic stromelysin-1 expression were inhibited by PD98059, staurosporine, and Ca(2+) chelation, but not by SB203580 or pyrrolidine dithiocarbamate. These results show that activation of astrocytic ET receptors stimulates the production of stromelysin-1, suggesting a role for ETs in stromelysin production in brain pathologies.

The involvement of astrocytes and kynurenine pathway in Alzheimer's disease

The kynurenine pathway (KP) and several of its neuroactive products, especially quinolinic acid (QUIN), are considered to be involved in the neuropathogenesis of Alzheimer's disease (AD). There is growing evidence suggesting that astrocytes play a critical role in the regulation of the excitotoxicity and inflammatory processes that occur during the evolution of AD. This review focuses on the role of astrocytes through their relation with the KP to the different features associated with AD including cytokine, chemokine and adhesion molecule production, cytoskeletal changes, astrogliosis, excitotoxicity, apoptosis and neurodegeneration.

Roles of the endogenous VEGF receptors flt-1 and flk-1 in astroglial and vascular remodeling after brain injury

Following trauma to the brain significant changes occur in both the astroglial and vascular components of the neuropil. Angiogenesis is required to re-establish metabolic support and astrocyte activation encompasses several functions including scar formation and the production of growth factors. VEGF has seminal involvement in the process of brain repair and is upregulated during many pathological events. VEGF signaling is regulated mainly through its two primary receptors: flk-1 (KDR/VEGF-R2) is expressed on vascular endothelium and some neurons and flt-1 (VEGF-R1) in the CNS, is expressed predominantly by activated astrocytes. Using an injury model of chronic minipump infusion of neutralizing antibodies (NA) to block VEGF receptor signaling, this study takes advantage of these differences in VEGF receptor distribution in order to understand the role the cytokine plays after brain injury. Infusion of NA to flk-1 caused a significant decrease in vascular proliferation and increased endothelial cell degeneration compared to control IgG infusions but had no effect on astrogliosis. By contrast infusion of NA to flt-1 significantly decreased astroglial mitogenicity and scar formation and caused some increase in endothelial degeneration. Neutralization of the flt-1 receptor function, but not flk-1, caused significant reduction in the astroglial expression of the growth factors, CNTF and FGF by 7days. These data suggest that after CNS injury, endogenous VEGF upregulation (by astrocytes) induces angiogenesis and, by autocrine signaling, increases both astrocyte proliferation and facilitates expression of growth factors. It is likely that VEGF plays an important role in aspects of astroglial scar formation.

Targeting of pancreatic glia in type 1 diabetes

OBJECTIVE

Type 1 diabetes reflects autoimmune destruction of beta-cells and peri-islet Schwann cells (pSCs), but the mechanisms of pSC death and the T-cell epitopes involved remain unclear.

RESEARCH DESIGN AND METHODS

Primary pSC cultures were generated and used as targets in cytotoxic T-lymphocyte (CTL) assays in NOD mice. Cognate interaction between pSC and CD8(+) T-cells was assessed by transgenic restoration of beta2-microglobulin (beta2m) to pSC in NOD.beta2m(-/-) congenics. I-A(g7) and K(d) epitopes in the pSC antigen glial fibrillary acidic protein (GFAP) were identified by peptide mapping or algorithms, respectively, and the latter tested by immunotherapy.

RESULTS

pSC cultures did not express major histocompatibility complex (MHC) class II and were lysed by ex vivo CTLs from diabetic NOD mice. In vivo, restoration of MHC class I in GFAP-beta2m transgenics significantly accelerated adoptively transferred diabetes. Target epitopes in the pSC autoantigen GFAP were mapped to residues 79-87 and 253-261 for K(d) and 96-110, 116-130, and 216-230 for I-A(g7). These peptides were recognized spontaneously in NOD spleens as early as 2.5 weeks of age, with proliferative responses peaking around weaning and detectable lifelong. Several were also recognized by T-cells from new-onset type 1 diabetic patients. NOD mouse immunotherapy at 8 weeks with the CD8(+) T-cell epitope, GFAP 79-87 but not 253-261, significantly inhibited type 1 diabetes and was associated with reduced gamma-interferon production to whole protein GFAP.

CONCLUSIONS

Collectively, these findings elucidate a role for pSC-specific CD8(+) T-cells in islet inflammation and type 1 diabetes pathogenesis, further supporting neuronal involvement in beta-cell demise.

Effect of a chronic GSM 900 MHz exposure on glia in the rat brain

Extension of the mobile phone technology raises concern about the health effects of 900 MHz microwaves on the central nervous system (CNS). In this study we measured GFAP expression using immunocytochemistry method, to evaluate glial evolution 10 days after a chronic exposure (5 days a week for 24 weeks) to GSM signal for 45 min/day at a brain-averaged specific absorption rate (SAR)=1.5 W/kg and for 15 min/day at a SAR=6 W/kg in the following rat brain areas: prefrontal cortex (PfCx), caudate putamen (Cpu), lateral globus pallidus of striatum (LGP), dentate gyrus of hippocampus (DG) and cerebellum cortex (CCx). In comparison to sham or cage control animals, rats exposed to chronic GSM signal at 6 W/kg have increased GFAP stained surface areas in the brain (p<0.05). But the chronic exposure to GSM at 1.5 W/kg did not increase GFAP expression. Our results indicated that chronic exposure to GSM 900 MHz microwaves (SAR=6 W/kg) may induce persistent astroglia activation in the rat brain (sign of a potential gliosis).

WT1 expression distinguishes astrocytic tumor cells from normal and reactive astrocytes

Particularly in small brain biopsies, it might be difficult to distinguish reactive astrogliosis from low-grade or infiltration zones of high-grade astrocytomas. So far no immunohistochemical marker allows a reliable distinction. Recently, the over-expression of Wilms' tumor gene product WT1 was reported in astrocytic tumor cells. However, no sufficient data on WT1 expression in normal or reactive astrocytes are available. Therefore, we investigated WT1 expression in paraffin-embedded brain sections from 28 controls, 48 cases with astrogliosis of various etiology and 219 astrocytomas [World Health Organization (WHO) grades I-IV] by immunohistochemistry. In normal brains and in astrogliosis, expression of WT1 was restricted to endothelial cells. In astrocytomas, WT1-positive tumor cells were found in pilocytic astrocytomas (66.7% of cases), diffuse astrocytomas (52.7%) WHO grade II (52.7%), anaplastic astrocytomas (83.4%) and glioblastomas (98.1%). Overall, the majority of all astrocytic neoplasms (84.5%) expressed WT1. Establishing a cut-off value of 0% immunoreactive tumor cells served to recognize neoplastic astrocytes with 100% specificity and 68% sensitivity and was associated with positive and negative predictive values of 1 and 0.68, respectively. Therefore, WT1 expression in astrocytes indicates a neoplastic origin and might represent an important diagnostic tool to differentiate reactive from neoplastic astrocytes by immunohistochemistry.

Protective role of reactive astrocytes in brain ischemia

Reactive astrocytes are thought to protect the penumbra during brain ischemia, but direct evidence has been lacking due to the absence of suitable experimental models. Previously, we generated mice deficient in two intermediate filament (IF) proteins, glial fibrillary acidic protein (GFAP) and vimentin, whose upregulation is the hallmark of reactive astrocytes. GFAP(-/-)Vim(-/-) mice exhibit attenuated posttraumatic reactive gliosis, improved integration of neural grafts, and posttraumatic regeneration. Seven days after middle cerebral artery (MCA) transection, infarct volume was 210 to 350% higher in GFAP(-/-)Vim(-/-) than in wild-type (WT) mice; GFAP(-/-), Vim(-/-) and WT mice had the same infarct volume. Endothelin B receptor (ET(B)R) immunoreactivity was strong on cultured astrocytes and reactive astrocytes around infarct in WT mice but undetectable in GFAP(-/-)Vim(-/-) astrocytes. In WT astrocytes, ET(B)R colocalized extensively with bundles of IFs. GFAP(-/-)Vim(-/-) astrocytes showed attenuated endothelin-3-induced blockage of gap junctions. Total and glutamate transporter-1 (GLT-1)-mediated glutamate transport was lower in GFAP(-/-)Vim(-/-) than in WT mice. DNA array analysis and quantitative real-time PCR showed downregulation of plasminogen activator inhibitor-1 (PAI-1), an inhibitor of tissue plasminogen activator. Thus, reactive astrocytes have a protective role in brain ischemia, and the absence of astrocyte IFs is linked to changes in glutamate transport, ET(B)R-mediated control of gap junctions, and PAI-1 expression.

Inhibition of injury-induced glial aromatase reveals a wave of secondary degeneration in the songbird brain

Mechanical or anoxic/ischemic brain insult results in reactive gliosis and a pronounced wave of apoptotic secondary degeneration (WSD). Reactive glia express aromatase (estrogen synthase) and glial estrogen synthesis decreases apoptosis and the volume of degeneration. Whether aromatization by glia affects gliosis itself or the initiation/maintenance of the WSD remains unknown. Adult male zebra finches (Taeniopygia guttata) were injured with a needle that contained the aromatase inhibitor fadrozole or vehicle into contralateral hemispheres. Birds were killed at 0, 2, 6, 24, 72h, 2 or 6 weeks postinjury. Gliosis and degeneration were measured with vimentin- and Fluoro-Jade B-expression, respectively. Reactive gliosis was detectable at 6 h, reached asymptote at 72 h, and continued until 6 weeks postinsult. Gliosis extended further around fadrozole-injury than vehicle, an effect driven by a larger area of gliosis around fadrozole- relative to vehicle-injury at 72 h postinsult. Glial aromatase was inhibited for about 2 weeks postinjury since aromatase relative optical density was higher around fadrozole-injury relative to vehicle-injury until this time-point. Degeneration around vehicle-injury reached asymptote at 2 h postinsult, but that around fadrozole-injury peaked 24-72 h postinjury and decreased thereafter. Thus, the injury-induced WSD as described in mammals is detectable in zebra finches only following glial aromatase inhibition. In the zebra finch, injury-induced estrogen provision may decrease reactive gliosis and severely dampen the WSD, suggesting that songbirds are powerful models for understanding the role of glial aromatization in secondary brain damage.

R6/2 neurons with intranuclear inclusions survive for prolonged periods in the brains of chimeric mice

The R6/2 mouse possesses mutant exon 1 of human Hdh, and R6/2 mice with 150 CAG repeats show neurological abnormalities by 10 weeks and die by 15 weeks. Few brain abnormalities, however, are evident at death, other than widespread ubiquitinated neuronal intranuclear inclusions (NIIs). We constructed R6/2t+/t- <--> wildtype (WT) chimeric mice to prolong survival of R6/2 cells and determine if neuronal death and/or neuronal injury become evident with longer survival. ROSA26 mice (which bear a lacZ transgene) were used as WT to distinguish between R6/2 and WT neurons. Chimeric mice consisting partly of R6/2 cells lived longer than pure R6/2 mice (up to 10 months), with the survival proportional to the R6/2 contribution. Genotypically R6/2 cells formed NIIs in the chimeras, and these NIIs grew only slightly larger than in 12-week pure R6/2 mice, even after 10 months. Additionally, neuropil aggregates formed near R6/2 neurons in chimeric mice older than 15 weeks. Thus, R6/2 neurons could survive well beyond 15 weeks in chimeras. Moreover, little neuronal degeneration was evident in either cortex or striatum by routine histological stains. Nonetheless, striatal shrinkage and ventricular enlargement occurred, and striatal projection neuron markers characteristically reduced in Huntington's disease were diminished. Consistent with such abnormalities, cortex and striatum in chimeras showed increased astrocytic glial fibrillary acidic protein. These results suggest that while cortical and striatal neurons can survive nearly a year with nuclear and extranuclear aggregates of mutant huntingtin, such lengthy survival does reveal cortical and striatal abnormality brought on by the truncated mutant protein.

Bioactive properties of nanostructured porous silicon for enhancing electrode to neuron interfaces

Many different types of microelectrodes have been developed for use as a direct brain-machine interface (BMI) to chronically recording single-neuron action potentials from ensembles of neurons. Unfortunately, the recordings from these microelectrode devices are not consistent and often last for only on the order of months. For most microelectrode types, the loss of these recordings is not due to failure of the electrodes, but most likely due to damage to surrounding tissue that results in the formation of non-conductive glial scar. Since the extracellular matrix consists of nanostructured fibrous protein assemblies, we have postulated that neurons may prefer a more complex surface structure than the smooth surface typical of thin-film microelectrodes. This porous structure could then act as a drug-delivery reservoir to deliver bioactive agents to aid in the repair or survival of cells around the microelectrode, further reducing the glial scar. We, therefore, investigated the suitability of a nanoporous silicon surface layer to increase the biocompatibility of our thin film ceramic-insulated multisite electrodes. In vitro testing demonstrated increased extension of neurites from PC12 pheochromocytoma cells on porous silicon surfaces compared to smooth silicon surfaces. Moreover, the size of the pores and the pore coverage did not interfere with this bioactive surface property, suggesting that large highly porous nanostructured surfaces can be used for drug delivery. The most porous nanoporous surfaces were then tested in vivo and found to be more biocompatible than smooth surface, producing less glial activation and allowing more neurons to remain close to the device. Collectively, these results support our hypothesis that nanoporous silicon may be an ideal material to improve biocompatibility of chronically implanted microelectrodes. The next step in this work will be to apply these surfaces to active microelectrodes, use them to deliver bioactive agents, and test that they do improve neural recordings.

Signal transduction pathways involved in protective effects of melatonin in C6 glioma cells

Melatonin (N-acetyl-5-methoxytryptamine), an indole hormone, is the chief secretory product of the pineal gland and is an efficient free radical scavenger and antioxidant, both in vitro and in vivo. The role of melatonin as an immunomodulator is, in some cases, contradictory. Although melatonin is reported to influence a variety of inflammatory and immune responses, evidence supporting its effects on important glioma cells-derived mediators is incomplete. We studied, in rat glioma cell line (C6), the role of melatonin (100 microm-1 mm) in the regulation of the expression of nitric oxide synthase (NOS) caused by incubation with lipopolysaccharide (LPS)/interferon (IFN)-gamma (1 microg/mL and 100 U/mL, respectively) and defined the mode of melatonin's action. Treatment with LPS/IFN-gamma for 24 hr elicited the induction of inducible (iNOS) activity as determined by nitrite and nitrate (NO(x)) accumulation in the culture medium. Preincubation with melatonin abrogated the mixed cytokines-mediated induction of iNOS. The effect of melatonin was concentration-dependent. Moreover, Western blot analysis showed that melatonin inhibited LPS/IFN-gamma-induced expression of COX-2 protein, but not that of constitutive cyclooxygenase. Inhibition of iNOS and COX-2 expression was associated with inhibition of activation of the transcription factor nuclear factor kappa B (NF-kappaB). The ability of melatonin to inhibit NF-kappaB activation was further confirmed by studies on the degradation of the inhibitor of NF-kappaB, IkappaB-alpha. Increased production of lipid peroxidation products using thiobarbituric acid assay were found in cellular contents from activated cultures. Lipid peroxidation was decreased by melatonin treatment in a concentration-dependent manner. Moreover, several genes having roles in heat-shock response were downregulated in melatonin-treated cells, such as 70 proteins, reflecting the reduced oxidative stress in these cells. The mechanisms underlying in vitro the neuroprotective properties of melatonin involve modulation of transcription factors and consequent altered gene expression, resulting in downregulation of inflammation.

Magnetic resonance microscopy and immunohistochemistry of the CNS of the mutant SOD murine model of ALS reveals widespread neural deficits

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease that primarily affects motor neurons and descending motor tracts of the CNS. We have evaluated the CNS of a murine model of familial ALS based on the over-expression of mutant human superoxide dismutase (mSOD; G93A) using magnetic resonance microscopy (MRM) and immunohistochemistry (IHC). Three-dimensional volumetric analysis was performed from 3D T2*-weighted images acquired at 17.6 T at isotropic resolutions of 40 mum. Compared to controls, mSOD mice had significant reductions in the volumes of total brain, substantia nigra, striatum, hippocampus, and internal capsule, with decreased cortical thickness in primary motor and somatosensory cortices. In the spinal cord, mSOD mice had significantly decreased volume of both the total grey and white matter; in the latter case, the volume change was confined to the dorsal white matter. Increased apoptosis, GFAP positive astrocytes, and/or activated microglia were observed in all those CNS regions that showed volume loss except for the hippocampus. The MRM findings in mSOD over-expressing mice are similar to data previously obtained from a model of ALS-parkinsonism dementia complex (ALS-PDC), in which neural damage occurred following a diet of washed cycad flour containing various neurotoxins. The primary difference between the two models involves a significantly greater decrease in spinal cord white matter volume in mSOD mice, perhaps reflecting variations in degeneration of the descending motor tracts. The extent to which several CNS structures are impacted in both murine models of ALS argues for a reevaluation of the nature of the pathogenesis of ALS since CNS structures involved in Parkinson's and Alzheimer's diseases appear to be affected as well.

Translocator protein 18 kDa is involved in the regulation of reactive gliosis

Translocator protein (18 kDa) (TSPO), previously known as peripheral-type benzodiazepine receptor, is a critical component of the mitochondrial permeability transition pore. Brain inflammation results in the induction of the expression of TSPO in glial cells and some TSPO ligands decrease reactive gliosis after brain injury. However, since some TSPO ligands are neuroprotective, their effects on reactive gliosis may be the consequence of a reduced neurodegeneration. To assess whether TSPO ligands can modulate reactive gliosis in absence of neuronal death, we have tested their effects on the inflammatory response induced in the hippocampus of male rats by the intracerebroventricular infusion of lipopolysaccharide (LPS). LPS treatment did not induce neuronal death, assessed by Fluoro jade-B staining, but increased the number of cells immunoreactive for vimentin and MHC-II, used as markers of reactive astrocytes and reactive microglia, respectively. Furthermore, LPS produced an increase in the number of proliferating microglia. The TSPO ligand PK11195 reduced the number of MHC-II immunoreactive cells and the proliferation of microglia in LPS treated rats. In contrast, another TSPO ligand, Ro5-4864, did not significantly affect the response of microglia to LPS. Neither PK11195 nor Ro5-4864 affected the LPS-mediated increase in the number of vimentin-immunoreactive astrocytes at the time point studied, although PK11195 reduced vimentin immunoreactivity. These findings identify TSPO as a potential target for controlling neural inflammation, showing that the TSPO ligand PK11195 may reduce microglia activation by a mechanism that is independent of the regulation of neuronal survival.

Protection against human immunodeficiency virus type 1 Tat neurotoxicity by Ginkgo biloba extract EGb 761 involving glial fibrillary acidic protein

Human immunodeficiency virus (HIV)-1 Tat protein is an important pathogenic factor in HIV-associated neuropathogenesis. Despite recent progress, the molecular mechanisms underlying Tat neurotoxicity are still not completely understood. However, few therapeutics have been developed to specifically target HIV infection in the brain. Recent development of an inducible brain-specific Tat transgenic mouse model has made it possible to define the mechanisms of Tat neurotoxicity and evaluate anti-neuroAIDS therapeutic candidates in the context of a whole organism. Herein, we demonstrate that administration of EGb 761, a standardized formulation of Ginkgo biloba extract, markedly protected Tat transgenic mice from Tat-induced developmental retardation, inflammation, death, astrocytosis, and neuron loss. EGb 761 directly down-regulated glial fibrillary acidic protein (GFAP) expression at both protein and mRNA levels. This down-regulation was, at least in part, attributable to direct effects of EGb 761 on the interactions of the AP1 and NF-kappaB transcription factors with the GFAP promoter. Most strikingly, Tat-induced neuropathological phenotypes including macrophage/microglia activation, central nervous system infiltration of T lymphocytes, and oxidative stress were significantly alleviated in GFAP-null/Tat transgenic mice. Taken together, these results provide the first evidence to support the potential for clinical use of EGb 761 to treat HIV-associated neurological diseases. Moreover, these findings suggest for the first time that GFAP activation is directly involved in Tat neurotoxicity, supporting the notion that astrocyte activation or astrocytosis may directly contribute to HIV-associated neurological disorders.

Astrocytes--friends or foes in multiple sclerosis?

In multiple sclerosis (MS), the presence of demyelinating plaques has concentrated researchers' minds on the role of the oligodendrocyte in its pathophysiology. Recently, with the rediscovery of early and widespread loss of axons in the disease, new emphasis has been put on the role of axons and axon-oligodendrocyte interactions in MS. Despite the fact that, in 1904, Müller claimed that MS was a disease of astrocytes, more recently, astrocytes have taken a back seat, except as the cells that form the final glial scar after all hope of demyelination is over. However, perhaps it is time for the return of the astrocyte to popularity in the pathogenesis of MS, with recent reports on the dual role of astrocytes in aiding degeneration and demyelination, by promoting inflammation, damage of oligodendrocytes and axons, and glial scarring, but also in creating a permissive environment for remyelination by their action on oligodendrocyte precursor migration, oligodendrocyte proliferation, and differentiation. We review these findings to try to provide a cogent view of astrocytes in the pathology of MS.

Endogenous transforming growth factor beta 1 suppresses inflammation and promotes survival in adult CNS

Transforming growth factor beta1 (TGFbeta1) is a pleiotropic cytokine with potent neurotrophic and immunosuppressive properties that is upregulated after injury, but also expressed in the normal nervous system. In the current study, we examined the regulation of TGFbeta1 and the effects of TGFbeta1 deletion on cellular response in the uninjured adult brain and in the injured and regenerating facial motor nucleus. To avoid lethal autoimmune inflammation within 3 weeks after birth in TGFbeta1-deficient mice, this study was performed on a T- and B-cell-deficient RAG2-/- background. Compared with wild-type siblings, homozygous deletion of TGFbeta1 resulted in an extensive inflammatory response in otherwise uninjured brain parenchyma. Astrocytes increased in GFAP and CD44 immunoreactivity; microglia showed proliferative activity, expression of phagocytosis-associated markers [alphaXbeta2, B7.2, and MHC1 (major histocompatibility complex type 1)], and reduced branching. Ultrastructural analysis revealed focal blockade of axonal transport, perinodal damming of axonal organelles, focal demyelination, and myelin debris in granule-rich, phagocytic microglia. After facial axotomy, absence of TGFbeta1 led to a fourfold increase in neuronal cell death (52 vs 13%), decreased central axonal sprouting, and significant delay in functional recovery. It also interfered with the microglial response, resulting in a diminished expression of early activation markers [ICAM1 (intercellular adhesion molecule 1), alpha6beta1, and alphaMbeta2] and reduced proliferation. In line with axonal and glial findings in the otherwise uninjured CNS, absence of endogenous TGFbeta1 also caused an approximately 10% reduction in the number of normal motoneurons, pointing to an ongoing and potent trophic role of this anti-inflammatory cytokine in the normal as well as in the injured brain.

Chronic erythropoietin-mediated effects on the expression of astrocyte markers in a rat model of contusive spinal cord injury

Using a standardized rat model of contusive spinal cord injury (SCI; [Gorio A, Gokmen N, Erbayraktar S, Yilmaz O, Madaschi L, Cichetti C, Di Giulio AM, Vardar E, Cerami A, Brines M (2002) Recombinant human erythropoietin counteracts secondary injury and markedly enhances neurological recovery from experimental spinal cord trauma. Proc Natl Acad Sci U S A 99:9450-9455]), we previously showed that the administration of recombinant human erythropoietin (rhEPO) improves both tissue sparing and locomotory outcome. In the present study, to better understand rhEPO-mediated effects on chronic astrocyte response to SCI in rat, we have used immunocytochemical methods combined with confocal and electron microscopy to investigate, 1 month after injury, the effects of a single rhEPO administration on the expression of a) aquaporin 4 (AQP4), the main astrocytic water channel implicated in edema development and resolution, and two molecules (dystrophin and syntrophin) involved in its membrane anchoring; b) glial fibrillary acidic protein (GFAP) and vimentin as markers of astrogliosis; c) chondroitin sulfate proteoglycans of the extracellular matrix which are upregulated after SCI and can inhibit axonal regeneration and influence neuronal and glial properties. Our results show that rhEPO administration after SCI modifies astrocytic response to injury by increasing AQP4 immunoreactivity in the spinal cord, but not in the brain, without apparent modifications of dystrophin and syntrophin distribution. Attenuation of astrogliosis, demonstrated by the semiquantitative analysis of GFAP labeling, was associated with a reduction of phosphacan/RPTP zeta/beta, whereas the levels of lecticans remained unchanged. Finally, the relative volume of a microvessel fraction was significantly increased, indicating a pro-angiogenetic or a vasodilatory effect of rhEPO. These changes were consistently associated with remarkable reduction of lesion size and with improvement in tissue preservation and locomotor recovery, confirming previous observations and underscoring the potentiality of rhEPO for the therapeutic management of SCI.

Expression profiling identifies a molecular signature of reactive astrocytes stimulated by cyclic AMP or proinflammatory cytokines

Specialized glia, termed reactive astrocytes, accompany numerous pathologic conditions affecting the central nervous system, including stroke, multiple sclerosis, and neoplasia. To better define this important cell type, we employed high-density microarray gene expression profiling using two in vitro models of reactive gliosis (stimulation with dbcAMP or IL-1beta/IFNgamma). We identified 44 differentially expressed transcripts common to both in vitro models and demonstrated that a subset of these genes are also differentially expressed in response to experimental autoimmune encephalomyelitis and focal cerebral ischemia in vivo. Moreover, this pattern of differential gene expression is not observed in hyperproliferating or neoplastic glia.

Formyl peptide receptor like 1 differentially requires mitogen-activated protein kinases for the induction of glial fibrillary acidic protein and interleukin-1α in human U87 astrocytoma cells

Mitogen-activated protein kinases (MAPKs) are not only pivotal mediators of signal transduction but they also regulate diverse biological processes ranging from survival, proliferation and differentiation to apoptosis. By using human U87 astrocytoma and transfected FPRL1/CHO cells, we have demonstrated that activation of FPRL1 with WKYMVM effectively phosphorylated JNK and ERK. Interestingly, p38 MAPK activation was only seen with FPRL1/CHO cells. The MAPK phosphorylations in response to WKYMVM were blocked by WRW(4) (a selective FPRL1 antagonist), but not cyclosporine H (a well-known FPR antagonist). The key signaling intermediates in the MAPK pathways were also delineated. G(i)/G(o) proteins, Src family tyrosine kinases, but not phosphatidylinositol-3 kinase, protein kinase C and calmodulin-dependent kinase II, were required to transmit signals from FPRL1 toward JNK, ERK and p38 MAPK. Furthermore, phospholipase Cbeta was distinctively involved in the regulation of JNK but not the other MAPKs. Importantly, WKYMVM-stimulated U87 cells triggered noticeable increases in glial fibrillary acidic protein (GFAP) and interleukin-1alpha (IL-1alpha), which are correlated with reactive astrocytosis. In contrast, GFAP expression was not altered following stimulation with N-formyl-methionyl-leucyl-phenylalanine. Moreover, inhibitions of G(i)/G(o) proteins and JNK completely abolished both GFAP and IL-1alpha upregulations by FPRL1, while blockade of the MEK/ERK cascade exclusively suppressed the GFAP production. Consistently, overexpression of MEK1 and constitutively active JNKK in U87 cells led to ERK and JNK activation, respectively, which was accompanied with markedly increased GFAP production. We have thus identified a possible linkage among FPRL1, MAPKs, astrocytic activation and the inflammatory response.

Growth factor function in the development and maintenance of midbrain dopaminergic neurons: concepts, facts and prospects for TGF-beta

Dopaminergic neurons of the nigrostriatal system are important in the control of motor performance and degenerate in Parkinson's disease. Therefore, in order to design novel strategies for the treatment of Parkinson's disease, it is important for us to understand their development, function, trophic factor requirements, plasticity and susceptibility to toxic influences. A large and still increasing number of growth factors have been implicated in the regulation of the survival and differentiation of dopaminergic neurons. These factors may also protect against a variety of toxic influences. On the basis of their localization, putative sources and mechanisms of actions, such growth factors fall into several categories: (i) local factors within the midbrain influencing proliferation, transmitter phenotype, migration, positioning and neurite growth of stem cells and early neurons; (ii) factors acting retrogradely from the striatum, which are responsible for intrastriatal sprouting and navigation of newly arrived axons as well as life-long maintenance of the dopaminergic nigrostriatal connection; (iii) factors coming into play when the system is toxically impaired; (iv) factors directly acting on dopaminergic neurons; and (v) factors provided by cytokinestimulated astroglia, microglia and neurons affecting dopaminergic neurons anterogradely. This article reviews actions of growth factors on dopaminergic neurons in vitro and in vivo, with a focus on members of the transforming growth factor (TGF)-beta superfamily. TGF-beta s may be particularly relevant to dopaminergic neurons, since they are expressed in the nigrostriatal system from early embryonic stages to adulthood and are significantly up-regulated in response to lesions.

Testosterone decreases reactive astroglia and reactive microglia after brain injury in male rats: role of its metabolites, oestradiol and dihydrotestosterone

Previous studies have shown that the neuroprotective hormone, testosterone, administered immediately after neural injury, reduces reactive astrogliosis. In this study we have assessed the effect of early and late therapy with testosterone or its metabolites, oestradiol and dihydrotestosterone, on reactive astroglia and reactive microglia after a stab wound brain injury in orchidectomized Wistar rats. Animals received daily s.c. injections of testosterone, oestradiol or dihydrotestosterone on days 0-2 or on days 5-7 after injury. The number of vimentin immunoreactive astrocytes and the volume fraction of major histocompatibility complex-II (MHC-II) immunoreactive microglia were estimated in the hippocampus in the lateral border of the wound. Both early and delayed administration of testosterone or oestradiol, but not dihydrotestosterone, resulted in a significant decrease in the number of vimentin-immunoreactive astrocytes. The volume fraction of MHC-II immunoreactive microglia was significantly decreased in the animals that received testosterone or oestradiol in both early and delayed treatments and in animals that received early dihydrotestosterone administration. Thus, both early and delayed administration of testosterone reduces reactive astroglia and reactive microglia and these effects may be at least in part mediated by oestradiol, while dihydrotestosterone may mediate part of the early effects of testosterone on reactive microglia. In conclusion, testosterone controls reactive gliosis and its metabolites, oestradiol and dihydrotestosterone, may be involved in this hormonal effect. The regulation of gliosis may be part of the neuroprotective mechanism of testosterone.

Transcriptional regulation of scar gene expression in primary astrocytes

The failure of the adult injured spinal cord to support axonal regeneration is in part attributed to the glial scar. Reactive astrocytes constitute a major cellular component of the glial scar and are heterogeneous with respect to the extracellular matrix proteins that they secrete. Astrocytes may produce antiregenerative molecules such as chondroitin sulphate proteoglycans (CSPGs) or proregenerative molecules such as laminin and fibronectin. While many different CSPGs are expressed after spinal cord injury (SCI) they all rely on the same enzymes, xylosyltransferase-I and -II (XT-I, XT-II) and chondroitin 4-sulfotransferase (C4ST) to add the repulsive chondroitin sulfate side chains to their core proteins. We show that XT-I, XT-II, and C4ST are part of a CSPG biosynthetic gene (CBG) battery. Using primary astrocyte cultures and quantitative PCR we demonstrate that TGFbeta2, PDGF, and IL-6 induce the expression of CBGs, laminin and fibronectin by several-fold. We further show that over-expression of the transcription factor SOX9 also strongly induces the expression of CBGs but does not increase the expression of laminin or fibronectin. Correspondingly, SOX9 knock-down in primary astrocytes causes a decrease in CBG and an increase in laminin and fibronectin mRNA levels. Finally, we show that the in vivo expression profiles of TGFbeta2, PDGF, IL-6, and SOX9 are consistent with their potential roles in differentially regulating CBGs, laminin and fibronectin gene expression in the injured spinal cord. This work suggests that SOX9 levels may be pivotal in determining the balance of pro- and anti-regenerative extracellular matrix molecules produced by astrocytes.

Temperature and nitric oxide control spontaneous calcium transients in astrocytes

Transient spontaneous increases in the intracellular Ca2+ concentration have been frequently observed in astrocytes in cell culture and in acutely isolated slices from several brain regions. Recent in vivo experiments, however, reported only a low frequency of spontaneous Ca2+ events in astrocytes. Since the ex vivo experiments were usually performed at temperatures lower than physiological body temperature, we addressed the question whether temperature could influence the spontaneous Ca2+ activity in astrocytes. Indeed, comparing the frequency and spike width of spontaneous Ca2+ transients in astrocytes at temperatures between 20 and 37 degrees C in culture as well as in acute cortical slices from mouse brain, revealed that spontaneous Ca2+ responses occurred frequently at low temperature and became less frequent at higher temperature. Moreover, the single Ca2+ events had a longer duration at low temperature. We found that nitric oxide (NO) mimicked the increase in spontaneous Ca2+ activity and that an NO-synthase inhibitor attenuated the effect of lowering the temperature. Thus, temperature and NO are major determinants of spontaneous astrocytic Ca2+ signalling.

Expression of pannexin2 protein in healthy and ischemized brain of adult rats

The expression pattern of the pannexin2 protein (Px2) in healthy and ischemized brains of adult rats was investigated. A polyclonal antibody for rat Px2 was generated in chicken and purified for affinity. This antibody was used to study by Western blot, Enzyme-Linked Immunosorbent Assay, and immunohistochemistry, the expression pattern of Px2 in healthy brain of adult rats and in the hippocampus of rats submitted to bilateral clamping of carotid arteries for 20 min, followed by different times of reperfusion (I/R) (8 h, 24 h, 48 h, 72 h, 14 days and 30 days). Immunohistochemical studies visualized the wide and complex expression pattern of Px2 in the healthy brain. All Px2(+) positive cells were neurons which also showed no puncta on their cellular membranes. Both pyramidal cells and interneurons, the majority of which were positive to parvalbumin, were stained in healthy hippocampus. The number of Px2 interneurons in the hippocampus showed a progressive reduction at successive time intervals after I/R, with a negative peak of about -40% after 72 h from I/R. Interneurons which were positive for both Px2 and parvalbumin, represented about the 85% of all parvalbumin cells stained in the hippocampus. This percentage rested grossly unmodified at different time intervals after I/R in spite of the progressive neuronal depletion. Concomitantly, an intense astrogliosis occurred in the hippocampus. Most of the astroglial cells expressed de novo and for a transient time (from 24 h to 14 days from I/R), Px2. Primary co-cultures of hippocampal neurons and astrocytes were submitted to transient ischemia-like injury. This set of experiments further confirmed the in vivo results by showing that Px2 is de novo and transiently expressed in astroglial cells following a transient ischemia-like injury. These results suggested the expression of Px2 in the astrocytes may be induced either from injured neurons or by biochemical pathways internal to the astrocyte itself. In conclusion, our results showed the transient expression of Px2 in astrocytes of reactive gliosis occurring in the hippocampus following I/R injury. We hypothesize that Px2 expression in astrocytes following an ischemic insult is principally involved in the formation of hemichannels for the release of signaling molecules devoted to influence the cellular metabolism and the redox status of the surrounding environment.