Astrocytes in cerebral ischemic injury: morphological and general considerations

c-Jun and c-Fos regulate the complement factor H promoter in murine astrocytes

The complement system is a critical component of innate immunity that requires regulation to avoid inappropriate activation. This regulation is provided by many proteins, including complement factor H (CFH), a critical regulator of the alternative pathway of complement activation. Given its regulatory function, mutations in CFH have been implicated in diseases such as age-related macular degeneration and membranoproliferative glomerulonephritis, and central nervous system diseases such as Alzheimer's disease, Parkinson's disease, and a demyelinating murine model, experimental autoimmune encephalomyelitis (EAE). There have been few investigations on the transcriptional regulation of CFH in the brain and CNS. Our studies show that CFH mRNA is present in several CNS cell types. The murine CFH (mCFH) promoter was cloned and examined through truncation constructs and we show that specific regions throughout the promoter contain enhancers and repressors that are positively regulated by inflammatory cytokines in astrocytes. Database mining of these regions indicated transcription factor binding sites conserved between different species, which led to the investigation of specific transcription factor binding interactions in a 241 base pair (bp) region at -416 bp to -175 bp that showed the strongest activity. Through supershift analysis, it was determined that c-Jun and c-Fos interact with the CFH promoter in astrocytes in this region. These results suggest a relationship between cell cycle and complement regulation, and how these transcription factors and CFH affect disease will be a valuable area of investigation.

Role of sodium/hydrogen exchanger isoform 1 in microglial activation and proinflammatory responses in ischemic brains

Our recent study reveals that Na⁺/H⁺ exchanger isoform 1 (NHE-1) mediates H⁺ extrusion during "respiratory bursting", which is important for microglial activation. In the present study, we further investigated whether NHE-1 plays a role in proinflammatory activation of microglia in vivo using a mouse model of transient focal cerebral ischemia and reperfusion (I/R). Activated microglial cells were identified by their expression of two microglial marker proteins (CD11b and Iba1) as well as by their transformation from a "ramified" to an "amoeboid" morphology. An immediate increase in activated microglial numbers was detected in the ipsilateral ischemic core area of NHE-1⁺/⁺ brains at 1 hour (h) I/1 h R, which gradually decreased during 6-24 h I/R. This was followed by a sharp rise in microglial activation in the peri-infarct area and an increase in proinflammatory cytokine formation at 3 day after I/R. Interestingly, HOE 642 (a potent NHE-1 inhibitor) -treated or NHE-1 heterozygous (NHE-1⁺/⁻) mice exhibited less microglia activation, less NADPH oxidase activation, or a reduced proinflammatory response at 3-7 day after I/R. Blocking NHE-1 activity also significantly decreased microglial phagocytosis in vitro. In contrast, astrogliosis formation in the peri-infarct area was not affected by NHE-1 inhibition. Taken together, our results demonstrate that NHE-1 protein was abundantly expressed in activated microglia and astrocytes. NHE-1 inhibition reduced microglial proinflammatory activation following ischemia.

Cannabidiol reduces brain damage and improves functional recovery after acute hypoxia-ischemia in newborn pigs

Newborn piglets exposed to acute hypoxia-ischemia (HI) received i.v. cannabidiol (HI + CBD) or vehicle (HI + VEH). In HI + VEH, 72 h post-HI brain activity as assessed by amplitude-integrated EEG (aEEG) had only recovered to 42 ± 9% of baseline, near-infrared spectroscopy (NIRS) parameters remained lower than normal, and neurobehavioral performance was abnormal (27.8 ± 2.3 points, normal 36). In the brain, there were fewer normal and more pyknotic neurons, while astrocytes were less numerous and swollen. Cerebrospinal fluid concentration of neuronal-specific enolase (NSE) and S100β protein and brain tissue percentage of TNFα(+) cells were all higher. In contrast, in HI + CBD, aEEG had recovered to 86 ± 5%, NIRS parameters increased, and the neurobehavioral score normalized (34.3 ± 1.4 points). HI induced histological changes, and NSE and S100β concentration and TNFα(+) cell increases were suppressed by CBD. In conclusion, post-HI administration of CBD protects neurons and astrocytes, leading to histological, functional, biochemical, and neurobehavioral improvements.

Glial fibrillary acidic protein as a brain injury biomarker in children undergoing extracorporeal membrane oxygenation

OBJECTIVE

To determine whether, in children, plasma glial fibrillary acidic protein is associated with brain injury during extracorporeal membrane oxygenation and with mortality.

DESIGN

Prospective, observational study.

SETTING

Pediatric intensive care unit in an urban tertiary care academic center.

PATIENTS

Neonatal and pediatric patients on extracorporeal membrane oxygenation (n = 22).

INTERVENTIONS

Serial blood sampling for glial fibrillary acidic protein measurements.

MEASUREMENTS AND MAIN RESULTS

Prospective patients age 1 day to 18 yrs who required extracorporeal membrane oxygenation from April 2008 to August 2009 were studied. Glial fibrillary acidic protein was measured using an electrochemiluminescent immunoassay developed at Johns Hopkins. Control samples were collected from 99 healthy children (0.5-16 yrs) and 59 neonatal intensive care unit infants without neurologic injury. In controls, the median glial fibrillary acidic protein concentration was 0.055 ng/mL (interquartile range, 0-0.092 ng/mL) and the 95th percentile of glial fibrillary acidic protein was 0.436 ng/mL. In patients on extracorporeal membrane oxygenation, plasma glial fibrillary acidic protein was measured at 6, 12, and every 24 hrs after cannulation. We enrolled 22 children who underwent extracorporeal membrane oxygenation. Median age was 7 days (interquartile range, 2 days to 9 yrs), and primary extracorporeal membrane oxygenation indication was: cardiac failure, six of 22 (27.3%); respiratory failure, 12 of 22 (54.5%); extracorporeal cardiopulmonary resuscitation, three of 22 (13.6%); and sepsis, one of 22 (4.6%). Seven of 22 (32%) patients developed acute neurologic injury (intracranial hemorrhage, brain death, or cerebral edema diagnosed by imaging). Fifteen of 22 (68%) survived to hospital discharge. In the extracorporeal membrane oxygenation group, peak glial fibrillary acidic protein levels were higher in children with brain injury than those without (median, 5.9 vs. 0.09 ng/mL, p = .04) and in nonsurvivors compared with survivors to discharge (median, 5.9 vs. 0.09 ng/mL, p = .04). The odds ratio for brain injury for glial fibrillary acidic protein >0.436 ng/mL vs. normal was 11.5 (95% confidence interval, 1.3-98.3) and the odds ratio for mortality was 13.6 (95% confidence interval, 1.7-108.5).

CONCLUSIONS

High glial fibrillary acidic protein during extracorporeal membrane oxygenation is significantly associated with acute brain injury and death. Brain injury biomarkers may aid in outcome prediction and neurologic monitoring of patients on extracorporeal membrane oxygenation to improve outcomes and benchmark new therapies.

Changes in lipid-sensitive two-pore domain potassium channel TREK-1 expression and its involvement in astrogliosis following cerebral ischemia in rats

Astrocytes play an active and important role in the pathophysiology of cerebral ischemia. We have previously shown that mature hipppocampal astrocytes functionally express two-pore domain K(+) channel TREK-1, which significantly contributes to the passive conductance and help to set the negative resting membrane potential essential for the optimal operation of some astrocytic homeostatic functions. However, its expression under ischemic conditions remains to be determined. In this study, we examined the expression of TREK-1 in rat brain under physiological and focal ischemia conditions. The results show that TREK-1 was broadly expressed on astrocytes and neurons in the cortex, CA1 region of hippocampus. After middle cerebral artery occlusion induced focal ischemia, the TREK-1 expression was significantly increased at days 3, 7 and 30 following reperfusion, which correlated with reactive astrogliosis in the cortex and hippocampus. Cultured cortical astrocytes also express TREK-1. TREK-1 inhibitor quinine inhibited the proliferation of astrocytes exposed to hypoxia condition. These data provide evidence showing the astrocytic TREK-1 involvement in ischemia pathology.

HIV-1 gp120 induces expression of IL-6 through a nuclear factor-kappa B-dependent mechanism: suppression by gp120 specific small interfering RNA

In addition to its role in virus entry, HIV-1 gp120 has also been implicated in HIV-associated neurocognitive disorders. However, the mechanism(s) responsible for gp120-mediated neuroinflammation remain undefined. In view of increased levels of IL-6 in HIV-positive individuals with neurological manifestations, we sought to address whether gp120 is involved in IL-6 over-expression in astrocytes. Transfection of a human astrocyte cell line with a plasmid encoding gp120 resulted in increased expression of IL-6 at the levels of mRNA and protein by 51.3±2.1 and 11.6±2.2 fold respectively; this effect of gp120 on IL-6 expression was also demonstrated using primary human fetal astrocytes. A similar effect on IL-6 expression was observed when primary astrocytes were treated with gp120 protein derived from different strains of X4 and R5 tropic HIV-1. The induction of IL-6 could be abrogated by use of gp120-specific siRNA. Furthermore, this study showed that the NF-κB pathway is involved in gp120-mediated IL-6 over-expression, as IKK-2 and IKKβ inhibitors inhibited IL-6 expression by 56.5% and 60.8%, respectively. These results were also confirmed through the use of NF-κB specific siRNA. We also showed that gp120 could increase the phosphorylation of IκBα. Furthermore, gp120 transfection in the SVGA cells increased translocation of NF-κB from cytoplasm to nucleus. These results demonstrate that HIV-1 gp120-mediated over-expression of IL-6 in astrocytes is one mechanism responsible for neuroinflammation in HIV-infected individuals and this is mediated by the NF-κB pathway.

Mechanisms underlying the protective effects of myricetin and quercetin following oxygen-glucose deprivation-induced cell swelling and the reduction in glutamate uptake in glial cells

The protective effects of the flavonoid polyphenols, myricetin and quercetin, were investigated on key features of ischemic injury in cultures including cell swelling and the reduction in glutamate uptake. C6 glial cells were exposed to oxygen-glucose deprivation (OGD) for 5 h and cell swelling was determined 90 min after the end of OGD. OGD-induced swelling was significantly blocked by both quercetin and myricetin although higher concentrations were required for quercetin. OGD-induced free radical production, a contributing factor in cell swelling, was significantly reduced by both myricetin and quercetin. However, depolarization of the inner mitochondrial membrane potential (ΔΨ(m)), the blockade of which generally reduces swelling, was significantly diminished by myricetin, but not quercetin. This indicated that quercetin could reduce swelling despite its inability to prevent depolarization of ΔΨ(m) possibly through other signaling pathways. Increased intracellular calcium ([Ca²+](i)) is an important characteristic of ischemic injury and is implicated in swelling. Both myricetin and quercetin attenuated the increase in [Ca²+](i). Further, a reduction in [Ca²+](i), through the use of nifedipine, nimodipine, verapamil, dantrolene, or BAPTA-AM, significantly reduced OGD-induced cell swelling indicating that one possible mechanism by which such flavonoids attenuate cell swelling may be through regulating [Ca²+](i). OGD-induced decrease in glutamate uptake was attenuated by myricetin, but not quercetin. Cyclosporin A, a blocker of the mitochondrial permeability transition (mPT) pore, but not FK506 (that does not block the mPT), attenuated the decline in glutamate uptake after OGD, indicating the involvement of the mPT in glutamate uptake. Our results indicated that while blockade of ΔΨ(m) may be sufficient to reduce swelling, it may not be a necessary factor, and that flavonoids reduce cell swelling by regulating [Ca²+](i). The differential effects of myricetin and quercetin on OGD-induced reduction on glutamate uptake may be due to their differential effects on mitochondria.

Enhanced angiogenesis and astrocyte activation by ecdysterone treatment in a focal cerebral ischemia rat model

BACKGROUND AND PURPOSE

We reported previously that ecdysterone (EDS) improves neurologic function after experimental stroke. However, the underlying mechanism remained unclear. The present study was conducted to test whether ecdysterone improves neurologic function by enhancing astrocyte activation and angiogenesis after focal cerebral ischemia in rats.

METHODS

Focal cerebral ischemia model was conducted by middle cerebral artery occlusion (MCAO). EDS was intraperitoneally injected at 20 mg kg1 daily for 7 days after MCAO. Neurologic recovery was assessed using the neurologic severity scores. Microvessel density and GFAP expression were detected with immunostaining and analyzed quantitatively with image system.

RESULTS

Treatment with EDS significantly improved functional recovery, along with increases in density of cerebral microvessels and astrocyte activation. Microvessel density was significantly higher in EDS treated group than in ischemia control group at all time points, and reached a peak on day 14. EDS treated group had substantial increment in GFAP immunoreactive cells, darker staining color, more and longer nerve processes, higher GFAP expression and area of immunoreactive cells at each time point.

CONCLUSION

Our data suggest that EDS treatment enhanced angiogenesis and astrocyte activation which could contribute to functional recovery.

Time-dependent changes in proinflammatory and neurotrophic responses of microglia and astrocytes in a rat model of osmotic demyelination syndrome

Osmotic demyelination syndrome (ODS) is a serious demyelinating disease in the central nervous system usually caused by rapid correction of hyponatremia. In an animal model of ODS, we previously reported microglial accumulation expressing proinflammatory cytokines. Microglia and astrocytes secreting proinflammatory cytokines and neurotrophic factors are reported to be involved in the pathogenesis of demyelinative diseases. Therefore, to clarify the role of microglial and astrocytic function in ODS, we examined the time-dependent changes in distribution, morphology, proliferation, and mRNA/protein expression of proinflammatory cytokines, neurotrophic factors, and matrix metalloproteinase (MMP) in microglia and astrocytes 2 days (early phase) and 5 days (late phase) after the rapid correction of hyponatremia in ODS rats. The number of microglia time dependently increased at demyelinative lesion sites, proliferated, and expressed tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, inducible nitric oxide synthase, and MMP2, 9, and 12 at the early phase. Microglia also expressed leukemia inhibitory factor (a neurotrophic factor) and phagocytosed myelin debris at the late phase. The number of astrocytes time dependently increased around demyelinative lesions, extended processes to lesions, proliferated, and expressed nerve growth factor and glial cell line-derived neurotrophic factor at the late phase. Moreover, treatment with infliximab, a monoclonal antibody against TNF-α, significantly attenuated neurological impairments. Our results suggest that the role of microglia in ODS is time dependently shifted from detrimental to protective and that astrocytes play a protective role at the late phase. Modulation of excessive proinflammatory responses in microglia during the early phase after rapid correction may represent a therapeutic target for ODS.

Alzheimer type II astrocytes in the brains of pigs with salt poisoning (water deprivation/intoxication)

The finding of Alzheimer type II astrocytes, in addition to the pathognomonic combination of laminar cerebrocortical necrosis and eosinophil infiltration, in the brains of pigs is reported for the first time in cases of indirect salt poisoning following water deprivation.

Modulation of NADPH oxidase activation in cerebral ischemia/reperfusion injury in rats

NADPH oxidase is a major complex that produces reactive oxygen species (ROSs) during the ischemic period and aggravates brain damage and cell death after ischemic injury. Although many approaches have been tested for preventing production of ROSs by NADPH oxidase in ischemic brain injury, the regulatory mechanisms of NADPH oxidase activity after cerebral ischemia are still unclear. The aim of this study is identifying apocynin as a critical modulator of NADPH oxidase and elucidating its role as a neuroprotectant in an experimental model of brain ischemia in rat. Treatment of apocynin 5min before of reperfusion attenuated cerebral ischemia in rats. Administration of apocynin showed marked reduction in infarct size compared with that of control rats. Medial carotid artery occlusion (MCAo)-induced cerebral ischemia was also associated with an increase in, nitrotyrosine formation, as well as IL-1β expression, IκB degradation and ICAM expression in ischemic regions. These expressions were markedly inhibited by the treatment of apocynin. We also demonstrated that apocynin reduces levels of apoptosis (TUNEL, Bax and Bcl-2 expression) resulting in a reduction in the infarct volume in ischemia-reperfusion brain injury. This new understanding of apocynin induced adaptation to ischemic stress and inflammation could suggest novel avenues for clinical intervention during ischemic and inflammatory diseases.

Relationship between activated astrocytes and hypoxic cerebral tissue in a rat model of cerebral ischemia/reperfusion

Following cerebral infarction, hypoxic tissues remains in the ischemic cortex for long periods of time. Glial fibrillary acidic protein (GFAP) is a specific marker of astrocytes, which is thought to be essential for neuronal survival. We aimed to clarify the relationship between hypoxic tissue and astrocytes following cerebral infarction. Rats with middle cerebral artery occlusion were randomly divided into a 1.5-hour ischemia-reperfusion(1.5-hour IR) group and a permanent ischemia (PI) group. Hypoxic tissue and GFAP fluorescence intensity in the ischemic cortex were observed postoperatively on days 1, 3, 7, and 14. Results showed that hypoxic tissue was present from day 1 to 14 in the 1.5-hour IR group and on days 1 and 3 in the PI group. The GFAP fluorescence intensity in the 1.5-hour IR group was stronger than that in the PI group at the same time point of observation. Over time, GFAP expression increased and peaked at 7 days in each group, followed by a decrease in signal. In hypoxic tissue, the GFAP fluorescence intensity was stronger than that in the surrounding tissue at all observation time points. These data indicate that astrocytes were strongly activated in hypoxic tissue induced by temporary ischemia followed by reperfusion. The activation of astrocytes may partially contribute to the survival and repair of hypoxic tissue following brain ischemia.

Biphasic actions of HMGB1 signaling in inflammation and recovery after stroke

Stroke induces a complex web of pathophysiology that may evolve over hours to days and weeks after onset. It is now recognized that inflammation is an important phenomenon that can dramatically influence outcomes after stroke. In this minireview, we explore the hypothesis that inflammatory signals after stroke are biphasic in nature. The high-mobility group box 1 (HMGB1) protein is discussed as an example of this idea. HMGB1 is normally present in the nucleus. Under ischemic conditions, it is released extracellularly from many types of cells. During the acute phase poststroke, HMGB1 promotes necrosis and influx of damaging inflammatory cells. However, during the delayed phase poststroke, HMGB1 can mediate beneficial plasticity and recovery in many cells of the neurovascular unit. These emerging findings support the hypothesis that inflammation after stroke can be both detrimental and beneficial, depending on the cellular situations involved.

Targeting astrocytes for stroke therapy

Stroke remains a major health problem and is a leading cause of death and disability. Past research and neurotherapeutic clinical trials have targeted the molecular mechanisms of neuronal cell death during stroke, but this approach has uniformly failed to reduce stroke-induced damage or to improve functional recovery. Beyond the intrinsic molecular mechanisms inducing neuronal death during ischemia, survival and function of astrocytes is absolutely required for neuronal survival and for functional recovery after stroke. Many functions of astrocytes likely improve neuronal viability during stroke. For example, uptake of glutamate and release of neurotrophins enhances neuronal viability during ischemia. Under certain conditions, however, astrocyte function may compromise neuronal viability. For example, astrocytes may produce inflammatory cytokines or toxic mediators, or may release glutamate. The only clinical neurotherapeutic trial for stroke that specifically targeted astrocyte function focused on reducing release of S-100β from astrocytes, which becomes a neurotoxin when present at high levels. Recent work also suggests that astrocytes, beyond their influence on cell survival, also contribute to angiogenesis, neuronal plasticity, and functional recovery in the several days to weeks after stroke. If these delayed functions of astrocytes could be targeted for enhancing stroke recovery, it could contribute importantly to improving stroke recovery. This review focuses on both the positive and the negative influences of astrocytes during stroke, especially as they may be targeted for translation to human trials.

Olfactory ensheathing cells moderate nuclear factor kappaB translocation in astrocytes

Nuclear factor kappaB (NFκB) is a key transcriptional regulator of inflammatory genes. We investigated the modulatory effects of olfactory ensheathing cells (OECs), microglia and meningeal fibroblasts on translocation of NFκB to astrocyte nuclei. The percentage of activated astrocytes in co-cultures with OECs was significantly less than for co-cultures with microglia (p<0.001) and fibroblasts (p<0.05). Phorbol myristate acetate (PMA) and calcium ionophore stimulation of p65 NFκB translocation to nuclei provided an in vitro model of astrocyte inflammatory activation. Soluble factors released by OECs significantly moderated the astrocytic NFκB translocation induced by either PMA/calcium ionophore or microglia-derived factors (p<0.001). Insulin-like growth factor-1 may contribute to these effects, since it is expressed by OECs and also significantly moderated the astrocytic NFκB translocation (p<0.05), albeit insufficiently to fully account for the OEC-induced moderation (p<0.01). Olfactory ensheathing cells significantly moderated the increased transcription of the pro-inflammatory cytokine, granulocyte macrophage-colony stimulating factor in the activated astrocytes (p<0.01). These results suggest that transplanted OECs could improve neural repair after CNS injury by moderating astrocyte activation.

Astroglial proteins as diagnostic markers of acute intracerebral hemorrhage-pathophysiological background and clinical findings

The time span from symptom onset to treatment initiation remains a critical variable determining the efficacy of thrombolysis in acute ischemic stroke. To date, performing a brain scan is indispensable prior to therapy in order to differentiate between patients with ischemic stroke and those with intracerebral hemorrhage (ICH). This causes substantial treatment delay, as thrombolysis cannot be applied prior to hospital admission at much earlier time points. Recently, brain-specific astroglial proteins (i.e., glial fibrillary acidic protein (GFAP), S100B) were identified to be released rapidly from the cytoplasm of destroyed cells in case of acute ICH. Elevated serum concentrations were found within the first 6 h after ICH onset. In contrast, in ischemic stroke, these proteins are released with delay, mirroring the more gradual occurrence of necrotic cell death and blood brain barrier disruption. S100B and GFAP may qualify as candidate serum biomarkers which are able to differentiate between ischemic stroke and ICH in the emergency phase of stroke. This minireview enlightens the pathophysiological background of this finding and provides an overview on currently available clinical data.

Human microglia transplanted in rat focal ischemia brain induce neuroprotection and behavioral improvement

Background and Purpose

Microglia are resident immunocompenent and phagocytic cells of central nervous system (CNS), which produce various cytokines and growth factors in response to injury and thereby regulate disease pathology. The purpose of this study is to investigate the effects of microglial transplantation on focal cerebral ischemia model in rat.

Methods

Transient middle cerebral artery occlusion (MCAO) in rats was induced by the intraluminal filament technique. HMO6 cells, human microglial cell line, were transplanted intravenously at 48 hours after MCAO. Functional tests were performed and the infarct volume was measured at 7 and 14 days after MCAO. Migration and cell survival of transplanted microglial cells and host glial reaction in the brain were studied by immunohistochemistry. Gene expression of neurotrophic factors, cytokines and chemokines in transplanted cells and host rat glial cells was determined by laser capture microdissection (LCM) and quantitative real time-PCR.

Results

HMO6 human microglial cells transplantion group demonstrated significant functional recovery compared with control group. At 7 and 14 days after MCAO, infarct volume was significantly reduced in the HMO group. In the HMO6 group, number of apoptotic cells was time-dependently reduced in the infarct core and penumbra. In addition, number of host rat microglia/macrophages and reactive astrocytes was significantly decreased at 7 and 14 days after MCAO in the penumbra. Gene expression of various neurotrophic factors (GDNF, BDNF, VEGF and BMP7) and anti-inflammatory cytokines (IL4 and IL5) was up-regulated in transplanted HMO6 cells of brain tissue compared with those in culture. The expression of GDNF and VEGF in astrocytes in penumbra was significantly up-regulated in the HMO6 group.

Conclusions

Our results indicate that transplantation of HMO6 human microglial cells reduces ischemic deficits and apoptotic events in stroke animals. The results were mediated by modulation of gliosis and neuroinflammation, and neuroprotection provided by neurotrophic factors of endogenous and transplanted cells-origin.

Regional heterogeneity and diversity in cytokine and chemokine production by astroglia: differential responses to HIV-1 Tat, gp120, and morphine revealed by multiplex analysis

HIV-infected individuals who abuse opiates show a faster progression to AIDS and higher incidence of encephalitis. The HIV-1 proteins Tat and gp120 have been shown to cause neurodegenerative changes either in vitro or when injected or expressed in the CNS, and we have shown that opiate drugs can exacerbate neurotoxic effects in the striatum through direct actions on pharmacologically discrete subpopulations of mu-opioid receptor-expressing astroglia. Opiate coexposure also significantly enhances release of specific inflammatory mediators by astroglia from the striatum, and we theorize that astroglial reactivity may underlie aspects of HIV neuropathology. To determine whether astroglia from different regions of the central nervous system have distinct, intrinsic responses to HIV-1 proteins and opiates, we used multiplex suspension array analyses to define and compare the inflammatory signature of cytokines released by murine astrocytes grown from cerebral cortex, cerebellum, and spinal cord. Results demonstrate significant regional differences in baseline secretion patterns, and in responses to viral proteins. Of importance for the disease process, astrocytes from all regions have very limited inflammatory response to gp120 protein, as compared to Tat protein, either in the presence or absence of morphine. Overall, the chemokine/cytokine release is higher from spinal cord and cortical astroglia than from cerebellar astroglia, paralleling the relatively low incidence of HIV-related neuropathology in the cerebellum.

Oncostatin M is a novel glucocorticoid-dependent neuroinflammatory factor that enhances oligodendrocyte precursor cell activity in demyelinated sites

The innate immune reaction to tissue injury is a natural process, which can have detrimental effects in the absence of negative feedbacks by glucocorticoids (GCs). Although acute lipopolysaccharide (LPS) challenge is relatively harmless to the brain parenchyma of adult animals, the endotoxin is highly neurotoxic in animals that are treated with the GC receptor antagonist RU486. This study investigated the role of cytokines of the gp130-related family in these effects, because they are essential components of the inflammatory process that provide survival signals to neurons. Intracerebral LPS injection stimulated expression of several members of this family of cytokines, but oncostatin M (Osm) was the unique ligand to be completely inhibited by the RU486 treatment. OSM receptor (Osmr) is expressed mainly in astrocytes and endothelial cells following LPS administration and GCs are directly responsible for its transcriptional activation in the presence of the endotoxin. In a mouse model of demyelination, exogenous OSM significantly modulated the expression of genes involved in the mobilization of oligodendrocyte precursor cells (OPCs), differentiation of oligodendrocyte, and production of myelin. In conclusion, the activation of OSM signaling is a mechanism activated by TLR4 in the presence of negative feedback by GCs on the innate immune system of the brain. OSM absence is associated with detrimental effects of LPS, whereas exogenous OSM favors repair response to demyelinated regions.

Caspase-11 mediates ischemia-induced astrocyte death: involvement of endoplasmic reticulum stress and C/EBP homologous protein

Astrocytes are essential cells for maintaining brain integrity. We have recently shown that the transcription factor C/EBP homologous protein (CHOP), associated with endoplasmic reticulum (ER) stress, plays a key role in the astrocyte death induced by ischemia. Meanwhile, mediators of apoptosis downstream of CHOP in the ER stress-dependent pathway remain to be elucidated. Our aim in this work was to determine whether caspase-11, able to activate apoptotic and proinflammatory pathways, is implicated in ER stress-dependent astrocyte death in ischemic conditions. According to our results, caspase-11 is up-regulated in primary astrocyte cultures following either oxygen and glucose deprivation (OGD) or treatment with the ER-stress inducers thapsigargin and tunicamycin. Moreover, these same stimuli increased caspase-11 mRNA levels and luciferase activity driven by a caspase-11 promoter, indicating that caspase-11 is regulated at the transcriptional level. Our data also illustrate the involvement of ER stress-associated CHOP in caspase-11 regulation, insofar as CHOP overexpression by means of an adenoviral vector caused a significant raise in caspase-11. In turn, caspase-11 suppression with siRNA rescued astrocytes from OGD- and ER stress-induced death, supporting the idea that caspase-11 is responsible for the deleterious effects of ischemia on astrocytes. Finally, inhibition of caspase-1 and caspase-3 significantly reduced astrocyte death, which indicates that these proteases act as death effectors of caspase-11. In conclusion, our work contributes to clarifying the pathways leading to astrocyte death in response to ischemia by defining caspase-11 as a key mediator of the ER stress response acting downstream of CHOP.

Role of ERK map kinase and CRM1 in IL-1beta-stimulated release of HMGB1 from cortical astrocytes

Reactive astrocytes are traditionally thought to impede brain plasticity after stroke. However, we previously showed that reactive astrocytes may also contribute to stroke recovery, partly via the release of a nuclear protein called high-mobility group box 1 (HMGB1). Here, we investigate the mechanisms that allow stimulated astrocytes to release HMGB1. Exposure of rat primary astrocytes to IL-1beta for 24 h elicited a dose-dependent HMGB1 response. Immunostaining and western blots of cell lysates showed increased intracellular levels of HMGB1. Western blots confirmed that IL-1beta induced a release of HMGB1 into astrocyte conditioned media. MAP kinase signaling was involved. Levels of phospho-ERK were increased by IL-1beta, and the MEK/ERK inhibitor U0126 decreased HMGB1 upregulation in the stimulated astrocytes. Since HMGB1 is a nuclear protein, the role of the nuclear protein exporter, chromosome region maintenance 1 (CRM1), was assessed as a candidate mechanism for linking MAP kinase signaling to HMGB1 release. IL-1beta increased CRM1 expression in concert with a translocation of HMGB1 from nucleus into cytoplasm. Blockade of IL-1beta-stimulated HMGB1 release with the ERK inhibitor U0126 was accompanied by a downregulation of CRM1. Our findings reveal that IL-1beta stimulates the release of HMGB1 from activated astrocytes via ERK MAP kinase and CRM1 signaling. These data suggest a novel pathway by which inflammatory cytokines may enhance the ability of reactive astrocytes to release prorecovery mediators after stroke.

GFAP expression in the rat brain following sub-chronic exposure to a 900 MHz electromagnetic field signal

PURPOSE

The rapid development and expansion of mobile communications contributes to the general debate on the effects of electromagnetic fields emitted by mobile phones on the nervous system. This study aims at measuring the glial fibrillary acidic protein (GFAP) expression in 48 rat brains to evaluate reactive astrocytosis, three and 10 days after long-term head-only sub-chronic exposure to a 900 MHz electromagnetic field (EMF) signal, in male rats.

METHODS

Sprague-Dawley rats were exposed for 45 min/day at a brain-averaged specific absorption rate (SAR) = 1.5 W/kg or 15 min/day at a SAR = 6 W/kg for five days per week during an eight-week period. GFAP expression was measured by the immunocytochemistry method in the following rat brain areas: Prefrontal cortex, cerebellar cortex, dentate gyrus of the hippocampus, lateral globus pallidus of the striatum, and the caudate putamen.

RESULTS

Compared to the sham-treated rats, those exposed to the sub-chronic GSM (Global System for mobile communications) signal at 1.5 or 6 W/kg showed an increase in GFAP levels in the different brain areas, three and ten days after treatment.

CONCLUSION

Our results show that sub-chronic exposures to a 900 MHz EMF signal for two months could adversely affect rat brain (sign of a potential gliosis).

Insulin-like growth factor -1 (IGF-1) derived neuropeptides, a novel strategy for the development of pharmaceuticals for managing ischemic brain injury

Insulin-Like Growth Factor-1 (IGF-1) is neuroprotective and improves long-term function after brain injury. However, its clinical application to neurological disorders is limited by its large molecular size, poor central uptake, and mitogenic potential. Glycine-proline-glutamate (GPE) is naturally cleaved from the IGF-1 N-terminal and is also neuroprotective after ischemic injury, thus providing a potential novel strategy of drug discovery for management of neurological disorders. GPE is not enzymatically stable, thus intravenous infusion of GPE becomes necessary for stable and potent neuroprotection. The broad effective dose range and treatment window of 3-7 h after the lesion suggest its potential for treating acute brain injuries. The neuroprotective action of GPE is not age selective, is not dependent on cerebral reperfusion, plasma glucose concentrations, and core body temperature. G-2mPE, a GPE analogue designed to be more resistant to enzymatic activity, has a prolonged plasma half-life and is more potent in neuroprotection. Neuroprotection by GPE and its analogue may be involved in modulation of inflammation, promotion of astrocytosis, inhibition of apoptosis, and in vascular remodeling. Small neuropeptides have advantages over growth factors in the treatment of brain injury, and modified neuropeptides, designed to overcome the limitations of their endogenous counterparts, represent a novel strategy of pharmaceutical discovery for neurological disorders.

Prolonged activation of ERK triggers glutamate-induced apoptosis of astrocytes: neuroprotective effect of FK506

Although, astrocytes are more resistant than neurons to ischemic injury, astrocyte death has been demonstrated in animal models of brain ischemia. Astrocytes death after ischemia/reperfusion may strongly affect neuronal survival because of the absence of their trophic and metabolic support to neurons, and astrocytic glutamate uptake. Early signals involved in astrocytes death are poorly understood. We demonstrated enhanced and mostly cytoplasmic activation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) during glutamate-induced apoptosis of cultured astrocytes. Treatment with UO126, inhibitor of MEK1, threo-beta-benzyloxyaspartic acid, glutamate transporter inhibitor, and FK506, a cytoprotective drug prevented ERK activation and glutamate-induced apoptosis. Over-expression of ERK dual specificity phosphatases 5 and 6 reduced apoptosis in transfected astrocytes. Prolonged ERK1/2 activation was observed in ischemic brain: in the nucleus and cytoplasm of astrocytes in the cerebral cortex, and exclusively in the cytoplasm of astrocytes in the striatum. Global gene expression profiling in the cortex revealed that FK506 blocks middle cerebral artery occlusion-induced expression of numerous genes associated with ERK signaling pathway and apoptosis. The results demonstrate a pro-apoptotic role of sustained activation of ERK1/2 signaling in glutamate-induced death of astrocytes and the ability of FK506 to block both ERK activation and astrocytic cell death in vitro and in ischemic brains.

Astrocytes are more resistant to focal cerebral ischemia than neurons and die by a delayed necrosis

Several recent reports proposed that astrocyte death might precede neuronal demise after focal ischemia, contrary to the conventional view that astrocytes are more resistant to injury than neurons. Interestingly, there are findings supporting each of these opposing views. To clarify these controversies, we assessed astrocyte viability after 2-h middle cerebral artery occlusion in mice. In contrast to neighboring neurons, astrocytes were alive and contained glycogen across the ischemic area 6 h after reperfusion, and at the expanding outer border of the infarct at later time points. These glycogen-positive astrocytes had intact plasma membranes. Astrocytes lost plasmalemma integrity much later than neurons: 19 +/- 22 (mean +/- standard deviation), 58 +/- 14 and 69 +/- 3% of astrocytes in the perifocal region became permeable to propidium iodide (PI) at 6, 24, 72 h after ischemia, respectively, in contrast to 81 +/- 2, 96 +/- 3, 97 +/- 2% of neurons. Although more astrocytes in the cortical and subcortical core regions were PI-positive, their numbers were considerably less than those of neurons. Lysosomal rupture (monitored by deoxyribonuclease II immunoreactivity) followed a similar time course. Cytochrome-c immunohistochemistry showed that astrocytes maintained mitochondrial integrity longer than neurons. EM confirmed that astrocyte ultrastructure including mitochondria and lysosomes disintegrated much later than that of neurons. We also found that astrocytes died by a delayed necrosis without significantly activating apoptotic mechanisms although they rapidly swelled at the onset of ischemia.

Optimizing the success of cell transplantation therapy for stroke

Stem cell transplantation has evolved as a promising experimental treatment approach for stroke. In this review, we address the major hurdles for successful translation from basic research into clinical applications and discuss possible strategies to overcome these issues. We summarize the results from present pre-clinical and clinical studies and focus on specific areas of current controversy and research: (i) the therapeutic time window for cell transplantation; (ii) the selection of patients likely to benefit from such a therapy; (iii) the optimal route of cell delivery to the ischemic brain; (iv) the most suitable cell types and sources; (v) the potential mechanisms of functional recovery after cell transplantation; and (vi) the development of imaging techniques to monitor cell therapy.

High extracellular glutamate modulates expression of glutamate transporters and glutamine synthetase in cultured astrocytes

Astroglial cells clear extracellular glutamate through the glutamate transporters, GLT-1 and GLAST, and subsequently convert the incorporated glutamate into glutamine by the enzyme, glutamine synthetase (GS). Several forms of acute brain injury are associated with the increased expression of GS and the decreased expression of GLT-1 and/or GLAST, eventually leading to the accumulation of excitotoxic extracellular glutamate concentrations. Although of clinical interest, the actual trigger of these injury-related changes of glial glutamate turnover remains unknown. Our present studies provide evidence that increases in extracellular glutamate, as present in many brain injuries, are sufficient to modulate the expression of glutamate transporters and GS. Subjecting cultured cortical astrocytes to glutamate concentrations of 0.5-20 mM resulted in a 25% loss of GLT-1 and GLAST protein levels after 24 h; GLT-1 and GLAST levels maximally decreased by 40% and 75%, respectively, after 72 h. This decline was not due to astroglial cell death, since glutamate up to 50 mM did not affect the survival of cultured astrocytes within 72 h. Major astrocytic cell death, however, occurred in cultures maintained under severe (4% O(2)), but not mild (9% O(2)), hypoxia, as well as in the presence of aspartate (>or=20 mM). Glutamate at >or=1 mM induced a prolonged increase of GS expression in contrast to glutamate transporters. Neither the decline of glutamate transporter expression nor the increase in GS expression induced by high extracellular glutamate was further modulated by mild hypoxia. Whereas the stimulatory influences of glutamate on GS expression were prevented by the non-competitive NMDA receptor antagonist, MK801, the inhibitory influences on glutamate transporter expression were neither sensitive to MK801, the non-competitive mGluR5 antagonist, MTEP, nor the non-competitive AMPA receptor antagonist, GYKI52466, implying that glutamate controls glial glutamate transport by a glutamate receptor-independent mechanism.

CD38 regulation in activated astrocytes: implications for neuroinflammation and HIV-1 brain infection

Reactive astrogliosis is a key pathological aspect of neuroinflammatory disorders including human immunodeficiency virus type 1 (HIV-1)-associated neurological disease. On the basis of previous data that showedastrocytes activated with interleukin (IL)-1beta induce neuronal injury, we analyzed global gene changes in IL-1beta-activated human astrocytes by gene microarray. Among the up-regulated genes, CD38, a 45-kDa type II single chain transmembrane glycoprotein, was a top candidate, with a 17.24-fold change that was validated by real-time polymerase chain reaction. Key functions of CD38 include enzymatic activities and involvement in adhesion and cell signaling. Importantly, CD38(+)CD8(+) T-cell expression is a clinical correlate for progression of HIV-1 infection and biological marker for immune activation. Thus, CD38 expression in HIV-1 and/or IL-1beta-stimulated human astrocytes and human brain tissues was analyzed. IL-1beta and HIV-1 activation of astrocytes enhanced CD38 mRNA levels. Both CD38 immunoreactivity and adenosine 5'-diphosphate (ADP)-ribosyl cyclase activity were up-regulated in IL-1beta-activated astrocytes. CD38 knockdown using specific siRNAs significantly reduced astrocyte proinflammatory cytokine and chemokine production. However, CD38 mRNA levels were unchanged in IL-1beta knockdown conditions, suggesting that IL-1beta autocrine loop is not implicated in this process. Quantitative immunohistochemical analysis of HIV-seropositive without encephalitis and HIV-1 encephalitis brain tissues showed significant up-regulation of CD38, which colocalized with glial fibrillary acidic protein-positive cells in areas of inflammation. These results suggest an important role of CD38 in the regulation of astrocyte dysfunction during the neuroinflammatory processes involved in neurodegenerative/neuroinflammatory disorders such as HIV-1 encephalitis.

Determinants of regional and local diversity within the astroglial lineage of the normal central nervous system

Astrocytes are a major component of the resident non-neuronal glial cell population of the CNS. They are ubiquitously distributed throughout the brain and spinal cord, where they were initially thought to function in both structural and homeostatic capacities, providing the framework and environment in which neurons performed their parenchymal duties. However, this stroma-like view of astrocytes is no longer satisfactory. Mounting evidence particularly within the last decade indicates that astrocytes do not simply support neuronal activity but directly contribute to it. Congruent with this evolving view of astrocyte function in information processing is the emergent notion that these glial cells are not a homogeneous population of cells. Thus, astrocytes in various anatomically distinct regions of the normal CNS possess unique phenotypic characteristics that may directly influence the particular neuronal activities that define these regions. Remarkably, regional populations of astrocytes appear to exhibit local heterogeneity as well. Many phenotypic traits of the astrocyte lineage are responsive to local environmental cues (i.e., are adaptable), suggesting that plasticity contributes to this diversity. However, compelling evidence suggests that astrocytes arise from multiple distinct progenitor pools in the developing CNS, raising the intriguing possibility that some astrocyte heterogeneity may result from intrinsic differences between these progenitors. The purpose of this review is to explore the evidence for and mechanistic determinants of regional and local astrocyte diversity.

Aquaporin 4 knockout resists negative regulation of neural cell proliferation by cocaine in mouse hippocampus

Our previous study revealed that aquaporin 4 (AQP4) knockout attenuated locomotor activity in cocaine exposure mice and reduced the extracellular dopamine levels in the nucleus accumbens, suggesting that AQP4 might participate in cocaine addiction. The aim of the present study was to investigate the impact of AQP4 on cell proliferation of dentate gyrus in the mouse hippocampus after repeated cocaine treatment and withdrawal. The immunohistochemistry results showed that repeated cocaine administration significantly decreased cellular proliferation in the subgranular zone, which was followed by a rebound increase after 2-wk withdrawal and a return to normal level after 3-wk withdrawal. AQP4 knockout resisted cocaine-induced reductions of neural cell proliferation. Further studies through immunohistochemistry and immunoblot analysis showed that AQP4 knockout sustained the levels of glial fibrillary acidic protein in the hippocampus, and suppressed the enhancement of extracellular signal-regulated kinase phosphorylation induced by repeated cocaine administration. Notably, AQP4 knockout increased protein kinase C activity examined by substrate protein phosphorylation method, which was not affected by cocaine administration or withdrawal. We also found that repeated cocaine administration could elevate the expression of AQP4 in wild-type mice. In conclusion, it is reported for the first time that AQP4 knockout resisted cocaine-mediated inhibition of neural cell proliferation via up-regulating PKC-mediated signal transduction, suggesting that AQP4 might regulate neurogenesis during drug addiction. Our findings may have helpful implications in the cell biology of neurogenesis.

Photothrombosis ischemia stimulates a sustained astrocytic Ca2+ signaling in vivo

Although there is significant information concerning the consequences of cerebral ischemia on neuronal function, relatively little is known about functional responses of astrocytes, the predominant glial-cell type in the central nervous system. In this study, we asked whether focal ischemia would impact astrocytic Ca(2+) signaling, a characteristic form of excitability in this cell type. In vivo Ca(2+) imaging of cortical astrocytes was performed using two-photon (2-P) microscopy during the acute phase of photothrombosis-induced ischemia initiated by green light illumination of circulating Rose Bengal. Although whisker evoked potentials were reduced by over 90% within minutes of photothrombosis, astrocytes in the ischemic core remained structurally intact for a few hours. In vivo Ca(2+) imaging showed that an increase in transient Ca(2+) signals in astrocytes within 20 min of ischemia. These Ca(2+) signals were synchronized and propagated as waves amongst the glial network. Pharmacological manipulations demonstrated that these Ca(2+) signals were dependent on activation of metabotropic glutamate receptor 5 (mGluR5) and metabotropic gamma-aminobutyric acid receptor (GABA(B)R) but not by P2 purinergic receptor or A1 adenosine receptor. Selective inhibition of Ca(2+) in astrocytes with BAPTA significantly reduced the infarct volume, demonstrating that the enhanced astrocytic Ca(2+) signal contributes to neuronal damage presumably through Ca(2+)-dependent release of glial glutamate. Because astrocytes offer multiple functions in close communication with neurons and vasculature, the ischemia-induced increase in astrocytic Ca(2+) signaling may represent an initial attempt for these cells to communicate with neurons or provide feed back regulation to the vasculature.

Green tea polyphenols attenuate glial swelling and mitochondrial dysfunction following oxygen-glucose deprivation in cultures

Astrocyte swelling is a major component of cytotoxic brain edema in ischemia. Oxidative stress and mitochondrial dysfunction have been hypothesized to contribute to such swelling in cultures. We investigated the protective effects of polyphenol-rich green tea extract (GTE) on key features of ischemic injury namely cell swelling, nitric oxide (NO) production, and depolarization of the inner mitochondrial membrane potential (Deltapsi(m)). C6 glial cultures were subjected to 5-h oxygen-glucose deprivation (OGD) and cell volume was determined using the 3-O-methyl-glucose method. At 90 min after the end of OGD, cell volume increased by > 33% and this increase was attenuated by GTE but not by the individual polyphenol components including catechin, epicatechin, or epigallocatechin gallate (EGCG). However, a combination of catechin, epicatechin and EGCG prevented swelling. OGD-induced increase in NO was further increased by GTE. OGD-induced decline in Deltapsi(m) was also attenuated by green tea extract, EGCG and a combination of catechin, epicatechin and EGCG but not by catechin or epicatechin alone. Our findings indicate a protective effect of GTE in cell swelling in ischemic injury and such protective effects may be mediated by its effect on the mitochondria. It appears that effects on cell swelling are mediated by the concerted action of more than one of the individual components of GTE.

Molecular and magnetic resonance imaging of human embryonic stem cell-derived neural stem cell grafts in ischemic rat brain

Real-time imaging of transplanted stem cells is essential for understanding their interactions in vivo with host environments, for tracking cell fate and function and for successful delivery and safety monitoring in the clinical setting. In this study, we used bioluminescence (BLI) and magnetic resonance imaging (MRI) to visualize the fate of grafted human embryonic stem cell (hESC)-derived human neural stem cells (hNSCs) in stroke-damaged rat brain. The hNSCs were genetically engineered with a lentiviral vector carrying a double fusion (DF) reporter gene that stably expressed enhanced green fluorescence protein (eGFP) and firefly luciferase (fLuc) reporter genes. The hNSCs were self-renewable, multipotent, and expressed markers for neural stem cells. Cell survival was tracked noninvasively by MRI and BLI for 2 months after transplantation and confirmed histologically. Electrophysiological recording from grafted GFP(+) cells and immuno-electronmicroscopy demonstrated connectivity. Grafted hNSCs differentiated into neurons, into oligodendrocytes in stroke regions undergoing remyelination and into astrocytes extending processes toward stroke-damaged vasculatures. Our data suggest that the combination of BLI and MRI modalities provides reliable real-time monitoring of cell fate.

IGF-1 derived small neuropeptides and analogues: a novel strategy for the development of pharmaceuticals for neurological conditions

Insulin-like growth factor-1 (IGF-1) is neuroprotective and improves long-term function after brain injury. However, its clinical application to neurological disorders is limited by its large molecular size, poor central uptake and mitogenic potential. Glycine-proline-glutamate (GPE) is naturally cleaved from the IGF-1 N-terminal and it is also neuroprotective after ischemic injury, which provided a novel strategy of drug discovery for neurological disorders. GPE is not enzymatically stable, thus intravenous infusion of GPE becomes necessary for stable and potent neuroprotection. The broad effective dose range and treatment window of 3-7 h after the lesion suggest its potential for treating acute brain injuries. G-2meth-PE, a GPE analogue designed to be more enzymatic resistant, has a prolonged plasma half-life and is more potent in neuroprotection. Neuroprotection by GPE and its analogue may involve modulation of inflammation, promotion of astrocytosis, inhibition of apoptosis and vascular remodelling. Acute administration of GPE also prevents 6-OHDA-induced nigrostrial dopamine depletion. Delayed treatment with GPE does not prevent dopamine loss, but improves long-term function. Cyclo-glycyl-proline (cyclic Gly-Pro) is an endogenous DKP that may be derived from GPE. Cyclic Gly-Pro and its analogue cyclo-L-glycyl-L-2-allylproline (NNZ 2591) are both neuroprotective after ischaemic injury. NNZ2591 is highly enzymatic resistant and centrally accessible. Its peripheral administration improves somatosensory-motor function and long-term histological outcome after brain injury. Our research suggests that small neuropeptides have advantages over growth factors in the treatment of brain injury, and that modified neuropeptides designed to overcome the limitations of their endogenous counterparts represent a novel strategy of pharmaceutical discovery for neurological disorders.

A systems approach to prion disease

Prions cause transmissible neurodegenerative diseases and replicate by conformational conversion of normal benign forms of prion protein (PrP^C) to disease-causing PrP^Sc isoforms. A systems approach to disease postulates that disease arises from perturbation of biological networks in the relevant organ. We tracked global gene expression in the brains of eight distinct mouse strain–prion strain combinations throughout the progression of the disease to capture the effects of prion strain, host genetics, and PrP concentration on disease incubation time. Subtractive analyses exploiting various aspects of prion biology and infection identified a core of 333 differentially expressed genes (DEGs) that appeared central to prion disease. DEGs were mapped into functional pathways and networks reflecting defined neuropathological events and PrP^Sc replication and accumulation, enabling the identification of novel modules and modules that may be involved in genetic effects on incubation time and in prion strain specificity. Our systems analysis provides a comprehensive basis for developing models for prion replication and disease, and suggests some possible therapeutic approaches.

Characterization of proteasome inhibition on astrocytes cell cycle

Increasing evidence indicates that proteasome inhibition occurs in multiple central nervous system (CNS) disorders, including Alzheimer's disease (AD) and Parkinson's disease (PD). Compared with the extensive studies on neurons, little attention is paid on the proteasome inhibition in astrocytes. Here, we demonstrated that lactacystin inhibited proteasome dose-dependently in cultured astrocytes. Simultaneously, lactacystin suppressed the expression of cell cycle proteins in astrocytes and caused the proliferating astrocytes arrested at G1/S checkpoint. Western blots showed that proteasome inhibition led to a decrease in cdk-2, cdk-4, cyclin D1 expression accompanied with an increase in p21waf1/cip1 expression. The effect of chronic low-level proteasome inhibition on astrocytes was consistent with that in acute proteasome inhibition. Furthermore, increased levels of interleukin-6 (IL-6) secretion, STAT-3 and phospho-STAT-3 expression were found, suggesting that proteasome inhibition in astrocytes could stabilize signals of grow arrest through the JAK/STAT signaling cascade.

Astroglia in dementia and Alzheimer's disease

Astrocytes, the most numerous cells in the brain, weave the canvas of the grey matter and act as the main element of the homoeostatic system of the brain. They shape the microarchitecture of the brain, form neuronal-glial-vascular units, regulate the blood-brain barrier, control microenvironment of the central nervous system and defend nervous system against multitude of insults. Here, we overview the pathological potential of astroglia in various forms of dementias, and hypothesise that both atrophy of astroglia and reactive hypertrophic astrogliosis may develop in parallel during neurodegenerative processes resulting in dementia. We also show that in the transgenic model of Alzheimer's disease, reactive hypertrophic astrocytes surround the neuritic plaques, whereas throughout the brain parenchyma astroglial cells undergo atrophy. Astroglial atrophy may account for early changes in synaptic plasticity and cognitive impairments, which develop before gross neurodegenerative alterations.

Hypoxic-ischemic brain injury activates early hippocampal stem/progenitor cells to replace vulnerable neuroblasts

Although the phenomenon of ongoing neurogenesis in the hippocampus is well described, it remains unclear what relevance this has in terms of brain self-repair following injury. In a highly regulated developmental program, new neurons are added to the inner granular cell layer of the dentate gyrus (DG) where slowly dividing radial glial-like type 1 neural stem/progenitors (NSPs) give rise to rapidly proliferating type 2 neural progenitors which undergo selection and maturation into functional neurons. The induction of these early hippocampal progenitors after injury may represent an endogenous mechanism for brain recovery and remodeling. To determine what role early hippocampal progenitors play in remodeling following injury, we utilized a model of hypoxic-ischemic injury on young transgenic mice that express green fluorescent protein (GFP) specifically in neural progenitors. We demonstrate that this injury selectively activates programmed cell death in committed but immature neuroblasts, which is followed by proliferation of both early type 1 and later type 2 progenitors. This subsequently leads to newly generated neurons becoming stably incorporated into the DG.

Adenosine A1 and A3 receptors protect astrocytes from hypoxic damage

Brain levels of adenosine are elevated during hypoxia. Through effects on adenosine receptors (A(1), A(2A), A(2B) and A(3)) on astrocytes, adenosine can influence functions such as glutamate uptake, reactive gliosis, swelling, as well as release of neurotrophic and neurotoxic factors having an impact on the outcome of metabolic stress. We have studied the roles of these receptors in astrocytes by evaluating their susceptibility to damage induced by oxygen deprivation or exposure to the hypoxia mimic cobalt chloride (CoCl(2)). Hypoxia caused ATP breakdown and purine release, whereas CoCl(2) (0.8 mM) mainly reduced ATP by causing cell death in human D384 astrocytoma cells. Further experiments were conducted in primary astrocytes prepared from specific adenosine receptor knock-out (KO) and wild type (WT) mice. In WT cells purine release following CoCl(2) exposure was mainly due to nucleotide release, whereas hypoxia-induced intracellular ATP breakdown followed by nucleoside efflux. N-ethylcarboxamidoadenosine (NECA), an unselective adenosine receptor agonist, protected from cell death following hypoxia. Cytotoxicity was more pronounced in A(1)R KO astrocytes and tended to be higher in WT cells in the presence of the A(1) receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX). Genetic deletion of A(2A) receptor resulted in less prominent effects. A(3)R KO glial cells were more affected by hypoxia than WT cells. Accordingly, the A(3) receptor agonist 2-chloro-N(6)-(3-iodobenzyl)-N-methyl-5'-carbamoyladenosine (CL-IB-MECA) reduced ATP depletion caused by hypoxic conditions. It also reduced apoptosis in human astroglioma D384 cells after oxygen deprivation. In conclusion, the data point to a cytoprotective role of adenosine mediated by both A(1) and A(3) receptors in primary mouse astrocytes.

Possible involvement of P2X7 receptor activation in microglial neuroprotection against focal cerebral ischemia in rats

Microglia play important roles in the pathogenic cascade following cerebral ischemia, since they express growth factors, chemokines and regulatory cytokines as well as free radicals and other toxic mediators. P2X7 receptor, a subtype of a family of P2 purinoceptors, is primarily expressed in microglia and macrophages, suggesting that it regulates immune function and inflammatory responses. However, the involvement of ATP in such microglial responses after cerebral ischemia is not yet understood. In this study, we investigated the possible involvement of ATP, especially through the P2X7 receptors, in a rat model of focal cerebral ischemia. In immunohistochemical analysis, P2X7 receptor-like immunoreactivity was predominantly detected in microglia, and then activated microglia accumulated in the ischemic region, in rats subjected to middle cerebral artery occlusion (MCAO) and reperfusion. Intracerebroventricular injection with P2X7 receptor agonist 2'-3'-O-(4-benzoylbenzoyl)adenosine 5'-triphosphate (BzATP) improved behavioral dysfunction accessed by rota-rod test and ischemic neural injury induced by MCAO. In contrast, P2X7 receptor antagonist adenosine 5'-triphosphate-2',3'-dialdehyde (OxATP) exacerbated ischemic brain damage. These results suggest that microglia play an important role in neuroprotection against rat cerebral ischemia, which is regulated by a P2X7 receptor-mediated ATP signal.

Gene expression profiling of astrocytes from hyperammonemic mice reveals altered pathways for water and potassium homeostasis in vivo

Acute hyperammonemia (HA) causes cerebral edema and brain damage in children with urea cycle disorders (UCDs) and in patients in acute liver failure. Chronic HA is associated with developmental delay and mental retardation in children with UCDs, and with neuropsychiatric symptoms in patients with chronic liver failure. Astrocytes are a major cellular target of hyperammonemic encephalopathy, and changes occurring in these cells are thought to be causally related to the brain edema of acute HA. To study the effect of HA on astrocytes in vivo, we crossed the Otc(spf) mouse, a mouse with the X-linked UCD ornithine transcarbamylase (OTC) deficiency, with the hGFAP-EGFP mouse, a mouse selectively expressing green fluorescent protein in astrocytes. We used FACS to purify astrocytes from the brains of hyperammonemic and healthy Otcspf/GFAP-EGFP mice. RNA isolated from these astrocytes was used in microarray expression analyses and qRT-PCR. When compared with healthy littermates, we observed a significant downregulation of the gap-junction channel connexin 43 (Cx43) the water channel aquaporin 4 (Aqp4) genes, and the astrocytic inward-rectifying potassium channel (Kir) genes Kir4.1 and Kir5.1 in hyperammonemic mice. Aqp4, Cx43, and Kir4.1/Kir5.1 are co-localized to astrocytic end-feet at the brain vasculature, where they regulate potassium and water transport. Since, NH4+ ions can permeate water and K+-channels, downregulation of these three channels may be a direct effect of elevated blood ammonia levels. Our results suggest that alterations in astrocyte-mediated water and potassium homeostasis in brain may be key to the development of the brain edema.