Signal transduction in neuronal death

The miR206-JunD Circuit Mediates the Neurotoxic Effect of Methylmercury in Cortical Neurons

Methylmercury (MeHg) causes neuronal death through different pathways. Particularly, we found that in cortical neurons it increased the expression of Repressor Element-1 Silencing Transcription Factor (REST), histone deacetylase (HDAC)4, Specificity Protein (Sp)1, Sp4, and reduced the levels of brain-derived neurotrophic factor (BDNF). Herein, in rat cortical neurons we investigated whether microRNA (miR)206 can modulate MeHg-induced cell death by regulating REST/HDAC4/Sp1/Sp4/BDNF axis. MeHg (1 µM) reduced miR206 expression after both 12 and 24 h and miR206 transfection prevented MeHg-induced neuronal death. Furthermore, miR206 reverted MeHg-induced REST and Sp4 increase and BDNF reduction at gene and protein level, and reverted HDAC4 protein increase, but not HDAC4 mRNA upregulation. Moreover, since no miR206 seed sequences were identified in the 3'-untranslated regions (3'-UTRs) of REST and SP4, we investigated the role of JunD, that presents a consensus motif on REST, Sp4, and BDNF promoters. Indeed, MeHg increased JunD mRNA and protein levels, and JunD knockdown counteracted MeHg-induced REST, Sp4 increase, but not BDNF reduction. Furthermore, we identified a miR206 binding site in the 3'-UTR of JunD mRNA (miR206/JunD) and mutagenesis of miR206/JunD site reverted JunD luciferase activity reduction induced by miR206. Finally, miR206 prevented MeHg-increased JunD binding to REST and Sp4 promoters, and MeHg-reduced BDNF expression was determined by the increase of HDAC4 binding on BDNF promoter IV. Collectively, these results suggest that miR206 downregulation induced by MeHg exposure determines an upregulation of HDAC4, that in turn downregulated BDNF, and the activation of JunD that, by binding REST and Sp4 gene promoters, increased their expression.

Low extracellular zinc increases neuronal oxidant production through nadph oxidase and nitric oxide synthase activation

A decrease in zinc (Zn) levels increases the production of cell oxidants, affects the oxidant defense system and triggers oxidant sensitive signals in neuronal cells. However, the underlying mechanisms are still unclear. This work tested the hypothesis that the increase in neuronal oxidants that occurs when cellular Zn decreases is mediated by the activation of the NMDA receptor. Differentiated PC12 cells were cultured in control, Zn-deficient or Zn-repleted media. The incubation in Zn deficient media led to a rapid increase in cellular calcium levels, which was prevented by a NMDA receptor antagonist (MK-801). Cellular calcium accumulation was associated with NADPH oxidase and nitric oxide synthase (NOS) activation, an increase in cell oxidant levels, and an associated activation of a redox-sensitive signal (AP-1). In cells incubated in the Zn deficient medium, NADPH oxidase activation was prevented by MK-801 and by a protein kinase C inhibitor. The rise in cell oxidants was prevented by inhibitors of NADPH oxidase, of the NOS and by MK-801. A similar pattern of inhibitor action was observed for zinc deficiency-induced AP-1 activation. Results demonstrate that a decrease in extracellular Zn leads to an increase in neuronal oxidants through the activation of the NMDAR that leads to calcium influx and to a calcium-mediated activation of protein kinase C/NADPH oxidase and NOS. Changes in extracellular Zn concentrations can be sensed by neurons, which using reactive oxygen and nitrogen species as second messengers, can regulate signaling involved in neuronal development and function.

Differential gene expression in the rat cochlea after exposure to impulse noise

Understanding the molecular biology of noise trauma is vital to developing effective and timely interventions. In a model of explosion-mediated impulse noise injury, differential gene expression was studied in whole rat cochlea preparations at 3 and 24 h following the exposure. We developed a technique using mRNA from a single cochlea on each oligonucleotide microarray to avoid pooling of mRNA samples. Application of a conservative statistical analysis approach resulted in the identification of 61 differentially expressed genes. Within 3 h after the exposure, there was an up-regulation of immediate early genes, mainly transcription factors and genes involved in the tissue's response to oxidative stress. No genes were found to be significantly down-regulated. At 24 h following the exposure, up-regulated genes included members of inflammatory and antioxidant pathways and one gene involved in glutathione metabolism was down-regulated. A subset of genes was confirmed by real-time reverse transcriptase-polymerase chain reaction (RT-PCR). The present study demonstrates the power of the microarray technique in providing a global view of the gene regulation following noise exposure, and in identifying genes that may be mechanistically important in hearing loss, and thereby serve as a basis for the development of therapeutic interventions.

Effect of acupuncture treatment on vascular dementia

OBJECTIVE

Recent studies have suggested that acupuncture can ameliorate some symptoms commonly associated with vascular dementia (VaD). The study was carried out to observe the clinical therapeutic effects for VaD of 'yi qi tiao xue, fu ben pei yuan' acupuncture method (supplementing vital force-matter and regulating blood, supporting the root and fostering the source).

METHODS

Sixty inpatients with VaD were randomly assigned to the treat group (TG) or control group (CG). Both the TG and the CG received routine treatment as other inpatients with VaD, including medication and traditional acupuncture treatment. After that, the TG was given the treatment of 'yi qi tiao xue, fu ben pei yuan' acupuncture, which included five body acupoints, namely, tanzhong (CV17), zhongwan (CV12), qihai (CV6), zusanli (ST36) and xuehai (SP10). The Treatment was performed once daily for 6 weeks. The mini-mental status examination (MMSE), the revised Hasegawa's dementia scale (HDS-R) and activities of daily living (ADL) exam were carried out before and after the experiment, to evaluate therapeutic effects of the acupuncture method.

RESULTS

The MMSE, HDS-R and ADL scores were significantly improved in the TG and CG (p<0.001). But the overall scores of MMSE and HDS-R for the subjects in the TG were notably higher than those in the CG (p<0.05). Patients in the TG showed remarkable improvement in memory, orientation, calculation and self-managing ability in daily living after treatment. The total effective rate was 80.0% in the TG versus 46.7% in the CG, where significant difference between the two groups exhibited (p<0.05).

CONCLUSIONS

These results suggested that 'yi qi tiao xue, fu ben pei yuan' acupuncture method had significant therapeutic effects and well tolerated in ameliorate the key clinical symptoms of VaD.

Cell cycle molecules and vertebrate neuron death: E2F at the hub

Vertebrate neuron cell death is both a normal developmental process and the catastrophic outcome of nervous system trauma or degenerative disorders. Although the mechanisms of such death include an evolutionarily conserved core apoptotic pathway that is highly homologous to that first described by Horvitz and co-workers in Caenorhabditis elegans, it appears that many instances of neuron death additionally require the transcription-dependent induction of proapoptotic molecules. One such proapoptotic transcriptional pathway revealed by studies over the past decade revolves about the transcription factor E2F and those molecules that either regulate E2F activity or that are direct or indirect transcriptional targets of E2F. Many of the molecules associated with the E2F apoptotic pathway in postmitotic neurons also participate in the cell cycle in proliferating cells. Observations in human material and in animal and cell culture models show widespread correlation between changes in expression, activity and subcellular localization of E2F-related cell cycle molecules and developmental and catastrophic neuron death. A variety of experimental approaches support a causal role for such changes in the death process and are beginning to indicate how the neuronal E2F pathway activates the core apoptotic machinery. The discovery and elaboration of the neuronal apoptotic E2F pathway provides abundant targets as well as small molecule candidates for potential therapeutic intervention in nervous system trauma and degenerative disease.

Acupuncture suppresses intrastriatal hemorrhage-induced apoptotic neuronal cell death in rats

Intracerebral hemorrhage is one of the most devastating types of stroke. In the present study, the effect of acupuncture on intrastriatal hemorrhage-induced neuronal cell death in rats was investigated via Nissl staining, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay, and immunohistochemistry for caspase-3. The present results showed that lesion size and apoptotic neuronal cell death in the striatum were significantly increased following intrastriatal hemorrhage in rats and that acupunctural treatment at the Zusanli acupoint suppressed the hemorrhage-induced increase in lesion size and apoptotic neuronal cell death in the striatum. In the present study, it can be suggested that acupunctural treatment, especially at the Zusanli acupoint, may aid in the recovery following central nervous system sequellae following intracerebral hemorrhage.

Dipyridamole is neuroprotective for cultured rat embryonic cortical neurons

The effects of a clinically useful cardiovascular agent, dipyridamole, were examined in a rodent tissue culture model of neuroprotection. Dipyridamole effectively protected rat embryonic day 18 (E18) cortical neurons from either 48 h trophic deprivation or 48 h exposure to the glutathione synthesis inhibitor, L-buthionine (R,S) sulfoximine. The neuron sparing actions of dipyridamole were time- and concentration-dependent and mimicked the actions of exogenously applied glutathione. These results demonstrate that dipyridamole protects primary neuronal cultures against either trophic or chemically mediated insults, and suggest that dipyridamole has a potent antioxidant ability that compensates for glutathione depletion in neuronal cultures.

Electro-acupuncture preconditioning abrogates the elevation of c-Fos and c-Jun expression in neonatal hypoxic-ischemic rat brains induced by glibenclamide, an ATP-sensitive potassium channel blocker

This study aimed to clarify the neuroprotective mechanism of electro-acupuncture (EA) preconditioning on hypoxic-ischemic brain injury (HIBI). Using Western blot, the expression of c-fos protein (c-Fos) and c-jun protein (c-Jun) induced by glibenclamide, an ATP-sensitive potassium (K(ATP)) channel blocker was examined from cerebral cortical and hippocampal samples in neonatal hypoxic-ischemic rats, with or without EA preconditioning. EA was performed on Hegu (LI4), a well-known acupoint commonly used in Oriental medicine for the treatment of neuronal injury resulting from hypoxia-ischemia (HI). Preconditioned rats were treated with either diazoxide, a K(ATP) channel opener, glibenclamide, or sterile saline injected into the left lateral ventricle (i.c.v.), with or without EA administration before HI insult. Interestingly, low c-Fos and c-Jun expressions were found both in diazoxide and EA groups, 24 h after HI. Furthermore, significant differences in relative optical density (ROD) were found between glibenclamide and HI control groups (P< or =0.05), as well as between the group administered glibenclamide after EA and the HI control group (P< or =0.05). However, the level of c-Fos and c-Jun expression in the group administered glibenclamide after EA was significantly lower than in the glibenclamide group (P< or =0.05). The present findings indicate that the effectiveness of EA preconditioning against HIBI may be mediated via the opening of K(ATP) channels.

Modulation of activator protein 1/DNA binding activity by acoustic overstimulation in the guinea-pig cochlea

Changes in gene expression are part of the homeostatic machinery with which cells respond to external stimuli or assaults. The activity of the early response transcriptional factor activator protein-1 (AP-1) can be modulated by a variety of environmental stimuli including those that alter the cellular oxidation/reduction status. This study investigates the activation of AP-1/DNA binding in the guinea-pig cochlea in response to acoustic overstimulation which produces reactive oxygen species. Electrophoretic mobility shift assays revealed that binding of AP-1 to its radiolabeled oligonucleotide probe markedly changed in nuclear extracts of inner ear tissues following intense noise exposure (4 kHz octave band, 115 dB, 5 h). AP-1/DNA binding increased in the organ of Corti and the lateral wall tissues immediately after the exposure, returning to near-baseline levels 5 h later. At 15 h after noise, a second peak of binding activity occurred in the organ of Corti whereas stria vascularis showed a lesser but more sustained activity. Binding in nuclear extracts from the spiral ganglion did not change. Incubation of nuclear extracts with antibodies against Fos/Jun family proteins prior to a supershift assay showed Fra-2 as a major component of the AP-1 complex immediately after the noise exposure. In the organ of Corti, Fra-2 immunoreactivity was localized to the middle turn, i.e. the region which is most affected by the 4-kHz octave band exposure. The results suggest the modulation of gene expression via the activation of AP-1 as a consequence of noise trauma but also demonstrate differential responses in cochlear tissues.

JNK-dependent phosphorylation of c-Jun on serine 63 mediates nitric oxide-induced apoptosis of neuroblastoma cells

c-Jun NH2-terminal kinases (JNKs) potentiate transcriptional activity of c-Jun by phosphorylating serines 63 and 73. Moreover, JNK and c-Jun can modulate apoptosis. However, an involvement of nitric oxide (NO)-induced phosphorylation of c-Jun on Ser-63 and Ser-73 in apoptosis has not been explored. We report that in SH-Sy5y neuroblastoma cells, NO induced apoptosis following JNK activation and phosphorylation of c-Jun almost exclusively on Ser-63. Importantly, NO-induced apoptosis and caspase-3 activity were inhibited in cells stably transformed with dominant-negative c-Jun in which Ser-63 is mutated to alanine (S63A), but not in cells transformed with dominant-negative c-Jun (S73A). Ser-63 of c-Jun (but not Ser-73) was required for NO-induced, c-Jun-dependent transcriptional activity. NO-induced apoptosis, Ser-63 phosphorylation of c-Jun, and caspase-3 activity were all inhibited in SH-Sy5y cells transformed with dominant-negative jnk. A caspase-3 inhibitor prevented apoptosis but not c-Jun phosphorylation. In a different neuroblastoma cell line, NO-induced Ser-63 phosphorylation of c-Jun and apoptosis were blocked by a specific JNK inhibitor. We conclude that NO-inducible apoptosis is mediated by JNK-dependent Ser-63 phosphorylation of c-Jun upstream of caspase-3 activation in neuroblastoma cells.

Treatment with the snail peptide CGX-1007 reduces DNA damage and alters gene expression of c-fos and bcl-2 following focal ischemic brain injury in rats

Delayed cell death following ischemic brain injury has been linked to alterations in gene expression. In this study we have evaluated the upregulation of several genes associated with delayed cell death (c-fos, bax, and bcl-2) during the initial 24 h of transient middle cerebral artery occlusion (MCAo) in the rat and the effects of postinjury treatment with the NR2B subunit specific NMDA receptor antagonist CGX-1007 (Conantokin-G, Con-G). C-fos mRNA levels peaked at 1 h postinjury in both cortical and subcortical ischemic brain regions (30-fold increase), remained elevated at 4 h and returned to within normal, preinjury levels 24 h postinjury. The increase in mRNA levels correlated to increased protein expression in the entire ipsilateral hemisphere at 1 h. Regions of necrosis at 4 h were void of C-Fos immunoreactivity with continued upregulation in surrounding regions. At 24 h, loss of C-Fos staining was observed in the injured hemisphere except for sustained increases along the border of the infarct and in the cingulate cortex of vehicle treated rats. CGX-1007 treatment reduced c-fos expression throughout the infarct region by up to 50%. No significant differences were measured in either bcl-2 or bax mRNA expression between treatment groups. However, at 24 h postinjury CGX-1007 treatment was associated with an increase in Bcl-2 immunoreactivity that correlated to a reduction in DNA fragmentation. In conclusion, CGX-1007 effectively attenuated gene expression associated with delayed cell death as related to a neuroprotective relief of cerebral ischemia.

Tumour necrosis factor-alpha- vs. growth factor deprivation-promoted cell death: different receptor requirements for mediating nerve growth factor-promoted rescue

Physiological and pathological aging of the central nervous system (CNS) is characterized by functional neuronal impairments which may lead to perturbed cell homeostasis and eventually to neuronal death. Many toxic events may underlie age-related neurodegeneration. These include the effects of beta amyloid, Tau and mutated presenilin proteins, free radicals and oxidative stress, pro-inflammatory cytokines and lack of growth factor support, which can be individually or collectively involved. Taken individually, these toxicants can induce very diverse cell responses, thus requiring individually targeted corrective interventions upstream of common cell death (apoptotic) pathways. Recent preliminary evidence suggests that the pro-inflammatory cytokine tumour necrosis factor alpha (TNFalpha) and growth factor withdrawal can both activate a common apoptotic pathway in nerve growth factor (NGF)-responsive PC12 cells involving caspase 3, albeit through very distinct upstream pathways: the former through active signalling and the latter through passive or lack of survival signalling. Here, we show that NGF can rescue PC12 cells from both growth factor withdrawal- and TNFalpha-promoted cell death. However, NGF rescue from growth factor withdrawal requires NGF signalling through the high-affinity tyrosine kinase receptor (TrkA), while NGF rescue from TNFalpha-promoted cell death requires NGF signalling through the low-affinity p75NTR receptor. These results strengthen the idea that prevention of age- or pathology-associated neurodegeneration may require varied molecular approaches reflecting the diversity of the toxicants involved, possibly acting simultaneously.

Attenuated transcriptional responses to oxidative stress in the aged rat brain

The aged nervous system displays impaired cognitive functions, and these impairments are exacerbated in several neurodegenerative diseases. A role for oxidative stress has been suggested for several of these age-associated dysfunctions. In addition, recovery from more acute traumatic insults that also generate oxidative stress is impaired in the aged. Here we examine the response of aged rat hippocampi to normobaric hyperoxia treatments and demonstrate an attenuation in the DNA binding activity of the AP-1 and nuclear factor-kappa B transcription factors, which are important components of stress response signal transduction pathways and can determine shifts in cellular commitments to necrosis, apoptosis, or functional recovery in the central nervous system.

Neuronal differentiation and protection from nitric oxide-induced apoptosis require c-Jun-dependent expression of NCAM140

c-Jun, a crucial component of the dimeric transcription factor activating protein 1 (AP-1), can regulate apoptosis induced by oxidative stress and has been implicated in neuronal differentiation, but the mechanisms are largely unknown. We found that specific inhibition of transcription or stable transfection with cDNA encoding dominant-negative c-Jun sensitized SH-SY5Y neuroblastoma cells (TAM-67 cells) to apoptosis induced by the nitric oxide (NO) donor sodium nitroprusside or SIN-1. TAM-67 cells also became refractory to nerve growth factor (NGF)-induced neuronal differentiation. Dominant-negative c-Jun abolished expression of a 140-kDa neural cell adhesion molecule (NCAM140) and dramatically enhanced the expression of NCAM180 in TAM-67 cells. Inhibition of c-Jun in TAM-67 cells also resulted in a corresponding decrease in the amount of NCAM140 mRNA and an increase in the amount of NCAM180 mRNA. Reexpression of NCAM140 in TAM-67 cells restored NGF-induced neuronal differentiation and resistance to NO-induced apoptosis. Our results show that c-Jun/AP-1, through up-regulation of NCAM140, plays an important role in both NGF-induced neuronal differentiation and resistance to apoptosis induced by NO in neuroblastoma cells. As NCAM140 and NCAM180 are translated from differentially spliced mRNAs transcribed from the same gene, alternative splicing of NCAM pre-mRNA (and consequently the synthesis of the smaller NCAM140 species) appears to be regulated by c-Jun/AP-1.

Localization of activator protein-1 complex with DNA binding activity in mitochondria of murine brain after in vivo treatment with kainate

To elucidate mechanisms underlying mitochondrial dysfunctions induced by glutamate, we have examined the effects of in vivo treatment with the ionotropic glutamate receptor agonist kainate on localization of the transcription factor activator protein-1 (AP-1) in mitochondria as well as nuclei of murine brain. A systemic administration of kainate dramatically enhanced AP-1 DNA binding in both mitochondrial and nuclear extracts of mouse cerebral cortex and hippocampus 1 hr to 3 d later. Unlabeled AP-1 probe selectively competed for AP-1 DNA binding in mitochondrial extracts of cortex and hippocampus obtained from mice injected with kainate. Supershift and immunoblotting analyses revealed participation of c-Fos, Fos-B, and Jun-B proteins in potentiation by kainate of mitochondrial AP-1 DNA binding in cortex and hippocampus. An immunohistochemical study demonstrated marked expression by kainate of c-Fos protein in the pyramidal and dentate granular layers, whereas an immunoelectron microscopic analysis showed localization of c-Fos protein within mitochondria, as well as nuclei, of the CA1 pyramidal and dentate granular cells in hippocampus obtained 2 hr after the administration of kainate. Mitochondrial AP-1 DNA binding was inhibited by particular unlabeled oligonucleotides containing sequences similar to the AP-1 site found in the noncoding region of mitochondrial DNA. Kainate markedly potentiated binding of radiolabeled oligonucleotide probes containing sequences effective in competing for AP-1 DNA binding in hippocampal mitochondrial extracts. These results suggest that kainate may facilitate expression of the AP-1 complex and subsequent translocation into mitochondria to participate in mechanisms associated with transcriptional regulation of mitochondrial DNA in murine hippocampus.

Regional distribution of heme oxygenase, HSP70, and glutathione in brain: relevance for endogenous oxidant/antioxidant balance and stress tolerance

It is generally recognized that lipid peroxides play an important role in the pathogenesis of several diseases and that sulfhydryl groups are critically involved in cellular defense against endogenous or exogenous oxidants. Recent evidence indicates that lipid peroxides directly participate in induction of cytoprotective proteins, such as heat shock proteins (Hsps), which play a central role in the cellular mechanisms of stress tolerance. Heme oxygenase (HO) is a stress protein that has been implicated in defense mechanisms against agents that may induce oxidative injury, such as endotoxins, cytokines and heme and its induction represents a common feature in a number of neurodegenerative diseases. In the present report we studied regional distribution of heme oxygenase (HO) activity and protein expression, together with that of Hps70, in brain of C57BL6 mice. Endogenous lipid peroxidation was investigated on the basis of the analysis of ultra weak chemiluminescence, hydro peroxides and lipid soluble fluorescent products, and compared to the regional distribution of thiols, antioxidant enzymes and trace metals. Our results show that levels of HO activity and expression of inducible Hsp70 and the ratio of GSH/GSSG in the different brain regions examined were positively correlated with the content of peroxides. Substantia Nigra was the brain area exhibiting the highest levels of HO-2, constitutive and inducible Hsp70, GSSG, peroxides, iron, and calcium, in contrast with the lowest content in GSH, GSH/GSSG ratio and glutathione reductase activity, compared to the other cerebral regions examined. Among these, cortex showed the lowest levels of HO-2, Hsp70, GSSG and peroxides that were associated with the highest levels of GSH and GSH/GSSG ratio. These data support the hypothesis that the glutathione redox state and basal peroxides can directly participate in the signaling pathways of heat shock protein expression and hence of stress tolerance.

Dual role of the NF-kappaB transcription factor in the death of immature neurons

We have previously shown that the extent of axotomy-induced death of retinal ganglion cells is reduced by cycloheximide, an inhibitor of protein synthesis, and that an earlier sublethal oxidative insult induced by buthionine sulfoximine, a glutathione synthesis inhibitor, enhances the protective effects of cycloheximide. Thus, axotomy-induced ganglion cell death seems to involve an interaction between the redox status and genetic expression. The redox-sensitive transcription factor nuclear factor-kappaB (NF-kappaB) is a logical candidate for providing this interaction. In the present study, we injected intraocularly selective inhibitors of NF-kappaB in chick embryos either unlesioned, or after a unilateral tectal lesion, which axotomizes ganglion cells. The number of dying cells in the retina contralateral to the lesion was reduced in embryos receiving NF-kappaB inhibitors as compared with vehicle-injected controls. In contrast, the same NF-kappaB inhibitors administered as pretreatment before intraocular injection of buthionine sulfoximine and cycloheximide drastically raised neuronal death and induced fulgurant degenerative changes in the retina. The most parsimonious interpretation of our results is that in axotomized retinal ganglion cells of chick embryos NF-kappaB may have either death-promoting or death-inhibiting effects. We propose a theoretical model to explain these dual effects assuming the existence of parallel death pathways differently affected by NF-kappaB. These results may have implications for future redox-based therapeutic strategies for neuroprotection.

Expression of c-Fos after noise-induced temporary threshold shift in the guinea pig cochlea

c-Fos is known to be a component of a transcription factor, activator protein-1, which is induced by oxidative stress. Guinea pigs were exposed to 4 kHz band noise of 110 dB SPL for 1 or 5 h and the expression of c-Fos in the organ of Corti was determined using Western blotting analysis and immunocytochemistry. c-Fos was expressed only after the noise exposure. The c-Fos expression was mainly found in the Hensen's cells, Claudius' cells and Deiter's cells of the basal and second turns of the cochlea. Since the threshold shift was temporary, the expression of c-Fos is therefore considered to contribute to the survival or protective function of the organ of Corti.

Differential postreceptor signaling events triggered by excitotoxic stimulation of different ionotropic glutamate receptors in retinal neurons

The aim of this work was to investigate whether excitotoxicity induced by overstimulation of different ionotropic glutamate receptors could trigger different intracellular signaling cascades. Cultured chick neuronal retina cells, essentially amacrine-like, were particularly sensitive to the toxicity induced by non-NMDA glutamate receptor agonists. One hour stimulation with 100 microM kainate induced a reduction of cell viability of about 44%, as assessed by the MTT test 24 hr after stimulation. Kainate-induced toxicity was mediated through AMPA receptors. Glutamate (100 microM, 1 hr) reduced cell viability by 26%, essentially acting through N-methyl-D-aspartate receptors. Five hours after stimulation, neuronal retina cells had an apoptotic-like nuclear morphology. In retinal neurons, the excitotoxic stimulation, with either glutamate or kainate, induced a calcium-dependent enhancement of the DNA-binding activity of the activating protein-1 (AP-1) transcription factor, which was maximal 2 hr after stimulation. Glutamate induced a greater increase in the AP-1 DNA-binding activity than did kainate. Supershift assays using antibodies directed against different members of the Fos and Jun protein families showed that the AP-1 complex in retinal neurons includes proteins of the Fos family, namely, Fra-2, c-Jun, and Jun D. The DNA-binding activity of the nuclear factor-kappaB transcription factor was not significantly changed upon excitotoxic stimulation with any agonist. Stimulation of glutamate receptors with 100 microM kainate or 100 microM glutamate for 2 min was sufficient to induce the activation of the extracellular signal-regulated kinase (ERK). Inhibition of the ERK activation with the MEK inhibitors U 0126 and PD 98059 increased the toxicity induced by kainate but was without effect on the toxicity induced by glutamate. These results indicate that, although stimulation with both glutamate receptor agonists increased ERK phosphorylation, only kainate-induced ERK activation correlates with the activation of a survival signaling pathway. Our results suggest that, in chick embryo retinal neurons, the signaling pathways that mediate excitotoxic cell death and neuroprotection are stimulus specific.

Inhibition of calpain-mediated apoptosis by E-64 d-reduced immediate early gene (IEG) expression and reactive astrogliosis in the lesion and penumbra following spinal cord injury in rats

Upregulation of calpain, a Ca(2+)-activated cysteine protease, has been implicated in apoptosis and tissue degeneration in spinal cord injury (SCI) that over time spreads from the site of injury to the surrounding regions. We examined calpain content and activity, regulation of immediate early genes (IEGs) such as c-jun and c-fos, reactive astrogliosis as the expression of glial fibrillary acidic protein (GFAP), and apoptosis-related features such as caspase-3 mRNA expression and internucleosomal DNA fragmentation in 1-cm long spinal cord segments (S1, distant rostral; S2, adjacent rostral; S3, lesion or injury; S4, adjacent caudal; and S5, distant caudal) following SCI in rats. Calpain content and production of 150 kD calpain-cleaved alpha-fodrin fragment, expression of IEGs, reactive astrogliosis, and apoptotic features were highly increased in the lesion (S3), moderately in adjacent areas (S2 and S4), and slightly in distant areas (S1 and S5) in SCI rats when compared to sham animals. Administration of the calpain-specific inhibitor E-64-d (1 mg/kg) to SCI rats continuously for 24 h inhibited calpain activity and other factors contributing to apoptosis in the lesion and surrounding areas, indicating that calpain played a key role in the pathophysiology of SCI. The results obtained from this animal model of SCI suggest that calpain inhibitor can provide neuroprotection in patients with SCI.

Gene array analysis reveals changes in peripheral nervous system gene expression following stimuli that result in reactivation of latent herpes simplex virus type 1: induction of transcription factor Bcl-3

The earliest events within the peripheral mammalian nervous system that cause herpes simplex virus type 1 (HSV-1) to reactivate from latency are unknown but are highly likely to include altered regulation of cellular transcription factors. Using gene array analysis, we have examined the changes that occur in cellular mRNA levels in mouse trigeminal ganglia following explantation, a stimulus that results in HSV-1 reactivation from latency. We have detected both increased and decreased expression levels of particular cellular transcripts, which include RNAs encoding neuronal factors, transcription factors, and factors involved in the cell cycle. Among the transcription factors that are upregulated is Bcl-3, a coactivator for NFkappaB. We have confirmed these increases in Bcl-3 transcription levels using reverse transcription-PCR and S1 nuclease protection assays. In addition, we have shown Bcl-3 upregulation at the protein level. Importantly, Bcl-3 RNA levels were found to increase specifically in neuronal cells within the trigeminal ganglia. We discuss a potential role for this factor in upregulating ICP0 transcription, which is an important viral event for initiation of HSV-1 reactivation.

[Delayed apoptosis and its regulation in astrocytes]

Astrocytes, the most abundant glial cell type in the brain, are considered to have physiological and pathological roles in neuronal activities. We found that reperfusion of cultured astrocytes after Ca2+ depletion causes Ca2+ overload followed by delayed cell death and the Na(+)-Ca2+ exchanger in the reverse mode is responsible for this Ca(2+)-mediated cell injury (Ca2+ paradox injury). The Ca2+ paradox injury of cultured astrocytes is considered to be an in vitro model of ischemia/reperfusion injury, since a similar paradoxical change in extracellular Ca2+ concentration is reported in ischemic brain tissue. This review summarizes the mechanisms underlying the Ca(2+)-mediated injury of astrocytes and the protective effects of drugs against Ca2+ reperfusion injury. This study shows that Ca2+ reperfusion injury of astrocytes is accompanied by apoptosis as evidenced by DNA fragmentation and nuclear condensation. Calpain, reactive oxygen species, calcineurin, caspase-3, and NF-kappa B are involved in Ca2+ reperfusion-induced delayed apoptosis of astrocytes. Several drugs including CV-2619, T-588 and ibudilast protect astrocytes against the delayed apoptosis. CV-2619 prevents astrocytes from the delayed apoptosis by production of nerve growth factor, resulting in an activation of mitogen-activated protein (MAP)/extracellular signal-regulated kinase (ERK) and phosphatidylinositol-3 (PI3) kinase signal pathways. The protective effect of T-588 is mainly mediated by an activation of MAP/ERK signal cascade. Moreover, ibudilast prevents the Ca2+ reperfusion-induced delayed apoptosis of astrocytes via cyclic GMP signaling pathway. Further studies in this system will contribute to the development of new drugs that attenuate ischemia/reperfusion injury via modulation of astrocytes.

Characterization of ceramide-induced apoptotic death in cerebellar granule cells in culture

Sphingomyelin signalling system has been involved in several examples of cell death through apoptosis. We have characterised the effect of exposure to the cell permeable ceramide analogue, C2-ceramide, on cultures of differentiated cerebellar granule cells. C(2)-ceramide was toxic to granule cells in a dose- and time-dependent way at concentrations higher than 10 microM. Ceramide exposure was accompanied by characteristic alterations of cell morphology, namely swollen cell bodies and punctuate appearance and arcuate direction of processes. The final outcome of ceramide exposure was a form of cell death largely apoptotic in nature. Hoechst stain, followed by counts of nuclei with normal appearance and size or with condensed chromatin and reduced size, revealed a large increase of the proportion of shrunken nuclei in treated cultures. In situ visualisation of fragmented DNA through the TUNEL technique, additionally marked cells undergoing apoptosis as a consequence of ceramide treatment. Accordingly, the DNA extracted from cultures exposed to C2-ceramide and subjected to agarose gel electrophoresis showed the peculiar ladder of fragmented low molecular weight DNA. Treatments with inhibitors of two caspases or of nitric oxide synthase were unable to rescue neurons exposed to ceramide, thus suggesting a neurotoxic action not primarily dependent on activation of death proteases or on nitric oxide production.

TrkA induces differentiation but not apoptosis in C6-2B glioma cells

Nerve growth factor (NGF) binds to the TrkA tyrosine kinase and the p75 neurotrophin receptors. Depending upon which receptor is activated, NGF can induce differentiation or apoptosis. C6-2B glioma cells express the p75 receptor, but NGF decreases their growth only when TrkA is introduced (C6trk). It is unclear, however, whether TrkA reduces C6-2B cell growth by apoptosis or differentiation. To examine which mechanisms account for the anti-proliferative effect of NGF in these cells, we first analyzed whether NGF causes apoptosis by flow cytometry, two-site immunoassay and in situ TUNEL. None of these methods indicated that C6trk undergo apoptosis. Additional apoptotic markers, such as Bcl-2, Bax, Bad, p53, caspase 3, and NF-kappaB were also used. C6trk cells exhibited lower levels of Bcl-2 compared with the parental C6 mock cells, but no changes in the levels of other apoptotic proteins. Moreover, NGF increased AP-1 binding activity in C6trk cells, suggesting that NGF may induce differentiation. We then examined whether TrkA changes the glioma phenotype. In C6trk cells, but not in C6mock cells, NGF enhanced the levels of neuron-specific enolase as well as the levels of A2B5 and 2', 3'-cyclic nucleotide 3'-phosphodiesterase, markers for oligodendrocytes, without affecting the expression of other neuronal markers. Our data suggest that the antiproliferative properties of TrkA may rely on its ability to induce differentiation of C6 cells from undifferentiated glioma to oligodendrocytes.

Behavioral and biochemical effects of glutathione depletion in the rat brain

Glutathione serves the function of providing reducing equivalents for the maintenance of oxidant homeostasis, and besides it plays roles in intra- and intercellular signaling in the brain. Our purpose was to test the effects of depleting tissue glutathione by diethylmaleate (5.3 mmol/kg, intraperitoneal) on brain antioxidant metabolism, nerve growth factor levels, and cognitive performance in rats. Six hours after the treatment, glutathione level in the hippocampus dropped down to 30% of the mean value of vehicle-treated animals and glutathione peroxidase activity also declined. Twenty-four hours after the injection the values had been partially restored. Moreover, the hippocampal and cortical levels of nerve growth factor protein did not change in response to diethylmaleate treatment. Glutathione depletion did not influence the performance of animals in the step-through passive avoidance test, but impairs acquisition in the Morris water maze when given before training. However, when diethylmaleate was administered after acquisition in the same paradigm, it did not affect the retention tested at the following day. Our results suggest that glutathione status is important during acquisition, but not for retention, of spatial memory in maze tasks and they support the hypothesis of the oxidant/antioxidant equilibrium as a key piece acting in the regulation of brain function.

The NF-kappaB inhibitor diethyldithiocarbamate (DDTC) increases brain cell death in a transient middle cerebral artery occlusion model of ischemia

A transient ischemic middle cerebral artery occlusion model of stroke was used to examine the role of the transcription factor NF-kappaB in cell death as measured by DNA fragmentation and infarction volume. The left middle cerebral artery was occluded for either 30 min or 2 h in rats. One set of animals was pretreated with diethyldithiocarbamate (DDTC), an inhibitor of NF-kappaB, 30 min prior to reperfusion. The animals were reperfused and allowed to survive for 2 or 7 days. DNA fragmentation was assayed by in situ end labeling in the stroke core and penumbral regions. Specific cortical and subcortical regions were measured using quantitative image analysis. DNA fragmentation was seen only on the ischemic side of the brains in all cases. Overall, the DDTC-treated groups showed significantly increased DNA fragmentation within the ischemic side compared to the saline control groups. DDTC treatment also caused an increase in stroke volume based on triphenyl tetrazolium chloride staining. Electrophoretic mobility shift assays showed NF-kappaB activation peaking 15 min following reperfusion and that this activation was blocked by the DDTC treatment. This study suggests that the use of NF-kappaB inhibitors to block cell death following stroke needs to be carefully examined because global inhibitors may not promote neuronal survival.

Alterations in signal transduction cascade in young and adult rat brain and lymphocytes

Signal transduction cascade, phosphoinositide metabolism, and protein kinases were studied from discrete areas of rat brain like cerebral hemispheres, cerebellum, brainstem, and diencephalon as well as lymphocytes isolated from three different age groups of rats; young (1 month), young adult (3-4 months), and adult (12 months) rats. The activities of protein kinase A, protein kinase C, phospholipase A(2) and phospholipase C and inositol 1, 4, 5-triphosphate, diacylglycerol, cyclic adenosine monophosphate contents were assayed from different brain areas and lymphocytes from these three age group rats. An upregulatory effect on the signal transduction system was observed from 1 month to 3-4-month age group, whereas, the brain tissue and lymphocytes of adult rats showed lower contents and activities of signal transduction components as compared to young adults. In view of the established 'cross talk' between signal transduction system, the present results suggests that molecular/cellular changes in brain and immune cells signal transduction pathway along with neuronal cell loss may contribute to age-related decline in nervous as well as immune system functions.

NO synthase and NO-dependent signal pathways in brain aging and neurodegenerative disorders: the role of oxidant/antioxidant balance

Nitric oxide and other reactive nitrogen species appear to play several crucial roles in the brain. These include physiological processes such as neuromodulation, neurotransmission and synaptic plasticity, and pathological processes such as neurodegeneration and neuroinflammation. There is increasing evidence that glial cells in the central nervous system can produce nitric oxide in vivo in response to stimulation by cytokines and that this production is mediated by the inducible isoform of nitric oxide synthase. Although the etiology and pathogenesis of the major neurodegenerative and neuroinflammatory disorders (Alzheimer's disease, amyothrophic lateral sclerosis, Parkinson's disease, Huntington's disease and multiple sclerosis) are unknown, numerous recent studies strongly suggest that reactive nitrogen species play an important role. Furthermore, these species are probably involved in brain damage following ischemia and reperfusion, Down's syndrome and mitochondrial encephalopathies. Recent evidence also indicates the importance of cytoprotective proteins such as heat shock proteins (HSPs) which appear to be critically involved in protection from nitrosative and oxidative stress. In this review, evidence for the involvement of nitrosative stress in the pathogenesis of the major neurodegenerative/ neuroinflammatory diseases and the mechanisms operating in brain as a response to imbalance in the oxidant/antioxidant status are discussed.

Nitric oxide synthase induction in astroglial cell cultures: effect on heat shock protein 70 synthesis and oxidant/antioxidant balance

Glial cells in the nervous system can produce nitric oxide in response to cytokines. This production is mediated by the inducible isoform of nitric oxide synthase. Radical oxygen species (ROS) and nitric oxide (NO) derivatives have been claimed to play a crucial role in many different processes, both physiological such as neuromodulation, synaptic plasticity, response to glutamate, and pathological such as ischemia and various neurodegenerative disorders. In the present study we investigated the effects of NO synthase (iNOS) induction in astrocyte cultures on the synthesis of heat shock proteins, the activity of respiratory chain complexes and the oxidant/antioxidant balance. Treatment of astrocyte cultures for 18 hr with LPS and INFgamma produced a dose dependent increase of iNOS associated with an increased synthesis of hsp70 stress proteins. This effect was abolished by the NO synthase inhibitor L-NMMA and significantly decreased by addition of SOD/CAT in the medium. Time course experiments showed that iNOS induced protein expression increased significantly by 2 hr after treatment with LPS and INFgamma and reached a plateau at 18 hr; hsp70 protein synthesis peaked around 18 and 36 hr after the same treatment. Addition to astrocytes of the NO donor sodium nitroprusside resulted in a dose dependent increase in hsp70 protein that was comparable to that found after a mild heat shock. Additionally, a decrease in cytochrome oxidase activity, a marked decrease in ATP and protein sulfhydryl contents, an increase in the activity of the antioxidant enzymes mt-SOD and catalase were found which were abolished by L-NMMA. These findings suggest the importance of mitochondrial energy impairment as a critical determinant of the susceptibility of astrocytes to neurotoxic processes and point to a possible pivotal role of hsp70 in the signalling pathways of stress tolerance.

Kainate receptor-mediated activation of the AP-1 transcription factor complex in cultured rat cerebellar granule cells

The sequence-specific DNA-binding activity of the AP-1 transcription factor complex was measured in cultured rat cerebellar granule cells by electrophoretic mobility shift assay. A low concentration of kainate (KA; 10 microM), but not alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA; 10 microM), enhanced DNA-binding of the AP-1 transcription factor in cultures pretreated with Concanavalin A (Con A), to prevent KA receptor desensitization. In the presence of cyclothiazide (an inhibitor of AMPA receptor desensitization), KA (10 microM) caused only a slight increase of AP-1 DNA-binding, in contrast to the threefold enhancement produced by AMPA (10 or 30 microM) or by a higher concentration of KA (30 microM), suggesting that the effect of KA, in the presence of Con A, is mediated by activation of putative KA receptors. To confirm this, the effects of the AMPA receptor-selective, non-competitive antagonist, 1-(4-aminophenyl)-3-methylcarbamoyl-4-methyl-3,4-dihydro-7, 8-methylenedioxy-5H-2,3-benzodiazepine (GYKI 53655; 50 microM), the mixed AMPA/KA receptor competitive antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 50 microM), and the AMPA and GluR5 KA receptor competitive antagonist, (-)(3S,4aR,6R, 8aR)-6-[2-(1(2)H-tetrazole-5-yl)ethyl]-1,2,3,4,4a,5,6,7,8, 8a-decahydroisoquinoline-3-carboxylic acid monohydrate (LY 326325; 100 microM), were examined on AMPA- and KA-induced AP-1 activation, respectively. Our results suggest that stimulation of native KA receptors is responsible for the observed KA-specific activation of the AP-1 transcription factor complex.

NF-kappaB inhibits apoptosis in murine mammary epithelia

The transcription factor NF-kappaB is a key modulator of apoptosis in a variety of cell types, but to date this specific function of NF-kappaB has not been demonstrated in epithelia. Here, we describe the activation of NF-kappaB during post-lactational involution of the mouse mammary gland, a period of extensive apoptosis of luminal epithelial cells. Significantly, active NF-kappaB localized exclusively to nonapoptotic epithelial cells both in vivo and in the mammary epithelial cell line, KIM-2, transduced with an NF-kappaB-dependent green fluorescent protein reporter. Activation of NF-kappaB in vitro coincided with a decrease in the cytosolic repressor, IkappaBalpha. Furthermore, induction of NF-kappaB either by extracellular ligands or, more specifically, by inhibition of the IkappaB repressor with adenoviral constructs expressing antisense mRNA, resulted in enhanced survival of KIM-2 cells. Therefore, although coincident with induction of apoptosis both in vivo and in vitro, NF-kappaB appeared to exert a selective survival function in epithelial cells. This study highlights for the first time a role for NF-kappaB in modulating apoptosis in epithelium.

Glyceraldehyde-3-phosphate dehydrogenase and apoptosis

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) has long been recognized as playing an integral role in glycolysis. During the past 20 years, however, a number of novel, additional functions for GAPDH have been described. These include acting as an uracil DNA glycosylase, activator of transcription, binding to RNA, and an involvement in tubulin assembly. One of the most intriguing functions which has recently been recognized is an involvement in the initiation of apoptosis. Further, GAPDH associates with proteins implicated in human neurodegenerative disorders. This review summarizes the evidence implicating GAPDH in the initiation of one or more apoptotic cascades. The possible functions of GAPDH in the nucleus which could result in the initiation of apoptosis are also discussed.

Hwansodan protects PC12 cells against serum-deprivation-induced apoptosis via a mechanism involving Ras and mitogen-activated protein (MAP) kinase pathway

Hwansodan has been used as a prescription for senile and vascular dementia in Oriental medicine. We investigated the neuroprotective effects of Hwansodan water extract on the apoptotic death of PC12 cells by serum deprivation. Hwansodan significantly rescued PC12 cells from apoptotic death by serum deprivation in a dose-dependent manner. The nuclear staining of PC12 cells clearly showed that Hwansodan attenuated nuclear condensation and fragmentation, which represents typical neuronal apoptotic characteristics. Hwansodan also prevents DNA fragmentation and caspase-3-like protease activation in serum-deprived PC12 cells and induces the tyrosine phosphorylation of proteins around 44 kDa, which was identified as ERK1 with electrophoretic gel mobility shift by Western blot. In addition, MEK inhibitor PD98059 and Ras inactivator, alpha-hydroxyfarnesylphosphonic acid and mevastatin, attenuated the neuroprotective effects of Hwansodan in serum-deprived PC12 cells. These results indicate that Ras/MEK/ERK signaling pathway plays a role in neuroprotective effects of Hwansodan in serum-deprived PC12 cells.

HSP70 induction in the brain following ethanol administration in the rat: regulation by glutathione redox state

Changes in glutathione (GSH) and glutathione disulfide (GSSG) levels and/or redox status have been suggested to mediate the induction of heat shock proteins (HSPs) that follows exposure to oxidizing agents such as ethanol. Here we report the effects of ethanol administration to rats at intracellular levels of GSH, GSSG, HSP70, and protein carbonyls in brain and liver. Following 7 days of ethanol administration, there was a significant decrease in GSH, a significant induction of HSP70, and a significant increase in protein carbonyls in all brain regions studied and in liver. In cortex, striatum, and hippocampus there was a significant correlation between (a) the decrease in GSH, (b) the increase in GSSG, and (c) the decrease in GSH/GSSG ratio and HSP70 levels induced in response to ethanol. These data support the hypothesis that a redox mechanism may be involved in the heat-shock signal pathway responsible for HSP70 induction in the brain.

Model for aging in the basal forebrain cholinergic system

A key component of the cognitive deficits associated with aging is the loss of function of cholinergic neurons in the basal forebrain due to neuronal losses and decreased cholinergic function of spared neurons. A model to mimic one aspect of this phenomenon is to kill cholinergic neurons selectively in the basal forebrain via administration of the immunotoxin IgG-192-saporin. Here we discuss apoptotic regulators, such as nerve growth factor, in age-associated changes present in the cholinergic system and the role of the NF-kappaB signaling system in cellular commitment to apoptosis. We also examine the age-associated decline in intrinsic response mechanisms, which may account for the age-associated reduction in recovery from both acute and chronic insults to the central nervous system.

Apoptosis and the nervous system

Apoptosis is now recognized as a normal feature in the development of the nervous system and may also play a role in neurodegenerative diseases and aging. This phenomenon has been investigated intensively during the last 6-7 years, and the progress made in this field is reviewed here. Besides a few in vivo studies, a variety of neuronal preparations from various parts of the brain, the majority of which were primary cultures, and some cell lines have been investigated. Several apoptosis-inducing agents have been identified, and these include lack of neurotrophic support, neurotransmitters, neurotoxicants, modulators of protein phosphorylation and calcium homeostasis, DNA-damaging agents, oxidative stress, nitric oxide, and ceramides. The precise signaling cascade is not well established, and there are lacunae in many suggested pathways. However, it appears certain that the Bcl family of proteins is involved in the apoptotic pathway, and these proteins in turn affect the processing of interleukin-1beta converting enzyme (ICE)/caspases. The available evidence suggests that there may be several apoptotic pathways that may depend on the cell type and the inducing agent, and most of the pathways may converge at the ICE/caspases step.

Activation of AP-1 and nuclear factor-kappaB transcription factors is involved in hydrogen peroxide-induced apoptotic cell death of oligodendrocytes

H2O2-induced onset and execution of programmed cell death in mature rat brain oligodendrocytes in culture is accompanied by the induction and nuclear translocation of the transcription factors AP-1 and nuclear factor-kappaB (NF-kappaB), both of which have been discussed as regulators of cell death and survival. Supershift analysis of nuclear extracts indicated that the AP-1 complex consists of c-Jun, c-Fos, JunD, and possibly JunB proteins, and that the NF-kappaB complex contains p50, p65, and c-Rel proteins. The first signs of DNA fragmentation were seen already during the first hour after the treatment. DNA fragmentation could be prevented by the antioxidants pyrrolidine dithiocarbamate and vitamin E, by the nuclease inhibitor aurintricarboxylic acid, and by preincubation with the iron chelator deferoxamine (DFO). Additionally, DFO protected oligodendrocytes from H2O2-induced cytotoxic effects as assessed by the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay, and suppressed the formation of free radicals. DFO alone led to a slight increase and in combination with H2O2 synergistically induced DNA-binding activities of AP-1 and NF-kappaB in oligodendrocytes. Our data suggest that although low levels of H2O2 directly activate AP-1 and NF-kappaB and might contribute to signal transduction pathways promoting cell survival, the formation and action of hydroxyl radicals promote cell death mechanisms that can be attenuated by the iron chelator DFO.

Apoptosis in Ca2 + reperfusion injury of cultured astrocytes: roles of reactive oxygen species and NF-kappaB activation

We previously reported that incubation of cultured astrocytes in Ca2 + -containing medium after exposure to Ca2 + -free medium caused Ca2 + influx followed by delayed cell death. Here, we studied the mechanisms underlying the Ca2 + -mediated injury of cultured astrocytes. Our results show that Ca2 + reperfusion injury of astrocytes appears to be mediated by apoptosis, as demonstrated by DNA fragmentation and prevention of death by caspase-3 inhibitors. Paradoxical Ca2 + challenge stimulated rapidly reactive oxygen species (ROS) production. Ca2 + reperfusion injury of astrocytes was influenced by several reagents which modified ROS production. When astrocytes were exposed to hydrogen peroxide (H2O2) for 30 min and then incubated without H2O2 for 1-5 days, cell toxicity including apoptosis was observed. Ca2 + reperfusion injury induced by Ca2 + depletion or H2O2 exposure was blocked by the iron chelator 1, 10-phenanthroline, the NF-kappaB inhibitor pyrrolidinedithiocarbamate and the calcineurin inhibitor FK506. Incubation in normal medium after H2O2 exposure rapidly increased the level of nuclear NF-kappaB p65 subunit, and the effect was blocked by 1,10-phenanthroline, pyrrolidinedithiocarbamate and FK506. These findings indicate that Ca2 + reperfusion-induced apoptosis is mediated at least partly by ROS production and ROS cause NF-kappaB activation in cultured astrocytes.

Induction of an immediate early gene egr-1 by zinc through extracellular signal-regulated kinase activation in cortical culture: its role in zinc-induced neuronal death

Egr-1 is one of the immediate early transcription factors that are induced after brain insults. However, the mechanism and the role of Egr-1 induction are not yet determined. In the present study, using mouse cortical cultures, we examined the ionic mechanism of Egr-1 induction and its role in neuronal death. Although zinc, NMDA, or ionomycin induced comparable neuronal death in cortical culture, only zinc increased Egr-1 expression, which was attenuated by blocking zinc influx. It is intriguing that brief exposure to zinc induced sustained extracellular signal-regulated kinase (Erk) activation. PD098059, an inhibitor of the Erk 1/2 upstream kinase mitogen-activated protein kinase kinase 1 (MEK1), blocked Erk 1/2 activation, Egr-1 induction, and neuronal death by zinc. The present study has demonstrated that zinc, rather than calcium, induces lasting Egr-1 expression in cortical culture by activating Erk 1/2, which is part of a cascade that may play an active role in zinc neurotoxicity. We propose that translocation of endogenous zinc may be the key mechanism of Egr-1 induction and neuronal death in brain ischemia.

The potential of neuroprotection in glaucoma treatment

Visual field loss in glaucoma is due to death of retinal ganglion cells. Reducing or slowing down the loss of ganglion cells in glaucoma, a concept known as neuroprotection, would appear to be the only way forward. This does not imply that treatment of risk factors, such as elevated intraocular pressure, must not be continuously implemented. In this paper we point out that very little is known about the mechanisms of ganglion cell death in glaucoma and that data derived from studies on the "ideal animal model for glaucoma" must not be overemphasized. We also propose that the death processes of neurones in various diseases are fundamentally the same but vary in cause. Experimental data show that the death rate of neuronal populations is dependent on the impact of the insult and that neuroprotectants are more likely to benefit a patient in diseases in which the neurones die slowly, as in glaucoma, than in a disease in which the death of a set of neurones is rapid. We conclude that if a putative neuroprotectant can be administered in such a way that it reaches the retina in appropriate amounts and has insignificant side effects, it is likely to attenuate ganglion cell death and thus benefit the glaucoma patient.

Effect of NGF treatment on outcome measures in a rat model of middle cerebral artery occlusion

Ischemic insults to the brain result in a time-dependent increase in neuronal death that is responsible for some of the functional deficits associated with stroke. Our working hypothesis is that ischemia results in a prompt depletion of high energy phosphate species resulting in decreased pH and glutathione levels in brain in a temporal and spatial pattern that disrupts nerve growth factor homeostasis and increases neuronal apoptosis. Here we show hemispheric depletion of active phosphate species after ischemia. Also, we observed that the striatum is an early target for oxidative stress that is followed by energy metabolic impairment and altered neurotrophin levels that were detected by noninvasive magnetic resonance imaging (MRI) measurements of cytotoxicity and conventional biochemical determinations of apoptosis, glutathione, and nerve growth factor (NGF) protein levels in a pattern distinct from that observed in the hippocampus. Furthermore, early assessment of intracellular pH by 31P-magnetic resonance spectroscopy (31P-MRS) was a predictor of later infarct development as determined by MRI. We also show that pretreatment with pharmacological doses of NGF did not have overall significant beneficial consequences on irreversible ischemia in an intraluminal unilateral irreversible model of stroke in rat brain.