Oxygen-induced apoptosis in PC12 cells with special reference to the role of Bcl-2

The influence of oxygen supply on metabolism of neural cells cultured on a gas-permeable PTFE foil

The influence of oxygen on neural stem cell proliferation, differentiation, and apoptosis is of great interest for regenerative therapies in neurodegenerative disorders, such as Parkinson's disease. These oxygen depending mechanisms have to been considered for the optimization of neural cell culture conditions. In this study, we used a cell culture system with an oxygen-permeable polytetrafluorethylene (PTFE) foil to investigate the effect of oxygen on metabolism and survival of neural cell lines in vitro. Human glial astrocytoma-derived cells (GOS-3) and rat pheochromacytoma cells (PC12) were cultured on the gas-permeable PTFE foil as well as a conventional non oxygen-permeable cell culture substrate at various oxygen concentrations. Analyses of metabolic activity, gene expression of apoptotic grade, and dopamine synthesis were performed. Under low oxygen partial pressure (2%, 5%) the anaerobic metabolism and apoptotic rate of cultured cells is diminished on PTFE foil when compared with the conventional culture dishes. In contrast, under higher oxygen atmosphere (21%) the number of apoptotic cells on the PTFE foil was enhanced. This culture model demonstrates a suitable model for the improvement of oxygen dependent metabolism under low oxygen conditions as well as for induction of oxidative stress by high oxygen atmosphere without supplementation of neurotoxins.

Cooperative roles of c-Abl and Cdk5 in regulation of p53 in response to oxidative stress

The p53 tumor suppressor protein, a critical modulator of cellular stress responses, is activated through diverse mechanisms that result in its stabilization and transcriptional activation. p53 activity is controlled by transcriptional, translational, and post-translational regulation. The major mechanisms of p53 regulation occur primarily through interactions with HDM2, an E3 ubiquitin ligase that leads to p53 nuclear export and degradation. Here, we demonstrate that hydrogen peroxide-induced oxidative stress elicits down-regulation of HDM2. c-Abl mediates down-regulation of HDM2, leading to an increase of p53 level. Moreover, Cdk5 (cyclin-dependent kinase 5), a proline-directed Ser/Thr kinase, additionally increases p53 stability via post-translational modification of p53 in response to hydrogen peroxide. The p53 protein stabilized by c-Abl and Cdk5 is transcriptionally active; however, transcription of its target gene is differentially regulated with selective binding of p53 on promoter regions of its target genes by c-Abl. In addition, c-Abl modulates Cdk5 activity via phosphorylation of tyrosine 15 in cooperation with cleavage of p35 to p25. Our results show that c-Abl and Cdk5 cooperatively regulate maximal activation of p53, resulting in neuronal death in response to oxidative stress by hydrogen peroxide. These findings aid in clarifying the mechanism underlying the occurrence of neuronal apoptosis as a result of c-Abl and Cdk5-mediated p53 stabilization and transcriptional activation.

Stabilization and activation of p53 induced by Cdk5 contributes to neuronal cell death

The p53 tumor suppressor protein is a key regulator of cellular functions including responses to numerous stress signals, and triggers apoptosis in many cell types, including neurons. The major mechanisms known to regulate p53 stabilization and activation include phosphorylation and ubiquitin ligase-mediated proteasomal degradation. Cyclin-dependent kinase 5 (Cdk5), a proline-directed serine/threonine kinase, is most active in the central nervous system and plays a variety of roles in neuronal degeneration. Here, we demonstrate for the first time that Cdk5 interacts with p53 and increases its stability through posttranslational regulation, leading to accumulation of p53, particularly in the nucleus. We show that Cdk5 phosphorylates p53 on Ser15, Ser33 and Ser46 in vitro, and that increased Cdk5 activity in the nucleus mediates these phosphorylation events in response to genotoxic and oxidative stresses. Cdk5 mediates disruption of the interaction between p53 and Hdm2 (also known as Mdm2), and prevents Hdm2-induced p53 ubiquitylation and downregulation. Cdk5 additionally enhances phosphorylation-dependent binding of the p300 coactivator, inducing acetylation of p53. Cdk5-stabilized p53 protein is transcriptionally active, resulting in the induction of pro-apoptotic genes and subsequent mitochondria-mediated apoptosis in response to genotoxic or oxidative stress. Collectively, these novel findings help define the mechanisms underlying neuronal apoptosis occurring as a result of Cdk5-mediated p53 stabilization and transcriptional activation.

Regulation of cyclin-dependent kinase 5 and p53 by ERK1/2 pathway in the DNA damage-induced neuronal death

DNA damage is known to be an initiator of neuronal death in neurodegenerative conditions such as Parkinson's and Alzheimer's diseases. The mechanism linking DNA damage and neuronal death is not completely understood. Here, we delineate the mechanism by which neuronal death evoked by DNA damage is controlled. Using mouse cortical neurons and SH-SY5Y human neuroblastoma cells, we identify a critical role of ERK signaling in neuronal death induced by DNA damage upon mitomycin C treatment. In addition, we provide evidence that the ERK signaling regulates Cyclin-dependent kinase 5 (Cdk5) activity and stability of tumor suppressor p53. Mitomycin C increased expression of p35, a specific activator of neuronal Cdk5 in an ERK1/2-dependent manner. Moreover, stability of p53 was increased by its phosphorylation on Ser33 and Ser46 by Cdk5, leading to neuronal death. Finally, we show that activated ERK induced increased expression of the Egr-1 transcription factor, which then bound to the promoter region of p35. We suggest subsequent increase of p35 expression and Cdk5 activity contribute to p53-dependent neuronal death. Thus, the present finding provides a new insight into a molecular mechanism underlying DNA damage-induced neuronal death.

Expression of cystatin C prevents oxidative stress-induced death in PC12 cells

Cystatin C, an inhibitor of cysteine proteinases, is suggested to be involved in oxidative stress-induced apoptosis of cultured CNS neurons and various neuronal diseases in vivo; however, little is known about its mechanism of action. To address the role cystatin C plays in oxidative stress-induced neuronal cell death, we established PC12 cell lines that stably expressed rat cystatin C. These cystatin C-expressing PC12 cells showed remarkable resistance to high (50%) oxygen atmosphere. This resistance correlate with expression levels of cystatin C, demonstrating that cystatin C has a protective effect on high oxygen-induced cell death. In contrast, in a normal (20%) oxygen atmosphere neither control nor cystatin C-expressing PC12 cells showed a significant change in the number of living cells, indicating that cystatin C does not play an important role in the regulation of cellular proliferation. Furthermore, the cystatin C-expressing cell line also resisted other oxidative stresses, including glutamate- and 13-L-hydroperoxylinoleic acid (LOOH)-induced cell death. These results demonstrate that cystatin C has protective effects against various oxidative stresses that induce cell death.

Free radical-dependent nuclear localization of Bcl-2 in the central nervous system of aged rats is not associated with Bcl-2-mediated protection from apoptosis

We have previously reported that Bcl-2 is up-regulated in the CNS of aged F344 rats as a consequence of oxidative stress. In addition to increased levels of expression, we now report that there is a subcellular redistribution of Bcl-2 in the CNS of aged F344 rats. Using western blotting, we found Bcl-2 predominantly located in the cytosol of young rats. However, in aged rats Bcl-2 was found primarily in the nucleus. This distribution, in the hippocampus and cerebellum, was reversed by treatment with the nitrone spin trap N-tert-butyl-alpha-phenylnitrone (PBN). Paradoxically, PBN treatment in young rats had the opposite effect, changing Bcl-2 from predominantly cytosolic to nuclear. We also detected an increase in Bax in aged hippocampal samples (both nuclear and cytosolic), which was reversed by treatment with PBN. The distribution of Bcl-2 and Bax in the cytosol of aged rats dramatically decreased the Bcl-2/Bax ratio, a probable indicator of neuronal vulnerability, which was restored upon treatment with PBN. In order to assess the effect of nuclear association of Bcl-2 we used PC12 cells stably transfected with a Bcl-2 construct to which we added the nuclear localization sequence of the SV40 large T antigen to the N-terminus which resulted in nuclear targeting of Bcl-2. Measurement of cell death using lactate dehydrogenase assays showed that, contrary to wild-type Bcl-2, Bcl-2 localized to the nucleus was not effective in protecting cells from treatment with 250 microm H2O2. These results suggest that nuclear localization of Bcl-2 observed in the aged CNS may not reflect a protective mechanism against oxidative stress, a major component of age-associated CNS impairments.

Protective effects of sesamin and sesamolin on hypoxic neuronal and PC12 cells

Reactive oxygen species (ROS) are important mediators of a variety of pathological processes, including inflammation and ischemic injury. The neuroprotective effects of sesame antioxidants, sesamin and sesamolin, against hypoxia or H2O2-induced cell injury were evaluated by cell viability or lactate dehydrogenase (LDH) activity. Sesamin and sesamolin reduced LDH release of PC12 cells under hypoxia or H2O2-stress in a dose-dependent manner. Dichlorofluorescein (DCF)-sensitive ROS production was induced in PC12 cells by hypoxia or H2O2-stress but was diminished in the presence of sesamin and sesamolin. We evaluated further the role of mitogen-activated protein kinases (MAPKs) and caspase-3 in hypoxia-induced PC12 cell death. Extracellular signal-regulated protein kinase (ERK) 1, c-jun N-terminal kinase (JNK), and p38 MAPKs of signaling pathways were activated during hypoxia. We found that the inhibition of MAPKs and caspase-3 by sesamin and sesamolin correlated well with the reduction in LDH release under hypoxia. Furthermore, the hypoxia-induced apoptotic-like cell death in cultured cortical cells as detected by a fluorescent DNA binding dye was reduced significantly by sesamin and sesamolin. Taken together, these results suggest that the protective effect of sesamin and sesamolin on hypoxic neuronal and PC12 cells might be related to suppression of ROS generation and MAPK activation.

Combined nimodipine and citicoline reduce infarct size, attenuate apoptosis and increase bcl-2 expression after focal cerebral ischemia

Cerebral ischemia triggers a multitude of pathophysiological and biochemical events that separately affect the evolution of focal ischemia and, therefore, stroke treatment should logically employ all known neuroprotective agents. We hypothesized that a treatment combining nimodipine and citicoline might have a potential neuroprotective effect. To assess this idea, Sprague-Dawley rats underwent transient bilateral common carotid artery ligation with simultaneous middle cerebral artery occlusion for 60 min. Four treatment groups were established. Animals received either: a) saline (control group); b) intracarotid nimodipine infusion during 30 min in the ischemia-reperfusion (nimodipine group); c) i.p. postischemic citicoline injections once daily for 7 days (citicoline group); or d) intracarotid nimodipine bolus during ischemia-reperfusion plus i.p. postichemic citicoline injections (combination group). They were killed after either 7 or 3 days after reperfusion. In the first case, the volume of the infarcted tissue was studied by a stereological procedure and in the second case, in situ end-labeling of nuclear DNA fragmentation (TUNEL) and Bcl-2 expression were employed to determine the level of apoptosis. The infarct volume was significantly reduced in both the nimodipine and the citicoline treatment groups after 7 days of reperfusion; combination of both drugs produced an additive effect. After 3 days of reperfusion, the number of Bcl-2-positive neurons was significantly increased while that of TUNEL-positive cells significantly decreased at the infarct border in the combined-treatment animals. Our findings demonstrate a neuroprotective effect from an acute single dose of nimodipine during ischemia-reperfusion and prolonged post-ischemic treatment with citicoline in a model of focal cerebral ischemia. These results suggest that a possible mechanism of neuroprotective action would be mediated by increased Bcl-2 expression and decreased apoptosis within the boundary zone of the infarct together with neutralization of the ischemia-reperfusion injury.

Gamma-tocopheryl quinone stimulates apoptosis in drug-sensitive and multidrug-resistant cancer cells

Chemotherapy-induced cell death is linked to apoptosis, and there is increasing evidence that multidrug-resistance in cancer cells may be the result of a decrease in the ability of a cell to initiate apoptosis in response to cytotoxic agents. In previous studies, we synthesized two classes of electrophilic tocopheryl quinones (TQ), nonarylating alpha-TQ and arylating gamma- and delta-TQ, and found that gamma- and delta-TQ, but not alpha-TQ, were highly cytotoxic in human acute lymphoblastic leukemia cells (CEM) and multidrug-resistant (MDR) CEM/VLB100. We have now extended these studies on tumor biology with CEM, HL60 and MDR HL60/MX2 human promyelocytic leukemia, U937 human monocytic leukemia, and ZR-75-1 breast adenocarcinoma cells. gamma-TQ, but not alpha-TQ or tocopherols, showed concentration and incubation time-dependent effects on loss of plasma membrane integrity, diminished viable cell number, and stimulation of apoptosis. Its cytotoxicity exceeded that of doxorubicin in HL60/MX2 cells, which express MRP, an MDR-associated protein. Apoptosis was confirmed by TEM, TUNEL, and DNA gel electrophoresis. Kinetic studies showed that an induction period was required to initiate an irreversible multiphase process. Gamma-TQ released mitochondrial cytochrome c to the cytosol, induced the cleavage of poly(ADP-ribose)polymerase, and depleted intracellular glutathione. Unlike xenobiotic electrophiles, gamma-TQ is a highly cytotoxic arylating electrophile that stimulates apoptosis in several cancer cell lines including cells that express MDR through both P-glycoprotein and MRP-associated proteins. The biological properties of arylating TQ electrophiles are closely associated with cytotoxicity and may contribute to other biological effects of these highly active agents.

Brain-derived neurotrophic factor accelerates nitric oxide donor-induced apoptosis of cultured cortical neurons

Brain-derived neurotrophic factor (BDNF) is known to have important functions in neuronal survival, differentiation, and plasticity. In addition to its role as a survival-promoting factor, BDNF reportedly can enhance neuronal cell death in some cases, for example, the death caused by excitotoxicity or glucose deprivation. The cellular mechanism of the death-enhancing effect of BDNF remains unknown, in contrast to that of its survival-promoting effect. In this work, we found that BDNF markedly accelerated the nitric oxide (NO) donor-induced death of cultured embryonic cortical neurons. BDNF increased the number of cells with nuclear condensation and DNA fragmentation 24 h after treatment with the NO donor, but it did not change the number of those cells 36 h after the treatment. The BDNF-accelerated death of cortical neurons was inhibited by the addition of actinomycin D or cycloheximide. These results suggest that BDNF can accelerate apoptotic cell death elicited by NO donor. TrkB-IgG and K252a blocked the BDNF-induced acceleration of the death, indicating that the death-accelerating effect by BDNF is mediated by TrkB. In addition, the BDNF-accelerated apoptosis was inhibited by the addition of SB202190 and SB203580, specific inhibitors of p38 mitogen-activated protein kinase (MAPK), and U0126, a specific inhibitor of MAPK/ERK kinase 1, indicating that the activation of both p38 MAPK and ERK is involved in the signaling cascade of the BDNF-accelerated, NO donor-induced apoptosis.

Mitochondria and neuronal survival

Mitochondria play a central role in the survival and death of neurons. The detailed bioenergetic mechanisms by which isolated mitochondria generate ATP, sequester Ca(2+), generate reactive oxygen species, and undergo Ca(2+)-dependent permeabilization of their inner membrane are currently being applied to the function of mitochondria in situ within neurons under physiological and pathophysiological conditions. Here we review the functional bioenergetics of isolated mitochondria, with emphasis on the chemiosmotic proton circuit and the application (and occasional misapplication) of these principles to intact neurons. Mitochondria play an integral role in both necrotic and apoptotic neuronal cell death, and the bioenergetic principles underlying current studies are reviewed.

Carnosine protects against excitotoxic cell death independently of effects on reactive oxygen species

The role of carnosine, N-acetylcarnosine and homocarnosine as scavengers of reactive oxygen species and protectors against neuronal cell death secondary to excitotoxic concentrations of kainate and N-methyl-D-aspartate was studied using acutely dissociated cerebellar granule cell neurons and flow cytometry. We find that carnosine, N-acetylcarnosine and homocarnosine at physiological concentrations are all potent in suppressing fluorescence of 2',7'-dichlorofluorescein, which reacts with intracellularly generated reactive oxygen species. However, only carnosine in the same concentration range was effective in preventing apoptotic neuronal cell death, studied using a combination of the DNA binding dye, propidium iodide, and a fluorescent derivative of the phosphatidylserine-binding dye, Annexin-V. Our results indicate that carnosine and related compounds are effective scavengers of reactive oxygen species generated by activation of ionotropic glutamate receptors, but that this action does not prevent excitotoxic cell death. Some other process which is sensitive to carnosine but not the related compounds is a critical factor in cell death. These observations indicate that at least in this system reactive oxygen species generation is not a major contributor to excitotoxic neuronal cell death.

Brain-derived neurotropic factor prevents superoxide anion-induced death of PC12h cells stably expressing TrkB receptor via modulation of reactive oxygen species

In our previous report (Satoh et al., 1999. Regulation of reactive oxygen species by nerve growth factor but not by Bcl-2 as a novel mechanism of protection of PC12 cells from superoxide anion-induced death. J. Biochem. 125, 952-959), we reported that nerve growth factor (NGF) protected PC12 cells from superoxide anion (O2-)-induced cell death through a novel regulation of reactive oxygen species (ROS) which increased O2- and decreased hydrogen peroxide (H2O2), indicating that decreasing conversion from O2- to H2O2 is a critical process for the protection by NGF. In the present study, we performed a comparative study on protective mechanisms between NGF and brain-derived neurotrophic factor (BDNF) using TrkB-expressing PC12h cells. When compared with NGF, BDNF induced a weaker but significant protective effect on the cells from O2- induced death. BDNF did not seem to change the total amount of ROS in the cells treated with xanthine and xanthine oxidase. On the other hand, BDNF increased O2- and decreased H2O2- levels in the same cells, although not so strongly as NGF. These results suggest that decreasing conversion from O2- to H2O2 is also critical for the protection by BDNF, which is considered to play a central role in survival and differentiation of CNS neurons.

CNS-specific prostacyclin ligands as neuronal survival-promoting factors in the brain

Prostacyclin (PGI2) is a critical regulator of the cardiovascular system, via dilatation of vascular smooth muscle and inhibition of platelet aggregation (Moncada, S. 1982, Br. J. Pharmacol., 76, 3). Our previous studies demonstrated that a novel subtype of PGI2 receptor, which is clearly distinct from a peripheral subtype in terms of ligand specificity, is expressed in the rostral region of the brain, e.g. cerebral cortex, hippocampus, thalamus and striatum, and that (15R)-16-m-17,18,19,20-tetranorisocarbacyclin (15R-TIC) and 15-deoxy-16-m-17,18,19,20-tetranorisocarbacyclin (15-deoxy-TIC) specifically bind to the central nervous system (CNS)-specific PGI2 receptor. Here, we report that these CNS-specific PGI2 receptor ligands, including PGI2 itself, prevented the neuronal death. They prevented apoptotic cell death of hippocampal neurons induced by high (50%) oxygen atmosphere, xanthine + xanthine oxidase, and serum deprivation. IC50s for neuronal death were approximately 30 and 300 nM for 15-deoxy-TIC and 15R-TIC, respectively, which well correlated with the binding potency for the CNS-specific PGI2 receptor. 6-Keto-PGF1alpha (a stable metabolite of PGI2), peripheral nervous system-specific PGI2 ligands and other prostaglandins (PGs) than PGI2 did not show such neuroprotective effects. In vivo, 15R-TIC protected CA1 pyramidal neurons against ischaemic damage in gerbils. These results indicate that CNS-specific PGI2 ligands have neuronal survival-promoting activity both in vitro and in vivo, and may represent a new type of therapeutic drug for neurodegeneration.

Regulation of Bcl-2 protein expression during oxidative stress in neuronal and in endothelial cells

The relationship between oxidative stress and Bcl-2 expression was investigated in two different experimental models of oxidative stress. Acute oxidative stress was assessed by measuring, with fluorescence microscopy and cytofluorimetry, the increase in fluorescence of the oxidation-sensitive probe dihydrorhodamine 123, both in retinal rod receptor cells exposed to bright light (0.32 mW/cm(2) for 15 minutes) and in human endothelial cells treated with the immunosuppressant cyclosporin A (200 microM for 21 h). In both cell types, acute oxidative stress reduced Bcl-2 expression and also caused a significant increase in the level of nucleosomes. Interestingly, chronic treatment with clinical concentrations of cyclosporin A (0.5-2.5 microM for 8 days) led to a significant increase in Bcl-2 expression, while nucleosomes were similar to control level. This suggests that up-regulation of Bcl-2 protein by low levels of oxidants may represent a critical factor in cellular adaptation to drug toxicity.

The beta2-adrenoceptor agonist clenbuterol modulates Bcl-2, Bcl-xl and Bax protein expression following transient forebrain ischemia

It is well known that proteins encoded by the Bcl-2 gene family play a major role in the regulation of apoptosis. We have demonstrated previously that neuronal apoptosis can be induced in the hippocampus and striatum after global ischemia. Clenbuterol, a beta2-adrenoceptor agonist, showed considerable activity against neuronal apoptosis. In the present study, we attempted to find out whether the members of the Bcl-2 family are induced after ischemia, and whether expression of these genes could be altered by clenbuterol. Transient forebrain ischemia was performed in male Wistar rats by clamping both common carotid arteries and reducing the blood pressure to 40 mmHg for 10 min. Clenbuterol (0.5 mg/kg, i.p.) or vehicle were injected 3 h before onset of ischemia or in non-ischemic rats. The hippocampus and striatum were taken from non-ischemic rats 3, 6 and 24 h after injection of clenbuterol, as well as from drug-treated and untreated rats 6 and 24 h after ischemia. Eighty micrograms/lane total protein were loaded on a 15% sodium dodecyl sulfate-polyacrylamide gel for western blotting. Bcl-2, Bax and Bcl-xl proteins were detectable in the non-ischemic hippocampus and the striatum. Clenbuterol up-regulated the expression of Bcl-2 protein at 3, 6 and 24 h after administration. Enhanced Bcl-xl signals were found in the non-ischemic striatum 3, 6 and 24 h after clenbuterol treatment, but no change of Bcl-xl expression by clenbuterol was seen in the non-ischemic hippocampus. Bax expression was not altered by clenbuterol in the non-ischemic hippocampus and striatum. Bcl-2 was up-regulated in both detected regions at 24 h after ischemia, while the increase in Bax and Bcl-xl protein expression had appeared already at 6 h and also 24 h after ischemia. Clenbuterol further increased the expression of Bcl-2 at 6 and 24 h after ischemia. In contrast, Bax protein level was down-regulated by clenbuterol at 6 and 24 h after ischemia. Clenbuterol also increased Bcl-xl level in the ischemic striatum. The results suggest that global ischemia induces proto-oncogenes which are associated with apoptosis. Clenbuterol not only increased Bcl-2 expression in the non-ischemic hippocampus and striatum, but also up-regulated Bcl-2 and down-regulated Bax expression in the ischemic hippocampus and striatum. The increase in the ratio of Bcl-2 and Bax may contribute to the anti-apoptotic effect of clenbuterol. The present study indicates that pharmacological modulation of Bcl-2 family member expression could become a new strategy to interfere with neuronal damage.

Generation of reactive oxygen species, release of L-glutamate and activation of caspases are required for oxygen-induced apoptosis of embryonic hippocampal neurons in culture

Oxygen-induced cell death in embryonic neurons is a useful in vitro model of neuronal apoptosis to study the molecular mechanisms underlying the cell death induced by oxidative stress. In the present study, we examined the involvement of reactive oxygen species and glutamate in the high (50%) oxygen-induced death of cultured hippocampal neurons. During the course of cell death, increases in O2- and hydrogen peroxide (H2O2) levels were observed. On the other hand, superoxide dismutase (SOD), catalase and deferoxamine (DFX), which have inhibitory effects on the generation of O2-, H2O2 and hydroxyl radicals, respectively, protected the neurons. These results suggested that both O2- and H2O2 play important roles in this apoptosis. Antagonists of NMDA and AMPA/kinate (AMPA/KA) receptors and an inhibitor of glutamate release partially prevented the apoptosis, suggesting that exposure to high oxygen enhances glutamate release, which results in activation of NMDA receptor and AMPA/KA receptor. In addition, specific nitric oxide (NO) scavenger and NO synthetase inhibitors blocked the apoptosis, indicating that NO and/or peroxynitrite are involved in this mechanism of cell death. Caspase inhibitors also blocked the neuronal apoptosis. These results suggested that multiple effectors including generation of reactive oxygen species, release of L-glutamate and activation of caspases are activated during the death induced by high oxygen.

Efficacy of a low volume recirculating superfusion chamber for long term administration of expensive drugs and dyes

We have characterized the efficacy of a low volume (2 ml) two-compartment experimental chamber in which a gas inflow equilibrates and recirculates the bathing fluid. This type of chamber is suitable for experiments employing en bloc preparations that require the administration of expensive molecular probes. The fluid in the chamber is pumped from a compartment holding the preparation to an elevated reservoir compartment using gas bubbles. The fluid returns via gravity along a different path. The flow rate of superfusate in the chamber was 30 ml min(-1). To determine the effectiveness of the chamber in dissolving gas, we filled the chamber with bicarbonate-buffered physiological saline and measured pH and P(O(2)) with ion-selective and Clark-style microelectrodes. Steady state values of pH and P(O(2)) in the chamber were almost identical to those in an external tonometer bubbled vigorously with the same gas mixture. When CO(2) was increased from 2 to 4.4%, the chamber pH fell with a time constant of 56 s (about twice that of the tonometer). To determine the effectiveness of gas exchange between a brain preparation and the fluid in the chamber we measured pH and P(O(2)) depth profiles of the in vitro tadpole brainstem. We found virtually no unstirred layer owing to excellent mixing and the high flow created by the recirculating mechanism. We demonstrate that despite the high flow rates, preparations are mechanically stable allowing intracellular electrophysiological recordings.

Oxygen toxicity induces apoptosis in neuronal cells

1. A high oxygen atmosphere induced apoptosis in cultured neuronal cells including PC12 cells and rat embryonic cortical, hippocampal, and basal forebrain neurons associated with DNA fragmentation and nuclear condensation. 2. The sensitivity of CNS neurons to a high-oxygen atmosphere was the following order; cortex > basal forebrain > hippocampus. 3. Cycloheximide and actinomycin-D inhibited the apoptosis, indicating that it depends on new macromolecular synthesis. In contrast, cultured postnatal CNS neurons were resistant to oxidative stress. 4. Neurotrophic factors such as nerve growth factor (NGF), fibroblast growth factor (FGF), and epidermal growth factor (EGF) blocked the apoptosis induced by a high-oxygen atmosphere.

Changes in c-Jun but not Bcl-2 family proteins in p53-dependent apoptosis of mouse cerebellar granule neurons induced by DNA damaging agent bleomycin

Tumor suppressor gene p53 is a critical regulator of the cellular response to DNA damage. To examine the function of p53 in postmitotic CNS neurons, we cultured cerebellar granule cells from 15-day-old wild type and p53-deficient mice, and analyzed changes of protein expression in apoptosis elicited by DNA damage. When cerebellar granule cells from wild type mice were treated with bleomycin, a DNA strand-break inducing agent, neuronal death occurred. In contrast, cells from p53-deficient mice were resistant to bleomycin-induced neuronal death. Furthermore, cells from p53 heterozygous mice showed an intermediate resistance between wild type and p53-deficient mice. These results show that p53 is required for the bleomycin-induced cerebellar granule cell death. To examine which proteins are involved in this apoptosis, we examined changes in protein levels of the Bcl-2 family, including Bcl-2, Bcl-X and Bax. The relative amounts of these proteins did not change after bleomycin treatment, suggesting that the changes in the levels of these Bcl-2 family proteins are not necessary for apoptosis in this system. In contrast, the levels of c-Jun protein significantly increased 6 h after treatment with bleomycin in wild type but not in p53-deficient cerebellar granule cells. These results raise the possibility that c-Jun is required for p53-dependent neuronal apoptosis induced by bleomycin.

Upregulation of the anti-apoptotic protein Bcl-2 may be an early event in neurodegeneration: studies on Parkinson's and incidental Lewy body disease

Apoptosis and oxidative stress have been suggested to be involved in Parkinson's disease (PD). However, whether this is a cause or consequence of neurodegeneration is unknown. Incidental Lewy Body disease (ILBD) appears to be a presymptomatic form of Parkinson's disease where individuals are neurologically normal, but after post-mortem examination pathology similar to Parkinson's disease is present. Thus, ILBD can be used to examine the early stages of the pathological process in PD. We investigated the levels of Bcl-2, an anti-apoptotic protein known to decrease cell death induced by several mechanisms, including oxidative stress. Our data show that Bcl-2 is significantly raised in the basal ganglia regions of PD patients as compared to age-matched controls. A similar trend is also found in ILBD. We propose that Bcl-2 increases in some brain regions as an early event and that these brain regions are under a stress for perhaps many years before any symptomatic changes occur.

Changes in mitochondrial membrane potential during oxidative stress-induced apoptosis in PC12 cells

We examined the effects of various types of oxidative stress on cell survival and on mitochondrial membrane potential (delta psi m) in PC12 cells transfected with BCL-2. Several types of oxidative stress such as exposure to hydrogen peroxide, 13-L-hydroperoxylinoleic acid, and xanthine + xanthine oxidase triggered apoptotic nuclear condensation and DNA fragmentation in normal PC12 cells. These types of oxidative stress induced significant increases in level of reactive oxygen species (ROS) before cell death. By contrast, BCL-2 prevented the apoptosis induced by these oxidative stresses. However, BCL-2 did not reduce ROS levels, indicating that it functions downstream of ROS generation. We measured delta psi m as a potential target of ROS during oxidative stress-induced cell death. Hydrogen peroxide, 13-L-hydroperoxylinoleic acid, and xanthine + xanthine oxidase induced a significant loss of delta psi m simultaneously with cell death. BCL-2 prevented the decrease in delta psi m as well as apoptosis induced by oxidative stress. These observations suggest that the oxidative stress triggers apoptosis associated with both increased generation of ROS and decreases in level of delta psi m and that BCL-2 prevents cell death as well as delta psi m but not ROS production.

Decreased glutathione results in calcium-mediated cell death in PC12

Neuronal damage in certain cellular populations in the brain has been linked to oxidative stress accompanied by an elevation in intracellular calcium. Many questions remain about how such oxidative stress occurs and how it affects calcium homeostasis. Glutathione (GSH) is a major regulator of cellular redox status in the brain, and lowered GSH levels have been associated with dopaminergic cell loss in Parkinson's disease (PD). We found that transfection of antisense oligomers directed against glutamylcysteine synthetase (GCS), the rate-limiting enzyme in GSH synthesis, into PC12 cells resulted in decreased GSH and increased levels of ROS. Decreased GSH levels also correlated with an increase in intracellular calcium levels. Data from this study suggest that dopaminergic neurons are very sensitive to decreases in the internal oxidant buffering capacity of the cell caused by reductions in GSH levels, and that alterations in this parameter can result in disruption of calcium homeostasis and cell death. These results may be of particular significance for therapeutic treatment of PD, as those dopaminergic neurons that are spared in this disorder appear to contain the calcium binding protein, calbindin.