A transient inhibition of mitochondrial ATP synthesis by nitric oxide synthase activation triggered apoptosis in primary cortical neurons

Liver proteome analysis in a rodent model of alcoholic steatosis

Alcoholic steatosis (AS) is the initial pathology associated with early stage alcoholic liver disease (ALD) and is characterized by the accumulation of fat in the liver. AS is considered clinically benign because it is reversible, and the progression of AS to alcoholic steatohepatitis (ASH) is a key step in the development of ALD. A two-dimensional gel electrophoresis (2DE)-mass spectrometry (MS) proteomic approach was used to investigate the protein expression pattern underlying AS, as the first step toward determining liver tissue biomarkers for early stage ALD. Several proteins involved in fatty acid and amino acid metabolism were up-regulated in 3- and 6-week ethanol-fed rats relative to isocaloric controls, which suggest a higher energy demand upon chronic exposure to ethanol. In addition, the expression of two proteins associated with alcohol-induced oxidative stress, peroxiredoxin 6 (PRDX6) and aldehyde dehydrogenase 2 (ALDH2), was down-regulated in ethanol fed rats, and suggests an increase in reactive oxygen species and oxidative stress. To investigate if irreversible protein modification arising from oxidative stress during AS impacts protein levels, the extent of carbonylated proteins in the ethanol and isocaloric groups was identified using mass spectrometry. The detection of modified proteins involved in antioxidant functions further supports the notion that oxidative modification of these proteins leads to protein turnover during AS. In addition, the carbonylation of betaine-homocysteine S-methyltransferase, a protein implicated in fatty liver development, in 3-week and 6-week ethanol exposed samples suggests that this protein could be a marker for early stage AS.

Role of cyclophilin D-dependent mitochondrial permeability transition in glutamate-induced calcium deregulation and excitotoxic neuronal death

In the present study we tested the hypothesis that the cyclophilin D-dependent (CyD) mitochondrial permeability transition (CyD-mPT) plays an important role in glutamate-triggered delayed calcium deregulation (DCD) and excitotoxic neuronal death. We used cultured cortical neurons from wild-type C57BL/6 and cyclophilin D-knockout mice (Ppif(-/-)). Induction of the mPT was identified by following the rapid secondary acidification of mitochondrial matrices monitored with mitochondrially targeted pH-sensitive yellow fluorescent protein. Suppression of the CyD-mPT due to genetic CyD ablation deferred DCD and mitochondrial depolarization, and increased the survival rate after exposure of neurons to 10 microM glutamate, but not to 100 microM glutamate. Ca(2+) influx into Ppif(-/-) neurons was not diminished in comparison with WT neurons judging by (45)Ca accumulation. In both types of neurons, 100 microM glutamate produced greater Ca(2+) influx than 10 microM glutamate. We hypothesize that greater Ca(2+) influx produced by higher glutamate rapidly triggered the CyD-independent mPT in both WT and Ppif(-/-) neurons equalizing their responses to supra-physiologic excitotoxic insults. In neurons exposed to moderate but pathophysiologically-relevant glutamate concentrations, an induction of the CyD-mPT appears to play an important role in mitochondrial injury contributing to DCD and cell death.

Adaptation to G93Asuperoxide dismutase 1 in a motor neuron cell line model of amyotrophic lateral sclerosis: the role of glutathione

Motor neuron degeneration in amyotrophic lateral sclerosis involves oxidative damage. Glutathione (GSH) is critical as an antioxidant and a redox modulator. We used a motor neuronal cell line (NSC-34) to investigate whether wild-type and familial amyotrophic lateral sclerosis-linked G93A mutant Cu,Zn superoxide dismutase (wt/G93ASOD1) modified the GSH pool and glutamate cysteine ligase (GCL), the rate-limiting enzyme for GSH synthesis. We studied the effect of various G93ASOD1 levels and exposure times. Mutant Cu,Zn superoxide dismutase induced an adaptive process involving the upregulation of GSH synthesis, even at very low expression levels. However, cells with a high level of G93ASOD1 cultured for 10 weeks showed GSH depletion and a decrease in expression of the modulatory subunit of GCL. These cells also had lower levels of GSH and GCL activity was not induced after treatment with the pro-oxidant tert-butylhydroquinone. Cells with a low level of G93ASOD1 maintained higher GSH levels and GCL activity, showing that the exposure time and the level of the mutant protein modulate GSH synthesis. We conclude that failure of the regulation of the GSH pathway caused by G93ASOD1 may contribute to motor neuron vulnerability and we identify this pathway as a target for therapeutic intervention.

Nitric oxide in health and disease of the nervous system

Nitric oxide (NO) is an important messenger molecule in a variety of physiological systems. NO, a gas, is produced from L-arginine by different isoforms of nitric oxide synthase (NOS) and serves many normal physiologic purposes, such as promoting vasodilation of blood vessels and mediating communication between nervous system cells. In addition to its physiologic actions, free radical activity of NO can cause cellular damage through a phenomenon known as nitrosative stress. Here, we review the role of NO in health and disease, focusing on its role in function and dysfunction of the nervous system. Substantial evidence indicates that NO plays a key role in most common neurodegenerative diseases, and, although the mechanism of NO-mediated neurodegeneration remains uncertain, studies suggest several possibilities. NO has been shown to modify protein function by nitrosylation and nitrotyrosination, contribute to glutamate excitotoxicity, inhibit mitochondrial respiratory complexes, participate in organelle fragmentation, and mobilize zinc from internal stores. In this review, we discuss and analyze the evidence for each of these mechanisms in different neurodegenerative diseases and propose future directions for research of the role of NO in neurodegeneration.

Cdk5 phosphorylates Cdh1 and modulates cyclin B1 stability in excitotoxicity

Anaphase-promoting complex/cyclosome (APC/C), an E3 ubiquitin ligase that destabilizes cell cycle proteins, is activated by Cdh1 in post-mitotic neurons, where it regulates axonal growth, synaptic plasticity and survival. The APC/C-Cdh1 substrate, cyclin B1, has been found to accumulate in degenerating brain areas in Alzheimer's disease and stroke. This highlights the importance of elucidating cyclin B1 regulation by APC/C-Cdh1 in neurons under stress conditions relevant to neurological disease. Here, we report that stimulation of N-methyl-D-aspartate receptors (NMDARs) that occurs in neurodegenerative diseases promoted the accumulation of cyclin B1 in the nuclei of cortical neurons; this led the neurons to undergo apoptotic death. Moreover, we found that the Ser-40, Thr-121 and Ser-163 triple phosphorylation of Cdh1 by the cyclin-dependent kinase-5 (Cdk5)-p25 complex was necessary and sufficient for cyclin B1 stabilization and apoptotic death after NMDAR stimulation. These results reveal Cdh1 as a novel Cdk5 substrate that mediates cyclin B1 neuronal accumulation in excitotoxicity.

PACAP38 protects rat cortical neurons against the neurotoxicity evoked by sodium nitroprusside and thrombin

Pituitary adenylate cyclase-activating polypeptide (PACAP) 38 is a multifunctional anti-inflammatory and anti-apoptotic neuropeptide widely distributed in the nervous system. The objective of this study is to determine whether PACAP38 is neuroprotective against sodium nitroprusside (SNP) and thrombin, two mechanistically distinct neurotoxic agents. Treatment of primary cortical neuronal cultures with 1 mM SNP for 4 h causes neuronal cell death that is significantly reduced by 100 nM PACAP38. PACAP38 down-regulates SNP-induced cell cycle protein (cyclin E) expression and up-regulates p57(KIP2), a cyclin-dependent kinase inhibitor as well as the anti-apoptotic protein Bcl-2. Similarly, neuronal death induced by 100 nM thrombin or the thrombin receptor activating peptide (TRAP 6) is reduced by PACAP38 treatment. Thrombin-stimulated cell cycle protein (cdk4) expression is decreased by PACAP38 while PACAP38 inhibits thrombin-mediated reduction of p57(KIP2). However, the decrease in Bcl-2 evoked by thrombin is not affected by PACAP38. Finally, both SNP and thrombin (or TRAP) increase caspase 3 activity, an effect that is decreased by PACAP38. These data show that PACAP38 supports neuronal survival in vitro suppressing cell cycle progression and enhancing anti-apoptotic proteins. Our results support the possibility that PACAP could be a useful therapeutic agent for reducing neuronal cell death in neurodegenerative diseases.

Enhanced expression of RNase L as a novel intracellular signal generated by NMDA receptors in mouse cortical neurons

Recently we showed that the level of mitochondrial mRNA was decreased prior to neuronal death induced by glutamate. As the level of mRNA is regulated by ribonuclease (RNase), we examined RNase activity and its expression in the primary cultures of cortical neurons after glutamate treatment in order to evaluate the involvement of RNase in glutamate-induced neuronal death. A 15-min exposure of the cultures to glutamate at the concentration of 100 microM produced marked neuronal damage (more than 70% of total cells) at 24-h post-exposure. Under the experimental conditions used, RNA degradation was definitely observed at a period of 4-12-h post-exposure, a time when no damage was seen in the neurons. Glutamate-induced RNA degradation was completely prevented by the N-methyl-d-aspartic acid (NMDA) receptor channel blocker MK-801 or the NR2B-containing NMDA receptor antagonist ifenprodil. Glutamate exposure produced enhanced expression of RNase L at least 2-12h later, which was absolutely abolished by MK-801. However, no significant change was seen in the level of RNase H1 mRNA at any time point post-glutamate treatment. Immunocytochemical studies revealed that RNase L expressed in response to glutamate was localized within the nucleus, mitochondria, and cytoplasm in the neurons. Taken together, our data suggest that expression of RNase L is a signal generated by NMDA receptor in cortical neurons. RNase L expression and RNA degradation may be events that cause neuronal damage induced by NMDA receptor activation.

Curcuma oil modulates the nitric oxide system response to cerebral ischemia/reperfusion injury

The antioxidant activity of C.oil in cerebral stroke has been reported earlier. We have attempted here to clarify the mechanisms underlying the neuroprotection against experimental cerebral ischemia by Curcuma oil (C.oil), isolated from the rhizomes of Curcuma longa. C.oil (250 mg/kg i.p.) was given 30 min before focal ischemia in rats caused by occlusion of the middle cerebral artery (1h of occlusion, 24h of reflow). Ischemia, leads to elevation in [Ca(2+)] this sets into motion a cascades of ischemic injury which was attenuated by C.oil. C.oil reduced post-ischemic brain neutrophil infiltration in the ischemic area, controlled tissue NOx levels and the neuronal levels of nitric oxide, peroxynitrite and reactive oxygen species when measured after 24h of reflow. Double immunofluorescence staining analysis and Western immunoblot analysis with C.oil treatment showed that the expression of nitric oxide synthase (NOS) isoforms were decreased significantly compared to the untreated ischemia group. Ischemia is associated with increased in TUNEL (TdT-mediated dUTP nick-end labeling) positive cells in brain sections indicating DNA fragmentation. The C.oil treated group showed a significant decrease in numbers of apoptotic cells compared to the untreated ischemia group, as seen in the flowcytometric analysis of the neurons. Results of immunohistochemistry and Western immunoblot indicate that C.oil suppressed the elevated protein level of Bax, and aided mitochondrial translocation and activation of Bcl-2 by altered mitochondrial membrane potential. It also inhibits the cytosolic release of apoptogenic molecules like cytochrome c, inhibits the activation of caspase-3 and the expression of p53 ultimately inhibiting apoptosis. Our observations suggest that high levels of NO generated by NOS isoforms are partially responsible for exacerbating the neuronal damage induced by MCAo by intraluminal filament.

Regulation of glycolysis and pentose-phosphate pathway by nitric oxide: impact on neuronal survival

Besides its essential role at regulating neural functions through cyclic GMP, nitric oxide is emerging as an endogenous physiological modulator of energy conservation for the brain. Thus, nitric oxide inhibits cytochrome c oxidase activity in neurones and glia, resulting in down-regulation of mitochondrial energy production. The subsequent increase in AMP facilitates the activation of 5'-AMP-dependent protein kinase, which rapidly triggers the activation of 6-phosphofructo-1-kinase--the master regulator of the glycolytic pathway--and Glut1 and Glut3--the main glucose transporters in the brain. In addition, nitric oxide activates glucose-6-phosphate dehydrogenase, the first and rate-limiting step of the pentose-phosphate pathway. Here, we review recent evidences suggesting that nitric oxide exerts a fine control of neuronal energy metabolism by tuning the balance of glucose-6-phosphate consumption between glycolysis and pentose-phosphate pathway. This may have important implications for our understanding of the mechanisms controlling neuronal survival during oxidative stress and bioenergetic crisis.

Changes in ATP content in cerebellar granule cells during hyperstimulation of glutamate receptors: possible role of NO and nitrite ions

In primary 7-8-day culture of cerebellar granule cells, glutamate exposure (100 microM, 10-240 min) induced a 60-30% drop in ATP level; during the postglutamate period ATP level completely recovered after 24 h. Inhibition of NO-synthase with L-NAME during glutamate application resulted in less pronounced decrease in ATP level immediately after its application and had no effect on ATP recovery after 24 h. It was found that hyperstimulation of glutamate receptors elevates concentration of NO products (nitrites and nitrates), while NO2(-) ions can increase ATP content.

Linking glycolysis with oxidative stress in neural cells: a regulatory role for nitric oxide

NO (nitric oxide) participates in a considerable number of physiological functions. At the biochemical level, most of its actions can be ascribed to its ability to bind, and activate, soluble guanylate cyclase. However, mounting evidence now strongly suggests that the NO-mediated inhibition of cytochrome c oxidase, the terminal complex of the mitochondrial respiratory chain, may be a further step of a cell signalling process involved in the regulation of important cellular functions. In most cells, including neurons and astrocytes, NO reversibly, and irreversibly, modulates O(2) consumption, a phenomenon through which NO signals certain pathways relevant for neuronal survival. Here, we propose that besides the control of mitochondrial bioenergetics, NO finely modulates the balance between glucose consumption through the glycolytic pathway and the pentose phosphate pathway in neurons. This may have implications for our understanding of the mechanisms of neurodegeneration due to oxidative and nitrosative stress.

Nitric oxide evokes an adaptive response to oxidative stress by arresting respiration

Aerobic metabolism generates biologically challenging reactive oxygen species (ROS) by the endogenous autooxidation of components of the electron transport chain (ETC). Basal levels of oxidative stress can dramatically rise upon activation of the NADPH oxidase-dependent respiratory burst. To minimize ROS toxicity, prokaryotic and eukaryotic organisms express a battery of low-molecular-weight thiol scavengers, a legion of detoxifying catalases, peroxidases, and superoxide dismutases, as well as a variety of repair systems. We present herein blockage of bacterial respiration as a novel strategy that helps the intracellular pathogen Salmonella survive extreme oxidative stress conditions. A Salmonella strain bearing mutations in complex I NADH dehydrogenases is refractory to the early NADPH oxidase-dependent antimicrobial activity of IFNgamma-activated macrophages. The ability of NADH-rich, complex I-deficient Salmonella to survive oxidative stress is associated with resistance to peroxynitrite (ONOO(-)) and hydrogen peroxide (H(2)O(2)). Inhibition of respiration with nitric oxide (NO) also triggered a protective adaptive response against oxidative stress. Expression of the NDH-II dehydrogenase decreases NADH levels, thereby abrogating resistance of NO-adapted Salmonella to H(2)O(2). NADH antagonizes the hydroxyl radical (OH(.)) generated in classical Fenton chemistry or spontaneous decomposition of peroxynitrous acid (ONOOH), while fueling AhpCF alkylhydroperoxidase. Together, these findings identify the accumulation of NADH following the NO-mediated inhibition of Salmonella's ETC as a novel antioxidant strategy. NO-dependent respiratory arrest may help mitochondria and a plethora of organisms cope with oxidative stress engendered in situations as diverse as aerobic respiration, ischemia reperfusion, and inflammation.

Oxidative Stress and Cardiac Repair/Remodeling Following Infarction

Extensive cardiac remodeling after myocardial infarction (MI) contributes significantly to ventricular dysfunction. Factors regulating left ventricular remodeling at different stages after MI are under investigation. There is growing recognition and experimental evidence that oxidative stress mediated by reactive oxygen species plays a role in the pathogeneses of myocardial repair/remodeling in various cardiac diseases. After acute MI, oxidative stress is developed in both infarcted and noninfarcted myocardium. Accumulating evidence has demonstrated that oxidative stress participates in several aspects of cardiac repair/remodeling after infarction that include cardiomyocyte apoptosis, inflammatory/fibrogenic responses, and hypertrophy. The exact pathways on reactive oxygen species-mediated myocardial remodeling are under investigation. The therapeutic potential of oxidative stress-directed drugs in myocardial remodeling after infarction has not been fully realized.

Nitric oxide from neuronal nitric oxide synthase sensitises neurons to hypoxia-induced death via competitive inhibition of cytochrome oxidase

Hypoxia/ischaemia is known to trigger neuronal death, but the role of neuronal nitric oxide synthase (nNOS) in this process is controversial. Nitric oxide (NO) inhibits cytochrome oxidase in competition with oxygen. We tested whether NO derived from nNOS synergises with hypoxia to induce neuronal death by inhibiting mitochondrial cytochrome oxidase. Sixteen hours of hypoxia (2% oxygen) plus deoxyglucose (an inhibitor of glycolysis) caused extensive, excitotoxic death of neurons in rat cerebellar granule cell cultures. Three different nNOS inhibitors (including the selective inhibitor N-4S-4-amino-5-2-aminoethyl-aminopentyl-N'-nitroguanidine) decreased this neuronal death by half, indicating a contribution of nNOS to hypoxic death. The selective nNOS inhibitor did not, however, block neuronal death induced either by added glutamate or by added azide (an uncompetitive inhibitor of cytochrome oxidase), indicating that nNOS does not act downstream of glutamate or cytochrome oxidase. Hypoxia plus deoxyglucose-induced glutamate release and neuronal depolarisation, and the nNOS inhibitor decreased this. Hypoxia inhibited cytochrome oxidase activity in the cultures, but a selective nNOS inhibitor prevented this inhibition, indicating NO from nNOS was inhibiting cytochrome oxidase in competition with oxygen. These data indicate that hypoxia synergises with NO from nNOS to induce neuronal death via cytochrome oxidase inhibition causing neuronal depolarisation. This mechanism might contribute to ischaemia/stroke-induced neuronal death in vivo.

Decreased level of mitochondrial RNA by glutamate in cultured cortical neurons

Mitochondrial injury is induced by a decline in mitochondrial function as well as by damaged mitochondrial DNA. In this study, we evaluate the effects of glutamate exposure on the level of mitochondrial mRNA in cultured cortical neurons of mice. Glutamate exposure for 15 min significantly reduced cell viability 24 h later. Under these experimental conditions, glutamate was effective in reducing the level of mitochondrial mRNAs, especially the mRNAs of NADH-ubiquinone oxidoreductase subunits (nd1 and nd6), 6 h after the exposure. Southern blot analysis, however, revealed no significant change in that of the mitochondrial DNA at any time after glutamate exposure. These results suggest that the activation of glutamate signals negatively regulated the expression of mitochondrial mRNA, without affecting the level of mitochondrial DNA.

Progesterone maintains basal intracellular adenosine triphosphate levels and viability of spontaneously immortalized granulosa cells by promoting an interaction between 14-3-3sigma and ATP synthase beta/precursor through a protein kinase G-dependent mechanism

The present studies were designed to 1) describe changes in both the mitochondrial membrane potential and ATP content of spontaneously immortalized granulosa cells as they undergo apoptosis, 2) identify some of the downstream events that are activated by progesterone (P4), and 3) relate these downstream events to changes in mitochondrial function and apoptotic cell death. These studies revealed that in response to serum deprivation, the mitochondrial membrane potential initially hyperpolarizes and ATP content increases. That this increase in ATP is required for apoptosis was demonstrated by the finding that oligomycin inhibited the increase in ATP and apoptosis. Piridoxalphosphate-6-azopeyl-2'-4'-disulfonic acid, an inhibitor of purinergic receptors, which are activated by ATP, also inhibited apoptosis due to serum withdrawal. This study provides additional support for ATP's causative role in apoptosis. Moreover, 8-Br-cGMP, a protein kinase G (PKG) activator, mimicked P4's action, whereas a PKG antagonist, DT-3, attenuated P4's suppressive effect on ATP and apoptosis. Finally, DT-3 treatment was shown to attenuate P4-regulated phosphorylation of 14-3-3sigma and its binding partner, ATP synthasebeta/precursor and the amount of ATP synthasebeta/precursor that bound to 14-3-3sigma. Based on these data, it is proposed that P4 prevents apoptosis in part by activating PKG, which in turn maintains the interaction between ATP synthasebeta/precursor and 14-3-3sigma. In the absence of P4-induced PKG activity, we further propose that some ATP synthasebeta precursor dissociates from 14-3-3sigma, resulting in its activation and incorporation into the ATP synthase complex, which ultimately results in an increase in ATP and apoptosis.

Nitric Oxide Synthase 3-Mediated Neurodegeneration After Intracerebral Gene Delivery

In Alzheimer disease (AD), increased nitric oxide synthase 3 (NOS3) expression correlates with apoptosis in cortical neurons and colocalizes with amyloid precursor protein (APP)-amyloid beta (Abeta) deposits in the brain. In the present study we examined the potential role of NOS3 in relation to AD-type neurodegeneration using an in vivo model of gene delivery. Long Evans rat pups were given a single intracerebral injection of recombinant plasmid DNA containing the human NOS3 cDNA (p-hNOS3) or the luciferase (p-Luc) gene as a negative control, and complexed with polyamine reagent. Overexpression of NOS3 in the brain increased the levels of APP, APP-Abeta, p53, Tau, glial fibrillary acidic protein, and peroxisome proliferator activated receptors (PPAR) delta and gamma and decreased the levels of Hu (neuronal marker) mRNA, phosphorylated glycogen synthase kinase 3beta, ATP synthase, and choline acetyltransferase expression as demonstrated by real-time quantitative reverse-transcribed polymerase chain reaction, Western blot analysis, or immunohistochemical staining. These effects of NOS3 overexpression were accompanied by increased single-stranded DNA immunoreactivity, reflecting DNA damage. The results suggest that increased cerebral expression of NOS3 causes several molecular abnormalities related to AD-type neurodegeneration, including oxidative stress, mitochondrial dysfunction, and impaired acetylcholine homeostasis. The coexisting increases in PPAR-delta and -gamma expression suggest that the adverse effects of NOS3 overexpression may be abated by PPAR agonist treatment.

Early cell death in the brain of fetal preterm lambs after hypoxic-ischemic injury

The objective of the present study was to evaluate using premature fetal lambs the effect of cerebral hypoxia-ischemia induced by partial occlusion of the umbilical cord on the type of cell death which occurs in different brain regions and to ascertain some of the neural pathways which may underlie the associated pathologies. Lambs were sacrificed either immediately after a 1 h hypoxic-ischemic insult or 3 h later. Brains were fixed by perfusion and blocks of the different brain territories were processed for light microscopy (hematoxylin-eosin, Nissl staining), electron transmission microscopy and quantification of apoptosis by the TUNEL method. Other fixed brains were dissociated and labeled by nonyl acridine orange to determine mitochondrial integrity. Non-fixed brains were also used for membrane asymmetry studies, in which cell suspensions were analyzed by flow cytometry to quantify apoptosis. In both hypoxic-ischemic groups, necrotic-like neurons were observed mainly in the mesencephalon, pons, deep cerebellar nuclei and basal nuclei, whereas apoptotic cells were extensively found both in white and gray matter and were not limited to regions where necrotic neurons were present. The 3 h post-partial cord occlusion group, but not the 0 h group, showed a generalized alteration of cell membrane asymmetry and mitochondrial integrity as revealed by Annexin V/PI flow cytometry and nonyl acridine orange studies, respectively. Our results show that the apoptotic/necrotic patterns of cell death occurring early after hypoxic-ischemic injury are brain-region-specific and have distinct dynamics and suggest that therapeutic strategies aimed at rescuing cells from the effects of hypoxia/ischemia should be aimed at blocking the apoptotic components of brain damage.

Inhibition of PTEN by peroxynitrite activates the phosphoinositide-3-kinase/Akt neuroprotective signaling pathway

Peroxynitrite is usually considered as a neurotoxic nitric oxide-derivative. However, an increasing body of evidence suggests that, at low concentrations, peroxynitrite affords transient cytoprotection, both in vitro and in vivo. Here, we addressed the signaling mechanism responsible for this effect, and found that rat cortical neurons in primary culture acutely exposed to peroxynitrite (0.1 mmol/L) rapidly elicited Akt-Ser(473) phosphorylation. Inhibition of phosphoinositide-3-kinase (PI3K)/Akt pathway with wortmannin or Akt small hairpin RNA (shRNA) abolished the ability of peroxynitrite to prevent etoposide-induced apoptotic death. Endogenous peroxynitrite formation by short-term incubation of neurons with glutamate stimulated Akt-Ser(473) phosphorylation, whereas Akt shRNA enhanced the vulnerability of neurons against glutamate. We further show that Akt-Ser(473) phosphorylation was consequence of the oxidizing, but not the nitrating properties of peroxynitrite. Peroxynitrite failed to nitrate or phosphorylate neurotrophin tyrosine kinase receptors (Trks), and it did not modify the ability of brain-derived neurotrophic factor (BDNF), to phosphorylate its cognate receptor, TrkB; however, peroxynitrite enhanced BDNF-mediated Akt-Ser(473) phosphorylation. Finally, we found that peroxynitrite-stimulated Akt-Ser(473) phosphorylation was associated with an increased proportion of oxidized phosphoinositide phosphatase, PTEN, in neurons. Moreover, peroxynitrite prevented the increase of apoptotic neuronal death caused by over-expression of PTEN. Thus, peroxynitrite exerts neuroprotection by inhibiting PTEN, hence activating the anti-apoptotic PI3K/Akt pathway in primary neurons.

Street heroin induces mitochondrial dysfunction and apoptosis in rat cortical neurons

Cortical function has been suggested to be highly compromised by repeated heroin self-administration. We have previously shown that street heroin induces apoptosis in neuronal-like PC12 cells. Thus, we analysed the apoptotic pathways involved in street heroin neurotoxicity using primary cultures of rat cortical neurons. Our street heroin sample was shown to be mainly composed by heroin, 6-monoacetylmorphine and morphine. Exposure of cortical neurons to street heroin induced a slight decrease in metabolic viability, without loss of neuronal integrity. Early activation of caspases involved in the mitochondrial apoptotic pathway was observed, culminating in caspase 3 activation, Poly-ADP Ribose Polymerase (PARP) cleavage and DNA fragmentation. Apoptotic morphology was completely prevented by the non-selective caspase inhibitor z-VAD-fmk, indicating an important role for caspases in neurodegeneration induced by street heroin. Ionotropic glutamate receptors, opioid receptors and oxidative stress were not involved in caspase 3 activation. Interestingly, street heroin cytotoxicity was shown to be independent of a functional mitochondrial respiratory chain, as determined using NT-2 rho(0) cells. Nonetheless, in street heroin-treated cortical neurons, cytochrome c was released, accompanied by a decrease in mitochondrial potential and Bcl-2/Bax. Pure heroin hydrochloride similarly decreased metabolic viability but only slightly activated caspase 3. Altogether, our data suggest an important role for mitochondria in mediating street heroin neurotoxic effects.

Mechanisms of nitric oxide-induced apoptosis in bovine chromaffin cells: Role of mitochondria and apoptotic proteins

The aim of this work was to establish the possible involvement of mitochondria in the apoptotic event triggered by nitric oxide (NO) in chromaffin cells. Using bovine chromaffin cells in primary culture and several NO donors (SNP, SNAP, and GSNO) at apoptotic concentrations (50 microM-1 mM), we have shown that NO induces a time-dependent decrease in the mitochondrial transmembrane potential (DeltaPsi(m)), which correlates with the appearance of hypodiploid cells. Disruption in DeltaPsi(m) is followed by cytochrome c release to the cytosol, which in turn precedes caspase 3 activation. In this mechanism participates the Bcl-2 protein family, because NO donors downregulate the expression of anti-apoptotic members of the family such as Bcl-2 and Bcl-XL, and increase the expression of pro-apoptotic members, Bax and Bcl-Xs, inductors of cytochrome c release to cytosol. Different cell signaling pathways seem to regulate Bax induction and Bcl-2 inhibition because decreased Bcl-2 levels are detected later than enhanced Bax expression. The tumour suppressor protein p53 is also upregulated in a very early phase (30 min) of the NO-induced apoptosis and may be responsible for the further induction of Bax expression. Finally, the translocation of NF-kappaB to the nucleus seems to be another early event in NO-induced apoptosis and it may be involved in the regulation of p53 expression. These results support strongly the participation of mitochondrial mechanisms in NO-induced apoptosis in chromaffin cells and suggest that these cells may be good models for the investigation of molecular basis of neurodegeneration and neuroprotection.

D-beta-hydroxybutyrate prevents glutamate-mediated lipoperoxidation and neuronal damage elicited during glycolysis inhibition in vivo

Excitotoxic neuronal death mediated by over-activation of glutamate receptors has been implicated in ischemia, hypoglycemia and some neurodegenerative diseases. It involves oxidative stress and is highly facilitated during impairment of energy metabolism. We have shown previously that in vivo systemic glycolysis inhibition with iodoacetate (IOA), exacerbates glutamate excitotoxicity. We have now investigated whether this effect involves oxidative damage to membrane lipids, as evaluated by the presence of thiobarbituric acid-reactive substances. We have also tested whether the ketone body, D-beta-hydroxybutyrate (D-BHB), prevents lipoperoxidation and tissue damage. Results show that glutamate intrastriatal injection in control rats transiently enhances lipoperoxidation, while in IOA-treated animals increased lipoperoxidation is sustained. Treatment with D-BHB significantly reduces striatal lesions and lipoperoxidation. Vitamin E also reduced neuronal damage and lipoperoxidation. Results suggest that glycolysis impairment favors a pro-oxidant condition and situates oxidative damage as an important mediator of in vivo induced excitotoxicity. Results provide evidence for the neuroprotective effect of D-BHB against glutamate toxicity.

Inducible and neuronal nitric oxide synthases (NOS) have complementary roles in recovery sleep induction

Sleep homeostasis is the process by which recovery sleep is generated by prolonged wakefulness. The molecular mechanisms underlying this important phenomenon are poorly understood. We have previously shown that nitric oxide (NO) generation increases in the basal forebrain (BF) during sleep deprivation (SD). Moreover, both NO synthase (NOS) inhibition and a NO scavenger prevented recovery sleep induction, while administration of a NO donor during the spontaneous sleep-wake cycle increased sleep, indicating that NO is necessary and sufficient for the induction of recovery sleep. Next we wanted to know which NOS isoform is involved in the production of recovery sleep. Using in vivo microdialysis we infused specific inhibitors of NOS into the BF of rats during SD, and found that an inhibitor of inducible NOS (iNOS), 1400W, prevented non-rapid eye movement (NREM) recovery, while an inhibitor of neuronal NOS (nNOS), L-N-propyl-arginine, decreased REM recovery but did not affect NREM recovery. Using immunoblot analysis we found that iNOS was not expressed during the spontaneous sleep-wake cycle, but was induced by prolonged wakefulness (increased by 278%). A known iNOS inducer, lipopolysaccharide, evoked an increase in sleep that closely resembled recovery sleep, and its effects were abolished by 1400W. These results suggest that the elevation of NO produced by induction of iNOS in the BF during prolonged wakefulness is a specific mechanism for producing NREM recovery sleep and that the two NOS isoforms have a complementary role in NREM and REM recovery induction.

Optical and pharmacological tools to investigate the role of mitochondria during oxidative stress and neurodegeneration

Mitochondria are critical for cellular adenosine triphosphate (ATP) production; however, recent studies suggest that these organelles fulfill a much broader range of tasks. For example, they are involved in the regulation of cytosolic Ca(2+) levels, intracellular pH and apoptosis, and are the major source of reactive oxygen species (ROS). Various reactive molecules that originate from mitochondria, such as ROS, are critical in pathological events, such as ischemia, as well as in physiological events such as long-term potentiation, neuronal-vascular coupling and neuronal-glial interactions. Due to their key roles in the regulation of several cellular functions, the dysfunction of mitochondria may be critical in various brain disorders. There has been increasing interest in the development of tools that modulate mitochondrial function, and the refinement of techniques that allow for real time monitoring of mitochondria, particularly within their intact cellular environment. Innovative imaging techniques are especially powerful since they allow for mitochondrial visualization at high resolution, tracking of mitochondrial structures and optical real time monitoring of parameters of mitochondrial function. The techniques discussed include classic imaging techniques, such as rhodamine-123, the highly advanced semi-conductor nanoparticles (quantum dots), and wide field microscopy as well as high-resolution multiphoton imaging. We have highlighted the use of these techniques to study mitochondrial function in brain tissue and have included studies from our laboratories in which these techniques have been successfully applied.

Nitric oxide, cell bioenergetics and neurodegeneration

Following stimulation of NMDA receptors, neurons transiently synthesize nitric oxide (NO) in a calcium/calmodulin-dependent manner through the activation of neuronal NO synthase. Nitric oxide acts as a messenger, activating soluble guanylyl cyclase and participating in the transduction signalling pathways involving cyclic GMP. Nitric oxide also binds to cytochrome c oxidase, and is able to inhibit cell respiration in a process that is reversible and in competition with oxygen. This action can also lead to the release of superoxide anion from the mitochondrial respiratory chain. Here, we discuss recent evidence that this mitochondrial interaction represents a molecular switch for cell signalling pathways involved in the control of physiological functions. These include superoxide- or oxygen-dependent modulation of gene transcription, calcium-dependent cell signalling responses, changes in the mitochondrial membrane potential or AMP-activated protein kinase-dependent control of glycolysis. In pathophysiological conditions, such as brain ischaemia or neurological disorders, NO is formed excessively by NMDA receptor over-activation in neurons, or by inducible NO synthase from neighbouring glia (microglial cells and astrocytes). Elevated NO concentrations can then interact with superoxide anion, generated by the mitochondria or by other mechanisms, leading to the formation of the powerful oxidant species peroxynitrite. During pathological conditions activation of the NAD(+)-consuming enzyme poly(APD-ribose) polymerase-1 (PARP-1) is also a likely mechanism for NO-mediated energy failure and neurotoxicity. Activation of PARP-1 is, however, a repair process, which in milder forms of oxidative stress protects neurons from death. Thus, whilst NO plays a physiological role in neuronal cell signalling, its over-production may cause neuronal energy compromise leading to neurodegeneration.

Mitochondrial involvement in nitric oxide-induced cellular death in cortical neurons in culture

Nitric oxide (NO) is an unstable molecule with physiological and pathological properties. In brain, NO acts as a modulator of neurotransmission as well as a protector against neuronal death from several death stimuli. However, beside this protector effect, high NO concentrations produce neuronal death by a mechanism in which the caspase pathway is implicated. In this work, we demonstrate that in cortical neurons the NO toxicity is mediated by mitochondrial dysfunction. SNAP, an NO donor, induces apoptosis in these cells because it 1) increases the p53 and 2) induces cytochrome c release and activation of caspase-9 and caspase-3. SNAP also induces necrosis, through 1) breakdown of the mitochondrial membrane potential, 2) ATP decrease, 3) ROS formation, and 4) LDH and ATP release, indicative of oxidative stress and death by necrosis. To sum up, in cortical neurons, high NO concentrations produced cellular death by both an apoptotic and a necrotic mechanism in which the mitochondria are implicated.

Modulation of astroglial energy metabolism by nitric oxide

Activated astroglial cells produce large amounts of nitric oxide (NO) which, through the binding to soluble guanylyl cyclase, rapidly increases cyclic GMP concentrations. In addition, through the binding with the a-a (3) binuclear center of cytochrome c oxidase, NO rapidly decreases the affinity of this complex for O(2), hence reversibly inhibiting the mitochondrial electron flux and ATP synthesis. Despite promoting a profound degree of mitochondrial inhibition, astrocytes show remarkable resistance to NO and peroxynitrite, whereas neurons are highly vulnerable. Recent evidence suggests that the inhibition of mitochondrial respiration by these nitrogen-derived reactive species leads to the modulation of key regulatory steps of glucose metabolism. Thus, upregulation of glucose uptake, the stimulation of glycolysis and the activation of pentose-phosphate pathway appear to be important sites of action. The stimulation of these glucose-metabolizing pathways by NO would represent a transient attempt by the glial cells to compensate for energy impairment and oxidative stress, and thus to emerge from an otherwise pathological outcome.

Voltage-dependent potassium channels are involved in glutamate-induced apoptosis of rat hippocampal neurons

The role of voltage-dependent potassium channel currents in glutamate-treated rat hippocampal neurons was investigated. Cell viability was evaluated by MTT reduction assay and morphological changes. Apoptosis was detected by Hoechst33342 staining with fluorescent microscopy and propidium iodide staining with flow cytometry. Membrane potassium channel currents were recorded with whole-cell patch clamp recordings. Results showed that after shortly exposed to glutamate, about 25 and 50% cells died in 3 h and 24 h, respectively. Meanwhile, the enhancement of IK was observed within 6 h after the glutamate insult. TEA selectively blocked IK and significantly reduced cell apoptosis. IA did not change in the insult though 4-AP, the blocker of this current, showed a protective effect against the injury. These data were in consistent with the hypothesis that K+ efflux contributed to glutamate-triggered apoptosis and IK channels might have a therapeutic effect on the treatment of cerebral ischemia.

Contribution of reduced and oxidized glutathione to signals detected by magnetic resonance spectroscopy as indicators of local brain redox state

The reduced form of glutathione (GSH; gamma-glutamyl cysteinyl glycine) is supposedly the most powerful reducing battery in the central nervous system against oxidative stress. We evaluated the contribution of GSH and GSSG to MEGA-PRESS (a frequency-selective refocusing technique) signals assessed by magnetic resonance spectroscopy (MRS). GSH gave a single positive signal (2.95 ppm) by the MEGA-PRESS. In contrast, GSSG gave a multiplet of reversed signals (3.03, 3.23, and 3.34 ppm). A phantom solution mimicking the normal in vivo condition (GSH:GSSG=100:1) gave a single positive peak. Even when the ratio was changed to 10:1, corresponding to toxic oxidative stress, GSH was prominent and GSSG signals were minimal. Thus, GSSG signals could be negligible. In the phantom solution (creatine:GSH:aspartate:gamma-aminobutyric acid=7:3:1:1), the creatine signal overshadowed the other signals. Through the MEGA-PRESS, a single peak of GSH stood out over other signals. In vivo, the brains of healthy volunteers gave similar signals as the in vitro phantom solution, indicating that the signal originated from GSH. The estimated concentration of GSH in the human brain was 1.9+/-0.37 mM (mean+/-S.D., n=4). In conclusion, MEGA-PRESS allowed us to assess GSH levels in vivo non-invasively.

15,16-dihydrotanshinone I suppresses the activation of BV-2 cell, a murine microglia cell line, by lipopolysaccharide

Microglial activation has been implicated in neurodegenerative diseases. Therefore, inhibition of inflammation mediated by microglia is a strategy in neurodegenerative disease therapy. In this study, we isolated cryptotanshinone and 15,16-dihydrotanshinone I from Salvia miltiorrhiza, a traditional Korean herb medicine, by bioactivity-guided fractionation based on inhibitory effect on nitric oxide in a lipopolysaccharide-stimulated BV-2 cells, a murine microglial cell line. 15,16-Dihydotanshinoe I suppressed the expression of not only inducible nitric oxide synthase but also of interleukin-1beta, tumor necrosis factor-alpha, and of TNF-alpha converting enzyme.

Knockdown of Glutamate-Cysteine Ligase by Small Hairpin RNA Reveals That Both Catalytic and Modulatory Subunits Are Essential for the Survival of Primary Neurons

Glutathione deficiency is an early biochemical feature that occurs during apoptotic neuronal death associated with certain neurological disorders such as Parkinson disease. However, whether specific targeting of glutathione biosynthesis in neurons is sufficient to trigger neurodegeneration remains undetermined. To address this issue, we used a vector-based small hairpin RNA (shRNA) strategy to knock down each subunit of glutamate-cysteine ligase (GCL; gamma-glutamylcysteine synthetase), the heterodimeric enzyme that catalyzes the rate-limiting step of glutathione biosynthesis. Independent targeting of the catalytic and modulatory subunits by shRNA caused disruption of GCL as assessed by Northern and Western blotting, enzyme activity, and glutathione concentrations. Silencing each subunit in primary cortical neurons spontaneously elicited time-dependent apoptotic death, an effect that was synergistic with glutamate or nitric oxide treatment. Moreover, neuronal apoptosis by GCL knockdown was rescued by expressing the corresponding subunit full-length cDNA carrying silent mutations within the shRNA target cDNA sequence and by incubating neurons with gamma-glutamylcysteine or glutathione ethyl ester. In contrast, supplying glutathione precursors to neurons from co-cultured astrocytes did not prevent the apoptotic death triggered by GCL knockdown. Finally, overexpressing the catalytic (but not modulatory) GCL subunit full-length cDNA increased enzyme activity and glutathione concentrations, yielding neurons more resistant to glutamate- or nitric oxide-mediated apoptosis. Thus, specific and independent disruption of each subunit of GCL in neurons can be said to cause a primary decrease in glutathione that is sufficient to promote neurodegeneration.

D-beta-hydroxybutyrate is neuroprotective against hypoxia in serum-free hippocampal primary cultures

Hypoxia decreased survival of cultured rat primary hippocampal neurons in a time dependent manner. Addition of 4 mM Na D-beta-hydroxybutyrate (bHB), a ketone body, protected the cells for 2 hr and maintained the increase in survival compared to that of controls for up to 6 hr. Trypan blue exclusion indicated that acute cell death was reduced markedly after 2-hr exposure to hypoxia in the bHB-treated group. The presence of bHB also decreased the number of neurons exhibiting condensed nuclei visualized by propidium iodide, indicative of apoptosis. The mitochondrial transmembrane potential (Em/c) was maintained for up to 2 hr exposure to hypoxia in the bHB-treated group, whereas the potential in the control group was decreased. Furthermore, cytochrome C release, caspase-3 activation, and poly (ADP-ribose) polymerase (PARP) cleavage were decreased in the bHB-treated group for the first 2 hr of exposure. These findings indicate that ketone bodies may be a candidate for widening the therapeutic window before thrombolytic therapy and at the same time decreasing apoptotic damage in the ischemic penumbra.

Cerebral blood flow and morphological changes after hypoxic-ischaemic injury in preterm lambs

AIM

To evaluate the effect of cerebral hypoxia-ischaemia induced by partial occlusion of the umbilical cord on the relationship of the regional cerebral blood flow and the cerebral cell death in near-term fetal lambs.

METHODS

Fifteen near-term lambs were assigned to two hypoxic-ischaemic groups with or without life support (3 h), and a healthy one. Hypoxia-ischaemia was induced by partial occlusion of the umbilical cord (60 min). Routine light and electron microscopy, and the TUNEL method for apoptosis were performed. Regional cerebral blood flow was measured by coloured microspheres. Cardiovascular, gas exchange and pH parameters were also evaluated.

RESULTS

Both hypoxic-ischaemic groups produced a transient acidosis and a decrease of base excess in comparison to the healthy group. Cortical and cerebellar zones, where the regional cerebral blood flow values were similar to baseline, showed an increased number of oligodendrocyte-like apoptotic cells. In contrast, in the inner zones, where regional cerebral blood flow was increased, the number of apoptotic cells did not increase. Necrotic neurons were observed in the basal nuclei, mesencephalon, pons and deep cerebellar nuclei.

CONCLUSION

Our results suggest that regional cerebral blood flow and the presence of apoptotic cells, 3 h after hypoxic-ischemic injury, are correlated.

An increase in the ATP levels occurs in cerebellar granule cells en route to apoptosis in which ATP derives from both oxidative phosphorylation and anaerobic glycolysis

Although it is recognized that ATP plays a part in apoptosis, whether and how its level changes en route to apoptosis as well as how ATP is synthesized has not been fully investigated. We have addressed these questions using cultured cerebellar granule cells. In particular, we measured the content of ATP, ADP, AMP, IMP, inosine, adenosine and L-lactate in cells undergoing apoptosis during the commitment phase (0-8 h) in the absence or presence of oligomycin or/and of citrate, which can inhibit totally the mitochondrial oxidative phosphorylation and largely the substrate-level phosphorylation in glycolysis, respectively. In the absence of inhibitors, apoptosis was accompanied by an increase in ATP and a decrease in ADP with 1:1 stoichiometry, with maximum ATP level found at 3 h apoptosis, but with no change in levels of AMP and its breakdown products and with a relatively low level of L-lactate production. Consistently, there was an increase in the cell energy charge and in the ratio ([ATP][AMP])/[ADP](2). When the oxidative phosphorylation was completely blocked by oligomycin, a decrease of the ATP content was found both in control cells and in cells undergoing apoptosis, but nonetheless cells still died by apoptosis, as shown by checking DNA laddering and by death prevention due to actinomycin D. In this case, ATP was provided by anaerobic glycolysis, as suggested by the large increase of L-lactate production. On the other hand, citrate itself caused a small decrease in ATP level together with a huge decrease in L-lactate production, but it had no effect on cell survival. When ATP level was further decreased due to the presence of both oligomycin and citrate, death occurred via necrosis at 8 h, as shown by the lack of DNA laddering and by death prevention found due to the NMDA receptor antagonist MK801. However, at a longer time, when ATP level was further decreased, cells died neither via apoptosis nor via glutamate-dependent necrosis, in a manner similar to something like to energy catastrophe. Our results shows that cellular ATP content increases in cerebellar granule cell apoptosis, that the role of oxidative phosphorylation is facultative, i.e. ATP can also derive from anaerobic glycolysis, and that the type of cell death depends on the ATP availability.

Increased mitochondrial respiration maintains the mitochondrial membrane potential and promotes survival of cerebellar neurons in an endogenous model of glutamate receptor activation

It is thought that the combination of extracellular glutamate accumulation and mitochondrial damage is involved in neuronal death associated with brain ischemia and hypoglycemia, and some neurodegenerative diseases such as Huntington's disease. However, the mechanism whereby those two factors interact together to trigger neurodegeneration in this and other neurodegenerative disorders is still elusive. Here, we have addressed this issue using a model of mild and sustained accumulation of extracellular glutamate in cerebellar cultured neurons, which are mostly glutamatergic and commonly used to study glutamate neurotoxicity. The resulting stimulation of glutamate receptors triggered a approximately 50% persistent increase in mitochondrial respiration that was associated with free radicals formation, and which was found to be necessary to prevent the collapse of the mitochondrial membrane potential (Deltapsim) and apoptotic cell death. In fact, hampering the glutamate-mediated increase in mitochondrial respiration with an inhibitor of the mitochondrial respiratory chain stopped neurons from producing free radicals, but led them to undergo rapid and profound Deltapsim collapse and apoptotic cell death. Thus, we suggest that the formation of reactive oxygen species by glutamate receptor activation is the unavoidable consequence of an increase in the mitochondrial respiration aimed to prevent Deltapsim collapse and neurodegeneration. These results may be relevant to understand the pathophysiology of those neurodegenerative diseases associated with both mitochondrial respiratory chain and glutamate transporter defects.

Glutamate-induced deregulation of calcium homeostasis and mitochondrial dysfunction in mammalian central neurones

Delayed neuronal death following prolonged (10-15 min) stimulation of Glu receptors is known to depend on sustained elevation of cytosolic Ca(2+) concentration ([Ca(2+)](i)) which may persist far beyond the termination of Glu exposure. Mitochondrial depolarization (MD) plays a central role in this Ca(2+) deregulation: it inhibits the uniporter-mediated Ca(2+) uptake and reverses ATP synthetase which enhances greatly ATP consumption during Glu exposure. MD-induced inhibition of Ca(2+) uptake in the face of continued Ca(2+) influx through Glu-activated channels leads to a secondary increase of [Ca(2+)](i) which, in its turn, enhances MD and thus [Ca(2+)](i). Antioxidants fail to suppress this pathological regenerative process which indicates that reactive oxygen species are not involved in its development. In mature nerve cells (>11 DIV), the post-glutamate [Ca(2+)](i) plateau associated with profound MD usually appears after 10-15 min Glu (100 microM) exposure. In contrast, in young cells (<9 DIV) delayed Ca(2+) deregulation (DCD) occurs only after 30-60 min Glu exposure. This difference is apparently determined by a dramatic increase in the susceptibility of mitochondia to Ca(2+) overload during nerve cells maturation. The exact mechanisms of Glu-induced profound MD and its coupling with the impairment of Ca(2+) extrusion following toxic Glu challenge is not clarified yet. Their elucidation demands a study of dynamic changes in local concentrations of ATP, Ca(2+), H(+), Na(+) and protein kinase C using novel methodological approaches.

Apoptosis to necrosis switching downstream of apoptosome formation requires inhibition of both glycolysis and oxidative phosphorylation in a BCL-X(L)- and PKB/AKT-independent fashion

Human T-lymphoma Jurkat cells treated with several intrinsic death stimuli readily undergo a stepwise apoptotic program. Treatment with 1,9-dideoxyforskolin (ddFSK), an inactive analogue of the adenylate cyclase activator forskolin, induces necrotic cell death and switches to necrosis the response to the apoptosis inducers in Jurkat and in other cell models. Yet, in the presence of ddFSK, mitochondrial changes are enhanced and apoptosome formation takes place. We show that ddFSK does not inhibit the catabolic steps of apoptosis, but rather elicits a profound ATP depletion that in turn tunes the mode of cell demise towards necrosis. Treatment with ddFSK impairs both glycolysis and oxidative phosphorylation in a Bcl-X(L)- and PKB/Akt-independent fashion, and inhibition of both processes is needed to affect apoptosis progression. Apoptosis is not blocked per se by ATP depletion, as engagement of the Fas receptor directly activates caspases, thus bypassing ddFSK inhibition.

Neuronal NOS activation during oxygen and glucose deprivation triggers cerebellar granule cell death in the later reoxygenation phase

The present study investigated the temporal relationship between neuronal nitric oxide synthase (nNOS) activity and expression and the development of neuronal damage occurring during anoxia and anoxia followed by reoxygenation. For this purpose, cerebellar granule cells were exposed to 2 hr of oxygen and glucose deprivation (OGD) and 24 hr of reoxygenation. To clarify the consequences of nNOS activity inhibition on neuronal survival, cerebellar granule cells were exposed to OGD, both in the absence of extracellular Na(+) ([Na(+)](e)), a condition that by reducing intracellular Ca(2+) ([Ca(2+)](I)) prevents Ca(2+)-dependent nNOS activation, and in the presence of selective and nonselective nNOS inhibitors, such as N(omega)-L-allyl-L-arginine (L-ALA), N(omega)-propyl-L-arginine (NPLA), and L-nitro-arginine-methyl-ester (L-NAME), respectively. The results demonstrated that the removal of [Na(+)](e) hampered the [Ca(2+)](i) increase and decreased expression and activity of nNOS. Similarly, the increase of free radical production present in cerebellar neurons, exposed previously to OGD and OGD/reoxygenation, was abolished completely in the absence of [Na(+)](e). Furthermore, the absence of [Na(+)](e) in cerebellar neurons exposed to 2 hr of OGD led to the improvement of mitochondrial activity and neuronal survival, both after the OGD phase and after 24 hr of reoxygenation. Finally, the exposure of cerebellar neurons to L-ALA (200 nM), and L-NAME (500 microM) was able to effectively reduce NO(*) production and caused an increase in mitochondrial oxidative activity and an improvement of neuronal survival not only during OGD, but also during reoxygenation. Similar results during OGD were obtained also with NPLA (5 nM), another selective nNOS inhibitor. These data suggest that the activation of nNOS is highly accountable for the neuronal damage occurring during the OGD and reoxygenation phases.

Differential mechanisms of nitric oxide- and peroxynitrite-induced cell death

Nitric oxide (NO) contributes to cellular degeneration in various disorders, particularly in the nervous system. NO targets cell proteins such as soluble guanylyl cyclase, but its detrimental effects are generally attributed to its reaction product with superoxide, peroxynitrite. To understand the mechanisms of NO-induced cell stress, we studied the effects of the NO donors diethylenetriamine and spermine NONOate and the peroxynitrite donor 5-amino-3-(4-morpholinyl)-1,2,3-oxadiazolium chloride (SIN-1) in SH-SY5Y and NG108-15 neuroblastoma cells. All three compounds induced a dose- and time-dependent decrease in viable cells, which was not blocked by the soluble guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one. The two NONOates were approximately 15-fold more potent in SH-SY5Y than in NG108-15 cells, whereas the EC50 values of SIN-1 in SH-SY5Y and NG108-15 cells were in the same order. This led us to conclude that the mechanisms of NO and peroxynitrite did not converge. This was supported by our other findings. NONOates induced DNA fragmentation and an increase in cellular caspase-3 activity that preceded the gradual decline in cell viability. In contrast, SIN-1 induced a transient decline in ATP levels and a delayed loss of cell viability with no significant increase in caspase-3 activity or DNA laddering. Moreover, post-treatment with insulin inhibited caspase-3 activation and loss of cell viability in NONOate- but not in SIN-1-exposed cells. These findings suggest that NO is a potent toxin independent of peroxynitrite formation.

Adenine nucleotide metabolism and cell fate after oxidant exposure of rat cortical neurons: effects of inhibition of poly(ADP-ribose) polymerase

We exposed cultured neurons prelabeled with 14C-adenine to H2O2 with or without the poly(ADP-ribose) polymerase (PARP) inhibitor 3,4-Dihydro-5-[4-(1-piperidinyl)butoxy]-1(2H)-isoquinolinone (DPQ) to quantify its effects on acute ATP depletion, later ATP synthesis, cellular and nuclear morphology, extent of DNA fragmentation, and PARP cleavage. According to the extent of the acute ATP depletion, the exposures were classified as 'mild' (50 microM H2O2), 'moderate' (100-250 microM H2O2), or 'severe' (500 microM-1 mM H2O2) insults. Mild exposure had no significant effects on the parameters studied. In the 'moderately' exposed neurons, ATP depletion to 59+/-6% of control was associated with a decrease in the cell counts, apoptotic morphology, and cleavage of PARP. In this group, DPQ prevented the acute ATP (to 95+/-15% of control), preserved cell morphology, and improved cell survival. In the 'severe' group, ATP depletion to 18+/-4% was associated with necrosis and intact PARP. DPQ elevated ATP levels (to 44+/-12% of control) and post-insult ATP synthesis, improved cell counts, and altered cell morphology towards apoptosis rather than necrosis. Post-insult application of DPQ was less effective. Our results show that the extent of oxidant-induced ATP depletion and cell fate can be modified by PARP inhibition, to some extent also after the insult.

The tyrosine phosphatase SHP2 modulates MAP kinase p38 and caspase 1 and 3 to foster neuronal survival

1. The Src homology protein tyrosine phosphatase SHP2 is associated with cytoskeletal maintenance, cell division, and cell differentiation, but the role of SHP2 during central nervous system injury requires further definition. We therefore characterized the role of SHP2 during nitric oxide (NO)-induced programmed cell death (PCD). 2. Employing primary hippocampal neurons from mice with a dominant negative SHP2 mutant to render the phosphatase site of the SHP2 protein biologically inactive, but functionally capable of binding substrate, neuronal injury was evaluated by trypan blue, DNA fragmentation, membrane phosphatidyl serine (PS) exposure, mitogen-activated protein (MAP) kinase phosphorylation, and cysteine protease activity. NO was administered through the NO generators SIN-1 (300 microM) or NOC-9 (300 microM). 3. Following NO exposure, neuronal survival decreased from 89 +/- 3% in untreated controls to 37 +/- 2% in wild-type neurons and to 21 +/- 4% in SHP2 mutant neurons. In sister cultures following NO exposure, this increased susceptibility to neuronal injury paralleled enhanced genomic DNA degradation and membrane PS exposure with PCD induction increasing in SHP2 mutant neurons by approximately 42% during specified time periods when compared to wild-type neurons. Interestingly, modulation of the MAP kinase p38 appears to represent an initial level of neuronal protection employed by SHP2. In addition, both the rate and degree of caspase 1- and caspase 3-like activities in SHP2 mutant neurons were significantly increased over a 24-h course when compared to wild-type neurons. Inhibition of caspase 1- and caspase 3-like activities reversed the progression of neuronal PCD, suggesting that inhibition of cysteine protease activity is a downstream mechanism for SHP2 to afford neuronal protection. 4. Our work supports the premise that the tyrosine phosphatase SHP2 plays a dominant role during NO-induced PCD and may offer a potential molecular "checkpoint" against neurodegenerative disease.

Regulation of glucose metabolism by nitrosative stress in neural cells

Following brain inflammatory stimuli, astrocytes actively synthesize nitric oxide and peroxynitrite. These nitrogen-derived species trigger a repertoire of biochemical effects, including alteration of mitochondrial function and redox status both in astrocytes and neighboring neurons. Furthermore, under such nitrosative stress astrocytes show remarkable resistance in spite of having their mitochondria impaired, whereas the neighboring neurons show vulnerability. In this review, we discuss recent evidence strongly suggesting that nitrogen-derived species modulate key regulatory steps of glucose metabolism. These involve up-regulation of high-affinity glucose transporter, stimulation of glycolysis at 6-phosphofructo-1-kinase, and activation of pentose-phosphate pathway at glucose-6-phosphate dehydrogenase. We conclude that the orchestrated stimulation of glucose-metabolising pathways by nitric oxide would be a transient attempt of certain neural cells to compensate for the impaired energy status and oxidised glutathione and thus emerge from an otherwise neuropathological outcome.

Glutamate uptake inhibitor L-trans-pyrrolidine 2,4-dicarboxylate becomes neurotoxic in the presence of subthreshold concentrations of mitochondrial toxin 3-nitropropionate: involvement of mitochondrial reducing activity and ATP production

An increased concentration of extracellular glutamate is associated with neuronal damage induced by cerebral ischemia. We have demonstrated previously that exposure of cultured cerebellar granule neurons to L-trans-pyrrolidine-2,4-dicarboxylate (PDC), a glutamate uptake inhibitor, increases extracellular glutamate levels but does not induce neuronal damage. Coincubation of PDC, however, with a subthreshold concentration of the mitochondrial toxin, 3-nitropropionic acid (3-NP), results in severe damage to these neurons. We have investigated the time course of changes in mitochondrial reducing capacity and ATP levels in cerebellar granule cells after simultaneous exposure to 3-NP and PDC, and its relation to cell viability and nuclear condensation. Although individually, 3-NP and PDC treatments are not harmful to neurons, the simultaneous exposure to both compounds results in a progressive decline in mitochondrial reducing capacity during the first 4 hr, and a rapid decrease in ATP levels. At 4 hr, cells lose plasma membrane integrity and show condensed nuclei. In the presence of the energy substrates pyruvate and acetoacetate, the N-methyl-D-apartate (NMDA) receptor antagonist, MK-801, and the spin trapper alpha-phenyl-N-tert-butylnitrone (PBN), the decline in mitochondrial activity and ATP levels is prevented, the number of condensed nuclei is reduced, and plasma membrane integrity is preserved. In contrast, the broad-spectrum caspase inhibitor Z-Asp-DCB (Z-Asp-CH2-DCB) prevents nuclear condensation but has no effect on mitochondrial reducing capacity or cell survival. Our results show that glutamate uptake impairment rapidly induces neuronal death during inhibition of succinate dehydrogenase by a mechanism involving mitochondrial dysfunction that, if not prevented, leads to cell death.

Transcription factor activator protein-1 expressed by kainate treatment can bind to the non-coding region of mitochondrial genome in murine hippocampus

We have demonstrated previously that the transcription factor activator protein-1 (AP-1) complex is translocated into mitochondria into the nucleus in murine hippocampus after systemic kainate injection (Ogita et al. [2002] J. Neurosci. 22:2561-2570). The present study investigates whether the mitochondrial AP-1 complex translocated in response to kainate treatment binds to AP-1-like sites located at the non-coding region of the mitochondrial genome in mouse hippocampus. There are 10 sites with sequences similar to the nuclear AP-1 site in the non-coding region. Of 10 pieces (MT-1-MT-10) of synthesized double-stranded oligonucleotides, each containing a mitochondrial AP-1-like site, MT-3, MT-4, and MT-9 were effective in inhibiting mitochondrial AP-1 DNA binding enhanced by kainate. Electrophoresis mobility shift analysis using radiolabeled MT-3 and MT-9 probes demonstrated marked enhancement with binding of these 2 probes in hippocampal mitochondrial extracts prepared 2-6 hr after kainate treatment. Unlabeled AP-1 probe was more potent than unlabeled MT-9 probe in inhibiting the mitochondrial MT-9 binding. Supershift analysis revealed participation of particular Fos/Jun family proteins, such as c-Fos, Fos-B, c-Jun, Jun-B, and Jun-D, in MT-9 binding in hippocampal mitochondrial extracts prepared 4 hr after kainate treatment. Immunoprecipitation analysis using anti-c-Fos antibody demonstrated that c-Fos associated with the mitochondrial genome in hippocampal mitochondria prepared from kainate-treated animals. These results suggest that the AP-1 complex expressed by in vivo kainate treatment would bind to AP-1-like sites in the non-coding region of the mitochondrial genome after translocation into mitochondria from murine hippocampus.

Mitochondrial peroxiredoxin-3 protects hippocampal neurons from excitotoxic injury in vivo

Mitochondria are involved in excitotoxic damage of nerve cells. Following the breakdown of the calcium-buffering ability of mitochondria, mitochondrial calcium overload induces reactive oxygen species (ROS) bursts that produce free radicals and open permeability transition pores, ultimately leading to neuronal cell death. In the present study, we focused on a mitochondrial antioxidant protein, peroxiredoxin-3 (Prx-3), to investigate the mechanism by which toxic properties of ROS were up-regulated in mitochondria of damaged nerve cells. Immunohistochemical analysis revealed that Prx-3 protein exists in mitochondria of rat hippocampus, whereas we found a significant decrease in Prx-3 mRNA and protein levels associated with an increase in nitrated proteins in the rat hippocampus injured by microinjection of ibotenic acid. Furthermore, in vivo adenoviral gene transfer of Prx-3 completely inhibited protein nitration and markedly reduced gliosis, a post-neuronal cell death event. Since mitochondrial Prx-3 seems to be neuroprotective against oxidative insults, our findings suggest that Prx-3 up-regulation might be a useful novel approach for the management of neurodegenerative diseases.

Inflammatory neurodegeneration mediated by nitric oxide, glutamate, and mitochondria

In inflammatory, infectious, ischemic, and neurodegenerative pathologies of the central nervous system (CNS) glia become "activated" by inflammatory mediators, and express new proteins such as the inducible isoform of nitric oxide synthase (iNOS). Although these activated glia have benefi- cial roles, in vitro they potently kill cocultured neurons, and there is increasing evidence that they contribute to pathology in vivo. Nitric oxide (NO) from iNOS appears to be a key mediator of such glial-induced neuronal death. The high sensitivity of neurons to NO is partly due to NO causing inhibition of respiration, rapid glutamate release from both astrocytes and neurons, and subsequent excitotoxic death of the neurons. NO is a potent inhibitor of mitochondrial respiration, due to reversible binding of NO to cytochrome oxidase in competition with oxygen, resulting in inhibition of energy production and sensitization to hypoxia. Activated astrocytes or microglia cause a potent inhibition of respiration in cocultured neurons due to glial NO inhibiting cytochrome oxidase within the neurons, resulting in ATP depletion and glutamate release. In some conditions, glutamate- induced neuronal death can itself be mediated by N-methyl-D-aspartate (NMDA)-receptor activation of the neuronal isoform of NO synthase (nNOS) causing mitochondrial damage. In addition NO can be converted to a number of reactive derivatives such as peroxynitrite, NO2, N2O3, and S-nitrosothiols that can kill cells in part by inhibiting mitochondrial respiration or activation of mitochondrial permeability transition, triggering neuronal apoptosis or necrosis.