Cytosolic redistribution of cytochrome c after transient focal cerebral ischemia in rats

Signaling of cell death and cell survival following focal cerebral ischemia: life and death struggle in the penumbra

Focal ischemia by middle cerebral artery occlusion (MCAO) results in necrosis at the infarct core and activation of complex signal pathways for cell death and cell survival in the penumbra. Recent studies have shown activation of the extrinsic and intrinsic pathways of caspase-mediated cell death, as well as activation of the caspase-independent signaling pathway of apoptosis in several paradigms of focal cerebral ischemia by transient MCAO to adult rats and mice. The extrinsic pathway (cell-death receptor pathway) is initiated by activation of the Fas receptor after binding to the Fas ligand (Fas-L); increased Fas and Fas-L expression has been shown following focal ischemia. Moreover, focal ischemia is greatly reduced in mice expressing mutated (nonfunctional) Fas. Increased expression of caspase-1, -3, -8, and -9, and of cleaved caspase-8, has been observed in the penumbra. Activation of the intrinsic (mitochondrial) pathway following focal ischemia is triggered by Bax translocation to and competition with Bcl-2 and other members of the Bcl-2 family in the mitochondria membrane that is followed by cytochrome c release to the cytosol. Bcl-2 over-expression reduces infarct size. Cytochrome c binds to Apaf-1 and dATP and recruits and cleaves pro-caspase-9 in the apoptosome. Both caspase-8 and caspase-9 activate caspase-3, among other caspases, which in turn cleave several crucial substrates, including the DNA-repairing enzyme poly(ADP-ribose) polymerase (PARP), into fragments of 89 and 28 kDa. Inhibition of caspase-3 reduces the infarct size, further supporting caspase-3 activation following transient MCAO. In addition, caspase-8 cleaves Bid, the truncated form of which has the capacity to translocate to the mitochondria and induce cytochrome c release. The volume of brain infarct is greatly reduced in Bid-deficient mice, thus indicating activation of the mitochondrial pathway by cell-death receptors following focal ischemia. Recent studies have shown the mitochondrial release of other factors; Smac/DIABLO (Smac: second mitochondrial activator of caspases: DIABLO: direct IAP binding protein with low pI) binds to and neutralizes the effects of the X-linked inhibitor of apoptosis (XIAP). Finally, apoptosis-inducing factor (AIF) translocates to the mitochondria and the nucleus following focal ischemia and produces peripheral chromatin condensation and large-scale DNA strands, thus leading to the caspase-independent cell death pathway of apoptosis. Delineation of the pro-apoptotic and pro-survival signals in the penumbra may not only increase understanding of the process but also help to rationalize strategies geared to reducing brain damage targeted at the periphery of the infarct core.

Apoptosis and brain ischaemia

There is increasing evidence that some neuronal death after brain ischaemia is mediated by the action of cysteine-requiring aspartate-directed proteases (caspases), the proteases responsible for apoptosis in mammals, although this form of neuronal death is not always accompanied by the morphological changes that are typical of apoptosis in other tissues. Caspase-mediated neuronal death is more extensive after transient than permanent focal brain ischaemia and may contribute to delayed loss of neurons from the penumbral region of infarcts. The activation of caspases after brain ischaemia is largely consequent on the translocation of Bax, Bak, and other BH3-only members of the Bcl-2 family to the mitochondrial outer membrane and the release of cytochrome c, procaspase-9, and apoptosis activating factor-1 (Apaf-1) from the mitochondrial intermembrane space. How exactly ischaemia induces this translocation is still poorly understood. NF-kappaB, the c-jun N-terminal kinase-c-Jun pathway, p53, E2F1, and other transcription factors are probably all involved in regulating the expression of BH3-only proteins after brain ischaemia, and mitochondrial translocation of Bad from sequestering cytosolic proteins is promoted by inactivation of the serine-threonine kinase, Akt. Other processes that are probably involved in the activation of caspases after brain ischaemia include the mitochondrial release of the second mitochondrial activator of caspases (Smac) or direct inhibitor-of-apoptosis-binding protein with low pI (DIABLO), the accumulation of products of lipid peroxidation, a marked reduction in protein synthesis, and the aberrant reentry of neurons into the cell cycle. Non-caspase-mediated neuronal apoptosis may also occur, but there is little evidence to date that this makes a significant contribution to brain damage after ischaemia. The intracellular processes that contribute to caspase-mediated neuronal death after ischaemia are all potential targets for therapy. However, anti-apoptotic interventions in stroke patients will require detailed evaluation using a range of outcome measures, as some such interventions seem simply to delay neuronal death and others to preserve neurons but not neuronal function.

To die or not to die for neurons in ischemia, traumatic brain injury and epilepsy: a review on the stress-activated signaling pathways and apoptotic pathways

After a severe episode of ischemia, traumatic brain injury (TBI) or epilepsy, it is typical to find necrotic cell death within the injury core. In addition, a substantial number of neurons in regions surrounding the injury core have been observed to die via the programmed cell death (PCD) pathways due to secondary effects derived from the various types of insults. Apart from the cell loss in the injury core, cell death in regions surrounding the injury core may also contribute to significant losses in neurological functions. In fact, it is the injured neurons in these regions around the injury core that treatments are targeting to preserve. In this review, we present our cumulated understanding of stress-activated signaling pathways and apoptotic pathways in the research areas of ischemic injury, TBI and epilepsy and that gathered from concerted research efforts in oncology and other diseases. However, it is obvious that our understanding of these pathways in the context of acute brain injury is at its infancy stage and merits further investigation. Hopefully, this added research effort will provide a more detailed knowledge from which better therapeutic strategies can be developed to treat these acute brain injuries.

Cytochrome C and caspase-9 expression in Huntington's disease

There is increasing evidence implicating apoptosis-mediated cell death in the pathogenesis of neurodegenerative diseases. One important event in the apoptotic cascade is the release of cytochrome c by mitochondria into the cytoplasm, activating caspase-9, leading to the subsequent activation of downstream executioner caspases. In the present study, we examined the distribution of cytochrome c and caspase-9 in Huntington's disease (HD) patients and in a transgenic model of HD (R6/2 line). Neuronal cytochrome c immunoreactivity increased with neuropathological severity in HD patients. Concomitant with this finding, Western-blot analysis showed a shift in the distribution of cytochrome c from the mitochondrial to the cytosolic fraction with incremental cytosolic expression associated with greater striatal degeneration. Active caspase-9 immunoreactivity was present in both HD striatal neurons and in Western blots of severe-grade specimens. Similar findings were observed in the R6/2 mice. There was a temporal increase in expression and shift of cytochrome c from the mitochondrial to the cytosolic fraction from 4-13 wk of age. Activated caspase-9 and caspase 3 activities were present only at endstage disease. Although the present results provide evidence that key components of the intrinsic mitochondrial apoptotic pathway are activated in both HD patients and a transgene murine model of HD, these phenomena are prominent in only severe neuropathological grades in HD patients and HD mice, suggesting that apoptosis may play a greater role in neuronal death at endstage disease.

Inhibition of the alpha-ketoglutarate dehydrogenase complex alters mitochondrial function and cellular calcium regulation

Mitochondrial dysfunction occurs in many neurodegenerative diseases. The alpha-ketoglutarate dehydrogenase complex (KGDHC) catalyzes a key and arguably rate-limiting step of the tricarboxylic acid cycle (TCA). A reduction in the activity of the KGDHC occurs in brains and cells of patients with many of these disorders and may underlie the abnormal mitochondrial function. Abnormalities in calcium homeostasis also occur in fibroblasts from Alzheimer's disease (AD) patients and in cells bearing mutations that lead to AD. Thus, the present studies test whether the reduction of KGDHC activity can lead to the alterations in mitochondrial function and calcium homeostasis. alpha-Keto-beta-methyl-n-valeric acid (KMV) inhibits KGDHC activity in living N2a cells in a dose- and time-dependent manner. Surprisingly, concentration of KMV that inhibit in situ KGDHC by 80% does not alter the mitochondrial membrane potential (MMP). However, similar concentrations of KMV induce the release of cytochrome c from mitochondria into the cytosol, reduce basal [Ca(2+)](i) by 23% (P<0.005), and diminish the bradykinin (BK)-induced calcium release from the endoplasmic reticulum (ER) by 46% (P<0.005). This result suggests that diminished KGDHC activities do not lead to the Ca(2+) abnormalities in fibroblasts from AD patients or cells bearing PS-1 mutations. The increased release of cytochrome c with diminished KGDHC activities will be expected to activate other pathways including cell death cascades. Reductions in this key mitochondrial enzyme will likely make the cells more vulnerable to metabolic insults that promote cell death.

Calcium-induced mitochondrial swelling and cytochrome c release in the brain: its biochemical characteristics and implication in ischemic neuronal injury

The objective of the present study was to determine the biochemical characteristics of Ca(2+)-induced mitochondrial swelling (mitochondrial permeability transition; mPT) and cytochrome c release in the brain, and to clarify its role in neuronal injury following transient forebrain ischemia. Mitochondria were isolated from rat brain and liver. Changes in mitochondrial volume were measured via light absorbance at 540 nm. Using Western blot analysis, we examined the in vitro release of mitochondrial cytochrome c under these conditions. Transient forebrain ischemia was induced by 5 min occlusion of the common carotid arteries in the gerbil. Cyclosporin A (CsA), a specific mPT blocker, and/or trifluoperazine, a blocker of phospholipase A(2), were given before and 24 h after ischemia. The number of surviving neurons in the hippocampal CA1 sector was counted 7 days after ischemia. Calcium induced a moderate decrease of light absorbance in brain mitochondria, which was inhibited by CsA. However, calcium induced a much larger decrease of light absorbance in liver mitochondria. Calcium induced a moderate release of cytochrome c from brain mitochondria, which was not inhibited by CsA. However, calcium induced the release of a larger amount of cytochrome c from liver mitochondria. Selective neuronal injury due to transient forebrain ischemia was significantly ameliorated by treatment with high-dose CsA. The biochemical properties of Ca(2+)-induced mitochondrial swelling in the brain are different from those in the liver. Cytochrome c is released from brain mitochondria through an mPT-independent mechanism. CsA potentially ameliorates delayed neuronal injury in the hippocampus due to transient forebrain ischemia.

Mitochondrial oxidative stress after global brain ischemia in rats

Vulnerable neurons in the hippocampus die 2-3 days after transient global brain ischemia. In the present study, rat brain mitochondria were isolated at different time points (4 h, 24 h and 48 h) after transient global ischemia. Detection of mitochondrially-generated reactive oxygen species, measured through dichlorodihydrofluorescein oxidation, was increased up to 40% relative to control in hippocampal mitochondria at 4 h and 48 h of reperfusion. Ischemia-stimulated oxidative stress was observed with mitochondria oxidizing substrates linked to nicotinamide adenine dinucleotide or flavin adenine dinucleotide, but not in the presence of the respiratory chain inhibitor antimycin A. A slightly decreased Ca(2+) uptake capacity was observed in hippocampal mitochondria during reperfusion. We conclude that transient brain ischemia induces oxidative stress in hippocampal mitochondria.

A caspase-3-dependent pathway is predominantly activated by the excitotoxin pregnenolone sulfate and requires early and late cytochrome c release and cell-specific caspase-2 activation in the retinal cell death

This study investigates the implication of mitochondria- and caspase-dependent pathways in the death of retinal neurones exposed to the neurosteroid pregnenolone sulfate (PS) shown to evoke apoptosis and contribute to amplification and propagation of excitotoxicity. After a brief PS challenge of intact retinas, caspase-3 and caspase-2 activation and cytochrome c release occur early and independent of changes in the oxidative state measured by superoxide dismutase activity. The temporal and spatial relationship of these events suggests that a caspase-3-dependent pathway is activated in response to cytochrome c release and requires caspase-2 activation and a late cytochrome c release in specific cellular subsets of retinal layers. The protection by caspase inhibitors indicates a predominant role of the pathway in PS-induced retinal apoptosis, although a limited use of caspase inhibitors is upheld on a conceivable shift from apoptosis toward necrosis. Conversely, 3alpha-hydroxy-5beta-pregnan-20-one sulfate and 17beta-oestradiol provide complete prevention of PS-induced retinal death.

Overexpression of SOD1 protects vulnerable motor neurons after spinal cord injury by attenuating mitochondrial cytochrome c release

Defective Cu,Zn-superoxide dismutase (SOD1) is responsible for some types of amyotrophic lateral sclerosis, and ventral horn motor neurons (VMN) have been shown to die through a mitochondria-dependent apoptotic pathway after chronic exposure to high levels of reactive oxygen species (ROS). VMN are also selectively vulnerable to mild spinal cord injury (SCI); however, the involvement of SOD1, ROS, and apoptosis in their death has not been clarified. Mild compression SCI was induced in SOD1-overexpressing transgenic rats and wild-type littermates. Superoxide production, mitochondrial release of cytochrome c, and activation of caspase-9 were examined, and apoptotic DNA injury was also characterized. In the wild-type animals, increased superoxide production, mitochondrial release of cytochrome c, and cleaved caspase-9 were observed exclusively in VMN after SCI. Subsequently, a majority of VMN (75%) selectively underwent delayed apoptotic cell death. Transgenic animals showed less superoxide production, mitochondrial cytochrome c release, and caspase-9 activation, resulting in death of only 45% of the VMN. These results suggest that the ROS-initiated mitochondrial signaling pathway possibly plays a pivotal role in apoptotic VMN death after SCI and that increased levels of SOD1 in VMN reduce oxidative stress, thereby attenuating the activation of the pathway and delayed cell death.

Ischemic intensity influences the distribution of delayed infarction and apoptotic cell death following transient focal cerebral ischemia in rats

The aim of this study was to investigate whether the apoptotic process contributes to the delayed infarction that follows a middle cerebral artery (MCA) occlusion of 20 min (mild ischemia group) and to compare this with the delayed component of infarct following 2 h of MCA occlusion (severe ischemia group). Adult male Sprague-Dawley rats underwent left MCA occlusion for either 20 min or 2 h and were reperfused for 12, 24 and 72 h. On 2,3,5-triphenyltetrazolium chloride-stained coronal sections, delayed infarction was observed to develop in the whole MCA territory after mild ischemia, and also in the frontoparietal cortex after severe ischemia. At 24 h after 20 min of MCA occlusion, characteristic apoptotic features, including chromatin condensation and apoptotic bodies were frequently observed by electron microscopy. In both ischemic groups, Hoechst 33342 staining showed typically condensed and fragmented nuclei in the area showing delayed infarction, where TdT-dUTP nick end labeling (TUNEL)-positive cells were also significantly increased. Caspase-3 activity was also found to be elevated 24 and 72 h after reperfusion and this peaked at 24 h in both groups. These findings suggest that ischemic severity may influence the distribution of delayed infarction, and that apoptosis is the underlying pathophysiologic mechanism.

Bid-mediated mitochondrial pathway is critical to ischemic neuronal apoptosis and focal cerebral ischemia

We have investigated the role of the BH3-only pro-death Bcl-2 family protein, Bid, in ischemic neuronal death in a murine focal cerebral ischemia model. Wild-type and bid-deficient mice of inbred C57BL/6 background were subjected to 90-min ischemia induced by left middle cerebral artery occlusion followed by 72-h reperfusion. The volume of ischemic infarct was significantly smaller in the bid-deficient brains than in the wild-type brains, suggesting that Bid participated in the ischemic neuronal death. Indeed, following the ischemic treatment there was a significant reduction of apoptosis in the ischemic areas, particularly in the inner infarct border zone (the penumbra), of the bid-deficient brains. In addition, activation of Bid in the wild-type brains could be readily detected at approximately 3 h after ischemia, as evidenced by its proteolytic cleavage and translocation to the mitochondria as determined using Western blot analysis and immunofluorescence staining. Correspondingly, mitochondrial release of cytochrome c could be detected around the same time Bid was cleaved in the wild-type brains. However, no significant cytochrome c release was detected in the bid-deficient brains until 24 h later. This suggests that, although the mitochondrial apoptosis pathway might be activated by multiple mechanisms during focal cerebral ischemia, Bid is critical to its early activation. This notion was further supported by the finding that caspase-3 activation was severely impaired in the bid-deficient brains, whereas activation of caspase-8 was much less affected. Taken together, these data suggest that Bid is activated early in neuronal ischemia in a caspase-8-dependent fashion and that Bid is perhaps one of the earliest and most potent activators of the mitochondrial apoptosis pathway. Thus, the role of Bid in the induction of ischemic neuronal death may render this molecule an attractive target for future therapeutic intervention.

Cytochrome c associated apoptosis during ATP recovery after hypoxia in neonatal rat cerebrocortical slices

Cellular injury was evaluated in superfused cerebrocortical slices (350 micro m) from 7-day-old Sprague-Dawley rats exposed to 30 min hypoxia followed by 4 h of reoxygenation. At the end of hypoxia homogenous cytosolic immunoreactivity of cytochrome c increased approximately fourfold, cytochrome c intensity in western blot analyses increased more than fivefold, and whole cell and cytosolic cleaved caspase-9 underwent 50% and 100% increases, respectively. Immunostaining of sections taken 1.5 h after hypoxia showed: (i) more than a threefold increase in cleaved caspase-9; (ii) localization of cleaved caspase-9 to the interior and peripheral exterior of nuclei; and (iii) homogeneously distributed cytochrome c in the cytosol. Western blot analysis for 1.5 h after hypoxia showed that cytosolic caspase-9 returned to control values, while whole cell caspase-9 stayed approximately the same, suggesting translocation of caspase-9 to nuclei. By 4 h after hypoxia there was significant nuclear fragmentation and an increase in TUNEL positive staining. 31P/1H nuclear magnetic resonance (NMR) confirmed substantial decreases of ATP and phosphocreatine during hypoxia, with rapid but incomplete recovery being close to steady state 1 h after reoxygenation. At all time points after hypoxia the primary injury was cytochrome c associated apoptosis.

Cytochrome c release and caspase activation after traumatic brain injury

Experimental traumatic brain injury (TBI) results in a rapid and significant necrosis of cortical tissue at the site of injury. In the ensuing hours and days, secondary injury exacerbates the primary damage resulting in significant neurological dysfunction. The identification of cell death pathways that mediate this secondary traumatic injury have not been elucidated, however recent studies have implicated a role for apoptosis in the neuropathology of traumatic brain injury. The present study utilized a controlled cortical impact model of brain injury to assess the involvement of apoptotic pathways: release of cytochrome c from mitochondria and the activation of caspase-1- and caspase-3-like proteases in the injured cortex at 6, 12 and 24 h post-injury. Collectively, these results demonstrate cytochrome c release from mitochondria and its redistribution into the cytosol occurs in a time-dependent manner following TBI. The release of cytochrome c is accompanied by a time-dependent increase in caspase-3-like protease activity with no apparent increase in caspase-1-like activity. However, pretreatment with a general caspase inhibitor had no significant effect on the amount of cortical damage observed at 7 days post-injury. Our data suggest that several pro-apoptotic events occur following TBI, however the translocation of cytochrome c itself and/or other events upstream of caspase activation/inhibition may be sufficient to induce neuronal cell death.

NXY-059 maintains Akt activation and inhibits release of cytochrome C after focal cerebral ischemia

Stroke is the third leading cause of death in the US, with a prevalence of 750,000 patients per year, and a social cost estimated at $50 billion. Current therapeutics are targeted at restoring blood flow rather than on preventing the actual mechanisms associated with neuronal cell death. Here, we show that, following transient (2 h) middle cerebral artery occlusion (tMCAO) in male, Wistar rats, neuronal damage determined using MAP-2 staining increased progressively after the tMCAO. Notably, such neuronal degeneration was first associated with a decrease in p-Akt in both the focus and penumbra of the infarct region and, later with an increase in cytosolic cytochrome C levels in cortical neurons in the infarct area. These findings implicate that Akt alterations and consequent release of cytochrome C are involved in neuronal death. To further address this issue, NXY-059 (disodium 4-[(tert.-butylimino)methyl]benzene-1,3-disulfonate N-oxide) administered i.v. (30 mg/kg bolus, followed by 30 mg/kg/h infusion for up to 24 h), commencing 1 h after reperfusion, not only prevented the increase in infarct area but also attenuated the postreperfusion increase in neuronal cytosolic cytochrome C and the postperfusion decrease in neuronal p-Akt. Thus, NXY-059, by preventing mitochondrial cytochrome C release by maintaining activation of the Akt pathway, appears to protect neurons from damage after ischemia.

N-methyl-D-aspartate receptor and L-type voltage-gated Ca(2+) channel antagonists suppress the release of cytochrome c and the expression of procaspase-3 in rat hippocampus after global brain ischemia

Transient global ischemia reportedly results in glutamate receptor stimulation and harmful Ca(2+)-overloading, then activates some proteins involved in cell apoptosis in vivo and in vitro, but underlying mechanisms remain to be elucidated. Here we evaluated the role of N-methyl-D-aspartate (NMDA) receptor antagonist and L-type voltage-gated Ca(2+) channel (L-VGCC) antagonist in mediating the release of cytochrome c and the expression of caspase-3 precursor protein (procaspase-3). Cytochrome c release from mitochondria is a critical step in the cell apoptotic process. We examined whether cytochrome c was translocated from mitochondria to the cytosol by Western blot in rat hippocampus after 15 min global ischemia. Released cytochrome c interacts with apoptotic protease activating factor-1 and caspase-9, both of which play important roles in the cytochrome c-dependent mitochondrial pathway of apoptosis by activating caspase-3. Our studies demonstrated that the inactive precursor and active cleaved subunits of caspase-3 protease increased dramatically with the extent of reperfusion time. Following pretreatment with ketamine (a non-competitive NMDA receptor antagonist) and nifedipine (L-VGCC antagonist), cytosolic cytochrome c and the expression of procaspase-3 dramatically decreased, which might result in less neuron damage after ischemia.

Cloning and characterization of rat caspase-9: implications for a role in mediating caspase-3 activation and hippocampal cell death after transient cerebral ischemia

Delayed hippocampal neurodegeneration after transient global ischemia is mediated, at least in part, through the activation of terminal caspases, particularly caspase-3, and the subsequent proteolytic degradation of critical cellular proteins. Caspase-3 may be activated by the membrane receptor-initiated caspase-8-dependent extrinsic pathway and the mitochondria-initiated caspase-9-dependent intrinsic pathway; however, the precise role of these deduced apoptosis-signaling pathways in activating caspase-3 in ischemic neurons remains elusive. The authors cloned the caspase-9 gene from the rat brain and investigated its potential role in mediating ischemic neuronal death in a rat model of transient global ischemia. Caspase-9 gene expression and protease activity were extremely low in the adult brain, whereas they were developmentally upregulated in newborn rats, especially at postnatal 12 weeks, a finding consistent with the theory of an essential role for caspase-9 in neuronal apoptosis during brain development. After 15-minute transient global ischemia, caspase-9 was overexpressed and proteolytically activated in the hippocampal CA1 neurons at 8 to 72 hours of reperfusion. The temporal profile of caspase-9 activation coincided with that of cytochrome c release and caspase-3 activation, but preceded CA1 neuronal death. Immunoprecipitation experiments revealed that there was enhanced formation of Apaf-1/caspase-9 complex in the hippocampus 8 and 24 hours after ischemia. Furthermore, intracerebral ventricular infusion of the relatively specific caspase-9 inhibitor N-benzyloxycarbonyl-Leu-Glu-His-Asp-fluoro-methylketone before ischemia attenuated caspase-3-like activity and significantly enhanced neuronal survival in the CA1 sector. In contrast, inhibition of caspase-8 activity had no significant effect on caspase-3 activation or neuronal survival. These results suggest that the caspase-9-dependent intrinsic pathway may be the primary mechanism responsible for the activation of caspase-3 in ischemic hippocampal neurons.

Effect of NXY-059 on secondary mitochondrial dysfunction after transient focal ischemia; comparison with cyclosporin A

The free radical trapping agents NXY-059 and alpha-phenyl-N-tert.-butylnitrone (PBN) markedly reduce infarct volume, even when given 1 or 3 h after the start of recirculation, following 2 h of middle cerebral artery (MCA) occlusion in rats. Their anti-ischemic effects are shared by the two immunosuppressants cyclosporin A (CsA) and FK506. Interestingly, CsA causes an additional reduction in infarct volume when given after only 5 min of recirculation, possibly reflecting blockade of a mitochondrial permeability transition (MPT) pore. PBN, CsA and FK506 are known to ameliorate the secondary dysfunction of mitochondrial function, as assessed in vitro, which occurs during the first 4-6 h of recirculation. The present experiments were undertaken to assess whether NXY-059 reduces tissue damage by acting directly on mitochondrial membranes, and provided that this is the case, if blockade of an MPT is involved. The results were compared to those of CsA, which thus served as a reference compound. NXY-059 was given i.v. after 5 min and 1 h, and CsA after 5 min of recirculation. Both NXY-059 and CsA reduced infarct volumes to about 30% of control, prevented the secondary decline in mitochondrial respiratory function during recirculation, and reduced the mitochondrial release of cytochrome c after 6 and 24 h of recirculation. However, NXY-059 failed to block the effect of Ca(2+) on mitochondrial swelling in vitro, as CsA did. Furthermore, NXY-059, given after 5 min of recirculation, did not reproduce the effects of CsA. The results thus suggest that NXY-059 exerts its effects on mitochondria by indirect mechanisms.

Angiotensin protects cortical neurons from hypoxic-induced apoptosis via the angiotensin type 2 receptor

The effects of angiotensin on mouse cortical neuronal cultures exposed to chemical-induced hypoxia was investigated. Cultures exposed to 10 mM sodium azide for 5 min showed a 17% increase in apoptosis when assayed 24 h postinsult. The N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 blocked sodium azide-induced cell death suggesting that the NMDA receptor contributes to the mediated cell death. Pretreatment of cultured neurons with angiotensin decreased sodium azide-induced apoptosis by 94%. When the AT(1) receptor was blocked by its receptor antagonist, losartan, angiotensin activation of the AT(2) receptor completely inhibited sodium azide-induced apoptosis. Pretreatment of neurons with the AT(2) receptor antagonist PD123319 resulted in angiotensin reducing sodium azide-induced apoptosis by 48%. These results demonstrate that angiotensin can significantly attenuate sodium azide-induced apoptosis primarily through activation of the AT(2) receptor and suggests that angiotensin may have a protective role in neurons undergoing ischemic injury.

Caspase-3-associated apoptotic cell death in excitotoxic necrosis of the entorhinal cortex following intraperitoneal injection of kainic acid in the rat

The present study is directed to study: (a) bax translocation and cytochrome c release as mediators of the mitochondrial pathway of apoptosis; (b) Fas-L (Fas-ligand) expression as an indicator of the possible involvement of the Fas/Fas-L signaling pathway; and (c) active caspase-3 expression as the main executioner of caspase-mediated apoptosis, in rats receiving an intraperitoneal injection of the glutamate analogue kainic acid (KA) at a dose of 9 mg/kg, which is sufficient to produce generalized seizures and excitotoxic cell death in the entorhinal cortex. Sub-fractionation studies of entorhinal cortex homogenates have shown cytochrome c and cytochrome oxidase IV localized in the mitochondrial fraction, and Bax localized in the cytosolic fraction. No modifications in the sub-cellular distribution of cytochrome c and Bax have been observed at 6 h and 24 h in KA-treated rats. Morphological studies have shown cytoplasmic shrinkage and nuclear condensation consistent with necrosis in the entorhinal cortex. Many neurons (about 30% of dying cells) are stained with the method of in situ end-labeling of nuclear DNA fragmentation. Yet only about 5% of dying cells have apoptotic morphology. A percentage of dying cells (5% at 6 h and 40% at 24 h) over-express Fas-L but only about 2% of dying cells at 24 h post-injection express cleaved caspase-3 (17 kD). The present data further support the concept that necrosis is the predominant form of cell death in the entorhinal cortex, although caspase-3-dependent apoptotic cell death may play a limited role, in the present paradigm of KA-induced excitotoxicity.

Induction of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) expression in rat brain after focal ischemia/reperfusion

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), a glycolytic enzyme, has been recently identified to be involved in the initiation of neuronal apoptosis. To investigate the serial changes and cellular localization of GAPDH expression, and its role in ischemia/reperfusion-induced neuronal apoptosis, the authors analyzed immunohistochemically brain areas of rats subjected to middle cerebral artery occlusion (MCAO) and reperfusion. Nuclear overexpression of GAPDH was noted in the ischemic core area after 2 hours of MCAO without reperfusion. During the subsequent reperfusion, nuclear accumulation of GAPDH in this area decreased in a time-dependent manner. However, cytoplasmic and nuclear GAPDH immunoreactivity was detected in neurons of the penumbra area of the parietal cortex, in rats subjected to 2-hour MCAO followed by 3-hour reperfusion. The increase of nuclear GAPDH immunoreactivity was persistently noted up to 48 hours of reperfusion, whereas cytoplasmic immunoreactivity correlated inversely with the duration of reperfusion. Moreover, double staining revealed colocalization of nuclear GAPDH and TUNEL in the penumbra area. The authors' study demonstrated that overexpression of GAPDH and nuclear translocation occurred in both the ischemic core and penumbra area soon after focal ischemia. These processes could be viewed as an early marker of ischemia/reperfusion-induced apoptotic neuronal death. The results suggest that GAPDH may play a critical role in the progression and spread of ischemic neuronal damage.

Overexpression of copper/zinc superoxide dismutase in transgenic rats protects vulnerable neurons against ischemic damage by blocking the mitochondrial pathway of caspase activation

Mitochondria are known to be involved in the early stage of apoptosis by releasing cytochrome c, caspase-9, and the second mitochondria-derived activator of caspases (Smac). We have reported that overexpression of copper/zinc superoxide dismutase (SOD1) reduced superoxide production and ameliorated neuronal injury in the hippocampal CA1 subregion after global ischemia. However, the role of oxygen free radicals produced after ischemia/reperfusion in the mitochondrial signaling pathway has not been clarified. Five minutes of global ischemia was induced in male SOD1-transgenic (Tg) and wild-type (Wt) littermate rats. Cytosolic expression of cytochrome c and Smac and activation of caspases were evaluated by immunohistochemistry, Western blot, and caspase activity assay. Apoptotic cell death was characterized by DNA nick end and single-stranded DNA labeling. In the Wt animals, early superoxide production, mitochondrial release of cytochrome c, Smac, and cleaved caspase-9 were observed after ischemia. Active caspase-3 was subsequently increased, and 85% of the hippocampal CA1 neurons showed apoptotic DNA damage 3 d after ischemia. Tg animals showed less superoxide production and cytochrome c and Smac release. Subsequent active caspase-3 expression was not evident, and only 45% of the neurons showed apoptotic DNA damage. A caspase-3 inhibitor (N-benzyloxycarbonyl-val-ala-asp-fluoromethyl ketone) reduced cell death only in Wt animals. These results suggest that overexpression of SOD1 reduced oxidative stress, thereby attenuating the mitochondrial release of cytochrome c and Smac, resulting in less caspase activation and apoptotic cell death. Oxygen free radicals may play a pivotal role in the mitochondrial signaling pathway of apoptotic cell death in hippocampal CA1 neurons after global ischemia.

Mitochondrial permeability transition in acute neurodegeneration

Acute neurodegeneration in man is encountered during and following stroke, transient cardiac arrest, brain trauma, insulin-induced hypoglycemia and status epilepticus. All these severe clinical conditions are characterized by neuronal calcium overload, aberrant cell signaling, generation of free radicals and elevation of cellular free fatty acids, conditions that favor activation of the mitochondrial permeability transition pore (mtPTP). Cyclosporin A (CsA) and its analog N-methyl-valine-4-cyclosporin A (MeValCsA) are potent blockers of the mtPTP and protect against neuronal death following excitotoxicity and oxygen glucose deprivation. Also, CsA and MeValCsA diminish cell death following cerebral ischemia, trauma, and hypoglycemia. Here we present data that strongly imply the mtPT in acute neurodegeneration in vivo. Compounds that readily pass the blood-brain-barrier (BBB) and block the mtPT may be neuroprotective in stroke.

Selective vulnerability of late oligodendrocyte progenitors to hypoxia-ischemia

In the premature infant, hypoxic-ischemic damage to the cerebral white matter [periventricular leukomalacia (PVL)] is a common and leading cause of brain injury that often results in chronic neurologic disability from cerebral palsy. The cellular basis for the propensity of white matter injury to occur in the developing brain and the greater resistance of the adult white matter to similar injury remains unknown. By using a neonatal rat model of hypoxic-ischemic injury, we found that the mechanism of perinatal white matter injury involved maturation-dependent vulnerability in the oligodendroctye (OL) lineage. The timing of appearance of late OL progenitors was the major developmental factor that accounted for the susceptibility of the neonatal white matter to injury. Late OL progenitors were the major OL lineage stage killed by apoptosis, whereas early OL progenitors and more mature OLs were highly resistant. The density of pyknotic late OL progenitors was significantly increased in the ischemic hemisphere (67 +/- 31 cells/mm2) versus the control hemisphere (2.2 +/- 0.4 cells/mm2; mean +/- SEM; p = 0.05), which resulted in the death of 72 +/- 6% of this OL stage. Surviving late OL progenitors displayed a reactive response in which an increase in cell density was accompanied by accelerated maturation to a P27/kip1-positive oligodendrocyte. Because we showed recently that late OL progenitors populate human cerebral white matter during the high risk period for PVL (Back et al., 2001), maturation-dependent vulnerability of OL progenitors to hypoxia-ischemia may underlie the selective vulnerability to PVL of the white matter in the premature infant.

Mild hypothermia reduces apoptosis of mouse neurons in vitro early in the cascade

Recent experimental work has shown that hypothermia with even small decreases in temperature is broadly neuroprotective, but the mechanism of this protection remains unclear. Although reduction of metabolism could explain protection by deep hypothermia, it does not explain the robust protection found with mild hypothermia. Several reports have suggested that ischemic apoptosis is reduced by hypothermia. The authors examined the effects of hypothermia on neuronal apoptosis using serum deprivation, a well-accepted model that induces neuronal apoptosis. Mild hypothermia (33 degrees C) significantly reduced the number of morphologically apoptotic neurons to less than half the number seen in normothermic culture temperatures (37 degrees C) after 48 hours. They examined the effect of hypothermia on several steps in the cascade. Caspase-3, -8, and -9 activity was significantly increased after 24 hours at 37 degrees C, and was significantly lower in cultures deprived of serum at 33 degrees C. Cytochrome c translocation was reduced by hypothermia. Western blot analysis failed to detect significant changes in Bax, bcl -2, or hsp -70 at early time points, whereas hypothermia significantly reduced cJun N-terminal kinase activation. The authors conclude that small decreases in temperature inhibit apoptosis very early, possibly at the level of the initiation of apoptosis, as suggested by reduced cJun N-terminal kinase activation and before the translocation of cytochrome c, with subsequent prevention of caspase activation.

Mild hypothermia attenuates cytochrome c release but does not alter Bcl-2 expression or caspase activation after experimental stroke

Mild hypothermia protects the brain from ischemia, but the underlying mechanisms of this effect are not well known. The authors previously found that hypothermia reduces the density of apoptotic cells, but it is not certain whether temperature alters associated biochemical events. Mitochondrial release of cytochrome c has recently been shown to be a key trigger in caspase activation and apoptosis via the intrinsic pathway. Using a model of transient focal cerebral ischemia, the authors determined whether mild hypothermia altered expression of Bcl-2 family proteins, mitochondrial release of cytochrome c, and caspase activation. Mild hypothermia significantly decreased the amount of cytochrome c release 5 hours after the onset of ischemia, but mitochondrial translocation of Bax was not observed until 24 hours. Mild hypothermia did not alter Bcl-2 and Bax expression, and caspase activation was not observed. The present study provides the first evidence that intraischemic mild hypothermia attenuates the release of cytochrome c in the brain, but does not appear to affect other biochemical aspects of the intrinsic apoptotic pathway. They conclude that necrotic processes may have been interrupted to prevent cytochrome c release, and that the ameliorative effect of mild hypothermia may be a result of maintaining mitochondrial integrity. Furthermore, the authors show it is unlikely that mild hypothermia alters the intrinsic apoptotic pathway.

BID mediates neuronal cell death after oxygen/ glucose deprivation and focal cerebral ischemia

Mitochondria and cytochrome c release play a role in the death of neurons and glia after cerebral ischemia. In the present study, we investigated whether BID, a proapoptotic promoter of cytochrome c release and caspase 8 substrate, was expressed in brain, activated after an ischemic insult in vivo and in vitro, and contributed to ischemic cell death. We detected BID in the cytosol of mouse brain and primary cultured mouse neurons and demonstrated, by using recombinant caspase 8, that neuronal BID also is a caspase 8 substrate. After 2 h of oxygen/glucose deprivation, BID cleavage was detected in neurons concurrent with caspase 8 activation but before caspase 3 cleavage. Bid(-/-) neurons were resistant to death after oxygen/glucose deprivation, and caspase 3 cleavage was significantly reduced; however, caspase 8 cleavage did not differ from wild type. In vivo, BID was cleaved 4 h after transient middle cerebral artery occlusion. Infarct volumes and cytochrome c release also were less in Bid(-/-) mice (-67% and -41%, respectively) after mild focal ischemia. These findings suggest that BID and the mitochondrial-amplification pathway promoting caspase activation contributes importantly to neuronal cell death after ischemic insult.

Ischemic preconditioning preserves mitochondrial function after global cerebral ischemia in rat hippocampus

Ischemic tolerance in brain develops when sublethal ischemic insults occur before "lethal" cerebral ischemia. Two windows for the induction of tolerance by ischemic preconditioning (IPC) have been proposed: one that occurs within 1 hour after IPC, and another that occurs 1 or 2 days after IPC. The authors tested the hypotheses that IPC would reduce or prevent ischemia-induced mitochondrial dysfunction. IPC and ischemia were produced by bilateral carotid occlusions and systemic hypotension (50 mm Hg) for 2 and 10 minutes, respectively. Nonsynaptosomal mitochondria were harvested 24 hours after the 10-minute "test" ischemic insult. No significant changes were observed in the oxygen consumption rates and activities for hippocampal mitochondrial complexes I to IV between the IPC and sham groups. Twenty-four hours of reperfusion after 10 minutes of global ischemia (without IPC) promoted significant decreases in the oxygen consumption rates in presence of substrates for complexes I and II compared with the IPC and sham groups. These data suggest that IPC protects the integrity of mitochondrial oxidative phosphorylation after cerebral ischemia.

Implications of CAD and DNase II in ischemic neuronal necrosis specific for the primate hippocampus

The exact molecular mechanism of ischemic neuronal death still remains unclear from rodents to primates. A number of studies using lower species animals have suggested implication of apoptosis cascade, while using monkeys the authors recently claimed necrosis cascade by calpain-induced leakage of lysosomal cathepsins (calpain-cathepsin hypothesis). This paper is to study implications of apoptotic versus necrotic cascades for the development of hippocampal CA1 neuronal death in the primate brain undergoing complete global ischemia. Here, we focused on two terminal cell death effectors; caspase-activated DNase (CAD) and lysosomal enzyme DNase II, in the monkey CA1 sector undergoing 18 min ischemia. The expressions of their mRNA and proteins, and the subcellular localizations as well as ultrastructure and specific DNA gel electrophoresis were examined. Expression of CAD was much less in the normal brain, compared with the lymph node or heart tissues. On day 1 after ischemia, however, CAD mRNA and protein were significantly increased in the CA1 sector, and then CAD protein immunohistochemically showed a translocation from the perikarya into the nucleus. Activated DNase II protein was significantly increased on days 2 and 3 after ischemia, and also showed a similar translocation indicating lysosomal leakage. Although the post-ischemic CA1 neurons showed positive terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling (TUNEL) staining on days 3-5, they showed eosinophilic coagulation necrosis on light microscopy, and frank membrane disruption and mild chromatin condensation on electron microscopy. Furthermore, DNA smear pattern typical for necrosis was observed instead of DNA laddering. These data altogether suggest that the post-ischemic CA1 neuronal death of the monkey occurs not by apoptosis but by necrosis with participations of lysosomal enzymes DNase II and cathepsins as well as CAD. The interactions between apoptotic (caspase-3 and CAD) and necrotic (calpain, cathepsin and DNase II) cascades should be studied further.

Evidence of phosphorylation of Akt and neuronal survival after transient focal cerebral ischemia in mice

The serine-threonine kinase, Akt, prevents apoptosis by phosphorylation at serine-473 in several cell systems. After phosphorylation, activated Akt inactivates other apoptogenic factors, such as Bad or caspase-9, thereby inhibiting cell death. The present study examined phosphorylation of Akt at serine-473 and DNA fragmentation after transient focal cerebral ischemia in mice subjected to 60 minutes of focal cerebral ischemia by intraluminal blockade of the middle cerebral artery. Phospho-Akt was analyzed by immunohistochemistry and Western blot analysis. The DNA fragmentation was evaluated by terminal deoxynucleotidyl transferase-mediated uridine 5-triphosphate-biotin nick end-labeling (TUNEL). Immunohistochemistry showed the expression of phospho-Akt was markedly increased in the middle cerebral artery territory cortex at 4 hours of reperfusion compared with the control, whereas it was decreased by 24 hours. Western blot analysis showed a significant increase of phospho-Akt 4 hours after focal cerebral ischemia in the cortex, whereas phospho-Akt was decreased in the ischemic core. Double staining with phospho-Akt and TUNEL showed different cellular distributions of phospho-Akt and TUNEL-positive staining. Phosphorylation of Akt was prevented after focal cerebral ischemia by LY294002, a phosphatidylinositol 3-kinase inhibitor, which facilitated subsequent DNA fragmentation. These results suggest that phosphorylation of Akt may be involved in determining cell survival or cell death after transient focal cerebral ischemia.

Delayed treatment with polynitroxyl albumin reduces infarct size after stroke in rats

Nitroxides are antioxidants that are known to protect cells from oxidative damage. Polynitroxyl albumin (PNA) is a compound of human serum albumin covalently labeled with nitroxides that exhibits a prolonged half-life and an enhanced antioxidant activity. Adult male Sprague-Dawley rats were subjected to 90 min intraluminal middle cerebral artery occlusion and the drug was administered intravenously immediately or 2 h after reperfusion. The effects of the drug were evaluated 24 h after reperfusion. Infarct volume was significantly reduced in immediate (79% reduction) and delayed (53% reduction) PNA-treated groups. The efficacy of a single, delayed i.v. injection of PNA suggests that PNA has great promise in the treatment of acute human stroke.

Cycloheximide reduces infarct volume when administered up to 6 h after mild focal ischemia in rats

We have previously described a rodent model of brief (30 min) middle cerebral artery occlusion followed by reperfusion, in which infarction develops gradually, reaching completion more than 3 days after ischemia, accompanied by morphological, biochemical, and pharmacological evidence of apoptosis. In the present study, we tested the hypotheses that delayed administration of a protein synthesis inhibitor would be effective in reducing tissue injury in this slowly evolving ischemic infarction, and that efficacy of this treatment would wane with more prolonged ischemia. Focal cerebral ischemia was induced in Long-Evans rats by occlusion of the right middle cerebral artery. Infarction volume was analyzed using triphenyl tetrazolium chloride staining, and morphology was studied using hematoxylin and eosin stained sections. Following 30 min middle cerebral artery occlusion and reperfusion, the core ischemic region exhibited vacuolization in the neuropil by 36 h after ischemia, and infarction reached full size by 7 days after ischemia. Cycloheximide reduced infarct volume when given up to 6 h after ischemia. If the duration of ischemic insult was increased to 90 min, the therapeutic window for delayed cycloheximide was only 30 min. In permanent middle cerebral artery occlusion, cycloheximide was ineffective even when given prior to ischemia onset. After mild, but not severe, ischemic insults, cerebral infarction develops slowly and may be treatable with protein synthesis inhibitors, even when treatment is delayed for up to 6 h after the onset of ischemia.

Superoxide during reperfusion contributes to caspase-8 expression and apoptosis after transient focal stroke

BACKGROUND AND PURPOSE

Reactive oxygen species produced during reperfusion may play a detrimental role in focal cerebral ischemia (FCI). We examined the protein expression of caspase-8, which plays a major role in both Fas-dependent and cytochrome c-dependent apoptotic pathways after FCI with or without reperfusion. Caspase-8 expression after transient FCI was compared between wild-type and transgenic mice that overexpress the cytosolic antioxidant copper/zinc superoxide dismutase (SOD1).

METHODS

Adult male CD-1 mice were subjected to 1 hour of FCI and reperfusion or to permanent FCI by intraluminal blockade of the middle cerebral artery. DNA fragmentation was evaluated by genomic DNA gel electrophoresis. Caspase-8 expression was analyzed by Western blot.

RESULTS

Caspase-8 was significantly induced 4 hours after transient FCI and remained at an increased level until 24 hours, whereas it was not modified after permanent FCI. Genomic DNA gel electrophoresis showed DNA laddering in a pattern similar to that seen in apoptosis, with a small amount of background smear 24 hours after transient FCI, whereas 25 hours of permanent FCI resulted in less DNA laddering with a strong background smear. Caspase-8 induction was significantly reduced in SOD1 transgenic mice compared with wild-type mice 4 hours after transient FCI.

CONCLUSIONS

The results suggest that increased reactive oxygen species production during reperfusion may contribute to the induction of caspase-8, thereby exacerbating apoptosis after FCI.

Cytochrome c release into cytosol with subsequent caspase activation during warm ischemia in rat liver

Apoptosis plays an important role in liver ischemia and reperfusion (I/R) injury. However, the molecular basis of apoptosis in I/R injury is poorly understood. The aims of this study were to ascertain when and how apoptotic signal transduction occurs in I/R injury. The apoptotic pathway in rats undergoing 90 min of warm ischemia with reperfusion was compared with that of rats undergoing prolonged ischemia alone. During ischemia, mitochondrial cytochrome c was released into the cytosol in a time-dependent manner in hepatocytes and sinusoidal endothelial cells, and caspase-3 and an inhibitor of caspase-activated DNase were cleaved. However, apoptotic manifestation and DNA fragmentation were not observed. After reperfusion, nuclear condensation, cells positive for terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling, and DNA fragmentation were observed and caspase-8 and Bid cleavage occurred. In contrast, prolonged ischemia alone induced necrosis rather than apoptosis. In summary, our results show that release of mitochondrial cytochrome c and caspase activation proceed during ischemia, although apoptosis is manifested after reperfusion.

Nitric oxide is involved in ischemia-induced apoptosis in brain: a study in neuronal nitric oxide synthase null mice

Nitric oxide can promote or inhibit apoptosis depending on the cell type and coexisting metabolic or experimental conditions. We examined the impact of nitric oxide on development of apoptosis 6, 24, and 72 h after permanent middle cerebral artery occlusion in mutant mice that lack the ability to generate nitric oxide from neuronal nitric oxide synthase. Adjacent coronal sections passing through the anterior commissure were stained with hematoxylin and eosin or terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL). Immunoblotting was used to identify changes in the anti- and proapoptotic proteins Bcl-2 and Bax, respectively. Activation of caspases was assessed by appearance of actin cleavage products using a novel antiserum directed against 32-kDa actin fragment (fractin). In the neuronal nitric oxide synthase mutant mouse, infarct size and TUNEL positive apoptotic neurons were reduced compared to the wild-type controls. At 6 h, Bcl-2 levels in the ischemic hemisphere were increased in mutants but decreased in the wild-type strain. Bax levels did not change significantly. Caspase-mediated actin cleavage appeared in the ischemic hemisphere at this time point, and was significantly less in mutant brains at 72 h compared to the wild-type. The reduction in the number of TUNEL and fractin positive apoptotic cells appears far greater than anticipated based on the smaller lesion size in mutant mice.Hence, from these data we suggest that a deficiency in neuronal nitric oxide production slows the development of apoptotic cell death after ischemic injury and is associated with preserved Bcl-2 levels and delayed activation of effector caspases.

The mitochondrial permeability transition pore and nitric oxide synthase mediate early mitochondrial depolarization in astrocytes during oxygen-glucose deprivation

Recent studies suggest that the degree of mitochondrial dysfunction in cerebral ischemia may be an important determinant of the final extent of tissue injury. Although loss of mitochondrial membrane potential (psi(m)), one index of mitochondrial dysfunction, has been documented in neurons exposed to ischemic conditions, it is not yet known whether astrocytes, which are relatively resistant to ischemic injury, experience changes in psi(m) under similar conditions. To address this, we exposed cortical astrocytes cultured alone or with neurons to oxygen-glucose deprivation (OGD) and monitored psi(m) using tetramethylrhodamine ethyl ester. Both neurons and astrocytes exhibited profound loss of psi(m) after 45-60 min of OGD. However, although this exposure is lethal to nearly all neurons, it is hours less than that needed to kill astrocytes. Astrocyte psi(m) was rescued during OGD by cyclosporin A, a permeability transition pore blocker, and (G)N-nitro-arginine, a nitric oxide synthase inhibitor. Loss of mitochondrial membrane potential in astrocytes was not accompanied by depolarization of the plasma membrane. Recovery of astrocyte psi(m) after reintroduction of O(2) and glucose occurred over a surprisingly long period (>1 hr), suggesting that OGD caused specific, reversible changes in astrocyte mitochondrial physiology beyond the simple lack of O(2) and glucose. Decreased psi(m) was associated with a cyclosporin A-sensitive loss of cytochrome c but not with activation of caspase-3 or caspase-9. Our data suggest that astrocyte mitochondrial depolarization could be a previously unrecognized event early in ischemia and that strategies that target the mitochondrial component of ischemic injury may benefit astrocytes as well as neurons.

Different expression of glycogen synthase kinase-3beta between young and old rat brains after transient middle cerebral artery occlusion

Ischemia is a common stress to human brain and is difficult to cure in older individuals. To examine the differences of the response to cerebral ischemia between young and old rat brains, distributions of glycogen synthase kinase-3beta (GSK3beta) and tau proteins were analyzed after 90 min of transient middle cerebral artery occlusion (MCAO) in young (10-11 weeks) and old (15 months) rats by immunohistochemical analyses. At 4 h of reperfusion, strong cytoplasmic and nuclear immunoreactivity for GSK3beta was induced in neurons of lamina I, II, V and VI of the cerebral cortex and dorsal caudate in young brains, while the induction was not observed in lamina I and II of old cerebral cortex. The staining in lamina V and VI and dorsal caudate then gradually decreased until seven days of reperfusion in both animal groups. The staining of tau protein and terminal deoxynucleotidyl transferase-mediated dUTP-biotin in situ nick end labeling (TUNEL) did not show any positive signals in the control brain, but showed positive signals after ischemia with a peak at 24 h and 3 days, respectively. No significant difference was observed in the temporal and spatial patterns of tau and TUNEL stainings between these two groups. These data suggest that GSK3beta may have a role in ischemic neuronal cell death, and that the different spatial expression of GSK3beta between young and old rat brains may partly explain the vulnerability of older neurons after ischemia.

Appearance of shortened Bcl-2 and Bax proteins and lack of evidence for apoptosis in rat forebrain after severe experimental traumatic brain injury

To investigate whether apoptosis plays a role in traumatic brain injury (TBI), we examined the expression of Bcl-2 and Bax proteins and the release of mitochondrial cytochrome c in rat brains using Western blot analysis. Bcl-2 at the predicted 26 kDa was not detected in controls and TBI groups. However, at 1 h post-TBI, a shortened Bcl-2 protein with a molecular size of approximately 14.5 kDa was detected in the injured hemisphere (R). At 4 and 12 h post TBI, an additional bcl-2 band ( approximately 10 kDa) was detected in R. Both bands disappeared at 14 days post-injury. The predicted 21-kDa band of Bax was detected in both controls and TBI animals. In addition, two shortened Bax proteins ( approximately 18 kDa) were detected after TBI. The time course of appearance was similar to that of Bcl-2 described above. In the present study, neither cytochrome c release from mitochondria nor DNA fragmentation was detected in the forebrains of sham and TBI groups. Treatment of animals with an antioxidant N-acetylcysteine administered ip greatly diminished the levels of shortened Bcl-2 and Bax proteins. These findings suggest that the induction of shortened Bcl-2 and Bax proteins in rat brains may be associated with reactive oxygen species generated after TBI.

Oxidative stress-dependent release of mitochondrial cytochrome c after traumatic brain injury

Mitochondrial cytochrome c translocation to the cytosol initiates the mitochondrial-dependent apoptotic pathway. This event has not been previously reported in traumatic brain injury (TBI). The authors determined the expression of cytochrome c in cytosolic and mitochondrial fractions after severe TBI produced by the controlled cortical impact model in the mouse. One hour after trauma there was an increase in cytosolic cytochrome c immunoreactivity. The increases in cytosolic cytochrome c preceded DNA fragmentation, which started at 4 hours. Western blots of mitochondrial and cytosolic fractions confirmed that there was a translocation of cytochrome c from the mitochondria after TBI. Mice deficient in manganese superoxide dismutase (MnSOD) showed an increased loss of mitochondrial cytochrome c after trauma, but less apoptotic cell death 4 and 24 hours after injury compared with wild-type control mice. However, the overall cell death was increased in MnSOD mice, as illustrated by a larger cortical lesion in these animals. The results show that cytochrome c is released from the mitochondria after severe TBI partly by a free radical-dependent mechanism, and that massive mitochondrial cytochrome c release is a predictor of necrotic cell death rather than apoptosis.

Is caspase-3 inhibition a valid therapeutic strategy in cerebral ischemia?

Neurodegenerative diseases are characterized by progressive impairment of brain function as a consequence of ongoing neuronal cell death. Apoptotic mechanisms have been implicated in this process and a major involvement of caspase-3, a typical pro-apoptotic executioner protease, has been claimed. In this review, the role of caspase-3 in neuronal cell loss in animal models of stroke is discussed and critically evaluated. In summary, it is concluded that the biochemical evidence favoring caspase-3 as a therapeutic target in cerebral ischemia is not convincing, and the development of selective caspase-3 inhibitors for the treatment of human stroke must be viewed as high risk.

Maintaining Mitochondrial Membrane Impermeability

Apoptosis may contribute to retinal ganglion cell loss in glaucoma and glaucoma models. Recent research has suggested that mitochondrially dependent apoptosis signaling may contribute to apoptosis in a rat model of glaucoma involving chronic increases in intraocular pressure. In some forms of apoptosis, mitochondrially dependent signaling involves increases in mitochondrial membrane permeability and the mitochondrial release of factors that signal for cell degradation. Opening of a multi-protein, mitochondrial megapore is one factor that contributes to the increased permeability and some anti-apoptotic proteins, particularly BCL-2 and BCL-X(L), bind at the megapore and facilitate megapore closure and reduce increases in mitochondrial membrane permeability. Phosphorylated protein kinase B (Akt) serves as an integrator for cellular survival signals and facilitates the megapore actions of BCL-2 and BCL-X(L), which could protect retinal ganglion cells against insults that induce apoptosis. Several anti-apoptotic agents are being evaluated for use in glaucoma, including brimonidine and propargylamines, which oppose mitochondrially dependent apoptosis through pathways involving phosphorylated Akt.

Manganese Superoxide Dismutase Affects Cytochrome c Release and Caspase-9 Activation After Transient Focal Cerebral Ischemia in Mice

Release of cytochrome c from mitochondria to cytosol is a critical step in the mitochondrial-dependent signaling pathways of apoptosis. The authors have reported that manganese superoxide dismutase (Mn-SOD) attenuated cytochrome c release and apoptotic cell death after focal cerebral ischemia (FCI). To investigate downstream to the cytochrome c-dependent pathway, the authors examined caspase-9 activation after transient FCI by immunohistochemistry and Western blotting in both wild-type and Sod2 -/+ mice. Mice were subjected to 60 minutes of middle cerebral artery occlusion followed by 1, 2, 4, or 24 hours of reperfusion. Two hours after reperfusion, cytochrome c and caspase-9 were observed in the cytosol and significantly increased in Sod2 -/+ mutants compared with wild-type mice as shown by Western blotting. Immunofluorescent double labeling for cytochrome c and caspase-9 showed cytosolic cytochrome c 1 hour after transient FCI. Cleaved caspase-9 first appeared in the cytosol at 2 hours and colocalized with cytochrome c. Terminal deoxynucleotidyl transferase-mediated uridine 5;-triphosphate-biotin nick and labeling (TUNEL) showed significant increase of positive cells in Sod2 -/+ mice compared with the wild-type in the cortex, but not in the caudate putamen. The current study revealed Mn-SOD might affect cytochrome c translocation and downstream caspase activation in the mitochondrial-dependent cell death pathway after transient FCI.

Intracellular Bax translocation after transient cerebral ischemia: implications for a role of the mitochondrial apoptotic signaling pathway in ischemic neuronal death

Activation of terminal caspases such as caspase-3 plays an important role in the execution of neuronal cell death after transient cerebral ischemia. Although the precise mechanism by which terminal caspases are activated in ischemic neurons remains elusive, recent studies have postulated that the mitochondrial cell death-signaling pathway may participate in this process. The bcl-2 family member protein Bax is a potent proapoptotic molecule that, on translocation from cytosol to mitochondria, triggers the activation of terminal caspases by increasing mitochondrial membrane permeability and resulting in the release of apoptosis-promoting factors, including cytochrome c. In the present study, the role of intracellular Bax translocation in ischemic brain injury was investigated in a rat model of transient focal ischemia (30 minutes) and reperfusion (1 to 72 hours). Immunochemical studies revealed that transient ischemia induced a rapid translocation of Bax from cytosol to mitochondria in caudate neurons, with a temporal profile and regional distribution coinciding with the mitochondrial release of cytochrome c and caspase-9. Further, in postischemic caudate putamen in vivo and in isolated brain mitochondria in vitro, the authors found enhanced heterodimerization between Bax and the mitochondrial membrane permeabilization-related proteins adenine nucleotide translocator (ANT) and voltage-dependent anion channel. The ANT inhibitor bongkrekic acid prevented Bax and ANT interactions and inhibited Bax-triggered caspase-9 release from isolated brain mitochondria in vitro. Bongkrekic acid also offered significant neuroprotection against ischemia-induced caspase-3 and caspase-9 activation and cell death in the brain. These results strongly suggest that the Bax-mediated mitochondrial apoptotic signaling pathway may play an important role in ischemic neuronal injury.

Induction of mitochondrial heat shock protein 60 and 10 mRNAs following transient focal cerebral ischemia in the rat

Heat shock proteins (HSPs) 60 and 10 are stress-inducible mitochondrial matrix proteins that form a chaperonin complex that is important for mitochondrial protein folding and function. The effect of cerebral ischemia on mitochondrial HSPs is unclear. The topographical and chronological patterns of HSP60 and HSP10 messenger ribonucleic acid (mRNA) expression and induction were investigated in the rat focal cerebral ischemia model. Focal cerebral ischemia was produced by transient middle cerebral artery occlusion for 30 or 90 min. Expression of mRNAs was analyzed using reverse transcription-polymerase chain reaction (RT-PCR) and in situ hybridization. RT-PCR analysis showed that both HSP60 and HSP10 mRNA levels increased significantly in the ischemic cortex from 4 to 24 h of reperfusion after 30 min of occlusion. In situ hybridization analysis demonstrated significant induction of both mRNAs in the whole ischemic cortex after 30 min of occlusion and in the dorsomedial border (penumbra) of the ischemic cortex and ipsilateral hippocampus after 90 min of occlusion. Expression patterns and the timing of the induction of both HSP60 and HSP10 mRNAs were identical throughout the experiments. Simultaneous induction of the mRNAs for the mitochondrial chaperonins, HSP60 and HSP10, in various regions in focal cerebral ischemia demonstrates that mitochondrial stress conditions persist concomitantly with cytosolic stress conditions in focal cerebral ischemia.

Hypoglycaemia-induced cell death: features of neuroprotection by the P2 receptor antagonist basilen blue

Our previous work in neuronal cultures has shown that several antagonists of P2 ATP receptors prevent cell death evoked by hypoglycaemia, chemical hypoxia, mitochondria dysfunction, as well as glutamate-dependent excitotoxicity and low potassium-induced apoptosis. Experiments are now designed to examine which biological pathway contributes to cell death/survival under glucose starvation. We show here that, consequently to hypoglycaemic insults, cerebellar granule neurones undergo a combination of apoptosis and necrosis both inhibited by the P2 receptor antagonist basilen blue. This is demonstrated by morphological and biochemical features, such as TdT-mediated dUTP-biotin nick end-labelling, fluorescent staining of nuclear chromatin using Hoechst 33258, direct counting of intact viable nuclei and extracellular releasing of the cytosolic enzyme LDH. Furthermore, we show that hypoglycaemia induces outflow of cytochrome c from mitochondria and it up-regulates heat-shock proteins HSP70, but not HSP90, glucose-regulated proteins GRP75 and GRP78, as well as expression and activity of the enzyme caspase-2. Basilen blue can modulate only some of these effects. Our data contribute to dissect the role played by P2 receptor antagonism in sustaining neuroprotection against metabolic stresses.

Increased cytochrome c-mediated DNA fragmentation and cell death in manganese-superoxide dismutase-deficient mice after exposure to subarachnoid hemolysate

BACKGROUND AND PURPOSE

We sought to investigate the mechanisms for oxidative injury caused by subarachnoid hemolysate, a pro-oxidant.

METHODS

Injection of 50 microL of subarachnoid hemolysate or saline was performed in CD1 mice (n=75), mutant mice deficient in Mn-superoxide dismutase (Sod2+/-; n=23), and their wild-type littermates (n=23). Subcellular location of cytochrome c was studied by immunocytochemistry, immunofluorescence, and immunoblotting of cellular fractions. DNA fragmentation was assessed though DNA laddering and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling (TUNEL). Cell death was examined through basic histology.

RESULTS

Cytochrome c immunoreactivity was present in the cytosol of neurons at 2 hours after hemolysate injection and increased by 4 hours compared with saline-injected animals (P:<0.02). Cytosolic cytochrome c was more abundant in Sod2+/- mutants. DNA fragmentation was evident at 24 hours, but not 4 hours, after hemolysate injection as determined by DNA laddering and TUNEL staining (P:<0.02). DNA fragmentation colocalized to cells with cytosolic cytochrome c and iron. In Sod2+/- mutants, the extent of fragmentation was increased as determined by TUNEL staining (52% increase; P:<0.02) and DNA laddering (optical density=0.819 versus 0.391; P:<0.01). Cell death was evident on basic histology as early as 4 hours after hemolysate injection. No cell death was evident in controls. In Sod2+/- mutants, cell death was increased by 51% compared with wild-type littermates (P:<0.05).

CONCLUSIONS

These results demonstrate that subarachnoid blood products are associated with the presence of cytochrome c in the cytosol and subsequent cell death in neurons. It appears that Mn-superoxide dismutase plays a role in preventing cell death after exposure to subarachnoid blood products.

Reduction of copper, zinc-superoxide dismutase in knockout mice does not affect edema or infarction volumes and the early release of mitochondrial cytochrome c after permanent focal cerebral ischemia

Copper,zinc-superoxide dismutase (SOD1) was shown to be highly protective against ischemia/reperfusion injury in the brain. We have recently reported that SOD1 prevents the release of mitochondrial cytochrome c and subsequent apoptosis after ischemia/reperfusion in mice. To investigate its dose dependent effect on permanent focal cerebral ischemia, we examined neurological deficit scores, infarction volume, and the amount of hemisphere enlargement after 24 h of focal cerebral ischemia in both knockout mutants of SOD1 (Sod1 -/+ and Sod1 -/-) and wild-type littermates. We also examined the release of cytochrome c and subsequent DNA fragmentation after ischemia. There were no differences in the neurological deficit scores, infarction volumes and edema formation. There was also no difference of the amount cytosolic cytochrome c at 2 h and of the amount of DNA fragmentation at 24 h after focal cerebral ischemia. The results indicate that the SOD1 enzyme does not appear to affect cerebral infarction, cerebral edema nor the mitochondrial signaling pathway for apoptosis following permanent focal cerebral ischemia where there is no reperfusion injury.

Reactive oxygen radicals in signaling and damage in the ischemic brain

Reactive oxygen species have been implicated in brain injury after ischemic stroke. These oxidants can react and damage the cellular macromolecules by virtue of the reactivity that leads to cell injury and necrosis. Oxidants are also mediators in signaling involving mitochondria, DNA repair enzymes, and transcription factors that may lead to apoptosis after cerebral ischemia. Transgenic or knockout mice with cell- or site-specific prooxidant and antioxidant enzymes provide useful tools in dissecting the events involving oxidative stress in signaling and damage in ischemic brain injury.

Mild hypothermia mitigates post-ischemic neuronal death following focal cerebral ischemia in rat brain: immunohistochemical study of Fas, caspase-3 and TUNEL

Mild hypothermia is considered to have a protective effect during ischemic neuronal cell death. The present study provides experimental evidence for this beneficial role of mild hypothermia using reversible middle cerebral artery occlusion (MCAo) in a Sprague-Dawley (SD) rat model. MCAo was induced in rats for 1 h followed by reperfusion at different periods. Hematoxylin-eosin (HE) staining in normothermic (NT) 37 degrees C and hypothermic (HT) 33 degrees C groups of rats confirmed cerebral infarcts. The mean per cent infarct area was significantly reduced in the HT group of rats. Immunohistochemical analysis was done using anti-Fas and caspase-3 antibodies. The immunohistochemical expression of Fas and caspase-3 was demonstrable as early as 5 h after reperfusion, but the expression pattern maximized at 24 h after reperfusion. The expression of Fas and caspase-3 proteins showed a clear decrease in the HT group over the NT group. In situ detection of DNA fragmentation was done using the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling method (TUNEL). TUNEL-positive cells were first observed at 5h after reperfusion and progressively increased by 24h. A higher number of TUNEL-positive cells was found in the NT group, but they were significantly decreased in the HT group. Further, DNA fragmentation was confirmed by size fractionation in agarose gel. These findings demonstrate a positive relation between the expression of Fas, caspase-3 and TUNEL-positive cells.

Involvement of oxidative stress and caspase-3 in cortical infarction after photothrombotic ischemia in mice

Apoptosis-related cell death is linked to oxidative stress and caspases in experimental cerebral ischemia. However, the role of oxidative stress in caspase activation and subsequent apoptotic cell death after cerebral ischemia is unknown. The authors evaluated the role of oxidative stress in ischemic cerebral infarction after photothrombosis and the relation between oxidative stress and caspase-related cell death 6 and 24 hours after ischemia with and without U-74389G, a potent free radical scavenger (10 mg/kg, 30 minutes before and after ischemia induction). Reactive oxygen species, detected by hydroethidine oxidation, and cytosolic cytochrome c were detected in early ischemic lesions. Western blot analysis showed the cleaved form and the increased level of the proform of caspase-3 in the ischemic lesion 24 hours after ischemia. Decreased caspase-3 immunoreactivity was detected in the antioxidant-treated group after ischemia. Decreased DNA fragmentation and laddering were detected and the lesion was smaller in the treated group after ischemia compared with the untreated group. Oxidative stress and cytochrome c release occur in the ischemic lesion after photothrombotic ischemia. The free radical scavenger attenuated caspase-3 up-regulation, DNA fragmentation, and the final lesion. The authors concluded that oxidative stress may mediate caspase-related apoptotic cell death and subsequent cortical infarction after photothrombotic ischemia.

Molecular mechanisms of ischemic neuronal injury

Brain ischemia triggers a complex cascade of molecular events that unfolds over hours to days. Identified mechanisms of postischemic neuronal injury include altered Ca(2+) homeostasis, free radical formation, mitochondrial dysfunction, protease activation, altered gene expression, and inflammation. Although many of these events are well characterized, our understanding of how they are integrated into the causal pathways of postischemic neuronal death remains incomplete. The primary goal of this review is to provide an overview of molecular injury mechanisms currently believed to be involved in postischemic neuronal death specifically highlighting their time course and potential interactions.