Cytochrome c release from mitochondria to the cytosol was suppressed in the ischemia-tolerance-induced hippocampal CA1 region after 5-min forebrain ischemia in gerbils

Neuroprotection of ischemic preconditioning is mediated by thioredoxin 2 in the hippocampal CA1 region following a subsequent transient cerebral ischemia

Preconditioning by brief ischemic episode induces tolerance to a subsequent lethal ischemic insult, and it has been suggested that reactive oxygen species are involved in this phenomenon. Thioredoxin 2 (Trx2), a small protein with redox-regulating function, shows cytoprotective roles against oxidative stress. Here, we had focused on the role of Trx2 in ischemic preconditioning (IPC)-mediated neuroprotection against oxidative stress followed by a subsequent lethal transient cerebral ischemia. Animals used in this study were randomly assigned to six groups; sham-operated group, ischemia-operated group, IPC plus (+) sham-operated group, IPC + ischemia-operated group, IPC + auranofin (a TrxR2 inhibitor) + sham-operated group and IPC + auranofin + ischemia-operated group. IPC was subjected to a 2 minutes of sublethal transient ischemia 1 day prior to a 5 minutes of lethal transient ischemia. A significant loss of neurons was found in the stratum pyramidale (SP) of the hippocampal CA1 region (CA1) in the ischemia-operated-group 5 days after ischemia-reperfusion; in the IPC + ischemia-operated-group, pyramidal neurons in the SP were well protected. In the IPC + ischemia-operated-group, Trx2 and TrxR2 immunoreactivities in the SP and its protein level in the CA1 were not significantly changed compared with those in the sham-operated-group after ischemia-reperfusion. In addition, superoxide dismutase 2 (SOD2) expression, superoxide anion radical ( O2-) production, denatured cytochrome c expression and TUNEL-positive cells in the IPC + ischemia-operated-group were similar to those in the sham-operated-group. Conversely, the treatment of auranofin to the IPC + ischemia-operated-group significantly increased cell damage/death and abolished the IPC-induced effect on Trx2 and TrxR2 expressions. Furthermore, the inhibition of Trx2R nearly cancelled the beneficial effects of IPC on SOD2 expression, O2- production, denatured cytochrome c expression and TUNEL-positive cells. In brief, this study shows that IPC conferred neuroprotection against ischemic injury by maintaining Trx2 and suggests that the maintenance or enhancement of Trx2 expression by IPC may be a legitimate strategy for therapeutic intervention of cerebral ischemia.

Signaling pathways leading to ischemic mitochondrial neuroprotection

There is extensive evidence that ischemic/reperfusion mediated mitochondrial dysfunction is a major contributor to ischemic damage. However data also indicates that mild ischemic stress induces mitochondrial dependent activation of ischemic preconditioning. Ischemic preconditioning is a neuroprotective mechanism which is activated upon a brief sub-injurious ischemic exposure and is sufficient to provide protection against a subsequent lethal ischemic insult. Current research demonstrates that mitochondria are not only the inducers of but are also an important target of ischemic preconditioning mediated protection. Numerous proteins and signaling pathways are activated by ischemic preconditioning which protect the mitochondria against ischemic damage. In this review we examine some of the proteins activated by ischemic precondition which counteracts the deleterious effects of ischemia/reperfusion thereby maintaining normal mitochondrial activity and lead to ischemic tolerance.

Apoptosis-related protein expression in rabbits with blast brain injury following early hyperbaric oxygen therapy

We treated detonator-explosion-induced craniocerebral injury in rabbits with hyperbaric oxygen 1-24 hours post-injury. Expression of the apoptosis-regulating protein cytochrome c, the pro-apoptotic protein Bax and the apoptosis marker caspase-3 in the tissues surrounding the area of injury was significantly reduced, while that of the anti-apoptotic protein Bcl-2 was significantly increased. Our findings indicate that the curative effects of early hyperbaric oxygen on cortical cell apoptosis is associated with suppression of cytochrome c release from mitochondria. This mechanism underlies the observed reduction in Bax expression and upregulation of Bcl-2 expression.

Revisiting Cerebral Postischemic Reperfusion Injury: New Insights in Understanding Reperfusion Failure, Hemorrhage, and Edema

Cerebral postischemic reperfusion injury is defined as deterioration of ischemic brain tissue that parallels and antagonizes the benefits of restoring cerebral circulation after therapeutic thrombolysis for acute ischemic stroke. To understand the paradox of injury caused by treatment, we first emphasize the phenomenon in which recanalization of an occluded artery does not lead to tissue reperfusion. Additionally, no-reflow after recanalization may be due to injury of the neurovascular unit, distal microthrombosis, or both, and certainly worsens outcome. We examine the mechanism of molecular and sub-cellular damage in the neurovascular unit, notably oxidative stress, mitochondrial dysfunction, and apoptosis. At the level of the neurovascular unit, which mediates crosstalk between the damaged brain and systemic responses in blood, we summarize emerging evidence demonstrating that individual cell components play unique and cumulative roles that lead to damage of the blood–brain barrier and neurons. Furthermore, we review the latest developments in establishing a link between the immune system and microvascular dysfunction during ischemic reperfusion. Progress in assessing reperfusion injury has also been made, and we review imaging studies using various magnetic resonance imaging modalities. Lastly, we explore potential treatment approaches, including ischemic preconditioning, postconditioning, pharmacologic agents, and hypothermia.

Inhibition of caspase-9 activation and apoptosis is involved in ischemic preconditioning-induced neuroprotection in rat brain

OBJECTIVES

Cerebral ischemic pre-conditioning (IPC) is capable of protecting hippocampal neurons from ischemia/reperfusion (I/R) injury. In the current study, we investigated the role of activated caspase-9 in the protective process induced by IPC and related it to cytochrome c release and apoptosis.

METHODS

I/R injury was induced by a four-vessel occlusion model in Wistar rats which were randomly divided into ischemia/reperfusion group (I/R), ischemic pre-conditioning + I/R group (IPC + I/R) and control group. Histologic changes in the pyramidal layer of the hippocampal CA1 region were determined by hematoxylin and eosin (H&E) staining. The relative proportion of apoptotic neurons in this area was assessed with TUNEL staining. The redistribution of cytochrome c and activation of caspase-9 were detected in the same area with immunohistochemistry and Western blotting respectively.

RESULTS

Compared to the I/R group, IPC increased the number of surviving neurons in the hippocampal CA1 region (p<0.001), markedly reduced the number of apoptotic pyramidal neurons (p<0.001), inhibited the release of cytochrome c from mitochondria to cytoplasm (p<0.001 for positively stained neurons) and decreased the amount of activated caspase-9 (p<0.001).

DISCUSSION

These findings confirm that IPC is capable of protecting neurons from injury by apoptosis. The release of cytochrome c to the cytosol demonstrates that the mitochondrial pathway was involved, and the reduction in this release caused by IPC was clearly associated with reduced caspase-9 activation. Together, these results suggest that IPC protects neurons via action on the mitochondrial/caspase-9 pathway of apoptosis.

Changes in the expression of mitochondrial peroxiredoxin and thioredoxin in neurons and glia and their protective effects in experimental cerebral ischemic damage

We observed chronological changes in the mitochondrial-specific antioxidant enzymes peroxiredoxin 3 (Prx3) and thioredoxin 2 (Trx2) and their neuroprotective effects in the hippocampal CA1 region after 5 min of transient cerebral ischemia in gerbils. In the sham-operated group, weak Prx3 and Trx2 immunoreactivity was detected in the stratum pyramidale. Prx3 immunoreactivity was increased in pyramidal neurons and expressed in microglia 1 and 3 days, respectively, after ischemia/reperfusion (I/R). Trx2 immunoreactivity in pyramidal neurons increased 30 min and 1 day after I/R and decreased 6 h after I/R. Trx2 immunoreaction was expressed in astrocytes at 3 days postischemia. The intraventricular administration of Prx3 or Prx3/Trx2 (16 microg/20 microl, icv) using an osmotic pump significantly reduced ischemia-induced hyperactivity in a spontaneous motor test and protected CA1 pyramidal neurons from the ischemic damage. In addition, the activation of astrocytes and microglia was decreased in the ischemic CA1 region after Prx3/Trx2 treatment. In addition, treatment with Prx3 or Prx3/Trx2 significantly reduced lipid peroxidation and the release of cytochrome c from mitochondria and cytoplasm in the ischemic CA1 region. These results suggest that changes in the expression of Prx3 and Trx2 in the hippocampal CA1 region after I/R may be associated with the delayed neuronal death of CA1 pyramidal cells induced by transient cerebral ischemia, and that treatment with Prx3 or Prx3/Trx2 in ischemic brains shows a potent neuroprotective effect against ischemic damage by reducing lipid peroxidation and mitochondrial-mediated apoptosis by I/R.

Human neural stem cell transplantation attenuates apoptosis and improves neurological functions after cerebral ischemia in rats

BACKGROUND

Neuroprotection is a major therapeutic approach for ischemic brain injury. We investigated the neuroprotective effects induced by transplantation of human embryonic neural stem cells (NSCs) into the cortical penumbra 24 h after focal cerebral ischemia.

METHODS

NSCs were prepared from human embryonic brains obtained at 8 weeks of gestation. Focal cerebral ischemia was induced in adult rats by permanent occlusion of the middle cerebral artery. Animals were randomly divided into two groups: NSCs-grafted group and medium-grafted group (control). Infarct size was assessed 28 days after transplantation by hematoxylin and eosin staining. Neurological severity scores were evaluated before ischemia and at 1, 7, 14, and 28 days after transplantation. The terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay and immunohistochemical analysis of Bcl-2 and Bax were performed at 7, 14, and 28 days after transplantation.

RESULTS

Physiological parameters of the two groups were comparable, but not significantly different. NSC transplantation significantly improved neurological function (P<0.05) but did not reduce the infarct size significantly (P>0.05). Compared with the control, NSC transplantation significantly reduced the number of TUNEL- and Bax-positive cells in the penumbra at 7 days. Interestingly, the number of Bcl-2-positive cells in the penumbra after NSC transplantation was significantly higher than that after medium transplantation (P<0.05).

CONCLUSIONS

The results indicate that NSC transplantation has anti-apoptotic activity and can improve the neurological function; these effects are mediated by the up-regulation of Bcl-2 expression in the penumbra.

Both ischemic preconditioning and ghrelin administration protect hippocampus from ischemia/reperfusion and upregulate uncoupling protein-2

BACKGROUND

A major endogenous protective mechanism in many organs against ischemia/reperfusion (I/R) injury is ischemic preconditioning (IPC). By moderately uncoupling the mitochondrial respiratory chain and decreasing production of reactive oxygen species (ROS), IPC reduces apoptosis induced by I/R by reducing cytochrome c release from the mitochondria. One element believed to contribute to reduce ROS production is the uncoupling protein UCP2 (and UCP3 in the heart). Although its implication in IPC in the brain has been shown in vitro, no in vivo study of protein has shown its upregulation. Our first goal was to determine in rat hippocampus whether UCP2 protein upregulation was associated with IPC-induced protection and increased ROS production. The second goal was to determine whether the peptide ghrelin, which possesses anti-oxidant and protective properties, alters UCP2 mRNA levels in the same way as IPC during protection.

RESULTS

After global forebrain ischemia (15 min) with 72 h reperfusion (I/R group), we found important neuronal lesion in the rat hippocampal CA1 region, which was reduced by a preceding 3-min preconditioning ischemia (IPC+I/R group), whereas the preconditioning stimulus alone (IPC group) had no effect. Compared to control, UCP2 protein labelling increased moderately in the I/R (+39%, NS) and IPC+I/R (+28%, NS) groups, and substantially in the IPC group (+339%, P < 0.05). Treatment with superoxide dismutase (10000 U/kg ip) at the time of a preconditioning ischemia greatly attenuated (-73%, P < 0.001) the increase in UCP2 staining at 72 h, implying a role of oxygen radicals in UCP2 induction.Hippocampal UCP2 mRNA showed a moderate increase in I/R (+33%, P < 0.05) and IPC+I/R (+40%, P < 0.05) groups versus control, and a large increase in the IPC group (+333%, P < 0.001). In ghrelin experiments, the I/R+ghrelin group (3 daily administrations) showed considerable protection of CA1 neurons versus I/R animals, and increased hippocampal UCP2 mRNA (+151%, P < 0.001).

CONCLUSION

We confirm that IPC causes increased expression of UCP2 protein in vivo, at a moment appropriate for protection against I/R in the hippocampus. The two dissimilar protective strategies, IPC and ghrelin administration, were both associated with upregulated UCP2, suggesting that UCP2 may often represent a final common pathway in protection from I/R.

The neuroprotective mechanism of brain ischemic preconditioning

Brain ischemia is one of the most common causes of death and the leading cause of adult disability in the world. Brain ischemic preconditioning (BIP) refers to a transient, sublethal ischemia which results in tolerance to later, otherwise lethal, cerebral ischemia. Many attempts have been made to understand the molecular and cellular mechanisms underlying the neuroprotection offered by ischemic preconditioning. Many studies have shown that neuroprotective mechanisms may involve a series of molecular regulatory pathways including activation of the N-methyl-D-aspartate (NMDA) and adenosine receptors; activation of intracellular signaling pathways such as mitogen activated protein kinases (MAPK) and other protein kinases; upregulation of Bcl-2 and heat shock proteins (HSPs); and activation of the ubiquitin-proteasome pathway and the autophagic-lysosomal pathway. A better understanding of the processes that lead to cell death after stroke as well as of the endogenous neuroprotective mechanisms by which BIP protects against brain ischemic insults could help to develop new therapeutic strategies for this devastating neurological disease. The purpose of the present review is to summarize the neuroprotective mechanisms of BIP and to discuss the possibility of mimicking ischemic preconditioning as a new strategy for preventive treatment of ischemia.

Molecular physiology of preconditioning-induced brain tolerance to ischemia

Ischemic tolerance describes the adaptive biological response of cells and organs that is initiated by preconditioning (i.e., exposure to stressor of mild severity) and the associated period during which their resistance to ischemia is markedly increased. This topic is attracting much attention because preconditioning-induced ischemic tolerance is an effective experimental probe to understand how the brain protects itself. This review is focused on the molecular and related functional changes that are associated with, and may contribute to, brain ischemic tolerance. When the tolerant brain is subjected to ischemia, the resulting insult severity (i.e., residual blood flow, disruption of cellular transmembrane gradients) appears to be the same as in the naive brain, but the ensuing lesion is substantially reduced. This suggests that the adaptive changes in the tolerant brain may be primarily directed against postischemic and delayed processes that contribute to ischemic damage, but adaptive changes that are beneficial during the subsequent test insult cannot be ruled out. It has become clear that multiple effectors contribute to ischemic tolerance, including: 1) activation of fundamental cellular defense mechanisms such as antioxidant systems, heat shock proteins, and cell death/survival determinants; 2) responses at tissue level, especially reduced inflammatory responsiveness; and 3) a shift of the neuronal excitatory/inhibitory balance toward inhibition. Accordingly, an improved knowledge of preconditioning/ischemic tolerance should help us to identify neuroprotective strategies that are similar in nature to combination therapy, hence potentially capable of suppressing the multiple, parallel pathophysiological events that cause ischemic brain damage.

Interrupting reperfusion as a stroke therapy: ischemic postconditioning reduces infarct size after focal ischemia in rats

Cerebral ischemic preconditioning protects against stroke, but is clinically feasible only when the occurrence of stroke is predictable. Reperfusion plays a critical role in cerebral injury after stroke; we tested the hypothesis that interrupting reperfusion lessens ischemic injury. We found for the first time that such postconditioning with a series of mechanical interruptions of reperfusion significantly reduces ischemic damage. Focal ischemia was generated by permanent distal middle cerebral artery (MCA) occlusion plus transient bilateral common carotid artery (CCA) occlusion. After 30 secs of CCA reperfusion, ischemic postconditioning was performed by occluding CCAs for 10 secs, and then allowing for another two cycles of 30 secs of reperfusion and 10 secs of CCA occlusion. Infarct size was measured 2 days later. Cerebral blood flow (CBF) was measured in animals subjected to permanent MCA occlusion plus 15 mins of bilateral CCA occlusion, which demonstrates that postconditioning disturbed the early hyperemia immediately after reperfusion. Postconditioning dose dependently reduced infarct size in animals subjected to permanent MCA occlusion combined with 15, 30, and 60 mins of bilateral CCA occlusion, by reducing infarct size approximately 80%, 51%, and 17%, respectively. In addition, postconditioning blocked terminal deoxynucleotidyl transferase-mediated uridine 5'-triphosphate-biotin nick end labeling-positive staining, a marker of apoptosis, in the penumbra 2 days after stroke. Furthermore, in situ superoxide detection using hydroethidine suggested that postconditioning attenuated superoxide products during early reperfusion after stroke. In conclusion, postconditioning reduced infarct size, most plausibly by blocking apoptosis and free radical generation. With further study it may eventually be clinically applicable for stroke treatment.

Mechanisms of neuroprotection during ischemic preconditioning: lessons from anoxic tolerance

Different physiological adaptations for anoxia resistance have been described in the animal kingdom. These adaptations are particularly important in organs that are highly susceptible to energy deprivation such as the heart and brain. Among vertebrates, turtles are one of the species that are highly tolerant to anoxia. In mammals however, insults such as anoxia, ischemia and hypoglycemia, all cause major histopathological events to the brain. However, in mammals even ischemic or anoxic tolerance is found when a sublethal ischemic/anoxic insult is induced sometime before a lethal ischemic/anoxic insult is induced. This phenomenon is defined as ischemic preconditioning. Better understanding of the mechanisms inducing both anoxic tolerance in turtles or ischemic preconditioning in mammals may provide novel therapeutic interventions that may aide mammalian brain to resist the ravages of cerebral ischemia. In this review, we will summarize some of the mechanisms implemented in both models of tolerance, emphasizing physiological and biochemical similarities.

The preconditioning modified neuronal expression of apoptosis-related proteins of Bcl-2 superfamily following severe hypobaric hypoxia in rats

The patterns of expression of the Bcl-2, Bax, and Bcl-xL proteins were examined immunocytochemically in rat hippocampus and neocortex after severe hypobaric hypoxia (180 Torr for 3 h) and severe hypoxia preconditioned by intermittent mild hypoxia (360 Torr for 2 h daily, for 3 consecutive days, 24 h prior to severe hypoxia). As revealed by TUNEL assay, severe hypobaric hypoxia produced extensive apoptotic damage to the neurons of hippocampal CA1-CA4 and the neocortex but not the dentate gyrus granule cells. Remarkable posthypoxic up-regulation of Bax expression maximal at 24 h was detected in the CA1-CA4 areas of hippocampus and neocortex 3-72 h after severe hypoxia. The preconditioning to severe hypoxia protected neurons from the posthypoxic apoptotic transformations, the up-regulation of Bax expression, and resulted in persistent overexpression of Bcl-2 and Bcl-xL. We conclude that the protective action of hypoxic preconditioning is at least in part mediated by shifting of neuronal Bax/Bcl-2-Bcl-xL ratio to a favor of antiapoptotic proteins Bcl-2 and Bcl-xL.

Ischaemic preconditioning: therapeutic implications for stroke?

Ischaemic preconditioning (IPC), also known as ischaemic tolerance (IT), is a phenomenon whereby tissue is exposed to a brief, sublethal period of ischaemia, which activates endogenous protective mechanisms, thereby reducing cellular injury that may be caused by subsequent lethal ischaemic events. The first description of this phenomenon was in the heart, which was reported by Murry and co-workers in 1986. Subsequent studies demonstrated IPC in lung, kidney and liver tissue, whereas more recent studies have concentrated on the brain. The cellular mechanisms underlying the beneficial effects of IPC remain largely unknown. This phenomenon, which has been demonstrated by using various injury paradigms in both cultured neurons and animal brain tissue, may be utilised to identify and characterise therapeutic targets for small-molecule, antibody, or protein intervention. This review will examine the experimental evidence demonstrating the phenomenon termed IPC in models of cerebral ischaemia, the cellular mechanisms that may be involved and the therapeutic implications of these findings.

Effect of the first window of ischemic preconditioning on mitochondrial dysfunction following global cerebral ischemia

Rats may develop sustained tolerance against lethal cerebral ischemia after exposure to a sublethal ischemic insult (ischemic preconditioning (IPC)). Two windows for the induction of tolerance by IPC have been proposed, one that occurs within 1h following IPC, and the other one that occurs 1-3 days after IPC. An important difference between these two windows is that in contrast to the second window, neuroprotection against lethal ischemia is transient in the first window. We tested the hypothesis that rapid IPC would reduce or prevent ischemia-induced changes in mitochondrial function. IPC and ischemia were produced by bilateral carotid occlusions and systemic hypotension (50 mmHg) for 2 and 10 min, respectively. The non-synaptosomal mitochondria were harvested 30 min following the 10 min 'test' ischemia. Mitochondrial rate of respiration decreased by 10% when the substrates were pyruvate and malate, and 29% when the substrates were ascorbic acid and N,N,N',N'-tetramethyl-p-phenylenediamine ( P< 0.01). The activities of complex I-III decreased in ischemic group by 16, 23 (P < 0.05) and 24%, respectively. IPC was unable to prevent decreases in the rate of respiration and activities of different complexes. These data suggest that rapidly induced IPC is unable to protect the integrity of mitochondrial oxidative phosphorylation following cerebral ischemia, perhaps explaining why IPC only provides transitory protection in the 'first window'.

Growth arrest and DNA damage-inducible gene 153 increases transiently in the thalamus following focal cerebral infarction

The thalamus degenerates following cerebral infarction in the territory supplied by the middle cerebral artery (MCA), and apoptosis is suspected to be the mechanism of this phenomenon. The author studied the role of the growth arrest and DNA damage-inducible gene (GADD) 153 in this thalamic degeneration. The MCA was occluded in stroke-prone spontaneously hypertensive rats. The expression of GADD 153 and Bcl-2, and the release of cytochrome c from the mitochondria to cytosol, were examined in the thalamus until 7 days after ischemia using in situ hybridization, immunoblot, immunohistochemistry and RT-PCR analyses. Gadd153 mRNA expression and GADD153 protein increased transiently at 2, 3, 5 and 7 days, and at 3 and 5 days after ischemia. Bcl-2 mRNA expression and Bcl-2 protein decreased at 3 and 5 days. The release of cytochrome c from the mitochondria was detected at 5 days. These results suggest that increased GADD 153 suppresses Bcl-2 expression, which causes the release of cytochrome c from the mitochondria and leads to thalamic degeneration.

Preconditioning enhances the expression of mitochondrial antioxidant thioredoxin-2 in the forebrain of rats exposed to severe hypobaric hypoxia

The impact of severe hypoxia and preconditioning on the expression of the mitochondrial antioxidant thioredoxin-2 (Trx-2) in rat hippocampus (CA1, CA2, CA3 fields, and dentate gyrus) and neocortex was studied by immunocytochemistry. The preconditioning consisted of three trials of mild hypobaric hypoxia (360 Torr, 2 hr) spaced at 24 hr. The last trial was followed by severe hypobaric hypoxia (180 Torr, 3 hr) 24 hr later. Both in hippocampus and in neocortex, severe hypobaric hypoxia resulted in enhanced Trx-2 expression at 3 hr, followed by a slight decline in Trx-2 levels, which nevertheless remained increased at 24 hr elsewhere except for the CA1 region. The preconditioning considerably augmented severe hypoxia-induced Trx-2 immunoreactivity, affecting both the number of immunoreactive cells and the intensity of immunostaining. The findings suggest a role for Trx-2 in the formation of brain hypoxic/ischemic tolerance accomplished by the preconditioning.

The augmentation of brain thioredoxin-1 expression after severe hypobaric hypoxia by the preconditioning in rats

Induction of endogenous antioxidants is one of the key molecular mechanisms of cell resistance to hypoxia/ischemia. The effect of severe hypoxia on the expression of cytosolic antioxidant thioredoxin-1 (Trx) in hippocampus and neocortex was studied in preconditioned and non-preconditioned rats. The preconditioning consisted of three trials of mild hypobaric hypoxia (360 Torr, 2 h) spaced at 24 h. Twenty-four hours after the last trial rats were subjected to severe hypobaric hypoxia (180 Torr, 3 h). Trx expression was studied by immunocytochemistry. In hippocampus severe hypobaric hypoxia rapidly induced Trx expression, which remained elevated still at 24 h. In neocortex the enhanced expression appeared only at 24 h. The preconditioning significantly augmented severe hypoxia-induced Trx-immunoreactivity at 3 h but not at 24 h. These findings point out that Trx contributes to mechanisms of brain tolerance to hypobaric hypoxia, especially in early periods after the exposure.

Bcl-2 and Bax proteins are increased in neocortical but not in thalamic apoptosis following devascularizing lesion of the cerebral cortex in the rat: an immunohistochemical study

The hypothesis that devascularization of somatosensory and motor cortex causes apoptosis in infarcted regions and in the linked thalamic nuclei was evaluated. To unravel whether Bcl-related proteins, known to regulate apoptosis, participate in neuronal and glial responses to devascularization, we analyzed immunohistochemically the distribution and intensity of staining of Bcl-2 and Bax proteins at different time points after lesion. Both early (up to 6 h) and late (1-7 days) responses were studied. Devascularization led to rapid (within hours) apoptosis in the cortex and to a delayed (within 3-7 days) apoptosis in thalamic nuclei. In control groups, Bcl-2 and Bax immunoreactivity (IR) was detected in neurons and oligodendrocytes but not in astrocytes or microglia. Following devascularization, Bcl-2 IR and Bax IR increased in neurons before the onset of the apoptosis. In the ischemic focus, the increase reached maximal values 3 h after the lesion. The increase was of slower onset in the penumbra zone (24 h and after), a region in which both proteins were induced in astrocytes also. The change of Bax IR intensity exceeded four times that of Bcl-2 at all time points investigated, indicating a diminution of Bcl-2/Bax ratio that may direct neurons to apoptotic pathway. In numerous neurons, an increase of IR in the cytoplasm was accompanied by induction of nuclear staining. No changes of Bcl-2 and Bax IR were found in thalamic nuclei. Our results point to different mechanisms underlying apoptosis of cortical and thalamic neurons. Nuclear appearance of Bcl-2 and Bax suggests they possess regulatory role of gene expression changes triggered by cortical infarct.

Role of protein synthesis in the ischemic tolerance acquisition induced by transient forebrain ischemia in the rat

Although ischemic preconditioning of the heart and brain is a well-documented neuroprotective phenomenon, the mechanism underlying the increased resistance to severe ischemia induced by a preceding mild ischemic exposure remains unclear. In this study we have determined the effect of ischemic preconditioning on ischemia/reperfusion-associated translation inhibition in the neocortex and hippocampus of the rat. We studied the effect of the duration on the sublethal ischemic episode (3, 4, 5 or 8 min), as well as the amount of time elapsed between sublethal and lethal ischemia on the cell death 7 days after the last ischemic episode. In addition, the rate of protein synthesis in vitro and expression of the 72-kD heat shock protein (hsp) were determined under the different experimental conditions. Our results suggest that two different mechanisms are essential for the acquisition of ischemic tolerance, at least in the CA1 sector of hippocampus. The first mechanism implies a highly significant reduction in translation inhibition after lethal ischemia, especially at an early time of reperfusion, in both vulnerable and nonvulnerable neurons. For the acquisition of full tolerance, a second mechanism, highly dependent on the time interval between preconditioning (sublethal ischemia) and lethal ischemia, is absolutely necessary; this second mechanism involves synthesis of protective proteins, which prevent the delayed death of vulnerable neurons.

Ischemic pre-conditioning preserves brain mitochondrial functions during the middle cerebral artery occlusion in rat

It is well known that a brief period of ischemia increases tolerance to a subsequent severe ischemic episode. In the present study, bilateral carotid arteries occlusion (BCAO) was applied as pre-conditioning to testify whether this kind of ischemia could preserve the function of mitochondria with the impairment induced by middle cerebral artery occlusion (MCAO) in brain. The activities of respiratory enzyme complex I to IV, mitochondria swelling, membrane potential, and membrane fluidity were investigated. The results showed that the percentage of infarct area decreased greatly due to the ischemic pre-conditioning (IP) revealing the preventive effect of IP on infarct size. The activities of respiratory enzyme complex III, IV were effectively preserved (p < 0.05, p < 0.05) compared with MCAO group through ischemic pre-conditioning. Mitochondrial swelling and membrane fluidity were protected by IP, and also an increased trend was found in membrane potential, which indicated that the integrity of mitochondrial membrane was maintained. It suggested that the function of mitochondrial energy metabolism in brain ischemia was effectively protected by this kind of pre-conditioning.

Hypoxic preconditioning prevents cortical infarction by transient focal ischemia-reperfusion

One of the proposed pathologic actions underlying brain infarction is excess free radicals resulting from reoxygenation. In this paper we report an investigation of the neuroprotective effect of hypoxic preconditioning on transient focal ischemia-reperfusion injuries in rat brain. Female Wistar rats were subjected to 380 mmHg in an altitude chamber for 15 hours/day. Our ex vivo studies showed that auto-oxidation and iron-induced lipid peroxidation of brain homogenates of the four-week hypoxia-preconditioned rats were significantly lower than those of the normoxic rats. A focal infarction in the cerebral cortex of normoxic rats was consistently observed 24 hours after a 60-minute transient ischemic occlusion of the right middle cerebral artery and bilateral common carotid arteries. Hypoxic preconditioning in fact attenuated cortical infarction in a duration-dependent manner. Induction of the neuroprotection required two weeks of hypoxic preconditioning. Four weeks of hypoxic preconditioning significantly reduced the cortical infarcted area, the elevated lipid peroxidation, and resulted in an acute increase in cytosolic cytochrome c in the infarcted cortex of normoxic rats. The protective effect of four weeks of hypoxic preconditioning lasted seven days under a renormoxic condition. Our data suggest that oxidative stress may result in apoptosis in the transient focal ischemia-reperfusion injuries. Furthermore, hypoxic preconditioning attenuated cortical infarction in the rat brain. Although supplementation of antioxidants may encounter difficulty at the blood-brain barrier, hypoxic preconditioning is very likely to protect CNS targets from oxidative injuries without any barrier.

Axotomy induces cytochrome c release in retinal ganglion cells

Activation of caspase-3 and -9 has been implicated in the death of axotomized retinal ganglion cells (RGCs). The upstream pathways involved in the activation of these caspases, however, remain unknown. The aim of the current study is to examine the role of cytochrome c release in axotomized RGC death using immuno-histochemistry. We found that while only a low level of cytochrome c immunoreactivity was evident in normal retina, cytochrome c immunoreactivity increased markedly at 1 day post-axotomy, peaked at 3 days post-axotomy, and decreased thereafter. In addition, cytochrome c immunoreactivity localized almost exclusively to RGCs, suggesting that the cytochrome c release observed was injury-related. Our data indicate that cytochrome c release potentially contributes to the death of axotomized RGCs.

Down-regulation of parkin protein in transient focal cerebral ischemia: A link between stroke and degenerative disease?

Ubiquitylated protein aggregates are characteristic features of neurodegenerative disorders that are also found in acute pathological states of the brain such as stroke. Many of the proteins connected to neurodegenerative diseases play a role in the ubiquitin-proteasomal pathway. Mutation of one of these proteins, the E3 ubiquitin ligase parkin, is the cause of autosomal recessive juvenile Parkinson's disease. Here we show that transient focal cerebral ischemia of 1-h duration induces marked depletion of parkin protein levels, to 60%, 36%, 33%, and 25% of controls after 1, 3, 6, and 24 h of reperfusion, but that ischemia does not cause lower protein levels of E2 ubiquitin-conjugating enzymes Ubc6, Ubc7, or Ubc9. After 3 h of reperfusion, when parkin protein levels were already reduced to <40% of control, ATP levels were almost completely recovered from ischemia and we did not observe DNA fragmentation, suggesting that parkin depletion preceded development of neuronal cell death. Up-regulation of the expression of parkin has been shown to protect cells from injury induced by endoplasmic reticulum (ER) dysfunction, and this form of cellular stress is also triggered by transient cerebral ischemia. However, in contrast to observations in neuroblastoma cells, we saw no up-regulation of parkin expression in primary neuronal cell cultures after induction of ER dysfunction. Our data thus suggest that ischemia-induced depletion of parkin protein may contribute to the pathological process resulting in cell injury by increasing the sensitivity of neurons to ER dysfunction and the aggregation of ubiquitylated proteins during the reperfusion period.

Role of caspase 3-dependent Bcl-2 cleavage in potentiation of apoptosis by Bcl-2

Previous studies from our laboratory have demonstrated that Bcl-2 has a proapoptotic effect on neocarzinostatin (NCS)-treated PC12 pheochromocytoma cells. In the present study, we examine the mechanisms of this effect and demonstrate its relevance for the in vivo situation. Four hours after NCS treatment, a 23-kDa cleavage product of Bcl-2 was detected in whole cell lysates of bcl-2-transfected PC12 cells. In contrast, bcl-2 transfection protected PC12 cells from cisplatin-induced apoptosis, and cisplatin treatment did not result in Bcl-2 cleavage. Similarly, Bcl-2 cleavage did not occur and Bcl-2-mediated protection from, rather than potentiation of apoptosis was observed after NCS treatment of MCF-7 breast cancer cells. The caspase 3-specific inhibitor Ac-DEVD-CHO prevented Bcl-2 cleavage and attenuated NCS-induced apoptosis in bcl-2-transfected PC12 cells, whereas it had no effect on NCS-induced apoptosis in mock-transfected PC12 cells. Furthermore, MCF-7 cells do not express caspase 3, a finding in concert with the lack of Bcl-2 cleavage in this line. In in vivo experiments, xenografts of bcl-2-transfected PC12 cells were more susceptible to NCS toxicity than were xenografts of mock-transfected PC12 cells. Caspase 3-mediated Bcl-2 cleavage therefore plays an important role in the potentiation by Bcl-2 of NCS-induced apoptosis.

Both caspase-dependent and caspase-independent pathways may be involved in hippocampal CA1 neuronal death because of loss of cytochrome c From mitochondria in a rat forebrain ischemia model

In a rat forebrain ischemia model, the authors examined whether loss of cytochrome c from mitochondria correlates with ischemic hippocampal CA1 neuronal death and how cytochrome c release may shape neuronal death. Forebrain ischemia was induced by bilateral common carotid artery occlusion with simultaneous hypotension for 10 minutes. After reperfusion, an early rapid depletion of mitochondrial cytochrome c and a late phase of diffuse redistribution of cytochrome c occurred in the hippocampal CA1 region, but not in the dentate gyrus and CA3 regions. Intracerebroventricular administration of Z-DEVD-FMK, a relatively selective caspase-3 inhibitor, provided limited but significant protection against ischemic neuronal damage on day 7 after reperfusion. Treatment with 3 minutes of ischemia (ischemic preconditioning) 48 hours before the 10-minute ischemia attenuated both the early and late phases of cytochrome c redistribution. In another subset of animals treated with cycloheximide, a general protein synthesis inhibitor, the late phase of cytochrome c redistribution was inhibited, whereas most hippocampal CA1 neurons never regained mitochondrial cytochrome c. Examination of neuronal survival revealed that ischemic preconditioning prevents, whereas cycloheximide only delays, ischemic hippocampal CA1 neuronal death. DNA fragmentation detected by terminal deoxytransferase-mediated dUTP-nick end labeling (TUNEL) in situ was largely attenuated by ischemic preconditioning and moderately reduced by cycloheximide. These results indicate that the loss of cytochrome c from mitochondria correlates with hippocampal CA1 neuronal death after transient cerebral ischemia in relation to both caspase-dependent and -independent pathways. The amount of mitochondrial cytochrome c regained may determine whether ischemic hippocampal CA1 neurons survive or succumb to late-phase death.

Histochemical cytochrome c oxidase activity and caspase-3 in gerbil hippocampal CA1 neurons after transient forebrain ischemia

We examined the cytochrome c oxidase (COX) activity in gerbil hippocampal CA1 neurons after 5-min ischemia by a histochemical method in the presence or absence of exogenous cytochrome c. In the CA1 neurons, COX activity without exogenous cytochrome c decreased from 1 h after ischemia, but was restored by the addition of exogenous cytochrome c in the following 6 h after ischemia. These results suggest that it is not COX activity but endogenous cytochrome c that is changed in the early phase after ischemia, and that COX activity begins to decrease 9 h after ischemia. We examined caspase-3 in the CA1 region by immunoblotting, as caspase-3 is known to take part in the cell-death cascade downstream from cytochrome c. Although pro-caspase-3 was strongly detected, active caspase-3 was not detected before and until 84 h after 5-min ischemia. Our data suggested that delayed neuronal death is likely to progress via cytochrome c-release but not via caspase-3 activation.