Expression of redox factor-1, p53-activated gene 608 and caspase-3 messenger RNAs following repeated unilateral common carotid artery occlusion in gerbils--relationship to delayed cell injury and secondary failure of energy state

Notch signaling and neuronal death in stroke

Ischemic stroke is a leading cause of morbidity and death, with the outcome largely determined by the amount of hypoxia-related neuronal death in the affected brain regions. Cerebral ischemia and hypoxia activate the Notch1 signaling pathway and four prominent interacting pathways (NF-κB, p53, HIF-1α and Pin1) that converge on a conserved DNA-associated nuclear multi-protein complex, which controls the expression of genes that can determine the fate of neurons. When neurons experience a moderate level of ischemic insult, the nuclear multi-protein complex up-regulates adaptive stress response genes encoding proteins that promote neuronal survival, but when ischemia is more severe the nuclear multi-protein complex induces genes encoding proteins that trigger and execute a neuronal death program. We propose that the nuclear multi-protein transcriptional complex is a molecular mediator of neuronal hormesis and a target for therapeutic intervention in stroke.

Induction of parkinsonism-related proteins in the spinal motor neurons of transgenic mouse carrying a mutant SOD1 gene

Amyotrophic lateral sclerosis is a progressive and fatal disease caused by selective death of motor neurons, and a number of these patients carry mutations in the superoxide dismutase 1 (SOD1) gene involved in ameliorating oxidative stress. Recent studies indicate that oxidative stress and disruption of mitochondrial homeostasis is a common mechanism for motor neuron degeneration in amyotrophic lateral sclerosis and the loss of midbrain dopamine neurons in Parkinson's disease. Therefore, the present study investigated the presence and alterations of familial Parkinson's disease-related proteins, PINK1 and DJ-1, in spinal motor neurons of G93ASOD1 transgenic mouse model of amyotrophic lateral sclerosis. Following onset of disease, PINK1 and DJ-1 protein expression increased in the spinal motor neurons. The activated form of p53 also increased and translocated to the nuclei of spinal motor neurons, followed by increased expression of p53-activated gene 608 (PAG608). This is the first report demonstrating that increased expression of PAG608 correlates with activation of phosphorylated p53 in spinal motor neurons of an amyotrophic lateral sclerosis model. These results provide further evidence of the profound correlations between spinal motor neurons of amyotrophic lateral sclerosis and parkinsonism-related proteins.

Biochemical evaluation of focal non-reperfusion cerebral ischemia by middle cerebral artery occlusion in rats

Cerebral ischemia is an important event in clinical and surgical neurological practice since it is one of the diseases that most compromise the human species. In the present study 40 adult rats were submitted to periods of focal ischemia of 30, 60 and 90 min without reperfusion and animals submitted to a sham procedure were used as controls. We analyzed the levels of ATP, malondialdehyde and caspase-3. No significant differences in the biochemical measurements were observed between the right and left brain hemispheres of the same animal in each experimental group. Reduced ATP levels were observed after the three periods of ischemia compared to the sham group. No significant increase in malondialdehyde or caspase-3 levels was observed. Despite significant changes in ATP levels, the results indicated cell viability in the ischemic region as shown by the low rates of lipid peroxidation and apoptosis, findings probably related to the lack of reperfusion.

Direct experimental occlusion of the distal middle cerebral artery induces high reproducibility of brain ischemia in mice

Several investigators have used murine models to investigate the pathophysiology of brain ischemia. The focal ischemic model is a closer approximation to human stroke which includes a necrotic core, penumbra, and undamaged tissue. Occlusion of a unilateral artery, especially the middle cerebral artery (MCA), is performed in this model, but collateral circulation often induces variation of ischemic lesions both qualitatively and quantitatively. It is likely that the more proximal the artery which is unilaterally occluded is, the more inconsistent the outcomes. The present study was designed to examine the reproducibility of infarct lesion by distal or proximal artery occlusion. Direct occlusion of the distal MCA was performed and compared with unilateral common carotid artery occlusion (CCAO) in C57BL/6 mice. Direct MCA occlusion (MCAO) consistently induced ischemic lesions in cortical areas. All model animals (n=14) survived 24 h after occlusion, and exhibited a maximum infarct volume (20.0 +/- 5.0%). In contrast, permanent and transient unilateral CCAO models had mortality rates of 62.5 and 25.0%, and showed severe to absent lesions with the infarct volumes of 29.0 +/- 20.8 and 33.2 +/- 24.2%, respectively. In conclusion, distal MCAO produces high reproducibility of ischemic insults and survivability compared to unilateral CCAO. Thus, distal MCAO is a useful method for the focal ischemic model.

Specific induction of PAG608 in cranial and spinal motor neurons of L-DOPA-treated parkinsonian rats

We identified p53-activated gene 608 (PAG608) as a specifically induced gene in striatal tissue of L-DOPA (100mg/kg)-injected hemi-parkinsonian rats using differential display assay. In the present study, we further examined morphological distribution of PAG608 in the central nervous system of L-DOPA-treated hemi-parkinsonian rats. PAG608 expression was markedly induced in fibers and neuronal cells of the lateral globus pallidus and reticular thalamic nucleus adjacent to internal capsule, specifically in the parkinsonian side of L-DOPA-treated models. The protein was also constitutively expressed in motor neurons specifically in either side of the pontine nucleus and motor nuclei of trigeminal and facial nerves. Furthermore, L-DOPA-induced PAG608 expression on motor neurons in the contralateral side of the ventral horn of the spinal cord and the lateral corticospinal tract without cell loss. The specific induction of PAG608 6-48h after L-DOPA injection in the extrapyramidal tracts, pyramidal tracts and corresponding lower motor neurons of the spinal cords suggests its involvement in molecular events in stimulated motor neurons. Taken together with the constitutive expression of PAG608 in the motor nuclei of cranial nerves, PAG608 may be a useful marker of stressed or activated lower motor neurons.

Suppression of p53-activated gene, PAG608, attenuates methamphetamine-induced neurotoxicity

The p53-activated gene 608 (PAG608) is a proapoptotic gene activated and regulated by p53 expression in oxidative stress-induced apoptosis of neuronal cells. In this study, we determined the role of PAG608 in methamphetamine-induced neurotoxicity. Treatment of mouse dopaminergic CATH.a cells with 2 mM methamphetamine increased PAG608 expression at 3h followed by increase in phosphorylated p53 expression. Transient transfection of PAG608 antisense cDNA or RNA interference using PAG608 small interfering RNA significantly attenuated the dose-dependent decrease in cell viability of CATH.a cells by methamphetamine (1-4 mM) exposure. In monoaminergic neuronal B65 cells, which contain serotonin rather than dopamine, methamphetamine-induced cell death was also significantly but partially protected by transient transfection of PAG608 antisense cDNA. Furthermore, cell death of PC12 cells produced by methamphetamine (1-5 mM) was almost completely prevented by stable expression of PAG608 antisense cDNA, compared with significant reduction of cell viability in control PC12 cells. Our results showed that suppression of PAG608 using transient and stable transfection with PAG608 antisense cDNA or small interfering RNA attenuates methamphetamine-induced death of various monoaminergic neuronal cells, suggesting that methamphetamine neurotoxicity in monoaminergic cells is related, at least in part, to induction of PAG608 expression.

Adrenomedullin Gene Delivery Protects Against Cerebral Ischemic Injury by Promoting Astrocyte Migration and Survival

Adrenomedullin (AM) has been shown to protect against ischemia/reperfusion-induced myocardial infarction and apoptosis. In the present study, we examined the potential neuroprotective action of delayed AM gene transfer in cerebral ischemia. Three days after a 1-hr occlusion of the middle cerebral artery (MCAO), rats were injected intravenously with adenovirus harboring human AM cDNA. The experiment was terminated 7 days after MCAO. AM gene transfer significantly reduced cerebral infarct size compared with that of rats before virus injection and compared with that of rats injected with control virus. The expression of recombinant human AM was identified in ischemic brain by immunostaining. Morphological analyses showed that AM gene transfer enhanced the survival and migration of astrocytes into the ischemic core. Cerebral ischemia markedly increased astrocyte apoptosis, and AM gene delivery significantly reduced apoptosis to near normal levels as seen in sham control rats. Similarly, in primary cultured astrocytes, AM stimulated cell migration and inhibited hypoxia/reoxygenation-induced apoptosis. The effects of AM on both migration and apoptosis were abolished by calcitonin gene-related peptide [CGRP(8-37)], an AM receptor antagonist. Enhanced cell survival after AM gene transfer was accompanied by markedly increased cerebral nitric oxide and Bcl-2 levels, as well as Akt and GSK-3beta phosphorylation, but reduced NADPH oxidase activity and superoxide production. Inactivation of GSK-3beta by phosphorylation led to reduced GSK-3beta activity and caspase- 3 activation. These results indicate that exogenous AM provides neuroprotection against cerebral ischemia injury by enhancing astrocyte survival and migration and inhibiting apoptosis through suppression of oxidative stress-mediated signaling events.

Human neural stem/progenitor cells, expanded in long-term neurosphere culture, promote functional recovery after focal ischemia in Mongolian gerbils

Transplantation of human neural stem cells (NSCs) is a promising potential therapy for neurologic dysfunctions after the hyperacute stage of stroke in humans, but large amounts of human NSCs must be expanded in long-term culture for such therapy. To determine their possible therapeutic potential for human stroke, human fetal neural stem/progenitor cells (NSPCs) (i.e., neurosphere-forming cells) were isolated originally from forebrain tissues of one human fetus, and expanded in long-term neurosphere culture (exceeding 24 weeks), then xenografted into the lesioned areas in the brains of Mongolian gerbils 4 days after focal ischemia. Sensorimotor and cognitive functions were evaluated during the 4 weeks after transplantation. The total infarction volume in the NSPC-grafted animals was significantly lower than that in controls. Approximately 8% of the grafted NSPCs survived, mainly in areas of selective neuronal death, and were costained with antibodies against neuronal nuclei antibody (NeuN), microtubule associated protein (MAP-2), glial fibrillary acidic protein (GFAP), and anti-2'3' cyclic nucleotide 3'-phosphodiesterase (CNPase). Synaptic structures between NSPCs-derived neurons and host neurons were observed. Furthermore, gradual improvement of neurologic functions was observed clearly in the NSPC-grafted animals, compared to that in controls. Human NSPCs, even from long-term culture, remarkably improved neurologic functions after focal ischemia in the Mongolian gerbil, and maintained their abilities to migrate around the infarction, differentiate into mature neurons, and form synapses with host neuronal circuits. These results indicate that in vitro-expanded human neurosphere cells are a potential source for transplantable material for treatment of stroke.

Protective effect of green tea polyphenol EGCG against neuronal damage and brain edema after unilateral cerebral ischemia in gerbils

Previous studies have demonstrated that a green tea polyphenol, (-)-epigallocatechine gallate (EGCG), has a potent free radical scavenging and antioxidant effect. Glutamate leads to excitotoxicity and oxidative stress, which are important pathophysiologic responses to cerebral ischemia resulting in brain edema and neuronal damage. We investigated the effect of EGCG on excitotoxic neuronal damage in a culture system and the effect on brain edema formation and lesion after unilateral cerebral ischemia in gerbils. In vitro, excitotoxicity was induced by 24-hr incubation with N-methyl-D-aspartate (NMDA; 10 microM), AMPA (10 microM), or kainate (20 microM). EGCG (5 microM) was added to the culture media alone or with excitotoxins. We examined malondialdehyde (MDA) level and neuronal viability to evaluate the effect of EGCG. In vivo, unilateral cerebral ischemia was induced by occlusion of the right common carotid artery for 30, 60, or 90 min and followed by reperfusion of 24 hr. Brain edema, MDA, and infarction were examined to evaluate the protective effect of EGCG. EGCG (25 or 50 mg/kg, intraperitoneally) was administered twice, at 30 min before and immediately after ischemia. EGCG reduced excitotoxin-induced MDA production and neuronal damage in the culture system. In the in vivo study, treatment of gerbils with the lower EGCG dose failed to show neuroprotective effects; however, the higher EGCG dose attenuated the increase in MDA level caused by cerebral ischemia. EGCG also reduced the formation of postischemic brain edema and infarct volume. These results demonstrate EGCG may have future possibilities as a neuroprotective agent against excitotoxicity-related neurologic disorders such as brain ischemia.

Ischemic neuronal death in the rat hippocampus: the calpain-calpastatin-caspase hypothesis

Inappropriate imbalances between proteases and protease inhibitors are known to occur under cerebral ischemia and neurodegenerative processes, and could be contributors to various diseases that are characterized by excessive (ischemia, AIDS) or inadequate (cancer, autoimmunity) cell death. For instance, calpain is activated in various necrotic and apoptotic conditions, whereas caspase-3 is only activated in neuronal apoptosis. Caspases and calpains are cysteine proteases that require proteolytic cleavage for activation. The substrates cleaved by caspases include cytoskeletal and associated proteins, kinases, members of the Bcl-2 family of apoptosis-related proteins, presenilins, and DNA-modulating enzymes. Calpain substrates include cytoskeletal and associated proteins, kinases and phosphatases, membrane receptors and transporters, and steroid receptors. This article provides a review of the properties of caspases and calpains, their roles in cell death pathways following cerebral ischemia, and the substrates upon which they act. Because calpain inhibitors and caspase inhibitors appear to protect brain tissue by distinct mechanisms in cerebral ischemia, the possible therapeutic interactions between these drugs in a well-defined rodent model of global ischemia are briefly discussed and documented.

Caspase inhibitors as anti-inflammatory and antiapoptotic agents

The striking efficacy of Z-VAD-fmk in the various animal models presented above may reflect its ability to inhibit multiple enzymes including caspases. In accord with this, more selective, reversible inhibitors usually show low efficacy in multifactorial models such as ischaemia, but may offer some protection against NMDA-induced excitotoxicity and hepatitis. Importantly, caspase inhibitors may exhibit significant activity in vivo even when they are applied post insult. As far as the CNS is concerned, the first systemically active inhibitors have emerged. Functional recovery could be achieved in some ischaemia models, but long-term protection by caspase inhibitors is still being questioned. Recent developments in drug design enabled the first caspase inhibitors to enter the clinic. Although initially directed towards peripheral indications such as rheumatoid arthritis, caspase inhibitors will no doubt eventually be used to target CNS disorders. For this purpose the peptidic character of current inhibitors will have to be further reduced. Small molecule, nonpeptidic caspase inhibitors, which have appeared recently, indicate that this goal can be accomplished. Unfortunately, many fundamental questions still remain to be addressed. In particular, the necessary spectrum of inhibitory activity required to achieve the desired effect needs to be determined. There is also a safety aspect associated with prolonged administration. Therefore, the next therapeutic areas for broader-range caspase inhibitors are likely to involve acute treatment. Recent results with synergistic effects between MK-801 and caspase inhibitors in ischaemia suggest that caspase inhibitors may need to be used in conjunction with other drugs. It can be expected that, in the near future, research on caspases and their inhibitors will remain a rapidly developing area of biology and medicinal chemistry. More time, however, may be needed for the first caspase inhibitors to appear on the market.

The p53-activated gene, PAG608, requires a zinc finger domain for nuclear localization and oxidative stress-induced apoptosis

The p53-activated gene PAG608, which encodes a nuclear zinc finger protein, is a p53-inducible gene that contributes to p53-mediated apoptosis. However, the mechanisms by which PAG608 is involved in the apoptosis of neuronal cells are still obscure. In this study, we demonstrated that expression of p53 was induced by 100 microm 6-hydroxydopamine (6-OHDA), accompanied by increased PAG608 expression in PC12 cells. On the other hand, transient or permanent transfection of antisense PAG608 cDNA into PC12 cells significantly prevented apoptotic cell death induced by 100 microm 6-OHDA or 200 microm hydrogen peroxide but not by 250 microm 1-methyl-4-phenylpyridinium ion. The 6-OHDA-induced activation of caspase-3, DNA fragmentation, loss of mitochondrial membrane potential, and induction of p53 and Bax were also prevented in PC12 cells that stably expressed antisense PAG608 cDNA. These results suggest that PAG608 is associated with the apoptotic pathway induced by these oxidative stress-generating reagents, upstream of the collapse in the mitochondrial membrane potential in PC12 cells. Interestingly, transient transfection with PAG608 cDNA increased p53 expression in both PC12 cells and B65 cells, indicating that PAG608 induced by p53 is able to induce p53 expression in these cells inversely. Furthermore, transient transfection of a truncated mutant PAG608 cDNA, lacking the first zinc finger domain, inhibited 6-OHDA-induced cell death and altered the nuclear and nucleolar localization of wild-type PAG608 in PC12 cells. These results suggest that PAG608 may induce or regulate p53 expression and translocate to the nucleus and nucleolus using its first zinc finger domain during oxidative stress-induced apoptosis of catecholamine-containing cells.

A catalytic antioxidant (AEOL 10150) attenuates expression of inflammatory genes in stroke

Oxidative stress is a major source of injury from cerebral ischemia and reperfusion. We hypothesized that a catalytic antioxidant AEOL 10150 [manganese (III) meso-tetrakis (di-N-ethylimidazole) porphyrin] would attenuate changes in brain gene expression in a mouse model of transient middle cerebral artery occlusion (MCAO). C57BL/6J mice were subjected to either sham surgery or 60 min of right MCAO. AEOL 10150 or phosphate-buffered saline was given intravenously 5 min after onset of reperfusion (n = 6 per group). Six hours later, parenchyma within the MCA distribution was harvested. RNA from the six brains in each group was pooled and mRNA expression determined using an Affymetrix murine MG_U74A v. 2.0 expression microarray. Each experiment was performed three times. The largest changes in expression occurred in stress response and inflammatory genes such as heat shock protein, interleukin-6, and macrophage inflammatory protein-2. Treatment with AEOL 10150 attenuated only the increase in expression of inflammatory genes. This suggests that AEOL 10150 protects brain by attenuating the immune response to ischemia and reperfusion.

Relationship between metabolic dysfunctions, gene responses and delayed cell death after mild focal cerebral ischemia in mice

The evolution of brain injury was examined in mice subjected to focal cerebral ischemia as induced by 30 min of intraluminar thread occlusion of the middle cerebral artery, followed by 3 h to 3 days of reperfusion. Metabolic dysfunctions were studied by 3H-leucine autoradiography for the measurement of cerebral protein synthesis and by regional ATP bioluminescent imaging. Metabolic changes were compared with responses of the genes c-fos, c-jun, heat-shock protein gene (hsp)72, p53-activated gene (pag)608 and caspase-3, which were investigated by in situ hybridization histochemistry and immunocytochemistry, and correlated with the degree of DNA fragmentation, as assessed by the terminal TdT-mediated dUTP-biotin nick end labeling method. Intraluminar thread occlusion led to a reproducible reduction of cerebral laser Doppler flow to 20-30% of control. Thread withdrawal was followed by a short-lasting post-ischemic hyperperfusion to approximately 120%. In non-ischemic control animals, fractional protein synthesis values of 0.81+/-0.26 and 0.94+/-0.23 were obtained. Thread occlusion resulted in a suppression of protein synthesis throughout the territory of the middle cerebral artery after 3 h of reperfusion (0.04+/-0.08 in caudate-putamen and 0.14+/-0.19 in somatosensory cortex, P<0.05). Protein synthesis partly recovered in the cortex after 24 h and 3 days (0.71+/-0.40 and 0.63+/-0.26, respectively), but remained suppressed in the caudate-putamen (0.14+/-0.22 and 0.28+/-0.28). Regional ATP levels did not show any major disturbances at the reperfusion times examined. Thread occlusion resulted in a transient increase of c-fos mRNA levels in ischemic and non-ischemic parts of the cortex and caudate-putamen at 3 h after ischemia, which suggests that spreading depressions were elicited in the tissue. At the same time, c-jun and hsp72 mRNAs were elevated only in ischemic brain areas showing inhibition of protein synthesis. C-fos and c-jun responses completely disappeared within 24 h of reperfusion. Hsp72 mRNA levels remained elevated in the cortex after 24 h, but decreased to basal values in the caudate-putamen. Twenty-four hours after reperfusion, pag608 and caspase-3 mRNA levels increased in the caudate-putamen, where protein synthesis rates were still reduced, and remained elevated even after 3 days. However, pag608 and caspase-3 mRNA levels did not increase in the cortex, where protein synthesis recovered. After 24 h and 3 days, functionally active p20 fragment of caspase-3 was detected in the caudate-putamen, closely associated with the appearance of DNA fragmented cells. Neither activated caspase-3 nor DNA fragmentation were noticed in the cortex.In summary, the suppression of protein synthesis is reversible in the ischemia-resistant cortex following 30 min of thread occlusion in mice, but persists in the vulnerable caudate-putamen. In the caudate-putamen, apoptotic programs are induced, closely in parallel with the manifestation of delayed cell death. Thus, the recovery of protein synthesis may be a major factor influencing tissue survival after transient focal ischemia.