It is well-established that a brief period of global brain ischemia causes delayed cell death in hippocampal CA1 pyramidal neurons days after reperfusion in animals and humans. Although numerous factors have been indicated in this phenomenon, the mechanisms underlying this delayed neuronal cell death are still poorly understood. We have demonstrated that cerebral infarction and neurological deficits are significantly reduced in transgenic mice over-expressing CuZn-superoxide dismutase (Sod1) activity after acute focal stroke, whereas vasogenic edema, infarction and neurological deficits are exacerbated in mutant mice deficient in SOD1 or in mitochondrial manganese SOD (Sod2) activities. But the role of these antioxidant enzymes on the delayed hippocampal neuronal injury after global ischemia is still unknown. Our hypothesis is that oxidative stress induced by mild ischemia and reperfusion causes the delayed hippocampal neuronal injury and death through pathways involving both necrosis and apoptosis, and that the latter is exacerbated when mitochondrial dysfunction occurs during reperfusion. It is our aim to test our hypothesis using transgenic mice over-expressing Sod1 and Sod2 activities and knockout mutant mice that contain no SOD1 -/- (homozygous), half (heterozygous, Sod1 +/-) or SOD2 +/- activities. In order to dissect out the role of mitochondrial dysfunction in ischemic brain injury, we will study the cytosolic distribution of mitochondrial dysfunction in ischemic brain injury, we will study the cytosolic distribution of mitochondrial proteins cytochrome c and cytochrome c oxidase in ischemic brain tissue. Cytochrome c release from mitochondria has been attributed to the activation of caspase 3 and subsequent apoptosis in cells following exogenous apoptotic stimuli. In order to elucidate the oxidative role of subcellular compartmentation (i.e., cytosolic versus mitochondria) in necrosis and apoptosis, we will generate mice that contain genotypes with combinations of increased Sod1 expression and Sod2 +/- knockout mutants. We will investigate whether increased cytosolic CuZnSOD (SOD1) activity will reduce neuronal apoptosis in Sod2 +/- knockout mice that are vulnerable to transient forebrain ischemia. We believe these are unique and fresh approaches that will provide insights into the oxidative mechanism in mitochondria that underlies apoptosis in delayed hippocampal cell death after global cerebral ischemia and reperfusion.
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