Manganese Superoxide Dismutase Mediates the Early Release of Mitochondrial Cytochrome C and Subsequent DNA Fragmentation after Permanent Focal Cerebral Ischemia in Mice

Abstract

Recent studies have shown that release of mitochondrial cytochrome c is a critical step in the apoptosis process. We have reported that cytosolic redistribution of cytochrome cin vivooccurred after transient focal cerebral ischemia (FCI) in rats and preceded the peak of DNA fragmentation. Although the involvement of reactive oxygen species in the cytosolic redistribution of cytochrome cin vitrohas been suggested, the detailed mechanism by which cytochrome c release is mediatedin vivohas not yet been established. Also, the role of mitochondrial oxidative stress in cytochrome c release is unknown. These issues can be addressed using knock-out mutants that are deficient in the level of the mitochondrial antioxidant manganese superoxide dismutase (Mn-SOD). In this study we examined the subcellular distribution of the cytochrome c protein in both wild-type mice and heterozygous knock-outs of the Mn-SOD gene (Sod2 −/+) after permanent FCI, in which apoptosis is assumed to participate. Cytosolic cytochrome c was detected as early as 1 hr after ischemia, and correspondingly, mitochondrial cytochrome c showed a significant reduction 2 hr after ischemia (p< 0.01). Cytosolic accumulation of cytochrome c was significantly higher in Sod2 −/+ mice compared with wild-type animals (p< 0.05).N-benzyloxycarbonyl-val-ala-asp-fluoromethyl ketone (z-VAD.FMK), a nonselective caspase inhibitor, did not affect cytochrome c release after ischemia. A significant amount of DNA laddering was detected 24 hr after ischemia and increased in Sod2 −/+ mice. These data suggest that Mn-SOD blocks cytosolic release of cytochrome c and could thereby reduce apoptosis after permanent FCI.