Effects of Hsp70.1 gene knockout on the mitochondrial apoptotic pathway after focal cerebral ischemia

Background and Purpose - Murine heat-shock protein 70 (HSP70) protein, which is produced from 2 genes, hsp70.1 and hsp70.3, is known to protect the brain against ischemic injury. However, little information is available on the antiapoptotic mechanism of HSP70.1 protein after cerebral ischemia. To evaluate the role of HSP70.1 protein in ischemia, we analyzed the mitochondrial apoptotic pathway using hsp70.1 knockout ( KO) mice and their wild-type (WT) mice. Methods - hsp70.1 KO and WT mice underwent focal ischemia for 120 minutes. DNA fragmentation was evaluated by TUNEL staining. Cytochrome c release and the activation of caspase-3 were analyzed by Western blotting and immunohistochemistry. Results - hsp70.1 mRNA was not detected in hsp70.1 KO mice after ischemia, and HSP70 protein expression was markedly suppressed versus WT mice. KO mice showed a significantly greater infarction volume and DNA fragmentation in the cortex than WT mice at 24 hours after ischemia. At 8 hours, cytochrome c release into the cytoplasm was markedly higher in KO mice than in WT mice. Caspase-3 activation was also significantly enhanced in KO mice versus WT mice, as evidenced by higher levels of activated caspase-3 and cleaved gelsolin. Conclusions - These findings suggest that the deletion of the hsp70.1 gene increases cytochrome c release into the cytoplasm and subsequent caspase-3 activation, thereby exacerbating apoptosis after focal cerebral ischemia.