Heat-Shock Protein 70 Attenuates Caspase-3 Activation and DNA Fragmentation Following Focal Cerebral Ischemia

ABSTRACT

BACKGROUND: Recently, HSP70 has been shown to act as an inhibitor of apoptotic pathways in the cell culture following heat shock; however, little information is available on the mechanism of neuroprotection after cerebral ischemia. In this study, our purpose is to investigate whether the HSP70 protein can protect apoptotic cell death after focal cerebral ischemia. METHODS: hsp70.1 knockout (KO) and wild-type (WT) mice were subjected to transient middle cerebral artery occlusion for 2 hours. At 22 hours, we measured infarction volumes, and detected DNA fragmentation with TUNEL staining. HSP70 and hsp70.1 mRNA expression were analyzed by Western blots and Northern blots, respectively. Caspase-3 activation was examined with Western blots and caspase-3 activity assay. RESULTS: hsp70.1 mRNA was not detected in hsp70.1 KO mice after ischemia, and HSP70 expression was markedly suppressed in KO mice versus WT mice. The infarction volume was significantly larger in the KO (82.1 +/- 9.5 mm3) than in the WT (58.4 +/- 10.3 mm3; p<0.05) 24hours later. 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, as determined by Western blotting and caspase-3 activity assay. TUNEL-positive apoptotic cells were much higher in the KO (1.94 +/- 0.61 X 10(3)/mm2) than in the WT (1.05 +/- 0.35 X 10(3)/mm2; p<0.05) in the cortex, but not in the striatum. CONCLUSIONS: We conclude that that HSP70 acts as a strong inhibitor of apoptosis via blocking caspase-3 activation following focal cerebral ischemia.