Combined and individual mitochondrial HSP60 and HSP10 expression in cardiac myocytes protects mitochondrial function and prevents apoptotic cell deaths induced by simulated ischemia-reoxygenation

Background-The mitochondrial heat-shock proteins HSP60 and HSP10 form a mit ochondrial chaperonin complex, and previous studies have shown that their i ncreased expression exerts a protective effect against ischemic injury when cardiac myocytes are submitted to simulated ischemia, The more detailed me chanisms by which such a protective effect occurs are currently unclear. We wanted to determine whether HSP60 and HSP10 could exert a protection again st simulated ischemia and reoxygenation (SI/RO)-induced apoptotic cell deat h and whether such protection results from decreased mitochondrial cytochro me c release and caspase-3 activation and from the preservation of ATP leve ls by preservation of the electron transport chain complexes. In addition, we explored whether increased expression of HSP60 or HSP10 by itself exerts a protective effect. Methods and Results-We overexpressed HSP60 and HSP10 together or separately in rat neonatal cardiac myocytes using an adenoviral vector and then subje cted the myocytes to SI/RO. Cell death and apoptosis in myocytes were quant ified by parameters such as enzyme release, DNA fragmentation, and caspase- 3 activation. Overexpression of the combination of HSP60 and HSP10 and of H SP60 or HSP10 individually protected myocytes against apoptosis. This prote ction is accompanied by decreases in mitochondrial cytochrome c release and in caspase-3 activity and increases in ATP recovery and activities of comp lex III and IV in mitochondria after SI/RO. Conclusions-These results suggest: that mitochondrial chaperonins HSP60 and HSP10 in combination or individually play an important role in maintaining mitochondrial integrity and capacity for ATP generation, which are the cru cial factors in determining survival of cardiac myocytes undergoing ischemi a/reperfusion injury.