Release of mitochondrial cytochrome c and activation of cytosolic caspasesinduced by myocardial ischaemia

It has previously been shown that apoptosis is increased in ischaemic/reper fused heart. However, little is known about the mechanism of induction of a poptosis in myocardium during ischaemia. We investigated whether prolonged myocardial ischaemia causes activation of caspases and whether this activat ion is related to cytochrome c release from mitochondria to cytosol during ischaemia. Using an in vitro model of heart ischaemia, we show that 60 min ischaemia leads to a significant accumulation of cytochrome c in the cytoso l and a decrease in mitochondrial content of cytochrome c but not cytochrom e a. The release of cytochrome c from mitochondria was accompanied by activ ation of caspase-3-like proteases (measured by cleavage of fluorogenic pept ide substrate DEVD-amc) and a large increase in number of cells with DNA st rand breaks (measured by TUNEL staining). Caspase-1-like proteases (measure d by YVAD-amc cleavage) were not activated during ischaemia. Addition of 14 muM cytochrome c to cytosolic extracts prepared from control hearts induce d ATP-dependent activation of caspase-3-like protease activity. Our data su ggest that extended heart ischaemia can cause apoptosis mediated by release of cytochrome c from mitochondria and subsequent activation of caspase-3. (C) 2001 Elsevier Science BN. All rights reserved.