ARC inhibits cytochrome c release from mitochondria and protects against hypoxia-induced apoptosis in heart-derived H9c2 cells

Ischemia induces apoptosis as well as necrosis of cardiac myocytes. We rece ntly reported the cloning of a cDNA chat encodes an apoptotic inhibitor, AR C, that is expressed predominantly in cardiac and skeletal muscle, in the p resent study, we examined the ability of ARC to protect rat embryonic heart -derived H9c2 cells from apoptosis induced by hypoxia, a component of ische mia, We found that H9c2 cells express ARC and that exposure to hypoxia subs tantially reduces ARC expression while inducing apoptosis. Transfected H9c2 cells in which cytosolic ARC protein levels remain elevated during hypoxia were significantly more resistant to hypoxia-induced apoptosis than parent al H9c2 cells or H9c2, cells transfected with a control vector. Loss of end ogenous ARC in the cytosol of H9c2 cells was associated with translocation of ARC from the cytosol to intracellular membranes, release of cytochrome c from the mitochondria, activation of caspase-3, poly(ADP-ribose)polymerase (PARP) cleavage, and DNA fragmentation. All of these events were inhibited in H9c2 cells overexpressing ARC when compared with control cells, In cont rast, caspase inhibitors prevented PARP cleavage but not cytochrome c relea se, suggesting that exogenously expressed ARC acts upstream of caspase acti vation in this model of apoptosis, These results demonstrate that ARC can p rotect heart myogenic H9c2 cells from hypoxia-induced apoptosis, and that A RC prevents cytochrome c release by acting upstream of caspase activation, perhaps at the mitochondrial level. The full text, of this article is avail able at http://.www.circresaha.org.