Protein Kinase Cδ Activation Induces Apoptosis in Response to Cardiac Ischemia and Reperfusion Damage

Abstract

Heart attacks caused by occlusion of coronary arteries are often treated by mechanical or enzymatic removal of the occlusion and reperfusion of the ischemic heart. It is now recognized that reperfusion per se contributes to myocardial damage, and there is a great interest in identifying the molecular basis of this damage. We recently showed that inhibiting protein kinase C␦ (PKC␦) protects the heart from ischemia and reperfusion-induced damage. Here, we demonstrate that PKC␦ activity and mitochondrial translocation at the onset of reperfusion mediates apoptosis by facilitating the accumulation and dephosphorylation of the pro-apoptotic BAD (Bcl-2-associated death promoter), dephosphorylation of Akt, cytochrome c release, PARP (poly(ADPribose) polymerase) cleavage, and DNA laddering. Our data suggest that PKC␦ activation has a critical proapoptotic role in cardiac responses following ischemia and reperfusion.

δPKC participates in the endoplasmic reticulum stress-induced response in cultured cardiac myocytes and ischemic heart

“…δPKC levels were normalized using calnexin, an ER resident chaperone protein. Since δPKC is known to translocate to mitochondria [13,15], we confirmed that mitochondria are not present in this ER fraction using Western blotting against the mitochondrial protein, adenine nucleotide translocase (ANT) [17] (Fig. 3A; ANT is detected in the mitochondrial fraction, though Fig.…”

“…Using dominant negative mutants of δPKC, broad spectrum inhibitors or a specific δPKC antagonist peptide, δPKC was further demonstrated to be a mediator of apoptosis [13,18,37,38]. Few studies have reported an antiapoptotic role for δPKC [39,40].…”

“…Various apoptotic stimuli induce δPKC translocation to mitochondria [13,15,28]. Because we found that δPKC regulates ER stress-mediated signaling events, we next determined whether δPKC directly translocates to the ER under these conditions.…”

“…Together, these data show that active δPKC translocates to ER upon Tm-induced ER stress. δPKC translocation to the ER mediates, at least in part, ER stress response of the myocardium in a model of ischemia-reperfusion injury Inhibition of δPKC protects the heart from ischemia-reperfusion injury partly through reducing mitochondria-mediated cell death [13,16]. Increasing evidence suggests that ischemia/ reperfusion in the heart also activates the ER stress response resulting in cellular injury [5,8,9,[30][31][32].…”

“…δPKC is also a substrate of caspase 3, which activates this enzyme by proteolysis [12]. We previously demonstrated that myocardial ischemiareperfusion results in δPKC translocation to cardiac mitochondria, inducing a pro-apoptotic response including release of cytochrome-c, caspase 3 and 9 activation and inhibition of PARP degradation, all hallmarks of mitochondria-dependent apoptosis [13]. In the present study, we demonstrate for the first time that δPKC also translocates to the ER following ischemia and reperfusion in whole hearts as well as following tunicamycin treatment of cultured cardiac myocytes.…”