Roles of phospho-GSK-3β in myocardial protection afforded by activation of the mitochondrial K_ATP channel

Abstract 

The aim of this study was to determine the roles of glycogen synthase kinase-3β (GSK-3β) in cardioprotection by activation of the mitochondrial ATP-sensitive K⁺ channel (mK_ATP channel). In isolated rat hearts, an mK_ATP activator, diazoxide, and a GSK-3β inhibitor, SB216763, similarly limited infarct size and the combination of these agents did not afford further protection. The protection by pre-ischemic treatment with diazoxide was abolished by inhibition of protein kinase C-ε (PKC-ε) or phosphatidylinositol-3-kinase (PI3K) upon reperfusion. Infusion of a GSK-3β inhibitor (LiCl), but not diazoxide, during reperfusion limited infarct size. Inhibition of PKC-ε or PI3K did not affect the protection by LiCl. Diazoxide infusion alone did not induce GSK-3β phosphorylation. However, diazoxide infusion before ischemia increased mitochondrial phospho-GSK-3β level and reduced cyclophilin-D (CypD) binding to adenine nucleotide translocase (ANT) at 10min after reperfusion. This diazoxide-induced GSK-3β phosphorylation was inhibited by blockade of the mK_ATP channel before ischemia and by blockade of PKC-ε, PI3K or the adenosine A2b receptor at the time of reperfusion. Inhibition of GSK-3β by LiCl during reperfusion increased phospho-GSK-3β but had no significant effect on CypD–ANT binding. These results suggest that GSK-3β phosphorylation at the time of reperfusion by a PKC-ε, PI3K- and A2b receptor-dependent mechanism contributes to prevention of myocardial necrosis by pre-ischemic activation of the mK_ATP channel. Inhibition of CypD–ANT interaction may contribute to mK_ATP-induced myocardial protection, though it is not the sole mechanism of phospho-GSK-3β-mediated cytoprotection.

Keywords: Glycogen synthase kinase-3ß, Mitochondria, ATP-sensitive potassium channel, Infarct size, Reperfusion injury