Ischemic Preconditioning Attenuates Myocardial Apoptosis through Regulation of Hypoxia Inducible Factor-1αand Heat Shock Protein 70

Abstract

Ischemic preconditioning (IPC) increases expression of several cardioprotective genes and attenuates myocardial dysfunction after ischemia-reperfusion (IR) injury. However, the precise cellular mechanisms by which IPC confers myocardial protection are incompletely understood. We hypothesized that the beneficial effect of IPC in the heart is due to upregulation of two key transcription factors, Hypoxia Inducible Factor-1α (HIF-1α) and Heat Shock Protein 70 (HSP70). In this study, neonatal rat cardiomyoblasts (H9c2 cells) were subjected to IPC (four cycles of 15-min hypoxia/15-min reoxygenation), followed by 12-hr hypoxia-reoxygenation (HR). HIF-1α and HSP70 expression were measured by ELISA and immunoblot. Apoptosis was assessed by DNA fragmentation and caspase-3 activity. The results showed that IPC induced HIF-1α and HSP70 expression and attenuated apoptosis after 12-hr HR. Pretreatment with DMOG, an HIF-1α activator, showed a similar protective effect as IPC. An HIF-1α inhibitor (CAY10585) or HSP70 inhibitor (KNK437) decreased IPC-induced HIF-1α or HSP70 expression, respectively, and abrogated the anti-apoptotic effect of IPC. In summary, IPC is associated with increased HIF-1α and HSP70 expression and a subsequent decreased apoptosis in neonatal cardiomyoblasts exposed to HR. These results suggest that HIF-1α and HSP70play important roles in IPC-induced cardioprotection, and these endogenous transcription factors may provide a novel therapeutic target to prevent myocardial IR injury in vivo.