Dynamic regulation of Apoptosis, Autophagy, and Necroptosis in Ischemic Postconditioning Cardioprotection: The Importance of Adiponectin

Abstract

Apoptosis, autophagy, and necroptosis are three major forms of programmed cell death during myocardial ischemia reperfusion (IR) injury. Induction of apoptosis and necroptosis exacerbate while induction of autophagy attenuates myocardial IR injury. Ischemic postconditioning (IPo) protects the hearts against myocardial IR injury which requires the activation of adiponectin (APN). IPo by reducing apoptosis and/or inducing autophagy confers cardioprotection. However, the dynamic changes of these three forms of programmed cell death (i.e., apoptosis, autophagy, and necroptosis) during myocardial IR and IPo is unclear and their interplay with APN is unknown. This study aims to investigate the changes of apoptosis, autophagy and necroptosis during myocardial IR and IPo and their association with APN.Adult male mice were either sham-operated or subjected to myocardial IR (30 minutes of coronary occlusion followed, respectively, by 0, 1, 2, 4, 12, 36 hours of reperfusion) without or with IPo (3 cycles of 10 seconds of ischemia and 10 seconds of reperfusion, applied immediately at the onset of reperfusion). Cell necrosis was evaluated by detecting plasma lactate dehydrogenase (LDH) release. Myocardial apoptosis was assessed by measuring levels of protein expression of Caspase3, Cleaved-caspase3, Bax, Bcl-2. Necroptosis was assessed by measuring protein expression of receptor interacting protein (RIP)1 and RIP3. Autophagy was assessed by examining protein expression of LC3II, LC3I and p62.Myocardial cell necrosis was progressively and significantly increased from 2 to 12 hours of reperfusion and peaked at 12 hours evidenced as continuously elevated LDH release. Myocardial apoptosis became more and more serious from 0 to 12 hours of reperfusion and peaked at 12 hours of reperfusion manifested as increasing levels of protein expression of Cleaved-caspase 3/ Caspase3 and Bax/Bcl-2 ratio. Myocardial autophagy was significantly down-regulated from 1 to 4 hours of reperfusion and recovered from 12 hours to 36 hours of reperfusion evidenced by reduction of LC3II/LC3I and increase of p62 protein expression. Necroptosis was progressively and significantly increased from 0 to 12 hours of reperfusion and peaked at 4 hours of reperfusion evidenced by increases of RIP3 and RIP1 protein expression. These myocardial IR-induced cell deaths were associated with increases of cardiac APN protein expression at 2 and 4 hours of reperfusion. IPo significantly reduced cell necrosis/necroptosis and apoptosis, but increased autophagy (All P<0.05 vs. corresponding IR group). IPo significantly increased cardiac APN protein expression from 0 to 4 hours of reperfusion (All P<0.05 vs. corresponding IR group). It is concluded that during myocardial IR, reduction of autophagy and increase of necroptosis are induced and processed earlier than the increase of apoptosis, which jointly lead to increase of cell death (cell necrosis) at the late stage of reperfusion. IPo attenuates cell death in myocardial IR by increasing cardiac APN at the early stage of reperfusion.