Abstract 1256: Reperfusion But Not Ischemia Initiates Autophagy And Inhibition Of Autophagy Protects The Heart From Reperfusion Injury
The exact role of autophagy in myocardial ischemia/reperfusion injury remains unknown. We aimed to test if and how autophagy contributes to the pathogenesis of ischemia/reperfusion injury in the heart. Isolated rat hearts were subjected to 30 min regional ischemia followed by 2 h of reperfusion or sham operation. Myocardial biopsies were taken from ischemic area. Ischemia did not increase the LC3-II to LC3-I ratio (LC3-II/LC3-I), an established marker of autophagy, compared to the sham group. In contrast, LC3-II/LC3-I was markedly increased upon reperfusion (1.4, 2.2, 2.9, and 2.2-fold increases at 10, 30, 60, and 120 min of reperfusion; n = 6)). These observations suggest that reperfusion but not ischemia triggers autophagy. In support of this finding, electron microscopic analysis revealed a significant increase in the number of cytoplasmic autophagosome in myocardium upon reperfusion but not during ischemia. To confirm that the above observations were of autophagic origin, we tested if 3-methyladenine (3-MA), a classic inhibitor of autophagy, prevents reperfusion-induced LC3-II/LC3-I increase. Our data showed that 3-MA given at reperfusion prevented LC3-II/LC3-I increases, assuring that reperfusion indeed enhances autophagic activity. Interestingly, 3-MA also reduced infarct size in rat hearts subjected to 30 min ischemia plus 2 h of reperfusion (27.4 ± 0.8 % in 3-MA vs. 37.9 ± 3.1 in control %; p < 0.05; n = 6), suggesting that autophagy during reperfusion is detrimental and prevention of autophagy results in cardioprotection. To investigate the pathway that leads to autophagy during reperfusion, we determined the expression levels of Beclin-1, an important mammalian autophagy protein. Neither ischemia nor reperfusion increased Beclin-1 expression, implying that this protein is not involved in reperfusion-induced autophagy. Taken together, reperfusion but not ischemia initiates autophagy in isolated rat hearts and autophagy may play an important role in the pathogenesis of reperfusion injury. Inhibition of autophagy may serve as a unique strategy for prevention of reperfusion injury.