Abstract 1259: Ischemic Preconditioning Of the Myocardium Augments Autophagy in Association with BAG-1 Protein
Autophagy is an intracellular event in which cell digests its own constituents. Since cardiac myocytes are terminally differentiated, they maintain homeostasis mainly by activation of degrading pathways, namely, autophagy. Inefficient or lack of autophagy causes poor performance of the myocardium. Moreover, the mechanism of autophagy remains largely unknown. BAG-1 (Bcl2-associated athanogene-1) is multifunctional protein that protects cells from a range of apoptotic stimuli. In this study, we found that 30 min of ischemia and 2 hr of reperfusion (IR) in isolated rat heart or 3 hr of hypoxia and 2 hrs of reoxygenation in myocardium derived H9c2 myoblasts slightly elevated the proteins expression of BAG-1, autophagosomal membrane specific protein MAP1LC3-II, and Beclin1, a marker of autophagy. The above proteins were significantly increased in both cytosol and nuclear fractions when preconditioning (PC; four cyclic episodes of 5 min of ischemia/hypoxia and 10 min of reperfusion/reoxygenation) the myocardium preceded IR. Our co-immunoprecipitation as well as co-immunofluorescence analyses revealed that BAG-1 was bound with MAP1LC3-II, where the binding was enhanced in PC heart. BAG-1 was also found to be bound with Beclin-1 and Hsp70. Further, treatment of rats with either rapamycin, an inducer of autophagy (0.25 mg/kg; i.p.) or Wortmannin, a proven inhibitor of autophgy (15 μg/kg; i.p.) given 30 min before isolation of heart, which were then subjected to IR with or without PC. Rapamycin treatment in the preconditioned heart enhanced the protein expression of BAG-1, Beclin-1 and MAP1LC3-II; however, rapamycin treatment did not alter the above protein expressions in IR injury. Treatment with Wortmannin abolished the preconditioning-induced induction of BAG-1, Beclin-1, and MAP1LC3-II. Wortmannin treatment did not alter the above proteins in IR injury. In conclusion, our results show that autophagy plays a crucial role in the PC-induced protection of the myocardium against IR injury by inducing the survival of cells in association with BAG-1 protein.