Impaired Autophagosome Clearance Contributes to Cardiomyocyte Death in Ischemia-Reperfusion Injury
Background—In myocardial ischemia, induction of autophagy via the AMP-induced protein kinase (AMPK) pathway is protective, whereas reperfusion stimulates autophagy with BECLIN-1 upregulation, and is implicated in causing cell death. We examined flux through the macro-autophagy pathway as a determinant of the discrepant outcomes in cardiomyocyte cell death in this setting
Methods and Results—Reversible left anterior descending coronary artery ligation was performed in mice with cardiomyocyte-restricted expression of GFP-tagged microtubule associated protein light chain-3 (LC3) to induce ischemia (120 minutes) or ischemia-reperfusion (IR, 30-90 minutes) with saline or chloroquine (CQ) pretreatment (n=4/group). Autophagosome clearance, assessed as the ratio of punctate LC3 abundance in saline to CQ treated samples was markedly impaired with IR as compared with sham controls. Reoxygenation increased cell death in neonatal rat cardiomyocytes (NRCMs) as compared with hypoxia alone; markedly increased autophagosomes but not autolysosomes (assessed as punctate dual fluorescent mCherry-GFP tandem tagged LC3 expression); and impaired clearance of polyglutamine aggregates, indicating impaired autophagic flux. The resultant autophagosome accumulation was associated with increased reactive oxygen species (ROS) and mitochondrial permeabilization leading to cell death, which was attenuated by cyclosporine A pretreatment. Hypoxia-reoxygenation injury was accompanied by ROS-mediated BECLIN-1 upregulation and reduction in Lysosome Associated Membrane Protein-2 (LAMP2), a critical determinant of autophagosome-lysosome fusion. Restoration of LAMP2 levels synergizes with partial BECLIN-1 knockdown to restore autophagosome processing and attenuate cell death following hypoxia-reoxygenation.
Conclusions—Ischemia-reperfusion injury impairs autophagosome clearance mediated in part by ROS-induced decline in LAMP2 and upregulation of BECLIN-1, contributing to increased cardiomyocyte death.
- Received May 5, 2011.
- Accepted May 4, 2012.
- Copyright © 2012, American Heart Association, Inc. All rights reserved. Unauthorized use prohibited