Enhancing Macroautophagy Protects against Ischemia/Reperfusion Injury in Cardiac Myocytes

• Published in: The Journal of biological chemistry 2006-10, Vol.281 (40), p.29776-29787
• Main Authors: Hamacher-Brady, Anne, Brady, Nathan R., Gottlieb, Roberta A.
• Format: Article
• Language: English
• Subjects: Animals; Apoptosis - physiology; Autophagy - physiology; Cell Line; Heart Atria - cytology; Heart Atria - pathology; Mice; Myocardial Ischemia - pathology; Myocardial Ischemia - prevention & control; Myocardial Reperfusion Injury - pathology; Myocardial Reperfusion Injury - prevention & control; Myocytes, Cardiac - pathology; Myocytes, Cardiac - physiology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M603783200

Cardiac myocytes undergo programmed cell death as a result of ischemia/reperfusion (I/R). One feature of I/R injury is the increased presence of autophagosomes. However, to date it is not known whether macroautophagy functions as a protective pathway, contributes to programmed cell death, or is an irrelevant event during cardiac I/R injury. We employed simulated I/R of cardiac HL-1 cells as an in vitro model of I/R injury to the heart. To assess macroautophagy, we quantified autophagosome generation and degradation (autophagic flux), as determined by steady-state levels of autophagosomes in relation to lysosomal inhibitor-mediated accumulation of autophagosomes. We found that I/R impaired both formation and downstream lysosomal degradation of autophagosomes. Overexpression of Beclin1 enhanced autophagic flux following I/R and significantly reduced activation of pro-apoptotic Bax, whereas RNA interference knockdown of Beclin1 increased Bax activation. Bcl-2 and Bcl-xL were protective against I/R injury, and expression of a Beclin1 Bcl-2/-xL binding domain mutant resulted in decreased autophagic flux and did not protect against I/R injury. Overexpression of Atg5, a component of the autophagosomal machinery downstream of Beclin1, did not affect cellular injury, whereas expression of a dominant negative mutant of Atg5 increased cellular injury. These results demonstrate that autophagic flux is impaired at the level of both induction and degradation and that enhancing autophagy constitutes a powerful and previously uncharacterized protective mechanism against I/R injury to the heart cell.