Published online before print March 1, 2007, doi: 10.1161/01.RES.0000261924.76669.36
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Submitted on December 1, 2006
Revised on January 31, 2007
Accepted on January 20, 2007
Distinct Roles of Autophagy in the Heart During Ischemia and Reperfusion. Roles of AMP-Activated Protein Kinase and Beclin 1 in Mediating Autophagy
Yutaka Matsui ;
From the Cardiovascular Research Institute (Y.M., H.T., M.A., J.S.), Department of Cell Biology and Molecular Medicine, University of Medicine and Dentistry of New Jersey, New Jersey Medical School, Newark; Departments of Internal Medicine and Microbiology (X.Q., B.L.), University of Texas Southwestern Medical Center, Dallas; Department of Internal Medicine (H.S.), Graduate School of Medicine, University of Tokyo, Japan; and Division of Molecular Medical Science (T.A.), Programs for Biomedical Research, Hiroshima University, Japan.
* To whom correspondence should be addressed. E-mail: Sadoshju{at}umdnj.edu.
Autophagy is an intracellular bulk degradation process for proteins and organelles. In the heart, autophagy is stimulated by myocardial ischemia. However, the causative role of autophagy in the survival of cardiac myocytes and the underlying signaling mechanisms are poorly understood. Glucose deprivation (GD), which mimics myocardial ischemia, induces autophagy in cultured cardiac myocytes. Survival of cardiac myocytes was decreased by 3-methyladenine, an inhibitor of autophagy, suggesting that autophagy is protective against GD in cardiac myocytes. GD-induced autophagy coincided with activation of AMP-activated protein kinase (AMPK) and inactivation of mTOR (mammalian target of rapamycin). Inhibition of AMPK by adenine 9-
-D-arabinofuranoside or dominant negative AMPK significantly reduced GD-induced autophagy, whereas stimulation of autophagy by rapamycin failed to cause an additive effect on GD-induced autophagy, suggesting that activation of AMPK and inhibition of mTOR mediate GD-induced autophagy. Autophagy was also induced by ischemia and further enhanced by reperfusion in the mouse heart, in vivo. Autophagy resulting from ischemia was accompanied by activation of AMPK and was inhibited by dominant negative AMPK. In contrast, autophagy during reperfusion was accompanied by upregulation of Beclin 1 but not by activation of AMPK. Induction of autophagy and cardiac injury during the reperfusion phase was significantly attenuated in beclin 1+/- mice. These results suggest that, in the heart, ischemia stimulates autophagy through an AMPK-dependent mechanism, whereas ischemia/reperfusion stimulates autophagy through a Beclin 1-dependent but AMPK-independent mechanism. Furthermore, autophagy plays distinct roles during ischemia and reperfusion: autophagy may be protective during ischemia, whereas it may be detrimental during reperfusion.
Key words: autophagy • AMP-activated protein kinase (AMPK) • beclin 1 • ischemia/reperfusion
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