Abstract 032: Impaired Cardiac Autophagy In Metabolic Syndrome Despite Intact AMPK And mTOR Signaling
Objective: We previously reported that basal cardiac autophagy is lower in the setting of metabolic syndrome (MetS) (obesity, dyslipidemia, insulin resistance) and is associated with attenuation of cardioprotection after ischemic preconditioning. To understand the underlying mechanisms and exclude effects of the extracellular milieu, we investigated the roles of two major cellular energy sensing pathways, adenosine monophosphate-activated protein kinase (AMPK), and mammalian target of rapamycin (mTOR), using adult rat ventricular cardiomyocytes (ARVM) isolated from Sprague Dawley (SD) and Zucker obese (ZO) rats.
Methods: ARVM were cultured overnight and subjected to nutrient deprivation (1 hr), or treated with 1µM phenformin (Ph), an AMPK activator, or 5µM rapamycin (Rap), an mTOR inhibitor. Immunoblotting was used to measure phosphorylation of AMPK, p70S6 kinase (a downstream target of mTOR), LC3-I, -II, and p62 (autophagic clearance).
Results: In ARVM from SD rats, starvation or Ph increased p-AMPK and decreased p-p70S6K, accompanied by increased LC3-II and 50% reduction in p62. Rapamycin decreased phosphorylation of p70S6K, increased LC3-II and decreased p62. In ZO ARVM, Ph and Rap also activated AMPK and inhibited mTOR; however, LC3-II was unchanged (Fig.) and p62 clearance was blunted.
Conclusions: Despite appropriate activation of AMPK and inhibition of mTOR, autophagy is impaired in ARVM from ZO rats. These cells retain the MetS phenotype, facilitating efforts to delineate the molecular basis of impaired autophagy and vulnerability to ischemia/reperfusion injury in MetS. This could lead to new approaches to myocardial protection in at-risk patients.
- © 2013 by American Heart Association, Inc.