Abstract 3711: Role of Adiponectin in Modulating Oxidative-Stress Induced Cardiomyocyte Autophagy
Introduction: Reactive oxygen species (ROS) induce autophagy, a highly regulated process of protein and organelle degradation. Autophagy serves as a survival mechanism in response to stressors, but if excessive results in type-II programmed cell death. The mTOR signaling pathway negatively regulates autophagy, while AMPK phosphorylation leads to mTOR inhibition, thereby promoting autophagy. Adiponectin (APN), an adipose-derived adipokine, mediates cardioprotective effects, although little is known about the role of APN in regulating cardiomyocyte autophagy. We tested the hypothesis that APN protects against ROS-induced autophagy in cardiomyocytes and the mechanisms involved in the regulation of ROS-induced cardiomyocyte autophagy by APN.
Methods: Isolated adult rat ventricular myocytes (ARVM) were pretreated with APN (30μg/mL, 18hrs) followed by H2O2 exposure (1mM). Following 6hrs of H2O2 exposure, autophagy was determined by assessing protein expression of LC3II/LC3I ratio (indicative of autophagosome formation) and other autophagy-related proteins (n=4 –5/experiment). Phosphorylated mTOR and AMPK expression were also measured.
Results: Pretreatment of ARVM with APN had no effect on LC3II/LC3I expression vs. control. H2O2 induced LC3I to LC3II conversion by a factor of 3.4±1.0 (P<0.05 vs. control), which was abrogated by pre-treatment with APN by 44.5±10% (P<0.05 vs. control). Neither H2O2 nor APN significantly affected ATG5, ATG7, or Beclin-1 expression, also key autophagy-related proteins. Interestingly, H2O2 increased AMPK phosphorylation by 48.9±6.0% (P<0.001 vs. control), while pretreatment with APN decreased this phosphorylation by 25.8±4.4% (P<0.01 vs. H2O2 only-treated ARVM). H2O2 decreased mTOR phosphorylation by 31±7.8% (P<0.01 vs. control), which was restored by APN pretreatment by 48±14% (P<0.05 vs. H2O2 only-treated ARVM).
Conclusion: These data suggest that ROS induces autophagy through an AMPK/mTOR-dependent mechanism in ARVM. APN ameliorates ROS-induced cardiomyocyte autophagy, in part through inhibition of H2O2-induced AMPK phosphorylation. This finding provides insight into the anti-oxidant potential of APN, and underscores its importance in the protection against cardiovascular diseases.