ABSTRACT
AMP kinase (AMPK) plays an important role in the regulation of energy metabolism in cardiac cells. Furthermore, activation of AMPK protects the heart from myocardial infarction and heart failure. The present study examines whether or not AMPK affects the peroxisome proliferator-activated receptor-α (PPARα)/mitochondria pathway in response to acute oxidative stress in cultured cardiomyocytes. Cultured H9c2 rat embryonic cardioblasts were exposed to H2O2-induced acute oxidative stress in the presence or absence of metformin, compound C (AMPK inhibitor), GW6471 (PPARα inhibitor), or A-769662 (AMPK activator). Results showed that AMPK activation by metformin reverted oxidative stress-induced inactivation of AMPK and prevented oxidative stress-induced cell death. In addition, metformin attenuated reactive oxygen species generation and depolarization of the inner mitochondrial membrane. The antioxidative effects of metformin were associated with the prevention of mitochondrial DNA damage in cardiomyocytes. Coimmunoprecipitation studies revealed that metformin abolished oxidative stress-induced physical interactions between PPARα and cyclophilin D (CypD), and the abolishment of these interactions was associated with inhibition of permeability transition pore formation. The beneficial effects of metformin were not due to acetylation or phosphorylation of PPARα in response to oxidative stress. In conclusion, this study demonstrates that the protective effects of metformin-induced AMPK activation against oxidative stress converge on mitochondria and are mediated, at least in part, through the dissociation of PPARα-CypD interactions, independent of phosphorylation and acetylation of PPARα and CypD.
Subject(s)
Adenylate Kinase/metabolism , Antioxidants/pharmacology , Cyclophilins/metabolism , Enzyme Activators/pharmacology , Metformin/pharmacology , Myocytes, Cardiac/drug effects , Oxidative Stress/drug effects , PPAR alpha/metabolism , Adenylate Kinase/antagonists & inhibitors , Animals , Biphenyl Compounds , Cell Death/drug effects , Cell Line , Dose-Response Relationship, Drug , Enzyme Activation , Membrane Potential, Mitochondrial/drug effects , Mitochondria, Heart/drug effects , Mitochondria, Heart/enzymology , Mitochondrial Membrane Transport Proteins/metabolism , Mitochondrial Permeability Transition Pore , Myocytes, Cardiac/enzymology , Myocytes, Cardiac/pathology , Oxidants/pharmacology , PPAR alpha/antagonists & inhibitors , Protein Binding , Protein Kinase Inhibitors/pharmacology , Pyrones/pharmacology , Rats , Reactive Oxygen Species/metabolism , Signal Transduction/drug effects , Thiophenes/pharmacologyABSTRACT
AMP-kinase (AMPK) activation reduces cardiac hypertrophy, although underlying molecular mechanisms remain unclear. In this study, we elucidated the anti-hypertrophic action of metformin, specifically, the role of the AMPK/eNOS/p53 pathway. H9c2 rat cardiomyocytes were treated with angiotensin II (AngII) for 24 hrs in the presence or absence of metformin (AMPK agonist), losartan [AngII type 1 receptor (AT1R) blocker], Nω-nitro-L-arginine methyl ester (L-NAME, pan-NOS inhibitor), splitomicin (SIRT1 inhibitor) or pifithrin-α (p53 inhibitor). Results showed that treatment with metformin significantly attenuated AngII-induced cell hypertrophy and death. Metformin attenuated AngII-induced activation (cleavage) of caspase 3, Bcl-2 down-regulation and p53 up-regulation. It also reduced AngII-induced AT1R up-regulation by 30% (P < 0.05) and enhanced AMPK phosphorylation by 99% (P < 0.01) and P-eNOS levels by 3.3-fold (P < 0.01). Likewise, losartan reduced AT1R up-regulation and enhanced AMPK phosphorylation by 54% (P < 0.05). The AMPK inhibitor, compound C, prevented AT1R down-regulation, indicating that metformin mediated its effects via AMPK activation. Beneficial effects of metformin and losartan converged on mitochondria that demonstrated high membrane potential (Δψm ) and low permeability transition pore opening. Thus, this study demonstrates that the anti-hypertrophic effects of metformin are associated with AMPK-induced AT1R down-regulation and prevention of mitochondrial dysfunction through the SIRT1/eNOS/p53 pathway.