Crosstalk between AMPK activation and angiotensin II- induced hypertrophy in cardiomyocytes: the role of mitochondria

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 24hrs in the presence or absence of metformin (AMPK agonist), losartan [AngII type 1 receptor (AT1R) blocker], N-nitro-L-arginine methyl ester (L-NAME, pan-NOS inhibitor), splitomicin (SIRT1 inhibitor) or pifithrin- (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 ((m)) 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.