AMPK activators, like resveratrol or metformin, inhibit pathological cardiac hypertrophy. However, despite evidence for their anti-hypertrophic effect, it seems that this phenomenon is mainly circumstantial. Indeed, those agents induce a rather non-specific AMPK activation by increasing the AMP/ATP ratio or by mimicking AMP. Hence, the aim of this study was to test the ability of a more specific AMPK activator, called A-769662, to prevent phenylephrine (PE)-induced hypertrophy in cultured neonatal rat ventricular myocytes (NRVM) and in adult rat ventricular myocytes (ARVM).

Alpha-actinin immunostaining, radio labelled amino acid incorporation, nuclear factor of activated T-cells (NFAT) activity, hypertrophy-linked gene expression and protein phosphorylation were analysed to determine NRVM hypertrophy. Cell surface area and protein phosphorylation were analysed to define ARVM hypertrophy.

Using dose–response experiments and genetic AMPK silencing, we show here that A-769662 is able to prevent the development of PE-induced NRVM hypertrophy by an AMPK-dependant mechanism. This hypertrophy prevention correlates with the modification of AMPK-related key regulators of cardiac hypertrophy including ~50% lower protein synthesis (p<0.05) and a 3-fold decreased phosphorylation of p70S6K (p<0.05) but also a significant decrease in ERK1/2 (~50%, p<0.05) and NFAT signalling (~90%, p<0.05) when high concentrations of A-769662 were used in combination with PE vsPE alone. However, while low dose of A-769662 (12.5μM) still efficientlyM) efficiently prevents PE-induced NRVM hypertrophy (p<0.05) none of the known AMPK downstream targets are modified at this dose, showing a discrepancy between hypertrophy prevention and known AMPK target regulation. The same discrepancy was observed in ARVM at low dose of A-769662.

Collectively, our results using low dose of A-769662 suggest a yet to be identified mechanism by which AMPK can regulate cardiac hypertrophy.