Beta 3 adrenoreceptors protect from hypertrophic remodelling through AMP-activated protein kinase and autophagy

Aims The abundance of beta 3-adrenergic receptors (beta 3-ARs) is upregulated in diseased human myocardium. We previously showed that cardiac-specific expression of beta 3-AR inhibits the hypertrophic response to neurohormonal stimulation. Here, we further analysed signalling pathways involved in the anti-hypertrophic effect of beta 3-AR. Methods and results In vitro hypertrophic responses to phenylephrine (PE) were analysed in neonatal rat ventricular myocytes (NRVM) infected with a recombinant adenovirus expressing the human beta 3-AR (AdVh beta 3). We confirmed results in mice with cardiomyocyte-specific moderate expression of human beta 3-AR (beta 3-TG) and wild-type (WT) littermates submitted to thoracic transverse aortic constriction (TAC) for 9 weeks. We observed a colocalization of beta 3-AR with the AMP-activated protein kinase (AMPK) both in neonatal rat and in adult mouse cardiomyocytes. Treatment of NRVM with PE induced hypertrophy and a decrease in phosphorylation of Thr172-AMPK (/2, P = 0.0487) and phosphorylation of Ser79-acetyl-CoA carboxylase (ACC) (/2.6, P = 0.0317), inducing an increase in phosphorylated Ser235/236 S6 protein (x2.5, P = 0.0367) known to be involved in protein synthesis. These effects were reproduced by TAC in WT mice but restored to basal levels in beta 3-AR expressing cells/mice. siRNA targeting of AMPK partly abrogated the anti-hypertrophic effect of beta 3-AR in response to PE in NRVM. Concomitant with hypertrophy, autophagy was decreased by PE, as measured by microtubule-associated protein 1 light chain 3 (LC3)-II/LC3-I ratio (/2.6, P = 0.0010) and p62 abundance (x3, P = 0.0016) in NRVM or by TAC in WT mice (LC3-II/LC3-I ratio: /5.4, P = 0.0159), but preserved in human beta 3-AR expressing cells and mice, together with reduced hypertrophy. Conclusions Cardiac-specific moderate expression of beta 3-AR inhibits the hypertrophic response in part through AMPK activation followed by inhibition of protein synthesis and preservation of autophagy. Activation of the cardiac beta 3-AR pathway may provide future therapeutic avenues for the modulation of hypertrophic remodelling.