Purpose: Although cAMP is one of the most well-known signaling molecules produced by β-adrenergic receptors (β-AR) stimulation, its mechanism of action in cardiac hypertrophy is not fully understood. Here, we investigated the involvement of the cAMP sensor Epac1 in β-AR-induced cardiac remodeling using knock-out mice for Epac1 (Epac1-/-) and cardiotropic adeno-associated viruses encoding Epac1 (AAV9-Epac1).
Methods and Results: Epac1-/- was obtained by crossbreeding the LoxP-Epac1 mouse line with the Desmin-CRE-recombinase line. We found that Epac1-/- mice displayed an improved cardiac contractile function and were protected against cardiac hypertrophy following chronic infusion of a non-selective β-AR agonist, Isoprenaline (ISO) for 28 days. Histological analysis of AAV9-Epac1 treated mice revealed a significant increase in cardiomyocyte size indicating that AAV9-increased Epac1 expression cardiac promoted cardiac myocyte hypertrophy. Interestingly, activation of β-AR-Epac1 pathway induced the accumulation of ubiquitinated proteins as well as the expression of a proteotoxic stress sensor, p62/SQSTM1 during hypertrophy. Subsequent autophagy was triggered as shown by the up-regulation of autophagy markers (Beclin 1, LC3-II) revealed by immunoblot. ISO- induced autophagy was prevented both in Epac1-/- mice and rat neonatal ventricular myocytes pre-treated with a specific Epac1 pharmacological inhibitor, CE3F4. Of particular interest, pharmacological inhibition of autophagy using 3-methyladenine or down-regulation of Beclin 1 or Atg5 by specific siRNA potentiated Epac1 hypertrophic effects.
Conclusions: Altogether these data show that Epac1 is involved in pathological cardiac remodelling during chronic β-AR activation. Autophagy antagonizes Epac1-induced cardiac hypertrophy.