cAMP-mediated β-adrenergic signaling negatively regulates Gq-coupled receptor-mediated fetal gene response in cardiomyocytes

The treatment with β-blockers causes an enhancement of the norepinephrine-induced fetal gene response in cultured cardiomyocytes. Here, we tested whether the activation of cAMP-mediated β-adrenergic signaling antagonizes α1-adrenergic receptor (AR)-mediated fetal gene response. To address this question, the fetal gene program, of which atrial natriuretic peptide (ANP) and the β-isoform of myosin heavy chain are classical members, was induced by phenylephrine (PE), an α1-AR agonist. In cultured neonatal rat cardiomyocytes, we found that stimulation of β-ARs with isoproterenol, a β-AR agonist, inhibited the fetal gene expression induced by PE. Similar results were also observed when cardiomyocytes were treated with forskolin (FSK), a direct activator of adenylyl cyclase, or 8-CPT-6-Phe-cAMP, a selective activator of protein kinase A (PKA). Conversely, the PE-induced fetal gene expression was further upregulated by H89, a selective PKA inhibitor. To evaluate whether these results could be generalized to Gq-mediated signaling and not specifically to α1-ARs, cardiomyocytes were treated with prostaglandin F2α, another Gq-coupled receptor agonist, which is able to promote fetal gene expression. This treatment caused an increase of both ANP mRNA and protein levels, which was almost completely abolished by FSK treatment. The capability of β-adrenergic signaling to regulate the fetal gene expression was also evaluated in vivo conditions by using β1- and β2-AR double knockout mice, in which the predominant cardiac β-AR subtypes are lacking, or by administering isoproterenol (ISO), a β-AR agonist, at a subpressor dose. A significant increase of the fetal gene expression was found in β1- and β2-AR gene deficient mice. Conversely, we found that ANP, β-MHC and skACT mRNA levels were significantly decreased in ISO-treated hearts. Collectively, these data indicate that cAMP-mediated β-adrenergic signaling negatively regulates Gq cascade activation-induced fetal gene expression in cultured cardiomyocytes and that this inhibitory regulation is already operative in the mouse heart under physiological conditions.