Heterologous desensitization of cardiac β-adrenergic signal via hormone-induced βAR/arrestin/PDE4 complexes

Cardiac beta-adrenergic receptor (beta AR) signalling is susceptible to heterologous desensitization by different neurohormonal stimuli in clinical conditions associated with heart failure. We aim to examine the underlying mechanism of cross talk between beta ARs and a set of G-protein coupled receptors (GPCRs) activated by hormones/agonists. Rat ventricular cardiomyocytes were used to determine heterologous phosphorylation of beta ARs under a series of GPCR agonists. Activation of G(s)-coupled dopamine receptor, adenosine receptor, relaxin receptor and prostaglandin E2 receptor, and G(q)-coupled alpha(1) adrenergic receptor and angiotensin II type 1 receptor promotes phosphorylation of beta(1)AR and beta(2)AR at putative protein kinase A (PKA) phosphorylation sites; but activation of G(i)-coupled alpha(2) adrenergic receptor and activation of protease-activated receptor does not. The GPCR agonists that promote beta(2)AR phosphorylation effectively inhibit beta AR agonist isoproterenol-induced PKA phosphorylation of phospholamban and contractile function in ventricular cardiomyocytes. Heterologous GPCR stimuli have minimal to small effect on isoproterenol-induced beta(2)AR activation and G-protein coupling for cyclic adenosine monophosphate (cAMP) production. However, these GPCR stimuli significantly promote phosphorylation of phosphodiesterase 4D (PDE4D), and recruit PDE4D to the phosphorylated beta(2)AR in a beta-arrestin 2 dependent manner without promoting beta(2)AR endocytosis. The increased binding between beta(2)AR and PDE4D effectively hydrolyzes cAMP signal generated by subsequent stimulation with isoproterenol. Mutation of PKA phosphorylation sites in beta(2)AR, inhibition of PDE4, or genetic ablation of PDE4D or beta-arrestin 2 abolishes this heterologous inhibitory effect. Ablation of beta-arrestin 2 or PDE4D gene also rescues beta-adrenergic stimuli-induced myocyte contractile function. These data reveal essential roles of beta-arrestin 2 and PDE4D in a common mechanism for heterologous desensitization of cardiac beta ARs under hormonal stimulation, which is associated with impaired cardiac function during the development of pathophysiological conditions.