β-Adrenergic Receptor Stimulation and Activation of Protein Kinase A Protect Against α1-Adrenergic–Mediated Phosphorylation of Protein Kinase D and Histone Deacetylase 5

IntroductionChronic activation of β1-adrenergic receptor (β1-AR) signaling can have deleterious effects on the heart, and animal models overexpressing β1-ARs develop a dilated cardiomyopathy and heart failure. In the classic β-AR pathway, receptor occupancy by an agonist results in increased cyclic adenosine monophosphate (cAMP) levels and activation of protein kinase A (PKA). However, the role of PKA-dependent signaling in the development and progression of cardiomyopathies and heart failure is controversial, because β-AR signal transduction is generally desensitized in the failing heart and PKA activity is not increased.Methods and ResultsNeonatal rat ventricular myocytes were acutely (15 minutes) or chronically (48 hours) treated with isoproterenol, and phosphorylation of protein kinase D (PKD) and histone deacetylase 5 (HDAC5) was measured. Acute β1-AR stimulation or expression of constitutively active (CA) PKA reduced α1-adrenergic-mediated phosphorylation of HDAC5 and PKD by activation of a phosphatase. Overexpression of CA-PKA also reduced α1-adrenergic–mediated increased expression of contractile protein fetal isoforms and promoted repression of adult isoforms, but had no effect on α1-adrenergic–mediated cellular hypertrophy.ConclusionsThese data indicate that the PKA-dependent arm of β-AR signaling can be antihypertrophic and presumably beneficial, through dephosphorylation of PKD and HDAC5 and reduction of hypertrophic fetal isoform gene expression.