Cardiomyocyte PKA Ablation Enhances Basal Contractility While Eliminates Cardiac β-Adrenergic Response Without Adverse Effects on the Heart

Abstract

Rationale: PKA (Protein Kinase A) is a major mediator of β-AR (β-adrenergic) regulation of cardiac function, but other mediators have also been suggested. Reduced PKA basal activity and activation are linked to cardiac diseases. However, how complete loss of PKA activity impacts on cardiac physiology and if it causes cardiac dysfunction have never been determined. Objectives: We set to determine how the heart adapts to the loss of cardiomyocyte PKA activity and if it elicits cardiac abnormalities. Methods and Results: (1) Cardiac PKA activity was almost completely inhibited by expressing a PKA inhibitor peptide in cardiomyocytes (cPKAi) in mice; (2) cPKAi reduced basal phosphorylation of 2 myofilament proteins (TnI [troponin I] and cardiac myosin binding protein C), and one longitudinal SR (sarcoplasmic reticulum) protein (PLB [phospholamban]) but not of the sarcolemmal proteins (Cav1.2 α1c and PLM [phospholemman]), dyadic protein RyR2, and nuclear protein CREB (cAMP response element binding protein) at their PKA phosphorylation sites; (3) cPKAi increased the expression of CaMKII (Ca 2+ /calmodulin-dependent kinase II), the Cav1.2 β subunits and current, but decreased CaMKII phosphorylation and CaMKII-mediated phosphorylation of PLB and RyR2; (4) These changes resulted in significantly enhanced myofilament Ca 2+ sensitivity, prolonged contraction, slowed relaxation but increased myocyte Ca 2+ transient and contraction amplitudes; (5) Isoproterenol-induced PKA and CaMKII activation and their phosphorylation of proteins were prevented by cPKAi; (6) cPKAi abolished the increases of heart rate, and cardiac and myocyte contractility by a β-AR agonist (isoproterenol), showing an important role of PKA and a minimal role of PKA-independent β-AR signaling in acute cardiac regulation; (7) cPKAi mice have partial exercise capability probably by enhancing vascular constriction and ventricular filling during β-AR stimulation; and (8) cPKAi mice did not show any cardiac functional or structural abnormalities during the 1-year study period. Conclusions: PKA activity suppression induces a unique Ca 2+ handling phenotype, eliminates β-AR regulation of heart rates and cardiac contractility but does not cause cardiac abnormalities.

Mechanisms of ryanodine receptor 2 dysfunction in heart failure

“…of RYR2 at both Ser2808 and Ser2030 in isoprenaline-treated hearts 5 . Moreover, transgenic mice expressing RYR2-Ser2030Ala have an incomplete β-adrenergic response 6 .…”

PRKAR1A deficiency impedes hypertrophy and reduces heart size

“…adenylyl cyclase, cAMP, cardiomyopathy, catecholamine, myocardial development 1 | INTRODUCTION Myocardial 3',5'-cyclic adenosine monophosphate (cAMP)-dependent protein kinase (protein kinase A, PKA) is a key regulator of heart rate and cardiac contractility, through phosphorylation of multiple calcium-handling proteins involved in excitation-contraction coupling (Zhang et al, 2019). The PKA holoenzyme consists of two regulatory and two catalytic subunits.…”

Hepatic PKA inhibition accelerates the lipid accumulation in liver

“…In our mouse model, the overexpression of PKAi-GFP successfully inhibited PKA activity in the liver, thus allowing us for the precise and comprehensive study of the roles of PKA in liver tissue. In future studies, it is possible to study the effects of different degrees of PKA inhibitions on the development of NAFLD by screening out transgenic mouse strains with different abundance of PKAi expression, and even achieve the functional PKA ablation model through extremely high expression as reported recently [43].…”