AMPKγ2 Regulates Cardiac Hypertrophy and Arrhythmias via Interacting With Myosin

Variants in PRKAG2 cause hypertrophic cardiomyopathy and conduction disturbances. Although prior studies associated PRKAG2-related hypertrophy with increased glycogen storage, many hypertrophic cardiomyopathy phenotypes remain unexplained. We aimed to uncover how PRKAG2 variants induce myocyte hypertrophy and electrical changes during early cardiac development.

We generated transgenic zebrafish expressing wild-type or pathogenic variant Prkag2 under a myocardium-specific promoter, Tg(cmcl2:Prkag2^WT) (Tg^WT) and Tg(cmcl2: Prkag2^R299Q) (Tg^R299Q), respectively, and examined cardiac electrophysiology, contractile function, and cytoarchitecture during cardiogenesis and in adult hearts.

Tg^R299Q fish showed hypertrophic cardiomyocytes and progressive contractile abnormalities, recapitulating human hypertrophic cardiomyopathy phenotypes. Cardiomyocyte glycogen was elevated in adult but not embryonic hearts. Despite the absence of glycogen accumulation at 6 days post-fertilization, Tg^R299Q hearts showed electrical abnormalities, including reduced conduction velocity and prolonged action potential and Ca²⁺ transient durations, compared to Tg^WT and wild-type (Tübingen/AB [TuAB]). We observed decreased AMPK (AMP-activated protein kinase) phosphorylation in the Tg^R299Q hearts. However, AMPK activation did not rescue the electrophysiological abnormalities in Tg^R299Q. Proximity ligation assays and coimmunoprecipitation identified a physical interaction between AMPKγ2 and myosin, enhanced by the R299Q variant and accompanied by increased AMPKγ2 localization to the myofilament. NCX (Na⁺/Ca²⁺ exchanger) inhibition increased Ca²⁺ duration and diastolic Ca²⁺ in Tg^WT but not Tg^R299Q hearts, indicating reduced free cytosolic Ca²⁺ for NCX-mediated extrusion in Tg^R299Q. These findings suggest that enhanced AMPKγ2-myosin interaction may promote myofilament Ca²⁺ retention, thereby prolonging Ca²⁺ transient duration and action potential duration in the mutant. Notably, the myosin inhibitor mavacamten reduced AMPKγ2-myosin interaction in Tg^R299Q hearts, and both mavacamten and vmhcl knockdown rescued the early electrophysiological abnormalities.

The PRKAG2 variant altered cardiac excitability, contractility, and Ca²⁺ handling during cardiogenesis, independent of glycogen accumulation. Enhanced interactions between AMPKγ2 and myosin contributed to these early changes. Our study revealed a novel link between cellular energy sensing and contractile machinery, with therapeutic potential for modulating contractile function in cardiomyopathies.