Beyond Glycogen Storage: AMPKγ2 Regulates Cardiac Hypertrophy and Electrophysiology via Myosin Interaction

Variants in PRKAG2 cause hypertrophic cardiomyopathy (HCM) and conduction disturbances. While prior studies associated PRKAG2 -related hypertrophy with increased glycogen storage, many HCM 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 (Tg ^WT ) or pathogenic variant (Tg ^R299Q ) Prkag2 cDNA under a myocardium-specific promoter, 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 HCM phenotypes. Cardiomyocyte glycogen was elevated in adult but not embryonic hearts. Despite the absence of glycogen accumulation at 6-day post-fertilization, Tg ^R299Q hearts showed electrical abnormalities, including reduced conduction velocity and prolonged action potential and Ca ²⁺ transient durations. We observed decreased AMPK phosphorylation in the Tg ^R299Q hearts. However, AMPK activation did not rescue the electrophysiological abnormalities in Tg ^R299Q . Proximity ligation assays and co-immunoprecipitation identified a physical interaction between AMPKγ2 and myosin, enhanced by the R299Q variant and accompanied by increased AMPKγ2 localization to the myofilament. Na⁺/Ca²⁺ exchanger (NCX) inhibition increased Ca ²⁺ duration and diastolic Ca ²⁺ in Tg ^WT but not Tg ^R299Q hearts, indicating reduced free cytosolic Ca ²⁺ 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 APD 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 Ca ²⁺ 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.