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

We generated transgenic zebrafish expressing wild-type (TgWT) or pathogenic variant (TgR299Q) Prkag2 cDNA under a myocardium-specific promoter, and examined cardiac electrophysiology, contractile function, and cytoarchitecture during cardiogenesis and in adult hearts. Results: TgR299Q 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, TgR299Q hearts showed electrical abnormalities, including reduced conduction velocity and prolonged action potential and Ca2+ transient durations. We observed decreased AMPK phosphorylation in the TgR299Q hearts. However, AMPK activation did not rescue the electrophysiological abnormalities in TgR299Q.

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 Ca2+ duration and diastolic Ca2+ in TgWT but not TgR299Q hearts, indicating reduced free cytosolic Ca2+ for NCX-mediated extrusion in TgR299Q. 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 TgR299Q hearts, and both mavacamten and vmhcl knockdown rescued the early electrophysiological abnormalities. Conclusions: 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.