A transgenic mouse model to study a novel PRKAG2 mutation (K475E) causing infantile‐onset hypertrophic cardiomyopathy

Background PRKAG2 encodes the γ2 subunit isoform of AMPK, a heterotrimeric enzyme with major roles in regulation of energy metabolism in response to cellular stress. Mutations in PRKAG2 have been implicated in hypertrophic cardiomyopathy (HCM). We identified a novel PRKAG2 mutation in a neonate with prenatal onset of HCM noted on a 27‐week prenatal ultrasound. Molecular testing for HCM revealed a de novo PRKAG2 mutation (K475E). We have demonstrated that overexpressing the K475E mutant in vitro leads to activation of cell growth pathway. We also have demonstrated that K475E mutation led to increases in cell size and area which can be reversed by rapamycin. Objective To developed transgenic mouse models to confirm K475E‐induced cardiac phenotype, determine the downstream signaling pathways involved, and test targeted therapy for K475E‐induced HCM using rapamycin. Methods Human WT and K475E DNA constructs were inserted into a pBluescript vector with the mouse α‐myosin heavy chain promoter. Transgenic mice with the cardiac‐specific overexpression of WT (TgWT) or the K475E mutation (TgK475E) were established by pronucleus microinjection. Survival curve and cardiac hypertrophy were examined and cardiac function changes were monitored by echocardiography. Results Male TgK475E mice were prone to sudden death with only 50% survived by 13‐week old. Hypertrophy in TgK475E mice was confirmed by their significant increases in heart weight/body weight and heart weight/tibial length ratios versus the non‐transgenic control and TgWT mice. Histology revealed large vacuoles and high glycogen content in TgK475E myocytes throughout the ventricles. Echocardiography confirmed that LV mass dramatically increased in TgK475E mice starting from 5 weeks of age. At 6‐week old, ejection fraction (EF) was more than 70% in TgK475E mice, which then decreased to less than 30% by 18‐week old. Fraction shortening (FS) in TgK475E mice showed similar trend. In contrast, EF and FS in non‐transgenic control and TgWT mice were not significantly changed. Compared to nontransgenic control and TgWT mice, Vd, Vs, LIVD (d) and LIVD (s) were all significantly increased in TgK475E mice starting at 7‐week of age. 4‐week Rapamycin treatment dramatically decreased the ratios of heart weight/body weight and heart weight/tibia length in TgK475E mice. Conclusion These results indicate the transgenic mouse model reflects the early onset phenotype of the K475E mutation‐induced HCM. Targeted therapeutic strategy with mTOR inhibition is partially effective and should be studied further. Support or Funding Information This study was supported by NIH P30GM114750 (J.P., Y.‐T.T.) and Oh‐Zopfi Research Award, Women & Infant's Hospital (Y.‐T.T.). We thank the COBRE in Perinatal Biology Core and Kilguss Core Facility for the excellent molecular and microscopy supports.