Myh7 is a classic biomarker for cardiac remodeling and a potential target to attenuate cardiomyocyte (CM) hypertrophy. This study aimed to identify the dominant function of Myh7 after birth and determine whether its removal would affect CM maturation or contribute to reversal of pathological hypertrophy phenotypes. The CASAAV (CRISPR/Cas9-AAV9-based somatic mutagenesis) technique was used to deplete Myh6 and Myh7, and an AAV dosage of 5 × 109 vg/g was used to generate a mosaic CM depletion model to explore the function of Myh7 in adulthood. CM hypertrophy was induced by transverse aortic constriction (TAC) in Rosa26Cas9-P2A-GFP mice at postnatal day 28 (PND28). Heart function was measured by echocardiography. Isolated CMs and in situ imaging were used to analyze the structure and morphology of CM. We discovered that CASAAV successfully silenced Myh6 and Myh7 in CMs, and early depletion of Myh7 led to mild adulthood lethality. However, the Myh7 PND28-knockout mice had normal heart phenotype and function, with normal cellular size and normal organization of sarcomeres and T-tubules. The TAC mice also received AAV-Myh7-Cre to produce Myh7-knockout CMs, which were also of normal size, and echocardiography demonstrated a reversal of cardiac hypertrophy. In conclusion, Myh7 has a role during the maturation period but rarely functions in adulthood. Thus, the therapeutic time should exceed the period of maturation. These results confirm Myh7 as a potential therapeutic target and indicate that its inhibition could help reverse CM hypertrophy.
Keywords: CASAAV; Cardiomyocyte hypertrophy; Myh6; Myh7.