Abstract Body (Do not enter title and authors here): Background: Hypertrophic cardiomyopathy (HCM) is an autosomal dominant genetic disorder and the leading cause of sudden death in young individuals under 35 years of age. Mutation in the myosin heavy chain 7 (MYH7) gene, which encodes the contractile protein β-myosin heavy chain (β-MHC), represent a major genetic determinant of HCM. In this study, we identified a novel MYH7 T265I mutation in a familial HCM proband and his father, the functional consequences of which were previously unknown.
Methods: The CRISPR/Cas9 technology was used to construct heterozygous mutant (Myh7^T265I/+) and homozygous mutant (Myh7^T265I/T265I) mice. These mice were assigned to a sedentary group and an 8-week moderate exercise group. The effect of the gene mutation on cardiac function was evaluated using nuclear magnetic resonance, echocardiography, Masson, WGA, qRT-PCR, western blot and transmission electron microscopy. The Myh7^T265I/+-AC16 cells were constructed to investigate the effects of gene mutation on myocardial cell function and signaling pathways, thereby elucidating its pathogenic mechanism.
Results: The study family presented with two confirmed HCM cases and a history of multiple sudden death. Whole exome sequencing identified a novel MYH7 T265I mutation in the proband and affected family members. Bioinformatics analysis predicted that MYH7^T265I/+ variant disrupts hydrogen bond formation in β-MHC, impairing its function and reducing ATP-binding affinity. In 8-week-old mutant mice, left ventricular wall thickness was increased, but no significant changes were observed in ejection fraction, diastolic function or fibrosis. However, mitochondrial dysfunction was already evident. By 6 months of age, both Myh7^T265I/+ and Myh7^T265I/T265I mice developed myocardial hypertrophy, and progressive mitochondrial damage—phenotypes that were ameliorated by exercise intervention. Cardiac hypertrophy became markedly more severe by 12 months of age. In vitro studies in AC16 cardiomyocytes confirmed that Myh7^T265I/+ induced hypertrophic growth. Functional assays revealed decreased ATP levels, calcium overload, and mitochondrial structural abnormalities, including cristae rupture and vacuolation.
Conclusion: The novel MYH7 T265I mutation induces HCM pathogenesis through a cascade of energy metabolism dysfunction (reduced ATP production), calcium homeostasis disruption, and mitochondrial damage. Notably, moderate exercise attenuated the HCM phenotype in mutant mice.