Effects of the MYH7 R369Q Dilated Cardiomyopathy-causing Mutation on Myosin Crossbridge Kinetics and Cardiomyocyte Contractility

Abstract

The R369Q mutation in the MYH7 gene is a likely pathogenic variant of familial dilated cardiomyopathy (DCM). This mutation is located in loop 4 of β-myosin heavy chain actin-binding surface and may alter actin-myosin interaction that facilitates cardiomyocyte contraction. There are limited insights into the nature and implications of this mutation on the contractile system within a cardiomyocyte that results in hypocontractility. To better understand the biochemical and biophysical effects of R369Q mutation, this study utilized CRISPR/Cas9-edited R369Q homozygous human induced pluripotent stem cell-derived cardiomyocytes to investigate its effect on the myosin crossbridge cycle kinetics and cell contractility. The rate of ATP binding to isolated myofibrils, as measured using the stopped-flow technique, was observed to be slower for the R369Q myosin variant. As contractility is driven by transient rise of intracellular calcium, there is no significant difference between the calcium transient of healthy and R369Q mutant cardiomyocytes. These effects may contribute to the development of DCM and highlight the importance of understanding the molecular consequences of genetic mutations.