Effects of changes in myosin biomechanics on canonical and non-canonical signaling and HCM phenotypes.

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Myosin heavy chain 7 (MYH7) mutations are among the most commonly found in patients with hypertrophic cardiomyopathy (HCM). To address cellular responses to biomechanical alternations due to mutations in MYH7, we employed human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) as an in vitro model and deeply phenotyped the transcriptional changes in these cells using single cell RNA sequencing (scRNAseq). We profiled hiPSC-CMs carrying heterozygous G265E mutant and control wild type MYH7 alleles at 30 and 60 day after differentiation and found potential disruption in hypertrophic gene expression as well as genes regulating mitochondrial metabolism. Intriguingly, the gene expression phenotype in these mutant lines appear somewhat subtle and vary considerably from line to line and differentiation batch to batch. To assess whether the mutant cells are more susceptible to physiological stress, we treated day 30 hiPSC-CMs with isoproterenol and observed an increased in their metabolic gene defect that was corroborated using a Seahorse metabolic assay. Given the more subtle phenotype of MYH7 G256E heterozygous mutant line, we considered whether a homozygous mutant would provide a more robust phenotype manifestation at the transcriptional level. To address this, we profiled day 30 hiPSC-CM from a MYH R369Q homozygous mutant line and found a significantly greater consistency in transcriptional phenotype among different lines and batches of differentiation. In summary, our work revealed the power of MYH7 mutation-specific hiPSC-CMs as an in vitro model of HCM and the ability of scRNAseq to deeply phenotype these cells to reveal their aberrant cellular signaling and metabolic response. When combined with a comprehensive understanding of MYH7 mutation effects at the single molecular and whole tissue level, we hope to enable future development of novel therapy against HCM.