Metabolic Characterization of HiPSC-CMs derived from a Hypertrophic Cardiomyopathy Patient Harboring the MYH7 p.R403L Variant

Abstract

2 Abstract Hypertrophic cardiomyopathy (HCM) is a severe hypercontractile disorder of the heart affecting 1 in 500 individuals. It is often caused by variants in sarcomere proteins, including the β-myosin heavy chain (MYH7), leading to abnormalities in calcium handling and cellular metabolism. Although the pathogenic variants in MYH7 are linked to mitochondrial dysfunction, the exact mechanism in HCM remains unknown. In this study, we first metabolically matured human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) derived from an HCM patient resembling the HCM phenotype. Hereafter, we functionally characterized our model by examining contractile function and mitochondrial respiration. Additionally, we treated the cells with metabolic inhibitors (oligomycin, carbonyl cyanide-4 (trifluoromethoxy) phenylhydrazone, and rotenone/antimycin A) and enhancers (fenofibrate and bezafibrate) and evaluated the metabolic changes using seahorse and immunofluorescent imaging, respectively. In our diseased cell lines, we observed prolonged cardiac contraction, decreased fatty acid oxidation, and minor response upon metabolic inhibition. By re-activating the metabolic activities with fenofibrate, proliferator-activated receptor alpha (PPARA) levels were boosted while hydroxyacyl-CoA dehydrogenase trifunctional multienzyme complex subunit alpha (HADHA) levels remained unchanged. Immunofluorescent staining of sarcomeres using alpha actinin (ACTN2) and MYH7 antibodies revealed sarcomere disarray in diseased cells and recurrence of the variant in one of the isogenic control cell lines. Taken together, our study shows aberrant contractile function, impaired myocardial energy metabolism, and sarcomere disarray in a hiPSC-CMs model carrying the MYH7_R403L variant. Future research should include routine sequencing of hiPSC-CMs lines and improve maturation strategies to model HCM in vitro. Additionally, the time point of fibrate administration during pre-clinical in vitro studies in HCM should be further optimized.