Hypercontractility by hypertrophic cardiomyopathy mutant iPSC-CMs induces hippo-yap activation through enhanced nuclear deformation.

Abstract

Hypertrophy Cardiomyopathy (HCM) is the most prevalent hereditary cardiovascular disease - affecting >1:500 individuals. Advanced forms of HCM clinically present with hypercontractility, hypertrophy and fibrosis. Several single-point mutations in β-myosin heavy chain (MYH7) have been associated with HCM and increased contractility at the organ level. Different MYH7 mutations have resulted in increased, decreased, or unchanged force production at the molecular level. Yet how these molecular kinetics link to cell and tissue pathogenesis remains unclear. The Hippo Pathway has been demonstrated to be reactivated in pathological hypertrophic growth, intriguing because it signals proliferative growth during developmental growth and is quiescent during cardiac homeostasis. We hypothesized that changes in force production (intrinsically or extrinsically) directly alter the homeostatic mechano-signaling of the Hippo pathway through changes in stresses on the nucleus. Using human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), we asked whether homeostatic mechanical signaling through the canonical growth regulator, Hippo-YAP, is altered 1) by changes in the biomechanics of single HCM mutant cardiomyocytes and 2) by alterations in the mechanical environment. We use genetically edited hiPSC-CM with point mutations in MYH7 associated with HCM, and their matched controls, combined with micropatterned traction force microscopy substrates of different stiffness to measure changes in contractility and cell size. Mutant hiPSC-CMs display hypercontractile phenotypes and activated Hippo-YAP (% of hiPSC-CMs with nuclear localized YAP, mutants: 56.4% +/-6.85%, control: 32.1% +/-4.67%). The modulation of contractility in healthy hiPSC-CMs by treatment with inotropic drugs or culture in fibrotic-like stiff conditions also activated YAP compared to untreated controls. We hypothesize the activation of YAP in both HCM mutants and healthy hiPSC-CMs treated with contractility modulators is through enhanced nuclear deformation (nuclear aspect ratio amplitude, mutants: 0.063 +/-0.016, control: 0.027 +/-0.005).