HCM and DCM associated TNNT2 sarcomeric variants induce nucleus remodeling in human iPSC-CMs.

Abstract

Hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM) are associated with sarcomeric protein mutations in thick- and thin-filament genes, particularly in the gene TNNT2, which encodes cardiac troponin T (cTnT). Mutations in cTnT can lead to altered contractility dynamics and a high incidence of sudden cardiac death. Human-induced pluripotent stem cells cardiomyocytes (hiPSC-CMs) model offers an effective method to investigate cardiac diseases in vitro. We analyze morphological and functional alterations in two common mutations associated with HCM and DCM, cTnT I79N and cTnT R141W, respectively. We performed experiments in physiologically relevant microenvironment and in the presence of two clinically relevant drugs to treat cardiomyopathies, mavacamten and omencativ mercabil. Cellular characterization confirmed successful maturation of cardiomyocytes and altered contractility consistent with human phenotypes. Stiffer microenvironment determined potential physiological conditions of our model to the human system. In addition, cardiomyocytes under constant physical influence respond to microenvironmental changes, such as energetic metabolism, signal transduction and propagation of electrical stimuli. Through mechanotransduction, the sarcomeric contractility is translated intracellularly to other organelles, including the nucleus. We analyze the mechanical effect of altered sarcomeric contraction, due to TNNT2 mutations, on the nuclear morphology and stiffness of hiPSC-CMs. We observed altered nuclear circularity, aspect ratio and area. We also observed alterations in the nucleus stiffness and protein expression for both HCM and DCM, with opposite effects. Drug treatment showed promising results for the model to correct both contractility and nuclear stiffness. Increased or diminished contractility imposed by TNNT2 pathogenic variants can trigger nuclear remodeling, potentially compromising cellular structure and composition. This supports that sarcomeric variants associated with cardiomyopathy plays a role in cardiomyocyte mechanotransduction.