Project Summary/Abstract Misregulated extracellular matrix (ECM) remodeling is associated with both hypertrophic and dilated cardiomyopathy (HCM, DCM). Cardiac fibrosis, characterized by the increased deposition and reorganization of ECM components, is a hallmark of cardiomyopathy. Fibrotic ECM remodeling results in changes to the mechanical properties of the myocardium, such as increased elasticity (stiffness) compared to healthy tissue, and these mechanical changes can significantly disrupt cardiomyocyte (CM) function and phenotype. Fibrotic ECM remodeling in other organs and tissues has also been shown to alter tissue viscoelasticity, or ability of the tissue to dissipate energy through viscous flow upon loading. Substrates of varying viscoelasticity can differentially regulate cell contractility and phenotype, including in muscle myoblasts. However, how myocardial viscoelasticity changes during HCM or DCM progression is not well established. Further, how CMs, the motor units of the heart, respond to viscoelastic mechanical environments that mimic healthy or diseased tissue is unknown. The objective of this proposal is to determine how ECM remodeling during cardiomyopathy alters tissue viscoelasticity and the extent to which those mechanical changes can drive disease progression. We will address the critical outstanding question of how myocardial viscoelasticity varies between health and disease and to what extent disease-associated mechanical changes accelerate disease progression through two Specific Aims. Aim 1: Does cardiomyopathy-driven ECM remodeling alter myocardial viscoelasticity? and Aim 2: Does matrix viscoelasticity regulate cardiomyocyte phenotype and function? We will mechanically characterize human and porcine myocardium from DCM and HCM patients or models respectively, as well as assessing the contribution of ECM remodeling in driving mechanical changes. Then, we will use wildtype and mutant hiPSC- CMs with HCM mutations and culture them on hydrogel substrates with tunable viscoelasticity and assess key indicators their phenotype. Our results are expected to have positive translational impact as they can inform a more comprehensive interpretation of diagnostic imaging modalities, such as ultrasound elastography, by assessing viscoelasticity as a marker of disease progression. Additionally, incorporating substrate viscoelasticity into in vitro human CMs culture models would more accurately represent the pathophysiological context CMs experience in diseased tissue. Especially when combined with other advantages of iPSC models, such as patient specificity, these advanced platforms could yield novel biological insights or enable identification of potential therapeutic targets.

Project Narrative Cardiomyopathies are known to alter the structure and stiffness of cardiac tissue. However, how the time- dependent mechanical properties of cardiac tissue, known as viscoelasticity, change in cardiomyopathy and what impact these changes have on cardiomyocytes is currently unknown. We will directly measure cardiac tissue viscoelasticity and then test cardiomyocyte responses using a viscoelastic biomaterial platform.