Hypertrophic Cardiomyopathy (HCM) is the most common inherited heart disease and the most common cause of sudden death in young people. While genetic studies have identified specific sarcomere genes associated with HCM, they fail to predict which patients will develop HCM. This proposal is motivated by mounting clinical and animal model evidence for mechanical epigenetic factors possibly explaining this variance. These data suggest that mechanical overload on the heart, caused by hypertension, can act together with sarcomere mutations to cause maladaptive hypertrophic remodeling in HCM. We are also motivated by the need to identify the factors underlying the failure of drug treatments to reverse HCM: although medicines that reduce blood pressure can reverse idiopathic (non-genetic) hypertrophy, they fail to reverse the course of symptomatic HCM. Based upon these prior data, we hypothesize that HCM mutations alter the magnitude of cardiac overload required to induce hypertrophic remodeling and shorten the timeframe over which remodeling is reversible. We aim to dissect the molecular mechanisms through which mechanical loading integrates with sarcomere mutations to cause structural and functional pathology in HCM linked to mutations in Myosin Binding Protein C (MYBPC3). This is possible for the first time because we have developed a medium-throughput, human induced pluripotent stem cell (iPSC) derived micro-heart muscle model system that allows us to apply a controlled magnitude of mechanical overload to iPSC-derived cardiomyocytes. This system will enable us to characterize the effects of overload on micro-heart muscle derived from both iPSC without disease mutations, and from iPSC engineered to harbor HCM patient specific MYPBC3 mutations (Aim 1). We will extend our magnetic hydrogel technologies to dynamically control the magnitude of mechanical overload on micro- heart muscles in situ, enabling us to determine mechanisms through which HCM mutations render cardiomyocytes resistant to blood pressure reducing therapeutics (Aim 2). Finally, we will determine molecular mechanisms linking mechanical overload and MYBPC3 mutations with hypertrophic remodeling (Aim 3).