This project will elucidate the biological mechanisms by which obesity alters the myocardium in patients with heart failure and a preserved ejection fraction (HFpEF) to ultimately derive sorely needed precision- guided therapies. HFpEF currently represents more than half of all heart failure worldwide, its prevalence is rising, morbidity and mortality are substantial, and yet we still have very few effective therapies. It is a major unmet medical need and a disease priority for the NIH. One of the factors that has made it difficult to treat is a major transformation over the past two decades such that most patients are now obese, many severely, with diabetes and metabolic syndrome also very common. This obesity-metabolic syndrome (OMS-HFpEF) phenotype has altered disease manifestations and progression and worsened prognosis. Yet our knowledge of the underlying myocardial pathobiology effects from obesity are limited. Johns Hopkins has established a dedicated clinical HFpEF Center that obtains detailed phenotyping of HFpEF patients, the majority being OMS-HFpEF, African American, and female. The phenotyping includes obtaining myocardial biopsies that have already provided novel insights into cellular and molecular features. Our recent studies revealed less fibrosis than predicted, and that fat metabolism and glucose metabolism seem both to be depressed in OMS-HFpEF, pairing abnormalities found in HF with reduced EF and obesity/diabetes respectively, in essence a worst of both worlds that limits fuel flexibility. Yet unlike HFrEF, oxidative phosphorylation seems enhanced particularly in obese patients. We also find a strong inverse correlation between obesity and calcium-stimulated myofilament function – being very depressed in OMS-HFpEF ± diabetes, hypertension, or LV hypertrophy. Obesity is thus a major driver for fundamental changes in HFpEF. This R35 Program dissects metabolic and sarcomeric dysregulation in OMS-HFpEF, starting with analysis of human myocardial tissues, and testing abnormalities in animal models that have both marked OMS and cardiac hemodynamic stress. Models are benchmarked to pair with human molecular/cellular pathobiology, rather than only organ level physiology as historically done. Our metabolic studies will determine the fuel substrates used by OMS-HFpEF heart, where bottlenecks in fuel metabolism occur, how these maybe circumvented and what the impact is, which metabolites are formed that can impact epigenetics (histone modifications) to alter gene programs controlling metabolism and other key cellular functions. Major interest is on Krebs cycle intermediates such as citrate, succinate and fumarate and polyamines, that can impact histone methylation and acetylation. Our myocyte studies will determine how obesity depresses sarcomere function, find the protein(s) and structural changes involved, their causes, and prove causality. Lastly, we will test therapies to improve metabolic flexibility and sarcomere performance in O...