Project Title: C-terminal Peptide of Cardiac Troponin I for the Treatment of Diastolic Heart Failure Project Summary Myocardial contractility is essential for cardiac function. Troponin-mediated thin myofilament regulation controls cardiac muscle contraction and relaxation. The troponin complex consists of three protein subunits: the calcium receptor troponin C (TnC), the inhibitory subunit troponin I (TnI), and the tropomyosin-binding subunit troponin T (TnT). Cardiac TnI plays a pivotal role in myofilament activation and deactivation, determining the kinetics of cardiac muscle contraction and relaxation, and pumping efficiency of the heart. Our research project focuses on a novel therapeutic peptide derived from the conserved C-terminal end mobile domain of cardiac TnI (cTnI-C27) for its effect on enhancing myocardial relaxation and the underlying mechanisms. Biochemical, genetic and physiological approaches and mouse models of diastolic cardiac dysfunction are employed to study cTnI-C27 peptide to understand its selective enhancement of diastolic function of the heart. The ultimate goal is to develop a targeted treatment for diastolic heart failure (HFpEF) that presently lacks an effective treatment. Three Specific Aims are proposed in the research plan: Aim 1 is to characterize the mechanism for exogenous cTnI-C27 peptide to modulate myofilament function as an activated state-specific myofilament Ca2+- desensitizer. We shall determine the binding site of cTnI-C27 peptide on tropomyosin in thin filament and characterize its effect on contractile kinetics and endogenous troponin regulation of myofibril actomyosin ATPase in reconstituted myofilaments and skinned cardiac muscle. The results will determine how exogenous cTnI-C27 peptide modulates cardiac muscle contractility, especially the enhanceing of Frank-Starling response without increasing sarcomere length. Aim 2 is to study the delivery of cTnI-C27 peptide into cardiomyocytes for functional effect. Heart-homing fusion peptide, AAV9 and inducible transgenic expression of cTnI-C27 peptide will be studied in vivo and in ex vivo working hearts. Effects on cardiac muscle contractility and heart function will be examined for therapeutic efficacy in normal and diastolic dysfunctional and fibrotic mouse hearts to evaluate the therapeutic potential of cTnI-C27 peptide. Aim 3 is to determine the chronic effects of exogenous cTnI-C27 peptide on cardiac function and remodeling. To develop the cTnI-C27 peptide for the treatment of chronic heart failure, we need to understand the effects of chronic presence of cTnI-C27 peptide on cardiac muscle. We shall examine the therapeutic and side-effects of chronic transgenic expression of cTnI-C27 peptide in normal and failing mouse heart. In vivo and ex vivo cardiac function, tolerance to hemodynamic stresses, and myocardial remodeling will be examined in young and aging mice to collect informative longitudinal data. With combined expertise in myofilament prot...