Engineering the Cardiac Fuel Supply: Elevation of 2-deoxy-ATP for Myofilament-Targeted Treatment of Heart Failure

Abstract

Heart failure is a syndrome characterized by the inability of the heart to fill with, or eject, blood. There are many causes of heart failure including toxins (e.g. alcohol, chemotherapy), inherited cardiomyopathies, viral infections, and coronary artery disease. All of these conditions can impair left ventricular function, which initiates a cascade of compensatory events as the heart attempts to maintain cardiac output. While initially beneficial, these compensatory responses eventually become maladaptive, and ultimately lead to heart failure. Because the majority of patients with heart failure have impaired systolic dysfunction that initiates the cycle of decompensation, therapeutic approaches to prevent or reverse heart failure are aimed at improving left ventricular function. Despite advances in therapy, however, the five-year mortality for heart failure is ~50%. In an effort to increase the contractility of myocardium and improve left ventricular function, we propose novel, myofilament-targeted inotrope to treat heart failure. Using reductionist techniques, we have shown that dATP is a more effective substrate than ATP for contraction of cardiac muscle, increasing force and the rate of force development. Our biochemical and mechanical analysis suggests that dATP increases the rates of myosin binding and product release, translating to enhanced contractility and, perhaps, relaxation. This project spans from molecular mechanisms to translational research, determining how dATP improves myosin function and how this translates to improved cardiac function in normal and damaged hearts. The research presented in this dissertation (1) characterizes the effects of increased dATP in vivo on cardiac function in both normal hearts and those following injury (myocardial infarction), and (2) details the effects of dATP binding on the structure of myosin, which elucidates a molecular mechanism by which increased dATP concentration results in contractile enhancements. Life-long elevation of [dATP] in transgenic mice and cardiac-specific, viral-mediated elevation in [dATP] overexpression increased performance in healthy mice ex vivo. The performance improvement in healthy mice motivated us to examine the therapeutic potential of RR overexpression in an infarct model. Preliminary echocardiography measurements showed that AAV-mediated RR overexpression improved in vivo performance in infarcted mice. MD simulations of myosin in the showed that dADP.Pi altered the conformation of the nucleotide binding pocket, the cleft, and the actin binding surface on myosin, stabilizing a conformation of myosin that binds actin more favorably than the stable conformation of myosin bound to ADP.Pi. These studies provide a potential mechanism that underlies the dATP-mediated increase in contractility observed. Elevating cardiac dATP may be a viable therapy to improve performance in patients suffering systolic dysfunction. This approach is being commercialized and pre-clinical, large animal studies are underway.