Biophysical Society Thematic Meeting | Canterbury 2023

Towards a More Perfect Union: Multi-Scale Models of Muscle and Their Experimental Validation

Tuesday Speaker Abstracts

EXPERIMENTAL AND COMPUTATIONAL APPROACHES FOR MECHANISTIC ANALYSIS AND THERAPEUTIC DEVELOPMENT OF 2-DEOXY ATP TO TREAT HEART FAILURE Michael Regnier 1 ; Charles Murry 2 ; Ketaki Mhatre 3 ; 1 University of Washington, Bioengineering, Seattle, WA, USA 2 University of Washington, Pathology & Lab Medicine, Seattle, WA, USA 3 University of Washington, Heart and Muscle Mechanics Lab, Seattle, WA, USA 2-deoxy-ATP (dATP) is a naturally occurring myosin activator that improves contractility without impairing relaxation. ATP is converted to dATP by the enzyme Ribonucleotide Reductase (RNR). In post-mitotic cardiomyocytes RNR is downregulated but over-expression of the enzyme results in elevation from < 0.1% to ~1% of the ATP pool. In transgenic mice that have 1% dATP, left ventricular (LV) pressure development is increased by ~30% and the rate of pressure development (+dP/dT) and decline (-dP/dT) are increased. We have used contractile mechanics and protein biochemistry to determine that dATP increases crossbridge cycling rate and NTPase activity, speeding the rate of myosin attachment to actin, and the release of NTP hydrolysis products, and that contractile force is augmented with as little as 1-2% dATP. We used x-ray diffraction of demembranated pig LV muscle to demonstrate that this level of dATP results in significant movement of myosin heads away from the thick filament and towards thin filaments. Stiffness measurements indicate weak binding with actin is also increased. We used Molecular Dynamics (MD) modeling to demonstrate this is likely due to a dADP.Pi induced increase in positive charge of the actin binding surface on myosin. MD simulations were also used to demonstrate that M.ADP.Pi may destabilize the interacting heads motif (IHM) of myosin on the thick filament backbone, providing a mechanism for increased myosin recruitment during contractions. Multi-scale modeling predicts that the increased recruitment and cycling rate of myosin can explain the increases in LV hemodynamics. We recently demonstrated that human stem cell-derived cardiomyocytes, engineered to over-express RNR, result in 1-2% dATP in the cells. When these cells are transplanted into rats at one-month post-myocardial infarct, they couple with host myocardium and deliver dATP through gap junctions. This results in improved LV function for at least three months post-transplant.

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