Abstract 17554: A Unique Synergistic Approach That Uncovers MLC2v Phosphorylation as an Early Marker for Heart Disease
Currently it is understood that the major proteins that activate heart muscle contraction during each heartbeat are from the calcium-dependent actin regulatory family. In contrast, myosin regulatory proteins such as ventricular myosin light chain-2 (MLC2v) are thought to play a minor role in this context. Evidence from human cardiac disease and in vitro studies challenge this concept and suggest a direct influence of myosin regulatory proteins, such as MLC2v, on activation of muscle contraction through phosphorylation. However, the direct role of MLC2v phosphorylation in heart muscle contraction and human heart disease remain unknown. Using a novel multi-scale computational model we show that MLC2v phosphorylation controls early dynamics of muscle contraction activation and the known critical twisting motion (torsion) of the heart during contraction in vivo. This is achieved by directly increasing the stiffness of the myosin neck domain and the extent of myosin head movement away from the myosin filament backbone, rendering the myosin head more “accessible” to dictate feedback and control activation of muscle contraction. To test the computational model's predictions on loss of these mechanisms in vivo, we produced novel gene-targeted MLC2v phosphorylation knock-in mutant mouse models, only one of which exhibited a significant loss of MLC2v phosphorylation in the heart. Phosphorylation mutant mice showed early defects in heart contraction dynamics and torsion, consistent with the computational model's predictions and prior to the onset of “classic” early markers of heart disease. These mice subsequently developed overt heart failure in the form of dilated cardiomyopathy, leading to premature death as well as an increased susceptibility to heart muscle dysfunction following stress. Our results uncover early mechanisms by which MLC2v and myosin can dictate activation of heart muscle contraction as well as contribute to decreased heart torsion, the latter of which is gaining attention as an early clinical functional marker of heart disease in children and adults. We highlight an unappreciated role for myosin-based phosphorylation gradients in the adult heart while shedding light on the early mechanisms underlying human heart disease and failure.
- © 2010 by American Heart Association, Inc.