Mouse and computational models link Mlc2v dephosphorylation to altered myosin kinetics in early cardiac disease
Farah Sheikh, … , Andrew D. McCulloch, Ju Chen
Farah Sheikh, … , Andrew D. McCulloch, Ju Chen
Published March 19, 2012
Citation Information: J Clin Invest. 2012;122(4):1209-1221. https://doi.org/10.1172/JCI61134.
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Research Article Cardiology

Mouse and computational models link Mlc2v dephosphorylation to altered myosin kinetics in early cardiac disease

Abstract

Actin-myosin interactions provide the driving force underlying each heartbeat. The current view is that actin-bound regulatory proteins play a dominant role in the activation of calcium-dependent cardiac muscle contraction. In contrast, the relevance and nature of regulation by myosin regulatory proteins (for example, myosin light chain-2 [MLC2]) in cardiac muscle remain poorly understood. By integrating gene-targeted mouse and computational models, we have identified an indispensable role for ventricular Mlc2 (Mlc2v) phosphorylation in regulating cardiac muscle contraction. Cardiac myosin cycling kinetics, which directly control actin-myosin interactions, were directly affected, but surprisingly, Mlc2v phosphorylation also fed back to cooperatively influence calcium-dependent activation of the thin filament. Loss of these mechanisms produced early defects in the rate of cardiac muscle twitch relaxation and ventricular torsion. Strikingly, these defects preceded the left ventricular dysfunction of heart disease and failure in a mouse model with nonphosphorylatable Mlc2v. Thus, there is a direct and early role for Mlc2 phosphorylation in regulating actin-myosin interactions in striated muscle contraction, and dephosphorylation of Mlc2 or loss of these mechanisms can play a critical role in heart failure.

Authors

Farah Sheikh, Kunfu Ouyang, Stuart G. Campbell, Robert C. Lyon, Joyce Chuang, Dan Fitzsimons, Jared Tangney, Carlos G. Hidalgo, Charles S. Chung, Hongqiang Cheng, Nancy D. Dalton, Yusu Gu, Hideko Kasahara, Majid Ghassemian, Jeffrey H. Omens, Kirk L. Peterson, Henk L. Granzier, Richard L. Moss, Andrew D. McCulloch, Ju Chen

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Figure 3

A computational model identifies dual molecular roles for ventricular Mlc2 phosphorylation (Mlc2v-p) in regulating cardiac actin-myosin interactions that underlie twitch relaxation defects in DM mice.

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A computational model identifies dual molecular roles for ventricular Ml...
The effects of Mlc2v-p on (A) myosin head diffusion (17) and (B) myosin lever arm stiffness (18, 20) were tested. (C) A recent model of myofilament function (21) was modified to include Mlc2v-p mechanisms (orange, mechanism 1; green, mechanism 2). Refer to Supplemental Methods and Supplemental Tables 1 and 2 for details. (D) Model parameters for 0% Mlc2v-p were adjusted such that model fit matched maximum tension, Ca2+ sensitivity to force (pCa50), and relative maximum rate of force redevelopment (ktr) in dephosphorylated skinned mouse myocardium (28, 29). Model fit to experimental data in phosphorylated skinned myocardium (28, 29) was obtained with both mechanisms. (E) Model fits (lines) to experimental data from steady-state force-pCa curves measured in dephosphorylated (red circle) and phosphorylated (blue circle) skinned myocardium (digitized from Stelzer et al., ref. 29) were only obtained with both mechanisms. (F) Ca2+ transient and muscle twitch tension measurements in 6-week-old papillary muscles at 25°C. Muscle simulations used parameters of 0% (red trace) and 31% MLC2v-p (blue trace, value measured in WT myocardium in Figure 1A). Maximum tension and twitch relaxation defects in DM muscle were recapitulated by model simulations. Arrow denotes leftward shift (acceleration) when normalized to tension. Values for fit are in Supplemental Tables 1 and 2. (G) Model fit of TP50-T in WT and DM muscle using both mechanisms is shown.