Myosin Regulatory Light Chain Phosphorylation Attenuates Cardiac Hypertrophy

Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA.
Journal of Biological Chemistry (Impact Factor: 4.57). 08/2008; 283(28):19748-56. DOI: 10.1074/jbc.M802605200
Source: PubMed


Hyperphosphorylation of myosin regulatory light chain (RLC) in cardiac muscle is proposed to cause compensatory hypertrophy. We therefore investigated potential mechanisms in genetically modified mice. Transgenic (TG) mice were generated to overexpress Ca2+/calmodulin-dependent myosin light chain kinase specifically in cardiomyocytes. Phosphorylation of sarcomeric cardiac RLC and cytoplasmic nonmuscle RLC increased markedly in hearts from TG mice compared with hearts from wild-type (WT) mice. Quantitative measures of RLC phosphorylation revealed no spatial gradients. No significant hypertrophy or structural abnormalities were observed up to 6 months of age in hearts of TG mice compared with WT animals. Hearts and cardiomyocytes from WT animals subjected to voluntary running exercise and isoproterenol treatment showed hypertrophic cardiac responses, but the responses for TG mice were attenuated. Additional biochemical measurements indicated that overexpression of the Ca2+/calmodulin-binding kinase did not perturb other Ca2+/calmodulin-dependent processes involving Ca2+/calmodulin-dependent protein kinase II or the protein phosphatase calcineurin. Thus, increased myosin RLC phosphorylation per se does not cause cardiac hypertrophy and probably inhibits physiological and pathophysiological hypertrophy by contributing to enhanced contractile performance and efficiency.

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    • "Attenuation of RLC phosphorylation in cardiac MLCK knock-out mice led to ventricular myocyte hypertrophy, fibrosis and to mild dilated cardiomyopathy (Chang et al. 2015; Ding et al. 2010). Any change in RLC phosphorylation is then expected to cause abnormal heart performance, presumably through morphological and/or functional alterations (change in force, myofilament calcium sensitivity, ATPase activity, etc.) (Huang et al. 2008; Morano 1999; Sweeney et al. 1993). Constitutive RLC-mutant pseudo-phosphorylation was recently shown to prevent the development of HCM in mice (Yuan et al. 2015). "
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    ABSTRACT: We discuss here the potential mechanisms of action associated with hypertrophic (HCM) or dilated (DCM) cardiomyopathy causing mutations in the myosin regulatory (RLC) and essential (ELC) light chains. Specifically, we focus on four HCM mutations: RLC-A13T, RLC-K104E, ELC-A57G and ELC-M173V, and one DCM RLC-D94A mutation shown by population studies to cause different cardiomyopathy phenotypes in humans. Our studies indicate that RLC and ELC mutations lead to heart disease through different mechanisms with RLC mutations triggering alterations of the secondary structure of the RLC which further affect the structure and function of the lever arm domain and impose changes in the cross bridge cycling rates and myosin force generation ability. The ELC mutations exert their detrimental effects through changes in the interaction of the N-terminus of ELC with actin altering the cross talk between the thick and thin filaments and ultimately resulting in an altered force-pCa relationship. We also discuss the effect of mutations on myosin light chain phosphorylation. Exogenous myosin light chain phosphorylation and/or pseudo-phosphorylation were explored as potential rescue tools to treat hypertrophy-related cardiac phenotypes.
    Full-text · Article · Sep 2015 · Journal of Muscle Research and Cell Motility
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    • "change in force, myofilament calcium sensitivity , ATPase activity, etc. [7] [8] [9]. Consistent with this notion, it was shown that RLC phosphorylation in vivo may prevent the development of the hypertrophic phenotype [10]. Thus, both regions of RLC, the calcium binding site and the phosphorylation domain, are important regulators of RLC function and any mutations located in these sites or their vicinity are expected to affect cardiac muscle contraction. "
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    ABSTRACT: We have examined, for the first time, the effects of the familial hypertrophic cardiomyopathy (HCM)- associated Lys104Glu mutation in the myosin regulatory light chain (RLC). Transgenic mice expressing the Lys104Glu substitution (Tg-MUT) were generated and the results compared to Tg-WT (wild-type human ventricular RLC) mice. Echocardiography with pulse wave Doppler in 6month-old Tg-MUT showed early signs of diastolic disturbance with significantly reduced E/A transmitral velocities ratio. Invasive hemodynamics in 6month-old Tg-MUT mice also demonstrated a borderline significant prolonged isovolumic relaxation time (Tau) and a tendency for slower rate of pressure decline, suggesting alterations in diastolic function in Tg-MUT. Six month-old mutant animals had no LV hypertrophy; however, at >13months they displayed significant hypertrophy and fibrosis. In skinned papillary muscles from 5-6 month-old mice a mutation induced reduction in maximal tension and slower muscle relaxation rates were observed. Mutated cross-bridges showed increased rates of binding to the thin filaments and a faster rate of the power stroke. In addition, ~2-fold lower level of RLC phosphorylation was observed in the mutant compared to Tg-WT. In line with the higher mitochondrial content seen in Tg-MUT hearts, the MUT-myosin ATPase activity was significantly higher than WT-myosin, indicating increased energy consumption. In the in vitro motility assay, MUT-myosin produced higher actin sliding velocity under zero load, but the velocity drastically decreased with applied load in the MUT vs. WT myosin. Our results suggest that diastolic disturbance (impaired muscle relaxation, lower E/A) and inefficiency of energy use (reduced contractile force and faster ATP consumption) may underlie the Lys104Glu-mediated HCM phenotype.
    Full-text · Article · Jun 2014 · Journal of Molecular and Cellular Cardiology
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    • "Consistent with these findings, a transgenic mouse model overexpressing cardiac MLCK in the heart displayed an increase in MLC2v phosphorylation, while revealing an attenuated response to stress-induced hypertrophy mediated by pressure overload (Warren et al., 2012). Interestingly, overexpression of skeletal MLCK in the heart also attenuated catecholamine-and exercise (treadmill)-induced hypertrophy in mice (Huang et al., 2008). These results provide striking evidence that increased MLC2v phosphorylation can be used as a therapeutic strategy to alleviate stress-induced cardiac disease. "
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    ABSTRACT: Thin (actin) filament accessory proteins are thought to be the regulatory force for muscle contraction in cardiac muscle; however, compelling new evidence suggests that thick (myosin) filament regulatory proteins are emerging as having independent and important roles in regulating cardiac muscle contraction. Key to these new findings is a growing body of evidence that point to an influential and, more recently, direct role for ventricular myosin light chain-2 (MLC2v) phosphorylation in regulating cardiac muscle contraction, function, and disease. This includes the discovery and characterization of a cardiac-specific myosin light chain kinase capable of phosphorylating MLC2v as well as a myosin phosphatase that dephosphorylates MLC2v in the heart, which provides added mechanistic insights on MLC2v regulation within cardiac muscle. Here, we review evidence for an emerging and critical role for MLC2v phosphorylation in regulating cardiac myosin cycling kinetics, function, and disease, based on recent studies performed in genetic mouse models and humans. We further provide new perspectives on future avenues for targeting these pathways as therapies in alleviating cardiac disease.
    Full-text · Article · Aug 2013 · Trends in cardiovascular medicine
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