The effect of myosin RLC phosphorylation in normal and cardiomyopathic mouse hearts

• Published in: Journal of cellular and molecular medicine Vol. 16; no. 4; pp. 911 - 919
• Main Authors: Muthu, Priya, Kazmierczak, Katarzyna, Jones, Michelle, Szczesna‐Cordary, Danuta
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.04.2012; John Wiley & Sons, Inc
• Subjects: Amino acids; Animal welfare; Animals; Antibodies; Aspartic acid; Calcium; Calmodulin; cardiac hypertrophy; Cardiac muscle; Cardiomyopathies - metabolism; Cardiomyopathies - pathology; Cardiomyopathy; Familial hypertrophic cardiomyopathy; Kinases; Laboratory animals; Mice; Mice, Transgenic; Muscle contraction; muscle fibres; Mutation; Myocardium - metabolism; Myocardium - pathology; Myofibrils; Myosin Light Chains - genetics; Myosin Light Chains - metabolism; myosin regulatory light chain; Myosin-light-chain kinase; Original; Phenotypes; Phosphorylation; Proteins; Transgenic mice; Valine
• ISSN: 1582-1838; 1582-4934
• DOI: 10.1111/j.1582-4934.2011.01371.x

Phosphorylation of the myosin regulatory light chain (RLC) by Ca2+‐calmodulin–activated myosin light chain kinase (MLCK) is known to be essential for the inotropic function of the heart. In this study, we have examined the effects of MLCK‐phosphorylation of transgenic (Tg) mouse cardiac muscle preparations expressing the D166V (aspartic acid to valine)–RLC mutation, identified to cause familial hypertrophic cardiomyopathy with malignant outcomes. Our previous work with Tg‐D166V mice demonstrated a large increase in the Ca2+ sensitivity of contraction, reduced maximal ATPase and force and a decreased level of endogenous RLC phosphorylation. Based on studies demonstrating the beneficial and/or protective effects of cardiac myosin phosphorylation for heart function, we hypothesized that an ex vivo phosphorylation of Tg‐D166V cardiac muscle may rescue the detrimental contractile phenotypes observed earlier at the level of single myosin molecules and in Tg‐D166V papillary muscle fibres. We showed that MLCK‐induced phosphorylation of Tg‐D166V cardiac myofibrils and muscle fibres was able to increase the reduced myofibrillar ATPase and reverse an abnormally increased Ca2+ sensitivity of force to the level observed for Tg‐wild‐type (WT) muscle. However, in contrast to Tg‐WT, which displayed a phosphorylation‐induced increase in steady‐state force, the maximal tension in Tg‐D166V papillary muscle fibres decreased upon phosphorylation. With the exception of force generation data, our results support the notion that RLC phosphorylation works as a rescue mechanism alleviating detrimental functional effects of a disease causing mutation. Further studies are necessary to elucidate the mechanism of this unexpected phosphorylation‐induced decrease in maximal tension in Tg‐D166V–skinned muscle fibres.