title: The effect of myosin RLC phosphorylation in normal and cardiomyopathic mouse hearts.
abstract: Phosphorylation of the myosin regulatory light chain (RLC) by Ca(2+)-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 Ca(2+) 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 Ca(2+) 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.
authors.affiliation: Department of Molecular and Cellular Pharmacology, University of Miami Miller School of Medicine, Miami, FL 33136, USA.
authors.forename: Priya
authors.initials: P
authors.lastname: Muthu
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Kazmierczak
authors.forename: Michelle
authors.initials: M
authors.lastname: Jones
authors.forename: Danuta
authors.initials: D
authors.lastname: Szczesna-Cordary
mesh_terms: D000818:Animals; D009202:Cardiomyopathies / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D008822:Mice, Transgenic; D009154:Mutation; D009206:Myocardium / Q000378:metabolism* / Q000473:pathology; D018994:Myosin Light Chains / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation
chemical_list: D018994:Myosin Light Chains