title: Discrete effects of A57G-myosin essential light chain mutation associated with familial hypertrophic cardiomyopathy.
abstract: The functional consequences of the familial hypertrophic cardiomyopathy A57G (alanine-to-glycine) mutation in the myosin ventricular essential light chain (ELC) were assessed in vitro and in vivo using previously generated transgenic (Tg) mice expressing A57G-ELC mutant vs. wild-type (WT) of human cardiac ELC and in recombinant A57G- or WT-protein-exchanged porcine cardiac muscle strips. Compared with the Tg-WT, there was a significant increase in the Ca²⁺ sensitivity of force (ΔpCa₅₀ ≅ 0.1) and an ~1.3-fold decrease in maximal force per cross section of muscle observed in the mutant preparations. In addition, a significant increase in passive tension in response to stretch was monitored in Tg-A57G vs. Tg-WT strips indicating a mutation-induced myocardial stiffness. Consistently, the hearts of Tg-A57G mice demonstrated a high level of fibrosis and hypertrophy manifested by increased heart weight-to-body weight ratios and a decreased number of nuclei indicating an increase in the two-dimensional size of Tg-A57G vs. Tg-WT myocytes. Echocardiography examination showed a phenotype of eccentric hypertrophy in Tg-A57G mice, enhanced left ventricular (LV) cavity dimension without changes in LV posterior/anterior wall thickness. Invasive hemodynamics data revealed significantly increased end-systolic elastance, defined by the slope of the pressure-volume relationship, indicating a mutation-induced increase in cardiac contractility. Our results suggest that the A57G allele causes disease by means of a discrete modulation of myofilament function, increased Ca²⁺ sensitivity, and decreased maximal tension followed by compensatory hypertrophy and enhanced contractility. These and other contributing factors such as increased myocardial stiffness and fibrosis most likely activate cardiomyopathic signaling pathways leading to pathologic cardiac remodeling.
authors.affiliation: Department of Molecular and Cellular Pharmacology, University of Miami Miller School of Medicine, Miami, Florida; and.
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Kazmierczak
authors.forename: Ellena C
authors.initials: EC
authors.lastname: Paulino
authors.forename: Wenrui
authors.initials: W
authors.lastname: Huang
authors.forename: Priya
authors.initials: P
authors.lastname: Muthu
authors.forename: Jingsheng
authors.initials: J
authors.lastname: Liang
authors.forename: Chen-Ching
authors.initials: CC
authors.lastname: Yuan
authors.forename: Ana I
authors.initials: AI
authors.lastname: Rojas
authors.forename: Joshua M
authors.initials: JM
authors.lastname: Hare
authors.forename: Danuta
authors.initials: D
authors.lastname: Szczesna-Cordary
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D002118:Calcium / Q000378:metabolism; D024741:Cardiomyopathy, Hypertrophic, Familial / Q000000981:diagnostic imaging / Q000235:genetics* / Q000378:metabolism* / Q000503:physiopathology; D004195:Disease Models, Animal; D056966:Excitation Contraction Coupling; D005355:Fibrosis; D020022:Genetic Predisposition to Disease; D006439:Hemodynamics; D006801:Humans; D007700:Kinetics; D051379:Mice; D008822:Mice, Transgenic; D009154:Mutation; D009200:Myocardial Contraction; D009210:Myofibrils / Q000378:metabolism; D018994:Myosin Light Chains / Q000235:genetics* / Q000378:metabolism*; D010210:Papillary Muscles / Q000378:metabolism* / Q000473:pathology; D010641:Phenotype; D010766:Phosphorylation; D013552:Swine; D014463:Ultrasonography; D016277:Ventricular Function, Left; D020257:Ventricular Remodeling
chemical_list: D018994:Myosin Light Chains; D002118:Calcium
keywords: Ca2+ sensitivity of contraction; echocardiography; hypertrophic cardiomyopathy; myosin essential light chain; pressure-volume loops