title: Cardiac myosin heavy chain isoform exchange alters the phenotype of cTnT-related cardiomyopathies in mouse hearts.
abstract: Familial hypertrophic cardiomyopathy, FHC, is a clinically heterogeneous, autosomal-dominant disease of the cardiac sarcomere leading to extensive remodeling at both the whole heart and molecular levels. The remodeling patterns are mutation-specific, a finding that extends to the level of single amino acid substitutions at the same peptide residue. Here we utilize two well-characterized transgenic FHC mouse models carrying independent amino acid substitutions in the TM-binding region of cardiac troponin T (cTnT) at residue 92. R92Q and R92L cTnT domains have mutation-specific average peptide conformation and dynamics sufficient to alter thin filament flexibility and cross-bridge formation and R92 mutant myocytes demonstrate mutation-specific temporal molecular remodeling of Ca(2+) kinetics and impaired cardiac contractility and relaxation. To determine if a greater economy of contraction at the crossbridge level would rescue the mechanical defects caused by the R92 cTnT mutations, we replaced the endogenous murine alpha-myosin heavy chain (MyHC) with the beta-MyHC isoform. While beta-MyHC replacement rescued the systolic dysfunction in R92Q mice, it failed to rescue the defects in diastolic function common to FHC-associated R92 mutations. Surprisingly, a significant component of the whole heart and molecular contractile improvement in the R92Q mice was due to improvements in Ca(2+) homeostasis including SR uptake, [Ca2+](i) amplitude and phospholamban phosphorylation. Our data demonstrate that while genetically altering the myosin composition of the heart bearing a thin filament FHC mutation is sufficient to improve contractility, diastolic performance is refractory despite improved Ca(2+) kinetics. These data reveal a previously unrecognized role for MyHC isoforms with respect to Ca(2+) homeostasis in the setting of cardiomyopathic remodeling and demonstrate the overall dominance of the thin filament mutation in determining the degree of diastolic impairment at the myofilament level.
authors.affiliation: Department of Physiology and Biophysics, Albert Einstein College of Medicine, Yeshiva University, 1300 Morris Park Avenue, Ullmann, Room 316, Bronx, NY 10461, USA.
authors.forename: Ron
authors.initials: R
authors.lastname: Rice
authors.forename: Pia
authors.initials: P
authors.lastname: Guinto
authors.forename: Candice
authors.initials: C
authors.lastname: Dowell-Martino
authors.forename: Huamei
authors.initials: H
authors.lastname: He
authors.forename: Kirsten
authors.initials: K
authors.lastname: Hoyer
authors.forename: Maike
authors.initials: M
authors.lastname: Krenz
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Robbins
authors.forename: Joanne S
authors.initials: JS
authors.lastname: Ingwall
authors.forename: Jil C
authors.initials: JC
authors.lastname: Tardiff
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D024741:Cardiomyopathy, Hypertrophic, Familial / Q000378:metabolism*; D006352:Heart Ventricles / Q000166:cytology; D006801:Humans; D066298:In Vitro Techniques; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009210:Myofibrils / Q000378:metabolism; D018995:Myosin Heavy Chains / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D020033:Protein Isoforms / Q000378:metabolism*; D012518:Sarcomeres / Q000378:metabolism; D020107:Troponin T / Q000235:genetics / Q000378:metabolism*
chemical_list: D020033:Protein Isoforms; D020107:Troponin T; D018995:Myosin Heavy Chains; D002118:Calcium