title: Long term ablation of protein kinase A (PKA)-mediated cardiac troponin I phosphorylation leads to excitation-contraction uncoupling and diastolic dysfunction in a knock-in mouse model of hypertrophic cardiomyopathy.
abstract: The cardiac troponin I (cTnI) R21C (cTnI-R21C) mutation has been linked to hypertrophic cardiomyopathy and renders cTnI incapable of phosphorylation by PKA in vivo. Echocardiographic imaging of homozygous knock-in mice expressing the cTnI-R21C mutation shows that they develop hypertrophy after 12 months of age and have abnormal diastolic function that is characterized by longer filling times and impaired relaxation. Electrocardiographic analyses show that older R21C mice have elevated heart rates and reduced cardiovagal tone. Cardiac myocytes isolated from older R21C mice demonstrate that in the presence of isoproterenol, significant delays in Ca(2+) decay and sarcomere relaxation occur that are not present at 6 months of age. Although isoproterenol and stepwise increases in stimulation frequency accelerate Ca(2+)-transient and sarcomere shortening kinetics in R21C myocytes from older mice, they are unable to attain the corresponding WT values. When R21C myocytes from older mice are treated with isoproterenol, evidence of excitation-contraction uncoupling is indicated by an elevation in diastolic calcium that is frequency-dissociated and not coupled to shorter diastolic sarcomere lengths. Myocytes from older mice have smaller Ca(2+) transient amplitudes (2.3-fold) that are associated with reductions (2.9-fold) in sarcoplasmic reticulum Ca(2+) content. This abnormal Ca(2+) handling within the cell may be attributed to a reduction (2.4-fold) in calsequestrin expression in conjunction with an up-regulation (1.5-fold) of Na(+)-Ca(2+) exchanger. Incubation of permeabilized cardiac fibers from R21C mice with PKA confirmed that the mutation prevents facilitation of mechanical relaxation. Altogether, these results indicate that the inability to enhance myofilament relaxation through cTnI phosphorylation predisposes the heart to abnormal diastolic function, reduced accessibility of cardiac reserves, dysautonomia, and hypertrophy.
authors: Department of Biomedical Sciences, Florida State University College of Medicine, Tallahassee, Florida 32306-4300.
authors: David
authors: D
authors: Dweck
authors: Department of Biomedical Sciences, Florida State University College of Medicine, Tallahassee, Florida 32306-4300,; Family Institute, Florida State University, Tallahassee, Florida 32306.
authors: Marcos A
authors: MA
authors: Sanchez-Gonzalez
authors: Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9040.
authors: Audrey N
authors: AN
authors: Chang
authors: Interdisciplinary Stem Cell Institute, University of Miami Miller School of Medicine, Miami, Florida 33136, and.
authors: Raul A
authors: RA
authors: Dulce
authors: Department of Biomedical Sciences, Florida State University College of Medicine, Tallahassee, Florida 32306-4300.
authors: Crystal-Dawn
authors: CD
authors: Badger
authors: Department of Biomedical Sciences, Florida State University College of Medicine, Tallahassee, Florida 32306-4300.
authors: Andrew P
authors: AP
authors: Koutnik
authors: Department of Biomedical Sciences, Florida State University College of Medicine, Tallahassee, Florida 32306-4300.
authors: Edda L
authors: EL
authors: Ruiz
authors: Department of Biomedical Sciences, Florida State University College of Medicine, Tallahassee, Florida 32306-4300.
authors: Brittany
authors: B
authors: Griffin
authors: Department of Molecular and Cellular Pharmacology, University of Miami Miller School of Medicine, Miami, Florida 33136.
authors: Jingsheng
authors: J
authors: Liang
authors: Department of Biomedical Sciences, Florida State University College of Medicine, Tallahassee, Florida 32306-4300.
authors: Mohamed
authors: M
authors: Kabbaj
authors: Family Institute, Florida State University, Tallahassee, Florida 32306.
authors: Frank D
authors: FD
authors: Fincham
authors: Interdisciplinary Stem Cell Institute, University of Miami Miller School of Medicine, Miami, Florida 33136, and.
authors: Joshua M
authors: JM
authors: Hare
authors: Department of Biomedical Sciences, Florida State University College of Medicine, Tallahassee, Florida 32306-4300.
authors: J Michael
authors: JM
authors: Overton
authors: Department of Biomedical Sciences, Florida State University College of Medicine, Tallahassee, Florida 32306-4300,. Electronic address: jose.pinto@med.fsu.edu.
authors: Jose R
authors: JR
authors: Pinto
mesh_terms: D000818:Animals; D020013:Calcium Signaling; D002312:Cardiomyopathy, Hypertrophic / Q000235:genetics / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism*; D003971:Diastole; D004195:Disease Models, Animal; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D032383:Myocytes, Cardiac / Q000378:metabolism* / Q000473:pathology; D010766:Phosphorylation / Q000502:physiology; D012519:Sarcoplasmic Reticulum / Q000235:genetics / Q000378:metabolism; D019210:Troponin I / Q000235:genetics / Q000378:metabolism*
chemical_list: D019210:Troponin I; D017868:Cyclic AMP-Dependent Protein Kinases
keywords: Calcium; Cardiac Hypertrophy; Cardiac Muscle; Cardiac Troponin I; Heart Rate Variability; Hypertrophic Cardiomyopathy; Knock-in Mice; Mouse; R21C; Troponin