Chad M Warren1, Chehade N Karam1, Beata M Wolska1, Tomoyoshi Kobayashi1, Pieter P de Tombe1, Grace M Arteaga1, J Martijn Bos1, Michael J Ackerman1, R John Solaro2. 1. From the Department of Physiology and Biophysics, Center for Cardiovascular Research (C.M.W., C.N.K., B.M.W., T.K., R.J.S.) and Division of Cardiology, Department of Medicine (B.M.W.), University of Illinois at Chicago; Department of Cell and Molecular Physiology, Stritch School of Medicine, Loyola University Chicago, Maywood, IL (P.P.d.T.); and Division of Pediatric Critical Care and Physiology, Department of Pediatrics (G.M.A.), Department of Molecular Pharmacology and Experimental Therapeutics, Windland Smith Rice Sudden Death Genomics Laboratory (J.M.B., M.J.A.), Division of Pediatric Cardiology, Department of Pediatrics (J.M.B., M.J.A.), and Division of Cardiovascular Diseases, Department of Medicine (M.J.A.), Mayo Clinic, Rochester, MN. 2. From the Department of Physiology and Biophysics, Center for Cardiovascular Research (C.M.W., C.N.K., B.M.W., T.K., R.J.S.) and Division of Cardiology, Department of Medicine (B.M.W.), University of Illinois at Chicago; Department of Cell and Molecular Physiology, Stritch School of Medicine, Loyola University Chicago, Maywood, IL (P.P.d.T.); and Division of Pediatric Critical Care and Physiology, Department of Pediatrics (G.M.A.), Department of Molecular Pharmacology and Experimental Therapeutics, Windland Smith Rice Sudden Death Genomics Laboratory (J.M.B., M.J.A.), Division of Pediatric Cardiology, Department of Pediatrics (J.M.B., M.J.A.), and Division of Cardiovascular Diseases, Department of Medicine (M.J.A.), Mayo Clinic, Rochester, MN. solarorj@uic.edu.
Abstract
BACKGROUND: Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiovascular disease characterized by thickening of ventricular walls and decreased left ventricular chamber volume. The majority of HCM-associated mutations are found in genes encoding sarcomere proteins. Herein, we set out to functionally characterize a novel HCM-associated mutation (K206I-TNNI3) and elucidate the mechanism of dysfunction at the level of myofilament proteins. METHODS AND RESULTS: The male index case was diagnosed with HCM after an out-of-hospital cardiac arrest, which was followed by comprehensive clinical evaluation, transthoracic echocardiography, and clinical genetic testing. To determine molecular mechanism(s) of the mutant human cardiac troponin I (K206I), we tested the Ca(2+) dependence of thin filament-activated myosin-S1-ATPase activity in a reconstituted, regulated, actomyosin system comparing wild-type human troponin complex, 50% mix of K206I/wildtype, or 100% K206I. We also exchanged native troponin detergent extracted fibers with reconstituted troponin containing either wildtype or a 65% mix of K206I/wildtype and measured force generation. The Ca(2+) sensitivity of the myofilaments containing the K206I variant was significantly increased, and when treated with 20 µmol/L (-)-epigallocatechin gallate (green tea) was restored back to wild-type levels in ATPase and force measurements. The K206I mutation impairs the ability of the troponin I to inhibit ATPase activity in the absence of calcium-bound human cardiac troponin C. The ability of calcium-bound human cardiac troponin C to neutralize the inhibition of K206I was greater than with wild-type TnI. CONCLUSIONS: Compromised interactions of K206I with actin and hcTnC may lead to impaired relaxation and HCM.
BACKGROUND:Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiovascular disease characterized by thickening of ventricular walls and decreased left ventricular chamber volume. The majority of HCM-associated mutations are found in genes encoding sarcomere proteins. Herein, we set out to functionally characterize a novel HCM-associated mutation (K206I-TNNI3) and elucidate the mechanism of dysfunction at the level of myofilament proteins. METHODS AND RESULTS: The male index case was diagnosed with HCM after an out-of-hospital cardiac arrest, which was followed by comprehensive clinical evaluation, transthoracic echocardiography, and clinical genetic testing. To determine molecular mechanism(s) of the mutant humancardiac troponin I (K206I), we tested the Ca(2+) dependence of thin filament-activated myosin-S1-ATPase activity in a reconstituted, regulated, actomyosin system comparing wild-type human troponin complex, 50% mix of K206I/wildtype, or 100% K206I. We also exchanged native troponin detergent extracted fibers with reconstituted troponin containing either wildtype or a 65% mix of K206I/wildtype and measured force generation. The Ca(2+) sensitivity of the myofilaments containing the K206I variant was significantly increased, and when treated with 20 µmol/L (-)-epigallocatechin gallate (green tea) was restored back to wild-type levels in ATPase and force measurements. The K206I mutation impairs the ability of the troponin I to inhibit ATPase activity in the absence of calcium-bound humancardiac troponin C. The ability of calcium-bound humancardiac troponin C to neutralize the inhibition of K206I was greater than with wild-type TnI. CONCLUSIONS: Compromised interactions of K206I with actin and hcTnC may lead to impaired relaxation and HCM.
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