title: Gene-Targeted Mice with the Human Troponin T R141W Mutation Develop Dilated Cardiomyopathy with Calcium Desensitization.
abstract: Most studies of the mechanisms leading to hereditary dilated cardiomyopathy (DCM) have been performed in reconstituted in vitro systems. Genetically engineered murine models offer the opportunity to dissect these mechanisms in vivo. We generated a gene-targeted knock-in murine model of the autosomal dominant Arg141Trp (R141W) mutation in Tnnt2, which was first described in a human family with DCM. Mice heterozygous for the mutation (Tnnt2R141W/+) recapitulated the human phenotype, developing left ventricular dilation and reduced contractility. There was a gene dosage effect, so that the phenotype in Tnnt2R141W/+mice was attenuated by transgenic overexpression of wildtype Tnnt2 mRNA transcript. Male mice exhibited poorer survival than females. Biomechanical studies on skinned fibers from Tnnt2R141W/+ hearts showed a significant decrease in pCa50 (-log[Ca2+] required for generation of 50% of maximal force) relative to wildtype hearts, indicating Ca2+ desensitization. Optical mapping studies of Langendorff-perfused Tnnt2R141W/+ hearts showed marked increases in diastolic and peak systolic intracellular Ca2+ ([Ca2+]i), and prolonged systolic rise and diastolic fall of [Ca2+]i. Perfused Tnnt2R141W/+ hearts had slower intrinsic rates in sinus rhythm and reduced peak heart rates in response to isoproterenol. Tnnt2R141W/+ hearts exhibited a reduction in phosphorylated phospholamban relative to wildtype mice. However, crossing Tnnt2R141W/+ mice with phospholamban knockout (Pln-/-) mice, which exhibit increased Ca2+ transients and contractility, had no effect on the DCM phenotype. We conclude that the Tnnt2 R141W mutation causes a Ca2+ desensitization and mice adapt by increasing Ca2+-transient amplitudes, which impairs Ca2+ handling dynamics, metabolism and responses to β-adrenergic activation.
authors.affiliation: Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin, Madison, WI, United States of America.|Cardiology Section, Medical Service, William. S. Middleton Memorial Veterans Hospital, Madison, WI, United States of America.|UPMC Heart and Vascular Institute and Division of Cardiology, Department of Medicine, University of Pittsburgh, Pittsburgh, PA, United States of America.
authors.forename: Mohun
authors.initials: M
authors.lastname: Ramratnam
authors.affiliation: UPMC Heart and Vascular Institute and Division of Cardiology, Department of Medicine, University of Pittsburgh, Pittsburgh, PA, United States of America.
authors.forename: Guy
authors.initials: G
authors.lastname: Salama
authors.affiliation: UPMC Heart and Vascular Institute and Division of Cardiology, Department of Medicine, University of Pittsburgh, Pittsburgh, PA, United States of America.
authors.forename: Ravi K
authors.initials: RK
authors.lastname: Sharma
authors.affiliation: UPMC Heart and Vascular Institute and Division of Cardiology, Department of Medicine, University of Pittsburgh, Pittsburgh, PA, United States of America.
authors.forename: David Wen Rui
authors.initials: DW
authors.lastname: Wang
authors.affiliation: Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States of America.
authors.forename: Stephen H
authors.initials: SH
authors.lastname: Smith
authors.affiliation: UPMC Heart and Vascular Institute and Division of Cardiology, Department of Medicine, University of Pittsburgh, Pittsburgh, PA, United States of America.
authors.forename: Sanjay K
authors.initials: SK
authors.lastname: Banerjee
authors.affiliation: UPMC Heart and Vascular Institute and Division of Cardiology, Department of Medicine, University of Pittsburgh, Pittsburgh, PA, United States of America.
authors.forename: Xueyin N
authors.initials: XN
authors.lastname: Huang
authors.affiliation: Division of Cardiovascular Medicine, Department of Internal Medicine, University of Iowa Carver College of Medicine, Iowa City, IA, United States of America.|Abboud Cardiovascular Research Center, University of Iowa, Iowa City, IA, United States of America.
authors.forename: Lindsey M
authors.initials: LM
authors.lastname: Gifford
authors.affiliation: UPMC Heart and Vascular Institute and Division of Cardiology, Department of Medicine, University of Pittsburgh, Pittsburgh, PA, United States of America.
authors.forename: Michele L
authors.initials: ML
authors.lastname: Pruce
authors.affiliation: UPMC Heart and Vascular Institute and Division of Cardiology, Department of Medicine, University of Pittsburgh, Pittsburgh, PA, United States of America.
authors.forename: Bethann E
authors.initials: BE
authors.lastname: Gabris
authors.affiliation: UPMC Heart and Vascular Institute and Division of Cardiology, Department of Medicine, University of Pittsburgh, Pittsburgh, PA, United States of America.
authors.forename: Samir
authors.initials: S
authors.lastname: Saba
authors.affiliation: Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States of America.
authors.forename: Sanjeev G
authors.initials: SG
authors.lastname: Shroff
authors.affiliation: UPMC Heart and Vascular Institute and Division of Cardiology, Department of Medicine, University of Pittsburgh, Pittsburgh, PA, United States of America.|Division of Cardiovascular Medicine, Department of Internal Medicine, University of Iowa Carver College of Medicine, Iowa City, IA, United States of America.|Abboud Cardiovascular Research Center, University of Iowa, Iowa City, IA, United States of America.
authors.forename: Ferhaan
authors.initials: F
authors.lastname: Ahmad
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002311:Cardiomyopathy, Dilated / Q000235:genetics* / Q000378:metabolism* / Q000503:physiopathology; D005260:Female; D055879:Gene Knock-In Techniques; D018390:Gene Targeting; D006321:Heart / Q000503:physiopathology*; D006801:Humans; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D009200:Myocardial Contraction; D017354:Point Mutation; D020107:Troponin T / Q000235:genetics*
chemical_list: D020107:Troponin T; D002118:Calcium