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.
Highlights
Familial cardiomyopathies are primary disorders of the myocardium caused by heritable mutations in single genes, the most common of which are hypertrophic (HCM) and dilated cardiomyopathy (DCM) [1, 2]
A intriguing discovery has been that mutations in some of the same genes, such as the gene encoding cardiac troponin T can lead to either DCM or HCM [4]. cTnT is a component of the troponin complex within the thin filament of the sarcomere which allows actomyosin interaction and contraction to occur in response to Ca2+
Gene-targeted mice with a mutation in Tnnt2 previously discovered in human families with DCM [14] were generated by homologous recombination (Fig 1A)
Summary
Familial cardiomyopathies are primary disorders of the myocardium caused by heritable mutations in single genes, the most common of which are hypertrophic (HCM) and dilated cardiomyopathy (DCM) [1, 2]. Considerable progress has been made in the past two decades in determining the molecular genetic basis for DCM and HCM, with mutations in genes encoding sarcomere proteins accounting for a significant fraction of DCM and a majority of HCM cases. A intriguing discovery has been that mutations in some of the same genes, such as the gene encoding cardiac troponin T (cTnT, TNNT2) can lead to either DCM or HCM [4]. CTnT is a component of the troponin complex within the thin filament of the sarcomere which allows actomyosin interaction and contraction to occur in response to Ca2+ A intriguing discovery has been that mutations in some of the same genes, such as the gene encoding cardiac troponin T (cTnT, TNNT2) can lead to either DCM or HCM [4]. cTnT is a component of the troponin complex within the thin filament of the sarcomere which allows actomyosin interaction and contraction to occur in response to Ca2+
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
