Characterization of Troponin T Dilated Cardiomyopathy Mutations in the Fetal Troponin Isoform

Venkatraman, Gayathri; Gomes, Aldrin V.; Kerrick, W. Glenn L.; Potter, James D.

doi:10.1074/jbc.m409337200

Cited by 35 publications

(34 citation statements)

References 43 publications

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“…This effect of different HCTnT isoforms on the Ca 2ϩ sensitivity of force development has been reported several times by our laboratory (15,16,21). We have also observed an additive increase of Ca 2ϩ sensitivity in fibers reconstituted with SSTnI⅐CTnC compared with the CTnI⅐CTnC.…”

Section: Effect Of Hctnt Rcm Mutant Isoforms On the Casupporting

confidence: 86%

A Troponin T Mutation That Causes Infantile Restrictive Cardiomyopathy Increases Ca2+ Sensitivity of Force Development and Impairs the Inhibitory Properties of Troponin

Pinto

Parvatiyar

Jones

et al. 2008

Journal of Biological Chemistry

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Restrictive cardiomyopathy (RCM) is a rare disorder characterized by impaired ventricular filling with decreased diastolic volume. We are reporting the functional effects of the first cardiac troponin T (CTnT) mutation linked to infantile RCM resulting from a de novo deletion mutation of glutamic acid 96. The mutation was introduced into adult and fetal isoforms of human cardiac TnT (HCTnT3-⌬E96 and HCTnT1-⌬E106, respectively) and studied with either cardiac troponin I (CTnI) or slow skeletal troponin I (SSTnI). Skinned cardiac fiber measurements showed a large leftward shift in the Ca 2؉ sensitivity of force development with no differences in the maximal force. HCTnT1-⌬E106 showed a significant increase in the activation of actomyosin ATPase with either CTnI or SSTnI, whereas HCTnT3-⌬E96 was only able to increase the ATPase activity with CTnI. Both mutants showed an impaired ability to inhibit the ATPase activity. The capacity of the CTnI⅐CTnC and SSTnI⅐CTnC complexes to fully relax the fibers after TnT displacement was also compromised. Experiments performed using fetal troponin isoforms showed a less severe impact compared with the adult isoforms, which is consistent with the cardioprotective role of SSTnI and the rapid onset of RCM after birth following the isoform switch. These data indicate that troponin mutations related to RCM may have specific functional phenotypes, including large leftward shifts in the Ca 2؉ sensitivity and impaired abilities to inhibit ATPase and to relax skinned fibers. All of this would account for and contribute to the severe diastolic dysfunction seen in RCM.

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Section: Effect Of Hctnt Rcm Mutant Isoforms On the Casupporting

confidence: 86%

A Troponin T Mutation That Causes Infantile Restrictive Cardiomyopathy Increases Ca2+ Sensitivity of Force Development and Impairs the Inhibitory Properties of Troponin

Pinto

Parvatiyar

Jones

et al. 2008

Journal of Biological Chemistry

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“…Fluorescence Labeling of CTnC-Monocysteine CTnC derivatives were engineered using cDNAs previously cloned for G159D, L29Q, and WT CTnC by substituting Cys 35 for Ser in order to direct specific IAANS incorporation to Cys 84 (denoted -CTnC(C84) IA ). The CTnCs were also doubly labeled with IAANS at Cys 35 and Cys 84 (denoted -CTnC IA ).…”

Section: Methodsmentioning

confidence: 99%

“…The CTnCs were also doubly labeled with IAANS at Cys 35 and Cys 84 (denoted -CTnC IA ). Fluorescent incorporation and subsequent purification of labeled CTnC followed previous methods (38).…”

Section: Methodsmentioning

confidence: 99%

Challenging Current Paradigms Related to Cardiomyopathies

Dweck

Hus

Potter

2008

Journal of Biological Chemistry

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Two novel mutations (G159D and L29Q) in cardiac troponin C (CTnC) associate their phenotypic outcomes with dilated (DCM) and hypertrophic cardiomyopathy (HCM), respectively. Current paradigms propose that sarcomeric mutations associated with DCM decrease the myofilament Ca 2؉ sensitivity, whereas those associated with HCM increase it. Therefore, we incorporated the mutant CTnCs into skinned cardiac muscle in order to determine if their effects on the Ca 2؉ sensitivities of tension and ATPase activity coincide with the current paradigms and phenotypic outcomes. The G159D-CTnC decreases the Ca 2؉ sensitivity of tension and ATPase activation and reduces the maximal ATPase activity when incorporated into regulated actomyosin filaments. Under the same conditions, the L29Q-CTnC has no effect. Surprisingly, changes in the apparent G159D-CTnC Ca 2؉ affinity measured by tension in fibers do not occur in the isolated CTnC, and large changes measured in the isolated L29Q-CTnC do not manifest in the fiber. These counterintuitive findings are justified through a transition in Ca 2؉ affinity occurring at the level of cardiac troponin and higher, implying that the true effects of these mutations become apparent as the hierarchical level of the myofilament increases. Therefore, the contractile apparatus, representing a large cooperative machine, can provide the potential for a change (G159D) or no change (L29Q) in the Ca 2؉ regulation of contraction. In accordance with the clinical outcomes and current paradigms, the desensitization of myofilaments from G159D-CTnC is expected to weaken the contractile force of the myocardium, whereas the lack of myofilament changes from L29Q-CTnC may preserve diastolic and systolic function.Cardiomyopathies are diseases of the myocardium that often lead to cardiac remodeling to compensate for deficiencies in cardiac output (1). In the case of dilated cardiomyopathy (DCM), 2 heart failure is characterized by a systolic dysfunction (i.e. reduced ejection fraction), whereas hypertrophic (HCM) and restrictive cardiomyopathies are characterized as having diastolic dysfunctions (i.e. impaired relaxation) (2). In many cases, the cardiac contractile dysfunction is attributed to inherited sarcomeric gene mutations. The functional effects of more than 40 thin filament mutations associated with cardiomyopathies assessed in vitro suggest that these mutations affect the Ca 2ϩ responsiveness of the myofilament in the absence of CTnI phosphorylation. As the number of in vitro-characterized mutations continues to grow, a developing paradigm emerges that associates decreases in the myofilament Ca 2ϩ sensitivity with DCM (3-7) and associates increases with HCM (4, 6 -12) and restrictive cardiomyopathy (13)(14)(15)(16)(17). This suggests that distinct effects on the Ca 2ϩ -dependent processes of the myofilament are critical determinants of the severity and molecular pathologies of these diseases.The first cardiac troponin C (CTnC) mutation (E59D/D75Y) was found in an explanted heart from an adult male who died fr...

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“…Most biochemical thin filament studies have been performed using non-human cardiac myosin (e.g. Szczesna et al, 2000;Venkatraman et al, 2005Venkatraman et al, , 2003 or skeletal myosin (e.g. Kobayashi et al, 2013;Lin et al, 1996;Mirza et al, 2005;Tobacman et al, 1999).…”

Section: + -Desensitizing Respectivelymentioning

confidence: 99%

Effects of hypertrophic and dilated cardiomyopathy mutations on power output by human β-cardiac myosin

Spudich

Aksel

Bartholomew

et al. 2016

Journal of Experimental Biology

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Hypertrophic cardiomyopathy is the most frequently occurring inherited cardiovascular disease, with a prevalence of more than one in 500 individuals worldwide. Genetically acquired dilated cardiomyopathy is a related disease that is less prevalent. Both are caused by mutations in the genes encoding the fundamental forcegenerating protein machinery of the cardiac muscle sarcomere, including human β-cardiac myosin, the motor protein that powers ventricular contraction. Despite numerous studies, most performed with non-human or non-cardiac myosin, there is no clear consensus about the mechanism of action of these mutations on the function of human β-cardiac myosin. We are using a recombinantly expressed human β-cardiac myosin motor domain along with conventional and new methodologies to characterize the forces and velocities of the mutant myosins compared with wild type. Our studies are extending beyond myosin interactions with pure actin filaments to include the interaction of myosin with regulated actin filaments containing tropomyosin and troponin, the roles of regulatory light chain phosphorylation on the functions of the system, and the possible roles of myosin binding protein-C and titin, important regulatory components of both cardiac and skeletal muscles.

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Characterization of Troponin T Dilated Cardiomyopathy Mutations in the Fetal Troponin Isoform

Cited by 35 publications

References 43 publications

A Troponin T Mutation That Causes Infantile Restrictive Cardiomyopathy Increases Ca2+ Sensitivity of Force Development and Impairs the Inhibitory Properties of Troponin

A Troponin T Mutation That Causes Infantile Restrictive Cardiomyopathy Increases Ca2+ Sensitivity of Force Development and Impairs the Inhibitory Properties of Troponin

Challenging Current Paradigms Related to Cardiomyopathies

Effects of hypertrophic and dilated cardiomyopathy mutations on power output by human β-cardiac myosin

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