Effects of Missense Mutations Phe110Ile and Glu244Asp in Human Cardiac Troponin T on Force Generation in Skinned Cardiac Muscle Fibers

1999 ◽  
Vol 126 (3) ◽  
pp. 457-460 ◽  
Author(s):  
H. Nakaura ◽  
F. Yanaga ◽  
I. Ohtsuki ◽  
S. Morimoto
Keyword(s):  
Cardiac Muscle ◽  
Cardiac Troponin ◽  
Troponin T ◽  
Muscle Fibers ◽  
Force Generation ◽  
Cardiac Troponin T ◽  
Missense Mutations ◽  
Cardiac Muscle Fibers

Increase in tension-dependent ATP consumption induced by cardiac troponin T mutation

2005 ◽  
Vol 289 (5) ◽  
pp. H2112-H2119 ◽  
Author(s):  
Murali Chandra ◽  
Matthew L. Tschirgi ◽  
Jil C. Tardiff
Keyword(s):  
Cardiac Myocytes ◽  
Cardiac Troponin ◽  
Troponin T ◽  
Muscle Fibers ◽  
Familial Hypertrophic Cardiomyopathy ◽  
Mechanical Activity ◽  
Cardiac Troponin T ◽  
Skinned Muscle ◽  
Plasmic Reticulum ◽  
Cardiac Muscle Fibers

How different mutations in cardiac troponin T (cTnT) lead to distinct secondary downstream cellular remodeling in familial hypertrophic cardiomyopathy (FHC) remains elusive. To explore the molecular basis for the distinct impact of different mutations in cTnT on cardiac myocytes, we studied mechanical activity of detergent-skinned muscle fiber bundles from different lines of transgenic (TG) mouse hearts that express wild-type cTnT (WTTG), R92W cTnT, R92L cTnT, and Delta-160 cTnT (deletion of amino acid 160). The amount of mutant cTnT is ∼50% of the total myocellular cTnT in both R92W and R92L TG mouse hearts and ∼35% in Delta-160 TG mouse hearts. Myofilament Ca2+ sensitivity was enhanced in all mutant cTnT TG cardiac muscle fibers. Compared with the WTTG fibers, Ca2+ sensitivity increased significantly at short sarcomere length (SL) of 1.9 μm ( P < 0.001) in R92W TG fibers by 2.2-fold, in R92L by 2.0-fold, and in Delta-160 by 1.3-fold. At long SL of 2.3 μm, Ca2+ sensitivity increased significantly ( P < 0.01) in a similar manner (R92W, 2.5-fold; R92L, 1.9-fold; Delta-160, 1.3-fold). Ca2+-activated maximal tension remained unaltered in all TG muscle fibers. However, tension-dependent ATP consumption increased significantly in Delta-160 TG muscle fibers at both short SL (23%, P < 0.005) and long SL (37%, P < 0.0001), suggesting a mutation-induced change in cross-bridge detachment rate constant. Chronic stresses on relative cellular ATP level in cardiac myocytes may cause a strain on energy-dependent Ca2+ homeostatic mechanisms. This may result in pathological remodeling that we observed in Delta-160 TG cardiac myocytes where the ratio of sarco(endo)plasmic reticulum Ca2+-ATPase 2/phospholamban decreased significantly. Our results suggest that different types of stresses imposed on cardiac myocytes would trigger distinct cellular signaling, which leads to remodeling that may be unique to some mutants.

scholarly journals Hypertrophic cardiomyopathy mutation in cardiac troponin T (R95H) attenuates length-dependent activation in guinea pig cardiac muscle fibers

2017 ◽  
Vol 313 (6) ◽  
pp. H1180-H1189 ◽  
Author(s):  
Alexis V. Mickelson ◽  
Murali Chandra
Keyword(s):  
Hypertrophic Cardiomyopathy ◽  
Guinea Pig ◽  
Central Region ◽  
Cardiac Troponin ◽  
Sarcomere Length ◽  
Troponin T ◽  
Cardiac Troponin T ◽  
Cross Bridge ◽  
Cardiac Muscle Fibers ◽  
Length Dependent Activation

The central region of cardiac troponin T (TnT) is important for modulating the dynamics of muscle length-mediated cross-bridge recruitment. Therefore, hypertrophic cardiomyopathy mutations in the central region may affect cross-bridge recruitment dynamics to alter myofilament Ca2+ sensitivity and length-dependent activation of cardiac myofilaments. Given the importance of the central region of TnT for cardiac contractile dynamics, we studied if hypertrophic cardiomyopathy-linked mutation (TnTR94H)-induced effects on contractile function would be differently modulated by sarcomere length (SL). Recombinant wild-type TnT (TnTWT) and the guinea pig analog of the human R94H mutation (TnTR95H) were reconstituted into detergent-skinned cardiac muscle fibers from guinea pigs. Steady-state and dynamic contractile measurements were made at short and long SLs (1.9 and 2.3 µm, respectively). Our results demonstrated that TnTR95H increased pCa50 (−log of free Ca2+ concentration) to a greater extent at short SL; TnTR95H increased pCa50 by 0.11 pCa units at short SL and 0.07 pCa units at long SL. The increase in pCa50 associated with an increase in SL from 1.9 to 2.3 µm (ΔpCa50) was attenuated nearly twofold in TnTR95H fibers; ΔpCa50 was 0.09 pCa units for TnTWT fibers but only 0.05 pCa units for TnTR95H fibers. The SL dependency of rate constants of cross-bridge distortion dynamics and tension redevelopment was also blunted by TnTR95H. Collectively, our observations on the SL dependency of pCa50 and rate constants of cross-bridge distortion dynamics and tension redevelopment suggest that mechanisms underlying the length-dependent activation cardiac myofilaments are attenuated by TnTR95H. NEW & NOTEWORTHY Mutant cardiac troponin T (TnTR95H) differently affects myofilament Ca2+ sensitivity at short and long sarcomere length, indicating that mechanisms underlying length-dependent activation are altered by TnTR95H. TnTR95H enhances myofilament Ca2+ sensitivity to a greater extent at short sarcomere length, thus attenuating the length-dependent increase in myofilament Ca2+ sensitivity.

scholarly journals Coexistence of cardiac troponin T variants reduces heart efficiency

2010 ◽  
Vol 299 (1) ◽  
pp. H97-H105 ◽  
Author(s):  
Han-Zhong Feng ◽  
J.-P. Jin
Keyword(s):  
Cardiac Muscle ◽  
Transgenic Mouse ◽  
Cardiac Troponin ◽  
Troponin T ◽  
Ex Vivo ◽  
Heart Function ◽  
Left Ventricular Pressure ◽  
Left Ventricular ◽  
Cardiac Troponin T ◽  
Myofilament Activation

Corresponding to the synchronized contraction of the myocardium and rhythmic pumping function of the heart, a single form of cardiac troponin T (cTnT) is present in the adult cardiac muscle of humans and most other vertebrate species. Alternative splicing variants of cTnT are found in failing human hearts and animal dilated cardiomyopathies. Biochemical analyses have shown that these cTnT variants are functional and produce shifted myofilament Ca2+ sensitivity. We proposed a hypothesis that the coexistence of two or more functionally distinct TnT variants in the adult ventricular muscle that is normally activated as a syncytium may decrease heart function and cause cardiomyopathy (Huang et al., Am J Physiol Cell Physiol 294: C213–C222, 2008). In the present study, we studied transgenic mouse hearts expressing one or two cTnT variants in addition to normal adult cTnT to investigate whether desynchronized myofilament activation decreases ventricular efficiency. The function of ex vivo working hearts was examined in the absence of systemic neurohumoral influence. The results showed that the transgenic mouse hearts produced lower maximum left ventricular pressure, slower contractile and relaxation velocities, and decreased stroke volume compared with wild-type controls. Ventricular pumping efficiency, calculated by the ejection integral versus total systolic integral and cardiac work versus oxygen consumption, was significantly lower in transgenic mouse hearts and corresponded to the number of cTnT variants present. The results indicated a pathogenic mechanism in which the coexistence of functionally different cTnT variants in cardiac muscle reduces myocardial efficiency due to desynchronized thin filament activation.

P1617Contractile imbalance as trigger for HCM pathogenesis: evidence from mutations in different sarcomeric proteins

2019 ◽  
Vol 40 (Supplement_1) ◽  
Author(s):  
J Montag ◽  
V Burkart ◽  
J Beck ◽  
D Aldag-Niebling ◽  
B Piep ◽  
...  
Keyword(s):  
Cardiac Troponin ◽  
Troponin I ◽  
Troponin T ◽  
Calcium Sensitivity ◽  
Force Generation ◽  
Mutant Protein ◽  
Common Mechanism ◽  
Fluorescence Intensity Ratio ◽  
Missense Mutations ◽  
Sarcomeric Proteins

Abstract Hypertrophic cardiomyopathy (HCM) is mostly caused by mutations in sarcomeric proteins. About 90% of mutation-positive patients have mutations in one of four proteins: the β-myosin heavy chain (β-MyHC, MYH7), cardiac myosin binding protein C (cMyBP-C, MYBPC3), cardiac troponin I (cTnI, TNNI3), and cardiac troponin T. Almost all patients are heterozygous; they express the wildtype and the mutant protein isoform. For patients with β-MyHC missense mutations we have reported previously that individual cardiomyocytes show a significant variability in force generation and calcium-sensitivity, ranging from essentially donor–like to highly altered function. We provided evidence that the MYH7-alleles are switched on and off stochastically and independently from each other in each cell. This burst-like expression leads to highly variable fractions of mutant and wildtype mRNA between the cardiomyocytes, presumably causing variable fractions of mutant protein. We assume that this variability underlies the determined contractile imbalance leading to stronger cells that over-contract and over-stretch weaker cells. This could trigger development of HCM-hallmarks like myocyte disarray, fibrosis and hypertrophy. To test whether contractile imbalance may provide a common mechanism of HCM-development, we extended our analysis to additional sarcomeric proteins with HCM-mutations. Analysis of cardiomyocytes from a patient with missense mutation R145W in cTnI revealed highly variable calcium-sensitivity between individual cardiomyocytes, substantially higher than for donor cardiomyocytes. This functional heterogeneity was associated with highly variable fractions of mutant TNNI3-mRNA from cell-to-cell. This suggests that not only missense mutations in β-MyHC but also in cTnI induce hallmarks of HCM via the contractile imbalance mechanism. In contrast to missense mutations, truncation mutations in cMyBP-C presumably cause HCM via haploinsufficiency. Degradation of truncated proteins causes a lack of functional cMyBP-C and thereby alters function of the sarcomere. We hypothesized that different levels of haploinsufficiency from cell-to-cell may also cause contractile imbalance. Therefore we examined a patient with truncation mutation c.927–2A>G in cMyBP-C. Western blot analysis revealed no truncated protein and reduced levels of wildtype-cMyBP-C, consistent with haploinsufficiency. We also observed a significantly higher variability in fluorescence intensity ratio (MyBPC/Alpha-Actinin) for cardiomyocytes of the HCM-patient than in donor cardiomyocytes. The patchy distribution of cMyBP-C in histological tissue section indicated variable levels of functional protein from cell-to-cell. Functional analysis revealed significantly more variable isometric force generation from cell to cell of patient cardiomyocytes compared to donor, suggesting contractile imbalance. We conclude that contractile imbalance may be a potential common mechanism of HCM pathogenesis. Acknowledgement/Funding German Research Foundation (DFG)

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