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Different functional properties of troponin T mutants that cause dilated cardiomyopathy
Gayathri Venkatraman1, Keita Harada, Aldrin V Gomes
1Department of Molecular and Cellular Pharmacology, University of Miami School Of Medicine, 1600 NW 10th Avenue, Miami, FL 33101, USA.
Abstract:
The effects of Troponin T (TnT) mutants R141W and DeltaK210, the only two currently known mutations in TnT that cause dilated cardiomyopathy(DCM) independent of familial hypertrophic cardiomyopathy (FHC), and TnT-K273E, a mutation that leads to a progression from FHC to DCM, were investigated. Studies on the Ca2+ sensitivity of force development in porcine cardiac fibers demonstrated that TnT-DeltaK210 caused a significant decrease in Ca2+ sensitivity, whereas the TnT-R141W did not result in any change in Ca2+ sensitivity when compared with human cardiac wild-type TnT (HCWTnT). TnT-DeltaK210 also caused a decrease in maximal force when compared with HCWTnT and TnT-R141W. In addition, the TnT-DeltaK210 mutant decreased maximal ATPase activity in the presence of Ca2+. However, the TnT-K273E mutation caused a significant increase in Ca2+ sensitivity but behaved similarly to HCWTnT in actomyosin activation assays. Inhibition of ATPase activity in reconstituted actin-activated myosin ATPase assays was similar for all three TnT mutants and HCWTnT. Additionally, circular dichroism studies suggest that the secondary structure of all three TnT mutants was similar to that of the HCWTnT. These results suggest that a rightward shift in Ca2+ sensitivity is not the only determinant for the phenotype of DCM.
Insights
Investigating Troponin T (TnT) mutations reveals that altered Ca2+ sensitivity and force are key in dilated cardiomyopathy (DCM). These findings suggest Ca2+ sensitivity shifts alone do not fully explain DCM development.
Area of Science:
- Cardiovascular Biology
- Molecular Cardiology
- Biochemistry
Background:
- Dilated cardiomyopathy (DCM) and familial hypertrophic cardiomyopathy (FHC) are significant heart muscle diseases.
- Troponin T (TnT) mutations are implicated in cardiomyopathies, but their precise functional impact requires further elucidation.
- Specific TnT mutations, R141W and DeltaK210, are linked to DCM independently of FHC, while K273E progresses from FHC to DCM.
Purpose of the Study:
- To investigate the functional effects of specific Troponin T (TnT) mutants (R141W, DeltaK210, K273E) on cardiac muscle mechanics.
- To determine the impact of these TnT mutations on calcium (Ca2+) sensitivity, force generation, and ATPase activity.
- To explore the relationship between altered Ca2+ sensitivity and the development of DCM phenotypes.
Main Methods:
- Experiments utilized porcine cardiac fibers to assess Ca2+ sensitivity of force development.
- Actomyosin activation assays were performed to evaluate myosin ATPase activity.
- Circular dichroism spectroscopy was employed to analyze the secondary structure of TnT mutants.
Main Results:
- TnT-DeltaK210 significantly decreased Ca2+ sensitivity and maximal force, along with reduced maximal ATPase activity.
- TnT-R141W showed no change in Ca2+ sensitivity but exhibited altered maximal force compared to wild-type.
- TnT-K273E increased Ca2+ sensitivity but showed normal actomyosin activation and ATPase inhibition, with similar secondary structures across all mutants.
Conclusions:
- Altered Ca2+ sensitivity and force dynamics are critical factors in the pathogenesis of DCM caused by specific TnT mutations.
- The TnT-K273E mutation's impact on Ca2+ sensitivity does not fully explain its role in DCM progression.
- These findings indicate that a simple rightward shift in Ca2+ sensitivity is insufficient to account for the DCM phenotype, highlighting the complexity of TnT's role in cardiac function.