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Analysis of the molecular pathogenesis of cardiomyopathy-causing cTnT mutants I79N, ΔE96, and ΔK210
Fan Bai1, Hannah M Caster, Jose R Pinto
1Department of Anatomy and Cell Biology, The University of Iowa, Iowa City, Iowa, USA.
Insights
Cardiac troponin T (TnT) mutations cause distinct cardiomyopathies. This study reveals unique molecular mechanisms for each TnT mutation, impacting cardiac muscle force generation differently.
Area of Science:
- Cardiovascular Biology
- Molecular Cardiology
- Biophysics
Background:
- Cardiac troponin T (TnT) mutations are linked to various cardiomyopathies, including hypertrophic, restrictive, and dilated forms.
- Understanding the molecular basis of these mutations is crucial for developing targeted therapies.
Purpose of the Study:
- To investigate the functional effects of specific TnT mutants (I79N, ΔE96, ΔK210) on cardiac muscle mechanics.
- To elucidate the distinct molecular mechanisms underlying different TnT mutation-related cardiomyopathies.
Main Methods:
- Utilized thin-filament extraction/reconstitution technique to study TnT mutants.
- Assessed effects of Ca(2+), ATP, phosphate, and ADP on force and transients at 25°C.
- Employed sinusoidal analysis to deduce equilibrium constants related to cross-bridge cycling.
Main Results:
- The ΔK210 mutant showed significantly reduced maximal Ca(2+) tension and Ca(2+)-activatable tension compared to wild-type (WT).
- TnT mutants I79N and ΔE96 exhibited increased Ca(2+) sensitivity, while ΔK210's sensitivity was similar to WT.
- All mutants displayed altered ADP association (K0), force generation (K4), and cross-bridge detachment (K2) equilibrium constants compared to WT.
Conclusions:
- The molecular pathogenesis of cardiac TnT mutation-related cardiomyopathies differs for each mutation.
- Specific TnT mutations lead to distinct alterations in cardiac muscle force generation and cross-bridge kinetics.
- Findings highlight the complex interplay between TnT structure, function, and disease phenotypes.
Abstract:
Three troponin T (TnT) mutants that cause hypertrophic, restrictive, and dilated cardiomyopathy (I79N, ΔE96, and ΔK210, respectively), were examined using the thin-filament extraction/reconstitution technique. Effects of Ca(2+), ATP, phosphate, and ADP concentrations on force and its transients were studied at 25°C. Maximal Ca(2+) tension (THC) and Ca(2+)-activatable tension (Tact), respectively, were similar among I79N, ΔE96, and WT, whereas ΔK210 led to a significantly lower THC (∼20% less) and Tact (∼25% less) than did WT. In pCa solution containing 8 mM Pi and ionic strength adjusted to 200 mM, the Ca(2+) sensitivity (pCa50) of I79N (5.63 ± 0.02) and ΔE96 (5.60 ± 0.03) was significantly greater than that of WT (5.45 ± 0.04), but the pCa50 of ΔK210 (5.54 ± 0.04) remained similar to that of WT. Five equilibrium constants were deduced using sinusoidal analysis. All three mutants showed significantly lower K0 (ADP association constant) and larger K4 (equilibrium constant of force generation step) relative to the corresponding values for WT. I79N and ΔK210 were associated with a K2 (equilibrium constant of cross-bridge detachment step) significantly lower than that of ΔE96 and WT. These results demonstrated that at pCa 4.66, the force/cross-bridge is ∼18% less in I79N and ∼41% less in ΔK210 than that in WT. These results indicate that the molecular pathogenesis of the cardiac TnT mutation-related cardiomyopathies is different for each mutation.
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