Hypertrophic and Dilated Cardiomyopathy-Associated Troponin T Mutations R130C and ΔK210 Oppositely Affect Length-Dependent Calcium Sensitivity of Force Generation

Marcel Groen; Alfredo Jesus López-Dávila; Stefan Zittrich; Gabriele Pfitzer; Robert Stehle

doi:10.3389/fphys.2020.00516

Hypertrophic and Dilated Cardiomyopathy-Associated Troponin T Mutations R130C and ΔK210 Oppositely Affect Length-Dependent Calcium Sensitivity of Force Generation

Front Physiol. 2020 Jun 3:11:516. doi: 10.3389/fphys.2020.00516. eCollection 2020.

Authors

Marcel Groen¹, Alfredo Jesus López-Dávila², Stefan Zittrich³, Gabriele Pfitzer⁴, Robert Stehle³

Affiliations

¹ Department of Neurology and Neurogeriatry, Johannes Wesling Medical Center, Ruhr-University Bochum, Bochum, Germany.
² Department of Molecular and Cell Physiology, Hannover Medical School, Hanover, Germany.
³ Institute of Vegetative Physiology, University of Cologne, Cologne, Germany.
⁴ Institute of Neurophysiology, University of Cologne, Cologne, Germany.

Abstract

Length-dependent activation of calcium-dependent myocardial force generation provides the basis for the Frank-Starling mechanism. To directly compare the effects of mutations associated with hypertrophic cardiomyopathy and dilated cardiomyopathy, the native troponin complex in skinned trabecular fibers of guinea pigs was exchanged with recombinant heterotrimeric, human, cardiac troponin complexes containing different human cardiac troponin T subunits (hcTnT): hypertrophic cardiomyopathy-associated hcTnT^R130C, dilated cardiomyopathy-associated hcTnT^ΔK210 or the wild type hcTnT (hcTnT^WT) serving as control. Force-calcium relations of exchanged fibers were explored at short fiber length defined as 110% of slack length (L ₀) and long fiber length defined as 125% of L ₀ (1.25 L ₀). At short fiber length (1.1 L ₀), calcium sensitivity of force generation expressed by -log [Ca²⁺] required for half-maximum force generation (pCa₅₀) was highest for the hypertrophic cardiomyopathy-associated mutation R130C (5.657 ± 0.019), intermediate for the wild type control (5.580 ± 0.028) and lowest for the dilated cardiomyopathy-associated mutation ΔK210 (5.325 ± 0.038). Lengthening fibers from 1.1 L ₀ to 1.25 L ₀ increased calcium sensitivity in fibers containing hcTnT^R130C (delta-pCa₅₀ = +0.030 ± 0.010), did not alter calcium sensitivity in the wild type control (delta-pCa₅₀ = -0.001 ± 0.010), and decreased calcium sensitivity in fibers containing hcTnT^ΔK210 (delta-pCa₅₀ = -0.034 ± 0.013). Length-dependent activation indicated by the delta-pCa₅₀ was highly significantly (P < 0.001) different between the two mutations. We hypothesize that primary effects of mutations on length-dependent activation contribute to the development of the diverging phenotypes in hypertrophic and dilated cardiomyopathy.

Keywords: calcium sensitivity; cardiomyopathy; contractility; force generation; length dependent activation; sarcomere length; thin filament regulation; troponin.