Engineered Troponins Modulate the Ca2+ Sensitivity of the Failing Human Myocardium

Abstract

The amount of force generated by cardiac sarcomeres depends in part on the sensitivity of the myofilaments to Ca2+. We tested the hypothesis that force development of the failing human heart can also be increased or decreased by Ca2+ sensitized and/or desensitized troponin (Tn). All procedures were approved by the University of Kentucky Institutional Review Board. Utilizing permeabilized multicellular preparations isolated from the hearts of patients with heart failure, we exchanged the native troponin with Tn containing either human recombinant wild-type subunits, engineered TnCs or phosphomimetic TnIs that increase or decrease myofilament Ca2+ sensitivity. The results show that compared to the wild-type Tn, our Ca2+ sensitizing L48Q TnC and S150D TnI Tn exchanges both increased (p < 0.001) pCa50 from ∼5.48 to ∼5.84 and ∼5.68, respectively. Conversely, the Ca2+ desensitizing D73N TnC and Y26E TnI Tn exchanges both decreased (p < 0.001) pCa50 to ∼5.05 and ∼5.29, respectively. In the presence of saturating Ca2+, the maximal force per cross-sectional area, shortening velocity, rate of tension redevelopment (ktr) and power were all similar for the exchanged Tns suggesting the modified Tns have a negligible direct impact on myosin function (except for Y26E TnI, which slowed ktr by ∼25%). This study demonstrates that the myofilament responsiveness of the failing human heart to Ca2+ can be modulated by engineering either TnC or TnI. These findings open the door to potential new Tn targeted therapies for heart disease.