Altered regulation of cardiac muscle contraction by troponin T mutations that cause familial hypertrophic cardiomyopathy

To study the effect of troponin (Tn) T mutations that cause familial hypert rophic cardiomyopathy (FHC) on cardiac muscle contraction, wild-type, and t he following recombinant human cardiac TnT mutants were cloned and expresse d: I79N, R92Q, F110I, E163K, R278C, and intron 16(G(1) --> A) (In16). These TnT FHC mutants were reconstituted into skinned cardiac muscle preparation s and characterized for their effect on maximal steady state force activati on, inhibition, and the Ca2+ sensitivity of force development. Troponin com plexes containing these mutants were tested for their ability to regulate a ctin-tropomyosin(Tm)-activated myosin-ATPase activity. TnT(R278C) and TnT(F 110I) reconstituted preparations demonstrated dramatically increased Ca2+ s ensitivity of force development, while those with TnT(R92Q) and TnT(I79N) s howed a moderate increase. The deletion mutant, TnT(In16), significantly de creased both the activation and the inhibition of force, and substantially decreased the activation and the inhibition of actin-Tm-activated myosin-AT Pase activity. ATPase activation was also impaired by TnT(F110I), while its inhibition was reduced by TnT(R278C). The TnT(E163K) mutation had the smal lest effect on the Ca2+ sensitivity of force; however, it produced an eleva ted activation of the ATPase activity in reconstituted thin filaments. Thes e observed changes in the Ca2+ regulation of force development caused by th ese mutations would likely cause altered contractility and contribute to th e development of FHC.