Electromechanical and energetic dysfunction in HCM mouse models carrying troponin T mutations

Many of cTnT mutations linked to cardiomyopathies fall the TNT1 domain/N terminal tail region of unresolved high definition structure. This region (∼94–170) of cTnT is critical to Tm binding and contraction regulation. Here, the impact of the E163R mutation in cTnT-TNT1 on contractile function and tension cost was investigated using intact and skinned preparations from WT and transgenic mouse hearts. Methods: Left and right ventricular trabeculae were dissected from non-transgenic wild type (WT) and heterozygous (E163R or R92Q) mouse hearts and mounted isometrically to record twitch tension or, when skinned, Ca2+ activated force. Myofibrillar ATPase activity was measured by fluorimetric enzyme coupled assay (de Tombe and Stienen, 1995). In this thesis we aimed to assess the primary alterations of the contractile function and of tension cost caused by E163R cTnT-TNT1domain mutation, using skinned preparations or single myofibrils from WT and transgenic mouse hearts. Than we aimed to characterize the E-C coupling and pro-arrhythmogenic changes occurring in heterozygous transgenic mice carrying E163R cTnT and understand how they concur with the primary effects of the mutation to determine the contractile performance of intact E163R myocardium; to compare these Ca2+ handling abnormalities to those identified in widely described cTnT mouse model carrying R92Q mutation, and to test the effects of specific pharmacological interventions, which may be effective to acutely reverse some of the E-C coupling and mechanical alterations observed. Conclusions: We observed that primary myofilament changes in R92Q (increased Ca2+ sensitivity) are associated with a large spectrum of EC-coupling and sarcolemmal alterations, which appear to be the major contributor to the observed mechanical dysfunction and arrhythmogeneicity in this mouse line, resembling advanced human disease. In E163R instead, in the absence of major EC-coupling changes, the impairment of myofilament function (increased Ca2+ sensitivity and higher Tension Cost) appear to be the leading element determining mechanical abnormalities.