Abstract 58: Differential Ventricular Remodeling Induced by Thin Filament Mutational Effects on the Tropomyosin Overlap Structure

Inherited mutations in cardiac thin filament proteins create primary alterations in structure. These changes then lead to pathologic remodeling of the heart. We have proposed that two mutations, tropomyosin (Tm) D230N which leads to dilated cardiomyopathy (DCM) and cardiac troponin T (cTnT) R92L, which leads to hypertrophic cardiomyopathy (HCM), directly affect the Tm overlap, a crucial structure regulating myofilament activation. These mutations lead to divergent ventricular remodeling, which we hypothesize is caused by differential effects on the Tm overlap, an inherently dynamic system. In order to investigate this hypothesis, we used time-resolved Forster resonance energy transfer (FRET) to measure discrete distances across the proteins of the overlap, and differential scanning calorimetry (DSC) in order to characterize the baseline structure of this region as well as the effects of mutants. We found that the cTnT R92L mutant increased interprotein distance at the proximal N-terminal end of this region. In contrast, the Tm D230N mutant decreases interprotein distance at the proximal C-terminal end of the overlap. DSC studies showed a significant increase in the association of Tm with actin in the presence of Tm D230N, predicted to increase cooperativity of thin filament activation. These finding are in agreement both with the human population who carry the disease, as well as the mouse lines in our lab, which phenocopy the human disease. Overall, the study further characterized the wild type structure of the Tm overlap, and revealed the differential structural effects of the mutants, thereby, for the first time linking local changes in structure to phenotypic changes and ventricular remodeling leading to HCM and DCM. Further studies will investigate the role of isoform and phosphorylation modifiers, elucidating how these modify human disease in the presence and absence of cardiomyopathy linked mutations.