Abstract 11999: Molecular and Cellular Characterization of RyR2 Mutations Linked to Long-QT Syndrome

Long-QT syndrome (LQTS) is a cardiac disorder characterized by prolonged QT interval and abnormal T waves on the electrocardiogram. Electrical abnormality can lead to severe arrhythmias, syncope and sudden cardiac death. Mutations in the Na + and K + channels or associated proteins account for the majority of cases; however, the genetic causes of about 20% of LQTS cases remain poorly understood. Recent genetic studies revealed novel LQTS-associated variants on the cardiac ryanodine receptor (RyR2), a Ca 2+ channel responsible for Ca 2+ -induced Ca 2+ release and excitation-contraction coupling. Given the important roles of RyR2 in the electrical activity of heart and previous evidence of RyR2 mutations in other inherited arrhythmias, we hypothesized that RyR2 mutations lead to functional alterations of the channels and contribute to dysregulated Ca 2+ release and pathological electrical remodeling. Eleven novel RyR2 mutations were identified in genetic studies of LQTS patients, including S166C, H877P, R1760W, G2094S, R2824W, R2920Q, R3673W, Y4287N, V4298M, P4534S and K4594Q. [3H] ryanodine (RyR2 ligand) binding assays revealed variable effects of the mutations on the opening probability of the RyR2 channel. In cell lines with stable expression of RyR2, Ca 2+ overload activates RyR2 channels and leads to spontaneous Ca 2+ release into the cytoplasm. Compared to WT RyR2, LQTS-associated RyR2 mutations cause an increase in the proportion of cells that exhibit spontaneous Ca 2+ release at various Ca 2+ concentrations, suggesting an increase in luminal Ca 2+ sensitivity of the channels. A transgenic mouse model carrying the R2920Q mutation was used to investigate the cellular and molecular pathways leading to LQTS. Homozygous mice showed prolonged QT interval and QTc at 5 months. Electrophysiological studies of the isolated cardiomyocytes revealed a depolarized resting membrane potential in the homozygous R2920Q cardiomyocytes and prolonged action potential duration in both heterozygous and homozygous R2920Q cardiomyocytes, compared to the WT cells. The availability of a mouse model that recapitulates the cardinal signs of LQTS will allow for deeper mechanistic insight into the role of RyR2 dysfunction as a driver of this arrhythmogenic syndrome.