Functional Studies on Ion Channel Mutations in Hereditary Sudden Cardiac Death Syndrome in Taiwan

• Main Authors: Chia-Hisang Hsueh, 薛嘉祥
• Other Authors: 賴凌平
• Format: Others
• Language: en_US
• Online Access: http://ndltd.ncl.edu.tw/handle/07436277256943403636

博士 === 國立臺灣大學 === 藥理學研究所 === 97 === Hereditary sudden cardiac death syndromes are major causes of unexpected death especially in young individuals. However, current treatment modalities for these syndromes are not satisfactory, presumably due to poor understanding of the underlying mechanisms that lead to the pathogenesis of these diseases. For the past decades, several responsible genes for these syndromes have been identified and studied. In our studies, we screened patients with LQTS or Brugada syndrome in Taiwan and identified three mutations in KCNH2 responsible for LQTS and three mutations in SCN5A responsible for Brugada syndrome. Functional studies were performed to elucidate the possible mechanisms of the disease-causing mutations. KCNH2, or hERG, encodes the pore forming subunit of the rapid activating delayed rectifier potassium channel (IKr), which plays important roles in the repolarization process during the late phase of cardiac action potential. The three LQTS-related mutations of the KCNH2 genes all lead to a reduced IKr and might be related to the prolongation of action potential duration and the prolongation of QT interval in ECG. These mutations are p.N633D, p.R744fs, and p.P923fs. When expressed in HEK293T cells, p.N633D and p.R744fs channels displayed no current while p.P923fs channel elicited current with significantly lower current density and faster inactivation kinetics. In western blotting analysis, pR744fs was the only one with glycosylation defect. In confocal microscopic studies, p.R744fs-GFP also revealed trafficking defect. However, p.R744fs-GFP differed from pR744fs in being fully glycosylated while p.R744fs fusion with GFP at the N-terminus revealed glycosylation defect. In co-immunoprecipitation studies, the assembling capacity of p.N633D, and p.P923fs were intact p.R744fs failed to interact with neither WT nor itself to form tetramers. SCN5A is the most well known responsible gene that causes Brugada syndrome. Until now, more than a hundred mutations in SCN5A responsible for Brugada syndrome have been described. Functional studies of some of the mutations have been performed and showed that a reduction of human cardiac sodium current accounts for the pathogenesis of Brugada syndrome. Here we reported three novel SCN5A mutations identified in patients with Brugada syndrome in Taiwan (p.I848fs, p.R965C, and p.1876insM). Their electrophysiological properties were altered in patch clamp analysis. The p.I848fs mutant generated no sodium current. The p.R965C and p.1876insM mutants produced channels with steady state inactivation shifted to a more negative potential (9.4mV and 8.5mV respectively), and slower recovery from inactivation. Besides, the steady state activation of p.1876insM was altered and was shifted to a more positive potential (7.69mV). With increasing understanding of the underlying mechanisms of hereditary sudden cardiac death, we expect advances in the diagnosis, treatment, and prevention of these syndromes.