Abstract
Simple SummaryIn this study, the induced pluripotent stem cell-derived cardiomyocyte model from a patient with long QT syndrome harboring a heterozygous Nav1.5 R1623Q mutation exhibited prolonged field potential duration corrected by Fridericia’s formula (FPDcF, analogous to QTcF). FPDcF was shortened with mexiletine treatment and increased the frequency of arrhythmia-like EAD events following E4031, an Ikr blocker, administration. These characteristics partly reflect the patient phenotypes. As the R1623Q mutation is related to severe congenital LQT syndrome in fetuses and neonates, the effect of the neonatal variants on the electrophysiological properties of the R1623Q mutant was examined using an automated patch-clamp system. Our results demonstrated that both R1623Q and neonatal R1623Q delayed inactivation of INa and increased late Na current. We speculated that neonatal Nav1.5 ameliorates QTc prolongation. Developmental switching of neonatal/adult Nav1.5 isoforms might play a role in the mechanisms underlying severe long QT syndrome in fetuses and neonates.The SCN5A R1623Q mutation is one of the most common genetic variants associated with severe congenital long QT syndrome 3 (LQT3) in fetal and neonatal patients. To investigate the properties of the R1623Q mutation, we established an induced pluripotent stem cell (iPSC) cardiomyocyte (CM) model from a patient with LQTS harboring a heterozygous R1623Q mutation. The properties and pharmacological responses of iPSC-CMs were characterized using a multi-electrode array system. The biophysical characteristic analysis revealed that R1623Q increased open probability and persistent currents of sodium channel, indicating a gain-of-function mutation. In the pharmacological study, mexiletine shortened FPDcF in R1623Q-iPSC-CMs, which exhibited prolonged field potential duration corrected by Fridericia’s formula (FPDcF, analogous to QTcF). Meanwhile, E4031, a specific inhibitor of human ether-a-go-go-related gene (hERG) channel, significantly increased the frequency of arrhythmia-like early after depolarization (EAD) events. These characteristics partly reflect the patient phenotypes. To further analyze the effect of neonatal isoform, which is predominantly expressed in the fetal period, on the R1623Q mutant properties, we transfected adult form and neonatal isoform SCN5A of control and R1623Q mutant SCN5A genes to 293T cells. Whole-cell automated patch-clamp recordings revealed that R1623Q increased persistent Na+ currents, indicating a gain-of-function mutation. Our findings demonstrate the utility of LQT3-associated R1623Q mutation-harboring iPSC-CMs for assessing pharmacological responses to therapeutic drugs and improving treatment efficacy. Furthermore, developmental switching of neonatal/adult Nav1.5 isoforms may be involved in the pathological mechanisms underlying severe long QT syndrome in fetuses and neonates.
Highlights
Type 3 long QT syndrome (LQT3), which is caused by SCN5A gain-of-function mutations, is a potentially life-threatening disease with a high risk of sudden cardiac death resulting from torsade de points (TdP) [1,2,3]
The co-administration of lidocaine was effective in suppressing sustained ventricular tachycardia (VT)
E-4031 promoted the formation of an early after depolarization (EAD)- and triggered activity (TA)-like field p tential waveform in the R1623Q mutation-harboring induced pluripotent stem cell (iPSC)-CMs but not in the WT iPS
Summary
Type 3 long QT syndrome (LQT3), which is caused by SCN5A gain-of-function mutations, is a potentially life-threatening disease with a high risk of sudden cardiac death resulting from torsade de points (TdP) [1,2,3]. SCN5A encodes the α subunit of the cardiac voltage-gated sodium channel (Nav1.5), which allows Na+ flux in response to a depolarizing stimulus [4]. We were the first to report a de novo missense mutation of SCN5A R1623Q at an external position in segment S4 of the highly conserved DIV in a female Japanese patient [5]. DIV is important for the inactivation of sodium channels [6]. Miller et al [10] reported that recurrent third-trimester fetal loss or sudden infant death can result from the R1623Q mutation. Previous studies have reported that the SCN5A R1623Q mutation is one of the most frequent genetic variations in severe congenital LQT syndrome among fetuses and neonates [5,10,11,12,13,14,15,16,17,18]
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