Abstract
SUMMARYLong QT syndrome (LQTS) is caused by functional alterations in cardiac ion channels and is associated with prolonged cardiac repolarization time and increased risk of ventricular arrhythmias. Inherited type 2 LQTS (LQT2) and drug-induced LQTS both result from altered function of the hERG channel. We investigated whether the electrophysiological characteristics of LQT2 can be recapitulated in vitro using induced pluripotent stem cell (iPSC) technology. Spontaneously beating cardiomyocytes were differentiated from two iPSC lines derived from an individual with LQT2 carrying the R176W mutation in the KCNH2 (HERG) gene. The individual had been asymptomatic except for occasional palpitations, but his sister and father had died suddenly at an early age. Electrophysiological properties of LQT2-specific cardiomyocytes were studied using microelectrode array and patch-clamp, and were compared with those of cardiomyocytes derived from control cells. The action potential duration of LQT2-specific cardiomyocytes was significantly longer than that of control cardiomyocytes, and the rapid delayed potassium channel (IKr) density of the LQT2 cardiomyocytes was significantly reduced. Additionally, LQT2-derived cardiac cells were more sensitive than controls to potentially arrhythmogenic drugs, including sotalol, and demonstrated arrhythmogenic electrical activity. Consistent with clinical observations, the LQT2 cardiomyocytes demonstrated a more pronounced inverse correlation between the beating rate and repolarization time compared with control cells. Prolonged action potential is present in LQT2-specific cardiomyocytes derived from a mutation carrier and arrhythmias can be triggered by a commonly used drug. Thus, the iPSC-derived, disease-specific cardiomyocytes could serve as an important platform to study pathophysiological mechanisms and drug sensitivity in LQT2.
Highlights
Signal propagation between cardiomyocytes is a very tightly regulated system
The repolarization time was significantly prolonged in cultured LQTS type 2 (LQT2)-specific cardiac cells, compared with control cells, at low beating rates, and this is consistent with the clinical observation that, at slow beating rate, the QT interval is prolonged more in LQT2 patients compared with healthy individuals (Swan et al, 1999)
Plat-E (Cell Biolabs, San Diego, CA), irradiated SNL-76/7 (HPA Culture Collections, Salisbury, UK) and mouse embryonic fibroblast (MEF; Millipore, Billerica, MA) cells were cultured without antibiotics. induced pluripotent stem cell (iPSC) and human embryonic stem cells (hESCs) were maintained in KSR medium: knockout (KO)-Dulbecco’s Modified Eagle’s Medium (DMEM) (Invitrogen) containing 20% KO serum replacement (KO-SR, Invitrogen), non-essential amino acids (NEAA), L-glutamine, penicillin/streptomycin, 0.1 mmol/l 2-mercaptoethanol and 4 ng/ml basic fibroblast growth factor
Summary
Signal propagation between cardiomyocytes is a very tightly regulated system. Mutations in ion channels involved in this system can cause electrical alterations that, in certain circumstances, such as during exercise or emotional stress, could trigger arrhythmias. (LQTS) can either be genetic or acquired (e.g. drug-induced) in nature and is due to defective functioning of cardiac ion channels. A total of 12 congenital LQTS subtypes are presently known (Hedley et al, 2009) Two of these subtypes account for more than 90% of all genetically identified LQTS cases and both are due to defective functioning of potassium channels. LQTS type 1 (LQT1) is the most common subtype, resulting from mutations in the KCNQ1 gene, which encodes the -subunit of the slow component of the delayed rectifier potassium current (IKs) channel (Chiang and Roden, 2000). LQTS type 2 (LQT2) is due to defective functioning of the subunit of the rapid delayed potassium channel (IKr), encoded by the KCNH2 [ known as human ether-a-go-go-related gene (HERG)] gene (Curran et al, 1995). The acquired form of LQTS is due to altered functioning of the same KCNH2 ion channel
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