Department of Pharmacology, College of Physicians and Surgeons, Columbia University Medical Center, New York, NY 10032, USA.
J Gen Physiol. 2013 Jan;141(1):61-72. doi: 10.1085/jgp.201210899.
Understanding the basis for differential responses to drug therapies remains a challenge despite advances in genetics and genomics. Induced pluripotent stem cells (iPSCs) offer an unprecedented opportunity to investigate the pharmacology of disease processes in therapeutically and genetically relevant primary cell types in vitro and to interweave clinical and basic molecular data. We report here the derivation of iPSCs from a long QT syndrome patient with complex genetics. The proband was found to have a de novo SCN5A LQT-3 mutation (F1473C) and a polymorphism (K897T) in KCNH2, the gene for LQT-2. Analysis of the biophysics and molecular pharmacology of ion channels expressed in cardiomyocytes (CMs) differentiated from these iPSCs (iPSC-CMs) demonstrates a primary LQT-3 (Na(+) channel) defect responsible for the arrhythmias not influenced by the KCNH2 polymorphism. The F1473C mutation occurs in the channel inactivation gate and enhances late Na(+) channel current (I(NaL)) that is carried by channels that fail to inactivate completely and conduct increased inward current during prolonged depolarization, resulting in delayed repolarization, a prolonged QT interval, and increased risk of fatal arrhythmia. We find a very pronounced rate dependence of I(NaL) such that increasing the pacing rate markedly reduces I(NaL) and, in addition, increases its inhibition by the Na(+) channel blocker mexiletine. These rate-dependent properties and drug interactions, unique to the proband's iPSC-CMs, correlate with improved management of arrhythmias in the patient and provide support for this approach in developing patient-specific clinical regimens.
尽管遗传学和基因组学取得了进步，但要了解药物治疗反应差异的基础仍然是一个挑战。诱导多能干细胞（iPSC）为在体外研究治疗和遗传上相关的原发性细胞类型中疾病过程的药理学提供了前所未有的机会，并将临床和基础分子数据交织在一起。我们在此报告了从一位具有复杂遗传学的长 QT 综合征患者中衍生 iPSC 的情况。该先证者被发现存在 SCN5A LQT-3 突变（F1473C）和 KCNH2 中的多态性（K897T），KCNH2 是 LQT-2 的基因。对从这些 iPSC 分化而来的心肌细胞（CM）中表达的离子通道的生物物理学和分子药理学分析表明，主要的 LQT-3（Na+通道）缺陷是导致心律失常的原因，而不受 KCNH2 多态性的影响。F1473C 突变发生在通道失活门，增强了晚期 Na+通道电流（I(NaL)），该电流由未能完全失活的通道携带，并在长时间去极化期间传导增加的内向电流，导致复极化延迟、QT 间期延长和致命性心律失常风险增加。我们发现 I(NaL)的非常明显的速率依赖性，即增加起搏速率会显著降低 I(NaL)，并且还会增加其被 Na+通道阻滞剂美西律的抑制作用。这些与患者的 iPSC-CM 相关的速率依赖性特性和药物相互作用，为心律失常的改善管理提供了支持，并为开发针对患者的临床方案提供了支持。
