Mechanisms of postpartum-related arrhythmogenesis in long-QT syndrome

心源性猝死（SCD）在年轻、表面健康的个体中，通常继发于罕见的遗传性心律失常性通道病变。遗传性长qt综合征2型（LQT2）是其中一种致心律失常疾病，重极化HERG离子通道基因的功能缺失突变延长心脏复极，增加室性心动过速、晕厥和SCD的风险。患有LQT2的成年女性发生致命性心律失常的风险高于男性。在产后阶段，这种风险进一步增加了4倍。尽管有这样的临床观察，但没有研究调查产后分泌的催产素和催乳素是否以及如何具有促心律失常的作用。我们假设催产素和催乳素通过调节致心律失常底物（心脏复极的区域异质性延长）以及对促心律失常交感神经刺激的易感性而增加了产后心律失常风险。我们已经产生了转基因LQT2兔模型（hergg - g628s），模仿人类LQTS表型，QT间期延长，自发性室性心动过速和心源性猝死，并且与人类受试者相似，在产后阶段由于致命性室性心律失常而死亡率特别高。因此，这些转基因LQT家兔是在体内、离体全心、组织、细胞和分子水平上研究产后相关心律失常发生机制的有用工具。在本项目中，我们将利用转基因LQT2家兔研究催产素和催乳素对心律失常发生、（局部）心脏复极以及心脏离子通道和转运体的表达、磷酸化和功能的影响。为了从多个层面评估产后心律失常的机制，我们将使用体内ECG监测，离体单相动作电位测量，实时PCR和western blot分析心脏离子通道和Ca2+处理蛋白的mRNA和蛋白表达，以及细胞贴片夹紧。实验数据最终将整合到一个硅LQT2心脏模型中，以测试激素诱导的变化是否易导致心律失常。我们的长期目标是将我们关于产后相关心律失常发生机制的发现转化为临床（诊断和治疗）常规，特别是将这些发现用于LQTS患者母乳喂养和催产素给药的建议。

Sudden cardiac death (SCD) in younger, apparently healthy individuals, most often occurs secondary to rare inherited arrhythmogenic channelopathies. The inherited long-QT syndrome type 2 (LQT2) is one of these arrhythmogenic diseases, in which loss-of-function mutations in the gene of repolarizing HERG ion channels prolong cardiac repolarization and increase the risk for ventricular tachyarrhythmia, syncope and SCD. Adult women with LQT2 have a higher risk for lethal arrhythmia than men. During the postpartum phase, this risk is further increased by 4-fold. Despite this clinical observation, no studies have investigated whether and how oxytocin and prolactin that are secreted during the postpartum phase have pro-arrhythmic effects.We hypothesize that oxytocin and prolactin contribute to the heightened postpartal arrhythmogenic risk by modulating the arrhythmogenic substrate (regionally heterogeneous prolongation of cardiac repolarization) as well as the susceptibility to pro-arrhythmic sympathetic stimuli. We have generated transgenic LQT2 rabbit models (HERG-G628S) mimicking the human LQTS phenotype with QT interval prolongations, spontaneous ventricular tachycardia and sudden cardiac death - and similarly as in human subjects - a particularly high mortality during the postpartum phase due to lethal ventricular arrhythmia. These transgenic LQT rabbits are thus useful tools to investigate mechanisms of postpartum-related arrhythmogenesis on in vivo, ex vivo whole heart, tissue, cellular and molecular levels.In this project, we will utilize transgenic LQT2 rabbits to investigate how oxytocin and prolactin affect arrhythmogenesis, (regional) cardiac repolarization and the expression, phosphorylation and function of cardiac ion channels and transporters. To assess mechanisms of postpartum arrhythmia on multiple levels, we will use in vivo ECG monitoring, ex vivo monophasic action potential measurements, real-time PCR and western blot analyses of mRNA and protein expression of cardiac ion channels and Ca2+-handling proteins, and cellular patch clamping. The experimental data will finally be integrated into an in silico LQT2 heart model to test whether the hormone-induced changes predispose to arrhythmia.Our longterm goal is to translate our findings on the mechanisms of postpartum-related arrhythmogenesis into clinical (diagnostic and therapeutic) routines, specifically, use these findings for recommendations regarding breastfeeding and oxytocin administration in LQTS patients.