Mechanisms of Long QT Syndrome 1 in Heart

 描述（由申请人提供）：在人心脏中，成孔KCNQ 1（KV7.1; Q1）亚基与辅助KCNE 1（E1）亚基组装形成缓慢激活的延迟整流钾电流（IKs），这是正常心脏动作电位（AP）复极化所必需的。心脏IKs降低会延长心室动作电位时程（APD），导致长QT综合征（LQTS），这是一种易发生劳力触发的致命性心律失常和心源性猝死（SCD）的疾病。LQTS占美国每年约400，000例SCD病例的很大一部分，影响从婴儿到老年人的所有年龄组。目前LQTS的治疗选择（β受体阻滞剂治疗、植入式起搏器、左心交感神经去神经支配）不能纠正潜在的复极异常，并且都具有显著的局限性。心脏IKs的病理性降低可能是由于通道亚基（Q1─ LQT 1; E1─ LQT 5）的遗传性突变引起的，也可能是在衰竭的心脏中获得的，可能是这种情况下不利的神经激素环境的结果。从机制上讲，心脏IK降低可能是由于：（i）通道亚基组装不当;（ii）Q1和/或E1亚基向心脏细胞表面的运输减少;（iii）表面通道的异常生物物理特性（包括Po减少和通道激活电压依赖性的向右移动）;和（iv）交感神经调节受损。在大多数遗传性和获得性LQTS病例中，心脏IKs密度和/或功能调节降低的确切分子机制尚不清楚。这种缺乏明确性是合理开发这种危险状况的新疗法的关键障碍。导致缺乏进展的因素是：（1）在常用的小鼠模型中，IKs不存在，并且不有助于动作电位复极;（2）缺乏定量评估IKs的工具。 监测心脏中动态IKs通道运输;（3）缺乏直接在成年心肌细胞中研究LQT 1突变的功能影响的研究。我们的长期目标是阐明生理和病理条件下控制心脏Q1/E1通道表面密度和功能调节的分子机制，并为LQTS和危及生命的心律失常的个性化治疗提供机制上的见解。我们已经做出了几项创新来推进这些目标，包括开发光学工具来测量Q1/E1组装，表面密度和活细胞中的动态运输，并建立两个互补的成人培养心肌细胞模型系统来直接阐明心脏细胞中的LQT 1机制。我们提出了三个具体的目标：（1）利用光学方法阐明心脏Q1/E1通道复合物表面密度的控制机制。(2)阐明Q1 C端不同LQT 1突变损害成人心室心肌细胞IKs功能的机制。(3)确定心力衰竭中慢性升高的蛋白激酶对心脏Q1/E1表面密度、运输、功能和调节的影响。

 DESCRIPTION (provided by applicant): In human heart, pore-forming KCNQ1 (KV7.1; Q1) subunits assemble with auxiliary KCNE1 (E1) subunits to form the slowly activating, delayed rectifier potassium current, IKs, which is essential for normal cardiac action potential (AP) repolarization. Decreased cardiac IKs prolongs the ventricular action potential duration (APD), resulting in long QT syndrome (LQTS), a disorder that predisposes to exertion-triggered fatal arrhythmias and sudden cardiac death (SCD). LQTS accounts for a significant portion of ~400,000 cases of SCD in the United States each year affecting all age groups from infants to the elderly. Current treatment options for LQTS (β- blocker therapy, implantable defibrillators, left cardiac sympathetic denervation) do not correct the underlying repolarization abnormality and all have significant limitations. Pathological decreases in cardiac IKs can arise due to inherited mutations in channel subunits (Q1─ LQT1; E1─ LQT5), or can be acquired in the failing heart, potentially as a consequence of the adverse neuro-hormonal milieu in this condition. Mechanistically, reduced cardiac IKs may be due to: (i) improper assembly of channel subunits; (ii) diminished trafficking of Q1 and/or E1 subunits to the heart cell surface; (iii) abnormal biophysical properties of surface channels (including diminished Po and rightward shifts in voltage-dependence of channel activation); and (iv) impaired sympathetic regulation. The precise molecular mechanisms underlying reductions in cardiac IKs density and/or functional regulation in most cases of inherited and acquired LQTS is unknown. This lack of clarity is a critical barrier to rational development of new therapies for this dangerous condition Factors contributing to the lack of progress are: (1) IKs is absent and does not contribute to action potential repolarization in popularly used mouse models; (2) lack of tools to quantitatively monitor dynamic IKs channel trafficking in heart; and (3) paucity of studies investigating functional impact of LQT1 mutations directly in adult cardiomyocytes. Our long term objective is to elucidate the molecular mechanisms controlling the surface density and functional regulation of Q1/E1 channels in heart under both physiological and pathological conditions, and to bridge the mechanistic insights to advance personalized therapy for LQTS and life-threatening cardiac arrhythmias. We have made several innovations to advance these objectives including developing optical tools to measure Q1/E1 assembly, surface density, and dynamic trafficking in live cells, and establishing two complementary adult cultured cardiomyocyte model systems to elucidate LQT1 mechanisms directly in heart cells. We propose three specific Aims: (1) Utilize optical approaches to illuminate mechanisms controlling surface density of Q1/E1 channel complexes in heart. (2) Elucidate mechanisms by which distinct LQT1 mutations in Q1 C-terminus impair IKs function in adult ventricular cardiomyocytes. (3) Determine the impact of protein kinases that are chronically elevated in heart failure on Q1/E1 surface density, trafficking, function, and regulation in heart.