Mechanisms of Long QT Syndrome 1 in Heart

 描述(申请人提供)：在人体心脏，形成孔洞的KCNQ1(KV7.1；Q1)亚基与辅助的KCNE1(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)复极所必需的。心脏iKs减少会延长心室动作电位时程，导致长QT综合征(LQTS)，这是一种易发生力竭触发的致命性心律失常和心脏性猝死(SCD)的疾病。在美国每年约40万例SCD病例中，LQTS占相当大的比例，影响到从婴儿到老年人的所有年龄段。目前LQTS的治疗方案(β阻滞剂治疗、植入型除颤器、左心交感神经切断)不能纠正潜在的复极异常，而且都有显著的局限性。心脏IKs的病理性减少可能是由于通道亚单位(Q1─LQT1；E1─LQT5)的遗传突变引起的，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，心肌Ik减少可能是由于：(I)通道亚单位的不正确组装；(Ii)Q1和/或E1亚单位向心肌细胞表面转运减少；(Iii)表面通道的异常生物物理特性(包括通道激活电压依赖性的Po减小和右移)；以及(Iv)交感神经调节受损。在大多数遗传性和获得性LQT病例中，心脏IKs密度和/或功能调节减少的确切分子机制尚不清楚。这种缺乏清晰度是合理开发治疗这种危险情况的新疗法的关键障碍。导致缺乏进展的因素是：(1)IKs缺失，并且不有助于在普遍使用的小鼠模型中进行动作电位复极；(2)缺乏量化工具 监测心脏中动态的IKS通道运输；以及(3)缺乏直接研究LQT1突变对成年心肌细胞功能影响的研究。我们的长期目标是阐明在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，并为推进LQTS和危及生命的心律失常的个性化治疗铺平机制桥梁。为了推进这些目标，我们进行了几项创新，包括开发光学工具来测量活细胞中Q1/E1的组装、表面密度和动态运输，以及建立两个互补的成人培养心肌细胞模型系统来直接阐明LQT1在心肌细胞中的作用机制。我们提出了三个具体目标：(1)利用光学方法阐明心脏中Q1/E1通道复合体表面密度的控制机制。(2)阐明Q1C末端不同的LQT1突变损害成人心肌细胞IKS功能的机制。(3)确定心力衰竭时慢性升高的蛋白激酶对Q1/E1表面密度、转运、功能和心脏调节的影响。

 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.