CaMKII in Sinus Node Physiology and Disease

描述(由申请人提供)：令人兴奋的最新证据支持这样一种观点，即窦房结(SAN)心脏起搏细胞通过促进肌浆网(SR)钙离子释放和肌膜Na+/钙离子交换器(NCX)携带的去极化内向电流增加而导致心率加快。收缩心肌细胞的兴奋-收缩偶联和细胞钙循环的蛋白质被保存在窦房结细胞中，我们的研究表明，尽管窦房结细胞表现出最小的机械活动，但窦房结细胞和心室肌细胞具有相似的SR钙含量，以细胞膜电容为指标。多功能钙和钙调蛋白依赖的蛋白激酶II(CaMKII)是一种丝氨酸-苏氨酸激酶，调节SR相关的钙稳态蛋白、磷蛋白(PLN)和兰尼定受体(RyR)。我们的新数据支持这样一种观点，即CaMKII在肾上腺素能受体(？AR)介导的窦房结‘战或逃’生理反应中起核心作用。此外，在过度的病理性AR刺激条件下，抑制CaMKII可增强窦房结细胞的存活率，并预防窦性心律失常。我们假设：1)CaMKII通过抑制SR钙超载和减少SR钙泄漏，调节SR钙的摄取和释放，作为生理窦房结对AR刺激反应的细胞机制的一部分；2)CaMKII抑制通过防止SR钙超载和减少SR钙泄漏来保护窦房结心律失常、窦房结细胞死亡和肥大；3)内向NCX电流是SR钙释放激活的主要肌膜靶点，导致4相细胞膜去极化增强和心率加快。我们的实验室已经适应和发展了可靠地分离小鼠和兔的SAN细胞，并进行体内病毒基因转移到SAN细胞和体外病毒基因转移到培养的SAN细胞的新方法。这些创新方法将使我们能够全面测试CaMKII、SR、Ca~(2+)和NCX在心脏起搏中的作用。公共卫生相关性：在美国，窦房结(SAN)心脏起搏器衰竭是发病率和死亡率的重要原因。我们每年在永久性的、通过手术植入的起搏器上花费超过20亿美元。起搏器是一种成功但极不完美的治疗方法，不能治疗潜在的疾病，容易发生机械故障、感染，需要反复手术替换。因此，针对SAN衰竭的改进的非侵入性治疗将为美国人带来重要的公共健康好处。此外，窦房结衰竭是房颤患者的常见症状，并与心力衰竭死亡率的增加有关。尽管这些特殊的SAN细胞具有明显的重要性，但在理解SAN细胞信号和细胞内钙离子与SAN细胞电输出之间的耦合方面，关键的知识缺口仍然存在。提高对SAN细胞生物学的了解是开发改进的治疗方法以调节SAN功能和延长SAN生存的必要的第一步。我们的建议侧重于CaMKII作为诱发SAN疾病的中心但被忽视的信号的作用。

DESCRIPTION (provided by applicant): Exciting recent evidence supports a view that sinoatrial node (SAN) cardiac pacemaker cells cause heart rate increases by enhancement of sarcoplasmic reticulum (SR) Ca2+ release and augmentation of depolarizing inward current carried by the sarcolemmal Na+/Ca2+ exchanger (NCX). Proteins dedicated to excitation-contraction coupling and cellular Ca2+ cycling in contracting cardiomyocytes are preserved in SAN cells, and our studies show SAN cells and ventricular myocytes have similar SR Ca2+ content, indexed for cell membrane capacitance, despite the fact that SAN cells exhibit minimal mechanical activity. The multifunctional Ca2+ and calmodulin-dependent protein kinase II (CaMKII) is a serine- threonine kinase that regulates the SR-associated Ca2+ homeostatic proteins, phospholamban (PLN) and ryanodine receptors (RyR). Our new data support a view that CaMKII plays a central role in ¿adrenergic receptor (¿AR) mediated SAN 'fight or flight' physiological responses. Furthermore, under conditions of excessive, pathological ¿AR stimulation, CaMKII inhibition enhances SAN cell survival and protects against SAN arrhythmias. We hypothesize that 1) CaMKII regulates SR Ca2+ uptake and release as part of a cellular mechanism for physiological SAN responses to ¿AR stimulation; 2) CaMKII inhibition protects against SAN arrhythmias, SAN cell death and hypertrophy by preventing SR Ca2+ overload and reducing SR Ca2+ leak; 3) inward NCX current is the major sarcolemmal target activated by SR Ca2+ release, leading to enhanced phase 4 cell membrane depolarization and faster heart rates. Our laboratory has adapted and developed new methods for reliably isolating mouse and rabbit SAN cells, and performing in vivo viral gene transfer to the SAN and in vitro viral gene transfer to cultured SAN cells. These innovative approaches will allow us to comprehensively test the role of CaMKII, SR Ca2+ and NCX in cardiac pacing. PUBLIC HEALTH RELEVANCE: Sinoatrial nodal (SAN) cardiac pacemaker failure is a significant cause of morbidity and mortality in the United States. We spend over 2 billion dollars on permanent, surgically-implanted pacemakers annually. Pacemakers are a successful but highly imperfect therapy that do not treat the underlying disease and are subject to mechanical failure, infection and require repetitive surgical replacement. Thus, improved, non-invasive therapies for SAN failure would produce important public health benefits for Americans. Furthermore, SAN failure is a frequent finding in patients with atrial fibrillation and is associated with increased mortality in heart failure. Despite the clear importance of these specialized SAN cells, critical knowledge gaps remain for understanding SAN cell signaling and the coupling between intracellular Ca2+ and SAN cell electrical outputs. Improved understanding of SAN cell biology is a necessary first step to developing improved therapies for regulating SAN function and extending SAN survival. Our proposal focuses on the role of CaMKII as a central, but neglected, signal for inducing SAN disease.