Control of KATP channel expression by CaMKII: role in heart failure resistance

描述（由申请人提供）：心力衰竭在美国是一个巨大的公共卫生问题。在过去的二十年里，慢性心力衰竭的治疗已经取得了相当大的进展，然而，即使使用最好的现代治疗方法，心力衰竭仍然与50%的5年死亡率有关。因此，寻找治疗和预防心力衰竭的新方法是医学的主要挑战之一。atp敏感钾（KATP）通道是最丰富的心脏膜蛋白复合物之一，具有调节膜兴奋性以响应细胞能量状态变化的独特能力。当细胞代谢需求增加激活时，KATP通道依赖的钾外排缩短了心脏动作电位持续时间（APD）。这种钾的外流限制了钠和钙进入细胞，从而减少了离子稳态和收缩的能量需求，并延长了支持心肌松弛和ATP补充的舒张期。我们最近的研究发现，心脏优化APD和能量利用的能力取决于KATP通道的膜表达水平，这影响了KATP电流适应工作量变化的速度和效率。全面了解控制膜KATP通道表达的机制可能会揭示提高心脏能量效率和抵抗心力衰竭的新途径。基于我们的初步数据，我们假设细胞膜KATP通道的表达通过钙/钙调素依赖性蛋白激酶II （CaMKII）与整体心功能耦合。这种密集表达的多功能激酶靶向许多参与兴奋收缩偶联和兴奋性的蛋白质，以支持增强心脏性能，而其在病理生理条件下的持续激活可促进心肌细胞死亡和功能障碍。我们提出了一个以前未被识别的CaMKII激活的下游信号通路，通过Kir6.2成孔KATP通道亚基的磷酸化和随后的KATP通道的内吞作用。在CaMKII持续激活的情况下，随之而来的KATP通道表达的减少会加剧心脏能量资源的消耗，从而导致心肌损伤、细胞死亡和心力衰竭。我们预测，CaMKII抑制对心脏应激抵抗的已知有益作用将在很大程度上取决于KATP通道的膜保留。在Aim1中，我们将通过在心肌细胞和HEK293T细胞中使用标记重组KATP通道亚基、共聚焦免疫荧光成像、分子生物学和膜片钳技术来定义camkii依赖性KATP通道内吞作用的机制。在Aim 2中，我们将研究在具有KATP通道表达缺陷和心脏选择性CaMKII抑制的遗传小鼠模型中诱导的心力衰竭，以了解CaMKII依赖的KATP通道表达调节在产生能量和功能缺陷中定义心力衰竭的作用。

DESCRIPTION (provided by applicant): Heart failure is an enormous public health problem in the United States. Over the past two decades, there has been considerable progress in the treatment of chronic heart failure yet, even with the best of modern therapy, heart failure is stil associated with a 5-year mortality rate of 50%. Therefore, the search for new approaches to treatment and prevention of heart failure is one of the major challenges in medicine. The ATP-sensitive potassium (KATP) channel, one of the most abundant cardiac membrane protein complexes, has the unique ability to adjust membrane excitability in response to changes in the energetic status of the cell. When activated by increased cellular metabolic demand, KATP channel-dependent potassium efflux shortens cardiac action potential duration (APD). This potassium efflux limits sodium and calcium entry into the cell and thus reduces energy requirements for ion homeostasis and contraction, as well as prolongs the diastolic interval that supports myocardial relaxation and replenishment of ATP. Our recent work uncovered that that the ability of the heart to optimize APD and energy utilization depends on the membrane expression level of KATP channels which affects how quickly and efficiently KATP current can adapt to changes in workload. A complete understanding of mechanisms that control membrane KATP channel expression may reveal new avenues to promote cardiac energy efficiency and resistance to heart failure. Based on our preliminary data, we hypothesize that membrane KATP channel expression is coupled with overall cardiac function by calcium/calmodulin dependent protein kinase II (CaMKII). This densely expressed multifunctional kinase targets numerous proteins involved in excitation contraction coupling and excitability to support enhanced cardiac performance, while its persistent activation under pathophysiological conditions promotes cardiomyocyte death and dysfunction. We propose a previously unrecognized downstream signaling pathway of CaMKII activation through phosphorylation of the Kir6.2 pore-forming KATP channel subunit and consequent endocytosis of KATP channels. Under persistent CaMKII activation, the consequent reduction in KATP channel expression would aggravate depletion of cardiac energy resources thus contributing to myocardial injury, cell death and heart failure. We predict that the known beneficial effects on cardiac stress resistance that occur with CaMKII inhibition will depend significantly on membrane retention of KATP channels. In Aim1 we will define the mechanism for CaMKII-dependent endocytosis of KATP channels by use of tagged recombinant KATP channel subunits, confocal immunofluorescence imaging, and molecular biology and patch clamp techniques in cardiomyocytes and HEK293T cells. In Aim 2 we will study heart failure, induced in genetic mouse models with KATP channel expression deficits and cardioselective CaMKII inhibition, to understand the role of CaMKII-dependent KATP channel expression regulation in the generation of the energetic and functional deficits defining heart failure.