Aldosterone-independent regulation of ENaC by systemic salt

描述（由申请人提供）：众所周知，醛固酮影响远端肾单位中的ENaC活性，以调节钠平衡，从而调节血压。这项建议挑战了我们目前的观点，如何ENaC活动响应饮食中的盐摄入量的变化，确定醛固酮的独立手段，这一规定。具体而言，我们已经开发出的证据表明，协调刺激性血管紧张素II和抑制性缓激肽（BK）级联之间的耦合是必要的ENaC活性的适当适应饮食钠的变化。我们的初步工作有力地支持了我们的中心假设，即Ang II直接刺激哺乳动物醛固酮敏感性远端肾单位（ASDN）中ENaC介导的Na+重吸收，并且这种调节对于醛固酮对ENaC的作用是非冗余的。此外，我们推测，在钠限制期间，Ang II级联的激活通过限制BK信号对ENaC的抑制作用进一步增强ENaC活性。相比之下，BK信号传导对于在盐摄入量升高期间抑制ENaC活性是必需的，其在缺乏B2受体的小鼠中的功能障碍导致由于ENaC活性升高而导致的过度Na+保守。重要的是，B2受体缺失的小鼠会发生盐敏感性高血压。为了验证这一假设，我们提出了3个具体目标：1）确定全身盐摄入量对ENaC的醛固酮非依赖性调节的生理重要性。明确ENaC中Ang II调节在此过程中的作用。2)明确血管紧张素II调节哺乳动物ASDN中ENaC活性的作用机制和细胞信号通路。3)确定Ang II和BK信号级联之间的功能耦合如何控制ENaC活性以响应全身盐的变化，并建立破坏B2 -/-小鼠中这种调节的病理生理后果。我们的实验方法范围从天然远端肾单位细胞的电生理学到整个动物平衡研究，并将联合收割机1）在分裂开放的小鼠远端肾单位中ENaC活性的膜片钳测量与通过蛋白质印迹/RPPA和免疫组织化学探测的ENaC表达水平，和2）平衡研究，以在小鼠中用分子遗传工具评估肾Na+排泄，以确定醛固酮的生理作用。肾脏对ENaC和钠处理的独立调节。从药理学的角度来看，这项工作的重要性将促使开发B2激动剂作为纠正远端肾单位钠处理以控制血压的工具。

DESCRIPTION (provided by applicant): It is well known that aldosterone affects ENaC activity in the distal nephron to regulate sodium balance and, consequently blood pressure. This proposal challenges our current view on how ENaC activity responds to variations in dietary salt intake by identifying aldosterone-independent means of this regulation. Specifically, we have developed evidence that coordinated coupling between stimulatory Ang II and inhibitory Bradykinin (BK) cascades is necessary for proper adaptation of ENaC activity to variations in dietary sodium. Our preliminary work strongly supports our central hypothesis that Ang II directly stimulates ENaC-mediated Na+- reabsorption in the mammalian aldosterone-sensitive distal nephron (ASDN) and this regulation is non- redundant to aldosterone actions on ENaC. In addition, we hypothesize that the activation of Ang II cascade during sodium restriction further augments ENaC activity by limiting inhibitory actions of BK signaling on ENaC. In contrast, BK signaling is necessary to suppress ENaC activity during elevated salt intake with its dysfunction in mice lacking B2 receptors causing excessive Na+ conservation as a result of elevated ENaC activity. Importantly, mice with deleted B2 receptors develop salt-sensitive hypertension. To test this hypothesis we address 3 specific aims: 1) Establish the physiological importance of aldosterone-independent regulation of ENaC by systemic salt intake. Define the role of Ang II regulation of ENaC in this process. 2) Define the mechanism of action and delineate the cellular signaling pathway of Ang II regulation of ENaC activity in mammalian ASDN. 3) Determine how functional coupling between Ang II and BK signaling cascades controls ENaC activity in response to changes in systemic salt and establish the patho-physiological consequences of disrupting this regulation in B2 -/- mice. Our experimental approach ranges from electrophysiology in native distal nephron cells to whole animal balance studies and will combine 1) patch clamp measurements of ENaC activity in the split-open murine distal nephrons with ENaC expression levels probed by western blotting/RPPA and immunohistochemistry, and 2) balance studies to assess renal Na+ excretion with molecular genetic tools in mice to define a physiological role of aldosterone-independent regulation of ENaC and sodium handling by the kidney. From a pharmacological standpoint, the importance of this work will urge the development of B2 agonists as tools for correction of sodium handling in the distal nephron to control blood pressure.