Defining the Contribution of ENaC to ADH-mediated Water and Sodium Excretion

定义 ENaC 对 ADH 介导的水和钠排泄的贡献

• 批准号: 9105117
• 负责人: ALAN C PAO
• 金额: $ 32.43万
• 依托单位: PALO ALTO VETERANS INSTIT FOR RESEARCH
• 依托单位国家: 美国
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-07-25 至 2020-03-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/9105117
• 关键词: Adrenalectomy; Agonist; Aldosterone; Animals; Binding; Blood; Blood Pressure; Cells; Chronic; Conflict (Psychology); Disease; Distal; Duct (organ) structure; Elements; Epithelial; Equilibrium; Excretory function; Extracellular Fluid; Feedback; Gap Junctions; Homeostasis; Hypertension; Hyponatremia; Inappropriate ADH Syndrome; Infusion procedures; Kidney; Knockout Mice; Knowledge; Lead; Link; Liquid substance; Mediating; Medical; Methodology; Movement; Mus; Nature; Nephrons; Osmolalities; Outcome; Pathogenesis; Pathologic; Permeability; Plasma; Play; Positioning Attribute; Prevention; Reagent; Receptor Activation; Receptor Signaling; Regulation; Renin-Angiotensin-Aldosterone System; Research; Role; Serum; Signal Pathway; Signal Transduction; Sodium; Sodium Channel; System; Systemic blood pressure; Testing; Thinking; Thyroid Gland; Tubular formation; Urine; Vasopressins; Water; Water Movements; Wild Type Mouse; absorption; aquaporin-2; blood pressure regulation; clinically significant; collecting tubule structure; defined contribution; driving force; epithelial Na+ channel; gain of function mutation; hormone regulation; in vivo; insight; kidney interstitial tissue; kidney medulla; mouse model; novel; patch clamp; patient population; public health relevance; receptor; solute; treatment strategy; ubiquitin-protein ligase; water channel

 DESCRIPTION (provided by applicant): Antidiuretic hormone (ADH) plays a key role in regulating water balance by controlling renal water transport. ADH binds to the vasopressin-2 receptor (V2R) and increases expression of aquaporin 2 (AQP2) water channels in collecting duct cells to increase renal tubular water permeability. A steep solute corticomedullary gradient in the medullary interstitium provides the driving force for water absorption from tubular fluid in the distal nephron. We and others have demonstrated that ADH also stimulates activity of the epithelial sodium channel (ENaC) in the collecting duct and that ENaC possibly facilitates urine concentration. However, ENaC is traditionally regarded as the end-effector of the renin-angiotensin-aldosterone system (RAAS) and the final element that controls renal Na+ excretion and thus blood pressure. Yet we have shown that in some cases of hyponatremia, such as after adrenalectomy, ENaC activity is surprisingly robust. After adrenalectomy, serum ADH levels rise, leading to an increase in ADH-mediated ENaC activity. This increase in ENaC activity occurs in the absence of aldosterone, raising many new questions about ADH regulation of ENaC. The notion that ENaC can respond to both ADH and RAAS is at odds with the accepted role of this channel in merely controlling renal Na+ reabsorption and blood pressure. To reconcile the apparent conflicting roles of ADH in regulating both water and balance, we propose a unifying paradigm that defines the contribution of ENaC as a regulator of water and Na+ balance. We hypothesize that simultaneous activation of ENaC and AQP2 by ADH promotes urine concentration and plasma dilution. If parallel signaling pathways stimulate ENaC activity to a sufficiently high level, then ADH-mediated ENaC activation will induce Na+ retention beyond what is needed for urine concentration and lead to hypertension. We will use state-of-the-art methodologies (e.g., patch clamp studies of isolated split-open collecting duct in mice) and novel reagents (connecting segment/collecting duct-specific Nedd4-2 knockout mice) to test three Specific Aims: 1) Test whether ENaC contributes to pathologic renal water reabsorption and hyponatremia, 2) Test whether V2R activation can induce renal Na+ retention and high blood pressure, and 3) Test whether V2R signals through Nedd4-2 to stimulate ENaC in vivo. This proposal will provide mechanistic insights into how ADH, AQP2, and ENaC interact and ultimately control water and Na+ homeostasis. This knowledge is clinically significant because it may suggest new strategies, which are already currently available to clinicians, for the treatment of hyponatremia and hypertension.

 描述（由申请人提供）：抗利尿激素（ADH）通过控制肾水运输在调节水平衡中发挥关键作用。 ADH 与加压素 2 受体 (V2R) 结合，增加集合管细胞中水通道蛋白 2 (AQP2) 水通道的表达，从而增加肾小管水渗透性。髓质间质中的陡峭溶质皮质髓质梯度为从髓质中的管状液体吸收水提供了驱动力 远端肾单位。我们和其他人已经证明，ADH 还会刺激集合管中上皮钠通道 (ENaC) 的活性，并且 ENaC 可能促进尿液浓缩。然而，ENaC 传统上被认为是肾素-血管紧张素-醛固酮系统 (RAAS) 的末端效应器，也是控制肾脏 Na+ 排泄从而控制血压的最终元件。然而我们已经证明，在某些低钠血症病例中，例如肾上腺切除术后，ENaC 活性出人意料地强劲。肾上腺切除术后，血清 ADH 水平升高，导致 ADH 介导的 ENaC 活性增加。 ENaC 活性的增加是在醛固酮不存在的情况下发生的，这引发了有关 ENaC 的 ADH 调节的许多新问题。 ENaC 可以对 ADH 和 RAAS 均有反应的观点与该通道仅控制肾 Na+ 重吸收和血压的公认作用不一致。为了调和 ADH 在调节水和平衡方面明显相互冲突的作用，我们提出了一个统一的范式，将 ENaC 的贡献定义为水和 Na+ 平衡的调节剂。我们假设 ADH 同时激活 ENaC 和 AQP2 可促进尿液浓度和血浆稀释。如果并行信号通路将 ENaC 活性刺激到足够高的水平，那么 ADH 介导的 ENaC 激活将导致 Na+ 潴留超过尿液浓度所需，并导致高血压。我们将使用最先进的方法（例如，对小鼠分离的裂开集合管进行膜片钳研究）和新型试剂（连接节段/集合管特异性 Nedd4-2 敲除小鼠）来测试三个具体目标：1）测试 ENaC 是否有助于病理性肾水重吸收和低钠血症，2）测试 V2R 激活是否会诱导肾 Na+ 潴留和高血钾 压力，以及3)测试V2R是否通过Nedd4-2发出信号来刺激体内的ENaC。该提案将为 ADH、AQP2 和 ENaC 如何相互作用并最终控制水和 Na+ 稳态提供机制见解。这一知识具有重要的临床意义，因为它可能提出治疗低钠血症和高血压的新策略，而这些策略目前已经可供临床医生使用。