Integrated control of collecting duct function and endothelin synthesis

 描述(申请人提供)：集合管(CD)内皮素-1(ET-1)系统在调节血压(BP)和尿钠排泄方面起着关键作用。ET-1直接抑制Cd、Na+和水的重吸收；Cd特异性敲除ET-1导致盐敏感型高血压。ET受体拮抗剂引起的液体滞留是限制这些药物在临床试验中成功的一个主要因素，很大程度上是由于阻断了CDET-1的作用。鉴于CD ET-1调节体液容量(BFV)的动态平衡，确定该系统如何通过BFV状态的变化来调节是很重要的。尿液ET-1排泄量随着盐或水负荷的增加而增加；由于尿液ET-1主要来源于CD，这些发现提示BFV调节CD ET-1的产生。补肾活血方扩张促进CD-ET-1合成的机制(S)尚不完全清楚。我们发现，FLOW通过激活钙依赖的信号通路促进内髓CD(IMCD)产生ET-1，可能需要初级纤毛和多囊蛋白-1和-2；这些发现提出了初级纤毛和多囊蛋白在CD ET-1和CD盐和水重吸收调节中的令人兴奋的可能性。此外，我们还发现，嘌呤能受体P2Y2和P2X7可能在IMCD ET-1血流反应中起重要作用，提示CD中急性作用(ATP)和慢性作用(ET-1)的利钠利尿因子之间存在联系。我们还发现，一氧化氮(NO)可能通过NO合成酶3对IMCD ET-1的流动刺激是必需的；由于NO从未被证明能增加ET-1，这是一个新的和重要的研究领域。综上所述，这些新发现构成了我们关键假说的基础：1)FLOW通过纤毛、多囊蛋白-1和-2、P2Y2和P2X7受体、NO和钙依赖信号之间的相互作用增加IMCD ET-1的产生；以及2)纤毛、多囊蛋白-1和-2、P2Y2和P2X7受体，以及CD ET-1的NO调节影响CD盐和水处理以及血压。具体目标如下：1)评估纤毛和多囊藻毒素对CD、ET-1合成和肾功能的调节。这包括确定在生理条件下CD中的纤毛和多囊蛋白-1和-2是否调节血压以及盐和水的排泄，ET-1是否在这种调节中发挥作用，以及CD中的纤毛和多囊蛋白-1和-2如何调节ET-1的产生。2)探讨嘌呤能对CD-ET-1合成和肾功能的调节作用。这包括确定生理条件下P2Y2和P2X7是否调节血压和尿盐和水的排泄，CD ET-1是否在这种调节中发挥作用，以及CD中的P2Y2和P2X7如何调节ET-1的产生。3)评价NO对CDET-1合成和肾功能的调节作用。这包括确定CD中特定的NOS亚型在生理条件下调节血压和尿盐和水排出中的作用，CD ET-1是否在这种调节中发挥作用，以及CD中的NOS亚型如何调节ET-1的产生。综上所述，这项研究将极大地加深对肾小管液体流动如何调节镉的盐和水的重吸收以及ET-1在这一过程中的作用的理解。

 DESCRIPTION (provided by applicant): The collecting duct (CD) endothelin-1 (ET-1) system plays a key role in regulating blood pressure (BP) and urinary Na+ excretion. ET-1 directly inhibits CD Na+ and water reabsorption; CD-specific knockout of ET-1 causes salt-sensitive hypertension. ET receptor antagonist-induced fluid retention, a major factor limiting the success of these agents in clinical trials, is largely due to blockade of CD ET-1 actions. Given that CD ET-1 modulates body fluid volume (BFV) homeostasis, it is important to define how this system is regulated by changes in BFV status. Urinary ET-1 excretion is increased in response to salt or water loading; since urinary ET-1 largely derives from the CD, these findings suggest that BFV regulates CD ET-1 production. The mechanism(s) by which BFV expansion enhances CD ET-1 synthesis are incompletely understood. We have found that flow enhances ET-1 production by the inner medullary CD (IMCD) through activation of Ca2+- depending signaling and may require primary cilia and polycystins-1 and -2; these findings raise exciting possibilities about te role of primary cilia and polycystins in the regulation of CD ET-1 and CD salt and water reabsorption. In addition, we found that the purinergic receptors P2Y2 and P2X7 may be important in the IMCD ET-1 flow response, suggesting a link between acutely (ATP) and chronically (ET-1) acting natriuretic and diuretic factors in the CD. We have also found that nitri oxide (NO), likely via NO synthase 3, is necessary for flow stimulation of IMCD ET-1; since NO has never been shown to increase ET-1, this represents a novel and important area of investigation. Taken together, these new findings form the basis for our key hypotheses: 1) Flow increases IMCD ET-1 production through an interplay between cilia, polycystins-1 and -2, P2Y2 and P2X7 receptors, NO and Ca2+-depending signaling; and 2) Cilia, polycystins-1 and -2, P2Y2 and P2X7 receptors, and NO modulation of CD ET-1 affects CD salt and water handling and BP. The following specific aims will be addressed: 1) Evaluate cilia and polycystin regulation of CD ET-1 synthesis and renal function. This involves determining if cilia and polycystins-1 and -2 in the CD regulate BP and salt and water excretion under physiological conditions, if ET-1 plays a role in such regulation, and how cilia and polycystins-1 and -2 in the CD modulate ET-1 production. 2) Evaluate purinergic regulation of CD ET-1 synthesis and renal function. This involves determining if P2Y2 and P2X7 modulate BP and urinary salt and water excretion under physiological conditions, if CD ET-1 plays a role in such regulation, and how P2Y2 and P2X7 in the CD modulate ET-1 production. 3) Evaluate NO regulation CD ET-1 synthesis and renal function. This involves identification of the role of specific NOS isoforms in the CD in modulating BP and urinary salt and water excretion under physiological conditions, if CD ET-1 plays a role in such regulation, and how NOS isoforms in the CD modulate ET-1 production. Taken together, this studies will greatly enhance understanding of how tubule fluid flow regulates CD salt and water reabsorption and the role of ET-1 in this process.