Regulation of sodium transport and blood pressure by SPAK/OSR1 kinases

高血压影响着美国6000万成年人，是中风的主要独立危险因素， 心肌梗塞和充血性心力衰竭，以及终末期肾病的主要原因。超过 一半的高血压患者有盐敏感成分，约30%的高血压患者 主要是由于肾脏对钠的处理异常。激酶SPAK和OSR 1发挥作用， 在肾脏钠转运的调节中起重要作用。在体外，这两种激酶都能激活钠离子， 转运蛋白NKCC 2和NCC，但对SPAK和OSR 1激活它们的途径知之甚少 整个动物。在小鼠中的研究表明，OSR 1对NKCC 2的激活更重要，而SPAK 是NCC的主要激活剂。最近的证据表明，多种形式的SPAK和OSR 1存在于 肾脏，其中一些抑制钠转运，与SPAK和OSR 1仅 降低血压的刺激（例如饮食盐限制），或给予激素， 增加血压（如醛固酮、血管加压素和血管紧张素II），降低抑制性 SPAK和OSR 1，但增加激活形式的水平。肾脏钠转运和血液的调节 因此，SPAK和OSR 1的压力比以前认为的更复杂。本提案的目的是 确定SPAK和OSR 1调节肾钠转运的机制。R 01将 为主要研究者提供必要的资源，以检验SPAK和OSR 1 同种型差异调节肾钠转运，并差异介导生理反应， 改变血压的刺激。为了检验这一假设，提出了三个具体目标。目标1： 研究SPAK和OSR 1亚型差异调节肾钠转运的机制。 SPAK和OSR 1同种型抑制NKCC 2活性的机制将使用 非洲爪蟾卵母细胞和哺乳动物细胞。目的2是确定调节异构体的生理因子 表情使用野生型、SPAK敲除和肾OSR 1敲除小鼠， 醛固酮输注和诱导性高血压对SPAK和OSR 1水平及肾定位的影响 将确定同种型以及这些作用的机制和时间。目标3是研究如何 SPAK和OSR 1调节整个动物的肾钠转运和血压。急性的影响 和慢性醛固酮、加压素或血管紧张素II给药对NCC和NKCC 2磷酸化的影响 并在野生型、SPAK敲除和肾OSR 1敲除小鼠中测定活性。两者都缺乏的小鼠 还将表征肾脏中的SPAK和OSR 1。这些研究将使我们能够分配具体的 SPAK或OSR 1亚型的生理功能，这是了解如何发挥作用的一个重大进展。 在体外激活相同靶点的两种密切相关的激酶在体内具有非常不同的作用。此外，本发明还提供了一种方法， 我们将深入了解独立于SPAK/OSR 1激活阳离子共转运蛋白的途径。

Hypertension affects 60 million adults in the United States, and is a major independent risk factor for stroke, myocardial infarction, and congestive heart failure, and a major cause of end-stage renal disease. More than half of hypertensive patients have a salt-sensitive component, and in approximately 30%, hypertension is predominantly due to abnormalities in sodium handling by the kidney. The kinases SPAK and OSR1 play important roles in the regulation of renal sodium transport. In vitro, both kinases activate the sodium transporters NKCC2 and NCC, but little is known about the pathways via which SPAK and OSR1 activate them in whole animals. Studies in mice indicate that OSR1 is more important for activation of NKCC2, while SPAK is the main activator of NCC. Recent evidence shows that multiple forms of SPAK and OSR1 exist in the kidney, some of which inhibit sodium transport, contrary to the prevailing view that SPAK and OSR1 only activate it. Stimuli that lower blood pressure (e.g. dietary salt restriction), or administration of hormones that increase blood pressure (e.g. aldosterone, vasopressin and angiotensin II), reduce the levels of inhibitory SPAK and OSR1, but increase levels of activating forms. Regulation of renal sodium transport and blood pressure by SPAK and OSR1 is thus more complex than previously believed. The objective of this proposal is to determine the mechanisms by which SPAK and OSR1 regulate renal sodium transport. The R01 Grant will provide the necessary resources for the principal investigator to test the hypothesis that SPAK and OSR1 isoforms differentially regulate renal sodium transport, and differentially mediate responses to physiological stimuli that alter blood pressure. To test this hypothesis, three specific aims are proposed. Aim 1 is to examine the mechanisms by which SPAK and OSR1 isoforms differentially regulate renal sodium transport. The mechanisms by which SPAK and OSR1 isoforms inhibit activity of NKCC2 will be determined using Xenopus oocytes and mammalian cells. Aim 2 is to identify the physiological factors that modulate isoform expression. Using wild-type, SPAK knockout and renal OSR1 knockout mice, the effects of sodium restriction, aldosterone infusion and induced-hypertension on the levels and renal localization of SPAK and OSR1 isoforms, as well as the mechanism and timing of these effects, will be determined. Aim 3 is to examine how SPAK and OSR1 regulate renal sodium transport and blood pressure in whole animals. The effects of acute and chronic aldosterone, vasopressin or angiotensin II administration on NCC and NKCC2 phosphorylation and activity will be determined in wild-type, SPAK knockout and renal OSR1 knockout mice. Mice lacking both SPAK and OSR1 in the kidney will also be characterized. These studies will enable us to assign specific physiological functions to either SPAK or OSR1 isoforms, a significant advance towards understanding how two closely related kinases that activate the same targets in vitro have very different roles in vivo. In addition, we will gain insight into the pathways that activate cation cotransporters independently of SPAK/OSR1.