Renal ACE, salt sensitivity and blood pressure control

描述(由申请人提供)：最近的研究强调了肾脏炎症在引起肾脏钠处理缺陷方面的重要性，这是盐敏感型高血压的一个主要特征。然而，肾脏炎症导致肾钠滞留的确切机制尚不完全清楚。我们最近发表的研究表明，肾组织中血管紧张素转换酶(ACE)的活性在实验性高血压的发生发展中起着不可或缺的作用。具体地说，由于局部(肾脏)Ang II生成受损，缺乏肾脏ACE的小鼠对传统的高血压模型具有抵抗力。肾脏血管紧张素Ⅱ对几种关键的钠离子转运体的活性至关重要，包括粗大的升肢Na+/K+/2Cl-转运体(NKCC2)和远端小管氯化钠共转运体(NCC)；肾脏血管紧张素转换酶促进局部血管紧张素Ⅱ的合成导致钠和水滞留和高血压。基于这些发现，这一建议将解决这样的假设，即肾脏ACE/Ang II途径是沿肾单位钠运输的主开关，炎症或其他肾脏损伤不适当地激活这一开关会触发肾脏钠调节失调，最终导致盐敏感型高血压。我们使用后L命名的高血压模型进行了初步研究。在此过程中，短暂接触L-NAME(4周)之后是恢复期(1周)，最后是高盐饮食(3周)。最初的侮辱(L 名称)可引起肾脏炎症，并导致先前正常(即耐盐)的小鼠对盐敏感和高血压。我们现在提出的证据表明，肾脏组织中缺乏血管紧张素转换酶的小鼠不会出现L名字后的盐敏感性。此外，缺乏肾脏ACE的小鼠对高盐保持正常的肾脏反应，尽管该方案诱导了大量的肾脏炎症。为了进一步研究这些非常新颖的观察结果，提出了两个目标：目标1是确定肾小管上皮血管紧张素转换酶在盐敏感型高血压中的定量贡献。我们的假设是，肾单位上皮细胞的血管紧张素转换酶是引起盐敏感性的实质炎症反应中局部血管紧张素Ⅱ的主要来源。为此，我们创建了一个转基因模型，在该模型中，管状血管紧张素转换酶的表达可以打开/关闭；我们将研究这些小鼠对后L命名模型的反应。目的2研究肾脏血管紧张素转换酶/血管紧张素转换酶II主开关的体内生化基础。我们的假设是，肾脏ACE局部合成Ang II增加了NCC的丰度、NKCC2和NCC的磷酸化(通过激酶Spak)以及细胞表面NKCC2和NCC的表达。为了验证这一点，我们将测定野生型和缺乏肾脏ACE的小鼠在后L高血压期间NKCC2和NCC的调节。通过研究肾脏损伤和肾脏血管紧张素转换酶主控开关之间的这种新的和强制性的相互作用，我们的研究将为盐敏感型高血压的起源提供新的和机械的见解，每2名高血压患者中就有1名受到影响。

DESCRIPTION (provided by applicant): Recent studies emphasize the importance of renal inflammation in causing defective sodium handling by the kidneys, a central feature of salt-sensitive hypertension. Yet, the precise mechanisms by which renal inflammation leads to renal sodium retention are not fully understood. We recently published that the activity of the angiotensin-converting enzyme (ACE) in renal tissues is indispensable for the development of experimental hypertension. Specifically, mice lacking renal ACE are resistant to traditional models of hypertension due to impaired local (renal) Ang II generation. Renal Ang II appears critical to the activity of several key sodium transporters, including the thick ascending limb Na+/K+/2Cl- transporter (NKCC2) and the distal tubule NaCl co- transporter (NCC); increased local Ang II synthesis by renal ACE results in sodium and water retention and hypertension. Based on these findings, this proposal will address the hypothesis that the renal ACE/Ang II pathway is a master switch of sodium transport along the nephron, and inappropriate activation of this switch by inflammation or other renal injury triggers the renal sodium dysregulation that ultimately causes salt- sensitive hypertension. We conducted preliminary studies using the post-L NAME hypertension model. In this, the transient exposure to L-NAME (4 weeks) is followed by a recovery phase (1 week) and finally exposure to a high salt diet (3 weeks). The initial insult (L NAME) induces renal inflammation and leads to salt-sensitivity and hypertension in previously normal (i.e. salt resistant) mice. We now present evidence that mice lacking ACE in renal tissues do NOT develop post L-NAME salt-sensitivity. Further, mice lacking renal ACE maintain a normal renal response to high salt despite substantial levels of renal inflammation induced by the protocol. Two aims are proposed to further investigate these very novel observations: Aim 1 is to determine the quantitative contribution of tubular epithelial ACE to salt-sensitive hypertension. Our hypothesis is that ACE from the epithelial cells of the nephron is the major source of local Ang II in response to the parenchymal inflammation inducing salt-sensitivity. To do this, we created a transgenic model in which tubular ACE expression can be turned on/off; we will investigate the responses of these mice to the post-L NAME model. Aim 2 is to study the in vivo biochemical basis of the renal ACE/Ang II master switch. Our hypothesis is that local Ang II synthesis by renal ACE increases NCC abundance, NKCC2 and NCC phosphorylation (via the kinase SPAK) and cell surface expression of NKCC2 and NCC. To test this, we will determine the regulation of NKCC2 and NCC in wild-type and mice lacking renal ACE during post-L NAME hypertension. By studying this very novel and obligatory interaction between renal injury and the master switch of renal ACE, our studies will provide novel and mechanistic insights into the origins of salt-sensitive hypertension, a condition affecting 1 in every 2 hypertensive patients.