Role of Proximal Tubule NHE3 in Angiotensin II-induced Hypertension

描述（由申请人提供）：高血压是慢性心力衰竭、中风和慢性肾脏疾病的主要危险因素。尽管许多人认为高血压不再是一个主要问题，但高血压发展的终身风险>80%，并且仍然只有50%的高血压患者达到适当的血压控制。导致高血压发展的因素以及老年患者血压难以控制的原因仍不完全清楚。尽管人们已经认识到，无论高血压的遗传原因如何，高血压的发展都需要将压力尿钠排泄关系重置为更高的压力，但负责压力尿钠排泄的机制及其在高血压中的重置仍有待确定。我们的理由是，增加钠（Na+）的重吸收在肾近端小管通过钠和氢交换器3（NHE 3）由于组织血管紧张素II（ANG II）的不适当的升高可能有助于重置的压力尿钠排泄反应在高血压。我们最近已经证明，细胞外和细胞内ANG II增加NHE 3的表达和活性在近端小管细胞在体外和在大鼠和小鼠的近端小管通过AT 1a受体。此外，我们已经产生了令人兴奋的初步数据，近端小管选择性删除NHE 3显着减弱压力尿钠排泄和血压反应血管紧张素II诱导的高血压。使用创新的分子，基因组和药理学方法，这项建议将测试的假设，NHE 3在近端小管中起着关键作用，在介导压力尿钠排泄和近端小管选择性删除NHE 3防止重置压力尿钠排泄和衰减ANG II诱导的高血压的发展。设计了三个具体目标来检验这一假设。在具体目标1中，我们将使用近端小管特异性NHE 3-KO小鼠确定NHE 3在近端小管中的选择性过表达是否会刺激近端小管Na+重吸收、重置压力性尿钠排泄和促进盐敏感性高血压的发展，而NHE 3的缺失是否会抑制近端小管Na+重吸收、钝性压力性尿钠排泄和降低基础血压，tgNhe 3-/-和SGLT 2-Cre+ Nhe 3flox/flox。在具体目标2中，我们将使用tgNhe 3-/-和SGLT 2-Cre+ Nhe 3flox/flox小鼠，确定输注降压剂量的ANG II加高盐饮食是否会刺激近端小管Na+重吸收，重置压力性尿钠排泄，并通过增加近端小管中NHE 3的表达诱导高血压，而缺失NHE 3是否会减弱ANG II诱导的高血压。在具体目标3中，我们将在ANG II亚型诱导的高血压模型中检测近端小管中NHE 3表达的分子敲低或NHE 3的药理学抑制的治疗效果。该项目产生的新知识将帮助我们更好地了解高血压的肾脏机制，并开发新的NHE 3抑制剂来治疗控制不良的老年高血压患者。

DESCRIPTION (provided by applicant): Hypertension is the major risk factor for chronic heart failure, stroke, and chronic kidney diseases. Although many think hypertension is no longer a major concern, the lifetime risk for the development of hypertension is >80% and, still only 50% of hypertensive patients attain adequate blood pressure control. The factors contributing to the development of hypertension, and the reason why blood pressure is difficult to control in elderly patients remain incompletely understood. Although it is well recognized that regardless of genetic cause of the hypertension, the development of hypertension requires the resetting of the pressure natriuresis relationship to higher pressures, the mechanisms responsible for pressure natriuresis and its resetting in hypertension remain to be determined. We reason that increased sodium (Na+) reabsorption in the renal proximal tubule via the sodium and hydrogen exchanger 3 (NHE3) due to inappropriately elevated tissue angiotensin II (ANG II) may contribute to the resetting of pressure natriuresis responses in hypertension. We have recently demonstrated that both extracellular and intracellular ANG II increases the expression and activity of NHE3 in proximal tubule cells in vitro and in the proximal tubule of rats and mice via AT1a receptors. Further, we have generated exciting preliminary data that proximal tubule-selective deletion of NHE3 markedly attenuates pressure natriuresis and blood pressure responses in ANG II-induced hypertension. Using innovative molecular, genomic and pharmacological approaches, this proposal will test the hypothesis that NHE3 in the proximal tubule plays a critical role in mediating pressure natriuresis and that proximal tubule-selective deletion of NHE3 prevents the resetting pressure natriuresis and attenuate the development of ANG II-induced hypertension. Three specific aims are designed to test this hypothesis. In Specific Aim 1, we will determine whether the overexpression of NHE3 selectively in the proximal tubule will stimulate proximal tubule Na+ reabsorption, reset pressure natriuresis, and promote the development of salt- sensitive hypertension, whereas deletion of NHE3 will inhibit proximal tubule Na+ reabsorption, blunt pressure natriuresis and decrease basal blood pressure using proximal tubule-specific NHE3-KO mice, tgNhe3-/-and SGLT2-Cre+Nhe3flox/flox. In Specific Aim 2, we will determine whether infusion of a subpressor dose of ANG II plus a high salt diet will stimulate proximal tubule Na+ reabsorption, resets pressure natriuresis, and induces hypertension by increasing the expression of NHE3 in the proximal tubule, whereas deletion of NHE3 will attenuate ANG II-induced hypertension using tgNhe3-/-and SGLT2-Cre+Nhe3flox/flox mice. In Specific Aim 3, we will test the therapeutic efficacy of molecular knockdown of the expression of NHE3 in the proximal tubule or pharmacological inhibition of NHE3 in a subpressor ANG II-induced hypertension model. The new knowledge generated by this project will help us better understand the renal mechanisms of hypertension and develop new NHE3 inhibitors to treat elderly patients with poorly-controlled hypertension.