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，但高血压终生发展的风险为80%，仍然只有50%的高血压患者得到适当的血压控制。导致高血压发生的因素以及老年患者血压难以控制的原因尚不完全清楚。尽管众所周知，无论高血压的遗传原因如何，高血压的发展都需要重置压力钠尿与高血压的关系，但高血压中压力钠尿及其重置的机制仍有待确定。我们认为，由于组织血管紧张素II （ANG II）不适当升高，肾近端小管通过钠氢交换器3 （NHE3）增加的钠（Na+）重吸收可能有助于高血压患者压力钠尿反应的重置。我们最近证明，细胞外和细胞内的ANG II通过AT1a受体在体外近端小管细胞和大鼠和小鼠近端小管中增加NHE3的表达和活性。此外，我们已经获得了令人兴奋的初步数据，即近端小管选择性缺失NHE3可显著减轻angii诱导的高血压患者的压力性尿钠和血压反应。采用创新的分子、基因组和药理学方法，本研究将验证近端小管中NHE3在介导压力性钠尿中起关键作用的假设，以及近端小管选择性缺失NHE3可阻止重置压力性钠尿并减轻ANG ii诱导的高血压的发展。为了验证这一假设，设计了三个具体目标。在Specific Aim 1中，我们将通过近端小管特异性NHE3- ko小鼠、tgNhe3-/和SGLT2-Cre+Nhe3flox/flox来确定NHE3在近端小管选择性过表达是否会刺激近端小管Na+重吸收、重置压力钠尿并促进盐敏感性高血压的发展，而NHE3的缺失会抑制近端小管Na+重吸收、钝化压力钠尿并降低基础血压。在Specific Aim 2中，我们将通过使用tgNhe3-/和SGLT2-Cre+Nhe3flox/flox小鼠，确定注入亚压剂量的ANG II和高盐饮食是否会刺激近端小管Na+重吸收，重置压力性尿钠，并通过增加近端小管中NHE3的表达诱导高血压，而NHE3的缺失会减轻ANG II诱导的高血压。在Specific Aim 3中，我们将在一个亚压型angii诱导的高血压模型中测试NHE3在近端小管中表达的分子敲除或药理抑制的治疗效果。本项目产生的新知识将有助于我们更好地了解高血压的肾脏机制，并开发新的NHE3抑制剂来治疗老年控制不良的高血压患者。

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.