Role of NOX4 In Kidney Function In Salt-Sensitive Hypertension

 描述（由申请人提供）：肾脏对钠和水的调节在高血压中起关键作用，并且可被氧化应激途径显著损害。两种肾小管元件在建立Na+稳态中具有重要意义，并且已知它们都参与盐敏感型高血压，即髓厚汉勒升支（mTAL）和醛固酮敏感性远端肾单位（ASDN）。SS大鼠的mTAL产生过量的ROS，并且过氧化氢酶（H2 O2的清除剂）的慢性髓内输注使SS大鼠中的盐诱导的高血压降低近50%。相反，向正常大鼠的髓质输注H2 O2减少MBF和Na+排泄，导致盐敏感型高血压。高盐饮食喂养的SS大鼠ASDN节段中ENaC的表达和活性也更高，导致Na+的重吸收和盐诱导的高血压的增强。肾脏中ROS和H2 O2的主要来源是NADPH氧化酶，但特定的Nox亚型如Nox 1、2和4的作用及其影响肾功能的机制尚未得到很好的阐明。肾脏中最丰富的同种型是Nox 4，其独特之处在于它主要释放H2 O2。然而，还没有研究已经进行，以确定在Na+稳态和高血压的Nox 4的作用。我们假设Nox 4通过两种方式在决定SS大鼠的血压盐敏感性中起主导作用：1）通过在Henle（mTAL）的肾外髓粗升支中过量产生H2 O2，其扩散到周围的直血管（VR）周细胞，引起MBF的收缩和减少; 2）通过H2 O2介导的ASDN中ENaC活性的增加。 为了探索Nox 4的作用，我们建立了一种新的大鼠模型，在SS大鼠中具有Nox 4的无效突变。我们将比较这种突变大鼠SSNox 4-/-与SS大鼠的反应，具体目的如下：1-确定SS大鼠中Nox 4无效突变（SSNox 4-/-）对全肾功能（MBF和GFR）、肾氧化应激、压力-尿钠排泄、盐诱导的高血压和肾损伤的生理后果。2-（新目标）确定SSNox 4-/-大鼠中肾损伤减少的程度是较低肾灌注压相对于固有肾内ROS产生减少的结果（肾灌注压研究的伺服控制）。3-确定Nox 4是否在mTAL中响应于增加的管腔Na+递送而重要参与H2 O2产生，以及H2 O2是否可以从mTAL扩散到收缩周围VR。4-确定SS大鼠ASDN中H2 O2的产生和ENaC表达/活性是否是Nox 4依赖性的。研究是多尺度设计的，从细胞内到那些利用慢性仪器大鼠监测MBF和GFR变化数周。这些结果有望大大提高我们对Nox 4在肾功能中作用的理解，并为高血压和肾脏疾病的治疗提供新的靶向氧化应激途径。

 DESCRIPTION (provided by applicant): Sodium and water regulation by the kidney plays a key role in hypertension and can be significantly compromised by pathways of oxidative stress. Two tubular elements are of major importance in establishing Na+ homeostasis and both are known to participate in salt-sensitive forms of hypertension, the medullary thick ascending limb of Henle (mTAL) and the aldosterone sensitive distal nephron (ASDN). The mTAL of SS rats produces excess ROS and the chronic intramedullary infusion of catalase, a scavenger of H2O2, reduces salt- induced hypertension nearly 50% in SS rats. Conversely, medullary infusion of H2O2 to normal rats reduces MBF and Na+ excretion resulting in a salt-sensitive form of hypertension. SS rats fed a high salt diet also exhibit greater expression and activity of ENaC in the ASDN segments leading to greater reabsorption of Na+ and enhancement of salt-induced hypertension. The major source of ROS and H2O2 in the kidney is NADPH oxidase but the roles of specific Nox isoforms such as Noxs 1, 2 and 4 and the mechanisms whereby they affect renal function have not been well elucidated. The most abundant isoform in the kidney is Nox4 which is unique in that it releases predominantly H2O2. Yet no studies have been carried out to determine the role of Nox4 in Na+ homeostasis and hypertension. We hypothesize that Nox4 plays a dominant role in determining blood pressure salt-sensitivity in the SS rat in two ways: 1) By excess production of H2O2 in the renal outer medullary thick ascending limbs of Henle (mTAL) which diffuses to surrounding vasa recta (VR) pericytes causing constriction and reduction of MBF; 2) Through H2O2-mediated increases of ENaC activity in the ASDN. To explore the role of Nox4, we have created a novel rat model with a null mutation of Nox4 in the SS rat. We will compare the responses of this mutant rat, SSNox4-/-, to those of the SS rat in four Specific Aims: 1- Determine physiological consequences of a null mutation of Nox4 in SS rats (SSNox4-/-) upon whole kidney function (MBF and GFR), renal oxidative stress, pressure-natriuresis, salt-induced hypertension and renal injury. 2-(New Aim) Determine the extent to which the reduced renal injury in SSNox4-/- rats is a consequence of a lower renal perfusion pressure versus an inherent intrarenal reduction of ROS production (servo-control of renal perfusion pressure studies). 3-Determine if Nox4 is importantly involved in H2O2 production in mTAL in response to increased luminal Na+ delivery and whether H2O2 can diffuse from mTAL to constrict surrounding VR. 4-Determine if production of H2O2 and ENaC expression/activity in ASDN of SS rats is Nox4-dependent. Studies are multiscale in design ranging from intracellular to those utilizing chronically instrumented rats which monitor changes in MBF and GFR over several weeks. The results are expected to greatly enhance our understanding of the role of Nox4 in renal function and lead to novel ways to target pathways of oxidative stress in the treatment of hypertension and renal disease.