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着关键作用，并可通过氧化应激途径显著受损。有两个小管元件在建立Na+稳态中起着重要作用，它们都参与了盐敏感型高血压的形成，即延髓粗大的Henle升支(MTAL)和对醛固酮敏感的远端肾单位(ASDN)。SS大鼠的mTAL产生过量的ROS，慢性髓内注射过氧化氢酶(一种H_2O_2的清除剂)可使SS大鼠的盐源性高血压降低近50%。相反，向正常大鼠延髓注射过氧化氢可以减少MBF和Na+的排泄，从而导致盐敏感型高血压。喂食高盐饮食的SS大鼠在ASDN节段ENaC的表达和活性也较高，导致Na+重吸收增加，盐诱导的高血压加重。肾脏中ROS和H_2O_2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很好地阐明。肾脏中含量最丰富的异构体是NOX4，它的独特之处在于它主要释放过氧化氢。然而，还没有研究确定NOX4在钠离子动态平衡和高血压中的作用。我们推测，NOX4在SS大鼠血压盐敏感性的决定中起主导作用有两种方式：1)通过肾脏外髓增厚的Henle升支(MTAL)产生过量的H_2O_2，扩散到周围的直肠血管(Vr)周细胞，导致MBF收缩和减少；(2)通过H_2O_2介导的ASDN中ENaC活性的增加。为了探讨NOX4的作用，我们在SS大鼠中建立了一种新的NOX4零突变的大鼠模型。我们将在四个特定目标上比较这一突变大鼠SSNox4-/-与SS大鼠的反应：1-确定SS大鼠中NOX4零突变(SSNox4-/-)对整个肾功能(MBF和GFR)、肾脏氧化应激、压力-钠尿、盐源性高血压和肾脏损伤的生理后果。2-(新目标)确定SSNox4-/-大鼠肾脏损伤的减少在多大程度上是肾灌注压降低与肾内ROS产生固有减少的结果(肾灌注压的伺服控制研究)。3-确定NOX4是否在mTAL因腔内Na+供应增加而产生H_2O_2的过程中起重要作用，以及H_2O_2是否可以从m_TAL扩散到收缩周围的VR。4-确定SS大鼠ASDN中H_2O_2的产生和ENaC的表达/活性是否依赖于NOX4。研究是多尺度的设计，从细胞内到那些利用长期仪器监测MBF和GFR在几周内变化的大鼠。这些结果有望极大地提高我们对NOX4在肾功能中作用的理解，并导致在高血压和肾脏疾病的治疗中针对氧化应激途径的新途径。

 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.