Role of Insulin Receptors in the Kidney

描述（由申请人提供）：肥胖和糖尿病导致高循环胰岛素水平和高血压（BP）。然而，这些关联背后的机制亟需澄清。例如，在肾脏中，胰岛素通过其自身的受体可导致钠潴留，并激活上皮钠通道（ENaC）。尽管如此，胰岛素也可以增加一氧化氮（NO）的产生，这已被证明可以降低ENaC的活性。因此，预计胰岛素的这两种作用对BP具有相反的作用。为了更好地阐明胰岛素受体在肾脏中的作用，我们已经开发了一种具有“敲除”（KO）或肾远端小管中胰岛素受体（IR）缺失（IRKO）的转基因小鼠。这些小鼠存活并正常生长，但具有显著较高的基础BP。它们快速排泄NaCl负荷的能力也受损，并且在基础状态和胰岛素治疗后，尿硝酸盐和亚硝酸盐（NO的尿形式）排泄的增加变钝。因此，我们的假设是，IR在肾脏中可能有一个以前未被认识到的作用，促进容量排泄和维持正常的血压。我们进一步表明，这些缺陷直接产生的结果受损的NO生产与随后的过度活动的ENaC。下文概述了三个主要目标。目的1是确定是否减少肾NOS活性在远端小管是一个机制决定因素的钠排泄缺陷和血压升高的IRKO小鼠。将在进食和禁食IRKO和WT小鼠的内髓质、外髓质和皮质以及显微解剖的近端小管、粗升支和集合管中测量肾一氧化氮合酶（NOS）活性。我们还将测试胰岛素对内髓集合管（IMCD）培养物中NOS活性和NO水平的直接影响。最后，我们将测试一氧化氮供体莫西多明是否能恢复一氧化氮水平，以及使IRKO小鼠的血压和钠排泄正常化。目的2是确定上皮钠通道（ENaC）活性增加是否是IRKO小鼠钠排泄缺陷和血压升高的机制决定因素。为此，我们将测试是否benzamil，ENaC的拮抗剂，消除血压和尿钠排泄的差异。将在天然组织和原代IMCD细胞中检查ENaC调节。最后，在目标3中，我们确定在IRKO小鼠IMCD中是否改变了与ENaC活化和NO产生相关的不同IR信号传导。将评价参与从受体到ENaC和一氧化氮合酶激活的IR信号传递的关键蛋白质的磷酸化。这些蛋白质包括但不限于胰岛素受体底物（IRS）、磷酸肌醇-3-激酶（PI-3 K）以及血清和糖皮质激素调节激酶（SGK 1）。总体而言，这些研究将高度阐明胰岛素在远端小管中在血液控制和钠调节中的作用。此外，他们可能会提供深入了解与代谢综合征相关的高血压的病理基础。

DESCRIPTION (provided by applicant): Obesity and diabetes lead to high circulating levels of insulin and high blood pressure (BP). However, mechanisms underlying these associations are in dire need of clarification. For example, in the kidney, insulin, through its own receptor, can lead to sodium retention, and activate the epithelial sodium channel (ENaC). Nonetheless, insulin can also increase the production of nitric oxide (NO), which has been shown to reduce the activity of ENaC. Thus, these two actions of insulin would be expected to have opposing effects on BP. To better elucidate the role of the insulin receptor in the kidney, we have developed an transgenic mouse with "knockout" (KO) or deletion of the insulin receptor (IR) in the distal tubule of the kidney (IRKO). These mice survive and grow normally, but have significantly higher basal BP. They are also impaired in their ability to rapidly excrete a NaCl load, as well as, have blunted rise in urinary nitrates plus nitrites (a urinary form of NO) excretion in the basal state and after insulin treatment. Thus our hypothesis is that IR in the kidney may have a previously unappreciated role in facilitating volume excretion and in the maintenance of normal BP. We further suggest these deficiencies arise directly as the result of impaired NO production with subsequent over-activity of ENaC. Three main aims are outlined below. Aim 1 is to determine whether reduced renal NOS activity in the distal tubule is a mechanistic determinant of the sodium-excretory defect and elevated BP in the IRKO mice. Renal nitric oxide synthase (NOS) activity will be measured in inner medulla, outer medulla, and cortex, as well as, microdissected proximal tubule, thick ascending limb, and collecting duct from fed and fasted IRKO and WT mice. We will also test the direct effects of insulin on NOS activity and NO levels in inner medullary collecting duct (IMCD) cultures. Finally, we will test whether molsidomine, an NO donor, restores NO levels, as well as normalizes BP and sodium excretion in IRKO mice. Aim 2 is to determine whether increased activity of the epithelial sodium channel (ENaC) is a mechanistic determinant of the sodium-excretory defect and elevated BP in the IRKO mice. For this aim, we will test whether benzamil, an antagonist of ENaC, abolishes differences in BP and natriuresis. ENaC regulation will be examined in native tissue and in primary IMCD cells. Finally, in Aim 3 we determine whether distinct IR signaling relating to ENaC activation and NO generation is altered in the IRKO mouse IMCD. Phosphorylation of critical proteins involved in IR signal transmission from the receptor to the activation of ENaC and nitric oxide synthase will be evaluated. These proteins include, but are not limited to, the insulin receptor substrate (IRS), phosphoinositide-3-kinase (PI-3K), and the serum and glucocorticoid-regulated kinase (SGK1). Overall, these studies will highly elucidate the role of insulin in the the distal tubule with regard to its role in blood control and sodium regulation. Moreover, they may provide insight into the pathology underlying hypertension associated with the metabolic syndrome.