ENaC Transport in Insulin Resistance: Role of Insulin & IGF-1 Receptors

描述（由申请人提供）：高血压影响美国6000万成年人，并且胰岛素抵抗综合征在这些个体中的大约一半中诱导盐敏感型高血压。在胰岛素抵抗综合征中，由外周阻力引起的代偿性高胰岛素血症通过对肾小管的直接作用增加钠潴留，从而增加血压。在集合管的主细胞中表达的上皮钠通道（ENaC）是该过程的基础。然而，在胰岛素抵抗综合征中传播胰岛素诱导的ENaC刺激的主细胞中的受体尚未建立。关于胰岛素受体在介导肾钠重吸收中的作用，实验研究产生了相互矛盾的结果。另一方面，一些研究表明，胰岛素样生长因子-1（IGF-1）受体的激活可以通过ENaC增强钠的重吸收。本提案的目的是确定在胰岛素抵抗模型中特异性调节ENaC活性的机制。R 01基金将为主要研究者（PI）提供必要的资源，以检验外周胰岛素抵抗引起的高胰岛素血症通过激活胰岛素和/或IGF-1受体、启动下游信号级联反应和增强ENaC介导的钠转运诱导盐敏感性高血压的假设。为了检验这一假设，提出了两个具体目标。目的1是确定胰岛素和/或IGF-1受体在胰岛素抵抗小鼠模型中对血压、钠重吸收和ENaC介导的钠转运的贡献。使用野生型和主要细胞特异性胰岛素或IGF-1受体敲除小鼠，PI将在这些小鼠中诱导胰岛素抵抗，然后测量全身血压、存在和不存在ENaC特异性抑制剂的尿钠排泄以及跨体外微灌注集合管的钠转运。目的2是确定胰岛素介导的胰岛素和/或IGF-1受体激活刺激主细胞中ENaC介导的钠转运的细胞机制。PI将测量对照与胰岛素抵抗野生型小鼠中的受体活化;测量胰岛素抵抗野生型与基因敲除小鼠中的ENaC表达;并使用新技术比较ENaC介导的电流和受体信号传导途径，以从野生型和基因敲除小鼠中分离主细胞。所提出的目标的预期结果是确定刺激ENaC所需的受体和受体后信号通路，从而确定胰岛素抵抗综合征中的盐敏感性高血压。我们预计，这些结果将显着推进该领域确定适当的目标，预防和治疗高血压的疾病与胰岛素抵抗，如肥胖和2型糖尿病。拟议的研究是创新的，因为我们将直接比较胰岛素和IGF-1受体，并采用新的技术来挑战高胰岛素血症的单方面范例，简单地激活集合管ENaC表达主细胞中的胰岛素受体。 公共卫生相关性：随着一般人群中胰岛素抵抗发病率的增加，高血压和心血管疾病的发病率也会增加。肾脏是胰岛素敏感的，而其他器官是胰岛素抵抗的;因此，在胰岛素抵抗综合征中，高血浆胰岛素水平刺激肾集合管中的钠重吸收，并诱导盐敏感型高血压。胰岛素如何刺激钠重吸收的机制尚未建立，通过在胰岛素抵抗小鼠中研究这些机制，我们可以更多地了解胰岛素抵抗如何导致盐敏感性高血压，以及如何为这部分人设计特定的治疗方法。

DESCRIPTION (provided by applicant): Hypertension affects 60 million adults in the United States, and the insulin resistance syndrome induces a salt- sensitive form of hypertension in approximately half of these individuals. In the insulin resistance syndrome compensatory hyperinsulinemia provoked by peripheral resistance increases sodium retention and hence, blood pressure via direct effects on the renal tubule. The epithelial sodium channel (ENaC) expressed in principal cells of the collecting duct is fundamental to this process. However, the receptors in principal cells which propagate insulin-induced ENaC stimulation in the insulin resistance syndrome are not established. Experimental studies have yielded conflicting results on the role of the insulin receptor in mediating renal sodium reabsorption. On the other hand, several studies have suggested that activation of the insulin-like growth factor-1 (IGF-1) receptor can enhance sodium reabsorption via ENaC. The objective in this proposal is to determine the mechanisms that specifically regulate ENaC activity in models of insulin resistance. The R01 Grant will provide the necessary resources for the principal investigator (PI) to test the hypothesis that hyperinsulinemia provoked by peripheral insulin resistance induces salt-sensitive hypertension via activation of the insulin and/or the IGF-1 receptor, initiation of downstream signaling cascades, and enhancement of ENaC- mediated sodium transport. To test this hypothesis, two specific aims are proposed. Aim 1 is to define the contribution of the insulin and/or IGF-1 receptor to blood pressure, sodium reabsorption, and ENaC-mediated sodium transport in mouse models of insulin resistance. Using wild-type and principal cell-specific insulin or IGF-1 receptor knockout mice, the PI will induce insulin resistance in these mice and then measure systemic blood pressure, urine sodium excretion in the presence and absence of an ENaC-specific inhibitor, and sodium transport across in vitro microperfused collecting duct. Aim 2 is to determine the cellular mechanisms by which insulin-mediated activation of the insulin and/or IGF-1 receptor stimulates ENaC-mediated sodium transport in principal cells. The PI will measure receptor activation in control vs. insulin-resistant wild-type mice; measure ENaC expression in insulin-resistant wild-type vs. knockout mice; and compare ENaC-mediated currents and receptor signaling pathways using a novel technique to isolate principal cells from wild-type and knockout mice. The expected outcomes of the proposed aims are to identify the receptors and post-receptor signaling pathways required for stimulation of ENaC and hence, salt-sensitive hypertension in the insulin resistance syndrome. We anticipate that these results will significantly advance the field by identifying appropriate targets for the prevention and treatment of hypertension in diseases associated with insulin resistance, such as obesity and Type 2 diabetes mellitus. The proposed research is innovative in that we will directly compare the insulin and IGF-1 receptor and employ novel techniques to challenge the unilateral paradigm of hyperinsulinemia simply activating the insulin receptor in ENaC-expressing principal cells of the collecting duct. PUBLIC HEALTH RELEVANCE: As the incidence of insulin resistance increases in the general population, so will the incidence of hypertension and cardiovascular disease. The kidney is insulin-sensitive while other organs are insulin-resistant; thus, in the insulin resistance syndrome high plasma levels of insulin stimulate sodium reabsorption in kidney collecting duct and induce a salt-sensitive form of hypertension. The mechanisms of how insulin stimulates sodium reabsorption are not established, and by studying these mechanisms in insulin-resistant mice, we can learn more about how insulin resistance causes salt-sensitive hypertension and how to design specific therapies for this subset of individuals.