Endothelin-1 in Obesity and Insulin Resistance

项目摘要 胰岛素抵抗（IR）是美国的一个主要健康问题。 患有肥胖症的患者，两者都是心血管疾病的主要危险因素。目前， 导致IR的机制尚未完全理解。ET-1是一种血管活性肽，主要由 内皮细胞ET-1在肥胖患者中升高，并与IR相关。 缺氧，这发生在肥胖症患者身上。它激活两种受体，ETA和ETB， 在生理上相互对立。我们的初步数据表明，抑制啮齿类动物的ETB受体， 遗传或非遗传的，改善胰岛素耐受性并降低空腹血糖。这 血糖控制的改善与血浆脂联素和脂肪脂联素的增加有关 和过氧化物酶体增殖物激活受体γ（PPAR-γ）mRNA。此外，脂肪细胞特异性ETB 功能增加的小鼠对高脂喂养的反应是葡萄糖耐受不良，而脂肪细胞 与floxed对照同窝出生的小鼠相比，ETB敲除小鼠具有改善的葡萄糖和胰岛素耐受性。这些 数据表明脂肪组织是ET-1诱导的胰岛素信号传导减少的可能靶点。已经 先前显示，在培养的脂肪细胞上ETB受体的激活抑制了 胰岛素此外，ETB受体的阻断改善了睡眠呼吸暂停啮齿动物模型中的胰岛素敏感性。 这些数据表明，肥胖患者中观察到的ET-1增加可能通过ETB促进IR 受体的因此，我们推测肥胖诱导的组织缺氧促进了ET-1/ETB受体的表达， 脂肪中的活化导致脂肪细胞上的IR、PPAR-γ抑制和脂联素释放减少 从而引起肌肉和肝脏组织的IR。为了验证这一假设，我们将在 体内和体外技术。首先，使用培养的脂肪细胞，我们将确定是否激活ETB 受体抑制PPAR-γ，减少脂联素分泌，并引起脂肪细胞的胰岛素抵抗。下一个是 我们将在饮食诱导的肥胖和IR模型中使用临床批准的ET-1受体抑制剂， 将利用我们实验室生产的两种新型小鼠模型，使我们能够过度表达或敲除 ETB。为了检验这一假设，将检验以下具体目标： 具体目的1：检验ETB受体激活直接抑制胰岛素信号传导的假设。 通过抑制PPAR-γ减少脂联素的产生。 具体目的2：检验脂肪细胞上ETB受体活化促进胰岛素抵抗的假设 通过抑制小鼠体内的过氧化物酶体增殖体激活受体-γ和减少脂联素的释放。 具体目的3：检验ETB受体阻断剂增加血浆脂联素并改善血浆脂联素水平的假设。 肥胖小鼠的胰岛素抵抗。

Project Summary Insulin resistance (IR) is a major health problem in the U.S. It precludes type II diabetes and is often present in patients suffering from obesity, both being major risk factors for cardiovascular disease. Currently, mechanisms leading to IR are not fully understood. ET-1 is a vasoactive peptide primarily released by endothelial cells. It is increased in patients with obesity and associated with IR. ET-1 is elevated in response to hypoxia, which occurs in individuals with obesity. It activates two receptors, ETA and ETB, which typically oppose each other physiologically. Our preliminary data indicate that inhibiting ETB receptors in rodents, either genetically or pharmacologically, improves insulin tolerance and reduces fasting blood glucose. This improvement in glucose control is associated with an increase in plasma adiponectin and adipose adiponectin and peroxisome proliferator-activated receptor gamma (PPAR-γ) mRNA. In addition, adipocyte specific ETB gain of function mice have exacerbated glucose intolerance in response to high fat feeding, while adipocyte ETB knockout mice have improved glucose and insulin tolerance compared to floxed control littermates. These data suggest the adipose tissue as a possible target for ET-1 induced reduction in insulin signaling. It has been previously shown that activation of ETB receptors on cultured adipocytes inhibits the anti-lipolytic effects of insulin. Furthermore, blockade of ETB receptors improves insulin sensitivity in a rodent model of sleep apnea. These data suggest that increased ET-1 observed in patients with obesity may promote IR via the ETB receptor. Thus, we hypothesize that that obesity induced tissue hypoxia promotes ET-1/ETB receptor activation in adipose leading to IR on adipocytes, PPAR-γ inhibition and reduced Adiponectin release by adipocytes thereby causing IR in muscle and liver tissue. To test this hypothesis, we will utilize both in vivo and in vitro techniques. First, using cultured adipocytes, we will determine whether activation of ETB receptors inhibits PPAR-γ, reduces adiponectin secretion, and causes insulin resistance on adipocytes. Next, we will used clinically approved inhibitors of ET-1 receptors in a model of diet induced obesity and IR, and we will utilize two novel mouse models that were produced by our lab that allow us to over-express or knockout the ETB. To test this hypothesis, the following specific aims will be tested: Specific aim 1: To test the hypothesis that ETB receptor activation directly inhibits insulin signaling on adipocytes and reduces adiponectin production by inhibiting PPAR-γ. Specific aim 2: To test the hypothesis that ETB receptor activation on adipocytes promotes insulin resistance by inhibiting PPAR-γ and reducing adiponectin release in mice. Specific aim 3: To test the hypothesis that ETB receptor blockade increases plasma adiponectin and improves insulin resistance in obese mice.