NR4A Orphan Receptors And Insulin Resistance

描述(申请人提供)：胰岛素抵抗是2型糖尿病(T2 DM)和代谢综合征发病机制的核心，增加胰岛素敏感性的药物或生活方式干预是有效的治疗和预防措施。噻唑烷二酮类药物(TZD)通过激活核转录因子(即PPAR3)来增强胰岛素敏感性；然而，TZD治疗伴随着不良反应，包括体重增加和心力衰竭。这些不良影响限制了临床应用，并突显了直接作用于肌肉的替代胰岛素增敏药物的必要性。我们将研究NR4A家族的孤儿核受体，这些受体在我们的人类肌肉基因芯片上被鉴定为差异表达的基因。大量的初步数据表明：(I)NR4A3在胰岛素抵抗的人和啮齿动物中的表达水平较低；(Ii)TZD诱导NR4A3，这表明NR4A3可能位于TZD作用的下游；(Iii)MCK-NR4A3转基因小鼠表现出胰岛素敏感的表型；(Iv)NR4A3受体的增加可以增强胰岛素信号转导和刺激葡萄糖转运；(V)PGA2以NR4A3依赖的方式增强胰岛素敏感性。为了进行这些新的观察，我们的总体目标是增加我们对NR4A受体在调节胰岛素作用中的作用，它们在人类胰岛素抵抗中的作用，以及它们作为治疗药物靶点的理论基础的理解。为了实现这一目标，我们将利用我们实验室的翻译研究能力，包括人类新陈代谢、人类肌肉和脂肪组织活组织检查、转基因小鼠和培养细胞系统。基于大量的初步数据，具体目的是：(1)评估NR4A受体在胰岛素敏感、胰岛素抵抗和T2 DM患者减肥和TZD治疗前后的肌肉和脂肪中的表达，以及在胰岛素抵抗动物模型中的表达。(2)通过对骨骼肌特异性高表达NR4A3的转基因小鼠进行表型鉴定，确定NR4A3的代谢作用。在人类和小鼠中，NR4A的表达将被评估其在全身和单个细胞和组织水平上影响胰岛素敏感性和底物代谢的能力。(3)通过研究NR4A3在培养的肌肉和脂肪细胞中的稳定高表达和shRNA介导的抑制作用，确定NR4A3调节胰岛素作用的机制。这些研究将针对我们的初步数据，这些数据表明NR4A3调节胰岛素刺激的葡萄糖运输、GLUT4易位和胰岛素介导的信号分子的磷酸化。(4)根据初步数据确定NR4A3的脂质介质激动剂，这些数据表明PGA2以NR4A3依赖的方式增加胰岛素敏感性。因此，这项工作将阐明导致胰岛素抵抗的新分子和病理生理过程，并开发新的潜在药物靶点，用于治疗和预防糖尿病和心脏代谢性疾病。公共卫生相关性：胰岛素抵抗是导致2型糖尿病和代谢综合征的关键因素。治疗胰岛素抵抗可以预防糖尿病和控制已经患有这种疾病的患者的血糖；然而，现有的药物具有严重的副作用，限制了它们的使用。这项研究将首次阐明一个新的孤儿核转录因子家族(NR4A)在胰岛素抵抗原因中的作用，以及它们作为治疗和预防2型糖尿病新药靶点的潜力。

DESCRIPTION (provided by applicant): Insulin resistance is central to the pathogenesis of Type 2 Diabetes (T2DM) and the Metabolic Syndrome, and drugs or lifestyle interventions that increase insulin sensitivity constitute effective therapy and prevention. Thiazolidinedione drugs (TZDs) act through agonism of nuclear transcription factors (i.e., PPAR3) to enhance insulin sensitivity; however, TZD therapy is associated with adverse effects, including weight gain and heart failure. These untoward effects limit clinical utility, and highlight the need for alternative insulin-sensitizing medications that can act directly on muscle. We will study the NR4A family of orphan nuclear receptors, which were identified as differentially expressed genes on our human muscle cDNA microarrays. Extensive preliminary data indicate that: (i) NR4A3 is expressed at lower levels in insulin-resistant humans and rodents; (ii) TZDs induce NR4A3 suggesting that NR4A3 may be downstream of TZD action; (iii) MCK-NR4A3 transgenic mice exhibit an insulin sensitive phenotype; (iv) an increase in NR4A3 receptors can augment insulin signaling and stimulation of glucose transport; (v) PGA2 acts to increase insulin sensitivity in a NR4A3 dependent manner. To pursue these novel observations, our overall goal is to increase our understanding of the role of NR4A receptors in modulating insulin action, their role in human insulin resistance, and their rationale as a therapeutic drug target. To achieve this goal, we will apply our laboratory's capacity for translational research including human metabolism, human muscle and adipose tissue biopsies, transgenic mice, and cultured cell systems. Based on extensive preliminary data, the specific aims are: (1) Assess expression of NR4A receptors in muscle and fat in insulin sensitive, insulin resistant, and T2DM humans, before and after weight loss and TZD treatment, and in insulin resistant rodent models. (2) Establish metabolic role of NR4A3 by phenotyping transgenic mice with specific hyperexpression of NR4A3 in skeletal muscle. In both human and mouse, NR4A expression will be assessed for its ability to affect insulin sensitivity and substrate metabolism at the level of whole body and individual cells and tissues. (3) Determine mechanisms by which NR4A3 regulates insulin action by studying stable hyperexpression and shRNA- mediated suppression of NR4A3 in cultured muscle and adipose cells. These studies will address our preliminary data indicating that NR4A3 modulates insulin-stimulated glucose transport, GLUT4 translocation, and insulin-mediated phosphorylation of signaling molecules. (4) Identify lipid mediator agonists of NR4A3 based on preliminary data indicating that PGA2 increases insulin sensitivity in a NR4A3 dependent manner. Thus, this work will elucidate novel molecules and pathophysiologic processes contributing to insulin resistance, and develop new potential drug targets for the treatment and prevention of diabetes and cardiometabolic disease. PUBLIC HEALTH RELEVANCE: Insulin resistance is a critical factor causing Type 2 Diabetes and the Metabolic Syndrome. Treatment of insulin resistance can prevent diabetes and control blood sugars in patients who already have the disease; however, the available medications have serious side effects which limit their use. This research will elucidate, for the first time, the role of a novel family of orphan nuclear transcription factors (NR4A) in the cause of insulin resistance, and their potential as targets for new drugs to treat and prevent Type 2 Diabetes.