Mechanism of Defective Incretin Action in Beta Cells during Type 2 Diabetes Mellitus

项目总结/摘要 肠促胰岛素介导的葡萄糖刺激的胰岛素分泌增强（GSIS）占50%， 餐后胰岛素分泌，并且是生理血糖调节所必需的。在营养刺激下， 两种主要肠促胰岛素激素葡萄糖依赖性促胰岛素肽（GIP）和胰高血糖素样肽-1 GLP-1分别从肠内分泌K细胞和L细胞分泌，并通过循环到达β细胞， 在那里它们结合其受体，GIP受体（GIPR）和GLP-1受体（GLP-1 R）以扩增GSIS。 虽然循环肠促胰岛素水平不受2型糖尿病的影响，但肠促胰岛素对β细胞GSIS的作用是 在T2 DM患者中显著降低。然而，糖尿病相关的确切机制 β-细胞中肠降血糖素信号传导的钝化仍不清楚。 在T2 DM中，增加循环GLP-1水平的药理学方法可改善GSIS和血糖控制。 相比之下，T2 DM中明显不存在GIP介导的肠促胰岛素效应; 循环GIP浓度不符合任何GSIS改善。的分子机制 T2 DM患者对GLP-1的应答减弱和对GIP的应答缺失仍知之甚少。 2型糖尿病部分与慢性炎症状态有关，局部和循环中 炎性细胞因子对外周组织中的胰岛素作用产生负面影响， 内分泌胰腺因此，我们研究了促炎性细胞因子的作用，这些细胞因子在炎症反应中升高。 T2 DM对胰岛β细胞中肠促胰岛素信号传导的影响。相反，我们还询问了抗炎药 胆碱能信号系统通过烟碱乙酰胆碱受体（nAchR）调节肠促胰岛素信号。 基于我们的初步研究，我们假设TNFα通过其受体TNFR 1在β- 细胞-以非经典方式激活Ser/Thr G蛋白受体激酶2（GKR 2），以抑制Gαs- 通过配体活化的GIPR和GLP-1 R的活化和cAMP合成。因此，我们的研究结果建立了一个 T2 DM中炎性细胞因子与β细胞中肠促胰岛素信号传导减少之间的机制联系。 我们的初步研究还表明，在T2 DM的小鼠模型中，刺激α7烟碱样受体， 乙酰胆碱受体（α7-nAchR）重新激活β细胞中的GIPR信号传导，以增强GSIS并改善 - 是的我们的机制研究表明，α7-nAchR信号磷酸化（TNFα激活）GRK 2， 丝氨酸670以抵消其对GIPR和GLP-1 R介导的cAMP合成的抑制作用。 我们现在寻求扩大我们的新的和令人兴奋的发现，特别是a）了解TNFR 1的作用， GRK 2介导的信号传导对体内β细胞功能、GIP和GLP-1 R作用以及TNFR 1信号传导如何影响 在肥胖和2型糖尿病背景下调节α细胞基因表达; B）具体了解 GRK 2在T2 DM中介导对β细胞肠促胰岛素作用的抵抗;以及c）了解抗GRK 2的有益作用。 T2 DM背景下β细胞中的炎性α7-nAchR信号传导。 我们将使用互补的体内和体外方法来阐明这些重要的信号通路 使用新生成的独特小鼠模型在β细胞中以及在体外在人胰岛和β细胞中进行。 我们的研究结果将对T2 DM的炎症细胞因子如何影响 肠促胰岛素信号传导和β细胞功能。我们提出的研究还将为以下影响提供新的见解： β-细胞中的烟碱乙酰胆碱信号传导。最后，我们的研究确定了潜在的新受体靶点， 改善T2 DM中β细胞功能障碍的潜力。 .

PROJECT SUMMARY/ABSTRACT The incretin-mediated potentiation of glucose-stimulated insulin secretion (GSIS) accounts for 50% of postprandial insulin secretion and is essential for physiologic glycemic regulation. Upon nutrient stimulus, the two principal incretin hormones glucose-dependent insulinotropic peptide (GIP) and glucagon-like peptide-1 (GLP-1) are secreted, respectively, from intestinal endocrine K- and L-cells and reach β-cells via the circulation, where they bind their receptors, GIP receptor (GIPR) and GLP-1 receptor (GLP-1R) to amplify GSIS. While circulating incretin hormone levels are not impacted by T2DM, incretin effects on β-cell GSIS are significantly diminished in T2DM patients. However, the precise mechanisms underlying diabetes-associated blunting of incretin signaling in β-cells remain unclear. In T2DM, pharmacologic means to increase circulating GLP-1 levels improves GSIS and glycemic control. In contrast, the GIP-mediated incretin effect is notably absent in T2DM; and pharmacologic means to increase circulating GIP concentrations is not met with any GSIS improvement. The molecular mechanisms underlying diminished response to GLP-1 and absent response to GIP in T2DM remain poorly understood. T2DM is in part linked to a chronic inflammatory state with increased levels of local and circulating inflammatory cytokines that negatively impact insulin action in peripheral tissues and negatively impact the endocrine pancreas. We have therefore examined the role of pro-inflammatory cytokines that are elevated in T2DM on incretin signaling in islet -cells. Conversely, we have also interrogated the anti-inflammatory cholinergic signaling system through nicotinic acetylcholine receptors (nAchR) in modulating incretin signaling. Based on our preliminary studies, we hypothesize that TNFα - signaling through its receptor TNFR1 on β- cells - activates the Ser/Thr G-protein receptor kinase 2 (GKR2) in a non-canonical manner to suppress Gαs- activation and cAMP synthesis by ligand activated GIPR and by GLP-1R. Thus, our findings establish a mechanistic link between inflammatory cytokines in T2DM with diminished incretin signaling in β-cells. Our preliminary studies also indicate that in a murine model of T2DM, stimulating the α7 nicotinic acetylcholine receptor (α7-nAchR) reactivates GIPR signaling in β-cells to potentiate GSIS and improve glycemia. Our mechanistic studies indicate that α7-nAchR signaling phosphorylates (TNFα-activated) GRK2 at serine 670 to counteract its inhibitory effects on GIPR and GLP-1R-mediated cAMP synthesis. We now seek to expand our novel and exciting findings specifically a) to understand the role of TNFR1- GRK2-mediated signaling on in vivo β-cell function, on GIP and GLP-1R action as well as how TNFR1 signaling modulates α-cell gene expression in the context of obesity and T2DM; b) to specifically understand the role of GRK2 in mediating resistance to β-cell incretin action in T2DM; and c) to understand the beneficial role of anti- inflammatory α7-nAchR signaling in β-cells in the context of T2DM. We will use complementary in vivo and in vitro approaches to elucidate these important signaling pathways in β-cells using newly generated unique mouse models as well as in vitro in human islets and β-cells. The outcomes of our studies will yield important insights into how inflammatory cytokines of T2DM impact incretin signaling and β-cell function. Our proposed studies will also provide new insights into the effects of nicotinic acetylcholine signaling in β-cells. Finally, our studies identify potentially new receptor targets with the potential to ameliorate β-cell dysfunction in T2DM. .