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

项目摘要/摘要 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，对生理血糖调节是必不可少的。在营养刺激下， 两种主要的胰岛素激素--葡萄糖依赖的促胰岛素肽(GIP)和胰升糖素样肽-1 (GLP-1)分别由肠道内分泌K细胞和L细胞分泌，并通过循环到达β细胞， 它们与其受体GIP受体(GIPR)和GLP-1受体(GLP-1R)结合以扩增GSIS。 虽然T2 DM对循环中的胰岛素水平没有影响，但胰岛素对β细胞GSI的影响是 在T2 DM患者中显著降低。然而，与糖尿病相关的确切机制 β细胞中INTIN信号的钝化仍不清楚。 在T2 DM患者中，提高循环GLP-1水平的药物手段可改善GSIS和血糖控制。 相反，GIP介导的胰岛素效应在T2 DM中明显不存在；药物手段增加 循环的GIP浓度没有得到任何GSIS的改善。潜在的分子机制 T2 DM患者对GLP-1的反应减弱和对GIP的反应缺失仍然知之甚少。 T2 DM部分与慢性炎症状态有关，局部和循环水平增加 炎性细胞因子对周围组织中胰岛素的作用产生负面影响，并对 内分泌胰腺。因此，我们研究了促炎症细胞因子的作用，这些细胞因子在 T2 DM对胰岛细胞胰岛素信号转导的影响相反，我们也审问了消炎药 胆碱能信号系统通过烟碱型乙酰胆碱受体(NAchR)调节胰岛素信号。 根据我们的初步研究，我们假设肿瘤坏死因子α信号通过其在β上的受体TNFR 1- 细胞-以非规范方式激活丝氨酸/苏氨酸G蛋白受体激酶2以抑制GαS- 配体激活GIPR和GLP-1R激活和合成cAMP。因此，我们的发现建立了一个 T2 DM的炎性细胞因子与β细胞中INTIN信号减弱之间的机制联系。 我们的初步研究还表明，在T2 DM小鼠模型中，刺激α7尼古丁 乙酰胆碱受体(α7-nAchR)重新激活β-细胞中的GIPR信号，增强GSI并改善 血糖升高。我们的机制研究表明，α7-nAchR信号磷酸化(肿瘤坏死因子α激活)GRK2at 丝氨酸670拮抗其对GIPR和GLP-1R介导的cAMP合成的抑制作用。 我们现在寻求扩展我们的新颖和令人兴奋的发现，特别是a)了解TNFR1的作用- GRK2介导的体内β细胞功能、GIP和GLP-1R的作用及其信号转导途径 在肥胖和T2 DM的背景下调节α细胞基因的表达；b)具体了解 GRK2在介导T2 DM对β细胞的胰岛素抵抗中的作用；以及c)了解抗GRK2的有益作用 2型糖尿病背景下α7-nAchR在β细胞中的炎性信号转导 我们将使用体内和体外互补的方法来阐明这些重要的信号通路。 在使用新产生的独特小鼠模型的β细胞中，以及在体外的人类胰岛和β细胞中。 我们的研究结果将对T2 DM的炎性细胞因子如何影响提供重要的见解 胰岛素信号与β细胞功能。我们建议的研究也将为我们提供关于 烟碱型乙酰胆碱在β细胞中的信号转导。最后，我们的研究确定了潜在的新受体靶点 改善T2 DM患者β细胞功能障碍的可能性。 。

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. .