Endothelial Basis of Obesity-induced Insulin Resistance

项目总结/摘要 Fc受体（FcR）在免疫细胞中的效应细胞中调节IgG结合后的细胞内信号传导。 系统我们以前发现，称为FcγRIIB的抑制性FcR也在骨骼肌中表达， 肌肉微血管内皮，并且整体FcγRIIB敲除小鼠免受高脂饮食的影响 （HFD）诱导的胰岛素抵抗。为了探讨内皮FcγRIIB在胰岛素代谢中的作用，我们 通过与floxed Fcγ RIIB杂交，产生了内皮细胞特异性缺乏Fcγ RIIB的小鼠品系 (FcγRIIBfl/fl）与VE钙粘蛋白-Cre小鼠（FcγRIIBfl/fl：VECad-Cre）的对照组，并用对照饮食或HFD喂养它们。 我们发现FcγRIIBfl/fl：VECad-Cre小鼠可免受HFD诱导的外周胰岛素抵抗 以及葡萄糖向骨骼肌的输送受损。此外，我们发现IgG 分离自HFD喂养的野生型小鼠（HFD-IgG），但不分离自对照饮食喂养的小鼠（Con-IgG）的IgG， 当转移到FcγRIIB中缺乏内源性IgG的小鼠（B-/-小鼠）中时， 与Con-IgG相比，HFD-IgG在其Fc结构域中的唾液酸化较少。治疗 用N-乙酰基-D-甘露糖胺（ManNAc）增加蛋白质唾液酸化的野生型小鼠， HFD诱导的胰岛素抵抗。此外，从肥胖型2型糖尿病（T2 DM）中分离的IgG 患者，但非T2 DM受试者，通过FcγRIIB诱导B-/-小鼠的胰岛素抵抗。基于 这些新的发现，拟议项目的总体目标是确定IgG唾液酸化是如何 饮食诱导的肥胖症（DIO）中的失调以及内皮FcγRIIB如何促成发病机制 DIO相关的胰岛素抵抗使用小鼠模型和培养细胞。目标1将决定如何 HFD降低IgG的唾液酸化，集中于调节IgG唾液酸化的B细胞中的过程。我们 还将确定ManNAc如何预防HFD诱导的胰岛素抵抗。目标2将决定如何 内皮FcγRIIB介导HFD诱导的外周胰岛素抵抗，验证了以下假设： HFD-IgG激活内皮FcγRIIB可启动细胞内信号传导， 胰岛素的跨内皮转运。目的3将确定IgG唾液酸化及其诱导 小鼠的胰岛素抵抗与人的DIO相关的胰岛素抵抗相关，使用现有的 具有一系列肥胖和胰岛素敏感性的受试者队列。使用高度平移的方法， 我们将测试新的概念，即内皮中的FcγRIIB和B细胞中IgG的修饰是至关重要的， 参与胰岛素抵抗和T2 DM的发病机制。我们预计新的知识 将导致新的预防和治疗措施，以打击胰岛素抵抗， 其特征在于肥胖症和其它慢性炎性病症。

Project Summary/Abstract Fc receptors (FcR) modulate intracellular signaling upon IgG binding in the effector cells in the immune system. We have previously found that the inhibitory FcR known as FcγRIIB is also expressed in skeletal muscle microvascular endothelium, and that global FcγRIIB null mice are protected from high-fat diet (HFD)-induced insulin resistance. To explore the role of endothelial FcγRIIB in insulin metabolism, we generated the mouse strain lacking FcγRIIB specifically in endothelial cells by crossing floxed FcγRIIB (FcγRIIBfl/fl) with VE Cadherin-Cre mice (FcγRIIBfl/fl:VECad-Cre), and fed them with control diet or HFD. We found that FcγRIIBfl/fl:VECad-Cre mice are protected from HFD-induced peripheral insulin resistance and from impairment of glucose delivery to the skeletal muscle. Furthermore, we discovered that IgG isolated from HFD-fed wild-type mice (HFD-IgG), but not IgG from control diet-fed mice (Con-IgG), induces insulin resistance when transferred into mice lacking endogenous IgG (B-/- mice) in an FcγRIIB dependent manner, and that HFD-IgG is less sialylated in its Fc domain compared to Con-IgG. Treatment of wild-type mice with N-Acetyl-D-mannosamine (ManNAc) that increases protein sialylation ameliorated HFD-induced insulin resistance. Moreover, IgG isolated from obese type 2 diabetes mellitus (T2DM) patients, but not from non-T2DM subjects, induced insulin resistance in B-/- mice via FcγRIIB. Based upon these novel findings, the overall goal of the proposed project is to determine how IgG sialylation is dysregulated in diet-induced obesity (DIO) and how endothelial FcγRIIB contributes to the pathogenesis of DIO-related insulin resistance using both mouse models and cultured cells. Aim 1 will determine how HFD decreases sialylation of IgG, focusing on the process in B cells that modulates IgG sialylation. We will also determine how ManNAc prevents HFD-induced insulin resistance. Aim 2 will determine how endothelial FcγRIIB mediates HFD-induced peripheral insulin resistance, testing the hypothesis that activation of endothelial FcγRIIB by HFD-IgG initiates intracellular signaling that leads to attenuation of transendothelial transport of insulin. Aim 3 will determine whether IgG sialylation and its ability to induce insulin resistance in mice are associated with DIO-related insulin resistance in humans, using existing cohorts of subjects with a range of obesity and insulin sensitivity. Using a highly translational approach, we will test the novel concept that FcγRIIB in endothelium and modification of IgG in B cells are critically involved in the pathogenesis of insulin resistance and T2DM. We anticipate that the new knowledge gained will lead to novel preventative and treatment measures to combat the insulin resistance that characterizes obesity and other chronic inflammatory conditions.