Toll样受体-3在PM2.5诱导胰岛素抵抗中的作用及调控机制研究

Previously, we and others have demonstrated a strong link between the concentration of particulate matter (PM) in air and diabetes. Adipose tissue macrophages polarization plays a pivotal role in PM2.5-induced insulin resistance. TLR3, one of important pattern recognition receptors, leads to M1 macrophage polarization when activated, and then participates in metabolic diseases by regulating inflammation response. However, whether TLR3 is involved in the PM2.5-mediated insulin resistance remains unknown. We hypothesized that TLR3 deficiency should increase insulin sensitivity by balancing M1/M2 polarization. The present study will investigate this issue with focusing on visceral adipose tissue. Firstly, the effect of PM2.5 inhalation on insulin resistance and the expression and location of TLR3 in adipose tissue will be examined. Then, whether TLR3 deficiency could ameliorate PM2.5-induced insulin resistance will be investigated. Next, by comparing the macrophages infiltration, macrophages polarization and inflammation levels of adipose tissue in wild type and TLR3-/- mice, the role of TLR3 during the process will be determined. Finally, the underlying mechanism of it will be explored by examining the TLR3 and insulin signaling pathways. The present study will open new direction for the etiology and underlying mechanism of diabetes, provide new evidence for the increasing incidence of diabetes, propose new targets for treatment and prevention of diabetes, rendering significant importance to human health.

糖尿病发病率增加迅速与污染空气中颗粒物密切相关，内脏脂肪巨噬细胞极性改变是PM2.5颗粒引起胰岛素抵抗（IR）的重要机制。TLR3是重要的模式识别受体，其激活可诱导巨噬细胞向M1型转化，通过调控炎症反应参与糖尿病的发生。但TLR3是否介导PM2.5诱发的IR，尚无报道。本项目将围绕内脏脂肪首先探讨PM2.5对IR及TLR3表达和分布的影响；进一步分析TLR3功能缺失能否改善PM2.5诱发的IR；并通过比较野生型和TLR3基因敲除型小鼠内脏脂肪巨噬细胞浸润、极化状态和炎症水平确定其在这一过程中的作用；接下来对TLR3和胰岛素信号通路进行鉴定，深入探讨TLR3调节PM2.5诱发IR的机制。本项目将为糖尿病发病病因和机制提出新的研究方向，为PM2.5引起糖尿病发病率迅速增加提供新的证据，也为糖尿病防治提出新的研究标靶。

糖尿病发病率增加迅速与饮食和污染空气中颗粒物密切相关，内脏脂肪巨噬细胞极性改变是胰岛素抵抗（IR）的重要机制。CCR2作为炎症因子趋化受体在炎性细胞向局部组织募集中发挥重要作用；TLR3是重要的模式识别受体，其激活可诱导巨噬细胞向M1型转化，通过调控炎症反应参与糖尿病的发生。我们认为CCR2或者TLR3功能缺失会通过改变内脏脂肪M1/M2平衡增加胰岛素的敏感性。本研究利用CCR2基因敲除型小鼠、TLR3基因敲除型小鼠以及C57BL/6野生型小鼠，深入探讨了CCR2以及TLR3在胰岛素抵抗中的调控作用。研究结果表明：1）在正常饮食小鼠，PM2.5暴露引起小鼠内脏脂肪组织巨噬细胞浸润，CCR2基因敲除虽然改善这一现象并抑制血液中炎症水平，但并未改善PM2.5吸入引起的空腹血糖的升高以及胰岛素敏感性异常。该作用与PM2.5吸入引起CCR2非依赖性肝脏糖异生限速酶表达和炎症反应增加有关。2）在高脂饮食小鼠，由饮食诱导的糖耐量受损和胰岛素敏感性降低、内脏脂肪形态和功能出现异常；上述改变被TLR3功能缺失所改善。其机制可能为高脂饮食上调TLR3基因表达，激活TBK1/IKKβ/NFκB炎症信号通路，引起巨噬细胞向内脏脂肪组织浸润和极化，从而抑制胰岛素信号通路，进一步抑制脂肪水解酶HSL和ATGL的活性和表达。3）在正常饮食小鼠，PM2.5暴露4周引起雌性和雄性小鼠血糖均升高，但长期暴露后，此血糖差异消失。在雌性小鼠，ITT实验显示PM2.5吸入显著抑制了胰岛素敏感性，该作用强于雄性小鼠。PM2.5吸入引起内脏脂肪组织巨噬细胞向M1型极化，该现象被TLR3基因敲除所阻断。本项目将为糖尿病发病病因和机制提出新的研究方向，为PM2.5引起糖尿病发病率迅速增加提供新的证据，也为糖尿病防治提出新的标靶。