治疗肥胖性胰岛素抵抗的新靶点PPARδ通过GSTP1-NLRP3炎性体通路抗炎的作用和机制研究

Peroxisome proliferator-activated receptor (PPAR) δ is a nuclear receptor that has represented as a potential new therapeutic target for obesity-induced insulin resistance (IR). Emerging evidence suggests that PPARδ attenuates IR by repression of IL-1β production in macrophages; however, the mechanisms underpinning this anti-inflammatory property of PPARδ have not been fully understood. Previously, it is shown that NLRP3 inflammasome activation is required for IL-1β production in macrophages; however, we found that PPARδ activation could attenuate NLRP3 mRNA level. We also found that, activation of PPARδ resulted in a highly enriched gene expression of GSTP1. Moreover, overexpress GSTP1 in macrophages repressed NLRP3 gene expression as indicated by our preliminary data. Therefore, we propose that PPARδ exerts inhibitory effect on IL-1β production through transcriptional induction of GSTP1 which further suppresses NLRP3 inflammasome activation in macrophages. In the present study, we will first induce-or-reduce PPARδ expression in macrophages to investigate its role in regulating NLRP3 inflammasome activation. Secondly, luciferase reporter gene will be used to identify regulatory mechanism of PPARδ on GSTP1 expression. Thirdly, we will test if GSTP1 could modulate the activation process of NLRP3 inflammasome. At last, our hypothesis will be verified in obesity-induced IR mice model using the PPARδ-deficient bone marrow chimaeras mice. This study will provide a new mechanism underlying PPARδ inhibitory effect on obesity-induced IR, and also offer new evidence for development and application of PPARδ agonists as an anti-obesity-induced IR drug.

核转录因子PPARδ是肥胖性胰岛素抵抗（IR）的新型治疗靶点，其作用机理与抑制巨噬细胞产生IL-1β有关，但PPARδ抑制巨噬细胞产生IL-1β的机制不完全清楚。IL-1β的产生依赖NLRP3炎性体的活化，而我们发现激活PPARδ可抑制NLRP3的基因表达；我们还发现激活PPARδ后，GSTP1是表达量升高最显著的基因之一，其过表达可使NLRP3的表达降低。故推测：PPARδ可通过上调GSTP1的表达，抑制NLRP3炎性体的活化，从而抑制IL-1β产生。本研究首先改变PPARδ的表达，探寻其对NLRP3炎性体的调控作用；然后用荧光素酶报告基因揭示PPARδ对GSTP1的调控机制；再考察GSTP1对NLRP3炎性体的影响；最后在骨髓细胞敲除PPARδ基因的小鼠中建立肥胖性IR模型，验证体外试验的结果。本项目旨在完善PPARδ抑制肥胖性IR的机制，为PPARδ激动剂的开发应用提供新的科学依据。

本课题首次发现M2型巨噬细胞可发挥抗自身死亡的重要生理功能，该生理功能解释了M2型巨噬细胞在肥胖症中对机体的保护机制。同时该课题的研究成果还说明激活Pparδ/Pparγ以及Stat6是抑制脂毒性引起的NLRP3炎性体和IL-1β的有效手段，这为肥胖症的治疗提供了新手段和新靶点。具体的研究成果如下：.1.通过比较M2型巨噬细胞诱导剂白细胞介素-4（IL-4）以及GW501516[过氧化物酶体增殖物激活受体δ/γ(Pparδ/Pparγ)的激动剂]所引起的基因表达的改变，我们发现M2型巨噬细胞可上调促细胞存活和抗细胞死亡的基因的表达。.2.体外试验证明Pparδ/γ或信号传导子及转录激活子(Stat6)在巨噬细胞中的敲除可加剧棕榈酸诱导的巨噬细胞死亡和NLRP3炎性体激活，相反激活Pparδ/γ或Stat6则抑制棕榈酸诱导的巨噬细胞死亡和NLRP3炎性体激活。这说明Pparδ/γ或Stat6的激动剂（例如GW501516、GW0742或Il-4）是抑制脂毒性所引起的NLRP3炎性体反应和IL-1β的有效新方法。 .3.小鼠体内实验表明β-肾上腺素能受体激动剂所引发的脂解效应使得骨髓细胞Pparδ/γ特异性敲除的小鼠（Mac-Pparδ/γ-/-）以及Stat6全身性敲除小鼠(Stat6-/-)的脂肪组织巨噬细胞表现出更多的细胞死亡和炎症反应，进一步说明Pparδ/γ和Stat6是抑制IL-1β相关的炎症反应的有潜力的新靶点。