细粒棘球蚴感染小鼠Bregs分化调控及其糖代谢重编程事件研究

The larval stages of Echinococcus granulosus (E. granulosus) can significantly down-regulate the immune response in hosts, leading to the immune escape, however, the underlying mechanisms are still largely unexplored. Our previous study has reported the expansion of regulatory B cells (Bregs) in mice post-infection, which thus represents one strategy of immune escape adopted by the parasite. Our In vitro experiment further shows that the excretory-secretory products (ESPs) of the parasite can directly induce the differentiation of Bregs via TLR-2 signaling, and significantly regulate the expression of Phosphatase and Tensin homolog (PTEN) and the Glucose Transporter 4 (GLUT4) in B cells, which suggests that the metabolic regrogramming events of glucose in B cells may be linked with TLR-2 signaling, thereby affecting the differentiation of Bregs. Moreover, our transcriptome analysis of the parasite has found a complete set of transcripts that related with glycolysis and gluconeogenesis processes in the putative ESPs, which also implies that the parasite may regulate the host immune response through interacting with glucose metabolism. Combining with the above results, the present study is to furhter investigate the regulation of Bregs differentiation both in in vitro and in vivo levels using whole profile of gene expression and metabonomics, with a special focus on the role and the mechanism of the metabolic programming events of glucose mediated by the TLR-2/PTEN in the differentiation process. This study will provide several novel information on the understanding of the mechanism of immune downregulation adopted by E. granulosus.

细粒棘球蚴感染显著下调宿主免疫应答，是其免疫逃避的重要手段，但具体机制尚不清楚。课题组前期研究发现，该寄生虫感染可诱导调节性B细胞（Bregs）比例升高，是其发挥免疫逃避作用的机制之一。体外实验进一步发现，其排泄分泌物（ESPs）可依赖TLR-2直接诱导Bregs分化，并调节B细胞上磷酸酶-张力蛋白同系物（PTEN）和葡萄糖转运子4的表达，提示ESPs可能通过TLR-2调控B细胞糖代谢重编程事件以影响Bregs分化。而转录组测序发现，ESPs含有全套糖酵解、糖异生相关酶类的转录本，提示该寄生虫可能通过干扰糖代谢调节宿主免疫应答。本项目在此基础上，拟联合应用全基因组表达谱及代谢组学等技术，从体外、体内水平进一步明确细粒棘球蚴感染对小鼠Bregs分化的调控作用，重点阐述TLR-2/PTEN介导的糖代谢重编程事件在此调控过程中的作用及机制，将为细粒棘球蚴下调宿主免疫应答的机制提供新的见解。

本项目从免疫代谢学视角，探究细粒棘球蚴（Echinococcus granulosus, Eg）感染下调宿主免疫应答、改善代谢紊乱的作用及机制。本项目发现（1）Eg促进小鼠Bregs分化及其代谢重编程机制。在体内，Eg感染可促进Bregs细胞比例增多；且在体外发现，Eg来源排泄分泌物（excretory-secretory products，ESPs）可诱导B细胞分化为Bregs。机制上，ESPs依赖TLR-2上调PTEN表达，后者通过促进脂肪酸代谢促进B细胞产生高水平IL-10。B细胞代谢组学显示，在阳离子模式下，共鉴定出340个差异代谢物；在阴离子模式，共鉴定出216个差异代谢物。这些代谢物富集于64条通路，包括甲状腺激素合成、谷胱甘肽/果糖/甘露糖/甘油磷脂代谢过程。B细胞转录组共鉴定出413个差异表达基因（differentially expressed genes，DEGs）。其中，与炎症以及趋化相关DEGs在感染后被上调。与此相对应的是，上调的DEGs主要与脂肪酸氧化、脂质合成/分解/转运和胆固醇代谢有关。Co-expression网络分析显示免疫与代谢相关的DEGs存在密切相互作用。尤其，胆固醇合成过程中甲羟戊酸生成相关酶HMGCR表达上调，其可能通过上调BLIMP1促进Bregs分化。本项目发现（2）Eg具有调控脂肪生成及改善肥胖相关认知障碍的潜力。Eg感染小鼠脂肪重量降低、脂肪细胞直径变小；伴随系统性碳水化合物氧化减低、脂肪酸氧化增强。脂肪组织全基因表达谱发现，Eg感染上调“脂肪氧合酶”、“精氨酸和脯氨酸代谢”；而下调“糖酵解”、“三羧酸循环”、“脂质从头合成”、“脂滴生成”等代谢通路。尤其，我们首次在国际上发现Eg来源分子ESPs可通过调节肠道菌群-肠-脑轴，改善肥胖小鼠的认知功能损伤。这些研究结果为寄生虫调控宿主免疫与代谢的机制提供了全新的见解。