沙蒿多糖靶向肠道A.muciniphila菌调节小鼠肝脏脂肪酸代谢的机制及组-效关系探究

Recent findings show that microbiota A. muciniphila plays a key role in hepatic lipid homeostasis metabolism. Our preliminary study demonstrated that crude Artemisia Sphaerocephala Krasch polysaccharide (ASKP) can increase the abundance of A. muciniphila, and ameliorate the fatty acid metabolism disorder in mice. However, it is still unclear with which structural domain characteristics of ASKP fraction targets the A. muciniphila proliferation, and whether A. muciniphila mediates the improvement effects of ASKP on hepatic lipid metabolism disorder. In this project, ASKP is purified into a series of homogeneous fractions, and the primary structure of ASKP fractions are characterized. We will study the relationship between different ASKP fractions and A. muciniphila proliferation (compositon-activity), and screen out the active ASKP fraction which could significant increase A. muciniphila abundance. The methods including antibiotic treatment, faecal microbiota transplantation, and microbiota supplementation will be used to investigate whether A. muciniphila mediates the improvement effects of ASKP on hepatic lipid metabolism disorder. The effects of ASKP on the expression of ileum and colon tight junction proteins ZO-1, Occludin et al. and hepatic fatty acid metabolism-related protein SREBP-1c/ACC/FAS et al. will also be studied. This study will elucidate the molecular mechanism of ASKP regulating fatty acid homeostasis metabolism through A. muciniphila-intestinal mucosal barrier-hepatic SREBP-1c axis, and provide a theoretical basis for ASKP on regulation of lipid metabolism.

新近报道，肠道A. muciniphila（AM）菌与肝脂稳态代谢密切相关，我们初步发现沙蒿粗多糖可大幅增加AM菌丰度，并改善小鼠肝脏脂肪酸代谢紊乱。然而，何种结构域特性的沙蒿多糖组分选择性增殖AM菌及该菌是否介导沙蒿多糖的肝脂代谢改善效应尚不清楚。本项目拟将沙蒿多糖纯化为不同的系列均一组分，表征其一级结构，研究不同组分沙蒿多糖与AM菌调节效应的关系（组-效关系），筛选对AM菌有显著增殖特性的沙蒿多糖组分。采用抗生素处理、粪菌移植、菌种回补方法，研究AM菌是否介导沙蒿多糖的肝脂调节效应，考察沙蒿多糖对回肠及结肠ZO-1、Occludin等肠上皮细胞紧密连接蛋白与肝脏SREBP-1c/ACC/FAS等脂肪酸代谢相关蛋白表达的影响。阐明沙蒿多糖靶向AM菌-肠粘膜屏障-肝SREBP-1c轴调控脂肪酸稳态代谢的分子机制，为完善沙蒿多糖调节脂代谢的机制提供理论依据。

最近，在Gut等国际顶级期刊上相继报道了多种膳食功能糖与肠道微生物互作调节糖脂代谢的作用机制，而作为生物大分子的沙蒿多糖（ASKP）难以被人体直接吸收，其体内调节糖脂代谢的分子机制不明，为此我们以肠道菌群为切入点系统研究了沙蒿多糖体内调节糖脂代谢的分子机理。研究发现ASKP可改善肥胖小鼠肠道菌群失调，并大幅靶向提高肠道A. muciniphila（AKK）菌丰度，促进小鼠腹股沟白色脂肪（iWAT）和褐色脂肪（WAT）中产热蛋白PGC-1α、UCP-1和CIDEA的表达，加速肝脏和iWAT中甘油三酯的分解。同时，采用广谱抗生素饮用水构建了“伪无菌鼠”模型，发现抗生素处理显著废除了ASKP调控肝脂代谢稳态的益生效应，表明肠道菌群在介导沙蒿多糖体内调控糖脂代谢过程中发挥了关键作用。进一步，我们将ASKP分离纯化为三种单一组分ASKP1、ASKP2与ASKP3，在小鼠体内发现相对于ASKP2和ASKP3，ASKP1表现出更好地缓解肥胖小鼠肝脂代谢紊乱的益生效应，并可大幅靶向增殖特征肠道AKK菌丰度。. 进一步，通过菌种回补试验发现，发现无论AKK活菌还是死菌（巴氏杀菌处理）均可提高肥胖小鼠糖肠道黏膜蛋白ZO-1、Occludin和Claudin-1的表达修复肠屏障损伤，改善糖脂代谢异常。同时，我们与与瓦格宁根大学教授Willem M. De Vos开展合作，获得AKK菌外膜蛋白Amuc_1100，发现Amuc_1100可作用于肠道TLR2-Myd88通路诱导ILC3细胞分泌IL-22，通过激活肠上皮细胞（ECs）中表达的岩藻糖转移酶2（Fut2）介导肠细胞岩藻糖基化（UEA-1表达上调），降低肠屏障通透性并减少内毒素进入体循环，抑制肝脏ACC1、FAS和SREBP1蛋白表达进而调控脂代谢稳态。我们的结果表明，AKK菌的活性位点可能是其膜外蛋白Amuc_1100，通过肠粘膜屏障-肝SREBP-1c轴调控肝脏脂代谢稳态。. 相关研究成果在农业食品科学研究领域 Food & Function, Journal of Agricultural and Food Chemistry等国际顶级SCI期刊上共发表高水平科研论文7篇，影响因子均在4.0以上，且受到国内外学术界高度关注，被 SCI 期刊大量引用。此外，部分研究成果正在整理中，拟发表在更高水平的杂志上。