肠道菌群与其代谢物在鹅肥肝形成中的变化规律及作用机理

In mammalian animals, severe hepatic steatosis is often accompanied with inflammation and fibrosis. In contrast, no overt pathological symptoms are observed in goose liver with severe steatosis, suggesting goose may host a unique mechanism underlying the development of its fatty liver. It is known that disorders in gut microbiota and their metabolites can induce several diseases including non-alcoholic fatty liver disease (NAFLD) in mammalian animals (e.g., human and mouse). However, it is unclear whether gut microbiota and their metabolites contribute to goose fatty liver. Our preliminary data indicate dramatic constitutive changes in gut microbiota in the development of goose fatty liver. To further address this, the structural and functional changes in gut microbiota will be determined by de novo metagenomics analysis in this study. Intestinal transcriptome analysis will also be performed to reveal the mediating role of intestine in the participation of gut microbiota to the formation of goose fatty liver. Moreover, the metabolites from gut content as well as hepatic and blood metabolites will be analyzed so that the fingerprint of metabolites of gut microbiota may be identified. Based on these analyses, in vitro and vivo studies will be further employed for validation, thus it may become clear whether gut microbiota and their metabolites are involved in the unique mechanism underlying goose fatty liver. The completion of this project will not only promotes the understanding of mechanism for the development of goose fatty liver, but also provides new solution to NAFLD-associated problems in human and other economic animals.

哺乳动物肝脏脂肪变性常伴有炎症和纤维化，而鹅肝脏可沉积大量脂肪而不发生明显的病理症状，提示鹅脂肪肝(或肥肝)的形成存在某种独特机制。在哺乳动物（如人和鼠）中，肠道菌群及其代谢物的紊乱可诱发脂肪肝等多种疾病。然而，肠道菌群是否参与鹅肥肝的形成尚不清楚。本课题组前期研究发现，鹅肥肝的形成伴有明显的肠道菌群结构变化。为阐明肠道菌群及其代谢物与鹅肥肝形成的关系和作用机制，本研究拟采用宏基因组学方法分析鹅肥肝形成过程中肠道菌群的结构和功能变化，通过对宿主肠道组织的转录组分析，揭示肠道在菌群参与脂肪肝形成中的介导作用，以及对肠道内容物、血液和肝脏代谢组进行分析，识别肠道菌群代谢物的指纹特征。在此基础上，利用体外细胞试验和活体试验进行部分验证，从而明确肠道菌群及其代谢物在鹅肥肝形成中的变化规律和作用机理。该项目的完成不仅有助于深入阐明鹅肥肝的形成机制，而且为人类和其他动物脂肪肝的研究提供参考。

肠道菌群可以通过肠-肝轴参与非酒精性脂肪肝的发生和发展。以肠道菌群为研究对象，应用宏基因组学技术对菌群的结构进行分析，寻找与脂肪肝相关的菌群，已成为脂肪肝研究的一种重要手段。本研究以鹅肥肝为研究模型，对朗德鹅填饲不同阶段的肠道微生物进行宏基因组分析，并结合肠道内容物的代谢组学分析以及肠道组织的转录组分析，探索肠道菌群与宿主在脂肪肝形成过程中的相互作用方式与途径。研究结果表明，朗德鹅肠道微生物主要由厚壁菌门、变形菌门、拟杆菌门、放线菌门等少数丰度较高的优势菌门及其属水平上的叶杆菌属、拟杆菌属、螺杆菌属、乳酸杆菌属等优势菌属组成；填饲在一定程度上降低了肠道菌群的多样性，且这种影响在盲肠中最为显著；填饲过程中以厚壁菌门为代表的有益菌门显著增加，以蓝藻菌门为代表的有害菌门先降低然后恢复到稳定的水平。转录组数据表明，肠道组织中部分与炎症相关的差异基因，如FGB、C8A的表达水平显著下调，与紧密连接相关的SOCS3表达水平下调，而ZO-1（TJP1）和OCLN的mRNA表达量没有显著差异；进一步分析发现，填饲24天鹅的回肠和盲肠的差异表达基因主要富集于鞘脂代谢通路中。相应的，代谢组学研究表明参与鞘脂类物质合成的底物--乙醇胺（或胆胺）和磷酸乙醇胺在填饲组与对照组间存在显著差异；此外，四氢皮质甾酮、CYP27A1等通过对胆固醇、甾醇等脂质物质合成的影响进而促进脂肪的合成。动物试验表明，填饲饲粮中添加乳酸菌和乳酸可以抑制鹅肥肝的形成。本研究结果不仅有助于深入全面地阐明鹅肥肝的形成机制，而且为人类和其他动物脂肪肝的研究提供参考。