调节肠道菌群生成不同浓度硫化氢影响GLP-1分泌及宿主糖代谢的机制研究

Type 2 diabetes (T2D) is the severe threat to human’s health. The disorder of gut microbiota may play an important role in T2D process. The applicant formerly prompted gut microbiota to produce the short chain acid (SCFA), so as to enhance the secretion of GLP-1 and then improve T2D. Simultaneously, H2S production was inhibited. This work has been published on the journal of Science. It was reported that various levels of H2S had the different effects on GLP-1 secretion and glucose homeostasis. However, the regulatory mechanism of these effects still remained unclear. The applicant further revealed that the amount of sulfide quinone oxidoreductase (SQR) in intestinal cells which can decrease the H2S level might be modulated by the beneficial bacterium. The enzyme further increased the secretion of GLP-1 by regulating the amount of SCFA receptors. Based on this work, the applicant speculated that various levels of H2S modulated by gut microbiota might influence the secretion of GLP-1 and hosts’ glucose homeostasis differently via the different effect on the SCFA receptors. This study plans to study the different influence and mechanism of different levels of H2S on the SCFA receptor, secretion of GLP-1 and glucose homeostasis of mice by applying microencapsulated methionine to regulate the abundance of H2S producers and those bacterium which can promote the production of SQR, together with the gene knockout mice. This study will help to set up a novel treatment method by the modulation of the physiological effect levels of H2S produced by gut microbiota.

T2D严重威胁人类健康。研究表明，肠道菌群失调可能参与T2D进展。申请人前期通过调节肠道菌群产生短链脂肪酸（SCFA），促进GLP-1分泌并改善了T2D。同时，H2S生成被抑制（该工作发表在《Science》上）。据报道，不同浓度H2S对GLP-1分泌和糖代谢的影响不同，然而其调控机制有待进一步研究。申请人后续研究提示，发挥降低H2S浓度作用的肠道细胞SQR酶受有益菌调控，并通过调节SCFA受体数量促进GLP-1分泌。基于此，申请人推测调节肠道菌群生成不同浓度H2S，可能通过对SCFA受体的不同作用，产生对GLP-1分泌和糖代谢的不同影响。本项目拟采用微囊化蛋氨酸，调节H2S产生菌和促SQR生成菌丰度，结合基因敲除小鼠模型，研究不同浓度H2S通过调节SCFA受体作用，对GLP-1分泌和糖代谢产生不同的影响及机制。本研究将为调控肠道菌群生成生理作用浓度H2S，建立治疗T2D的新方案奠定基础。

2型糖尿病的发生发展与肠道菌群失调之间存在密切联系，蛋氨酸限制饮食可以改变肠道菌群的结构和功能。过量的蛋氨酸摄入会导致高同型半胱氨酸血症的发生，探究肠道菌群在宿主蛋氨酸代谢过程中的作用有助于为高同型半胱氨酸血症的治疗提供新思路。本研究通过给予小鼠肠道菌群不同剂量蛋氨酸，使其通过肠道菌群代谢。通过观察小鼠血糖相关各项指标、脂肪代谢指标、组织病理变化及粪便菌群基因组分析，评价蛋氨酸是否通过肠道菌群对宿主糖脂代谢及健康产生不同影响，进一步为预防及治疗2型糖尿病、高同型半胱氨酸血症和促进机体健康提供新的思路。研究发现，限制和增加蛋氨酸摄入均可以降低小鼠体重及血糖。小鼠肠道菌群鸟枪法宏基因组测序结果显示，限制（无/低）蛋氨酸饮食均能通过降低果糖和甘露糖代谢通路降低血糖，但这些小鼠在进行胰岛素抵抗试验中均因低血糖出现晕厥现象，提示限制蛋氨酸饮食可能通过降低该通路导致营养不良。高蛋氨酸饮食通过K00558 (编码DNA (cytosine-5)-methyltransferase 1, DNA甲基转移酶)参与半胱氨酸和蛋氨酸代谢通路，该通路是产生同型半胱氨酸的重要通路。研究发现，随着蛋氨酸摄入浓度的增加，血清同型半胱氨酸浓度也逐渐增加，提示该组小鼠糖代谢异常可能与肠道菌群同型半胱氨酸代谢有关，亦提示高蛋氨酸饮食带来的体重和血糖水平降低可能也并不意味着小鼠处于一种健康状态。进一步通过对SPF小鼠、伪无菌小鼠和菌群移植小鼠采用低蛋氨酸饮食、正常蛋氨酸饮食和高蛋氨酸饮食进行干预，结果表明，低蛋氨酸与高蛋氨酸浓度喂养小鼠体重比正常蛋氨酸浓度喂养小鼠低，低蛋氨酸摄入可能导致营养不良，而高蛋氨酸摄入可能引起宿主棕色脂肪组织增加，产能增加，从而降低小鼠体重。高蛋氨酸饮食小鼠出现肝脂肪病变，伪无菌造模小鼠肝脏无此变化。推测肠道菌群在蛋氨酸代谢对宿主糖脂代谢产生影响的过程中所发挥的作用可能较宿主自身代谢更为重要。总之，正常摄入蛋氨酸对维持机体健康非常重要。