Gut symbionts alleviate MASH through a secondary bile acid biosynthetic pathway

Cell

Volume 187, Issue 11, May 23, 2024, p2717-2734.e33

Qixing Nie, Xi Luo, Kai Wang, Yong Ding, Shumi Jia, Qixiang Zhao, Meng Li, Jinxin Zhang, Yingying Zhuo, Jun Lin, Chenghao Guo, Zhiwei Zhang, Huiying Liu, Guangyi Zeng, Jie You, Lulu Sun, Hua Lu, Ming Ma, Yanxing Ji, Ming Hua Zheng, Yanli Pang, Changtao Jiang

https://doi.org/10.1016/j.cell.2024.03.034

ABSTRACT: The gut microbiota has been found to play an important role in the progression of metabolic dysfunctionassociated steatohepatitis (MASH), but the mechanisms have not been established. Here, by developing a click-chemistry-based enrichment strategy, we identified several microbial-derived bile acids, including the previously uncharacterized 3-succinylated cholic acid (3-sucCA), which is negatively correlated with liver damage in patients with liver-tissue-biopsy-proven metabolic dysfunction-associated fatty liver disease (MAFLD). By screening human bacterial isolates, we identified Bacteroides uniformis strains as effective producers of 3-sucCA both in vitro and in vivo. By activity-based protein purification and identification, we identified an enzyme annotated as b-lactamase in B. uniformis responsible for 3-sucCA biosynthesis. Furthermore, we found that 3-sucCA is a lumen-restricted metabolite and alleviates MASH by promoting the growth of Akkermansia muciniphila. Together, our data offer new insights into the gut microbiota-liver axis that may be leveraged to augment the management of MASH.

摘要：肠道菌群已被发现在代谢功能障碍相关脂肪性肝炎 (MASH) 的进展中发挥重要作用，但其机制尚未确定。在此，通过开发基于点击化学的富集策略，我们鉴定出几种微生物衍生的胆汁酸，包括之前未表征的3-琥珀酰胆酸 (3-sucCA)，它与肝组织活检证实的代谢功能障碍相关脂肪肝疾病 (MAFLD) 患者的肝损伤呈负相关。通过筛选人体细菌分离株，我们鉴定出Bacteroides uniformis菌株在体外和体内均为3-sucCA的有效生产者。通过基于活性的蛋白质纯化和鉴定，我们在Bacteroides uniformis菌中鉴定出一种β-内酰胺酶，该酶负责3-sucCA的生物合成。此外，我们发现3-sucCA是一种管腔限制性代谢物，可通过促进Akkermansia muciniphila的生长来缓解MASH 。总之，我们的数据为肠道菌群-肝脏轴提供了新的见解，或许可以用于增强MASH的管理。

Keywords: gut microbiota; bile acid; acylated bile acids; 3-sucCA; biosynthesis; BAS-suc; MAFLD

关键词：肠道微生物群；胆汁酸；?；ㄖ?；3-琥珀酰胆酸；生物合成；BAS-suc；代谢功能障碍相关脂肪肝疾病

SUMMARY: This study focused on the mechanism by which gut symbionts alleviate metabolic dysfunction-associated steatohepatitis (MASH). Employing a click chemistry-based enrichment strategy, a microbially derived bile acid-3-succinylated cholic acid (3-sucCA)-was identified. Levels of 3-sucCA were lower in patients with metabolically associated fatty liver disease (MAFLD) confirmed by liver tissue biopsy, and this bile acid exhibited a negative correlation with the degree of liver damage. The study further identified Bacteroides uniformis as the primary producer of 3-sucCA. Through activity-based protein purification and characterization, an enzyme annotated as a β-lactamase in this bacterium (designated BAS-suc) was found to be the key enzyme driving 3-sucCA biosynthesis. Additional experiments demonstrated that 3-sucCA is a gut lumen-restricted metabolite: it does not act directly on the bile acid receptors FXR and TGR5, but instead exerts its effects by promoting the growth of Akkermansia muciniphila. Specifically, 3-sucCA can activate the Amuc-NagB enzyme in Akkermansia muciniphila, facilitating glucosamination and peptidoglycan synthesis, which in turn accelerates the proliferation of Akkermansia muciniphila. The increased abundance of Akkermansia muciniphila enhances intestinal barrier function and reduces endotoxemia, thereby alleviating MASH via the LPS-TLR4 pathway. In animal models, supplementation with either 3-sucCA or 3-sucCA-producing Bacteroides uniformis (harboring the BAS-suc gene) reduced hepatic steatosis, inflammation, and fibrosis in mice. However, this protective effect was abolished when BAS-suc was knocked out in Bacteroides uniformis or when Akkermansia muciniphila was depleted. Analysis of clinical samples revealed that the fecal abundances of Bacteroides uniformis, Akkermansia muciniphila, and 3-sucCA content in MAFLD patients decreased with disease severity. Furthermore, the abundance of the bas-suc gene was positively correlated with both 3-sucCA levels and Akkermansia muciniphila abundance, while being negatively correlated with liver damage markers. In conclusion, this study uncovers a novel pathway: Bacteroides uniformis synthesizes 3-sucCA via BAS-suc, which in turn enriches Akkermansia muciniphila to alleviate MASH. This finding provides a microbial metabolic target for MASH therapy.

总结：该研究聚焦肠道共生菌缓解代谢相关脂肪性肝炎（MASH）的机制，通过点击化学富集策略发现微生物衍生胆汁酸3-琥珀酰胆酸（3-sucCA），其在经肝组织活检证实的代谢相关脂肪性肝?。∕AFLD）患者中含量较低，且与肝损伤程度呈负相关。研究筛选出拟杆菌（Bacteroides uniformis）为3-sucCA的主要产生菌，通过基于活性的蛋白质纯化鉴定，发现该菌中一种β-内酰胺酶（命名为BAS-suc）是3-sucCA生物合成的关键酶。进一步实验表明，3-sucCA是肠腔限制性代谢物，不直接作用于胆汁酸受体FXR和TGR5，而是通过促进阿克曼氏菌（Akkermansia muciniphila）生长发挥作用——3-sucCA可激活阿克曼氏菌中Amuc-NagB酶，促进葡萄糖胺化及肽聚糖合成，从而加速其增殖；阿克曼氏菌的增加能改善肠道屏障功能、降低内毒素血症，进而通过LPS-TLR4通路缓解MASH。在动物模型中，补充3-sucCA或能产生3-sucCA的拟杆菌Bacteroides uniformis（含BAS-suc基因），可减轻小鼠肝脏脂肪变性、炎症和纤维化，而敲除BAS-suc 的拟杆菌或阿克曼氏菌，该保护作用消失。临床样本分析显示，MAFLD患者粪便中拟杆菌、阿克曼氏菌丰度及3-sucCA含量均随疾病严重程度降低，且BAS-suc基因丰度与3-sucCA、阿克曼氏菌丰度正相关，与肝损伤指标负相关。综上，该研究揭示了拟杆菌通过BAS-suc合成3-sucCA，进而富集阿克曼氏菌缓解MASH的新通路，为MASH的治疗提供了微生物代谢靶点。