Table_1_Impact of gut microbiota on nonalcoholic fatty liver disease: insights from a leave-one-out cross-validation study.xlsx

IntroductionEnteric dysbacteriosis is strongly associated with nonalcoholic fatty liver disease (NAFLD). However, the underlying causal relationship remains unknown. Thus, the present study aimed to investigate the relationship between gut microbiota and NAFLD using Mendelian randomization (MR) and analyze the target genes potentially regulated by specific microbiota.
MethodsBidirectional two-sample MR analysis was performed using inverse variance weighted (IVW) supplemented by MR-Egger, weighted median, simple mode, and weighted mode methods. Data were pooled from gut microbiota and NAFLD association studies. The least absolute shrinkage, selection operator regression, and the Support Vector Machine algorithm were used to identify genes regulated by these intestinal flora in NAFLD. The liver expression of these genes was verified in methionine choline-deficient (MCD) diet-fed mice.
ResultsIVW results confirmed a causal relationship between eight specific gut microbes and NAFLD. Notably, the order Actinomycetales, NB1n, the family Actinomycetaceae, Oxalobacteraceae and the genus Ruminococcaceae UCG005 were positively correlated, whereas Lactobacillaceae, the Christensenellaceae R7 group, and Intestinibacter were negatively correlated with NAFLD onset. In NAFLD, these eight bacteria regulated four genes: colony-stimulating factor 2 receptor β, fucosyltransferase 2, 17-beta-hydroxysteroid dehydrogenase 14, and microtubule affinity regulatory kinase 3 (MAPK3). All genes, except MARK3, were differentially expressed in the liver tissues of MCD diet-fed mice.
DiscussionThe abundance of eight gut microbiota species and NAFLD progression displayed a causal relationship based on the expression of the four target genes. Our findings contributed to the advancement of intestinal microecology-based diagnostic technologies and targeted therapies for NAFLD.

引言
肠道菌群失调与非酒精性脂肪性肝病（nonalcoholic fatty liver disease, NAFLD）密切相关，但其潜在的因果关联仍未明确。本研究旨在利用孟德尔随机化（Mendelian randomization, MR）探究肠道菌群与非酒精性脂肪性肝病的关联，并分析特定菌群可能调控的靶基因。
方法
本研究采用逆方差加权（inverse variance weighted, IVW）法，并辅以MR-Egger、加权中位数、简单模态法及加权模态法，开展双向两样本孟德尔随机化分析。研究数据整合自肠道菌群与非酒精性脂肪性肝病的关联研究。本研究采用最小绝对收缩和选择算子（least absolute shrinkage and selection operator, LASSO）回归与支持向量机（Support Vector Machine, SVM）算法，筛选非酒精性脂肪性肝病中受上述肠道菌群调控的基因，并在甲硫氨酸胆碱缺乏（methionine choline-deficient, MCD）饮食喂养的小鼠中验证这些基因的肝脏表达水平。
结果
逆方差加权分析结果证实，8种特定肠道菌群与非酒精性脂肪性肝病存在因果关联。具体而言，放线菌目（Actinomycetales）、NB1n、放线菌科（Actinomycetaceae）、草酸杆菌科（Oxalobacteraceae）以及瘤胃球菌科UCG005属（Ruminococcaceae UCG005）的丰度与非酒精性脂肪性肝病发病呈正相关；而乳杆菌科（Lactobacillaceae）、克里斯滕森菌科R7群（Christensenellaceae R7 group）以及Intestinibacter属的丰度与该病发病呈负相关。在非酒精性脂肪性肝病中，上述8种菌群调控4个靶基因：集落刺激因子2受体β亚基、岩藻糖基转移酶2、17β-羟类固醇脱氢酶14以及微管亲和调节激酶3（MAPK3）。除MARK3外，其余所有基因在甲硫氨酸胆碱缺乏饮食喂养小鼠的肝组织中均存在差异表达。
讨论
基于4个靶基因的表达情况，本研究证实8种肠道菌群的丰度与非酒精性脂肪性肝病进展存在因果关联。本研究结果为基于肠道微生态的非酒精性脂肪性肝病诊断技术与靶向治疗手段的发展提供了理论支撑。