Supplementary Material for: Altered intestinal microbial flora and metabolism in patients with idiopathic membranous nephropathy

Introduction: Dysbiosis of the intestinal microbiome and related metabolites have been observed in chronic kidney disease (CKD), yet their roles in idiopathic membranous nephropathy (IMN) is poorly understood. Methods: In this study, we describe the variation of intestinal bacteria and fecal metabolites in patients with IMN in Chinese population. Stool samples are collected from 41 IMN patients at the beginning of diagnosis confirmation and 41 gender and age matched healthy control (HC). Microbial communities are investigated by sequencing of 16S rRNA genes and functional profiles predicted using Tax4Fun, and the correlation between intestinal bacteria and IMN clinical characteristics is also analyzed. Untargeted metabolomic analysis is performed to explore the relationship between colon’s microbiota and fecal metabolites. Results: IMN gastrointestinal microbiota demonstrates lower richness and diversity compared to HC, and exhibits a marked taxonomic and inferred functional dysbiosis when compared to HC. Some genera are closely related to the clinical parameters, such as Citrobacter and Akkermansia. 20 characteristic microbial biomarkers are selected to establish a disease prediction model with a diagnostic accuracy of 93.53%. Fecal metabolomics shows that tryptophan metabolism is reduced in IMN patients but uremic toxin accumulation in feces is not noticeable. Fecal microbiota transplantation demonstrates that gut dysbiosis impairs gut permeability in microbiota-depleted mice and induces NOD-like receptor activation in kidneys. Discussion/Conclusions: Clarifying the changes in intestinal microbiota in IMN patients will help further know the pathogenesis of this disease, and microbiota-targeted biomarkers will provide a potentially powerful tool for diagnosing and treating IMN.

引言：肠道菌群失调及其相关代谢物已在慢性肾脏病（CKD）中被观测到，但其在特发性膜性肾病（IMN）中的作用尚不明晰。
方法：本研究针对中国人群中的特发性膜性肾病（IMN）患者，分析其肠道菌群与粪便代谢物的变化。我们收集了41例确诊初期的IMN患者以及41例性别、年龄匹配的健康对照（HC）的粪便样本。通过16S rRNA基因（16S rRNA genes）测序对微生物群落进行分析，并利用Tax4Fun预测菌群功能谱，同时分析肠道菌群与IMN临床特征之间的相关性。此外，开展非靶向代谢组学分析（Untargeted metabolomic analysis），以探究结肠菌群与粪便代谢物之间的关联。
结果：与健康对照相比，IMN患者的胃肠道菌群丰富度和多样性均更低，且在分类学组成及预测功能层面均呈现显著失调。部分菌属与临床参数密切相关，例如柠檬酸杆菌属（Citrobacter）和嗜黏蛋白阿克曼菌属（Akkermansia）。我们筛选出20个特征性微生物生物标志物，构建了疾病预测模型，其诊断准确率可达93.53%。粪便代谢组学分析显示，IMN患者的色氨酸代谢通路活性降低，但粪便中尿毒症毒素的积累并不显著。粪便菌群移植实验证实，肠道菌群失调会破坏菌群缺陷小鼠的肠道屏障通透性，并诱导肾脏内NOD样受体（NOD-like receptor）的激活。
讨论与结论：明确IMN患者肠道菌群的变化，有助于进一步阐明该疾病的发病机制，而以菌群为靶点的生物标志物将为IMN的诊断与治疗提供极具潜力的有力工具。