Hirsutella sinensis fungus Alleviates Ulcerative Colitis via Modulating Gut microbiota-derived Ursodeoxycholic Acid Biosynthesis to Inhibit Th17 Cell Differentiation

• Hirsutella sinensis fungus is special in nutrients and can effectively relieve colonic inflammation and inhibit Th17 cell differentiation • Hirsutella sinensis fungus increases the abundance of Ruminococcus and Lactobacillus • Hirsutella sinensis fungus increases microbiota-driven ursodeoxycholic acid synthesis • IL-6/JAK2/STAT3 signaling signaling is the key mechanism by which Hirsutella sinensis fungus alleviates UC Hirsutella sinensis fungus (HSF) is an edible fungus used in traditional chinese medicine. Although its potential in regulating immunity and improving the tumor microenvironment has been recognized, it has not been sufficiently studied in the context of Ulcerative colitis (UC). In this study, we used ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry to identify the nutritional components of HSF, and clarified its effect on UC by detecting the effects of HSF on gut microbiota, bile acid metabolism and T helper 17 (Th17) cells cell differentiation. Results from 16S rRNA sequencing, fecal microbiota transplantation (FMT), and antibiotics (ABX) experiments indicate that HSF exerts its protective effects against UC by correcting gut microbiota imbalances and modulating Th17 cell differentiation. Additionally, untargeted metabolomics and targeted bile acid analysis reveal that HSF regulates bile acid metabolism, particularly ursodeoxycholic acid (UDCA) synthesis, through remodeling the gut microbiota. Supplementation with exogenous UDCA inhibits Th17 cell differentiation and restores damaged intestinal barriers, thereby mitigating UC. Mechanistically, HSF regulates the imbalance of intestinal flora, especially the abundance of Ruminococcus and Lactobacillus , promotes UDCA synthesis, inhibits Interleukin-6 (IL-6)/ janus kinase 2 (JAK2)/ signal transducer and activator of transcription 3 (STAT3) signaling and Th17 cell differentiation. This study demonstrated that HSF modulates Th17 cell differentiation via the intestinal microbiota-UDCA metabolic axis and enhances intestinal barrier integrity, offering a promising new approach for the treatment of UC.