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Background Faecalibacterium prausnitzii ( F. prausnitzii) has been recognized for its various intestinal and extraintestinal benefits to humans. Extracellular vesicles(EVs) have diverse functions in host-to-cell communication. Both F.prausnitzii and its derived EVs(FPEVs) hold therapeutic potential for inflammatory bowel disease (IBD). However, clinical translation is hindered by strict anaerobiosis and poor colonization capacity, which pose challenges for large-scale application. Therefore, we want to pinpoint the specific active component in FPEVs. Then we want to explore the potential role of the component on intestinal inflammation and intestinal barrier in Ulcerative Colitis (UC) and related molecular mechanisms.Methods The effects of FPEVs and its bioactive component on DSS-induced intestinal inflammation and intestinal epithelial barrier were observed and evaluated by histologic images, QPCR, Western blot and Immunofluorescence. The bioactive component of FPEVs was identified by using untargeted metabolomics. The specific protective molecular mechanisms of the component were analyzed by RNA-sequencing, and verified by QPCR, Western blot and Immunofluorescence in vitro using mice colonic organoids and in vivo.Results FPEVs significantly alleviated intestinal inflammation and epithelial damage in DSS-induced murine model (IDDF2026-ABS-0190 Figure 1(A-F)).Phytosphingosine(PHS) was identified as the specific active component in FPEVs by using untargeted metabolomics (IDDF2026-ABS-0190 Figure 2(A)). PHS was also effective in alleviating inflammation and conferring protection to the intestinal barrier in DSS-induced colitis model (IDDF2026-ABS-0190 Figure 2(B-F)) and in colonic organoids derived from mice (IDDF2026-ABS-0190 Figure 2(G)).RNA-sequencing on the intestinal epithelial cell showed that PHS enhanced stem cell activity and promoted cell proliferation (IDDF2026-ABS-0190 Figure 3(A-C)), and targeted the downstream pathway to Wnt/β-catenin pathway (IDDF2026-ABS-0190 Figure 5(A)). These results were verified in mice (IDDF2026-ABS-0190 Figure 4(A-C), IDDF2026-ABS-0190 Figure 5(B-C)) and colonic organoids (IDDF2026-ABS-0190 Figure 4(D-E), IDDF2026-ABS-0190 Figure 5(D)).The biological effect of PHS was mediated through its direct binding to LRP6, which was verified by molecular docking analysis and Surface plasmon resonance (IDDF2026-ABS-0190 Figure 5(E-F)). Inhibition of LRP6 attenuated the therapeutic efficacy of PHS (IDDF2026-ABS-0190 Figure 6(A-D)).Conclusions FPEVs and the bioactive component PHS, both alleviate colitis and preserve intestinal barrier integrity. Mechanistically, PHS directly interacts with LRP6, which is the receptor of Wnt in Wnt/β-catenin pathway. This interaction activates Wnt/β-catenin signaling pathway, thereby promoting the proliferation and differentiation of intestinal stem cells to drive repair.Abstract IDDF2026-ABS-0190 Figure 1Abstract IDDF2026-ABS-0190 Figure 2Abstract IDDF2026-ABS-0190 Figure 3Abstract IDDF2026-ABS-0190 Figure 4Abstract IDDF2026-ABS-0190 Figure 5Abstract IDDF2026-ABS-0190 Figure 6