Portulaca oleracea L. polysaccharide alleviates colitis-associated bone loss through Muribaculaceae-enriched gut microbiota and elevated colonic melatonin

AIMS: Colitis and its associated bone loss are major global health concerns with limited therapeutic options. Portulaca oleracea L. polysaccharide (POP) has been suggested to ameliorate both conditions via microbiota modulation. The study aimed to explore whether POP can alleviate colitis-associated bone loss and its underling mechanism. METHODS: A murine model of dextran sodium sulfate (DSS)-induced colitis with bone loss was used to assess the effects of POP. The 16S rRNA sequencing and ex vivo fecal microbiota transplantation (ex-FMT) were employed to identify bacterial taxa potentially associated with POP's protective effects. The functional impact of microbial metabolites was evaluated by treating cells with fecal supernatants (FS), and their compositional profiles were analyzed using fecal metabolomics. RESULTS: POP mitigated DSS-induced colitis and bone loss and reshaped gut microbial composition, featuring enrichment of Muribaculaceae. Transplantation of POP-modulated microbiota (POPFMT) replicated the therapeutic benefits, which were maintained following gentamicin treatment (GENFMT) but abolished by vancomycin (VANFMT). Compared with the DSSFMT group, Muribaculaceae abundance was significantly higher in the POPFMT group. This increase was maintained in the GENFMT group but markedly reduced in the VANFMT group. FS from POP group maintained gut barrier function by increasing ZO-1 and Occludin expression, while suppressing apoptosis in HT-29 cells. FS from POPFMT group suppressed inflammatory osteoclastogenesis of RAW 264.7 cells via the TRAF6/p65-NFATc1 signaling axis. Metabolomics revealed distinct tryptophan-related profiles, with POPFMT and GENFMT were characterized by elevated melatonin abundance, DSSFMT by increased indole, and VANFMT by increased indole derivatives. Colonic melatonin levels were consistently higher in the POP-treated, POPFMT, and GENFMT groups. Exogenous melatonin ameliorated DSS-induced colitis and bone loss, whereas the 4P-PDOT attenuated its protective effects. CONCLUSION: POP ameliorates DSS-induced colitis and bone loss by modulating the gut microbiota. The POP-modulated gut microbiota is characterized by enrichment of Muribaculaceae and is associated with increased colonic melatonin levels, which contributes to the observed attenuation of colitis and bone loss.