Ulcerative colitis-driven gut dysbiosis exacerbates periodontal bone loss through the gut–oral axis /Th17/Treg imbalance

Ulcerative colitis (UC) and periodontitis, both microbial dysbiosis-driven chronic inflammatory disorders, coexist and mutually exacerbate, but the causal mechanisms remain unclear. Using ligature-induced periodontitis plus DSS-colitis mice, we found UC doubles alveolar bone loss, heightens systemic inflammation, oxidative stress, and osteoclastogenesis. 16S rRNA and LC–MS metabolomics showed UC enriches oral pathogens, depletes gut Firmicutes, expands Bacteroides, and correlates with suppressed amino-acid/bile-acid biosynthesis. Fecal microbiota transplantation (FMT) from DSS donors into antibiotic-pretreated periodontitis-prone mice replicated aggravated bone loss, systemic inflammation, gut-barrier leakage, and Th17/Treg imbalance, while healthy-donor FMT protected. GC–MS revealed 35–60% reductions in acetate, propionate, and butyrate; keystone taxa Parabacteroides and Muribaculum inversely correlated with SCFAs and host inflammatory genes. Collectively, UC-driven gut dysbiosis is a transmissible causal factor that simultaneously remodels oral and intestinal biofilms, erodes epithelial barriers, and amplifies osteoclastic bone resorption. SCFAs-producing microbes or supplementation may be potential therapeutics for UC-associated periodontitis patients.