6-formylindolo[3, 2-b]carbazole alters gut microbiota and prevents the progression of ankylosing spondylitis in mice.

• Bacteroidetes/Firmicutes was involved in the development of ankylosing spondylitis (AS). • 6-formylindolo[3, 2-b]carbazole (FICZ) modulated intestinal homeostasis. • FICZ reduced the severity of AS. • FICZ improved intestinal mucosal barrier function. • FICZ altered the composition of the gut microbiota thus reversing the process of AS. Ankylosing spondylitis (AS), is known as a chronic inflammatory autoimmune disease, there is evidence to suggest that gut microbiota disorders may be related to the occurrence and development of AS. Studies have shown that 6-formylindolo[3, 2-b]carbazole (FICZ) has the ability to modulate intestinal homeostasis and inhibit inflammatory responses. The purpose of this work is to evaluate the protective role of FICZ in treating AS and elucidate potential mechanisms. FICZ was administered to the proteoglycan (PG)-induced AS mice for 7 consecutive weeks. The effects of FICZ on AS mice were evaluated by the disease severity, intestinal histopathology, proinflammatory cytokine levels, and intestinal mucosal barrier function. The gut microbiota compositions were profiled through 16S rDNA high-throughput sequencing. We found that FICZ significantly reduced the severity of AS and resulted in the downregulating of TNF-α and IL-17A inflammatory cytokines. Moreover, FICZ ameliorated pathological changes in the ileal and improved intestinal mucosal barrier function. Furthermore, FICZ altered the composition of the gut microbiota by increasing the Bacteroidetes/Firmicutes phylum ratio and enriched the genes related to "glycan biosynthesis and metabolism", thus reversing the process of AS. In conclusion, FICZ suppressed the progression of AS and altered gut microbiota in AS mice, which provided new insight into AS therapy strategy. [ABSTRACT FROM AUTHOR]