Bacterially-derived indole modulates murine arthritis through alteration of B cell glycosylation enzymes

Abstract

Abstract Indole, a bacteria-derived immunomodulatory metabolite that binds the aryl hydrocarbon receptor (AhR), is produced by bacterial tryptophanase in the intestinal tract of both mice and humans. Our studies using the murine collagen-induced arthritis (CIA) model of inflammatory arthritis demonstrated that intestinal bacteria influence disease severity through modulation of autoantibody glycosylation, and indole significantly correlated with the development of disease (P<0.0001). Therefore, we hypothesized that indole modulates CIA through modulation of B cell glycosylation enzymes via AhR signaling. Mice with CIA that were protected by treatment with broad-spectrum antibiotics at the time of booster injection (CIA+Abx), lost the protective effect of antibiotics when dosed with indole (arthritis score 3.6±0.75 CIA+Abx+Indole vs. 1±0.00 CIA+Abx, p<0.001). Mice with CIA, compared to CIA+Abx, demonstrated significantly increased expression of β1,4-galactosyltransferase 1 (GalT) and β-galactoside α2, 6-sialyltransferase 1 (St6gal1), two enzymes important in mediating pathogenic antibody glycosylation; this effect was reversed in CIA+Abx+Indole. We further demonstrate that Ramos cells, a human B cell line, upregulate glycosylation enzymes and AhR expression in response to indole exposure, with a fold change expression of 3.315±0.92 of B4GALT5 in indole-treated cells as compared to untreated (p=0.05). While the requirement of AhR and the glycosylation status of antibodies in our studies need to be confirmed, these results suggest that microbiome changes in CIA result in indole signaling on B cells, affecting glycosylation enzymes that modulate autoantibody effector function towards a proinflammatory profile.