Microbiota-dependent indole production stimulates the development of collagen-induced arthritis in mice
Brenda J. Seymour, … , Sean P. Colgan, Kristine A. Kuhn
Brenda J. Seymour, … , Sean P. Colgan, Kristine A. Kuhn
Published December 19, 2023
Citation Information: J Clin Invest. 2024;134(4):e167671. https://doi.org/10.1172/JCI167671.
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Research Article Autoimmunity

Microbiota-dependent indole production stimulates the development of collagen-induced arthritis in mice

Abstract

Altered tryptophan catabolism has been identified in inflammatory diseases like rheumatoid arthritis (RA) and spondyloarthritis (SpA), but the causal mechanisms linking tryptophan metabolites to disease are unknown. Using the collagen-induced arthritis (CIA) model, we identified alterations in tryptophan metabolism, and specifically indole, that correlated with disease. We demonstrated that both bacteria and dietary tryptophan were required for disease and that indole supplementation was sufficient to induce disease in their absence. When mice with CIA on a low-tryptophan diet were supplemented with indole, we observed significant increases in serum IL-6, TNF, and IL-1β; splenic RORγt+CD4+ T cells and ex vivo collagen-stimulated IL-17 production; and a pattern of anti-collagen antibody isotype switching and glycosylation that corresponded with increased complement fixation. IL-23 neutralization reduced disease severity in indole-induced CIA. Finally, exposure of human colonic lymphocytes to indole increased the expression of genes involved in IL-17 signaling and plasma cell activation. Altogether, we propose a mechanism by which intestinal dysbiosis during inflammatory arthritis results in altered tryptophan catabolism, leading to indole stimulation of arthritis development. Blockade of indole generation may present a unique therapeutic pathway for RA and SpA.

Authors

Brenda J. Seymour, Brandon Trent, Brendan E. Allen, Adam J. Berlinberg, Jimmy Tangchittsumran, Widian K. Jubair, Meagan E. Chriswell, Sucai Liu, Alfredo Ornelas, Andrew Stahly, Erica E. Alexeev, Alexander S. Dowdell, Sunny L. Sneed, Sabrina Fechtner, Jennifer M. Kofonow, Charles E. Robertson, Stephanie M. Dillon, Cara C. Wilson, Robert M. Anthony, Daniel N. Frank, Sean P. Colgan, Kristine A. Kuhn

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Figure 5

Indole alters complement activation, IgG subclass, and glycosylation.

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Indole alters complement activation, IgG subclass, and glycosylation. Si...
Six-week-old male DBA/1 mice were fed a TL or TS diet starting on day –1 and through the duration of the experiment. Following induction of CIA, mice were treated with indole (200 μL of a 10 mM solution) or vehicle control (0.33% methanol) by oral gavage every other day starting on day 0. (A) Day 35 serum was evaluated by ELISA for C3 binding to anti–CII IgG. n = 5–10 per group from 1 independent experiment. (B) Formalin-fixed, paraffin-embedded (FFPE) joints were stained for complement C3 by immunohistochemistry, and staining intensity was scored. Each data point represents the average complement deposition score of all 4 paws for 1 mouse (maximum score = 3 per paw). n = 10–15 per group, pooled from 2 independent experiments. (C and D) Day 35 serum was evaluated by ELISA for anti–CII IgG2a (C) and anti–CII IgG2b (D). n = 5–10 per group from 1 independent experiment. (E) Diagram of possible glycosylation patterns on N297 of the IgG Fc domain. Blue squares denote N-acetylglucosamine; green circles denote mannose; yellow circles denote galactose; purple diamonds denote sialic acid. (F and G) Total IgG was purified from serum, and IgG glycosylation patterns were assessed by LC-MS/MS. The percentage of galactosylation (Gal) and the percentage of sialylation (Sia) are plotted, respectively. Galactosylation and sialylation were calculated as a percentage of all glycoforms (G0, G1, G2, S1, and S2). n = 8 per group from 1 independent experiment. (H and I) In a separate experiment, anti–CII IgG was purified using CII-linked CNBr Sepharose 4B beads. IgG glycosylation patterns were assessed by LC-MS/MS. Galactosylation and sialylation are plotted as the percentage of G1, G2, S1, and S2 glycoforms only. n = 5–10 per group from 1 representative experiment. For all panels, values are plotted as individual mice (symbols) and the mean ± SEM (bars). *P < 0.05, **P < 0.01, ***P < 0.001, and ****P < 0.0001, by 1-way ANOVA with Bonferroni’s correction for multiple comparisons (A–D, H, and I) and unpaired Student’s t test (F and G). rel., relative.