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 6

Indole skews toward Th17 cells.

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Indole skews toward Th17 cells. Six-week-old male DBA/1 mice were fed a ...
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. Spleens were harvested on day 35 for analysis by flow cytometry. (A) Splenic naive (CD44–CD62L+) T cells as a percentage of CD4+ T cells. (B) Splenic effector T cells (CD44+CD62L–) as a percentage of CD4+ T cells. (C) Splenic central memory T cells (CD44+CD62L+) as a percentage of CD4+ T cells. n = 5–10 per group from 1 independent experiment for A–C. (D) Splenic FoxP3+RORγt–CD25+ Tregs are plotted as a percentage of total CD4+ T cells. (E) Splenic CD3+CD4+FoxP3–RORγt+ Th17 cells are plotted as a percentage of total CD4+ T cells. (F) Ratio of splenic Th17 to Tregs at CIA days 21 and 35. n = 10–20 per group, pooled from 2 independent experiments (day 35 [d35]) (D–F) and n = 10 per group (day 21 [d21]) from 1 independent experiment (F). (G and H) Total splenocytes from CIA day 35 were harvested and restimulated (stim) with bovine type II collagen (G) or CD3/CD28 Dynabeads (H); supernatant was saved and IL-17A/F was measured by Meso Scale Discovery (MSD). One statistical outlier was identified in the TS+Vehicle group using Grubb’s test and was excluded from analysis. n = 4 (TS+Vehicle) and n = 5 (TL+Indole, TL+Vehicle) per group from 1 independent experiment. (I) TL+Indole-treated mice received i.p. injections of 100 μg anti–IL-23p19 or isotype (anti-HRP) on CIA days 0, 7, 14, and 21, and CIA severity was monitored. n = 10 (TL+Indole+anti–IL-23), n = 10 (TL+Indole+Isotype), and n = 4 (TS+Vehicle). Asterisks show the comparison between TL+Indole+Isotype versus TL+Indole+anti–IL-23. 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–H) or 2-way ANOVA with Bonferroni’s correction for multiple comparisons (I).