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 3

Indole minimally affects bacterial dysbiosis imparted by a TL diet during CIA.

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Indole minimally affects bacterial dysbiosis imparted by a TL diet durin...
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. CIA was induced, and indole (200 μL of a 10 mM solution) or vehicle control (0.33% methanol) was added by oral gavage every other day starting on day 0. On day 35, fecal pellets were harvested, genomic DNA was isolated, and 16S rRNA-Seq was performed to assess microbial diversity for TS+Vehicle (TS, n = 5), TL+Vehicle (TL, n = 10), and TL+Indole (TLI, n = 10). (A–C) α-Diversity indices are shown for each group. *P < 0.05 and **P < 0.01, by 1-way ANOVA with pairwise P values determined by Tukey’s honest significance difference tests for differences between groups. Richness: measured by the Chao1 index. Shannon Diversity: measured by Shannon’s diversity index, H. Evenness: measured by H/Hmax where Hmax = the maximum H for a subject. (D) PCA, in which smaller, lighter symbols represent individual mice and large, darker symbols represent group means plus 95% CIs for PC1 and PC2. (E) Bar charts showing mean distributions of taxa for each group. Taxa with relative abundances of less than 1.0% were collapsed into the “Other” category to simplify the figure. OTU, operational taxonomic units. Differences in β-diversity between groups were assessed using PERMANOVA tests with the weighted Aitchison dissimilarity index: **P < 0.01 and ***P < 0.001. (F–I) Volcano and effect size plots generated by ANOVA-like differential expression (ALDEx2) analysis indicate taxa that were significantly enriched or depleted (FDR-corrected P value < 0.05) in mice with CIA on 1 diet compared with another: TS+Vehicle versus TL+Vehicle (F and G), TL+Vehicle versus TL+Indole (H and I).