# Influence of bacterial tryptophan metabolism on inflammatory arthritis

> **NIH NIH R01** · UNIVERSITY OF COLORADO DENVER · 2024 · $549,209

## Abstract

ABSTRACT
Despite the observation of microbial dysbiosis in the intestines of individuals at risk for and with rheumatoid
arthritis (RA) and spondyloarthritis (SpA), the mechanisms by which dysbiosis promotes inflammatory arthritis
remain unknown. Our group has made the following key discoveries: (1) In patients with axial SpA, paired
bacterial metagenomics with intestinal tissue metabolomics screening connected bacterial dysbiosis to
tryptophan catabolism into indoles. (2) We identified a novel indole-producing bacterium Subdoligranulum
didolesgii present in and targeted by autoantibodies and T cells from individuals at risk for and with RA that can
stimulate joint swelling when transferred into mice, whereas a non-indole producing isogenic strain does not. (3)
Using the CIA model, we demonstrated that a tryptophan low diet or microbiome depletion with antibiotics results
in protection from arthritis, and supplementation with indole is sufficient for disease by modulating both Th17 cell
differentiation and autoantibody pathogenicity. The goal of this proposal is to connect these observations and
demonstrate the immunologic pathway of indole from its generation by dysbiosis in RA to pathogenic immune
functions. Based on ongoing studies, we hypothesize that bacterial dysbiosis associated with RA results in
increased tryptophan catabolism into indole, which signals in intestinal dendritic cells to produce cytokines
leading to Th17 cell differentiation required for pathogenic autoantibody generation. In Aim 1, we will use paired
stool and plasma samples from an established cohort of controls, individuals with RA, and individuals at risk for
RA with some of whom transition to disease, to perform bacterial metagenomics of the stool and targeted
metabolomics of the plasma for the tryptophan pathway. We hypothesize that bacterial metagenomics will reveal
a pattern of tryptophan catabolism to indoles with increased plasma indole metabolites that correspond with the
development of RA. Aim 2 will then identify the cellular target of indole in vivo using dual single cell ATAC and
RNA sequencing of mesenteric lymph nodes harvested from mice fed a tryptophan low diet ± indole and induced
for CIA. Traditional immunologic and molecular biology techniques will then be performed to confirm the signaling
pathway and immune effects imparted by indole in human cells. Finally, Aim 3 will examine the requirement of
indole-stimulated Th17 differentiation for pathogenic autoantibody formation. We hypothesize that indole-
stimulated Th17 differentiation results in IL-21 that is necessary for B cell isotype switching and expression of
key glycosylation enzymes. We will block IL-23 and IL-21 in our indole-CIA model and human primary B cells to
dissect B cell functions associated with Th17 cell differentiation. Successful completion of these studies will
reveal a targetable pathway and disease population for potential therapeutic development by blocking indole in
treating RA...

## Key facts

- **NIH application ID:** 10979436
- **Project number:** 2R01AR075033-06
- **Recipient organization:** UNIVERSITY OF COLORADO DENVER
- **Principal Investigator:** Kristine A. Kuhn
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $549,209
- **Award type:** 2
- **Project period:** 2019-04-10 → 2029-07-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10979436

## Citation

> US National Institutes of Health, RePORTER application 10979436, Influence of bacterial tryptophan metabolism on inflammatory arthritis (2R01AR075033-06). Retrieved via AI Analytics 2026-05-27 from https://api.ai-analytics.org/grant/nih/10979436. Licensed CC0.

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