# Tryptophan derivatives in EHEC pathogenesis

> **NIH NIH R01** · UT SOUTHWESTERN MEDICAL CENTER · 2022 · $143,243

## Abstract

PROJECT SUMMARY
The colon contains tryptophan derivatives such as indole, which is a microbiota-derived signaling molecule, and
the host-derived serotonin neurotransmitter that is primarily synthesized in the GI tract. Indole is also known to
be absorbed by host cells and helps strengthen the integrity of the intestinal barrier, being regarded as a
beneficial chemical cue within microbial/host interactions. Indole is synthesized by tryptophanase, which is
encoded by the tnaA gene. We have shown that the concentration of indole is significantly higher in the lumen
of the colon (the compartment where the microbiota resides) compared to colonic tissues (where indole is
absorbed by intestinal epithelial cells). Serotonin is synthesized in enterochromaffin cells by the enzyme
tryptophan hydroxylase (TpH1). Upon its synthesis, serotonin is released into the lamina propria and is secreted
into the lumen. Serotonin signaling in the intestinal mucosa is terminated by removal of serotonin by the
serotonin selective reuptake transporter (SERT), which is expressed by epithelial cells. We showed that both
serotonin and indole converge to decrease virulence gene expression from enterohemorrhagic E. coli (EHEC)
and Citrobacter rodentium, a murine pathogen employed as a surrogate animal model for EHEC. We also
identified the bacterial receptor for these signals as CpxA. Upon sensing serotonin and/or indole, CpxA
functions primarily as a phosphatase, dephosphorylating itself and CpxR, that activates virulence in its
phosphorylated state. Through transcriptome studies we also identified the Indole Sequestering Receptor (Isr),
which in the absence of indole directly activates virulence expression. However, in the presence of indole, Isr is
no longer able to activate transcription of virulence genes. Using TpH1 pharmacological inhibitors (decrease the
levels of serotonin in the gut) and SERT knockout mice (have increased levels of luminal serotonin), we showed
that the presence of higher levels of serotonin in the intestine of mice decreased virulence in C. rodentium,
while decreased levels of serotonin are conducive to increased pathogenesis. Moreover, we synthetically
altered the concentration of indole in the GI tract of mice. This allowed us to assess the role of self-produced
versus microbiota-produced indole, and show that decreased indole concentrations promote bacterial
pathogenesis, while increased levels of indole decreases bacterial virulence gene expression during murine
infection. Altogether, both serotonin and indole decrease virulence of C. rodentium during murine infection. Our
studies show that fluctuations in the levels of indole and the serotonin neurotransmitter significantly impact
disease prognosis. However several questions regarding this exquisite signaling regulation of bacterial
virulence remain unanswered. Consequently the specific aims of this grant are: Aim 1. Define the CpxA/CpxR
and Isr serotonin/indole signaling cascade. Aim 2. Invest...

## Key facts

- **NIH application ID:** 10333398
- **Project number:** 5R01AI155398-02
- **Recipient organization:** UT SOUTHWESTERN MEDICAL CENTER
- **Principal Investigator:** VANESSA SPERANDIO
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $143,243
- **Award type:** 5
- **Project period:** 2021-02-01 → 2022-08-07

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10333398

## Citation

> US National Institutes of Health, RePORTER application 10333398, Tryptophan derivatives in EHEC pathogenesis (5R01AI155398-02). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10333398. Licensed CC0.

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