# A247 ACTIVATION OF VISCERAL AFFERENT NEURONS INVOLVED IN NOCICEPTION BY A BACTERIUM ASSOCIATED WITH INFLAMMATORY BOWEL DISEASE

## TL;DR

This study shows that a gut bacterium linked to inflammatory bowel disease can activate pain-sensing nerves in the gut, potentially explaining the severe abdominal pain in IBD.

## Contribution

The study demonstrates that Bacteroides vulgatus can directly activate visceral afferent neurons and sensitize TRPV1, linking bacterial proteases to IBD-related pain.

## Key findings

- B. vulgatus supernatant increases basal firing and mechanosensitivity of colonic afferent axons.
- B. vulgatus supernatant elevates Ca2+ influx and sensitizes TRPV1 in dorsal root ganglia neurons.
- B. vulgatus selectively activates high-threshold nociceptor units but not wide-dynamic range units.

## Abstract

Inflammatory bowel disease (IBD) is characterized by chronic relapsing inflammation of the gastrointestinal tract. Severe abdominal pain is a common symptom of IBD, yet effective pain treatments are limited. Proteolytic activity is elevated in IBD compared to healthy individuals. Recently, protease production by the gut bacterium Bacteroides vulgatus has been correlated with the severity of IBD.

Since proteases acting on protease-activated receptor 2 (PAR-2) can activate visceral pain pathways, we test the hypothesis that mediators from B. vulgatus activate visceral pain pathways and can directly activate dorsal root ganglia (DRG) neurons, altering pain signalling.

The effects of B. vulgatus ATCC 8482 supernatant or brain heart infusion (BHI) growth media on nociceptive neurons were assessed using ex-vivo single-unit afferent nerve recordings from C57bl/6 mouse colons. To further examine cellular mechanisms, Ca2+ imaging was performed on dissociated DRG neurons following the superfusion of B. vulgatus culture supernatant. As TRPV1 is an ion channel expressed mainly on nociceptive neurons, the effect of B vulgatus culture supernatant on Ca2+ influx in response to the TRPV1 agonist capsaicin was also quantified. “N” represents mice, while “n” represents single afferent units or DRG neurons.

Perfusion of B. vulgatus supernatant (1:20) through the lumen of murine colons significantly increased basal firing frequency by 50% (p < 0.001, N = 8, n = 38) and mechanosensitivity of colonic afferent axons by 48% (p < 0.05, N = 8). Interestingly, only the putative nociceptor high-threshold units were activated upon perfusion of this bacterial supernatant (p < 0.01, N = 8, n = 13), while the wide-dynamic range units were unaffected (p > 0.05, N = 8, n = 30). The BHI growth media did not alter basal activity (p > 0.05, N = 6, n = 23) or afferent nerve mechanosensitivity (p > 0.05, N = 6). Superfusion of B. vulgatus supernatant (1:100) increased intracellular [Ca2+] by 16% (p < 0.0001, N= 7, n = 51). Furthermore, exposure to the B. vulgatus supernatant significantly elevated Ca2+ influx in response to the TRPV1 agonist capsaicin (100 nM; p < 0.0001, n = 77, N = 7), while the BHI media did not alter intracellular [Ca2+] in response to capsaicin (p > 0.05, n = 66, N = 7).

Mediators released by Bacteroides vulgatus can activate visceral afferent nerves involved in nociception. Additionally, B. vulgatus can directly modulate DRG neuronal Ca2+ homeostasis and sensitize TRPV1 in these neurons. Future studies will explore whether proteases are responsible.

CIHR