Sustained neurochemical plasticity in central terminals of mouse DRG neurons following colitis

A role for interleukin 17A in IBD-related neuroplasticity

BACKGROUND

Changes to the structure and function of the innervation of the gut contribute to symptom generation in inflammatory bowel diseases (IBD). However, delineation of the mechanisms of these effects has proven difficult. Previous work on sympathetic neurons identified interleukin (IL)-17A as a novel neurotrophic cytokine. Since IL-17A is involved in IBD pathogenesis, we tested the hypothesis that IL-17A contributes to neuroanatomical remodeling during IBD.

METHODS

Immunohistochemistry for tyrosine hydroxylase was used to identify sympathetic axons in mice with dextran sulphate sodium (DSS)-induced colitis and controls. Axon outgrowth from sympathetic neurons in response to incubation in cytokines or endoscopic patient biopsy supernatants was quantified.

KEY RESULTS

DSS-induced colitis led to an increase in tyrosine hydroxylase immunoreactivity in the inflamed colon but not the spleen. Colonic supernatants from mice with colitis and biopsy supernatants from Crohn's disease patients increased axon outgrowth from mouse sympathetic neurons compared to supernatants from uninflamed controls. An antibody that neutralized IL-17A blocked the ability of DSS-induced colitis and Crohn's disease supernatants to induce axon extension.

CONCLUSIONS AND INFERENCES

These findings identify IL-17A as a potential mediator of neuroanatomical remodeling of the gut innervation during IBD.

Demonstration of elevated levels of active cathepsin S in dextran sulfate sodium colitis using a new activatable probe

BACKGROUND

Proteases play a major role in inflammatory diseases of the gastrointestinal tract. Activatable probes are a major technological advance, enabling sensitive detection of active proteases in tissue samples. Our aim was to synthesize an activatable probe for cathepsin S and validate its use in a mouse model of colitis.

METHODS

We designed and synthesized a new fluorescent activatable probe, NB200, for the detection of active cathepsin S. Colitis was induced in C57BL/6 mice by the administration of 3% dextran sulfate sodium (DSS). Homogenized mouse colons, with or without the addition of the specific cathepsin S inhibitor MV026031, were incubated with NB200 in a fluorescent plate reader.

KEY RESULTS

NB200 selectively detected purified cathepsin S and not other common inflammatory proteases. Homogenates of colon from mice with DSS colitis induced a significant fluorescent increase when compared to control animals (control vs DSS: p < 0.05 at 200 min and p < 0.01 at 220-240 min), indicating cathepsin S activation. The cathepsin S inhibitor abolished this increase in fluorescence (DSS vs DSS + MV026031: p < 0.05 at 140 min, p < 0.01 at 180 min, p < 0.001 at 200-240 min), which confirms cathepsin S activation. Cathepsin S activity correlated with the disease activity index (Spearman r = 0.77, p = 0.017).

CONCLUSIONS & INFERENCES

Our investigation has demonstrated the utility of activatable probes for detecting protease activity in intestinal inflammation. Panels of such probes may allow 'signature' protease profiles to be established for a range of inflammatory diseases and disorders.