IL-17 sensitises sensory neurons and colonic afferents to noxious stimuli in a PI3K dependent manner
Managing visceral pain associated with gastrointestinal (GI) disease remains a significant challenge due to the gut-related side effects and contraindicated use of many commonly used painkillers in people with inflammatory bowel disease (IBD). Consequently, it is crucial to deepen our understanding of the mediators and mechanisms underlying inflammatory pain in people with IBD. To do this, we compared bulk RNA sequencing data from colonic biopsy samples from people with IBD with single-cell RNA sequencing data from colon projecting dorsal root ganglion (DRG) neurons in mice to generate an interactome of putative pro-nociceptive cytokine signalling pathways. This in silico analysis revealed a 10-fold increase in IL17A expression in samples from people with ulcerative colitis (UC) alongside marked co-expression of Il17ra with Trpv1 in colon-projecting DRG neurons in mice, highlighting a likely role for interleukin-17 (IL-17) in colonic nociceptor signalling in people with UC. In support of this, Ca2+ imaging studies demonstrated that IL-17 stimulates DRG sensory neurons co-sensitive to capsaicin with a similar proportion responding in neuron-enriched cultures generated by magnetic-activated cell sorting, thus confirming that IL-17 directly activates DRG neurons. IL-17-evoked Ca2+ signals were attenuated by TRPV1 inhibition, consistent with nociceptor activation, and blocked by inhibition of phosphoinositide 3-kinase (PI3K) activity, consistent with the known role for PI3K as a downstream effector of IL-17 receptor signalling. In keeping with these observations, IL-17 enhanced murine colonic afferent responses to colorectal distension at noxious distension pressures, an effect also blocked by PI3K inhibition. Overall, these findings demonstrate a pro-nociceptive effect of IL-17 in the GI tract, thus highlighting the potential utility of IL-17-targeting therapies to reduce pain in people with UC.