Welsh, F. | bioRxiv Science

bioRxiv2022

Sensitisation of colonic nociceptors by IL-13 is dependent on JAK and p38 MAPK activity

The effective management of visceral pain is a significant unmet clinical need for those affected by gastrointestinal diseases, such as inflammatory bowel disease (IBD). The rational design of novel analgesics requires a greater understanding of the mediators and mechanisms underpinning visceral pain. Interleukin-13 (IL-13) production by immune cells residing in the gut is elevated in IBD, and IL-13 appears to be important in the development of experimental colitis. Whats more, receptors for IL-13 are expressed by neurons innervating the colon, though it is not known whether IL-13 plays any role in visceral nociception per se. To resolve this, we employed Ca2+ imaging of cultured sensory neurons and ex vivo electrophysiological recording from the lumbar splanchnic nerve innervating the distal colon. Ca2+ imaging revealed the stimulation of small-diameter, capsaicin-sensitive sensory neurons by IL-13, indicating that IL-13 likely stimulates nociceptors. IL-13-evoked Ca2+ signals were attenuated by inhibition of Janus (JAK) and p38 kinases. In the lumbar splanchnic nerve, IL-13 did not elevate baseline firing, nor sensitise the response to capsaicin application, but did enhance the response to distention of the colon. In line with Ca2+ imaging experiments, IL-13-mediated sensitisation of the afferent response to colon distention was blocked by inhibition of either JAK or p38 kinase signalling. Together, these data highlight a potential role for IL-13 in visceral nociception and implicate JAK and p38 kinases in pro-nociceptive signalling downstream of IL-13. Key Points SummaryThe pro-inflammatory cytokine IL-13 is elevated in gastrointestinal (GI) diseases and known to sensitise sensory neurons. This study confirms a role for IL-13 in colonic afferent sensitisation and defines a role for downstream JAK and p38 MAPK signalling in colonic mechanosensitisation. IL-13-mediated increase in [Ca2+]i in capsaicin-sensitive sensory neurons is dependent on p38 MAPK and JAK signalling. IL-13-induced sensitisation of colonic afferents to noxious mechanical distension is abolished by inhibition of p38 MAPK and JAK. We have built on the current understanding of IL-13 and its neuronal interactions, highlighting the therapeutic potential of targeting p38 MAPK and JAK signalling pathways to treat visceral pain in GI disease.

physiology↗

bioRxiv2022

Sensitisation of colonic nociceptors by TNFα is dependent on TNFR1 expression and p38 MAPK activity

Visceral pain is a leading cause of morbidity in gastrointestinal diseases, which is exacerbated by the gut related side-effects of many analgesics. New treatments are needed and further understanding of the mediators and mechanisms underpinning visceral nociception in disease states is required to facilitate this. The pro-inflammatory cytokine TNF is linked to pain in both patients with inflammatory bowel disease and irritable bowel syndrome, and has been shown to sensitise colonic sensory neurons. Somatic, TNF- triggered thermal and mechanical hypersensitivity is mediated by TRPV1 signalling and p38 MAPK activity respectively, downstream of TNFR1 receptor activation. We therefore hypothesised that TNFR1-evoked p38 MAPK activity may also be responsible for TNF sensitisation of colonic afferent responses to the TRPV1 agonist capsaicin, and noxious distension of the bowel. Using Ca2+ imaging of dorsal root ganglion sensory neurons, we observed TNF-mediated increases in intracellular [Ca2+] and sensitisation of capsaicin responses. The sensitising effects of TNF were dependent on TNFR1 expression and attenuated by p38 MAPK inhibition. Consistent with these findings, ex vivo colonic afferent fibre recordings demonstrated enhanced response to noxious ramp distention of the bowel and bath application of capsaicin following TNF pre-treatment. Responses were reversed by p38 MAPK inhibition and absent in tissue from TNFR1 knockout mice. Our findings demonstrate a contribution of TNFR1, p38 MAPK and TRPV1 to TNF-induced sensitisation of colonic afferents, highlighting the potential utility of these drug targets for the treatment of visceral pain in GI disease. Abstract figure legendTNF sensitised Ca2+ responses to the TRPV1 agonist capsaicin in dorsal root ganglion sensory neurons. Sensitisation was TNFR1-dependent and attenuated by inhibition of p38 MAPK. Direct Ca2+ responses to TNF were TRPV1-and TRPA1-dependent. In ex vivo colonic afferent recordings, TNF increased sensitivity to noxious ramp distension and capsaicin, both of which were absent in TNFR1-/- tissue or blocked by inhibition of p38 MAPK. These findings establish a role for TNFR1, p38 MAPK and TRPV1 in TNF-mediated sensitisation of colonic afferents. Key Points SummaryO_LITNF sensitises sensory neurons and colonic afferents to the TRPV1 agonist capsaicin. C_LIO_LITNF-mediated sensitisation of sensory neurons and colonic nociceptors is dependent on TNFR1 expression. C_LIO_LITNF sensitisation of sensory neurons and colonic afferents to capsaicin and noxious ramp distension is abolished by inhibition of p38 MAPK. C_LI

neuroscience↗