Biology subjects

Barker, K. H.

Publications and source records attributed to Barker, K. H..

4 recordsLinked to original sources

bioRxiv2023

GPR35 inhibits TRPA1-mediated colonic afferent hypersensitivity through suppression of Substance P release

The development of non-opioid analgesics for the treatment of chronic abdominal pain is a pressing area of unmet clinical need. To address this, we examined the expression of Gi/o-coupled receptors in colonic sensory neurons, which, like opioid receptors, have the potential to inhibit nociceptor activation due to their inhibitory G protein coupling. This led to the identification of the orphan receptor GPR35 as a visceral analgesic drug target due to its marked co-expression with TRPA1, a mediator of noxious mechanotransduction in the bowel. Consistent with in silico docking studies which identified binding sites for the mast cell stabiliser cromolyn and phosphodiesterase inhibitor zaprinast at GPR35, we demonstrated, using GPR35 knockout mice, that the antinociceptive effects of these drugs on TRPA1-mediated colonic nociceptor activation and mechanosensitisation were GPR35-dependent. Further work showed these antinociceptive effects occurred through the inhibition of substance P (SP) release. This confirmed both the pronociceptive effect of SP on colonic afferents, and the contribution of SP to TRPA1-mediated colonic nociceptor activation and sensitisation. We also found that TRPA1-induced contraction of the colon was mediated by SP signalling and could be inhibited by cromolyn in a GPR35-dependent manner. Our data identify GPR35, through its inhibition of SP-mediated colonic contractility and nociceptor activation and sensitisation, as a putative mechanism for the reported clinical efficacy of cromolyn in the treatment of irritable bowel syndrome. These findings highlight the potential utility of GPR35 agonists to deliver non-opioid analgesia for the treatment of abdominal pain associated with gastrointestinal diseases such as irritable bowel syndrome and inflammatory bowel disease.

physiology↗

bioRxiv2023

Transcriptomic profiling reveals a pro-nociceptive role for Angiotensin II in inflammatory bowel disease

ObjectiveVisceral pain is a leading cause of morbidity in inflammatory bowel disease (IBD), contributing significantly to reduced quality of life. Currently available analgesics often lack efficacy or have intolerable side-effects, driving the need for a more complete understanding of the mechanisms causing pain. MethodsWhole transcriptome gene expression analysis was performed by bulk RNA sequencing of colonic biopsies from patients with ulcerative colitis (UC) and Crohns disease (CD) reporting abdominal pain and compared with non-inflamed control biopsies. Putative pro-nociceptive mediators were identified based on pathway analysis of differentially expressed genes in IBD tissue and single cell gene expression in colonic neurons. Pro-nociceptive activity of identified mediators was assessed in assays of sensory neuron and colonic afferent activity. ResultsRNA sequencing analysis highlighted a 7.6-fold increase in the expression of angiotensinogen transcripts, Agt, the precursor to angiotensin II (Ang II), in samples from UC patients (p = 3.2x10-8). Consistent with the marked expression of the angiotensin AT1 receptor in colonic neurons, Ang II elicited an increase in intracellular Ca2+ in capsaicin-sensitive, voltage gated sodium channel subtype NaV1.8-positive sensory neurons. Ang II also evoked action potential discharge in high-threshold colonic nociceptors. These effects were inhibited by the AT1 receptor antagonist valsartan. ConclusionFindings from our study identify AT1 receptor-mediated colonic nociceptor activation as a novel pathway of visceral nociception in IBD patients with UC. This work highlights the potential utility of angiotensin receptor blockers, such as valsartan, as treatments for pain in IBD.

neuroscience↗

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↗