Background: The activation of pain sensing nerves (nociceptors), which innervate the gut, by mediators released from the inflamed bowel is thought to be a principal cause of pain in Crohn's disease. Our current understanding of this process is limited, and further investigation is needed to provide insight into the mechanisms of nociception in Crohn's disease, which can then be targeted to relieve abdominal pain. To address this, we have developed an experimental approach to study visceral nociception in colitis by comparing transcript expression in patient biopsy samples, with the ability of supernatants generated from the biopsy to stimulate nociceptors. Using this system, we have identified matrix metalloproteinase-12 (MMP-12) as a putative mediator of nociception in Crohn's disease (Tranter et al (2016). World Congress on Pain, IASP). Here, we confirm a role for MMP-12 in nociception by describing its direct effects on nociceptor signalling.
Methods: Nociceptor activity (serosal and mesenteric) was recorded from teased splanchnic nerve fibres using an in vitro mouse colon flat-sheet preparation as described previously (Hockley et al (2014) Pain; 155 (10), 1962–1975). Changes in firing were determined following direct application of MMP-12 (or vehicle) alone; application of MMP-12 in combination with an experimental soup of inflammatory mediators (bradykinin, histamine, 5-HT, PGE2, ATP); or in response to mechanical stimulation following MMP-12 administration. Responses were expressed as mean ± sem values, and statistically compared using a Student's t-test, significance set at p<0.05.
Results: Application of MMP-12 (20nM); stimulated visceral nociceptor activity in 3/9 preparations tested, producing a significant increase in nerve discharge compared to vehicle (e.g. 11.4±1.8 spikes/ min vs 1.8±1.2 spikes/ min, MMP-12 vs vehicle n=3, p<0.01), and enhanced nociceptor firing in response to inflammatory mediators (e.g. 52% increase in activity vs vehicle n=5, p<0.05). Additionally pre-treatment with MMP-12 promoted mechanical hypersensitivity to von Frey hair probing of receptive field by 24% n=8, p<0.01.
Conclusions: The data demonstrates a novel role for MMP-12 in nociceptor activation and sensitisation, which in combination with our previous study suggests that MMP-12 may be an important mediator of abdominal pain in Crohn's disease.