Original ResearchBasic and Translational—Alimentary TractTRPA1 and Substance P Mediate Colitis in Mice
Section snippets
Animals
Mice were killed in a 100% CO2 atmosphere (approved by the Animal Protection Authority, District Government Mittelfranken, Ansbach, Germany). Initial breeding pairs of TRPV1+/– and TRPA1+/– mice were donated by Dr Davis (Glaxo Smith Kline, Harlow, UK)36 and Drs Kwan and Corey (Harvard, Boston, MA),37 respectively, and CGRP+/− and SP+/− mice were donated by Dr Zimmer (University Bonn, Bonn, Germany). For details of mouse breeding and genotyping see the Supplementary Material and Methods.
Release of CGRP and SP
The
TNBS Activates TRPA1 in Sensory Neurons
Whether TNBS directly activates colonic sensory nerves and functions through the irritant receptor TRPA1 to release neuropeptides was investigated using an established ex vivo mouse colon preparation.38 TNBS induced CGRP and SP release in a concentration-dependent manner, similar to the established TRPA1 agonist AITC-induced CGRP release (Figure 1A and B). TNBS-induced (1 mmol/L) CGRP release was abolished in a calcium-free extracellular solution (Figure 1C), indicating a physiological
Discussion
We identified a TRPA1- and SP-dependent sensory neuronal mechanism of TNBS and DSS inducing colitis in mice. TRPA1 receptor and SP expression in extrinsic primary afferent neurons was required for the development of TNBS colitis, and a pharmacologic block of TRPA1 improved chronic colitis. In addition, primary chronic DSS colitis was ameliorated in TRPA1−/− and in WT littermates treated with the selective TRPA1 antagonist HC-030031, it was abrogated in SP−/− but aggravated in CGRP−/− mice.
Conclusions
Along with our results, evidence is growing for the etiologic relevance of neuroimmune interactions in colitis. The present study expands the established concept of hapten-induced TNBS and cytotoxic DSS colitis by sensory neuronal factors that finally lead to a loss in immune tolerance. Sensitization of the TRPA1 receptor by endogenous mediators of inflammation and metabolites of oxidative stress, which lead to increased SP release, may play a decisive role in the pathogenesis of human
Acknowledgments
The authors thank A. Kuhn and S. Haux-Oertel for technical assistance, J. Schramm and R. Fischer for excellent maintenance of animal breeding, and D. Metzner for graphic assistance (Institute of Physiology and Pathophysiology). The authors also thank K. Loeschner, H. Symowski, and A. Hecht for preparing the histologic slides (Institute of Anatomy I).
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Conflicts of interest The authors disclose no conflicts.
Funding Peter Reeh and Matthias Engel were supported by the Federal Ministry of Education and Res. (BMBF0315449C); Matthias Engel received additional support from the Marohn-Stiftung of the Friedrich-Alexander-Universität Erlangen-Nürnberg; Alexandru Babes was supported by grant PN2 Idei 164/2007 from the Romanian Government and by a visiting scientist grant from the Humboldt Foundation; and the chemical analytic work by Miloš Filipović and Ivana Ivanović–Burmazović was supported by the Deutsche Forschungsgemeinschaft.