Role of Neuronal and Non-Neuronal Transient Receptor Potential Vanilloid Type 1 and Sensory Neuropeptides in DSS-Induced Peripheral Inflammatory Changes

BACKGROUND & AIMS: The activation of transient receptor potential vanilloid type 1 (TRPV1) leads to release of sensory neuropeptides such as substance P (SP), neurokinin A (NKA) and calcitonin gene-related peptide (CGRP) from the nerve endings, and these neuropeptides in turn initiate the biochemical cascade known as neurogenic inflammation. TRPV1 channels and the sensory neuropeptides are expressed not only in sensory nerve fibers but also in non-neuronal cells in the mucosa of large intestine. The aim of this study was to investigate alteration of the sensory neuropeptides and TRPV1 channels in mucosa of DSS-induced colitis mice and to characterize their non-neuronal cells. METHODS: Colitis was induced by 3% dextran sulfate sodium (DSS) solution given as drinking water for 7 days in C57BL/6 mice. To evaluate visceral nociception, colorectal distension was performed in mice treated with vehicle or BCTC on day 7 of DSS treatment. Immunohistochemical analysis was performed using rectal tissues of mice. SP, NKA, CGRP, 5-HT, F4/80, keratin, TNF-α, CD11c, and CD4 were detected by indirect staining with their specific antibodies. TRPV1-immunoreactivity was detected by using immunohistochemical staining with fluorescein-conjugated tyramide amplification. RESULTS: TRPV1 antagonist BCTC significantly attenuated the visceral hyperalgesia to control level in DSS-induced colitis model. We compared the number of the nerve fibers and non-neuronal cells expressing TRPV1 channels and sensory neuropeptides in normal and DSS-induced colitis model mice. The number of TRPV1and CGRP-expressing nerve fibers is significantly increased in colitis model. The non-neuronal TRPV1 cells were markedly increased but non-neuronal CGRP-expressing cells were not observed in colitis model. No significant alteration in the number of SP and NKA positive nerve fibers was detected. On the other hand, SP and NKA positive cells were drastically increased in colitis model. Next, double labeling studies were carried out to characterize TRPV1-, SP-, and NKA-expressing cells under inflammatory state. We found two types of non-neuronal TRPV1-expressing cells in mucosa of colitis model. One is keratin positive cells located upper part of mucosa. Another is TNF-α and/or F4/80 positive cells located middle part of the mucosa. Both types of TRPV1-expressing cells did not colocalize with CD4 and CD11c. SP and NKA positive cells almost completely colocalized with 5-HT in experimental colitis model mice. CONCLUSION: These results suggest that TRPV1immunopositive epithelial cells and macrophage are associated with visceral hyperalgesia in colitis.