visceral hypersensitivity and serotonin : an important mechanism for Potentiation of TRPV 4 signalling by histamine

Background Although evidence points to a role for histamine and serotonin in visceral hypersensitivity, activation of calcium channels such as transient receptor potential vanilloid 4 (TRPV4) also causes visceral hypersensitivity. We hypothesised that TRPV4 is important for the generation of hypersensitivity, mediating histamineand serotonin-induced visceral hypersensitivity. Methods In response to histamine, serotonin and/or TRPV4 agonist (4aPDD), calcium signals and TRPV4 localisation studies were performed on dorsal root ganglia (DRG) neurons projecting from the colon. To evaluate visceral nociception, colorectal distension (CRD) was performed in mice treated with serotonin or histamine and with 4aPDD. Intrathecal injection of TRPV4 silencer RNA (SiRNA) or mismatch SiRNA was used to target TRPV4 expression. Results Pre-exposure of DRG neurons projecting from the colon, to histamine or serotonin, increased Ca responses induced by 4aPDD by a protein kinase C (PKC), phospholipase Cb (PLCb), mitogen-activated protein kinase kinase (MAPKK) and phospholipase A2 (PLA2)-dependent mechanisms. Serotonin or histamine treatments enhanced TRPV4 expression at the plasma membrane by a MAPKK mechanism. Hypersensitivity induced by serotonin or histamine were both significantly inhibited by TRPV4 SiRNA intrathecal injection. Administration of sub-nociceptive doses of serotonin or histamine potentiated 4aPDD-induced hypersensitivity in response to CRD. Conclusions Serotonin and histamine sensitise TRPV4 response to 4aPDD both in vivo (increased visceral hypersensitivity) and in vitro, in sensory neurons, by a PKC, PLA2, PLCb and MAPKK-dependent mechanism. Serotonin and histamine caused a MAPKK-dependent increase in TRPV4 expression in colonic sensory neurons plasma membranes. Further, histamineor serotoninmediated visceral hypersensitivity depend on TRPV4 expression in sensory neurons. TRPV4 appears as a common mechanism to several known mediators of visceral hypersensitivity. INTRODUCTION Transient receptor potential vanilloid 4 (TRPV4) is a widely expressed cation channel of the transient receptor potential (TRP) superfamily. TRP channels are intrinsic membrane receptor channels with six transmembrane spans and a cation-permeable pore region. TRPV4 can be activated by physical stimuli such as cell swelling or innocuous warmth, and by chemical ligands. Among other cell types, TRPV4 has been shown to be expressed on sensory neurons, where it caused Ca mobilisation, but also the release of nociceptive peptides such as substance P and calcitonin gene-related peptide (CGRP). Overall, different studies have defined a role for TRPV4 in the transduction of pain in somatic models, and, more recently, we have demonstrated that TRPV4 activation was a major component of visceral nociception. Further, we have shown that TRPV4 activation was a downstream signal of the visceral hypersensitivity symptoms induced by the activation of the protease-activated receptor-2 (PAR2), a G protein-coupled receptor that has been implicated in the peripheral generation of pain signals.Considering the recently demonstrated importance of protease signalling and PAR2 activation in pain symptoms related to inflammatory Significance of this study What is already known about this subject? < Histamine and serotonin play a role in visceral hypersensitivity < Transient receptor potential vanilloid 4 (TRPV4) caused visceral hypersensitivity < Hypotheses: TRPV4 is mediating histamineand serotonin-induced visceral hypersentivity What are the new findings? < Histamine or serotonin increased Ca responses induced by 4aPDD by a protein kinase C (PKC), phospholipase Cb (PLCb), mitogen-activated protein kinase kinase (MAPKK) and phospholipase A2 (PLA2)-dependent mechanism < Serotonin or histamine treatments enhanced TRPV4 expression at the plasma membrane by a MAPKK mechanism < Histamineor serotonin-mediated visceral hypersensitivity depend on TRPV4 expression in sensory neurons How might it impact on clinical practice in the foreseeable future? TRPV4 appears as a common mechanism to several known mediators of visceral hypersensitivity. Thus, TRPV4 directly or its regulation could be a new potential therapeutic target in patients with inflammatory bowel syndrome (IBS) for the treatment of abdominal pain. INSERM U563, Centre de Physiopathologie de Toulouse Purpan, Toulouse, France Université Toulouse III Paul Sabatier, Toulouse, France Department of Physiology and Pharmacology, University of Calgary, Calgary, Alberta, Canada Correspondence to Dr Nathalie Vergnolle, INSERM U 563, CHU Purpan, BP 3028, 31024 Toulouse Cedex, France; nathalie.vergnolle@inserm.fr NC and CA contributed equally to this work. Revised 9 October 2009 Accepted 17 November 2009 Gut 2010;59:481e488. doi:10.1136/gut.2009. 192567 481 Neurogastroenterology group.bmj. com on March 27, 2010 Published by gut.bmj. com Downloaded from