Mo1692 Vascular Endothelial Transient Receptor Potential Vanilloid 4 Links Colonic Inflammation in Dextran Sulfate Sodium-Induced Colitis Model Mice

Abstract

BACKGROUND&AIMS: Transient receptor potential vanilloid 4 (TRPV4) is a nonselective cation channel, and involved in physical sensing in various types of tissues. TRPV4 is expressed in sensory neuron and vascular endothelial cells in various organs. In gastrointestinal tracts, TRPV4 activation in epithelial cells increases in intracellular calcium concentrations and induces colitis. However, the localization and the role of the TRPV4 channel expressed in vascular endothelial cells in colitis are still poorly defined. In the present study, we investigated the alteration of TRPV4 expression in the colonic vascular endothelial cells during dextran sulfate sodium (DSS)-induced colitis. METHODS: Eight week-old wild type (WT) and TRPV4 knock-out (TRPV4 KO) mice were used. Colitis was induced by 2% DSS solution given as drinking water for 7 days. The disease activity index (DAI) was evaluated during the treatment, while colon length, histological damage, and myeloperoxidase (MPO) activity were examined post-DSS treatment. Immunohistochemical analysis was performed in distal colon. TRPV4-immunoreactivity was detected by using immunohistochemical staining with fluorescein-conjugated tyramide amplification. CD31, CD105, CD11b, CD68, Ly6B.2, and VEGF receptor-2 were detected by indirect staining with their specific antibodies. Vascular leakage was investigated using Evans blue dye extrusion assay. RESULTS: TRPV4 KO mice protected against DSS-induced weight loss, neutrophil (MPO), colon shortening, diarrhea, occult-fecal blood, and histological damage. TRPV4 immunoreactivities were detected mostly in epithelial cells of normal distal colon. DSS treatment drastically increased TRPV4 expression in vascular endothelial cells of mucosa and submucosal layer which colocalized with CD31, CD105, and VEGF receptor-2, but not epithelial cells. Repeated intrarectal and intravenous administration of TRPV4 agonist GSK1016790A exacerbated the severity of DSS colitis. Increased vascular permeability was observed following single intravenous administration of GSK1016790A in DSS colitis and this effect was abolished with TRPV4 antagonist RN1734. CD11b, CD68, Ly6B.2 immunopositive cells were detected around TRPV4 positive vascular endothelial cells in mucosa and submucosal layer in DSS colitis. CONCLUSION: These findings indicate that the alteration of TRPV4 in vascular endothelial cells may contribute to progression of colonic inflammation via increasing vascular permeability.