Transient receptor potential vanilloid 4 (TRPV4) regulates vascular endothelial permeability during colonic inflammation in dextran sulfate sodium‐induced murine colitis

Background & Aim Transient receptor potential vanilloid 4 (TRPV4) is a non‐selective cation channel and responds to physical stimuli and various endogenous ligands such as arachidonic acid metabolites. The activation of TRPV4 in epithelial cells is known to release inflammatory cytokines and promote colitis. In contrast, several studies demonstrated that TRPV4 is also expressed in vascular endothelial cells in various organs. However, the localization and role of TRPV4 channel expression in colonic vascular endothelial cells are not clearly defined. The present study attempted to clarify the function and expression of TRPV4 in colonic vascular endothelial cells during dextran sulfate sodium (DSS)‐induced colitis. Methods Eight‐week‐old WT and TRPV4 KO mice were used. Colitis was induced by 2% DSS solution given in drinking water for 7 days. The disease activity index (DAI) was evaluated during DSS treatment while colon length, histological damage, and myeloperoxidase (MPO) activity were examined on day 7. Immunohistochemical analyses were also performed on frozen sections of colon using various specific antibodies. Vascular leakage was investigated using Evans blue dye extrusion assay. Expression of TRPV4 and vascular endothelial cadherin was also examined by western blotting in cultured mouse aortic endothelial cells and mouse distal colon. Results DSS treatment caused severe colitis accompanied by increase in DAI, MPO activity, histological score, and shortening of colon length. These responses were significantly attenuated in TRPV4 KO mice compared with WT mice. Repeated intrarectal (20 μg/kg once daily) administration of GSK1016790A, a TRPV4 agonist, exacerbated the severity of DSS‐induced colitis. DSS treatment upregulated the expression of TRPV4 co‐localized with endothelial marker of CD31 but not with lymph node marker lymphatic vessel endothelial hyaluronan receptor‐1 in vascular endothelial cells of the mucosal and submucosal layers of distal colon. Increased TRPV4 expression in vascular endothelial cells was detected in distal colon but not in proximal colon. Increased vascular permeability was observed following a single intravenous administration of GSK1016790A (3 μg/kg) in colitis and this effect was abolished by intravenous injection of TRPV4 antagonist RN1734 (600 μg/kg). TRPV4 KO mice had significantly reduced DSS‐induced vascular permeability in the colon. Furthermore, TRPV4 was co‐localized with vascular endothelial (VE)‐cadherin, the major endothelial adhesion molecule that regulates endothelial adherence junctions. The VE‐cadherin area was significantly decreased following repeated intravenous administration of GSK1016790A in DSS‐induced colitis compared with DSS‐vehicle treated group. Furthermore, activation of TRPV4 decreased the VE‐cadherin in mouse aortic endothelial cell. Conclusion These findings indicate that the alteration of TRPV4 in vascular endothelial cells contributes to progression of colonic inflammation via increased vascular permeability. Support or Funding Information We thank Dr. Atsuko Mizuno (Jichi Medical School) and Dr. Makoto Suzuki for providing us with TRPV4‐deficient mice. We also thank RIKEN BioResource Center for providing the MAEC. This work was supported in part by Grants‐in‐Aid for Scientific Research from the Ministry of Education, Science, Sports, and Culture of Japan (#25860395 and 16K08287) and Takeda Science Foundation.