Abstract
Background & AimG‐protein coupled receptor 35 (GPR35), a receptor for kynurenic acid and lysophosphatidic acid, is expressed in immune, central nervous, and gastrointestinal systems. Recently, GPR35 has been implicated in the onset of inflammatory bowel disease (IBD); polymorphism of this receptor was associated with Crohn's disease and ulcerative colitis. Mucosal repair is a critical event for suppression of inflammation and improvement of epithelial barrier functions, and has several processes including epithelial migration and proliferation. However, the role of GPR35 in physiological and pathological processes for mucosal repair in the colon remains undefined. In this study, we investigated the contribution of GPR35‐mediated signaling to mucosal repair of colonic epithelium in IBD, using colonic epithelial cells and mice.MethodsThe monolayer of young adult mouse colonic epithelium cells (YAMC) was damaged (1 mm in diameter) and the closure of the damage was determined at 6 and 24 h later. Cell proliferation, mRNA expression of fibronectin, integrin α5 and EGF receptors (EGFR), and activation of ERK were determined using MTT assay, quantitative RT‐PCR, and western blot, respectively. Experimental colitis was induced in male C57BL/6 mice by daily administration of 2 % Dextran sulfate sodium (DSS) in drinking water. The body weight loss and diarrhea were evaluated daily while the severity of colitis was examined on 7 days after the onset of DSS treatment. The expression and distribution of fibronectin and integrin α5 in the colonic epithelium in mice was determined using western blot and immunohistochemical stain, respectively.ResultsThe apparent protein expression of GPR35 was detected in YAMC cells. GPR35 agonists such as YE120, zaprinast, and pamoic acid promoted wound repair in concentration‐dependent manner without any influence on cell proliferation. YE120‐induced wound repair was significantly abolished by a specific GPR35 antagonist (CID2745687), forskolin and pertussis toxin. YE120 significantly increased the mRNA expression of fibronectin and integrin α5, and ERK phosphorylation, but these responses were attenuated by CID2745687 and forskolin. Furthermore, the severity of DSS‐induced colitis was significantly reduced by daily subcutaneous administration of pamoic acid. Daily injection of pamoic acid induced the expression of fibronectin and integrin α5 in the colonic epithelium of DSS‐treated mice.ConclusionGPR35 signaling promotes mucosal repair via upregulation of fibronectin and integrin α5 expression, coupling to Gi protein, and activating ERK1/2 in colonic epithelial cells. Thus, GPR35 may be a novel therapeutic target for activation of mucosal repair in IBD.Support or Funding InformationAll this work was supported by Japan Society for the Promotion of Science (JSPS) under the Grant‐in‐Aid for Scientific‐Research Program (KAKENHI; grant number 15H06727). The authors would like to thank Dr. Robert Whitehead for providing YAMC cells.
Published Version
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