Activation Of Aryl Hydrocarbon Receptor Up-regulates Epithelial Cells Derived IL-10 Expression And Meliorates Dextran Sulfate Sodium-induced Murine Colitis

Background:Inflammatory bowel disease(IBD),consisting of ulcerative colitis and Crohn’s disease,is a major chronic disorder that affects the GI tract of humans.Although the precise pathogenesis of colitis is inadequately understood,present evidence indicates that is caused by dysregulated mucosal immune response and epithelial barrier dysfunction.The aryl hydrocarbon receptor(AhR)is a cytoplasmic transcription factor activated by a large variety of environmental agents.Activation of the AhR is involved in the control of intestinal mucosal homeostasis.Evidences have suggested that AhR is suppressed in the intestines of IBD patients,and activation of AhR by ligands such as FICZ or TCDD inhibits the inflammatory response in murine colitis models.Although a number of studies have suggested a protective role for AhR in colitis,the precise underlying mechanism remains unclear.Interleukin-10(IL-10)is an important anti-inflammatory cytokine that ameliorates mucosal inflammation.The goal of this study was to investigate the role of AhR activation in alleviating intestinal inflammation by upregulating IL-10 in intestinal epithelial cells(IECs).Methods:1.Colitis was induced in mice by the administration of 4% dextran sulphate sodium(DSS)for 7 days.The mice were given injections of the AhR agonist 6-formylindolo(3,2-b)carbazole(FICZ)starting 2 days after the first administration of DSS.Mice were weighted,colon tissues were collected and measured,and histology analyses were performed.2.IECs were isolated from colon,and the expression of IL-10 in IECs was assessed by Western blot analysis.The mRNA levels of inflammatory cytokines were assessed by quantitative real-time polymerase chain reaction(QRT-PCR)3.Caco-2 cells were treated with FICZ in the presence or absence of lipopolysaccharide(LPS).The expression of P-STAT3 and IL-10 proteins were assessed by Western blotting.The mRNA levels of inflammatory cytokines were assessed by quantitative real-time polymerase chain reaction(QRT-PCR)Results:1.Administration of FICZ significantly alleviated the weight loss induced by DSS.After treated with DSS,the colon of mice was nearly half shorter with edema and congestion,but FICZ alleviated that.Histological analysis indicated that DSS-treated mice exhibited severe damage with loss of epithelial surface and entire crypts,while DSS+FICZ group had moderate injure.2.FICZ up-regulated the epithelial IL-10 expression compared to DSS treatment.DSS treatment up-regulated the mRNA levels of these pro-inflammatory cytokines,while FICZ attenuated these changes.3.Caco-2 cells were treated with FICZ in the presence or absence of LPS for 24 hours.LPS greatly up-regulated the mRNA levels of IL-1β and IL-6,whereas FICZ alleviated it.Meanwhile the expression of IL-10 were also increased in both mRNA and protein levels when treated with FICZ in the presence or absence of LPS.4.Caco-2 cells were treated with FICZ for 24 hours.We found that though STAT3 expression was almost not affected,P-STAT3 expression was obviously up-regulated when treated with FICZ.Conclusion:1.FICZ induced AhR activation could ameliorate DSS-induced murine experimental colitis.2.FICZ induced AhR activation could decrease the levels of inflammatory cytokines both in vitro and vivo.3.Activation of AhR could increase the expression of epithelial-derived P-STAT3 and IL-10.