Protective role of 1,25(OH)2 vitamin D3 in the mucosal injury and epithelial barrier disruption in DSS-induced acute colitis in mice.

Intestinal hyper-permeability plays a critical role in the etiopathogenesis of inflammatory bowel disease (IBD) by affecting the penetration of pathogens, toxic compounds and macromolecules. 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], the active form of vitamin D, has been shown to be an important regulator of IBD and recent epidemiology suggests that patients with IBD have an impaired vitamin D status. The purpose of this study is to investigate the possible protective effects of 1,25(OH)2D3 on mucosal injury and epithelial barrier disruption on dextran sulfate sodium (DSS)-induced acute colitis model. We used DSS-induced acute colitis model to investigate the protective effects of 1,25(OH)2D3 on mucosal injury and epithelial barrier integrity. Severity of colitis was evaluated by disease activity index (DAI), body weight (BW) change, colon length, histology, myeloperoxidase (MPO) activity, and proinflammatory cytokine production including tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ). In vitro the protective role of 1,25(OH)2D3 was assessed by incubating Caco-2 cells with or without DSS and measuring transepithelial electrical resistance (TEER) and fluorescein isothiocyanate dextran (FITC-D). The intestinal permeability was analyzed by FITC-D, bacterial translocation and measurement of lipopolysaccharide (LPS). Ultrastructural features of the colon tissue and Caco-2 cell monolayer were observed by electron microscopy. Expressions of tight junction (TJ) proteins in the colon mucosa and Caco-2 cells were detected by immunohistochemistry, immunofluorescence, Western blot and real-time fluorescent quantitative PCR, respectively. DSS-induced acute colitis model was characterized by a reduced BW, AUC of BW, serum calcium, higher DAI, AUC of DAI, shortened colon length, elevated MPO activity, worsened histologic inflammation, increased mononuclear cell numbers in mesenteric lymph nodes (MLNs) and colonic lamina propria (LP), and enhanced proteins and mRNA levels of TNF-α and IFN-γ. 1,25(OH)2D3 markedly increased expressions of TJ proteins and mRNA and decreased the FITC-D permeability and the level of LPS. Furthermore, 1,25(OH)2D3 abrogated bacterial translocation to MLNs and ameliorated ultrastructural features of the colon epithelium by scanning electron microscopy (SEM). In vitro, 1,25(OH)2D3 increased TEER, TJ proteins and mRNA expressions, decreased the FITC-D permeability, and preserved structural integrity of the TJ in Caco-2 cells. 1,25(OH)2D3 may play a protective role in mucosal barrier homeostasis by maintaining the integrity of junction complexes and in healing capacity of the colon epithelium. 1,25(OH)2D3 may represent an attractive and novel therapeutic agent for the adjuvant therapy of IBD.

Zhao H ，Zhang H ，Wu H ，Li H ，Liu L ，Guo J ，Li C ，Shih DQ ，Zhang X ... -  《BMC GASTROENTEROLOGY》

Effect of toll-like receptor 3 agonist poly I:C on intestinal mucosa and epithelial barrier function in mouse models of acute colitis.

Zhao HW ，Yue YH ，Han H ，Chen XL ，Lu YG ，Zheng JM ，Hou HT ，Lang XM ，He LL ，Hu QL ，Dun ZQ ... -  《-》

Novel role of the vitamin D receptor in maintaining the integrity of the intestinal mucosal barrier.

Emerging evidence supports a pathological link between vitamin D deficiency and the risk of inflammatory bowel disease (IBD). To explore the mechanism we used the dextran sulfate sodium (DSS)-induced colitis model to investigate the role of the vitamin D receptor (VDR) in mucosal barrier homeostasis. While VDR(+/+) mice were mostly resistant to 2.5% DSS, VDR(-/-) mice developed severe diarrhea, rectal bleeding, and marked body weight loss, leading to death in 2 wk. Histological examination revealed extensive ulceration and impaired wound healing in the colonic epithelium of DSS-treated VDR(-/-) mice. Severe ulceration in VDR(-/-) mice was preceded by a greater loss of intestinal transepithelial electric resistance (TER) compared with VDR(+/+) mice. Confocal and electron microscopy (EM) revealed severe disruption in epithelial junctions in VDR(-/-) mice after 3-day DSS treatment. Therefore, VDR(-/-) mice were much more susceptible to DSS-induced mucosal injury than VDR(+/+) mice. In cell cultures, 1,25-dihydroxy-vitamin D(3) [1,25(OH)(2)D(3)] markedly enhanced tight junctions formed by Caco-2 monolayers by increasing junction protein expression and TER and preserved the structural integrity of tight junctions in the presence of DSS. VDR knockdown with small interfering (si)RNA reduced the junction proteins and TER in Caco-2 monolayers. 1,25(OH)(2)D(3) can also stimulate epithelial cell migration in vitro. These observations suggest that VDR plays a critical role in mucosal barrier homeostasis by preserving the integrity of junction complexes and the healing capacity of the colonic epithelium. Therefore, vitamin D deficiency may compromise the mucosal barrier, leading to increased susceptibility to mucosal damage and increased risk of IBD.

Kong J ，Zhang Z ，Musch MW ，Ning G ，Sun J ，Hart J ，Bissonnette M ，Li YC ... -  《AMERICAN JOURNAL OF PHYSIOLOGY-GASTROINTESTINAL AND LIVER PHYSIOLOGY》

Effects and Mechanism of Constitutive TL1A Expression on Intestinal Mucosal Barrier in DSS-Induced Colitis.

The role of TL1A in the intestinal mucosa barrier in inflammatory bowel disease (IBD) is still unclear. This study was aimed to investigate the expression levels of tight junction protein (TJ), myosin light chain kinase (MLCK), MyD88 and tumor necrosis factor (TNF) receptor-associated factor-6 (TRAF6) and how TL1A influences the intestinal barrier in IBD. The mouse models of IBD were built using FMS-TL1A-GFP-transgenic mice and wild-type mice. The morphological and histopathological changes, bacterial translocation, permeability of colonic mucosa, and LPS level were assessed. Caco-2 cells were used to further investigate the association between TL1A and TNF-α and LPS. The protein level and mRNA changes of TJ proteins including ZO-1, occluding, JAMA, claudin-1, claudin-2, and claudin-3 were investigated using Western blot and real-time PCR. Protein changes of MLCK, MyD88 and TNF receptor-associated factor-6 (TRAF6), and TNF-α mRNA in the mouse colon were further assessed. The IBD models were successfully built. Cooper HS score and histopathological score of the colon were higher in DSS/WT group than in control/WT group (P < 0.05), higher in DSS/Tg group than in control/Tg group (P < 0.05), and higher in DSS/Tg group than in DSS/WT group. PAS, colonic permeability of the colon, and FITC-D examination showed the similar results and trends. Compared with control/WT group, the levels of TL1A and claudin-2 were higher and the levels of ZO-1, occludin, JAMA, claudin-1, and claudin-3 were lower in DSS/WT group (P < 0.05). Compared with control/Tg group, the levels of TL1A and claudin-2 were higher and the levels of ZO-1, occludin, JAMA, claudin-1, and claudin-3 were lower in DSS/Tg group. Compared with Caco-2 + TNF-α group, the expression level of occludin and claudin-1 in Caco-2 + LV-TNFSF15 + TNF-α group was significantly lower (P < 0.05); p-MLC level was significantly higher. Compared with Caco-2 + LPS group, the expression level of occludin and claudin-1 significantly decreased in Caco-2 + LV-TNFSF15 + LPS group; MyD88 and TRAF6 expression level significantly increased. The results suggested that TL1A could impair intestinal epithelial barrier in the mouse model of IBD and might regulate TJ expression via MLCK/p-MLC pathway and LPS-mediated MyD88/TRAF6 pathway.

Yang M ，Jia W ，Wang D ，Han F ，Niu W ，Zhang H ，Shih DQ ，Zhang X ... -  《-》

Fermented barley and soybean (BS) mixture enhances intestinal barrier function in dextran sulfate sodium (DSS)-induced colitis mouse model.

Woo JK ，Choi S ，Kang JH ，Kim DE ，Hurh BS ，Jeon JE ，Kim SY ，Oh SH ... -  《BMC Complementary and Alternative Medicine》