Altered intestinal barrier function is postulated to be a central predisposing factor to intestinal diseases, including inflammatory bowel diseases and food allergies. However, the mechanisms involved in maintaining homeostatic intestinal barrier integrity remain undefined. In this study, we demonstrate that mice deficient in mast cells ( Kit ^W-sh/W-sh [Wsh]) or mast cell chymase (Mcpt4 ^−/− ) have significantly decreased basal small intestinal permeability compared with wild-type (WT) mice. Altered intestinal barrier function was linked to decreased intestinal epithelial cell migration along the villus/crypt axis, altered intestinal morphology, and dysregulated claudin-3 crypt expression. Remarkably, engraftment of Wsh mice with WT but not Mcpt4 ^−/− mast cells restored intestinal epithelial cell migration, morphology, and intestinal epithelial barrier function. Collectively, these findings identify a mechanism by which mast cells regulate homeostatic intestinal epithelial migration and barrier function.

We tested the hypothesis that increased production of nitric oxide (NO.) associated with lipopolysaccharide (LPS)-induced systemic inflammation leads to functionally significant alterations in the expression and/or targeting of key tight junction (TJ) proteins in ileal and colonic epithelium. Wild-type or inducible NO. synthase (iNOS) knockout male C57B1/6J mice were injected intraperitoneally with 2 mg/kg Escherichia coli O111:B4 LPS. iNOS was inhibited using intraperitoneal L-N(6)-(1-iminoethyl)lysine (L-NIL; 5 mg/kg). Immunoblotting of total protein and NP-40 insoluble proteins revealed decreased expression and decreased TJ localization, respectively, of the TJ proteins, zonula occludens (ZO)-1, ZO-2, ZO-3, and/or occludin in ileal mucosa and colonic mucosa (total protein only) after injection of C57B1/6J mice with LPS. Immunohistochemistry showed deranged distribution of ZO-1 and occludin in both tissues from endotoxemic mice. Endotoxemia was associated with evidence of gut epithelial barrier dysfunction evidenced by increased ileal mucosal permeability to fluorescein isothiocyanate-dextran (Mr=4 kDa) and increased bacterial translocation to mesenteric lymph nodes. Pharmacologic inhibition of iNOS activity using L-NIL or genetic ablation of the iNOS gene ameliorated LPS-induced changes in TJ protein expression and gut mucosal barrier function. These results support the view that at least one mechanism contributing to the pathogenesis of gastrointestinal epithelial dysfunction secondary to systemic inflammation is increased iNOS-dependent NO. production leading to altered expression and localization of key TJ proteins.

Intestinal epithelial barrier function is impaired after the exposure of enterocytes to proinflammatory cytokines. The mechanism(s) responsible for this phenomenon remain incompletely understood. We used cultured monolayers of Caco-2 enterocyte-like cells to characterize the effect of cytomix, a mixture of interferon-γ, tumor necrosis factor-α, and interleukin-1β, on the expression and localization of several tight junctions proteins. Cells were stimulated with cytomix in the presence or absence of 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), an NO· scavenger. Some cells were treated with (Z)-1-[2-(2-aminoethyl)-N-(2-ammonioethyl) amino]diazen-1-ium-1,2-diolate] (DETA-NONOate), an NO· donor. Tight junction protein expression was measured in cellular extracts by Western blotting and localized in cells using immunofluorescence. Steady-state mRNA levels were determined using semi-quantitative reverse-transcription polymerase chain reaction. Incubation of cells with DETA-NONOate or cytomix decreased epithelial barrier function, decreased expression of ZO-1 mRNA, decreased expression of ZO-1, ZO-3, and occludin protein, and increased expression of claudin-1 protein. The effects of cytomix on barrier function and tight junction protein expression were modulated by cPTIO. Cytomix caused incorrect subcellular localization of ZO-1, occludin, and claudin-1, and this was modulated by co-incubation with cPTIO. DETA-NONOate caused similar protein mislocalization as observed with cytomix. The effectiveness of cPTIO in maintaining tight junction protein expression and correct subcellular localization was less apparent at early time points (12 h) compared with later points, suggesting an NO·-independent effect of cytokines on barrier function. Thus, cytomix appears to increase the permeability of Caco-2 monolayers through NO·-dependent and -independent mechanisms that are associated with changes in the expression and/or targeting of proteins involved in tight junction function.

We sought to determine the role of IL-6 as a mediator of the alterations in gut barrier function that occur after hemorrhagic shock and resuscitation (HS/R). C57Bl/6 wild-type (WT) and IL-6 knockout (KO) mice on a C57Bl/6 background were subjected to either a sham procedure or HS/R. Organ and tissue samples were obtained 4 h after resuscitation. In WT mice, HS/R significantly increased ileal mucosal permeability to fluorescein isothiocyanate-labeled dextran (average molecular mass, 4 kDa) and bacterial translocation to mesenteric lymph nodes. These alterations in gut barrier function were not observed in IL-6 KO animals. HS/R increased ileal steady-state mRNA levels for IL-6, TNF, and IL-10 in WT but not in IL-6 KO mice. Ileal mucosal expression of the tight junction protein, ZO-1, decreased after HS/R in WT but not IL-6 KO mice. Collectively, these data support the view that expression of IL-6 is essential for the development of gut barrier dysfunction after HS/R.

Background. While activation of the IL-6-dependent transcription factor signal transducer and activator of transcription 3 (STAT3) has been implicated in the pa