It has been suggested that prolonged inflammatory bowel diseases (IBD) may lead to colitis-associated carcinogenesis (CAC). We previously observed that the NF-κB activation in colonic epithelial cells is associated with increased tumor necrosis factor receptor 2 (TNFR2) expression in CAC development. However, the mechanism by which epithelial NF-κB activation leading to CAC is still unclear. Myosin light chain kinase (MLCK) has been reported to be responsible for the epithelial permeability associated with TNF signaling. Therefore we focused on the role of MLCK expression via TNFR2 signaling on CAC development. Pro-tumorigenic cytokines such as IL-1β, IL-6 and MIP-2 production as well as INF-γ and TNF production at the lamina propria were increased in the setting of colitis, and further in tumor tissues in associations with up-regulated TNFR2 and MLCK expressions in the epithelial cells of a CAC model. The up-regulated MLCK expression was observed in TNF-stimulated colonic epithelial cells in a dose-dependent fashion in association with up-regulation of TNFR2. Silencing TNFR2, but not TNFR1, resulted in restoration of epithelial tight junction (TJ) associated with decreased MLCK expression. Antibody-mediated blockade of TNF signaling also resulted in restoration of TJ in association with suppressed MLCK expression, and interestingly, similar results were observed with suppressing TNFR2 and MLCK expressions by inhibiting MLCK in the epithelial cells. Silencing of MLCK also resulted in suppressed TNFR2, but not TNFR1, expression, suggesting that the restored TJ leads to reduced TNFR2 signaling. Such suppression of MLCK as well as blockade of TNFR2 signaling resulted in restored TJ, decreased pro-tumorigenic cytokines and reduced CAC development. These results suggest that MLCK may be a potential target for the prevention of IBD-associated tumor development.

ObjectiveAlthough immunoglobulin A (IgA) is abundantly expressed in the gut and known to be an important component of mucosal barriers against luminal pathogens, its precise function remains unclear. Therefore, we tried to elucidate the effect of IgA on gut homeostasis maintenance and its mechanism.DesignWe generated various IgA mutant mouse lines using the CRISPR/Cas9 genome editing system. Then, we evaluated the effect on the small intestinal homeostasis, pathology, intestinal microbiota, cytokine production, and immune cell activation using intravital imaging.ResultsWe obtained two lines, with one that contained a <50 base pair deletion in the cytoplasmic region of the IgA allele (IgA tail-mutant; IgAtm/tm) and the other that lacked the most constant region of the IgH α chain, which resulted in the deficiency of IgA production (IgA−/−). IgA−/− exhibited spontaneous inflammation in the ileum but not the other parts of the gastrointestinal tract. Associated with this, there were significantly increased lamina propria CD4+ T cells, elevated productions of IFN-γ and IL-17, increased ileal segmented filamentous bacteria and skewed intestinal microflora composition. Intravital imaging using Ca2+ biosensor showed that IgA−/− had elevated Ca2+ signalling in Peyer’s patch B cells. On the other hand, IgAtm/tm seemed to be normal, suggesting that the IgA cytoplasmic tail is dispensable for the prevention of the intestinal disorder.ConclusionIgA plays an important role in the mucosal homeostasis associated with the regulation of intestinal microbiota and protection against mucosal inflammation especially in the ileum.

Prolonged inflammatory bowel diseases (IBD) may lead to colitis-associated carcinogenesis (CAC). Previous studies had shown that nuclear factor-κB (NF-κB) activation in both macrophages and epithelia in inflamed colonic tissue is associated with CAC development. However, the mechanism by which epithelial NF-κB activation leading to CAC development had not previously been rigorously studied. We and others had observed the increased expression of the type 2 receptor for tumor necrosis factor (TNFR2/TNFRSF1b/p75) in IBD models. Myosin light chain kinase (MLCK) is suggested to be associated with epithelial permeability via TNF signaling. Therefore, the relationship between epithelial MLCK expression and NF-κB activation via TNFR2 signaling on CAC development was investigated. Pro-tumorigenic cytokines such as interleukin (IL)-1ß, IL-6 and macrophage inflammatory protein-2 at the lamina propria were increased in the setting of colitis and further increased in tumor tissues with upregulated epithelial TNFR2 and MLCK expressions in an animal model of CAC. The upregulated MLCK expression was also observed in TNF-stimulated colonic epithelial cells in vitro in association with the upregulation of TNFR2 but not TNFR1/TNFRSF1a/p55. Gene silencing of tnfrsf1b, but not tnfrsf1a, resulted in restoration of epithelial tight junction (TJ) associated with decreased MLCK expression. The presence of anti-TNF antibody also resulted in restoration of TJ in association with suppressed MLCK expression, and interestingly, similar results including the suppressed TNFR2 and MLCK expressions were observed by inhibiting MLCK in the epithelial cells. MLCK silencing also led to suppressed TNFR2 expression, suggesting that the restored TJ leads to reduced TNFR2 signaling. Such suppression of MLCK as well as blockade of TNFR2 signaling resulted in reduced CAC development, restored TJ, and decreased pro-tumorigenic cytokines. These imply that TNF-induced NF-κB activation and MLCK expression may be a potential target for the prevention of IBD-associated carcinogenesis.

Chronic diarrhea is one of the major symptoms in gastroenterology. However, this may be caused by pathologic conditions for which the diagnosis is critical. Villous atrophy, as an endoscopic lesion, accompanied by chronic diarrhea can occasionally be observed in the patients with inflammatory diseases of the gastrointestinal (GI) tract. Herein, we present a case with persistent diarrhea accompanied by intestinal wall thickening without any other significant endoscopic features other than villous atrophy in the jejunum and the ileum, where we diagnosed as an indolent T cell lymphoproliferative disorder (T-LPD) of the GI tract, defined in the 2016–2017 revised World Health Organization classification, via single-balloon enteroscopy (SBE). Interestingly, we found the same lymphocyte infiltration from the distal third portion of the duodenum, where gastroscopy could not reach, via SBE, even though no endoscopic findings were observed such as villous atrophy. Since infiltrating cells in the intestinal tissues were CCR4+, mogamulizumab was administered with resulting durable symptomatic remission for more than 2 years. Patients with persistent diarrhea may have serious small intestinal disorder including not only chronic inflammatory diseases but also lymphoid neoplasmic conditions including T-LPD of GI tract.

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