Fructo-oligosaccharide-mediated alteration in claudin expression in small intestinal absorptive Caco-2 cells is positively associated with the induction of inflammatory genes and the glucan receptor gene CLEC7A

Indigestible carbohydrates may strengthen tight junctions (TJ) independently of intestinal bacteria. Here, we investigated whether indigestible carbohydrates, i.e., fructo-oligosaccharides (FOS), promote TJ directly to intestinal absorptive Caco-2 cells and examined the association between the expression of genes constructing TJ and other genes using mRNA microarray analysis. Caco-2 cells at 1.0 × 105/mL were seeded in a type I collagen plate and cultured in high glucose-Dulbecco's modified Eagle medium (DMEM) supplemented with 10% fetal calf serum (FCS); the cells reached confluence at 7 days after seeding. Ten days after the cells reached confluency, they were cultured for 24 h in 10% FCS-containing DMEM medium supplemented with 0%, 5%, or 10% FOS. We performed mRNA microarray to identify the genes, whose expression was altered by FOS. Subsequently, qRT-PCR was performed for these altered genes including CLEC7A encoding the glucan receptor, and for the claudin (CLDN) family genes. The expression of CLDN2, CLDN4, and CLEC7A proteins was assessed using western blot analysis. FOS decreased the mRNA and protein expression of CLDN2, which weakens TJ and increased those of CLDN4, which strengthens TJ, in Caco-2 cells. FOS treatment (10%) reduced the mRNA expression of anti-oxidative genes and induced the expression of immune response-related genes, including CLEC7A, CCL2, and ITGA2. Furthermore, the expression of CLEC7A was enhanced by FOS. Induction of TJ-strengthening CLDN4 and reduction of TJ-weakening CLDN2 by FOS treatment in small intestinal absorptive Caco-2 cells is positively associated with the induction of inflammatory genes, including CLEC7A.