CHARACTERIZATION OF EPITHELIAL GENE EXPRESSION DURING DEXTRAN SULFATE SODIUM-INDUCED COLITIS.

Abstract

101 In ulcerative colitis the colonic epithelium is severly damaged, leading to an impaired colonic function. Aim: Characterization of epithelial gene expression during onset of disease and active disease in an experimental colitis model in order to develop therapeutic regimes to induce epithelial regeneration. Methods: To induce colitis, rats received 7% dextran sulfate sodium (DSS) in their drinking water. Colonic segments were excised on various days after the beginning of the DSS treatment. Next to standard histological evaluation, cell function was studied by the expression of cell type specific markers at mRNA (in situ hybridization, RNA dot blots) and protein levels (immunohistochemistry, protein dot blots). Carbonic anhydrase I and IV (CAI and CAIV), and intestinal fatty acid binding protein(IFABP) were used as markers for enterocytes, mucin (MUC2) and intestinal trefoil factor (ITF) as markers for goblet cells. Results: During the onset of disease colonic damage is characterized by flattening of the surface epithelium, an increase of goblet cells in the surface epithelium (day 2), and focal crypt dilatation together with infiltration of leucocytes (day 5). Next to areas with a covering surface epithelium and elongated crypts, ulcerated areas with massive infiltration of inflammatory cells and loss of entire crypts were observed during active disease (day 7). At the mRNA level the expression of CAI, CAIV and IFABP was strongly decreased at the onset of disease (day 2-5), and at day 7 (active disease) these markers were even undetectable. The decrease in mRNA expression levels of these enterocyte markers is followed by a decrease in their protein expression levels. The expression of the goblet cell marker, MUC2, was largely unaffected at mRNA and protein levels during both phases of disease. In normal epithelium ITF is expressed in the upper 2/3 of the crypts. However, during active disease, in areas with a covering surface epithelium and elongated crypts. ITF expression was confined to the goblet cells of the surface epithelium.Conclusions: DSS-induced histological changes in rat colon are similar to the histological changes seen in patients with ulcerative colitis. The DSS-induced decreases in CAI, CAIV and IFABP at both mRNA and protein levels during the onset of disease demonstrate increasing loss of enterocyte cell function before ulceration. During DSS administration, the epithelium largely remains its MUC2 production. As MUC2 is the main component of the mucus layer, the unaltered MUC2 expression seems one of the primary defence mechanisms against DSS. Moreover, since ITF stimulates epithelial repair, the reduced ITF expression implies a DSS-induced decrease in epithelial repair capacity.