P077 Aberrant Muc1 and Muc13 expression in association with Par polarity complex and Vip dysfunction in a colitis T-cell transfer model

Abstract Background There is emerging evidence that loss of the gastrointestinal mucosal barrier integrity is a significant contributor to the pathophysiology of inflammatory bowel disease (IBD). Mucins represent the major components of the mucus barrier and inappropriate overexpression of transmembrane mucins can affect the barrier integrity by disrupting cell polarity and cell-cell interactions resulting in tight junction dysfunction.1 Aberrant expression of Muc1, Muc4, and Muc13, in particular, is observed in colonic tissue samples of IBD patients.2, 3 Nevertheless, the role of mucins in mucosal barrier disruption in IBD remains elusive. In this study, we investigated the expression patterns of transmembrane mucins and the mediators involved in barrier homeostasis during the progression of colitis in mice. Methods Colitis was induced in immunocompromised SCID mice by the adoptive transfer of CD4+CD25-CD62L+ T cells from the spleens of BALB/c donor mice. At 2, 4, and 6 weeks post-colitis, animals were sacrificed and colonic tissue collected for RNA and protein analysis of membrane-bound mucins (Muc1, Muc4, and Muc13), polarity proteins, and the vasointestinal polypeptide (Vip). This latter protein is implicated in the regulation of tight junction and mucin expression (Hokari et al., 2005). Apoptotic cells in tissue sections were detected using a terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) assay. Results Our data showed that Muc1 expression was significantly increased after 4 weeks of colitis (Figure a). Interestingly, a significant decrease of Muc13 expression was observed during acute colitis (2 weeks) whereas a remarkable turnover in expression was noted during chronic colitis (4–6 weeks; Figure b). Normal intestinal MUC13 expression plays crucial roles in epithelial proliferation, differentiation and apoptosis but inappropriate overexpression of this mucin could lower the level of protection. Indeed, a higher number of apoptotic cells was seen in tissue of chronic colitis-induced mice (Figure d). Furthermore, the polarity proteins Par3 and aPKC as well as Vip (Figure c) were significantly reduced in expression from week 2 onwards suggesting a disturbance in cell polarity. Figure. Relative expression of Muc1 (a), Muc13 (b), Vip (c) in the colon of mice with acute (2w) and chronic (4–6w) colitis. (d) Number of apoptotic cells in healthy and chronic colitis mice. Asterisk indicates significance (one-way ANOVA; p < 0.05). Conclus