P097 Intestinal barrier dysfunction in association with fibrosis during experimental acute and chronic colitis in mice

Abstract Background Intestinal barrier dysfunction is a significant contributor to the pathophysiology of Inflammatory bowel diseases (IBD). Furthermore, chronic inflammation and barrier dysfunction may result in the mucosal and submucosal deposition of the extracellular matrix, which progressively leads to structural fibrosis, a major complication in IBD. Here, we aimed at investigating intestinal inflammation, barrier function and the development of fibrosis using the dextran sodium sulphate (DSS) colitis mouse model. Methods Seven-week old C57BL6/J mice were treated with 3 subsequent cycles of 2% DSS in their drinking water for 7 days followed by a recovery phase of 7 days with normal drinking water to induce acute (cycle 1) and chronic colitis (cycle 2 and 3). Control animals received only drinking water. Disease activity was daily monitored. At the end of each DSS treatment (Day 7, 21 and 35), mice were used for compliance measurements to investigate the viscoelastic properties of the colon. Thereafter, at euthanasia, colonic tissue was collected to investigate inflammation (H&E), fibrosis (Masson’s trichrome), MPO activity and expression of tight junctions (Cldn1, Cldn2, Ocln, Cdh1, Zo-1, Zo-3), cell polarity proteins (Par3-Par6-aPKC, Crb3) and cytokines (Tnf-α, Il-1β, Il-6, Il-10, Il-22). Intestinal permeability was determined via oral gavage (4 h before euthanasia) of 4 kDa FITC-dextran, followed by measuring the fluorescence in the blood. Results Acute colitis in mice was correlated with marked intestinal inflammation (Figure 1A-C), increased expression of several pro-inflammatory cytokines (Tnf-α, Il-1β and Il-22; Figure 1D-E), increased intestinal permeability (Figure 1F), aberrant expression of Cldn1, Cldn2, Zo-3 and Par3 (Figure 1G-M) and a remarkable decrease in colonic compliance at lower balloon distension volumes (120 µl, p < 0.05) and fibrotic lesions. Although intestinal permeability was not significantly altered anymore at Day 21 and 35 (Figure 1F), barrier mediators, such as Cldn2, Zo-3 and Par3 (Figure 1G–M), were still changed. Abstract PO97 – Figure 1. (A) Representative H&E stained colon sections of control and DSS-treated mice. (B) Scoring of microscopic inflammation which was based on immune cell infiltration, goblet cell loss and epit