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P059 Two new genetic mouse models for ulcerative colitis based on lateral tight junction disruption.

W. Stremmel*1, S. Staffer2, M. Schneider3, H. Gan-Schreier2, A. Wannhoff2, A. Gauss4, H. Wolburg5, M. Bach6, A. Swidsinski7, T. Efferth3

1University Hospital of Heidelberg, Internal Medicine IV, Dept. of Gastroenterology, Heidelberg, Germany, 2University Hospital of Heidelberg, Internal Medicine IV, Div. of Gastroenterology, Heidelberg, Germany, 3Johannes Gutenberg University, Institute of Pharmacy & Biochemistry, Mainz, Germany, 4University Hospital of Heidelberg, Gastroenterology, Heidelberg, Germany, 5University Medical School Tuebingen, Pathology and Neuropathology, Tuebingen, Germany, 6Kirchhoff Institute of Physics, Physics, Heidelberg, Germany, 7Charité - University Hospital Berlin, Berlin, Germany

Background

Genetic mouse models for IBD mostly focus on the knockdown of key mediators of immune response. However, previous studies indicated the crucial role of tight junctions (TJ) for the pathogenesis of IBD. Kindlin 1 and 2 operate through integrin activation as adapter proteins either at the basal membrane (kindlin 1) or cell-cell adhesion (kindlin 2) site. Knockdown of both kindlins was expected to induce an IBD phenotype, if TJ were involved in the pathogenesis.

Methods

Male C57BL6 wild-type and tamoxifen-inducible kindlin 1 and 2 intestine-specific knockout mice were a gift from R. Faessler (MPI Munich, Germany). Mice (12 weeks old) were i.p. injected with 0.2 mg tamoxifen for up to 3 days. After 2 days of tamoxifen exposure in absence of a gross inflammatory phenotype, the morphologic appearance of TJs and the functional capability of phosphatidylcholine (PC) secretion into ileal and colonic lumen, the concentration of PC in mucus, the hydrophobicity of the mucosal surface, and the mucosal penetration of intestinal microbiota were analysed. After 3 days of tamoxifen exposure, the overt mucosal inflammation was assessed by macroscopic and histologic colitis scores.

Results

Freeze fracture electron microscopy of mucosal biopsies of kindlin 1 and 2(-/-) mice revealed a loosening of lateral TJ already after 2 days of tamoxifen exposure. The loss of cell adhesion caused in both mutants an expansion of the crypt lumina of the mucosal layer when assessed by randomly taken biopsies. Phosphatidylcholine secretion into the mucus was reduced by 66.3 ± 9.7 and 76 ± 12.1 % in kindlin 1 and 2(-/-) mice, respectively. Accordingly the mucus PC content dropped from 80 ± 23 in controls to 39 ± 27 and 27 ± 19 nmol • mg mucin 2-1 in kindlin 1 and 2(-/-) mice, respectively. In parallel the hydrophobicity was reduced as shown by contact angle goniometry values from 72 ± 6° in controls to 30 ± 2° and 35 ± 1° in kindlin 1 and 2(-/-) mice, respectively (p < 0.001). This allowed penetration of microbiota into the submucosa, as shown by FISH technology employing the segmented filamentous bacteria (SFB) Cy3 probe. Consequently, after 3 days of tamoxifen exposure, a full-blown intestinal inflammation was present with loose bloody stools and macroscopic and histologic features of colitis corresponding to a total major colitis score of 18 (17–18) and 19.5 (18–21) in kindlin 1 and 2(-/-) mice, respectively.

Conclusion

Genetic mouse models with intestinal deletion of kindlin 1 and 2 resulted in TJ disruption, widened crypt diameters, impaired mucus PC secretion with significant loss of mucus PC, and, thus, reduced mucus hydrophobicity, leading to penetration of the microbiota inducing mucosal inflammation, compatible with an ulcerative colitis phenotype.