A265 INVOLVEMENT OF LRP6 IN INTESTINAL HOMEOSTASIS AND INFLAMMATION

Abstract

Background

Self-renewal of the intestinal epithelium is tightly regulated by interacting intracellular signaling pathways, which control stem cell proliferation and differentiation. In particular, Wnt/b-catenin signalling controls crypt cell proliferation and survival and is required for maintenance of intestinal stem cells. Additionally, maturation of Paneth cells in the intestine also depends on this pathway. Wnt signals are transduced through Frizzled receptor and LRP5/LRP6 coreceptor to downregulate GSK3β activity, resulting in increased nuclear β-catenin. Recently, LRP6 was identified as a new candidate gene in ileal Crohn’s Disease (Koslowski, PLoS Genet 2012).

Aims

In the present study we would like to explored whether LRP6 is required for the maintenance of intestinal homeostasis and barrier function.

Methods

Using the Cre/loxP system, mice with an intestinal epithelial cell-specific deletion of LRP6 (LRP6^IEC-KO mice) were generated. Tissue architecture was visualized with hematoxylin-eosin staining and Paneth cells by lysozyme staining. Intestinal permeability was evaluated by dextran-FITC method. Crypts were isolated from control and mutant mice and organoid cultures were established as an ex vivo model of epithelial regeneration. The sensitivity of mice to inflammation was evaluated by giving 2% DSS to mice for 7 days. Mice were scored based on a scale of 0 to 4 for stool consistency, rectal bleeding, colon hardness and blood loss, and a cumulative disease activity index (DAI) was calculated.

Results

Loss of LRP6 expression was validated in LRP6^IEC-KO mice compared to control mice. At 4 weeks of age, no difference in body weight of LRP6^IEC-KO mice was noticed in comparison to control mice. Histological analyses indicate that the architecture of the small and large intestine was apparently not altered. Surprisingly, the number of proliferative cells remained unchanged in LRP6^IEC-KO mice and no difference in Paneth cell number was seen. However, intestinal permeability was markedly increased in 3-month-old LRP6^IEC-KO mice compared to control littermates. Furthermore, deletion of LRP6 clearly impaired organoid development as determined by measurement of both organoid growth and budding. Finally, LRP6^IECKO mice were much more sensitive to DSS treatment in comparison to control littermates.

Conclusions

These results suggest that LRP6 regulates IEC-mediated mucosal homeostatic and inflammatory responses.

Funding Agencies

CIHRCRCHUS