Laminins regulate crypt-villus architecture and epithelial cell behavior in the mouse intestine.

The organization of the lining of the gastrointestinal tube is similar for the stomach, small intestine and colon. It is composed of a continuous simple epithelium and underlying mesenchyme, including blood vessels, fibroblasts/myofibroblasts and immune cells. Individual organs contain modifications of this mucosa that are critical for their functions. We hypothesize that changes in the composition of the epithelial basement membrane are a critical determinant for structure and function of the local mucosa. Laminins are excellent candidates for such a role, as they comprise a large family of αβγ heterotrimeric glycoproteins that demonstrate developmental, organ and cell type specificity. We have found that adult mice lacking the normal villus laminin, α5, demonstrate a compensatory increase in α1 and α4, which are normally present in the colon. This laminin switch results in colonic metaplasia of the distal small intestine, which showed deepened crypts, villus atrophy and subsequent replacement by flat surface epithelial structures, and expression of colonic markers. This change was associated with aberrant intestinal epithelial cell proliferation, differentiation and migration. Here, unlike pathologic processes in humans that result in colonic metaplasia, there was no infiltration of inflammatory cells. These observations highlight the important and distinct roles of different laminin isoforms on the patterning of intestinal crypt-villus architecture and the regulation of intestinal epithelial cell behavior. Our data also suggest that differences in laminin composition along the gut's rostrocaudal axis contribute to its regionalization into small and large intestine. [ABSTRACT FROM AUTHOR]