Basement membrane formation and re‐distribution of the β1 integrins in a human intestinal co‐culture system

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Abstract
We have developed a co‐culture system suited for the study of epithelial‐mesenchymal interactions in the human fetal small intestine. As the epithelial component of this model, we used the human intestinal cell line Caco‐2 that is unique in its property to differentiate in vitro into a mature fetal enterocyte‐like cell type. A sheet of human intestinal mesenchymal cells, which we derived from an 18‐week‐old fetus, was used as mesenchymal element. Expression and distribution of cell‐specific markers (cytokeratin 18 and dipeptidyl peptidase IV), major basement membrane components, and β1 integrins were analyzed. In 14‐day co‐cultures, Caco‐2 cells formed a cytokeratin 18‐positive epithelial‐like sheet covering the vimentin‐positive HIM cell layers. As assessed by brush border dipeptidyl peptidase IV expression, co‐cultured Caco‐2 cells achieved cytodifferentiation as when cultured on plastic. A complete deposition of all known major human fetal intestinal basement membrane components occurred at the Caco‐2/HIM interface. Type IV collagen and tenascin were produced from the mesenchymal compartment, whereas laminin and fibronectin were contributed by both cell types. Interestingly, synthesis and deposition of basement membrane heparan sulfate proteoglycan were exclusively observed in co‐cultures, suggesting modulation of epithelial expression of this molecule by HIM cells. Finally, we observed that epithelial integrin‐β1 chains redistributed at the basal domain of co‐cultured Caco‐2 cells. Taken to gether, these observations indicate that the Caco‐2/HIM co‐culture model is a valuable system to study in vitro human basement membrane formation in the context of intestinal epithelial‐mesenchymal interactions.