Identification of Epithelial to Mesenchymal Transition as a Novel Source of Fibroblasts in Intestinal Fibrosis

Abstract

Intestinal fibrosis is a major complication of Crohn disease (CD), but the precise mechanism by which it occurs is incompletely understood. As a result, specific therapies to halt or even reverse fibrosis have not been explored. Here, we evaluated the contribution of epithelial to mesenchymal transition (EMT) to intestinal fibrosis associated with a mouse model of CD and also human inflammatory bowel disease. Mice administered intrarectal 2,4,6-trinitrobenzene sulfonic acid (TNBS) develop inflammation and fibrosis that resembles CD both histologically and by immunologic profile. We utilized this model to molecularly probe the contribution of EMT to intestinal fibrosis. Additionally, we utilized double-transgenic VillinCre; R26Rosa-lox-STOP-lox-LacZ mice, in which removal of the STOP cassette by Cre recombinase in villin(+) intestinal epithelial cells activates permanent LacZ expression, to lineage trace epithelial cells that might undergo EMT upon TNBS administration. TNBS-induced fibrosis is associated with the presence of a significant number of cells that express both epithelial and mesenchymal markers. In the lineage tagged transgenic mice, the appearance of LacZ(+) cells that also express the fibroblast marker FSP1 unequivocally demonstrates EMT. Transforming growth factor (TGF)-beta 1, a known inducer of EMT in epithelial cells, induces EMT in rat intestinal epithelial cells in vitro, and bone morphogenic protein-7, an antagonist of TGF-beta 1, inhibits EMT and fibrosis both in vitro and in the TNBS-treated mice. Our study demonstrates that EMT contributes to intestinal fibrosis associated with the TNBS-induced model of Crohn colitis and that inhibition of TGF-beta 1 with recombinant human bone morphogenic protein-7 prevents this process and prevents fibrosis.