Abnormal Mucosal Extracellular Matrix Deposition Is Associated with Increased TGF-β Receptor-expressing Mesenchymal Cells in a Mouse Model of Colitis

Transforming growth factor-β (TGF-β) depresses mucosal inflammation and upregulates extracellular matrix (ECM) deposition. We analyzed TGF-β receptors RI and RII as well as ECM components using the CD4+ T-cell-transplanted SCID mouse model of colitis. The principal change in colitis was an increased proportion of TGF-β RII+ mucosal mesenchymal cells, predominantly α-smooth muscle actin (SMA)+ myofibroblasts, co-expressing vimentin and basement membrane proteins, but not type I collagen. TGF-β RII+ SMA− fibroblasts producing type I collagen were also increased, particularly in areas of infiltration and in ulcers. Type IV collagen and laminin were distributed throughout the gut lamina propria in disease but were restricted to the basement membrane in controls. In areas of severe epithelial damage, type IV collagen was lost and increased type I collagen was observed. To examine ECM production by these cells, mucosal mesenchymal cells were isolated. Cultured cells exhibited a similar phenotype and matrix profile to those of in vivo cells. The data suggested that there were at least two populations of mesenchymal cells responsible for ECM synthesis in the mucosa and that ligation of TGF-β receptors on these cells resulted in the disordered and increased ECM production observed in colitic mucosa.