Vascular smooth muscle cells and pericytes express MMP-1, MMP-9, TIMP-1 and type I procollagen in inflammatory bowel disease.

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Matrix metalloproteinases (MMPs) are involved in tissue remodelling, which is one of the important aspects of inflammatory disease. To assess the balance between the matrix degradation and production, we analysed the in situ expression of MMP-1, -3, -8 and -9, tissue inhibitor of metalloproteinases (TIMP)-1 and -2, and type I procollagen (PC-I) in inflammatory bowel disease. Immunohistochemistry using frozen sections was performed in 17 patients with ulcerative colitis (UC) and 16 with Crohn's disease (CD). In both UC and CD, MMPs and TIMPs were expressed by inflammatory cells as well as by fibroblastic cells most prominently in actively inflamed areas in ulcer bases, but sparsely in intact inflamed mucosa in both UC and CD. In UC, inflamed mucosa with erosions expressed these substances focally. Fibroblasts also expressed PC-I. We identified that vascular smooth muscle cells of venules in ulcer bases expressed MMP-1 and -9, TIMP-1 and PC-I. These venules also expressed E-selectin, a cell adhesion molecule to facilitate the leucocyte extravasation, and vascular endothelial growth factor (VEGF) receptor 2, consistent with their property of newly formed vessels. Our results suggest that MMPs are involved in the tissue remodelling, angiogenesis and promotion of leucocyte extravasation in the actively inflamed area in the ulcer base in both UC and CD. MMP-1 expression in the mucosa may be related to the initial step of ulceration in UC. Therapeutic manipulation of extracellular matrix turnover would be an effective therapy to alleviate active inflammation and accelerate ulcer healing.