Endogenous IGFBP-3 Regulates Excess Collagen Expression in Intestinal Smooth Muscle Cells of Crohn's Disease Strictures

Background: Stricture formation occurs in approximate to 30% of patients with Crohn's disease (CD) and is a significant cause of morbidity. Strictures are characterized by intestinal smooth muscle cell hyperplasia, smooth muscle cell hypertrophy, and fibrosis due to excess net extracellular matrix production, including collagen. Transforming growth factor-beta 1 (TGF-beta 1) has profibrotic effects in many tissues due to its ability to regulate collagen expression and extracellular matrix dynamics. We previously showed that both insulin-like growth factor (IGF) binding protein-3 (IGFBP-3) and TGF-beta 1 are expressed by normal human intestinal smooth muscle cells, bind to, and activate TGF-beta RII/I receptors in these cells. Methods: Smooth muscle cells isolated from the muscularis propria of patients were used to prepare RNA, protein lysates, or placed into primary culture. IGFBP-3, TGF-beta 1, and collagen I alpha I expression was measured with quantitative reverse-transcription polymerase chain reaction (RT-PCR) and protein levels by enzyme-linked immunosorbent assay (ELISA) or immunoblot. Results: Expression and production of IGFBP-3, TGF-beta 1, and collagen I alpha I were significantly increased specifically in smooth muscle cells isolated from regions of strictured intestine in CD compared to nonstrictured histologically normal resection margin. IGFBP-3 and TGF-beta 1 regulated collagen I alpha I expression and production via a TGF-beta RII/I-dependent and Smad2/3-dependent mechanism. Upregulated (excess) collagen I alpha I expression and production in smooth muscle cells of strictures and basal collagen I alpha I in smooth muscle cells of normal margin were inhibited by immunoneutralization of IGFBP-3 or TGF-beta 1. Conclusions: The findings indicate that upregulated endogenous IGFBP-3 and TGF-beta 1 expression regulates excess collagen I alpha I production and contributes to fibrosis and stricture formation in CD.