Background/Aims Insulin-like growth factor-I (IGF-I) regulates human intestinal smooth muscle growth by stimulating proliferation and inhibiting apoptosis. IGF-I-stimulated growth is augmented when αvβ3 integrin is occupied by its ligands, fibronectin and vitronectin. Increased IGF-I expression and muscle cell hyperplasia are features of stricturing Crohn's disease, however, the role of IGF-I in stricture formation is unknown. The aim was to identify the functional role of endogenous IGF-I and αvβ3 integrin ligands in regulating muscle cell hyperplasia in stricturing Crohn's disease. Methods Smooth muscle cells were isolated from muscularis propria of stricturing Crohn's disease or normal margins. Quantitative PCR, immunoblot analysis and ELISA were used to measure fibronectin, vitronectin, αVβ3 integrin, and IGF-I levels. Activation of the IGF-I receptor, Erk1/2, p70S6 kinase and GSK-3β was measured by immunoblot. Proliferation was quantified by Ki67 immunostaining and [3H]thymidine incorporation. Apoptosis was measured from caspase-3 cleavage and nucleosome accumulation. Results IGF-I, vitronectin and fibronectin RNA and protein levels were increased 1.8 – 3.4 fold in muscle cells from strictures over normal margins. Basal IGF-I receptor phosphorylation was increased 320% in strictured over normal muscle and basal Erk1/2, p70S6 kinase and GSK-3β phosphorylation was increased 205 - 292% in strictures. In muscle cells from strictures, Ki67 immunoreactivity and [3H]thymidine incorporation were increased and apoptosis was decreased compared to normal margins. Antagonists of the IGF-I receptor or αVβ3 integrin reversed these changes. Conclusion Smooth muscle cell hyperplasia in stricturing Crohn's disease is regulated by increased endogenous IGF-I and αVβ3 integrin ligands that regulate augmented proliferation and diminished apoptosis.
Background Stricture formation occurs in ≈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-β1 (TGF-β1) 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-β1 are expressed by normal human intestinal smooth muscle cells, bind to, and activate TGF-βRII/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-β1, and collagen IαI 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-β1, and collagen IαI 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-β1 regulated collagen IαI expression and production via a TGF-βRII/I-dependent and Smad2/3-dependent mechanism. Upregulated (excess) collagen IαI expression and production in smooth muscle cells of strictures and basal collagen IαI in smooth muscle cells of normal margin were inhibited by immunoneutralization of IGFBP-3 or TGF-β1. Conclusions The findings indicate that upregulated endogenous IGFBP-3 and TGF-β1 expression regulates excess collagen IαI production and contributes to fibrosis and stricture formation in CD.
Background Strictures develop in >30% of Crohn’s disease. No available medication prevents stricture development in susceptible patients. In Crohn’s strictures, but not adjacent normal intestine, TGF-β1 increases in muscularis smooth muscle, increasing collagen I production and strictures. Muscle cells express αVβ3 integrin containing an RGD binding domain. The aim was to determine whether increased TGF-β1 levels in strictures was the result of latent TGF-β1, which contains an RGD sequence , binding to and activation by αVβ3; and whether cilengitide, which is an RGD-containing αVβ3 integrin inhibitor, decreases TGF-β1 activation and development of fibrosis in chronic TNBS-induced colitis Design Muscle cells were isolated from Crohn’s disease strictures and normal resection margin and from colon of rats after 42 d of chronic TNBS-induced colitis were used to prepare RNA, protein lysates and initiate primary cultures. The mechanisms leading to increased TGF-β1 activation, collagen I production and fibrosis were examined in human muscle and in rats. Human cultured cells in vitro and rats in vivo were treated with cilengitide to determine it efficacy to decrease TGF-β1-activation, collagen production and decrease the development of fibrosis. Results Latent TGF-β1 is activated by the αVβ3 RGD domain in human and rat intestinal smooth muscle. Increased activation of TGF-β1 in Crohn’s disease and in TNBS-induced colitis causes increased collagen production, and fibrosis that could be inhibited by cilengitide. Conclusions Cilengitide, a αVβ3 integrin RGD inhibitor, could be a novel treatment to diminish excess TGF-β1 activation, collagen I production and development of fibrosis in Crohn’s disease.
Hazelgrove KB, Flynn RS, Qiao LY, Grider JR, Kuemmerle JF. Endogenous IGF-I and ␣v3 integrin ligands regulate increased smooth muscle growth in TNBS-induced colitis. Am J Physiol Gastrointest Liver Physiol 296: G1230 -G1237, 2009. First published April 9, 2009 doi:10.1152/ajpgi.90508.2008.-Endogenous insulinlike growth factor-I (IGF-I) regulates intestinal smooth muscle growth by concomitantly stimulating proliferation and inhibiting apoptosis. IGF-I-stimulated growth is augmented by the ␣v3 integrin ligands vitronectin and fibronectin. IGF-I expression in smooth muscle is increased in both TNBS-induced colitis and Crohn's disease. We hypothesized that intestinal inflammation increased vitronectin and fibronectin expression by smooth muscle and, along with IGF-I upregulation, increased intestinal muscle growth. Intestinal smooth muscle cells were examined 7 days following the induction of TNBS-induced colitis. Although ␣ v3 integrin expression was not altered by TNBSinduced colitis, vitronectin and fibronectin levels were increased by 80 Ϯ 10% and 90 Ϯ 15%, above control levels, respectively. Basal IGF-I receptor phosphorylation in inflamed muscle from TNBStreated rats was increased by 86 Ϯ 8% over vehicle-treated controls. Basal ERK1/2, p70S6 kinase, and GSK-3 phosphorylation in muscle cells of TNBS-treated rats were also increased by 140 -180%. TNBS treatment increased basal muscle cell proliferation by 130 Ϯ 15% and decreased apoptosis by 20 Ϯ 2% compared with that in vehicletreated controls. The changes in proliferation and apoptosis were reversed by an IGF-I receptor tyrosine kinase inhibitor or an ␣v3 integrin antagonist. The results suggest that smooth muscle hyperplasia in TNBS-induced colitis partly results from the upregulation of endogenous IGF-I and ligands of ␣ v3 integrin that mediate increased smooth muscle cell proliferation and decreased apoptosis. This paper has identified one mechanism regulating smooth muscle hyperplasia, a feature of stricture formation that occurs in the chronically inflamed intestine of TNBS-induced colitis and potentially Crohn's disease.
Background & Aims-Strictures occur in ~30% of patients with Crohn's disease and are characterized by intestinal smooth muscle hyperplasia, hypertrophy, and fibrosis due to excess extracellular matrix production including collagen. Insulin-like Growth Factor-I (IGF-I) expression is increased in smooth muscle cells of the muscularis propria in Crohn's disease and in animal models of Crohn's disease, including TNBS-induced colitis. While upregulated IGF-I is conjectured to cause smooth muscle cell growth and collagen production in the inflamed intestine, its role in the development of fibrosis has not been directly demonstrated.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.