Submitted on August 20, 2008
Revised on March 31, 2009
Accepted on March 31, 2009
Endogenous IGF-I and 
V
3 Integrin Ligands Regulate Increased Smooth Muscle Growth in TNBS-induced Colitis
Krystina B. Hazelgrove, Robert S Flynn1, Li-Ya Qiao1, John R Grider1, and John F. Kuemmerle2*
1 Virginia Commonwealth University
2 Med Col Virginia, VCU
* To whom correspondence should be addressed. E-mail: jkuemmerle{at}hsc.vcu.edu.
Endogenous Insulin-like 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 
V
3 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 seven days following the induction of TNBS-induced colitis. While V3 integrin expression was not altered by TNBS-induced colitis, vitronectin and fibronectin levels were increased by 80 ± 10% and 90 ± 15% above control levels. Basal IGF-I receptor phosphorylation in inflamed muscle from TNBS-treated rats was increased by 86 ± 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 ± 15% and decreased apoptosis by 20 ± 2% compared to that in vehicle-treated 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.
