Inflammation location, but not type, determines the increase in TGF‐β1 and IGF‐1 expression and collagen deposition in IBD intestine

Background and Aims Inflammatory bowel disease (IBD) is frequently complicated by extracellular matrix (ECM) changes that may result in fibrosis. Transforming growth factor (TGF)‐β1 and insulin‐like growth factor (IGF)‐1 mediate numerous ECM changes. Our aim was to determine whether TGF‐β1 and IGF‐1 are involved in intestinal ECM collagen regulation and what impact the inflammatory infiltrate has on their expression. Methods TGF‐β1 and IGF‐1 mRNA and protein were assessed in fibrosed Crohn's disease (CD), inflamed CD, inflamed ulcerative colitis (UC), and control intestine using in situ hybridization and immunohistochemistry. Collagen types I and III were quantified by electron immunohistochemistry. Results In CD, increased TGF‐β1 and IGF‐1 mRNA expression was transmural. In UC, the increase was confined to the lamina propria and submucosa. In both, distribution of TGF‐β1 and IGF‐1 protein matched mRNA expression and coincided with the distribution of the inflammatory infiltrate. An increase in the collagen type III:I ratio in both CD and UC also coincided with the inflammatory infiltrate. Conclusions These findings suggest that TGF‐β1 and IGF‐1 are involved in intestinal ECM remodeling in IBD, and their enhanced expression depends on the presence and location of inflammatory infiltrates rather than the type of IBD.