Evidence for a differential expression of fibronectin splice forms ED-A and ED-B in Crohn's disease (CD) mucosa

Background and aims Fibronectin (FN) is an essential factor for the induction of migration of primary colonic lamina propria fibroblasts (CLPF). The FN isoform ED-A is an important inducer of migration. Recently, we have shown that CLPF isolated from inflamed Crohn's disease (CD) mucosa migrated significantly less than control CLPF. We, therefore, investigated changes in IN or integrin expression that could be relevant for CLPF migration. Materials and methods mRNA of control-CLPF and CLPF isolated from fibrotic mucosa of CD patients was subtractively hybridized. Expression of FN, ED-A, and ED-B in frozen sections from intestinal mucosa was determined by immunohistochemistry. The mRNA expression of the FN isoforms in control, CD, and fibrosis biopsies was quantified by real-time polymerase chain reaction (PCR). Integrin alpha 5 beta 1 protein and mRNA expression was analyzed by fluorescence activated cell sorting (FACS) and PCR, respectively. Results Subtractive hybridization indicated differential regulation of FN isoform expression in CD. The immunohistochemical analysis of FN protein revealed a reduction of FN isoforrns in inflamed CD mucosa compared to control mucosa. In CD fistulae, the ED-A and ED-B isoforms were virtually absent. In fibrotic mucosa, both proteins were increased. Real-time PCR showed a decrease of FN and ED-A expression during mucosal inflammation in CD in contrast to UC and a significant increase of FN and isoforms in CD fibrosis. No difference was found for protein and mRNA of integrin alpha 5 beta 1 in control, CD, and fibrosis CLPF by FACS and PCR. Conclusion Downregulated expression of migration-inducing FN-isoforrns in contrast to unchanged FN receptor expression may contribute to the observed alterations of CD CLPF migration.