Potential role for SNAIL family transcription factors in the etiology of Crohn's disease-associated fistulae.

BACKGROUND: Fistulae represent an important clinical complication of Crohn's disease (CD). The fistula tracts are covered by flat, myofibroblast-like cells with an epithelial origin (transitional cells, TC). We recently demonstrated a role of epithelial mesenchymal transition (EMT) in the pathogenesis of CD-associated fistulae. EMT is associated with an increased migratory and invasive potential of epithelial cells in different tissues. Here we investigated whether cytokines or growth factors as well as EMT-associated SNAIL family transcription factors are expressed in CD fistulae.

METHODS: By immunohistochemistry we analyzed seven perianal fistulae from seven CD and two perianal fistulae from two non-inflammatory bowel disease (IBD) control patients. Hematoxylin and eosin staining or immunohistochemistry for the expression of tumor necrosis factor (TNF), TNF-receptor I (TNF-RI), SNAIL1, SLUG, fibroblast growth factors (FGF) 1, 2, 4, 7, epidermal growth factor (EGF), and TWIST were performed using standard techniques.

RESULTS: Immunohistochemical staining of surgical specimens from CD patients revealed a strong expression of TNF and TNF-RI in and around fistula tracts. While SNAIL1 was also heavily expressed in the nuclei of TC, indicative of transcriptionally active protein, SLUG, FGF-1, and FGF-2 were detected rather in the fibrotic periphery of CD fistulae than in TC. In contrast, we did not detect considerable protein staining for FGF-4 and FGF-7 nor of EGF or the transcription factor, TWIST.

CONCLUSIONS: Our data demonstrate that SNAIL1 and TNF are strongly expressed in TC of CD-associated fistulae. These observations support our previous data and indicate the onset of EMT-associated events in the pathogenesis of CD fistulae.