Crohn’s & Colitis Congress™

Sessions Speakers Exhibitors Floor Plan Buzz

P033 - EPIGENETIC SILENCING OF SMAD7 CONTRIBUTES TO FIBROSIS IN STRICTURING CROHN’S DISEASE (Room Poster Hall)

TGF-β1 is a central pro-fibrotic cytokine in stricturing Crohn’s disease. Its affects are normally inhibited by increased Smad7 expression. We have shown that Smad7 is silenced in stricturing Crohn’s disease by TGF-β1 activated, Smad3-dependent expression of miR-21 resulting in sustained Smad3 activity and increased collagen I production. Smad7 expression can also be silenced by CpG island methylation or its protein levels diminished by deacetylation which allows E3 ubiquitin ligase-dependent proteosomal degradation via Smurf1/2. AIM: To determine whether Smad7 is silenced by increased promoter methylation or whether Smad7 is deacetylated and targeted for ubiquitination by Smurf1/2. METHODS: Subepithelial myofibroblasts (SEMF) were isolated separately from normal and strictured in the same patient with stricturing Crohn’s disease and placed into primary culture for these studies. SEMF were used for treatment with inhibitors or transfected with siRNA. RESULTS: TGF-β1 treatment of normal ileal SEMF elicited Smad3-dependent increase in Smurf1 and 2 and a concomitant decrease in Smad7 levels. Levels of acetylated Smad7 were lower and levels of Smad7 ubiquitination higher in SEMF of strictured compared to normal ileum. HDAC1 activity and HDAC1-dependent Smad7 deacetylation were also increased in these cells. Treatment of SEMF from strictured ileum with Smurf 1 or 2 inhibitors, or siRNA mediated knockdown resulted in increased Smad7 levels. DNA methyltransferase-1 was increased is SEMF of strictured ileum compared to normal. Treatment of SEMF with 5’Aza, a demethylating agent, increased Smad7 levels by decreasing CpG island methylation in its promoter. CONCLUSION: Smad7 is silenced in SEMF of ileum in patients with stricturing Crohn’s disease via miR-21 mediated mRNA degradation, DNMT-1 mediated promoter methylation, and also by Smurf1/2 mediated ubiquitination. This results in sustained TGF- β1 signaling, excess collagen I expression and development of fibrosis.