Knockdown of Smad7 With a Specific Antisense Oligonucleotide Attenuates Colitis and Colitis-Driven Colonic Fibrosis in Mice

Background: In Crohn's disease (CD), the pathogenic immune response is associated with high Smad7, an inhibitor of TGF-beta 1 signaling. Smad7 knockdown with Mongersen, a specific antisense oligonucleotide-containing compound, restores TGF-beta 1 activity leading to inhibition of inflammatory signals and associates with clinical benefit in CD patients. As TGF-beta 1 is pro-fibrogenic, it remains unclear whether Mongersen-induced Smad7 inhibition increases the risk of intestinal fibrosis. We assessed the impact of Smad7 inhibition on the course of colitis-driven intestinal fibrosis in mice. Methods: BALB/c mice were rectally treated with increasing doses of trinitrobenzene sulfonic acid (TNBS) for 8 or 12 weeks. The effect of oral Smad7 antisense or control oligonucleotide, administered to mice starting from week 5 or week 8, respectively, on mucosal inflammation and colitis-associated colonic fibrosis was assessed. Mucosal samples were analyzed for Smad7 by immunoblotting and immunohistochemistry, TGF beta 1 by enzyme-linked immunosorbent assay, and collagen by immunohistochemistry. Results: TNBS-induced chronic colitis was associated with colonic deposition of collagen I and fibrosis, which were evident at week 8 and became more pronounced at week 12. TNBS treatment enhanced Smad7 in both colonic epithelial and lamina propria mononuclear cells. Colitic mice treated with Smad7 antisense oligonucleotide exhibited reduced signs of colitis, less collagen deposition, and diminished fibrosis. These findings were associated with diminished synthesis of TGF-beta 1 and reduced p-Smad3 protein expression. Conclusion: Attenuation of colitis with Smad7 antisense oligonucleotide limits development of colonic fibrosis.