Inhibition of Smad7 With a Specific Antisense Oligonucleotide Facilitates TGF-β1–Mediated Suppression of Colitis

Background & Aims: Defective transforming growth factor (TGF)-β1 signaling due to high levels of Smad7 is a feature of inflammatory bowel disease (IBD). In this study, we analyzed the effect of reducing Smad7 levels with antisense oligonucleotide on mouse models of colitis. Methods: Mucosal samples taken from colitic tissue of mice with colitis due to either haptenating reagents (trinitrobenzene sulfonic acid [TNBS] or oxazolone) or to transfer of T cells (SCID transfer colitis) were analyzed for Smad3 and/or Smad7 expression by Western blotting and, in some cases, content of TGF-β1 by enzyme-linked immunosorbent assay. The effect of oral Smad7 antisense oligonucleotide on mucosal inflammation was assessed. Results: TGF-β1 levels were increased in the inflamed tissues of mice with colitis induced by either TNBS or oxazolone. Nevertheless, TGF-β1 did not exert a regulatory effect, probably because TGF-β1 signaling was blocked, as indicated by the presence of reduced Smad3 phosphorylation and high levels of Smad7. Oral administration of Smad7 antisense oligonucleotide to colitic mice restored TGF-β1 signaling via Smad3 and ameliorated inflammation in hapten-induced colitis. In addition, Smad7 antisense oligonucleotide had a therapeutic effect on relapsing TNBS-induced colitis but not on cell-transfer colitis. Conclusions: These data suggest that colitis models associated with high endogenous TGF-β1 levels and defective TGF-β1 signaling due to high levels of Smad7 can be ameliorated by down-regulation of Smad7 and by oral administration of Smad7 antisense oligonucleotide. This may represent a new approach to the control of IBD, particularly during active phases when its Smad7 profile resembles that of hapten-induced colitis.