NF-E2-Related Factor 2 Suppresses Intestinal Fibrosis by Inhibiting Reactive Oxygen Species-Dependent TGF-β1/SMADs Pathway

This study aimed to evaluate the antifibrotic effects of NF-E2-Related Factor 2 (Nrf2) on intestinal fibrosis. Intestinal fibrosis is a common complication of Crohn's disease; however, its mechanism of intestinal fibrosis is largely unclear. BALB/c mice received 2,4,6-trinitrobenzene sulfonic acid weekly via intrarectal injections to induce chronic fibrotic colitis. They also diet containing received 1% (w/w) tert-butylhydroquinone (tBHQ), which is an agonist of Nrf2. Human intestinal fibroblasts (CCD-18Co cells) were pretreated with tBHQ or si-Nrf2 followed by stimulation with transforming growth factor-beta 1 (TGF-beta 1), which transformed the cells into myofibroblasts. The main fibrosis markers such as alpha-smooth muscle actin, collagen I, tissue inhibitor of metalloproteinase-1, and TGF-beta 1/SMADs signaling pathway were detected by quantitative real-time RT-PCR, immunohistochemical analysis, and Western blot analysis. Levels of cellular reactive oxygen species (ROS) were detected by dichlorodihydrofluorescein diacetate. tBHQ suppressed the intestinal fibrosis through the TGF-beta 1/SMADs signaling pathway in TNBS-induced colitis and CCD-18Co cells. Moreover, Nrf2 knockdown enhanced the TGF-beta 1-induced differentiation of CCD-18Co cells. ROS significantly increased in TGF-beta 1-stimulated CCD-18Co cells. Pretreatment with H2O2, the primary component of ROS, was demonstrated to block the effect of tBHQ on reducing the expression of TGF-beta 1. Moreover, scavenging ROS by N-acetyl cysteine could inhibit the increasing expression of TGF-beta 1 promoted by Nrf2 knockdown. The results suggested that Nrf2 suppressed intestinal fibrosis by inhibiting ROS/TGF-beta 1/SMADs pathway in vivo and in vitro.