MBNL1 Promotes Intestinal Fibrosis via RAS-MAPK Pathway-Mediated Fibroblast Activation and Proliferation

Background: Intestinal fibrosis is a severe complication of Crohn's disease (CD) with no effective therapies currently available. Muscleblind-like protein 1 (MBNL1) is an RNA-binding protein that has been implicated in fibrosis across multiple organs, but its role in CD-associated intestinal fibrosis remains unexplored. This study aims to investigate the expression, functional role, and underlying mechanism of MBNL1 in intestinal fibrosis. Methods: MBNL1 expression was examined in a TNBS-induced mouse model and in stenotic intestinal tissues from CD patients. In vitro, human colonic fibroblasts (CCD-18Co) were stimulated with transforming growth factor-β1 (TGF-β1) to model fibrosis. MBNL1 was knocked down or overexpressed to assess its effects on fibroblast activation, proliferation (5-ethynyl-2'-deoxyuridine, EdU; Cell Counting Kit-8, CCK-8), and apoptosis (flow cytometry). Potential downstream pathways were predicted using BioGRID and DAVID analyses and validated by Western blot. A rescue experiment with the RAS activator ML-097 was performed to confirm pathway dependency. Results: MBNL1 expression was significantly upregulated in fibrotic tissues from both the mouse model and CD patients, as well as in TGF-β1-stimulated CCD-18Co. MBNL1 knockdown suppressed TGF-β1-induced fibroblast activation and proliferation while promoting apoptosis, whereas MBNL1 overexpression had the opposite effect. Mechanistically, MBNL1 positively regulated the RAS-MAPK signaling pathway. Reactivation of this pathway with ML-097 reversed the inhibitory effects of MBNL1 knockdown on fibroblast activation and proliferation. Conclusions: MBNL1 promotes colonic fibroblast activation and proliferation by activating the RAS-MAPK signaling pathway, establishing it as a potential therapeutic target for intestinal fibrosis in Crohn's disease.