Roflumilast Inhibits Fibrogenic Activation in Human Intestinal Myofibroblasts via Inhibition of Myocardin-Related Transcription Factor/Serum Response Factor Signaling.

The lack of effective anti-fibrotic agents remains a significant unmet need in the treatment of intestinal fibrosis, a condition largely driven by transforming growth factor-β1 (TGF-β1)-mediated myofibroblast activation. Phosphodiesterase 4 (PDE4) inhibitors, known to increase intracellular cAMP levels, exhibit anti-inflammatory and potential anti-fibrotic properties, though their efficacy in intestinal fibrosis is poorly defined. In this study, we investigated the anti-fibrotic effects and underlying mechanisms of PDE4 inhibitors (rolipram, roflumilast, piclamilast, and mesopram) in human intestinal myofibroblasts (HIMFs) stimulated with TGF-β1. All PDE4 inhibitors significantly reduced TGF-β1-induced mRNA expression of collagen1A1 (COL1A1) and fibronectin (FN1), with mesopram additionally reducing α-smooth muscle actin (ACTA2) mRNA expression. At the protein level, however, only roflumilast significantly decreased procollagen1A1 (Procol1A1) and FN expression. Mechanistically, roflumilast, rolipram, and mesopram significantly reduced serum response factor (SRF) mRNA expression, whereas piclamilast and mesopram significantly inhibited myocardin-related transcription factor A (MRTFA) mRNA expression. Rolipram and roflumilast exhibited a decreasing trend in MRTFA mRNA expression without statistical significance. Notably, roflumilast demonstrated superior inhibitory effects, significantly decreasing both MRTF-A and SRF protein expression and effectively reducing nuclear localization of MRTF-A. Additionally, rolipram and roflumilast significantly attenuated TGF-β1-induced phosphorylation of Smad2. These findings indicate that PDE4 inhibitors, particularly roflumilast, effectively suppress TGF-β1-induced fibrogenic activation in HIMFs by modulating MRTF/SRF and Smad-dependent pathways, highlighting the value of roflumilast for further preclinical investigation as a potential therapeutic strategy for intestinal fibrosis.