Sinominine alleviates pulmonary fibrosis by suppressing macrophage-to-myofibroblast transition via inhibition of the Frem1/NF-κB/IL-1β axis

Background: Idiopathic pulmonary fibrosis (IPF) is a lethal interstitial lung disease with limited therapeutic options. Macrophage-to-myofibroblast transition (MMT) is a pivotal source of matrix-producing process in fibrosis, yet its regulatory mechanisms remain incompletely understood. Methods: We employed a bleomycin (BLM)-induced murine model of IPF and an in vitro MMT model using MH-S alveolar macrophages. Histological (H&E, Masson's trichrome) and molecular (qPCR, Western blot, immunofluorescence) analyses were utilized to assess fibrosis, MMT, and pathway activity. Flow cytometry characterized macrophage populations. Key findings were validated through gene silencing ( Frem1 ) and molecular docking. Results: Sinominine significantly alleviated BLM-induced pulmonary fibrosis and collagen deposition. Mechanistically, SIN potently inhibited the MMT process, as evidenced by reduced expression of Acta2 and Col1a1 . We identified Frem1 as a direct target of SIN, and demonstrated its central role in a pro-fibrotic IL-1β signaling axis. The upregulation of Frem1 activates the MyD88/NF-κB signaling pathway and establishes a pathogenic positive feedback loop that amplifies IL-1β production. Both genetic ablation of Frem1 and direct IL-1β stimulation confirmed its non-redundant role in driving MMT. Crucially, the anti-fibrotic and anti-MMT effects of SIN were mediated through the targeted suppression of this Frem1/NF-κB/IL-1β pathway. Conclusion: Our study unveils a novel mechanism whereby SIN ameliorates pulmonary fibrosis by directly targeting Frem1 to disrupt an IL-1β-driven positive feedback loop and subsequent MMT. • SIN represents a novel therapeutic candidate for IPF by targeting the specific molecular node of Frem1 on macrophages, thereby interrupting the key pathogenic process of Macrophage-to-Myofibroblast Transition (MMT). • Monitoring IL-1β signaling activity or macrophage phenotypic shifts could serve as potential pharmacodynamic biomarkers in future clinical trials to assess SIN's target engagement and efficacy. • This study identifies the Frem1/MyD88/NF-κB/IL-1β axis as a druggable pathway, providing a new mechanistic framework for developing anti-fibrotic therapies that act at the intersection of inflammation and fibroblast activation.