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

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. 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. 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. 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.