Sophocarpine, a bioactive alkaloid derived from Sophora flavescens, alleviates subretinal fibrosis by suppressing epithelial-mesenchymal transition

Subretinal fibrosis (SF) is a vision-threatening complication of neovascular age-related macular degeneration (nAMD) with no effective treatment. Epithelial-mesenchymal transition (EMT) of retinal pigment epithelial (RPE) cells, driven by TGF-β signaling, is a key driver of SF. Sophocarpine (SOP) shows anti-fibrotic potential in other organs, but its role in ocular fibrosis remains unknown. To evaluate SOP’s therapeutic efficacy against SF and elucidate whether it inhibits TGF-β-induced RPE-EMT. Retinal safety of intravitreal SOP was assessed in C57BL/6J mice by electroretinography and histology. A laser-induced choroidal neovascularization (CNV) mouse model was used to evaluate SOP effects on SF in vivo. In vitro, TGF-β1-induced EMT models in ARPE-19 and iPSC-RPE cells were established. EMT markers were analyzed by qPCR, Western blot, and immunofluorescence. Functional assays included wound healing, Transwell migration, and gel contraction. RNA-seq and molecular docking explored mechanisms. Intravitreal SOP (200 µM) showed no detectable acute retinal toxicity. SOP reduced CNV lesion size, collagen deposition, and α-SMA/RPE65 co-localization in laser-induced mice. In vitro, SOP suppressed TGF-β1-induced upregulation of fibronectin, α-SMA, and vimentin, preserved ZO-1, and reduced migration and contraction in RPE cells. Mechanistically, SOP preferentially reduced MEK/ERK and p38 MAPK phosphorylation without affecting Smad2/3. Molecular docking and molecular dynamics simulations predict binding of SOP to MEK1, MEK2, and ERK2. SOP attenuated experimental SF and suppressed TGF-β1-induced EMT-like changes in RPE cells, in association with reduced MEK/ERK and p38 MAPK signaling. SOP represents a promising preclinical candidate that warrants further investigation.