Effect of the BMP4-Smad pathway on corneal immune double-arm and mechanism study.

Corneal neovascularization (CNV) and corneal lymphangiogenesis (CL) disrupt corneal immune privilege after injury and drive transplant rejection. This study investigated how the bone morphogenetic protein 4 (BMP4)-Smad pathway regulates both vascular arms of the corneal wound response. Bioinformatic analysis of a rat corneal suture-injury dataset showed that sustained injury induced a coordinated inflammatory, angiogenic, lymphangiogenic, and BMP/TGFβ-Smad transcriptional program, with predicted SMAD5-binding motifs in vascular- and lymphatic-related gene promoters. In vitro, BMP4 inhibited the proliferation and migration of human umbilical vein endothelial cells (HUVEC) and human lymphatic endothelial cells (HLEC) and downregulated CD31, VEGFA, LYVE-1, and VEGFC, whereas the BMP antagonist Noggin reversed these effects. BMP4 increased phosphorylated Smad1/5/8 (p-Smad1/5/8) and promoted its nuclear translocation, confirming canonical pathway activation. In a rat corneal suture model, BMP4 reduced inflammatory-cell infiltration and suppressed CNV and CL, as demonstrated by slit-lamp examination, lineage-resolved CD31/CD45 and LYVE-1/Prox1 co-staining, transmission electron microscopy, and molecular assays; Noggin antagonized each effect. BMP4 further activated corneal p-Smad1/5/8 signaling and induced endogenous BMP4 expression in a Noggin-sensitive manner, suggesting a self-amplifying loop. Together, these findings indicate that BMP4 coordinately restrains the vascular and lymphatic arms of the corneal immune response through canonical BMP4-Smad1/5/8 signaling and may help preserve corneal immune privilege during injury repair.