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Published on: August 20, 2016
Effect of the BMP4-Smad pathway on corneal immune double-arm and mechanism study
Yuxiao Guo1, Yan Niu1, Qi Zhu2
1The Second Clinical Medical College of Jilin University, Changchun 130012, Jilin Province, China.
Abstract:
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.
Insights
Bone morphogenetic protein 4 (BMP4) restrains corneal neovascularization and lymphangiogenesis by activating the BMP4-Smad pathway, preserving immune privilege after eye injury.
Area of Science:
- Ophthalmology
- Immunology
- Molecular Biology
Background:
- Corneal neovascularization (CNV) and lymphangiogenesis (CL) impair corneal immune privilege and lead to transplant rejection.
- The BMP4-Smad pathway's role in regulating these vascular responses in the cornea is not fully understood.
Purpose of the Study:
- To investigate how the bone morphogenetic protein 4 (BMP4)-Smad pathway regulates both vascular and lymphatic components of the corneal wound healing response.
Main Methods:
- Bioinformatic analysis of corneal suture-injury datasets.
- In vitro studies using endothelial cells (HUVEC, HLEC) treated with BMP4 and Noggin.
- In vivo studies using a rat corneal suture model with BMP4 and Noggin administration.
- Immunohistochemistry, electron microscopy, and molecular assays to assess vascularization and inflammation.
Main Results:
- BMP4 inhibited endothelial cell proliferation and migration in vitro and suppressed CNV and CL in vivo.
- BMP4 activated the canonical BMP4-Smad1/5/8 signaling pathway, confirmed by increased p-Smad1/5/8 and nuclear translocation.
- BMP4 reduced inflammatory cell infiltration and induced endogenous BMP4 expression, suggesting a self-amplifying loop.
Conclusions:
- BMP4 coordinately restrains both vascular and lymphatic corneal neovascularization via the BMP4-Smad1/5/8 pathway.
- BMP4 may be a therapeutic target to preserve corneal immune privilege during injury repair.
