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Y. Jin, S. K. Chauhan, P. Sage, A. Sharpe, R. Dana; Regulatory Effect of Vascular Endothelial Cell PD-L1 on Angiogenesis. Invest. Ophthalmol. Vis. Sci. 2010;51(13):49.
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To investigate the role of program death ligand-1 (PD-L1) expression on vascular endothelial cell (VEC) proliferation and corneal angiogenesis.
Expression levels of PD-L1, PD-1 and CD80 (B7.1) in MS1 cells (mouse VEC cell line) and primary VEC from murine lung and heart were analyzed using real-time PCR and flow cytometry. PD-L1 and CD80 expression levels in the MS1 cells were inhibited using respective siRNA, and the cell proliferation was then analyzed by BrdU incorporation assay. Neovascularization in the PD-L1 knockout (KO) mice and wild-type (WT) mice were scored during 2 weeks after suture-placement in the cornea using slit-lamp biomicroscopy, and the percentage of CD31hiLYVE-1- blood vessels in the corneas were measured on Day 14 using confocal microscopy. The expression levels of VEGF-A and VEGFR2 on the MS1 cells or the suture-placed corneas were analyzed by real-time PCR.
Both primary murine VEC and MS1 cells expressed PD-L1 and CD80, but not PD-1, at mRNA and protein levels. After inhibition of PD-L1 or CD80 expression in the MS1 cells by siRNA transfection, the mRNA expression level of VEGFR2 and the cell proliferation level were significantly enhanced, compared to the control group (p<0.01, t-test). After suture placement in the cornea, the expression level of VEGFR2 was significantly higher in the PD-L1 KO mice vs. WT mice (p<0.05, t-test). The CD31hiLYVE-1- blood vessel density was significantly promoted in the PDL-1KO group relative to the WT group (22+2% vs.11+1%, n=6 per group, p<0.001, t-test).
The expression of PD-L1 and its receptor CD80 on VEC has an inhibitory function on VEC proliferation and angiogenesis.
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