Abstract
Purpose: :
To investigate the role of program death ligand-1 (PD-L1) expression on vascular endothelial cell (VEC) proliferation and corneal angiogenesis.
Methods: :
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.
Results: :
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).
Conclusions: :
The expression of PD-L1 and its receptor CD80 on VEC has an inhibitory function on VEC proliferation and angiogenesis.
Keywords: neovascularization • cornea: basic science • vascular endothelial growth factor