Involvement Of Apelin/APJ System In Laser-induced Choroidal Neovascularization

Abstract

Purpose: : The apelin/apelin receptor (APJ) system has been reported to modulate developmental angiogenesis during early embryogenesis and pathogenic angiogenesis. The deficiency of apelin was reported to inhibit abnormal vessels in a mouse model of oxygen-induced retinopathy. We investigated its potential role in the formation of choroidal neovascularization (CNV) in a laser-induced CNV mouse model.

Methods: : CNV was induced in normal wild-type (WT) and apelin knockout (KO) mice by laser photocoagulation. The gene expression of apelin and APJ at 2, 4, and 7 days after laser photocoagulation was determined by quantitative real-time reverse transcription-polymerase chain reaction. The expression of APJ in laser induced CNV of WT mice was examined by immunohistochemistry with rat monoclonal anti- PECAM-1. The incidence and the size of CNV were compared in between apelin KO mice and WT mice 7 days after laser administration using the image of Alexa488-isolectin B4 labeled tissue in the choroidal flat mounts on a fluorescence microscope.

Results: : In WT mice, the expression of apelin significantly increased with a peak at 2 days after laser application (n=6, 5.98 ± 0.31 fold at 2 days (p<0.0001), 2.31 ± 0.27 fold at 4 days (p=0.099) and 1.92 ± 0.27 fold at 7 days (p=0.307) versus control). The APJ expression significantly increased at day 4 and day 7 (n=5, 2.94 ± 0.35 fold at 2 days (p=0.272), 7.13 ± 0.23 fold at 4 days (p<0.0001) and 7.74 ± 0.25 fold at 7 days (p<0.0001) versus control). APJ was detected in PECAM-1 positive endothelial cells in CNV by immunohistochemistry. The incidence of CNV visualized was similar, 75.0% (33 lesions / 44 shots) and 78.1% (50 lesions / 64 shots) in WT and apelin-KO mice, respectively. On the other hand, the size of CNV lesions in the apelin KO mice (22800 ± 6200μm², n=9) were significantly smaller than those in the WT mice (36300 ± 9600μm² , n=10)(p=0.047).

Conclusions: : The endogenous expression of apelin and APJ increased thorough the course of the development of CNV. The size of laser-induced CNV in apelin-KO mice was reduced comparing with WT mice. Those results suggest the involvement of apelin/APJ system in the formation of CNV.

Keywords: age-related macular degeneration • choroid: neovascularization • pathology: experimental