Domain I-IV of ß2-glycoprotein I inhibits advanced glycation end product-induced angiogenesis by down-regulating vascular endothelial growth factor 2 signaling.

Advanced glycation end products (AGEs) are a contributing factor in the angiogenesis that is characteristic of proliferative diabetic retinopathy. However, a previous study made a promising observation that domain I­IV of ß2­glycoprotein I (DI­IV) inhibits angiogenesis in human umbilical vein cells. The present study aimed to confirm the inhibition of AGE­induced angiogenesis in retinal endothelial cells by DI­IV and to investigate the potential underlying mechanisms. The RF/6A rhesus macaque choroid­retinal vascular endothelial cell line was cultured in vitro and treated with AGEs in the presence or absence of different concentrations of DI­IV. The proliferation, migration and tube formation of the RF/6A cells were evaluated using MTS assays, in vitro wound healing assays and in vitro Matrigel angiogenesis assays, respectively. The mRNA expression of vascular endothelial growth factor (VEGF), VEGF receptor (VEGFR) 2, VEGFR 1 and receptor for AGE (RAGE) were quantified by reverse transcription quantitative polymerase chain reaction. The expression of VEGFR­1, VEGFR­2 and the activation of protein kinase B (Akt) and extracellular signal­regulated kinase (ERK) were also assessed by western blot analysis. The results indicated that AGEs promoted the migration, proliferation and tube formation of RF/6A cells in vitro (P<0.05), increased the expression of VEGF, VEGFR­2 and RAGE (P<0.05) and increased the phosphorylation of Akt and ERK (P<0.05). DI­IV inhibited the increase in VEGFR­2 mRNA and protein, but did not inhibit the increase in VEGF or RAGE mRNAs. These results led to the conclusion that DI­IV inhibited AGE­induced angiogenesis in the RF/6A cells, which was accompanied by a downregulation in the expression of VEGFR­2 and its downstream phosphatidylinosol 3­kinase/Akt and mitogen­activated protein kinase/ERK1/2 pathways. These findings provide further support towards the treatment of proliferative diabetic retinopathy by interventions that act via a mechanism similar to that of DI­IV.

Reduced ß­2­glycoprotein І inhibits hypoxia­induced retinal angiogenesis in neonatal mice through the vascular endothelial growth factor pathway.

ß­2­glycoprotein I (ß2GPI), also known as apolipoprotein H, is a phospholipid­binding plasma protein consisting of five homologous repeated units. ß2GPI downregulates vascular endothelial growth factor (VEGF) signaling pathways and inhibits angiogenesis in vitro. However, the in vivo roles and effectors of reduced ß2GPI and ß2GPI in retinal angiogenesis are still not fully understood. In this study, an oxygen­induced retinopathy model was used to investigate the effects of reduced ß2GPI and ß2GPI, and to monitor the expression of VEGF, VEGF receptor (VEGFR) 1, VEGFR­2 and hypoxia­inducible factor 1 (HIF­1) mRNA and the phosphorylation of extracellular signal­regulated kinase (ERK) and Akt. The data showed that both ß2GPI and reduced ß2GPI inhibited retinal angiogenesis and suppressed the expression of VEGF, VEGFR­1, VEGFR­2, HIF­1, phosphorylated- (p­) ERK and p­Akt. The effects of reduced ß2GPI were significantly stronger than those of ß2GPI. In conclusion, this study showed that ß2GPI and reduced ß2GPI could inhibit retinal angiogenesis by downregulating the expression of VEGF and its downstream targets. This suggests that ß2GPI and reduced ß2GPI may have potential anti­angiogenic activity in vivo.