Regulation of vascular endothelial growth factor expression by advanced glycation end products

Advanced glycation end products (AGEs) are generated during long term diabe tes and are correlated with the development of diabetic complications, such as retinopathy. Diabetic retinopathy is characterized by an increased reti nal neovascularization due to the action of the angiogenic factor, vascular endothelial growth factor (VEGF). In this report, we show that injection o f insulin and glycated albumin (Alb-AGE) to mice increases VEGF mRNA expres sion in eyes. Insulin and Alb-AGE stimulate VEGF mRNA and protein expressio n in retinal epithelial cells (ARPE-19). Alb-AGE-induced VEGF expression is not modulated by the use of antioxidants, N-acetyl-L-cysteine or pyrrolidi nedithiocarbamate, or by an inhibitor of phosphatidylinositol 3-kinase (PI3 K), wortmannin. However, using an inhibitor of ERK activation, U0126, we sh ow that Alb-AGE stimulates VEGF expression through an ERK-dependent pathway . Accordingly, we found that Alb-AGE activated mitogen-activate protein kin ase, ERK1/2, JNK1/2, but not p38, and that Alb-AGE did not activate PI3K an d PKB. Moreover, Alb-AGE activated the transcription factor, hypoxia induci ble factor-1 (HIF-1) DNA binding activity. This activation is mediated by a n increase in accumulation of the HIF-1 alpha protein through an ERK-depend ent pathway. Thus, stimulation of VEGF expression by Alb-AGE, through the a ctivation of HIF-1, could play an important role in the development of diab etic retinopathy.