Pigment epithelium-derived factor inhibits TNF-α-induced interleukin-6 expression in endothelial cells by suppressing NADPH oxidase-mediated reactive oxygen species generation

Pigment epithelium-derived factor (PEDF) has recently been shown to be involved in the pathogenesis of proliferative diabetic retinopathy. Atherosclerosis is an inflammatory-fibroproliferative disease as well. Oxidative stress plays a major role in retinopathy and atherosclerosis. Accordingly, we investigated effects of PEDF on reactive oxygen species (ROS) generation, NF-κB activation and interleukin (IL)-6 expression in TNF-α-exposed HUVEC. TNF-α significantly increased intracellular ROS generation, which was completely blocked by PEDF or diphenylene iodonium, an inhibitor of NADPH oxidase. Further, PEDF completely prevented the TNF-α-induced increase in NADPH oxidase activity. PEDF or an antioxidant, N-acetylcysteine, significantly inhibited the TNF-α-induced NF-κB activation. PEDF inhibited TNF-α-induced expression of IL-6 at both mRNA and protein levels. Moreover, TNF-α downregulated PEDF mRNA levels. Ligand blot analysis revealed that HUVEC possessed a membrane protein with binding affinity for PEDF. The results demonstrated that PEDF inhibited TNF-α-induced NF-κB activation and subsequent IL-6 overexpression in HUVEC by suppressing NADPH oxidase-mediated ROS generation. Our present study suggests that PEDF may play an important role in the development and progression of atherosclerosis.