The mitochondrial uncoupling protein 2 (UCP2) decreases reactive oxygen species (ROS) formation by mitochondria. Our group previously showed that the UCP2 -866A allele was associated with risk of diabetic retinopathy (DR), which is caused by hyperglycemia-induced oxidative stress. To date, it is still unclear if the -866A allele directly affects UCP2 expression in endothelial cells. Thus, we investigated the effect of the A allele on UCP2 promoter activity in HUVECs treated with high glucose (HG) or hydrogen peroxide (H2O2). To quantify UCP2 promoter activity, HUVECs were transfected with pGL3 plasmids containing the UCP2 promoter and the firefly luciferase coding sequence. Experimental groups were: (1) pGL3-866G-transfected cells and (2) pGL3-866A cells, both under normal (4 mM) or HG (25 mM) concentrations for 24 h and 48 h or incubated with H2O2 (0.1 mM) for 1 h. UCP2 promoter activity was monitored by Luminescent Dual-luciferase Assay. HG induced an upregulation of UCP2 promoter activity in PGL3-866G cells after 24 h of treatment (P = 0.027), but not after 48 h. Compared to pGL3-866G cells, pGL3-866A cells seems to have reduced UCP2 promoter activity following 24 h and 48 h of normal glucose treatment (P = 0.087 and P = 0.022). After HG treatment, pGL3-866A cells had more marked UCP2 downregulation (24 h: - 3.2-folds, P < 0.001; and 48 h: - 2.5-folds, P < 0.001 vs. G cells). Both pGL3-866G and pGL3-866A cells treated with H2O2 showed a ≅ 4-fold increase in UCP2 promoter activity (both P < 0.001). The -866A allele modifies UCP2 promoter activity in HUVECs under HG treatment but not in the H2O2 condition.
Keywords: Diabetic retinopathy; Endothelial cells; High glucose; Oxidative stress; UCP2 polymorphism.