Oscillating glucose and constant high glucose induce endoglin expression in endothelial cells: the role of oxidative stress

High glucose-induced oxidative stress has been suggested as one of the mediators of endothelial damage in diabetes. The major endothelial protein, endoglin, has been found overexpressed in the vessels during pathological situations, but little is known about its relation to diabetic vascular complications. To clarify the role of endoglin in endothelial injury, we sought to determine the effects of high and oscillating glucose on its expression. Furthermore, the activation of the Kruppel-like factor 6 (KLF-6) and the hypoxia-inducible factor-1 alpha (HIF-1 alpha) as possible regulators of endoglin expression has been evaluated. The possible role of the oxidative stress has been studied evaluating the effects of the antioxidant alpha-lipoic acid (ALA) and the cellular antioxidant response mediated by NAD(P)H:quinine-oxido-reductase-1 (NQO-1) and heme oxygenase-1 (HO-1). Primary HUVECs were cultured for 21 days in normal, high and oscillating glucose (5, 25 and 5/25 mmol/l every 24 h, respectively) with/without ALA. In oscillating and high glucose total endoglin, its soluble form (sEng), KLF-6 and HIF-1 alpha were significantly increased. Simultaneously, the oxidative DNA stress markers 8-OHdG and H2A.X were elevated. Moreover, ENG gene transcriptional rate increased during glucose exposures concomitantly with increased KLF-6 nuclear translocations. ALA significantly reduced all these phenomena. Interestingly, during oscillating and chronic high glucose, NQO-1 and HO-1 did not increase, but ALA induced their overexpression. Together, these findings provide novel clue about endoglin in the regulation of high glucose-mediated vascular damage in HUVECs and the role of oxidative stress in this regulation.