The natural protective mechanism against hyperglycemia in vascular endothelial cells: Roles of the lipid peroxidation product 4-hydroxydodecadienal and peroxisome proliferator-activated receptor δ

OBJECTIVE - Vascular endothelial cells (VECs) downregulate their rate of glucose uptake in response to hyperglycemia by decreasing the expression of their typical glucose transporter GLUT-1. Hitherto, we discovered critical roles for the protein calreticulin and the arachidonic acid-metabolizing enzyme 12-lipoxygenase in this autoregulatory process. The hypothesis that 4-hydroxydodeca-(2E,6Z)-dienal (4-HDDE), the peroxidation product of 12-lipoxygenase, mediates this downregulatory mechanism by activating peroxisome proliferator-activated receptor (PPAR) δ was investigated. RESEARCH DESIGN AND METHODS - Effects of 4-HDDE and PPARδ on the glucose transport system and calreticulin expression in primary bovine aortic endothelial cells were evaluated by pharmacological and molecular interventions. RESULTS - Using GW501516 (PPARδ agonist) and GSK0660 (PPARδ antagonist), we discovered that high-glucose-induced downregulation of the glucose transport system in VECs is mediated by PPARδ. A PPAR-sensitive luciferase reporter assay in VECs revealed that high glucose markedly increased luciferase activity, while GSK0660 abolished it. High-performance liquid chromatography analysis showed that high-glucose incubation substantially elevated the generation of 4-HDDE in VECs. Treatment of VECs, exposed to normal glucose, with 4-HDDE mimicked high glucose and downregulated the glucose transport system and increased calreticulin expression. Like high glucose, 4-HDDE significantly activated PPARδ in cells overexpressing human PPAR (hPPAR)δ but not hPPARα, -γ1, or -γ2. Moreover, silencing of PPARδ prevented high-glucose-dependent alterations in GLUT-1 and calreticulin expression. Finally, specific binding of PPARδ to a PPAR response element in the promoter region of the calreticulin gene was identified by utilizing a specific chromatin immunoprecipitation assay. CONCLUSIONS - Collectively, our data show that 4-HDDE plays a central role in the downregulation of glucose uptake in VECs by activating PPARδ.