PEROXISOME PROLIFERATOR-ACTIVATED RECEPTOR γ IS REQUIRED FOR THE INHIBITORY EFFECT OF CIGLITAZONE BUT NOT 15-DEOXY-Δ12,14-PROSTAGLANDIN J2ON THE NFκB PATHWAY IN HUMAN ENDOTHELIAL CELLS

Peroxisome proliferator-activated receptor γ (PPARγ) is a ligand-activated nuclear receptor with effects on inflammation, atherosclerosis, and apoptosis. The endogenous PPARγ ligand, 15-deoxy-Δ12,14-PGJ2(15d-PGJ2), and the synthetic ligand, ciglitazone, have anti-inflammatory properties in endothelial cells. In addition to PPARγ-dependent effects on the anti-inflammatory process, it has been proposed that PPARγ ligands may also inhibit the nuclear transcription factor κB (NFκB) pathway in a PPARγ-independent manner. The purpose of this study was to compare the effects of 15d-PGJ2and ciglitazone on the cytokine-induced activation of the NFκB pathway. Human umbilical vein endothelial cells (HUVECs) were transiently transfected with NFκB-luciferase or PPARγ elements-luciferase reporter constructs for 48 h. The HUVECs were pretreated with 15d-PGJ2or ciglitazone (30 μM) for 1 h, followed by a 4-h stimulation with tumor necrosis factor α (100 U/mL). Luciferase assay was performed to determine reporter activity. Additionally, HUVECs were transiently transfected with a dominant-negative mutant, which retains ligand and DNA binding but exhibits markedly reduced transactivation. Stimulation of HUVEC with tumor necrosis factor α increased NFκB activation while decreasing PPARγ activity. Overexpression of a dominant-negative PPARγ mutant prevented the inhibitory effect of ciglitazone on cytokine-induced NFκB activation in transfected human endothelial cells. Conversely, 15d-PGJ2inhibited the cytokine-induced NFκB activation even in the absence of PPARγ. Our data suggest that 15d-PGJ2exerts direct inhibitory effects on the NFκB pathway through a PPARγ-independent mechanism. On the contrary, the inhibitory effect of ciglitazone on the NFκB pathway seems to require PPARγ activation.