Peroxisome proliferator-activated receptor γ is required for the inhibitory effect of ciglitazone but not 15-deoxy-Δ12,14-prostaglandin J2 on the NFκB pathway in human endothelial cells

Peroxisome proliferator-activated receptor gamma (PPAR gamma) is a ligand-activated nuclear receptor with effects on inflammation, atherosclerosis, and apoptosis. The endogenous PPAR gamma ligand, 15-deoxy-Delta (12,14)- PGJ(2) (15d-PGJ(2)), and the synthetic ligand, ciglitazone, have anti-inflammatory properties in endothelial cells. In addition to PPAR gamma-dependent effects on the anti-inflammatory process, it has been proposed that PPAR gamma ligands may also inhibit the nuclear transcription factor kappa B (NF kappa B) pathway in a PPAR gamma-independent manner. The purpose of this study was to compare the effects of 15d-PGJ(2) and ciglitazone on the cytokine-induced activation of the NF kappa B pathway. Human umbilical vein endothelial cells (HUVECs) were transiently transfected with NFKB-luciferase or PPAR gamma elements-lucif erase reporter constructs for 48 h. The HUVECs were pretreated with 15d-PGJ(2) or ciglitazone (30 P mu M) for 1 h, followed by a 4-h stimulation with tumor necrosis factor a (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 a increased NF kappa B activation while decreasing PPAR gamma activity. Overexpression of a dominant-negative PPAR gamma mutant prevented the inhibitory effect of ciglitazone on cytokine-induced NF gamma B activation in transfected human endothelial cells. Conversely, 15d-PGJ(2) inhibited the cytokine-induced NF kappa B activation even in the absence of PPAR gamma. Our data suggest that 15d-PGJ(2) exerts direct inhibitory effects on the NF kappa B pathway through a PPAR gamma-independent mechanism. On the contrary, the inhibitory effect of ciglitazone on the NF kappa B pathway seems to require PPAR gamma activation.