15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2) signals through retinoic acid receptor-related orphan receptor-α but not peroxisome proliferator-activated receptor-γ in human vascular endothelial cells -: The effect of 15d-PGJ2 on tumor necrosis factor-α-induced gene expression

Objective - 15- Deoxy-Delta(12,14)- prostaglandin J(2) (15d-PGJ2), a natural ligand of the peroxisome proliferator - activated receptor-gamma (PPAR gamma), has been shown to inhibit proinflammatory gene expression, but the signaling mechanisms involved remain unclear. Because retinoic acid receptor - related orphan receptor-alpha (ROR alpha) has been reported to suppress tumor necrosis factor-alpha (TNF-alpha) -induced expression of proinflammatory genes, we hypothesized that 15d-PGJ2 may induce ROR alpha expression resulting in inhibition of proinflammatory gene expression. Methods and Results - We demonstrate that 15d-PGJ2 induced ROR alpha 1 and ROR alpha 4 expression and inhibited TNF-alpha induced vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1) expression in human umbilical vein endothelial cells (HUVECs). In contrast, the synthetic PPAR gamma ligand pioglitazone weakly induced ROR alpha 4 expression but did not affect ROR alpha 1 expression or TNF-alpha-induced gene expression. Biphenol A diglycidyl ether, a PPAR gamma antagonist, did not block the effect of 15d-PGJ2 on ROR alpha expression. Adenovirus-mediated overexpression of ROR alpha 1 inhibited TNF-alpha-induced VCAM-1 and ICAM-1 expression, and overexpression of a mutant form of ROR alpha 1 (ROR alpha 1 Delta), which inhibited transcriptional activity of ROR alpha 1 and ROR alpha 4, attenuated its inhibition. Furthermore, we found that ROR alpha 1 Delta attenuated the inhibitory actions of 15d-PGJ2 on TNF-alpha-induced VCAM-1 and ICAM-1 expression. Conclusions - These results suggest that 15d-PGJ2 inhibits TNF-alpha - induced expression of proinflammatory genes mediated in part via induction of ROR alpha in HUVECs. This mechanism provides a novel insight into PPAR gamma-independent actions of 15d-PGJ2.