The antiinflammatory effect of laminar flow:: The role of PPARγ, epoxyeicosatrienoic acids, and soluble epoxide hydrolase

We previously reported that laminar flow activates peroxisome proliferator-activated receptor gamma (PPAR gamma) in vascular endothelial cells in a ligand-dependent manner that involves phospholipase A2 and cytochrome P450 epoxygenases. In this study, we investigated whether epoxyeicosatrienoic acids (EETs), the catalytic products of cytochrome P450 epoxygenases, are PPAR gamma ligands. Competition and direct binding assays revealed that EETs bind to the ligand-binding domain of PPAR gamma with K-d in the mu M range. In the presence of adamantyl-ureido-dodecanoic acid (AUDA), a soluble epoxide hydrolase (sEH)-specific inhibitor, EETs increased PPAR gamma transcription activity in endothelial cells and 3T3-L1 preadipocytes. Inclusion of AUDA in the perfusing media enhanced, but overexpression of sEH reduced, the laminar flow-induced PPAR gamma activity. Furthermore, laminar flow augmented cellular levels of EETs but decreased sEH at the levels of mRNA, protein, and activity. Blocking PPAR gamma by GW9662 abolished the EET/AUDA-mediated antiinflammatory effect, which indicates that PPAR gamma is an effector of EETs.