Peroxisome proliferator-activated receptor γ ligands stimulate endothelial nitric oxide production through distinct peroxisome proliferator-activated receptor γ-dependent mechanisms

Objective - We recently reported that the peroxisome proliferator-activated receptor gamma (PPAR gamma) ligands 15-deoxy-gamma(12,14)-prostaglandin J(2) (15d-PGJ(2)) and ciglitazone increased cultured endothelial cell nitric oxide ( NO) release without increasing the expression of endothelial nitric oxide synthase ( eNOS). The current study was designed to characterize further the molecular mechanisms underlying PPAR gamma-ligand-stimulated increases in endothelial cell NO production. Methods and Results - Treating human umbilical vein endothelial cells ( HUVEC) with PPAR gamma ligands ( 10 mu mol/L 15d-PGJ(2), ciglitazone, or rosiglitazone) for 24 hours increased NOS activity and NO release. In selected studies, HUVEC were treated with PPAR gamma ligands and with the PPAR gamma antagonist GW9662 ( 2 mu mol/L), which fully inhibited stimulation of a luciferase reporter gene, or with small interfering RNA to PPAR gamma, which reduced HUVEC PPAR gamma expression. Treatment with either small interfering RNA to PPAR gamma or GW9662 inhibited 15d-PGJ(2)-, ciglitazone-, and rosiglitazone-induced increases in endothelial cell NO release. Rosiglitazone and 15d-PGJ(2), but not ciglitazone, increased heat shock protein 90-eNOS interaction and eNOS ser(1177) phosphorylation. The heat shock protein 90 inhibitor geldanamycin attenuated 15d-PGJ(2)- and rosiglitazone-stimulated NOS activity and NO production. Conclusions - These findings further clarify mechanisms involved in PPAR gamma-stimulated endothelial cell NO release and emphasize that individual ligands exert their effects through distinct PPAR gamma-dependent mechanisms.