15-Deoxy-delta12,14-prostaglandin-J2 up-regulates cyclooxygenase-2 but inhibits prostaglandin-E2 production through a thiol antioxidant-sensitive mechanism

15-Deoxy-delta12,14-prostaglandin-J2 (15d-PGJ2) has potent anti-inflammatory effects including the inhibition of interleukin-1β (IL-1β)-induced expression of cyclooxygenase-2 (COX-2) and prostaglandin E2 (PGE2) production in several cell types. 15d-PGJ2 contains an α,β-unsaturated electrophilic ketone and several evidences suggest that thiol reducing agents prevent or revert the cellular effects of 15d-PGJ2. The present study was devoted to analyze the effect of 15d-PGJ2 on COX-2 expression in cultured human mesangial cells (HMC). 15d-PGJ2 induced an increase in the reduced glutathione (GSH) content and up-regulated COX-2 protein expression, but not COX-1, in a manner which was unaffected by selective peroxisome proliferator-activated receptor γ (PPARγ) blockade nor mimicked by ciglitazone, a PPARγ agonist. N-acetylcysteine (NAC), a thiol reducing agent, but not reactive oxygen species scavengers, prevented 15d-PGJ2-induced COX-2 up-regulation. Depletion of GSH by buthionine sulfoximine, which diminishes thiol antioxidant activity, cooperated with 15d-PGJ2 to accumulate COX-2. Therefore, 15d-PGJ2 up-regulated COX-2 through a thiol antioxidant-sensitive mechanism. Interestingly, NAC did not inhibit the COX-2 expression induced by the electrophilic α,β-unsaturated compound PGA2. Up-regulation of COX-2 by 15d-PGJ2 did not result in increased PGE2 production. Furthermore, preincubation with 15d-PGJ2 inhibited IL-1β-induced PGE2 production although IL-1β-induced COX-2 expression remained unaffected by the treatment with 15d-PGJ2. On the contrary, PGA2 elicited an increase in PGE2 production and it acted synergistically with IL-1β to enhance PGE2 production. These results indicate for the first time that 15d-PGJ2 inhibits PGE2 production independently of its effect on COX-2 expression.