Effect of Peroxisome Proliferator Activated Receptor (PPAR)7 agonists on prostaglandins cascade in joint cells

摘要

In response to inflammatory cytokines, chondrocytes and synovial fibroblasts produce high amounts of prostaglandins (PG) which self-perpetuate locally the inflammatory reaction. Prostaglandins act primarily through membrane receptors coupled to G proteins but also bind to nuclear Peroxisome Proliferator-Activated Receptors (PPARs). Amongst fatty acids, the cyclopentenone metabolite of PGD2,15-deoxy-A12,14PGJ2 (15d-PGJ2), was shown to be a potent ligand of the PPAR7 isotype prone to inhibit the production of inflammatory mediators. As the stimulated synthesis of PGE2 originates from the preferential coupling of inducible enzymes, cyclooxygenase-2 (COX-2) and membrane PGE synthase-1 (m PGES-1), we investigated the potency of 15d-PGJ2 to regulate prostaglandins synthesis in rat chondrocytes stimulated with interleukin-1beta (IL-lbeta). We demonstrated that 15d-PGJ2, but not the high-affinity PPAR7 ligand rosiglitazone, decreased almost completely PGE2 synthesis and m PGES-1 expression. The inhibitory potency of 15d-PGJ2 was unaffected by changes in PPAR7 expression and resulted from inhibition of NF-re B nuclear binding and I獴alpha sparing, secondary to reduced phosphorylation of IKKbeta. Consistently with 15d-PGJ2 being a putative endogenous regulator of the inflammatory reaction if synthesized in sufficient amounts, the present data confirm the variable PPAR7-dependency of its effects in joint cells while underlining possible species and cell types specificities.