Downregulation of microsomal prostaglandin E synthase-1 (mPGES-1) expression in chondrocytes is regulated by MAP kinase phosphatase-1 (MKP-1)

Objectives: Microsomal prostaglandin E synthase-1 (mPGES-1) catalyses the formation of PGE(2) in inflammatory tissues. It is considered a potential drug target in inflammatory conditions to achieve clinical benefits comparable to NSAIDs with a better tolerability. Inhibitors of mPGES-1 are under development but the pharmacological regulation of mPGES-1 expression remains poorly known. MAP kinase phosphatase-1 (MKP-1) is an enzyme that limits the activity of pro-inflammatory MAP kinases p38 and JNK. In the present study, we discovered that dexamethasone down-regulates mPGES-1 expression in articular chondrocytes in an MKP-1 and p38 kinase dependent manner. Methods: Primary human chondrocytes were isolated from cartilage samples obtained from osteoarthritis (OA) patients undergoing knee replacement surgery. Primary mouse chondrocytes were isolated from cartilage samples of MKP-1 deficient (knock-out, KO) and corresponding wild type (WT) mice. Expression of mPGES-1 and MKP-1 were measured by quantitative reverse transcription polymerase chain reaction (qRT-PCR) and Western blot, and MAP kinase phosphorylation by Western blot. Results: Dexamethasone inhibited the expression of mPGES-1 in primary human chondrocytes and in chondrocytes from wild type but not from MKP-1 deficient mice. Dexamethasone enhanced MKP-1 expression in chondrocytes from wild type mice as well as in primary human OA chondrocytes. Dexamethasone induced the dephosphorylation of both p38 and JNK, whereas mPGES-1 expression was downregulated by selective inhibitors of p38 only. Conclusions: The results show that MICP-1 is a crucial mediator of pharmacological control of inflammatory mPGES-1 expression by glucocorticoids, and underline MKP-1 as a potential anti-inflammatory drug target.