Prostaglandin E2 synthesis in cartilage explants under compression: mPGES-1 is a mechanosensitive gene
1 UMR 7079 CNRS, Physiology and Physiopathology Laboratory, University Paris 6, quai St-Bernard, Paris, 75252 Cedex 5, France
2 Department of Rheumatology, UFR Pierre et Marie Curie, Saint-Antoine Hospital, 75012 Paris, France
3 CNE Neuroendocrine Cellular Interactions, UMR CNRS 6544, Mediterranean University, Faculty of Medecine, 13916 Marseille Cedex 20, France
4 Laboratory on Oro-facial Repair and Replannings EA 2496, University Paris Descartes, Faculty of Odontology, 92120 Montrouge, France
Arthritis Research & Therapy 2006, 8:R135 doi:10.1186/ar2024Published: 27 July 2006
Knee osteoarthritis (OA) results, at least in part, from overloading and inflammation leading to cartilage degradation. Prostaglandin E2 (PGE2) is one of the main catabolic factors involved in OA. Its synthesis is the result of cyclooxygenase (COX) and prostaglandin E synthase (PGES) activities whereas NAD+-dependent 15 hydroxy prostaglandin dehydrogenase (15-PGDH) is the key enzyme implicated in the catabolism of PGE2. For both COX and PGES, three isoforms have been described: in cartilage, COX-1 and cytosolic PGES are constitutively expressed whereas COX-2 and microsomal PGES type 1 (mPGES-1) are inducible in an inflammatory context. COX-3 (a variant of COX-1) and mPGES-2 have been recently cloned but little is known about their expression and regulation in cartilage, as is also the case for 15-PGDH. We investigated the regulation of the genes encoding COX and PGES isoforms during mechanical stress applied to cartilage explants. Mouse cartilage explants were subjected to compression (0.5 Hz, 1 MPa) for 2 to 24 hours. After determination of the amount of PGE2 released in the media (enzyme immunoassay), mRNA and proteins were extracted directly from the cartilage explants and analyzed by real-time RT-PCR and western blotting respectively. Mechanical compression of cartilage explants significantly increased PGE2 production in a time-dependent manner. This was not due to the synthesis of IL-1, since pretreatment with interleukin 1 receptor antagonist (IL1-Ra) did not alter the PGE2 synthesis. Interestingly, COX-2 and mPGES-1 mRNA expression significantly increased after 2 hours, in parallel with protein expression, whereas COX-3 and mPGES-2 mRNA expression was not modified. Moreover, we observed a delayed overexpression of 15-PGDH just before the decline of PGE2 synthesis after 18 hours, suggesting that PGE2 synthesis could be altered by the induction of 15-PGDH expression. We conclude that, along with COX-2, dynamic compression induces mPGES-1 mRNA and protein expression in cartilage explants. Thus, the mechanosensitive mPGES-1 enzyme represents a potential therapeutic target in osteoarthritis.