Up‐regulation of microsomal prostaglandin E synthase 1 in osteoarthritic human cartilage: Critical roles of the ERK‐1/2 and p38 signaling pathways

Abstract

Objective. Microsomal prostaglandin E synthase 1 (mPGES-1) is the final enzyme of the cascade that produces prostaglandin E 2 (PGE 2 ), a key actor in arthritis. To study mPGES-1 synthesis in human cartilage and its regulation by interleukin-1␤ (IL-1␤), we used human cartilage and an immortalized human chondrocyte cell line. Furthermore, we investigated the signaling pathways involved in mPGES-1 expression.Methods. We used real-time quantitative reverse transcription-polymerase chain reaction, Northern blotting, and Western blotting to measure mPGES-1 messenger RNA (mRNA) and protein expression in human chondrocytes. PGE 2 production was measured by enzyme-linked immunosorbent assay.Results. Cartilage specimens from osteoarthritis (OA) patients contained far greater amounts of mPGES-1 and cyclooxygenase 2 (COX-2) mRNA than did normal cartilage. Incubation with IL-1␤ markedly increased mPGES-1 mRNA and protein in a dosedependent and time-dependent manner, in parallel with an increase in PGE 2 levels. Both PD98059, an ERK pathway inhibitor, and SB203580, a p38␣/␤ MAPK inhibitor, abolished the increases in mPGES-1 mRNA and protein in response to IL-1␤. The specific p38␣ MAPK inhibitor SC906 suppressed IL-1␤-induced COX-2 expression but not IL-1␤-induced mPGES-1 expression, suggesting preferential involvement of p38␤ MAPK in IL-1␤-induced mPGES-1 expression.Conclusion. This study is the first to show that mPGES-1 is stimulated in human chondrocytes by the proinflammatory cytokine IL-1␤ via activation of both ERK-1/2 and p38 MAPK in an isoform-specific manner. We postulate that mPGES-1 may be a novel target for OA therapy.Prostaglandin E 2 (PGE 2 ) plays an important role in cartilage metabolism. Its many effects on chondrocytes (for review, see ref. 1) include enhanced production of matrix metalloproteinase 3 (2), modulation of proteoglycan and collagen synthesis (2,3), and stimulation of chondrocyte apoptosis (4,5). The synovial fluid of patients with osteoarthritis (OA) and rheumatoid arthritis contains high concentrations of PGE 2 (4), and cartilage and chondrocytes from OA patients spontaneously release more PGE 2 than does normal cartilage (2,6,7). These results suggest that PGE 2 may be actively involved in cartilage breakdown in OA patients. PGE 2 is synthesized by the isoenzymes cyclooxygenase 1 (COX-1) and COX-2, both of which act on arachidonic acid to form the prostaglandin endoperoxide H 2 (PGH 2 ). The prostanoid synthase prostaglandin E synthase (PGES) produces PGE 2 from PGH 2 . Three

Heme oxygenase-1 induction modulates microsomal prostaglandin E synthase-1 expression and prostaglandin E2 production in osteoarthritic chondrocytes

“…mPGES-1 is induced by pro-inflammatory cytokines in many cell types and has been proposed as a target in inflammatory diseases [45] and OA [10,46]. Recent studies have revealed that EGR-1 could be a key regulator of mPGES-1 transcription in response to cytokine stimulation [47].…”

“…The arachidonic acid metabolite PGE 2 , a mediator of inflammation and pain, is produced in OA chondrocytes stimulated by IL-1 by the coordinated induction of cyclooxygenase-2 (COX-2) and microsomal PGE synthase 1 (mPGES-1) [10]. Previous studies have suggested the interest of this last enzyme as a novel target for OA [10].…”

Inhibition of Matrix Metalloproteinase-3 and -13 Synthesis Induced by IL-1β in Chondrocytes from Mice Lacking Microsomal Prostaglandin E Synthase-1

“…Previous studies demonstrated that IL-1b markedly increased mPGES-1 mRNA and protein expression, in parallel with an increase in PGE 2 levels in chondrocytes (9,10). Interestingly, accumulating evidences involve mPGES-1 in cartilage degradation (9)(10)(11)(12)(13)(14).…”

Prostaglandin E2 Exerts Catabolic Effects in Osteoarthritis Cartilage: Evidence for Signaling via the EP4 Receptor

“…Gene expression analysis of both intact and damaged cartilage obtained from OA patients has shown a concomitant increase in the expression of microsomal PG synthase, a terminal synthase required for COX-2-derived PGE 2 production in diseased, but not normal cartilage (12). The coordinate expression of COX-2 and mPGES can be further up-regulated in chondrocytes by the proinflammatory cytokines IL-1␤ and TNF-␣ (13)(14)(15). Recently, Beier's group (16) confirmed up-regulation of COX-2 in vivo in a surgically induced model of OA.…”