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Prostaglandin E2is an enhancer for IL-1β-induced expression of membrane-associated prostaglandin E synthase in rheumatoid synovial fibroblasts
Arthritis Res Thervolume 5, Article number: 65 (2003)
Membrane-associated prostaglandin E synthase (mPGES) is a recently identified terminal enzyme of arachidonic acid cascade that catalyzes prostaglandin (PG)H2 to PGE2. We recently reported that expression of mPGES in rheumatoid synovial fibroblasts (RSF) was upregulated by IL-1β, and that the time-course of its expression was delayed and prolonged when compared with that of cyclooxygenase-2 (COX-2).
To identify the regulating factors of mPGES expression in RSF.
RSF from patients with rheumatoid arthritis (RA) on surgery, who gave written consent to the use of tissues for this research, were treated with IL-1β, rofecoxib, NS-398, and meloxicam (selective COX-2 inhibitors). The effects of PGE2 and selective EP1, EP2, EP3, and EP4 receptor agonists (DI-004, AE1-259-01, AE-243, and AE1-329, respectively; Ono Pharmaceutical Co., Osaka, Japan) were also studied in various conditions. Expression of the mRNA and protein of mPGES and COX-2 were analyzed by northern and Western blot analyses, respectively. Expression of PGE2 receptor mRNA in RSF was determined by RT-PCR. PGE2 and cAMP production was measured by an ELISA.
Enhanced expression of mPGES mRNA and protein in IL-1β-stimulated RSF was attenuated by rofecoxib, NS-398, or meloxicam. This attenuation was restored by addition of PGE2. Exogenous PGE2 only (without IL-1β stimulation) did not induce expression of mPGES in RSF, indicating that PGE2 was an enhancer of mPGES expression in the IL-1β-stimulated condition.
We then examined which PGE2 receptor was important in the enhancing action of PGE2 in RSF. EP2 and EP4 receptor mRNA was detected in RSF; however, EP1 and EP3 were negative. Addition of AE1-259-01 (EP2 agonist) or AE1-329 (EP4 agonist) as well as PGE2 restored the inhibitory effects of mPGES expression by rofecoxib. In addition, the restoration by PGE2 was mimicked by forskolin, a direct activator of adenylate cyclase. Intracellular cAMP was increased by IL-1β and it was inhibited by rofecoxib.
The enhancing property of PGE2 via EP2/EP4 receptors on mPGES expression may play an important role in the cytokine-stimulated articular inflammation in RA patients. It also seems that COX-2 inhibitors effectively decrease PGE2 production not only by COX-2 inhibition, but also by reduction of mPGES expression.
This work was supported in part by grants from the Ministry of Education, Culture, Sports, Science and Technology of the Japanese Government.