Microsomal prostaglandin E synthase‐1, which is not coupled to a particular cyclooxygenase isoenzyme, is essential for prostaglandin E2 biosynthesis in vascular smooth muscle cells

Summary. Background: Prostaglandin (PG) E2 induces expression of matrix metalloproteinases and angiogenic factors, thereby contributing to plaque instability. Objective: To study the influence of cyclooxygenase (COX) and PGE synthase (PGES) isoenzyme expression on PGE2 and PGI2 biosynthesis in vascular smooth muscle cells (VSMC) in culture. Methods: Cells were treated with human recombinant IL-1β over different periods of time. Expression of PGI synthase, and COX and PGES isoenzymes was determined by real-time reverse transcriptase polymerase chain reaction and immunoblotting. Biosynthesis of prostanoids from exogenous or endogenous substrate was analyzed by high-performance liquid chromatography or enzyme-immunoassay after incubation of cells with labeled arachidonic acid or thrombin, respectively. Results: Cytosolic PGES and microsomal PGES (mPGES) -1 and -2 were expressed in VSMC. PGES activity was mainly linked to mPGES-1. IL-1β induced COX-2 and mPGES-1 with a different time course. VSMC ability to synthesize PGE2 and PGI2 fitted mPGES-1 and COX-2 expression, respectively. The ability of VSMC to produce PGI2 was downregulated by mPGES-1 expression and was restored when mPGES-1 expression was silenced. Results from COX-1 and COX-2 silencing and selective inhibition showed that both COX-1 and COX-2 were involved in the biosynthesis of PGE2 and their relative contribution depended on the time of incubation with IL-1β. Conclusions: mPGES-1 is the main PGES responsible for PGE2 biosynthesis by VSMC and its induction downregulates VSMC ability to produce PGI2. These results support the concept that under inflammatory conditions VSMC could significantly contribute to plaque instability and that mPGES-1 may be a target for therapeutic intervention in patients with cardiovascular risk.