Type IIA secretory phospholipase A₂ up-regulates cyclooxygenase-2 and amplifies cytokine-mediated prostaglandin production in human rheumatoid synoviocytes

Human type IIA secretory phospholipase A₂ (sPLA₂-IIA) is induced in association with several immune-mediated inflammatory conditions. We have evaluated the effect of sPLA₂-IIA on PG production in primary synovial fibroblasts from patients with rheumatoid arthritis (RA). At concentrations found in the synovial fluid of RA patients, exogenously added sPLA₂-IIA dose-dependently amplified TNF-α-stimulated PGE₂ production by cultured synovial fibroblasts. Enhancement of TNF-α-stimulated PGE₂ production in synovial cells was accompanied by increased expression of cyclooxygenase (COX)-2 and cytosolic phospholipase A₂ (cPLA₂)-α. Blockade of COX-2 enzyme activity with the selective inhibitor NS-398 prevented both TNF-α-stimulated and sPLA₂-IIA-amplified PGE₂ production without affecting COX-2 protein induction. However, both sPLA₂-IIA-amplified PGE₂ production and enhanced COX-2 expression were blocked by the sPLA₂ inhibitor LY311727. Colocalization studies using triple-labeling immunofluorescence microscopy showed that sPLA₂-IIA and cPLA₂-α are coexpressed with COX-2 in discrete populations of CD14-positive synovial macrophages and synovial tissue fibroblasts from RA patients. Based on these findings, we propose a model whereby the enhanced expression of sPLA₂-IIA by RA synovial cells up-regulates TNF-α-mediated PG production via superinduction of COX-2. Therefore, sPLA₂-IIA may be a critical modulator of cytokine-mediated synovial inflammation in RA.