Toxoplasma gondii induces prostaglandin E2 synthesis in macrophages via signal pathways for calcium-dependent arachidonic acid production and PKC-dependent induction of cyclooxygenase-2

Abstract

In this study, the intracellular signaling pathway of PGE2 synthesis in macrophages (RAW264.7) induced by Toxoplasma gondii was investigated. The T. gondii-induced PGE2 production in macrophages increased in a time-dependent manner, as PGE2 induction began at 4 h, peaked at 12 h, and then plateaued at a high level. COX-2 mRNA in macrophages was detectable as early as 4 h after treatment; the maximal expression was observed at 8 h. The earliest induction of COX-2 protein occurred at 4 h and peaked at 16 h; meanwhile, COX-1 mRNA level and protein production remained unchanged throughout. Indomethacin and nimesulide inhibited tachyzoite-induced PGE2 production and COX-2 mRNA expression in macrophages but they had no significant effect on COX-2 protein expression. EGTA, TFP and BAPTA/AM inhibited both arachidonic acid (AA) and PGE2 production without effecting COX-2 protein expression, but verapamil inhibited neither AA nor PGE2 production. H7 was found to inhibit PGE2 production, and COX-2 mRNA expression and protein expression by tachyzoite or LPS stimulated macrophages in a dose-dependent manner. Our results demonstrate that T. gondii induces PGE2 biosynthesis in RAW264.7 macrophages by regulating AA production through a calcium-dependent pathway and induction of COX-2 expression by a PKC-dependent pathway.