Interleukin-1β Induces Prostaglandin G/H Synthase-2 (Cyclooxygenase-2) in Primary Murine Astrocyte Cultures

Abstract: Activation of glial cells and the consequent release of cytokines, proteins, and other intercellular signaling molecules is a well-recognized phenomenon in brain injury and neurodegenerative disease. We and others have previously described an inducible prostaglandin G/H synthase, known as PGHS-2 or cyclooxygenase-2, that is up-regulated in many cell systems by cytokines and growth factors and down-regulated by glucocorticoid hormones. In cultured mouse astrocytes we observed increased production of prostaglandin E₂ (PGE₂) after stimulation with either interleukin-1β (IL-1β) or the protein kinase C activator phorbol 12-myristate 13-acetate (TPA). This increase in PGE₂ content was blocked by pretreatment with dexamethasone and correlated with increases in cyclooxygenase activity measured at 4 h. Northern blots revealed concomitant increases in PGHS-2 mRNA levels that peaked at 2 h and were dependent on the dosage of IL-1β. Dexamethasone inhibited this induction of PGHS-2 mRNA by IL-1β. TPA, basic fibroblast growth factor, and the proinflammatory factors tumor necrosis factor α and lipopolysaccharide, but not interleukin-6, also stimulated PGHS-2 mRNA expression. Relative to IL-1β, the greater increases in PGE₂ production and cyclooxygenase activity caused by TPA correlated with a greater induction of PGHS-2 mRNA. Furthermore, NS-398, a specific inhibitor of cyclooxygenase-2, blocked >80% of the cyclooxygenase activity in TPA-treated astrocytes. These findings indicate that increased expression of PGHS-2 contributes to prostaglandin production in cultured astrocytes exposed to cytokines and other factors.