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

Abstract

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 E 2 (PGE 2) after stimulation with either interleukin‐1β (IL‐1β) or the protein kinase C activator phorbol 12‐myristate 13‐acetate (TPA). This increase in PGE 2 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 PGE 2 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.