Interferon-γ reduces cyclooxygenase-2-mediated prostaglandin E 2 production from primary mouse astrocytes independent of nitric oxide formation

Abstract

Nitric oxide (NO) and prostaglandins (PGs) modulate inflammatory and immune responses in the central nervous system (CNS). Both NO and PG synthesis have been described in appropriately stimulated astrocytes. In other systems, both positive and negative modulation of cyclooxygenase (COX) activity, hence PG synthesis, have been described by NO. Since interferon (IFN)-γ is known to upregulate the production of NO from astrocytes, the present study was designed to investigate the effect of IFNγ on PG production from activated astrocytes and to determine whether this effect is mediated by NO. Astrocytic PG production was induced by exposure of murine cortical cultures to lipopolysaccharide (LPS). This induction was time- and concentration-dependent, and prevented by inhibitors of transcription and translation, as well as the selective COX-2 inhibitor, NS-398. LPS-induced expression of COX-2 mRNA and protein was confirmed by reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blot analysis, respectively. Exposure of LPS-treated astrocytes to IFNγ resulted in a concentration-dependent decrease in PGE 2 accumulation which was accompanied by a striking parallel increase in NO formation. However, the NOS inhibitors, N G-nitro- l-arginine or N 6-(1-iminoethyl)-lysine, failed to reverse the IFNγ-mediated diminution of LPS-induced PGE 2 production, indicating that the IFNγ-mediated reduction in COX-2-dependent PGE 2 production occurred independent of NO formation. Additional experiments demonstrated that IFNγ acted mainly by downregulating the expression of COX-2 protein. Present results indicate that PG and NO synthesis in mouse cortical astrocytes in vitro are under the direct reciprocal control of IFNγ.