Interferon-gamma reduces cyclooxygenase-2-mediated prostaglandin E2 production from primary mouse astrocytes independent of nitric oxide formation.

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)-gamma is known to upregulate the production of NO from astrocytes, the present study was designed to investigate the effect of IFNgamma 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 IFNgamma resulted in a concentration-dependent decrease in PGE2 accumulation which was accompanied by a striking parallel increase in NO formation. However, the NOS inhibitors, N(G)-nitro-L-arginine or N6-(1-iminoethyl)-lysine, failed to reverse the IFNgamma-mediated diminution of LPS-induced PGE2 production, indicating that the IFN-gamma-mediated reduction in COX-2-dependent PGE2 production occurred independent of NO formation. Additional experiments demonstrated that IFN-gamma 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 IFNgamma.