ENDOGENOUS NITRIC-OXIDE ACTIVATES PROSTAGLANDIN-F2-ALPHA PRODUCTION IN HUMAN MICROGLIAL CELLS BUT NOT IN ASTROCYTES - A STUDY OF INTERACTIONS BETWEEN EICOSANOIDS, NITRIC-OXIDE, AND SUPEROXIDE ANION (O-2(-)) REGULATORY PATHWAYS

Secretion of the eicosanoids, nitric oxide (NO.) and superoxide anion (O-2(.-)) was evaluated in human embryonic astrocytes and microglia. A n inducible form of cyclo-oxygenase (COX 2) was demonstrated in astroc ytes and microglia after IL-1 beta plus IFN-gamma stimulation, since 1 ) large amounts of PGF(2 alpha) were released; 2) PCF2 alpha secretion required protein synthesis and was blocked by indomethacin; and 3) th e response was delayed and persistent. Using the same inducers, astroc ytes, but not microglial cells, produced NO. and had an inducible form oi nitric oxide synthase. Conversely, microglial cells were induced b y IL-1 beta and IFN-gamma to generate surperoxide anions (O-2(.-)) thr ough an NADPH oxidase-dependent pathway. We then investigated interact ions between these different pathways of synthesis by inhibition exper iments. The cytokine-induced production of PGF(2 alpha) in astrocytes was not affected by exposure to N-omega-monomethyl-L-arginine, which i nhibits NO. production, whereas it was reduced by 40% in microglia. Si nce microglia did not secrete any detectable NO. in their supernatant, intracellular production of NO. could occur in these cells that posit ively regulated PGF(2 alpha) production. Exposure to indomethacin, whi ch prevented PGF(2 alpha) production in both astrocytes and microglia, resulted in a 64% increase in cytokine-induced NO degrees production by astrocytes and a 70% inhibition of O-2(.-) generation by stimulated microglia. Finally, superoxide dismutase depletion of O-2(.-) in astr ocytes and microglia had no effect on PGF(2 alpha) production in these cells, These results demonstrate that there are important interaction s between the pathways of synthesis of inflammatory mediators in glial cells that could unveil additional regulatory mechanisms.