THE KINETICS AND REGULATION OF THE INDUCTION OF TYPE-II NITRIC-OXIDE SYNTHASE AND NITRIC-OXIDE IN HUMAN FETAL GLIAL-CELL CULTURES

Our understanding of how human glial cells are induced to produce nitr ic oxide and how the production is regulated may allow us to better de sign therapeutic strategies for treating inflammatory diseases of the central nervous system in man. Cultures of human fetal astrocytes and microglia produce inducible nitric oxide synthase and nitric oxide in response to Interferon gamma and Interleukin 1 beta. The mRNA for the enzyme was induced by 2 h and returned to baseline by day 2; the prote in was expressed by 24 h and was present in cells for the entire 7 day s of culture. Nitric oxide was not seen in cell supernatants until day 3 reaching a peak by day 7. Footprints of nitric oxide production suc h as NADPH diaphorase and nitrotyrosine staining as well as cGMP produ ction were not significantly above background until day 3 to day 4, ri sing steadily until day 7. These data suggest that while the type II n itric oxide synthase is induced in human glial cells within 24 h of st imulation, it is not a functionally active enzyme until 48-72 h later, implying that there is a posttranslational regulation of the enzyme l imiting nitric oxide production in these cells.