PROTEIN-TYROSINE KINASE INHIBITORS SUPPRESS THE PRODUCTION OF NITRIC-OXIDE IN MIXED GLIA, MICROGLIA-ENRICHED OR ASTROCYTE-ENRICHED CULTURES

Nitric oxide (NO) produced bq glial cells has been implicated in the n europathogenesis of various diseases. However, the signaling transduct ion pathway(s) for the production of NO in these cells is not well und erstood, To test whether protein tyrosine kinases (PTKs) are required for signaling events of NO production in glial cells, this study exami ned the effects of genistein and tyrphostin A25, two potent inhibitors of PTKs, on the production of NO in mouse primary mixed glia, microgl ia-enriched or astrocyte-enriched cultures exposed to lipopolysacchari de (LPS) ora combination of LPS and interferon-gamma (IFN gamma). LPS induced a dose-dependent increase in NO production from the mixed glia cultures. The LPS-induced NO production was significantly enhanced by stimulating the cells with IFN gamma. Genistein or tyrphostin A25 inh ibited the production of NO in both LPS- and LFN gamma/LPS-stimulated mixed glia cultures. The production of NO in the stimulated microglia- enriched or astrocyte-enriched cultures was also inhibited by tyrphost in A25. To verify the cellular sources of NO, immunocytochemical stain ing of inducible NO synthase (iNOS) was followed by staining with the microglia marker Mac-1 or the astrocyte marker glial fibrillary acid p rotein (GFAP) in microglia-enriched or astrocyte-enriched cultures. Th e expression of iNOS and the production of NO in microglia-enriched cu ltures were significantly higher than those in the identically stimula ted astrocyte-enriched cultures. These results demonstrate that PTKs a re involved in the signaling events of LPS-induced NO production in mi croglia and astrocytes, and that microglia are more responsive than as trocytes to stimuli which induce NO. These results may provide insight s into therapeutic interventions In the pathway for NO production in t he brain.