INTERFERON-GAMMA AND LIPOPOLYSACCHARIDE REDUCE CAMP RESPONSES IN CULTURED GLIAL-CELLS - REVERSAL BY A TYPE-IV PHOSPHODIESTERASE INHIBITOR

The aim of the present study was to determine whether two classical ma crophage activators, bacterial lipopolysaccharide (LPS) and interferon -gamma (IFN-gamma) could affect the accumulation of the second messeng er cAMP in cultured rat microglia and astrocytes. Purified microglia a nd astrocyte secondary cultures obtained from the neonatal rat were gr own for 3 days in basal medium Eagle (BME) +/- 10% fetal calf serum (F CS). Exposure of microglia to LPS resulted into a dose- and time-depen dent decrease in the accumulation of cAMP induced by receptor-mediated (isoproterenol or prostaglandin E(2)) or direct (forskolin) activatio n of adenylate cyclase. The inhibitory effect of LPS was rapid (a 10 m in preincubation was sufficient to approach a maximal effect), occurre d at low doses (IC50 = 1.2 ng/ml), and was not abrogated by pertussis toxin. A selective inhibitor of type IV phosphodiesterase (rolipram, 1 00 nM) prevented the effect of LPS on cAMP accumulation, while inhibit ors of other forms of phosphodiesterase were unable to do so. IFN-gamm a (100 u/ml) also caused a depression of the evoked cAMP accumulation in microglia after a 10 min preincubation, and its effect was prevente d by rolipram, as in the case of LPS. Astrocytes differed from microgl ia in that LPS (1-100 ng/ml) did not inhibit the accumulation of cAMP induced by either isoproterenol or forskolin; on the other hand, IFN-g amma did have an inhibitory effect (though less pronounced than in mic roglia) that could be prevented by rolipram. Our observations indicate that two potent activators of microglia acting at different receptors , LPS and IFN-gamma, can diminish the accumulation of cAMP through a c ommon mechanism, the stimulation of a specific form of cAMP phosphodie sterase. The fact that IFN-gamma, but not LPS, was effective in astroc ytes suggests that LPS receptors are scarcely, if at all, expressed in these cells, or that they are differently coupled to second messenger s. Selective inhibitors of type TV phosphodiesterase might prevent som e of the obnoxious actions of LPS or IFN-gamma in the living organism. (C) 1995 Wiley-Liss, Inc.