REGULATION OF NERVE GROWTH-FACTOR SECRETION AND MESSENGER-RNA EXPRESSION BY BACTERIAL LIPOPOLYSACCHARIDE IN PRIMARY CULTURES OF RAT ASTROCYTES

The present work was undertaken to study the effect of bacterial lipop olysaccharide (LPS), a potent activator of the host inflammatory respo nse, on the synthesis of nerve growth factor (NGF) by newborn rat brai n astrocytes. Treatment of primary rat astroglial cells cultured in ch emically defined medium with LPS resulted in a dose-dependent accumula tion of NGF mRNA, and an increased release of NGF protein in the cell medium. NGF mRNA levels were maximal after 24 hr of stimulation (8-fol d increase), whereas extracellular NGF peaked after 72 hours of treatm ent (17-fold increase). This dramatic increase of extracellular NGF wa s abrogated if cells were treated with actinomycin D or cycloheximide, a fact which implies that the accumulation of extracellular NGF by UP S-treated cells requires DNA transcription and RNA translation. Stimul ation of NGF synthesis and secretion was: (i) unaffected by treatment with the protein kinase C inhibitor bisindolylmaleimide, and (ii) prev ented by forskolin and 3-isobutyl-1-methylxanthine, two agents which i ncrease cAMP levels. Inhibition of LPS effect was also obtained with a pigenin, a proposed inhibitor of the mitogen-activated protein kinase pathway. Results thus show that LPS stimulates NGF synthesis by astrog lial cells through a mechanism that is independent of protein kinase C (PKC), antagonized by cAMP-elevating agents, and probably mediated by the mitogen-activated protein kinase cascade. The data raise the poss ibility that LPS exerts stimulatory effects on NGF synthesis that are independent of those elicited by astrocyte-derived inflammatory lympho kines such as IL-1 beta, TNF alpha or TGF beta 1. (C) 1997 Wiley-Liss, Inc.