Possible involvement of 5α-reduced neurosteroids in adrenergic and serotonergic stimulation of GFAP gene expression in rat C6 glioma cells

Abstract

Influence of adrenergic and serotonergic stimulation on glial fibrillary acidic protein (GFAP) gene expression in rat C6 glioma cells was first examined as an in vitro model experiment for investigating the neuronal regulation of glial cell differentiation. Stimulation of these cells with isoproterenol and serotonin elevated GFAP mRNA levels followed by an increase in its protein contents, thus suggesting that both adrenergic and serotonergic stimulation might induce the differentiation of the glioma cells. In addition, progesterone and its 5α-reduced metabolite dihydroprogesterone also elevated GFAP mRNA levels in rat C6 glioma cells, consistent with their stimulatory actions on GFAP gene expression observed in rat astrocytes (Melcangi, R.C., Riva, M.A., Fumagalli, F., Magnaghi, V., Racagni, G., Martini, L., 1996. Effect of progesterone, testosterone and their 5α-reduced metabolites on GFAP gene expression in type 1 astrocytes, Brain Res. 711, 10–15). Further studies showed that the elevation of GFAP mRNA levels induced by isoproterenol and serotonin as well as progesterone was abolished by pretreatment of the glioma cells with finasteride, an inhibitor of 5α-reduced steroid production. Moreover, the stimulatory actions of isoproterenol and serotonin on GFAP gene expression were inhibited by pretreatment with a GABA A receptor antagonist bicuculline and a progesterone receptor antagonist RU486. These findings suggest that both adrenergic and serotonergic stimulation may indirectly activate GFAP gene expression probably through the production of 5α-reduced steroid metabolites in rat C6 glioma cells, proposing the possibility that 5α-reduced neurosteroids may play a potential role in the neuronal regulation of glial cell differentiation.