Intracellular increases of cAMP induce opposite effects in glutamic acid decarboxylase (GAD67) and glial fibrillary acidic protein immunoreactivities in C6 cells.

C6 is a cell line that expresses glial and neuronal markers. Treatments that increase intracellular cAMP levels induce the differentiation of these cells. We had previously demonstrated that forskolin, an agent that activates adenylate cyclase, produced changes in gene expression in C6 cells. As a consequence of this treatment, glutamic acid decarboxylase (GAD) activity and the mRNA for GAD67, one of the isoforms of the enzyme, decreased. In contrast, this treatment increased the transcription of the glial fibrillary acidic protein (GFAP) gene. We now show, by immunocytochemistry, that the changes in gene expression are phenotypically reflected by corresponding changes in the levels of the proteins encoded by the GAD67 and GFAP genes. Computer-assisted image analysis demonstrated that both the increase in GFAP immunofluorescence, and the decrease in GAD67 immunofluorescence are statistically significant. The changes in gene expression and in protein immunoreactivity are part of the differentiation process of the C6 cells towards a more mature glial phenotype.