Role of c-Fos protein on glutamate toxicity in primary neural hippocampal cells.

The hippocampus is extremely sensitive to microenvironmental signals and toxic events, including massive glutamate release. Despite the extensive literature related to the cascade of molecular events triggered in postsynaptic neurons, the distinction between proapoptotic and survival pathways is still being discussed. In this study, we have investigated the role of c-Fos in glutamate-induced toxicity in primary cultures of hippocampal neurons by using antisense oligonucleotide (ASO) technology. Exposure of cells (5 days in vitro; DIV) to glutamate 0.5 mM for 24 hr caused massive nuclear alteration. An increase in the number of caspase-3-positive cells was also observed 24 hr after glutamate treatment. The expression of c-fos and c-jun immediate-early genes was increased 30 min after glutamate exposure. The study of c-Fos and c-Jun protein expression revealed an increase in the number of cells positive for both antibodies. To investigate whether the expression of c-Fos protein after glutamate treatment was related to cell death activation or cell survival pathways, cells were exposed to 5 muM of c-fos ASO at 4 DIV, 24 hr before glutamate treatment. The presence of the ASO in the medium significantly decreased the number of altered nuclei, and this was associated with a significant reduction in the number of c-Fos-positive cells after glutamate treatment. Exposure of cells to the c-fos ASO under the conditions described above decreased caspase-3 immunostaining induced by glutamate. These results suggest that the synthesis of c-Fos protein after glutamate exposure favors cell death pathway activation in which caspase-3 is also involved.