TNFalpha and TNF receptor 1 expression in the mixed neuronal-glial cultures of hippocampal dentate gyrus exposed to glutamate or trimethyltin.

We examined the expression and cellular localization of tumor necrosis factor alpha (TNFalpha) and its type 1 receptor (TNFR1) in mixed neuronal-glial cultures of rat hippocampal dentate gyrus exposed to glutamate (GLU) or trimethyltin (TMT). Our previous studies demonstrated that both pathogenic factors evoked neuronal apoptosis, however, TMT was more potent and caused cell death in almost 90% of neurons. Observed neurodegeneration was accompanied by morphological changes of microglia. In the current study, using RT-PCR and Western blotting analysis, we found that GLU and TMT induced increase in TNFalpha mRNA and protein levels. The induction of transcription was stronger following GLU treatment, however the protein production was much more intensive after TMT exposure. Double fluorescent labeling for TNFalpha, TNFR1 and cellular markers revealed cytokine expression in microglia and some neurons. On the other hand, majority of neuronal cells displayed TNFR1 immunoreactivity, in control and in treated cultures. Moreover, TMT led to a strong increase in TNFR1 expression in astrocytes, which displayed remarkable, granular staining for the cytokine receptor. Western blotting for TNFR1 revealed enhanced protein expression only in cultures treated with TMT. This is the first report demonstrating the changes of expression of TNFalpha and TNFR1 in hippocampal dentate gyrus cultures treated with GLU or TMT. Our results indicate that TNFalpha may be involved in the mechanism of neurotoxic effects evoked by both pathogenic factors and suggest that astrocytes via TNFR1 may enhance TMT-induced injury.