Tumor necrosis factor alpha inhibits glutamate uptake by primary human astrocytes - Implications for pathogenesis of HIV-1 dementia

Human immunodeficiency virus (HIV) infection is commonly associated with neurological disease that occurs in the apparent absence of extensive infection of brain cells by HIV, suggesting that indirect mechanisms account for neuropathogenesis in the CNS, perhaps including changes in the normal neuroprotective functions of astrocytes. To test this hypothesis, we examined the effect of the pro-inflammatory cytokine, tumor necrosis factor alpha (TNF alpha), produced by HIV-1-infected macrophages and microglia, on glutamate transport by primary human fetal astrocytes (PHFAs). A dose-dependent inhibition of high affinity glutamate uptake sites was observed 12-24 h after addition of exogenous recombinant human TNF alpha to PHFAs. This effect was specific since it was blocked by a neutralizing monoclonal antibody directed against TNF alpha. Furthermore, the inhibitory effect was reproduced by a monoclonal antibody that is an agonist at the 55-kDa TNF receptor. These results suggest that the neurotoxic effects of TNF alpha may be due in part to its ability to inhibit glutamate uptake by astrocytes, which in turn may result in excitotoxic concentrations of glutamate in synapses.