AIMS: As many as 50% of AIDS patients suffer from multiple neurological symptoms collectively termed AIDS-related dementia. The neurotoxicity of the HIV-1 envelope protein gp120 has been implicated in the neuropathology of AIDS. Results from several lines of research suggest that gp120 causes the death of neurons through the activation of microglia which release neurotoxic substances, such as proinflammatory cytokines and nitric oxide (NO). However, the direct evidence indicating the link between neurotoxicity of gp120 and microglia in the brain is still lacking. The purpose of this project is to provide this link using a mixed neuron/glia culture. ACCOMPLISHMENTS: In order to examine the roles of brain microglia in the neurotoxicity of g 120, we have established a mixed neuro/ glia culture prepared from the midbrain region of E 14 rat embryos. This type of culture is enriched in tyrosine hydroxylase-positive neurons, which are crucial for the production of dopamine. Degeneration of these neurons in the midbrain cause Parkinsons disease in humans. We have studied the roles of microglia in the neurotoxic effects of gp120 in this co-culture system. Nanomolar concentrations of gp120 produced time-dependent degeneration of dopamine-containing neurons based on their capability to take up tritiated-dopamine, which is a reliabe functional measurement of the viability of dopamine neurons. An analysis by immunostainning of tyrosine hydroxylase-positive cells confirmed the neurodegenerative effect of gp120. Similar experiments were performed in enriched neuronal cultures without the presence of glial cells, no neurotoxicity was observed by the same concentrations of gp 120. This study confirmed the notion that microglia are essential for the expression of gp120- induced neurotoxicity in the brain. Biochemical measurements of pro- inflammatory cytokines and free radicals indicated increased production of nitric oxide and release of TNF-a in neuron/glia cell cultures, which were mainly produced from microglia. Co-treatment with a nitric oxide synthase inhibitor or immunoneutralization with TNF -a antibodies effectively abolished gp120-induced neurotoxicity, further indicating the important role of microglia in the mediation of the toxic effects of gp120 . Studies are underway to examine the possible roles of endogenous opioid peptides in modulating the neurotoxicity of gp120, since both exogenous opiates and endogenous opioid system have been implicated in AIDS-related dementia. - AIDS, neurotoxicity, HIV-1 neurotoxic effects
