| Astrocytosis and neuron death are two hallmarks of HIV-associated neuropathogenesis. In the brain, neurons are not infected by HIV-1. Thus, indirect effects resulting from HIV-1 infected microglia/macrophages and astrocytes have been proposed for neuronal damage in the brain of HIV infected individuals. HIV Tat protein can be secreted from HIV-infected and Tat-expressing cells, and is able to be taken up into neighboring cells. However, the molecular pathways of Tat neurotoxicity are not yet fully defined. In this study, we established Tat-expressing neuronal and glioblastoma cell lines and determined Tat effects on cell growth and function. We also used primary astrocytes isolated from the brain-targeted Tat transgenic mice. Our results showed that Tat expression resulted in growth inhibition, but not apoptosis of astrocytes, neurons, as well as non-glial cells. We also showed that Tat interacted with a number of cell cycle-related proteins, suggesting that the interactions between Tat and multiple cell cycle-regulators may account for Tat-induced anti-proliferative effect. In addition, we found that Tat expression resulted in a significant increase in GFAP expression, a cellular marker of astrocytosis. Furthermore, we found, for the first time, that Tat expression impaired glutamate uptake by astrocytes. Importantly, cell culture supernatants from Tat-expressing astrocytes caused rapid neuron death. Taken together, our studies provide direct evidence for the first time to link Tat, astrocyte dysfunction, and neuron death. These results also suggest disruption of astrocytes-neuron homeostasis also contributes to Tat neurotoxicity. |
