Dopaminergic neurotoxicity of HIV-1 gp120: Reactive oxygen species as signaling intermediates

We examined the role of reactive oxygen species (ROS) in loss of dopaminergic neurons (DNs) from the substantia nigra (SN) in neuroAIDS. The frequency of Parkinson-like symptomatology, and DN loss, in neuroAIDS is often attributed to nonspecific DN fragility to oxidative stress. Cultured DN are more sensitive to ROS than non-dopaminergic neurons (RN): DN underwent apoptosis at far lower H2O2 concentrations than RN. Gene delivery of glutathione peroxidase (GPx1), which detoxifies H2O2, largely protected both neuron types. HIV-1 envelope, gp120, which elicits oxidative stress in neurons, caused apoptosis more readily in DN than in RN. However, unlike apoptosis caused by H2O2, gp120-induced DN apoptosis was specific: DNs were specifically more sensitive than RN to receptor-mediated [Ca2+]i fluxes triggered by gp120. Gp120-induced Ca2+ signaling in both neuron types was inhibited by GPx1 or Cu/Zn superoxide dismutase (SOD1), implicating superoxide and peroxide in ligand (gp120)-induced signaling upstream of Ca2+ release from intracellular stores. In vivo, rats given 10 ng of gp120 stereotaxically showed rapid DN loss within the SN, while loss of RN in the SN and caudate–putamen (CP) was slower and required ≥ 100 ng of gp120. Furthermore, gp120 injected into the CP was transported axonally retrograde to the SN, causing delayed DN loss there. This, too, was prevented by SOD1 or GPx1. DNs are therefore specifically hypersensitive to gp120-induced apoptosis, signaling for which involves ROS intermediates. These findings may help explain why DN loss and Parkinson's-like dysfunction predominate in neuroAIDS and may apply to other neurodegenerative diseases involving the SN.