HIV-1 transactivator of transcription protein induces mitochondrial hyperpolarization and synaptic stress leading to apoptosis

Abstract

Despite the efficacy of highly active antiretroviral therapy in reducing viral burden, neurologic disease associated with HIV-1 infection of the CNS has not decreased in prevalence. HIV-1 does not induce disease by direct infection of neurons, although extensive data suggest that intra-CNS viral burden correlates with both the severity of virally induced neurologic disease, and with the generation of neurotoxic metabolites. Many of these molecules are capable of inducing neuronal apoptosis in vitro, but neuronal apoptosis in vivo does not correlate with CNS dysfunction, thus prompting us to investigate cellular and synaptic events occurring before cell death that may contribute to HIV-1-associated neurologic disease. We now report that the HIV-1 regulatory protein transactivator of transcription protein (Tat) increased oxidative stress, ATP levels, and mitochondrial membrane potential in primary rodent cortical neurons. Additionally, a proinflammatory cellular metabolite up-regulated by Tat, platelet-activating factor, also induced oxidative stress and mitochondrial hyperpolarization in neurons, suggesting that this type of metabolic dysfunction may occur on a chronic basis during HIV-1 infection of the CNS. Tat-induced mitochondrial hyperpolarization could be blocked with a low dose of the protonophore FCCP, or the mitochondrial KATP channel antagonist, tolbutamide. Importantly, blocking the mitochondrial hyperpolarization attenuated Tat-induced neuronal apoptosis, suggesting that increased mitochondrial membrane potential may be a causal event in precipitating neuronal apoptosis in cell culture. Finally, Tat and platelet-activating factor also increased neuronal vesicular release, which may be related to increased mitochondrial bioenergetics and serve as a biomarker for early damage to neurons.