The role of extracellular human immunodeficiency virus type 1 viral protein R in neuropathogenesis

Human immunodeficiency virus type 1 (HIV-1), the etiological agent of acquired immunodeficiency syndrome (AIDS), is treatable by antiretroviral therapy but may not be eradicated due to presence of long-lived cellular reservoirs in specific tissues such as the central nervous system (CNS). HIV-1enters the CNS early after infection, although the most severe symptoms of progressive neurocognitive impairment manifest during late stage disease, including inflammatory conditions such as excessive molecular oxidation and decreased intracellular glutathione (GSH), the main cellular antioxidant. In the context of neuropathogenesis, both directly infected cells as well as inflammatory cytokines and secreted viral proteins play a pivotal role in disease progression. Among the latter is Vpr, a virion-associated protein, which functions both in post-entry steps and during the HIV-1 life cycle. Vpr has been detected as a virionfree protein in the serum and cerebrospinal fluid of HIV-1-infected patients, and has the ability to enter cells. This leads to formation of mitochondrial permeability transition pores, which affect membrane potential and ATP translocation. Additionally, late-stage disease patients manifest increased extracellular Vpr levels in the blood. These premises led us to investigate the role of extracellular Vpr in inducing oxidative stress and its contribution to disease progression. We focused our attention on astrocytes, as the intimate regulators of neuronal fate, and found that extracellular Vpr induces declines in ATP and GSH levels, along with increased production of reactive oxygen species (ROS) and decreased GSH/GSSG ratio. These events are driven by Vpr-induced impairment of GAPDH activity and possibly glycolysis. Exposure to Vpr increased secretion of IL-6, IL-8, MCP-1 and MIF-1, with possible increased chemotaxis of cells from the periphery. Several genes of the oxidative stress pathway were dysregulated in response to extracellular Vpr exposure, which may cause a vicious cycle and further decrease intracellular GSH levels. In conclusion, we propose a model of HIV-1 disease progression wherein increased levels of extracellular Vpr, as within the CNS of late-stage HIV-1-infected patients, contribute to impair astrocytic functionality and affect the astrocytic-neuronal network, essential for brain homeostasis. This dissertation provides new insights to the field with respect to the conditions observed in late-stage patients.