Mitochondrial Glutaminase Release Contributes to Glutamate-Mediated Neurotoxicity during Human Immunodeficiency Virus-1 Infection

Abstract

Human immunodeficiency virus (HIV) induces a neurological disease culminating in frank dementia referred to as HIV-associated dementia (HAD). Neurotoxins from HIV-1-infected and activated mononuclear phagocytes contribute to the neuropathogenesis of HAD. Glutamate is the predominant excitatory neurotransmitter in the mammalian central nervous system (CNS) and functions through activation of multiple receptors. Excessive glutamate production by HIV-infected macrophages in HAD may contribute to neuronal injury. Our previous studies have suggested that mitochondrial glutaminase is responsible for the excessive production of glutamate. However, how HIV-1 infection regulates glutamate over-production remains unclear. In this study, we propose that HIV infection-induced oxidative stress contributes to mitochondrial glutaminase release, which results in the excessive production of glutamate and subsequent neuronal injury. We collected conditioned media from HIV-1 infected macrophages and analyzed glutamate concentration in the media by RP-HPLC, and found that the cyclosporine A (CsA), an inhibitor of HIV-1 replication and mitochondrial permeability transition pore, and N-acetylcysteine (NAC), a remover of reactive oxygen species (ROS), not only blocked the excessive glutamate production, but also decreased the glutamate-mediated neurotoxicity. In addition, HIV-infection-induced ROS generation was accompanied with the excessive glutamate production, suggesting that oxidative stress was involved in glutamate regulation. Using the isolated rat brain mitochondria as an ex vivo model and over-expressing GFP-glutaminase fusion protein in mammalian cells as a cell model, we confirm oxidative stress-mediated mitochondrial glutaminase release during HIV-1 infection contributes to glutamate over-production and the subsequent neurotoxicity. These results may provide insight into HAD pathogenesis and a therapeutic strategy for HAD treatment.

Glutamate metabolism in HIV-1 infected macrophages: Role of HIV-1 Vpr

“…Increase in glutamate levels has been reported to be glutamine-dependent, and the glutamatemediated neurotoxicity has been shown to be augmented by the mitochondrial glutaminase release. 17,20 Similar to these reports, we have observed a significant increase in the levels of GLS in the media by HIV-1 Vpr overexpression in macrophages (Fig. 4E) resulting in increased extracellular release of glutamate.…”

“…17,20 We hypothesize that the observed increase in extracellular levels of glutamate in the context of HIV-1 infection of macrophages is mediated by Vpr induced glycolysis, and TCA cycle activation in HIV-1 infected macrophages. To test this hypothesis we employed U937 cells activated by phorbol-12-myristate-13-acetate (PMA), to promote cell cycle arrest and induction of a differentiation program into macrophages, characterized by phenotypic and functional changes.…”

“…16 HAD has been linked to macrophage toxin production including glutamate. [17][18][19][20] Increased glutamate levels are also seen in the plasma, and cerebrospinal fluid (CSF) of HIV-1 infected patients. 18,21 In addition, the observation that soluble Vpr is detected in the CSF of HIV-1 infected individuals 22 suggests that Vpr can have bystander effects on uninfected cells and on neuronal cells 23 and contribute to glutamate-mediated neurodegeneration.…”

Glutaminase C overexpression in the brain induces learning deficits, synaptic dysfunctions, and neuroinflammation in mice

“…Glutaminase has been implicated in the neurotoxic effect of various CNS cell types in vitro , including macrophages, microglia (Huang et al, 2011; Tian et al, 2012; Zhao et al, 2004), and neurons (Hoffman et al, 2016; Ye et al, 2013). Furthermore, glutamianse is associated with various neurodegenerative and neuroinflammatory disesases such as HIV-1 associated dementia, multiple sclerosis, amyotrophic lateral sclerosis, and Alzheimer's disease (Burbaeva et al, 2014; D'Alessandro et al, 2011; Huang et al, 2011; Werner et al, 2001; Zhao et al, 2012), as well as neuropsychiatric diseases such as schizophrenia (Gluck et al, 2002).…”

Adenosine Triphosphate Released from HIV-Infected Macrophages Regulates Glutamatergic Tone and Dendritic Spine Density on Neurons

“…Even in cART treated individuals, certain populations of HIV-infected macrophages transmigrate into the CNS and can be found in perivascular cuffs and in parenchyma (Langford et al, 2003; Gras and Kaul, 2010; Buckner et al, 2011). These infected monocytes have altered metabolic functions that increase the release of immunomodulatory factors and amino acids such as arachidonic acid and glutamate (Tian et al, 2012; Koenig et al, 1986; Dreyer and Lipton, 1995; Yadav and Collman, 2009; Yao et al, 2010; Thompson et al, 2011). The removal of viral and proteinaceous components from the media of HIV-infected macrophages (HIV/MDM) revealed that a low molecular weight compounds acting through glutamatergic receptors were toxic to neurons (O'Donnell et al, 2006; Erdmann et al, 2007; Erdmann et al, 2009).…”