Mitochondrial glutaminase release contributes to glutamate-mediated neurotoxicity during human immunodeficiency virus-1 infection

NMDA receptor blockade attenuates Japanese encephalitis virus infection-induced microglia activation

Neurodegeneration and neuroinflammation are key components in the pathogenesis of Japanese Encephalitis caused by Japanese Encephalitis Virus (JEV) infection. The N-methyl-D-aspartate (NMDA)-type glutamate receptor displays excitatory neurotoxic and pro-inflammatory properties in a cell context-dependent manner. Herein, potential roles of the NMDA receptor in excitatory neurotoxicity and neuroinflammation and effects of NMDA receptor blockade against JEV pathogenesis were investigated in rat microglia, neuron/glia, neuron cultures, and C57BL/6 mice. In microglia, JEV infection induced glutamate release and activated post-receptor NMDA signaling, leading to activation of Ca2+ mobilization and Calcium/Calmodulin-dependent Protein Kinase II (CaMKII), accompanied by pro-inflammatory NF-κB and AP-1 activation and cytokine expression. Additionally, increased Dynamin-Related Protein-1 protein phosphorylation, NAPDH Oxidase-2/4 expression, free radical generation, and Endoplasmic Reticulum stress paralleled with the reactive changes of microglia after JEV infection. JEV infection-induced biochemical and molecular changes contributed to microglia reactivity and pro-inflammatory cytokine expression. NMDA receptor antagonists MK801 and memantine alleviated intracellular signaling and pro-inflammatory cytokine expression in JEV-infected microglia. JEV infection induced neuronal cell death in neuron/glia culture associated with the concurrent production of pro-inflammatory cytokines. Conditioned media of JEV-infected microglia compromised neuron viability in neuron culture. JEV infection-associated neuronal cell death was alleviated by MK801 and memantine. Activation of NMDA receptor-related inflammatory changes, microglia activation, and neurodegeneration as well as reversal effects of memantine were revealed in the brains of JEV-infected mice. The current findings highlight a crucial role of the glutamate/NMDA receptor axis in linking excitotoxicity and neuroinflammation during the course of JEV pathogenesis, and proposes the anti-inflammatory and neuroprotective potential of NMDA receptor blockade.

Neuroinflammation in HIV-Related Neuropathic Pain

In the management of human immunodeficiency virus (HIV) infection around the world, chronic complications are becoming a new problem along with the prolonged life expectancy. Chronic pain is widespread in HIV infected patients and even affects those with a low viral load undergoing long-term treatment with antiviral drugs, negatively influencing the adherence to disease management and quality of life. A large proportion of chronic pain is neuropathic pain, which defined as chronic pain caused by nervous system lesions or diseases, presenting a series of nervous system symptoms including both positive and negative signs. Injury caused by HIV protein, central and peripheral sensitization, and side effects of antiretroviral therapy lead to neuroinflammation, which is regarded as a maladaptive mechanism originally serving to promote regeneration and healing, constituting the main mechanism of HIV-related neuropathic pain. Gp120, as HIV envelope protein, has been found to be the major toxin that induces neuropathic pain. Particularly, the microglia, releasing numerous pro-inflammatory substances (such as TNFα, IL-1β, and IL-6), not only sensitize the neurons but also are the center part of the crosstalk bridging the astrocytes and oligodendrocytes together forming the central sensitization during HIV infection, which is not discussed detailly in recent reviews. In the meantime, some NRTIs and PIs exacerbate the neuroinflammation response. In this review, we highlight the importance of clarifying the mechanism of HIV-related neuropathic pain, and discuss about the limitation of the related studies as future research directions.

Alzheimer's disease-like perturbations in HIV-mediated neuronal dysfunctions: understanding mechanisms and developing therapeutic strategies

Excessive exposure to toxic substances or chemicals in the environment and various pathogens, including viruses and bacteria, is associated with the onset of numerous brain abnormalities. Among them, pathogens, specifically viruses, elicit persistent inflammation that plays a major role in Alzheimer's disease (AD) as well as dementia. AD is the most common brain disorder that affects thought, speech, memory and ability to execute daily routines. It is also manifested by progressive synaptic impairment and neurodegeneration, which eventually leads to dementia following the accumulation of Aβ and hyperphosphorylated Tau. Numerous factors contribute to the pathogenesis of AD, including neuroinflammation associated with pathogens, and specifically viruses. The human immunodeficiency virus (HIV) is often linked with HIV-associated neurocognitive disorders (HAND) following permeation through the blood-brain barrier (BBB) and induction of persistent neuroinflammation. Further, HIV infections also exhibited the ability to modulate numerous AD-associated factors such as BBB regulators, members of stress-related pathways as well as the amyloid and Tau pathways that lead to the formation of amyloid plaques or neurofibrillary tangles accumulation. Studies regarding the role of HIV in HAND and AD are still in infancy, and potential link or mechanism between both is not yet established. Thus, in the present article, we attempt to discuss various molecular mechanisms that contribute to the basic understanding of the role of HIV-associated neuroinflammation in AD and HAND. Further, using numerous growth factors and drugs, we also present possible therapeutic strategies to curb the neuroinflammatory changes and its associated sequels.

The Glutamate System as a Crucial Regulator of CNS Toxicity and Survival of HIV Reservoirs

Glutamate (Glu) is the most abundant excitatory neurotransmitter in the central nervous system (CNS). HIV-1 and viral proteins compromise glutamate synaptic transmission, resulting in poor cell-to-cell signaling and bystander toxicity. In this study, we identified that myeloid HIV-1-brain reservoirs survive in Glu and glutamine (Gln) as a major source of energy. Thus, we found a link between synaptic compromise, metabolomics of viral reservoirs, and viral persistence. In the current manuscript we will discuss all these interactions and the potential to achieve eradication and cure using this unique metabolic profile.

Microglia Mediate HIV-1 gp120-Induced Synaptic Degeneration in Spinal Pain Neural Circuits

HIV-1 infection of the nervous system causes various neurological diseases, and synaptic degeneration is likely a critical step in the neuropathogenesis. Our prior studies revealed a significant decrease of synaptic protein, specifically in the spinal dorsal horn of patients with HIV-1 in whom pain developed, suggesting a potential contribution of synaptic degeneration to the pathogenesis of HIV-associated pain. However, the mechanism by which HIV-1 causes the spinal synaptic degeneration is unclear. Here, we identified a critical role of microglia in the synaptic degeneration. In primary cortical cultures (day in vitro 14) and spinal cords of 3- to 5-month-old mice (both sexes), microglial ablation inhibited gp120-induced synapse decrease. Fractalkine (FKN), a microglia activation chemokine specifically expressed in neurons, was upregulated by gp120, and knockout of the FKN receptor CX3CR1, which is predominantly expressed in microglia, protected synapses from gp120-induced toxicity. These results indicate that the neuron-to-microglia intercellular FKN/CX3CR1 signaling plays a role in gp120-induced synaptic degeneration. To elucidate the mechanism controlling this intercellular signaling, we tested the role of the Wnt/β-catenin pathway in regulating FKN expression. Inhibition of Wnt/β-catenin signaling blocked both gp120-induced FKN upregulation and synaptic degeneration, and gp120 stimulated Wnt/β-catenin-regulated FKN expression via NMDA receptors (NMDARs). Furthermore, NMDAR antagonist APV, Wnt/β-catenin signaling suppressor DKK1, or knockout of CX3CR1 alleviated gp120-induced mechanical allodynia in mice, suggesting a critical contribution of the Wnt/β-catenin/FKN/CX3R1 pathway to gp120-induced pain. These findings collectively suggest that HIV-1 gp120 induces synaptic degeneration in the spinal pain neural circuit by activating microglia via Wnt3a/β-catenin-regulated FKN expression in neurons.SIGNIFICANCE STATEMENT Synaptic degeneration develops in the spinal cord dorsal horn of HIV patients with chronic pain, but the patients without the pain disorder do not show this neuropathology, indicating a pathogenic contribution of the synaptic degeneration to the development of HIV-associated pain. However, the mechanism underlying the synaptic degeneration is unclear. We report here that HIV-1 gp120, a neurotoxic protein that is specifically associated with the manifestation of pain in HIV patients, induces synapse loss via microglia. Further studies elucidate that gp120 activates microglia by stimulating Wnt/β-catenin-regulated fractalkine in neuron. The results demonstrate a critical role of microglia in the pathogenesis of HIV-associated synaptic degeneration in the spinal pain neural circuit.

Evidence of adaptation of maternofetal transport of glutamine relative to placental size in normal mice, and in those with fetal growth restriction

Key points

Fetal growth restriction (FGR) is a major risk factor for stillbirth and has significant impact upon lifelong health.

A small, poorly functioning placenta, as evidenced by reduced transport of nutrients to the baby, underpins FGR. It remains unclear how a small but normal placenta differs from the small FGR placenta in terms of ability to transfer nutrients to the fetus.

Placental transport of glutamine and glutamate, key amino acids for fetal growth, was assessed in normal mice and those with FGR.

Glutamine and glutamate transport was greater in the lightest versus heaviest placenta in a litter of normally grown mice. Placentas of mice with FGR had increased transport capacity in mid‐pregnancy, but this adaptation was insufficient in late pregnancy.

Placental adaptations, in terms of increased nutrient transport (per gram) to compensate for small size, appear to achieve appropriate fetal growth in normal pregnancy. Failure of this adaptation might contribute to FGR.

Abstract

Fetal growth restriction (FGR), a major risk factor for stillbirth, and neonatal and adulthood morbidity, is associated with reduced placental size and decreased placental nutrient transport. In mice, a small, normal placenta increases its nutrient transport, thus compensating for its reduced size and maintaining normal fetal growth. Whether this adaptation occurs for glutamine and glutamate, two key amino acids for placental metabolism and fetal growth, is unknown. Additionally, an assessment of placental transport of glutamine and glutamate between FGR and normal pregnancy is currently lacking. We thus tested the hypothesis that the transport of glutamine and glutamate would be increased (per gram of tissue) in a small normal placenta [C57BL6/J (wild‐type, WT) mice], but that this adaptation fails in the small dysfunctional placenta in FGR [insulin‐like growth factor 2 knockout (P0) mouse model of FGR]. In WT mice, comparing the lightest versus heaviest placenta in a litter, unidirectional maternofetal clearance (K_mf) of ¹⁴C‐glutamine and ¹⁴C‐glutamate (^glutamineK_mf and ^glutamateK_mf) was significantly higher at embryonic day (E) 18.5, in line with increased expression of LAT1, a glutamine transporter protein. In P0 mice, ^glutamineK_mf and ^glutamateK_mf were higher (P0 versus wild‐type littermates, WTL) at E15.5. At E18.5, ^glutamineK_mf remained elevated whereas ^glutamateK_mf was similar between groups. In summary, we provide evidence that ^glutamineK_mf and ^glutamateK_mf adapt according to placental size in WT mice. The placenta of the growth‐restricted P0 fetus also elevates transport capacity to compensate for size at E15.5, but this adaptation is insufficient at E18.5; this may contribute to decreased fetal growth.

Fetal growth restriction (FGR) is a major risk factor for stillbirth and has significant impact upon lifelong health.

A small, poorly functioning placenta, as evidenced by reduced transport of nutrients to the baby, underpins FGR. It remains unclear how a small but normal placenta differs from the small FGR placenta in terms of ability to transfer nutrients to the fetus.

Placental transport of glutamine and glutamate, key amino acids for fetal growth, was assessed in normal mice and those with FGR.

Glutamine and glutamate transport was greater in the lightest versus heaviest placenta in a litter of normally grown mice. Placentas of mice with FGR had increased transport capacity in mid‐pregnancy, but this adaptation was insufficient in late pregnancy.

Placental adaptations, in terms of increased nutrient transport (per gram) to compensate for small size, appear to achieve appropriate fetal growth in normal pregnancy. Failure of this adaptation might contribute to FGR.

Glutamine Antagonist JHU083 Normalizes Aberrant Glutamate Production and Cognitive Deficits in the EcoHIV Murine Model of HIV-Associated Neurocognitive Disorders

HIV-associated neurocognitive disorders (HAND) have been linked to dysregulation of glutamate metabolism in the central nervous system (CNS) culminating in elevated extracellular glutamate and disrupted glutamatergic neurotransmission. Increased glutamate synthesis via upregulation of glutaminase (GLS) activity in brain immune cells has been identified as one potential source of excess glutamate in HAND. However, direct evidence for this hypothesis in an animal model is lacking, and the viability of GLS as a drug target has not been explored. In this brief report, we demonstrate that GLS inhibition with the glutamine analogue 6-diazo-5-oxo-L-norleucine (DON) can reverse cognitive impairment in the EcoHIV-infected mouse model of HAND. However, due to peripheral toxicity DON is not amenable to clinical use in a chronic disease such as HAND. We thus tested JHU083, a novel, brain penetrant DON prodrug predicted to exhibit improved tolerability. Systemic administration of JHU083 reversed cognitive impairment in EcoHIV-infected mice similarly to DON, and simultaneously normalized EcoHIV-induced increases in cerebrospinal fluid (CSF) glutamate and GLS activity in microglia-enriched brain CD11b + cells without observed toxicity. These studies support the mechanistic involvement of elevated microglial GLS activity in HAND pathogenesis, and identify JHU083 as a potential treatment option. Graphical Abstract Please provide Graphical Abstract caption.Glutamine Antagonist JHU083 Normalizes Aberrant Glutamate Production and Cognitive Deficits in the EcoHIV Murine Model of HIV-Associated Neurocognitive Disorders .

Transcriptome analysis reveals the activation of neuroendocrine-immune system in shrimp hemocytes at the early stage of WSSV infection

Background

Functional communications between nervous, endocrine and immune systems are well established in both vertebrates and invertebrates. Circulating hemocytes act as fundamental players in this crosstalk, whose functions are conserved during the evolution of the main groups of metazoans. However, the roles of the neuroendocrine-immune (NEI) system in shrimp hemocytes during pathogen infection remain largely unknown.

Results

In this study, we sequenced six cDNA libraries prepared with hemocytes from Litopenaeus vannamei which were injected by WSSV (white spot syndrome virus) or PBS for 6 h using Illumina Hiseq 4000 platform. As a result, 3444 differentially expressed genes (DEGs), including 3240 up-regulated genes and 204 down-regulated genes, were identified from hemocytes after WSSV infection. Among these genes, 349 DEGs were correlated with innate immunity and categorized into seven groups based on their predictive function. Interestingly, 18 genes encoded putative neuropeptide precursors were induced significantly by WSSV infection. Furthermore, some genes were mapped to several typical processes in the NEI system, including proteolytic processing of prohormones, amino acid neurotransmitter pathways, biogenic amine biosynthesis and acetylcholine signaling pathway.

Conclusions

The data suggested that WSSV infection triggers the activation of NEI in shrimp, which throws a light on the pivotal roles of NEI system mediated by hemocytes in shrimp antiviral immunity.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5614-4) contains supplementary material, which is available to authorized users.

Glutaminase 1 regulates the release of extracellular vesicles during neuroinflammation through key metabolic intermediate alpha-ketoglutarate

Background

Extracellular vesicles (EVs) are important in the intercellular communication of the central nervous system, and their release is increased during neuroinflammation. Our previous data demonstrated an increased release of EVs during HIV-1 infection and immune activation in glial cells. However, the molecular mechanism by which infection and inflammation increase EV release remains unknown. In the current study, we investigated the role of glutaminase 1 (GLS1)-mediated glutaminolysis and the production of a key metabolic intermediate α-ketoglutarate on EV release.

Methods

Human monocyte-derived macrophage primary cultures and a BV2 microglia cell line were used to represent the innate immune cells in the CNS. Transmission electron microscopy, nanoparticle tracking analysis, and Western blots were used to determine the EV regulation. GLS1 overexpression was performed using an adenovirus vector in vitro and transgenic mouse models in vivo. Data were evaluated statistically by ANOVA, followed by the Bonferroni post-test for paired observations.

Results

Our data revealed an increased release of EVs in GLS1-overexpressing HeLa cells. In HIV-1-infected macrophages and immune-activated microglia BV2 cells, treatment with bis-2-(5-phenylacetamido-1,2,4-thiadiazol-2-yl)ethyl sulfide (BPTES) or CB839, two specific GLS inhibitors, significantly decreased EV release, suggesting a critical role of GLS1 in EV release. Furthermore, addition of α-ketoglutarate or ceramide rescued EV release during BPTES treatment, implicating α-ketoglutarate and ceramide as critical downstream effectors for GLS inhibitors. These findings were further corroborated with the investigation of brain tissues in GLS1-transgenic mice. The EV levels were significantly higher in GLS1 transgenic mice than those in control mice, suggesting that GLS1 increases EV release in vivo.

Conclusions

These findings suggest that GLS1-mediated glutaminolysis and its downstream production of α-ketoglutarate are essential in regulating EV release during HIV-1 infection and immune activation. These new mechanistic regulations may help understand how glutamine metabolism shapes EV biogenesis and release during neuroinflammation.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1120-x) contains supplementary material, which is available to authorized users.

The interaction between mitochondria and oncoviruses

Mitochondria play important roles in multiple aspects of viral tumorigenesis. Mitochondrial genomes contribute to the host's genetic background. After viruses enter the cell, they modulate mitochondrial function and thus alter bioenergetics and retrograde signaling pathways. At the same time, mitochondria also regulate and mediate viral oncogenesis. In this context, oncogenesis by oncoviruses like Hepatitis B virus (HBV), Hepatitis C virus (HCV), Human papilloma virus (HPV), Human Immunodeficiency virus (HIV) and Epstein-Barr virus (EBV) will be discussed.

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

Glutaminolysis, a metabolic process that converts glutamine to glutamate, is particularly important for the central nervous system since glutamate is the major transmitter of excitatory synapses. Glutaminase is the mitochondrial enzyme that catalyzes the first step of glutaminolysis. Two genes encode at least four isoforms of glutaminase in humans. Gls1 gene encodes isoforms kidney-type glutaminase (KGA) and glutaminase C (GAC) through alternative splicing, whereas Gls2 gene encodes liver-type glutaminase isoforms. KGA and GAC have been associated with several neurological diseases. However, it remains unclear whether changes in their expressions can directly cause brain abnormalities. Using a transgenic approach, we generated mice that overexpressed GAC in the brain. The resulting transgenic mice had severe impairments in spatial and fear learning compared with littermate controls. The learning deficits were consistent with diminished hippocampal long-term potentiation in the hippocampal slices of the GAC transgenic mice. Furthermore, we found increases in astrocyte and microglia markers, inflammatory factors, and a decrease in synapse marker synaptophysin, suggesting neuroinflammation and synaptic changes in the GAC transgenic mouse brains. In conclusion, these findings provide the first evidence that GAC overexpression in the brain has deleterious effects on learning and synaptic integrity in vivo.

HIV-associated synaptic degeneration

Human immunodeficiency virus (HIV) infection induces neuronal injuries, with almost 50% of infected individuals developing HIV-associated neurocognitive disorders (HAND). Although highly activate antiretroviral therapy (HAART) has significantly reduced the incidence of severe dementia, the overall prevalence of HAND remains high. Synaptic degeneration is emerging as one of the most relevant neuropathologies associate with HAND. Previous studies have reported critical roles of viral proteins and inflammatory responses in this pathogenesis. Infected cells, including macrophages, microglia and astrocytes, may release viral proteins and other neurotoxins to stimulate neurons and cause excessive calcium influx, overproduction of free radicals and disruption of neurotransmitter hemostasis. The dysregulation of neural circuits likely leads to synaptic damage and loss. Identification of the specific mechanism of the synaptic degeneration may facilitate the development of effective therapeutic approaches to treat HAND.

N-(Pivaloyloxy)alkoxy-carbonyl Prodrugs of the Glutamine Antagonist 6-Diazo-5-oxo-l-norleucine (DON) as a Potential Treatment for HIV Associated Neurocognitive Disorders

Aberrant excitatory neurotransmission associated with overproduction of glutamate has been implicated in the development of HIV-associated neurocognitive disorders (HAND). The glutamine antagonist 6-diazo-5-oxo-l-norleucine (DON, 14) attenuates glutamate synthesis in HIV-infected microglia/macrophages, offering therapeutic potential for HAND. We show that 14 prevents manifestation of spatial memory deficits in chimeric EcoHIV-infected mice, a model of HAND. 14 is not clinically available, however, because its development was hampered by peripheral toxicities. We describe the synthesis of several substituted N-(pivaloyloxy)alkoxy-carbonyl prodrugs of 14 designed to circulate inert in plasma and be taken up and biotransformed to 14 in the brain. The lead prodrug, isopropyl 6-diazo-5-oxo-2-(((phenyl(pivaloyloxy)methoxy)carbonyl)amino)hexanoate (13d), was stable in swine and human plasma but liberated 14 in swine brain homogenate. When dosed systemically in swine, 13d provided a 15-fold enhanced CSF-to-plasma ratio and a 9-fold enhanced brain-to-plasma ratio relative to 14, opening a possible clinical path for the treatment of HAND.

TNF-α promotes extracellular vesicle release in mouse astrocytes through glutaminase

Background

Extracellular vesicles (EVs) are membrane-contained vesicles shed from cells. EVs contain proteins, lipids, and nucleotides, all of which play important roles in intercellular communication. The release of EVs is known to increase during neuroinflammation. Glutaminase, a mitochondrial enzyme that converts glutamine to glutamate, has been implicated in the biogenesis of EVs. We have previously demonstrated that TNF-α promotes glutaminase expression in neurons. However, the expression and the functionality of glutaminase in astrocytes during neuroinflammation remain unknown. We posit that TNF-α can promote the release of EVs in astrocytes through upregulation of glutaminase expression.

Results

Release of EVs, which was demonstrated by electron microscopy, nanoparticle tracking analysis (NTA), and Western Blot, increased in mouse astrocytes when treated with TNF-α. Furthermore, TNF-α treatment significantly upregulated protein levels of glutaminase and increased the production of glutamate, suggesting that glutaminase activity is increased after TNF-α treatment. Interestingly, pretreatment with a glutaminase inhibitor blocked TNF-α-mediated generation of reactive oxygen species in astrocytes, which indicates that glutaminase activity contributes to stress in astrocytes during neuroinflammation. TNF-α-mediated increased release of EVs can be blocked by either the glutaminase inhibitor, antioxidant N-acetyl-l-cysteine, or genetic knockout of glutaminase, suggesting that glutaminase plays an important role in astrocyte EV release during neuroinflammation.

Conclusions

These findings suggest that glutaminase is an important metabolic factor controlling EV release from astrocytes during neuroinflammation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-017-0853-2) contains supplementary material, which is available to authorized users.

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

HIV-1 infected macrophages play a significant role in the neuropathogenesis of AIDS. HIV-1 viral protein R (Vpr) not only facilitates HIV-1 infection but also contribute to long-lived persistence in macrophages. Our previous studies using SILAC-based proteomic analysis showed that the expression of critical metabolic enzymes in the glycolytic pathway and tricarboxylic acid (TCA) cycle were altered in response to Vpr expression in macrophages. We hypothesized that Vpr-induced modulation of glycolysis and TCA cycle regulates glutamate metabolism and release in HIV-1 infected macrophages. We assessed the amount of specific metabolites induced by Vpr and HIV-1 in macrophages at the intracellular and extracellular level in a time-dependent manner utilizing multiple reaction monitoring (MRM) targeted metabolomics. In addition, stable isotope-labeled glucose and an MRM targeted metabolomics assay were used to evaluate the de novo synthesis and release of glutamate in Vpr overexpressing macrophages and HIV-1 infected macrophages, throughout the metabolic flux of glycolytic pathway and TCA cycle activation. The metabolic flux studies demonstrated an increase in glucose uptake, glutamate release and accumulation of α-ketoglutarate (α-KG) and glutamine in the extracellular milieu in Vpr expressing and HIV-1 infected macrophages. Interestingly, glutamate pools and other intracellular intermediates (glucose-6-phosphate (G6P), fructose-6-phosphate (F6P), citrate, malate, α-KG, and glutamine) showed a decreased trend except for fumarate, in contrast to the glutamine accumulation observed in the extracellular space in Vpr overexpressing macrophages. Our studies demonstrate that dysregulation of mitochondrial glutamate metabolism induced by Vpr in HIV-1 infected macrophages commonly seen, may contribute to neurodegeneration via excitotoxic mechanisms in the context of NeuroAIDS.

Disruption of TCA Cycle and Glutamate Metabolism Identified by Metabolomics in an In Vitro Model of Amyotrophic Lateral Sclerosis

This study aims to develop a cellular metabolomics model that reproduces the pathophysiological conditions found in amyotrophic lateral sclerosis in order to improve knowledge of disease physiology. We used a co-culture model combining the motor neuron-like cell line NSC-34 and the astrocyte clone C8-D1A, with each over-expressing wild-type or G93C mutant human SOD1, to examine amyotrophic lateral sclerosis (ALS) physiology. We focused on the effects of mutant human SOD1 as well as oxidative stress induced by menadione on intracellular metabolism using a metabolomics approach through gas chromatography coupled with mass spectrometry (GC-MS) analysis. Preliminary non-supervised analysis by Principal Component Analysis (PCA) revealed that cell type, genetic environment, and time of culture influenced the metabolomics profiles. Supervised analysis using orthogonal partial least squares discriminant analysis (OPLS-DA) on data from intracellular metabolomics profiles of SOD1^G93C co-cultures produced metabolites involved in glutamate metabolism and the tricarboxylic acid cycle (TCA) cycle. This study revealed the feasibility of using a metabolomics approach in a cellular model of ALS. We identified potential disruption of the TCA cycle and glutamate metabolism under oxidative stress, which is consistent with prior research in the disease. Analysis of metabolic alterations in an in vitro model is a novel approach to investigation of disease physiology.

Glutaminase-containing microvesicles from HIV-1-infected macrophages and immune-activated microglia induce neurotoxicity

BACKGROUND

HIV-1-infected and/or immune-activated microglia and macrophages are pivotal in the pathogenesis of HIV-1-associated neurocognitive disorders (HAND). Glutaminase, a metabolic enzyme that facilitates glutamate generation, is upregulated and may play a pathogenic role in HAND. Our previous studies have demonstrated that glutaminase is released to the extracellular fluid during HIV-1 infection and neuroinflammation. However, key molecular mechanisms that regulate glutaminase release remain unknown. Recent advances in understanding intercellular trafficking have identified microvesicles (MVs) as a novel means of shedding cellular contents. We posit that during HIV-1 infection and immune activation, microvesicles may mediate glutaminase release, generating excessive and neurotoxic levels of glutamate.

RESULTS

MVs isolated through differential centrifugation from cell-free supernatants of monocyte-derived macrophages (MDM) and BV2 microglia cell lines were first confirmed in electron microscopy and immunoblotting. As expected, we found elevated number of MVs, glutaminase immunoreactivities, as well as glutaminase enzyme activity in the supernatants of HIV-1 infected MDM and lipopolysaccharide (LPS)-activated microglia when compared with controls. The elevated glutaminase was blocked by GW4869, a neutral sphingomyelinase inhibitor known to inhibit MVs release, suggesting a critical role of MVs in mediating glutaminase release. More importantly, MVs from HIV-1-infected MDM and LPS-activated microglia induced significant neuronal injury in rat cortical neuron cultures. The MV neurotoxicity was blocked by a glutaminase inhibitor or GW4869, suggesting that the neurotoxic potential of HIV-1-infected MDM and LPS-activated microglia is dependent on the glutaminase-containing MVs.

CONCLUSIONS

These findings support MVs as a potential pathway/mechanism of excessive glutamate generation and neurotoxicity in HAND and therefore MVs may serve as a novel therapeutic target.

Macrophages treated with particulate matter PM2.5 induce selective neurotoxicity through glutaminase-mediated glutamate generation

Exposure to atmospheric particulate matter PM2.5 (aerodynamic diameter ≤ 2.5 μm) has been epidemiologically associated with respiratory illnesses. However, recent data have suggested that PM2.5 is able to infiltrate into circulation and elicit a systemic inflammatory response. Potential adverse effects of air pollutants to the central nervous system (CNS) have raised concerns, but whether PM2.5 causes neurotoxicity remains unclear. In this study, we have demonstrated that PM2.5 impairs the tight junction of endothelial cells and increases permeability and monocyte transmigration across endothelial monolayer in vitro, indicating that PM2.5 is able to disrupt blood-brain barrier integrity and gain access to the CNS. Exposure of primary neuronal cultures to PM2.5 resulted in decrease in cell viability and loss of neuronal antigens. Furthermore, supernatants collected from PM2.5 -treated macrophages and microglia were also neurotoxic. These macrophages and microglia significantly increased extracellular levels of glutamate following PM2.5 exposure, which were negatively correlated with neuronal viability. Pre-treatment with NMDA receptor antagonist MK801 alleviated neuron loss, suggesting that PM2.5 neurotoxicity is mediated by glutamate. To determine the potential source of excess glutamate production, we investigated glutaminase, the main enzyme for glutamate generation. Glutaminase was reduced in PM2.5 -treated macrophages and increased in extracellular vesicles, suggesting that PM2.5 induces glutaminase release through extracellular vesicles. In conclusion, these findings indicate PM2.5 as a potential neurotoxic factor, crucial to understanding the effects of air pollution on the CNS.

HIV effects on age-associated neurocognitive dysfunction: premature cognitive aging or neurodegenerative disease?

Marked improvements in survival and health outcome for people infected with HIV have occurred since the advent of combination antiretroviral therapy over a decade ago. Yet HIV-associated neurocognitive disorders continue to occur with an alarming prevalence. This may reflect the fact that infected people are now living longer with chronic infection. There is mounting evidence that HIV exacerbates age-associated cognitive decline. Many middle-aged HIV-infected people are experiencing cognitive decline similar that to that found among much older adults. An increased prevalence of vascular and metabolic comorbidities has also been observed and is greatest among older adults with HIV. Premature age-associated neurocognitive decline appears to be related to structural and functional brain changes on neuroimaging, and of particular concern is the fact that pathology indicative of neurodegenerative disease has been shown to occur in the brains of HIV-infected people. Yet notable differences also exist between the clinical presentation and brain disturbances occurring with HIV and those occurring in neurodegenerative conditions such as Alzheimer’s disease. HIV interacts with the aging brain to affect neurological structure and function. However, whether this interaction directly affects neurodegenerative processes, accelerates normal cognitive aging, or contributes to a worsening of other comorbidities that affect the brain in older adults remains an open question. Evidence for and against each of these possibilities is reviewed.

Heme oxygenase-1 dysregulation in the brain: implications for HIV-associated neurocognitive disorders

Heme oxygenase-1 (HO-1) is a highly inducible and ubiquitous cellular enzyme that subserves cytoprotective responses to toxic insults, including inflammation and oxidative stress. In neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease and multiple sclerosis, HO-1 expression is increased, presumably reflecting an endogenous neuroprotective response against ongoing cellular injury. In contrast, we have found that in human immunodeficiency virus (HIV) infection of the brain, which is also associated with inflammation, oxidative stress and neurodegeneration, HO-1 expression is decreased, likely reflecting a unique role for HO-1 deficiency in neurodegeneration pathways activated by HIV infection. We have also shown that HO-1 expression is significantly suppressed by HIV replication in cultured macrophages which represent the primary cellular reservoir for HIV in the brain. HO-1 deficiency is associated with release of neurotoxic levels of glutamate from both HIV-infected and immune-activated macrophages; this glutamate-mediated neurotoxicity is suppressed by pharmacological induction of HO-1 expression in the macrophages. Thus, HO-1 induction could be a therapeutic strategy for neuroprotection against HIV infection and other neuroinflammatory brain diseases. Here, we review various stimuli and signaling pathways regulating HO-1 expression in macrophages, which could promote neuronal survival through HO-1-modulation of endogenous antioxidant and immune modulatory pathways, thus limiting the oxidative stress that can promote HIV disease progression in the CNS. The use of pharmacological inducers of endogenous HO-1 expression as potential adjunctive neuroprotective therapeutics in HIV infection is also discussed.

Adenosine triphosphate released from HIV-infected macrophages regulates glutamatergic tone and dendritic spine density on neurons

Despite wide spread use of combination antiretroviral therapy (cART) in developed countries, approximately half of HIV-infected patients will develop impairments in cognitive function. Accumulating evidence suggests that neuronal dysfunction can be precipitated by HIV-infection of macrophages by mechanisms that involve alterations in innate and adaptive immune responses. HIV-infection of macrophages is known to increase the release of soluble neurotoxins. However, the composition of products released from infected macrophages is complex and not fully known. In this study we provide evidence that ATP and other immuno-/neuromodulatory nucleotides are exported from HIV-infected macrophages and modify neuronal structure. Supernatants collected from HIV-infected macrophages (HIV/MDM) contained large amounts of ATP, ADP, AMP and small amounts of adenosine, in addition to glutamate. Dilutions of these supernatants that were sub-threshold for glutamate receptor activation evoked rapid calcium flux in neurons that were completely inhibited by the enzymatic degradation of ATP, or by blockade of calcium permeable purinergic receptors. Applications of these highly diluted HIV/MDM onto neuronal cultures increased the amount of extracellular glutamate by mechanisms dependent on purinergic receptor activation, and downregulated spine density on neurons by mechanisms dependent on purinergic and glutamate receptor activation. We conclude from these data that ATP released from HIV-infected macrophages downregulates dendritic spine density on neurons by a mechanism that involves purinergic receptor mediated modulation of glutamatergic tone. These data suggest that neuronal function may be depressed in HIV infected individuals by mechanisms that involve macrophage release of ATP that triggers secondary effects on glutamate handling.

IL-1β and TNF-α induce neurotoxicity through glutamate production: a potential role for neuronal glutaminase

Glutaminase 1 is the main enzyme responsible for glutamate production in mammalian cells. The roles of macrophage and microglia glutaminases in brain injury, infection, and inflammation are well documented. However, little is known about the regulation of neuronal glutaminase, despite neurons being a predominant cell type of glutaminase expression. Using primary rat and human neuronal cultures, we confirmed that interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α), two pro-inflammatory cytokines that are typically elevated in neurodegenerative disease states, induced neuronal death and apoptosis in vitro. Furthermore, both intracellular and extracellular glutamate levels were significantly elevated following IL-1β and/or TNF-α treatment. Pre-treatment with N-Methyl-D-aspartate (NMDA) receptor antagonist MK-801 blocked cytokine-induced glutamate production and alleviated the neurotoxicity, indicating that IL-1β and/or TNF-α induce neurotoxicity through glutamate. To determine the potential source of excess glutamate production in the culture during inflammation, we investigated the neuronal glutaminase and found that treatment with IL-1β or TNF-α significantly upregulated the kidney-type glutaminase (KGA), a glutaminase 1 isoform, in primary human neurons. The up-regulation of neuronal glutaminase was also demonstrated in situ in a murine model of HIV-1 encephalitis. In addition, IL-1β or TNF-α treatment increased the levels of KGA in cytosol and TNF-α specifically increased KGA levels in the extracellular fluid, away from its main residence in mitochondria. Together, these findings support neuronal glutaminase as a potential component of neurotoxicity during inflammation and that modulation of glutaminase may provide therapeutic avenues for neurodegenerative diseases.

Astrocytic expression of HIV-1 Nef impairs spatial and recognition memory

Despite the widespread use of antiretroviral therapy that effectively limits viral replication, memory impairment remains a dilemma for HIV infected people. In the CNS, HIV infection of astrocytes leads to the production of the HIV-1 Nef protein without viral replication. Post mortem studies have found Nef expression in hippocampal astrocytes of people with HIV associated dementia suggesting that astrocytic Nef may contribute to HIV associated cognitive impairment even when viral replication is suppressed. To test whether astrocytic expression of Nef is sufficient to induce cognitive deficits, we examined the effect of implanting primary rat astrocytes expressing Nef into the hippocampus on spatial and recognition memory. Rats implanted unilaterally with astrocytes expressing Nef showed impaired novel location and novel object recognition in comparison with controls implanted with astrocytes expressing green fluorescent protein (GFP). This impairment was correlated with an increase in chemokine ligand 2 (CCL2) expression and the infiltration of peripheral macrophages into the hippocampus at the site of injection. Furthermore, the Nef exposed rats exhibited a bilateral loss of CA3 neurons. These results suggest that Nef protein expressed by the implanted astrocytes activates the immune system leading to neuronal damage and spatial and recognition memory deficits. Therefore, the continued expression of Nef by astrocytes in the absence of viral replication has the potential to contribute to HIV associated cognitive impairment.