The glutamate-glutamine cycle as an inducible, protective face of macrophage activation

The acute neurotoxicity of inorganic mercury in Mactra chinensis philippi

Inorganic mercury (IHg) is hazardous to marine organisms especially resulting in neurotoxicity, bivalves are sensitive to pollutants as "ocean sentinel", but data on the neurotoxicity of IHg in bivalves are sparse. So we chosed M. chinensis philippi with typical neural structures in bivalves to investigate the neurotoxicity of IHg, which could be helpful to understand the specificity of neural regulation and the response characteristics of bivalves. After acute exposed to IHg (HgCl2) for 24 h, the metabolites of ganglion tissues in M. chinensis philippi were evaluated using 1H-nuclear magnetic resonance based metabolomics; Ca2+, neurotransmitters (nitric oxide, glutamate, acetylcholine) and related enzymes (calcineurin, nitric oxide synthase and acetylcholinesterase) were measured using biochemical detection. Compared to the control group, the levels of the nitric oxide (81.04 ± 12.84 μmol/g prot) and acetylcholine (30.93 ± 12.57 μg/mg prot) in M. chinensis philippi of IHg-treated were decreased, while glutamate (2.11 ± 0.61 mmol/L) increased significantly; the activity of nitric oxide synthase (679.34 ± 135.33 U/mg prot) was increased, while acetylcholinesterase (1.39 ± 0.44 U/mg prot) decreased significantly, and the activity of calcineurin (0.52 ± 0.02 U/mg prot) had a statistically insignificant increasing tendency. The concentration of Ca2+ (0.92 ± 0.46 mmol/g prot) in the IHg-treated group was significantly higher than that in the control group. OPLS-DA was performed to reveal the difference in metabolites between the control and IHg-challenged groups, the metabolites of glucose, glutamine, inosine, succinate, glutamate, homarine, and alanine were sensitive to IHg, subsequently metabolic pathways that were affected including glucose metabolism, glutamine metabolism, nucleotide metabolism, Krebs cycle, amino acid metabolism and osmotic regulation. In our study, IHg interfered with metabolites in M. chinensis philippi, thus the corresponding metabolic pathways were changed, which influenced the neurotransmitters subsequently. Furthermore, Ca2+overload affected the synthesis or degradation of the neurotransmitters, and then the altered neurotransmitters involved in changes in metabolic pathways again. Overall, we hypothesized that the neurotoxic effects of IHg on bivalve were in close contact with metabolism, neurotransmitters, related enzymes and Ca2+, which could be effective neurotoxic biomarkers for marine environmental quality assessment, and also provide effective data for the study of the regulatory mechanism of the nervous system in response to IHg in bivalves.

Effects of Psychotherapy on Glutamatergic Neurotransmission

INTRODUCTION

Psychodynamic psychotherapy is an effective and widely used treatment for major depressive disorder (MDD); however, little is known about neurobiological changes associated with induced symptom improvement.

METHODS

Proton magnetic resonance spectroscopy with a two-dimensional J-resolved sequence served to test the relationship between glutamate (Glu) and glutamine (Gln) levels, measured separately in pregenual anterior cingulate cortex (pgACC) and the anterior midcingulate cortex (aMCC) as a control region, with change in depression symptoms after 6 months of weekly psychodynamic psychotherapy sessions in MDD patients. Depressed (N = 45) and healthy (N = 30) subjects participated in a baseline proton magnetic resonance spectroscopy measurement and a subgroup of MDD subjects (N = 21) then received once-a-week psychodynamic psychotherapy and participated in a second proton magnetic resonance spectroscopy measurement after 6 months. Change in depression symptoms was assessed using the Hamilton Depression Rating Scale (HAMD).

RESULTS

Higher pretreatment pgACC Gln concentrations in MDD patients compared to healthy controls were associated with symptom severity. Patients and controls did not differ regarding Gln levels in aMCC nor regarding Glu levels in both regions. The association of pgACC Gln concentration and severity of depressive symptoms was reversed after 6 months of psychotherapy in MDD subjects. Regarding Gln in aMCC as well as Glu in both regions, there were no significant associations with improvement of depressive symptoms in the course of psychotherapy.

DISCUSSION

Findings indicate specific regional effects of psychodynamic psychotherapy on glutamatergic neurotransmission and thereby highlight the key role of the pgACC in both depression pathophysiology and recovery.

Microglial reprogramming by Hv1 antagonism protects neurons from inflammatory and glutamate toxicity

Although the precise mechanisms determining the neurotoxic or neuroprotective activation phenotypes in microglia remain poorly characterized, metabolic changes in these cells appear critical for these processes. As cellular metabolism can be tightly regulated by changes in intracellular pH, we tested whether pharmacological targeting of the microglial voltage-gated proton channel 1 (Hv1), an important regulator of intracellular pH, is critical for activated microglial reprogramming. Using a mouse microglial cell line and mouse primary microglia cultures, either alone, or co-cultured with rat cerebrocortical neurons, we characterized in detail the microglial activation profile in the absence and presence of Hv1 inhibition. We observed that activated microglia neurotoxicity was mainly attributable to the release of tumor necrosis factor alpha, reactive oxygen species, and zinc. Strikingly, pharmacological inhibition of Hv1 largely abrogated inflammatory neurotoxicity not only by reducing the production of cytotoxic mediators but also by promoting neurotrophic molecule production and restraining excessive phagocytic activity. Importantly, the Hv1-sensitive change from a pro-inflammatory to a neuroprotective phenotype was associated with metabolic reprogramming, particularly via a boost in NADH availability and a reduction in lactate. Most critically, Hv1 antagonism not only reduced inflammatory neurotoxicity but also promoted microglia-dependent neuroprotection against a separate excitotoxic injury. Our results strongly suggest that Hv1 blockers may provide an important therapeutic tool against a wide range of inflammatory neurodegenerative disorders.

Acute effects of ketamine on the pregenual anterior cingulate: linking spontaneous activation, functional connectivity, and glutamate metabolism

Ketamine exerts its rapid antidepressant effects via modulation of the glutamatergic system. While numerous imaging studies have investigated the effects of ketamine on a functional macroscopic brain level, it remains unclear how altered glutamate metabolism and changes in brain function are linked. To shed light on this topic we here conducted a multimodal imaging study in healthy volunteers (N = 23) using resting state fMRI and proton (¹H) magnetic resonance spectroscopy (MRS) to investigate linkage between metabolic and functional brain changes induced by ketamine. Subjects were investigated before and during an intravenous ketamine infusion. The MRS voxel was placed in the pregenual anterior cingulate cortex (pgACC), as this region has been repeatedly shown to be involved in ketamine's effects. Our results showed functional connectivity changes from the pgACC to the right frontal pole and anterior mid cingulate cortex (aMCC). Absolute glutamate and glutamine concentrations in the pgACC did not differ significantly from baseline. However, we found that stronger pgACC activation during ketamine was linked to lower glutamine concentration in this region. Furthermore, reduced functional connectivity between pgACC and aMCC was related to increased pgACC activation and reduced glutamine. Our results thereby demonstrate how multimodal investigations in a single brain region could help to advance our understanding of the association between metabolic and functional changes.

Nature of glutamate alterations in substance dependence: A systematic review and meta-analysis of proton magnetic resonance spectroscopy studies

Animal studies have reported the brain glutamatergic dysfunction in substance dependence. However, proton magnetic resonance spectroscopy (¹H-MRS) studies of glutamate in substance-dependent patients published contradicting results. In order to investigate the characteristics of brain glutamatergic alterations in substance-dependent patients, we conducted systematic reviews and meta-analyses of ¹H-MRS studies that have investigated the glutamate, glutamine, and Glx (glutamate + glutamine) concentration in substance-dependent patients. Multiple databases were searched until Sep 10, 2020. Twenty-nine studies comprising 982 patients and 787 controls were included. There was significantly decreased glutamate level in dorsolateral prefrontal cortex in patients compared with controls. Higher glutamate levels in medial prefrontal cortex and basal ganglia region were also demonstrated in patients compared with controls. Subgroup analyses based on the substance type and abstinence period (short vs medium-term abstinence period) were performed. The results revealed Glx and glutamate concentrations in all investigated brain regions were not different in patients with any types of substance dependence compared with controls. The abstinence period had no effect on the glutamate levels. In summary, substance dependence is associated with glutamatergic dysfunction of prefrontal cortex and basal ganglia. Present findings partially support the hypothesis that addiction is associated with abnormal brain glutamatergic neurotransmission.

Metabolic and inflammatory reprogramming of macrophages by ONC201 translates in a pro-inflammatory environment even in presence of glioblastoma cells

Tumor-associated macrophages facilitate tumor progression and resistance to therapy. Their capacity for metabolic and inflammatory reprogramming represents an attractive therapeutic target. ONC201/TIC10 is an anticancer molecule that antagonizes the dopamine receptor D2 and affects mitochondria integrity in tumor cells. We examined whether ONC201 induces a metabolic and pro-inflammatory switch in primary human monocyte-derived macrophages that reactivates their antitumor activities, thus enhancing the onco-toxicity of ONC201. Contrary to glioblastoma cells, macrophages exhibited a low ratio of dopamine receptors D2/D5 gene expression and were resistant to ONC201 cytotoxicity. Macrophages responded to ONC201 with a severe loss of mitochondria integrity, a switch to glycolytic ATP production, alterations in glutamate transport, and a shift towards a pro-inflammatory profile. Treatment of macrophages-glioblastoma cells co-cultures with ONC201 induced similar alterations in glutamatergic and inflammatory gene expression profiles of macrophages. It induced as well metabolic changes and a pro-inflammatory switch of the co-culture milieu. However, these changes did not translate into increased onco-toxicity. This study provides the first evidence that ONC201 affects macrophage immunometabolism and leads to a pro-inflammatory tumor environment. This speaks in favor of implementing ONC201 in combinatorial therapies and warrants further investigation of the mechanisms of action of ONC201 in macrophages and other immune cells.

Altered neurometabolism in major depressive disorder: A whole brain 1H-magnetic resonance spectroscopic imaging study at 3T

INTRODUCTION

Major depressive disorder (MDD) is a severe mental disorder with a neurobiological basis that is poorly understood. Several studies demonstrated widespread, functional and neurometabolic alterations in MDD. However, little is known about whole brain neurometabolic alterations in MDD.

METHOD

Thirty-two patients with MDD and 32 paired on a one-to-one basis healthy controls (CTRL) underwent ¹H-whole brain spectroscopic (¹H-WBS) imaging. Lobar and cerebellar metabolite concentrations of brain N-acetylaspartate (NAA), total choline (tCho), total creatine (tCr), glutamine (Gln), glutamate (Glu), and myo-Inositol (mI) were assessed in patients and controls.

RESULTS

Decreased NAA, tCho, and tCr were found in the right frontal and right parietal lobe in MDD compared to CTRL, and to a lesser extent in the left frontal lobe. Furthermore, in MDD increased glutamine was observed in the right frontal lobe and bitemporal lobes, and increased glutamate in the cerebellum.

CONCLUSION

Altered global neurometabolism examined using ¹H-WBS imaging in MDD may be interpreted as signs of neuronal dysfunction, altered energy metabolism, and oligodendrocyte dysfunction. In particular, the parallel decrease in NAA, tCr and tCho in the same brain regions may be indicative of neuronal dysfunction that may be counterbalanced by an increase of the neuroprotective metabolite glutamine. Future prospective investigations are warranted to study the functional importance of these findings.

The Human SLC1A5 Neutral Amino Acid Transporter Catalyzes a pH-Dependent Glutamate/Glutamine Antiport, as Well

ASCT2 is a neutral amino acid transporter, which catalyzes a sodium-dependent obligatory antiport among glutamine and other neutral amino acids. The human ASCT2 over-expressed in Pichia pastoris and reconstituted in proteoliposomes has been employed for identifying alternative substrates of the transporter. The experimental data highlighted that hASCT2 also catalyzes a sodium-dependent antiport of glutamate with glutamine. This unconventional antiport shows a preferred sidedness: glutamate is inwardly transported in exchange for glutamine transported in the counter direction. The orientation of the transport protein in proteoliposomes is the same as in the cell membrane; then, the observed sidedness corresponds to the transport of glutamate from the extracellular to the intracellular compartment. The competitive inhibition exerted by glutamate on the glutamine transport together with the docking analysis indicates that the glutamate binding site is the same as that of glutamine. The affinity for glutamate is lower than that for neutral amino acids, while the transport rate is comparable to that measured for the asparagine/glutamine antiport. Differently from the neutral amino acid antiport that is insensitive to pH, the glutamate/glutamine antiport is pH-dependent with optimal activity at acidic pH on the external (extracellular) side. The stimulation of glutamate transport by a pH gradient suggests the occurrence of a proton flux coupled to the glutamate transport. The proton transport has been detected by a spectrofluorometric method. The rate of proton transport correlates well with the rate of glutamate transport indicating a 1:1 stoichiometry H⁺: glutamate. The glutamate/glutamine antiport is also active in intact HeLa cells. On a physiological point of view, the described antiport could have relevance in some districts in which a glutamate/glutamine cycling is necessary, such as in placenta.

Histidine Utilization Is a Critical Determinant of Acinetobacter Pathogenesis

Acinetobacter baumannii is a nosocomial pathogen capable of causing a range of diseases, including respiratory and urinary tract infections and bacteremia. Treatment options are limited due to the increasing rates of antibiotic resistance, underscoring the importance of identifying new targets for antimicrobial development. During infection, A. baumannii must acquire nutrients for replication and survival. These nutrients include carbon- and nitrogen-rich molecules that are needed for bacterial growth. One possible nutrient source within the host is amino acids, which can be utilized for protein synthesis or energy generation. Of these, the amino acid histidine is among the most energetically expensive for bacteria to synthesize; therefore, scavenging histidine from the environment is likely advantageous. We previously identified the A. baumannii histidine utilization (Hut) system as being linked to nutrient zinc homeostasis, but whether the Hut system is important for histidine-dependent energy generation or vertebrate colonization is unknown. Here, we demonstrate that the Hut system is conserved among pathogenic Acinetobacter and regulated by the transcriptional repressor HutC. In addition, the Hut system is required for energy generation using histidine as a carbon and nitrogen source. Histidine was also detected extracellularly in the murine lung, demonstrating that it is bioavailable during infection. Finally, the ammonia-releasing enzyme HutH is required for acquiring nitrogen from histidine in vitro, and strains inactivated for hutH are severely attenuated in a murine model of pneumonia. These results suggest that bioavailable histidine in the lung promotes Acinetobacter pathogenesis and that histidine serves as a crucial nitrogen source during infection.

Assessing the reliability of gene expression measurements in very-low-numbers of human monocyte-derived macrophages

Tumor-derived primary cells are essential for in vitro and in vivo studies of tumor biology. The scarcity of this cellular material limits the feasibility of experiments or analyses and hence hinders basic and clinical research progress. We set out to determine the minimum number of cells that can be analyzed with standard laboratory equipment and that leads to reliable results, unbiased by cell number. A proof-of-principle study was conducted with primary human monocyte-derived macrophages, seeded in decreasing number and constant cell density. Gene expression of cells stimulated to acquire opposite inflammatory states was analyzed by quantitative PCR. Statistical analysis indicated the lack of significant difference in the expression profile of cells cultured at the highest (100,000 cells) and lowest numbers (3,610 cells) tested. Gene Ontology, pathway enrichment and network analysis confirmed the reliability of the data obtained with the lowest cell number. This statistical and computational analysis of gene expression profiles indicates that low cell number analysis is as dependable and informative as the analysis of a larger cell number. Our work demonstrates that it is possible to employ samples with a scarce number of cells in experimental studies and encourages the application of this approach on other cell types.

Combined Glia Inhibition and Opioid Receptor Agonism Afford Highly Potent Analgesics without Tolerance

Commonly prescribed opioid analgesics produce tolerance upon chronic use due in part to induction of hyperalgesia. Given that two reported bivalent ligands (MMG22 and MCC22) produce potent antinociception without tolerance only in inflamed mice, we have investigated the possible cellular and receptor targets of these ligands. The selective microglia inhibitors, minocycline and SB290157, antagonized intrathecal (i.t.) MCC22 antinociception orders of magnitude more potently than MMG22, suggesting that MCC22 selectively targets activated microglia. The astrocyte toxin, l-α-aminoadipic acid antagonized MMG22 antinociception 126-fold without reducing the potency of MCC22, indicating that activated astrocytes are targets of MMG22. MK-801 and Ro25-6981 antagonism of MMG22 antinociception, but not MCC22, is consistent with selective inhibition of activated NMDAR in astrocytes. The antinociception produced by i.t. MMG22 or MCC22 were both antagonized by the selective mu opioid receptor antagonist, β-FNA, implicating interaction of these ligands with MOR in spinal afferent neurons. MCC22 antinociception was potently blocked by kainate or AMPA ion channel antagonists (LY382884; NBQX), in contrast to MMG22. It is concluded that i.t. MMG22 and MCC22 produce exceptional antinociception via potent inhibition of activated spinal glia, thereby leading to desensitization of spinal neurons and enhanced activation of neuronal MOR. Thus, the present study suggests a new approach to treatment of chronic inflammatory pain without tolerance through a single molecular entity that simultaneously inhibits activated glia and stimulates MOR in spinal neurons.

Memantine ameliorates pulmonary inflammation in a mice model of COPD induced by cigarette smoke combined with LPS

An enhanced chronic inflammatory response in the airways has been regarded as a critical characteristic of chronic obstructive pulmonary disease (COPD). Memantine, an N-methyl-d-aspartate (NMDA) receptors antagonist, has been reported to alleviate lung inflammation. In this study, we investigated the effect and mechanism of memantine on the COPD model induced by cigarette smoke (CS) combined with LPS. Mice and RAW264.7 cells were treated with LPS in the presence or absence of CS. We performed H&E staining to analysis the lung histopathological characteristics. Cytokines (IL-6, TNF-α, and IFN-γ) levels in bronchoalveolar lavage fluid (BALF), lung tissue homogenates and RAW264.7 cell culture medium were determined. Glutamate levels in plasma and culture medium of RAW264.7 were determined. The intracellular Ca2+ flux in RAW264.7 cells was measured by fluo-3 AM staining. The protein levels of NR-1, xCT, ERK1/2, and AKT signaling in the lung tissue and cells were investigated. The result showed that CS and LPS stimulation caused inflammation response, a significant increase in the release of cytokines, including TNF-α, IL-6, and IFN-γ, the elevated release of glutamate and protein levels of NR-1 and xCT, increased Ca2+ influx, and the activation of the ERK1/2 pathway in vitro and in vivo. The above effects of CS and LPS stimulation could be significantly attenuated by memantine treatment. In conclusion, memantine can effectively ameliorate pulmonary inflammation in CS + LPS-induced COPD in mice via reducing NR-1 and xCT expression, glutamate release, Ca2+ influx, and the phosphorylation of Erk1/2. We provided a possible mechanism by which memantine ameliorates COPD in mice.

The role of 13N-ammonia in the differential diagnosis of gliomas and brain inflammatory lesions

OBJECTIVE

To investigate the utility of ¹³N-ammonia PET/CT imaging in the differential diagnosis of gliomas and brain inflammations.

METHODS

¹³N-ammonia PET/CT imaging data of 77 patients with gliomas and 34 patients with brain inflammations were retrospectively analyzed. No patients received any treatment before ¹³N-ammonia imaging. All the patients were diagnosed by stereotactic biopsy or clinical follow-up. Visual and semi-quantitative analysis was performed to analyze the results of ¹³N-ammonia imaging. Finally, the uptake ratios of each lesion were calculated and its differences among different groups were tested with one-way ANOVA.

RESULTS

29.4% inflammations, 51.6% low-grade gliomas and 91.3% high-grade gliomas were positive by visual analysis in ¹³N-ammonia imaging. The sensitivity, specificity and accuracy for the diagnosis of gliomas were 75.3%, 55.8% and 67.8%, respectively. As for semi-quantitative analysis, the T/G ratios of inflammatory lesions, low-grade gliomas and high-grade gliomas were 0.88 ± 0.24, 1.04 ± 0.43 and 1.43 ± 0.49, respectively. One-way ANOVA revealed that the T/G ratios of high-grade gliomas were significantly higher than those of low-grade gliomas and inflammations (P < 0.05), but there was no statistical difference between low-grade gliomas and inflammations (P = 0.118). Among the inflammatory lesions, T/G ratios were not statistically different between infectious and demyelinating lesions (P > 0.05). ROC curve analysis showed that the optimal cut-off value of T/G ratio in distinguishing gliomas from inflammations was 1.21 with the AUC 0.78. The sensitivity, specificity, accuracy, PPV and NPV were 52.9%, 94.4%, 65.3%, 95.7% and 45.9%, respectively. ROC curve analysis showed that the optimal cut-off value of T/G ratio in distinguishing high-grade gliomas from low-grade gliomas was 1.06 with the AUC 0.78. The sensitivity, specificity, accuracy, PPV and NPV were 81.5%, 67.7%, 76.5%, 81.5% and 67.7%, respectively. ROC curve analysis showed that the optimal cut-off value of T/G ratio in distinguishing high-grade gliomas from low-grade gliomas and inflammations was 1.19 with the AUC 0.84. The sensitivity, specificity, accuracy, PPV and NPV were 70.4%, 85.1%, 78.5%, 79.2% and 78.1%, respectively.

CONCLUSIONS

¹³N-ammonia imaging is effective in distinguishing high-grade gliomas from low-grade gliomas and inflammations, but its role in the differential diagnosis of low-grade gliomas and brain inflammatory lesions is limited, and the accuracy needs to be improved.

Glutamine Synthetase: Localization Dictates Outcome

Glutamine synthetase (GS) is the adenosine triphosphate (ATP)-dependent enzyme that catalyses the synthesis of glutamine by condensing ammonium to glutamate. In the circulatory system, glutamine carries ammonia from muscle and brain to the kidney and liver. In brain reduction of GS activity has been suggested as a mechanism mediating neurotoxicity in neurodegenerative disorders. In cancer, the delicate balance between glutamine synthesis and catabolism is a critical event. In vitro evidence, confirmed in vivo in some cases, suggests that reduced GS activity in cancer cells associates with a more invasive and aggressive phenotype. However, GS is known to be highly expressed in cells of the tumor microenvironment, such as fibroblasts, adipocytes and immune cells, and their ability to synthesize glutamine is responsible for the acquisition of protumoral phenotypes. This has opened a new window into the complex scenario of the tumor microenvironment, in which the balance of glutamine consumption versus glutamine synthesis influences cellular function. Since GS expression responds to glutamine starvation, a lower glutamine synthesizing power due to the absence of GS in cancer cells might apply a metabolic pressure on stromal cells. This event might push stroma towards a GS-high/protumoral phenotype. When referred to stromal cells, GS expression might acquire a ‘bad’ significance to the point that GS inhibition might be considered a conceivable strategy against cancer metastasis.

Contribution of Brain Tissue Oxidative Damage in Hypothyroidism-associated Learning and Memory Impairments

The brain is a critical target organ for thyroid hormones, and modifications in memory and cognition happen with thyroid dysfunction. The exact mechanisms underlying learning and memory impairments due to hypothyroidism have not been understood yet. Therefore, this review was aimed to compress the results of previous studies which have examined the contribution of brain tissues oxidative damage in hypothyroidism-associated learning and memory impairments.

The role of system Xc- in methamphetamine-induced dopaminergic neurotoxicity in mice

The cystine/glutamate antiporter (system Xc^-, Sxc) transports cystine into cell in exchange for glutamate. Since xCT is a specific subunit of Sxc, we employed xCT knockout mice and investigated whether this antiporter affected methamphetamine (MA)-induced dopaminergic neurotoxicity. MA treatment significantly increased striatal oxidative burdens in wild type mice. xCT inhibitor [i.e., S-4-carboxy-phenylglycine (CPG), sulfasalazine] or an xCT knockout significantly protected against these oxidative burdens. MA-induced increases in Iba-1 expression and Iba-1-labeled microglial immunoreactivity (Iba-1-IR) were significantly attenuated by CPG or sulfasalazine administration or xCT knockout. CPG or sulfasalazine significantly attenuated MA-induced TUNEL-positive cell populations in the striatum of Taconic ICR mice. The decrease in excitatory amino acid transporter-2 (or glutamate transporter-1) expression and increase in glutamate release were attenuated by CPG, sulfasalazine or xCT knockout. In addition, CPG, sulfasalazine or xCT knockout significantly protected against dopaminergic loss (i.e., decreases in tyrosine hydroxylase expression and immunoreactivity, and an increase in dopamine turnover rate) induced by MA. However, CPG, sulfasalazine or xCT knockout did not significantly affect the impaired glutathione system [i.e., decrease in reduced glutathione (GSH) and increase in oxidized glutathione (GSSG)] induced by MA. Our results suggest that Sxc mediates MA-induced neurotoxicity via facilitating oxidative stress, microgliosis, proapoptosis, and glutamate-related toxicity.

Blockade of Glutamine Synthetase Enhances Inflammatory Response in Microglial Cells

AIMS

Microglial cells are brain-resident macrophages engaged in surveillance and maintained in a constant state of relative inactivity. However, their involvement in autoimmune diseases indicates that in pathological conditions microglia gain an inflammatory phenotype. The mechanisms underlying this change in the microglial phenotype are still unclear. Since metabolism is an important modulator of immune cell function, we focused our attention on glutamine synthetase (GS), a modulator of the response to lipopolysaccharide (LPS) activation in other cell types, which is expressed by microglia.

RESULTS

GS inhibition enhances release of inflammatory mediators of LPS-activated microglia in vitro, leading to perturbation of the redox balance and decreased viability of cocultured neurons. GS inhibition also decreases insulin-mediated glucose uptake in microglia. In vivo, microglia-specific GS ablation enhances expression of inflammatory markers upon LPS treatment. In the spinal cords from experimental autoimmune encephalomyelitis (EAE), GS expression levels and glutamine/glutamate ratios are reduced.

INNOVATION

Recently, metabolism has been highlighted as mediator of immune cell function through the discovery of mechanisms that (behind these metabolic changes) modulate the inflammatory response. The present study shows for the first time a metabolic mechanism mediating microglial response to a proinflammatory stimulus, pointing to GS activity as a master modulator of immune cell function and thus unraveling a potential therapeutic target.

CONCLUSIONS

Our study highlights a new role of GS in modulating immune response in microglia, providing insights into the pathogenic mechanisms associated with inflammation and new strategies of therapeutic intervention. Antioxid. Redox Signal. 26, 351-363.

Neuropathology of mood disorders: do we see the stigmata of inflammation?

A proportion of cases with mood disorders have elevated inflammatory markers in the blood that conceivably may result from stress, infection and/or autoimmunity. However, it is not yet clear whether depression is a neuroinflammatory disease. Multiple histopathological and molecular abnormalities have been found postmortem but the etiology of these abnormalities is unknown. Here, we take an immunological perspective of this literature. Increases in activated microglia or perivascular macrophages in suicide victims have been reported in the parenchyma. In contrast, astrocytic markers generally are downregulated in mood disorders. Impairment of astrocytic function likely compromises the reuptake of glutamate potentially leading to excitotoxicity. Inflammatory cytokines and microglia/macrophage-derived quinolinic acid (QA) downregulate the excitatory amino acid transporters responsible for this reuptake, while QA has the additional effect of inhibiting astroglial glutamine synthetase, which converts glutamate to glutamine. Given that oligodendroglia are particularly vulnerable to inflammation, it is noteworthy that reductions in numbers or density of oligodendrocyte cells are one of the most prominent findings in depression. Structural and/or functional changes to GABAergic interneurons also are salient in postmortem brain samples, and may conceivably be related to early inflammatory insults. Although the postmortem data are consistent with a neuroimmune etiology in a subgroup of depressed individuals, we do not argue that all depression-associated abnormalities are reflective of a neuroinflammatory process or even that all immunological activity in the brain is deleterious. Rather, we highlight the pervasive role of immune signaling pathways in brain function and provide an alternative perspective on the current postmortem literature.

Interactions of Opioids and HIV Infection in the Pathogenesis of Chronic Pain

Over 50% of HIV-1/AIDS patients suffer chronic pain. Currently, opioids are the cornerstone medications for treating severe pain in these patients. Ironically, emerging clinical data indicates that repeated use of opiate pain medicines might in fact heighten the chronic pain states in HIV patients. Both laboratory-based and clinical studies strongly suggest that opioids exacerbate the detrimental effects of HIV-1 infection on the nervous system, both on neurons and glia. The combination of opioids and HIV-1infection may promote the damage of neurons, including those in the pain sensory and transmission pathway, by activating both caspase-dependent and caspase-independent pro-apoptotic pathways. In addition, the opiate-HIV-1 interaction may also cause widespread disturbance of glial function and elicit glial-derived pro-inflammatory responses that dysregulate neuronal function. The deregulation of neuron-glia cross-talk that occurs with the combination of HIV-1 and opioids appears to play an important role in the development of the pathological pain state. In this article, we wish to provide an overview of the potential molecular and cellular mechanisms by which opioids may interact with HIV-1 to cause neurological problems, especially in the context of HIV-associated pathological pain. Elucidating the underlying mechanisms will help researchers and clinicians to understand how chronic use of opioids for analgesia enhances HIV-associated pain. It will also assist in optimizing therapeutic approaches to prevent or minimize this significant side effect of opiate analgesics in pain management for HIV patients.

Integrated metabolic modelling reveals cell-type specific epigenetic control points of the macrophage metabolic network

BACKGROUND

The reconstruction of context-specific metabolic models from easily and reliably measurable features such as transcriptomics data will be increasingly important in research and medicine. Current reconstruction methods suffer from high computational effort and arbitrary threshold setting. Moreover, understanding the underlying epigenetic regulation might allow the identification of putative intervention points within metabolic networks. Genes under high regulatory load from multiple enhancers or super-enhancers are known key genes for disease and cell identity. However, their role in regulation of metabolism and their placement within the metabolic networks has not been studied.

METHODS

Here we present FASTCORMICS, a fast and robust workflow for the creation of high-quality metabolic models from transcriptomics data. FASTCORMICS is devoid of arbitrary parameter settings and due to its low computational demand allows cross-validation assays. Applying FASTCORMICS, we have generated models for 63 primary human cell types from microarray data, revealing significant differences in their metabolic networks.

RESULTS

To understand the cell type-specific regulation of the alternative metabolic pathways we built multiple models during differentiation of primary human monocytes to macrophages and performed ChIP-Seq experiments for histone H3 K27 acetylation (H3K27ac) to map the active enhancers in macrophages. Focusing on the metabolic genes under high regulatory load from multiple enhancers or super-enhancers, we found these genes to show the most cell type-restricted and abundant expression profiles within their respective pathways. Importantly, the high regulatory load genes are associated to reactions enriched for transport reactions and other pathway entry points, suggesting that they are critical regulatory control points for cell type-specific metabolism.

CONCLUSIONS

By integrating metabolic modelling and epigenomic analysis we have identified high regulatory load as a common feature of metabolic genes at pathway entry points such as transporters within the macrophage metabolic network. Analysis of these control points through further integration of metabolic and gene regulatory networks in various contexts could be beneficial in multiple fields from identification of disease intervention strategies to cellular reprogramming.

Suppression of neurite outgrowth of primary cultured hippocampal neurons is involved in impairment of glutamate metabolism and NMDA receptor function caused by nanoparticulate TiO2

Numerous studies have indicated that nano-titanium dioxide (TiO2) can induce neurotoxicity in vitro and in vivo, however, it is unclear whether nano-TiO2 affects neurite outgrowth of hippocampal neurons. In order to investigate the mechanism of neurotoxicity, rat primary cultured hippocampal neurons on the fourth day of culture were exposed to 5, 15, and 30 μg/mL nano-TiO2 for 24 h, and nano-TiO2 internalization, dendritic growth, glutamate metabolism, expression of N-methyl-D-aspartate (NMDA) receptor subunits (NR1, NR2A and NR2B), calcium homeostasis, sodium current (INa) and potassium current (IK) were examined. Our findings demonstrated that nano-TiO2 crossed the membrane into the cytoplasm or nucleus, and significantly suppressed dendritic growth of primary cultured hippocampal neurons in a concentration-dependent manner. Furthermore, nano-TiO2 induced a marked release of glutamate to the extracellular region, decreased glutamine synthetase activity and increased phosphate-activated glutaminase activity, elevated intracellular calcium ([Ca(2+)]i), down-regulated protein expression of NR1, NR2A and NR2B, and increased the amplitudes of the INa and IK. In addition, nano-TiO2 increased nitric oxide and nitrice synthase, attenuated the activities of Ca(2+)-ATPase and Na(+)/K(+)-ATPase, and increased the ADP/ATP ratio in the primary neurons. Taken together, these findings indicate that nano-TiO2 inhibits neurite outgrowth of hippocampal neurons by interfering with glutamate metabolism and impairing NMDA receptor function.

Glutamine synthetase desensitizes differentiated adipocytes to proinflammatory stimuli by raising intracellular glutamine levels

The role of glutamine synthetase (GS) during adipocyte differentiation is unclear. Here, we assess the impact of GS on the adipocytic response to a proinflammatory challenge at different differentiation stages. GS expression at the late stages of differentiation desensitized mature adipocytes to bacterial lipopolysaccharide (LPS) by increasing intracellular glutamine levels. Furthermore, LPS-activated mature adipocytes were unable to produce inflammatory mediators; LPS sensitivity was rescued following GS inhibition and the associated drop in intracellular glutamine levels. The ability of adipocytes to differentially respond to LPS during differentiation negatively correlates to GS expression and intracellular glutamine levels. Hence, modulation of intracellular glutamine levels by GS expression represents an endogenous mechanism through which mature adipocytes control the inflammatory response.

Domoic acid-induced seizures in California sea lions (Zalophus californianus) are associated with neuroinflammatory brain injury

California sea lions (CSLs) exposed to the marine biotoxin domoic acid (DA) develop an acute or chronic toxicosis marked by seizures and act as sentinels of the disease. Experimental evidence suggests that oxidative stress and neuroinflammation are important mechanisms underlying the seizurogenic potential of environmental toxicants but these pathways are relatively unstudied in CSLs. In the current study, we investigated the role of glutamate-glutamine changes and gliosis in DA-exposed CSLs to better understand the neurotoxic mechanisms occurring during DA toxicity. Sections from archived hippocampi from control and CSLs diagnosed with DA toxicosis were immunofluorescently stained for markers of gliosis, oxidative/nitrative stress and changes in glutamine synthetase (GS). Quantitative assessment revealed increasing loss of microtubule associated protein-2 positive neurons with elevations in 4-hydroxynonenal correlating with chronicity of exposure, whereas the pattern of activated glia expressing nitric oxide synthase 2 and tumor necrosis factor followed pathological severity. There was no significant change in the amount of GS positive cells but there was increased 3-nitrotyrosine in GS expressing cells and in neurons, particularly in animals with chronic DA toxicosis. These changes were consistently seen in the dentate gyrus and in the cornu ammonis (CA) sectors CA3, CA4, and CA1. The results of this study indicate that gliosis and resultant changes in GS are likely important mechanisms in DA-induced seizure that need to be further explored as potential therapies in treating exposed wildlife.

Glutamate metabolism and HIV-associated neurocognitive disorders

HIV-1 infection can lead to neurocognitive impairment collectively known as HIV-associated neurocognitive disorders (HAND). Although combined antiretroviral treatment (cART) has significantly ameliorated HIV's morbidity and mortality, persistent neuroinflammation and neurocognitive dysfunction continue. This review focuses on the current clinical and molecular evidence of the viral and host factors that influence glutamate-mediated neurotoxicity and neuropathogenesis as an important underlying mechanism during the course of HAND development. In addition, discusses potential pharmacological strategies targeting the glutamatergic system that may help prevent and improve neurological outcomes in HIV-1-infected subjects.

A glutamate-dependent redox system in blood cells is integral for phagocytosis in Drosophila melanogaster

Glutamate transport is highly regulated as glutamate directly acts as a neurotransmitter and indirectly regulates the synthesis of antioxidants. Although glutamate deregulation has been repeatedly linked to serious human diseases such as HIV infection and Alzheimer's, glutamate's role in the immune system is still poorly understood. We find that a putative glutamate transporter in Drosophila melanogaster, polyphemus (polyph), plays an integral part in the fly's immune response. Flies with a disrupted polyph gene exhibit decreased phagocytosis of microbial-derived bioparticles. When infected with S. aureus, polyph flies show an increase in both susceptibility and bacterial growth. Additionally, the expression of two known glutamate transporters, genderblind and excitatory amino acid transporter 1, in blood cells affects the flies' ability to phagocytose and survive after an infection. Consistent with previous data showing a regulatory role for glutamate transport in the synthesis of the major antioxidant glutathione, polyph flies produce more reactive oxygen species (ROS) as compared to wild-type flies when exposed to S. aureus. In conclusion, we demonstrate that a polyph-dependent redox system in blood cells is necessary to maintain the cells' immune-related functions. Furthermore, our model provides insight into how deregulation of glutamate transport may play a role in disease.

Congenital hypothyroidism alters the oxidative status, enzyme activities and morphological parameters in the hippocampus of developing rats

Congenital hypothyroidism is associated with delay in cell migration and proliferation in brain tissue, impairment of synapse formation, misregulation of neurotransmitters, hypomyelination and mental retardation. However, the mechanisms underlying the neuropsychological deficits observed in congenital hypothyroidism are not completely understood. In the present study we proposed a mechanism by which hypothyroidism leads to hippocampal neurotoxicity. Congenital hypothyroidism induces c-Jun-N-terminal kinase (JNK) pathway activation leading to hyperphosphorylation of the glial fibrillary acidic protein (GFAP), vimentin and neurofilament subunits from hippocampal astrocytes and neurons, respectively. Moreover, hyperphosphorylation of the cytoskeletal proteins was not reversed by T3 and poorly reversed by T4. In addition, congenital hypothyroidism is associated with downregulation of astrocyte glutamate transporters (GLAST and GLT-1) leading to decreased glutamate uptake and subsequent influx of Ca(2+) through N-methyl-D-aspartate (NMDA) receptors. The Na(+)-coupled (14)C-α-methyl-amino-isobutyric acid ((14)C-MeAIB) accumulation into hippocampal cells also might cause an increase in the intracellular Ca(2+) concentration by opening voltage-dependent calcium channels (VDCC). The excessive influx of Ca(2+) through NMDA receptors and VDCCs might lead to an overload of Ca(2+) within the cells, which set off glutamate excitotoxicity and oxidative stress. The inhibited acetylcholinesterase (AChE) activity might also induce Ca(2+) influx. The inhibited glucose-6-phosphate dehydrogenase (G6PD) and gamma-glutamyl transferase (GGT) activities, associated with altered glutamate and neutral amino acids uptake could somehow affect the GSH turnover, the antioxidant defense system, as well as the glutamate-glutamine cycle. Reduced levels of S100B and glial fibrillary acidic protein (GFAP) take part of the hypothyroid condition, suggesting a compromised astroglial/neuronal neurometabolic coupling which is probably related to the neurotoxic damage in hypothyroid brain.

Targeting microglial K(ATP) channels to treat neurodegenerative diseases: a mitochondrial issue

Neurodegeneration is a complex process involving different cell types and neurotransmitters. A common characteristic of neurodegenerative disorders is the occurrence of a neuroinflammatory reaction in which cellular processes involving glial cells, mainly microglia and astrocytes, are activated in response to neuronal death. Microglia do not constitute a unique cell population but rather present a range of phenotypes closely related to the evolution of neurodegeneration. In a dynamic equilibrium with the lesion microenvironment, microglia phenotypes cover from a proinflammatory activation state to a neurotrophic one directly involved in cell repair and extracellular matrix remodeling. At each moment, the microglial phenotype is likely to depend on the diversity of signals from the environment and of its response capacity. As a consequence, microglia present a high energy demand, for which the mitochondria activity determines the microglia participation in the neurodegenerative process. As such, modulation of microglia activity by controlling microglia mitochondrial activity constitutes an innovative approach to interfere in the neurodegenerative process. In this review, we discuss the mitochondrial K_ATP channel as a new target to control microglia activity, avoid its toxic phenotype, and facilitate a positive disease outcome.

Glutamine modifies immune responses of mice infected with porcine circovirus type 2

The present study was conducted to evaluate the immune-enhancing effects of dietaryl-glutamine supplementation in porcine circovirus type 2 (PCV2)-infected mice, and to examine the clearance effects of glutamine against PCV2 in experimentally infected mice. A total of sixty Kunming female mice were infected with PCV2 at a dose of 100 TCID50(50 % tissue culture infection dose) by intraperitoneal injection after 2 weeks of dietaryl-glutamine supplementation orl-alanine supplementation (as the control (isonitrogenous) group). The measured variables on 3rd, 5th, 7th, 9th and 11th d post-infection (dpi) included: (1) PCV2 virus loaded in the liver, spleen, heart, lung, kidney, ovary and serum was determined by real-time PCR; (2) IL-2, IL-6, IL-10, interferon (IFN)-α, IFN-γ and C-reactive protein levels in serum were measured by ELISA; (3) serum total superoxide dismutase activity was measured spectrophotometrically at 550 nm absorbance. Dietaryl-glutamine supplementation significantly increased serum IL-2 levels on the 3rd (P< 0·01), 5th (P< 0·01), 7th (P< 0·05) and 9th dpi, significantly (P< 0·05) increased serum IL-6 levels on 3rd dpi, significantly (P< 0·05) increased serum IFN-γ levels on the 9th and 11th dpi and significantly decreased (P< 0·01) serum IL-10 levels on the 9th and 11th dpi, compared with those in the control group. Meanwhile, the PCV2 virus genome was detected sporadically throughout the experimental period in both groups. Taken together, the present results suggest that dietaryl-glutamine supplementation enhances immune function in PCV2-infected mice.

A Modified Bacillus Calmette-Guérin (BCG) Vaccine with Reduced Activity of Antioxidants and Glutamine Synthetase Exhibits Enhanced Protection of Mice despite Diminished in Vivo Persistence

Early attempts to improve BCG have focused on increasing the expression of prominent antigens and adding recombinant toxins or cytokines to influence antigen presentation. One such modified BCG vaccine candidate has been withdrawn from human clinical trials due to adverse effects. BCG was derived from virulent Mycobacterium bovis and retains much of its capacity for suppressing host immune responses. Accordingly, we have used a different strategy for improving BCG based on reducing its immune suppressive capacity. We made four modifications to BCG Tice to produce 4dBCG and compared it to the parent vaccine in C57Bl/6 mice. The modifications included elimination of the oxidative stress sigma factor SigH, elimination of the SecA2 secretion channel, and reductions in the activity of iron co-factored superoxide dismutase and glutamine synthetase. After IV inoculation of 4dBCG, 95% of vaccine bacilli were eradicated from the spleens of mice within 60 days whereas the titer of BCG Tice was not significantly reduced. Subcutaneous vaccination with 4dBCG produced greater protection than vaccination with BCG against dissemination of an aerosolized challenge of M. tuberculosis to the spleen at 8 weeks post-challenge. At this time, 4dBCG-vaccinated mice also exhibited altered lung histopathology compared to BCG-vaccinated mice and control mice with less well-developed lymphohistiocytic nodules in the lung parenchyma. At 26 weeks post-challenge, 4dBCG-vaccinated mice but not BCG-vaccinated mice had significantly fewer challenge bacilli in the lungs than control mice. In conclusion, despite reduced persistence in mice a modified BCG vaccine with diminished antioxidants and glutamine synthetase is superior to the parent vaccine in conferring protection against M. tuberculosis. The targeting of multiple immune suppressive factors produced by BCG is a promising strategy for simultaneously improving vaccine safety and effectiveness.

Effects of 18-kDa translocator protein knockdown on gene expression of glutamate receptors, transporters, and metabolism, and on cell viability affected by glutamate

OBJECTIVE

Previously, several important roles for glutamate have been described for the biology of primary brain tumors. For example, glutamate has been suggested to promote glioma cell proliferation by the activation of the 2-amino-3-(5-methyl-3-oxo-1,2-oxazol-4-yl)propanoic acid (AMPA) subtype of glutamate receptors. In the present study, we determined the potential regulatory roles of the 18-kDa translocator protein (TSPO) in the glutamatergic system in relation to cell death of brain tumor cells through knockdown of the TSPO by genetic manipulation.

MATERIALS AND METHODS

With microarray analysis and validation of gene expression of particular genes using real-time PCR, we found effects because of small inhibitory RNA knockdown of the TSPO in human U118MG glioblastoma cells on gene expression of glutamate receptors, glutamate transporters, and enzymes for glutamate metabolism. We also applied antisense RNA to silence TSPO in rat C6 glioblastoma cells and assayed the effects on DNA fragmentation, indicative of apoptosis, because of glutamate exposure.

RESULTS

In particular, the effects of TSPO silencing in human U118MG cells related to glutamate metabolism indicate a net effect of a reduction in glutamate levels, which may potentially protect the cells in question from cell death. The TSPO knockdown in C6 cells showed that TSPO is required for the induction of apoptosis because of glutamate exposure.

CONCLUSION

These findings show that interactions between the TSPO and the glutamatergic system may play a role in tumor development of glioblastoma cells. This may also have implications for our understanding of the involvement of the TSPO in secondary brain damage and neurodegenerative diseases.

The role of non-synaptic extracellular glutamate

Although there are some mechanisms which allow the direct crossing of substances between the cytoplasm of adjacent cells (gap junctions), most substances use the extracellular space to diffuse between brain cells. The present work reviews the behavior and functions of extracellular glutamate (GLU). There are two extracellular pools of glutamate (GLU) in the brain, a synaptic pool whose functions in the excitatory neurotransmission has been widely studied and an extrasynaptic GLU pool although less known nonetheless is gaining attention among a growing number of researchers. Evidence accumulated over the last years shows a number of mechanisms capable of releasing glial GLU to the extracellular medium, thus modulating neurons, microglia and oligodendrocytes, and regulating the immune response, cerebral blood flow, neuronal synchronization and other brain functions. This new scenario is expanding present knowledge regarding the role of GLU in the brain under different physiological and pathological conditions. This article is part of a Special Issue entitled 'Extrasynaptic ionotropic receptors'.

Opiate drug use and the pathophysiology of neuroAIDS

Opiate abuse and HIV-1 have been described as interrelated epidemics, and even in the advent of combined anti-retroviral therapy, the additional abuse of opiates appears to result in greater neurologic and cognitive deficits. The central nervous system (CNS) is particularly vulnerable to interactive opiate-HIV-1 effects, in part because of the unique responses of microglia and astroglia. Although neurons are principally responsible for behavior and cognition, HIV-1 infection and replication in the brain is largely limited to microglia, while astroglia and perhaps glial progenitors can be latently infected. Thus, neuronal dysfunction and injury result from cellular and viral toxins originating from HIV-1 infected/exposed glia. Importantly, subsets of glial cells including oligodendrocytes, as well as neurons, express µ-opioid receptors and therefore can be direct targets for heroin and morphine (the major metabolite of heroin in the CNS), which preferentially activate µ-opioid receptors. This review highlights findings that neuroAIDS is a glially driven disease, and that opiate abuse may act at multiple glial-cell types to further compromise neuron function and survival. The ongoing, reactive cross-talk between opiate drug and HIV-1 co-exposed microglia and astroglia appears to exacerbate critical proinflammatory and excitotoxic events leading to neuron dysfunction, injury, and potentially death. Opiates enhance synaptodendritic damage and a loss of synaptic connectivity, which is viewed as the substrate of cognitive deficits. We especially emphasize that opioid signaling and interactions with HIV-1 are contextual, differing among cell types, and even within subsets of the same cell type. For example, astroglia even within a single brain region are heterogeneous in their expression of µ-, δ-, and κ-opioid receptors, as well as CXCR4 and CCR5, and Toll-like receptors. Thus, defining the distinct targets engaged by opiates in each cell type, and among brain regions, is critical to an understanding of how opiate abuse exacerbates neuroAIDS.

Translational magnetic resonance spectroscopy reveals excessive central glutamate levels during alcohol withdrawal in humans and rats

BACKGROUND

In alcoholism, excessive glutamatergic neurotransmission has long been implicated in the acute withdrawal syndrome and as a key signal for dependence-related neuroplasticity. Our understanding of this pathophysiological mechanism originates largely from animal studies, but human data are needed for translation into successful medication development.

METHODS

We measured brain glutamate levels during detoxification in alcohol-dependent patients (n = 47) and in healthy control subjects (n = 57) as well as in a rat model of alcoholism by state-of-the-art ¹H-magnetic magnetic resonance spectroscopy at 3 and 9.4 T, respectively.

RESULTS

We found significantly increased glutamate levels during acute alcohol withdrawal in corresponding prefrontocortical regions of treatment-seeking alcoholic patients and alcohol-dependent rats versus respective control subjects. The augmented spectroscopic glutamate signal is likely related to increased glutamatergic neurotransmission because, enabled by the high field strength of the animal scanner, we detected a profoundly elevated glutamate/glutamine ratio in alcohol-dependent rats during acute withdrawal. All dependence-induced metabolic alterations normalize within a few weeks of abstinence in both humans and rats.

CONCLUSIONS

Our data provide first-time direct support from humans for the glutamate hypothesis of alcoholism, demonstrate the comparability of human and animal magnetic resonance spectroscopy responses, and identify the glutamate/glutamine ratio as potential biomarker for monitoring disease progression.

Effects of bee venom on glutamate-induced toxicity in neuronal and glial cells

Bee venom (BV), which is extracted from honeybees, is used in traditional Korean medical therapy. Several groups have demonstrated the anti-inflammatory effects of BV in osteoarthritis both in vivo and in vitro. Glutamate is the predominant excitatory neurotransmitter in the central nervous system (CNS). Changes in glutamate release and uptake due to alterations in the activity of glutamate transporters have been reported in many neurodegenerative diseases, including Parkinson's disease, Alzheimer's disease, and amyotrophic lateral sclerosis. To assess if BV can prevent glutamate-mediated neurotoxicity, we examined cell viability and signal transduction in glutamate-treated neuronal and microglial cells in the presence and absence of BV. We induced glutamatergic toxicity in neuronal cells and microglial cells and found that BV protected against cell death. Furthermore, BV significantly inhibited the cellular toxicity of glutamate, and pretreatment with BV altered MAP kinase activation (e.g., JNK, ERK, and p38) following exposure to glutamate. These findings suggest that treatment with BV may be helpful in reducing glutamatergic cell toxicity in neurodegenerative diseases.

Glutamine synthetase is a genetic determinant of cell type-specific glutamine independence in breast epithelia

Although significant variations in the metabolic profiles exist among different cells, little is understood in terms of genetic regulations of such cell type-specific metabolic phenotypes and nutrient requirements. While many cancer cells depend on exogenous glutamine for survival to justify the therapeutic targeting of glutamine metabolism, the mechanisms of glutamine dependence and likely response and resistance of such glutamine-targeting strategies among cancers are largely unknown. In this study, we have found a systematic variation in the glutamine dependence among breast tumor subtypes associated with mammary differentiation: basal- but not luminal-type breast cells are more glutamine-dependent and may be susceptible to glutamine-targeting therapeutics. Glutamine independence of luminal-type cells is associated mechanistically with lineage-specific expression of glutamine synthetase (GS). Luminal cells can also rescue basal cells in co-culture without glutamine, indicating a potential for glutamine symbiosis within breast ducts. The luminal-specific expression of GS is directly induced by GATA3 and represses glutaminase expression. Such distinct glutamine dependency and metabolic symbiosis is coupled with the acquisition of the GS and glutamine independence during the mammary differentiation program. Understanding the genetic circuitry governing distinct metabolic patterns is relevant to many symbiotic relationships among different cells and organisms. In addition, the ability of GS to predict patterns of glutamine metabolism and dependency among tumors is also crucial in the rational design and application of glutamine and other metabolic pathway targeted therapies.

Region and state specific glutamate downregulation in major depressive disorder: a meta-analysis of (1)H-MRS findings

For major depressive disorder (MDD), magnetic resonance spectroscopy ((1)H-MRS) studies of glutamate, glutamine and Glx (the composite measure of mainly glutamate and glutamine) have yielded inconclusive or seemingly inconsistent results. We therefore systematically reviewed whether in vivo concentrations of glutamate, glutamine and Glx measured with (1)H-MRS differ between MDD patients and controls. Meta-analysis including meta-regression, sensitivity, statistical heterogeneity, and publication bias analyses were conducted. Glutamate and Glx concentrations were found to be lower in the anterior cingulate cortex (ACC) in patients compared to controls (standardized mean difference (SMD) for glutamate with 95% CIs: -0.86, -1.55 to -0.17; and for Glx: -1.15, -1.86 to -0.44). In addition, Glx was decreased in all brain regions together in current episode patients (SMD: -0.62, -1.17 to -0.07). We conclude that in MDD, glutamate and possibly glutamine are downregulated primarily in the ACC and during depressive states. These results fit the central role of the ACC in depressive symptomatology and suggest that in MDD changes in glutamatergic neurotransmission are state-dependent.

HIV-1 infection and alcohol abuse: neurocognitive impairment, mechanisms of neurodegeneration and therapeutic interventions

Clinical studies indicate that alcohol dependence has an additive effect on cognitive deficits associated with HIV-1 infection. Findings in humans and animal models suggest that alcohol, similar to HIV-1, induces inflammatory processes in the brain leading to neurodegeneration. The causes of HIV-1-associated neurotoxicity are comparable to those mediating alcohol-induced neuronal injury. This review aims to present the mechanisms of the combined effects of HIV-1 and alcohol abuse in the brain and to discuss neuroprotective therapies. Oxidative stress, overproduction of pro-inflammatory factors, impairment of blood-brain barrier and glutamate associated neurotoxicity appear to play important roles in alcohol driven neurodegeneration. Diminution of neuroinflammation constitutes a logical approach for prevention of HIV-1 and alcohol mediated neurodegeneration. Agonists of cannabinoid receptor 2 (CB₂) possess potent anti-inflammatory and neuroprotective properties. We address multifaceted beneficial effects of CB₂ activation in the setting of HIV-1 brain infection and alcohol abuse.

Microglial self-defence mediated through GLT-1 and glutathione

Glutamate is stored in synaptic vesicles in presynaptic neurons. It is released into the synaptic cleft to provide signalling to postsynaptic neurons. Normally, the astroglial glutamate transporters GLT-1 and GLAST take up glutamate to mediate a high signal-to-noise ratio in the synaptic signalling, and also to prevent excitotoxic effects by glutamate. In astrocytes, glutamate is transformed into glutamine, which is safely transported back to neurons. However, in pathological conditions, such as an ischemia or virus infection, astroglial transporters are down-regulated which could lead to excitotoxicity. Lately, it was shown that even microglia can express glutamate transporters during pathological events. Microglia have two systems for glutamate transport: GLT-1 for transport into the cells and the x (c) (-) system for transport out of the cells. We here review results from our work and others, which demonstrate that microglia in culture express GLT-1, but not GLAST, and transport glutamate from the extracellular space. We also show that TNF-α can induce increased microglial GLT-1 expression, possibly associating the expression with inflammatory systems. Furthermore, glutamate taken up through GLT-1 may be used for direct incorporation into glutathione and to fuel the intracellular glutamate pool to allow cystine uptake through the x (c) (-) system. This can lead to a defence against oxidative stress and have an antiviral function.

EAAT expression by macrophages and microglia: still more questions than answers

Glutamate is the main excitatory amino acid, but its presence in the extracellular milieu has deleterious consequences. It may induce excitotoxicity and also compete with cystine for the use of the cystine-glutamate exchanger, blocking glutathione neosynthesis and inducing an oxidative stress-induced cell death. Both mechanisms are critical in the brain where up to 20% of total body oxygen consumption occurs. In normal conditions, the astrocytes ensure that extracellular concentration of glutamate is kept in the micromolar range, thanks to their coexpression of high-affinity glutamate transporters (EAATs) and glutamine synthetase (GS). Their protective function is nevertheless sensitive to situations such as oxidative stress or inflammatory processes. On the other hand, macrophages and microglia do not express EAATs and GS in physiological conditions and are the principal effector cells of brain inflammation. Since the late 1990s, a number of studies have now shown that both microglia and macrophages display inducible EAAT and GS expression, but the precise significance of this still remains poorly understood. Brain macrophages and microglia are sister cells but yet display differences. Both are highly sensitive to their microenvironment and can perform a variety of functions that may oppose each other. However, in the very particular environment of the healthy brain, they are maintained in a repressed state. The aim of this review is to present the current state of knowledge on brain macrophages and microglial cells activation, in order to help clarify their role in the regulation of glutamate under pathological conditions as well as its outcome.

Macrophage signaling in HIV-1 infection

The human immunodeficiency virus-1 (HIV-1) is a member of the lentivirus genus. The virus does not rely exclusively on the host cell machinery, but also on viral proteins that act as molecular switches during the viral life cycle which play significant functions in viral pathogenesis, notably by modulating cell signaling. The role of HIV-1 proteins (Nef, Tat, Vpr, and gp120) in modulating macrophage signaling has been recently unveiled. Accessory, regulatory, and structural HIV-1 proteins interact with signaling pathways in infected macrophages. In addition, exogenous Nef, Tat, Vpr, and gp120 proteins have been detected in the serum of HIV-1 infected patients. Possibly, these proteins are released by infected/apoptotic cells. Exogenous accessory regulatory HIV-1 proteins are able to enter macrophages and modulate cellular machineries including those that affect viral transcription. Furthermore HIV-1 proteins, e.g., gp120, may exert their effects by interacting with cell surface membrane receptors, especially chemokine co-receptors. By activating the signaling pathways such as NF-kappaB, MAP kinase (MAPK) and JAK/STAT, HIV-1 proteins promote viral replication by stimulating transcription from the long terminal repeat (LTR) in infected macrophages; they are also involved in macrophage-mediated bystander T cell apoptosis. The role of HIV-1 proteins in the modulation of macrophage signaling will be discussed in regard to the formation of viral reservoirs and macrophage-mediated T cell apoptosis during HIV-1 infection.

Nitrated alpha-synuclein and microglial neuroregulatory activities

Microglial neuroinflammatory responses affect the onset and progression of Parkinson's disease (PD). We posit that such neuroinflammatory responses are, in part, mediated by microglial interactions with nitrated and aggregated alpha-synuclein (alpha-syn) released from Lewy bodies as a consequence of dopaminergic neuronal degeneration. As disease progresses, secretions from alpha-syn-activated microglia can engage neighboring glial cells in a cycle of autocrine and paracrine amplification of neurotoxic immune products. Such pathogenic processes affect the balance between a microglial neurotrophic and neurotoxic signature. We now report that microglia secrete both neurotoxic and neuroprotective factors after exposure to nitrated alpha-syn (N-alpha-syn). Proteomic (surface enhanced laser desorption-time of flight, 1D sodium dodecyl sulfate electrophoresis, and liquid chromatography-tandem mass spectrometry) and limited metabolomic profiling demonstrated that N-alpha-syn-activated microglia secrete inflammatory, regulatory, redox-active, enzymatic, and cytoskeletal proteins. Increased extracellular glutamate and cysteine and diminished intracellular glutathione and secreted exosomal proteins were also demonstrated. Increased redox-active proteins suggest regulatory microglial responses to N-alpha-syn. These were linked to discontinuous cystatin expression, cathepsin activity, and nuclear factor-kappa B activation. Inhibition of cathepsin B attenuated, in part, N-alpha-syn microglial neurotoxicity. These data support multifaceted microglia functions in PD-associated neurodegeneration.

Neuronal damage accompanies perinatal white-matter damage

Extremely low-gestational-age newborns have a prominently increased risk of brain dysfunctions attributed to white-matter damage, which is thought to result from the vulnerability of the oligodendrocyte. This white-matter damage now appears to be accompanied by cerebral-cortex and deep-gray-matter abnormalities, including excess apoptosis without replacement and the impairment of surviving neurons and resulting interference with synaptogenesis and connectivity. Recent advances in corticogenesis suggest that neurons migrate from the germinative zones through the white matter to the cortex when the white matter is most vulnerable and perhaps is being injured. Advances in developmental neuroscience also suggest that the excitotoxic and inflammatory processes that probably contribute to white-matter damage are also able to damage developing neurons. Together, these advances support the untested hypothesis that white-matter damage in the preterm newborn is accompanied by the death of neurons as they migrate through the dangerous minefield of white matter undergoing injury.

Oxidative stress and the pathogenesis of neurodegenerative disorders

Microglia-derived inflammatory neurotoxins play a principal role in the pathogenesis of neurodegenerative disorders including Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and HIV-associated dementia; chief among these is reactive oxygen species. The detrimental effects of oxidative stress in the brain and nervous system are primarily a result of the diminished capacity of the central nervous system to prevent ongoing oxidative damage. A spectrum of environmental cues, mitochondrial dysfunction, accumulation of aberrant misfolded proteins, inflammation, and defects in protein clearance are known to evolve and form as a result of disease progression. These factors likely affect glial function serving to accelerate the tempo of disease. Understanding the relationships between disease progression, free radical formation, neuroinflammation, and neurotoxicity is critical to elucidating disease mechanisms and the development of therapeutic modalities to combat disease processes. In an era where populations continue to age, the prevalence and incidence of age-related neurodegenerative diseases are on the rise; therefore, the need for novel therapeutic strategies that attenuate neuroinflammation and protect neurons against oxidative stress is ever more immediate.

Advances in macrophage and dendritic cell biology in HIV-1 infection stress key understudied areas in infection, pathogenesis, and analysis of viral reservoirs

The continued quest to intervene in HIV-1 infection by halting transmission, suppressing replication, or eradicating disease in infected subjects stresses the significance of dendritic cell and macrophage biology as early and persistent players in the relationship between infection and disease. As highlighted by new data and presentations at the Sixth International Workshop on HIV and Cells of Macrophage/Dendritic Lineage and Other Reservoirs, a greater emphasis is currently underway in studying the potential of targeting these cell types by intervention early in infection, better defining viral phenotypes and entry mechanisms with a more precise nomenclature system, identifying new, intrinsic cellular factors that may restrict infection within these cell types, and pursuing novel roles for macrophage activation and trafficking. Other key areas include examination of these cells as sources of viral persistence in patients, their roles in coinfection, and their metabolic function in HIV pathogenesis and drug toxicity. This issue of JLB contains reviews and original research reports from the workshop, which highlight new findings, current research questions, and key areas in need of future investigation as a result of their significance to HIV prevention and pathogenesis.