GCP II inhibition rescues neurons from gp120IIIB-induced neurotoxicity

Methamphetamine Enhancement of HIV-1 gp120-Mediated NLRP3 Inflammasome Activation and Resultant Proinflammatory Responses in Rat Microglial Cultures

Human Immunodeficiency Virus type 1 (HIV-1)-associated neurocognitive disorders (HANDs) remain prevalent in HIV-1-infected individuals despite the evident success of combined antiretroviral therapy (cART). The mechanisms underlying HAND prevalence in the cART era remain perplexing. Ample evidence indicates that HIV-1 envelope glycoprotein protein 120 (gp120), a potent neurotoxin, plays a pivotal role in HAND pathogenesis. Methamphetamine (Meth) abuse exacerbates HANDs, but how this occurs is not fully understood. We hypothesize that Meth exacerbates HANDs by enhancing gp120-mediated neuroinflammation. To test this hypothesis, we studied the effect of Meth on gp120-induced microglial activation and the resultant production of proinflammatory cytokines in primary rat microglial cultures. Our results show that Meth enhanced gp120-induced microglial activation, as revealed by immunostaining and Iba-1 expression, and potentiated gp120-mediated NLRP3 expression and IL-1β processing and release, as assayed by immunoblotting and ELISA. Meth also augmented the co-localization of NLRP3 and caspase-1, increased the numbers of NLRP3 puncta and ROS production, increased the levels of iNOS expression and NO production, and increased the levels of cleaved gasderminD (GSDMD-N; an executor of pyroptosis) in gp120-primed microglia. The Meth-associated effects were attenuated or blocked by MCC950, an NLRP3 inhibitor, or Mito-TEMPO, a mitochondrial superoxide scavenger. These results suggest that Meth enhances gp120-associated microglial NLRP3 activation and the resultant proinflammatory responses via mitochondria-dependent signaling.

Comparative proteomic analysis of cerebral cortex revealed neuroprotective mechanism of esculentoside A on Alzheimer's disease

Esculentoside A (EsA), isolated from phytolacca esculenta, is a saponin showing neuroprotective effect in the mouse models of Alzheimer's disease (AD). To investigate its action target and underlying mechanism, this study used the proteomics technique of isobaric tags for relative and absolute quantification (iTRAQ) to analyze the differentially expressed proteins (DEPs) in the cerebral cortex of EsA-treated and untreated triple-transgenic 3 × Tg-AD model mice. Proteomic comparison revealed 250, 436, and 903 DEPs in three group pairs, i.e. AD/Wild-type (WT), AD+5 mg/kg EsA/AD, AD+10 mg/kg EsA/AD, respectively. Among them 28 DEPs were commonly shared by three group pairs, and 25 of them showed reversed expression levels in the diseased group under the treatment of both doses of EsA. Bioinformatics analysis revealed that these DEPs were mainly linked to metabolism, synapses, apoptosis, learning and memory. EsA treatment restored the expression of these proteins, including amyloid precursor protein (APP), cathepsin B (Cstb), 4-aminobutyrate aminotransferase (Abat), 3-phosphoinositide-dependent protein kinase-1 (PDK1), carnitine palmitoyltransferase1 (Cpt1) and synaptotagmin 17 (Syt17), thereby ameliorated the spatial learning and memory of AD mice. Collectively, this study reveals for the first time the profound effect of EsA on the cerebral cortex of AD mice, which might be a potential therapeutic agent for the treatment of AD.

Methamphetamine enhancement of HIV-1 gp120-mediated NLRP3 inflammasome activation and resultant proinflammatory responses in rat microglial cultures

Background

Human Immunodeficiency Virus type 1 (HIV-1)-associated neurocognitive disorders (HAND) remain prevalent in HIV-1-infected individuals despite the evident success of combined antiretroviral therapy (cART). The mechanisms under HAND prevalence in the cART era remain perplexing. Ample evidence indicates that HIV-1 envelope glycoprotein protein 120 (gp120), a potent neurotoxin, plays a pivotal role in the HAND pathogenesis. Methamphetamine (Meth) abuse exacerbates HAND. How Meth exacerbates HAND is not fully understood. This study was to test the hypothesis that Meth exacerbates HAND by enhancing gp120-mediated proinflammatory responses in the brain, worsening the pathogenesis of HAND.

Methods

Experiments were carried out on primary microglial cultures prepared from neonatal SD rats. The purity of microglia was determined by staining with anti-CD11b. Meth and gp120 were applied to microglial cultures. Microglial activation was revealed by immunostaining and Iba-1 expression. The protein expression levels of Pro-IL-1β, Il-1β, Iba-1, iNOS, NLRP3, GSDMD and GSDMD-N were detected by western blotting analyses. The levels of proinflammatory cytokine and NO production in the microglia culture supernatants were assayed by ELISA and Griess reagent systems, respectively. NLRP3 activation was uncovered by fluorescent microscopy images displaying NLRP3 puncta labeled by anti-NLRP3 antibody. NLRP3 co-localization with caspase-1 was labeled with antibodies. One-way ANOVA with post hoc Tukey's multiple comparison tests was employed for statistical analyses.

Results

Meth enhanced gp120-induced microglia activation revealed by immunostaining and Iba-1 expression, and potentiated gp120-mediated NLRP3 expression, IL-1β processing and release assayed by immunoblot and ELISA. Meth also augmented the co-localization of NLRP3 and caspase-1, increased the numbers of NLRP3 puncta and ROS production, elevated levels of iNOS expression and NO production, and enhanced levels of cleaved gasderminD (GSDMD-N, an executor of pyroptosis) in gp120-primed microglia. The Meth-associated effects were attenuated or blocked by MCC950, an NLRP3 inhibitor, or Mito-TEMPO, a mitochondrial superoxide scavenger, indicating the involvement of mitochondria in Meth enhancement of NLRP3 inflammasome activation in gp120-primed microglia.

Conclusions

These results suggest that Meth enhanced gp120-associated microglial NLRP3 activation and resultant proinflammatory responses via mitochondria-dependent signaling.

HIV-associated neurocognitive disorder--pathogenesis and prospects for treatment

In the past two decades, several advancements have improved the care of HIV-infected individuals. Most importantly, the development and deployment of combination antiretroviral therapy (CART) has resulted in a dramatic decline in the rate of deaths from AIDS, so that people living with HIV today have nearly normal life expectancies if treated with CART. The term HIV-associated neurocognitive disorder (HAND) has been used to describe the spectrum of neurocognitive dysfunction associated with HIV infection. HIV can enter the CNS during early stages of infection, and persistent CNS HIV infection and inflammation probably contribute to the development of HAND. The brain can subsequently serve as a sanctuary for ongoing HIV replication, even when systemic viral suppression has been achieved. HAND can remain in patients treated with CART, and its effects on survival, quality of life and everyday functioning make it an important unresolved issue. In this Review, we describe the epidemiology of HAND, the evolving concepts of its neuropathogenesis, novel insights from animal models, and new approaches to treatment. We also discuss how inflammation is sustained in chronic HIV infection. Moreover, we suggest that adjunctive therapies--treatments targeting CNS inflammation and other metabolic processes, including glutamate homeostasis, lipid and energy metabolism--are needed to reverse or improve HAND-related neurological dysfunction.

A Novel Role of Proline Oxidase in HIV-1 Envelope Glycoprotein-induced Neuronal Autophagy

Proline oxidase (POX) catalytically converts proline to pyrroline-5-carboxylate. This catabolic conversion generates reactive oxygen species (ROS) that triggers cellular signaling cascades including autophagy and apoptosis. This study for the first time demonstrates a role of POX in HIV-1 envelope glycoprotein (gp120)-induced neuronal autophagy. HIV-1 gp120 is a neurotoxic factor and is involved in HIV-1-associated neurological disorders. However, the mechanism of gp120-mediated neurotoxicity remains unclear. Using SH-SY5Y neuroblastoma cells as a model, this study demonstrates that gp120 treatment induced POX expression and catalytic activity. Concurrently, gp120 also increased intracellular ROS levels. However, increased ROS had a minimal effect on neuronal apoptosis. Further investigation indicated that the immediate cellular response to increased ROS paralleled with induction of autophagy markers, beclin-1 and LC3-II. These data lead to the hypothesis that neuronal autophagy is activated as a cellular protective response to the toxic effects of gp120. A direct and functional role of POX in gp120-mediated neuronal autophagy was examined by inhibition and overexpression studies. Inhibition of POX activity by a competitive inhibitor "dehydroproline" decreased ROS levels concomitant with reduced neuronal autophagy. Conversely, overexpression of POX in neuronal cells increased ROS levels and activated ROS-dependent autophagy. Mechanistic studies suggest that gp120 induces POX by targeting p53. Luciferase reporter assays confirm that p53 drives POX transcription. Furthermore, data demonstrate that gp120 induces p53 via binding to the CXCR4 co-receptor. Collectively, these results demonstrate a novel role of POX as a stress response metabolic regulator in HIV-1 gp120-associated neuronal autophagy.

Glutamate carboxypeptidase II inhibition behaviorally and physiologically improves pyridoxine-induced neuropathy in rats

Pyridoxine is used as a supplement for treating conditions such as vitamin deficiency as well as neurological disorders such as depression, epilepsy and autism. A significant neurologic complication of pyridoxine therapy is peripheral neuropathy thought to be a result of long-term and high dose usage. Although pyridoxine-induced neuropathy is transient and can remit after its withdrawal, the process of complete recovery can be slow. Glutamate carboxypeptidase II (GCP II) inhibition has been shown to improve symptoms of both chemotherapy- and diabetic-induced neuropathy. This study evaluated if GCP II inhibition could behaviorally and physiologically improve pyridoxine-induced neuropathy. In the current study, high doses of pyridoxine (400 mg/kg, twice a day for seven days) were used to induce neuropathy in rats. An orally bioavailable GCP II inhibitor, 2-(3-mercaptopropyl) pentanedioic acid (2-MPPA), was administered daily at a dose of 30 mg/kg starting from the onset of pyridoxine injections. Body weight, motor coordination, heat sensitivity, electromyographical (EMG) parameters and nerve morphological features were monitored. The results show beneficial effects of GCP II inhibition including normalization of hot plate reaction time, foot fault improvements and increased open field distance travelled. H wave frequency, amplitude and latency as well as sensory nerve conduction velocity (SNCV) were also significantly improved by 2-MPPA. Lastly, GCP II inhibition resulted in morphological protection in the spinal cord and sensory fibers in the lumbar region dorsal root ganglia (DRG). In conclusion, inhibition of GCP II may be beneficial against the peripheral sensory neuropathy caused by pyridoxine.

Existence of glia mitigated ketamine-induced neurotoxicity in neuron-glia mixed cultures of neonatal rat cortex and the glia-mediated protective effect of 2-PMPA

The present study compared ketamine-induced neurotoxicity in the neuron-glia mixed cultures and neuronal cultures and further explored the neuroprotective effect of the NAAG peptidase inhibitor 2-(phosphonomethyl) pentanedioic acid (2-PMPA). Firstly, Rosenfeld's staining and immunofluorescence staining of microtubule-associated protein 2 (MAP2) and glial fibrillary acidic protein (GFAP) were used to address the difference of morphology in the mixed cultures and neuronal cultures. Our results showed that neurons and astrocytes grew in good conditions. The ratio of neurons and astrocytes in the mixed cultures was around 1:1, and the purity of neurons in the neuronal cultures is 91.3%. Furthermore, ketamine was used to test the hypothesis that the presence of a higher proportion of glia in the mixed cultures would be protective against ketamine-induced neurotoxicity in the mixed cultures compared with neuronal cultures. The results showed that ketamine-induced morphological changes, cell viability decrease and lactate dehydrogenase (LDH) levels increase were significantly mitigated in neuron-glia mixed cultures compared with neuronal cultures. Furthermore, 2-PMPA was included to further explore efficient protective drug for ketamine-induced neurotoxicity. Our results showed that 2-PMPA reduced ketamine-induced decrease of cell viability and increase of LDH levels in the mixed cultures but not in the neuronal cultures. Further morphological changes of neurons and astrocytes also indicated that 2-PMPA could improve ketamine damaged neurons in the mixed cultures instead of neuronal cultures. These results indicate that glia protect neurons from ketamine-induced neurotoxicity. These data further suggest that glia mediate the neuroprotective effect of 2-PMPA and 2-PMPA has the potential to treat ketamine-induced neurotoxicity in vivo. Delineating the mechanisms underlying the communication between neurons and glia and the neuroprotective effects of 2-PMPA in the mixed cultures to ketamine-induced neurotoxicity require further investigation.

Targeting the glutamatergic system for the treatment of HIV-associated neurocognitive disorders

The accumulation of excess glutamate in the extracellular space as a consequence of CNS trauma, neurodegenerative diseases, infection, or deregulation of glutamate clearance results in neuronal damage by excessive excitatory neurotransmission. Glutamate excitotoxicity is thought to be one of several mechanisms by which HIV exerts neurotoxicity that culminates in HIV-associated neurocognitive disorders (HAND). Excess glutamate is released upon HIV infection of macrophage/microglial cells and has been associated with neurotoxicity mediated by gp120, transactivator of transcription (Tat) and other HIV proteins. Several strategies have been used over the years to try to prevent glutamate excitotoxicity. Since the main toxic effects of excess glutamate are thought to be due to excitotoxicity from over activation of glutamate receptors, antagonists of these receptors have been popular therapeutic targets. Early work to ameliorate the effects of excess extracellular glutamate focused on NMDA receptor antagonism, but unfortunately, potent blockade of this receptor has been fraught with side effects. One alternative to direct receptor blockade has been the inhibition of enzymes responsible for the production of glutamate such as glutaminase and glutamate carboxypeptidase II. Another approach has been to regulate the transporters responsible for modulation of extracellular glutamate such as excitatory amino acid transporters and the glutamate-cystine antiporter. There is preliminary experimental evidence that these approaches have potential therapeutic utility for the treatment of HAND. These efforts however, are at an early stage where the next steps are dependent on the identification of drug-like inhibitors as well as the development of predictive neuroAIDS animal models.

Inhibition of glutamate carboxypeptidase II (GCPII) activity as a treatment for cognitive impairment in multiple sclerosis

Half of all patients with multiple sclerosis (MS) experience cognitive impairment, for which there is no pharmacological treatment. Using magnetic resonance spectroscopy (MRS), we examined metabolic changes in the hippocampi of MS patients, compared the findings to performance on a neurocognitive test battery, and found that N-acetylaspartylglutamate (NAAG) concentration correlated with cognitive functioning. Specifically, MS patients with cognitive impairment had low hippocampal NAAG levels, whereas those with normal cognition demonstrated higher levels. We then evaluated glutamate carboxypeptidase II (GCPII) inhibitors, known to increase brain NAAG levels, on cognition in the experimental autoimmune encephalomyelitis (EAE) model of MS. Whereas GCPII inhibitor administration did not affect physical disabilities, it increased brain NAAG levels and dramatically improved learning and memory test performance compared with vehicle-treated EAE mice. These data suggest that NAAG is a unique biomarker for cognitive function in MS and that inhibition of GCPII might be a unique therapeutic strategy for recovery of cognitive function.

Glutamate carboxypeptidase II (GCPII) inhibitor displays anti-glutamate and anti-cocaine effects in an invertebrate assay

Glutamate carboxypeptidase II (GCPII) inhibitors are promising anti-glutamatergic and anti-addictive agents. We hypothesized that a GCPII inhibitor 2 (phosphonomethyl) pentanedioic acid (2-PMPA) would display anti-stereotypical activity in planarians. Experiments revealed that 2-PMPA displayed no overt behavioral activity by itself but attenuated stereotypical counts (C-shape hyperkinesias) elicited by four compounds (2-PMPA rank order potency: glutamate>NMDA>pilocarpine>cocaine). These data suggest GCPII inhibitors display broad-spectrum efficacy against behavioral activity produced by glutamatergic and non-glutamatergic compounds in an invertebrate assay.