Nrf2 gene deletion fails to alter psychostimulant-induced behavior or neurotoxicity

P2X7 receptor augments kainic acid-induced nitrosative stress by abrogating GS-HSP25-mediated iNOS inhibition and GSH synthesis in the mouse hippocampus

Glutathione (GSH) and heat shock protein 25 (HSP25) reciprocally regulate each other, which maintain redox homeostasis. Since P2X7 receptor (P2X7R) regulates GSH biosynthesis and HSP25 induction, the present study was conducted to explore the role of P2X7R in the reciprocal regulation between HSP25 and GSH in response to kainic acid (KA)-induced nitrosative stress and the related signal pathways, which are largely unknown. The present data demonstrate that P2X7R deletion attenuated KA-induced reductions in total GSH level and nuclear factor-erythroid 2-related factor 2 (Nrf2) intensity/nuclear translocation in astrocytes. P2X7R ablation increased Nrf2 intensity/nuclear translocation in microglia following KA treatment. P2X7R deletion also ameliorated KA-induced inducible nitric oxide synthase (iNOS) and S-nitrosylated-cysteine (SNO-Cys) inductions in microglia and astrocytes. However, P2X7R ablation could not affect KA-induced nuclear Nrf2 translocation and SNO-Cys production in CA3 neurons. Furthermore, P2X7R ablation mitigated S-nitrosylations of glutamine synthase (GS) and alanine-serine-cysteine transporter 2 (ASCT2) induced by KA. HSP25 knockdown increased GSH consumption, astroglial iNOS level and S-nitrosylations of GS and ASCT2, but decreased Nrf2 intensity/nuclear translocation in astrocytes of P2X7R-/- mice following KA injection. These findings indicate that P2X7R facilitated iNOS upregulation by inhibiting HSP25 induction and nuclear Nrf2 translocation in astrocytes, which augmented nitrosative stress-mediated reduction in GSH biosynthesis in response to KA. Therefore, our data suggest that the targeting of P2X7R-Nrf2-iNOS-GS-HSP25 pathway may be required for the maintenance of GSH-mediated redox homeostasis against nitrosative stress, which would prevent the progression of undesirable consequences from seizures and neuroinflammation.

Intraperitoneal injection of buprenorphine on anxiety-like behavior and alteration in expression of Gfap and Nrf2 in methamphetamine treated rats

The effects of buprenorphine (BUP) on anxiety-like behavior and the expression of the glial fibrillary acidic protein (Gfap) and nuclear factor erythroid 2-related factor 2 (Nrf2) in methamphetamine (METH)-treated rats were investigated in this study. Twenty-eight male Wistar rats were randomly divided into four groups including control (saline), METH (10.00 mg kg^-1), BUP (10.00 mg kg^-1), and BUP+METH groups and treated for five days. On the final day of treatment, gene expression levels and anxiety were evaluated using elevated plus-maze (EPM). According to the results, five days of METH injection reduced open arm exploration in the EPM. In contrast, the open arm entries and the time spent in the open arms were increased in the BUP+METH group compared to the METH group. The expression levels of Gfap and Nrf2 were lower in METH-treated rats compared to controls, whereas Gfap and Nrf2 expression levels were higher in the METH+BUP-treated rats compared to the METH-treated rats, however, it was similar to the controls. These findings suggested that co-administration of BUP+METH could decrease anxiety-like behavior through increasing the activity of the antioxidant protection system and might have therapeutic potential for preventing anxiety in METH users.

P2X7 Receptor Augments LPS-Induced Nitrosative Stress by Regulating Nrf2 and GSH Levels in the Mouse Hippocampus

P2X7 receptor (P2X7R) regulates inducible nitric oxide synthase (iNOS) expression/activity in response to various harmful insults. Since P2X7R deletion paradoxically decreases the basal glutathione (GSH) level in the mouse hippocampus, it is likely that P2X7R may increase the demand for GSH for the maintenance of the intracellular redox state or affect other antioxidant defense systems. Therefore, the present study was designed to elucidate whether P2X7R affects nuclear factor-erythroid 2-related factor 2 (Nrf2) activity/expression and GSH synthesis under nitrosative stress in response to lipopolysaccharide (LPS)-induced neuroinflammation. In the present study, P2X7R deletion attenuated iNOS upregulation and Nrf2 degradation induced by LPS. Compatible with iNOS induction, P2X7R deletion decreased S-nitrosylated (SNO)-cysteine production under physiological and post-LPS treated conditions. P2X7R deletion also ameliorated the decreases in GSH, glutathione synthetase, GS and ASCT2 levels concomitant with the reduced S-nitrosylations of GS and ASCT2 following LPS treatment. Furthermore, LPS upregulated cystine:glutamate transporter (xCT) and glutaminase in P2X7R^+/+ mice, which were abrogated by P2X7R deletion. LPS did not affect GCLC level in both P2X7R^+/+ and P2X7R^−/− mice. Therefore, our findings indicate that P2X7R may augment LPS-induced neuroinflammation by leading to Nrf2 degradation, aberrant glutamate-glutamine cycle and impaired cystine/cysteine uptake, which would inhibit GSH biosynthesis. Therefore, we suggest that the targeting of P2X7R, which would exert nitrosative stress with iNOS in a positive feedback manner, may be one of the important therapeutic strategies of nitrosative stress under pathophysiological conditions.

Targeting the renin angiotensin system for the treatment of anxiety and depression

Emotional disorders like anxiety and depression are responsible for considerable morbidity and mortality all over the world. Several antidepressant and anxiolytic medications are available for the treatment of anxiety and depression. However, a significant number of patients either do not respond to these medications or respond inadequately. Hence, there is a need to identify novel targets for the treatment of anxiety and depression. In this review we focus on the renin angiotensin system (RAS) as a potential target for the treatment of these disorders. We review work that has evaluated the effects of various compounds targeting the RAS on anxiety- and depression-like behaviors. Further, we suggest future work that must be carried out to fully exploit the RAS for the treatment of anxiety and depression. The RAS provides an attractive target for both the identification of novel anxiolytic and antidepressant medications and/or for enhancing the efficacy of currently available medications used for the treatment of anxiety and depression.

Extinction Training after Cocaine Self-Administration Influences the Epigenetic and Genetic Machinery Responsible for Glutamatergic Transporter Gene Expression in Male Rat Brain

Glutamate is a key excitatory neurotransmitter in the central nervous system. The balance of glutamatergic transporter proteins allows long-term maintenance of glutamate homeostasis in the brain, which is impaired during cocaine use disorder. The aim of this study was to investigate changes in the gene expression of SLC1A2 (encoding GLT-1), and SLC7A11 (encoding xCT), in rat brain structures after short-term (3 days) and long-term (10 days) extinction training using microarray analysis and quantitative real-time PCR. Furthermore, we analyzed the expression of genes encoding transcription factors, i.e., NFKB1 and NFKB2 (encoding NF-κB), PAX6, (encoding Pax6), and NFE2L2 (encoding Nrf2), to verify the correlation between changes in glutamatergic transporters and changes in their transcriptional factors and microRNAs (miRNAs; miR-124a, miR-543-3p and miR-342-3p) and confirm the epigenetic mechanism. We found reduced GLT-1 transcript and mRNA level in the prefrontal cortex (PFCTX) and dorsal striatum (DSTR) in rats that had previously self-administered cocaine after 3 days of extinction training, which was associated with downregulation of PAX6 (transcript and mRNA) and NFKB2 (mRNA) level in the PFCTX and with upregulation of miR-543-3p and miR-342-3p in the DSTR. The xCT mRNA level was reduced in the PFCTX and DSTR, and NFE2L2 transcript level in the PFCTX was decreased on the 3rd day of extinction training. In conclusion, 3-day drug-free period modulates GLT-1 and xCT gene expression through genetic and epigenetic mechanisms, and such changes in expression seem to be potential molecular targets for developing a treatment for cocaine-seeking behavior.

Reactive Oxygen Species/Hypoxia-Inducible Factor-1α/Platelet-Derived Growth Factor-BB Autocrine Loop Contributes to Cocaine-Mediated Alveolar Epithelial Barrier Damage

Abuse of psychostimulants, such as cocaine, has been shown to be closely associated with complications of the lung, such as pulmonary hypertension, edema, increased inflammation, and infection. However, the mechanism by which cocaine mediates impairment of alveolar epithelial barrier integrity that underlies various pulmonary complications has not been well determined. Herein, we investigate the role of cocaine in disrupting the alveolar epithelial barrier function and the associated signaling cascade. Using the combinatorial electric cell-substrate impedance sensing and FITC-dextran permeability assays, we demonstrated cocaine-mediated disruption of the alveolar epithelial barrier, as evidenced by increased epithelial monolayer permeability with a concomitant loss of the tight junction protein zonula occludens-1 (Zo-1) in both mouse primary alveolar epithelial cells and the alveolar epithelial cell line, L2 cells. To dissect the signaling pathways involved in this process, we demonstrated that cocaine-mediated induction of permeability factors, platelet-derived growth factor (PDGF-BB) and vascular endothelial growth factor, involved reactive oxygen species (ROS)-dependent induction of hypoxia-inducible factor (HIF)-1α. Interestingly, we demonstrated that ROS-dependent induction of another transcription factor, nuclear factor erythroid-2-related factor-2, that did not play a role in cocaine-mediated barrier dysfunction. Importantly, this study identifies, for the first time, that ROS/HIF-1α/PDGF-BB autocrine loop contributes to cocaine-mediated barrier disruption via amplification of oxidative stress and downstream signaling. Corroboration of these cell culture findings in vivo demonstrated increased permeability of the alveolar epithelial barrier, loss of expression of Zo-1, and a concomitantly increased expression of both HIF-1α and PDGF-BB. Pharmacological blocking of HIF-1α significantly abrogated cocaine-mediated loss of Zo-1. Understanding the mechanism(s) by which cocaine mediates barrier dysfunction could provide insights into the development of potential therapeutic targets for cocaine-mediated pulmonary hypertension.

WITHDRAWN: Melatonin improves methamphetamine-induced blood brain barrier impairment through NADPH oxidase-2 in primary rat brain microvascular endothelium cells

The Publisher regrets that this article is an accidental duplication of an article that has already been published in 〈BRES, 1646 (2016) 182-192〉, 10.1016/j.brainres.2016.05.049. The duplicate article has therefore been withdrawn. The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy.

Methamphetamine oxidative stress, neurotoxicity, and functional deficits are modulated by nuclear factor-E2-related factor 2

Activation of redox-sensitive transcription factors like nuclear factor-E2-related factor 2 (Nrf2) can enhance the transcription of cytoprotective genes during oxidative stress. We investigated whether Nrf2 is activated by methamphetamine (METH) thereby altering neurotoxicity in Nrf2 +/+ and -/- adult mouse brain. A single dose of METH can induce the mRNA levels of Nrf2-regulated antioxidant and cytoprotective proteins in mouse brain. Multiple-day dosing with METH enhanced DNA oxidation and decreased tyrosine hydroxylase and dopamine transporter staining in the striatum, indicating dopaminergic nerve terminal toxicity, which was more severe in -/- mice, as were deficits in motor coordination and olfactory discrimination. These Nrf2-dependent effects were independent of changes in METH metabolism or the induction of hyperthermia. Similarly, METH increased striatal glial fibrillary acidic protein, indicating neurotoxicity. METH neurotoxicity was also observed in the glial cells and in the GABAergic system of the olfactory bulbs and was enhanced in -/- mice, whereas dopaminergic parameters were unaffected. With one-day dosing of METH, there were no differences between +/+ and -/- mice in either basal or METH-enhanced DNA oxidation and neurotoxicity markers. Nrf2-mediated pathways accordingly may protect against the neurodegenerative effects and functional deficits initiated by METH and perhaps other reactive oxygen species-enhancing neurotoxicants, when there is time for transcriptional activation and protein induction. In human users of METH, this mechanism may be essential when differences in drug abuse patterns may alter the induction and duration of Nrf2 activation thereby modulating susceptibility to the neurotoxic effects of METH.

Developmental role of nuclear factor E2-related factor 2 in mitigating methamphetamine fetal toxicity and postnatal neurodevelopmental deficits

Nuclear factor E2-related factor 2 (Nrf2) is a transcription factor that mediates protective responses to oxidative stress, but its developmental role is unknown. Herein, we treated pregnant Nrf2-deficient knockout mice with methamphetamine (METH) (5-40 mg/kg ip), which increases fetal reactive oxygen species (ROS) and oxidatively damaged DNA in fetal brain tissue. METH-exposed Nrf2(-/-) fetuses were unable to increase mRNA levels of ROS-protective heme oxygenase-1, NAD(P)H:quinone oxidoreductase, or oxoguanine glycosylase 1, unlike wild-type controls, and exhibited enhanced DNA oxidation, fetal resorption, edema, and reduced fetal weight, with greater toxicity in female Nrf2(-/-) fetuses. Postnatal neurodevelopmental deficits in activity and olfactory function were exacerbated, with gender-dependent differences, and the olfactory bulb GABAergic marker GAD-65 was decreased in Nrf2(-/-) offspring exposed in utero to METH. In utero METH-initiated olfactory deficits may be a sensitive postnatal functional test for long-term neurotoxicity, and indicated a broad fetal role for Nrf2. The results show that fetal Nrf2 deficiency enhances METH-initiated oxidative DNA damage and toxicity, suggesting that Nrf2 activation of cytoprotective proteins mitigates the effects of ROS and their oxidative damage to cellular macromolecules, thereby protecting the developing fetus from adverse structural and postnatal neurodevelopmental consequences.

Hypoxic preconditioning involves system Xc- regulation in mouse neural stem cells

In animals, hypoxic preconditioning has been used as a form of neuroprotection. The exact mechanism involved in neuroprotective hypoxic preconditioning has not been described, yet could be valuable for possible neuroprotective strategies. The overexpression of the cystine-glutamate exchanger, system Xc-, has been demonstrated as being neuroprotective (Shih, Erb et al. 2006). Here, using immunohistochemistry, we demonstrate that C57BL/6 mice exposed to hypoxia showed an increase in system Xc- expression, with the highest level of intensity in the hippocampus. Western Blot analysis also showed an almost 2-fold increase in system Xc- protein in hypoxia-exposed versus control mice. The mRNA for the regulatory subunit of system Xc-, xCT, and the xCT/actin ratio were also increased under hypoxic conditions. Experiments using hypoxia-inducible factor (HIF-1α) siRNA showed a statistically significant decrease in HIF-1α and system Xc- expression. Under hypoxic conditions, system Xc- activity, as determined by cystine uptake, increased 2-fold. Importantly, hypoxic preconditioning was attenuated in neural stem cells by pharmacological inhibition of system Xc- activity with S4-carboxyphenylglycine. These data provide the first evidence of hypoxic regulation of the cystine glutamate exchanger system Xc-.

Nrf2 deficiency potentiates methamphetamine-induced dopaminergic axonal damage and gliosis in the striatum

Oxidative stress that correlates with damage to nigrostriatal dopaminergic neurons and reactive gliosis in the basal ganglia is a hallmark of methamphetamine (METH) toxicity. In this study, we analyzed the protective role of the transcription factor Nrf2 (nuclear factor-erythroid 2-related factor 2), a master regulator of redox homeostasis, in METH-induced neurotoxicity. We found that Nrf2 deficiency exacerbated METH-induced damage to dopamine neurons, shown by an increase in loss of tyrosine hydroxylase (TH)- and dopamine transporter (DAT)-containing fibers in striatum. Consistent with these effects, Nrf2 deficiency potentiated glial activation, indicated by increased striatal expression of markers for microglia (Mac-1 and Iba-1) and astroglia (GFAP) one day after METH administration. At the same time, Nrf2 inactivation dramatically potentiated the increase in TNFα mRNA and IL-15 protein expression in GFAP+ cells in the striatum. In sharp contrast to the potentiation of striatal damage, Nrf2 deficiency did not affect METH-induced dopaminergic neuron death or expression of glial markers or proinflammatory molecules in the substantia nigra. This study uncovers a new role for Nrf2 in protection against METH-induced inflammatory and oxidative stress and striatal degeneration.

Cellular stress responses, the hormesis paradigm, and vitagenes: novel targets for therapeutic intervention in neurodegenerative disorders

Despite the capacity of chaperones and other homeostatic components to restore folding equilibrium, cells appear poorly adapted for chronic oxidative stress that increases in cancer and in metabolic and neurodegenerative diseases. Modulation of endogenous cellular defense mechanisms represents an innovative approach to therapeutic intervention in diseases causing chronic tissue damage, such as in neurodegeneration. This article introduces the concept of hormesis and its applications to the field of neuroprotection. It is argued that the hormetic dose response provides the central underpinning of neuroprotective responses, providing a framework for explaining the common quantitative features of their dose-response relationships, their mechanistic foundations, and their relationship to the concept of biological plasticity, as well as providing a key insight for improving the accuracy of the therapeutic dose of pharmaceutical agents within the highly heterogeneous human population. This article describes in mechanistic detail how hormetic dose responses are mediated for endogenous cellular defense pathways, including sirtuin and Nrf2 and related pathways that integrate adaptive stress responses in the prevention of neurodegenerative diseases. Particular attention is given to the emerging role of nitric oxide, carbon monoxide, and hydrogen sulfide gases in hormetic-based neuroprotection and their relationship to membrane radical dynamics and mitochondrial redox signaling.

Nrf2-mediated neuroprotection in the MPTP mouse model of Parkinson's disease: Critical role for the astrocyte

Oxidative stress has been implicated in the etiology of Parkinson's disease (PD) and in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) animal model of PD. It is known that under conditions of oxidative stress, the transcription factor NF-E2-related factor (Nrf2) binds to antioxidant response element (ARE) to induce antioxidant and phase II detoxification enzymes. To investigate the role of Nrf2 in the process of MPTP-induced toxicity, mice expressing the human placental alkaline phosphatase (hPAP) gene driven by a promoter containing a core ARE sequence (ARE-hPAP) were used. ARE-hPAP mice were injected (30 mg/kg) once per day for 5 days and killed 7 days after the last MPTP injection. In response to this design, ARE-dependent gene expression was decreased in striatum whereas it was increased in substantia nigra. The same MPTP protocol was applied in Nrf2(+/+) and Nrf2(-/-) mice; Nrf2 deficiency increases MPTP sensitivity. Furthermore, we evaluated the potential for astrocytic Nrf2 overexpression to protect from MPTP toxicity. Transgenic mice with Nrf2 under control of the astrocyte-specific promoter for the glial fribillary acidic protein (GFAP-Nrf2) on both a Nrf2(+/+) and Nrf2(-/-) background were administered MPTP. In the latter case, only the astrocytes expressed Nrf2. Independent of background, MPTP-mediated toxicity was abolished in GFAP-Nrf2 mice. These striking results indicate that Nrf2 expression restricted to astrocytes is sufficient to protect against MPTP and astrocytic modulation of the Nrf2-ARE pathway is a promising target for therapeutics aimed at reducing or preventing neuronal death in PD.

Neuronal pentraxins modulate cocaine-induced neuroadaptations

Neuronal pentraxins (NPs) function in the extracellular matrix to bind alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. Three NPs have been described, neuronal activity-regulated pentraxin (Narp), which is regulated as an immediate early gene, NP1, and neuronal pentraxin receptor (NPR). Narp and NP1 enhance synaptogenesis and glutamate signaling by clustering AMPA receptors, whereas NPR contributes to removing AMPA receptors during group I metabotropic glutamate receptor-dependent long-term depression. Here, we examine mice with genetic deletions [knockout (KO)] of each NP to assess their contributions to cocaine-induced neuroplasticity. Consistent with a shared AMPA receptor clustering function for Narp and NP1, deletion of either NP caused similar behavioral alterations. Thus, although both Narp and NP1 deletion promoted cocaine-induced place preference, NPR deletion was without effect. In addition, although Narp and NP1 KO showed reduced time in the center of a novel environment, NPR KO mice spent more time in the center. Finally, although Narp and NP1 KO mice showed blunted locomotion after AMPA microinjection into the accumbens 3 weeks after discontinuing repeated cocaine injections, the AMPA response was augmented in NPR KO. Likewise, endogenous glutamate release elicited less motor activity in Narp KO mice. Consistent with reduced AMPA responsiveness after chronic cocaine in Narp KO mice, glutamate receptor 1 was reduced in the PSD fraction of Narp KO mice withdrawn from cocaine. These data indicate that NPs differentially contribute to cocaine-induced plasticity in a manner that parallels their actions in synaptic plasticity.

Regulation of glutathione synthesis via interaction between glutamate transport-associated protein 3-18 (GTRAP3-18) and excitatory amino acid carrier-1 (EAAC1) at plasma membrane

Regulation of the cysteine transporter known as excitatory amino acid carrier-1 (EAAC1) for intracellular glutathione (GSH) content was investigated using human embryonic kidney (HEK) 293 cells as a model system. GSH content was significantly reduced by l-aspartate-beta-hydroxamate (50-250 microM), an inhibitor of both EAAC1 and GLT1, both of which are transporters to take up cysteine, whereas dihydrokainate (1-100 microM), a specific inhibitor of GLT1, failed to do so. This indicates that EAAC1 is involved in GSH content in HEK293 cells. We examined the effect of glutamate transport-associated protein 3-18 (GTRAP3-18), which is capable of interacting with EAAC1. The GSH content decreased when the GTRAP3-18 protein level at the plasma membrane was increased by methyl-beta-cyclodextrin (250 microM), rendering the cells more vulnerable to oxidative stress. Intracellular GSH increased when the GTRAP3-18 protein level at the plasma membrane was decreased by antisense oligonucleotides, rendering the cells more resistant to oxidative stress. Furthermore, we found that the increase in GSH content produced by stimulating protein kinase C, a translocator and activator of EAAC1, was inhibited by an increase in cell surface GTRAP3-18 protein. These results show GTRAP3-18 to negatively and dominantly regulate cellular GSH content via interaction with EAAC1 at the plasma membrane.

Cellular interplay between neurons and glia: toward a comprehensive mechanism for excitotoxic neuronal loss in neurodegeneration

Astrocytes perform vital maintenance, functional enhancement, and protective roles for their associated neurons; however these same mechanisms may become deleterious for neurons under some conditions. In this review, we highlight two normally protective pathways, the endoplasmic reticulum (ER) stress response and an endogenous antioxidant response, which may become neurotoxic when activated in astrocytes during the inflammation associated with neurodegeneration. Stimulation of these multifaceted pathways affects a panoply of cellular processes. Of particular importance is the effect these pathways have on the homeostasis of the excitatory amino acid neurotransmitter, glutamate. The endogenous antioxidant response increases extracellular glutamate in the pursuit of making the cellular antioxidant, glutathione, by increasing expression of the xCT subunit of the cystine/glutamate antiporter. Meanwhile, inflammatory mediators such as TNFα reduce levels of membrane-bound glutamate scavenging proteins such as the excitatory amino acid transporters. Together, these cellular activities may result in a net increase in extracellular glutamate that could alter neuronal function and lead to excitotoxicity. Here we discuss the role of N-methyl-D-aspartate receptors, which, when excessively stimulated by glutamate, can cause neuronal dysfunction and loss via activation of calpains. While there are other pathways acting in concert or parallel to those we describe here, this review explores a rationale to explain how two protective mechanisms may result in neuronal loss during neurodegeneration.