Activation of transcription factor Nrf-2 and its downstream targets in response to moloney murine leukemia virus ts1-induced thiol depletion and oxidative stress in astrocytes

The Multifaceted Roles of NRF2 in Cancer: Friend or Foe?

Physiological concentrations of reactive oxygen species (ROS) play vital roles in various normal cellular processes, whereas excessive ROS generation is central to disease pathogenesis. The nuclear factor erythroid 2-related factor 2 (NRF2) is a critical transcription factor that regulates the cellular antioxidant systems in response to oxidative stress by governing the expression of genes encoding antioxidant enzymes that shield cells from diverse oxidative alterations. NRF2 and its negative regulator Kelch-like ECH-associated protein 1 (KEAP1) have been the focus of numerous investigations in elucidating whether NRF2 suppresses tumor promotion or conversely exerts pro-oncogenic effects. NRF2 has been found to participate in various pathological processes, including dysregulated cell proliferation, metabolic remodeling, and resistance to apoptosis. Herein, this review article will examine the intriguing role of phase separation in activating the NRF2 transcriptional activity and explore the NRF2 dual impacts on tumor immunology, cancer stem cells, metastasis, and long non-coding RNAs (LncRNAs). Taken together, this review aims to discuss the NRF2 multifaceted roles in both cancer prevention and promotion while also addressing the advantages, disadvantages, and limitations associated with modulating NRF2 therapeutically in cancer treatment.

A Study on the Planarian Model Confirms the Antioxidant Properties of Tameron against X-ray- and Menadione-Induced Oxidative Stress

Ionizing radiation and radiation-related oxidative stress are two important factors responsible for the death of actively proliferating cells, thus drastically reducing the regeneration capacity of living organisms. Planarian flatworms are freshwater invertebrates that are rich in stem cells called neoblasts and, therefore, present a well-established model for studies on regeneration and the testing of novel antioxidant and radioprotective substances. In this work, we tested an antiviral and antioxidant drug Tameron (Monosodium α-Luminol or 5-amino-2,3-dihydro-1,4-phthalazinedione sodium salt) for its ability to reduce the harm of X-ray- and chemically induced oxidative stress on a planarian model. Our study has revealed the ability of Tameron to effectively protect planarians from oxidative stress while enhancing their regenerative capacity by modulating the expression of neoblast marker genes and NRF-2-controlled oxidative stress response genes.

Glutathione and Related Molecules in Parkinsonism

Glutathione (GSH) is the most abundant intrinsic antioxidant in the central nervous system, and its substrate cysteine readily becomes the oxidized dimeric cystine. Since neurons lack a cystine transport system, neuronal GSH synthesis depends on cystine uptake via the cystine/glutamate exchange transporter (xCT), GSH synthesis, and release in/from surrounding astrocytes. Transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2), a detoxifying master transcription factor, is expressed mainly in astrocytes and activates the gene expression of various phase II drug-metabolizing enzymes or antioxidants including GSH-related molecules and metallothionein by binding to the antioxidant response element (ARE) of these genes. Accumulating evidence has shown the involvement of dysfunction of antioxidative molecules including GSH and its related molecules in the pathogenesis of Parkinson’s disease (PD) or parkinsonian models. Furthermore, we found several agents targeting GSH synthesis in the astrocytes that protect nigrostriatal dopaminergic neuronal loss in PD models. In this article, the neuroprotective effects of supplementation and enhancement of GSH and its related molecules in PD pathology are reviewed, along with introducing new experimental findings, especially targeting of the xCT-GSH synthetic system and Nrf2–ARE pathway in astrocytes.

Activation of anti-oxidant Keap1/Nrf2 pathway modulates efficacy of dihydroartemisinin-based monotherapy and combinatory therapy with ionizing radiation

The efficacy of radiotherapy depends not only on DNA damage but also on ROS production, both induced by ionizing radiation. Massive ROS production can induce cell death or activate protective pathways such as Keap1/Nrf2 pathway, which regulates intracellular cysteine availability through upregulation of SLC7A11, a subunit of xCT transporter, and subsequently glutathione synthesis, thus improving antioxidative defense. The anti-malaria drug dihydroartemisinin (DHA) shows anti-neoplastic potential. Previous publications suggested that DHA increased ROS production. We intended to enhance oxidative stress with DHA to improve the efficacy of radiotherapy. Therefore, we first analyzed the oxidative response to DHA in HCT116 colorectal and NCI-H460 lung adenocarcinoma cells. In response to DHA, we detected lipid peroxidation and protein oxidation, which resulted in mitochondrial damage and eventually in iron-dependent cell death. Concurrently, DHA activated Keap1/Nrf2 pathway in HCT116 cells, leading to increased SLC7A11 expression and glutathione level. In Keap1-mutant NCI-H460 cells, Nrf2 was constantly activated and responsible for high SLC7A11 and glutathione levels. Pancancer analysis revealed that lung cancer is the tumor entity with the most frequent Keap1 alterations. Although NCI-H460 cells reacted more refractory to DHA-induced cell death than HCT116 cells, eradication of clonogenic cells by DHA was more efficient in both cell lines when Keap1/Nrf2 pathway was inhibited. When applied simultaneously, radiotherapy and DHA more efficiently eradicated clonogenic cells than either therapy alone, but treatment schedule can mitigate the combinatory effect in HCT116 cells. In summary, DHA improved efficacy of radiotherapy, but treatment schedule must be considered with care especially in Keap1-wildtype cells.

xCT: A Critical Molecule That Links Cancer Metabolism to Redox Signaling

System x_c^- cystine/glutamate antiporter, composed of a light-chain subunit (xCT, SLC7A11) and a heavy-chain subunit (CD98hc, SLC3A2), is mainly responsible for the cellular uptake of cystine in exchange for intracellular glutamate. In recent years, the xCT molecule has been found to play an important role in tumor growth, progression, metastasis, and multidrug resistance in various types of cancer. Interestingly, xCT also exhibits an essential function in regulating tumor-associated ferroptosis. Despite significant progress in targeting the system x_c^- transporter in cancer treatment, the underlying mechanisms still remain elusive. It is also unclear why solid tumors are more sensitive to xCT inhibitors such as sulfasalazine, as compared to hematological malignancies. This review mainly focuses on the role of xCT cystine/glutamate transporter in regard to tumor growth, chemoresistance, tumor-selective ferroptosis, and the mechanisms regulating xCT gene expression. The potential therapeutic implications of targeting the system x_c^- and its combination with chemotherapeutic agents or immunotherapy to suppress tumor growth and overcome drug resistance are also discussed.

Taurine Chloramine Prevents Neuronal HT22 Cell Damage Through Nrf2-Related Heme Oxygenase-1

Oxidative cell damages are able to contribute to neuronal degeneration in several diseases of the central nervous system (CNS) including stroke as well as ischemia. Heme oxygenase (HO)-1 plays a major role in the pathogenesis of neuronal disorder. Taurine chloramine (TauCl) has been shown to possess strong neuronal activities; however, the direct effects of TauCl on neuronal cell death remain to be determined. Therefore, this study was designed to assess the neuroprotective effect of TauCl using oxidative stress-stimulated mouse hippocampal HT22 cells. TauCl showed protective effects against oxidative stress-induced neurotoxicity and inhibited the reactive oxygen species (ROS) production by inducing the heme oxygenase (HO)-1 expression in HT22 cells. TauCl upregulated HO-1 expression and it also increased the nuclear factor E2-related factor 2 (Nrf2) translocation to nuclear. Using an inhibitor of HO-1 activity, we verified that the oxidative stress-related HT22 cell death was significantly suppressed by TauCl. In addition, we found reduced TauCl-induced HO-1 expression and cytoprotection following treatment of the cells with an extracellular signal-regulated kinase (ERK) inhibitor (PD98059) or a p38 inhibitor (SB203580), but not following treatment with a SP600125 as a c-Jun NH2-terminal kinase (JNK) inhibitor. These findings suggest that TauCl improves cellular damage induced by glutamate or H2O2 through ERK and p38, Nrf2, and HO-1 pathways in HT22 cells.

Cytoplasmic vacuolization in cell death and survival

Cytoplasmic vacuolization (also called cytoplasmic vacuolation) is a well-known morphological phenomenon observed in mammalian cells after exposure to bacterial or viral pathogens as well as to various natural and artificial low-molecular-weight compounds. Vacuolization often accompanies cell death; however, its role in cell death processes remains unclear. This can be attributed to studying vacuolization at the level of morphology for many years. At the same time, new data on the molecular mechanisms of the vacuole formation and structure have become available. In addition, numerous examples of the association between vacuolization and previously unknown cell death types have been reported. Here, we review these data to make a deeper insight into the role of cytoplasmic vacuolization in cell death and survival.

Why should neuroscientists worry about iron? The emerging role of ferroptosis in the pathophysiology of neuroprogressive diseases

Ferroptosis is a unique form of programmed death, characterised by cytosolic accumulation of iron, lipid hydroperoxides and their metabolites, and effected by the fatal peroxidation of polyunsaturated fatty acids in the plasma membrane. It is a major driver of cell death in neurodegenerative neurological diseases. Moreover, cascades underpinning ferroptosis could be active drivers of neuropathology in major psychiatric disorders. Oxidative and nitrosative stress can adversely affect mechanisms and proteins governing cellular iron homeostasis, such as the iron regulatory protein/iron response element system, and can ultimately be a source of abnormally high levels of iron and a source of lethal levels of lipid membrane peroxidation. Furthermore, neuroinflammation leads to the upregulation of divalent metal transporter1 on the surface of astrocytes, microglia and neurones, making them highly sensitive to iron overload in the presence of high levels of non-transferrin-bound iron, thereby affording such levels a dominant role in respect of the induction of iron-mediated neuropathology. Mechanisms governing systemic and cellular iron homeostasis, and the related roles of ferritin and mitochondria are detailed, as are mechanisms explaining the negative regulation of ferroptosis by glutathione, glutathione peroxidase 4, the cysteine/glutamate antiporter system, heat shock protein 27 and nuclear factor erythroid 2-related factor 2. The potential role of DJ-1 inactivation in the precipitation of ferroptosis and the assessment of lipid peroxidation are described. Finally, a rational approach to therapy is considered, with a discussion on the roles of coenzyme Q₁₀, iron chelation therapy, in the form of deferiprone, deferoxamine (desferrioxamine) and deferasirox, and N-acetylcysteine.

The Genomic Basis of Noise-induced Hearing Loss: A Literature Review Organized by Cellular Pathways

OBJECTIVE

Using Reactome, a curated Internet database, noise-induced hearing loss studies were aggregated into cellular pathways for organization of the emerging genomic and epigenetic data in the literature.

DATA SOURCES

PubMed and Reactome.org, a relational data base program systematizing biological processes into interactive pathways and subpathways based on ontology, cellular constituents, gene expression, and molecular components.

STUDY SELECTION

Peer-reviewed population and laboratory studies for the previous 15 years relating genomics and noise and hearing loss were identified in PubMed. Criteria included p values <0.05 with correction for multiple genes, a fold change of >1.5, or duplicated studies.

DATA EXTRACTION AND SYNTHESIS

One-hundred fifty-eight unique HGNC identifiers from 77 articles met the selection criteria, and were uploaded into the analysis program at http://reactome.org. These genes participated in a total of 621 cellular interactions in 21 of 23 pathways. Cellular response to stress with its attenuation phase, particularly in response to heat stress, detoxification of ROS, and specific areas of the immune system are predominant pathways identified as significantly 'overrepresented' (p values <0.1e-5 and false discovery rates <0.01).

CONCLUSION

Twenty-one of 23 of the designated pathways in Reactome have significant influence on noise-induced hearing loss, signifying a confluence of molecular pathways in reaction to acoustic trauma; however, cellular response to stress, including heat shock response, and other small areas of immune response were highly overrepresented. Yet-to-be-explored genomics areas include miRNA, lncRNA, copy number variations, RNA sequencing, and human genome-wide association study.

Neuroprotective potential of astroglia

Astroglia are the homoeostatic cells of the central nervous system, which participate in all essential functions of the brain. Astrocytes support neuronal networks by handling water and ion fluxes, transmitter clearance, provision of antioxidants, and metabolic precursors and growth factors. The critical dependence of neurons on constant support from the astrocytes confers astrocytes with intrinsic neuroprotective properties. On the other hand, loss of astrocytic support or their pathological transformation compromises neuronal functionality and viability. Manipulating neuroprotective functions of astrocytes is thus an important strategy to enhance neuronal survival and improve outcomes in disease states. © 2017 The Authors Journal of Neuroscience Research Published by Wiley Periodicals, Inc.

Tryptanthrin Suppresses the Activation of the LPS-Treated BV2 Microglial Cell Line via Nrf2/HO-1 Antioxidant Signaling

Microglia are the resident macrophages in the central nervous system (CNS) and play essential roles in neuronal homeostasis and neuroinflammatory pathologies. Recently, microglia have been shown to contribute decisively to neuropathologic processes after ischemic stroke. Furthermore, natural compounds have been reported to attenuate inflammation and pathologies associated with neuroinflammation. Tryptanthrin (indolo[2,1-b]quinazoline-6,12-dione) is a phytoalkaloid with known anti-inflammatory effects in cells. In present study, the authors confirmed middle cerebral artery occlusion (MCAO) injury triggers the activation of microglia in brain tissue, and investigated whether tryptanthrin influences the function of mouse murine BV2 microglia under LPS-induced inflammatory conditions in vitro. It was found tryptanthrin protected BV2 microglia cells against LPS-induced inflammation and inhibited the induction of M1 phenotype microglia under inflammatory conditions. In addition, tryptanthrin reduced the production of pro-inflammatory cytokines in BV2 microglia cells via nuclear factor erythroid 2-related factor 2 (Nrf2)/heme oxygenase 1 (HO-1) signaling and NF-κB signaling. The authors suggest that tryptanthrin might alleviate the progress of neuropathologies by controlling microglial functions under neuroinflammatory conditions.

Role of miR-182 in response to oxidative stress in the cell fate of human fallopian tube epithelial cells

High grade serous ovarian carcinoma (HGSC) is a DNA instable tumor and its precursor is commonly found originating from the fimbriated end of the fallopian tube secretory epithelial (FTSE) cells. The local stresses via ovulation and related inflammation are risks for HGSC. In this study, we examined the cellular and molecular responses of FTSE cells to stress. We found that excess intracellular reactive oxygen species (ROS) in normal FTSE cells upregulated a subset of microRNA expression (defined as ROSmiRs). Most ROSmiRs' expression and function were influenced and regulated by p53, and together they drove the cells into stress-induced premature senescence (SIPS). However, ROS-induced miR-182 is regulated by β-catenin, not by p53. In normal FTSE cells, miR-182 overexpression triggers cellular senescence by p53-mediated upregulation of p21. Conversely, in cells with p53 mutations, miR-182 overexpression no longer enhances p21 but functions as an “Onco-miR”. p53 dysfunction is a prerequisite for miR-182-mediated tumorigenesis. In addition, we found that human follicular fluid could significantly induce intracellular ROS in normal FTSE cells. These findings suggest that ROS and p53 mutations may trigger a series of events, beginning with overexpressing miR-182 by ROS and β-catenin, impairing the DNA damage response, promoting DNA instability, bypassing senescence and eventually leading to DNA instable tumors in FTSE cells.

Serotonin 1A Receptors on Astrocytes as a Potential Target for the Treatment of Parkinson's Disease

Astrocytes are the most abundant neuron-supporting glial cells in the central nervous system. The neuroprotective role of astrocytes has been demonstrated in various neurological disorders such as amyotrophic lateral sclerosis, spinal cord injury, stroke and Parkinson’s disease (PD). Astrocyte dysfunction or loss-of-astrocytes increases the susceptibility of neurons to cell death, while astrocyte transplantation in animal studies has therapeutic advantage. We reported recently that stimulation of serotonin 1A (5-HT_1A) receptors on astrocytes promoted astrocyte proliferation and upregulated antioxidative molecules to act as a neuroprotectant in parkinsonian mice. PD is a progressive neurodegenerative disease with motor symptoms such as tremor, bradykinesia, rigidity and postural instability, that are based on selective loss of nigrostriatal dopaminergic neurons, and with non-motor symptoms such as orthostatic hypotension and constipation based on peripheral neurodegeneration. Although dopaminergic therapy for managing the motor disability associated with PD is being assessed at present, the main challenge remains the development of neuroprotective or disease-modifying treatments. Therefore, it is desirable to find treatments that can reduce the progression of dopaminergic cell death. In this article, we summarize first the neuroprotective properties of astrocytes targeting certain molecules related to PD. Next, we review neuroprotective effects induced by stimulation of 5-HT_1A receptors on astrocytes. The review discusses new promising therapeutic strategies based on neuroprotection against oxidative stress and prevention of dopaminergic neurodegeneration.

Butein provides neuroprotective and anti-neuroinflammatory effects through Nrf2/ARE-dependent haem oxygenase 1 expression by activating the PI3K/Akt pathway

BACKGROUND AND PURPOSE

Butein, 3,4,2',4'-tetrahydroxychalcone, has various pharmacological effects. However, no study has demonstrated the specific neurobiological mechanisms of the effects of butein in neuronal cells. The present study examined the role of butein as an antioxidative and anti-inflammatory inducer of haem oxygenase 1 (HO1) in mouse hippocampal HT22, BV2 microglial and primary mouse hippocampus neurons.

EXPERIMENTAL APPROACH

We investigated the neuroprotective effects of butein on glutamate-induced HT22 cell and primary mouse hippocampal neuron death and its anti-neuroinflammatory effects on LPS-induced activation of BV2 cells. We elucidated the underlying mechanisms by assessing the involvement of NF-κB, HO1, nuclear factor-E2-related factor 2 (Nrf2) and Akt signalling.

KEY RESULTS

Butein decreased cellular oxidative injury and the production of ROS in glutamate-treated HT22 cells and primary mouse hippocampal neurons. Furthermore, butein suppressed LPS-induced pro-inflammatory enzymes and mediators in BV2 microglia. Butein inhibited IL-6, IL-1β and TNF-α production and mRNA expression. In addition, butein decreased NO and PGE2 production and inducible NOS and COX-2 expression through the NF-κB signalling pathway. Butein up-regulated Nrf2/ARE-mediated HO1 expression through the PI3K/Akt pathway and this was positively associated with its cytoprotective effects and anti-neuroinflammatory actions.

CONCLUSION AND IMPLICATIONS

Our results indicate that butein effectively prevents glutamate-induced oxidative damage and LPS-induced activation and that the induction of HO1 by butein through the PI3K/Akt pathway and Nrf2 activation appears to play a pivotal role in its effects on neuronal cells. Our results provide evidence for the neuroprotective properties of butein.

The herbal extract KCHO-1 exerts a neuroprotective effect by ameliorating oxidative stress via heme oxygenase-1 upregulation

KCHO-1 is a novel product comprised of 30% ethanol extracts obtained from nine medical herbs, which are commonly used in traditional Korean and Chinese medicine. The nine herbs include Curcuma longa, Salvia miltiorrhiza, Gastrodia elata, Chaenomeles sinensis, Polygala tenuifolia, Paeonia japonica, Glycyrrhiza uralensis, Atractylodes japonica and processed Aconitum carmichaeli. Recent studies have reported the beneficial effects of these herbs. The present study aimed to investigate the direct neuroprotective effects of KCHO‑1 on HT22 mouse hippocampal cells, and to determine the possible underlying mechanisms. KCHO‑1 significantly suppressed glutamate‑ and hydrogen peroxide (H2O2)‑induced cell damage, and reactive oxygen species generation. In addition, KCHO‑1 increased the mRNA and protein expression levels of heme oxygenase (HO)‑1. Tin protoporphyrin, which is an inhibitor of HO activity, partially suppressed the effects of KCHO‑1. Furthermore, KCHO‑1 significantly upregulated nuclear factor erythroid‑derived 2‑related factor‑2 (Nrf2) nuclear translocation. Extracellular signal‑regulated kinase (ERK) activation also appeared to be associated with KCHO‑1‑induced HO‑1 expression, since the ERK inhibitor PD98059 suppressed HO‑1 expression and prevented KCHO‑1‑induced cytoprotection. The results of the present study suggested that KCHO‑1 may effectively prevent glutamate‑ or H2O2‑induced oxidative damage via Nrf2/ERK mitogen‑activated protein kinase‑dependent HO‑1 expression. These data suggest that KCHO‑1 may be useful for the treatment of neurodegenerative diseases.

Splicing of Friend Murine Leukemia Virus env-mRNA Enhances Its Ability to Form Polysomes

Friend murine leukemia virus (MLV) belongs to the gamma retroviruses of the Retroviridae family. The positive-sense RNA of its genome contains a 5' long terminal repeat (LTR), 5' leader sequence, gag, pol, env, and 3' LTR. Transcription from proviral DNA begins from the R region of the 5' LTR and ends at the polyadenylation signal located at the R region of the other end of the 3' LTR. There is a 5' splice site in the 5' leader sequence and a 3' splice site at the 3' end of the pol region. Both full-length unspliced mRNAs and a singly spliced mRNA (env-mRNA) are produced in MLV-infected cells. The MLV Env protein plays important roles both in viral adsorption to host cells and in neuropathogenic disease in MLV-infected mice and rats. Understanding the regulatory mechanisms controlling Env expression is important for determining the functions of the Env protein. We have previously shown that splicing increases env-mRNA stability and translation efficiency. Generally, mRNA polysome formation correlates with translation efficiency. Therefore, here we investigated the effects of env-mRNA splicing on polysome formation to identify mechanisms for Env up-regulation due to splicing. We performed polysome profile analyses using Env-expression plasmids producing spliced or unspliced env-mRNA and showed that the former formed polysomes more efficiently than the latter. Thus, splicing of env-mRNA facilitated polysome formation, suggesting that this contributes to up-regulation of Env expression. We replaced the env region of the expression plasmids with a luciferase (luc) gene, and found that in this case both unspliced and spliced luc-mRNA formed polysomes to a similar extent. Thus, we conclude that whether mRNA polysome formation is affected by splicing depends on the structure of gene in question.

Acerogenin A from Acer nikoense Maxim Prevents Oxidative Stress-Induced Neuronal Cell Death through Nrf2-Mediated Heme Oxygenase-1 Expression in Mouse Hippocampal HT22 Cell Line

Oxidative cell damage contributes to neuronal degeneration in many central nervous system (CNS) diseases such as Parkinson's disease, Alzheimer's disease, and ischemia. Inducible heme oxygenase (HO)-1 acts against oxidants that are thought to play a key role in the pathogenesis of neuronal diseases. The stem bark of Acer nikoense Maxim (Aceraceae) is indigenous to Japan; it has been used in folk medicine as a treatment of hepatic disorders and eye diseases. Acerogenin A, a natural compound isolated from Japanese folk medicine A. nikoense, showed neuroprotective effects and reactive oxygen species (ROS) reduction on glutamate-induced neurotoxicity by inducing the expression of HO-1 in mouse hippocampal HT22 cells. Furthermore, acerogenin A caused the nuclear accumulation of nuclear factor-E2-related factor 2 (Nrf2) and the activation of the PI3K/AKT signaling pathways. In this study, we demonstrated that acerogenin A effectively prevents glutamate-induced oxidative damage, and HO-1 induction via PI3K/Akt and Nrf2 pathways appears to play a key role in the protection of HT22 cells. Therefore, this study implies that the Nrf2/HO-1 pathway represents a biological target and that acerogenin A might be a candidate for the prevention of neurodegeneration.

Expression of xCT and activity of system xc(-) are regulated by NRF2 in human breast cancer cells in response to oxidative stress

Cancer cells adapt to high levels of oxidative stress in order to survive and proliferate by activating key transcription factors. One such master regulator, the redox sensitive transcription factor NF E2 Related Factor 2 (NRF2), controls the expression of cellular defense genes including those encoding intracellular redox-balancing proteins involved in glutathione (GSH) synthesis. Under basal conditions, Kelch-like ECH-associated protein 1 (KEAP1) targets NRF2 for ubiquitination. In response to oxidative stress, NRF2 dissociates from KEAP1, entering the nucleus and binding to the antioxidant response element (ARE) in the promoter of its target genes. Elevated reactive oxygen species (ROS) production may deplete GSH levels within cancer cells. System xc(-), an antiporter that exports glutamate while importing cystine to be converted into cysteine for GSH synthesis, is upregulated in cancer cells in response to oxidative stress. Here, we provided evidence that the expression of xCT, the light chain subunit of system xc(-), is regulated by NRF2 in representative human breast cancer cells. Hydrogen peroxide (H2O2) treatment increased nuclear translocation of NRF2, also increasing levels of xCT mRNA and protein and extracellular glutamate release. Overexpression of NRF2 up-regulated the activity of the xCT promoter, which contains a proximal ARE. In contrast, overexpression of KEAP1 repressed promoter activity and decreased xCT protein levels, while siRNA knockdown of KEAP1 up-regulated xCT protein levels and transporter activity. These results demonstrate the importance of the KEAP1/NRF2 pathway in balancing oxidative stress in breast cancer cells through system xc(-). We have previously shown that xCT is upregulated in various cancer cell lines under oxidative stress. In the current investigation, we focused on MCF-7 cells as a model for mechanistic studies.

Lack of effect of Theiler's murine encephalomyelitis virus infection on system xc⁻

Changes in the expression of xCT, the specific subunit of system xc(-) or the cystine/glutamate antiporter, have been associated with several neurological disorders and system xc(-) was recently proposed as a potential target for the development of new treatment strategies for multiple sclerosis (MS). In this study we used Theiler's murine encephalomyelitis virus (TMEV) infection, both in vitro and in vivo, as a model to further evaluate the involvement of system xc(-) in MS. Protein levels of xCT, as well as activity of system xc(-) were unaffected in RAW264.7 macrophages after infection with the demyelinating DA strain of TMEV. Also, protein expression of xCT remained stable in spinal cord and brain of FVB mice 1-2 and 6 weeks after intracranial injection of the DA strain of TMEV. These results demonstrate that TMEV infection of macrophages or FVB mice has no effect on system xc(-) and as such cannot be used as a model to study the involvement of system xc(-) in MS.

p53 as a retrovirus-induced oxidative stress modulator

Infection of astrocytes by the neuropathogenic mutant of Moloney murine leukemia virus, ts1, exhibits increased levels of reactive oxygen species (ROS) and signs of oxidative stress compared with uninfected astrocytes. Previously, we have demonstrated that ts1 infection caused two separate events of ROS upregulation. The first upregulation occurs during early viral establishment in host cells and the second during the virus-mediated apoptotic process. In this study, we show that virus-mediated ROS upregulation activates the protein kinase, ataxia telangiectasia mutated, which in turn phosphorylates serine 15 on p53. This activation of p53 however, is unlikely associated with ts1-induced cell death. Rather p53 appears to be involved in suppressing intracellular ROS levels in astrocytes under oxidative stress. The activated p53 appears to delay retroviral gene expression by suppressing NADPH oxidase, a superoxide-producing enzyme. These results suggest that p53 plays a role as a retrovirus-mediated oxidative stress modulator.

Chitooligosaccharides inhibit ethanol-induced oxidative stress via activation of Nrf2 and reduction of MAPK phosphorylation

Chitooligosaccharides (COS) are hydrolyzed products of chitosan and have been proven to exhibit various biological functions. The aims of this study were to investigate the mechanisms underlying the hepatoprotective effects of COS against ethanol-induced oxidative stress in vitro. Human L02 normal liver cells were pretreated with COS (0.25, 0.5 and 1.0 mg/ml) and then hepatotoxicity was stimulated by the addition of ethanol (80 mM). Pretreatment with COS protected L02 cells from ethanol-induced cell cytotoxicity through inhibition of reactive oxygen species generation. Furthermore, ethanol-induced lipid peroxidation and glutathione depletion was inhibited by COS. The antioxidant potential of COS was correlated with the induction of antioxidant genes including HO-1, NQO1 and SOD via the transcriptional activation of nuclear factor erythroid-2‑related factor-2 (Nrf2). Additionally, the protective effects of COS against ethanol were blocked by Nrf2 knockdown. Moreover, signal transduction studies showed that COS was able to suppress the ethanol-induced phosphorylation of p38 MAPK, JNK and ERK. In conclusion, the COS-mediated activation of Nrf2 and reduction of MAPK phosphorylation may be important for its hepatoprotective action.

MED12 and HMGA2 mutations: two independent genetic events in uterine leiomyoma and leiomyosarcoma

Recent identification of somatic MED12 mutations in most uterine leiomyomas brings a new venue for the study of the tumorigenesis of leiomyomas. We are particularly interested in the correlation of MED12 and HMGA2 gene products in leiomyomas and leiomyosarcomas with and without MED12 mutations. To address these issues, in this study we examined MED12 mutations in a large cohort of usual type leiomyomas (178 cases) and uterine leiomyosarcomas (32 cases). We found that 74.7% (133/178) of leiomyomas had MED12 mutations, which was consistent with several independent studies. In contrast, only 9.7% (3/32) of leiomyosarcomas harbored MED12 mutations. Expression analysis by western blot and immunohistochemistry revealed that those leiomyomas with complex MED12 mutations had significantly lower protein products than the matched myometrium. Interestingly, most leiomyosarcomas without MED12 mutations also had very low levels of MED12 expression in comparison to the matched myometrium. These findings suggest a potential functional role of MED12 in both benign and malignant uterine smooth muscle tumors. When we further examined HMGA2 expression in all leiomyomas and leiomyosarcomas, we found that HMGA2 overexpression was exclusively present in those leiomyomas with no MED12 mutation, accounting for 10.1% (18/178) of total leiomyomas and 40% (18/45) of non-MED12 mutant leiomyomas. Twenty-five percent (8/32) of leiomyosarcomas had HMGA2 overexpression, and no MED12 mutations were found in HMGA2 positive leiomyosarcoma. These findings strongly suggest that MED12 mutations and HMGA2 overexpression are independent genetic events that occur in leiomyomas, and they may act differently in the tumorigenesis of uterine leiomyomas.

Autophagy defends pancreatic β cells from human islet amyloid polypeptide-induced toxicity

Type 2 diabetes (T2D) is characterized by a deficiency in β cell mass, increased β cell apoptosis, and extracellular accumulation of islet amyloid derived from islet amyloid polypeptide (IAPP), which β cells coexpress with insulin. IAPP expression is increased in the context of insulin resistance, the major risk factor for developing T2D. Human IAPP is potentially toxic, especially as membrane-permeant oligomers, which have been observed to accumulate within β cells of patients with T2D and rodents expressing human IAPP. Here, we determined that β cell IAPP content is regulated by autophagy through p62-dependent lysosomal degradation. Induction of high levels of human IAPP in mouse β cells resulted in accumulation of this amyloidogenic protein as relatively inert fibrils within cytosolic p62-positive inclusions, which temporarily averts formation of toxic oligomers. Mice hemizygous for transgenic expression of human IAPP did not develop diabetes; however, loss of β cell-specific autophagy in these animals induced diabetes, which was attributable to accumulation of toxic human IAPP oligomers and loss of β cell mass. In human IAPP-expressing mice that lack β cell autophagy, increased oxidative damage and loss of an antioxidant-protective pathway appeared to contribute to increased β cell apoptosis. These findings indicate that autophagy/lysosomal degradation defends β cells against proteotoxicity induced by oligomerization-prone human IAPP.

Unfolded protein response in hepatitis C virus infection

Hepatitis C virus (HCV) is a single-stranded, positive-sense RNA virus of clinical importance. The virus establishes a chronic infection and can progress from chronic hepatitis, steatosis to fibrosis, cirrhosis, and hepatocellular carcinoma (HCC). The mechanisms of viral persistence and pathogenesis are poorly understood. Recently the unfolded protein response (UPR), a cellular homeostatic response to endoplasmic reticulum (ER) stress, has emerged to be a major contributing factor in many human diseases. It is also evident that viruses interact with the host UPR in many different ways and the outcome could be pro-viral, anti-viral or pathogenic, depending on the particular type of infection. Here we present evidence for the elicitation of chronic ER stress in HCV infection. We analyze the UPR signaling pathways involved in HCV infection, the various levels of UPR regulation by different viral proteins and finally, we propose several mechanisms by which the virus provokes the UPR.

Kinetic studies of the effect of a 17-nucleotide difference in the 0.3-kb region containing the R-U5-5' leader sequence of Friend murine leukemia virus on viral gene expression

In addition to the env gene, a 0.3-kb fragment containing the R-U5-5' leader sequence is essential for the induction of spongiform neurodegeneration by Friend murine leukemia virus (Fr-MLV) clone A8 and it also influences expression of the Env protein. Kinetic studies were carried out using two recombinant viruses, R7f, carrying the A8 0.3-kb fragment, and Rec5, carrying the 0.3-kb fragment of the non-neuropathogenic Fr-MLV clone 57. These analyses suggested that the 0.3-kb fragment influenced the expression level of the Env protein by regulating the amount of spliced env-mRNA rather than the amount of total viral mRNA or viral production.

Decursin Isolated from Angelica gigas Nakai Rescues PC12 Cells from Amyloid β-Protein-Induced Neurotoxicity through Nrf2-Mediated Upregulation of Heme Oxygenase-1: Potential Roles of MAPK

Decursin (D), purified from Angelica gigas Nakai, has been proven to exert neuroprotective property. Previous study revealed that D reduced A β 25 ‒ 35-induced cytotoxicity in PC12 cells. Our study explored the underlying mechanisms by which D mediates its therapeutic effects in vitro. Pretreatment of cells with D diminished intracellular generation of ROS in response to A β 25 ‒ 35. Western blot revealed that D significantly increased the expression and activity of HO-1, which was correlated with its protection against A β 25 ‒ 35-induced injury. Addition of ZnPP, an HO-1 competitive inhibitor, significantly attenuated its protective effect in A β 25 ‒ 35-treated cells, indicating the vital role of HO-1 resistance to oxidative injury. Moreover, D induced Nrf2 nuclear translocation, the upstream of HO-1 expression. While investigating the signaling pathways responsible for HO-1 induction, D activated ERK and dephosphorylated p38 in PC12 cells. Addition of U0126, a selective inhibitor of ERK, blocked D-induced Nrf2 activation and HO-1 induction and meanwhile reversed the protection of D against A β 25 ‒ 35-induced cell death. These findings suggest D augments cellular antioxidant defense capacity through both intrinsic free radical scavenging activity and activation of MAPK signal pathways that leads to Nrf2 activation, and subsequently HO-1 induction, thereby protecting the PC12 cells from A β 25 ‒ 35-induced oxidative cytotoxicity.

Tight junction proteins and oxidative stress in heavy metals-induced nephrotoxicity

Kidney is a target organ for heavy metals. They accumulate in several segments of the nephron and cause profound alterations in morphology and function. Acute intoxication frequently causes acute renal failure. The effects of chronic exposure have not been fully disclosed. In recent years increasing awareness of the consequences of their presence in the kidney has evolved. In this review we focus on the alterations induced by heavy metals on the intercellular junctions of the kidney. We describe that in addition to the proximal tubule, which has been recognized as the main site of accumulation and injury, other segments of the nephron, such as glomeruli, vessels, and distal nephron, show also deleterious effects. We also emphasize the participation of oxidative stress as a relevant component of the renal damage induced by heavy metals and the beneficial effect that some antioxidant drugs, such as vitamin A (all-trans-retinoic acid) and vitamin E (α-tocopherol), depict on the morphological and functional alterations induced by heavy metals.

System xc⁻ cystine/glutamate antiporter: an update on molecular pharmacology and roles within the CNS

System x(c)(-) is an amino acid antiporter that typically mediates the exchange of extracellular l-cystine and intracellular L-glutamate across the cellular plasma membrane. Studied in a variety of cell types, the import of L-cystine through this transporter is critical to glutathione production and oxidative protection. The exchange-mediated export of L-glutamate takes on added significance within the CNS, as it represents a non-vesicular route of release through which this excitatory neurotransmitter can participate in either neuronal signalling or excitotoxic pathology. When both the import of L-cystine and the export of L-glutamate are taken into consideration, system x(c)(-) has now been linked to a wide range of CNS functions, including oxidative protection, the operation of the blood-brain barrier, neurotransmitter release, synaptic organization, viral pathology, drug addiction, chemosensitivity and chemoresistance, and brain tumour growth. The ability to selectively manipulate system x(c)(-), delineate its function, probe its structure and evaluate it as a therapeutic target is closely linked to understanding its pharmacology and the subsequent development of selective inhibitors and substrates. Towards that goal, this review will examine the current status of our understanding of system x(c)(-) pharmacology and the structure-activity relationships that have guided the development of an initial pharmacophore model, including the presence of lipophilic domains adjacent to the substrate binding site. A special emphasis is placed on the roles of system x(c)(-) within the CNS, as it is these actions that are among the most exciting as potential long-range therapeutic targets.

Inhibition of nuclear factor erythroid 2-related factor 2 exacerbates HIV-1 gp120-induced oxidative and inflammatory response: role in HIV associated neurocognitive disorder

The HIV epidemic continues to be the most severe public health problem and concern within USA and across the globe. In spite of the highly active antiretroviral therapy, HIV infected subjects experience major neurological complications that range from HIV associated dementia to moderate neurocognitive and motor impairments collectively termed as HIV associated neurocognitive disorders (HAND). Astrocytes play an important role in the neuropathogenesis of HAND. Further, in the recent years it has been shown that oxidative stress plays a major role in the neuropathogenesis of HAND. Nuclear factor erythroid 2-related factor 2 (Nrf2), a leucine zipper redox-sensitive transcription factor, is an important regulator of cell survival and adaptive mechanisms and has been shown to possess a protective role in a variety of neurological and inflammatory disorders. Earlier we have shown that Nrf2 is upregulated in response to HIV-1 gp120 and such upregulation of Nrf2 may be a protective mechanism against the HIV-induced oxidative stress. We hypothesize that Nrf2-mediated antioxidant pathways are important in regulating the HIV-induced oxidative stress and that the disruption of Nrf2 makes the cells more susceptible to HIV gp120-induced deleterious effects. Our results indicate that when astrocytes are exposed to gp120 there is an increase in the expression of NOX2, a subunit of NADPH oxidase, and also an upregulated expression of nuclear factor kappa B, tumor necrosis factor-α (TNF-α) and matrix metalloproteinase-9 (MMP-9). However, the degree of expression was significantly higher in those cells where Nrf2 was silenced by siRNA. Taken together, these results suggest a possible protective role of Nrf2 in regulating the levels of pro-oxidative and pro-inflammatory molecules in HAND.

Involvement of Heme Oxygenase-1 Induction in the Cytoprotective and Immunomodulatory Activities of Viola patrinii in Murine Hippocampal and Microglia Cells

A number of diseases that lead to injury of the central nervous system are caused by oxidative stress and inflammation in the brain. In this study, NNMBS275, consisting of the ethanol extract of Viola patrinii, showed potent antioxidative and anti-inflammatory activity in murine hippocampal HT22 cells and BV2 microglia. NNMBS275 increased cellular resistance to oxidative injury caused by glutamate-induced neurotoxicity and reactive oxygen species generation in HT22 cells. In addition, the anti-inflammatory effects of NNMBS275 were demonstrated by the suppression of proinflammatory mediators, including proinflammatory enzymes (inducible nitric oxide synthase and cyclooxygenase-2) and cytokines (tumor necrosis factor-α and interleukin-1β). Furthermore, we found that the neuroprotective and anti-inflammatory effects of NNMBS275 were linked to the upregulation of nuclear transcription factor-E2-related factor 2-dependent expression of heme oxygenase-1 in HT22 and BV2 cells. These results suggest that NNMBS275 possesses therapeutic potential against neurodegenerative diseases that are induced by oxidative stress and neuroinflammation.

Activation of AMP-activated protein kinase in cerebella of Atm-/- mice is attributable to accumulation of reactive oxygen species

Ataxia telangiectasia (A-T) is an inherited disease, the most prominent feature of which is ataxia caused by degeneration of cerebellar neurons and synapses. The mechanisms underlying A-T neurodegeneration are still unclear, and many factors are likely to be involved. AMP-activated protein kinase (AMPK) is a sensor of energy balance, and research on its function in neural cells has gained momentum in the last decade. The dual roles of AMPK in neuroprotection and neurodegeneration are complex, and they need to be identified and characterized. Using an Atm (ataxia telangiectasia mutated) gene deficient mouse model, we showed here that: (a) upregulation of AMPK phosphorylation and elevation of reactive oxygen species (ROS) coordinately occur in the cerebella of Atm-/- mice; (b) hydrogen peroxide induces AMPK phosphorylation in primary mouse cerebellar astrocytes in an Atm-independent manner; (c) administration of the novel antioxidant monosodium luminol (MSL) to Atm-/- mice attenuates the upregulation of both phosphorylated-AMPK (p-AMPK) and ROS, and corrects the neuromotor deficits in these animals. Together, our results suggest that oxidative activation of AMPK in the cerebellum may contribute to the neurodegeneration in Atm-/- mice, and that ROS and AMPK signaling pathways are promising therapeutic targets for treatment of A-T and other neurodegenerative diseases.

Narrowing down the critical region within env gene for determining neuropathogenicity of murine leukemia virus A8

Friend murine leukemia virus clone A8 causes spongiform neurodegeneration in the rat brain, and the env gene of A8 is a primary determinant of neuropathogenicity. In order to narrow down the critical region within the env gene that determines neuropathogenicity, we constructed chimeric viruses having chimeric env between A8 and non-neuropathogenic 57 on the background of A8 virus. After replacement of the BamHI (at nucleotide 5715)-AgeI (at nucleotide 6322) fragment of A8 virus with the corresponding fragment of 57, neuropathogenicity was lost. In contrast, the chimeric viruses that have the BamHI (5715)-AgeI (6322) fragment of A8 induced spongiosis in 100% of infected rats at the same or slightly lower intensity than A8 virus. These results indicate that the BamHI (5715)-AgeI (6322) fragment of A8, which contains the signal sequence and the N-terminal half of RBD, is crucial for the induction of spongiform neurodegeneration. In the BamHI (5715)-AgeI (6322) fragment, seven amino acids differed between A8 and 57, one in the signal sequence and six in RBD, which suggests that these amino acids significantly contribute to the neuropathogenicity of A8.

Multiple stress signals activate mutant p53 in vivo

p53 levels are tightly regulated in normal cells, and thus, the wild-type p53 protein is nearly undetectable until stimulated through a variety of stresses. In response to stress, p53 is released from its negative regulators, mainly murine double minute 2 (Mdm2), allowing p53 to be stabilized to activate cell-cycle arrest, senescence, and apoptosis programs. Many of the upstream signals that regulate wild-type p53 are known; however, limited information for the regulation of mutant p53 exists. Previously, we showed that wild-type and mutant p53R172H are regulated in a similar manner in the absence of Mdm2 or p16. In addition, this stabilization of mutant p53 is responsible for the gain-of-function metastatic phenotype observed in the mouse. In this report, we examined the role of oncogenes, DNA damage, and reactive oxygen species, signals that stabilize wild-type p53, on the stabilization of mutant p53 in vivo and the consequences of this expression on tumor formation and survival. These factors stabilized mutant p53 protein which oftentimes contributed to exacerbated tumor phenotypes. These findings, coupled with the fact that patients carry p53 mutations without stabilization of p53, suggest that personalized therapeutic schemes may be needed for individual patients depending on their p53 status.

The novel Nrf2-interacting factor KAP1 regulates susceptibility to oxidative stress by promoting the Nrf2-mediated cytoprotective response

The transcription factor Nrf2 (nuclear factor-erythroid 2-related factor 2) co-ordinately regulates ARE (antioxidant-response element)-mediated induction of cytoprotective genes in response to electrophiles and oxidative stress; however, the molecular mechanism controlling Nrf2-dependent gene expression is not fully understood. To identify factors that regulate Nrf2-dependent transcription, we searched for proteins that interact with the Nrf2-NT (N-terminal Nrf2 transactivation domain) by affinity purification from HeLa nuclear extracts. In the present study, we identified KAP1 [KRAB (Krüppel-associated box)-associated protein 1] as a novel Nrf2-NT-interacting protein. Pull-down analysis confirmed the interaction between KAP1 and Nrf2 in cultured cells and demonstrated that the N-terminal region of KAP1 binds to Nrf2-NT in vitro. Reporter assays showed that KAP1 facilitates Nrf2 transactivation activity in a dose-dependent manner. Furthermore, the induction of the Nrf2-dependent expression of HO-1 (haem oxygenase-1) and NQO1 [NAD(P)H quinone oxidoreductase 1] by DEM (diethyl maleate) was attenuated by KAP1 knockdown in NIH 3T3 fibroblasts. This finding established that KAP1 acts as a positive regulator of Nrf2. Although Nrf2 nuclear accumulation was unaffected by KAP1 knockdown, the ability of Nrf2 to bind to the regulatory region of HO-1 and NQO1 was reduced. Moreover, KAP1 knockdown enhanced the sensitivity of NIH 3T3 cells to tert-butylhydroquinone, H2O2 and diamide. These results support our contention that KAP1 participates in the oxidative stress response by maximizing Nrf2-dependent transcription.

HIV-1 gp120 induces antioxidant response element-mediated expression in primary astrocytes: role in HIV associated neurocognitive disorder

HIV infection affects the central nervous system resulting in HIV associated neurocognitive disorder (HAND), which is characterized by depression, behavioral and motor dysfunctions. The HIV-1 viral envelope protein gp120 is known to induce the release of neurotoxic factors which lead to apoptotic cell death. Although the exact mechanisms involved in HIV-1 gp120-induced neurotoxicity are not completely understood, oxidative stress is suggested to play a vital role in the neuropathogenesis of HAND. Astrocytes represent major population of the non-neuronal cell type in the brain and play a critical role in the neuropathogenesis of HAND. Increased oxidative stress is known to induce nuclear factor erythroid derived 2-related factor 2 (Nrf2), a basic leucine zipper transcription factor which is known to regulate the antioxidant defensive mechanism. However, the role of Nrf2 in HAND has not been elucidated. We report that gp120 significantly upregulates Nrf2 in human astrocytes and is associated with stimulation of key antioxidant defensive enzymes Hemoxygenase (HO-1) and NAD(P)H dehydrogenase quinone1 (Nqo1). Pretreatment of the astrocytes with antioxidants or a specific calcium chelator BAPTA-AM, significantly blocked the upregulation of Nrf2, HO-1 and Nqo1. These results suggest a possible role of the intracellular calcium and oxidative stress in Nrf2 mediated antioxidant defense mechanism, which may have protective role in promoting cell survival.

Effects of excessive selenium supplementation to diet contaminated with deoxynivalenol on blood phagocytic activity and antioxidative status of broilers

This study examined the effects of excessive dietary supplementation with organic selenium on phagocytic activity and antioxidative status of chickens for fattening fed diet contaminated with deoxynivalenol (DON). Sixty chickens of Ross 308 hybrids were at day of hatching divided into four groups with 15 birds in each. The background DON dietary levels in both negative and positive control groups were 0.2 mg/kg. The complete feed for positive control group was supplemented with Se dose 1 mg/kg in the form of Se-yeast. Group 3 was fed diet with DON level 3 mg/kg while diet for group 4 combined DON level 3 mg/kg with a excessive supplement of Se-yeast (Se dose 1 mg/kg). After 6 weeks of dietary intake, six randomly-chosen chickens from each group were sampled. Feeding of contaminated diet resulted in significantly reduced blood phagocytic activity (19.5 ± 1.1% in the negative control vs. 12.8 ± 0.8% in the DON-treated group, p < 0.05). Se-yeast supplemented to the DON contaminated diet prevented suppression of phagocytic activity. Dietary intake of DON at levels 3 mg/kg did not influence the plasma α-tocopherol level while excessive dietary Se dose reduced it in both Se supplemented groups. Neither the birds of DON-treated group nor the birds from group 4 with DON and Se-yeast showed any response in plasma γ-glutamyltransferase (GGT) activity. Subtoxic dietary level of DON significantly increased the activity of glutathione peroxidase (GPx) in the duodenal mucosa, while additional Se supplementation prevented such a response to mycotoxin. On the other hand, both Se supplemented groups showed significantly elevated GPx activities in blood, liver and kidney, (p < 0.05). The results suggest a potential ability of excessive supplementation of organic selenium to prevent the blood phagocytic activity suppression and changes in GPx activity in duodenal tissue induced in broilers by subtoxic dietary levels of DON.

Regulation of the system x(C)- cystine/glutamate exchanger by intracellular glutathione levels in rat astrocyte primary cultures

The system x(C)- (Sx(C)-) transporter functions to mediate the exchange of extracellular cystine (L-Cys(2)) and intracellular glutamate (L-Glu). Internalized L-Cys(2) serves as a rate-limiting precursor for the biosynthesis of glutathione (GSH), while the externalized L-Glu can contribute to either excitatory signaling or excitotoxicity. In the present study the influence of culture conditions (with and without dibutyryl-cAMP) and GSH levels on the expression of Sx(C)- were investigated in primary rat astrocyte cultures. Sx(C)- activity in dbcAMP-treated cells was nearly sevenfold greater than in untreated astrocytes and increased further (∼threefold) following the depletion of intracellular GSH with buthionine sulfoximine. This increase in Sx(C)- triggered by GSH depletion was only observed in the dbcAMP-treated phenotype and was distinct from the Nrf2-mediated response initiated by exposure to electrophiles. Changes in Sx(C)- activity correlated with increases in both protein and mRNA levels of the xCT subunit of the Sx(C)- heterodimer, an increase in the V(max) for L-Glu uptake and was linked temporally to GSH levels. This induction of Sx(C)- was not mimicked by hydrogen peroxide nor attenuated by nonspecific antioxidants but was partially prevented by the co-administration of the cell-permeant thiols GSH-ethyl ester and N-acetylcysteine. These findings demonstrate that the expression of Sx(C)- on astrocytes is dynamically regulated by intracellular GSH levels in a cell- and phenotype-dependent manner. The presence of this pathway likely reflects the inherent vulnerability of the CNS to oxidative damage and raises interesting questions as to the functional consequences of changes in Sx(C)- activity in CNS injury and disease.

Phenylbutyric acid suppresses protein accumulation-mediated ER stress in retrovirus-infected astrocytes and delays onset of paralysis in infected mice

Many neurodegenerative diseases are associated with accumulation of misfolded proteins in cells of the central nervous system (CNS). We have previously reported that accumulation of the precursor envelope protein gPr80(env) of ts1, a mutant of Moloney murine leukemia virus (MoMuLV), in the endoplasmic reticulum (ER) of infected astrocytes, results in ER stress, oxidative stress and cell death, subsequently leading to ts1-mediated neurodegeneration in infected mice. In the present study, we assessed whether treatments that reduce the accumulation of gPr80(env) in the ER of ts1-infected astrocytes provided a protective effect against ER stress and cell death. We show that treatment with phenylbutyric acid (PBA) can prevent the unfolded protein response (UPR), ER stress and cell death in cultured ts1-infected astrocytes. The protective effect of PBA is associated with its ability to reduce gPr80(env) accumulation and to increase the expression of proteins involved in protein folding in the ER, such as protein disulfide isomerase (PDI) and ERp44, rather than by decrease mRNA levels of gPr80(env) or alter the proteasomal degradation process for gPr80(env). In infected mice treated with PBA we also noted a reduction in the severity of the neuropathology in brainstem tissues and a delayed onset of paralysis. These results show that PBA is a potentially effective drug for the treatment of neurodegeneration caused by protein accumulation in cells of the CNS.

System x(c)- and thioredoxin reductase 1 cooperatively rescue glutathione deficiency

GSH is the major antioxidant and detoxifier of xenobiotics in mammalian cells. A strong decrease of intracellular GSH has been frequently linked to pathological conditions like ischemia/reperfusion injury and degenerative diseases including diabetes, atherosclerosis, and neurodegeneration. Although GSH is essential for survival, the deleterious effects of GSH deficiency can often be compensated by thiol-containing antioxidants. Using three genetically defined cellular systems, we show here that forced expression of xCT, the substrate-specific subunit of the cystine/glutamate antiporter, in gamma-glutamylcysteine synthetase knock-out cells rescues GSH deficiency by increasing cellular cystine uptake, leading to augmented intracellular and surprisingly high extracellular cysteine levels. Moreover, we provide evidence that under GSH deprivation, the cytosolic thioredoxin/thioredoxin reductase system plays an essential role for the cells to deal with the excess amount of intracellular cystine. Our studies provide first evidence that GSH deficiency can be rescued by an intrinsic genetic mechanism to be considered when designing therapeutic rationales targeting specific redox enzymes to combat diseases linked to GSH deprivation.

Methylmercury induces acute oxidative stress, altering Nrf2 protein level in primary microglial cells

The neurotoxicity of methylmercury (MeHg) is well documented in both humans and animals. MeHg causes acute and chronic damage to multiple organs, most profoundly the central nervous system (CNS). Microglial cells are derived from macrophage cell lineage, making up approximately 12% of cells in the CNS, yet their role in MeHg-induced neurotoxicity is not well defined. The purpose of the present study was to characterize microglial vulnerability to MeHg and their potential adaptive response to acute MeHg exposure. We examined the effects of MeHg on microglial viability, reactive oxygen species (ROS) generation, glutathione (GSH) level, redox homeostasis, and Nrf2 protein expression. Our data showed that MeHg (1-5 microM) treatment caused a rapid (within 1 min) concentration- and time-dependent increase in ROS generation, accompanied by a statistically significant decrease in the ratio of GSH and its oxidized form glutathione disulfide (GSSG) (GSH:GSSG ratio). MeHg increased the cytosolic Nrf2 protein level within 1 min of exposure, followed by its nuclear translocation after 10 min of treatment. Consistent with the nuclear translocation of Nrf2, quantitative real-time PCR revealed a concentration-dependent increase in the messenger RNA level of Ho-1, Nqo1, and xCT 30 min post MeHg exposure, whereas Nrf2 knockdown greatly reduced the upregulation of these genes. Furthermore, we observed increased microglial death upon Nrf2 knockdown by the small hairpin RNA approach. Taken together, our study has demonstrated that microglial cells are exquisitely sensitive to MeHg and respond rapidly to MeHg by upregulating the Nrf2-mediated antioxidant response.

Neuroprotective effects of the drug GVT (monosodium luminol) are mediated by the stabilization of Nrf2 in astrocytes

Oxidative stress is implicated in various kinds of neurological disorders, including human immunodeficiency virus (HIV) associated dementia (HAD). Our laboratory has been studying the murine retrovirus ts1, a pathogenic mutant of the Moloney murine leukemia virus (MoMuLV), as a model for HAD. Like HIV in humans, ts1 induces oxidative stress and progressive neurodegeneration in mice. We have shown previously that an antioxidant and anti-inflammatory drug GVT or MSL (monosodium luminol) suppresses ts1-induced oxidative stress, attenuates the development of spongiform encephalopathy, and delays hind limb paralysis in infected mice. It is known that upregulation of the nuclear transcription factor NF-E2-related factor 2 (Nrf2) is involved in upregulating cellular antioxidant defenses. Since Nrf2 is associated with elevation of antioxidant defenses in general, and since GVT suppresses ts1-induced neurodegeneration, our aim in this study was to determine whether GVT neuroprotection is linked to Nrf2 upregulation in the brain. We report here that GVT upregulates the levels of Nrf2, both in primary astrocyte cultures and in brainstem of ts1-infected mice. Significant upregulation of Nrf2 expression by GVT occurs in both the cytosolic and nuclear fractions of cultured astrocytes and brainstem cells. Notably, although GVT treatment increases Nrf2 protein levels in cultured astrocytes and brainstem tissues, Nrf2 mRNA levels are not altered. This suggests that the neuroprotective effects of GVT may be mediated by the stabilization of the Nrf2 protein, allowing continuous upregulation of Nrf2 levels in the astrocytes.

alpha-Luminol prevents decreases in glutamate, glutathione, and glutamine synthetase in the retinas of glaucomatous DBA/2J mice

OBJECTIVE

To test the hypothesis that in DBA/2J mice, oxidative stress decreases glutamine synthetase (GS) levels resulting in a loss of neuronal glutamate and that the antioxidant alpha-luminol (GVT) decreases this stress and glutamate loss in some types of glaucoma.

ANIMALS

DBA/2J mice were separated into two groups, of which one was not treated, and the other treated with GVT in the drinking water. At 7 months of age, retinas were examined from five untreated DBA/2J mice, seven GVT-treated mice, and five C57BL/6 mice (negative controls).

METHODS

Serial 0.5 microm plastic sections were immunogold stained for glutamate, GS, and total glutathione, followed by image analysis for staining patterns and density.

RESULTS

Focal decreases in glutamate immunostaining were common in the inner nuclear layer (INL) of DBA/2J retinas, but not in C57BL/6 or GVT-treated DBA/2J retinas. Decreases in glutathione and GS immunostaining were found in DBA/2J retinal regions where neuronal glutamate immunostaining was reduced. Retinas from GVT-treated DBA/2J had no significant decreases in INL levels of glutamate, glutathione, or GS.

CONCLUSIONS

Retinas of dogs with primary glaucoma are reported to have focal depletion of neuronal glutamate. In DBA/2J mice, similar changes occur prior to the development of clinical disease. In these focal glutamate-depleted regions, levels of glutathione and GS are also reduced, consistent with the hypothesis that oxidative stress contributes to retinal changes in glaucoma. The ability of GVT, an antioxidant, to inhibit retinal abnormalities in DBA/2J mice provides further support for this hypothesis.

Activation of transcription factor Nrf2 by hepatitis C virus induces the cell-survival pathway

Oxidative stress has been implicated in various human diseases, including the pathogenesis of hepatitis C virus (HCV). Previous studies have shown the induction of oxidative stress in cultured cells expressing HCV genes. The transcription factor Nrf2 is known to be activated in response to oxidative stress, but the mechanism of its activation is not clearly understood. In this study, we first determined the induction of Nrf2 and then investigated the mechanism of Nrf2 activation in human hepatoma cells infected with HCV (JFH-1). Our results showed the induction and nuclear translocation of Nrf2 in a time-dependent manner. The HCV-mediated activation of Nrf2 was abrogated in the presence of an antioxidant, PDTC (pyrrolidine dithiocarbamate), and a Ca(2+) chelator, BAPTA-AM [1,2-bis(aminophenoxy)ethane N,N,N,N-tetraacetic acid tetra(acetoxymethyl) ester], which suggests a role for both reactive oxygen species and Ca(2+) signalling in the Nrf2-activation process. By using inhibitors of cellular kinases, we showed further that HCV-mediated phosphorylation/activation of Nrf2 is mediated by the mitogen-activated protein (MAP) kinases p38 MAPK and janus kinase. We also observed enhanced phosphorylation of Akt and its downstream substrate Bad in HCV-infected cells. Furthermore, by using a small interfering RNA approach, our results suggest a potential role for HCV-mediated Nrf2 activation in the survival of HCV-infected cells, a condition favourable for liver oncogenesis. Taken together, these results provide an insight into the mechanisms by which HCV induces intracellular events relevant to chronic HCV infection.

Attenuation of oxidative stress, inflammation and apoptosis by minocycline prevents retrovirus-induced neurodegeneration in mice

The ts1 mutant of the Moloney murine leukemia virus (MoMuLV) causes neurodegeneration in infected mice that resembles HIV-associated dementia. We have shown previously that ts1 infects glial cells in the brain, but not neurons. The most likely mechanism for ts1-mediated neurodegeneration is loss of glial redox support and glial cell toxicity to neurons. Minocycline has been shown to have neuroprotective effects in various models of neurodegeneration. This study was designed to determine whether and how minocycline prevents paralysis and death in ts1-infected mice. We show here that minocycline delays neurodegeneration in ts1-infected mice, and that it prevents death of cultured astrocytes infected by ts1 through attenuating oxidative stress, inflammation and apoptosis. Although minocycline reduces virus titers in the CNS of infected mice, it does not affect virus titers in infected mice thymi, spleens or infected C1 astrocytes. In addition, minocycline prevents death of primary neurons when they are cocultured with ts1-infected astrocytes, through mechanisms involving both inhibition of oxidative stress and upregulation of the transcription factor NF-E2-related factor 2 (Nrf2), which controls cellular antioxidant defenses. We conclude that minocycline delays retrovirus ts1-induced neurodegeneration involving antioxidant, anti-inflammation and anti-apoptotic mechanisms.

The degree of folding instability of the envelope protein of a neurovirulent murine retrovirus correlates with the severity of the neurological disease

A small group of ecotropic murine retroviruses cause a spongiform neurodegenerative disease manifested by tremor, paralysis, and wasting. The neurovirulence of these viruses has long been known to be determined by the sequence of the viral envelope protein, although the nature of the neurotoxicity remains to be clarified. Studies on the neurovirulent viruses FrCas(NC) and Moloney murine leukemia virus ts1 indicate that the nascent envelope protein misfolds, is retained in the endoplasmic reticulum (ER), and induces an unfolded protein response. In the present study we constructed a series of viruses with chimeric envelope genes containing segments from virulent and avirulent retroviruses. Each of the viruses studied was highly neuroinvasive but differed in the severity of the neurological disease they induced. Only viruses that contained the receptor-binding domain (RBD) of the neurovirulent virus induced neurological disease. Likewise, only viruses containing the RBD of the neurovirulent virus exhibited increased binding of the ER chaperone BiP to the envelope precursor protein and induced the unfolded protein response. Thus, the RBD determined both neurovirulence and folding instability. Among viruses carrying the neurovirulent RBD, the severity of the disease was increased when envelope sequences from the neurovirulent virus outside the RBD were also present. Interestingly, these sequences appeared to further increase the degree of folding instability (BiP binding) of the viral envelope protein. These results provide strong support for the hypothesis that this spongiform neurodegenerative disease represents a virus-induced protein folding disorder.