The Nrf2-antioxidant response element signaling pathway and its activation by oxidative stress

ROS-mediated lipid peroxidation and RES-activated signaling

Nonenzymatic lipid oxidation is usually viewed as deleterious. But if this is the case, then why does it occur so frequently in cells? Here we review the mechanisms of membrane peroxidation and examine the genesis of reactive electrophile species (RES). Recent evidence suggests that during stress, both lipid peroxidation and RES generation can benefit cells. New results from genetic approaches support a model in which entire membranes can act as supramolecular sinks for singlet oxygen, the predominant reactive oxygen species (ROS) in plastids. RES reprogram gene expression through a class II TGA transcription factor module as well as other, unknown signaling pathways. We propose a framework to explain how RES signaling promotes cell "REScue" by stimulating the expression of genes encoding detoxification functions, cell cycle regulators, and chaperones. The majority of the known biological activities of oxygenated lipids (oxylipins) in plants are mediated either by jasmonate perception or through RES signaling networks.

Ginsenoside Rg1 reduces toxicity of PM(2.5) on human umbilical vein endothelial cells by upregulating intracellular antioxidative state

Ambient airborne particulate matter (PM) is an important environmental pollutant responsible for many human diseases. Oxidative stress is suggested to be involved in PM-induced cell injury. The present study is designed to study unsalutary effects of the organic extracts of PM with an aerodynamic diameter of less than 2.5μm (PM(2.5)) and protective effect of Ginsenoside Rg1 (Rg1) against PM(2.5) on human umbilical vein endothelial cells (HUVECs) in vitro. Cytotoxic effects of the organic extract PM(2.5) on HUVECs were measured by means of HUVEC cell viability and the generation of intracellular reactive oxygen species (ROS). Expression of heme oxygenase-1(HO-1) and Nuclear factor-erythroid 2-related factor 2 (Nrf2) and Nrf2 cytoplasm-nucleus location were assayed. The present results showed that PM(2.5) (50-800μg/ml) decreased HUVEC viability and increased intracellular generation of ROS and malondialdehyde (MDA) in a concentration dependent manner, but increased HO-1 expression without concentration dependence. Rg1 (10 and 40μg/ml) diminished PM(2.5)-induced HUVEC viability, decrease ROS and MDA generation, increased HO-1 and Nrf2 expression and promoted Nrf2 translocation to nucleus in a concentration dependent manner. These results suggested that organic extracts of PM(2.5) increase oxidative stress and decrease cell viability; Rg1 antagonize PM(2.5)-induced excess oxidative stress; HO-1 expression increase and Nrf2 translocation to nucleus may be involved in the effects of both PM(2.5) and Rg1 on HUVECs.

Nrf2-Keap1 antioxidant defense and cell survival signaling are upregulated by 17β-estradiol in homocysteine-treated dopaminergic SH-SY5Y cells

BACKGROUND AND AIMS

A recent neuroimaging study discovered the neurotoxicity effects of homocysteine (Hcy), which is only seen in elderly women. Estrogens exert a variety of actions on brain function that influence cognitive function, mood, and neuroprotection. The Kelch-like ECH-associated protein 1 (Keap1)/nuclear factor erythroid 2-related factor 2 (Nrf2) antioxidant defense pathway has been well-known to afford neuroprotection. Here, we first demonstrate the roles of Nrf2-Keap1 in 17β-estradiol (E2) cytoprotection and Hcy toxicity and the protective mechanisms of E2 on Hcy cytotoxicity in human dopaminergic SH-SY5Y cells.

METHODS

Cell viability was determined by trypan blue method. Protein expression was determined by Western blot analysis. Superoxide dismutase (SOD) activity was determined by ELISA. Reactive oxygen species (ROS) production was determined by flow cytometry.

RESULTS

In Hcy-treated SH-SY5Y cells, E2 increased cell viability, attenuated ROS production, activated Akt signaling and inhibited glycogen synthase kinase-3β (GSK-3β), a kinase known to participate in neurodegeneration. Moreover, E2 treatment led to Nrf2 dissociation from Keap1, the main negative regulator of Nrf2 activity in the cytoplasm, and increased the protein level of Nrf2 in the nucleus, with a significant increase in HO-1 expression and SOD activity in Hcy-treated cells. E2-induced Nrf2 activation was attenuated by the PI3K inhibitor LY294002 and the estrogen receptor antagonist ICI 182,780. Further, E2 decreased Hcy-induced apoptotic death by upregulating the antiapoptotic protein Bcl-2, decreasing cytochrome c release from mitochondria, and attenuating apoptotic cascade activation (Bax, caspase-9, and caspase-3).

CONCLUSION

E2 activates cell survival signaling and Nrf2-Keap1 antioxidant defense pathway and attenuates Hcy cytotoxicity.

Alterations in glutathione levels and apoptotic regulators are associated with acquisition of arsenic trioxide resistance in multiple myeloma

Arsenic trioxide (ATO) has been tested in relapsed/refractory multiple myeloma with limited success. In order to better understand drug mechanism and resistance pathways in myeloma we generated an ATO-resistant cell line, 8226/S-ATOR05, with an IC50 that is 2–3-fold higher than control cell lines and significantly higher than clinically achievable concentrations. Interestingly we found two parallel pathways governing resistance to ATO in 8226/S-ATOR05, and the relevance of these pathways appears to be linked to the concentration of ATO used. We found changes in the expression of Bcl-2 family proteins Bfl-1 and Noxa as well as an increase in cellular glutathione (GSH) levels. At low, clinically achievable concentrations, resistance was primarily associated with an increase in expression of the anti-apoptotic protein Bfl-1 and a decrease in expression of the pro-apoptotic protein Noxa. However, as the concentration of ATO increased, elevated levels of intracellular GSH in 8226/S-ATOR05 became the primary mechanism of ATO resistance. Removal of arsenic selection resulted in a loss of the resistance phenotype, with cells becoming sensitive to high concentrations of ATO within 7 days following drug removal, indicating changes associated with high level resistance (elevated GSH) are dependent upon the presence of arsenic. Conversely, not until 50 days without arsenic did cells once again become sensitive to clinically relevant doses of ATO, coinciding with a decrease in the expression of Bfl-1. In addition we found cross-resistance to melphalan and doxorubicin in 8226/S-ATOR05, suggesting ATO-resistance pathways may also be involved in resistance to other chemotherapeutic agents used in the treatment of multiple myeloma.

Ethyl 3',4',5'-trimethoxythionocinnamate modulates NF-κB and Nrf2 transcription factors

Recently, we identified a novel cinnamate analog, ethyl 3',4',5'-trimethoxythionocinnamate (ETMTC) as a potent inhibitor of cell adhesion molecules (CAMs), such as intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1) and E-selectin. However, its mechanism of action has not been elucidated so far. Since, nuclear factor-kappa B (NF-κB) is the major transcription factor involved in the regulation of ICAM-1, VCAM-1 and E-selectin expression, we determined the status of NF-κB activation in ETMTC treated human endothelial cells. Here, we demonstrate that ETMTC inhibits TNF-α-induced nuclear translocation and activation of NF-κB by inhibiting phosphorylation and degradation of IκBα. The inhibition of IκBα phosphorylation and degradation by ETMTC was found to be due to its ability to inhibit IκB kinase activity. In addition, oxidative stress is known to regulate NF-κB activation through TNF-α signaling cascade, therefore, we examined the effect of ETMTC on TNF-α-induced reactive oxygen species generation. We observed that ETMTC significantly inhibits TNF-α-induced reactive oxygen species generation in endothelial cells. To further elucidate the anti-oxidant potential of ETMTC, we examined its effect on induction of anti-oxidant genes viz. glutamate-cysteine ligase, modifier subunit (GCLM), heme oxygenase-1 (HO1) and NAD (P)H:quinone oxidoreductase 1 (NQO1) in human bronchial epithelial cells. Interestingly, ETMTC significantly induces the anti-oxidant genes viz. GCLM, HO1 and NQO1 by activating nuclear factor-erythroid 2 p45-related factor 2 (Nrf2). Thus, ETMTC could be useful towards developing potent anti-inflammatory molecules.

Water quality assessment using the AREc32 reporter gene assay indicative of the oxidative stress response pathway

The reporter gene assay AREc32 is based on the induction of the Nrf2 mediated oxidative stress response pathway in the human breast cancer cell line MCF7, where eight copies of the antioxidant response element (ARE) are linked to a reporter gene encoding for luciferase. The Nrf2-ARE pathway is responsive to many chemicals that cause oxidative stress, among them a large number of pesticides and skin irritants. We adopted and validated the AREc32 bioassay for water quality testing. tert-Butylhydroquinone served as the positive control, phenol as the negative control and other reactive chemicals were assessed for their specificity. An environmentally relevant reference chemical, benzo(a)pyrene was the most potent inducer of all tested chemicals. The concentration causing an induction ratio (IR) of 1.5 (EC(IR1.5)) was chosen as the effect benchmark value. The assay was applied to 21 water samples ranging from sewage to drinking water, including secondary treatment and various tertiary treatment options (ozonation, biologically activated carbon filtration, membrane filtration, reverse osmosis, advanced oxidation, chlorination, chloramination). The samples were enriched by solid phase extraction. In most samples the oxidative stress response was far more sensitive than cytotoxicity. The primary and secondary treated effluent exceeded the effect threshold IR 1.5 at a relative enrichment factor (REF) of 1, i.e., the native samples were active. All tertiary treated samples were less potent and their EC(IR1.5) lay between REF 1 and 10. The Nrf2 pathway was induced at a REF of approximately 10 for surface waters and drinking water, and above this enrichment cytotoxicity took over in most samples and quenched the induction. The blank (ultrapure water run through the sample enrichment process) was cytotoxic at an REF of 100, which is the limit of concentrations range that can be evaluated. Treatment typically decreased both the cytotoxicity and oxidative stress response apart from drinking water treatment where chlorination caused an increase in oxidative stress response, presumably due to the formation of disinfection by-products. This study demonstrates the relevance and applicability of the oxidative stress response pathway for water quality monitoring.

Identification of novel microRNAs in post-transcriptional control of Nrf2 expression and redox homeostasis in neuronal, SH-SY5Y cells

Nuclear factor-erythroid 2-related factor 2 (Nrf2/NFE2L2), a redox-sensitive transcription factor plays a critical role in adaptation to cellular stress and affords cellular defense by initiating transcription of antioxidative and detoxification genes. While a protein can be regulated at multiple levels, control of Nrf2 has been largely studied at post-translational regulation points by Keap1. Importantly, post-transcriptional/translational based regulation of Nrf2 is less understood and to date there are no reports on such mechanisms in neuronal systems. In this context, studies involving the role of microRNAs (miRs) which are normally considered as fine tuning regulators of protein production through translation repression and/or post-transcriptional alterations, are in place. In the current study, based on in-silico analysis followed by immunoblotting and real time analysis, we have identified and validated for the first time that human NFE2L2 could be targeted by miR153/miR27a/miR142-5p/miR144 in neuronal, SH-SY5Y cells. Co-transfection studies with individual miR mimics along with either WT 3′ UTR of human Nrf2 or mutated miRNA targeting seed sequence within Nrf2 3′ UTR, demonstrated that Nrf2 is a direct regulatory target of these miRs. In addition, ectopic expression of miR153/miR27a/miR142-5p/miR144 affected Nrf2 mRNA abundance and nucleo-cytoplasmic concentration of Nrf2 in a Keap1 independent manner resulting in inefficient transactivating ability of Nrf2. Furthermore, forced expression of miRs diminished GCLC and GSR expression resulting in alteration of Nrf2 dependent redox homeostasis. Finally, bioinformatics based miRNA-disease network analysis (MDN) along with extended computational network analysis of Nrf2 associated pathologic processes suggests that if in a particular cellular scenario where any of these miR153/miR27a/miR142-5p/miR144 either individually or as a group is altered, it could affect Nrf2 thus triggering and/or determining the fate of wide range of disease outcomes.

A novel small molecule, N-(4-(2-pyridyl)(1,3-thiazol-2-yl))-2-(2,4,6-trimethylphenoxy) acetamide, selectively protects against oxidative stress-induced cell death by activating the Nrf2-ARE pathway: therapeutic implications for ALS

Antioxidant defense is crucial in restoring cellular redox homeostasis. Recent findings have suggested that oxidative stress plays pivotal roles in the pathogenesis of many neurodegenerative diseases. Thus, an anti-oxidative stress remedy might be a promising means for the treatment of such disorders. In this study, we employed a novel ligand-based virtual screening system and identified a novel small molecule, N-(4-(2-pyridyl)(1,3-thiazol-2-yl))-2-(2,4,6-trimethylphenoxy) acetamide (CPN-9), which selectively suppressed oxidative stress-induced cell death in a cell-type-independent manner. CPN-9 upregulates NF-E2-related factor 2 (Nrf2), a key transcriptional regulator of the expression of phase II detoxification enzymes and antioxidant proteins, and Nrf2-regulated factors such as heme oxygenase-1 (HO-1), NAD(P)H quinone oxidoreductase 1 (NQO1), and glutamate-cysteine ligase modifier subunit (GCLM). The CPN-9-mediated upregulation of HO-1, NQO1, and GCLM was abolished by Nrf2 knockdown. Moreover, the antioxidant N-acetylcysteine reduced the protective effect of CPN-9 against oxidative stress-induced cell death with concomitant diminishing of Nrf2 nuclear translocation. These results indicate that CPN-9 exerts its activity via the reactive oxygen species-dependent activation of the Nrf2 signaling pathway in cultured cells. It is noteworthy that the postonset systemic administration of CPN-9 to a transgenic ALS mouse model carrying the H46R mutation in the human Cu/Zn superoxide dismutase (SOD1) gene sustained motor functions and delayed disease progression after onset. Collectively, CPN-9 is a novel Nrf2 activator and a neuroprotective candidate for the treatment of neurodegenerative diseases, including ALS.

Plants vs. cancer: a review on natural phytochemicals in preventing and treating cancers and their druggability

Cancer remains to be one of the leading causes of death in the United States and around the world. The advent of modern drug-targeted therapies has undeniably improved cancer patients' cares. However, advanced metastasized cancer remains untreatable. Hence, continued searching for a safer and more effective chemoprevention and treatment is clearly needed for the improvement of the efficiency and to lower the treatment cost for cancer care. Cancer chemoprevention with natural phytochemical compounds is an emerging strategy to prevent, impede, delay, or cure cancer. This review summarizes the latest research in cancer chemoprevention and treatment using the bioactive components from natural plants. Relevant molecular mechanisms involved in the pharmacological effects of these phytochemicals are discussed. Pharmaceutical developmental challenges and opportunities in bringing the phytochemicals into the market are also explored. The authors wish to expand this research area not only for their scientific soundness, but also for their potential druggability.

Transcriptome profiling of peripheral blood cells identifies potential biomarkers for doxorubicin cardiotoxicity in a rat model

Aims

Doxorubicin (DOX), a widely used anticancer agent, can cause an unpredictable cardiac toxicity which remains a major limitation in cancer chemotherapy. There is a need for noninvasive, sensitive and specific biomarkers which will allow identifying patients at risk for DOX-induced cardiotoxicity to prevent permanent cardiac damage. The aim of this study was to investigate whether the expression of specific genes in the peripheral blood can be used as surrogate marker(s) for DOX-induced cardiotoxicity.

Methods/Results

Rats were treated with a single dose of DOX similar to one single dose that is often administered in humans. The cardiac and peripheral blood mononuclear cells (PBMCs) genome-wide expression profiling were examined using Illumina microarrays. The results showed 4,409 differentially regulated genes (DRG) in the hearts and 4,120 DRG in PBMC. Of these 2411 genes were similarly DRG (SDRG) in both the heart and PBMC. Pathway analysis of the three datasets of DRG using Gene Ontology (GO) enrichment analysis and Ingenuity Pathways Analysis (IPA) showed that most of the genes in these datasets fell into pathways related to oxidative stress response and protein ubiquination. IPA search for potential eligible biomarkers for cardiovascular disease within the SDRG list revealed 188 molecules.

Conclusions

We report the first in-depth comparison of DOX-induced global gene expression profiles of hearts and PBMCs. The high similarity between the gene expression profiles of the heart and PBMC induced by DOX indicates that the PBMC transcriptome may serve as a surrogate marker of DOX-induced cardiotoxicity. Future directions of this research will include analysis of PBMC expression profiles of cancer patients treated with DOX-based chemotherapy to identify the cardiotoxicity risk, predict DOX-treatment response and ultimately to allow individualized anti-cancer therapy.

The 'N-factors' in pancreatic cancer: functional relevance of NF-κB, NFAT and Nrf2 in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) represents one of the deadliest malignancies, with an overall life expectancy of 6 months. Despite considerable advances in the understanding of the molecular mechanisms involved in the carcinogenesis of PDAC, the outcome of the disease was not significantly improved over the last 20 years. Although some achievements in molecular-targeted therapies have been made (that is, targeting the epidermal growth factor receptor by erlotinib), which already entered clinical settings, and despite the promising outcome of the FOLFIRINOX trial, there is an urgent need for improvement of the chemotherapy in this disease. A plethora of molecular alterations are thought to be responsible for the profound chemoresistance, including mutations in oncogenes and tumor suppressors. Besides these classical hallmarks of cancer, the constitutive or inducible activity of transcription factor pathways are characteristic changes in PDAC. Recently, three transcription factors-nuclear factor-κB (NF-κB), nuclear factor of activated T cells (NFAT) and nuclear factor-E2-related factor-2 (Nrf2)-have been shown to be crucial for tumor development and chemoresistance in pancreatic cancer. These transcription factors are key regulators of a variety of genes involved in nearly all aspects of tumorigenesis and resistance against chemotherapeutics and death receptor ligands. Furthermore, the pathways of NF-κB, NFAT and Nrf2 are functional, interacting on several regulatory steps, and, especially, natural compounds such as curcumin interfere with more than one pathway. Thus, targeting these pathways by established inhibitors or new drugs might have great potential to improve the outcome of PDAC patients, most likely in combination with established anticancer drugs. In this article, we summarize recent progress in the characterization of these transcription-factor pathways and their role in PDAC and therapy resistance. We also discuss future concepts for the treatment of PDAC relying on these pathways.

Thioredoxin reductase inhibition elicits Nrf2-mediated responses in Clara cells: implications for oxidant-induced lung injury

AIMS

Pulmonary oxygen toxicity contributes to lung injury in newborn and adult humans. We previously reported that thioredoxin reductase (TrxR1) inhibition with aurothioglucose (ATG) attenuates hyperoxic lung injury in adult mice. The present studies tested the hypothesis that TrxR1 inhibition protects against the effects of hyperoxia via nuclear factor E2-related factor 2 (Nrf2)-dependent mechanisms.

RESULTS

Both pharmacologic and siRNA-mediated TrxR1 inhibition induced robust Nrf2 responses in murine-transformed Clara cells (mtCC). While TrxR1 inhibition did not alter the susceptibility of cells to the effects of hyperoxia, glutathione (GSH) depletion after TrxR1 inhibition markedly enhanced the hyperoxic susceptibility of cultured mtCCs. Finally, in vivo data revealed dose-dependent increases in the expression of the Nrf2 target gene NADPH:quinone oxidoreductase 1 (NQO1) in the lungs of ATG-treated adult mice.

INNOVATION

TrxR1 inhibition activates Nrf2-dependent antioxidant responses in mtCCs in vitro and in adult murine lungs in vivo, providing a plausible mechanism for the protective effects of TrxR1 inhibition in vivo.

CONCLUSION

GSH-dependent enzyme systems in mtCCs may be of greater importance for protection against hyperoxic exposure than are TrxR-dependent systems. The induction of Nrf2 activation via TrxR1 inhibition represents a novel therapeutic strategy that attenuates oxidant-mediated lung injury. Similar expression levels of TrxR1 in newborn and adult mouse or human lungs broaden the potential clinical applicability of the present findings to both neonatal and adult oxidant lung injury.

Mitochondrial decay in ageing: 'Qi-invigorating' schisandrin B as a hormetic agent for mitigating age-related diseases

1. The mitochondrial free radical theory of ageing (MFRTA) proposes a primary role for mitochondrial reactive oxygen species (ROS) in the ageing process. The reductive hot spot hypothesis of mammalian ageing serves as a supplement to the MFRTA by explaining how the relatively few cells that have lost oxidative phosphorylation capacity due to mitochondrial DNA mutations can be toxic to the rest of the body and result in the development of age-related diseases. 2. Schisandrin B (SchB), which can induce both a glutathione anti-oxidant and a heat shock response via redox-sensitive signalling pathways, is a hormetic agent potentially useful for increasing the resistance of tissues to oxidative damage. The enhanced cellular/mitochondrial anti-oxidant status and heat shock response afforded by SchB can preserve the structural and functional integrity of mitochondria, suggesting a potential role for SchB in ameliorating age-related diseases. 3. Future studies will focus on investigating whether SchB can produce the hormetic response in humans.

Inhibition of the Nrf2 transcription factor by the alkaloid trigonelline renders pancreatic cancer cells more susceptible to apoptosis through decreased proteasomal gene expression and proteasome activity

Evidence accumulates that the transcription factor nuclear factor E2-related factor 2 (Nrf2) has an essential role in cancer development and chemoresistance, thus pointing to its potential as an anticancer target and undermining its suitability in chemoprevention. Through the induction of cytoprotective and proteasomal genes, Nrf2 confers apoptosis protection in tumor cells, and inhibiting Nrf2 would therefore be an efficient strategy in anticancer therapy. In the present study, pancreatic carcinoma cell lines (Panc1, Colo357 and MiaPaca2) and H6c7 pancreatic duct cells were analyzed for the Nrf2-inhibitory effect of the coffee alkaloid trigonelline (trig), as well as for its impact on Nrf2-dependent proteasome activity and resistance to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and anticancer drug-induced apoptosis. Chemoresistant Panc1 and Colo357 cells exhibit high constitutive Nrf2 activity, whereas chemosensitive MiaPaca2 and H6c7 cells display little basal but strong tert-butylhydroquinone (tBHQ)-inducible Nrf2 activity and drug resistance. Trig efficiently decreased basal and tBHQ-induced Nrf2 activity in all cell lines, an effect relying on a reduced nuclear accumulation of the Nrf2 protein. Along with Nrf2 inhibition, trig blocked the Nrf2-dependent expression of proteasomal genes (for example, s5a/psmd4 and α5/psma5) and reduced proteasome activity in all cell lines tested. These blocking effects were absent after treatment with Nrf2 siRNA, a condition in which proteasomal gene expression and proteasome activity were already decreased, whereas siRNA against the related transcription factor Nrf1 did not affect proteasome activity and the inhibitory effect of trig. Depending on both Nrf2 and proteasomal gene expression, the sensitivity of all cell lines to anticancer drugs and TRAIL-induced apoptosis was enhanced by trig. Moreover, greater antitumor responses toward anticancer drug treatment were observed in tumor-bearing mice when receiving trig. In conclusion, representing an efficient Nrf2 inhibitor capable of blocking Nrf2-dependent proteasome activity and thereby apoptosis protection in pancreatic cancer cells, trig might be beneficial in improving anticancer therapy.

Direct oxidation of the [2Fe-2S] cluster in SoxR protein by superoxide: distinct differential sensitivity to superoxide-mediated signal transduction

The [2Fe-2S] transcription factor SoxR is activated by reversible one-electron oxidation of its [2Fe-2S] cluster, leading to enhanced production of various antioxidant proteins through induction of the soxRS regulon in Escherichia coli. Recently, there has been considerable debate about whether superoxide (O(2)(•)) activates SoxR directly. To elucidate the underlying activation mechanism, we investigated SoxR interaction with O(2)(•) using pulse radiolysis. Radiolytically generated hydrated electrons reduced the oxidized form of the [2Fe-2S] cluster of SoxR within 2 μs. A subsequent increase in absorption in the visible region corresponding to reoxidation of the [2Fe-2S] cluster was observed on a time scale of milliseconds. Addition of human copper/zinc superoxide dismutase inhibited this delayed oxidation in a concentration-dependent fashion (I(50) = 1.0 μm), indicating that O(2)(•) oxidized the reduced form of SoxR directly. The second-order rate constant of this process was estimated to be 5 × 10(8) m(-1) s(-1). A similar result was observed after pulse radiolysis of Pseudomonas aeruginosa SoxR. However, superoxide dismutase inhibited the oxidation of reduced SoxR much more effectively in P. aeruginosa, even at a lower concentration (I(50) = 80 nm), indicating that the soxRS response is much more sensitive to O(2)(•) in E. coli than in P. aeruginosa. These results suggest that SoxR proteins play a distinct regulatory role in the activation of O(2)(•).

Deficiency in the nuclear-related factor erythroid 2 transcription factor (Nrf1) leads to genetic instability

Nuclear factor erythroid-derived 2-related factor 1 (Nrf1) regulates cellular stress response genes, and has also been suggested to play a role in other cellular processes. We previously demonstrated that hepatocyte-specific deletion of Nrf1 in mice resulted in spontaneous apoptosis, inflammation, and development of liver tumors. Here, we showed that both fibroblasts derived from Nrf1 null mouse embryos and fibroblasts expressing a conditional Nrf1 allele showed increased micronuclei and formation of abnormal nuclei. Lentiviral shRNA-mediated knockdown of Nrf1 in SAOS-2 cells also resulted in increased micronuclei, abnormal mitosis and multi-nucleated cells. Metaphase analyses showed increased aneuploidy in Nrf1(-/-) embryonic fibroblasts. Nuclear defects in Nrf1-deficient cells were associated with decreased expression of various genes encoding kinetochore and mitotic checkpoint proteins. Our findings suggest that Nrf1 may play a role in maintaining genomic integrity, and that Nrf1 dysregulation may induce tumorigenesis.

Ferulic acid induces heme oxygenase-1 via activation of ERK and Nrf2

This study investigated the effect of ferulic acid (FA) on the up-regulation of heme oxygenase-1 (HO-1) in lymphocytes and the molecular mechanisms involved. Lymphocytes were treated with FA (0.001-0.1 μM) for certain times. Cell viability, the activity and level of expression of HO-1, and signal pathways were analyzed. FA significantly upregulated HO-1 expression both at the level of mRNA and protein in lymphocytes. Moreover, FA induced NF-E2-related factor (Nrf2) nuclear translocation and transcriptional activity, which is upstream of FA induced HO-1 expression. In addition, lymphocytes treated with FA exhibited activation of extracellular regulated kinase (ERK) and treatments with U0126 (an ERK kinase inhibitor) attenuated the FA induced activation of Nrf2, resulting in a decrease in HO-1 expression. Zinc protoporphyrin (ZnPP, a HO-1 inhibitor) markedly suppressed cytoprotection from radiation-induced cell damage by FA. Results suggested that the ERK signaling pathway controlled the anti-oxidation of FA by regulating the expression of the antioxidant enzyme HO-1.

Activator protein-1 regulation of murine aldehyde dehydrogenase 1a1

Previously we demonstrated that aldehyde dehydrogenase (ALDH) 1a1 is the major ALDH expressed in mouse liver and is an effective catalyst in metabolism of lipid aldehydes. Quantitative real-time polymerase chain reaction analysis revealed a ≈2.5- to 3-fold induction of the hepatic ALDH1A1 mRNA in mice administered either acrolein (5 mg/kg acrolein p.o.) or butylated hydroxylanisole (BHA) (0.45% in the diet) and of cytosolic NAD⁺-dependent ALDH activity. We observed ≈2-fold increases in ALDH1A1 mRNA levels in both Nrf2⁺/⁺ and Nrf2⁻/⁻ mice treated with BHA compared with controls, suggesting that BHA-induced expression is independent of nuclear factor E2-related factor 2 (Nrf2). The levels of activator protein-1 (AP-1) mRNA and protein, as well as the amount of phosphorylated c-Jun were significantly increased in mouse liver or Hepa1c1c7 cells treated with either BHA or acrolein. With use of luciferase reporters containing the 5'-flanking sequence of Aldh1a1 (-1963/+27), overexpression of c-Jun resulted in an ≈4-fold induction in luciferase activity, suggesting that c-Jun transactivates the Aldh1a1 promoter as a homodimer and not as a c-Jun/c-Fos heterodimer. Promoter deletion and mutagenesis analyses demonstrated that the AP-1 site at position -758 and possibly -1069 relative to the transcription start site was responsible for c-Jun-mediated transactivation. Electrophoretic mobility shift assay analysis with antibodies against c-Jun and c-Fos showed that c-Jun binds to the proximal AP-1 site at position -758 but not at -1069. Recruitment of c-Jun to this proximal AP-1 site by BHA was confirmed by chromatin immunoprecipitation analysis, indicating that recruitment of c-Jun to the mouse Aldh1a1 gene promoter results in increased transcription. This mode of regulation of an ALDH has not been described before.

Emerging applications for zebrafish as a model organism to study oxidative mechanisms and their roles in inflammation and vascular accumulation of oxidized lipids

With the advent of genetic engineering, zebrafish (Danio rerio) were recognized as an attractive model organism to study many biological processes. Remarkably, the small size and optical transparency of zebrafish larvae enable high-resolution imaging of live animals. Zebrafish respond to various environmental and pathological factors with robust oxidative stress. In this article, we provide an overview of the molecular mechanisms involved in oxidative stress and antioxidant response in zebrafish. Existing applications of genetically encoded fluorescent sensors allow imaging, in real time, of the production of H(2)O(2) and studying its involvement in inflammatory responses, as well as activation of the oxidation-sensitive transcription factors HIF and NRF2. Oxidative stress, combined with hyperlipidemia, leads to oxidation of lipoproteins, the process that contributes significantly to the development of atherosclerosis in humans. Recent work found that feeding zebrafish a high-cholesterol diet results in hypercholesterolemia, vascular lipid accumulation, and extreme lipoprotein oxidation. Generation of a transgenic zebrafish expressing a green fluorescent protein-tagged human antibody to malondialdehyde (MDA)-modified LDL makes possible the in vivo visualization of MDA epitopes in the vascular wall and testing of the efficacy of antioxidants and dietary interventions. Thus, using zebrafish as a model organism provides important advantages in studying the roles of reactive oxygen species and lipid oxidation in basic biologic and pathologic processes.

Mitochondria as a source and target of lipid peroxidation products in healthy and diseased heart

The heart is a highly oxidative organ in which cardiomyocyte turnover is virtually absent, making it particularly vulnerable to accumulation of lipid peroxidation products (LPP) formed as a result of oxidative damage. Reactive oxygen and nitrogen species are the most common electrophiles formed during lipid peroxidation and lead to the formation of both stable and unstable LPP. Of the LPP formed, highly reactive aldehydes are a well-recognized causative factor in ageing and age-associated diseases, including cardiovascular disease and diabetes. Recent studies have identified that the mitochondria are both a primary source and target of LPP, with specific emphasis on aldehydes in cardiomyocytes and how these affect the electron transport system and Ca(2+) balance. Numerous studies have found that there are functional consequences in the heart following exposure to specific aldehydes (acrolein, trans-2-hexanal, 4-hydroxynonenal and acetaldehyde). Because these LPP are known to form in heart failure, cardiac ischaemia-reperfusion injury and diabetes, they may have an underappreciated role in the pathophysiology of these disease processes. Lipid peroxidation products are involved in the transcriptional regulation of endogenous anti-oxidant systems. Recent evidence demonstrates that transient increases in LPP may be beneficial in cardioprotection by contributing to mitohormesis (i.e. induction of anti-oxidant systems) in cardiomyocytes. Thus, exploitation of the cardioprotective actions of the LPP may represent a novel therapeutic strategy for future treatment of heart disease.

Molecular and genomic approach for understanding the gene-environment interaction between Nrf2 deficiency and carcinogenic nickel-induced DNA damage

Nickel (II) is a toxic and carcinogenic metal which induces a redox imbalance following oxidative stress. Nuclear factor erythroid-2 related factor 2 (Nrf2) is a redox factor that regulates oxidation/reduction status and consequently mediates cytoprotective responses against exposure to environmental toxicants. In this study, we investigated the protective roles of the Nrf2 gene against oxidative stress and DNA damage induced by nickel at sub-lethal doses. Under nickel exposure conditions, we detected significantly increased intracellular ROS generation, in addition to higher amounts of DNA damage using comet assay and γ-H2AX immunofluorescence staining in Nrf2 lacking cells, as compared to Nrf2 wild-type cells. In addition, we attempted to identify potential nickel and Nrf2-responsive targets and the relevant pathway. The genomic expression data were analyzed using microarray for the selection of synergistic effect-related genes by Nrf2 knockdown under nickel treatment. In particular, altered expressions of 6 upregulated genes (CAV1, FOSL2, MICA, PIM2, RUNX1 and SLC7A6) and 4 downregulated genes (APLP1, CLSPN, PCAF and PRAME) were confirmed by qRT-PCR. Additionally, using bioinformatics tool, we found that these genes functioned principally in a variety of molecular processes, including oxidative stress response, necrosis, DNA repair and cell survival. Thus, we describe the potential biomarkers regarded as molecular candidates for Nrf2-related cellular protection against nickel exposure. In conclusion, these findings indicate that Nrf2 is an important factor with a protective role in the suppression of mutagenicity and carcinogenicity by environmental nickel exposure in terms of gene-environment interaction.

Differential activities of the two closely related withanolides, Withaferin A and Withanone: bioinformatics and experimental evidences

Background and Purpose

Withanolides are naturally occurring chemical compounds. They are secondary metabolites produced via oxidation of steroids and structurally consist of a steroid-backbone bound to a lactone or its derivatives. They are known to protect plants against herbivores and have medicinal value including anti-inflammation, anti-cancer, adaptogenic and anti-oxidant effects. Withaferin A (Wi-A) and Withanone (Wi-N) are two structurally similar withanolides isolated from Withania somnifera, also known as Ashwagandha in Indian Ayurvedic medicine. Ashwagandha alcoholic leaf extract (i-Extract), rich in Wi-N, was shown to kill cancer cells selectively. Furthermore, the two closely related purified phytochemicals, Wi-A and Wi-N, showed differential activity in normal and cancer human cells in vitro and in vivo. We had earlier identified several genes involved in cytotoxicity of i-Extract in human cancer cells by loss-of-function assays using either siRNA or randomized ribozyme library.

Methodology/Principal Findings

In the present study, we have employed bioinformatics tools on four genes, i.e., mortalin, p53, p21 and Nrf2, identified by loss-of-function screenings. We examined the docking efficacy of Wi-N and Wi-A to each of the four targets and found that the two closely related phytochemicals have differential binding properties to the selected cellular targets that can potentially instigate differential molecular effects. We validated these findings by undertaking parallel experiments on specific gene responses to either Wi-N or Wi-A in human normal and cancer cells. We demonstrate that Wi-A that binds strongly to the selected targets acts as a strong cytotoxic agent both for normal and cancer cells. Wi-N, on the other hand, has a weak binding to the targets; it showed milder cytotoxicity towards cancer cells and was safe for normal cells. The present molecular docking analyses and experimental evidence revealed important insights to the use of Wi-A and Wi-N for cancer treatment and development of new anti-cancer phytochemical cocktails.

Development and validation of a new in vitro assay designed to measure contact allergen-triggered oxidative stress in dendritic cells

BACKGROUND

Selected contact allergens are known to induce phenotypic and functional maturation of dendritic cells (DCs). Such changes occurring in DCs have been employed as assay readouts to predict skin-sensitizing potentials of small chemicals.

OBJECTIVE

To respond to the urgent needs for reliable in vitro tests to identify contact allergens, we sought to develop a DC-based assay designed to detect early change(s) induced by sensitizers.

METHODS

Signature gene expression profiles of skin sensitization were determined by GeneChip and quantitative RT-PCR analyses of RNA samples harvested from mouse skin and XS106 DC line after exposure to dinitrofluorobenzene (DNFB). Production of reactive oxygen species (ROS) was examined indirectly by measuring the level of oxidative stress-XS106 DCs were labeled with a fluorescent dye, CM-H(2)DCFDA, exposed to test chemicals, and then examined for fluorescence signals by flow cytometer.

RESULTS

DNFB induced abundant mRNA expression of several redox regulatory genes in both mouse skin and XS106DCs. Expression of these genes was inducible by hydrogen peroxide and blocked by a ROS inhibitor, diphenyleneiodonium. Rapid and significant ROS production was induced by 25 of the 28 tested skin sensitizers, but only by 3 of the 21 tested skin irritants.

CONCLUSIONS

Our small-scale validation study demonstrates the practical utility of our DC-based ROS production assay to detect structurally diverse contact allergens with varying sensitizing potencies. It is tempting to speculate that ROS production in DCs may represent an early event during the sensitization phase.

Baicalein protects against 6-OHDA-induced neurotoxicity through activation of Keap1/Nrf2/HO-1 and involving PKCα and PI3K/AKT signaling pathways

Baicalein, one of the major flavonoids found in Scutellaria baicalensis Georgi, displays neuroprotective effects on experimental models of Parkinson's disease (PD) in vitro and in vivo. Although the antioxidative and/or anti-inflammatory activity of baicalein likely contributes to these neuroprotective effects, other modes of action remain largely uncharacterized. In the present study, baicalein pretreatment significantly prevented cells from 6-hydroxydopamine (6-OHDA)-induced damage by attenuating cellular apoptosis. However, post-treatment with baicalein did not show any restorative effect against 6-OHDA-induced cellular damage. We found that baicalein increased transcriptional factor NF-E2-related factor 2 (Nrf2)/hemo oxygenase 1(HO-1) protein expression and decreased Kelch-like ECH-associated protein 1 (Keap1) in a time- and concentration-dependent manner in PC12 cells. In addition, baicalein induced Nrf2 nuclear translocation and enhanced antioxidant response element (ARE) transcriptional activity, which conferred cytoprotection against 6-OHDA-induced oxidative injury. Moreover, we demonstrated that cytoprotective effects of baicalein could be attenuated by Nrf2 siRNA transfection and the HO-1 inhibitor zinc protoporphyrin (Znpp) as well as the proteasome inhibitor MG132. Furthermore, PKCα and AKT protein phosphorylation were up-regulated by baicalein pretreatment, and selective inhibitors targeted to PKC, PI3K, and AKT could block the cytoprotective effects of baicalein. Taken together, our results indicate that baicalein prevented PC12 cells from 6-OHDA-induced oxidative damage via the activation of Keap1/Nrf2/HO-1, and it also involves the PKCα and PI3K/AKT signaling pathway. Ultimately, the neuroprotective effects of baicalein may endue baicalein as a promising candidate for the prevention of PD.

Mutant p53R273H attenuates the expression of phase 2 detoxifying enzymes and promotes the survival of cells with high levels of reactive oxygen species

Uncontrolled accumulation of reactive oxygen species (ROS) causes oxidative stress and induces harmful effects. Both high ROS levels and p53 mutations are frequent in human cancer. Mutant p53 forms are known to actively promote malignant growth. However, no mechanistic details are known about the contribution of mutant p53 to excessive ROS accumulation in cancer cells. Herein, we examine the effect of p53(R273H), a commonly occurring mutated p53 form, on the expression of phase 2 ROS-detoxifying enzymes and on the ability of cells to readopt a reducing environment after exposure to oxidative stress. Our data suggest that p53(R273H) mutant interferes with the normal response of human cells to oxidative stress. We show here that, upon oxidative stress, mutant p53(R273H) attenuates the activation and function of NF-E2-related factor 2 (NRF2), a transcription factor that induces the antioxidant response. This effect of mutant p53 is manifested by decreased expression of phase 2 detoxifying enzymes NQO1 and HO-1 and high ROS levels. These findings were observed in several human cancer cell lines, highlighting the general nature of this phenomenon. The failure of p53(R273H) mutant-expressing cells to restore a reducing oxidative environment was accompanied by increased survival, a known consequence of mutant p53 expression. These activities are attributable to mutant p53(R273H) gain of function and might underlie its well-documented oncogenic nature in human cancer.

Dietary heme-mediated PPARα activation does not affect the heme-induced epithelial hyperproliferation and hyperplasia in mouse colon

Red meat consumption is associated with an increased colon cancer risk. Heme, present in red meat, injures the colon surface epithelium by luminal cytotoxicity and reactive oxygen species. This surface injury is overcompensated by hyperproliferation and hyperplasia of crypt cells. Transcriptome analysis of mucosa of heme-fed mice showed, besides stress- and proliferation-related genes, many upregulated lipid metabolism-related PPARα target genes. The aim of this study was to investigate the role of PPARα in heme-induced hyperproliferation and hyperplasia. Male PPARα KO and WT mice received a purified diet with or without heme. As PPARα is proposed to protect against oxidative stress and lipid peroxidation, we hypothesized that the absence of PPARα leads to more surface injury and crypt hyperproliferation in the colon upon heme-feeding. Heme induced luminal cytotoxicity and lipid peroxidation and colonic hyperproliferation and hyperplasia to the same extent in WT and KO mice. Transcriptome analysis of colonic mucosa confirmed similar heme-induced hyperproliferation in WT and KO mice. Stainings for alkaline phosphatase activity and expression levels of Vanin-1 and Nrf2-targets indicated a compromised antioxidant defense in heme-fed KO mice. Our results suggest that the protective role of PPARα in antioxidant defense involves the Nrf2-inhibitor Fosl1, which is upregulated by heme in PPARα KO mice. We conclude that PPARα plays a protective role in colon against oxidative stress, but PPARα does not mediate heme-induced hyperproliferation. This implies that oxidative stress of surface cells is not the main determinant of heme-induced hyperproliferation and hyperplasia.

Established Principles and Emerging Concepts on the Interplay between Mitochondrial Physiology and S-(De)nitrosylation: Implications in Cancer and Neurodegeneration

S-nitrosylation is a posttranslational modification of cysteine residues that has been frequently indicated as potential molecular mechanism governing cell response upon redox unbalance downstream of nitric oxide (over)production. In the last years, increased levels of S-nitrosothiols (SNOs) have been tightly associated with the onset of nitroxidative stress-based pathologies (e.g., cancer and neurodegeneration), conditions in which alterations of mitochondrial homeostasis and activation of cellular processes dependent on it have been reported as well. In this paper we aim at summarizing the current knowledge of mitochondria-related proteins undergoing S-nitrosylation and how this redox modification might impact on mitochondrial functions, whose impairment has been correlated to tumorigenesis and neuronal cell death. In particular, emphasis will be given to the possible, but still neglected implication of denitrosylation reactions in the modulation of mitochondrial SNOs and how they can affect mitochondrion-related cellular process, such as oxidative phosphorylation, mitochondrial dynamics, and mitophagy.

Role of sulfiredoxin as a regulator of peroxiredoxin function and regulation of its expression

Peroxiredoxins (Prxs) constitute a family of peroxidases in which cysteine serves as the primary site of oxidation during the reduction of peroxides. Members of the 2-Cys Prx subfamily of Prxs (Prx I to IV in mammals) are inactivated via hyperoxidation of the active-site cysteine to sulfinic acid (Cys-SO(2)H) during catalysis and are reactivated via an ATP-consuming reaction catalyzed by sulfiredoxin (Srx). This reversible hyperoxidation reaction has been proposed to protect H(2)O(2) signaling molecules from premature removal by 2-Cys Prxs or to upregulate the chaperone function of these enzymes. In addition to its sulfinic acid reductase activity, Srx catalyzes the removal of glutathione (deglutathionylation) from modified proteins. The physiological relevance of both the reversible hyperoxidation of 2-Cys Prxs and the deglutathionylation catalyzed by Srx remains unclear. Recent findings have revealed that Srx expression is induced in mammalian cells under a variety of conditions, such as in metabolically stimulated pancreatic β cells, in immunostimulated macrophages, in neuronal cells engaged in synaptic communication, in lung cells exposed to hyperoxia or cigarette smoke, in hepatocytes of ethanol-fed animals, and in several types of cells exposed to chemopreventive agents. Such induction of Srx in mammalian cells is regulated at the transcriptional level, predominantly via activator protein-1 and/or nuclear factor erythroid 2-related factor 2. Srx expression is also regulated at the translational level in Saccharomyces cerevisiae.

Profiling environmental chemicals for activity in the antioxidant response element signaling pathway using a high throughput screening approach

BACKGROUND

Oxidative stress has been implicated in the pathogenesis of a variety of diseases ranging from cancer to neurodegeneration, highlighting the need to identify chemicals that can induce this effect. The antioxidant response element (ARE) signaling pathway plays an important role in the amelioration of oxidative stress. Thus, assays that detect the up-regulation of this pathway could be useful for identifying chemicals that induce oxidative stress.

OBJECTIVES

We used cell-based reporter methods and informatics tools to efficiently screen a large collection of environmental chemicals and identify compounds that induce oxidative stress.

METHODS

We utilized two cell-based ARE assay reporters, β-lactamase and luciferase, to screen a U.S. National Toxicology Program 1,408-compound library (NTP 1408, which contains 1,340 unique compounds) for their ability to induce oxidative stress in HepG2 cells using quantitative high throughput screening (qHTS).

RESULTS

Roughly 3% (34 of 1,340) of the unique compounds demonstrated activity across both cell-based assays. Based on biological activity and structure-activity relationship profiles, we selected 50 compounds for retesting in the two ARE assays and in an additional follow-up assay that employed a mutated ARE linked to β-lactamase. Using this strategy, we identified 30 compounds that demonstrated activity in the ARE-bla and ARE-luc assays and were able to determine structural features conferring compound activity across assays.

CONCLUSIONS

Our results support the robustness of using two different cell-based approaches for identifying compounds that induce ARE signaling. Together, these methods are useful for prioritizing chemicals for further in-depth mechanism-based toxicity testing.

The time course of the adaptations of human muscle proteome to bed rest and the underlying mechanisms

In order to get a comprehensive picture of the complex adaptations of human skeletal muscle to disuse and further the understanding of the underlying mechanisms, we participated in two bed rest campaigns, one lasting 35 days and one 24 days. In the first bed rest (BR) campaign, myofibrillar proteins, metabolic enzymes and antioxidant defence systems were found to be down-regulated both post-8 days and post-35 days BR by proteomic analysis of vastus lateralis muscle samples from nine subjects. Such profound alterations occurred early (post-8 days BR), before disuse atrophy developed, and persisted through BR (post-35 days BR). To understand the mechanisms underlying the protein adaptations observed, muscle biopsies from the second bed rest campaign (nine subjects) were used to evaluate the adaptations of master controllers of the balance between muscle protein breakdown and muscle protein synthesis (MuRF-1 and atrogin-1; Akt and p70S6K), of autophagy (Beclin-1, p62, LC3, bnip3, cathepsin-L), of expression of antioxidant defence systems (NRF2) and of energy metabolism (PGC-1α, SREBP-1, AMPK). The results indicate that: (i) redox imbalance and remodelling of muscle proteome occur early and persist through BR; (ii) impaired energy metabolism is an early and persistent phenomenon comprising both the oxidative and glycolytic one; (iii) although both major catabolic systems, ubiquitin proteasome and autophagy, could contribute to the progression of atrophy late into BR, a decreased protein synthesis cannot be ruled out; (iv) a decreased PGC-1α, with the concurrence of SREBP-1 up-regulation, is a likely trigger of metabolic impairment, whereas the AMPK pathway is unaltered.

Cre-mediated stress affects sirtuin expression levels, peroxisome biogenesis and metabolism, antioxidant and proinflammatory signaling pathways

Cre-mediated excision of loxP sites is widely used in mice to manipulate gene function in a tissue-specific manner. To analyze phenotypic alterations related to Cre-expression, we have used AMH-Cre-transgenic mice as a model system. Different Cre expression levels were obtained by investigation of C57BL/6J wild type as well as heterozygous and homozygous AMH-Cre-mice. Our results indicate that Cre-expression itself in Sertoli cells already has led to oxidative stress and lipid peroxidation (4-HNE lysine adducts), inducing PPARα/γ, peroxisome proliferation and alterations of peroxisome biogenesis (PEX5, PEX13 and PEX14) as well as metabolic proteins (ABCD1, ABCD3, MFP1, thiolase B, catalase). In addition to the strong catalase increase, a NRF2- and FOXO3-mediated antioxidative response (HMOX1 of the endoplasmic reticulum and mitochondrial SOD2) and a NF-κB activation were noted. TGFβ1 and proinflammatory cytokines like IL1, IL6 and TNFα were upregulated and stress-related signaling pathways were induced. Sertoli cell mRNA-microarray analysis revealed an increase of TNFR2-signaling components. 53BP1 recruitment and expression levels for DNA repair genes as well as for p53 were elevated and the ones for related sirtuin deacetylases affected (SIRT 1, 3-7) in Sertoli cells. Under chronic Cre-mediated DNA damage conditions a strong downregulation of Sirt1 was observed, suggesting that the decrease of this important coordinator between DNA repair and metabolic signaling might induce the repression release of major transcription factors regulating metabolic and cytokine-mediated stress pathways. Indeed, caspase-3 was activated and increased germ cell apoptosis was observed, suggesting paracrine effects. In conclusion, the observed wide stress-induced effects and metabolic alterations suggest that it is essential to use the correct control animals (Cre/Wt) with matched Cre expression levels to differentiate between Cre-mediated and specific gene-knock out-mediated effects.

Requirement for the histone deacetylase Hdac3 for the inflammatory gene expression program in macrophages

Histone deacetylases (HDACs) regulate inflammatory gene expression, as indicated by the potent antiinflammatory activity of pan-HDAC inhibitors. However, the specific contribution of each of the 11 HDAC proteins to the inflammatory gene expression program is unknown. Using an integrated genomic approach, we found that Hdac3-deficient macrophages were unable to activate almost half of the inflammatory gene expression program when stimulated with LPS. A large part of the activation defect was attributable to loss of basal and LPS-inducible expression of IFN-β, which maintains Stat1 protein levels in unstimulated cells and acts in an autocrine/paracrine manner after stimulation to promote a secondary wave of Stat1-dependent gene expression. Loss of Hdac3-mediated repression of nuclear receptors led to hyperacetylation of thousands of genomic sites and associated gene derepression. The up-regulation of the constitutively expressed prostaglandin endoperoxide synthase, Ptgs1 (Cox-1), a nuclear receptor target, had a causative role in the phenotype because its chemical inhibition reverted, albeit partially, the Ifn-β activation defect. These data indicate a central role for Hdac3 in inflammation and may have relevance for the use of selective Hdac inhibitors as antiinflammatory agents.

6-shogaol-rich extract from ginger up-regulates the antioxidant defense systems in cells and mice

The rhizome of ginger (Zingiber officinale Roscoe) is known to have several bioactive compounds including gingerols and shogaols which possess beneficial health properties such as anti-inflammatory and chemopreventive effects. Based on recent observations that 6-shogaol may have more potent bioactivity than 6-gingerol, we obtained a 6-shogaol-rich extract from ginger and examined its effects on the nuclear factor E2-related factor2 (Nrf2)/antioxidant response element (ARE) pathway in vitro and in vivo. 6-Shogaol-rich extract was produced by extracting ginger powder with 95% ethanol at 80 °C after drying at 80 °C (GEE8080). GEE8080 contained over 6-fold more 6-shogaol compared to the room temperature extract (GEE80RT). In HepG2 cells, GEE8080 displayed much stronger inductions of ARE-reporter gene activity and Nrf2 expression than GEE80RT. GEE8080 stimulated phosphorylations of mitogen-activated protein kinases (MAPKs) such as ERK, JNK, and p38. Moreover, the GEE8080-induced expressions of Nrf2 and HO-1 were attenuated by treatments of SB202190 (a p38 specific inhibitor) and LY294002 (an Akt specific inhibitor). In a mouse model, the GEE8080 decreased the diethylnitrosamine (DEN)-mediated elevations of serum aspartate transaminase and alanine transaminase as well as the DEN-induced hepatic lipid peroxidation. Inductions of Nrf2 and HO-1 by GEE8080 were also confirmed in the mice. In addition, the administration of GEE8080 to the mice also restored the DEN-reduced activity and protein expression of hepatic antioxidant enzymes such as superoxide dismutase, glutathione peroxidase and catalase. In conclusion, GEE8080, a 6-shogaol-rich ginger extract, may enhance antioxidant defense mechanism through the induction of Nrf2 and HO-1 regulated by p38 MAPK and PI3k/Akt pathway in vitro and in vivo.

Exercise tames the wild side of the Myc network: a hypothesis

We propose that the well-documented therapeutic actions of repeated physical activities over human lifespan are mediated by the rapidly turning over proto-oncogenic Myc (myelocytomatosis) network of transcription factors. This transcription factor network is unique in utilizing promoter and epigenomic (acetylation/deacetylation, methylation/demethylation) mechanisms for controlling genes that include those encoding intermediary metabolism (the primary source of acetyl groups), mitochondrial functions and biogenesis, and coupling their expression with regulation of cell growth and proliferation. We further propose that remote functioning of the network occurs because there are two arms of this network, which consists of driver cells (e.g., working myocytes) that metabolize carbohydrates, fats, proteins, and oxygen and produce redox-modulating metabolites such as H₂O₂, NAD⁺, and lactate. The exercise-induced products represent autocrine, paracrine, or endocrine signals for target recipient cells (e.g., aortic endothelium, hepatocytes, and pancreatic β-cells) in which the metabolic signals are coupled with genomic networks and interorgan signaling is activated. And finally, we propose that lactate, the major metabolite released from working muscles and transported into recipient cells, links the two arms of the signaling pathway. Recently discovered contributions of the Myc network in stem cell development and maintenance further suggest that regular physical activity may prevent age-related diseases such as cardiovascular pathologies, cancers, diabetes, and neurological functions through prevention of stem cell dysfunctions and depletion with aging. Hence, regular physical activities may attenuate the various deleterious effects of the Myc network on health, the wild side of the Myc-network, through modulating transcription of genes associated with glucose and energy metabolism and maintain a healthy human status.

Genetic and cellular mechanisms regulating anterior foregut and esophageal development

Separation of the single anterior foregut tube into the esophagus and trachea involves cell proliferation and differentiation, as well as dynamic changes in cell-cell adhesion and migration. These biological processes are regulated and coordinated at multiple levels through the interplay of the epithelium and mesenchyme. Genetic studies and in vitro modeling have shed light on relevant regulatory networks that include a number of transcription factors and signaling pathways. These signaling molecules exhibit unique expression patterns and play specific functions in their respective territories before the separation process occurs. Disruption of regulatory networks inevitably leads to defective separation and malformation of the trachea and esophagus and results in the formation of a relatively common birth defect, esophageal atresia with or without tracheoesophageal fistula (EA/TEF). Significantly, some of the signaling pathways and transcription factors involved in anterior foregut separation continue to play important roles in the morphogenesis of the individual organs. In this review, we will focus on new findings related to these different developmental processes and discuss them in the context of developmental disorders or birth defects commonly seen in clinics.

Vitiligo-inducing phenols activate the unfolded protein response in melanocytes resulting in upregulation of IL6 and IL8

Vitiligo is characterized by depigmented skin patches due to loss of epidermal melanocytes. Oxidative stress may play a role in vitiligo onset, while autoimmunity contributes to disease progression. In this study we sought to identify mechanisms that link disease triggers and spreading of lesions. A hallmark of melanocytes at the periphery of vitiligo lesions is dilation of the endoplasmic reticulum (ER). We hypothesized that oxidative stress results in redox disruptions that extend to the ER, causing accumulation of misfolded peptides, which activates the unfolded protein response (UPR). We used 4-tertiary butyl phenol (4-TBP) and monobenzyl ether of hydroquinone (MBEH), known triggers of vitiligo. We show that expression of key UPR components, including the transcription factor X-box binding protein 1 (XBP1), are increased following exposure of melanocytes to phenols. XBP1 activation increases production of immune mediators interleukin-6 (IL6) and IL8. Co-treatment with XBP1 inhibitors reduced IL6 and IL8 production induced by phenols, while over-expression of XBP1 alone increased their expression. Thus, melanocytes themselves produce cytokines associated with activation of an immune response following exposure to chemical triggers of vitiligo. These results expand our understanding of the mechanisms underlying melanocyte loss in vitiligo and pathways linking environmental stressors and autoimmunity.

Staying cool in difficult times: mitochondrial dynamics, quality control and the stress response

One of the critical problems with the combustion of sugar and fat is the generation of cellular oxidation. The ongoing consumption of oxygen results in damage to lipids, protein and mtDNA, which must be repaired through essential pathways in mitochondrial quality control. It has long been established that intrinsic protease pathways within the matrix and intermembrane space actively degrade unfolded and oxidized mitochondrial proteins. However, more recent work into the field of quality control has established distinct roles for both mitochondrial fragmentation and hyperfusion in different aspects of quality control and survival. In addition, mitochondrial derived vesicles have recently been shown to carry cargo directly to the lysosome, adding further insight into the integration of mitochondrial dynamics in cellular homeostasis. This review will focus on the mechanisms and emerging questions concerning the links between mitochondrial dynamics and quality control. This article is part of a Special Issue entitled: Protein Import and Quality Control in Mitochondria and Plastids.

Mitochondrial- and endoplasmic reticulum-associated oxidative stress in Alzheimer's disease: from pathogenesis to biomarkers

Alzheimer's disease (AD) is the most common cause of dementia in the elderly, affecting several million of people worldwide. Pathological changes in the AD brain include the presence of amyloid plaques, neurofibrillary tangles, loss of neurons and synapses, and oxidative damage. These changes strongly associate with mitochondrial dysfunction and stress of the endoplasmic reticulum (ER). Mitochondrial dysfunction is intimately linked to the production of reactive oxygen species (ROS) and mitochondrial-driven apoptosis, which appear to be aggravated in the brain of AD patients. Concomitantly, mitochondria are closely associated with ER, and the deleterious crosstalk between both organelles has been shown to be involved in neuronal degeneration in AD. Stimuli that enhance expression of normal and/or folding-defective proteins activate an adaptive unfolded protein response (UPR) that, if unresolved, can cause apoptotic cell death. ER stress also induces the generation of ROS that, together with mitochondrial ROS and decreased activity of several antioxidant defenses, promotes chronic oxidative stress. In this paper we discuss the critical role of mitochondrial and ER dysfunction in oxidative injury in AD cellular and animal models, as well as in biological fluids from AD patients. Progress in developing peripheral and cerebrospinal fluid biomarkers related to oxidative stress will also be summarized.

The intersection between aging and cardiovascular disease

The average lifespan of humans is increasing, and with it the percentage of people entering the 65 and older age group is growing rapidly and will continue to do so in the next 20 years. Within this age group, cardiovascular disease will remain the leading cause of death, and the cost associated with treatment will continue to increase. Aging is an inevitable part of life and unfortunately poses the largest risk factor for cardiovascular disease. Although numerous studies in the cardiovascular field have considered both young and aged humans, there are still many unanswered questions as to how the genetic pathways that regulate aging in model organisms influence cardiovascular aging. Likewise, in the molecular biology of aging field, few studies fully assess the role of these aging pathways in cardiovascular health. Fortunately, this gap is beginning to close, and these two fields are merging together. We provide an overview of some of the key genes involved in regulating lifespan and health span, including sirtuins, AMP-activated protein kinase, mammalian target of rapamycin, and insulin-like growth factor 1 and their roles regulating cardiovascular health. We then discuss a series of review articles that will appear in succession and provide a more comprehensive analysis of studies carried out linking genes of aging and cardiovascular health, and perspectives of future directions of these two intimately linked fields.

E3 ubiquitin ligases in protein quality control mechanism

In living cells, polypeptide chains emerging from ribosomes and preexisting polypeptide chains face constant threat of misfolding and aggregation. To prevent protein aggregation and to fulfill their biological activity, generally, protein must fold into its proper three-dimensional structure throughout their lifetimes. Eukaryotic cell possesses a quality control (QC) system to contend the problem of protein misfolding and aggregation. Cells achieve this functional QC system with the help of molecular chaperones and ubiquitin-proteasome system (UPS). The well-conserved UPS regulates the stability of various proteins and maintains all essential cellular function through intracellular protein degradation. E3 ubiquitin ligase enzyme determines specificity for degradation of certain substrates via UPS. New emerging evidences have provided considerable information that various E3 ubiquitin ligases play a major role in cellular QC mechanism and principally designated as QC E3 ubiquitin ligases. Nevertheless, very little is known about how E3 ubiquitin ligase maintains QC mechanism against abnormal proteins under various stress conditions. Here in this review, we highlight and discuss the functions of various E3 ubiquitin ligases implicated in protein QC mechanism. Improving our knowledge about such processes may provide opportunities to modulate protein QC mechanism in age-of-onset diseases that are caused by protein aggregation.

Glutathione/thioredoxin systems modulate mitochondrial H2O2 emission: an experimental-computational study

The net emission of hydrogen peroxide (H(2)O(2)) from mitochondria results from the balance between reactive oxygen species (ROS) continuously generated in the respiratory chain and ROS scavenging. The relative contribution of the two major antioxidant systems in the mitochondrial matrix, glutathione (GSH) and thioredoxin (Trx), has not been assessed. In this paper, we examine this key question via combined experimental and theoretical approaches, using isolated heart mitochondria from mouse, rat, and guinea pig. As compared with untreated control mitochondria, selective inhibition of Trx reductase with auranofin along with depletion of GSH with 2,4-dinitrochlorobenzene led to a species-dependent increase in H(2)O(2) emission flux of 17, 11, and 6 fold in state 4 and 15, 7, and 8 fold in state 3 for mouse, rat, and guinea pig mitochondria, respectively. The maximal H(2)O(2) emission as a percentage of the total O(2) consumption flux was 11%/2.3% for mouse in states 4 and 3 followed by 2%/0.25% and 0.74%/0.29% in the rat and guinea pig, respectively. A minimal computational model accounting for the kinetics of GSH/Trx systems was developed and was able to simulate increase in H(2)O(2) emission fluxes when both scavenging systems were inhibited separately or together. Model simulations suggest that GSH/Trx systems act in concert. When the scavenging capacity of either one of them saturates during H(2)O(2) overload, they relieve each other until complete saturation, when maximal ROS emission occurs. Quantitatively, these results converge on the idea that GSH/Trx scavenging systems in mitochondria are both essential for keeping minimal levels of H(2)O(2) emission, especially during state 3 respiration, when the energetic output is maximal. This suggests that the very low levels of H(2)O(2) emission observed during forward electron transport in the respiratory chain are a result of the well-orchestrated actions of the two antioxidant systems working continuously to offset ROS production.

Suppression of the Nrf2-dependent antioxidant response by glucocorticoids and 11β-HSD1-mediated glucocorticoid activation in hepatic cells

Background

Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) is a key transcription factor regulating a plethora of detoxifying enzymes and antioxidant genes involved in drug metabolism and defence against oxidative stress. The glucocorticoid receptor (GR) is a ligand-induced transcription factor involved in the regulation of energy supply for metabolic needs to cope with various stressors. GR activity is controlled by glucocorticoids, which are synthesized in the adrenal glands and regenerated mainly in the liver from inactive cortisone by 11β-hydroxysteroid dehydrogenase-1 (11β-HSD1).

Methods and Principal Findings

Using transfected HEK-293 cells and hepatic H4IIE cells we show that glucocorticoids, activated by 11β-HSD1 and acting through GR, suppress the Nrf2-dependent antioxidant response. The expression of the marker genes NQO1, HMOX1 and GST2A was suppressed upon treatment of 11β-HSD1 expressing cells with cortisone, an effect that was reversed by 11β-HSD1 inhibitors. Furthermore, our results demonstrate that elevated glucocorticoids lowered the ability of cells to detoxify H₂O₂. Moreover, a comparison of gene expression in male and female rats revealed an opposite sexual dimorphism with an inverse relationship between 11β-HSD1 and Nrf2 target gene expression.

Conclusions

The results demonstrate a suppression of the cellular antioxidant defence capacity by glucocorticoids and suggest that elevated 11β-HSD1 activity may lead to impaired Nrf2-dependent antioxidant response. The gender-specific differences in hepatic expression levels of 11β-HSD1 and Nrf2 target genes and the impact of pharmacological inhibition of 11β-HSD1 on improving cellular capacity to cope with oxidative stress warrants further studies in vivo.