Induction of phospholipid hydroperoxide glutathione peroxidase in human polymorphonuclear neutrophils and HL60 cells stimulated with TNF-alpha

Inhibition of ferroptosis alleviates high-power microwave-induced myocardial injury

Background

The use of high-power microwave (HPM) in our daily live is becoming more and more widespread, but the safety has also caused our concern. And ferroptosis is a newly discovered modality that can regulate cell death in recent years. The aim of our study was to demonstrate whether ferroptosis is an important cause of myocardial injury caused by HPM. And whether myocardial injury caused by HPM can be alleviated by inhibiting ferroptosis.

Methods

We verified the extent of myocardial damage by different doses of HPM through in vivo and in vitro assays, respectively. In addition, GPX4 was knocked down and overexpressed in cardiac myocytes to verify the altered sensitivity of cardiac myocytes to HPM. Finally, the therapeutic effect of Fer-1 and tanshinoneIIA on myocardial injury caused by HPM was verified in in vivo and in vitro assays.

Results

We found that cardiac tissue and cardiomyocyte injury in mice gradually increased with increasing HPM dose, while ferroptosis markers were consistent with the injury trend. Gpx4 had an important role in ferroptosis in cardiomyocytes caused by HPM. Finally, tanshinoneIIA and Fer-1 could attenuate the damage of cardiac tissues and cardiomyocytes caused by HPM.

Conclusions

In conclusion, our study found that ferroptosis, a novel mode of cell death, is present in myocardial injury caused by HPM. Moreover, tanshinone, a drug already in clinical use, can significantly reduce myocardial injury caused by HPM, which is promising to provide new therapeutic ideas for myocardial injury caused by HPM.

Edaravone ameliorates depressive and anxiety-like behaviors via Sirt1/Nrf2/HO-1/Gpx4 pathway

Background

The inflammation and oxidative stress (OS) have been considered crucial components of the pathogenesis of depression. Edaravone (EDA), a free radical scavenger, processes strong biological activities including antioxidant, anti-inflammatory and neuroprotective properties. However, its role and potential molecular mechanisms in depression remain unclear. The present study aimed to investigate the antidepressant activity of EDA and its underlying mechanisms.

Methods

A chronic social defeat stress (CSDS) depression model was performed to explore whether EDA could produce antidepressant effects. Behaviors tests were carried out to examine depressive, anxiety-like and cognitive behaviors including social interaction (SI) test, sucrose preference test (SPT), open field test (OFT), elevated plus maze (EPM), novel object recognition (NOR), tail suspension test (TST) and forced swim test (FST). Hippocampal and medial prefrontal cortex (mPFC) tissues were collected for Nissl staining, immunofluorescence, targeted energy metabolomics analysis, enzyme-linked immunosorbent assay (ELISA), measurement of MDA, SOD, GSH, GSH-PX, T-AOC and transmission electron microscopy (TEM). Western blotting (WB) and quantitative real-time polymerase chain reaction (qRT-PCR) detected the Sirt1/Nrf2/HO-1/Gpx4 signaling pathway. EX527, a Sirt1 inhibitor and ML385, a Nrf2 inhibitor were injected intraperitoneally 30 min before EDA injection daily. Knockdown experiments were performed to determine the effects of Gpx4 on CSDS mice with EDA treatment by an adeno-associated virus (AAV) vector containing miRNAi (Gpx4)–EGFP infusion.

Results

The administrated of EDA dramatically ameliorated CSDS-induced depressive and anxiety-like behaviors. In addition, EDA notably attenuated neuronal loss, microglial activation, astrocyte dysfunction, oxidative stress damage, energy metabolism and pro-inflammatory cytokines activation in the hippocampus (Hip) and mPFC of CSDS-induced mice. Further examination indicated that the application of EDA after the CSDS model significantly increased the protein expressions of Sirt1, Nrf2, HO-1 and Gpx4 in the Hip. EX527 abolished the antidepressant effect of EDA as well as the protein levels of Nrf2, HO-1 and Gpx4. Similarly, ML385 reversed the antidepressant and anxiolytic effects of EDA via decreased expressions of HO-1 and Gpx4. In addition, Gpx4 knockdown in CSDS mice abolished EDA-generated efficacy on depressive and anxiety-like behaviors.

Conclusion

These findings suggest that EDA possesses potent antidepressant and anxiolytic properties through Sirt1/Nrf2/HO-1/Gpx4 axis and Gpx4-mediated ferroptosis may play a key role in this effect.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02400-6.

Selenium can regulate the differentiation and immune function of human dendritic cells

Selenium is an essential trace element that can regulate the function of immnue cells via selenoproteins. However, the effects of selenium on human dendritic cell (DCs) remain unclear. Thus, selenoprotein levels in monocytes, immature DCs (imDCs) and mature DCs (mDCs) treated with or without Na₂SeO₃ were evaluated using RT-PCR, and then the immune function of imDCs and mDCs was detected by flow cytometry, cell counting and the CCK8 assay. In addition, the effects of Se on cytokine and surface marker expression were investigated by RT-PCR. The results revealed different expression levels of selenoprotein in monocytes, imDCs and mDCs, and selenoproeins could be regulated by Se. Moreover, it was indicated that anti-phagocytic activity was improved by 0.1 µM Se, whereas it was suppressed by 0.2 µM Se in imDCs; The migration of imDCs and mDCs was improved by 0.1 µM Se, whereas their migration was inhibited by treatment with 0.05 or 0.2 µM Se; The mixed lymphocyte reaction of mDCs was improved by 0.1 µM Se, and it was inhibited by 0.05 and 0.2 µM Se. In addition, 0.1 µM Se improved the immune function of DCs through the regulation of CD80, CD86, IL12-p35 and IL12-p40. Wheres 0.05 and 0.2 µM Se impaired immune function of DCs by up-regulation of interleukin (IL-10) in imDCs and down-regulation of CD80, CD86, IL12-p35 and IL12-p40 in mDCs. In conclusion, 0.1 µM Se might improve the immune function of human DCs through selenoproteins.

Targeted reduction of cholesterol uptake in cholesterol-addicted lymphoma cells blocks turnover of oxidized lipids to cause ferroptosis

Normal human cells can either synthesize cholesterol or take it up from lipoproteins to meet their metabolic requirements. In some malignant cells, de novo cholesterol synthesis genes are transcriptionally silent or mutated, meaning that cholesterol uptake from lipoproteins is required for survival. Recent data suggest that lymphoma cells dependent upon lipoprotein-mediated cholesterol uptake are also subject to ferroptosis, an oxygen- and iron-dependent cell death mechanism triggered by accumulation of oxidized lipids in cell membranes unless the lipid hydroperoxidase, glutathione peroxidase 4 (GPX4), reduces these toxic lipid species. To study mechanisms linking cholesterol uptake with ferroptosis and determine the potential role of the high-density lipoprotein (HDL) receptor as a target for cholesterol depleting therapy, we treated lymphoma cell lines known to be sensitive to the reduction of cholesterol uptake with HDL-like nanoparticles (HDL NPs). HDL NPs are a cholesterol-poor ligand that binds to the receptor for cholesterol-rich HDLs, scavenger receptor type B1 (SCARB1). Our data reveal that HDL NP treatment activates a compensatory metabolic response in treated cells toward increased de novo cholesterol synthesis, which is accompanied by nearly complete reduction in expression of GPX4. As a result, oxidized membrane lipids accumulate, leading to cell death through a mechanism consistent with ferroptosis. We obtained similar results in vivo after systemic administration of HDL NPs in mouse lymphoma xenografts and in primary samples obtained from patients with lymphoma. In summary, targeting SCARB1 with HDL NPs in cholesterol uptake-addicted lymphoma cells abolishes GPX4, resulting in cancer cell death by a mechanism consistent with ferroptosis.

Regulatory Phenomena in the Glutathione Peroxidase Superfamily

Significance: The selenium-containing Glutathione peroxidases (GPxs)1-4 protect against oxidative challenge, inhibit inflammation and oxidant-induced regulated cell death. Recent Advances: GPx1 and GPx4 dampen phosphorylation cascades predominantly via prevention of inactivation of phosphatases by H₂O₂ or lipid hydroperoxides. GPx2 regulates the balance between regeneration and apoptotic cell shedding in the intestine. It inhibits inflammation-induced carcinogenesis in the gut but promotes growth of established cancers. GPx3 deficiency facilitates platelet aggregation likely via disinhibition of thromboxane biosynthesis. It is also considered a tumor suppressor. GPx4 is expressed in three different forms. The cytosolic form proved to inhibit interleukin-1-driven nuclear factor κB activation and leukotriene biosynthesis. Moreover, it is a key regulator of ferroptosis, because it reduces hydroperoxy groups of complex lipids and silences lipoxygenases. By alternate substrate use, the nuclear form contributes to chromatin compaction. Mitochondrial GPx4 forms the mitochondrial sheath of spermatozoa and, thus, guarantees male fertility. Out of the less characterized GPxs, the cysteine-containing GPx7 and GPx8 are unique in contributing to oxidative protein folding in the endoplasmic reticulum by reacting with protein isomerase as an alternate substrate. A yeast 2-Cysteine glutathione peroxidase equipped with CP and CR was reported to sense H₂O₂ for inducing an adaptive response. Critical Issues: Most of the findings compiled are derived from tissue culture and/or animal studies only. Their impact on human physiology is sometimes questionable. Future Directions: The expression of individual GPxs and GPx-dependent regulatory phenomena are to be further investigated, in particular in respect to human health.

Germination Improves the Polyphenolic Profile and Functional Value of Mung Bean (Vigna radiata L.)

The use of legumes as functional foods has gained increasing attention for the prevention and treatment of the so called non-communicable diseases that are highly prevalent worldwide. In this regard, biotechnological approaches for the enhancement of legumes' nutritional and functional value have been extensively employed. In the present study, the process of germination increased several parameters of mung bean (Vigna radiata L.) functionality, including extract yield, total phenolic content and in vitro antioxidant capacity. In addition, 3-day-germinated mung bean proved to be an interesting source of dietary essential minerals and exhibited a greater variety of polyphenolic compounds compared to raw mung bean. These properties resulted in enhanced cytoprotective features of the 3-day mung bean extracts against radical oxygen species in human colorectal (HT29) and monocyte (U937) cell lines. Moreover, the antiproliferative effects were tested in different colon cancer cell lines, T84 and drug-resistant HCT-18, as well as in a non-tumor colon CCD-18 line. Altogether, our results demonstrate that the germination process improves the mung bean's nutritional value and its potential as a functional food.

Selenium and selenoproteins in prostanoid metabolism and immunity

Selenium (Se) is an essential trace element that functions in the form of the 21st amino acid, selenocysteine (Sec) in a defined set of proteins. Se deficiency is associated with pathological conditions in humans and animals, where incorporation of Sec into selenoproteins is reduced along with their expression and catalytic activity. Supplementation of Se-deficient population with Se has shown health benefits suggesting the importance of Se in physiology. An interesting paradigm to explain, in part, the health benefits of Se stems from the observations that selenoprotein-dependent modulation of inflammation and efficient resolution of inflammation relies on mechanisms involving a group of bioactive lipid mediators, prostanoids, which orchestrate a concerted action toward maintenance and restoration of homeostatic immune responses. Such an effect involves the interaction of various immune cells with these lipid mediators where cellular redox gatekeeper functions of selenoproteins further aid in not only dampening inflammation, but also initiating an effective and active resolution process. Here we have summarized the current literature on the multifaceted roles of Se/selenoproteins in the regulation of these bioactive lipid mediators and their immunomodulatory effects.

Endomorphin-2- and Neurotensin- Based Chimeric Peptide Attenuates Airway Inflammation in Mouse Model of Nonallergic Asthma

We examined anti-inflammatory potency of hybrid peptide-PK20, composed of neurotensin (NT) and endomorphin-2 (EM-2) pharmacophores in a murine model of non-atopic asthma induced by skin sensitization with 2,4-dinitrofluorobenzene and intratracheal challenge of cognate hapten. Mice received intraperitoneally PK20, equimolar mixture of its structural elements (MIX), dexamethasone (DEX), or NaCl. Twenty-four hours following hapten challenge, the measurements of airway responsiveness to methacholine were taken. Bronchoalveolar lavage (BALF) and lungs were collected for further analyses. Treatment with PK20, similarly to dexamethasone, reduced infiltration of inflammatory cells, concentration of mouse mast cell protease, IL-1β, IL-12p40, IL-17A, CXCL1, RANTES in lungs and IL-1α, IL-2, IL-13, and TNF-α in BALF. Simple mixture of NT and EM-2 moieties was less potent. PK20, DEX, and MIX significantly decreased malondialdehyde level and secretory phospholipase 2 activity in lungs. Intensity of NF-κB immunoreactivity was diminished only after PK20 and DEX treatments. Neither PK20 nor mixture of its pharmacophores were as effective as DEX in alleviating airway hyperresponsiveness. PK20 effectively inhibited hapten-induced inflammation and mediator and signaling pathways in a manner seen with dexamethasone. Improved anti-inflammatory potency of the hybrid over the mixture of its moieties shows its preponderance and might pose a promising tool in modulating inflammation in asthma.

Differential acute effects of selenomethionine and sodium selenite on the severity of colitis

The European population is only suboptimally supplied with the essential trace element selenium. Such a selenium status is supposed to worsen colitis while colitis-suppressive effects were observed with adequate or supplemented amounts of both organic selenomethionine (SeMet) and inorganic sodium selenite. In order to better understand the effect of these selenocompounds on colitis development we examined colonic phenotypes of mice fed supplemented diets before the onset of colitis or during the acute phase. Colitis was induced by treating mice with 1% dextran sulfate sodium (DSS) for seven days. The selenium-enriched diets were either provided directly after weaning (long-term) or were given to mice with a suboptimal selenium status after DSS withdrawal (short-term). While long-term selenium supplementation had no effect on colitis development, short-term selenite supplementation, however, resulted in a more severe colitis. Colonic selenoprotein expression was maximized in all selenium-supplemented groups independent of the selenocompound or intervention time. This indicates that the short-term selenite effect appears to be independent from colonic selenoprotein expression. In conclusion, a selenite supplementation during acute colitis has no health benefits but may even aggravate the course of disease.

Binge drinking during adolescence disrupts Se homeostasis and its main hepatic selenoprotein expression

BACKGROUND

Binge drinking (BD) is the most common ethanol (EtOH) intake consumption model among teenagers, but little is known about its effects on the liver. During its hepatic metabolism, acute alcohol exposure produces a great amount of reactive oxygen species which contributes to alcohol-induced liver injury. Selenium (Se) plays a key role in antioxidant defense as it forms part of selenoproteins, such as the antioxidant glutathione peroxidases (GPxs) or the selenoprotein P (SelP), synthesized mainly in liver. Chronic EtOH consumption decreases both Se deposits and this tissue's antioxidant activity.

METHODS

Two BD administration routes (oral and intraperitoneal) were used in adolescent rats to analyze Se homeostasis; the main hepatic selenoproteins' expression: GPx1, GPx4, and SelP, and their biological roles related to oxidation. Their relationship with inflammatory processes was also determined by analyzing the expression of the transcriptional factor nuclear factor-kappa beta (NF-κB).

RESULTS

It has been demonstrated for the first time that BD in adolescents alters Se homeostasis regardless of the administration route employed, despite the fact that the BD oral group ingested less Se in diet. This decrease of Se in serum and liver is directly related to a decrease in serum GPx3 and hepatic GPx1 activity, contributing to the oxidative imbalance found. The depletion of Se detected in liver affects GPx1 expression and, surprisingly, GPx4 expression. This could be related to the lower expression of the transcriptional factor NF-κB in the liver, a key player in the regulation of inflammatory processes.

CONCLUSIONS

Due to the above, and to find whether a Se supplementation therapy improves these situations, it would be interesting to explore in more depth the relationship between Se, the high oxidation found, and the depressed immune response reported in BD adolescents.

The role of selenium in inflammation and immunity: from molecular mechanisms to therapeutic opportunities

Dietary selenium (]Se), mainly through its incorporation into selenoproteins, plays an important role in inflammation and immunity. Adequate levels of Se are important for initiating immunity, but they are also involved in regulating excessive immune responses and chronic inflammation. Evidence has emerged regarding roles for individual selenoproteins in regulating inflammation and immunity, and this has provided important insight into mechanisms by which Se influences these processes. Se deficiency has long been recognized to negatively impact immune cells during activation, differentiation, and proliferation. This is related to increased oxidative stress, but additional functions such as protein folding and calcium flux may also be impaired in immune cells under Se deficient conditions. Supplementing diets with above-adequate levels of Se can also impinge on immune cell function, with some types of inflammation and immunity particularly affected and sexually dimorphic effects of Se levels in some cases. In this comprehensive article, the roles of Se and individual selenoproteins in regulating immune cell signaling and function are discussed. Particular emphasis is given to how Se and selenoproteins are linked to redox signaling, oxidative burst, calcium flux, and the subsequent effector functions of immune cells. Data obtained from cell culture and animal models are reviewed and compared with those involving human physiology and pathophysiology, including the effects of Se levels on inflammatory or immune-related diseases including anti-viral immunity, autoimmunity, sepsis, allergic asthma, and chronic inflammatory disorders. Finally, the benefits and potential adverse effects of intervention with Se supplementation for various inflammatory or immune disorders are discussed.

Combined astaxanthin and fish oil supplementation improves glutathione-based redox balance in rat plasma and neutrophils

The present study aimed to investigate the effects of daily (45 days) intake of fish oil (FO; 10mg EPA/kg body weight (BW) and 7 mg DHA/kg BW) and/or natural ASTA (1mg ASTA/kg BW) on oxidative stress and functional indexes of neutrophils isolated from Wistar rats by monitoring superoxide (O(2)(-)), hydrogen peroxide (H(2)O(2)), and nitric oxide (NO()) production compared to the progression of auto-induced lipid peroxidation and Ca(2+) release in activated neutrophils. Furthermore, phagocytic capacity, antioxidant enzyme activities, glutathione-recycling system, and biomarkers of lipid and protein oxidation in neutrophils were compared to the redox status. Our results show evidence of the beneficial effects of FO+ASTA supplementation for immune competence based on the redox balance in plasma (significant increase in GSH-dependent reducing power), non-activated neutrophils (increased activity of the glutathione-recycling enzymes GPx and GR) and PMA-activated neutrophils (lower O(2)(-), H(2)O(2), and NO() generation, reduced membrane oxidation, but higher phagocytic activity). Combined application of ASTA and FO promoted hypolipidemic/hypocholesterolemic effects in plasma and resulted in increased phagocytic activity of activated neutrophils when compared with ASTA or FO applied alone. In PMA-activated neutrophils, ASTA was superior to FO in exerting antioxidant effects. The bulk of data reinforces the hypothesis that habitual consumption of marine fish (e.g. salmon, which is a natural source of both astaxanthin and fish oil) is beneficial to human health, in particular by improving immune response and lowering the risk of vascular and infectious diseases.

New Strategy of Functional Analysis of PHGPx Knockout Mice Model Using Transgenic Rescue Method and Cre-LoxP System

Phospholipid hydroperoxide glutathione peroxidase (PHGPx) is an intracellular antioxidant enzyme that directly reduces peroxidized phospholipids. PHGPx is transcribed from one gene into three types of mRNA, mitochondrial, non-mitochondrial and nucleolar PHGPx by alternative transcription. In this review, we focus on our recent experiments on the regulation of promoter activity of the types of PHGPx and on the novel strategy of functional analysis of a PHGPx knockout mice model using the transgenic rescue method and Cre-LoxP system. PHGPx is especially high in testis and spermatozoa. A deficiency is implicated in human infertility. We established spermatocyte-specific PHGPx knockout (KO) mice using a Cre-loxP system. Targeted disruption of all exons of the PHGPx gene in mice by homologous recombination caused embryonic lethality at 7.5 days post coitum. The PHGPx-loxP transgene rescued PHGPx KO mice from embryonic lethality. These rescued floxed PHGPx mice were mated with spermatocyte specific Cre expressing mice. All the spermatocyte-specific PHGPx KO male mice were infertile and displayed a significant decrease in the number of spermatozoa and significant reductions in forward motility by mitochondrial dysfunction of spermatozoa. These results demonstrate that depletion of PHGPx in spermatozoa may be one of the causes of male infertility in mice and humans.

Transcriptional regulation of mammalian selenoprotein expression

BACKGROUND

Selenoproteins contain the twenty-first amino acid, selenocysteine, and are involved in cellular defenses against oxidative damage, important metabolic and developmental pathways, and responses to environmental challenges. Elucidating the mechanisms regulating selenoprotein expression at the transcriptional level is a key to understanding how these mechanisms are called into play to respond to the changing environment.

METHODS

This review summarizes published studies on transcriptional regulation of selenoprotein genes, focused primarily on genes whose encoded protein functions are at least partially understood. This is followed by in silico analysis of predicted regulatory elements in selenoprotein genes, including those in the aforementioned category as well as the genes whose functions are not known.

RESULTS

Our findings reveal regulatory pathways common to many selenoprotein genes, including several involved in stress-responses. In addition, tissue-specific regulatory factors are implicated in regulating many selenoprotein genes.

CONCLUSIONS

These studies provide new insights into how selenoprotein genes respond to environmental and other challenges, and the roles these proteins play in allowing cells to adapt to these changes.

GENERAL SIGNIFICANCE

Elucidating the regulatory mechanisms affecting selenoprotein expression is essential for understanding their roles in human diseases, and for developing diagnostic and potential therapeutic approaches to address dysregulation of members of this gene family.

Src tyrosine kinases mediate activations of NF-kappaB and integrin signal during lipopolysaccharide-induced acute lung injury

Src tyrosine kinases (TKs) are signaling proteins involved in cell signaling pathways toward cytoskeletal, membrane and nuclear targets. In the present study, using a selective Src TK inhibitor, PP1, we investigated the roles of Src TKs in the key pulmonary responses, NF-kappaB activation, and integrin signaling during acute lung injury in BALB/C mice intratracheally treated with LPS. LPS resulted in c-Src phosphorylation in lung tissue and the phospho-c-Src was predominantly localized in recruited neutrophils and alveolar macrophages. PP1 inhibited LPS-induced increases in total protein content in bronchoalveolar lavage fluid, neutrophil recruitment, and increases in the production or activity of TNF-alpha and matrix metalloproteinase-9. PP1 also blocked LPS-induced NF-kappaB activation, and phosphorylation and degradation of IkappaB-alpha. The inhibition of NF-kappaB activation by PP1 correlated with a depression of LPS-induced integrin signaling, which included increases in the phosphorylations of integrin beta(3), and of the focal adhesion kinase (FAK) family members, FAK and Pyk2, in lung tissue, and reductions in the fibrinogen-binding activity of alveolar macrophages. Moreover, treatment with anti-alpha(v), anti-beta(3), or Arg-Gly-Asp-Ser (RGDS), inhibited LPS-induced NF-kappaB activation. Taken together, our findings suggest that Src TKs play a critical role in LPS-induced activations of NF-kappaB and integrin (alpha(v)beta(3)) signaling during acute lung injury. Therefore, Src TK inhibition may provide a potential means of ameliorating inflammatory cascade-associated lung injury.

Identification of a responsible promoter region and a key transcription factor, CCAAT/enhancer-binding protein epsilon, for up-regulation of PHGPx in HL60 cells stimulated with TNF alpha

In the present study we investigated promoter regions of the PHGPx [phospholipid hydroperoxide GPx (glutathione peroxidase)] gene and transcription factors involved in TNFalpha (tumour necrosis factor alpha)-induced up-regulation of PHGPx in non-differentiated HL60 cells. Non-differentiated HL60 cells displayed up-regulation of non-mitochondrial and mitochondrial PHGPx mRNA in response to TNFalpha stimulation. The promoter activity was up-regulated by TNFalpha stimulation in cells transfected with a luciferase reporter vector encoding the region from -282 to -123 of the human PHGPx gene compared with the non-stimulated control. The up-regulated promoter activity was effectively abrogated by a mutation in the C/EBP (CCAAT/enhancer-binding protein)-binding sequence in this region. ChIP (chromatin immunoprecipitation) assays demonstrated that C/EBPepsilon bound to the -247 to -34 region in HL60 cells, but C/EBPalpha, beta, gamma and delta did not. The binding of C/EBPepsilon to the promoter region was increased in HL60 cells stimulated with TNFalpha compared with that of the non-stimulated control. An increased binding of nuclear protein to the C/EBP-binding sequence was observed by EMSA (electrophoretic mobility-shift assay) in cells stimulated with TNFalpha, and it was inhibited by pre-treatment with an anti-C/EBPepsilon antibody, but not with other antibodies. The C/EBPepsilon mRNA was expressed in PMNs (polymorphonuclear cells), non-differentiated HL60 cells and neutrophil-like differentiated HL60 cells displaying TNFalpha-induced up-regulation of PHGPx mRNA, but not in macrophage-like differentiated HL60 cells, HEK-293 cells (human embryonic kidney-293 cells) and other cell lines exhibiting no up-regulation. The up-regulation of PHGPx mRNA, however, was detected in HEK-293 cells overexpressing C/EBPepsilon as a result of TNFalpha stimulation. These results indicate that C/EBPepsilon is a critical transcription factor in TNFalpha-induced up-regulation of PHGPx expression.

The cystine/cysteine cycle: a redox cycle regulating susceptibility versus resistance to cell death

The glutathione-dependent system is one of the key systems regulating cellular redox balance, and thus cell fate. Cysteine, typically present in its oxidized form cystine in the extracellular space, is regarded as the rate-limiting substrate for glutathione (GSH) synthesis. Cystine is transported into cells by the highly specific amino-acid antiporter system xc-. Since Burkitt's Lymphoma (BL) cells display limited uptake capacity for cystine, and are thus prone to oxidative stress-induced cell death, we stably expressed the substrate-specific subunit of system xc-, xCT, in HH514 BL cells. xCT-overexpressing cells became highly resistant to oxidative stress, particularly upon GSH depletion. Contrary to previous predictions, the increase of intracellular cysteine did not affect the cellular GSH pool, but concomitantly boosted extracellular cysteine concentrations. Even though cells were depleted of bulk GSH, xCT overexpression maintained cellular integrity by protecting against lipid peroxidation, a very early event in cell death progression. Our results show that system xc- protects against oxidative stress not by elevating intracellular GSH levels, but rather creates a reducing extracellular environment by driving a highly efficient cystine/cysteine redox cycle. Our findings show that the cystine/cysteine redox cycle by itself must be viewed as a discrete major regulator of cell survival.

From selenium to selenoproteins: synthesis, identity, and their role in human health

The requirement of the trace element selenium for life and its beneficial role in human health has been known for several decades. This is attributed to low molecular weight selenium compounds, as well as to its presence within at least 25 proteins, named selenoproteins, in the form of the amino acid selenocysteine (Sec). Incorporation of Sec into selenoproteins employs a unique mechanism that involves decoding of the UGA codon. This process requires multiple features such as the selenocysteine insertion sequence (SECIS) element and several protein factors including a specific elongation factor EFSec and the SECIS binding protein 2, SBP2. The function of most selenoproteins is currently unknown; however, thioredoxin reductases (TrxR), glutathione peroxidases (GPx) and thyroid hormone deiodinases (DIO) are well characterised selenoproteins involved in redox regulation of intracellular signalling, redox homeostasis and thyroid hormone metabolism. Recent evidence points to a role for selenium compounds as well as selenoproteins in the prevention of some forms of cancer. A number of clinical trials are either underway or being planned to examine the effects of selenium on cancer incidence. In this review we describe some of the recent progress in our understanding of the mechanism of selenoprotein synthesis, the role of selenoproteins in human health and disease and the therapeutic potential of some of these proteins.

Glutathione peroxidases and redox-regulated transcription factors

Analysis of the selenoproteome identified five glutathione peroxidases (GPxs) in mammals: cytosolic GPx (cGPx, GPx1), phospholipid hydroperoxide GPx (PHGPX, GPx4), plasma GPx (pGPX, GPx3), gastrointestinal GPx (GI-GPx, GPx2) and, in humans, GPx6, which is restricted to the olfactory system. GPxs reduce hydroperoxides to the corresponding alcohols by means of glutathione (GSH). They have long been considered to only act as antioxidant enzymes. Increasing evidence, however, suggests that nature has not created redundant GPxs just to detoxify hydroperoxides. cGPx clearly acts as an antioxidant, as convincingly demonstrated in GPx1-knockout mice. PHGPx specifically interferes with NF-kappaB activation by interleukin-1, reduces leukotriene and prostanoid biosynthesis, prevents COX-2 expression, and is indispensable for sperm maturation and embryogenesis. GI-GPx, which is not exclusively expressed in the gastrointestinal system, is upregulated in colon and skin cancers and in certain cultured cancer cells. GI-GPx is a target for Nrf2, and thus is part of the adaptive response by itself, while PHGPx might prevent cancer by interfering with inflammatory pathways. In conclusion, cGPx, PHGPx and GI-GPx have distinct roles, particularly in cellular defence mechanisms. Redox sensing and redox regulation of metabolic events have become attractive paradigms to unravel the specific and in part still enigmatic roles of GPxs.