Selenium regulation of the selenoprotein and nonselenoprotein transcriptomes in rodents

Processive Recoding and Metazoan Evolution of Selenoprotein P: Up to 132 UGAs in Molluscs

Selenoproteins typically contain a single selenocysteine, the 21st amino acid, encoded by a context-redefined UGA. However, human selenoprotein P (SelenoP) has a redox-functioning selenocysteine in its N-terminal domain and nine selenium transporter-functioning selenocysteines in its C-terminal domain. Here we show that diverse SelenoP genes are present across metazoa with highly variable numbers of Sec-UGAs, ranging from a single UGA in certain insects, to 9 in common spider, and up to 132 in bivalve molluscs. SelenoP genes were shaped by a dynamic evolutionary process linked to selenium usage. Gene evolution featured modular expansions of an ancestral multi-Sec domain, which led to particularly Sec-rich SelenoP proteins in many aquatic organisms. We focused on molluscs, and chose Pacific oyster Magallana gigas as experimental model. We show that oyster SelenoP mRNA with 46 UGAs is translated full-length in vivo. Ribosome profiling indicates that selenocysteine specification occurs with ∼5% efficiency at UGA1 and approaches 100% efficiency at distal 3' UGAs. We report genetic elements relevant to its expression, including a leader open reading frame and an RNA structure overlapping the initiation codon that modulates ribosome progression in a selenium-dependent manner. Unlike their mammalian counterparts, the two SECIS elements in oyster SelenoP (3'UTR recoding elements) do not show functional differentiation in vitro. Oysters can increase their tissue selenium level up to 50-fold upon supplementation, which also results in extensive changes in selenoprotein expression.

Bioefficacy of hydroxy-selenomethionine as a selenium supplement in pregnant dairy heifers and on the selenium status of their calves

This study aimed to determine the effects of supplementing pregnant heifers with the organic selenium (Se) source 2-hydroxy-4-methylselenobutanoic acid (HMSeBA) during the last 8 wk of pregnancy on dam and calf Se status. A total of 42 in-calf heifers were recruited to the study and randomly allocated to 1 of 3 treatments; a negative control (Con), sodium selenite (NaSe), or HMSeBA. Animals were blocked by body weight, body condition score, and expected calving date before treatment allocation. Following enrollment, all animals underwent a 7-wk wash-out period, after which they received their respective supplements, top-dressed daily onto a basal diet for the last 8 wk of pregnancy. Heifer blood samples were taken at weekly intervals from enrollment until 2 wk before expected calving date and as soon as possible after calving for determination of whole-blood glutathione peroxidase activity (GSH-Px) and plasma Se and malondialdehyde (MDA) concentrations. Selenized AA were determined in plasma samples taken at 3 wk precalving. A colostrum sample was taken as close to parturition as possible for determination of colostrum total Se, selenized AA, and IgG concentration. Calves were blood sampled as close to birth as possible for determination of whole-blood GSH-Px activity and plasma Se and MDA concentrations. Differences in whole-blood GSH-Px activity did not become apparent until calving; GSH-Px activity was lowest in Con heifers but similar between NaSe and HMSeBA heifers. Plasma Se was lowest in unsupplemented heifers and greatest in those supplemented with HMSeBA; this was attributable to greater selenomethionine concentrations in the plasma of HMSeBA heifers. Colostrum Se was lowest in Con heifers and greatest in HMSeBA heifers. The greater Se concentration of HMSeBA heifers was attributable to a greater proportion of total Se comprising selenocysteine; the reason for this is not known. There was no effect of supplementation on colostrum IgG concentration. Plasma Se was lowest in calves born to Con heifers and greatest in those born to HMSeBA heifers. There were no effects of treatment on calf whole-blood GSH-Px activity or plasma MDA concentration. The enhanced Se status associated with HMSeBA supplementation is likely a consequence of selenomethionine supply and may confer benefits to both the dam and her calf postpartum.

Prioritized brain selenium retention and selenoprotein expression: Nutritional insights into Parkinson's disease

Selenium (Se), an essential trace mineral, confers its physiological functions mainly through selenoproteins, most of which are oxidoreductases. Results from animal, epidemiological, and human genetic studies link Parkinson's disease to Se and certain selenoproteins. Parkinson's disease is characterized by multiple motor and non-motor symptoms that are difficult to diagnose at early stages of the pathogenesis. While irreversible, degenerative and age-related, the onset of Parkinson's disease may be delayed through proper dietary and environmental controls. One particular attribute of Se biology is that brain has the highest priority to receive and retain this nutrient even in Se deficiency. Thus, brain Se deficiency is rare; however, a strong body of recent evidence implicates selenoprotein dysfunction in Parkinson's disease. Direct and indirect evidence from mouse models implicate selenoprotein T, glutathione peroxidase 1, selenoprotein P and glutathione peroxidase 4 in counteracting Parkinson's disease through Se transportation to the brain and reduced oxidative stress. It is of future interest to further characterize the full selenoproteomes in various types of brain cells and elucidate the mechanism of their actions in Parkinson's disease.

The Thioredoxin-Like Family of Selenoproteins: Implications in Aging and Age-Related Degeneration

The thioredoxin-like (Rdx) family proteins contain four selenoproteins (selenoprotein H, SELENOH; selenoprotein T, SELENOT; selenoprotein V, SELENOV; selenoprotein W, SELENOW) and a nonselenoprotein Rdx12. They share a CxxU or a CxxC (C, cysteine; x, any amino acid; U, selenocysteine) motif and a stretch of eGxFEI(V) sequence. From the evolutionary perspective, SELENOW and SELENOV are clustered together and SELENOH and SELENOT are in another branch. Selenoproteins in the Rdx family exhibit tissue- and organelle-specific distribution and are differentially influenced in response to selenium deficiency. While SELENOH is nucleus-exclusive, SELENOT resides mainly in endoplasmic reticulum and SELENOW in cytosol. SELENOV is expressed essentially only in the testes with unknown cellular localization. SELENOH and SELENOW are more sensitive than SELENOT and SELENOV to selenium deficiency. While physiological functions of the Rdx family of selenoproteins are not fully understand, results from animal models demonstrated that (1) brain-specific SELENOT knockout mice are susceptible to 1-methyl-4-phenylpyridinium-induced Parkinson's disease in association with redox imbalance and (2) adult zebrafishes with heterozygous SELENOH knockout are prone to dimethylbenzanthracene-induced tumorigenesis together with increased DNA damage and oxidative stress. Further animal and human studies are needed to fully understand physiological roles of the Rdx family of selenoproteins in redox regulation, genome maintenance, aging, and age-related degeneration.

Effects of dietary sodium selenite and organic selenium sources on immune and inflammatory responses and selenium deposition in growing pigs

The study was conducted to compare effects of different dietary Se sources (sodium selenite [NaSe], Se-enriched yeast [Se yeast] or L-selenomethionine [SeMet]) and one Se-deficient control diet on the expression of selected genes, hematological and clinical biochemical parameters, and muscle morphology in two parallel trials with finisher pigs. Se concentrations in blood plasma and tissues were also monitored. From the pigs in one of the parallel groups, muscle samples obtained from Musculus longissimus dorsi (LD) before and during the trial were examined. The pigs in the other parallel group were challenged once with lipopolysaccharide (LPS) intravenously. Transcriptional analyses of LD showed that selenogenes SelenoW and H were higher expressed in pigs fed Se-supplemented diets compared with control. Furthermore, the expression of interferon gamma and cyclooxygenase 2 was lower in the Se-supplemented pigs versus control. In whole blood samples prior to LPS, SelenoN, SelenoS and thioredoxin reductase 1 were higher expressed in pigs fed NaSe supplemented feed compared with the other groups, possibly indicating a higher level of oxidative stress. After LPS exposure glutathione peroxidase 1 and SelenoN were more reduced in pigs fed NaSe compared with pigs fed organic Se. Products of most above-mentioned genes are intertwined with the oxidant-antioxidant system. No significant effects of Se-source were found on hematologic parameters or microscopic anatomy. The Se-concentrations in various skeletal muscles and heart muscle were significantly different between the groups, with highest concentrations in pigs fed SeMet, followed by those fed Se yeast, NaSe, and control diet. Consistent with previous reports our results indicate that dietary Se at adequate levels can support the body's antioxidant system. Our results indicate that muscle fibers of pigs fed organic Se are less vulnerable to oxidative stress compared with the other groups.

Evolution, regulation, and function of porcine selenogenome

Much less research on regulation and function of selenoproteins has been conducted in domestic pigs than in rodents or humans, although pigs are an excellent model of human nutrition and medicine and pork is a widely consumed meat in the world. Phylogenetically, the 25 identified porcine selenoproteins fell into two primitive groups, and might be further divided into three parallel branches. Despite a high similarity to that of humans and rodents, the porcine selenoproteome exhibited the closest evolutionary relationship with that of sheep and cattle among eight domestic species. Expression (mRNA, protein, and/or enzyme activity) of 2/3 of the 25 porcine selenoproteins in various tissues of pigs was affected by dietary Se intakes, and 14 of them showed responses to a high fat diet. When dietary Se deficiency mainly down-regulated the expression of selected selenoproteins, dietary Se excess exerted rather diverse effects on their expression. Overdosing pigs with dietary Se induced hyperinsulinemia, along with lipid accumulation and protein increase, in the liver and muscle by affecting key genes and(or) proteins involved in the metabolisms of glucose, lipid, and protein. In conclusion, expression of porcine selenoproteins was highly responsive to dietary Se and fat intakes, and was involved in body glucose, lipid, and protein metabolism as those of rodents and humans.

Beneficial and paradoxical roles of selenium at nutritional levels of intake in healthspan and longevity

Accumulation of genome and macromolecule damage is a hallmark of aging, age-associated degeneration, and genome instability syndromes. Although processes of aging are irreversible, they can be modulated by genome maintenance pathways and environmental factors such as diet. Selenium (Se) confers its physiological functions mainly through selenoproteins, but Se compounds and other proteins that incorporate Se nonspecifically also impact optimal health. Bruce Ames proposed that the aging process could be mitigated by a subset of low-hierarchy selenoproteins whose levels are preferentially reduced in response to Se deficiency. Consistent with this notion, results from two selenotranscriptomic studies collectively implicate three low-hierarchy selenoproteins in age or senescence. Experimental evidence generally supports beneficial roles of selenoproteins in the protection against damage accumulation and redox imbalance, but some selenoproteins have also been reported to unexpectedly display harmful functions under sporadic conditions. While longevity and healthspan are usually thought to be projected in parallel, emerging evidence suggests a trade-off between longevity promotion and healthspan deterioration with damage accumulation. We propose that longevity promotion under conditions of Se deficiency may be attributed to 1) stress-response hormesis, an advantageous event of resistance to toxic chemicals at low doses; 2) reduced expression of selenoproteins with paradoxical functions to a lesser extent. In particular, selenoprotein H is an evolutionally conserved nuclear selenoprotein postulated to confer Se functions in redox regulation, genome maintenance, and senescence. This review highlights the need to pinpoint roles of specific selenoproteins and Se compounds in healthspan and lifespan for a better understanding of Se contribution at nutritional levels of intake to healthy aging.

Selenium at the redox interface of the genome, metabolome and exposome

Selenium (Se) is a redox-active environmental mineral that is converted to only a small number of metabolites and required for a relatively small number of mammalian enzymes. Despite this, dietary and environmental Se has extensive impact on every layer of omics space. This highlights a need for global network response structures to provide reference for targeted, hypothesis-driven Se research. In this review, we survey the Se research literature from the perspective of the responsive physical and chemical barrier between an organism (functional genome) and its environment (exposome), which we have previously termed the redox interface. Recent advances in metabolomics allow molecular phenotyping of the integrated genome-metabolome-exposome structure. Use of metabolomics with transcriptomics to map functional network responses to supplemental Se in mice revealed complex network responses linked to dyslipidemia and weight gain. Central metabolic hubs in the network structure in liver were not directly linked to transcripts for selenoproteins but were, instead, linked to transcripts for glucose transport and fatty acid β-oxidation. The experimental results confirm the survey of research literature in showing that Se interacts with the functional genome through a complex network response structure. The results imply that systematic application of data-driven integrated omics methods to models with controlled Se exposure could disentangle health benefits and risks from Se exposures and also serve more broadly as an experimental paradigm for exposome research.

Role of glutathione peroxidase 1 in glucose and lipid metabolism-related diseases

Glutathione peroxidase 1 (GPX1) is a selenium-dependent enzyme that reduces intracellular hydrogen peroxide and lipid peroxides. While past research explored regulations of gene expression and biochemical function of this selenoperoxidase, GPX1 has recently been implicated in the onset and development of chronic diseases. Clinical data have shown associations of human GPX1 gene variants with elevated risks of diabetes. Knockout and overexpression of Gpx1 in mice may induce types 1 and 2 diabetes-like phenotypes, respectively. This review assembles the latest advances in this new field of selenium biology, and attempts to postulate signal and molecular mechanisms mediating the role of GPX1 in glucose and lipid metabolism-related diseases. Potential therapies by harnessing the beneficial effects of this ubiquitous redox-modulating enzyme are briefly discussed.

Selenium-Related Transcriptional Regulation of Gene Expression

The selenium content of the body is known to control the expression levels of numerous genes, both so-called selenoproteins and non-selenoproteins. Selenium is a trace element essential to human health, and its deficiency is related to, for instance, cardiovascular and myodegenerative diseases, infertility and osteochondropathy called Kashin–Beck disease. It is incorporated as selenocysteine to the selenoproteins, which protect against reactive oxygen and nitrogen species. They also participate in the activation of the thyroid hormone, and play a role in immune system functioning. The synthesis and incorporation of selenocysteine occurs via a special mechanism, which differs from the one used for standard amino acids. The codon for selenocysteine is a regular in-frame stop codon, which can be passed by a specific complex machinery participating in translation elongation and termination. This includes a presence of selenocysteine insertion sequence (SECIS) in the 3′-untranslated part of the selenoprotein mRNAs. Nonsense-mediated decay is involved in the regulation of the selenoprotein mRNA levels, but other mechanisms are also possible. Recent transcriptional analyses of messenger RNAs, microRNAs and long non-coding RNAs combined with proteomic data of samples from Keshan and Kashin–Beck disease patients have identified new possible cellular pathways related to transcriptional regulation by selenium.

A Quantitative Chemoproteomic Platform to Monitor Selenocysteine Reactivity within a Complex Proteome

Mammalian selenocysteine (Sec)-containing proteins, selenoproteins, are important to (patho)physiological processes, including redox homeostasis. Sec residues have been recalcitrant to mass spectrometry-based chemoproteomic methods that enrich for reactive cysteine (Cys) residues with electrophilic chemical probes, despite confirmed reactivity of Sec with these electrophiles. Highly abundant Cys peptides likely suppress low-abundant Sec peptides. By exploiting the decreased pK_a of Sec relative to Cys, we have developed a chemoproteomic platform that relies on low pH (pH 5.75) electrophile labeling, reducing Cys reactivity and enhancing identification of Sec-containing peptides across mouse tissues and cell lines. The utility of this Sec-profiling platform is underscored by evaluation of the selectivity of auranofin, an inhibitor of the selenoprotein, thioredoxin reductase, against both reactive Cys- and Sec-containing proteins. Platform limitations pertain to the non-physiological low-pH conditions that could perturb protein structure and function. Future work necessitates the discovery of Sec-selective electrophiles that function at physiological pH.

Selenium-Dependent Antioxidant Enzymes: Actions and Properties of Selenoproteins

Unlike other essential trace elements that interact with proteins in the form of cofactors, selenium (Se) becomes co-translationally incorporated into the polypeptide chain as part of 21st naturally occurring amino acid, selenocysteine (Sec), encoded by the UGA codon. Any protein that includes Sec in its polypeptide chain is defined as selenoprotein. Members of the selenoproteins family exert various functions and their synthesis depends on specific cofactors and on dietary Se. The Se intake in productive animals such as chickens affect nutrient utilization, production performances, antioxidative status and responses of the immune system. Although several functions of selenoproteins are unknown, many disorders are related to alterations in selenoprotein expression or activity. Selenium insufficiency and polymorphisms or mutations in selenoproteins' genes and synthesis cofactors are involved in the pathophysiology of many diseases, including cardiovascular disorders, immune dysfunctions, cancer, muscle and bone disorders, endocrine functions and neurological disorders. Finally, heavy metal poisoning decreases mRNA levels of selenoproteins and increases mRNA levels of inflammatory factors, underlying the antagonistic effect of Se. This review is an update on Se dependent antioxidant enzymes, presenting the current state of the art and is focusing on results obtained mainly in chicken.

Translation regulation of mammalian selenoproteins

BACKGROUND

Interest in selenium research has considerably grown over the last decades owing to the association of selenium deficiencies with an increased risk of several human diseases, including cancers, cardiovascular disorders and infectious diseases. The discovery of a genetically encoded 21^st amino acid, selenocysteine, is a fascinating breakthrough in molecular biology as it is the first addition to the genetic code deciphered in the 1960s. Selenocysteine is a structural and functional analog of cysteine, where selenium replaces sulfur, and its presence is critical for the catalytic activity of selenoproteins.

SCOPE OF REVIEW

The insertion of selenocysteine is a non-canonical translational event, based on the recoding of a UGA codon in selenoprotein mRNAs, normally used as a stop codon in other cellular mRNAs. Two RNA molecules and associated partners are crucial components of the selenocysteine insertion machinery, the Sec-tRNA^[Ser]Sec devoted to UGA codon recognition and the SECIS elements located in the 3'UTR of selenoprotein mRNAs.

MAJOR CONCLUSIONS

The translational UGA recoding event is a limiting stage of selenoprotein expression and its efficiency is regulated by several factors.

GENERAL SIGNIFICANCE

The control of selenoproteome expression is crucial for redox homeostasis and antioxidant defense of mammalian organisms. In this review, we summarize current knowledge on the co-translational insertion of selenocysteine into selenoproteins, and its layers of regulation.

Selenium Supplementation Alters Hepatic Energy and Fatty Acid Metabolism in Mice

Background

Human and animal studies have raised concerns that supplemental selenium can increase the risk of metabolic disorders, but underlying mechanisms are unclear.

Objective

We used an integrated transcriptome and metabolome analysis of liver to test for functional pathway and network responses to supplemental selenium in mice.

Methods

Male mice (8-wk-old, C57BL/6J) fed a standard diet (0.41 ppm Se) were given selenium (Na2SeO4, 20 μmol/L) or vehicle (drinking water) for 16 wk. Livers were analyzed for selenium concentration, activity of selenoproteins, reduced glutathione (GSH) redox state, gene expression, and high-resolution metabolomics. Transcriptomic and nontargeted metabolomic data were analyzed with biostatistics, bioinformatics, pathway enrichment analysis, and combined transcriptome-metabolome-wide association study (TMWAS).

Results

Mice supplemented with selenium had greater body mass gain from baseline to 16 wk (55% ± 5%) compared with controls (40% ± 3%) (P < 0.05); however, no difference was observed in liver selenium content, selenoenzyme transcripts, or enzyme activity. Selenium was higher in the heart, kidney, and urine of mice supplemented with selenium. Gene enrichment analysis showed that supplemental selenium altered pathways of lipid and energy metabolism. Integrated transcriptome and metabolome network analysis showed 2 major gene-metabolite clusters, 1 centered on the transcript for the bidirectional glucose transporter 2 (Glut2) and the other centered on the transcripts for carnitine-palmitoyl transferase 2 (Cpt2) and acetyl-CoA acyltransferase (Acaa1). Pathway analysis showed that highly associated metabolites (P < 0.05) were enriched in fatty acid metabolism and bile acid biosynthesis, including acylcarnitines, triglycerides and glycerophospholipids, long-chain acyl-coenzyme As, phosphatidylcholines, and sterols. TMWAS of body weight gain confirmed changes in the same pathways.

Conclusions

Supplemental selenium in mice alters hepatic fatty acid and energy metabolism and causes increases in body mass. A lack of effect on hepatic selenium content suggests that signaling involves an extrahepatic mechanism.

Selenium-regulated hierarchy of human selenoproteome in cancerous and immortalized cells lines

BACKGROUND

Selenoproteins (25 genes in human) co-translationally incorporate selenocysteine using a UGA codon, normally used as a stop signal. The human selenoproteome is primarily regulated by selenium bioavailability with a tissue-specific hierarchy.

METHODS

We investigated the hierarchy of selenoprotein expression in response to selenium concentration variation in four cell lines originating from kidney (HEK293, immortalized), prostate (LNCaP, cancer), skin (HaCaT, immortalized) and liver (HepG2, cancer), using complementary analytical methods. We performed (i) enzymatic activity, (ii) RT-qPCR, (iii) immuno-detection, (iv) selenium-specific mass spectrometric detection after non-radioactive ⁷⁶Se labeling of selenoproteins, and (v) luciferase-based reporter constructs in various cell extracts.

RESULTS

We characterized cell-line specific alterations of the selenoproteome in response to selenium variation that, in most of the cases, resulted from a translational control of gene expression. We established that UGA-selenocysteine recoding efficiency, which depends on the nature of the SECIS element, dictates the response to selenium variation.

CONCLUSIONS

We characterized that selenoprotein hierarchy is cell-line specific with conserved features. This analysis should be done prior to any experiments in a novel cell line.

GENERAL SIGNIFICANCE

We reported a strategy based on complementary methods to evaluate selenoproteome regulation in human cells in culture.

Selenium supplementation prevents metabolic and transcriptomic responses to cadmium in mouse lung

BACKGROUND

The protective effect of selenium (Se) on cadmium (Cd) toxicity is well documented, but underlying mechanisms are unclear.

METHODS

Male mice fed standard diet were given Cd (CdCl₂, 18 μmol/L) in drinking water with or without Se (Na₂SeO_4, 20 μmol/L) for 16 weeks. Lungs were analyzed for Cd concentration, transcriptomics and metabolomics. Data were analyzed with biostatistics, bioinformatics, pathway enrichment analysis, and combined transcriptome-metabolome-wide association study.

RESULTS

Mice treated with Cd had higher lung Cd content (1.7 ± 0.4 pmol/mg protein) than control mice (0.8 ± 0.3 pmol/mg protein) or mice treated with Cd and Se (0.4 ± 0.1 pmol/mg protein). Gene set enrichment analysis of transcriptomics data showed that Se prevented Cd effects on inflammatory and myogenesis genes and diminished Cd effects on several other pathways. Similarly, Se prevented Cd-disrupted metabolic pathways in amino acid metabolism and urea cycle. Integrated transcriptome and metabolome network analysis showed that Cd treatment had a network structure with fewer gene-metabolite clusters compared to control. Centrality measurements showed that Se counteracted changes in a group of Cd-responsive genes including Zdhhc11, (protein-cysteine S-palmitoyltransferase), Ighg1 (immunoglobulin heavy constant gamma-1) and associated changes in metabolite concentrations.

CONCLUSION

Co-administration of Se with Cd prevented Cd increase in lung and prevented Cd-associated pathway and network responses of the transcriptome and metabolome. Se protection against Cd toxicity in lung involves complex systems responses.

GENERAL SIGNIFICANCE

Environmental Cd stimulates proinflammatory and profibrotic signaling. The present results indicate that dietary or supplemental Se could be useful to mitigate Cd toxicity.

Regulation and function of avian selenogenome

BACKGROUND

Selenium (Se) is an essential micronutrient required by avian species. Dietary Se/vitamin E deficiency induces three classical diseases in chicks: exudative diathesis, nutritional pancreatic atrophy, and nutritional muscular dystrophy.

SCOPE OF REVIEW

This review is to summarize and analyze the evolution, regulation, and function of avian selenogenome and selenoproteome and their relationship with the three classical Se/vitamin E deficiency diseases.

MAJOR CONCLUSIONS

There are 24 selenoproteins confirmed in chicks, with two avian-specific members (SELENOU and SELENOP2) and two missing mammalian members (GPX6 and SELENOV). There are two forms of SELENOP containing 1 or 13 selenocysteine residues. In addition, a Gallus gallus gene was conjectured to be the counterpart of the human SEPHS2. Expression of selenoprotein genes in the liver, pancreas, and muscle of chicks seemed to be highly responsive to dietary Se changes. Pathogeneses of the Se/vitamin E deficient diseases in the chicks were likely produced by missing functions of selected selenoproteins in regulating cellular and tissue redox balance and inhibiting oxidative/reductive stress-induced cell death.

GENERAL SIGNIFICANCE

Gene knockout models, similar to those of rodents, will help characterize the precise functions of avian selenoproteins and their comparisons with those of mammalian species.

Effects of Selenium Supplementation on the Diabetic Condition Depend on the Baseline Selenium Status in KKAy Mice

Oxidative stress in obesity leads to insulin resistance in type 2 diabetes. Some selenoproteins possess antioxidant properties, suggesting that selenium (Se) may protect against type 2 diabetes; however, evidence from epidemiological studies is contradictory. We hypothesized that Se status before supplementation (baseline) contributes to the supplementation outcome. This study aimed to clarify the influence of baseline Se status on the effect of Se supplementation on the diabetic condition. Six-week-old KKAy mice were fed a diet without supplemental Se or with 0.1 ppm Se in the form of L-selenomethionine (SeM) for 2 weeks to create low-Se and sufficient-Se baseline statuses, respectively. For the next 4 weeks, low-Se mice were given a SeM (0.5 ppm Se)-supplemented diet, and sufficient-Se mice were given either a SeM (0.5 ppm Se)- or sodium selenite (0.5 ppm Se)-supplemented diet; control groups continued on baseline diets. Serum Se concentrations, glutathione peroxidase (GPx) activities, adiponectin levels, glucose tolerance, and insulin sensitivity were analyzed. All mice became diabetic during the 2-week baseline induction period. At the end of the supplementation period, Se-receiving groups demonstrated significantly higher Se concentrations and GPx activities than their respective controls. Sufficient-Se mice receiving SeM had lower blood glucose levels and better insulin sensitivity than control and sodium selenite-receiving mice, whereas low-Se mice receiving SeM showed no such improvements compared with their controls. Our results suggest that Se supplementation in the form of SeM may help prevent type 2 diabetes aggravation in people taking the 55 μg/day Se recommended dietary allowance.

Selenium requirements based on muscle and kidney selenoprotein enzyme activity and transcript expression in the turkey poult (Meleagris gallopavo)

The current NRC selenium (Se) requirement for turkeys is 0.2 μg Se/g diet. We previously fed turkey poults a Se-deficient diet (0.005 μg Se/g) supplemented with 10 graded levels of Se (0, 0.025, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.75, 1.0 μg Se/g as Na2SeO3, 5/treatment) for 4 wk, and found that the minimum dietary Se requirement was 0.3 μg Se/g based on selenoprotein enzyme activity in blood, liver, gizzard and pancreas. Because the turkey is primarily a production animal, we expanded this analysis to kidney, heart, breast and thigh. Se concentrations in Se-deficient poults were 5.0, 9.8, 33, and 15% of levels in poults fed 0.4 μg Se/g in liver, kidney, thigh and breast, respectively. Increasing Se supplementation resulted in hyperbolic response curves for all tissues; breakpoint analysis indicated minimum Se requirements of 0.34-0.36 μg Se/g based on tissue Se levels in liver, kidney and thigh. Similarly, GPX1 activity in muscle tissues and kidney responded hyperbolically to increasing dietary Se, reaching well-defined plateaus with breakpoints at 0.30-0.36 μg Se/g. Minimum Se requirements based on GPX4 activity were 0.30-0.32 μg Se/g for breast and thigh. Selenoprotein transcript expression decreased significantly in Se deficiency for only 2, 3, 5, and 6 mRNA in breast, thigh, heart, and kidney, respectively, out of 24 known avian selenoproteins. Se response curves for regulated selenoprotein transcripts were hyperbolic, and reached well-defined plateaus with breakpoints in a narrow range of 0.08-0.19 μg Se/g. No selenoprotein transcript was altered by supernutritional Se. In summary, these results clearly indicate that the NRC dietary Se requirement should be raised to 0.4 μg Se/g, at least for poults, to meet the nutritional needs of the young turkey. The Se response curve plateaus further show that limits for turkey supplementation with selenite could safely be raised to 0.5 μg Se/g diet.

Selenoprotein P-neutralizing antibodies improve insulin secretion and glucose sensitivity in type 2 diabetes mouse models

Selenoprotein P (SeP) functions as a selenium (Se)-supply protein. SeP is identified as a hepatokine, promoting insulin resistance in type 2 diabetes. Thus, the suppression of Se-supply activity of SeP might improve glucose metabolism. Here, we develop an anti-human SeP monoclonal antibody AE2 as with neutralizing activity against SeP. Administration of AE2 to mice significantly improves glucose intolerance and insulin resistance that are induced by human SeP administration. Furthermore, excess SeP administration significantly decreases pancreas insulin levels and high glucose-induced insulin secretion, which are improved by AE2 administration. Epitope mapping reveals that AE2 recognizes a region of human SeP adjacent to the first histidine-rich region (FHR). A polyclonal antibody against the mouse SeP FHR improves glucose intolerance and insulin secretion in a mouse model of diabetes. This report describes a novel molecular strategy for the development of type 2 diabetes therapeutics targeting SeP.

Selenoprotein P is secreted by the liver and when present in excess it promotes development of type 2 diabetes. Here the authors develop neutralizing antibodies to target human and mouse selenoprotein P, and show that they improve insulin secretion and glucose tolerance in mouse models.

Human selenoprotein P and S variant mRNAs with different numbers of SECIS elements and inferences from mutant mice of the roles of multiple SECIS elements

Dynamic redefinition of the 10 UGAs in human and mouse selenoprotein P (Sepp1) mRNAs to specify selenocysteine instead of termination involves two 3' UTR structural elements (SECIS) and is regulated by selenium availability. In addition to the previously known human Sepp1 mRNA poly(A) addition site just 3' of SECIS 2, two further sites were identified with one resulting in 10-25% of the mRNA lacking SECIS 2. To address function, mutant mice were generated with either SECIS 1 or SECIS 2 deleted or with the first UGA substituted with a serine codon. They were fed on either high or selenium-deficient diets. The mutants had very different effects on the proportions of shorter and longer product Sepp1 protein isoforms isolated from plasma, and on viability. Spatially and functionally distinctive effects of the two SECIS elements on UGA decoding were inferred. We also bioinformatically identify two selenoprotein S mRNAs with different 5' sequences predicted to yield products with different N-termini. These results provide insights into SECIS function and mRNA processing in selenoprotein isoform diversity.

Analyses of Selenotranscriptomes and Selenium Concentrations in Response to Dietary Selenium Deficiency and Age Reveal Common and Distinct Patterns by Tissue and Sex in Telomere-Dysfunctional Mice

Background: The hierarchies of tissue selenium distribution and selenotranscriptomes are thought to critically affect healthspan and longevity.Objective: We determined selenium status and selenotranscriptomes in response to long-term dietary selenium deficiency and age in tissues of male and female mice.Methods: Weanling telomerase RNA component knockout C57BL/6 mice were fed a selenium-deficient (0.03 mg Se/kg) Torula yeast-based AIN-93G diet or a diet supplemented with sodium selenate (0.15 mg Se/kg) until age 18 or 24 mo. Plasma, hearts, kidneys, livers, and testes were collected to assay for selenotranscriptomes, selected selenoproteins, and tissue selenium concentrations. Data were analyzed with the use of 2-factor ANOVA (diet × age) in both sexes.Results: Dietary selenium deficiency decreased (P ≤ 0.05) selenium concentrations (65-72%) and glutathione peroxidase (GPX) 3 (82-94%) and selenoprotein P (SELENOP) (17-41%) levels in the plasma of both sexes of mice and mRNA levels (9-68%) of 4, 4, and 12 selenoproteins in the heart, kidney, and liver of males, respectively, and 5, 16, and 14 selenoproteins, respectively, in females. Age increased selenium concentrations and SELENOP levels (27% and 30%, respectively; P ≤ 0.05) in the plasma of males only but decreased (12-46%; P < 0.05) mRNA levels of 1, 5, and 13 selenoproteins in the heart, kidney, and liver of males, respectively, and 6, 5, and 0 selenoproteins, respectively, in females. Among these mRNAs, selenoprotein H (Selenoh), selenoprotein M (Selenom), selenoprotein W (Selenow), methionine-R-sulfoxide reductase 1 (MsrB1), Gpx1, Gpx3, thioredoxin reductase 1 (Txnrd1), Txnrd2, selenoprotein S (Selenos), selenoprotein F (Selenof), and selenoprotein O (Selenoo) responded in parallel to dietary selenium deficiency and age in ≥1 tissue or sex, or both. Dietary selenium deficiency upregulated (40-160%; P ≤ 0.05) iodothyronine deiodinase 2 (Dio2) and selenoprotein N (Selenon) in the kidneys of males. Age upregulated (11-44%; P < 0.05) Selenon in the kidneys of males, selenoprotein K (Selenok) and selenoprotein I (Selenoi) in the kidneys of females, and Selenof and Selenok in the testes.Conclusions: These results illustrate tissue-specific sexual dimorphisms of selenium status and selenotranscriptomes because of dietary selenium deficiency and age.

The effect of dietary bacterial organic selenium on growth performance, antioxidant capacity, and Selenoproteins gene expression in broiler chickens

Background

Selenium (Se) is an essential trace mineral in broilers, which has several important roles in biological processes. Organic forms of Se are more efficient than inorganic forms and can be produced biologically via Se microbial reduction. Hence, the possibility of using Se-enriched bacteria as feed supplement may provide an interesting source of organic Se, and benefit broiler antioxidant system and other biological processes. The objective of this study was to examine the impacts of inorganic Se and different bacterial organic Se sources on the performance, serum and tissues Se status, antioxidant capacity, and liver mRNA expression of selenoproteins in broilers.

Results

Results indicated that different Se sources did not significantly (P ≤ 0.05) affect broiler growth performance. However, bacterial organic Se of T5 (basal diet +0.3 mg /kg feed ADS18 Se), T4 (basal diet +0.3 mg /kg feed ADS2 Se), and T3 (basal diet +0.3 mg /kg feed ADS1 Se) exhibited significantly (P ≤ 0.05) highest Se concentration in serum, liver, and kidney respectively. Dietary inorganic Se and bacterial organic Se were observed to significantly affect broiler serum ALT, AST, LDH activities and serum creatinine level. ADS18 supplemented Se of (Stenotrophomonas maltophilia) bacterial strain showed the highest GSH-Px activity with the lowest MDA content in serum, and the highest GSH-Px and catalase activity in the kidney, while bacterial Se of ADS2 (Klebsiella pneumoniae) resulted in a higher level of GSH-Px1 and catalase in liver. Moreover, our study showed that in comparison with sodium selenite, only ADS18 bacterial Se showed a significantly higher mRNA level in GSH-Px1, GSH-Px4, DIO1, and TXNDR1, while both ADS18 and ADS2 showed high level of mRNA of DIO2 compared to sodium selenite.

Conclusions

The supplementation of bacterial organic Se in broiler chicken, improved tissue Se deposition, antioxidant status, and selenoproteins gene expression, and can be considered as an effective alternative source of Se in broiler chickens.

Antioxidants selenomethionine and D-pantethine decrease the negative side effects of doxorubicin in NL/Ly lymphoma-bearing mice

Aim

To investigate the potential tissue-protective effects of antioxidants selenomethionine and D-pantethine applied together with doxorubicin (Dx) on NK/Ly lymphoma-bearing mice. The impact of this chemotherapy scheme on animal survival, blood cell profile, hepatotoxicity, glutathione level, and activity of glutathione-converting enzymes in the liver was compared with the action of Dx applied alone.

Methods

The hematological profile of animals was studied by the analysis of blood smears under light microscopy. Hepatotoxicity of studied drugs was evaluated measuring the activity of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) enzymes, De Ritis ratio, and coenzyme A fractions by McDougal assay. Glutathione level in animal tissues was measured with Ellman reagent, and the activity of glutathione reductase, transferase, and peroxidase was measured using standard biochemical assays.

Results

D-pantethine (500 mg/kg) and, to a lower extent, selenomethionine (600 µg/kg) partially reduced the negative side effects (leukocytopenia and erythropenia) of Dx (5 mg/kg) in NK/Ly lymphoma bearing animals on the 14th day of their treatment. This increased animal survival time from 47-48 to 60+ days and improved the quality of their life. This ability of D-pantethine and selenomethionine was realized via hepatoprotective and immunomodulating activities. D-pantethine also restored the levels of acid-soluble and free CoA in the liver of tumor-bearing animals, while selenomethionine caused the recovery of glutathione peroxidase levels in the liver, which was significantly diminished under Dx treatment. Both compounds decreased glutathione level in the liver, which was considerably induced by Dx.

Conclusions

Antioxidants selenomethionine and D-pantethine partially reversed the negative side effects of Dx in NK/Ly lymphoma-bearing mice and significantly increased the therapeutic efficiency of this drug in tumor treatment.

GPx1 knockdown suppresses chondrogenic differentiation of ATDC5 cells through induction of reductive stress

Glutathione peroxidase 1 (GPx1) is a selenium (Se)-containing protein and is induced in cartilage formation. GPx1 eliminates reactive oxygen species (ROS), which are required for chondrogenic induction. The physiological properties of GPx1 in cartilage and the redox mechanisms involved are not known. The effects of GPx1 on chondrogenic differentiation of ATDC5 cells were examined through short hairpin RNA-mediated gene silencing. The results demonstrated that GPx1 knockdown impaired gene expression of sex determining region Y-box 9, collagen II (Col II), and aggrecan. GPx1 knockdown suppressed the accumulation of cartilage glycosaminoglycans (GAGs) and the proliferation of chondrocyte. GPx1 knockdown also induced cell apoptosis. However, cell sensitivity toward exogenous oxidative stress was not increased after GPx1 knockdown. Unexpectedly, GPx1 knockdown not only induced oxidative stress characterized by the increased production of ROS but also caused reductive stress indicated by an elevation of glutathione (GSH)/oxidized GSH (GSSG) ratio. Furthermore, GPx1 knockdown-mediated reductive and oxidative stress could be antagonized by a thiol-oxidizing agent diamide and a thiol-containing compound N-acetylcysteine (NAC), respectively. Moreover, NAC attenuated GPx1 knockdown-induced cell apoptosis, while diamide prevented GPx1 knockdown-suppressed chondrocyte proliferation. Finally, diamide but not NAC could rescue GPx1 knockdown-mediated impaired chondrogenic differentiation. In summary, GPx1 is essential for chondrogenic induction in ATDC5 cells mainly through modulation of intracellular GSH/GSSG ratio, rather than an antioxidant enzyme to detoxify ROS. In addition, GPx1 knockdown-induced impaired chondrogenesis may participate in the pathogenesis of the endemic osteoarthropathy due to Se deficiency. These observations offer novel insights for the development of therapeutic target during cartilage degeneration.

The Selenocysteine-Specific Elongation Factor Contains Unique Sequences That Are Required for Both Nuclear Export and Selenocysteine Incorporation

Selenocysteine (Sec) is a critical residue in at least 25 human proteins that are essential for antioxidant defense and redox signaling in cells. Sec is inserted into proteins cotranslationally by the recoding of an in-frame UGA termination codon to a Sec codon. In eukaryotes, this recoding event requires several specialized factors, including a dedicated, Sec-specific elongation factor called eEFSec, which binds Sec-tRNASec with high specificity and delivers it to the ribosome for selenoprotein production. Unlike most translation factors, including the canonical elongation factor eEF1A, eEFSec readily localizes to the nucleus of mammalian cells and shuttles between the cytoplasmic and nuclear compartments. The functional significance of eEFSec's nuclear localization has remained unclear. In this study, we have examined the subcellular localization of eEFSec in the context of altered Sec incorporation to demonstrate that reduced selenoprotein production does not correlate with changes in the nuclear localization of eEFSec. In addition, we identify several novel sequences of the protein that are essential for localization as well as Sec insertion activity, and show that eEFSec utilizes CRM1-mediated nuclear export pathway. Our findings argue for two distinct pools of eEFSec in the cell, where the cytoplasmic pool participates in Sec incorporation and the nuclear pool may be involved in an as yet unknown function.

Insights for Setting of Nutrient Requirements, Gleaned by Comparison of Selenium Status Biomarkers in Turkeys and Chickens versus Rats, Mice, and Lambs

To gain insights into nutrient biomarkers and setting of dietary nutrient requirements, selenium biomarker levels and requirements in response to multiple graded levels of dietary selenium were compared between day-old turkeys and chickens versus weanling rats and mice and 2-d-old lambs supplemented with sodium selenite. In rodents, there was no significant effect of dietary selenium on growth, indicating that the minimum selenium requirement was <0.007 μg Se/g diet. In contrast, there was a significant effect in turkeys, chicks, and lambs, which showed selenium requirements for growth of 0.05, 0.025, and 0.05 μg Se/g diet, respectively. Liver glutathione peroxidase (GPX) 1 activity fell in all species to <4% of selenium-adequate levels, plasma GPX3 activity fell to <3% in all species except for mice, and liver GPX4 activity fell to <10% in avians but only to ∼50% of selenium-adequate levels in rodents. Selenium-response curves for these biomarkers reached well-defined plateaus with increasing selenium supplementation in all species, collectively indicating minimum selenium requirements of 0.06-0.10 μg Se/g for rats, mice, and lambs but 0.10-0.13 μg Se/g for chicks and 0.23-0.33 μg Se/g for turkeys. In contrast, increasing dietary selenium did not result in well-defined plateaus for erythrocyte GPX1 activity and liver selenium in most species. Selenium-response curves for GPX1 mRNA for rodents and avians had well-defined plateaus and similar breakpoints. GPX4 mRNA was not significantly regulated by dietary selenium in rodents, but GPX4 mRNA in avians decreased in selenium deficiency to ∼35% of selenium-adequate plateau levels. Notably, no selenoprotein activities or mRNA were effective biomarkers for supernutritional selenium status. Robust biomarkers, such as liver GPX1 and plasma GPX3 activity for selenium, should be specific for the nutrient, fall dramatically in deficiency, and reach well-defined plateaus. Differences in biomarker-response curves may help researchers better understand nutrient metabolism and targeting of tissues in deficiency, thus to better characterize requirements.

Protective Effects of Selol Against Sodium Nitroprusside-Induced Cell Death and Oxidative Stress in PC12 Cells

Selol is an organic selenitetriglyceride formulation containing selenium at +4 oxidation level that can be effectively incorporated into catalytic sites of of Se-dependent antioxidants. In the present study, the potential antioxidative and cytoprotective effects of Selol against sodium nitroprusside (SNP)-evoked oxidative/nitrosative stress were investigated in PC12 cells and the underlying mechanisms analyzed. Spectrophoto- and spectrofluorimetic methods as well as fluorescence microscopy were used in this study; mRNA expression was quantified by real-time PCR. Selol dose-dependently improved the survival and decreased the percentage of apoptosis in PC12 cells exposed to SNP. To determine the mechanism of this protective action, the effect of Selol on free radical generation and on antioxidative potential was evaluated. Selol offered significant protection against the elevation of reactive oxidative species (ROS) evoked by SNP. Moreover, this compound restored glutathione homeostasis by ameliorating the SNP-evoked disturbance of GSH/GSSG ratio. The protective effect exerted by Selol was associated with the prevention of SNP-mediated down-regulation of antioxidative enzymes: glutathione peroxidase (Se-GPx), glutathione reductase (GR), and thioredoxin reductase (TrxR). Finally, GPx inhibition significantly abolished the cytoprotective effect of Selol. In conclusion, these results suggest that Selol effectively protected PC12 cells against SNP-induced oxidative damage and death by adjusting free radical levels and antioxidant system, and suppressing apoptosis. Selol could be successfully used in the treatments of diseases that involve oxidative stress and resulting apoptosis.

Effect of Inorganic Dietary Selenium Supplementation on Selenoprotein and Lipid Metabolism Gene Expression Patterns in Liver and Loin Muscle of Growing Lambs

Effect of selenium (Se) supplementation on the selenoprotein and lipid metabolism gene expression patterns in ruminants, especially in lambs is not yet fully understood. The aim of study was to evaluate the effect of Se supplementation on the messenger RNA (mRNA) expression patterns of selected selenoproteins and genes related to lipid metabolism in growing lambs. The experiment was conducted on 48 Polish Merino lambs divided into two groups (n = 24): control (C)-lambs fed with a basal diet (BD) with no Se supplementation, and supplemented (S)-lambs fed with a BD, supplemented with 0.5 mg Se/kg as sodium selenate for 8 weeks. Expression of 12 selenoproteins and six genes related to lipid metabolism was analyzed in the liver and longissimus dorsi (LD) muscle of growing lambs by qPCR. Significant differences were found in the expression of GPX1, GPX2, SEPM, SEPW1, SEP15, SEPGS2, and TXNRD1 in the liver, and GPX1, SEPP1, SEPN1, SEPW1, SEP15, and MSRB1 in the LD muscle between S and C lambs. Se supplementation mainly upregulated SEPW1, SEP15 (P < 0.001; P < 0.01) mRNA expression in the liver, and GPX1, SEPP1, SEPN1, SEPW1 (P < 0.001; P < 0.01) in the muscle of S group. On the other hand, significant decrease in GPX2 (P < 0.01), SEPM (P < 0.001), and SEPHS2 (P < 0.01) mRNA expression levels were observed in the liver of S group of lambs. Se supplementation did not affect PON1, LXRα, and PPARα mRNA expression levels, but a significant increase in mRNA levels of APOE and LPL in the LD muscle (P < 0.05) as well as LPL (P < 0.05) in the liver were noticed in the group of Se supplemented lambs. Our study confirmed that, in lambs, similarly to other species, mRNA expression patterns of several selenoproteins highly depend on dietary Se levels, and their expression is ruled by hierarchical principles and tissue-specific mechanisms. Moreover, the study showed that changes Se intake leads to different levels of genes expression related with lipid metabolism.

Modeling and gene knockdown to assess the contribution of nonsense-mediated decay, premature termination, and selenocysteine insertion to the selenoprotein hierarchy

The expression of selenoproteins, a specific group of proteins that incorporates selenocysteine, is hierarchically regulated by the availability of Se, with some, but not all selenoprotein mRNA transcripts decreasing in abundance with decreasing Se. Selenocysteine insertion into the peptide chain occurs during translation following recoding of an internal UGA stop codon. There is increasing evidence that this UGA recoding competes with premature translation termination, which is followed by nonsense-mediated decay (NMD) of the transcript. In this study, we tested the hypothesis that the susceptibility of different selenoprotein mRNAs to premature termination during translation and differential sensitivity of selenoprotein transcripts to NMD are major factors in the selenoprotein hierarchy. Selenoprotein transcript abundance was measured in Caco-2 cells using real-time PCR under different Se conditions and the data obtained fitted to mathematical models of selenoprotein translation. A calibrated model that included a combination of differential sensitivity of selenoprotein transcripts to NMD and different frequency of non-NMD related premature translation termination was able to fit all the measurements. The model predictions were tested using SiRNA to knock down expression of the crucial NMD factor UPF1 (up-frameshift protein 1) and selenoprotein mRNA expression. The calibrated model was able to predict the effect of UPF1 knockdown on gene expression for all tested selenoproteins, except SPS2 (selenophosphate synthetase), which itself is essential for selenoprotein synthesis. These results indicate an important role for NMD in the hierarchical regulation of selenoprotein mRNAs, with the exception of SPS2 whose expression is likely regulated by a different mechanism.

Glutathione peroxidase 4 and vitamin E cooperatively prevent hepatocellular degeneration

The selenoenzyme glutathione peroxidase 4 (Gpx4) is an essential mammalian glutathione peroxidase, which protects cells against detrimental lipid peroxidation and governs a novel form of regulated necrotic cell death, called ferroptosis. To study the relevance of Gpx4 and of another vitally important selenoprotein, cytosolic thioredoxin reductase (Txnrd1), for liver function, mice with conditional deletion of Gpx4 in hepatocytes were studied, along with those lacking Txnrd1 and selenocysteine (Sec) tRNA (Trsp) in hepatocytes. Unlike Txnrd1- and Trsp-deficient mice, Gpx4^−/− mice died shortly after birth and presented extensive hepatocyte degeneration. Similar to Txnrd1-deficient livers, Gpx4^−/− livers manifested upregulation of nuclear factor (erythroid-derived)-like 2 (Nrf2) response genes. Remarkably, Gpx4^−/− pups born from mothers fed a vitamin E-enriched diet survived, yet this protection was reversible as subsequent vitamin E deprivation caused death of Gpx4-deficient mice ~4 weeks thereafter. Abrogation of selenoprotein expression in Gpx4^−/− mice did not result in viable mice, indicating that the combined deficiency aggravated the loss of Gpx4 in liver. By contrast, combined Trsp/Txnrd1-deficient mice were born, but had significantly shorter lifespans than either single knockout, suggesting that Txnrd1 plays an important role in supporting liver function of mice lacking Trsp. In sum our study demonstrates that the ferroptosis regulator Gpx4 is critical for hepatocyte survival and proper liver function, and that vitamin E can compensate for its loss by protecting cells against deleterious lipid peroxidation.

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Conditional Gpx4 loss causes hepatocellular degeneration and early death of mice.

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Dietary vitamin E supplementation rescues death of liver-specific Gpx4 null mice.

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Nutritional vitamin E content in diet may severely impact experimental outcome.

Selenoprotein Transcript Level and Enzyme Activity as Biomarkers for Selenium Status and Selenium Requirements of Chickens (Gallus gallus)

The NRC selenium (Se) requirement for broiler chicks is 0.15 μg Se/g diet, based primarily on weight gain and feed intake studies reported in 1986. To determine Se requirements in today’s rapidly growing broiler chick, day-old male chicks were fed Se-deficient basal diets supplemented with graded levels of Se (0, 0.025, 0.05, 0.075, 0.1, 0.2, 0.3, 0.5, 0.75, and 1.0 μg Se/g) as Na₂SeO₃ (5/treatment). Diets contained 15X the vitamin E requirement, and there were no gross signs of Se-deficiency. At 29 d, Se-deficient chicks weighed 62% of Se-supplemented chicks; 0.025 μg Se/g reversed this effect, indicating a minimum Se requirement of 0.025 μg Se/g diet for growth for male broiler chicks. Enzyme activities in Se-deficient chicks for plasma GPX3, liver and gizzard GPX1, and liver and gizzard GPX4 decreased dramatically to 3, 2, 5, 10 and 5%, respectively, of Se-adequate levels, with minimum Se requirements of 0.10–0.13 μg Se/g, and with defined plateaus above these levels. Pancreas GPX1 and GPX4 activities, however, lacked defined plateaus, with breakpoints at 0.3 μg Se/g. qPCR measurement of all 24 chicken selenoprotein transcripts, plus SEPHS1, found that SEPP1 in liver, GPX3 in gizzard, and SEPP1, GPX3 and SELK in pancreas were expressed at levels comparable to housekeeping transcripts. Only 33%, 25% and 50% of selenoprotein transcripts were down-regulated significantly by Se deficiency in liver, gizzard and pancreas, respectively. No transcripts could be used as biomarkers for supernutritional Se status. For export selenoproteins SEPP1 and GPX3, tissue distribution, high expression and Se-regulation clearly indicate unique Se metabolism, which may underlie tissues targeted by Se deficiency. Based on enzyme activities in liver, gizzard, and plasma, the minimum Se requirement in today’s broiler chick is 0.15 μg Se/g diet; pancreas data indicate that the Se requirement should be raised to 0.2 μg Se/g diet to provide a margin of safety.

Dietary Selenium Status Regulates the Transcriptions of Selenoproteome and Activities of Selenoenzymes in Chicken Kidney at Low or Super-nutritional Levels

To determine dietary selenium (Se) status regulates the transcriptions of selenoproteome and activities of selenoenzymes in chicken kidney, 1-day-old chickens received low Se (0.028 mg Se per kg of diet) or super-nutritional Se (3.0 or 5.0 mg Se per kg of diet) in their diets for 8 weeks. It was observed that dietary low or super-nutritional Se did not make renal appearance pathological changes in chicken. Low Se significantly reduced total antioxidant capability (T-AOC), glutathione (GSH) content, but malondialdehyde (MDA) content in the kidney increased and decreased glutathione peroxidase (Gpx) and thioredoxin reductase (TrxR) activity with changes in their mRNA levels. Super-nutritional Se (3.0 mg/kg) increased T-AOC and GSH contents then made them reduce, but it reduced MDA content significantly, elevated then reduced Gpx activity, and decreased TrxR activity with changes in their mRNA levels. Dietary low Se downregulated the mRNA expressions of Gpx1-4, Txnrd3, Sepn1, Selw, Sepx1, Selh, and SEPSECS. At super-nutritional Se, most selenoproteins were upregulated in chicken kidney, but Sepp2 and Sep15 was only upregulated in Se excess (5.0 mg/kg) bird. These results indicated that dietary Se status stabilizes normal renal physiology function via regulation of the selenoprotemic transcriptions and selenoenzyme activities in avian.

HIV-1 Gag Blocks Selenite-Induced Stress Granule Assembly by Altering the mRNA Cap-Binding Complex

Stress granules (SGs) are dynamic accumulations of stalled preinitiation complexes and translational machinery that assemble under stressful conditions. Sodium selenite (Se) induces the assembly of noncanonical type II SGs that differ in morphology, composition, and mechanism of assembly from canonical SGs. Se inhibits translation initiation by altering the cap-binding activity of eukaryotic translation initiation factor 4E (eIF4E)-binding protein 1 (4EBP1). In this work, we show that human immunodeficiency virus type 1 (HIV-1) Gag is able to block the assembly of type II noncanonical SGs to facilitate continued Gag protein synthesis. We demonstrate that expression of Gag reduces the amount of hypophosphorylated 4EBP1 associated with the 5′ cap potentially through an interaction with its target, eIF4E. These results suggest that the assembly of SGs is an important host antiviral defense that HIV-1 has evolved for inhibition through several distinct mechanisms.

The antiviral stress response is an important host defense that many viruses, including HIV-1, have evolved to evade. Selenite induces a block in translation and leads to stress granule assembly through the sequestration of eIF4E by binding hypophosphorylated 4EBP1. In this work, we demonstrate that in the face of selenite-induced stress, HIV-1 is able to maintain Gag mRNA translation and to elicit a blockade to selenite-induced stress granule assembly by altering the amount of hypophosphorylated 4EBP1 on the 5′ cap.

Selenoprotein Transcript Level and Enzyme Activity as Biomarkers for Selenium Status and Selenium Requirements in the Turkey (Meleagris gallopavo)

The current National Research Council (NRC) selenium (Se) requirement for the turkey is 0.2 μg Se/g diet. The sequencing of the turkey selenoproteome offers additional molecular biomarkers for assessment of Se status. To determine dietary Se requirements using selenoprotein transcript levels and enzyme activities, day-old male turkey poults were fed a Se-deficient diet supplemented with graded levels of Se (0, 0.025, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.75, 1.0 μg Se/g diet) as selenite, and 12.5X the vitamin E requirement. Poults fed less than 0.05 μg Se/g diet had a significantly reduced rate of growth, indicating the Se requirement for growth in young male poults is 0.05 μg Se/g diet. Se deficiency decreased plasma GPX3 (glutathione peroxidase), liver GPX1, and liver GPX4 activities to 2, 3, and 7%, respectively, of Se-adequate levels. Increasing Se supplementation resulted in well-defined plateaus for all blood, liver and gizzard enzyme activities and mRNA levels, showing that these selenoprotein biomarkers could not be used as biomarkers for supernutritional-Se status. Using selenoenzyme activity, minimum Se requirements based on red blood cell GPX1, plasma GPX3, and pancreas and liver GPX1 activities were 0.29–0.33 μg Se/g diet. qPCR analyses using all 10 dietary Se treatments for all 24 selenoprotein transcripts (plus SEPHS1) in liver, gizzard, and pancreas found that only 4, 4, and 3 transcripts, respectively, were significantly down-regulated by Se deficiency and could be used as Se biomarkers. Only GPX3 and SELH mRNA were down regulated in all 3 tissues. For these transcripts, minimum Se requirements were 0.07–0.09 μg Se/g for liver, 0.06–0.15 μg Se/g for gizzard, and 0.13–0.18 μg Se/g for pancreas, all less than enzyme-based requirements. Panels based on multiple Se-regulated transcripts were effective in identifying Se deficiency. These results show that the NRC turkey dietary Se requirement should be raised to 0.3 μg Se/g diet.

Effect of 4-week feeding of deoxynivalenol- or T-2-toxin-contaminated diet on lipid peroxidation and glutathione redox system in the hepatopancreas of common carp (Cyprinus carpio L.)

The purpose of study was to investigate the effects of T-2 toxin (4.11 mg T-2 toxin and 0.45 mg HT-2 toxin kg(-1) feed) and deoxynivalenol (5.96 and 0.33 mg 15-acetyl deoxynivalenol (DON) kg(-1) feed) in 1-year-old common carp juveniles in a 4-week feeding trial. The exposure of mycotoxins resulted in increased mortality in both groups consuming mycotoxin-contaminated diet. Parameters of lipid peroxidation were not affected during the trial, and antioxidant defence also did not show response to oxidative stress; however, glutatione peroxidase activity slightly, but significantly, decreased in the T-2 toxin group. Glutathione S-transferase activity showed moderate decrease as effect of T-2 toxin, which suggests its effect on xenobiotic transformation. Reduced glutathione concentration showed moderate changes as effect of DON exposure, but T-2 toxin has no effect. Expression of phospholipid hydroperoxide glutathione peroxidase (GPx4) genes showed different response to mycotoxin exposure. T-2 toxin caused dual response in the expression of gpx4a (early and late downregulation and mid-term upregulation), but continuous upregulation was found as effect of deoxynivalenol. Expression of the other gene, gpx4b, was upregulated by both trichothecenes during the whole period. The results suggested that trichothecenes have some effect on free radical formation and antioxidant defence, but the changes depend on the duration of exposure and the dose applied, and in case of glutathione peroxidase, there was no correlation between expression of genes and enzyme activity.

Diphenyl Diselenide Protects Against Mortality, Locomotor Deficits and Oxidative Stress in Drosophila melanogaster Model of Manganese-Induced Neurotoxicity

Several experimental and epidemiological reports have associated manganese exposure with induction of oxidative stress and locomotor dysfunctions. Diphenyl diselenide (DPDS) is widely reported to exhibit antioxidant, anti-inflammatory and neuroprotective effects in in vitro and in vivo studies via multiple biochemical mechanisms. The present study investigated the protective effect of DPDS on manganese-induced toxicity in Drosophila melanogaster. The flies were exposed, in a dietary regimen, to manganese alone (30 mmol per kg) or in combination with DPDS (10 and 20 µmol per kg) for 7 consecutive days. Exposure to manganese significantly (p < 0.05) increased flies mortality, whereas the survivors exhibited significant locomotor deficits with increased acetylcholinesterase (AChE) activity. However, dietary supplementation with DPDS caused a significant decrease in mortality, improvement in locomotor activity and restoration of AChE activity in manganese-exposed flies. Additionally, the significant decreases in the total thiol level, activities of catalase and glutathione-S-transferase were accompanied with significant increases in the generation of reactive oxygen and nitrogen species and thiobarbituric acid reactive substances in flies exposed to manganese alone. Dietary supplementation with DPDS significantly augmented the antioxidant status and prevented manganese-induced oxidative stress in the treated flies. Collectively, the present data highlight that DPDS may be a promising chemopreventive drug candidate against neurotoxicity resulting from acute manganese exposure.

Gene expression profiling of selenophosphate synthetase 2 knockdown in Drosophila melanogaster

Selenium (Se) is an important trace element for many organisms and is incorporated into selenoproteins as selenocysteine (Sec). In eukaryotes, selenophosphate synthetase SPS2 is essential for Sec biosynthesis. In recent years, genetic disruptions of both Sec biosynthesis genes and selenoprotein genes have been investigated in different animal models, which provide important clues for understanding the Se metabolism and function in these organisms. However, a systematic study on the knockdown of SPS2 has not been performed in vivo. Herein, we conducted microarray experiments to study the transcriptome of fruit flies with knockdown of SPS2 in larval and adult stages. Several hundred differentially expressed genes were identified in each stage. In spite that the expression levels of other Sec biosynthesis genes and selenoprotein genes were not significantly changed, it is possible that selenoprotein translation might be reduced without impacting the mRNA level. Functional enrichment and network-based analyses revealed that although different sets of differentially expressed genes were obtained in each stage, they were both significantly enriched in the carbohydrate metabolism and redox processes. Furthermore, protein-protein interaction (PPI)-based network clustering analysis implied that several hub genes detected in the top modules, such as Nimrod C1 and regucalcin, could be considered as key regulators that are responsible for the complex responses caused by SPS2 knockdown. Overall, our data provide new insights into the relationship between Se utilization and several fundamental cellular processes as well as diseases.

Supranutritional dietary selenium induced hyperinsulinemia and dyslipidemia via affected expression of selenoprotein genes and insulin signal-related genes in broiler

The purpose of this study was to investigate the effects of supranutritional selenium (Se) on the mRNA expression of selenoprotein genes and insulin signal-related genes in the liver, muscle and pancreas of the broiler.

Sodium selenite suppresses hepatitis B virus transcription and replication in human hepatoma cell lines

Hepatitis B virus (HBV) infection is one of the most serious and prevalent health problems worldwide. Current anti‐HBV medications have a number of drawbacks, such as adverse effects and drug resistance; thus, novel potential anti‐HBV reagents are needed. Selenium (Se) has been shown to be involved in both human immunodeficiency virus and hepatitis C virus infections, but its role in HBV infection remains unclear. To address this, sodium selenite (Na₂SeO₃) was applied to three HBV cell models: HepG2.2.15 cells, and HuH‐7 cells transfected with either 1.1 or 1.3× HBV plasmids. Cytotoxicity of Na₂SeO₃ was examined by Cell Counting Kit‐8. Levels of viral antigen expression, transcripts, and encapsidated viral DNA were measured by enzyme‐linked immunosorbent assay, northern blot, and Southern blot, respectively. There was no obvious cytotoxicity in either HepG2.2.15 or HuH‐7 cells with <2.5 µM Na₂SeO₃. Below this concentration, Na₂SeO₃ suppressed HBsAg and HBeAg production, HBV transcript level, and amount of genomic DNA in all three tested models, and suppression level was enhanced in line with increases in Na₂SeO₃ concentration or treatment time. Moreover, the inhibitory effect of Na₂SeO₃ on HBV replication can be further enhanced by combined treatment with lamivudine, entecavir, or adefovir. Thus, the present study clearly proves that Na₂SeO₃ suppresses HBV protein expression, transcription, and genome replication in hepatoma cell models in a dose‐ and time‐dependent manner. J. Med. Virol. 88:653–663, 2016. © 2015 Wiley Periodicals, Inc.

Update on selenoprotein biosynthesis

SIGNIFICANCE

Selenium is an essential trace element that is incorporated in the small but vital family of proteins, namely the selenoproteins, as the selenocysteine amino acid residue. In humans, 25 selenoprotein genes have been characterized. The most remarkable trait of selenoprotein biosynthesis is the cotranslational insertion of selenocysteine by the recoding of a UGA codon, normally decoded as a stop signal.

RECENT ADVANCES

In eukaryotes, a set of dedicated cis- and trans-acting factors have been identified as well as a variety of regulatory mechanisms, factors, or elements that control the selenoprotein expression at the level of the UGA-selenocysteine recoding process, offering a fascinating playground in the field of translational control. It appeared that the central players are two RNA molecules: the selenocysteine insertion sequence (SECIS) element within selenoprotein mRNA and the selenocysteine-tRNA([Ser]Sec); and their interacting partners.

CRITICAL ISSUES

After a couple of decades, despite many advances in the field and the discovery of many essential and regulatory components, the precise mechanism of UGA-selenocysteine recoding remains elusive and more complex than anticipated, with many layers of control. This review offers an update of selenoproteome biosynthesis and regulation in eukaryotes.

FUTURE DIRECTIONS

The regulation of selenoproteins in response to a variety of pathophysiological conditions and cellular stressors, including selenium levels, oxidative stress, replicative senescence, or cancer, awaits further detailed investigation. Clearly, the efficiency of UGA-selenocysteine recoding is the limiting stage of selenoprotein synthesis. The sequence of events leading Sec-tRNA([Ser]Sec) delivery to ribosomal A site awaits further analysis, notably at the level of a three-dimensional structure.

Nonsense-mediated mRNA decay: an intricate machinery that shapes transcriptomes

Nonsense-mediated mRNA decay (NMD) is probably the best characterized eukaryotic RNA degradation pathway. Through intricate steps, a set of NMD factors recognize and degrade mRNAs with translation termination codons that are positioned in abnormal contexts. However, NMD is not only part of a general cellular quality control system that prevents the production of aberrant proteins. Mammalian cells also depend on NMD to dynamically adjust their transcriptomes and their proteomes to varying physiological conditions. In this Review, we discuss how NMD targets mRNAs, the types of mRNAs that are targeted, and the roles of NMD in cellular stress, differentiation and maturation processes.

Dietary Selenium Levels Affect Selenoprotein Expression and Support the Interferon-γ and IL-6 Immune Response Pathways in Mice

Selenium is an essential element that is required to support a number of cellular functions and biochemical pathways. The objective of this study was to examine the effects of reduced dietary selenium levels on gene expression to assess changes in expression of non-selenoprotein genes that may contribute to the physiological consequences of selenium deficiency. Mice were fed diets that were either deficient in selenium or supplemented with selenium in the form of sodium selenite for six weeks. Differences in liver mRNA expression and translation were measured using a combination of ribosome profiling, RNA-Seq, microarrays, and qPCR. Expression levels and translation of mRNAs encoding stress-related selenoproteins were shown to be up-regulated by increased selenium status, as were genes involved in inflammation and response to interferon-γ. Changes in serum cytokine levels were measured which confirmed that interferon-γ, as well as IL-6, were increased in selenium adequate mice. Finally, microarray and qPCR analysis of lung tissue demonstrated that the selenium effects on immune function are not limited to liver. These data are consistent with previous reports indicating that adequate selenium levels can support beneficial immune responses, and further identify the IL-6 and interferon-γ pathways as being responsive to dietary selenium intake.

Characterization and Expression of Chicken Selenoprotein U

Selenoprotein U (SelU) may regulate a myriad of biological processes through its redox function. In chicks, neither the nucleotide sequence nor the amino acid sequence is known. The main objectives of this study were to clone and characterize the chicken Selu gene and investigate Selu messenger RNA (mRNA) and protein expression in chicken tissues. The coding sequence (CDS) of Selu contained 387 bases with a typical mammalian selenocysteine insertion sequence (SECIS) located in the 3'-untranslated region. The deduced amino acid sequence of chicken SelU contains 224 amino acids with UAA as the stop codon. Like all SelU genes identified in different species, chicken SelU contains one well-conserved selenocysteine (Sec) at the 85th position encoded by the UGA codon. The SECIS element was with the conserved denosine (--AAA--) rather than the motif cytidine (--CC--) motif. Moreover, the expression pattern of Selu mRNA in muscle, liver, kidney, heart, spleen, lung, testis, and brain was analyzed with real-time quantitative PCR in young male chickens fed a Se-deficient corn-soybean meal basal diet supplemented with 0.0 and 0.3 mg Se/kg in the form of sodium selenite. We found that the abundance of Selu mRNA in muscle, liver, kidney, heart, spleen, and lung was downregulated (P < 0.05) by Se deficiency. However, it was not affected by dietary Se concentrations in testis and brain. Furthermore, protein abundance of SelU in these seven tissues was consistent with the mRNA abundance. Hence, we suggest that Selu might play an important role in the biochemical function of Se in birds.

Expression of Selenoprotein Genes Is Affected by Obesity of Pigs Fed a High-Fat Diet

BACKGROUND

Relations of the 25 mammalian selenoprotein genes with obesity and the associated inflammation remain unclear.

OBJECTIVE

This study explored impacts of high-fat diet-induced obesity on inflammation and expressions of selenoprotein and obesity-related genes in 10 tissues of pigs.

METHODS

Plasma and 10 tissues were collected from pigs (n = 10) fed a corn-soy-based control diet or that diet containing 3-7% lard from weanling to finishing (180 d). Plasma concentrations (n = 8) of cytokines and thyroid hormones and tissue mRNA abundance (n = 4) of 25 selenoprotein genes and 16 obesity-related genes were compared between the pigs fed the control and high-fat diets. Stepwise regression was applied to analyze correlations among all these measures, including the previously reported body physical and plasma biochemical variables.

RESULTS

The high-fat diet elevated (P < 0.05) plasma concentrations of tumor necrosis factor α, interleukin-6, leptin, and leptin receptor by 29-42% and affected (P < 0.05-0.1) tissue mRNA levels of the selenoprotein and obesity-related genes in 3 patterns. Specifically, the high-fat diet up-regulated 12 selenoprotein genes in 6 tissues, down-regulated 13 selenoprotein genes in 7 tissues, and exerted no effect on 5 genes in any tissue. Body weights and plasma triglyceride concentrations of pigs showed the strongest regressions to tissue mRNA abundances of selenoprotein and obesity-related genes. Among the selenoprotein genes, selenoprotein V and I were ranked as the strongest independent variables for the regression of phenotypic and plasma measures. Meanwhile, agouti signaling protein, adiponectin, and resistin genes represented the strongest independent variables of the obesity-related genes for the regression of tissue selenoprotein mRNA.

CONCLUSIONS

The high-fat diet induced inflammation in pigs and affected their gene expression of selenoproteins associated with thioredoxin and oxidoreductase systems, local tissue thyroid hormone activity, endoplasmic reticulum protein degradation, and phosphorylation of lipids. This porcine model may be used to study interactive mechanisms between excess fat intake and selenoprotein function.