Selective up-regulation of human selenoproteins in response to oxidative stress

Selenium May Be Involved in Esophageal Squamous Cancer Prevention by Affecting GPx3 and FABP1 Expression: A Case-Control Study Based on Bioinformatic Analysis

The role of selenium in the developmental process of esophageal cancer (EC) requires further investigation. To explore the relationship between selenium-related factors and EC through bioinformatic analysis, a case-control study was conducted to verify the results. Utilizing the GEPIA and TCGA databases, we delineated the differential expression of glutathione peroxidase 3 (GPx3) in EC and normal tissues, identified differentially expressed genes (DEGs), and a performed visualization analysis. Additionally, 100 pairs of dietary and plasma samples from esophageal precancerous lesions (EPLs) of esophageal squamous cancer (ESCC) cases and healthy controls from Huai'an district, Jiangsu, were screened. The levels of dietary selenium, plasma selenium, and related enzymes were analyzed using inductively coupled plasma mass spectrometry (ICP-MS) or ELISA kits. The results showed lower GPx3 expression in tumor tissues compared to normal tissues. Further analysis revealed that DEGs were mainly involved in the fat digestion and absorption pathway, and the core protein fatty acid binding protein 1 (FABP1) was significantly upregulated and negatively correlated with GPx3 expression. Our case-control study found that selenium itself was not associated with EPLs risk. However, both the decreased concentration of GPx3 and the increase in FABP1 were positively correlated with the EPLs risk (p for trend = 0.035 and 0.046, respectively). The different expressions of GPx3 and FABP1 reflect the potential of selenium for preventing ESCC at the EPLs stage. GPx3 may affect myocardial infarction through FABP1, which remains to be further studied.

Regorafenib activates oxidative stress by inhibiting SELENOS and potentiates oxaliplatin-induced cell death in colon cancer cells

Colorectal cancer (CRC) is the third most common cancer, and is one of the leading causes of cancer-related death worldwide. At the time of diagnosis, about 20% of patients with CRC present metastatic disease. Regorafenib, an oral multi-kinase inhibitor, has been demonstrated the efficacy and tolerability in patients with metastatic CRC. Oxaliplatin is a frontline treatment regimen for CRC, and combination treatments with oxaliplatin and other chemotherapeutic agents exert superior therapeutic effects. However, side effects and drug resistance limited their further clinical application. Here, we found that combined treatment with regorafenib and oxaliplatin synergistically enhanced anti-tumor activities in CRC by activating reactive oxygen species (ROS) mediated endoplasmic reticulum (ER) stress, C-Jun-amino-terminal kinase (JNK) and p38 signaling pathways. Regorafenib promoted ROS production by suppressing the expression of selenoprotein S (SELENOS). Knocking down SELENOS sensitized ROS-mediated anti-tumor effects of regorafenib in CRC cells. Furthermore, mouse xenograft models demonstrated that synergistic anti-tumor effects of combined treatment with regorafenib and oxaliplatin. This study provided solid experimental evidences for the combined treatment with regorafenib and oxaliplatin in CRC.

A homozygous mutation in the human selenocysteine tRNA gene impairs UGA recoding activity and selenoproteome regulation by selenium

The selenocysteine (Sec) tRNA (tRNA[Ser]Sec) governs Sec insertion into selenoproteins by the recoding of a UGA codon, typically used as a stop codon. A homozygous point mutation (C65G) in the human tRNA[Ser]Sec acceptor arm has been reported by two independent groups and was associated with symptoms such as thyroid dysfunction and low blood selenium levels; however, the extent of altered selenoprotein synthesis resulting from this mutation has yet to be comprehensively investigated. In this study, we used CRISPR/Cas9 technology to engineer homozygous and heterozygous mutant human cells, which we then compared with the parental cell lines. This C65G mutation affected many aspects of tRNA[Ser]Sec integrity and activity. Firstly, the expression level of tRNA[Ser]Sec was significantly reduced due to an altered recruitment of RNA polymerase III at the promoter. Secondly, selenoprotein expression was strongly altered, but, more surprisingly, it was no longer sensitive to selenium supplementation. Mass spectrometry analyses revealed a tRNA isoform with unmodified wobble nucleotide U34 in mutant cells that correlated with reduced UGA recoding activities. Overall, this study demonstrates the pleiotropic effect of a single C65G mutation on both tRNA phenotype and selenoproteome expression.

Biological and Catalytic Properties of Selenoproteins

Selenocysteine is a catalytic residue at the active site of all selenoenzymes in bacteria and mammals, and it is incorporated into the polypeptide backbone by a co-translational process that relies on the recoding of a UGA termination codon into a serine/selenocysteine codon. The best-characterized selenoproteins from mammalian species and bacteria are discussed with emphasis on their biological function and catalytic mechanisms. A total of 25 genes coding for selenoproteins have been identified in the genome of mammals. Unlike the selenoenzymes of anaerobic bacteria, most mammalian selenoenzymes work as antioxidants and as redox regulators of cell metabolism and functions. Selenoprotein P contains several selenocysteine residues and serves as a selenocysteine reservoir for other selenoproteins in mammals. Although extensively studied, glutathione peroxidases are incompletely understood in terms of local and time-dependent distribution, and regulatory functions. Selenoenzymes take advantage of the nucleophilic reactivity of the selenolate form of selenocysteine. It is used with peroxides and their by-products such as disulfides and sulfoxides, but also with iodine in iodinated phenolic substrates. This results in the formation of Se-X bonds (X = O, S, N, or I) from which a selenenylsulfide intermediate is invariably produced. The initial selenolate group is then recycled by thiol addition. In bacterial glycine reductase and D-proline reductase, an unusual catalytic rupture of selenium-carbon bonds is observed. The exchange of selenium for sulfur in selenoproteins, and information obtained from model reactions, suggest that a generic advantage of selenium compared with sulfur relies on faster kinetics and better reversibility of its oxidation reactions.

Effect of Organic Selenium on the Homeostasis of Trace Elements, Lipid Peroxidation, and mRNA Expression of Antioxidant Proteins in Mouse Organs

(1) In this study we determined the effect of long-term selenomethionine administration on the oxidative stress level and changes in antioxidant protein/enzyme activity; mRNA expression; and the levels of iron, zinc, and copper. (2) Experiments were performed on 4-6-week-old BALB/c mice, which were given selenomethionine (0.4 mg Se/kg b.w.) solution for 8 weeks. The element concentration was determined via inductively coupled plasma mass spectrometry. mRNA expression of SelenoP, Cat, and Sod1 was quantified using real-time quantitative reverse transcription. Malondialdehyde content and catalase activity were determined spectrophotometrically. (3) After long-term SeMet administration, the amount of Se increased by 12-fold in mouse blood, 15-fold in the liver, and 42-fold in the brain, as compared to that in the control. Exposure to SeMet decreased amounts of Fe and Cu in blood, but increased Fe and Zn levels in the liver and increased the levels of all examined elements in the brain. Se increased malondialdehyde content in the blood and brain but decreased it in liver. SeMet administration increased the mRNA expression of selenoprotein P, dismutase, and catalase, but decreased catalase activity in brain and liver. (4) Eight-week-long selenomethionine consumption elevated Se levels in the blood, liver, and especially in the brain and disturbed the homeostasis of Fe, Zn, and Cu. Moreover, Se induced lipid peroxidation in the blood and brain, but not in the liver. In response to SeMet exposure, significant up-regulation of the mRNA expression of catalase, superoxide dismutase 1, and selenoprotein P in the brain, and especially in the liver, was determined.

The role of selenium in shaping mice brain metabolome and selenoproteome through the gut-brain axis by combining metabolomics, metallomics, gene expression and amplicon sequencing

Selenium (Se) is a trace element crucial for human health. Recently, the impact of Se supplementation on gut microbiota has been pointed out as well as its influence on the expression of certain selenoproteins and gut metabolites. This study aims to elucidate the link between Se supplementation, brain selenoproteins and brain metabolome as well as the possible connection with the gut-brain axis. To this end, an in vivo study with 40 BALB/c mice was carried out. The study included conventional (n=20) and mice model with microbiota depleted by antibiotics (n=20) under a regular or Se supplemented diet. Brain selenoproteome was determined by a transcriptomic/gene expression profile, while brain metabolome and gut microbiota profiles were accomplished by untargeted metabolomics and amplicon sequencing, respectively. The total content of Se in brain was also determined. The selenoproteins genes Dio and Gpx isoenzymes, SelenoH, SelenoI, SelenoT, SelenoV and SelenoW and 31 metabolites were significantly altered in the brain after Se supplementation in conventional mice, while 11 selenoproteins and 26 metabolites were altered in microbiota depleted mice. The main altered brain metabolites were related to glyoxylate and dicarboxylate metabolism, amino acid metabolism, and gut microbiota that have been previously related with the gut-brain axis (e.g., members of Lachnospiraceae and Ruminococcaceae families). Moreover, specific associations were determined between brain selenoproteome and metabolome, which correlated with the same bacteria, suggesting an intertwined mechanism. Our results demonstrated the effect of Se on brain metabolome through specific selenoproteins gene expression and gut microbiota.

Selenocompounds and Sepsis-Redox Bypass Hypothesis: Part B-Selenocompounds in the Management of Early Sepsis

Significance: Endothelial barrier damage, which is in part caused by excess production of reactive oxygen, halogen and nitrogen species (ROHNS), especially peroxynitrite (ONOO^-), is a major event in early sepsis and, with leukocyte hyperactivation, part of the generalized dysregulated immune response to infection, which may even become a complex maladaptive state. Selenoenzymes have major antioxidant functions. Their synthesis is related to the need to limit deleterious oxidant redox cycling by small selenocompounds, which may be of therapeutic cytotoxic interest. Plasma selenoprotein-P is crucial for selenium transport from the liver to the tissues and for antioxidant endothelial protection, especially against ONOO^-. Above micromolar concentrations, sodium selenite (Na₂SeO₃) becomes cytotoxic, with a lower cytotoxicity threshold in activated cells, which has led to cancer research. Recent Advances: Plasma selenium (<2% of total body selenium) is mainly contained in selenoprotein-P, and concentrations decrease rapidly in the early phase of sepsis, because of increased selenoprotein-P binding and downregulation of hepatic synthesis and excretion. At low concentrations, Na₂SeO₃ acts as a selenium donor, favoring selenoprotein-P synthesis in physiology, but probably not in the acute phase of sepsis. Critical Issues: The cytotoxic effects of Na₂SeO₃ against hyperactivated leukocytes, especially the most immature forms that liberate ROHNS, may be beneficial, but they may also be harmful for activated endothelial cells. Endothelial protection against ROHNS by selenoprotein-P may reduce Na₂SeO₃ toxicity, which is increased in sepsis. Future Direction: The combination of selenoprotein-P for endothelial protection and the cytotoxic effects of Na₂SeO₃ against hyperactivated leukocytes may be a promising intervention for early sepsis. Antioxid. Redox Signal. 37, 998-1029.

Emerging roles of ER-resident selenoproteins in brain physiology and physiopathology

The brain has a very high oxygen consumption rate and is particularly sensitive to oxidative stress. It is also the last organ to suffer from a loss of selenium (Se) in case of deficiency. Se is a crucial trace element present in the form of selenocysteine, the 21st proteinogenic amino acid present in selenoproteins, an essential protein family in the brain that participates in redox signaling. Among the most abundant selenoproteins in the brain are glutathione peroxidase 4 (GPX4), which reduces lipid peroxides and prevents ferroptosis, and selenoproteins W, I, F, K, M, O and T. Remarkably, more than half of them are proteins present in the ER and recent studies have shown their involvement in the maintenance of ER homeostasis, glycoprotein folding and quality control, redox balance, ER stress response signaling pathways and Ca2+ homeostasis. However, their molecular functions remain mostly undetermined. The ER is a highly specialized organelle in neurons that maintains the physical continuity of axons over long distances through its continuous distribution from the cell body to the nerve terminals. Alteration of this continuity can lead to degeneration of distal axons and subsequent neuronal death. Elucidation of the function of ER-resident selenoproteins in neuronal pathophysiology may therefore become a new perspective for understanding the pathophysiology of neurological diseases. Here we summarize what is currently known about each of their molecular functions and their impact on the nervous system during development and stress.

Quantifying Turnover Dynamics of Selenoproteome by Isotopic Perturbation

Selenium, as an essential trace element of life, is closely related to human health and is required to produce selenoproteins, a family of important functional proteins in many living organisms. All selenoproteins contain a special amino acid, selenocysteine, which often serves as their active-site residue, and the expression and activity of selenoproteins are fine-tuned. However, the turnover dynamics of selenoproteome has never been systematically investigated, especially in a site-specific manner for selenocysteines. In the current work, we developed a chemical proteomic strategy named "SElenoprotein Turnover Rate by Isotope Perturbation (SETRIP)" to quantitatively monitor the turnover dynamics of selenoproteins at the proteomic level. The kinetic rates and half-lives of nine selenoproteins were accurately measured by combining Na₂⁷⁴SeO₃ metabolic labeling with pulse-chase chemoproteomics. The half-lives of selenoproteins were measured to range from 6 to 32 h with the housekeeping selenoprotein glutathione peroxidases (GPX4) showing a faster turnover rate, implying that the hierarchy regulation also exists in the turnover of selenoproteins in addition to expression and activity. Our study generated a global portrait of dynamic changes in the selenoproteome and provided important clues to study the roles of selenium in biology.

Anomalous HIV-1 RNA, How Cap-Methylation Segregates Viral Transcripts by Form and Function

The acquisition of m7G-cap-binding proteins is now recognized as a major variable driving the form and function of host RNAs. This manuscript compares the 5'-cap-RNA binding proteins that engage HIV-1 precursor RNAs, host mRNAs, small nuclear (sn)- and small nucleolar (sno) RNAs and sort into disparate RNA-fate pathways. Before completion of the transcription cycle, the transcription start site of nascent class II RNAs is appended to a non-templated guanosine that is methylated (m7G-cap) and bound by hetero-dimeric CBP80-CBP20 cap binding complex (CBC). The CBC is a nexus for the co-transcriptional processing of precursor RNAs to mRNAs and the snRNA and snoRNA of spliceosomal and ribosomal ribonucleoproteins (RNPs). Just as sn/sno-RNAs experience hyper-methylation of m7G-cap to trimethylguanosine (TMG)-cap, so do select HIV RNAs and an emerging cohort of mRNAs. TMG-cap is blocked from Watson:Crick base pairing and disqualified from participating in secondary structure. The HIV TMG-cap has been shown to license select viral transcripts for specialized cap-dependent translation initiation without eIF4E that is dependent upon CBP80/NCBP3. The exceptional activity of HIV precursor RNAs secures their access to maturation pathways of sn/snoRNAs, canonical and non-canonical host mRNAs in proper stoichiometry to execute the retroviral replication cycle.

The effect of stocking rate and supplementary selenium on the fatty acid composition and subsequent peroxidisability of poultry muscle tissues

Selenium (Se) plays a crucial role in protecting biological materials from oxidative damage through the action of the selenoprotein glutathione peroxidase (GSH-Px), and the effectiveness of this protection is often dependent upon Se supply. Recent evidence has indicated that GSH-Px mRNA expression can be upregulated in response to potential oxidative damage risk, and that this upregulation is independent of Se supply. The current study aimed to determine the effect of Se supplementation, stocking rate and tissue fatty acid profile on GSH-Px activity in breast and thigh tissue of commercial broilers. A total of 168 Ross 308 broiler chicks were enrolled onto the study. Prior to enrolment, birds were brooded as a single group and received a starter diet containing no additional Se. The study was a 2 × 2 factorial design comprising of two levels of dietary Se (high Se, 0.5 mg/kg total Se, low Se background Se only), and two stocking rates (high, 30 kg/m², and low, 15 kg/m²). At 15 days of age, birds were blocked by live weight and randomly allocated to one of the four treatments, with six pen replicates per treatment. At 42 days of age, one bird was randomly selected from each pen replicate, euthanased and breast and thigh tissue harvested. GSH-Px activity, thiobarbituric acid reactive substances (TBARS), and fatty acid (FA) content of these tissues were determined. There was no effect (P > 0.05) of stocking rate on GSH-Px activity or TBARS. GSH-Px activity did not differ between tissue types but was greater in high Se birds (P < 0.001) compared to low Se. TBARS concentrations were greater in thigh tissue (P < 0.001), and these thigh concentrations were greater in high Se birds (P < 0.05). There were marked differences between breast and thigh tissue in most FAs (P < 0.001), with breast generally containing greater proportions of polyunsaturated FA, so that breast tissue had a higher (P < 0.001) peroxidisability index (PI) than thigh. A positive correlation between GSH-Px activity and PI in the thigh tissue of high Se birds (Pearson Correlation 0.668; P = 0.025) may indicate that increasing susceptibility to peroxidisation in lipid-rich tissues may also upregulate GSH-Px activity in Se-replete birds. This study suggests that ensuring adequate dietary selenium could be a useful tool to mitigate adverse effects on meat quality caused by oxidation, particularly in lipid-rich meat.

Examining xCT-mediated selenium uptake and selenoprotein production capacity in cells

The production of selenoproteins in cancer cells is dependent on uptake of selenium and processing via the selenocysteine biosynthesis pathway. Both the uptake and processing of selenium has recently shown to be upregulated in subsets of cancer cells due to their increased expression of xCT transporter, and the resulting increased expression of selenoproteins such as GPX4 can play multiple roles in cancer cells such as providing protection against ferroptotic insults. Here, we describe a set of protocols designed to measure this process in cancer cell culture-the measurement of xCT transporter expression and activity, the intracellular uptake of selenium in cancer cells, and the expression of selenoproteins as the final functional readout of this process. The successful measurement of xCT requires non-denaturing western blotting of xCT subunits, while its activity is determined by the measurement of reduced thiol groups that accumulate over time, as determined by Ellman's reagent. Selenium uptake is determined by supplementing a selenium source and then measuring total intracellular selenium levels, which is determined from digested cellular material using a reactive fluorescent probe or via inductively coupled plasma mass spectrometry. Finally, specific tips for efficiently determining the expression level of a set of "indicator" selenoproteins is provided. These parameters allow one to determine the "selenophilicity" of cells, i.e., the ability of cells to utilize selenite to upregulate their selenoprotein production and thus antioxidant defenses.

Selenoproteins in the Human Placenta: How Essential Is Selenium to a Healthy Start to Life?

Selenium is an essential trace element required for human health, and selenium deficiency has been associated with many diseases. The daily recommended intake of selenium is 60 µg/day for adults, which increases to 65 µg/day for women when pregnant. Selenium is incorporated into the 21st amino acid, selenocysteine (sec), a critical component of selenoproteins that plays an important role in a variety of biological responses such as antioxidant defence, reactive oxygen species (ROS) signalling, formation of thyroid hormones, DNA synthesis and the unfolded protein response in the endoplasmic reticulum (ER). Although 25 selenoproteins have been identified, the role of many of these is yet to be fully characterised. This review summarises the current evidence demonstrating that selenium is essential for a healthy pregnancy and that poor selenium status leads to gestational disorders. In particular, we focus on the importance of the placental selenoproteome, and the role these proteins may play in a healthy start to life.

Interplay between Selenium, Selenoproteins and HIV-1 Replication in Human CD4 T-Lymphocytes

The infection of CD4 T-lymphocytes with human immunodeficiency virus (HIV), the etiological agent of acquired immunodeficiency syndrome (AIDS), disrupts cellular homeostasis, increases oxidative stress and interferes with micronutrient metabolism. Viral replication simultaneously increases the demand for micronutrients and causes their loss, as for selenium (Se). In HIV-infected patients, selenium deficiency was associated with a lower CD4 T-cell count and a shorter life expectancy. Selenium has an important role in antioxidant defense, redox signaling and redox homeostasis, and most of these biological activities are mediated by its incorporation in an essential family of redox enzymes, namely the selenoproteins. Here, we have investigated how selenium and selenoproteins interplay with HIV infection in different cellular models of human CD4 T lymphocytes derived from established cell lines (Jurkat and SupT1) and isolated primary CD4 T cells. First, we characterized the expression of the selenoproteome in various human T-cell models and found it tightly regulated by the selenium level of the culture media, which was in agreement with reports from non-immune cells. Then, we showed that selenium had no significant effect on HIV-1 protein production nor on infectivity, but slightly reduced the percentage of infected cells in a Jurkat cell line and isolated primary CD4 T cells. Finally, in response to HIV-1 infection, the selenoproteome was slightly altered.

Selenoproteome Expression Studied by Non-Radioactive Isotopic Selenium-Labeling in Human Cell Lines

Selenoproteins, in which the selenium atom is present in the rare amino acid selenocysteine, are vital components of cell homeostasis, antioxidant defense, and cell signaling in mammals. The expression of the selenoproteome, composed of 25 selenoprotein genes, is strongly controlled by the selenium status of the body, which is a corollary of selenium availability in the food diet. Here, we present an alternative strategy for the use of the radioactive ⁷⁵Se isotope in order to characterize the selenoproteome regulation based on (i) the selective labeling of the cellular selenocompounds with non-radioactive selenium isotopes (⁷⁶Se, ⁷⁷Se) and (ii) the detection of the isotopic enrichment of the selenoproteins using size-exclusion chromatography followed by inductively coupled plasma mass spectrometry detection. The reliability of our strategy is further confirmed by western blots with distinct selenoprotein-specific antibodies. Using our strategy, we characterized the hierarchy of the selenoproteome regulation in dose–response and kinetic experiments.

Nrf2 in Cancer, Detoxifying Enzymes and Cell Death Programs

Reactive oxygen species (ROS) play an important role in cell proliferation and differentiation. They are also by-products of aerobic living conditions. Their inherent reactivity poses a threat for all cellular components. Cells have, therefore, evolved complex pathways to sense and maintain the redox balance. Among them, Nrf2 (Nuclear factor erythroid 2-related factor 2) plays a crucial role: it is activated under oxidative conditions and is responsible for the expression of the detoxification machinery and antiapoptotic factors. It is, however, a double edge sword: whilst it prevents tumorigenesis in healthy cells, its constitutive activation in cancer promotes tumour growth and metastasis. In addition, recent data have highlighted the importance of Nrf2 in evading programmed cell death. In this review, we will focus on the activation of the Nrf2 pathway in the cytoplasm, the molecular basis underlying Nrf2 binding to the DNA, and the dysregulation of this pathway in cancer, before discussing how Nrf2 contributes to the prevention of apoptosis and ferroptosis in cancer and how it is likely to be linked to detoxifying enzymes containing selenium.

Genetic risk of clozapine-induced leukopenia and neutropenia: a genome-wide association study

BACKGROUND

Clozapine is considered to be the most effective antipsychotic medication for schizophrenia. However, it is associated with several adverse effects such as leukopenia, and the underlying mechanism has not yet been fully elucidated. The authors performed a genome-wide association study (GWAS) in a Chinese population to identify genetic markers for clozapine-induced leukopenia (CIL) and clozapine-induced neutropenia (CIN).

METHODS

A total of 1879 patients (225 CIL cases, including 43 CIN cases, and 1,654 controls) of Chinese descent were included. Data from common and rare single nucleotide polymorphisms (SNPs) were tested for association. The authors also performed a trans-ancestry meta-analysis with GWAS results of European individuals from the Clozapine-Induced Agranulocytosis Consortium (CIAC).

RESULTS

The authors identified several novel loci reaching the threshold of genome-wide significance level (P < 5 × 10^-8). Three novel loci were associated with CIL while six were associated with CIN, and two T cell related genes (TRAC and TRAT1) were implicated. The authors also observed that one locus with evidence close to genome-wide significance (P = 5.08 × 10^-8) was near the HLA-B gene in the major histocompatibility complex region in the trans-ancestry meta-analysis.

CONCLUSIONS

The associations provide novel and valuable understanding of the genetic and immune causes of CIL and CIN, which is useful for improving clinical management of clozapine related treatment for schizophrenia. Causal variants and related underlying molecular mechanisms need to be understood in future developments.

Comparative study on protective effect of different selenium sources against cadmium-induced nephrotoxicity via regulating the transcriptions of selenoproteome

Cadmium (Cd) is a ubiquitous environmental pollutant, which mainly input to the aquatic environment through discharge of industrial and agricultural waste, can be a threat to human and animal health. Selenium (Se) possesses a beneficial role in protecting animals and ameliorating the toxic effects of Cd. However, the comparative antagonistic effects of different Se sources such as inorganic, organic Se and nano-form Se on Cd toxicity are still under-investigated. Hence, the purpose of this study was to evaluate the comparative of Se sources antagonism on Cd-induced nephrotoxicity via oxidative stress and selenoproteome transcription. In the present study, Cd-diet disturbed in the system balance of 5 trace elements (Zinc (Zn), copper (Cu), Iron (Fe), Se, Cd) and impaired renal function. Se sources, including nano- Se (NS), Se- yeast (SY), sodium selenite (SS) and mixed selenium (MS) significantly recovered the balance of 4 trace elements (Zn, Cu, Cd, Se) and renal impaired indexes (blood urea nitrogen (BUN) and creatinine (CREA)). Histological appearance of Cd-treated kidney indicated renal tubular epithelial vacuoles, particle degeneration and enlarged capsular space. Ultrastructure observation results illustrated that Cd-induced mitochondrial cristae reduction, membrane disappearance, and nuclear deformation. Treatment with Se sources, NS appeared a better impact on improving kidney tissues against the pathological alterations resulting from Cd administration. Meanwhile, NS reflected a significant impact on relieving Cd-induced kidney oxidative damage, and significantly restored the antioxidant defense system of the body. Our findings also showed NS ameliorated the Cd-induced downtrends expression of selenoproteome and selenoprotein synthesis related transcription factors. Overall, NS was the most effective Se source in avoiding of Cd cumulative toxicity, improving antioxidant capacity and regulating of selenoproteome transcriptome and selenoprotein synthesis related transcription factors expression, which contributes to ameliorate Cd-induced nephrotoxicity in chickens. These results demonstrated diet supplement with NS may prove to be an effective approach for alleviating Cd toxicity and minimizing Cd -induced health risk.

Association between fatality rate of COVID-19 and selenium deficiency in China

BACKGROUND

COVID-19 has impacted populations around the world, with the fatality rate varying dramatically across countries. Selenium, as one of the important micronutrients implicated in viral infections, was suggested to play roles.

METHODS

An ecological study was performed to assess the association between the COVID-19 related fatality and the selenium content both from crops and topsoil, in China.

RESULTS

Totally, 14,045 COVID-19 cases were reported from 147 cities during 8 December 2019-13 December 2020 were included. Based on selenium content in crops, the case fatality rates (CFRs) gradually increased from 1.17% in non-selenium-deficient areas, to 1.28% in moderate-selenium-deficient areas, and further to 3.16% in severe-selenium-deficient areas (P = 0.002). Based on selenium content in topsoil, the CFRs gradually increased from 0.76% in non-selenium-deficient areas, to 1.70% in moderate-selenium-deficient areas, and further to 1.85% in severe-selenium-deficient areas (P < 0.001). The zero-inflated negative binomial regression model showed a significantly higher fatality risk in cities with severe-selenium-deficient selenium content in crops than non-selenium-deficient cities, with incidence rate ratio (IRR) of 3.88 (95% CIs: 1.21-12.52), which was further confirmed by regression fitting the association between CFR of COVID-19 and selenium content in topsoil, with the IRR of 2.38 (95% CIs: 1.14-4.98) for moderate-selenium-deficient cities and 3.06 (1.49-6.27) for severe-selenium-deficient cities.

CONCLUSIONS

Regional selenium deficiency might be related to an increased CFR of COVID-19. Future studies are needed to explore the associations between selenium status and disease outcome at individual-level.

Risk of breast cancer in relation to dietary intake of selenium and serum selenium as a marker of dietary intake: a prospective cohort study within The Malmö Diet and Cancer Study

Purpose

Selenium has been suggested to be protective against breast cancer, but the evidence remains inconclusive. Hence, it is important to further examine the potential protective effect. This prospective cohort study investigates pre-diagnostic selenium intake in relation to breast cancer risk. In addition, we analyze serum selenium as a marker of dietary intake.

Methods

This study includes 17,035 women in the Malmö Diet and Cancer cohort. Dietary assessment and serum samples were collected at baseline (1991–1996). During 344,584 person-years of follow-up, 1,427 incident cases were retrieved. Cox regression analysis examined breast cancer risks adjusted for potential confounding factors. In addition, odds ratios (ORs) were estimated for 1186 cases and an equal number of controls in relation to quartiles (Q) of selenium intake and groups consisting of a combination of intake and serum selenium levels.

Results

No overall association between selenium intake, or a combination of intake and serum levels, and breast cancer risk was found. The adjusted relative risk for breast cancer in selenium intake Q4 versus Q1 was 0.96 (0.83–1.12) (P_trend = 0.65). Similarly, adjusted the OR for breast cancer in selenium intake for Q4 versus Q1 was 0.97 (0.76–1.23). The kappa value, 0.096 (p = 0.001), showed poor agreement between serum selenium and selenium intake.

Conclusion

Our findings suggest that there is no overall association between selenium intake, or a combination of intake and serum levels, and breast cancer risk. Finally, our results showed a poor correlation between estimated selenium intake and serum selenium.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10552-021-01433-1.

T-2 Toxin Induces Epiphyseal Plate Lesions via Decreased SECISBP2-Mediated Selenoprotein Expression in DA Rats, Exacerbated by Selenium Deficiency

OBJECTIVE

Both selenium (Se) deficiency and mycotoxin T2 lead to epiphyseal plate lesions, similar to Kashin-Beck disease (KBD). However, regulation of selenoproteins synthesis mediated by SECISBP2, in response to these 2 environmental factors, remained unclear. The present study proposed to explore the mechanism behind the cartilage degradation resulting from Se deficiency and mycotoxin T2 exposure.

DESIGN

Deep chondrocyte necrosis and epiphyseal plate lesions were replicated in Dark Agouti (DA) rats by feeding them T2 toxin/Se deficiency artificial synthetic diet for 2 months.

RESULTS

Se deficiency led to decreased expression of COL2α1, while T2 treatment reduced the heparan sulfate 6-O-sulfotransferase 2 (HS6ST2) expression, both of which affected the cartilage extracellular matrix metabolism in the rat models. The expression of Col2α1, Acan, Hs6st2, Secisbp2, Gpx1, and Gpx4 were all significantly decreased in cartilage tissues from DA rats, fed a Se-deficient diet or exposed to T2 toxin, contrary to Adamts4, whose expression was increased in both conditions. In addition, T2 treatment led to the decreased expression of SBP2, GPX1, GPX4, and total GPXs activity in C28/I2 cells.

CONCLUSION

DA rats exposed to T2 toxin and/or Se-deficient conditions serve as the perfect model of KBD. The 2 environmental risk factors of KBD, which serve as a "double whammy," can intensify the extracellular matrix metabolic imbalance and the antioxidant activity of chondrocytes, leading to articular cartilage degradation and epiphyseal plate abnormalities similar to those observed in KBD.

Food for thought: nano-selenium in poultry nutrition and health

In recent years, nanoparticles have become a fashionable subject of research due to their sizes, shapes, and unique intrinsic physicochemical properties. In particular for the last 5 years, nano-Se has received tremendous attention in terms of its production, characteristic, and possible application for poultry/animal science and medical sciences. Indeed, Nano-Se is shown to be a potential source of Se for poultry/animal nutrition. However, there is an urgent need to address the questions related to nano-Se absorption, assimilation, and metabolism. It is not clear at present if major biological effects of nano-Se are due to Se-protein synthesis, direct antioxidant/prooxidant effects, or both. It is necessary to understand how metallic nano-Se can be converted into H2Se and further to SeCys to be incorporated into selenoproteins. The aforementioned issues must be resolved before nano-Se finds its way to animal/poultry production as a feed supplement and clearly this subject warrants further investigation.

Selenoprotein T: An Essential Oxidoreductase Serving as a Guardian of Endoplasmic Reticulum Homeostasis

Significance: Selenoproteins incorporate the essential nutrient selenium into their polypeptide chain. Seven members of this family reside in the endoplasmic reticulum (ER), the exact function of most of which is poorly understood. Especially, how ER-resident selenoproteins control the ER redox and ionic environment is largely unknown. Since alteration of ER function is observed in many diseases, the elucidation of the role of selenoproteins could enhance our understanding of the mechanisms involved in ER homeostasis. Recent Advances: Among selenoproteins, selenoprotein T (SELENOT) is remarkable as the most evolutionarily conserved and the only ER-resident selenoprotein whose gene knockout in mouse is lethal. Recent data indicate that SELENOT contributes to ER homeostasis: reduced expression of SELENOT in transgenic cell and animal models promotes accumulation of reactive oxygen and nitrogen species, depletion of calcium stores, activation of the unfolded protein response and impaired hormone secretion. Critical Issues: SELENOT is anchored to the ER membrane and associated with the oligosaccharyltransferase complex, suggesting that it regulates the early steps of N-glycosylation. Furthermore, it exerts a selenosulfide oxidoreductase activity carried by its thioredoxin-like domain. However, the physiological role of the redox activity of SELENOT is not fully understood. Likewise, the nature of its redox partners needs to be further characterized. Future Directions: Given the impact of ER stress in pathologies such as neurodegenerative, cardiovascular, metabolic and immune diseases, understanding the role of SELENOT and developing derived therapeutic tools such as selenopeptides to improve ER proteostasis and prevent ER stress could contribute to a better management of these diseases.

Copper interferes with selenoprotein synthesis and activity

Selenium and copper are essential trace elements for humans, needed for the biosynthesis of enzymes contributing to redox homeostasis and redox-dependent signaling pathways. Selenium is incorporated as selenocysteine into the active site of redox-relevant selenoproteins including glutathione peroxidases (GPX) and thioredoxin reductases (TXNRD). Copper-dependent enzymes mediate electron transfer and other redox reactions. As selenoprotein expression can be modulated e.g. by H2O2, we tested the hypothesis that copper status affects selenoprotein expression. To this end, hepatocarcinoma HepG2 cells and mice were exposed to a variable copper and selenium supply in a physiologically relevant concentration range, and transcript and protein expression as well as GPX and TXNRD activities were compared. Copper suppressed selenoprotein mRNA levels of GPX1 and SELENOW, downregulated GPX and TXNRD activities and decreased UGA recoding efficiency in reporter cells. The interfering effects were successfully suppressed by applying the copper chelators bathocuproinedisulfonic acid or tetrathiomolybdate. In mice, a decreased copper supply moderately decreased the copper status and negatively affected hepatic TXNRD activity. We conclude that there is a hitherto unknown interrelationship between copper and selenium status, and that copper negatively affects selenoprotein expression and activity most probably via limiting UGA recoding. This interference may be of physiological relevance during aging, where a particular shift in the selenium to copper ratio has been reported. An increased concentration of copper in face of a downregulated selenoprotein expression may synergize and negatively affect the cellular redox homeostasis contributing to disease processes.

Association between Serum Essential Metal Elements and the Risk of Schizophrenia in China

Numerous essential metal elements (EMEs) are necessary to maintain the proper function of human body. In this case-control study, we investigated the associations of 11 EMEs [Calcium (Ca), potassium (K), magnesium (Mg), sodium (Na), manganese (Mn), selenium (Se), cobalt (Co), Molybdenum (Mo), copper (Cu), zinc (Zn), and iron (Fe)] in serum with the risk of schizophrenia. We recruited first-episode and drug-naïve schizophrenic patients (cases = 99) and age-sex-matched normal subjects (controls = 99) from Tangshan, Hebei Province, China. The 11 EMEs in serum from cases and controls were quantified by inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry. We observed that a higher level of Mn (OR = 2.390; 95%CI: 1.504–3.796) and lower levels of Ca (OR = 0.939; 95%CI: 0.890–0.990), Mg (OR = 0.806; 95%CI: 0.669–0.972), Na (OR = 0.995; 95%CI: 0.993–0.998), and Se (OR = 0.954; 95%CI: 0.937–0.972) were associated with an elevated risk of schizophrenia. Dose–response relationships between serum EME concentrations and the risk of schizophrenia were observed in most of the schizophrenia-associated EMEs. Moreover, the serum concentrations of these schizophrenia-associated EMEs in patients were correlated with the severity of their clinical symptoms. Significant correlations were found between EMEs and biomarkers associated with schizophrenia related to metabolic and oxidative stress. This study suggested that the concentration and profile of EMEs were different between schizophrenic patients and normal controls and revealed potential metabolisms associated with EMEs and schizophrenia, suggesting EMEs might act as biomarkers of schizophrenia to improve the current situation of diagnosis and treatment.

Role of the Thyroid Gland in Expression of the Thyroid Phenotype of Sbp2-Deficient Mice

Selenocysteine insertion sequence-binding protein 2, SBP2 (SECISBP2), is required for selenoprotein synthesis. Partial SBP2 deficiency syndrome manifests characteristic thyroid function tests. The Sbp2 deficiency mouse model, Sbp2 inducible conditional knockout (iCKO), replicates this thyroid phenotype and was used for pathophysiologic investigations. As selenoproteins have an antioxidative role in thyroid gland function, their deficiencies have potential to affect thyroid hormone (TH) synthesis. Sbp2 iCKO mice had larger thyroids relative to body weight and increased thyroidal thyroxine (T4) and triiodothyronine (T3) content while 5' deiodinases enzymatic activities were decreased. Possible mechanisms for the discrepancy between the increased thyroidal T3 and normal circulating T3 were investigated in dynamic experiments. Treatment with bovine thyroid-stimulating hormone (TSH) resulted in increased delta T4 in Sbp2 iCKO mice, indicating increased availability of preformed thyroidal TH. Next, the recovery of TH levels was evaluated after withdrawal of chemical suppression. At one day, Sbp2 iCKO mice had higher serum and thyroidal T3 concomitant with lower TSH, confirming increased capacity of TH synthesis in Sbp2 deficiency. Decreased TH secretion was ruled out as serum and thyroidal TH were high in Sbp2 iCKO mice. Treatment with a low-iodine diet also ruled out thyroidal secretion defect as both serum levels and thyroidal TH content similarly declined over time in Sbp2-deficient mice compared to wild-type (Wt) mice. This study provides evidence for unsuspected changes in the thyroid gland that contribute to the thyroid phenotype of Sbp2 deficiency, with increased thyroidal T4 and T3 content in the setting of increased TH synthesis capacity contributing to the circulating TH levels while thyroidal secretion is preserved.

Proteomic analysis of infected primary human leucocytes revealed PSTK as potential treatment-monitoring marker for active and latent tuberculosis

Markers for monitoring clearance of Mycobacterium tuberculosis (Mtb) infection during anti-TB drug treatment could facilitate management of tuberculosis (TB) treatment, but are lacking. We aimed to screen for Mtb clearance markers from in-vitro-infected leucocytes and to evaluate these markers in followed-up active TB (ATB) patients and latent TB (LTBI) cases after anti-TB drug treatment. Extracellular proteins from primary leucocytes infected with each of the Mtb lineages (East-Asian, Indo-Oceanic, Euro-American and the laboratory strain H37Rv) were screened as possible clearance markers. Leucocytes infected with Staphylococcus aureus acted as controls. The proteomic analysis was performed using GeLC-MS/MS. Several quantitative and qualitative candidate clearance markers were found. These proteins were suppressed during the infection stage of all Mtb lineages and re-expressed after bacillary clearance. PSTK, FKBP8 and MGMT were common clearance markers among the four Mtb lineages in our model. Only PSTK was a potential clearance marker based on western blot validation analysis from culture supernatants. The PSTK marker was further validated with western blot analysis using serum samples (n = 6) from ATB patients and LTBI cases during anti-TB drug treatment, and from healthy controls (n = 3). Time-dependent increase of PSTK was found both in ATB and LTBI patients during the course of anti-TB drug treatment, but not in healthy controls. We have demonstrated that PSTK is a potential treatment-monitoring marker for active and latent TB.

Cul5-type Ubiquitin Ligase KLHDC1 Contributes to the Elimination of Truncated SELENOS Produced by Failed UGA/Sec Decoding

The UGA codon signals protein translation termination, but it can also be translated into selenocysteine (Sec, U) to produce selenocysteine-containing proteins (selenoproteins) by dedicated machinery. As Sec incorporation can fail, Sec-containing longer and Sec-lacking shorter proteins co-exist. Cul2-type ubiquitin ligases were recently shown to destabilize such truncated proteins; however, which ubiquitin ligase targets truncated proteins for degradation remained unclear. We report that the Cul5-type ubiquitin ligase KLHDC1 targets truncated SELENOS, a selenoprotein, for proteasomal degradation. SELENOS is involved in endoplasmic reticulum (ER)-associated degradation, which is linked to reactive oxygen species (ROS) production, and the knockdown of KLHDC1 in U2OS cells decreased ER stress-induced cell death. Knockdown of SELENOS increased the cell population with lower ROS levels. Our findings reveal that, in addition to Cul2-type ubiquitin ligases, KLHDC1 is involved in the elimination of truncated oxidoreductase-inactive SELENOS, which would be crucial for maintaining ROS levels and preventing cancer development.

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KLHDC1 is a Cul5-type ubiquitin ligase

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KLHDC1 targets immature SELENOS for proteasomal degradation

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KLHDC1 knockdown in U2OS cells decreases ER stress-induced cell death

Dietary Selenium Supplementation Ameliorates Female Reproductive Efficiency in Aging Mice

Female reproductive (ovarian) aging is distinctively characterized by a markedly reduced reproductive function due to a remarkable decline in quality and quantity of follicles and oocytes. Selenium (Se) has been implicated in playing many important biological roles in male fertility and reproduction; however, its potential roles in female reproduction, particularly in aging subjects, remain poorly elucidated. Therefore, in the current study we used a murine model of female reproductive aging and elucidated how different Se-levels might affect the reproductive efficiency in aging females. Our results showed that at the end of an 8-week dietary trial, whole-blood Se concentration and blood total antioxidant capacity (TAOC) were significantly reduced in Se-deficient (0.08 mg Se/kg; Se-D) mice, whereas both of these biomarkers were significantly higher in inorganic (0.33 mg/kg; ISe-S) and organic (0.33 mg/kg; OSe-S) Se-supplemented groups. Similarly, compared to the Se-D group, Se supplementation significantly ameliorated the maintenance of follicles and reduced the rate of apoptosis in ovaries. Meanwhile, the rate of in vitro-produced embryos resulting from germinal vesicle (GV) oocytes was also significantly improved in Se-supplemented (ISe-S and OSe-S) groups compared to the Se-D mice, in which none of the embryos developed to the hatched blastocyst stage. RT-qPCR results revealed that mRNA expression of Gpx1, Gpx3, Gpx4, Selenof, p21, and Bcl-2 genes in ovaries of aging mice was differentially modulated by dietary Se levels. A considerably higher mRNA expression of Gpx1, Gpx3, Gpx4, and Selenof was observed in Se-supplemented groups compared to the Se-D group. Similarly, mRNA expression of Bcl-2 and p21 was significantly lower in Se-supplemented groups. Immunohistochemical assay also revealed a significantly higher expression of GPX4 in Se-supplemented mice. Our results reasonably indicate that Se deficiency (or marginal levels) can negatively impact the fertility and reproduction in females, particularly those of an advancing age, and that the Se supplementation (inorganic and organic) can substantiate ovarian function and overall reproductive efficiency in aging females.

Sex Differences in Glutathione Peroxidase Activity and Central Obesity in Patients with Type 2 Diabetes at High Risk of Cardio-Renal Disease

Women with type 2 diabetes (T2DM) have an increased susceptibility of developing cardio-renal disease compared to men, the reasons and the mechanisms of this vulnerability are unclear. Since oxidative stress plays a key role in the development of cardio-renal disease, we investigated the relationship between sex, plasma antioxidants status (glutathione peroxidase (GPx-3 activity), vitamin E and selenium), and adiposity in patients with T2DM at high risk of cardio-renal disease. Women compared to men had higher GPx-3 activity (p = 0.02), bio-impedance (p ≤ 0.0001), and an increase in waist circumference in relation to recommended cut off-points (p = 0.0001). Waist circumference and BMI were negatively correlated with GPx-3 activity (p ≤ 0.05 and p ≤ 0.01, respectively) and selenium concentration (p ≤ 0.01 and p ≤ 0.02, respectively). In multiple regression analysis, waist circumference and sex were independent predictors of GPx-3 activity (p ≤ 0.05 and p ≤ 0.05, respectively). The data suggest that increased central fat deposits are associated with reduced plasma antioxidants which could contribute to the future risk of cardio-renal disease. The increased GPx-3 activity in women could represent a preserved response to the disproportionate increase in visceral fat. Future studies should be aimed at evaluating if the modulation of GPx-3 activity reduces cardio-renal risk in men and women with T2DM.

Effects of Sodium Selenite, L-Selenomethionine, and Selenium Nanoparticles During Late Pregnancy on Selenium, Zinc, Copper, and Iron Concentrations in Khalkhali Goats and Their Kids

The objective of this study was to evaluate the effect of organic, inorganic, and selenium nanoparticle supplements at the final stage of pregnancy on selenium, zinc, copper, and iron concentrations of goats and placental, colostrum, and milk transfer of these trace minerals from goats to their kids. Forty pregnant Khalkhali goats (30 ± 5 kg) were randomly allocated to four treatments including (1) no supplement (control), 0.6 mg Se head^-1 day^-1 of selenomethionine (SM), 0.6 mg Se head^-1 day^-1 of selenium nanoparticles (SN), and 0.6 mg Se head^-1 day^-1 of sodium selenite (SS), from 4 weeks before the expected day of delivery to delivery day. Blood samples were taken from the goats 4 weeks before the expected day of delivery and on the kidding day. Colostrum samples were collected from the goats immediately after kidding. Instantly after delivery, newborn kids were taken apart from their dams and their blood samples were collected from the jugular vein, before they drank their first colostrums and at 7, 14, 21, and 28 after birthday. The results demonstrated that the whole blood and serum Se concentration was greater in Se-supplemented goats compared with the control (P < 0.05). The total Se content of the whole blood and serum was higher in SN than in SM (P < 0.05) and SS goats (P < 0.05). At birth, the whole blood and serum concentration of Se was decreased (P < 0.05) in kids of SN-treated goats contrasted with the control ones (P < 0.05). The copper content of goats and their kids in treated goats was greater compared with control goats except for SN treated, which was decreased (P < 0.05). It was totally vice versa with Zn content trend in the whole blood, serum, and colostrum (P < 0.05), which was also concomitant with an increase in Fe content of kids of supplemented goats at birth and first week of life (P < 0.05). These results seem to indicate a higher efficacy of placental and colostral transfer of Se into kids of SM-treated goats when contrasted with either receiving comparable doses of SN or SS. It could be concluded that Se supplementation can affect and correlate with Cu, Zn, and Fe levels, and this effect depends a lot on the chemical or physical variety of Se supplementation.

Progress in the emerging role of selenoproteins in cardiovascular disease: focus on endoplasmic reticulum-resident selenoproteins

Cardiovascular diseases represent one of the most important health problems of developed countries. One of the main actors involved in the onset and development of cardiovascular diseases is the increased production of reactive oxygen species that, through lipid peroxidation, protein oxidation and DNA damage, induce oxidative stress and cell death. Basic and clinical research are ongoing to better understand the endogenous antioxidant mechanisms that counteract oxidative stress, which may allow to identify a possible therapeutic targeting/application in the field of stress-dependent cardiovascular pathologies. In this context, increasing attention is paid to the glutathione/glutathione-peroxidase and to the thioredoxin/thioredoxin-reductase systems, among the most potent endogenous antioxidative systems. These key enzymes, belonging to the selenoprotein family, have a well-established function in the regulation of the oxidative cell balance. The aim of the present review was to highlight the role of selenoproteins in cardiovascular diseases, introducing the emerging cardioprotective role of endoplasmic reticulum-resident members and in particular one of them, namely selenoprotein T or SELENOT. Accumulating evidence indicates that the dysfunction of different selenoproteins is involved in the susceptibility to oxidative stress and its associated cardiovascular alterations, such as congestive heart failure, coronary diseases, impaired cardiac structure and function. Some of them are under investigation as useful pathological biomarkers. In addition, SELENOT exhibited intriguing cardioprotective effects by reducing the cardiac ischemic damage, in terms of infarct size and performance. In conclusion, selenoproteins could represent valuable targets to treat and diagnose cardiovascular diseases secondary to oxidative stress, opening a new avenue in the field of related therapeutic strategies.

Selenium, Selenoproteins and Viral Infection

Reactive oxygen species (ROS) are frequently produced during viral infections. Generation of these ROS can be both beneficial and detrimental for many cellular functions. When overwhelming the antioxidant defense system, the excess of ROS induces oxidative stress. Viral infections lead to diseases characterized by a broad spectrum of clinical symptoms, with oxidative stress being one of their hallmarks. In many cases, ROS can, in turn, enhance viral replication leading to an amplification loop. Another important parameter for viral replication and pathogenicity is the nutritional status of the host. Viral infection simultaneously increases the demand for micronutrients and causes their loss, which leads to a deficiency that can be compensated by micronutrient supplementation. Among the nutrients implicated in viral infection, selenium (Se) has an important role in antioxidant defense, redox signaling and redox homeostasis. Most of biological activities of selenium is performed through its incorporation as a rare amino acid selenocysteine in the essential family of selenoproteins. Selenium deficiency, which is the main regulator of selenoprotein expression, has been associated with the pathogenicity of several viruses. In addition, several selenoprotein members, including glutathione peroxidases (GPX), thioredoxin reductases (TXNRD) seemed important in different models of viral replication. Finally, the formal identification of viral selenoproteins in the genome of molluscum contagiosum and fowlpox viruses demonstrated the importance of selenoproteins in viral cycle.

Role of Selenium and Selenoproteins in Male Reproductive Function: A Review of Past and Present Evidences

Selenium (Se) is an important trace mineral having many essential roles at the cellular and organismal levels in animal and human health. The biological effects of Se are mainly carried out by selenoproteins (encoded by 25 genes in humans and 24 in mice). As an essential component of selenoproteins, Se performs structural and enzymic roles; in the latter context it is well known for its catalytic and antioxidative functions. Studies involving different animal models have added great value to our understanding regarding the potential implications of Se and selenoproteins in mammalian fertility and reproduction. In this review, we highlight the implications of selenoproteins in male fertility and reproduction followed by the characteristic biological functions of Se and selenoproteins associated with overall male reproductive function. It is evident from observations of past studies (both animal and human) that Se is essentially required for spermatogenesis and male fertility, presumably because of its vital role in modulation of antioxidant defense mechanisms and other essential biological pathways and redox sensitive transcription factors. However, bearing in mind the evidences from mainstream literature, it is also advisable to perform more studies focusing on the elucidation of additional roles played by the peculiar and canonical selenoproteins i.e., glutathione peroxidase 4 (GPX4) and selenoprotein P (SELENOP) in the male reproductive functions. Nevertheless, search for the elucidation of additional putative mechanisms potentially modulated by other biologically relevant selenoproteins should also be included in the scope of future studies. However, as for the implication of Se in fertility and reproduction in men, though a few clinical trials explore the effects of Se supplementation on male fertility, due to inconsistencies in the recruitment of subjects and heterogeneity of designs, the comparison of such studies is still complicated and less clear. Therefore, further research focused on the roles of Se and selenoproteins is awaited for validating the evidences at hand and outlining any therapeutic schemes intended for improving male fertility. As such, new dimensions could be added to the subject of male fertility and Se supplementation.

Selenized Plant Oil Is an Efficient Source of Selenium for Selenoprotein Biosynthesis in Human Cell Lines

Selenium is an essential trace element which is incorporated in the form of a rare amino acid, the selenocysteine, into an important group of proteins, the selenoproteins. Among the twenty-five selenoprotein genes identified to date, several have important cellular functions in antioxidant defense, cell signaling and redox homeostasis. Many selenoproteins are regulated by the availability of selenium which mostly occurs in the form of water-soluble molecules, either organic (selenomethionine, selenocysteine, and selenoproteins) or inorganic (selenate or selenite). Recently, a mixture of selenitriglycerides, obtained by the reaction of selenite with sunflower oil at high temperature, referred to as Selol, was proposed as a novel non-toxic, highly bioavailable and active antioxidant and antineoplastic agent. Free selenite is not present in the final product since the two phases (water soluble and oil) are separated and the residual water-soluble selenite discarded. Here we compare the assimilation of selenium as Selol, selenite and selenate by various cancerous (LNCaP) or immortalized (HEK293 and PNT1A) cell lines. An approach combining analytical chemistry, molecular biology and biochemistry demonstrated that selenium from Selol was efficiently incorporated in selenoproteins in human cell lines, and thus produced the first ever evidence of the bioavailability of selenium from selenized lipids.

A Versatile Strategy to Reduce UGA-Selenocysteine Recoding Efficiency of the Ribosome Using CRISPR-Cas9-Viral-Like-Particles Targeting Selenocysteine-tRNA[Ser]Sec Gene

The translation of selenoprotein mRNAs involves a non-canonical ribosomal event in which an in-frame UGA is recoded as a selenocysteine (Sec) codon instead of being read as a stop codon. The recoding machinery is centered around two dedicated RNA components: The selenocysteine insertion sequence (SECIS) located in the 3′ UTR of the mRNA and the selenocysteine-tRNA (Sec-tRNA^[Ser]Sec). This translational UGA-selenocysteine recoding event by the ribosome is a limiting stage of selenoprotein expression. Its efficiency is controlled by the SECIS, the Sec-tRNA^[Ser]Sec and their interacting protein partners. In the present work, we used a recently developed CRISPR strategy based on murine leukemia virus-like particles (VLPs) loaded with Cas9-sgRNA ribonucleoproteins to inactivate the Sec-tRNA^[Ser]Sec gene in human cell lines. We showed that these CRISPR-Cas9-VLPs were able to induce efficient genome-editing in Hek293, HepG2, HaCaT, HAP1, HeLa, and LNCaP cell lines and this caused a robust reduction of selenoprotein expression. The alteration of selenoprotein expression was the direct consequence of lower levels of Sec-tRNA^[Ser]Sec and thus a decrease in translational recoding efficiency of the ribosome. This novel strategy opens many possibilities to study the impact of selenoprotein deficiency in hard-to-transfect cells, since these CRISPR-Cas9-VLPs have a wide tropism.

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.

The hsa-miR-181a-5p reduces oxidation resistance by controlling SECISBP2 in osteoarthritis

BACKGROUND

The phenotypes of osteoarthritis (OA) consist of cartilage extracellular matrix (ECM) metabolism disorder and the breakdown of cartilage homeostasis, which are induced by pro-inflammatory factors and oxidative stress. Selenoproteins regulated by selenocysteine insertion sequence binding protein 2 (SBP2) are highly effective antioxidants, but their regulatory mechanisms, particularly the involvement of miRNAs, are not fully understood.

METHODS

To explore whether miR-181a-5p and SBP2 are involved in OA pathogenesis, we established an IL-1β model using the chondrocyte SW1353 cell line. Next, we up- or down-regulated SBP2 and miRNA-181a-5p expression in the cells. Finally, we measured the expression of miRNA-181a-5p, SBP2 and three selenoproteins in OA cartilage and peripheral blood.

RESULTS

The results showed that IL-1β increased hsa-miR-181a-5p and decreased SBP2 in a time- and dose-dependent manner. GPX1 and GPX4, which encode crucial glutathione peroxidase antioxidant enzymes, were up-regulated along with SBP2 and miR-181a-5p. Furthermore, SBP2 showed a significant negative correlation with miR-181a-5p during induced ATDC5 cell differentiation. There was lower GPX1 and GPX4 mRNA expression and SBP2 protein expression in damaged cartilage than in smooth cartilage from the same OA sample, and hsa-miR-181a-5p expression on the contrary. Similar results were observed in peripheral blood. In conclusion, we have reported a novel pathway in which pro-inflammatory factors, miRNA, SBP2 and selenoproteins are associated with oxidation resistance in cartilage.

CONCLUSION

Overall, this study provides the first comprehensive evidence that pro-inflammatory factors cause changes in the cartilage antioxidant network and describes the discovery of novel mediators of cartilage oxidative stress and OA pathophysiology. Our data suggest that miR-181a-5p may be used to develop novel early-stage diagnostic and therapeutic strategies for OA.

Selenium-sensitive miRNA-181a-5p targeting SBP2 regulates selenoproteins expression in cartilage

Selenium (Se) deficiency brings about defects in the biosynthesis of several selenoproteins and has been associated with aberrant chondrogenesis. Selenocysteine (Sec) Insertion Sequence (SECIS) and SECIS binding protein 2 (SBP2) interaction is a very critical node for the metabolic balance between Se and selenoproteins. The Gpx1, Gpx4 and SelS have different binding affinities with SBP2 in cells. According to our results, both miR‐181a‐5p and SBP2 appeared to be selenium‐sensitive and regulated the expression of selenoproteins in C28/I2 cells under Se sufficient environment. However, they showed significantly opposite expression trend in Se deficiency rats cartilage and SeD C28/I2 cells. The SBP2 is a direct target gene of miR‐181a‐5p in C28/I2 cells as determined by reporter gene and off‐target experiments. And the miR‐181a‐5p could regulate SBP2 and the selenoproteins in C28/I2 cells. Depending upon the Se supply levels, C28/I2 cells were divided into three groups, that is normal Se, SeD and SeS, which underwent through a 7‐day Se deprivation process, then SBP2 was knocked‐down and overexpressed in all the groups. Moreover, the selected selenoproteins were down‐regulated in second‐generation low Se diet rat cartilage. The selenoproteins expression was decreased by Se deficiency which depended on the Selenium‐sensitive miR‐181a‐5p to participate and regulate SBP2 at post‐transcriptional level. It involves a series of antioxidant and ECM (extracellular matrix) genes, to overcome the ROS‐related stress for the protection of essential physiological functions and to maintain the balance between anabolism and catabolism of the cartilage.

Nonradioactive Isotopic Labeling and Tracing of Selenoproteins in Cultured Cell Lines

Selenium (Se) is an essential component of genetically encoded selenoproteins, in the form of a rare amino acid, namely the selenocysteine (Sec). Radioactive ⁷⁵Se has been widely used to trace selenoproteins in vitro and in vivo (cell models and animals). Alternatively, its unique isotopic pattern can be used to detect and characterize nonradioactive Se-compounds in cellular extracts using molecular or elemental mass spectrometry at ppm levels. However, when studying trace levels of Se-compounds, such as selenoproteins (ppt levels), the distribution of the signal between its six naturally abundant isotopes reduces its sensitivity. Here, we describe the use of isotopically enriched forms of Se as an alternative strategy to radioactive ⁷⁵Se, for the labeling and tracing of selenoproteins in cultured cell lines.

Detection of Selenoproteins by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP MS) in Immobilized pH Gradient (IPG) Strips

In contrast to other trace elements that are cofactors of enzymes and removed from proteins under denaturing conditions, Se is covalently bound to proteins when incorporated into selenoproteins, since it is a component of selenocysteine aminoacid. It implies that selenoproteins can undergo several biochemical separation methods in stringent and chaotropic conditions and still maintain the presence of selenium in the primary sequence. This feature has been used to develop a method for the detection of trace levels of human selenoproteins in cell extracts without the use of radioactive isotopes. The selenoproteins are separated as a function of their isoelectric point (pI) using iso-electrofocusing (IEF) electrophoretic strips and detected by laser ablation-inductively coupled plasma mass spectrometry (LA-ICP MS). This method, therefore referred to as IEF-LA-ICP MS, allowed the detection of several selenoproteins in human cell lines, including Gpx1, Gpx4, TXNRD1, TXNRD2, and SELENOF.

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.

SELENOPROTEIN O is a chloroplast protein involved in ROS scavenging and its absence increases dehydration tolerance in Arabidopsis thaliana

The evolutionary conserved family of Selenoproteins performs redox-regulatory functions in bacteria, archaea and eukaryotes. Among them, members of the SELENOPROTEIN O (SELO) subfamily are located in mammalian and yeast mitochondria, but their functions are thus far enigmatic. Screening of T-DNA knockout mutants for resistance to the proline analogue thioproline (T4C), identified mutant alleles of the plant SELO homologue in Arabidopsis thaliana. Absence of SELO resulted in a stress-induced transcriptional activation instead of silencing of mitochondrial proline dehydrogenase, and also high elevation of Δ(1)-pyrroline-5-carboxylate dehydrogenase involved in degradation of proline, thereby alleviating T4C inhibition and lessening drought-induced proline accumulation. Unlike its animal homologues, SELO was localized to chloroplasts of plants ectopically expressing SELO-GFP. The protein was co-fractionated with thylakoid membrane complexes, and co-immunoprecipitated with FNR, PGRL1 and STN7, all involved in regulating PSI and downstream electron flow. The selo mutants displayed extended survival under dehydration, accompanied by longer photosynthetic activity, compared with wild-type plants. Enhanced expression of genes encoding ROS scavenging enzymes in the unstressed selo mutant correlated with higher oxidant scavenging capacity and reduced methyl viologen damage. The study elucidates SELO as a PSI-related component involved in regulating ROS levels and stress responses.

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.

Emerging roles of endoplasmic reticulum-resident selenoproteins in the regulation of cellular stress responses and the implications for metabolic disease

Chronic metabolic stress leads to cellular dysfunction, characterized by excessive reactive oxygen species, endoplasmic reticulum (ER) stress and inflammation, which has been implicated in the pathogenesis of obesity, type 2 diabetes and cardiovascular disease. The ER is gaining recognition as a key organelle in integrating cellular stress responses. ER homeostasis is tightly regulated by a complex antioxidant system, which includes the seven ER-resident selenoproteins - 15 kDa selenoprotein, type 2 iodothyronine deiodinase and selenoproteins S, N, K, M and T. Here, the findings from biochemical, cell-based and mouse studies investigating the function of ER-resident selenoproteins are reviewed. Human experimental and genetic studies are drawn upon to highlight the relevance of these selenoproteins to the pathogenesis of metabolic disease. ER-resident selenoproteins have discrete roles in the regulation of oxidative, ER and inflammatory stress responses, as well as intracellular calcium homeostasis. To date, only two of these ER-resident selenoproteins, selenoproteins S and N have been implicated in human disease. Nonetheless, the potential of all seven ER-resident selenoproteins to ameliorate metabolic dysfunction warrants further investigation.

On elongation factor eEFSec, its role and mechanism during selenium incorporation into nascent selenoproteins

BACKGROUND

Selenium, an essential dietary micronutrient, is incorporated into proteins as the amino acid selenocysteine (Sec) in response to in-frame UGA codons. Complex machinery ensures accurate recoding of Sec codons in higher organisms. A specialized elongation factor eEFSec is central to the process.

SCOPE OF REVIEW

Selenoprotein synthesis relies on selenocysteinyl-tRNA^Sec (Sec-tRNA^Sec), selenocysteine inserting sequence (SECIS) and other selenoprotein mRNA elements, an in-trans SECIS binding protein 2 (SBP2) protein factor, and eEFSec. The exact mechanisms of discrete steps of the Sec UGA recoding are not well understood. However, recent studies on mammalian model systems have revealed the first insights into these mechanisms. Herein, we summarize the current knowledge about the structure and role of mammalian eEFSec.

MAJOR CONCLUSIONS

eEFSec folds into a chalice-like structure resembling that of the archaeal and bacterial orthologues SelB and the initiation protein factor IF2/eIF5B. The three N-terminal domains harbor major functional sites and adopt an EF-Tu-like fold. The C-terminal domain 4 binds to Sec-tRNA^Sec and SBP2, senses distinct binding domains, and modulates the GTPase activity. Remarkably, GTP hydrolysis does not induce a canonical conformational change in eEFSec, but instead promotes a slight ratchet of domains 1 and 2 and a lever-like movement of domain 4, which may be critical for the release of Sec-tRNA^Sec on the ribosome.

GENERAL SIGNIFICANCE

Based on current findings, a non-canonical mechanism for elongation of selenoprotein synthesis at the Sec UGA codon is proposed. Although incomplete, our understanding of this fundamental biological process is significantly improved, and it is being harnessed for biomedical and synthetic biology initiatives. This article is part of a Special Issue entitled "Selenium research" in celebration of 200 years of selenium discovery, edited by Dr. Elias Arnér and Dr. Regina Brigelius-Flohe.

SeMet attenuates OTA-induced PCV2 replication promotion by inhibiting autophagy by activating the AKT/mTOR signaling pathway

Porcine circovirus type 2 (PCV2) is recognized as the causative agent of porcine circovirus-associated diseases. PCV2 replication could be promoted by low doses of ochratoxin A (OTA) as in our previous study and selenium has been shown to attenuate PCV2 replication. However, the underlying mechanism remains unclear. The aim of the study was to investigate the effects of selenomethionine (SeMet), the major component of organic selenium, on OTA-induced PCV2 replication promotion and its potential mechanism. The present study demonstrates that OTA could promote PCV2 replication as measured by cap protein expression, viral titer, viral DNA copies and the number of infected cells. In addition, OTA could activate autophagy as indicated by up-regulated light chain 3 (LC3)-II and autophagy-related protein 5 expressions and autophagosome formation. Further, OTA could down-regulate p-AKT and p-mTOR expressions and OTA-induced autophagy was inhibited when insulin was applied. SeMet at 2, 4 and 6 μM had significant inhibiting effects against OTA-induced PCV2 replication promotion. Furthermore, SeMet could attenuate OTA-induced autophagy and up-regulate OTA-induced p-AKT and p-mTOR expression inhibition. Rapamycin, an inhibitor of AKT/mTOR, could reverse the effects of SeMet on OTA-induced autophagy and the PCV2 replication promotion. In conclusion, SeMet could block OTA-induced PCV2 replication promotion by inhibiting autophagy by activating the AKT/mTOR pathway. Therefore, SeMet supplementation could be an effective prophylactic strategy against PCV2 infections and autophagy may be a potential marker to develop novel anti-PCV2 drugs.

Comparison of analytical methods using enzymatic activity, immunoaffinity and selenium-specific mass spectrometric detection for the quantitation of glutathione peroxidase 1

Glutathione peroxidase 1 (Gpx1), one of the most responsive selenoproteins to the variation of selenium concentration, is often used to evaluate "selenium status" at a cellular or organismal level. The four major types of analytical methodologies to quantify Gpx1 were revisited. They include (i) an enzymatic assay, (ii, iii) polyacrylamide gel electrophoresis (PAGE) with (ii) western blot detection of protein or (iii) inductively coupled plasma mass spectrometry (ICP MS) detection of selenium, and (iv) size-exclusion chromatography with ICP MS detection. Each of the four methods was optimized for the quantification of Gpx1 with maximum sensitivity. The methods based on the enzymatic and immunodetection offer a much higher sensitivity but their accuracy is compromised by the limited selectivity and limited dynamic range. The advantages, drawbacks and sources of error of each technique are critically discussed and the need for the cross-validation of the results using the different techniques to assure the quality assurance of quantitative analysis is emphasized.