Guiding bar motif of thioredoxin reductase 1 modulates enzymatic activity and inhibitor binding by communicating with the co-factor FAD and regulating the flexible C-terminal redox motif

Thioredoxin reductase (TXNRD) is a selenoprotein that plays a crucial role in cellular antioxidant defense. Previously, a distinctive guiding bar motif was identified in TXNRD1, which influences the transfer of electrons. In this study, utilizing single amino acid substitution and Excitation-Emission Matrix (EEM) fluorescence spectrum analysis, we discovered that the guiding bar communicates with the FAD and modulates the electron flow of the enzyme. Differential Scanning Fluorimetry (DSF) analysis demonstrated that the aromatic amino acid in guiding bar is a stabilizer for TXNRD1. Kinetic analysis revealed that the guiding bar is vital for the disulfide reductase activity but hinders the selenocysteine-independent reduction activity of TXNRD1. Meanwhile, the guiding bar shields the selenocysteine residue of TXNRD1 from the attack of electrophilic reagents. We also found that the inhibition of TXNRD1 by caveolin-1 scaffolding domain (CSD) peptides and compound LCS3 did not bind to the guiding bar motif. In summary, the obtained results highlight new aspects of the guiding bar that restrict the flexibility of the C-terminal redox motif and govern the transition from antioxidant to pro-oxidant.

The mechanism of selenium regulating the permeability of vascular endothelial cells through selenoprotein O

Vascular diseases, a leading cause of death in human, are strongly associated with pathological damage to blood vessels. The selenoprotein (Sel) have been reported to play important roles in vascular disease. However, the role of SelO in vascular disease has not been conclusively investigated. The present experiment was to investigate the regulatory mechanism of the effect of SelO on the permeability of vascular endothelial. The H.E staining, FITC-Dextran staining, Dil-AC-LDL staining and FITC-WGA staining showed that vascular structure was damaged, and intercellular junctions were disrupted with selenium (Se)-deficient. Immunohistochemistry, qPCR and Western blot revealed decreased expression of the adhesion plaque proteins vinculin, talin and paxillin, decreased expression of the vascular connectivity effector molecules connexin, claudin-1 and E-cadherin and increased expression of JAM-A and N-cadherin, as well as decreased expression of the ZO-1 signaling pathways ZO-1, Rock, rhoGEF, cingulin and MLC-2. In a screening of 24 Sel present in mice, SelO showed the most pronounced changes in vascular tissues, and a possible association between SelO and vascular intercellular junction effectors was determined using IBM SPSS Statistics 25. Silencing of SelO, vascular endothelial intercellular junction adverse effects present. The regulatory relationship between SelO and vascular endothelial intercellular junctions was determined. The results showed that Se deficiency lead to increased vascular endothelial permeability and vascular tissue damage by decreasing SelO expression, suggesting a possible role for SelO in regulating vascular endothelial permeability.

Comparative investigation of selenium-enriched Pleurotus ostreatus and Ganoderma lucidum as natural sources of selenium supplementation

Selenium (Se) is an essential trace element for human health, but its nutritional supply is insufficient in large parts of the world. Mushrooms can be enriched in selenium and can serve as alternative and natural source of selenium supplementation. In the present study, two common mushroom species (Pleurotus ostreatus and Ganoderma lucidum), were enriched with two selenium compounds (selenite and selenate) to test their suitability as natural sources of selenium supplementation. Sharp differences in the the metabolic patterns of the fortified selenium were observed. Selenium was effectively metabolized in P. ostreatus but remained in inorganic form in G. lucidum. However, mushrooms extracts were effective in enhancing selenoprotein expression in cell lines. The present study highlights the importance of employing selenium speciation analysis with an element-selective technique to examine the metabolic products following mushroom fortification for nutritional purposes due to the different toxicological profile and bioavailability of different selenium biotransformation products.

Sodium selenite (Na2SeO3) attenuates T-2 toxin-induced iron death in LMH cells through the ROS/PI3K/AKT/Nrf2 pathway

T-2 toxin, is a monotrichous mycotoxin commonly found in animal feed and agricultural products that can damage tissues and organs through oxidative stress. Selenium is a trace element with favorable antioxidant effects. However, it is unclear whether T-2 toxin-induces ferroptosis in LMH cells and whether Na2SeO3 has a protective role in this process. To investigate the process of hepatic injury by T-2 toxin and its antagonistic effect by Na2SeO3, we used 20 ng/mL T-2 toxin as well as 160 nmol/L Na2SeO3 to treat the LMH cells. The results demonstrated that exposure to the T-2 toxin induced iron death by increasing the quantity of ROS, leading to oxidative damage, decreasing the quantities of SOD, GPx, and T-AOC, and increasing the accumulation of MDA and H2O2, which resulted in the accumulation of Fe2+ and the down-regulation of the manifestation of linked genes and proteins including FTH1, Gpx4, NQO-1, and HO-1. After the addition of Na2SeO3, the PI3K/AKT/Nrf2 pathway is activated by regulating the selenoproteins gene level, and the above abnormal changes are reversed. In summary, Na2SeO3 alleviated T-2 toxin-induced iron death via the PI3K/AKT/Nrf2 pathway. These study not only broaden the cytotoxic knowledge regarding T-2 toxin, but also serve as a foundation for the use of Na2SeO3 in daily life.

Selenomethionine alleviates environmental heat stress induced hepatic lipid accumulation and glycogen infiltration of broilers via maintaining mitochondrial and endoplasmic reticulum homeostasis

With the increasing of global mean surface air temperature, heat stress (HS) induced by extreme high temperature has become a key factor restricting the poultry industry. Liver is the main metabolic organ of broilers, HS induces liver damage and metabolic disorders, which impairs the health of broilers and affects food safety. As an essential trace element for animals, selenium (Se) involves in the formation of antioxidant system, and its biological functions are generally mediated by selenoproteins. However, the mechanism of Se against HS induced liver damage and metabolic disorders in broilers is inadequate. Therefore, we developed the chronic heat stress (CHS) broiler model and investigated the potential protection mechanism of organic Se (selenomethionine, SeMet) on CHS induced liver damage and metabolic disorders. In present study, CHS caused liver oxidative damage, and induced hepatic lipid accumulation and glycogen infiltration of broilers, which are accompanied by mitochondrial dysfunction, abnormal mitochondrial tricarboxylic acid (TCA) cycle and endoplasmic reticulum (ER) stress. Dietary SeMet supplementation increased the hepatic Se concentration and exhibited protective effects via promoting the expression of selenotranscriptome and several key selenoproteins (GPX4, TXNRD2, SELENOK, SELENOM, SELENOS, SELENOT, GPX1, DIO1, SELENOH, SELENOU and SELENOW). These key selenoproteins synergistically improved the antioxidant capacity, and mitigated the mitochondrial dysfunction, abnormal mitochondrial TCA cycle and ER stress, thus recovered the hepatic triglyceride and glycogen concentration. What's more, SeMet supplementation suppressed lipid and glycogen biosynthesis and promoted lipid and glycogen breakdown in liver of broilers exposed to CHS though regulating the AMPK signals. Overall, our present study reveals a potential mechanism that Se alleviates environment HS induced liver damage and glycogen and lipid metabolism disorders in broilers, which provides a preventive and/or treatment measure for environment HS-dependent hepatic metabolic disorders in poultry industry.

Selenium modulates AR/IGF-1R/EGFR and TROP2 signaling pathways and improves anticancer efficacy in murine mammary carcinoma 4T1

The micronutrient selenium (Se) has been shown to exert potential anticancer properties. This study aimed to evaluate the effects of Se (in Se yeast form) on the selenoproteins (SELENO), AR/IGF-1R/EGFR, PI3K/Akt/mTOR and Ras/Raf/ERK cascades, and immune checkpoint blockade in TNBC murine 4T1 cells. We also assessed the effects of combination treatment with chemotherapeutic doxorubicin and Se on trophoblast cell surface antigen 2 (TROP2) levels. Compared with the control groups, cells incubated with Se (0.25, 0.5, 0.75, 1.0, 1.5 µg Se/mL) have lower viability, raised intracellular Se concentrations and SELENO expression, and higher malondialdehyde products in a dose-dependent manner. Se induced the inactivation of AR/IGF-1R/EGFR and downregulation of the PI3K/Akt/mTOR and Ras/Raf/ERK signaling molecules. Se-treated cells also exhibited decreased mitochondrial membrane potential, reduced levels of the cell cycle regulatory protein cyclin D1, cancer stemness, metastatic and EMT-related markers, and increased apoptosis. Subsequently, Se treatment significantly suppressed PD-1/PD-L1 and CTLA-4 mRNA levels and proteins. Doxorubicin decreased 4T1 cell viability and TROP2 expression levels, but the addition of Se to doxorubicin contributed to further reductions. Similar responses to Se treatment were also observed in the human MDA-MB-231 and MCF-7 breast cancer cells. These results show that Se upregulates SELENO and anti-AR/IGF-1R/EGFR signaling in TNBC cells, thus inducing oxidative stress-dependent apoptosis and cell cycle arrest, stemness, EMT, and metastasis, as well as blocking the immune checkpoint molecules. TROP2 down-regulation with Se is also a potential anti-TNBC therapeutic target.

Comparison of Nutritional Availability of Biogenic Selenium Nanoparticles and Chemically Synthesized Selenium Nanoparticles

Selenium (Se) is an essential micronutrient, and animals biosynthesize selenoproteins from various selenocompounds such as inorganic salts and organic selenocompounds as a Se source. In addition to the inorganic and organic forms of Se, it is also known that elemental Se is biologically synthesized at the nanoscale in nature. Biologically synthesized Se nanoparticles (Se-NPs), i.e., biogenic Se-NPs (Se-BgNPs), have not been fully investigated as a Se source compared with the other forms of Se. In this study, we evaluated the nutritional availability of Se-BgNPs biosynthesized in E. coli and revealed that Se-BgNPs were less assimilated into selenoproteins in rats as a Se source than inorganic Se salt or chemically synthesized Se-NPs. Se-BgNPs showed tolerance toward digestion and low absorbability in gut, which resulted in the low nutritional availability. Se-BgNPs seem to be coated with a biomaterial that functions to reduce their toxicity toward E. coli and at the same time lowers their availability to animals.

Improving Catalytic Activity, Acid-Tolerance, and Thermal Stability of Glutathione Peroxidase by Systematic Site-Directed Selenocysteine Incorporation

Glutathione peroxidase (GPx) is an important antioxidant enzyme. Selenocysteine (Sec)-containing GPxs (Sec-GPxs) are usually superior to their conventional cysteine-containing counterparts (Cys-GPxs), which make up the majority of the natural GPxs but display unsuitable activity and stability for industrial applications. This study first heterologously expressed and characterized a Cys-GPx from Lactococcus lactis (LlGPx), systematically exchanged all the three Cys to Sec and introduced an extra Sec. The results showed that the insertion of Sec at the active site could effectively increase the enzyme activity and confer a lower optimal pH value on the mutants. The double mutant C36U/L157U increased by 2.65 times (5.12 U/mg). The thermal stability of the C81U mutant was significantly improved. These results suggest that site-directed Sec incorporation can effectively improve the enzymatic properties of LlGPx, which may be also used for the protein engineering of other industrial enzymes containing catalytic or other functional cysteine residues.

Development of an assay pipeline for the discovery of novel small molecule inhibitors of human glutathione peroxidases GPX1 and GPX4

Selenoprotein glutathione peroxidases (GPX), like ubiquitously expressed GPX1 and the ferroptosis modulator GPX4, enact antioxidant activities by reducing hydroperoxides using glutathione. Overexpression of these enzymes is common in cancer and can be associated with the development of resistance to chemotherapy. GPX1 and GPX4 inhibitors have thus shown promise as anti-cancer agents, and targeting other GPX isoforms may prove equally beneficial. Existing inhibitors are often promiscuous, or modulate GPXs only indirectly, so novel direct inhibitors identified through screening against GPX1 and GPX4 could be valuable. Here, we developed optimized glutathione reductase (GR)-coupled GPX assays for the biochemical high-throughput screen (HTS) of almost 12,000 compounds with proposed mechanisms of action. Initial hits were triaged using a GR counter-screen, assessed for isoform specificity against an additional GPX isoform, GPX2, and were assessed for general selenocysteine-targeting activity using a thioredoxin reductase (TXNRD1) assay. Importantly, 70% of the GPX1 inhibitors identified in the primary screen, including several cephalosporin antibiotics, were found to also inhibit TXNRD1, while auranofin, previously known as a TXNRD1 inhibitor, also inhibited GPX1 (but not GPX4). Additionally, every GPX1 inhibitor identified (including omapatrilat, tenatoprazole, cefoxitin and ceftibuten) showed similar inhibitory activity against GPX2. Some compounds inhibiting GPX4 but not GPX1 or GPX2, also inhibited TXNRD1 (26%). Compounds only inhibiting GPX4 included pranlukast sodium hydrate, lusutrombopag, brilanestrant, simeprevir, grazoprevir (MK-5172), paritaprevir, navitoclax, venetoclax and VU0661013. Two compounds (metamizole sodium and isoniazid sodium methanesulfate) inhibited all three GPXs but not TXNRD1, while 2,3-dimercaptopropanesulfonate, PI4KIII beta inhibitor 3, SCE-2174 and cefotetan sodium inhibited all tested selenoproteins (but not GR). The detected overlaps in chemical space suggest that the counter screens introduced here should be imperative for identification of specific GPX inhibitors. With this approach, we could indeed identify novel GPX1/GPX2- or GPX4-specific inhibitors, thus presenting a validated pipeline for future identification of specific selenoprotein-targeting agents. Our study also identified GPX1/GPX2, GPX4 and/or TXNRD1 as targets for several previously developed pharmacologically active compounds.

Carrimycin, a first in-class anti-cancer agent, targets selenoprotein H to induce nucleolar oxidative stress and inhibit ribosome biogenesis

Carrimycin is a synthetic macrolide antibiotic that has been shown to have anti-cancer activity; however, its exact mechanism of action and molecular target were previously unknown. It was recently elucidated that Isovalerylspiramycin I (ISP I), the active component of carrimycin, targets selenoprotein H (SelH), a nucleolar reactive oxygen species-scavenging enzyme in the selenoprotein family. ISP I treatment accelerates SelH degradation, resulting in oxidative stress, disrupted ribosomal biogenesis, and apoptosis in tumor cells. Specifically, ISP I disrupts the association between RNA polymerase I and ribosomal DNA in the nucleolus. This inhibits ribosomal RNA transcription and subsequent ribosomal assembly, which prevents cancer cells from sustaining elevated rates of protein synthesis and cellular proliferation that are necessary for tumor growth and malignancy. In this review, we (1) describe the historical categorization and evolution of anti-cancer agents, including macrolide antibiotics, (2) outline the discovery of SelH as a target of ISP I, and (3) summarize the ways in which carrimycin has been used both clinically and at the bench to date and propose additional potential therapeutic uses.

Serine Administration Improves Selenium Status, Oxidative Stress, and Mitochondrial Function in Longissimus Dorsi Muscle of Piglets with Intrauterine Growth Retardation

Intrauterine growth retardation (IUGR) causes oxidative stress in the skeletal muscle. Serine and selenoproteins are involved in anti-oxidative processes; however, whether IUGR affects selenium status and whether serine has beneficial effects remain elusive. Here, we investigated the effects of serine administration on selenium nutritional status and oxidative stress in the longissimus dorsi muscle of piglets with IUGR. Six newborn Min piglets having normal birth weight were administered saline, and 12 IUGR piglets were either administered saline or 0.8% serine. The results showed a lower selenium content in skeletal muscle in IUGR piglets, which was restored after serine administration. IUGR piglets showed a disturbed expression of genes encoding selenoproteins, with decreased expression of GPX2, GPX4, TXNRD1, and TXNRD3 and increased expression of DIO1, DIO2, SELF, SELM, SELP, and SELW. Notably, serine administration restored the expression levels of these genes. In accordance with the changes in gene expression, the activity of GPX, TXNRD, and DIO and the content of GSH and SELP were also altered, whereas serine administration restored their contents and activities. Moreover, we observed severe oxidative stress in the skeletal muscle of IUGR piglets, as indicated by decreased GSH content and increased MDA and PC content, whereas serine administration alleviated these changes. In conclusion, our results indicate that IUGR piglets showed a disturbed expression of genes encoding selenoproteins, accompanied by severe oxidative stress. Serine administration can improve selenium status, oxidative stress, and mitochondrial function in the longissimus dorsi muscle of piglets with IUGR. These results suggest that serine could potentially be used in the treatment of IUGR in piglets.

Selenoprotein Gene mRNA Expression Evaluation During Renal Ischemia-Reperfusion Injury in Rats and Ebselen Intervention Effects

Effects of selenoproteins on many renal diseases have been reported. However, their role in renal ischemia-reperfusion (I/R) injury is unclear. The present study was performed to investigate the impact of ebselen and renal I/R injury on the expression of selenoproteins. Sprague-Dawley rats were pretreated with or without ebselen (10 mg/kg) through a daily single oral administration from 3 days before renal I/R surgery. RT-qPCR (real-time quantitative PCR) was performed to determine the mRNA expression of 25 selenoprotein genes in the renal tissues. The expression levels of two selenoproteins, including GPX3 (glutathione peroxidase 3) and DIO1 (iodothyronine deiodinase 1), were evaluated by Western blot or/and IHF (immunohistofluorescence) assays. Furthermore, renal function, renal damage, oxidative stress, and apoptosis were assessed. The results showed that in renal I/R injury, the mRNA levels of 15 selenoprotein genes (GPX1, GPX3, GPX4, DIO1, DIO2, TXNRD2, TXNRD3, SEPHS2, MSRB1, SELENOF, SELENOK, SELENOO, SELENOP, SELENOS, and SELENOT) were decreased, whereas those of eight selenoprotein genes (GPX2, GPX6, DIO3, TXNRD1, SELENOH, SELENOM, SELENOV, and SELENOW) were increased. I/R also induced a reduction in the expression levels of GPX3 and DIO1 proteins. In addition, our results indicated that ebselen reversed the changes in those selenoprotein genes, excluding SELENOH, SELENOM, SELENOP, and SELENOT, in renal I/R injury and alleviated I/R-induced renal dysfunction, tissue damage, oxidative stress, and apoptosis. To our knowledge, this is the first study to investigate the changes of 25 mammalian selenoprotein genes in renal I/R injury kidneys. The present study also provided more evidence for the roles of ebselen against renal I/R injury.

Side-by-side comparison of recombinant human glutathione peroxidases identifies overlapping substrate specificities for soluble hydroperoxides

Five out of eight human glutathione peroxidases (GPXs) are selenoproteins, representing proteins that contain selenium as part of the amino acid selenocysteine. The GPXs are important for reducing hydroperoxides in a glutathione-consuming manner and thus regulate cellular redox homeostasis. GPX1, GPX2, and GPX4 represent the three main cytosolic GPXs, but they differ in their expression patterns with GPX1 and GPX4 being expressed ubiquitously, whereas GPX2 is mainly expressed in epithelial cells. GPX1 and GPX2 have been described to reduce soluble hydroperoxides, while GPX4 reduces complex lipid hydroperoxides, thus protecting cells from lipid peroxidation and ferroptosis. But most of these data are derived from cells that are devoid of one of the isoforms and thus, compensation or other cellular effects might affect the conclusions. So far, the use of isolated recombinant human selenoprotein glutathione peroxidases in pure enzyme assays has not been employed to study their substrate specificities side by side. Using recombinant GPX1, GPX2, and GPX4 produced in E. coli we here assessed their GPX activities by a NADPH-consuming glutathione reductase-coupled assay with 17 different peroxides (all at 50 μM) as substrates. GPX4 was clearly the only isoform able to reduce phosphatidylcholine hydroperoxide. In contrast, small soluble hydroperoxides such as H₂O₂, cumene hydroperoxide, and tert-butyl hydroperoxide were reduced by all three isoforms, but with approximately 10-fold higher efficiency for GPX1 in comparison to GPX2 and GPX4. Also, several fatty acid-derived hydroperoxides were reduced by all three isoforms and again GPX1 had the highest activity. Interestingly, the stereoisomerism of the fatty acid-derived hydroperoxides clearly affected the activity of the GPX enzymes. Overall, distinct substrate specificity is obvious for GPX4, but not so when comparing GPX1 and GPX2. Clearly GPX1 was the most potent isoform of the three GPXs in terms of turnover in reduction of soluble and fatty-acid derived hydroperoxides.

Macranthoidin B (MB) Promotes Oxidative Stress-Induced Inhibiting of Hepa1-6 Cell Proliferation via Selenoprotein

The aim of this study was to investigate the role of selenoproteins in Macranthoidin B (MB) with regard to the inhibition of hepa1-6 cell proliferation. The CCK8 method was used to detect the inhibition rate in hepa1-6 cell of proliferation. The production of ROS, MDA, GSH levels, and GSH-Px and SOD activities was detected according to corresponding reagent kits. We determined the mRNA expressions of 25 selenoproteins in hepa1-6 cells via real-time quantitative PCR (qRT-PCR); moreover, the heat map and principal component analysis were used for further bioinformatics analysis. The results revealed that with an increasing concentration of MB, the inhibitory effect on hepa1-6 cell proliferation intensified. Compared with the control group, the treatment group showed significantly increased ROS levels, elevated MDA contents, and decreased GSH level, GSH-Px activity, and SOD activity. Increasing MB concentration treatment induced remarkable degradation of Txnrd1, Txnrd2, Txnrd3, Gpx1, Gpx2, Gpx3, Gpx6, Dio1, Dio2, Selt, Selp, Selh, Selk, Selw, Seln, and Dio3. Principal component analysis revealed that Txnrd 3, Selk, Selo, Selw, Selt, Dio2, Txnrd1, Dio3, Gpx6, and Dio1 were highly correlated with MB. In conclusion, MB dose dependently inhibited hepa1-6 cell proliferation and induced oxidative stress. Based on bioinformatics analysis, with MB treatment, Txnrd 3, Selk, Selo, Selw, Selt, Dio2, Txnrd1, Dio3, Gpx6, and Dio1 exhibited critical role in the inhibition of hepa1-6 cells proliferation. The functions of these selenoproteins were associated with oxidative stress.

Alleviating effects of selenium on fluoride-induced testosterone synthesis disorder and reproduction toxicity in rats

Fluoride (F) exists widely in food, water and other natural resources, and can cause damage to the reproductive system of human and animals. Studies have shown that selenium (Se) is a necessary trace element to maintain the normal male reproductive system. However, it is not clear whether it can alleviate the damage of reproductive system induced by F. Hence, sodium fluoride (NaF) was administered singly in drinking water at 100 mg L^-1 alone and co-administered by drinking with sodium selenite (Na₂SeO₃) at 0.5, 1.0, 2.0 mg L^-1 for 10 consecutive weeks. The results demonstrated that the sperm deformity rate were increased significantly by F, however, it was improved significantly after the addition of 2.0 mg L^-1 Na₂SeO₃. The contents of glutathione peroxidase 4 (GPX-4), selenoprotein P (SePP), pregnenolone (PREG), androstenedione (ASD), and testosterone (T) were reduced obviously in the F group, however, it was increased significantly after adding 0.5, 1.0 and 2.0 mg L^-1 Na₂SeO₃. F decreased noticeably the mRNA and protein expression levels of steroidogenic acute regulatory protein (StAR), cytochrome P450 cholesterol side chain lyase (P450scc), 3β-hydroxysteroid dehydrogenase (3β-HSD), cytochrome P450 17α-hydroxylase (P450c17) and 17β-hydroxysteroid dehydrogenase (17β-HSD), which was increased obviously after the addition of 1.0 and 2.0 mg L^-1 Na₂SeO₃. In summary, 2.0 mg L^-1 Na₂SeO₃ can alleviate testosterone synthesis disorder induced by F via reducing oxidative stress, increasing the level of selenoprotein in testis and regulating the content of related hormones and enzyme activity during testosterone synthesis pathway.

Deiodinases control local cellular and systemic thyroid hormone availability

Iodothyronine deiodinases (DIO) are a family of selenoproteins controlling systemic and local availability of the major thyroid hormone l-thyroxine (T4), a prohormone secreted by the thyroid gland. T4 is activated to the active 3,3'-5-triiodothyronine (T3) by two 5'-deiodinases, DIO1 and DIO2. DIO3, a 5-deiodinase selenoenzyme inactivates both the prohormone T4 and its active form T3. DIOs show species-specific different patterns of temporo-spatial expression, regulation and function and exhibit different mechanisms of reaction and inhibitor sensitivities. The main regulators of DIO expression and function are the thyroid hormone status, several growth factors, cytokines and altered pathophysiological conditions. Selenium (Se) status has a modest impact on DIO expression and translation. DIOs rank high in the priority of selenium supply to various selenoproteins; thus, their function is impaired only during severe selenium deficiency. DIO variants, polymorphisms, SNPs and rare mutations have been identified. Development of DIO isozyme selective drugs is ongoing. A first X-ray structure has been reported for DIO3. This review focusses on the biochemical characteristics and reaction mechanisms, the relationships between DIO selenoproteins and their importance for local and systemic provision of the active hormone T3. Nutritional, pharmacological, and environmental factors and inhibitors, such as endocrine disruptors, impact DIO functions.

Seizures, ataxia and parvalbumin-expressing interneurons respond to selenium supply in Selenop-deficient mice

Mice with constitutive disruption of the Selenop gene have been key to delineate the importance of selenoproteins in neurobiology. However, the phenotype of this mouse model is exquisitely dependent on selenium supply and timing of selenium supplementation. Combining biochemical, histological, and behavioral methods, we tested the hypothesis that parvalbumin-expressing interneurons in the primary somatosensory cortex and hippocampus depend on dietary selenium availability in Selenop-/- mice. Selenop-deficient mice kept on adequate selenium diet (0.15 mg/kg, i.e. the recommended dietary allowance, RDA) developed ataxia, tremor, and hyperexcitability between the age of 4-5 weeks. Video-electroencephalography demonstrated epileptic seizures in Selenop-/- mice fed the RDA diet, while Selenop± heterozygous mice behaved normally. Both neurological phenotypes, hyperexcitability/seizures and ataxia/dystonia were successfully prevented by selenium supplementation from birth or transgenic expression of human SELENOP under a hepatocyte-specific promoter. Selenium supplementation with 10 μM selenite in the drinking water on top of the RDA diet increased the activity of glutathione peroxidase in the brains of Selenop-/- mice to control levels. The effects of selenium supplementation on the neurological phenotypes were dose- and time-dependent. Selenium supplementation after weaning was apparently too late to prevent ataxia/dystonia, while selenium withdrawal from rescued Selenop-/- mice eventually resulted in ataxia. We conclude that SELENOP expression is essential for preserving interneuron survival under limiting Se supply, while SELENOP appears dispensable under sufficiently high Se status.

Selenium Deficiency Induces Inflammatory Response and Decreased Antimicrobial Peptide Expression in Chicken Jejunum Through Oxidative Stress

Selenium deficiency can affect the level of selenoprotein in organs and tissues and cause inflammation. However, the mechanism of selenium deficiency on jejunal injury in chickens remains unclear. In this study, we established a selenium deficiency model in chickens by feeding a low selenium diet and observed ultrastructural and pathological changes in the jejunum. The expression levels of 25 selenoproteins, the levels of oxidative stress, tight junction (TJ) proteins, and antimicrobial peptides (AMP), as well as the expression levels of factors related to inflammatory signaling pathways, were examined in the intestine and analyzed using principal component analysis (PCA). The results of PCA and quantitative real-time PCR (qRT-PCR) showed that selenium deficiency mainly affected the expression of antioxidant selenoproteins in chicken jejunum, especially glutathione peroxidases, thioredoxin reductase, and iodothyronine deiodinase, thus weakening the antioxidant function in the intestine and inducing oxidative stress. We also found disruption of intestinal TJ structures, a significant reduction in TJ protein expression, and downregulation of antimicrobial peptide levels, suggesting that selenium deficiency led to damage of the intestinal barrier. In addition, a significant increase in inflammatory cell infiltration and expression of inflammatory factors was observed in the jejunum, indicating that selenium deficiency induces inflammatory injury. In conclusion, selenium deficiency downregulates antioxidant selenoproteins levels, induces oxidative stress, decreases intestinal AMP levels, and leads to inflammatory injury and disruption of the intestinal barrier in the jejunum. These results shed new light on the molecular mechanisms of intestinal damage caused by selenium deficiency.

The selenoprotein methionine sulfoxide reductase B1 (MSRB1)

Methionine (Met) can be oxidized to methionine sulfoxide (MetO), which exist as R- and S-diastereomers. Present in all three domains of life, methionine sulfoxide reductases (MSR) are the enzymes that reduce MetO back to Met. Most characterized among them are MSRA and MSRB, which are strictly stereospecific for the S- and R-diastereomers of MetO, respectively. While the majority of MSRs use a catalytic Cys to reduce their substrates, some employ selenocysteine. This is the case of mammalian MSRB1, which was initially discovered as selenoprotein SELR or SELX and later was found to exhibit an MSRB activity. Genomic analyses demonstrated its occurrence in most animal lineages, and biochemical and structural analyses uncovered its catalytic mechanism. The use of transgenic mice and mammalian cell culture revealed its physiological importance in the protection against oxidative stress, maintenance of neuronal cells, cognition, cancer cell proliferation, and the immune response. Coincident with the discovery of Met oxidizing MICAL enzymes, recent findings of MSRB1 regulating the innate immunity response through reversible stereospecific Met-R-oxidation of cytoskeletal actin opened up new avenues for biological importance of MSRB1 and its role in disease. In this review, we discuss the current state of research on MSRB1, compare it with other animal Msrs, and offer a perspective on further understanding of biological functions of this selenoprotein.

Selenium status and type 2 diabetes risk

Optimal selenium (Se) status is necessary for overall health. That status can be affected by food intake pattern, age, sex, and health status. At nutritional levels of intake, Se functions metabolically as an essential constituent of some two dozen selenoproteins, most, if not all, of which have redox functions. Insufficient dietary intake of Se reduces, to varying degrees, the expression of these selenoproteins. Recent clinical and animal studies have indicated that both insufficient and excessive Se intakes may increase risk of type 2 diabetes mellitus (T2D), perhaps by way of selenoprotein actions. In this review, we discuss the current evidence linking Se status and T2D risk, and the roles of 14 selenoproteins and other proteins involved in selenoprotein biosynthesis. Understanding such results can inform the setting of safe and adequate Se intakes.

New insights on selenoproteins and neuronal function

Fifty years have passed since the discovery of the first selenoprotein by Rotruck and colleagues. In that time, the essential nature of selenium has come to light including the dependence of the brain on selenium to function properly. Animal models have shown that a lack of certain selenoproteins in the brain is detrimental for neuronal health, sometimes leading to neurodegeneration. There is also potential for selenoprotein-mediated redox balance to impact neuronal activity, including neurotransmission. Important insights on these topics have been gained over the past several years. This review briefly summarizes the known roles of specific selenoproteins in the brain while highlighting recent advancements regarding selenoproteins in neuronal function. Hypothetical models of selenoprotein function and emerging topics in the field are also provided.

Characterization of a new selenoprotein methionine sulfoxide reductase from Haematococcus pluvialis and its antioxidant activity in response to high light intensity, hydrogen peroxide, glyphosate, and cadmium exposure

Selenium incorporates into selenocysteine (Sec) which is a key component of selenoproteins implicated in antioxidant defense and redox homeostasis. Methionine sulfoxide reductases (Msr) play crucial roles in cellular defense against environmental stress. Whereas mammals have the MsrB selenoprotein form, unicellular organisms have MsrA. The Sec residue at the conserved catalytic sites of selenoprotein MsrA confers a metabolic advantage over the non-selenoprotein type MsrA. In the present study, the novel selenoprotein HpMsrA from Haematococcus pluvialis was cloned by the rapid amplification of cDNA ends and transformed into the model green alga Chlamydomonas reinhardtii. Alignment of homologs revealed the presence of the conserved catalytic domain GUFW and showed that the HpMsrA protein comprises Sec (U) at the N-terminus but no recycled Cys at the C-terminus. We studied the response of HpMsrA expression to selenite, high light intensity, hydrogen peroxide, cadmium nitrate, and glyphosate exposure via real-time quantitative PCR and enzyme activity analysis. The results demonstrated that HpMsrA protects cellular proteins against oxidative and environmental stressors. Compared with wild type C. reinhardtii, the transformant exhibited a superior antioxidant ability. The discoveries made herein shed light on the antioxidant physiology and environmental stress resistance mechanisms of the selenoproteins in microalgae. This information may aid in conducting environmental risk assessments of aquatic ecosystems involving microalgae known to respond rapidly and quantitatively to abiotic stress factors promoting excessive reactive oxygen species generation.

Yeast Selenium Exerts an Antioxidant Effect by Regulating the Level of Selenoprotein to Antagonize Cd-Induced Pyroptosis of Chicken Liver

Cadmium (Cd) exposure can cause multiple organ damage in humans and animals by causing oxidative stress. Organic selenium can antagonize the toxic damage of heavy metals by exerting antioxidant effects. Oxidative stress can activate NLRP3/Caspase1-dependent pyroptosis, but it is not clear whether yeast selenium (Se Y) can antagonize Cd-induced pyroptosis in the chicken liver. In this experiment, we studied the effects of CdCl₂ single, Se Y single, and combined exposure on the pyroptosis of chicken liver. The results showed that Cd exposure induced oxidative stress in the chicken liver, and the expression of Sepx1, SelU, SelT, GPx1, GPx4, Dio1, Dio2, Dio3, TrxR1, TrxR2, TrxR3, SelH, SelI, SelO, SelK, SelPb, Selpp, and Sel15 decreased. In addition, NLRP3 inflammasome complex (NOD-like receptor protein 3 (NLRP3), apoptosis-associated speck-like protein containing (ASC), and pro-Caspase1), Cysteinyl aspartate specific proteinase (Caspase1), Interleukin-β (IL-1β), and Interleukin-18 (IL-18) were upregulated. The combined treatment of Se Y and Cd found that the antioxidant level and the expression level of selenoprotein recovered to the Se group, and the liver pyroptosis decreased. Principal component analysis and correlation analysis screened out that selenoprotein O (SelO) is negatively correlated with pyroptosis-related genes. In short, our data shows that Se Y exerts an antioxidant effect by increasing the expression of selenoproteins and antagonizing the pyroptosis of chicken liver induced by Cd. This study provides new ideas for the field of heavy metal toxicology research. And the selected SelO has an important reference significance for follow-up research.

Comprehensive proteomic analysis to elucidate the anti-heat stress effects of nano-selenium in rainbow trout (Oncorhynchus mykiss)

Because of the continuous intensification of global warming, extreme climate fluctuations, and high-density farming, cold-water rainbow trout (Oncorhynchus mykiss) are exposed to conditions of heat stress, which has severely impacted their survival and yield. Nano-selenium (nano-Se) shows higher biological activity and lower toxicity and has emerged as an ideal and ecological Se formulation. Herein rainbow trout were fed either a basal diet (control group) or basal diet plus 5 mg/kg nano-Se (treatment group). Samples were collected before (18 °C for 9 days; CG18, Se18) and after (24 °C for 8 h; CG24, Se24) heat stress. The DIA/SWATH approach was then applied to compare changes at the proteome level. We found 223 and 269 differentially abundant proteins in the CG18-CG24 and Se18-Se24 groups, respectively, which mainly included apoptosis-, heat stress-, and lipid-related proteins. In comparison with the CG18-CG24 group, the Se18-Se24 group showed higher abundance of molecular chaperone, such as Hsp70, Hsp90a.1, Hspa8, Hsp30, DNAJA4, Dnajb1, Bag2 and Ahsa1; on nano-Se supplementation, the heat stress-induced decline in the abundance of the selenoprotein MsrB2 was partially restored. Furthermore, nano-Se supplementation downregulated the abundance of lipid-related (CYP51, EBP, DHCR7, DHCR24, and APOB) and pro-apoptotic (caspase-8 and Bad) proteins. Protein-protein interaction analyses suggested that nano-Se inhibits apoptosis by upregulating the expression of Hsp70, Hsp90a.1, Hspa8, and Dnajb1; further, Hsp70/Hspa8 and MsrB2 appear to play a synergistic role in antioxidant defense under heat stress. Overall, our findings provide novel insights into nano-Se-mediated tolerance of heat stress, demonstrating that nano-Se exerts its anti-heat stress effects in rainbow trout by promoting protein repair, enhancing recovery of antioxidant enzyme activity, and alleviating lipid metabolism and apoptosis.

Dysregulation of Transcription Profile of Selenoprotein in Patients with Kashin-Beck Disease and Its Effect on Se Deficiency-Induced Chondrocyte Apoptosis

Kashin-Beck disease (KBD) is a chronic, degenerative osteoarthropathy related to selenium (Se) deficiency. Se participates in the synthesis of selenoprotein in the form of selenocysteine. In total, 25 selenoproteins, encoded by 25 genes, are currently found in humans; however, the effects of selenoprotein genes on chondrocyte apoptosis, particularly in apoptosis-related genes, remain poorly elucidated. Therefore, in the current study, the expression of selenoprotein genes and apoptosis-related genes were determined by RT-qPCR in patients and chondrocytes and the correlations between them were analyzed using Pearson and Spearman's rank correlation, and the chondrocyte apoptosis rate was detected by Annexin V-FITC/PI. The results showed that the mRNA levels of 17 selenoprotein genes were downregulated, whereas two genes were upregulated in patients with KBD. The BAX/BCL2 ratio and the mRNA levels of BAX and P53 were increased, but the mRNA levels of BCL2 and NF-κB p65 were decreased in patients with KBD. The mRNA levels of GPX2, GPX3, DIO1, TXNRD1, TXNRD3, and SPS2 were most closely associated with apoptosis-related genes in patients with KBD. Moreover, in the Se deficiency group, the mRNA levels of GPX3, DIO1, and TXNRD1 were downregulated and GPX activity was decreased, but the late apoptosis rate, the mRNA levels of BAX and P53, and the BAX/BCL2 ratio were increased; the opposite trend was observed in the Se supplement group. Collectively, these results indicate that selenoprotein transcription profile is dysregulated in patients with KBD. Furthermore, the expression of GPX3, DIO1, and TXNRD1 genes might be involved in the development of chondrocyte apoptosis by affecting antioxidant capacity.

coli host strain

Selenoproteins containing the rare amino acid selenocysteine (Sec), typically being enzymes utilizing the selenium atom of Sec for promoted catalysis of redox reactions, are challenging to obtain at high amounts in pure form. The technical challenges limiting selenoprotein supply derive from intricacies in their translation, necessitating the recoding of a UGA stop codon to a sense codon for Sec. This, in turn, involves the interactions of a Sec-dedicated elongation factor, either directly or indirectly, with a structure in the selenoprotein-encoding mRNA called a SECIS element (Selenocysteine Insertion Sequence), a dedicated tRNA species for Sec with an anticodon for the UGA, and several accessory enzymes and proteins involved in the selenoprotein synthesis. Here, we describe an alternative method for recombinant selenoprotein production using UAG as the Sec codon in a specific strain of E. coli lacking other UAG codons and lacking the release factor RF1 that normally terminates translation at UAG. We also describe how such recombinant selenoproteins can be purified and further analyzed for final Sec contents. The methodology can be used for production of natural selenoproteins in recombinant form as well as for production of synthetic selenoproteins that may be designed to use the unique biophysical properties of Sec for diverse biotechnological applications.

Determination of optimal dietary selenium levels by full expression of selenoproteins in various tissues of broilers from 22 to 42 d of age

The current NRC dietary selenium (Se) requirement (0.15 mg/kg) of broilers from 22 to 42 d of age is primarily based on a previous study reported in 1986, which might not be applicable to modern classes of rapidly growing broilers. The present experiment was conducted to determine the optimal dietary Se level for meeting metabolic and functional Se requirements of broilers fed a corn-soybean meal diet from 22 to 42 d of age. A total of 336 Arbor Acres male broilers at 22 d old were randomly assigned to 1 of 6 treatments with 7 replicates and fed a basal corn-soybean meal diet (control, containing 0.014 mg Se/kg) and the basal diet supplemented with 0.10, 0.20, 0.30, 0.40, or 0.50 mg Se/kg from Na₂SeO₃ for 21 d. The results showed that the Se concentrations in plasma, liver, kidney, pancreas, breast and thigh muscles, the activity of glutathione peroxidase (GPX) in plasma, liver and kidney, the mRNA expression levels of Gpx4, selenoprotein (Seleno) h and Selenou in liver, Selenop and Selenoh in kidney, and the protein expression levels of GPX4 in the liver and kidney of broilers were affected (P < 0.05) by supplemental Se level, and increased quadratically (P < 0.05) with the increase of supplemental Se level. The estimates of optimal dietary Se levels were 0.10 to 0.49 mg/kg based on the fitted broken-line or asymptotic models (P < 0.0001) of the above Se concentration indices, and 0.08 to 0.37 mg/kg based on the fitted broken-line, quadratic or asymptotic models (P < 0.007) of the above selenoprotein expression indices. These results indicate that the optimal dietary Se levels would be 0.49 mg/kg to support the maximum Se concentrations and 0.37 mg/kg to support the full expression of selenoproteins in plasma and various tissues of broilers fed a corn-soybean meal diet from 22 to 42 d of age.

Selenium Deficiency Leads to Changes in Renal Fibrosis Marker Proteins and Wnt/β-Catenin Signaling Pathway Components

Renal fibrosis is the final result of the progression of chronic kidney disease (CKD) to end-stage renal disease (ESRD). Earlier studies confirmed that selenium (Se) displays a close association with kidney diseases. However, the correlation between Se and fibrosis has rarely been explored. Thus, this article mainly aimed to investigate the effect of Se deficiency on renal fibrosis and the Wnt/β-catenin signaling pathway. Twenty BALB/c mice were fed a diet containing 0.02-mg/kg Se (Se-deficient diet) or 0.18-mg/kg Se (standard diet) for 20 weeks. A human glomerular mesangial cell (HMC) cell line was transfected with lentiviral TRNAU1AP-shRNA vector to establish a stable Se deficiency model in vitro. As indicated in this study, the glutathione (GSH) content in the Se-deficient group displayed an obvious decline compared with that in the control group, whereas the content of malondialdehyde (MDA) was obviously elevated. The results of Masson staining showed fibrosis around the renal tubules, and the results of immunohistochemistry showed that the area of positive fibronectin expression increased. In the Se-deficient group, the levels of collagen I, collagen III, matrix metalloproteinase 9 (MMP9), and other fibrosis-related proteins changed significantly in vivo and in vitro. Compared with the control group, the TRNAU1AP-shRNA group showed markedly reduced cell proliferation and migration abilities. Our data indicate that Se deficiency can cause kidney damage and renal fibrosis. Furthermore, the Wnt pathway is critical for the development of tissue and organ fibrosis. The data of this study demonstrated that the expression of Wnt5a, β-catenin, and dishevelled 1 (Dvl-1) was significantly upregulated in the Se-deficient group. Therefore, the Wnt/β-catenin pathway may play an important role in renal fibrosis caused by Se deficiency.

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.

Serine Supplementation in the Diets of Late Gestating and Lactating Sows Improves Selenium Nutritional Status in Sows and Their Offspring

Serine can regulate selenoprotein expression, and dietary serine is correlated with the contents of plasma selenoprotein P (Sepp1) and milk selenium (Se) in lactating mothers. Based on this, we investigated the effects of serine supplementation in the diets of late gestating and lactating sows on Sepp1 and Se contents in sows and their offspring. A total of 72 sows were assigned to four groups. During the experiment, sows were fed either a basal diet or basal diets supplemented with three different levels of serine. The results showed that maternal dietary serine had no effect on the Se content in the serum of sows and their offspring, whereas it significantly increased the Se content in the liver of piglets at the age of 21 days. Maternal dietary serine significantly increased Sepp1 content, either in the serum of sows or that in their offspring at the ages of 3 days, 7 days, and 21 days. Additionally, maternal dietary serine significantly increased litter weight and the average body weight of piglets at the age of 11 days. Notably, a positive correlation was found between the average body weight of piglets at the age of 11 days and serum Sepp1 content in piglets, at the age of either 3 days or 7 days. In conclusion, maternal dietary serine supplementation could improve Se nutritional status in sows and their offspring. These beneficial changes may contribute to the higher body weight of the offspring.

Meta-analysis of Association Studies of Selenoprotein Gene Polymorphism and Kashin-Beck Disease: an Updated Systematic Review

To evaluate the association between selenoprotein gene polymorphisms and Kashin-Beck disease (KBD) susceptibility through a systematic review and updated meta-analysis. PubMed, Google Scholar, Cochrane library, and Chinese National Knowledge Infrastructure (CNKI) were electronically searched using the terms "selenoprotein" and "Kashin-Beck disease" or "KBD" with a search time from the establishment of the database to January 2021. The Newcastle-Ottawa Scale (NOS) was used for methodological quality evaluation of the included studies. Stata 14.0 software was used to pooled odds ratio (OR) and 95% confidence interval. There were a total of eight included case-control studies covering 2025 KBD patients and 1962 controls. Meta-analysis results show that the pooled odds ratios (OR) and 95% confidence intervals (CI) for DIO2 (rs225014) were 0.69 (0.52, 0.91), 0.69 (0.50, 0.96), and 0.72 (0.52, 0.99) in the allele, heterozygote, and dominant models, respectively. The OR and 95%CI for SEPS1 (-105G>A) were 2.47 (1.85, 3.29), 9.36 (4.58, 19.12), 2.17 (1.53, 3.08), and 8.60 (4.25, 17.38) in the allele, homozygote, dominant, and recessive models, respectively. In addition, the OR and 95%CI for Sep15 (rs5859) were 2.05 (1.06, 3.96) in the allele model. These results illustrate that there was a significant association between DIO2 (rs225014), SEPS1 (-105G>A), Sep15 (rs5859), and KBD. For GPX1 (rs1050450, rs1800668, rs3811699), DIO2 (rs225014, rs1352815, rs1388382), TrxR2 (rs1139793, rs5746841), GPX4 (rs713041, rs4807542), and SEPP1 (rs7579, 25191g/a), there was no significant statistical difference between the KBD and control groups (P>0.05). We conclude that the DIO2 (rs225014), SEPS1 (-105G>A), and Sep15 (rs5859) gene polymorphism are associated with susceptibility to KBD.

Selenium exerts protective effects against heat stress-induced barrier disruption and inflammation response in jejunum of growing pigs

BACKGROUND

Heat stress (HS) has a negative impact on the intestinal barrier and immune function of pigs. Selenium (Se) may improve intestinal health through affecting selenoproteins. Thus we investigate the protective effect of new organic Se (2-hydroxy-4-methylselenobutanoic acid, HMSeBA) on jejunal damage in growing pigs upon HS and integrate potential roles of corresponding selenoproteins.

RESULTS

HS decreased the villus height and increased (P < 0.05) the protein abundance of HSP70, and downregulated (P < 0.05) protein levels of tight junction-related proteins (CLDN-1 and OCLD). HS-induced jejunal damage was associated with the upregulation of four inflammation-related genes and ten selenoprotein-encoding genes, downregulation (P < 0.05) of four selenoprotein-encoding genes and decreased (P < 0.05) the protein abundance of GPX4 and SELENOS. Compared with the HS group, HMSeBA supplementation not only elevated the villus height and the ratio of V/C (P < 0:05), but also reduced (P < 0.05) the protein abundance of HSP70 and MDA content, and increased (P < 0.05) the protein abundance of OCLD. HMSeBA supplementation downregulated the expression of seven inflammation-related genes, changed the expression of 12 selenoprotein-encoding genes in jejunum mucosa affected by HS, and increased the protein abundance of GPX4, TXNRD1 and SELENOS.

CONCLUSION

Organic Se supplementation beyond nutritional requirement alleviates the negative effect of HS on the jejunum of growing pigs, and its protective effect is related to the response of corresponding selenoproteins. © 2021 Society of Chemical Industry.

Do Concentration or Activity of Selenoproteins Change in Acute Stroke Patients? A Systematic Review and Meta-Analyses

INTRODUCTION

Stroke is characterized by deleterious oxidative stress. Selenoprotein enzymes are essential endogenous antioxidants, and detailed insight into their role after stroke could define new therapeutic treatments. This systematic review aimed to elucidate how blood selenoprotein concentration and activity change in the acute phase of stroke.

METHODS

We searched PubMed, EMBASE, and Medline databases for studies measuring serial blood selenoprotein concentration or activity in acute stroke patients or in stroke patients compared to non-stroke controls. Meta-analyses of studies stratified by the type of stroke, blood compartment, and type of selenoprotein measurement were conducted.

RESULTS

Eighteen studies and data from 941 stroke patients and 708 non-stroke controls were included in this review. Glutathione peroxidase (GPx) was the only identified selenoprotein, and its activity was most frequently measured. Results from 12 studies and 693 patients showed that compared to non-stroke controls in acute ischaemic stroke patients, the GPx activity increased in haemolysate (standardized mean difference [SMD]: 0.27, 95% CI: 0.07-0.47) but decreased in plasma (mean difference [MD]: -1.08 U/L, 95% CI: -1.94 to -0.22) and serum (SMD: -0.54, 95% CI: -0.91 to -0.17). From 4 identified studies in 106 acute haemorrhagic stroke patients, the GPx activity decreased in haemolysate (SMD: -0.40, 95% CI: -0.68 to -0.13) and remained unchanged in plasma (MD: -0.10 U/L, 95% CI: -0.81 to 0.61) and serum (MD: -5.00 U/mL, 95% CI: -36.17 to 26.17) compared to non-stroke controls. Results from studies assessing the GPx activity in the haemolysate compartment were inconsistent and characterized by high heterogeneity.

CONCLUSIONS

Our results suggest a reduction of the blood GPx activity in acute ischaemic stroke patients, a lack of evidence regarding a role for GPx in haemorrhagic stroke patients, and insufficient evidence for other selenoproteins.

Harnessing selenocysteine to enhance microbial cell factories for hydrogen production

Hydrogen is a clean, renewable energy source, that when combined with oxygen, produces heat and electricity with only water vapor as a biproduct. Furthermore, it has the highest energy content by weight of all known fuels. As a result, various strategies have engineered methods to produce hydrogen efficiently and in quantities that are of interest to the economy. To approach the notion of producing hydrogen from a biological perspective, we take our attention to hydrogenases which are naturally produced in microbes. These organisms have the machinery to produce hydrogen, which when cleverly engineered, could be useful in cell factories resulting in large production of hydrogen. Not all hydrogenases are efficient at hydrogen production, and those that are, tend to be oxygen sensitive. Therefore, we provide a new perspective on introducing selenocysteine, a highly reactive proteinogenic amino acid, as a strategy towards engineering hydrogenases with enhanced hydrogen production, or increased oxygen tolerance.

Expression of selenoproteins via genetic code expansion in mammalian cells

Selenoproteins, which contain the 21st amino acid selenocysteine, play roles in maintaining cellular redox homeostasis. Many open questions remain in the field of selenoprotein biology, including the functions of a number of uncharacterized human selenoproteins, and the properties of selenocysteine compared to its analogous amino acid cysteine. The mechanism of selenocysteine incorporation involves an intricate machinery that deviates from the mechanism of incorporation for the canonical 20 amino acids. As a result, recombinant expression of selenoproteins has been historically challenging, and has hindered a deeper evaluation of selenoprotein biology. Genetic code expansion methods, which incorporate protected analogs of selenocysteine, allow the endogenous selenocysteine incorporation mechanism to be bypassed entirely to facilitate selenoprotein expression. Here we present a method for incorporating a photocaged selenocysteine amino acid (DMNB-Sec) into human selenoproteins directly in mammalian cells. This approach offers the opportunity to study human selenoproteins in their native cellular environment and should advance our understanding of selenoprotein biology.

Missense mutation in selenocysteine synthase causes cardio-respiratory failure and perinatal death in mice which can be compensated by selenium-independent GPX4

Selenoproteins are a small family of proteins containing the trace element selenium in form of the rare amino acid selenocysteine (Sec), which is decoded by the UGA codon. In humans, a number of pathogenic variants in genes encoding distinct selenoproteins or selenoprotein biosynthesis factors have been identified. Pathogenic variants in selenocysteine synthase (SEPSECS), which catalyzes the last step in Sec-tRNA[Ser]Sec biosynthesis, were reported in children suffering from progressive cerebello-cerebral atrophy. To understand the pathomechanism associated with SEPSECS deficiency, we generated a novel mouse model recapitulating the respective human pathogenic p.Y334C variant in the murine Sepsecs gene (SepsecsY334C). Unlike in patients, pups homozygous for the p.Y334C variant died perinatally with signs of cardio-respiratory failure. Perinatal death is reminiscent of the Sedaghatian spondylometaphyseal dysplasia disorder in humans, which is caused by pathogenic variants in the gene encoding the selenoprotein and key ferroptosis regulator glutathione peroxidase 4 (GPX4). Protein expression levels of distinct selenoproteins in SepsecsY334C/Y334C mice were found to be generally reduced in brain and isolated cortical neurons, while transcriptomics analysis uncovered an upregulation of NRF2-regulated genes. Crossbreeding of SepsecsY334C/Y334C mice with mice harboring a targeted mutation of the catalytically active Sec to Cys in GPX4 rescued perinatal death of SepsecsY334C/Y334C mice, showing that the cardio-respiratory defects of SepsecsY334C/Y334C mice were caused by the lack of GPX4. Like in SepsecsY334C/Y334C mice, selenoprotein expression levels remained low and NRF2-regulated genes remained highly expressed in these compound mutant mice, indicating that selenium-independent GPX4, along with a sustained antioxidant response are sufficient to compensate for dysfunctional Sec-tRNA[Ser]Sec biosynthesis. Our findings imply that children with pathogenic variants in SEPSECS or GPX4 may even benefit from treatments that incompletely compensate for impaired GPX4 activity.

Determination of optimal dietary selenium levels by full expression of selenoproteins in various tissues of broilers from 1 to 21 d of age

The current NRC dietary selenium (Se) requirement (0.15 mg/kg) of broilers is primarily based on growth performance data reported in 1986. Our study aimed to determine optimal dietary Se levels of broilers fed a practical corn-soybean meal diet for the full expression of selenoproteins in various tissues. A total of 384 one-d-old male broilers (n = 8 replicates/diet) were fed a basal corn-soybean meal diet or the basal diet supplemented with 0.1, 0.2, 0.3, 0.4 or 0.5 mg Se/kg in the form of Na₂SeO₃ for 21 d. Regression analysis was conducted to evaluate the optimal dietary Se levels using broken-line, quadratic or asymptotic models. The activity of glutathione peroxidase (GPX) in the plasma, liver, kidney and pancreas, iodothyronine deiodinase (DIO) in the plasma, liver and pancreas, and thioredoxin reductase (Txnrd) in the liver and pancreas, the mRNA levels of Gpx1, Gpx4, Dio1, selenoprotein (Seleno) h, Selenop and Selenou in the liver, Gpx4, Dio1, Txnrd1, Txnrd2, Selenoh, Selenop and Selenou in the kidney, and Gpx1, Gpx4, Selenoh and Selenou in the pancreas, and the protein levels of GPX4 in the liver and kidney of broilers were influenced (P < 0.05) by added Se levels, and increased quadratically (P < 0.05) with the increase of added Se levels. The estimates of optimal dietary Se levels were 0.07 to 0.36 mg/kg based on the fitted broken-line, quadratic or asymptotic models (P < 0.001) of the aforementioned selenoprotein expression in the plasma, liver and kidney, and 0.09 to 0.46 mg/kg based on the fitted broken-line models (P < 0.001) of the aforementioned selenoprotein expression in the pancreas. The results indicate that the optimal dietary Se levels would be 0.36 mg/kg to support the full expression of selenoproteins in the plasma, liver and kidney, and 0.46 mg/kg to support the full expression of selenoproteins in the pancreas of broilers fed a practical corn-soybean meal diet from 1 to 21 d of age.

Fungal genomes: suffering with functional annotation errors

Background

The genome sequence data of more than 65985 species are publicly available as of October 2021 within the National Center for Biotechnology Information (NCBI) database alone and additional genome sequences are available in other databases and also continue to accumulate at a rapid pace. However, an error-free functional annotation of these genome is essential for the research communities to fully utilize these data in an optimum and efficient manner.

Results

An analysis of proteome sequence data of 689 fungal species (7.15 million protein sequences) was conducted to identify the presence of functional annotation errors. Proteins associated with calcium signaling events, including calcium dependent protein kinases (CDPKs), calmodulins (CaM), calmodulin-like (CML) proteins, WRKY transcription factors, selenoproteins, and proteins associated with the terpene biosynthesis pathway, were targeted in the analysis. Gene associated with CDPKs and selenoproteins are known to be absent in fungal genomes. Our analysis, however, revealed the presence of proteins that were functionally annotated as CDPK proteins. However, InterproScan analysis indicated that none of the protein sequences annotated as “calcium dependent protein kinase” were found to encode calcium binding EF-hands at the regulatory domain. Similarly, none of a protein sequences annotated as a “selenocysteine” were found to contain a Sec (U) amino acid. Proteins annotated as CaM and CMLs also had significant discrepancies. CaM proteins should contain four calcium binding EF-hands, however, a range of 2–4 calcium binding EF-hands were present in the fungal proteins that were annotated as CaM proteins. Similarly, CMLs should possess four calcium binding EF-hands, but some of the CML annotated fungal proteins possessed either three or four calcium binding EF-hands. WRKY transcription factors are characterized by the presence of a WRKY domain and are confined to the plant kingdom. Several fungal proteins, however, were annotated as WRKY transcription factors, even though they did not contain a WRKY domain.

Conclusion

The presence of functional annotation errors in fungal genome and proteome databases is of considerable concern and needs to be addressed in a timely manner.

Supplementary Information

The online version contains supplementary material available at 10.1186/s43008-021-00083-x.

Diverse cytoprotective actions of vitamin E isoforms- role as peroxyl radical scavengers and complementary functions with selenoproteins

Vitamin E, a generic term for tocopherol (T) and tocotrienol (T3), is one of the most potent lipid-soluble antioxidants in the body. It is classified into T and T3 based on the difference in the side chain structure. T and T3 have four isoforms: α-, β-, γ-, and δ, which have different chroman rings. Both T and T3 exhibit a similar ability to scavenge free radicals, and the extent of this ability depends on the difference in the chroman structure. However, they display unique cytoprotective activities in cultured cells depending on the difference in the side chain structure. The cytoprotective effects of vitamin E have received much attention in the prevention of ferroptosis, which is a distinct form of cell death involving iron-dependent lipid peroxidation. This review focuses on the cytoprotective actions of vitamin E isoforms against oxidative stress, particularly the difference between T and T3 and its relation to cellular uptake and distribution. Moreover, the molecular mechanism for cytoprotection of vitamin E oxidation products is explained, and the complementary role of vitamin E and selenoproteins to prevent lipid peroxidation and ferroptosis is described. Furthermore, the evaluation of vitamin E's radical scavenging activity in vivo using oxidative stress markers is discussed, particularly based on kinetic data and the physiological molar ratio of vitamin E to substrates, and the limited role of vitamin E as a peroxyl radical scavenger is described. The future directions and unresolved issues related to vitamin E and lipid peroxidation are also discussed.

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

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

Effect of organic and inorganic dietary selenium supplementation on gene expression in oviduct tissues and Selenoproteins gene expression in Lohman Brown-classic laying hens

Background

The oviduct of a hen provides a conducive environment for egg formation, which needs a large amount of mineral elements from the blood via trans-epithelial permeability. Eggshell is the calcified layer on the outside of an egg that provides protection and is critical for egg quality. However, little is known about the genes or proteins involved in eggshell formation, and their relationship to dietary microminerals. We hypothesized that dietary selenium supplementation in chickens will influence genes involved in eggshell biomineralization, and improve laying hen antioxidant capacity. The objective of this research was to investigate how organic and inorganic dietary selenium supplementation affected mRNA expression of shell gland genes involved in eggshell biomineralization, and selenoproteins gene expression in Lohman Brown-Classic laying hens.

Results

Shell gland (Uterus) and liver tissue samples were collected from hens during the active growth phase of calcification (15–20 h post-ovulation) for RT-PCR analysis. In the oviduct (shell gland and magnum) and liver of laying hens, the relative expression of functional eggshell and hepatic selenoproteins genes was investigated. Results of qPCR confirmed the higher (p < 0.05) mRNA expression of OC-17 and OC-116 in shell gland of organic Se hen compared to inorganic and basal diet treatments. Similarly, dietary Se treatments affected the mRNA expression of OCX-32 and OCX-36 in the shell gland of laying hens. In the magnum, mRNA expression of OC-17 was significantly (p < 0.05) higher in hens fed-bacterial organic, while OC-116 mRNA expression was down-regulated in dietary Se supplemented groups compared to non-Se supplemented hens. Moreover, when compared to sodium selenite, only ADS18 bacterial Se showed significantly (p < 0.05) higher mRNA levels in GPX1, GPX4, DIO1, DIO2 and SELW1, while Se-yeast showed significantly (p < 0.05) higher mRNA levels in TXNRD1 than the non-Se group.

Conclusions

Dietary Se supplementation especially that from a bacterial organic source, improved shell gland and hepatic selenoproteins gene expression in laying hens, indicating that it could be used as a viable alternative source of Se in laying hens. The findings could suggest that organic Se upregulation of shell gland genes and hepatic selenoproteins in laying hens is efficient.

Menadione inhibits thioredoxin reductase 1 via arylation at the Sec498 residue and enhances both NADPH oxidation and superoxide production in Sec498 to Cys498 substitution

The selenoprotein thioredoxin reductase 1 (TrxR1; TXNRD1) participates in multiple cellular processes and is regarded as a cellular target in anti-tumor drug discovery and development. TrxR1 has been reported to reduce menadione to menadiol and to produce superoxide anion radicals. However, the details of TrxR1-mediated menadione reduction have rarely been studied. In this study, we found that wild-type TrxR1 could reduce menadione in a less efficient way, but the U498C mutant variant supported high-efficiency menadione reduction in a Sec-independent manner. Meanwhile, the site-directed mutagenesis results showed that Cys⁶⁴ mutant increased the K_m values and decreased the catalytic efficiency, which was associated with a charge-transfer complex between FAD-Cys⁶⁴. Mass spectrometry (MS) revealed that in NADPH pre-reduced TrxR1 but not oxidized TrxR1, the highly active Sec⁴⁹⁸ of wild-type TrxR1 was arylated by menadione and strongly impaired the DTNB reducing activity in a dose-dependent manner. TrxR1 reduced menadione more efficiently than glutathione reductase (GR), and interestingly menadione did not inhibit the GSSG reducing activity of GR. In summary, our results demonstrate that TrxR1 catalyzes the reduction of menadione in a Sec-independent manner, which highly depend on Cys⁴⁹⁸ instead of N-terminal redox motif, and the Sec⁴⁹⁸ of TrxR1 is the primary target of menadione. The interaction between menadione and TrxR1 revealed in this study may provide a valuable reference for the development of anticancer drugs targeting selenoprotein TrxR1.

Loss of Selenov predisposes mice to extra fat accumulation and attenuated energy expenditure

Selenoprotein V (SELENOV) is a new and the least conserved member of the selenoprotein family. Herein we generated Selenov knockout (KO) mice to determine its in vivo function. The KO led to 16-19% increases (P < 0.05) in body weight that were largely due to 54% higher (P < 0.05) fat mass accumulation, compared with the wild-type (WT) controls. The extra fat accumulation in the KO mice was mediated by up-regulations of genes and proteins involved in lipogenesis (Acc, Fas, Dgat, and Lpl; up by 40%-1.1-fold) and down-regulations of lipolysis (Atgl, Hsl, Ces1d, and Cpt1a; down by 36-89%) in the adipose tissues. The KO also decreased (P < 0.05) VO₂ consumption (14-21%), VCO₂ production (14-16%), and energy expenditure (14-23%), compared with the WT controls. SELENOV and O-GlcNAc transferase (OGT) exhibited a novel protein-protein interaction that explained the KO-induced decreases (P < 0.05) of OGT protein (15-29%), activity (33%), and function (O-GlcNAcylation, 10-21%) in the adipose tissues. A potential cascade of SELENOV-OGT-AMP-activated protein kinase might serve as a central mechanism to link the biochemical and molecular responses to the KO. Overall, our data revealed a novel in vivo function and mechanism of SELENOV as a new inhibitor of body fat accumulation, activator of energy expenditure, regulator of O-GlcNAcylation, and therapeutic target of such related disorders.

Selenogenome and AMPK signal insight into the protective effect of dietary selenium on chronic heat stress-induced hepatic metabolic disorder in growing pigs

BACKGROUND

Chronic heat stress (CHS) disrupts hepatic metabolic homeostasis and jeopardizes product quality of pigs. Selenium (Se) may regulate the metabolic state through affect selenoprotein. Thus, we investigate the protective effect of dietary hydroxy-4-methylselenobutanoic acid (HMSeBA) on CHS induced hepatic metabolic disorder in growing pigs, and the corresponding response of selenoprotein.

METHODS

Forty crossbreed growing pigs were randomly assigned to five groups: control group raised in the thermoneutral environment (22 ± 2 °C) with basal diet; four CHS groups raised in hyperthermal condition (33 ± 2 °C) with basal diet and supplied with 0.0, 0.2, 0.4, and 0.6 mg Se/kg HMSeBA, respectively. The trial lasted 28 d. The serum biochemical, hepatic metabolism related enzyme, protein and gene expression and 25 selenoproteins in liver tissue were determined by real-time PCR, ELISA and western blot.

RESULTS

CHS significantly increased the rectal temperature, respiration rate, serum aspartate aminotransferase (AST) and low-density lipoprotein cholesterol (LDL-C) of pigs, up-regulated hepatic heat shock protein 70 (HSP70) and induced lower liver weight, glycogen content, hepatic glucokinase and glutathione peroxidase (GSH-Px). The CHS-induced liver metabolic disorder was associated with the aberrant expression of 6 metabolism-related gene and 11 selenoprotein encoding genes, and decreased the protein abundance of GCK, GPX4 and SELENOS. HMSeBA improved anti-oxidative capacity of liver. 0.4 or 0.6 mg Se/kg HMSeBA supplementation recovered the liver weight, glycogen content and rescue of mRNA abundance of genes related to metabolism and protein levels of GCK. HMSeBA supplementation changed expressions of 15 selenoprotein encoding genes, and enhanced protein expression of GPX1, GPX4 and SELENOS in the liver affected by CHS. CHS alone showed no impact while HMSeBA supplementation increased protein levels of p-AMPKα in the liver.

CONCLUSIONS

In summary, HMSeBA supplementation beyond nutrient requirement mitigates CHS-induced hepatic metabolic disorder, recovered the liver glycogen content and the processes that are associated with the activation of AMPK signal and regulation of selenoproteins in the liver of growing pigs.

Small molecule selenium-containing compounds: Recent development and therapeutic applications

Selenium (Se) is an essential micronutrient of organism and has important function. It participates in the functions of selenoprotein in several manners. In recent years, Se has attracted much attention because of its therapeutic potential against several diseases. Many natural and synthetic organic Se-containing compounds were studied and explored for the treatment of cancer and other diseases. Studies have showed that incorporation of Se atom into small molecules significantly enhanced their bioactivities. In this paper, according to different applications and structural characteristics, the research progress and therapeutic application of Se-containing compounds are reviewed, and more than 110 Se-containing compounds were selected as representatives which showed potent activities such as anticancer, antioxidant, antifibrolytic, antiparasitic, antibacterial, antiviral, antifungal and central nervous system related effects. This review is expected to provide a basis for further study of new promising Se-containing compounds.

SARS-CoV-2 suppresses mRNA expression of selenoproteins associated with ferroptosis, endoplasmic reticulum stress and DNA synthesis

Higher selenium status has been shown to improve the clinical outcome of infections caused by a range of evolutionally diverse viruses, including SARS-CoV-2. However, the impact of SARS-CoV-2 on host-cell selenoproteins remains elusive. The present study investigated the influence of SARS-CoV-2 on expression of selenoprotein mRNAs in Vero cells. SARS-CoV-2 triggered an inflammatory response as evidenced by increased IL-6 expression. Of the 25 selenoproteins, SARS-CoV-2 significantly suppressed mRNA expression of ferroptosis-associated GPX4, DNA synthesis-related TXNRD3 and endoplasmic reticulum-resident SELENOF, SELENOK, SELENOM and SELENOS. Computational analysis has predicted an antisense interaction between SARS-CoV-2 and TXNRD3 mRNA, which is translated with high efficiency in the lung. Here, we confirmed the predicted SARS-CoV-2/TXNRD3 antisense interaction in vitro using DNA oligonucleotides, providing a plausible mechanism for the observed mRNA knockdown. Inhibition of TXNRD decreases DNA synthesis which is thereby likely to increase the ribonucleotide pool for RNA synthesis and, accordingly, RNA virus production. The present findings provide evidence for a direct inhibitory effect of SARS-CoV-2 replication on the expression of a specific set of selenoprotein mRNAs, which merits further investigation in the light of established evidence for correlations between dietary selenium status and the outcome of SARS-CoV-2 infection.

An unusual thioredoxin system in the facultative parasite Acanthamoeba castellanii

The free-living amoeba Acanthamoeba castellanii occurs worldwide in soil and water and feeds on bacteria and other microorganisms. It is, however, also a facultative parasite and can cause serious infections in humans. The annotated genome of A. castellanii (strain Neff) suggests the presence of two different thioredoxin reductases (TrxR), of which one is of the small bacterial type and the other of the large vertebrate type. This combination is highly unusual. Similar to vertebrate TrxRases, the gene coding for the large TrxR in A. castellanii contains a UGA stop codon at the C-terminal active site, suggesting the presence of selenocysteine. We characterized the thioredoxin system in A. castellanii in conjunction with glutathione reductase (GR), to obtain a more complete understanding of the redox system in A. castellanii and the roles of its components in the response to oxidative stress. Both TrxRases localize to the cytoplasm, whereas GR localizes to the cytoplasm and the large organelle fraction. We could only identify one thioredoxin (Trx-1) to be indeed reduced by one of the TrxRases, i.e., by the small TrxR. This thioredoxin, in turn, could reduce one of the two peroxiredoxins tested and also methionine sulfoxide reductase A (MsrA). Upon exposure to hydrogen peroxide and diamide, only the small TrxR was upregulated in expression at the mRNA and protein levels, but not the large TrxR. Our results show that the small TrxR is involved in the A. castellanii's response to oxidative stress. The role of the large TrxR, however, remains elusive.

Cell-penetrating, antioxidant SELENOT mimetic protects dopaminergic neurons and ameliorates motor dysfunction in Parkinson's disease animal models

Parkinson's disease (PD) is a neurodegenerative disorder characterized by motor dysfunction for which there is an unmet need for better treatment options. Although oxidative stress is a common feature of neurodegenerative diseases, notably PD, there is currently no efficient therapeutic strategy able to tackle this multi-target pathophysiological process. Based on our previous observations of the potent antioxidant and neuroprotective activity of SELENOT, a vital thioredoxin-like selenoprotein, we designed the small peptide PSELT from its redox active site to evaluate its antioxidant properties in vivo, and its potential polyfunctional activity in PD models. PSELT protects neurotoxin-treated dopaminergic neurons against oxidative stress and cell death, and their fibers against neurotoxic degeneration. PSELT is cell-permeable and acts in multiple subcellular compartments of dopaminergic neurons that are vulnerable to oxidative stress. In rodent models of PD, this protective activity prevented neurodegeneration, restored phosphorylated tyrosine hydroxylase levels, and led to improved motor skills. Transcriptomic analysis revealed that gene regulation by PSELT after MPP+ treatment negatively correlates with that occurring in PD, and positively correlates with that occurring after resveratrol treatment. Mechanistically, a major impact of PSELT is via nuclear stimulation of the transcription factor EZH2, leading to neuroprotection. Overall, these findings demonstrate the potential of PSELT as a therapeutic candidate for treatment of PD, targeting oxidative stress at multiple intracellular levels.

Lipid peroxidation products as a mediator of toxicity and adaptive response - The regulatory role of selenoprotein and vitamin E

Lipid peroxidation and its products have been investigated extensively and their biological importance, particularly in relation to physiological and pathophysiological conditions, has received considerable attention. Lipids are oxidized by three distinct mechanisms, i.e., enzymatic oxidation, nonenzymatic, free radical-mediated oxidation, and nonenzymatic, nonradical-mediated oxidation, which respectively yield specific products. Lipid hydroperoxides are the major primary products formed and are reduced to the corresponding hydroxides by antioxidative enzymes such as selenoproteins, and/or undergo secondary oxidation, generating various products with electrophilic properties, such as 4-hydroxy-2-nonenal. Lipid peroxidation induces a loss of fine structure and natural function of lipids, and can produce cytotoxicity and/or novel biological activity. This review broadly discusses the mechanisms of lipid peroxidation and its products, its utility as a biomarker for oxidative stress, the biological effects of lipid peroxidation products, including their action as a mediator of the adaptive response, and the role of the antioxidant system, particularly selenoproteins and vitamin E, in preventing lipid peroxidation and ferroptosis.

Biogeographic and Evolutionary Patterns of Trace Element Utilization in Marine Microbial World

Trace elements are required by all organisms, which are key components of many enzymes catalyzing important biological reactions. Many trace element-dependent proteins have been characterized; however, little is known about their occurrence in microbial communities in diverse environments, especially the global marine ecosystem. Moreover, the relationships between trace element utilization and different types of environmental stressors are unclear. In this study, we used metagenomic data from the Global Ocean Sampling expedition project to identify the biogeographic distribution of genes encoding trace element-dependent proteins (for copper, molybdenum, cobalt, nickel, and selenium) in a variety of marine and non-marine aquatic samples. More than 56,000 metalloprotein and selenoprotein genes corresponding to nearly 100 families were predicted, becoming the largest dataset of marine metalloprotein and selenoprotein genes reported to date. In addition, samples with enriched or depleted metalloprotein/selenoprotein genes were identified, suggesting an active or inactive usage of these micronutrients in various sites. Further analysis of interactions among the elements showed significant correlations between some of them, especially those between nickel and selenium/copper. Finally, investigation of the relationships between environmental conditions and metalloprotein/selenoprotein families revealed that many environmental factors might contribute to the evolution of different metalloprotein and/or selenoprotein genes in the marine microbial world. Our data provide new insights into the utilization and biological roles of these trace elements in extant marine microbes, and might also be helpful for the understanding of how these organisms have adapted to their local environments.