Selenoprotein H is an essential regulator of redox homeostasis that cooperates with p53 in development and tumorigenesis

Synergistic Effect of Maternal Micronutrient Supplementation on ORFV DNA Vaccine Immune Response in a Pregnant Model

Contagious ecthyma is a contagious zoonotic disease caused by the Orf virus that can infect farm animals and humans, but no vaccine is available for pregnant mothers. Excessive oxidative stress during pregnancy can suppress the vaccine immune response in pregnant mothers; hence, maternal micronutrient supplementation could effectively improve the immune response, health, and oxidative status during pregnancy. In this study, we employed an 8-week-old pregnant rat model to receive a single intramuscular dose of 200 µg of ORF DNA vaccine with or without vitamin E and selenium supplementation to evaluate their effect on immune responses (specific IgG and IgG isotypes), oxidative stress, liver enzymes, and blood glucose levels in maternal-neonatal serum and milk secretions. Additionally, antioxidant-related gene expressions were analyzed in the maternal placenta and pups' liver. The results showed that supplementation of vitamin E and selenium with ORF DNA vaccination increased the production of specific antibody and IgG isotypes (IgG1 and IgG2a) and reduced the oxidative stress in neonatal-maternal serum and milk compared to both the control group and those vaccinated without supplementation (p < 0.05). Notably, the ORF DNA vaccine did not cause oxidative stress and hepatic damage. However, combined supplementation of vitamin E and selenium with DNA vaccination significantly decreased serum malondialdehyde (MDA) levels and improved the antioxidant-related enzyme activities of glutathione peroxidase (GPX), superoxide dismutase 1 (SOD1), and selenoprotein P (SELP) in the maternal placenta and liver of pups (p < 0.05). In conclusion, maternal supplementation of vitamin E and selenium enhanced the immune responses of the ORF DNA vaccine by mitigating oxidative stress in pregnant rats and could thus be a promising strategy for better health outcomes for both mothers and neonates.

Selenium metabolism and selenoproteins function in brain and encephalopathy

Selenium (Se) is an essential trace element of the utmost importance to human health. Its deficiency induces various disorders. Se species can be absorbed by organisms and metabolized to hydrogen selenide for the biosynthesis of selenoproteins, selenonucleic acids, or selenosugars. Se in mammals mainly acts as selenoproteins to exert their biological functions. The brain ranks highest in the specific hierarchy of organs to maintain the level of Se and the expression of selenoproteins under the circumstances of Se deficiency. Dyshomeostasis of Se and dysregulation of selenoproteins result in encephalopathy such as Alzheimer's disease, Parkinson's disease, depression, amyotrophic lateral sclerosis, and multiple sclerosis. This review provides a summary and discussion of Se metabolism, selenoprotein function, and their roles in modulating brain diseases based on the most currently published literature. It focuses on how Se is utilized and transported to the brain, how selenoproteins are biosynthesized and function physiologically in the brain, and how selenoproteins are involved in neurodegenerative diseases. At the end of this review, the perspectives and problems are outlined regarding Se and selenoproteins in the regulation of encephalopathy.

Selenocysteine tRNA methylation promotes oxidative stress resistance in melanoma metastasis

Selenocysteine-containing proteins play a central role in redox homeostasis. Their translation is a highly regulated process and is dependent on two tRNASec isodecoders differing by a single 2'-O-ribose methylation called Um34. Here we characterized FTSJ1 as the Um34 methyltransferase and show that its activity is required for efficient selenocysteine insertion at the UGA stop codon during translation. Specifically, loss of Um34 leads to ribosomal stalling and decreased UGA recoding. FTSJ1-deficient cells are more sensitive to oxidative stress and show decreased metastatic colonization in xenograft models of melanoma metastasis. We found that FTSJ1 mediates efficient translation of selenoproteins essential for the cellular antioxidant response. Our findings uncover a role for tRNASec Um34 modification in oxidative stress resistance and highlight FTSJ1 as a potential therapeutic target specific for metastatic disease.

Human selenocysteine synthase, SEPSECS, has evolved to optimize binding of a tRNA-based substrate

The evolution of the genetic code to incorporate selenocysteine (Sec) enabled the development of a selenoproteome in all domains of life. O-phosphoseryl-tRNASec selenium transferase (SepSecS) catalyzes the terminal reaction of Sec synthesis on tRNASec in archaea and eukaryotes. Despite harboring four equivalent active sites, human SEPSECS binds no more than two tRNASec molecules. Though, the basis for this asymmetry remains poorly understood. In humans, an acidic, C-terminal, α-helical extension precludes additional tRNA-binding events in two of the enzyme monomers, stabilizing the SEPSECS•tRNASec complex. However, the existence of a helix exclusively in vertebrates raised questions about the evolution of the tRNA-binding mechanism in SEPSECS and the origin of its C-terminal extension. Herein, using a comparative structural and phylogenetic analysis, we show that the tRNA-binding motifs in SEPSECS are poorly conserved across species. Consequently, in contrast to mammalian SEPSECS, the archaeal ortholog cannot bind unacylated tRNASec and requires an aminoacyl group. Moreover, the C-terminal α-helix 16 is a mammalian innovation, and its absence causes aggregation of the SEPSECS•tRNASec complex at low tRNA concentrations. Altogether, we propose SEPSECS evolved a tRNASec binding mechanism as a crucial functional and structural feature, allowing for additional levels of regulation of Sec and selenoprotein synthesis.

Optimized methods to image hepatic lipid droplets in zebrafish larvae

The optical transparency of zebrafish larvae enables visualization of subcellular structures in intact organs, and these vertebrates are widely used to study lipid biology and liver disease. Lipid droplet (LD) presence is a prevalent feature of healthy cells, but, under conditions such as nutrient excess, toxicant exposure or metabolic imbalance, LD accumulation in hepatocytes can be a harbinger of more severe forms of liver disease. We undertook a comprehensive analysis of approaches useful to investigate LD distribution and dynamics in physiological and pathological conditions in the liver of zebrafish larvae. This comparative analysis of the lipid dyes Oil Red O, Nile Red, LipidTox and LipidSpot, as well as transgenic LD reporters that rely on EGFP fusions of the LD-decorating protein perilipin 2 (PLIN2), demonstrates the strengths and limitations of each approach. These protocols are amenable to detection methods ranging from low-resolution stereomicroscopy to confocal imaging, which enables measurements of hepatic LD size, number and dynamics at cellular resolution in live and fixed animals. This resource will benefit investigators studying LD biology in zebrafish disease models.

Selenoprotein H mediates low selenium-related cognitive decline through impaired oligodendrocyte myelination with disrupted hippocampal lipid metabolism in female mice

Low selenium levels are closely associated with reduced cognitive performance and lipid dysregulation, yet the mechanism of action remains unclear. The physiological function of selenium is primarily mediated by selenoproteins. Selenoprotein H (SELENOH), as one of the selenium-containing proteins, has an unelucidated role in regulating cognitive status and lipid metabolism. In this study, we established a Selenoh gene knockout (HKO) mouse model to investigate whether Selenoh mediates the impact of selenium on cognitive function. We found that HKO mice showed a significant decline in cognition compared with the wild-type (HWT) littermates, and were not affected by deficient or excessive selenium, while no differences in anxiety and depression behavior were observed. HKO mice showed reduced myelin basic protein expression in hippocampal oligodendrocytes, with decreased glycolipid levels and increased phospholipid and sphingolipid levels in the hippocampus. Furthermore, the high-fat diet (HFD) exerted no effect on cognition and limited impact on the gene profile in the hippocampus of HKO mice. Compared with those of HWT mice, the myelination pathways in the hippocampus of HKO mice were downregulated as revealed by RNA-seq, which was further confirmed by the reduced expression levels of myelin-related proteins. Finally, HKO increased the expression of hippocampal fatty acid transporter (FATP) 4, and HFD increased the FATP4 expression in HWT mice but not in HKO mice. In summary, our study demonstrated that HKO induced cognitive decline by impairing myelination in oligodendrocytes with disrupted hippocampal lipid metabolism, which provided a novel viewpoint on the selenoprotein-mediated neurodegenerative diseases of selenium.

Selenium as a Modulator of Redox Reactions in the Prevention and Treatment of Cardiovascular Diseases

Cardiovascular diseases stand as the predominant global cause of mortality, exerting a profound impact on both life expectancy and its quality. Given their immense public health burden, extensive efforts have been dedicated to comprehending the underlying mechanisms and developing strategies for prevention and treatment. Selenium, a crucial participant in redox reactions, emerges as a notable factor in maintaining myocardial cell homeostasis and influencing the progression of cardiovascular disorders. Some disorders, such as Keshan disease, are directly linked with its environmental deficiency. Nevertheless, the precise extent of its impact on the cardiovascular system remains unclear, marked by contradictory findings in the existing literature. High selenium levels have been associated with an increased risk of developing hypertension, while lower concentrations have been linked to heart failure and atrial fibrillation. Although some trials have shown its potential effectiveness in specific groups of patients, large cohort supplementation attempts have generally yielded unsatisfactory outcomes. Consequently, there persists a significant need for further research aimed at delineating specific patient cohorts and groups of diseases that would benefit from selenium supplementation.

The beneficial and toxic effects of selenium on zebrafish. A systematic review of the literature

Selenium is an important and essential trace element in organisms, but its effects on organisms are also a "double-edged sword". Selenium deficiency or excess can endanger the health of humans and animals. In order to thoroughly understand the nutritional value and toxicity hazards of selenium, researchers have conducted many studies on the model animal zebrafish. However, there is a lack of induction and summary of relevant research on which selenium acts on zebrafish. This paper provides a review of the reported studies. Firstly, this article summarizes the benefits of selenium on zebrafish from three aspects: Promoting growth, Enhancing immune function and anti-tumor ability, Antagonizing some pollutants, such as mercury. Then, three aspects of selenium toxicity to zebrafish are introduced: nervous system and behavior, reproductive system and growth, and damage to some organs. This article also describes how different forms of selenium compounds have different effects on zebrafish health. Finally, prospects for future research directions are presented.

Comparative transcriptomics coupled to developmental grading via transgenic zebrafish reporter strains identifies conserved features in neutrophil maturation

Neutrophils are evolutionarily conserved innate immune cells playing pivotal roles in host defense. Zebrafish models have contributed substantially to our understanding of neutrophil functions but similarities to human neutrophil maturation have not been systematically characterized, which limits their applicability to studying human disease. Here we show, by generating and analysing transgenic zebrafish strains representing distinct neutrophil differentiation stages, a high-resolution transcriptional profile of neutrophil maturation. We link gene expression at each stage to characteristic transcription factors, including C/ebp-β, which is important for late neutrophil maturation. Cross-species comparison of zebrafish, mouse, and human samples confirms high molecular similarity of immature stages and discriminates zebrafish-specific from pan-species gene signatures. Applying the pan-species neutrophil maturation signature to RNA-sequencing data from human neuroblastoma patients reveals association between metastatic tumor cell infiltration in the bone marrow and an overall increase in mature neutrophils. Our detailed neutrophil maturation atlas thus provides a valuable resource for studying neutrophil function at different stages across species in health and disease.

Selenoproteins and tRNA-Sec: regulators of cancer redox homeostasis

In the past two decades significant progress has been made in uncovering the biological function of selenium. Selenium, an essential trace element, is required for the biogenesis of selenocysteine which is then incorporated into selenoproteins. These selenoproteins have emerged as central regulators of cellular antioxidant capacity and maintenance of redox homeostasis. This review provides a comprehensive examination of the multifaceted functions of selenoproteins with a particular emphasis on their contributions to cellular antioxidant capacity. Additionally, we highlight the promising potential of targeting selenoproteins and the biogenesis of selenocysteine as avenues for therapeutic intervention in cancer. By understanding the intricate relationship between selenium, selenoproteins, and reactive oxygen species (ROS), insights can be gained to develop therapies that exploit the inherent vulnerabilities of cancer cells.

The semisynthesis of nucleolar human selenoprotein H

The human selenoprotein H is the only selenocysteine-containing protein that is located in the cell's nucleolus. In vivo studies have suggested that it plays some role in DNA binding, consumption of reactive oxygen species, and may serve as a safeguard against cancers. However, the protein has never been isolated and, as a result, not yet fully characterized. Here, we used a semi-synthetic approach to obtain the full selenoprotein H with a S43T mutation. Using biolayer interferometry, we also show that the Cys-containing mutant of selenoprotein H is capable of binding DNA with sub-micromolar affinity. Employing state-of-the-art expressed protein ligation (EPL), our devised semi-synthetic approach can be utilized for the production of numerous, hard-to-obtain proteins of biological and therapeutic relevance.

"Alphabet" Selenoproteins: Their Characteristics and Physiological Roles

Selenium (Se) is a metalloid that is recognized as one of the vital trace elements in our body and plays multiple biological roles, largely mediated by proteins containing selenium-selenoproteins. Selenoproteins mainly have oxidoreductase functions but are also involved in many different molecular signaling pathways, physiological roles, and complex pathogenic processes (including, for example, teratogenesis, neurodegenerative, immuno-inflammatory, and obesity development). All of the selenoproteins contain one selenocysteine (Sec) residue, with only one notable exception, the selenoprotein P (SELENOP), which has 10 Sec residues. Although these mechanisms have been studied intensely and in detail, the characteristics and functions of many selenoproteins remain unknown. This review is dedicated to the recent data describing the identity and the functions of several selenoproteins that are less known than glutathione peroxidases (Gpxs), iodothyronine deiodinases (DIO), thioredoxin reductases (TRxRs), and methionine sulfoxide reductases (Msrs) and which are named after alphabetical letters (i.e., F, H, I, K, M, N, O, P, R, S, T, V, W). These "alphabet" selenoproteins are involved in a wide range of physiological and pathogenetic processes such as antioxidant defense, anti-inflammation, anti-apoptosis, regulation of immune response, regulation of oxidative stress, endoplasmic reticulum (ER) stress, immune and inflammatory response, and toxin antagonism. In selenium deficiency, the "alphabet" selenoproteins are affected hierarchically, both with respect to the particular selenoprotein and the tissue of expression, as the brain or endocrine glands are hardly affected by Se deficiency due to their equipment with LRP2 or LRP8.

"Alphabet" Selenoproteins: Implications in Pathology

Selenoproteins are a group of proteins containing selenium in the form of selenocysteine (Sec, U) as the 21st amino acid coded in the genetic code. Their synthesis depends on dietary selenium uptake and a common set of cofactors. Selenoproteins accomplish diverse roles in the body and cell processes by acting, for example, as antioxidants, modulators of the immune function, and detoxification agents for heavy metals, other xenobiotics, and key compounds in thyroid hormone metabolism. Although the functions of all this protein family are still unknown, several disorders in their structure, activity, or expression have been described by researchers. They concluded that selenium or cofactors deficiency, on the one hand, or the polymorphism in selenoproteins genes and synthesis, on the other hand, are involved in a large variety of pathological conditions, including type 2 diabetes, cardiovascular, muscular, oncological, hepatic, endocrine, immuno-inflammatory, and neurodegenerative diseases. This review focuses on the specific roles of selenoproteins named after letters of the alphabet in medicine, which are less known than the rest, regarding their implications in the pathological processes of several prevalent diseases and disease prevention.

Apical and mechanistic effects of 6PPD-quinone on different life-stages of the fathead minnow (Pimephales promelas)

N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone (6PPD-quinone) is an emerging contaminant of concern that is generated through the environmental oxidation of the rubber tire anti-degradant 6PPD. Since the initial report of 6PPD-quinone being the cause of urban runoff mortality syndrome of Coho salmon, numerous species have been identified as either sensitive or insensitive to acute lethality caused by 6PPD-quinone. In sensitive species, acute lethality might be caused by uncoupling of mitochondrial respiration in gills. However, little is known about effects of 6PPD-quinone on insensitive species. Here we demonstrate that embryos of fathead minnows (Pimephales promelas) are insensitive to exposure to concentrations as great as 39.97 μg/L for 168 h, and adult fathead minnows are insensitive to exposure to concentrations as great as 9.4 μg/L for 96 h. A multi-omics approach using a targeted transcriptomics array, (EcoToxChips), and proton nuclear magnetic resonance (1H NMR) was used to assess responses of the transcriptomes and metabolomes of gills and livers from adult fathead minnows exposed to 6PPD-quinone for 96 h to begin to identify sublethal effects of 6PPD-quinone. There was little agreement between results of the EcoToxChip and metabolomics analyses, likely because genes present on the EcoToxChip were not representative of pathways suggested to be perturbed by metabolomic analysis. Changes in abundances of transcripts and metabolites in livers and gills suggest that disruption of one‑carbon metabolism and induction of oxidative stress might be occurring in gills and livers, but that tissues differ in their sensitivity or responsiveness to 6PPD-quinone. Overall, several pathways impacted by 6PPD-quinone were identified as candidates for future studies of potential sublethal effects of this chemical.

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.

Bioconversion of inorganic selenium to less toxic selenium forms by microbes: A review

In recent years, microbial conversion of inorganic selenium into an efficient and low-toxic form of selenium has attracted much attention. With the improvement of scientific awareness and the continuous progress of nanotechnology, selenium nanoparticles can not only play the unique functions of organic selenium and inorganic selenium but also have higher safety, absorption and biological activity than other selenium forms. Therefore, the focus of attention has gradually shifted beyond the level of selenium enrichment in yeast to the combination of biosynthetic selenium nanoparticles (BioSeNPs). This paper primarily reviews inorganic selenium and its conversion to less toxic organic selenium and BioSeNPs by microbes. The synthesis method and potential mechanism of organic selenium and BioSeNPs are also introduced, which provide a basis for the production of specific forms of selenium. The methods to characterize selenium in different forms are discussed to understand the morphology, size and other characteristics of selenium. In general, to obtain safer and higher selenium content products, it is necessary to develop yeast resources with higher selenium conversion and accumulation.

Ercc2/Xpd deficiency results in failure of digestive organ growth in zebrafish with elevated nucleolar stress

Mutations in ERCC2/XPD helicase, an important component of the TFIIH complex, cause distinct human genetic disorders which exhibit various pathological features. However, the molecular mechanisms underlying many symptoms remain elusive. Here, we have shown that Ercc2/Xpd deficiency in zebrafish resulted in hypoplastic digestive organs with normal bud initiation but later failed to grow. The proliferation of intestinal endothelial cells was impaired in ercc2/xpd mutants, and mitochondrial abnormalities, autophagy, and inflammation were highly induced. Further studies revealed that these abnormalities were associated with the perturbation of rRNA synthesis and nucleolar stress in a p53-independent manner. As TFIIH has only been implicated in RNA polymerase I-dependent transcription in vitro, our results provide the first evidence for the connection between Ercc2/Xpd and rRNA synthesis in an animal model that recapitulates certain key characteristics of ERCC2/XPD-related human genetic disorders, and will greatly advance our understanding of the molecular pathogenesis of these diseases.

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Ercc2/Xpd deficiency results in failure of digestive organ growth in zebrafish

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Ercc2/Xpd-deficient intestinal endothelial cells exhibit impaired proliferation

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Mitochondrial abnormalities, autophagy, and inflammation are highly induced

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rRNA synthesis perturbation leads to nucleolar stress in a p53-independent manner

The Role of Some Selenoproteins in the Etiopathogenesis of Breast Cancer

Amaç: Meme kanseri, kadınlarda kanser kaynaklı ölümlerde akciğer kanserinden sonra ikinci sırada yer alır. Çeşitli çalışmalarda, selenoproteinlerin kanserogenezin bazı evrelerini baskıladığı ve kanser hücrelerinin çoğalma hızını azalttığı gösterilmiştir. Ancak bu mekanizmalar tam olarak açıklanamamıştır. Kanser tedavisinde radyoterapi, kemoterapiyle birlikte en çok tercih edilen tedavi yöntemlerindendir. Çalışmanın amacı, radyoterapi alan meme kanserli hastaların tedavi öncesi ve sonrası selenoprotein düzeylerindeki değişiklikleri değerlendirerek hastalığın etiyopatogenezine olası etkilerini incelemektir.Yöntem: Çalışmamıza meme kanseri teşhisi konmuş, radyoterapi öncesi ve radyoterapi sonrası örnekleri alınan 35 kadın hasta ile herhangi bir ilaç tedavisi almayan 25 sağlıklı kadın gönüllü dahil edildi. Hasta ve sağlıklı kontrol gruplarını oluşturan bireylerden kan örnekleri alındı. Serum örneklerinde selenoprotein K (Sel-K), selenoprotein W1 (Sel-W1) ve selenoprotein P (Sel-P) düzeyleri ELISA (Enzyme-Linked Immunosorbent Assay) yöntemi ile ölçüldü. İstatistiksel analiz, Wilcoxon ve Mann-Whitney U testleri kullanılarak yapıldı. Hesaplamalar için Statistical Package for the Social Sciences – SPSS 21.0 for Windows (SPSS Inc, Chicago, IL, ABD) kullanıldı. p&lt;0.05, istatistiksel olarak anlamlı bir farkı belirtmek için kabul edildi.Bulgular: Serum Sel-K düzeyleri tedavi öncesi ve kontrol grubu karşılaştırıldığında, tedavi öncesi grupta anlamlı olarak düşük bulundu. Sel- P düzeyleri hem tedavi öncesi hem de tedavi sonrasında kontrol grubu ile karşılaştırıldığında her iki grupta da kontrol grubuna göre düşük bulundu. Sel-W1 düzeylerinde gruplar arasında herhangi bir anlamlılık bulunmadı.Sonuç: Meme kanserinde bazı selenoproteinlerin hastalığın etiyopatogenezinde önemli bir rolü olmakla birlikte daha fazla örneklem grubu ve ileri çalışmalar ile hastalığın progresyonu ve selenoprotein düzeyleri arasındaki ilişkinin araştırılmasına ihtiyaç duyulmaktadır.

Gene Signatures Induced by Ionizing Radiation as Prognostic Tools in an In Vitro Experimental Breast Cancer Model

This study aimed to analyze the expression of genes involved in radiation, using an Affymetrix system with an in vitro experimental breast cancer model developed by the combined treatment of low doses of high linear energy transfer (LET) radiation α particle radiation and estrogen yielding different stages in a malignantly transformed breast cancer cell model called Alpha model. Altered expression of different molecules was detected in the non-tumorigenic Alpha3, a malignant cell line transformed only by radiation and originally derived from the parental MCF-10F human cell line; that was compared with the Alpha 5 cell line, another cell line exposed to radiation and subsequently grown in the presence 17β-estradiol. This Alpha5, a tumorigenic cell line, originated the Tumor2 cell line. It can be summarized that the Alpha 3 cell line was characterized by greater gene expression of ATM and IL7R than control, Alpha5, and Tumor2 cell lines, it presented higher selenoprotein gene expression than control and Tumor2; epsin 3 gene expression was higher than control; stefin A gene expression was higher than Alpha5; and metallothionein was higher than control and Tumor2 cell line. Therefore, radiation, independently of estrogen, induced increased ATM, IL7R, selenoprotein, GABA receptor, epsin, stefin, and metallothioneins gene expression in comparison with the control. Results showed important findings of genes involved in cancers of the breast, lung, nervous system, and others. Most genes analyzed in these studies can be used for new prognostic tools and future therapies since they affect cancer progression and metastasis. Most of all, it was revealed that in the Alpha model, a breast cancer model developed by the authors, the cell line transformed only by radiation, independently of estrogen, was characterized by greater gene expression than other cell lines. Understanding the effect of radiotherapy in different cells will help us improve the clinical outcome of radiotherapies. Thus, gene signature has been demonstrated to be specific to tumor types, hence cell-dependency must be considered in future treatment planning. Molecular and clinical features affect the results of radiotherapy. Thus, using gene technology and molecular information is possible to improve therapies and reduction of side effects while providing new insights into breast cancer-related fields.

Identification of Selenoprotein H Isoforms and Impact of Selenoprotein H Overexpression on Protein But Not mRNA Levels of 2 Other Selenoproteins in 293T Cells

BACKGROUND

Selenoprotein H (SELONOH), a member of the thioredoxin-like family proteins, is prioritized to degradation in selenium (Se) insufficiency. Recent studies implicate protective roles of SELENOH in oxidative stress, cellular senescence, and intestinal tumorigenesis. Although the nonselenoprotein H0YE28 is suggested as shortened SELENOH according to genomic and proteomic data repositories, this variant has not been verified biochemically.

OBJECTIVES

We sought to identify SELENOH isoforms and explore the impact of Se flux on selenoprotein expression in SELENOH-overexpressing cells.

METHODS

A vector expressing a FLAG (the DYKDDDDK sequence) tag on the N-terminal end of wild-type SELENOH was constructed and transiently transfected into 293T cells incubated with graded concentrations of Na2SeO3 (0-200 nM). Cells were subjected to immunoprecipitation, LC-MS/MS protein analysis, immunoblotting, qRT-PCR, and senescence assays. Data were analyzed by 1-way or 2-way ANOVA.

RESULTS

Results of anti-FLAG immunoblotting showed that FLAG-SELENOH transfection increased (3.7-fold; P < 0.05) protein levels of the long, but not the short, SELENOH variants in the presence of Na2SeO3 (100 nM). By contrast, SELENOH mRNA levels were increased by 53-fold upon FLAG-SELENOH transfection but were comparable with or without supplemental Se (100 nM). LC-MS/MS analyses of anti-FLAG immunoprecipitates designated both anti-FLAG bands as SELENOH and co-identified three 60S ribosomal and 9 other proteins. Overexpression of FLAG-SELENOH 1) reduced glutathione peroxidase 1 and thioredoxin reductase 1 expression at the protein rather than the mRNA level in the absence but not presence of supplemental Se (100 nM; P < 0.05); 2) increased mRNA levels of 3 heat shock proteins (HSP27, HSP70-1A, and HSP70-1B; P < 0.05); and 3) reduced senescence induced by H2O2 (20 μM, 4 hours; P < 0.05).

CONCLUSIONS

These cellular studies demonstrate a Se-independent, shortened SELENOH variant and suggest competition of overexpressed FLAG-SELENOH with 2 other selenoproteins for the expression at the protein but not the mRNA level in Se insufficiency.

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.

Selenium Deficiency Due to Diet, Pregnancy, Severe Illness, or COVID-19-A Preventable Trigger for Autoimmune Disease

The trace element selenium (Se) is an essential part of the human diet; moreover, increased health risks have been observed with Se deficiency. A sufficiently high Se status is a prerequisite for adequate immune response, and preventable endemic diseases are known from areas with Se deficiency. Biomarkers of Se status decline strongly in pregnancy, severe illness, or COVID-19, reaching critically low concentrations. Notably, these conditions are associated with an increased risk for autoimmune disease (AID). Positive effects on the immune system are observed with Se supplementation in pregnancy, autoimmune thyroid disease, and recovery from severe illness. However, some studies reported null results; the database is small, and randomized trials are sparse. The current need for research on the link between AID and Se deficiency is particularly obvious for rheumatoid arthritis and type 1 diabetes mellitus. Despite these gaps in knowledge, it seems timely to realize that severe Se deficiency may trigger AID in susceptible subjects. Improved dietary choices or supplemental Se are efficient ways to avoid severe Se deficiency, thereby decreasing AID risk and improving disease course. A personalized approach is needed in clinics and during therapy, while population-wide measures should be considered for areas with habitual low Se intake. Finland has been adding Se to its food chain for more than 35 years-a wise and commendable decision, according to today's knowledge. It is unfortunate that the health risks of Se deficiency are often neglected, while possible side effects of Se supplementation are exaggerated, leading to disregard for this safe and promising preventive and adjuvant treatment options. This is especially true in the follow-up situations of pregnancy, severe illness, or COVID-19, where massive Se deficiencies have developed and are associated with AID risk, long-lasting health impairments, and slow recovery.

Fic and non-Fic AMPylases: protein AMPylation in metazoans

Protein AMPylation refers to the covalent attachment of an AMP moiety to the amino acid side chains of target proteins using ATP as nucleotide donor. This process is catalysed by dedicated AMP transferases, called AMPylases. Since this initial discovery, several research groups have identified AMPylation as a critical post-translational modification relevant to normal and pathological cell signalling in both bacteria and metazoans. Bacterial AMPylases are abundant enzymes that either regulate the function of endogenous bacterial proteins or are translocated into host cells to hijack host cell signalling processes. By contrast, only two classes of metazoan AMPylases have been identified so far: enzymes containing a conserved filamentation induced by cAMP (Fic) domain (Fic AMPylases), which primarily modify the ER-resident chaperone BiP, and SelO, a mitochondrial AMPylase involved in redox signalling. In this review, we compare and contrast bacterial and metazoan Fic and non-Fic AMPylases, and summarize recent technological and conceptual developments in the emerging field of AMPylation.

Selenium(Ⅳ) alleviates chromium(Ⅵ)-induced toxicity in the green alga Chlamydomonas reinhardtii

The wide range of industrial applications of chromium (Cr) has led to an increasing risk of water contamination by Cr(Ⅵ). However, efficient methods to remove or decrease the toxicity of Cr(Ⅵ) in situ are lacking. The main aim of this study was to investigate the mechanisms by which selenite alleviates chromium(Ⅵ)-induced toxicity in Chlamydomonas reinhardtii. Our results showed that K₂Cr₂O₇ had toxic effects on both the structure and physiology of C. reinhardtii in a dose-dependent manner. Adding selenite significantly alleviated chromium accumulation and toxicity in cells. RNA-seq data showed that the expression level of selenoproteins such as SELENOH was significantly increased. Both SELENOH-amiRNA knockdown mutants and selenoh insertional mutant produced more reactive oxygen species (ROS) and grew slower than the wild type, suggesting that SELENOH can reduce chromium toxicity by decreasing the levels of ROS produced by Cr(Ⅵ). We also demonstrated that selenite can reduce the absorption of Cr(Ⅵ) by cells but does not affect the process of Cr(Ⅵ) adsorption and efflux. This information on the molecular mechanism by which selenite alleviates Cr(Ⅵ) toxicity can be used to increase the bioremediation capacity of algae and reduce the human health risks associated with Cr(Ⅵ) toxicity.

Effects of Di-Isononyl Phthalate (DiNP) on Follicular Atresia in Zebrafish Ovary

Di-isononyl phthalate (DiNP) is a plasticizer reported to elicit hormone-like activity and disrupt metabolism and reproduction in fish and other vertebrates. In general, phthalates have been used at high concentrations beyond reported environmental levels to assess their adverse effects on fish gonadal physiology. The present study exposed adult female zebrafish to a wide range of DiNP concentrations [0.42 µg L^-1 (10^-9 M), 4.2 µg L^-1 (10^-8 M), and 42 µg L^-1 (10^-7 M)] for 21 days. We evaluated gene expression profiles related to apoptosis, autophagy, and oxidative stress; DNA fragmentation (TUNEL assay: terminal deoxynucleotidyl transferase dUTP nick end labeling) and caspase activity (CAS3) were also examined. Exposure to 0.42 and 4.2 µg L^-1 upregulated the genes coding for tnfa and baxa, sod1, prkaa1, respectively. CAS3 immunohistochemistry revealed a higher number of positive vitellogenic oocytes in ovaries exposed to 0.42 µg L^-1. Subsequently, we examined the relationship between CAS3 signaling and DNA fragmentation. Accordingly, DNA fragmentation was observed in vitellogenic follicles of fish exposed to 0.42 and 4.2 μg L^-1. Our results demonstrate that follicular atresia can occur after exposure to environmental levels of DiNP for 21 days, which may adversely affect the reproductive performance of female zebrafish in a non-monotonic manner.

Zebrafish: An emerging model system to study liver diseases and related drug discovery

The zebrafish has emerged as a powerful vertebrate model for studying liver-associated disorders. Liver damage is a crucial problem in the process of drug development and zebrafish have proven to be an important tool for the high-throughput screening of drugs for hepatotoxicity. Although the structure of the zebrafish liver differs to that of mammals, the fundamental physiologic processes, genetic mutations and manifestations of pathogenic responses to environmental insults exhibit much similarity. The larval transparency of the zebrafish is a great advantage for real-time imaging in hepatic studies. The zebrafish has a broad spectrum of cytochrome P450 enzymes, which enable the biotransformation of drugs via similar pathways as mammals, including oxidation, reduction and hydrolysis reactions. In the present review, we appraise the various drugs, chemicals and toxins used to study liver toxicity in zebrafish and their similarities to the rodent models for liver-related studies. Interestingly, the zebrafish has also been effectively used to study the pathophysiology of nonalcoholic and alcoholic fatty liver disease. The genetic models of liver disorders and their easy manipulation provide great opportunity in the area of drug development. The zebrafish has proven to be an influential model for the hepatic system due to its invertebrate-like advantages coupled with its vertebrate biology. The present review highlights the pivotal role of zebrafish in bridging the gap between cell-based and mammalian models.

Chemical Elements in Electronic Cigarette Solvents and Aerosols Inhibit Mitochondrial Reductases and Induce Oxidative Stress

INTRODUCTION

Chemical elements and their toxicity were evaluated in electronic cigarette (EC) solvents, fluids, and aerosols.

AIMS AND METHODS

Element identification and quantification in propylene glycol (PG), glycerin (G), refill fluids before and after use, and aerosols was done using inductively coupled plasma optical emission spectrometry. Cytotoxicity and oxidative stress were evaluated using in vitro assays.

RESULTS

Seven elements were present in PG, G, and popular refill fluids, and they transferred to aerosols made with ECs. Selenium was in all products (0.125-0.292 mg/L), while arsenic, aluminum, and tin were frequently in solvent and refill fluid samples at lower concentrations. Iron, chromium, copper, nickel, zinc, and lead were only detected in fluid after EC use, indicating they came from heated atomizers. Elements transferred most efficiently to aerosols made with second-/third-generation ECs. Of the elements in fluid, selenium and arsenic were the most cytotoxic to human bronchial epithelial cells (BEAS-2B) and pulmonary fibroblasts in the 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide assay. Selenium increased superoxide production in mitochondria and nucleoli and elevated selenoprotein H in nucleoli of BEAS-2B cells at concentrations found in EC aerosols (10 nM or 0.002 mg/L).

CONCLUSIONS

Elements in EC aerosols came from both e-fluids and atomizing units. Within second-/third-generation products, transfer became more efficient as power increased. In vitro responses occurred at concentrations of selenium found in some EC aerosols. Human exposure to chemical elements in ECs could be reduced by regulating (decreasing) allowable EC power and by improving the purity of PG and G.

IMPLICATIONS

PG, G, refill fluids, and e-fluids contained potentially toxic chemical elements that transferred to aerosols. Transfer was more efficient in second- and third-generation EC products and increased as power increased. Selenium and arsenic were the most cytotoxic of the elements tested in the 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide assay. Selenium tetrachloride-induced oxidative stress in BEAS-2B cells, but not in human pulmonary fibroblasts. All fluids contained selenium above the concentration that induced oxidative stress in human bronchial epithelial cells. Selenium increased superoxide in mitochondria and nucleoli and increased selenoprotein H, a redox responsive DNA-binding protein that is upregulated by superoxide and an indicator of nucleolar stress. EC users are exposed to elements in aerosols, which may with chronic exposure contribute to diseases associated with oxidative stress.

Accessing the transcriptional status of selenoproteins in skin cancer-derived cell lines

BACKGROUND

Selenoproteins are selenocysteine (Sec)-containing proteins that exhibit numerous physiological functions, mainly antioxidative activities. Studies have suggested that several human selenoproteins play an important role in tumor initiation and progression, including melanoma.

METHODS

Using RNA-seq data set from Sequence Reads Archive (SRA) experiments published at the National Center for Biotechnology Information (NCBI), we determined and compared the transcriptional levels of the 25 selenoproteins-coding sequences found in 16 human-derived melanoma cell lines and compared to four melanocyte controls.

RESULTS

15 selenoprotein-coding genes were found to be expressed in melanoma and normal melanocyte cells, and their mRNA levels varied among the cell lines. All melanoma cells analyzed with BRAF or NRAS mutations presented upregulated levels of SELENOI, TXNRD1, and SELENOT transcripts and downregulated levels of SELENOW and SELENON transcripts in comparison with melanocytes controls. Moreover, SELENOW, SELENON, SELENOI, TXNRD1, and SELENOT-coding transcripts were affected when BRAF-mutated A375 cells were treated with CPI203, A771726 or Vorinostat drugs.

CONCLUSION

Our results indicate that melanoma cells can modify, in a different manner, the selenoprotein transcript levels, as a possible mechanism to control tumor progression. We suggest that the usage of diet and supplements containing selenium should be carefully used for patients with melanoma.

Selenoproteins and their emerging roles in signaling pathways

The functional activity of selenoproteins has a wide range of effects on complex pathogenetic processes, including teratogenesis, immuno-inflammatory, neurodegenerative. Being active participants and promoters of many signaling pathways, selenoproteins support the lively interest of a wide scientific community. This review is devoted to the analysis of recent data describing the participation of selenoproteins in various molecular interactions mediating important signaling pathways. Data processing was carried out by the method of complex analysis. For convenience, all selenoproteins were divided into groups depending on their location and function. Among the group of selenoproteins of the ER membrane, selenoprotein N affects the absorption of Ca2+ by the endoplasmic reticulum mediated by oxidoreductin (ERO1), a key player in the CHOP/ERO1 branch, a pathogenic mechanism that causes myopathy. Another selenoprotein of the ER membrane selenoprotein K binding to the DHHC6 protein affects the IP3R receptor that regulates Ca2+ flux. Selenoprotein K is able to affect another protein of the endoplasmic reticulum CHERP, also appearing in Ca2+ transport. Selenoprotein S, associated with the lumen of ER, is able to influence the VCP protein, which ensures the incorporation of selenoprotein K into the ER membrane. Selenoprotein M, as an ER lumen protein, affects the phosphorylation of STAT3 by leptin, which confirms that Sel M is a positive regulator of leptin signaling. Selenoprotein S also related to luminal selenoproteins ER is a modulator of the IRE1α-sXBP1 signaling pathway. Nuclear selenoprotein H will directly affect the suppressor of malignant tumours, p53 protein, the activation of which increases with Sel H deficiency. The same selenoprotein is involved in redox regulation. Among the cytoplasmic selenoproteins, abundant investigations are devoted to SelP, which affects the PI3K/Akt/Erk signaling pathway during ischemia/reperfusion, is transported into the myoblasts through the plasmalemma after binding to the apoER2 receptor, and into the neurons to the megaline receptor and in general, selenoprotein P plays the role of a pool that stores the necessary trace element and releases it, if necessary, for vital selenoproteins. The thioredoxin reductase family plays a key role in the invasion and metastasis of salivary adenoid cystic carcinoma through the influence on the TGF-β-Akt/GSK-3β pathway during epithelial-mesenchymal transition. The deletion of thioredoxin reductase 1 affects the levels of messengers of the Wnt/β-catenin signaling pathway. No less studied is the glutathione peroxidase group, of which GPX3 is able to inhibit signaling in the Wnt/β-catenin pathway and thereby inhibit thyroid metastasis, as well as suppress protein levels in the PI3K/Akt/c-fos pathway. A key observation is that in cases of carcinogenesis, a decrease in GPX3 and its hypermethylation are almost always found. Among deiodinases, deiodinase 3 acts as a promoter of the oncogenes BRAF, MEK or p38, while stimulating a decrease in the expression of cyclin D1. The dependence of the level of deiodinase 3 on the Hedgehog (SHH) signaling pathway is also noted. Methionine sulfoxide reductase A can compete for the uptake of ubiquitin, reduce p38, JNK and ERK promoters of the MAPK signaling pathway; methionine sulfoxide reductase B1 suppresses MAPK signaling messengers, and also increases PARP and caspase 3.

The Role of Selenium in Oxidative Stress and in Nonthyroidal Illness Syndrome (NTIS): An Overview

Selenium is a trace element, nutritionally classified as an essential micronutrient, involved in maintaining the correct function of several enzymes incorporating the selenocysteine residue, namely the selenoproteins. The human selenoproteome including 25 proteins is extensively described here. The most relevant selenoproteins, including glutathione peroxidases, thioredoxin reductases and iodothyronine deiodinases are required for the proper cellular redox homeostasis as well as for the correct thyroid function, thus preventing oxidative stress and related diseases. This review summarizes the main advances on oxidative stress with a focus on selenium metabolism and transport. Moreover, thyroid-related disorders are discussed, considering that the thyroid gland contains the highest selenium amount per gram of tissue, also for future possible therapeutic implication.

Increased RLIP76 expression in IDH1 wild‑type glioblastoma multiforme is associated with worse prognosis

Mutation of the isocitrate dehydrogenase (IDH) gene is regarded a novel indicator for the prognosis of patients with glioma. However, the role of the IDH1 gene mutations in carcinogenesis and the mechanisms underlying their function in glioblastoma multiforme (GBM) remain unknown. The present study aimed to determine whether the association of RLIP76 with the different IDH1 mutational status could serve as a putative biomarker for improving disease prognosis. Quantitative PCR, western blotting and immunohistochemical staining assays were used to investigate the expression levels of RLIP76 in 124 patients with GBM with different IDH1 mutational status. In addition, the association between RLIP76 expression, IDH1 mutational status and clinicopathological characteristics was investigated. The effects of RLIP76 expression and IDH1 mutational status on cell proliferation, cell apoptosis, and cell signaling were examined by Cell Counting Kit-8, flow cytometry and western blot assays, respectively. The data demonstrated that IDH1 wild-type (IDH1^Wt) patients with low RLIP76 expression exhibited improved overall and progression-free survival. This effect was not observed in patients with IDH1 mutant (IDH1^Mut) GBM. In vitro assays demonstrated that knockdown of IDH1 or overexpression of the IDH1 R132H mutation suppressed cell proliferation and promoted cell apoptosis in U87 glioma cells. Mechanistic studies further indicated that although the IDH1 R132H mutant phenotype exhibited similar antitumor effects on GBM cells as those observed with the IDH1 knockdown, it acted via a different mechanism with regard to the regulation of the apoptosis signaling pathway. IDH1 R132H mutant cells promoted p53-induced apoptosis, while the IDH1 knockdown inhibited the RLIP76-dependent apoptotic pathway in glioma cells. The findings of the present study provided insight to the contribution of IDH1 mutation in the development of GBM and indicated that RLIP76 may be considered as a prognostic biomarker of IDH1^Wt GBM.

There Is Something Fishy About Liver Cancer: Zebrafish Models of Hepatocellular Carcinoma

The incidence of hepatocellular carcinoma (HCC) and the mortality resulting from HCC are both increasing. Most patients with HCC are diagnosed at advanced stages when curative treatments are impossible. Current drug therapy extends mean overall survival by only a short period of time. Genetic mutations associated with HCC vary widely. Therefore, transgenic and mutant animal models are needed to investigate the molecular effects of specific mutations, classify them as drivers or passengers, and develop targeted treatments. Cirrhosis, however, is the premalignant state common to 90% of HCC patients. Currently, no specific therapies are available to halt or reverse the progression of cirrhosis to HCC. Understanding the genetic drivers of HCC as well as the biochemical, mechanical, hormonal, and metabolic changes associated with cirrhosis could lead to novel treatments and cancer prevention strategies. Although additional therapies recently received Food and Drug Administration approval, significant clinical breakthroughs have not emerged since the introduction of the multikinase inhibitor sorafenib, necessitating alternate research strategies. Zebrafish (Danio rerio) are effective for disease modeling because of their high degree of gene and organ architecture conservation with human beings, ease of transgenesis and mutagenesis, high fecundity, and low housing cost. Here, we review zebrafish models of HCC and identify areas on which to focus future research efforts to maximize the advantages of the zebrafish model system.

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

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

Utilization of selenocysteine in early-branching fungal phyla

Selenoproteins are a diverse group of proteins containing selenocysteine (Sec)-the twenty-first amino acid-incorporated during translation via a unique recoding mechanism^1,2. Selenoproteins fulfil essential roles in many organisms¹, yet are not ubiquitous across the tree of life^3-7. In particular, fungi were deemed devoid of selenoproteins^4,5,8. However, we show here that Sec is utilized by nine species belonging to diverse early-branching fungal phyla, as evidenced by the genomic presence of both Sec machinery and selenoproteins. Most fungal selenoproteins lack consensus Sec recoding signals (SECIS elements⁹) but exhibit other RNA structures, suggesting altered mechanisms of Sec insertion in fungi. Phylogenetic analyses support a scenario of vertical inheritance of the Sec trait within eukaryotes and fungi. Sec was then lost in numerous independent events in various fungal lineages. Notably, Sec was lost at the base of Dikarya, resulting in the absence of selenoproteins in Saccharomyces cerevisiae and other well-studied fungi. Our results indicate that, despite scattered occurrence, selenoproteins are found in all kingdoms of life.

Dissecting metabolism using zebrafish models of disease

Zebrafish (Danio rerio) are becoming an increasingly powerful model organism to study the role of metabolism in disease. Since its inception, the zebrafish model has relied on unique attributes such as the transparency of embryos, high fecundity and conservation with higher vertebrates, to perform phenotype-driven chemical and genetic screens. In this review, we describe how zebrafish have been used to reveal novel mechanisms by which metabolism regulates embryonic development, obesity, fatty liver disease and cancer. In addition, we will highlight how new approaches in advanced microscopy, transcriptomics and metabolomics using zebrafish as a model system have yielded fundamental insights into the mechanistic underpinnings of disease.

Selenoprotein H controls cell cycle progression and proliferation of human colorectal cancer cells

Selenoprotein H (SELENOH) is supposed to be involved in redox regulation as well as in tumorigenesis. However, its role in healthy and transformed cells of the gastrointestinal tract remains elusive. We analyzed SELENOH expression in cells depending on their selenium supply and differentiation status and found that SELENOH expression was increased in tumor tissue, in undifferentiated epithelial cells from mice and in colorectal cancer lines as compared to more differentiated ones. Knockdown studies in human colorectal cancer cells revealed that repression of SELENOH decreased cellular differentiation and increased proliferation and migration. In addition, SELENOH knockdown cells have a higher competence to form colonies or tumor xenografts. In parallel, they show a faster cell cycle transition. The high levels of SELENOH in tumors as well as in undifferentiated, proliferative cells together with its inhibitory effects on proliferation and G1/S phase transition suggest SELENOH as a key regulator for cell cycle progression and for prevention of uncontrolled proliferation. As SELENOH expression is highly dependent on the selenium status, effects of selenium supplementation on cancer initiation and progression appear to involve SELENOH.

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

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

Yap regulates glucose utilization and sustains nucleotide synthesis to enable organ growth

The Hippo pathway and its nuclear effector Yap regulate organ size and cancer formation. While many modulators of Hippo activity have been identified, little is known about the Yap target genes that mediate these growth effects. Here, we show that yap ^-/- mutant zebrafish exhibit defects in hepatic progenitor potential and liver growth due to impaired glucose transport and nucleotide biosynthesis. Transcriptomic and metabolomic analyses reveal that Yap regulates expression of glucose transporter glut1, causing decreased glucose uptake and use for nucleotide biosynthesis in yap ^-/- mutants, and impaired glucose tolerance in adults. Nucleotide supplementation improves Yap deficiency phenotypes, indicating functional importance of glucose-fueled nucleotide biosynthesis. Yap-regulated glut1 expression and glucose uptake are conserved in mammals, suggesting that stimulation of anabolic glucose metabolism is an evolutionarily conserved mechanism by which the Hippo pathway controls organ growth. Together, our results reveal a central role for Hippo signaling in glucose metabolic homeostasis.

Transcriptional responses and mechanisms of copper nanoparticle toxicology on zebrafish embryos

Copper nanoparticles (CuNPs) are used widely due to their attractive antimicrobial properties. However, their biosafety and kinetics on vertebrate embryogenesis are still limited. In this study, CuNPs were revealed to induce eye hypoplasia and almost no digestive gut in zebrafish embryos in a dose-dependent manner. Then, transcriptional responses of zebrafish embryos to CuNPs were investigated, and it was revealed that the genes related to wound healing and stimulus responses were up-regulated, but the genes associated with phototransduction and metabolisms were down-regulated. Differentially expressed genes (DEGs) in CuNPs-exposed and Cu²⁺-exposed embryos were compared further. Increased VEGF signaling and expression of fli1 were observed in CuNPs rather than Cu²⁺ treated embryos, but increased reactive oxygen species (ROS) and the resulting enhanced hemoglobin were observed in both CuNPs and Cu²⁺ treated embryos. This study for the first time revealed that CuNPs and Cu²⁺ both down-regulated the genes related to phototransduction and metabolisms, but up-regulated the genes associated with hemoglobin. Additionally, compared with Cu²⁺, CuNPs might be more effective in elevating blood vessels in embryos. Our results suggest that the biological effects of CuNPs are organogenesis-specific during fish embryogenesis, and both particles and ions might mediate their biological effects on embryogenesis.

Overexpression of selenoprotein H prevents mitochondrial dynamic imbalance induced by glutamate exposure

Selenium and selenoproteins play important roles in neuroprotection against glutamate‑induced cell damage, in which mitochondrial dysfunction is considered a major pathogenic feature. Recent studies have revealed that mitochondrial fission could activates mitochondrial initiated cell death pathway. The objectives of the study are to determine whether glutamate induced cell death is mediated through mitochondrial initiated cell death pathway and activation of autophagy, and whether overexpression of selenoprotein H can protect cells from glutamate toxicity by preserving mitochondrial morphology and suppressing autophagy. Vector- or human selenoprotein H (SelH)-transfected HT22 cells (V-HT22 and SelH-HT22, respectively) were exposed to glutamate. The results showed that glutamate-induced cytotoxicity was associated with increased ROS production and imbalance in mitochondrial dynamics and autophagy. These alterations were reversed and cellular integrity restored by overexpression of SelH in HT22 cells.

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

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

Selenoproteins and Metastasis

Cancer survival is largely impacted by the dissemination of cancer cells from the original tumor site to secondary tissues or organs through metastasis. Targets for antimetastatic therapies have recently become a focus of research, but progress will require a better understanding of the molecular mechanisms driving metastasis. Selenoproteins play important roles in many of the cellular activities underlying metastasis including cell adhesion, matrix degradation and migration, invasion into the blood and extravasation into secondary tissues, and subsequent proliferation into metastatic tumors along with the angiogenesis required for growth. In this review the roles identified for different selenoproteins in these steps and how they may promote or inhibit metastatic cancers is discussed. These roles include selenoenzyme modulation of redox tone and detoxification of reactive oxygen species, calcium homeostasis and unfolded protein responses regulated by endoplasmic reticulum selenoproteins, and the multiple physiological responses influenced by other selenoproteins.

The Regulation of Pathways of Inflammation and Resolution in Immune Cells and Cancer Stem Cells by Selenium

Cancer is a complex disease where cancer stem cells (CSCs) maintain unlimited replicative potential, but evade chemotherapy drugs through cellular quiescence. CSCs are able to give rise to bulk tumor cells that have the capability to override antiproliferative signals and evade apoptosis. Numerous pathways are dysregulated in tumor cells, where increased levels of prooxidant reactive oxygen and nitrogen species can lead to localized inflammation to exacerbate all three stages of tumorigenesis: initiation, progression, and metastasis. Modulation of cellular metabolism in tumor cells as well as immune cells in the tumor microenvironment (TME) can impact inflammatory networks. Altering these pathways can potentially serve as a portal for therapy. It is well known that selenium, through selenoproteins, modulates inflammatory pathways in addition to regulating redox homeostasis in cells. Therefore, selenium has the potential to impact the interaction between tumor cells, CSCs, and immune cells. In the sections later, we review the current status of knowledge regarding this interaction, with reference to leukemia stem cells, and the importance of selenium-dependent regulation of inflammation as a potential mechanism to affect the TME and tumor cell survival.