Selenium deficiency-induced multiple tissue damage with dysregulation of immune and redox homeostasis in broiler chicks under heat stress.

Broiler chicks are fast-growing and susceptible to dietary selenium (Se) deficiency. This study sought to reveal the underlying mechanisms of how Se deficiency induces key organ dysfunctions in broilers. Day-old male chicks (n=6 cages/diet, 6 chicks/cage) were fed with a Se-deficient diet (Se-Def, 0.047 mg Se/kg) or the Se-Def+0.3 mg Se/kg (Control, 0.345 mg Se/kg) for 6 weeks. The serum, liver, pancreas, spleen, heart, and pectoral muscle of the broilers were collected at week 6 to assay for Se concentration, histopathology, serum metabolome, and tissue transcriptome. Compared with the Control group, Se deficiency induced growth retardation and histopathological lesions and reduced Se concentration in the five organs. Integrated transcriptomics and metabolomics analysis revealed that dysregulation of immune and redox homeostasis related biological processes and pathways contributed to Se deficiency-induced multiple tissue damage in the broilers. Meanwhile, four metabolites in the serum, daidzein, epinephrine, L-aspartic acid and 5-hydroxyindoleacetic acid, interacted with differentially expressed genes with antioxidative effects and immunity among all the five organs, which contributed to the metabolic diseases induced by Se deficiency. Overall, this study systematically elucidated the underlying molecular mechanisms in the pathogenesis of Se deficiency-related diseases, which provides a better understanding of the significance of Se-mediated heath in animals.

Selenoproteins Protect Against Avian Liver Necrosis by Metabolizing Peroxides and Regulating Receptor Interacting Serine Threonine Kinase 1/Receptor Interacting Serine Threonine Kinase 3/Mixed Lineage Kinase Domain-Like and Mitogen-Activated Protein Kinase Signaling.

Liver necroptosis of chicks is induced by selenium (Se)/vitamin E (VE) deficiencies and may be associated with oxidative cell damage. To reveal the underlying mechanisms of liver necrosis, a pool of the corn-soy basal diet (10 µg Se/kg; no VE added), a basal diet plus all-rac-α-tocopheryl acetate (50 mg/kg), Se (sodium selenite at 0.3 mg/kg), or both of these nutrients were provided to day-old broiler chicks (n = 40/group) for 6 weeks. High incidences of liver necrosis (30%) of chicks were induced by -SE-VE, starting at day 16. The Se concentration in liver and glutathione peroxidase (GPX) activity were decreased (P < 0.05) by dietary Se deficiency. Meanwhile, Se deficiency elevated malondialdehyde content and decreased superoxide dismutase (SOD) activity in the liver at weeks 2 and 4. Chicks fed with the two Se-deficient diets showed lower (P < 0.05) hepatic mRNA expression of Gpx1, Gpx3, Gpx4, Selenof, Selenoh, Selenok, Selenom, Selenon, Selenoo, Selenop, Selenot, Selenou, Selenow, and Dio1 than those fed with the two Se-supplemented diets. Dietary Se deficiency had elevated (P < 0.05) the expression of SELENOP, but decreased the downregulation (P < 0.05) of GPX1, GPX4, SELENON, and SELENOW in the liver of chicks at two time points. Meanwhile, dietary Se deficiency upregulated (P < 0.05) the abundance of hepatic proteins of p38 mitogen-activated protein kinase, phospho-p38 mitogen-activated protein kinase, c-Jun N-terminal kinase, phospho-c-Jun N-terminal kinase, extracellular signal-regulated kinase, phospho-mitogen-activated protein kinase, receptor-interacting serine-threonine kinase 1 (RIPK1), receptor-interacting serine-threonine kinase 3 (RIPK3), and mixed lineage kinase domain-like (MLKL) at two time points. In conclusion, our data confirmed the differential regulation of dietary Se deficiency on several key selenoproteins, the RIPK1/RIPK3/MLKL, and mitogen-activated protein kinase signaling pathway in chicks and identified new molecular clues for understanding the etiology of nutritional liver necrosis.

Dietary Selenium Regulates microRNAs in Metabolic Disease: Recent Progress.

Selenium (Se) is an essential element for the maintenance of a healthy physiological state. However, due to environmental and dietary factors and the narrow safety range of Se, diseases caused by Se deficiency or excess have gained considerable traction in recent years. In particular, links have been identified between low Se status, cognitive decline, immune disorders, and increased mortality, whereas excess Se increases metabolic risk. Considerable evidence has suggested microRNAs (miRNAs) regulate interactions between the environment (including the diet) and genes, and play important roles in several diseases, including cancer. MiRNAs target messenger RNAs to induce changes in proteins including selenoprotein expression, ultimately generating disease. While a plethora of data exists on the epigenetic regulation of other dietary factors, nutrient Se epigenetics and especially miRNA regulated mechanisms remain unclear. Thus, this review mainly focuses on Se metabolism, pathogenic mechanisms, and miRNAs as key regulatory factors in Se-related diseases. Finally, we attempt to clarify the regulatory mechanisms underpinning Se, miRNAs, selenoproteins, and Se-related diseases.

Knockout of Selenoprotein V Affects Regulation of Selenoprotein Expression by Dietary Selenium and Fat Intakes in Mice.

BACKGROUND: The metabolic function of selenoprotein V (SELENOV) remains unknown. OBJECTIVES: Two experiments were conducted to determine effects of the Selenov knockout (KO) on selenium concentration and mRNA, protein, and/or activity of 4 major selenoproteins [glutathione peroxidase (GPX) 1, GPX4, thioredoxin reductase-1 (TXNRD1), and selenoprotein P (SELENOP)] in the serum, liver, testis, and/or white adipose tissue (WAT) of mice fed different dietary selenium and fat concentrations. METHODS: In Experiment (Expt) 1, 40 KO and 40 wild-type (WT) mice (males, 8 wk old) were fed (n = 10/genotype) a casein-sucrose basal diet plus 0, 0.3, 1, or 3 mg Se/kg (as sodium selenite) for 32 wk . In Expt 2, 20 KO and 20 WT mice (males, 8 wk old) were fed (n  = 10/genotype) a normal-fat diet (NF; 10% calories from fat) or a high-fat diet (HF; 60% calories from fat) for 19 wk. RESULTS: In Expt 1, the KO caused consistent or substantial decreases (P < 0.05) of mRNA amounts of Gpx1, Txnrd1, and Selenop in the testis (≤52%), but selenium concentrations (19-29%) and GPX activities (≤ 50%) were decreased in the liver across different dietary selenium concentrations . Hepatic and testis GPX1 protein was elevated (≤31%) and decreased (≤45%) by the KO, respectively. In Expt 2, the genotype and dietary fat intake exerted interaction effects ( P < 0.05) on Gpx1 mRNA amounts in the WAT; Gpx1, Txnrd1, and Selenop mRNA amounts and TXNRD activities in the testis; and selenium concentrations in the serum and liver. However, these 2 treatments produced largely independent or additive effects (P < 0.05) on the GPX1 and SELENOP protein amounts in the liver and testis (up to ± 50% changes). CONCLUSIONS: The KO-mediated changes in the tissue selenium concentrations and functional expression of 3 major selenoproteins implied potential for SELENOV in regulating body selenium metabolism in the mouse.

Avian selenogenome: response to dietary Se and vitamin E deficiency and supplementation.

Selenium (Se) is an essential nutrient for humans and all food-producing animal species. Nutritional deficiencies of Se and (or) vitamin E induce exudative diathesis, nutritional pancreatic atrophy, and nutritional muscular dystrophy in chicks. Although these diseases are presumably associated with the need of Se for the synthesis of the 21st amino acid, selenocysteine (Sec, U) in selenoproteins, metabolic functions of the 25 selenoproteins identified in avian species remain largely unknown. This paper reviews regulations of the whole selenogenome and selected selenoproteins by different concentrations and chemical forms of dietary Se and (or) vitamin E in various affected tissues. The avian selenogenome may be divided into 2 groups: responders and non-responders, based on its response to dietary Se and vitamin E changes. Mechanisms for the gene-, tissue-, and age-dependent responses and the correlation with the stress and cell death signaling are explored. Overall, this review intends to link the novel regulation and function of avian selenogenome to the protection by Se against oxidative insults associated with the classical Se/vitamin E deficiency diseases in chicks.

A Novel Organic Selenium Compound Exerts Unique Regulation of Selenium Speciation, Selenogenome, and Selenoproteins in Broiler Chicks.

Background: A new organic selenium compound, 2-hydroxy-4-methylselenobutanoic acid (SeO), displayed a greater bioavailability than sodium selenite (SeNa) or seleno-yeast (SeY) in several species.Objective: This study sought to determine the regulation of the speciation of selenium, expression of selenogenome and selenocysteine biosynthesis and degradation-related genes, and production of selenoproteins by the 3 forms of selenium in the tissues of broiler chicks.Methods: Day-old male chicks (n = 6 cages/diet, 6 chicks/cage) were fed a selenium-deficient, corn and soy-based diet [base diet (BD), 0.05 mg Se/kg] or the BD + SeNa, SeY, or SeO at 0.2 mg Se/kg for 6 wk. Plasma, livers, and pectoral and thigh muscles were collected at weeks 3 and 6 to assay for total selenium, selenomethionine, selenocysteine, redox status, and selected genes, proteins, and enzymes.Results: Although both SeY and SeO produced greater concentrations (P < 0.05) of total selenium (20-172%) and of selenomethionine (≤15-fold) in the liver, pectoral muscle, and thigh than those of SeNa, SeO further raised (P < 0.05) these concentrations by 13-37% and 43-87%, respectively, compared with SeY. Compared with the BD, only SeO enhanced (P < 0.05) the mRNA of selenoprotein (Seleno) s and methionine sulfoxide reductase B1 (Msrb1) in the liver and thigh (62-98%) and thioredoxin reductase (TXRND) activity in the pectoral and thigh muscles (20-37%) at week 3. Furthermore, SeO increased (P < 0.05) the expression of glutathione peroxidase (Gpx) 3, GPX4, SELENOP, and SELENOU relative to the SeNa group by 26-207%, and the expression of Selenop, O-phosphoseryl-transfer RNA (tRNA):selenocysteinyl-tRNA synthase, GPX4, and SELENOP relative to the SeY group by 23-55% in various tissues.Conclusions: Compared with SeNa or SeY, SeO demonstrated a unique ability to enrich selenomethionine and total selenium depositions, to induce the early expression of Selenos and Mrsb1 mRNA and TXRND activity, and to enhance the protein production of GPX4, SELENOP, and SELENOU in the tissues of chicks.

Characterization of Selenoprotein M and Its Response to Selenium Deficiency in Chicken Brain.

Selenoprotein M (SelM) may function as thiol disulfide oxidoreductase that participates in the formation of disulfide bonds and can be implicated in calcium responses. SelM may have a functional role in catalyzing free radicals and has been associated with Alzheimer's disease (AD). However, studies of SelM in chicken remain very limited. In this study, two groups of day-old broiler chicks (n = 40/group) were fed a corn-soy basal diet (BD, 13 µg Se/kg) and BD supplemented with Se (as sodium selenite) at 0.3 mg/kg. The brain was collected at 14, 21, 28, and 42 days of age. We performed a sequence analysis and predicted the structure and function of SelM. We also investigated the effects of Se deficiency on the expression of Selt, Selw, and Selm and the Se status in the chicken brain. The results show that Se deficiency induced the lower (P < 0.05) Se content, glutathione peroxidase (GPx), and catalase (CAT) activities; increased (P < 0.05) malondialdehyde (MDA) content; and reduced (P < 0.05) the expression of Selm messenger RNA (mRNA) and protein abundance of SelM in the brain. However, there were no significant brain Selt and Selw mRNA levels by dietary Se deficiency in chicks. The different regulations of these three redox (Rdx) protein expressions by Se deficiency represent a novel finding of the present study. Our results demonstrated that SelM may have an important role in protecting against oxidative damage in the brain of chicken, which might shed light on the role of SelM in human neurodegenerative disease. More studies are needed to confirm our conclusion.

Selenoproteins protect against avian nutritional muscular dystrophy by metabolizing peroxides and regulating redox/apoptotic signaling.

Nutritional muscular dystrophy (NMD) of chicks is induced by dietary selenium (Se)/vitamin E (Vit. E) deficiencies and may be associated with oxidative cell damage. To reveal the underlying mechanisms related to the presumed oxidative cell damage, we fed four groups of 1-day-old broiler chicks (n = 40/group) with a basal diet (BD; 10 µg Se/kg; no Vit. E added, -Se -Vit. E) or the BD plus all-rac-α-tocopheryl acetate at 50mg/kg (-Se +Vit. E), Se (as sodium selenite) at 0.3mg/kg (+Se -Vit. E), or both of these nutrients (+Se +Vit. E) for 6 weeks. High incidences of NMD (93%) and mortality (36%) of the chicks were induced by the BD, starting at week 3. Dietary Se deficiency alone also induced muscle fiber rupture and coagulation necrosis in the pectoral muscle of chicks at week 3 and thereafter, with increased (P < 0.05) malondialdehyde, decreased (P < 0.05) total antioxidant capacity, and diminished (P < 0.05) glutathione peroxidase activities in the muscle. To link these oxidative damages of the muscle cells to the Se-deficiency-induced NMD, we first determined gene expression of the potential 26 selenoproteins in the muscle of the chicks at week 2 before the onset of symptoms. Compared with the +Se chicks, the -Se chicks had lower (P < 0.05) muscle mRNA levels of Gpx1, Gpx3, Gpx4, Sepp1, Selo, Selk, Selu, Selh, Selm, Sepw1, and Sep15. The -Se chicks also had decreased (P < 0.05) production of 6 selenoproteins (long-form selenoprotein P (SelP-L), GPx1, GPx4, Sep15, SelW, and SelN), but increased levels (P < 0.05) of the short-form selenoprotein P in muscle at weeks 2 and 4. Dietary Se deficiency elevated (P < 0.05) muscle p53, cleaved caspase 3, cleaved caspase 9, cyclooxygenase 2 (COX2), focal adhesion kinase (FAK), phosphatidylinositol 3-kinase (PI3K), phospho-Akt, nuclear factor-κB (NF-κB), p38 mitogen-activated protein kinase (p38 MAPK), phospho-p38 MAPK, phospho-JNK, and phospho-ERK and decreased (P < 0.05) muscle procaspase 3, procaspase 9, and NF-κB inhibitor α. In conclusion, the downregulation of SelP-L, GPx1, GPx4, Sep15, SelW, and SelN by dietary Se deficiency might account for induced oxidative stress and the subsequent peroxidative damage of chick muscle cells via the activation of the p53/caspase 9/caspase 3, COX2/FAK/PI3K/Akt/NF-κB, and p38 MAPK/JNK/ERK signaling pathways. Metabolism of peroxides and redox regulation are likely to be the mechanisms whereby these selenoproteins prevented the onset of NMD in chicks.

Porcine serum can be biofortified with selenium to inhibit proliferation of three types of human cancer cells.

Our objectives were to determine if porcine serum could be enriched with selenium (Se) by feeding pigs with high concentrations of dietary Se and if the Se-biofortified serum inhibited proliferation of 3 types of human cancer cells. In Expt. 1, growing pigs (8 wk old, n = 3) were fed 0.02 or 3.0 mg Se/kg (as sodium selenite) for 16 wk and produced serum with 0.5 and 5.4 µmol/L Se, respectively. In Expt. 2, growing pigs (5 wk old, n = 6) were fed 0.3 or 1.0 mg Se/kg (as Se-enriched yeast) for 6 wk and produced serum with 2.6 and 6.2 µmol/L Se, respectively. After the Se-biofortified porcine sera were added at 16% in RPMI 1640 to treat NCI-H446, DU145, and HTC116 cells for 144 h, they decreased (P < 0.05) the viability of the 3 types of human cancer cells by promoting apoptosis, compared with their controls. This effect was replicated only by adding the appropriate amount of methylseleninic acid to the control serum and was mediated by a downregulation of 8 cell cycle arrest genes and an upregulation of 7 apoptotic genes. Along with 6 previously reported selenoprotein genes, selenoprotein T (Selt), selenoprotein M (Selm), selenoprotein H (Selh), selenoprotein K (Selk), and selenoprotein N (Sepn1) were revealed to be strongly associated with the cell death-related signaling induced by the Se-enriched porcine serum. In conclusion, porcine serum could be biofortified with Se to effectively inhibit the proliferation of 3 types of human cancer cells and the action synchronized with a matrix of coordinated functional expression of multiple selenoprotein genes.

Gene expression of endoplasmic reticulum resident selenoproteins correlates with apoptosis in various muscles of se-deficient chicks.

Dietary selenium (Se) deficiency causes muscular dystrophy in various species, but the molecular mechanism remains unclear. Our objectives were to investigate: 1) if dietary Se deficiency induced different amounts of oxidative stress, lipid peroxidation, and cell apoptosis in 3 skeletal muscles; and 2) if the distribution and expression of 4 endoplasmic reticulum (ER) resident selenoprotein genes (Sepn1, Selk, Sels, and Selt) were related to oxidative damages in these muscles. Two groups of day-old layer chicks (n = 60/group) were fed a corn-soy basal diet (33 µg Se/kg; produced in the Se-deficient area of Heilongjiang, China) or the diet supplemented with Se (as sodium selenite) at 0.15 mg/kg for 55 d. Dietary Se deficiency resulted in accelerated (P < 0.05) cell apoptosis that was associated with decreased glutathione peroxidase activity and elevated lipid peroxidation in these muscles. All these responses were stronger in the pectoral muscle than in the thigh and wing muscles (P < 0.05). Relative distribution of the 4 ER resident selenoprotein gene mRNA amounts and their responses to dietary Se deficiency were consistent with the resultant oxidative stress and cell apoptosis in the 3 muscles. Expression of Sepn1, Sels, and Selt in these muscles was correlated with (r > 0.72; P < 0.05) that of Sepsecs encoding a key enzyme for biosynthesis of selenocysteine (selenocysteinyl-tRNA synthase). In conclusion, the pectoral muscle demonstrated unique expression patterns of the ER resident selenoprotein genes and GPx activity, along with elevated susceptibility to oxidative cell death, compared with the other skeletal muscles. These features might help explain why it is a primary target of Se deficiency diseases in chicks.

A high-selenium diet induces insulin resistance in gestating rats and their offspring.

Although supranutrition of selenium (Se) is considered a promising anti-cancer strategy, recent human studies have shown an intriguing association between high body Se status and diabetic risk. This study was done to determine if a prolonged high intake of dietary Se actually induced gestational diabetes in rat dams and insulin resistance in their offspring. Forty-five 67-day-old female Wistar rats (n=15/diet) were fed a Se-deficient (0.01 mg/kg) corn-soy basal diet (BD) or BD+Se (as Se-yeast) at 0.3 or 3.0mg/kg from 5 weeks before breeding to day 14 postpartum. Offspring (n=8/diet) of the 0.3 and 3.0mg Se/kg dams were fed with the same respective diet until age 112 days. Compared with the 0.3mg Se/kg diet, the 3.0mg/kg diet induced hyperinsulinemia (P<0.01), insulin resistance (P<0.01), and glucose intolerance (P<0.01) in the dams at late gestation and/or day 14 postpartum and in the offspring at age 112 days. These impairments concurred with decreased (P<0.05) mRNA and/or protein levels of six insulin signal proteins in liver and muscle of dams and/or pups. Dietary Se produced dose-dependent increases in Gpx1 mRNA or GPX1 activity in pancreas, liver, and erythrocytes of dams. The 3.0mg Se/kg diet decreased Selh (P<0.01), Sepp1 (P=0.06), and Sepw1 (P<0.01), but increased Sels (P<0.05) mRNA levels in the liver of the offspring, compared with the 0.3mg Se/kg diet. In conclusion, supranutrition of Se as a Se-enriched yeast in rats induced gestational diabetes and insulin resistance. Expression of six selenoprotein genes, in particular Gpx1, was linked to this metabolic disorder.

The selenium deficiency disease exudative diathesis in chicks is associated with downregulation of seven common selenoprotein genes in liver and muscle.

Fast-growing broiler chicks are susceptible to Se deficiency diseases including exudative diathesis (ED). Our objective was to determine if ED could be induced by feeding a current, practical diet and if the incidence was related to selenogenome expression in liver and muscle of chicks. Four groups of day-old broiler chicks (n = 60/group) were fed a corn-soy basal diet (BD; 14 µg Se/kg; produced in the Se-deficient area of Sichuan, China and not supplemented with Se or vitamin E), the BD and all-rac-α-tocopheryl acetate at 50 mg/kg and Se (as sodium selenite) at 0.3 mg/kg, or both of these nutrients for 6 wk. A high incidence of ED and mortality of chicks were induced by the BD. The incidences and mortality were completely prevented by supplemental dietary Se but were only partially decreased by supplemental α-tocopherol acetate. Dietary Se deficiency decreased (P < 0.05) mRNA levels of 7 common selenoprotein genes (Gpx1, Gpx4, Sepw1, Sepn1, Sepp1, Selo, and Selk) in muscle and liver. Whereas supplementing α-tocopherol acetate enhanced (P < 0.05) only the muscle Sepx1 mRNA level, it actually decreased (P < 0.05) hepatic Gpx1, Seli, Txnrd1, and Txnrd2 mRNA levels. In conclusion, dietary Se protected chicks from the Se deficiency disease ED, probably by upregulating selenoprotein genes coding for oxidation- and/or lesion-protective proteins. The protection by vitamin E might be mediated via selenoproteins not assayed in this study and/or Se-independent mechanisms. The inverse relationship between hepatic expression of 4 redox-related selenoprotein genes and vitamin E status revealed a novel interaction between Se and vitamin E in vivo.