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OBJECTIVES: The trace element selenium (Se) is known mainly for its antioxidant properties and is critical for proper brain function. The role of Se in regulating energy metabolism, and the sexually dimorphic nature of Se functions, however, are underappreciated, and warrant increased attention. Recent work in our lab has highlighted the importance of Se utilization in hypothalamic regulation of energy metabolism. Dietary Se is incorporated into selenoproteins in the form of the unique amino acid selenocysteine (Sec). The objective of this study was to assess the role of selenoproteins in Agouti-related peptide (Agrp)-positive neurons, an orexigenic sub-population of the hypothalamus. METHODS: We generated mice with Agrp-Cre-driven deletion of selenocysteine tRNA (Trsp-Agrp KO mice), which is essential for Sec incorporation into selenoproteins, thus ablating selenoprotein synthesis in Agrp-positive neurons. The metabolic phenotype of Trsp-Agrp KO mice challenged with a high-fat diet was characterized via glucose tolerance test (i.p. injection) and the use of analytical chambers to measure food intake and respiratory metabolism. Prior to sacrifice, mice were challenged with leptin (i.p. injection) to assess neuronal leptin responsivity via immunohistochemistry and western blot. Brown adipose tissue (BAT) morphology and thermogenic protein expression were also analyzed. RESULTS: Female Trsp-Agrp KO mice displayed resistance to diet-induced obesity, which was accompanied by improved glucose tolerance and elevated energy expenditure levels without changes in food intake. Female Trsp-Agrp KO mice also had greater leptin sensitivity and showed signs of elevated BAT thermogenesis. Male Trsp-Agrp KO mice displayed no changes in metabolic phenotype. CONCLUSIONS: Loss of selenoproteins in Agrp-positive neurons of the hypothalamus promotes energy expenditure and reduces diet-induced obesity in a sexually dimorphic manner, leading to resistance to a high-fat diet in females. FUNDING SOURCES: This work was funded by grant support from the National Institute of Diabetes and Digestive and Kidney Diseases (MJB) and Ola HAWAII, a grant from the National Institute on Minority Health and Health Disparities.

OBJECTIVES: Americans are a selenium-replete population with high use of statins, a drug commonly prescribed to ameliorate hypercholesterolemia. Statins act by inhibiting the first step of cholesterol biosynthesis in the liver, the mevalonate pathway. This pathway is also important for the maturation of the selenocysteine tRNA, responsible for the expression of selenoproteins. Selenoprotein deficits were suggested as responsible for side effects of statins, such as increased oxidative stress leading to muscle cramps and myopathies. Selenium for selenoprotein synthesis can be provided by diet or by the actions of the selenium recycling enzyme selenocysteine lyase (Scly). Our objective was to investigate the effects of the use of statins in an animal model lacking the enzyme Scly and fed a high-fat, Se-supplemented diet. METHODS: Age-matched homozygous littermates wild-type C57BL/6 N (WT) and Scly knockout (Scly KO) mice were fed a high-fat diet containing a 1 ppm blend of selenite plus selenomethionine, and were daily treated with simvastatin (5 mg/kg of body weight) for 21 days. We analyzed serum cholesterol levels, oxidative stress and creatine kinase (CK) activity, and liver and skeletal muscle gene expression of selenoproteins and enzymes involved in creatine metabolism. RESULTS: Obese Scly KO mice had a sex-dependent response statin treatment. While female Scly KO mice improved their body weight after statin treatment, male Scly KO mice further gained weight. Statin treatment improved serum oxidative stress in the Scly KO mice, despite sharp elevation of CK activity. Statin treatment did not affect hepatic selenoprotein gene expression of Scly KO mice, but impaired glutathione peroxidase 1 expression in the muscle of male Scly KO mice, while enhancing it in females. CONCLUSIONS: Responses to statin treatment in Scly KO mice fed a high-fat, Se-supplemented diet vary according to sex, benefiting more female than male mice, and are mostly independent of selenoprotein expression. FUNDING SOURCES: National Institutes of Health (NIH) grants U54MD007601 Ola Hawaii (subproject 5544) and R01DK47320, and Fundação de Amparo à Pesquisa do Estado de São Paulo fellowship 2018/0,9478–4. The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH.

Selenoprotein P (Sel P) is a selenium-rich glycoprotein believed to play a key role in selenium (Se) transport throughout the body. Development of a Sel P knockout mouse model has supported this notion and initial studies have indicated that selenium supply to various tissues is differentially affected by genetic deletion of Sel P. Se in the form of the amino acid, selenocysteine, is incorporated into selenoproteins at UGA codons. Thus, Se availability affects not only selenoprotein levels, but also the turnover of selenoprotein mRNAs via the nonsense-mediated decay pathway. We investigated how genetic deletion of Sel P in mice affected levels of the mRNAs encoding all known members of the murine selenoprotein family, as well as three non-selenoprotein factors involved in their synthesis, selenophosphate synthetase 1 (SPS1), SECIS-binding protein 2 (SBP2) and SECp43. Our findings present a comprehensive description of selenoprotein mRNA expression in the following murine tissues: brain, heart, intestine, kidney, liver, lung, spleen and testes. We also describe how abundance of selenoproteins and selenoprotein-synthesis factors are affected by genetic deletion of Sel P in some of these tissues, providing insight into how the presence of this selenoprotein influences selenoprotein mRNA levels, and thus, the selenoproteome.

Selenoproteins are a diverse group of proteins/nusually misidentified and misannotated in sequence/ndatabases. The presence of an in-frame UGA (stop)/ncodon in the coding sequence of selenoprotein/ngenes precludes their identification and correct/nannotation. The in-frame UGA codons are recoded/nto cotranslationally incorporate selenocysteine,/na rare selenium-containing amino acid. The development/nof ad hoc experimental and, more recently,/ncomputational approaches have allowed the efficient/nidentification and characterization of the/nselenoproteomes of a growing number of species./nToday, dozens of selenoprotein families have been/ndescribed and more are being discovered in recently/nsequenced species, but the correct genomic annotation/nis not available for the majority of these/ngenes. SelenoDB is a long-term project that aims to/nprovide, through the collaborative effort of experimental/nand computational researchers, automatic/nand manually curated annotations of selenoprotein/ngenes, proteins and SECIS elements. Version 1.0 of/nthe database includes an initial set of eukaryotic/ngenomic annotations, with special emphasis on the/nhuman selenoproteome, for immediate inspection/nby selenium researchers or incorporation into more/ngeneral databases. SelenoDB is freely available at/nhttp://www.selenodb.org.

Selenocysteine incorporation at UGA codons requires cis-acting mRNA secondary structures and several specialized trans-acting factors. The latter include a selenocysteine-specific tRNA, an elongation factor specific for this tRNA and a SECIS-binding protein, SBP2, which recruits the elongation factor to the selenoprotein mRNA. Overexpression of selenoprotein mRNAs in transfected cells results in inefficient selenocysteine incorporation due to limitation of one or more of these factors. Using a transfection-based competition assay employing overexpression of selenoprotein mRNAs to compete for selenoprotein synthesis, we investigated the ability of the trans-acting factors to overcome competition and restore selenocysteine incorporation. We report that co-expression of SBP2 overcomes the limitation produced by selenoprotein mRNA overexpression, whereas selenocysteyl-tRNA and the selenocysteine-specific elongation factor do not. Competition studies indicate that once bound to SECIS elements, SBP2 does not readily exchange between them. Finally, we show that SBP2 preferentially stimulates incorporation directed by the seleno protein P and phospholipid hydroperoxide glutathione peroxidase SECIS elements over those of other selenoproteins. The mechanistic implications of these findings for the hierarchy of selenoprotein synthesis and nonsense-mediated decay are discussed.