Selenoprotein W, Selenium and Glutathione Peroxidase in Rat and Sheep Brains and in Brain Cell Cultures

Selenoprotein W deficiency does not affect oxidative stress and insulin sensitivity in the skeletal muscle of high-fat diet-fed obese mice

Selenoprotein W (SelW) is a selenium-containing protein with a redox motif found abundantly in the skeletal muscle of rodents. Previous in vitro studies suggest that SelW plays an antioxidant role; however, relatively few in vivo studies have addressed the antioxidant role of SelW. Since oxidative stress is a causative factor for the development of insulin resistance in obese subjects, we hypothesized that if SelW plays a role as an antioxidant, SelW deficiency could aggravate the oxidative stress and insulin resistance caused by a high-fat diet. SelW deficiency did not affect insulin sensitivity and H₂O₂ levels in the skeletal muscle of control diet-fed mice. SelW levels in the skeletal muscle were decreased by high-fat diet feeding for 12 wk. High-fat diet induced obesity and insulin resistance and increased the levels of H₂O₂ and oxidative stress makers, which were not affected by SelW deficiency. High-fat diet feeding increased the expression of antioxidant enzymes; however, SelW deficiency did not affect the expression levels of antioxidants. These results suggest that SelW does not play a protective role against oxidative stress and insulin resistance in the skeletal muscle of high-fat diet-fed obese mice.

Identification of FAM96B as a novel selenoprotein W binding partner in the brain

Selenoprotien W (SelW) plays a key role in brain development, although the exact biological function and mechanisms remain unclear. We performed a yeast two-hybrid screen on a human fetal brain cDNA library and identified FAM96B as a novel binding partner of SelW. FRET analyses confirmed the interaction between SelW' and FAM96B. The mutated SelW' construct was cloned and overexpressed in E. coli, and a pull-down assay verified a direct interaction between SelW' and FAM96B. Finally, Co-Immunoprecipitation on murine brain tissue proteins demonstrated an endogenous interaction between the two proteins in the brain. Taken together, our findings prove a direct interaction between SelW and FAM96B, which may provide new insights into the role of SelW in brain development and neurodegenerative diseases.

Molecular cloning and sequence analysis of selenoprotein W gene and its mRNA expression patterns in response to metabolic status and cadmium exposure in goldfish, Carassius auratus

Selenoprotein W (SelW) is a low molecular weight and selenocysteine containing protein with redox activity involved in the antioxidant response. In the present study, the full-length cDNA of goldfish (Carassius auratus) selenoprotein W (gfSelW) was successfully cloned from the liver tissue by rapid amplification of cDNA ends technique. The obtained gfSelW cDNA was 730 bp long with a 79 bp 5'-untranslated region (UTR), a 390 bp 3'-UTR containing the consensus polyadenylation signal AATAAA and a 261 bp open reading frame coding a protein of 86 amino acid residues. gfSelW mRNA was observed in all regions of brain and peripheral tissues by semi-quantitative RT-PCR, and the most abundant was detected in testis. After fasting for 1 week, gfSelW mRNA expression levels were significantly decreased compared to the fed group in hypothalamus and liver. After refeeding for 7 days, gfSelW mRNA expression levels were increased back. Furthermore, the mRNA expressions of gfSelW in hypothalamus and liver were varied in periprandial changes and significantly up-regulated after meal 2 h and 4 h, respectively. With cadmium exposure for 24 h, gfSelW mRNA expression levels in gill and leucocytes were significantly decreased at different cadmium concentrations changing from 0.5 ppm to 10 ppm. However, the gfSelW mRNA expression level was sharply increased in liver, relatively to the control about 4.98-fold at 0.5 ppm. The results in this study provide molecular characterization of SelW in goldfish and imply that SelW mRNA expression may be associated with metabolic status and oxidative stress and regulated by metabolic factors and cadmium in fish.

Effects of dietary selenium on selenoprotein W gene expression in the chicken immune organs

Selenoprotein W (SelW) is expressed in the immune systems of mammals. However, its pattern of expression in the immune organs of birds is still unclear. To investigate the distribution of SelW and effects of dietary Se levels on the SelW mRNA expression in the immune organs of birds, 1-day-old male chickens were fed either a commercial diet or an Se-supplemented diet containing 0.601, 1.058, 1.514, or 2.427 mg Se per kilogram, and 1.0, 2.0, 3.0 or 5.0 mg sodium selenite per kilogram for 90 days. The immune organs (spleen, thymus, and bursa of Fabricius) were collected and examined for Se content and SelW mRNA levels. The mRNA expression of SelW was detected in all the tissues. Although Se content was the highest in the spleen, the remarkable stability of the SelW mRNA level was observed in this organ during different times of dietary Se supplementation. Se-supplemented diet can make the SelW expression levels higher within a certain range in thymus and bursa of Fabricius. The present study demonstrates that SelW is widely expressed in immune organs of birds and that Se-supplementation of the feed increases SelW expression in the thymus and the bursa of Fabricius.

Effect of copper, zinc and cadmium on the promoter of selenoprotein W in glial and myoblast cells

Rat selenoprotein W (SeW) promoter activity was investigated using different concentrations of cadmium, copper, and zinc. Two fragments (404 and 1265 bp) of the SeW promoter, containing a single metal response element (MRE), were ligated into the multiple cloning site of a pGL3-Basic reporter plasmid. The constructs were transfected into cultured C6 (rat glial) and L8 (myoblast) cells and promoter activity measured by means of luciferase reporter gene fused to the SeW promoter fragments in the reporter plasmid. With post-transfection exposure of these cell lines to these metals, copper and zinc, but not cadmium, significantly increased promoter activity of the unmutated 1265 bp (not 404 bp) construct (p<0.05) only in the C6 cells. Mutation of the MRE sequence abolished promoter response to metal exposure but did not eliminate promoter activity. The results suggest that SeW expression in glial cells can be increased on exposure to copper and zinc and that this response is dependent on the MRE sequence present in the SeW promoter.

Selenium and the brain: a review

Similar to other tissues selenium from selenomethionine is deposited in the brain at higher concentrations than selenium in other forms. Vitamin E has a greater effect than selenium in reducing lipid peroxidation in various brain regions. Selenium does not have as great effect on glutathione peroxidase (GPX) activity in the brain as in most other organs. Prolonged selenium and iodine deficiencies will compromise thyroid hormone homeostatus in the brain and this is due to changes in deiodinases activities and lipid peroxidation. Even though selenium deficiency results in reduced GPX activity and selenium content in the brain, there is no reduction in thioredoxin reductase activity or selenoprotein W levels. Selenoprotein P is taken up in greater amounts by the brain but not by other organs in selenium deficient animals, suggesting a critical function of this selenoprotein in this organ. Selenium will influence compounds with hormonal activity (and neurotransmitters) in the brain, and this is postulated to be the reason selenium affects moods in humans and behavior in animals. Even though selenium counteracts the neurotoxicity of mercury, cadmium, lead and vanadium, it causes them to accumulate in the brain, presumably in a nontoxic complex.