Roger A. Sunde, Ph.D.

Professor of Nutritional Sciences; Ph.D., 1980

Emphasis Group
Biochemical & Molecular Nutrition
Human Nutrition

Principal Research Interest
Our research is focused on studying four related questions regarding the molecular nutrition and biochemistry of selenium.

Research Summary:
Can molecular biology techniques be used to better establish nutrient requirements? We evaluated the Se requirement in young, rapidly growing male and female rats by determining growth, liver Se, liver glutathione peroxidase (GPX1) activity and liver mRNA. For pups that are Se-adequate initially, there is no apparent Se requirement for growth in Se deficiency, in spite GPX1 activity at effectively zero and GPX1 mRNA levels at 10% of adequate levels (Fig. 1). In both sexes, GPX activity reaches a plateau at 0.1 µg Se/g diet, even in female rat liver with 2.5 times more GPX than the male, and liver GPX1 mRNA levels reach a plateau at 0.05 µg Se/g which is half of the dietary Se level needed for plateau GPX1 activity. These studies were used in establishing the NRC95 Se requirements. We have recently extended this approach to ages of the life-cycle that are less easily evaluated, and we found that the Se requirement does not increase during pregnancy and lactation, and is not affected by vitamin E status. New studies are modifying these techniques for use to determine Se requirements in humans using Se-deficient Chinese subjects. We are also evaluating the molecular basis for the higher Se requirements of turkeys.

What are 'critical' biochemical roles for Se? We isolated and sequenced full-length cDNA clones to a new selenoperoxidase, pig and rat phospholipid hydroperoxide glutathione peroxidase (GPX4), and were the first to report that GPX4 mRNA levels are little affected by Se deficiency in the same samples that show a 90% decrease in GPX1 mRNA levels (Fig. 1). We also developed a second-generation Se-deficient rat model with growth at half the rate of Se-supplemented litter mates. In this model, growth is significantly increased growth with a single injection of as little as 1 µg Se/100 g rat. We have shown that increases in circulating tri-iodothyronine hormone are not associated with the increased growth and are now looking at Se-dependent thioredoxin reductase.

What is the biological role of GPX1? Our research suggests the hypothesis that GPX1 functions as a "biological Se buffer." We have used SDS-PAGE electrophoresis to show that 75Se flux into GPX1 rises only after 75Se incorporation into GPX4 is saturated. We have recently used GPX1-knockout mice to study the impact on other Se-dependent parameters when the GPX1 Se buffer no longer is present. Future work will involve recombinant selenoproteins to further test this hypothesis in transfected cultured cells and animals.

What is the molecular mechanism used to accomplish Se regulation of GPX1 mRNA? We have postulated that GPX1 mRNA possesses elements that specifically target GPX1 mRNA for degradation in Se deficiency. To investigate this mechanism, we studied the Se regulation of endogenous GPX1 and stably-transfected recombinant GPX1 mRNAs in CHO cells. Site-directed mutations which delete or alter the GPX1 SECIS result in loss of Se regulation, and mutations that restore the stem loop structure restore Se regulation. We have shown that the GPX4 3'UTR can substitute for the GPX1 3'UTR in mediating Se regulation (Fig 2), and that GPX1 coding-region sequences or organization are necessary for Se regulation of an mRNA species. This work indicates that Se regulation of GPX1 mRNA stability occurs by nonsense-mediated decay requiring the UGA in front of an exon. And we were able to use this approach to make Se-regulated beta-globin (Fig 2). More recently, we are determining the effect of selenium status on transcript abundance (mRNA copies/cell) and translational efficiency (selenoproteins made/mRNA).

Representative Publications

Weiss, S.L., Evenson, J.K., Thompson, K.M., and Sunde, R.A. 1997. Dietary selenium regulation of glutathione peroxidase mRNA and other selenium-dependent parameters in male rats. J. Nutr. Biochem. 8: 85-91.

Sunde, R.A. 1997. Selenium. In: Handbook of Nutritionally Essential Mineral Elements (O'Dell, B.L., and Sunde, R.A., eds.), Marcel Dekker, Inc., New York, pp. 493-556.

Weiss, S.L., and Sunde, R.A. 1997. Selenium regulation of classical glutathione peroxidase expression requires the 3-untranslated region in transfected Chinese hamster ovary cells. J. Nutr. 127: 1304-1310.

Sunde, R.A., Thompson, B.M., Palm, M.D., Weiss, S.L., Thompson, K.M., and Evenson, J.K. 1997. Selenium regulation of selenium-dependent glutathione peroxidases. Biomed. Environ. Sci. 10: 346-355.

Thompson, K.M., Haibach, H., and Sunde, R.A. 1998. Liver selenium and testis phospholipid hydroperoxide glutathione peroxidase are associated with growth during Se repletion of second-generation Se-deficient male rats. J. Nutr. 128: 1289-1295.

Weiss, S.L. & Sunde, R.A. 1998. Cis-acting elements are required for selenium regulation of glutathione peroxidase-1 mRNA levels. RNA 4: 816-827.

Wen, W., Weiss, S.L. & Sunde, R.A. 1998. UGA codon position affects the efficiency of selenocysteine incorporation into glutathione peroxidase-1. J. Biol. Chem. 273: 28533-28541.

Sunde, R.A. 2000. Selenium. In: Biochemical and Physiological Aspects of Human Nutrition (Stipanuk, M. H. ed.), W.B. Sanders, New York. Pp. 782-809.

Sunde, R.A. and Evenson, J.K. 2000. Control of expression of glutathione peroxidase-1 and other selenoproteins in rats and cultured cells. In: Trace Elements in Man and Animals 10 (Roussel, A.M., R.A. Anderson, & Favier, A. E., eds.), pp. 21-27. Plenum Publishers, New York.

Sachdev,S.W. & Sunde,R.A. 2001. Selenium regulation of transcript abundance and relative translational efficiency of glutathione peroxidase 1 and 4 in rat liver. Biochem. J. 357: 851-858.

Sunde,R.A. 2001. Regulation of selenoprotein expression. In: Selenium: Its Molecular Biology and Role in Human Health (Hatfield,D.L., ed.), pp. 81-96. Kluwer Academic Publishers, Norwood, MA.

Sunde,R.A. 2001. Selenium. In: Present Knowledge in Nutrition, 8th Ed. (Bowman, BA, & Russell, R.M., eds.), pp. 352-365. The Nutrition Foundation, Washington, D.C.

Hadley, K.B. and Sunde, R.A. 2001. Selenium regulation of thioredoxin reductase activity and mRNA levels in rat liver. J. Nutr. Biochem. 12: 693-702.