Selenoprotein Gene Expression in Thyroid and Pituitary of Young Pigs Is Not Affected by Dietary Selenium Deficiency or Excess

Abstract

Expression and function of selenoproteins in endocrine tissues remain unclear, largely due to limited sample availability. Pigs have a greater metabolic similarity and tissue size than rodents as a model of humans for that purpose. We conducted 2 experiments: 1) we cloned 5 novel porcine selenoprotein genes; and 2) we compared the effects of dietary selenium (Se) on mRNA levels of 12 selenoproteins, activities of 4 antioxidant enzymes, and Se concentrations in testis, thyroid, and pituitary with those in liver of pigs. In Experiment 1, porcine Gpx2, Sephs2, Sep15, Sepn1, and Sepp1 were cloned and demonstrated 84-94% of coding sequence homology to human genes. In Experiment 2, weanling male pigs (n = 30) were fed a Se-deficient (0.02 mg Se/kg) diet added with 0, 0.3, or 3.0 mg Se/kg as Se-enriched yeast for 8 wk. Although dietary Se resulted in dose-dependent increases (P < 0.05) in Se concentrations and GPX activities in all 4 tissues, it did not affect the mRNA levels of any selenoprotein gene in thyroid or pituitary. Testis mRNA levels of Txnrd1 and Sep15 were decreased (P < 0.05) by increasing dietary Se from 0.3 to 3.0 mg/kg. Comparatively, expressions of Gpx2, Gpx4, Dio3, and Sep15 were high in pituitary and Dio1, Sepp1, Sephs2, and Gpx1 were high in liver. In conclusion, the mRNA abundances of the 12 selenoprotein genes in thyroid and pituitary of young pigs were resistant to dietary Se deficiency or excess.

High Dietary Selenium Intake Alters Lipid Metabolism and Protein Synthesis in Liver and Muscle of Pigs

“…Alterations of these factors were associated with expressions of 12 selenoproteins (1,3,5,9,18,19). However, to the best of our knowledge, there was no information on effects of dietary selenium, in particular high selenium intake, on body protein metabolism, although protein synthesis was reported to negatively regulate insulin sensitivity (20,21) and a high protein diet inhibited the development of type 2 diabetes (22).…”

“…As shown in our previous studies (3,18), the high-selenium diet resulted in a moderate (20-50%) increase in GPX activities in both liver and muscle. Overproduction of GPX activity by Gpx1 overexpression in mice led to type 2 diabetes-like phenotypes, including hyperlipidemia and fatty liver (1,9,19), and the selenium deficiency partially rescued those disorders (9).…”

Insights for Setting of Nutrient Requirements, Gleaned by Comparison of Selenium Status Biomarkers in Turkeys and Chickens versus Rats, Mice, and Lambs

“…A number of other studies in various species reported that >75% of selenoprotein transcripts examined were downregulated significantly by selenium deficiency when just a selenium-deficient and a selenium-adequate group were compared (47)(48)(49)(50), and several reported that the majority of selenoprotein transcripts examined were downregulated significantly by selenium deficiency when 3 groups (selenium-deficient, seleniumadequate, high-selenium) were studied (51,52). In contrast, when multiple levels of selenium supplementation were used, resulting in well-defined biomarker plateaus, far fewer selenoprotein transcripts were significantly altered by selenium deficiency (20), especially in avian studies that used commercial (outbred) strains (26,27).…”

Selenium and diabetes - evidence from animal studies

“…While Zhou et al [116] found little effect of dietary Se concentrations (0.02, 0.3, and 3.0 mg/ kg diet) on mRNA levels of 12 selenoprotein genes in thyroid, pituitary, liver, or muscle, Liu et al [62] reported that mRNA expression of the remaining 13 selenoproteins in 10 tissues of pigs responded to dietary Se in three patterns. But, there was no common regulation for any given gene across all tissues or for any given tissue across all genes [62].…”

“…This antioxidant effect was in accordance with increased plasma GPx3 activity by high Se over adequate Se supplements, although the high selenite diet had no effect on the activities of GPx1 and SOD in the liver, and even decreased catalase activity. Using the Se-enriched yeast [116], Zhou et al have demonstrated that 3.0 mg of Se/ kg of diet enhanced (43-88%) GPx activity among four tissues of pigs (liver, testis, thyroid, and pituitary) compared to those fed 0.3 mg of Se/kg of diet. However, the high Se diet did not affect activities of plasma GPx3 and other three antioxidant enzymes in any of the four tissues.…”