Selenoprotein gene expression in thyroid and pituitary of young pigs is not affected by dietary selenium deficiency or excess

[Nutrimail]

Testis, thyroid, and pituitary glands are three major endocrine organs in the body that regulate growth, reproduction, and metabolism. The discovery of the impaired thyroid hormone metabolism in selenium (Se)-deficient animals and the subsequent identification of deiodinases signified the crucial roles of Se in endocrine functions. Expression and function of selenoproteins in endocrine tissues remain unclear, largely due to limited sample availability.

Two different experiments were conducted: 1) Five novel porcine selenoprotein genes were cloned; and 2) the effects of dietary selenium (Se) on mRNA levels of 12 selenoproteins were compared; 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. The lack of responses of mRNA levels of Gpx1 and other selenoprotein genes in any of the tissues to dietary Se increases from 0.3 to 3 mg/kg suggests limitation of these indicators to assess body Se status when Se supply exceeds the requirement.

tags: nutrition protein

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