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Synthesis and Metabolism of Thyroid Hormones Is Preferentially Maintained in Selenium-Deficient Transgenic Mice

Institute for Experimental Endocrinology (L.S., C.R., M.M., E.G., U.S., J.K.), Neurobiology of Selenium (U.S.), Charité-Universitaetsmedizin Berlin, D-10117 Berlin, Germany; Department of Endocrinology (M.O.K.), Centre Hospitalier et Universitaire de Nancy, 54042 Nancy, France; and Institut de Physique Biologique (R.S.), Unité d’Analyses Endocriniennes, Hopital Civil, 67091 Strasbourg Cedex, France

Address all correspondence and requests for reprints to: Dr. Lutz Schomburg, Institut für Experimentelle Endokrinologie, Charité-Universitaetsmedizin Berlin, Schumannstrasse 20/21, D-10117 Berlin, Germany. E-mail: lutz.schomburg{at}charite.de.

The thyroid gland is rich in selenium (Se) and expresses a variety of selenoproteins that are involved in antioxidative defense and metabolism of thyroid hormones (TH). Se deficiency impairs regular synthesis of selenoproteins and adequate TH metabolism. We recently generated mice that lack the plasma Se carrier, selenoprotein P (SePP). SePP-knockout mice display decreased serum Se levels and manifest growth defects and neurological abnormalities partly reminiscent of thyroid gland dysfunction or profound hypothyroidism. Thus, we probed the TH axis in developing and adult SePP-knockout mice. Surprisingly, expression of Se-dependent 5'-deiodinase type 1 was only slightly altered in liver, kidney, or thyroid at postnatal d 60, and 5'-deiodinase type 2 activity in brain was normal in SePP-knockout mice. Thyroid gland morphology, thyroid glutathione peroxidase activity, thyroid Se concentration, and serum levels of TSH, T₄, or T₃ were within normal range. Pituitary TSHß transcripts and hepatic 5'-deiodinase type 1 mRNA levels were unchanged, indicating regular T₃ bioactivity in thyrotropes and hepatocytes. Cerebellar granule cell migration as a sensitive indicator of local T₃ action during development was undisturbed. Collectively, these findings demonstrate that low levels of serum Se or SePP in the absence of other challenges do not necessarily interfere with regular functioning of the TH axis. 5'-deiodinase isozymes are preferentially supplied, and Se-dependent enzymes in the thyroid are even less-dependent on serum levels of Se or SePP than in brain. This indicates a top priority of the thyroid gland and its selenoenzymes with respect to the hierarchical Se supply within the organism.

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