Selenoprotein Transcript Level and Enzyme Activity as Biomarkers for Selenium Status and Selenium Requirements in the Turkey (Meleagris gallopavo).

Rachel M Taylor,Roger A Sunde,Stephen L Clarke

doi:10.1371/journal.pone.0151665

Abstract

The current National Research Council (NRC) selenium (Se) requirement for the turkey is 0.2 μg Se/g diet. The sequencing of the turkey selenoproteome offers additional molecular biomarkers for assessment of Se status. To determine dietary Se requirements using selenoprotein transcript levels and enzyme activities, day-old male turkey poults were fed a Se-deficient diet supplemented with graded levels of Se (0, 0.025, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.75, 1.0 μg Se/g diet) as selenite, and 12.5X the vitamin E requirement. Poults fed less than 0.05 μg Se/g diet had a significantly reduced rate of growth, indicating the Se requirement for growth in young male poults is 0.05 μg Se/g diet. Se deficiency decreased plasma GPX3 (glutathione peroxidase), liver GPX1, and liver GPX4 activities to 2, 3, and 7%, respectively, of Se-adequate levels. Increasing Se supplementation resulted in well-defined plateaus for all blood, liver and gizzard enzyme activities and mRNA levels, showing that these selenoprotein biomarkers could not be used as biomarkers for supernutritional-Se status. Using selenoenzyme activity, minimum Se requirements based on red blood cell GPX1, plasma GPX3, and pancreas and liver GPX1 activities were 0.29–0.33 μg Se/g diet. qPCR analyses using all 10 dietary Se treatments for all 24 selenoprotein transcripts (plus SEPHS1) in liver, gizzard, and pancreas found that only 4, 4, and 3 transcripts, respectively, were significantly down-regulated by Se deficiency and could be used as Se biomarkers. Only GPX3 and SELH mRNA were down regulated in all 3 tissues. For these transcripts, minimum Se requirements were 0.07–0.09 μg Se/g for liver, 0.06–0.15 μg Se/g for gizzard, and 0.13–0.18 μg Se/g for pancreas, all less than enzyme-based requirements. Panels based on multiple Se-regulated transcripts were effective in identifying Se deficiency. These results show that the NRC turkey dietary Se requirement should be raised to 0.3 μg Se/g diet.

Highlights

The current National Research Council (NRC) Se requirement for the turkey is 0.2 μg Se/g diet for growing turkeys at all stages [1]
0.05 μg Se/g diet is sufficient for growth and 0.1 μg Se/g diet is required for maximum glutathione peroxidase (GPX) activity [8]
The objectives of this study are: 1) to determine the Se requirement of a modern commercial strain of male turkey poults based on tissue selenoprotein enzyme activity; 2) to identify which selenoprotein transcripts are regulated by Se status and to use these as molecular biomarkers to assess Se status and Se requirements; 3) to evaluate selenoprotein mRNA for potential as biomarkers of supernutritional-Se status

Summary

Introduction

The current National Research Council (NRC) Se requirement for the turkey is 0.2 μg Se/g diet for growing turkeys at all stages [1]. Subsequent studies found that plasma Se and plasma glutathione peroxidase (GPX) activities were 15 and 25%, respectively, of levels in poults fed diets containing 0.23 μg Se/g diet regardless of vitamin E supplementation [3], and that 0.13–0.17 μg Se/g diet or more was necessary to maximized plasma GPX activity [4]. These dietary Se requirements to prevent disease, maintain growth, and maximize GPX activity in the turkey stand out relative to other species. We began studying selenoenzyme expression in the turkey to better understand Se requirements, and found that at least 0.2 μg Se/g diet was required to maximize plasma and liver GPX activity [10]

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Conclusion