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" Response to High Inorganic Selenium in Hepatic Turkey Selenoproteome, Transcriptome and Selenometabolome "
Taylor, Rachel M.
Sunde, Roger A.
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Latin Dissertation
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English
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| Record Number
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1105875
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| Doc. No
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TLpq2337193065
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| Main Entry
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Sunde, Roger A.
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Taylor, Rachel M.
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| Title & Author
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Response to High Inorganic Selenium in Hepatic Turkey Selenoproteome, Transcriptome and Selenometabolome\ Taylor, Rachel M.Sunde, Roger A.
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| College
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The University of Wisconsin - Madison
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| Date
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2019
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| student score
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2019
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| Degree
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Ph.D.
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| Page No
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129
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| Abstract
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The National Research Council turkey selenium (Se) requirement is 0.2 µg Se/g diet for all life stages, but our previous research indicates that the requirement for today’s commercial strain of rapidly growing poult is 0.4 µg Se/g, based on selenoenzyme activity, selenoprotein transcript expression and tissue Se concentration in a variety of turkey tissues. However, no established biomarker is markedly altered by high dietary Se (> 1.0 µg Se/g diet). The research questions that this report will address are: 1) How do established Se status biomarkers in the turkey respond to high selenium? 2) What transcriptomic markers or pathways are altered by high dietary Se? 3) What unique Se-specific metabolites are produced in the liver of turkeys fed high Se? The FDA currently limits Se inclusion in premixed diets for poultry and other livestock species to 0.3 µg Se/g diet. Thus, there is a need to investigate the effect of high dietary Se in turkeys. Our first experiment fed day-old male poults 0.4 (Se-adequate), 2.0 or 5.0 µg Se/g diet to characterize tissue Se accumulation in poults fed high dietary inorganic Se and to evaluate the efficacy of selenoprotein activity and transcript expression as biomarkers of high Se status. There was no significant effect of Se supplementation on poult growth. Supplementation with 5 µg Se/g diet resulted in Se concentrations that were 5.6×, 1.7×, 1.9×, and 2.0× greater than Se-adequate levels in liver, kidney, breast, and thigh, respectively, and GPX activities in plasma, red cells, liver, kidney, and heart that were ≤ 2× Se-adequate values. In all tissues examined, no selenoprotein transcript was increased ≥ 2.0×, and no selenoprotein transcript was decreased ≤ 0.5× by 2 or 5 µg Se/g diet as compared to Se-adequate poults. Of the 112 Se status biomarkers reported in this study, liver Se concentration was the only biomarker markedly altered by high Se status. This study provides evidence of no adverse effects in turkey poults fed up to 5 µg Se/g diet as inorganic Se. Thus we conclude the FDA limit for Se supplementation in turkey feed can be safely raised to 0.5 µg Se/g diet. Given the increase in liver Se concentration in high Se-fed poults, our next study assessed the full hepatic transcriptome for the effect of Se status from Se-deficient to high-Se. We conducted RNA-seq analysis on liver mRNA from turkey poults fed 0, 0.025, 0.4, 0.75 and 1.0 µg Se/g in experiment 1, and fed 0.4, 2.0 and 5.0 µg Se in experiment 2. Our objectives were to identify transcript biomarkers for high Se status, which in turn would suggest proteins and pathways used by animals to adapt to high Se. We found that in response to high Se intake, there were only a limited number of significant differentially expressed transcripts, all with relatively small fold changes; no transcript showed a consistent pattern of altered expression in response to high Se intakes across the 1, 2 and 5 µg Se/g treatments, and there were no associated metabolic pathways and biological functions that were consistently found with high Se supplementation. A comparison of differentially expressed transcript sets with high Se transcript sets identified in parallel studies in rodents fed high Se also failed to identify common differentially expressed transcripts between these three species. This study indicates that turkeys do not alter gene expression as a homeostatic mechanism to adapt to high Se. Given the lack of transcriptomic changes, we investigated the selenometabolome in Se-deficient, Se-adequate, and high-Se turkey liver using HPLC-ICP-MS and HPLC-ESI-MS/MS. In liver from turkeys fed a true Se-deficient diet and supplemented with inorganic Se, no selenomethionine (SeMet)was detected showing that the turkey cannot synthesize SeMet de novo from inorganic Se. Selenocysteine (Sec) content in liver of turkeys fed high Se only doubled compared with Se-adequate liver, indicating that the 6-fold increase in liver Se in these birds was not due to increases in selenoproteins. What increased dramatically in high Se liver were the low molecular weight (MW) selenometabolites, glutathione-, cysteine- and methyl- conjugates of the selenosugar, seleno-N-acetyl galactoseamine (SeGalNac). In addition, size-exclusion chromatography and follow-up analysis demonstrated that a substantial amount of Se in Se-adequate liver was present as selenosugars decorating general proteins via mixed-disulfide links. These analyses show that in Se-adequate liver far more Se is present as the selenosugar moiety, mostly decorating general proteins, than is present as Sec in selenoproteins. With high Se supplementation, increased selenosugar formation occurs, further increasing selenosugar-decorated proteins, but also increasing selenosugar linked to low MW thiols, leading to the formation of methyl-SeGalNac. This report demonstrates that most established Se status biomarkers in the turkey poult are not altered by high Se status, except for liver Se concentration. Additionally, minimal hepatic transcriptome changes are seen even in poults fed 5 µg Se/g diet, indicating that this level of Se is not toxic to the poult and metabolism of high Se is not mediated through altering hepatic gene expression. When fed high-Se diets, turkeys apparently increase production of hepatic selenosugars attached to thiols and general proteins. Selenosugars and related compounds may offer the best biomarkers of high Se status in the turkey poult.
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Animal sciences
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Nutrition
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