J. Anim Sci. 2006. 84:2382-2390. doi:10.2527/jas.2005-372
© 2006 American Society of Animal Science
Effect of selenium intake and fetal age on mRNA levels of two selenoproteins in porcine fetal and maternal liver
C. E. Hostetler*,
J. Michal
,
M. Robison
,
T. L. Ott and
R. L. Kincaid,1
* School of Molecular Biosciences, Washington State University, Pullman 99164-4660;
and
Department of Animal Sciences, Washington State University, Pullman 99164-6351; and
and
Department of Animal and Veterinary Sciences, Center for Reproductive Biology, University of Idaho, Moscow 83844-2330
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Abstract
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The objective of this study was to determine if levels of mRNA encoding cytosolic glutathione peroxidase (cGPx) and thioredoxin reductase (TrxR-1) change during fetal development, and if maternal Se intake during gestation affects the mRNA levels of these proteins. Prepubertal gilts (n = 24) were randomly assigned to either Se-adequate (0.39 ppm of Se; n = 12) or Se-deficient (0.05 ppm of Se; n = 12) diets, 6 wk before breeding. Maternal liver was collected at d 10, 45, 70, and 114 of pregnancy, and fetal liver samples were collected at the same times except d 10. Complementary DNA sequences encoding cGPx and TrxR-1 were cloned and sequenced. Quantitative real-time PCR analysis indicated that levels of mRNA for cGPx in fetal liver decreased more than 3-fold between d 45 and 114 of gestation. Although the gilts were only marginally deficient in Se, and maternal Se intake did not affect cGPx mRNA levels in fetal liver, the low-Se diet tended (P = 0.1) to reduce fetal TrxR-1 mRNA levels. In the liver of the dams, the low Se intake did not affect mRNA levels for either cGPx or TrxR-1. Compared with the liver of the dams, mRNA levels for cGPx were about 3.5 times lower in fetal liver. Results of this study support the hypothesis that neonatal pigs are born with reduced cGPx corresponding to reduced cGPx mRNA levels during late gestation.
Key Words: glutathione peroxidase • mRNA • pig • selenium • thioredoxin reductase
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INTRODUCTION
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Cellular glutathione peroxidase (cGPx, EC 1.11.1.9), the first identified selenoprotein (Flohé et al., 1973
; Rotruck et al., 1973), is the most abundant (and is present in the greatest quantity) in the liver. All of the selenoproteins have enzymatic properties, and most are involved in the catabolism of peroxides (Burk, 1991). Glutathione peroxidase catalyzes the reduction of hydrogen peroxide and lipid peroxides. As Se intake decreases, cGPx mRNA and enzymatic activity decrease (Lei et al., 1998).
Thioredoxin reductase (TrxR-1, EC 1.6.4.5), an Se-dependent flavoprotein, catalyzes the reduction of thioredoxin (Moore et al., 1964; Williams, 1995). Lack of thioredoxin is embryonically lethal because many transcription factors require thioredoxin reduction for DNA binding (Matsui et al., 1996). Additionally, thioredoxin has been identified as the "early pregnancy factor," which has lymphocyte modifying activity and is induced within hours of fertilization (Clarke et al., 1991). Mammalian TrxR-1 has a selenocysteine (SeCys) residue in the highly conserved C-terminal sequence: –Gly-Cys-SeCys-Gly (Gladyshev et al., 1996). In rodents, TrxR-1 mRNA and enzymatic activity are regulated by dietary Se (Hill et al., 1997; Hadley and Sunde, 2001).
Embryonic loss during the first 30 d of pregnancy is about 30% in swine (Pope, 1988, 1992). Most conceptus loss occurs from d 11 to 15, which is the critical period of pregnancy recognition (Pope, 1988). Little is known about the causes of early embryonic mortality; however, nutritional factors have been implicated (Wilmut et al., 1986; McArdle and Ashworth, 1999; Ashworth and Antipatis, 2001). Synchronization of embryo development with the uterine environment is paramount to embryonic survival (Pope, 1988) and generation of free radicals may occur when more-developed embryos stimulate the uterus to advance beyond the stage of less-developed embryos (Roberts et al., 1993).
Because of the role of selenoproteins as antioxidants, the objectives of the current study were to determine if levels of mRNA for cGPX and TrxR-1 change during fetal development and if maternal Se intake affects mRNA expression.
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MATERIALS AND METHODS
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Diets, Animals, and Sampling
Diets were prepared at the Washington State University Animal Feed Preparation Laboratory in 898-kg batches. Gilts were fed 2.25 kg of feed per head per day and housed in pens made of galvanized pipe on partially slatted, concrete floors. Diets were based on barley and peas grown locally on Se-deficient soils, and the Se pre-mix-supplementation was removed to create an Se-deficient diet (Table 1). Analysis of Se in feeds was done by hydride-generation atomic absorption spectrophotometry (Holm Research Center, University of Idaho, Moscow). Water was available for ad libitum consumption.
All procedures using animals were approved by the Washington State University Institutional Animal Care and Use Committee. Prepubertal crossbred gilts (n = 24) were selected from a growing and finishing facility and randomly assigned to either Se-adequate (NRC, 1998; 0.39 ppm of Se; n = 12) or Se-deficient (0.05 ppm of Se; n = 12) diets, 6 wk before breeding. Gilts were bred at the onset (d 1) of their second estrous period, and then at 12-h intervals until no longer in estrus, by using AI with fresh semen collected daily and containing at least 4 billion sperm per insemination.
For the cloning of cGPx and TrxR-1 from early embryos, 2 gilts were humanely killed by captive-bolt stunning followed by exsanguination at d 13 of pregnancy for conceptus (embryo and associated membranes) collection directly into TRIzol reagent (Life Technologies, Frederick, MD) and subsequent extraction of total RNA. These 2 gilts were in addition to the 24 animals used in the study and were generated specifically for the collection of conceptus tissue to be used for RNA extraction and subsequent cloning of cDNA for cGPX and TrxR-1. Before tissue collection, these gilts were fed an adequate-Se gestation diet identical to that in Table 1
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Gilts consuming the experimental diets were slaughtered by using the same method described above, at 10, 45, and 70 d of pregnancy (n = 3 per diet per period). Three gilts from each treatment were not killed while gestating, but allowed to give birth (114 d) for collection of newborn piglet liver. Newborn piglets were killed by administering an overdose of Na pentobarbital (30 mg/ kg, 4% solution, given by cardiac puncture) before suckling. Liver samples of the sows that were allowed to farrow were collected after weaning (d 21). Tissue samples were collected at a local abattoir, frozen immediately in liquid N, and subsequently stored at –80°C until analysis. Fetal liver samples were collected from 2 fetuses per pregnancy from d 30 to 114 and maternal liver was collected at all gestational ages.
Total RNA Extraction
Total RNA was extracted from conceptus and fetal and maternal liver using the TRIzol reagent according to the manufacturer’s instructions. Briefly, frozen tissues collected at slaughter were ground in liquid nitrogen (approximately 1 g of tissue) with an RNase-free mortar and pestle and homogenized. Chloroform (0.2 mL/mL of TRIzol) was added to each sample, which was then mixed vigorously, and subsequently centrifuged at 12,000 x g for 15 min at 6°C to achieve phase separation. The upper, aqueous phase was decanted into a new 1.5-mL tube (USA Scientific, Ocala, FL), and isopropyl alcohol (0.5 mL/mL of TRIzol) was added to precipitate the RNA. The RNA was resuspended in diethyl pyrocarbonate-(Sigma, St. Louis, MO) treated water and quantified by measuring optical density (OD) at 260 nm (BioPhotometer, Eppendorf, Hamburg, Germany). The purity of the RNA preparation was estimated using the OD260:OD280 ratio, and RNA integrity was verified by 1.5% agarose, 2.2 M formaldehyde gel electrophoresis according to standard procedures (Sambrook et al., 1989).
Primer Design for Quantitative Real-Time PCR and Sequencing
Primers for quantitative real-time (Q) PCR amplification of cGPx (Figure 1) and TrxR-1 (Figure 2) were designed using Primer3 software (http://frodo.wi.mit.edu/cgi-bin/primer3/primer3_www.cgi) and were synthesized by Life Technologies. The 2 sets of primers for cGPx were designed based on a published bovine nucleotide sequence (Catherwood, 1998; GenBank Accession No. X13684, 828 nucleotides) because the published porcine embryo sequence (Lee et al., 2000; Gen-Bank Accession No. AJ010340, 348 nucleotides) did not contain the full coding sequence. The 3 sets of primers for TrxR-1 were designed based on the published porcine nucleotide sequence (Altschul et al., 1990; Gen-Bank Accession No. AF277894, 1,533 nucleotides) established from reticulocytes. Initial sequencing of the cDNA was conducted using T3 and T7 primers. Nested primers for each cDNA were used for subsequent sequencing, and both the top and bottom cDNA strand was sequenced for 2 positive clones for cGPx and 1 positive clone for TrxR-1.
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Figure 1. Nucleotide sequence of the cDNA encoding cellular glutathione peroxidase (cGPx) in the d 13 porcine embryo; complete coding sequence reading 5' to 3', 803 nucleotides. Nucleotides corresponding to the in-frame start (13 to 15) and stop (637 to 639) codons appear in uppercase bold type; nucleotide triplet encoding insertion of selenocysteine appears in uppercase, bold, italic type (160 to 162); nucleotides corresponding to primers used for amplification and sequencing of the gene appear in bold type; and arrows indicate the direction of amplification. Primers used in quantitative real-time PCR appear in bold and underlined type. Forward primer was 285 bp and reverse primer was 346 bp.
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Figure 2. Nucleotide sequence of the gene encoding thioredoxin reductase-1 (TrxR-1) in the d 13 porcine embryo; partial coding sequence reading 5' to 3', 1,441 nucleotides. Nucleotides corresponding to primers used for amplification and sequencing of the gene are shown in bold type, and arrows indicate the direction of amplification. Primers used for quantitative real-time PCR are shown in bold and underlined type. Forward primer was 797 bp and reverse primer was 874 bp.
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Reverse Transcription PCR
Total RNA (2 µg) was reverse-transcribed using SuperScript II (Invitrogen) to obtain first-strand cDNA. The cDNA was amplified using a PCR optimization kit (PCR Optimizer Kit, Life Technologies). The polymerase used in the PCR reaction was Thermalace (Life Technologies). Agarose gel electrophoresis was used to determine the number and sizes of the resulting PCR product(s).
Cloning and Transformation
The products of the PCR reaction were cloned directly into an expression vector (pCR4Blunt-TOPO, Invitrogen) and chemically competent Escherichia coli (DH5
E. coli, Life Technologies) were transformed with the purified plasmid DNA. The transformation reaction was streaked onto Luria broth agar (Research Products International, Mt. Prospect, IL) plates containing 100 µg of ampicillin/mL and grown overnight at 37°C. Six individual colonies were picked from the plates and placed into tubes containing 5 mL of Luria broth with ampicillin (100 µg/mL). Tubes were placed in a shaking incubator at 37°C overnight, and bacteria were harvested by centrifugation at 500 x g for 5 min at 4°C.
Plasmid Purification
Plasmid DNA was purified using the Plasmid Mini Purification kit according to the manufacturer’s instructions (Qiagen, Valencia, CA). Yield of plasmid DNA was determined spectrophotometrically at a wavelength of 206 nm. The cDNA were released by digestion with the EcoRI restriction enzyme (Life Technologies) and separated using agarose gel (1%) electrophoresis. The cDNA from 2 positive clones for cGPx and 1 positive clone for TrxR-1 were submitted to the Molecular Biology Core Facility (School of Molecular Biosciences, Washington State University, Pullman) for sequencing of the top and bottom strands using the appropriate T3 and T7 primers and gene-specific nested primers. The double-stranded nucleotide sequence was obtained from the clones and compared with published sequences (Blast, NCBI; Altschul et al., 1990).
mRNA Levels
Two-step Q-PCR was used to determine mRNA levels of cGPx and TrxR-1 in maternal and conceptus liver. Messenger RNA isolated as described above was treated with RNase-free deoxyribonuclease 1 (Fermentas Life Sciences, Hanover, MD) and synthesized into cDNA with Superscript II reverse transcriptase (Invitrogen) and oligo(dT)12–18 primers (Invitrogen). Briefly, 2 µg of RNA was mixed with 1 µL of oligo(dT)12–18 primers (0.5 µg/µL) and 1 µL of dinucleotide triphosphate (dNTP; 10 mM for each dinucleotide) in a total volume of 12 µL, heated at 65°C for 5 min, and cooled immediately on ice. First-strand buffer (4 µL), 0.1 M dithiothreitol (2 µL), and 40 units of RNaseOUT ribonuclease inhibitor (Invitrogen,) were added to the tube, which was then incubated for 2 min at 42°C. Superscript II reverse transcriptase (200 units) was then added and the reaction was incubated at 42°C for 50 min, followed by inactivation at 70°C for 15 min. Complementary DNA was subsequently diluted 5-fold in diethyl pyrocarbonate-treated water.
Primer3 software was used for primer design. Parameters were set so the primers were 19 to 25 bp long, with melting temperatures of 58 to 60°C, and the products were 60 to 100 bp in length. Gene-specific primers for cGPx (forward, 5'-GGAGATCCTGAATTGCCTCAA G-3'; reverse, 5'-GCATGAAGTTGGGCTCGAA-3'; Figure 1) and TrxR-1 (forward, 5'-AGGCCACTAACAGTG ACGAA-3'; reverse, 5'-TTGTGCAAGCATCGCTTCCT-3'; Figure 2) were based on the sequences determined above, whereas primers for ß-actin mRNA (forward, 5'-GACAGGATGCAGAAGGAGAT-3'; reverse, 5'-GATCC ACACGGAGTACTTGC-3'; Figure 3), the endogenous control used for data normalization, were based on Gen-Bank Accession No. U07786.
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Figure 3. Location of ß-actin primers (based on GenBank Accession No. U07786). Primers used for quantitative real-time PCR appear in bold and underlined type. Forward primer was 565 bp and reverse primer was 657 bp.
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Polymerase chain reactions were conducted on an iCycler iQ Real Time PCR Detection System (BioRad Laboratories, Hercules, CA), and cDNA synthesis measured with SYBR green fluorescence (iQ SYBR Green Supermix; BioRad Laboratories). Before actual mRNA quantification, primer concentrations were optimized and absence of primerdimers was verified using melting curve analysis (Technical Bulletin 2684, BioRad Laboratories). Relative efficiencies of amplification of cGPx, TrxR-1, and ß-actin were validated as approximately equal by running a serial dilution of cDNA from the liver of an adult sow.
Duplicate PCR reactions for each gene were conducted in a final volume of 20 µL that contained 10 µL of iQ SYBR (BioRad Laboratories), optimal primer concentrations, and 1 µL of diluted cDNA. No-template and no-reverse transcriptase controls were included for each sample to verify the absence of nonspecific amplification and genomic DNA contamination, respectively. Thermocycling conditions were as follows: initial denaturation at 95°C for 2 min 30 s; followed by 40 cycles of 30 s at 95°C, 30 s at 58°C, and 30 s at 72°C. After the completion of the last cycle, a melting curve analysis was performed to verify specific amplification. Statistical analysis of ß-actin mRNA levels in maternal and fetal liver revealed no effect of gestational age or diet.
Statistical Analysis
Data for cGPX and TrxR-1 were normalized to the housekeeping gene ß-actin, and mRNA level was quantified using the relative standard curve method (Applied Biosystems, 1997). The PROC GLM procedure of SAS (version 9.1, SAS Inst., Inc., Cary, NC) was used to analyze relative quantities of cGPX and TrxR-1 mRNA in fetal or sow liver. The model included Se treatment, day of gestation, and their interaction. Pairwise comparisons of least squares means were performed using a protected t-test.
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RESULTS AND DISCUSSION
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The Se-dependent enzymes, cGPx and TrxR-1, were cloned from d 13 porcine conceptuses. Agarose gel electrophoresis was conducted using the cDNA product resulting from Q-PCR of the embryo RNA. The amplified gene product derived from Q-PCR using primers specific for cGPx migrated at approximately 800 nucleotides. This was consistent with expected size of 801 nucleotides based on the location of the primers in the published bovine sequence (Catherwood, 1998; Accession No. X13684, 828 nucleotides). The amplified gene product derived from Q-PCR using primers specific for TrxR-1 migrated at approximately 1,400 nucleotides. This was consistent with the expected size of 1,417 nucleotides based on the location of the primers in the published porcine sequence (Altschul et al., 1990; Accession No. AF277894, 1,533 nucleotides). The top and bottom strands corresponding to the cDNA of these products were sequenced using the appropriate T3 and T7 primers. Nucleotide sequence analysis determined that the 803-nucleotide product was cGPx, and the sequence was subsequently published online through GenBank (Hostetler et al., 2002a; Accession No. AF532927). This is the complete coding sequence for cGPx with the in-frame start codon located at nucleotides 7 to 9 and the stop codon located at nucleotides 627 to 629. The base triplet encoding insertion of selenocysteine is at nucleotides 160 to 162. Searching the nucleotide database for nearly exact matches revealed significant homologies with a number of published nucleotide sequences. There was homology with several partial porcine sequences (98 to 99%), a full-length bovine sequence (89%), and several human sequences (85 to 87%). The partial porcine sequence submitted by Catherwood (1998; Accession No. AJ010340) is only 348 nucleotides long. This sequence was 98% homologous to a region corresponding to the middle (nucleotides 244 to 591) of the cGPx cDNA. Another sequence for cGPx from the pig has been reported (Hamasima and Suzuki, 1998; Accession No.C94913). This sequence was cloned from a porcine backfat cDNA library and is 300 nucleotides in length. Comparison of this sequence with the sequence report revealed that 294 of 295 nucleotides (99%) match in the 3' region of the cGPx cDNA cloned from the d 13 porcine conceptus. Similarly, Liu and Ding (2004) reported a sequence derived from porcine adipocytes (AY743601) that shares 99% homology between bp 2 and 256 of the sequence reported here.
The bovine cGPx sequence (Mullenbach et al., 1988; Accession No. X13684) used to design the primers for our sequence was derived from bovine pituitary and was 80% homologous to our sequence. Multiple human sequences were roughly 85 to 87% homologous with the porcine embryo cGPx sequence.
Sequence analysis of the TrxR-1 clone revealed amplification of a 1,441-nucleotide product with significant homologies to other published mammalian TrxR-1 cDNA. The TrxR-1 nucleotide sequence reported here was subsequently published on GenBank (Hostetler et al., 2002b; Accession No. AF537300). This is a partial coding sequence because the putative in-frame start sequence is roughly 18 nucleotides 5' to the beginning of the porcine TrxR-1 reported here. The base triplets encoding insertion of selenocysteine and the stop codon are approximately 54 and 57 nucleotides 3' of the end of our sequence, respectively. The pTrxR-1 sequence shares nucleotide sequence homology with previously published bovine (90%), porcine (93%), and human (89%) sequences. The previously published bovine sequence (Terashima, 1998; Accession No. AF053984) is from the small intestine, is 3,535 nucleotides long, and contains the entire 3' untranslated region. The previously published porcine sequence (Lee et al., 2000; Accession No. AF277894) was cloned from porcine reticulocytes, is 1,533 nucleotides in length, and was used to design primers for PCR to amplify the porcine conceptus TrxR-1 cDNA. This sequence shares nucleotide homology in the region spanning nucleotides 1 through 1,423 of our sequence. Interestingly, this sequence is only 93% (1,324 of 1,423 nucleotides) homologous to our sequence. The human sequence published by Strausberg (2001; BC018122) from a cDNA library as part of the human genome project was 89% homologous to pTrxR-1.
Our intent in feeding the low-Se diet was to reduce maternal Se intake, but not to a level that impaired reproduction because we wanted to study the effects of maternal intake of Se on the fetus. The effects of the low maternal intake of Se during pregnancy on Se concentrations and GPx activities in maternal and fetal liver have been published previously (Hostetler and Kincaid, 2004a,b). By the end of the gestation period, the concentration of Se in blood was reduced to levels considered deficient for maternal whole blood and marginally deficient for liver by the low Se diet (Figure 4, adapted from Hostetler and Kincaid, 2004a; Puls, 1988). The activity of GPx in liver homogenates of sows also was reduced by the low-Se diet (Figure 5, adapted from Hostetler and Kincaid, 2004b). However, concentrations of cGPx mRNA in liver of sows were not significantly affected by either day of pregnancy or Se intake (Figure 6). Similarly, levels of TrxR-1 mRNA in sow liver also were not affected by the low Se diet or day of pregnancy (Figure 7).
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Figure 4. Effect of dietary Se on gestational changes in the concentration of Se in whole blood and liver of sows (n = 3 sows/diet per period). The effect of dietary Se on concentrations of Se in whole blood and liver were significant (P < 0.05; adapted from Hostetler and Kincaid, 2004a).
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Figure 5. Effect of dietary Se on gestational changes in cellular glutathione peroxidase (cGPx) activity in maternal and fetal liver homogenates (n = 3 sows/diet per period). The effect of dietary Se on sow liver cGPx activity was significant (P < 0.05). The effect of gestational age on fetal liver cGPx activity was significant (P < 0.01; adapted from Hostetler and Kincaid, 2004b).
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Figure 6. Effect of Se intake and day of gestation on cellular glutathione peroxidase (cGPx) mRNA levels in liver of sows (n = 3 sows/diet per period). Quantities of mRNA are normalized relative to the housekeeping gene, ß-actin.
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Figure 7. Effect of Se intake and day of gestation on thioredoxin reductase-1 (TrxR-1) mRNA levels in liver of sows (n = 3 sows/diet per period). Quantities of mRNA are normalized relative to the housekeeping gene, ß-actin.
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Selenium concentrations in fetal liver decreased with gestational age from d 45 to 114 and were lower for fetuses of sows fed the low Se diet compared with fetuses of sows fed the adequate Se diet (0.095 vs. 0.230 ppm Se wet weight, respectively; Hostetler and Kincaid, 2004a). Although maternal Se intake did not affect GPx activity in fetal liver, GPx activities in fetal liver decreased sharply between d 90 and 114 of pregnancy (Figure 5). Accordingly, levels of cGPx mRNA in fetal liver decreased (P < 0.01) more than 3-fold from gestational d 45 to 114 (Figure 8), but maternal Se intake did not affect fetal cGPx mRNA levels (Figure 8). Levels of TrxR-1 mRNA tended (P = 0.1) to be reduced by the low Se intake of the dam but did not change significantly during gestation (Figure 9).
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Figure 8. Effect of maternal Se intake and gestational age on cellular glutathione peroxidase (cGPx) mRNA expression in liver of fetuses and neonates (n = 3 sows/ diet per period). Quantities of mRNA are normalized relative to the housekeeping gene, ß-actin. There was a significant effect of gestational age on cGPx mRNA expression (P < 0.01).
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Figure 9. Effect of maternal Se intake and gestational age on thioredoxin reductase-1 (TrxR-1) mRNA expression in liver of fetuses and neonates (n = 3 sows/diet per period). Quantities of mRNA are normalized relative to the housekeeping gene, ß-actin.
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Newborn pigs, regardless of maternal Se intake, have lower GPx activity in serum and liver compared with the dam (Loudenslager, et al., 1986; Mahan and Kim, 1996; Hostetler and Kincaid, 2004b). A comparison of the relative mRNA levels for cGPx in liver of sows and fetuses were 0.93 vs. 0.26, respectively; that is, cGPx mRNA levels were about 3.5 times higher in sow liver than in fetal liver. Relative levels of mRNA for TrxR-1 were 1.64 in sow liver and 0.99 in fetal liver. To our knowledge this is the first report of the mRNA levels for maternal and fetal porcine liver cGPx and Trx-R1.
The low maternal intake of Se for 42 d before conception did not affect levels of cGPx mRNA in maternal liver, nor was cGPx activity in maternal liver affected (Hostetler and Kincaid, 2004b). Similarly, the low maternal Se intake did not affect cGPx mRNA levels in fetal liver. Thus, based upon cGPx activity and cGPx mRNA levels in liver, the sows fed the low Se diet were not Se deficient although they would be classified as at least marginally deficient based upon their Se concentrations in liver and whole blood (Puls, 1988). However, the concentrations of H2O2 and malondialdehyde, indicators of oxidative stress, were increased in both fetal and maternal liver by the low Se diet (Hostetler and Kincaid, 2004b). Whether the increased H2O2 in maternal and fetal liver in the low-Se–fed sows was due to increased production of H2O2 or because of a reduced rate of conversion of H2O2 to H2O and O2 is not known.
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IMPLICATIONS
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Factors that influence conceptus growth and development are also likely to affect embryonic survival and development. Because the fetus relies on the dam for nutrients, maternal intake of trace elements may affect fetal development and survival if the dam does not have adequate Se stores. We hypothesize that exposure to free radicals may increase fetal and newborn mortality. However, Se use by the fetus, known to affect antioxidant capacity, has not been thoroughly investigated. In fetal liver, mRNA levels for cellular glutathione peroxidase, but not thioredoxin reductase-1, were markedly reduced by d 70 of gestation. When sows were fed an Se-deficient diet, mRNA levels for thioredoxin reductase-1 tended to be reduced. However, the reduced levels of mRNA for cellular glutathione peroxidase during later gestation were not explained by the dam’s Se intake because mRNA levels for cellular glutathione peroxidase decreased regardless of the sow’s dietary treatment.
1 Corresponding author: rkincaid{at}wsu.edu
Received for publication July 11, 2005.
Accepted for publication March 23, 2006.
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Abstract
INTRODUCTION
