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ARS Home » Plains Area » Clay Center, Nebraska » U.S. Meat Animal Research Center » Livestock Bio-Systems » Research » Publications at this Location » Publication #314050
Title: Pig endometrium expresses the polyol pathway enzymes necessary to convert glucose to fructose prior to implantation with a shift to chorion expression post-implantation

Author
item STEINHAUSER, C - Texas A&M University
item LANDERS, M - Texas A&M University
item MYATT, L - Texas A&M University
item BURGHARDT, R - Texas A&M University
item WU, G - Texas A&M University
item Vallet, Jeff
item BAZER, FULLER - Texas A&M University
item JOHNSON, G - Texas A&M University

Submitted to: Society for the Study of Reproduction Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 3/20/2015
Publication Date: 6/2/2015
Citation: Steinhauser, C.B., Landers, M., Myatt, L., Burghardt, R.C., Wu, G., Vallet, J., Bazer, F.W., Johnson, G.A. 2015. Pig endometrium expresses the polyol pathway enzymes necessary to convert glucose to fructose prior to implantation with a shift to chorion expression post-implantation [abstract]. Society for the Study of Reproduction Annual Meeting. pp. 20-21 (Abstract #53). Available: https://www.ssr.org/

Interpretive Summary:

Technical Abstract: Glucose and fructose are abundant hexose sugars in pig conceptuses (embryo/fetus and associated placenta). While glucose is mostly catabolized for energy, in vitro studies implicate fructose as a substrate for the biosynthesis of glycoaminoglycans, phospholipids, and nucleic acids as well as a signaling molecule for the mechanistic target of rapamycin (MTOR) pathway. The uterine flushings of pregnant gilts contain greater than 5 mM fructose and, as pregnancy progresses, so do the fetal fluids. Fructose cannot be detected in maternal blood, which suggests local fructose production. Fructose can be synthesized from glucose without using ATP via the polyol pathway. Glucose is converted to sorbitol by aldose reductase (AKR1B1) and sorbitol to fructose by sorbitol dehydrogenase (SORD). The fructose can then be utilized by cells following conversion to fructose-1-phosphate by keto-hexokinase (KHK) after being transported across cell membranes by the solute carriers SLC2A5 and SLC2A8. Therefore, our hypothesis is that specific cell types in the endometrium and chorioallantois utilize the polyol pathway to convert glucose to fructose for use by the conceptus. AKR1B1, SORD, KHK, SLC2A5, and SLC2A8 mRNAs and proteins were analyzed in the endometrium and placentae of gilts from Days 9 to 85 of gestation and Days 5 to 17 of the estrous cycle using qPCR and in situ hybridization or immunohistochemistry. AKR1B1 mRNA increased between Days 9 and 11 in the endometrium of pregnant gilts and then decreased to levels similar to cyclic gilts by Day 15. AKR1B1 protein was detected in uterine luminal epithelium (LE) on Days 13 through 20 of gestation. However, after Day 20 of pregnancy, AKR1B1 protein was undetectable in LE, but detectable in the chorion, except for the areolae. SORD mRNA peaked in endometrium on Days 5 through 9 of the estrous cycle and pregnancy, and protein was localized to LE, uterine glandular epithelium (GE), and conceptus trophectoderm (Tr) throughout the peri-implantation period. Interestingly, by Day 20 of pregnancy the majority of SORD protein was localized to the entire chorion, and to a lesser extent the GE. Only low levels of KHK mRNA and protein were detected in endometrium, however, KHK protein was detected in Tr on Day 11 of pregnancy and expression increased through Day 15. KHK protein continued to be expressed in the chorion, especially in the tall columnar cells and areolae through Day 85. KHK protein localization in the Tr/chorion is particularly interesting because KHK catalyzes the conversion of fructose to fructose-1-phosphate, which can be used for synthesis of hexosamines, lipids, and ATP, as well as for regulating the glucokinase, MTOR, and proinflammatory pathways. SLC2A8 mRNA increased on Day 9 in endometria from both cyclic and pregnant gilts, and peaked on Day 11. SLC2A8 protein was detected in GE beginning on Day 9 of the estrous cycle and pregnancy, while LE expression became detectable on Day 13. After Day 20 of pregnancy, SLC2A8 protein was detected primarily in the areolae. SLC2A5 mRNA localized to the LE, GE, and chorion throughout pregnancy. These results are the first to establish that the molecular components for conversion of glucose to fructose and for transport of fructose are present in the LE and Tr/chorion. The intriguing shift in expression of the polyol enzymes from LE to chorion during pregnancy suggests that the free-floating and elongating conceptuses are supported by fructose synthesized by the LE. However, after implantation is established at the maternal/conceptus interface, the chorion becomes self-sufficient for the synthesis and transport of fructose.