Hexose Sugar Transport and Metabolism at the Porcine Uterine-Placental Interface
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Commercial sows experience a high incidence of prenatal loss and substantial variation in birthweight among piglets in a litter. These outcomes negatively impact efficiency and profitability in the swine industry and are hypothesized to result from insufficient endometrial support and placental development during pregnancy. This study examined how glucose and fructose are synthesized, transported, and metabolized at the uterine-placental interface of pigs to support development and growth of the placenta and embryo/fetus. Total tissue mRNA expression and mRNA or protein cellular localization for glucose transporters and polyol pathway enzymes were determined in endometrial and/or placental tissues collected from gilts throughout the estrous cycle and pregnancy. SLC2A1 is the most abundant glucose transporter in the endometrium and is expressed by luminal (LE) and glandular epithelia (GE) throughout pregnancy. SLC2A3 is expressed by trophectoderm/chorion throughout pregnancy. SLC2A5, a fructose transporter, is expressed by LE and chorion after Day 30 of gestation. SLC2A8, a glucose and fructose transporter, is expressed by LE, GE, and select fetal tissues during the peri-implantation period of pregnancy. SLC2A1 mRNA and SLC2A8 protein are upregulated in the uterine epithelia in response to E2 and P4. The conversion of glucose to fructose involves aldose reductase (AKR1B1) and sorbitol dehydrogenase (SORD). AKR1B1 is expressed by uterine LE during the peri-implantation period, then by chorion after Day 20. SORD is expressed initially by uterine LE, GE, and trophectoderm, but is barely detectable in the endometrium by Day 20. Ketohexokinase (KHK), which phosphorylates fructose, is expressed by trophectoderm/chorion throughout pregnancy, especially in the tall columnar cells and areolae. These results establish the presence of the molecular components for hexose sugar transport, conversion of glucose to fructose, and fructose utilization at the uterine-placental interface of pigs. The shift in expression of AKR1B1 and SORD from uterine LE to chorion during pregnancy suggests that the free-floating conceptuses are supported by fructose synthesized and secreted into the uterine lumen by uterine LE. After placentation is initiated, the chorion becomes self-sufficient for fructose synthesis and transport to the conceptus. With this knowledge, future studies can be designed to manipulate the availability and transport of hexose sugars across the uterine-placental interface to decrease prenatal loss and variability in birth weights within litters, leading to increased efficiency and profitability for the swine industry.
Steinhauser, Chelsie Burroughs (2015). Hexose Sugar Transport and Metabolism at the Porcine Uterine-Placental Interface. Doctoral dissertation, Texas A & M University. Available electronically from