Possible roles of transporters SLC2A5 and SLC2A8 in fructose movement between maternal and fetal tissues during pig pregnancy

Authors: BURROUGHS, CHELSIE - Texas A&M University; Vallet, Jeff; WU, GUOYAO - Texas A&M University; BURGHARDT, ROBERT - Texas A&M University; BAZER, FULLER - Texas A&M University; JOHNSON, GREGORY - Texas A&M University

Submitted to: Society for the Study of Reproduction Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 3/28/2013
Publication Date: 7/1/2013
Citation: Burroughs, C., Vallet, J., Wu, G., Burghardt, R., Bazer, F., Johnson, G. 2013. Possible roles of transporters SLC2A5 and SLC2A8 in fructose movement between maternal and fetal tissues during pig pregnancy [abstract]. Biology of Reproduction Supplement (46th Annual Meeting of the Society for the Study of Reproduction). pp. 228-229 (Abstract #490).

Interpretive Summary:

Technical Abstract: Fetal fluids in porcine conceptuses contain high concentrations of fructose, but compared to glucose, fructose plays a minor role as an energy source. Fructose can be converted to glucosamine, a precursor for synthesis of glycosaminoglycans, such as hyaluronan, which are necessary for placental stroma development. Additional pathways for fructose metabolism lead to synthesis of phospholipids and nucleic acids that support development of the conceptus. While these anabolic pathways may explain the requirement for a fructose reservoir in allantoic fluid, the mechanisms for fructose transport between maternal and fetal tissues have not been fully elucidated. Therefore, we determined the gene expression for SLC2A5, a facilitated fructose transporter, and SLC2A8, a facilitated glucose/fructose transporter, in pig endometria and placenta. Q-PCR was performed using Perfecta SYBR Green to determine transcript levels of SLC2A5 and SLC2A8 in 3 animals (each measured in triplicate) in the following experiments with endogenous GAPDH used for normalization. Statistical analyses were performed on the deltaCt values using one-way ANOVA for each gene within each experiment and Tukey’s HSD in Exp 1 and student’s t-test within each gene in Exp 2 and 3. In Exp 1, gilts were hysterectomized on either Day 5, 9, 10, 12, 13, 14, 15, 20, 25, 30, 35, 40, 60, or 85 of pregnancy. Additionally, placenta from Days 45 and 85 were collected. SLC2A8 expression was greatest at 4.15±0.28 on Day 10 after which time transcript levels declined to 0.75±0.08 on Day 12 and 0.19±0.01 on Day 20 and values remained low, but detectable, to Day 85 of pregnancy. In contrast, SLC2A5 expression was low in early pregnancy (0.005±0.0002), peaked on Day 30 (0.53±0.03) and remained abundant to Day 85. Both SLC2A5 and SLC2A8 were present in Day 45 and 85 placenta. In Exp 2, cyclic gilts were injected daily (Days 11-14) with estradiol benzoate (i.m.) or vehicle and hysterectomized on Day 15 or 90 of pseudopregnancy. Both SLC2A5 and SLC2A8 transcript levels were similar at Days 15 and 90 in the pregnant and pseudopregnant gilts (p>0.05). In Exp 3, gilts were ovariectomized on Day 12, injected daily with progesterone (i.m.) or vehicle for 28 days, and hysterectomized on Day 40. Progesterone (P4) increased expression of SLC2A5 (0.14±0.03) as compared to controls (0.01±0.002; p<0.05). There was no effect of P4 on SLC2A8 expression. SLC2A8 transcript levels were elevated during the peri-implantation period when luminal epithelium secretions are high, while SLC2A5 transcript levels were elevated when the uterine glandular epithelium is the major source of histotroph between Days 30 and 85 of pregnancy. The temporal expression patterns indicate that both SLC2A5 and SLC2A8 may serve to transport fructose in the uterus throughout pregnancy. In addition, SLC2A5 expression is progesterone dependent. These results suggest that the endometrium can metabolize fructose, and the placenta can release fructose into the fetal circulation during pregnancy, which provides insight into the significance of the abundance of fructose in fetal fluids.