Human placental glucose transport in fetoplacental growth and metabolism

Abstract

While efficient glucose transport is essential for all cells, in the case of the human placenta, glucose transport requirements are two-fold; provision of glucose for the growing fetus in addition to the supply of glucose required the changing metabolic needs of the placenta itself. The rapidly evolving environment of placental cells over gestation has significant consequences for the development of glucose transport systems. The two-fold transport requirement of the placenta means also that changes in expression will have effects not only for the placenta but also for fetal growth and metabolism. This review will examine the localization, function and evolution of placental glucose transport systems as they are altered with fetal development and the transport and metabolic changes observed in pregnancy pathologies.

Keywords: Diabetes; Glucose transporters; IUGR; Placenta, human; Preeclampsia; Pregnancy.

Fig. 1.

Distribution of placental glucose transporters in first and third trimester human placenta. This figure shows the distribution of glucose transporters in first and third trimester human placenta as described in Section 3. The localization of GLUT8, 9a and 9b in the first trimester is unknown. No information is available on GLUT10 localization in either first or third trimester. MVM, microvillous membrane; BM, basal membrane; STB, syncytiotrophoblast; CTB, cytotrophoblast; EC, endothelial cell; VS, villous stromal cell.

Fig. 2.

Factors affecting glucose transfer kinetics across the human placenta. Glucose will diffuse, or be transported by facilitative diffusion transporters from regions of high to low concentration. Maternal diet and hepatic glucose release keep maternal glucose high while fetal consumption reduces fetal levels. Glucose concentrations decrease progressively from the maternal artery to vein and from [glucose]A > [glucose]B > [glucose]C ≫ [glucose]H (note that [glucose]B may vary in different regions of the placenta). The glucose concentration in any region will be determined by the rate at which glucose diffuses out in the fetal direction and the rate at which new glucose diffuses in from the maternal side. Glucose metabolism within the syncytiotrophoblast and uptake by other placental cells will also affect glucose concentrations in specific regions. It should be noted that there is no fixed relationship between the direction of maternal blood flow and blood flow within the villi. (Adapted, with permission, from Day, PE et al., Placenta 34 (2013), 953–958)