There is substantial evidence to show that fetal weight is closely associated with placental weight, that fetal weight is affected by maternal nutritional status and that fetal growth, as observed clearly in extremes such as macrosomia and fetal growth restriction, is related to availability of nutrients such as glucose and the amino acids. We hypothesize that fetal nutrient availability coordinates fetoplacental growth with the expression and activity of placental nutrient transporters either directly, or via fetal and placental growth factors. The proposed studies will examine this hypothesis by comparison of normal and fetal growth restricted pregnancies and by in vitro investigation of the mechanisms involved in regulation of growth factor release and transporter expression.
The specific aims of this proposal are (1) to compare uterine and umbilical blood flows, transplacental glucose and amino acid transfer, fetal plasma glucose and amino acid concentrations and fetal plasma protein synthesis in normal and growth restricted pregnancies, (2a) to measure maternal and fetal circulating growth factors (IGF-1 and placental growth hormone, pGH), their binding proteins and trophoblast expression of growth factor binding proteins and receptors, (2b) to determine the effect of glucose, amino acids and IGF-1 on the release of pGH in placental tissue explants and trophoblast cells, (3a) to measure the expression and activity of the GLUT1 glucose transporter and the ATA1/2 and LAT-1/2 amino acid transporters in normal and growth restricted pregnancies, (3b) to measure the effects of glucose, amino acids, IGF-1 and pGH on the expression and activity of the GLUT1 glucose transporter and the ATA1/2 and LAT-1/2 amino acid transporters in tissue explants and trophoblast cells and (3c) to determine whether nutrient availability modulates nutrient transporter expression in trophoblast cells via the nutrient-sensing protein kinase, mTOR (mammalian target of rapamycin). These studies will use two well-defined groups, a group of normal pregnancies and a group suffering from fetal growth restriction (FGR). These groups will be defined not only by birthweight, but also by growth trajectory and by umbilical blood flow, ensuring that measurements are performed in conditions of true fetal growth restriction. These studies will, for the first time, generate integrated data on this pathology, data concerning blood flow, fetal nutrient availability, transplacental nutrient flux, growth factor release and nutrient transporter expression. These studies will lay the foundation for the more complex investigations of fetal growth restriction in pathologies such as preeclampsia and diabetes and will provide the basis for exploration of the signaling pathways by which nutrient availability is converted to signals which regulate gene expression and protein synthesis.
