Tracking nutrient transfer at the human maternofetal interface from 4 weeks to term

In this study we have tracked glycogen and glycoprotein flux associated with nutrient uptake into trophoblast in early deciduochorial and later haemochorial placenta.

α-amylase, glycogen synthase and glycogen phosphorylase were immunohistochemically localised in 6-14 week and term placenta and first trimester decidua. Placentae of 4-18 weeks' gestation and term were also stained with 22 biotinylated lectins.

Histochemical data were consistent with glycogenolysis in decidual gland epithelium and placental cyto- and syncytiotrophoblast; α-amylase was present in decidual secretions but absent in placenta. Glycogen and glycogen synthase were both apparent in villous cytotrophoblast cells and columns. Profound changes were observed in placental glycosylation during gestation. Syncytial microvilli were richly glycosylated as were first trimester vacuoles but, by term, syncytiotrophoblast showed little lectin binding except in microvillous and basal membranes. Cytotrophoblast Golgi bodies were active in the first trimester; at term the cells were generally more glycosylated than syncytiotrophoblast.

We deduce that decidual cell glycogen is broken down for transport into the placenta where the products may be reassembled into glycogen or used for metabolic processes. First trimester histiotrophe is internalised by syncytiotrophoblast, then broken down in apical vacuoles containing lysosomal markers. This process declines after haemotrophic nutrition commences. Transition from histiotrophic to haemotrophic nutrition involves reduced amounts of uterine secretory derivatives reaching the placenta, and reduction in internalisation of glycoprotein by syncytiotrophoblast, presumably reflecting the shift to low molecular weight nutrients. Glycogen accumulates in cytotrophoblast from early pregnancy and is mobilised for utilisation by fetoplacental tissues.