Transport of cholesterol across a BeWo cell monolayer

Abstract

The placental transport of various compounds, such as glucose and fatty acids, has been well studied. However, the transport of cholesterol, a sterol essential for proper fetal development, remains undefined in the placenta. Therefore, the purpose of these studies was to examine the transport of cholesterol across a placental monolayer and its uptake by various cholesterol acceptors. BeWo cells, which originated from a human choriocarcinoma, were grown on transwells for 3 days to form a confluent monolayer. The apical side of the cells was radiolabeled with either free cholesterol or LDL cholesteryl ester. After 24 h, the radiolabel was removed and cholesterol acceptors were added to the basolateral chamber. Cholesterol was found to be taken up by the apical surface of the placental monolayer, transported to the basolateral surface of the cell, and effluxed to fetal human serum, fetal HDL, or phospholipid vesicles, but not to apolipoprotein A-I. In addition, increasing the cellular cholesterol concentration further increased the amount of cholesterol transported to the basolateral acceptors. These are the first studies to demonstrate the movement of cholesterol across a placental cell from the maternal circulation (apical side) to the fetal circulation (basolateral side).

Novel Insights into Concepts and Directionality of Maternal–Fetal Cholesterol Transfer across the Human Placenta

“…Other investigations demonstrated a greater protein expression level of ABCG1 in BeWo as compared to placenta tissues [48], but again ABCA1 expression was not shown. A study investigating vectorial cholesterol transport in BeWo cells failed to demonstrate the efflux of cholesterol to apoA-1 at the basal (fetal) side [49]. However, basally oriented transport was observed when fetal human serum or phospholipid vesicles were used as acceptors.…”

“…However, basally oriented transport was observed when fetal human serum or phospholipid vesicles were used as acceptors. Despite the apparent importance of ABCA1-mediated cholesterol efflux, no ABCA1 mRNA or protein expression data were reported [49]. Of note, BeWo cells are derived from a first trimester placenta.…”

Placental ABC Transporters: Biological Impact and Pharmaceutical Significance

“…Both these discoveries suggested a possible role of ABCA1 in lipid transport. Schmid et al performed the first studies in humans that demonstrated cholesterol transport from maternal to fetal compartment using BeWo cells as a model of placental monolayer function (21). However, these studies did not precisely determine the involvement of ABCA1 in efflux of cholesterol from placenta.…”

Review: Transport of maternal cholesterol to the fetal circulation

“…BeWo cells synthesize placental hormones and express trophoblast proteins [reviewed in (18, 19)]. Subclone 30 of BeWo cells becomes a confluent monolayer that is polarized when grown on transwells allowing for the study of unilateral transport across a polarized cell.…”

“…In all studies, cells were grown to confluence, and incubated with LDL radiolabeled with cholesteryl ester. After removal of apical LDL, various acceptors were added to the basal side as described (18). The percent cholesterol effluxed is the radiolabel in the basal media as a percentage of radiolabel taken up by the cells.…”