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

Abstract

Cholesterol is indispensable for cellular membrane composition and function. It is also a precursor for the synthesis of steroid hormones, which promote, among others, the maturation of fetal organs. A role of the ATP-binding-cassette-transporter-A1 (ABCA1) in the transport of maternal cholesterol to the fetus was suggested by transferring cholesterol to apolipoprotein-A-1 (apo-A1), but the directionality of the apoA-1/ABCA1-dependent cholesterol transport remains unclear. We isolated primary trophoblasts from term placentae to test the hypotheses that (1) apoA-1/ABCA1 dispatches cholesterol mainly towards the fetus to support fetal developmental maturation at term, and (2) differentiated syncytiotrophoblasts (STB) exert higher cholesterol transport activity than undifferentiated cytotrophoblasts (CTB). As experimental models, we used (1) trophoblast monolayers grown on Transwell® system consisting of apical (maternal-like) and basal (fetal-like) compartments, and (2) trophoblasts grown on conventional culture plates at CTB and STB stages. Surprisingly, apoA-1-mediated cholesterol efflux operated almost exclusively at the apical-maternal side, where ABCA1 was also localized by immunofluorescence. We found greater cholesterol efflux capacity in STB, which was increased by liver-X-receptor agonist treatment and decreased by ABCA1 inhibition. We conclude that at term the apoA-1/ABCA1 pathway is rather involved in cholesterol transport to the mother than in transfer to the fully developed fetus.

Small molecule inhibitors provide insights into the relevance of LAT1 and LAT2 in materno‐foetal amino acid transport

“…The collected tissue was used to isolate primary cytotrophoblasts as previously described 32 . Isolated cells were cultured on Cell‐BIND plates in Dulbecco's modified Eagle's medium containing 4.5 g/L glucose (DMEM‐highGlucose; Gibco, Paisley, UK) and characterized by analysing the expression of cytokeratin‐7 and vimentin as previously described 33 . Primary trophoblasts were evaluated for leucine uptake at the cytotrophoblast (CTB) and syncytiotrophoblast (STB) stage (ie after 12 and 48 hours of culture, respectively) when spontaneous differentiation and fusion has occurred.…”

Cholesterol uptake and efflux are impaired in human trophoblast cells from pregnancies with maternal supraphysiological hypercholesterolemia

“…The efflux of cholesterol from trophoblast cells to acceptors such as HDL or ApoA-I has been previously reported. Classically, it has been described that the efflux to HDL is mediated by ABCG1 and to ApoA-I by ABCA1 19,20,[48][49][50] . Our results of in situ localization are in agreement with previous papers describing ABCA1 in the syncytiotrophoblast layer of the placenta 20,49,[51][52][53] .…”

“…Therefore, the cholesterol efflux may occur to the maternal and/or the foetal side of this tissue, directionality that was not possible to be determined with our 2D model. Then, it is required to determine the efflux rates in cultured polarized PHT to improve our understanding of the directionality of the cholesterol efflux (to apical/maternal or basal/ foetal) 48,50 . However, and based on: (1) the placental localization of ABCA1 (transport to ApoA-I) and ABCG1 (transport to HDL), (2) recent evidence showing that the efflux to ApoA-I in PHT is mainly to the apical side 48 , (3) that the expression of ApoA-I in the neonatal lipoproteins is very low compared to maternal concentration of this apolipoproteina 29 ; we speculate that in PHT from MSPH placentas, the increased efflux to ApoA-I could be to the maternal circulation and the reduced efflux to HDL could be to the fetal circulation maybe as a possible regulation to control increased cholesterol flux to the foetal circulation.…”

Elevated Glucose and Insulin Levels Decrease DHA Transfer across Human Trophoblasts via SIRT1-Dependent Mechanism

“…The cells were cultured in proprietary trophoblast medium with fetal bovine serum, growth supplements, and antibiotics (penicillin/streptomycin) (ScienCell) in a humidified incubator under a 5% CO 2 atmosphere at 37 • C. Trophoblasts were seeded at a density of 0.5 × 10 6 cells/cm 2 and 0.1 × 10 6 cells/cm 2 in 6-well plates or 12-well Transwell plates coated with human placental collagen (0.01% w/v). The medium was replenished every day for seven days to allow syncytialization of cells, which was confirmed by hPL and hCG mRNA expression and secretion of hCG, as described previously [39,40]. The insulin-resistant GDM trophoblast cell model was established by treating day four culture with 25-mmol/L glucose and 10 −7 -mol/L insulin for 72 h, as described previously [41].…”