Trophoblast Differentiation Affects Crucial Nutritive Functions of Placental Membrane Transporters.

Cytotrophoblasts are progenitor cells that proliferate and fuse to form the multinucleated syncytiotrophoblast layer, implicated in placental endocrine and transport functions. While membrane transporters play a critical role in the distribution of nutrients, hormones, and xenobiotics at the maternal-fetal interface, their selectivity to the syncytiotrophoblast layer is poorly characterized. We aimed to evaluate the regulation of placental transporters in response to trophoblast differentiation in vitro. Experiments were carried out in isolated primary human trophoblast cells before and after syncytialization. Gene expression of six molecular markers and thirty membrane transporters was investigated by qPCR analysis. Subsequently, functional expression was evaluated for proteins involved in the transplacental transfer of essential nutrients i.e., cholesterol (ABCA1, ABCG1), glucose (SLC2A1), leucine (SLC3A2, SLC7A5), and iron (transferrin receptor, TfR1). We identified that human chorionic gonadotropin, placental lactogen, endoglin, and cadherin-11 serve as optimal gene markers for the syncytialization process. We showed that trophoblast differentiation was associated with differential gene expression (mostly up-regulation) of several nutrient and drug transporters. Further, we revealed enhanced protein expression and activity of ABCG1, SLC3A2, SLC7A5, and TfR1 in syncytialized cells, with ABCA1 and GLUT1 displaying no change. Taken together, these results indicate that the syncytiotrophoblast has a dominant role in transporting essential nutrients cholesterol, leucine, and iron. Nonetheless, we present evidence that the cytotrophoblast cells may also be linked to transport functions that could be critical for the cell fusion processes. Our findings collectively yield new insights into the cellular functions associated with or altered by the trophoblast fusion. Importantly, defective syncytialization could lead to nutrient transfer imbalance, ultimately compromising fetal development and programming.

Comparative expression patterns of selected membrane transporters in differentiated BeWo and human primary trophoblast cells.

Although placental membrane transporters have an important impact on materno-fetal nutrient transfer, placental cell models are poorly characterized regarding transporter expression. We assessed the mRNA expression of 26 physiologically important solute carriers and ABC transporters in BeWo (b30 clone) and primary human trophoblast cells (PHT) before and after syncytialization. 77% of the transporters showed similar mRNA expression changes between BeWo and PHT after syncytialization. Selected transporters, however, were either lacking in BeWo or showed different trends after syncytialization. In conclusion, BeWo cells generally represent an apt model for transporter studies, but their suitability should be confirmed for each transporter by comparison with PHT.