Drug transporter expression during in vitro differentiation of first-trimester and term human villous trophoblasts

Revealing the molecular landscape of human placenta: a systematic review and meta-analysis of single-cell RNA sequencing studies

BACKGROUND

With increasing significance of developmental programming effects associated with placental dysfunction, more investigations are devoted to improving the characterization and understanding of placental signatures in health and disease. The placenta is a transitory but dynamic organ adapting to the shifting demands of fetal development and available resources of the maternal supply throughout pregnancy. Trophoblasts (cytotrophoblasts, syncytiotrophoblasts, and extravillous trophoblasts) are placental-specific cell types responsible for the main placental exchanges and adaptations. Transcriptomic studies with single-cell resolution have led to advances in understanding the placenta's role in health and disease. These studies, however, often show discrepancies in characterization of the different placental cell types.

OBJECTIVE AND RATIONALE

We aim to review the knowledge regarding placental structure and function gained from the use of single-cell RNA sequencing (scRNAseq), followed by comparing cell-type-specific genes, highlighting their similarities and differences. Moreover, we intend to identify consensus marker genes for the various trophoblast cell types across studies. Finally, we will discuss the contributions and potential applications of scRNAseq in studying pregnancy-related diseases.

SEARCH METHODS

We conducted a comprehensive systematic literature review to identify different cell types and their functions at the human maternal-fetal interface, focusing on all original scRNAseq studies on placentas published before March 2023 and published reviews (total of 28 studies identified) using PubMed search. Our approach involved curating cell types and subtypes that had previously been defined using scRNAseq and comparing the genes used as markers or identified as potential new markers. Next, we reanalyzed expression matrices from the six available scRNAseq raw datasets with cell annotations (four from first trimester and two at term), using Wilcoxon rank-sum tests to compare gene expression among studies and annotate trophoblast cell markers in both first trimester and term placentas. Furthermore, we integrated scRNAseq raw data available from 18 healthy first trimester and nine term placentas, and performed clustering and differential gene expression analysis. We further compared markers obtained with the analysis of annotated and raw datasets with the literature to obtain a common signature gene list for major placental cell types.

OUTCOMES

Variations in the sampling site, gestational age, fetal sex, and subsequent sequencing and analysis methods were observed between the studies. Although their proportions varied, the three trophoblast types were consistently identified across all scRNAseq studies, unlike other non-trophoblast cell types. Notably, no marker genes were shared by all studies for any of the investigated cell types. Moreover, most of the newly defined markers in one study were not observed in other studies. These discrepancies were confirmed by our analysis on trophoblast cell types, where hundreds of potential marker genes were identified in each study but with little overlap across studies. From 35 461 and 23 378 cells of high quality in the first trimester and term placentas, respectively, we obtained major placental cell types, including perivascular cells that previously had not been identified in the first trimester. Importantly, our meta-analysis provides marker genes for major placental cell types based on our extensive curation.

WIDER IMPLICATIONS

This review and meta-analysis emphasizes the need for establishing a consensus for annotating placental cell types from scRNAseq data. The marker genes identified here can be deployed for defining human placental cell types, thereby facilitating and improving the reproducibility of trophoblast cell annotation.

Modeling the Progression of Placental Transport from Early- to Late-Stage Pregnancy by Tuning Trophoblast Differentiation and Vascularization

The early-stage placental barrier is characterized by a lack of fetal circulation and by a thick trophoblastic barrier, whereas the later-stage placenta consists of vascularized chorionic villi encased in a thin, differentiated trophoblast layer, ideal for nutrient transport. In this work, predictive models of early- and late-stage placental transport are created using blastocyst-derived placental stem cells (PSCs) by modulating PSC differentiation and model vascularization. PSC differentiation results in a thinner, fused trophoblast layer, as well as an increase in human chorionic gonadotropin secretion, barrier permeability, and secretion of certain inflammatory cytokines, which are consistent with in vivo findings. Further, gene expression confirms this shift toward a differentiated trophoblast subtype. Vascularization results in a molecule type- and size-dependent change in dextran and insulin permeability. These results demonstrate that trophoblast differentiation and vascularization have critical effects on placental barrier permeability and that this model can be used as a predictive measure to assess fetal toxicity of xenobiotic substances at different stages of pregnancy.

An update on placental drug transport and its relevance to fetal drug exposure

Pregnant women are often complicated with diseases that require treatment with medication. Most drugs administered to pregnant women are off-label without the necessary dose, efficacy, and safety information. Knowledge concerning drug transfer across the placental barrier is essential for understanding fetal drug exposure and hence drug safety and efficacy to the fetus. Transporters expressed in the placenta, including adenosine triphosphate (ATP)-binding cassette efflux transporters and solute carrier uptake transporters, play important roles in determining drug transfer across the placental barrier, leading to fetal exposure to the drugs. In this review, we provide an update on placental drug transport, including in vitro cell/tissue, ex vivo human placenta perfusion, and in vivo animal studies that can be used to determine the expression and function of drug transporters in the placenta as well as placental drug transfer and fetal drug exposure. We also describe how the knowledge of placental drug transfer through passive diffusion or active transport can be combined with physiologically based pharmacokinetic modeling and simulation to predict systemic fetal drug exposure. Finally, we highlight knowledge gaps in studying placental drug transport and predicting fetal drug exposure and discuss future research directions to fill these gaps.

A Glyphosate-Based Formulation but Not Glyphosate Alone Alters Human Placental Integrity

Glyphosate (G)-based herbicidal formulations, such as the most commonly used one, Roundup (R), are major pesticides used worldwide on food and feed. Pregnant women may be frequently exposed to R compounds. These are composed of G, which is declared as the active principle, and other products contained in formulations, named formulants, which have been declared as inerts and diluents by the manufacturers. These formulants have, in fact, been demonstrated to be much more toxic than G, in particular to placental and embryonic human cells. In this work, we thus compared the effect of G and a GT+ formulation named R, using placental perfusion ex vivo. R, but not G alone, was demonstrated to alter the placental permeability of a known small model molecule, antipyrine. Similar results were observed for the fetal venous flow rate. The transfer of G alone increases with time, but is significantly decreased in presence of its formulants. The perfusion of R provokes a destruction of fetal vessels, as demonstrated by immunohistochemistry. Formulants obviously alter the fetal-placental circulation and placental integrity according to time of exposure. Therefore, G does not appear to be the main toxic agent of R. Formulants, although undeclared, include polyoxyethanolamines, PAHs, or heavy metals, and may be responsible for this toxicity. These compounds are also present in other pesticides. The progressive blood flow reduction due to the toxic compounds of formulations may diminish the nutrient supply to the fetus, alter the development, and may enhance the poisoning effects. Although these are preliminary results, they could at least partially explain some adverse pregnancy outcomes in mothers exposed to pesticides or other environmental pollutants. The debate on glyphosate alone is proven insufficient for the understanding of the toxicity.

Multiple Drug Transporters Contribute to the Placental Transfer of Emtricitabine

Emtricitabine (FTC) is a first-line antiviral drug recommended for the treatment of AIDS during pregnancy. We hypothesized that transporters located in the placenta contribute to FTC transfer across the blood-placenta barrier. BeWo cells, cell models with stable or transient expression of transporter genes, primary human trophoblast cells (PHTCs), and small interfering RNAs (siRNAs) were applied to demonstrate which transporters were involved. FTC accumulation in BeWo cells was reduced markedly by inhibitors of equilibrative nucleoside transporters (ENTs), concentrative nucleoside transporters (CNTs), organic cation transporters (OCTs), and organic cation/carnitine transporter 1 (OCTN1) and increased by inhibitors of breast cancer resistance protein (BCRP) and multidrug resistance-associated proteins (MRPs). ENT1, CNT1, OCTN1, MRP1/2/3, and BCRP, but not ENT2, CNT3, OCTN2, or multidrug resistance protein 1 (MDR1), were found to transport FTC. FTC accumulation in PHTCs was decreased significantly by inhibitors of ENTs and OCTN1. These results suggest that ENT1, CNT1, and OCTN1 probably contribute to FTC uptake from maternal circulation to trophoblasts and that ENT1, CNT1, and MRP1 are likely involved in FTC transport between trophoblasts and fetal blood, whereas BCRP and MRP1/2/3 facilitate FTC transport from trophoblasts to maternal circulation. Coexistence of tenofovir or efavirenz with FTC in the cell medium did not influence FTC accumulation in BeWo cells or PHTCs.

Analysis of the effects of polyunsaturated fatty acids on transporter expressions using a PCR array: Induction of xCT/SLC7A11 in human placental BeWo cells

OBJECTIVE

Polyunsaturated fatty acids (PUFAs), including arachidonic acid (AA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), are essential for adequate fetal growth. The aim of the present study was to elucidate the effects of PUFAs on the expression and function of placental transporters, which play important roles in placental functions including the supply of nutrients to the fetus, excretion of metabolites, and protection of the fetus from xenobiotics.

METHODS

Human placental choriocarcinoma BeWo cells were used as a trophoblast model. PUFA-induced alteration in the gene expression of 84 transporters was investigated by a commercially available PCR array. Protein levels and the activity of transporters were assessed by western blotting and uptake experiments, respectively. The placental expression of the transporters was analyzed using pregnant Wistar rats.

RESULTS

PUFAs (AA, EPA, and DHA) increased cystine/glutamate transporter xCT/SLC7A11, which mediates the cellular uptake of cystine coupled with the efflux of glutamate in human placental choriocarcinoma BeWo cells. These PUFAs also increased [¹⁴C]-cystine uptake in BeWo cells. PUFA-induced xCT/SLC7A11 mRNA expression was not blocked by nuclear factor-erythroid 2-related factor-2 (NRF2) knockdown. Reverse transcription (RT)-PCR analysis indicated that xCT/Slc7a11 mRNA was detected in rat placenta and the expression level at gestational day (GD) 12 was higher than that at GD 20.

CONCLUSION

These results indicate that PUFAs promoted cystine uptake in placental cells by inducing xCT/SLC7A11 expression and NRF2 did not contribute to upregulation of xCT/SLC7A11 by PUFAs. Furthermore, xCT expression in rat placenta may change during pregnancy.

Chemotherapy in pregnancy: exploratory study of the effects of paclitaxel on the expression of placental drug transporters

Introduction The use of paclitaxel in pregnant cancer patients is feasible in terms of fetal safety, but little is known about the effects of paclitaxel on the placenta. Using three experimental models, we aimed to assess the effects of paclitaxel on the expression of placental drug transporters. Methods In the in vitro model (human primary trophoblast culture), trophoblasts were isolated from normal term placentas and subsequently exposed to paclitaxel. The transcriptional regulation of 84 genes encoding for drug transporters, and the protein expression of ABCB1/P-gp and ABCG2/BCRP were assessed. In the in vivo model, placental tissues isolated from pregnant cancer patients treated with paclitaxel were analyzed to assess the protein expression of ABCB1/P-gp and ABCG2/BCRP. The same parameters were assessed in extracts from human placental cotyledons perfused ex vivo with paclitaxel. Results In the in vitro model, the expression of twelve drug-transporters genes was found to be significantly down-regulated after exposure to paclitaxel, including ABCC10, SLC28A3, SLC29A2, and ATP7B (involved in the transport of taxanes, antimetabolites, and cisplatin, respectively). The protein expression of ABCB1/P-gp increased by 1.3-fold after paclitaxel administration. Finally, the protein expression of ABCB1/P-gp and ABCG2/BCRP was higher in cotyledons from mothers treated with multiple doses of paclitaxel during pregnancy than in cotyledons perfused with a single dose of paclitaxel. Discussion Paclitaxel modulates the expression of placental drug transporters involved in the disposition of various anticancer agents. Further studies will be needed to assess the impact of repeated or prolonged exposure to paclitaxel on the expression and function of placental drug transporters.

Transport mechanism of ursodeoxycholic acid in human placental BeWo cells

Ursodeoxycholic acid (UDCA) is a first-line drug to treat intrahepatic cholestasis of pregnancy (ICP). However, its effects on the fetus are not clearly known. To better guide its clinical use, we aimed to study the mechanism underlying the placental transport of UDCA. The uptake and efflux of UDCA across placental apical membranes were studied using BeWo cells; effects of different exposure durations, UDCA concentrations, temperatures, and inhibitors of transporters were studied. A transwell assay was performed, and UDCA concentration in both fetal and maternal sides was measured using LC-MS/MS. Higher unidirectional transport of UDCA was observed in the basolateral-to-apical direction than in the apical-to-basolateral direction. Ko143 and verapamil, which are typical inhibitors of efflux transporters, significantly increased UDCA transport from different directions. UDCA uptake from the apical membrane of BeWo cells was time-dependent, but sodium-independent. It was inhibited by inhibitors of energy metabolism and of organic anion transporters, indicating an active transport mechanism. UDCA uptake from the apical membranes of BeWo cells could be mediated by organic anion-transporting polypeptides, whereas its efflux could be mediated by breast cancer resistance protein and multidrug resistant protein 3. The results of the present study may provide a basis for UDCA use in pregnancy.

Buprenorphine, Norbuprenorphine, R-Methadone, and S-Methadone Upregulate BCRP/ABCG2 Expression by Activating Aryl Hydrocarbon Receptor in Human Placental Trophoblasts

Opioid dependence during pregnancy is a rising concern. Maintaining addicted pregnant women on long-acting opioid receptor agonist is the most common strategy to manage drug abuse in pregnant women. Methadone (MET) and buprenorphine (BUP) are widely prescribed for opiate maintenance therapy. Norbuprenorphine (NBUP) is the primary active metabolite of BUP. These medications can cross the placenta to the fetus, leading to postpartum neonatal abstinence syndrome. Despite their use during pregnancy, little is known about the cellular changes in the placenta brought about by these drugs. In this study, we showed that BUP, NBUP, and MET at clinically relevant plasma concentrations significantly induced BCRP mRNA up to 10-fold in human model placental JEG3 and BeWo cells and in primary human villous trophoblasts, and this induction was abrogated by CH223191, an aryl hydrocarbon receptor (AhR)-specific antagonist. These drugs increased AhR recruitment onto the AhR-response elements and significantly induced breast cancer resistance protein (BCRP) gene transcription. AhR overexpression further increased BCRP mRNA and protein expression. Knockdown of AhR by shRNA decreased BCRP expression, and this decrease was reversed by rescuing AhR expression. Finally, induction of BCRP expression in JEG3 and BeWo cells was accompanied by an increase in its efflux activity. Collectively, we have demonstrated, for the first time, that BUP, NBUP, and MET are potent AhR agonists and can induce BCRP in human placental trophoblasts by activating AhR. Given the critical role of BCRP in limiting fetal exposure to drugs and xenobiotics, long-term use of these medications may affect fetal drug exposure by altering BCRP expression in human placenta.

Placental ABC Transporters: Biological Impact and Pharmaceutical Significance

The human placenta fulfills a variety of essential functions during prenatal life. Several ABC transporters are expressed in the human placenta, where they play a role in the transport of endogenous compounds and may protect the fetus from exogenous compounds such as therapeutic agents, drugs of abuse, and other xenobiotics. To date, considerable progress has been made toward understanding ABC transporters in the placenta. Recent studies on the expression and functional activities are discussed. This review discusses the placental expression and functional roles of several members of ABC transporter subfamilies B, C, and G including MDR1/P-glycoprotein, the MRPs, and BCRP, respectively. Since placental ABC transporters modulate fetal exposure to various compounds, an understanding of their functional and regulatory mechanisms will lead to more optimal medication use when necessary in pregnancy.

[Tyrosine kinase inhibitors and pregnancy: A risk to the fetus?]

The association of cancer and pregnancy is increasingly frequent. This is related, partially, to the increasingly belated age of pregnancy. The management of cancer in pregnancy is a complicated issue. The use of tyrosine kinase inhibitors (TKIs) during pregnancy remains rare and only few data are available concerning their transplacental passage. The aim of this work is to review the data described in the literature, in order to highlight the risks incurred by the fetus, associated with these TKIs' treatment. Up to 189 pregnancies of women treated with TKIs during part or throughout their pregnancy have been described. Clinical data are reassuring and would be in favor of taking the treatment in terms of the balance maternal profit versus fetal risk. These data must, nevertheless, be interpreted with caution.