Proteomic analyses of primary human villous trophoblasts exposed to flame retardant BDE-47 using SWATH-MS

Polybrominated diphenyl ethers (PBDEs) are a class of brominated flame retardants and recognized developmental toxicants that are detectable in placental tissues. Higher levels of in utero PBDE exposure have been associated with an increased risk of adverse birth outcomes. During pregnancy, cytotrophoblasts (CTBs) from the placenta play critical roles in the formation of the maternal-fetal interface via uterine invasion and vascular remodeling. The differentiation of these cells towards an invasive phenotype is crucial for proper placental development. We previously have shown that BDE-47 can impact CTB viability and hinder the ability of these cells to migrate and invade. To expand on potential toxicological mechanisms, we utilized quantitative proteomic approaches to identify changes in the global proteome of mid-gestation primary human CTBs after exposure to BDE-47. Using sequential window acquisition of all theoretical fragment-ion spectra (SWATH), we identified 3024 proteins in our CTB model of differentiation/invasion. Over 200 proteins were impacted as a function of BDE-47 exposure (1 μM and 5 μM) across the treatment period (15, 24, and 39 h). The differentially expressed molecules displayed time- and concentration-dependent changes in expression and were enriched in pathways associated with aggregatory and adhesive processes. Network analysis identified CYFIP1, a molecule previously unexplored in a placental context, to be dysregulated at BDE-47 concentrations previously seen to impact CTB migration/invasion. Our SWATH-MS dataset thus demonstrates BDE-47 impacts the global proteome of differentiating CTBs and serves as a valuable resource for further understanding of the relationship between environmental chemical exposures and placental development and function. AVAILABILITY OF DATA AND MATERIAL: Raw chromatograms are deposited on the MassIVE proteomic database (https://massive.ucsd.edu) under accession number MSV000087870. Normalized relative abundances are also available as Table S1

Placental syncytiotrophoblast constitutes a major barrier to vertical transmission of Listeria monocytogenes.

Listeria monocytogenes is an important cause of maternal-fetal infections and serves as a model organism to study these important but poorly understood events. L. monocytogenes can infect non-phagocytic cells by two means: direct invasion and cell-to-cell spread. The relative contribution of each method to placental infection is controversial, as is the anatomical site of invasion. Here, we report for the first time the use of first trimester placental organ cultures to quantitatively analyze L. monocytogenes infection of the human placenta. Contrary to previous reports, we found that the syncytiotrophoblast, which constitutes most of the placental surface and is bathed in maternal blood, was highly resistant to L. monocytogenes infection by either internalin-mediated invasion or cell-to-cell spread. Instead, extravillous cytotrophoblasts-which anchor the placenta in the decidua (uterine lining) and abundantly express E-cadherin-served as the primary portal of entry for L. monocytogenes from both extracellular and intracellular compartments. Subsequent bacterial dissemination to the villous stroma, where fetal capillaries are found, was hampered by further cellular and histological barriers. Our study suggests the placenta has evolved multiple mechanisms to resist pathogen infection, especially from maternal blood. These findings provide a novel explanation why almost all placental pathogens have intracellular life cycles: they may need maternal cells to reach the decidua and infect the placenta

Invasive Extravillous Trophoblasts Restrict Intracellular Growth and Spread of Listeria monocytogenes

Listeria monocytogenes is a facultative intracellular bacterial pathogen that can infect the placenta, a chimeric organ made of maternal and fetal cells. Extravillous trophoblasts (EVT) are specialized fetal cells that invade the uterine implantation site, where they come into direct contact with maternal cells. We have shown previously that EVT are the preferred site of initial placental infection. In this report, we infected primary human EVT with L. monocytogenes. EVT eliminated ∼80% of intracellular bacteria over 24-hours. Bacteria were unable to escape into the cytoplasm and remained confined to vacuolar compartments that became acidified and co-localized with LAMP1, consistent with bacterial degradation in lysosomes. In human placental organ cultures bacterial vacuolar escape rates differed between specific trophoblast subpopulations. The most invasive EVT—those that would be in direct contact with maternal cells in vivo—had lower escape rates than trophoblasts that were surrounded by fetal cells and tissues. Our results suggest that EVT present a bottleneck in the spread of L. monocytogenes from mother to fetus by inhibiting vacuolar escape, and thus intracellular bacterial growth. However, if L. monocytogenes is able to spread beyond EVT it can find a more hospitable environment. Our results elucidate a novel aspect of the maternal-fetal barrier

Regionally distinct trophoblast regulate barrier function and invasion in the human placenta

The human placenta contains two specialized regions: the villous chorion where gases and nutrients are exchanged between maternal and fetal blood, and the smooth chorion (SC) which surrounds more than 70% of the developing fetus but whose cellular composition and function is poorly understood. Here, we use single cell RNA-sequencing to compare the cell types and molecular programs between these two regions in the second trimester human placenta. Each region consists of progenitor cytotrophoblasts (CTBs) and extravillous trophoblasts (EVTs) with similar gene expression programs. While CTBs in the villous chorion differentiate into syncytiotrophoblasts, they take an alternative trajectory in the SC producing a previously unknown CTB population which we term SC-specific CTBs (SC-CTBs). Marked by expression of region-specific cytokeratins, the SC-CTBs form a stratified epithelium above a basal layer of progenitor CTBs. They express epidermal and metabolic transcriptional programs consistent with a primary role in defense against physical stress and pathogens. Additionally, we show that SC-CTBs closely associate with EVTs and secrete factors that inhibit the migration of the EVTs. This restriction of EVT migration is in striking contrast to the villous region where EVTs migrate away from the chorion and invade deeply into the decidua. Together, these findings greatly expand our understanding of CTB differentiation in these distinct regions of the human placenta. This knowledge has broad implications for studies of the development, functions, and diseases of the human placenta

Polysialic acid enhances the migration and invasion of human cytotrophoblasts

Polysialic acid (polySia) is a large, cell-surface linear homopolymer composed of α2,8-linked sialic acid residues. Most extensively studied in the nervous system, this unique glycan modulates development by enhancing cell migration and regulating differentiation. PolySia also functions in developing and adult immune systems and is a signature of many cancers. In this study, we demonstrated that human placental trophoblasts, an epithelial lineage, also display this glycan. Cytotrophoblasts and syncytiotrophoblasts expressed polySia in the first trimester and downregulated it during the course of pregnancy. PolySia promoted cytotrophoblast migration in an explant model of chorionic villous growth. Removal of this glycan also reduced cytotrophoblast penetration of basement membranes in an in vitro model of invasion. Finally, we showed that polySia was overexpressed in biopsies from patients with gestational trophoblastic diseases, including benign molar pregnancies and malignant choriocarcinomas. These results demonstrated, for the first time, functional roles for polySia during normal human placental development and implicated these unusual oligosaccharides in the unrestrained invasion of trophoblast tumors

An Investigation of the Single and Combined Phthalate Metabolite Effects on Human Chorionic Gonadotropin Expression in Placental Cells.

BackgroundObservational studies have reported associations between maternal phthalate levels and adverse outcomes at birth and in the health of the child. Effects on placental function have been suggested as a biologic basis for these findings.ObjectiveWe evaluated the effects of phthalates on placental function in vitro by measuring relevant candidate genes and proteins.Materials and methodsHuman trophoblast progenitor cells were isolated at 7-14 wk of pregnancy (two female and three male concepti), and villous cytotrophoblast cells (vCTBs) were isolated at 15-20 wk (three female and four male concepti). Cells were cultured in vitro with four phthalate metabolites and their combination at concentrations based on levels found previously in the urine of pregnant women: mono-n-butyl (MnBP, 200 nM), monobenzyl (MBzP, 3μM), mono-2-ethylhexyl (MEHP, 700 nM), and monoethyl (MEP, 1.5μM) phthalates. mRNA levels of CGA, CGB, PPARG, CYP19A1, CYP11A1, PTGS2, EREG, and the intracellular β subunit of human chorionic gonadotropin (hCGβ) and peroxisome proliferator activated receptor γ (PPARγ) were measured in the cellular extracts, and protein levels for four forms of secreted hCG were measured in the conditioned media.ResultsPreviously reported associations between maternal phthalates and placental gene expression were reproduced experimentally: MnBP with CGA, MBzP with CYP11A1, and MEHP with PTGS2. CGB and hCGβ were up-regulated by MBzP. In some cases, there were marked, even opposite, differences in response by sex of the cells. There was evidence of agonism in female cells and antagonism in male cells of PPARγ by simultaneous exposure to multiple phthalates.ConclusionsConcentrations of MnBP, MBzP and MEHP similar to those found in the urine of pregnant women consistently altered hCG and PPARγ expression in primary placental cells. These findings provide evidence for the molecular basis by which phthalates may alter placental function, and they provide a preliminary mechanistic hypothesis for opposite responses by sex. https://doi.org/10.1289/EHP1539

<i>L. monocytogenes</i> infects villous cytotrophoblasts when syncytiotrophoblast is removed.

<p>(<b>A</b>) Placental explant treated with collagenase-containing solution to degrade the syncytiotrophoblast (SYN). Treatment varies; some areas of syncytiotrophoblast remain (e.g. between arrowheads). All villi anchor to form extravillous cytotrophoblasts (EVT). Bar = 1 mm. (<b>B</b>) Left: histological section of enzymatically-treated villus arm, 8 h postinoculation (p.i.). No syncytiotrophoblast remains, permitting infection of both villous cytotrophoblasts (CTB) and extravillous cytotrophoblasts (EVT). Red = E-cadherin (Ecad). Green = <i>L. monocytogenes</i>. Blue = DAPI. Asterisk = Matrigel. Right: Green channel only, color inverted to show <i>L. monocytogenes</i> (solid black) with background fluorescence (faint grey) to show explant outline. Bar = 100 µm. (<b>C</b>) Distribution of infected cell types in enzymatically-treated explants compared to that in untreated explants at 8 h p.i. Here, sCTB refers to villous trophoblasts, which are subsyncytial in untreated explants but exposed after syncytiotrophoblast removal in enzymatically-treated explants. Each condition represents two sections from each of three explants. For syncytiotrophoblast (SYN) and basally accessible syncytiotrophoblast (bSYN), a “cell” was considered to be the area around a single nucleus, roughly the size of a cytotrophoblast. Bars = SEM.</p

<i>L. monocytogenes</i> enters the placenta primarily at invasive villus tips.

<p>(<b>A</b>) Consecutive histological sections of a permissively infected explant at 8 h post-inoculation, frozen and stained for <i>L. monocytogenes</i> (green) and DNA (blue). Left panel and inset 1: red = cytokeratin (CK), expressed by cytotrophoblasts (CTB). In middle panel with insets 2 and 3: red = βHCG (HCG), which primarily stains syncytiotrophoblast (SYN). Subsyncytial cytotrophoblasts (sCTB) underlie the syncytiotrophoblast. Where cytotrophoblasts invade from the villus into the decidua, syncytiotrophoblast breaks, exposing basal surfaces (bSYN). Scattered, isolated bacteria are found mainly in proximal extravillous cytotrophoblasts (EVT). Bar = 100 µm. (<b>B</b>) Distribution of infected cell types in explants infected with ΔActA (top) or 10403S wild type <i>L. monocytogenes</i> (bottom). Each graph represents two sections in each of three explants (average of infected cells counted per explant = 135). For SYN and bSYN, a “cell” was considered to be the area around a single nucleus, roughly the size of a cytotrophoblast. Bars are SEM. (<b>C</b>) Projection of a 3D confocal image showing a whole explant permissively infected with GFP-expressing <i>L. monocytogenes</i> and fixed at 8 h. Anchoring villi (AV), which include invading extravillous cytotrophoblasts, and floating villi (FV), which remain covered with syncytiotrophoblast, are indicated. Red = F-actin. Green = <i>L. monocytogenes</i>. Blue = DNA. Left and top: reconstructed Z series. Because of high F-actin levels in extravillous cytotrophoblasts, bacteria appear yellow. Right and bottom: sum of total GFP intensity over 70 µm Z stack for each X/Y position after background subtraction shows the majority of bacteria are in anchoring villi, in extravillous cytotrophoblasts. Bar = 100 µm.</p

<i>L. monocytogenes</i> grows variably in placental explants.

<p>(<b>A</b>) Intracellular survival of <i>L. monocytogenes</i> in 86 explants from 18 placentas infected with ∼2×10⁶ 10403S (filled circles) or EGDe (open circles) wild type strains for 30 min. Gentamicin was added at 60<i> </i>min to kill extracellular bacteria and maintained in media thereafter. Infection is highly variable and growth is slower than in most cell lines. Bars = median values. (<b>B</b>) Number of internalized bacteria at 2 h post inoculation (p.i.) correlates with the number of anchoring villi in the explant (n = 30 explants, r² = 0.49). (<b>C</b>) Histological section of explant frozen and sliced at 8 h p.i., then stained for <i>L. monocytogenes</i> (green), DNA (blue), and EGFR (red), which stains trophoblast membranes. Bacteria are found in extravillous cytotrophoblasts (EVT) but not syncytiotrophoblast (SYN). Matrigel (MAT) and stroma (STR) are also indicated. Bar = 100 µm.</p