Diverse subtypes and developmental origins of trophoblast giant cells in the mouse placenta

Identification of transcriptional signature change and critical transcription factors involved during the differentiation of mouse trophoblast stem cell into maternal blood vessel associated trophoblast giant cell

The placenta is essential organ for oxygen and nutrient exchange between the mother and the developing fetus. Trophoblast lineage differentiation is closely related to the normal function of the placenta. Trophoblast stem cells (TSCs) can differentiate into all placental trophoblast subtypes and are widely used as in vitro stem cell models to study placental development and trophoblast lineage differentiation. Although extensive research has been conducted on the differentiation of TSCs, the possible parallels between trophoblast giant cells (TGCs) that are differentiated from TSCs in vitro and the various subtypes of TGC lineages in vivo are still poorly understood. In this study, mouse TSCs (mTSCs) were induced to differentiate into TGCs, and our mRNA sequencing (RNA-seq) data revealed that mTSCs and TGCs have distinct transcriptional signatures. We conducted a comparison of mTSCs and TGCs transcriptomes with the published transcriptomes of TGC lineages in murine placenta detected by single-cell RNA-seq and found that mTSCs tend to differentiate into maternal blood vessel-associated TGCs in vitro. Moreover, we identified the transcription factor (TF) ZMAT1, which may be responsible for the differentiation of mTSCs into sinusoid TGCs, and the TFs EGR1 and MITF, which are likely involved in the differentiation of mTSCs into spiral artery-associated TGCs. Thus, our findings provide a valuable resource for the mechanisms of trophoblast lineage differentiation and placental deficiency-associated diseases development.

Cross-Species Insights into Trophoblast Invasion During Placentation Governed by Immune-Featured Trophoblast Cells

Proper development of the placenta, the transient support organ forms after embryo implantation, is essential for a successful pregnancy. However, the regulation of trophoblast invasion, which is most important during placentation, remains largely unknown. Here, rats, mice, and pigs are used as biomedical models, used scRNA-seq to comparatively elucidate the regulatory mechanism of placental trophoblast invasion, and verified it using a human preeclampsia disease model combined with scStereo-seq. A dual-featured type of immune-featured trophoblast (iTrophoblast) is unexpectedly discovered. Interestingly, iTrophoblast only exists in invasive placentas and regulates trophoblast invasion during placentation. In a normally developing placenta, iTrophoblast gradually transforms from an immature state into a functional mature state as it develops. Whereas in the developmentally abnormal preeclamptic placenta, disordered iTrophoblast transformation leads to the accumulation of immature iTrophoblasts, thereby disrupting trophoblast invasion and ultimately leading to the progression of preeclampsia.

Fetal MAVS and type I IFN signaling pathways control ZIKV infection in the placenta and maternal decidua

The contribution of placental immune responses to congenital Zika virus (ZIKV) syndrome remains poorly understood. Here, we leveraged a mouse model of ZIKV infection to identify mechanisms of innate immune restriction exclusively in the fetal compartment of the placenta. ZIKV principally infected mononuclear trophoblasts in the junctional zone, which was limited by mitochondrial antiviral-signaling protein (MAVS) and type I interferon (IFN) signaling mechanisms. Single nuclear RNA sequencing revealed MAVS-dependent expression of IFN-stimulated genes (ISGs) in spongiotrophoblasts but not in other placental cells that use alternate pathways to induce ISGs. ZIKV infection of Ifnar1-/- or Mavs-/- placentas was associated with greater infection of the adjacent immunocompetent decidua, and heterozygous Mavs+/- or Ifnar1+/- dams carrying immunodeficient fetuses sustained greater maternal viremia and tissue infection than dams carrying wild-type fetuses. Thus, MAVS-IFN signaling in the fetus restricts ZIKV infection in junctional zone trophoblasts, which modulates dissemination and outcome for both the fetus and the pregnant mother.

Inhibition of HDAC activity directly reprograms murine embryonic stem cells to trophoblast stem cells

Embryonic stem cells (ESCs) can differentiate into all cell types of the embryonic germ layers. ESCs can also generate totipotent 2C-like cells and trophectodermal cells. However, these latter transitions occur at low frequency due to epigenetic barriers, the nature of which is not fully understood. Here, we show that treating mouse ESCs with sodium butyrate (NaB) increases the population of 2C-like cells and enables direct reprogramming of ESCs into trophoblast stem cells (TSCs) without a transition through a 2C-like state. Mechanistically, NaB inhibits histone deacetylase activities in the LSD1-HDAC1/2 corepressor complex. This increases acetylation levels in the regulatory regions of both 2C- and TSC-specific genes, promoting their expression. In addition, NaB-treated cells acquire the capacity to generate blastocyst-like structures that can develop beyond the implantation stage in vitro and form deciduae in vivo. These results identify how epigenetics restrict the totipotent and trophectoderm fate in mouse ESCs.

Placenta Extracellular Vesicles: Messengers Connecting Maternal and Fetal Systems

The placenta operates during gestation as the primary communication organ between the mother and fetus. It is essential for gas, nutrient exchange, and fetal waste transfer. The placenta also produces a wide range of hormones and other factors that influence maternal physiology, including survival and activity of the corpus luteum of the ovary, but the means whereby the placenta shapes fetal development remain less clear, although the fetal brain is thought to be dependent upon the placenta for factors that play roles in its early differentiation and growth, giving rise to the term "placenta-brain axis". Placental hormones transit via the maternal and fetal vasculature, but smaller placental molecules require protection from fetal and maternal metabolism. Such biomolecules include small RNA, mRNA, peptides, lipids, and catecholamines that include serotonin and dopamine. These compounds presumably shuttle to maternal and fetal systems via protective extracellular vesicles (EVs). Placental EVs (pEVs) and their components, in particular miRNA (miRs), are known to play important roles in regulating maternal systems, such as immune, cardiovascular, and reproductive functions. A scant amount is known about how pEVs affect fetal cells and tissues. The composition of pEVs can be influenced by gestational diseases. This review will provide critical insight into the roles of pEVs as the intermediary link between maternal and fetal systems, the impact of maternal pathologies on pEV cargo contents, and how an understanding of biomolecular changes within pEVs in health and disease might be utilized to design early diagnostic and mitigation strategies to prevent gestational diseases and later offspring disorders.

Single-cell RNA sequencing reveals placental response under environmental stress

The placenta is crucial for fetal development, yet the impact of environmental stressors such as arsenic exposure remains poorly understood. We apply single-cell RNA sequencing to analyze the response of the mouse placenta to arsenic, revealing cell-type-specific gene expression, function, and pathological changes. Notably, the Prap1 gene, which encodes proline-rich acidic protein 1 (PRAP1), is significantly upregulated in 26 placental cell types including various trophoblast cells. Our study shows a female-biased increase in PRAP1 in response to arsenic and localizes it in the placenta. In vitro and ex vivo experiments confirm PRAP1 upregulation following arsenic treatment and demonstrate that recombinant PRAP1 protein reduces arsenic-induced cytotoxicity and downregulates cell cycle pathways in human trophoblast cells. Moreover, PRAP1 knockdown differentially affects cell cycle processes, proliferation, and cell death depending on the presence of arsenic. Our findings provide insights into the placental response to environmental stress, offering potential preventative and therapeutic approaches for environment-related adverse outcomes in mothers and children.

Placental glycosylation senses the anti-angiogenic milieu induced by human sFLT1 during pregnancy

Abnormal placental angiogenesis during gestation resulting from high levels of anti-angiogenic factors, soluble fms-like tyrosine kinase-1 (sFLT1) and soluble endoglin, has been implicated in the progression of preeclampsia (PE). This heterogeneous syndrome (defined by hypertension with or without proteinuria after 20 weeks of pregnancy) remains a major global health burden with long-term consequences for both mothers and child. Previously, we showed that in vivo systemic human (hsFLT1) overexpression led to reduced placental efficiency and PE-like syndrome in mice. Galectins (gal-1, -3 and -9) are critical determinants of vascular adaptation to pregnancy and dysregulation of the galectin-glycan circuits is associated with the development of this life-threatening disease. In this study, we assessed the galectin-glycan networks at the maternal-fetal interface associated with the hsFLT1-induced PE in mice. We observed an increase on the maternal gal-1 expression in the decidua and junctional zone layers of the placenta derived from hs FLT1high pregnancies. In contrast, placental gal-3 and gal-9 expression were not sensitive to the hsFLT1 overexpression. In addition, O- and N-linked glycan expression, poly-LacNAc sequences and terminal sialylation were down-regulated in hsFLT1 high placentas. Thus, the gal-1-glycan axis appear to play an important role counteracting the anti-angiogenic status caused by sFLT1, becoming critical for vascular adaptation at the maternal-fetal interface.

A Single Trophoblast Layer Acts as the Gatekeeper at the Endothelial-Hematopoietic Crossroad in the Placenta

During embryonic development the placental vasculature acts as a major hematopoietic niche, where endothelial to hematopoietic transition ensures emergence of hematopoietic stem cells (HSCs). However, the molecular mechanisms that regulate the placental hematoendothelial niche are poorly understood. Using a parietal trophoblast giant cell (TGC)-specific knockout mouse model and single-cell RNA-sequencing, we show that the paracrine factors secreted by the TGCs are critical in the development of this niche. Disruptions in the TGC-specific paracrine signaling leads to the loss of HSC population and the concomitant expansion of a KDR+/DLL4+/PROM1+ hematoendothelial cell-population in the placenta. Combining single-cell transcriptomics and receptor-ligand pair analyses, we also define the parietal TGC-dependent paracrine signaling network and identify Integrin signaling as a fundamental regulator of this process. Our study elucidates novel mechanisms by which non-autonomous signaling from the primary parietal TGCs maintain the delicate placental hematopoietic-angiogenic balance and ensures embryonic and extraembryonic development.

Vitamin C inactivates c-Jun N-terminal kinase to stabilize heart and neural crest derivatives expressed 1 (Hand1) in regulating placentation and maintenance of pregnancy

Vitamin C (VC) serves as a pivotal nutrient for anti-oxidation process, metabolic responses, and stem cell differentiation. However, its precise contribution to placenta development and gestation remains obscure. Here, we demonstrated that physiological levels of VC act to stabilize Hand1, a key bHLH transcription factor vital for the development trajectory of trophoblast giant cell (TGC) lineages, thereby promoting the differentiation of trophoblast stem cells into TGC. Specifically, VC administration inactivated c-Jun N-terminal kinase (JNK) signaling, which directly phosphorylates Hand1 at Ser48, triggering the proteasomal degradation of Hand1. Conversely, a loss-of-function mutation at Ser48 on Hand1 not only significantly diminished both intrinsic and VC-induced stabilization of Hand1 but also underscored the indispensability of this residue. Noteworthy, the insufficiency of VC led to severe defects in the differentiation of diverse TGC subtypes and the formation of labyrinth's vascular network in rodent placentas, resulting in failure of maintenance of pregnancy. Importantly, VC deficiency, lentiviral knockdown of JNK or overexpression of Hand1 mutants in trophectoderm substantially affected the differentiation of primary and secondary TGC in E8.5 mouse placentas. Thus, these findings uncover the significance of JNK inactivation and consequential stabilization of Hand1 as a hitherto uncharacterized mechanism controlling VC-mediated placentation and perhaps maintenance of pregnancy.

Novel high throughput screen reports that benzo(a)pyrene overrides mouse trophoblast stem cell multipotency, inducing SAPK activity, HAND1 and differentiated trophoblast giant cells

INTRODUCTION

Cultured mouse trophoblast stem cells (mTSC) maintain proliferation/normal stemness (NS) under FGF4, which when removed, causes normal differentiation (ND). Hypoxic, or hyperosmotic stress forces trophoblast giant cells (TGC) differentiate. Hypoxic, hyperosmotic, and genotoxic benzo(a)pyrene (BaP), which is found in tobacco smoke, force down-regulation of inhibitor of differentiation (Id)2, enabling TGC differentiation. Hypoxic and hyperosmotic stress induce TGC by SAPK-dependent HAND1 increase. Here we test whether BaP forces mTSC-to-TGC while inducing SAPK and HAND1.

METHODS

Hand1 and SAPK activity were assayed by immunoblot, mTSC-to-TGC growth and differentiation were assayed at Tfinal after 72hr exposure of BaP, NS, ND, Retinoic acid (RA), or sorbitol. Nuclear-stained cells were micrographed automatically by a live imager, and assayed by ImageJ/FIJI, Biotek Gen 5, AIVIA proprietary artificial intelligence (AI) software or open source, CellPose artificial intelligence/AI software.

RESULTS

BaP (0.05-1μM) activated SAPK and HAND1 without diminishing growth. TSC-to-TGC differentiation was assayed with increasingly accuracy for 2-4 N cycling nuclei and >4 N differentiating TGC nuclei, using ImageJ/FIJI, Gen 5, AIVIA, or CellPose AI software. The AIVIA and Cellpose AI software matches human accuracy. The lowest BaP effects on SAPK activation/HAND1 increase are >10-fold more sensitive than similar effects for mESC. RA induces 44-47% 1st lineage TGC differentiation, but the same RA dose induces only 1% 1st lineage mESC differentiation.

DISCUSSION

First, these pilot data suggest that mTSC can be used in high throughput screens (HTS) to predict toxicant exposures that force TGC differentiation. Second, mTSC differentiated more cells than mESC for similar stress exposures, Third, open source AI can replace human micrograph quantitation and enable a miscarriage-predicting HTS.

The influence of high-speed train's transient pressure change on the fetal growth of SD rats

This research aims to explore the influence of transient pressure fluctuation inside high-speed trains passing throught tunnels on the fetal growth of Sprague - Dawley (SD) rats. A pressure variation simulation system was designed and exposure experiments were performed on SD rats. Forty-eight SD rats are divided into two control groups and two experimental groups, and are then exposed to transient pressure alternation (-1200 Pa ~1200 Pa) from gestation day 0 to gestation day 5 (GD 0-5). Fetal growth and development indicators on GD12 and GD18 between experimental and control groups were compared. Statistical results showed that, compared to the control group, the key indicators in the experimental group, including placental weight, placental diameter, fetal weight, and crown-to-rump length have decreased by 4.77%, 3.38%, 6.20%, and 3.75% respectively on GD18. The findings imply that the pressure fluctuation environment of high-speed trains has potential effects on the fetal growth of SD rats.

Lipid nanoparticle structure and delivery route during pregnancy dictate mRNA potency, immunogenicity, and maternal and fetal outcomes

Treating pregnancy-related disorders is exceptionally challenging because the threat of maternal and/or fetal toxicity discourages the use of existing medications and hinders new drug development. One potential solution is the use of lipid nanoparticle (LNP) RNA therapies, given their proven efficacy, tolerability, and lack of fetal accumulation. Here, we describe LNPs for efficacious mRNA delivery to maternal organs in pregnant mice via several routes of administration. In the placenta, our lead LNP transfected trophoblasts, endothelial cells, and immune cells, with efficacy being structurally dependent on the ionizable lipid polyamine headgroup. Next, we show that LNP-induced maternal inflammatory responses affect mRNA expression in the maternal compartment and hinder neonatal development. Specifically, pro-inflammatory LNP structures and routes of administration curtailed efficacy in maternal lymphoid organs in an IL-1β-dependent manner. Further, immunogenic LNPs provoked the infiltration of adaptive immune cells into the placenta and restricted pup growth after birth. Together, our results provide mechanism-based structural guidance on the design of potent LNPs for safe use during pregnancy.

The GATA transcriptional program dictates cell fate equilibrium to establish the maternal-fetal exchange interface and fetal development

The placenta establishes a maternal-fetal exchange interface to transport nutrients and gases between the mother and the fetus. Establishment of this exchange interface relies on the development of multinucleated syncytiotrophoblasts (SynT) from trophoblast progenitors, and defect in SynT development often leads to pregnancy failure and impaired embryonic development. Here, we show that mouse embryos with conditional deletion of transcription factors GATA2 and GATA3 in labyrinth trophoblast progenitors (LaTPs) have underdeveloped placenta and die by ~embryonic day 9.5. Single-cell RNA sequencing analysis revealed excessive accumulation of multipotent LaTPs upon conditional deletion of GATA factors. The GATA factor-deleted multipotent progenitors were unable to differentiate into matured SynTs. We also show that the GATA factor-mediated priming of trophoblast progenitors for SynT differentiation is a conserved event during human placentation. Loss of either GATA2 or GATA3 in cytotrophoblast-derived human trophoblast stem cells (human TSCs) drastically inhibits SynT differentiation potential. Identification of GATA2 and GATA3 target genes along with comparative bioinformatics analyses revealed that GATA factors directly regulate hundreds of common genes in human TSCs, including genes that are essential for SynT development and implicated in preeclampsia and fetal growth retardation. Thus, our study uncovers a conserved molecular mechanism, in which coordinated function of GATA2 and GATA3 promotes trophoblast progenitor-to-SynT commitment, ensuring establishment of the maternal-fetal exchange interface.

Extracellular vesicles from mouse trophoblast cells: Effects on neural progenitor cells and potential participants in the placenta-brain axis†

The fetal brain of the mouse is thought to be dependent upon the placenta as a source of serotonin (5-hydroxytryptamine; 5-HT) and other factors. How factors reach the developing brain remains uncertain but are postulated here to be part of the cargo carried by placental extracellular vesicles (EV). We have analyzed the protein, catecholamine, and small RNA content of EV from mouse trophoblast stem cells (TSC) and TSC differentiated into parietal trophoblast giant cells (pTGC), potential primary purveyors of 5-HT. Current studies examined how exposure of mouse neural progenitor cells (NPC) to EV from either TSC or pTGC affect their transcriptome profiles. The EV from trophoblast cells contained relatively high amounts of 5-HT, as well as dopamine and norepinephrine, but there were no significant differences between EV derived from pTGC and from TSC. Content of miRNA and small nucleolar (sno)RNA, however, did differ according to EV source, and snoRNA were upregulated in EV from pTGC. The primary inferred targets of the microRNA (miRNA) from both pTGC and TSC were mRNA enriched in the fetal brain. NPC readily internalized EV, leading to changes in their transcriptome profiles. Transcripts regulated were mainly ones enriched in neural tissues. The transcripts in EV-treated NPC that demonstrated a likely complementarity with miRNA in EV were mainly up- rather than downregulated, with functions linked to neuronal processes. Our results are consistent with placenta-derived EV providing direct support for fetal brain development and being an integral part of the placenta-brain axis.

Overexpression of Human sFLT1 in the Spongiotrophoblast Is Sufficient to Induce Placental Dysfunction and Fetal Growth Restriction in Transgenic Mice

Preeclampsia (PE) is characterized by maternal hypertension and placental dysfunction, often leading to fetal growth restriction (FGR). It is associated with an overexpression of the anti-angiogenic sFLT1 protein, which originates from the placenta and serves as a clinical biomarker to predict PE. To analyze the impact of sFLT1 on placental function and fetal growth, we generated transgenic mice with placenta-specific human sFLT1 (hsFLT1) overexpression. Immunohistochemical, morphometrical, and molecular analyses of the placentas on 14.5 dpc and 18.5 dpc were performed with a focus on angiogenesis, nutrient transport, and inflammation. Additionally, fetal development upon placental hsFLT1 overexpression was investigated. Dams exhibited a mild increase in serum hsFLT1 levels upon placental hsFLT1 expression and revealed growth restriction of the fetuses in a sex-specific manner. Male FGR fetuses expressed higher amounts of placental hsFLT1 mRNA compared to females. FGR placentas displayed an altered morphology, hallmarked by an increase in the spongiotrophoblast layer and changes in labyrinthine vascularization. Further, FGR placentas showed a significant reduction in placental glycogen storage and nutrient transporter expression. Moreover, signs of hypoxia and inflammation were observed in FGR placentas. The transgenic spongiotrophoblast-specific hsFLT1 mouse line demonstrates that low hsFLT1 serum levels are sufficient to induce significant alterations in fetal and placental development in a sex-specific manner.

Murine trophoblast organoids as a model for trophoblast development and CRISPR-Cas9 screening

The placenta becomes one of the most diversified organs during placental mammal radiation. The main in vitro model for studying mouse trophoblast development is the 2D differentiation model of trophoblast stem cells, which is highly skewed to certain lineages and thus hampers systematic screens. Here, we established culture conditions for the establishment, maintenance, and differentiation of murine trophoblast organoids. Murine trophoblast organoids under the maintenance condition contain stem cell-like populations, whereas differentiated organoids possess various trophoblasts resembling placental ones in vivo. Ablation of Nubpl or Gcm1 in trophoblast organoids recapitulated their deficiency phenotypes in vivo, suggesting that those organoids are valid in vitro models for trophoblast development. Importantly, we performed an efficient CRISPR-Cas9 screening in mouse trophoblast organoids using a focused sgRNA (single guide RNA) library targeting G protein-coupled receptors. Together, our results establish an organoid model to investigate mouse trophoblast development and a practicable approach to performing forward screening in trophoblast lineages.

Epigenetic control of the imprinted growth regulator Cdkn1c in cadmium-induced placental dysfunction

Cadmium (Cd) is a toxic metal ubiquitous in the environment. In utero, Cd is inefficiently transported to the foetus but causes foetal growth restriction (FGR), likely through impairment of the placenta where Cd accumulates. However, the underlying molecular mechanisms are poorly understood. Cd can modulate the expression of imprinted genes, defined by their transcription from one parental allele, which play critical roles in placental and foetal growth. The expression of imprinted genes is governed by DNA methylation at Imprinting Control Regions (ICRs), which are susceptible to environmental perturbation. The imprinted gene Cdkn1c/CDKN1C is a major regulator of placental development, is implicated in FGR, and shows increased expression in response to Cd exposure in mice. Here, we use a hybrid mouse model of in utero Cd exposure to determine if the increase in placental Cdkn1c expression is caused by changes to ICR DNA methylation and loss of imprinting (LOI). Consistent with prior studies, Cd causes FGR and impacts placental structure and Cdkn1c expression at late gestation. Using polymorphisms to distinguish parental alleles, we demonstrate that increased Cdkn1c expression is not driven by changes to DNA methylation or LOI. We show that Cdkn1c is expressed primarily in the placental labyrinth which is proportionally increased in size in response to Cd. We conclude that the Cd-associated increase in Cdkn1c expression can be fully explained by alterations to placental structure. These results have implications for understanding mechanisms of Cd-induced placental dysfunction and, more broadly, for the study of FGR associated with increased Cdkn1c/CDKN1C expression.

Stromal cells-specific retinoic acid determines parturition timing at single-cell and spatial-temporal resolution

The underlying mechanisms governing parturition remain largely elusive due to limited knowledge of parturition preparation and initiation. Accumulated evidences indicate that maternal decidua plays a critical role in parturition initiation. To comprehensively decrypt the cell heterogeneity in decidua approaching parturition, we investigate the roles of various cell types in mouse decidua process and reveal previously unappreciated insights in parturition initiation utilizing single-cell RNA sequencing (scRNA-seq). We enumerate the cell types in decidua and identity five different stromal cells populations and one decidualized stromal cells. Furthermore, our study unravels that stromal cells prepare for parturition by regulating local retinol acid (RA) synthesis. RA supplement decreases expression of extracellular matrix-related genes in vitro and accelerates the timing of parturition in vivo. Collectively, the discovery of contribution of stromal cells in parturition expands current knowledge about parturition and opens up avenues for the intervention of preterm birth (PTB).

Involvement of metalloproteinase and nitric oxide synthase/nitric oxide mechanisms in early decidual angiogenesis-vascularization of normal and experimental pathological mouse placenta related to maternal alcohol exposure

Successful pregnancy for optimal fetal growth requires adequate early angiogenesis and remodeling of decidual spiral arterioles during placentation. Prior to the initiation of invasion and endothelial replacement by trophoblasts, interactions between decidual stromal cells and maternal leukocytes, such as uterine natural killer cells and macrophages, play crucial roles in the processes of early maternal vascularization, such as proliferation, apoptosis, migration, differentiation, and matrix and vessel remodeling. These placental angiogenic events are highly dependent on the coordination of several mechanisms at the early maternal-fetal interface, and one of them is the expression and activity of matrix metalloproteinases (MMPs) and endothelial nitric oxide synthases (NOSs). Inadequate balances of MMPs and nitric oxide (NO) are involved in several placentopathies and pregnancy complications. Since alcohol consumption during gestation can affect fetal growth associated with abnormal placental development, recently, we showed, in a mouse model, that perigestational alcohol consumption up to organogenesis induces fetal malformations related to deficient growth and vascular morphogenesis of the placenta at term. In this review, we summarize the current knowledge of the early processes of maternal vascularization that lead to the formation of the definitive placenta and the roles of angiogenic MMP and NOS/NO mechanisms during normal and altered early gestation in mice. Then, we propose hypothetical defective decidual cellular and MMP and NOS/NO mechanisms involved in abnormal decidual vascularization induced by perigestational alcohol consumption in an experimental mouse model. This review highlights the important roles of decidual cells and their MMP and NOS balances in the physiological and pathophysiological early maternal angiogenesis-vascularization during placentation in mice.

Trophoblast Differentiation: Mechanisms and Implications for Pregnancy Complications

Placental development is a tightly controlled event, in which cell expansion from the trophectoderm occurs in a spatiotemporal manner. Proper trophoblast differentiation is crucial to the vitality of this gestational organ. Obstructions to its development can lead to pregnancy complications, such as preeclampsia, fetal growth restriction, and preterm birth, posing severe health risks to both the mother and offspring. Currently, the only known treatment strategy for these complications is delivery, making it an important area of research. The aim of this review was to summarize the known information on the development and mechanistic regulation of trophoblast differentiation and highlight the similarities in these processes between the human and mouse placenta. Additionally, the known biomarkers for each cell type were compiled to aid in the analysis of sequencing technologies.

Fetal manipulation of maternal metabolism is a critical function of the imprinted Igf2 gene

Maternal-offspring interactions in mammals involve both cooperation and conflict. The fetus has evolved ways to manipulate maternal physiology to enhance placental nutrient transfer, but the mechanisms involved remain unclear. The imprinted Igf2 gene is highly expressed in murine placental endocrine cells. Here, we show that Igf2 deletion in these cells impairs placental endocrine signaling to the mother, without affecting placental morphology. Igf2 controls placental hormone production, including prolactins, and is crucial to establish pregnancy-related insulin resistance and to partition nutrients to the fetus. Consequently, fetuses lacking placental endocrine Igf2 are growth restricted and hypoglycemic. Mechanistically, Igf2 controls protein synthesis and cellular energy homeostasis, actions dependent on the placental endocrine cell type. Igf2 loss also has additional long-lasting effects on offspring metabolism in adulthood. Our study provides compelling evidence for an intrinsic fetal manipulation system operating in placenta that modifies maternal metabolism and fetal resource allocation, with long-term consequences for offspring metabolic health.

LncRNA Tuna is activated in cadmium-induced placental insufficiency and drives the NRF2-mediated oxidative stress response

Cadmium (Cd) is a toxic heavy metal found throughout the environment and one of the top ten toxicants of major public health concern identified by the World Health Organization. In utero Cd exposure causes fetal growth restriction, malformation, and spontaneous abortion; however, the mechanisms by which Cd impacts these outcomes are poorly understood. Cd accumulates in the placenta, suggesting that these negative outcomes may be a consequence of disrupted placental function and placental insufficiency. To understand the impact of Cd on gene expression within the placenta, we developed a mouse model of Cd-induced fetal growth restriction through maternal consumption of CdCl2 and performed RNA-seq on control and CdCl2 exposed placentae. The top differentially expressed transcript was the Tcl1 Upstream Neuron-Associated (Tuna) long non-coding RNA, which was upregulated over 25-fold in CdCl2 exposed placentae. Tuna has been shown to be critical for neural stem cell differentiation. However, within the placenta, there is no evidence that Tuna is normally expressed or functional at any developmental stage. To determine the spatial expression of Cd-activated Tuna within the placenta, we used in situ hybridization as well as placental layer-specific RNA isolation and analysis. Both methods confirmed the absence of Tuna expression in control samples and determined that Cd-induced Tuna expression is specific to the junctional zone. Since many lncRNAs regulate gene expression, we hypothesized that Tuna forms part of the mechanism of Cd-induced transcriptomic changes. To test this, we over-expressed Tuna in cultured choriocarcinoma cells and compared gene expression profiles to those of control and CdCl2 exposed cells. We demonstrate significant overlap between genes activated by Tuna overexpression and genes activated by CdCl2 exposure, with enrichment in the NRF2-mediated oxidative stress response. Herein we analyze the NRF2 pathway and show that Tuna increases NRF2/NRF2 both at the transcript and protein levels. Tuna drives increased NRF2 target gene expression, a result that is abrogated with the use of an NRF2 inhibitor, confirming that Tuna activates oxidative stress response genes through this pathway. This work identifies the lncRNA Tuna as a potential novel player in Cd-induced placental insufficiency.

Myc promotes polyploidy in murine trophoblast cells and suppresses senescence

The placenta is essential for reproductive success. The murine placenta includes polyploid giant cells that are crucial for its function. Polyploidy occurs broadly in nature but its regulators and significance in the placenta are unknown. We have discovered that many murine placental cell types are polyploid and have identified factors that license polyploidy using single-cell RNA sequencing. Myc is a key regulator of polyploidy and placental development, and is required for multiple rounds of DNA replication, likely via endocycles, in trophoblast giant cells. Furthermore, MYC supports the expression of DNA replication and nucleotide biosynthesis genes along with ribosomal RNA. Increased DNA damage and senescence occur in trophoblast giant cells without Myc, accompanied by senescence in the neighboring maternal decidua. These data reveal Myc is essential for polyploidy to support normal placental development, thereby preventing premature senescence. Our study, combined with available literature, suggests that Myc is an evolutionarily conserved regulator of polyploidy.

Animal models of the placenta accreta spectrum: current status and further perspectives

Placenta accreta spectrum disorder (PAS) is a kind of disease of placentation defined as abnormal trophoblast invasion of part or all of the placenta into the myometrium, even penetrating the uterus. Decidual deficiency, abnormal vascular remodeling in the maternal-fetal interface, and excessive invasion by extravillous trophoblast (EVT) cells contribute to its onset. However, the mechanisms and signaling pathways underlying such phenotypes are not fully understood, partly due to the lack of suitable experimental animal models. Appropriate animal models will facilitate the comprehensive and systematic elucidation of the pathogenesis of PAS. Due to the remarkably similar functional placental villous units and hemochorial placentation to humans, the current animal models of PAS are based on mice. There are various mouse models induced by uterine surgery to simulate different phenotypes of PAS, such as excessive invasion of EVT or immune disturbance at the maternal-fetal interface, which could define the pathological mechanism of PAS from the perspective of the "soil." Additionally, genetically modified mouse models could be used to study PAS, which is helpful to exploring the pathogenesis of PAS from the perspectives of both "soil" and "seed," respectively. This review details early placental development in mice, with a focus on the approaches of PAS modeling. Additionally, the strengths, limitations and the applicability of each strategy and further perspectives are summarized to provide the theoretical foundation for researchers to select appropriate animal models for various research purposes. This will help better determine the pathogenesis of PAS and even promote possible therapy.

The Fgf/Erf/NCoR1/2 repressive axis controls trophoblast cell fate

Placental development relies on coordinated cell fate decisions governed by signalling inputs. However, little is known about how signalling cues are transformed into repressive mechanisms triggering lineage-specific transcriptional signatures. Here, we demonstrate that upon inhibition of the Fgf/Erk pathway in mouse trophoblast stem cells (TSCs), the Ets2 repressor factor (Erf) interacts with the Nuclear Receptor Co-Repressor Complex 1 and 2 (NCoR1/2) and recruits it to key trophoblast genes. Genetic ablation of Erf or Tbl1x (a component of the NCoR1/2 complex) abrogates the Erf/NCoR1/2 interaction. This leads to mis-expression of Erf/NCoR1/2 target genes, resulting in a TSC differentiation defect. Mechanistically, Erf regulates expression of these genes by recruiting the NCoR1/2 complex and decommissioning their H3K27ac-dependent enhancers. Our findings uncover how the Fgf/Erf/NCoR1/2 repressive axis governs cell fate and placental development, providing a paradigm for Fgf-mediated transcriptional control.

A differentiation roadmap of murine placentation at single-cell resolution

The placenta is one of the most important yet least understood organs. Due to the limitations of conventional research approaches, we are still far from a comprehensive understanding of mouse placentation, especially regarding the differentiation of trophoblast lineages at the early developmental stage. To decipher cell compositions and developmental processes, we systematically profile the single-cell transcriptomes of trophoblast cells from extraembryonic tissues (embryonic day 7.5 (E7.5) and E8.5) and placentae (E9.5-E14.5) at one-day intervals. We identify distinct trophoblast cell types during mouse placentation, including unreported progenitor cells and intermediate precursor cells. An updated differentiation roadmap of mouse trophoblast lineages is presented following systematic transcriptome analyses. Based on transcriptomic regulatory network inference, we specify transcription factors responsible for the regulation of dynamic developmental processes during lineage diversification. We map lineage differentiation trajectories and find that sinusoid trophoblast giant cells arise from the subpopulation of ectoplacental cone cells. We provide a comprehensive single-cell data resource to shed light on future mechanistic studies of the gene regulatory networks governing hemochorial placentation.

Effects of Stevioside on the Expressions of GLUT 1, GLUT 3, and GLUT 4 Proteins in Diabetic Rat Placenta

The placenta provides maternal-fetal nutrient transport. The primary source of energy for fetus development is glucose and maternal-fetal glucose transport occurs through glucose transporters (GLUTs). Stevioside, a component of Stevia rebaudiana Bertoni, is used for medicinal and commercial purposes. We aim to determine the effects of stevioside on GLUT 1, GLUT 3, and GLUT 4 proteins expressions in diabetic rat placentas. The rats are divided into four groups. A single dose of streptozotocin (STZ) is administered to form the diabetic groups. Pregnant rats receive stevioside to form the stevioside and diabetic + stevioside groups. According to immunohistochemistry results, GLUT 1 protein is found in both the labyrinth and junctional zones. GLUT 3 protein is limited in the labyrinth zone. GLUT 4 protein is detected in trophoblast cells. According to Western blotting results, on the 15th and 20th days of pregnancy, there is no difference in the expression of GLUT 1 protein between groups. On the 20th day of pregnancy, the expression of GLUT 3 protein in the diabetic group is statistically higher compared to the control group. On the 15th day and 20th day of pregnancy, the expression of GLUT 4 protein in the diabetic group is statistically lower compared to the control group. Insulin levels in blood samples derived from rat abdominal aorta are determined by the ELISA method. According to the ELISA results, there is no difference in insulin protein concentration between groups. Stevioside treatment reduces GLUT 1 protein expression under diabetic conditions.

Epidermal growth factor represses differentiation of mouse trophoblast stem cells into spongiotrophoblast cells via epidermal growth factor receptor

The mouse placenta is composed of three different trophoblast layers that are occupied by particular trophoblast subtypes to maintain placental function and pregnancy. Accurate control of trophoblast differentiation is required for proper placental function; however, the molecular mechanisms underlying cell fate decisions in trophoblast stem cells remain poorly understood. Epidermal growth factor (EGF) signaling is involved in multiple biological processes including cell survival, proliferation, and differentiation. The effect of EGF on trophoblast function has been reported in various species; however, the role of EGF signaling in mouse trophoblast specification remains unclear. In this study, we aimed to elucidate the role of EGF signaling in mouse trophoblast differentiation using mouse trophoblast stem cells (mTSCs) in an in vitro culture system. EGF stimulation at the early stage of differentiation repressed mTSC differentiation into spongiotrophoblast cells (SpT). Gene deletion and inhibitor experiments showed that the effect of EGF exposure went through epidermal growth factor receptor (Egfr) activity in mTSCs. EGF stimuli induced acute downstream activation of MAPK/ERK, PI3K/AKT, and JNK pathways, and inhibition of the MAPK/ERK pathway, but not others, alleviated EGF-mediated repression of SpT differentiation. Moreover, expression of Mash2, a master regulator of SpT differentiation, was repressed by EGF stimulation, and MAPK/ERK inhibition counteracted this repression. The Mash2 overexpression recovered SpT marker expression, indicating that the decrease in Mash2 expression was due to abnormal SpT differentiation in EGF-treated mTSCs. Our findings suggest that the EGF-Egfr-MAPK/ERK-Mash2 axis is a core regulatory mechanism for the EGF-mediated repression of SpT differentiation.

Trans-differentiation of trophoblast stem cells: implications in placental biology

Trophoblast invasion is a hallmark of hemochorial placentation. Invasive trophoblast cells replace the endothelial cells of uterine spiral arteries. The mechanism by which the invasive trophoblast cells acquire this phenotype is unknown. Here, we demonstrate that, during differentiation, a small population of trophoblast stem (TS) cells trans-differentiate into a hybrid cell type expressing markers of both trophoblast (TC) and endothelial (EC) cells. In addition, a compendium of EC-specific genes was found to be associated with TS cell differentiation. Using functional annotation, these genes were categorized into angiogenesis, cell adhesion molecules, and apoptosis-related genes. HES1 repressed transcription of EC genes in TS cells. Interestingly, differentiated TCs secrete TRAIL, but its receptor DR4 is expressed only in ECs and not in TCs. TRAIL induced apoptosis in EC but not in TC. Co-culture of ECs with TC induced apoptosis in ECs via extrinsic apoptotic pathway. These results highlight that (a) TS cells possess the potential to trans-differentiate into "trophendothelial" phenotype, regulated by HES1 and (b) trophoblast differentiation-induced TRAIL secretion directs preferential demise of ECs located in their vicinity.

Estrogen Actions in Placental Vascular Morphogenesis and Spiral Artery Remodeling: A Comparative View between Humans and Mice

Estrogens, mainly 17β-estradiol (E2), play a critical role in reproductive organogenesis, ovulation, and fertility via estrogen receptors. E2 is also a well-known regulator of utero-placental vascular development and blood-flow dynamics throughout gestation. Mouse and human placentas possess strikingly different morphological configurations that confer important reproductive advantages. However, the functional interplay between fetal and maternal vasculature remains similar in both species. In this review, we briefly describe the structural and functional characteristics, as well as the development, of mouse and human placentas. In addition, we summarize the current knowledge regarding estrogen actions during utero-placental vascular morphogenesis, which includes uterine angiogenesis, the control of trophoblast behavior, spiral artery remodeling, and hemodynamic adaptation throughout pregnancy, in both mice and humans. Finally, the estrogens that are present in abnormal placentation are also mentioned. Overall, this review highlights the importance of the actions of estrogens in the physiology and pathophysiology of placental vascular development.

Paternal obesity induces epigenetic aberrations and gene expression changes in placenta and fetus

Paternal epigenome regulates placental and fetal growth. However, the effect of paternal obesity on placenta and its subsequent effect on the fetus via sperm remains unknown. We previously discovered abnormal methylation of imprinted genes involved in placental and fetal development in the spermatozoa of obese rats. In the present study, elaborate epigenetic characterization of sperm, placenta, and fetus was performed. For 16 weeks, male rats were fed either control or a high-fat diet. Following mating studies, sperm, placenta, and fetal tissue were collected. Significant changes were observed in placental weights, morphology, and cell populations. Methylation status of imprinted genes-Igf2, Peg3, Cdkn1c, and Gnas in spermatozoa, correlated with their expression in the placenta and fetus. Placental DNA methylating enzymes and 5-methylCytosine levels increased. Furthermore, in spermatozoa, DNA methylation of a few genes involved in pathways associated with placental endocrine function-gonadotropin-releasing hormone, prolactin, estrogen, and vascular endothelial growth factor, correlated with their expression in placenta and fetus. Changes in histone-modifying enzymes were also observed in the placenta. Histone marks H3K4me3, H3K9me3, and H4ac were downregulated, while H3K27me3 and H3ac were upregulated in placentas derived from obese male rats. This study shows that obesity-related changes in sperm methylome translate into abnormal expression in the F1-placenta fathered by the obese male, presumably affecting placental and fetal development.

Are there foetal extracellular vesicles in maternal blood? Prospects for diagnostic biomarker discovery

Prenatal diagnosis of congenital disease improves clinical outcomes; however, as many as 50% of congenital heart disease cases are missed by current ultrasound screening methods. This indicates a need for improved screening technology. Extracellular vesicles (EVs) have attracted enormous interest in recent years for their potential in diagnostics. EVs mediate endocrine signalling in health and disease and are known to regulate aspects of embryonic development. Here, we critically evaluate recent evidence suggesting that EVs released from the foetus are able to cross the placenta and enter the maternal circulation. Furthermore, EVs from the mother appear to be transported in the reverse direction, whilst the placenta itself acts as a source of EVs. Experimental work utilising rodent models employing either transgenically encoded reporters or application of fluorescent tracking dyes provide convincing evidence of foetal-maternal crosstalk. This is supported by clinical data demonstrating expression of placental-origin EVs in maternal blood, as well as limited evidence for the presence of foetal-origin EVs. Together, this work raises the possibility that foetal EVs present in maternal blood could be used for the diagnosis of congenital disease. We discuss the challenges faced by researchers in translating these basic science findings into a clinical non-invasive prenatal test.

Perturbation of placental protein glycosylation by endoplasmic reticulum stress promotes maladaptation of maternal hepatic glucose metabolism

Placental hormones orchestrate maternal metabolic adaptations to support pregnancy. We hypothesized that placental ER stress, which characterizes early-onset pre-eclampsia (ePE), compromises glycosylation, reducing hormone bioactivity and these maladaptations predispose the mother to metabolic disease in later life. We demonstrate ER stress reduces the complexity and sialylation of trophoblast protein N-glycosylation, while aberrant glycosylation of vascular endothelial growth factor reduced its bioactivity. ER stress alters the expression of 66 of the 146 genes annotated with "protein glycosylation" and reduces the expression of sialyltransferases. Using mouse placental explants, we show ER stress promotes the secretion of mis-glycosylated glycoproteins. Pregnant mice carrying placentas with junctional zone-specific ER stress have reduced blood glucose, anomalous hepatic glucose metabolism, increased cellular stress and elevated DNA methyltransferase 3A. Using pregnancy-specific glycoproteins as a readout, we also demonstrate aberrant glycosylation of placental proteins in women with ePE, thus providing a mechanistic link between ePE and subsequent maternal metabolic disorders.

The trophoblast giant cells of cricetid rodents

Giant cells are a prominent feature of placentation in cricetid rodents. Once thought to be maternal in origin, they are now known to be trophoblast giant cells (TGCs). The large size of cricetid TGCs and their nuclei reflects a high degree of polyploidy. While some TGCs are found at fixed locations, others migrate throughout the placenta and deep into the uterus where they sometimes survive postpartum. Herein, we review the distribution of TGCs in the placenta of cricetids, including our own data from the New World subfamily Sigmodontinae, and attempt a comparison between the TGCs of cricetid and murid rodents. In both families, parietal TGCs are found in the parietal yolk sac and as a layer between the junctional zone and decidua. In cricetids alone, large numbers of TGCs, likely from the same lineage, accumulate at the edge of the placental disk. Common to murids and cricetids is a haemotrichorial placental barrier where the maternal-facing layer consists of cytotrophoblasts characterized as sinusoidal TGCs. The maternal channels of the labyrinth are supplied by trophoblast-lined canals. Whereas in the mouse these are lined largely by canal TGCs, in cricetids canal TGCs are interspersed with syncytiotrophoblast. Transformation of the uterine spiral arteries occurs in both murids and cricetids and spiral artery TGCs line segments of the arteries that have lost their endothelium and smooth muscle. Since polyploidization of TGCs can amplify selective genomic regions required for specific functions, we argue that the TGCs of cricetids deserve further study and suggest avenues for future research.

A chemically defined system supports two distinct types of stem cell from a single blastocyst and their self-assembly to generate blastoid

The pluripotent stem cells exist in a narrow window during early development and its derivation depends on intrinsic and extrinsic growth signalling in vitro. It has remained challenging to derive two or three distinct cell lines that are representative of blastocyst-stage lineages from one preimplantation embryo simultaneously in a chemical defined condition. Therefore, it is desirable to establish a system by manipulating extrinsic signalling in culture to derive multiple types of stem cells from a single blastocyst. This study used a defined medium containing Activin A, WNT activator and LIF (ACL medium), enabling establishment of ACL-ESCs and ACL-XEN cells from one blastocyst. ACL-blastoids were generated by suspending ACL-ESCs and ACL-XEN cells with ACL-blastoid medium in three-dimensional culture system. Lineage markers expression of ACL-blastoids were performed by immunofluorescence. Our results indicate that ACL-ESCs and ACL-XEN cells derived from one blastocyst represent ICM and PrE lineages. Importantly, we obtained ACL-blastoid from ACL-ESCs and ACL-XEN cells self-aggregation, partially recapitulating early development and initiation of early implantation events. This study would not only provide ACL culture system for derivation and maintenance of two types of cell lines corresponding to ICM as well as PrE, but also reconstruct blastoids with them to deepen our understanding of early embryogenesis and widen insights into translational application of stem cells.

Possible transfer of lncRNA H19-derived miRNA miR-675-3p to adjacent H19-non-expressing trophoblast cells in near-term mouse placenta

LncRNA H19 serves as a regulatory RNA in mouse placental development. However, there is little information available on the in situ expression of H19 in the late-gestation mouse placenta. In this study, we performed quantitative polymerase chain reaction (qPCR) and in situ hybridization (ISH) analyses of lncRNA H19 and its exon 1-derived miRNA miR-675-3p to identify cell types expressing these non-coding RNAs in the mouse placenta during mid-to-late gestation. By qPCR analysis, we confirmed that H19 was highly expressed during mid-to-late gestation (E10.5-E18.5) and that H19-derived miRNA miR-675-3p was remarkably upregulated in the E18.5 placenta. ISH analysis revealed trophoblast cell type-specific expression of lncRNA H19 and miR-675-3p during later stages of gestation. In the junctional zone and decidua of late-gestation placenta, H19 was expressed in trophoblast giant cells and glycogen trophoblast cells; however, H19 was absent in spongiotrophoblast cells. In the labyrinth and chorionic plate, H19 was present in sinusoidal mononuclear trophoblast giant cells, fetal vascular endothelial cells, and basal chorionic trophoblast cells, but not in syncytiotrophoblasts. As expected, these lncRNA H19-expressing cells exhibited miR-675-3p in the E18.5 placenta. Intriguingly, miR-675-3p was also present in H19-negative spongiotrophoblast cells and syncytiotrophoblasts, implying the possible transfer of miR-675-3p from H19-exprssing cells to adjacent H19-non-expressing trophoblast cells. These findings suggest that the mouse placenta expresses lncRNA H19 in a trophoblast cell type-specific fashion during later stages of gestation.

HIF1 inhibitor acriflavine rescues early-onset preeclampsia phenotype in mice lacking placental prolyl hydroxylase domain protein 2

Preeclampsia is a serious pregnancy disorder that lacks effective treatments other than delivery. Improper sensing of oxygen changes during placentation by prolyl hydroxylases (PHDs), specifically PHD2, causes placental hypoxia-inducible factor-1 (HIF1) buildup and abnormal downstream signaling in early-onset preeclampsia, yet therapeutic targeting of HIF1 has never been attempted. Here we generated a conditional (placenta-specific) knockout of Phd2 in mice (Phd2-/- cKO) to reproduce HIF1 excess and to assess anti-HIF therapy. Conditional deletion of Phd2 in the junctional zone during pregnancy increased placental HIF1 content, resulting in abnormal placentation, impaired remodeling of the uterine spiral arteries, and fetal growth restriction. Pregnant dams developed new-onset hypertension at midgestation (E9.5) in addition to proteinuria and renal and cardiac pathology, hallmarks of severe preeclampsia in humans. Daily injection of acriflavine, a small molecule inhibitor of HIF1, to pregnant Phd2-/- cKO mice from E7.5 (prior to hypertension) or E10.5 (after hypertension had been established) to E14.5 corrected placental dysmorphologies and improved fetal growth. Moreover, it reduced maternal blood pressure and reverted renal and myocardial pathology. Thus, therapeutic targeting of the HIF pathway may improve placental development and function, as well as maternal and fetal health, in preeclampsia.

Adgrg1 is a new transcriptional target of Hand1 during trophoblast giant cell differentiation

The placenta, forming the maternal-fetal interface, is essential for the survival and development of the fetus. It has been shown that the basic helix-loop-helix (bHLH) transcription factor Hand1 plays an important role in trophoblast giant cells (TGCs) differentiation during placental development in mice. However, the underlying molecular mechanism remains elusive. We hereby report that Adgrg1 (GPR56), a G protein coupled receptor, was a new transcriptional target of Hand1. Hand1 activated the expression of Adgrg1 by binding to its promoter region during TGCs differentiation. Double in situ hybridization revealed co-expression of Hand1 and Adgrg1 in Prl2c2⁺ TGCs located in the junctional zone of the placenta. Knockdown of Adgrg1 not only led to increased Prl2c2 expression, but also the improvement of cell migration and invasion during TGC differentiation. Moreover, the ligand of Adgrg1, Tgm2, was expressed in Prl2c2⁺ TGCs located in the placental junctional zone and Tgm2 Knockdown increased cell migration and invasion, suggesting Tgm2 is a potential ligand involved in the functions of Adgrg1 during TGC differentiation in the manners of autocrine. Collectively, these results demonstrate that Adgrg1 is a new transcriptional target of Hand1, affecting Prl2c2 expression as well as cell migration and invasion during TGCs differentiation. As a transmembrane receptor, Adgrg1 perhaps could act as a potential therapeutic target for placental-associated diseases caused by abnormal trophoblast migration and invasion, providing new insights for the preventions and therapies of placenta-related diseases.

Loss of the placental iron exporter ferroportin 1 causes embryonic demise in late-gestation mouse pregnancy

Fetal development relies on adequate iron supply by the placenta. The placental syncytiotrophoblasts (SCTB) express high levels of iron transporters, including ferroportin1 (Fpn1). Whether they are essential in the placenta has not been tested directly, mainly due to the lack of gene manipulation tools in SCTB. Here, we aimed to generate a SCTB-specific Cre mouse and use it to determine the role of placental Fpn1. Using CRISPR/Cas9 technology, we created a syncytin b (Synb) Cre line (SynbCre) targeting the fetal-facing SCTB layer in mouse placental labyrinth. SynbCre deleted Fpn1 in late gestation mouse placentas reliably with high efficiency. Embryos without placental Fpn1 were pale and runted, and died before birth. Fpn1 null placentas had reduced transferrin receptor expression, increased oxidative stress and detoxification responses, and accumulated ferritin in the SCTB instead of the fetal endothelium. In summary, we demonstrate that SynbCre is an effective and specific tool to investigate placental gene function in vivo. The loss of Fpn1 in late gestation mouse placenta is embryonically lethal, providing direct evidence for an essential role of Fpn1 in placental iron transport.

The Innate Defense in the Zika-Infected Placenta

Zika virus (ZIKV) is an arthropod-borne virus that belongs to the Flaviviridae family, genus Flavivirus and was first isolated 1947 in Uganda, Africa, from the serum of a sentinel Rhesus monkey. Since its discovery, the virus was responsible for major outbreaks in several different countries, being linked to severe complications in pregnant women, neonatal birth defects and the congenital zika syndrome. Maternal-fetal transmission of ZIKV can occur in all trimesters of pregnancy, and the role of the placenta and its cells in these cases is yet to be fully understood. The decidua basalis and chorionic villi, maternal-fetal components of the placenta, contain a rich immunological infiltrate composed by Hofbauer cells, mastocytes, dendritic cells and macrophages, primary cells of the innate immune response that have a role that still needs to be better investigated in ZIKV infection. Recent studies have already described several histopathological features and the susceptibility and permissiveness of placenta cells to infection by the Zika virus. In this review, we address some of the current knowledge on the innate immune responses against ZIKV, especially in the placenta.

Postmitotic centriole disengagement and maturation leads to centrosome amplification in polyploid trophoblast giant cells

DNA replication is normally coupled with centriole duplication in the cell cycle. Trophoblast giant cells (TGCs) of the placenta undergo endocycles resulting in polyploidy but their centriole state is not known. We used a cell culture model for TGC differentiation to examine centriole and centrosome number and properties. Before differentiation, trophoblast stem cells (TSCs) have either two centrioles before duplication or four centrioles after. We find that the average nuclear area increases approximately eight-fold over differentiation, but most TGCs do not have more than four centrioles. However, these centrioles become disengaged, acquire centrosome proteins, and can nucleate microtubules. In addition, some TGCs undergo further duplication and disengagement of centrioles, resulting in substantially higher numbers. Live imaging revealed that disengagement and separation are centriole autonomous and can occur asynchronously. Centriole amplification, when present, occurs by the standard mechanism of one centriole generating one procentriole. PLK4 inhibition blocks centriole formation in differentiating TGCs but does not affect endocycle progression. In summary, centrioles in TGC endocycles undergo disengagement and conversion to centrosomes. This increases centrosome number but to a limited extent compared with DNA reduplication.

Using high throughput screens to predict miscarriages with placental stem cells and long-term stress effects with embryonic stem cells

A problem in developmental toxicology is the massive loss of life from fertilization through gastrulation, and the surprising lack of knowledge of causes of miscarriage. Half to two-thirds of embryos are lost, and environmental and genetic causes are nearly equal. Simply put, it can be inferred that this is a difficult period for normal embryos, but that environmental stresses may cause homeostatic responses that move from adaptive to maladaptive with increasing exposures. At the lower 50% estimate, miscarriage causes greater loss-of-life than all cancers combined or of all cardio- and cerebral-vascular accidents combined. Surprisingly, we do not know if miscarriage rates are increasing or decreasing. Overshadowed by the magnitude of miscarriages, are insufficient data on teratogenic or epigenetic imbalances in surviving embryos and their stem cells. Superimposed on the difficult normal trajectory for peri-gastrulation embryos are added malnutrition, hormonal, and environmental stresses. An overarching hypothesis is that high throughput screens (HTS) using cultured viable reporter embryonic and placental stem cells (e.g., embryonic stem cells [ESC] and trophoblast stem cells [TSC] that report status using fluorescent reporters in living cells) from the pre-gastrulation embryo will most rapidly test a range of hormonal, environmental, nutritional, drug, and diet supplement stresses that decrease stem cell proliferation and imbalance stemness/differentiation. A second hypothesis is that TSC respond with greater sensitivity in magnitude to stress that would cause miscarriage, but ESC are stress-resistant to irreversible stemness loss and are best used to predict long-term health defects. DevTox testing needs more ESC and TSC HTS to model environmental stresses leading to miscarriage or teratogenesis and more research on epidemiology of stress and miscarriage. This endeavor also requires a shift in emphasis on pre- and early gastrulation events during the difficult period of maximum loss by miscarriage.

Transcription factor networks in trophoblast development

The placenta sustains embryonic development and is critical for a successful pregnancy outcome. It provides the site of exchange between the mother and the embryo, has immunological functions and is a vital endocrine organ. To perform these diverse roles, the placenta comprises highly specialized trophoblast cell types, including syncytiotrophoblast and extravillous trophoblast. The coordinated actions of transcription factors (TFs) regulate their emergence during development, subsequent specialization, and identity. These TFs integrate diverse signaling cues, form TF networks, associate with chromatin remodeling and modifying factors, and collectively determine the cell type-specific characteristics. Here, we summarize the general properties of TFs, provide an overview of TFs involved in the development and function of the human trophoblast, and address similarities and differences to their murine orthologs. In addition, we discuss how the recent establishment of human in vitro models combined with -omics approaches propel our knowledge and transform the human trophoblast field.

Maternal exposure to ambient PM2.5 causes fetal growth restriction via the inhibition of spiral artery remodeling in mice

BACKGROUND

Maternal exposure to ambient fine particulate matters (PM_2.5) is associated with low birth weight (LBW) in offspring, but the underlying biological mechanisms are not yet fully understood. As the bridge that connects mother and fetus, the placenta plays a crucial role in fetal development by providing the fetus with nutrients and oxygen. However, whether PM_2.5 exposure would impact the placental development and the related mechanisms are unclear.

RESULTS

In the present study, female C57Bl/6j mice were exposed to filtered air (FA) or concentrated ambient PM_2.5 (CAP) during pregestational and gestational periods, and the fetal development and placental structure were investigated. Our results showed that maternal exposure to CAP induced fetal growth restriction (FGR) and LBW. The placenta from CAP-exposed mice exhibited abnormal development including significant decrease of surface area, smaller junctional zone and impaired spiral artery remodeling. Meanwhile, CAP exposure altered trophoblast lineage differentiation and disrupted the balance between angiogenic and angiostatic factors in placenta. In addition, the inflammatory cytokines levels in lung, placenta and serum were significantly increased after ambient PM_2.5 exposure.

CONCLUSION

Our findings indicate that maternal exposure to PM_2.5 disrupts normal structure and spiral artery remodeling of placenta and further induces FGR and LBW. This effect may be caused by the placental inflammation response subsequent to the pulmonary and systemic inflammation induced by ambient PM_2.5 exposure.

Altered expression of Notch signaling, Tlr receptors, and surfactant protein expression after prostaglandin inhibition may be associated with the delayed labor in LPS-induced mice

PURPOSE

This study aims to investigate whether indomethacin (IND) delays preterm birth by regulating the Notch pathway, Tlr receptors, and Sp-A in the placenta in lipopolysaccharide (LPS)-induced preterm labor (PTL) model.

METHODS

CD-1 mice were distributed to the pregnant control (PC), Sham, PBS, IND (2 mg/kg; i.p.), LPS (25 μg/100 μl; intrauterine), and LPS + IND groups. The injections were performed on day 14.5 of pregnancy. Placentae were collected on day 15.5 of pregnancy, and immunohistochemical analyzes were performed. Differences in staining intensities between the Cox-1, Notch-1 (N1), Dll-1, Jagged-2 (Jag-2), Tlr-2, and Tlr-4 proteins were compared.

RESULTS

Preterm labor rates were 100% and 66% (preterm delivery delayed 5 h) in the LPS and LPS + IND groups, respectively. In LPS-treated mice, a general morphological deterioration was observed in the placenta. Total placental mid-sagittal measurement was significantly reduced in the LPS-treated group, while it was similar to the PC group in the LPS + IND group. Cox-1 expression in the LZ increased, and Sp-A expression decreased after LPS injection, and IND administration diminished this increase. N1 expression increased in the labyrinth zone (LZ) and the junctional zone (JZ). Dll-1 and Jag-2 expression increased in the JZ after LPS injection (p < 0.0001). IND administration diminished Tlr-2 expression in the LZ and Tlr-4 expression in the JZ after LPS injection.

CONCLUSION

In conclusion, PG (prostaglandin) inhibition may alter Notch signaling, Tlr, and Sp-A protein expression and may be associated with delayed labor in LPS-induced mice.

Placenta-specific lncRNA 1600012P17Rik is expressed in spongiotrophoblast and glycogen trophoblast cells of mouse placenta

A few long noncoding RNAs (long ncRNAs, lncRNAs) exhibit trophoblast cell type-specific expression patterns and functional roles in mouse placenta. However, the cell- and stage-specific expression patterns and functions of most placenta-derived lncRNAs remain unclear. In this study, we explored mouse placenta-associated lncRNAs using a combined bioinformatic and experimental approach. We used the FANTOM5 database to survey lncRNA expression in mouse placenta and found that 1600012P17Rik (MGI: 1919275, designated P17Rik), a long intergenic ncRNA, was the most highly expressed lncRNA at gestational day 17. Polymerase chain reaction analysis confirmed that P17Rik was exclusively expressed in placenta and not in any of the adult organs examined in this study. In situ hybridization analysis revealed that it was highly expressed in spongiotrophoblast cells and to a lesser extent in glycogen trophoblast cells, including migratory glycogen trophoblast cells invading the decidua. Moreover, we found that it is a polyadenylated lncRNA localized mainly to the cytoplasm of these trophoblast cells. As these trophoblast cells also expressed the neighboring protein-coding gene, pappalysin 2 (Pappa2), we investigated the effects of P17Rik on Pappa2 expression using Pappa2-expressing MC3T3-E1 cells and found that P17Rik transfection increased the messenger RNA (mRNA) and protein levels of Pappa2. These results indicate that mouse placenta-specific lncRNA P17Rik modulates the expression of the neighboring protein-coding gene Pappa2 in spongiotrophoblast and glycogen trophoblast cells of mouse placenta during late gestation.

Evaluating the Effects of BPA and TBBPA Exposure on Pregnancy Loss and Maternal-Fetal Immune Cells in Mice

BACKGROUND

Bisphenol A (BPA) exposure has been linked to miscarriages and pregnancy complications in humans. In contrast, the potential reproductive toxicity of BPA analogs, including tetrabromobisphenol A (TBBPA), is understudied. Furthermore, although environmental exposure has been linked to altered immune mediators, the effects of BPA and TBBPA on maternal-fetal immune tolerance during pregnancy have not been studied. The present study investigated whether exposure resulted in higher rates of pregnancy loss in mice, lower number of regulatory T cells (Tregs), and lower indoleamine 2,3 deoxygenase 1 (Ido1) expression, which provided evidence for mechanisms related to immune tolerance in pregnancy.

OBJECTIVES

The purpose of this investigation was to characterize the effects of BPA and TBBPA exposure on pregnancy loss in mice and to study the percentage and number of Tregs and Ido1 expression and DNA methylation.

METHODS

Analysis of fetal resorption and quantification of maternal and fetal immune cells by flow cytometry were performed in allogeneic and syngeneic pregnancies. Ido1 mRNA and protein expression, and DNA methylation in placentas from control and BPA- and TBBPA-exposed mice were analyzed using real-time quantitative polymerase chain reaction, immunofluorescence, and bisulfite sequencing analyses.

RESULTS

BPA and TBBPA exposure resulted in higher rates of hemorrhaging in early allogeneic, but not syngeneic, conceptuses. In allogeneic pregnancies, BPA and TBBPA exposure was associated with higher fetal resorption rates and lower maternal Treg number. Importantly, these differences were associated with lower IDO1 protein expression in trophoblast giant cells and higher mean percentage Ido1 DNA methylation in embryonic day 9.5 placentas from BPA- and TBBPA-exposed mice.

DISCUSSION

BPA- and TBBPA-induced pregnancy loss in mice was associated with perturbed IDO1-dependent maternal immune tolerance. https://doi.org/10.1289/EHP10640.

Vaginal Exposure to Candida albicans During Early Gestation Results in Adverse Pregnancy Outcomes via Inhibiting Placental Development

Vulvovaginal candidiasis (VVC) is considered the second most common cause of vaginitis after bacterial vaginosis and the most common lower genital tract infection during pregnancy. Candida albicans (C. albicans), an opportunistic pathogen, is the major species causing VVC. Recently, increasing researches have shown that lower reproductive tract infection during pregnancy can lead to various adverse pregnancy outcomes. However, the underlying mechanisms are not fully understood. Hence, we successfully established a mouse model of vaginal C. albicans infection and characterized the adverse pregnancy outcomes. C. albicans infection strikingly increased abortion rate and decreased litter size. Further analysis of placental development demonstrated that placental structure was abnormal, including that the area of spongiotrophoblast (Spo) and labyrinth (Lab) was reduced, and the formation of placental vessel was decreased in Lab zone. Accordingly, the expression of marker genes during placental development was downregulated. Collectively, the above findings revealed that vaginal C. albicans infection during pregnancy can inhibit placental development and ultimately lead to adverse pregnancy outcomes. This study enhances our comprehension of the effect of VVC on pregnancy, and placental dysplasia as a feasible orientation to explore VVC during pregnancy.

Protein O-GlcNAcylation as a nutrient sensor signaling placental dysfunction in hypertensive pregnancy

INTRODUCTION

During pregnancy, arterial hypertension may impair placental function, which is critical for a healthy baby's growth. Important proteins during placentation are known to be targets for O-linked β-N-acetylglucosamine modification (O-GlcNAcylation), and abnormal protein O-GlcNAcylation has been linked to pathological conditions such as hypertension. However, it is unclear how protein O-GlcNAcylation affects placental function and fetal growth throughout pregnancy during hypertension.

METHODS

To investigate this question, female Wistar and spontaneously hypertensive rats (SHR) were mated with male Wistar rats, and after pregnancy confirmation by vaginal smear, rats were divided into groups of 14, 17, and 20 days of pregnancy (DOPs). On the 14th, 17th, and 20th DOP, rats were euthanized, fetal parameters were measured, and placentas were collected for western blot, immunohistochemical, and morphological analyses.

RESULTS

SHR presented a higher blood pressure than the Wistar rats (p=0.001). Across all DOPs, SHR showed reduced fetal weight and an increase in small-for-gestational-age fetuses. While near-term placentas were heavier in SHR (p=0.006), placental efficiency decreased at 17 (p=0.01) and 20 DOPs (p<0.0001) in this group. Morphological analysis revealed reduced junctional zone area and labyrinth vasculature changes on SHR placentas in all DOPs. O-GlcNAc protein expression was lower in placentas from SHR compared with Wistar at 14, 17, and 20 DOPs. Decreased expression of O-GlcNAc transferase (p=0.01) and O-GlcNAcase (p=0.002) enzymes was found at 14 DOPs in SHR. Immunohistochemistry showed reduced placental O-GlcNAc content in both the junctional zone and labyrinth of the placentas from SHR. Periodic acid-Schiff analysis showed decreased glycogen cell content in the placentas from SHR at 14, 17, and 20 DOPs. Moreover, glucose transporter 1 expression was decreased in placentas from SHR in all DOPs.

CONCLUSIONS

These findings suggest that decreased protein O-GlcNAcylation caused by insufficient placental nutritional apport contributes to placental dysfunction during hypertensive pregnancy, impairing fetal growth.