Fetal Endothelium Research Articles

Unique Ultrastructural Alterations in the Placenta Associated With Macrosomia Induced by Gestational Diabetes Mellitus

Abstract Objective To investigate the morphological and ultrastructural alterations in placentas from pregnancies with gestational diabetes mellitus (GDM)–induced macrosomia, term nondiabetic macrosomia, and normal pregnancies. Methods Sixty full-term placentas were collected, and clinical data along with informed consent were obtained from pregnant women who underwent regular visit checks and delivered their newborns in Northwest Women’s and Children’s Hospital between May and December 2022. Placentas were divided into three equal groups: normal pregnancy (control group), nondiabetic macrosomia group, and macrosomia complicated with GDM (diabetic macrosomia) group. Gross morphological data of placentas were recorded, and placental samples were processed for examination of ultrastructural and stereological changes using transmission electron microscopy. Analysis of variance and chi-squared test were used to examine the differences among the three groups for continuous and categorical variables, respectively. Results The baseline characteristics of mothers and neonates did not differ across the three groups, except for a significantly higher birth weight in the diabetic macrosomia group (4172.00 ± 151.20 vs. 3192.00 ± 328.70, P < 0.001) and nondiabetic macrosomia group (4138.00 ± 115.20 vs. 3192.00 ± 328.70, P < 0.001) compared with control group. Examination of the placentas revealed that placental weight was also highest in the diabetic macrosomia group compared with control group (810.00 ± 15.81 vs. 490.00 ± 51.48, P < 0.001) and nondiabetic macrosomia group (810.00 ± 15.81 vs. 684.00 ± 62.69, P < 0.001), but the ratio of neonatal birth weight to placental weight (BW/PW) was significantly lower in the diabetic macrosomia group compared with that in the control group (5.15 ± 0.19 vs. 6.54 ± 0.63, P < 0.001) and nondiabetic macrosomia group (5.15 ± 0.19 vs. 6.09 ± 0.52, P < 0.001) group. In contrast, the BW/PW ratio in nondiabetic macrosomia did not differ significantly from that in the control group. Distinct ultrastructural changes in terminal villi and stereological alterations in microvilli were observed in the diabetic macrosomia group, including changes in the appearance of cytoplasmic organelles and the fetal capillary endothelium and thickness of the vasculo-syncytial membrane and basal membrane. Conclusion Significant ultrastructural and stereological alterations were discovered in the placentas from pregnant women with macrosomia induced by GDM. These alterations may be the response of the placenta to the hyperglycemia condition encountered during pregnancies complicated with GDM.

406 A CTS Team Approach to Identifying Risk of Neonatal Hypoglycemia and its Relationship with Endothelial Dysfunction

OBJECTIVES/GOALS: Neonatal hypoglycemia is seen in 65% of maternally diabetic pregnancies, and can lead to severe neurological damage. Neonatal glycemia may also be an indicator of placental function in these pregnancies. The purpose of this study is to identify patterns of neonatal glycemia, and associated endothelial dysfunction, by maternal diabetes subtype. METHODS/STUDY POPULATION: Pregnancies with maternal Type 1 (T1DM), Type 2 (T2DM), and gestational diabetes mellitus (GDM) are being enrolled. Maternal hemoglobin A1c (HbA1c) and umbilical cord insulin/glucose are being collected from 20 pregnancies in each group, 10 of which also undergo placental/umbilical cord tissue collection. Following delivery, neonatal blood glucose levels are also collected every 3-4 hours (4+ measurements) to determine rate of glycemic change. Linear regression modeling will be used to determine associations with placental and umbilical endothelial RNA expression, umbilical cord insulin levels, and maternal HbA1c within each diabetic subtype and between normoglycemic and hypoglycemic neonates. Endothelial gene expression will be compared using paired t-tests with Benjamini-Hochberg correction. RESULTS/ANTICIPATED RESULTS: Thus far, 5 T1DM, 10 T2DM, and 13 GDM samples have been collected. Gestational age at delivery and birth weight were similar between groups (38.1 ± 1.05 weeks; 3.6 ± 0.59 kilograms) and delivery method is evenly distributed (Cesarean section or vaginal delivery). Currently, with limited cohort size, no association is evident between maternal HbA1c and umbilical cord glucose/insulin (p=0.114) or neonatal hypoglycemia diagnosis (p=0.674) when controlled for gestational age and infant birthweight. We hypothesize that, with pending analyses, maternal HbA1c and umbilical cord insulin levels will correlate negatively with the rate of neonatal glycemic change, and positively with the level of inflammatory and angiogenic transcription identified in placental and umbilical endothelium. DISCUSSION/SIGNIFICANCE: Characterization of postnatal glucose control is key to prognosis and risk stratification of infants of diabetic mothers. Understanding placental response to glucose, as well as sequela in the fetal endothelium, is also critical to understanding the pathogenesis of neonatal hypoglycemia and other adverse outcomes of diabetic pregnancy.

A novel technique to estimate intravillous fetal vasculature on routine placenta histologic sections

Placental histopathologic lesions are dichotomized into “present” or “absent” and have limited inter-rater reliability. Continuous metrics are needed to characterize placental health and function. Tissue sections (N = 64) of human placenta were stained with CD34 antibody and hematoxylin. Proportion of the villous space occupied by fetal vascular endothelium (%FVE; pixels positive for CD34/total pixels) was evaluated for effect sizes associated with pregnancy outcomes, smoking status, and subtypes of lesions (n = 30). Time to fixation>60 min significantly increased the quantification. Large effect sizes were found between %FVE and both preterm birth and intrauterine growth restriction. These results demonstrate proof-of-concept for this vascular estimation.

Immunomodulation of Antibody Glycosylation through the Placental Transfer

Establishing an immune balance between the mother and fetus during gestation is crucial, with the placenta acting as the epicenter of immune tolerance. The placental transfer of antibodies, mainly immunoglobulin G (IgG), is critical in protecting the developing fetus from infections. This review looks at how immunomodulation of antibody glycosylation occurs during placental transfer and how it affects fetal health. The passage of maternal IgG antibodies through the placental layers, including the syncytiotrophoblast, stroma, and fetal endothelium, is discussed. The effect of IgG subclass, glycosylation, concentration, maternal infections, and antigen specificity on antibody transfer efficiency is investigated. FcRn-mediated IgG transport, influenced by pH-dependent binding, is essential for placental transfer. Additionally, this review delves into the impact of glycosylation patterns on antibody functionality, considering both protective and pathological effects. Factors affecting the transfer of protective antibodies, such as maternal vaccination, are discussed along with reducing harmful antibodies. This in-depth examination of placental antibody transfer and glycosylation provides insights into improving neonatal immunity and mitigating the effects of maternal autoimmune and alloimmune conditions.

Volume electron microscopy reveals placental ultrastructure in 3D

Many structures necessary for placental function can only be visualised at the ultrastructural scale. Recent technological advances have made Volume electron microscopy (volume EM) approaches much more accessible. Volume EM allows the ultrastructure of tissues, cells and organelles to be visualised in 3D. It also allows the 3D spatial relationships between these structures to be determined. This review will highlight the potential for volume EM to advance our understanding of placental ultrastructure. It will focus on the human term placenta highlighting key findings spanning the placental barrier from trans-syncytial nanopores in the syncytiotrophoblast to tunnelling nanotubes in the fetal capillary endothelium. Volume EM is advancing our understanding of placental ultrastructure, but to fully exploit its potential, it will be necessary to use it as part of multimodal and correlative workflows. The complementary strengths of these different approaches can complement volume EM and reveal the biological significance of its novel observations. The use of volume EM also highlighted how ultrastructural features might underpin pregnancy pathologies and demonstrates the need for more research in this underrepresented area.

Analysis of global DNA methylation and epigenetic modifiers (DNMTs and HDACs) in human foetal endothelium exposed to gestational and type 2 diabetes

ABSTRACT Foetuses exposed to maternal gestational diabetes (GDM) and type 2 diabetes (T2D) have an increased risk of adverse perinatal outcomes. Epigenetic mechanisms, including DNA methylation and histone modifications, may act as mediators of persistent metabolic memory in endothelial cells (ECs) exposed to hyperglycaemia, even after glucose normalization. Therefore, we investigated alterations in global DNA methylation and epigenetic modifier expression (DNMT1, DNMT3a, DNMT3b, HDAC1, and HDAC2) in human umbilical vein ECs (HUVECs) from the umbilical cords of mothers with GDM (n = 8) and T2D (n = 3) compared to that of healthy mothers (n = 6). Global DNA alteration was measured using a 5-methylation cytosine colorimetric assay, followed by quantitative real-time polymerase chain reaction to measure DNA methyltransferase and histone acetylase transcript expression. We revealed that DNA hypermethylation occurs in both GDM- and T2D-HUVECs compared to that in Control-HUVECs. Furthermore, there was a significant increase in HDAC2 mRNA levels in GDM-HUVECs and increase in DNMT3b mRNA levels in T2D-HUVECs. Overall, our results suggest that GDM and T2D are associated with global DNA hypermethylation in foetal endothelial cells under normoglycemic conditions and the aberrant mRNA expression of HDAC2 and DNMT3b could play a role in this dysregulation.

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.

Comparative Characteristics of Sialoglycans Expression Disorders in the Placental Barrier Structures in Preeclampsia and Fetal Growth Restriction.

We compared the expression profiles of α2,3- and α2,6-sialoglycans in the glycocalyx of the placental barrier structures in early and late forms of preeclampsia and fetal growth restriction using the method of lectin histochemistry. It was found that the expression of α2,3-sialoglycans in the syncytiotrophoblast and fetal endothelium of the terminal villi of the placenta was reduced in preeclampsia in comparison with normal placenta and, on the contrary, was increased in fetal growth restriction. Significant differences were found in both clinical phenotypes of preeclampsia and fetal growth restriction. Changes in the expression pattern of α2,6-sialoglycans in the endothelium of terminal villi were more pronounced than in syncytiotrophoblast. In early and late-onset preeclampsia, a significant increase in the expression of α2,6-sialoglycans was revealed only in the fetal endothelium; in early fetal growth restriction, the expression of α2,6-sialoglycans was reduced in the endothelium, but increased in syncytiotrophoblast in late fetal growth restriction. The features of the expression of sialoglycans in structures of the placental barrier in preeclampsia and fetal growth restriction were revealed, which may indicate the pathogenetic involvement of sialoglycans in the inflammatory activation cascade in fetal growth restriction, and in preeclampsia, apparently, they are associated with impaired fetal tolerance.

Vertical Zika Virus Transmission at the Maternal-Fetal Interface

Zika virus (ZIKV) is spread by mosquito bites or via sexual or vertical transmission. ZIKV-infected adults are generally asymptomatic, but can display mild symptoms including fever, joint pain, rash and conjunctivitis. However, during pregnancy, vertical ZIKV transmission can cause placental dysfunction and elicit severe fetal defects, including microcephaly, retinopathy, fetal growth restriction and/or stillbirth. Since no FDA-approved vaccine or anti-viral agents are currently available, ZIKV infection poses a global maternal-fetal health challenge. The maternal-fetal interface consists of maternal decidual and immune cells as well as fetal-derived trophoblasts. Compared to other cell types at the maternal-fetal interface, syncytiotrophoblasts, which form the outer layer of floating villi, are less-permissive to ZIKV, thereby preventing ZIKV transmission to the underlying cytotrophoblasts and/or other cells such as Hofbauer cells or fetal endothelium in the villi. However, anchoring villi are tightly attached to the decidua and their cytotrophoblastic cell columns are ZIKV-permissive, suggesting this location as the most likely site of ZIKV vertical transmission. Thus, at the maternal-fetal interface, maternal decidual cells likely serve as a reservoir of ZIKV persistence since they: 1) overexpress viral entry molecules compared to trophoblasts; 2) are highly permissive to ZIKV infection in a gestational age-dependent manner (more easily infected earlier in gestation); 3) augment ZIKV infection of weakly permissive primary cytotrophoblast cultures; and 4) display local maternal-immune tolerance, which prolongs ZIKV survival to facilitate fetal transmission. This review focuses on molecular mechanisms underlying ZIKV infection of cells at the human maternal-fetal interface, thus highlighting how decidual cells enhance propagation of ZIKV in extravillous cytotrophoblasts and why development of agents that eliminate ZIKV persistence in reproductive tissues before pregnancy is crucial to prevent perinatal ZIKV transmission.

Mapping the developing human cardiac endothelium at single-cell resolution identifies MECOM as a regulator of arteriovenous gene expression.

Coronary vasculature formation is a critical event during cardiac development, essential for heart function throughout perinatal and adult life. However, current understanding of coronary vascular development has largely been derived from transgenic mouse models. The aim of this study was to characterize the transcriptome of the human foetal cardiac endothelium using single-cell RNA sequencing (scRNA-seq) to provide critical new insights into the cellular heterogeneity and transcriptional dynamics that underpin endothelial specification within the vasculature of the developing heart. We acquired scRNA-seq data of over 10 000 foetal cardiac endothelial cells (ECs), revealing divergent EC subtypes including endocardial, capillary, venous, arterial, and lymphatic populations. Gene regulatory network analyses predicted roles for SMAD1 and MECOM in determining the identity of capillary and arterial populations, respectively. Trajectory inference analysis suggested an endocardial contribution to the coronary vasculature and subsequent arterialization of capillary endothelium accompanied by increasing MECOM expression. Comparative analysis of equivalent data from murine cardiac development demonstrated that transcriptional signatures defining endothelial subpopulations are largely conserved between human and mouse. Comprehensive characterization of the transcriptional response to MECOM knockdown in human embryonic stem cell-derived EC (hESC-EC) demonstrated an increase in the expression of non-arterial markers, including those enriched in venous EC. scRNA-seq of the human foetal cardiac endothelium identified distinct EC populations. A predicted endocardial contribution to the developing coronary vasculature was identified, as well as subsequent arterial specification of capillary EC. Loss of MECOM in hESC-EC increased expression of non-arterial markers, suggesting a role in maintaining arterial EC identity.

Environmental Nanoparticles Reach Human Fetal Brains.

Anthropogenic ultrafine particulate matter (UFPM) and industrial and natural nanoparticles (NPs) are ubiquitous. Normal term, preeclamptic, and postconceptional weeks(PCW) 8–15 human placentas and brains from polluted Mexican cities were analyzed by TEM and energy-dispersive X-ray spectroscopy. We documented NPs in maternal erythrocytes, early syncytiotrophoblast, Hofbauer cells, and fetal endothelium (ECs). Fetal ECs exhibited caveolar NP activity and widespread erythroblast contact. Brain ECs displayed micropodial extensions reaching luminal NP-loaded erythroblasts. Neurons and primitive glia displayed nuclear, organelle, and cytoplasmic NPs in both singles and conglomerates. Nanoscale Fe, Ti, and Al alloys, Hg, Cu, Ca, Sn, and Si were detected in placentas and fetal brains. Preeclamptic fetal blood NP vesicles are prospective neonate UFPM exposure biomarkers. NPs are reaching brain tissues at the early developmental PCW 8–15 stage, and NPs in maternal and fetal placental tissue compartments strongly suggests the placental barrier is not limiting the access of environmental NPs. Erythroblasts are the main early NP carriers to fetal tissues. The passage of UFPM/NPs from mothers to fetuses is documented and fingerprinting placental single particle composition could be useful for postnatal risk assessments. Fetal brain combustion and industrial NPs raise medical concerns about prenatal and postnatal health, including neurological and neurodegenerative lifelong consequences.

Infrequent Placental and Fetal Involvement in SARS-CoV-2 Infection: Pathology Data from a Large Medical Center

In order to determine the frequency of SARS-CoV-2 placental and fetal involvements, we analyzed placentas of 197 women positive for infection at delivery and fetal tissues in cases of pregnancy loss in women positive by SARS-CoV-2 PCR (N = 2) and COVID-19 serology (N = 4), using in situ hybridization (ISH), immunohistochemistry (IHC) and, in selected cases, RT-PCR of tissue homogenates. The virus was identified in situ, accompanied by intervillositis, in 2 of 197 placentas (1.02%). In three more cases, SARS-CoV-2 was detected by tissue PCR without in situ localization and placental inflammation. There were no maternal mortality or association of placental infection with the clinical severity of COVID-19. All tested neonates born to SARS-CoV-2-positive women (N = 172) were negative for the virus. There were three pregnancy losses among 197 infected women and in two cases available fetal tissues were negative for SARS-CoV-2. In one of four fetal autopsies performed in women with positive COVID-19 serology, the mother-to-child transmission (MTCT) could be inferred based on positive SARS-CoV-2 nucleocapsid IHC in fetal pulmonary endothelium. Placental involvement by SARS-CoV-2 is rare, but may be underestimated due to its transient nature. MTCT is even rarer, supporting the protective role of placenta in SARS-CoV-2 infection.

Local fluid shear stress operates a molecular switch to drive fetal semilunar valve extension.

While much is known about the genetic regulation of early valvular morphogenesis, mechanisms governing fetal valvular growth and remodeling remain unclear. Hemodynamic forces strongly influence morphogenesis, but it is unknown whether or how they interact with valvulogenic signaling programs. Side-specific activity of valvulogenic programs motivates the hypothesis that shear stress pattern-specific endocardial signaling controls the elongation of leaflets. We determined that extension of the semilunar valve occurs via fibrosa sided endocardial proliferation. Low OSS was necessary and sufficient to induce canonical Wnt/β-catenin activation in fetal valve endothelium, which in turn drives BMP receptor/ligand expression, and pSmad1/5 activity essential for endocardial proliferation. In contrast, ventricularis endocardial cells expressed active Notch1 but minimal pSmad1/5. Endocardial monolayers exposed to LSS attenuate Wnt signaling in a Notch1 dependent manner. Low OSS is transduced by endocardial cells into canonical Wnt signaling programs that regulate BMP signaling and endocardial proliferation. In contrast, high LSS induces Notch signaling in endocardial cells, inhibiting Wnt signaling and thereby restricting growth on the ventricular surface. Our results identify a novel mechanically regulated molecular switch, whereby fluid shear stress drives the growth of valve endothelium, orchestrating the extension of the valve in the direction of blood flow.

ACE2 Is Expressed in Immune Cells That Infiltrate the Placenta in Infection-Associated Preterm Birth.

COVID-19 is associated with increased incidence of preterm birth (PTB). We assessed pathways by which SARS-CoV-2 could access the placenta. Placentae, from PTB with or without chorioamnionitis (ChA), or from term pregnancies (n = 12/13/group) were collected. Peripheral blood was collected from healthy pregnant women (n = 6). Second trimester placental explants (16–20 weeks, n = 5/group) were treated with lipopolysaccharide (LPS, to mimic bacterial infection) and ACE2, CCL2, IL-6/8 and TNFα mRNA was assessed. ChA-placentae exhibited increased ACE2 and CCL2 mRNA expression (p < 0.05). LPS increased cytokine and ACE2 mRNA in placental explants. Placental ACE2 protein localized to syncytiotrophoblast, fetal endothelium, extravillous trophoblast and in immune cells-subsets (M1/M2 macrophage and neutrophils) within the villous stroma. Significantly increased numbers of M1 macrophage and neutrophils were present in the ChA-placenta (p < 0.001). Subsets of peripheral immune cells from pregnant women express the ACE2 mRNA and protein. A greater fraction of granulocytes was positive for ACE2 protein expression compared to lymphocytes or monocytes. These data suggest that in pregnancies complicated by ChA, ACE2 positive immune cells in the maternal circulation have the potential to traffic SARS-CoV-2 virus to the placenta and increase the risk of vertical transmission to the placenta/fetus.

Endocytosis in the placenta: An undervalued mediator of placental transfer

Endocytosis is an essential mechanism for cellular uptake in many human tissues. A range of endocytic mechanisms occur including clathrin-dependent and -independent mechanisms. However, the role of endocytosis in the placenta and the spatial localisation of individual mechanisms is not well understood. The two principal cell layers that comprise the placental barrier to maternal-fetal transfer are the syncytiotrophoblast and fetal capillary endothelium. Endocytic uptake into the syncytiotrophoblast has been demonstrated for physiological maternal molecules such as transferrin-bound iron and low density lipoprotein (LDL) and may play an important role in the uptake of several other micronutrients, serum proteins, and therapeutics at both major placental cell barriers. These mechanisms may also mediate placental uptake of some viruses and nanoparticles. This review introduces the mechanisms of cargo-specific endocytosis and what is known about their localisation in the placenta, focussing predominantly on the syncytiotrophoblast. A fuller understanding of placental endocytosis is necessary to explain both fetal nutrition and the properties of the placental barrier. Characterising placental endocytic mechanisms and their regulation may allow us to identify their role in pregnancy pathologies and provide new avenues for therapeutic intervention.

1112HAND1 knockdown disrupts trophoblast but not placental endothelial global gene expression

We previously reported disrupted placental structure, and vascular changes in placentas from fetuses with Congenital Heart Defects. Signaling between trophoblast and villous endothelium is proposed for proper placental development and function. We hypothesize that disruption of genes associated with CHD within the trophoblast impacts fetal endothelium and results in dysregulated placental vasculature in CHD fetuses. A model of human cytotrophoblast, BeWo choriocarcinoma cells and isolated human placental microvascular endothelial cells (HPMVEC) were treated for 48 hrs with HAND1 siRNA/lipofectamine. Additionally, control HPMVECs were exposed to conditioned BeWo media (+/- HAND1) for 48 hrs. Cells were harvested and total RNA isolated. RNA was sequenced on an Illumina NextSeq 550 platform (single end reads 85bp, read depth 25M). The Galaxy Bioinformatic Platform was used for quality control, alignment (Bowtie2) and generation of read counts (Feature Counts). Normalization and differential gene expression analyses were conducted using general linear modeling in edgeR package from Bioconductor. Significance was determined using a fold change cut off of >1.5 and raw p<0.05. Overrepresentation analysis was performed using Panther DB for Reactome pathways and GO terms Direct HAND1 knockdown in the BeWo choriocarcinoma cell line caused downregulation of 632 genes, and upregulation of 102 genes. Overrepresentation analysis identified disruption to pathways including cell differentiation, neurogenesis, localization, and cell projection organization. In contrast, direct HAND1 knockdown in HPMVECs resulted in minimal disruption to global gene expression with differential expression in just 18 genes. Indirect HAND1 disruption did not alter HPMVEC gene expression. Disruption to HAND1 expression significantly alters gene expression profile in trophoblast but not HPMVEC, either directly or indirectly. Disruption to the structure and vasculature of the placenta in cases of CHD is likely primarily due to abnormal trophoblast development.

Cotton Rat Placenta Anatomy and Fc Receptor Expression and Their Roles in Maternal Antibody Transfer.

Respiratory syncytial virus (RSV) is the leading cause of bronchiolitis and viral pneumonia in infants and young children worldwide. Currently no vaccine is available to prevent RSV infection, but virus-neutralizing monoclonal antibodies can be given prophylactically, emphasizing the protective potential of antibodies. One concept of RSV vaccinology is mothers' immunization to induce high antibody titers, leading to passive transfer of high levels of maternal antibody to the fetus through the placenta and to the neonate through colostrum. Cotton rats are an excellent small animal model for RSV infection and have been used to test maternal immunization. To mechanistically understand antibody transfer in the cotton rat model, we characterized the cotton rat placenta and Fc receptor localization. Placentas from cotton rats at midgestation (approximately day 14) and at late gestation (approximately day 25) and neonatal (younger than 1 wk) gastrointestinal tracts were collected for light microscopy, immunohistochemistry, and transmission electron microscopy. The cotton rat placenta is hemotrichorial and has 5 distinct layers: decidua, junctional zone, labyrinth, chorionic plate, and yolk sac. Consistent with the transfer of maternal antibodies, the majority of the Fc receptors are present in the yolk sac endoderm and fetal capillary endothelium of the chorionic plate, involving 10% of the cells within the labyrinth. In addition, Fc receptors are present on duodenal and jejunal enterocytes in cotton rats, similar to humans, mice, and rats. These findings provide the structural basis for the pre- and postnatal transfer of maternal antibodies described in cotton rats.

Materno-fetal cholesterol transport during pregnancy.

Cholesterol is a major nutrient required for fetal growth. It is also a precursor for the synthesis of steroid hormones and essential for the development and maturation of fetal organs. During pregnancy, the placenta controls the transport of cholesterol from the mother to the fetus and vice versa. Cholesterol originating from the maternal circulation has to cross two main membrane barriers to reach the fetal circulation: Firstly, cholesterol is acquired by the apical side of the syncytiotrophoblast (STB) from the maternal circulation as high-density lipoprotein (HDL)-, low-density lipoprotein (LDL)- or very-low-density lipoprotein (VLDL)-cholesterol and secreted at the basal side facing the villous stroma. Secondly, from the villous stroma cholesterol is taken up by the endothelium of the fetal vasculature and transported to the fetal vessels. The proteins involved in the uptake of HDL-, LDL-, VLDL- or unesterified-cholesterol are scavenger receptor type B class 1 (SR-B1), cubulin, megalin, LDL receptor (LDLR) or Niemann-Pick-C1 (NPC1) which are localized at the apical and/or basal side of the STB or at the fetal endothelium. Through interaction with apolipoproteins (e.g. apoA1) cholesterol is effluxed either to the maternal or fetal circulation via the ATP-binding-cassette (ABC)-transporter A1 and ABCG1 localized at the apical/basal side of the STB or the endothelium. In this mini-review, we summarize the transport mechanisms of cholesterol across the human placenta, the expression and localization of proteins involved in the uptake and efflux of cholesterol, and the expression pattern of cholesterol transport proteins in pregnancy pathologies such as pre-eclampsia, gestational diabetes mellitus and intrauterine growth retardation.

2010 - IDENTIFYING NECESSARY CHROMATIN STATES AND TARGETS FOR HEMOGENIC SPECIFICATION AND REPROGRAMMING

Hematopoietic stem cells (HSCs) originate from a subset of endothelium in the embryo known as hemogenic endothelium. Hemogenic endothelium must undergo an endothelial to hematopoietic transition (EHT) to form HSCs. EHT requires the activity of the transcription factor (TF) RUNX1. Ectopic pan-endothelial expression of RUNX1 in mouse embryos is able to specify embryonic endothelium as hemogenic. However, as compared to embryonic endothelium, RUNX1 is not as effective at specifying fetal endothelium as hemogenic. To understand the difference in the competency of embryonic versus fetal endothelium to be specified as hemogenic, we examined differences in chromatin at these two developmental stages. ATAC-seq revealed that RUNX1 appears to be specifying embryonic endothelium through a canonical EHT program. To orchestrate this EHT transcriptional program, RUNX1 participates with other hematopoietic TFs, such as FLI1, ETS1, SPI1, and GFI1. Following RUNX1 induction in embryonic endothelium, immune genes and motility related genes are upregulated. In fetal endothelium, however, RUNX1 induction results in a more complex picture. To determine if these differences were due to underlying chromatin differences between fetal and embryonic endothelium, we examined control embryonic and fetal endothelium using stochastic optical reconstruction microscopy (STORM). STORM imaging suggests that there are global differences in chromatin structure between fetal and embryonic endothelium. Fetal endothelium appears to have more densely packed chromatin that is located more peripherally than embryonic endothelium. Taken together, these data show that the reduced specification efficiency by RUNX1 observed between embryonic and fetal endothelium is due, at least in part, to chromatin structure.

Secondary Placental Defects in Cxadr Mutant Mice.

The Coxsackie virus and adenovirus receptor (CXADR) is an adhesion molecule known for its role in virus-cell interactions, epithelial integrity, and organogenesis. Loss of Cxadr causes numerous embryonic defects in mice, notably abnormal development of the cardiovascular system, and embryonic lethality. While CXADR expression has been reported in the placenta, the precise cellular localization and function within this tissue are unknown. Since impairments in placental development and function can cause secondary cardiovascular abnormalities, a phenomenon referred to as the placenta-heart axis, it is possible placental phenotypes in Cxadr mutant embryos may underlie the reported cardiovascular defects and embryonic lethality. In the current study, we determine the cellular localization of placental Cxadr expression and whether there are placental abnormalities in the absence of Cxadr. In the placenta, CXADR is expressed specifically by trophoblast labyrinth progenitors as well as cells of the visceral yolk sac (YS). In the absence of Cxadr, we observed altered expression of angiogenic factors coupled with poor expansion of trophoblast and fetal endothelial cell subpopulations, plus diminished placental transport. Unexpectedly, preserving endogenous trophoblast Cxadr expression revealed the placental defects to be secondary to primary embryonic and/or YS phenotypes. Moreover, further tissue-restricted deletions of Cxadr suggest that the secondary placental defects are likely influenced by embryonic lineages such as the fetal endothelium or those within the extraembryonic YS vascular plexus.