Three-Dimensional In Vitro Human Placental Organoids from Mononuclear Villous Trophoblasts or Trophoblast Stem Cells to Understand Trophoblast Dysfunction in Fetal Growth Restriction

The placenta plays a critical role in the efficient delivery of nutrients and oxygen from mother to fetus to maintain normal fetal growth. Human placental development and function is a highly orchestrated process, which is spatially and temporally controlled by hormones and growth factors. Specialized epithelial cells called trophoblasts play key roles in placental exchange capacity, and their abnormal function and development contribute to many pregnancy complications, including fetal growth restriction (FGR), a condition in which the fetus does not reach its full growth potential in utero. Great variation in the anatomy and development of the placenta in animal model systems (in vivo) and 2D culture model systems of trophoblasts (in vitro) limits our ability to understand pregnancy disorders. Generating in vitro models that recapitulate the unique features of the human placenta has been challenging. Here, we describe detailed methods to isolate mononuclear villous trophoblasts (containing cytotrophoblasts and trophoblast stem cells) from first trimester placentae, and use both these and trophoblast stem cell populations that can be grown long term in a three-dimensional (3D) placental organoid culture system.

Human placental vascular and perivascular cell heterogeneity differs between first trimester and term, and in pregnancies affected by foetal growth restriction

Growth-restricted placentae have a reduced vascular network, impairing exchange of nutrients and oxygen. However, little is known about the differentiation events and cell types that underpin normal/abnormal placental vascular formation and function. Here, we used 23-colour flow cytometry to characterize placental vascular/perivascular populations between first trimester and term, and in foetal growth restriction (FGR). First-trimester endothelial cells had an immature phenotype (CD144+/lowCD36-CD146low), while term endothelial cells expressed mature endothelial markers (CD36+CD146+). At term, a distinct population of CD31low endothelial cells co-expressed mesenchymal markers (CD90, CD26), indicating a capacity for endothelial to mesenchymal transition (EndMT). In FGR, compared with normal pregnancies, endothelial cells constituted 3-fold fewer villous core cells (P < 0.05), contributing to an increased perivascular: endothelial cell ratio (2.6-fold, P < 0.05). This suggests that abnormal EndMT may play a role in FGR. First-trimester endothelial cells underwent EndMT in culture, losing endothelial (CD31, CD34, CD144) and gaining mesenchymal (CD90, CD26) marker expression. Together this highlights how differences in villous core cell heterogeneity and phenotype may contribute to FGR pathophysiology across gestation.

The transposable element-derived transcript of LIN28B has a placental origin and is not specific to tumours

Transposable elements (TEs) are genetic elements that have evolved as crucial regulators of human development and cancer, functioning as both genes and regulatory elements. When TEs become dysregulated in cancer cells, they can serve as alternate promoters to activate oncogenes, a process known as onco-exaptation. This study aimed to explore the expression and epigenetic regulation of onco-exaptation events in early human developmental tissues. We discovered co-expression of some TEs and oncogenes in human embryonic stem cells and first trimester and term placental tissues. Previous studies identified onco-exaptation events in various cancer types, including an AluJb SINE element-LIN28B interaction in lung cancer cells, and showed that the TE-derived LIN28B transcript is associated with poor patient prognosis in hepatocellular carcinoma. This study further characterized the AluJb-LIN28B transcript and confirmed that its expression is restricted to the placenta. Targeted DNA methylation analysis revealed differential methylation of the two LIN28B promoters between placenta and healthy somatic tissues, indicating that some TE-oncogene interactions are not cancer-specific but arise from the epigenetic reactivation of developmental TE-derived regulatory events. In conclusion, our findings provide evidence that some TE-oncogene interactions are not limited to cancer and may originate from the epigenetic reactivation of TE-derived regulatory events that are involved in early development. These insights broaden our understanding of the role of TEs in gene regulation and suggest the potential importance of targeting TEs in cancer therapy beyond their conventional use as cancer-specific markers.

Applying Scientific Rationale to the Current Perceptions and Explanations of Massage and Miscarriage in the First Trimester

Miscarriage is a relatively common occurrence, impacting 8-15% of clinically recognised pregnancies, and up to 30% of all conceptions. The public perception of the risk factors associated with miscarriage does not match the evidence. Evidence indicates that there are very few modifiable factors to prevent miscarriage, and the majority of the time little could have been done to prevent a spontaneous miscarriage. However, the public perception is that consuming drugs, lifting a heavy object, previous use of an intrauterine device, or massage can all contribute to miscarriage. While misinformation about the causes and risk factors of miscarriage continues to circulate, pregnant women will experience confusion about what activities they can (and cannot) do in early pregnancy, including receiving a massage. Pregnancy massage is an important component of massage therapy education. The resources that underpin pregnancy massage coursework consist of educational print content that includes direction and caution that massage in the first trimester, if done 'incorrectly' or in the 'wrong' location, can contribute to adverse outcomes such as miscarriage. The most common statements, perceptions and explanations for massage and miscarriage cover three broad areas: 1) maternal changes from massage affects the embryo/fetus; 2) massage leads to damage of the fetus/placenta; and 3) aspects of the massage treatment in the first trimester initiate contractions. The goal of this paper is to use scientific rationale to critically consider the validity of the current perceptions and explanations of massage therapy and miscarriage. Whilst direct evidence from clinical trials was lacking, considerations of physiological mechanisms regulating pregnancy and known risk factors associated with miscarriage provide no evidence that massage in pregnancy would increase a patient's risk of miscarriage. This scientific rationale should be addressed when teaching pregnancy massage courses.

Modelling human placental villous development: designing cultures that reflect anatomy

The use of in vitro tools to study trophoblast differentiation and function is essential to improve understanding of normal and abnormal placental development. The relative accessibility of human placentae enables the use of primary trophoblasts and placental explants in a range of in vitro systems. Recent advances in stem cell models, three-dimensional organoid cultures, and organ-on-a-chip systems have further shed light on the complex microenvironment and cell-cell crosstalk involved in placental development. However, understanding each model's strengths and limitations, and which in vivo aspects of human placentation in vitro data acquired does, or does not, accurately reflect, is key to interpret findings appropriately. To help researchers use and design anatomically accurate culture models, this review both outlines our current understanding of placental development, and critically considers the range of established and emerging culture models used to study this, with a focus on those derived from primary tissue.

Predicting pregnancy specific uterine vascular reactivity: A data driven computational model of shear-dependent, myogenic, and mechanical radial artery features

The entire maternal circulation adapts to pregnancy, and this adaption is particularly extensive in the uterine circulation where the major vessels double in size to facilitate an approximately 15-fold increase in blood supply to this organ over the course of pregnancy. Several factors may play a role in both the remodelling and biomechanical function of the uterine vasculature including the paracrine microenvironment, passive properties of the vessel wall, and active components of vascular function (incorporating the myogenic response and response to shear stress induced by intravascular blood flow). However, the interplay between these factors, and how this plays out in an organ-specific manner to induce the extent of remodelling observed in the uterus is not well understood. Here we present an integrated assessment of the uterine radial arteries, likely rate-limiters to flow of oxygenated maternal blood to the placental surface, via computational modelling and pressure myography. We show that uterine radial arteries behave differently to other systemic vessels (higher compliance and shear mediated constriction) and that their properties change with the adaptation to pregnancy (higher myogenic tone, higher compliance, and ability to tolerate higher flow rates before constricting). Together, this provides a useful tool to improve our understanding of the role of uterine vascular adaptation in normal and abnormal pregnancies and highlights the need for vascular bed specific investigations of vascular function in health and disease.

The Chondrogenic Potential of First-Trimester and Term Placental Mesenchymal Stem/Stromal Cells

OBJECTIVES

Mesenchymal stem/stromal cells (MSCs) are a well-established cell source for cartilage engineering, but challenges remain as differentiation often results in chondrocyte hypertrophy. Chondrogenic potential also varies with MSC source and donor age. We assessed the chondrogenic potential of first-trimester and term placental MSCs and compared their response to commonly used bone marrow MSCs (BM-MSCs).

DESIGN

MSCs were isolated from first-trimester and term placentae. BM-MSCs were commercially obtained. Chondrogenesis was induced by micromass culture in commercial chondrogenic media for 7, 14, or 21 days. Pellets were assessed for glycosaminoglycan (GAG) content, and types I, II, and X collagen. Gene expression was profiled using Qiagen RT2 human MSC arrays.

RESULTS

At day 0, first-trimester and term MSCs expression levels of many chondrogenic genes to BM-MSC after 21 days of culture. Only first trimester MSCs showed significant changes in chondrogenic gene expression during induction compared to day 0 undifferentiated MSCs (greater BMP4, KAT2B, and reduced GDF6 expression). Additionally, first-trimester MSCs showed significantly greater expression of ABCB1 (at days 14 and 21) and BMP4 (at days 7, 14, 21) compared with term MSCs. Both first-trimester and term pellets showed increased GAG content over time and term MSCs had significantly GAG greater compared with BM-MSCs at days 7 and 14. Type II collagen was present in all pellets but unlike BM-MSCs, type I collagen was not observed in first-trimester or term MSC pellets.

CONCLUSIONS

These data highlight differences in BM-MSC and placental MSC chondrogenesis and demonstrate that placental MSCs may be an alternative cell source.

From stem cells to spiral arteries: A journey through early placental development

Early placental development lays the foundation of a healthy pregnancy, and numerous tightly regulated processes must occur for the placenta to meet the increasing nutrient and oxygen exchange requirements of the growing fetus later in gestation. Inadequacies in early placental development can result in disorders such as fetal growth restriction that do not present clinically until the second half of gestation. Indeed, growth restricted placentae exhibit impaired placental development and function, including reduced overall placental size, decreased branching of villi and the blood vessels within them, altered trophoblast function, and impaired uterine vascular remodelling, which together combine to reduce placental exchange capacity. This review explores the importance of early placental development across multiple anatomical aspects of placentation, from the stem cells and lineage hierarchies from which villous core cells and trophoblasts arise, through extravillous trophoblast invasion and spiral artery remodelling, and finally remodelling of the larger uterine vessels.

Know the game: Insights to help early career researchers successfully navigate academia

Career trajectories in science are often unpredictable, with many early and mid-career researchers working multiple successive fixed-term contracts, and physically relocating to take up employment opportunities. Whilst this can provide exciting opportunities to change research direction, acquire new skills, and see the world, the precarity of this scenario is also a significant cause of anxiety for many, and can have a negative impact on their ability to maintain career momentum and trajectory, access institutional financial benefits, or make long term career or financial plans. Here, we build on a pair of workshops held at the 2021 International Federation of Placenta Associations annual conference to discuss two key areas important to help early career researchers navigate their careers - building an academic profile, and the financial ramifications of academic careers.

Differences in human placental mesenchymal stromal cells may impair vascular function in FGR

Placentae from pregnancies with foetal growth restriction (FGR) exhibit poor oxygen and nutrient exchange, in part due to impaired placental vascular development. Placental mesenchymal stromal cells (pMSCs) reside in a perivascular niche, where they may influence blood vessel formation/function. However, the role of pMSCs in vascular dysfunction in FGR is unclear. To elucidate the mechanisms by which pMSCs may impact placental vascularisation we compared the transcriptomes of human pMSCs isolated from FGR (<5th centile) (n = 7) and gestation-matched control placentae (n = 9) using Affymetrix microarrays. At the transcriptome level, there were no statistically significant differences between normal and FGR pMSCs; however, several genes linked to vascular function exhibited notable fold changes, and thus the dataset was used as a hypothesis-generating tool for possible dysfunction in FGR. Genes/proteins of interest were followed up by real-time PCR, western blot and immunohistochemistry. Gene expression of ADAMTS1 and FBLN2 (fibulin-2) were significantly upregulated, whilst HAS2 (hyaluronan synthase-2) was significantly downregulated, in pMSCs from FGR placentae (n = 8) relative to controls (n = 7, P < 0.05 for all). At the protein level, significant differences in the level of fibulin-2 and hyaluronan synthase-2, but not ADAMTS1, were confirmed between pMSCs from FGR and control pregnancies by Western blot. All three proteins demonstrated perivascular expression in third-trimester placentae. Fibulin-2 maintains vessel elasticity, and its increased expression in FGR pMSCs could help explain the increased distensibility of FGR blood vessels. ADAMTS1 and hyaluronan synthase-2 regulate angiogenesis, and their differential expression by FGR pMSCs may contribute to the impaired angiogenesis in these placentae.

Three-dimensional visualisation of the feto-placental vasculature in humans and rodents

Adequate development of the feto-placental circulation is critical for placental exchange function and healthy fetal growth. Understanding the structure of this circulation and how it informs fetal outcomes is important both in the human placenta, and the rodent, a purported comparative experimental model. Vascular casting and micro-CT imaging approaches enable detailed quantification of the complex vascular relationships in the feto-circulation, and provide detailed data to parameterise in silico models. Here, to assist researchers to apply these technically challenging methods we provide detailed approaches to cast and image; 1) human placentas at the cotyledon-level, and 2) whole rodent placentas.

Multiscale and multimodal imaging of utero-placental anatomy and function in pregnancy

Placental structures at the nano-, micro-, and macro scale each play important roles in contributing to its function. As such, quantifying the dynamic way in which placental structure evolves during pregnancy is critical to both clinical diagnosis of pregnancy disorders, and mechanistic understanding of their pathophysiology. Imaging the placenta, both exvivo and invivo, can provide a wealth of structural and/or functional information. This review outlines how imaging across modalities and spatial scales can ultimately come together to improve our understanding of normal and pathological pregnancies. We discuss how imaging technologies are evolving to provide new insights into placental physiology across disciplines, and how advanced computational algorithms can be used alongside state-of-the-art imaging to obtain a holistic view of placental structure and its associated functions to improve our understanding of placental function in health and disease.

Something old, something new: digital quantification of uterine vascular remodelling and trophoblast plugging in historical collections provides new insight into adaptation of the utero-placental circulation

STUDY QUESTION

What is the physiological extent of vascular remodelling in and trophoblast plugging of the uterine circulation across the first half of pregnancy?

SUMMARY ANSWER

All levels of the uterine vascular tree (arcuate, radial and spiral arteries (SAs)) dilate ∼2.6- to 4.3-fold between 6 and 20 weeks of gestation, with significant aggregates of trophoblasts persisting in the decidual and myometrial parts of SAs beyond the first trimester.

WHAT IS KNOWN ALREADY

In early pregnancy, endovascular trophoblasts form 'plugs' in the SAs, transiently inhibiting blood flow to the placenta, whilst concurrently the uterine vasculature undergoes significant adaption to facilitate increased blood delivery to the placenta later in gestation. These processes are impaired in pregnancy disorders, but quantitative understanding of the anatomical changes even in normal pregnancy is poor.

STUDY DESIGN, SIZE, DURATION

Serial sections of normal placentae in situ (n = 22) of 6.1-20.5 weeks of gestation from the Boyd collection and Dixon collection (University of Cambridge, UK) were digitalized using a slide scanner or Axio Imager.A1 microscope.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Spiral (n = 45), radial (n = 40) and arcuate (n = 39) arteries were manually segmented. Using custom-written scripts for Matlab® software, artery dimensions (Feret diameters; major axes; luminal/wall area) and endovascular trophoblast plug/aggregate (n = 24) porosities were calculated. Diameters of junctional zone SAs within the myometrium (n = 35) were acquired separately using a micrometre and light microscope. Decidual thickness and trophoblast plug depth was measured using ImageJ.

MAIN RESULTS AND THE ROLE OF CHANCE

By all measures, radial and arcuate artery dimensions progressively increased from 6.1 to 20.5 weeks (P < 0.01). The greatest increase in SA calibre occurred after 12 weeks of gestation. Trophoblast aggregates were found to persist within decidual and myometrial parts of SA lumens beyond the first trimester, and up to 18.5 weeks of gestation, although those present in the second trimester did not appear to prevent the passage of red blood cells to the intervillous space. Trophoblasts forming these aggregates became more compact (decreased in porosity) over gestation, whilst channel size between cells increased (P = 0.01). Decidual thickness decreased linearly over gestation (P = 0.0003), meaning plugs occupied an increasing proportion of the decidua (P = 0.02).

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

Although serial sections were assessed, two-dimensional images cannot completely reflect the three-dimensional properties and connectivity of vessels and plugs/aggregates. Immersion-fixation of the specimens means that vessel size may be under-estimated.

WIDER IMPLICATIONS OF THE FINDINGS

Uterine vascular remodelling and trophoblast plug dispersion is a progressive phenomenon that is not completed by the end of the first trimester. Our quantitative findings support the concept that radial arteries present a major site of resistance until mid-gestation. Their dimensional increase at 10-12 weeks of gestation may explain the rapid increase in blood flow to the placenta observed by others at ∼13 weeks. Measured properties of trophoblast plugs suggest that they will impact on the resistance, shear stress and nature of blood flow within the utero-placental vasculature until mid-gestation. The presence of channels within plugs will likely lead to high velocity flow streams and thus increase shear stress experienced by the trophoblasts forming the aggregates. Quantitative understanding of utero-placental vascular adaptation gained here will improve in silico modelling of utero-placental haemodynamics and provide new insights into pregnancy disorders, such as fetal growth restriction.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by a Royal Society Te Aparangi Marsden Grant [18-UOA-135]. A.R.C. is supported by a Rutherford Discovery Fellowship [14-UOA-019]. The authors have no conflict of interest to declare.

Structure-function relationships in the feto-placental circulation from in silico interpretation of micro-CT vascular structures

A well-functioning placenta is critical for healthy fetal development, as the placenta brings fetal blood in close contact with nutrient rich maternal blood, enabling exchange of nutrients and waste between mother and fetus. The feto-placental circulation forms a complex branching structure, providing blood to fetal capillaries, which must receive sufficient blood flow to ensure effective exchange, but at a low enough pressure to prevent damage to placental circulatory structures. The branching structure of the feto-placental circulation is known to be altered in complications such as fetal growth restriction, and the presence of regions of vascular dysfunction (such as hypovascularity or thrombosis) are proposed to elevate risk of placental pathology. Here we present a methodology to combine micro-computed tomography and computational model-based analysis of the branching structure of the feto-placental circulation in ex vivo placentae from normal term pregnancies. We analyse how vascular structure relates to function in this key organ of pregnancy; demonstrating that there is a 'resilience' to placental vascular structure-function relationships. We find that placentae with variable chorionic vascular structures, both with and without a Hyrtl's anastomosis between the umbilical arteries, and those with multiple regions of poorly vascularised tissue are able to function with a normal vascular resistance. Our models also predict that by progressively introducing local heterogeneity in placental vascular structure, large increases in feto-placental vascular resistances are induced. This suggests that localised heterogeneities in placental structure could potentially provide an indicator of increased risk of placental dysfunction.

Influence of culture media on the derivation and phenotype of fetal-derived placental mesenchymal stem/stromal cells across gestation

INTRODUCTION

Derivation of pure fetal placental mesenchymal stem/stromal cells (pMSCs) is key to understand their role in placental development. However, isolated pMSCs are often contaminated by maternal-derived decidual MSCs (dMSCs). EGM-2 medium promotes the derivation of term fetal pMSCs, but the extent of first-trimester maternal pMSC contamination remains unclear. Culture media can also affect MSC phenotype. Here, we examined the effects of culture media on maternal pMSC contamination and fetal pMSC phenotype across gestation.

METHODS

pMSCs were derived from first-trimester or term placentae in advanced-DMEM/F12 medium or EGM-2 medium. Proportions of maternal (XX) and fetal (XY) cells in male pMSC cultures were determined by fluorescence in-situ hybridization. pMSC phenotype was analysed by flow cytometry, immunohistochemistry and Alamar blue proliferation assays.

RESULTS

When derived in advanced-DMEM/F12, all first trimester pMSC isolates exhibited maternal contamination (>72% XX cells, n = 5), whilst 7/9 term pMSC isolates were >98% fetal. When derived in EGM-2, all first trimester (n = 4) and term (n = 9) pMSC isolates contained 95-100% fetal cells. Fetal pMSCs in EGM-2 proliferated 2-fold (first-trimester) or 4-fold (term) faster than those in advanced-DMEM/F12 (p < 0.05, n = 3). Fetal pMSCs in both media expressed the generic MSC marker profile (CD90⁺, CD105+, CD73⁺, CD31-, CD34-, CD144-). However, pMSCs transferred from EGM-2 to advanced-DMEM/F12 increased expression of smooth muscle cell markers calponin and α-smooth muscle actin, and decreased expression of the vascular cell marker VEGFR2 (n = 3).

CONCLUSIONS

Deriving first-trimester pMSC in EGM-2 dramatically reduces maternal dMSC contamination. Media affects fetal pMSC phenotype, and careful consideration should be given to application specific culture conditions.

Computational modeling of the interactions between the maternal and fetal circulations in human pregnancy

In pregnancy, fetal growth is supported by its placenta. In turn, the placenta is nourished by maternal blood, delivered from the uterus, in which the vasculature is dramatically transformed to deliver this blood an ever increasing volume throughout gestation. A healthy pregnancy is thus dependent on the development of both the placental and maternal circulations, but also the interface where these physically separate circulations come in close proximity to exchange gases and nutrients between mum and baby. As the system continually evolves during pregnancy, our understanding of normal vascular anatomy, and how this impacts placental exchange function is limited. Understanding this is key to improve our ability to understand, predict, and detect pregnancy pathologies, but presents a number of challenges, due to the inaccessibility of the pregnant uterus to invasive measurements, and limitations in the resolution of imaging modalities safe for use in pregnancy. Computational approaches provide an opportunity to gain new insights into normal and abnormal pregnancy, by connecting observed anatomical changes from high-resolution imaging to function, and providing metrics that can be observed by routine clinical ultrasound. Such advanced modeling brings with it challenges to scale detailed anatomical models to reflect organ level function. This suggests pathways for future research to provide models that provide both physiological insights into pregnancy health, but also are simple enough to guide clinical focus. We the review evolution of computational approaches to understanding the physiology and pathophysiology of pregnancy in the uterus, placenta, and beyond focusing on both opportunities and challenges. This article is categorized under: Reproductive System Diseases >Computational Models.

The placenta in fetal growth restriction: What is going wrong?

The placenta is essential for the efficient delivery of nutrients and oxygen from mother to fetus to maintain normal fetal growth. Dysfunctional placental development underpins many pregnancy complications, including fetal growth restriction (FGR) a condition in which the fetus does not reach its growth potential. The FGR placenta is smaller than normal placentae throughout gestation and displays maldevelopment of both the placental villi and the fetal vasculature within these villi. Specialized epithelial cells called trophoblasts exhibit abnormal function and development in FGR placentae. This includes an altered balance between proliferation and apoptotic death, premature cellular senescence, and reduced colonisation of the maternal decidual tissue. Thus, the placenta undergoes aberrant changes at the macroscopic to cellular level in FGR, which can limit exchange capacity and downstream fetal growth. This review aims to compile stereological, in vitro, and imaging data to create a holistic overview of the FGR placenta and its pathophysiology, with a focus on the contribution of trophoblasts.

Establishment of maternal blood supply to the placenta: insights into plugging, unplugging and trophoblast behaviour from an agent-based model

The ability of the baby to receive nutrients and oxygen in utero depends on the healthy development of the placenta. For maternal blood to adequately perfuse the placenta, it dramatically alters the arteries in the uterus that supply it with nutrient-rich blood right from the start of pregnancy. Placental cells (trophoblasts) invade both into the tissue of the uterus and into the maternal blood vessels nearest to the site of implantation (the spiral arteries (SAs)) and transform these allowing a relatively high and steady flow of nutrient-rich blood to perfuse the placenta. Trophoblasts also form plugs that occlude SAs, preventing maternal blood flow to the placenta until the late first trimester, at which point these plugs dislodge or disintegrate. Here we present an agent-based model of trophoblast migration within plugged SAs to tease apart the impact of chemical signals and mechanical factors on trophoblast behaviour. The model supports our previous in vitro hypothesis that plugging of the maternal arteries in early pregnancy can act to promote trophoblast invasion by providing a 'low flow' environment and extends our understanding by suggesting 'weak spots' in plug structure can lead to plug degeneration, allowing increased blood flow through the materno-fetal circulation.

Differences in placental capillary shear stress in fetal growth restriction may affect endothelial cell function and vascular network formation

Fetal growth restriction (FGR) affects 5-10% of pregnancies, leading to clinically significant fetal morbidity and mortality. FGR placentae frequently exhibit poor vascular branching, but the mechanisms driving this are poorly understood. We hypothesize that vascular structural malformation at the organ level alters microvascular shear stress, impairing angiogenesis. A computational model of placental vasculature predicted elevated placental micro-vascular shear stress in FGR placentae (0.2 Pa in severe FGR vs 0.05 Pa in normal placentae). Endothelial cells cultured under predicted FGR shear stresses migrated significantly slower and with greater persistence than in shear stresses predicted in normal placentae. These cell behaviors suggest a dominance of vessel elongation over branching. Taken together, these results suggest (1) poor vascular development increases vessel shear stress, (2) increased shear stress induces cell behaviors that impair capillary branching angiogenesis, and (3) impaired branching angiogenesis continues to drive elevated shear stress, jeopardizing further vascular formation. Inadequate vascular branching early in gestation could kick off this cyclic loop and continue to negatively impact placental angiogenesis throughout gestation.

Placental formation in early pregnancy: how is the centre of the placenta made?

BACKGROUND

Correct development of the placenta is critical to establishing pregnancy and inadequate placentation leads to implantation failure and miscarriage, as well as later gestation pregnancy disorders. Much attention has been focused on the placental trophoblasts and it is clear that the trophoblast lineages arise from the trophectoderm of the blastocyst. In contrast, the cells of the placental mesenchyme are thought to arise from the inner cell mass, but the details of this process are limited. Due to ethical constraints and the inaccessibility of very early implantation tissues, our knowledge of early placentation has been largely based on historical histological sections. More recently, stem cell technologies have begun to shed important new light on the origins of the placental mesenchymal lineages.

OBJECTIVE AND RATIONALE

This review aims to amalgamate the older and more modern literature regarding the origins of the non-trophoblast lineages of the human placenta. We highlight ways in which rapidly developing stem cell technologies may shed new light on these crucial peri-implantation events.

SEARCH METHODS

Relevant articles were identified using the PubMed database and Google Scholar search engines. A pearl growing method was used to expand the scope of papers relevant to the cell differentiation events of non-trophoblast placental lineages.

OUTCOMES

At the start of pregnancy, cells of the extraembyronic mesoderm migrate to underlie the primitive trophoblast layers forming the first placental villi. The mesenchymal cells in the villus core most likely originate from the hypoblast of the embryo, but whether cells from the epiblast also contribute is yet to be determined. This is important because, following the formation of the villus core, vasculogenesis and haematopoiesis take place in the nascent placenta before it is connected to the embryonic circulation, making it likely that haematopoietic foci, placental macrophages, endothelial cells and vascular smooth muscle cells all arise in the placenta de novo. Evidence from the stem cell field indicates that these cells could directly differentiate from the extraembryonic mesoderm. However, the lineage hierarchy involved in cell fate decisions has not been well-established. Mesodermal progenitors capable of differentiating into both vascular and haematopoietic lineages can be derived from human embryonic stem cells, but the identification of such stem cells in the placenta is lacking. Future work profiling rare progenitor populations in early placentae will aid our understanding of early placentation.

WIDER IMPLICATIONS

Understanding the origins of the cell lineages of the normal placenta will help us understand why so many pregnancies fail and address mechanisms that may salvage some of these losses.

The role of DNA methylation in human trophoblast differentiation

The placenta is a vital fetal exchange organ connecting mother and baby. Specialised placental epithelial cells, called trophoblasts, are essential for adequate placental function. Trophoblasts transform the maternal vasculature to allow efficient blood flow to the placenta and facilitate adequate nutrient uptake. Placental development is in part regulated by epigenetic mechanisms. However, our understanding of how DNA methylation contributes to human trophoblast differentiation is limited. To better understand how genome-wide methylation differences affect trophoblast differentiation, reduced representation bisulfite sequencing (RRBS) was conducted on four matched sets of trophoblasts; side-population trophoblasts (a candidate human trophoblast stem cell population), cytotrophoblasts (an intermediate progenitor population), and extravillous trophoblasts (EVT, a terminally differentiated population) each isolated from the same first trimester placenta. Each trophoblast population had a distinct methylome. In line with their close differentiation relationship, the methylation profile of side-population trophoblasts was most similar to cytotrophoblasts, whilst EVT had the most distinct methylome. In comparison to mature trophoblast populations, side-population trophoblasts exhibited differential methylation of genes and miRNAs involved in cell cycle regulation, differentiation, and regulation of pluripotency. A combined methylomic and transcriptomic approach was taken to better understand cytotrophoblast differentiation to EVT. This revealed methylation of 41 genes involved in epithelial to mesenchymal transition and metastatic cancer pathways, which likely contributes to the acquisition of an invasive EVT phenotype. However, the methylation status of a gene did not always predict gene expression. Therefore, while CpG methylation plays a role in trophoblast differentiation, it is likely not the only regulatory mechanism involved in this process.

Human trophoblasts are primarily distinguished from somatic cells by differences in the pattern rather than the degree of global CpG methylation

The placenta is a fetal exchange organ connecting mother and baby that facilitates fetal growth in utero. DNA methylation is thought to impact placental development and function. Global DNA methylation studies using human placental lysates suggest that the placenta is uniquely hypomethylated compared to somatic tissue lysates, and this hypomethylation is thought to be important in conserving the unique placental gene expression patterns required for successful function. In the placental field, methylation has frequently been examined in tissue lysates, which contain mixed cell types that can confound results. To better understand how DNA methylation influences placentation, DNA from isolated first trimester trophoblast populations underwent reduced representation bisulfite sequencing and was compared to publicly available data of blastocyst-derived and somatic cell populations. First, this revealed that, unlike murine blastocysts, human trophectoderm and inner cell mass samples did not have significantly different levels of global methylation. Second, our work suggests that differences in global CpG methylation between trophoblasts and somatic cells are much smaller than previously reported. Rather, our findings suggest that different patterns of CpG methylation may be more important in epigenetically distinguishing the placenta from somatic cell populations, and these patterns of methylation may contribute to successful placental/trophoblast function.

Summary: The placenta may not be as uniquely hypomethylated as previously reported, rather differences in the pattern of CpG methylation are what make it epigenetically distinct.

Placental Nano-vesicles Target to Specific Organs and Modulate Vascular Tone In Vivo

STUDY QUESTION

How do nano-vesicles extruded from normal first trimester human placentae affect maternal vascular function?

SUMMARY ANSWER

Placental nano-vesicles affect the ability of systemic mesenteric arteries to undergo endothelium- and nitric oxide- (NO-) dependent vasodilation in vivo in pregnant mice.

WHAT IS KNOWN ALREADY

Dramatic cardiovascular adaptations occur during human pregnancy, including a substantial decrease in total peripheral resistance in the first trimester. The human placenta constantly extrudes extracellular vesicles that can enter the maternal circulation and these vesicles may play an important role in feto-maternal communication.

STUDY DESIGN, SIZE, DURATION

Human placental nano-vesicles were administered into CD1 mice via a tail vein and their localization and vascular effects at 30 min and 24 h post-injection were investigated.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Nano-vesicles from normal first trimester human placentae were collected and administered into pregnant (D12.5) or non-pregnant female mice. After either 30 min or 24 h of exposure, all major organs were dissected for imaging (n = 7 at each time point) while uterine and mesenteric arteries were dissected for wire myography (n = 6 at each time point). Additional in vitro studies using HMEC-1 endothelial cells were also conducted to investigate the kinetics of interaction between placental nano-vesicles and endothelial cells.

MAIN RESULTS AND THE ROLE OF CHANCE

Nano-vesicles from first trimester human placentae localized to the lungs, liver and kidneys 24 h after injection into pregnant mice (n = 7). Exposure of pregnant mice to placental nano-vesicles for 30 min in vivo increased the vasodilatory response of mesenteric arteries to acetylcholine, while exposure for 24 h had the opposite effect (P < 0.05, n = 6). These responses were prevented by L-NAME, an NO synthase inhibitor. Placental nano-vesicles did not affect the function of uterine arteries or mesenteric arteries from non-pregnant mice. Placental nano-vesicles rapidly interacted with endothelial cells via a combination of phagocytosis, endocytosis and cell surface binding in vitro.

LARGE SCALE DATA

N/A.

LIMITATIONS REASONS FOR CAUTION

As it is not ethical to administer labelled placental nano-vesicles to pregnant women, pregnant CD1 mice were used as a model of pregnancy.

WIDER IMPLICATIONS OF THE FINDINGS

This is the first study to report the localization of placental nano-vesicles and their vascular effects in vivo. This work provides new insight into how the dramatic maternal cardiovascular adaptations to pregnancy may occur and indicates that placental extracellular vesicles may be important mediators of feto-maternal communication in a healthy pregnancy.

STUDY FUNDING/COMPETING INTEREST(S)

This research was supported by the Faculty of Medical and Health Science (FMHS) School of Medicine PBRF research fund to L.W.C. M.T. is a recipient of a University of Auckland Health Research Doctoral Scholarship and the Freemasons Postgraduate Scholarship. No authors have any competing interests to disclose.

Understanding abnormal uterine artery Doppler waveforms: A novel computational model to explore potential causes within the utero-placental vasculature

INTRODUCTION

Uterine artery (UtA) Doppler indices are one of the most commonly employed screening tests for pre-eclampsia worldwide. Abnormal indices appear to result from increased uterine vascular resistance, but anatomical complexity and lack of appropriate animal models mean that little is known about the relative contribution of each of the components of the uterine vasculature to the overall UtA Doppler waveform. Previous computational models suggested that trophoblast-mediated spiral artery remodeling has a dominant effect on the UtA Doppler waveform. However, these models did not incorporate the myometrial arterio-venous anastomoses, which have significant potential to affect utero-placental haemodynamics.

METHODS

We present a more anatomically complete computational model, explicitly incorporating a structural description of each component of the uterine vasculature, and crucially including myometrial arterio-venous anastomoses as parallel pathways for blood-flow away from the placental bed. Wave transmission theory was applied to the network to predict UtA waveforms.

RESULTS

Our model shows that high UtA resistance indices, combined with notching, reflect an abnormal remodeling of the entire uterine vasculature. Incomplete spiral artery remodeling alone is unlikely to cause abnormal UtA Doppler waveforms as increased resistance in these arteries can be 'buffered' by upstream anastomoses. Critically, our results indicate that the radial arteries, may have a more important effect on utero-placental flow dynamics, and the UtA Doppler waveform than previously thought.

CONCLUSIONS

This model suggests that to appropriately interpret UtA Doppler waveforms they must be considered to be reflecting changes in the entire system, rather than just the spiral arteries.

Association of Placental Jets and Mega-Jets With Reduced Villous Density

Spiral arteries (SAs) lie at the interface between the uterus and placenta, and supply nutrients to the placental surface. Maternal blood circulation is separated from the fetal circulation by structures called villous trees. SAs are transformed in early pregnancy from tightly coiled vessels to large high-capacity channels, which is believed to facilitate an increased maternal blood flow throughout pregnancy with minimal increase in velocity, preventing damage to delicate villous trees. Significant maternal blood flow velocities have been theorized in the space surrounding the villi (the intervillous space, IVS), particularly when SA conversion is inadequate, but have only recently been visualized reliably using pulsed wave Doppler ultrasonography. Here, we present a computational model of blood flow from SA openings, allowing prediction of IVS properties based on jet length. We show that jets of flow observed by ultrasound are likely correlated with increased IVS porosity near the SA mouth and propose that observed mega-jets (flow penetrating more than half the placental thickness) are only possible when SAs open to regions of the placenta with very sparse villous structures. We postulate that IVS tissue density must decrease at the SA mouth through gestation, supporting the hypothesis that blood flow from SAs influences villous tree development.

Antiphospholipid antibodies increase the levels of mitochondrial DNA in placental extracellular vesicles: Alarmin-g for preeclampsia

The pathogenesis of preeclampsia remains unclear but placental factors are known to play a crucial role causing maternal endothelial cell dysfunction. One potential factor is placental micro- and nano- vesicles. Antiphospholipid antibodies (aPL) increase the risk of preeclampsia ten-fold, in part by damaging the mitochondria in the syncytiotrophoblast. Since mitochondrial DNA (mtDNA) is a danger- associated molecular pattern (DAMP/alarmin) that may activate endothelial cells, the aims of the current study were to investigate whether aPL affect the number of placental vesicles extruded, their mtDNA content and their ability to activate endothelial cells. Exposure of first trimester human placental explants to aPL affected neither the number nor size of extruded micro- and nano- vesicles (n = 5), however their levels of mtDNA were increased (n = 6). These vesicles significantly activated endothelial cells (n = 5), which was prevented by blocking toll-like receptor 9 (TLR-9), a receptor for extracellular DNA. Thus, aPL may increase the risk of preeclampsia in part by increasing the amount of mtDNA associated with placental vesicles. That mitochondrial DNA is recognised as a DAMP by TLR-9 to cause endothelial cell activation, raises the possibility that placental vesicles or TLR-9 might be a target for pharmaceutical intervention to reduce the consequences of aPL in pregnancy.

Placental trophoblast debris mediated feto-maternal signalling via small RNA delivery: implications for preeclampsia

To profile the small RNA cargo carried by trophoblast debris derived from the placenta during normal and preeclamptic pregnancies and to determine whether trophoblast debris can deliver its small RNAs to endothelial cells with functional consequences. We confirmed that trophoblast debris can deliver its small RNAs contents to recipient endothelial cells during the co-culture. Next generation sequencing was employed to profile the small RNA contents in both normotensive and preeclamptic trophoblast debris. We identified 1278 mature miRNAs and 2646 non-miRNA small RNA fragments contained. Differential expression analysis identified 16 miRNAs (including miR-145), 5 tRNA fragments from 3 different tRNAs, 13 snRNA fragments and 85 rRNA fragments that were present in different levels between preeclamptic and normotensive trophoblast debris. We loaded a miR-145 mimic into normotensive trophoblast debris via transfection of placental explants from which the debris was derived and found the miR-145 loaded debris induced transcriptomic changes in endothelial cells similar to those induced by preeclamptic trophoblast debris. Trophoblast debris deported into maternal circulation can deliver its small RNA contents to maternal cells thereby contributing to feto-maternal communication. Small RNAs that are dysregulated in preeclamptic trophoblast debris might contribute to the endothelial cell activation which is a hallmark of preeclampsia.

Feeding Your Baby In Utero: How the Uteroplacental Circulation Impacts Pregnancy

The utero-placental circulation links the maternal and fetal circulations during pregnancy, ensuring adequate gas and nutrient exchange, and consequently fetal growth. However, our understanding of this circulatory system remains incomplete. Here, we discuss how the utero-placental circulation is established, how it changes dynamically during pregnancy, and how this may impact on pregnancy success, highlighting how we may address knowledge gaps through advances in imaging and computational modeling approaches.

In vivo targets of human placental micro-vesicles vary with exposure time and pregnancy

Throughout human gestation, the placenta extrudes vast quantities of extracellular vesicles (EVs) of different sizes into the maternal circulation. Although multinucleated macro-vesicles are known to become trapped in the maternal lungs and do not enter the peripheral circulation, the maternal organs and cells that smaller placental micro-vesicles interact with in vivo remain unknown. This study aimed to characterise the interaction between placental micro-vesicles and endothelial cells in vitro and to elucidate which organs placental micro-vesicles localise to in vivo Placental macro- and micro-vesicles were isolated from cultured human first trimester placental explants by sequential centrifugation and exposed to human microvascular endothelial cells for up to 72 h. In vivo, placental macro- and micro-vesicles were administered to both non-pregnant and pregnant CD1 mice, and after two or 30 min or 24 h, organs were imaged on an IVIS Kinetic Imager. Placental EVs rapidly interacted with endothelial cells via phagocytic and clathrin-mediated endocytic processes in vitro, with over 60% of maximal interaction being achieved by 30 min of exposure. In vivo, placental macro-vesicles were localised exclusively to the lungs regardless of time of exposure, whereas micro-vesicles were localised to the lungs, liver and kidneys, with different distribution patterns depending on the length of exposure and whether the mouse was pregnant or not. The fact that placental EVs can rapidly interact with endothelial cells and localise to different organs in vivo supports that different size fractions of placental EVs are likely to have different downstream effects on foeto-maternal communication.

Micro- and Nano-vesicles from First Trimester Human Placentae Carry Flt-1 and Levels Are Increased in Severe Preeclampsia

BACKGROUND/OBJECTIVES

Preeclampsia is a life-threatening hypertensive disease affecting 3-5% of pregnancies. While the pathogenesis of preeclampsia remains unclear, it is known that placenta-derived factors trigger the disease by activating maternal endothelial cells prior to the onset of clinical symptoms. Extracellular vesicles (EVs) of different sizes extruded by the placenta may be one factor. The truncated/secreted form of Flt-1 (sFlt-1) has also been implicated in the pathogenesis of preeclampsia. We investigated whether placental EV production is altered in preeclampsia such that they induce endothelial cell activation, and whether (s)Flt-1 is involved.

METHODS

Macro-, micro-, and nano-vesicles were collected from normal and preeclamptic (PE) placental explants, and separated by differential centrifugation. The number and size of micro- and nano-vesicles was measured by nanoparticle tracking analysis and their ability to activate endothelial cells was quantified by endothelial cell intercellular adhesion molecule 1 expression and monocyte adhesion. The levels of Flt-1 were measured by western blots and ELISA.

RESULTS

PE placentae extruded significantly more micro- and nano-vesicles than control placentae and the extruded micro-vesicles were larger than those from control placentae. Micro- and nano-vesicles from both first trimester and term human placentae carried Flt-1 and levels were significantly increased in EVs from severe, but not mild, PE compared to normotensive placentae. All fractions of EVs from PE placentae activated endothelial cells, and for micro- and nano-vesicles, activation was reduced in the presence of exogenous vascular endothelial growth factor (VEGF), a Flt-1 neutralizing antibody, or by pre-treatment with VEGF. While EV-bound VEGF constituted over 20% of the total detected VEGF secreted by PE and normotensive placentae, EV-bound Flt-1 did not significantly contribute to the total level of sFlt-1/Flt-1 released by human third trimester placentae.

DISCUSSION

Micro- and nano-vesicles extruded by human placentae carry Flt-1 across gestation and in severe preeclampsia, the levels of vesicle-bound Flt-1 are upregulated. All fractions of PE placental EVs activated endothelial cells and for micro- and nano-vesicles, this was in part due to the ability of EV-bound Flt-1 to sequester VEGF. That placental EVs can activate endothelial cells supports the contention that EVs are one placental toxin contributing to the pathogenesis of preeclampsia.

Stem cell insights into human trophoblast lineage differentiation

BACKGROUND

The human placenta is vital for fetal development, yet little is understood about how it forms successfully to ensure a healthy pregnancy or why this process is inadequate in 1 in 10 pregnancies, leading to miscarriage, intrauterine growth restriction or preeclampsia. Trophoblasts are placenta-specific epithelial cells that maximize nutrient exchange. All trophoblast lineages are thought to arise from a population of trophoblast stem cells (TSCs). However, whilst the isolation of murine TSC has led to an explosion in understanding murine placentation, the isolation of an analogous human TSC has proved more difficult. Consequently, alternative methods of studying human trophoblast lineage development have been employed, including human embryonic stem cells (hESCs), induced pluripotent stem cells (iPS) and transformed cell lines; but what do these proxy models tell us about what is happening during early placental development?

OBJECTIVE AND RATIONALE

In this systematic review, we evaluate current approaches to understanding human trophoblast lineage development in order to collate and refine these models and inform future approaches aimed at establishing human TSC lines.

SEARCH METHODS

To ensure all relevant articles were analysed, an unfiltered search of Pubmed, Embase, Scopus and Web of Science was conducted for 25 key terms on the 13th May 2016. In total, 47 313 articles were retrieved and manually filtered based on non-human, non-English, non-full text, non-original article and off-topic subject matter. This resulted in a total of 71 articles deemed relevant for review in this article.

OUTCOMES

Candidate human TSC populations have been identified in, and isolated from, both the chorionic membrane and villous tissue of the placenta, but further investigation is required to validate these as 'true' human TSCs. Isolating human TSCs from blastocyst trophectoderm has not been successful in humans as it was in mice, although recently the first reported TSC line (USFB6) was isolated from an eight-cell morula. In lieu of human TSC lines, trophoblast-like cells have been induced to differentiate from hESCs and iPS. However, differentiation in these model systems is difficult to control, culture conditions employed are highly variable, and the extent to which they accurately convey the biology of 'true' human TSCs remains unclear, particularly as a consensus has not been met among the scientific community regarding which characteristics a human TSC must possess.

WIDER IMPLICATIONS

Human TSC models have the potential to revolutionize our understanding of trophoblast differentiation, allowing us to make significant gains in understanding the underlying pathology of pregnancy disorders and to test potential therapeutic interventions on cell function in vitro. In order to do this, a collaborative effort is required to establish the criteria that define a human TSC to confirm the presence of human TSCs in both primary isolates and to determine how accurately trophoblast-like cells derived from current model systems reflect trophoblast from primary tissue. The in vitro systems currently used to model early trophoblast lineage formation have provided insights into early human placental formation but it is unclear whether these trophoblast-like cells are truly representative of primary human trophoblast. Consequently, continued refinement of current models, and standardization of culture protocols is essential to aid our ability to identify, isolate and propagate 'true' human TSCs from primary tissue.

IFPA meeting 2015 workshop report IV: placenta and obesity; stem cells of the feto-maternal interface; placental immunobiology and infection

Workshops are an important part of the IFPA annual meeting as they allow for discussion of specialised topics. At the 2015 IFPA annual meeting there were 12 themed workshops, three of which are summarized in this report. These workshops related to various aspects of placental biology and collectively covered areas of obesity and the placenta, stem cells of the feto-maternal interface, and placental immunobiology and infection.

A multiscale model of placental oxygen exchange: The effect of villous tree structure on exchange efficiency

The placenta is critical to fetal health during pregnancy as it supplies oxygen and nutrients to maintain life. It has a complex structure, and alterations to this structure across spatial scales are associated with several pregnancy complications, including intrauterine growth restriction (IUGR). The relationship between placental structure and its efficiency as an oxygen exchanger is not well understood in normal or pathological pregnancies. Here we present a computational framework that predicts oxygen transport in the placenta which accounts for blood and oxygen transport in the space around a placental functional unit (the villous tree). The model includes the well-defined branching structure of the largest villous tree branches, as well as a smoothed representation of the small terminal villi that comprise the placenta's gas exchange interfaces. The model demonstrates that oxygen exchange is sensitive to villous tree geometry, including the villous branch length and volume, which are seen to change in IUGR. This is because, to be an efficient exchanger, the architecture of the villous tree must provide a balance between maximising the surface area available for exchange, and the opposing condition of allowing sufficient maternal blood flow to penetrate into the space surrounding the tree. The model also predicts an optimum oxygen exchange when the branch angle is 24 °, as villous branches and TBs are spread out sufficiently to channel maternal blood flow deep into the placental tissue for oxygen exchange without being shunted directly into the DVs. Without concurrent change in the branch length and angles, the model predicts that the number of branching generations has a small influence on oxygen exchange. The modelling framework is presented in 2D for simplicity but is extendible to 3D or to incorporate the high-resolution imaging data that is currently evolving to better quantify placental structure.

Proteomic characterization of macro-, micro- and nano-extracellular vesicles derived from the same first trimester placenta: relevance for feto-maternal communication

STUDY QUESTION

What proteins are carried by extracellular vesicles (EVs) released from normal first trimester placentae?

SUMMARY ANSWER

One thousand five hundred and eighty-five, 1656 and 1476 proteins were characterized in macro-, micro- and nano-vesicles, respectively, from first trimester placentae, with all EV fractions being enriched for proteins involved in vesicle transport and inflammation.

WHAT IS KNOWN ALREADY

Placental EVs are being increasingly recognized as important mediators of both healthy and pathological pregnancies. However, current research has focused on detecting changes in specific proteins in particular fractions of vesicles during disease. This is the first study to investigate the full proteome of different-sized fractions of EVs from the same first trimester placenta and highlights the differences/similarities between the vesicle fractions.

STUDY DESIGN, SIZE, DURATION

A well-established ex vivo placental explant culture model was used to generate macro-, micro- and nano-vesicles from 56 first trimester placentae. Vesicle fractions were collected by differential ultracentrifugation, quantified and characterized.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Placental macro-, micro- and nano-vesicles were characterized by microscopy, dynamic light scattering and nanoparticle tracking analysis. The proteome of each EV fraction was interrogated using liquid chromatography-coupled tandem mass spectrometry. Results were validated by semi-quantitative western blotting.

MAIN RESULTS AND THE ROLE OF CHANCE

A total of 1585, 1656 and 1476 proteins were identified in macro-, micro- and nano-vesicles, respectively. One thousand one hundred and twenty-five proteins were shared between all three fractions while up to 223 proteins were unique to each fraction. Gene Ontology pathway analysis showed an enrichment of proteins involved in vesicle transport and inflammation in all three fractions of EVs. The expression levels of proteins involved in internalization of vesicles (annexin V, calreticulin, CD31, CD47), the complement pathway [C3, decay-accelerating factor (DAF), membrane cofactor protein (MCP), protectin] and minor histocompatibility antigens [ATP-dependent RNA helicase (DDX3), ribosomal protein S4 (RPS4)] were different between different-sized EVs.

LIMITATIONS, REASONS FOR CAUTION

This study is largely hypothesis-generating in nature. It is important to validate these findings using EVs isolated from maternal plasma and the function of the different EV fractions would need further investigation.

WIDER IMPLICATIONS OF THE FINDINGS

Our results support the concept that various EV factions can interact with different maternal cells and have unique effects to mediate feto-maternal communication during early pregnancy. This study also provides a list of candidate proteins, which may inform the identification of robust markers that can be used to isolate placental vesicles from the maternal blood in the future.

STUDY FUNDING/COMPETING INTERESTS

M.T. is a recipient of the University of Auckland Health Research Doctoral Scholarship and the Freemasons Postgraduate Scholarship. This project was supported by a School of Medicine Performance-based research fund (PBRF) grant awarded to L.W.C. No authors have any conflicts of interest to disclose.

Stem Cells and Pregnancy Disorders: From Pathological Mechanisms to Therapeutic Horizons

Blastocyst implantation, placental development, and fetal growth are all dependent on the interactions between the developing placenta and the decidualized endometrium. Adult stem cell populations resident in both the placenta and endometrium play key roles in directing cell fate and tissue organization throughout pregnancy. As we begin to understand how these stem cell populations contribute to successful pregnancies, we can begin to ask what roles they play in the pathogenesis of pregnancy disorders from implantation failure and miscarriage through fetal growth restriction and preeclampsia. Furthermore, as our understanding of the therapeutic applications of stem cells in other organs rapidly expands, can we make stem cell therapies a clinical reality in obstetric medicine? This review aims to summarize our current understanding of the role reproductive stem cells play in pregnancy success, and how they may help us better understand the underlying pathogenesis of pregnancy disorders to offer novel therapeutic solutions in the future.

Isolation and characterisation of a novel trophoblast side-population from first trimester placentae

The placenta is responsible for all nutrient and gas exchange between mother and baby during pregnancy. The differentiation of specialised placental epithelial cells called trophoblasts is essential for placental function, but we understand little about how these populations arise. Mouse trophoblast stem cells have allowed us to understand many of the factors that regulate murine trophoblast lineage development, but the human placenta is anatomically very different from the mouse, and it is imperative to isolate a human trophoblast stem cell to understand human placental development. Here we have developed a novel methodology to isolate a Hoechst side-population of trophoblasts from early gestation placentae and compared their transcriptome to differentiated trophoblast populations (cytotrophoblasts and extravillous trophoblasts) using microarray technology. Side-population trophoblasts clustered as a transcriptomically distinct population but were more closely related to cytotrophoblasts than extravillous trophoblasts. Side-population trophoblasts up-regulated a number of genes characteristic of trophectoderm and murine trophoblast stem cells in comparison to cytotrophoblasts or extravillous trophoblasts and could be distinguished from both of these more mature populations by a unique set of 22 up-regulated genes, which were enriched for morphogenesis and organ development and the regulation of growth functions. Cells expressing two of these genes (LAMA2 and COL6A3) were distributed throughout the cytotrophoblast layer at the trophoblast/mesenchymal interface. Comparisons to previously published trophoblast progenitor populations suggest that the side-population trophoblasts isolated in this work are a novel human trophoblast population. Future work will determine whether these cells exhibit functional progenitor/stem cell attributes.

IL-1 beta but not the NALP3 inflammasome is an important determinant of endothelial cell responses to necrotic/dangerous trophoblastic debris

INTRODUCTION

Necrotic but not apoptotic trophoblastic debris can induce endothelial cell activation but the mechanism by which endothelial cells distinguish apoptotic from necrotic debris is unclear. The NALP3 inflammasome is a pattern recognition receptor that macrophages employ to recognise "danger signals" in necrotic cell corpses. In this study, we hypothesized that endothelial cells can identify and respond to necrotic trophoblastic debris via the NALP3 inflammasome.

METHODS

The effect of trophoblastic debris on endothelial expression of NALP3 inflammasome components was investigated using qRT-PCR, immunoassays and fluorescent caspase 1 activity assay. IL-1β in was quantified by ELISA. Endothelial cell activation was measured by cell surface ICAM expression and monocytes adhesion assay.

RESULTS

The NALP3 inflammasome was expressed in resting vascular endothelial cells and is involved in endothelial response to danger signals. However, exposure to necrotic trophoblastic debris did not significantly alter the expression of any of the three components of the NALP3 inflammasome at the mRNA level, nor was caspase-1 activation increased. Conditioned media from endothelial cells exposed to necrotic trophoblastic debris contained elevated levels of IL-1β which was derived from the necrotic debris and which contributed to endothelial cell activation.

DISCUSSION

Necrotic trophoblastic debris induced endothelial cell activation through the IL-1β/IL-1R pathway. However, the NALP3 inflammasome in endothelial cells was not involved in this process.

Multiscale modelling of the feto-placental vasculature

The placenta provides all the nutrients required for the fetus through pregnancy. It develops dynamically, and, to avoid rejection of the fetus, there is no mixing of fetal and maternal blood; rather, the branched placental villi 'bathe' in blood supplied from the uterine arteries. Within the villi, the feto-placental vasculature also develops a complex branching structure in order to maximize exchange between the placental and maternal circulations. To understand the development of the placenta, we must translate functional information across spatial scales including the interaction between macro- and micro-scale haemodynamics and account for the effects of a dynamically and rapidly changing structure through the time course of pregnancy. Here, we present steps towards an anatomically based and multiscale approach to modelling the feto-placental circulation. We assess the effect of the location of cord insertion on feto-placental blood flow resistance and flow heterogeneity and show that, although cord insertion does not appear to directly influence feto-placental resistance, the heterogeneity of flow in the placenta is predicted to increase from a 19.4% coefficient of variation with central cord insertion to 23.3% when the cord is inserted 2 cm from the edge of the placenta. Model geometries with spheroidal and ellipsoidal shapes, but the same volume, showed no significant differences in flow resistance or heterogeneity, implying that normal asymmetry in shape does not affect placental efficiency. However, the size and number of small capillary vessels is predicted to have a large effect on feto-placental resistance and flow heterogeneity. Using this new model as an example, we highlight the importance of taking an integrated multi-disciplinary and multiscale approach to understand development of the placenta.

The relationship between TGFβ, low oxygen and the outgrowth of extravillous trophoblasts from anchoring villi during the first trimester of pregnancy

BACKGROUND

During the first trimester of human pregnancy, specialised placental cells called extravillous trophoblasts (EVTs) grow out from anchoring villi, invade the maternal decidua and remodel the uterine spiral arteries. Inadequate EVT invasion is associated with pregnancy complications including intrauterine growth restriction (IUGR) and pre-eclampsia. During early pregnancy, the placenta exists in a physiologically normal low oxygen environment, which may regulate EVT outgrowth. One potential oxygen responsive regulator of EVTs is the transforming growth factor-beta (TGFβ) family of cytokines. This work aimed to determine the role of TGFβ1, β2 and β3 in regulating EVT outgrowth in the low oxygen environment of early pregnancy.

RESULTS

Using a quantitative high-throughput first trimester villous explant model of EVT outgrowth we demonstrated no significant difference in the frequency of EVT outgrowth between explants treated with TGFβ1, β2 or β3. However, explants treated with TGFβ2, but not β1 or β3, produced EVT outgrowths with a significantly smaller area in comparison to untreated controls (p=0.03). When explants were cultured in 1.5% oxygen, TGFβ2, but not β1 or β3, in the conditioned medium of explants that produced EVT outgrowth was significantly reduced in comparison to 8% oxygen (p<0.05). There was no significant difference in the concentration of TGFβ2 or TGFβ3 from isolated primary EVTs cultured in 1.5% or 8% oxygen.

CONCLUSIONS

TGFβ2 inhibits EVT outgrowth expansion from first trimester anchoring villi. As TGFβ2 secretion from anchoring villi is down-regulated in low oxygen, these findings suggest that the low oxygen environment in early pregnancy may be important to allow EVT outgrowth expansion and promote adequate placentation.

Impact of sildenafil on marital and sexual adjustment in patients and their wives after radiotherapy and short-term androgen suppression for prostate cancer: analysis of RTOG 0215

PURPOSE

The Radiation Therapy Oncology Group (RTOG) 0215 investigated the efficacy of sildenafil in improving erectile dysfunction following radiotherapy and neoadjuvant/concurrent androgen deprivation therapy among prostate cancer patients and found a significant improvement on drug but only in 21% of study participants. This paper reports on a secondary aim to investigate the effect of sildenafil on overall sexual and marital adjustment among both patients and their wives.

METHODS

RTOG 0215 was a placebo-controlled, double-blind, crossover trial of sildenafil. Participation of wives was optional. Twenty-four married heterosexual couples (33% of heterosexual couples in study) completed the Sexual Adjustment Questionnaire and Locke's Marital Adjustment Test. Treatment differences in mean change scores were evaluated by paired t-tests, and the proportion of patients achieving a clinically meaningful change was evaluated using chi-square tests. Spearman's correlation coefficients were used to determine the association of adjustment between patients and wives.

RESULTS

There was no significant change in either sexual or marital adjustment for patients. For wives, there was a trend for improvement in sexual adjustment but no significant change in marital adjustment. Change in marital adjustment between patients and wives was weakly related (r(s) = 0.15, p = 0.48), and for sexual adjustment, there was a moderate, but nonsignificant relationship (r(s) = 0.40, p = 0.09).

CONCLUSIONS

Larger studies are warranted to further examine possible differences in sexual experiences and treatment needs between prostate cancer patients and their wives, as well as to assess predictors of sildenafil response.

Human placentation from nidation to 5 weeks of gestation. Part II: Tools to model the crucial first days

Human pregnancy is unusual with respect to monthly spontaneous decidualisation as well as the degree of placental invasion and interaction with the decidualised endometrial stroma. This review covers in vivo animal models and in vitro cell culture models that have been used to study the earliest stages of human implantation and placentation from nidation to 5 weeks of gestation. The field has expanded rapidly in recent years due to the generation of human embryonic stem cell lines and the ability of some scientists to culture human blastocysts. These models have enabled researchers to begin to elucidate the interactions involved in human blastocyst apposition, adhesion and implantation. However, we still understand very little about the differentiation processes involved in the formation of the placenta. Continued improvements to current models, including the potential isolation of a human trophoblast stem cell, will significantly enhance our ability to define the molecular and structural events occurring during human implantation and early placental development.

Remodelling at the maternal–fetal interface: relevance to human pregnancy disorders

In human pregnancy, successful placentation and remodelling of the uterine vasculature require the integration of a number of stages, which are crucial for a healthy pregnancy. As the demands of the developing fetus for nutrients and oxygen increase, the capacity of the maternal blood vessels to supply this must be altered radically, with deficiencies in this process implicated in a number of dangerous pregnancy complications. The complex signalling networks that regulate these tightly co-ordinated events are becoming clearer as more studies of early pregnancy are performed. It is the aim of this review to draw together our knowledge of events that occur to facilitate a successful pregnancy ranging from the preparation for implantation, through the invasion and differentiation of the trophoblast and the regulation of these processes by other cells within the decidual environment, to the active role that the trophoblast and maternal immune cells play in facilitating the remodelling of the uterine spiral arteries. The events involved in a healthy pregnancy will then be compared to aberrant placentation and remodelling, which are characteristics of many pregnancy disorders, and recent advances in detection of abnormal placental development will also be discussed.

Pre-eclampsia: fitting together the placental, immune and cardiovascular pieces

The success of pregnancy is a result of countless ongoing interactions between the placenta and the maternal immune and cardiovascular systems. Pre-eclampsia is a serious pregnancy complication that arises from multiple potential aberrations in these systems. The pathophysiology of pre-eclampsia is established in the first trimester of pregnancy, when a range of deficiencies in placentation affect the key process of spiral artery remodelling. As pregnancy progresses to the third trimester, inadequate spiral artery remodelling along with multiple haemodynamic, placental and maternal factors converge to activate the maternal immune and cardiovascular systems, events which may in part result from increased shedding of placental debris. As we understand more about the pathophysiology of pre-eclampsia, it is becoming clear that the development of early- and late-onset pre-eclampsia, as well as intrauterine growth restriction (IUGR), does not necessarily arise from the same underlying pathology.

The isolation and characterization of a population of extravillous trophoblast progenitors from first trimester human placenta

BACKGROUND

It is widely accepted that most if not all villous cytotrophoblasts from term placentae are committed to differentiate into syncytiotrophoblast, but that early in gestation villous cytotrophoblasts are bipotential and capable of differentiating into either extravillous trophoblasts (EVTs) or syncytiotrophoblast. In contrast, our previous work has suggested that two separate populations of cytotrophoblast exist in the first trimester, one committed to EVT differentiation and the other to syncytiotrophoblast differentiation. In this work, we have isolated and characterized the population of 'EVT progenitors'.

METHODS

First trimester villous explants were cultured for 10 days then subjected to sequential trypsinization. Viable cells that adhered to Matrigel following trypsinization were cultured for up to 5 days and characterized by immunohistochemistry.

RESULTS

The isolation protocol yielded >90% cytokeratin positive trophoblasts, which expressed markers characteristic of EVT progenitors. Over 5 days of culture, these isolated putative EVT progenitors did not syncytialize, but approximately 20% differentiated into HLA-G positive EVTs.

CONCLUSIONS

It is likely that the isolated putative EVT progenitors are the population of EVT progenitors previously identified in vivo. The characteristics of these isolated putative EVT progenitors provides further evidence for separate progenitors of EVT and syncytiotrophoblast in the first trimester.