Aspects Of Placental Development Research Articles

Trophoblast organoids with physiological polarity model placental structure and function.

Human trophoblast organoids (TOs) are a three-dimensional ex vivo culture model that can be used to study various aspects of placental development, physiology and pathology. However, standard culturing of TOs does not recapitulate the cellular orientation of chorionic villi in vivo given that the multi-nucleated syncytiotrophoblast (STB) develops largely within the inner facing surfaces of these organoids (STBin). Here, we developed a method to culture TOs under conditions that recapitulate the cellular orientation of chorionic villi in vivo. We show that culturing STBin TOs in suspension with gentle agitation leads to the development of TOs containing the STB on the outer surface (STBout). Using membrane capacitance measurements, we determined that the outermost surface of STBout organoids contain large syncytia comprising >50 nuclei, whereas STBin organoids contain small syncytia (<10 nuclei) and mononuclear cells. The growth of TOs under conditions that mimic the cellular orientation of chorionic villi in vivo thus allows for the study of a variety of aspects of placental biology under physiological conditions.

Placental Mitochondrial Function and Dysfunction in Preeclampsia.

The placenta is a vital organ of pregnancy, regulating adaptation to pregnancy, gestational parent/fetal exchange, and ultimately, fetal development and growth. Not surprisingly, in cases of placental dysfunction-where aspects of placental development or function become compromised-adverse pregnancy outcomes can result. One common placenta-mediated disorder of pregnancy is preeclampsia (PE), a hypertensive disorder of pregnancy with a highly heterogeneous clinical presentation. The wide array of clinical characteristics observed in pregnant individuals and neonates of a PE pregnancy are likely the result of distinct forms of placental pathology underlying the PE diagnosis, explaining why no one common intervention has proven effective in the prevention or treatment of PE. The historical paradigm of placental pathology in PE highlights an important role for utero-placental malperfusion, placental hypoxia and oxidative stress, and a critical role for placental mitochondrial dysfunction in the pathogenesis and progression of the disease. In the current review, the evidence of placental mitochondrial dysfunction in the context of PE will be summarized, highlighting how altered mitochondrial function may be a common feature across distinct PE subtypes. Further, advances in this field of study and therapeutic targeting of mitochondria as a promising intervention for PE will be discussed.

A Bioengineered Model for Studying Vascular-Pericyte Interactions of the Placenta.

Investigating the complex cellular interactions of the placenta has remained, until now, a challenge in the field. Given the ethical limitations of studying human placentae, and the interspecies differences that exist between mammals, in vitro models are a valuable tool for investigating developmental and pathologic processes related to the human placenta. A number of in vitro models have been recently employed to investigate various aspects of placental development, with many focusing on the maternal-fetal interface including the trophoblasts and an endothelial barrier. One critical aspect in mimicking the physiology of the placenta is to include perfusable microvessels. As this organ is highly vascularized, it is pertinent to represent the exchange of oxygen and nutrients from the maternal blood to the embedded vessels of the fetus. Using hydrogel-laden microfluidics, it is now possible to bioengineer these and other microvessels in a reproducible manner. By using HUVEC, fetal-like vessels can be generated on a chip and can be studied in a controlled manner. This chapter introduces the concept of generating a triculture vasculature on-chip system, which can be employed to study placental pericyte-endothelial interactions. We describe strategies for generating the vessels on-chip, as well as for quantifying vascular morphology and function. This methodology allows for unique microvessel-related biological questions to be addressed, including how stromal cells impact vascular remodeling over time.

Mechanisms of early placental development in mouse and humans

The importance of the placenta in supporting mammalian development has long been recognized, but our knowledge of the molecular, genetic and epigenetic requirements that underpin normal placentation has remained remarkably under-appreciated. Both the in vivo mouse model and in vitro-derived murine trophoblast stem cells have been invaluable research tools for gaining insights into these aspects of placental development and function, with recent studies starting to reshape our view of how a unique epigenetic environment contributes to trophoblast differentiation and placenta formation. These advances, together with recent successes in deriving human trophoblast stem cells, open up new and exciting prospects in basic and clinical settings that will help deepen our understanding of placental development and associated disorders of pregnancy.

(Epi)genetic control of human trophoblast invasion

During pregnancy the placenta is essential for the growing fetus as it provides oxygen and nutrients and accomplishes waste disposal by connecting the maternal and fetal circulations. To form a functional placenta the fetomaternal interface must be properly developed. For this, fetal extravillous trophoblasts need to invade the maternal placental bed thereby remodeling the maternal spiral arteries from low-capacity high-resistance to high-capacity low-resistance vessels. Inadequate trophoblast invasion can be found at the origin of a variety of pregnancy complications and diseases, such as IUGR (Intra Uterine Growth Restriction), familial early-onset pre-eclampsia, and the HELLP syndrome (Hemolysis, Elevated Liver Enzymes, Low Platelets). This research topic will discuss the various genetic and epigenetic aspects that so far have been identified to control this biological process of trophoblast invasion. The first level of control on invasion is control on trophoblast differentiation. Trophoblasts differentiate from villous cytotrophoblasts to proliferating column extravillous trophoblasts and finally to non-proliferating invasive extravillous trophoblasts. Important players in this differentiation cascade are Wnt signaling components (Knofler and Pollheimer, 2013), microRNAs (Doridot et al., 2013) and DNA methylation (Novakovic and Saffery, 2013) and its regulators, i.e., DNA methyltransferases and TET proteins (Logan et al., 2013). Knofler and Pollheimer (2013) describe how the Wnt signaling pathway contributes to differentiation of extravillous trophoblasts and their invasive properties is indicated by the translocation of β-catenin to the nucleus and the upregulation of TCF-4. Canonical Wnt activity has been shown to promote trophoblast invasion, where hyperactivation leads to trophoblast disorders such as choriocarcinoma and hydatidiform moles, while downregulation of the Wnt signaling cascade can be found in pre-eclampsia. MicroRNAs (miRNAs) are able to affect gene expression by modulating mRNA stability and/or translation. Doridot et al. (2013) describe the role of miRNAs in regulating various aspects of placental development. Particular focus is on the effects of miRNAs on Notch signaling leading to aberrant trophoblast differentiation and invasion, and affecting angiogenesis at the fetomaternal interface. Secondly, differentiation of the villous cytotrophoblasts into syncytiotrophoblasts under miRNA control is discussed. Another important function of miRNAs involves modulation of the immunological balance of the uterine-embryo contact. Furthermore, two specific aspects are highlighted, i.e., miRNAs induced by hypoxia and miRNAs originating from imprinting clusters, as both play an important role in placental development. DNA methyltransferases (DNMTs) and TET proteins, methylate and demethylate DNA, respectively, leading to changes in transcription. Logan et al. (2013) discuss their role in trophoblast differentiation from trophoblast stem cells to cytotrophoblasts to syncytiotrophoblasts and proliferating column trophoblasts. Partly under control of DNMTs and TETs the latter subsequently differentiate from an epithelial to a highly invasive mesenchymal phenotype. The perspective by Novakovic and Saffery (2013) describes the extensive parallels that exist between trophoblast invasion and tumorigenesis. Not only molecular pathways are shared but also epigenetic mechanisms. The DNA methylation similarities between the placenta and cancer are discussed from global hypomethylation to placenta-specific tumor suppressor methylation to the occurrence of loss-of-imprinting. Furthermore, a common origin of epigenetic features in placenta and cancer is speculated from the simple explanation of the independent use of similar pathways or the more intriguing observation that placental mammals have a higher incidence of cancers indicating a reactivation of placental pathways in cancer. Specific genes involved in aberrant trophoblast invasion have been identified via genome-wide linkage studies in families suffering from pregnancy-associated diseases like pre-eclampsia and the HELLP-syndrome as well as via candidate gene approaches (van Dijk and Oudejans, 2013). The potential functions of these genes in the etiology of disease are discussed including the role of epigenetic inheritance. Thulluru et al. (2013) describe a study on Nodal expression in the maternal decidua affecting, potentially via Activin-A upregulation, Nodal and STOX1 expression in extravillous trophoblasts. STOX1 was identified by genome-wide linkage analysis and inhibits trophoblast differentiation and invasion. Nodal is found to be upregulated in pre-eclamptic placentas and inhibits invasion of extravillous trophoblasts, while Activin-A is increased in serum of pre-eclamptic patients. As decidua-specific Nodal knockout mice show clear signs of poor placentation, i.e., IUGR and preterm birth, this study links multiple candidate genes involved in trophoblast invasion. The contributions to this research topic clearly show the diversity of genetic and epigenetic components that individually play a role in the control of human trophoblast invasion in both healthy and diseased states of the placenta.

EG-VEGF: a key endocrine factor in placental development

Endocrine gland-derived vascular endothelial growth factor (EG-VEGF), also named prokineticin 1, is the canonical member of the prokineticin family. Numerous reports suggest a direct involvement of this peptide in normal and pathological reproductive processes. Recent advances propose EG-VEGF as a key endocrine factor that controls many aspects of placental development and suggest its involvement in the development of preeclampsia (PE), the most threatening pathology of human pregnancy. This review describes the finely tuned action and regulation of EG-VEGF throughout human pregnancy, argues for its clinical relevance as a potential diagnostic marker of the onset of PE, and discusses future research directions for therapeutic targeting of EG-VEGF.

The Role of Macrophages in Utero-placental Interactions During Normal and Pathological Pregnancy

The intimate association between maternal and placental tissues elicits an interesting immunological paradox. Placental tissue contains paternal antigens, but under normal circumstances the semi-allogeneic fetus and placenta are not attacked by the maternal immune system. Interestingly, this tolerance to fetal antigens occurs in the presence of a large number of maternal leukocytes, almost all of which are members of the innate immune system. Macrophages are one of the most abundant leukocytes in the decidua and their numbers remain constant throughout gestation. They are recruited to the decidua by both stromal cells and trophoblast cells, where they adopt a specialized phenotype that may assist in various aspects of decidual homeostasis, placental development, and tolerance to the semi-allogeneic trophoblast. Aberrant behavior of these macrophages can affect trophoblast function and placental development, potentially leading to a spectrum of adverse pregnancy outcomes ranging from pre-eclampsia to fetal growth restriction or demise. This review will focus on the phenotype and putative functions of decidual macrophages in normal pregnancy, and how abnormal activation of these cells can affect various aspects of placental development.

PPAR Signaling in Placental Development and Function

With the major attention to the pivotal roles of PPARs in diverse aspects of energy metabolism, the essential functions of PPAR and PPAR in placental development came as a surprise and were often considered a nuisance en route to their genetic analysis. However, these findings provided an opportune entrée into placental biology. Genetic and pharmacological studies, primarily of knockout animal models and cell culture, uncovered networks of PPAR and PPAR, their heterodimeric RXR partners, associated transcriptional coactivators, and target genes, that regulate various aspects of placental development and function. These studies furnish both specific information about trophoblasts and the placenta and potential hints about the functions of PPARs in other tissues and cell types. They reveal that the remarkable versatility of PPARs extends beyond the orchestration of metabolism to the regulation of cellular differentiation, tissue development, and trophoblast-specific functions. This information and its implications are the subject of this review.