Understanding placental nutrient transfer--why bother? New biomarkers of fetal growth

Computational Modelling of Paracellular Diffusion and OCT3 Mediated Transport of Metformin in the Perfused Human Placenta

Metformin is an antidiabetic drug, increasingly prescribed in pregnancy and has been shown to cross the human placenta. The mechanisms underlying placental metformin transfer remain unclear. This study investigated the roles of drug transporters and paracellular diffusion in the bidirectional transfer of metformin across the human placental syncytiotrophoblast using placental perfusion experiments and computational modelling. 14C-metformin transfer was observed in the maternal to fetal and fetal to maternal directions and was not competitively inhibited by 5 mM unlabelled metformin. Computational modelling of the data was consistent with overall placental transfer via paracellular diffusion. Interestingly, the model also predicted a transient peak in fetal 14C-metformin release due to trans-stimulation of OCT3 by unlabelled metformin at the basal membrane. To test this hypothesis a second experiment was designed. OCT3 substrates (5 mM metformin, 5 mM verapamil and 10 mM decynium-22) added to the fetal artery trans-stimulated release of 14C-metformin from the placenta into the fetal circulation, while 5 mM corticosterone did not. This study demonstrated activity of OCT3 transporters on the basal membrane of the human syncytiotrophoblast. However, we did not detect a contribution of either OCT3 or apical membrane transporters to overall materno-fetal transfer, which could be represented adequately by paracellular diffusion in our system.

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.

Effect of Maternal Iron Deficiency Anaemia on the Expression of Iron Transport Proteins in the Third Trimester Placenta

BackgroundDuring pregnancy, iron is transferred from mother to fetus with placental iron transport proteins (Transferrin receptor, Divalent metal transporter/DMT1, ferroportin/FPN1 and Zyklopen). The aim of the study was to evaluate the effect of maternal iron deficiency anemia on placental iron transporters. Study Design: Two hundred pregnant women, in third trimester of pregnancy were divided into anemic (Hemoglobin/Hb < 11g/dl) and non-anemic groups (Hb ≥ 11 g/dl). After delivery, placental expression of iron transport proteins were studied by immunohistochemistry and by mRNA analysis. Results: Of the 200 subjects, 59% were anemic. All 3 placental proteins showed statistically significant increase in immunohistochemical expression, proportionate to the severity of maternal anemia. The mRNA expression of DMT-1 gene was only significantly elevated in placentas of anemic mothers. Conclusion: Although in our study mRNA expression of only the DMT-1 gene was significantly high, immunohistochemically however all the 3 proteins showed significantly higher expression in placentas of anemic mothers.

Lipid signatures reflect the function of the murine primary placentation

The placenta regulates maternal-fetal communication, and its defect leads to significant pregnancy complications. The maternal and embryonic circulations are primitively connected in early placentation, but the function of the placenta during this developmentally essential period is relatively unknown. We thus performed a comparative proteomic analysis of the placenta before and after primary placentation and found that the metabolism and transport of lipids were characteristically activated in this period. The placental fatty acid (FA) carriers in specific placental compartments were upregulated according to gestational age, and metabolomic analysis also showed that the placental transport of FAs increased in a time-dependent manner. Further analysis of two mutant mice models with embryonic lethality revealed that lipid-related signatures could reflect the functional state of the placenta. Our findings highlight the importance of the nutrient transport function of the primary placenta in the early gestational period and the role of lipids in embryonic development.

Advancements in Microfluidic Systems for the Study of Female Reproductive Biology

The female reproductive tract is a highly complex physiological system that consists of the ovaries, fallopian tubes, uterus, cervix, and vagina. An enhanced understanding of the molecular, cellular, and genetic mechanisms of the tract will allow for the development of more effective assisted reproductive technologies, therapeutics, and screening strategies for female specific disorders. Traditional 2-dimensional and 3-dimensional static culture systems may not always reflect the cellular and physical contexts or physicochemical microenvironment necessary to understand the dynamic exchange that is crucial for the functioning of the reproductive system. Microfluidic systems present a unique opportunity to study the female reproductive tract, as these systems recapitulate the multicellular architecture, contacts between different tissues, and microenvironmental cues that largely influence cell structure, function, behavior, and growth. This review discusses examples, challenges, and benefits of using microfluidic systems to model ovaries, fallopian tubes, endometrium, and placenta. Additionally, this review also briefly discusses the use of these systems in studying the effects of endocrine disrupting chemicals and diseases such as ovarian cancer, preeclampsia, and polycystic ovarian syndrome.

Praegnatio Perturbatio-Impact of Endocrine-Disrupting Chemicals

The burden of adverse pregnancy outcomes such as preterm birth and low birth weight is considerable across the world. Several risk factors for adverse pregnancy outcomes have been identified. One risk factor for adverse pregnancy outcomes receiving considerable attention in recent years is gestational exposure to endocrine-disrupting chemicals (EDCs). Humans are exposed to a multitude of environmental chemicals with known endocrine-disrupting properties, and evidence suggests exposure to these EDCs have the potential to disrupt the maternal-fetal environment culminating in adverse pregnancy and birth outcomes. This review addresses the impact of maternal and fetal exposure to environmental EDCs of natural and man-made chemicals in disrupting the maternal-fetal milieu in human leading to adverse pregnancy and birth outcomes-a risk factor for adult-onset noncommunicable diseases, the role lifestyle and environmental factors play in mitigating or amplifying the effects of EDCs, the underlying mechanisms and mediators involved, and the research directions on which to focus future investigations to help alleviate the adverse effects of EDC exposure.

Impact of maternal iron deficiency anaemia on the expression of the newly discovered multi-copper ferroxidase, Zyklopen, in term placentas

In the present study, we investigated the effect of maternal iron deficiency anaemia (IDA) on expression of the newly discovered iron transporter, Zyklopen in term placenta, in 200 pregnant women. Placental expression of Zyklopen was studied by mRNA analysis and immunohistochemistry for the protein. In addition neonatal anthropometric parameters were also analysed. 58.8% of 200 subjects were anaemic. Both Zyklopen mRNA as well as protein expression in the placenta showed a statistically significant increase with increasing severity of anaemia. Although all the neonatal anthropometric parameters were lower in newborns of anaemic mothers, none showed any statistical significance. Zp mRNA levels did not show any significant correlation with newborn and placental parameters (except newborn skinfold thickness and head circumference). Similar to mRNA expression, Zp IHC expression correlated positively, albiet non-significantly, with newborn length and Hb levels, the correlation was however negative with birth weight, head circumference, mid-arm circumference unlike the mRNA expression, where it positively correlated with the above parameters. Our study for the first time demonstrated a definite increase in expression of Zyklopen at both mRNA and protein levels in term placenta, in maternal IDA.IMPACT STATEMENTWhat is already known on this subject? Iron deficiency anaemia (IDA) in a pregnant mother can lead to anaemia in the developing foetus; which is frequently observed to be of lesser severity than that in the mother. Recently a copper-containing oxidase called Zyklopen was discovered which was involved in iron efflux in BeWo cells. The gene encoding Zyklopen has been identified with a putative C-terminal membrane-spanning sequence and high sequence identitical to hephaestin (Heph) and ceruloplasmin (Cp), the other known vertebrate multicopper ferroxidase (MCF). Protein expression of this new MCF was observed in multiple diverse mouse tissues, including placenta and mammary gland.What do the results of this study add? Zyklopen protein immunohistochemical expression showed a statistically significant increase with increasing severity of anaemia. Similarly, placental mRNA expression of the Zyklopen gene was observed to be higher in anaemic mothers when compared to non-anaemic mothers. Our study for the first time demonstrated a definite increase in expression of Zyklopen at both protein and mRNA levels in term placenta, in maternal IDA.What are the implications of these findings for clinical practice and/or further research? This study will help us to understand better, the increased potential for influx of iron from mother to foetus in the condition of maternal iron deficiency. This study will help to determine how placental iron transport proteins can be regulated in response to maternal and neonatal iron status and will further our existing knowledge on relationships between maternal and neonatal iron status and mechanisms by which placental iron transport is modified in relation to these parameters.

Increased homocysteine mediated oxidative stress as key determinant of hepatitis E virus (HEV) infected pregnancy complication and outcome: A study from Northeast India

With the background of association of oxidative stress and Hepatitis E virus (HEV) infection in pregnancy complications the present novel study aimed to evaluate the significance of changes in maternal homocysteine levels and the related mechanism(s) in the pathophysiology of HEV related pregnancy complications and negative outcomes. Term delivery (TD, N = 194) and HEV-IgM positive pregnancy cases [N = 109] were enrolled. Serum and placental homocysteine levels were evaluated by ELISA and immunofluorescence and in turn correlated with serum Vitamin B12 levels. Distribution of variant MTHFR C➔T and TYMS1494del6bp genotyping were studied by PCR-RFLP. Differential folate receptor alpha (FR-α) expression in placenta was evaluated by real-time PCR and immunofluorescence respectively. The HEV viral load was significantly higher in both FHF and AVH cases. Higher serum homocysteine levels was associated with preterm delivery (PTD) and fetal death in HEV infected cases and was significantly inversely correlated with serum VitaminB12 levels in HEV cases. Placental homocysteine expression was upregulated in HEV cases, and in cases with negative pregnancy outcome. A Homocysteine level was associated with MTHFR C677T status. Genetic alterations in folate pathway was associated with increased risk of PTD in HEV infected pregnancy cases, disease severity, and negative pregnancy outcome in AVH and FHF groups. FR-α expression was downregulated in placental tissues of HEV infected pregnancy.Placental stress caused by HEV inflicted increased homocysteine due to alterations in maternal vitamin B12 levels and folate pathway components is detrimental mechanism in PTD and negative pregnancy outcome in HEV infected pregnancy cases and holds prognostic and therapeutic significance.

Maternal Vitamin and Mineral Supplementation and Rate of Maternal Weight Gain Affects Placental Expression of Energy Metabolism and Transport-Related Genes

Maternal nutrients are essential for proper fetal and placental development and function. However, the effects of vitamin and mineral supplementation under two rates of maternal weight gain on placental genome-wide gene expression have not been investigated so far. Furthermore, biological processes and pathways in the placenta that act in response to early maternal nutrition are yet to be elucidated. Herein, we examined the impact of maternal vitamin and mineral supplementation (from pre-breeding to day 83 post-breeding) and two rates of gain during the first 83 days of pregnancy on the gene expression of placental caruncles (CAR; maternal placenta) and cotyledons (COT; fetal placenta) of crossbred Angus beef heifers. We identified 267 unique differentially expressed genes (DEG). Among the DEGs from CAR, we identified ACAT2, SREBF2, and HMGCCS1 that underlie the cholesterol biosynthesis pathway. Furthermore, the transcription factors PAX2 and PAX8 were over-represented in biological processes related to kidney organogenesis. The DEGs from COT included SLC2A1, SLC2A3, SLC27A4, and INSIG1. Our over-representation analysis retrieved biological processes related to nutrient transport and ion homeostasis, whereas the pathways included insulin secretion, PPAR signaling, and biosynthesis of amino acids. Vitamin and mineral supplementation and rate of gain were associated with changes in gene expression, biological processes, and KEGG pathways in beef cattle placental tissues.

Targeting the Dysfunctional Placenta to Improve Pregnancy Outcomes Based on Lessons Learned in Cancer

In recent decades, our understanding of the disrupted mechanisms that contribute to major obstetrical diseases, including preeclampsia, fetal growth restriction, preterm birth, and gestational diabetes, has increased exponentially. Common to many of these obstetric diseases is placental maldevelopment and dysfunction; the placenta is a significant component of the maternal-fetal interface involved in coordinating, facilitating, and regulating maternal and fetal nutrient, oxygen and waste exchange, and hormone and cytokine production. Despite the advances in our understanding of placental development and function, there are currently no treatments for placental maldevelopment and dysfunction. However, given the transient nature and accessibility from the maternal circulation, the placenta offers a unique opportunity to develop targeted therapeutics for routine obstetric practices. Furthermore, given the similar developmental paradigms between the placenta and cancer, there is an opportunity to appropriate current knowledge from advances in targeted therapeutics in cancer treatments. In this review, we highlight the similarities between early placental development and cancer and introduce a number of targeted therapies currently being explored in cancer and pregnancy. We also propose a number of new effectors currently being targeted in cancer research that have the potential to be targeted in the development of treatments for pregnancy complications. Finally, we describe a method for targeting the placenta using nonviral polymers that are capable of delivering plasmids, small interfering RNA, and other effector nucleic acids, which could ultimately improve fetal and maternal outcomes from complicated pregnancies.

Developmental origins of metabolic diseases

Almost 2 billion adults in the world are overweight, and more than half of them are classified as obese, while nearly one-third of children globally experience poor growth and development. Given the vast amount of knowledge that has been gleaned from decades of research on growth and development, a number of questions remain as to why the world is now in the midst of a global epidemic of obesity accompanied by the "double burden of malnutrition," where overweight coexists with underweight and micronutrient deficiencies. This challenge to the human condition can be attributed to nutritional and environmental exposures during pregnancy that may program a fetus to have a higher risk of chronic diseases in adulthood. To explore this concept, frequently called the developmental origins of health and disease (DOHaD), this review considers a host of factors and physiological mechanisms that drive a fetus or child toward a higher risk of obesity, fatty liver disease, hypertension, and/or type 2 diabetes (T2D). To that end, this review explores the epidemiology of DOHaD with discussions focused on adaptations to human energetics, placental development, dysmetabolism, and key environmental exposures that act to promote chronic diseases in adulthood. These areas are complementary and additive in understanding how providing the best conditions for optimal growth can create the best possible conditions for lifelong health. Moreover, understanding both physiological as well as epigenetic and molecular mechanisms for DOHaD is vital to most fully address the global issues of obesity and other chronic diseases.

An assessment of serum-dependent impacts on intracellular accumulation and genomic response of per- and polyfluoroalkyl substances in a placental trophoblast model

Per- and polyfluoroalkyl substances (PFAS), a class of environmental contaminants, have been detected in human placenta and cord blood. The mechanisms driving PFAS-induced effects on the placenta and adverse pregnancy outcomes are not well understood. This study investigated the impact of perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid (PFOA), and a replacement PFAS known as hexafluoropropylene oxide dimer acid (HFPO-DA, tradename GenX) on placental trophoblasts in vitro. Several key factors were addressed. First, PFAS levels in cell culture reagents at baseline were quantified. Second, the role of supplemental media serum in intracellular accumulation of PFAS in a human trophoblast (JEG3) cell line was established. Finally, the impact of PFAS on the expression of 96 genes involved in proper placental function in JEG3 cells was evaluated. The results revealed that serum-free media (SFM) contained no detectable PFAS. In contrast, fetal bovine serum-supplemented media (SSM) contained PFNA, PFUdA, PFTrDA, and 6:2 FTS, but these PFAS were not detected internally in cells. Intracellular accumulation following 24 hr treatments was significantly higher when cultured in SFM compared to SSM for PFOS and PFOA, but not HFPO-DA. Treatment with PFAS was associated with gene expression changes (n = 32) in pathways vital to placental function, including viability, syncytialization, inflammation, transport, and invasion/mesenchymal transition. Among the most robust PFAS-associated changes were those observed in the known apoptosis-related genes, BAD and BAX. These results suggest a complex relationship between PFAS, in vitro culture conditions, and altered expression of key genes necessary for proper placentation.

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.

Region-specific changes in the mRNA and protein expression of LCPUFA biosynthesis enzymes and transporters in the placentae of women with preeclampsia

The biosynthesis and transport of long chain polyunsaturated fatty acids (LCPUFA) require the activity of fatty acid desaturase (FADS) enzymes, fatty acid transport proteins (FATP) and fatty acid binding proteins (FABP). In a previous study we have demonstrated region-specific changes in the LCPUFA levels in preeclampsia (PE) as compared to the normotensive control (NC) placentae.

AIM

To understand the region-specific changes in the mRNA levels and protein expression of biosynthesis enzymes and transporters of LCPUFA in PE and NC placentae.

METHODS

In this cross-sectional study, 20 NC women and 44 women with PE (23 term (TPE) and 21 preterm PE (PTPE)) were recruited. The samples were collected from four regions of the placentae considering cord insertion as the center (CM, central maternal/basal; CF, central fetal/chorionic; PM, peripheral maternal/basal and PF, peripheral fetal/chorionic). The mRNA levels were estimated using qRT-PCR. Statistical analysis was done using both post hoc least significant difference (LSD) test and Benjamini Hochberg correction in the analysis of covariance. Preliminarily, localization and expression of proteins were studied by immunohistochemistry (n = 3/group).

RESULTS

The mRNA levels of FADS1, FADS2 and FATP1 were lower in the central regions (CM and CF) of the PE placentae (both TPE and PTPE) as compared to NC. These differences in the mRNA levels were observed by the LSD test and were not significant after the Benjamini Hochberg correction. Preliminary findings of IHC indicate that the protein expression of FADS1 and FATP4 was higher in the basal regions (CM and PM) of the PE placentae as compared to NC. FADS1, FADS2 and FATP4 proteins were localized in the syncytiotrophoblasts, cytotrophoblasts, mesenchymal cells, endothelial cells of the fetal capillaries and extravillous trophoblasts of the placenta.

CONCLUSION

FADS enzymes are detected in the placentae of Indian women. In PE placentae, there are region-specific alterations in the mRNA and protein levels of LCPUFA biosynthesis enzymes (FADS1 and FADS2) and transporters (FATP1, FATP4 and FABP3) as compared to term NC. These changes were more pronounced toward the basal side and region around the cord insertion.

Double-label immunohistochemistry to assess labyrinth structure of the mouse placenta with stereology

In mice, the labyrinth zone of the placenta exchanges nutrients and gases between mother and fetus. This placental zone is complex in structure and defects in its morphogenesis can compromise substrate exchange and thus, fetal growth and viability. Numerous mouse models involving genetic and environmental manipulation show abnormalities in labyrinth zone size. However, further structural analysis, normally undertaken using ultrathin resin sections, can pose practical constraints. Here, we validate the use of stereology on paraffin-embedded sections double-labelled for lectin and cytokeratin as a cheap, fast and robust alternative for analysing the structure of the mouse placental labyrinth.

Expression of iron transport protein Divalent metal transporter 1 (DMT1) increases in response to maternal iron deficiency anemia in near term to term placenta

Introduction: Iron deficiency anemia (IDA) is the most prevalent nutritional deficiency disorder in pregnant women. During pregnancy, placental transport protein Divalent metal transporter1 (DMT1) plays a crucial role in transit of iron across placenta. The developing fetus is observed to be immune to anemia despite presence of anemia in the mother. Hence, we planned the present study to explore the effect of maternal IDA on the expression of DMT1 in the placenta.Materials and methods: Two hundred pregnant women recruited, were divided into anemic and nonanemic groups based on their predelivery hemoglobin levels (<11 g/dL and ≥11 g/dL respectively). After delivery, placental expression of DMT1 was studied by immunohistochemistry and mRNA analysis and neonatal anthropometry was performed.Results: Of the 200 women recruited, 58.8% were anemic with 60.35% having moderate anemia. Most of the red cell parameters were observed to be higher in cord blood than mothers. DMT1 protein immunohistochemical expression showed a statistically significant increase with increasing severity of anemia. Similarly, placental mRNA expression levels of DMT1 gene were observed to be higher in anemic mothers in comparison with nonanemic mothers.Conclusion: Our study thus demonstrated a definite increase in expression of DMT1 at both protein and mRNA levels in term placenta, in maternal IDA.

Maternal malnutrition impacts placental morphology and transporter expression: an origin for poor offspring growth

The placenta promotes fetal growth through nutrient transfer and selective barrier systems. An optimally developed placenta can adapt to changes in the pregnancy environment, buffering the fetus from adverse exposures. We hypothesized that the placenta adapts differently to suboptimal maternal diets, evidenced by changes in placental morphology, developmental markers and key transport systems. Mice were fed a control diet (CON) during pregnancy, undernourished (UN) by 30% of control intake from gestational day (GD) 5.5-18.5 or fed 60% high-fat diet (HF) 8 weeks before and during pregnancy. At GD18.5, placental morphometry, development and transport were assessed. Junctional and labyrinthine areas of UN and HF placentae were smaller than CON by >10%. Fetal blood space area and fetal blood space:fetal weight ratios were reduced in HF vs. CON and UN. Trophoblast giant cell marker Ctsq mRNA expression was lower in UN vs. HF, and expression of glycogen cell markers Cx31.1 and Pcdh12 was lower in HF vs. UN. Efflux transporter Abcb1a mRNA expression was lower in HF vs. UN, and Abcg2 expression was lower in UN vs. HF. mRNA expression of fatty acid binding protein Fabp_pm was higher in UN vs. CON and HF. mRNA and protein levels of the lipid transporter FAT/CD36 were lower in UN, and FATP4 protein levels were lower in HF vs. UN. UN placentae appear less mature with aberrant transport, whereas HF placentae adapt to excessive nutrient supply. Understanding placental adaptations to common nutritional adversities may reveal mechanisms underlying the developmental origins of later disease.

Using Experimental Models to Assess Effects of Bisphenol A (BPA) and Phthalates on the Placenta: Challenges and Perspectives

The placenta is critical for all aspects of fetal development. Bisphenol A (BPA) and phthalates are endocrine disruptors with ubiquitous exposure in pregnant women-their effects on the placenta is an area of growing research interest. Therefore, our objectives were to (1) summarize research related to the effects BPA or phthalates on placental outcomes in animal and cell models, and (2) evaluate the challenges for using such models to study the impacts of these chemicals on placental endpoints. Overall, studies in cells and animal models suggest that BPA and phthalates impact placental hormones, some epigenetic endpoints, increase inflammation and oxidative stress, and decrease cell viability and nutrient transfer. However, few animal or cell studies have assessed these outcomes at concentrations relevant to humans. Furthermore, it is unclear whether effects of BPA/phthalates on the placenta in animal models mediate fetal outcomes, as most studies have dosed after the earliest stages of placental and fetal development. It is also unclear whether effects of these chemicals are sex-specific, as few studies have considered placental sex. Finally, while there is substantial evidence for effects of mono-(2-ethylhexyl) phthalate (the major metabolite of di-(2-ethylhexyl) phthalate), on placental endpoints in cells, little is currently known about effects of other phthalates to which pregnant women are exposed. Moving forward, these limitations will need to be addressed to help us understand the precise mechanisms of action of these chemicals within the placenta, and how these reported perturbations impact fetal health.

Biosensors for Detection of Human Placental Pathologies: A Review of Emerging Technologies and Current Trends

Substantial growth in the biosensor research has enabled novel, sensitive and point-of-care diagnosis of human diseases in the last decade. This paper presents an overview of the research in the field of biosensors that can potentially predict and diagnosis of common placental pathologies. A survey of biomarkers in maternal circulation and their characterization methods is presented, including markers of oxidative stress, angiogenic factors, placental debris, and inflammatory biomarkers that are associated with various pathophysiological processes in the context of pregnancy complications. Novel biosensors enabled by microfluidics technology and nanomaterials is then reviewed. Representative designs of plasmonic and electrochemical biosensors for highly sensitive and multiplexed detection of biomarkers, as well as on-chip sample preparation and sensing for automatic biomarker detection are illustrated. New trends in organ-on-a-chip based placental disease models are highlighted to illustrate the capability of these in vitro disease models in better understanding the complex pathophysiological processes, including mass transfer across the placental barrier, oxidative stress, inflammation, and malaria infection. Biosensor technologies that can be potentially embedded in the placental models for real time, label-free monitoring of these processes and events are suggested. Merger of cell culture in microfluidics and biosensing can provide significant potential for new developments in advanced placental models, and tools for diagnosis, drug screening and efficacy testing.

Nutrient sensor signaling pathways and cellular stress in fetal growth restriction

Fetal growth restriction is one of the most common obstetrical complications resulting in significant perinatal morbidity and mortality. The most frequent etiology of human singleton fetal growth restriction is placental insufficiency, which occurs secondary to reduced utero-placental perfusion, abnormal placentation, impaired trophoblast invasion and spiral artery remodeling, resulting in altered nutrient and oxygen transport. Two nutrient-sensing proteins involved in placental development and glucose and amino acid transport are mechanistic target of rapamycin (mTOR) and O-linked N-acetylglucosamine transferase (OGT), which are both regulated by availability of oxygen. Impairment in either of these pathways is associated with fetal growth restriction and accompanied by cellular stress in the forms of hypoxia, oxidative and endoplasmic reticulum (ER) stress, metabolic dysfunction and nutrient starvation in the placenta. Recent evidence has emerged regarding the potential impact of nutrient sensors on fetal stress response, which occurs in a sexual dysmorphic manner, indicating a potential element of genetic gender susceptibility to fetal growth restriction. In this mini review, we focus on the known role of mTOR and OGT in placental development, nutrient regulation and response to cellular stress in human fetal growth restriction with supporting evidence from rodent models.

Assessment of Placental Transport Function in Studies of Disease Programming

Environmental conditions during pregnancy affect fetal growth and development and program the offspring for poor future health. These effects may be mediated by the placenta, which develops to transfer nutrients from the mother to the fetus for growth. The ability to measure the unidirectional maternofetal transfer of non-metabolizable radio-analogues of glucose and amino acid by the placenta in vivo has thus been invaluable to our understanding of the regulation of fetal growth, particularly in small animal models. Herein, I describe the method by which in vivo placental transfer function can be quantified in the mouse, an animal model widely used in studies of in utero disease programming.

Serial block-face scanning electron microscopy of erythrocytes protruding through the human placental syncytiotrophoblast

The syncytiotrophoblast forms a continuous barrier between the maternal and fetal circulations. Here we present a serial block‐face scanning electron microscopy (SBFSEM) study, based on a single image stack, showing pooling of fetal blood underneath a region of stretched syncytiotrophoblast that has become detached from the basement membrane. Erythrocytes are protruding from discrete holes in the syncytiotrophoblast suggesting that, under specific circumstances, the syncytiotrophoblast may be permeable to fetal cells. This observation represents a pathological process but it poses questions about the physical properties and permeability of the syncytiotrophoblast and may represent an early stage in the formation of fibrin deposits in areas of syncytial denudation. This study also illustrates how the 3D images generated by SBFSEM allow the interpretation of structures that could not be understood from a single histological section.

[Expression of FABP7 in mouse placenta tissue and human trophoblast HTR-8/Svneo cells]

OBJECTIVE

To detect the expression of FABP7 in the placenta of pregnant mice and in HTR-8/Svneo cells.

METHODS

Real-time PCR and immunofluorescence were used to detect FABP7 mRNA and protein expressions in the uterine and placental tissue of pregnant mice at different days of gestation. FABP7 expression was also detected in cultured HTR-8/Svneo cells using immunofluorescence assay. The mice were treated with E₂, P₄ or their combination for 6 and 24 h and Fabp7 mRNA level in the uterus was detected with real-time PCR.

RESULTS

At 7.5-10.5 days of gestation, the pregnant mice showed positive expressions of Fabp7 mRNA in the uterus and placenta, and FABP7 protein was detected in the decidualized cells and trophoblast giant cells. The expressions of FABP7 were detected at both the mRNA and protein levels in cultured HTR-8/Svneo cells. In mice treated with P4 alone or with E₂+P₄ for 6 and 24 h, the expression level of Fabp7 mRNA was upregulated in the uterus. Fabp7 upregulation was observed in mice at 24 h following E₂ treatment but not at 6 h.

CONCLUSION

FABP7 is expressed in trophoblast giant cells and decidual cells in the placental tissue of mice and in cultured HTR-8/Svneo cells, suggesting the involvement of FABP7 in placental development and in maintenance of pregnancy. E₂ and P₄ can regulate the expression of FABP7 in mouse uterus.

mRNA Levels of Placental Iron and Zinc Transporter Genes Are Upregulated in Gambian Women with Low Iron and Zinc Status

Background: The role of the placenta in regulating micronutrient transport in response to maternal status is poorly understood.

Objective: We investigated the effect of prenatal nutritional supplementation on the regulation of placental iron and zinc transport.

Methods: In a randomized trial in rural Gambia [ENID (Early Nutrition and Immune Development)], pregnant women were allocated to 1 of 4 nutritional intervention arms: 1) iron and folic acid (FeFol) tablets (FeFol group); 2) multiple micronutrient (MMN) tablets (MMN group); 3) protein energy (PE) as a lipid-based nutrient supplement (LNS; PE group); and 4) PE and MMN (PE+MMN group) as LNS. All arms included iron (60 mg/d) and folic acid (400 μg/d). The MMN and PE+MMN arms included 30 mg supplemental Zn/d. In a subgroup of ∼300 mother-infant pairs, we measured maternal iron status, mRNA levels of genes encoding for placental iron and zinc transport proteins, and cord blood iron levels.

Results: Maternal plasma iron concentration in late pregnancy was 45% and 78% lower in the PE and PE+MMN groups compared to the FeFol and MMN groups, respectively (P < 0.001). The mRNA levels of the placental iron uptake protein transferrin receptor 1 were 30–49% higher in the PE and PE+MMN arms than in the FeFol arm (P < 0.031), and also higher in the PE+MMN arm (29%; P = 0.042) than in the MMN arm. Ferritin in infant cord blood was 18–22% lower in the LNS groups (P < 0.024). Zinc supplementation in the MMN arm was associated with higher maternal plasma zinc concentrations (10% increase; P < 0.001) than in other intervention arms. mRNA levels for intracellular zinc-uptake proteins, in this case zrt, irt-like protein (ZIP) 4 and ZIP8, were 96–205% lower in the PE+MMN arm than in the intervention arms without added zinc (P < 0.025). Furthermore, mRNA expression of ZIP1 was 85% lower in the PE+MMN group than in the PE group (P = 0.003).

Conclusion: In conditions of low maternal iron and in the absence of supplemental zinc, the placenta upregulates the gene expression of iron and zinc uptake proteins, presumably in order to meet fetal demands in the face of low maternal supply. The ENID trial was registered at www.controlled-trials.com as ISRCTN49285450.

The Fascinating and Complex Role of the Placenta in Pregnancy and Fetal Well-being

Existing evidence implicates the placenta as the origin of some common pregnancy complications. Moreover, some maternal conditions, such as inadequate nutrition, diabetes, and obesity, are known to adversely affect placental function, with subsequent negative impact on the fetus and newborn. The placenta may also contribute to fetal programming with health consequences into adulthood, such as cardiovascular, metabolic, and mental health disorders. There is evidence that altered placental development, specifically impaired trophoblast invasion and spiral artery remodeling in the first trimester, is the origin of preeclampsia. Prenatal care providers who understand the relationships between placental health and maternal-newborn health can better inform and guide women to optimize health early in pregnancy and prior to conception. This article reviews the current understanding of placental function; placental contributions to normal fetal brain development and timing of birth; and impact of maternal nutrition, obesity, and diabetes on the placenta.

A microphysiological model of the human placental barrier

During human pregnancy, the fetal circulation is separated from maternal blood in the placenta by two cell layers - the fetal capillary endothelium and placental trophoblast. This placental barrier plays an essential role in fetal development and health by tightly regulating the exchange of endogenous and exogenous materials between the mother and the fetus. Here we present a microengineered device that provides a novel platform to mimic the structural and functional complexity of this specialized tissue in vitro. Our model is created in a multilayered microfluidic system that enables co-culture of human trophoblast cells and human fetal endothelial cells in a physiologically relevant spatial arrangement to replicate the characteristic architecture of the human placental barrier. We have engineered this co-culture model to induce progressive fusion of trophoblast cells and to form a syncytialized epithelium that resembles the syncytiotrophoblast in vivo. Our system also allows the cultured trophoblasts to form dense microvilli under dynamic flow conditions and to reconstitute expression and physiological localization of membrane transport proteins, such as glucose transporters (GLUTs), critical to the barrier function of the placenta. To provide a proof-of-principle for using this microdevice to recapitulate native function of the placental barrier, we demonstrated physiological transport of glucose across the microengineered maternal-fetal interface. Importantly, the rate of maternal-to-fetal glucose transfer in this system closely approximated that measured in ex vivo perfused human placentas. Our "placenta-on-a-chip" platform represents an important advance in the development of new technologies to model and study the physiological complexity of the human placenta for a wide variety of applications.

Computational modelling of placental amino acid transfer as an integrated system

Placental amino acid transfer is essential for fetal development and its impairment is associated with poor fetal growth. Amino acid transfer is mediated by a broad array of specific plasma membrane transporters with overlapping substrate specificity. However, it is not fully understood how these different transporters work together to mediate net flux across the placenta. Therefore the aim of this study was to develop a new computational model to describe how human placental amino acid transfer functions as an integrated system. Amino acid transfer from mother to fetus requires transport across the two plasma membranes of the placental syncytiotrophoblast, each of which contains a distinct complement of transporter proteins. A compartmental modelling approach was combined with a carrier based modelling framework to represent the kinetics of the individual accumulative, exchange and facilitative classes of transporters on each plasma membrane. The model successfully captured the principal features of transplacental transfer. Modelling results clearly demonstrate how modulating transporter activity and conditions such as phenylketonuria, can increase the transfer of certain groups of amino acids, but that this comes at the cost of decreasing the transfer of others, which has implications for developing clinical treatment options in the placenta and other transporting epithelia.

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First computational model of placental amino acid transfer as an integrated system

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Increased activity of a transporter does not mean increased transfer to the fetus.

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Increasing transfer of certain amino acids can reduce the transfer of others.

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Amino acid composition as well as concentration determines transfer to the fetus.

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Modelling of phenylketonuria suggests inhibition by excess maternal phenylalanine.

Phenylalanine transfer across the isolated perfused human placenta: an experimental and modeling investigation

Membrane transporters are considered essential for placental amino acid transfer, but the contribution of other factors, such as blood flow and metabolism, is poorly defined. In this study we combine experimental and modeling approaches to understand the determinants of [(14)C]phenylalanine transfer across the isolated perfused human placenta. Transfer of [(14)C]phenylalanine across the isolated perfused human placenta was determined at different maternal and fetal flow rates. Maternal flow rate was set at 10, 14, and 18 ml/min for 1 h each. At each maternal flow rate, fetal flow rates were set at 3, 6, and 9 ml/min for 20 min each. Appearance of [(14)C]phenylalanine was measured in the maternal and fetal venous exudates. Computational modeling of phenylalanine transfer was undertaken to allow comparison of the experimental data with predicted phenylalanine uptake and transfer under different initial assumptions. Placental uptake (mol/min) of [(14)C]phenylalanine increased with maternal, but not fetal, flow. Delivery (mol/min) of [(14)C]phenylalanine to the fetal circulation was not associated with fetal or maternal flow. The absence of a relationship between placental phenylalanine uptake and net flux of phenylalanine to the fetal circulation suggests that factors other than flow or transporter-mediated uptake are important determinants of phenylalanine transfer. These observations could be explained by tight regulation of free amino acid levels within the placenta or properties of the facilitated transporters mediating phenylalanine transport. We suggest that amino acid metabolism, primarily incorporation into protein, is controlling free amino acid levels and, thus, placental transfer.

Fatty Acid Binding Protein 3 Is Involved in n-3 and n-6 PUFA transport in mouse trophoblasts

BACKGROUND

Low placental fatty acid (FA) transport during the embryonic period has been suggested to result in fetal developmental disorders and various adult metabolic diseases, but the molecular mechanism by which FAs are transported through the placental unit remains largely unknown.

OBJECTIVE

The aim of this study was to examine the distribution and functional relevance of FA binding protein (FABP), a cellular chaperone of FAs, in the mouse placenta.

METHODS

We clarified the localization of FABPs and sought to examine their function in placental FA transport through the phenotypic analysis of Fabp3-knockout mice.

RESULTS

Four FABPs (FABP3, FABP4, FABP5, and FABP7) were expressed with spatial heterogeneity in the placenta, and FABP3 was dominantly localized to the trophoblast cells. In placentas from the Fabp3-knockout mice (both sexes), the transport coefficients for linoleic acid (LA) were significantly reduced compared with those from wild-type mice by 25% and 44% at embryonic day (E) 15.5 and E18.5, respectively, whereas those for α-linolenic acid (ALA) were reduced by 19% and 17%, respectively. The accumulation of LA (18% and 27% at E15.5 and E18.5) and ALA (16% at E15.5) was also significantly less in the Fabp3-knockout fetuses than in wild-type fetuses. In contrast, transport and accumulation of palmitic acid (PA) were unaffected and glucose uptake significantly increased by 23% in the gene-ablated mice compared with wild-type mice at E18.5. Incorporation of LA (51% and 52% at 1 and 60 min, respectively) and ALA (23% at 60 min), but not PA, was significantly less in FABP3-knockdown BeWo cells than in controls, whereas glucose uptake was significantly upregulated by 51%, 50%, 31%, and 33% at 1, 20, 40, and 60 min, respectively.

CONCLUSIONS

Collectively FABP3 regulates n-3 (ω-3) and n-6 (ω-6) polyunsaturated FA transport in trophoblasts and plays a pivotal role in fetal development.

Maternal-fetal nutrient transport in pregnancy pathologies: the role of the placenta

Appropriate in utero growth is essential for offspring development and is a critical contributor to long-term health. Fetal growth is largely dictated by the availability of nutrients in maternal circulation and the ability of these nutrients to be transported into fetal circulation via the placenta. Substrate flux across placental gradients is dependent on the accessibility and activity of nutrient-specific transporters. Changes in the expression and activity of these transporters is implicated in cases of restricted and excessive fetal growth, and may represent a control mechanism by which fetal growth rate attempts to match availability of nutrients in maternal circulation. This review provides an overview of placenta nutrient transport with an emphasis on macro-nutrient transporters. It highlights the changes in expression and activity of these transporters associated with common pregnancy pathologies, including intrauterine growth restriction, macrosomia, diabetes and obesity, as well as the potential impact of maternal diet. Molecular signaling pathways linking maternal nutrient availability and placenta nutrient transport are discussed. How sexual dimorphism affects fetal growth strategies and the placenta’s response to an altered intrauterine environment is considered. Further knowledge in this area may be the first step in the development of targeted interventions to help optimize fetal growth.

Differential levels of amino acid transporters System L and ASCT2, and the mTOR protein in placenta of preeclampsia and IUGR

Background

Sufficient amino acid transport activity (AAT) is indispensable for appropriate fetal growth. Studies suggest that placental nutrient uptake activity is responsive to both maternal and fetal nutrient demands. We hypothesize that under conditions of limited nutrient availability to the fetus, as often present in preeclampsia, intrauterine growth restriction (IUGR), and insufficient weight-gain during pregnancy, a general adaptive response aimed to increase amino acid transport activity may be observed in the placenta.

Method

A total of 40 placentas from full-term (n = 10) and pre-term (average gestational period = 34.8 weeks, n = 10) normal pregnancies, IUGR (n = 10), and preeclampsia (n = 10) associated pregnancies were looked at by immunohistochemistry followed by relative qualitative scoring to compare expression levels and localization of System L, ASCT2, and mTOR proteins.

Result

Microvillous syncytiotrophoblast (ST) in placenta of pregnancies complicated by IUGR or preeclampsia (PE) showed significant increases in the levels of System L amino acid transport proteins 4F2hc and LAT1 compared to both full-term control and pre-term (early gestation control) pregnancies seperately (p < 0.05). Elevated mTOR protein was uniquely higher in IUGR placentas compared to full-term controls (P = 0.0026). Total cellular ASCT2 transporter protein levels were similar in all groups, however, levels of ASCT2 protein localized to the ST microvillous membrane (MVM) were significantly lower in IUGR compared to both full-term and pre-term pregnancies (P = 0.0006, 0.03, respectively). Additionally, ASCT2 and mTOR protein levels were positively associated with maternal pre-pregnancy BMI (P = 0.046, 0.048, respectively).

Conclusion

There are three important findings based upon the present study. First, in conditions of limited nutrient availability, such as PE or IUGR, there is an overall increase in the level of System L and mTOR protein expression in the ST, suggestive of an adaptive response. Second, a decrease in ASCT2 protein at the ST MVM suggests a post-translational event that may decrease AAT activity in IUGR placentas. Third, a physiological link between transporter expression and pre-pregnancy BMI is suggested based upon a positive association observed with ASCT2 and mTOR expression values.

Detrimental effects of ethanol and its metabolite acetaldehyde, on first trimester human placental cell turnover and function

Fetal alcohol spectrum disorder (FASD) describes developmental issues from high maternal alcohol intake, which commonly results in fetal growth restriction and long term morbidity. We aimed to investigate the effect of alcohol and acetaldehyde, on the first trimester placenta, the period essential for normal fetal organogenesis. Normal invasion and establishment of the placenta during this time are essential for sustaining fetal viability to term. We hypothesise that alcohol (ethanol) and acetaldehyde have detrimental effects on cytotrophoblast invasion, turnover and placental function. Taurine is an important amino acid for neuronal and physiological development, and so, its uptake was assayed in cells and placental explants exposed to alcohol or acetaldehyde. First trimester villous explants and BeWo cells were treated with 0, 10, 20, 40 mM ethanol or 0, 10, 20, 40 µM acetaldehyde. The invasive capacity of SGHPL4, a first trimester extravillous cytotrophoblast cell line, was unaffected by ethanol or acetaldehyde (p>0.05; N = 6). The cells in-cycle were estimated using immunostaining for Ki67. Proliferating trophoblast cells treated with ethanol were decreased in both experiments (explants: 40% at 20 mM and 40 mM, p<0.05, N = 8–9) (cell line: 5% at 20 mM and 40 mM, p<0.05, N = 6). Acetaldehyde also reduced Ki67-positive cells in both experiments (explants at 40 µM p<0.05; N = 6) (cell line at 10 µM and 40 µM; p<0.05; N = 7). Only in the cell line at 20 µM acetaldehyde demonstrated increased apoptosis (p<0.05; N = 6). Alcohol inhibited taurine transport in BeWo cells at 10 mM and 40 mM (p<0.05; N = 6), and in placenta at 40 mM (p<0.05; N = 7). Acetaldehyde did not affect taurine transport in either model (P<0.05; N = 6). Interestingly, system A amino acid transport in placental explants was increased at 10 µM and 40 µM acetaldehyde exposure (p<0.05; N = 6). Our results demonstrate that exposure to both genotoxins may contribute to the pathogenesis of FASD by reducing placental growth. Alcohol also reduces the transport of taurine, which is vital for developmental neurogenesis.

What factors determine placental glucose transfer kinetics?

INTRODUCTION

Transfer of glucose across the human placenta is directly proportional to maternal glucose concentrations even when these are well above the physiological range. This study investigates the relationship between maternal and fetal glucose concentrations and transfer across the placenta.

METHODS

Transfer of d-glucose, (3)H-3-o-methyl-d-glucose ((3)H-3MG) and (14)C-l-glucose across the isolated perfused human placental cotyledon was determined for maternal and fetal arterial d-glucose concentrations between 0 and 20 mmol/l.

RESULTS

Clearance of (3)H-3MG or (14)C-l-glucose was not affected by maternal or fetal d-glucose concentrations in either circulation.

DISCUSSION

Based on the arterial glucose concentrations and the reported KM for GLUT1, the transfer of d-glucose and (3)H-3MG would be expected to show signs of saturation as d-glucose concentrations increased but this did not occur. One explanation for this is that incomplete mixing of maternal blood and the rate of diffusion across unstirred layers may lower the effective concentration of glucose at the microvillous membrane and subsequently at the basal membrane. Uncertainties about the affinity of GLUT1 for glucose, both outside and inside the cell, may also contribute to the difference between the predicted and observed kinetics.

CONCLUSION

These factors may therefore help explain why the observed and predicted kinetics differ and they emphasise the importance of understanding the function of transport proteins in their physiological context. The development of a computational model of glucose transfer may improve our understanding of how the determinants of placental glucose transfer interact and function as a system.

Saturated fat-rich diet increases fetal lipids and modulates LPL and leptin receptor expression in rat placentas

Metabolic alterations in obese and overweight mothers impact the placenta and the fetus, leading to anomalies in fetal growth and lipid accretion. The primary aim of the study was to examine the effect of a saturated fat-rich diet (FD) on growth, lipid accretion, and lipases, leptin and leptin receptor (ObR) expression in the placenta and fetal liver. We also aimed to find a role for fetal leptin in the modulation of placental and fetal liver lipase and ObR expression. Six-week-old rats were fed with a standard rat chow (control) or a 25% FD for 7 weeks until mating and during pregnancy. Also, in a group of control rats, fetuses were injected with leptin on days 19, 20, and 21 of pregnancy. On day 21, we assessed lipidemia, insulinemia, and leptinemia in mothers and fetuses. In the placenta and fetal liver, lipid concentration was assessed by thin layer chromatography (TLC) and the gene expression of lipoprotein lipase (LPL), endothelial lipase, insulin receptor (Insr), leptin, and ObR by RT-PCR. The FD induced hypertriglyceridemia and hyperleptinemia (P<0.01) in mothers and fetuses, an increase in maternal (P<0.05) and fetal weight (P<0.01), overaccumulation of lipids in fetal liver (P<0.01), and enhanced leptin expression in the placenta and fetal liver (P<0.05). Placental expression of IR and LPL was increased (P<0.05), and ObR decreased (P<0.05) in the FD group. Fetal administration of leptin induced the placental and fetal liver downregulation of ObR (P<0.05) and upregulation of LPL expression (P<0.05). The FD led to increased fetal lipid levels, which may result from high maternal lipid availability and fetal leptin effects.

Plasmodium falciparum malaria elicits inflammatory responses that dysregulate placental amino acid transport

Placental malaria (PM) can lead to poor neonatal outcomes, including low birthweight due to fetal growth restriction (FGR), especially when associated with local inflammation (intervillositis or IV). The pathogenesis of PM-associated FGR is largely unknown, but in idiopathic FGR, impaired transplacental amino acid transport, especially through the system A group of amino acid transporters, has been implicated. We hypothesized that PM-associated FGR could result from impairment of transplacental amino acid transport triggered by IV. In a cohort of Malawian women and their infants, the expression and activity of system A (measured by Na⁺-dependent ¹⁴C-MeAIB uptake) were reduced in PM, especially when associated with IV, compared to uninfected placentas. In an in vitro model of PM with IV, placental cells exposed to monocyte/infected erythrocytes conditioned medium showed decreased system A activity. Amino acid concentrations analyzed by reversed phase ultra performance liquid chromatography in paired maternal and cord plasmas revealed specific alterations of amino acid transport by PM, especially with IV. Overall, our data suggest that the fetoplacental unit responds to PM by altering its placental amino acid transport to maintain adequate fetal growth. However, IV more profoundly compromises placental amino acid transport function, leading to FGR. Our study offers the first pathogenetic explanation for FGR in PM.

Malaria infection during pregnancy can cause fetal growth restriction and low birthweight associated with high infant mortality and morbidity rates. The pathogenesis of fetal growth restriction in placental malaria is largely unknown, but in other pathological pregnancies, impaired transplacental amino acid transport has been implicated. In a cohort of Malawian women and their infants, we found that placental malaria, especially when associated with local inflammation, was associated with decreased expression and activity of an important group of amino acid placental transporters. Using an in vitro model of placental malaria with local inflammation, we discovered that maternal monocyte products could impair the activity of amino acid transporters on placental cells. Amino acid concentrations in paired maternal and cord plasmas revealed specific alterations of amino acid transport by placental malaria, especially with local inflammation. Overall, our data suggest that, more than malaria infection per se, the local inflammation it triggers compromises placental amino acid transport function, leading to fetal growth restriction. Greater understanding of the mechanisms involved, combined with interventions to improve fetal growth in malaria, are important priorities in areas of the world where the co-existence of malaria and maternal malnutrition threatens the health and lives of millions of young babies.

Expression of flotillins in the human placenta: potential implications for placental transcytosis

A proteomics survey of human placental syncytiotrophoblast (ST) apical plasma membranes revealed peptides corresponding to flotillin-1 (FLOT1) and flotillin-2 (FLOT2). The flotillins belong to a class of lipid microdomain-associated integral membrane proteins that have been implicated in clathrin- and caveolar-independent endocytosis. In the present study, we characterized the expression of the flotillin proteins within the human placenta. FLOT1 and FLOT2 were coexpressed in placental lysates and BeWo human trophoblast cells. Immunofluorescence microscopy of first-trimester and term placentas revealed that both proteins were more prominent in villous endothelial cells and cytotrophoblasts (CTs) than the ST. Correspondingly, forskolin-induced fusion in BeWo cells resulted in a decrease in FLOT1 and FLOT2, suggesting that flotillin protein expression is reduced following trophoblast syncytialization. The flotillin proteins co-localized with a marker of fluid-phase pinocytosis, and knockdown of FLOT1 and/or FLOT2 expression resulted in decreased endocytosis of cholera toxin B subunit. We conclude that FLOT1 and FLOT2 are abundantly coexpressed in term villous placental CTs and endothelial cells, and in comparison, expression of these proteins in the ST is reduced. These findings suggest that flotillin-dependent endocytosis is unlikely to be a major pathway in the ST, but may be important in the CT and endothelium.

Pharmacotherapy in pregnancy; effect of ABC and SLC transporters on drug transport across the placenta and fetal drug exposure

Pharmacotherapy during pregnancy is often inevitable for medical treatment of the mother, the fetus or both. The knowledge of drug transport across placenta is, therefore, an important topic to bear in mind when deciding treatment in pregnant women. Several drug transporters of the ABC and SLC families have been discovered in the placenta, such as P-glycoprotein, breast cancer resistance protein, or organic anion/cation transporters. It is thus evident that the passage of drugs across the placenta can no longer be predicted simply on the basis of their physical-chemical properties. Functional expression of placental drug transporters in the trophoblast and the possibility of drug-drug interactions must be considered to optimize pharmacotherapy during pregnancy. In this review we summarize current knowledge on the expression and function of ABC and SLC transporters in the trophoblast. Furthermore, we put this data into context with medical conditions that require maternal and/or fetal treatment during pregnancy, such as gestational diabetes, HIV infection, fetal arrhythmias and epilepsy. Proper understanding of the role of placental transporters should be of great interest not only to clinicians but also to pharmaceutical industry for future drug design and development to control the degree of fetal exposure.

Placental adaptations to the maternal-fetal environment: implications for fetal growth and developmental programming

The placenta is a transient organ found in eutherian mammals that evolved primarily to provide nutrients for the developing fetus. The placenta exchanges a wide array of nutrients, endocrine signals, cytokines and growth factors with the mother and the fetus, thereby regulating intrauterine development. Recent studies show that the placenta is not just a passive organ mediating maternal-fetal exchange. It can adapt its capacity to supply nutrients in response to intrinsic and extrinsic variations in the maternal-fetal environment. These dynamic adaptations are thought to occur to maximize fetal growth and viability at birth in the prevailing conditions in utero. However, some of these adaptations may also affect the development of individual fetal tissues, with patho-physiological consequences long after birth. Here, this review summarizes current knowledge on the causes, possible mechanisms and consequences of placental adaptive responses, with a focus on the regulation of transporter-mediated processes for nutrients. This review also highlights the emerging roles that imprinted genes and epigenetic mechanisms of gene regulation may play in placental adaptations to the maternal-fetal environment.

Antenatal dexamethasone treatment in midgestation reduces system A-mediated transport in the late-gestation murine placenta

Clinically, approximately 30% of women who receive synthetic glucocorticoids (sGC) for risk of preterm labor carry to term. In vitro studies have shown that sGC acutely regulate the placental system A amino acid transporter, but there are no comparable data in vivo. Hence, the objective of our study was to examine the acute [embryonic day (E)15.5] and longer-term (E17.5 and E18.5) consequences of midgestation antenatal sGC [dexamethasone (DEX); 0.1 mg/kg on E13.5 and E14.5] on placental system A-mediated transfer in the mouse (measured in vivo as maternal-fetal unidirectional (14)C-methylaminoisobutyric acid transfer per gram of placenta). System A transfer and Slc38a mRNA expression significantly increased from E12.5 to E18.5 (P < 0.05), corresponding to increased fetal growth. DEX treatment had no acute effect at E15.5 or longer-term effect at E17.5 but significantly decreased system A-mediated transfer before term (E18.5; P < 0.05) in placentae of male and female fetuses. There was no effect of DEX on Slc38a gene expression. Administration of DEX in this regime had no effect on birth weight. We conclude that sGC treatment in midgestation leads to a substantial decrease in placental system A-mediated transport in late gestation, suggesting that prenatal sGC therapy may lead to a reduction in availability of neutral amino acids to the fetus if gestation persists to term.

Placental-specific Igf2 deficiency alters developmental adaptations to undernutrition in mice

The pattern of fetal growth is a major determinant of the subsequent health of the infant. We recently showed in undernourished (UN) mice that fetal growth is maintained until late pregnancy, despite reduced placental weight, through adaptive up-regulation of placental nutrient transfer. Here, we determine the role of the placental-specific transcript of IGF-II (Igf2P0), a major regulator of placental transport capacity in mice, in adapting placental phenotype to UN. We compared the morphological and functional responses of the wild-type (WT) and Igf2P0-deficient placenta in WT mice fed ad libitium or 80% of the ad libitium intake. We observed that deletion of Igf2P0 prevented up-regulation of amino acid transfer normally seen in UN WT placenta. This was associated with a reduction in the proportion of the placenta dedicated to nutrient transport, the labyrinthine zone, and its constituent volume of trophoblast in Igf2P0-deficient placentas exposed to UN on d 16 of pregnancy. Additionally, Igf2P0-deficient placentas failed to up-regulate their expression of the amino acid transporter gene, Slc38a2, and down-regulate phosphoinositide 3-kinase-protein kinase B signaling in response to nutrient restriction on d 19. Furthermore, deleting Igf2P0 altered maternal concentrations of hormones (insulin and corticosterone) and metabolites (glucose) in both nutritional states. Therefore, Igf2P0 plays important roles in adapting placental nutrient transfer capacity during UN, via actions directly on the placenta and/or indirectly through the mother.