Mechanisms of maternofetal exchange across the human placenta

Association between placental efficiency with anthropometry and nutritional phenotypes in full-term newborns from the 2010/2011 BRISA birth cohort

OBJECTIVE

To study the association between placental efficiency with anthropometry and nutritional phenotypes in full-term newborns from a birth cohort.

METHOD

This was a secondary cross-sectional analysis of data obtained in a cohort study (Brazilian RibeirãoPreto and São Luís Birth Cohort Studies - BRISA), whose deliveries were performed between 2010 and 2011. Standardized questionnaires were applied to mothers, and placentas and newborns were evaluated shortly after delivery. Placental efficiency was assessed using the ratio between birth weight and placental weight (BW/PW ratio); values below the lower quartile (25th percentile for gestational age) were considered to have low placental efficiency. Newborn phenotypes were small and large for gestational age, stunted and wasted, evaluated using the INTERGROWTH-21 growth standard. To identify the confounding variables theoretical model was constructed using Directed Acyclic Graphs, and unadjusted and adjusted logistic regression were performed. Placental measurements were obtained blindly from pregnancy and delivery data.

RESULTS

723 mother-placenta-child triads were studied. 3.2 % of newborns were small-for-gestational-age (SGA), 6.5 %large-for-gestational-age (LGA), 5.7 %had stunting, and 0.27 % wasting. A significantly higher risk was found between low placental efficiency and SGA (OR 2.82;95 % CI 1.05-7.57), stunting (OR 2.23; 95 % CI 1.07-4.65), and wasting (OR 8.22; 95 % CI 1.96-34.37). No relationship was found between LGA and placental efficiency.

CONCLUSIONS

Low placental efficiency was associated with increased risk for small-for-gestational-age, stunting, and wasting. Placental morphometry can provide valuable information on intrauterine conditions and neonatal health, helping to identify newborns at higher risk of future comorbidities.

Feto-placental Unit: From Development to Function

The placenta is an intriguing organ that allows us to survive intrauterine life. This essential organ connects both mother and fetus and plays a crucial role in maternal and fetal well-being. This chapter presents an overview of the morphological and functional aspects of human placental development. First, we describe early human placental development and the characterization of the cell types found in the human placenta. Second, the human placenta from the second trimester to the term of gestation is reviewed, focusing on the morphology and specific pathologies that affect the placenta. Finally, we focus on the placenta's primary functions, such as oxygen and nutrient transport, and their importance for placental development.

Placenta: an organ with high energy requirements

Placenta is a unique organ, without which the very phenomenon of human pregnancy is impossible. Semiallogeneous nature, localization of the placenta, complex and heterogeneous cellular composition determines its complex and multifaceted role in the course of physiological pregnancy, indicates the importance of studying this organ in a number of reproductive pathologies. The purpose of this review was to analyze the literature sources illustrating the importance of energydependent processes in placental metabolism and to determine the molecular basis of placental energy conversion. Publications of foreign and Russian authors from PubMed database and scientific electronic library eLIBRARY.ru were used when writing the review. The review highlights the main functions of the placenta: transport and synthetic functions in terms of their place in the structure of energy expenditure of the organ. The systems by which the transport of ions and gases from maternal blood through the placental barrier is performed, are considered. The role of the placenta in the synthesis of steroid hormones and glucocorticoids is detailed. The main bioenergetic systems are also considered: placental glucose metabolism, the functional activity of mitochondria and the creatine kinase system of the placenta. These data allow us to put the placenta on a par with other organs with high energy requirements (brain, transverse striated skeletal muscles, heart, kidneys, liver), which are most susceptible to metabolic disorders. Maintaining a balance between expenditure and synthesis of macroergic compounds in the placenta is critical for an adequate course of physiological pregnancy, and imbalances can lead to such pathologies as fetal retardation syndrome or preeclampsia. Further study of placental energy supply systems seems important for understanding the mechanisms of intrauterine development disorders and developing their pathogenetic treatment.

Fetal and Neonatal Anesthesia

Anesthesia for fetal and neonatal surgery requires subspecialized knowledge and expertise. Attention to important anatomic, physiologic, and metabolic differences seen in pregnancy and at birth are essential for the optimal care of these patients. Thorough preoperative evaluations tailored intraoperative strategies and careful postoperative management are critical when devising the anesthetic approach for each of these cases.

Immunohistopathological changes in the placenta of malaria-infected women in unstable transmission setting of Aligarh

INTRODUCTION

Pregnant women are more susceptible to malaria due to a combination of physiological and immunological changes. The infection may even affect the growth and survival of the foetus, which mainly occur when parasite enters the placenta. The sequestration of infected erythrocytes may trigger the host response, leading to placental inflammation and altered development, affecting the structure and nutrient transport of placenta. These factors collectively impair placental functions and affect foetal growth.

METHODS

Pregnant women with peripheral parasitaemia for P. falciparum and P. vivax (20 each) were included in the present study, along with 15 age-matched uninfected healthy pregnant women. Placentae were analysed for the presence of local parasitaemia along with pathological lesions caused due to the parasite. Immunohistochemical staining for CD20, CD45 and CD68 cells was performed for examining the specific leucocytes in the intervillous space of the placenta.

RESULTS

Of the 20 individuals with P. falciparum, only seven placentae showed parasitaemia, whereas individuals with P. vivax showed no placental infection. The pathological changes observed in the P. falciparum-infected placenta include syncytial knotting, excess fibrinoid deposition, syncytiotrophoblast necrosis, syncytial rupture, thickening of trophoblast basement membrane and increased collagen deposition. Immunohistochemical staining showed a significant increase in B cells (CD20), leucocytes (CD45) and monocytes and macrophages (CD68) in the P. falciparum-infected placenta (p < 0.0001).

DISCUSSION

The result implies that P. falciparum is responsible for pathological alterations in placenta, affecting the nutrient transport across placenta and foetal growth. The immune cells also migrate to the placenta and accumulate in the intervillous space to show humoral and cell-mediated immunity against the parasite.

The Pivotal Role of the Placenta in Normal and Pathological Pregnancies: A Focus on Preeclampsia, Fetal Growth Restriction, and Maternal Chronic Venous Disease

The placenta is a central structure in pregnancy and has pleiotropic functions. This organ grows incredibly rapidly during this period, acting as a mastermind behind different fetal and maternal processes. The relevance of the placenta extends far beyond the pregnancy, being crucial for fetal programming before birth. Having integrative knowledge of this maternofetal structure helps significantly in understanding the development of pregnancy either in a proper or pathophysiological context. Thus, the aim of this review is to summarize the main features of the placenta, with a special focus on its early development, cytoarchitecture, immunology, and functions in non-pathological conditions. In contraposition, the role of the placenta is examined in preeclampsia, a worrisome hypertensive disorder of pregnancy, in order to describe the pathophysiological implications of the placenta in this disease. Likewise, dysfunction of the placenta in fetal growth restriction, a major consequence of preeclampsia, is also discussed, emphasizing the potential clinical strategies derived. Finally, the emerging role of the placenta in maternal chronic venous disease either as a causative agent or as a consequence of the disease is equally treated.

Altered protein O-GlcNAcylation in placentas from mothers with diabetes causes aberrant endocytosis in placental trophoblast cells

Women with pre-existing diabetes have an increased risk of poor pregnancy outcomes, including disordered fetal growth, caused by changes to placental function. Here we investigate the possibility that the hexosamine biosynthetic pathway, which utilises cellular nutrients to regulate protein function via post-translationally modification with O-linked N-acetylglucosamine (GlcNAc), mediates the placental response to the maternal metabolic milieu. Mass spectrometry analysis revealed that the placental O-GlcNAcome is altered in women with type 1 (n = 6) or type 2 (n = 6) diabetes T2D (≥ twofold change in abundance in 162 and 165 GlcNAcylated proteins respectively compared to BMI-matched controls n = 11). Ingenuity pathway analysis indicated changes to clathrin-mediated endocytosis (CME) and CME-associated proteins, clathrin, Transferrin (TF), TF receptor and multiple Rabs, were identified as O-GlcNAcylation targets. Stimulating protein O-GlcNAcylation using glucosamine (2.5 mM) increased the rate of TF endocytosis by human placental cells (p = 0.02) and explants (p = 0.04). Differential GlcNAcylation of CME proteins suggests altered transfer of cargo by placentas of women with pre-gestational diabetes, which may contribute to alterations in fetal growth. The human placental O-GlcNAcome provides a resource to aid further investigation of molecular mechanisms governing placental nutrient sensing.

Calcium and lactate in the fetal-to-neonatal transition

OBJECTIVE

To explore the relationship between calcium and lactate in arterial cord blood of healthy term neonates in response to the stress of labor.

METHODS

This was a prospective cohort study of consecutive, vaginal, term births in a community medical center (April 2029 to February 2020). Calcium and lactate were measured in cord blood gas analysis immediately after delivery.

RESULTS

In the arterial cord blood of 480 neonates, calcium levels were 1.5 (1.4; 1.5) mmol/L and lactate levels were 3.8 (2.9; 4.9) mmol/L. Calcium and lactate showed a statistically significant positive correlation (Pearson's correlation, r = 0.15, p = .001). Calcium levels had a significant positive correlation with PaCO₂ and a significant negative correlation with pH, PaO₂, HCO₃^-, and ABE levels. Multivariable analysis models confirmed that calcium levels were associated with HCO₃^-, gestational age, and birth weight, all accounting for 7% of the variability.

CONCLUSION

In healthy term vaginally delivered neonates, it was found that calcium and lactate were strongly correlated, together pointing to a neonatal response to the stress of labor and delivery. Cord blood calcium regulation may have an ancillary role in defining neonatal adaptation to extrauterine life.

Validation studies of a fluorescent method to measure placental glucose transport in mice

INTRODUCTION

Proper placental function is essential for optimal fetal growth in utero. Placental transfer of nutrients to the fetus can be measured using radiolabelled tracers, but non-radioactive methods have potential advantages. This study aimed to develop a fluorescence-based method to measure placental glucose transport in mice.

METHODS

Time course and localisation of the IRDye 800CW 2-deoxyglucose were recorded (Lumina IVIS Live Imaging System) following tail vein injection into anaesthetised late pregnant mice. Fluorescent signals in placental and fetal tissues were assessed after injecting conscious dams with 10 nmol IRDye 800CW 2-deoxyglucose (3, 30, 60, 120 min) or vehicle. Specificity of dye uptake was determined by comparing uptake of IRDye 800CW conjugated to 2-deoxyglucose or carboxylate, at 2 and 24 h. Finally, we assessed relationships of fetal size and umbilical blood flow velocities with relative dye uptake.

RESULTS

In late pregnant mice, uterine fluorescent signal localised rapidly over placentas and remained consistent for >1 h. Signal intensity in whole and homogenised tissues increased in fetuses and decreased in placentas after 3 min and stabilised by 30 min post-injection. Relative fetal dye uptake at 2 and 24 h was greater in littermates with the highest compared to lowest placental efficiency; signals were similar for 2-deoxyglucose- or carboxylate-conjugated dyes. Relative fetal dye uptake correlated positively with fetal weight and placental efficiency and negatively with umbilical artery resistance indices.

CONCLUSIONS

Fetal uptake of IRDye 800CW correlates with markers of placental blood flow and fetal growth, but does not specifically measure placental glucose transport.

Human placental oxygenation in late gestation: experimental and theoretical approaches

The placenta is crucial for life. It is an ephemeral but complex organ acting as the barrier interface between maternal and fetal circulations, providing exchange of gases, nutrients, hormones, waste products and immunoglobulins. Many gaps exist in our understanding of the detailed placental structure and function, particularly in relation to oxygen handling and transfer in healthy and pathological states in utero. Measurements to understand oxygen transfer in vivo in the human are limited, with no general agreement on the most appropriate methods. An invasive method for measuring partial pressure of oxygen in the intervillous space through needle electrode insertion at the time of Caesarean sections has been reported. This allows for direct measurements in vivo whilst maintaining near normal placental conditions; however, there are practical and ethical implications in using this method for determination of placental oxygenation. Furthermore, oxygen levels are likely to be highly heterogeneous within the placenta. Emerging non-invasive techniques, such as MRI, and ex vivo research are capable of enhancing and improving current imaging methodology for placental villous structure and increase the precision of oxygen measurement within placental compartments. These techniques, in combination with mathematical modelling, have stimulated novel cross-disciplinary approaches that could advance our understanding of placental oxygenation and its metabolism in normal and pathological pregnancies, improving clinical treatment options and ultimately outcomes for the patient.

Placental physiology monitored by hyperpolarized dynamic 13C magnetic resonance

Placental functions, including transport and metabolism, play essential roles in pregnancy. This study assesses such processes in vivo, from a hyperpolarized MRI perspective. Hyperpolarized urea, bicarbonate, and pyruvate were administered to near-term pregnant rats, and all metabolites displayed distinctive behaviors. Little evidence of placental barrier crossing was observed for bicarbonate, at least within the timescales allowed by ¹³C relaxation. By contrast, urea was observed to cross the placental barrier, with signatures visible from certain fetal organs including the liver. This was further evidenced by the slower decay times observed for urea in placentas vis-à-vis other maternal compartments and validated by mass spectrometric analyses. A clear placental localization, as well as concurrent generation of hyperpolarized lactate, could also be detected for [1-¹³C]pyruvate. These metabolites also exhibited longer lifetimes in the placentas than in maternal arteries, consistent with a metabolic activity occurring past the trophoblastic interface. When extended to a model involving the administration of a preeclampsia-causing chemical, hyperpolarized MR revealed changes in urea's transport, as well as decreases in placental glycolysis vs. the naïve animals. These distinct behaviors highlight the potential of hyperpolarized MR for the early, minimally invasive detection of aberrant placental metabolism.

Localization of TASK and TREK, Two-Pore Domain K+ Channels, in Human Cytotrophoblast Cells

OBJECTIVE

Two-pore domain K+ channels (K2P), an emerging K+ channel subfamily, contribute to setting membrane potential in both electrically excitable and nonexcitable cells and, as such, influence cellular function. The multinucleate syncytiotrophoblast of human placenta, formed from the fusion of mononucleate cytotrophoblast cells, is a transporting epithelium whose function likely depends on the activity of K+ channels. We have therefore investigated the gene expression of two members of this family, TASK and TREK, in cultured human cytotrophoblast cells, and have also investigated protein expression in cytotrophoblast cells and placenta.

METHODS

We used reverse transcriptase-polymerase chain reaction (RT-PCR), Western blotting, and immunocytochemistry to investigate the gene and protein expression of TASK and TREK isoforms in both isolated cytotrophoblast cells and term placental tissue.

RESULTS

In cytotrophoblast cells, mRNAs encoding TASK1, 2, 4, 5, and TREK1 were detected, whereas weak or no signals were observed for TASK3 and TREK2. Western blotting for TASK1 in cytotrophoblast cells gave two bands of approximately 78 and 150 kd; TREK1 gave bands of approximately 90 and 130 kd. TASK1 immunofluorescence in placenta colocalized with cytokeratin-7, a trophoblast-specific marker. TREK1 predominantly stained cells around the villous perimeter and this staining was colocalized with propidium iodide nuclear staining.

CONCLUSION

Human cytotrophoblast cells from term placenta are a site of expression for various K2P genes, two of which, namely, TASK1 and TREK1, are transcribed into protein.

Maternal obesity is associated with a reduction in placental taurine transporter activity

Background/Objectives:

Maternal obesity increases the risk of poor pregnancy outcome including stillbirth, pre-eclampsia, fetal growth restriction and fetal overgrowth. These pregnancy complications are associated with dysfunctional syncytiotrophoblast, the transporting epithelium of the human placenta. Taurine, a β-amino acid with antioxidant and cytoprotective properties, has a role in syncytiotrophoblast development and function and is required for fetal growth and organ development. Taurine is conditionally essential in pregnancy and fetal tissues depend on uptake of taurine from maternal blood. We tested the hypothesis that taurine uptake into placental syncytiotrophoblast by the taurine transporter protein (TauT) is lower in obese women (body mass index (BMI)⩾30 kg m⁻²) than in women of ideal weight (BMI 18.5–24.9 kg m⁻²) and explored potential regulatory factors.

Subjects/Methods:

Placentas were collected from term (37–42-week gestation), uncomplicated, singleton pregnancies from women with BMI 19–49 kg m⁻². TauT activity was measured as the Na⁺-dependent uptake of ³H-taurine into placental villous fragments. TauT expression in membrane-enriched placental samples was investigated by western blot. In vitro studies using placental villous explants examined whether leptin or IL-6, adipokines/cytokines that are elevated in maternal obesity, regulates TauT activity.

Results:

Placental TauT activity was significantly lower in obese women (BMI⩾30) than women of ideal weight (P<0.03) and inversely related to maternal BMI (19–49 kg m⁻²; P<0.05; n=61). There was no difference in TauT expression between placentas of ideal weight and obese class III (BMI⩾40) subjects. Long-term exposure (48 h) of placental villous explants to leptin or IL-6 did not affect TauT activity.

Conclusions:

Placental TauT activity at term is negatively related to maternal BMI. We propose that the reduction in placental TauT activity in maternal obesity could lower syncytiotrophoblast taurine concentration, compromise placental development and function, and reduce the driving force for taurine efflux to the fetus, thereby increasing the risk of poor pregnancy outcome.

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.

Expression and function of thyroid hormone transporters in the microvillous plasma membrane of human term placental syncytiotrophoblast

The transplacental passage of thyroid hormones (THs) from mother to fetus in humans has been deduced from observational clinical studies and is important for normal fetoplacental development. To investigate the transporters that regulate TH uptake by syncytiotrophoblast (the primary barrier to maternal-fetal exchange, which lies in direct contact with maternal blood), we isolated the microvillous plasma membrane (MVM) of human term syncytiotrophoblasts. We have demonstrated that MVM vesicles express plasma membrane TH transporter proteins, including system-L (L-type amino acid transporter 1 and CD98), monocarboxylate transporters (MCTs) 8 and 10, organic anion-transporting polypeptides 1A2 and 4A1. We provide the first definitive evidence that the human syncytiotrophoblast MVM is capable of rapid, saturable T(4) and T(3) uptake at similar rates and in a Na(+)-independent manner. These two major forms of THs could not significantly inhibit each others' uptake, suggesting that each is mediated by largely different transporters. No single transporter was noted to play a dominant role in either T(4) or T(3) uptake. Using combinations of transporter inhibitors that had an additive effect on TH uptake, we provide evidence that 67% of saturable T(4) uptake is facilitated by system-L and MCT10 with a minor role played by organic anion-transporting polypeptides, whereas 87% of saturable T(3) uptake is mediated by MCT8 and MCT10. Our data demonstrate that syncytiotrophoblast may control the quantity and forms of THs taken up by the human placenta. Thus, syncytiotrophoblast could be critical in regulating transplacental TH supply from the mother to the fetus.

Animal models for prenatal gene therapy: choosing the right model

Testing in animal models is an essential requirement during development of prenatal gene therapy for -clinical application. Some information can be derived from cell lines or cultured fetal cells, such as the efficiency of gene transfer and the vector dose that might be required. Fetal tissues can also be maintained in culture for short periods of time and transduced ex vivo. Ultimately, however, the use of animals is unavoidable since in vivo experiments allow the length and level of transgene expression to be measured, and provide an assessment of the effect of the delivery procedure and the gene therapy on fetal and neonatal development. The choice of animal model is determined by the nature of the disease and characteristics of the animal, such as its size, lifespan, and immunology, the number of fetuses and their development, parturition, and the length of gestation and the placentation. The availability of a disease model is also critical. In this chapter, we discuss the various animal models that can be used and consider how their characteristics can affect the results obtained. The projection to human application and the regulatory hurdles are also presented.

Placental chloride channels: a review

The human placental syncytiotrophoblast (hSTB) is a polarized epithelial structure, that forms the main barrier to materno-fetal exchange. The chloride (Cl(-)) channels in other epithelial tissues contribute to several functions, such as maintenance of the membrane potential, volume regulation, absorption and secretion. Additionally, the contributions of Cl(-) channels to these functions are demonstrated by certain diseases and knock-out animal models. There are multiple lines of evidence for the presence of Cl(-) channels in the hSTB, which could contribute to different placental functions. However, both the mechanism by which these channels are involved in the physiology of the placenta, and their molecular identities are still unclear. Furthermore, a correlation between altered Cl(-) channels functions and pathological pregnancies is beginning to emerge. This review summarizes recent developments on conductive placental chloride transport, and discusses its potential implications for placental physiology.

Glial cell missing-1 transcription factor is required for the differentiation of the human trophoblast

Mammalian placentation is a highly regulated process and is dependent on the proper development of specific trophoblast cell lineages. The two major types of trophoblast, villous and extravillous, show mitotic arrest during differentiation. In mice, the transcription factor, glial cell missing-1 (Gcm1), blocks mitosis and is required for syncytiotrophoblast formation and morphogenesis of the labyrinth, the murine equivalent of the villous placenta. The human homolog GCM1 has an analogous expression pattern, but its function is presently unknown. We studied GCM1 function in the human-derived BeWo choriocarcinoma cell line and in first trimester human placental villous and extravillous explants. The GCM1 expression was either inhibited by siRNA and antisense oligonucleotides methods or upregulated by forskolin treatment. Inhibition of GCM1 resulted in an increased rate of proliferation, but prevented de novo syncytiotrophoblast formation in syncytially denuded floating villous explants. GCM1 inhibition prevented extravillous differentiation along the invasive pathway in extravillous explants on matrigel. By contrast, forskolin-induced expression of GCM1 reduced the rate of proliferation and increased the rate of syncytialization in the floating villous explant model. Our studies show that GCM1 has a distinct role in the maintenance, development and turnover of the human trophoblast. Alterations in GCM1 expression or regulation may explain several aspects of two divergent severe placental insufficiency syndromes, namely preeclampsia and intrauterine growth restriction, which cause extreme preterm birth.

Human fetal growth and organ development: 50 years of discoveries

Knowledge about human fetal growth and organ development has greatly developed in the last 50 years. Anatomists and physiologists had already described some crucial aspects, for example, the circulation of blood during intrauterine life through the fetal heart, the liver as well as the placenta. However, only in the last century physiologic studies were performed in animal models. In the human fetus, the introduction of ultrasound and Doppler velocimetry has provided data about the growth and development of the fetus and of the circulation through the different fetal districts. Moreover, in the last 2 decades we have learned about fetal oxygenation and fetal nutrient supply caused by the availability of fetal blood samples obtained under relatively steady state conditions. These studies, together with studies using stable isotope methodologies, have clarified some aspects of the supply of the major nutrients for the fetus such as glucose, amino acids, and fatty acids. At the same time, the relevance of placental function has been recognized as a major determinant of fetal diseases leading to intrauterine growth restriction. More recently, the availability of new tools such as 3-dimensional ultrasound and magnetic resonance imaging, have made possible the evaluation of the growth and development of fetal organs. This knowledge in the healthy fetus will improve the ability of clinicians to recognize abnormal phenotypes of the different fetal organs, thus allowing to stage fetal diseases.

Ontogeny of hematological cell and biochemical profiles in maternal and fetal baboons (Papio species)

The normal ranges of hematological cell profiles and biochemistry are documented in adult non-pregnant, pregnant, juvenile, and neonatal baboons. Despite the extensive use of the baboon as a model for the study of various aspects of pregnancy, there is no data from paired mothers and their fetuses at different stages of gestation. Hematologic and biochemical profile data were obtained from eight non-pregnant female baboons, 37 mothers and 38 fetal baboons at 30 +/- 2, 90 +/- 2, 125 +/- 2, and 175 +/- 2 days of gestation (mean +/- range; dGA; term, 180 dGA). Changes observed in fetal and maternal blood during normal baboon pregnancy were similar to those reported in human pregnancy. The level of alkaline phosphatase was two times higher in fetal blood circulation than that reported in human pregnancy.

Development of structures and transport functions in the mouse placenta

The placenta is essential for sustaining the growth of the fetus during gestation, and defects in its function result in fetal growth restriction or, if more severe, fetal death. Several molecular pathways have been identified that are essential for development of the placenta, and mouse mutants offer new insights into the cell biology of placental development and physiology of nutrient transport.

Syncytiotrophoblast Degradation and the Pathophysiology of the Malaria-infected Placenta

Malaria is associated with excessive parasitic infection of the placenta and a reduction in neonatal birthweight. This study has investigated placental cell death in women with active and past malarial infection. Term placentae, with and without malarial pathology, were obtained from women in The Gambia. Active and past malaria infections were identified in placental sections and histological examination was used to determine the number of villi, the incidence of apoptosis, syncytial degradation, fibrinoid deposition and the frequency of syncytial knots. Placentae with active malaria infection showed erythrocyte adhesion of infected cells to syncytiotrophoblast, syncytial degradation, increased syncytial knotting and, in rare cases, localized destruction of the villi. Past malarial infection was characterized by syncytiotrophoblast disruption and fibrin-type fibrinoid (FTF) deposition. Perivillous FTF deposition was consistent with increased syncytial lesions and both increased lesions and syncytial knots were associated with birthweight reductions. Active malaria infection produced no alteration in placental apoptosis. The numbers of chorionic villi remained unchanged and infiltration of inflammatory cells, although not measured directly, appeared to be non-pervasive within the infected tissue. These observations establish a direct link between malaria parasitic infection and syncytiotrophoblast damage. The placental rejection of parasite-affected syncytia may invoke structural changes to compensate for inadequate placental exchange. Syncytial destruction could have serious implications; impairing fetal growth and in some rare cases, providing a previously unrecognized pathway to congenital infection.

Placental-fetal interrelationship in IUGR fetuses--a review

The role of placental function in maintaining an adequate fetal growth has been addressed by many different laboratories. The relationship between maternal and fetal circulation in the placenta is crucial for efficient exchanges of oxygen and nutrients. Moreover, maturational changes are taking place throughout gestation within the placenta in order to increase the transfer capacities while fetal/placental weight ratio is significantly decreasing. In human pregnancies, an impairment in the invasion of fetal trophoblast cells into the maternal decidua has been hypothesized as a cause of placental insufficiency leading to intrauterine growth restriction (IUGR). This condition has been associated with a number of adaptive changes taking place in both placenta and fetus. Adaptive changes can be followed by pathology leading to fetal death and therefore staging of the disease is fundamental for timing of delivery.A classification of the severity of IUGR in human pregnancies has been proposed based upon fetal heart rate (FHR) and Doppler velocimetry of the umbilical artery (pulsatility index or PI). This classification of clinical severity reflects different degrees of placental insufficiency and is associated with significant differences in placental nutrient exchange. Only those IUGR with pathological PI and FHR are associated with increasing degrees of hypoxemia and lacticacidemia. Furthermore, significant differences are observed in the transplacental glucose gradient in the most severe cases and the placental transport of essential amino acids is significantly reduced both in vivo and in vitro. These findings suggest that both placental metabolism and transport are altered in intrauterine growth restriction in humans.

Regulation of placental transfer: the Na(+)/H(+) exchanger--a review

This review article considers the purposes and mechanisms of regulation of placental transfer in general terms and then illustrates some key points with reference to the Na(+)/H(+) exchanger (NHE), a transport protein found in the syncytiotrophoblast. NHE probably has a role in the homeostasis of syncytiotrophoblast intracellular pH and may also be involved in syncytiotrophoblast cell volume regulation as well as H(+) loss from and Na(+) transfer to the fetus. The activity and expression of NHE in the microvillous plasma membrane of the syncytiotrophoblast is reduced in placentas from preterm, growth restricted babies as compared to their gestationally matched normally grown counterparts. There are differential effects of gestation in normal pregnancy on NHE mRNA, NHE protein and NHE activity. There is also evidence of acute modulation of NHE activity. Regulation of NHE in syncytiotrophoblast is therefore complex with control at transcription, post transcription and post translational loci.

The functional regeneration of syncytiotrophoblast in cultured explants of term placenta

We have investigated the functional characteristics of term human placental villous explants kept in long-term (7-11 days) culture. Fragments of placental villous tissue (approximately 5-10 mg wet wt) were cultured in supplemented CMRL-1066 culture medium for up to 11 days. After the first day of culture, the syncytiotrophoblast appeared vacuolated and eventually degenerated. However, a new syncytiotrophoblast developed by day 4, being indistinguishable from that of a fresh placenta by 11 days. Release of human chorionic gonadotrophin increased and activity of lactate dehydrogenase in culture medium decreased with culture time. Transport variables were measured over the first 7 days of culture. Basal (86)Rb efflux was reduced with time in culture and was inhibited by Ba2+, suggesting the efflux was mediated by K+ channels. At all stages of culture, (86)Rb efflux was stimulated by ATP, hyposmotic medium, and ANG II. A complex pattern of efflux changes with culture time and type of stimulator was observed, suggesting that several compartments of the tissue contributed to stimulated efflux. This culture system provides opportunities for studies of chronic regulation of placental function.

Activity and expression of the Na(+)/H(+) exchanger in the microvillous plasma membrane of the syncytiotrophoblast in relation to gestation and small for gestational age birth

The effect of gestational age, low birth weight, and umbilical plasma pH on the activity and expression of the Na(+)/H(+) exchanger in the microvillous plasma membrane (MVM) of the placental syncytiotrophoblast was investigated. MVM were isolated from placentas of fetuses delivered in the first and second trimesters and from appropriately grown for gestational age (AGA) and small for gestational age (SGA) babies born at term. Na(+)/H(+) exchange activity (amiloride-sensitive Na(+) uptake) was higher (p<0.05) in second trimester and term AGA MVM versus first trimester MVM (median [range]: 1.80 [1.01-3.03], 1.72 [1.16-3.15] versus 1.48 [0.92-1.66] nmol/mg protein/30s, respectively, n = 6, 12, and 9). As regards exchanger isoforms, Western blotting showed that NHE1 expression did not change across gestation, but NHE2 and NHE3 expression were lower (p<0.01) in the first and second trimesters than in term AGA MVM. There were no differences in Na(+)/H(+) exchanger activity or in NHE1-3 expression in term AGA MVM versus SGA (n = 11) MVM. There was no correlation between exchanger activity and umbilical artery or vein plasma pH, although with a relatively small number of samples (n = 12 and 15, respectively). We conclude that there is differential regulation of the activity and expression of Na(+)/H(+) exchanger isoforms in the MVM over the course of gestation in normal pregnancy; this is not affected in pregnancies resulting in SGA babies at term.

Development and polarization of cationic amino acid transporters and regulators in the human placenta

We have investigated L-arginine transport systems in the human placental syncytiotrophoblast across gestation using purified microvillous (MVM) and basal (BM) plasma membrane vesicles. In MVM from first-trimester and term placentas, L-arginine transport was by systems y(+) and y(+)L. In BM (term placentas), however, there was evidence for system y(+)L only. The Michaelis constant of system y(+)L was significantly lower (P < 0.05) in first-trimester compared with term MVM and lower in term MVM compared with BM (P < 0.05). There was no functional evidence for system b(0+) in term MVM or BM. Cationic amino acid transporter (CAT) 1, CAT 4, and 4F2hc were detected using RT-PCR in placentas throughout gestation. rBAT was not detected in term placentas. An approximately 85-kDa and an approximately 135-kDa protein was detected by Western blotting in MVM under reducing and nonreducing conditions, respectively, consistent with the 4F2hc monomer and the 4F2hc-light chain dimer, and their expression was significantly higher (P < 0.05) in term compared with first-trimester MVM. These proteins were not detected in BM despite functional evidence for system y(+)L. These data suggest different roles for 4F2hc in the development and polarization of cationic amino acid transporters in the syncytiotrophoblast.

Sites of mRNA expression of the cystic fibrosis (CF) and multidrug resistance (MDR1) genes in the human placenta of early pregnancy: No evidence for complementary expression

The aims of this study were to establish the sites of mRNA expression of both the cystic fibrosis (CF) and multidrug resistance (MDR1) genes in human placental sections from early pregnancy (first, early and mid-second trimesters). Riboprobes specific for each of these two genes were generated and used for in situ hybridization experiments. The results show parallel mRNA expression for the CF and MDR1 genes, with the signal detected in the syncytiotrophoblast and cytotrophoblast cells of the placental villi. Other cell types within the villous core were negative. Similar results were obtained at all stages of pregnancy studied.

System A amino acid transporter activity in human placental microvillous membrane vesicles in relation to various anthropometric measurements in appropriate and small for gestational age babies

Fetal growth and development is dependent on the transfer of amino acids from maternal to fetal blood across the microvillous plasma membrane (MVM) and basal plasma membrane of placental syncytiotrophoblast. The aim of this study was to determine the relationship of system A amino acid transporter (SysA) activity in MVM to a variety of measurements of size at birth in a group of term small for gestational age (SGA) babies and in a group of appropriate for gestational age (AGA) babies. Mean SysA activities (nmol/mg vesicle protein/30 s +/- SEM) were: SGA, 0.027 +/- 0.004 (n = 25) and AGA, 0.045 +/- 0.005 (n = 24); p = 0.006. Spearman rank correlations were calculated for SGA (n = 19-25) and AGA (n = 21-24) groups for SysA activity against the following anthropometric measurements: abdominal circumference, birth weight, length, midarm circumference (MAC), head circumference, midarm circumference:head circumference ratio, placental weight (PW), placental ratio (placental weight:birth weight), birth weight:length ratio, Ponderal index (birth weight/length3) and triceps and subscapular skin-fold thicknesses (tsft and ssft). In SGA babies, SysA activity was positively correlated (p < 0.05) with subscapular skin-fold thicknesses (r = 0.48), triceps skin-fold thicknesses (r = 0.42), PW (r = 0.42), and placental ratio (r = 0.46). In AGA babies, the only significant correlation was an inverse one with placental ratio (r = -0.50). These data suggest there are differences in the relationship between placental SysA activity and fetal proportion in term AGA compared with SGA babies.