The placenta: a multifaceted, transient organ.

The placenta is arguably the most important organ of the body, but paradoxically the most poorly understood. During its transient existence, it performs actions that are later taken on by diverse separate organs, including the lungs, liver, gut, kidneys and endocrine glands. Its principal function is to supply the fetus, and in particular, the fetal brain, with oxygen and nutrients. The placenta is structurally adapted to achieve this, possessing a large surface area for exchange and a thin interhaemal membrane separating the maternal and fetal circulations. In addition, it adopts other strategies that are key to facilitating transfer, including remodelling of the maternal uterine arteries that supply the placenta to ensure optimal perfusion. Furthermore, placental hormones have profound effects on maternal metabolism, initially building up her energy reserves and then releasing these to support fetal growth in later pregnancy and lactation post-natally. Bipedalism has posed unique haemodynamic challenges to the placental circulation, as pressure applied to the vena cava by the pregnant uterus may compromise venous return to the heart. These challenges, along with the immune interactions involved in maternal arterial remodelling, may explain complications of pregnancy that are almost unique to the human, including pre-eclampsia. Such complications may represent a trade-off against the provision for a large fetal brain.This is the accepted manuscript. It's currently embargoed until 19/01/2016. the final version is available from Royal Society Publishing at http://rstb.royalsocietypublishing.org/content/370/1663/2014006

Glucocorticoids as regulatory signals during intrauterine development.

What is the topic of this review? This review discusses the role of the glucocorticoids as regulatory signals during intrauterine development. It examines the functional significance of these hormones as maturational, environmental and programming signals in determining offspring phenotype. What advances does it highlight? It focuses on the extensive nature of the regulatory actions of these hormones. It highlights the emerging data that these actions are mediated, in part, by the placenta, other endocrine systems and epigenetic modifications of the genome. Glucocorticoids are important regulatory signals during intrauterine development. They act as maturational, environmental and programming signals that modify the developing phenotype to optimize offspring viability and fitness. They affect development of a wide range of fetal tissues by inducing changes in cellular expression of structural, transport and signalling proteins, which have widespread functional consequences at the whole organ and systems levels. Glucocorticoids, therefore, activate many of the physiological systems that have little function in utero but are vital at birth to replace the respiratory, nutritive and excretory functions previously carried out by the placenta. However, by switching tissues from accretion to differentiation, early glucocorticoid overexposure in response to adverse conditions can programme fetal development with longer term physiological consequences for the adult offspring, which can extend to the next generation. The developmental effects of the glucocorticoids can be direct on fetal tissues with glucocorticoid receptors or mediated by changes in placental function or other endocrine systems. At the molecular level, glucocorticoids can act directly on gene transcription via their receptors or indirectly by epigenetic modifications of the genome. In this review, we examine the role and functional significance of glucocorticoids as regulatory signals during intrauterine development and discuss the mechanisms by which they act in utero to alter the developing epigenome and ensuing phenotype.We would like to thank the many members of the Department of Physiology, Development and Neuroscience who have contributed to discussions and helped with our own studies cited here. We are also grateful for financial support from the BBSRC (BB/I011773/1), Horserace Betting Levy Board (VET/PRJ/736) and the Centre for Trophoblast Research at the University of Cambridge.This is the author accepted manuscript. The final version is available from Wiley via http://dx.doi.org/10.1113/EP08521

Placental Origins of Chronic Disease.

Epidemiological evidence links an individual's susceptibility to chronic disease in adult life to events during their intrauterine phase of development. Biologically this should not be unexpected, for organ systems are at their most plastic when progenitor cells are proliferating and differentiating. Influences operating at this time can permanently affect their structure and functional capacity, and the activity of enzyme systems and endocrine axes. It is now appreciated that such effects lay the foundations for a diverse array of diseases that become manifest many years later, often in response to secondary environmental stressors. Fetal development is underpinned by the placenta, the organ that forms the interface between the fetus and its mother. All nutrients and oxygen reaching the fetus must pass through this organ. The placenta also has major endocrine functions, orchestrating maternal adaptations to pregnancy and mobilizing resources for fetal use. In addition, it acts as a selective barrier, creating a protective milieu by minimizing exposure of the fetus to maternal hormones, such as glucocorticoids, xenobiotics, pathogens, and parasites. The placenta shows a remarkable capacity to adapt to adverse environmental cues and lessen their impact on the fetus. However, if placental function is impaired, or its capacity to adapt is exceeded, then fetal development may be compromised. Here, we explore the complex relationships between the placental phenotype and developmental programming of chronic disease in the offspring. Ensuring optimal placentation offers a new approach to the prevention of disorders such as cardiovascular disease, diabetes, and obesity, which are reaching epidemic proportions.The authors thank the various funding agencies that have generously supported their research over the years; GJB, the Medical Research Council, the Wellcome Trust and Action Medical Research; ALF, the Biotechnology and Biological Sciences Council, the Medical Research Council and the Wellcome Trust; KLT, the National Institutes of Child Health and Human Development, the Nation Heart Lung and Blood Institute, the National Institute of Diabetes and Digestive and Kidney Diseases, the National Institute of Aging, the American Heart Association and the M. Lowell Edwards Endowment.This is the author accepted manuscript. The final version is available from the American Physiological Society via https://doi.org/10.1152/physrev.00029.201

Hypoxia, fetal and neonatal physiology: 100 years on from Sir Joseph Barcroft.

This is the author accepted manuscript. The final version is available from Wiley via http://dx.doi.org/10.1113/JP27200

Maternal and fetal genomes interplay through phosphoinositol 3-kinase(PI3K)-p110α signaling to modify placental resource allocation.

Pregnancy success and life-long health depend on a cooperative interaction between the mother and the fetus in the allocation of resources. As the site of materno-fetal nutrient transfer, the placenta is central to this interplay; however, the relative importance of the maternal versus fetal genotypes in modifying the allocation of resources to the fetus is unknown. Using genetic inactivation of the growth and metabolism regulator, Pik3ca (encoding PIK3CA also known as p110α, α/+), we examined the interplay between the maternal genome and the fetal genome on placental phenotype in litters of mixed genotype generated through reciprocal crosses of WT and α/+ mice. We demonstrate that placental growth and structure were impaired and associated with reduced growth of α/+ fetuses. Despite its defective development, the α/+ placenta adapted functionally to increase the supply of maternal glucose and amino acid to the fetus. The specific nature of these changes, however, depended on whether the mother was α/+ or WT and related to alterations in endocrine and metabolic profile induced by maternal p110α deficiency. Our findings thus show that the maternal genotype and environment programs placental growth and function and identify the placenta as critical in integrating both intrinsic and extrinsic signals governing materno-fetal resource allocation.Centre for Trophoblast Research award of a Next Generation Fellowship, Erasmus Exchange scheme scholarshipThis is the author accepted manuscript. The final version is available from the National Academy of Sciences via http://dx.doi.org/10.1073/pnas.160201211

Pancreas deficiency modifies bone development in the ovine fetus near term.

Hormones have an important role in the regulation of fetal growth and development, especially in response to nutrient availability in utero. Using micro-CT and an electromagnetic three-point bend test, this study examined the effect of pancreas removal at 0.8 fraction of gestation on the developing bone structure and mechanical strength in fetal sheep. When fetuses were studied at 10 and 25 days after surgery, pancreatectomy caused hypoinsulinaemia, hyperglycaemia and growth retardation which was associated with low plasma concentrations of leptin and a marker of osteoclast activity and collagen degradation. In pancreatectomized fetuses compared to control fetuses, limb lengths were shorter, and trabecular (Tb) bone in the metatarsi showed greater bone volume fraction, Tb thickness, degree of anisotropy and porosity, and lower fractional bone surface area and Tb spacing. Mechanical strength testing showed that pancreas deficiency was associated with increased stiffness and a greater maximal weight load at fracture in a subset of fetuses studied near term. Overall, pancreas deficiency in utero slowed the growth of the fetal skeleton and adapted the developing bone to generate a more compact and connected structure. Maintenance of bone strength in growth-retarded limbs is especially important in a precocial species in preparation for skeletal loading and locomotion at birth

Maternal Dexamethasone Treatment Alters Tissue and Circulating Components of the Renin-Angiotensin System in the Pregnant Ewe and Fetus.

Antenatal synthetic glucocorticoids promote fetal maturation in pregnant women at risk of preterm delivery and their mechanism of action may involve other endocrine systems. This study investigated the effect of maternal dexamethasone treatment, at clinically relevant doses, on components of the renin-angiotensin system (RAS) in the pregnant ewe and fetus. From 125 days of gestation (term, 145 ± 2 d), 10 ewes carrying single fetuses of mixed sex (3 female, 7 male) were injected twice im, at 10-11 pm, with dexamethasone (2 × 12 mg, n = 5) or saline (n = 5) at 24-hour intervals. At 10 hours after the second injection, maternal dexamethasone treatment increased angiotensin-converting enzyme (ACE) mRNA levels in the fetal lungs, kidneys, and heart and ACE concentration in the circulation and lungs, but not kidneys, of the fetuses. Fetal cardiac mRNA abundance of angiotensin II (AII) type 2 receptor decreased after maternal dexamethasone treatment. Between the two groups of fetuses, there were no significant differences in plasma angiotensinogen or renin concentrations; in transcript levels of renal renin, or AII type 1 or 2 receptors in the lungs and kidneys; or in pulmonary, renal or cardiac protein content of the AII receptors. In the pregnant ewes, dexamethasone administration increased pulmonary ACE and plasma angiotensinogen, and decreased plasma renin, concentrations. Some of the effects of dexamethasone treatment on the maternal and fetal RAS were associated with altered insulin and thyroid hormone activity. Changes in the local and circulating RAS induced by dexamethasone exposure in utero may contribute to the maturational and tissue-specific actions of antenatal glucocorticoid treatment.The study was supported by the Biotechnology and Biological Sciences Research Council and Tommy’s, the baby charity.This is the final version. It was first published by the Endocrine Society at http://press.endocrine.org/doi/abs/10.1210/en.2015-119

Proximity to Delivery Alters Insulin Sensitivity and Glucose Metabolism in Pregnant Mice.

In late pregnancy, maternal insulin resistance occurs to support fetal growth, but little is known about insulin-glucose dynamics close to delivery. This study measured insulin sensitivity in mice in late pregnancy at day 16 (D16) and near term at D19. Nonpregnant (NP) and pregnant mice were assessed for metabolite and hormone concentrations, body composition by DEXA, tissue insulin signaling protein abundance by Western blotting, glucose tolerance and utilization, and insulin sensitivity using acute insulin administration and hyperinsulinemic-euglycemic clamps with [(3)H]glucose infusion. Whole-body insulin resistance occurred in D16 pregnant dams in association with basal hyperinsulinemia, insulin-resistant endogenous glucose production, and downregulation of several proteins in hepatic and skeletal muscle insulin signaling pathways relative to NP and D19 values. Insulin resistance was less pronounced at D19, with restoration of NP insulin concentrations, improved hepatic insulin sensitivity, and increased abundance of hepatic insulin signaling proteins. At D16, insulin resistance at whole-body, tissue, and molecular levels will favor fetal glucose acquisition, while improved D19 hepatic insulin sensitivity will conserve glucose for maternal use in anticipation of lactation. Tissue sensitivity to insulin, therefore, alters differentially with proximity to delivery in pregnant mice, with implications for human and other species.We are grateful to the Medical Research Council for funding the research through a studentship to Barbara Musial and an in vivo skills award (MR/J500458/1 and MRC CORD G0600717).This is the author accepted manuscript. The final version is available from the American Diabetes Association via http://dx.doi.org/10.2337/db15-153