Placental metabolic reprogramming: do changes in the mix of energy-generating substrates modulate fetal growth?

Cause of fetal growth restriction during high-altitude pregnancy

High-altitude pregnancy increases the incidence of fetal growth restriction and reduces birth weight. This poses a significant clinical challenge as both are linked to adverse health outcomes, including raised infant mortality and the development of the metabolic syndrome in later life. While this reduction in birth weight is mostly understood to be driven by the hypobaric hypoxia of high altitude, the causative mechanism is unclear. Moreover, it is now recognized that highland ancestry confers protection against this reduction in birth weight. Here, we analyze the evidence that pregnancy at high altitude reduces birth weight and that highland ancestry confers protection, discussing mechanisms contributing to both effects.

Placentae of small appropriately-grown-for-gestational-age neonates exhibit sexually dimorphic transcriptomic changes representative of placental insufficiency

INTRODUCTION

Previous studies have reported that neonates less than the 25th BWC especially if they were male, were more likely to be associated with birth complications suggesting small neonates often identified as appropriately grown are at risk of adverse outcomes. We have questioned whether smaller neonates not typically categorized as "small for gestational age" may not reach their genetically determined growth due to placental insufficiency.

METHODS

RNA-Seq was performed on the Illumina NovaSeq 600 using term placentae from neonates that were less than the 10th birthweight centile (BWC) (n = 39), between the 10th and the 30th BWC (n = 15) or greater than the 30th BWC (n = 23). Bioinformatic analyses were conducted and statistical significance was assessed at a level of P < 0.05 for single comparisons or FDR <0.05 unless otherwise noted.

RESULTS

Gene set enrichment analysis revealed differences between BWC groups and in relation to the sex of the placenta. Genes associated with hypoxia, inflammatory responses, estrogen responsive genes, and androgen responsive genes were enriched (FDR <0.1) for in placentae of neonates <10th BWC regardless of sex and also in male placentae of neonates between the 10th-30th BWC. Female placenta of neonates between the 10th-30th BWC were comparable to placentae of neonates >30th BWC.

DISCUSSION

These findings provide evidence that small male neonates may be at a greater risk of an adverse outcome than females due to changes in gene expression that are associated with placental dysfunction. The current data raises questions of whether placental pathology for smaller appropriately grown neonates should be scientifically and clinically examined in more depth.

Placental physioxia is based on spatial and temporal variations of placental oxygenation throughout pregnancy

For obvious reasons, in vivo measurements of placental oxygenation are extremely rare and hence, scientists need to focus on the few studies that revealed at least some data on the topic. The scarcity of real in vivo data resulted in the development of hypotheses on placental oxygenation that blocked an objective view on the topic for decades. Only now, new hypotheses are emerging adding new views and ideas on the topic. Especially in the field of preeclampsia, hypotheses on placental oxygenation have mislead a whole generation of scientists. This review article displays the available in vivo placental oxygen data from 8 to 40 weeks of gestation. It also compares these physiological oxygen concentrations, called physioxia, with the situation in pre-placental hypoxia, i.e. pregnancies at high altitude. Finally, it summarizes what we know today about oxygen measurements in cases with preeclampsia. In early-onset preeclampsia cases, all in vivo data available today point to increased oxygen values in the intervillous space of the placenta. This is due to a reduced oxygen transfer of the placental barrier from maternal to fetal blood, resulting in hypoxia of fetal blood and the fetus.

Adaptive responses in uteroplacental metabolism and fetoplacental nutrient shuttling and sensing during placental insufficiency

Glucose, lactate, and amino acids are major fetal nutrients. During placental insufficiency-induced intrauterine growth restriction (PI-IUGR), uteroplacental weight-specific oxygen consumption rates are maintained, yet fetal glucose and amino acid supply is decreased and fetal lactate concentrations are increased. We hypothesized that uteroplacental metabolism adapts to PI-IUGR by altering nutrient allocation to maintain oxidative metabolism. Here, we measured nutrient flux rates, with a focus on nutrients shuttled between the placenta and fetus (lactate-pyruvate, glutamine-glutamate, and glycine-serine) in a sheep model of PI-IUGR. PI-IUGR fetuses weighed 40% less and had decreased oxygen, glucose, and amino acid concentrations and increased lactate and pyruvate versus control (CON) fetuses. Uteroplacental weight-specific rates of oxygen, glucose, lactate, and pyruvate uptake were similar. In PI-IUGR, fetal glucose uptake was decreased and pyruvate output was increased. In PI-IUGR placental tissue, pyruvate dehydrogenase (PDH) phosphorylation was decreased and PDH activity was increased. Uteroplacental glutamine output to the fetus and expression of genes regulating glutamine-glutamate metabolism were lower in PI-IUGR. Fetal glycine uptake was lower in PI-IUGR, with no differences in uteroplacental glycine or serine flux. These results suggest increased placental utilization of pyruvate from the fetus, without higher maternal glucose utilization, and lower fetoplacental amino acid shuttling during PI-IUGR. Mechanistically, AMP-activated protein kinase (AMPK) activation was higher and associated with thiobarbituric acid-reactive substances (TBARS) content, a marker of oxidative stress, and PDH activity in the PI-IUGR placenta, supporting a potential link between oxidative stress, AMPK, and pyruvate utilization. These differences in fetoplacental nutrient sensing and shuttling may represent adaptive strategies enabling the placenta to maintain oxidative metabolism.NEW & NOTEWORTHY These results suggest increased placental utilization of pyruvate from the fetus, without higher maternal glucose uptake, and lower amino acid shuttling in the placental insufficiency-induced intrauterine growth restriction (PI-IUGR) placenta. AMPK activation was associated with oxidative stress and PDH activity, supporting a putative link between oxidative stress, AMPK, and pyruvate utilization. These differences in fetoplacental nutrient sensing and shuttling may represent adaptive strategies enabling the placenta to maintain oxidative metabolism at the expense of fetal growth.

Decreased Vitamin D Levels and Altered Placental Vitamin D Gene Expression at High Altitude: Role of Genetic Ancestry

High-altitude hypoxia challenges reproduction; particularly in non-native populations. Although high-altitude residence is associated with vitamin D deficiency, the homeostasis and metabolism of vitamin D in natives and migrants remain unknown. We report that high altitude (3600 m residence) negatively impacted vitamin D levels, with the high-altitude Andeans having the lowest 25-OH-D levels and the high-altitude Europeans having the lowest 1α,25-(OH)2-D levels. There was a significant interaction of genetic ancestry with altitude in the ratio of 1α,25-(OH)2-D to 25-OH-D; with the ratio being significantly lower in Europeans compared to Andeans living at high altitude. Placental gene expression accounted for as much as 50% of circulating vitamin D levels, with CYP2R1 (25-hydroxylase), CYP27B1 (1α-hydroxylase), CYP24A1 (24-hydroxylase), and LRP2 (megalin) as the major determinants of vitamin D levels. High-altitude residents had a greater correlation between circulating vitamin D levels and placental gene expression than low-altitude residents. Placental 7-dehydrocholesterol reductase and vitamin D receptor were upregulated at high altitude in both genetic-ancestry groups, while megalin and 24-hydroxylase were upregulated only in Europeans. Given that vitamin D deficiency and decreased 1α,25-(OH)2-D to 25-OH-D ratios are associated with pregnancy complications, our data support a role for high-altitude-induced vitamin D dysregulation impacting reproductive outcomes, particularly in migrants.

Mitochondrial Dysfunction in the Pathogenesis of Preeclampsia

PURPOSE OF REVIEW

Preeclampsia complicates 5-10% of all pregnancies and is a leading cause of maternal and perinatal mortality and morbidity. The placenta plays a pivotal role in determining pregnancy outcome by supplying the fetus with oxygen and nutrients and by synthesizing hormones. Placental function is highly dependent on energy supplied by mitochondria. It is well-known that preeclampsia is originated from placental dysfunction, although the etiology of it remains elusive.

RECENT FINDINGS

During the last three decades, substantial evidence suggests that mitochondrial abnormality is a major contributor to placental dysfunction. In addition, mitochondrial damage caused by circulating bioactive factors released from the placenta may cause endothelial dysfunction and subsequent elevation in maternal blood pressure. In this review, we summarize the current knowledge of mitochondrial abnormality in the pathogenesis of preeclampsia and discuss therapeutic approaches targeting mitochondria for treatment of preeclampsia.

Prenatal Hypoxia Affects Foetal Cardiovascular Regulatory Mechanisms in a Sex- and Circadian-Dependent Manner: A Review

Prenatal hypoxia during the prenatal period can interfere with the developmental trajectory and lead to developing hypertension in adulthood. Prenatal hypoxia is often associated with intrauterine growth restriction that interferes with metabolism and can lead to multilevel changes. Therefore, we analysed the effects of prenatal hypoxia predominantly not associated with intrauterine growth restriction using publications up to September 2021. We focused on: (1) The response of cardiovascular regulatory mechanisms, such as the chemoreflex, adenosine, nitric oxide, and angiotensin II on prenatal hypoxia. (2) The role of the placenta in causing and attenuating the effects of hypoxia. (3) Environmental conditions and the mother's health contribution to the development of prenatal hypoxia. (4) The sex-dependent effects of prenatal hypoxia on cardiovascular regulatory mechanisms and the connection between hypoxia-inducible factors and circadian variability. We identified that the possible relationship between the effects of prenatal hypoxia on the cardiovascular regulatory mechanism may vary depending on circadian variability and phase of the days. In summary, even short-term prenatal hypoxia significantly affects cardiovascular regulatory mechanisms and programs hypertension in adulthood, while prenatal programming effects are not only dependent on the critical period, and sensitivity can change within circadian oscillations.

Tissue-specific responses that constrain glucose oxidation and increase lactate production with the severity of hypoxemia in fetal sheep

Fetal hypoxemia decreases insulin and increases cortisol and norepinephrine concentrations and may restrict growth by decreasing glucose utilization and altering substrate oxidation. Specifically, we hypothesized that hypoxemia would decrease fetal glucose oxidation and increase lactate and pyruvate production. We tested this by measuring whole body glucose oxidation and lactate production, and molecular pathways in liver, muscle, adipose, and pancreas tissues of fetuses exposed to maternal hypoxemia for 9 days (HOX) compared with control fetal sheep (CON) in late gestation. Fetuses with more severe hypoxemia had lower whole body glucose oxidation rates, and HOX fetuses had increased lactate production from glucose. In muscle and adipose tissue, expression of the glucose transporter GLUT4 was decreased. In muscle, pyruvate kinase (PKM) and lactate dehydrogenase B (LDHB) expression was decreased. In adipose tissue, LDHA and lactate transporter (MCT1) expression was increased. In liver, there was decreased gene expression of PKLR and MPC2 and phosphorylation of PDH, and increased LDHA gene and LDH protein abundance. LDH activity, however, was decreased only in HOX skeletal muscle. There were no differences in basal insulin signaling across tissues, nor differences in pancreatic tissue insulin content, β-cell area, or genes regulating β-cell function. Collectively, these results demonstrate coordinated metabolic responses across tissues in the hypoxemic fetus that limit glucose oxidation and increase lactate and pyruvate production. These responses may be mediated by hypoxemia-induced endocrine responses including increased norepinephrine and cortisol, which inhibit pancreatic insulin secretion resulting in lower insulin concentrations and decreased stimulation of glucose utilization.NEW & NOTEWORTHY Hypoxemia lowered fetal glucose oxidation rates, based on severity of hypoxemia, and increased lactate production. This was supported by tissue-specific metabolic responses that may result from increased norepinephrine and cortisol concentrations, which decrease pancreatic insulin secretion and insulin concentrations and decrease glucose utilization. This highlights the vulnerability of metabolic pathways in the fetus and demonstrates that constrained glucose oxidation may represent an early event in response to sustained hypoxemia and fetal growth restriction.

Impact of reduced uterine perfusion pressure model of preeclampsia on metabolism of placenta, maternal and fetal hearts

Preeclampsia is a cardiovascular pregnancy complication characterised by new onset hypertension and organ damage or intrauterine growth restriction. It is one of the leading causes of maternal and fetal mortality in pregnancy globally. Short of pre-term delivery of the fetus and placenta, treatment options are limited. Consequently, preeclampsia leads to increased cardiovascular disease risk in both mothers and offspring later in life. Here we aim to examine the impact of the reduced uterine perfusion pressure (RUPP) rat model of preeclampsia on the maternal cardiovascular system, placental and fetal heart metabolism. The surgical RUPP model was induced in pregnant rats by applying silver clips around the aorta and uterine arteries on gestational day 14, resulting in ~ 40% uterine blood flow reduction. The experiment was terminated on gestational day 19 and metabolomic profile of placentae, maternal and fetal hearts analysed using high-resolution ¹H NMR spectroscopy. Impairment of uterine perfusion in RUPP rats caused placental and cardiac hypoxia and a series of metabolic adaptations: altered energetics, carbohydrate, lipid and amino acid metabolism of placentae and maternal hearts. Comparatively, the fetal metabolic phenotype was mildly affected. Nevertheless, long-term effects of these changes in both mothers and the offspring should be investigated further in the future.

Uteroplacental nutrient flux and evidence for metabolic reprogramming during sustained hypoxemia

Gestational hypoxemia is often associated with reduced birth weight, yet how hypoxemia controls uteroplacental nutrient metabolism and supply to the fetus is unclear. This study tested the effects of maternal hypoxemia (HOX) between 0.8 and 0.9 gestation on uteroplacental nutrient metabolism and flux to the fetus in pregnant sheep. Despite hypoxemia, uteroplacental and fetal oxygen utilization and net glucose and lactate uptake rates were similar in HOX (n = 11) compared to CON (n = 7) groups. HOX fetuses had increased lactate and pyruvate concentrations and increased net pyruvate output to the utero-placenta. In the HOX group, uteroplacental flux of alanine to the fetus was decreased, as was glutamate flux from the fetus. HOX fetuses had increased alanine and decreased aspartate, serine, and glutamate concentrations. In HOX placental tissue, we identified hypoxic responses that should increase mitochondrial efficiency (decreased SDHB, increased COX4I2) and increase lactate production from pyruvate (increased LDHA protein and LDH activity, decreased LDHB and MPC2), both resembling metabolic reprogramming, but with evidence for decreased (PFK1, PKM2), rather than increased, glycolysis and AMPK phosphorylation. This supports a fetal-uteroplacental shuttle during sustained hypoxemia whereby uteroplacental tissues produce lactate as fuel for the fetus using pyruvate released from the fetus, rather than pyruvate produced from glucose in the placenta, given the absence of increased uteroplacental glucose uptake and glycolytic gene activation. Together, these results provide new mechanisms for how hypoxemia, independent of AMPK activation, regulates uteroplacental metabolism and nutrient allocation to the fetus, which allow the fetus to defend its oxidative metabolism and growth.

Chemical Induction of Trophoblast Hypoxia by Cobalt Chloride Leads to Increased Expression of DDIT3

Choriocarcinoma cells BeWo b30 are used to model human placental trophoblast hypoxia using cobalt (II) chloride and hydroxyquinoline derivative (HD) as chemical inducers of hypoxia-inducible factor (HIF). In this study, it was shown that both substances activate the hypoxic pathway and the epithelial–mesenchymal transition and inhibit the pathways of cell proliferation. However, CoCl₂ caused activation of the apoptosis pathway, increased the activity of effector caspases 3 and 7, and increased the expression of the unfolded protein response target DDIT3. The mTORC1 pathway was activated upon exposition to CoCl₂, while HD suppressed this pathway, as it happens during real trophoblast hypoxia. Thus, effect of CoCl₂ on BeWo cells can be a model of severe hypoxia with activation of apoptosis, while HD mimics moderate hypoxia.

Global proteomic analyses of human cytotrophoblast differentiation/invasion

During human pregnancy, cytotrophoblasts (CTBs) from the placenta differentiate into specialized subpopulations that play crucial roles in proper fetal growth and development. A subset of these CTBs differentiate along an invasive pathway, penetrating the decidua and anchoring the placenta to the uterus. A crucial hurdle in pregnancy is the ability of these cells to migrate, invade and remodel spiral arteries, ensuring adequate blood flow to nourish the developing fetus. Although advances continue in describing the molecular features regulating the differentiation of these cells, assessment of their global proteomic changes at mid-gestation remain undefined. Here, using sequential window acquisition of all theoretical fragment-ion spectra (SWATH), which is a data-independent acquisition strategy, we characterized the protein repertoire of second trimester human CTBs during their differentiation towards an invasive phenotype. This mass spectrometry-based approach allowed identification of 3026 proteins across four culture time points corresponding to sequential stages of differentiation, confirming the expression dynamics of established molecules and offering new information into other pathways involved. The availability of a SWATH CTB global spectral library serves as a beneficial resource for hypothesis generation and as a foundation for further understanding CTB differentiation dynamics.

Levels of miR-374 increase in BeWo b30 cells exposed to hypoxia

In humans, trophoblast hypoxia during placental development can be a cause of serious pregnancy complications, such as preeclampsia and fetal growth restriction. The pathogenesis of these conditions is not fully clear and may be associated with changed expression of some genes and regulatory molecules, including miRNA, in trophoblast cells. The aim of this study was to analyze miRNA profiles and measure the expression of their target genes in a model of trophoblast hypoxia. Human choriocarcinoma BeWo b30 cells were used as a trophoblast model. Hypoxia was induced by cobalt chloride (CoCl2) and an oxyquinoline derivative. MRNA and miRNA expression profiles were evaluated by means of next generation sequencing (NGS); the expression of individual genes was analyzed by PCR. We studied the secondary structure of mRNAs of target genes for those miRNAs whose expression had changed significantly and analyzed potential competition between these miRNAs for the binding site. The observed changes in the expression of the key genes involved in the response to hypoxia confirmed the feasibility of using CoCl2 and the oxyquinoline derivative as hypoxia inducers. The analysis revealed an increase in miR-374 levels following the activation of the hypoxia pathway in our trophoblast model. The changes were accompanied by a reduction in FOXM1 mRNA expression; this mRNA is a target for hsa-miR-374a-5p and hsa-miR374b-5p, which can compete with hsa-miR-21-5p for the binding sites on FOXM1 mRNA. The involvement of FOXM1 in the regulation of the invasive cell potential suggests the role of miR-374 and FOXM1 in the pathogenesis of disrupted trophoblast invasion during placental development as predisposing for fetal growth restriction and preeclampsia.

Adaptations of the human placenta to hypoxia: opportunities for interventions in fetal growth restriction

BACKGROUND

The placenta is the functional interface between the mother and the fetus during pregnancy, and a critical determinant of fetal growth and life-long health. In the first trimester, it develops under a low-oxygen environment, which is essential for the conceptus who has little defense against reactive oxygen species produced during oxidative metabolism. However, failure of invasive trophoblasts to sufficiently remodel uterine arteries toward dilated vessels by the end of the first trimester can lead to reduced/intermittent blood flow, persistent hypoxia and oxidative stress in the placenta with consequences for fetal growth. Fetal growth restriction (FGR) is observed in ∼10% of pregnancies and is frequently seen in association with other pregnancy complications, such as preeclampsia (PE). FGR is one of the main challenges for obstetricians and pediatricians, as smaller fetuses have greater perinatal risks of morbidity and mortality and postnatal risks of neurodevelopmental and cardio-metabolic disorders.

OBJECTIVE AND RATIONALE

The aim of this review was to examine the importance of placental responses to changing oxygen environments during abnormal pregnancy in terms of cellular, molecular and functional changes in order to highlight new therapeutic pathways, and to pinpoint approaches aimed at enhancing oxygen supply and/or mitigating oxidative stress in the placenta as a mean of optimizing fetal growth.

SEARCH METHODS

An extensive online search of peer-reviewed articles using PubMed was performed with combinations of search terms including pregnancy, placenta, trophoblast, oxygen, hypoxia, high altitude, FGR and PE (last updated in May 2020).

OUTCOMES

Trophoblast differentiation and placental establishment are governed by oxygen availability/hypoxia in early pregnancy. The placental response to late gestational hypoxia includes changes in syncytialization, mitochondrial functions, endoplasmic reticulum stress, hormone production, nutrient handling and angiogenic factor secretion. The nature of these changes depends on the extent of hypoxia, with some responses appearing adaptive and others appearing detrimental to the placental support of fetal growth. Emerging approaches that aim to increase placental oxygen supply and/or reduce the impacts of excessive oxidative stress are promising for their potential to prevent/treat FGR.

WIDER IMPLICATIONS

There are many risks and challenges of intervening during pregnancy that must be considered. The establishment of human trophoblast stem cell lines and organoids will allow further mechanistic studies of the effects of hypoxia and may lead to advanced screening of drugs for use in pregnancies complicated by placental insufficiency/hypoxia. Since no treatments are currently available, a better understanding of placental adaptations to hypoxia would help to develop therapies or repurpose drugs to optimize placental function and fetal growth, with life-long benefits to human health.

Shedding New Light on Cancer Metabolism: A Metabolic Tightrope Between Life and Death

Since the earliest findings of Otto Warburg, who discovered the first metabolic differences between lactate production of cancer cells and non-malignant tissues in the 1920s, much time has passed. He explained the increased lactate levels with dysfunctional mitochondria and aerobic glycolysis despite adequate oxygenation. Meanwhile, we came to know that mitochondria remain instead functional in cancer cells; hence, metabolic drift, rather than being linked to dysfunctional mitochondria, was found to be an active act of direct response of cancer cells to cell proliferation and survival signals. This metabolic drift begins with the use of sugars and the full oxidative phosphorylation via the mitochondrial respiratory chain to form CO₂, and it then leads to the formation of lactic acid via partial oxidation. In addition to oncogene-driven metabolic reprogramming, the oncometabolites themselves alter cell signaling and are responsible for differentiation and metastasis of cancer cells. The aberrant metabolism is now considered a major characteristic of cancer within the past 15 years. However, the proliferating anabolic growth of a tumor and its spread to distal sites of the body is not explainable by altered glucose metabolism alone. Since a tumor consists of malignant cells and its tumor microenvironment, it was important for us to understand the bilateral interactions between the primary tumor and its microenvironment and the processes underlying its successful metastasis. We here describe the main metabolic pathways and their implications in tumor progression and metastasis. We also portray that metabolic flexibility determines the fate of the cancer cell and ultimately the patient. This flexibility must be taken into account when deciding on a therapy, since singular cancer therapies only shift the metabolism to a different alternative path and create resistance to the medication used. As with Otto Warburg in his days, we primarily focused on the metabolism of mitochondria when dealing with this scientific question.

Exposure to Trichloroethylene Metabolite S-(1,2-Dichlorovinyl)-L-cysteine Causes Compensatory Changes to Macronutrient Utilization and Energy Metabolism in Placental HTR-8/SVneo Cells

Trichloroethylene (TCE) is a widespread environmental contaminant following decades of use as an industrial solvent, improper disposal, and remediation challenges. Consequently, TCE exposure continues to constitute a risk to human health. Despite epidemiological evidence associating exposure with adverse birth outcomes, the effects of TCE and its metabolite S-(1, 2-dichlorovinyl)-L-cysteine (DCVC) on the placenta remain undetermined. Flexible and efficient macronutrient and energy metabolism pathway utilization is essential for placental cell physiological adaptability. Because DCVC is known to compromise cellular energy status and disrupt energy metabolism in renal proximal tubular cells, this study investigated the effects of DCVC on cellular energy status and energy metabolism pathways in placental cells. Human extravillous trophoblast cells, HTR-8/SVneo, were exposed to 5–20 μM DCVC for 6 or 12 h. After establishing concentration and exposure duration thresholds for DCVC-induced cytotoxicity, targeted metabolomics was used to evaluate overall energy status and metabolite concentrations from energy metabolism pathways. The data revealed glucose metabolism perturbations including a time-dependent accumulation of glucose-6-phosphate+frutose-6-phosphate (G6P+F6P) as well as independent shunting of glucose intermediates that diminished with time, with modest energy status decline but in the absence of significant changes in ATP concentrations. Furthermore, metabolic profiling suggested that DCVC stimulated compensatory utilization of glycerol, lipid, and amino acid metabolism to provide intermediate substrates entering downstream in the glycolytic pathway or the tricarboxylic acid cycle. Lastly, amino acid deprivation increased susceptibility to DCVC-induced cytotoxicity. Taken together, these results suggest that DCVC caused metabolic perturbations necessitating adaptations in macronutrient and energy metabolism pathway utilization to maintain adequate ATP levels.

Global population variation in placental size and structure: Evidence from Cebu, Philippines

INTRODUCTION

Placental morphology influences the intrauterine environment and fetal growth, which help set life-course health trajectories across generations. Little is known about placental characteristics in populations with chronic nutritional insufficiency where birth weights tend to be lower, and how these relationships between birth and placental weights vary across populations.

METHODS

We collected weights and stereologically-determined villous mass and surface area of 21 placentas from offspring of women enrolled in a birth cohort study in metropolitan Cebu, Philippines, a low-income population. We identified 15 samples from other global populations ranging from low to high income that had similar data to ours to assess patterns of variation between birth and placental weights and microscopic characteristics. We ranked the population samples in order for each characteristic.

RESULTS

Mean birth weight in Cebu was 3162 ± 80 g (ranked 9/16) and placental weight was 454 ± 32 g (ranked 12/16). Birth:placental weight ratio was 7.0 (ranked 3/16). Average villous surface area for Cebu placentas was 6.5 m2 (ranked 9/12); Birth weight:villous surface area was 0.048 g/m2 (ranked 4/12).

DISCUSSION

Placentas from Cebu produced heavier neonates per units of placental weight and villous surface area than most other populations, despite lower villous surface areas and less complex surface-to-volume topography. This range of placental efficiency spurs questions about the mechanisms by which placental morphology optimizes efficiency in different environmental contexts during gestation. Placental variation both within and across populations is likely due to many intersecting environmental, metabolic, and (epi)genetic factors that will require additional research to clarify.

Use of Glucose, Glutamine and Fatty Acids for Trophoblast Respiration in Lean, Obese and Gestational Diabetic Women

PURPOSE

Maternal obesity and gestational diabetes (GDM) are associated with adverse outcomes particularly with a male fetus. The composition and amount of substrate supplied to the placenta is altered in these conditions. We hypothesized that there are sexually dimorphic differences in utilization of glucose, fatty acids and glutamine between trophoblast of lean, obese and GDM women.

METHODS

Trophoblast were isolated from term male or female placentas from lean, obese or GDM women (n = 4-6/group) and syncytiotrophoblast formed over 72 hr before measuring mitochondrial respiration by fuel flex assay (Seahorse XF96 analyzer). Dependency, capacity and flexibility for use of glucose, glutamine and fatty acids was measured with western blot of glucose transporter GLUT1, glutaminase and carnitine palmitoyl-transferase 1A, (CPT1A).

RESULTS

Sexual dimorphism in syncytiotrophoblast fuel utilization was seen in GDM vs lean with a significant increase in glucose dependency in male and glucose capacity in female, whereas for glutamine capacity significantly decreased in male and female but dependency only in female. Fatty acid dependency and capacity significantly increased in male and capacity in female trophoblast of GDM vs either lean or obese. In male but not female trophoblast flexibility to use all three fuels significantly decreased from lean to obese and GDM. In male trophoblast there were significant associations between GLUT1 and glucose dependency (positive) and flexibility (negative).

MAIN CONCLUSIONS

Human syncytiotrophoblast utilizes glutamine for mitochondrial respiration. Utilization of glucose, fatty acids and glutamine changes in a sexually dimorphic manner with obesity and GDM predominantly with a male placenta.

Mitochondrial implications in human pregnancies with intrauterine growth restriction and associated cardiac remodelling

Intrauterine growth restriction (IUGR) is an obstetric complication characterised by placental insufficiency and secondary cardiovascular remodelling that can lead to cardiomyopathy in adulthood. Despite its aetiology and potential therapeutics are poorly understood, bioenergetic deficits have been demonstrated in adverse foetal and cardiac development. We aimed to evaluate the role of mitochondria in human pregnancies with IUGR. In a single‐site, cross‐sectional and observational study, we included placenta and maternal peripheral and neonatal cord blood mononuclear cells (PBMC and CBMC) from 14 IUGR and 22 control pregnancies. The following mitochondrial measurements were assessed: enzymatic activities of mitochondrial respiratory chain (MRC) complexes I, II, IV, I + III and II + III, oxygen consumption (cell and complex I‐stimulated respiration), mitochondrial content (citrate synthase [CS] activity and mitochondrial DNA copy number), total ATP levels and lipid peroxidation. Sirtuin3 expression was evaluated as a potential regulator of bioenergetic imbalance. Intrauterine growth restriction placental tissue showed a significant decrease of MRC CI enzymatic activity (P < 0.05) and CI‐stimulated oxygen consumption (P < 0.05) accompanied by a significant increase of Sirtuin3/β‐actin protein levels (P < 0.05). Maternal PBMC and neonatal CBMC from IUGR patients presented a not significant decrease in oxygen consumption (cell and CI‐stimulated respiration) and MRC enzymatic activities (CII and CIV). Moreover, CS activity was significantly reduced in IUGR new‐borns (P < 0.05). Total ATP levels and lipid peroxidation were preserved in all the studied tissues. Altered mitochondrial function of IUGR is especially present at placental and neonatal level, conveying potential targets to modulate obstetric outcome through dietary interventions aimed to regulate Sirtuin3 function.

Placental mitochondria adapt developmentally and in response to hypoxia to support fetal growth

Mitochondria respond to a range of stimuli and function in energy production and redox homeostasis. However, little is known about the developmental and environmental control of mitochondria in the placenta, an organ vital for fetal growth and pregnancy maintenance in eutherian mammals. Using respirometry and molecular analyses, the present study examined mitochondrial function in the distinct transport and endocrine zones of the mouse placenta during normal pregnancy and maternal inhalation hypoxia. The data show that mitochondria of the two zones adopt different strategies in modulating their respiration, substrate use, biogenesis, density, and efficiency to best support the growth and energy demands of fetoplacental tissues during late gestation in both normal and hypoxic conditions. The findings have important implications for environmentally induced adaptations in mitochondrial function in other tissues and for compromised human pregnancy in which hypoxia and alterations in placental mitochondrial function are associated with poor outcomes like fetal growth restriction.

Metabolic Reprogramming of Trophoblast Cells in Response to Hypoxia

Hypoxia of trophoblast cells is an important regulator of normal development of the placenta. However, some pathological states associated with hypoxia, e.g. preeclampsia, impair the functions of placental cells. Oxyquinoline derivative inhibits HIF-prolyl hydroxylase by stabilizing HIF-1 transcription complex, thus modeling cell response to hypoxia. In human choriocarcinoma cells BeWo b30 (trophoblast model), oxyquinoline increased the expression of a core hypoxia response genes along with up-regulation of NOS3, PDK1, and BNIP3 genes and down-regulation of the PPARGC1B gene. These changes in the expression profile attest to activation of the metabolic cell reprogramming mechanisms aimed at reducing oxygen consumption by enabling the switch from aerobic to anaerobic glucose metabolism and the respective decrease in number of mitochondria. The possibility of practical use of the therapeutic properties of oxyquinoline derivatives is discussed.

Human placental glucose transport in fetoplacental growth and metabolism

While efficient glucose transport is essential for all cells, in the case of the human placenta, glucose transport requirements are two-fold; provision of glucose for the growing fetus in addition to the supply of glucose required the changing metabolic needs of the placenta itself. The rapidly evolving environment of placental cells over gestation has significant consequences for the development of glucose transport systems. The two-fold transport requirement of the placenta means also that changes in expression will have effects not only for the placenta but also for fetal growth and metabolism. This review will examine the localization, function and evolution of placental glucose transport systems as they are altered with fetal development and the transport and metabolic changes observed in pregnancy pathologies.

Physiological effects of high-altitude trekking on gonadal, thyroid hormones and macrophage migration inhibitory factor (MIF) responses in young lowlander women

Altitude hypoxia is often associated with impairment of human reproduction. In this study, hormones and macrophage migration inhibitory factor (MIF, a proinflammatory cytokine with key roles in human reproduction) were determined in seven regularly menstruating, lowlander native women living at sea level participating in 14 days of trekking at moderate and high altitude. Blood and saliva samples were collected from each subject at high altitude (5050 m a.s.l. [above sea level]), and at sea level before and after the expedition. Testosterone level was lowered by high altitude and was restored after the end of the expedition, while progesterone decreased significantly in all participants at the end of the expedition, although most of the participants were in the luteal phase. The salivary concentration of MIF decreased greatly at altitude, but its levels were completely restored after the return to sea level. Our findings showed high sensitivity and rapid changes in the determined parameters in response to the high‐altitude hypoxic environment, particularly MIF.

Serial Uterine Artery Embolization for the Treatment of Placenta Percreta in the First Trimester: A Case Report

Two patients with placenta percreta underwent uterine artery embolization (UAE) for abnormally invasive placenta (AIP) in the first trimester. Patient 1 had a 9-week cervical ectopic, while Patient 2 had a 9-week cesarean scar pregnancy. Elective termination of pregnancy was performed in both patients. UAE was performed with tris-acryl gelatin microspheres as well as gelfoam until stasis and was repeated in cases of revascularization. Both patients were followed with US/MRI/MRA scans and β-hCG levels. Revascularization occurred in both patients following UAE, requiring multiple embolizations to achieve complete placental involution. Serial bland UAE may be an effective technique in the treatment of first-trimester AIP, with the distinct advantage of maintaining a patient's fertility.

LEVEL OF EVIDENCE

Level IV.

Soluble Fms-Like Tyrosine Kinase-1 Alters Cellular Metabolism and Mitochondrial Bioenergetics in Preeclampsia

Preeclampsia is a maternal hypertensive disorder that affects up to 1 out of 12 pregnancies worldwide. It is characterized by proteinuria, endothelial dysfunction, and elevated levels of the soluble form of the vascular endothelial growth factor receptor-1 (VEGFR-1, known as sFlt-1). sFlt-1 effects are mediated in part by decreasing VEGF signaling. The direct effects of sFlt-1 on cellular metabolism and bioenergetics in preeclampsia, have not been established. The goal of this study was to evaluate whether sFlt-1 causes mitochondrial dysfunction leading to disruption of normal functioning in endothelial and placental cells in preeclampsia. Endothelial cells (ECs) and first-trimester trophoblast (HTR-8/SVneo) were treated with serum from preeclamptic women rich in sFlt-1 or with the recombinant protein. sFlt-1, dose-dependently inhibited ECs respiration and acidification rates indicating a metabolic phenotype switch enhancing glycolytic flux. HTR-8/SVneo displayed a strong basal glycolytic metabolism, remaining less sensitive to sFlt-1-induced mitochondrial impairment. Moreover, results obtained in ECs exposed to serum from preeclamptic subjects demonstrated that increased sFlt-1 leads to metabolic perturbations accountable for mitochondrial dysfunction observed in preeclampsia. sFlt-1 exacerbated mitochondrial reactive oxygen species (ROS) formation and mitochondrial membrane potential dissipation in ECs and trophoblasts exposed to serum from preeclamptic women. Forcing oxidative metabolism by culturing cells in galactose media, further sensitized cells to sFlt-1. This approach let us establish that sFlt-1 targets mitochondrial function in ECs. Effects of sFlt-1 on HTR-8/SVneo cells metabolism were amplified in galactose, demonstrating that sFlt-1 only target cells that rely mainly on oxidative metabolism. Together, our results establish the early metabolic perturbations induced by sFlt-1 and the resulting endothelial and mitochondrial dysfunction in preeclampsia.

Gestational differences in murine placenta: Glycolytic metabolism and pregnancy parameters

The placenta is a complex and essential organ composed largely of fetal-derived cells, including several different trophoblast subtypes that work in unison to support nutrient transport to the fetus during pregnancy. Abnormal placental development can lead to pregnancy-associated disorders that often involve metabolic dysfunction. The scope of dysregulated metabolism during placental development may not be fully representative of the in vivo state in defined culture systems, such as cell lines or isolated primary cells. Thus, assessing metabolic function in intact placental tissue would provide a better assessment of placental metabolism. In this study, we describe a methodology for assaying glycolytic function in structurally-intact mouse placental tissue, ex vivo, without culturing or tissue dissociation, that more closely resembles the in vivo state. Additionally, we present data highlighting sex-dependent differences of two mouse strains (C57BL/6 and ICR) in the pre-hypertrophic (E14.5) and hypertrophic (E18.5) placenta. These data establish a foundation for investigation of metabolism throughout gestation and provides a comprehensive assessment of glycolytic function during placental development.

In Vivo Quantification of Placental Insufficiency by BOLD MRI: A Human Study

Fetal health is critically dependent on placental function, especially placental transport of oxygen from mother to fetus. When fetal growth is compromised, placental insufficiency must be distinguished from modest genetic growth potential. If placental insufficiency is present, the physician must trade off the risk of prolonged fetal exposure to placental insufficiency against the risks of preterm delivery. Current ultrasound methods to evaluate the placenta are indirect and insensitive. We propose to use Blood-Oxygenation-Level-Dependent (BOLD) MRI with maternal hyperoxia to quantitatively assess mismatch in placental function in seven monozygotic twin pairs naturally matched for genetic growth potential. In-utero BOLD MRI time series were acquired at 29 to 34 weeks gestational age. Maps of oxygen Time-To-Plateau (TTP) were obtained in the placentas by voxel-wise fitting of the time series. Fetal brain and liver volumes were measured based on structural MR images. After delivery, birth weights were obtained and placental pathological evaluations were performed. Mean placental TTP negatively correlated with fetal liver and brain volumes at the time of MRI as well as with birth weights. Mean placental TTP positively correlated with placental pathology. This study demonstrates the potential of BOLD MRI with maternal hyperoxia to quantify regional placental function in vivo.

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.

Oxygen tension regulates the miRNA profile and bioactivity of exosomes released from extravillous trophoblast cells - Liquid biopsies for monitoring complications of pregnancy

Our understanding of how cells communicate has undergone a paradigm shift since the recent recognition of the role of exosomes in intercellular signaling. In this study, we investigated whether oxygen tension alters the exosome release and miRNA profile from extravillous trophoblast (EVT) cells, modifying their bioactivity on endothelial cells (EC). Furthermore, we have established the exosomal miRNA profile at early gestation in women who develop pre-eclampsia (PE) and spontaneous preterm birth (SPTB). HTR-8/SVneo cells were used as an EVT model. The effect of oxygen tension (i.e. 8% and 1% oxygen) on exosome release was quantified using nanocrystals (Qdot®) coupled to CD63 by fluorescence NTA. A real-time, live-cell imaging system (Incucyte™) was used to establish the effect of exosomes on EC. Plasma samples were obtained at early gestation (<18 weeks) and classified according to pregnancy outcomes. An Illumina TrueSeq Small RNA kit was used to construct a small RNA library from exosomal RNA obtained from EVT and plasma samples. The number of exosomes was significantly higher in EVT cultured under 1% compared to 8% oxygen. In total, 741 miRNA were identified in exosomes from EVT. Bioinformatic analysis revealed that these miRNA were associated with cell migration and cytokine production. Interestingly, exosomes isolated from EVT cultured at 8% oxygen increased EC migration, whilst exosomes cultured at 1% oxygen decreased EC migration. These changes were inversely proportional to TNF-α released from EC. Finally, we have identified a set of unique miRNAs in exosomes from EVT cultured at 1% oxygen and exosomes isolated from the circulation of mothers at early gestation, who later developed PE and SPTB. We suggest that aberrant exosomal signalling by placental cells is a common aetiological factor in pregnancy complications characterised by incomplete SpA remodeling and is therefore a clinically relevant biomarker of pregnancy complications.

AMPK Knockdown in Placental Labyrinthine Progenitor Cells Results in Restriction of Critical Energy Resources and Terminal Differentiation Failure

Placental abnormalities can cause Pregnancy-Associated Disorders, including preeclampsia, intrauterine growth restriction, and placental insufficiency, resulting in complications for both the mother and fetus. Trophoblast cells within the labyrinthine layer of the placenta facilitate the exchange of nutrients, gases, and waste between mother and fetus; therefore, the development of this cell layer is critical for fetal development. As trophoblast cells differentiate, it is assumed their metabolism changes with their energy requirements. We hypothesize that proper regulation of trophoblast metabolism is a key component of normal placental development; therefore, we examined the role of AMP-activated kinase (AMPK, PRKAA1/2), a sensor of cellular energy status. Our previous studies have shown that AMPK knockdown alters both trophoblast differentiation and nutrient transport. In this study, AMPKα1/2 shRNA was used to investigate the metabolic effects of AMPK knockdown on SM10 placental labyrinthine progenitor cells before and after differentiation. Extracellular flux analysis confirmed that AMPK knockdown was sufficient to reduce trophoblast glycolysis, mitochondrial respiration, and ATP coupling efficiency. A reduction in AMPK in differentiated trophoblasts also resulted in increased mitochondrial volume. These data indicate that a reduction in AMPK disrupts cellular metabolism in both progenitors and differentiated placental trophoblasts. This disruption correlates to abortive trophoblast differentiation that may contribute to the development of Pregnancy-Associated Disorders.

Cytotrophoblast, Not Syncytiotrophoblast, Dominates Glycolysis and Oxidative Phosphorylation in Human Term Placenta

The syncytiotrophoblast (SCT) at the maternal-fetal interface has been presumed to be the primary driver of placental metabolism, and the underlying progenitor cytotrophoblast cells (CTB) an insignificant contributor to placental metabolic activity. However, we now show that the metabolic rate of CTB is much greater than the SCT. The oxygen consumption and extracellular acidification rate, a measure of glycolysis, are both greater in CTB than in SCT in vitro (CTB: 96 ± 16 vs SCT: 46 ± 14 pmol O₂ × min⁻¹ × 100 ng DNA⁻¹, p < 0.001) and (CTB: 43 ± 6.7 vs SCT 1.4 ± 1.0 ∆mpH × min⁻¹ × 100 ng DNA⁻¹, p < 0.0001). Mitochondrial activity, as determined by using the mitochondrial activity-dependent dye Mitotracker CM-H₂TMRosa, is higher in CTB than in SCT in culture and living explants. These data cast doubt on the previous supposition that the metabolic rate of the placenta is dominated by the SCT contribution. Moreover, differentiation into SCT leads to metabolic suppression. The normal suppression of metabolic activity during CTB differentiation to SCT is prevented with a p38 MAPK signaling inhibitor and epidermal growth factor co-treatment. We conclude that the undifferentiated CTB, in contrast to the SCT, is highly metabolically active, has a high level of fuel flexibility, and contributes substantially to global metabolism in the late gestation human placenta.

Role of placental insufficiency and intrauterine growth restriction on the activation of fetal hepatic glucose production

Glucose is the major fuel for fetal oxidative metabolism. A positive maternal-fetal glucose gradient drives glucose across the placenta and is sufficient to meet the demands of the fetus, eliminating the need for endogenous hepatic glucose production (HGP). However, fetuses with intrauterine growth restriction (IUGR) from pregnancies complicated by placental insufficiency have an early activation of HGP. Furthermore, this activated HGP is resistant to suppression by insulin. Here, we present the data demonstrating the activation of HGP in animal models, mostly fetal sheep, and human pregnancies with IUGR. We also discuss potential mechanisms and pathways that may produce and support HGP and hepatic insulin resistance in IUGR fetuses.

Placental origins of adverse pregnancy outcomes: potential molecular targets: an Executive Workshop Summary of the Eunice Kennedy Shriver National Institute of Child Health and Human Development

Although much progress is being made in understanding the molecular pathways in the placenta that are involved in the pathophysiology of pregnancy-related disorders, a significant gap exists in the utilization of this information for the development of new drug therapies to improve pregnancy outcome. On March 5-6, 2015, the Eunice Kennedy Shriver National Institute of Child Health and Human Development of the National Institutes of Health sponsored a 2-day workshop titled Placental Origins of Adverse Pregnancy Outcomes: Potential Molecular Targets to begin to address this gap. Particular emphasis was given to the identification of important molecular pathways that could serve as drug targets and the advantages and disadvantages of targeting these particular pathways. This article is a summary of the proceedings of that workshop. A broad number of topics were covered that ranged from basic placental biology to clinical trials. This included research in the basic biology of placentation, such as trophoblast migration and spiral artery remodeling, and trophoblast sensing and response to infectious and noninfectious agents. Research findings in these areas will be critical for the formulation of the development of future treatments and the development of therapies for the prevention of a number of pregnancy disorders of placental origin that include preeclampsia, fetal growth restriction, and uterine inflammation. Research was also presented that summarized ongoing clinical efforts in the United States and in Europe that has tested novel interventions for preeclampsia and fetal growth restriction, including agents such as oral arginine supplementation, sildenafil, pravastatin, gene therapy with virally delivered vascular endothelial growth factor, and oxygen supplementation therapy. Strategies were also proposed to improve fetal growth by the enhancement of nutrient transport to the fetus by modulation of their placental transporters and the targeting of placental mitochondrial dysfunction and oxidative stress to improve placental health. The roles of microRNAs and placental-derived exosomes, as well as messenger RNAs, were also discussed in the context of their use for diagnostics and as drug targets. The workshop discussed the aspect of safety and pharmacokinetic profiles of potential existing and new therapeutics that will need to be determined, especially in the context of the unique pharmacokinetic properties of pregnancy and the hurdles and pitfalls of the translation of research findings into practice. The workshop also discussed novel methods of drug delivery and targeting during pregnancy with the use of macromolecular carriers, such as nanoparticles and biopolymers, to minimize placental drug transfer and hence fetal drug exposure. In closing, a major theme that developed from the workshop was that the scientific community must change their thinking of the pregnant woman and her fetus as a vulnerable patient population for which drug development should be avoided, but rather be thought of as a deprived population in need of more effective therapeutic interventions.

Human placental renin-angiotensin system in normotensive and pre-eclamptic pregnancies at high altitude and after acute hypoxia-reoxygenation insult

A functioning placental renin-angiotensin system (RAS) appears necessary for uncomplicated pregnancy and is present during placentation, which occurs under low oxygen tensions. Placental RAS is increased in pre-eclampsia (PE), characterised by placental dysfunction and elevated oxidative stress. We investigated the effect of high altitude hypoxia on the RAS and hypoxia-inducible factors (HIFs) by measuring mRNA and protein expression in term placentae from normotensive (NT) and PE women who delivered at sea level or above 3100 m, using an explant model of hypoxia-reoxygenation to assess the impact of acute oxidative stress on the RAS and HIFs. Protein levels of prorenin (P = 0.049), prorenin receptor (PRR; P = 0.0004), and angiotensin type 1 receptor (AT1R, P = 0.006) and type 2 receptor (AT2R, P = 0.002) were all significantly higher in placentae from NT women at altitude, despite mRNA expression being unaffected. However, mRNA expression of all RAS components was significantly lower in PE at altitude than at sea level, yet PRR, angiotensinogen (AGT) and AT1R proteins were all increased. The increase in transcript and protein expression of all the HIFs and NADPH oxidase 4 seen in PE compared to NT at sea level was blunted at high altitude. Experimentally induced oxidative stress stimulated AGT mRNA (P = 0.04) and protein (P = 0.025). AT1R (r = 0.77, P < 0.001) and AT2R (r = 0.81, P < 0.001) mRNA both significantly correlated with HIF-1β, whilst AT2R also correlated with HIF-1α (r = 0.512, P < 0.013). Our observations suggest that the placental RAS is responsive to changes in tissue oxygenation: this could be important in the interplay between reactive oxygen species as cell-signalling molecules for angiogenesis and hence placental development and function.

Placental phenotype and resource allocation to fetal growth are modified by the timing and degree of hypoxia during mouse pregnancy

Key points

Hypoxia is a major cause of fetal growth restriction, particularly at high altitude, although little is known about its effects on placental phenotype and resource allocation to fetal growth.

In the present study, maternal hypoxia induced morphological and functional changes in the mouse placenta, which depended on the timing and severity of hypoxia, as well as the degree of maternal hypophagia.

Hypoxia at 13% inspired oxygen induced beneficial changes in placental morphology, nutrient transport and metabolic signalling pathways associated with little or no change in fetal growth, irrespective of gestational age.

Hypoxia at 10% inspired oxygen adversely affected placental phenotype and resulted in severe fetal growth restriction, which was due partly to maternal hypophagia.

There is a threshold between 13% and 10% inspired oxygen, corresponding to altitudes of ∼3700 m and 5800 m, respectively, at which the mouse placenta no longer adapts to support fetal resource allocation. This has implications for high altitude human pregnancies.

Abstract

The placenta adapts its transport capacity to nutritional cues developmentally, although relatively little is known about placental transport phenotype in response to hypoxia, a major cause of fetal growth restriction. The present study determined the effects of both moderate hypoxia (13% inspired O₂) between days (D)11 and D16 or D14 and D19 of pregnancy and severe hypoxia (10% inspired O₂) from D14 to D19 on placental morphology, transport capacity and fetal growth on D16 and D19 (term∼D20.5), relative to normoxic mice in 21% O₂. Placental morphology adapted beneficially to 13% O₂; fetal capillary volume increased at both ages, exchange area increased at D16 and exchange barrier thickness reduced at D19. Exposure to 13% O₂ had no effect on placental nutrient transport on D16 but increased placental uptake and clearance of ³H‐methyl‐d‐glucose at D19. By contrast, 10% O₂ impaired fetal vascularity, increased barrier thickness and reduced placental ¹⁴C‐methylaminoisobutyric acid clearance at D19. Consequently, fetal growth was only marginally affected in 13% O₂ (unchanged at D16 and −5% at D19) but was severely restricted in 10% O₂ (−21% at D19). The hypoxia‐induced changes in placental phenotype were accompanied by altered placental insulin‐like growth factor (IGF)‐2 expression and insulin/IGF signalling, as well as by maternal hypophagia depending on the timing and severity of the hypoxia. Overall, the present study shows that the mouse placenta can integrate signals of oxygen and nutrient availability, possibly through the insulin‐IGF pathway, to adapt its phenotype and optimize maternal resource allocation to fetal growth during late pregnancy. It also suggests that there is a threshold between 13% and 10% inspired O₂ at which these adaptations no longer occur.

Hypoxia is a major cause of fetal growth restriction, particularly at high altitude, although little is known about its effects on placental phenotype and resource allocation to fetal growth.

In the present study, maternal hypoxia induced morphological and functional changes in the mouse placenta, which depended on the timing and severity of hypoxia, as well as the degree of maternal hypophagia.

Hypoxia at 13% inspired oxygen induced beneficial changes in placental morphology, nutrient transport and metabolic signalling pathways associated with little or no change in fetal growth, irrespective of gestational age.

Hypoxia at 10% inspired oxygen adversely affected placental phenotype and resulted in severe fetal growth restriction, which was due partly to maternal hypophagia.

There is a threshold between 13% and 10% inspired oxygen, corresponding to altitudes of ∼3700 m and 5800 m, respectively, at which the mouse placenta no longer adapts to support fetal resource allocation. This has implications for high altitude human pregnancies.

Placenta: the forgotten organ

The placenta sits at the interface between the maternal and fetal vascular beds where it mediates nutrient and waste exchange to enable in utero existence. Placental cells (trophoblasts) accomplish this via invading and remodeling the uterine vasculature. Amazingly, despite being of fetal origin, trophoblasts do not trigger a significant maternal immune response. Additionally, they maintain a highly reliable hemostasis in this extremely vascular interface. Decades of research into how the placenta differentiates itself from embryonic tissues to accomplish these and other feats have revealed a previously unappreciated level of complexity with respect to the placenta's cellular composition. Additionally, novel insights with respect to roles played by the placenta in guiding fetal development and metabolism have sparked a renewed interest in understanding the interrelationship between fetal and placental well-being. Here, we present an overview of emerging research in placental biology that highlights these themes and the importance of the placenta to fetal and adult health.

Intrauterine programming

In mammals, the intrauterine condition has an important role in the development of fetal physiological systems in later life. Suboptimal maternal environment can alter the regulatory pathways that determine the normal development of the fetus in utero, which in post-natal life may render the individual more susceptible to cardiovascular or metabolic adult-life diseases. Changes in the intrauterine availability of nutrients, oxygen and hormones can change the fetal tissue developmental regulatory planning, which occurs genomically and non-genomically and can cause permanent structural and functional changes in the systems, leading to diseases in early years of life and those that particularly become overt in adulthood. In this review we take a brief look at the main elements which program the fetal system development and consequently induce a crucial impact on the cardiovascular, nervous and hormonal systems in adulthood.

Endocannabinoid crosstalk between placenta and maternal fat in a baboon model (Papio spp.) of obesity

INTRODUCTION

Maternal obesity (MO) remains a serious obstetric problem with acute and chronic morbidities for both mothers and offspring. The mechanisms underlying these adverse consequences of MO remain unknown. Endocannabinoids (ECB) are neuromodulatory lipids released from adipocytes and other tissues. Metabolic crosstalk between placenta and adipocytes may mediate sequelae of MO. The goal of this study was to elucidate placental and systemic ECB in MO.

MATERIAL AND METHODS

Placentas, sera, and subcutaneous fat were collected at Cesarean sections performed near term (0.9 G) in four non-obese (nOB) and four obese (OB) baboons (Papio spp.). Concentrations of anandamide (AEA) and 2-arachidonoylglycerol (2-AG) were measured by liquid chromatography coupled to tandem mass spectrometry. AEA and 2-AG pathways were characterized in placentas by Q-RT-PCR, Western blot and immunohistochemistry.

RESULTS

Placental 2-AG levels were lower and maternal fat AEA levels were higher in OB (1254.1 ± 401.3 nmol/kg and 17.3 ± 4 nmol/kg) vs. nOB (3124.2 ± 557.3 nmol/kg and 3.1 ± 0.6 nmol/kg) animals. Concentrations of 2-AG correlated positively between maternal fat and placenta (r = 0.82, p = 0.013), but correlated negatively with maternal leptin concentrations (r = -0.72, p = 0.04 and r = -0.83, p = 0.01, respectively).

CONCLUSION

This is the first study to demonstrate differential ECB pathway regulation in maternal fat and placenta in MO. Differential regulation and function exist for AEA and 2-AG as the major ECB pathways in placenta.

Enhanced trimethylation of histone h3 mediates impaired expression of hepatic glucose 6-phosphatase expression in offspring from rat dams exposed to hypoxia during pregnancy

Given that hepatic glucose 6-phosphatase (G6Pase, involved in gluconeogenesis) has been demonstrated to be altered long term in animal models of intrauterine growth restriction (IUGR), we hypothesized that hypoxia in utero may regulate G6Pase expression via epigenetic mechanisms. To address this further, a rat model of maternal hypoxia leading to IUGR and impaired liver growth was utilized. In the 12-month-old male offspring of pregnant rat dams exposed to 11.5% atmospheric oxygen from gestational day (gd) 15 to gd 21, nonfasting glucose was lower in association with decreased hepatic G6Pase messenger RNA and protein levels. This was concomitant with enhanced methylation of histone H3 [K9] surrounding the promoter of G6Pase. Moreover, when McA-RH7777 hepatoma cells were exposed to various concentrations of oxygen for 48 hours, we observed an oxygen-dependent decrease in G6Pase expression associated with enhanced histone H3 [K9] methylation. Collectively, these results indicate that hypoxia directly and indirectly impairs G6Pase expression through enhanced methylation of histone H3 [K9].

Suppression of mitochondrial electron transport chain function in the hypoxic human placenta: a role for miRNA-210 and protein synthesis inhibition

Fetal growth is critically dependent on energy metabolism in the placenta, which drives active exchange of nutrients. Placental oxygen levels are therefore vital, and chronic hypoxia during pregnancy impairs fetal growth. Here we tested the hypothesis that placental hypoxia alters mitochondrial electron transport chain (ETS) function, and sought to identify underlying mechanisms. We cultured human placental cells under different oxygen concentrations. Mitochondrial respiration was measured, alongside levels of ETS complexes. Additionally, we studied placentas from sea-level and high-altitude pregnancies. After 4 d at 1% O₂ (1.01 KPa), complex I-supported respiration was 57% and 37% lower, in trophoblast-like JEG3 cells and fibroblasts, respectively, compared with controls cultured at 21% O₂ (21.24 KPa); complex IV-supported respiration was 22% and 30% lower. Correspondingly, complex I levels were 45% lower in placentas from high-altitude pregnancies than those from sea-level pregnancies. Expression of HIF-responsive microRNA-210 was increased in hypoxic fibroblasts and high-altitude placentas, whilst expression of its targets, iron-sulfur cluster scaffold (ISCU) and cytochrome c oxidase assembly protein (COX10), decreased. Moreover, protein synthesis inhibition, a feature of the high-altitude placenta, also suppressed ETS complex protein levels. Our results demonstrate that mitochondrial function is altered in hypoxic human placentas, with specific suppression of complexes I and IV compromising energy metabolism and potentially contributing to impaired fetal growth.

Environmental regulation of placental phenotype: implications for fetal growth

Environmental conditions during pregnancy determine birthweight, neonatal viability and adult phenotype in human and other animals. In part, these effects may be mediated by the placenta, the principal source of nutrients for fetal development. However, little is known about the environmental regulation of placental phenotype. Generally, placental weight is reduced during suboptimal conditions like maternal malnutrition or hypoxaemia but compensatory adaptations can occur in placental nutrient transport capacity to help maintain fetal growth. In vivo studies show that transplacental glucose and amino acid transfer adapt to the prevailing conditions induced by manipulating maternal calorie intake, dietary composition and hormone exposure. These adaptations are due to changes in placental morphology, metabolism and/or abundance of specific nutrient transporters. This review examines environmental programming of placental phenotype with particular emphasis on placental nutrient transport capacity and its implications for fetal growth, mainly in rodents. It also considers the systemic, cellular and molecular mechanisms involved in signalling environmental cues to the placenta. Ultimately, the ability of the placenta to balance the competing interests of mother and fetus in resource allocation may determine not only the success of pregnancy in producing viable neonates but also the long-term health of the offspring.

Developmental perturbation induced by maternal asthma during pregnancy: the short- and long-term impacts on offspring

Maternal asthma is a common disease to complicate human pregnancy. Epidemiological studies have identified that asthma during pregnancy increases the risk of a number of poor outcomes for the neonate including growth restriction, lower birthweight, preterm delivery, neonatal resuscitation, and stillbirth. Asthma therefore represents a significant health burden to society and could have an impact on the lifelong health of the children of women with asthma. Our research has identified that maternal asthma in pregnancy induces placental dysfunction and developmental perturbation in the fetus in a sex specific manner. These alterations in development could increase the risk of metabolic disease in adulthood of children of asthmatic mothers, especially females. In this paper, we will discuss the evidence currently available that supports the hypothesis that children of mothers with asthma may be at risk of lifelong health complications which include diabetes and hypertension.

Oxygen delivery and fetal-placental growth: beyond a question of supply and demand?

Towards the end of the first trimester, blood flow and oxygenation rise within the placenta, supporting an increased capacity for mitochondrial oxidative metabolism in both the placenta and developing fetus. In this regard, the placenta acts uniquely as both a conduit of oxygen to the fetal circulation and a significant consumer of oxygen in order to support its own energy demands for the processes of nutrient transport and protein synthesis for hormone production and growth. When the supply of oxygen becomes restricted, for example during chronic exposure to hypobaric hypoxia at high altitude, placental and fetal tissues respond in order to optimise the allocation of oxygen between competing demands. In this case, the placenta appears to remodel its metabolism to decrease oxygen consumption, probably by increasing ATP production via glycolysis. This process can maintain oxygen supply to the fetus but is still associated with growth restriction. Oxidative stress, a feature of pre-eclampsia, might elicit similar metabolic changes in the absence of hypoxia. This review considers what is known about the metabolic response of the placenta and fetal tissues to hypoxia and oxidative stress, and suggests possible mechanisms that might underlie such metabolic remodelling using lessons from other tissues and organ systems. Aspects of the hypoxia response that remain to be addressed are highlighted and future studies suggested. Much remains unknown about the coordinated metabolic response of the fetal-placental unit to chronic hypoxia and oxidative stress, but it would appear to be more than a simple question of supply and demand.

Evidence of endoplasmic reticulum stress and protein synthesis inhibition in the placenta of non-native women at high altitude

Pregnancy at high altitude is associated with a reduction in birth weight of ∼100 g/1000 m of ascent. The underlying mechanisms are unclear but may involve alteration in energy-demanding activities, such as protein synthesis. To test this hypothesis, both in vivo and in vitro approaches were used. Placental tissues from pregnant women residing at 3100 m were studied, and placental cells were incubated under hypoxia. In the 3100-m placentas, we observed dilation of endoplasmic reticulum (ER) cisternae, increased phosphorylation of eukaryotic initiation factor 2 subunit α (P-eIF2α), reduced AKT phosphorylation, and reduced P-4E-BP1 but increased 4E-BP1 protein compared to sea level controls. These findings suggest the presence of ER stress and protein synthesis inhibition. Hypoxia (1% O(2)) reduced proliferation of trophoblast-like JEG-3 cells, BeWo cells, and placental fibroblasts by ∼40, ∼60, and ∼18%, respectively. Sublethal dosage of salubrinal, an eIF2α phosphatase inhibitor, increased P-eIF2α and reduced BeWo cell and placental fibroblast proliferation by ∼50%. Administration of the PI-3K inhibitor LY294002 also reduced JEG-3 proliferation. Our results demonstrate that exposure to chronic hypobaric hypoxia causes mild placental ER stress, which, in turn, modulates protein synthesis and slows proliferation. These effects may account for the reduced placental villous volume, and contribute to the low birth weight that typifies high-altitude populations.

Review: The placenta and developmental programming: balancing fetal nutrient demands with maternal resource allocation

The placenta evolved to support development of the fetus, and so potentially plays a key role in the aetiology of developmental programming through its impact on nutrient transfer. Placental transport efficiency depends on a variety of parameters, including surface area for exchange, thickness of the interhaemal membrane and density of transporter proteins inserted into the trophoblast membranes. Here, we review recent studies that tested whether adaptations of placental efficiency are induced in the mouse placenta when maternal nutrient supply and fetal demand are manipulated experimentally. Naturally small placentas, and those exposed to maternal undernutrition, displayed structural changes indicative of accelerated maturation at E16, with enlargement of the labyrinth exchange zone at the expense of the endocrine junctional zone. These changes were associated with increased transport of a non-metabolisable amino acid analogue per gram of placenta, and expression of genes encoding specific System A transporters. Up-regulation of transporters was also observed when a mismatch between placental size and fetal demand was generated through genetic manipulation of the Igf2/H19 axis. Conversely, overgrowth of the placenta induced by deletion of H19 resulted in reduced transport capacity and expression of transporter genes. We conclude that under conditions when the maternal nutrient supply or placental size may be limiting for normal fetal growth, the placenta adapts so as to increase its transport capacity. Hence, it ameliorates the effects of environmental cues that would otherwise lead to more extensive developmental programming. The P0 transcript of Igf2 appears to be a strong candidate as a mediator of these adaptations in the mouse.