The expression and function of fatty acid transport protein-2 and -4 in the murine placenta

The role of candidate transport proteins in β-cell long-chain fatty acid uptake: Where are we now?

Type 2 diabetes (T2D) in humans is typically preceded by elevated levels of circulatory long-chain free fatty acids (LC-FFA). These excess LC-FFA are widely thought to be taken up by pancreatic β-cells, contributing to their dysfunction and death during the development of T2D; a process that has been termed lipotoxicity. Depending on their degree of saturation and carbon chain length, LC-FFA can exert different effects on pancreatic β-cells viability and function in vitro. Long-chain saturated fatty acids (LC-SFA) are thought to be toxic, whereas monounsaturated fatty acids are not and may even offer protection against the toxic effects of LC-SFAs. However, the mechanism of LC-FFA uptake into pancreatic β-cells is poorly understood, partly because it has been an understudied area of research. Determining how LC-FFA are taken up into β-cells is crucial for later formulation of therapies to prevent potential cellular overload of LC-FFA, thereby slowing the onset of T2D. In this work, we detail more than 40 years of literature investigating the role of membrane-associated transport proteins in LC-FFA uptake. By focussing on what is known in other cell types, we highlight where we can extrapolate our current understanding of protein-mediated transport to β-cells and uncover where further understanding is required.

Ectopic Lipid Accumulation Correlates with Cellular Stress in Rabbit Blastocysts from Diabetic Mothers

Maternal diabetes mellitus in early pregnancy leads to hyperlipidemia in reproductive tract organs and an altered embryonic environment. To investigate the consequences on embryonic metabolism, the effect of high environmental-lipid levels was studied in rabbit blastocysts cultured with a lipid mixture in vitro and in blastocysts from diabetic, hyperlipidemic rabbits in vivo. The gene and protein expression of marker molecules involved in lipid metabolism and stress response were analyzed. In diabetic rabbits, the expression of embryoblast genes encoding carnitine palmityl transferase 1 and peroxisome proliferator-activated receptors α and γ increased, whereas trophoblast genes encoding for proteins associated with fatty acid synthesis and β-oxidation decreased. Markers for endoplasmic (activating transcription factor 4) and oxidative stress (nuclear factor erythroid 2-related factor 2) were increased in embryoblasts, while markers for cellular redox status (superoxide dismutase 2) and stress (heat shock protein 70) were increased in trophoblasts from diabetic rabbits. The observed regulation pattern in vivo was consistent with an adaptation response to the hyperlipidemic environment, suggesting that maternal lipids have an impact on the intracellular metabolism of the preimplantation embryo in diabetic pregnancy and that embryoblasts are particularly vulnerable to metabolic stress.

The lipase cofactor CGI58 controls placental lipolysis

In eutherians, the placenta plays a critical role in the uptake, storage, and metabolism of lipids. These processes govern the availability of fatty acids to the developing fetus, where inadequate supply has been associated with substandard fetal growth. Whereas lipid droplets are essential for the storage of neutral lipids in the placenta and many other tissues, the processes that regulate placental lipid droplet lipolysis remain largely unknown. To assess the role of triglyceride lipases and their cofactors in determining placental lipid droplet and lipid accumulation, we assessed the role of patatin like phospholipase domain containing 2 (PNPLA2) and comparative gene identification-58 (CGI58) in lipid droplet dynamics in the human and mouse placenta. While both proteins are expressed in the placenta, the absence of CGI58, not PNPLA2, markedly increased placental lipid and lipid droplet accumulation. These changes were reversed upon restoration of CGI58 levels selectively in the CGI58-deficient mouse placenta. Using co-immunoprecipitation, we found that, in addition to PNPLA2, PNPLA9 interacts with CGI58. PNPLA9 was dispensable for lipolysis in the mouse placenta yet contributed to lipolysis in human placental trophoblasts. Our findings establish a crucial role for CGI58 in placental lipid droplet dynamics and, by extension, in nutrient supply to the developing fetus.

Transcriptomic analysis of lipid metabolism in zebrafish offspring of parental long-term exposure to bisphenol A

Bisphenol A (BPA) is one of the most common environmental endocrine disruptor chemicals (EDCs) and exhibits reproductive, cardiovascular, immune, and neurodevelopmental toxic effects. The development of the offspring was examined in the present investigation to determine the cross-generational effects of long-term exposure of parental zebrafish to environmental concentrations of BPA (15 and 225 µg/L). Parents were exposed to BPA for 120 days, and their offspring were evaluated at 7 days after fertilization in BPA-free water. The offspring exhibited higher mortality, deformity, and heart rates, and showed significant fat accumulation in abdominal region. RNA-Seq data showed that more lipid metabolism-related KEGG pathways, such as the PPAR signaling pathway, adipocytokine signaling pathway, and ether lipid metabolism pathway were enriched in the 225 µg/L BPA-treated offspring compared to 15 µg/L BPA-treated offspring, indicating greater effects of high dose BPA on offspring lipid metabolism. Lipid metabolism-related genes implied that BPA is responsible for disrupting lipid metabolic processes in the offspring through increased lipid production, abnormal transport, and disruption of lipid catabolism. The present study will be helpful for further evaluation of the reproductive toxicity of environmental BPA to organisms and the subsequent parent-mediated intergenerational toxicity.

Muscle Lipid Oxidation Is Not Affected by Obstructive Sleep Apnea in Diabetes and Healthy Subjects

The molecular mechanisms linking obstructive sleep apnea (OSA) with type 2 diabetes mellitus (T2DM) remain unclear. This study investigated the effect of OSA on skeletal muscle lipid oxidation in nondiabetic controls and in type 2 diabetes (T2DM) patients. Forty-four participants matched for age and adiposity were enrolled: nondiabetic controls (control, n = 14), nondiabetic patients with severe OSA (OSA, n = 9), T2DM patients with no OSA (T2DM, n = 10), and T2DM patients with severe OSA (T2DM + OSA, n = 11). A skeletal muscle biopsy was performed; gene and protein expressions were determined and lipid oxidation was analyzed. An intravenous glucose tolerance test was performed to investigate glucose homeostasis. No differences in lipid oxidation (178.2 ± 57.1, 161.7 ± 22.4, 169.3 ± 50.9, and 140.0 ± 24.1 pmol/min/mg for control, OSA, T2DM, and T2DM+OSA, respectively; p > 0.05) or gene and protein expressions were observed between the groups. The disposition index, acute insulin response to glucose, insulin resistance, plasma insulin, glucose, and HBA1C progressively worsened in the following order: control, OSA, T2DM, and T2DM + OSA (p for trend <0.05). No association was observed between the muscle lipid oxidation and the glucose metabolism variables. We conclude that severe OSA is not associated with reduced muscle lipid oxidation and that metabolic derangements in OSA are not mediated through impaired muscle lipid oxidation.

Fetal membranes exhibit similar nutrient transporter expression profiles to the placenta

INTRODUCTION

During pregnancy, the growth of the fetus is supported by the exchange of nutrients, waste, and other molecules between maternal and fetal circulations in the utero-placental unit. Nutrient transfer, in particular, is mediated by solute transporters such as solute carrier (SLC) and adenosine triphosphate-binding cassette (ABC) proteins. While nutrient transport has been extensively studied in the placenta, the role of human fetal membranes (FM), which was recently reported to have a role in drug transport, in nutrient uptake remains unknown.

OBJECTIVES

This study determined nutrient transport expression in human FM and FM cells and compared expression with placental tissues and BeWo cells.

METHODS

RNA sequencing (RNA-Seq) of placental and FM tissues and cells was done. Genes of major solute transporter groups, such as SLC and ABC, were identified. Proteomic analysis of cell lysates was performed via nano-liquid chromatography-tandem mass spectrometry (nanoLC-MS/MS) to confirm expression at a protein level.

RESULTS

We determined that FM tissues and cells derived from the fetal membrane tissues express nutrient transporter genes, and their expression is similar to that seen in the placenta or BeWo cells. In particular, transporters involved in macronutrient and micronutrient transfer were identified in both placental and FM cells. Consistent with RNA-Seq findings, carbohydrate transporters (3), vitamin transport-related proteins (8), amino acid transporters (21), fatty acid transport-related proteins (9), cholesterol transport-related proteins (6) and nucleoside transporters (3) were identified in BeWo and FM cells, with both groups sharing similar nutrient transporter expression.

CONCLUSION

This study determined the expression of nutrient transporters in human FMs. This knowledge is the first step in improving our understanding of nutrient uptake kinetics during pregnancy. Functional studies are required to determine the properties of nutrient transporters in human FMs.

Obesity phenotype induced by high-fat diet leads to maternal-fetal constraint, placental inefficiency, and fetal growth restriction in mice

The aim of this study was to investigate certain parameters regarding the maternal-fetal outcomes in a diet-induced obesity model. Obese, glucose-intolerant females who were exposed to a high-fat diet prior to pregnancy had lower placental efficiency and lower birth weight pups compared to the controls. Simple linear regression analyses showed that maternal obesity disrupts the proportionality between maternal and fetal outcomes during pregnancy. Maternal obesity is correlated with fetal outcomes, perhaps because of problems with hormonal signaling and exacerbation of inflammation in the maternal metabolic environment. The maternal obese phenotype altered the thickness of the placental layer, the transport of fatty acids, and the expression of growth factors. For example, lower expression of epidermal growth factor receptor (EGFR) mRNA in the obesity-prone group may have contributed to the rupture of the placental layers, leading to adverse fetal outcomes. Furthermore, maintenance of maternal glucose homeostasis and overexpression of placental growth factor (PGF) in the obesity-resistant group likely protected the placenta and fetuses from morphological and functional damage.

Assessing hypoxic damage to placental trophoblasts by measuring membrane viscosity of extracellular vesicles

INTRODUCTION

As highly sophisticated intercellular communication vehicles in biological systems, extracellular vesicles (EVs) have been investigated as both promising liquid biopsy-based disease biomarkers and drug delivery carriers. Despite tremendous progress in understanding their biological and physiological functions, mechanical characterization of these nanoscale entities remains challenging due to the limited availability of proper techniques. Especially, whether damage to parental cells can be reflected by the mechanical properties of their EVs remains unknown.

METHODS

In this study, we characterized membrane viscosities of different types of EVs collected from primary human trophoblasts (PHTs), including apoptotic bodies, microvesicles and small extracellular vesicles, using fluorescence lifetime imaging microscopy (FLIM). The biochemical origin of EV membrane viscosity was examined by analyzing their phospholipid composition, using mass spectrometry.

RESULTS

We found that different EV types derived from the same cell type exhibit different membrane viscosities. The measured membrane viscosity values are well supported by the lipidomic analysis of the phospholipid compositions. We further demonstrate that the membrane viscosity of microvesicles can faithfully reveal hypoxic injury of the human trophoblasts. More specifically, the membrane of PHT microvesicles released under hypoxic condition is less viscous than its counterpart under standard culture condition, which is supported by the reduction in the phosphatidylethanolamine-to-phosphatidylcholine ratio in PHT microvesicles.

DISCUSSION

Our study suggests that biophysical properties of released trophoblastic microvesicles can reflect cell health. Characterizing EV's membrane viscosity may pave the way for the development of new EV-based clinical applications.

Lipid signatures reflect the function of the murine primary placentation

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

Uteroplacental Insufficiency with Hypoxia Upregulates Placental PPARγ-KMT5A Axis in the Rat

The placenta represents a critical node in fetal lipid acquisition, yet the mechanisms by which the placenta handles lipids under normal and pathologic conditions are incompletely understood. A key player in placental lipid handling is peroxisome proliferator-activated receptor gamma (PPARγ). PPARγ influences global gene expression via its regulation of the epigenetic modifier lysine methyltransferase 5A (KMT5A), which places a methyl group on histone 4 lysine 20 (H4K20me) of target genes. Here we test the hypothesis that KMT5A is present in both the human and rat placentas and is affected by uteroplacental insufficiency (UPI) in the rat in association with increased placental lipid accumulation. We assessed levels and localization of KMT5A, as well as lipid droplet accumulation, in human placental tissue collected from maternal donors after delivery by planned cesarean section. Using a rat model of UPI, we also evaluated the effects of UPI on lipid accumulation, PPARγ, KMT5A, and H4K20me in the rat placenta. In this study, we show for the first time the presence and activity of KMT5A, in human and in rat placentas. We also demonstrate that in the rat placenta, UPI increases hypoxia, KMT5a expression, and activity in association with increased lipid accumulation in placenta supporting male fetuses. Placental PPARγ-KMT5A axis may be an important mediator of placental lipid handling.

FATP2-targeted therapies - A role beyond fatty liver disease

Fatty acid transport protein 2 (FATP2) is a multifunctional protein whose specific function is determined by the type of located cell, its intracellular location, or organelle-specific interactions. In the different diseases setting, a newfound appreciation for the biological function of FATP2 has come into view. Two main functions of FATP2 are to activate long-chain fatty acids (LCFAs) as a very long-chain acyl-coenzyme A (CoA) synthetase (ACSVL) and to transport LCFAs as a fatty acid transporter. FATP2 is not only involved in the occurrence of nonalcoholic fatty liver disease (NAFLD) and type 2 diabetes mellitus (T2DM), but also plays an important role in lithogenic diet-induced cholelithiasis, the formation of cancer tumor immunity, the progression of chronic kidney disease (CKD), and the regulation of zoledronate-induced nephrotoxicity. Herein, we review the updated information on the role of FATP2 in related diseases. In particular, we discuss the new functions of FATP2 and propose that FATP2 is a potential clinical biomarker and therapeutic target. In conclusion, regulatory strategies for FATP2 may bring new treatment options for cancer and lipid metabolism-related disorders.

Transgenic expression of human C19MC miRNAs impacts placental morphogenesis

INTRODUCTION

The chromosome 19 miRNA cluster (C19MC) encodes a large family of microRNAs (miRNAs) that are abundantly expressed in the placenta of higher primates and also in certain cancers. In the placenta, miRNAs from this cluster account for nearly 40% of all miRNAs present in trophoblasts. However, the function of these miRNAs in the placenta remains poorly understood. Recent observations reveal a role for these miRNAs in cell migration, and suggest that they are involved in the development and function of the human placenta. Here, we examine the placenta in transgenic mice expressing the human C19MC miRNAs.

METHODS

We produced transgenic mice using pronuclear microinjection of a bacterial artificial chromosome plasmid carrying the entire human C19MC locus and derived a homozygous line using crossbreeding. We performed morphological characterization and profiled gene expression changes in the placentas of the transgenic mice.

RESULTS

C19MC transgenic mice delivered on time with no gross malformations. The placentas of transgenic mice expressed C19MC miRNAs and were larger than wild type placentas. Histologically, we found that the transgenic placenta exhibited projections of spongiotrophoblasts that penetrated deep into the labyrinth. Gene expression analysis revealed alterations in the expression of several genes involved in cell migration, with evidence of enhanced cell proliferation.

DISCUSSION

Mice that were humanized for transgenically overexpressed C19MC miRNAs exhibit enlarged placentas with aberrant delineation of cell layers. The observed phenotype and the related gene expression changes suggest disrupted migration of placental cell subpopulations.

Physical Activity During Pregnancy Is Associated with Increased Placental FATP4 Protein Expression

Placental function is of utmost importance to ensure proper fetal development in utero. Among the placenta's many roles includes the passage of sufficient macronutrients, such as glucose, amino acids, and fatty acids, to the fetus. Macronutrients are carried from maternal circulation to the fetus across transporters within the placenta. The objective of this study was to examine the impact of (i) an acute bout of exercise and (ii) chronic exercise participation on placenta nutrient transporter expression and localization. To investigate the effect of acute exercise, pre- and post-exercise serum was collected from pregnant (n = 5) and non-pregnant (n = 5) women who underwent a moderate-intensity exercise session and used to treat BeWo cells. To assess chronic physical activity, we analyzed term placenta from women categorized as active (n = 10) versus non-active (n = 10). Protein expression and localization for the transporters GLUT1, SNAT1, and FATP4 were examined for both groups. GLUT1 expression in BeWo cells treated with serum from pregnant women was higher compared with that from non-pregnant, independent of exercise. FATP4 protein expression was elevated in the term placenta of active women. Immunohistochemistry analysis of term placenta illustrated increased staining of FATP4 in placental tissue from active women and differential staining pattern of GLUT1 depending on physical activity status. Chronic exercise during pregnancy increases the expression of placental FATP4 in vivo, suggesting greater metabolism and usage of fatty acids. Additionally, serum from pregnant women could contain factors that increase GLUT1 protein expression in vitro. BeWo cells treated with pre- and post-exercise serum from pregnant women resulted in greater GLUT1 expression compared with those treated with pre- and post-exercise serum from non-pregnant women. Physical activity appears to differentially impact key placental transporters involved in the transfer and availability of nutrients from mother to fetus. Future research ought to examine the mechanisms involved in regulating these changes and their impact on fetal growth and health.

Changes in Placental Nutrient Transporter Protein Expression and Activity Across Gestation in Normal and Obese Women

Fetal growth and development are dependent on placental nutrient transport. The syncytiotrophoblast (ST) and its two polarized plasma membranes, the maternal-facing microvillous membrane (MVM) and fetal-facing basal membrane (BM), represent the primary barrier in the human placenta, controlling transplacental transfer of small solutes. MVM and BM nutrient transporter expression and activity are increased in obese mothers delivering large babies. However, placental nutrient transporter expression and activity in early gestation in normal and obese women are largely unknown. Placentas from normal BMI and obese women at 6-24 weeks of gestation, and term placentas from normal BMI women, were collected and ST plasma membranes isolated. The activity and protein expression of amino acid, glucose, and fatty acid transporters was assessed. No significant differences were observed in placental nutrient transporter protein expression between normal BMI and obese women in early pregnancy. In the MVM, system A amino acid activity (p = 0.02), SNAT2 (p < 0.0001), SNAT4 (p < 0.001), and GLUT1 (p = 0.01) protein expression were higher at term compared with early gestation. In contrast, MVM system L activity (p = 0.001), FATP4 (p = 0.03), and FATP6 (p = 0.009) protein expression were lower at term compared with early pregnancy. In the BM, there was no change in system L activity across gestation; however, BM FATP6 (p = 0.002) protein expression was lower at term compared with early pregnancy. These results suggest that placental transport of amino acids, glucose, and fatty acids are subjected to coordinated regulation across gestation to meet a fetal nutrient demand that changes with advancing pregnancy.

Complex, coordinated and highly regulated changes in placental signaling and nutrient transport capacity in IUGR

The most common cause of intrauterine growth restriction (IUGR) in the developed world is placental insufficiency, a concept often used synonymously with reduced utero-placental and umbilical blood flows. However, placental insufficiency and IUGR are associated with complex, coordinated and highly regulated changes in placental signaling and nutrient transport including inhibition of insulin and mTOR signaling and down-regulation of specific amino acid transporters, Na+/K+-ATPase, the Na+/H+-exchanger, folate and lactate transporters. In contrast, placental glucose transport capacity is unaltered and Ca2+-ATPase activity and the expression of proteins involved in placental lipid transport are increased in IUGR. These findings are not entirely consistent with the traditional view that the placenta is dysfunctional in IUGR, but rather suggest that the placenta adapts to reduce fetal growth in response to an inability of the mother to allocate resources to the fetus. This new model has implications for the understanding of the mechanisms underpinning IUGR and for the development of intervention strategies.

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

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

The effect of high glucose on lipid metabolism in the human placenta

Diabetes mellitus (DM) during pregnancy can result in fetal overgrowth, likely due to placental dysfunction, which has health consequences for the infant. Here we test our prediction from previous work using a placental cell line that high glucose concentrations affect placental lipid metabolism. Placentas from women with type 1 (n = 13), type 2 (n = 6) or gestational (n = 12) DM, BMI-matched to mothers without DM (n = 18), were analysed for lipase and fatty acid transport proteins and fatty acid and triglyceride content. Explants from uncomplicated pregnancies (n = 6) cultured in physiological or high glucose were similarly analysed. High glucose levels did not alter placental lipase or transporter expression or the profile and abundance of fatty acids, but triglyceride levels were higher (p < 0.05), suggesting reduced β- oxidation. DM did not affect placental protein expression or fatty acid profile. Triglyceride levels of placentas from mothers with pre-existing DM were similar to controls, but higher in obese women with gestational DM. Maternal hyperglycemia may not affect placental fatty acid uptake and transport. However, placental β-oxidation is affected by high glucose and reduced in a subset of women with DM. Abnormal placental lipid metabolism could contribute to increased maternal-fetal lipid transfer and excess fetal growth in some DM pregnancies.

Downregulations of placental fatty acid transporters during cadmium-induced fetal growth restriction

Cadmium (Cd) is one of the environmental pollutants, which has multiple toxic effects on fetuses and placentas. Placental fatty acid (FA) uptake and transport are critical for the fetal and placental development. We aimed to analyze the triglyceride (TG) level, the expression patterns of several key genes involved in FA uptake and transport, and the molecular mechanisms for the altered gene expressions in placentas in response to Cd treatment. Our results showed that the placental TG level was significantly decreased in the Cd-exposed placentas. Fatty acid transporting protein 1 (FATP1), FATP6 and fatty acid binding protein 3 (FABP3) were significantly down-regulated in the placentas from Cd-exposed mice. The expression level of phospho-p38 MAPK was increased by Cd treatment, while the protein level of total p38 MAPK remained unchanged. The expression levels of peroxisome proliferator-activated receptor-γ (PPAR-γ) and the hypoxia-inducible factor-1α (HIF-1α) were significantly decreased in the Cd-exposed placentas. The methylation levels of the promoter regions of FATP1, FATP6 and FABP3 showed no significant differences between the treatment and control groups. In addition, the circulating non-esterified fatty acid (NEFA), total cholesterol (TC), and TG levels were not decreased in the maternal serum from the Cd-exposed mice. Therefore, our results suggest Cd exposure dose not reduce the maternal FA supply, but reduces the placental TG level. Cd treatment also downregulates the placental expressions of FATP1, FATP6 and FABP3, respectively associated with p38-MAPK, p38 MAPK/PPAR-γ and HIF-1α pathways.

PLIN2 Is Essential for Trophoblastic Lipid Droplet Accumulation and Cell Survival During Hypoxia

Trophoblast hypoxia and injury, key components of placental dysfunction, are associated with fetal growth restriction and other complications of pregnancy. Accumulation of lipid droplets has been found in hypoxic nonplacental cells. Unique to pregnancy, lipid accumulation in the placenta might perturb lipid transport to the fetus. We tested the hypothesis that hypoxia leads to accumulation of lipid droplets in human trophoblasts and that trophoblastic PLIN proteins play a key role in this process. We found that hypoxia promotes the accumulation of lipid droplets in primary human trophoblasts. A similar accretion of lipid droplets was found in placental villi in vivo from pregnancies complicated by fetal growth restriction. In both situations, these changes were associated with an increased level of cellular triglycerides. Exposure of trophoblasts to hypoxia led to reduced fatty acid efflux and oxidation with no change in fatty acid uptake or synthesis. We further found that hypoxia markedly stimulated PLIN2 mRNA synthesis and protein expression, which colocalized to lipid droplets. Knockdown of PLIN2, but not PLIN3, enhanced trophoblast apoptotic death, and overexpression of PLIN2 promoted cell viability. Collectively, our data indicate that hypoxia enhances trophoblastic lipid retention in the form of lipid droplets and that PLIN2 plays a key role in this process and in trophoblast defense against apoptotic death. These findings also imply that this protective mechanism may lead to diminished trafficking of lipids to the developing fetus.

Fatty acid transporting proteins: Roles in brain development, aging, and stroke

Polyunsaturated fatty acids are required for the brain development and significantly impact aging and stroke. Due to the hydrophobicity of fatty acids, fatty acids transportation related proteins that include fatty acid binding proteins (FABPs), long chain acyl-coA synthase (ACS), fatty acid transportation proteins (FATPs), fatty acid translocase (FAT/CD36) and newly reported major facilitator superfamily domain-containing protein (Mfsd2a) play critical roles in the uptake of various fatty acids, especially polyunsaturated fatty acids. They are not only involved in neurodevelopment, but also have great impact on neurological disease, such as aging related dementia and stroke.

The Effect of Hypoxia and Metformin on Fatty Acid Uptake, Storage, and Oxidation in L6 Differentiated Myotubes

Metabolic impairments associated with obstructive sleep apnea syndrome (OSA) are linked to tissue hypoxia, however, the explanatory molecular and endocrine mechanisms remain unknown. Using gas-permeable cultureware, we studied the chronic effects of mild and severe hypoxia on free fatty acid (FFA) uptake, storage, and oxidation in L6 myotubes under 20, 4, or 1% O₂. Additionally, the impact of metformin and the peroxisome proliferator-activated receptor (PPAR) β/δ agonist, called GW501516, were investigated. Exposure to mild and severe hypoxia reduced FFA uptake by 37 and 32%, respectively, while metformin treatment increased FFA uptake by 39% under mild hypoxia. GW501516 reduced FFA uptake under all conditions. Protein expressions of CD36 (cluster of differentiation 36) and SCL27A4 (solute carrier family 27 fatty acid transporter, member 4) were reduced by 17 and 23% under severe hypoxia. Gene expression of UCP2 (uncoupling protein 2) was reduced by severe hypoxia by 81%. Metformin increased CD36 protein levels by 28% under control conditions and SCL27A4 levels by 56% under mild hypoxia. Intracellular lipids were reduced by mild hypoxia by 18%, while in controls only, metformin administration further reduced intracellular lipids (20% O₂) by 36%. Finally, palmitate oxidation was reduced by severe hypoxia, while metformin treatment reduced non-mitochondrial O₂ consumption, palmitate oxidation, and proton leak at all O₂ levels. Hypoxia directly reduced FFA uptake and intracellular lipids uptake in myotubes, at least partially, due to the reduction in CD36 transporters. Metformin, but not GW501516, can increase FFA uptake and SCL27A4 expression under mild hypoxia. Described effects might contribute to elevated plasma FFA levels and metabolic derangements in OSA.

Transplacental Nutrient Transport Mechanisms of Intrauterine Growth Restriction in Rodent Models and Humans

Although the causes of intrauterine growth restriction (IUGR) have been intensively investigated, important information is still lacking about the role of the placenta as a link from adverse maternal environment to adverse pregnancy outcomes of IUGR and preterm birth. IUGR is associated with an increased risk of cardiovascular, metabolic, and neurological diseases later in life. Determination of the most important pathways that regulate transplacental transport systems is necessary for identifying marker genes as diagnostic tools and for developing drugs that target the molecular pathways. Besides oxygen, the main nutrients required for appropriate fetal development and growth are glucose, amino acids, and fatty acids. Dysfunction in transplacental transport is caused by impairments in both placental morphology and blood flow, as well as by factors such as alterations in the expression of insulin-like growth factors and changes in the mTOR signaling pathway leading to a change in nutrient transport. Animal models are important tools for systematically studying such complex events. Debate centers on whether the rodent placenta is an appropriate tool for investigating the alterations in the human placenta that result in IUGR. This review provides an overview of the alterations in expression and activity of nutrient transporters and alterations in signaling associated with IUGR and compares these findings in rodents and humans. In general, the data obtained by studies of the various types of rodent and human nutrient transporters are similar. However, direct comparison is complicated by the fact that the results of such studies are controversial even within the same species, making the interpretation of the results challenging. This difficulty could be due to the absence of guidelines of the experimental design and, especially in humans, the use of trophoblast cell culture studies instead of clinical trials. Nonetheless, developing new therapy concepts for IUGR will require the use of animal models for gathering robust data about mechanisms leading to IUGR and for testing the effectiveness and safety of the intervention among pregnant women.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Exercise rescues obese mothers' insulin sensitivity, placental hypoxia and male offspring insulin sensitivity

The prevalence of obesity during pregnancy continues to increase at alarming rates. This is concerning as in addition to immediate impacts on maternal wellbeing, obesity during pregnancy has detrimental effects on the long-term health of the offspring through non-genetic mechanisms. A major knowledge gap limiting our capacity to develop intervention strategies is the lack of understanding of the factors in the obese mother that mediate these epigenetic effects on the offspring. We used a mouse model of maternal-diet induced obesity to define predictive correlations between maternal factors and offspring insulin resistance. Maternal hyperinsulinemia (independent of maternal body weight and composition) strongly associated with offspring insulin resistance. To test causality, we implemented an exercise intervention that improved maternal insulin sensitivity without changing maternal body weight or composition. This maternal intervention prevented excess placental lipid deposition and hypoxia (independent of sex) and insulin resistance in male offspring. We conclude that hyperinsulinemia is a key programming factor and therefore an important interventional target during obese pregnancy, and propose moderate exercise as a promising strategy to improve metabolic outcome in both the obese mother and her offspring.

Role of Insulin in Placental Transport of Nutrients in Gestational Diabetes Mellitus

BACKGROUND

Gestational diabetes mellitus (GDM) is associated with increased fetal adiposity, which may increase the risk of obesity in adulthood. The placenta has insulin receptors and maternal insulin can activate its signaling pathways, affecting the transport of nutrients to the fetus. However, the effects of diet or insulin treatment on the placental pathophysiology of GDM are unknown.

SUMMARY

There are very few studies on possible defects in the insulin signaling pathway in the GDM placenta. Such defects could influence the placental transport of nutrients to the fetus. In this review we discuss the state of insulin signaling pathways in placentas of women with GDM, as well as the role of exogenous insulin in placental nutrient transport to the fetus, and fetal adiposity. Key Messages: Maternal insulin in the third trimester is correlated with fetal abdominal circumference at that time, suggesting the important role of insulin in this process. Since treatment with insulin at the end of pregnancy may activate placental nutrient transport to the fetus and promote placental fatty acid transfer, it would be interesting to improve maternal hyperlipidemia control in GDM subjects treated with this hormone. More research in this area with high number of subjects is necessary.

Isolation of human trophoblastic extracellular vesicles and characterization of their cargo and antiviral activity

INTRODUCTION

Primary human trophoblasts release a repertoire of extracellular vesicles (EVs). Among them are nano-sized exosomes, which we found to suppress the replication of a wide range of diverse viruses. These exosomes contain trophoblastic microRNAs (miRNAs) that are expressed from the chromosome 19 miRNA cluster and exhibit antiviral properties. Here, we report our investigation of the cargo of placental EVs, focusing on the composition and the antiviral properties of exosomes, microvesicles, and apoptotic blebs.

METHODS

We isolated EVs using ultracentrifugation and defined their purity using immunoblotting, electron microscopy, and nanoparticle tracking. We used liquid chromatography-electrospray ionization-mass spectrometry, protein mass spectrometry, and miRNA TaqMan card PCR to examine the phospholipids, proteins, and miRNA cargo of trophoblastic EVs and an in vitro viral infection assay to assess the antiviral properties of EVs.

RESULTS

We found that all three EV types contain a comparable repertoire of miRNA. Interestingly, trophoblastic exosomes harbor a protein and phospholipid profile that is distinct from that of microvesicles or apoptotic blebs. Functionally, trophoblastic exosomes exhibit the highest antiviral activity among the EVs. Consistently, plasma exosomes derived from pregnant women recapitulate the antiviral effect of trophoblastic exosomes derived from in vitro cultures of primary human trophoblasts.

DISCUSSION

When compared to other trophoblastic EVs, exosomes exhibit a unique repertoire of proteins and phospholipids, but not miRNAs, and a potent viral activity. Our work suggests that human trophoblastic EVs may play a key role in maternal-placental-fetal communication.

Maternal obesity modulates intracellular lipid turnover in the human term placenta

BACKGROUND

Obesity before pregnancy is associated with impaired metabolic status of the mother and the offspring later in life. These adverse effects have been attributed to epigenetic changes in utero, but little is known about the role of placental metabolism and its contribution to fetal development.

OBJECTIVES

We examined the impact of maternal pre-pregnancy obesity on the expression of genes involved in placental lipid metabolism in lean and obese women.

SUBJECTS/METHODS

Seventy-three lean and obese women with healthy pregnancy were recruited at term elective cesarean delivery. Metabolic parameters were measured on maternal venous blood samples. Expression of 88 genes involved in lipid metabolism was measured in whole placenta tissue. Proteins of genes differently expressed in response to maternal obesity were quantified, correlated with maternal parameters and immunolocalized in placenta sections. Isolated primary trophoblasts were used for in vitro assays.

RESULTS

Triglyceride (TG) content was increased in placental tissue of obese (1.10, CI 1.04-1.24 mg g^-1, P<0.05) vs lean (0.84, CI 0.72-1.02 mg g^-1) women. Among target genes examined, six showed positive correlation (P<0.05) with maternal pre-pregnancy BMI, namely ATGL (PNPLA2), FATP1 (SLC27A1), FATP3 (SLC27A3), PLIN2, PPARG and CGI-58 (ABHD5). CGI-58 protein abundance was twofold higher (P<0.001) in placentas of obese vs lean women. CGI-58 protein levels correlated positively with maternal insulin levels and pre-pregnancy body mass index (R=0.63, P<0.001 and R=0.64, P<0.001, respectively). CGI-58 and PLIN2 were primarily located in the syncytiotrophoblast and, were upregulated (1.38- and 500-fold, respectively) upon oleic acid and insulin treatment of cultured trophoblast cells.

CONCLUSION

Pre-gravid obesity significantly modifies the expression of placental genes related to transport and storage of neutral lipids. We propose that the upregulation of CGI-58, a master regulator of TG hydrolysis, contributes to the turnover of intracellular lipids in placenta of obese women, and is tightly regulated by metabolic factors of the mother.

The effect of gestational age on expression of genes involved in uptake, trafficking and synthesis of fatty acids in the rat placenta

Gestation triggers a tight coordination among maternal tissues to provide fatty acids (FA) to the fetus through placental transport; however, there is insufficient evidence regarding regulation of proteins involved in placental transport of FA according to gestational age. The aim of this study was to determine the role of gestational age on the expression of genes involved in FA uptake, trafficking and synthesis in the rat placenta to support fetal demands. Gene expression of encoding proteins for placental transport and synthesis of FA was measured in placenta. Also, FA composition was measured in placenta, fetuses and newborns. mRNA expression of lipoprotein lipase (lpl) and fatp-1 (for uptake) was 4.4- and 1.43-fold higher, respectively, during late gestation than at P14, but expression of p-fabp-pm decreased 0.37-fold at late pregnancy in comparison with P14. Only mRNA fabp-4 member for trafficking of FA was 2.95-fold higher at late gestation than at P14. mRNA of fasn and elovl-6 participating in saturated FA and enzymes for the polyunsaturated FA synthesis were downregulated during late gestation and their regulator srebf-1c increased at P16. This study suggests that gestational age has an effect on expression of some genes involved in uptake, trafficking and synthesis of FA in the rat placenta; mRNA expression of lpl and, fatp-1 for uptake and fabp-4 implicated in trafficking was expressed at high levels at late gestation. In addition, placenta expresses the mRNAs involved in FA synthesis; these genes were expressed at low levels at late gestation. Additionally, mRNAs of Srebf-1c transcriptional regulator of desaturases and elongases was highly expressed during late gestation. Finally, these changes in the rat placenta allowed the placenta to partially supply saturated and monounsaturated FA to the fetus.

Real-Time Tracking of BODIPY-C12 Long-Chain Fatty Acid in Human Term Placenta Reveals Unique Lipid Dynamics in Cytotrophoblast Cells

While the human placenta must provide selected long-chain fatty acids to support the developing fetal brain, little is known about the mechanisms underlying the transport process. We tracked the movement of the fluorescently labeled long-chain fatty acid analogue, BODIPY-C₁₂, across the cell layers of living explants of human term placenta. Although all layers took up the fatty acid, rapid esterification of long-chain fatty acids and incorporation into lipid droplets was exclusive to the inner layer cytotrophoblast cells rather than the expected outer syncytiotrophoblast layer. Cytotrophoblast is a progenitor cell layer previously relegated to a repair role. As isolated cytotrophoblasts differentiated into syncytialized cells in culture, they weakened their lipid processing capacity. Syncytializing cells suppress previously active genes that regulate fatty-acid uptake (SLC27A2/FATP2, FABP4, ACSL5) and lipid metabolism (GPAT3, LPCAT3). We speculate that cytotrophoblast performs a previously unrecognized role in regulating placental fatty acid uptake and metabolism.

Protein expression of fatty acid transporter 2 is polarized to the trophoblast basal plasma membrane and increased in placentas from overweight/obese women

BACKGROUND

Obese and overweight women are more likely to deliver a large infant or an infant with increased adiposity, however the underlying mechanisms are not well established. We tested the hypothesis that placental capacity to transport fatty acid is increased in overweight/obese women.

METHODS

Pregnant women with body mass index (BMI) ranging from 18.4 to 54.3 kg/m(2) and with uncomplicated term pregnancies were recruited for collection of blood samples and placental tissue. Maternal and fetal levels of non-esterified fatty acids (NEFAs) were measured in plasma. The expression and localization of CD36/fatty acid translocase (FAT), fatty acid transport protein (FATP)2, and FATP4 was determined in fixed placental tissue and in isolated syncytiotrophoblast plasma membranes from normal and high BMI mothers.

RESULTS

Maternal and fetal plasma NEFA levels did not correlate (n = 42). FATP2 and FATP4 expressions were higher in the basal plasma membrane (BPM) compared to the microvillous membrane (P < 0.001; n = 7) per unit membrane protein. BPM expression of FATP2 correlated with maternal BMI (P < 0.01; n = 30); there was no association between CD36/FAT or FATP4 expression and maternal BMI.

CONCLUSION

The polarization of FATPs to the BPM will facilitate fatty acid transfer across the placenta. In overweight/obese pregnancies, the increased FATP2 expression could contribute to increased fatty acid delivery to the fetus and while we have no direct data we speculate that this could lead accelerated fetal growth or increased fat deposition.

Investigation of the fatty acid transporter-encoding genes SLC27A3 and SLC27A4 in autism

The solute carrier 27A (SLC27A) gene family encodes fatty acid transport proteins (FATPs) and includes 6 members. During fetal and postnatal periods of development, the growing brain requires a reliable supply of fatty acids. Because autism spectrum disorders (ASD) are now recognized as disorders caused by impaired early brain development, it is possible that functional abnormalities of SLC27A genes may contribute to the pathogenesis of ASD. Here, we confirmed the expression of SLC27A3 and SLC27A4 in human neural stem cells derived from human induced pluripotent stem cells, which suggested their involvement in the developmental stage of the central nervous system. Additionally, we resequenced the SLC27A3 and SLC27A4 genes using 267 ASD patient and 1140 control samples and detected 47 (44 novel and 29 nonsynonymous) and 30 (17 novel and 14 nonsynonymous) variants for the SLC27A3 and SLC27A4, respectively, revealing that they are highly polymorphic with multiple rare variants. The SLC27A4 Ser209 allele was more frequently represented in ASD samples. Furthermore, we showed that a SLC27A4 Ser209 mutant resulted in significantly higher fluorescently-labeled fatty acid uptake into bEnd3 cells, a mouse brain capillary-derived endothelial cell line, compared with SLC27A4 Gly209, suggesting that the functional change may contribute to ASD pathophysiology.

Increased placental fatty acid transporter 6 and binding protein 3 expression and fetal liver lipid accumulation in a mouse model of obesity in pregnancy

Obesity in pregnancy is associated with increased fetal growth and adiposity, which, in part, is determined by transplacental nutrient supply. Trophoblast uptake and intracellular trafficking of lipids are dependent on placental fatty acid transport proteins (FATP), translocase (FAT/CD36), and fatty acid binding proteins (FABP). We hypothesized that maternal obesity in mice leads to increased placental expression of FAT/CD36, FATPs, and FABPs, and lipid accumulation in the fetal liver. C57/BL6J female mice were fed either a control (C; n = 10) or an obesogenic (OB; n = 10) high-fat, high-sugar diet before mating and throughout pregnancy. At E18.5, placentas and fetal livers were collected. Trophoblast plasma membranes (TPM) were isolated from placental homogenates. Expression of FAT/CD36 and FATP (TPM) and FABP (homogenates) was determined by immunoblotting. Gene expression was assessed by RT-quantitative PCR. Sections of fetal livers were stained for Oil Red O, and lipid droplets were quantified. TPM protein expression of FAT/CD36, FATP 2, and FATP 4 was comparable between C and OB groups. Conversely, TPM FATP 6 expression was increased by 35% in OB compared with C placentas without changes in mRNA expression. FABPs 1, 3-5 and PPARγ were expressed in homogenates, and FABP 3 expression increased 27% in OB compared with C placentas; however, no changes were observed in mRNA expression. Lipid droplet accumulation was 10-fold higher in the livers of fetuses from OB compared with C group. We propose that increased lipid transport capacity in obese mice promotes transplacental fatty acid transport and contributes to excess lipid accumulation in the fetal liver.

Fatty acid transport proteins in disease: New insights from invertebrate models

The dysregulation of lipid metabolism has been implicated in various diseases, including diabetes, cardiopathies, dermopathies, retinal and neurodegenerative diseases. Mouse models have provided insights into lipid metabolism. However, progress in the understanding of these pathologies is hampered by the multiplicity of essential cellular processes and genes that modulate lipid metabolism. Drosophila and Caenorhabditis elegans have emerged as simple genetic models to improve our understanding of these metabolic diseases. Recent studies have characterized fatty acid transport protein (fatp) mutants in Drosophila and C. elegans, establishing new models of cardiomyopathy, retinal degeneration, fat storage disease and dermopathies. These models have generated novel insights into the physiological role of the Fatp protein family in vivo in multicellular organisms, and are likely to contribute substantially to progress in understanding the etiology of various metabolic disorders. Here, we describe and discuss the mechanisms underlying invertebrate fatp mutant models in the light of the current knowledge relating to FATPs and lipid disorders in vertebrates.

The expression and post-transcriptional regulation of FSTL1 transcripts in placental trophoblasts

INTRODUCTION

Follistatin-like-1 (FSTL1) is a widely expressed secreted protein with diverse but poorly understood functions. Originally described as a pro-inflammatory molecule, it has recently been reported to play a role in signaling pathways that regulate development and homeostasis. Distinctively, FSTL1 harbors within its 3'-UTR the sequence encoding microRNA-198 (miR-198), shown to be inversely regulated relative to FSTL1 expression and to exhibit opposite actions on cellular processes such as cell migration. We sought to investigate the expression of FSTL1 and to assess its interplay with miR-198 in human trophoblasts.

METHODS

We used a combination of northern blot analyses, quantitative PCR, small RNA sequencing, western blot and immunohistochemistry to characterize FSTL1 and miR-198 expression in placental trophoblasts. We also used reporter assays to examine the post-transcriptional regulation of FSTL1 and assess its putative regulation by miR-198.

RESULTS

We detected the expression of FSTL1 transcript in both the human extravillous trophoblast line HTR-8/SVneo and in primary term human villous trophoblasts. We also found that the expression of FSTL1 was largely restricted to extravillous trophoblasts. Hypoxia enhanced the expression of FSTL1 protein in cultured primary villous trophoblasts. Interestingly, we did not detect any evidence for expression or function of mature miR-198 in human trophoblasts.

DISCUSSION

Our data indicate that placental FSTL1 is expressed particularly in extravillous trophoblasts. We also found no evidence for placental expression of miR-198, or for its regulation of FSTL1, implying that the post-transcriptional regulation of FSTL1 by miR-198 is tissue specific.

Regulation of fatty acid binding proteins by hypoxia inducible factors 1α and 2α in the placenta: relevance to pre-eclampsia

Pre-eclampsia is characterized by placental hypoxia and dyslipidemia. Arachidonic and docosahexanoic acids are essential maternal nutrients for fetal development. They are transported via placental trophoblast cells by membrane and cytosolic fatty acid binding proteins. Others report the expressions of these proteins which are increased in hypoxic trophoblasts. Using bioinformatics, BeWo cells, reporter assays, quantitative real-time PCR and immunoblotting we tested the hypothesis that hypoxia inducible factors 1α (HIF-1α) and/or 2α (HIF-2α) regulate the expressions of FABP1, FABP3, FABP4 and FATP2 proteins. Three hypoxia responsive elements (HRE) were identified in FABP1 which cumulatively responded strongly to HIF-1α and weakly to HIF-2α. FABP3 expression partially responded to HIF-1α. Two putative HRE were validated in FABP4 both of which responded weakly to HIF-1α and HIF-2α. FATP2 protein expression reacted positively to hypoxia. Thus, fetal essential fatty acid supply via the placenta is protected under hypoxia. It will be interesting to determine if our findings are replicated in human pre-eclamptic placenta.

Placental adaptations in growth restriction

The placenta is the primary interface between the fetus and mother and plays an important role in maintaining fetal development and growth by facilitating the transfer of substrates and participating in modulating the maternal immune response to prevent immunological rejection of the conceptus. The major substrates required for fetal growth include oxygen, glucose, amino acids and fatty acids, and their transport processes depend on morphological characteristics of the placenta, such as placental size, morphology, blood flow and vascularity. Other factors including insulin-like growth factors, apoptosis, autophagy and glucocorticoid exposure also affect placental growth and substrate transport capacity. Intrauterine growth restriction (IUGR) is often a consequence of insufficiency, and is associated with a high incidence of perinatal morbidity and mortality, as well as increased risk of cardiovascular and metabolic diseases in later life. Several different experimental methods have been used to induce placental insufficiency and IUGR in animal models and a range of factors that regulate placental growth and substrate transport capacity have been demonstrated. While no model system completely recapitulates human IUGR, these animal models allow us to carefully dissect cellular and molecular mechanisms to improve our understanding and facilitate development of therapeutic interventions.

The influence of ligand-activated LXR on primary human trophoblasts

INTRODUCTION

The Liver X Receptors (LXRs) are critical transcriptional regulators of cellular metabolism that promote cholesterol efflux and lipogenesis in response to excess intracellular cholesterol. In contrast, the Sterol Response Element Binding Protein-2 (SREBP2) promotes the synthesis and uptake of cholesterol. Oxysterols are products of cholesterol oxidation that accumulate in conditions associated with increased cellular levels of reactive oxygen species, such as hypoxia and oxidative stress, activating LXR and inhibiting SREBP2. While hypoxia and oxidative stress are commonly implicated in placental injury, the impact of the transcriptional regulation of cholesterol homeostasis on placental function is not well characterized.

METHODS

We measured the effects of the synthetic LXR ligand T0901317 and the endogenous oxysterol 25-hydroxycholesterol (25OHC) on differentiation, cytotoxicity, progesterone synthesis, lipid droplet formation, and gene expression in primary human trophoblasts.

RESULTS

Exposure to T0901317 promoted lipid droplet formation and inhibited differentiation, while 25OHC induced trophoblast toxicity, promoted hCG and progesterone release at lower concentrations with inhibition at higher concentrations, and had no effect on lipid droplet formation. The discrepant effect of these ligands was associated with distinct changes in expression of LXR and SREBP2 target genes, with upregulation of ABCA1 following 25OHC and T090317 exposure, exclusive activation of the lipogenic LXR targets SREBP1c, ACC1 and FAS by T0901317, and exclusive inhibition of the SREBP2 targets LDLR and HMGCR by 25OHC.

CONCLUSION

These findings implicate cholesterol oxidation as a determinant of trophoblast function and activity, and suggest that placental gene targets and functional pathways are selectively regulated by specific LXR ligands.

Sub-chronically exposing mice to a polycyclic aromatic hydrocarbon increases lipid accumulation in their livers

The potential for exposing humans and wildlife to environmental polycyclic aromatic hydrocarbons (PAHs) has increased. Risk assessments describing how PAHs disturb lipid metabolism and induce hepatotoxicity have only received limited attention. In the present study, seven-week-old male ICR mice received intraperitoneal injections of 0, 0.01, 0.1 or 1mg/kg body weight 3-methylcholanthrene (3MC) per week for 10 weeks. A high-fat diet was provided during the exposure. Histopathological lipid accumulation and lipid metabolism-related genes were measured. We observed that sub-chronic 3MC exposure significantly increased lipid droplet and triacylglycerol (TG) levels in the livers. A low dose of 3MC activated the aryl hydrocarbon receptor, which negatively regulated lipid synthesis in the livers. The primary genes including acetyl-CoA carboxylase (Acc), fatty acid synthase (Fas) and stearoyl-CoA desaturase 1 (Scd1) decreased significantly when compared with those in the control group, indicating that de novo fatty acid synthesis in the hepatocytes was significantly inhibited by the sub-chronic 3MC exposure. However, the free fatty acid (FFA) synthesis in the adipose tissue was greatly enhanced by up-regulating the expression of peroxisome proliferator-activated receptor γ (PPARγ) and sterol regulatory element binding protein-1c (SREBP1C) and target genes including Acc, Fas and Scd1. The synthesized FFA was released into the blood and then transported into the liver by the up-regulation of Fat and Fatp2, which resulted in the gradual accumulation of lipids in the liver. In conclusion, histological examinations and molecular level analyses highlighted the development of lipid accumulation and confirmed that 3MC significantly impaired lipid metabolism in mice.

Fatty acid binding protein-4 is expressed in the mouse placental labyrinth, yet is dispensable for placental triglyceride accumulation and fetal growth

INTRODUCTION

Fatty Acid Binding Protein-4 (FABP4) is a member of a family of FABP proteins that regulate intracellular lipid trafficking in diverse tissues. We recently showed that FABP4 regulates triglyceride accumulation in primary human trophoblasts. To assess the function of placental FABP4 in vivo, we tested the hypothesis that FABP4 is expressed in the murine placenta, and regulates placenta triglyceride accumulation.

METHODS

C57Bl/6 wild type or Fabp4-null mice were time-bred, and fetuses and placentas harvested at different time points during pregnancy. Placental FABP4 expression was assessed at different gestational ages, using quantitative PCR, immunohistochemistry, immunofluorescence and western immunoblotting. FABPs expression was examined by RT-qPCR. Placental lipids were extracted using the Folch method and triglyceride levels determined using a colorimetric quantification kit.

RESULTS

Using immunohistochemistry, we found that FABP4 was expressed in the placental labyrinthine layer, predominantly in endothelial cells in association with CD31 positive fetal capillaries. The level of placental FABP4 mRNA and protein increased from E12.5 to E16.5 and slightly decreased at E18.5. Breeding of Fabp4 heterozygous mice resulted in embryonic genotypes that followed a Mendelian distribution and exhibited normal weight and morphology, triglyceride content, and expression of other FABP family members. Exposure to hypoxia (O2 = 12%) between E12.5-E18.5 did not uncover a difference between wild type and Fabp4-null mice.

CONCLUSIONS

FABP4 is expressed in the mouse placental labyrinth, with highest expression at E16.5. FABP4 is dispensable for feto-placental growth and placental lipid accumulation.

Potential first trimester metabolomic biomarkers of abnormal birth weight in healthy pregnancies

OBJECTIVE

Macrosomia and low birth weight (LBW) can be associated with pregnancy complications and may affect the long-term health of the child. The aim of this study was to evaluate the metabolomic serum profiles of healthy pregnant women to identify early biomarkers of macrosomia and LBW and to understand mechanisms leading to abnormal fetal growth not related to mother's body mass index or presence of gestational diabetes.

METHOD

Serum samples from 770 women were collected between the 12th and 14th gestational week. Delivery samples were divided into three groups according to the infant birth weight as follows: low, <2500 g; normal, 2500-4000 g; and high >4000 g. Samples from women with any complications of pregnancy were excluded. Serum fingerprinting was performed by LC-QTOF-MS.

RESULTS

Lower levels of phospholipids, lysophospholipids, and monoacylglycerols; low vitamin D3 metabolites; and increased bilirubin level were associated with macrosomia. Because most changes involved lipids, as a concept of validation, adipocyte fatty acid-binding protein (A-FABP) levels were measured and found correlated with the studied lipids and birth weight.

CONCLUSION

Serum fingerprinting in early pregnancy can predict the risk of macrosomia. Serum levels of A-FABP and several lipids are promising prognostic markers for macrosomia in healthy pregnancies.

Acyl-CoA metabolism and partitioning

Long-chain fatty acyl-coenzyme As (CoAs) are critical regulatory molecules and metabolic intermediates. The initial step in their synthesis is the activation of fatty acids by one of 13 long-chain acyl-CoA synthetase isoforms. These isoforms are regulated independently and have different tissue expression patterns and subcellular locations. Their acyl-CoA products regulate metabolic enzymes and signaling pathways, become oxidized to provide cellular energy, and are incorporated into acylated proteins and complex lipids such as triacylglycerol, phospholipids, and cholesterol esters. Their differing metabolic fates are determined by a network of proteins that channel the acyl-CoAs toward or away from specific metabolic pathways and serve as the basis for partitioning. This review evaluates the evidence for acyl-CoA partitioning by reviewing experimental data on proteins that are believed to contribute to acyl-CoA channeling, the metabolic consequences of loss of these proteins, and the potential role of maladaptive acyl-CoA partitioning in the pathogenesis of metabolic disease and carcinogenesis.

Maternal diabetes leads to unphysiological high lipid accumulation in rabbit preimplantation embryos

According to the "developmental origin of health and disease" hypothesis, the metabolic set points of glucose and lipid metabolism are determined prenatally. In the case of a diabetic pregnancy, the embryo is exposed to higher glucose and lipid concentrations as early as during preimplantation development. We used the rabbit to study the effect of maternal diabetes type 1 on lipid accumulation and expression of lipogenic markers in preimplantation blastocysts. Accompanied by elevated triglyceride and glucose levels in the maternal blood, embryos from diabetic rabbits showed a massive intracellular lipid accumulation and increased expression of fatty acid transporter 4, fatty acid-binding protein 4, perilipin/adipophilin, and maturation of sterol-regulated element binding protein. However, expression of fatty acid synthase, a key enzyme for de novo synthesis of fatty acids, was not altered in vivo. During a short time in vitro culture of rabbit blastocysts, the accumulation of lipid droplets and expression of lipogenic markers were directly correlated with increasing glucose concentration, indicating that hyperglycemia leads to increased lipogenesis in the preimplantation embryo. Our study shows the decisive effect of glucose as the determining factor for fatty acid metabolism and intracellular lipid accumulation in preimplantation embryos.

NDRG1 deficiency attenuates fetal growth and the intrauterine response to hypoxic injury

Intrauterine mammalian development depends on the preservation of placental function. The expression of the protein N-myc downstream-regulated gene 1 (NDRG1) is increased in placentas of human pregnancies affected by fetal growth restriction and in hypoxic primary human trophoblasts, where NDRG1 attenuates cell injury. We sought to assess the function of placental NDRG1 in vivo and tested the hypothesis that NDRG1 deficiency in the mouse embryo impairs placental function and consequently intrauterine growth. We found that Ndrg1 knock-out embryos were growth restricted in comparison to wild-type or heterozygous counterparts. Furthermore, hypoxia reduced the survival of female, but not male, knock-out embryos. Ndrg1 deletion caused significant alterations in placental gene expression, with a marked reduction in transcription of several lipoproteins in the placental labyrinth. These transcriptional changes were associated with reduced fetal:maternal serum cholesterol ratio exclusively in hypoxic female embryos. Collectively, our findings indicate that NDRG1 promotes fetal growth and regulates the metabolic response to intrauterine hypoxic injury in a sexually dichotomous manner.

Chronic exposure of mice to environmental endocrine-disrupting chemicals disturbs their energy metabolism

We evaluated the effects of a 20-week chronic exposure of mice to a low dose of cypermethrin (CYP), atrazine (ATZ) and 17α-ethynyestradiol (EE2) on energy metabolism. Here, male mice were exposed to 50 μg/kg BW/day CYP, 100 μg/kg BW/day ATZ or 1 μg/kg BW/day EE2 supplied in their drinking water for 20 weeks. During the exposure, mice were fed a high energy diet (HD). The bodyweights were not significantly affected by chronic exposure to EDCs, while the serum-free fatty acids (FFA) levels, hepatic lipid accumulation and triacylglycerol (TG) contents increased significantly in the ATZ- and CYP-HD groups. To determine the mechanism involved, we determined the expression levels of the genes in the glucose and fat metabolism pathways in the liver and adipose tissue. The results showed that chronic exposure to ATZ and CYP increased the mRNA levels of a number of key genes involved in both the de novo FFA synthesis pathway and the transport of FFA from blood. The increased amount of FFA was partially consumed as energy through β-oxidation in the mitochondria. Some of the FFA was used to synthesize TG in the liver by up-regulating primary genes, which resulted in increased TG levels and lipid accumulation. The results indicate that chronic exposure to EDCs has the potential to cause energy metabolic dysregulation and hepatotoxicity in mice.

The expression and localization of N-myc downstream-regulated gene 1 in human trophoblasts

The protein N-Myc downstream-regulated gene 1 (NDRG1) is implicated in the regulation of cell proliferation, differentiation, and cellular stress response. NDRG1 is expressed in primary human trophoblasts, where it promotes cell viability and resistance to hypoxic injury. The mechanism of action of NDRG1 remains unknown. To gain further insight into the intracellular action of NDRG1, we analyzed the expression pattern and cellular localization of endogenous NDRG1 and transfected Myc-tagged NDRG1 in human trophoblasts exposed to diverse injuries. In standard conditions, NDRG1 was diffusely expressed in the cytoplasm at a low level. Hypoxia or the hypoxia mimetic cobalt chloride, but not serum deprivation, ultraviolet (UV) light, or ionizing radiation, induced the expression of NDRG1 in human trophoblasts and the redistribution of NDRG1 into the nucleus and cytoplasmic membranes associated with the endoplasmic reticulum (ER) and microtubules. Mutation of the phosphopantetheine attachment site (PPAS) within NDRG1 abrogated this pattern of redistribution. Our results shed new light on the impact of cell injury on NDRG1 expression patterns, and suggest that the PPAS domain plays a key role in NDRG1’s subcellular distribution.

SLC27 fatty acid transport proteins

The uptake and metabolism of long chain fatty acids (LCFA) are critical to many physiological and cellular processes. Aberrant accumulation or depletion of LCFA underlie the pathology of numerous metabolic diseases. Protein-mediated transport of LCFA has been proposed as the major mode of LCFA uptake and activation. Several proteins have been identified to be involved in LCFA uptake. This review focuses on the SLC27 family of fatty acid transport proteins, also known as FATPs, with an emphasis on the gain- and loss-of-function animal models that elucidate the functions of FATPs in vivo and how these transport proteins play a role in physiological and pathological situations.

Placental oleic acid uptake is lower in male offspring of obese women

INTRODUCTION

The fetus is dependent on the placenta for its supply of long chain polyunsaturated fatty acids (LCPUFA), which are essential in fetal growth and development. Previous work suggests that high maternal body mass index (BMI) inhibits fetal LCPUFA delivery and males have greater fatty acid requirements than females during development. We hypothesized that male placental fatty acid uptake would be more sensitive to maternal BMI compared to females.

METHODS

Term placental samples were collected from healthy women receiving Cesarean section (n = 38). Placental fatty acid transporter and binding protein gene expression and uptake of oleic acid (OA), arachidonic acid, (AA) and docosahexanoic acid (DHA) were measured. Two-way ANOVA was used to assess the effects of fetal sex and maternal overweight/obesity (BMI >26 kg/m2).

RESULTS

Placental fatty acid uptake of OA was 43% lower in male offspring and 73% higher in female offspring of obese compared to normal BMI women (P < 0.05). The interaction between fetal sex and maternal BMI had a significant effect on both OA (P = 0.002) and AA uptake (P = 0.01). DHA uptake was not affected by fetal sex or maternal obesity. Placental fatty acid transporter CD36 and binding protein FABP5 gene expression levels were lower in male offspring of obese mothers but were not affected by BMI among females.

CONCLUSION

Maternal obesity and fetal sex significantly affect the placental uptake of oleate and arachidonate. Placental fatty acid uptake in both male and female fetuses is sensitive to maternal BMI, but males may have inadequate acquisition of the unsaturated fatty acid OA, when exposed to maternal obesity.

Regulation of nutrient transport across the placenta

Abnormal fetal growth, both growth restriction and overgrowth, is associated with perinatal complications and an increased risk of metabolic and cardiovascular disease later in life. Fetal growth is dependent on nutrient availability, which in turn is related to the capacity of the placenta to transport these nutrients. The activity of a range of nutrient transporters has been reported to be decreased in placentas of growth restricted fetuses, whereas at least some studies indicate that placental nutrient transport is upregulated in fetal overgrowth. These findings suggest that changes in placental nutrient transport may directly contribute to the development of abnormal fetal growth. Detailed information on the mechanisms by which placental nutrient transporters are regulated will therefore help us to better understand how important pregnancy complications develop and may provide a foundation for designing novel intervention strategies. In this paper we will focus on recent studies of regulatory mechanisms that modulate placental transport of amino acids, fatty acids, and glucose.