Placental Amino Acid Transport Research Articles

Trophoblast-specific overexpression of adiponectin receptor 2 causes fetal growth restriction in pregnant mice.

Maternal obesity in pregnancy is strongly associated with complications such as fetal overgrowth and infants of obese mothers have an increased risk to develop obesity, diabetes, and cardiovascular disease later in life. However, the underlying mechanisms are not well established. Circulating levels of adiponectin are low in obese pregnant women and maternal circulating adiponectin is negatively associated with birth weight. We have reported that normalizing maternal adiponectin in obese pregnant mice prevents placental dysfunction, fetal overgrowth, and programming of offspring cardio-metabolic disease. However, the mechanistic link between maternal adiponectin, placental function, and fetal growth remains to be established. We hypothesized that trophoblast-specific overexpression of the adiponectin receptor 2 (Adipor2) in healthy pregnant mice inhibits placental mTORC1 signaling and nutrient transport, resulting in fetal growth restriction. Using lentiviral transduction of blastocysts with a mammalian gene expression lentiviral vector for up-regulation of Adipor2 (Adipor2-OX), we achieved a ~ 3-fold increase in placenta Adipor2 mRNA levels and a 2-fold increase of the ADIPOR2 protein in the trophoblast plasma membrane. Placenta-specific Adipor2-OX increased placental peroxisome proliferator-activated receptor-α phosphorylation, ceramide synthase expression and ceramide concentrations. Furthermore, Adipor2-OX inhibited placental mTORC1 signaling and reduced invivo placental transport of glucose and amino acids. Lastly, Adipor2-OX reduced fetal weight by 11%. These data provide mechanistic evidence that placental Adipor2 signaling directly affects fetal growth. We propose that low circulating adiponectin in maternal obesity causes fetal overgrowth and programs the offspring for cardio-metabolic disease mediated by a direct effect on placental function.

Trophoblast-specific overexpression of the LAT1 increases transplacental transport of essential amino acids and fetal growth in mice.

Placental System L amino acid transporter activity is decreased in pregnancies complicated by intrauterine growth restriction (IUGR) and increased in fetal overgrowth. However, it is unknown if changes in the expression/activity of placental Large Neutral Amino Acid Transporter Small Subunit 1 (Slc7a5/LAT1) are mechanistically linked to placental function and fetal growth. We hypothesized that trophoblast-specific Slc7a5 overexpression increases placental transport of essential amino acids, activates the placental mechanistic target of rapamycin (mTOR) signaling, and promotes fetal growth in mice. Using lentiviral transduction of blastocysts with a Slc7a5 transgene, we achieved trophoblast-specific overexpression of Slc7a5 (Slc7a5 OX) with increased fetal (+27%) and placental weights (+10%). Trophoblast-specific Slc7a5 overexpression increased trophoblast plasma membrane (TPM) LAT1 protein abundance and TPM System L transporter (+53%) and System A transporter activity (+ 21%). Slc7a5 overexpression also increased transplacental transport of leucine (+ 85%) but not of the System A tracer, 14C-methylamino isobutyric acid, in vivo. Trophoblast-specific overexpression of Slc7a5 activated placental mTORC1, as assessed by increased (+44%) phosphorylation of S6 ribosomal protein (Ser 235/236), and mTORC2 as indicated by phosphorylation of PKCα-Tyr-657 (+47%) and Akt-Ser 473 (+96%). This is the first demonstration that placental transport of essential amino acids is mechanistically linked to fetal growth. The decreased placental System L activity in human IUGR and the increased placental activity of this transporter in some cases of fetal overgrowth may directly contribute to the development of these pregnancy complications.

Fetal growth delay caused by loss of non-canonical imprinting is resolved late in pregnancy and culminates in offspring overgrowth.

Germline epigenetic programming, including genomic imprinting, substantially influences offspring development. Polycomb Repressive Complex 2 (PRC2) plays an important role in Histone 3 Lysine 27 trimethylation (H3K27me3)-dependent imprinting, loss of which leads to growth and developmental changes in mouse offspring. In this study, we show that offspring from mouse oocytes lacking the PRC2 protein Embryonic Ectoderm Development (EED) were initially developmentally delayed, characterised by low blastocyst cell counts and substantial growth delay in mid-gestation embryos. This initial developmental delay was resolved as offspring underwent accelerated fetal development and growth in late gestation resulting in offspring that were similar stage and weight to controls at birth. The accelerated development and growth in offspring from Eed-null oocytes was associated with remodelling of the placenta, which involved an increase in fetal and maternal tissue size, conspicuous expansion of the glycogen-enriched cell population, and delayed parturition. Despite placental remodelling and accelerated offspring fetal growth and development, placental efficiency, and fetal blood glucose levels were low, and the fetal blood metabolome was unchanged. Moreover, while expression of the H3K27me3-imprinted gene and amino acid transporter Slc38a4 was increased, fetal blood levels of individual amino acids were similar to controls, indicating that placental amino acid transport was not enhanced. Genome-wide analyses identified extensive transcriptional dysregulation and DNA methylation changes in affected placentas, including a range of imprinted and non-imprinted genes. Together, while deletion of Eed in growing oocytes resulted in fetal growth and developmental delay and placental hyperplasia, our data indicate a remarkable capacity for offspring fetal growth to be normalised despite inefficient placental function and the loss of H3K27me3-dependent genomic imprinting.

Regulation of placental amino acid transport in health and disease.

Abnormal fetal growth, i.e., intrauterine growth restriction (IUGR) or fetal growth restriction (FGR) and fetal overgrowth, is associated with increased perinatal morbidity and mortality and is strongly linked to the development of metabolic and cardiovascular disease in childhood and later in life. Emerging evidence suggests that changes in placental amino acid transport may contribute to abnormal fetal growth. This review is focused on amino acid transport in the human placenta, however, relevant animal models will be discussed to add mechanistic insights. At least 25 distinct amino acid transporters with different characteristics and substrate preferences have been identified in the human placenta. Of these, System A, transporting neutral nonessential amino acids, and System L, mediating the transport of essential amino acids, have been studied in some detail. Importantly, decreased placental Systems A and L transporter activity is strongly associated with IUGR and increased placental activity of these two amino acid transporters has been linked to fetal overgrowth in human pregnancy. An array of factors in the maternal circulation, including insulin, IGF-1, and adiponectin, and placental signaling pathways such as mTOR, have been identified as key regulators of placental Systems A and L. Studies using trophoblast-specific gene targeting in mice have provided compelling evidence that changes in placental Systems A and L are mechanistically linked to altered fetal growth. It is possible that targeting specific placental amino acid transporters or their upstream regulators represents a novel intervention to alleviate the short- and long-term consequences of abnormal fetal growth in the future.

Identification and verification of feature biomarkers associated with immune cells in recurrent pregnancy loss.

The aim of this study was to investigate the causes, diagnostic markers, and treatment methods for recurrent pregnancy loss (RPL) using bioinformatics approaches. Bioinformatics methods were utilized to analyze gene expression databases to identify key genes and modules associated with RPL. Weighted gene co-expression network analysis (WGCNA) was employed to identify gene sets related to maternal-fetal immunity. Gene set variation analysis (GSVA) and protein-protein interaction networks were used to explore signaling pathways and molecular interactions in RPL. Immune cell infiltration was assessed using single-sample gene set enrichment analysis (ssGSEA). Thirteen genes were identified as potential diagnostic markers, some of which were involved in placental amino acid transport, glucose absorption, and reactive oxygen species production. Several gene sets related to protein transport, steroid synthesis, and glycosaminoglycan degradation were found to be associated with RPL. Immune cell infiltration analysis found that CD56bright NK cells and monocytes showed significantly increased infiltration in RPL and were associated with key hub genes. The validation of hub genes, including PCSK5, CCND2, SLC5A3, RASAL1, MYZAP, MFAP4, and P2RY14, as potential diagnostic markers, showed promising value. This study contributes to a better understanding of the etiology of RPL and potential diagnostic markers. The identified immune-related gene sets, signaling pathways, and immune cell infiltrations provide valuable insights for future research and therapeutic advancements in RPL.

Oleic acid stimulation of amino acid uptake in primary human trophoblast cells is mediated by phosphatidic acid and mTOR signaling.

Normal fetal development is critically dependent on optimal nutrient supply by the placenta, and placental amino acid transport has been demonstrated to be positively associated with fetal growth. Mechanistic target of rapamycin (mTOR) is a positive regulator of placental amino acid transporters, such as System A. Oleic acid (OA) has been previously shown to have a stimulatory role on placental mTOR signaling and System A amino acid uptake in primary human trophoblast (PHT) cells. We investigated the mechanistic link between OA and System A activity in PHT. We found that inhibition of mTOR complex 1 or 2, using small interfering RNA to knock down raptor or rictor, prevented OA-stimulated System A amino acid transport indicating the interaction of OA with mTOR. Phosphatidic acid (PA) is a key intermediary for phospholipid biosynthesis and a known regulator of the mTOR pathway; however, phospholipid biosynthetic pathways have not been extensively studied in placenta. We identified placental isoforms of acyl transferase enzymes involved in de novo phospholipid synthesis. Silencing of 1-acylglycerol-3-phosphate-O-acyltransferase-4, an enzyme in this pathway, prevented OA mediated stimulation of mTOR and System A amino acid transport. These data indicate that OA stimulates mTOR and amino acid transport in PHT cells mediated through de novo synthesis of PA. We speculate that fatty acids in the maternal circulation, such as OA, regulate placental functions critical for fetal growth by interaction with mTOR and that late pregnancy hyperlipidemia may be critical for increasing nutrient transfer to the fetus.

CHOP upregulation and dysregulation of the mature form of the SNAT2 amino acid transporter in the placentas from small for gestational age newborns.

The placentas from newborns that are small for gestational age (SGA; birth weight < -2 SD for gestational age) may display multiple pathological characteristics. A key determinant of fetal growth and, therefore, birth weight is placental amino acid transport, which is under the control of the serine/threonine kinase mechanistic target of rapamycin (mTOR). The effects of endoplasmic reticulum (ER) stress on the mTOR pathway and the levels of amino acid transporters are not well established. Placentas from SGA and appropriate for gestational age (AGA) newborns and the human placental BeWo cell line exposed to the ER stressor tunicamycin were used. We detected a significant increase in the levels of C/EBP homologous protein (CHOP) in the placentas from SGA newborns compared with those from AGA newborns, while the levels of other ER stress markers were barely affected. In addition, placental mTOR Complex 1 (mTORC1) activity and the levels of the mature form of the amino acid transporter sodium-coupled neutral amino acid transporter 2 (SNAT2) were also reduced in the SGA group. Interestingly, CHOP has been reported to upregulate growth arrest and DNA damage-inducible protein 34 (GADD34), which in turn suppresses mTORC1 activity. The GADD34 inhibitor guanabenz attenuated the increase in CHOP protein levels and the reduction in mTORC1 activity caused by the ER stressor tunicamycin in the human placental cell line BeWo, but it did not recover mature SNAT2 protein levels, which might be reduced as a result of defective glycosylation. Collectively, these data reveal that GADD34A activity and glycosylation are key factors controlling mTORC1 signaling and mature SNAT2 levels in trophoblasts, respectively, and might contribute to the SGA condition. Video Abstract.

Dietary rumen-protected L-arginine or N-carbamylglutamate enhances placental amino acid transport and suppresses angiogenesis and steroid anabolism in underfed pregnant ewes

This study aimed to investigate the effects of dietary supplementation of underfed Hu ewes from d 35 to 110 of gestation with either rumen-protected L-arginine (RP-Arg) or N-carbamylglutamate (NCG) on placental amino acid (AA) transport, angiogenic gene expression, and steroid anabolism. On d 35 of gestation, 32 Hu ewes carrying twin fetuses were randomly divided into four treatment groups, each consisting of eight ewes, and were fed the following diets: A diet providing 100% of NRC's nutrient requirements for pregnant ewes (CON); A diet providing 50% of NRC's nutrient requirements for pregnant ewes (RES); RES diet plus 5 g/d NCG (RES + NCG); or RES diet plus 20 g/d RP-Arg (RES + ARG). On the d 110 of pregnancy, blood samples were taken from the mother, and samples were collected from type A cotyledons (COT; the fetal portions of the placenta). The levels of 17β-estradiol and progesterone in the maternal serum and both the capillary area density (CAD) and capillary surface density (CSD) in type A COT were decreased in response to Arg or NCG supplementation when compared to the RES group. The concentrations of arginine, leucine, putrescine and spermidine in type A COT were higher (P < 0.05) in the RES + ARG or RES + NCG group than in the RES group. The mRNA expression levels of inducible nitric oxide synthase (iNOS) and solute carrier family 15, member 1 (SLC15A1) were increased (P < 0.05) while those of progesterone receptor (PGR) and fibroblast growth factor 2 (FGF2) were decreased in type A COT by supplementation with either NCG or RP-Arg compared to the RES group. The results suggest that providing underfed pregnant ewes from d 35 to 110 of gestation with a diet supplemented with NCG or RP-Arg improves placental AA transport, and reduces the expression of angiogenic growth factor genes and steroid anabolism, leading to better fetal development.

Insulin like growth factor 1 (IGF-1) and IGF binding proteins in obese pregnant women and their babies: Potential effects on placental function and fetal growth

Introduction: The placenta expresses significant amounts of insulin and IGF1 receptors at distinct locations on both fetal and maternal surfaces. This makes the IGF1 and the insulin receptor accessible to fetal and/or maternal insulin, IGF1 and IGF2. IGFs are involved in the receptor-mediated regulation of placental growth and transport, and placental angiogenesis. Maternal obesity during gestation mediates significant changes in the metabolism of mothers, placentas as well as fetal growth. Objectives: In obese women. the role of the insulin like growth factor system IGFs, IGF receptors, IGF-binding proteins (IGFBPs) and IGFBP proteases during gestation, and their effect on placental growth and fetal anthropometric changes need further clarification. In this update we reviewed the literature on the detected changes in the maternal and fetal IGFs in relation to placental growth and function and to fetal growth and newborn size in pregnant obese mothers. Eighteen research articles fitted the criteria of this update. Results: Twenty-three research papers were including 2817 pregnant obese and non-obese women (controls) and their babies were selected and reviewed. Results showed that obesity and excessive nutrient intake during gestation increase maternal IGF1and decreases IGBP1. Increased maternal IGF1 and/or its availability due to decreased IGFBP1 can increase the size (weight) and development of the placenta, stimulate mTOR signaling which stimulates protein synthesis, mitochondrial function, and upregulate specific placental amino acid transporter isoforms (amino acids transport), GLUT-1, (glucose transport) and possibly lipid transport to the fetus which can induce fetal IGF1 secretion and lead to overgrowth. Conclusions: In obese women during pregnancy, increased level of IGF1 and/or its availability due to decreased IGFBP1 can increase the size (weight) and development of the placenta, stimulate mTOR signaling which stimulates protein synthesis, mitochondrial function, and upregulate placental transport of amino acids, glucose and possibly fatty acids.

Maternal, placental, and fetal Insulin-Like Growth Factor-I (IGF-1) and IGF Binding proteins (IGFBPs) in Diabetic pregnancies: Effects on fetal growth and birth size.

Introduction: During gestation, IGF1 secretion and availability in the maternal blood and at the maternal-fetal interface is mainly regulated by IGF-binding proteins (IGFBP) such as IGFBP-1 synthesized by the decidua. Data about the interaction between maternal, placental, and fetal IGF1/IGFBP in relation to fetal growth and newborn size during diabetic pregnancy (gestational Diabetes (GDM) and Type 1 DM (T1DM) is not clear. Aim of the study and Methods: We reviewed the research papers published in Pubmed, Google scholar, Research gate, and Scopus in the past 20 years on the relationship between maternal, placental, and fetal/infantile/ IGF1/IGFBP-1 in relation to birth size in pregnancies associated with maternal diabetes. Results: Twenty-eight research papers were selected and reviewed (patients’ number = 1902). In GDM pregnancies, higher maternal IGF1 levels and/or its availability due to lower IGFBP1 levels can increase the size (weight) and functions of the placenta. These include the upregulation of specific placental amino acid transporter isoforms and GLUT-1, stimulation of mTOR signaling which stimulates protein synthesis, increasing mitochondrial functions, and accelerating nutrient transport which significantly contributes to fetal growth and newborn birth size. On the other hand, in pregnant women with T1DM, lower maternal IGF1 is associated with subsequent underweight placenta and lower birthweight.

Assisted reproductive technology causes reduced expression of amino acid transporters in human full-term placentas.

In the mouse model, manipulations of assisted reproductive technology (ART) can lead to enlarged placentas and influence the expression of amino acid transporters in placentas during mid-to late-gestation. However, it is uncertain whether those abnormal changes presented in ART mouse placentas also occur in human ART placentas. We choose the placenta tissue of pregnant woman by ART in term birth (ART group) and by natural pregnancy in term birth (control group) to compare the birth weight of the baby, placental weight and ratio of the fetal/placental weight of these two groups. We then detect the mRNA and protein expression of placental amino acid transporter genes (SNAT1, SNAT2, SNAT4, LAT1 and LAT2) in these two groups by real-time quantitative PCR, Western blot and immunofluorescence staining. Additionally, the PI3K-AKT-mTOR signaling activity was also analyzed. There were no statistical differences in new birth weight between the ART group and the control group. Compared with the control group, the placenta weight of baby was significantly higher in ART group and ratio of the fetal/placental weight was significantly lower in ART group. We found that the mRNA and protein expression of A system of amino acid transporter SNAT1, SNAT2 and SNAT4 in placenta were significantly down-regulated in ART group compared with placentas from natural pregnancies. Additionally, there were no statistical differences of the mRNA and protein expression of L system of amino acid transporter LAT1 between these two groups, but amino acid transporter LAT2 in placenta was significantly down-regulated in ART group. Furthermore, the PI3K-AKT-mTOR signaling activity was inhibited in ART group. ART leads to the expressions of amino acid transporter genes SNAT1, SNAT2, SNAT4 and LAT2 significantly down-regulated in placenta accompanied by the PI3K-AKT-mTOR signaling inhibition, which suggests that ART may affect the function of placenta amino acid transporter during the late pregnancy, leading to enlarged placentas and probably low birth weight.

COVID-19 Vaccines and the Virus: Impact on Drug Metabolism and Pharmacokinetics.

This article reports on an American Society of Pharmacology and Therapeutics, Division of Drug Metabolism and Disposition symposium held at Experimental Biology on April 2, 2022, in Philadelphia. As of July 2022, over 500 million people have been infected with SARS-CoV-2 (the virus causing COVID-19) and over 12 billion vaccine doses have been administered. Clinically significant interactions between viral infections and hepatic drug metabolism were first recognized over 40 years ago during a cluster of pediatric theophylline toxicity cases attributed to reduced hepatic drug metabolism amid an influenza B outbreak. Today, a substantive body of research supports that the activated innate immune response generally decreases hepatic cytochrome P450 activity. The interactions extend to drug transporters and other organs and have the potential to impact drug absorption, distribution, metabolism, and excretion (ADME). Based on this knowledge, altered ADME is predicted with SARS-CoV-2 infection or vaccination. The report begins with a clinical case exploring the possibility of SARS-CoV-2 vaccination increasing clozapine levels. This is followed by discussions of how SARS-CoV-2 infection or vaccines alter the metabolism and disposition of complex drugs, such as nanoparticles and biologics and small molecule therapies. The review concludes with a discussion of the effects of viral infections on placental amino acid transport and their potential to impact fetal development. The session improved our understanding of the impact of emerging viral infections and vaccine technologies on drug metabolism and disposition, which will help mitigate drug toxicity and improve drug and vaccine safety and effectiveness. SIGNIFICANCE STATEMENT: Altered pharmacokinetics of small molecule and complex molecule drugs and fetal brain distribution of amino acids following SARS-CoV-2 infection or immunization are possible. The proposed mechanisms involve decreased liver cytochrome P450 metabolism of small molecules, enhanced innate immune system metabolism of complex molecules, and altered placental and fetal blood-brain barrier amino acid transport, respectively. Future research is needed to understand the effects of these interactions on adverse drug responses, drug and vaccine safety, and effectiveness and fetal neurodevelopment.

Maternal immune activation in rats induces dysfunction of placental leucine transport and alters fetal brain growth.

Maternal infection during pregnancy increases the offspring risk of developing a variety of neurodevelopmental disorders (NDDs), including schizophrenia. While the mechanisms remain unclear, dysregulation of placental function is implicated.We hypothesised that maternal infection, leading to maternal immune activation and stimulated cytokine production, alters placental and yolk sac amino acid transport, affecting fetal brain development and thus NDD risk. Using a rat model of maternal immune activation induced by the viral mimetic polyinosinic:polycytidylic acid (poly(I:C)), we investigated placental and yolk sac expression of system L amino acid transporter subtypes which transport several essential amino acids including branched-chain amino acids (BCAA), maternal and fetal BCAA concentration, placental 14C-leucine transport activity and associated impacts on fetal growth and development.Poly(I:C) treatment increased acutely maternal IL-6 and TNFα concentration, contrasting with IL-1β. Transcriptional responses for these pro-inflammatory cytokines were found in placenta and yolk sac following poly(I:C) treatment. Placental and yolk sac weights were reduced by poly(I:C) treatment, yet fetal body weight was unaffected, while fetal brain weight was increased. Maternal plasma BCAA concentration was reduced 24 h post-poly(I:C) treatment, yet placental, but not yolk sac, BCAA concentration was increased. Placental and yolk sac gene expression of Slc7a5, Slc7a8 and Slc43a2 encoding LAT1, LAT2 and LAT4 transporter subtypes, respectively, was altered by poly(I:C) treatment. Placental 14C-leucine transport was significantly reduced 24 h post-treatment, contrasting with a significant increase 6 days following poly(I:C) treatment.Maternal immune activation induces dysregulated placental transport of amino acids affecting fetal brain development, and NDD risk potential in offspring.

Impact of inflammation and infection on the expression of amino acid transporters in the placenta: A minireview.

Amino acid transporters expressed in the placenta help to regulate the transfer of amino acids from maternal to fetal circulation. Nutritional or hormonal factors are known to potentially impact the expression of amino acid transporters in the placenta. A relatively new field of inquiry has also demonstrated that inflammation, whether associated with infection or not, also alters the expression of amino acid transporters in the placenta. Indeed, studies over the past 15 years have demonstrated that malaria, viral and bacterial models of infection, preeclampsia, and direct administration of proinflammatory cytokines can alter placental amino acid transporter expression. While such studies have largely focused on System A and System L transporters, other transporters are also affected. p38 MAPK, STAT3, mTORC1, and AMPK signaling have all been implicated in these changes, but the underlying mechanism(s) remain to be fully elucidated. Furthermore, the implications of such changes warrant further investigation. This review will summarize studies that have investigated the impact of inflammation on placental amino acid transporter expression, identify questions that remain unanswered, and propose future areas of research to advance the field. As amino acid transporters are now being considered for drug targeting and drug delivery, furthering our understanding of the regulation of these transporters during disease states will be of increasing clinical value. Significance Statement While this is a relatively new field of research, multiple studies have demonstrated that inflammation alters placental amino acid transporter expression. This review will serve to summarize, for the first time, studies in this field and identify gaps in current knowledge as research in this area moves beyond identifying changes in transporter expression to investigating the implications of such changes and the mechanisms underlying them.

Infection During Pregnancy Downregulates the Expression of Amino Acid Transporters in Rat and Human Placentas

Maternal immune activation (MIA) resulting from infection during pregnancy increases the chance of offspring having a neurodevelopmental disorder such as autism or schizophrenia. However, the mechanism underlying this association is unknown. Placental transport of amino acids from maternal to fetal circulation is essential for proper fetal neurodevelopment. We hypothesized that MIA could alter the expression of placental amino acid transporters, thereby altering fetal exposure to the amino acids required for proper brain development. Thus, the objective of this study was to examine whether MIA impacts the expression of amino acid transporters in the placentas of rats and humans. MIA was induced in pregnant rats through the administration of the viral mimetic poly(I:C) on gestational day 14. Placental and fetal tissues were collected 24 and 48 hours later. Human placentas isolated at term from pregnancies complicated with either chorioamnionitis (n = 17) or an unidentified active infection causing flu‐like symptoms (n = 6) were compared to healthy gestational age‐matched controls (n = 18). Protein expression of amino acid transporters in rat or human placentas, as well as fetal rat brains, was determined using immunoblotting. Levels of free amino acids in fetal rat brains were also quantified using reverse‐phase HPLC. In rats, poly(I:C) significantly downregulated the amino acid transporters ASCT1 and EAAT2 in the placenta, with a trend towards decreased SNAT2. SNAT5, EAAT1, and GLYT1 were also significantly reduced in fetal brains from poly(I:C)‐treated dams. Furthermore, the levels of multiple amino acids were significantly altered in fetal brains of poly(I:C)‐treated rats. In human placentas, ASCT1 was significantly downregulated in active infection cases, but not in chorioamnionitis cases. A pronounced trend of decreased SNAT2 expression was also seen in active infection cases, but this did not reach significance. To conclude, MIA decreases the expression of amino acid transporters in the placentas of rats and is associated with altered levels of free amino acids in fetal rat brains. Moreover, decreased expression of amino acid transporters is also seen in human placentas obtained from pregnancies with active infection. As amino acids are required for proper neurodevelopment, these changes in transport could provide a link between MIA and neurodevelopmental disorders.

Vitamin D stimulates placental L-type amino acid transporter 1 (LAT1) in preeclampsia

Vitamin D insufficiency/deficiency has been linked to an increased risk of preeclampsia. Impaired placental amino acid transport is suggested to contribute to abnormal fetal intrauterine growth in pregnancies complicated by preeclampsia. However, if vitamin D-regulated amino acid transporter is involved in the pathophysiologic mechanism of preeclampsia has not been clarified yet. The aberrant expression of key isoform of L-type amino acid transporter LAT1 was determined by western blot and immunohistochemistry in the placenta from normotensive and preeclamptic pregnancies. The role for vitamin D on placental LAT1 expression was investigated through the exposure of HTR-8/SVneo human trophoblast cells to the biologically active 1,25(OH)2D3 and the oxidative stress-inducer cobalt chloride (CoCl2). Our results showed that placental LAT1 expression was reduced in women with preeclampsia compared to normotensive pregnancies, which was associated with decreased expression of vitamin D receptor (VDR). 1,25(OH)2D3 significantly upregulated LAT1 expression in placental trophoblasts, and also prevented the decrease of mTOR activity under CoCl2-induced oxidative stress. siRNA targeting VDR significantly attenuated 1,25(OH)2D3-stimulated LAT1 expression and mTOR signaling activity. Moreover, treatment of rapamycin specifically inhibited the activity of mTOR signaling and resulted in decrease of LAT1 expression. In conclusion, LAT1 expression was downregulated in the placenta from women with preeclampsia. 1,25(OH)2D3/VDR could stimulate LAT1 expression, which was likely mediated by mTOR signaling in placental trophoblasts. Regulation on placental amino acid transport may be one of the mechanisms by which vitamin D affects fetal growth in preeclampsia.

Mechanistic Target of Rapamycin Complex 2 Regulation of the Primary Human Trophoblast Cell Transcriptome.

Mechanistic Target of Rapamycin Complex 2 (mTORC2) regulates placental amino acid and folate transport. However, the role of mTORC2 in modulating other placental functions is largely unexplored. We used a gene array following the silencing of rictor to identify genes regulated by mTORC2 in primary human trophoblast (PHT) cells. Four hundred and nine genes were differentially expressed; 102 genes were down-regulated and 307 up-regulated. Pathway analyses demonstrated that inhibition of mTORC2 resulted in increased expression of genes encoding for pro-inflammatory IL-6, VEGF-A, leptin, and inflammatory signaling (SAPK/JNK). Furthermore, down-regulated genes were functionally enriched in genes involved in angiogenesis (Osteopontin) and multivitamin transport (SLC5A6). In addition, the protein expression of leptin, VEGFA, IL-6 was increased and negatively correlated to mTORC2 signaling in human placentas collected from pregnancies complicated by intrauterine growth restriction (IUGR). In contrast, the protein expression of Osteopontin and SLC5A6 was decreased and positively correlated to mTORC2 signaling in human IUGR placentas. In conclusion, mTORC2 signaling regulates trophoblast expression of genes involved in inflammation, micronutrient transport, and angiogenesis, representing novel links between mTOR signaling and multiple placental functions necessary for fetal growth and development.

Fetal Sex Does Not Impact Placental Blood Flow or Placental Amino Acid Transfer in Late Gestation Pregnant Sheep With or Without Placental Insufficiency.

Pregnant sheep have been used to model complications of human pregnancies including placental insufficiency and intrauterine growth restriction. Some of the hallmarks of placental insufficiency are slower uterine and umbilical blood flow rates, impaired placental transport of oxygen and amino acids, and lower fetal arterial concentrations of anabolic growth factors. An impact of fetal sex on these outcomes has not been identified in either human or sheep pregnancies. This is likely because most studies measuring these outcomes have used small numbers of subjects or animals. We undertook a secondary analysis of previously published data generated by our laboratory in late-gestation (gestational age of 133 ± 0days gestational age) control sheep (n = 29 male fetuses; n = 26 female fetuses; n = 3 sex not recorded) and sheep exposed to elevated ambient temperatures to cause experimental placental insufficiency (n = 23 male fetuses; n = 17 female fetuses; n = 1 sex not recorded). The primary goal was to determine how fetal sex modifies the effect of the experimental insult on outcomes related to placental blood flow, amino acid and oxygen transport, and fetal hormones. Of the 112 outcomes measured, we only found an interaction between fetal sex and experimental insult for the uterine uptake rates of isoleucine, phenylalanine, and arginine. Additionally, most outcomes measured did not show a difference based on fetal sex when adjusting for the impact of placental insufficiency. Exceptions included fetal norepinephrine and cortisol concentrations, which were higher in female compared to male fetuses. For the parameters measured in the current analysis, the impact of fetal sex was not widespread.

Maternal intermittent fasting during pregnancy: a translational research challenge for an important clinical scenario.

In volume 135, issue 11 of Clinical Science, Alkhalefah et al. report that, in pregnant rats, repeated, cyclic fasting, mimicking the fasting experienced by observant Muslim pregnant women during Ramadan, alters placental amino acid transport and increases the incidence of low birth weight. Though Muslim women are exempt, many observe Ramadan: >500 million fetuses worldwide may be exposed to Ramadan fasting in each generation, and low birth weight increases the risk of developing chronic disease in the future adult. Several mechanisms, including altered circadian rhythm, maternal stress, undernutrition or compensatory overeating at the breaking of fast, could, in theory, impact fetal growth during Ramadan. Limitations of the experimental model obviously prevent direct extrapolation to humans. Whether Ramadan fasting indeed affect fetal growth therefore remains unclear, as there is no clear-cut evidence from epidemiological studies. The paper illustrates the need to design further case-controlled studies in large cohorts of women who fasted at various stages of pregnancy, compared to appropriately matched women who did not fast, as well as more experimental studies focused on this issue of public health relevance.

Reduction of In Vivo Placental Amino Acid Transport Precedes the Development of Intrauterine Growth Restriction in the Non-Human Primate.

Intrauterine growth restriction (IUGR) is associated with reduced placental amino acid transport (AAT). However, it remains to be established if changes in AAT contribute to restricted fetal growth. We hypothesized that reduced in vivo placental AAT precedes the development of IUGR in baboons with maternal nutrient restriction (MNR). Baboons were fed either a control (ad libitum) or MNR diet (70% of control diet) from gestational day (GD) 30. At GD 140, in vivo transplacental AA transport was measured by infusing nine (13)C- or (2)H-labeled essential amino acids (EAAs) as a bolus into the maternal circulation at cesarean section. A fetal vein-to-maternal artery mole percent excess ratio for each EAA was measured. Microvillous plasma membrane (MVM) system A and system L transport activity were determined. Fetal and placental weights were not significantly different between MNR and control. In vivo, the fetal vein-to-maternal artery mole percent excess ratio was significantly decreased for tryptophan in MNR. MVM system A and system L activity was markedly reduced in MNR. Reduction of in vivo placental amino acid transport precedes fetal growth restriction in the non-human primate, suggesting that reduced placental amino acid transfer may contribute to IUGR.