Mammalian target of rapamycin signalling modulates amino acid uptake by regulating transporter cell surface abundance in primary human trophoblast cells

Placental function in maternal obesity

Maternal obesity is associated with pregnancy complications and increases the risk for the infant to develop obesity, diabetes and cardiovascular disease later in life. However, the mechanisms linking the maternal obesogenic environment to adverse short- and long-term outcomes remain poorly understood. As compared with pregnant women with normal BMI, women entering pregnancy obese have more pronounced insulin resistance, higher circulating plasma insulin, leptin, IGF-1, lipids and possibly proinflammatory cytokines and lower plasma adiponectin. Importantly, the changes in maternal levels of nutrients, growth factors and hormones in maternal obesity modulate placental function. For example, high insulin, leptin, IGF-1 and low adiponectin in obese pregnant women activate mTOR signaling in the placenta, promoting protein synthesis, mitochondrial function and nutrient transport. These changes are believed to increase fetal nutrient supply and contribute to fetal overgrowth and/or adiposity in offspring, which increases the risk to develop disease later in life. However, the majority of obese women give birth to normal weight infants and these pregnancies are also associated with activation of inflammatory signaling pathways, oxidative stress, decreased oxidative phosphorylation and lipid accumulation in the placenta. Recent bioinformatics approaches have expanded our understanding of how maternal obesity affects the placenta; however, the link between changes in placental function and adverse outcomes in obese women giving birth to normal sized infants is unclear. Interventions that specifically target placental function, such as activation of placental adiponectin receptors, may prevent the transmission of metabolic disease from obese women to the next generation.

Down-regulation of placental Cdc42 and Rac1 links mTORC2 inhibition to decreased trophoblast amino acid transport in human intrauterine growth restriction

Intrauterine growth restriction (IUGR) increases the risk for perinatal complications and metabolic and cardiovascular disease later in life. The syncytiotrophoblast (ST) is the transporting epithelium of the human placenta, and decreased expression of amino acid transporter isoforms in the ST plasma membranes is believed to contribute to IUGR. Placental mechanistic target of rapamycin Complex 2 (mTORC2) signaling is inhibited in IUGR and regulates the trafficking of key amino acid transporter (AAT) isoforms to the ST plasma membrane; however, the molecular mechanisms are unknown. Cdc42 and Rac1 are Rho-GTPases that regulate actin-binding proteins, thereby modulating the structure and dynamics of the actin cytoskeleton. We hypothesized that inhibition of mTORC2 decreases AAT expression in the plasma membrane and amino acid uptake in primary human trophoblast (PHT) cells mediated by down-regulation of Cdc42 and Rac1. mTORC2, but not mTORC1, inhibition decreased the Cdc42 and Rac1 expression. Silencing of Cdc42 and Rac1 inhibited the activity of the System L and A transporters and markedly decreased the trafficking of LAT1 (System L isoform) and SNAT2 (System A isoform) to the plasma membrane. mTORC2 inhibition by silencing of rictor failed to decrease AAT following activation of Cdc42/Rac1. Placental Cdc42 and Rac1 protein expression was down-regulated in human IUGR and was positively correlated with placental mTORC2 signaling. In conclusion, mTORC2 regulates AAT trafficking in PHT cells by modulating Cdc42 and Rac1. Placental mTORC2 inhibition in human IUGR may contribute to decreased placental amino acid transfer and reduced fetal growth mediated by down-regulation of Cdc42 and Rac1.

Maternal L-proline supplementation enhances fetal survival, placental development, and nutrient transport in mice†

L-Proline (proline) in amniotic fluid was markedly increased during pregnancy in both pigs and sheep. However, in vivo data to support a beneficial effect of proline on fetal survival are not available. In this study, pregnant C57BL/6J mice were fed a purified diet supplemented with or without 0.50% proline from embryonic day 0.5 (E0.5) to E12.5 or term. Results indicated that dietary supplementation with proline to gestating mice enhanced fetal survival, reproductive performance, the concentrations of proline, arginine, aspartic acid, and tryptophan in plasma and amniotic fluid, while decreasing the concentrations of ammonia and urea in plasma and amniotic fluid. Placental mRNA levels for amino acid transporters, including Slc36a4, Slc38a2, Slc38a4, Slc6a14, and Na+/K+ ATPase subunit-1α (Atp1a1), fatty acid transporter Slc27a4, and glucose transporters Slc2a1 and Slc2a3, were augmented in proline-supplemented mice, compared with the control group. Histological analysis showed that proline supplementation enhanced labyrinth zone in the placenta of mice at E12.5, mRNA levels for Vegf, Vegfr, Nos2, and Nos3, compared with the controls. Western blot analysis showed that proline supplementation increased protein abundances of phosphorylated (p)-mTORC1, p-ribosomal protein S6 kinase (p70S6K), and p-eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1), as well as the protein level of GCN2 (a negative regulator of mTORC1 signaling). Collectively, our results indicate a novel functional role of proline in improving placental development and fetal survival by enhancing placental nutrient transport, angiogenesis, and protein synthesis.

Is there a definite relationship between placental mTOR signaling and fetal growth?

Fetal growth restriction and overgrowth are common obstetrical complications that result in adverse perinatal outcomes and long-term health risks later in life, including neurodevelopmental dysfunction and adult metabolic syndrome. The placenta plays a critical role in the nutrition transfer from mother to fetus and even exerts adaptive mechanism when the fetus is under poor developmental conditions. The mammalian/mechanistic target of rapamycin (mTOR) signaling serves as a critical hub of cell growth, survival, and metabolism in response to nutrients, growth factors, energy, and stress signals. Placental mTOR signaling regulates placental function, including oxygen and nutrient transport. Therefore, placental mTOR signaling is hypothesized to have a positive relationship with fetal growth. In this review, we summarize that most studies support the current evidence that there is connection between placental mTOR signaling and abnormal fetal growth; however, but more studies should be performed following a vigorous and unanimous method for assessment to determine placental mTOR activity.

Consumption of a Branched-Chain Amino Acid (BCAA) during Days 2-10 of Pregnancy Causes Abnormal Fetal and Placental Growth: Implications for BCAA Supplementation in Humans

A relatively large branched-chain amino acid (BCAA) supplement, consumed for more than 10 days, appears to be especially effective at alleviating muscle damage and soreness during intense human training. However, perturbations in amino acid and protein consumption could have unwanted transgenerational effects on male and female reproduction. This paper hypothesizes that isoleucine consumption by female mice from days 2 to 10 of pregnancy will alter fetal and placental growth later in gestation. Mice that had received 118 mM isoleucine in their drinking water delivered pups on day 19 of pregnancy that were 9% larger than normal, whereas the reverse was true for pups born on day 20. Moreover, the inverse correlation between birth weight and litter size was lost in mice that previously consumed excess isoleucine. Similarly, the normal correlations between fetal and placental weights were lost by day 18 of pregnancy in mice that had consumed excess isoleucine. Mice that consumed excess isoleucine had placentas smaller than, and fetuses larger than normal on day 18 of pregnancy, but the reverse was true on day 15. Other unintended and unexpected effects of BCAA consumption should be studied more thoroughly due to the increasing use of BCAAs to alleviate muscle damage and soreness in athletes.

Downregulation of Placental Amino Acid Transporter Expression and mTORC1 Signaling Activity Contributes to Fetal Growth Retardation in Diabetic Rats

Alterations in placental transport may contribute to abnormal fetal intrauterine growth in pregnancies complicated by diabetes, but it is not clear whether the placental amino acid transport system is altered in diabetic pregnancies. We therefore studied the changes in the expressions of placental amino acid transporters in a rat model of diabetes induced by streptozotocin, and tested the effects of hyperglycemia on trophoblast amino acid transporter in vitro. Our results showed that the expressions for key isoforms of system L amino acid transporters were significantly reduced in the placentas of streptozotocin-induced diabetic pregnant rats, which was associated with the decreased birthweight in the rats. A decreased placental efficiency and decreased placental mammalian target of rapamycin (mTOR) complex 1 (mTORC1) activity were also found in the rat model. In addition, hyperglycemia in vitro could inhibit amino acid transporter expression and mTORC1 activity in human trophoblast. Inhibition of mTORC1 activity led to reduced amino acid transporter expression in placental trophoblast. We concluded that reduced placental mTORC1 activity during pregnancy resulted in decreased placental amino acid transporter expression and, subsequently, contributed to fetal intrauterine growth restriction in pregnancies complicated with diabetes.

mTOR complex 2 is an integrator of cancer metabolism and epigenetics

Metabolic reprogramming is a central hallmark of cancer and is driven by abnormalites of oncogenes and tumor suppressors. This enables tumor cells to obtain the macromolecular precursors and energy needed for rapid tumor growth. Accelerated metabolism also translates into cancer cell aggression through epigenetic changes. The aberrant signaling cascades activated by oncogenes coordinate metabolic reprogramming with epigenetic shifts and subsequent global transcriptional changes through the dysregulation of rate-limiting metabolic enzymes as well as by facilitating the production of intermediary metabolites. As the landscape of cancer cell metabolism has been elucidated, it is now time for this knowledge to be translated into benefit for patients. Here we review the recently identified central regulatory role for mechanistic/mammalian target of rapamycin complex 2 (mTORC2), a downstream effector of many cancer-causing mutations, in reprogramming the metabolic and epigenetic landscape. This leads to tumor cell survival and cancer drug resistance.

Nanoparticle mediated increased insulin-like growth factor 1 expression enhances human placenta syncytium function

INTRODUCTION

Placental dysfunction is an underlying cause of many major obstetric diseases and treatment options for complications like fetal growth restriction (FGR) are limited .We previously demonstrated nanoparticle delivery of the human insulin-like growth factor 1 (hIGF1) transgene under control of the trophoblast-specific PLAC1 promoter maintains normal fetal growth in a surgically-induced FGR mouse model. However, uptake by human placental syncytiotrophoblast has yet to be determined.

METHODS

An ex vivo human placenta perfusion model, term placenta villous fragments, and other in vitro syncytiotrophoblast models were used to determine nanoparticle uptake, transgene expression, and functional responses under oxidative stress conditions.

RESULTS

In the ex vivo perfusion, fluorescence from a Texas-Red conjugated nanoparticle increased in maternal perfusate upon nanoparticle addition and declined by the conclusion of the experiment (P < 0.001. Fluorescent histology confirmed localization in the syncytiotrophoblasts. No Texas-Red fluorescence was detected in the fetal perfusate. Transgene expression of hIGF1 in differentiated BeWo cells, isolated primary trophoblasts and fragments was increased compared to untreated (55,000-fold, P = 0.0003; 95-fold, P = 0.003; 400-fold, P < 0.001, respectively). Functionally, increased hIGF1 expression in villous fragments resulted in translocation of glucose transporter 1 to the syncytiotrophoblast cell membrane and under conditions of oxidative stress in BeWo cells, protected against increased cell death (P < 0.01) and decreased mitochondrial activity (P < 0.01).

CONCLUSION

The current study confirms that our nanoparticle is capable of uptake in human placental syncytium which results in enhanced transgene expression, functional changes to cellular activity and protection against increased oxidative stress.

Reduced Na+ K+ -ATPase activity may reduce amino acid uptake in intrauterine growth restricted fetal sheep muscle despite unchanged ex vivo amino acid transporter activity

KEY POINTS

Fetuses with intrauterine growth restriction (IUGR) have reduced muscle mass that persists postnatally, which may contribute to their increased risk for adult onset metabolic diseases, such as diabetes and obesity. Amino acid transporter-mediated histidine uptake and system L amino acid transporter activity were similar in sarcolemmal membranes isolated from control and IUGR hindlimb skeletal muscle. Activity of Na⁺ K⁺ -ATPase, which is responsible for establishing the sodium gradient necessary for system A and N amino acid transporter function, was significantly reduced in IUGR skeletal muscle sarcolemma compared to control. ATP content was lower in IUGR skeletal muscle. Expression and phosphorylation of proteins in the mechanistic target of rapamycin pathway were similar in control and IUGR skeletal muscle homogenate. Our data suggest that lower Na⁺ K⁺ -ATPase activity, which reduces the driving force for active amino acid transport, and lower ATP availability contribute to reduced amino acid uptake and protein synthesis in IUGR fetal skeletal muscle.

ABSTRACT

Fetuses with intrauterine growth restriction (IUGR) have lower muscle mass that persists postnatally. Using a sheep model of placental insufficiency and IUGR, we have previously demonstrated lower net total uptake of amino acids by the fetal hindlimb and lower skeletal muscle protein synthesis rates. To investigate the mechanisms underlying these changes, we tested the hypothesis that ex vivo amino acid transporter and Na⁺ K⁺ -ATPase activity is reduced, and ex vivo ATP levels are lower in hindlimb skeletal muscle of the IUGR fetus. We developed a novel protocol to measure transporter-mediated histidine uptake, system L amino acid transporter activity and Na⁺ K⁺ -ATPase activity using sarcolemmal membranes isolated from hindlimb muscle of control (CON, n = 11-12) and IUGR (n = 12) late gestation fetal sheep. We also determined ATP content and the activity of insulin and mechanistic target of rapamycin (mTOR) signalling, which are involved in regulating cellular amino acid uptake and protein synthesis, by measuring the expression and phosphorylation of AKT, 4E-BP1, eIF2α, AMPKα, p70 S6 kinase and rpS6 in muscle homogenates. Transporter-mediated histidine uptake and system L activity were similar in control and IUGR sarcolemma, although ex vivo Na⁺ K⁺ -ATPase activity was lower by 64% (P = 0.019) in IUGR sarcolemma. ATP content was lower by 25% (P = 0.007) in IUGR muscle. Insulin, AMPK, and mTOR signalling activity was similar in control and IUGR muscle. We speculate that reduced muscle sarcolemmal Na⁺ K⁺ -ATPase activity and lower ATP content diminishes the sodium gradient in vivo, resulting in a reduced driving force for sodium-dependent transporters and subsequently lower muscle amino acid uptake.

Curcumin Protects Human Trophoblast HTR8/SVneo Cells from H2O2-Induced Oxidative Stress by Activating Nrf2 Signaling Pathway

Pregnancy complications are associated with oxidative stress induced by accumulation of trophoblastic ROS in the placenta. We employed the human trophoblast HTR8/SVneo cell line to determine the effect of curcumin pre-treatment on H₂O₂-induced oxidative damage in HTR8/Sveo cells. Cells were pretreated with 2.5 or 5 μM curcumin for 24 h, and then incubated with 400 μM H₂O₂ for another 24 h. The results showed that H₂O₂ decreased the cell viability and induced excessive accumulation of reactive oxygen species (ROS) in HTR8/Sveo cells. Curcumin pre-treatment effectively protected HTR8/SVneo cells against oxidative stress-induced apoptosis via increasing Bcl-2/Bax ratio and decreasing the protein expression level of cleaved-caspase 3. Moreover, curcumin pre-treatment alleviated the excessive oxidative stress by enhancing the activity of antioxidative enzymes. The antioxidant effect of curcumin was achieved by activating Nrf2 and its downstream antioxidant proteins. In addition, knockdown of Nrf2 by Nrf2-siRNA transfection abolished the protective effects of curcumin on HTR8/SVneo cells against oxidative damage. Taken together, our results show that curcumin could protect HTR8/SVneo cells from H₂O₂-induced oxidative stress by activating Nrf2 signaling pathway.

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.

Effect of high altitude on human placental amino acid transport

Women residing at high altitudes deliver infants of lower birth weight than at sea level. Birth weight correlates with placental system A-mediated amino acid transport capacity, and severe environmental hypoxia reduces system A activity in isolated trophoblast and the mouse placenta. However, the effect of high altitude on human placental amino acid transport remains unknown. We hypothesized that microvillous membrane (MVM) system A and system L amino acid transporter activity is lower in placentas of women living at high altitude compared with low-altitude controls. Placentas were collected at term from healthy pregnant women residing at high altitude (HA; >2,500 m; n = 14) or low altitude (LA; <1,700 m; n = 14) following planned, unlabored cesarean section. Birth weight, but not placenta weight, was 13% lower in HA pregnancies (2.88 ± 0.11 kg) compared with LA (3.30 ± 0.07 kg, P < 0.01). MVM erythropoietin receptor abundance, determined by immunoblot, was greater in HA than in LA placentas, consistent with lower placental oxygen levels at HA. However, there was no effect of altitude on MVM system A or L activity, determined by Na⁺-dependent [¹⁴C]methylaminoisobutyric acid uptake and [³H]leucine uptake, respectively. MVM abundance of glucose transporters (GLUTs) 1 and 4 and basal membrane GLUT4 were also similar in LA and HA placentas. Low birth weights in the neonates of women residing at high altitude are not a consequence of reduced placental amino acid transport capacity. These observations are in general agreement with studies of IUGR babies at low altitude, in which MVM system A activity is downregulated only in growth-restricted babies with significant compromise.NEW & NOTEWORTHY Babies born at high altitude are smaller than at sea level. Birth weight is dependent on growth in utero and, in turn, placental nutrient transport. We determined amino acid transport capacity in placentas collected from women resident at low and high altitude. Altitude did not affect system A amino acid transport across the syncytiotrophoblast microvillous membrane, suggesting that impaired placental amino acid transport does not contribute to reduced birth weight in this high-altitude population.

Vasoactive Intestinal Peptide induces glucose and neutral amino acid uptake through mTOR signalling in human cytotrophoblast cells

The transport of nutrients across the placenta involves trophoblast cell specific transporters modulated through the mammalian target of rapamycin (mTOR). The vasoactive intestinal peptide (VIP) has embryotrophic effects in mice and regulates human cytotrophoblast cell migration and invasion. Here we explored the effect of VIP on glucose and System A amino acid uptake by human trophoblast-derived cells (Swan 71 and BeWo cell lines). VIP activated D-glucose specific uptake in single cytotrophoblast cells in a concentration-dependent manner through PKA, MAPK, PI3K and mTOR signalling pathways. Glucose uptake was reduced in VIP-knocked down cytotrophoblast cells. Also, VIP stimulated System A amino acid uptake and the expression of GLUT1 glucose transporter and SNAT1 neutral amino acid transporter. VIP increased mTOR expression and mTOR/S6 phosphorylation whereas VIP silencing reduced mTOR mRNA and protein expression. Inhibition of mTOR signalling with rapamycin reduced the expression of endogenous VIP and of VIP-induced S6 phosphorylation. Our findings support a role of VIP in the transport of glucose and neutral amino acids in cytotrophoblast cells through mTOR-regulated pathways and they are instrumental for understanding the physiological regulation of nutrient sensing by endogenous VIP at the maternal-foetal interface.

Glucocorticoid regulation of amino acid transport in primary human trophoblast cells

Excess maternal glucocorticoids reduce placental amino acid transport and fetal growth, but whether these effects are mediated directly on the syncytiotrophoblast remains unknown. We hypothesised that glucocorticoids inhibit mechanistic target of rapamycin (mTOR) signaling and insulin-stimulated System A amino acid transport activity in primary human trophoblast (PHT) cells. Syncytialised PHTs, isolated from term placentas (n = 15), were treated with either cortisol (1 μM) or dexamethasone (1 μM), ± insulin (1 nM) for 24 h. Compared to vehicle, dexamethasone increased mRNA expression, but not protein abundance of the mTOR suppressor, regulated in development and DNA damage response 1 (REDD1). Dexamethasone enhanced insulin receptor abundance, activated mTOR complex 1 and 2 signaling and stimulated System A activity, measured by Na+-dependent 14C-methylaminoisobutyric acid uptake. Cortisol also activated mTORC1 without significantly altering insulin receptor or mTORC2 read-outs or System A activity. Both glucocorticoids downregulated expression of the glucocorticoid receptor and the System A transporter genes SLC38A1, SLC38A2 and SLC38A4, without altering SNAT1 or SNAT4 protein abundance. Neither cortisol nor dexamethasone affected System L amino acid transport. Insulin further enhanced mTOR and System A activity, irrespective of glucocorticoid treatment and despite downregulating its own receptor. Contrary to our hypothesis, glucocorticoids do not inhibit mTOR signaling or cause insulin resistance in cultured PHT cells. We speculate that glucocorticoids stimulate System A activity in PHT cells by activating mTOR signaling, which regulates amino acid transporters post-translationally. We conclude that downregulation of placental nutrient transport in vivo following excess maternal glucocorticoids is not mediated by a direct effect on the placenta.

Multifaceted regulation of the system A transporter Slc38a2 suggests nanoscale regulation of amino acid metabolism and cellular signaling

Amino acids are essential for cellular protein synthesis, growth, metabolism, signaling and in stress responses. Cell plasma membranes harbor specialized transporters accumulating amino acids to support a variety of cellular biochemical pathways. Several transporters for neutral amino acids have been characterized. However, Slc38a2 (also known as SA1, SAT2, ATA2, SNAT2) representing the classical transport system A activity stands in a unique position: Being a secondarily active transporter energized by the electrochemical gradient of Na⁺, it creates steep concentration gradients for amino acids such as glutamine: this may subsequently drive the accumulation of additional neutral amino acids through exchange via transport systems ASC and L. Slc38a2 is ubiquitously expressed, yet in a cell-specific manner. In this review, we show that Slc38a2 is regulated at the transcriptional and translational levels as well as by ions and proteins through direct interactions. We describe how Slc38a2 senses amino acid availability and passes this onto intracellular signaling pathways and how it regulates protein synthesis, cellular proliferation and apoptosis through the mechanistic (mammalian) target of rapamycin (mTOR) and general control nonderepressible 2 (GCN2) pathways. Furthermore, we review how this extensively regulated transporter contributes to cellular osmoadaptation and how it is regulated by endoplasmic reticulum stress and various hormonal stimuli to promote cellular metabolism, cellular signaling and cell survival. This article is part of the issue entitled 'Special Issue on Neurotransmitter Transporters'.

LAT1-like transporters regulate dopaminergic transmission and sleep in Drosophila

Amino acid transporters are involved in functions reportedly linked to the sleep/wake cycle: neurotransmitter synthesis and recycling, the regulation of synaptic strength, protein synthesis, and energy metabolism. In addition, the existence of bidirectional relationships among extracellular content, transport systems, and sleep/wake states is receiving emerging support. Nevertheless, the connection between amino acid transport and sleep/wake regulation remains elusive. To address this question, we used Drosophila melanogaster and investigated the role of LAT1 (large neutral amino acid transporter 1) transporters. We show that the two Drosophila LAT1-like transporters: Juvenile hormone Inducible-21 and minidiscs (Mnd) are required in dopaminergic neurons for sleep/wake regulation. Down-regulating either gene in dopaminergic neurons resulted in higher daily sleep and longer sleep bout duration during the night, suggesting a defect in dopaminergic transmission. Since LAT1 transporters can mediate in mammals the uptake of L-DOPA, a precursor of dopamine, we assessed amino acid transport efficiency by L-DOPA feeding. We find that downregulation of JhI-21, but not Mnd, reduced the sensitivity to L-DOPA as measured by sleep loss. JhI-21 downregulation also attenuated the sleep loss induced by continuous activation of dopaminergic neurons. Since LAT1 transporters are known to regulate target of rapamycin (TOR) signaling, we investigated the role of this amino acid sensing pathway in dopaminergic neurons. Consistently, we report that TOR activity in dopaminergic neurons modulates sleep/wake states. Altogether, this study provides evidence that LAT1-mediated amino acid transport in dopaminergic neurons is playing a significant role in sleep/wake regulation and is providing several entry points to elucidate the role of nutrients such as amino acids in sleep/wake regulation.

Fetal and trophoblast PI3K p110α have distinct roles in regulating resource supply to the growing fetus in mice

Studies suggest that placental nutrient supply adapts according to fetal demands. However, signaling events underlying placental adaptations remain unknown. Here we demonstrate that phosphoinositide 3-kinase p110α in the fetus and the trophoblast interplay to regulate placental nutrient supply and fetal growth. Complete loss of fetal p110α caused embryonic death, whilst heterozygous loss resulted in fetal growth restriction and impaired placental formation and nutrient transport. Loss of trophoblast p110α resulted in viable fetuses, abnormal placental development and a failure of the placenta to transport sufficient nutrients to match fetal demands for growth. Using RNA-seq we identified genes downstream of p110α in the trophoblast that are important in adapting placental phenotype. Using CRISPR/Cas9 we showed loss of p110α differentially affects gene expression in trophoblast and embryonic stem cells. Our findings reveal important, but distinct roles for p110α in the different compartments of the conceptus, which control fetal resource acquisition and growth.

Apelin is a novel regulator of human trophoblast amino acid transport

Apelin is an insulin-sensitizing hormone increased in abundance with obesity. Apelin and its receptor, APJ, are expressed in the human placenta, but whether apelin regulates placental function in normal body mass index (BMI) and obese pregnant women remains unknown. We hypothesized that apelin stimulates amino acid transport in cultured primary human trophoblast (PHT) cells and that maternal circulating apelin levels are elevated in obese pregnant women delivering large babies. Treating PHT cells with physiological concentrations of the pyroglutamated form [Pyr¹]apelin-13 (0.1-10.0 ng/ml) for 24 h dose-dependently increased System A amino acid transport (P < 0.05) but did not affect System L transport activity. Mechanistic target of rapamycin (mTOR), extracellular signal-regulated kinase-1/2 (ERK1/2), and AMP-activated protein kinase-α (AMPKα) signaling were unaffected by apelin (P > 0.05). Plasma apelin was not different in obese women (BMI 35.8 ± 0.7, n = 21) with large babies compared with normal-BMI women (23.1 ± 0.5, n = 16) delivering normal birth weight infants. Apelin was highly expressed in placental villous tissue (20-fold higher vs. adipose), and APJ was present in syncytiotrophoblast microvillous membrane, but neither differed in abundance between normal-BMI and obese women. Phosphorylation (Thr¹⁷²) of placental AMPKα strongly correlated with microvillous membrane APJ expression (P < 0.01, R = 0.63) but negatively correlated with placental apelin abundance (P < 0.01, R = -0.62). Neither placental APJ nor apelin abundance correlated with maternal BMI, plasma insulin, birth weight, or mTOR or ERK1/2 signaling (P > 0.05). Hence, apelin stimulates trophoblast amino acid uptake, establishing a novel mechanism regulating placental function. We found no evidence that apelin constitutes an endocrine link between maternal obesity and fetal overgrowth.

Maternal obesity results in decreased syncytiotrophoblast synthesis of palmitoleic acid, a fatty acid with anti-inflammatory and insulin-sensitizing properties

The fetus is dependent on delivery of fatty acids (FAs) by the syncytiotrophoblast, the transporting epithelium of the human placenta. Obese pregnant women have dyslipidemia; however, whether obesity impacts placental lipid transport and metabolism remains to be fully established. Palmitoleic acid (POA), an FA with anti-inflammatory and insulin-sensitizing properties, is synthesized from palmitic acid (PA) catalyzed by stearoyl-coenzyme A desaturase (SCD) activity. We hypothesized that the uptake and incorporation of FAs and POA synthesis are reduced in primary human trophoblasts (PHTs) isolated from pregnancies complicated by maternal obesity. Villous cytotrophoblasts were isolated from 7 placentas of obese [body mass index (BMI) = 37.5 ± 1.9] and 12 normal (BMI = 23.6 ± 0.6) mothers. FA uptake and incorporation were assessed using uniformly labeled (U[¹³C])-FA mixtures of PA, oleic acid (OA), linoleic acid, and docosahexaenoic acid. Cellular [¹³C] FAs were quantified both in total cellular lipids and in lipid classes by GC-MS. Uptake and incorporation of [¹³C] FAs in total cellular lipids were not different in PHTs isolated from obese mothers compared with normal mothers. Only the concentration of OA was increased in the triglyceride fraction (P < 0.05) if the mother was obese. We found an isotopic enrichment of POA after U[¹³C]-PA treatment, demonstrating SCD activity in PHT cells. Labeled POA content and the POA:PA ratio were significantly lower in PHTs isolated from placentas of obese mothers compared with normal, healthy controls. Decreased syncytiotrophoblast POA synthesis may contribute to insulin resistance and low-grade inflammation in the mother, placenta, or fetus (or a combination of the 3) in pregnancies complicated by obesity.-Ferchaud-Roucher, V., Barner, K., Jansson, T., Powell, T. L. Maternal obesity results in decreased syncytiotrophoblast synthesis of palmitoleic acid, a fatty acid with anti-inflammatory and insulin-sensitizing properties.

Novel roles of mechanistic target of rapamycin signaling in regulating fetal growth†

Mechanistic target of rapamycin (mTOR) signaling functions as a central regulator of cellular metabolism, growth, and survival in response to hormones, growth factors, nutrients, energy, and stress signals. Mechanistic TOR is therefore critical for the growth of most fetal organs, and global mTOR deletion is embryonic lethal. This review discusses emerging evidence suggesting that mTOR signaling also has a role as a critical hub in the overall homeostatic control of fetal growth, adjusting the fetal growth trajectory according to the ability of the maternal supply line to support fetal growth. In the fetus, liver mTOR governs the secretion and phosphorylation of insulin-like growth factor binding protein 1 (IGFBP-1) thereby controlling the bioavailability of insulin-like growth factors (IGF-I and IGF-II), which function as important growth hormones during fetal life. In the placenta, mTOR responds to a large number of growth-related signals, including amino acids, glucose, oxygen, folate, and growth factors, to regulate trophoblast mitochondrial respiration, nutrient transport, and protein synthesis, thereby influencing fetal growth. In the maternal compartment, mTOR is an integral part of a decidual nutrient sensor which links oxygen and nutrient availability to the phosphorylation of IGFBP-1 with preferential effects on the bioavailability of IGF-I in the maternal-fetal interface and in the maternal circulation. These new roles of mTOR signaling in the regulation fetal growth will help us better understand the molecular underpinnings of abnormal fetal growth, such as intrauterine growth restriction and fetal overgrowth, and may represent novel avenues for diagnostics and intervention in important pregnancy complications.

Mechanistic Target of Rapamycin Complex 1 Promotes the Expression of Genes Encoding Electron Transport Chain Proteins and Stimulates Oxidative Phosphorylation in Primary Human Trophoblast Cells by Regulating Mitochondrial Biogenesis

Trophoblast oxidative phosphorylation provides energy for active transport and protein synthesis, which are critical placental functions influencing fetal growth and long-term health. The molecular mechanisms regulating trophoblast mitochondrial oxidative phosphorylation are largely unknown. We hypothesized that mechanistic Target of Rapamycin Complex 1 (mTORC1) is a positive regulator of key genes encoding Electron Transport Chain (ETC) proteins and stimulates oxidative phosphorylation in trophoblast and that ETC protein expression is down-regulated in placentas of infants with intrauterine growth restriction (IUGR). We silenced raptor (mTORC1 inhibition), rictor (mTORC2 inhibition) or DEPTOR (mTORC1/2 activation) in cultured term primary human trophoblast (PHT) cells. mTORC1 inhibition caused a coordinated down-regulation of 18 genes encoding ETC proteins representing all ETC complexes. Inhibition of mTORC1, but not mTORC2, decreased protein expression of ETC complexes I–IV, mitochondrial basal, ATP coupled and maximal respiration, reserve capacity and proton leak, whereas activation of mTORC1 had the opposite effects. Moreover, placental protein expression of ETC complexes was decreased and positively correlated to mTOR signaling activity in IUGR. By controlling trophoblast ATP production, mTORC1 links nutrient and O₂ availability and growth factor signaling to placental function and fetal growth. Reduced placental mTOR activity may impair mitochondrial respiration and contribute to placental insufficiency in IUGR pregnancies.

Chronic heat stress affects muscle hypertrophy, muscle protein synthesis and uptake of amino acid in broilers via insulin like growth factor-mammalian target of rapamycin signal pathway

Heat stress markedly impairs the growth performance of broilers, such as the reduction of breast muscle mass and yield. The aim of this study was to examine the molecular mechanism of depressed muscle mass and yield caused by heat stress. A total of 144 (28-day-old) male broilers were allocated randomly into 3 treatment groups: (1) the normal control group (environment temperature was 22°C), (2) the heat stress group (environment temperature was 32°C), (3) the pair-fed group (environment temperature was 22°C and pair-fed to heat stress group). The experiment lasted for 14 d (from the age of 28 to 42 d). After 14 d of heat exposure, heat stress decreased (P < 0.05) broiler average daily gain, breast muscle mass, and muscle yield, and increased (P < 0.05) feed to gain ratio. After 14 d of heat exposure, heat stress increased (P < 0.05) the activities of aspartate aminotransferase and the concentrations of uric acid and most amino acids in serum, and reduced (P < 0.05) the concentration of insulin like growth factor 1 (IGF-1) in serum. Additionally, heat stress decreased (P < 0.05) the mRNA expressions of IGF-1, IGF-1 receptor, insulin receptor substrate 1, mammalian target of rapamycin (mTOR), the 70 kD ribosomal protein S6 kinase, myogenic differentiation, myogenin, solute carrier family 38 member 2, solute carrier family 7 member 5, and solute carrier family 3 member 2 of the breast muscle. In conclusion, chronic heat stress resulted in lower breast muscle mass and yield, and decreased muscle protein synthesis and amino acid transportation by downregulating IGFs-mTOR signal pathway. These findings have important practical significance in discovering effective means to alleviate muscle loss caused by chronic heat stress.

A systems perspective on placental amino acid transport

Placental amino acid transfer is a complex process that is essential for fetal development. Impaired amino acid transfer causes fetal growth restriction, which may have lifelong health consequences. Transepithelial transfer of amino acids across the placental syncytiotrophoblast requires accumulative, exchange and facilitated transporters on the apical and basal membranes to work in concert. However, transporters alone do not determine amino acid transfer and factors that affect substrate availability, such as blood flow and metabolism, may also become rate-limiting for transfer. In order to determine the rate-limiting processes, it is necessary to take a systems approach which recognises the interdependence of these processes. New technologies have the potential to deliver targeted interventions to the placenta and help poorly growing fetuses. While many factors are necessary for amino acid transfer, novel therapies need to target the rate-limiting factors if they are going to be effective. This review will outline the factors which determine amino acid transfer and describe how they become interdependent. It will also highlight the role of computational modelling as a tool to understand this process.

Amino acid profile in women with gestational diabetes mellitus treated with metformin or insulin

AIMS

We compared the effects of metformin and insulin treatments of gestational diabetes mellitus (GDM) on amino acid metabolism.

METHODS

217 pregnant women diagnosed with GDM were randomized to receive either metformin or insulin. ¹H nuclear magnetic spectroscopy was used to determine serum concentrations of alanine, glutamine, glycine, isoleucine, leucine, valine, histidine, phenylalanine, tyrosine, glucose and lactate at the time of diagnosis and at 36 gestational weeks (gw).

RESULTS

Majority of the amino acid concentrations increased from 30 to 36 gw. The rise in alanine (16% vs. 8%, p < 0.0001), isoleucine (11% vs. 5%, p = 0.035) and lactate (29% vs. 14% p = 0.015) was larger in the metformin group compared to insulin group. Baseline alanine, glycine, isoleucine, leucine, valine and tyrosine were positively related to slightly earlier delivery. Alanine at 36 gw was positively associated with birth weight and glutamine with gestational hypertension or preeclampsia. Lactate at 36 gw was not associated with any adverse outcome.

CONCLUSIONS

Compared to insulin metformin caused a greater increase in serum alanine, isoleucine and lactate concentrations. Although the observed differences in the metabolic variables were relatively small and not outright concerning, additional studies and follow-up data are required to ensure the safety of metformin use in pregnancy. The trial was registered in Clinicaltrials.gov, NCT01240785; http://clinicaltrials.gov/ct2/show/NCT01240785.

Weighing In on mTOR Complex 2 Signaling: The Expanding Role in Cell Metabolism

In all eukaryotes, the mechanistic target of rapamycin (mTOR) signaling emerges as a master regulator of homeostasis, which integrates environmental inputs, including nutrients, energy, and growth factors, to regulate many fundamental cellular processes such as cell growth and metabolism. mTOR signaling functions through two structurally and functionally distinct complexes, mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2), which correspond to two major branches of signal output. While mTORC1 is well characterized for its structure, regulation, and function in the last decade, information of mTORC2 signaling is only rapidly expanding in recent years, from structural biology, signaling network, to functional impact. Here we review the recent advances in many aspects of the mTORC2 signaling, with particular focus on its involvement in the control of cell metabolism and its physiological implications in metabolic diseases and aging.

Trophoblast: The central unit of fetal growth, protection and programming

The placenta is the first organ to be created during mammalian development. As the main link between the mother and the fetus it has more diverse functions than any other organ, serving as a digestive, excretory, respiratory, endocrine, and immune system. The outer layer of the placenta, the trophoblast, plays a key role in fetal development by orchestrating all these functions. Recent research has associated perturbations of maternal conditions (such as malnutrition, stress or inflammation) with alterations of the trophoblasts' endocrine, transport and metabolic processes. As reviewed here, adaptations to these conditions enable the fetus to survive, but at the cost of permanently changing its physiology and structure. Moreover, these adaptations trigger fetal programming that increases predisposition to various pathological conditions in adult life, typically metabolic, cardiovascular or CNS diseases.

Down-regulation of placental folate transporters in intrauterine growth restriction

Folate deficiency in pregnancy is associated with neural tube defects, restricted fetal growth and fetal programming of diseases later in life. Fetal folate availability is dependent on maternal folate levels and placental folate transport capacity, mediated by two key transporters, Folate Receptor-α and Reduced Folate Carrier (RFC). We tested the hypothesis that intrauterine growth restriction (IUGR) is associated with decreased folate transporter expression and activity in isolated syncytiotrophoblast microvillous plasma membranes (MVM). Women with pregnancies complicated by IUGR (birth weight <3rd percentile, mean birth weight 1804±110 g, gestational age 35.7±0.61 weeks, n=25) and women delivering an appropriately-for gestational age infant (control group, birth weight 25th-75th centile, mean birth weight 2493±216 g, gestational age 33.9±0.95 weeks, n=19) were recruited and placentas were collected at delivery. MVM was isolated and folate transporter protein expression was measured using Western blot and transporter activity was determined using radiolabelled methyltetrahydrofolic acid and rapid filtration. Whereas the expression of FR-α was unaffected, MVM RFC protein expression was significantly decreased in the IUGR group (-34%, P<.05). IUGR MVM had a significantly lower folate uptake compared to the control group (-38%, P<.05). In conclusion, placental folate transport capacity is decreased in IUGR, which may contribute to the restricted fetal growth and intrauterine programming of childhood and adult disease. These findings suggest that continuation of folate supplementation in the second and third trimester is of particular importance in pregnancies complicated by IUGR.

Diet Enriched with Olive Oil Attenuates Placental Dysfunction in Rats with Gestational Diabetes Induced by Intrauterine Programming

SCOPE

Offspring from rats with mild diabetes develop gestational diabetes mellitus (GDM). We tested the hypothesis that an olive oil-supplemented diet attenuates placental oxidative stress/inflammation, activation of mTOR signaling, and inhibition of peroxisome proliferator-activated receptor γ (PPARγ) and fetal overgrowth in GDM offspring from mild diabetic rats.

METHODS AND RESULTS

Female offspring from rats with mild diabetes (group that developed GDM) and controls were fed with either a standard diet or a 6% olive oil-supplemented diet during pregnancy. On day 21 of pregnancy, plasma glucose levels in mothers and fetuses were increased in the GDM group independently of the diet. Fetal overgrowth and activation of placental mTOR signaling were partially prevented in the olive oil-treated GDM group. Placental PPARγ protein expression was decreased in GDM rats, independently of the diet. However, increases in placental lipoperoxidation, connective tissue growth factor, and matrix metalloproteinase 2 levels were prevented by the olive oil-enriched diet.

CONCLUSION

Diets enriched with olive oil attenuate placental dysfunction and fetal overgrowth in rats with GDM induced by intrauterine programming.

Maternal serum AMP-activated protein kinase levels in mild and severe preeclampsia

OBJECTIVE

To investigate Phosphorylated adenosine monophosphate activated protein kinase (AMPK) levels in healthy pregnant women and pregnant women with preeclampsia (PE).

METHODS

Twenty-eight women with mild-PE, 22 with severe-PE, and 30 normotensive controls were included in this cross-sectional study. The serum AMPK levels of these patients were analyzed. The patients were followed up to delivery.

RESULTS

No statistically significant difference was found between the groups for age, gravida, parity, and gestational age at the time the blood samples were obtained (p > .05). No significant difference between the group with mild-PE and the control group was found, while in the severe-PE group, serum AMPK levels were significantly higher relative to both the mild-PE and control groups (p < .001 and p < .001, respectively). No correlation was detected between serum AMPK levels and age, body mass index (BMI), and gestational age at the time the blood samples were collected. A negative correlation was found between AMPK levels and gestational week and birthweight at delivery, while a positive correlation was detected between systolic and diastolic blood pressures and AMPK levels.

CONCLUSIONS

Serum AMPK was higher in patients with severe-PE compared with healthy pregnant women and patients with PE without severe features so it might be a new biomarker for the prediction of disease and its severity.

The effects of L-type amino acid transporter 1 on milk protein synthesis in mammary glands of dairy cows

The mammary gland requires the uptake of AA for milk protein synthesis during lactation. The L-type amino acid transporter 1 (LAT1, encoded by SLC7A5), found in many different types of mammalian cells, is indispensable as a transporter of essential AA to maintain cell growth and protein synthesis. However, the function of LAT1 in regulating milk protein synthesis in the mammary gland of the dairy cow remains largely unknown. For the current study, we characterized the relationship between LAT1 expression and milk protein synthesis in lactating dairy cows and investigated whether the mammalian target of rapamycin complex 1 (mTORC1) signaling controls the expression of LAT1 in their mammary glands. We found that LAT1 and the heavy chain of its chaperone, 4F2, were expressed in mammary tissues of lactating cows, with the expression levels of LAT1 and the 4F2 heavy chain being significantly greater in lactating mammary tissues with high-milk protein content (milk yield, 33.8 ± 2.1 kg/d; milk protein concentration >3%, wt/vol,; n = 3) than in tissues from cows with low-milk protein content (milk yield, 33.7 ± 0.5 kg/d; milk protein concentration <3%, wt/vol; n = 3). Immunofluorescence staining of sectioned mammary tissues from cows with high and low milk protein content showed that LAT1 was located on the whole plasma membrane of alveolar epithelial cells, suggesting that LAT1 provides essential AA to the mammary gland. In cultured mammary epithelial cells from the dairy cows with high-milk protein content, knockdown of LAT1 expression decreased cell viability and β-casein expression; in contrast, overexpression of LAT1 had the opposite effect. Inhibition of mTORC1 by rapamycin attenuated the phosphorylation of molecules related to mTORC1 signaling and caused a marked decrease in LAT1 expression in the cultured cells; expression of β-casein also decreased significantly. These results suggest that LAT1 is involved in milk protein synthesis in the mammary glands of lactating dairy cows and that the mTORC1 signaling pathway might be a control point for regulation of LAT1 expression, which could ultimately be used to alter milk protein synthesis.

Fibroblast-like synoviocyte migration is enhanced by IL-17-mediated overexpression of L-type amino acid transporter 1 (LAT1) via the mTOR/4E-BP1 pathway

In rheumatoid arthritis (RA), activated synovial fibroblasts have the ability to invade joint cartilage, actively contributing to joint destruction in RA. The mechanisms underlying this cell migration and invasion remain unclear. Our previous results and data from the GEO profile indicate that the L-type amino acid transporter gene, LAT1, is overexpressed in the synovium of RA. To identify its potential role in RA, fibroblast-like synoviocytes (FLS) from patients with RA were used to determine the effects of suppressing the LAT1 genes using RNA interference and the LAT inhibitor, BCH. We found that BCH exposure reduced the phosphorylation of mTOR and its downstream target 4EBP1, radiolabeled leucine uptake, and migration of RA FLS. LAT1 silencing by siRNA presented effects similar to BCH inhibition. Treatment of cells with IL-17 stimulated the expression of LAT1. In contrast, applying an inhibitor of mTOR pathway, temsirolimus, or silencing eIF4E neutralized the stimulation of IL-17 on LAT1. BCH and siLAT1 also resulted in lower IL-17-stimulated leucine uptake and cell migration. These results suggest that the migration of RA FLS is aggravated by IL-17-mediated overexpression of LAT1 via mTOR/4E-BP1 pathway. In conclusion, further investigation is warranted into LAT1 as a potential target for drug therapies aimed at attenuating migration of transformed-appearing fibroblasts and subsequently preventing further erosion of bone and cartilage.

Supplementation with polyunsaturated fatty acids in pregnant rats with mild diabetes normalizes placental PPARγ and mTOR signaling in female offspring developing gestational diabetes

Maternal diabetes impairs fetoplacental development and programs metabolic diseases in the offspring. We have previously reported that female offspring of pregnant rats with mild diabetes develop gestational diabetes mellitus (GDM) when they become pregnant. Here, we studied the effects of supplementation with polyunsaturated fatty acids (PUFAs) in pregnant mild diabetic rats (F0) by feeding a 6% safflower-oil-enriched diet from day 1 to 14 followed by a 6% chia-oil-enriched diet from day 14 of pregnancy to term. We analyzed maternal metabolic parameters and placental signaling at term in pregnant offspring (F1). The offspring of both PUFAs-treated and untreated mild diabetic rats developed GDM. Although gestational hyperglycemia was not prevented by dietary PUFAs treatment in F0, triglyceridemia and cholesterolemia in F1 mothers were normalized by F0 PUFAs dietary treatment. In the placenta of F1 GDM rats, PPARγ levels were reduced and lipoperoxidation was increased, changes that were prevented by the maternal diets enriched in PUFAs in the F0 generation. Moreover, fetal overgrowth and placental activation of mTOR signaling pathways were reduced in F1 GDM rats whose mothers were treated with PUFAs diets. These results suggest that F0 PUFAs dietary treatment in pregnancies with mild diabetes improves maternal dyslipidemia, fetal overgrowth and placental signaling in female offspring when they become pregnant. We speculate that an increased PUFAs intake in pregnancies complicated by diabetes may prove effective to ameliorate metabolic programming in the offspring, thereby improving the health of future generations.

Impaired placental autophagy in placental malaria

Background

Placental malaria is a major cause of low birthweight, principally due to impaired fetal growth. Intervillositis, a local inflammatory response to placental malaria, is central to the pathogenesis of poor fetal growth as it impairs transplacental amino acid transport. Given the link between inflammation and autophagy, we investigated whether placental malaria-associated intervillositis increased placental autophagy as a potential mechanism in impaired fetal growth.

Methods

We examined placental biopsies collected after delivery from uninfected women (n = 17) and from women with Plasmodium falciparum infection with (n = 14) and without (n = 7) intervillositis. Western blotting and immunofluorescence staining coupled with advanced image analysis were used to quantify the expression of autophagic markers (LC3-II, LC3-I, Rab7, ATG4B and p62) and the density of autophagosomes (LC3-positive puncta) and lysosomes (LAMP1-positive puncta).

Results

Placental malaria with intervillositis was associated with higher LC3-II:LC3-I ratio, suggesting increased autophagosome formation. We found higher density of autophagosomes and lysosomes in the syncytiotrophoblast of malaria-infected placentas with intervillositis. However, there appear to be no biologically relevant increase in LC3B/LAMP1 colocalization and expression of Rab7, a molecule involved in autophagosome/lysosome fusion, was lower in placental malaria with intervillositis, indicating a block in the later stage of autophagy. ATG4B and p62 expression showed no significant difference across histological groups suggesting normal autophagosome maturation and loading of cargo proteins into autophagosomes. The density of autophagosomes and lysosomes in the syncytiotrophoblast was negatively correlated with placental amino acid uptake.

Conclusions

Placental malaria-associated intervillositis is associated with dysregulated autophagy that may impair transplacental amino acid transport, possibly contributing to poor fetal growth.

FTY720-induced endocytosis of yeast and human amino acid transporters is preceded by reduction of their inherent activity and TORC1 inhibition

FTY720 is a sphingoid base analog that acts as an anticancer agent in animal models. Its effect on tumor cells stems largely from its ability to trigger endocytosis of several nutrient transporters. The observation that FTY720 similarly stimulates downregulation of amino acid permeases in yeast suggests that the cellular mechanisms it targets, which are still poorly characterized, are evolutionarily conserved. We here report that adding FTY720 to yeast cells results in rapid inhibition of the intrinsic activity of multiple permeases. This effect is associated with inhibition of the TORC1 kinase complex, which in turn promotes ubiquitin-dependent permease endocytosis. Further analysis of the Gap1 permease showed that FTY720 elicits its ubiquitylation via the same factors that promote this modification when TORC1 is inhibited by rapamycin. We also show that FTY720 promotes endocytosis of the LAT1/SLC7A5 amino acid transporter in HeLa cells, this being preceded by loss of its transport activity and by mTORC1 inhibition. Our data suggest that in yeast, TORC1 deactivation resulting from FTY720-mediated inhibition of membrane transport elicits permease endocytosis. The same process seems to occur in human cells even though our data and previous reports suggest that FTY720 promotes transporter endocytosis via an additional mechanism insensitive to rapamycin.

Placentome Nutrient Transporters and Mammalian Target of Rapamycin Signaling Proteins Are Altered by the Methionine Supply during Late Gestation in Dairy Cows and Are Associated with Newborn Birth Weight

Background: To our knowledge, most research demonstrating a link between maternal nutrition and both fetal growth and offspring development after birth has been performed with nonruminants. Whether such relationships exist in large ruminants is largely unknown.Objective: We aimed to investigate whether increasing the methionine supply during late pregnancy would alter uteroplacental tissue nutrient transporters and mammalian target of rapamycin (mTOR) and their relation with newborn body weight.Methods: Multiparous Holstein cows were used in a randomized complete block design experiment. During the last 28 d of pregnancy, cows were fed a control diet or the control diet plus ethylcellulose rumen-protected methionine (0.9 g/kg dry matter intake) (Mepron; Evonik Nutrition & Care GmbH) to achieve a 2.8:1 ratio of lysine to methionine in the metabolizable protein reaching the small intestine. We collected placentome samples at parturition and used them to assess mRNA and protein expression and the phosphorylation status of mTOR pathway proteins.Results: Newborn body weight was greater in the methionine group than in the control group (44.1 kg and 41.8 kg, respectively; P ≤ 0.05). Increasing the methionine supply also resulted in greater feed intake (15.8 kg/d and 14.6 kg/d), plasma methionine (11.9 μM and 15.3 μM), and plasma insulin (1.16 μg/L and 0.81 μg/L) in cows during late pregnancy. As a result, mRNA expression of genes involved in neutral amino acid transport [solute carrier (SLC) family members SLC3A2, SLC7A5, SLC38A1, and SLC38A10], glucose transport [SLC2A1, SLC2A3, and SLC2A4], and the mTOR pathway [mechanistic target of rapamycin and ribosomal protein S6 kinase B1] were upregulated (P ≤ 0.07) in methionine-supplemented cows. Among 6 proteins in the mTOR pathway, increasing the methionine supply led to greater (P ≤ 0.09) protein expression of α serine-threonine kinase (AKT), phosphorylated (p)-AKT, p-eukaryotic elongation factor 2, and the p-mTOR:mTOR ratio.Conclusion: Supplemental methionine during late gestation increases feed intake and newborn body weight in dairy cows, and this effect may be mediated by alterations in the uteroplacental transport of nondispensable and dispensable amino acids and glucose at least in part through changes in gene transcription and mTOR signaling.

Metformin, the aspirin of the 21st century: its role in gestational diabetes mellitus, prevention of preeclampsia and cancer, and the promotion of longevity

Metformin is everywhere. Originally introduced in clinical practice as an antidiabetic agent, its role as a therapeutic agent is expanding to include treatment of prediabetes mellitus, gestational diabetes mellitus, and polycystic ovarian disease; more recently, experimental studies and observations in randomized clinical trials suggest that metformin could have a place in the treatment or prevention of preeclampsia. This article provides a brief overview of the history of metformin in the treatment of diabetes mellitus and reviews the results of metaanalyses of metformin in gestational diabetes mellitus as well as the treatment of obese, non-diabetic, pregnant women to prevent macrosomia. We highlight the results of a randomized clinical trial in which metformin administration in early pregnancy did not reduce the frequency of large-for-gestational-age infants (the primary endpoint) but did decrease the frequency of preeclampsia (a secondary endpoint). The mechanisms by which metformin may prevent preeclampsia include a reduction in the production of antiangiogenic factors (soluble vascular endothelial growth factor receptor-1 and soluble endoglin) and the improvement of endothelial dysfunction, probably through an effect on the mitochondria. Another potential mechanism whereby metformin may play a role in the prevention of preeclampsia is its ability to modify cellular homeostasis and energy disposition, mediated by rapamycin, a mechanistic target. Metformin has a molecular weight of 129 Daltons and therefore readily crosses the placenta. There is considerable evidence to suggest that this agent is safe during pregnancy. New literature on the role of metformin as a chemotherapeutic adjuvant in the prevention of cancer and in prolonging life and protecting against aging is reviewed briefly. Herein, we discuss the mechanisms of action and potential benefits of metformin.

Maternal folate deficiency causes inhibition of mTOR signaling, down-regulation of placental amino acid transporters and fetal growth restriction in mice

Maternal folate deficiency is linked to restricted fetal growth, however the underlying mechanisms remain to be established. Here we tested the hypothesis that mTOR functions as a folate sensor in vivo in mice and that maternal folate deficiency inhibits placental mTOR signaling and amino acid transporter activity and causes fetal growth restriction. Folate deficient mice had lower serum folate (−60%). In late pregnancy, fetal weight in the folate deficient group was decreased (−17%, p < 0.05), whereas placental weight, litter size and crown rump length were unaltered. Maternal folate deficiency inhibited placental mTORC1 and mTORC2 signaling and decreased trophoblast plasma membrane System A and L amino acid transporter activities and transporter isoform expression. Folate deficiency also caused a decrease in phosphorylation of specific functional readouts of mTORC1 and mTORC2 signaling in multiple maternal and fetal tissues. We have identified a novel specific molecular link between maternal folate availability and fetal growth, involving regulation of placental mTOR signaling by folate, resulting in changes in placental nutrient transport. mTOR folate sensing may have broad biological significance because of the critical role of folate in normal cell function and the wide range of disorders, including cancer, that have been linked to folate availability.

Mechanistic Target of Rapamycin Is a Novel Molecular Mechanism Linking Folate Availability and Cell Function

Folate deficiency has been linked to a wide range of disorders, including cancer, neural tube defects, and fetal growth restriction. Folate regulates cellular function mediated by its involvement in the synthesis of nucleotides, which are needed for DNA synthesis, and its function as a methyl donor, which is critical for DNA methylation. Here we review current data showing that folate sensing by mechanistic target of rapamycin (mTOR) constitutes a novel and distinct pathway by which folate modulates cell functions such as nutrient transport, protein synthesis, and mitochondrial respiration. The mTOR signaling pathway responds to growth factors and changes in nutrient availability to control cell growth, proliferation, and metabolism. mTOR exists in 2 complexes, mTOR complex (mTORC) 1 and mTORC2, which have distinct upstream regulators and downstream targets. Folate deficiency in pregnant mice caused a marked inhibition of mTORC1 and mTORC2 signaling in multiple maternal and fetal tissues, downregulation of placental amino acid transporters, and fetal growth restriction. In addition, folate deficiency in primary human trophoblast (PHT) cells resulted in inhibition of mTORC1 and mTORC2 signaling and decreased the activity of key amino acid transporters. Folate sensing by mTOR in PHT cells is independent of the accumulation of homocysteine and requires the proton-coupled folate transporter (PCFT; solute carrier 46A1). Furthermore, mTORC1 and mTORC2 regulate trophoblast folate uptake by modulating the cell surface expression of folate receptor α and the reduced folate carrier. These findings, which provide a novel link between folate availability and cell function, growth, and proliferation, may have broad biological significance given the critical role of folate in normal cell function and the multiple diseases that have been associated with decreased or excessive folate availability. Low maternal folate concentrations are linked to restricted fetal growth, and we propose that the underlying mechanisms involve trophoblast mTOR folate sensing resulting in inhibition of mTORC1 and mTORC2 and downregulation of placental amino acid transporters.

mTOR folate sensing links folate availability to trophoblast cell function

KEY POINTS

Folate deficiency during pregnancy is associated with restricted fetal growth, although the underlying mechanisms are poorly understood. Here we show that mechanistic target of rapamycin (mTOR) functions as a folate sensor in primary human trophoblast (PHT) cells. Folate sensing by mTOR in PHT cells involves both mTOR Complex 1 and 2 and requires the proton-coupled folate transporter. We report a previously unknown molecular mechanism by which folate regulates trophoblast cell function. Because mTOR is a positive regulator of placental amino acid transport and mitochondrial function, placental mTOR folate sensing may constitute the mechanistic link between maternal folate status and fetal growth. These findings provide new insight into how folate influences human cell physiology and may have implications for our understanding of how altered folate availability causes diseases such as fetal growth restriction, fetal malformations and cancer.

ABSTRACT

Folate is a water-soluble B vitamin that is essential for cellular methylation reactions and DNA synthesis and repair. Low maternal folate levels in pregnancy are associated with fetal growth restriction, but the underlying mechanisms are poorly understood. Mechanistic target of rapamycin (mTOR) links nutrient availability to cell growth and function by regulating gene expression and protein translation. Here we show that mTOR functions as a folate sensor in primary human trophoblast (PHT) cells. Folate deficiency in PHT cells caused inhibition of mTOR signalling and decreased the activity of key amino acid transporters. Folate sensing by mTOR in PHT cells involves both mTOR Complex 1 and 2 and requires the proton-coupled folate transporter (PCFT, SLC46A1). The involvement of PCFT in mTOR folate sensing is not dependent on its function as a plasma membrane folate transporter. Increasing levels of homocysteine had no effect on PHT mTOR signalling, suggesting that mTOR senses low folate rather than high homocysteine. In addition, we demonstrate that maternal serum folate is positively correlated to placental mTORC1 and mTORC2 signalling activity in human pregnancy. We have identified a previously unknown molecular link between folate availability and cell function involving PCFT and mTOR signalling. We propose that mTOR folate sensing in trophoblast cells matches placental nutrient transport, and therefore fetal growth, to folate availability. These findings may have implications for our understanding of how altered folate availability causes human diseases such as fetal growth restriction, fetal malformations and cancer.

Fatty acid and lipid profiles in primary human trophoblast over 90h in culture

Little is known about the mechanisms underlying the preferential transport of long chain polyunsaturated fatty acids (LCPUFA) to the fetus by the syncytiotrophoblast and the role of cytotrophoblasts in placental lipid metabolism and transport. We studied primary human trophoblast (PHT) cells cultured for 90h to determine the fatty acid and lipid composition of cytotrophoblast (18h culture) and syncytiotrophoblast (90h culture) cells. In cultured PHT total lipid fatty acids were significantly (P < 0.05) reduced at 90h compared to 18h in culture including lower levels of palmitic acid (PA, 16:0, -37%), palmitoleic acid (POA, 16:1n-7, -30%), oleic acid (OA, 18:1n-9, -31%), LCPUFA arachidonic acid (AA, 20:4n-6, -28%) and α-linolenic acid (ALA, 18:3n-3, -55%). In major lipid classes, OA and most of the n-3 and n-6 LCPUFA were markedly lower at 90h in TG (-57 to -76%; p < 0.05). In the cellular NEFA, n-6 LCPUFA, dihomo-γ-linolenic acid (DGLA, 20:3n-6) and AA were both reduced by -51% and DHA was -55% lower (p < 0.05) at 90h. In contrast, phospholipid FA content did not change between cytotrophoblasts and syncytiotrophoblast except for OA, which decreased by -62% (p < 0.05). Decreasing PHT TG and NEFA lipid content at 90h in culture is likely due to processes related to differentiation such as alterations in lipase activity that occur as cytotrophoblast cells differentiate. We speculate that syncytiotrophoblast prioritizes PL containing AA and DHA for transfer to the fetus by mobilizing FA from storage lipids.

Optimal ratios of essential amino acids stimulate β-casein synthesis via activation of the mammalian target of rapamycin signaling pathway in MAC-T cells and bovine mammary tissue explants

Amino acids are the building blocks of proteins and serve as key molecular components upstream of the signaling pathways that regulate protein synthesis. The objective of this study was to systematically investigate the effect of essential AA ratios on milk protein synthesis in vitro and to elucidate some of the underlying mechanisms. Triplicate cultures of MAC-T cells and bovine mammary tissue explants (MTE) were incubated with the optimal AA ratio (OPAA; Lys:Met, 2.9:1; Thr:Phe, 1.05:1; Lys:Thr, 1.8:1; Lys:His, 2.38:1; and Lys:Val, 1.23:1) in the presence of rapamycin (control), OPAA, a Lys:Thr ratio of 2.1:1, a Lys:Thr ratio of 1.3:1, a Lys:His ratio of 3.05:1, or a Lys:Val ratio of 1.62:1 for 12 h; the other AA concentrations were equal to OPAA. In some experiments, the cells were cultured with OPAA with or without rapamycin (100 ng/mL) or with mammalian target of rapamycin (mTOR) small interference RNA, and the MTE were exposed to OPAA with rapamycin for β-casein expression. Among the treatments, the expression of β-casein was greatest in the MTE cultured with OPAA. In MAC-T cells, the OPAA upregulated the mRNA expression of SLC1A5 and SLC7A5 but downregulated the expression of IRS1, AKT3, EEF1A1, and EEF2 compared with the control. The OPAA had no effect on the mTOR phosphorylation status but increased the phosphorylation of S6K1 and RPS6. When the MTE were treated with rapamycin in the presence of OPAA, the expression of β-casein was markedly decreased. The phosphorylation of RPS6 and 4EBP1 also was reduced in MAC-T cells. A similar negative effect on the expression of RPS6KB1 and EIF4EBP1 was detected when the cells were cultured with either rapamycin or mTOR small interference RNA. The optimal AA ratio stimulated β-casein expression partly by enhancing the transport of AA into the cells, cross-talk with insulin signaling and a subsequent enhancement of mTOR signaling, or translation elongation in both MAC-T cells and bovine MTE.

Essential Roles of L-Type Amino Acid Transporter 1 in Syncytiotrophoblast Development by Presenting Fusogenic 4F2hc

The layers of the epithelial syncytium, i.e., syncytiotrophoblasts, differentiate from chorionic trophoblasts via cell fusion and separate maternal and fetal circulations in hemochorial placentas. L-type amino acid transporter 1 (LAT1) and its covalently linked ancillary subunit 4F2hc are colocalized on both maternal and fetal surfaces of syncytiotrophoblasts, implying their roles in amino acid transfer through the placental barrier. In this study, LAT1 knockout, in addition, revealed a novel role of LAT1 in syncytiotrophoblast development. LAT1 at midgestation was selectively expressed in trophoblastic lineages in the placenta, exclusively as a LAT1-4F2hc heterodimer. In LAT1 homozygous knockout mice, chorionic trophoblasts remained largely mononucleated, and the layers of syncytiotrophoblasts were almost completely absent. The amount of 4F2hc protein, which possesses a fusogenic function in trophoblastic cells, as well as in virus-infected cells, was drastically reduced by LAT1 knockout, with less affecting the mRNA level. Knockdown of LAT1 in trophoblastic BeWo cells also reduced 4F2hc protein and suppressed forskolin-induced cell fusion. These results demonstrate a novel fundamental role of LAT1 to support the protein expression of 4F2hc via a chaperone-like function in chorionic trophoblasts and to promote syncytiotrophoblast formation by contributing to cell fusion in the developing placenta.

Prenatal high-fat diet alters placental morphology, nutrient transporter expression, and mtorc1 signaling in rat

OBJECTIVE

This study aimed to determine how the rat placenta and fetus respond to maternal high-fat (HF) diet during gestation and to identify the possible mechanisms.

METHODS

Pregnant Sprague-Dawley rats were fed with standard chow (13.5% fat) or HF (60% fat) diet during gestation. Placentas were collected on gestation day 21.

RESULTS

HF dams had greater fat mass, higher plasma leptin, lower plasma adiponectin, and impaired glucose tolerance during pregnancy. The placental labyrinth thickness was reduced in both male and female fetuses of HF dams. In HF male placentas, glucose transporter 3 gene expression, system A amino acid transporter (SNAT) 2 gene expression, and SNAT2 protein expression were increased through the activation of the mTORC1 4EBP1 branch. In HF female placentas, gene expression of insulin-like growth factor 2 (IGF2) and IGF2 receptor was elevated compared to placentas of females fed standard chow. Although male and female placentas responded differently to prenatal HF diet exposure, both male and female fetal weight was not altered by maternal HF diet.

CONCLUSIONS

Placenta responds and adapts to maternal metabolic changes by altering placental layer thickness, mTORC1 signaling, expression of nutrient transporters, and growth factors in a sex-specific manner.

Exposure of pregnant mice to triclosan impairs placental development and nutrient transport

Triclosan (TCS) is associated with spontaneous abortions and fetal growth restriction. Here, we showed that when pregnant mice were treated with 8 mg/kg TCS (8-TCS mice) on gestational days (GD) 6–18 fetal body weights were lower than controls. Placental weights and volumes were reduced in 8-TCS mice. The placental proliferative cells and expression of PCNA and Cyclin D3 on GD13 were remarkably decreased in 8-TCS mice. The decreases in activities and expression of placental System A amino acid or glucose transporters on GD14 and GD17 were observed in 8-TCS mice. Levels of serum thyroxine (T4) and triiodothyronine (T3) were lower in 8-TCS mice than those in controls. Declines of placental Akt, mTOR and P70S6K phosphorylation in 8-TCS mice were corrected by L-thyroxinein (T4). Treating 8-TCS mice with T4 rescued the placental cell proliferation and recovered the activity and expression of amino acid and glucose transporters, which were sensitive to mTOR inhibition by rapamycin. Furthermore, the replacement of T4 could rescue the decrease in fetal body weight, which was blocked by rapamycin. These findings indicate that TCS-induced hypothyroxinemia in gestation mice through reducing Akt-mTOR signaling may impair placental development and nutrient transfer leading to decreases in fetal body weight.

1,25-Dihydroxy vitamin D3 stimulates system A amino acid transport in primary human trophoblast cells

Vitamin D deficiency during pregnancy is linked to adverse perinatal outcomes such as small for gestational age infants. Recent evidence suggests that changes in placental amino acid transport contribute to altered fetal growth. We tested the hypothesis that 1,25-dihydroxy vitamin D3 increases the gene expression of System A and L amino acid transporter isoforms and stimulates placental amino acid transport activity in cultured primary human trophoblast cells mediated by mTOR signaling. Treatment with 1,25-dihydroxy vitamin D3 significantly increased mRNA expression of the System A isoform SNAT2 and System A activity, but had no effect on System L and did not affect mTOR signaling. siRNA silencing of the vitamin D receptor prevented 1,25-dihydroxy vitamin D3-stimulated System A transport. In conclusion, 1,25-dihydroxy vitamin D3 regulates System A activity through increased mRNA expression of SNAT2 transporters. Effects on placental amino acid transport may be the mechanism underlying the association between maternal vitamin D status and fetal growth.

Inhibition of placental mTOR signaling provides a link between placental malaria and reduced birthweight

BACKGROUND

Placental Plasmodium falciparum malaria can trigger intervillositis, a local inflammatory response more strongly associated with low birthweight than placental malaria infection alone. Fetal growth (and therefore birthweight) is dependent on placental amino acid transport, which is impaired in placental malaria-associated intervillositis. Here, we tested the hypothesis that mechanistic target of rapamycin (mTOR) signaling, a pathway known to regulate amino acid transport, is inhibited in placental malaria-associated intervillositis, contributing to lower birthweight.

METHODS

We determined the link between intervillositis, mTOR signaling activity, and amino acid uptake in tissue biopsies from both uninfected placentas and malaria-infected placentas with and without intervillositis, and in an in vitro model using primary human trophoblast (PHT) cells.

RESULTS

We demonstrated that (1) placental mTOR activity is lower in cases of placental malaria with intervillositis, (2) placental mTOR activity is negatively correlated with the degree of inflammation, and (3) inhibition of placental mTOR activity is associated with reduced placental amino acid uptake and lower birthweight. In PHT cells, we showed that (1) inhibition of mTOR signaling is a mechanistic link between placental malaria-associated intervillositis and decreased amino acid uptake and (2) constitutive mTOR activation partially restores amino acid uptake.

CONCLUSIONS

Our data support the concept that inhibition of placental mTOR signaling constitutes a mechanistic link between placental malaria-associated intervillositis and decreased amino acid uptake, which may contribute to lower birthweight. Restoring placental mTOR signaling in placental malaria may increase birthweight and improve neonatal survival, representing a new potential therapeutic approach.

Metabolic Reprogramming in Brain Tumors

Next-generation sequencing has substantially enhanced our understanding of the genetics of primary brain tumors by uncovering several novel driver genetic alterations. How many of these genetic modifications contribute to the pathogenesis of brain tumors is not well understood. An exciting paradigm emerging in cancer biology is that oncogenes actively reprogram cellular metabolism to enable tumors to survive and proliferate. We discuss how some of these genetic alterations in brain tumors rewire metabolism. Furthermore, metabolic alterations directly impact epigenetics well beyond classical mechanisms of tumor pathogenesis. Metabolic reprogramming in brain tumors is also influenced by the tumor microenvironment contributing to drug resistance and tumor recurrence. Altered cancer metabolism can be leveraged to noninvasively image brain tumors, which facilitates improved diagnosis and the evaluation of treatment effectiveness. Many of these aspects of altered metabolism provide novel therapeutic opportunities to effectively treat primary brain tumors.