Fredrick J. Rosario

Activation of Placental mTOR Signaling and Amino Acid Transporters in Obese Women Giving Birth to Large Babies

CONTEXT Babies of obese women are often large at birth, which is associated with perinatal complications and metabolic syndrome later in life. The mechanisms linking maternal obesity to fetal overgrowth are largely unknown. OBJECTIVE We tested the hypothesis that placental insulin/IGF-I and mammalian target of rapamycin (mTOR) signaling is activated and amino acid transporter activity is increased in large babies of obese women. DESIGN AND SETTING Pregnant women were recruited prospectively for collection of placental tissue at a university hospital and academic biomedical center. PATIENTS OR OTHER PARTICIPANTS Twenty-three Swedish pregnant women with first trimester body mass index ranging from 18.5 to 44.9 kg/m(2) and with uncomplicated pregnancies participated in the study. INTERVENTIONS There were no interventions. MAIN OUTCOME MEASURES We determined the phosphorylation of key signaling molecules (including Akt, IRS-1, S6K1, 4EBP-1, RPS6, and AMPK) in the placental insulin/IGF-I, AMPK, and mTOR signaling pathways. The activity and protein expression of the amino acid transporter systems A and L were measured in syncytiotrophoblast microvillous plasma membranes. RESULTS Birth weights (range, 3025-4235 g) were positively correlated to maternal body mass index (P < 0.05). The activity of placental insulin/IGF-I and mTOR signaling was positively correlated (P < 0.001), whereas AMPK phosphorylation was inversely (P < 0.05) correlated to birth weight. Microvillous plasma membrane system A, but not system L, activity and protein expression of the system A isoform SNAT2 were positively correlated to birth weight (P < 0.001). CONCLUSIONS Up-regulation of specific placental amino acid transporter isoforms may contribute to fetal overgrowth in maternal obesity. This effect may be mediated by activation of insulin/IGF-I and mTOR signaling pathways, which are positive regulators of placental amino acid transporters.

Maternal Protein Restriction in the Rat Inhibits Placental Insulin, mTOR, and STAT3 Signaling and Down-Regulates Placental Amino Acid Transporters

The mechanisms underlying reduced fetal growth in response to maternal protein restriction are not well established. Maternal levels of insulin, IGF-I, and leptin are decreased in rats fed a low protein (LP) diet. Because these hormones stimulate placental amino acid transporters in vitro, we hypothesized that maternal protein restriction inhibits placental leptin, insulin/IGF-I, and mammalian target of rapamycin signaling and down-regulates the expression and activity of placental amino acid transporters. Pregnant rats were fed either an isocaloric low protein (LP, 4% protein) or control diet (18% protein) and studied at gestational day (GD)15, GD19, or GD21 (term 23). At GD19 and GD21, placental expression of phosphorylated eukaryotic initiation factor 4E binding protein 1 (Thr-36/46 or Thr-70) and phosphorylated S6 ribosomal protein (Ser-235/236) was decreased in the LP group. In addition, placental expression of phosphorylated S6 kinase 1 (Thr-389), phosphorylated Akt (Thr-308), and phosphorylated signal transducer and activator of transcription 3 (Tyr-705) was reduced at GD21. In microvillous plasma membranes (MVM) isolated from placentas of LP animals, protein expression of the sodium-coupled neutral amino acid transporter (SNAT)2 and the large neutral amino acid transporters 1 and 2 was reduced at GD19 and GD21. MVM SNAT1 protein expression was reduced at GD21 in LP rats. SNAT4 and 4F2 heavy chain expression in MVM was unaltered. System A and L amino acid transporter activity was decreased in MVM from LP animals at GD19 and GD21. In conclusion, maternal protein restriction inhibits placental insulin, mammalian target of rapamycin signaling, and signal transducer and activator of transcription 3 signaling, which is associated with a down-regulation of placental amino acid transporters. We speculate that maternal endocrine and metabolic control of placental nutrient transport reduces fetal growth in response to protein restriction.

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

Inadequate nutrient supply during fetal life results in intrauterine growth restriction (IUGR), which may lead to obesity, diabetes, and cardiovascular disease later in life. A decreased placental amino acid transporter activity has been implicated in the pathophysiology of IUGR; however, the mechanisms regulating placental amino acid transporters in the human are largely unknown. We show that inhibition of mammalian target of rapamycin complex 1 or 2 markedly decreases the activity of key placental amino acid transporters in cultured primary human placental cells, mediated by modulating the movement of specific transporter isoforms between the cell interior and the plasma membrane. Because mTOR signalling is inhibited in the IUGR placenta, these findings identify one possible mechanism by which fetal nutrient supply is reduced in this pregnancy complication. Our data may help us better understand the regulation of amino acid transporters and the molecular mechanisms underlying IUGR.

Down-regulation of placental mTOR, insulin/IGF-I signaling, and nutrient transporters in response to maternal nutrient restriction in the baboon

The mechanisms by which maternal nutrient restriction (MNR) causes reduced fetal growth are poorly understood. We hypothesized that MNR inhibits placental mechanistic target of rapamycin (mTOR) and insulin/IGF‐I signaling, down‐regulates placental nutrient transporters, and decreases fetal amino acid levels. Pregnant baboons were fed control (ad libitum, n=11) or an MNR diet (70% of controls, n=11) from gestational day (GD) 30. Placenta and umbilical blood were collected at GD 165. Western blot was used to determine the phosphorylation of proteins in the mTOR, insulin/IGF‐I, ERK1/2, and GSK‐3 signaling pathways in placental homogenates and expression of glucose transporter 1 (GLUT‐1), taurine transporter (TAUT), sodium‐dependent neutral amino acid transporter (SNAT), and large neutral amino acid transporter (LAT) isoforms in syncytiotrophoblast microvillous membranes (MVMs). MNR reduced fetal weights by 13%, lowered fetal plasma concentrations of essential amino acids, and decreased the phosphorylation of placental S6K, S6 ribosomal protein, 4E‐BP1, IRS‐1, Akt, ERK‐1/2, and GSK‐3. MVM protein expression of GLUT‐1, TAUT, SNAT‐2 and LAT‐1/2 was reduced in MNR. This is the first study in primates exploring placental responses to maternal undernutrition. Inhibition of placental mTOR and insulin/IGF‐I signaling resulting in down‐regulation of placental nutrient transporters may link maternal undernutrition to restricted fetal growth.—Kavitha, J. V., Rosario, F. J., Nijland, M. J., McDonald, T. J., Wu, G., Kanai, Y., Powell, T. L., Nathanielsz, P. W., Jansson, T. Down‐regulation of placental mTOR, insulin/IGF‐I signaling, and nutrient transporters in response to maternal nutrient restriction in the baboon. FASEB J. 28, 1294–1305 (2014). www.fasebj.org

Chronic maternal infusion of full‐length adiponectin in pregnant mice down‐regulates placental amino acid transporter activity and expression and decreases fetal growth

•  Fetal growth is positively correlated to maternal adiposity, but the underlying mechanisms remain largely unknown. •  Maternal circulating levels of adiponectin, a hormone secreted by adipose tissue, are negatively correlated to maternal adiposity and fetal growth, suggesting that maternal adiponectin may limit fetal growth. •  Here we report that chronic administration of adiponectin to pregnant mice inhibits placental insulin and mammalian target of rapamycin (mTOR) signalling, down‐regulates the activity and expression of key placental nutrient transporters, and decreases fetal growth. •  We have identified a novel physiological mechanism by which the endocrine functions of maternal adipose tissue influence fetal growth by altering placental function. •  These findings may help us better understand the factors determining birth weight in normal pregnancies and in pregnancy complications associated with altered maternal adiponectin levels such as obesity and gestational diabetes.

Adiponectin supplementation in pregnant mice prevents the adverse effects of maternal obesity on placental function and fetal growth.

Significance Obesity and metabolic syndrome may, in part, originate in fetal life. In particular, babies of mothers with obesity and/or gestational diabetes mellitus (GDM) are often large at birth and have increased adiposity, which predisposes them to the development of metabolic disease later in life. Maternal obesity and GDM are typically associated with low circulating levels of adiponectin (ADN), and we found that ADN supplementation to pregnant obese mice completely normalized the changes in placental function and prevented fetal overgrowth caused by maternal obesity. These findings suggest that strategies to increase ADN levels in maternal obesity and GDM may alleviate the adverse effects of these pregnancy complications on the fetus. Mothers with obesity or gestational diabetes mellitus have low circulating levels of adiponectin (ADN) and frequently deliver large babies with increased fat mass, who are susceptible to perinatal complications and to development of metabolic syndrome later in life. It is currently unknown if the inverse correlation between maternal ADN and fetal growth reflects a cause-and-effect relationship. We tested the hypothesis that ADN supplementation in obese pregnant dams improves maternal insulin sensitivity, restores normal placental insulin/mechanistic target of rapamycin complex 1 (mTORC1) signaling and nutrient transport, and prevents fetal overgrowth. Compared with dams on a control diet, female C57BL/6J mice fed an obesogenic diet before mating and throughout gestation had increased fasting serum leptin, insulin, and C-peptide, and reduced high-molecular-weight ADN at embryonic day (E) 18.5. Placental insulin and mTORC1 signaling was activated, peroxisome proliferator-activated receptor-α (PPARα) phosphorylation was reduced, placental transport of glucose and amino acids in vivo was increased, and fetal weights were 29% higher in obese dams. Maternal ADN infusion in obese dams from E14.5 to E18.5 normalized maternal insulin sensitivity, placental insulin/mTORC1 and PPARα signaling, nutrient transport, and fetal growth without affecting maternal fat mass. Using a mouse model with striking similarities to obese pregnant women, we demonstrate that ADN functions as an endocrine link between maternal adipose tissue and fetal growth by regulating placental function. Importantly, maternal ADN supplementation reversed the adverse effects of maternal obesity on placental function and fetal growth. Improving maternal ADN levels may serve as an effective intervention strategy to prevent fetal overgrowth caused by maternal obesity.

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

BackgroundPlacental 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.MethodsWe 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.ResultsWe 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.ConclusionsOur 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.

Increased placental nutrient transport in a novel mouse model of maternal obesity with fetal overgrowth

To identify possible mechanisms linking obesity in pregnancy to increased fetal adiposity and growth, a unique mouse model of maternal obesity associated with fetal overgrowth was developed, and the hypothesis that maternal obesity causes up‐regulation of placental nutrient transporter expression and activity was tested.

Increased ubiquitination and reduced plasma membrane trafficking of placental amino acid transporter SNAT-2 in human IUGR.

Inhibition of placental mechanistic target of rapamycin (mTOR) signalling, which activates NEDD4-2 (neural precursor cell expressed developmentally down-regulated protein 4-2) ubiquitin ligase leading to increased sodium-coupled neutral amino acid transporter 2 (SNAT-2) ubiquitination and removal from the syncytiotrophoblast plasma membrane may constitute a key mechanism underlying decreased placental amino acid transport in human IUGR.

Activation of placental insulin and mTOR signaling in a mouse model of maternal obesity associated with fetal overgrowth

Fetal overgrowth is common in obese women and is associated with perinatal complications and increased risk for the child to develop metabolic syndrome later in life. Placental nutrient transport capacity has been reported to be increased in obese women giving birth to large infants; however, the underlying mechanisms are not well established. Obesity in pregnancy is characterized by elevated maternal serum insulin and leptin, hormones that stimulate placental amino acid transporters in vitro. We hypothesized that maternal obesity activates placental insulin/IGF-I/mTOR and leptin signaling pathways. We tested this hypothesis in a mouse model of obesity in pregnancy that is associated with fetal overgrowth. C57BL/6J female mice were fed a control (C) or a high-fat/high-sugar (HF/HS) pelleted diet supplemented by ad libitum access to sucrose (20%) solution. Placentas were collected at embryonic day 18.5. Using Western blot analysis, placental mTOR activity was determined along with energy, inflammatory, leptin, and insulin signaling pathways (upstream modulators of mTOR). Phosphorylation of S6 ribosomal protein (S-235/236), 4E-BP1 (T-37/46), Insulin receptor substrate 1 (Y-608), Akt (T-308), and STAT-3 (Y-705) was increased in obese dams. In contrast, expression of placental caspase-1, IкBα, IL-1β, and phosphorylated-JNK(p46/54-T183/Y185) was unaltered. Fetal amino acid availability is a key determinant of fetal growth. We propose that activation of placental insulin/IGF-I/mTOR and leptin signaling pathways in obese mice stimulates placental amino acid transport and contributes to increased fetal growth.