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Differential levels of amino acid transporters System L and ASCT2, and the mTOR protein in placenta of preeclampsia and IUGR.

Aiko Y, Askew DJ, Aramaki S, Myoga M, Tomonaga C, Hachisuga T, Suga R, Kawamoto T, Tsuji M, Shibata E - BMC Pregnancy Childbirth (2014)

Bottom Line: Total cellular ASCT2 transporter protein levels were similar in all groups, however, levels of ASCT2 protein localized to the ST microvillous membrane (MVM) were significantly lower in IUGR compared to both full-term and pre-term pregnancies (P = 0.0006, 0.03, respectively).Additionally, ASCT2 and mTOR protein levels were positively associated with maternal pre-pregnancy BMI (P = 0.046, 0.048, respectively).Third, a physiological link between transporter expression and pre-pregnancy BMI is suggested based upon a positive association observed with ASCT2 and mTOR expression values.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Obstetrics and Gynecology, School of Medicine, University of Occupational and Environmental Health, Kitakyushu, Fukuoka, Japan. age-s@med.uoeh-u.ac.jp.

ABSTRACT

Background: Sufficient amino acid transport activity (AAT) is indispensable for appropriate fetal growth. Studies suggest that placental nutrient uptake activity is responsive to both maternal and fetal nutrient demands. We hypothesize that under conditions of limited nutrient availability to the fetus, as often present in preeclampsia, intrauterine growth restriction (IUGR), and insufficient weight-gain during pregnancy, a general adaptive response aimed to increase amino acid transport activity may be observed in the placenta.

Method: A total of 40 placentas from full-term (n = 10) and pre-term (average gestational period = 34.8 weeks, n = 10) normal pregnancies, IUGR (n = 10), and preeclampsia (n = 10) associated pregnancies were looked at by immunohistochemistry followed by relative qualitative scoring to compare expression levels and localization of System L, ASCT2, and mTOR proteins.

Result: Microvillous syncytiotrophoblast (ST) in placenta of pregnancies complicated by IUGR or preeclampsia (PE) showed significant increases in the levels of System L amino acid transport proteins 4F2hc and LAT1 compared to both full-term control and pre-term (early gestation control) pregnancies seperately (p < 0.05). Elevated mTOR protein was uniquely higher in IUGR placentas compared to full-term controls (P = 0.0026). Total cellular ASCT2 transporter protein levels were similar in all groups, however, levels of ASCT2 protein localized to the ST microvillous membrane (MVM) were significantly lower in IUGR compared to both full-term and pre-term pregnancies (P = 0.0006, 0.03, respectively). Additionally, ASCT2 and mTOR protein levels were positively associated with maternal pre-pregnancy BMI (P = 0.046, 0.048, respectively).

Conclusion: There are three important findings based upon the present study. First, in conditions of limited nutrient availability, such as PE or IUGR, there is an overall increase in the level of System L and mTOR protein expression in the ST, suggestive of an adaptive response. Second, a decrease in ASCT2 protein at the ST MVM suggests a post-translational event that may decrease AAT activity in IUGR placentas. Third, a physiological link between transporter expression and pre-pregnancy BMI is suggested based upon a positive association observed with ASCT2 and mTOR expression values.

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ASCT2 protein localization within the syncytiotrophoblast. ASCT2 protein was detected by immunohistochemistry in the placenta of A, full-term control, B, pre-term control, C, preeclampsia and D, intrauterine growth restriction-associated pregnancies. E, ASCT2 protein expression levels were estimated in the syncytiotrophoblast, including subcellular localization at the plasma membrane (PM), microvillus membrane (MVM), and the intracellular compartment (IC) (* P < 0.05, size bar = 40 mM).
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Figure 4: ASCT2 protein localization within the syncytiotrophoblast. ASCT2 protein was detected by immunohistochemistry in the placenta of A, full-term control, B, pre-term control, C, preeclampsia and D, intrauterine growth restriction-associated pregnancies. E, ASCT2 protein expression levels were estimated in the syncytiotrophoblast, including subcellular localization at the plasma membrane (PM), microvillus membrane (MVM), and the intracellular compartment (IC) (* P < 0.05, size bar = 40 mM).

Mentions: In addition to overall protein levels within the ST layer, we also wished to compare AAT protein localization, a common mechanism of AAT activity regulation[30,41]. By IHC, both 4F2hc and LAT1 appeared relatively diffuse, with proteins being detected in ST cytoplasm and MVM, making a quantitative estimation with respect to localization very difficult. ASCT2 exhibited strong staining of the cytotrophoblast as well as ST basal plasma membrane, and this staining appeared consistent across all samples. However, different patterns of staining with respect to ST intracellular cytoclasmic space and MVM localization were present within the sample set (Figure 4, A-D). The same blinded scoring system was employed to grade ST cytoplasmic and MVM localized staining intensity for ASCT2. Pre-term control and PE placenta samples both exhibited reduced levels of ASCT2 at the MVM and in the intracellular compartment compared to full-term controls, but these differences were non-significant. The IUGR group exhibited the lowest ASCT2 levels at the MVM (ASCT2MVM) and in the intracellular compartment (ASCT2IC) (Figure 4). IUGR ASCT2MVM levels were significantly different from both full-term and pre-term control groups (P = 0.0006, 0.017, respectively), and IUGR ASCT2IC was significantly lower than the full-term control group (P = 0.03, Figure 4E).


Differential levels of amino acid transporters System L and ASCT2, and the mTOR protein in placenta of preeclampsia and IUGR.

Aiko Y, Askew DJ, Aramaki S, Myoga M, Tomonaga C, Hachisuga T, Suga R, Kawamoto T, Tsuji M, Shibata E - BMC Pregnancy Childbirth (2014)

ASCT2 protein localization within the syncytiotrophoblast. ASCT2 protein was detected by immunohistochemistry in the placenta of A, full-term control, B, pre-term control, C, preeclampsia and D, intrauterine growth restriction-associated pregnancies. E, ASCT2 protein expression levels were estimated in the syncytiotrophoblast, including subcellular localization at the plasma membrane (PM), microvillus membrane (MVM), and the intracellular compartment (IC) (* P < 0.05, size bar = 40 mM).
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4060848&req=5

Figure 4: ASCT2 protein localization within the syncytiotrophoblast. ASCT2 protein was detected by immunohistochemistry in the placenta of A, full-term control, B, pre-term control, C, preeclampsia and D, intrauterine growth restriction-associated pregnancies. E, ASCT2 protein expression levels were estimated in the syncytiotrophoblast, including subcellular localization at the plasma membrane (PM), microvillus membrane (MVM), and the intracellular compartment (IC) (* P < 0.05, size bar = 40 mM).
Mentions: In addition to overall protein levels within the ST layer, we also wished to compare AAT protein localization, a common mechanism of AAT activity regulation[30,41]. By IHC, both 4F2hc and LAT1 appeared relatively diffuse, with proteins being detected in ST cytoplasm and MVM, making a quantitative estimation with respect to localization very difficult. ASCT2 exhibited strong staining of the cytotrophoblast as well as ST basal plasma membrane, and this staining appeared consistent across all samples. However, different patterns of staining with respect to ST intracellular cytoclasmic space and MVM localization were present within the sample set (Figure 4, A-D). The same blinded scoring system was employed to grade ST cytoplasmic and MVM localized staining intensity for ASCT2. Pre-term control and PE placenta samples both exhibited reduced levels of ASCT2 at the MVM and in the intracellular compartment compared to full-term controls, but these differences were non-significant. The IUGR group exhibited the lowest ASCT2 levels at the MVM (ASCT2MVM) and in the intracellular compartment (ASCT2IC) (Figure 4). IUGR ASCT2MVM levels were significantly different from both full-term and pre-term control groups (P = 0.0006, 0.017, respectively), and IUGR ASCT2IC was significantly lower than the full-term control group (P = 0.03, Figure 4E).

Bottom Line: Total cellular ASCT2 transporter protein levels were similar in all groups, however, levels of ASCT2 protein localized to the ST microvillous membrane (MVM) were significantly lower in IUGR compared to both full-term and pre-term pregnancies (P = 0.0006, 0.03, respectively).Additionally, ASCT2 and mTOR protein levels were positively associated with maternal pre-pregnancy BMI (P = 0.046, 0.048, respectively).Third, a physiological link between transporter expression and pre-pregnancy BMI is suggested based upon a positive association observed with ASCT2 and mTOR expression values.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Obstetrics and Gynecology, School of Medicine, University of Occupational and Environmental Health, Kitakyushu, Fukuoka, Japan. age-s@med.uoeh-u.ac.jp.

ABSTRACT

Background: Sufficient amino acid transport activity (AAT) is indispensable for appropriate fetal growth. Studies suggest that placental nutrient uptake activity is responsive to both maternal and fetal nutrient demands. We hypothesize that under conditions of limited nutrient availability to the fetus, as often present in preeclampsia, intrauterine growth restriction (IUGR), and insufficient weight-gain during pregnancy, a general adaptive response aimed to increase amino acid transport activity may be observed in the placenta.

Method: A total of 40 placentas from full-term (n = 10) and pre-term (average gestational period = 34.8 weeks, n = 10) normal pregnancies, IUGR (n = 10), and preeclampsia (n = 10) associated pregnancies were looked at by immunohistochemistry followed by relative qualitative scoring to compare expression levels and localization of System L, ASCT2, and mTOR proteins.

Result: Microvillous syncytiotrophoblast (ST) in placenta of pregnancies complicated by IUGR or preeclampsia (PE) showed significant increases in the levels of System L amino acid transport proteins 4F2hc and LAT1 compared to both full-term control and pre-term (early gestation control) pregnancies seperately (p < 0.05). Elevated mTOR protein was uniquely higher in IUGR placentas compared to full-term controls (P = 0.0026). Total cellular ASCT2 transporter protein levels were similar in all groups, however, levels of ASCT2 protein localized to the ST microvillous membrane (MVM) were significantly lower in IUGR compared to both full-term and pre-term pregnancies (P = 0.0006, 0.03, respectively). Additionally, ASCT2 and mTOR protein levels were positively associated with maternal pre-pregnancy BMI (P = 0.046, 0.048, respectively).

Conclusion: There are three important findings based upon the present study. First, in conditions of limited nutrient availability, such as PE or IUGR, there is an overall increase in the level of System L and mTOR protein expression in the ST, suggestive of an adaptive response. Second, a decrease in ASCT2 protein at the ST MVM suggests a post-translational event that may decrease AAT activity in IUGR placentas. Third, a physiological link between transporter expression and pre-pregnancy BMI is suggested based upon a positive association observed with ASCT2 and mTOR expression values.

Show MeSH
Related in: MedlinePlus