PPARγ Involved In The Regulation Of Amino Acid Transporters In Human Placen1Syncytiotrophob Lasts And Its Mechanism

The exchange of nutrients across the placenta is indispensable for the growth of fetusover the course of gestation. The dysfunction of placental transportation is considered to beone of major cause of fetal overgrowth and intrauterine growth restriction (IUGR), apregnancy complication not only associated with maternal and perinatal morbidity, but alsoregarded as a risk factor for diabetes and cardiovascular disease in adult age. Amino acids,which are essential for synthesis of protein and many other substances, play an importantrole in fetal growth. The smooth transportation of amino acids via the placenta relies oncooperation of various transporters in the microvillous membranes (MVM) and basalplasma membranes (BM) of the syncytiotrophoblasts, the main functional cells in theplacenta. There is so many evidence that the activity of system A amino acid transporter inIUGR group is significantly lower compared with normal pregnancies, and the activity ispositively related to the severity of IUGR. The same phenomenon also occurred in systemL and TAUT amino acid transporter.PPAR γ is one of the isoforms of PPARs, which is belonging to nuclear receptorsuperfamily. PPAR γ, known as the ‘master’ gene of fat cell biology and differentiation,appears to have a pivotal role in placental development. Waite shown that the activators ofPPAR-γ (fatty acids and lipid metabolites) in maternal circulation elevated obviously(about twofold) during normal pregnancy, indicating that increased activation of PPAR γ isrequired for maternal metabolism throughout pregnancy. Recently, Marta Díaz et al hasdemonstrated that PPAR γ mRNA expression was found to be low in placentas of SGAfetuses and to associate positively to fetal and placental weights, suggesting that there maybe a closely link between PPAR γ in placentas and fetal growth.So we carry out this experiment to investigate whether PPAR γ can regulate theexpression of system A, L and TAUT amino acid transporters in human placental cells, andthe mechanism involved in it.We take human placental trophoblast cells as the object of study. Using the PPAR γagonist rosiglitazone and antagonist GW9662to treat the cells, we revealed thephenomenon that rosiglitazone can regulate the expression of subtypes of three systemamino acid transporters. Then chromatin immunoprecipitation and siRNA interferencewere utilized to explore the molecular mechanism. Finally we collected human placentaltissue which from the women who give birth to small-for-gestational-age, apprioate-for-gestational-age and large-for-gestational-age babies, and measured theprotein expression of PPAR γ and subtypes of amino acid transporters.Main results and conclusions are as follows:1. PPAR γ involved in the regulation of subtypes of three systemamino acid transporters in human placental cellsThe mRNA and protein levels of ATA1、ATA2、ATA4、LAT1、LAT2、TAUT weredetected in placental trophoblast cells. PPAR γ agonist rosiglitazone dose-dependentlystimulated the expression of LAT1、LAT2、TAUT, but have no effect on the expression ofATA1、ATA2、ATA4.2. Mechanism of PPAR γ on LAT1、LAT2、TAUT expression1. Treating placental cells with PPAR γ antagonist GW9662, nature-ligand15d-PGJ2and highly selective agonist GW1929respectively, we found that not only15d-PGJ2butalso GW1929can up-regulate the expression of LAT1、LAT2、TAUT, and GW9662reversed the effects of rosiglitazone. And transfected the placental cells with PPAR γsiRNA also abolished the effect by rosiglitazone.2. Transfecting placental cells with RXRa siRNA, we found that the effect ofrosiglitazone was abolished.3. Using the protein synthesis inhibitor CHX to treat cells, we found that the effect ofrosiglitazone on LAT1and TAUT was abolished, while the effect of rosiglitazone onLAT2was not influenced.4. The Mithramycin A treatment on cells can reverse the effects of rosiglitazone onLAT1and TAUT.5. The chromatin immunoprecipitation certify that rosiglitazone can promote thecombination of SP-1and promoter of LAT1and TAUT genes.3.The expression of LAT1、LAT2、TAUT and PPARγin placentaltissue from the women who give birth to small-for-gestational-age(SGA),apprioate-for-gestational-age(AGA) and large-for-gestational-age(LGA)babiesCompared with AGA and LGA, the protein level of LAT1, LAT2and PPARγ werereduced remarkablely in the tissue of SGA, and there is a positive correlation existed between the expression of LAT1, LAT2and PPARγ and birth weight. But there is nodifference of TAUT protein expression among SGA, AGA and LGA. And there is apositive correlation existed between the expression of LAT1, LAT2, TAUT and PPARγprotein expression.In summary, the above results demonstrated:Rosiglitazone can stimulate the expression of LAT1, LAT2, TAUT; PPARγ andRXRa are essential for the effect of rosiglitazone on LAT1, LAT2, TAUT; the effect ofPPARγ on LAT1and TAUT depended on SP-1; rosiglitazone can not only up-regulate theexpression of SP-1, but also promote the combination of SP-1and promoter of LAT1andTAUT genes; lower expression of LAT1, LAT2and PPARγ may be an major cause ofSGA.