Trophoblast mTOR: a critical hub linking maternal nutrient supply to placental function, fetal growth and fetal islet function

胎儿宫内生长受限和胎儿过度生长都会增加围生期并发症的风险 并使个体在儿童时期易患肥胖症、糖尿病和心血管疾病， 成年年龄。因此，对胎儿生长调节机制的理解对于确定胎儿生长的机制是至关重要的。 主要妊娠并发症的原因和成人疾病的发育规划。胎盘mTOR信号在IUGR中被抑制，在胎儿过度生长的妊娠中被激活。滋养层mTOR信号传导响应于一系列不同的母体营养和代谢信号。例如，滋养层mTOR被胰岛素/IGF-I、葡萄糖和氨基酸、脂肪酸和叶酸激活，并被皮质醇、脂联素、感染和子宫胎盘血流减少抑制。此外，mTOR是滋养层氨基酸和叶酸转运以及线粒体呼吸的正调节剂。总的来说，这些数据表明滋养层mTOR信号传导作为连接母体营养供应与胎盘功能、胎儿生长和发育编程的关键枢纽发挥作用。然而，缺乏证明滋养层mTOR信号传导的变化直接调节体内胎盘功能，导致异常胎儿生长和程序成人疾病的数据，这代表了知识上的主要差距和未来靶向滋养层mTOR信号传导以减轻IUGR和胎儿过度生长的障碍。我们的中心假设是滋养层mTOR信号传导的抑制与胎盘营养转运和线粒体呼吸减少、胎儿生长受限和胎儿胰岛β细胞功能受损在机制上相关。我们的方法将是在培养的原代人滋养层（PHT）细胞和滋养层特异性诱导mTOR敲低小鼠，我们最近开发的基因靶向。在目的1中，我们将确定滋养层mTOR信号转导在胎盘功能和胎儿生长调节中的机制作用。我们假设：（1）恢复正常的mTOR信号转导挽救了从IUGR妊娠中分离的PHT细胞的表型，（2）小鼠滋养层特异性mTOR敲低降低了胎盘营养转运和线粒体呼吸，并抑制了胎儿生长。在目标2中，我们将建立滋养层mTOR信号传导在调节胎儿胰岛功能中的机制作用。我们的工作假设是，滋养层mTOR信号传导的抑制抑制了由释放到胎儿循环中的外泌体miRNA介导的胎儿胰岛功能。拟议的工作是重要的，因为它将产生新的机制信息，导致更好地了解异常胎儿生长和代谢疾病的子宫内编程的基础，这将对该领域产生持续和重大的影响。所提出的工作是创新的，因为滋养层特异性诱导mTOR敲除小鼠，使用piggyBac转座子介导的转基因产生，代表了第一个小鼠模型与诱导滋养层特异性基因靶向。

Both intrauterine growth restriction (IUGR) and fetal overgrowth increase the risk for perinatal complications and predispose the individual for developing obesity, diabetes and cardiovascular disease in childhood and adult age. Thus, a mechanistic understanding of the regulation of fetal growth is critical for identifying the causes of major pregnancy complications and developmental programming of adult disease. Placental mTOR signaling is inhibited in IUGR and activated in pregnancies complicated by fetal overgrowth. Trophoblast mTOR signaling responds to an array of diverse maternal nutritional and metabolic signals. For example, trophoblast mTOR is activated by insulin/IGF-I, glucose and amino acids, fatty acids and folate, and inhibited by cortisol, adiponectin, infection and reduced uteroplacental blood flow. In addition, mTOR is a positive regulator of trophoblast amino acid and folate transport and mitochondrial respiration. Collectively, this data suggest that trophoblast mTOR signaling functions as a critical hub linking maternal nutrient supply to placental function, fetal growth and developmental programming. However, data demonstrating that changes in trophoblast mTOR signaling directly regulates placental function in vivo, causes abnormal fetal growth and programs adult disease is lacking, representing a major gap in knowledge and a roadblock for future targeting of trophoblast mTOR signaling to mitigate IUGR and fetal overgrowth. Our central hypothesis is that inhibition of trophoblast mTOR signaling is mechanistically linked to decreased placental nutrient transport and mitochondrial respiration, fetal growth restriction and impaired fetal pancreatic isletcell function. Our approach will be to use gene targeting in cultured primary human trophoblast (PHT) cells and a trophoblast specific inducible mTOR knockdown mouse that we have recently developed. In Aim 1 we will determine the mechanistic role of trophoblast mTOR signaling in the regulation of placental function and fetal growth. We hypothesize that (1) restoring normal mTOR signaling rescues the phenotype in PHT cells isolated from IUGR pregnancies and that (2) trophoblast-specific mTOR knockdown in mice decreases placental nutrient transport and mitochondrial respiration and inhibits fetal growth. In Aim 2, we will establish the mechanistic role of trophoblast mTOR signaling in regulating fetal islet function Our working hypothesis is that inhibition of trophoblast mTOR signaling inhibits fetal islet function mediated by exosomal miRNAs released into the fetal circulation. The proposed work is significant because it will generate novel mechanistic information leading to a better understanding of the underpinnings of abnormal fetal growth and in utero programming of metabolic disease, which will have a sustained and significant impact on the field. The proposed work is innovative because the trophoblast specific inducible mTOR knockout mouse, generated using piggyBac transposon mediated transgenesis, represents the first mouse model with inducible trophoblast specific gene targeting.