Intrauterine growth restriction (IUGR) increases the risk for perinatal complications and predisposes for adult disease. Fetal growth is strongly dependent on nutrient availability, which is determined by placental nutrient transfer. The activity of key placental amino acid transporters and mitochondrial respiration is decreased in IUGR, which is believed to cause or contribute to decreased fetal nutrient availability and reduced fetal growth. Currently, there are no specific treatments available for IUGR. We recently reported that silencing of placental mechanistic Target of Rapamycin (mTOR) Complex 1 and/or C2 markedly inhibits trophoblast amino acid transport activity. Silencing of DEPTOR, an endogenous inhibitor of mTORC1 and C2, in primary human trophoblast cells activates mTORC1 and C2 signaling, which, in turn increased trophoblast amino acid transport and mitochondrial respiration. Here we propose a novel and innovative strategy to modulate placental DEPTOR in vivo, based on transposable elements that are able to efficiently introduce constructs into the host genome while exhibiting low toxicity and low immune response. We have previously reported a minimally invasive in vivo method, sonoporation to deliver piggyBac transposon-based plasmids to the mouse liver achieving long-term transgene expression. We propose that sonoporation can also mediate tissue-specific delivery of plasmids to the placenta, an organ that is readily accessible to ultrasound. Our central hypothesis is that placenta-specific in vivo reduction in DEPTOR expression and consequent restoration of normal mTORC1 and mTORC2 signaling reestablishes placental amino acid transport and mitochondrial respiration resulting in normalization of fetal growth in a rat model of IUGR. Our hypothesis is based on our preliminary data which demonstrates that normalization of mTORC1 and mTORC2 signaling by DEPTOR silencing in cultured primary trophoblast isolated from IUGR baboons completely restores normal amino acid transport capacity and mitochondrial respiration. We will utilize a well-established rat model of maternal protein restriction, which is associated with inhibition of placental mTOR and amino acid transport and IUGR.
Specific Aims : (1) Develop an efficient approach for trophoblast-specific activation of mTORC1 and mTORC2 signaling by means of DEPTOR RNA knockdown. (2) Determine the effect of trophoblast specific DEPTOR knock down on placental mTOR signaling, amino acid transport and mitochondrial respiration and fetal growth in a rat model of IUGR. This proposal is significant because it will provide novel mechanistic information with respect to the role of placental mTOR signaling in regulating placental function and fetal growth. Furthermore, the proposed non-viral approach for placental gene transfer may be adapted to the human in the future and be used as an early intervention strategy in IUGR pregnancies. Because the placenta is a tissue with a finite life span, essential for fetal development but discarded after birth, it is well suited for improving fetal wellbeing, without causing previous problems associated with gene transfer directly into the host genome.
Intrauterine growth restriction (IUGR) due to placental insufficiency is a major cause of fetal and neonatal mortality and morbidity and increases the risk for the development of obesity, diabetes, and cardiovascular disease in childhood and later in life. Currently there are no specific and effective treatments available for IUGR in humans. The proposed research will lead to a better understanding of the mechanisms underlying IUGR and could result in the development of a novel treatment for IUGR in women with the potential to improve public health for pregnant women, her baby and the next generation.
