Intrauterine growth restriction (IUGR) increases the risk for perinatal complications and predisposes for adult disease. However, the mechanisms mediating the restricted growth and programming of long-term health remain to be fully established. We have previously provided compelling evidence that trophoblast mammalian target of rapamycin (mTOR) signaling functions as a placental nutrient sensor, indirectly influencing fetal growth by regulating placental nutrient transporters. In this proposal we will tet the innovative hypothesis that placental mTOR signaling directly influences fetal metabolism and growth. Our central hypothesis is that inhibition of trophoblast mTOR signaling in response to restricted nutrient availability alters the release of humoral factors that cause increased secretion and phosphorylation of IGFBP-1 and decreased secretion of IGF-I from the fetal liver. We propose two specific aims:
Aim 1 : Determine the role of trophoblast mTOR in the regulation of IGF-I and IGFBP-1 secretion and IGFBP-1 phosphorylation in fetal liver cells in vitro and Aim 2: Establish the effect of placental specific mTOR knock down on fetal liver IGF-I and IGFBP-1 secretion and IGFBP-1 phosphorylation in the mouse.
In Aim 1, we will obtain conditioned media (CM) from cultured human primary trophoblast cells of two types: 1. Cells isolated from normal term placentas and transfected with scrambled siRNA or siRNA targeting the mTOR signaling pathway and 2. Cells isolated from IUGR and Appropriate-for-Gestational-Age (AGA) placentas. Human HepG2 cells and primary fetal baboon liver cells will be incubated in trophoblast CM and secretion and phosphorylation of IGFBP-1 (Western blot, 2-D immunoblotting, ELISA and mass spectrometry approaches) as well as IGF-I secretion (ELISA) will be determined. In addition, candidates for the putative humoral factors will be identified using mass spectrometry based quantitative labeling approaches.
In Aim 2, we will develop a conditional trophoblast specific mTOR knock down mouse using transfection of blastocysts from mTOR-floxed mice by lentiviral vectors containing ERT2-Cre-constructs. The expression and phosphorylation of IGFBP-1 and expression of IGF-I in fetal liver and fetal levels of IGF-I and IGFBP-1 as well as fetal growth will be studied after induction of trophoblast specific mTOR knock down by tamoxifen. Significance: Abnormal fetal growth is a major contributor to perinatal morbidity and has profound impact on long-term health. This work has the potential to identify a molecular mechanism by which the placenta directly influences fetal metabolism and growth and programs the fetus for disease later in life. Innovation: The hypothesis that the placenta directly regulates fetal growth by modulating fetal liver function is a conceptually novel idea. Furthermore, we propose to develop an approach allowing conditional trophoblast specific gene targeting in the mouse, which has - to the best of our knowledge - not previously been reported. Thus, the proposed work is also methodologically innovative.
Abnormal fetal growth affects 10-15% of all babies and increases the risk for injuries at delivery and to develop obesity, diabetes, and cardiovascular disease in childhood and later in life. In this proposal we will test the novel hypothesis that the placenta directly regulates fetal growth and metabolism by the release of circulating factors affecting fetal growth factor secretion. This research will increase our understanding of the role of the placenta in determining the short- and long-term health of the baby and may help design novel treatments to alleviate abnormal fetal growth.
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