Placental DEPTOR as a stress sensor during pregnancy

Abstract

DEPTOR [DEP-domain-containing and mTOR (mammalian target of rapamycin)-interacting protein] is a modulator of mTOR signalling that binds to mTORC (mTOR complex) 1 and mTORC2. However, to date, the precise functions of DEPTOR are not fully elucidated, particularly in reproductive tissues where mTOR acts as a placental nutrient sensor. Pregnancy is associated with major physiological and psychosocial changes and adaptation to these changes is crucial for normal fetal development. In the present study, we tested the hypothesis that maternal stress can affect mTOR signalling at term, and, as a result, influence placental growth. We first investigated the expression of DEPTOR, mTOR, rictor (rapamycin-insensitive companion of mTOR) and raptor (regulatory associated protein of mTOR) from human placentas (n=23) using Q-PCR (quantitative PCR), and correlated these data to days of pregnancy and maternal stress, as well as placental and fetal weight. Maternal and fetal cortisol levels were also measured. JEG-3 and BeWo cells, used as placental in vitro models, were treated with cortisol and DEPTOR expression was assessed using Q-PCR. DEPTOR appears to be the predominant transcript in the human placenta compared with mTOR, rictor and raptor in both term (n=13) and preterm (n=10) placentas as assessed by Q-PCR. There was a significantly lower level only of log-DEPTOR gene expression in the high stress group (-1.34) than in the low stress group (0.07; t₂₀=2.41, P=0.026). Interestingly, mothers with high stress had significantly elevated levels of cortisol (8555 pg/ml) compared with those with low stress (4900 pg/ml). We then tested the hypothesis that cortisol can directly affect DEPTOR expression. When BeWo cells were treated with cortisol 10, 100 and 1000 nM, the expression of DEPTOR was significantly down-regulated by 50, 41 and 39% (all P<0.05) respectively when compared with basal levels. Treatment of JEG-3 cells with cortisol, led to a significant decrease of DEPTOR expression at 100 nM (39%, P<0.05) and at 1000 nM (73%, P<0.01). These novel findings are indicative of a higher order of complexity of DEPTOR signalling in the human placenta that is affected by maternal stress, which could affect pregnancy outcome.