Modulatory role of mTOR in trophoblast adaptive response in the early stage of placentation in sheep

Abstract

During the early stage of placentation in sheep, normal conceptus development is affected by trophoblast cell functionality, whose dysregulation results in early pregnancy loss. Trophoblast metabolism is supported mainly by histotrophic factors, including fibroblast growth factor-2 (FGF2), which are involved in cell differentiation and function through the modulation of specific cellular mechanisms. The mechanistic target of rapamycin (mTOR) is known as a cellular ‘nutrient sensor’, but its downstream regulation remains poorly understood. The hypothesis was that during trophoblast development the FGF2 effect is mediated by mTOR signalling pathway modulation. Primary trophoblast cells from 21-day-old sheep placenta were characterised and subjected to FGF2 and rapamycin treatment to study the effects on cell functionality, gene and protein expression profiles. The model showed mainly mononuclear cells with epithelial cell-like growth and placental morphological properties, expressing peculiar trophoblast markers. FGF2 promoted cell proliferation and migration under normal culture conditions, whereas mTOR inhibition reversed this effect. When the mTOR signalling pathway was activated, FGF2 failed to influence invasion activity. mTOR inhibition significantly reduced cell motility, but FGF2 supplementation restored motility even when mTOR was inhibited. Interestingly, mTOR inhibition influenced endocrine trophoblast marker regulation. Although FGF2 supplementation did not affect ovine placenta lactogen expression, as observed in the control, interferon-tau was drastically reduced. This study provides new insights into the mechanism underlying mTOR inhibitory effects on trophoblast cell functionality. In addition, as mTOR is involved in the expression of hormonal trophoblast markers, it may play a crucial role in early placenta growth and foetal–maternal crosstalk.