mTOR is an essential gate in adapting the functional response of ovine trophoblast cells under stress-inducing environments

Introduction: During the early stage of pregnancy trophoblast cells adapt to adverse uterine environments characterized by oxygen and nutrient deprivation. Autophagy is an intracellular degradation process that aims to promote cell survival in response to stressful conditions. Autophagy activation passes through the mechanistic target of rapamycin (mTOR), also known as a placental nutrient sensor. Here, we tested the hypothesis that ovine trophoblast cells may adapt to a suboptimal environment through an mTOR dependent regulation of cell survival with relevant implications for key placental functionality. Methods: Primary ovine trophoblast cells subjected to mTOR inhibitor and low-nutrient conditions were used to explore how autophagy affects cellular functionality and expression of solute carriers' genes (SLCs). Results: Autophagy activation was confirmed both in rapamycin-treated and low-nutrient conditions, through the detection of specific autophagic markers. However, p-mTOR activation seems to be severely modified only following rapamycin treatment whereas 24h of starvation allowed p-mTOR reactivation. Starvation promoted migration compared to normal culture conditions whereas all trophoblast functional activities were decreased in rapamycin treatment. Interestingly in both conditions, the autophagy-activated environment did not affect the progesterone release. mRNA expression of amino acid transporters remains largely undisturbed except for SLC43A2 and SLC38A4 which are downregulated in starved and rapamycin-treated cells, respectively. Discussion: The study demonstrates that sheep trophoblast cells can adapt to adverse conditions in the early stage of placentation by balancing, in an mTOR dependent manner, nutrient recycling and transport with relevant effects for in vitro functional properties, which could potentially impact conceptus development and survival.