Melatonin mitigates autophagy: unlocking conditional resilience in sheep trophoblast cells exposed to a hypoxic environment

Melatonin is a key molecule in supporting pregnancy success in sheep, particularly under suboptimal conditions. In humans, melatonin is also known for its antioxidant properties. In addition, it has recently been reported that melatonin differentially drives cell fate in normal vs altered trophoblast cells. Given that, we hypothesize that melatonin is a potential partner for trophoblasts to overcome a hypoxic environment during the early stage of pregnancy. Here, we explore the effect of melatonin on early trophoblast cell behavior and its potential mitigating effect in CoCl2-induced hypoxia. Cell functionality and autophagy modulation were studied on ovine primary trophoblast cells (oTCs) 24 h treated with 250 mu M melatonin with/without 200 mu M CoCl2. First, melatonin exerts its antioxidant effects by reducing H2O2 levels under hypoxic cellular conditions (P < 0.0001). CoCl2 suppressed cell proliferation and migration (P < 0.0001); however, melatonin supplementation partially restored oTCs functionality (P < 0.05). Melatonin-mediated cytoprotective effects are manifested even through the modulation of cell fate mechanisms, particularly autophagy and apoptosis. Increased protein expression of autophagic markers (BCLN1 and LC3BII/LC3BI ratio) in concomitance with a decreased phosphorylation of mTOR was observed in CoCl2-treated cells (P < 0.01), while a reduced rate of autophagy was detected following melatonin co-treatment (P < 0.01). Similarly, melatonin attenuates the CoCl2-induced increase in apoptosis when administered concurrently (5.5 vs 1.8%, P < 0.01). These findings suggest that melatonin promotes autophagy over apoptosis, indicating a shift toward cell survival mechanisms. In addition, melatonin enhances cell functionality under hypoxia, suggesting the conceptus benefits from melatonin, particularly when it is forced to grow in a suboptimal environment.Lay summaryMelatonin is known for its role in regulating reproduction in sheep; however, very little is known about the role it plays in the development of the placenta. Here, we take you through how melatonin helps the placental cells survive in a low-oxygen environment, a condition called hypoxia. In this environment, we found that melatonin helps the placental cells function and reduces their death rate by helping them recycle damaged parts to survive. Overall, our findings highlight melatonin as a powerful molecule playing a role in placental cells' survival and how they function under stressful conditions. Since hypoxia is a common cause of pregnancy complications, melatonin could be a valuable aid for both animals and humans. Indeed, this study shows that melatonin is not just a sweet little pill; it is mighty and should only be used when truly needed.