Placental apoptosis increased by hypoxia inducible Factor-1 stabilization is counteracted by leptin.

Abstract

During pregnancy, apoptosis is a physiological event critical in the remodeling and aging of the placenta. Increasing evidence has pointed towards the relevance of hypoxia as modulator of trophoblast cell death. Previous reports have shown that leptin, a placental cytokine, promotes cell survival in both cell culture and placental explant models. The aim of this work is to establish the role of leptin in apoptosis under hypoxic condition in trophoblast cells. In this study, we evaluated the effect of cobalt chloride, a hypoxia mimicking agent that stabilizes the expression of hypoxia inducible factor-1 alpha (HIF-1α), on Swan-71 and human placental explants. Hypoxia chamber was also used to generate 2% oxygen. Apoptosis was determined by the presence of apoptotic nucleus, fragmentation of DNA and Caspase-3 and PARP-1 cleavage. The pro-apoptotic proteins BAX, BID, BAD and BAK and the anti-apoptotic effectors BCL-2, BCL-xL and MCL-1 were also analyzed. We found that HIF-1α stabilization increased the appearance of apoptotic nucleus, fragmentation of DNA, and Caspase-3 and PARP-1 cleavage. Hypoxia mimicking conditions enhanced the expression of pro-apoptotic effectors BAX, BID, BAD and BAK. HIF-1α stabilization also downregulated the level of BCL-2, BCL-xL and MCL-1. All these apoptotic parameters changes were reversed with leptin treatment. Moreover, we showed that leptin action on apoptosis modulation involves PI3K and MAPK signaling pathways. Obtained data demonstrate that HIF-1α stabilization induces apoptosis in human placenta and leptin counteracts this effect, reinforcing its role as a survival cytokine.