CONICET | Buscador de Institutos y Recursos Humanos

The process of embryo implantation and trophoblast invasion is currently considered as the most limiting factor for the establishment of pregnancy. Leptin has been proposed to play a relevant role in the regulation of the embryo implantation as well as its maintenance. Leptin is a 16000 MW protein product of the obese gene, originally considered as an adipocyte-derived signaling molecule for the central control of metabolism. However, leptin has been suggested to be involved in other functions during pregnancy, particularly in placenta, where it was found to be expressed. In our work we aimed to study the signal transduction pathways activated by leptin in placenta and to elucidate the mechanisms that mediate the antiapoptotic effect of leptin. Moreover, we attempted to study the regulation of leptin expression in placenta. BeWo and JEG-3 choriocarcinoma cell line, as well as trophoblastic cells from human placenta explants were used. Western blot analyses were carried out to detect leptin expression as well as the phosphorylated form of proteins involved in mayor signaling pathways. Apoptosis was assayed by flow cytometry and by western blot of caspase-3 fragmentation. Transient transfection assays with a plasmid construction containing different leptin promoter regions and the reporter gene luciferase, and expression vectors for some intermediates of signaling pathways were used to determine the transcriptional regulation of leptin. qRT-PCR was performed to determine leptin mRNA expression. We have found that leptin stimulates JAK-STAT, MAPK and PI3K pathways in placental cells and in human placental explants. The effect of leptin on JEG-3 survival was completely reversed by blocking p42/44 MAPK activation employing the MEK inhibitor PD98059. We have also found that hCG added to BeWo and JEG-3 cells showed a stimulatory effect on leptin expression. Moreover, hCG treatment enhanced leptin promoter activity and mRNA expression .Similar results were obtained with placental explants evidencing physiological relevance. We found that dbcAMP counteracted hCG effect on leptin expression. Moreover, hCG effect on leptin is mediated by the MAPK pathway. We showed that cAMP stimulates leptin expression in placental cells. More interestingly, we demonstrated that the cAMP effect on leptin expression probably involves both the PKA classic signaling pathway and the MAPK signal transduction pathway. A cross talk between these pathways would be responsible for the observed effects. In summary, our results further support the importance of leptin in the biology of reproduction

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