Expression and Regulation by PPARγ of hCG α- and β-subunits: Comparison between Villous and Invasive Extravillous Trophoblastic Cells☆

Abstract 

During human placental development trophoblast follows two differentiation pathways: the extravillous (EVCT) and the villous cytotrophoblasts (VCT) that display different phenotypes and functions. It is well established that human chorionic gonadotropin hormone (hCG) is mainly secreted by the endocrine VCT (syncytiotrophoblast) into the maternal compartment and stimulates the formation of the syncytiotrophoblast (ST) in an autocrine manner. We recently reported that the invasive EVCT also produces hCG that promotes trophoblast invasion in vitro. Herein, we compared hCG gene expression in primary culture of villous and extravillous trophoblasts obtained from the same first trimester human chorionic villi and differentiated in vitro into ST and invasive EVCT, respectively. Total hCG, free α and free β subunits were quantified in cell supernatants by immunometric assays and normalized to DNA content. α and β transcript levels were quantified by Q-PCR and normalized to cytokeratin 7. We show that free α-, free β-subunits and total hCG are differently expressed and secreted by the two trophoblast subtypes during their differentiation in vitro. We found an α/β ratio 100 times lower in invasive EVCT in comparison to the ST suggesting that β subunit may not be step limiting for hCG production in EVCT. Finally we investigated the regulation of hCG gene expression by PPARγ, a nuclear receptor that controls trophoblast differentiation and invasion. Interestingly, activation of PPARγ by the agonist rosiglitazone gave opposite results in the endocrine VCT and invasive EVCT: α and β subunit transcript levels and protein secretions were up regulated in VCT, whereas they were down regulated in EVCT. Our results demonstrated that hCG gene expression is differentially regulated in the two trophoblast lineages during their in vitro differentiation and modulated in an opposite way by PPARγ.

Keywords: Human placenta, Trophoblast differentiation, Trophoblast invasion, Syncytiotrophoblast, Rosiglitazone, hCG gene expression