Estrogen-Related Receptor γ (ERRγ) Regulates Oxygen-Dependent Expression of Voltage-gated Potassium (K+) Channels and Tissue Kallikrein during Human Trophoblast Differentiation

Estrogen-related receptor gamma (ERR gamma) serves a critical O-2-dependent regulatory role in the differentiation of human cytotrophoblasts to syncytiotrophoblast. In this study, we investigated expression of genes encoding tissue kallikrein (KLK1) and voltage-gated K+ channels (K(V)7) during differentiation of human trophoblasts in culture and the roles of ERR gamma and O-2 tension in their regulation. Expression of KLK1 and the K(V)7 channel subunits, KCNQ1, KCNE1, KCNE3, and KCNE5, increased during differentiation of cultured human trophoblast cells in a 20% O-2 environment. Notably, together with ERR gamma, expression of KLK1, KCNQ1, KCNE1, KCNE3, and KCNE5 was markedly reduced when cells were cultured in a hypoxic environment (2% O-2). Moreover, upon transduction of trophoblast cells with short hairpin RNAs for endogenous ERR gamma, KLK1, KCNQ1, KCNE1, and KCNE3 expression was significantly decreased. Promoter and site-directed mutagenesis studies in transfected cells identified putative ERR gamma response elements within the KLK1 and KCNE1 5'-flanking regions required for ERR gamma stimulated transcriptional activity. Binding of endogenous ERR gamma to these ERR gamma response elements increased during trophoblast differentiation in culture and was inhibited by hypoxia. The K(V)7 blocker linopirdine reduced human chorionic gonadotropin secretion and aggregation of cultured human trophoblasts, suggesting a possible role of K(V)7 channels in cell fusion and differentiation. Illumina gene expression arrays of cultured human trophoblast cells revealed several genes upregulated during syncytiotrophoblast differentiation and downregulated upon ERR gamma knockdown involved in cell differentiation, adhesion, and synthesis of steroid and peptide hormones required for placental development and function. Collectively, these findings suggest that ERR gamma mediates O-2-dependent expression of genes involved in human trophoblast differentiation, function, and vascular homeostasis.