胎儿过多暴露于糖皮质激素是发育源性疾病的重要致病原因，因此研究胎盘糖皮质激素屏障建立的分子机制对于保证胎儿的正常发育意义重大。胎盘糖皮质激素屏障是由绒毛小叶合体滋养层表达的糖皮质激素灭活酶11beta-HSD2承担的，滋养细胞合体化过程中11beta-HSD2大幅上调是此屏障建立的关键事件，申请人以往工作表明，组蛋白表观遗传学修饰可能是此屏障建立的关键机制。本课题首次从沉默转录的组蛋白密码H3K27甲基化及其相关酶EZH2入手，利用人原代滋养细胞探讨合体化过程是否通过下调EZH2和H3K27的甲基化促进11beta-HSD2的大量表达；探讨引起EZH2下调的原因是否由合体化过程中产生的重要激素hCG激活cAMP通路，导致调控EZH2转录的CDK4/pRB/E2F1通路下调引起的。此设想具有充分的理论依据和工作基础，并具备预实验结果支持。此机制的阐明将诠释胎盘糖皮质激素屏障的建立机制。

Overexposure to glucocorticoids in utero is an important cause of diseases with fetal origins, thus understanding the mechanisms of the establisment of placental glucocorticoid barrier is crucial for ensuring the normal development of the fetus. 11beta-hydroxysteroid 2 (11beta-HSD2) in the syncytiotrophoblasts of the placental villi is recognized as the placenta glucocorticoid barrier and it forms the front line of defence against maternal cortisol. The upregulation of 11beta-HSD2 during syncytialization of the cytotrophoblasts is believed to be the crucial event in the establishment of this barrier. Our previous work has proved that the histone codes may play an important role in this event. This proposed project will explore, for the first time, the role of H3K27 methyalion and methylaton-related enzymes such as EZH2 in the establishment of this barrier by using cultured primary human placental trophoblasts. We propose that hCG produced in large amounts during syncytiolization may inhibit the transcription machinery ( CDK4/pRB/E2F1 ) required for EZH2 expression by activating the cAMP signaling pathway, thereby lowering the levels of H3K27 methyaltion associated with 11beta-HSD2 promoter and leading to the abrupt up-regulation of 11beta-HSD2 during syncytiolization. This proposed project is based on solid rationals and supported by our previous work and the preliminary data. We believe that the sucessful carry-out of this project will help us elucidate the mechanism underlying the establishment of placental glucocorticoid barrier.