LAUSR

Establishment of endometrial surface receptivity is crucial for the initiation of embryo implantation, yet the molecular mechanisms are not well understood especially in the human. We have recently discovered that podocalyxin (PODXL) is a critical negative regulator of human endometrial surface receptivity. PODXL is highly expressed in all epithelial and endothelial cells in the non-receptive endometrium, but down-regulated specifically in the luminal epithelium at receptivity. We have further shown that PODXL inhibits embryo implantation, and that PODXL down-regulation is essential for endometrial surface receptivity. Our previous study also indicated that progesterone down-regulates PODXL, however, the exact molecular regulations are unknown. Here we investigated whether progesterone suppresses PODXL via microRNAs (miRNAs). We first bioinformatically predicted 13 miRNAs that may potentially target human PODXL, then experimentally determined whether any of these 13 miRNAs are altered in primary human endometrial epithelial cells (HEECs) by progesterone, and whether the identified miRNAs can affect PODXL expression in Ishikawa cells without progesterone and alter receptivity to embryo implantation. Progesterone significantly up-regulated miR-145 and miR-199 while suppressing PODXL in HEECs. When these two miRNAs were transfected into Ishikawa cells, both significantly down-regulated PODXL mRNA and protein in the absence of progesterone. Moreover, both miR-145 and miR-199 significantly enhanced receptivity of the Ishikawa monolayer to embryo implantation in in-vitro models. This study thus provides in-vitro evidence that PODXL is down-regulated by progesterone partly via miR-145 and miR-199 during the development of human endometrial epithelial receptivity. These results also reveal the likely importance of hormonal regulation of microRNAs for embryo implantation.