Abstract
The establishment of uterine receptivity is a prerequisite for embryo implantation and begins with the transformation of the luminal epithelium. MicroRNAs (miRNAs) have been widely reported to be involved in the regulation of embryo implantation, but their roles in establishing uterine receptivity remain unclear. In this study, through small RNA sequencing analysis, we showed that a low level of miR-192-5p is essential for initiating implantation in mice, and transient upregulation of miR-192-5p led to implantation failure. In situ hybridization results revealed that miR-192-5p was primarily expressed in the endometrial epithelium, and dysregulation of miR-192-5p interfered with the performance of the luminal epithelium, resulting in inadequate receptivity. By manipulating miR-192-5p expression in mouse uterus and an endometrial epithelial cell line, we showed that miR-192-5p maintains cell polarity through stabilizing adherens junction protein E-cadherin, thereby preventing epithelial-mesenchymal transition. Furthermore, miR-192-5p preserved the pattern of microvilli as well as Muc1 expression on the apical membrane of epithelial cells, thereby avoiding embryo adhesion. Moreover, miR-192-5p was found to be regulated by ovarian steroids. Collectively, this study demonstrated that the physiological role of miR-192-5p in mouse uterus is to maintain the nonreceptive state of epithelial cells and prevent their transformation to the receptive state. Thus, a sustained high level of miR-192-5p is detrimental to embryo implantation. These findings help elucidate the mechanisms involved in miRNA-based regulation of uterine physiology in early pregnancy, and may even contribute to the diagnosis and treatment of infertility.