Research Insights

Dynamic uterine fluid volume is essential for successful early pregnancy. Uterine fluid volume is the net result of secretion and absorption, which are respectively promoted by ovarian estradiol (E2) and progesterone (P4) through the uterine epithelium. Dysregulated uterine fluid movement has been associated with impaired early pregnancy, particularly in women with endometriosis undergoing ovarian stimulation for in vitro fertilization-embryo transfer (IVF-ET) who often experience uterine fluid retention and implantation failure. Na+ and Cl- are the dominant ions in the uterine fluid. Amiloride-sensitive epithelial Na+ channel (ENaC) and cystic fibrosis transmembrane conductance regulator (CFTR) have been implicated in their movements across the uterine epithelial cell membrane to generate osmotic gradients for facilitating fluid movement through the epithelial membrane water channels, aquaporins (AQPs). Despite the essential roles of sex hormones and ion/water channels in regulating dynamic uterine fluid movement during early pregnancy, the precise hormonal and ionic mechanisms remains elusive. Our preliminary data in mouse models revealed inhibition of uterine fluid absorption by amiloride on day 0.5 post-coitus (D0.5) but not D3.5, dynamic expression of genes for ion/water channels in D0.5 and D3.5 luminal epithelium (embryo implantation initiates ~D4.0 in mice) by mRNA-seq, and a novel function of E2-estrogen receptor α (ERα) in regulating uterine fluid absorption. In human models, we developed a microphysiological system that enables a microfluidic co-culture of ovarian follicles and human endometrial (Endo) organoids for engineering a female reproductive tract-on-a-chip (FRT-Chip), and our preliminary data showed the longterm survival and 3D architecture of Endo organoids in vitro as well as the regulation of ENaC and CFTR by cocultured follicles. Herein, we formulate our central hypothesis that ERα and PR converge on hormonal and ionic mechanisms to finely coordinate temporal uterine fluid absorption during early pregnancy, while dysregulation of ion/water channels in eutopic endometriosis endometrium or under ovarian stimulation for IVF leads to disrupted uterine fluid dynamics and impaired early pregnancy. There are two Specific Aims. In Aim 1, we will use transgenic mouse models with ERα or PR deficiency in the uterine epithelium to determine in vivo functions and regulatory mechanisms of selected Na+ channels, Cl- channels, and water channels in the uterine epithelium for uterine fluid absorption during early pregnancy. In Aim 2, we will collect normal and endometriosis endometrium biopsies from menstruating women and IVF-ET patients to compare ion/water channels in human endometrium biopsies and perform a microfluidic co-culture of follicles and Endo organoids to engineer an FRT-Chip and investigate mechanisms regulating human uterine fluid movement under physiological and pathological conditions. The successful completion of these studies will generate a comprehensive molecular atlas of uterine fluid movement. Identification of local uterine epithelial factors is a crucial first step for developing treatments to regulate uterine fluid movement, improve embryo implantation success, and reduce early pregnancy loss. 

Funder: National Institutes of Health 

Amount: $3,910,102 

PI: Xiaoqin Ye, College of Veterinary Medicine