The molecular regulation of embryo implantation: the roles of the G protein-coupled receptors KISS1R and GPR83
Creators: name: Schaefer, Jennifer Nicole
Publisher: name: No Publisher Supplied
Year: 2024

description: During early pregnancy, the endometrium of the uterus undergoes structural and functional remodelling to promote an embryo-receptive state allowing for successful embryo implantation. To date, molecular defects of the endometrium represent major causes of female infertility. Of the numerous molecular mediators of early pregnancy, several G protein-coupled receptors (GPCRs) are expressed in the uterus during the peri-implantation period. However, studies using knockout mouse models, have only implicated a limited number of uterine GPCRs (ex. LGR4, LPAR3, and KISS1R) as regulators of embryo implantation. Furthermore, studies with human mid-secretory phase endometrial biopsies and pregnant wild-type mice demonstrated the uterus expresses a functional kisspeptin (KP)/KISS1R and PEN/GPR83 signaling systems during the window of embryo implantation. The purpose of this dissertation research was to determine the roles of endometrial GPCRs (KISS1R and GPR83) in the molecular regulation of embryo implantation. Reproductive profiling in pregnant conditional uterine knockout of Kiss1r (KO) mice generated using the Pgr-Cre driver revealed while KO females exhibited normal ovarian function and mated successfully to stud males, they exhibited implantation failure. Further assessment of the uterus on D4 of pregnancy, the day of embryo implantation, revealed loss of uterine KISS1R led to aberrantly persistent epithelial ERα/ESR1 transcriptional activity. This led to the temporal misexpression of several genes that increase fluid secretion into the uterine lumen which likely disrupted embryo-endometrial interactions contributing to the reduced implantation events. In human endometrial biopsies, KP and KISS1R protein were greatly expressed in the mid-secretory endometrium during the window of implantation in stromal cells. In vitro decidualization of primary human endometrial stromal cells (HESCs) demonstrated KISS1R declines with progression of decidualization and when overexpressed inhibits decidualization by significantly reducing ESR1 expression and transcriptional activity. Furthermore, overexpression of ESR1-46 isoform, known to antagonize ESR1 signaling ablated ESR1-66 and ESR1-54 protein levels and inhibited decidualization comparable to HESCs expressing exogenous KISS1R. Thus, endometrial KISS1R positively regulates embryo implantation by negatively regulating ESR1 expression ensuring ESR1/ERα transcriptional activity is in check to allow the endometrium to acquire a receptive state and stromal fibroblasts to decidualize in a timely manner. Finally, decidualizing HESCs, exhibit PEN/GPR83 signaling evident by the increased mRNA expression of GRP83 and the enzymatic machinery to process its ligand PEN, along with the mid-secretory phase endometrium being able to produce PEN. Gain-of-function studies overexpressing GPR83 in PEN-treated decidualizing HESCs increased critical targets of decidualization such as FOXO1 and IGFBP1. These findings suggest GPR83 acts via FOXO1-mediated activation of IGFBP1 to positively regulate endometrial decidualization. In the eutopic endometrium of infertile women exhibiting molecular evidence of defective decidualization, GPR83 mRNA is abnormally elevated likely as a compensatory mechanism to correct the defect. Taken together, these data provide evidence that the uterine Gαq/11-coupled receptors, KISS1R and GPR83, are essential in the establishment of a healthy pregnancy through the molecular regulation of endometrial receptivity and decidualization and thereby embryo implantation. These findings will be vital for the development of novel targeted therapies in the treatment of female infertility and provide insight into the potential mechanisms underlying the action and effects of endocrine acting chemicals on the female reproduction system during early pregnancy.