Progesterone control of human endometrial cells

Abstract

The coordination of events and cellular interactions within the uterus is vital to the establishment of pregnancy, a process constrained to a narrow window of time within the ovarian cycle. The transformation of the endometrium into decidua is one such event and is considered essential to embryo implantation and to the maintenance of pregnancy. In humans these changes are most dramatic in the stromal compartment and are influenced by progesterone, secreted by the Corpus Luteum (CL). This hormone is believed to be the main factor inducing such differentiation in the oestradiol-primed stroma. However, mediators with the ability to activate the protein kinase A/cAMP pathway, such as Prostaglandin E₂ (PGE₂) and relaxin, are potent inducers of decidualisation when administered alongside progesterone in endometrial stromal cells (ESCs) in vitro. Uterine Natural Killer (uNK) cells increase in number in secretory phase endometrial stroma, implying the control of progesterone on their expansion. However, they lack the nuclear progesterone receptor and growth and differentiation may depend on interactions with ESCs. uNK cells replicate upon Interleukin-15 (IL-15) administration in vitro and this cytokine is expressed in the epithelial and stromal cells. The aims of this research project have been to investigate in vitro decidualisation of ESCs and regulation of IL-15 and uNK cells in order to extrapolate how ESCs and uNK cells may interact during the secretory phase and early pregnancy.The present study has explored the factors involved in decidualisation using primary human ESC cultures. Quantitative real-time PCR (Q RT-PCR) and Enzyme-linked Immunoabsorbant Assays (ELISA) have been used to investigate effective in vitro stimuli of decidualisation. A combination of treatment with a progestin and either 8- Bromo cAMP or PGE₂ was capable of stimulating decidualisation in ESC cultures as determined by increases in two markers of this process, prolactin and insulin-like growth factor-binding protein-1 (IGFBP-1). Further analysis has revealed the changes taking place within the PGE₂ pathway in decidualising ESCs, including an upregulation in the EP₂ prostaglandin receptor messenger RNA (mRNA) upon treatment with 8-Bromo cAMP plus a progestin.The results present here have demonstrated a rise in IL-15 mRNA levels in parallel with in vitro decidualisation. It appears that both progesterone and the intracellular messenger, cAMP, are involved in decidualisation and IL-15 expression. IL-15 secretion from the cells is shown to be IFN-y dependent. The expression of IL-15 and interferon-y (IFN-y) mRNA across the menstrual cycle has been established. Immunohistochemistry was used to determine IL-15 expression during simulated early pregnancy compared with normal luteal controls and has shown that secretions of the CL, including progesterone and/or relaxin, have the ability to increase IL-15 expression in vivo. Primary cultures of human uNK and peripheral blood NK cells have been used for studying the T helper 2-type cytokine IL-10 which is believed important for the support of early pregnancy. In response to PGE2 treatment, uNK cells expressed and secreted raised levels of IL-10, an anti-inflammatory cytokine.Further investigation into the interactions between the convergence of the cAMP and progesterone intracellular pathways and their receptors would be important in clarifying the exact mechanisms controlling ESC decidualisation and IL-15 regulation. The interactions between ESCs and uNK cells need to be clarified further to assess the roles of uNK cells in reproductive processes.