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.