The human endometrium is a complex multicellular tissue, located within the cavity of the uterus. Its luminal surface is defined by a layer of epithelial cells supported on a multicellular stroma containing fibroblasts, glands (lined by a secretory epithelium), blood vessels (lined with endothelial cells) and several populations of immune cells; the latter includes a unique population of natural killer (uNK) cells. The endometrium undergoes dynamic remodelling across the menstrual cycle in response to fluctuating levels of sex steroids secreted by ovarian cells. The phases of the endometrial cycle include an oestrogendominated proliferative phase, a progesterone-dominated secretory phase and menses (endometrial shedding precipitated by falling levels of progesterone). A key feature of the secretory phase is differentiation (decidualisation) of endometrial stromal fibroblasts (ESC) an event characterised by transformation of cell shape, secretion of growth factors/cytokines, angiogenesis/vascular remodelling and an increase in the numbers of resident immune cells. Decidualisation ensures an appropriate nutritional and hormonal environment exists during the establishment of pregnancy. Studies in mice suggest that de novo biosynthesis of oestrogen within the uterus may play an essential role in regulation of decidualisation but no data exist for human. Endometrial endothelial and uNK cells both contain oestrogen receptors but the impact of oestrogens on their function has not been explored. In the current studies three questions have been addressed: 1. Is oestrogen biosynthesis a feature of human endometrial stromal cell decidualisation? 2. What is the impact of oestrogen on uNK cell function? 3. What role (if any) does oestrogen play in the interplay between decidual, immune and vascular cells within the human endometrial stroma? Results obtained provide the first evidence that de novo biosynthesis of oestrogens occurs during decidualisation of human ESC. This was attributed to changes in expression patterns of mRNAs encoding proteins that play a critical role in regulation of oestrogen biosynthesis (STAR, CYP11A1, CYP19A1 [aromatase], HSD17B2 [17βHSD2] and STS [steroid sulphatase]). Changes in the pattern of metabolism were confirmed using thin layer chromatography and analysis of concentrations of oestrone (E1) and oestradiol (E2) in culture media. Secretion of E1 and E2 was reduced by addition of an aromatase inhibitor. Data derived from studies described within this thesis also show for the first time that incubation of uNK cells with E2 not only enhanced cell migration but also stimulated secretion of factors that had a significant impact on endothelial cell angiogenesis. These findings were supported by novel evidence that E2 had a significant impact on expression of genes associated with cell motility and angiogenesis. In addition, factors, including E1/E2, secreted by decidualised stromal cells, stimulated chemotaxis of uNK cells. Future experiments will focus on determining the identity of the angiogenic factors secreted by uNK cells in response to E2 and the mechanisms responsible for uNK cell movement. In summary, new data presented in this thesis provide evidence that local biosynthesis of oestrogens within the endometrial stroma may play a previously unrecognised role in regulating the function of uNK cells and endometrial endothelial cells in women. These results have implications for treatment of disorders such as infertility, heavy menstrual bleeding and endometriosis.

Chlamydia trachomatis (Ct), the most common sexually transmitted bacterium, has been associated with adverse pregnancy outcomes including controversial data on miscarriage, intrauterine growth restriction and low birth weight, however the causative mechanisms are unknown. A successful pregnancy requires normal endometrial stromal cell (ESC) decidualisation and trophoblast invasion, processes that involve chemokine action and lead to successful implantation. My objectives were to determine whether Ct infection impacts upon ESC decidualisation and chemokine secretion on human primary ESC invitro, to investigate the role of Ct infection in pregnancy in-vivo using a murine model of pregnancy and to investigate the role of Ct in miscarriage in a statistically powered case control study. A novel finding is that Ct can infect and proliferate in ESC, resulting in suboptimal decidualisation as measured by decidualisation marker prolactin’s reduced mRNA and protein levels in infected ESC. Furthermore, the altered secreted chemokine profile of decidualised ESC suggests an attenuated innate immune response from infected ESC. Focusing on chemokines C-X-C motif chemokine 12 (CXCL12) and CXCL16, important for trophoblast invasion, decreased mRNA and protein concentrations were detected in infected decidualised cells. From the in-vivo mouse model of past Ct infection in pregnancy, it was demonstrated that Ct infection did neither affect the fertility of the mice, pregnancy or resorption numbers in C3H mice nor alter embryonic and placental weight on e12 embryos. However, Ct infection caused reduction of embryo and placenta weight on e14 embryos. Finally, preliminary data from the case control study indicate that past Ct infection is not associated with miscarriage. Our in house PGP3 ELISA that detects past Ct infection was more sensitive than a commercially available MOMP ELISA. My data suggests that Ct infection affects pregnancy during the implantation stage by impairing decidualisation and altering chemokine secretion predisposing for adverse pregnancy outcomes that include growth restriction during later gestation.