Endometriosis is a debilitating disease that is diagnosed in 0.5-5% fertile and 25-40% of infertile women, but the underlying mechanisms involved in progression of the disease as well as the associated infertility are yet unclear. Research now shows evidence that the immune system has a pivotal role in endometriosis development as well as the related infertility. Among other immune cells, the T-helper lymphocytes accumulate in the normal endometrium during the mid- to late-secretory phase of the menstrual cycle and are considered essential for endometrial receptivity. The goal of this project was to 1) study the relationship between anti-inflammatory T-regulatory (Treg) and pro-inflammatory T-helper-17 (Th17) lymphocytes in the eutopic endometrium of patients with the primary complaint of infertility; 2) explore the involvement of interleukin-17 (IL-17) in the promotion of a pro-inflammatory environment and the consequences of this altered microenvironment on eutopic endometrial and ectopic endometriotic cells; and 3) characterize EMMPRIN expression in the eutopic endometrium in women with endometriosis-related infertility and its correlation to elevated IL-17 expression.
Endometrial biopsy samples collected from patients during the mid- to late-secretory phase of their menstrual cycles were evaluated for Treg and Th17 lymphocyte subsets and the Th17 specific cytokine, IL-17 expression. These data were compared to the fertility status in these patients. Overall, Treg cell counts were higher and Th17 cell counts were lower in patients who conceived compared to those that did not get pregnant. Conversely, patients who maintained their infertile status had a lower Treg cell count and higher Th17 cell count in their eutopic endometrium. The ratio of Treg:Th17 cell counts was significantly correlated to their fertility status. Patients with a ratio less than 3 failed to conceive in spite of medical or surgical intervention. Laparoscopic intervention for ectopic lesion excision had a boosting effect on the endometrial Treg cell population which was in turn correlated to a positive pregnancy outcome. The IL-17 expression was elevated in both the glandular and stromal compartments of the endometrium in patients with a low Treg:high Th17 cell ratio.
IL-17 is associated with various inflammatory conditions including endometriosis. IL-17 treatment did not have any effect on cell proliferation in endometrial or endometriotic cell type. But IL-17 did positively affect cell migration and invasion in the endometriotic cells, though not in the endometrial cells. To understand this differential effect we assessed IL-17 receptor (IL-17R) expression in both cell types and observed that the receptor expression was fairly similar in both cell types. Thus we concluded that the differential effect was probably due to specific interaction processes of IL-17 with different cell types or another co-receptor expressed specifically on the endometriotic cells could mediate this effect. The inflammatory NFkB pathway is the hallmark of IL-17 activity, but our results showed that in our uterine cell lines, IL-17 did not induce the NFkB pathway. Instead IL-17 activated an alternate MAPK signal transduction pathway, but only in the endometriotic 12Z cells.
Because it is known that cell motility requires MMP induction, we also evaluated changes in EMMPRIN expression in these cells when treated with IL-17. Endometriotic cells showed a transient increase in EMMPRIN expression post treatment which could partially explain their enhanced motility in the presence of IL-17. We also assessed the correlation between IL-17 and EMMPRIN expression in the eutopic endometrial samples from patients with endometriosis. We found that IL-17 expression positively correlated with EMMPRIN expression in about 90% of the samples tested.
Our experiments using IL-17 may reveal the mechanisms involved with the creation of a pro-inflammatory environment and its consequence on eutopic endometrial cells as well as processes involved in the establishment of ectopic endometriotic lesions. We believe this project addresses questions that will greatly increase our understanding of how a specific immune cell niche may regulate endometrial receptivity. Moreover, a better understanding of the mechanisms of Epithelial to Mesenchymal Transition will aid research in the field of endometriosis as well as cancer
