Defining the effects of chronic endometritis on the endometrium through menstrual effluent

Background Chronic endometritis (CE) is defined by persistent inflammation of the endometrium, typically associated with microbial infections, including LPS-producing E. coli and Chlamydia. CE diagnosis occurs mainly in the setting of infertility. CE is commonly diagnosed by counting CD138+ plasma cells in stromal-dense areas of an endometrial biopsy. However, there is no standardized diagnostic criteria and plasma cells alone may be insufficient to reliably diagnose CE. Pathological diagnosis may be improved by measuring endometrial edema and increased endometrial stromal cell (eSC) density. Human eSCs express TLRs, including TLR4 and thus, are targets of LPS and other pathogen-associated molecular patterns (PAMPs). While previous studies identified increased eSC density and aberrant eSC functions in the setting of CE, these alterations have not been well-defined. In humans and the few species that menstruate, eSCs proliferate during the luteal phase and then eSCs decidualize (a differentiation process critical for implantation) during the mid-secretory phase. Our laboratory has pioneered the use of menstrual effluent (ME, shed endometrial tissue) for studying endometriosis. We hypothesize that infection-related alterations in eSCs will help better understand and diagnose CE. Methods Using ME collected from women (18-40 years) with no history of pelvic inflammatory disease, polycystic ovary syndrome, or endometriosis, eSCs were isolated and grown in culture media until confluency. Low passage ME-derived eSCs were treated with LPS (0-500 ng/ml) for 3 days and then analyzed for proliferation by CyQuant assay and decidualization potential by measuring the production of Insulin-like Growth Factor Binding Protein 1 (IGFBP1, a decidualization marker) by ELISA. Results Overall, proliferation assays revealed a significant increase in eSC numbers following LPS treatment compared to vehicle: 0 ng/ml vs. 25 ng/ml (p = 0.014), 0 ng/ml vs. 50 ng/ml (p < 0.0001), 0 ng/ml vs. 250 ng/ml (p = 0.0017). By contrast, decidualization assays revealed a significant decrease in IGFBP1 concentrations in LPS-treated conditions compared to vehicle: 0 ng/ml vs. 10 ng/ml (p = 0.0078), 0 ng/ml vs. 25 ng/ml (p = 0.0078). Conclusion LPS has opposing effects on eSC proliferation and decidualization. An increase in proliferation following LPS exposure supports the increased eSC density reported in the endometrium during CE and may promote endometrial polyp formation in confirmed CE cases. The decreased decidualization following LPS may contribute to the infertility observed in CE. Further research is needed to elucidate the potential mechanisms underlying these altered eSC phenotypes.