(254) Selective Ablation of ESR1 in an ESR2+ Cell Lineage Results in Endometrial Hyperplasia and Uterine Inflammation

Mary Bunnell¹, Po-Ching Patrick Lin¹, Ji-Eun Oh ¹, CheMyong Jay Ko¹

¹Department of Comparative Biosciences, University of Illinois Urbana-Champaign, Urbana, IL, USA

Abstract Text:

In the uterus, the actions of estradiol (E2) are regulated by two distinct nuclear receptors, estrogen receptors alpha (ESR1) and beta (ESR2). ESR1, the predominant subtype in the adult uterus, is essential for uterine development and regulates epithelial cell proliferation. ESR2 regulates stromal signaling and modulates ESR1-driven gene transcription, primarily to prevent hyperproliferation. Disruptions to E2 signaling through these receptors are associated with uterine pathologies such as endometrial hyperplasia and cancers, which have significant consequences for fertility and quality of life in women. Our recent studies utilizing a novel mouse model in which ESR1 is selectively ablated in the ESR2-expressing cell lineage (Esr1 ^flox/flox Esr2 ^iCre/WT; Esr2-Esr1KO mice) revealed that a loss of ESR1 in ESR2+ cells causes female infertility, endometrial hyperplasia, and uterine inflammation. Therefore, in this study, we hypothesized that ESR1+ cells that arise from an ESR2+ cell lineage are vital regulators of cell proliferation and inflammation in the uterus. To test this hypothesis, histological analyses and immunohistochemistry (IHC) were conducted at different stages of reproductive maturity utilizing our unique Esr2-Esr1KO model, which we compared with wild-type (WT) and global ESR1 knockout (Esr1KO) mice. Interestingly, IHC of 40-day-old uteri revealed a heterogenous loss of ESR1 expression in discrete clusters of luminal and glandular epithelial cells in Esr2-Esr1KO mice, whereas ESR1 was uniformly expressed in the epithelium in WT mice. Unlike Esr1KO mice, which exhibited uterine hypoplasia, Esr2-Esr1KO mice displayed normal uterine size and structure at day 40, indicating that ESR1 ablation in ESR2+ lineage does not impair early stage uterine development. However, by 4 months of age, 100% of Esr2-Esr1KO females developed prominent abdominal distention, lethargy, and signs of discomfort. Histological analysis of adult and peri-pubertal uteri revealed that Esr2-Esr1KOs developed age-dependent uterine pathology, including chronic inflammation, epithelial and stromal immune cell infiltration, pus within the lumen, endometrial hyperplasia, and abnormal architecture in the luminal and glandular epithelium. The endometrial hyperplasia was confirmed using IHC, which showed a higher expression of Ki67 in the Esr2-Esr1KO uterine epithelium compared to WT. In conclusion, Esr2-Esr1KO mice exhibited uterine pathology distinct from that of WT and Esr1KO mice, characterized by a loss of ESR1 expression in a subpopulation of luminal and glandular epithelial cells, epithelial hyperplasia, inflammation, and immune cell infiltration into the tissue that worsen with age. These findings provide compelling evidence that ESR1+ cells derived from ESR2+ lineages are essential for maintaining uterine homeostasis by regulating epithelial proliferation and modulating inflammatory responses.