Uterine epithelial estrogen receptor α temporally regulates preimplantation uterine immunity involving interleukin-1β signaling.

Abstract

Objective: Estrogen receptor α (ERα/Esr1) is essential for uterine function during early pregnancy. The uterus has a dynamic immune environment, including transient endometrial inflammation in response to post-coital semen. The uterine epithelium is the first contact for uterine lumen contents (e.g., semen). We aimed to determine the function and mechanism of uterine epithelial ERα in regulating the uterine immune response to semen.

Methods: Uterine tissues and uterine flushes were collected from naturally mated uterine epithelial ERα-deficient epiERα ^-/- (Esr1 ^f/- Wnt7a ^Cre/+ ) mice and Esr1 ^f/- control mice on day 0.5 post-coitus (D0.5) and D3.5. Histology, immunohistochemistry, mRNA-seq, real-time polymerase chain reaction (PCR), flow cytometry, and cytokine assays were employed to determine the spatiotemporal distribution of immune cells and assess their functional states.

Results: There was a sharp decline in neutrophils from D0.5 to D3.5 in both Esr1 ^f/- and epiERα ^-/- uteri. Immunohistochemistry detected ~7-fold ELANE+ neutrophils in the uterine luminal epithelium (LE) layer and ~1.5-fold in the stromal layer of D0.5 epiERα ^-/- uterus compared to D0.5 Esr1 ^f/- counterparts. Gelled uterine lumen contents with varied densities of neutrophils and sperm were detected in both D0.5 Esr1 ^f/- and epiERα ^-/- mice. Flow cytometry revealed significantly increased percentages of neutrophils among CD45⁺ leukocytes in uterine digests with a trend of increased neutrophil cell number and proportions in uterine flushes from D0.5 epiERα ^-/- mice. Dysregulation of immune genes at both mRNA and protein levels was noted in D0.5 epiERα ^-/- LE/uterus, especially an upregulation of inflammatory cytokines. In particular, upregulation of genes involved in signaling by interleukin (IL)-1β, a potent pro-inflammatory cytokine involved in mating-induced uterine inflammation, was observed in both the uterine tissue and uterine flush.

Conclusion: These findings demonstrate an essential function of uterine epithelial ERα in controlling mating-induced inflammation in the LE layer, stromal layer, and uterine lumen, and highlight the IL-1β signaling pathway among the molecular mechanisms involved in regulation of uterine inflammation by uterine epithelial ERα.