Forkhead box protein O1 and progesterone receptor expression in endometrial epithelial cells at embryo transfer time: case-control and mechanistic study.

OBJECTIVE

To study the nuclear expression of transcription factor forkhead box protein O1 (FOXO1) and progesterone receptor (PGR) loss in the endometrial epithelial cells (EEC) at embryo transfer time, in assisted reproductive technologies cycles (ART) and to study the effect of elevated estradiol concentration on serum and glucocorticoid/kinase-1 (SGK1) cytoplasmic increase and FOXO1 nuclear reduction using primary EEC (p-EEC).

DESIGN

Case control observational study and mechanistic study by in vitro assay using cell culture of p-EEC. The protein expression of FOXO1 and PGR was determined by immunohistochemistry and quantified by digital score. Progesterone receptor messenger RNA (mRNA) levels were measured in laser capture microdissected (LCM) EECs, using quantitative real time polymerase chain reaction. Primary EEC were incubated with varying estradiol (E2) concentrations to assess SGK1 and FOXO1 nuclear expression. The FOXO1 expression was analyzed using multiple linear regression with E2, progesterone (P), and PGR as independent variables.

SUBJECTS: (Cases): Infertile women subjected to in vitro fertilization (IVF) or expecting frozen-thawed embryo transfer (FET). (Controls): Fertile women during the midluteal phase of natural cycles.

EXPOSURE: Controlled ovarian stimulation for IVF or hormonal replacement therapy for FET (HRT-FET). Cell culture of p-EEC with different E2 concentrations.

MAIN OUTCOME MEASURE: FOXO1 and PGR protein expression and PGR mRNA levels.

RESULTS

No statistically significant differences were observed among the groups with respect to age, body mass index, or endometrial thickness. FOXO1 expression was significantly higher in controls compared with IVF and HRT groups. The PGR expression was lower in controls compared with IVF and HRT cases. The PGR mRNA levels from LCM-EEC were lower in controls vs. IVF and HRT. Multiple linear regression showed that higher E2 levels were strongly associated with lower FOXO1 levels. In vitro, elevated E2 increased cytoplasmic SGK1 and concomitantly decreased nuclear FOXO1.

CONCLUSION

The fertile implantation window is characterized by nuclear FOXO1 expression and PGR loss in EECs. In ART cycles, supraphysiological E2 levels appear to disrupt this profile, likely via SGK1 upregulation, resulting in retained PGR and reduced nuclear FOXO1, potentially compromising receptivity.