Mitochondrial Dysfunction Induced by High Estradiol Concentrations in Endometrial Epithelial Cells

Abstract

Context: A supraphysiological estradiol (E2) concentration after ovarian stimulation is known to result in lower embryo implantation rates in in vitro fertilization. Endometrial epithelial cell (EEC) apoptosis occurs after the stimulation with high E2 concentrations, and mitochondria play important roles in cell apoptosis.

Objective: To investigate the mitochondrial function in EECs after the stimulation with high E2 concentrations.

Materials and methods: Human EECs were purified and cultured with different E2 concentrations (10-10, 10-9, 10-8, 10-7 M) in vitro, in which 10-7 M is supraphysiologically high. Eight-week-old female mouse endometrium was obtained 5.5 days after the injection of 1.25 IU or 20 IU equine chorionic gonadotropin, roughly during the embryo implantation window, to examine the in vivo effects of high E2 concentrations on mouse EECs.

Results: In vivo and in vitro experiments demonstrated decreased mitochondrial DNA contents and ATP formation after EECs were stimulated with supraphysiologically high E2 concentrations than those stimulated with a physiologic E2 concentration. Less prominent immunofluorescence mitochondrial staining, fewer mitochondria numbers under electron microscopy, lower 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolylcarbocyanine iodide aggregate/monomer ratio, and greater reactive oxygen species (ROS) production were found after EECs were stimulated with supraphysiologically high E2 concentrations. The high E2-induced ROS production was reduced when EECs were pretreated with N-acetyl-cysteine in vitro, but remained unchanged after the pretreatment with coenzyme Q10.

Conclusion: High E2 concentrations increase extramitochondrial ROS production in EECs and subsequently result in mitochondrial dysfunction.

Keywords: embryo implantation; endometrial epithelial cell; high estradiol concentration; mitochondria; reactive oxygen species.