Endometrial regeneration with endometrial epithelium: homologous orchestration with endometrial stroma as a feeder

BACKGROUND

Thin endometrium adversely affects reproductive success rates with fertility treatment. Autologous transplantation of exogenously prepared endometrium can be a promising therapeutic option for thin endometrium; however, endometrial epithelial cells have limited expansion potential, which needs to be overcome in order to make regenerative medicine a therapeutic strategy for refractory thin endometrium. Here, we aimed to perform long-term culture of endometrial epithelial cells in vitro.

METHODS

We prepared primary human endometrial epithelial cells and endometrial stromal cells and investigated whether endometrial stromal cells and human embryonic stem cell-derived feeder cells could support proliferation of endometrial epithelial cells. We also investigated whether three-dimensional culture can be achieved using thawed endometrial epithelial cells and endometrial stromal cells.

RESULTS

Co-cultivation with the feeder cells dramatically increased the proliferation rate of the endometrial epithelial cells. We serially passaged the endometrial epithelial cells on mouse embryonic fibroblasts up to passage 6 for 4 months. Among the human-derived feeder cells, endometrial stromal cells exhibited the best feeder activity for proliferation of the endometrial epithelial cells. We continued to propagate the endometrial epithelial cells on endometrial stromal cells up to passage 5 for 81 days. Furthermore, endometrial epithelium and stroma, after the freeze-thaw procedure and sequential culture, were able to establish an endometrial three-dimensional model.

CONCLUSIONS

We herein established a model of in vitro cultured endometrium as a potential therapeutic option for refractory thin endometrium. The three-dimensional culture model with endometrial epithelial and stromal cell orchestration via cytokines, membrane-bound molecules, extracellular matrices, and gap junction will provide a new framework for exploring the mechanisms underlying the phenomenon of implantation. Additionally, modified embryo culture, so-called "in vitro implantation", will be possible therapeutic approaches in fertility treatment.

The gasotransmitter hydrogen sulfide inhibits transepithelial anion secretion of pregnant mouse endometrial epithelium

Endometrial epithelium exhibits a robust ion transport activity required for dynamical regulation of uterine fluid environment and thus embryo implantation. However, there still lacks a thorough understanding of the ion transport processes and regulatory mechanism in peri-implantation endometrial epithelium. As a gaseous signaling molecule or gasotransmitter, hydrogen sulfide (H₂S) regulates a myriad of cellular and physiological processes in various tissues, including the modulation of ion transport proteins in epithelium. This study aimed to investigate the effects of H₂S on ion transport across mouse endometrial epithelium and its possible role in embryo implantation. The existence of endogenous H₂S in pregnant mouse uterus was tested by the detection of two key H₂S-generating enzymes and measurement of H₂S production rate in tissue homogenates. Transepithelial ion transport processes were electrophysiologically assessed in Ussing chambers on early pregnant mouse endometrial epithelial layers, demonstrating that H₂S suppressed the anion secretion by blocking cystic fibrosis transmembrane conductance regulator (CFTR). H₂S increased intracellular Cl^- concentration ([Cl^-]_i) in mouse endometrial epithelial cells, which was abolished by pretreatment with the CFTR selective inhibitor CFTR_inh-172. The cAMP level in mouse endometrial epithelial cells was not affected by H₂S, indicating that H₂S blocked CFTR in a cAMP-independent way. In vivo study showed that interference with H₂S synthesis impaired embryo implantation. In conclusion, our study demonstrated that H₂S inhibits the transepithelial anion secretion of early pregnant mouse endometrial epithelium via blockade of CFTR, contributing to the preparation for embryo implantation.