P-801 Human endometrial Organoids (hEOs): a non invasive powerful tool to study receptivity and a step forward precision medicine in IVF
Authors: Luongo F.P , Luddi A , Paccagnini E , Morgante G , De Leo V , Piomboni P 
Published: June 2022

Abstract

Study question
Organoids from menstrual blood (MB) can mimic human receptive endometrium?

Summary answer
This research provides a reliable and less invasive 3D endometrial model able to mimic the window of implantation (WOI).

What is known already
Investigating the physiology and function of the normal cycling endometrium is challenging due to its great individual variability. hEOs are considered a new step forward in precision medicine and a tool for the study of endometrial biology, associated diseases (i.e. endometriosis) and to understand the complex mechanism surrounding endometrium-embryo cross talk. During the WOI apical cytoplasmic protrusions traditionally called “pinopodes” are reported to be a specific marker of endometrial receptivity.Initially hypothesized to form at the sites of blastocyst attachment, pinopodes have typically been correlated with successful implantation and are strongly regulated by the ovarian steroid hormones.

Study design, size, duration
hEOs are usually obtained from endometrial biopsy, here a much less invasive source was employed. Menstrual blood (MB) retrieved by menstrual cups was processed to isolate epithelial (Ep) and stromal endometrial cells (hESC). hEOswere created to investigate the morphological changes occurring in vivo during the menstrual cycle, specifically at the WOI. For a proof of concept, we recruited five healthy volunteers from January 2021 to december 2022 signing an informed written consent for this study.

Participants/materials, setting, methods
All the participants provided written informed consent for the use of their MB samples. Female healthy volunteers received instruction for the use of menstrual cups. hEOs obtained from MB have been exposed to hormonal treatments to mimic the endometrial hormonal milieu typical of the proliferative and mid secretory phase of the menstrual cycle. Cultured hEOs were then observed in a Quanta 400 (FEI) scanning electron microscope (SEM).

Main results and the role of chance
In this study we succeeded to establish a reliable 3Dmodel using both Ep cells and hESC using a less invasive approach. The hEOs generated from the co-culture of these two types of cells were used to mimic the mid secretory phase. The expansion media has been supplemented with 10 − 8 M E2 + 10 − 6 M P4 and 50 mM cAMP. Treated hEOs have been cultured for 4 days; washed with PBS and fixed for 2 h at 4 °C in cold Karnovsky’s. Using Scanning electron Microscopy, we closely observed the luminal surface of hEOs in the proliferative phase. The inner side of Ep cells was characterized by the presence of pinopodes large 5-10 μm, apical plasma membrane of uterine epithelial cells protrusions, not present in unstimulated hEOs. Generally, during days 17-19 of the menstrual cycle, cellular bulging increases with the formation of small (1-2 μm) pinopodes. Their full development was reported to be present at day 20and is a specific marker of the WOI.

Limitations, reasons for caution
There are discrepancies in the literature regarding pinopode morphology on specific days of the cycle, and of course, these changes may vary between individuals. Further studies, comprising individuals undergoing IVF treatments should be explored.

Wider implications of the findings
Effective and reliable embryo implantation modeling is necessary to mimic the molecular event cascade that occurs in vivo. Pinopodes responds to stimuli, in particular to Progesterone, these findings can be used to calibrate hormonal treatments of women undergoing IVF.

Trial registration number
Not applicable