O-217 Associations between endometrial stem cells quantities, serum levels of progesterone and estradiol and expression of their respective receptors in endometrial tissue during the mid-luteal phase
Authors: Ruseva M , Parvanov D , Ganeva R , Handzhiyska M , Vidolova N , Metodiev D , Stamenov G 
Published: June 2022

Abstract

Study question
Is the percentage of endometrial stem cells linked to serum progesterone, serum estradiol, and their receptors expression in human endometrium during the mid-luteal phase?

Summary answer
We found an association between CD117+ endometrial stem cells and serum progesterone, estradiol, as well as with the expression of their receptors in the endometrium.

What is known already
Various types of stem cells including NOTCH1+ and CD117+ stromal cells have been found in the endometrium. Their quantities have been hypothesised to fluctuate with the menstrual cycle and to have a link with endometrial receptivity. It has been well established that progesterone and estradiol play a crucial role in the preparation of the endometrium for implantation and the expression of their receptors also varies with the menstrual cycle. Nonetheless, the relationship between stem cells and other established markers of endometrial receptivity, such as the sex hormones signaling system, constitutes a novel field of research.

Study design, size, duration
The present observational study included 87 women aged 26-56 (mean 39.5 years old) undergoing in-vitro fertilisation and for whom a peripheral blood sample and an endometrial biopsy were obtained during the mid-luteal phase (LH + 7) of a natural cycle. Immunohistochemical (IHC) markers for NOTCH1 (E-AB-12815, Elabscience), CD117 (CD117/c-Kit/SCF-Receptor RB-9038-RQ, Epredia), progesterone (PR) and estrogen receptors (ER) (1-PR026-07, 1-ES006-07, Quartett) were used to stain endometrial tissue. The investigation was carried out between March 2020 and January 2022.

Participants/materials, setting, methods
Serum progesterone and estradiol were measured via electrochemiluminescence using Cobas e411 analyser (Roche Diagnostics, Germany) on the day of obtaining the endometrial biopsy. Stem cells (count and percentage) and the expression of hormone receptors (6-point scale) were determined using ImageJ. Stem cells percentage was compared between groups with high and low progesterone (analogously for estradiol) using Wilcoxon signed-rank test. To assess the link between stem cell percentages and receptor expression, Spearman correlation was used.

Main results and the role of chance
The mean percentage of positively stained NOTCH1 endometrial stromal stem cells was 0.13 ± 0.29% and CD117+ cells was 0.034 ± 0.039%. The hormone serum levels ranged from 0.2 to 60 ng/mL (median of 14.9 ng/mL) for progesterone and from 12 to 1985 pg/mL (median of 135.6 pg/mL) for estradiol.
While the quantities of the two stem cell types demonstrated a positive correlation with each other (R = 0.379, p &lt; 0.001), the percentage of NOTCH1+ stem cells showed no difference between the studied serum hormone levels (p &gt; 0.05), nor revealed a relationship with the expression of their receptors (p &gt; 0.05). In contrast, the amount of CD117+ cells differed significantly between patients with high and low serum progesterone (cutoff 14.9 ng/mL, p = 0.001) and estradiol levels (cutoff 135.6 pg/mL, p = 0.019). Furthermore, the quantity of stem cells positive for CD117 correlated positively with the two hormone receptor levels in the endometrium – PR (R = 0.277, p = 0.019) and ER (R = 0.318, p = 0.007).

Limitations, reasons for caution
A limitation of the study was the sample size. These findings should be confirmed using a larger population. In addition, confounding variables such as the immunological profile of the tissue should also be taken into account.

Wider implications of the findings
This study shows that certain endometrial stem cell types (CD117+) but not others (NOTCH1+) are associated with sex hormone signaling during the mid-luteal phase. This relationship highlights the role these cells play in preparing the endometrium for embryo implantation and their quantity might be an indirect indicator of endometrial receptivity.

Trial registration number
not applicable