P-317 Associations between endometrial microbiome composition and cellular senescence
Authors: Parvanov D , Stamenov G , Tihomirova T , Ganeva R , Ruseva M , Handzhiyska M , Vidolova N , Metodiev D , Chapanova S , Staneva R , Rukova B , Pancheva M , Serafimova M , Hadjidekova S 
Published: June 2023

Abstract

Study question
Is there an association between the percentage of senescent cells and microbiome composition in human endometrium?

Summary answer
We found that cellular senescence is negatively associated with the relative abundance of certain bacterial taxa.

What is known already
Recent studies indicated that endometrial microbiome characteristics and certain levels of cellular senescence are essential for the establishment of normal endometrial receptivity and successful embryo implantation. The secretion of senescence-associated secretory phenotype (SASP) components is responsible for immune cell activation and might cause endometrial dysbiosis. On the other hand, some studies suggest that the presence of specific metabolic groups of bacteria and their metabolites could influence cellular stress response that might suppress the development of senescent cells. However, the direct relationship between the quantity of senescent cells and microbiome content in the endometrium has never been studied.

Study design, size, duration
This was a prospective observational cohort study performed between April 2021 and January 2023. Endometrial biopsies were collected from 30 women aged between 34 and 45 during the mid-luteal phase (LH + 7) in a natural cycle. Each biopsy was divided for genetic and immunohistochemical analyses. The exclusion criteria were history of recent inflammatory disease, chronic endometritis, recent antibiotic treatment, endocrinological disorders, autoimmune diseases, oncological diseases, moderate or severe endometriosis, adenomyosis, uterine hyperplasia, and endometrial polyps.

Participants/materials, setting, methods
We used immunohistochemical biomarker p16ink4a (MAD-000690QD–7, Master Diagnostica) to identify senescent cells. The percentages of positively stained cells in the endometrial stroma and in the luminal epithelium were calculated by HALO image analysis software (version 2.3, IndicaLabs). Endometrial microbiota composition was analyzed after DNA isolation from the endometrial samples using 16S rRNA (v4-v5 region) gene sequencing. Statistical analysis was performed by Spearman’s correlation test using SPSS v.21 (IBM Corp., Armonk, NY, USA).

Main results and the role of chance
A total of 271 distinct bacterial species and 668 genera were identified across the studied 30 endometrial samples. The percentage of p16+ senescent endometrial stromal cells ranged from 0 to 1.7%, with a mean value of 0.37%, while the percentage of p16+ luminal epithelial cells ranged between 2.5% and 74.0%, with a mean value of 21.5%
Spearman analysis revealed significant negative correlation between the percentage of p16+ stromal cells and the relative abundance of Porphyromonas sp. (R = −0.41, p = 0.03) and Sphingobacterium sp. (R = −0.37, p = 0.05). The percentage of p16+ luminal senescent cells correlated negatively with the abundance of Micrococcus luteus (R = −0.44, p = 0.02), Moraxella osloensis (R = −0.37, p = 0.05), Rubellimicrobium sp. (R = −0.46, p = 0.02), Stenotrophomonas sp. (R = − 0.45, p = 0.03), Chryseobacterium sp. (R = −0.41, p = 0.04), Carnobacterium sp. (R = −0.40, p = 0.04), Deinococcus sp. (R = −0.38, p = 0.05), and Enhydrobacter sp. (R = − 0.37, p = 0.05).

Limitations, reasons for caution
The study was limited in sample size. The assessment includes only endometrial samples from the mid-luteal phase of the cycle.

Wider implications of the findings
We found that the level of senescence is negatively associated with the relative abundance of certain bacteria taxa in human endometrium, including some related to impaired reproductive function and early embryonic development arrest. These findings suggest a possible specific interaction between senescent cells and microbiome that might influence endometrial receptivity.

Trial registration number
The current research was funded by National Science Fund, Ministry of Education, Bulgaria, Contract № KP-06-N53/14/16.11.2021