P-650 Follicular extracellular vesicles of older women inhibit oocyte maturation
Authors: Liu C , Yao H , Cui M , Gong X , Chen Y 
Published: June 2023

Abstract

Study question
Whether follicular extracellular vesicles of older women interfere with the quality of oocytes.

Summary answer
OLD-EVs induced the oxidative stress in the oocytes and inhibited oocyte maturation by increasing the abnormal mitochondria distribution and abnormal spindle rates.

What is known already
Ovary is a critical regulator of female fertility and the source of oocytes. With the modern tendency of delaying childbearing, ovarian aging has become an age-related disease. Ovarian aging is generally characterized by a gradual decrease in both the quantity and quality of oocytes. The pregnancy outcomes of older women were far from satisfying with higher abortion rates, birth defects rates, and lower live birth rates even after the assistance of IVF. However, the detailed mechanisms of decreased oocyte quality of aging women have not been clarified.

Study design, size, duration
Extracellular vesicles (EVs) were isolated from follicular fluid of older women (aged 40-50, n = 7, OLD-EVs) and younger women (aged 25-30, n = 6, YOUNG-EVs) via ultracentrifugation. Germinal vesicle (GV) oocytes from female ICR mice were co-cultured with OLD-EVs, YOUNG-EVs, or PBS (blank control), respectively. GV breakdown (GVBD) rate and maturation rate were calculated at two-hour and fourteen-hour of co-culture, respectively. Besides, oocyte mitochondria distribution, meiosis spindle morphology, and oxidative status were assessed in different groups.

Participants/materials, setting, methods
EVs were determined by western blotting, nanoparticle tracking analysis, and transmission electron microscopy. Fluorescence labeled EVs were used to visualize internalization by oocytes. Oocytes mitochondria and mitosis spindles were stained with fluorescence, and abnormal mitochondria rate or abnormal spindle rate was calculated. Reactive oxygen species (ROS) level was detected in the differently treated oocytes. Moreover, the expression of CAT, GSS, and SOD was determined in the oocytes using quantitative reverse transcription polymerase chain reaction.

Main results and the role of chance
Both OLD-EVs and YOUNG-EVs are bilayered vesicles, ranging from 100 to 150 nm and enriched in Alix, TSG101, and CD9. EVs could be internalized by oocytes within one hour. After coculture, GVBD rate was similar among the three groups; whereas maturation rate was significantly decreased in the OLD-EV group compared with YOUNG-EV group or PBS group. In addition, the abnormal mitochondria distribution rate or abnormal spindle rate were significantly increased in the OLD-EV group compared with PBS or YOUNG-EV group. The ROS level was increased in the PCOS-EV group compared with YOUNG-EV group, and the expression of CAT, GSS, and SOD was increased in the OLD-EV-treated oocytes.

Limitations, reasons for caution
Our study did not identify the contents of OLD-EVs and YOUNG-EVs, and the molecular mechanisms of dysregulations induced by OLD-EVs need further researches to investigate.

Wider implications of the findings
This work confirmed that EV-conducted cellular communication played an important role in oocyte maturation. The dysregulation of oocytes induced by OLD-EVs might be related to the poor oocyte quality of aging women, which provide a novel target to improve pregnancy outcomes of these patients.

Trial registration number
not applicable