O-233 Follicular fluid extracellular vesicles as a potential tool for human spermatozoa selection in vitro
Authors: Anastasiya S , Makarova N , Nepsha O , Zingerenko B , Silachev D , Shevtsova Y , Goryunov K , Chagovets V , Novoselova A , Kalinina E 
Published: June 2023

Abstract

Study question
What characteristics and features of follicular fluid (FF) extracellular vesicles (EVs) of women of different ages can affect the functional characteristics of spermatozoa?

Summary answer
The size, lipid composition, and progesterone levels of the FF EVs change with a woman's age and affect the fertilizing ability of spermatozoa.

What is known already
Aging influences on molecular composition of the FF, reducing fertilization processes occurring in the fallopian tubes. FF is an important factor in activating spermatozoa during oocyte fertilization, enhancing the process of sperm hyperactivation and capacitation. FF progesterone is one of the main chemoattractants in the female genital tract, attracting sperm to the oocyte and starting the fertilization processes. Our previous studies have shown a significant effect of FF EVs of young women compared to advanced maternal age women (AMA) on the hyperactivation and motility of spermatozoa. The binding of FF EVs to the acrosoma of the sperm also was detected.

Study design, size, duration
FF EVs were obtained by sequential centrifugation at different rotational speeds. The sperm fraction was isolated, washed by differential centrifugation in a density gradient, suspended in the saline to a concentration of 10*6/ml and incubated with EVs (1:2) at 37 °C in CO2-incubator for 1 h. Next steps: immunofluorescent staining, test for acrosomal reaction of spermatozoa after incubation, NTA analysis, the lipid profile and progesterone measuring of FF EVs of women of different ages.

Participants/materials, setting, methods
All study participants signed a voluntary informed consent for the use of biological samples for research purposes. Sperm samples were isolated from seminal fluid (n = 21) aged 28-36. FF EVs were obtained from young (n = 14) aged 22-30 and AMA patients (n = 14) aged 42-47. The methods used in this work also include immunofluorescence microscopy, nanoparticle tracking analysis, flow cytometry, liquid chromatography–mass spectrometry, statistical data analysis. Lipids were extracted from EVs using a modified Folch extraction protocol.

Main results and the role of chance
Progesterone levels were significantly higher in FF EVs samples from young women compared to FF EVs samples from AMA women and controls (3951000 a.u., 598500 a.u., 6701 a.u.). This may explain the increase in sperm hyperactivation and motility after incubation with FF EVs. The difference in size (144.78 nm ± 9.92 VS 127.03 nm ± 17.17) and lipid composition of young women's FF EVs may explain the more significant functional and therapeutic effect on spermatozoa compared to AMA women FF EVs. A total of 389 vesicle lipids were identified. The level of cholesterol esters, cholesterol, lysophosphatidylcholines, phosphatidylcholines was 1,5 times higher in FF EVs of young women. The level of di- and triglycerides, ceramides, oxidized forms of phosphatidylcholines was higher in FF EVs of AMA women. The level of spontaneous acrosomal reaction was almost 3 times lower in sperm samples after incubation with FF EVs compared to the control (11,21% VS 32,88%). This supports the hypothesis that FF EVs may restrain premature acrosomal reaction in the fallopian tubes. Age-related changes are reflected in reproductive important biological processes, which leads to a change in the composition and functions of FF and affect the functional role of FF EVs.

Limitations, reasons for caution
Small amount of data. To be completely confident in the importance of the participation of FF EVs in the activation of spermatozoa, it is necessary to perform proteomic analyses of FF EVs to discuss the possible mechanisms underlying the effects of FF EVs of different age groups on sperm characteristics.

Wider implications of the findings
Further studies may help not only to complement the fundamental understanding of the processes of fertilization and the impact on spermatozoa morphofunctional characteristics, but also to develop a tool for improving ART outcomes in couples with male infertility. The solutions could be the use of FF EVs from young donors.

Trial registration number
not applicable