Extracellular vesicles from follicular fluid may improve the nuclear maturation rate of in vitro matured mare oocytes.

The research explores how extracellular vesicles (EVs) from follicular fluid can potentially enhance the in vitro maturation (IVM) rate of horse (mare) eggs or oocytes, which could result in further improvement of assisted reproductive techniques (ART) in horses.

Introduction and Hypothesis

• The study was embarked upon in response to inconsistencies observed in the in vitro maturation of equine oocytes. These inconsistencies pose a hindrance to advancements in assisted reproductive techniques.
• The researchers hypothesized that follicular fluid EVs (ffEVs) drawn from small ovarian follicles (less than 20mm in size) could potentially improve the in vitro maturation rate of mare oocytes.

Methodology

• Equine ovarian follicular fluid was aspirated, and the ffEVs were isolated by performing ultracentrifugation. The isolated EVs were characterized using nanoparticle tracking analysis and flow cytometry.
• The researchers also labeled ffEVs using an ExoGlow-protein EV labeling kit. Cumulus-oocyte complexes (COCs) were matured using two methods: a one-step method that entails continuous culture for 24-38 hours, and a two-step method with initial denudation after 24 hours.
• These maturing processes were done either in the presence of ffEVs (200 μg protein/ml) or without.

Results and Importance

• The findings indicated that ffEVs were ingested by equine cumulus cells and surprisingly by oocytes for the first time. They observed that the ffEV treatment during the two-step culture positively affected the maturation rate of compacted COCs as opposed to the control group
• However, there was no observed effect of the ffEV supplementation on the maturation rate during the one-step culture.
• While the research presents significant results, it also indicates areas requiring further study, such as the influence of follicular size on the presence and concentration of follicular fluid extracellular vesicles, and the specific role these vesicles play in the maturation of oocytes.
• The results demonstrate the potential of ffEVs supplementation to improve the in vitro maturation rate of mare oocytes. These could be substantial findings for both equine assisted reproduction and the broader field of veterinary science.