92 Extracellular vesicles from oviductal spheroids and uterine horn epithelial cells show different uptake times by equine spermatozoa and act upon capacitation.

The research investigates how extracellular vesicles, secreted by specific cells in the female horse reproductive tract, interact with horse sperm in vitro. The results indicate these vesicles can stimulate horse sperm, potentially improving fertilization rates.

Research Background and Objective

• The study starts by highlighting how the microenvironment in female reproductive tracts, specifically in the uterine and tubal epithelial cells, supports and regulates interaction with sperm during transit.
• The researchers aimed to understand the nature of this interaction in horses, especially for In Vitro Fertilization (IVF) applications.
• Extracellular vesicles (EVs), which are crucial for cell-to-cell communication, were the key aspect of this interaction under examination.

Methodology

• After obtaining three horse genital tracts from a slaughterhouse, uterine explants were digested with enzymes to obtain cells to culture on an air-liquid interface (ALI) system, enabling them to polarise.
• The oviducts were squeezed to obtain spheroids, which along with the epithelial cells were cultured for three days to produce EVs.
• Sperm samples were then prepared, incubated with the EVs and monitored over several hours using confocal microscopy.
• Then, to analyze the EVs’ impact on the sperm, the researchers evaluated capacitation-related events, sperm motility, rates of acrosomal reaction (AR) and apoptosis.

Findings

• The study found that the size and concentration of EVs from uterine and oviductal tissues varied.
• Uterine EVs were detected in the head of sperm cells after 4 hours of incubation, whereas oviductal EVs were found in the middle piece after 1 hour.
• The rate of AR (a process in sperm to help penetrate the egg) was higher when sperm was incubated with uterine and oviductal EVs.
• Furthermore, the AR rate was the highest when the two types of EVs were combined.
• There were changes to the sperm motility consistent with hyperactivation when incubated with these EVs.

Conclusion

• The researchers concluded that EVs from the female genital tract stimulate equine sperm hyperactivation in vitro and induce AR. This implies potential improvements in fertilization rates.