Protective roles of seminal plasma exosomes and microvesicles during human sperm cryopreservation

Abstract

Research question

Do seminal plasma microvesicles and exosomes, as two subtypes of extracellular vesicles, exert cryoprotective properties in sperm cryopreservation?

Design

Microvesicles and exosomes isolated from normozoospermic semen samples (n = 10) by serial ultracentrifugation were determined using scanning electron microscopy, dynamic light scattering and western blot analysis. The interactions between extracellular vesicles and spermatozoa were detected using Dil labelling. Purified spermatozoa from different normozoospermic samples (n = 25) were then treated individually with exosomes or microvesicles for 1 h and subsequently cryopreserved. The effects of extracellular vesicles during cryopreservation were investigated by determining post-thaw sperm motility, morphology, viability, reactive oxygen species (ROS) generation, lipid peroxidation, total antioxidant capacity (TAC), mitochondrial membrane potential (MMP), DNA integrity, and apoptosis rate.

Results

Microvesicles and exosomes displayed a round-shape morphology, with about 70% of exosomes ranging from 43–144 nm, microvesicles ranging from 144.5–486 nm and both expressed tetraspanin markers. Fluorescence microscopy showed that exosomes and microvesicles absorbed mainly in the sperm head and less frequently in the neck and tail. The post-thawing results indicated that the diluent with exosomes or microvesicles had improved sperm motility (P = 0.007), morphology (P < 0.001) and viability (P < 0.001) compared with untreated samples. The ROS levels decreased significantly (P = 0.001), with a consequent decrease in DNA damage (P = 0.001). The TAC activity (P = 0.001) and MMP levels (P = 0.001) were also significantly improved; levels of malondialdehyde (MDA) (P = 0.62) and apoptosis rate (P = 1.000) remained unchanged.

Conclusion

Seminal plasma microvesicles and exosomes could protect spermatozoa from cryopreservation chilling injuries.