In vitro cultured human endometrial cells release extracellular vesicles that can be uptaken by spermatozoa

Extracellular vesicles (EVs) derived from different parts of the male reproductive tract can be internalized by human spermatozoa affecting their maturation and regulating their functions. Here we demonstrate that EVs derived from the female tract can be uptaken by sperm and affect their competence. Primary endometrial cells release EVs with a diameter between 50 and 350 nm and bear the standard vesicle and exosome marker proteins CD63, CD9, TSG101 and ALIX. The uptake of dye-labelled endometrial cell-derived EVs by spermatozoa, quantified as fluorescence intensity, was significantly higher when EVs were derived from cells in the proliferative phase. Vital, motile fluorescent sperm could be appreciated after a 48-hour co-incubation with endometrial cells previously labelled with the Vybrant™ DiO dye. EV internalization by sperm was blocked at 4 °C and by incubation with filipin, suggesting an energy-dependent process probably attributable to the lipid-raft domain mediated-endocytosis. Sperm ability to undergo capacitation and acrosome reaction was stimulated by endometrial cell-derived EVs as manifested by the increased protein tyrosine phosphorylation and evident reactivity when stimulated with a calcium ionophore. Based on these findings, EVs exchange may be suggested as an emerging way through which female reproductive tract cells can interact with the passing spermatozoa.