Objective
To characterize in depth and investigate the role of exosomes present in seminal plasma in affecting parameters underlying sperm activity. Design: In vitro experimental study. Setting: Research hospital. Patient(s): Normozoospermic, severe asthenozoospermic, and post-vasectomy azoospermic men 18-55 years of age were considered for the study. Seminal plasma was collected and processed to separate spermatozoa and exosomes. Intervention(s): None. Main outcomes measure(s): Exosomes from seminal plasma were isolated and characterized by means of nanoparticle tracking analysis, transmission electron microscopy and Western blot. Exosome uptake by spermatozoa was monitored by means of immunofluorescence and flow cytometry. The effect of exosomes on spermatozoa was determined by evaluating progressive motility and capacitation, the latter assessed by means of tyrosine phosphorylation and acrosome reaction. Result(s): We isolated and characterized exosomes from seminal plasma of normo-, astheno-, and azoospermic patients. They display similar features in terms of shape, size, expression of canonic exosome markers and proteins involved in spermatozoa maturation, and fertilization capacity. After ejaculation, sperm cells are still receptive and are able to take up exosomes in a time- and pH-dependent manner. Exosomes derived from normozoospermic but not from asthenozoospermic individuals improve spermatozoa motility and trigger capacitation. Transfer of cysteine-rich secretory protein 1 from exosomes to spermatozoa may have a role in these phenomena.