Infertility has become a global health issue, with approximately 50% of infertility cases generated by disorders in male reproduction. Spermatozoa are conveyed towards female genital tracts in a safe surrounding provided by the seminal plasma. Interestingly, this dynamically changing medium is a rich source of proteins, essential not only for sperm transport, but also for its protection and maturation. Most of the seminal proteins are acquired by spermatozoa in transit through exosomes (epididymosomes and prostasomes). The high number of seminal proteins, the increasing knowledge of their origins and biological functions and their differential expression in the case of azoospermia, asthenozoospermia, oligozoospermia and teratozoospermia or other conditions of male infertility have allowed the identification of a wide variety of biomarker candidates and their involvement in biological pathways, thus to strongly suggest that the proteomic landscape of seminal plasma may be a potential indicator of sperm dysfunction. This review summarizes the current knowledge in seminal plasma proteomics and its potentiality as a diagnostic tool in different degrees of male infertility.

Summary: Kisspeptin, the product of the KISS1 gene, plays an essential role in the regulation of spermatogenesis acting primarily at the hypothalamic level of the gonadotropic axis. However, the presence of kisspeptin and its canonical receptor, KISS1R, in spermatozoa has not been explored nor the direct effects of kisspeptin on sperm function have been studied so far. In the present study, we analysed the expression of kisspeptin and its receptor in sperm cells by western blot and immunocytochemistry assays and evaluated the effects of exposure to kisspeptin on sperm intracellular Ca²⁺ concentration, [Ca²⁺]i, sperm motility, sperm hyperactivation and the acrosome reaction. Changes in [Ca²⁺]i were monitored using Fura‐2, sperm kinematic parameters were measured using computer‐assisted sperm analysis (CASA), and the acrosome reaction was measured using fluorescein isothiocyanate‐coupled Pisum sativum agglutinin lectin (FITC–PSA method). We found that kisspeptin and its receptor are present in sperm cells, where both are mainly localized in the sperm head, around the neck and in the flagellum midpiece. Exposure to kisspeptin caused a slow, progressive increase in [Ca²⁺]i, which reached a plateau about 3–6 min after kisspeptin exposure. In addition, kisspeptin modulated sperm progressive motility causing a biphasic (stimulatory and inhibitory) response and also induced transient sperm hyperactivation. The effects of kisspeptin on sperm motility and hyperactivation were inhibited by the antagonist of KISS1R, peptide 234. Kisspeptin did not induce the acrosome reaction in human spermatozoa. These data show for the first time that kisspeptin and its receptor are present in human spermatozoa and modulate key parameters of sperm function. This may represent an additional mechanism for their crucial function in the control of male fertility.