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BackgroundPlasma membranes of ejaculated sperm are covered by epididymal and accessory glands secreted proteins that must be released from sperm surface during the female reproductive tract passage in order to capacitate and fertilize the oocyte.ObjectivesAs human sperm plasma membrane‐associated proteins (SMAP) have not yet been investigated, the aim of this study was to characterize the SMAP released during in vitro human capacitation and to study their possible role as decapacitation factors.Materials and MethodsSMAP were characterized by 2‐dimensional electrophoresis and mass spectrometry analysis. Besides, we explored SMAP effects on motility, protein tyrosine phosphorylation, and calcium ionophore‐induced acrosome reaction of spermatozoa either incubated for 6 h in capacitating medium ± SMAP or for 5 h in capacitating medium alone followed by incubation for 1 h ± SMAP.ResultsMass spectrometry analysis allowed the identification of 29 proteins, all of which have previously been identified in the human seminal fluid. Spermatozoa incubated for 6 h under capacitating conditions in the presence of the SMAP showed a significant decrease in the incidence of non‐progressive motility, hyperactivation, protein tyrosine phosphorylation, and calcium ionophore‐induced acrosome reaction. However, spermatozoa incubated for 5 h in capacitating medium and further incubated for 1 h with the SMAP showed a lower percentage of spermatozoa with non‐progressive motility and hyperactivated cells but no effects on protein tyrosine phosphorylation were detected.Discussion and ConclusionsOur results indicate that SMAP inhibit the progress of human sperm capacitation, but only motility changes related to capacitation may be reversed by these proteins. The study of the identified proteins on sperm function and their mechanisms of action on this cell may contribute to the understanding of their role during capacitation.

Sperm residency in female reproductive tract is essential to undergo functional changes that allow the cell to encounter the oocyte and fertilize it. Those changes, known as capacitation, are modulated by molecules located in the uterotubal surface and fluids. During the fertile window, there is a notable increase in some reproductive hormones such as progesterone, estradiol, and luteinizing hormone in the female reproductive tract, so spermatozoa are exposed to these hormones in an environment that must favor gamete encountering and fusion. This spatiotemporal coincidence suggests that they are suitable candidates to modulate sperm function in order to synchronize the events that ultimately allow the success of fertilization. The presence of receptors for these hormones in the human sperm has been described, but their physiological relevance and mechanisms of action have been either subject of controversy or not properly investigated. This review intends to summarize the evidence that support the participation of these hormones in the regulation of sperm capacitation.

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