Proteomic characterization of human sperm plasma membrane-associated proteins and their role in capacitation.

Abstract

Plasma 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. As human sperm plasma membrane-associated proteins (SMAP) have not yet been investigated, the aim of this study was to characterize the SMAP released during invitro human capacitation and to study their possible role as decapacitation factors. SMAP 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 6h in capacitating medium±SMAP or for 5h in capacitating medium alone followed by incubation for 1h±SMAP. Mass spectrometry analysis allowed the identification of 29 proteins, all of which have previously been identified in the human seminal fluid. Spermatozoa incubated for 6h 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 5h in capacitating medium and further incubated for 1h 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. Our 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.