Effect of seminal plasma proteins on the motile sperm subpopulations in ram ejaculates

It has been proposed that seminal plasma proteins (SPP) support survival of ram spermatozoa, exerting a dual effect, both capacitating and decapacitating. In this study, changes in motility patterns of ram spermatozoa capacitated in the presence of epidermal growth factor (EGF) were evaluated. Clustering procedures were used to determine the presence of sperm subpopulations with specific motion characteristics. Four sperm subpopulations (SP) were defined after the application of a principal component analysis procedure. Progressive spermatozoa with high straightness (STR) were found in SP1, reflected in the high linearity (LIN) and STR values and low amplitude of lateral head movement (ALH; rapid, non-hyperactivated spermatozoa). SP2 spermatozoa seemed to be starting to acquire hyperactivated motility, while the SP3 group consisted of rapid, hyperactivated spermatozoa. SP4 showed less-vigorous spermatozoa, with non-linear motility. The addition of SPP before in vitro capacitation with EGF induced a decrease in SP1 and an increase in SP3. However, a reduction in the chlortetracycline-capacitated sperm rate and protein tyrosine phosphorylation was found, which corroborates with the hypothesis that the SPP protective effect on spermatozoa is related to their decapacitating role. These findings allow us to deduce that ram spermatozoa are able to undergo capacitation with no hyperactivation and that SPP are able to induce hyperactivation in spermatozoa but maintain them in a decapacitated state.