Uteroglobin and transglutaminase modulate human sperm functions

\During the process of capacitation, spermatozoa undergo significant change s in membrane composition, including removal of decapacitating factors (DFs ), which are present in seminal plasma, that lead to increased sensitivity to physiological stimuli of the acrosome reaction. In the present study we investigated the presence, localization, and effects on human spermatozoa o f 2 proteins of seminal plasma origin, uteroglobin (UG) and transglutaminas e (TG). These 2 proteins interact with one another because TG promotes cova lent links of UG to sperm surface proteins. We found that UG is localized a round the entire surface of ejaculated human sperm, whereas TG is predomina ntly localized in the neck. FACScan analysis confirmed the surface localiza tion of both antigens and demonstrated that swim-up selection of spermatozo a was associated with a significant reduction in the contents of the 2 subs tances when compared with unselected samples. Western blot analysis of UG i n total sperm lysates confirmed the lower content of the protein in swim-up -selected sperm. Swim-up-selected sperm were characterized by their ability to undergo a spontaneous, time-dependent increase of capacitation-characte ristic chlortetracycline pattern of fluorescence and increase in responsive ness to progesterone. Such changes were not observed in unselected sperm. E xogenous addition of TG, together with recombinant rabbit UG, prevented the spontaneous increase in responsiveness to progesterone (acrosome reaction and intracellular calcium) at 24 hours in swim-up-selected sperm, suggestin g the occurrence of a capacitation-inhibiting activity of the 2 substances. In addition, we found that endogenous UG and TG contents, as determined by FACScan analysis, were negatively correlated (P < .0001) with sperm motili ty and that exogenous addition of the 2 substances resulted in a substantia l reduction of progressive motility (P < .01). Collectively, these data ind icate that TG and UG represent 2 DFs, and contribute to understanding the b iochemical mechanisms that characterize the process of capacitation.