Zona pellucida-induced acrosome reaction in human sperm: dependency on activation of pertussis toxin-sensitive Gi protein and extracellular calcium, and priming effect of progesterone and follicular fluid

Abstract

In these studies, we aimed to characterize the effects of the physiological, homologous agonists of the acrosome reaction, i.e. the zona pellucida (ZP) and progesterone/follicular fluid, on human sperm. The specific aims of our studies were: (i) to examine the dependency of the solubilized ZP-induced acrosome reaction on G(i) protein activation and presence of extracellular calcium; and (ii) to determine whether progesterone/follicular fluid exert a priming or synergist effect on the solubilized ZP-induced acrosome reaction. Highly motile sperm from fertile donors were exposed to the agonists in a microassay and the acrosomal status of live sperm was determined by indirect immunofluorescence using PSA-FITC/Hoechst double-staining. Pretreatment with pertussis-toxin (100 ng/ml) and EGTA (2.5 mmol/l) significantly inhibited the ZP-induced acrosome reaction without affecting the spontaneous rate of exocytosis. Progesterone (1.25 microg/ml) and human follicular fluid (10%) exerted a priming, time-dependent effect on the ZP-induced acrosome reaction. These studies demonstrated that: (i) acrosomal exocytosis of capacitated human sperm triggered by the homologous ZP is dependent on the activation of G(i) proteins (pertussis toxin-sensitive) and the presence of extracellular calcium; and (ii) progesterone and follicular fluid exert a priming effect on the ZP-induced acrosome reaction.

Progesterone primes zona pellucida‐induced activation of phospholipase A2 during acrosomal exocytosis in guinea pig spermatozoa

“…At low concentrations (2.5 mM; about one third of the maximal effective concentration, and within the range of concentrations seen in the oocyte vestments), progesterone enhanced exocytosis triggered by half-maximal concentrations of ZP. These results agree with our previous finding showing that the steroid primes the action of ZP in mouse sperm acrosomal exocytosis (Roldan et al, 1994a), and similar conclusions from experiments using boar (Melendrez et al, 1994) and human (Schuffner et al, 2002) spermatozoa. Therefore, it seems that the progesterone priming effect in eliciting exocytosis is a widespread phenomenon in mammalian spermatozoa, and consistent with the expected sequence of interactions of the sperm cell with the oocyte coats.…”

Dynamic resolution of acrosomal exocytosis in human sperm

“…Second, the acrosomal content disperses, revealing a new surface membranethe inner acrosomal membrane (IAM) -which is a requirement for fertilisation. The AR is induced by binding to the zona pellucida (Kopf and Gerton, 1991), probably after 'priming' by progesterone released from the oocyte and surrounding cells (Roldan et al, 1994;Schuffner et al, 2002;Harper et al, 2004). Exposure of acrosomal content therefore occurs when the sperm reaches the outer surface of the zona pellucida, yet for proteolytic activity of the enzymes to be of significance they must be present throughout zona pellucida penetration [a process that takes minutes (Yanagimachi, 1994)].…”

EFECTO DEL FLUIDO FOLICULAR SOBRE LA CAPACIDAD DE UNIÓN A ZONA PELÚCIDA DE ESPERMATOZOIDES EPIDIDIMARIOS DE ALPACA (Vicugna pacos)

“…Anteriormente, se ha podido reconocer para otras especies que el fluido folicular favorece ciertas funciones asociadas con la capacidad fecundante como la movilidad y la reacción acrosomal (Yanagimachi, 1969;Tesarík, 1985;Suarez et al, 1986;Morales et al, 1989;Ravnik et al, 1990;Hansen et al, 1991;McNutt y Killian, 1991;Ravnik et al, 1992;McNutt et al, 1994;Cheng et al, 1998;Jeon et al, 2001;Thérien et al, 2001;Briton-Jones et al, 2001;Schuffner et al, 2002;Getpook y Wirotkarun, 2007;Esmaeilpour et al, 2014;Leemans et al, 2015). Estudios previos en nuestro laboratorio determinaron que el fluido folicular favorece la movilidad espermática en alpaca (Bravo y Valdivia, 2017).…”