Human Sperm Plasma Membrane Progesterone Receptor(s) and the Acrosome Reaction1

Abstract

Progesterone initiation of te human sperm acrosome reaction (AR) includes stimulation of a transient Ca2+ influx and a transient Cl- efflux. A role for one or more plasma membrane receptors has been suggested, but, except for evidence supporting the involvement of a sperm GABAA-like receptor/Cl- channel, there is little information about possible receptor identity. Here, we attempt to identify plasma membrane progesterone receptors in human sperm using a mouse monoclonal antibody (mAb-C262) raised against the C-terminal steroid-binding domain of the human intracellular progesterone receptor. C-262 inhibited the progesterone-initiated AR in a dose-dependent manner. Maximum inhibition was 77% as detected by fluorescein isothiocyanate (FITC)-concanavalin A (conA). Motility was unaffected. A control mouse mAb (h-151) raised against the human estrogen receptor did not inhibit the progesterone-initiated AR. Western blotting with C-262, but not with h-151, detected a major sperm protein band of 50-52 kDa. In indirect immunofluorescence localization studies, live and ethanol-fixed uncapacitated sperm and fixed capacitated sperm incubated with C-262, but not with h-151, displayed fluorescence at the equatorial segment region of the sperm head plasma membrane. In spectrofluorometric studies using capacitated sperm loaded with the Ca2+ probe Fura-2 or the Cl- probe MEQ, C-262 but not h-151 inhibited both Ca2+ influx and Cl- efflux. These ion fluxes could be due to the binding of progesterone to two different receptor/channels or to its binding to one and cross talk with the other. Our results strongly support the involvement of sperm plasma membrane receptors in the progesterone-initiated AR and provide a candidate for one such receptor.

Suppression of progesterone-enhanced hyperactivation in hamster spermatozoa by estrogen

“…It also stimulates ZP penetration and the AR in hamster spermatozoa (Libersky & Boatman 1995b, Llanos & Anabalon 1996. Although spermatozoa do not have a classic intracellular progesterone receptor (PGR), a PGR is present in the cell membrane (Sabeur et al 1996, Baldi et al 1998, 2009, Lösel & Wehling 2003, Luconi et al 2004, Jang & Yi 2005. Moreover, it has been suggested that progesterone binds to the acrosome region, and PGR is localized to the same region in human (Gadkar et al 2002) and hamster spermatozoa (Noguchi et al 2008).…”

Spermatozoa Epididymal Maturation in the Mexican Big-Eared Bat (Corynorhinus Mexicanus)

“…At least 200 spermatozoa were counted and classified according to their acrosome fluorescence. The acrosome reaction was induced in previously capacitated spermatozoa, either by the addition of 100 ml of A23187 diluted stock solution to a final concentration of 10 mM of the ionophore, or by the addition of progesterone to a final concentration of 3.18 mM [Sabeur et al 1996] in the capacitating medium and the incubation was continued under the same conditions. After 15, 30, 45 and 60 min at 371C, in accord with our previous results [García-Macedo et al 2001;Á valos-Rodríguez et al 2004], samples were removed, fixed, and the percentage of acrosome reacted spermatozoa was determined by CBB staining [Miller et al 1993].…”

Biphasic Effect of GABA on Rat Sperm Acrosome Reaction: Involvement of GABA A and GABA B Receptors

“…Progesterone induces AR in human sperm by interacting with a steroid receptor located in the plasma membrane. This membrane receptor is distinctly di erent from the classical nuclear receptor [4,22,26,30] and may be related to the GABA A receptor=Cl 7 channel [21].…”