Inhibition of G protein in human sperm and its influence on acrosome reaction and zona pellucida binding
Objective: To evaluate human sperm acrosomal status, zona pellucida (ZP)-binding capacity, and sperm motion characteristics after treatment with pertussis toxin followed by exposure to increasing concentrations of solubilized human ZP. Design: Prospective analytical study. Setting: Normal human sperm donors in an academic research environment. Intervention: Sperm were prepared with a wash and swim-up method and treated with a final concentration of 100 ng/mL pertussis toxin. Acrosomal status were determined using a Pisum sativum agglutinin-fluorescein-isothiocyanate method after exposure of sperm to 0.25, 0.5, 0.75, and 1.00 ZP/μL solutions of human ZP. Zona binding potential was recorded using intact zona-binding assays. Motion characteristics were recorded with a semen analyzer. Main Outcome Measure: Percentage acrosome-reacted sperm, number of zona-bound sperm, and sperm motion parameters. Results: Spermatozoa treated with 100 ng/mL pertussis toxin, followed by ZP-mediated acrosome reaction induction, showed a significant decrease in the percentage of acrosome-reacted sperm compared with untreated controls. Motion characteristics of 3-hour capacitated sperm after treatment with either phosphate-buffered saline (PBS) or pertussis toxin were not different. Pertussis toxin-treated sperm populations bound significantly more sperm to the ZP after 4 hours incubation compared with the PBS-control groups: 137.1 ± 8.0 compared with 96.3 ± 7.0 (mean ± SEM). Conclusions: The data support the concept of the controlling mechanism and importance of G proteins during the ZP-mediated acrosome reaction. Intact acrosomes correlate with and are needed to ensure tight zona binding.