Acrosome Reaction Induced by Recombinant Human Zona Pellucida 3 Peptides rhuZP3a22∼176 and rhuZP3b177∼348 and Their Mechanism

ABSTRACT: To explore the biological characteristics of the recombinant zona pellucida 3 (ZP3) peptides of rhuZP3a^22∼176 and rhuZP3b^177∼348, we examined whether rhuZP3a^22∼176 or rhuZP3b^177∼348 trigger the acrosome reaction (AR) of human spermatozoa and we investigated the underlying mechanism. The assessment of AR was performed using chlortetracycline staining. The intracellular free calcium concentration ([Ca²⁺]i) in Fura-2/AM-loaded human sperm was monitored with a spectrofluorophotometer. We found that rhuZP3a^22∼176 and rhuZP3b^177∼348 were capable of eliciting AR at different concentrations. With the addition of either peptide, the [Ca²⁺]i level was raised to a peak with or without a plateau. The AR could be inhibited by pertussis toxin (PTX), EGTA, and pimozide (a T-type calcium channel blocker), whereas verapamil was less effective in this regard. The results of the present study suggest that peptides rhuZP3a^22∼176 and rhuZP3b^177∼348 have a role similar to human ZP3, and that the mechanism of the response to the peptides involves influx of calcium, the G protein pathway, and a T-type calcium channel.