FACTORS AFFECTING FERTILIZATION - ENDOMETRIAL PLACENTAL PROTEIN-14 REDUCES THE CAPACITY OF HUMAN SPERMATOZOA TO BIND TO THE HUMAN ZONA-PELLUCIDA

Objective: To examine whether placental protein 14 (PP14) may affect d irectly those sperm functions crucial to fertilization and early embry o development. Design: In these prospective studies, we evaluated seme n samples of fertile men incubated under capacitating conditions with and without PP14. Setting: Academic tertiary institution. Intervention s: Biologically active PP14 was purified from human midtrimester amnio tic fluid by anion exchange and immunoaffinity chromatography. After s eparation of the motile fraction, spermatozoa were incubated for 30 mi nutes with or without PP14 (concentration range of 0.01 to 100 mu g/mL ), washed, and then aliquots were prepared for use in the different as says. Human sperm-zona pellucida (ZP) binding was assessed using the h emizona assay (HZA) in a 4-hour gametes coincubation period. Sperm mot ility parameters were evaluated using a computerized semen analyzer. T he acrosome reaction (AR) was determined by fluorescein isothiocyanate -conjugated Pisum sativum agglutinin and indirect immunofluorescence. Main Outcome Measures: Sperm-ZP binding, sperm motility patterns, and AR. Results: Preincubation of sperm (and not the hemizonae) with PP14 produced a significant and dose-dependent inhibition of binding in the HZA. Monoclonal antibodies generated against PP14 showed no direct ef fect in the HZA and partially neutralized the inhibitory activity of P P14 in the HZA. Insulin-like growth factor binding protein-1 (IGFBP-1) , and endometrial stromal cell product, showed no effect in the HZA. N either PP14 nor IGFBP-1 interfered with sperm motility parameters or t he AR. Conclusions: Placental protein 14 produced a potent, fast, and dose-dependent inhibition of binding of human spermatozoa to the human ZP without affecting other prefertilization events (i.e., hyperactiva ted motility or AR). The detrimental effect on sperm-zona interaction seems to be specific for this endometrial epithelial protein (not obse rved with an endometrial stromal product) and may have fundamental bea rance to the fertilization process thus providing a mechanism for endo metriosis-related infertility.