Inhibition of acrosin activity with a trypsin inhibitor blocks human sperm penetration of the zona pellucida.
To evaluate the role of acrosin in human sperm penetration of the zona pellucida (ZP), sperm-oocyte interaction was studied after acrosin activity was blocked with soybean trypsin inhibitor (SBTI). Oocytes that had failed to fertilize because of sperm pathology in a clinical in vitro fertilization program were used to assess sperm binding to and penetration into the ZP. The acrosome reaction of sperm bound to the ZP was determined using fluorescein-labeled Pisum sativum agglutinin after sperm were removed from the ZP. Acrosin activity, determined by a gelatin substrate film method, was severely inhibited by 2 mg/ml SBTI. Sperm motility and movement characteristics, assessed by a Hamilton-Thorn motility analyzer, were unchanged after 6-h incubation with SBTI. Inhibition of acrosin activity did not affect the number of sperm bound to the ZP but completely blocked sperm penetration of the ZP after a 5-h incubation. SBTI did not influence the spontaneous acrosome loss of sperm in culture medium after 6-h and 20-h incubations, but the percentage of acrosome-reacted sperm bound to the ZP was significantly reduced. It was concluded that acrosin activity plays a key role in sperm-zona interaction in humans. Motile sperm are unable to penetrate the ZP when acrosin activity is inhibited. This might result from interference with a phase of the sperm-ZP binding reaction or with a lytic action of acrosin. Also, acrosin may be involved in the acrosome reaction induced by sperm binding to the ZP.
Liu
D Y
DY
Department of Obstetrics and Gynaecology, University of Melbourne, Victoria, Australia.
Baker
H W
HW
D000176:Acrosin / Q000502:physiology*; D000177:Acrosome / Q000502:physiology; D005260:Female; D006801:Humans; D006868:Hydrolysis / Q000187:drug effects; D066298:In Vitro Techniques; D008297:Male; D011506:Proteins / Q000378:metabolism; D013081:Sperm Motility / Q000187:drug effects; D013084:Sperm-Ovum Interactions / Q000187:drug effects*; D014361:Trypsin Inhibitors / Q000494:pharmacology*; D015044:Zona Pellucida / Q000502:physiology*
D011506:Proteins; D014361:Trypsin Inhibitors; D000176:Acrosin