Reactive Oxygen Species Block Sperm-Egg Fusion via Oxidation of Sperm Sulfhydryl Proteins in Mice

Abstract

The effects of reactive oxygen species (ROS) on mouse sperm-egg fusion were determined. Sperm were treated with superoxide and hydrogen peroxide generated by addition of xanthine oxidase (XO: 10–200 mlU/ml) to hypoxanthine (HX: 1 mM). While XO at concentrations higher than 100 mlU/ml decreased the motility and lipid peroxidation of sperm, XO at less than 50 mlU/ml had no such effect. However, 20–50 mlU/ml XO significantly suppressed sperm fusion with zona-free eggs. Two ROS scavengers, superoxide dismutase and catalase, attenuated the inhibition of sperm-egg fusion by HX-XO. The sulfhydryl (SH) reductant, dithiothreitol, also reversed the inhibition. The sperm SH-rich fusion-related proteins were highly sensitive to ROS. These results suggest that ROS at low concentrations may inhibit sperm-egg fusion via oxidation of the SH-proteins in the sperm membrane, without causing loss of motility.