ИСТИНА

Sperm-specific glycolytic enzymes, first of all glyceraldehyde-3-phosphate dehydrogenase (GAPDS), play a crucial role in the energy supply for the motility of sperms of mammals including human. The significance of GAPDS for the progressive motility of mammalian sperms is confirmed by the presence of a special isoform of the enzyme that is firmly attached to the cytoskeleton of the sperm flagellum only in mammals. Inactivation of GAPDS by reactive oxygen species (ROS) results in the loss of the sperm motility. A high sensitivity to the action of ROS is related to the high reactivity of the sulfhydryl group of the active site of GAPDS, which was demonstrated for the purified recombinant human enzyme. This process may be prevented by the addition of different antioxidants, but the inactivation of GAPDS in sperms in situ is irreversible. However, low doses of ROS exert an opposite effect on the sperm motility. Incubation of semen samples with 10 and 100 µM hydrogen peroxide increased the content of spermatozoa with progressive motility by 20 and 18%, respectively, and enhanced the activity of GAPDS in the sperm cells by 27 and 20% compared to the semen sample incubated without additions. It was also shown that incubation with 10 µM hydrogen peroxide increased the content of reduced glutathione (GSH) in sperm cells by 50% on average compared to that in the control samples. It is supposed that low concentrations of hydrogen peroxide activate the pentose phosphate pathway, resulting in NADPH synthesis and the reduction of the oxidized glutathione by glutathione reductase yielding GSH. The formed GSH reduces the oxidized cysteine residues of the GAPDS active site, increasing the activity of the enzyme, which in turn enhances the content of sperm cells with progressive motility. Thus, the increase of motile spermatozoa in the presence of low concentrations of hydrogen peroxide may serve as an indicator of normal functioning of the antioxidant defense system in sperm cells. Acknowledgments: This work was supported by grants from the Russian Foundation for Basic Research №13-04-00823 and № 14-04-00331.