The importance of redox regulated pathways in sperm cell biology.

Redox regulated events are fundamental to our understanding of many cellular pathways and pathological processes. On the one hand, production of reactive oxygen species by mammalian spermatozoa has been associated with a loss of cell function and DNA integrity as a consequence of oxidative stress. These cells are exquisitely sensitive to such damage as a consequence of their relative lack of cytosolic antioxidant enzymes and relative abundance of polyunsaturated fatty acids. Given this susceptibility, it is surprising to discover that spermatozoa are intensely redox active cells and professional generators of reactive oxygen species. The latter are physiologically important to the spermatozoa in regulating every aspect of sperm function examined, including their movement characteristics, capacitation, sperm-zona interaction, the acrosome reaction and sperm-oocyte fusion. The molecular basis of this redox drive is still poorly understood in terms of the source of the reactive oxygen species and the mechanisms by which these reactive metabolites enhance sperm function. Recent advances include the discovery of NOX5 in the male germ line and elucidation of the role of reactive oxygen species in controlling a unique signal transduction cascade associated with sperm capacitation. Given the central importance of redox chemistry in the control of sperm function further research in this area may uncover valuable targets for contraceptive intervention.