Sperm Capacitation as an Oxidative Event

Eve de Lamirande and Cristian O'Flaherty

Abstract Capacitation is associated with a mild oxidative stress. Spermatozoa are the only cell type in which a reciprocal reactive oxygen species (ROS)-induced ROS formation is demonstrated, the superoxide anion (O2'-) promoting nitric oxide (NO') synthesis and vice versa. Both O2'- and NO' are essential and are synthesized by sperm enzymes, an oxidase, and nitric oxide synthase (NOS), and they have specific targets. Semenogelin, zinc ions, and the sulfhydryl/disulfide couple are natural regulator for both the oxidase and NOS and are also expected to directly regulate some of the enzymes involved in transduction cascades triggered by O2'- and NO'. ROS promote all the signal transduction pathways involved during capacitation leading to the late protein Tyr phosphorylation. Sperm hyperactivation and acrosome reaction are also modulated by ROS. Therefore, ROS play major role in sperm activation and related stimulation of several processes, multiplicity of enzymatic pathways and types of regulation, cross talks, apparent redundancy of mechanisms, etc. This is expected to insure that spermatozoa acquire their fertility potential.

Keywords Sperm capacitation • Mild oxidative event • Reactive oxygen species • Cell physiology • Sperm activation • Targets for ROS

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