Changes of the Protein CoAlation Pattern in Response to Oxidative Stress and Capacitation in Human Spermatozoa.

The spermatozoa have limited antioxidant defences, a high polyunsaturated fatty acids content and the impossibility of synthesizing proteins, thus being susceptible to oxidative stress. High levels of reactive oxygen species (ROS) harm human spermatozoa, promoting oxidative damage to sperm lipids, proteins and DNA, leading to infertility. Coenzyme A (CoA) is a key metabolic integrator in all living cells. Recently, CoA was shown to function as a major cellular antioxidant mediated by a covalent modification of surface-exposed cysteines by CoA (protein CoAlation) under oxidative or metabolic stresses. Here, the profile of protein CoAlation was examined in sperm capacitation and in human spermatozoa treated with different oxidizing agents (hydrogen peroxide, (H2O2), diamide and tert-butyl hydroperoxide (t-BHP). Sperm viability and motility were also investigated. We found that H2O2 and diamide produced the highest levels of protein CoAlation and the greatest reduction of sperm motility without impairing viability. Protein CoAlation levels are regulated by 2-Cys peroxiredoxins (PRDXs). Capacitated spermatozoa showed lower levels of protein CoAlation than non-capacitation cells. This study is the first to demonstrate that PRDXs regulate protein CoAlation, which is part of the antioxidant response of human spermatozoa and participates in the redox regulation associated with sperm capacitation.

Redox Regulation to Modulate Phosphorylation Events in Human Spermatozoa.

Significance: Spermatozoa are complex and compartmentalized cells that undergo capacitation, a series of biochemical and morphological changes to acquire the ability to fertilize oocytes. Reactive oxygen species (ROS) have a prominent dual role in capacitation. At physiological levels, ROS regulate numerous cellular processes, including increases of cyclic adenosine monophosphate, calcium, and activation of phosphorylation events needed for capacitation. On the contrary, at high concentrations that do not impair sperm viability, ROS can cause loss of motility and inhibition of capacitation. Higher ROS concentrations promote oxidation of lipids, proteins, and DNA leading to cell death, and these damages have been associated with male infertility. Critical Issues: When incubated under specific conditions, spermatozoa can produce low and controlled amounts of ROS that are not harmful but instead regulate numerous cellular processes, including the phosphorylation of tyrosine, serine, and threonine residues in critical proteins needed for sperm capacitation. Here, we outline the complex redox signaling in human spermatozoa needed to achieve fertility and the role of ROS as physiological mediators that trigger phosphorylation cascades. Moreover, we illustrate the importance of various phosphoproteins in spermatozoa capacitation, viability, and hyperactive motility. Future Directions: Further studies to elucidate the different phosphorylation players during sperm capacitation and acrosome reaction (the regulated exocytotic event that releases proteolytic enzymes allowing the spermatozoon to penetrate the zona pellucida and fertilize the oocyte) are essential to understand how the spermatozoon acquires the fertilizing ability to fertilize the oocyte. This knowledge will serve to develop novel diagnostic tools and therapy for male infertility. Antioxid. Redox Signal. 37, 437-450.