Levels of Protein CoAlation Regulate Redox Signaling Events of Human Sperm Capacitation

Infertility is a global health problem, with male factors contributing to nearly half of all cases. Up to 30% of male infertility is classified as idiopathic, in part because routine semen analysis does not assess sperm fertilizing competence. Capacitation is a complex process that endows spermatozoa with the competence to fertilize the oocyte, and it depends on oxidant-driven phosphorylation events. These events include increased PKA substrate and tyrosine phosphorylation, which promote hyperactivated motility and the acrosome reaction. These pathways are normally restrained by decapacitation factors that must be relieved in the female reproductive tract before capacitation can proceed. Protein CoAlation is an antioxidant modification of protein thiols through a disulfide bond with coenzyme A (CoASH). We previously detected protein CoAlation in human spermatozoa and observed that its levels decline during capacitation, but its function was unknown. We hypothesized that protein CoAlation functions as a decapacitation mechanism that prevents redox signalling, enabling oxidative activation of phosphorylation events during capacitation. Using spermatozoa from healthy human donors, we leveraged subcellular fractionation, immunocytochemistry, computer-assisted sperm analysis (CASA), and immunoblotting to determine the sperm protein CoAlation profile, assess CoASH biosynthetic enzymes, and test how pharmacological modulation of CoAlation levels influences capacitation. CoAlated proteins were distributed across intracellular sperm compartments, and spermatozoa possess the CoASH biosynthetic enzymes PANK2 and CoASY, indicating an intrinsic capacity for CoAlation. Inhibition of CoASH biosynthesis reduced CoAlation and enhanced PKA substrate phosphorylation, tyrosine phosphorylation, hyperactivated motility, and the progesterone-induced acrosome reaction under capacitating conditions. Pantothenic acid supplementation increased CoAlation and suppressed these processes without impairing viability or baseline motility. These findings indicate that high levels of protein CoAlation in several protein bands are a pre-existing feature of the non-capacitated state that restrains the redox-regulated events of capacitation and that its decline is required to permit sperm capacitation. CoAlation levels may emerge as a biomarker of sperm capacitation and fertilizing competence.