The achievement of boar sperm in vitro capacitation is related to an increase of disrupted disulphide bonds and intracellular reactive oxygen species levels

Abstract

The aim of this work was to determine the relationship of intracellular reactive oxygen species (ROS) and the disulphide bonds established between sperm proteins with the achievement of capacitation in boar spermatozoa. With this purpose, spermatozoa were incubated in a specifically designed in vitro capacitation medium (CM) in the presence or absence of reduced glutathione (GSH). Incubation of boar spermatozoa in CM for 4 h significantly (p < 0.05) increased free cysteine residues, which is a marker of disrupted disulphide bonds, and also intracellular ROS levels. The addition of GSH to the medium prevented most capacitation‐like changes in sperm motility, membrane lipid disorder, mitochondrial membrane potential, intracellular calcium levels and localization of tyrosine‐phosphorylated proteins (pTyr), but not in tyrosine phosphorylation of P32. These effects were accompanied by the inhibition of the ability of sperm cells to trigger the acrosome exocytosis in response to progesterone. When GSH was added together with progesterone after 4 h of incubation, acrosome exocytosis was not altered, but the subsequent decrease in intracellular calcium observed in controls cells was inhibited. Furthermore, co‐incubation of oocytes with spermatozoa previously incubated in CM in the presence of GSH for 4 h significantly (p < 0.05) increased the number of spermatozoa attached to the oocyte surface but decreased normal fertilization rates. Our results suggest that boar sperm capacitation is related to an increase in disrupted disulphide bonds and intracellular ROS levels and that both events are related to the regulation of hyperactivated motility, intracellular calcium dynamics, sperm binding ability to the oocyte and achievement of proper nuclear decondensation upon oocyte penetration.