Differential proteome association study of freeze-thaw damage in ram sperm

In this study proteomics analysis was performed to investigate damage caused to ram sperm by the freeze-thaw process. Sperm motility, viability, reactive oxygen species (ROS) and adenosine triphosphate (ATP) content were measured to evaluate sperm quality. Compared with fresh groups, motility, viability and ATP content were all lower in freeze-thawed sperm (P < 0.001), and ROS content was higher (P < 0.001). Moreover, 25 differential protein spots were detected in two-dimensional gels using PDQuest 8.0 software and the corresponding proteins were identified using matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometry (MALDI-TOF-TOF MS) coupled with searching of the NCBI protein sequence database. Among these proteins, hexokinase1 (HXK1), the enzyme that catalyzes the first step of glycolysis in the sperm glycolytic pathway, is known to be associated with sperm motility. Casein kinase II subunit alpha (CSNK2A2), a serine/threonine-selective protein kinase, is associated with sperm apoptosis. We used immunoblotting and immunofluorescence to analyze the expression and localization of these two proteins. HXK1 and CSNK2A2 expression levels in fresh sperm were significantly higher than that in freeze-thawed sperm (P < 0.001). HXK1 and CSNK2A2 were detected in the main part of the sperm flagellum, and the immunofluorescence signal from these proteins was weakened in the freeze-thawed group. Decreased expression of HXK1 and CSNK2A2 may be associated with decreased sperm motility and viability following freeze-thawing.