Triosephosphate isomerase (TPI) and epididymal secretory glutathione peroxidase (GPX5) are markers for boar sperm quality

• We studied the relationship between boar sperm quality and five sperm and seminal plasma proteins.
• Normalised levels of TPI and GPX5 were associated with boar sperm quality.
• No significant correlation was found between ACRBP, ODF1 and FN1 with sperm quality.
• Sperm TPI content and amounts of GPX5 in seminal plasma may be used as quality markers of boar sperm.

The present study sought to determine the relationship of three sperm proteins (acrosin binding protein, ACRBP; outer dense fibre protein 1, ODF1; and triosephosphate isomerase, TPI), and two seminal plasma proteins (fibronectin, FN1; and epididymal secretory glutathione peroxidase, GPX5) to conventional sperm quality parameters (sperm membrane integrity, morphology and motility) in pigs. With this purpose, 22 boar ejaculates were split into two groups according to their sperm quality (mean ± standard error of the mean, % viable sperm: 95.25 ± 0.53 vs. 78.22 ± 1.93; % morphologically normal sperm: 96.30 ± 0.66 vs. 80.81 ± 2.28). The amounts of these five proteins were evaluated through Western blot analysis and subsequently compared between these two groups through a t-test for independent samples. Normalised levels of TPI in sperm were significantly higher in the low than in the high sperm quality group. In addition, TPI was found to be negatively correlated with sperm membrane integrity, morphology and several parameters describing sperm motility. On the other hand, amounts of GPX5 in seminal plasma were also significantly higher in the low than in the high quality group, and this protein was also found to be negatively correlated with sperm membrane integrity and total and progressive sperm motility. By contrast, sperm content in ACRBP and ODF1 amounts of seminal plasma protein FN1 did not significantly differ between the two groups of sperm quality. Thus, we can conclude that sperm TPI content and amounts of GPX5 in seminal plasma may be used as quality markers of boar sperm.