Seminal plasma proteins of adult boars and correlations with sperm parameters

The present study was conducted to identify the major seminal plasma protein profile of boars and its associations with semen criteria. Semen samples were collected from 12 adult boars and subjected to evaluation of sperm parameters (motility, morphology, vitality, and percent of cells with intact acrosome). Seminal plasma was obtained by centrifugation, analyzed by two-dimensional SDS-PAGE, and proteins identified by mass spectrometry (electrospray ionization quadrupole time-of-flight). We tested regression models using spot intensities related to the same proteins as independent variables and semen parameters as dependent variables (P ≤ 0.05). One hundred twelve spots were identified in the boar seminal plasma gels, equivalent to 39 different proteins. Spermadhesin porcine seminal protein (PSP)-I and PSP-II, as well as spermadhesins AQN-1, AQN-3 and AWN-1 represented 45.2 ± 8% of the total intensity of all spots. Other proteins expressed in the boar seminal plasma included albumin, complement proteins (complement factor H precursor, complement C3 precursor and adipsin/complement factor D), immunoglobulins (IgG heavy chain precursor, IgG delta heavy chain membrane bound form, IgG gamma-chain, Ig lambda chain V-C region PLC3, and CH4 and secreted domains of swine IgM), IgG-binding proteins, epididymal-specific lipocalin 5, epididymal secretory protein E1 precursor, epididymal secretory glutathione peroxidase precursor, transferrin, lactotransferrin and fibronectin type 1 (FN1). On the basis of the regression analysis, the percentage of sperm with midpiece defects was related to the amount of CH4 and secreted domains of swine IgM and FN1 (r² = 0.58, P = 0.006), IgG-binding protein (r² = 0.41, P = 0.024), complement factor H precursor (r² = 0.61, P = 0.014) and lactadherin (r² = 0.45, P = 0.033). The percentage of sperm with tail defects was also related to CH4 and secreted domains of swine IgM and FN1 (r² = 0.40, P = 0.034), IgG-binding protein (r² = 0.35, P = 0.043) and lactadherin (r² = 0.74, P = 0.001). Sperm motility, in turn, had association with the intensities of spots identified as lactadherin (r² = 0.48, P = 0.027). In conclusion, we presently describe the major proteome of boar seminal plasma and significant associations between specific seminal plasma proteins and semen parameters. Such relationships will serve as the basis for determination of molecular markers of sperm function in the swine species.