Sperm and seminal plasma proteomics of high- versus low-fertility Holstein bulls

Sperm are highly specialized compartmentalized cells, with unique compositional, morphological and functional properties, including a plasma membrane that undergoes dynamic protein remodeling and surface modifications. Seminal plasma is a highly complex biological fluid containing proteins, amino acids, enzymes, fructose and other carbohydrates, lipids, major minerals and trace elements. Seminal plasma proteins are involved in regulation of osmotic pressure and pH of seminal plasma, transport of ions, lipid and hormones. The objective was to compare sperm and seminal plasma proteomes of bulls with differing fertility and to relate differences to biological processes. Semen was collected from bulls with high or low fertility (4 bulls in each category). Sperm and seminal plasma proteins were isolated, purified, subjected to 2-D gel electrophoresis, protein identification and ontology. In sperm and seminal plasma, binder of sperm proteins (BSP)-1, -3 and -5, and spermadhesin-1, ALB, TIMP, AKI and PEBP1 were higher for high-versus low-fertility bulls (P < 0.05), whereas proteins CLU, CCT5 and 8, ELSPbP1, and PSMA6 were more abundant in sperm and seminal plasma of low- versus high-fertility bulls (P < 0.05). Further, HSP90, ZFP34, IFNRF4, BCL62, NADHD, TUBB3 and Histone H1 were in greater abundance in sperm of high- compared with low-fertility bulls. The two key biological processes of proteins differentially expressed in high- and low-fertility bulls were metabolic processes and biological regulation. The most prominent molecular functions for proteins that differed are binding, catalytic and receptor activities. The main cellular components for proteins that differed are cellular, extracellular, and plasma membrane. Since protein content differed in high- versus low-fertility bulls, we inferred that the efficiency of associated sperm functions that are necessary for fertility may also differ between high- and low-fertility semen. In conclusion, differences between high- and low-fertility bulls regarding abundance of sperm and seminal plasma proteins likely contributed to differences in fertility.