Comparative Proteomic Analysis of Young and Adult Bull (Bos taurus) Cryopreserved Semen

SIMPLE SUMMARY: In this study, we compared sperm quality parameters and proteomic profile of the cryopreserved semen (spermatozoa and supernatant) obtained from young (2 years old) and adult (4 years old) Holstein Friesian bulls. We found differences in proteome composition between sperm from young and adult bulls and identified important age-related proteins both in spermatozoa and supernatant after thawing. Our results indicate higher maturity of adult bull spermatozoa compared to the spermatozoa of young bulls, which might contribute to an increased ability to fertilize an oocyte. On the other hand, young bull spermatozoa were equipped with proteins involved in cytoskeleton development, suggesting that developmental processes are still in progress. ABSTRACT: The age of the bull is widely accepted to influence the production of sperm, affecting the amount and quality of produced semen, which in turn impacts the results of cryopreservation. However, the exact influence of the maturation process on cryopreserved sperm, as well as the underlying molecular mechanisms of this process, are not fully understood. The goal of this study was to evaluate changes in the proteome of thawed semen (spermatozoa and supernatant) collected from young and adult bulls (n = 6) using the 2D-DIGE approach. The quality of semen was assessed using a CASA system and flow cytometry. We found no significant age-related variation in semen quality, with the exception of the average path velocity of sperm movement, which was higher in adult bulls. Proteomic analysis indicated 15 spermatozoa proteins and 10 supernatant proteins with significant age-related changes. Our results suggest that semen from adult bulls is better equipped with proteins related to energy production, protection of spermatozoa against oxidative stress and fertilizing ability. Proteins increased in abundance in young bull spermatozoa were connected to the cytoskeleton and its development, which strongly suggests that developmental processes are still in progress. In conclusion, our results provide novel insight into the mechanism of the development of the male reproductive system of cattle.