Interpretive Summary: Identification of oxidatively modified proteins during cryopreservation of carp semen.By: Dr. Caitlin Vonderohe
The ability to freeze semen represents a valuable opportunity to improve fish breeding and conservation programs. However, the act of freezing, or cryopreserving, can seriously damage or even kill spermatozoa. Cryopreservation can result in the formation of reactive oxygen species that can severely damage the plasma membrane of sperm which can be fatal to the sperm cells. In “Identification of oxidatively modified proteins due to cryopreservation of carp semen,” published in the Journal of Animal Science in April 2018, the authors compared the degree of protein oxidation between fresh, fresh-diluted and cryopreserved carp semen. The authors used the degree of protein carbonylation as a marker of protein oxidation in fresh, fresh-diluted and cryopreserved carp semen. Semen was collected from healthy male carp housed at the Institute of Ichthyobiology and Aquaculture of the Polish Academy of Sciences in Golysz, Poland, in the middle of spawning season. The semen was evaluated for quality to select samples that met the minimum quality requirements for freezing. The semen samples were diluted in a semen extender. One part of this diluted sample was further analyzed for changes that occur in the spermatozoa due to dilution, while the other part of this sample was frozen in liquid nitrogen.
The fresh, fresh-diluted and cryopreserved semen were analyzed for motility parameters, viability measures, and oxidative stress. The diluted semen and cryopreserved had decreased motility parameters, particularly in trajectory, compared to the fresh semen. Dilution did not reduce the viability of sperm compared to fresh semen, but cryopreservation resulted in a 40.2% reduction in sperm viability.
Three protein spots on the spermatozoa were altered by dilution with semen extender, and 22 spots were affected by cryopreservation. The majority of the affected proteins were part of the structure and motor center of the sperm flagella, and therefore significantly affect sperm motility. The authors also noted that the cryopreservation process also resulted in reactive oxygen species production, which could have contributed protein and plasma membrane damage, further reducing sperm viability.
Overall, the authors conclude that cryopreservation can result in oxidative damage to proteins involved in intracellular transport, membrane stability, motility, and signal transduction, among other vital cellular functions. Cryopreservation may also result in impaired cell energy metabolism and can cause damage that results in sperm motility disorders. The addition of an antioxidant may help reduce the number of reactive oxygen species that cause oxidative damage, in the sample after cryopreservation. Therefore additional studies should be done to discover new ways to cryopreserve carp semen to minimize oxidative damage.
To view the full article, visit the Journal of Animal Science.