Cryopreservation of rooster semen: Evidence for the epigenetic modifications of thawed sperm

Although semen cryopreservation is an important, widely used technique for long-term sperm storage, it not only induces partially irreversible damages to sperm but might also deteriorate anatomical, biochemical, and structural organelles. These cellular and epigenetic modifications are the main reasons underlying the decline in sperm motility and fertility during the freeze-thaw process. Using the two Lake and Beltsville semen extenders, the present study aims to evaluate the epigenetic patterns (DNA methylation and histone modification), cellular parameters (e.g., membrane integrity, viability, DNA stability, mitochondria activity, and apoptosis status), and fertility potential of rooster semen collected from six mature roosters before and after cryopreservation according to a standard protocol. The results show that cryopreservation leads to significantly (P < 0.05) reduced values of the parameters examined when compared with those of fresh sperms. While the extenders used exhibit no difference with respect to DNA methylation (DNMT), the Lake extender leads to significant reductions (P < 0.05) in H3K9 acetylation (17.4 ± 1.8) and H3K4 methylation (42 ± 2.3) compared to the Beltsville (9.2 ± 1.8 and 23 ± 2.3, respectively). Compared to the Beltsville extender, the Lake one is also observed to yield a significantly (P < 0.05) superior sperm quality in terms of total motility (TM; 77.2 ± 1.6 vs. 68.3 ± 1.6), average path velocity (VAP; 71 ± 1.4 vs. 53 ± 1.4), and straight-line velocity (VSL; 52 ± 1.5 vs. 34 ± 1.5) as well as significantly (P < 0.05) higher viability (60 ± 1.69 vs. 51 ± 1.69) and membrane functionality (55 ± 3.2 vs. 46 ± 3.2). The Lake extender is also found to outperform the Beltsville one due to its significantly (P < 0.05) higher fertility rate (59.5% vs. 47.2%). The two extenders, however, exhibit no differences in DNA fragmentation, mitochondrial activity, or hatchability rate. The Beltsville extender showed to be superior to the Lake one due to its significantly greater reactive oxygen species percentage (ROS; 45.9 ±.3.2 vs. 28.5 ± 3.2) and apoptosis (29 ± 2.3 vs. 27 ± 2.3). It may be concluded that the Lake extender is capable of improving the cellular and epigenetic parameters of rooster sperms during cryopreservation due to the crucial roles it plays in the protection of sperms against cryo-damages.