Investigation of the efficacy of different cryoprotectants in the freezing of testicular tissue and epididymal sperm: Spermatological parameters, tissue viability and PARP-1 gene expression

The presented study covers testicular tissue and epididymal spermatozoa cryopreservation processes in bulls and aims to investigate the effects of these applications on spermatological parameters, cell viability in testicular tissue, and the expression of the PARP-1 gene, a DNA repair enzyme. Testes of 20 bulls over 2 years old, slaughtered in a slaughterhouse, were used in the study. After spermatological evaluations, the semen obtained from the cauda epididymis was frozen in liquid nitrogen vapor according to the straw method and stored in liquid nitrogen (−196 °C). Testicular tissue pieces obtained from the testicles were frozen by the slow freezing method in cryotubes in diluents containing Dimethylsulfoxide (DMSO) and Ethylene Glycol (EG) cryoprotectants and stored in liquid nitrogen (−196 °C). The total motility (TM) (85.89 ± 12.83 %), progressive motility (PM) (54.02 ± 15.77 %), and kinematic parameter values of fresh sperm were significantly higher compared to the TM (57.62 ± 13.13 %), PM (29.60 ± 10.76 %), and kinematic parameter values after thawing (P < 0.05). Significant decreases in plasma membrane integrity (PMI) and viability and an increase in chromatin condensation and morphological disorders in the head, middle part, and tail regions were observed in post-thaw semen samples (P < 0.05). When the effects of DMSO and EG on cell viability after thaw in frozen testicular tissue were evaluated, it was observed that the cell viability values of testicular tissues frozen with EG (45.70 ± 10.00) were statistically significantly lower than those frozen with DMSO (51.20 ± 7.70) (P < 0.05). When the effects of both cryoprotectants on gene expression in tissue and semen samples were examined, it was determined that gene expression increased on average 0.19 ± 0.27 times in the tissue samples in the DMSO group compared to fresh tissue samples and 0.17 ± 0.19 times in the tissue samples in the EG group. It was determined that gene expression levels increased by an average of 1.20 ± 1.08 times in post-thaw epididymal spermatozoa samples compared to fresh semen samples. The results show that cryopreservation can activate cellular repair mechanisms by stimulating PARP-1 gene expression and affect gene expression by activating specific pathways in tissues and cells.