SIRT1 gene methylation in sperm differs in rams with high and low fertility

Recently, more evidences of epigenetic impact on the male fertility, particularly on sperm DNA methylation have been reported. Data related to this issue in livestock males is still limited. The present study analyzed the DNA methylation status of the important gene for spermatogenesis, SIRT1, in ram sperm and its correspondence with semen quality and fertilizing ability. The ejaculates of 10 rams (5 rams - 1.5 years old, and 5 rams - 4 years old) from Synthetic Population Bulgarian Milk breed were evaluated and used for the artificial insemination of 174 ewes in breeding season. Two semen samples from each animal were used for DNA extraction followed by bisulfite conversion. The DNA methylation status of SIRT1 was detected through quantitative methylation-specific PCR using two sets of primers designed specifically for bisulfite-converted DNA sequences to attach methylated and unmethylated sites. On the base of age and conception rate the rams were divided in different groups. Data of semen quality, DNA methylation status of SIRT1 and reproductive performances of each group were statistically processed. Results showed a high average value of DNA methylation of SIRT1 in ram sperm (78.5±23.9%) and wide individual variability among investigated animals, with a coefficient of variation of 34.4%. The 1.5 years old animals tended to have a higher level of SIRT1 methylation than 4 years old animals. The rams in group with high fertilizing ability had significantly higher DNA methylation of SIRT1 in sperm than those with low fertilizing ability. In conclusion, results of this study provided evidence that the alteration of sperm SIRT1 methylation is associated with fertility performances of the rams and, probably, with their age.