The Correlation Between Sperm DNA Methylation and DNA Damage: A Comparison of Comet and TUNEL

Hailey Elizabeth Zimmerman ^* Tim Jenkins ^*

• Brigham Young University, Provo, United States

It has been suggested that DNA damage correlates with global DNA methylation patterns in the sperm methylome. To assess this relationship more comprehensively, we analyzed the relationship between sperm DNA damage (as measured by both the comet and TUNEL assays) and DNA methylation with CpG resolution data (EPIC array) in the largest publicly available sperm DNA methylation dataset. Samples were classified by DNA damage score, in both comet and TUNEL, and subgroups were produced from these based on the highest and lowest values for each assay. These subgroups were used to assess differential methylation, epigenetic age, and epigenetic instability as a function of DNA damage. Furthermore, we compared the TUNEL and comet measurements of damage and their correlations to DNA methylation alterations. A regional analysis of differential methylation revealed 3387 significantly altered regions between the high and low comet categories, and 23 regions between high and low DNA fragmentation index (DFI) values. Although a regression demonstrates comet and TUNEL scores have a positive relationship, we found that the comet assay seems to have a much better fit with methylation disruption. Methylation disturbance as predicted by the comet assay also showed a significant relationship to gene ontology pathways related to germline development. It is noteworthy however that high and low comet scores were of far higher magnitude than differences between high and low TUNEL scores. These findings suggest comet scores offer a more comprehensive picture of sperm cell abnormalities.