Abstract
The impact of aging on reproductive outcomes has received considerable critical attention; however, there is much less information available on the effects of paternal age compared to the effects of maternal age. In this study, methylation levels of sperm rDNA promoter regions and Long Interspersed Nucleotide Element 1 (LINE-1) were measured using pyrosequencing and fertilization, day 3 good-quality embryo, pregnancies, and implantation results were assessed. We observed significantly increasing levels of DNA methylation in the sperm rDNA promoter regions with age based on stratifying the samples by age alone (P = 0.0001) and performing linear regression analysis (P < 0.0001). Meanwhile, no statistically significant correlations were observed between global LINE-1 methylation with age. No statistically significant correlations were observed between sperm rDNA promoter methylation levels and either the day 3 good-quality embryo rate or clinical pregnancy rate. In contrast, the correlation between sperm rDNA promoter methylation levels and fertilization (2 pronuclei) rate was nearly significant (P = 0.0707), especially the methylation levels of some individual CpG units (CpG_10, P = 0.0176; CpG_11, P = 0.0438; CpG_14, P = 0.0232) and rDNA promoter methylation levels measured using primerS2 (P = 0.0513). No significant correlation was found between sperm rDNA promoter methylation levels and fertilization rates (2 pronuclei, 1 pronuclei, and 1 polypronuclei). Our results demonstrate that sperm are susceptible to age-associated alterations in methylation levels of rDNA promoter regions, suggesting that sperm rDNA promoter methylation levels can be applied to DNA methylation-based age prediction, and that the aberrant methylation of rDNA promoters may be partially responsible for enhanced disease susceptibility of offspring sired by older fathers. Methylation levels of sperm rDNA promoter regions may correlate with polypronuclei rates of IVF programs.
Highlights
The impact of aging on reproductive outcomes has received considerable critical attention, as there are significant trends toward delayed births
Recent research investigated sperm DNA methylation patterns in 17 fertile donors collected from each individual 9–19 years apart using a methylation array approach and identified 139 regions that are significantly hypomethylated with age and 8 regions that are significantly hypermethylated with age (Jenkins et al, 2014)
This study aimed to assess the between correlation of sperm ribosomal DNA (rDNA) promoter methylation levels and paternal age and evaluate their influence on in vitro fertilization (IVF) outcomes
Summary
The impact of aging on reproductive outcomes has received considerable critical attention, as there are significant trends toward delayed births. Advanced paternal age is associated with delayed time to pregnancy and an increased risk of neuropsychiatric diseases in offspring. The causes remain unclear, there is some evidence that alterations in DNA methylation likely occur with increasing age (Jenkins et al, 2015; Kimura et al, 2018). RRNA gene activation and associated nucleolus formation can be used as a marker for the activation of the embryonic genome and for evaluation of the developmental potential of embryos (Hyttel et al, 2000). The expression of rRNA genes is subject to complex regulation, including methylation of the ribosomal DNA (rDNA) promoter (Ghoshal et al, 2004; Santoro and Grummt, 2005)
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