Paternal aging and associated intraindividual alterations of global sperm 5-methylcytosine and 5-hydroxymethylcytosine levels

Abstract

Objective: To evaluate the relative intraindividual changes in sperm 5-methylcytosine (5-mC) and 5-hydroxymethylcytosine (5-hmC) levels associated with age and to compare the levels of 5-hmC in mature human sperm to blood DNA.

Design: Prospective research study.

Setting: University-based andrology and in vitro fertilization (IVF) laboratory.

Patient(s): Fifteen known fertile sperm donors, 22 other known fertile controls, and 41 male blood donors from a general population tissue bank.

Intervention(s): None.

Main outcome measure(s): Measurements of global 5-mC and 5-hmC levels via an enzyme-linked immunosorbent assay (ELISA)-based assay.

Result(s): Global sperm 5-mC levels exhibit a statistically significant increase with age, and a similar trend was seen in 5-hmC levels. On average, in the age ranges we analyzed, 5-mC increased by 1.76% per year, and 5-hmC, though more variable, increased by approximately 5% per year. Additionally, we found that 5-hmC levels in sperm are 32.59% of that found in blood DNA.

Conclusion(s): Global sperm DNA methylation patterns are stable over short periods of time but increase with age, which raises important questions regarding the risks of advanced paternal age. Additionally, as we would predict for a transcriptionally quiescent cell type, 5-hmC levels are statistically significantly lower in human sperm than in blood DNA.

Keywords: 5-hydroxymethylcytosine; 5-methylcytosine; Advanced paternal age; global DNA methylation; sperm DNA methylation.