Impact of excess sugar on the whole genome DNA methylation pattern in human sperm

Dietary factors may regulate the epigenome. We aimed to explore whether a diet intervention, including excess sugar, affects the methylome in human sperm, and to describe the sperm methylome. We used Whole Genome Bisulfite Sequencing (WGBS) to analyze DNA methylation in sperm taken at three time points from 15 males during a diet intervention; i) at baseline, ii) after one week on a standardized diet, and iii) after an additional week on a high-sugar diet providing 150% of their estimated total energy expenditure.

We identified seven nominal diet-associated differentially methylated regions in sperm (p < 0.05). The diet was nominally associated with methylation of 143 sites linked to fertility (e.g. AHRR, GNAS, and HDAC4), 313 sites in imprinted genes (e.g. GLIS3, PEG10, PEG3, and SNURF), and 42 sites in top 1%-expressed genes (e.g. CHD2) (p < 0.05). In sperm, 3'UTRs and introns had the highest levels of methylation, while 5'UTRs and CpG islands had the lowest levels. Non-expressed genes in human sperm were hypomethylated in exons compared with transcribed genes.

In human sperm, DNA methylation levels were linked to gene expression, and excess sugar had modest effects on methylation on imprinted and highly expressed genes, and genes affecting fertility.