Age-related methylation changes are associated with altered transcriptional circuitry [Methyl-seq]

Altered DNA methylation patterns represent an attractive mechanism for the phenotypic changes associated with human aging. Several studies have described age-related methylation changes to various extents, but their functional significance has remained largely unclear. We have now used an integrated methylome and transcriptome sequencing approach to characterize age-related methylation changes in the human epidermis and to analyze their impact on gene expression. Our results show limited and localized methylation differences between young and old methylomes at single-base resolution. Similarly, the comparison of transcriptomes from young and old samples revealed a highly defined set of differentially expressed genes with functional annotations in skin homeostasis. Further data analysis showed a robust correlation between age-related promoter hypermethylation and gene silencing, particularly at promoters that were pre-marked with stem cell-specific chromatin features. In addition, we also observed age-related methylation changes at transcription factor binding sites, with a significant enrichment of stem cell regulatory networks. Our results provide a high-resolution analysis of age-related methylation changes and suggest that they result in highly defined alterations in the transcriptional programme of the human epidermis. Interestingly, several of our findings can be interpreted to reflect epigenetic changes in aging stem cells, thus supporting a critical role of stem cells in human aging.