With age, cells tend to be hypomethylated globally, but show hypermethylation locally (e.g. at promoter CpG islands). This combination is also referred to as "epigenetic drift" and is a typical characteristic of epigenetic ageing.
Epigenetic ageing
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Global hypomethylation:
- With increasing age, the total amount of DNA methylation in the genome decreases.
- Repetitive elements (LINEs, SINEs, satellite DNA) are particularly affected.
- Consequence: genomic instability, increased mutation rate.
Regional hypermethylation:
- At the same time, focal hypermethylation occurs at certain CpG islands in promoter regions.
- This often affects tumor suppressor genes and cell cycle regulation genes.
- Consequence: potentially reduced gene expression of important protective genes.