Figure 1.

A systemic representation of DNA methylation and demethylation. By means of the action of DNA methyltransferases, the methyl group is transferred to the 5th carbon in cytosine. Generally, DNA methylation is initiated by DNMT3A/3B (de novo pathway) and is maintained by DNMT1. Most gene expression is suppressed by DNA methylation, which contributes to the development of neurodegeneration. On the other hand, methylated cytosine turned into cytosine through an active/passive demethylation process. This cycle regulates the gene expression, while under certain environmental conditions, abnormality in this cycle may contribute to the development of neurodegenerative diseases.