Comprehensive overview of epigenetic mechanisms in neurodegeneration: DNA methylation, histone modifications, non-coding RNAs, TET enzymes, SIRT1, and EZH2
Epigenetic dysregulation has emerged as a central mechanism in neurodegenerative diseases, providing a molecular link between genetic susceptibility and environmental factors. These heritable yet reversible modifications to chromatin structure regulate gene expression without altering the DNA sequence, and their dysfunction contributes to the transcriptional programs that drive neuronal death.
The epigenetic landscape in neurodegeneration involves:
This mechanistic page covers the major epigenetic pathways and their cross-disease implications.
DNA methylation typically involves the addition of a methyl group to cytosine residues in CpG dinucleotides, forming 5-methylcytosine. In neurodegeneration, global patterns are altered[1]:
Alzheimer's Disease:
Parkinson's Disease:
ALS/FTD:
The DNMT family coordinates methylation patterns[4]:
| Enzyme | Function | Changes in Neurodegeneration |
|---|---|---|
| DNMT1 | Maintenance methylation | Upregulated in AD |
| DNMT3A | De novo methylation | Reduced in PD |
| DNMT3B | De novo methylation | Altered in ALS |
Histone acetylation at lysine residues relaxes chromatin, promoting transcription. The balance between histone acetyltransferases (HATs) and histone deacetylases (HDACs) is critical[5].
HDAC Dysregulation in Disease:
| HDAC | AD | PD | ALS | HD |
|---|---|---|---|---|
| HDAC1 | ↑ | ↑ | ↓ | ↑ |
| HDAC2 | ↑↑ | ↑ | ↑ | ↑ |
| HDAC3 | ↑ | — | ↑ | ↑ |
| HDAC6 | ↑ | ↑ | — | ↑ |
HDAC2 in Alzheimer's Disease[6]:
HDAC6 and Tau[7]:
H3K9me3 marks constitutive heterochromatin and is essential for genome stability[8]:
H3K27me3 is deposited by Polycomb Repressive Complex 2 (PRC2/EZH2):
H3K27ac distinguishes active enhancers from poised ones[9]:
TET (Ten-Eleven Translocation) enzymes convert 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC), an intermediate in active demethylation[10]:
| TET Enzyme | Brain Expression | Function |
|---|---|---|
| TET1 | High (neurons) | Active demethylation, 5hmC generation |
| TET2 | Moderate | Hematopoietic, some neuronal |
| TET3 | High (neurons) | Maternal DNA demethylation |
5-hydroxymethylcytosine is abundant in the brain and has distinct regulatory functions[11]:
SIRT1 is a NAD+-dependent deacetylase with broad neuroprotective effects[13]:
| Compound | Target | Stage | Notes |
|---|---|---|---|
| Resveratrol | SIRT1 activator | Phase 2 | Mixed results in AD |
| SRT2104 | SIRT1 activator | Preclinical | Better brain penetration |
| EX-527 | SIRT1 inhibitor | Research | Used in cancer |
EZH2 is the catalytic subunit of PRC2, depositing H3K27me3 and repressing gene expression[15]:
ALS[16]:
AD[17]:
| Strategy | Approach | Status |
|---|---|---|
| EZH2 inhibitors | Tazemetostat, GSK343 | Preclinical |
| PRC2 disruption | EED inhibitors | Research |
| H3K27me3 modulation | HDAC inhibitors | Varies |
MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression post-transcriptionally[18]:
Key miRNAs in AD[19]:
Key miRNAs in PD[21]:
Key miRNAs in ALS:
| miRNA | Target Disease | Approach | Status |
|---|---|---|---|
| miR-146a antagomir | AD | Anti-miR therapy | Preclinical |
| miR-7 mimic | PD | miRNA delivery | Preclinical |
| miR-124 delivery | ALS/PD | Cell therapy | Research |
| Mechanism | AD | PD | ALS | FTD | HD |
|---|---|---|---|---|---|
| Global hypomethylation | +++ | ++ | + | ++ | + |
| HDAC2 elevation | +++ | ++ | + | ++ | ++ |
| miR-146a upregulation | +++ | + | ++ | + | + |
| 5hmC loss | ++ | ++ | + | — | — |
| PRC2 dysregulation | ++ | + | ++ | ++ | — |
HDAC inhibitors show broad potential:
Other approaches:
Epigenetic dysregulation represents a unifying feature of neurodegenerative diseases, creating self-perpetuating cycles of transcriptional dysfunction. The reversible nature of epigenetic modifications makes them attractive therapeutic targets, though delivery to the CNS remains challenging.
Key Takeaways:
DNA methylation in neurodegenerative disease. Nat Rev Neurol. 2020. ↩︎
Epigenetic clock and neurodegeneration. Aging Cell. 2021. ↩︎
SNCA promoter methylation in PD. Neurology. 2010. ↩︎
DNA methyltransferases in neurodegeneration. J Mol Neurosci. 2020. ↩︎
Histone acetylation in synaptic plasticity. Nat Rev Neurosci. 2021. ↩︎
HDAC2 and memory deficits in AD. Nature. 2008. ↩︎
HDAC6 and tau pathology. Mol Neurodegener. 2020. ↩︎
H3K9me3 and heterochromatin in neurodegeneration. Nat Rev Neurosci. 2019. ↩︎
H3K27ac alterations in AD. J Neurosci. 2019. ↩︎
TET enzymes and 5hmC in neurodegeneration. Nat Rev Neurol. 2020. ↩︎
5-hydroxymethylcytosine in brain. Nat Rev Neurosci. 2015. ↩︎
TET1 and 5hmC in AD. Nat Neurosci. 2018. ↩︎
SIRT1 and neurodegeneration. Nat Rev Neurol. 2012. ↩︎
SIRT1 and tau pathology in mice. Cell. 2011. ↩︎
EZH2 and polycomb in neurodegeneration. Nat Rev Neurosci. 2020. ↩︎
EZH2-mediated repression in ALS. Nat Neurosci. 2020. ↩︎
EZH2 and tau pathology. Mol Brain. 2015. ↩︎
MicroRNAs in neurodegeneration. Nat Rev Neurol. 2019. ↩︎
miR-146a in AD neuroinflammation. Nat Rev Neurol. 2015. ↩︎
miR-124 and neuronal differentiation. Cell. 2014. ↩︎
miR-7 and miR-153 in PD. Nat Rev Neurol. 2018. ↩︎