Epigenetic Changes in PSP

Epigenetic Changes in Progressive Supranuclear Palsy

Overview

Progressive Supranuclear Palsy (PSP) is a rare but devastating neurodegenerative disorder characterized by progressive postural instability, vertical gaze palsy, parkinsonism, and cognitive decline. While PSP was once considered a "sporadic" disease, increasing evidence suggests that epigenetic alterations play a significant role in its pathogenesis [1](https://pubmed.ncbi.nlm.nih.gov/24717639/). Epigenetic changes—heritable modifications to DNA and chromatin that regulate gene expression without altering the DNA sequence—have emerged as key contributors to neurodegeneration in PSP and related tauopathies. [@graff2013]

Epigenetic dysregulation in PSP affects multiple molecular pathways, including those involved in tau protein metabolism, neuroinflammation, mitochondrial function, and neuronal survival. Understanding these epigenetic changes provides insights into disease mechanisms and potential therapeutic targets [2](https://pubmed.ncbi.nlm.nih.gov/25448807/). [@selkoe2004]

Epigenetic Changes in Progressive Supranuclear Palsy

Overview

Progressive Supranuclear Palsy (PSP) is a rare but devastating neurodegenerative disorder characterized by progressive postural instability, vertical gaze palsy, parkinsonism, and cognitive decline. While PSP was once considered a "sporadic" disease, increasing evidence suggests that epigenetic alterations play a significant role in its pathogenesis [1](https://pubmed.ncbi.nlm.nih.gov/24717639/). Epigenetic changes—heritable modifications to DNA and chromatin that regulate gene expression without altering the DNA sequence—have emerged as key contributors to neurodegeneration in PSP and related tauopathies. [@graff2013]

Epigenetic dysregulation in PSP affects multiple molecular pathways, including those involved in tau protein metabolism, neuroinflammation, mitochondrial function, and neuronal survival. Understanding these epigenetic changes provides insights into disease mechanisms and potential therapeutic targets [2](https://pubmed.ncbi.nlm.nih.gov/25448807/). [@selkoe2004]

<div class="infobox infobox-mechanism"> [@goedert2006]
<table> [@duyckaerts1997]
<tr><th>Mechanism Name</th><td>Epigenetic Changes in PSP</td></tr> [@williamsgray2016]
<tr><th>Category</th><td>Molecular Pathology</td></tr> [@litvan1996]
<tr><th>Related Diseases</th><td><a href="/diseases/progressive-supranuclear-palsy">Progressive Supranuclear Palsy</a></td></tr> [@ahlskog2011]
<tr><th>Key Processes</th><td>DNA methylation, histone modifications, non-coding RNAs</td></tr> [@kelley2012]
</table> [@zhang2019]
</div> [@miller2007]

DNA Methylation Alterations

Global Hypomethylation

One of the most prominent epigenetic changes in PSP is global DNA hypomethylation [3](https://pubmed.ncbi.nlm.nih.gov/24658389/). This reduction in methylated cytosine residues across the genome leads to:

• Activation of transposable elements: Normally silenced by methylation, transposons become active and can cause genomic instability
• Altered gene expression: Both increased expression of normally silenced genes and dysregulation of tissue-specific genes
• Chromatin relaxation: Reduced methylation promotes an open chromatin configuration

Gene-Specific Methylation Changes

Detailed studies have identified specific genes with altered methylation patterns in PSP brain tissue:

Tau-related genes:

• Altered methylation of microtubule-associated protein tau (MAPT) gene regulatory regions
• Changes in methylation of kinases that phosphorylate tau
• Methylation changes in tau-related transcription factors

• Dysregulated methylation of cytokine genes
• Altered patterns in immune response regulators
• Changes in glial cell-specific gene expression

• Reduced methylation of antioxidant enzyme genes
• Altered methylation of pro-survival factor promoters
• Changes in DNA repair gene methylation

Mechanisms of Methylation Dysregulation

Several factors contribute to DNA methylation alterations in PSP:

Histone Modifications

Histone Acetylation

Changes in histone acetylation patterns are observed in PSP [4](https://pubmed.ncbi.nlm.nih.gov/23353710/):

Reduced histone acetylation:

• Decreased H3 and H4 acetylation levels
• Associated with transcriptional repression
• Linked to reduced cognitive function

• Increased HDAC activity in PSP brain
• HDAC2 overexpression in affected regions
• Therapeutic potential of HDAC inhibitors

Histone Methylation

Altered histone methylation patterns contribute to PSP pathogenesis:

H3K4me3 (activating mark):

• Reduced levels in PSP prefrontal cortex
• Associated with transcriptional downregulation

• Altered distribution in PSP
• Affects development and differentiation genes

• Changes in heterochromatin stability
• Genomic instability implications

Histone Phosphorylation

Stress-activated kinases that phosphorylate histones are dysregulated in PSP:

• p38 MAPK activation leads to H3 phosphorylation
• JNK activation affects histone modifications
• Links between stress response and epigenetic changes

Non-Coding RNA Dysregulation

MicroRNAs (miRNAs)

Multiple miRNAs are dysregulated in PSP [5](https://pubmed.ncbi.nlm.nih.gov/25909221/):

Upregulated miRNAs:

• miR-124: Altered neuronal plasticity
• miR-128: Affects tau phosphorylation
• miR-219: Dysregulated in glia

• miR-7: Reduced in PSP brain
• miR-153: Targets tau kinase genes
• miR-132: Altered in PSP

Long Non-Coding RNAs (lncRNAs)

Emerging evidence suggests lncRNA involvement in PSP:

• NEAT1: Altered nuclear organization
• MALAT1: Splicing regulation changes
• HOTAIR: Affects developmental genes

Circular RNAs (circRNAs)

The role of circRNAs in PSP is beginning to be explored:

• Altered circRNA expression patterns
• Potential as biomarkers
• Regulatory functions in neuronal homeostasis

Tau Protein and Epigenetics

Tau Promoter Methylation

The MAPT gene shows altered methylation in PSP:

• Differential methylation of MAPT promoter affects expression
• H1 haplotype influence on methylation patterns
• Links between genetic background and epigenetic changes

Tau Acetylation and Degradation

Epigenetic mechanisms affect tau protein metabolism:

• Acetylation affects tau degradation
• HDAC6 regulation of tau acetylation
• Acetylation-mimicking mutations and pathology

Tau Pathology Spreading

Epigenetic changes may facilitate tau propagation:

• Cell-to-cell transmission mechanisms
• Role of extracellular vesicles
• Epigenetic reprogramming in recipient cells

Neuroinflammation and Epigenetics

Glial Cell Epigenetics

Epigenetic changes in microglia and astrocytes [6](https://pubmed.ncbi.nlm.nih.gov/25855099/):

• Altered cytokine gene methylation
• Changes in glial activation patterns
• NF-κB pathway epigenetic dysregulation

Peripheral Immune Epigenetics

Systemic immune changes in PSP:

• Altered immune cell methylation patterns
• Potential peripheral biomarkers
• Inflammatory epigenetic signatures

Mitochondrial Dysfunction and Epigenetics

Mitochondrial DNA Methylation

Mitochondrial genome shows epigenetic changes:

• Altered mtDNA methylation
• Correlations with mitochondrial dysfunction
• Implications for energy metabolism

Nuclear-Mitochondrial Cross-Talk

Epigenetic mechanisms affecting mitochondria:

• PGC-1α methylation changes
• Mitochondrial biogenesis dysregulation
• Metabolic consequences

Therapeutic Implications

Epigenetic Therapies

Potential treatment strategies targeting epigenetic changes [7](https://pubmed.ncbi.nlm.nih.gov/25855099/):

HDAC inhibitors:

• Vorinostat, Valproic acid
• Suberoylanilide hydroxamic acid (SAHA)
• Testing in tauopathy models

• 5-azacytidine
• Decitabine
• Limited CNS penetration challenges

• JQ1, I-BET762
• Target bromodomain proteins
• Emerging therapeutic potential

Lifestyle and Environmental Factors

Modifiable factors that may influence epigenetic changes:

• Diet and nutrition
• Exercise
• Cognitive stimulation
• Stress management

Biomarker Potential

Epigenetic Biomarkers

Epigenetic changes have biomarker potential in PSP:

• Peripheral blood mononuclear cell methylation
• miRNA signatures in CSF
• Exosomal epigenetic marks

Diagnostic and Prognostic Value

• Early detection potential
• Disease progression markers
• Treatment response monitoring

Research Methods

Detection Techniques

Epigenetic changes are studied using:

• Bisulfite sequencing: DNA methylation analysis
• ChIP-seq: Histone modification mapping
• RNA-seq: Non-coding RNA profiling
• ATAC-seq: Chromatin accessibility

Model Systems

Research relies on:

• Postmortem brain tissue
• Animal models of tauopathy
• Induced pluripotent stem cells (iPSCs)
• Cell culture models

Conclusion

Epigenetic alterations represent a fundamental aspect of PSP pathogenesis, contributing to disease progression through multiple interconnected mechanisms. The complex interplay between genetic susceptibility and epigenetic dysregulation provides insights into the heterogeneity of PSP presentations and the challenges of developing effective therapies. While targeting epigenetic mechanisms offers therapeutic promise, the complexity of the epigenetic landscape and the need for brain-penetrant drugs present significant challenges. Future research focusing on understanding the causal relationships between epigenetic changes and neurodegeneration, developing selective epigenetic modulators, and identifying reliable biomarkers will be essential for translating these findings into clinical benefits.

See Also

• [Progressive Supranuclear Palsy](/diseases/progressive-supranuclear-palsy)
• Tau Protein Pathology
• [Neuroinflammation](/mechanisms/neuroinflammation-pathway)
• [DNA Methylation](/entities/dna-methylation)
• [Histone Modifications](/entities/histone-modifications)
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Parkinson's Disease](/diseases/parkinsons-disease)
• [Frontotemporal Dementia](/diseases/frontotemporal-dementia)

External Links

• [OMIM: PSP](https://www.omim.org/entry/601104)
• [National Institute of Neurological Disorders and Stroke: PSP](https://www.ninds.nih.gov/Disorders/All-Disorders/Progressive-Supranuclear-Palsy-Information-Page)
• [CurePSP Foundation](https://www.psp.org/)

References