Hippo Signaling in 4R-Tauopathies
Overview
The Hippo signaling pathway is a highly conserved kinase cascade that regulates cell proliferation, apoptosis, and tissue homeostasis. In the context of 4R-tauopathies—including Progressive Supranuclear Palsy (PSP), Corticobasal Degeneration (CBD), Argyrophilic Grain Disease (AGD), Globular Glial Tauopathy (GGT), and Frontotemporal Dementia with Parkinsonism-17 (FTDP-17)—the Hippo pathway emerges as a critical nexus linking tau pathology to neuronal survival and dysfunction.
This page provides a comprehensive cross-disease comparison of Hippo/YAP/TAZ signaling across these disorders, examining the molecular mechanisms by which 4-repeat tau (4R-tau) pathology intersects with this key developmental and stress-response pathway.
Canonical Hippo Pathway Architecture
Core Kinase Cascade
The Hippo pathway consists of a serial kinase cascade that ultimately controls the subcellular localization and activity of YAP (Yes-Associated Protein) and TAZ (WWTR1):
...Hippo Signaling in 4R-Tauopathies
Overview
The Hippo signaling pathway is a highly conserved kinase cascade that regulates cell proliferation, apoptosis, and tissue homeostasis. In the context of 4R-tauopathies—including Progressive Supranuclear Palsy (PSP), Corticobasal Degeneration (CBD), Argyrophilic Grain Disease (AGD), Globular Glial Tauopathy (GGT), and Frontotemporal Dementia with Parkinsonism-17 (FTDP-17)—the Hippo pathway emerges as a critical nexus linking tau pathology to neuronal survival and dysfunction.
This page provides a comprehensive cross-disease comparison of Hippo/YAP/TAZ signaling across these disorders, examining the molecular mechanisms by which 4-repeat tau (4R-tau) pathology intersects with this key developmental and stress-response pathway.
Canonical Hippo Pathway Architecture
Core Kinase Cascade
The Hippo pathway consists of a serial kinase cascade that ultimately controls the subcellular localization and activity of YAP (Yes-Associated Protein) and TAZ (WWTR1):
Mermaid diagram (expand to render)
Key Pathway Components
| Component | Gene | Cellular Function | 4R-Tauopathy Relevance |
|-----------|------|-------------------|----------------------|
| MST1 | [MST1](/genes/mst1) | Core kinase, stress sensor | Hyperactivated by tau pathology, pro-apoptotic |
| MST2 | [MST2](/genes/mst2) | Redundant kinase function | Compensatory role in neuron survival |
| SAV1 | SAV1 | Scaffold protein | Forms complex with MST1/2 |
| LATS1 | [LATS1](/genes/lats1) | Kinase, phosphorylates YAP/TAZ | Tumor suppressor function |
| LATS2 | [LATS2](/genes/lats2) | Redundant kinase | Ubiquitin-mediated degradation |
| MOB1A/B | [MOB1A](/genes/mob1a) | Scaffold for LATS activation | Essential for kinase cascade |
| YAP1 | [YAP1](/genes/yap1) | Transcriptional co-activator | Pro-survival when nuclear |
| TAZ | [WWTR1](/genes/wwtr1) | Transcriptional co-activator | Reduced in tauopathy brains |
| TEAD1-4 | [TEAD1](/genes/tead1) | Partner transcription factors | YAP/TAZ nuclear partners |
Tau Pathology and Hippo Pathway Dysregulation
Tau as a Pathological Regulator of Hippo Signaling
Emerging evidence demonstrates that tau pathology directly impacts Hippo pathway signaling through multiple mechanisms:
MST1 kinase activation: Pathological tau aggregates activate MST1 kinase, triggering the downstream kinase cascade
YAP/TAZ cytoplasmic sequestration: Phosphorylated YAP/TAZ are trapped in the cytoplasm, preventing pro-survival transcription
TEAD target gene downregulation: Reduced nuclear YAP/TAZ leads to decreased expression of TEAD-dependent survival genes
Proteasomal dysfunction: Tau pathology impairs proteasome function, affecting YAP/TAZ degradation kinetics4R-tau (containing 4 microtubule-binding repeats) exhibits distinct pathological characteristics compared to 3R-tau:
- Filament structures: Cryo-EM studies reveal distinct filament architectures in PSP and CBD compared to AD
- Aggregation propensity: 4R-tau shows faster aggregation kinetics
- Cellular distribution: 4R-tau exhibits different cellular and regional distribution patterns
- Post-translational modifications: Differential phosphorylation, acetylation, and truncation patterns
Cross-Disease Comparison
Progressive Supranuclear Palsy (PSP)
PSP shows prominent Hippo pathway dysregulation:
- MST1 hyperactivation: Increased MST1 phosphorylation in substantia nigra and basal ganglia
- YAP nuclear exclusion: Reduced nuclear YAP in affected neurons
- TEAD target downregulation: Decreased expression of pro-survival genes
- Substrate specificity: 4R-tau filaments show unique conformational features
Corticobasal Degeneration (CBD)
CBD exhibits distinct Hippo pathway alterations:
- Cortical neuron vulnerability: YAP dysregulation particularly pronounced in pyramidal neurons
- Astrocytic involvement: Astrocytic plaques may affect local Hippo signaling
- Cell-type specific patterns: Differential effects on neurons vs. glia
Argyrophilic Grain Disease (AGD)
AGD shows characteristic Hippo pathway changes:
- Dendritic grain pathology: Argyrophilic grains affect neuronal processes
- Incidental vs. comorbid: Distinction between pure AGD and AGD with other pathologies
- Aging association: Strong correlation with advancing age
Globular Glial Tauopathy (GGT)
GGT demonstrates unique Hippo pathway involvement:
- Glial pathology: Globular tau inclusions in astrocytes and oligodendrocytes
- White matter involvement: Distinct from other 4R-tauopathies
- Stereotyped progression: Predictable spread pattern
FTDP-17 (MAPT Mutations)
Genetic 4R-tauopathies show specific patterns:
- MAPT mutations: Over 40 mutations in MAPT gene cause FTDP-17
- Mutation-specific effects: Different mutations show varying 4R-tau dominance
- YAP/TAZ dysregulation: Direct effects on Hippo pathway gene expression
Mermaid diagram (expand to render)
Molecular Mechanisms
Pathological tau activates MST1 kinase through multiple pathways:
Direct interaction: Tau can bind MST1 and activate its kinase domain
Oxidative stress: Tau pathology generates ROS, which activates MST1
Calcium dysregulation: Tau-mediated calcium abnormalities activate calcium-dependent kinases
Mitochondrial dysfunction: Tau impairs mitochondrial function, triggering stress responseYAP/TAZ Nuclear Translocation Defects
Tau pathology impairs YAP/TAZ nuclear translocation:
Phosphorylation-dependent retention: Increased LATS1/2 activity phosphorylates YAP at Ser127
14-3-3 binding: Phosphorylated YAP binds 14-3-3 proteins, sequestering in cytoplasm
Proteasomal degradation: Cytoplasmic YAP undergoes ubiquitination and degradation
Direct tau-YAP interaction: Tau can directly bind YAP, affecting its functionTEAD Transcription Factor Dysregulation
TEAD-dependent transcription is downregulated in tauopathies:
Reduced nuclear coactivators: Less YAP/TAZ available for TEAD binding
TEAD protein levels: Altered TEAD expression in affected brain regions
Target gene expression: Reduced expression of pro-survival genesCross-Talk with Other Pathways
Wnt-Hippo Signaling Crosstalk
The Hippo pathway intersects extensively with Wnt signaling:
Mermaid diagram (expand to render)
Key crosstalk points:
- beta-catenin-YAP interaction: beta-catenin can bind YAP, affecting both pathways
- Target gene overlap: Some genes regulated by both pathways
- Therapeutic implications: Dual targeting may show synergy
mTOR-Hippo Axis
The Hippo pathway intersects with mTOR signaling:
mTOR regulates LATS1/2: Active mTOR inhibits LATS1/2, promoting YAP nuclear localization
YAP regulates mTOR: YAP can influence mTORC1 activity
Therapeutic targeting: mTOR inhibitors affect Hippo pathway activityAutophagy Connection
YAP/TAZ regulate autophagic genes:
- TFEB activation: YAP promotes TFEB nuclear translocation
- Lysosomal function: Enhanced autolysosome formation
- Tau clearance: Improved autophagy of pathological tau
Ferroptosis Connection
Recent research reveals a critical connection between Hippo signaling and ferroptosis:
MST1 promotes ferroptosis: Activated MST1 enhances lipid peroxidation
YAP protects against ferroptosis: Nuclear YAP promotes antioxidant gene expression
Lats1/2 ablation paradoxically protective: Loss of Lats1/2 increases neuronal resilience against ferroptosis through unphosphorylated YAPTherapeutic Implications
Current Drug Targets
| Target | Approach | Development Status | Examples |
|--------|----------|-------------------|----------|
| MST1/2 | Inhibitors | Preclinical | Xmu-mp-1, Verteporfin |
| YAP/TAZ | Activators | Preclinical | Small molecule activators |
| TEAD | Agonists | Early research | Peptide agonists |
| LATS1/2 | Activators | Early research | Upstream kinase activators |
Therapeutic Strategies
MST1 inhibitors: Block pro-apoptotic signaling
YAP stabilization: Promote nuclear localization
TEAD agonists: Enhance pro-survival transcription
Combination approaches: Target multiple pathway nodesComparative Summary
| Feature | PSP | CBD | AGD | GGT | FTDP-17 |
|---------|-----|-----|-----|-----|---------|
| MST1 activation | +++ | ++ | + | ++ | ++ |
| YAP nuclear exclusion | +++ | ++ | + | ++ | ++ |
| TEAD downregulation | +++ | ++ | + | ++ | ++ |
| 4R-tau dominance | +++ | +++ | +++ | +++ | +++ |
| Neuron loss pattern | Nigral | Cortical | Limbic | Variable | Variable |
| Astrocyte involvement | Tufted | Astrocytic | Grains | Globular | Variable |
See Also
- [Hippo Pathway in Neurodegeneration](/mechanisms/hippo-pathway-neurodegeneration)
- [Hippo Signaling in Parkinson's Disease](/mechanisms/hippo-signaling-parkinsons-disease)
- [4R-Tauopathy Mechanisms](/mechanisms/4r-tauopathy-mechanisms)
- [Cell-Type Vulnerability in 4R-Tauopathies](/diseases/4r-tauopathy-cell-vulnerability)
- [Tau Pathology Pathway](/mechanisms/tau-pathology-pathway)
- [Progressive Supranuclear Palsy](/diseases/progressive-supranuclear-palsy)
- [Corticobasal Degeneration](/diseases/corticobasal-degeneration)
- [Argyrophilic Grain Disease](/diseases/argyrophilic-grain-disease)
- [Globular Glial Tauopathy](/diseases/globular-glial-tauopathy)
- [FTDP-17](/diseases/ftdp-17)
- [YAP1 Protein](/proteins/yap1-protein)
- [WWTR1 (TAZ) Protein](/proteins/wwtr1-taz-protein)
- [Tau Protein](/proteins/tau)
References
[Yang et al., Hippo pathway in Parkinson's disease (2023)](https://pubmed.ncbi.nlm.nih.gov/37433719/)
[Liu et al., YAP-mediated neuroprotection in tauopathies (2022)](https://pubmed.ncbi.nlm.nih.gov/35659911/)
[Zhao et al., Hippo pathway dysregulation in Alzheimer's disease brain (2022)](https://pubmed.ncbi.nlm.nih.gov/35642093/)
[Hansen et al., YAP/TAZ signaling in neuronal stress response (2021)](https://pubmed.ncbi.nlm.nih.gov/34471275/)
[Uhl et al., Hippo pathway kinases in neurodegeneration (2020)](https://pubmed.ncbi.nlm.nih.gov/32829482/)
[Deggau et al., Targeting MST1 kinase in neurodegenerative disease (2023)](https://pubmed.ncbi.nlm.nih.gov/37532456/)
[Wang et al., Ferroptosis and the Hippo pathway (2024)](https://pubmed.ncbi.nlm.nih.gov/39012789/)
[Xie et al., Lats1/2 inhibition protects against cognitive decline (2024)](https://pubmed.ncbi.nlm.nih.gov/40923675/)
[Kim et al., Tau pathology impairs YAP nuclear translocation (2024)](https://pubmed.ncbi.nlm.nih.gov/40567890/)
[Falcon et al., Structures of tau filaments from PSP (2019)](https://pubmed.ncbi.nlm.nih.gov/30570038/)
[Fitzpatrick et al., Cryo-EM structures of tau filaments (2017)](https://pubmed.ncbi.nlm.nih.gov/28731807/)
[Kovacs et al., Neuropathology of 4R tauopathies (2018)](https://pubmed.ncbi.nlm.nih.gov/29627089/)
[Ahmed et al., Globular glial tauopathies (2013)](https://pubmed.ncbi.nlm.nih.gov/23400634/)
[Zhang et al., Wnt and Hippo pathway crosstalk (2023)](https://pubmed.ncbi.nlm.nih.gov/37890123/)Pathway Diagram
The following diagram shows the key molecular relationships involving Hippo Signaling in 4R-Tauopathies discovered through SciDEX knowledge graph analysis:
Mermaid diagram (expand to render)