Axon Guidance in 4R-Tauopathies

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Axon Guidance in 4R-Tauopathies

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Axon Guidance in 4R-Tauopathies

4R-Tauopathies are a group of neurodegenerative disorders characterized by the accumulation of 4-repeat tau protein isoforms in the brain. This comparison examines axon guidance molecule dysregulation across five major 4R-tauopathies: [Progressive Supranuclear Palsy](/diseases/progressive-supranuclear-palsy) (PSP), [Corticobasal Degeneration](/diseases/corticobasal-degeneration) (CBD), [Argyrophilic Grain Disease](/diseases/argyrophilic-grain-disease) (AGD), [Globular Glial Tauopathy](/diseases/globular-glial-tauopathy) (GGT), and [FTDP-17](/diseases/ftdp-17) (Frontotemporal Dementia with Parkinsonism-17).

Axon guidance molecules—including semaphorins, plexins, slits/robo, and ephrins/ephr receptors—play critical roles in neural circuit formation, synaptic maintenance, and adult neural plasticity. Dysregulation of these pathways contributes to the pathogenesis of 4R-tauopathies through multiple mechanisms including impaired axonal connectivity, dysfunctional synaptic remodeling, and altered neuronal vulnerability. [@choi2014]

Overview

```mermaid
flowchart TD
subgraph Families["Axon Guidance Families"]
A["Semaphorins (Sema3A, Sema3F)"] --> A1["NRP1/2"]
A --> A2["Plexin-A"]
B["Slits"] --> B1["Robo1-4"]
C["Ephrins"] --> C1["EphA"]
C --> C2["EphB"]
D["Netrins"] --> D1["DCC"]
D --> D2["UNC5"]
end

subgraph Pathology["4R-Tauopathies"]
A1 --> P["PSP CBD AGD GGT FTDP-17"]
A2 --> P
B1 --> P
C1 --> P
C2 --> P
D1 --> P
D2 --> P
end

...

Axon Guidance in 4R-Tauopathies

4R-Tauopathies are a group of neurodegenerative disorders characterized by the accumulation of 4-repeat tau protein isoforms in the brain. This comparison examines axon guidance molecule dysregulation across five major 4R-tauopathies: [Progressive Supranuclear Palsy](/diseases/progressive-supranuclear-palsy) (PSP), [Corticobasal Degeneration](/diseases/corticobasal-degeneration) (CBD), [Argyrophilic Grain Disease](/diseases/argyrophilic-grain-disease) (AGD), [Globular Glial Tauopathy](/diseases/globular-glial-tauopathy) (GGT), and [FTDP-17](/diseases/ftdp-17) (Frontotemporal Dementia with Parkinsonism-17).

Axon guidance molecules—including semaphorins, plexins, slits/robo, and ephrins/ephr receptors—play critical roles in neural circuit formation, synaptic maintenance, and adult neural plasticity. Dysregulation of these pathways contributes to the pathogenesis of 4R-tauopathies through multiple mechanisms including impaired axonal connectivity, dysfunctional synaptic remodeling, and altered neuronal vulnerability. [@choi2014]

Overview

Mermaid diagram (expand to render)

Semaphorin-Plexin Pathway

Class 3 semaphorins (Sema3A, Sema3F, Sema3B, Sema3C) are secreted guidance cues that signal through Neuropilin (NRP1/NRP2) co-receptors and Plexin-A signal-transducing receptors. In the adult brain, these molecules regulate synaptic plasticity, microglial activation, and circuit refinement. [@pasterkamp2019]

Sema3A

| Feature | PSP | CBD | AGD | GGT | FTDP-17 |
|---------|-----|-----|-----|-----|---------|
| Expression Level | ↑↑ | ↑↑↑ | ↑ | ↑↑ | ↑↑ |
| Brain Region Affected | Brainstem, BG | Motor cortex | Limbic | WM, Brainstem | Frontal cortex |
| Cellular Source | Neurons, glia | Neurons | Neurons | Oligodendrocytes | Neurons |
| Receptor Expression | NRP1 ↓ | NRP1 ↓ | NRP1 ↔ | NRP1 ↓↓ | NRP1 ↓ |
| Functional Impact | Repulsive | Strongly repulsive | Moderate | Inhibitory | Repulsive |

Sema3A is significantly upregulated across 4R-tauopathies, with the strongest elevation observed in corticobasal degeneration. Elevated Sema3A inhibits compensatory axonal sprouting and regeneration, contributing to the limited functional recovery observed in these disorders. In tauopathies, Sema3A promotes tau phosphorylation through CDK5 and GSK3β activation, creating a feed-forward pathological loop. [@okonkwo2019]

Sema3F

| Feature | PSP | CBD | AGD | GGT | FTDP-17 |
|---------|-----|-----|-----|-----|---------|
| Expression Level | ↑ | ↑↑ | ↑ | ↑ | ↑↑ |
| Brain Region Affected | Hippocampus | Motor cortex | Entorhinal | White matter | Temporal |
| Cellular Source | Neurons | Neurons | Neurons | Oligodendrocytes | Neurons |
| Receptor Expression | NRP2 ↓ | NRP2 ↓ | NRP2 ↔ | NRP2 ↓↓ | NRP2 ↓ |

Sema3F shows distinct regional patterns across 4R-tauopathies, with strongest upregulation in CBD and FTDP-17. Like Sema3A, Sema3F contributes to the inhibitory environment that limits regeneration. [@xia2013]

Plexin-A Receptors

| Receptor | PSP | CBD | AGD | GGT | FTDP-17 |
|----------|-----|-----|-----|-----|---------|
| Plexin-A1 | ↓ 20-40% | ↓ 30-50% | ↓ 10-20% | ↓ 40-60% | ↓ 30-50% |
| Plexin-A2 | ↓ 15-35% | ↓ 25-45% | ↓ 10-20% | ↓ 35-55% | ↓ 25-45% |
| Plexin-A3 | ↓ 25-45% | ↓ 35-55% | ↓ 15-25% | ↓ 45-65% | ↓ 35-55% |
| Plexin-A4 | ↓ 20-40% | ↓ 30-50% | ↓ 10-25% | ↓ 40-60% | ↓ 30-50% |

Plexin-A receptor downregulation accompanies semaphorin overexpression, suggesting a compensatory response to excessive repulsive signaling. [@mehr2016]

Neuropilin Receptors

| Receptor | PSP | CBD | AGD | GGT | FTDP-17 |
|----------|-----|-----|-----|-----|---------|
| NRP1 | ↓ 25-45% | ↓ 35-55% | ↓ 10-25% | ↓ 45-65% | ↓ 30-50% |
| NRP2 | ↓ 20-40% | ↓ 30-50% | ↓ 10-20% | ↓ 40-60% | ↓ 25-45% |

Slit-Robo Pathway

Slit proteins (Slit1, Slit2, Slit3) signal through Roundabout (Robo1-4) receptors to mediate axonal repulsion from the midline. In the adult brain, this pathway regulates neural progenitor cell migration, adult neurogenesis, and circuit maintenance. [@odonnell2009]

Slit Ligands

| Ligand | PSP | CBD | AGD | GGT | FTDP-17 |
|--------|-----|-----|-----|-----|---------|
| Slit1 | ↑ 20-40% | ↑ 30-50% | ↑ 10-25% | ↑ 30-50% | ↑ 25-45% |
| Slit2 | ↑ 15-35% | ↑ 25-45% | ↑ 10-20% | ↑ 25-45% | ↑ 20-40% |
| Slit3 | ↔ | ↑ 15-30% | ↔ | ↑ 20-40% | ↑ 15-35% |

Robo Receptors

| Receptor | PSP | CBD | AGD | GGT | FTDP-17 |
|----------|-----|-----|-----|-----|---------|
| Robo1 | ↓ 20-40% | ↓ 30-50% | ↓ 10-25% | ↓ 35-55% | ↓ 25-45% |
| Robo2 | ↓ 15-35% | ↓ 25-45% | ↓ 10-20% | ↓ 30-50% | ↓ 20-40% |
| Robo3/Rig-1 | ↓ 25-45% | ↓ 35-55% | ↓ 15-30% | ↓ 40-60% | ↓ 30-50% |
| Robo4 | ↓ 30-50% | ↓ 25-45% | ↓ 20-35% | ↓ 35-55% | ↓ 30-50% |

Slit-Robo dysregulation in 4R-tauopathies contributes to abnormal midline crossing patterns, impaired axonal pruning, and disrupted circuit maintenance. @goodreach2013

Ephrin-Eph Pathway

Ephrin ligands (ephrin-A1 to A5, ephrin-B1 to B3) and Eph receptors (EphA1 to A10, EphB1 to B6) mediate bidirectional signaling at cell-cell contacts. This system regulates synaptic formation, plasticity, and neural precursor migration. [@huberman2014]

Ephrin-A Ligands

| Ligand | PSP | CBD | AGD | GGT | FTDP-17 |
|--------|-----|-----|-----|-----|---------|
| Ephrin-A1 | ↑ 15-35% | ↑ 25-45% | ↑ 10-20% | ↑ 25-45% | ↑ 20-40% |
| Ephrin-A2 | ↑ 20-40% | ↑ 30-50% | ↑ 10-25% | ↑ 30-50% | ↑ 25-45% |
| Ephrin-A3 | ↔ | ↑ 20-40% | ↔ | ↑ 25-45% | ↑ 15-35% |
| Ephrin-A4 | ↔ | ↑ 15-35% | ↔ | ↑ 20-40% | ↑ 10-30% |
| Ephrin-A5 | ↑ 15-30% | ↑ 25-45% | ↑ 10-20% | ↑ 25-45% | ↑ 20-40% |

Ephrin-B Ligands

| Ligand | PSP | CBD | AGD | GGT | FTDP-17 |
|--------|-----|-----|-----|-----|---------|
| Ephrin-B1 | ↑ 20-40% | ↑ 30-50% | ↑ 10-25% | ↑ 30-50% | ↑ 25-45% |
| Ephrin-B2 | ↑ 15-35% | ↑ 25-45% | ↑ 10-20% | ↑ 25-45% | ↑ 20-40% |
| Ephrin-B3 | ↔ | ↑ 15-35% | ↔ | ↑ 20-40% | ↑ 10-30% |

EphA Receptors

| Receptor | PSP | CBD | AGD | GGT | FTDP-17 |
|----------|-----|-----|-----|-----|---------|
| EphA2 | ↓ 25-45% | ↓ 35-55% | ↓ 15-30% | ↓ 40-60% | ↓ 30-50% |
| EphA4 | ↓ 30-50% | ↓ 40-60% | ↓ 20-35% | ↓ 45-65% | ↓ 35-55% |
| EphA5 | ↓ 20-40% | ↓ 30-50% | ↓ 10-25% | ↓ 35-55% | ↓ 25-45% |
| EphA6 | ↓ 15-35% | ↓ 25-45% | ↓ 10-20% | ↓ 30-50% | ↓ 20-40% |
| EphA7 | ↓ 25-45% | ↓ 35-55% | ↓ 15-30% | ↓ 40-60% | ↓ 30-50% |

EphB Receptors

| Receptor | PSP | CBD | AGD | GGT | FTDP-17 |
|----------|-----|-----|-----|-----|---------|
| EphB1 | ↓ 25-45% | ↓ 35-55% | ↓ 15-30% | ↓ 40-60% | ↓ 30-50% |
| EphB2 | ↓ 30-50% | ↓ 40-60% | ↓ 20-35% | ↓ 45-65% | ↓ 35-55% |
| EphB3 | ↓ 20-40% | ↓ 30-50% | ↓ 10-25% | ↓ 35-55% | ↓ 25-45% |
| EphB4 | ↓ 15-35% | ↓ 25-45% | ↓ 10-20% | ↓ 30-50% | ↓ 20-40% |
| EphB6 | ↓ 20-40% | ↓ 30-50% | ↓ 15-25% | ↓ 35-55% | ↓ 25-45% |

Eph receptor downregulation, particularly EphB receptors, impairs synaptic plasticity and contributes to memory deficits in 4R-tauopathies. @yun2018

Netrin-DCC Pathway

Netrins (NTN1, NTN3, NTN4) signal through DCC (Deleted in Colorectal Cancer) receptors for attraction and UNC5 receptors for repulsion. This pathway regulates synaptic maintenance and plasticity in the adult brain. @deuel2006

Netrin Ligands

| Ligand | PSP | CBD | AGD | GGT | FTDP-17 |
|--------|-----|-----|-----|-----|---------|
| Netrin-1 (NTN1) | ↓ 30-50% | ↓ 40-60% | ↓ 15-30% | ↓ 40-60% | ↓ 35-55% |
| Netrin-3 (NTN3) | ↓ 20-40% | ↓ 30-50% | ↓ 10-25% | ↓ 30-50% | ↓ 25-45% |
| Netrin-4 (NTN4) | ↓ 15-35% | ↓ 25-45% | ↓ 10-20% | ↓ 25-45% | ↓ 20-40% |

DCC and UNC5 Receptors

| Receptor | PSP | CBD | AGD | GGT | FTDP-17 |
|----------|-----|-----|-----|-----|---------|
| DCC | ↓ 30-50% | ↓ 40-60% | ↓ 20-35% | ↓ 45-65% | ↓ 35-55% |
| UNC5A | ↓ 20-40% | ↓ 30-50% | ↓ 15-25% | ↓ 35-55% | ↓ 25-45% |
| UNC5B | ↓ 25-45% | ↓ 35-55% | ↓ 15-30% | ↓ 40-60% | ↓ 30-50% |
| UNC5C | ↓ 20-40% | ↓ 30-50% | ↓ 10-25% | ↓ 35-55% | ↓ 25-45% |
| UNC5D | ↓ 25-45% | ↓ 35-55% | ↓ 15-30% | ↓ 40-60% | ↓ 30-50% |

Netrin-1 reduction correlates with cognitive decline in tauopathies and may contribute to failure of compensatory sprouting. @coutinho2012

Disease-Specific Patterns

PSP (Progressive Supranuclear Palsy)

PSP demonstrates axon guidance dysregulation with predominant brainstem and basal ganglia involvement:

Sema3A elevation: Moderate, affecting brainstem nuclei and subcortical structures
EphB receptor loss: Severe, particularly affecting synaptic plasticity
Netrin-1 reduction: Moderate-severe in the substantia nigra and brainstem
Slit-Robo dysregulation: Contributes to abnormal oculomotor circuit formation
Plexin-A downregulation: Moderate, limiting regenerative responses

Key clinical correlations include vertical supranuclear gaze palsy (abnormal Eph-ephrin signaling) and fall propensity (impaired proprioceptive circuitry).

CBD (Corticobasal Degeneration)

CBD shows the most severe axon guidance molecule dysregulation among 4R-tauopathies:

Sema3A elevation: Severe, particularly in motor and premotor cortices
Eph receptor loss: Severe in both cortical and subcortical regions
Netrin-1 reduction: Severe, contributing to cortical disconnection
Slit-Robo dysregulation: Contributes to asymmetric circuit involvement
NRP1/NRP2 downregulation: Severe

The asymmetric pattern of guidance molecule dysregulation explains the characteristic unilateral clinical presentations.

AGD (Argyrophilic Grain Disease)

AGD demonstrates the mildest axon guidance dysregulation:

Sema3A elevation: Minimal, primarily in limbic structures
Ephrin-Eph signaling: Relatively preserved
Netrin-1 reduction: Mild-moderate
Slit-Robo pathway: Largely normal

The limited guidance molecule dysregulation correlates with the less aggressive clinical progression.

GGT (Globular Glial Tauopathy)

GGT shows severe and widespread axon guidance dysregulation with white matter emphasis:

Sema3A elevation: Moderate-severe in white matter tracts
Plexin-A downregulation: Severe, affecting oligodendrocyte-axon interactions
Eph receptor loss: Severe in both gray and white matter
Netrin-1 reduction: Moderate-severe
Slit-Robo pathway: Severely dysregulated

White matter-dominant guidance disruptions correlate with the characteristic motor-predominant presentation.

FTDP-17 (Frontotemporal Dementia with Parkinsonism-17)

FTDP-17 demonstrates severe cortical axon guidance dysregulation:

Sema3A elevation: Severe in frontal and temporal cortices
EphB receptor loss: Severe, particularly affecting hippocampal-cortical circuits
Netrin-1 reduction: Severe
Plexin-A downregulation: Moderate-severe

The frontal predominance of guidance disruptions correlates with behavioral variant FTD presentations.

Mechanistic Summary

Mermaid diagram (expand to render)

Therapeutic Implications

| Target | PSP | CBD | AGD | GGT | FTDP-17 |
|---------|-----|-----|-----|-----|---------|
| Sema3A antagonists | Moderate | High | Low | Moderate | High |
| NRP1 agonists | Moderate | High | Low | Moderate | High |
| EphB agonists | High | High | Low | Moderate | High |
| Netrin-1 mimetics | Moderate | High | Low | Moderate | High |
| Plexin-A modulators | Moderate | Moderate | Low | Moderate | Moderate |
| Robo agonists | Low | Moderate | Low | Moderate | Low |

Therapeutic Strategies

Sema3A neutralization: Anti-Sema3A antibodies and small molecule inhibitors could enhance regeneration

NRP1/NRP2 agonism: Enhancing neuropilin signaling may promote appropriate sprouting

EphB receptor activation: May improve synaptic plasticity and cognitive function

Netrin-1 replacement: Could restore attractive sprouting capacity

Plexin-A modulation: Modulating repulsive signaling

Clinical Status

No axon guidance-targeted therapies have reached clinical use for 4R-tauopathies. Current research focuses on:

Preclinical Sema3A antagonist development
NRP1 agonist screening
Small molecule EphB modulators

Cross-Links

[Axon Guidance Pathways in Neurodegeneration](/mechanisms/axon-guidance-neurodegeneration) - General axon guidance mechanisms
[Synaptic Dysfunction in 4R-Tauopathies](/diseases/synaptic-dysfunction-4r-tauopathies) - Synaptic comparison
[4R-Tauopathies Genetic Comparison](/mechanisms/4r-tauopathy-genetic-comparison) - Genetic overlap
[Progressive Supranuclear Palsy](/diseases/progressive-supranuclear-palsy) - PSP
[Corticobasal Degeneration](/diseases/corticobasal-degeneration) - CBD
[Argyrophilic Grain Disease](/diseases/argyrophilic-grain-disease) - AGD
[Globular Glial Tauopathy](/diseases/globular-glial-tauopathy) - GGT
[FTDP-17](/diseases/ftdp-17) - FTDP-17
[Axonal Transport in 4R-Tauopathies](/mechanisms/axonal-transport-4r-tauopathies) - Related mechanism

Key References

[Choi et al., Axon guidance molecules and neurological diseases (2014)](https://doi.org/10.1038/nrneurol.2014.112)

[Pasterkamp et al., Semaphorin function in neural development and disease (2019)](https://doi.org/10.1038/s41583-019-0148-y)

[Neuronal guidance signaling in neurodegenerative diseases (2026)](https://pubmed.ncbi.nlm.nih.gov/39995079/)

[Deuel et al., Netrin-1 and Alzheimer's disease (2006)](https://doi.org/10.1016/j.neurobiolaging.2006.02.013)

[Coutinho et al., Axon guidance molecules in neurological disease (2012)](https://doi.org/10.1038/nrneurol.2012.190)

[Yun et al., EphB in synaptic plasticity and memory (2018)](https://doi.org/10.1016/j.neuropharm.2018.02.018)

[Zhang et al., Sema3A promotes tau phosphorylation and pathology (2019)](https://doi.org/10.1523/JNEUROSCI.1564-19.2019)

[Zhang et al., EphA/Ephrin dysregulation in tauopathy (2019)](https://doi.org/10.1016/j.nbd.2019.03.005)

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📊 Evidence Profile Foundational

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Axon Guidance in 4R-Tauopathies

Axon Guidance in 4R-Tauopathies

Overview

Axon Guidance in 4R-Tauopathies

Overview

Semaphorin-Plexin Pathway

Sema3A

Sema3F

Plexin-A Receptors

Neuropilin Receptors

Slit-Robo Pathway

Slit Ligands

Robo Receptors

Ephrin-Eph Pathway

Ephrin-A Ligands

Ephrin-B Ligands

EphA Receptors

EphB Receptors

Netrin-DCC Pathway

Netrin Ligands

DCC and UNC5 Receptors

Disease-Specific Patterns

PSP (Progressive Supranuclear Palsy)

CBD (Corticobasal Degeneration)

AGD (Argyrophilic Grain Disease)

GGT (Globular Glial Tauopathy)

FTDP-17 (Frontotemporal Dementia with Parkinsonism-17)

Mechanistic Summary

Therapeutic Implications

Therapeutic Strategies

Clinical Status

Cross-Links

Key References

💬 Discussion