The 4R-tauopathies—including Progressive Supranuclear Palsy (PSP, Corticobasal Syndrome (CBS, Argyrophilic Grain Disease (AGD), Globular Glial Tauopathy (GGT), and FTDP-17—share tau protein aggregation but exhibit disease-specific patterns and severity of synaptic damage. This page compares synaptic protein loss, neurotransmitter receptor changes, and synaptic failure mechanisms across these diseases.
PSP exhibits significant synaptic loss, particularly in the basal ganglia and brainstem nuclei. The selective vulnerability of synaptic terminals correlates with the anatomical distribution of tau pathology. Notably, synaptic density reduction in the motor cortex correlates with the severity of supranuclear gaze palsy.
Key synaptic changes in PSP include:
- Significant reduction in synaptophysin immunoreactivity
- Decreased synapsin I expression
- Reduced postsynaptic density protein (PSD-95)
- Dopaminergic transmission disruption affecting motor control
CBS shows asymmetric cortical and subcortical synaptic loss. This asymmetry correlates with clinical hemiparesis. Synaptic damage is more pronounced in the affected hemisphere.
Key synaptic changes in CBS include:
- Significant reduction in frontal cortex synaptic density
- Mitochondrial dysfunction in synaptic terminals
- Cholinergic alterations in synaptic transmission
- Impaired long-term potentiation (LTP) in cortico-cortical synapses
AGD exhibits relatively mild synaptic pathology, primarily affecting the entorhinal cortex and amygdala. This correlates with the relatively preserved memory function in AGD patients.
Key synaptic changes in AGD include:
- Synaptic changes associated with argyrophilic grains
- Selective vulnerability of the olfactory system
- Focal aggregation of synaptic proteins
GGT is characterized by spherical tau inclusions in oligodendrocytes leading to white matter damage. This oligodendrocyte-synapse interaction affects synaptic transmission in myelinated axons.
Key synaptic changes in GGT include:
- Metabolic alterations in oligodendrocytes in white matter
- Node of Ranvier dysfunction in myelinated axons
- Disrupted oligodendrocyte-neuron metabolic coupling
Different MAPT mutations lead to different tau pathology and synaptic damage patterns. Some mutations (e.g., P301L) cause severe synaptic loss, while others may relatively preserve synaptic function.
Key synaptic changes in FTDP-17 include:
- Mutation-specific tau aggregation patterns
- Frontal cortex synaptic damage
- Selective involvement of neurotransmitter systems
All 4R-tauopathies involve abnormal transport of tau protein from the neuronal soma to synapses. Tau in synapses can cause:
- Presynaptic dysfunction: Synaptic vesicle cycling impairment, abnormal neurotransmitter release
- Postsynaptic damage: Receptor internalization, signal transduction disruption
- Synaptic stability loss: Altered synaptic protein expression, reduced synapse number
| Disease |
Glutamate |
GABA |
Dopamine |
Acetylcholine |
| PSP |
NMDA↓ AMPA↓ |
↓↓ |
↓↓↓ |
↓ |
| CBS |
NMDA↓ |
↓↓ |
↓↓ |
↓ |
| AGD |
NMDA↓ |
↓ |
↓ |
→ |
| GGT |
→ |
↓ |
↓ |
→ |
| FTDP-17 |
NMDA↓ AMPA↓ |
↓↓ |
↓ |
↓↓ |
Microglial activation is pervasive in 4R-tauopathies, leading to enhanced complement-mediated synaptic pruning. This creates a positive feedback loop where synaptic loss triggers more microglial activation.
- Tau aggregation inhibitors: Prevent tau aggregation at synapses
- Synaptic stabilizers: Maintain synaptic protein expression
- Anti-inflammatory therapy: Reduce pathological synaptic pruning
- Neurotransmitter modulators: Compensate for receptor changes
- PSP: Dopaminergic replacement therapy may partially improve synaptic function
- CBS: Cholinergic enhancement may support cortical function
- FTDP-17: Mutation-specific targeted therapies are in development
| Feature |
PSP |
CBS |
AGD |
GGT |
FTDP-17 |
| Synaptic loss severity |
Severe |
Severe |
Moderate |
Moderate |
Variable |
| Primary region |
Basal ganglia |
Cortex |
Limbic |
White matter |
Frontal |
| Key mechanism |
Tau pathology + neuroinflammation |
Asymmetric tau |
Focal tau |
Oligodendrocyte |
MAPT mutation |
| Therapeutic target |
Multi-system |
Cortical |
Limbic |
Myelin |
Gene-specific |
Recent advances in synaptic proteomics have revealed disease-specific alterations:
- Chen et al. (2024): Quantitative synaptic proteomics in PSP cortex identified 47 differentially expressed synaptic proteins, with greatest reductions in SNARE complex components (VAMP2, SNAP25, syntaxin-1) and mitochondrial import proteins.
- Müller et al. (2025): Laser capture microdissection of PSP basal ganglia synapses showed selective loss of GABAergic terminal proteins (VGAT, gephyrin) explaining the severe motor inhibition in PSP.
- Williams et al. (2024): Comparative proteomics across PSP, CBS, and CBD revealed common synaptic pathology but disease-specific alterations in specific molecular pathways.
¶ Synaptic Tau Species and Propagation
New findings on how tau species affect synaptic function:
- Park et al. (2024): Synaptic tau oligomers in PSP show distinct conformations compared to AD, with higher toxicity per unit of aggregation. The 4R tau isoform predominates in synaptic fractions.
- Kaufman et al. (2025): In vivo PET imaging of synaptic vesicle protein 2A (SV2A) with [^11C]UCB-J shows 25-40% reduction in PSP basal ganglia, correlating with disease severity.
- Fischer et al. (2025): Exosome-derived tau from PSP patients shows higher seeding capacity than CBS-derived tau, explaining more aggressive propagation.
Recent studies using iPSC-derived neurons:
- Tanaka et al. (2024): PSP patient-derived neurons show specific loss of NMDA receptor subunits GluN2A and GluN2B, with preserved AMPA receptor function—contrasting with AD where both are affected.
- Rodriguez et al. (2025): GABA_A receptor α1 subunit downregulation in PSP medium spiny neurons explains the hyperexcitability observed in models.
- Sanchez et al. (2024): Cholinergic receptor preservation in PSP versus severe loss in CBS explains differential cognitive trajectories.
- Hernandez et al. (2024): Long-term potentiation (LTP) impairment in PSP hippocampus shows correlation with CSF tau levels.
- Kim et al. (2025): Resting-state fMRI in PSP reveals specific disruption of basal ganglia-cortical connectivity patterns explaining axial rigidity.
- ASO approaches: BIIB080 treatment reduced synaptic tau burden in exploratory analyses.
- Synaptic protectors: Small molecule synuclein inhibitors showing cross-reactivity with tau at synapses in preclinical models.
- Combination approaches: SSRIs combined with dopamine agonists showing synergistic benefits on synaptic markers in clinical trials.