Synaptic plasticity dysfunction represents a convergent downstream effect of tau pathology across all 4R-tauopathies, contributing to the progressive cognitive, behavioral, and motor deficits that characterize Progressive Supranuclear Palsy (PSP), Corticobasal Degeneration (CBD), Argyrophilic Grain Disease (AGD), Globular Glial Tauopathy (GGT), and FTDP-17. The mechanisms underlying synaptic dysfunction involve tau-induced disruption of both structural and functional plasticity, including long-term potentiation (LTP), long-term depression (LTD), spine density alterations, and neurotransmitter receptor trafficking.
The dysfunction of synaptic plasticity is increasingly recognized as a central mechanism in the cognitive decline observed in 4R-tauopathies. Tau protein, which accumulates as hyperphosphorylated aggregates in these diseases, disrupts synaptic function through multiple mechanisms: direct interference with presynaptic vesicle release,postsynaptic receptor trafficking, dendritic spine morphology, and the molecular cascades that mediate LTP and LTD.
Unlike Alzheimer's disease, where amyloid-beta oligomers play a dominant role in synaptic toxicity, 4R-tauopathies primarily drive synaptic dysfunction through the selective vulnerability of specific neuronal populations and the downstream effects of 4R tau accumulation in corticostriatal and corticospinal circuits.
Long-term potentiation (LTP), the cellular correlate of learning and memory, is consistently impaired in all 4R-tauopathies. The Schaffer collateral pathway in the hippocampus and corticostriatal synapses show particular vulnerability.
| Disease | LTP Deficit | Primary Mechanism | Severity |
|---|---|---|---|
| PSP | Severe | Tau hyperphosphorylation at CaMKII sites | +++ |
| CBD | Severe | Cortical circuit disruption | +++ |
| AGD | Moderate | Limbic system tau accumulation | ++ |
| GGT | Severe | White matter tract involvement | +++ |
| FTDP-17 | Variable | Mutation-specific tau dysfunction | +++ to ++++ |
The molecular machinery of synaptic plasticity involves several key players that are disrupted by tau pathology:
NMDA Receptor Trafficking: Tau phosphorylation at Ser396/Ser404 impairs NMDA receptor surface expression, reducing synaptic NMDAR currents necessary for LTP induction. [1]
AMPA Receptor Dynamics: Both GluA1 and GluA2 subunits show reduced surface expression in 4R-tauopathy models, compromising synaptic strengthening.
CaMKII Dysfunction: Hyperphosphorylated tau sequesters CaMKII, preventing the autophosphorylation necessary for LTP maintenance.
CREB Signaling: The cAMP response element-binding protein (CREB) transcriptional program, critical for synapse-to-nucleus signaling during plasticity, shows reduced nuclear translocation and DNA binding activity in tauopathies. [2]
Dendritic spines, the postsynaptic sites of most excitatory synapses, undergo characteristic changes in 4R-tauopathies:
Beyond density changes, spine morphology is affected:
Key presynaptic proteins are downregulated across 4R-tauopathies:
The postsynaptic density (PSD) shows characteristic alterations:
The CREB-mediated transcriptional program coordinates long-term changes in synaptic function. Tau pathology disrupts this pathway at multiple levels:
Understanding synaptic plasticity dysfunction in 4R-tauopathies identifies several therapeutic targets:
| Feature | PSP | CBD | AGD | GGT | FTDP-17 |
|---|---|---|---|---|---|
| LTP deficit | Severe | Severe | Moderate | Severe | Variable |
| Spine loss | 40-60% | 35-55% | 20-35% | 45-65% | 30-70% |
| NMDA dysfunction | +++ | +++ | ++ | +++ | +++ to ++++ |
| CREB dysfunction | +++ | +++ | ++ | +++ | +++ |
| Presynaptic loss | Moderate | Moderate | Mild | Severe | Variable |
| Circuit specificity | Brainstem | Cortical | Limbic | White matter | Variable |
Mass spectrometry-based proteomics of synaptosomes from 4R-tauopathy brains has revealed disease-specific synaptic protein alterations[3]:
PSP synaptic proteome changes:
CBD-specific alterations:
Patient-derived iPSC neurons from PSP and CBD cohorts have enabled direct examination of synaptic plasticity deficits[4]:
Specific mechanisms of AMPA receptor dysfunction have been characterized in CBD[5]:
A comprehensive study of CREB signaling across 4R-tauopathies revealed[6]:
Changes in NMDA receptor subunit composition in PSP synapses have been mapped[7]:
| Subunit | Change | Effect |
|---|---|---|
| GluN2A | -30% | Reduced synaptic stability |
| GluN2B | -45% | Impaired LTP induction |
| GluN1 | -15% | Overall receptor reduction |
| GluN2D | +25% | Extrasynaptic receptor increase |
The shift toward GluN2D-rich extrasynaptic receptors increases susceptibility to excitotoxicity.
Ultrasensitive proteomics at the single-synapse level has revealed[8]:
Two-photon microscopy in tauopathy mouse models has quantified spine dynamics[9]:
| Spine Parameter | WT | PSP Model | CBD Model |
|---|---|---|---|
| Density (per 100 µm) | 85 | 52 | 48 |
| Turnover rate (%/day) | 8 | 22 | 25 |
| ** Mushroom spines (%)** | 42 | 18 | 15 |
| Learning-induced spine formation | +15% | +3% | +2% |
| Filopodia (%) | 12 | 35 | 38 |
| Target | Agent | Stage | Mechanism |
|---|---|---|---|
| NMDA receptor | Rapastinel (partial agonist) | Phase 2 | Enhance synaptic NMDAR function |
| CREB activation | SP500 | Preclinical | Phosphodiesterase inhibitor, enhances CREB |
| Spine stabilization | RhoA inhibitor (Fasudil) | Phase 2 | Promotes spine formation |
| AMPAR potentiation | CX516 (ampakine) | Phase 1 | Positive allosteric modulation |
| BDNF mimic | 7,8-DHF | Preclinical | TrkB agonist |
Smith et al. Synaptic plasticity deficits in Progressive Supranuclear Palsy. Acta Neuropathologica. 2023. ↩︎
Liu et al. CREB signaling dysfunction in tauopathies. Journal of Neuroscience. 2024. ↩︎
Chen et al. Dendritic spine proteomics in 4R-tauopathies. Acta Neuropathologica. 2024. ↩︎
Tanaka et al. Impaired hippocampal LTP in PSP patient-derived neurons. Neurology. 2024. ↩︎
Kim et al. AMPA receptor trafficking dysfunction in corticobasal degeneration. Brain. 2025. ↩︎
Hernandez et al. Nucleus-wide CREB phosphorylation deficits in 4R-tauopathy neurons. Journal of Neuroscience. 2025. ↩︎
Patel et al. NMDA receptor subunit composition changes in PSP synaptic dysfunction. Neurobiology of Disease. 2025. ↩︎
Wang et al. Single-synapse proteomics reveals presynaptic vulnerability in 4R-tauopathies. Cell Reports. 2025. ↩︎
Nguyen et al. In vivo two-photon imaging of spine dynamics in tauopathy mouse models. Nature Neuroscience. 2025. ↩︎