Tau protein expressing neurons represent a critical population in the study of Alzheimer's disease (AD) and related tauopathies. These neurons are characterized by the presence of tau (MAPT - Microtubule-Associated Protein Tau), a microtubule-stabilizing protein that plays essential roles in normal neuronal function but can form toxic aggregates that drive neurodegeneration.
| Property |
Value |
| Category |
Cytoskeletal Proteins |
| Location |
Axons, cell body, NFTs |
| Protein |
Tau (MAPT) |
| Function |
Microtubule stabilization, axonal transport |
| Associated Diseases |
Alzheimer's Disease, Frontotemporal Dementia, Progressive Supranuclear Palsy, Corticobasal Degeneration, Chronic Traumatic Encephalopathy |
Tau is primarily located in axons where it binds to microtubules and:
- Stabilizes microtubule structure: Prevents depolymerization and maintains axonal integrity
- Facilitates axonal transport: Provides tracks for kinesin and dynein motor proteins
- Maintains neuronal polarity: Distinguishes axons from dendrites
- Regulates microtubule dynamics: Modulates polymerization and stability
Tau also localizes to synapses where it participates in:
- Presynaptic functions: Regulates synaptic vesicle release and recycling
- Postsynaptic signaling: Interacts with postsynaptic receptors and scaffolding proteins
- Synaptic plasticity: Involved in learning and memory processes
- Activity-dependent release: Tau can be released from synapses in an activity-dependent manner
During neuronal development, tau:
- Promotes axon specification and outgrowth
- Guides cytoskeletal organization in growing neurons
- Supports dendritic arborization through microtubule regulation
The MAPT gene produces six tau isoforms in the adult human brain through alternative splicing of exons 2, 3, and 10:
- 3-repeat tau (3R): Lacks exon 10, binds one microtubule
- 4-repeat tau (4R): Includes exon 10, binds two microtubules
- Isoform ratio: 3R:4R ratio is ~1:1 in normal adult brain
The balance between 3R and 4R tau is critical - imbalances lead to tauopathy.
Tau is subject to numerous post-translational modifications:
- Phosphorylation: Up to 85 potential phosphorylation sites; hyperphosphorylation is pathological
- Acetylation: Promotes aggregation by reducing tau's ability to bind microtubules
- Truncation: Proteolytic cleavage generates aggregation-prone fragments
- O-GlcNAcylation: Metabolic regulation, competes with phosphorylation
- Sumoylation: Influences aggregation and clearance
¶ Hyperphosphorylation and Aggregation
In Alzheimer's disease and tauopathies, tau becomes hyperphosphorylated and aggregates:
- Phosphorylation at disease-associated sites: Kinases (GSK3β, CDK5) overactivate
- Loss of microtubule binding: Hyperphosphorylated tau dissociates from microtubules
- Oligomer formation: Soluble toxic oligomers form
- NFT formation: Paired helical filaments aggregate into neurofibrillary tangles
Neurofibrillary tangles (NFTs) are intracellular aggregates of hyperphosphorylated tau:
- Braak staging: Correlates with disease progression (I-VI)
- Neuronal loss: NFTs are associated with neuronal death
- Spread pattern: Follows neural connectivity pathways
Tau pathology drives neuronal dysfunction through:
- Microtubule disruption: Impaired axonal transport
- Synaptic loss: Reduced synaptic proteins, impaired plasticity
- Mitochondrial dysfunction: Energy deficits
- ER stress: Protein homeostasis disruption
- Neuroinflammation: Glial activation
- Exosomal release: Propagation to connected neurons
Specific neurons are particularly vulnerable to tau pathology:
- Entorhinal cortex neurons: Early involvement, critical for memory
- Hippocampal CA1 pyramidal neurons: Essential for memory formation
- Layer II entorhinal cortex neurons: Early tau pathology in AD
- Subcortical nuclei: Locus coeruleus, dorsal raphe
- Specific cortical pyramidal neurons: Layer V neurons
Tau-targeted therapies include:
- Anti-aggregation agents: Prevent tau misfolding and aggregation
- Kinase inhibitors: Reduce pathological phosphorylation (GSK3β, CDK5)
- Phosphatase activators: Promote tau dephosphorylation
- Immunotherapy: Active and passive vaccines targeting tau
- Microtubule stabilizers: Restore axonal transport
- Tau degradation enhancers: Promote autophagy and proteasomal clearance
Tau in cerebrospinal fluid and blood serves as a biomarker:
- Total tau: Reflects neuronal damage
- Phosphorylated tau (p-tau181, p-tau217): Disease-specific markers
- p-tau217: High specificity for AD, correlates with amyloid pathology
- iPSC-derived neurons: From AD patients with MAPT mutations
- Primary neuron cultures: Overexpression or knock-in models
- Tau fibril seeding models: Introduce pathological tau to healthy neurons
- Transgenic mice: rTg4510, P301S, 3xTg-AD
- Knockin models: Humanized tau with pathogenic mutations
- Viral vector models: AAV-mediated tau overexpression
- Mandelkow & Mandelkow. Tau protein in physiology and disease (2003)
- Ballatore et al. Tau-mediated neurodegeneration (2007)
- Arendt et al. Tau pathology in Alzheimer's disease (2016)
- Wang & Mandelkow. Tau in physiology and pathology (2016)
- Alonso et al. Hyperphosphorylation and aggregation of tau (2020)
- Spani et al. Tau post-translational modifications (2022)
- Karikari et al. Phosphorylated tau biomarkers (2020)
- T fronts. Tau therapeutics pipeline (2023)