4R-Tau refers to the tau protein isoform containing four microtubule-binding repeat domains, encoded by the MAPT (Microtubule-Associated Protein Tau) gene. Tau exists as six isoforms in the adult human brain, generated by alternative splicing of exon 10. The 3R-Tau isoforms (3 repeats) and 4R-Tau isoforms (4 repeats) are normally expressed in a 1:1 ratio. Dysregulation leading to increased 4R-Tau production is a hallmark of several neurodegenerative diseases collectively called 4R-tauopathies.
The 4R-tauopathies include Progressive Supranuclear Palsy (PSP), Corticobasal Degeneration (CBD), and certain forms of Alzheimer's disease. The presence of 4R-tau predominant pathology is a key diagnostic feature distinguishing these conditions from 3R-predominant diseases like Pick's disease.
- Protein Name: 4R-Tau - Tau Protein with Four Repeat Domains
- UniProt ID: P10636 (isoform 2)
- Gene: MAPT
- Molecular Weight: ~45-65 kDa (depending on isoform)
- Protein Class: Microtubule-associated protein
- Tissue Expression: Neurons (axons), astrocytes, oligodendrocytes
- Isoform Length: 383-441 amino acids (4R isoforms)
4R-tau isoforms contain:
- N-terminal projection domain: Projects away from microtubules, interacts with neuronal membranes
- Proline-rich region: Contains multiple phosphorylation sites (20+ ser/thr sites)
- 1N, 2N isoforms: Include N-terminal inserts from exon 2/3
¶ Microtubule-Binding Domain
- C-terminal microtubule-binding domain: Contains either 3 (3R-tau) or 4 (4R-tau) repeat regions
- Repeat domains R1-R4: Each repeat is ~31 amino acids
- PHF6 motif: Hexapeptide sequence essential for aggregation
- 4R-tau includes repeat R3: The additional repeat increases microtubule binding affinity
- Exon 10 inclusion: Results in 4R-tau isoforms
- Alternative splicing: Regulated by ASF/SF2 and SRRM2
Normal tau functions include:
- Promotes tubulin polymerization and microtubule stability
- Dynamic instability regulation
- Axonal transport support
- Facilitates vesicle and organelle movement along axons
- Kinesin/dynactin interactions
- Organelle positioning
- Maintains axonal identity
- Distinguishes axons from dendrites
- Regulates synapse formation
- Modulates synaptic vesicle trafficking
- Presynaptic and postsynaptic roles
- Activity-dependent regulation
- DNA protection under stress conditions
- Signal transduction scaffolding
- RNA metabolism support
The balance between 3R-tau and 4R-tau is critical:
- 1:1 ratio in normal adult brain
- 4R-tau has ~2-fold higher microtubule binding affinity
- Excess 4R leads to microtubule hyperstabilization
PSP is the prototypical 4R-tauopathy:
- 4R predominant: 4R-tau aggregates are the hallmark pathology
- Glial tauopathy: Tau in astrocytes (tufted astrocytes) and oligodendrocytes
- Neurofibrillary tangles: Composed of 4R-tau filaments
- Brainstem involvement: Substantia nigra, brainstem nuclei
- Splicing dysregulation: Exon 10 inclusion increased
- Aggregation propensity: 4R-tau forms paired helical filaments
- Prion-like propagation: Seeding of tau pathology
- Post-translational modifications: Hyperphosphorylation, acetylation
- Vertical gaze palsy
- Postural instability
- Parkinsonism
- Cognitive decline
CBD is another 4R-tauopathy with distinct pathology:
- 4R-tau pathology: Astrocytic plaques, thread-like processes
- Neuronal loss: Cortical and basal ganglia involvement
- Tau isoforms: Predominantly 4R-tau
- Astrocytic plaques: Characteristic lesion
- Altered splicing: Increased 4R-tau
- Specific mutations: Associated with CBD-causing MAPT mutations
- Propagation: Spreading through neural networks
AD shows mixed tau pathology with both 3R and 4R tau:
- Mixed pathology: Both 3R and 4R tau (AD-tau)
- NFT formation: Paired helical filaments of mixed composition
- Braak staging: Spread of pathology through brain
- Tau PET: Imaging of tau aggregates
- Age-related alterations in exon 10 splicing
- Early changes in 3R/4R balance
- Therapeutic target for splicing modulators
- Compounds that reduce exon 10 inclusion (reduce 4R)
- ASF/SF2 modulators
- Antisense oligonucleotides
- Prevent 4R-tau fibril formation
- Small molecule inhibitors
- Antibody-based approaches
- Tau-targeting antibodies
- Vaccines against tau
- Active vs passive immunization
- Goedert M, et al, Tau isoforms in Alzheimer's disease (1991)
- Kidd M, et al, Paired helical filaments in progressive supranuclear palsy (1963)
- Mandelkow EM, et al, Tau domain organization and microtubule binding (1995)
- Weingarten MD, et al, Tau as a microtubule-associated protein (1975)
- Buée L, et al, Tau protein isoforms, phosphorylation and role in neurodegenerative disorders (2000)
- Dickson DW, et al, Neuropathology of 4R-tauopathies (2010)
- Combs B, et al, Tau oligomers in neurodegeneration (2019)
- Vasquez VM, et al, Tau splicing and 4R-tauopathies (2019)
- Leger B, et al, Tau propagation and 4R-tauopathies (2018)
- Krestchev T, et al, Tau post-translational modifications in 4R-tauopathies (2020)