The 4R-tauopathies represent a group of neurodegenerative disorders characterized by the accumulation of hyperphosphorylated 4-repeat (4R) tau protein, including Progressive Supranuclear Palsy (PSP), Corticobasal Degeneration (CBD), Argyrophilic Grain Disease (AGD), Globular Glial Tauopathy (GGT), and Frontotemporal Dementia with Parkinsonism-17 (FTDP-17). While tau pathology is the hallmark of these disorders, emerging evidence demonstrates that RNA metabolism dysregulation plays a critical pathogenic role, with RNA-binding proteins (RBPs) such as TDP-43, FUS, and heterogeneous nuclear ribonucleoproteins (hnRNPs) contributing to disease progression[1][2].
This pathway model maps the complete landscape of RNA metabolism dysfunction in 4R-tauopathies, examining splicing alterations, RNA granule formation, translational dysregulation, and shared mechanisms with TDP-43 proteinopathies in Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Dementia (FTD).
TDP-43 is a nuclear DNA/RNA-binding protein encoded by the TARDBP gene, involved in multiple RNA processing functions including transcription regulation, alternative splicing, RNA transport, and stability[1:1]. In healthy neurons, TDP-43 predominantly localizes to the nucleus, but in disease states it mislocalizes to the cytoplasm where it forms inclusion bodies.
| Disease | TDP-43 Inclusions | Frequency | Reference |
|---|---|---|---|
| PSP | Neuronal and glial cytoplasmic inclusions | 10-30% | [@baker2021tdp] |
| CBD | Motor cortex and basal ganglia | 20-40% | [@koga2017tdp] |
| AGD | Limbic system, amygdala | 15-25% | [@yokota2020tdp] |
| GGT | White matter, oligodendrocytes | 5-15% | [@ahmed2013ggt] |
| FTDP-17 | Frontal cortex, brainstem | Variable | [@zheng2022tdp] |
Pathogenic mechanisms:
FUS is another DNA/RNA-binding protein involved in transcription, RNA splicing, transport, and translation[2:1]. Pathogenic FUS mutations cause familial ALS and FTD, but FUS pathology is also observed in 4R-tauopathies.
Key differences from ALS/FTD FUS:
The hnRNP family includes over 20 proteins (hnRNPA1, hnRNPA2B1, hnRNPK, hnRNPL, hnRNPU, etc.) that regulate RNA splicing, stability, transport, and translation[4].
| hnRNP | Function | Dysregulation in 4R-Tauopathies |
|---|---|---|
| hnRNPA1 | Splicing regulation, stress granule formation | Aggregate formation in PSP and CBD |
| hnRNPA2B1 | RNA splicing, transport | Mutations cause multisystem proteinopathy |
| HNRNPK | Transcription, RNA processing | Altered expression in CBD |
| hnRNPL | Alternative splicing | Dysregulated in PSP |
The MAPT gene produces six tau isoforms through alternative splicing of exons 2, 3, and 10. Exclusion of exon 10 produces 3R tau, while inclusion produces 4R tau. In 4R-tauopathies, there is a selective increase in 4R tau isoforms[5].
Splicing regulators affected:
TDP-43 depletion leads to the inclusion of cryptic exons in multiple transcripts [6]:
| Disease | Key Splicing Alterations | Reference |
|---|---|---|
| PSP | Aberrant splicing of neuronal transcripts, MAPT splice variants | [@lawton2012psp] |
| CBD | Splicing changes in cytoskeletal, synaptic genes | [@koga2018cbd] |
| AGD | Limbic system splicing alterations | [@mithihara2019agd] |
Stress granules (SGs) are cytoplasmic RNA-protein aggregates formed under stress conditions (oxidative stress, heat shock, viral infection) to stall translation and protect mRNAs [7]. They contain:
| Feature | PSP | CBD | AGD | GGT |
|---|---|---|---|---|
| TIA1-positive SGs | ++ | ++ | + | + |
| G3BP1-positive SGs | ++ | ++ | + | + |
| Co-localization with tau | Yes | Yes | Rare | Yes |
Pathogenic cascade:
P-bodies are cytoplasmic foci involved in mRNA decay and storage. Unlike stress granules, they are present constitutively and increase under specific conditions [8].
In 4R-tauopathies, P-body dysfunction contributes to:
4R-tauopathies exhibit widespread translational dysregulation:
| Target | Function | Dysregulation | Consequence |
|---|---|---|---|
| Synaptic proteins | Neurotransmission | Reduced synthesis | Synaptic dysfunction |
| Mitochondrial proteins | Energy metabolism | Impaired translation | Energy failure |
| Cytoskeletal proteins | Structure | Altered expression | Axonal transport defects |
The concept of "ribostasis" refers to the proper balance of ribosome biogenesis, translation, and mRNA decay [9]. In 4R-tauopathies:
| Mechanism | 4R-Tauopathies | ALS/FTD | Shared? |
|---|---|---|---|
| TDP-43 aggregation | + | +++ | Yes |
| Stress granule formation | ++ | +++ | Yes |
| Nuclear import defects | + | +++ | Yes |
| Cryptic exon splicing | + | +++ | Yes |
| FUS pathology | + | +++ | Partial |
| hnRNP dysfunction | ++ | +++ | Yes |
Antisense oligonucleotides (ASOs)
Small molecules
Gene therapy
| Target | Approach | Stage | Reference |
|---|---|---|---|
| TDP-43 nuclear import | Small molecule enhancers | Preclinical | [@neefjes2021] |
| Stress granule clearance | Autophagy modulators | Preclinical | [@wedge2021] |
| Splicing correction | ASO-mediated | Clinical (ALS) | [@corti2022] |
Baker M, Mackenzie IR. 'TDP-43 in tauopathies: Pathological interactions and therapeutic targets'. Acta Neuropathol. 2021. ↩︎ ↩︎
Dormann D, Haass C. 'FUS proteinopathy: Linking RNA metabolism and neurodegeneration'. Acta Neuropathol. 2021. ↩︎ ↩︎
Ahmed Z, Bigio EH, Budka H, et al. 'Globular glial tauopathies (GGT): Consensus recommendations'. Acta Neuropathol. 2013. ↩︎
Jean-Marc B. 'The expanding world of ribonucleoproteins: The role of heterogeneous nuclear ribonucleoproteins in neuronal function and disease'. J Neurochem. 2022. ↩︎
Wang J, Gao QS, Wang Y, et al. 'Tau exon 10 alternative splicing: Correlation with neurodegeneration and therapeutic targeting'. Nat Rev Neurosci. 2024. ↩︎
Ling JP, Pletnikova O, Troncoso JC, et al. TDP-43 repression of cryptic exons in Alzheimer's disease and Parkinson's disease. Science. 2025. ↩︎
Wolozin B, Ivanov P. Stress granules and neurodegeneration. Nat Rev Neurosci. 2022. ↩︎
Standart N, Weil D. 'P-bodies: Cytoplasmic foci of post-transcriptional gene regulation'. J Mol Biol. 2024. ↩︎
Hetauer C, Kramer A. 'Ribostasis: The regulation of ribosome biogenesis and translation fidelity in neuronal homeostasis'. Neuron. 2023. ↩︎