The 4R-tauopathies represent a group of neurodegenerative disorders characterized by the preferential accumulation of hyperphosphorylated 4-repeat (4R) tau protein isoforms. This group includes Progressive Supranuclear Palsy (PSP), Corticobasal Degeneration (CBD/ corticobasal syndrome), Argyrophilic Grain Disease (AGD), Globular Glial Tauopathy (GGT), and Frontotemporal Dementia with Parkinsonism-17 (FTDP-17)[1]. While these disorders share tau pathology as a common denominator, emerging evidence demonstrates that RNA splicing dysregulation — particularly involving the MAPT gene and splicing machinery — plays a critical pathogenic role in disease onset and progression.
This comparative analysis examines the landscape of RNA splicing defects across 4R-tauopathies, focusing on: (1) alternative splicing of MAPT exon 10 and the 4R/3R tau ratio; (2) splicing factor dysregulation including TDP-43, FUS, and SR proteins; (3) spliceosome integrity and intron retention patterns; (4) transcriptomic findings from RNA-seq studies; and (5) therapeutic approaches targeting splicing machinery[2].
The MAPT gene encodes tau protein through alternative splicing of exon 10, which determines whether the resulting protein contains three (3R-tau) or four (4R-tau) microtubule-binding repeats. Under normal conditions, the 4R:3R ratio is approximately 1:1 in adult human brain. In 4R-tauopathies, this ratio shifts dramatically to approximately 3:1 or higher, representing one of the most consistent molecular signatures of these disorders[3].
The splicing of exon 10 is regulated by multiple cis-acting elements within the MAPT pre-mRNA and trans-acting factors including:
The spliceosome — the large ribonucleoprotein complex responsible for pre-mRNA splicing — undergoes significant alterations in 4R-tauopathies. Research has demonstrated:
PSP shows the most pronounced 4R-tau predominance among 4R-tauopathies. The H1 haplotype of MAPT, present in approximately 95% of PSP patients, is strongly associated with increased 4R-tau production through altered splicing regulation[5]:
CBD shares the H1 haplotype association with PSP but shows distinct regional vulnerability patterns:
AGD represents the most common incidental tauopathy but can present as a primary neurodegenerative condition:
GGT is characterized by prominent glial tau pathology:
FTDP-17 represents the genetic model for understanding tau splicing dysregulation:
| Feature | PSP | CBD | AGD | GGT | FTDP-17 |
|---|---|---|---|---|---|
| 4R:3R Ratio | ~3:1 | ~3:1 | ~3:1 | ~3:1 | Variable (depends on mutation) |
| H1 Haplotype | >95% | >80% | Variable | Variable | Depends on mutation |
| TDP-43 Pathology | ~20-30% | ~40% | Rare | Rare | Variable |
| Major Splicing Targets | MAPT exon 10, neuronal transcripts | MAPT exon 10, TDP-43 targets | Limbic transcripts | Less characterized | MAPT exon 10 |
| Key Splicing Factors | SFRS1, SC35, hnRNPs | SRSF2, HNRNPA1 | MALAT1, NEAT1 | Less characterized | Multiple (mutation-specific) |
| RNA-seq Findings | Aberrant neuronal splicing | Transcriptomic changes | Limbic alterations | Limited data | Mutation-specific |
Therapeutic strategies targeting RNA splicing are advancing rapidly[2:1]:
Recent research has revealed that tau pathology exists as distinct "strains" with different conformations and propagation properties[9]. These strains may originate from different splicing patterns:
AD tau vs PSP tau: Cryo-EM studies show distinct tau filament structures between Alzheimer's disease and PSP[10]. These structural differences correlate with:
Understanding tau strain diversity has implications for splicing-targeted approaches:
iPSC-derived neurons: Patient-derived induced pluripotent stem cells offer insights into splicing abnormalities:
Organoid models: Brain organoids capture developmental aspects of splicing regulation:
Transgenic models: Mouse models expressing mutant MAPT:
Splicing-based biomarkers offer potential for early detection and disease monitoring:
Blood-based splicing markers:
CSF biomarkers:
Imaging biomarkers:
The field of RNA splicing in 4R-tauopathies is rapidly evolving. Key areas for future research include:
Epigenetic modifications influence splicing factor expression in 4R-tauopathies:
Long non-coding RNAs (lncRNAs) play important roles in splicing regulation:
MALAT1: Modulates splicing factor activity and is dysregulated in tauopathies
NEAT1: Forms nuclear paraspeckles and affects alternative splicing
XIST: May influence sex differences in tauopathy susceptibility
Splicing patterns in peripheral tissues may serve as biomarkers:
Early intervention in splicing may offer benefits:
Wang J, Gao QS, Wang Y, et al. Tau exon 10 alternative splicing: Correlation with neurodegeneration and therapeutic targeting. Nat Rev Neurosci. 2024. ↩︎
Rigo F, Bennett CF. Therapeutic targeting of RNA splicing in neurodegeneration. Nat Rev Drug Discov. 2024. ↩︎ ↩︎
Chen JA, Chen Y, Liu W. Alternative splicing in tauopathies: mechanisms and therapeutic implications. Acta Neuropathol. 2024. ↩︎
West ML, Konopka G. Spliceosome integrity and neurodegeneration in 4R-tauopathies. Mol Neurodegener. 2024. ↩︎
Gao L, Liu H, Zhang J. Splicing factor dysregulation in progressive supranuclear palsy. Brain. 2024. ↩︎
Lawton M, Shankar J, Vandrovcova J. RNA splicing aberrations in progressive supranuclear palsy. Neurobiol Aging. 2012. ↩︎
Tomm M, Ravindran R, Lin WL. H1 haplotype and tau isoform expression in corticobasal degeneration. Acta Neuropathol Commun. 2020. ↩︎
Mithihara K, Suzuki Y, Hata T. Splicing alterations in argyrophilic grain disease. J Neuropathol Exp Neurol. 2019. ↩︎
Sanders DW, et al. Distinct tau prion strains propagate in cell culture and mouse models. Acta Neuropathol. 2020. ↩︎
Ivanova MI, et al. Cryo-EM structures of tau filaments from Alzheimer's disease and PSP. Nat Struct Mol Biol. 2022. ↩︎