Tauopathy

Tauopathy belongs to a class of neurodegenerative diseases involving the aggregation of tau protein into neurofibrillary or gliofibrillary tangles (Neurofibrillary tangle) in the human brain. Tangles are formed by hyperphosphorylation of the microtubule protein known as tau, causing the protein to dissociate from microtubules and form insoluble aggregates.[1] (These aggregations are also called paired helical filaments.) The mechanism of tangle formation is not well understood, and whether tangles are a primary cause of Alzheimer's disease or play a peripheral role is unknown.

Tauopathy
Diagram of a normal microtubule and one affected by tauopathy
SpecialtyNeurology 

Detection and imaging

Post-mortem
Tau tangles are seen microscopically in stained brain samples.
Pre-mortem
In living patients tau tangle locations can be imaged with a PET scan using a suitable radio-emissive agent.[2]

Alzheimer's disease

Abnormal accumulation of tau protein in neuronal cell bodies (arrow) and neuronal extensions (arrowhead) in the neocortex of a patient who died with Alzheimer's disease. The bar = 25 microns (0.025 millimeters).

Neurofibrillary tangles were first described by Alois Alzheimer in one of his patients with Alzheimer's disease (AD). The tangles are considered a secondary tauopathy. AD is also classified as an amyloidosis because of the presence of senile plaques.[3]

When tau becomes hyperphosphorylated, the protein dissociates from the microtubules in axons.[4] Then, tau becomes misfolded and the protein begins to aggregate, which eventually forms the neurofibrillary tangles seen in Alzheimer's patients.[1] Microtubules also destabilize when tau is dissociated. The combination of the neurofibrillary tangles and destabilized microtubules result in disruption of processes such as axonal transport and neural communication.[5]

The degree of NFT involvement in AD is defined by Braak stages. Braak stages I and II are used when NFT involvement is confined mainly to the transentorhinal region of the brain, stages III and IV when there's also involvement of limbic regions such as the hippocampus, and V and VI when there's extensive neocortical involvement. This should not be confused with the degree of senile plaque involvement, which progresses differently.[6]

Other diseases

In both Pick's disease and corticobasal degeneration, tau proteins are deposited as inclusion bodies within swollen or "ballooned" neurons.

Argyrophilic grain disease (AGD), another type of dementia,[19][20][21] is marked by an abundance of argyrophilic grains and coiled bodies upon microscopic examination of brain tissue.[22] Some consider it to be a type of Alzheimer's disease.[22] It may co-exist with other tauopathies such as progressive supranuclear palsy and corticobasal degeneration,[3] and also Pick's disease.[23]

Tauopathies are often overlapped with synucleinopathies, possibly due to interaction between the synuclein and tau proteins.[24]

The non-Alzheimer's tauopathies are sometimes grouped together as "Pick's complex" due to their association with frontotemporal dementia, or frontotemporal lobar degeneration.[25]

See also

References

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  2. Alzheimer 'tau' protein far surpasses amyloid in predicting toll on brain tissue
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  15. Brat DJ, Gearing M, Goldthwaite PT, Wainer BH, Burger PC (June 2001). "Tau-associated neuropathology in ganglion cell tumours increases with patient age but appears unrelated to ApoE genotype". Neuropathology and Applied Neurobiology. 27 (3): 197–205. doi:10.1046/j.1365-2990.2001.00311.x. PMID 11489139. S2CID 36482221.
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  19. Ferrer I, Santpere G, van Leeuwen FW (June 2008). "Argyrophilic grain disease". Brain. 131 (Pt 6): 1416–32. doi:10.1093/brain/awm305. PMID 18234698.
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  24. Moussaud S, Jones DR, Moussaud-Lamodière EL, Delenclos M, Ross OA, McLean PJ (October 2014). "Alpha-synuclein and tau: teammates in neurodegeneration?". Molecular Neurodegeneration. 9: 43. doi:10.1186/1750-1326-9-43. PMC 4230508. PMID 25352339.
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