A protein that accumulates inside neurons and destroys their internal scaffolding in Alzheimer's disease.Tau is a protein found mainly inside neurons, where it normally binds to and stabilizes microtubules — the internal scaffolding that transports materials along the long extensions of nerve cells. In Alzheimer's disease and several other neurodegenerative conditions, tau becomes abnormally modified (hyperphosphorylated) and detaches from microtubules. It then clumps together into tangled filaments inside the neuron, called neurofibrillary tangles. These tangles disrupt the transport system, leading to the gradual destruction of the neuron's internal structure and eventually cell death. The seed definition captures this: tau accumulates inside neurons and destroys their internal scaffolding.
Why does tau matter? Because the loss of tau function and the gain of toxic tau aggregates correlate strongly with cognitive decline in Alzheimer's disease. While amyloid plaques (made of a different protein) are also a hallmark, the spread of tau pathology through the brain follows the pattern of clinical symptoms more closely. Tau tangles are also found in other tauopathies, such as frontotemporal dementia and chronic traumatic encephalopathy. Understanding tau is therefore central to diagnosing and treating these disorders.
Tau explains how a single protein can go from a helpful structural component to a destructive agent. When tau is hyperphosphorylated, it loses its grip on microtubules, which fall apart. The neuron can no longer move nutrients and organelles along its axons, and communication with other neurons fails. The aggregated tau also spreads from cell to cell in a prion-like manner, which may explain why Alzheimer's pathology progresses through connected brain regions.
Tau was discovered in 1975 by Marc Kirschner and colleagues as a microtubule-associated protein. Its role in Alzheimer's disease was established in the 1980s when it was identified as the main component of neurofibrillary tangles.
In a healthy neuron, tau binds to tubulin dimers and promotes microtubule assembly. Microtubules act as tracks for motor proteins (kinesin and dynein) that carry cargo. When tau is phosphorylated by certain enzymes (kinases), it detaches. If phosphorylation is excessive, tau molecules begin to stick to each other, forming paired helical filaments. These filaments accumulate into tangles. The loss of microtubule stability and the physical blockage by tangles impair axonal transport, leading to synaptic dysfunction and neuronal death. The process is gradual and can take years or decades.
Tau is a target for Alzheimer's diagnostics (PET imaging of tau tangles) and for experimental therapies that aim to prevent tau aggregation or spread.
Tau is normally soluble and unfolded, but in disease it forms insoluble filaments that can be stained with silver — the same technique Alois Alzheimer used in 1906 to see the tangles he described.