Dementia-Linked Tau Protein Is Made in Dendrites, Not Axons, Study Finds

A study has found that tau, a protein known to be involved in Alzheimer’s disease, is made in dendrites rather than axons, contrary to conventional thinking. The disease’s central problem may be a failure of quality control during protein production, not the “mislocalization of the protein.”

Researchers at Columbia University published the findings in the journal Nature Neuroscience on the 9th (local time).

Alzheimer’s disease is a leading neurodegenerative disease, affecting more than 50 million people worldwide. A defining pathological feature is the abnormal aggregation of tau inside nerve cells, forming neurofibrillary tangles.

Researchers had generally believed that tau resides mainly in axons, where it stabilizes microtubules, and that, as disease develops, it becomes hyperphosphorylated and mislocalizes to the cell body and dendrites, where it aggregates. Accordingly, drug development has focused on blocking the movement and spread of mature tau protein.

The team developed a new imaging technology called STARFISH, with single-molecule detection sensitivity and codon-level spatial resolution. The technology can directly visualize where endogenous mRNA is actually translated inside nerve cells, without chemical labeling.

The researchers found that Mapt mRNA, which encodes tau, was distributed throughout the cell body, dendrites and axons, but protein synthesis occurred only in MAP2-positive dendrites. Tau in axons had moved there after being synthesized in dendrites.

What earlier imaging methods had detected as new tau signals in the cell body turned out to be an artifact caused by the diffusion of labeled peptides.

Another finding concerned the quality-control system. About one-third of newly synthesized tau was removed within tens of seconds of translation by neuronal proteasomes attached to the cell membrane. This system filters out newly made peptide chains at the site of production before they can misfold.

When neuronal proteasome function was impaired, tau that escaped removal accumulated in the cell body and dendrites, became phosphorylated and formed aggregates with beta-sheet structures. Blocking protein translation at the same time completely suppressed pathological aggregation. This suggests that tau accumulation depends on the continued synthesis of new protein rather than the movement of existing protein.

The team explained that newly made tau peptides expose microtubule-binding repeat sequences that promote aggregation before folding is complete, leaving them structurally vulnerable. Neuronal proteasomes remove these high-risk intermediates; when this defense fails, a chain reaction of aggregation begins in dendrites.

The findings also point to the possibility of intervening earlier in treatment. The researchers said an approach could be to act within minutes of tau synthesis to protect or enhance the neuronal proteasome’s ability to remove it, or to prevent newly made peptides from misfolding.

However, because the findings came from experiments in primary neuronal cultures and transgenic mice, further research is needed to validate them in human brain tissue and assess their clinical application.

The team said the findings suggest that tau pathology in Alzheimer’s disease may not involve “the right protein ending up in the wrong place,” but rather a failure to remove “new tau protein born defective” in dendrites in time.