Fascinating study - thanks for pointing it out!

Possibly related: a study indicating how microglia might be the agent that spreads the seeds intercellularly: https://pubmed.ncbi.nlm.nih.gov/30227881/

For anyone not keeping up on this: tau tangles seem to arise when protein folding errors produce a 'seed' version of tau that can then work as a catalyst to cause the other tau proteins in the cell to also misfold. This, in turn, can cause collapse of microtubules, structures within a cell that other parts of the cell use to move nutrients around (look for "motor protein" on youtube for videos of this very cool process). If you just consider the shape of a neuron, it's clear how important moving molecules from one end to the other might be.

It's still not clear what causes a 'seed' to form - or the mechanism of how it goes from one cell to the next. The study linked in the article is an attempt to come up with a formula to describe the rate of spread (TL;DR: the doubling rate's a bit under five years).

Finally, I can't help but think about how this parallels the progression of bovine spongiform encephalopathy (AKA "mad cow disease") where a foreign protein called a 'prion' works as a catalyst to do apparently similar damage.