Tau protein stabilizes structures that transport supplies from the center of the cell to the extremities, but sometimes some tau is not bound to these microtubules and instead clumps together into neurofibrillary tangles — one of the hallmarks of Alzheimer's disease, and also linked to other neurodegenerative disorders. A new study supports the theory that ‘bad’ tau travels to different brain regions via the synapses — that is, it’s secreted with the signals passing between neurons.
(2014). Neuronal activity regulates extracellular tau in vivo.
The Journal of Experimental Medicine. 211(3), 387 - 393.