http://www.alzheimersreadingroom.com/2014/11/tau-not-amyloid-beta-causes-neuronal.html

 http://www.foxnews.com/health/2014/10/31/tau-protein-not-plaque-may-cause-alzheimers-study-says/

 New research has found that plaques are not the main cause of Alzheimer’s disease, but rather the protein tau, also known as “tangles.”

“For a very long time, we believed, for almost 100 years, that [amyloid-beta] plaques are the main culprit in Alzheimer’s disease,” the study's senior investigator, Charbel E-H Moussa, MB, assistant professor of neuroscience at Georgetown University Medical Center, told FoxNews.com. “This study shows it’s another protein -- a very, very important one, called tau, is basically the main guilty one.”

Researchers found that tau modulates how much amyloid protein stays inside a cell, and how much is secreted outside the cell to form plaque. This build-up is what leads to neuron death. The plaque that forms outside a cell are not toxic, as previously believed, they found.

If tau is functioning normally, the amyloid-beta (Abeta) protein in a cell is “digested,” and what is not degraded is expelled outside the cell and accumulated as plaque. This pool of amyloid builds up in the cell, causing it to die.

Moussa likened tau to a train track— if it’s functioning normally, the train can run. If it’s disrupted, the train can’t move debris from one end of the cell to the other. There needs to be a ratio of “good” to “bad” tau -- the “good” holds the tracks together, but the “bad” makes it fall apart.

“…We know that the ratio of amyloid inside the cell to the outside is very small,” Moussa said. “So what gets out is basically an attempt by the cell to expel toxic amyloid.”  more through link