The scientists measured the mice's memory loss with the help of a swimming test: the healthy mice quickly learn how to find a life-saving platform located under the surface of the water in a water basin. In contrast, the transgenic animals, which have the additional pro-aggregant tau gene paddle aimlessly around the basin until they accidentally stumble on the platform; they require over four times more time to do this than their healthy counterparts. However, if the mutated toxic tau gene is switched off again, the mice learn to reach "dry land" with ease just a few weeks later. As a control, the mice with the anti-aggregant form of tau have no defects in learning, just as normal non-transgenic mice.
Surprising tissue results
Tissue tests showed that, as expected, no tau clumps had formed in the brains of the first group of mice expressing anti-aggregant tau. In the second group the mice suffering from Alzheimer's co-aggregates from human tau and "mouse tau" were formed - against expectations, because tau protein from mice does not usually aggregate. "Even more astonishingly, weeks after the additional gene had been switched off, the aggregated human tau had dissolved again. However, the 'mouse tau' remained clumped. Despite this, the mice were able to learn and remember again," says Eckhard Mandelkow. More precise tests revealed that new synapses had actually formed in their brains.
The scientists concluded from this that mutated or pathological tau can alter healthy tau. It appears that pro-aggregant tau can act similar to a crystal nucleus once it has started to clump up, it drags neighboring "healthy" tau into the clumps as well. This is what makes the process so toxic to the neurons. "The really important discovery here, however, is that the progression of Alzheimer's disease can be
|Contact: Eva-Maria Mandelkow|