For the first time, researchers have observed tau proteins, one of the presumed causes of Alzheimer's disease, spreading from one neuron to another, just like a progressing infection in the tissues.
"If the idea of a trans-neonal spread is accepted, then the most connected brain areas should have the greatest accumulation of tau and transmit it to their connections. This is how lead author Thomas Cope concludes his study published in the journal Brain. It's the same thing we could see in an influenza epidemic: people with larger networks are more likely to catch the flu and then pass it on to others. That's exactly what we saw.”
In Alzheimer's disease, the cerebral region where the tau protein is located first in the area of the entorhinal cortex, next to the hippocampus. This is why the first symptoms of the disease are memory problems. The study just published in the journal Brain, suggests that tau protein then spreads into the brain by proximity, infecting and destroying nerve cells, while progressively worsening the patient's symptoms.
Stop the spread of tau
Transneuronal propagation is one of the three hypotheses that explain the distribution of tau proteins. The hypothesis of metabolic vulnerability implies that tau proteins are made in the nerve cells and that the ones that produce the most are the ones already infected. The hypothesis of "trophic support" suggests that certain areas of the brain are more sensitive than others and that it is linked to a lack of vascularization, and therefore of nutrition.
However, the researchers' observations did not find evidence for these two hypotheses.
The origin of the disease lies in the progression of 2 types of protein, beta-amyloid and tau protein.
The accumulation of these beta-amyloid proteins creates amyloid plaques outside brain cells, while tau proteins accumulate inside neurons. The latter end up inhibiting or even killing the brain cells in this way. Understanding how tau spreads through the brain is a real issue for future therapies. Such research could help develop drugs that can stop tau proteins before they progress through large areas of the brain.