Over the last 25 years, scientists have learned a lot about Alzheimer's disease and yet the cure remains elusive. Alzheimer's disease is characterized by the presence of tau protein (tauopathy) in the memory-forming regions of the brain and as the disease progresses, tauopathy spreads through different regions.
One of the challenges towards understanding how the disease progresses is trying to understand the mechanism of how the tau proteins 'move' from one neuron to another. Scientists are trying to tease out the mechanism of disease spread and envision that this information will allow them to design drugs to contain the spread of the disease.
There are two prevailing hypotheses on how the tau proteins spread from one neuron to the next. One is that some regions of the brain are more resistant to tau proteins than others and therefore resist the disease longer. The other theory is that tau proteins spread from neuron to neuron through the synapses and spread the disease.
Two recent studies identify the second mechanism, i.e. trans-synaptic spreading of the disease along neural networks as the method of propagation of the disease. The first study appeared in PLoS One, and the second study is to appear in the journal Neuron. Both of these studies independently developed a mouse model, wherein the mouse would express the abnormal human tau only in a local region. This turned out to be a very powerful animal model, because the researchers could now track how the disease progressed in the brain and correlate the appearance of tau protein with the disease progression. Both these studies confirmed that the disease progresses using a trans-synaptic mechanism.
The insights provided by these results have excited the Alzheimer's research groups and the larger community. It is not hard to imagine that these mouse models can be used to test different therapies to halt the progression of the disease, and that indeed is the next step for these researchers.