Researchers see Alzheimer's as a two-protein disease: amyloid plaque - target of attempts to produce an Alzheimer's vaccine - on the one hand and neurofibrillary tangles on the other, both somehow related to or responsible for neurodegeneration. One particularly interesting thread of Alzheimer's research involves exploring the theory that these neurofibrillary tangles are not in fact a root cause of mental degeneration associated with the disease. You can find a high level overview of the basics over at Nature:
The brains of people with Alzheimer's and some 50 other forms of dementia are known to have certain characteristic features, including messy bundles of fibres in nerve cells called neurofibrillary tangles. But no one has been sure whether the tangles are a cause or symptom of dementia.
Mice engineered to massively overproduce a protein called tau tend to grow more of the tangles and display the same problems with memory and learning as humans with dementia. Researchers think that it is a certain version of the tau protein, rather than a simple over-abundance, that leads to the tangles.
It has been speculated that these tau proteins, rather than the tangles, kill nerve cells.
They trained mice to navigate a maze partly submerged in water, and watched for signs of memory loss. By the age of three months, mice genetically engineered to express 13 times too much tau protein couldn't remember the route to dry land, and had developed tangles in their brains.
But surprisingly, when the researchers turned off the switch promoting tau expression, the mice began to gain back some lost memory.
Most promising. Progress towards understanding and defeating the most common neurodegenerative diseases is a vital part of healthy life extension science. After all, the worst case scenario for the future of your heart and other organs is that they will have to be replaced wholesale with new, healthy tissue grown from your own cells. This isn't an option for the brain - so we had better develop very effective means of in situ repair.