Alzheimer's disease seems to spread like an infection from brain cell to brain cell, two new studies in mice have found. But instead of viruses or bacteria, what is being spread is a distorted protein known as tau.
The surprising finding answers a longstanding question and has immediate implications for developing treatments, researchers said. And they suspect that other degenerative brain diseases like Parkinson's may spread in a similar way.
Alzheimer’s researchers have long known that dying, tau-filled cells first emerge in a small area of the brain where memories are made and stored. The disease then slowly moves outward to larger areas that involve remembering and reasoning.
But for more than a quarter-century, researchers have been unable to decide between two explanations. One is that the spread may mean that the disease is transmitted from neuron to neuron, perhaps along the paths that nerve cells use to communicate with one another. Or it could simply mean that some brain areas are more resilient than others and resist the disease longer.
The new studies provide an answer. And they indicate it may be possible to bring Alzheimer’s disease to an abrupt halt early on by preventing cell-to-cell transmission, perhaps with an antibody that blocks tau.
The studies, done independently by researchers at Columbia and Harvard, involved genetically engineered mice that could make abnormal human tau proteins, predominantly in the entorhinal (pronounced en-toh-RYE-nal) cortex, a sliver of tissue behind the ears, toward the middle of the brain, where cells first start dying in Alzheimer’s disease. As expected, tau showed up there. And, as also expected, entorhinal cortex cells in the mice started dying, filled with tangled, spaghettilike strands of tau.