Scientists at the Gladstone Institutes have traced a molecular chain of events that may explain why APOE4, the strongest known genetic risk factor for Alzheimer's disease, appears to alter the brain long before anyone notices a memory lapse. Writing in Nature Aging, the team reported that in mouse models, APOE4 drives up production of a protein called Nell2. Neurons exposed to those higher levels became smaller than normal and fired more than they should.
The timing detail is the striking part. Mice with the most pronounced brain hyperactivity early in life went on to develop the worst memory problems as they aged, suggesting the overactive firing is not merely a byproduct of damage but an early signal that something has already gone wrong.
When the researchers dialed Nell2 production back down, neurons in adult APOE4 mice moved back toward their usual size and firing patterns. That the correction worked in adult animals, rather than only in young ones, matters: it hints that this particular consequence of carrying APOE4 may not be locked in from birth, and that a treatment window could still exist well into life.
Millions of people carry APOE4, and none of them can change that fact, which is why a downstream target like Nell2 is of interest - it is a step in the chain that a drug might plausibly interrupt. This work was done in mice, and translating a molecular finding from mouse neurons to human brains is a long road, but it gives researchers a concrete protein to pursue rather than a risk gene they can only measure.