The Big Picture
Alzheimer’s disease is driven by the buildup of a toxic protein called Tau, which kills brain cells as it spreads. For years, researchers have known that as toxic Tau moves into new regions of the brain, symptoms grow worse — but exactly how Tau travels from one neuron to the next has remained a mystery. Now, researchers at the University of Utah have identified a surprising accomplice in that spread: a protein called Arc.
What’s Happening
In a new study published in the journal Cell, a team led by Jason Shepherd, PhD, professor of neurobiology at University of Utah Health, and first author Mitali Tyagi, PhD, found that Arc — a protein normally used by neurons to send helpful messages to one another — can be hijacked by toxic Tau to hitch a ride between cells.
Arc typically wraps itself in a tiny bubble called an extracellular vesicle (EV), which floats from one neuron to a neighboring one carrying important information. But the researchers discovered that in a mouse model of Alzheimer’s disease, sticky Tau “seeds” — fragments of the larger toxic Tau tangles that clump inside neurons — attach themselves to Arc and use these EVs to spread to healthy cells. Once inside a new neuron, a Tau seed can corrupt the healthy Tau already there, starting the disease process all over again.
When the researchers studied Alzheimer’s model mice that lacked Arc altogether, the results were striking: EVs in their brains contained almost no Tau, and the spread of disease to new cells was “almost gone.”
Why It Matters
The findings reveal Arc as a kind of double-edged sword. Ridding a sick cell of toxic Tau through Arc-carried EVs helps that cell survive longer — mice lacking Arc actually saw their sick cells die faster, because trapped Tau built up to toxic levels inside the neuron. But once that toxic Tau is released, it can infect neighboring healthy neurons and spread the disease further.
That means simply blocking Arc may not be the answer — but it does point toward a more targeted therapeutic strategy: stopping neighboring cells from absorbing toxic Tau, rather than preventing sick cells from releasing it in the first place. Notably, the team also found the same Arc-and-Tau-containing EVs in human brain tissue, suggesting this hitchhiking mechanism likely plays out in people as well as mice.
The Bottom Line
This discovery gives researchers a new way to think about how Alzheimer’s disease progresses from cell to cell — and a promising new angle for future treatments. The team is particularly interested in designing therapies that intercept Tau-carrying EVs “mid-flight,” after they leave a sick cell but before they reach a healthy one. Such a treatment wouldn’t undo existing brain damage, but it could stop the disease from progressing further.
The researchers caution that this work has so far been done in mice, and more research is needed before any therapy reaches patients. Still, as Shepherd puts it, the discovery “could open new avenues” toward treatments that finally slow — or stop — the spread of Alzheimer’s disease.