A protein best known for helping neurons communicate may also help Alzheimer’s disease pathology move through the brain, according to new research from University of Utah Health.
The study, published in Cell, identifies the neuronal protein Arc as a key factor that helps toxic tau move from diseased neurons into neighboring healthy cells. In mouse models, removing Arc sharply reduced the transfer of tau between brain cells, pointing to a potential new strategy for slowing disease progression rather than reversing damage that has already occurred.
“I’m excited by the fact that we’ve identified a new way of potentially stopping the progression of Alzheimer’s disease,” said Jason Shepherd, PhD, professor of neurobiology at University of Utah Health and senior author of the study.
A new route for tau spread
Alzheimer’s disease is marked by the accumulation of abnormal protein deposits, including amyloid plaques and tau tangles. While amyloid has historically dominated drug development, tau pathology is closely linked to neurodegeneration and cognitive decline. As tau spreads across connected brain regions, symptoms worsen, making the mechanisms of tau transmission a major focus for therapeutic research.
The new study centers on Arc, a protein involved in synaptic plasticity, memory formation, and communication between neurons. Arc can package itself into extracellular vesicles, small membrane-bound particles that move between cells and carry biological cargo.
The researchers found that tau can use this system to its advantage. In Alzheimer’s mouse models, Arc helped package tau into extracellular vesicles, allowing tau to move from one neuron to another. Once taken up by recipient neurons, tau seeds can corrupt normal tau and trigger new aggregation.
By comparing Alzheimer’s model mice with and without Arc, the team showed that Arc was required for efficient tau release in neuronal extracellular vesicles and for tau transmission between cells.
The ‘glue monster’ problem
Tau is normally present in neurons and helps support microtubules, structures that act like internal transport tracks. In Alzheimer’s disease and related tauopathies, tau becomes abnormally modified, misfolds, and forms aggregates that interfere with neuronal function.
Mitali Tyagi, PhD, first author of the study and now a postdoctoral research associate at Washington University in St. Louis, compared tau tangles to “glue monsters.”
“They glue together and block transportation within the neuron,” Tyagi said. “But they can break down into smaller glue monsters, called tau seeds, which can then get transferred to a new neuron. And once this tau seed comes into contact with healthy tau, it is able to corrupt it. So, the pathology starts all over again in a healthy neuron.”
The researchers found extracellular vesicles containing both Arc and tau in the brains of Alzheimer’s model mice. These vesicles could seed tau aggregation in cell-based assays. But when Arc was absent, the vesicles contained far less tau and had greatly reduced seeding activity.
“When we removed Arc, we saw that the transfer of tau was severely, severely reduced,” Tyagi said. “It was almost gone.”
A double role for Arc
The findings are not as simple as suggesting Arc should be eliminated entirely. Arc appears to play a double-edged role in Alzheimer’s biology.
On one hand, Arc helps neurons export tau, which may reduce toxic buildup inside the original diseased cell. On the other hand, that same export process allows tau to reach and damage neighboring neurons.
“When Arc is absent, tau becomes trapped inside neurons and accumulates to toxic levels. When Arc is present, tau can be released in extracellular vesicles. While this helps reduce tau buildup within the original neuron, the released tau can be taken up by neighboring healthy neurons, promoting the spread of pathology,” Tyagi said.
In mice lacking Arc, tau accumulated inside neurons and was associated with early signs of cell toxicity. Yet tau transfer between cells was markedly reduced. This suggests that simply blocking tau release may not be the best therapeutic approach, because it could worsen toxicity in neurons already burdened by tau.
Instead, the researchers suggest that a more precise strategy may be to intercept tau-containing vesicles after they leave sick neurons but before they enter healthy ones.
Human brain data support the mechanism
Although much of the work was done in mice and cell models, the team also examined human postmortem brain tissue. They found that human brain-derived extracellular vesicles contained both Arc and phosphorylated tau, a disease-associated form of the protein.
The study also reported a positive correlation between Arc levels and phosphorylated tau levels in extracellular vesicles isolated from human brain tissue, supporting the idea that Arc-mediated vesicle biology may be relevant to human disease.
However, the authors caution that the work is still early. The strongest causal evidence comes from mouse models, and more research is needed to determine whether the same mechanism drives tau spread in people with Alzheimer’s disease.
“Most of the work we’ve been doing is in mice, not in humans,” Shepherd said. “We have some clues that whatever is happening in these mice could also be happening in humans, but we don’t know that yet. And we’re far away from saying that we’re developing a treatment for anything. But it could open new avenues to get to that point.”
Toward therapies that slow progression
The findings arrive as Alzheimer’s treatment is beginning to shift from symptom management toward disease modification. Anti-amyloid therapies have shown that changing disease biology is possible, but there remains a major need for treatments that slow tau-driven neurodegeneration and preserve cognition for longer.
Targeting tau spread could be one way to do that. A therapy aimed at tau-containing extracellular vesicles would not be expected to restore neurons already lost to disease. But it could potentially slow the movement of pathology through the brain, especially in early disease stages.
“If we could target these particular EVs, that would be a really useful therapy strategy,” Shepherd said. “For someone with early-onset Alzheimer’s or dementia, if we could stop the spread, then we could prevent further damage and cognitive decline.”
The study positions Arc not only as a messenger of normal brain communication, but also as a possible vehicle for pathological tau spread. The next challenge will be determining whether that vehicle can be safely intercepted without disrupting Arc’s essential roles in memory and synaptic function.
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