Researchers Identify Key Protein Driving the Spread of Alzheimer’s Throughout the Brain

Alzheimer’s disease is characterized by the accumulation of Tau, a toxic protein that disrupts and eventually destroys brain cells. As this protein migrates into new regions of the brain, the disease progresses, resulting in escalating cognitive decline and memory loss.

Now, a team of researchers has identified an unexpected catalyst in this progression. In a study using mouse models, scientists discovered that a protein called Arc—which typically facilitates communication between neurons—also appears to enable the transmission of toxic Tau from diseased cells to healthy ones.

This discovery suggests a novel approach to slowing the progression of Alzheimer’s. Rather than attempting to eliminate Tau entirely, future interventions could focus on preventing the protein from infiltrating healthy brain cells.

“I’m excited by the fact that we’ve identified a new way of potentially stopping the progression of Alzheimer’s disease,” explained Jason Shepherd, PhD, professor of neurobiology at University of Utah Health and the study’s senior author.

The full findings were published in the journal Cell.

The Role of Arc in Tau Transmission

To understand how the disease spreads, researchers compared Alzheimer’s mouse models with and without the Arc protein. Their experiments revealed that Arc is essential for the movement of toxic Tau between neurons.

Under normal physiological conditions, Arc is vital for brain function. The protein organizes itself into small, membrane-bound sacs called extracellular vesicles (EVs), which transport critical cellular signals from one neuron to another.

The study found that toxic Tau hijacks this natural communication system. By attaching to Arc within these microscopic vesicles, Tau is transported from an infected neuron into a healthy one, facilitating the spread of the disease.

How Tau Corrupts Healthy Cells

While every neuron contains Tau, in Alzheimer’s patients, the protein clumps into sticky “tangles” that obstruct the cell’s internal transport system, eventually killing the neuron. Mitali Tyagi, PhD, a postdoctoral research associate at Washington University in St. Louis and the study’s lead author, describes these tangles as “glue monsters.”

“They glue together and block transportation within the neuron,” Tyagi explained. “But they can break down into smaller glue monsters, called Tau seeds, which can then get transferred to a new neuron. Once this Tau seed contacts healthy Tau, it corrupts it, and the pathology begins anew in a healthy neuron.”

In the mouse models, the team identified extracellular vesicles containing both Arc and “sticky” Tau in brain tissue. These vesicles were capable of invading healthy cells and triggering the formation of new Tau tangles.

The results shifted dramatically when Arc was removed; mice lacking the protein showed significantly fewer Tau-containing vesicles, and the disease failed to spread effectively to neighboring cells. “When we removed Arc, we saw that the transfer of Tau was severely, severely reduced,” Tyagi noted. “It was almost gone.”

The Dual Nature of the Arc Protein

Despite its role in spreading the disease, the researchers discovered that Arc also provides a protective benefit during the early stages of Alzheimer’s. By helping neurons expel excess toxic Tau, Arc allows damaged cells to survive longer. In mice lacking Arc, toxic Tau remained trapped, causing already compromised cells to perish more quickly.

“When Arc is absent, Tau becomes trapped inside neurons and accumulates to toxic levels,” Tyagi said. “When Arc is present, Tau can be released in extracellular vesicles. While this reduces Tau buildup within the original neuron, the released Tau can be taken up by neighboring healthy neurons, promoting the spread of pathology.”

These findings suggest that the most effective treatment may not be blocking the release of Tau from diseased cells, but rather preventing those toxic vesicles from entering healthy neurons.

A New Target for Therapeutic Intervention

The research team also detected extracellular vesicles containing both Arc and Tau in human brain tissue, suggesting the same mechanism may operate in humans. However, the authors emphasize that extensive research is still required before these findings can be translated into clinical therapies.

“Most of the work we’ve been doing is in mice, not in humans,” Shepherd noted. “We have some clues that whatever is happening in these mice could also be happening in humans, but we don’t know that yet. We are far from developing a treatment, but it opens new avenues to get to that point.”

One promising strategy involves intercepting Tau-containing vesicles after they leave a diseased neuron but before they reach a healthy one. While this would not reverse existing damage, it could potentially halt further spread.

“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.”

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