Scientists at UCLA Health and UC San Francisco have discovered why certain brain cells are better equipped than others to withstand the buildup of tau, a toxic protein closely linked to Alzheimer’s disease and related dementias. The findings point to biological differences that may help explain why some neurons survive longer, and they could open the door to new treatment strategies.
The research, published in the journal Cell, relied on an advanced CRISPR-based genetic screening technique in lab-grown human neurons. The goal was to map the internal systems that control how tau accumulates inside brain cells. When tau forms clumps, it damages and eventually kills neurons, contributing to conditions such as frontotemporal dementia and Alzheimer’s disease. Tau is the most common protein known to aggregate in neurodegenerative disorders, yet scientists have long puzzled over why some neurons are more vulnerable than others.
CRISPR Screening Reveals a Tau Cleanup System
Using human neurons grown in the lab along with a gene-silencing tool called CRISPRi, the team systematically tested which genes influence tau buildup. Their large-scale screen highlighted a protein complex known as CRL5SOCS4. This complex labels tau with molecular tags that direct it toward the cell’s waste disposal system for breakdown and removal.
The results suggest that boosting this natural cleanup pathway could form the basis of new therapies for neurodegenerative diseases, which affect millions of Americans and still lack effective treatments.
“We wanted to understand why some neurons are vulnerable to tau accumulation while others are more resilient,” said study first author Dr. Avi Samelson, assistant professor of Neurology at UCLA Health, who conducted the research while at UCSF. “By systematically screening nearly every gene in the human genome, we found both expected pathways and completely unexpected ones that control tau levels in neurons.”
In experiments using neurons derived from human stem cells, the researchers switched off individual genes to see how each one influenced toxic tau clumping. Out of more than 1,000 genes flagged in the screen, CRL5SOCS4 stood out. It works by attaching chemical markers to tau, signaling the cell’s recycling machinery to destroy it.
When the team examined brain tissue from people with Alzheimer’s disease, they found that neurons with higher levels of CRL5SOCS4 components were more likely to survive despite tau accumulation.
Mitochondrial Stress and a Harmful Tau Fragment
The study also uncovered an unexpected link between mitochondrial problems and tau toxicity. Mitochondria act as the cell’s energy generators. When the researchers disrupted these energy-producing structures, cells began producing a specific tau fragment measuring about 25 kilodaltons. This fragment closely matches a biomarker detected in the blood and spinal fluid of Alzheimer’s patients, known as NTA-tau.
“This tau fragment appears to be generated when cells experience oxidative stress, which is common in aging and neurodegeneration,” Samelson said. “We found that this stress reduces the efficiency of the proteasome, the cell’s protein recycling machine, causing it to improperly process tau.”
Laboratory experiments showed that this altered tau fragment changes how tau proteins cluster together, which may influence how the disease progresses.
New Paths Toward Alzheimer’s Treatments
The findings offer several potential therapeutic directions. Increasing CRL5SOCS4 activity might help neurons clear tau more effectively. At the same time, protecting the proteasome during periods of cellular stress could reduce the formation of harmful tau fragments.
“What makes this study particularly valuable is that we used human neurons carrying an actual disease-causing mutation,” Samelson said. “These cells naturally have differences in tau processing, giving us confidence that the mechanisms we identified are relevant to human disease.”
Beyond CRL5SOCS4, the large-scale genetic screen revealed additional biological pathways not previously tied to tau regulation. These include a protein modification process known as UFMylation and enzymes that help build membrane anchors within cells.
Although the results are promising, the researchers caution that more work is needed before these discoveries can be translated into treatments.
The study was funded by the Rainwater Charitable Foundation/Tau Consortium, the National Institutes of Health and other sources.
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