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A team led by Prof. Jeong Won-seok at IBS and KAIST has identified ‘ERBB4’ as a key protein that triggers and worsens Alzheimer’s disease, publishing the finding in Nature. It may explain why amyloid-beta-targeting drugs have had limited effectiveness for decades

📌 Post Summary

For decades, Alzheimer’s drug development has centered on ‘amyloid beta.’ Remove this toxic substance that builds up in the brain, the thinking went, and the disease should improve — and several drugs targeting it were indeed developed. But the results fell short of expectations. A KAIST team led by Prof. Jeong Won-seok has now identified a new key factor that may explain why, publishing the findings in Nature. Here’s what they found, and what it means.

① Why Removing Amyloid Alone Wasn’t Enough

Alzheimer’s disease is a degenerative brain disorder marked by gradual decline in memory and cognitive function. Its hallmark is the abnormal buildup of the toxic protein amyloid beta in the brain. But as the disease progresses, other abnormal changes also appear simultaneously — excessive excitation in neural circuits, loss of synapses (connections between neurons), and inflammatory responses from brain immune cells like astrocytes and microglia. The problem is that even though amyloid-clearing drugs were developed, they couldn’t address this whole complex of abnormal changes together, limiting their effectiveness. The research team focused on finding a single ‘common regulatory factor’ that could explain all these pathological changes at once.

② What Is ‘ERBB4’? — A Protein Showing Up Somewhere It Shouldn’t

ERBB4 (Erb-B2 Receptor Tyrosine Kinase 4) is a receptor protein on the cell membrane that senses external signals and regulates cell growth, differentiation, and neuronal function. The brain has ‘excitatory neurons’ that speed up electrical signals and ‘inhibitory neurons’ that slow them down. In a normal brain, ERBB4 is active only in inhibitory neurons and barely functions in excitatory ones. This division of labor matters — it’s what keeps the two types of neurons in balance so our bodies neither shut down into lethargy nor spiral into seizures. But the research team found that in a specific group of excitatory neurons in the normal brain, ERBB4 was markedly elevated beyond where it should ever appear. The team named these neurons ‘Early Responsive Excitatory Neurons’ (EREN) and identified ERBB4 as the key factor driving neural circuit abnormalities.

③ Mouse Experiments — Turn It Off, Get Better; Turn It On, Get Sick

Using gene-editing technology, the team selectively removed ERBB4 from the excitatory neurons of Alzheimer’s model mice. The result: the overactive excitatory neurons calmed down, while some of the previously suppressed inhibitory neurons recovered their activity. Brain inflammation disappeared, and notably, the amount of ‘amyloid plaque’ — clumps formed by the toxic amyloid beta protein — dropped by more than half. Even more interesting was the reverse experiment. When the team artificially induced ERBB4 expression in the excitatory neurons of normal mice with no amyloid plaques at all, the mice developed the same key changes seen in Alzheimer’s — circuit hyperexcitability, synaptic imbalance, and increased glial responses. In other words, ERBB4 alone can kick off the disease process even without a trace of amyloid. The team also demonstrated the underlying mechanism: rising ERBB4 levels overactivate the ‘mTOR’ signaling pathway, which regulates cell growth and metabolism, spreading the pathology outward.

④ A Chain Reaction That Pulls In Astrocytes and Microglia

The team also examined how the brain’s non-neuronal cells — astrocytes and microglia — get involved in this process. Normally, these cells maintain brain homeostasis by pruning unnecessary synapses. But once ERBB4 abnormally raised the activity of excitatory neurons, astrocytes and microglia ended up excessively pruning excitatory synapses while pruning relatively few inhibitory ones — a pattern that actually deepened the circuit imbalance rather than correcting it. In other words, the very immune and support cells meant to protect the brain end up being drawn into ERBB4’s abnormal signaling and pushed toward making the disease worse.

⑤ Confirmed in Human Data Too — 446 Brain Tissue Samples Analyzed

The findings didn’t stop at mouse experiments. The team analyzed publicly available human brain transcriptome (gene expression) data from 446 individuals. They found that ERBB4 expression in excitatory neurons was significantly elevated in Alzheimer’s patients, and higher expression levels correlated with more severe amyloid plaque accumulation and worse cognitive decline. It should be clearly noted that, unlike the mouse experiments, the human data only established a correlation — it did not test the treatment effect of directly manipulating ERBB4 in people. Even so, this correlation supports the idea that ERBB4 changes aren’t merely a side effect that accompanies Alzheimer’s, but a core regulatory factor driving the disease’s cascading progression.

⑥ What’s Next — Beyond Dementia to Other Neurodegenerative Diseases

The team isn’t stopping here. They plan to examine how the ERBB4 gene and protein change during normal aging, not just in Alzheimer’s disease. They also intend to analyze ERBB4’s changes and function in other neurodegenerative diseases — Parkinson’s disease, Huntington’s disease, and tau-protein-related disorders — to see whether it could become a therapeutic target applicable across multiple neurodegenerative conditions. Jeong Won-seok, IBS deputy director, said, “This research provides a new clue for understanding the amplification process of Alzheimer’s disease from multiple angles,” adding, “We hope it will contribute to pioneering new treatment strategies that target the core link in the disease’s vicious cycle to alleviate multiple complex pathologies at once.” The research was supported by South Korea’s Ministry of Science and ICT. Kim Sung-soo, the ministry’s R&D bureau director, said, “The key to overcoming intractable diseases comes from a fundamental exploration of the principles of life.”

📌 Things Worth Keeping in Mind

• This research does not mean a treatment targeting ERBB4 already exists. This is a basic-research stage discovery of a key regulatory factor — actual drug development and clinical trials will take considerable time.
• The human data only established a ‘correlation’ between ERBB4 and dementia symptoms; the treatment effect of directly manipulating ERBB4 in humans has not yet been proven.
• Because this offers a compelling clue as to why existing amyloid-clearing treatments had limited effect, it could lead to future research on combination treatment strategies.
• The team plans to extend its research on ERBB4’s role beyond dementia to other neurodegenerative diseases like Parkinson’s, so it’s worth watching for follow-up findings.

For a field of Alzheimer’s research long fixated on amyloid beta alone, this discovery offers a clue to the old question of why removing amyloid alone was never enough. It won’t lead to a treatment right away, but by identifying a new target that could address multiple pathologies at once, it’s being seen as a discovery that could shift the direction of dementia research.

References

• Kyunghyang Shinmun, “Closer to the ‘dream of conquering dementia’… Korean researchers find key reason behind Alzheimer’s” (khan.co.kr)
• Edaily, “Key factor triggering Alzheimer’s cascading pathology identified” (edaily.co.kr)
• Clinic Journal, “Key switch to break Alzheimer’s vicious cycle found” (clinicjournal.co.kr)
• IDSN News, “IBS identifies ‘ERBB4’ as Alzheimer’s-worsening regulator… improves cognitive function in mice” (idsn.co.kr)
• Nature, “Aberrant excitatory neuronal ERBB4 promotes Alzheimer’s disease pathology” (nature.com)
• KAIST Department of Brain and Cognitive Sciences, Prof. Jeong Won-seok profile page (bcs.kaist.ac.kr)