Repeated head injuries, such as concussions – a known risk factor for Alzheimer’s disease (AD) – may reactivate a common dormant virus in the brain, increasing the risk of AD and other neurodegenerative conditions.
Researchers found that mild brain trauma can trigger this chain reaction, leading to harmful changes associated with cognitive decline and memory loss.
In previous studies, the researchers demonstrated the roles that common viruses, such as herpes simplex virus type 1 (HSV-1) (the so-called cold sore virus) and the virus which causes chickenpox and shingles play in the development of AD.
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HSV-1 can lie dormant in human cells for a lifetime, but when it re-awakens it can cause changes that resemble changes observed in AD patients’ brains.
In the latest study, published in Science Signaling, the researchers used a small, 3D, bioengineered human brain tissue model to test the effects of physical trauma on the brain cells. When the brain tissues were exposed to repeated “mild blows,” similar to concussions, the previously dormant HSV-1 virus became active. This reactivation triggered inflammation, beta-amyloid plaque build-up, and the formation of harmful tau proteins, which can damage brain cells and impair memory.
Importantly, the researchers also found that blocking an inflammatory molecule called Interleukin-1 beta prevented many of these harmful effects in lab models, opening the door to potential new treatments for those at risk.
Professor Itzhaki, Visiting Professorial Fellow at the Oxford Institute of Population Ageing and Emeritus Professor at the University of Manchester, said: “Head injuries are already recognised as a major risk factor, as are the cumulative effect of common infections, for conditions such as Alzheimer’s and dementia, but this is the first time we have been able to demonstrate a mechanism for that process.
“What we’ve discovered is that in the brain model these injuries can reactivate a dormant virus, HSV1, setting off inflammation which, in the brain, would lead to the very changes we see in Alzheimer’s patients.
“Understanding both the risk factors for dementia and Alzheimer’s, and the mechanism by which they develop, is important in being able to target treatment and prevention at as early a point as possible.”
The researchers hope their work will pave the way for new treatments to protect against neurodegeneration, particularly for those at high risk due to repeated concussions.
The full paper, ‘Repetitive injury induces phenotypes associated with Alzheimer’s disease by reactivating HSV-1 in a human brain tissue model’, is published in Science Signaling.