Repeated head injuries, such as concussions, may increase the risk of Alzheimer's disease and dementia by reactivating the herpes simplex virus type 1 (HSV-1) in the brain.
The researchers used organoids of the human brain to compare the effects of physical trauma on brain cells that had a dormant HSV-1 infection and those that did not. The brain cells were either given a single hard blow with a piston to simulate a traumatic head injury or several smaller blows to mimic the effects of repeated milder concussions. The researchers found that when the brain cells were exposed to physical trauma, HSV-1 was reactivated, supporting previous research that has linked neuroinflammation to the development of Alzheimer's disease.
Professor Ruth Itzhaki, from the University of Oxford and co-lead author of the paper published in Science Signaling, said: 'What we've discovered is that in the brain organoid these injuries can reactivate a dormant virus, HSV-1, setting off inflammation which, in the brain, would lead to the very changes we see in Alzheimer's patients'.
HSV-1 is a common virus that is responsible for causing cold sores and genital herpes. It is thought that over 80 percent of adults aged 60 years or over have been infected with HSV-1 at some point in their lives. It can remain dormant, meaning that a person may experience no symptoms unless the virus is reactivated.
The researchers used two brain organoids – one that was subjected to infection with HSV-1, and one that was not. After repeated, mild controlled blows to the brain organoids, the researchers found that HSV-1 was reactivated in the brain organoid that was subjected to HSV-1. The reactivation triggered inflammation that led to the formation of amyloid plaques and tau proteins, which are both signs of Alzheimer's disease. These changes were not seen in the brain organoid that was not subjected to infection with HSV-1.
The researchers also demonstrated that the effects of HSV-1 reactivation could be reduced by blocking the inflammatory protein interleukin-1 beta (IL-1b), which they hope may provide an opportunity for future research into therapeutic options that block IL-1b and stop the harmful effects of HSV-1 reactivation in the brain.
Dr Dana Cairns, from Tufts University and lead author of the study, said: 'This opens the question as to whether antiviral drugs or anti-inflammatory agents might be useful as early preventive treatments after head trauma to stop HSV-1 activation in its tracks, and lower the risk of Alzheimer's disease'.
Sources and References
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New study reveals link between head injuries and viruses in Alzheimer's disease
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Repetitive injury induces phenotypes associated with Alzheimer’s disease by reactivating HSV-1 in a human brain tissue model
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Herpes virus and head injuries linked to Alzheimer's, mini-brain study finds
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Using lab-grown human mini-brains, scientists find links between head trauma, herpes, and Alzheimer's
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