New research from Arizona State University and Banner Alzheimer's Institute has uncovered a surprising connection between a common virus and the development of Alzheimer's disease in some individuals.
The cytomegalovirus (CMV) is a type of herpes virus many people encounter during childhood. While it typically remains dormant in most people, the study suggests that in certain cases, it may stay active in the gut and travel to the brain, contributing to Alzheimer's disease.
How CMV Travels to the Brain and May Contribute to Alzheimer's
CMV spreads through bodily fluids like saliva, blood, and semen and by the time people reach 80 years old, nearly 9 out of 10 will have antibodies to the virus. However, the virus doesn't always cause harm.
For most individuals, CMV remains inactive and doesn't pose a significant risk. However, researchers have found that in some cases, CMV stays active in the gut and can travel along the vagus nerve, a pathway that connects the digestive system to the brain.
Once in the brain, the virus may trigger immune responses that lead to the buildup of amyloid plaques and tau tangles, both of which may contribute to Alzheimer's disease.
This finding suggests that CMV could play a role in the development of Alzheimer's in a specific group of patients.
According to ScienceAlert, Dr. Ben Readhead, a lead author of the study, explained that this particular form of Alzheimer's could affect 25% to 45% of people with the disease.
This subtype of Alzheimer's shows the usual brain abnormalities, but it also has a distinct biological profile, with higher levels of virus, antibodies, and immune responses in the brain.
The research offers a new perspective on how infections might contribute to neurodegenerative diseases like Alzheimer's.
The researchers analyzed tissue samples from 101 body donors, including 66 who had Alzheimer's disease. They studied tissues from the brain, spinal fluid, intestines, and vagus nerve to track the presence of CMV.
Their findings showed that the virus could travel from the intestines to the brain, and in some cases, it was found in the vagus nerve, a key pathway for the virus's journey to the brain.
Furthermore, the study revealed that the presence of CMV in the brain led to the activation of microglia, the immune cells in the brain.
While microglia are crucial for protecting the brain, if they become overactive, they can cause chronic inflammation, leading to neuronal damage. The virus triggered microglia to express a gene, CD83 linked to Alzheimer's disease.
CMV Linked to Alzheimer's in Brain Cells, Paving the Way for Early Detection and Treatment
To further test their hypothesis, the researchers used human brain cell models, which showed that CMV exposure led to increased production of amyloid and tau proteins, contributing to neuron damage and degeneration, Knowridge said.
These findings suggest that in some individuals, CMV may directly impact the development of Alzheimer's disease.
Importantly, the research indicates that the connection between CMV and Alzheimer's disease may only affect a small group of people with chronic CMV infections in their intestines. While almost everyone is exposed to CMV, only a subset of people develop this type of Alzheimer's.
This discovery has raised hopes that antiviral drugs could help prevent or slow down the progression of this Alzheimer's subtype, particularly if doctors can develop a blood test to detect CMV infections early.
The team is working on creating a test, which could identify individuals with chronic CMV infections in the gut. If successful, antiviral treatments could be used to manage the virus and potentially prevent the development of Alzheimer's in at-risk individuals.
While more research is needed to confirm these findings, the study represents a promising new direction in Alzheimer's research and treatment.
