A new study has presented further evidence supporting a hypothesis suggesting that viral infections in the olfactory system may accelerate the progression of Alzheimer’s disease (AD). Instead of focusing on specific viruses, the research looked at the relationship between biomarkers of viral infections and neurodegeneration in the hippocampus.
For decades, researchers have reported an association between brain diseases and acute viral infections. The herpes simplex virus in particular has long been associated with the development of Alzheimer’s disease. But it’s not clear exactly how viral infections might be influencing neurodegeneration.
This new research focused specifically on the olfactory system. Loss of the sense of smell has been found to be a possible early marker of Alzheimer’s neurodegeneration. So the question being explored here is whether viral infections in the nose play a role in accelerating the deterioration of Alzheimer’s disease.
To investigate this, the researchers analyzed post-mortem brain tissue from several people who died with Alzheimer’s disease. Compared to tissue samples taken from age-matched cognitively healthy subjects, the Alzheimer’s group showed substantial markers of viral infection and inflammation in the olfactory tract, a key pathway leading to the hippocampus.
“Overall, the transcriptional profile we have observed in this study may be representative of an olfactory system routinely bombarded by pathogens and the resulting pathological ramifications, such as amyloid deposition, microglia activation, and potential myelination disturbances,” they write. the researchers in the new study. “Taken together with a parallel body of literature indicating that early AD is characterized by loss of smell, amyloid deposition in the olfactory epithelium and olfactory sensory neuron dysfunction, our study raises the possibility that viral infection of the olfactory bulb/olfactory tract accelerates Alzheimer’s disease.”
The study did not focus on which specific pathogens might be responsible for persistent infections. However, researchers speculate that herpes simplex virus type 1 (HSV-1) and varicella zoster virus (VZV) are the most likely culprits. Both viruses have previously been implicated in the progression of Alzheimer’s disease, and both are known to lead to lifelong latent infections.
Lead author of the new study, Andrew Bubak, hypothesizes that this virus-induced loss of the sense of smell ultimately accelerates hippocampal degeneration. So instead of our sense of smell being damaged by Alzheimer’s neurodegeneration, it’s actually the process of losing our sense of smell that subsequently causes further dementia-related brain damage.
“We know that one of the first signs of Alzheimer’s disease is the loss of the sense of smell,” Bubak said. “The entire olfactory pathway goes to the hippocampus. If you decrease signaling along that pathway, you’ll get less signaling to the hippocampus. If you don’t use it, you lose it.”
The new study was published in neurobiology of aging.
Source: University of Colorado Anschutz Medical Campus
Source: news.google.com