While scientists have observed neuroinflammation in people with Alzheimer’s before, the new study reveals for the first time its critical role in the development of the disease. The study appears in Nature Medicine. The research finds that activating the brain’s immune cells — its microglial cells — promotes the spread of tangled tau proteins that comprise amyloid plaque.
Lead author of the study, Dr. Tharick Pascoal, Ph.D., assistant professor of psychiatry and neurology at the University of Pittsburgh School of Medicine, PA, explains: A new study finds that inflammation in the brain drives the progression from the presence of amyloid plaque and tau tangles to the onset of dementia and Alzheimer’s disease.
“Many have amyloid plaques in their brains but never progress to developing Alzheimer’s disease. We know that amyloid accumulation on its own is not enough to cause dementia — our results suggest that it is the interaction between neuroinflammation and amyloid pathology that unleashes tau propagation and eventually leads to widespread brain damage and cognitive impairment.” However, amyloid plaque — consisting of broken pieces of protein that clump together — is also present in the brains of older adults who do not develop Alzheimer’s, suggesting another factor is triggering the disease.
Inflammation is not by itself associated with cognitive impairment, Dr. Pascoal told MNT. “However,” he said, “when neuroinflammation converges with amyloid pathology, the interaction potentiates tau pathology. As a consequence, the coexistence of these three processes in the brain — amyloid, neuroinflammation, and tau pathology — determines cognitive deterioration.” While experiments using cultured cells and laboratory animals have previously implicated microglial activation in the spread of tau fibers, the new study is the first to document their relationship in living people. “However,” adds Dr. Snyder, “a sustained inflammatory response, or a change from acute to chronic neuroinflammation, may contribute to the underlying biology of several neurodegenerative disorders.”
“Inflammation has an important role in fighting off infection and other pathogens in the body, including in the brain and central nervous system,” said Snyder. Microglia “help clear debris (damaged neurons, infections) from the brain.” Heather M. Snyder, Ph.D., Alzheimer’s Association vice president of medical and scientific relations, who was not involved in the study, explained the purpose of neuroinflammation to Medical News Today. The Alzheimer’s Association contributed funding to the research.
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