Researchers Alzheimer's plaques protect the brain from infections

Alzheimer's disease not only have negative effects on the body
Experts around the world are trying to better understand Alzheimer's disease in order to find more effective ways to treat and prevent it. Researchers have now discovered that a protein fragment found in Alzheimer's disease may form sticky plaques around the neurons in our brain, but it can also have beneficial effects on our health. Beta-amyloid (ß-amyloid) seems to protect our brain from some pathogens.

Degenerative diseases pose a major threat to our health. Researchers at the Massachusetts General Hospital (MGH) have now discovered in one study that the classic villain of Alzheimer's disease, a protein fragment called ß-amyloid, is not just negative Has effects on body and mind. Although the protein fragment stifles our neurons, it also seems to protect our brain from pathogens. The physicians published the results of their study in the journal "Science Translational Medicine".

Alzheimer's is a serious condition that leads to the loss of cognitive abilities. The disease makes sticky plaques around the neurons in our brain. These deposits do not seem to have only negative effects. (Image: Juan Gärtner / fotolia.com)

Study on worms and mice brings amazing results
In Alzheimer's disease, the ß-amyloid protein fragment forms sticky plaques around the neurons of our brain, explain the physicians. A new study on mice and worms supports the very controversial hypothesis that these plaques can also have beneficial effects on our body. Apparently these deposits are able to protect our brain from the threat of pathogens, the authors explain. The findings of the study may provide new ways to prevent deadly degenerative diseases in the future, say the experts. Beta-amyloid deposits can also damage many other organs besides the brain, including the heart, liver, and kidneys, says neuroscientist Rudolph Tanzi of the Massachusetts General Hospital.

ß-amyloid 100 times more deadly than penicillin for some microbes
Six years ago, Tanzi and neuroscientist Robert D. Moir decided to test whether β-amyloid behaves similarly to a class of proteins with known positive properties (called antimicrobial peptides or AMPs). Some AMPs also form fibers around cells, but they use them to trap and kill microbes throughout the body. To see if ß-amyloid works in a similar way, the team in lab shells tested the reaction with a number of different microbes. These include, for example, Candida albicans, bacteria such as Escherichia coli and various strains of streptococci, the authors explain. The malignant protein was just as toxic to many pathogens as the positive AMPs. In fact, it was more than 100 times more deadly than penicillin against some microbes, says Moir of Massachusetts General Hospital.

Study: In animals, beta-amyloid actually protects against pathogens
For the first time in animals, the new study shows that beta-amyloid can actually protect against pathogens, Tanzi says. Researchers used mice that were genetically engineered to produce excess levels of the human version of β-amyloid. Then the scientists injected the brains of the rodents Salmonella bacteria. These should normally cause an infection, say the experts. The physicians then observed whether the mice with additional ß-amyloid had a better defense against the microbes. All test mice died within 96 hours. However, it was found that mice with human amyloid lost less weight, had fewer bacteria in their brain and lived up to 30 hours longer, the researchers explain. Next, the scientists tested their hypothesis on the worm Caenorhabditis elegans. Worms with a strain of genetically engineered ß-amyloid in their gut survived up to 3 days longer after exposure to salmonella and yeast, add the physicians.

Amyloid plaques may behave like an antimicrobial peptide
Older mice usually do not produce amyloid plaques later in life. However, young mice form such sticky deposits immediately after Salmonella infection, says Tanzi. The fact that amyloid can behave like an antimicrobial peptide is truly surprising and could potentially open up a new perspective on Alzheimer's disease. Perhaps a microbial pathogen could cause the formation of plaques in Alzheimer's. To provide clarity, physicians would have to study the brain tissue of many people who have previously died of Alzheimer's disease, the researchers explain. Then they would have to look for different pathogens and determine if the microbes are surrounded by so-called amyloid plaques, adds Dr. Tanzi added.

Dozens of previous studies had already sought infectious agents that could trigger Alzheimer's. These investigations were not systematic enough to identify a real culprit, Tanzi explains. If scientists find that certain microbes in the human brain act as a trigger for amyloid deposition, then antibodies may be developed that are specifically designed to prevent this reaction. If ß-amyloid fulfills an important protective function in our brains, it might make sense to treat the protein fragment like cholesterol, the experts say. Cholesterol is needed by all cells, but with high cholesterol it can have dangerous consequences for our body. So maybe beta-amyloid just has to be slowed down and controlled, but in no way completely destroyed, the authors speculate. (As)