An international team of researchers, some from Queen’s and Western Ontario Universities in Canada, investigated the link between irisin and Alzheimer’s disease after recent studies showed that irisin appears to promote the development of neurons in the hippocampus, a region of the brain essential for learning and memory.
By examining tissues obtained from human brain banks, researchers measured reduced concentrations of irisin in the hippocampus of donors with Alzheimer’s disease.
Experiments in mice then showed that irisin seemed to protect the synapses and memory of animals. When irisin was neutralized in the hippocampus of healthy mice, synapses and memory decreased. Similarly, increasing irisin levels seemed to improve brain health.
Scientists wrote in Nature Medicine that mice that swam almost every day for five weeks did not have memory problems, even if they were injected with beta-amyloid – the protein that engulfs neurons and destroys the memory of Alzheimer’s patients.
Blocking the action of irisin completely neutralized the benefits of swimming and in memory tests, the little swimmers performed no better than their sedentary sisters who had been injected with beta-amyloid.
“It brings a new mechanism,” explained Frédéric Calon, who is a full professor in the Faculty of Pharmacy at Université Laval. (The researchers) argue that there is a problem with this protein in Alzheimer’s disease, and it was known that exercise has an effect on this protein in the muscles, and they say it could also have an effect in the brain.”
However, the study seems to have some shortcomings. In particular, Mr. Calon questions the model used by the researchers, and other experts have raised concerns.
“They’re going to say that irisin improves cognition in animals, which is interesting,” he said. But at the same time, we don’t quite agree on what the active molecule is. It’s like a big protein that’s cut differently, and only a fraction would be active.”
The impact of physical exercise on neurodegenerative diseases has been of interest to researchers for some time. However, their focus was mainly on Parkinson’s disease, which has an impact on motor skills and where the effect of exercise was therefore easier to measure.
“In Alzheimer’s, it’s a little more blurry, but there are still some indirect evidence,” Calon said. For example, we know that having type 2 diabetes, obesity, especially in the middle of life, will increase the chances of developing Alzheimer’s disease. We’re starting to see it more clearly. It is well known that exercise has positive effects on obesity, on all metabolic problems, well, we think that there is a good chance that exercise will have an effect on Alzheimer’s.”
Studies also suggest that physical activity has a positive impact on cognition and “several things suggest” that maintaining good cardiovascular health through exercise can eventually protect the brain, Calon said.
“But we are in prevention especially, we are especially in a situation where we know that there are no real risks, so it is easy to suggest exercising, because we know that it can’t really cause problems,” he concludes.