*rushes to treadmill*
A team of scientists from the United States and Germany has investigated why running on a treadmill can boost memory recall.
According to the findings, which have been published in the journal Cell Metabolism, a run increases the levels of a protein called cathepsin B in the blood of mice, monkeys, and humans and may have something to do with the memory boost.
"We wanted to cast a wide net. Rather than focus on a known factor, we did a screen for proteins that could be secreted by muscle tissue and transported to the brain, and among the most interesting candidates was cathepsin B," senior author Henriette van Praag, a neuroscientist at the National Institute on Aging in the United States, said in a press release
The researchers were tipped off to take a deeper look into the role of cathepsin B after finding that there were high levels of the protein in the blood and muscle cells of mice who spent time on exercise wheels daily for several weeks.
In their own experiment, the researchers gave two sets of mice — one set of normal mice and one set of mice lacking the ability to produce cathepsin B — daily swim tests in a Morris water maze, in which a mouse is placed in a small pool and has to learn to swim to a platform hidden just below the surface.
Normally, mice learn where to find the platform after doing the task for a few days. However, the researchers found that when both groups of mice ran before the swim test, the normal mice were better able to recall the platform’s location, while the mice with blocked cathepsin B production couldn’t remember its location.
"Nobody has shown before cathepsin B's effect on spatial learning," says van Praag. "We also have converging evidence from our study that cathepsin B is upregulated in blood by exercise for three species--mice, Rhesus monkeys, and humans.”
“Moreover, in humans who exercise consistently for four months, better performance on complex recall tasks, such as drawing from memory, is correlated with increased cathepsin B levels,” she continued.
Interestingly, cathepsin B appears to be involved in a number of bodily mechanisms — but not all healthy ones. It’s known to be secreted by tumors, and other research has implicated the protein in amyloid plaque formation in the onset of Alzheimer’s disease. Contrasted with these previous findings, the link between cathepsin B and a memory boost may seem counterintuitive, and the researchers speculate it may be controversial.
However, van Praag hypothesizes that different physiological conditions and different levels of the protein likely yield different effects, which could explain the stark differences in research findings.
“This is a super exciting area. Exercise has so many health benefits, yet we know so little about many of these effects at a molecular level,” biologist David James of the University of Sydney, who did not participate in the work, told The Scientist.
Next, the researchers hope to explore how cathepsin B crosses the blood-brain barrier, and how it activates neuronal growth and connections. They also plan to look into how cathepsin B production changes with age.
"Overall, the message is that a consistently healthy lifestyle pays off," van Praag concludes. "People often ask us, how long do you have to exercise, how many hours? The study supports that the more substantial changes occur with the maintenance of a long-term exercise regimen."
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