Running regularly for a few months may boost your memory, say scientists who have identified a novel protein that fuels exercise-induced neuron growth.
The protein cathepsin B can be directly traced from the muscles to the brain in mice, researchers said. Also, after a run, protein levels increased in blood in mice, monkeys, and humans.
"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," said Henriette van Praag, a neuroscientist at the National Institute on Ageing in the US.
After exposing muscle cells in a dish to compounds that mimic exercise, researchers observed that the presence of cathepsin B production noticeably increased in the conditioned media of the cultures.
High levels of the protein were also found in the blood and muscle cells of mice that spent time daily for several weeks on their exercise wheels.
Additionally, when cathepsin B was applied to brain cells, it spurred the production of molecules related to neurogenesis.
Researchers then compared memory recall in normal mice with that in mice lacking the ability to produce cathepsin B under both sedentary and running conditions.
Over the course of a week, both sets of mice were given a daily swim test in the Morris water maze, in which a mouse is placed in a small pool and must learn to swim to a platform that is hidden just below the surface of the water.
After doing this task for a few days, normal mice eventually learn where to find the platform.
However, when both groups ran before their daily swim test, the normal mice were better able to recall the location of the platform, while the mice unable to make cathepsin B could not remember its location.
"Nobody has shown before cathepsin B's effect on spatial learning," said 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," he said.
"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," said van Praag.
This previously unrecognised function of cathepsin B may be controversial. The protein is known to be secreted by tumours and has been implicated in cell death and amyloid plaque formation in the brain.
Other studies have found that cathepsin B is neuroprotective and can clear amyloid plaques.
Researchers hypothesise that different levels of the protein and different physiological conditions may yield different effects.
The study was published in the journal Cell Metabolism.
