The physical and mental benefits of exercise are undeniable, but a new study by MIT engineers finds that the benefits may go even deeper. The researchers’ findings show how physical activity that causes muscles to contract leads to the release of biological signaling substances that may have the power to repair damaged nerve cells.
Clarifying “exercise factors”
Humans recognized very early on that exercise was good for you, but for many years scientists weren’t sure exactly what was happening when you flexed your muscles. People reasoned that some kind of chemical messenger must be released from the muscle fibers, but they didn’t have a clear idea of what it was. referred to as a somewhat ambiguous “work factor” or “exercise factor.”
next, 2000it was discovered that skeletal muscle releases interleukin-6 (IL-6), a well-known cytokine most commonly associated with the immune system. Further studies suggested that IL-6 alone was unlikely to explain all the effects of exercise, so the term ‘myokine’ was used to cover all similar factors that may be subsequently discovered. was created.
Although it is clear that muscles have the ability to release hundreds of different peptides, we still have a long way to go before we understand all of their biological functions.
For example, we know that proper training can lift your mood, relieve stress, and benefit your nervous system, but less is known about the effects of exercise at the level of individual neurons. . This is what the MIT team began exploring.
Muscles “talk” to nerves
The spark of an idea is 2023 survey Lead author Ritu Raman and colleagues found that muscle damage in mice can be healed by transplanting new muscle tissue and repeatedly stimulating it, or exercising. They hypothesized that new muscle tissue produces myokines that promote nerve and blood cell repair.
“This was interesting because we always think that nerves control muscles, but we don’t think that muscles fight back against nerves,” Raman said in the paper. said. statement. “So we started thinking that stimulating the muscles might be promoting nerve growth.”
However, proving this experimentally is a different story.
“People said maybe,” Raman added. “But there are hundreds of other types of cells in animals, and it’s very difficult to prove that nerves are growing more because of muscles rather than the immune system or other factors that play a role. I am fulfilling my role.”
Now, the researchers have developed a method to grow mouse muscle cells into fibers that then fuse to form stable sheets of muscle tissue that are about a quarter of the size. Genetic modification allows the muscles to contract in response to light, allowing them to be repeatedly “worked out” to mimic a workout.
After contracting the muscles, the researchers collected samples of the fluid around the sheets to see if the cells were releasing myokines. Raman tantalizingly explains: It is also effective against nerves and things unrelated to nerves. Muscles secrete myokines almost all the time, but when you exercise they secrete even more myokines. ”
They then applied this soup to motor neurons cultured in a similar manner. After adding myokine, the researchers saw that neurons began to grow four times faster than normal. “And the effects are immediate,” Raman said.
Genetic analysis revealed that the addition of myokines not only upregulated genes responsible for growth, but also promoted neuronal function and maturation.
Let’s train our bodies
Obviously, exercise is not just a chemical process; there are also mechanical forces that cause muscles to contract and relax. You may have never thought about it, but every time you stretch a muscle, you also stretch all the nerve fibers it’s attached to.
To simulate this, Raman and team grew another batch of motor neurons, this time on a surface studded with tiny magnets. They exercised their muscles for 30 minutes every day by applying an external magnet and wiggling the surface back and forth.
Physically exercising neurons made them grow longer, just as they observed with direct application of myokine.
“This is a good sign because it shows that both the biochemical and physical effects of exercise are equally important,” Raman says.
These green spheres are bundles of nerve cells that grow outward with long tails called axons. Images show growth over 5 days in response to biochemical (left) and physical (right) movement signals.
Myocaine is currently a hot topic. Another recent but unrelated study showed how drugs containing myokines could one day be used as an “exercise therapy” to protect the brain from age-related dementia.
Raman and his colleagues hope their new research will uncover new ways to repair damaged nerves and help people with other neurodegenerative diseases such as amyotrophic lateral sclerosis. There is much more to do and much more to discover about these mysterious messengers.
“This is just the first step toward understanding and controlling exercise as a medicine,” Raman said.
The research will be published in a journal advanced healthcare materials.
