by Samantha Rey, Imperial College London

MSMP activation or inhibition elicit rapid neural activity with muscle contraction or impair muscle activity in response to stretch, respectively. Credit: Nature (2024). DOI: 10.1038/s41586-024-08272-5

Researchers at Imperial College London have discovered that specialist macrophages—a type of white blood cell—play a key role in the control of muscle contraction and locomotion. The discovery overturns previous assumptions that muscle contraction and movement is controlled solely by the nervous system—including the brain and spinal cord.

In a study in mice, the researchers found that specially adapted macrophages in the muscle spindles, which were also found in human muscle, directly regulated neural activity and muscle contraction. They behaved similarly to neurons by releasing the neurotransmitter glutamate. When the macrophages were blocked in a group of mice, the affected muscles didn't move properly.

The researchers, led by Professor Simone di Giovanni at the Department of Brain Sciences, also found that macrophages play a role in supporting the metabolism of the nervous system during muscle contraction and locomotion to avoid exhaustion. The paper is published in the journal Nature.

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Z-stack of MSMP in proximity to MS. Credit: Nature (2024). DOI: 10.1038/s41586-024-08272-5

While more research is needed to confirm that the same mechanism applies for human muscles, the researchers believe the potential is clear.

Professor di Giovanni said, "The discovery, not just of these immune cells in close contact to muscle spindles but also that they play a key role in movement, is very exciting. This knowledge has implications for conditions like chronic fatigue syndrome and other diseases of the immune, muscular and nervous system that directly affect movement."

Macrophages can be found within many organs in the body, including the liver, brain, bones, and lungs, as well as in the blood, particularly at sites of infection, but this is the first time they've been found in muscle itself. They play an important role in the human immune system and carry out various functions including engulfing and digesting microorganisms and clearing out debris and dead cells.

More information: Yuyang Yan et al, Macrophages excite muscle spindles with glutamate to bolster locomotion, Nature (2024). DOI: 10.1038/s41586-024-08272-5

Journal information: Nature 

Provided by Imperial College London