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Snapshots of Life: Building Muscle in a Dish

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Fibers from cultured muscle stem cells

Credit: Kevin Murach, Charlotte Peterson, and John McCarthy, University of Kentucky, Lexington

As many of us know from hard experience, tearing a muscle while exercising can be a real pain. The good news is that injured muscle will usually heal quickly for many of us with the help of satellite cells. Never heard of them? They are the adult stem cells in our skeletal muscles long recognized for their capacity to make new muscle fibers called myotubes.

This striking image shows what happens when satellite cells from mice are cultured in a lab dish. With small adjustments to the lab dish’s growth media, those cells fuse to form myotubes. Here, you see the striated myotubes (red) with multiple cell nuclei (blue) characteristic of mature muscle fibers. The researchers also used a virus to genetically engineer some of the muscle to express a fluorescent protein (green).

The NIH-funded team—including Kevin Murach, Charlotte Peterson, and John McCarthy at the University of Kentucky, Lexington—snapped this image using a standard fluorescent microscope. It was selected as a winner in the Federation of American Societies for Experimental Biology’s 2017 BioArt competition.

While this image shows what happens when normal satellite cells are isolated and grown in the lab, the researchers are also using the same viruses in parallel experiments to tinker with potentially important genes in satellite cells. Their goal is to learn how those genetic changes help or hinder the way stem cells contribute to the formation and adaptation of muscle fibers.

Their studies in lab dishes and animals have already yielded some surprises. For instance, scientists had long thought satellite cells were essential not just for repairing damaged muscles but also for building muscle mass with exercise. But the team’s studies have shown that adult mice missing satellite cells continue to build larger muscles with exercise [1]. However, the new muscle is abnormal, producing an unusual amount of fibrous tissue.

The findings suggest that satellite cells play important roles in influencing the environment and characteristics of muscle. While the work is ongoing, it suggests the loss of satellite cells, which occurs as we age, may help to explain why our muscles can grow weaker and increasingly fibrotic over the years. That’s why a weekly exercise regimen is so important as we age, to stay fit and keep building healthy muscle fibers like those shown in this impressive BioArt winner. It’s always a good week to hit the gym!

References:

[1] Starring or Supporting Role? Satellite Cells and Skeletal Muscle Fiber Size Regulation. Murach KA, Fry CS, Kirby TJ, Jackson JR, Lee JD, White SH, Dupont-Versteegden EE, McCarthy JJ, Peterson CA. Physiology (Bethesda). 2018 Jan 1;33(1):26-38.

Links:

4 Types of Exercise (National Institute on Aging/NIH)

Kevin Murach (University of Kentucky, Lexington)

Charlotte Peterson (University of Kentucky)

John McCarthy (University of Kentucky)

University of Kentucky Center for Muscle Biology

BioArt (Federation of American Societies for Experimental Biology, Bethesda, MD)

NIH Support: National Institute of Arthritis and Musculoskeletal and Skin Diseases; National Institute on Aging

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