February 6, 2019 – Why are fat deposits more likely to occur after tears in the shoulder rotator cuff compared to other types of muscle damage? An increased tendency for stem cells within rotator cuff muscles to develop into fat cells can explain the difference, reports a study in February 6, 2019, the issue of Journal of Bone & Joint Surgery. The journal is published in the Lippincott portfolio in collaboration with Wolters Kluwer.
"Satellite" stem cells in the rotator cuff are more likely to develop into fat cells and less likely to develop into muscle cells as compared to calf muscle cells, according to the experimental study by Christopher L. Mendias, PhD, ATC and colleagues of the University of Michigan Medical School. , Ann Arbor, and Hospital for Special Surgery, New York. The researchers write, "There appears to be a cellular and genetic basis behind the generally poor prices of rotator cuff muscle healing."
& # 39; Satellite Cells & # 39; May be shaped more fat than muscle after rotator cuff tears
The researchers performed a number of experiments using muscle cells from mice to assess the properties of a type of stem cell called satellite cells. Stem cells are specialized cells with the potential to develop into different types of cells. Satellite cells that lie between muscle fibers play an important role in repairing after muscle damage.
Tears of shoulder rotator cuff are a common problem. Particularly in chronic tears, fats often develop, contributing to the weakening and atrophy of rotator cuff muscles. This fat infiltration can continue even after a successful rotator cuff repair surgery.
Dr. Mendias and colleagues created cultures of satellite cells isolated from mouse rotator cuff and calf muscles. "Clinically, we know that the rotator cuff is one of the hardest muscle groups to rehabilitate after injury, and it is believed to occur due to the high fat that accumulates in the muscle of patients with chronic tears," author author Schubert says. , MD, MS, Chief resident in orthopedic surgery at the University of Michigan. "We thought there might be a genetic basis for explaining why the rotator cuff accumulates fat after injury, and the specialized transgenic model we used in this study allowed us to precisely test this."
Compared to the calf-muscle satellite cells, satellite cells from the rotor case developed to 23 percent fewer muscle cells, and they showed a decrease of 87 percent in a "marker" of muscle formation. The rotator cuff satellite cells also had a 4- to 65-fold increase in markers of genes involved in fat cell generation (adipogenesis).
DNA level (epigenetic) studies identified hundreds of differences in re-activation between satellite cells from rotator boxes against calf muscles. The affected genes were involved in pathways related to fat metabolism and adipogenesis, suggesting that the muscle stem cells from the rotator cage are programmed to become easier fat cells.
Based on previous studies, the new study shows increased "adipogenic differentiation capacity" of rotator cuff satellite cells. Increased potential for developing into fat cells – and reduced potential to develop into muscle cells – can be an important explanation for the high fat content of muscles in patients with chronic rotator cuff tears, even after rotator cuff surgery.
The study also has potential therapeutic findings. "Satellite cells can be isolated from other muscle groups with relative ease." says Dr. Mendias, an associate researcher at the hospital for specialty surgery and an adjunct associate professor at the University of Michigan. "While further studies are needed, it is possible that a patient's own stem cell from a muscle that heals well, such as the calf, could be transplanted into rotator cuff muscle at the time of surgical repair. These transplanted cells may be better able to regenerate the chronically damaged muscle than the resident stem cells. "
Additional researchers who have contributed to the study are Andrew Noah, MS, Jonathan Gumucio, PhD, and Asheesh Bedi, MD, all at the University of Michigan.
Click here to read "Reduced Myogenic and Increased Adipogenic Differentiation Capacity of Rotator Cuff Muscle Stem Cells"
DOI: 10,2106 / JBJS.18.00509
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