DNA content limits the size of muscle fibers

In two articles published today in the reputed journal Nature Communications, researchers at the Department of Biosciences at the University of Oslo, in collaboration with a group at the University of Cincinnati show that the DNA-content limits muscle cell size. Size matters, since force is proportional to size. The findings are based on material from both humans and animal experiments.

Muscle fibers are DNA-poor

The muscle cells are by far the largest cells in the body, with volumes 100,000 times larger than for other body cells. Even if the DNA-content increases by supplying new cell nuclei from stem cells in the tissue during growth, this does not keep pace with the increase in volume, and the researchers believe that this sets a limit to how large the cells can become. 

The largest muscle cells in humans can be more than 40 cm (15 inches) long, and while most cells contain only one nucleus with DNA, such a cell can contain more than 40,000 nuclei. When muscle cells grow during development, or due to strength training, the number of nuclei increases, but it does not keep pace with the increase in volume, thus he larger the cell become the more DNA poor it becomes. This DNA “dilution” might limit the growth.

Previous training and muscle memory

The findings strengthen the groups previous discovery of a so called muscle memory, which seems to aid re-training when previous strength-exercise has led to a higher DNA content by acquiring permanent cell nuclei. 

At the University of Oslo the study has been led by Professor Kristian Gundersen, with Kenth-Arne Hansson, Einar Eftestøl, Jo C. Bruusgaard, Inga Juvkam and Anders Malthe-Sørenssen as collaborators. The studies are a collaboration with a group led by Dr. Douglas P. Millay at the University of Cincinnati.