A report in the January issue of Cell Metabolism, a publication of Cell Press, provides new evidence explaining how stem cells known as satellite cells contribute to building muscles up in response to exercise. These findings could lead to treatments for reversing or improving the muscle loss that occurs in diseases such as cancer and AIDS as well as in the normal aging process, according to the researchers.
The researchers showed that a transient and local rise in an inflammatory signal, the cytokine known as interleukin-6 (IL-6), is essential for the growth of muscle fibers. The findings offer the first clear mechanism for the stem cells incorporation into muscle and the first evidence linking a cytokine to this process, said Pura Muoz-Cnoves of Universitat Pompeu Fabra in Barcelona, Spain. As we learn more about how muscles grow in adults, we may uncover new methods for restoring lost muscle mass in the elderly and ill, she added.
Skeletal muscles are made up of individual myofibers, each with many nuclei containing genetic material. As muscles are made to work harder, they adapt by bulking up each of those individual fibers, the researchers explained, but the mechanisms responsible have largely remained elusive.
Mounting evidence has shown that the growth of myofibers is limited by the need to maintain an equilibrium between the number of nuclei and the fibers overall volume. Because mature myofibers are incapable of cell division, new nuclei must be supplied by satellite cells (muscle stem cells). Once activated, satellite cells follow an ordered set of events, including proliferation, migration, and incorporation into the myofiber, leading to its growth.
Now, the researchers have found that IL-6 is an essential regulator in that process. While IL-6 was virtually undetectable in the muscles of control mice, animals whose muscles were made to work harder showed an increase in IL-6 after one day. That cytokine rise was maintained
|Contact: Cathleen Genova|