Scientists have found that secreted proteins help with muscle repair and growth

Scientists at Tokyo Metropolitan University have discovered that a protein called platelet-derived growth factor B sub-(PDGF-B) is continuously secreted from skeletal muscle cells and helps repair muscle by encouraging myoblasts (muscle
stem cells) to proliferate.
Unexpectedly, they found that PDGF-B also helps with the growth
of muscle fibers.
They confirmed that this corresponded
to stronger fiber shrinkage.
Their findings provide game-changing therapies
for the treatment of muscle wasting and injury.

Saratine is a small protein
secreted by skeletal muscle cells.
They have a wide range of functions and can act on cells
near or far from where they are generated.
The full picture of how muscle factors affect cellular processes is far from clear, but it is believed that they play an important role in exercise-related bodily functions, particularly the maintenance of
muscle tissue.

A team led by Yasuko Manabe, an associate professor at Tokyo Metropolitan University, has been studying how muscle factors affect the behavior of
muscle cells.
Through numerous experiments, they found that a muscle factor called platelet-derived growth factor sub-B (PDGF-B) is secreted by skeletal muscle in a constitutive way, i.
e.
, without any stimulation
.
To understand the role played by PDGF-B, they extracted myoblasts, precursor cells that continue to differentiate into muscle fibers, and exposed them to
PDGF-B.
They were able to clearly show that PDGF-B induced greater proliferation of myoblasts
.

Strangely, they also found that PDGF-B affects cells
that have already differentiated.
They remove the myotubes (the developmental stages of muscle fibers) and expose them to
the same sarcosine.
The myotube treated with this method shows pronounced maturation under the microscope with a marked increase
in diameter.
They also expressed more myosin heavy chains, a key part of the myosin protein structure, the molecular motor
responsible for muscle contraction.
Using a recently developed technique based on observing how the myotube responds to electrical impulses, this has been shown to directly correspond to increased contraction strength
.
Therefore, PDGF-B not only helps make more muscle, but also makes them
stronger.
But this does not mean that both processes are accelerated at will
.
They noted subtle differences in the PDGF-B signaling pathway between myotubes and myoblasts; The team believes that these differences may be related to
the shift of cells from the proliferation stage to the mature stage.

The team's work clearly shows that PDGF-B is involved in muscle regeneration and is a big step
forward in developing effective treatments for muscle injury and atrophy, as well as protocols to improve muscle performance.

This work was supported
by the Japan Association for the Promotion of Science (JSPS) KAKENHI Scientific Research Grant [grant numbers JP 17H02159, JP 26242068 and 18H04086], the Next Generation World-Leading Researchers Science Grant Promotion Program [JSPS Next Project No.
LS102], the University of Tokyo Innovation Research Project Strategic Research Fund, and the Tokyo Metropolitan Government Advanced Research Grant [RR -2].