Myokine increases both myoblast proliferation and myotube contractile strength.
Researchers from Tokyo Metropolitan University have found that that skeletal muscle cells continually release a protein called platelet-derived growth factor subunit B (PDGF-B), which aids in muscle repair by promoting the formation of myoblasts (muscle stem cells). Unexpectedly, the scientists discovered that PDGF-B also promotes the expansion of muscle fibres. They verified that this was consistent with fibres contracting more forcefully. Their research presents a revolutionary approach for the treatment of muscle damage and atrophy.
Small proteins known as myokines are secreted by skeletal muscle cells. They perform a variety of tasks and can influence cells both nearby and distant from the site of their creation. Although a complete understanding of how myokines affect cellular processes is still far from obvious, it is thought that they are crucial for exercise-related bodily functions, particularly the maintenance of muscle tissue.
At Tokyo Metropolitan University, a group under the direction of Associate Professor Yasuko Manabe has been examining how myokines influence the actions of muscle cells. Through extensive experiments, they found that a myokine known as platelet-derived growth factor subunit B, or PDGF-B, is secreted by skeletal muscles in a constitutive way i.e. without any stimulus. To better grasp the function it performs, they exposed myoblasts—precursor cells that eventually develop into muscle fibers—to PDGF-B. From it, they were able to demonstrate unequivocally how PDGF-B increased myoblast proliferation.
Curiously, they discovered that PDGF-B affected differentiated cells as well. They exposed myotubes, a developmental stage of muscle fibres, to the same myokine. Under a microscope, the treated myotubes showed noticeably increased maturation and a visible increase in diameter. Additionally, they expressed more Myosin Heavy Chain, a crucial component of the protein structure of myosin, which is the molecular motor responsible for muscle contraction. Using a recently developed method based on observing how myotubes react to an electric pulse, this was demonstrated to closely correlate with greater contractile strength. As a result, PDGF-B not only promotes muscle growth but also increases muscle strength. However, this does not imply that both processes are accelerated in a random manner. They observed minute variations in PDGF-B signalling pathways between myotubes and myoblasts; the team hypothesises that these variations may be responsible for cells transitioning from a proliferating phase to a maturing phase.
The team’s findings demonstrates that PDGF-B is involved in muscle regeneration and represents a significant advance in the creation of effective regimens for treating muscle injury and atrophy as well as enhancing muscle performance. [APBN]
Source: Hamaguchi et al. (2023). PDGF-B secreted from skeletal muscle enhances myoblast proliferation and myotube maturation via activation of the PDGFR signaling cascade. Biochemical and Biophysical Research Communications, 639, 169-175.