Tokyo, Japan – Researchers at Tokyo Metropolitan University have developed a way to characterize the force generated by the contraction of myotubes, the precursors of skeletal muscle fiber, combining electrostimulation and wrinkle analysis of the silicone substrate on which they are mounted. Existing methods rely on muscle mass or the expression of certain proteins, both of which are less strongly correlated with muscle strength. Accurate measurement of myotube strength promises more efficient screening of drug targets for the treatment of muscle atrophy.
Muscle atrophy, the breakdown of muscle tissue, can have a devastating effect on quality of life and is known to affect lifespan. The effects are particularly felt in aging populations, where the costs associated with medical interventions and day-to-day care are also significant. This makes the treatment and prevention of amyotrophy a key societal issue.
But the reality is that treatments for muscle atrophy remain very limited. One of the challenges holding back researchers is the lack of an effective screening system for new drug targets, particularly the impact of different compounds on muscle strength. Myotubes, the cylindrical clusters of cells that then form muscle fibers, can be isolated in the lab and studied in different biochemical environments, but measuring the force with which they contract remains difficult. That’s why existing methods look at proxy measures, such as muscle mass or the proteins they express, but these don’t always correlate strongly with how hard they can pull. In the past, it even led to clinical trials of drugs that seemed to show promise, but turned out not to lead to improved muscle strength.
Now, a team of researchers led by Associate Professor Yasuko Manabe of Tokyo Metropolitan University has found a simple way to directly measure the actual strength of myotubes. They examined myotubes mounted on a two-layer elastic silicone substrate, with a hard surface layer on top of a thicker, softer layer. When the myotubes were stimulated by an electrical pulse, the team found that the fibers contracted and deformed the surface of the substrate, forming a series of wrinkles clearly visible under a microscope. Through careful calibration experiments using a flexible needle of known stiffness, they were able to demonstrate that the total length of the wrinkles was directly correlated to the strength of the forces deforming the substrate. In the case of the myotubes, the length of the wrinkles corresponded to the force with which they could contract when stimulated.
Using known atrophic (weaker) and hypertrophic (stronger) myotubes, they found that their new “strength index” was much more sensitive to muscle strength than existing measures, such as muscle mass and expression. Myosin Heavy Chain (MHC) protein. The method is simple to deploy with standard microscopy and image analysis techniques, with wide scope for practical application in the laboratory. The team believe this will dramatically accelerate drug discovery in the fight against muscle atrophy.
This work was supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI Grant-in-Aid for Scientific Research (B) in the field of sports science (Grant Number JP 17H02159), the TMU Strategic Research Fund for innovative research projects and an advanced research grant from the Tokyo Metropolitan Government (R2-2).