Uniaxial cyclic strain drives assembly and differentiation of skeletal myocytes

Ex vivo engineering of skeletal muscle represents an exciting new area of biotechnology. Although the ability of skeletal muscle cells to sense and respond to mechanical forces is well known, strategies based on the use of mechanical stimuli to optimize myogenesis in vitro remain limited. In this work, we describe a simple but powerful method based on uniaxial cyclic tensile strain (CTS) to induce assembly and differentiation of skeletal myocytes in vitro. Confluent mouse myoblastic precursors cultured on flexible-bottomed culture plates were subjected to either uniaxial or equibiaxial CTS. The uniaxial CTS protocol resulted in a highly aligned array of cross-striated fibers, with the major axis of most cells aligned perpendicularly to the axis of strain. In addition, a short period of myogenin activation and significant increase in the myotube/myoblast ratio and percentage of myosin-positive myotubes was found, indicating an enhanced cell differentiation. In contrast, cells under equibiaxial strain regimen had no clear orientation and displayed signs of membrane damage and impaired differentiation. These results, thus, demonstrate that the selection of a proper paradigm is a key element when discussing the relevance of mechanical stimulation for myogenesis in vitro. This study provides a rational framework to optimize engineering of functional skeletal muscle.