Cyclic Tensile Stress Induces Skeletal Muscle Hypertrophy and Myonuclear Accretion in a 3D Model

Skeletal muscle is highly adaptive to mechanical stress due to its resident stem cells and the pronounced level of myotube plasticity. Herein, we study the adaptation to mechanical stress and its underlying molecular mechanisms in a tissue-engineered skeletal muscle model. We subjected differentiated 3D skeletal muscle-like constructs to cyclic tensile stress using a custom-made bioreactor system, which resulted in immediate activation of stress-related signal transducers (Erk1/2, p38). Cell cycle re-entry, increased proliferation, and onset of myogenesis indicated subsequent myoblast activation. Furthermore, elevated focal adhesion kinase and β-catenin activity in mechanically stressed constructs suggested increased cell adhesion and migration. After 3 days of mechanical stress, gene expression of the fusogenic markers MyoMaker and MyoMixer, myotube diameter, myonuclear accretion, as well as S6 activation, were significantly increased. Our results highlight that we established a promising tool to study sustained adaptation to mechanical stress in healthy, hypertrophic, or regenerating skeletal muscle. Impact statement Sustained adaption to mechanical stress presents a key feature for skeletal muscle functionality and growth. Knowledge of these processes, however, is mostly based on in vivo or 2D cell culture models, both of which entail significant shortcomings. Herein, we generated highly hypertrophic tissue-engineered skeletal muscle-like constructs that are comparable to the results of successful in vivo models of adaption to mechanical stimuli, achieving an outcome that only few in vitro approaches have reached. Second, we aimed at studying the underlying molecular mechanisms, which is of interest since there is little knowledge of the intracellular events during hypertrophy upon mechanical stimulation.