Skeletal muscle tissue engineering: a maturation model promoting long-term survival of myotubes, structural development of the excitation-contraction coupling apparatus and neonatal myosin heavy chain expression.

The use of defined in vitro systems to study the developmental and physiological characteristics of a variety of cell types is increasing, due in large part to their ease of integration with tissue engineering, regenerative medicine, and high-throughput screening applications. In this study, myotubes derived from fetal rat hind limbs were induced to develop several aspects of mature muscle including: sarcomere assembly, development of the excitation-contraction coupling apparatus and myosin heavy chain (MHC) class switching. Utilizing immunocytochemical analysis, anisotropic and isotropic band formation (striations) within the myotubes was established, indicative of sarcomere formation. In addition, clusters of ryanodine receptors were colocalized with dihydropyridine complex proteins which signaled development of the excitation-contraction coupling apparatus and transverse tubule biogenesis. The myotubes also exhibited MHC class switching from embryonic to neonatal MHC. Lastly, the myotubes survived significantly longer in culture (70-90 days) than myotubes from our previously developed system (20-25 days). These results were achieved by modifying the culture timeline as well as the development of a new medium formulation. This defined model system for skeletal muscle maturation supports the goal of developing physiologically relevant muscle constructs for use in tissue engineering and regenerative medicine as well as for high-throughput screening applications.