Fabricating Muscle-Neuron Constructs with Improved Contractile Force Generation.

Tissue-engineered skeletal muscle constructs have attracted significant attention in the field of regenerative medicine. However, the contractile force produced by tissue-engineered skeletal muscle constructs is not comparable with that of natural skeletal muscle tissues. To improve contractile force generation of tissue-engineered skeletal muscle constructs, we investigated the effects of co-culturing C2C12 myoblasts with PC12 neural cells in the fabrication of skeletal muscle tissue constructs. Immunocytochemical analysis revealed differentiation of C2C12 myotubes and outgrowth of PC12 neurites toward the aligned myotubes with improved βIII-tubulin-positive neuronal area, suggesting enhanced neural differentiation of PC12 cells. Furthermore, co-culturing with PC12 cells improved the formation of sarcomeres and contractile activities of C2C12 myotubes, while the addition of nerve growth factor enhanced PC12 neurite outgrowth and further enhanced C2C12 myotube contractile activities. Formation of neuromuscular junctions in the C2C12/PC12 co-culture system was evidenced by the formation of acetylcholine receptor clusters, chemical inhibition of contractile myotubes, and expression of agrin. We then applied this co-culture system to the fabrication of neuron-incorporated skeletal muscle constructs using the magnetic force-based tissue engineering technique. In response to electrical pulses, the co-cultured tissue constructs generated maximum twitch (65.8 μN/mm2 ) and tetanic (135.1 μN/mm2 ) forces that were twofold higher than those of C2C12 monocultured constructs (twitch force, 36.3 μN/mm2 ; tetanic force, 65.9 μN/mm2 ). These results indicate that the nerve cell-incorporated skeletal muscle tissues constructed in this study could be used in drug testing and biological research for neuromuscular diseases.