Effects of Dexamethasone Dose and Timing on Tissue-Engineered Skeletal Muscle Units.

Our lab showed that administration of dexamethasone (DEX) stimulated myogenesis and resulted in advanced structure in our engineered skeletal muscle units (SMU). While administration of 25 nM DEX resulted in the most advanced structure, 10 nM dosing resulted in the greatest force production. We hypothesized that administration of 25 nM DEX during the entire fabrication process was toxic to the cells and that administration of DEX at precise time points during myogenesis would result in SMU with a more advanced structure and function. Thus, we fabricated SMU with 25 nM DEX administered at early proliferation (days 0-4), late proliferation (days 3-5), and early differentiation (days 5-7) stages of myogenesis and compared them to SMU treated with 10 nM DEX (days 0-16). Cell proliferation was measured with a BrdU assay (day 4) and myogenesis was examined by immunostaining for MyoD (day 4), myogenin (day 7), and α-actinin (day 11). Following SMU formation, isometric tetanic force production was measured. An analysis of cell proliferation indicated that 25 nM DEX administered at early proliferation (days 0-4) provided 21.5% greater myogenic proliferation than 10 nM DEX (days 0-4). In addition, 25 nM DEX administered at early differentiation (days 5-7) showed the highest density of myogenin-positive cells, demonstrating the greatest improvement in differentiation of myoblasts. However, the most advanced sarcomeric structure and the highest force production were exhibited with sustained administration of 10 nM DEX (days 0-16). In conclusion, alteration of the timing of 25 nM DEX administration did not enhance the structure or function of our SMU. SMU were optimally fabricated with sustained administration of 10 nM DEX.