Effect of 20-hydroxyecdysone and its metabolites in the absence or presence of IGF-1 on regulation of skeletal muscle cell growth

Purpose: To investigate the effect of 20-hydroxyecdysone (20E) and its metabolites and their synergistic effect with IGF-1 on regulation of skeletal muscle cell growth. Methods: Mouse skeletal muscle cell line (C2C12) was solely treated with 20E and its metabolites (14- deoxy- 20-hydroxyecdysone, poststerone, and 14-deoxypoststerone) at doses of 0.1, 1, and 10 µM or co-treated with IGF-1 (10 ng/ml). Cell viability and proliferative capacity were evaluated using MTT and BrdU incorporation assays, respectively. Myogenic differentiation proteins [embryonic myosin heavy chain (EbMHC) and MHC], androgen receptor (AR), and IGF-1 receptor (IGF-1R) protein expression were investigated using immunocytochemistry. Results: Treatments of 20E and its metabolites had no toxicity on skeletal muscle cells or induced AR/IGF-1R expression. In addition, solely treatment of 20E and its metabolites or co-treatment with IGF-1 had no significant effect on cell proliferation and myogenic differentiation capacity. In contrast, IGF-1 treatment alone significantly increased EbMHC expression (p<0.0001), MHC expression (p<0.05), and myotube number (p<0.05). Conclusion: These results indicate that 20E and its metabolites have no direct or synergistic effect with IGF-1 on skeletal muscle cell growth. Nevertheless, the pharmacological effects of 20E on skeletal muscle mass and strength in vivo that raises its therapeutic potential may associate with its indirect action.