Muscle Atrophy in the C2C12 Myotube Model upon Treatment with Dexamethasone

Muscle atrophy is the decrease of muscle size that leads to a decrease in force production, and can affect individuals at every stage of life.  Muscle atrophy occurs in several conditions including starvation, immobilization, cancer, and aging, and as a side effect of anti-inflammatory glucocorticoid treatment.  Skeletal muscle mass is maintained by a balance between protein synthesis and protein degradation, and skeletal muscle is an important reservoir of amino acids under catabolic conditions. It is important to determine the pathways for muscle atrophy so that therapeutic targets to prevent atrophy can be discovered. Glucocorticoids induce muscle atrophy by binding to the glucocorticoid receptor (GR), a member of the nuclear hormone receptor superfamily. Two genes, MuRF1 and MAFbx, are E3 ubiquitin ligases and are up-regulated in skeletal muscle by synthetic glucocorticoids like dexamethasone (DEX).  These E3 ligases are proposed to target proteins within the sarcomere for degradation. Therefore, we are exploring the use of the Mus musculus myoblast cell line (C₂C₁₂) to help determine MuRF1 or MAFbx targets. C₂C₁₂ myoblasts are being differentiated into myotubes and treated with increasing concentrations of DEX for Western blot analysis of potential E3 ligase targets.  We hypothesize that DEX treatment will lead to decreases in protein levels of specific sarcomeric structural proteins coincident with increasing MuRF1 or MAFbx expression.  Further studies will include evaluation of new GR ligands designed to retain anti-inflammatory activity with fewer side effects like muscle atrophy, and exploring the use of primary myotubes derived from GR and MuRF1 knockout mice.