Dexamethasone leads to Zn 2+ accumulation and increased unbound Zn 2+ in C2C12 muscle and 3T3-L1 adipose cells

Skeletal muscle atrophy is associated with increases in circulating glucocorticoid levels and insulin resistance. Zinc accumulates in atrophic muscle, but the relationship between atrophy, insulin resistance, and Zn homeostasis remains unclear. In this study, the effect of the glucocorticoid dexamethasone (DEX) on insulin and Zn homeostasis was explored. Treatment of differentiated C2C12 skeletal myotubes and 3T3-L1 adipocytes with DEX significantly increased mRNA expression of the metal-binding proteins Mt1 and 2 and altered energy storage as shown by the increased size of lipid droplets in 3T3-L1 cells. In C2C12 cells the total cellular Zn was higher after DEX treatment, and in both C2C12 and 3T3-L1 adipocytes, free unbound Zn was increased. Insulin treatment led to a gradual increase in free Zn in C2C12 cells, and no significant change in DEX-treated cells such that concentrations were similar 10 min after insulin treatment. These data demonstrate that DEX disturbs Zn homeostasis in muscle and fat cells. Further study of the molecular pathways involved to identify novel therapeutic targets for treatment of skeletal muscle atrophy is warranted.