miR-379 links glucocorticoid treatment with mitochondrial response in Duchenne muscular dystrophy.

Duchenne Muscular Dystrophy (DMD) is a lethal muscle disorder, caused by mutations in the DMD gene and affects approximately 1:5000-6000 male births. In this report, we identified dysregulation of members of the Dlk1-Dio3 miRNA cluster in muscle biopsies of the GRMD dog model. Of these, we selected miR-379 for a detailed investigation because its expression is high in the muscle, and is known to be responsive to glucocorticoid, a class of anti-inflammatory drugs commonly used in DMD patients. Bioinformatics analysis predicts that miR-379 targets EIF4G2, a translational factor, which is involved in the control of mitochondrial metabolic maturation. We confirmed in myoblasts that EIF4G2 is a direct target of miR-379, and identified the DAPIT mitochondrial protein as a translational target of EIF4G2. Knocking down DAPIT in skeletal myotubes resulted in reduced ATP synthesis and myogenic differentiation. We also demonstrated that this pathway is GC-responsive since treating mice with dexamethasone resulted in reduced muscle expression of miR-379 and increased expression of EIF4G2 and DAPIT. Furthermore, miR-379 seric level, which is also elevated in the plasma of DMD patients in comparison with age-matched controls, is reduced by GC treatment. Thus, this newly identified pathway may link GC treatment to a mitochondrial response in DMD.