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The mRNA Binding Protein AUF1 Controls the Regenerative Potential of Activated Skeletal Muscle Stem Cells

AU‐rich mRNA binding factor 1 (AUF1) is a promoter of mRNA decay. AUF1‐/‐ mice show loss of skeletal muscle mass and muscle weakness similar to limb girdle muscular dystrophy (LGMD). A mutation in a family cohort affected with LGMD was association‐mapped to the chromosomal location of human AUF1. We found that AUF1 levels increase in satellite cells following injury. We compared the rate of skeletal muscle regeneration between wild type (WT) and AUF1‐/‐ mice. 15 days following injury WT mice show repair while the AUF1‐/‐ mice show no regeneration. Mouse fiber culture studies show that AUF1‐/‐ satellite cells are unable to express the late stage myogenic regulatory factor, myogenin. We also observed a loss of Pax7, an early satellite cell marker, in AUF1‐/‐ satellite cells. This suggests that in the absence of AUF1 satellite cells cannot differentiate or return to quiescence. To understand the molecular role of AUF1, we completed studies using C2C12 cells. When AUF1 is partially silenced we observe delayed myogenesis due to reduced expression of Myogenin. The expression of nascent Myogenin was also reduced leading us to examine Myogenin regulating transcription factors. When AUF1 is partially silenced there is a 2.5 fold increase in Twist1, a Myogenin transcriptional repressor. Using RNA immuno‐precipitation we identified a direct interaction between AUF1 and Twist1 mRNA. This suggests that AUF1 mediated decay of Twist1 mRNA is crucial for the ability of activated satellite cells to express Myogenin and complete regeneration. Without AUF1 the satellite cell population maintains a “stem‐like” phenotype and depletes the quiescent population.