Arrestin domain containing 2 is highly induced in response to disuse in young and aged muscle and is sufficient to lower C2C12 myotube diameter

Arrestin Domain Containing 2 and 3 (Arrdc2/3) are genes whose mRNA contents are decreased in young skeletal muscle following mechanical overload. Arrdc3 is linked to the regulation of signaling pathways in non-muscle cells that could influence skeletal muscle size. Despite a similar amino acid sequence, Arrdc2 function remains undefined. The purpose of this study was to further explore the relationship of Arrdc2/Arrdc3 expression with changes in mechanical load in young and aged muscle and define the effect of Arrdc2/3 expression on myotube diameter. In young and aged mice, mechanical load was decreased using hindlimb suspension while mechanical load was increased by reloading previously unloaded muscle or inducing high force contractions. Arrdc2 and Arrdc3 mRNAs were overexpressed in C2C12 myotubes using adenoviruses. Myotube diameter was determined 48 h post-transfection and RNA sequencing was performed on those samples. Arrdc2 and Arrdc3 mRNA content was higher in the unloaded muscle within 1 day of disuse and remained higher up through 10 days. The induction of Arrdc2 mRNA was more pronounced in aged muscle than young muscle in response to unloading. Reloading previously unloaded muscle of young and aged mice restored Arrdc2 and Arrdc3 levels to ambulatory levels. Increasing mechanical load beyond normal ambulatory levels lowered Arrdc2 but not Arrdc3 mRNA in young and aged muscle. Arrdc2, not Arrdc3, overexpression was sufficient to lower myotube diameter in C2C12 cells in part by altering the transcriptome favoring muscle atrophy. These data are consistent with Arrdc2 contributing to disuse atrophy, particularly in aged muscle. C2C12 myotubes were transfected 3 days post-differentiation using adenoviruses encoding Arrdc2+Gfp or only Gfp as a control. Forty-eight h post-transfection, C2C12 myotubes were harvested and RNA was extracted. RNA-Seq was used to compare differentially expressed genes between Arrdc2 overexpressing vs. Gfp only myotubes.