The Effect of Gas6‐Axl Double Knockout on Satellite Cell Proliferation and Skeletal Muscle Regeneration After Injury

Growth arrest‐specific 6 (Gas6) is an extracellular signaling molecule that is known to play a role in cell proliferation, inflammation and other processes through its interaction with Tyro3, Axl, and Mer receptors, but little is known about its role in skeletal muscle. The purpose of this study was to examine the effects of Gas6‐Axl double knockout (dKO) in skeletal muscle recovery after injury. Muscle injury was produced by injecting BaCl 2 into tibialis anterior (TA) muscles of wild type (WT) and dKO mice. Muscle tissue was harvested 3, 7, and 14 days after injury. Gas6 and Axl expression over the injury timecourse was characterized by western blotting and ELISA. Muscle damage and cross‐sectional fiber areas were assessed on hematoxylin and eosin (H&E) stained sections. Muscle satellite cell content and proliferation were assessed by Pax7/Ki‐67 staining. We found that both Gas6 and Axl protein expression increased substantially after injury in WT muscles, peaked at 3 days post injury, then declined toward basal levels thereafter. TA mass was lower for dKO muscles 14 days after injury, but fiber CSA was elevated in dKO muscles, suggesting a deficit in fiber number leading to compensatory hypertrophy of existing fibers. Pax7‐positive satellite cell number was unaffected by genotype in uninjured control muscles, but was ~3X higher in WT vs. dKO muscles at 3 days post injury, suggesting that the rate of satellite cell proliferation was suppressed or delayed by dKO. These results indicate that Gas6‐Axl signaling plays a role in regulating skeletal muscle regeneration after injury. Impaired Gas6 function may be linked to excess hypertrophy and loss of muscle mass after injury. Support or Funding Information This work was supported by a grant from the Flight Attendant’s Medical Research Institute (FAMRI) and a BYU Graduate Research Fellowship.