Skeletal muscle preservation in arctic ground squirrels during hibernation season

Reduced skeletal loading and inactivity leads to muscle atrophy in humans and most mammals. By contrast, hibernating mammals demonstrate limited loss of skeletal muscle mass and strength by the end of winter after being physically inactive for several months. The present study objective was to detect any signs of muscle atrophy and restoration in arctic ground squirrel (AGS) skeletal muscles during the hibernation season. Quadriceps muscles of juvenile AGS males were collected 1–2 weeks before hibernation, and at 2, 6, 10–12 and 16–22 weeks after onset of hibernation during interbout arousal when body temperature returns to euthermic level. Muscle mass, fiber cross-sectional area (CSA) and fiber type composition were determined, as well as total and ribosomal RNA content, and expression of key genes involved in protein degradation. We found that muscle mass, CSA and fiber size distribution were not different between the groups (P > 0.05). No difference was detected in myofiber composition between the hibernation groups compared to pre-hibernation. Total RNA and ribosomal RNA content were not significantly different between the groups during hibernation. Transcript levels of ubiquitin E3-ligase FBXO32 (Atrogin-1, MAFbx) and autophagy related genes MAP1LC3A and BECN1 were not different between the hibernation and pre-hibernation groups. However, ubiquitin E3-ligase TRIM63 (MuRF-1) was significantly higher expressed at 2 weeks of hibernation compared to the other timepoints. These results, for the first time, show that AGS preserve muscles during hibernation season.