Differential protein metabolism and regeneration in hypertrophic diaphragm and atrophic gastrocnemius muscles in hibernating Daurian ground squirrels

Abstract

41Whether differences in regulation of protein metabolism and regeneration are involved in the 42 different phenotypic adaptation mechanisms of muscle hypertrophy and atrophy in hibernators? 43Two fast-type muscles (diaphragm and gastrocnemius) in summer active and hibernating Daurian 44 ground squirrels were selected to detect changes in cross-sectional area (CSA), fiber type 45 distribution, and protein expression indicative of protein synthesis metabolism (protein expression 46 of P-Akt, P-mTORC1, P-S6K1, and P-4E-BP1), protein degradation metabolism (MuRF1, atrogin-47 1, calpain-1, calpain-2, calpastatin, desmin, troponin T, Beclin1, and LC3-II), and muscle 48 regeneration (MyoD, myogenin, and myostatin). Results showed the CSA of the diaphragm muscle 49 increased significantly by 26.1%, whereas the CSA of the gastrocnemius muscle decreased 50 significantly by 20.4% in the hibernation group compared with the summer active group. Both 51 muscles displayed a significant fast-to-slow fiber-type transition in hibernation. Our study further 52 indicated that increased protein synthesis, decreased protein degradation, and increased muscle 53 regeneration potential contributed to diaphragm muscle hypertrophy, whereas decreased protein 54 synthesis, increased protein degradation, and decreased muscle regeneration potential contributed 55 to gastrocnemius muscle atrophy. In conclusion, the differences in muscle regeneration and 56 regulatory pattern of protein metabolism may contribute to the different adaptive changes observed 57 in the diaphragm and gastrocnemius muscles of ground squirrels. 58 59

Torpor versus interbout arousal: what is more important for protein metabolism and regeneration?

“…In this issue of Experimental Physiology , Yan et al. (2021) shed light on the distinctive features of the molecular mechanisms involved in the development of the hypertrophic response in the diaphragm and the atrophic response in the gastrocnemius muscle in hibernating Daurian ground squirrels. In particular, the authors showed that a decrease in protein synthesis, an increase in protein degradation and a decrease in muscle regeneration potential contributed to the atrophy of the gastrocnemius muscles during torpor, while an increase in protein synthesis, a decrease in protein degradation and an increase in muscle regeneration potential contributed to diaphragm muscle hypertrophy.…”