Lack of skeletal muscle atrophy and myosin isoform changes in a rodent hibernator, Spermophilus lateralis, subjected to activity restriction

Abstract

Hibernating ground squirrels demonstrate a greatly reduced, or even an absence of, atrophy in a variety of skeletal muscles and the heart during 4‐6 months of winter dormancy. We test whether these muscles are equally insensitive to inactivity induced reductions in muscle mass and changes in myosin heavy‐chain (MyHC) isoform expression. Field‐caught ground squirrels were captured during their Summer‐active periods, and subjected to cage restriction (small, individual and larger, group cages). Soleus, plantaris, medial and lateral gastrocnemius, diaphragm and cardiac muscles were studied for changes in muscle mass, MyHC isoform expression, citrate synthase activity, and atrophy related genes. Citrate synthase activity and mass was unchanged in all skeletal muscles and the heart. Cardiac alpha MyHC isoform expression was significantly increased in cage‐restricted animals. MAFbx, MuRF1, FOXO1, IGF1 and IGFBP5, and myostatin mRNA expression were also determined through RT‐PCR. The results demonstrate that activity restriction does not significantly alter skeletal muscle mass or MyHC isoform expression even in non‐hibernating ground squirrels and mechanistically suggests that protection during hibernation is an intrinsic adaptation. Funding sources: NIH SCORE, NIH RISE, CSULB.