Genetic Variability and Sex Affect the Response of Skeletal Muscle to Extended Immobilization

Extended periods of mechanical disuse can cause changes to the musculoskeletal system, particularly impacting the composition and strength of the affected muscle. Genetics are known to play a role in the proportion of lean mass and risk for sarcopenia with age, though the role of genetic variability in muscle adaptation to disuse is largely unknown. A total of 77 DO mice were casted using the single limb immobilization for three weeks, then hindlimb muscle morphology and performance were quantified. Total RNAseq was performed on gastrocnemius muscles, then Ingenuity Pathway Analysis was used to analyze sequencing data. We found that casting decreased body mass and hindlimb muscle mass (p<0.0001). Analyzing skeletal muscle morphology, we found an increase in cross-sectional area and volume in males but not females (p<0.0001). Additionally, we found immobilized limbs had greater twitch torque, but there was no effect on tetanus torque (p<0.0001). RNA sequencing identified 47 total significant differentially expressed genes. Finally, pathway analysis revealed a sex-dependent response to immobilization. Taken together, these results indicate that single limb immobilization incudes physiological changes to skeletal muscle and changes gene expression in a sex-dependent manner. Ultimately, this work will allow researchers to develop treatments to combat disuse-induced muscle loss. Overall design: 16 week old Diversity Outbred (DO) mice were casted via single limb immobilization for a period of 3 weeks. RNA was isolated from gastrocnemius muscles and sequenced.