Changes to the Skeletal Muscle Gene Expression Signature in Response to Nutrient and/or Mechanical Stimuli

Abstract

Nutrient consumption and mechanical overload influence skeletal muscle metabolism and function. These metabolic and functional outcomes are mediated at least in part by changes to the types of genes that are expressed in skeletal muscle. The extent to which nutrient consumption and mechanical overload act synergistically or independent of each other to change the skeletal muscle gene expression signature remains ill defined. Therefore, the purpose of this study was to define the differential and conserved gene expression responses to either nutrient consumption or mechanical overload as well as the combination of these stimuli. Published RNA‐Seq data sets generated from the muscle of humans subjected to acute resistance exercise were uploaded into the Database for Annotation Visualization and Integrated Discovery (DAVID) to define important functional gene categories related to muscle metabolism and/or function. Genes from the functional categories of ‘cell cycle’, ‘FoxO pathway’, and ‘transcription’ were marked for analysis in a mouse model of acute feeding and mechanical overload. For this model, C57BL/6 mice were initially fasted beginning at 1700 hr. The next morning (0800‐1000 hr), mice were randomized to remain fasted or allowed access to food for 30 min. Then, a mechanical overload was placed upon the left tibialis anterior (TA) muscle of all mice by subjecting the muscle to 10 sets of 6 eccentric muscle contractions by unilateral electrical stimulation of the sciatic nerve. The contralateral TA served as the non‐overloaded control muscle. All mice were deprived of food following the contractions protocol until euthanasia 4 hr later. The relative mRNA expression of Gadd45a, Usp2, Foxo1, Foxo3, and Myod1 were determined by RT‐PCR. Feeding and contractions each decreased the mRNA expression of Gadd45a (cell cycle), Foxo1, and Foxo3 (FoxO pathway), with the combination of feeding and contractions acting to synergistically decrease the expression of each gene. Conversely, the mRNA expression of Usp2 (cell cycle) was decreased in response to muscle contractions, with no effect of feeding noted. Finally, the mRNA expression of Myod1 (transcription) was significantly increased in response to feeding, with contractions causing a differential change in direction of Myod1 mRNA expression depending upon the fasting/feeding state. These data show that nutrient consumption and mechanical overload have shared and differential effects on the skeletal muscle gene expression signature. A more thorough understanding of the genetic changes regulated by each stimulus alone, as well as the combination of stimuli, will provide novel insight for how nutrients and mechanical overload alter metabolism and function in muscle.