Conserved and species-specific transcriptional responses to daily programmed resistance exercise in rat and mouse.

Mice are often used in gain or loss of function studies to understand how genes regulate metabolism and adaptation to exercise in skeletal muscle. Once-daily resistance training with electrical nerve stimulation produces hypertrophy of the dorsiflexors in rat, but not in mouse. Using implantable pulse generators, we assessed the acute transcriptional response (1-hour post exercise) after 2, 10 and 20 days of training in free living mice and rats using identical nerve stimulation paradigms. RNA-sequencing revealed strong concordance in the timecourse of many transcriptional responses in the tibialis anterior muscles of both species including responses related to stress responses/immediate-early genes, and collagen homeostasis, ribosomal subunits, autophagy and focal adhesion. However, pathways associated with energy metabolism including carbon metabolism, oxidative phosphorylation, mitochondrial translation, propanoate metabolism and valine, leucine and isoleucine degradation were oppositely regulated between species. These pathways were suppressed in the rat but upregulated in the mouse. Our transcriptional analysis suggests that although many pathways associated with growth show remarkable similarities between species, absence of an actual growth response in the mouse may be because the mouse prioritises energy metabolism, specifically replenishment of fuel stores and intermediate metabolites.