Effects of defined voluntary running distances coupled with high-fat diet consumption on the murine skeletal muscle transcriptome
Exercise counters many adverse health effects of consuming a high-fat diet (HFD). However, the complex molecular changes that occur in skeletal muscle in response to exercising while consuming a HFD are not yet known. We investigated the interplay between diverse exercise regimes and HFD consumption for 12 weeks on the adaptation of the skeletal muscle transcriptome. C57BL/6 male mice were randomized into six groups – two sedentary control groups and four exercise groups. An unrestricted running group that averaged 8.3 km/day and exercise groups that were restricted to 75%, 50%, or 25% of unrestricted running that averaged 6.3, 4.2, and 2.1 km/day, respectively. Control groups were fed either an AIN93G diet or a HFD (HFD-C) and the exercise groups were fed the HFD. Total RNA was extracted from flash frozen gastrocnemius muscle for sequencing and transcriptome analyses. A total of 12053 transcripts were differentially expressed in the exercise groups compared to the HFD-C. When comparing the HFD-C and the different exercise groups, exercising at 50% of unrestricted access (HFD-50%) resulted in maximum differentially expressed transcripts. Genes down regulated in HFD-50% group were mostly associated with MAPK and cAMP signaling pathways, whereas up-regulated genes were associated with PPAR and JAK-STAT signaling pathways, along with tryptophan and nitrogen metabolism. These results demonstrate that running distance has a significant impact on the adaptation of the skeletal muscle transcriptome to exercise. Furthermore, transcriptome adaptations were more prominent in response to middle-distance running. Overall design: Three to four weeks old C57BL/6 male mice were randomly assigned to one of six groups – two sedentary control groups and four exercise groups. One of the sedentary control groups was fed the AIN93G diet (NFD-C) and the other sedentary control group was fed the HFD (HFD-C). The four exercise groups were fed the HFD and had access to an in-cage running wheel equipped with programmable brakes (Model 86120, Scurry Activity Monitoring Systems, Lafayette Instrument, Lafayette, Ind.). One group had unrestricted access to the running wheel and averaged 8.3 km/day (HFD-U). The running distance of the HFD-U was then used to calculate the running distance of the other groups so that running was restricted by 75%, 50%, or 25% with average running distances of 6.3, 4.2, and 2.1 km/day, respectively. Brakes were released at Zeitgeber time 12 (light off) for restricted runners and applied when they met their assigned daily running activities. After 12 weeks the mice were euthanized and both gastrocnemius muscles were collected, flash frozen, and store at -80°C.