ABSTRACT: We sought to determine skeletal muscle genome-wide DNA methylation and transcriptome changes to one bout of lower-load (LL) versus higher-load (HL) resistance exercise. Previously trained college-aged males (n=11, age: 23±4 years old, training experience: 4 ± 3 years) performed LL or HL bouts to failure separated by one week. The HL bout (a.k.a., 80 Fail) consisted of four sets of back squats and four sets of leg extensions to failure using 80% of their estimated one-repetition maximum (i.e., est. 1-RM from 3-RM testing), whereas the LL bout (a.k.a., 30 Fail) consisted of this same paradigm using 30% of their est. 1-RM. Vastus lateralis muscle biopsies were collected before, 3 hours, and 6 hours after each exercise bout. DNA and RNA were batch-isolated from muscle and analyzed for genome-wide DNA methylation and mRNA expression using the 850k Illumina MethylationEPIC array and Clariom S mRNA microarray, respectively. Although the total number of repetitions performed were significantly greater during the 30 Fail versus 80 Fail bout (p<0.001), total training volume (sets x reps x load) was not significantly different between conditions (p=0.571). Interestingly, 30 Fail led to decreased methylation across various promoter regions, albeit the transcriptome-wide responses between bouts were largely similar. According to bioinformatics, both bouts altered post-exercise mRNA profiles related to inflammatory signaling (e.g., Toll receptor, CCKR, chemokine and cytokine signaling), apoptosis, gonadotropin-releasing hormone, and integrin signaling. Also notable, more robust DNA methylation events occurred 3 hours versus 6 hours post-exercise regardless of bout (239,951 versus 12,419 CpG sites significantly hyper- or hypomethylated at these respective time points, p<0.01). Moreover, the percentage of significantly altered mRNAs that also demonstrated significantly inversed methylation patterns across one or more CpG sites was appreciably higher at 3 hours versus 6 hours following exercise (~75% versus ~15%, respectively). In conclusion, our transcriptomic data suggest that the molecular signaling events during the early post-exercise period are largely similar between LL and HL bouts, and this may explain why similar longer-term phenotypes (e.g., myofiber hypertrophy) result from these two training modalities. Additionally, our methylome data indicate that the majority of DNA methylation changes following an acute bout of resistance exercise occur rapidly (~3 hours) following exercise in previously trained men.
