The 24-Hour Time Course of Integrated Molecular Responses to Resistance Exercise in Human Skeletal Muscle Implicates MYC as a Hypertrophic Regulator

Molecular control of recovery after exercise in muscle is temporally dynamic. A time course of biopsies around resistance exercise (RE) combined with -omics is necessary to better comprehend the molecular choreography of skeletal muscle adaptation in humans. We collected vastus lateralis biopsies before and 30 minutes, 3-, 8-, and 24 hours after acute RE. RNA-sequencing defined the transcriptome and a time-point matched biopsy only group were controls. DNA methylomics and computational approaches complimented the transcriptome data. Moreover, we tested whether cyclic transient overexpression of transcription factor MYC for 4 weeks were sufficient to induce skeletal muscle hypertrophy in female mice. Thirteen recreationally active volunteers volunteered to participate in the study. Eight in the RE group (age of 32±5 years, height of 181±9 cm, weight of 83±8 kg, and body mass index (BMI) of 25.3±2.0), and five in the CON group (age of 30±4 years, height of 177±5 cm, weight of 85±12 kg, and finally a BMI of 27.3±3.6). Following an overnight fast, volunteers consumed a standardized amount of liquid formula for breakfast. One hour after the breakfast, skeletal muscle biopsies were collected from the vastus lateralis using a Bergström needle. Ninety minutes after breakfast, volunteers started a 45 minute standardized RE session (7 reps x 7 set on leg press and leg extension machines; RE group) or rested for 45 minutes (CON group). Biopsies were again collected at 30 minutes, 3-, 8-, and 24 hours after exercise cessation. Biopsies were time point matched in the CON group. A standardized lunch was administered following the biopsy at 3 hours post RE. Following the 8-hour biopsy, volunteers were sent home overnight and instructed to eat a healthy dinner. The morning after, volunteers again received a standardized breakfast prior to donating their final biopsy, 24 hours after RE. Approximately 25 mg of muscle tissue from each biopsy was homogenized in TRI Reagent (Sigma-Aldrich, St Louis, MO, USA). RNA isolated using bromochloropropane and centrifugation. Next, the RNA was processed using Direct-zol filter columns (Zymo Research, Irvine, CA, USA). Finally, the RNA was treated with DNAse and eluted in DEPC-treated water prior to storage at -80°C. The concentration and purity of the RNA were determined using a BioTek PowerWave XS microplate reader (BioTek Instruments Inc., Winooski, VT, USA). mRNA library preparation was done using Poly A enrichment, followed by RNA sequencing by an Illumina NovaSeq 6000 (Novogene Corp. Inc., Sacramento, CA, USA) using 150 bp paired-end sequencing.