Proteolytic mRNA expression in response to acute resistance exercise in human single skeletal muscle fibers

J Appl Physiol (1985). 2006 Nov;101(5):1442-50. doi: 10.1152/japplphysiol.00438.2006. Epub 2006 Jul 13.


The purpose of this study was to characterize changes in mRNA expression of select proteolytic markers in human slow-twitch [myosin heavy chain (MHC) I] and fast-twitch (MHC IIa) single skeletal muscle fibers following a bout of resistance exercise (RE). Muscle biopsies were obtained from the vastus lateralis of eight young healthy sedentary men [23 +/- 2 yr (mean +/- SD), 93 +/- 17 kg, 183 +/- 6 cm] before and 4 and 24 h after 3 x 10 repetitions of bilateral knee extensions at 65% of one repetition maximum. The mRNA levels of TNF-alpha, calpains 1 and 2, muscle RING (really interesting novel gene) finger-1 (MuRF-1), atrogin-1, caspase-3, B-cell leukemia/lymphoma (Bcl)-2, and Bcl-2-associated X protein (Bax) were quantified using real-time RT-PCR. Generally, MHC I fibers had higher (1.6- to 5.0-fold, P < 0.05) mRNA expression pre- and post-RE. One exception was a higher (1.6- to 3.9-fold, P < 0.05) Bax-to-Bcl-2 mRNA ratio in MHC IIa fibers pre- and post-RE. RE increased (1.4- to 4.8-fold, P < 0.05) MuRF-1 and caspase-3 mRNA levels 4-24 h post-RE in both fiber types, whereas Bax-to-Bcl-2 mRNA ratio increased 2.2-fold (P < 0.05) at 4 h post-RE only in MHC I fibers. These results suggest that MHC I fibers have a greater proteolytic mRNA expression pre- and post-RE compared with MHC IIa fibers. The greatest mRNA induction following RE was in MuRF-1 and caspase-3 in both fiber types. This altered and specific proteolytic mRNA expression among slow- and fast-twitch muscle fibers indicates that the ubiquitin/proteasomal and caspase pathways may play an important role in muscle remodeling with RE.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Adult
  • Biomarkers / metabolism
  • Biopsy
  • Exercise / physiology*
  • Gene Expression
  • Humans
  • Male
  • Muscle Fibers, Fast-Twitch / metabolism*
  • Muscle Fibers, Slow-Twitch / metabolism*
  • Muscle Proteins / genetics*
  • Muscle Proteins / metabolism
  • Myosin Heavy Chains / genetics
  • Myosin Heavy Chains / metabolism
  • Protein Isoforms / genetics
  • Protein Isoforms / metabolism
  • Quadriceps Muscle / metabolism
  • RNA, Messenger / analysis
  • RNA, Messenger / biosynthesis*
  • Reverse Transcriptase Polymerase Chain Reaction
  • Weight Lifting / physiology*


  • Biomarkers
  • Muscle Proteins
  • Protein Isoforms
  • RNA, Messenger
  • Myosin Heavy Chains