Key result
Acute resistance exercise increased MuRF-1 and caspase-3 mRNA levels 1.4- to 4.8-fold (P<0.05) at 4-24 hours post-exercise in both slow- and fast-twitch muscle fibers.
Effect estimate: 1.4- to 4.8-fold increase
p-value: p=< 0.05
Acute resistance exercise induces specific proteolytic mRNA expression, particularly MuRF-1 and caspase-3, in human skeletal muscle fibers, suggesting a role for ubiquitin/proteasomal and caspase pathways in muscle remodeling.
Hypothesis-generating for proteolytic activation after resistance exercise; leaves open effects on adaptation or clinical outcomes.
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.
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Yang et al. (2006) studied Healthy sedentary men (n=8). Resistance exercise vs. Pre-exercise baseline was evaluated on Changes in mRNA expression of select proteolytic markers in single skeletal muscle fibers (1.4- to 4.8-fold increase, p=< 0.05). Acute resistance exercise increased MuRF-1 and caspase-3 mRNA levels 1.4- to 4.8-fold (P<0.05) at 4-24 hours post-exercise in both slow- and fast-twitch muscle fibers.
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