Effect of resistance exercise intensity on the expression of PGC-1alpha isoforms and the anabolic and catabolic signaling mediators, IGF-1 and myostatin, in human skeletal muscle.

Proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α) is a protein mechanistically involved in skeletal muscle adaptations to exercise. Recently, novel isoforms of PGC-1α have been identified, one of which (PGC-1α4) may be important for the development of muscle hypertrophy and strength in response to resistance exercise. Studies are needed to elucidate the specific resistance exercise conditions for which mRNA expression of the various PGC-1α isoforms is stimulated, particularly in humans. The purpose of this study was to describe the mRNA expression of the PGC-1α isoforms, and genes potentially under their regulation, in response to two resistance exercise intensities. In a cross-over design, ten participants performed two separate testing sessions involving a lower-body resistance exercise component consisting of a lower-intensity (50% of 1-repetition maximum; 1-RM) protocol and a higher-intensity (80% of 1-RM) protocol of equal volumes. Muscle samples were obtained at baseline, 45-min post-exercise (PE), 3-hr PE, 24-hr PE, and 48-hr PE. From each muscle sample, mRNA expression of PGC-1α1, PGC-1α2, PGC-1α3, PGC-1α4, myostatin, insulin-like growth factor-1Ea (IGF-1Ea), mechano growth factor (MGF), myosin heavy chain (MHC) I, MHC IIa, MHC IIx, was determined. Two-way repeated-measures analyses of variance (ANOVA) were performed (p ≤ 0.05) with intensity and time as main effects. Significant main effects existed for time for all PGC-1α and MHC isoforms (p < .05). Compared with baseline, PGC-1α1 was decreased at 24-hr and 48-hr PE. Conversely, PGC-1α2, PGC-1α3, and PGC-1α4 mRNA expression increased in response to exercise, peaking at 3-hr PE. MHC I, IIa, and IIx mRNA expression decreased at all time points measured following exercise. A significant interaction between intensity and time for IGF-1Ea was observed (p < .05). For the higher-intensity session, IGF-1Ea was increased at 24-hr PE compared with baseline and the lower-intensity session at the same time point (p < .05). The results of this study demonstrate an effect of resistance exercise on the expression of the novel PGC-1α isoforms without influence of intensity. Future research should determine if resistance exercise alters the expression of these genes at the translational level and if these potential effects contribute to skeletal muscle training adaptations in humans.Ph.D