The effects of acute aerobic and resistance exercise on mTOR signaling and autophagy markers in untrained human skeletal muscle

Purpose Aerobic (AE) and resistance (RE) exercise elicit unique adaptations in skeletal muscle. The purpose here was to compare the post-exercise response of mTOR signaling and select autophagy markers in skeletal muscle to acute AE and RE. Methods In a randomized, cross-over design, six untrained men (27 +/- 3 years) completed acute AE (40 min cycling, 70% HRmax) and RE (8 sets, 10 repetitions, 65% 1RM). Muscle biopsies were taken at baseline, and at 1 h and 4 h following each exercise. Western blot analyses were performed to examine total and phosphorylated protein levels. Upstream regulator analyses of skeletal muscle transcriptomics were performed to discern the predicted activation states of mTOR and FOXO3. Results Compared to AE, acute RE resulted in greater phosphorylation (P < 0.05) of mTOR(Ser)(2448) at 4 h, S6K1(Thr)(389) at 1 h, and 4E- BP1(Thr37/46) during the post-exercise period. However, both AE and RE increased mTOR(Ser2448) and S6K1(Thr389) phosphorylation at 4 h (P < 0.05). Upstream regulator analyses revealed the activation state of mTOR was increased for both AE (z score, 2.617) and RE (z score, 2.789). No changes in LC3BI protein were observed following AE or RE (P > 0.05), however, LC3BII protein was decreased after both AE and RE at 1 h and 4 h (P < 0.05). p62 protein content was also decreased at 4 h following AE and RE (P < 0.05). Conclusion Both acute AE and RE stimulate mTOR signaling and similarly impact select markers of autophagy. These findings indicate the early adaptive response of untrained human skeletal muscle to divergent exercise modes is not likely mediated through large differences in mTOR signaling or autophagy.