Autophagy Response To High-intensity Interval Exercise And Moderate-intensity Continuous Exercise Is Dissimilar In Skeletal Muscle And Peripheral Blood Mononuclear Cells

Abstract

Few human data exist investigating the autophagic response to exercise in humans including the response to high-intensity interval training (HIIT) compared to moderate-intensity continuous training (MICT). Further, the relationship between post-exercise autophagy in distinct tissues including skeletal muscle and peripheral blood mononuclear cells (PBMCs) is not known. PURPOSE: The purpose of this study was to investigate the autophagy response in skeletal muscle and PBMCs following an acute bout of HIIT exercise and MICT exercise. METHODS: Using a crossover design, ten recreationally-active males (n=5) and females (n=5) performed a bout of MICT (60 minutes at 55% of max velocity [Vmax]]) and HIIT (6 bouts of 1 minute at 100% Vmax and 1 minute at 3 MPH, followed by 5 minutes at 3 MPH, followed by another 6 bouts of 1 minute and 100% Vmax and 1 minute at 3 MPH). Muscle biopsies from the vastus lateralis and PBMCs from venous blood were collected pre- and 3 hours post-exercise. Exercise bouts were separated by ≥72 hours and performed after abstaining from alcohol for ≥24 hours and food and caffeine for ≥8 hours. Muscle tissue and PBMCs were analyzed for protein expression of markers of autophagy LC3I, LC3II, and p62 via western blot analysis. RESULTS: No differences were detected in LC3I, LC3II, and p62 protein content 3 hours post-exercise compared to pre-exercise in both HIIT and MICT bouts in skeletal muscle or PBMCs (p>0.05). However, LC3II:I ratio 3 hours post-exercise was different between HIIT (108.1 ±: 54.5%) and MICT (64.3± 47.3%; p<0.05) in skeletal muscle. There were no differences in LC3II:I in PBMCs between HIIT and MICT. CONCLUSION: Our findings show that HIIT and MICT exercise results in distinct changes in autophagy flux as suggested by LC3II:I in human skeletal muscle, but not in PBMCs. Our data suggest that the autophagy response to acute exercise in skeletal muscle and PBMCs are dissimilar which may indicate that distinct exercise thresholds exist.