J. Max Michel1, Daniel L. Plotkin1, Joshua S. Godwin1, Paulo H.C. Mesquita1, Bradley A. Ruple1, Mason C. McIntosh1, Cleiton A. Libardi2, Andreas N. Kavazis1, Michael D. Roberts3,1. 1Auburn University, Auburn, AL. 2Federal University of Sao Carlos, Sao Carlos, Brazil. 3Edward Via College of Osteopathic Medicine-Auburn Campus, Auburn, AL.

BACKGROUND: Skeletal muscle is a highly plastic tissue that uniquely responds to different external stimuli. While resistance training (RT) induces skeletal muscle hypertrophy, the effects of high-intensity interval training (HIIT) are less clear, with certain evidence indicating mild hypertrophy and other evidence suggesting no change in measurable outcomes. Our laboratory recently observed an increase in vastus lateralis thickness after seven weeks of RT (2 d/wk), with values returning to pre-training levels following seven weeks of treadmill HIIT (3 d/wk). Given that proteolytic mechanisms were not previously investigated, the purpose of this study was to examine the effects of the aforementioned exercise paradigm on markers of the ubiquitin-proteasome system (UPS). METHODS: Vastus lateralis biopsies were collected from 11 untrained college-aged males at baseline (PRE), after seven weeks of RT (MID) and after a subsequent seven weeks of HIIT (POST). Tissue was analyzed for atrogene mRNA expression, proteins associated with the UPS, and 20S proteasome activity. Data were checked for normality using Shapiro-Wilk tests and analyzed via one-way ANOVAs. RESULTS: Muscle really interesting new gene (RING) finger 1 (MuRF1), Atrogin-1, and forkhead box O3a (FOXO3a) all achieved significance at the overall ANOVA level (p≤0.0129). These mRNAs were all significantly upregulated at POST as compared to both PRE (p≤0.0315), and MID (p≤0.0315). Poly-ubiquitinated proteins achieved overall ANOVA significance (p=0.0185) and trended toward a significant increase at both MID (p=0.0694) and POST (p=0.0529). Protein abundance of the 20S proteasome core demonstrated overall ANOVA significance (p=0.0096) and showed increases at POST as compared to both PRE (p=0.0311) and MID (p=0.0485). Finally, 20S proteasome activity demonstrated overall ANOVA significance (p=0.0031) and showed increases from PRE at both MID (p=0.0011) and POST (p=0.0040). CONCLUSIONS: Markers of the UPS were upregulated at POST at the mRNA, protein, and activity level suggesting that the UPS played a role in the HIIT-induced atrophy that occurred following a prior seven-week RT program.

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