Graded reductions in pre-exercise glycogen concentration do not augment exercise-induced nuclear AMPK and PGC-1α protein content in human muscle

Hearris, MA ORCID: https://orcid.org/0000-0003-4909-6755, Owens, DJ, Strauss, JA, Shepherd, SO ORCID: https://orcid.org/0000-0001-6292-1356, Sharples, AP, Morton, JP and Louis, JB ORCID: https://orcid.org/0000-0002-9109-0958 (2020) Graded reductions in pre-exercise glycogen concentration do not augment exercise-induced nuclear AMPK and PGC-1α protein content in human muscle. Experimental Physiology, 105 (11). pp. 1882-1894. ISSN 0958-0670

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Abstract

New Findings: What is the central question of this study? What is the absolute level of pre-exercise glycogen concentration required to augment the exercise-induced signalling response regulating mitochondrial biogenesis? What is the main finding and its importance? Commencing high-intensity endurance exercise with reduced pre-exercise muscle glycogen concentrations confers no additional benefit to the early signalling responses that regulate mitochondrial biogenesis. Abstract: We examined the effects of graded muscle glycogen on the subcellular location and protein content of AMP-activated protein kinase (AMPK) and peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) and mRNA expression of genes associated with the regulation of mitochondrial biogenesis and substrate utilisation in human skeletal muscle. In a repeated measures design, eight trained male cyclists completed acute high-intensity interval (HIT) cycling (8 × 5 min at 80% peak power output) with graded concentrations of pre-exercise muscle glycogen. Following initial glycogen-depleting exercise, subjects ingested 2 g kg−1 (L-CHO), 6 g kg−1 (M-CHO) or 14 g kg−1 (H-CHO) of carbohydrate during a 36 h period, such that exercise was commenced with graded (P < 0.05) muscle glycogen concentrations (mmol (kg dw)−1: H-CHO, 531 ± 83; M-CHO, 332 ± 88; L-CHO, 208 ± 79). Exercise depleted muscle glycogen to <300 mmol (kg dw)−1 in all trials (mmol (kg dw)−1: H-CHO, 270 ± 88; M-CHO, 173 ± 74; L-CHO, 100 ± 42) and induced comparable increases in nuclear AMPK protein content (∼2-fold) and PGC-1α (∼5-fold), p53 (∼1.5-fold) and carnitine palmitoyltransferase 1 (∼2-fold) mRNA between trials (all P < 0.05). The magnitude of increase in PGC-1α mRNA was also positively correlated with post-exercise glycogen concentration (P < 0.05). In contrast, neither exercise nor carbohydrate availability affected the subcellular location of PGC-1α protein or PPAR, SCO2, SIRT1, DRP1, MFN2 or CD36 mRNA. Using a sleep-low, train-low model with a high-intensity endurance exercise stimulus, we conclude that pre-exercise muscle glycogen does not modulate skeletal muscle cell signalling.