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

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.