Repeated-ischaemic exercise enhances mitochondrial and ion transport gene adaptations in human skeletal muscle – Role of muscle redox state and AMPK

Abstract

AbstractThis study assessed the effect of repeated-ischaemic exercise on the mRNA content of PGC-1α (total, 1α1, and 1α4) and Na+,K+-ATPase (NKA; α1-3, β1-3, and FXYD1) isoforms in human skeletal muscle, and studied some of the potential molecular mechanisms involved. Eight trained men (26 ± 5 y and 57.4 ± 6.3 mL·kg-1·min-1) completed three interval running sessions with (ISC) or without ischaemia (CON), or in hypoxia (HYP, ~3250 m), in a randomised, crossover fashion separated by 1 week. A muscle sample was collected from the dominant leg before (Pre) and after exercise (+0h, +3h) in all sessions to measure the mRNA content of PGC-1α and NKA isoforms, oxidative stress markers (i.e. catalase and HSP70 mRNA), muscle lactate, and phosphorylation of AMPK, ACC, CaMKII, and PLB protein in type I and II fibres. Muscle hypoxia (i.e. deoxygenated haemoglobin) was matched between ISC and HYP, which was higher than in CON (~90% vs. ~70%; p< 0.05). The levels of PGC-1α total, -1α1, −1α4, and FXYD1 mRNA increased in ISC only (p< 0.05). These changes were associated with increases in oxidative stress markers and higher p-ACCSer221/ACC in type I fibres, but were unrelated to muscle hypoxia, lactate, and CaMKII and PLB phosphorylation. These findings highlight that repeated-ischaemic exercise augments the skeletal muscle gene response related to mitochondrial biogenesis and ion transport in trained men. This effect seems attributable, in part, to increased oxidative stress and AMPK activation, whereas it appears unrelated to altered CaMKII signalling, and the muscle hypoxia and lactate accumulation induced by ischaemia.Summary in key pointsWe investigated if ischaemia would augment the exercise-induced mRNA response of PGC-1α and Na+,K+-ATPase (NKA) isoforms (α1-3, β1-3, and FXYD1), and examined whether this effect could be related to oxidative stress and fibre type-dependent AMPK and CaMKII signalling in the skeletal muscle of trained men.Repeated-ischaemic exercise increased the mRNA content of PGC-1α total, −1α1, and-1α4, and of the NKA regulatory subunit FXYD1, whereas exercise in systemic hypoxia or alone was without effect on these genes.These responses to ischaemia were complemented by increased oxidative stress (as assessed by catalase and HSP70 mRNA) and ACC phosphorylation (an indicator of AMPK activation) in type I fibres. However, they were unrelated to CaMKII signalling, muscle hypoxia, and lactate accumulation.Thus, repeated ischaemic exercise augments the muscle gene response associated with mitochondrial biogenesis and ion homeostasis in trained men. This effect seems partly attributable to promoted oxidative stress and AMPK activation.AbbreviationsACCAcetyl-CoA carboxylaseAMPK5’ AMP-activated protein kinase subunitβ2Mβ2 microglobulinCaMKIICa2+-calmodulin-dependent protein kinase isoform IICONcontrol sessionCTcycle thresholdCVcoefficient of variationFXYD1phospholemman isoform 1GAPDHglyceraldehyde 3-phosphate dehydrogenaseGXTgraded exercise testHHbdeoxygenated haemoglobinHSP70heat-shock protein 70HYPrepeated-hypoxic exercise sessionISCrepeated-ischaemic exercise sessionK+potassium ionLTlactate thresholdMHCmyosin heavy chainNa+sodium ionNIRSnear-infrared spectroscopyNKANa+, K+-ATPaseOXPHOSoxidative phosphorylationPGC-1αperoxisome proliferator-activated receptor-gamma coactivator 1 alphaPLBphospholambanROSreactive oxygen speciesSDSsodium dodecyl sulphateTBPTATA-binding proteinVO2maxmaximum oxygen uptake