Repeated-ischaemic exercise enhances mitochondrial and ion transport gene adaptations in human skeletal muscle – Role of muscle redox state and AMPK
Authors: Christiansen Danny , Murphy Robyn M. , Bangsbo Jens , Stathis Christos G. , Bishop David J. 
Published: June 2017

This 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.catalaseandHSP70mRNA), 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 ofPGC-1αtotal,-1α1, −1α4, andFXYD1mRNA 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 points

We 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 bycatalaseandHSP70mRNA) 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.

Abbreviations

ACC

Acetyl-CoA carboxylase

AMPK

5’ AMP-activated protein kinase subunit

β2M

β2 microglobulin

CaMKII

Ca2+-calmodulin-dependent protein kinase isoform II

CON

control session

CT

cycle threshold

CV

coefficient of variation

FXYD1

phospholemman isoform 1

GAPDH

glyceraldehyde 3-phosphate dehydrogenase

GXT

graded exercise test

HHb

deoxygenated haemoglobin

HSP70

heat-shock protein 70

HYP

repeated-hypoxic exercise session

ISC

repeated-ischaemic exercise session

K+

potassium ion

LT

lactate threshold

MHC

myosin heavy chain

Na+

sodium ion

NIRS

near-infrared spectroscopy

NKA

Na+, K+-ATPase

OXPHOS

oxidative phosphorylation

PGC-1α

peroxisome proliferator-activated receptor-gamma coactivator 1 alpha

PLB

phospholamban

ROS

reactive oxygen species

SDS

sodium dodecyl sulphate

TBP

TATA-binding protein

VO2max

maximum oxygen uptake