High–intensity exercise training induces the oxidative modification of malate dehydrogenase 2 in skeletal muscles

•High–intensity training causes mitochondrial dysfunction.•Oxidative modification in muscle mitochondria is higher following intense training.•Oxidative modifications of MDH2 were higher in the muscles of exercised mice.•A mitochondrial fission factor was increased by exercise.•The modifications may limit effective adaptation in response to exercise training. High–intensity exercise training abrogates the aerobic metabolic system in skeletal muscles. Mitochondria play a crucial role in aerobic metabolism and regulate energy supply for muscle contraction. Although the detailed mechanism of mitochondrial dysfunction remains unknown, excessive reactive oxygen species (ROS) generated in response to high–intensity exercise may be involved. Herein, we examined the oxidative modification of mitochondrial proteins in mouse muscle following high–intensity exercise training. Male ICR mice (10–week–old) were divided into sedentary and high–intensity exercise groups. Mice in the exercise group received treadmill training five times per week for two weeks. The levels of oxidative protein modifications and the factors related to mitochondrial biogenesis and dynamics in the gastrocnemius muscle were measured. The levels of hexanoyl lysine adduct (HEL) and 4–hydroxy–2–nonenal (HNE) modified proteins tended to be higher in the muscle mitochondrial fraction, but not whole extractions, of the exercise group than in that of the sedentary group. Specifically, HEL and HNE modifications of malate dehydrogenase 2 (MDH2), a citric acid cycle–related enzyme, were particularly higher in the exercise group mice. Although mitochondrial biogenesis factors were upregulated by exercise, higher phosphorylation of dynamin–related protein 1 (Ser637) was observed in the exercise group. These results suggest that oxidative modification of MDH2 impairs the metabolic system following high–intensity exercise training, which may be associated with attenuated adaptation.