Skeletal muscle endurance declines with impaired mitochondrial respiration and inadequate supply of acetyl-CoA during muscle fatigue in 5/6 nephrectomized rats.

Chronic kidney disease (CKD)-related cachexia increases the risks of reduced physical activity and mortality. However, the physiological phenotype of skeletal muscle fatigue and changes in intramuscular metabolites during muscle fatigue in CKD-related cachexia remain unclear. In the present study, we performed detailed muscle physiological evaluation, analysis of mitochondrial function, and comprehensive analysis of metabolic changes before and after muscle fatigue in a 5/6 nephrectomized rat model of CKD. Wistar rats were randomized to a sham-operation (Sham) group that served as a control group or a 5/6 nephrectomy (Nx) group. Eight weeks after the operation, in situ torque and force measurements in plantar flexor muscles in Nx rats using electrical stimulation revealed a significant decrease in muscle endurance during subacute phase related to mitochondrial function. Muscle mass was reduced without changes in the proportions of fiber type-specific myosin heavy chain isoforms in Nx rats. Pyruvate-malate-driven state 3 respiration in isolated mitochondria was impaired in Nx rats. Protein expression levels of mitochondrial respiratory chain complexes III and V were decreased in Nx rats. Metabolome analysis revealed that the increased supply of acetyl CoA in response to fatigue was blunted in Nx rats. These findings suggest that CKD deteriorates skeletal muscle endurance in association with mitochondrial dysfunction and inadequate supply of acetyl-CoA during muscle fatigue. Mitochondrial dysfunction is associated with decreased skeletal muscle endurance in chronic kidney disease (CKD), but the muscle physiological phenotype and major changes in intramuscular metabolites during muscle fatigue in CKD-related cachexia remain unclear. By using a 5/6 nephrectomized CKD rat model, the present study revealed that CKD is associated with reduced tetanic force in response to repetitive stimuli in a subacute phase, impaired mitochondrial respiration, and inadequate supply of acetyl-CoA during muscle fatigue.