Journal Article

Metabolic profiles of exercise in patients with McArdle disease or mitochondrial myopathy

Delaney, Nigel F., Tadvalkar, Laura, Sharma, Rohit, Clish, Clary B., Haller, Ronald G., Mootha, Vamsi K.

2017

Overview

McArdle disease and mitochondrial myopathy impair muscle oxidative phosphorylation (OXPHOS) by distinct mechanisms: the former by restricting oxidative substrate availability caused by blocked glycogen breakdown, the latter because of intrinsic respiratory chain defects. We applied metabolic profiling to systematically interrogate these disorders at rest, when muscle symptoms are typically minimal, and with exercise, when symptoms of premature fatigue and potential muscle injury are unmasked. At rest, patients with mitochondrial disease exhibit elevated lactate and reduced uridine; in McArdle disease purine nucleotide metabolites, including xanthine, hypoxanthine, and inosine are elevated. During exercise, glycolytic intermediates, TCA cycle intermediates, and pantothenate expand dramatically in both mitochondrial disease and control subjects. In contrast, in McArdle disease, these metabolites remain unchanged from rest; but urea cycle intermediates are increased, likely attributable to increased ammonia production as a result of exaggerated purine degradation. Our results establish skeletal muscle glycogen as the source of TCA cycle expansion that normally accompanies exercise and imply that impaired TCA cycle flux is a central mechanism of restricted oxidative capacity in this disorder. Finally, we report that resting levels of long-chain triacylglycerols in mitochondrial myopathy correlate with the severity of OXPHOS dysfunction, as indicated by the level of impaired O₂ extraction from arterial blood during peak exercise. Our integrated analysis of exercise and metabolism provides unique insights into the biochemical basis of these muscle oxidative defects, with potential implications for their clinical management.

• Publisher: National Academy of Sciences
• Subject: Adolescent / Adult / Aged / Ammonia / Biological Sciences / Citric Acid Cycle - genetics / Citric Acid Cycle - physiology / Defects / Disease control / Electron transport / Electron Transport - physiology / Energy Metabolism - physiology / Exercise / Exercise - physiology / Fatigue / Female / Glycogen / Glycogen - metabolism / Glycogen Storage Disease Type V - genetics / Glycogen Storage Disease Type V - pathology / Glycogens / Glycolysis / Heart Rate - physiology / Humans / Hypoxanthine / Intermediates / Lactic acid / Male / Metabolic disorders / Metabolism / Metabolites / Metabolome - physiology / Middle Aged / Mitochondria / Mitochondria - metabolism / Mitochondrial Myopathies - genetics / Mitochondrial Myopathies - pathology / Muscle, Skeletal - metabolism / Muscle, Skeletal - pathology / Muscles / Muscular fatigue / Muscular system / Myopathy / Nucleotides / Oxidative Phosphorylation / Oxygen Consumption - physiology / Patients / Phosphorylation / Physiology / Signs and symptoms / Skeletal muscle / Tricarboxylic acid cycle / Triglycerides / Triglycerides - metabolism / Urea / Uridine / Young Adult