Increased muscular beta-hydroxyacyl CoA dehydrogenase with McArdle's disease

Muscle molecular adaptations to endurance exercise training are conditioned by glycogen availability: a proteomics-based analysis in the McArdle mouse model

KEY POINTS

Although they are unable to utilize muscle glycogen, McArdle mice adapt favourably to an individualized moderate-intensity endurance exercise training regime. Yet, they fail to reach the performance capacity of healthy mice with normal glycogen availability. There is a remarkable difference in the protein networks involved in muscle tissue adaptations to endurance exercise training in mice with and without glycogen availability. Indeed, endurance exercise training promoted the expression of only three proteins common to both McArdle and wild-type mice: LIMCH1, PARP1 and TIGD4. In turn, trained McArdle mice presented strong expression of mitogen-activated protein kinase 12 (MAPK12).

ABSTRACT

McArdle's disease is an inborn disorder of skeletal muscle glycogen metabolism that results in blockade of glycogen breakdown due to mutations in the myophosphorylase gene. We recently developed a mouse model carrying the homozygous p.R50X common human mutation (McArdle mouse), facilitating the study of how glycogen availability affects muscle molecular adaptations to endurance exercise training. Using quantitative differential analysis by liquid chromatography with tandem mass spectrometry, we analysed the quadriceps muscle proteome of 16-week-old McArdle (n = 5) and wild-type (WT) (n = 4) mice previously subjected to 8 weeks' moderate-intensity treadmill training or to an equivalent control (no training) period. Protein networks enriched within the differentially expressed proteins with training in WT and McArdle mice were assessed by hypergeometric enrichment analysis. Whereas endurance exercise training improved the estimated maximal aerobic capacity of both WT and McArdle mice as compared with controls, it was ∼50% lower than normal in McArdle mice before and after training. We found a remarkable difference in the protein networks involved in muscle tissue adaptations induced by endurance exercise training with and without glycogen availability, and training induced the expression of only three proteins common to McArdle and WT mice: LIM and calponin homology domains-containing protein 1 (LIMCH1), poly (ADP-ribose) polymerase 1 (PARP1 - although the training effect was more marked in McArdle mice), and tigger transposable element derived 4 (TIGD4). Trained McArdle mice presented strong expression of mitogen-activated protein kinase 12 (MAPK12). Through an in-depth proteomic analysis, we provide mechanistic insight into how glycogen availability affects muscle protein signalling adaptations to endurance exercise training.

McArdle Disease and Exercise Physiology

McArdle disease (glycogen storage disease Type V; MD) is a metabolic myopathy caused by a deficiency in muscle glycogen phosphorylase. Since muscle glycogen is an important fuel for muscle during exercise, this inborn error of metabolism provides a model for understanding the role of glycogen in muscle function and the compensatory adaptations that occur in response to impaired glycogenolysis. Patients with MD have exercise intolerance with symptoms including premature fatigue, myalgia, and/or muscle cramps. Despite this, MD patients are able to perform prolonged exercise as a result of the “second wind” phenomenon, owing to the improved delivery of extra-muscular fuels during exercise. The present review will cover what this disease can teach us about exercise physiology, and particularly focuses on the compensatory pathways for energy delivery to muscle in the absence of glycogenolysis.

What can metabolic myopathies teach us about exercise physiology?

Exercise physiologists are interested in metabolic myopathies because they demonstrate how knocking out a component of a specific biochemical pathway can alter cellular metabolism. McArdle's disease (myophosphorylase deficiency) has often been studied in exercise physiology to demonstrate the influence of removing the major anaerobic energy supply to skeletal muscle. Studies of patients with McArdle's disease have shown the increased reliance on blood-borne fuels, the importance of glycogen to maximal aerobic capacity, and the use of nutritional strategies to bypass metabolic defects. Myoadenylate deaminase deficiency is the most common metabolic enzyme deficiency in human skeletal muscle. It is usually compensated for endogenously and does not have a major influence on high-energy power output. Nutritional interventions such as carbohydrate loading and carbohydrate supplementation during exercise are essential components of therapy for patients with fatty acid oxidation defects. Cases of mitochondrial myopathies illustrate the importance of peripheral oxygen extraction for maximal aerobic capacity and show how both exercise and nutritional interventions can partially compensate for these mutations. In summary, metabolic myopathies provide important insights into regulatory and nutritional aspects of the major biochemical pathways of intermediary metabolism in human skeletal muscle. Key words: myoadenylate deaminase deficiency, MELAS syndrome, McArdle's disease, mitochondrial disease, inborn errors of metabolism.

Rhabdomyolysis in childhood. A primer on normal muscle function and selected metabolic myopathies characterized by disordered energy production

Patients with rhabdomyolysis present an important clinical problem. In acute episodes immediate treatment may be necessary to prevent significant morbidity and mortality. Evaluation of affected patients necessitates an understanding of basic muscle pathophysiology and of the variety of disturbances that can interfere with muscle energy metabolism. The physician must then pursue a systematic stepwise evaluation (Table 6) that includes obtaining relevant history and laboratory studies, as well as arranging for appropriate provocative testing and muscle biopsy. Once the diagnosis is established, patient and family counseling is necessary, particularly in genetic disorders. Unfortunately, specific therapies have not proven entirely successful, and treatment generally has been directed at reducing the severity of rhabdomyolytic episodes.

McArdle's disease and gout

We report the first case of McArdle's disease (muscle phosphorylase deficiency) and tophaceous gout. To examine the contribution of adenine nucleotide degradation to the disturbance of uric acid metabolism, we labeled the adenine nucleotide pool with [8-14C]adenine, and measured plasma and urine purines following vigorous exercise tests. Plasma and urinary hypoxanthine and xanthine concentrations and the specific radioactivity of urinary purines increased markedly, but plasma urate levels and uric acid excretion were not substantially modified. We suggest that, in this patient, the association of McArcle's disease with gout is coincidental.

Metabolic response to a high-fat diet in neonatal and adult rat muscle

Neonatal rats were exposed to a high-fat low-carbohydrate diet to determine how substrate availability might affect the metabolic phenotype of muscle. Mixed-fiber homogenates of extensor digitorum longus, soleus, and diaphragm muscles were assayed for beta-hydroxyacyl-CoA dehydrogenase (beta-OAC), succinate dehydrogenase, malate dehydrogenase, lactate dehydrogenase, phosphofructokinase (PFK), adenylokinase, and creatine kinase. The three muscles showed significant increases in enzyme activity for fatty acid oxidation (beta-OAC) in weaned neonatal rats maintained on the high-fat diet compared with normal weaned controls. This effect persisted for 6 wk of the diet. The other consistent metabolic change was a decrease in PFK. Adult animals subjected to the same diet had similar increases in fatty acid oxidation and a fall in PFK after 1 wk, with most of these changes persisting for the 4 wk of the diet. Examination of individual fibers revealed enzyme changes in fibers of all types, but with the largest effect in type IIb fibers. The data indicate that both adult and neonatal muscles are similarly capable of adjusting their energy metabolism in response to dietary factors.