Metabolic aspects of glycogenolysis with special attention to McArdle disease.

The physiological function of muscle glycogen is to meet the energy demands of muscle contraction. The breakdown of glycogen occurs through two distinct pathways, primarily cytosolic and partially lysosomal. To obtain the necessary energy for their function, skeletal muscles utilise also fatty acids in the ß-oxidation. Ketogenesis is an alternative metabolic pathway for fatty acids, which provides an energy source during fasting and starvation. Diseases arising from impaired glycogenolysis lead to muscle weakness and dysfunction. Here, we focused on the lack of muscle glycogen phosphorylase (PYGM), a rate-limiting enzyme for glycogenolysis in skeletal muscles, which leads to McArdle disease. Metabolic myopathies represent a group of genetic disorders characterised by the limited ability of skeletal muscles to generate energy. Here, we discuss the metabolic aspects of glycogenosis with a focus on McArdle disease, offering insights into its pathophysiology. Glycogen accumulation may influence the muscle metabolic dynamics in different ways. We emphasize that a proper treatment approach for such diseases requires addressing three important and interrelated aspects, which include: symptom relief therapy, elimination of the cause of the disease (lack of a functional enzyme) and effective and early diagnosis.

FBP2-A New Player in Regulation of Motility of Mitochondria and Stability of Microtubules in Cardiomyocytes.

Recently, we have shown that the physiological roles of a multifunctional protein fructose 1,6-bisphosphatase 2 (FBP2, also called muscle FBP) depend on the oligomeric state of the protein. Here, we present several lines of evidence that in HL-1 cardiomyocytes, a forced, chemically induced reduction in the FBP2 dimer-tetramer ratio that imitates AMP and NAD+ action and restricts FBP2-mitochondria interaction, results in an increase in Tau phosphorylation, augmentation of FBP2-Tau and FBP2-MAP1B interactions, disturbance of tubulin network, marked reduction in the speed of mitochondrial trafficking and increase in mitophagy. These results not only highlight the significance of oligomerization for the regulation of FBP2 physiological role in the cell, but they also demonstrate a novel, important cellular function of this multitasking protein-a function that might be crucial for processes that take place during physiological and pathological cardiac remodeling, and during the onset of diseases which are rooted in the destabilization of MT and/or mitochondrial network dynamics.