In fact, during exercise or anabolic hormonal stimulation, muscles grow because new proteins and organelles accumulate in the cytosol increasing cellular volume, a process named hypertrophy. This organized structure implies that protein and organelle turnover have a major impact on myofiber size and function. Different from all the other cell types, the dense packaging of contractile proteins and organelles does not leave empty space in the cytosol. Skeletal and Cardiac muscle cells are peculiar because the cytoplasm is filled by contractile proteins that are surrounded by organelles, especially the mitochondria and endoplasmic reticulum. Consistently, the metabolic adaptations occurring in skeletal muscles are assumed to work as a disease modifier and the quality of muscle mass is an important predictor of mortality 1. Understanding the mechanisms that control muscle mass will provide therapeutic targets for the treatment of muscle loss in inherited and non-hereditary diseases and for the improvement of the quality of life during ageing.īeing the most abundant tissue (40–50% of the total mass in healthy-weight individual) and the protein reservoir in the human body, skeletal muscles not only control locomotion but they are fundamental for breathing, eating, energy expenditure, as well as for glucose, amino acids, and lipids homeostasis and for maintaining a high quality of life 1. Novel insights that control and orchestrate such complex network are continuously emerging and will be summarized in this review. Mechanical, oxidative, nutritional and energy stresses, as well as growth factors or cytokines modulate signaling pathways that, ultimately, converge on protein and organelle turnover. These systems are controlled by transcriptional dependent programs that adapt muscle cells to environmental and nutritional clues. Muscle function is influenced by different quality systems that regulate the function of contractile proteins and organelles. Therefore, it is not surprising that excessive muscle loss is a bad prognostic index of a variety of diseases ranging from cancer, organ failure, infections and unhealthy ageing. ![]() Consequently, the growth or the loss of muscle mass can influence general metabolism, locomotion, eating and respiration. Skeletal muscle is the protein reservoir of our body and an important regulator of glucose and lipid homeostasis.
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