Cellular and Molecular Mechanisms of Muscle Atrophy
The Ubiquitin-Proteasome System The ubiquitin-proteasome system is needed to rid muscles of sarcomeric proteins when there are muscle changes. “A decrease in muscle mass is associated with: (1) An increased conjugation of ubiquitin to muscle proteins; (2) an increased proteasomal ATP-dependent activity; (3) increased protein breakdown that can be efficiently blocked by proteasome inhibitors; and (4) upregulation of transcripts encoding ubiquitin, some ubiquitin-conjugating enzymes (E2), a few ubiquitin- protein ligases (E3) and several proteasome subunits” (Lecker et al., 2006, p. 25). Muscle atrophy is best defined as an active process that is controlled by a specific set of signaling pathways
…show more content…
It plays a role in both the conditions and responds to numerous stimuli which includes: nutrient deprivation, cytokines, cellular stress, and amino acid starvation (Mizushima et al., 2008). There have been three different cell mechanisms explained in mammals for delivery of autophagic components to lysosomes: microautophagy, macroautophagy, and chaperone-mediated autophagy (CMA). The extent that CMA is involved in homeostasis of muscles is undefined and should be addressed in detail in the future (Bonaldo & Sandri, 2012). Per analysis of multiple organs, it has been seen determined that skeletal muscle has one of the highest rates of vesicle formation of tissues during fasting. “Autophagy is primarily considered to be a non-selective degradation pathway, but the significance of more selective forms of autophagy is becoming increasingly evident” (Bonaldo & Sandri, 2012, p. 29). In mammals, it is seen that an inactivation of the gene parkin or PINK1, leads to abnormal mitochondria and regulates mitophagy. This gene brings parkin to the mitochondria and endorses mitophagy through ubiquitylation of outer mitochondrial membrane proteins, which brings autophagic vesicles to ubiquitylated mitochondrial proteins (Narenda and Youle, 2011). “The main crucial role of the auto-lysosome system in relation to skeletal muscle is confirmed by the fact that alterations to this process contribute to the pathogenesis …show more content…
A., Bedard, N., Baracos, V., Attaix, D. and Wing, S. S.
(2005). USP19 is a ubiquitin-specific protease regulated in rat skeletal muscle during catabolic states. Am. J. Physiol. Endocrinology and Metabolism. 288, E693-E700.
Judge, A. R., Koncarevic, A., Hunter, R. B., Liou, H. C., Jackman, R. W. and
Kandarian, S. C. (2007). Role for IkappaBalpha, but not c-Rel, in skeletal muscle atrophy. American Journal of Physiology: Cell Physiology. 292, C372-C382.
Lecker, S. H., Goldberg, A. L. and Mitch, W. E. (2006). Protein degradation by the ubiquitin-proteasome pathway in normal and disease states. Journal of the American Society of Nephrology. 17,1807-1819.
Mittal, A., Bhatnagar, S., Kumar, A., Lach-Trifilieff, E., Wauters, S., Li, H.,
Makonchuk, D. Y., Glass, D. J. and Kumar, A. (2010). The TWEAK-Fn14 system is a critical regulator of denervation-induced skeletal muscle atrophy in mice. The Journal of Cell Biology. 188, 833-849.
Mizushima, N., Levine, B., Cuervo, A. M. and Klionsky, D. J. (2008). Autophagy fights disease through cellular self-digestion. Nature. 451, 1069-1075.
Narendra, D. P. and Youle, R. J. (2011). Targeting mitochondrial dysfunction: role for
PINK1 and Parkin in mitochondrial quality control. Antioxidants and Redox Signaling. 14,
Duchenne Muscular Dystrophy is a disease which causes skeletal muscle to waste away, this wasting of muscle is caused by a mutation of the dystrophin gene (Meregalli et al., 2013, p. 4251).
To build muscles, you need protein. To build muscles, you must maintain a sufficient amount of protein. Your body alone does not produce enough protein and that's why we need to find other sources, such as a high protein diet or a protein supplement, to provide the protein our body needs. Proteins will create body heat and speed up your metabolism. As a result, protein affects your metabolism which is more than fat or carbohydrates. This explains why the muscle mass is stronger than the fat. Exercise will change the metabolism of a person's protein. The amount of exercise a person does is fully understood by any protein provided by his
Muscular Dystrophy is a genetic disease in which muscle fibers are usually susceptible to damage and cause muscle wasting and weakness. There are bundles of fibers that make up muscles; proteins are involved in these muscles and help to keep the muscle working properly. If
Duchenne Muscular Dystrophy (DMD) is a fatal genetic disorder that is caused by mutations in the gene DMD, which encodes the muscle protein, dystrophin. Dystrophin protein is crucial to preserve the strength, stability, and flexibility of muscle fibers, which protects them from injury as they contract and relax. The DMD gene is primarily located in skeletal and cardiac muscle. Duchenne Muscular Dystrophy is caused by mutations in the gene that produce premature stop codons. The premature stop codons work to bring protein synthesis to a halt, resulting in a greatly shortened and nonfunctional form of dystrophin (Pierce, 2013, pg. 286). According to the Muscular Dystrophy Association (2016), “Individuals with DMD experience rapid progressive
When a cell becomes damaged and undergoes apoptosis the muscle cells may not be able to regenerate at a proper rate to avoid a deficiency in the amount of the nuclei needed to maintain proper muscle mass. Support for this need and the suggestion that nuclei number may be size limiting and therefore a causation for atrophy was found in the study by the observation of damaged myonuclei were found in stage 3 mice but absent in stage 1, myonuclei reduction in the two muscle samples, nuclear domain size in regards to surface area was either maintained or increased, and the reappearance of a correlation between nuclei number and fiber size in stage 3 muscles. Particularly EDL IIb fibers may be most susceptible to sarcoma due to a generally lower nuclei number and that distribution of these fibers is impaired in the elderly which would not reduce capacity for synthesis but could increase transport distances causing decreased functionality. The nuclear shape also changed which has an unknown impact on functionality and may have been the cause of the nuclear fragmentation possibly leading to
Muscular dystrophy (MD) is a genetic disorder caused by incorrect or missing genetic information that leads to the gradual weakening of the muscle cells. Various causes lead to weak and deteriorating muscles depending on the type of muscular dystrophy the patient was affected by. However, there are many causes for muscular dystrophy due to the fact that there are thirty forms of muscular dystrophy, which are categorized under several categories. All are ultimately caused by autosomal recessive, autosomal dominant, sex-linked, and random mutations in very rare cases.
DMD is caused by a mutation in the X-linked dystrophin gene, which results in a dysfunctional dystrophin protein. Dystrophin is a cytoskeletal protein that provides mechanical stability to muscle cells by connecting the muscle sarcolemma to the basal lamina of the extracellular matrix (ECM), and without it there, the muscle cells typically undergo a process of degeneration and regeneration. This process is limited by the survival of satellite cells present since satellite cells can only undergo mitosis a limited amount of times. Sarcolemma instability typically results in excess intracellular amounts of both sodium and calcium, which causes ATP depletion and mitochondrial uncoupling (Horn & Schleip, 2012). Satellite cells only have a limited number times they can undergo mitosis, and once a patient can no longer generate healthy muscle cells, the patient will typically experience cell death. This cell death and necrosis usually
Duchenne muscular dystrophy (DMD) is caused by a mutated gene in the X chromosome. This flawed genes is passed on by the mother. However, most carrier of the gene do not show signs or symptoms of the disease. The The flawed gene causes the improper production of the protein dystrophin which is accompanied by “defective dystrophin-glycoprotein complex (DGC) in the sarcolemma and leads to progressive muscle degeneration” (Nakamura & Takeda, 2011). The Dystrophin protein is vital in providing a muscle integrity. Therefore, the absence of dystrophin production can lead to muscled atrophy.
Under normal conditions, satellite cells are inactive, but become activated when there’s a serious injury, and when muscles lose their nerve supply. Satellite cells repair muscle fibres, but when they become old, they disrupt signals and skeletal muscle cannot be prepared and regenerated effectively. This results in muscle fibre degeneration, an increase in connective tissue between single muscle cells, and weakens the single muscle cell and neuromuscular junction connection (Tsitkanou, Della Gatta, Russell,
Chaperones are proteins that ensure the correct folding of the CFTR within the endoplasmic reticulum. Hsp70 is an important cytosolic chaperone that complexes with CFTR and reduces aggregation [5]. The CFTR passes through the endoplasmic reticulum-associated degradation (ERAD) after folding in the ER. This quality control system involves the ubiquitin proteasome system (UPS) for which CFTR is a substrate [16]. If a protein is molded and targeted for degradation, then ubiquitin will covalently attach to lysine residues on the CFTR. Three enzymes are required for the process of ubiquitylation: E1 ubiquitin activating enzymes, E2 ubiquitin conjugating enzymes, and E3 ubiquitin protein ligases. E1 enzymes are activated through hydrolysis of ATP, which creates an activated ubiquitin that is transferred to an E2 active site. The activated ubiquitin is then covalently bound to a lysine on the protein by an E3 ligase. A polyubiquitin chain is then formed as ubiquitin molecules link together, and if there are four or more then the misfolded CFTR chain is removed form the ER membrane and targeted for degradation by the 26S proteasome
Of all the tissues in the body, skeletal muscle can adapt the easiest. —- On the outside of the muscle just deep to the sarcolemma, are small cells that lack cytoplasm and help with the reparation of muscles, called satellite cells. During an intense workout, the fibers within the muscle tissue become damaged as they break down and tear. The job of
Muscular dystrophy is a combination of diseases passed down through genes identified by progressive degeneration of the skeletal or voluntary muscles.(Alicia Foose,PhD, Patricia Ardovino,PhD,2008, p.141). This occurs due to mixture of hypertrophy, atrophy, and necrosis muscle cells. The muscle fibers increase in muscle size and results in muscle weakness while the muscle undergoes necrosis, fat and connective tissue replace the muscle fibers.(Sheila Grossman, Carol Mattson Porth,p.461).There are nine types of muscular dystrophy according to Alicia Foose, and Patricia Ardovino“Duchenne, Becker, Emery-Dreifuss, Limb-girdle, facioscapulohumeral, myotonic, oculopharyngeal distal, and congenital.”Each disease
A muscular dystrophy is a group of diseases that is associated with progressive weakness and loss of an individual’s muscle mass. The condition causes the abnormal genes to interfere with the production of proteins needed to form healthy muscles. There is no medical cure for muscular dystrophy and related diseases, but strategies such as medication and therapy are used to manage the symptoms and slow the course of the disease. There are more than 30 types of muscular dystrophy, and the difference is based on the genes that cause it, the age when the symptoms appear first, how quickly the disease progresses and the muscles it affects (Tecklin, 2015).
The contractile unit of a muscle cell is the sarcomere. Sarcomeres are mostly comprised of actin and myosin which pull and slide upon each other. These contractile units are linked end to end, like a chain, throughout the length of any given muscle. Certain proteins link the ends of these chains to the cell membrane. When a normally healthy individual exercises, some of these fibers, both in the sarcomere and at the connections to the cell wall, will be broken down due to damage (Leyva, 2013). Associated with this process includes the rebuilding of these fibers, in which the body builds back what was damaged stronger than before the damage occurred (Leyva, 2013). One of these end proteins is dystrophin. The purpose of this paper is to explore the implications of insufficient production of dystrophin, as in DMD.
Satellite cells are cells that can develop into skeletal muscle cells and have been shown to re-enter the cell cycle from G0 to initiate growth of muscle fibers (Lee, 2004). In comparing wild type mice to mutant mice for the myostatin gene it has been shown that there are a larger number of satellite cells in mice that mutant (Lee, 2004). This demonstrates that when the satellite cells leave G0 phase and enter the cell cycle, myoblast begin to develop into muscle fiber cells increasing the muscle mass (Lee, 2004). The growth of satellite cells is beneficial to the body for growth and repair of the muscle cells (Lee, 2004) but not necessary otherwise. In order to ensure normal function of the myostatin gene it is essential to have the cell cycle regulating the myoblasts to stay in a state of quiescent, the G0 phase (Lee, 2004) so they are not being expressed or