Duchenne muscular dystrophy (DMD) is the most common type of muscular dystrophy caused by the loss of functional dystrophin. DMD is characterized by scoliosis, muscle wasting, loss of ambulation and a reduced life span. The first line of treatment for DMD is glucocorticoids (GCs). GCs are prescribed primarily for their anti-inflammatory and immunosuppressive effects; however, GC treatment is known to cause significant muscle atrophy. In DMD, GC treatment has been shown to improve muscle strength for the first 6 months and stabilization of the disease for up to 3 years. However, long term treatment reduces muscle function and accelerates disease progression. It is paradoxical that we use a medication that causes muscle wasting to treat a muscle wasting disease. The regeneration and function of muscle is dependent on the proper regulation and functioning of muscle satellite cells (MuSCs) to restore and repair muscle tissue. The impact GCs have on MuSCs from activation to proliferation and differentiation into muscle fibers is not well understood. GCs have many mechanisms of action by acting as a ligand to the glucocorticoid receptor (GR) to cause downstream effects by direct DNA binding or indirectly by regulating proteins. To study the role of GCs, we examined the effects of GC treatment on myoblast morphology, the cytoskeletal network, post-translational modifications (PTMs) of tubulin subunits, and the organization of microtubule organizing centers (MTOCs) in proliferating and differentiating myoblasts. This study shows that the GR is an essential regulator of myotube morphology and proper myonuclei placement. Furthermore, dexamethasone (DEX) treatment causes branching of the MT network, as well as an increase in the expression of the stabilizing MT markers, acetylated and detyrosinated tubulin during early differentiation. DEX treatment was also found to misposition the Golgi complex, a primary MTOC for the cytoskeletal network, from the periphery of the nucleus to the center of the nucleus during early differentiation. Finally, we found very few differentially expressed genes between WT and GRMuSC-/- myoblasts between early and late differentiation, indicating that these morphological defects we see are not due to GCs regulating gene expression. Thus, GCs act through the GR to modify the MT network during early differentiation, causing morphological changes in myoblasts that persist throughout differentiation.
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/45734 |
| Date | 14 December 2023 |
| Creators | Dawe, Leanne |
| Contributors | Wiper, Nadine Louise, Copeland, John |
| Publisher | Université d'Ottawa / University of Ottawa |
| Source Sets | Université d’Ottawa |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
| Rights | CC0 1.0 Universal, http://creativecommons.org/publicdomain/zero/1.0/ |
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