No description available.

No description available.

Thesis (Ph. D.)--Ohio State University, 2004. / Title from first page of PDF file. Document formatted into pages; contains x, 66 p.; also includes graphics. Includes bibliographical references (p. 57-61).

Increased calcium-activated calpain proteolysis in the sarcolemma membrane is thought to be a primary mechanism in the pathophysiology of Duchenne Muscular Dystrophy (DMD). However, few studies have tested this possibility prior to the overt signs of the dystrophy. The purpose of this study was to test the hypothesis that there is greater calpain content and total relative calpain activity in membranes obtained from dystrophic (mdx; mdx:utrophin-deficient (mdx:utrn-/-)) compared to wildtype (wt) mouse skeletal muscles during maturation at ages 7- and 21-d,and at a post-maturation age of 35-d. Calpain activity was determined as the calcium-dependent cleavage of the flurogenic substrate SLY-AMC, and content was determined by Western analysis with an anti-calpain antibody. There were several intriguing findings: 1. There was an inverse relationship between calpain content and relative activity in the whole muscle in both wt and mdx mice from age 7- to 35-d: calpain content decreased, and relative calpain activity increased as the mice aged. This suggests a similar role for calpain in both genotypes, which might relate to specific maturation processes, possibly up to age 21-d. Although the inverse relation was evident at 35-d, the targets for calpain in mdx compared to wt likely differed. 2. The increased relative calpain activity in the membrane fraction of mdx mice at age 35-d (26.73 Arbitrary Units, (AU)) compared to that of age 7- (4.9AU; p<0.05) and 21-d (8.74AU; p<0.05) is temporally related to degeneration and regeneration processes, and may also indicate activation of apoptosis, in mdx muscles at this age. 3. At age 7-d, there were no significant differences in either calpain content or relative calpain activity in all subcellular fractions for wt and mdx mice. This result might suggest similar calpain distribution and activities that are related to the regulation of muscle maturation and differentiation in both genotypes. (Note:data were not obtained for the mdx:utrn-/- mice at age 7-d because of insufficient animals). 4. At age 21-d, there was greater relative calpain activity in the myofibrillar supernatant fraction in mdx (15.13AU) than wt mice (1.18AU; p<0.05). This could indicate calpain's role in the initiation of myofibrillar protein turnover and the proteolysis of submembranous networks in the mdx muscles. 5. At age 21-d, greater calpain content in the mdx (1.40ìg) compared to wt (0.23 ìg; p<0.05) membrane fraction might suggest a broader distribution of calpain along membranes that contributes to the onset of dystrophy in the mdx muscles. 6. At age 35-d, there was greater calpain content in the mdx:utrn-/- compared to the wt membrane (0.48ìg vs 0.13 ìg), cytosolic (0.88ìg vs 0.30ìg), and myofibrillar supernatant (0.49ìg vs 0.17ìg; p<0.05 ) fractions This increased content and broad distribution across several subcellular fractions may reflect degeneration and regeneration processes, and potentially activation of apoptosis, in the mdx:utrn-/- muscles. These data suggest that calpain activity contributes to dystrophic pathophysiology mainly in the membrane fraction of mdx skeletal muscles at age ~21-d, but appears to contribute later at 35-d and in more subcellular fractions in mdx:utrn-/- skeletal muscles. / Master of Science

No description available.

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.

No description available.

No description available.

No description available.

Abstract available in PDF document. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2008.