Duchenne muscular dystrophy (DMD) is the most devastating form of muscular
dystrophy caused by a mutation in the dystrophin gene. Defects in the dystrophin gene in
DMD, are homologous to that found in mdx mice, and result in profound muscle damage,
inflammation and weakness in diaphragm and limb muscles. Dystrophin, a scaffolding
protein located in the sarcolemmal cytoskeleton, helps cells to maintain their structural
integrity and associates with critical cell signaling molecules that regulate cell growth
and repair (e.g., nNOS).
While the contributing mechanisms leading to DMD-induced degenerative
muscle function and damage are multi-factorial, elevated oxidative stress has been
proposed as a central mechanism. In contrast, antioxidants can attenuate muscle damage
as well as improve contractile function in dystrophin-deficient muscles. However, it is
unknown if oxidative stress is a causal factor in dystrophin-deficient diaphragm muscle
pathology and specifically targeted antioxidant (e.g., EUK-134) treated early in the course of the disease (3-4 weeks) can modulate oxidative stress, functional damage and
weakness in mdx diaphragm.
Therefore, the purpose of this study was to determine the effects of
catalase/superoxide dismutase mimetic EUK-134 on damage, inflammation, and
contractile function of the diaphragm muscle in mdx mice. We hypothesized that (a)
EUK-134 would attenuate muscle damage and oxidative stress in mdx diaphragm, (b)
EUK-134 would reduce inflammatory cells and an important transcription factor
including nuclear factor-kappaB (NF-kB) in mdx diaphragm and (c) EUK-134 would
restore proteins that attach to dystrophin such as nNOS and cytoskeletal proteins back to
sarcolemmal region and improve muscle contractility in mdx diaphragm.
C57BL/10ScSn wild type and mdx mice were given EUK-134 (30mg/kg, i.p.,
injection) beginning at 20 days of age for 8 days. The mice were euthanized and the
diaphragm muscle was harvested at 4 weeks of age, the time of peak inflammation, and
analyzed to measure myofiber inflammation, NF-kB activation, cytoskeletal proteins and
oxidative stress markers using Western immunoblotting, ELISA, immunofluoresence,
and immunohistochemistry. We found that EUK-134 ameliorated muscle damage and
oxidative stress in mdx diaphragm. EUK-134 protected against inflammation by
decreasing NF-kB activation in the nucleosome fraction of mdx diaphragm. Further,
EUK-134 partially rescued nNOS and k-1 syntrophin back to sarcolemmal membranes
and recovered force generation even in acute application in vitro in mdx diaphragm.
These results are the first to demonstrate a causal relationship between oxidative
stress and pathology caused by dystrophin-deficient diaphragm muscle. Moreover, the data indicate that EUK-134 has a protective effect against muscle damage, inflammation,
and contractility in mdx diaphragm. We believe that the results from our investigation
will provide clinical significance, as we expect to elucidate mechanisms by which
oxidative stress contribute to tissue damage and weakness in dystrophic diaphragm.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2009-08-7133 |
| Date | 2009 August 1900 |
| Creators | Kim, Jong Hee |
| Contributors | Lawler, John M. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | application/pdf |
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