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MyoD and myogenin protein expression in skeletal muscles of senile rats
Eduard I Dedkov1, Tatiana Y Kostrominova, Andrei B Borisov
1Department of Cell and Developmental Biology, 4643 Medical Sciences II Building, University of Michigan, Ann Arbor, Michigan 48109, USA. ededkov@umich.edu
Abstract:
We analyzed the level of protein expression of two myogenic regulatory factors (MRFs), MyoD and myogenin, in senile skeletal muscles and determined the cellular source of their production in young adult (4 months old), old (24, 26, and 28 months old), and senile (32 months old) male rats. Immunoblotting demonstrated levels of myogenin approximately 3.2, approximately 4.0, and approximately 5.5 times higher in gastrocnemius muscles of 24-, 26-, and 32-month-old animals, respectively, than in those of young adult rats. Anti-MyoD antibody recognized two major areas of immunoreactivity in Western blots: a single MyoD-specific band (approximately 43-45 kDa) and a double (or triple) MyoD-like band (approximately 55-65 kDa). Whereas the level of MyoD-specific protein in the 43- to 45-kDa band remained relatively unchanged during aging compared with that of young adult rats, the total level of MyoD-like immunoreactivity within the 55- to 65-kDa bands was approximately 3.4, approximately 4.7, approximately 9.1, and approximately 11.7 times higher in muscles of 24-, 26-, 28-, and 32-month-old rats, respectively. The pattern of MRF protein expression in intact senile muscles was similar to that recorded in young adult denervated muscles. Ultrastructural analysis of extensor digitorum longus muscle from senile rats showed that, occasionally, the area of the nerve-muscle junction was partially or completely devoid of axons, and satellite cells with the features of activated cells were found on the surface of living fibers. Immunohistochemistry detected accumulated MyoD and myogenin proteins in the nuclei of both fibers and satellite cells in 32-month-old muscles. We suggest that the up-regulated production of MyoD and myogenin proteins in the nuclei of both fibers and satellite cells could account for the high level of MRF expression in muscles of senile rats.
Insights
Aging increases myogenic regulatory factors (MRFs) like myogenin and MyoD in rat skeletal muscle. This heightened expression in senile muscles, particularly in fibers and satellite cells, may drive age-related muscle changes.
Area of Science:
- Muscle physiology and aging research.
- Molecular biology of muscle regeneration.
Background:
- Skeletal muscle aging is associated with functional decline.
- Myogenic regulatory factors (MRFs) are crucial for muscle development and repair.
Purpose of the Study:
- To analyze the protein expression levels of MyoD and myogenin in aging rat skeletal muscles.
- To determine the cellular sources of MRF production in senile muscles.
Main Methods:
- Immunoblotting to quantify myogenin and MyoD protein levels.
- Western blotting to identify MyoD-specific and MyoD-like protein bands.
- Ultrastructural analysis of nerve-muscle junctions.
- Immunohistochemistry to localize MRF proteins within muscle fibers and satellite cells.
Main Results:
- Myogenin levels significantly increased with age, being 5.5 times higher in 32-month-old rats compared to young adults.
- MyoD-like protein expression (55-65 kDa bands) showed a marked age-dependent increase, up to 11.7 times higher in senile rats.
- MyoD-specific protein (43-45 kDa band) levels remained relatively unchanged.
- Senile muscles exhibited denervation signs and activated satellite cells.
- Accumulated MyoD and myogenin were found in the nuclei of both muscle fibers and satellite cells in aged rats.
Conclusions:
- Up-regulated MyoD and myogenin production in senile rat muscle fibers and satellite cells contributes to elevated MRF expression.
- Age-related changes in MRF expression patterns may be linked to denervation and satellite cell activation in aging muscle.