title: Nuclear translocation of EndoG at the initiation of disuse muscle atrophy and apoptosis is specific to myonuclei.
abstract: Skeletal muscle atrophy is associated with an increase in apoptosis, and we showed previously that endonuclease G (EndoG) is localized to nuclei following unloading. The goal of this study was to determine whether the onset of apoptosis in response to disuse was consistent with the hypothesis that EndoG is involved in myofiber nuclear loss. Atrophy was induced by hindlimb suspension for 12 h or 1, 2, 4 and 7 days in 6-mo-old rats. Soleus myofiber cross-sectional area decreased significantly by 2 days, whereas muscle mass and muscle-to-body mass ratio decreased by 4 and 7 days, respectively. By contrast, a significant increase in apoptosis, evidenced by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL)-positive nuclei, occurred as early as 12 h after suspension, preceding the elevation in muscle atrophy F-box gene expression. The early increase in apoptosis appeared to be specific to myofiber nuclei, whereas TUNEL-positive interstitial cells did not become significantly elevated until 2 days after suspension. Furthermore, TUNEL-positive myofiber nuclei colocalized with EndoG as early as 12 h after suspension, and no such localization was observed in interstitial cells. Although no significant change in total activated caspase-3, -7, or -12 protein abundance was apparent, activated caspase-3 was expressed in interstitial cells undergoing apoptosis, some of which were endothelial cells. These data indicate that apoptosis is an early, and therefore possibly causative, event in the process of muscle atrophy, and that EndoG nuclear translocation is specific for myofiber nuclear apoptosis, whereas interstitial cells may undergo apoptosis via a more classical, caspase-dependent pathway.
authors.affiliation: Department of Geriatrics, University of Arkansas for Medical Sciences, Little Rock, AR, USA. eedupo2@email.uky.edu
authors.forename: Esther E
authors.initials: EE
authors.lastname: Dupont-Versteegden
authors.forename: Beau A
authors.initials: BA
authors.lastname: Strotman
authors.forename: Cathy M
authors.initials: CM
authors.lastname: Gurley
authors.forename: Dana
authors.initials: D
authors.lastname: Gaddy
authors.forename: Micheal
authors.initials: M
authors.lastname: Knox
authors.forename: James D
authors.initials: JD
authors.lastname: Fluckey
authors.forename: Charlotte A
authors.initials: CA
authors.lastname: Peterson
mesh_terms: D021581:Active Transport, Cell Nucleus; D000818:Animals; D017209:Apoptosis; D002467:Cell Nucleus / Q000378:metabolism* / Q000473:pathology; D004706:Endodeoxyribonucleases / Q000378:metabolism*; D019417:Hindlimb Suspension / Q000009:adverse effects; D008297:Male; D018482:Muscle, Skeletal / Q000201:enzymology* / Q000473:pathology*; D020966:Muscular Disorders, Atrophic / Q000201:enzymology* / Q000209:etiology / Q000473:pathology*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D004706:Endodeoxyribonucleases; C052391:endonuclease G