title: The peculiar apoptotic behavior of skeletal muscle cells.
abstract: Apoptosis plays an active role in maintaining skeletal muscle homeostasis. Its deregulation is involved in several skeletal muscle disorders such as dystrophies, myopathies, disuse and sarcopenia. The aim of this work was to study in vitro the apoptotic behavior induced by etoposide, staurosporine and hydrogen peroxide in the C2C12 skeletal muscle cell line, comparing myoblast vs myotube sensitivity, investigated by means of morphological and cytofluorimetric analyses. Myotubes appeared more resistant than myoblasts to apoptotic induction. In myoblasts treated with etoposide, nuclei with chromatin condensation were observed, in the presence of a diffuse DNA fragmentation, as shown by confocal microscopy. The latter also appeared in myotubes, where apoptotic and normal nuclei coexisted inside the same syncytium. After staurosporine treatment, myobalsts evidenced late apoptotic features and a high number of TUNEL-positive nuclei. Secondary necrosis appeared in myotubes, where myonuclei with cleaved DNA again coexisted with normal myonuclei. After H₂O₂ exposure, myotubes, differently from myoblasts, showed a poor sensitivity to cell death. Intriguingly, autophagic granules appeared abundantly in myotubes after each treatment. In myotubes, mitochondria were better preserved than in myoblasts since those which were damaged were probably degraded through autophagic processes. These findings demonstrate a scarce sensitivity of myotubes to apoptotic stimuli due to acquisition of an apoptosis-resistant phenotype during differentiation. The presence of nuclear-dependent "territorial" death domains in the syncytium could explain a slower death of myotubes compared to mononucleated cells. In addition, autophagy could preserve and protect muscle cell integrity against chemical stimuli, making C2C12 cells, in particular myotubes, more resistant to apoptosis induction.
authors: Department of Earth, Life and Environmental Sciences, University of Urbino, Carlo Bo, Urbino, Italy.
authors: Sara
authors: S
authors: Salucci
authors: Sabrina
authors: S
authors: Burattini
authors: Valentina
authors: V
authors: Baldassarri
authors: Michela
authors: M
authors: Battistelli
authors: Barbara
authors: B
authors: Canonico
authors: Aurelio
authors: A
authors: Valmori
authors: Stefano
authors: S
authors: Papa
authors: Elisabetta
authors: E
authors: Falcieri
mesh_terms: D000818:Animals; D017209:Apoptosis; D001343:Autophagy; D002454:Cell Differentiation; D002460:Cell Line; D053938:DNA Fragmentation; D004791:Enzyme Inhibitors / Q000737:chemistry; D005047:Etoposide / Q000737:chemistry; D005434:Flow Cytometry; D006706:Homeostasis; D006801:Humans; D006861:Hydrogen Peroxide / Q000737:chemistry; D020287:In Situ Nick-End Labeling; D051379:Mice; D018613:Microscopy, Confocal; D008854:Microscopy, Electron; D018485:Muscle Fibers, Skeletal / Q000473:pathology*; D018482:Muscle, Skeletal / Q000166:cytology* / Q000473:pathology*; D032446:Myoblasts / Q000473:pathology*; D019311:Staurosporine / Q000737:chemistry; D059005:Topoisomerase II Inhibitors / Q000737:chemistry; D020298:U937 Cells
chemical_list: D004791:Enzyme Inhibitors; D059005:Topoisomerase II Inhibitors; D005047:Etoposide; D006861:Hydrogen Peroxide; D019311:Staurosporine