title: Skeletal muscle myocytes undergo protein loss and reactive oxygen-mediated NF-kappaB activation in response to tumor necrosis factor alpha.
abstract: Skeletal muscle atrophy and weakness are thought to be stimulated by tumor necrosis factor alpha (TNF-alpha) in a variety of chronic diseases. However, little is known about the direct effects of TNF-alpha on differentiated skeletal muscle cells or the signaling mechanisms involved. We have tested the effects of TNF-alpha on the mouse-derived C2C12 muscle cell line and on primary cultures from rat skeletal muscle. TNF-alpha treatment of differentiated myotubes stimulated time- and concentration-dependent reductions in total protein content and loss of adult myosin heavy chain (MHCf) content; these changes were evident at low TNF-alpha concentrations (1-3 ng/ml) that did not alter muscle DNA content and were not associated with a decrease in MHCf synthesis. TNF-alpha activated binding of nuclear factor kappaB (NF-kappaB) to its targeted DNA sequence and stimulated degradation of I-kappaBalpha, an NF-kappaB inhibitory protein. TNF-alpha stimulated total ubiquitin conjugation whereas a 26S proteasome inhibitor (MG132 10-40 microM) blocked TNF-alpha activation of NF-kappaB. Catalase 1 kU/ml inhibited NF-kappaB activation by TNF-alpha; exogenous hydrogen peroxide 200 microM activated NF-kappaB and stimulated I-kappaBalpha degradation. These data demonstrate that TNF-alpha directly induces skeletal muscle protein loss, that NF-kappaB is rapidly activated by TNF-alpha in differentiated skeletal muscle cells, and that TNF-alpha/NF-kappaB signaling in skeletal muscle is regulated by endogenous reactive oxygen species.
authors.affiliation: Department of Medicine, Baylor College of Medicine, Houston, Texas 77030, USA.
authors.forename: Y P
authors.initials: YP
authors.lastname: Li
authors.forename: R J
authors.initials: RJ
authors.lastname: Schwartz
authors.forename: I D
authors.initials: ID
authors.lastname: Waddell
authors.forename: B R
authors.initials: BR
authors.lastname: Holloway
authors.forename: M B
authors.initials: MB
authors.lastname: Reid
mesh_terms: D000818:Animals; D051379:Mice; D009124:Muscle Proteins / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism*; D051381:Rats; D017382:Reactive Oxygen Species / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
chemical_list: D009124:Muscle Proteins; D016328:NF-kappa B; D017382:Reactive Oxygen Species; D014409:Tumor Necrosis Factor-alpha