title: Role of TNF-{alpha} signaling in regeneration of cardiotoxin-injured muscle.
abstract: Recent data suggest a physiological role for the proinflammatory cytokine TNF-alpha in skeletal muscle regeneration. However, the underlying mechanism is not understood. In the present study, we analyzed TNF-alpha-activated signaling pathways involved in myogenesis in soleus muscle injured by cardiotoxin (CTX) in TNF-alpha receptor double-knockout mice (p55(-/-)p75(-/-)). We found that activation of p38MAPK, which is critical for myogenesis, was blocked in CTX-injured p55(-/-)p75(-/-) soleus on day 3 postinjury when myogenic differentiation was being initiated, while activation of ERK1/2 and JNK MAPK, as well as transcription factor NF-kappaB, was not reduced. Consequently, the phosphorylation of transcription factor myocyte enhancer factor-2C, which is catalyzed by p38 and crucial for the expression of muscle-specific genes, was blunted. Meanwhile, expression of p38-dependent differentiation marker myogenin and p21 were suppressed. In addition, expression of cyclin D1 was fivefold that in wild-type (WT) soleus. These results suggest that myogenic differentiation is blocked or delayed in the absence of TNF-alpha signaling. Histological studies revealed abnormalities in regenerating p55(-/-)p75(-/-) soleus. On day 5 postinjury, new myofiber formation was clearly observed in WT soleus but not in p55(-/-)p75(-/-) soleus. To the contrary, p55(-/-)p75(-/-) soleus displayed renewed inflammation and dystrophic calcification. On day 12 postinjury, the muscle architecture of WT soleus was largely restored. Yet, in p55(-/-)p75(-/-) soleus, multifocal areas of inflammation, myofiber death, and myofibers with smaller cross-sectional area were observed. Functional studies demonstrated an attenuated recovery of contractile force in injured p55(-/-)p75(-/-) soleus. These data suggest that TNF-alpha signaling plays a critical regulatory role in muscle regeneration.
authors.affiliation: Department of Medicine, Baylor College of Medicine, One Baylor Plaza 520B, Houston, TX 77030, USA.
authors.forename: Shuen-Ei
authors.initials: SE
authors.lastname: Chen
authors.forename: Eric
authors.initials: E
authors.lastname: Gerken
authors.forename: Yingmin
authors.initials: Y
authors.lastname: Zhang
authors.forename: Mei
authors.initials: M
authors.lastname: Zhan
authors.forename: Raja K
authors.initials: RK
authors.lastname: Mohan
authors.forename: Andrew S
authors.initials: AS
authors.lastname: Li
authors.forename: Michael B
authors.initials: MB
authors.lastname: Reid
authors.forename: Yi-Ping
authors.initials: YP
authors.lastname: Li
mesh_terms: D000818:Animals; D004179:Cobra Cardiotoxin Proteins / Q000633:toxicity*; D004789:Enzyme Activation / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout; D009119:Muscle Contraction / Q000502:physiology; D024510:Muscle Development / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D009135:Muscular Diseases / Q000139:chemically induced / Q000503:physiopathology; D018124:Receptors, Tumor Necrosis Factor / Q000235:genetics / Q000502:physiology*; D012038:Regeneration / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology*; D014409:Tumor Necrosis Factor-alpha / Q000502:physiology*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D004179:Cobra Cardiotoxin Proteins; D018124:Receptors, Tumor Necrosis Factor; D014409:Tumor Necrosis Factor-alpha; D048051:p38 Mitogen-Activated Protein Kinases