IFN-gamma does not mimic the catabolic effects of TNF-alpha.
Cachexia is common in chronic inflammatory diseases and is attributed, in part, to an elevation of circulating proinflammatory cytokines. TNF-alpha is the prototype in this category. IFN-gamma is also thought to play a role, but the evidence supporting this model is primarily indirect. To determine the direct effects of IFN-gamma stimulation on muscle cells, we selected key components of the procatabolic signaling pathways by which TNF-alpha stimulates protein loss. We tested two hypotheses: 1) IFN-gamma mimics TNF-alpha signaling by increasing intracellular oxidant activity and activating MAPKs and NF-kappaB and 2) IFN-gamma increases the expression of the ubiquitin ligases atrogin1/MAFbx and muscle-specific ring finger protein 1 (MuRF1). Results showed that treatment with IFN-gamma at 60 ng/ml increased Stat1 phosphorylation after 15 min, indicating receptor activation. IFN-gamma had no effect on cytosolic oxidant activity, as measured by 2',7'-dichlorofluorescein oxidation. Nor did IFN-gamma activate JNK, ERK1/2, or p38 MAPK, as assessed by Western blot. Treatment for up to 60 min did not decrease IkappaB-alpha protein levels, as measured by Western blot analysis, or the DNA binding activity of NF-kappaB, as measured by EMSA. After 6 h, IFN-gamma decreased Akt phosphorylation and increased atrogin1/MAFbx and MuRF1 mRNA. Daily treatment for up to 72 h did not alter adult fast-type myosin heavy chain content or the total protein-to-DNA ratio. These data show that responses of myotubes to IFN-gamma and TNF-alpha differ markedly and provide little evidence for a direct catabolic effect of IFN-gamma on muscle.
Smith
Melissa A
MA
Department of Physiology, University of Kentucky, Lexington, KY 40536-0298, USA. masmit8@uky.edu
Moylan
Jennifer S
JS
Smith
Jeffrey D
JD
Li
Wei
W
Reid
Michael B
MB
D000818:Animals; D002100:Cachexia / Q000378:metabolism; D002460:Cell Line; D004247:DNA / Q000378:metabolism; D007371:Interferon-gamma / Q000502:physiology*; D020935:MAP Kinase Signaling System / Q000502:physiology; D051379:Mice; D018485:Muscle Fibers, Skeletal / Q000378:metabolism*; D009124:Muscle Proteins / Q000378:metabolism; D018995:Myosin Heavy Chains / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism; D010084:Oxidation-Reduction; D012333:RNA, Messenger / Q000378:metabolism; D044843:SKP Cullin F-Box Protein Ligases / Q000378:metabolism; D000070584:Tripartite Motif Proteins; D014409:Tumor Necrosis Factor-alpha / Q000502:physiology*; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*
D009124:Muscle Proteins; D016328:NF-kappa B; D012333:RNA, Messenger; D000070584:Tripartite Motif Proteins; D014409:Tumor Necrosis Factor-alpha; D007371:Interferon-gamma; D004247:DNA; C486691:Fbxo32 protein, mouse; C486692:Fbxo32 protein, rat; D044843:SKP Cullin F-Box Protein Ligases; C499084:Trim63 protein, mouse; D044767:Ubiquitin-Protein Ligases; D018995:Myosin Heavy Chains