title: Tumor necrosis factor-alpha decreases insulin-like growth factor-I messenger ribonucleic acid expression in C2C12 myoblasts via a Jun N-terminal kinase pathway.
abstract: IGF-I is a major anabolic hormone for skeletal muscle in vivo. Yet the mechanisms by which GH and cytokines regulate IGF-I expression remain obscure. Lipopolysaccharide (LPS) dramatically alters the circulating concentration of both TNF alpha and IGF-I, and TNF alpha in part mediates the cachectic activity of LPS. Little is known about the local synthesis of IGF-I and TNF alpha in skeletal muscle per se. The purpose of the present study was to determine whether LPS alters the expression of TNF alpha and IGF-I in mouse skeletal muscle and whether TNF alpha directly inhibits IGF-I mRNA expression in C2C12 myoblasts. Intraperitoneal injection of LPS in C3H/SnJ mice increased the expression of TNF alpha protein in plasma (16-fold) and TNF alpha mRNA in skeletal muscle (8-fold). LPS also decreased the plasma concentration of IGF-I (30%) and IGF-I mRNA in skeletal muscle (50%, between 6 and 18 h after LPS administration). Addition of LPS or TNF alpha directly to C2C12 myoblasts decreased IGF-I mRNA by 50-80%. The TNF alpha-induced decrease in IGF-I mRNA was both dose and time dependent and occurred in both myoblasts and differentiated myotubes. TNF alpha selectively decreased IGF-I but not IGF-II mRNA levels, and the effect of TNF alpha was blocked by a specific TNF-binding protein. TNF alpha did not alter IGF-I mRNA levels in the presence of the protein synthesis inhibitor cycloheximide. TNF alpha did not change the half-life of IGF-I mRNA. TNF alpha completely prevented GH-inducible IGF-I mRNA expression, but this GH resistance was not attributable to impairment in signal transducer and activator of transcription-3 or -5 phosphorylation. TNF alpha increased both nitric oxide synthase-II mRNA and protein, and the nitric oxide donor sodium nitroprusside decreased IGF-I mRNA levels in C2C12 cells. Yet inhibitor studies indicate that nitric oxide did not mediate the effect of TNF alpha on IGF-I mRNA expression. TNF alpha stimulated the phosphorylation of c-Jun and specific inhibition of the Jun N-terminal kinase pathway, but not other MAPK pathways, completely prevented the TNF alpha-induced drop in IGF-I mRNA. These data suggest that LPS stimulates TNF alpha expression in mouse skeletal muscle and autocrine-derived cytokines may contribute to the reduced expression of IGF-I in this tissue.
authors.affiliation: Department of Cellular and Molecular Physiology, Pennsylvania State University, College of Medicine, Hershey, Pennsylvania 17033, USA. rfrost@psu.edu
authors.forename: Robert A
authors.initials: RA
authors.lastname: Frost
authors.forename: Gerald J
authors.initials: GJ
authors.lastname: Nystrom
authors.forename: Charles H
authors.initials: CH
authors.lastname: Lang
mesh_terms: D000818:Animals; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D013006:Growth Hormone / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000037:antagonists & inhibitors* / Q000235:genetics; D048031:JNK Mitogen-Activated Protein Kinases; D008070:Lipopolysaccharides / Q000494:pharmacology; D051379:Mice; D008809:Mice, Inbred C3H; D008894:Milk Proteins; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism; D032446:Myoblasts / Q000378:metabolism*; D020030:Nitric Oxide Donors / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000502:physiology; D010766:Phosphorylation; D014176:Protein Biosynthesis / Q000502:physiology; D012333:RNA, Messenger / Q000037:antagonists & inhibitors / Q000378:metabolism; D050796:STAT3 Transcription Factor; D050799:STAT5 Transcription Factor; D013997:Time Factors; D015534:Trans-Activators / Q000378:metabolism; D014158:Transcription, Genetic / Q000502:physiology; D014409:Tumor Necrosis Factor-alpha / Q000008:administration & dosage / Q000235:genetics / Q000494:pharmacology*
chemical_list: D004268:DNA-Binding Proteins; D008070:Lipopolysaccharides; D008894:Milk Proteins; D020030:Nitric Oxide Donors; D012333:RNA, Messenger; D050796:STAT3 Transcription Factor; D050799:STAT5 Transcription Factor; C494087:Stat3 protein, mouse; D015534:Trans-Activators; D014409:Tumor Necrosis Factor-alpha; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D019001:Nitric Oxide Synthase; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases