title: Proinflammatory cytokine impairment of insulin-like growth factor I-induced protein synthesis in skeletal muscle myoblasts requires ceramide.
abstract: GH and IGF-I control over 80% of postnatal growth. We recently established that TNFalpha impairs the ability of IGF-I to increase protein synthesis and promote expression of myogenin in myoblasts. Here we extend these results by showing that ceramide, a second messenger in both TNFalpha and IL-1beta receptor signaling pathways, is a key downstream sphingosine-based lipid that leads to IGF-I resistance. A cell-permeable ceramide analog, C2-ceramide, inhibits IGF-I-induced protein synthesis by 65% and blocks the ability of IGF-I to increase expression of two key myogenic factors, myogenin and MyoD. Identical results were obtained with both TNFalpha and IL-1beta (1 ng/ml). Consistent with these data, neutral sphingomyelinase (N-SMase), an enzyme that catalyzes formation of ceramide from sphingomyelin, blocks IGF-I-induced protein synthesis and expression of both myogenin and MyoD. The possibility that cytokine-induced ceramide production is required for disruption of IGF-I biologic activity was confirmed by treating C2C12 myoblasts with inhibitors of all three ceramide-generating pathways. A N-SMase inhibitor, glutathione, as well as an acidic sphingomyelinase (A-SMase) inhibitor, D609, reverse the cytokine inhibition of IGF-I-induced protein synthesis by 80% and 45%, respectively. Likewise, an inhibitor of de novo ceramide synthesis, FB1, causes a 50% inhibition. Similarly, all three inhibitors significantly impair the ability of both TNFalpha and IL-1beta to suppress IGF-I-driven expression of myogenin. These experiments establish that ceramide, derived both from sphingomyelin and de novo synthesis, is a key intermediate by which proinflammatory cytokines impair the ability of IGF-I to promote protein synthesis and expression of critical muscle-specific transcription factors.
authors.affiliation: University of Illinois, Laboratory of Immunophysiology, 207 Edward R. Madigan Laboratory, 1201 West Gregory Drive, Urbana, Illinois 61801, USA.
authors.forename: Klemen
authors.initials: K
authors.lastname: Strle
authors.forename: Suzanne R
authors.initials: SR
authors.lastname: Broussard
authors.forename: Robert H
authors.initials: RH
authors.lastname: McCusker
authors.forename: Wen-Hong
authors.initials: WH
authors.lastname: Shen
authors.forename: Rodney W
authors.initials: RW
authors.lastname: Johnson
authors.forename: Gregory G
authors.initials: GG
authors.lastname: Freund
authors.forename: Robert
authors.initials: R
authors.lastname: Dantzer
authors.forename: Keith W
authors.initials: KW
authors.lastname: Kelley
mesh_terms: D000818:Animals; D002460:Cell Line; D002518:Ceramides / Q000037:antagonists & inhibitors / Q000502:physiology*; D016207:Cytokines / Q000502:physiology*; D004357:Drug Synergism; D006801:Humans; D018836:Inflammation Mediators / Q000502:physiology*; D055504:Insulin Receptor Substrate Proteins; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007375:Interleukin-1 / Q000494:pharmacology; D051379:Mice; D009124:Muscle Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D018482:Muscle, Skeletal / Q000378:metabolism*; D017570:MyoD Protein / Q000037:antagonists & inhibitors; D032446:Myoblasts / Q000378:metabolism*; D018008:Myogenin / Q000037:antagonists & inhibitors; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D011994:Recombinant Proteins / Q000494:pharmacology; D013108:Sphingomyelin Phosphodiesterase / Q000494:pharmacology; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D014443:Tyrosine / Q000378:metabolism
chemical_list: D002518:Ceramides; D016207:Cytokines; C526292:IRS1 protein, human; D018836:Inflammation Mediators; D055504:Insulin Receptor Substrate Proteins; D007375:Interleukin-1; C526295:Irs1 protein, mouse; C503799:MYOG protein, human; D009124:Muscle Proteins; D017570:MyoD Protein; C503801:Myog protein, mouse; D018008:Myogenin; D010750:Phosphoproteins; D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha; D014443:Tyrosine; D007334:Insulin-Like Growth Factor I; D013108:Sphingomyelin Phosphodiesterase