Lipopolysaccharide regulates proinflammatory cytokine expression in mouse myoblasts and skeletal muscle.
The purpose of the present study was to examine the regulation of tumor necrosis factor (TNF)-alpha and interleukin (IL)-6 by lipopolysaccharide (LPS) in C2C12 myoblasts and mouse skeletal muscle. LPS produced dose- and time-dependent increases in TNF-alpha and IL-6 mRNA content in C2C12 myoblasts. The LPS-induced cytokine response could be mimicked by peptidoglycan from the cell wall of Staphylococcus aureus but not by zymosan A, a cell wall component from Saccharomyces cerevisiae. Ongoing protein synthesis was not necessary for the increase in the two cytokine mRNAs. The transcriptional inhibitor 5,6-dichloro-beta-D-ribofuranosyl-benzimidazole blocked LPS-stimulated IL-6 mRNA expression without changing its mRNA half-life. The anti-inflammatory glucocorticoid dexamethasone selectively blocked LPS-stimulated IL-6 mRNA accumulation but not TNF-alpha. In contrast, the proteasomal inhibitor MG-132 blocked TNF-alpha mRNA expression but not IL-6. Exposure of myoblasts to LPS was associated with a rapid decrease in the inhibitor of nuclear factor-kappaB (I kappaB, alpha, and epsilon), and this response was also blocked by MG-132. Treatment of myocytes with IL-1 or TNF-alpha also increased IL-6 mRNA content, but the increase in IL-6 mRNA due to LPS could not be prevented by pretreatment with antagonists to either IL-1 or TNF. Under in vivo conditions, LPS increased the plasma concentration of TNF-alpha and IL-6 and stimulated the accumulation of their mRNAs in multiple tissues including skeletal muscle from wild-type mice. In contrast, the ability of LPS to stimulate the same cytokines was markedly decreased in mice that harbor a mutation in the Toll-like receptor 4. Our data suggest that LPS stimulates cytokine expression not only in classical immune tissues but also in skeletal muscle.
Department of Cellular and Molecular Physiology, The Pennsylvania State University, College of Medicine, Hershey, Pennsylvania 17033, USA. rfrost@psu.edu
Robert A
RA
Frost
Gerald J
GJ
Nystrom
Charles H
CH
Lang
D000818:Animals; D000893:Anti-Inflammatory Agents / Q000494:pharmacology; D000970:Antineoplastic Agents / Q000494:pharmacology; D001425:Bacterial Outer Membrane Proteins / Q000494:pharmacology; D002478:Cells, Cultured; D003907:Dexamethasone / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects / Q000276:immunology; D007375:Interleukin-1 / Q000494:pharmacology; D015850:Interleukin-6 / Q000235:genetics*; D007976:Leupeptins / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000494:pharmacology*; D051379:Mice; D008809:Mice, Inbred C3H; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000187:drug effects / Q000276:immunology*; D018482:Muscle, Skeletal / Q000166:cytology* / Q000276:immunology; D014176:Protein Biosynthesis / Q000276:immunology; D012333:RNA, Messenger / Q000032:analysis; D014158:Transcription, Genetic / Q000276:immunology; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics* / Q000494:pharmacology
D000893:Anti-Inflammatory Agents; D000970:Antineoplastic Agents; D001425:Bacterial Outer Membrane Proteins; D007375:Interleukin-1; D015850:Interleukin-6; D007976:Leupeptins; D008070:Lipopolysaccharides; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha; D003907:Dexamethasone; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde