The JNK MAP kinase pathway contributes to the development of endotoxin-induced diaphragm caspase activation.
We previously demonstrated that endotoxin-induced sepsis results in caspase 8-mediated diaphragmatic dysfunction. The upstream signaling pathways modulating diaphragm caspase 8 activation in response to endotoxin administration are, however, unknown. The purpose of the present study was to test the hypothesis that the JNK (Jun N-terminal Kinase) pathway is activated in the diaphragm during sepsis and contributes to sepsis-induced diaphragm caspase 8 activation. Endotoxin was administered to intact animals to model the effects of sepsis. We first assessed the time course of JNK activation after endotoxin (12 mg/kg i.p.) administration to mice. We then determined whether JNK inhibitor administration (30 microm/kg i.p. SP600125) could prevent caspase 8 activation and diaphragm weakness in endotoxin-treated mice. Experiments were then repeated comparing the effects of endotoxin on control and transgenic JNK knockout mice. We finally determined whether cytomix (LPS, TNFalpha, IL1beta, and IFN-gamma) exposure activated caspase 8 in C2C12 muscle cells and whether caspase 8 activation was attenuated by either chemical inhibition of JNK (30 microM SP600125) or transfection with a dominant negative JNK construct. We found that endotoxin activated diaphragm JNK (P < 0.001) and increased active caspase 8 (P < 0.01). Inhibition of JNK with SP600125 or by use of JNK-deficient animals prevented diaphragm caspase 8 activation (P < 0.01) and prevented diaphragm weakness (P < 0.05). JNK inhibition also prevented caspase 8 activation in cytokine-treated muscle cells (P < 0.001). These data implicate JNK activation as a major factor mediating inflammation-induced skeletal muscle caspase 8 activation and weakness.
Supinski
Gerald S
GS
Division of Pulmonary, Critical Care and Sleep Medicine, University of Kentucky, Lexington, Kentucky, USA. gsupi2@email.uky.edu
Ji
Xinying
X
Callahan
Leigh Ann
LA
D000818:Animals; D000873:Anthracenes / Q000494:pharmacology; D053181:Caspase 8 / Q000187:drug effects / Q000378:metabolism*; D002460:Cell Line; D016207:Cytokines / Q000378:metabolism; D003964:Diaphragm / Q000187:drug effects / Q000201:enzymology* / Q000503:physiopathology; D004195:Disease Models, Animal; D004789:Enzyme Activation; D048031:JNK Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D008070:Lipopolysaccharides; D020935:MAP Kinase Signaling System / Q000187:drug effects; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009119:Muscle Contraction / Q000187:drug effects; D018485:Muscle Fibers, Skeletal / Q000201:enzymology; D053580:Muscle Strength / Q000187:drug effects; D018908:Muscle Weakness / Q000201:enzymology* / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D018805:Sepsis / Q000139:chemically induced / Q000150:complications / Q000201:enzymology* / Q000503:physiopathology; D013997:Time Factors; D014162:Transfection
D000873:Anthracenes; D016207:Cytokines; D008070:Lipopolysaccharides; D047428:Protein Kinase Inhibitors; C432165:pyrazolanthrone; D048031:JNK Mitogen-Activated Protein Kinases; C505526:Casp8 protein, mouse; D053181:Caspase 8