The JNK MAP kinase pathway contributes to the development of endotoxin-induced diaphragm caspase activation

Supinski GS, Ji X, Callahan LA. The JNK MAP kinase pathway contributes to the development of endotoxin-induced diaphragm caspase activation. Am J Physiol Regul Integr Comp Physiol 297: R825-R834, 2009. First published July 15, 2009; doi: 10.1152/ajpregu.90849.2008.-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 ip) administration to mice. We then determined whether JNK inhibitor administration (30 mu m/kg ip 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, TNF alpha, IL1 beta, 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 mu M 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.