p38 Mitogen-Activated Protein Kinase Modulates Endotoxin-Induced Diaphragm Caspase Activation

We postulated that the p38 pathway is activated in the diaphragm during sepsis and contributes to sepsis-induced diaphragm caspase activation and contractile dysfunction. This study determined whether: (1) endotoxin administration elicits p38 activation in the diaphragm; (2) cytokines activate p38 in isolated muscle cells; (3) activation of p38 is accompanied by caspase 8 activation; (4) inhibition of p38 prevents caspase 8 activation and; (5) inhibition of p38 prevents diaphragm dysfunction in endotoxin-treated animals. We first evaluated the time course of diaphragm p38 activation after endotoxin in mice. We then determined if p38 inhibitor administration could prevent caspase 8 activation in endotoxin-treated mice. We also assessed p38 and caspase 8 activation in C2C12 muscle cells treated with control media or a cytokine mixture, with or without concomitant chemical inhibition of p38 (using 58203580, 25 mu M) or loss of p38 function due to cell transfection with a dominant negative p38 genetic construct. Endotoxin administration activated diaphragm p38 (P < 0.001), and cytokines activated p38 in C2C12 cells (P < 0.05). In both the diaphragm and cells, p38 activation was accompanied by increases in active caspase 8 (P < 0.01). Inhibition of p38 with either SB203580 or with a dominant negative p38 construct prevented caspase activation (P < 0.001). p38 inhibitors also prevented endotoxin-induced diaphragm weakness (P < 0.001). p38 modulates cytokine-induced skeletal muscle caspase activation.