Muscle-Specific Inhibition of the Classical Nuclear Factor-κB Pathway Is Protective Against Diaphragmatic Weakness in Murine Endotoxemia

Objective: Diaphragmatic weakness and acute respiratory failure are common in sepsis. Nuclear factor-B acts as a general coordinator of the systemic inflammatory response, but its role within the diaphragm itself during sepsis is unknown. We investigated the potential protective effect upon the diaphragm of inhibiting nuclear factor-B only within muscle fibers during acute endotoxemia. Design: Prospective study in experimental animals. Setting: University research laboratory. Interventions: Wild-type and transgenic (muscle-specific IB super-repressor) mice with skeletal muscle-specific inhibition of the classical nuclear factor-B pathway were subjected to acute endotoxemia. Muscle-specific ubiquitin ligases (muscle RING-finger protein 1 and atrogin-1), caspase-3 activity, inhibitor of apoptosis proteins, proinflammatory cytokines (interleukin-1, monocyte chemoattractant protein-1, and tumor necrosis factor-), and diaphragmatic contractility were evaluated after 24 hours. Measurements and Main Results: In wild-type mice, endotoxemia significantly increased proinflammatory cytokines (fold-change messenger RNA: interleukin-1 = 7.6, monocyte chemoattractant protein-1 = 15.3, and tumor necrosis factor- = 2.2) and proteolysis effectors (fold-change messenger RNA: muscle RING-finger protein 1 = 5.7, atrogin-1 = 2.8; caspase-3 activity elevated by 28%) in the diaphragm, while reducing its force-generating capacity by 38%. In nonendotoxemic muscle-specific IB super-repressor diaphragms, caspase-3 activity was unexpectedly increased by 40% above basal wild-type levels and inhibitors of apoptosis proteins were down-regulated, but force production remained normal. In muscle-specific IB super-repressor mice subjected to endotoxemia, proinflammatory cytokines, muscle RING-finger protein 1, and atrogin-1 were not significantly increased above their basal levels, and diaphragmatic weakness and further increases in caspase-3 activity were completely prevented. Conclusions: These results suggest that nuclear factor-B signaling within skeletal muscle fibers is a key pathway leading to diaphragmatic weakness during acute endotoxemia, most likely via effects on multiple inflammatory mediators. In addition, inhibition of nuclear factor-B signaling within diaphragm muscle fibers has complex effects on caspase-3 activation, which could have implications for the treatment of sepsis-induced diaphragmatic dysfunction.