NF-κB activation is required for the transition of pulmonary inflammation to muscle atrophy

Disease exacerbations and muscle wasting comprise negative prognostic factors of chronic obstructive pulmonary disease (COPD). Transient systemic inflammation and malnutrition have been implicated in skeletal muscle wasting after acute exacerbations of COPD. However, the interactions between systemic inflammation and malnutrition in their contributions to muscle atrophy, as well as the molecular basis underlying the transition of systemic inflammation to muscle atrophy, remain unresolved. Pulmonary inflammation was induced in mice by an intratracheal instillation of LPS to model acute disease exacerbation. Systemic inflammation, nutritional intake, and body and muscle weights were determined. Muscle inflammatory signaling and atrophy signaling were examined, and the effect of the muscle-specific inactivation of NF-κB on muscle atrophy was assessed in genetically modified mice. The intratracheal LPS instillation was followed by markedly elevated circulating cytokine concentrations and NF-κB activation in extrapulmonary tissues, including skeletal muscle. The administration of intratracheal LPS increased the expression of muscle E3 ubiquitin ligases, which govern muscle proteolysis, in particular MuRF1, and caused a rapid loss of muscle mass. Reduced food intake only partly accounted for the observed muscle atrophy, and did not activate NF-κB in muscle. Rather, plasma transfer experiments revealed the presence of NF-κB-signaling and atrophy-signaling properties in the circulation of intratracheal LPS-treated mice. The genetic inhibition of muscle NF-κB activity suppressed intratracheal LPS-induced MuRF1 expression and resulted in a significant sparing of muscle tissue. Systemic inflammation and malnutrition contribute to the muscle wasting induced by acute pulmonary inflammation via distinct mechanisms, and muscle NF-κB activation is required for the transition from inflammatory to muscle atrophy signaling.