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-kB on muscle atrophy was assessed in genetically modified mice. The intratracheal LPS instillation was followed by markedly elevated circulating cytokine concentrations and NF-kB 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-kB in muscle. Rather, plasma transfer experiments revealed the presence of NF-kB-signaling and atrophy-signaling properties in the circulation of intratracheal LPStreated mice. The genetic inhibition of muscle NF-kB 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-kB activation is required for the transition from inflammatory to muscle atrophy signaling.Keywords: pulmonary inflammation; systemic inflammation; muscle atrophy; NF-kB; cytokines Acute exacerbations of chronic obstructive pulmonary disease (COPD) are accompanied by pulmonary and transient systemic inflammation and malnutrition, which have been implicated in the onset of stepwise weight loss, muscle wasting and increased mortality (1-6). The underlying mechanisms are unknown and difficult to unravel in patients during the acute phase of an exacerbation. In many instances, the acute loss of muscle mass is dependent on increased muscle protein breakdown mediated by the ubiquitin (Ub) 26S-proteasome system (UPS) (7). The rate-limiting enzymes of this process during acute muscle atrophy include the Ub-E3 ligation enzymes atrogin-1/MAFbx and MuRF1. The genetic deletion of these "atrogenes" attenuates muscle atrophy under various conditions (8, 9), and the increased expression of MuRF1 and atrogin-1 has been reported in quadriceps muscle during exacerbations of COPD (1). Inducible transcription factors, including NF-kB, have been implicated in the transcriptional regulation of atrogin-1 and MuRF1 (10). NF-k...

Lung neutrophilia is common to a variety of lung diseases. The production of reactive oxygen and nitrogen species during neutrophil oxidative burst has been associated with protein and DNA damage. Myeloperoxidase (MPO) is an enzyme stored in the azurophilic granula of neutrophils. It is important in host defense because it generates the reactive oxidant hypochlorous acid and has been described to play a role in the activation of neutrophils during extravasation. We hypothesized that MPO contributes directly to the development of acute lung neutrophilia via stimulation of neutrophil extravasation and indirectly to the subsequent production of cytokines and chemokines in the lung. To test this hypothesis, wild-type (WT) and Mpo−/− mice were given a single LPS instillation, after which the development of neutrophil-dominated lung inflammation, oxidative stress, and cytokine and chemokine levels were examined. Mpo−/− mice demonstrated a decreased lung neutrophilia that peaked earlier than neutrophilia in WT mice, which can be explained by decreased neutrophil chemoattractant levels in LPS-exposed Mpo−/− compared with WT mice. However, oxidative stress levels were not different in LPS-exposed WT and Mpo−/− mice. Furthermore, in vivo findings were confirmed by in vitro studies, using isolated neutrophils. These results indicate that MPO promotes the development of lung neutrophilia and indirectly influences subsequent chemokine and cytokine production by other cell types in the lung.

Muscle wasting impairs physical performance, increases mortality and reduces medical intervention efficacy in chronic diseases and cancer. Developing proficient intervention strategies requires improved understanding of the molecular mechanisms governing muscle mass wasting and recovery. Involvement of muscle protein- and myonuclear turnover during recovery from muscle atrophy has received limited attention. The insulin-like growth factor (IGF)-I signaling pathway has been implicated in muscle mass regulation. As glycogen synthase kinase 3 (GSK-3) is inhibited by IGF-I signaling, we hypothesized that muscle-specific GSK-3β deletion facilitates the recovery of disuse-atrophied skeletal muscle. Wild-type mice and mice lacking muscle GSK-3β (MGSK-3β KO) were subjected to a hindlimb suspension model of reversible disuse-induced muscle atrophy and followed during recovery. Indices of muscle mass, protein synthesis and proteolysis, and post-natal myogenesis which contribute to myonuclear accretion, were monitored during the reloading of atrophied muscle. Early muscle mass recovery occurred more rapidly in MGSK-3β KO muscle. Reloading-associated changes in muscle protein turnover were not affected by GSK-3β ablation. However, coherent effects were observed in the extent and kinetics of satellite cell activation, proliferation and myogenic differentiation observed during reloading, suggestive of increased myonuclear accretion in regenerating skeletal muscle lacking GSK-3β. This study demonstrates that muscle mass recovery and post-natal myogenesis from disuse-atrophy are accelerated in the absence of GSK-3β.

During extensive inflammation, neutrophils undergo secondary necrosis causing myeloperoxidase (MPO) release that may damage resident lung cells. Recent observations suggest that MPO has pro-inflammatory properties, independent of its enzymatic activity. The aims of the present study were to characterise MPO internalisation by lung epithelial cells and to investigate the effect of MPO on oxidative stress, DNA damage and cytokine production by lung epithelial cells.Human alveolar and bronchial epithelial cells were stimulated with MPO, with or without priming the cells with pro-inflammatory stimuli. MPO protein was detected in the cell cytoplasm. Expression of haemoxygenase (HO)-1 and DNA strand breakage were determined. The production of interleukin (IL)-8 and -6 were measured.Analyses of MPO-stimulated cells demonstrated MPO presence in the cells. HO-1 expression was increased after MPO stimulation and increased further when cells were primed before MPO stimulation. MPO exposure also induced DNA strand breakage. Interestingly, MPO inhibited IL-8 production in bronchial, but not alveolar epithelium.In conclusion, alveolar and bronchial epithelial cells can internalise myeloperoxidase. Stimulation with myeloperoxidase increases haemoxygenase-1 expression and DNA strand breakage, suggesting cell damaging capacity of myeloperoxidase. In addition, myeloperoxidase inhibited interleukin-8 production by bronchial epithelial cells, indicating a negative feedback loop for neutrophil recruitment.

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Asbestos fibers are carcinogens causing oxidative stress and inflammation, but the sources and ramifications of oxidant production by asbestos are poorly understood. Here, we show that inhaled chrysotile asbestos fibers cause increased myeloperoxidase activity in bronchoalveolar lavage fluids (BALF) and myeloperoxidase immunoreactivity in epithelial cells lining distal bronchioles and alveolar ducts, sites of initial lung deposition of asbestos fibers. In comparison with sham mice, asbestos-exposed myeloperoxidase-null (MPOÀ/À) and normal (MPO+/+) mice exhibited comparable increases in polymorphonuclear leukocytes, predominately neutrophils, in BALF after 9 days of asbestos inhalation. Differential cell counts on BALF revealed decreased proportions of macrophages and increased lymphocytes in all mice exposed to asbestos, but numbers were decreased overall in asbestosexposed myeloperoxidase-null versus normal mice. Asbestosassociated lung inflammation in myeloperoxidase-null mice was reduced (P V 0.05) in comparison with normal asbestosexposed mice at 9 days. Decreased lung inflammation in asbestos-exposed myeloperoxidase-null mice at 9 days was accompanied by increases (P V 0.05) in Ki-67-and cyclin D1-positive immunoreactive cells, markers of cell cycle reentry, in the distal bronchiolar epithelium. Asbestos-induced epithelial cell proliferation in myeloperoxidase-null mice at 30 days was comparable to that found at 9 days. In contrast, inflammation and epithelial cell proliferation in asbestos-exposed normal mice increased over time. These results support the hypothesis that myeloperoxidase status modulates early asbestos-induced oxidative stress, epithelial cell proliferation, and inflammation.

This study clearly demonstrates myofibrillar and not generic protein accretion in skeletal muscle following leucine supplementation, and suggests this involves pre-translational control of MyHC expression by leucine.

To investigate the role of bronchiolar epithelial NF-κB activity in the development of inflammation and fibrogenesis in a murine model of asbestos inhalation, we used transgenic (Tg) mice expressing an IκBα mutant (IκBαsr) resistant to phosphorylation-induced degradation and targeted to bronchial epithelium using the CC10 promoter. Sham and chrysotile asbestos-exposed CC10-IκBαsr Tg+ and Tg− mice were examined for altered epithelial cell proliferation and differentiation, cytokine profiles, lung inflammation, and fibrogenesis at 3, 9, and 40 days. KC, IL-6 and IL-1β were increased (p ≤ 0.05) in bronchoalveolar lavage fluid (BALF) from asbestos-exposed mice, but to a lesser extent (p ≤ 0.05) in Tg+ vs Tg− mice. Asbestos also caused increases in IL-4, MIP-1β, and MCP-1 in BALF that were more elevated (p ≤ 0.05) in Tg+ mice at 9 days. Differential cell counts revealed eosinophils in BALF that increased (p ≤ 0.05) in Tg+ mice at 9 days, a time point corresponding with significantly increased numbers of bronchiolar epithelial cells staining positively for mucus production. At all time points, asbestos caused increased numbers of distal bronchiolar epithelial cells and peribronchiolar cells incorporating the proliferation marker, Ki-67. However, bronchiolar epithelial cell and interstitial cell labeling was diminished at 40 days (p ≤ 0.05) in Tg+ vs Tg− mice. Our findings demonstrate that airway epithelial NF-κB activity plays a role in orchestrating the inflammatory response as well as cell proliferation in response to asbestos.