Jane Batt

Cellular Markers of Muscle Atrophy in Chronic Obstructive Pulmonary Disease

Skeletal muscle atrophy in individuals with advanced chronic obstructive pulmonary disease (COPD) is associated with diminished quality of life, increased health resource use, and worsened survival. Muscle wasting results from an imbalance between protein degradation and synthesis, and is enhanced by decreased regenerative repair. We investigated the activation of cellular signaling networks known to mediate muscle atrophy and regulate muscle regenerative capacity in rodent models, in individuals with COPD (FEV(1) < 50% predicted). Nine patients with COPD and nine control individuals were studied. Quadriceps femoris muscle isometric contractile force and cross-sectional area were confirmed to be significantly smaller in the patients with COPD compared with control subjects. The vastus lateralis muscle was biopsied and muscle transcript and/or protein levels of key components of ubiquitin-mediated proteolytic systems (MuRF1, atrogin-1, Nedd4), inflammatory mediators (IkappaBalpha, NF-kappaBp65/p50), AKT network (AKT, GSK3beta, p70S6 kinase), mediators of autophagy (beclin-1, LC3), and myogenesis (myogenin, MyoD, Myf5, myostatin) were determined. Atrogin-1 and Nedd4, two ligases regulating ubiquitin-mediated protein degradation and myostatin, a negative regulator of muscle growth, were significantly increased in the muscle of patients with COPD. MuRF1, Myf5, myogenin, and MyoD were not differentially expressed. There were no differences in the level of phosphorylation of AKT, GSK3beta, p70S6kinase, or IkappaBalpha, activation of NF-kappaBp65 or NF-kappaBp50, or level of expression of beclin-1 or LC3, suggesting that AKT signaling was not down-regulated and the NF-kappaB inflammatory pathway and autophagy were not activated in the COPD muscle. We conclude that muscle atrophy associated with COPD results from the recruitment of specific regulators of ubiquitin-mediated proteolytic pathways and inhibition of muscle growth.

Intensive care unit-acquired weakness: clinical phenotypes and molecular mechanisms.

Intensive care unit-acquired weakness (ICUAW) begins within hours of mechanical ventilation and may not be completely reversible over time. It represents a major functional morbidity of critical illness and is an important patient-centered outcome with clear implications for quality of life and resumption of prior work and lifestyle. There is heterogeneity in functional outcome related to ICUAW across various patient populations after an episode of critical illness. This state-of-the art review argues that this observed heterogeneity may represent a clinical spectrum of disability in which there are recognizable clinical phenotypes for outcome according to age, burden of comorbid illness, and ICU length of stay. It further argues that these functional outcomes are modified by mood, cognition, and caregiver physical and mental health. This proposed construct of clinical phenotypes will be used as a framework for a review of the current literature on the molecular biology of muscle and nerve injury. This translational approach for the development of models pairing clinical phenotypes for different functional outcomes after critical illness with molecular mechanism of injury may offer unique insights into the diagnosis and treatment of muscle and nerve lesions.

Activating Transcription Factor 3 Confers Protection against Ventilator-induced Lung Injury

RATIONALE Ventilator-induced lung injury (VILI) significantly contributes to mortality in patients with acute respiratory distress syndrome, the most severe form of acute lung injury. Understanding the molecular basis for response to cyclic stretch (CS) and its derangement during high-volume ventilation is of high priority. OBJECTIVES To identify specific molecular regulators involved in the development of VILI. METHODS We undertook a comparative examination of cis-regulatory sequences involved in the coordinated expression of CS-responsive genes using microarray analysis. Analysis of stretched versus nonstretched cells identified significant enrichment for genes containing putative binding sites for the transcription factor activating transcription factor 3 (ATF3). To determine the role of ATF3 in vivo, we compared the response of ATF3 gene-deficient mice to wild-type mice in an in vivo model of VILI. MEASUREMENTS AND MAIN RESULTS ATF3 protein expression and nuclear translocation is increased in the lung after mechanical ventilation in wild-type mice. ATF3-deficient mice have greater sensitivity to mechanical ventilation alone or in conjunction with inhaled endotoxin, as demonstrated by increased cell infiltration and proinflammatory cytokines in the lung and bronchoalveolar lavage, and increased pulmonary edema and indices of tissue injury. The expression of stretch-responsive genes containing putative ATF3 cis-regulatory regions was significantly altered in ATF3-deficient mice. CONCLUSIONS ATF3 deficiency confers increased sensitivity to mechanical ventilation alone or in combination with inhaled endotoxin. We propose ATF3 acts to counterbalance CS and high volume-induced inflammation, dampening its ability to cause injury and consequently protecting animals from injurious CS.

Skeletal Muscle Dysfunction in Idiopathic Pulmonary Arterial Hypertension

Despite improvements in survival with disease-targeted therapies, the majority of patients with pulmonary arterial hypertension (PAH) have persistent exercise intolerance that results from impaired cardiac function and skeletal muscle dysfunction. Our intent was to understand the molecular mechanisms mediating skeletal muscle dysfunction in PAH. A total of 12 patients with PAH and 10 matched control subjects were assessed. Patients with PAH demonstrated diminished exercise capacity (lower oxygen uptake max, lower anaerobic threshold and higher minute ventilation/CO2) compared with control subjects. Quadriceps muscle cross-sectional area was significantly smaller in patients with PAH. The vastus lateralis muscle was biopsied to enable muscle fiber morphometric assessment and to determine expression levels/activation of proteins regulating (1) muscle mass, (2) mitochondria biogenesis and shaping machinery, and (3) excitation-contraction coupling. Patients with PAH demonstrated a decreased type I/type II muscle fiber ratio, with a smaller cross-sectional area in the type I fibers. Diminished AKT and p70S6 kinase phosphorylation, with increased atrogin-1 and muscle RING-finger protein-1 transcript levels, were evident in the PAH muscle, suggesting engagement of cellular signaling networks stimulating ubiquitin-proteasome-mediated proteolysis of muscle, with concurrent depression of networks mediating muscle hypertrophy. Although there were no differences in expression/activation of proteins associated with mitochondrial biogenesis or fission (MTCO2 [cytochrome C oxidase subunit II]/succinate dehydrogenase flavoprotein subunit A, mitochondrial transcription factor A, nuclear respiratory factor-1/dynamin-related protein 1 phosphorylation), protein levels of a positive regulator of mitochondrial fusion, Mitofusin2, were significantly lower in patients with PAH. Patients with PAH demonstrated increased phosphorylation of ryanodine receptor 1 receptors, suggesting that altered sarcoplasmic reticulum Ca(++) sequestration may impair excitation-contraction coupling in the PAH muscle. These data suggest that muscle dysfunction in PAH results from a combination of muscle atrophy and intrinsically impaired contractility.

Hypertrophic Airway Smooth Muscle Mass Correlates with Increased Airway Responsiveness in a Murine Model of Asthma

The increase of airway smooth muscle (ASM) mass in asthma results from hypertrophic and hyperplastic stimuli, and leads to an increase in cellular contractile proteins. However, little evidence correlates the relative contributions of hypertrophic and hyperplastic muscle with functional effects on airway resistance. We performed a ventilator-based assessment of respiratory mechanics and responsiveness to methacholine in a murine model of acute (3-week) ovalbumin (OVA)-induced airway inflammation, compared with a chronic (12-week) model. We correlated functional changes in airways Newtonian resistance (RN), peripheral tissue damping (G), and elastance (H) with the relative contributions of proliferation, hypertrophy, and apoptosis to increased ASM mass. Immunohistochemical analyses of treated (OVA-sensitized and OVA-challenged; OVA/OVA) and control (OVA-sensitized and saline-challenged; OVA/PBS) murine lungs showed an increase in ASM area in chronic, but not acute, OVA/OVA-treated mice that correlated positively with increased airway resistance to methacholine. Acute OVA/OVA-treated ASM exhibited an increase in proliferation with diminished apoptosis, which resolved in the chronic OVA/OVA model. Chronic OVA/OVA-treated ASM exhibited hypertrophy. Distinct temporal differences exist in the response of murine airways to antigenic challenge. We report that ASM proliferation and diminished apoptosis occur during the acute phase, followed by the development of smooth muscle hypertrophy and an increased muscle mass with chronic challenge, that correlate strongly with increased airway Newtonian resistance. The identification of a functionally relevant hypertrophic bronchial muscle mass highlights the possibility of regulating airway muscle hypertrophy as a novel therapeutic target in asthma.

Neuromuscular Blocking Agent Cisatracurium Attenuates Lung Injury by Inhibition of Nicotinic Acetylcholine Receptor-α1.

Background:Neuromuscular blocking agents (NMBAs) bind the nicotinic acetylcholine receptor &agr;1 (nAChR&agr;1) that also contributes to inflammatory signaling. Thus, the author hypothesized that the use of NMBA mitigates lung injury by improving ventilator synchrony and decreasing inflammatory responses. Methods:Lung injury was induced by intratracheal instillation of hydrogen chloride in rats that were randomized to receive no NMBA with evidence of asynchronous ventilation (noNMBA/aSYNC, n = 10); no NMBA with synchronous ventilation (noNMBA/SYNC, n = 10); cisatracurium (CIS, n = 10); or pancuronium (PAN, n = 10). Mechanical ventilation was set at a tidal volume of 6 ml/kg and positive end-expiratory pressure 8 cm H2O for 3 h. Human lung epithelial, endothelial, and CD14+ cells were challenged with mechanical stretch, lipopolysaccharide, lung lavage fluids (bronchoalveolar lavage fluid), or plasma obtained from patients (n = 5) with acute respiratory distress syndrome, in the presence or absence of CIS or small-interfering RNA and small hairpin RNA to attenuate the cell expression of nAChR&agr;1. Results:The use of CIS and PAN improved respiratory compliance (7.2 ± 0.7 in noNMBA/aSYNC, 6.6 ± 0.5 in noNMBA/SYNC, 5.9 ± 0.3 in CIS, and 5.8 ± 0.4 cm H2O/l in PAN; P < 0.05), increased PaO2 (140 ± 54, 209 ± 46, 269 ± 31, and 269 ± 54 mmHg, respectively, P < 0.05), and decreased the plasma levels of tumor necrosis factor-&agr; (509 ± 252 in noNMBA, 200 ± 74 in CIS, and 175 ± 84 pg/ml in PAN; P < 0.05) and interleukin-6 (5789 ± 79, 1608 ± 534, and 2290 ± 315 pg/ml, respectively; P < 0.05). The use of CIS and PAN or silencing the receptor nAChR&agr;1 resulted in decreased cytokine release in the human cells in response to a variety of stimuli mentioned earlier. Conclusions:The use of NMBA is lung protective through its antiinflammatory properties by blocking the nAChR&agr;1.

Microarray Meta-Analysis and Cross-Platform Normalization: Integrative Genomics for Robust Biomarker Discovery.

The diagnostic and prognostic potential of the vast quantity of publicly-available microarray data has driven the development of methods for integrating the data from different microarray platforms. Cross-platform integration, when appropriately implemented, has been shown to improve reproducibility and robustness of gene signature biomarkers. Microarray platform integration can be conceptually divided into approaches that perform early stage integration (cross-platform normalization) versus late stage data integration (meta-analysis). A growing number of statistical methods and associated software for platform integration are available to the user, however an understanding of their comparative performance and potential pitfalls is critical for best implementation. In this review we provide evidence-based, practical guidance to researchers performing cross-platform integration, particularly with an objective to discover biomarkers.

ICU-acquired weakness: mechanisms of disability.

Purpose of reviewICU-acquired weakness (ICUAW) is now recognized as a major complication of critical illness. There is no doubt that ICUAW is prevalent – some might argue ubiquitous – after critical illness, but its true role, the interaction with preexisting nerve and muscle lesions as well as its contribution to long-term functional disability, remains to be elucidated. Recent findingsIn this article, we review the current state-of-the-art of the basic pathophysiology of nerve and muscle weakness after critical illness and explore the current literature on ICUAW with a special emphasis on the most important mechanisms of weakness. SummaryVariable contributions of structural and functional changes likely contribute to both early and late myopathy and neuropathy, although the specifics of the temporality of both processes, and the influence patient comorbidities, age, and nature of the ICU insult have on them, remain to be determined.

Muscle wasting and early mobilization in acute respiratory distress syndrome.

Survivors of acute respiratory distress syndrome often sustain muscle wasting and functional impairment related to intensive care unit (ICU)-acquired weakness (ICUAW) and this disability may persist for years after ICU discharge. Early diagnosis in cooperative patients by physical examination is recommended to identify patients at risk for weaning failure and to minimize prolongation of risk factors for ICUAW. When possible, early rehabilitation in critically ill patients improves functional outcomes, likely by reducing disuse atrophy. Interventions designed to correct the functional impairment are lacking and further research to delineate the molecular pathways that give rise to ICUAW are needed.

Transcriptomic analysis reveals abnormal muscle repair and remodeling in survivors of critical illness with sustained weakness

ICU acquired weakness (ICUAW) is a common complication of critical illness characterized by structural and functional impairment of skeletal muscle. The resulting physical impairment may persist for years after ICU discharge, with few patients regaining functional independence. Elucidating molecular mechanisms underscoring sustained ICUAW is crucial to understanding outcomes linked to different morbidity trajectories as well as for the development of novel therapies. Quadriceps muscle biopsies and functional measures of muscle strength and mass were obtained at 7 days and 6 months post-ICU discharge from a cohort of ICUAW patients. Unsupervised co-expression network analysis of transcriptomic profiles identified discrete modules of co-expressed genes associated with the degree of muscle weakness and atrophy in early and sustained ICUAW. Modules were enriched for genes involved in skeletal muscle regeneration and extracellular matrix deposition. Collagen deposition in persistent ICUAW was confirmed by histochemical stain. Modules were further validated in an independent cohort of critically ill patients with sepsis-induced multi-organ failure and a porcine model of ICUAW, demonstrating disease-associated conservation across species and peripheral muscle type. Our findings provide a pathomolecular basis for sustained ICUAW, implicating aberrant expression of distinct skeletal muscle structural and regenerative genes in early and persistent ICUAW.