Role of LPS-induced microfilament depolymerization in MIP-2 production from rat pneumocytes

Dexamethasone upregulates macrophage PIEZO1 via SGK1, suppressing inflammation and increasing ROS and apoptosis

The side effects of high-dose dexamethasone in anti-infection include increased ROS production and immune cell apoptosis. Dexamethasone effectively activates serum/glucocorticoid-regulated kinase 1 (SGK1), which upregulates various ion channels by activating store-operated calcium entry (SOCE), leading to Ca2+ oscillations. PIEZO1 plays a crucial role in macrophages' immune activity and function, but whether dexamethasone can regulate PIEZO1 by enhancing SOCE via SGK1 activation remains unclear. The effects of dexamethasone were assessed in a mouse model of sepsis, and primary BMDMs and the RAW264.7 were treated with overexpression plasmids, siRNAs, or specific activators or inhibitors to examine the relationships between SGK1, SOCE, and PIEZO1. The functional and phenotypic changes of mouse and macrophage models were detected. The results indicate that high-dose dexamethasone upregulated SGK1 by activating the macrophage glucocorticoid receptor, which enhanced SOCE and subsequently activated PIEZO1. Activation of PIEZO1 resulted in Ca2+ influx and cytoskeletal remodelling. The increase in intracellular Ca2+ mediated by PIEZO1 further increased the activation of SGK1 and ORAI1/STIM1, leading to intracellular Ca2+ peaks. In the context of inflammation, activation of PIEZO1 suppressed the activation of TLR4/NFκB p65 in macrophages. In RAW264.7 cells, PIEZO1 continuous activation inhibited the change in mitochondrial membrane potential, accelerated ROS accumulation, and induced autophagic damage and cell apoptosis in the late stage. CaMK2α was identified as a downstream mediator of TLR4 and PIEZO1, facilitating high-dose dexamethasone-induced macrophage immunosuppression and apoptosis. PIEZO1 is a new glucocorticoid target to regulate macrophage function and activity. This study provides a theoretical basis for the rational use of dexamethasone.

Antipseudomonal and Immunomodulatory Properties of Esc Peptides: Promising Features for Treatment of Chronic Infectious Diseases and Inflammation

Persistent infections, such as those provoked by the Gram-negative bacterium Pseudomonas aeruginosa in the lungs of cystic fibrosis (CF) patients, can induce inflammation with lung tissue damage and progressive alteration of respiratory function. Therefore, compounds having both antimicrobial and immunomodulatory activities are certainly of great advantage in fighting infectious diseases and chronic inflammation. We recently demonstrated the potent antipseudomonal efficacy of the antimicrobial peptide (AMP) Esc(1-21) and its diastereomer Esc(1-21)-1c, namely Esc peptides. Here, we confirmed this antimicrobial activity by reporting on the peptides’ ability to kill P. aeruginosa once internalized into alveolar epithelial cells. Furthermore, by means of enzyme-linked immunosorbent assay and Western blot analyses, we investigated the peptides’ ability to detoxify the bacterial lipopolysaccharide (LPS) by studying their effects on the secretion of the pro-inflammatory cytokine IL-6 as well as on the expression of cyclooxygenase-2 from macrophages activated by P. aeruginosa LPS. In addition, by a modified scratch assay we showed that both AMPs are able to stimulate the closure of a gap produced in alveolar epithelial cells when cell migration is inhibited by concentrations of Pseudomonas LPS that mimic lung infection conditions, suggesting a peptide-induced airway wound repair. Overall, these results have highlighted the two Esc peptides as valuable candidates for the development of new multifunctional therapeutics for treatment of chronic infectious disease and inflammation, as found in CF patients.

Escherichia coli lipopolysaccharide induces alveolar epithelial cell stiffening

INTRODUCTION

Application of lipopolysaccharide (LPS) is a widely employed model to mimic acute respiratory distress syndrome (ARDS). Available data regarding LPS-induced biomechanical changes on pulmonary epithelial cells are limited only to P. aeruginosa LPS. Considering that LPS from different bacteria could promote a specific mechanical response in epithelial cells, we aim to assess the effect of E. coli LPS, widely employed as a model of ARDS, in the biomechanics of alveolar epithelial cells.

METHODS

Young's modulus (E) of alveolar epithelial cells (A549) was measured by atomic force microscopy every 5 min throughout 60 min of experiment after treatment with LPS from E. coli (100 μg/mL). The percentage of cells presenting actin stress fibers (F-actin staining) was also evaluated. Control cells were treated with culture medium and the values obtained were compared with LPS-treated cells for each time-point.

RESULTS

Application of LPS induced significant increase in E after 20 min (77%) till 60 min (104%) in comparison to controls. Increase in lung epithelial cell stiffness induced by LPS was associated with a higher number of cells presenting cytoskeletal remodeling.

CONCLUSIONS

The observed effects of E. coli LPS on alveolar epithelial cells suggest that this widely-used LPS is able to promote a quick formation of actin stress fibers and stiffening cells, thereby facilitating the disruption of the pulmonary epithelial barrier.

Depolymerization of Actin Filament by Cytochalasin E Induces Interleukin-8 Production and Up-Regulates CD54 in the HeLa Epithelial Cell Line

We previously reported that the depolymerization of actin filament by cytochalasin E enhances low affinity Fcepsilon receptor II (CD23) expression on the human monocyte-like cell line, U937 (J. Clin. Immunol. 20: 235, 2000). In this study, we found that cytochalasin E strongly induces interleukin-8 through an epithelial cell line, HeLa, in dose- and time-dependent manners as assessed by enzyme-linked immunoassay and reverse transcription-polymerase chain reaction techniques. In addition, interleukin-8 production in the HeLa cells cultured with cytochalasin E was blocked in the presence of protein kinase C inhibitors, Go6976 and H-7. On the other hand, it was found that CD54 (intercellular adhesion molecule-1; ICAM-1) expression on the HeLa cells and the secretion of soluble CD54 were significantly up-regulated after culturing with cytochalasin E, and that these up-regulations of CD54 were also suppressed by Go6976. Taken together, these findings indicate that cytochalasin E activates protein kinase C under the depolymerization of actin filament, leading to the induction of interleukin-8 production and the up-regulation of CD54 in HeLa cells.

Adenosine-5'-triphosphate release by Mannheimia haemolytica, lipopolysaccharide, and interleukin-1 stimulated bovine pulmonary epithelial cells

Mannheimia haemolytica, one of the agents associated with bovine respiratory disease complex, can cause severe lung pathology including the leakage of vascular products into the airways and alveoli. Previous work by this laboratory has demonstrated that bovine lung endothelial and epithelial cells undergo dramatic permeability increases when exposed to adenosine-5'-triphosphate (ATP). Therefore, we wanted to determine if ATP levels were elevated in bronchoalveolar lavage (BAL) samples from calves experimentally infected with M. haemolytica. In addition, cultured bovine pulmonary epithelial (BPE) cells were stimulated with heat-killed and live M. haemolytica bacteria, lipopolysaccharide (LPS), lipoteichoic acid (LTA), interleukin-1 (IL-1), and zymosan activated plasma (ZAP) to determine whether they might release extracellular ATP during in vitro infection. Calves experimentally exposed to M. haemolytica had an approximately 2-fold higher level of ATP in their BAL samples compared to control. BPE cells exposed to increasing numbers of heat-killed or live M. haemolytica had significantly increased levels of ATP release as compared to time-matched controls. Finally, BPE cells treated with several concentrations of LPS and IL-1 had increases in ATP release as compared to time-matched controls. This increase appeared to be a result of active ATP secretion by the cells, as cell viability was similar between treated and non-treated cells. Neither ZAP nor LTA induced any ATP release by the cells. In conclusion, ATP levels are elevated in lung secretions from calves infected with M. haemolytica. In addition, lung epithelial cells can actively release ATP when exposed to heat-killed or live M. haemolytica, LPS or IL-1.

Cytoskeletal regulation of epithelial barrier function during inflammation

Increased epithelial permeability is a common and important consequence of mucosal inflammation that results in perturbed body homeostasis and enhanced exposure to external pathogens. The integrity and barrier properties of epithelial layers are regulated by specialized adhesive plasma membrane structures known as intercellular junctions. It is generally believed that inflammatory stimuli increase transepithelial permeability by inducing junctional disassembly. This review highlights molecular events that lead to disruption of epithelial junctions during inflammation. We specifically focus on key mechanisms of junctional regulation that are dependent on reorganization of the perijunctional F-actin cytoskeleton. We discuss critical roles of myosin-II-dependent contractility and actin filament turnover in remodeling of the F-actin cytoskeleton that drive disruption of epithelial barriers under different inflammatory conditions. Finally, we highlight signaling pathways induced by inflammatory mediators that regulate reorganization of actin filaments and junctional disassembly in mucosal epithelia.

Early physiological and biological features in three animal models of induced acute lung injury

INTRODUCTION

Critically ill patients often develop acute lung injury (ALI) in the context of different clinical conditions. We aimed to explore differences in early local and systemic features in three experimental animal models of ALI.

METHODS

Mechanically ventilated male Sprague-Dawley rats were randomized to high tidal volume (VT) ventilation (HVT) (n = 8, VT 24 ml/kg), massive brain injury (MBI) (n = 8, VT 8 ml/kg) or endotoxemia (LPS) (n = 8, VT 8 ml/kg). Each experimental group had its own control group of eight rats (VT 8 ml/kg). We measured arterial blood gases, mean arterial pressure, lung compliance, inflammatory mediators in plasma and their expression and gelatinase activity in the lungs after 3 h of injury.

RESULTS

Despite maintaining relatively normal lung function without evidence of important structural changes, we observed altered lung and systemic inflammatory responses in all three experimental models. LPS triggered the most robust inflammatory response and HVT the lowest systemic proinflammatory response. The HVT group had higher Il6, Tnf and Cxcl2 mRNA in lungs than MBI animals. Metalloproteinase activity/expression and neutrophilic recruitment in the lungs were higher in HVT than in LPS or MBI.

CONCLUSIONS

The early responses to direct or remote lung insult in our three models of ALI captured different physiological and biological features that could lead to respiratory and/or multiorgan failure.

Effect of cytoskeleton inhibitors on deadhesion kinetics of HepG2 cells on biomimetic surface

Cytochalasin-D (Cyto-D) and latrunculin-A (Lat-A) are known inhibitors of actin microfilaments and adversely affect the physiological functions of anchorage-dependent cells. Alternatively, doxorubicin (Dox), a chemotherapeutic drug is known to induce apoptosis and cell detachment of tumor cells. However, the intricate interplay between drug administration, cytoskeletal rearrangement and biophysical responses of live cells on immobilized layer of extracellular matrix (ECM) protein remains unknown. In this study, the deadhesion kinetics and actin remodeling of live HepG2 cells following the addition of the three drugs are probed with confocal reflectance interference contrast microscopy (C-RICM) and fluorescence confocal microscopy. First, it is shown that the reduction in two-dimensional spread area of HepG2 cells is 10.5%, 15.4% and 21.9% under the influence of 5 microM of Lat-A, Cyto-D and Dox, respectively. Secondly, C-RICM demonstrates the recession of strong adhesion contact against time of cell seeding upon the addition of the three drugs. Thirdly, the initial cell detachment rate and extent of reduction in the degree of cell deformation (a/R) are dependent on both the drug types and concentration. Lastly, oscillation-like responses of a/R and adhesion energy are uniquely found in Lat-A induced cell detachment. Overall, our biophysical approaches have been proven as a highly quantitative platform for elucidating the interfacial properties of adherent cells on biomimetic surfaces under cytoskeleton disruption.

Acute lung injury and cell death: how many ways can cells die?

Apoptosis has been considered as an underlying mechanism in acute lung injury/acute respiratory distress syndrome and multiorgan dysfunction syndrome. Recently, several alternative pathways for cell death (such as caspase-independent cell death, oncosis, and autophagy) have been discovered. Evidence of these pathways in the pathogenesis of acute lung injury has also come into light. In this article, we briefly introduce cell death pathways and then focus on studies related to lung injury. The different types of cell death that occur and the underlying mechanisms utilized depend on both experimental and clinical conditions. Lipopolysaccharide-induced acute lung injury is associated with apoptosis via Fas/Fas ligand mechanisms. Hyperoxia and ischemia-reperfusion injury generate reactive oxidative species, which induce complex cell death patterns composed of apoptosis, oncosis, and necrosis. Prolonged overexpression of inflammatory mediators results in increased production and activation of proteases, especially cathepsins. Activation and resistance to death of neutrophils also plays an important role in promoting parenchymal cell death. Knowledge of the coexisting multiple cell death pathways and awareness of the pharmacological inhibitors targeting different proteases critical to cell death may lead to the development of novel therapies for acute lung injury.

Antioxidants preserve macrophage phagocytosis of Pseudomonas aeruginosa during hyperoxia

Pseudomonas. aeruginosa (PA) is a leading cause of nosocomial pneumonia in patients receiving mechanical ventilation with hyperoxia. Exposure to supraphysiological concentrations of reactive oxygen species during hyperoxia may result in macrophage damage that reduces their ability to phagocytose PA. We tested this hypothesis in cultured macrophage-like RAW 264.7 cells and alveolar macrophages from mice exposed to hyperoxia. Exposure to hyperoxia induced a similarly impaired phagocytosis of both the mucoid and the nonmucoid forms of PA in alveolar macrophages and RAW cells. Compromised PA phagocytosis was associated with cytoskeleton disorganization and actin oxidation in hyperoxic macrophages. To test whether moderate concentrations of O(2) limit the loss of phagocytic function induced by > or =95% O(2), mice and RAW cells were exposed to 65% O(2). Interestingly, although the resulting lung injury/cell proliferation was not significant, exposure to 65% O(2) resulted in a marked reduction in PA phagocytosis that was comparable to that of > or =95% O(2). Treatment with antioxidants, even post hyperoxic exposure, preserved actin cytoskeleton organization and phagocytosis of PA. These data suggest that hyperoxia reduces macrophage phagocytosis through effects on actin functions which can be preserved by antioxidant treatment. In addition, administration of moderate rather than higher concentrations of O2 does not improve macrophage phagocytosis of PA.

Long pentraxin 3 in pulmonary infection and acute lung injury

Long pentraxin 3 (PTX3) is a newly discovered acute phase protein produced at the sites of infection and inflammation by tissue cells, macrophages, monocytes, and dendritic cells. PTX3 plays an important role in preventing infection of certain fungi, bacteria, and viruses in the lung. Recombinant PTX3 has been proposed as a potential antifungal molecule for therapy. However, under certain experimental conditions, such as intestinal ischemia-reperfusion, high volume mechanical ventilation, or severe bacterial infection, increased expression of PTX3 is associated with more severe lung injury. Therefore, it is necessary to further explore the sources of PTX3 in the lung and the regulatory mechanisms of its expression. It is also essential to further determine how PTX3 binds to pathogens, complement, and apoptotic cells, and to determine whether PTX3 has a specific receptor in targeted cells. These studies will provide insight into the pathological processes of pulmonary infection and acute lung injury and provide potential novel therapeutic strategies to control pulmonary infections without severe lung injury.

Lipopolysaccharide Transiently Activates THP-1 Cell Adhesion

Lipopolysaccharide stimulation of adherent THP-1 cells induces morphological changes that are associated with the reorganization of the actin cytoskeleton. We hypothesized that LPS would also increase THP-1 cell adhesion and sought to determine the signaling mechanisms regulating this response. We show that LPS significantly increases THP-1 cell attachment after 1 h, supporting the idea that LPS can stimulate integrin function. By 4 h however, the number of adherent cells returned to control levels. Importantly, detached cells were determined to be viable by propidium iodide staining, indicating that the increase in cell adhesion was transient. LPS-induced adhesion to fibrinogen- but not fibronectin-coated wells was also transient, suggesting that adhesion reflected beta2 integrin activation. This idea was supported by the fact that LPS-induced adhesion could be blocked by a function-blocking anti-beta2 integrin antibody. Interestingly, the protein tyrosine phosphatase (PTP) inhibitor, phenylarsine oxide, prevented cell detachment. Taken together, these data suggest that LPS-mediated integrin activation is transient and can be regulated by PTP-mediated signaling events.

Lipopolysaccharide accelerates caspase-independent but cathepsin B-dependent death of human lung epithelial cells

Caspase-independent cell death has drawn increasing attention. In the present study, we found that lipopolysaccharide (LPS) accelerated spontaneous death of human lung epithelial A549 cells in a serum- and cell density-dependent manner: while serum starvation has been demonstrated to induce apoptosis in the same cell line, LPS-induced cell death was only observed in the presence of serum; in addition, the cell death was not observed when the cells were seeded at 10- or 100-fold lower density. The apoptotic features were demonstrated by TUNEL assay, DNA laddering and Annexin V staining. However, treatment of cells with two commonly used pan-caspase inhibitors, zVAD.fmk or BOC-D.fmk, failed to block cell death. In contrast, two cathepsin B inhibitors, Ca074-Me or N-1845, reduced cell death significantly. A time-dependent activation of cathepsin B, but not caspase 3, was observed in both control and LPS-treated cells. Although LPS did not further activate cathepsin B or its release, it increased expression and translocation of apoptosis inducing factor from mitochondria to the nucleus, and increased release of cytochrome c from mitochondria. LPS-induced cell death was significantly attenuated by either N-acetyl-L-cysteine or pyrrolidine-dithiocarbamate, both free radical scavengers. Disruption of lipid raft formation with filipin or methyl-beta-cyclodextrin also reduced apoptosis significantly, suggesting that lipid raft-dependent signaling is essential. These data imply that confluent cells undergo spontaneous cell death mediated by cathepsin B; LPS may accelerate this caspase-independent cell death through release of mitochondrial contents and reactive oxygen species.

Chlamydophila pneumoniae induces expression of toll-like receptor 4 and release of TNF-alpha and MIP-2 via an NF-kappaB pathway in rat type II pneumocytes

Background

The role of alveolar type II cells in the regulation of innate and adaptive immunity is unclear. Toll-like receptors (TLRs) have been implicated in host defense. The purpose of the present study was to investigate whether Chlamydophila pneumoniae (I) alters the expression of TLR2 and/orTLR4 in type II cells in a (II) Rho-GTPase- and (III) NF-κB-dependent pathway, subsequently (IV) leading to the production of (IV) pro-inflammatory TNF-α and MIP-2.

Methods

Isolated rat type II pneumocytes were incubated with C. pneumoniae after pre-treatment with calcium chelator BAPTA-AM, inhibitors of NF-κB (parthenolide, SN50) or with a specific inhibitor of the Rho-GTPase (mevastatin). TLR2 and TLR4 mRNA expressions were analyzed by PCR. Activation of TLR4, Rac1, RhoA protein and NF-κB was determined by Western blotting and confocal laser scan microscopy (CLSM) and TNF-α and MIP-2 release by ELISA.

Results

Type II cells constitutively expressed TLR4 and TLR2 mRNA. A prominent induction of TLR4 but not TLR2 mRNA was detected after 2 hours of incubation with C. pneumoniae. The TLR4 protein expression reached a peak at 30 min, began to decrease within 1–2 hours and peaked again at 3 hours. Incubation of cells with heat-inactivated bacteria (56°C for 30 min) significantly reduced the TLR4 expression. Treated bacteria with polymyxin B (2 μg/ml) did not alter TLR4 expression. C. pneumoniae-induced NF-κB activity was blocked by TLR4 blocking antibodies. TLR4 mRNA and protein expression were inhibited in the presence of BAPTA-AM, SN50 or parthenolide. TNF-α and MIP-2 release was increased in type II cells in response to C. pneumoniae, whereas BAPTA-AM, SN50 or parthenolide decreased the C. pneumoniae-induced TNF-α and MIP-2 release. Mevastatin inhibited C. pneumoniae-mediated Rac1, RhoA and TLR4 expression.

Conclusion

The TLR4 protein expression in rat type II cells is likely to be mediated by a heat-sensitive C. pneumoniae protein that induces a fast Ca²⁺-mediated NF-κB activity, necessary for maintenance of TLR4 expression and TNF-α and MIP-2 release through possibly Rac and Rho protein-dependent mechanism. These results indicate that type II pneumocytes play an important role in the innate pulmonary immune system and in inflammatory response mechanism of the alveolus.

DNA microarray analysis of gene expression in alveolar epithelial cells in response to TNFalpha, LPS, and cyclic stretch

Recent evidence suggests that alveolar epithelial cells (AECs) may contribute to the development, propagation, and resolution of acute lung injury (ALI)/acute respiratory distress syndrome (ARDS). Proinflammatory cytokines, pathogen products, and injurious mechanical ventilation are important contributors of excessive inflammatory responses in the lung. In the present study, we used cDNA microarrays to define the gene expression patterns of A549 cells (an AEC line) in the early stages of three models of pulmonary parenchymal cell activation: cells treated with tumor necrosis factor-alpha (TNFalpha) (20 ng/ml), lipopolysaccharide (LPS, 1 microg/ml), or cyclic stretch (20% elongation) for either 1 h or 4 h. Differential gene expression profiles were determined by gene array analysis. TNFalpha induced an inflammatory response pattern, including induction of genes for chemokines, inflammatory mediators, and cell surface membrane proteins. TNFalpha also increased genes related to pro- and anti-apoptotic proteins, signal transduction proteins, and transcriptional factors. TNFalpha further induced a group of genes that may form a negative feedback loop to silence the NFkappaB pathway. Stimulation of AECs with mechanical stretch changed cell morphology and activated Src protein tyrosine kinase. The combination of TNFalpha plus stretch enhanced or attenuated expression of multiple genes. LPS decreased microfilament polymerization but had less impact on NFkappaB translocation and gene expression. Results from this study indicate that AECs can tailor their response to different stimuli or/and combination of stimuli and subsequently play an important role in acute inflammatory responses in the lung.

Calprotectin release from human neutrophils is induced by Porphyromonas gingivalis lipopolysaccharide via the CD-14-Toll-like receptor-nuclear factor kappaB pathway

OBJECTIVES

Calprotectin is a cytosolic protein with antibacterial action in leukocytes and its level increases in some inflammatory diseases, including periodontal diseases, rheumatoid arthritis and ulcerative colitis. Recently, we found that the lipopolysaccharide of Porphyromonas gingivalis (P-LPS) induced calprotectin release from human neutrophils. P-LPS, a major virulence factor of periodontal pathogens, is known to induce the production and release of inflammatory cytokines through CD14, Toll-like receptor (TLR) and nuclear factor kappaB (NF-kappaB). In the present study, we investigated whether calprotectin release by P-LPS is induced via the CD14-TLR-NF-kappaB pathway and the cellular mechanism of calprotectin release in human neutrophils.

MATERIAL AND METHODS

Human neutrophils were isolated from the peripheral blood of healthy donors and pre-incubated in medium containing antibodies against CD14, TLR2 and TLR4, or several inhibitors of NF-kappaB, microtubules and microfilaments, and then incubated with P-LPS. The calprotectin amount in the culture medium was determined using ELISA, and the nuclear extracts from cells were used for the examination of NF-kappaB binding activity using electrophoretic mobility shift assays.

RESULTS

P-LPS increased calprotectin release from neutrophils and its induction was inhibited by anti-CD14 and anti-TLR2 antibodies, but not by two anti-TLR4 antibodies. NF-kappaB inhibitors suppressed P-LPS-induced NF-kappaB binding activity and calprotectin release. The inhibitors of microtubule and microfilament polymerization significantly decreased P-LPS-induced calprotectin release.

CONCLUSION

These results suggest that calprotectin release is induced by P-LPS via the CD14-TLR2-NF-kappaB signal pathway in human neutrophils and may be dependent on microtubule and microfilament systems.

Cellular biomechanics in the lung

Mechanical forces affect both the function and phenotype of cells in the lung. In this symposium, recent studies were presented that examined several aspects of biomechanics in lung cells and their relationship to disease. Wound healing and recovery from injury in the airways involve epithelial cell spreading and migration on a substrate that undergoes cyclic mechanical deformation; enhanced green fluorescent protein-actin was used in a stable cell line to examine cytoskeletal changes in airway epithelial cells during wound healing. Eosinophils migrate into the airways during asthmatic attacks and can also be exposed to cyclic mechanical deformation; cyclic mechanical stretch caused a decrease in leukotriene C(4) synthesis that may be dependent on mechanotransduction mechanisms involving the production of reactive oxygen species. Recent studies have suggested that proinflammatory cytokines are increased in ventilator-induced lung injury and may be elevated by overdistention of the lung tissue; microarray analysis of human lung epithelial cells demonstrated that cyclic mechanical stretch alone profoundly affects gene expression. Finally, airway hyperresponsiveness is a basic feature of asthma, but the relationship between airway hyperresponsiveness and changes in airway smooth muscle (ASM) function remain unclear. New analysis of the behavior of the ASM cytoskeleton (CSK) suggests, however, that the CSK may behave as a glassy material and that glassy behavior may account for the extensive ASM plasticity and remodeling that contribute to airway hyperresponsiveness. Together, the presentations at this symposium demonstrated the remarkable and varied roles that mechanical forces may play in both normal lung physiology as well as pathophysiology.