Extravascular fibrin, plasminogen activator, plasminogen activator inhibitors, and airway hyperresponsiveness

Regulation of airway contractility by plasminogen activators through N-methyl-D-aspartate receptor-1

Reactive airway disease is mediated by smooth muscle contraction initiated through several agonist-dependent pathways. Activation of type 1 N-methyl-D-aspartate receptors (NMDA-R1s) by plasminogen activators (PAs) has been linked to control of vascular tone, but their effect on airway smooth muscle contractility has not previously been studied to our knowledge. We observed that NMDA-R1s are expressed by human airway smooth muscle cells and constitutively inhibit the contraction of isolated rat tracheal rings in response to acetylcholine (Ach). Both tissue-type PA (tPA) and urokinase-type PA (uPA) bind to NMDA-R1 and reverse this effect, thereby enhancing Ach-induced tracheal contractility. Tracheal contractility initiated by Ach is reduced in rings isolated from tPA(-/-) and uPA(-/-) mice compared with their wild-type counterparts. The procontractile effect of uPA or tPA was mimicked and augmented by the nitric oxide synthase inhibitor, l-NAME. uPA and tPA further enhanced the contractility of rings denuded of epithelium, an effect that was inhibited by the NMDA-R antagonist, MK-801. Binding of PAs to NMDA-R1 and the subsequent activation of the receptor were inhibited by PA inhibitor type 1, by a PA inhibitor type 1-derived hexapeptide that recognizes the tPA and uPA docking domains, as well as by specific mutations within the docking site of tPA. These studies identify involvement of PAs and NMDA-R1 in airway contractility, and define new loci that could lead to the development of novel interventions for reactive airway disease.

Strain-dependent activation of NF-kappaB in the airway epithelium and its role in allergic airway inflammation

NF-kappaB activation in the airway epithelium has been established as a critical pathway in ovalbumin (Ova)-induced airway inflammation in BALB/c mice (Poynter ME, Cloots R, van Woerkom T, Butnor KJ, Vacek P, Taatjes DJ, Irvin CG, Janssen-Heininger YM. J Immunol 173: 7003-7009, 2004). BALB/c mice are susceptible to the development of allergic airway disease, whereas other strains of mice, such as C57BL/6, are considered more resistant. The goal of the present study was to determine the proximal signals required for NF-kappaB activation in the airway epithelium in allergic airway disease and to unravel whether these signals are strain-dependent. Our previous studies, conducted in the BALB/c mouse background, demonstrated that transgenic mice expressing a dominant-negative version of IkappaBalpha in the airway epithelium (CC10-IkappaBalpha(SR)) were protected from Ova-induced inflammation. In contrast to these earlier observations, we demonstrate here that CC10-IkappaBalpha(SR) transgenic mice on the C57BL/6 background were not protected from Ova-induced allergic airway inflammation. Consistent with this finding, Ova-induced nuclear localization of the RelA subunit of NF-kappaB was not observed in C57BL/6 mice, in contrast to the marked nuclear presence of RelA in BALB/c mice. Evaluation of cytokine profiles in bronchoalveolar lavage demonstrated elevated expression of TNF-alpha in BALB/c mice compared with C57BL/6 mice after an acute challenge with Ova. Finally, neutralization of TNF-alpha by a blocking antibody prevented nuclear localization of RelA in BALB/c mice after Ova challenge. These data suggest that the mechanism of response of the airway epithelium of immunized C57BL/6 mice to antigen challenge is fundamentally different from that of immunized BALB/c mice and highlight the potential importance of TNF-alpha in regulating epithelial NF-kappaB activation in allergic airway disease.

Fibrinogen binding to ICAM-1 promotes EGFR-dependent mucin production in human airway epithelial cells

Mucous hypersecretion is a serious feature of chronic airway diseases such as asthma, chronic obstructive pulmonary disease (COPD), and cystic fibrosis. Although mucins are produced via activation of an EGF receptor (EGFR) signaling cascade, the mechanisms leading to exaggerated mucin production in mucous hypersecretory diseases are unknown. Because expression of ICAM-1 and of the ICAM-1 ligand fibrinogen is increased in the airways of subjects with mucous hypersecretory diseases, we hypothesized that fibrinogen binding to ICAM-1 could increase EGFR-dependent mucin production in human airway (NCI-H292) epithelial cells. Consistent with this hypothesis, we found that an ICAM-1 neutralizing antibody and an ICAM-1(8-22) peptide that binds fibrinogen decreased mucin production induced by the EGFR ligand transforming growth factor (TGF)-alpha dose-dependently. Exogenous fibrinogen and a fibrinogen(117-133) peptide that binds ICAM-1 rescued mucin production in cells treated with the ICAM-1(8-22) peptide. Surprisingly, the ICAM-1(8-22) peptide increased EGFR phosphotyrosine and phospho-ERK1/2 in cells treated with TGF-alpha. The ICAM-1(8-22) peptide-induced increases in EGFR phosphotyrosine and phospho-ERK1/2 were prevented by exogenous fibrinogen, by the fibrinogen(117-133) peptide, and by selective inhibitors of phospholipase C (PLC), protein kinase C (PKC)-alpha/beta, and metalloproteases. These results suggest that fibrinogen binding to ICAM-1 promotes mucin production by decreasing TGF-alpha-induced EGFR and ERK1/2 activation and that the fibrinogen-ICAM-1-dependent decrease in EGFR and ERK1/2 activation occurs via inhibition of an early positive feedback pathway involving PLC- and PKC-alpha/beta-dependent metalloprotease activation and subsequent metalloprotease-dependent EGFR reactivation.

Physiologic dysfunction of the asthmatic lung: what's going on down there, anyway?

Asthma is a syndrome of lung dysfunction characterized by airflow obstruction, reversibility to bronchodilators, and airways hyperresponsiveness (AHR). There is a growing body of evidence that suggests that the principle defect in asthma is the occlusion of the airway lumen by liquid, fibrin, and mucus. The fall in FEV(1) observed in asthma is best explained by a loss of communicating airspaces and the rise in residual lung volume. Imaging studies in both human patients and experimental animals support this hypothesis. An increased propensity for the airways to close can be a cause of AHR. We conclude that loss of lung volume plays a central role in determining the dysfunction of the asthmatic lung as measured by FEV(1). Together, these recent findings provide a better understanding of the causes of airflow obstruction and AHR, suggesting new avenues for the development of more effective asthma therapies.

A severe deficiency of coagulation factor VIIa results in attenuation of the asthmatic response in mice

Eosinophil counts in the bronchoalveolar lavage fluid of wild-type (WT) mice increased after ovalbumin (OVA) challenge, a response that was diminished in comparably challenged low-expressing coagulation factor VII (FVII(tTA/tTA)) mice. Levels of T helper type 2 (Th2) cytokines, IL-4, IL-5, and IL-13, and eosinophil-attracting chemokines, eotaxin and RANTES, were also lower in the OVA-challenged FVII(tTA/tTA) mice. Eosinophils purified from low-FVII mice underwent apoptosis at a faster rate compared with WT eosinophils, and eosinophil migration in response to eotaxin was reduced in eosinophils obtained from FVII(tTA/tTA) mice. Airway hyperresponsiveness and mucous layer thickness were reduced in OVA-treated FVII(tTA/tTA) mice, and addition of exogenous coagulation factor X (FX) enhanced mucin production in human epithelial NCI-H292 cells. Correspondingly, incubation of FX with NCI-H292 cells resulted in activated (a) FX production, suggesting that the components required for FX activation were present on NCI-H292 cells. These results demonstrate that FVIIa functions in the asthmatic response to an allergen by stimulating lung eosinophilia, airway hyperresponsiveness, and mucin production, this latter effect through its ability to activate FX in conjunction with tissue factor.

Targeting eosinophils in asthma

Recruitment of eosinophils has long been recognized as a hallmark of the inflammatory response in asthma. However, the functions of this population of cells in host defense remain poorly understood. Eosinophils play an important part in the inflammatory response and have key regulatory roles in the afferent arm of the immune response. More recently, eosinophils have been demonstrated to participate in host defense against respiratory viruses. The specific contributions of eosinophils to the pathophysiology of asthma remain controversial. However, the balance of evidence indicates that they have a significant role in the disease, suggesting that they may be appropriate targets for therapy. Towards this end, a novel intervention of considerable potential interest is the use of an antibody directed against the beta common chain of the receptor for interleukin-3, interleukin-5 and granulocyte-macrophage colony-stimulating factor. However, eliminating eosinophils may not be a risk-free therapeutic strategy, as there is potentially an increased likelihood of respiratory viral infections. This may predispose to the development of acute exacerbations of asthma, an outcome that would have significant clinical implications.

Steroid-resistant neutrophilic inflammation in a mouse model of an acute exacerbation of asthma

Neutrophilic inflammation in acute exacerbations of asthma tends to be resistant to treatment with glucocorticoids. This may be related to decreased activity and expression of histone deacetylase-2 (HDAC2), which down-regulates expression of proinflammatory genes via recruitment to the glucocorticoid receptor complex. We assessed airway inflammation and response to steroid treatment in a novel mouse model of an acute exacerbation of chronic asthma. Systemically sensitized mice received low-level challenge with aerosolized ovalbumin for 4 weeks, followed by a single moderate-level challenge to induce enhanced inflammation in distal airways. We assessed the effects of pre-treatment with dexamethasone on the accumulation of inflammatory cells in the airways, airway responsiveness to methacholine, expression and enzymatic activity of nuclear proteins including histone acetyl transferase (HAT) and HDAC2, and levels of transcripts for neutrophil chemoattractant and survival cytokines. Dexamethasone suppressed inflammation associated with eosinophil and T-lymphocyte recruitment, but did not prevent neutrophil accumulation or development of airway hyperresponsiveness. Increased activity of HAT was suppressed by steroid treatment, but the marked diminution of HDAC2 activity and increased activity of nuclear factor-kappaB were not reversed. Correspondingly, elevated expression of mRNA for TNF-alpha, granulocyte-macrophage colony-stimulating factor, IL-8, and p21(waf) were also not suppressed by dexamethasone. Levels of lipid peroxidation and protein nitration products were elevated in the acute exacerbation model. We conclude that impaired nuclear recruitment of HDAC2 could be an important mechanism of steroid resistance of the neutrophilic inflammation in exacerbations of asthma. Oxidative stress may contribute to decreased HDAC2 activity.

Angiopoietin-1 protects against airway inflammation and hyperreactivity in asthma

RATIONALE

The angiopoietins (Ang) comprise a family of growth factors mainly known for their role in blood vessel formation and remodeling. The best-studied member, Ang-1, exhibits antiapoptotic and antiinflammatory effects. Although the involvement of Ang-1 in angiogenesis is well recognized, little information exists about its role in respiratory physiology and disease. On the basis of its ability to inhibit vascular permeability, adhesion molecule expression, and cytokine production, we hypothesized that Ang-1 administration might exert a protective role in asthma.

OBJECTIVES

To determine changes in the expression of Ang and to assess the ability of Ang-1 to prevent the histologic, biochemical, and functional changes observed in an animal model of asthma.

METHODS

To test our hypothesis, a model of allergic airway disease that develops after ovalbumin (OVA) sensitization and challenge was used.

MEASUREMENTS AND MAIN RESULTS

Ang-1 expression was reduced at the mRNA and protein levels in lung tissue of mice sensitized and challenged with OVA, leading to reduced Tie2 phosphorylation. Intranasal Ang-1 treatment prevented the OVA-induced eosinophilic lung infiltration, attenuated the increase in IL-5 and IL-13, and reduced eotaxin and vascular cell adhesion molecule 1 expression. These antiinflammatory actions of Ang-1 coincided with higher levels of IkappaB and decreased nuclear factor-kappaB binding activity. More importantly, Ang-1 reversed the OVA-induced increase in tissue resistance and elastance, improving lung function.

CONCLUSIONS

We conclude that Ang-1 levels are decreased in asthma and that administration of Ang-1 might be of therapeutic value because it prevents the increased responsiveness of the airways to constrictors and ameliorates inflammation.

The synergistic interactions of allergic lung inflammation and intratracheal cationic protein

RATIONALE

Airways hyperresponsiveness (AHR) is a hallmark feature of asthma, and can be caused by various disparate mechanisms. Mouse models of AHR have been useful for studying these mechanisms in isolation, but such models still typically do not exhibit the same degree of AHR as seen in severe human asthma. We hypothesized that more severe AHR in mice could be achieved by imbuing them with more than one mechanism of AHR.

OBJECTIVES

We sought to determine if the airway wall thickening accompanying allergic inflammation and the exaggerated smooth muscle shortening induced by intratracheal cationic protein could act together to produce a severe form of AHR.

METHODS

We used the forced oscillation technique to measure methacholine responsiveness in BALB/c mice that had been sensitized and challenged with ovalbumin followed by an intratracheal instillation of poly-l-lysine.

MEASUREMENTS AND MAIN RESULTS

We found that both ovalbumin and poly-l-lysine treatment alone caused moderate levels of AHR. When the two treatments were combined, however, they synergized in terms of their effect on lung stiffness to an extent that could even be fatal, reflecting a significantly enhanced level of airway closure.

CONCLUSIONS

Our results suggest that mechanistic synergy between airway wall thickening and exaggerated smooth muscle shortening produces a more germane mouse model of asthma that may have particular relevance to the pathophysiology of the acute severe asthma exacerbation.

Genome-wide profiling identifies epithelial cell genes associated with asthma and with treatment response to corticosteroids

Airway inflammation and epithelial remodeling are two key features of asthma. IL-13 and other cytokines produced during T helper type 2 cell-driven allergic inflammation contribute to airway epithelial goblet cell metaplasia and may alter epithelial-mesenchymal signaling, leading to increased subepithelial fibrosis or hyperplasia of smooth muscle. The beneficial effects of corticosteroids in asthma could relate to their ability to directly or indirectly decrease epithelial cell activation by inflammatory cells and cytokines. To identify markers of epithelial cell dysfunction and the effects of corticosteroids on epithelial cells in asthma, we studied airway epithelial cells collected from asthmatic subjects enrolled in a randomized controlled trial of inhaled corticosteroids, from healthy subjects and from smokers (disease control). By using gene expression microarrays, we found that chloride channel, calcium-activated, family member 1 (CLCA1), periostin, and serine peptidase inhibitor, clade B (ovalbumin), member 2 (serpinB2) were up-regulated in asthma but not in smokers. Corticosteroid treatment down-regulated expression of these three genes and markedly up-regulated expression of FK506-binding protein 51 (FKBP51). Whereas high baseline expression of CLCA1, periostin, and serpinB2 was associated with a good clinical response to corticosteroids, high expression of FKBP51 was associated with a poor response. By using airway epithelial cells in culture, we found that IL-13 increased expression of CLCA1, periostin, and serpinB2, an effect that was suppressed by corticosteroids. Corticosteroids also induced expression of FKBP51. Taken together, our findings show that airway epithelial cells in asthma have a distinct activation profile and identify direct and cell-autonomous effects of corticosteroid treatment on airway epithelial cells that relate to treatment responses and can now be the focus of specific mechanistic studies.

Transforming growth factor-beta1 suppresses airway hyperresponsiveness in allergic airway disease

RATIONALE

Asthma is characterized by increases in airway resistance, pulmonary remodeling, and lung inflammation. The cytokine transforming growth factor (TGF)-beta has been shown to have a central role in asthma pathogenesis and in mouse models of allergic airway disease.

OBJECTIVES

To determine the contribution of TGF-beta to airway hyperresponsiveness (AHR), we examined the time course, source, and isoform specificity of TGF-beta production in an in vivo mouse asthma model. To then elucidate the function of TGF-beta in AHR, inflammation, and pulmonary fibrosis, we examined the effects of blocking TGF-beta signaling with neutralizing antibody.

METHODS

Mice were sensitized and challenged with ovalbumin (OVA) to establish allergic airway disease. TGF-beta activity was neutralized by intranasal administration of monoclonal antibody.

MEASUREMENTS AND MAIN RESULTS

TGF-beta1 protein levels were increased in OVA-challenged lungs versus naive controls, and airway epithelial cells were shown to be a likely source of TGF-beta1. In addition, TGF-beta1 levels were elevated in OVA-exposed IL-5-null mice, which fail to recruit eosinophils into the airways. Neutralization of TGF-beta1 with specific antibody had no significant effect on airway inflammation and eosinophilia, although anti-TGF-beta1 antibody enhanced OVA-induced AHR and suppressed pulmonary fibrosis.

CONCLUSIONS

These data show that TGF-beta1 is the main TGF-beta isoform produced after OVA challenge, with a likely cellular source being the airway epithelium. The effects of blocking TGF-beta1 signaling had differential effects on AHR, fibrosis, and inflammation. While TGF-beta neutralization may be beneficial to abrogating airway remodeling, it may be detrimental to lung function by increasing AHR.

The role of gamma delta T cells in airway epithelial injury and bronchial responsiveness after chlorine gas exposure in mice

Background

Acute exposure to chlorine (Cl₂) gas causes epithelial injury and airway dysfunction. γδ T cells are present in the mucosal surface of the airways and may contribute to the injury/repair response of the epithelium.

Methods

C57Bl/6J (wild type) and TCR-δ^-/- mice exposed to Cl₂ (400 ppm) for 5 minutes underwent measurements of airway responses to i.v. methacholine (MCh) at 1, 3, and 5 days after exposure. Bronchoalveolar lavage was performed to determine epithelial and leukocyte counts, and protein content. Tissue repair was assessed by proliferating cell nuclear antigen (PCNA) immunoreactivity and by expression of keratinocyte growth factor (KGF) mRNA by real-time PCR.

Results

Wild type mice developed a greater degree of airway hyperresponsiveness to MCh at 1 day post exposure to Cl₂ compared with TCR-δ^-/- mice. Epithelial cell counts in BAL after Cl₂ exposure were greater in TCR-δ^-/- mice, but macrophages showed a later peak and granulocyte numbers were lower in TCR-δ^-/- than in wild type mice. Both groups had increased levels of total protein content in BAL after Cl₂ exposure that resolved after 3 and 5 days, respectively. Epithelial proliferating cell nuclear antigen staining was increased at 1 and 3 days post exposure and was similar in the two groups. KGF mRNA was constitutively expressed in both groups and did not increase significantly after Cl₂ but expression was lower in TCR-δ^-/- mice.

Conclusion

The severity of airway epithelial injury after Cl₂ is greater in TCR-δ^-/- mice but the inflammatory response and the change in airway responsiveness to methacholine are reduced. The rates of epithelial regeneration are comparable in both groups.

Airway hyperresponsiveness in allergically inflamed mice: the role of airway closure

RATIONALE

Allergically inflamed mice exhibit airway hyperresponsiveness to inhaled methacholine, which computer simulations of lung impedance suggest is due to enhanced lung derecruitment and which we sought to verify in the present study.

METHODS

BALB/c mice were sensitized and challenged with ovalbumin to induce allergic inflammation; the control mice were sensitized but received no challenge. The mice were then challenged with inhaled methacholine and respiratory system impedance tracked for the following 10 minutes. Respiratory elastance (H) was estimated from each impedance measurement. One group of mice was ventilated with 100% O(2) during this procedure and another group was ventilated with air. After the procedure, the mice were killed and ventilated with pure N(2), after which the trachea was tied off and the lungs were imaged with micro-computed tomography (micro-CT).

RESULTS

H was significantly higher in allergic mice than in control animals after methacholine challenge. The ratio of H at the end of the measurement period between allergic and nonallergic mice ventilated with O(2) was 1.36, indicating substantial derecruitment in the allergic animals. The ratio between lung volumes determined by micro-CT in the control and the allergic mice was also 1.36, indicative of a corresponding volume loss due to absorption atelectasis. Micro-CT images and histograms of Hounsfield units from the lungs also showed increased volume loss in the allergic mice compared with control animals after methacholine challenge.

CONCLUSIONS

These results support the conclusion that airway closure is a major component of hyperresponsiveness in allergically inflamed mice.

Thrombin-activatable procarboxypeptidase B regulates activated complement C5a in vivo

Plasma procarboxypeptidase B (proCPB) is activated by the endothelial thrombin-thrombomodulin [corrected] complex. Activated proCPB [corrected] (CPB) functions as a fibrinolysis inhibitor, but it may play a broader role by inactivating inflammatory mediators. To test this hypothesis, C5a-induced alveolitis was studied in wild-type (WT) and proCPB-deficient mice (proCPB-/-). C5a-induced alveolitis, as measured by cell counts and total protein contents in bronchoalveolar lavage fluids, was markedly enhanced in the proCPB-/- mice. E229K thrombin, a thrombin mutant with minimal clotting activity but retaining its ability to activate protein C and proCPB, attenuated C5a-induced alveolitis in WT but not in proCPB-/- mice, indicating that its beneficial effect is mediated primarily by its activation of proCPB. Lung tissue histology confirmed these cellular inflammatory responses. Delayed administration of E229K thrombin after the C5a instillation was ineffective in reducing alveolitis in WT mice, suggesting that the beneficial effect of E229K thrombin is due to the direct inhibition of C5a by CPB. Our studies show that thrombin-activatable proCPB, in addition to its role in fibrinolysis, has intrinsic anti-inflammatory functions. Its activation, along with protein C, by the endothelial thrombin-TM complex represents a homeostatic response to counteract the inflammatory mediators generated at the site of vascular injury.

Coagulation factor Xa modulates airway remodeling in a murine model of asthma

RATIONALE

Previous studies have demonstrated that dysregulated coagulation and fibrinolysis contribute to the pathogenesis of asthma.

OBJECTIVE

The role of procoagulant factor X in a murine model of ovalbumin (OVA)-induced asthma was investigated.

METHODS

Biochemical, cellular, and physiologic in vivo and in vitro approaches were used to determine effects of factor X on the asthmatic response in mice.

MEASUREMENTS AND MAIN RESULTS

Factor X transcript levels and factor Xa activity were increased in lungs of asthmatic mice challenged with OVA, compared with controls treated with phosphate-buffered saline. Factor X was highly expressed in bronchoalveolar lavage fluid macrophages from asthmatic mice. Treatment of mice with the factor Xa inhibitor fondaparinux during the last 4 wk of OVA challenge resulted in the attenuation of airway hyperresponsiveness but did not alter infiltration of inflammatory cells into the lung. There was a significant decrease in the thickness of the mucosal layer and in lung collagen deposition in fondaparinux-treated mice. In vitro investigations using human mucus-producing NCI-H292 cells indicated that exogenous factor Xa enhanced mucin production in a dose-dependent manner. Levels of amphiregulin, a protein that induces mucin production, were also increased in cells stimulated by factor Xa.

CONCLUSIONS

The results of this study introduce a novel participant in the asthmatic response and indicate that factor Xa functions in airway remodeling in asthma by stimulating mucin production, through regulation of amphiregulin expression and collagen deposition.

A central regulatory role for eosinophils and the eotaxin/CCR3 axis in chronic experimental allergic airway inflammation

To clarify the role and regulation of eosinophils, we subjected several key eosinophil-related genetically engineered mice to a chronic model of allergic airway inflammation aiming to identify results that were independent of the genetic targeting strategy. In particular, mice with defects in eosinophil development (Deltadbl-GATA) and eosinophil recruitment [mice deficient in CCR3 (CCR3 knockout) and mice deficient in both eotaxin-1 and eotaxin-2 (eotaxin-1/2 double knockout)] were subjected to Aspergillus fumigatus-induced allergic airway inflammation. Allergen-induced eosinophil recruitment into the airway was abolished by 98%, 94%, and 99% in eotaxin-1/2 double knockout, CCR3 knockout, and Deltadbl-GATA mice, respectively. Importantly, allergen-induced type II T helper lymphocyte cytokine production was impaired in the lungs of eosinophil- and CCR3-deficient mice. The absence of eosinophils correlated with reduction in allergen-induced mucus production. Notably, by using global transcript expression profile analysis, a large subset (29%) of allergen-induced genes was eosinophil- and CCR3-dependent; pathways downstream from eosinophils were identified, including in situ activation of coagulation in the lung. In summary, we present multiple lines of independent evidence that eosinophils via CCR3 have a central role in chronic allergic airway disease.

Induction of the plasminogen activator system by mechanical stimulation of human bronchial epithelial cells

Mechanical stimulation of the airway epithelium, as would occur during bronchoconstriction, is a potent stimulus and can activate profibrotic pathways. We used DNA microarray technology to examine gene expression in compressed normal human bronchial epithelial cells (NHBE). Compressive stress applied continuously over an 8-h period to NHBE cells led to the upregulation of several families of genes, including a family of plasminogen-related genes that were previously not known to be regulated in this system. Real-time PCR demonstrated a peak increase in gene expression of 8.0-fold for urokinase plasminogen activator (uPA), 16.2-fold for urokinase plasminogen activator receptor (uPAR), 4.2-fold for plasminogen activator inhibitor-1 (PAI-1), and 3.9-fold for tissue plasminogen activator (tPA). Compressive stress also increased uPA protein levels in the cell lysates (112.0 versus 82.0 ng/ml, P = 0.0004), and increased uPA (4.7 versus 3.3 ng/ml, P = 0.02), uPAR (1.3 versus 0.86 ng/ml, P = 0.007), and PAI-1 (50 versus 36 ng/ml, P = 0.006) protein levels in cell culture media. Functional studies demonstrated increased urokinase-dependent plasmin generation in compression-stimulated cells (0.0090 versus 0.0033 OD/min, P = 0.03). In addition, compression led to increased activation of matrix metalloproteinase (MMP)-9 and MMP-2 in a urokinase-dependent manner. In postmortem human lung tissue, we observed an increase in epithelial uPA and uPAR immunostaining in the airways of two patients who died in status asthmaticus compared with minimal immunoreactivity noted in airways from seven lung donors without asthma. Together these observations suggest an integrated response of airway epithelial cells to mechanical stimulation, acting through the plasminogen-activating system to modify the airway microenvironment.

Airway hyperreactivity in exacerbation of chronic asthma is independent of eosinophilic inflammation

We have developed an animal model to investigate the mechanisms underlying an acute exacerbation of chronic asthma. Sensitized BALB/c mice were exposed to aerosolized ovalbumin, either as chronic low-level challenge (mass concentration approximately 3 mg/m(3)) for 4 wk, a single moderate-level challenge (approximately 30 mg/m(3)), or chronic low-level followed by single moderate-level challenge (the acute exacerbation group). Compared with animals receiving chronic challenge alone, mice in the acute exacerbation group exhibited a more marked inflammatory response, with involvement of intrapulmonary airways and lung parenchyma, and increased numbers of lymphocytes and eosinophils in bronchoalveolar lavage fluid. They also developed airway hyperreactivity (AHR) to methacholine, demonstrable as increased transpulmonary resistance and decreased compliance. This pattern of AHR was absent in chronically challenged animals, but was also present in animals given single moderate-level challenge. However, compared with animals receiving a single moderate-level challenge, inflammation and AHR were induced more rapidly in the acute exacerbation group. Eosinophil-deficient GATA1 Deltadbl mice exhibited undiminished AHR in the acute exacerbation model. We conclude that in mice with pre-existing airway lesions resembling mild chronic asthma, exposure to a moderately high concentration of inhaled antigen induces features of an acute exacerbation. The inflammatory response involves distal airways and is associated with a distinct pattern of AHR, which develops independent of the enhanced eosinophilic inflammation.

The SERPINE2 gene is associated with chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a complex human disease likely influenced by multiple genes, cigarette smoking, and gene-by-smoking interactions, but only severe alpha 1-antitrypsin deficiency is a proven genetic risk factor for COPD. Prior linkage analyses in the Boston Early-Onset COPD Study have demonstrated significant linkage to a key intermediate phenotype of COPD on chromosome 2q. We integrated results from murine lung development and human COPD gene-expression microarray studies with human COPD linkage results on chromosome 2q to prioritize candidate-gene selection, thus identifying SERPINE2 as a positional candidate susceptibility gene for COPD. Immunohistochemistry demonstrated expression of serpine2 protein in mouse and human adult lung tissue. In family-based association testing of 127 severe, early-onset COPD pedigrees from the Boston Early-Onset COPD Study, we observed significant association with COPD phenotypes and 18 single-nucleotide polymorphisms (SNPs) in the SERPINE2 gene. Association of five of these SNPs with COPD was replicated in a case-control analysis, with cases from the National Emphysema Treatment Trial and controls from the Normative Aging Study. Family-based and case-control haplotype analyses supported similar regions of association within the SERPINE2 gene. When significantly associated SNPs in these haplotypic regions were included as covariates in linkage models, LOD score attenuation was observed most markedly in a smokers-only linkage model (LOD 4.41, attenuated to 1.74). After the integration of murine and human microarray data to inform candidate-gene selection, we observed significant family-based association and independent replication of association in a case-control study, suggesting that SERPINE2 is a COPD-susceptibility gene and is likely influenced by gene-by-smoking interaction.

Allergic airway inflammation

Several genes, including ADAM33, DPP10, PHF11, GPRA, and TIM-1, have been implicated in the pathogenesis and susceptibility to atopy and asthma. Advances have been made in defining the mechanism for the control of allergic airway inflammation in response to inhaled antigens. There is growing evidence that associates asthma with a systemic propensity for allergic type 2 T-cell cytokines. Disordered coagulation and fibrinolysis could also exacerbate asthma symptoms. Major emphasis on immunotherapy for asthma during the past decade has been to direct the immune response to a type 1 response. Recent literature supports the pivotal role of plasmacytoid dendritic cells and allergen-specific T-regulatory cells in the development of tolerance to allergens. In this review article, we discuss the current information on the pathogenesis of allergic airway inflammation and potential allergen immunotherapies, which could be beneficial in the treatment of airway inflammation, allergy, and asthma.

Asthma

There have been four types of drug treatment of asthma that have been used over the past 100 years. Belladonna alkaloids, derived from the thorn-apple plant were used in 1905, and chemically synthesized entities in this class are still in use today. Western medicine began to use adrenergic stimulants approximately 100 years ago, but they were likely used in Asian medicine long before that. Systemic treatment with corticosteroids was introduced into the treatment of asthma in the mid-20th century; inhaled corticosteroids have been in use for over 35 years. The last 40 years have also seen the development of the first targeted asthma treatments: cromones, antileukotrienes, and anti-IgE. As we learn more of the biology of asthma, we anticipate that more effective targeted asthma treatments will be developed.

NF-kappa B activation in airways modulates allergic inflammation but not hyperresponsiveness

Airways display robust NF-kappaB activation and represent targets for anti-inflammatory asthma therapies, but the functional importance of NF-kappaB activation in airway epithelium remains enigmatic. Therefore, transgenic mice were created in which NF-kappaB activation is repressed specifically in airways (CC10-IkappaBalpha(SR) mice). In response to inhaled Ag, transgenic mice demonstrated significantly ameliorated inflammation, reduced levels of chemokines, T cell cytokines, mucus cell metaplasia, and circulating IgE compared with littermate controls. Despite these findings, Ag-driven airways hyperresponsiveness was not attenuated in CC10-IkappaBalpha(SR) mice. This study clearly demonstrates that airway epithelial NF-kappaB activation orchestrates Ag-induced inflammation and subsequent adaptive immune responses, but does not contribute to airways hyperresponsiveness, the cardinal feature that underlies asthma.

Coagulation-dependent mechanisms and asthma

In several clinical disorders, there are interactions between inflammation-dependent tissue injury and thrombin formation, fibrin deposition, and impaired fibrinolysis. New evidence generated from a mouse model of allergic airway hyperreactivity suggests that disordered coagulation and fibrinolysis may contribute to the pathogenesis of asthma. The inflammatory mechanisms that lead to airway smooth muscle contraction and airway hyperresponsiveness may be associated with accumulation of extravascular fibrin, plasma exudates, and inflammatory cells that can lead to airway closure.