Cathepsin L activity is increased in alveolar macrophages and bronchoalveolar lavage fluid of smokers

Impaired SERPIN-Protease Balance in the Peripheral Lungs of Stable COPD Patients

The protease-antiprotease balance is involved in many biological processes, including blood coagulation, tissue remodeling, inflammation and immune responses. The aim of this study is to determine the balance between SERPINs and some related proteases in the lungs of stable COPD patients. In this cross-sectional study, the expression and localization of human SERPINs (anti-proteases) and some related proteases were measured in the lung parenchyma of mild-moderate COPD (MCOPD, n = 13) patients, control smokers (CS, n = 14) and control nonsmokers (CNS, n = 12) using transcriptome analysis, immunohistochemistry, and ELISA tests. Peripheral lung transcriptomic data showed increased mRNA levels of tissue plasminogen activator (tPA), cathepsin-L and caspase-1 as well as increased SERPINs A6, B3, B5, B11, B13 in the COPD group compared to the CNS group. At the protein level, IHC analysis showed that tPA and cathepsin-L increased in the bronchiolar epithelium and alveolar septa of the CS and COPD groups compared to the CNS group, as well as SERPINB5 and B13 in the alveolar macrophages and alveolar septa of the CS and COPD groups compared to the CNS group. SERPINA6 was shown to be decreased in the bronchiolar epithelium, bronchiolar lamina propria, and alveolar septa of the CS and COPD groups compared to the CNS group and was positively correlated with lung function. SERPINB3 was decreased in the alveolar septa of the CS group compared to the CNS group. The ELISA tests showed that in the total lung extracts, decreased levels of SERPINA6 and increased caspase-1 were shown in the COPD group compared to the CNS or both control groups, respectively. These data show an imbalance, at the protein level, of SERPINs and some related proteases in the lungs of the CS and stable COPD groups. These alterations may play a role in damaging the lung parenchyma of susceptible COPD patients.

Elevated Circulating Procathepsin L as a Potential Biomarker of Inflamm-aging

Inflamm-aging is a condition of low-grade and chronic systemic inflammation characterized by a systemic increase in multiple inflammatory biomarkers such as tumor necrosis factor (TNF), interleukin 6 (IL-6), C-reactive protein (CRP), and CXCL9 (MIG) in experimental and clinical settings. However, despite the recent identification of extracellular procathepsin L (pCTS-L) as a novel mediator of inflammatory diseases such as sepsis, its possible role in inflamm-aging was previously not investigated. In the present study, we compared blood levels of pCTS-L and other 62 cytokines and chemokines between young and aged Balb/C mice by Western blotting and Cytokine Antibody Arrays. In light of the surprising finding of a marked increase in blood pCTS-L levels in aged mice, we propose that blood pCTS-L levels may serve as another biomarker of inflamm-aging. Given the capacity of pCTS-L in inducing various cytokines (e.g., TNF and IL-6), it will be important to test the hypothetic role of pCTS-L in inflamm-aging under experimental and clinical conditions.

The protease inhibitor E64d might attenuate the development of experimental anti-glomerular basement membrane disease through regulating the activation of Th1 cells

BACKGROUND

Cathepsins have been recently identified as a regulator in the activation of Th1 and Th17 cells, which play an important role in the pathogenesis of anti-glomerular basement membrane (GBM) disease. Whether cathepsins contribute to the development of anti-GBM disease through regulating the activation of CD4+ T cell is still unclear.

METHODS

Rats with experimental anti-GBM disease was established by immunization with the nephritogenic T cell epitope α3127-148. E64d, a cysteine cathepsin inhibitor, was administered in vitro and vivo to evaluate the effect of cathepsins on regulating the activation of antigen specific T cells and the development of anti-GBM disease.

RESULTS

In rats with experimental anti-GBM diseases, E64d treatment not only reduced the levels of proteinuria, serum creatinine and anti-GBM antibody, but also ameliorated the kidney injury with less glomerular IgG deposition, a lower percentage of crescents and less infiltration of CD4+ T cells, CD8+ T cells and macrophages, as well as a lower percentage of splenic Th1 cells. In vitro, E64d treatment could significantly reduce the production of IFN-γ in the supernatant which might be produced by the activation of Th1 cells after being recalled with the autoantigen α3127-148. We also found the CD4+ T cells of rats with anti-GBM disease had an increased expression of cathepsin L (Cts-L), and the percentage of CD4+ T cells with extracellular expression of Cts-L was obviously higher, indicating it as a potential key regulator.

CONCLUSIONS

E64d might attenuate the development of anti-GBM disease by participating in the activation of Th1 cells, indicating it as a potential drug for anti-GBM disease in the future.

A two-decade journey in identifying high mobility group box 1 (HMGB1) and procathepsin L (pCTS-L) as potential therapeutic targets for sepsis

INTRODUCTION

Microbial infections and resultant sepsis are leading causes of death in hospitals, representing approximately 20% of total deaths worldwide. Despite the difficulties in translating experimental insights into effective therapies for often heterogenous patient populations, an improved understanding of the pathogenic mechanisms underlying experimental sepsis is still urgently needed. Sepsis is partly attributable to dysregulated innate immune responses manifested by hyperinflammation and immunosuppression at different stages of microbial infections.

AREAS COVERED

Here we review our recent progress in searching for late-acting mediators of experimental sepsis and propose high mobility group box 1 (HMGB1) and procathepsin-L (pCTS-L) as potential therapeutic targets for improving outcomes of lethal sepsis and other infectious diseases.

EXPERT OPINION

It will be important to evaluate the efficacy of HMGB1- or pCTS-L-targeting agents for the clinical management of human sepsis and other infectious diseases in future studies.

Multiscale stiffness of human emphysematous precision cut lung slices

Emphysema is a debilitating disease that remodels the lung leading to reduced tissue stiffness. Thus, understanding emphysema progression requires assessing lung stiffness at both the tissue and alveolar scales. Here, we introduce an approach to determine multiscale tissue stiffness and apply it to precision-cut lung slices (PCLS). First, we established a framework for measuring stiffness of thin, disk-like samples. We then designed a device to verify this concept and validated its measuring capabilities using known samples. Next, we compared healthy and emphysematous human PCLS and found that the latter was 50% softer. Through computational network modeling, we discovered that this reduced macroscopic tissue stiffness was due to both microscopic septal wall remodeling and structural deterioration. Lastly, through protein expression profiling, we identified a wide spectrum of enzymes that can drive septal wall remodeling, which, together with mechanical forces, lead to rupture and structural deterioration of the emphysematous lung parenchyma.

Identification of procathepsin L (pCTS-L)-neutralizing monoclonal antibodies to treat potentially lethal sepsis

Antibody-based strategies have been attempted to antagonize early cytokines of sepsis, but not yet been tried to target inducible late-acting mediators. Here, we report that the expression and secretion of procathepsin-L (pCTS-L) was induced by serum amyloid A (SAA) in innate immune cells, contributing to its late and systemic accumulation in experimental and clinical sepsis. Recombinant pCTS-L induced interleukin-6 (IL-6), IL-8, GRO-α/KC, GRO-β/MIP-2, and MCP-1 release in innate immune cells and moderately correlated with blood concentrations of these cytokines/chemokines in clinical sepsis. Mechanistically, pCTS-L interacted with Toll-like receptor 4 (TLR4) and the receptor for advanced glycation end products (RAGE) to induce cytokines/chemokines. Pharmacological suppression of pCTS-L with neutralizing polyclonal and monoclonal antibodies attenuated pCTS-L-mediated inflammation by impairing its interaction with TLR4 and RAGE receptors, and consequently rescued animals from lethal sepsis. Our findings have suggested a possibility of developing antibody strategies to prevent dysregulated immune responses mediated by late-acting cytokines.

Impact of inhaled pollutants on response to viral infection in controlled exposures

Air pollutants are a major source of increased risk of disease, hospitalization, morbidity, and mortality worldwide. The respiratory tract is a primary target of potential concurrent exposure to both inhaled pollutants and pathogens, including viruses. Although there are various associative studies linking adverse outcomes to co- or subsequent exposures to inhaled pollutants and viruses, knowledge about causal linkages and mechanisms by which pollutant exposure may alter human respiratory responses to viral infection is more limited. In this article, we review what is known about the impact of pollutant exposure on antiviral host defense responses and describe potential mechanisms by which pollutants can alter the viral infection cycle. This review focuses on evidence from human observational and controlled exposure, ex vivo, and in vitro studies. Overall, there are a myriad of points throughout the viral infection cycle that inhaled pollutants can alter to modulate appropriate host defense responses. These alterations may contribute to observed increases in rates of viral infection and associated morbidity and mortality in areas of the world with high ambient pollution levels or in people using tobacco products. Although the understanding of mechanisms of interaction is advancing through controlled in vivo and in vitro exposure models, more studies are needed because emerging infectious pathogens, such as severe acute respiratory syndrome coronavirus 2, present a significant threat to public health.

Chronic E-Cigarette Use Increases Neutrophil Elastase and Matrix Metalloprotease Levels in the Lung

Rationale: Proteolysis is a key aspect of the lung's innate immune system. Proteases, including neutrophil elastase and MMPs (matrix metalloproteases), modulate cell signaling, inflammation, tissue remodeling, and leukocyte recruitment via cleavage of their target proteins. Excessive proteolysis occurs with chronic tobacco use and is causative for bronchiectasis and emphysema. The effect of e-cigarettes (vaping) on proteolysis is unknown.

Objectives: We used protease levels as biomarkers of harm to determine the impact of vaping on the lung.

Methods: We performed research bronchoscopies on healthy nonsmokers, cigarette smokers, and e-cigarette users (vapers), and determined protease levels in BAL. In parallel, we studied the effects of e-cigarette components on protease secretion in isolated human blood neutrophils and BAL-derived macrophages. We also analyzed the nicotine concentration in induced sputum and BAL.

Measurements and Main Results: Neutrophil elastase, MMP-2, and MMP-9 activities and protein levels were equally elevated in both vapers' and smokers' BAL relative to nonsmokers. In contrast, antiprotease levels were unchanged. We also found that exposure of isolated neutrophils and macrophages to nicotine elicited dose-dependent increases in protease release. After vaping, measurable levels of nicotine were detectable in sputum and BAL, which corresponded to the half-maximal effective concentration values for protease release seen in immune cells.

Conclusions: We conclude that vaping induces nicotine-dependent protease release from resident pulmonary immune cells. Thus, chronic vaping disrupts the protease-antiprotease balance by increasing proteolysis in lung, which may place vapers at risk of developing chronic lung disease. These data indicate that vaping may not be safer than tobacco smoking.

What are the respiratory effects of e-cigarettes?

Electronic cigarettes (e-cigarettes) are alternative, non-combustible tobacco products that generate an inhalable aerosol containing nicotine, flavors, propylene glycol, and vegetable glycerin. Vaping is now a multibillion dollar industry that appeals to current smokers, former smokers, and young people who have never smoked. E-cigarettes reached the market without either extensive preclinical toxicology testing or long term safety trials that would be required of conventional therapeutics or medical devices. Their effectiveness as a smoking cessation intervention, their impact at a population level, and whether they are less harmful than combustible tobacco products are highly controversial. Here, we review the evidence on the effects of e-cigarettes on respiratory health. Studies show measurable adverse biologic effects on organ and cellular health in humans, in animals, and in vitro. The effects of e-cigarettes have similarities to and important differences from those of cigarettes. Decades of chronic smoking are needed for development of lung diseases such as lung cancer or chronic obstructive pulmonary disease, so the population effects of e-cigarette use may not be apparent until the middle of this century. We conclude that current knowledge of these effects is insufficient to determine whether the respiratory health effects of e-cigarette are less than those of combustible tobacco products.

High levels of cathepsin D and cystatin B are associated with increased risk of coronary events

Objective

The majority of acute coronary syndromes are caused by plaque ruptures. Proteases secreted by macrophages play an important role in plaque ruptures by degrading extracellular matrix proteins in the fibrous cap. Matrix metalloproteinases have been shown to be markers for cardiovascular disease whereas the members of the cathepsin protease family are less studied.

Methods

Cathepsin D, cathepsin L and cystatin B were measured in plasma at baseline from 384 individuals who developed coronary events (CEs), and from 409 age-matched and sex-matched controls from the Malmö Diet and Cancer cardiovascular cohort.

Results

Cathepsin D (180 (142–238) vs 163 (128–210), p<0.001), cathepsin L (55 (44–73) vs 52 (43–67), p<0.05) and cystatin B levels (45 (36–57) vs 42 (33–52), p<0.001) were significantly increased in CE cases compared to controls. In addition, increased cathepsin D (220 (165–313) vs 167 (133–211), p<0.001), cathepsin L (61 (46–80) vs 53 (43–68), p<0.05) and cystatin B (46 (38–58) vs 43 (34–54), p<0.05) were associated with prevalent diabetes. Furthermore, cathepsin D and cystatin B were increased in smokers. The HRs for incident CE comparing the highest to the lowest tertile(s) of cathepsin D and cystatin B were 1.34 (95% CI 1.02 to 1.75) and 1.26 (95% CI 1.01 to 1.57), respectively, after adjusting for age, sex, low-density lipoprotein/high-density lipoprotein ratio, triglycerides, body mass index, hypertension and glucose, but these associations did not remain significant after further addition of smoking to the model. In addition, cathepsin D was increased in incident CE cases among smokers after adjusting for cardiovascular risk factors.

Conclusions

The associations of cathepsin D and cystatin B with future CE provide clinical support for a role of these factors in cardiovascular disease, which for cathepsin D may be of particular importance for smokers.

Antimicrobial proteins and peptides in human lung diseases: A friend and foe partnership with host proteases

Lung antimicrobial proteins and peptides (AMPs) are major sentinels of innate immunity by preventing microbial colonization and infection. Nevertheless bactericidal activity of AMPs against Gram-positive and Gram-negative bacteria is compromised in patients with chronic obstructive pulmonary disease (COPD), cystic fibrosis (CF) and asthma. Evidence is accumulating that expression of harmful human serine proteases, matrix metalloproteases and cysteine cathepsins is markedely increased in these chronic lung diseases. The local imbalance between proteases and protease inhibitors compromises lung tissue integrity and function, by not only degrading extracellular matrix components, but also non-matrix proteins. Despite the fact that AMPs are somewhat resistant to proteolytic degradation, some human proteases cleave them efficiently and impair their antimicrobial potency. By contrast, certain AMPs may be effective as antiproteases. Host proteases participate in concert with bacterial proteases in the degradation of key innate immunity peptides/proteins and thus may play immunomodulatory activities during chronic lung diseases. In this context, the present review highlights the current knowledge and recent discoveries on the ability of host enzymes to interact with AMPs, providing a better understanding of the role of human proteases in innate host defense.

Human cystatin C: a new biomarker of idiopathic pulmonary fibrosis?

PURPOSE

Human idiopathic pulmonary fibrosis (IPF) is a progressive interstitial lung disorder with a poor prognosis. The identification of a new and specific biomarker in bronchoalveolar lavage fluids (BALFs) may assist in the diagnosis of the disease.

EXPERIMENTAL DESIGN

Characterization of cysteine Cats and their endogenous inhibitor, cystatin C, was conducted by immunochemical analysis and measurement of endopeptidase activity of control (n = 11) and IPF (n = 25) BALFs (normalized conditions, 20 μg protein/assay).

RESULTS

Cathepsin (Cat) B was detected as proform and mature enzyme for both control and IPF samples, while Cats K, L, and S were found as zymogens with a strengthened staining in IPF BALFs. The overall endopeptidase activity related mainly to Cat B and did not vary significantly between control and IPF samples. Conversely a significant increase of immunoreactive cystatin C was measured in BALFs for each of three IPF grades.

CONCLUSIONS AND CLINICAL RELEVANCE

An excessive deposition of extracellular matrix proteins is the hallmark of fibrotic disorders. Cats are potent collagenases and might be essential for lung homeostasis. Taken together, increase of cystatin C in IPF BALFs may reflect abnormal regulation of proteolytic activity of Cats in lung, which in turn can promote the development of fibrosis.

Active cathepsins B, H, K, L and S in human inflammatory bronchoalveolar lavage fluids

BACKGROUND INFORMATION

Chronic inflammation and tissue remodelling result from an imbalance between proteolytic enzymes and their inhibitors in the lungs in favour of proteolysis. While many studies have examined serine proteases (e.g. cathepsin G and neutrophil elastase) and matrix metalloproteases, little is known about the role of papain-like CPs (cysteine proteases). The present study focuses on the thiol-dependent cathepsins (CPs) and their specific cystatin-like inhibitors [CPIs (CP inhibitors)] in human inflammatory BALFs (BAL fluids, where BAL stands for broncho-alveolar lavage).

RESULTS

Cathepsins B, K and S found were mostly zymogens, whereas cathepsins H and L were predominantly in their mature forms. Little immunoreactive cystatin C was found and the high- and low-molecular-mass ('weight') kininogens were extensively degraded. The BALF procathepsins B and L could be activated autocatalytically, indicating that alveolar fluid pro-CPs are reservoirs of mature enzymes. Hydrolysis patterns of 7-amino-4-methylcoumarin-derived peptide substrates showed that extracellular alveolar CPs remain proteolytically active, and that cathepsins B and L are the most abundant thiol-dependent endoproteases. The CP/CPI balance was significantly tipped in favour of cathepsins (3- or 5-fold), as confirmed by the extensive CP-dependent degradation of exogenous kininogens by BALFs.

CONCLUSIONS

Although their importance for inflammation remains to be clarified, the presence of active cathepsins L, K and S suggests that they contribute to the extracellular breakdown of the extracellular matrix.

Alveolar macrophage recruitment and activation by chronic second hand smoke exposure in mice

Approximately 15% of cases of COPD occur in non-smokers. Among the potential risk factors for COPD in non-smokers is second-hand smoke (SHS) exposure. However, the Surgeon General reported in 2006 that the evidence linking second hand smoke and COPD is insufficient to infer a causal relationship, largely because current evidence does not establish a biological link. The goal of this study was to determine whether SHS exposure can induce alveolar macrophage recruitment and expression of activation markers that we have previously demonstrated in human smokers and in mouse models of emphysema. To achieve these goals, we studied mice exposed to an ambient mixture of predominantly [89%] sidestream smoke at increasing doses over 3 months. We found that second hand smoke exposure induced a dose-dependent increase in alveolar macrophage recruitment (mean +/- sd; 224,511 +/- 52,330 vs 166,152 +/- 47,989 macrophages/ml of bronchoalveolar lavage in smoke-exposed vs air-exposed controls at 3 months, p = 0.003). We also found increased expression of several markers of alveolar macrophage activation (PLA2g7, dkfzp434l142, Trem-2, and pirin, all p < 0.01 at 3 months) and increased lavage levels of two inflammatory mediators associated with COPD (CCL2 [MCP-1], 58 +/- 12 vs. 43 +/- 22 pg/ml, p = 0.03; and TNFalpha, 138 +/- 43 vs 88 +/- 78 pg/ml, p = 0.04 at 3 months). These findings indicate that second smoke exposure can cause macrophage recruitment and activation, providing a biological link between second-hand smoke exposure and the development of inflammatory processes linked to COPD.

Transcriptomics does not show adverse effects of β-carotene in A/J mice exposed to smoke for 2 weeks

Beta-carotene (betaC) supplementation in smokers was unexpectedly associated with increased incidence of lung cancer versus smoking alone. We performed a study in A/J mice to explore possible betaC/cigarette smoke (CS) interactions potentially influencing lung cancer risk in smokers. A/J mice received a diet containing 120 or 600 ppm betaC for six weeks, and exposed to mainstream CS (140 mg total suspended particulates/m(3)) during the last two weeks. Lung transcriptomics analysis revealed that CS induced drug metabolism, oxidative stress, extracellular matrix (ECM) degradation, inflammation markers, and apoptosis. betaC reduced CS-induced inflammation markers and ECM degradation. betaC modulated the CS effect on apoptosis without a clear pro- or anti-apoptotic trend. betaC alone induced only minor changes of gene expression. In conclusion, betaC/CS interactions caused gene regulations in lungs. CS was the main effector. The gene regulations overall did not indicate that betaC exacerbated CS effects. Dose-dependency of betaC effects was minor and not detectable by genome-wide data mining.

Interaction between human cathepsins K, L, and S and elastins: mechanism of elastinolysis and inhibition by macromolecular inhibitors

Proteolytic degradation of elastic fibers is associated with a broad spectrum of pathological conditions such as atherosclerosis and pulmonary emphysema. We have studied the interaction between elastins and human cysteine cathepsins K, L, and S, which are known to participate in elastinolytic activity in vivo. The enzymes showed distinctive preferences in degrading elastins from bovine neck ligament, aorta, and lung. Different susceptibility of these elastins to proteolysis was attributed to morphological differences observed by scanning electron microscopy. Kinetics of cathepsin binding to the insoluble substrate showed that the process occurs in two steps. The enzyme is initially adsorbed on the elastin surface in a nonproductive manner and then rearranges to form a catalytically competent complex. In contrast, soluble elastin is bound directly in a catalytically productive manner. Studies of enzyme partitioning between the phases showed that cathepsin K favors adsorption on elastin; cathepsin L prefers the aqueous environment, and cathepsin S is equally distributed among both phases. Our results suggest that elastinolysis by cysteine cathepsins proceeds in cycles of enzyme adsorption, binding of a susceptible peptide moiety, hydrolysis, and desorption. Alternatively, the enzyme may also form a new catalytic complex without prior desorption and re-adsorption. In both cases the active center of the enzymes remains at least partly accessible to inhibitors. Elastinolytic activity was readily abolished by cystatins, indicating that, unlike enzymes such as leukocyte elastase, pathological elastinolytic cysteine cathepsins might represent less problematic drug targets. In contrast, thyropins were relatively inefficient in preventing elastinolysis by cysteine cathepsins.

Cysteine cathepsins and caspases in silicosis

Silicosis is an occupational pneumoconiosis caused by inhalation of crystalline silica. It leads to the formation of fibrohyalin nodes that result in progressive fibrosis. Alternatively, emphysema may occur, with abnormal destruction of collagen fibres in the advanced stages. Although the pathophysiological mechanisms remain unclear, it has been established that the lung responds to silica by massive enrollment of alveolar macrophages, triggering an inflammatory cascade of reactions. An imbalance in the expression of lung proteases and their inhibitors is implicated in extracellular matrix remodelling and basement membrane disruption. Moreover, exposure to silica can initiate apoptotic cell death of macrophages. This review summarises the current knowledge on cysteine cathepsins that have been ignored so far during silicosis and outlines the recent progress on cellular pathways leading to silica-induced caspase activation, which have been partly delineated.

The Epithelial Cell in Lung Health and Emphysema Pathogenesis

Cigarette smoking is the primary cause of the irreversible lung disease emphysema. Historically, inflammatory cells such as macrophages and neutrophils have been studied for their role in emphysema pathology. However, recent studies indicate that the lung epithelium is an active participant in emphysema pathogenesis and plays a critical role in the lung's response to cigarette smoke. Tobacco smoke increases protease production and alters cytokine expression in isolated epithelial cells, suggesting that these cells respond potently even in the absence of a complete inflammatory program. Tobacco smoke also acts as an immunosuppressant, reducing the defense function of airway epithelial cells and enhancing colonization of the lower airways. Thus, the paradigm that emphysema is strictly an inflammatory-cell based disease is shifting to consider the involvement of resident epithelial cells. Here we review the role of epithelial cells in lung development and emphysema. To better understand tobacco-epithelial interactions we performed microarray analyses of RNA from human airway epithelial cells exposed to smoke extract for 24 hours. These studies identified differential regulation of 425 genes involved in diverse biological processes, such as apoptosis, immune function, cell cycle, signal transduction, proliferation, and antioxidants. Some of these genes, including VEGF, glutathione peroxidase, IL-13 receptor, and cytochrome P450, have been previously reported to be altered in the lungs of smokers. Others, such as pirin, cathepsin L, STAT1, and BMP2, are shown here for the first time to have a potential role in smoke-associated injury. These data broaden our understanding of the importance of epithelial cells in lung health and cigarette smoke-induced emphysema.

Iron-binding drugs targeted to lysosomes: a potential strategy to treat inflammatory lung disorders

In many inflammatory lung disorders, an abnormal assimilation of redox-active iron will exacerbate oxidative tissue damage. It may be that the most important cellular pool of redox-active iron exists within lysosomes, making these organelles vulnerable to oxidative stress. In experiments employing respiratory epithelial cells and macrophages, the chelation of intra-lysosomal iron efficiently prevented lysosomal rupture and the ensuing cell death induced by hydrogen peroxide, ionising radiation or silica particles. Furthermore, cell-permeable iron-binding agents (weak bases) that accumulate within lysosomes due to proton trapping were much more efficient for cytoprotection than the chelator, desferrioxamine. On a molar basis, the weak base alpha-lipoic acid plus was 5000 times more effective than desferrioxamine at preventing lysosomal rupture and apoptotic cell death in cell cultures exposed to hydrogen peroxide. Thus, iron-chelating therapy that targets the lysosome might be a future treatment strategy for inflammatory pulmonary diseases.

Downregulation of type II bone morphogenetic protein receptor in hypoxic pulmonary hypertension

Heterozygous mutations in the type II receptor for bone morphogenetic protein (BMPR-II) and dysfunction of BMPR-II have been implicated in patients with primary pulmonary hypertension (PH). To clarify the possible involvement of BMP and BMPR-II in the development of hypoxic PH, the expression of BMP-2, BMPR-II, and their downstream signals were investigated in rat lung under normal and hypoxic conditions by RT-PCR, immunoblot, and immunohistochemical methods. In rats under normal conditions, BMP-2 is localized in the endothelium of the pulmonary artery, whereas BMPR-II is abundantly expressed in the endothelium, smooth muscle cells, and adventitial fibroblasts. After 0.5 and 3 days of exposure to hypoxia, upregulation of BMP-2 was observed in the intrapulmonary arteries. The change was accompanied by activation of its downstream signaling, p38 MAPK, and Erk1/2 MAPK, and the apoptotic process, measured by caspase-3 activity and TdT-mediated dUTP nick end labeling-positive cells. In contrast, a significant decrease in the expression of BMPR-II and inactivation of p38 MAPK and caspase-3 were observed in the pulmonary vasculature after 7–21 days of hypoxia exposure. Because BMP-2 is known to inhibit proliferation of vascular smooth muscle cells and promote cellular apoptosis, disruption of BMP signaling pathway through downregulation of BMPR-II in chronic hypoxia may result in pulmonary vascular remodeling due to the failure of critical antiproliferative/differentiation programs in the pulmonary vasculature. These results suggest abrogation of BMP signaling may be a common molecular pathogenesis in the development of PH with various pathophysiological events, including primary and hypoxic PH.

A distinctive alveolar macrophage activation state induced by cigarette smoking

RATIONALE

Macrophages are believed to play a central role in emphysema based largely on data from mouse models. However, the relevance of these models to smoking-related lung disease in humans is uncertain.

OBJECTIVES

We sought to comprehensively characterize the effects of smoking on gene expression in human alveolar macrophages and to compare these with effects seen in transgenic mouse models of emphysema.

METHODS

We used DNA microarrays with genomewide coverage to analyze alveolar macrophages from 15 smokers, 15 nonsmokers, and 15 subjects with asthma (disease control). Selected gene expression changes were validated by polymerase chain reaction and ELISA. Expression changes were compared with those identified by microarray analysis of interleukin-13-overexpressing and integrin-beta6-deficient mice, which both develop emphysema.

MEASUREMENTS AND MAIN RESULTS

All 15 smokers shared a common pattern of macrophage gene expression that distinguished them from nonsmokers, a finding not observed in subjects with asthma. We identified 110 genes as differentially expressed in smokers despite using conservative statistical methods. Matrix metalloproteinase 12, a proteinase that plays a critical role in mouse models, was the third most highly induced gene in smokers (ninefold, p < 0.0001). However, most changes in smokers were not reflected in mouse models. One such finding was increased osteopontin expression in smokers (fourfold, p = 0.006), which was confirmed at the protein level and correlated with the degree of airway obstruction.

CONCLUSIONS

Smoking induces a remarkably consistent and distinctive pattern of alveolar macrophage activation. These studies identify aspects of mouse models that are directly relevant to human smokers and also reveal novel potential mediators of smoking-related diseases.

Cysteine cathepsins in human silicotic bronchoalveolar lavage fluids

Mature, active cysteine cathepsins (CPs) were identified in human inflammatory bronchoalveolar lavage fluid (BALF) supernatants from patients suffering from silicosis by both western blot and surface plasmon resonance analyses. BALFs are not a reservoir of activatable proforms, since no autocatalytic maturation at acidic pH occurs. Cathepsin H is the most profuse among studied CPs (median value: 36.5 nM), while cathepsins B and L are the two most abundant thiol-dependent endoproteases. The overall concentration of active cathepsins B, H, K, L, and S is approximately 10-fold lower than their concentration in BALF supernatants from patients suffering from inflammatory acute lung injuries (962+/-347 nM).The cathepsins (approximately 70 nM)/cystatin-like inhibitors (approximately 9 nM) ratio is unbalanced in favor of enzymes ( approximately 8-fold). This presence of uncontrolled CPs suggests that they may contribute, in addition to matrix metalloproteases, to the lung tissue breakdown/remodeling occurring during silicosis, although their exact contribution to interstitial inflammation remains to be evaluated.

The relationship between asthma and COPD. Lessons from transgenic mice

Asthma is characterized by eosinophilic and mononuclear cell infiltration, mucous metaplasia, airway remodeling, reversible airflow obstruction, and airway hyperresponsiveness. COPD is typified by nonreversible or incompletely reversible airway obstruction, often accompanied by mucous metaplasia and alveolar destruction. There is considerable overlap in pathogenesis and clinical features between the conditions. However, asthma and COPD may be distinguished by their respective cytokine profiles. Studies in transgenic mice have illuminated the roles of the T helper (Th) 1-mediated cytokine interferon-gamma in COPD, supporting the British hypothesis, and the Th2-mediated cytokine interleukin-13 in asthma, supporting the Dutch hypothesis. COPD and asthma may represent disease states along a continuum, with varying degrees of each disease often present in the same patient.

Alveolar Macrophages as Orchestrators of COPD

Alveolar macrophages play a critical role in the pathophysiology of COPD and are a major target for future anti-inflammatory therapy. Macrophage numbers are markedly increased in the lung and alveolar space of patients with COPD and are localized to sites of alveolar destruction. The increased numbers of macrophages may result from increased recruitment of blood monocytes, prolonged survival in the lung and to a lesser extent to increased proliferation in the lung. Alveolar macrophages from COPD patients have an increased baseline and stimulated secretion of inflammatory proteins, including certain cytokines, chemokines, reactive oxygen species and elastolytic enzymes, which together could account for all of the pathophysiological features of COPD. Alveolar macrophages form COPD appear to be resistant to the anti-inflammatory effects of corticosteriods and this is linked to reduced activity and expression of histone deacetylase 2, a nuclear enzyme that switches off inflammatory genes activated through the transcription factor nuclear factor-KB. Alternative anti-inflammatory therapies that inhibit macrophages are therefore needed in the future to deal with the chronic inflammation of COPD. These drugs may include resveratrol, theophylline derivatives, MAP kinase inhibitors and phosphodiesterase-4 inhibitors.

Multiple types of skeletal muscle atrophy involve a common program of changes in gene expression

Skeletal muscle atrophy is a debilitating response to starvation and many systemic diseases including diabetes, cancer, and renal failure. We had proposed that a common set of transcriptional adaptations underlie the loss of muscle mass in these different states. To test this hypothesis, we used cDNA microarrays to compare the changes in content of specific mRNAs in muscles atrophying from different causes. We compared muscles from fasted mice, from rats with cancer cachexia, streptozotocin-induced diabetes mellitus, uremia induced by subtotal nephrectomy, and from pair-fed control rats. Although the content of >90% of mRNAs did not change, including those for the myofibrillar apparatus, we found a common set of genes (termed atrogins) that were induced or suppressed in muscles in these four catabolic states. Among the strongly induced genes were many involved in protein degradation, including polyubiquitins, Ub fusion proteins, the Ub ligases atrogin-1/MAFbx and MuRF-1, multiple but not all subunits of the 20S proteasome and its 19S regulator, and cathepsin L. Many genes required for ATP production and late steps in glycolysis were down-regulated, as were many transcripts for extracellular matrix proteins. Some genes not previously implicated in muscle atrophy were dramatically up-regulated (lipin, metallothionein, AMP deaminase, RNA helicase-related protein, TG interacting factor) and several growth-related mRNAs were down-regulated (P311, JUN, IGF-1-BP5). Thus, different types of muscle atrophy share a common transcriptional program that is activated in many systemic diseases.

Inactivation of human beta-defensins 2 and 3 by elastolytic cathepsins

beta-Defensins are antimicrobial peptides that contribute to the innate immune responses of eukaryotes. At least three defensins, human beta-defensins 1, 2, and 3 (HBD-1, -2, and -3), are produced by epithelial cells lining the respiratory tract and are active toward Gram-positive (HBD-3) and Gram-negative (HBD-1, -2, and -3) bacteria. It has been postulated that the antimicrobial activity of defensins is compromised by changes in airway surface liquid composition in lungs of patients with cystic fibrosis (CF), therefore contributing to the bacterial colonization of the lung by Pseudomonas and other bacteria in CF. In this report we demonstrate that HBD-2 and HBD-3 are susceptible to degradation and inactivation by the cysteine proteases cathepsins B, L, and S. In addition, we show that all three cathepsins are present and active in CF bronchoalveolar lavage. Incubation of HBD-2 and -3 with CF bronchoalveolar lavage leads to their degradation, which can be completely (HBD-2) or partially (HBD-3) inhibited by a cathepsin inhibitor. These results suggest that beta-defensins are susceptible to degradation and inactivation by host proteases, which may be important in the regulation of beta-defensin activity. In chronic lung diseases associated with infection, overexpression of cathepsins may lead to increased degradation of HBD-2 and -3, thereby favoring bacterial infection and colonization.

Importance of lysosomal cysteine proteases in lung disease

The human lysosomal cysteine proteases are a family of 11 proteases whose members include cathepsins B, C, H, L, and S. The biology of these proteases was largely ignored for decades because of their lysosomal location and the belief that their function was limited to the terminal degradation of proteins. In the past 10 years, this view has changed as these proteases have been found to have specific functions within cells. This review highlights some of these functions, specifically their roles in matrix remodeling and in regulating the immune response, and their relationship to lung diseases.

Patterns of gene expression in atrophying skeletal muscles: response to food deprivation

During fasting and many systemic diseases, muscle undergoes rapid loss of protein and functional capacity. To define the transcriptional changes triggering muscle atrophy and energy conservation in fasting, we used cDNA microarrays to compare mRNAs from muscles of control and food-deprived mice. Expression of >94% of genes did not change, but interesting patterns emerged among genes that were differentially expressed: 1) mRNAs encoding polyubiquitin, ubiquitin extension proteins, and many (but not all) proteasome subunits increased, which presumably contributes to accelerated protein breakdown; 2) a dramatic increase in mRNA for the ubiquitin ligase, atrogin-1, but not most E3s; 3) a significant suppression of mRNA for myosin binding protein H (but not other myofibrillar proteins) and IGF binding protein 5, which may favor cell protein loss; 4) decreases in mRNAs for several glycolytic enzymes and phosphorylase kinase subunits, and dramatic increases in mRNAs for pyruvate dehydrogenase kinase 4 and glutamine synthase, which should promote glucose sparing and gluconeogenesis. During fasting, metallothionein mRNA increased dramatically, mRNAs for extracellular matrix components fell, and mRNAs that may favor cap-independent mRNA translation rose. Significant changes occurred in mRNAs for many growth-related proteins and transcriptional regulators. These transcriptional changes indicate a complex adaptive program that should favor protein degradation and suppress glucose oxidation in muscle. Similar analysis of muscles atrophying for other causes is allowing us to identify a set of atrophy-specific changes in gene expression.

Acute cigarette smoke exposure induces apoptosis of alveolar macrophages

Alveolar macrophages (AMs) may play a critical role in cigarette smoke (CS)-related pulmonary diseases. This study was designed to determine whether CS induces apoptosis of AMs. In in vitro studies, mouse, rat, and human AMs and human blood monocyte-derived macrophages cultured with aqueous whole CS extracts underwent apoptosis that was detected by light and electron microscopy and terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling. The gas phase of CSE did not cause apoptosis. The CS-induced apoptosis was associated with increased oxidative stress, Bax protein accumulation, mitochondrial dysfunction, and mitochondrial cytochrome c release but was independent of p53, Fas, and caspase activation. This apoptosis was inhibited by antioxidants such as glutathione, ascorbic acid, and alpha-tocopherol. In in vivo studies where rats were exposed to the smoke from 10 cigarettes over 5 h in an exposure chamber, approximately 3% of AMs obtained by bronchoalveolar lavage after 24 h showed apoptosis. These results suggest that acute CS exposure is capable of inducing apoptosis of AMs.

Cathepsin B, L, and S cleave and inactivate secretory leucoprotease inhibitor

A number of serine proteases, matrix metalloproteases, and cysteine proteases were evaluated for their ability to cleave and inactivate the antiprotease, secretory leucoprotease inhibitor (SLPI). None of the serine proteases or the matrix metalloproteases examined cleaved the SLPI protein. However, incubation with cathepsins B, L, and S resulted in the cleavage and inactivation of SLPI. All three cathepsins initially cleaved SLPI between residues Thr(67) and Tyr(68). The proteolytic cleavage of SLPI by all three cathepsins resulted in the loss of the active site of SLPI and the inactivation of SLPI anti-neutrophil elastase capacity. Cleavage and inactivation were catalytic with respect to the cathepsins, so that the majority of a 400-fold excess of SLPI was inactivated within 15 min by cathepsins L and S. Analysis of epithelial lining fluid samples from individuals with emphysema indicated the presence of cleaved SLPI in these samples whereas only intact SLPI was observed in control epithelial lining fluid samples. Active cathepsin L was shown to be present in emphysema epithelial lining fluid and inhibition of this protease prevented the cleavage of recombinant SLPI added to emphysema epithelial lining fluid. Taken together with previous data that demonstrates that cathepsin L inactivates alpha(1)-antitrypsin, these findings indicate the involvement of cathepsins in the diminution of the lung antiprotease screen possibly leading to lung destruction in emphysema.

Serum concentration and circadian profiles of cathepsins B, H and L, and their inhibitors, stefins A and B, in asthma

BACKGROUND

In order to determine the effect of asthma on serum concentrations of cathepsins B, H and L, and stefins A and B, the circadian and concentration profiles were followed in steroid-independent and steroid-dependent asthmatics before and after 1-week treatment with methylprednisolone and cyclosporin A.

METHODS

Serum samples were taken at 4-h intervals throughout a 24-h period. Cathepsin and stefin concentrations were assayed using specific ELISAs. Data were analysed by one-way ANOVA and least squares fit of 24-h cosine.

RESULTS

Temporal analysis of these proteins revealed little or no significant changes with time over a 24-h period. In comparison to normal sera, cathepsin H concentrations were elevated in all asthmatic patients, concentrations of both stefins were decreased in steroid-independent asthmatics, and stefin A concentrations were increased in steroid-dependent asthmatics before therapy. The effect of methylprednisolone treatment was demonstrated on decreased cathepsin B and increased cathepsin L concentrations in post-therapy serum samples. On the other hand, cyclosporin A treatment led to increased concentrations of cathepsins H and L. However, concentrations of stefins A and B were unaffected.

CONCLUSIONS

This study associated alterations in balance of serum cysteine proteinases and their inhibitors in asthmatic patients, which has raised the possibility of their involvement in asthma pathogenesis. Validated rhythms of cathepsins and stefins in asthmatic sera exhibited temporal differences, which are too small to influence the time of sampling for their quantitative measurement over the course of a day.

Discrepant distribution of big endothelin (ET)-1 and ET receptors in the pulmonary artery

Since pulmonary vasculature is complex in terms of regional difference in structure and function, it is important to understand the site of endothelin (ET) synthesis and the distribution of the ET system along the axial pathways of pulmonary artery. The expression of big ET-1, ET converting enzyme (ECE) and ET(A) receptors were examined in rat pulmonary arteries under normal and hypoxic conditions using an immunohistochemical method and Northern blot analysis. In normal conditions, big ET-1 was expressed in the intima and media of pulmonary arteries with a predominant distribution in the distal segments and a preferential localization in the media, while ETA receptors were dominantly expressed in the proximal segments. ECE was constitutively expressed in the intima and media. Following exposure to hypoxia, messenger ribonucleic acid (mRNA) expression of ET-1 and ET(A) receptors were up-regulated by two-fold and immunoreactivities for big ET-1, ECE, and ET(A) receptors significantly increased by two to five-fold in the distal segments. Smooth muscle cells are an important source of endothelin-1 in the pulmonary artery. The distribution of big endothelin-1 and endothelin A receptors in pulmonary arteries was discrepant in normal conditions while their expression concomitantly increased in the distal segments in hypoxic conditions. This heterogeneity may play an important role in the regulation of pulmonary vascular tone.

Interleukin-6 and transforming growth factor-beta 1 control expression of cathepsins B and L in human lung epithelial cells

Cathepsins B and L are commonly expressed cysteine proteinases that play a major role in lysosomal bulk proteolysis, protein processing, matrix degradation, and tissue remodeling. Cathepsins are also implicated in tumor progression and metastasis, tissue injury, and inflammation. Cells at sites of inflammation often show upregulation and secretion of cathepsins. The regulation of cathepsin expression by inflammatory mediators is not well understood. The aims of this study were to investigate the effect of the cytokines interleukin-1 beta (IL-1 beta), IL-6, IL-10, transforming growth factor-beta 1 (TGF-beta 1), and hepatocyte growth factor (HGF) on expression of cathepsin B and cathepsin L mRNA (quantitative RT-PCR), on protein expression (ELISA, Western blot), and also on enzymatic activity of cathepsins B and L. Investigations were performed using the human lung epithelial cell line A-549. IL-6 was found to induce a concentration-dependent increase in mRNA expression, protein concentration, and enzymatic activity of cathepsin L. Cathepsin B mRNA and protein expression were not affected by IL-6. In contrast, TGF-beta 1 decreased the amount of cathepsin L mRNA and cathepsin B mRNA. At protein level, it was shown that TGF-beta 1 clearly reduced the concentration of cathepsin L but not cathepsin B. The cytokines IL-1 beta, IL-10, and HGF were found to exert no effect on cathepsin B and L expression. In conclusion, these results are the first to show that IL-6 and TGF-beta 1 have opposite effects on the regulation of expression of cathepsins B and L in A-549 human lung epithelial cells. The proinflammatory cytokine IL-6 induced an upregulation of cathepsin L, whereas TGF-beta 1 suppressed cathepsin B and L expression. Further studies are needed to clarify the mechanism that affects cathepsin B and L expression.

Interferon gamma induction of pulmonary emphysema in the adult murine lung

Chronic inflammation containing CD8(+) lymphocytes, neutrophils, and macrophages, and pulmonary emphysema coexist in lungs from patients with chronic obstructive pulmonary disease. Although this inflammatory response is believed to cause the remodeling that is seen in these tissues, the mechanism(s) by which inflammation causes emphysema have not been defined. Here we demonstrate that interferon gamma (IFN-gamma), a prominent product of CD8(+) cells, causes emphysema with alveolar enlargement, enhanced lung volumes, enhanced pulmonary compliance, and macrophage- and neutrophil-rich inflammation when inducibly targeted, in a transgenic fashion, to the adult murine lung. Prominent protease and antiprotease alterations were also noted in these mice. They included the induction and activation of matrix metalloproteinase (MMP)-12 and cathepsins B, H, D, S, and L, the elaboration of MMP-9, and the selective inhibition of secretory leukocyte proteinase inhibitor. IFN-gamma causes emphysema and alterations in pulmonary protease/antiprotease balance when expressed in pulmonary tissues.

Inducible targeting of IL-13 to the adult lung causes matrix metalloproteinase- and cathepsin-dependent emphysema

Cigarette smoke exposure is the major cause of chronic obstructive pulmonary disease (COPD). However, only a minority of smokers develop significant COPD, and patients with asthma or asthma-like airway hyperresponsiveness or eosinophilia experience accelerated loss of lung function after cigarette smoke exposure. Pulmonary inflammation is a characteristic feature of lungs from patients with COPD. Surprisingly, the mediators of this inflammation and their contributions to the pathogenesis and varied natural history of COPD are not well defined. Here we show that IL-13, a critical cytokine in asthma, causes emphysema with enhanced lung volumes and compliance, mucus metaplasia, and inflammation, when inducibly overexpressed in the adult murine lung. MMP-2, -9, -12, -13, and -14 and cathepsins B, S, L, H, and K were induced by IL-13 in this setting. In addition, treatment with MMP or cysteine proteinase antagonists significantly decreased the emphysema and inflammation, but not the mucus in these animals. These studies demonstrate that IL-13 is a potent stimulator of MMP and cathepsin-based proteolytic pathways in the lung. They also demonstrate that IL-13 causes emphysema via a MMP- and cathepsin-dependent mechanism(s) and highlight common mechanisms that may underlie COPD and asthma.

Cysteine proteinase cathepsin H in tumours and sera of lung cancer patients: relation to prognosis and cigarette smoking

In order to evaluate the role of cysteine peptidase cathepsin H (Cath H) in human lung cancer its protein levels were determined in 148 pairs of lung tumour tissue and adjacent non-tumourous lung parenchyma using the enzyme-linked immunosorbent assay technique. Additionally, Cath H levels were determined in sera of 171 patients with malignant tumours, 34 patients with benign lung diseases and 47 healthy controls. The median level of Cath H in tumour tissue was 0.64 times that in the corresponding lung parenchyma. Relating tumour levels with histological type we found higher Cath H levels in small-cell and adenocarcinomas and lower levels in squamous cell carcinoma, large-cell carcinoma and secondary tumours. A significant difference in Cath H level between lung tumour tissue and non-tumourous lung parenchyma was associated with the group of cigarette smokers (156 vs 263 ng mg(-1) protein, P < 0.001). For this group of patients Cath H tumour levels correlated with the survival rate, while for the entire patient population this was not the case. Smokers with high tumour levels of Cath H experienced poor survival. Cath H was significantly higher in sera of patients with malignant and benign lung diseases than in control sera (P < 0.001). The increase was significant for all histological types, being the highest in small-cell and squamous cell carcinomas. Our study reveals that in lung tumours there is different behaviour of Cath H compared with other cysteine peptidases, e.g. cathepsin B and cathepsin L. Variations between tissue and serum levels of Cath H indicate either reduced expression or enhanced secretion of this enzyme in lung tumours.

Cellular and connective tissue changes in alveolar septal walls in emphysema

Emphysema is commonly defined as enlargement of airspaces distal to terminal bronchioles accompanied by destruction of alveolar walls, but without obvious fibrosis. Morphometric techniques were used to correlate changes in components of the alveolar septa surrounding enlarged airspaces in human emphysema with the mean linear intercept (Lm) of those airspaces. Alveolar and capillary surface density decreased with increased Lm, but the ratio of these surface densities to each other remained close to normal for mild to moderate increases in Lm. This suggests that the decreased gas exchange observed in emphysema is initiated by a total loss of septa and not by selective pathological changes of the microvasculature. Increases in septal wall thickness directly correlated with increases in Lm. For the mild to moderate emphysema lesions included in this study, an increase of 100% in Lm correlated with a 130% increase in the relative volume of the alveolar septal interstitium. Significant increases occurred in both elastin (0.14 to 0.56 microm(3)/microm(2) basement membrane [BM]) and collagen (0.49 to 1. 63 microm(3)/microm(2) BM). The increase in elastin and collagen raises the possibility of a remodeling process in the connective matrix in alveolar walls. Whether or not the new connective tissue represents a disordered, nonfunctional regional response needs to be determined.

Localization and distribution of endothelin receptor subtypes in pulmonary vasculature of normal and hypoxia-exposed rats

To clarify the roles of two different endothelin (ET) receptors in the pulmonary vasculature, the localization and distribution of endothelin-A (ETA) and ETB receptors were investigated in rat lung under normal and hypoxic conditions by an immunohistochemical method. We also carried out in situ hybridization for ETB receptor. In normal rats, ETA receptor is localized in the media of the pulmonary artery and vein with predominant distribution in such proximal segments as elastic arteries and large muscular arteries. ETB receptor is expressed in the intima and media of pulmonary vessels. The distribution of ETB receptor in the media predominates in the distal segments of the pulmonary artery, whereas its distribution in the intima is greater in the proximal segments. Immunoreactivity for ETA receptor increases in the media of the distal segments of the pulmonary artery after exposure to hypobaric hypoxia. Semiquantitative evaluation showed immunoreactivity for ETA receptor in the pulmonary arteries accompanying the terminal bronchioles, respiratory bronchioles, and alveolar ducts to be increased by 2.5-, 5-, and 20-fold after 14 d exposure to hypoxia, respectively. The messenger RNA and immunoreactivity for ETB receptor increased significantly in the intima of the distal segments of pulmonary artery after 7 and 14 d exposure to hypoxia. These results suggest that the vasoconstrictive effects of ET-1 are exerted mainly through ETA receptor in the proximal segments of the pulmonary artery and vein, whereas its effects in the distal segments are mediated by ETA and ETB receptors in normal rats. ETA receptors that increase in resistance arteries after exposure to hypoxia appear to play an important role in the vascular remodeling associated with hypoxic pulmonary hypertension. Because ETB receptors in the endothelium mediate ET-1-induced vasodilatory effects, the increase in endothelial ETB receptors may counteract the development of hypoxic pulmonary hypertension.

Compromised inhibition of human lung lavage cell elastases

Increased elastinolytic activity has been correlated with the degree of lung damage occurring in a variety of lung diseases including cystic fibrosis; serine proteinase inhibitors are currently on trial for the treatment of some lung disorders. However, human lung lavage cells also secrete metallo-dependent elastases. Here we show, for the first time, that whilst these are readily inhibited by EDTA, inhibition of serine elastases using serpins (serine proteinase inhibitors) is not always possible. This may reflect inactivation of serpins by uninhibited metalloproteinases and oxidants in a low protein milieu. Thus, the therapeutic inhibition of excessive elastinolytic activity may require a combination of inhibitors to work efficiently.

Role of oxidants/antioxidants in smoking-induced lung diseases

An imbalance between oxidants and antioxidants has been considered in the pathogenesis of smoking-induced lung diseases, such as chronic obstructive pulmonary disease (COPD), particularly emphysema. Recent evidence indicates that increased neutrophil sequestration and activation occurs in the pulmonary microvasculature in smokers and in patients with COPD, with the potential to release reactive oxygen species (ROS). ROS generated by airspace phagocytes or inhaled directly from the environment also increase the oxidant burden and may contribute to the epithelial damage. Although much research has focused on the protease/antiprotease theory of the pathogenesis of emphysema, less attention has been paid to the role of ROS in this condition. The injurious effects of the increased oxidant burden in smokers and in patients with COPD are opposed by the lung antioxidant defences. Hence, determining the mechanisms regulating the antioxidant responses is critical to our understanding of the role of oxidants in the pathogenesis of smoking-induced lung disease and to devising future strategies for antioxidant therapy. In this article we have reviewed the evidence for the presence of an oxidant/antioxidant imbalance in smoking-induced lung disease and its relevance to therapy in these conditions.

Human cathepsin O2, a novel cysteine protease highly expressed in osteoclastomas and ovary molecular cloning, sequencing and tissue distribution

A 1.6-kilobase full-length cDNA of a novel human cysteine protease has been isolated and sequenced. The nucleotide sequence encodes a polypeptide of 329 amino acids composed of a 15-residue N-terminal signal peptide, a 99-residue propeptide, and a mature protein of 215 amino acids. The deduced amino acid sequence contains two potential N-glycosylation sites, one located in the proregion and one in the mature enzyme. Comparison of the amino acid sequence of cathepsin O2 with that of known human lysosomal cysteine proteases revealed a substantial degree of similarity to cathepsins L and S. Northern blot analysis indicates predominant levels of expression in osteoclastomas and ovary and therefore the enzyme was named cathepsin O2. The extremely high expression levels of human cathepsin O2 in osteoclastomas suggest a major role of this novel enzyme in bone remodelling and bone related diseases.

The role of thiol proteases in tissue injury and remodeling

Human lung macrophages express all four of the known lysosomal thiol proteases: cathepsins B, H, L, and S. These enzymes share a similar size and targeting mechanism for lysosomal accumulation and all have relatively indiscriminate substrate specificity in comparison with such highly selective serine proteases as urokinase or thrombin. These enzymes do have distinctive properties: only cathepsin B has C-terminal dipeptidase activity, only cathepsin H has potent aminopeptidase activity, and only cathepsin L and S are elastolytic. Cathepsin S is unique in that it is stable at neutral pH; indeed, at neutral pH it has elastolytic activity roughly comparable with that of neutrophil elastase. Recent studies of the differential expression of these cathepsins suggest they not only cooperate in terminal degradation of endocytized protein but also have specific functions such as proenzyme activation, antigen processing, and tissue remodeling, especially bone matrix resorption. Lysates of lung macrophages degrade elastin at neutral pH, suggesting that necrosis of macrophages at sites of macrophage accumulation, e.g., caseation necrosis, could contribute to tissue destruction. Tissue destruction and remodeling by thiol proteases expressed by live macrophages, however, is limited by tight compartmentalization of cathepsins to lysosomes. Nonetheless, macrophages accumulate at sites of known injury in cigarette smokers. Because these cells contain potent elastases, and because lysosomal enzyme release and cell surface acidification are regulated events, dysregulation of thiol protease expression in stimulated macrophages may contribute to the injury observed in cigarette smokers with non-alpha-1-protease inhibitor-type emphysema.