Matrix metalloproteinases 2, 9, and 13, and tissue inhibitors of metalloproteinases 1 and 2 in experimental lung silicosis

Unraveling the mechanism of tetrandrine combined with Buyang Huanwu Decoction against silicosis using network pharmacology and molecular docking analyses

Silicosis is an incurable chronic disease characterized by lung fibrosis and inflammation. The combination of tetrandrine and Buyang Huanwu Decoction (BYHWD) has a curative effect on silicosis. However, the mechanism of action and the key active constituent in BYHWD are still unclear. The present study employed network pharmacology and molecular docking to determine the mechanism of action and the key active components of BYHWD of Tetrandrine in combination with BYHWD for silicosis. The primary elements and targets of BYHWD were obtained from the Traditional Chinese Medicine Systems Pharmacology and analysis platform. The targets associated with tetrandrine and silicosis were identified and extracted from the Comparative Toxicogenomics Database and GeneCards database. The potential targets for the treatment of silicosis using a combination of Tetrandrine and BYHWD were identified by considering the overlapping targets between compound drugs and silicosis. These targets were then utilized to construct protein-protein interaction networks, compound drug-ingredient-target networks, and perform enrichment analyses. The top 5 active ingredients present in the compound drug-ingredient-target network are tetrandrine, quercetin, luteolin, kaempferol, and beta-carotene. Similarly, the top 6 hub genes in the protein-protein interaction network are FGF2, MMP-9, MMP-1, IL-10, IL-17A, and IL-6. The molecular docking suggested that the active components may easily access the active pocket of the hub gene. The in-silico investigation suggested that quercetin might be the active component in BYHWD responsible for therapeutic effectiveness against silicosis. This study identified the active compound and potential molecular mechanism underlying the therapeutic effects of BYHWD in combination with tetrandrine for treating silicosis. Notably, we found that quercetin may serve as the key compound in BYHWD for the treatment of silicosis.

The Role of Matrix Metalloproteinase in Inflammation with a Focus on Infectious Diseases

Matrix metalloproteinases (MMPs) are involved in extracellular matrix remodeling through the degradation of extracellular matrix components and are also involved in the inflammatory response by regulating the pro-inflammatory cytokines TNF-α and IL-1β. Dysregulation in the inflammatory response and changes in the extracellular matrix by MMPs are related to the development of various diseases including lung and cardiovascular diseases. Therefore, numerous studies have been conducted to understand the role of MMPs in disease pathogenesis. MMPs are involved in the pathogenesis of infectious diseases through a dysregulation of the activity and expression of MMPs. In this review, we discuss the role of MMPs in infectious diseases and inflammatory responses. Furthermore, we present the potential of MMPs as therapeutic targets in infectious diseases.

Protective effects of intranasal curcumin on silica-induced lung damage

OBJECTIVE

Being anti-inflammatory and an antioxidant in nature, curcumin has been studied for its anti-asthmatic effects, but its impact on silicosis has not been investigated before. It is a form of occupational lung illness caused by inhaling crystalline silica. It is particularly common among those who work in construction-related sectors. Therefore, present study has been undertaken to investigate impact of intranasal curcumin on silica induced lung damage in mice model of silicosis.

MATERIALS AND METHODS

Mice model of silicosis was developed by intranasal silica instillation (2.5 mg/mice) for different durations mainly 7, 14 and 21 days, where the longest duration of silica exposure (21 days) mimics chronic occupational exposure of silica dust leading to silicosis. Curcumin (5 mg/kg,i.n) and /or dexamethasone, a known corticosteroid (10 mg/kg,i.p) was administered an hour prior to silica administration.

RESULTS

Present study revealed silica induced lung damage in the mice model of silicosis characterized by airway inflammation, collagen deposition and enhanced expression of fibrosis markers (MMP-9, α-SMA, Hydroxyproline), which were significantly reduced in curcumin treatment groups. Inhibitory effects of curcumin were compared with standard drug, dexamethasone, a corticosteroid and was found better in protecting structural alterations in the lung. Damaged and abnormal mitochondria (enlarged and irregular shapes) were observed in silicosis group which were reduced in curcumin and dexamethasone treatment groups as revealed in transmission electron microscopic studies.

CONCLUSIONS

Present study shows protective effects of intranasal curcumin on silica-induced airway inflammation and structural changes thereby lung damage. Hence, it can be considered as an alternative and complementary medication for silicosis.

LXA4 Inhibits Lipopolysaccharide-Induced Inflammatory Cell Accumulation by Resident Macrophages in Mice

Introduction

Alveolar macrophages that regulate the inflammatory response in lungs are the main target cell for the treatment of inflammatory pulmonary pathologies, such as acute respiratory distress syndrome (ARDS). Yolk sac derived alveolar resident macrophages play an important role in the pulmonary inflammatory response. With regards to anti-inflammatory actions, lipoxin A4 (LXA4) has been identified as an inflammatory "braking signal".

Methods

In vivo, LXA4 (0.1 µg/mouse) was injected intraperitoneally after intratracheal (1 mg/kg) lipopolysaccharide (LPS) administration; flow cytometry was used to measure peripheral blood monocyte derived recruited macrophage and neutrophil numbers; resident alveolar macrophage was depleted by liposome clodronate; CXCL2, CCL2, MMP9 level was detected by RT-PCR and ELISA. In vitro, sorted resident macrophages (1×10⁶) were cultured with LPS (1 μg/mL) and LXA4 (100 nmol/mL) with or without BOC-2 (10 μM) for 24 h to gain a better understanding of the mechanisms of LXA4.

Results

LXA4 inhibited tumor necrosis factor-a (TNF-a) and interleukin-1β (IL-1β) production induced by LPS. LXA4 also mediated LPS-induced macrophage recruitment and showed that this was dependent on CCL2 secretion and release by resident macrophages. LXA4 protects lung tissue by inhibiting neutrophil recruitment, partly through the CXCL2/MMP-9 signaling pathway. CXCL2 and MMP-9 are mainly expressed by resident macrophages and neutrophils, respectively. Finally, LXA4's beneficial effects were abrogated by BOC-2, an LXA4 receptor inhibitor.

Conclusion

These results suggest that LXA4 may be a promising therapy for preventing and treating ARDS.

A Tale of Two Proteolytic Machines: Matrix Metalloproteinases and the Ubiquitin-Proteasome System in Pulmonary Fibrosis

Pulmonary fibrosis is a chronic and progressive lung disease characterized by the activation of fibroblasts and the irreversible deposition of connective tissue matrices that leads to altered pulmonary architecture and physiology. Multiple factors have been implicated in the pathogenesis of lung fibrosis, including genetic and environmental factors that cause abnormal activation of alveolar epithelial cells, leading to the development of complex profibrotic cascade activation and extracellular matrix (ECM) deposition. One class of proteinases that is thought to be important in the regulation of the ECM are the matrix metalloproteinases (MMPs). MMPs can be up- and down- regulated in idiopathic pulmonary fibrosis (IPF) lungs and their role depends upon their location and function. Furthermore, alterations in the ubiquitin-proteosome system (UPS), a major intracellular protein degradation complex, have been described in aging and IPF lungs. UPS alterations could potentially lead to the abnormal accumulation and deposition of ECM. A better understanding of the specific roles MMPs and UPS play in the pathophysiology of pulmonary fibrosis could potentially drive to the development of novel biomarkers that can be as diagnostic and therapeutic targets. In this review, we describe how MMPs and UPS alter ECM composition in IPF lungs and mouse models of pulmonary fibrosis, thereby influencing the alveolar epithelial and mesenchymal cell behavior. Finally, we discuss recent findings that associate MMPs and UPS interplay with the development of pulmonary fibrosis.

Regulation of the Proteolytic Activity of Cysteine Cathepsins by Oxidants

Besides their primary involvement in the recycling and degradation of proteins in endo-lysosomal compartments and also in specialized biological functions, cysteine cathepsins are pivotal proteolytic contributors of various deleterious diseases. While the molecular mechanisms of regulation via their natural inhibitors have been exhaustively studied, less is currently known about how their enzymatic activity is modulated during the redox imbalance associated with oxidative stress and their exposure resistance to oxidants. More specifically, there is only patchy information on the regulation of lung cysteine cathepsins, while the respiratory system is directly exposed to countless exogenous oxidants contained in dust, tobacco, combustion fumes, and industrial or domestic particles. Papain-like enzymes (clan CA, family C1, subfamily C1A) encompass a conserved catalytic thiolate-imidazolium pair (Cys25-His159) in their active site. Although the sulfhydryl group (with a low acidic pKa) is a potent nucleophile highly susceptible to chemical modifications, some cysteine cathepsins reveal an unanticipated resistance to oxidative stress. Besides an introductory chapter and peculiar attention to lung cysteine cathepsins, the purpose of this review is to afford a concise update of the current knowledge on molecular mechanisms associated with the regulation of cysteine cathepsins by redox balance and by oxidants (e.g., Michael acceptors, reactive oxygen, and nitrogen species).

Doxycycline alleviates paraquat-induced acute lung injury by inhibiting neutrophil-derived matrix metalloproteinase 9

Paraquat (PQ), a highly toxic herbicide, selectively accumulates in the lungs and causes pulmonary damage through oxidative and inflammatory processes after intentional or accidental poisoning. The resulting acute lung injury (ALI) is characterized by neutrophil infiltration and extensive inflammation with rapid respiratory failure. However, effective therapies are lacking. We tested the hypothesis that suppressing neutrophil-derived matrix metalloproteinase 9 (MMP9) would ameliorate the inflammatory milieu and alleviate PQ-induced ALI. Lung injury was assessed in mice intratracheally injected with PQ aerosol by measuring the lung static compliance, cell count and neutrophil percentage of the bronchoalveolar lavage fluid (BALF) and lung, alveolar-capillary permeability, and histopathological lung injury scores. MMP9/2 activity was assessed by gelatin zymography, and the location of neutrophils and MMP9 in the lung was evaluated by immunofluorescence costaining. In the neutrophil depletion experiment, mice received anti-Ly6G antibody intraperitoneally; for the MMP inhibition experiment, an MMP inhibitor, doxycycline (DOX), was administered by gavage. In PQ-induced ALI, the activity of neutrophil-derived MMP9 but not MMP2 increased significantly. Neutrophil depletion reduced the inflammatory burden, improved pulmonary edema, and reduced the PQ-induced overexpression of MMP9. Consistently, oral delivery of DOX to mice decreased the overexpression of MMP9 that was activated by PQ and phenocopied the resolution of PQ-induced ALI observed after neutrophil depletion. Taken together, our results show for the first time that DOX is involved in the resolution of PQ-induced ALI via a mechanism involving reducing the activity of neutrophil-derived MMP9. We speculate that DOX may represent a novel therapeutic strategy for PQ-induced ALI.

The protective effects of bone morphogenetic protein-7 against epithelial injury and matrix metalloproteases upregulation induced by silica in vitro

OBJECTIVE

We investigate the effects of bone morphogenetic protein-7 (BMP-7) on models with silica-induced and macrophage-mediated fibrosis and its possible mechanisms in vitro.

METHODS

Rat alveolar II epithelial (RLE-6TN) cells were incubated with the supernatant of mouse macrophage-like cells (RAW264.7) and treated with 0, 25, 50, and 100 μg/mL silica. Using Western blotting, the epithelial markers (surfactant proteins-C and E-cadherin) and the mesenchymal markers (fibronectin (FN) and viminten (Vim)) were detected. After neutralizing the BMP-7, the progress of fibrosis was assessed by the content of hydroxyproline (Hyp) and collagen I, III protein levels as well as the Smad signaling pathway proteins, including phosphorylated Smad1/5(P-Smad1/5) and phosphorylated Smad2/3(P-Smad2/3). Collagen I was also identified by immunofluorescence and pretreated with SB-431542, LDN-193189, or anti-BMP-7-neutralizing antibody. In addition, the levels of matrix metalloproteinase-2 (MMP-2) and MMP-9 were detected using Western blotting.

RESULTS

The model of RLE-6TN cells was established successfully, the expressions of Vim, FN, MMP-2, and MMP-9 were upregulated, while the concentration of silica is increased. Neutralizing BMP-7 stimulated the decrease of P-Smad1/5 and the increase of P-Smad2/3, as well as the collagen I, collagen III, FN, and Hyp via Smad signaling pathway. Furthermore, pretreated with LDN-193189 or anti-BMP-7-neutralizing antibody, the expression of collagen I was increased, yet it was decreased with SB-431542 intervention.

CONCLUSION

The activated BMP/Smad and suppressed transforming growth factor-β/Smad pathways could suppress silica-induced fibrosis via a MMP-dependent mechanism. BMP-7 is expected to be the optimized strategy of delaying the interstitial changes.

Aliskiren attenuates bleomycin-induced pulmonary fibrosis in rats: focus on oxidative stress, advanced glycation end products, and matrix metalloproteinase-9

Pulmonary fibrosis is a progressive lung disorder with high mortality rate and limited successful treatment. This study was designed to assess the potential anti-oxidant and anti-fibrotic effects of aliskiren (Alsk) during bleomycin (BLM)-induced pulmonary fibrosis. Male Wistar rats were used as control untreated or treated with the following: a single dose of 2.5 mg/kg of BLM endotracheally and BLM and Alsk (either low dose 30 mg/kg/day or high dose 60 mg/kg/day), and another group was given Alsk 60 mg/kg/day alone. Alsk was given by gavage. Alsk anti-oxidant and anti-fibrotic effects were assessed. BLM significantly increased relative lung weight and the levels of lactate dehydrogenase and total and differential leucocytic count in bronchoalveolar lavage that was significantly ameliorated by high-dose Alsk treatment. As markers of oxidative stress, BLM caused a significant increase in the levels of lipid peroxides and nitric oxide accompanied with a significant decrease of superoxide dismutase and glutathione transferase enzymes. High-dose Alsk treatment restored these markers toward normal values. Alsk counteracted the overexpression of advanced glycation end products, matrix metalloproteinase-9 (MMP-9), and tissue inhibitor of metalloproteinases-1 in lung tissue induced by BLM. Fibrosis assessed by measuring hydroxyproline content, which markedly increased in the BLM group, was also significantly reduced by Alsk. These were confirmed by histopathological and immunohistochemical examination which revealed that Alsk attenuates signs of pulmonary fibrosis and decreased the overexpressed MMP-9 and transforming growth factor β1. Collectively, these findings indicate that Alsk has a potential anti-fibrotic effect beside its anti-oxidant activity.

Proteomic profiling change during the early development of silicosis disease

BACKGROUND

Silicosis is one of several severe occupational diseases for which effective diagnostic tools during early development are currently unavailable. In this study we focused on proteomic profiling during the early stages of silicosis to investigate the pathophysiology and identify the proteins involved.

METHODS

Two-dimensional (2D) gel electrophoresis and MALDI-TOF-MS were used to assess the proteomic differences between healthy individuals (HI), dust-exposed workers without silicosis (DEW) and silicosis patients (SP). Proteins abundances that differed by a factor of two-fold or greater were subjected to more detailed analysis, and enzyme linked to immunosorbent assay (ELISA) was employed to correlate with protein expression data.

RESULTS

Compared with HI, 42 proteins were more abundant and 8 were less abundant in DEW, and these were also differentially accumulated in SP. Closer inspection revealed that serine protease granzyme A, alpha-1-B-glycoprotein (A1BG) and the T4 surface glycoprotein precursor (TSGP) were among the up-regulated proteins in DEW and SP. Significant changes in serine proteases, glycoproteins and proto-oncogenes may be associated with the response to cytotoxicity and infectious pathogens by activation of T cells, positive regulation of extracellular matrix structural constituents and immune response, and fibroblast proliferation. Up-regulation of cytokines included TNFs, interferon beta precursor, interleukin 6, atypical chemokine receptor 2, TNFR13BV, and mutant IL-17F may be involved in the increased and persistent immune response and fibrosis that occurred during silicosis development.

CONCLUSIONS

Granzymes, glycoproteins, cytokines and immune factors were dramatically involved in the immune response, metabolism, signal regulation and fibrosis during the early development of silicosis. Proteomic profiling has expanded our understanding of the pathogenesis of silicosis, and identified a number of targets that may be potential biomarkers for early diagnosis of this debilitating disease.

Cell-Based Therapy for Silicosis

Silicosis is the most common pneumoconiosis globally, with higher prevalence and incidence in developing countries. To date, there is no effective treatment to halt or reverse the disease progression caused by silica-induced lung injury. Significant advances have to be made in order to reduce morbidity and mortality related to silicosis. In this review, we have highlighted the main mechanisms of action that cause lung damage by silica particles and summarized the data concerning the therapeutic promise of cell-based therapy for silicosis.

Protective effect of emodin against airway inflammation in the ovalbumin-induced mouse model

OBJECTIVE

To investigate whether emodin exerts protective effects on mouse with allergic asthma.

METHODS

A mouse model of allergic airway inflflammation was employed. The C57BL/6 mice sensitized and challenged with ovalbumin (OVA) were intraperitoneally administered 10 or 20 mg/kg emodin for 3 days during OVA challenge. Animals were sacrificed 48 h after the last challenge. Inflammatory cell count in the bronchoalveolar lavage fluid (BALF) was measured. The levels of interleukin (IL)-4, IL-5, IL-13 and eotaxin in BALF and level of immunoglobulin E (IgE) in serum were measured with enzyme-linked immuno sorbent assay kits. The mRNA expressions of IL-4, IL-5, heme oxygenase (HO)-1 and matrix metalloproteinase-9 (MMP-9) were determined by real-time quantitative polymerase chain reaction.

RESULTS

Emodin induced significant suppression of the number of OVA-induced total inflammatory cells in BALF. Treatment with emodin led to significant decreases in the levels of IL-4, IL-5, IL-13 and eotaxin in BALF and total IgE level in serum. Histological examination of lung tissue revealed marked attenuation of allergen-induced lung eosinophilic inflammation. Additionally, emodin suppressed IL-4, IL-5 and MMP-9 mRNA expressions and induced HO-1 mRNA expression.

CONCLUSION

Emodin exhibits anti-inflammatory activity in the airway inflammation mouse model, supporting its therapeutic potential for the treatment of allergic bronchial asthma.

Overexpression of matrix metalloproteinases in lung tissue of patients with primary spontaneous pneumothorax

BACKGROUND

Although blebs and bullae are frequently found in the apexes of lungs of patients with primary spontaneous pneumothorax (PSP), its pathogens remain unclear.

OBJECTIVES

To examine the role of proteases [matrix metalloproteinase (MMP)-2, MMP-7 and MMP-9] and antiproteases [tissue inhibitors of metalloproteinase (TIMP)-1, TIMP-2, TIMP-3 and TIMP-4] in the pathogenesis of PSP.

METHOD

Fifty consecutive PSP patients who received standard surgical care were enrolled in the study. Lung tissues from 20 patients with stage I non-small cell lung cancer were used as a control. Immunohistochemistry (IHC), reverse transcription-polymerase chain reaction (RT-PCR) and gelatin zymography were used to evaluate the expression of MMP and TIMP in the lung tissue of patients with PSP.

RESULTS

Overexpression of MMP-2, MMP-7 and MMP-9 was found in the afflicted lung by IHC, zymography and RT-PCR. By IHC, higher expression of MMP-2 and MMP-9 in PSP patients was identified in alveolar macrophages and type II pneumocytes (88 and 92% of patients in macrophages, and 72 and 70% of patients in type II pneumocytes, respectively). MMP-2, MMP-7 and MMP-9 expression in patients was higher in mesothelial cells (66, 76 and 76%). Overexpression of TIMP-2 was detected in the extracellular matrix around bullae and blebs. Expression levels of TIMP-1, TIMP-3 and TIMP-4 were negligible (<10% of cells) in both PSP patients and controls.

CONCLUSIONS

MMP-2, MMP-9, MMP-7 and TIMP-2 were upregulated in PSP lesions. These results suggest that an imbalance between the expression of proteases and antiproteases may be involved in the pathogeneses of PSP.

Liver functions in silica-exposed workers in Egypt: possible role of matrix remodeling and immunological factors

BACKGROUND

Brick manufacturing constitutes an important industrial sector in Egypt with considerable exposure to silica.

OBJECTIVES

We aimed for evaluating hepatic functions in silica-exposed workers in the clay brick industry, and the possible role of matrix remodeling and immunological factors.

METHODS

A case-control study, 87 workers as exposed and 45 as control subjects. Questionnaire, clinical examination, and laboratory investigations: liver functions, matrix metalloproteinase-9, immunoglobulins G and E, and anti-liver kidney microsomal antibody.

RESULTS

In the exposed workers, mean levels of liver functions, matrix metalloproteinase-9 (MMP-9), and IgG and IgE were significantly higher. In the silicotic subgroup the mean level of GGT was almost twice the level in the non-silicotic subjects. Logistic regression showed that abnormal GGT and ALT were associated with production workers.

CONCLUSION

Workers in the clay brick industry showed evidence of liver disease that could be related to matrix remodeling.

Always cleave up your mess: targeting collagen degradation to treat tissue fibrosis

Pulmonary fibrosis is a vexing clinical problem with no proven therapeutic options. In the normal lung there is continuous collagen synthesis and collagen degradation, and these two processes are precisely balanced to maintain normal tissue architecture. With lung injury there is an increase in the rate of both collagen production and collagen degradation. The increase in collagen degradation is critical in preventing the formation of permanent scar tissue each time the lung is exposed to injury. In pulmonary fibrosis, collagen degradation does not keep pace with collagen production, resulting in extracellular accumulation of fibrillar collagen. Collagen degradation occurs through both extracellular and intracellular pathways. The extracellular pathway involves cleavage of collagen fibrils by proteolytic enzyme including the metalloproteinases. The less-well-described intracellular pathway involves binding and uptake of collagen fragments by fibroblasts and macrophages for lysosomal degradation. The relationship between these two pathways and their relevance to the development of fibrosis is complex. Fibrosis in the lung, liver, and skin has been associated with an impaired degradative environment. Much of the current scientific effort in fibrosis is focused on understanding the pathways that regulate increased collagen production. However, recent reports suggest an important role for collagen turnover and degradation in regulating the severity of tissue fibrosis. The objective of this review is to evaluate the roles of the extracellular and intracellular collagen degradation pathways in the development of fibrosis and to examine whether pulmonary fibrosis can be viewed as a disease of impaired matrix degradation rather than a disease of increased matrix production.

Diospyros blancoi attenuates asthmatic effects in a mouse model of airway inflammation

Asthma is a complex disease linked to various pathophysiological events, including proteinase activity. In this study, we examined whether a Diospyros blancoi methanolic extract (DBE) exerts protective effects on allergic asthma in a murine asthma model. To investigate the specific role of DBE, we employed a murine model of allergic airway inflammation. BALB/c mice sensitized and challenged with ovalbumin (OVA) were orally administered 20 or 40 mg/kg DBE for 3 days during OVA challenge. DBE induced significant suppression of the number of OVA-induced total inflammatory cells, including eosinophils, macrophages, and lymphocytes, in bronchoalveolar lavage fluid (BALF). Moreover, treatment with DBE led to significant decreases in interleukin (IL)-4, IL-5, and eotaxin levels in BALF and OVA-specific immunoglobulin (Ig)E and IgG1 levels in serum. Histological examination of lung tissue revealed marked attenuation of allergen-induced lung eosinophilic inflammation and mucus-producing goblet cells in the airway. Additionally, DBE suppressed matrix metalloproteinase-9 activity and induced heme oxygenase-1 expression. The present findings collectively suggest that DBE exhibits anti-inflammatory activity in an airway inflammation mouse model, supporting its therapeutic potential for the treatment of allergic bronchial asthma.

Induction of pulmonary fibrosis by cerium oxide nanoparticles

Cerium compounds have been used as a diesel engine catalyst to lower the mass of diesel exhaust particles, but are emitted as cerium oxide (CeO(2)) nanoparticles in the diesel exhaust. In a previous study, we have demonstrated a wide range of CeO(2)-induced lung responses including sustained pulmonary inflammation and cellular signaling that could lead to pulmonary fibrosis. In this study, we investigated the fibrogenic responses induced by CeO(2) in a rat model at various time points up to 84 days post-exposure. Male Sprague Dawley rats were exposed to CeO(2) by a single intratracheal instillation. Alveolar macrophages (AM) were isolated by bronchial alveolar lavage (BAL). AM-mediated cellular responses, osteopontin (OPN) and transform growth factor (TGF)-β1 in the fibrotic process were investigated. The results showed that CeO(2) exposure significantly increased fibrotic cytokine TGF-β1 and OPN production by AM above controls. The collagen degradation enzymes, matrix metalloproteinase (MMP)-2 and -9 and the tissue inhibitor of MMP were markedly increased in the BAL fluid at 1 day- and subsequently declined at 28 days after exposure, but remained much higher than the controls. CeO(2) induced elevated phospholipids in BAL fluid and increased hydroxyproline content in lung tissue in a dose- and time-dependent manner. Immunohistochemical analysis showed MMP-2, MMP-9 and MMP-10 expressions in fibrotic regions. Morphological analysis noted increased collagen fibers in the lungs exposed to a single dose of 3.5mg/kg CeO(2) and euthanized at 28 days post-exposure. Collectively, our studies show that CeO(2) induced fibrotic lung injury in rats, suggesting it may cause potential health effects.

Lipopolysaccharide-induced lung injury: role of P2X7 receptor

RATIONALE

P2X7 receptors have been involved in inflammatory and immunological responses, and their activation modulates pro-inflammatory cytokines production by LPS-challenged macrophages.

OBJECTIVES

To determine the role of P2X7R in LPS-induced acute lung injury in mice.

METHODS

Wild-type (C57BL/6) and P2X7 knockout mice received intratracheal injection of saline or Escherichia coli LPS (60 μg). After 24h, changes in lung mechanics were determined by the end-inflation occlusion method. Bronchoalveolar lavage was performed, and lungs were harvested for measurement of morphometry, fibers content, inflammatory cells and cytokine expression by histochemistry and immunohistochemistry.

RESULTS

Compared with saline, LPS increased lung mechanical parameters, mast cell, collagen and fibronectin deposition in lung parenchyma, as well as nitric oxide and lactate dehydrogenase release into bronchoalveolar fluid in wild-type, but not in P2X7R knockout mice. Alveolar collapse, lung influx of polymorphonuclear and CD14(+) cells, as well as TGF-β, MMP-2, and IL-1β release were higher in wild-type than knockout LPS-challenged mice, while MMP-9 release where similar between the two genotypes. LPS increased macrophage immunoreactivity in lung tissue in both genotypes, but macrophages were not activated in the P2X7R knockout mice. Furthermore, LPS administration increased P2X7R immunoexpression in lung parenchyma in wild-type mice, and TLR4 in both wild-type and P2X7R knockout mice.

CONCLUSION

P2X7 receptors are implicated in the pathophysiology of LPS-induced lung injury, modulating lung inflammatory and functional changes.

Alterations of serum biomarkers associated with lung ventilation function impairment in coal workers: a cross-sectional study

BACKGROUND

Previous studies have demonstrated that alterations in certain circulating biomarkers may be correlated with Coal workers' pneumoconiosis (CWP). This study investigated the relationship between changes of serum biomarkers and pulmonary function during the development of CWP.

METHODS

Lung function parameters and specific serum indices were measured in 69 non-smoking coal workers, including 34 miners with CWP, 24 asymptomatic miners and 11 miners with minimal symptoms. The associations between changes in pulmonary function and serum indices were tested with Pearson's correlation coefficients. Multivariable analysis was used to estimate the predictive power of potential determinant variables for lung function.

RESULTS

Compared to healthy miners, lung function (FVC, FEV1, FEF50, FEF75, FEF25-75 % of predicted values) was decreased in miners with CWP (p < 0.05). Increased serum matrix metalloproteinase-9 (MMP-9) was associated with decreased FVC% of predicted values in the asymptomatic miners (r = -0.503, p = 0.014).

CONCLUSIONS

In coal mine workers, alterations of lung function parameters are associated with the development of CWP and with changes in circulating MMP-9, TIMP-9, IL-13 and IL-18R. These serum biomarkers may likely reflect the pathogenesis and progression of CWP in coal workers, and may provide for the importance of serum indicators in the early diagnosis of lung function injury in coal miners.

Prevalence of connective tissue disease in silicosis (1985-2006)-a report from the state of Michigan surveillance system for silicosis

BACKGROUND

The risk of developing clinical connective tissue disease (CTD) has been reported to be increased among individuals with silica exposure.

METHODS

We reviewed the medical records of individuals reported to the Michigan Silicosis Surveillance system from 1985 to 2006 to confirm the diagnosis of silicosis and determine the presence of CTDs.

RESULTS

From 1985 to 2006, 1,022 cases were confirmed to have silicosis. Medical records of 790 cases were available. Thirty-three individuals had rheumatoid arthritis (RA) [prevalence 4.2% (prevalence ratio (RR) ranged from 2.26, 95% CI: 1.57-3.25 to 6.96, 95% CI: 2.93-16.53) depending on the reference rate used], two had scleroderma [prevalence 0.3% (RR 28.3, 95% CI: 6.09-129.98)], one had systemic lupus erythematosus [prevalence 0.1% (RR 2.53, 95% CI: 0.30-21.64)], two had Sjogrens syndrome [prevalence 0.3% (RR 0.42, 95% CI: 0.09-2.08)], and six had anti-neutrophil cytoplasm antibody (ANCA) vasculitis [prevalence 0.8% (RR 25.3, 95% CI: 6.34-101.04)]. There was no difference between those with and without CTD with respect to age, race, industry type, history of tuberculosis, application for workers' compensation, or severity of fibrotic changes on chest X-ray.

CONCLUSIONS

A two- to eightfold risk for RA and systemic lupus erythematosus, with a greater than 24-fold risk for scleroderma and ANCA vasculitis was found in individuals with silicosis. The most common CTD among silicotics in the Michigan disease registry was RA. Though not classically included in the category of CTD, ANCA-associated vasculitis was found to have a much greater prevalence amongst silicosis patients than the general population.

Endogenous Hydrogen Sulfide Regulates Pulmonary Artery Collagen Remodeling in Rats with High Pulmonary Blood Flow

The mechanisms responsible for the structural remodeling of pulmonary vasculature induced by increased pulmonary blood flow are not fully understood. This study explores the effect of endogenous hydrogen sulfide (H2S), a novel gasotransmitter, on collagen remodeling of the pulmonary artery in rats with high pulmonary blood flow. Thirty-two Sprague-Dawley rats were randomly divided into sham, shunt, sham+PPG (D,L-propargylglycine, an inhibitor of cystathionine-γ-lyase), and shunt+PPG groups. After 4 weeks of shunting, the relative medial thickness (RMT) of pulmonary arteries and H2S concentration in lung tissues were investigated. Collagen I and collagen III were evaluated by hydroxyproline assay, sirius-red staining, and immunohistochemistry. Pulmonary artery matrix metalloproteinase-13 (MMP-13), tissue inhibitor of metalloproteinase-1 (TIMP-1), and connective tissue growth factor (CTGF) were evaluated by immunohistochemistry. After 4 weeks of aortocaval shunting, resulting in an elevation of lung tissue H2S to 116.4%, rats exhibited collagen remodeling and increased CTGF expression in the pulmonary arteries. Compared with those of the shunt group, lung tissue H2S production was lowered by 23.4%, RMT of the pulmonary artery further increased by 39.5%, pulmonary artery collagen accumulation became obvious, and pulmonary artery CTGF expression elevated ( P < 0.01) in the shunted rats treated with PPG. However, pulmonary artery MMP-13 and TIMP-1 expressions decreased significantly in rats of shunt+PPG group ( P < 0.01). This study suggests that endogenous H2S exerts an important regulatory effect on pulmonary collagen remodeling induced by high pulmonary blood flow.

Effect of Long-Term Inhalation of Toner on Extracellular Matrix in the Lungs of Rats In Vivo

We assessed the effects of long-term inhalation of toner on the pathological changes and gene expression with the synthesis and degradation of collagenous extracellular matrix in a rat model. Female Wistar rats (10 wk old) were divided evenly into a high concentration exposure group (H: 15.2 mg/m3), a low concentration exposure group (L: 5.5 mg/m3), and a control group. The mass median aerodynamic diameter of toner was 4.5 microm. The rats were sacrificed at the termination of a 1-yr or 2-yr inhalation period. Pathological examination was performed from the left lung, and transcriptional levels of mRNA extracted from the right lung were assessed by semiquantitative reverse-transcription polymerase chain polymerase (RT-PCR). The pathological findings showed mild pulmonary fibrosis in 20% (L, 1 yr), 40% (H, 1 yr), 56% (L, 2 yr) and 62% (H, 2 yr), while lung cancer was not observed in any of the exposed groups. In the 1-yr high-concentration group, gene expression of matrix metalloproteinase-2 (MMP-2) and type I collagen mRNA in the rat lungs increased, while tissue inhibitors of metalloproteinase-2 (TIMP-2) decreased. The 2-yr high-concentration group increased in message level of type I collagen and TIMP-2 but not that of MMP-2. These data suggested that results of gene expression of MMP, TIMP, and collagen in the 2-yr exposure may lead to accumulation of collagen compared to the 1-yr exposure, and that the imbalance of the expression of MMPs, TIMPs, and extracellular matrix might be associated with pulmonary fibrosis induced by toner.

Epithelial expression of TIMP-1 does not alter sensitivity to bleomycin-induced lung injury in C57BL/6 mice

Matrix metalloproteinases (MMPs) are mediators of lung injury, and their activity has been associated with the development of pulmonary fibrosis. To understand how MMPs regulate the development of pulmonary fibrosis, we examined MMP expression in two strains of mice with differing sensitivities to the fibrosis-inducing drug bleomycin. After a single intratracheal injection of the drug, bleomycin-sensitive C57BL/6 mice showed increased expression for MMPs (-2, -7, -9, -13) at both 7 and 14 days posttreatment compared with the bleomycin-resistant BALB/c strain. In addition, TIMP-1, an endogenous inhibitor of MMPs, was upregulated in the lungs of C57BL/6 mice but not BALB/c mice. We designed two strategies to decrease MMP expression to potentially decrease sensitivity of C57BL/6 mice: 1) we engineered C57BL/6 mice that overexpressed TIMP-1 in their lungs via surfactant protein C (SP-C) promoter; and 2) we inhibited expression of MMPs independent of TIMP-1 by knocking out metallothionein (MT), a critical zinc binding protein. SP-C-TIMP-1 mice reduced MMP expression in response to bleomycin. However, they were equally sensitive to bleomycin as their wild-type counterparts, displaying similar levels of hydroxyproline in the lung tissue. MT null mice displayed decreased lung activity of MMPs with no change in TIMP-1. Nonetheless, there was no difference between the MT null and wild-type control littermates with regards to any of the lung injury parameters measured. We conclude that although TIMP-1 expression is differentially regulated in fibrosis-sensitive and fibrosis-resistant strains, epithelial overexpression of TIMP-1 does not appear to substantially alter fibrotic lung disease in mice.

Differences in both matrix metalloproteinase 9 concentration and zymographic profile between plasma and serum with clot activators are due to the presence of amorphous silica or silicate salts in blood collection devices

Matrix metalloproteinases (MMPs) are promising diagnostic tools, and blood sampling/handling alters MMP concentrations between plasma and serum and between serum with and without clot activators. To explain the higher MMP-9 expression in serum collected with clot accelerators relative to serum with no additives and to plasma, we analyzed the effects of increasing amounts of silica and silicates (components of clot activators) in citrate plasma, serum, and buffy coats collected in both plastic and glass tubes from 50 healthy donors, and we analyzed the effects of silica and silicate on cultured leukemia cells. The levels of MMP-2 did not show significant changes between glass and plastic tubes, between serum and plasma, between serum with and without clot accelerators, or between silica and silicate treatments. No modification of MMP-9 expression was obtained by the addition of silica or silicate to previously separated plasma and serum. Increasing the amounts of nonsoluble silica and soluble silicate added to citrate and empty tubes prior to blood collection resulted in increasing levels of MMP-9 relative to citrate plasma and serum. Silica and silicate added to buffy coats and leukemia cells significantly induced MMP-9 release/secretion, demonstrating that both silica and silicate induce the release of pro- and complexed MMP-9 forms. We recommend limiting the misuse of serum and avoiding the interfering effects of clot activators.

Protective role of matrix metalloproteinase-9 in ozone-induced airway inflammation

BACKGROUND

Exposure to ozone causes airway inflammation, hyperreactivity, lung hyper-permeability, and epithelial cell injury. An early inflammatory response induced by inhaled O(3) is characterized primarily by release of inflammatory mediators such as cytokines, chemokines, and airway neutrophil accumulation. Matrix metalloproteinases (MMPs) have been implicated in the pathogenesis of oxidative lung disorders including acute lung injury, asthma, and chronic obstructive pulmonary disease.

OBJECTIVE

We hypothesized that MMPs have an important role in the pathogenesis of O(3)-induced airway inflammation.

METHODS

We compared the lung injury responses in either Mmp7- (Mmp7(-/-)) or Mmp9-deficient (Mmp9(-/-)) mice and their wild-type controls (Mmp7(+/+), Mmp9(+/+)) after exposure to 0.3 ppm O(3) or filtered air.

RESULTS

Relative to air-exposed controls, MMP-9 activity in bronchoalveolar lavage fluid (BALF) was significantly increased by O(3) exposure in Mmp9(+/+) mice. O(3)-induced increases in the concentration of total protein (a marker of lung permeability) and the numbers of neutrophils and epithelial cells in BALF were significantly greater in Mmp9(-/-) mice compared with Mmp9(+/+) mice. Keratinocyte-derived chemokine (KC) and macrophage inflammatory protein (MIP)-2 levels in BALF were also significantly higher in Mmp9(-/-) mice than in Mmp9(+/+) mice after O(3) exposure, although no differences in mRNA expression for these chemokines were found between genotypes. Mean BALF protein concentration and numbers of inflammatory cells were not significantly different between Mmp7(+/+) and Mmp7(-/-) mice after O(3) exposure.

CONCLUSIONS

Results demonstrated a protective role of MMP-9 but not of MMP-7, in O(3)-induced lung neutrophilic inflammation and hyperpermeability. The mechanism through which Mmp9 limits O(3)-induced airway injury is not known but may be via posttranscriptional effects on proinflammatory CXC chemokines including KC and MIP-2.

Scar-associated macrophages are a major source of hepatic matrix metalloproteinase-13 and facilitate the resolution of murine hepatic fibrosis

Both the identity and source of the rodent collagenase(s) that mediates matrix remodeling in liver fibrosis remain elusive. We have recently demonstrated an unequivocal role for scar-associated macrophages (SAMs) in the spontaneous resolution of liver fibrosis and sought to determine whether SAMs are the source of matrix metalloproteinase (MMP) 13 (collagenase 3), considered to be the primary interstitial collagenase in rodents. In this study, we demonstrate an association between MMP13 expression and the presence of SAMs in the regression of experimental liver fibrosis. mmp13 gene expression was restricted to regions of fibrosis that were rich in SAMs. Both MMP13 mRNA and protein colocalized to large phagocytes within and directly apposed to hepatic scars. Using the CD11b-DTR-transgenic mouse to deplete SAMs in a model of chronic CCl(4) injury, we found that SAM depletion resulted in a 5-fold reduction in mmp13 message (p = 0.005). Furthermore, resolution of CCl(4)-induced fibrosis was retarded in MMP13-deficient mice. Thus, SAMs selectively, during resolution of fibrosis induce and use the major collagenase MMP13 to mediate the resorption of interstitial matrix and successfully remodel the fibrotic liver.

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.

Unexpected smoking-linked high MMP-9 in induced sputum of hazardous dust-exposed workers

We investigated whether metalloproteinase-9 (MMP-9) values in induced sputum (IS) and pulmonary function tests can serve as a marker of damage and intensity of exposure to hazardous dust. Thirty-nine factory employees (28 workers exposed to metal particles and 11 supposedly nonexposed office workers) underwent IS induction. Samples were processed by conventional methods within 2 hours. The proportion of particles with diameters of 0-2 mu in IS samples was significantly higher in nonexposed than exposed workers and in smoker compared to nonsmoker workers. MMP-9 and TIMP-1 levels were similar for both groups. A linear regression model for MMP-9 based on exposure, smoking habits, and proportion of particles < 5 mu revealed a positive correlation between each of the explanatory variables and MMP-9 values. MMP-9 may serve as a marker for pulmonary injury.

Mechanistically identified suitable biomarkers of exposure, effect, and susceptibility for silicosis and coal-worker's pneumoconiosis: a comprehensive review

Clinical detection of silicosis is currently dependent on radiological and lung function abnormalities, both late manifestations of disease. Markers of prediction and early detection of pneumoconiosis are imperative for the implementation of timely intervention strategies. Understanding the underlying mechanisms of the etiology of coal workers pneumoconiosis (CWP) and silicosis was essential in proposing numerous biomarkers that have been evaluated to assess effects following exposure to crystalline silica and/or coal mine dust. Human validation studies have substantiated some of these proposed biomarkers and argued in favor of their use as biomarkers for crystalline silica- and CWP-induced pneumoconiosis. A number of "ideal" biological markers of effect were identified, namely, Clara cell protein-16 (CC16) (serum), tumor necrosis factor-alpha (TNF-alpha) (monocyte release), interleukin-8 (IL-8) (monocyte release), reactive oxygen species (ROS) measurement by chemiluminescence (neutrophil release), 8-isoprostanes (serum), total antioxidant levels measured by total equivalent antioxidant capacity (TEAC), glutathione, glutathione peroxidase activity, glutathione S-transferase activity, and platelet-derived growth factor (PDGF) (serum). TNF-alpha polymorphism (blood cellular DNA) was identified as a biomarker of susceptibility. Further studies are planned to test the validity and feasibility of these biomarkers to detect either high exposure to crystalline silica and early silicosis or susceptibility to silicosis in gold miners in South Africa.

Matrix metalloproteinases promote inflammation and fibrosis in asbestos-induced lung injury in mice

Inhalation of asbestos fibers causes pulmonary inflammation and eventual pulmonary fibrosis (asbestosis). Although the underlying molecular events are poorly understood, protease/antiprotease and oxidant/antioxidant imbalances are believed to contribute to the disease. Implicated in other forms of pulmonary fibrosis, the matrix metalloproteinases (MMPs) have not been examined in asbestosis. We therefore hypothesized that MMPs play a pathogenic role in asbestosis development. Wild-type C57BL/6 mice were intratracheally instilled with 0.1 mg crocidolite asbestos, causing an inflammatory response at 1 d and a developing fibrotic response at 7, 14, and 28 d. Gelatin zymography demonstrated an increase in MMP-9 (gelatinase B) during the inflammatory phase, while MMP-2 (gelatinase A) was profoundly increased in the fibrotic phase. Immunohistochemistry revealed MMP-9 in and around bronchiolar and airspace neutrophils that were often associated with visible asbestos fibers. MMP-2 was found in fibrotic regions at 7, 14, and 28 d. No increases in RNA levels of MMP-2, MMP-9, or MMP-8 were found, but levels of MMP-7, MMP-12, and MMP-13 RNA did increase at 14 d. The MMP inhibitors, TIMP-1 and TIMP-2, were also increased at 7-28 d after asbestos exposure. To confirm the importance of MMP activity in disease progression, mice exposed to asbestos were given daily injections of the MMP inhibitor, GM6001. MMP inhibition reduced inflammation and fibrosis in asbestos-treated mice. Collectively, these data suggest that MMPs contribute to the pathogenesis of asbestosis through effects on inflammation and fibrosis development.

Transcriptional up‐regulation of MMPs 12 and 13 by asbestos occurs via a PKCδ‐dependent pathway in murine lung

Asbestos is a known inflammatory, carcinogenic, and fibrotic agent, but the mechanisms leading to asbestos-induced lung diseases are unclear. Using a murine inhalation model of fibrogenesis, we show that asbestos causes significant increases in mRNA levels of lung matrix metalloproteinases (MMPs 12 and 13) and tissue inhibitor of metalloproteinases (TIMP1), as well as increased activities of MMP 2, 9, and 12 in bronchoalveolar lavage fluids (BALF). Asbestos-exposed PKCdelta knockout (PKCdelta-/-) mice exhibited decreased expression of lung MMP12 and MMP13 compared with asbestos-exposed wild-type mice. Studies using small molecule inhibitors in murine alveolar epithelial type II cells (C10) and primary lung fibroblasts confirmed that asbestos transcriptionally up-regulates MMPs via an EGFR (or other growth factor receptors)/PI3K/PKCdelta/ERK1/2 pathway. Moreover, use of a broad-spectrum MMP inhibitor showed that MMPs play an important role in further enhancing asbestos-induced signaling events by activating EGFR. These data reveal a potentially important link between asbestos signaling and integrity of the extracellular matrix (ECM) that likely contributes to asbestos-induced lung remodeling and diseases.

Red blood cells increase secretion of matrix metalloproteinases from human lung fibroblasts in vitro

Tissue remodeling is an important process in many inflammatory and fibrotic lung disorders. RBC may in these conditions interact with extracellular matrix (ECM). Fibroblasts can produce and secrete matrix components, matrix-degrading enzymes (MMPs) and tissue inhibitors of metalloproteinases (TIMPs). Imbalance in matrix synthesis/degradation may result in rearrangement of tissue architecture and lead to diseases such as emphysema or fibrosis. Neutrophil elastase (NE), a protease released by neutrophils, is known to activate MMP. We hypothesized that RBC can stimulate secretion of MMPs from human lung fibroblasts and that NE can augment this effect. Human fetal lung fibroblasts were cultured in floating collagen gels with or without RBC. After 4 days, the culture medium was analyzed with gelatin zymography, Western blot, and ELISA for MMP-1, -2, -3 and TIMP-1, -2. RBC augmented NE-induced fibroblast-mediated collagen gel contraction compared with NE alone (18.4+/-1.6%, 23.7+/-1.4% of initial gel area, respectively). A pan-MMP inhibitor (GM-6001) completely abolished the stimulating effect of NE. Gelatin zymography showed that RBC stimulated MMP-2 activity and that NE enhanced conversion to the active form. Addition of GM-6001 completely inhibited MMP-2 activity in controls, whereas it only partially altered RBC-induced MMP activity. Western blot confirmed the presence of MMP-1 and MMP-3 in fibroblasts stimulated with RBC, and ELISA confirmed increased concentrations of pro-MMP-1. We conclude that stimulation of MMP secretion by fibroblasts may explain the ability of RBC to augment fibroblast-mediated collagen gel contraction. This might be a potential mechanism by which hemorrhage in inflammatory conditions leads to ECM remodeling.

Expression of clara cell secretory protein in the lungs of rats exposed to crystalline silica in vivo

It has been theorized that Clara cell secretion protein (CCSP) plays a critical role in regulating the acute inflammatory response in the lung. We hypothesized that CCSP is also related to lung injury induced by occupational dust. The present study was conducted to investigate the time course of the expression of CCSP in lungs exposed to crystalline silica in vivo. Male Wistar rats were administered 1 mg or 2 mg of silica suspended in saline by a single intratracheal instillation and were sacrificed at 3 d, 1 wk, 1 month, 3 months and 6 months of recovery time. The expression of CCSP was observed by RT-PCR and western blot analysis. Exposure to 2 mg of silica decreased in levels of CCSP mRNA at 3 d, 1 wk, 1 month and 6 months following intratracheal instillation. The protein level of CCSP in silica-exposed rats was decreased at 3 d, 7 d and 1 month after a single instillation of 2 mg. The decreases in CCSP at the acute phase in this experiment suggest that CCSP may regulate the acute injury of the lung exposed to silica.

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.

Matrix metalloproteinases in destructive pulmonary pathology

Matrix metalloproteinases (MMPs) are a family of proteolytic enzymes that have a number of important physiological roles including remodelling of the extracellular matrix, facilitating cell migration, cleaving cytokines, and activating defensins. However, excess MMP activity may lead to tissue destruction. The biology of MMP and the role of these proteases in normal pulmonary immunity are reviewed, and evidence that implicates excess MMP activity in causing matrix breakdown in chronic obstructive pulmonary disease (COPD), acute respiratory distress syndrome (ARDS), sarcoidosis, and tuberculosis is discussed. Evidence from both clinical studies and animal models showing that stromal and inflammatory cell MMP expression leads to immunopathology is examined, and the mechanisms by which excess MMP activity may be targeted to improve clinical outcomes are discussed.

Matrix metalloproteinase-2 (MMP-2) and MMP-9 in pulmonary pathology

The lung is affected by a variety of disease processes that can lead to considerable morbidity and mortality. As the lung is the only organ for respiration and gas exchange, the structural and functional integrity of the lung is of primary importance. Various pathological processes affect the extracellular matrix (ECM) of the lung in an adverse manner, causing destruction of tissue integrity followed by tissue remodeling, which together impair normal pulmonary function. Matrix metalloproteinases (MMPs) are neutral proteinases that are involved in the breakdown and remodeling of the ECM under a variety of physiological and pathological conditions. MMP-2 and MMP-9, collectively known as the gelatinases, are particularly important in the pathogenesis of inflammatory, infectious, and neoplastic diseases in many organs including the lung. This review examines the expression of MMP-2 and MMP-9 in disease of the lung and discusses the role these gelatinases may play in disease progression.

Poly(ADP-ribosyl)ation in asthma and other lung diseases

Inhibition of poly(ADP-ribosyl)ation in oxidative stress-related pathologies has recently emerged as a very effective anti-inflammatory intervention in animal models of arthritis, colitis, diabetes and shock. Recent data from three laboratories also support the role of poly(ADP-ribose) polymerase-1 (PARP-1) activation in asthma. Similarly to other inflammatory conditions, the protective effects of PARP inhibition and the PARP-1 knock out phenotype in asthma models have been attributed to inhibition of inflammatory signal transduction (mainly via NF-kappaB) and of oxidative stress-induced cell dysfunction and tissue injury. Here I discuss the complex role of poly(ADP-ribosyl)ation in the regulation of inflammatory cell migration, chemokine and cytokine production and expression of other inflammatory mediators (inducible nitric oxide synthase, matrix metalloproteinases) in asthma. The role of PARP-1 in other oxidative stress-related lung diseases such as asbestosis, silicosis, acute respiratory distress syndrome and ischemia-reperfusion injury is also reviewed.

Overexpression of cathepsin K during silica-induced lung fibrosis and control by TGF-beta

Background

Lung fibrosis is characterized by tissue remodeling resulting from an imbalance between synthesis and degradation of extracellular organic matrices. To examine whether cathepsin(s) (Cat) are important in the development of pulmonary fibrosis, we assessed the expression of four Cat known for their collagenolytic activity in a model of silica-induced lung fibrosis.

Methods

Different strains of mice were transorally instilled with 2.5 mg crystalline silica or other particles. Cat expression (Cat K, S, L and B) was quantified in lung tissue and isolated pulmonary cells by quantitative RT-PCR. In vitro, we assessed the effect of different cytokines, involved in lung inflammatory and fibrotic responses, on the expression of Cat K by alveolar macrophages and fibroblasts.

Results

In lung tissue, Cat K transcript was the most strongly upregulated in response to silica, and this upregulation was intimately related to the fibrotic process. In mouse strains known for their differential response to silica, we showed that the level of Cat K expression following silica treatment was inversely related to the level of TGF-β expression and the susceptibility of these strains to develop fibrosis. Pulmonary macrophages and fibroblasts were identified as Cat K overproducing cells in the lung of silicotic mice. In vitro, Cat K was downregulated in mouse and human lung fibroblasts by the profibrotic growth factor TGF-β1.

Conclusion

Altogether, these data suggest that while Cat K may contribute to control lung fibrosis, TGF-β appears to limit its overexpression in response to silica particles.

Tissue inhibitor of metalloproteinases-2 growth-stimulatory activity is mediated by nuclear factor-kappa B in A549 lung epithelial cells

Tissue inhibitors of metalloproteinases (TIMPs) are pleiotropic factors that function as key regulators of extracellular matrix remodeling. They exhibit multifunctional roles including cell growth-stimulating activities and protection from apoptosis. In the present study, we showed that human recombinant TIMP-2 (hrTIMP-2) promotes growth of A549 lung cells. This effect was accompanied by increase in nuclear factor-kappa B (NF-kappaB) activity 24h after exposure as determined by electrophoretic mobility shift assay (EMSA) analysis. This effect was correlated with downregulation of IkappaBalpha and beta proteins and later increases in Bcl-3, IkappaB, and cyclin D1 proteins. Blocking induction of NF-kappaB activity using a dominant-negative mutated version of IkappaBalpha abrogated NF-kappaB activation and cell proliferation.

Influence of receptor activator of nuclear factor kappa B on human aortic valve myofibroblasts

Calcific aortic valve stenosis, the main heart valve disease in the elderly, is based on progressive calcification and fibrous thickening of the valve. Several reports addressed the pathogenesis of tissue calcification in this disorder, but few data exist on the molecular mechanisms of the fibrosis and remodeling of the extracellular matrix. The cytokine "receptor activator of nuclear factor kappa B ligand" (RANKL), is expressed in stenotic aortic valves and involved in valvular calcification during calcific aortic valve stenosis. The present study aimed to assess the influence of RANKL on the molecular mechanisms of connective tissue remodeling. In an established cell culture model of primary human aortic valve myofibroblasts, stimulation with RANKL increased cell proliferation as compared to medium alone. Matrix metalloproteinase (MMP)-1 was detectable time-dependently in conditioned media from RANKL-stimulated cells, but absent in media from control cells. MMP-1 activity was increased by RANKL, as measured by collagenase activity assay. Zymography showed an increase in active MMP-2 in RANKL-stimulated cells. These results support the concept that MMPs are involved in the connective tissue remodeling during calcific aortic valve stenosis. RANKL might regulate this process by promoting cell proliferation and MMP expression and activation.

Matrix metalloproteinase induction in fibrosis and fibrotic nodule formation due to silica inhalation

Matrix metalloproteinases (MMPs) are the principle enzymes that initiate degradation of collagen. We examined the role of MMPs during alveolar wall fibrosis and fibrotic nodule formation from silica exposure. Rats were exposed to filtered air or 15 mg/m(3) silica by inhalation for 5 days/wk, 6 h/day. Lungs were preserved by intratracheal instillation of fixative at 20, 40, 60, 79, and 116 days of exposure. Additional groups were fixed after 20, 40, and 60 days of exposure followed by 36 days of recovery. The number of nodules, defined by a collagenous core and a bounding cell layer detached from the alveolar wall, was determined by morphometry. Lungs showed increased alveolar wall collagen and fibrotic nodules at 79 and 116 days of exposure with increased collagenase and gelatinase activity. The number of nodules per lung in exposed groups increased from 619 +/- 447 at 40 days to 13,221 +/- 1,096 at 116 days (means +/- SE, n = 5). No nodules were seen in control lungs. Silica-exposed rats with a 36-day recovery in filtered air showed enhanced MMP activity over exposure to silica for the same duration with no recovery. MMP-2 and MMP-9 were significantly elevated in alveolar macrophages after 40-day exposure. Stromelysin expression was demonstrated in alveolar macrophages and cells within fibrotic nodules. TIMP-1 expression was not significantly altered. In summary, MMP activity was upregulated at 40 days of silica exposure and progressively increased during ensuing fibrotic responses. Early expression of stromelysin was found in fibrosing alveolar walls and fibrotic nodules.

Smad3 null mice develop airspace enlargement and are resistant to TGF-beta-mediated pulmonary fibrosis

Transforming growth factor-beta 1 plays a key role in the pathogenesis of pulmonary fibrosis, mediating extracellular matrix (ECM) gene expression through a series of intracellular signaling molecules, including Smad2 and Smad3. We show that Smad3 null mice (knockout (KO)) develop progressive age-related increases in the size of alveolar spaces, associated with high spontaneous presence of matrix metalloproteinases (MMP-9 and MMP-12) in the lung. Moreover, transient overexpression of active TGF-beta 1 in lungs, using adenoviral vector-mediated gene transfer, resulted in progressive pulmonary fibrosis in wild-type mice, whereas no fibrosis was seen in the lungs of Smad3 KO mice up to 28 days. Significantly higher levels of matrix components (procollagen 3A1, connective tissue growth factor) and antiproteinases (plasminogen activator inhibitor-1, tissue inhibitor of metalloproteinase-1) were detected in wild-type lungs 4 days after TGF-beta 1 administration, while no such changes were seen in KO lungs. These data suggest a pivotal role of the Smad3 pathway in ECM metabolism. Basal activity of the pathway is required to maintain alveolar integrity and ECM homeostasis, but excessive signaling through the pathway results in fibrosis characterized by inhibited degradation and enhanced ECM deposition. The Smad3 pathway is involved in pathogenic mechanisms mediating tissue destruction (lack of repair) and fibrogenesis (excessive repair).