Vanadium stimulates human bronchial epithelial cells to produce heparin-binding epidermal growth factor-like growth factor: a mitogen for lung fibroblasts

Exploration of the Shared Gene Signatures and Molecular Mechanisms between Chronic Bronchitis and Antineutrophil Cytoplasmic Antibody-associated Glomerulonephritis: Evidence from Transcriptome Data

BACKGROUND

Chronic Bronchitis (CB) is a recurrent and persistent pulmonary inflammation disease. Growing evidence suggests an association between CB and Anti-neutrophil Cytoplasmic Antibody-associated Glomerulonephritis (ANCA-GN). However, the precise mechanisms underlying their association remain unclear.

AIMS

The purpose of this study was to further explore the molecular mechanism of the occurrence of chronic bronchitis (CB) associated with anti-neutrophil cytoplasmic antibody-associated glomerulonephritis (ANCA- GN).

OBJECTIVE

Our study aimed to investigate the potential shared pathogenesis of CB-associated ANCA-GN.

METHODS

Datasets of ANCA (GSE108113 and GSE104948) and CB (GSE151052 and GSE162635) were obtained from the Gene Expression Omnibus (GEO) datasets. Firstly, GSE108113 and GSE151052 were analyzed to identify common differentially expressed genes (DEGs) by Limma package. Based on common DEGs, protein-protein interaction (PPI) network and functional enrichment analyses, including GO, KEGG, and GSEA, were performed. Then, hub genes were identified by degree algorithm and validated in GSE104948 and GSE162635. Further PPI network and functional enrichment analyses were performed on hub genes. Additionally, a competitive ceRNA network was constructed through miRanda and spongeScan. Transcription factors (TFs) were predicted and verified using the TRRUST database. Furthermore, the CIBERSORT algorithm was employed to explore immune cell infiltration. The Drug Gene Interaction Database (DGIDB) was utilized to predict small-molecular compounds of CB and ANCA-GN.

RESULTS

A total of 963 DEGs were identified in the integrated CB dataset, and 610 DEGs were identified in the integrated ANCA-GN dataset. Totally, we identified 22 common DEGs, of which 10 hub genes (LYZ, IRF1, PIK3CG, IL2RG, NT5E, ARG2, HBEGF, NFATC2, ALPL, and FKBP5) were primarily involved in inflammation and immune responses. Focusing on hub genes, we constructed a ceRNA network composed of 323 miRNAs and 348 lncRNAs. Additionally, five TFs (SP1, RELA, NFKB1, HIF1A, and SP3) were identified to regulate the hub genes. Furthermore, immune cell infiltration results revealed immunoregulation in CB and ANCA-GN. Finally, some small-molecular compounds (Daclizumab, Aldesleukin, and NT5E) were predicted to predominantly regulate inflammation and immunity, especially IL-2.

CONCLUSION

Our study explores the inflammatory-immune pathways underlying CB-associated ANCA-GN and emphasizes the importance of NETs and lymphocyte differentiation, providing novel insights into the shared pathogenesis and therapeutic targets.

Airway epithelial ITGB4 deficiency induces airway remodeling in a mouse model

BACKGROUND

Airway epithelial cells (AECs) with impaired barrier function contribute to airway remodeling through the activation of epithelial-mesenchymal trophic units (EMTUs). Although the decreased expression of ITGB4 in AECs is implicated in the pathogenesis of asthma, how ITGB4 deficiency impacts airway remodeling remains obscure.

OBJECTIVE

This study aims to determine the effect of epithelial ITGB4 deficiency on the barrier function of AECs, asthma susceptibility, airway remodeling, and EMTU activation.

METHODS

AEC-specific ITGB4 conditional knockout mice (ITGB4^-/-) were generated and an asthma model was employed by the sensitization and challenge of house dust mite (HDM). EMTU activation-related growth factors were examined in ITGB4-silenced primary human bronchial epithelial cells of healthy subjects after HDM stimulation. Dexamethasone, the inhibitors of JNK phosphorylation or FGF2 were administered for the identification of the molecular mechanisms of airway remodeling in HDM-exposed ITGB4^-/- mice.

RESULTS

ITGB4 deficiency in AECs enhanced asthma susceptibility and airway remodeling by disrupting airway epithelial barrier function. Aggravated airway remodeling in HDM-exposed ITGB4^-/- mice was induced through the enhanced activation of EMTU mediated by Src homology domain 2-containing protein tyrosine phosphatase 2/c-Jun N-terminal kinase/Jun N-terminal kinase-dependent transcription factor/FGF2 (SHP2/JNK/c-Jun/FGF2) signaling pathway, which was partially independent of airway inflammation. Both JNK and FGF2 inhibitors significantly inhibited the aggravated airway remodeling and EMTU activation in HDM-exposed ITGB4^-/- mice.

CONCLUSIONS

Airway epithelial ITGB4 deficiency induces airway remodeling in a mouse model of asthma through enhanced EMTU activation that is regulated by the SHP2/JNK/c-Jun/FGF2 pathway.

The extracellular matrix as a multitasking player in disease

Extracellular matrices (ECMs) are highly specialized and dynamic three-dimensional (3D) scaffolds into which cells reside in tissues. ECM is composed of a variety of fibrillar components, such as collagens, fibronectin, and elastin, and non-fibrillar molecules as proteoglycans, hyaluronan, and glycoproteins including matricellular proteins. These macromolecular components are interconnected forming complex networks that actively communicate with cells through binding to cell surface receptors and/or matrix effectors. ECMs exert diverse roles, either providing tissues with structural integrity and mechanical properties essential for tissue functions or regulating cell phenotype and functions to maintain tissue homeostasis. ECM molecular composition and structure vary among tissues, and is markedly modified during normal tissue repair as well as during the progression of various diseases. Actually, abnormal ECM remodeling occurring in pathologic circumstances drives disease progression by regulating cell-matrix interactions. The importance of matrix molecules to normal tissue functions is also highlighted by mutations in matrix genes that give rise to genetic disorders with diverse clinical phenotypes. In this review, we present critical and emerging issues related to matrix assembly in tissues and the multitasking roles for ECM in diseases such as osteoarthritis, fibrosis, cancer, and genetic diseases. The mechanisms underlying the various matrix-based diseases are also discussed. Research focused on the highly dynamic 3D ECM networks will help to discover matrix-related causative abnormalities of diseases as well as novel diagnostic tools and therapeutic targets.

Novel Approaches for Extracellular Matrix Targeting in Disease Treatment

Extracellular matrix (ECM) macromolecules, apart from structural role for the surrounding tissue, have also been defined as crucial mediators in several cell mechanisms. The proteolytic and cross-linking cascades of ECM have fundamental importance in health and disease, which is increasingly becoming acknowledged. However, formidable challenges remain to identify the diverse and novel role of ECM molecules, especially with regard to their distinct biophysical, biochemical, and structural properties. Considering the heterogeneous, dynamic, and hierarchical nature of ECM, the characterization of 3D functional molecular view of ECM in atomic detail will be very useful for further ECM-related studies. Nowadays, the creation of a pioneer ECM multidisciplinary integrated platform in order to decipher ECM homeostasis is more possible than ever. The access to cutting-edge technologies, such as optical imaging and electron and atomic force microscopies, along with diffraction and X-ray-based spectroscopic methods can integrate spanning wide ranges of spatial and time resolutions. Subsequently, ECM image-guided site-directed proteomics can reveal molecular compositions in defined native and reconstituted ECM microenvironments. In addition, the use of highly selective ECM enzyme inhibitors enables the comparative molecular analyses within pre-classified remodeled ECM microenvironments. Mechanistic information which will be derived can be used to develop novel protein-based inhibitors for effective diagnostic and/or therapeutic modalities targeting ECM reactions within tissue microenvironment.

The impaired proteases and anti-proteases balance in Idiopathic Pulmonary Fibrosis

Idiopathic Pulmonary Fibrosis (IPF) is a devastating chronic, progressive and irreversible disease that remains refractory to current therapies. Matrix metalloproteinases (MMPs) and their inhibitors, tissue inhibitors of MMPs (TIMPs), have been implicated in the development of pulmonary fibrosis since decades. Coagulation signalling deregulation, which influences several key inflammatory and fibro-proliferative responses, is also essential in IPF pathogenesis, and a growing body of evidence indicates that Protease-Activated Receptors (PARs) inhibition in IPF may be promising for future evaluation. Therefore, proteases and anti-proteases aroused great biomedical interest over the past years, owing to the identification of their potential roles in lung fibrosis. During these last decades, numerous other proteases and anti-proteases have been studied in lung fibrosis, such as matriptase, Human airway trypsin-like protease (HAT), Hepatocyte growth factor activator (HGFA)/HGFA activator inhibitor (HAI) system, Plasminogen activator inhibitor (PAI)-1, Protease nexine (PN)-1, cathepsins, calpains, and cystatin C. Herein, we provide a general overview of the proteases and anti-proteases unbalance during lung fibrogenesis and explore potential therapeutics for IPF.

Emerging insights into the role of matrix metalloproteases as therapeutic targets in fibrosis

Fibrosis is the extensive accumulation and buildup of extracellular matrix components, especially fibrillar collagens, during wound healing in response to tissue injury. During all individual stages of fibrosis ECM proteases, mainly matrix metalloproteinases, have diverse roles. The functional role of MMPs and their endogenous inhibitors are differentiated among their family members, and according to the different stages of fibrosis. MMPs levels are elevated in several inflammatory and non-inflammatory fibrotic tissues contributing to the development, progression or resolution of the disease, whereas in other tissues their expression levels can be diminished or be stable to the baseline. The biological roles of MMPs during fibrosis are not fully resolved, but they seem to differ according the specific member of the family, the affected tissue and the stage of the fibrotic response. Remarkably, some members of the family exhibit profibrotic actions while other function as antifibrotic molecules. Diverse animal models indicate that MMPs are contributing in processes related to immunity, tissue repair and ECM turnover, providing significant impact on mechanisms related to fibrosis. For that purpose, these proteases are considered as pharmacological targets and new biological drugs have been developed in order to treat fibrosis.

Extracellular matrix remodeling in idiopathic pulmonary fibrosis. It is the 'bed' that counts and not 'the sleepers'

INTRODUCTION

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive interstitial lung disease characterized by irreversible fibrosis. Current disease pathogenesis assumes an aberrant wound healing process in response to repetitive injurious stimuli leading to apoptosis of epithelial cells, activation of fibroblasts and accumulation of extracellular matrix (ECM). Particularly, lung ECM is a highly dynamic structure that lies at the core of several physiological and developmental pathways. The scope of this review article is to summarize current knowledge on the role of ECM in the pathogenesis of IPF, unravel novel mechanistic data and identify future more effective therapeutic targets. Areas covered: The exact mechanisms through which lung microenvironment activates fibroblasts and inflammatory cells, regulates profibrotic signaling cascades through growth factors, integrins and degradation enzymes ultimately leading to excessive matrix deposition are discussed. Furthermore, the potential therapeutic usefulness of specific inhibitors of matrix deposition or activators of matrix degradation pathways are also presented. Expert commentary: With a gradually increasing worldwide incidence IPF still present a major challenge in clinical research due to its unknown etiopathogenesis and current ineffective treatment approaches. Today, there is an amenable need for more effective therapeutic targets and ECM components may represent one.

Matrix metalloproteinases as therapeutic targets for idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a restrictive lung disease that is associated with high morbidity and mortality. Current medical therapies are not fully effective at limiting mortality in patients with IPF, and new therapies are urgently needed. Matrix metalloproteinases (MMPs) are proteinases that, together, can degrade all components of the extracellular matrix and numerous nonmatrix proteins. MMPs and their inhibitors, tissue inhibitors of MMPs (TIMPs), have been implicated in the pathogenesis of IPF based upon the results of clinical studies reporting elevated levels of MMPs (including MMP-1, MMP-7, MMP-8, and MMP-9) in IPF blood and/or lung samples. Surprisingly, studies of gene-targeted mice in murine models of pulmonary fibrosis (PF) have demonstrated that most MMPs promote (rather than inhibit) the development of PF and have identified diverse mechanisms involved. These mechanisms include MMPs: (1) promoting epithelial-to-mesenchymal transition (MMP-3 and MMP-7); (2) increasing lung levels or activity of profibrotic mediators or reducing lung levels of antifibrotic mediators (MMP-3, MMP-7, and MMP-8); (3) promoting abnormal epithelial cell migration and other aberrant repair processes (MMP-3 and MMP-9); (4) inducing the switching of lung macrophage phenotypes from M1 to M2 types (MMP-10 and MMP-28); and (5) promoting fibrocyte migration (MMP-8). Two MMPs, MMP-13 and MMP-19, have antifibrotic activities in murine models of PF, and two MMPs, MMP-1 and MMP-10, have the potential to limit fibrotic responses to injury. Herein, we review what is known about the contributions of MMPs and TIMPs to the pathogenesis of IPF and discuss their potential as therapeutic targets for IPF.

Descriptive epidemiology of human thyroid cancer: experience from a regional registry and the "volcanic factor"

Thyroid cancer (TC), the most common endocrine tumor, has steadily increased worldwide due to the increase of the papillary histotype. The reasons for this spread have not been established. In addition to more sensitive thyroid nodule screening, the effect of environmental factors cannot be excluded. Because high incidences of TC were found in volcanic areas (Hawaii and Iceland), a volcanic environment may play a role in the pathogenesis of TC. In January 2002, the Regional Register for TC was instituted in Sicily. With a population of approximately five million inhabitants with similar genetic and lifestyle features, the coexistence in Sicily of rural, urban, industrial, moderate-to-low iodine intake, and volcanic areas provides a conducive setting for assessing the environmental influences on the etiology of TC. In Sicily, between 2002 and 2004, 1,950 new cases of TC were identified, with an age-standardized rate (world) ASR(w) = 17.8/10(5) in females and 3.7/10(5) in males and a high female/male ratio (4.3:1.0). The incidence of TC was heterogeneous within Sicily. There were 2.3 times more cases in the Catania province (where most of the inhabitants live in the volcanic area of Mt. Etna): ASR(w) = 31.7/10(5) in females and 6.4/10(5) in males vs. 14.1 in females and 3.0 in males in the rest of Sicily. Multivariate analysis documented that residents in the volcanic area of Mt. Etna had a higher risk of TC, compared to the residents in urban, industrial, and iodine deficient areas of Sicily. An abnormally high concentration of several chemicals was found in the drinking water of the Mt. Etna aquifer, which provides water to most of the residents in the Catania province. Our data suggest that environmental carcinogen(s) of volcanic origin may promote papillary TC. Additional analyses, including cancer biological and molecular features, will allow a better understanding of risk factors and etiopathogenetic mechanisms.

Pathogenesis and disease mechanisms of occupational asthma

Occupational asthma (OA) is one of the most common forms of work-related lung disease in all industrialized nations. The clinical management of patients with OA depends on an understanding of the multifactorial pathogenetic mechanisms that can contribute to this disease. This article discusses the various immunologic and nonimmunologic mechanisms and genetic susceptibility factors that drive the inflammatory processes of OA.

Latent infection by γherpesvirus stimulates profibrotic mediator release from multiple cell types

Although γherpesvirus infections are associated with enhanced lung fibrosis in both clinical and animal studies, there is limited understanding about fibrotic effects of γherpesviruses on cell types present in the lung, particularly during latent infection. Wild-type mice were intranasally infected with a murine γherpesvirus (γHV-68) or mock-infected with saline. Twenty-eight days postinfection (dpi), ∼14 days following clearance of the lytic infection, alveolar macrophages (AMs), mesenchymal cells, and CD19-enriched cell populations from the lung and spleen express M(3) and/or glycoprotein B (gB) viral mRNA and harbor viral genome. AMs from infected mice express more transforming growth factor (TGF)-β(1), CCL2, CCL12, TNF-α, and IFN-γ than AMs from mock-infected mice. Mesenchymal cells express more total TGF-β(1), CCL12, and TNF-α than mesenchymal cells from mock-infected mice. Lung and spleen CD19-enriched cells express more total TGF-β(1) 28 dpi compared with controls. The CD19-negative fraction of the spleen overexpresses TGF-β(1) and harbors viral genome, but this likely represents infection of monocytes. Purified T cells from the lung harbor almost no viral genome. Purified T cells overexpress IL-10 but not TGF-β(1). Intracellular cytokine staining demonstrated that lung T cells at 28 dpi produce IFN-γ but not IL-4. Thus infection with a murine γherpesvirus is sufficient to upregulate profibrotic and proinflammatory factors in a variety of lung resident and circulating cell types 28 dpi. Our results provide new information about possible contributions of these cells to fibrogenesis in the lungs of individuals harboring a γherpesvirus infection and may help explain why γHV-68 infection can augment or exacerbate fibrotic responses in mice.

Mesenchymal cell survival in airway and interstitial pulmonary fibrosis

Fibrotic reactions in the airways of the lung or the pulmonary interstitium are a common pathologic outcome after exposure to a wide variety of toxic agents, including metals, particles or fibers. The survival of mesenchymal cells (fibroblasts and myofibroblasts) is a key factor in determining whether a fibroproliferative response that occurs after toxic injury to the lung will ultimately resolve or progress to a pathologic state. Several polypeptide growth factors, including members of the platelet-derived growth factor (PDGF) family and the epidermal growth factor (EGF) family, are prosurvival factors that stimulate a replicative and migratory mesenchymal cell phenotype during the early stages of lung fibrogenesis. This replicative phenotype can progress to a matrix synthetic phenotype in the presence of transforming growth factor-β1 (TGF-β1). The resolution of a fibrotic response requires growth arrest and apoptosis of mesenchymal cells, whereas progressive chronic fibrosis has been associated with mesenchymal cell resistance to apoptosis. Mesenchymal cell survival or apoptosis is further influenced by cytokines secreted during Th1 inflammation (e.g., IFN-γ) or Th2 inflammation (e.g., IL-13) that modulate the expression of growth factor activity through the STAT family of transcription factors. Understanding the mechanisms that regulate the survival or death of mesenchymal cells is central to ultimately developing therapeutic strategies for lung fibrosis.

Heparan sulfate in lung morphogenesis: The elephant in the room

Heparan sulfate (HS) is a structurally complex polysaccharide located on the cell surface and in the extracellular matrix, where it participates in numerous biological processes through interactions with a vast number of regulatory proteins such as growth factors and morphogens. HS is crucial for lung development; disruption of HS synthesis in flies and mice results in a major aberration of airway branching, and in mice, it results in neonatal death as a consequence of malformed lungs and respiratory distress. Epithelial-mesenchymal interactions governing lung morphogenesis are directed by various diffusible proteins, many of which bind to, and are regulated by HS, including fibroblast growth factors, sonic hedgehog, and bone morphogenetic proteins. The majority of research into the molecular mechanisms underlying defective lung morphogenesis and pulmonary pathologies, such as bronchopulmonary dysplasia and pulmonary hypoplasia associated with congenital diaphragmatic hernia (CDH), has focused on abnormal protein expression. The potential contribution of HS to abnormalities of lung development has yet to be explored to any significant extent, which is somewhat surprising given the abnormal lung phenotype exhibited by mutant mice synthesizing abnormal HS. This review summarizes our current understanding of the role of HS and HS-binding proteins in lung morphogenesis and will present in vitro and in vivo evidence for the fundamental importance of HS in airway development. Finally, we will discuss the future possibility of HS-based therapeutics for ameliorating insufficient lung growth associated with lung diseases such as CDH.

Signaling pathways in the epithelial origins of pulmonary fibrosis

Pulmonary fibrosis complicates a number of disease processes and leads to substantial morbidity and mortality. Idiopathic pulmonary fibrosis (IPF) is perhaps the most pernicious and enigmatic form of the greater problem of lung fibrogenesis with a median survival of three years from diagnosis in affected patients. In this review, we will focus on the pathology of IPF as a model of pulmonary fibrotic processes, review possible cellular mechanisms, review current treatment approaches and review two transgenic mouse models of lung fibrosis to provide insight into processes that cause lung fibrosis. We will also summarize the potential utility of signaling pathway inhibitors as a future treatment in pulmonary fibrosis. Finally, we will present data demonstrating a minimal contribution of epithelial-mesenchymal transition in the development of fibrotic lesions in the transforming growth factor-alpha transgenic model of lung fibrosis.

The overexpression of heparin-binding epidermal growth factor is responsible for Th17-induced airway remodeling in an experimental asthma model

Th17 cells that produce IL-17 have been found to participate in the development of allergy-triggered asthma. However, whether they play a causative role in the pathogenesis of airway remodeling in chronic asthma remains unclear. In this study, we investigated the role of Th17 cells in airway remodeling and the possible involvement of epidermal growth factor (EGF) receptor signals downstream of Th17. We established a C57BL/6 mouse model of prolonged allergen challenge that exhibits many characteristics of airway remodeling. Prolonged allergen challenge induced a progressive increase in the number of airway-infiltrating Th17 cells, and Th17 counts positively correlated with the severity of airway remodeling. Increases in mucus production, airway smooth muscle (ASM) mass, peribronchial collagen deposition, and airway heparin-binding EGF (HB-EGF) expression have been observed in sensitized mice following prolonged allergen exposure or adoptive Th17 transfer; remarkably, these effects can be abrogated by treatment with anti-IL-17 mAb. Both the EFGR inhibitor AG1478 and an anti-HB-EGF mAb ameliorated all of these effects, except for peribronchial collagen deposition in the presence of high levels of IL-17. In vitro, Th17 cells enhanced the airway epithelial expression of HB-EGF in a coculture of the two cells. The conditioned medium obtained from this coculture system effectively promoted ASM proliferation; this response was dramatically abolished by anti-HB-EGF mAb but not Abs against other EGF receptor ligands or IL-17. These observations demonstrated that overexpression of airway HB-EGF induced by IL-17 secreted from redundant expanding Th17 cells might contribute to excessive mucus expression and ASM proliferation in chronic asthma.

The effect of PM10 on human lung fibroblasts

Asthma diagnoses are increasing nationally with the highest rates in the New England states. Epidemiological studies have suggested a relationship between airborne particulate matter (PM) and severity of an asthma attack. However, because particulate matter, PM, is such a complex mixture, it is difficult to isolate the exacerbating factors. In this paper we investigate the effect of NIST (National Institute of Standards and Technology) and Maine PM and the soluble metals released from the PM on the growth of human lung fibroblasts. While the NIST PM itself had the most pronounced effect on cell survival rates, solutions of metals extracted from the PM also affected cell survival. Treatment of cells with 10, 50, 100 and 200 ug/cm(2) resulted in 84 +/- 13%, 69 +/- 15%, 58 +/- 14% and 58 +/- 16% survival, respectively. Appropriate concentrations of eight acid soluble metals from NIST PM were determined and tested on cells giving 91 +/- 11%, 87 +/- 10%, 72 +/- 18% and 66 +/- 20% survival, respectively. Soluble metals from Maine PM were extracted and mixtures of appropriate concentrations of these metals were used to treat cells, resulting in 88 +/- 5%, 81 +/- 5%, 79 +/- 3% and 57 +/- 9% survival rate. To determine which, if any, of the metals individually affected the cells, Mn, Cu, V and As were used to treat the cells. At the metal concentrations tested, only As and V affected cell survival.

STAT-1 signaling in human lung fibroblasts is induced by vanadium pentoxide through an IFN-beta autocrine loop

The inhalation of vanadium pentoxide (V(2)O(5)) results in bronchitis and airway fibrosis. The lung fibrotic response to V(2)O(5) partially resolves where fibroblasts first proliferate and deposit collagen, but then undergo growth arrest and apoptosis. STAT-1 mediates fibroblast growth arrest and apoptosis. We previously reported that STAT-1 is a protective factor and mice lacking STAT-1 are more susceptible to lung fibrosis. We also reported that V(2)O(5)-induced STAT-1 phosphorylation in lung fibroblasts requires H(2)O(2) and de novo protein synthesis. In this study, we identified IFN-beta as the protein that mediates STAT-1 activation by V(2)O(5) in normal human lung fibroblasts and identified NADPH and xanthine oxidase systems as sources of H(2)O(2) that drive IFN-beta gene expression. STAT-1 phosphorylation was decreased with neutralizing Abs to IFN-beta as well as an inhibitor of JAK. V(2)O(5) also increased transcription of an IFN-inducible and STAT-1-dependent chemokine, CXCL10. Inhibition of H(2)O(2)-generating enzyme systems NADPH oxidase by apocynin and xanthine oxidase by allopurinol individually reduced STAT-1 phosphorylation. Apocynin and allopurinol also decreased V(2)O(5)-induced IFN-beta mRNA levels and CXCL10 expression. IFN-alpha transcription was inhibited only by allopurinol. Taken together, these data indicate that fibroblasts play a role in the innate immune response to vanadium-induced oxidative stress by synthesizing IFN-beta and activating STAT-1 to cause growth arrest and increase levels of CXCL10, a potent antifibrotic factor. This mechanism is postulated to counterbalance profibrogenic mechanisms that follow V(2)O(5) injury.

Secretion of IL-13 by airway epithelial cells enhances epithelial repair via HB-EGF

Inappropriate repair after injury to the epithelium generates persistent activation, which may contribute to airway remodeling. In the present study we hypothesized that IL-13 is a normal mediator of airway epithelial repair. Mechanical injury of confluent airway epithelial cell (AEC) monolayers induced expression and release of IL-13 in a time-dependent manner coordinate with repair. Neutralizing of IL-13 secreted from injured epithelial cells by shIL-13Ralpha2.FC significantly reduced epithelial repair. Moreover, exogenous IL-13 enhanced epithelial repair and induced epidermal growth factor receptor (EGFR) phosphorylation. We examined secretion of two EGFR ligands, epidermal growth factor (EGF) and heparin-binding EGF (HB-EGF), after mechanical injury. Our data showed a sequential release of the EGF and HB-EGF by AEC after injury. Interestingly, we found that IL-13 induces HB-EGF, but not EGF, synthesis and release from AEC. IL-13-induced EGFR phosphorylation and the IL-13-reparative effect on AEC are mediated via HB-EGF. Finally, we demonstrated that inhibition of EGFR tyrosine kinase activity by tyrphostin AG1478 increases IL-13 release after injury, suggesting negative feedback between EGFR and IL-13 during repair. Our data, for the first time, showed that IL-13 plays an important role in epithelial repair, and that its effect is mediated through the autocrine release of HB-EGF and activation of EGFR. Dysregulation of EGFR phosphorylation may contribute to a persistent repair phenotype and chronically increased IL-13 release, and in turn result in airway remodeling.

Eosinophils in the pathogenesis of allergic airways disease

Eosinophils are traditionally thought to form part of the innate immune response against parasitic helminths acting through the release of cytotoxic granule proteins. However, they are also a central feature in asthma. From their development in the bone marrow to their recruitment to the lung via chemokines and cytokines, they form an important component of the inflammatory milieu observed in the asthmatic lung following allergen challenge. A wealth of studies has been performed in both patients with asthma and in mouse models of allergic pulmonary inflammation to delineate the role of eosinophils in the allergic response. Although the long-standing association between eosinophils and the induction of airway hyper-responsiveness remains controversial, recent studies have shown that eosinophils may also promote airway remodelling. In addition, emerging evidence suggests that the eosinophil may also serve to modulate the immune response. Here we review the highly co-ordinated nature of eosinophil development and trafficking and the evolution of the eosinophil as a multi-factoral leukocyte with diverse functions in asthma.

Genomic analysis of human lung fibroblasts exposed to vanadium pentoxide to identify candidate genes for occupational bronchitis

BACKGROUND

Exposure to vanadium pentoxide (V2O5) is a cause of occupational bronchitis. We evaluated gene expression profiles in cultured human lung fibroblasts exposed to V2O5 in vitro in order to identify candidate genes that could play a role in inflammation, fibrosis, and repair during the pathogenesis of V2O5-induced bronchitis.

METHODS

Normal human lung fibroblasts were exposed to V2O5 in a time course experiment. Gene expression was measured at various time points over a 24 hr period using the Affymetrix Human Genome U133A 2.0 Array. Selected genes that were significantly changed in the microarray experiment were validated by RT-PCR.

RESULTS

V2O5 altered more than 1,400 genes, of which ~300 were induced while >1,100 genes were suppressed. Gene ontology categories (GO) categories unique to induced genes included inflammatory response and immune response, while GO categories unique to suppressed genes included ubiquitin cycle and cell cycle. A dozen genes were validated by RT-PCR, including growth factors (HBEGF, VEGF, CTGF), chemokines (IL8, CXCL9, CXCL10), oxidative stress response genes (SOD2, PIPOX, OXR1), and DNA-binding proteins (GAS1, STAT1).

CONCLUSION

Our study identified a variety of genes that could play pivotal roles in inflammation, fibrosis and repair during V2O5-induced bronchitis. The induction of genes that mediate inflammation and immune responses, as well as suppression of genes involved in growth arrest appear to be important to the lung fibrotic reaction to V2O5.

Lung fibrotic responses to particle exposure

Particles generated from numerous anthropogenic sources have the potential to cause or exacerbate lung diseases, including asthma, bronchitis, and COPD. Fibrotic reactions are a component of all of these pulmonary diseases, and involve the progressive deposition of collagen by pulmonary fibroblasts. The reactivity, toxicity, and fibrogenic potential of particles in the lung depends on a variety of factors including particle size, surface area, and composition. Smaller particles, particularly in the nanosized range, have more toxic and fibrogenic capacity due to a higher surface-to-mass ratio and greater oxidant-generating potential. Composition is also an important determinant in the fibrotic response to particles. Transition metals, bacterial lipopolysaccaride, and polycyclic aromatic hydrocarbons are some of the toxic components of particles that activate intracellular signaling pathways that culminate in the production of profibrotic cytokines and growth factors.

Toluene diisocyanate (TDI) induces production of inflammatory cytokines and chemokines by bronchial epithelial cells via the epidermal growth factor receptor and p38 mitogen-activated protein kinase pathways

Toluene diisocyanate (TDI) is known as one of causes of occupational asthma and hypersensitivity pneumonitis. To investigate the stimulatory effect on bronchial epithelial cells in response to TDI, the authors examined production of cytokines by the bronchial epithelial cell line BEAS-2B and intercellular signal transduction stimulated by TDI-human serum albumin (HSA) conjugate. The production of interleukin (IL)-8, granulocyte-macrophage colony-stimulating factor (GM-CSF), and regulated on activation normal T cell expressed and secreted (RANTES) from the bronchial epithelial cells were augmented by the TDI-HSA conjugate. Extracellular signal-regulated kinase (Erk) 1/2 and p38 mitogen-activated protein kinase (MAPK) were phosphorylated by the TDI-HSA conjugate. AG1478, SB203580, and dexamethasone prevented augmentation of these cytokine production. TDI-HSA conjugate did not augment release of epidermal growth factor (EGF) ligands from BEAS-2B. These results suggest that TDI directly induces production of proinflammatory cytokines and chemokines through p38 MAPK and EGF receptor (EGFR)-Erk pathway without an autocrine mechanism. Thus, TDI was shown to have a stimulatory effect on bronchial epithelial cells, suggesting the potent role of bronchial epithelial cells in TDI-induced asthma.

Activation of MAP kinases by hexavalent chromium, manganese and nickel in human lung epithelial cells

Epidemiological studies indicate that workers who perform welding operations are at increased risk for bronchitis, siderosis, occupational asthma and lung cancer due to fume exposure. Welding fumes are a complex chemical mixture, and the metal composition is hypothesized to be an etiological factor in respiratory disease due to this exposure. In the present study, human lung epithelial cells in vitro responded to hexavalent chromium, manganese and nickel over a concentration range of 0.2-200 microM with a significant increase in intracellular phosphoprotein (a measure of stress response pathway activation). The mitogen-activated protein kinases ERK1/2, SAPK/JNK and p38 were activated via phosphorylation following 1-h exposures. Hexavalent chromium up-regulated p-38 phosphorylation 23-fold and SAPK/JNK phosphorylation 17-fold, with a comparatively modest 4-fold increase in ERK1/2 phosphorylation. Manganese caused a two- to four-fold increase in SAPK/JNK and ERK 1/2 phosphorylation, with no observed effects on p38 kinase. Nickel caused increased (two-fold) phosphorylation of ERK 1/2 only, and was not cytotoxic over the tested concentration range. The observed effects of welding fume metals on cellular signaling in lung epithelium demonstrate a potentially significant interplay between stress-response signaling (p38 and SAPK/JNK) and anti-apototic signaling (ERK 1/2) that is dependant on the specific metal or combination of metals involved.

Blocking airway mucous cell metaplasia by inhibiting EGFR antiapoptosis and IL-13 transdifferentiation signals

Epithelial hyperplasia and metaplasia are common features of inflammatory and neoplastic disease, but the basis for the altered epithelial phenotype is often uncertain. Here we show that long-term ciliated cell hyperplasia coincides with mucous (goblet) cell metaplasia after respiratory viral clearance in mouse airways. This chronic switch in epithelial behavior exhibits genetic susceptibility and depends on persistent activation of EGFR signaling to PI3K that prevents apoptosis of ciliated cells and on IL-13 signaling that promotes transdifferentiation of ciliated to goblet cells. Thus, EGFR blockade (using an irreversible EGFR kinase inhibitor designated EKB-569) prevents virus-induced increases in ciliated and goblet cells whereas IL-13 blockade (using s-IL-13Ralpha2-Fc) exacerbates ciliated cell hyperplasia but still inhibits goblet cell metaplasia. The distinct effects of EGFR and IL-13 inhibitors after viral reprogramming suggest that these combined therapeutic strategies may also correct epithelial architecture in the setting of airway inflammatory disorders characterized by a similar pattern of chronic EGFR activation, IL-13 expression, and ciliated-to-goblet cell metaplasia.

Susceptibility of signal transducer and activator of transcription-1-deficient mice to pulmonary fibrogenesis

The signal transducer and activator of transcription (Stat)-1 mediates growth arrest and apoptosis. We postulated that lung fibrosis characterized by excessive proliferation of lung fibroblasts would be enhanced in Stat1-deficient (Stat1-/-) mice. Two weeks after bleomycin aspiration (3 U/kg), Stat1-/- mice exhibited a more severe fibroproliferative response and significantly elevated total lung collagen compared to wild-type mice. Growth factors [epidermal growth factor (EGF) or platelet-derived growth factor (PDGF)] enhanced [3H]thymidine uptake in lung fibroblasts isolated from Stat1-/- mice compared to wild-type mice. Interferon (IFN)-gamma, which signals growth arrest via Stat1, inhibited EGF- or PDGF-stimulated mitogenesis in wild-type fibroblasts but enhanced [3H]thymidine uptake in Stat1-/- fibroblasts. Moreover, IFN-gamma treatment in the absence of growth factors induced a concentration-dependent increase in [3H]thymidine uptake in Stat1-/- but not wild-type fibroblasts. Mitogen-activated protein kinase (ERK-1/2) phosphorylation in response to PDGF or EGF did not differ among Stat1-/- and wild-type fibroblasts. However, Stat3 phosphorylation induced by PDGF, EGF, or IFN-gamma increased twofold in Stat1-/- fibroblasts compared to wild-type fibroblasts. Our findings indicate that Stat1-/- mice are more susceptible to bleomycin-induced lung fibrosis than wild-type mice due to 1) enhanced fibroblast proliferation in response to growth factors (EGF and PDGF), 2) stimulation of fibroblast growth by a Stat1-independent IFN-gamma signaling pathway, and 3) increased activation of Stat3.

Discrimination of vanadium from zinc using gene profiling in human bronchial epithelial cells

We hypothesized that gene expression profiling may discriminate vanadium from zinc in human bronchial epithelial cells (HBECs). RNA from HBECs exposed to vehicle, V (50 microM), or Zn (50 microM) for 4 hr (n = 4 paired experiments) was hybridized to Affymetrix Hu133A chips. Using one-class t-test with p < 0.01, we identified 140 and 76 genes with treatment:control ratios > or = 2.0 or < or = 0.5 for V and Zn, respectively. We then categorized these genes into functional pathways and compared the number of genes in each pathway between V and Zn using Fisher's exact test. Three pathways regulating gene transcription, inflammatory response, and cell proliferation distinguished V from Zn. When genes in these three pathways were matched with the 163 genes flagged by the same statistical filtration for V:Zn ratios, 12 genes were identified. The hierarchical clustering analysis showed that these 12 genes discriminated V from Zn and consisted of two clusters. Cluster 1 genes (ZBTB1, PML, ZNF44, SIX1, BCL6, ZNF450) were down-regulated by V and involved in gene transcription, whereas cluster 2 genes (IL8, IL1A, PTGS2, DTR, TNFAIP3, CXCL3) were up-regulated and linked to inflammatory response and cell proliferation. Also, metallothionein 1 genes (MT1F, MT1G, MT1K) were up-regulated by Zn only. Thus, using microarray analysis, we identified a small set of genes that may be used as biomarkers for discriminating V from Zn. The novel genes and pathways identified by the microarray may help us understand the pathogenesis of health effects caused by environmental V and Zn exposure.

Chronic obstructive pulmonary disease is associated with enhanced bronchial expression of FGF-1, FGF-2, and FGFR-1

An important feature of chronic obstructive pulmonary disease (COPD) is airway remodelling, the molecular mechanisms of which are poorly understood. In this study, the role of fibroblast growth factors (FGF-1 and FGF-2) and their receptor, FGFR-1, was assessed in bronchial airway wall remodelling in patients with COPD (FEV1 < 75%; n = 15) and without COPD (FEV1 > 85%; n = 16). FGF-1 and FGFR-1 were immunolocalized in bronchial epithelium, airway smooth muscle (ASM), submucosal glandular epithelium, and vascular smooth muscle. Quantitative digital image analysis revealed increased cytoplasmic expression of FGF-2 in bronchial epithelium (0.35 +/- 0.03 vs 0.20 +/- 0.04, p < 0.008) and nuclear localization in ASM (p < 0.0001) in COPD patients compared with controls. Elevated levels of FGFR-1 in ASM (p < 0.005) and of FGF-1 (p < 0.04) and FGFR-1 (p < 0.001) in bronchial epithelium were observed. In cultured human ASM cells, FGF-1 and/or FGF-2 (10 ng/ml) induced cellular proliferation, as shown by [3H]thymidine incorporation and by cell number counts. Steady-state mRNA levels of FGFR-1 were elevated in human ASM cells treated with either FGF-1 or FGF-2. The increased bronchial expression of fibroblast growth factors and their receptor in patients with COPD, and the mitogenic response of human ASM cells to FGFs in vitro suggest a potential role for the FGF/FGFR-1 system in the remodelling of bronchial airways in COPD.

Amphiregulin expression in human mast cells and its effect on the primary human lung fibroblasts

BACKGROUND

Amphiregulin is a member of the epidermal growth factor family and has been shown to stimulate the proliferation of human keratinocytes in an autocrine manner.

OBJECTIVE

The aim of the present study was to examine the expression change of growth factors, especially amphiregulin, in human mast cells induced by IgE cross-linking.

METHODS

Microarray analysis and RT-PCR were used to analyze the gene expression profile of human cord blood-derived mast cells (CBMCs) stimulated with IgE cross-linking. Protein secretion in the supernatants of CBMCs was measured by means of ELISA. Double-immunofluorescence staining was used to analyze the expression in the lung mast cells.

RESULTS

Of the 64 different growth factor genes analyzed, 5 were found to be substantially upregulated. Among them, amphiregulin mRNA was induced by 44-fold in CBMCs on activation through IgE cross-linking. Secretion of amphiregulin protein was evident in CBMCs 8 hours after stimulation. Amphiregulin was also expressed in human lung mast cells from patients with asthma, as demonstrated by means of double-immunofluorescence staining. Amphiregulin promoted the proliferation of the primary human lung fibroblasts, and amphiregulin-treated primary human lung fibroblasts showed a marked increase in the expression of c-fos , a proto-oncogene that facilitates or is required for the proliferation of a wide variety of cells.

CONCLUSION

Human CBMCs secreted amphiregulin on IgE cross-linking, and the amphiregulin induced proliferation of primary human lung fibroblasts. These data suggest that local release of amphiregulin by human mast cells could play an important role in lung fibrosis by promoting the proliferation of primary human lung fibroblasts.

Bronchial epithelial compression regulates epidermal growth factor receptor family ligand expression in an autocrine manner

The epidermal growth factor receptor (EGFR), an important signaling pathway in airway biology, is stimulated by compressive stress applied to human airway epithelial cells. Although the EGFR ligand, heparin-binding epidermal growth factor-like growth factor (HB-EGF), is known to be released as a result of this stimulation, whether compressive stress enhances expression of other EGFR ligands, and the duration of mechanical compression required to initiate this response, is not known. Human airway epithelial cells were exposed to compressive stress, and expression of four EGFR ligands was examined by quantitative PCR. Cells were exposed to: (1) continuous compressive stress over 8 h, (2) compression with and without EGFR inhibitor (AG1478), or (3) time-limited compression (3.75, 7.5, 15, 30, and 60 min). Compressive stress produced a sustained upregulation of the EGFR ligands HB-EGF, epiregulin, and amphiregulin, but not transforming growth factor-alpha. Inhibition with AG1478 demonstrated that expression of HB-EGF, epiregulin, and amphiregulin is dependent on the signaling via the EGFR. Immunostaining for epiregulin protein demonstrated increased expression with compression and attenuation with EGFR inhibition. The response of all three EGFR ligands persisted long after the mechanical stimulus was removed. Taken together, these data suggest the possibility of a mechanically activated EGFR autocrine feedback loop involving selected EGFR ligands.

Roles of epidermal growth factor receptor activation in epithelial cell repair and mucin production in airway epithelium

The epithelial cells lining the airways serve protective functions. The "barrier function" of the epithelium protects the individual from damage by inhaled irritants. The epithelium produces mucins which become hydrated and form a viscoelastic gel which spreads over the epithelial surface. In healthy individuals inhaled foreign materials become entrapped in the mucus and are cleared by mucociliary transport and by coughing. In many chronic inflammatory airway diseases, however, excessive mucus is produced and is inadequately cleared, leading to mucous obstruction and infection. At present there is no specific treatment for hypersecretion. However, the discovery that an epidermal growth factor receptor (EGFR) cascade is involved in mucin production by a wide variety of stimuli suggests that blockade may provide specific treatment for hypersecretory diseases. EGFR pathways have also been implicated in the repair of damaged airway epithelium. The roles of EGFR in airway epithelial cell hypersecretion and epithelial damage and repair are reviewed and future potential treatments are suggested.

EGF-related growth factors in the pathogenesis of murine ARPKD11See Editorial by Wilson, p. 2441

BACKGROUND

Epidermal growth factor (EGF), transforming growth factor-alpha (TGF-alpha) and their receptor, EGFR, play key roles in polycystic kidney disease (PKD) pathogenesis. Renal expression of two related growth factors, amphiregulin and heparin-binding EGF, has not been examined previously in PKD. The aims of this study of murine autosomal-recessive polycystic kidney disease (ARPKD) were (1) to characterize amphiregulin and heparin-binding EGF expression in cystic versus normal kidneys and cells; and (2) to identify the functional effects of abnormal EGF-related growth factor expression.

METHODS

Amphiregulin and heparin-binding-EGF expression were examined by immunohistology and Western blot of kidneys and conditionally-immortalized collecting tubule cells obtained from cystic bpk mice (a murine model of ARPKD) and normal littermates. EGF, TGF-alpha, amphiregulin, and heparin-binding EGF in vitro effects on cystic and control collecting tubule cells were assessed by cell proliferation, cyst fluid mitogenicity, and EGFR activation.

RESULTS

By immunohistology, amphiregulin and heparin-binding EGF localized to apical and basolateral surfaces of proximal tubule cysts > normal proximal tubules. In cystic collecting tubules, heparin-binding EGF (but not amphiregulin) localized to both apical and basolateral surfaces; whereas in normal collecting tubules, amphiregulin and heparin-binding EGF localized to the basolateral surface only. Increased amphiregulin and heparin-binding EGF expression by Western blot was seen in cystic vs. normal kidneys and increased heparin-binding EGF (but not amphiregulin) expression was present in cystic collecting tubule cell lines vs. controls. EGF, TGF-alpha, amphiregulin, and heparin-binding EGF were all mitogenic to cystic > control collecting tubule cells. Immunoprecipitation of EGF and TGF-alpha reduced cyst fluid mitogenicity by almost 80%, whereas heparin-binding EGF and amphiregulin immunoprecipitations had minimal effects. Differential receptor activation was also seen: Heparin-binding EGF markedly activated EGFR (>EGF = TGF-alpha > amphiregulin), with a greater effect seen in cystic vs. control collecting tubule cells.

CONCLUSION

Multiple EGF-related growth factors are abnormally expressed in murine ARPKD and may have differential roles in disease pathogenesis. In particular, newly identified abnormalities in heparin-binding EGF expression in cystic kidneys and cells may have important implications for disease pathogenesis.

Heparin-binding epidermal growth factor cleavage mediates zinc-induced epidermal growth factor receptor phosphorylation

We have previously shown that exposure to zinc ions can activate epidermal growth factor (EGF) receptor (EGFR) signaling in murine fibroblasts and A431 cells through a mechanism involving Src kinase. While studying the effects of zinc ions in normal human bronchial epithelial cell, we uncovered evidence for an additional mechanism of Zn(2+)-induced EGFR activation. Exposure to Zn(2+) induced phosphorylation of EGFR at tyrosine 1068, a major autophosphorylation site, in a dose- and time-dependent fashion. This effect of Zn(2+) on EGFR was significantly blocked with an antibody against the ligand-binding domain of the receptor. Neutralizing antibodies against EGFR ligands revealed the involvement of heparin-binding EGF (HB-EGF) in Zn(2+)-induced EGFR phosphorylation. This observation was further supported by immunoblots showing elevated levels of HB-EGF released by Zn(2+)-exposed cells. Zymography showed the existence of matrix metalloproteinase-3 in Zn(2+)-challenged cells. Incubation with a specific matrix metalloproteinase-3 inhibitor suppressed Zn(2+)-induced EGFR phosphorylation as well as HB-EGF release. Therefore, these data support an autocrine or paracrine mechanism whereby Zn(2+) induces EGFR phosphorylation through the extracellular release of EGFR ligands, which may be mediated by metalloproteinases.

Fine particulate matter induces amphiregulin secretion by bronchial epithelial cells

Particulate matter (PM) is thought to be responsible for respiratory health problems. Epithelial cells exposed to particles release pro-inflammatory cytokines leading to inflammation of airways. However, the signaling cascades triggered by particles are poorly understood. We demonstrate that PM with an aerodynamic diameter < 2.5 microm (PM2.5) or diesel exhaust particles upregulate the expression of amphiregulin (AR), a ligand of the epidermal growth factor receptor (EGFR), in human bronchial epithelial cells. AR secretion was blocked by an inhibitor of the EGFR tyrosine kinase (AG1478), or a selective mitogen-activated protein (MAP) kinase/extracellular regulated kinase (Erk) inhibitor (PD98059), but not by the p38 MAP kinase inhibitor (SB203580). Thus, AR secretion is mediated through the activation of the EGFR and Erk MAP kinase pathway. In addition, AR secretion was inhibited by the antioxidant N-acetyl cysteine, but not by a neutralizing anti-EGFR, suggesting an EGFR transactivation via oxidative stress. AR may be involved in cytokine secretion, as AR can induce granulocyte macrophage-colony-stimulating factor (GM-CSF) release and a neutralizing anti-EGFR reduces the particle-induced GM-CSF release. This study indicates that PM2.5 induces the expression and secretion of AR, an EGFR ligand contributing to GM-CSF release, which may reflect an important mechanism for sustaining the proinflammatory response.

Conditional expression of transforming growth factor-alpha in adult mouse lung causes pulmonary fibrosis

To determine whether overexpression of transforming growth factor (TGF)-alpha in the adult lung causes remodeling independently of developmental influences, we generated conditional transgenic mice expressing TGF-alpha in the epithelium under control of the doxycycline (Dox)-regulatable Clara cell secretory protein promoter. Two transgenic lines were generated, and following 4 days of Dox-induction TGF-alpha levels in whole lung homogenate were increased 13- to 18-fold above nontransgenic levels. After TGF-alpha induction, transgenic mice developed progressive pulmonary fibrosis and body weight loss, with mice losing 15% of their weight after 6 wk of TGF-alpha induction. Fibrosis was detected within 4 days of TGF-alpha induction and developed initially in the perivascular, peribronchial, and pleural regions but later extended into the interstitium. Fibrotic regions were composed of increased collagen and cellular proliferation and were adjacent to airway and alveolar epithelial sites of TGF-alpha expression. Fibrosis progressed in the absence of inflammatory cell infiltrates as determined by histology, without changes in bronchiolar alveolar lavage total or differential cell counts and without changes in proinflammatory cytokines TNF-alpha or IL-6. Active TGF-beta in whole lung homogenate was not altered 1 and 4 days after TGF-alpha induction, and immunostaining was not increased in the peribronchial/perivascular areas at all time points. Chronic epithelial expression of TGF-alpha in adult mice caused progressive pulmonary fibrosis associated with increased collagen and extracellular matrix deposition and increased cellular proliferation. Induction of pulmonary fibrosis by TGF-alpha was independent of inflammation or early activation of TGF-beta.

Heparin-binding EGF-like growth factor regulates elastin and FGF-2 expression in pulmonary fibroblasts

Elastase degradation of elastin within alveolar walls is an important event in the development of pulmonary emphysema. In addition to elastolytic activities, elastases release growth factors from extracellular matrices and interstitial cell surfaces that can regulate elastogenesis and other cellular responses. In the present study, we demonstrate that brief treatment of matrix-laden rat pulmonary fibroblast cultures with pancreatic elastase results in the release of soluble heparin-binding epidermal growth factor-like growth factor (HB-EGF) concomitant with a decrease in HB-EGF binding to both heparan sulfate proteoglycan and receptor sites on the cells. In undigested, matrix-laden fibroblasts, HB-EGF significantly downregulates elastin mRNA via activation of epidermal growth factor receptor. Results from nuclear run-on analyses show that HB-EGF downregulates elastin mRNA via transcriptional suppression. HBEGF treatment stimulates MAP or ERK kinase (MEK)-dependent ERK1/2 phosphorylation and leads to nuclear accumulation of Fra-1. Blocking ERK1/2 activation by MEK1/2 inhibitors (PD-98059 or U-0126) diminishes HB-EGF-induced Fra-1 accumulation and subsequent downregulation of elastin mRNA. Coaddition of two elastase-released growth factors, HB-EGF and FGF-2, results in an additive inhibitory effect on elastin mRNA levels. Furthermore, HB-EGF addition to pulmonary fibroblasts increases FGF-2 mRNA and protein levels. These data suggest that HB-EGF and FGF-2 act in concert to regulate the synthesis of elastin in injury/repair situations.

Vanadium-induced HB-EGF expression in human lung fibroblasts is oxidant dependent and requires MAP kinases

Vanadium pentoxide (V(2)O(5)) is a transition metal derived from the burning of petrochemicals that causes airway fibrosis and remodeling. Vanadium compounds activate many intracellular signaling pathways via the generation of hydrogen peroxide (H(2)O(2)) or other reactive oxygen species. In this study, we investigated the regulation of heparin-binding epidermal growth factor-like growth factor (HB-EGF) in human lung fibroblasts after V(2)O(5) treatment. V(2)O(5)-induced HB-EGF mRNA expression was abolished by N-acetyl-l-cysteine, suggesting an oxidant-mediated effect. Exogenous H(2)O(2) (>10 microM) mimicked the effect of V(2)O(5) in upregulating HB-EGF expression. Fibroblasts spontaneously released low levels of H(2)O(2) (1-2 microM), and the addition of V(2)O(5) depleted the endogenous H(2)O(2) pool within minutes. V(2)O(5) caused a subsequent increase of H(2)O(2) into the culture medium at 12 h. However, the burst of V(2)O(5)-induced H(2)O(2) occurred after V(2)O(5)-induced HB-EGF mRNA expression at 3 h, indicating that the V(2)O(5)-stimulated H(2)O(2) burst did not mediate HB-EGF expression. Either V(2)O(5) or H(2)O(2) activated ERK-1/2 and p38 MAP kinase. Inhibitors of the ERK-1/2 pathway (PD-98059) or p38 MAP kinase (SB-203580) significantly reduced either V(2)O(5)- or H(2)O(2)-induced HB-EGF expression. These data indicate that vanadium upregulates HB-EGF via ERK and p38 MAP kinases. The induction of HB-EGF is not related to a burst of H(2)O(2) in V(2)O(5) treated cells, yet the action of V(2)O(5) in upregulating HB-EGF is oxidant dependent and could be due to the reaction of V(2)O(5) with endogenous H(2)O(2).

p38 mitogen-activated protein kinase regulates growth factor-induced mitogenesis of rat pulmonary myofibroblasts

Myofibroblast proliferation is a central feature of pulmonary fibrogenesis. Several growth factors, including platelet-derived growth factor (PDGF) and epidermal growth factor (EGF), stimulate myofibroblast growth by activating extracellular signal regulated kinases 1 and 2 (ERK1/2). In this report, we demonstrate that PDGF-BB and EGF also activate the p38 mitogen-activated protein (MAP) kinase. Inhibition of p38 activity with the pyridinylimidazole compound SB203580 enhanced both PDGF-BB and EGF-stimulated DNA synthesis in rat lung myofibroblasts. ERK1/2 phosphorylation in response to either PDGF-BB or EGF treatment was significantly increased by pretreatment of cells with SB203580. We also demonstrated that ERK1/2-induced phosphorylation of PHAS-1 substrate was enhanced by inhibition of p38 MAP kinase with SB203580. However, SB203580 did not significantly increase growth factor-induced activation of MEK, the upstream kinase that phosphorylates ERK1/2. p38 MAP kinase was co-immunoprecipitated with ERK-1/2 following growth factor stimulation. Collectively, these data demonstrate that p38 MAP kinase activation negatively regulates PDGF- and EGF-mediated growth responses by directly interacting with ERK1/2 and suppressing its phosphorylation.

Iron loading makes a nonfibrogenic model air pollutant particle fibrogenic in rat tracheal explants

To examine the potential role of particle iron in fibrogenicity, we loaded nonfibrogenic fine (0.12micro) TiO(2) with increasing amounts of Fe(II)-Fe(III) chloride. Dusts were applied to rat tracheal explants, which were maintained in air organ culture for 1 wk. Iron-loaded dust increased procollagen gene expression and tissue hydroxyproline. The active oxygen species (AOS) scavenger tetramethylthiourea prevented these effects. Iron loading caused nuclear factor (NF)-kappaB activation, decreased levels of total IkappaBalpha, but relatively increased levels of both IkappaBalpha-phosphoserine 32/36 and IkappaBalpha-phosphotyrosine. A citrate extract of iron-loaded dust increased procollagen expression. Gel shift using a probe consisting of the NF-kappaB consensus sequence from the prolyl-4-hydroxylase promoter and adjacent bases showed increased nuclear binding, and RT-PCR examination showed increased prolyl-hydroxylase alpha-chain gene expression after iron loading. We conclude that addition of surface iron can convert a nonreactive model air pollutant particle into a fibrogenic particle via AOS- and NF-kappaB-dependent pathways, probably through two different NF-kappaB activation pathways in two different anatomic compartments. This process may proceed in vivo through iron extracted from the dust into the cytoplasm. NF-kappaB activation may directly increase expression of prolyl hydroxylase, an enzyme involved in collagen synthesis. These findings suggest that air pollutant particles containing significant quantities of transition metals may produce airway wall fibrosis and lead to chronic obstructive pulmonary disease.

Bronchial epithelial compression regulates MAP kinase signaling and HB-EGF-like growth factor expression

Airway smooth muscle constriction leads to the development of compressive stress on bronchial epithelial cells. Normal human bronchial epithelial cells exposed to an apical-to-basal transcellular pressure difference equivalent to the computed stress in the airway during bronchoconstriction demonstrate enhanced phosphorylation of extracellular signal-regulated kinase (ERK). The response is pressure dependent and rapid, with phosphorylation increasing 14-fold in 30 min, and selective, since p38 and c-Jun NH(2)-terminal kinase phosphorylation remains unchanged after pressure application. Transcellular pressure also elicits a ninefold increase in expression of mRNA encoding heparin-binding epidermal growth factor-like growth factor (HB-EGF) after 1 h, followed by prominent immunostaining for pro-HB-EGF after 6 h. Inhibition of the ERK pathway with PD-98059 results in a dose-dependent reduction in pressure-induced HB-EGF gene expression. The magnitude of the HB-EGF response to transcellular pressure and tumor necrosis factor (TNF)-alpha (1 ng/ml) is similar, and the combined mechanical and inflammatory stimulus is more effective than either stimulus alone. These results demonstrate that compressive stress is a selective and potent activator of signal transduction and gene expression in bronchial epithelial cells.