Epithelial Cells In Idiopathic Pulmonary Fibrosis Research Articles

Increased expression of CXCL6 in secretory cells drives fibroblast collagen synthesis and is associated with increased mortality in idiopathic pulmonary fibrosis.

Recent data suggest that the localisation of airway epithelial cells in the distal lung in idiopathic pulmonary fibrosis (IPF) may drive pathology. We set out to discover whether chemokines expressed in these ectopic airway epithelial cells may contribute to the pathogenesis of IPF. We analysed whole lung and single-cell transcriptomic data obtained from patients with IPF. In addition, we measured chemokine levels in blood, bronchoalveolar lavage (BAL) of IPF patients and air-liquid interface cultures. We employed ex vivo donor and IPF lung fibroblasts and an animal model of pulmonary fibrosis to test the effects of chemokine signalling on fibroblast function. By analysis of whole-lung transcriptomics, protein and BAL, we discovered that CXCL6 (a member of the interleukin-8 family) was increased in patients with IPF. Elevated CXCL6 levels in the BAL of two cohorts of patients with IPF were associated with poor survival (hazard ratio of death or progression 1.89, 95% CI 1.16-3.08; n=179, p=0.01). By immunostaining and single-cell RNA sequencing, CXCL6 was detected in secretory cells. Administration of mCXCL5 (LIX, murine CXCL6 homologue) to mice increased collagen synthesis with and without bleomycin. CXCL6 increased collagen I levels in donor and IPF fibroblasts 4.4-fold and 1.7-fold, respectively. Both silencing of and chemical inhibition of CXCR1/2 blocked the effects of CXCL6 on collagen, while overexpression of CXCR2 increased collagen I levels 4.5-fold in IPF fibroblasts. CXCL6 is expressed in ectopic airway epithelial cells. Elevated levels of CXCL6 are associated with IPF mortality. CXCL6-driven collagen synthesis represents a functional consequence of ectopic localisation of airway epithelial cells in IPF.

The NLRP3-Inflammasome-Caspase-1 Pathway Is Upregulated in Idiopathic Pulmonary Fibrosis and Acute Exacerbations and Is Inducible by Apoptotic A549 Cells.

Idiopathic pulmonary fibrosis (IPF) is a relentlessly progressive disease harboring significant morbidity and mortality despite recent advances in therapy. Regardless of disease severity acute exacerbations (IPF-AEs) may occur leading to considerable loss of function and are the leading cause of death in IPF. Histologic features of IPF-AE are very similar to acute respiratory distress syndrome (ARDS), but the underlying mechanisms are incompletely understood. We investigated the role of the NLRP3 inflammasome in IPF and IPF-AE. Bronchoalveolar lavage (BAL) cells were sampled from patients with IPF (n = 32), IPF-AE (n = 10), ARDS (n = 7) and healthy volunteers (HV, n = 37) and the NLRP3-inflammasome was stimulated in-vitro. We found the NLRP3 inflammasome to be hyper-inducible in IPF compared to HV with increased IL-1ß and pro-IL-1ß levels on ELISA upon stimulation as well as increased caspase-1 activity measured by caspase-1p20 immunoblotting. In IPF-AE, IL-1ß was massively elevated to an extent similar to ARDS. To evaluate potential mechanisms, we co-cultured BAL cells with radiated A549 cells (a model to simulate apoptotic alveolar epithelial cells), which led to increased NLRP3 mRNA expression and increased caspase-1 dependent IL-1ß production. In the presence of a reactive oxygen species (ROS) inhibitor (diphenyleneiodonium) and a cathepsin B inhibitor (E64D), NLRP3 expression was suppressed indicating that induction of NLRP3 activation following efferocytosis of apoptotic A549 cells is mediated via ROS and cathepsin-B. In summary, we present evidence of involvement of the NLRP3 inflammasome-caspase pathway in the pathogenesis of IPF-AE, similarly to ARDS, which may be mediated by efferocytosis of apoptotic alveolar epithelial cells in IPF.

Toll interacting protein protects bronchial epithelial cells from bleomycin-induced apoptosis.

Idiopathic pulmonary fibrosis (IPF) is characterized by altered epithelial cell phenotypes, which are associated with myofibroblast accumulation in the lung. Atypical alveolar epithelial cells in IPF express molecular markers of airway epithelium. Polymorphisms within and around Toll interacting protein (TOLLIP) are associated with the susceptibility to IPF and mortality. However, the functional role of TOLLIP in IPF is unknown. Using lung tissues from IPF and control subjects, we showed that expression of TOLLIP gene in the lung parenchyma is globally lower in IPF compared to controls. Lung cells expressing significant levels of TOLLIP include macrophages, alveolar type II, and basal cells. TOLLIP protein expression is lower in the parenchyma of IPF lungs but is expressed in the atypical epithelial cells of the distal fibrotic regions. Using overexpression and silencing approaches, we demonstrate that TOLLIP protects cells from bleomycin-induced apoptosis using primary bronchial epithelial cells and BEAS-2B cells. The protective effects are mediated by reducing mitochondrial reactive oxygen species (ROS) levels and upregulating autophagy. Therefore, global downregulation of the TOLLIP gene in IPF lungs may predispose injured lung epithelial cells to apoptosis and to the development of IPF.

Divergence of tight and adherens junction factors in alveolar epithelium in pulmonary fibrosis

It has been proposed that an epithelial injury may be one of the multiple primary events in the pathogenesis of idiopathic pulmonary fibrosis (IPF). The aim of this study was to characterize the tight junction and adherens junction proteins in normal human lung, IPF, cryptogenic organizing pneumonia, and asbestosis. We determined the immunohistochemical cell-specific expression of tight junction proteins claudin-1, claudin-2, claudin-3, claudin-4, claudin-5, and claudin-7, as well as 3 adherens junction proteins, E-cadherin, N-cadherin, and β-catenin. We further analyzed the expression of claudin-1, claudin-3, and claudin-4 and E-cadherin, N-cadherin, and β-catenin at the transcriptional level by quantitative real-time reverse transcriptase polymerase chain reaction. The expression levels of both tight junction and adherens junction proteins were elevated in regenerative alveolar epithelium in pulmonary fibrosis as compared with the expression of these proteins in normal alveolar epithelium. In particular, the expression levels of claudins-1 and claudin-3 were clearly elevated in all diseases. Furthermore, the amounts of adherens junction proteins messenger RNAs (mRNAs) were also all increased in pulmonary fibroses in comparison with healthy controls, with N-cadherin showing the greatest increase in mRNA levels in all diseases. However, the amounts of claudin-1, claudin-3, and claudin-4 mRNAs in fibrotic lung were similar to or even lower than those measured in the healthy controls. It is possible that the diminished capacity to produce claudin mRNAs may be one explanation for poor repair capacity of alveolar epithelial cells in IPF.

In search of the fibrotic epithelial cell: opportunities for a collaborative network

Idiopathic pulmonary fibrosis (IPF) is a chronic progressive disease of unknown aetiology. It has a very poor prognosis and no effective treatment. There are two major barriers to the development...

Ectopic respiratory epithelial cell differentiation in bronchiolised distal airspaces in idiopathic pulmonary fibrosis

BackgroundBronchiolisation of distal airspaces is an unexplained feature of idiopathic pulmonary fibrosis (IPF). The authors sought to identify mechanisms driving the differentiation of mucus cells during the bronchiolisation process.MethodsPathways governing...

Dickkopf proteins influence lung epithelial cell proliferation in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a fatal interstitial lung disease with unknown pathogenesis. The WNT/β-catenin pathway has recently been reported to be operative in epithelial cells in IPF. Dickkopf (DKK) proteins are known to regulate WNT signalling via interaction with Kremen (KRM) receptors, yet their expression and role in the adult lung and in IPF has not been addressed. We analysed the expression, localisation and function of DKK and KRM proteins in IPF lungs using Western blotting, quantitative RT-PCR, immunohistochemistry, ELISA and functional in vitro studies. Enhanced expression of DKK1 and DKK4 and KRM1 was detected in lung homogenates of IPF patients compared with transplant donors. Immunohistochemistry revealed that DKK1 was predominantly localised in basal bronchial epithelial cells. Furthermore, prominent expression of all proteins was observed in hyperplastic alveolar epithelial cells in IPF. Quantitative measurement of DKK1 revealed enhanced protein expression in the bronchoalveolar lumen of IPF patients. Finally, functional studies using human bronchial and alveolar epithelial cell lines demonstrated that WNT-induced epithelial cell proliferation is regulated by DKK1 in a dose-dependent fashion. In summary, DKK proteins are expressed in the lung epithelium in IPF. DKK proteins influence epithelial cell proliferation and may, therefore, be suitable therapeutic targets for IPF.

Increased Expression of Ect2, a Guanine Nucleotide Exchange Factor for Rho GTPases, in Hyperplastic Alveolar Epithelial Cells in IPF

Rationale: Idiopathic pulmonary fibrosis (IPF) is a progressive and fatal lung disease characterized by fibroblast activation and extracellular matrix (ECM) remodelling, leading to distorted lung architecture and function. During disease progression, repetitive alveolar epithelial injury and repair processes lead to enhanced fibroblast activation and ECM deposition, but molecular mechanisms thereof remain elusive. Previously, we have reported altered gene expression profiles of alveolar epithelial cells (AEC) in IPF, leading to AEC hyperplasia.

Stress in the ER (Endoplasmic Reticulum)

Stress in the ER (Endoplasmic Reticulum)

Functional Wnt Signaling Is Increased in Idiopathic Pulmonary Fibrosis

BackgroundIdiopathic pulmonary fibrosis (IPF) is a fatal lung disease, characterized by distorted lung architecture and loss of respiratory function. Alveolar epithelial cell injury and hyperplasia, enhanced extracellular matrix deposition, and (myo)fibroblast activation are features of IPF. Wnt/β-catenin signaling has been shown to determine epithelial cell fate during development. As aberrant reactivation of developmental signaling pathways has been suggested to contribute to IPF pathogenesis, we hypothesized that Wnt/β-catenin signaling is activated in epithelial cells in IPF. Thus, we quantified and localized the expression and activity of the Wnt/β-catenin pathway in IPF.Methodology/Principal FindingsThe expression of Wnt1, 3a, 7b, and 10b, the Wnt receptors Fzd1-4, Lrp5-6, as well as the intracellular signal transducers Gsk-3β, β-catenin, Tcf1, 3, 4, and Lef1 was analyzed in IPF and transplant donor lungs by quantitative real-time (q)RT-PCR. Wnt1, 7b and 10b, Fzd2 and 3, β-catenin, and Lef1 expression was significantly increased in IPF. Immunohistochemical analysis localized Wnt1, Wnt3a, β-catenin, and Gsk-3β expression largely to alveolar and bronchial epithelium. This was confirmed by qRT-PCR of primary alveolar epithelial type II (ATII) cells, demonstrating a significant increase of Wnt signaling in ATII cells derived from IPF patients. In addition, Western blot analysis of phospho-Gsk-3β, phospho-Lrp6, and β-catenin, and qRT-PCR of the Wnt target genes cyclin D1, Mmp 7, or Fibronectin 1 demonstrated increased functional Wnt/β-catenin signaling in IPF compared with controls. Functional in vitro studies further revealed that Wnt ligands induced lung epithelial cell proliferation and (myo)fibroblast activation and collagen synthesis.Conclusions/SignificanceOur study demonstrates that the Wnt/β-catenin pathway is expressed and operative in adult lung epithelium. Increased Wnt/β-catenin signaling may be involved in epithelial cell injury and hyperplasia, as well as impaired epithelial-mesenchymal cross-talk in IPF. Thus, modification of Wnt signaling may represent a therapeutic option in IPF.

The Role of High Mobility Group Box1 in Pulmonary Fibrosis

High mobility group box1 protein (HMGB1) was originally discovered as a nuclear binding protein, and is known to play an important role in acute lung injury. However, the role of HMGB1 in pulmonary fibrosis has not been addressed. Therefore, we measured the HMGB1 levels in serum and bronchoalveolar lavage fluids (BALF) from patients with idiopathic pulmonary fibrosis (IPF), nonspecific interstitial pneumonia, interstitial pneumonia associated with collagen vascular diseases, and hypersensitivity pneumonitis (HP) by enzyme-linked immunosorbent assay. We also assessed the HMGB1 expression in bleomycin-induced pulmonary fibrosis in mice, and examined the effect of anti-HMGB1 antibody and ethyl pyluvate, which inhibits the HMGB1 secretion from alveolar macrophages. In addition, we examined the effect of HMGB1 on fibroblast proliferation, apoptosis, and collagen synthesis in vitro. Serum HMGB1 levels were not significantly increased in interstitial lung diseases compared with control subjects. BALF HMGB1 levels were significantly increased in IPF and HP compared with control subjects. HMGB1 protein was predominantly detected in inflammatory cells and hyperplasic epithelial cells in IPF. In bleomycin-induced pulmonary fibrosis in mice, HMGB1 protein was predominantly up-regulated in bronchiolar epithelial cells at early phase and in alveolar epithelial and inflammatory cells in fibrotic lesions at later phase. Intraperitoneal injection of anti-HMGB1 antibody or ethyl pyluvate significantly attenuated lung inflammation and fibrosis in this model. HMGB1 significantly induced proliferation, but not apoptosis or collagen synthesis on cultured fibroblasts. HMGB1 may be a promising target against pulmonary fibrosis as well as acute lung injury.

Expression of Apoptotic and Antiapoptotic Markers in Epithelial Cells in Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic, usually fatal lung disease of unknown etiology. A common feature is the presence of microscopic areas of epithelial cell dropout. Increased apoptosis of these cells could elucidate the speculative pathogenesis of the disease. Therefore, the aim of our study was to examine the expression of p53, p21, bcl-2, bax, and caspase-3 in association with DNA strand breaks in bronchial and alveolar epithelial cells in lung specimens from IPF patients and control subjects. We examined by immunohistochemistry the expression of p53, p21, bax, bcl-2, and caspase-3 in association with DNA strand breaks detected by terminal deoxynucleotide transferase-mediated deoxyuridine triphosphate-biotin nick end-labeling (TUNEL) in bronchial and alveolar epithelial cells in lung specimens taken by biopsy in 12 IPF patients and 10 control subjects. An independent tissue evaluation by two pathologists graded semiquantatively the degree of staining present. TUNEL was positive in epithelial cells in all IPF patients and only in one control subject. The expression of p53, p21, bax, and caspase-3 was up-regulated in IPF patients compared to control subjects. Bcl-2 was expressed less in IPF patients than in control subjects. These results confirm that apoptotic hyperplastic epithelial cells are present in patients with IPF and that the expression of p53, p21, bax, and caspase-3 appears to be up-regulated and that of bcl-2 down-regulated in these cells. The increased expression of proapoptotic molecules in epithelial cells in IPF may be involved in the inadequate and delayed reepithelialization, which in turn contributes to fibroblast proliferation.

B7-1, B7-2 and class II MHC molecules in idiopathic pulmonary fibrosis and bronchiolitis obliterans-organizing pneumonia

Interstitial lung diseases are thought to be associated with the infiltration of activated T-lymphocytes. To induce an effective immune response, antigen-presenting cells have to not only present antigenic peptide with major histocompatibility complex (MHC) molecules to T-lymphocytes but also express B7 molecules. Therefore, the expression of B7-1, B7-2 and class II MHC molecules was investigated in lung tissues from patients with idiopathic pulmonary fibrosis (IPF) and bronchiolitis obliterans-organizing pneumonia (BOOP), and in normal lung parenchyma as a control, using immunohistochemical localization. B7-1 and B7-2 were aberrantly expressed in bronchiolar and alveolar epithelial cells, and class II MHC molecules were also aberrantly expressed in bronchiolar epithelial cells in IPF. B7-1 was aberrantly expressed in bronchiolar epithelial cells in BOOP. There was no significant difference in the expression of these proteins in alveolar macrophages between IPF and control subjects. However, B7-2 and class II MHC molecule expression in alveolar macrophages was decreased in BOOP compared with that in control subjects. Expression of CD28 and CTLA4, receptors for B7 molecules, was detected in infiltrating lymphocytes in lung tissues in IPF and BOOP. It was concluded that bronchiolar and alveolar epithelial cells may actively participate in the pathophysiology of idiopathic pulmonary fibrosis through the aberrant expression of B7 and class II major histocompatibility complex molecules. The dysregulation of these molecules in epithelial cells may lead to the activation of autoreactive T-lymphocytes, which might contribute to the pathogenesis of fibrosing lung diseases.

B7‐1, B7-2 and class II MHC molecules in idiopathic pulmonary fibrosis and bronchiolitis obliterans-organizing pneumonia

Interstitial lung diseases are thought to be associated with the infiltration of activated T-lymphocytes. To induce an effective immune response, antigen-presenting cells have to not only present antigenic peptide with major histocompatibility complex (MHC) molecules to T-lymphocytes but also express B7 molecules. Therefore, the expression of B7-1, B7-2 and class II MHC molecules was investigated in lung tissues from patients with idiopathic pulmonary fibrosis (IPF) and bronchiolitis obliterans-organizing pneumonia (BOOP), and in normal lung parenchyma as a control, using immunohistochemical localization. B7-1 and B7-2 were aberrantly expressed in bronchiolar and alveolar epithelial cells, and class II MHC molecules were also aberrantly expressed in bronchiolar epithelial cells in IPF. B7-1 was aberrantly expressed in bronchiolar epithelial cells in BOOP. There was no significant difference in the expression of these proteins in alveolar macrophages between IPF and control subjects. However, B7-2 and class II MHC molecule expression in alveolar macrophages was decreased in BOOP compared with that in control subjects. Expression of CD28 and CTLA4, receptors for B7 molecules, was detected in infiltrating lymphocytes in lung tissues in IPF and BOOP. It was concluded that bronchiolar and alveolar epithelial cells may actively participate in the pathophysiology of idiopathic pulmonary fibrosis through the aberrant expression of B7 and class II major histocompatibility complex molecules. The dysregulation of these molecules in epithelial cells may lead to the activation of autoreactive T-lymphocytes, which might contribute to the pathogenesis of fibrosing lung diseases.

The involvement of Fas-Fas ligand pathway in fibrosing lung diseases.

Pulmonary fibrosis begins with alveolitis, which progresses to destruction of lung tissue and excess collagen deposition. This process could be the result of DNA damage and a form of apoptosis. Therefore, we hypothesized that Fas ligand (FasL), which induces apoptosis in cells expressing Fas antigen (Fas), is associated with pulmonary fibrosis. We examined frozen lung tissues from seven patients with idiopathic pulmonary fibrosis (IPF), and bronchoalveolar lavage fluid (BALF) cells from 19 patients with IPF and from 17 patients with interstitial pneumonia associated with collagen vascular diseases (CVD-IP). We used five frozen lungs with normal lung parenchyma and BALF cells from 10 patients with solitary pulmonary nodule as controls. Reverse transcription-polymerase chain reaction (RT-PCR) showed that FasL messenger RNA (mRNA) was expressed in BALF cells from all patients with IPF and from 15 of 16 patients with CVD-IP. FasL mRNA was not detected in BALF cells except in one of 10 controls. RT in situ PCR detected FasL mRNA in inflammatory cells in BALF from patients with IPF. Immunohistochemistry detected FasL protein in infiltrating lymphocytes and granulocytes in all of seven frozen lung tissues of IPF, but in none of five control lung tissues. Additionally, the expression of Fas appeared to be upregulated in bronchiolar and alveolar epithelial cells in IPF compared with normal lung parenchyma by immunohistochemistry. We conclude that Fas and FasL were upregulated in fibrosing lung diseases and may associate with DNA damage or apoptosis of bronchiolar and alveolar epithelial cells in this disorder.

Monocyte chemoattractant protein-1 in idiopathic pulmonary fibrosis and other interstitial lung diseases

Macrophages play a crucial role in the pathogenesis of idiopathic pulmonary fibrosis (IPF). To examine the mechanisms for increased monocyte/macrophage recruitment in IPF and nonIPF interstitial lung diseases (nonIPF) the localization of monocyte chemoattractant protein-1 (MCP-1) was investigated in 14 cases of IPF, seven cases of nonIPF, and seven normal control lungs (CTRL) by immunohistochemistry using a specific anti-MCP-1 monoclonal antibody, F9. By double immunohistochemical staining using F9 and one of the cell type specific antibodies significant differences in the staining pattern of MCP-1 were observed between IPF and nonIPF. In IPF MCP-1 was observed in cuboidal and flattened metaplastic epithelial cells, alveolar macrophages, and vascular endothelial cells. In contrast, no epithelial cells were stained for MCP-1 in nonIPF cases, although alveolar macrophages and vascular endothelial cells were labeled. Northern hybridization analysis of selected cases showed marked expression of MCP-1 messenger RNA (mRNA) in IPF and nonIPF compared with CTRL. These findings suggest that the MCP-1 production in IPF and nonIPF plays an important role in the recruitment of monocyte/macrophages. Monocyte chemoattractant protein-1 production by epithelial cells in IPF may be caused by the metaplastic nature of the epithelial cells and may be one of the key factors inducing the irreversible progression of IPF.