Pulmonary fibrosis: pathogenesis, etiology and regulation

Modulation of lung inflammation by the Epstein-Barr virus protein Zta

Several studies have implicated gamma-herpesviruses, particularly Epstein-Barr virus (EBV), in the progression of idiopathic pulmonary fibrosis. The data presented here examine the possible role that EBV plays in the potentiation of this disease by evaluating the pulmonary response to expression of the EBV lytic transactivator protein Zta. Expression of Zta in the lungs of mice via adenovirus-mediated delivery (Adv-Zta) produced profibrogenic inflammation that appeared most pronounced by day 7 postexposure. Relative to mice exposed to control GFP-expressing adenovirus (Adv-GFP), mice exposed to Adv-Zta displayed evidence of lung injury and a large increase in inflammatory cells, predominantly neutrophils, recovered by bronchoalveolar lavage (BAL). Cytokine and mRNA profiling of the BAL fluid and cells recovered from Adv-Zta-treated mice revealed a Th2 and Th17 bias. mRNA profiles from Adv-Zta-infected lung epithelial cells revealed consistent induction of mRNAs encoding Th2 cytokines. Coexpression in transient assays of wild-type Zta, but not a DNA-binding-defective mutant Zta, activated expression of the IL-13 promoter in lung epithelial cells, and detection of IL-13 in Adv-Zta-treated mice correlated with expression of Zta. Induction of Th2 cytokines in Zta-expressing mice corresponded with alternative activation of macrophages. In cell culture and in mice, Zta repressed lung epithelial cell markers. Despite the profibrogenic character at day 7, the inflammation resolves by 28 days postexposure to Adv-Zta without evidence of fibrosis. These observations indicate that the EBV lytic transactivator protein Zta displays activity consistent with a pathogenic role in pulmonary fibrosis associated with herpesvirus infection.

Increased deposition of chondroitin/dermatan sulfate glycosaminoglycan and upregulation of β1,3-glucuronosyltransferase I in pulmonary fibrosis

Pulmonary fibrosis (PF) is characterized by increased deposition of proteoglycans (PGs), in particular core proteins. Glycosaminoglycans (GAGs) are key players in tissue repair and fibrosis, and we investigated whether PF is associated with changes in the expression and structure of GAGs as well as in the expression of β1,3-glucuronosyltransferase I (GlcAT-I), a rate-limiting enzyme in GAG synthesis. Lung biopsies from idiopathic pulmonary fibrosis (IPF) patients and lung tissue from a rat model of bleomycin (BLM)-induced PF were immunostained for chondroitin sulfated-GAGs and GlcAT-I expression. Alterations in disaccharide composition and sulfation of chondroitin/dermatan sulfate (CS/DS) were evaluated by fluorophore-assisted carbohydrate electrophoresis (FACE) in BLM rats. Lung fibroblasts isolated from control (saline-instilled) or BLM rat lungs were assessed for GAG structure and GlcAT-I expression. Disaccharide analysis showed that 4- and 6-sulfated disaccharides were increased in the lungs and lung fibroblasts obtained from fibrotic rats compared with controls. Fibrotic lung fibroblasts and transforming growth factor-β(1) (TGF-β(1))-treated normal lung fibroblasts expressed increased amounts of hyaluronan and 4- and 6-sulfated chondroitin, and neutralizing anti-TGF-β(1) antibody diminished the same. TGF-β(1) upregulated GlcAT-I and versican expression in lung fibroblasts, and signaling through TGF-β type I receptor/p38 MAPK was required for TGF-β(1)-mediated GlcAT-I and CS-GAG expression in fibroblasts. Our data show for the first time increased expression of CS-GAGs and GlcAT-I in IPF, fibrotic rat lungs, and fibrotic lung fibroblasts. These data suggest that alterations of sulfation isomers of CS/DS and upregulation of GlcAT-I contribute to the pathological PG-GAG accumulation in PF.

Phosphoinositide 3-kinase γ plays a critical role in bleomycin-induced pulmonary inflammation and fibrosis in mice

PI3Kγ is central in signaling diverse arrays of cellular functions and inflammation. Pulmonary fibrosis is associated with pulmonary inflammation, angiogenesis, and deposition of collagen and is modeled by instillation of bleomycin. The role of PI3Kγ in mediating bleomycin-induced pulmonary inflammation and fibrosis in mice and potential mechanisms involved was investigated here. WT or PI3Kγ KO mice were instilled with bleomycin and leukocyte subtype influx, cytokine and chemokine levels, and angiogenesis and tissue fibrosis evaluated. The activation of lung-derived leukocytes and fibroblasts was evaluated in vitro. The relevance of PI3Kγ for endothelial cell function was evaluated in HUVECs. PI3Kγ KO mice had greater survival and weight recovery and less fibrosis than WT mice after bleomycin instillation. This was associated with decreased production of TGF-β(1) and CCL2 and increased production of IFN-γ and IL-10. There was reduced expression of collagen, fibronectin, α-SMA, and von Willebrand factor and decreased numbers and activation of leukocytes and phosphorylation of AKT and IκB-α. PI3Kγ KO mice had a reduced number and area of blood vessels in the lungs. In vitro, treatment of human endothelial cells with the PI3Kγ inhibitor AS605240 decreased proliferation, migration, and formation of capillary-like structures. AS605240 also decreased production of collagen by murine lung-derived fibroblasts. PI3Kγ deficiency confers protection against bleomycin-induced pulmonary injury, angiogenesis, and fibrosis through the modulation of leukocyte, fibroblast, and endothelial cell functions. Inhibitors of PI3Kγ may be beneficial for the treatment of pulmonary fibrosis.

The pathogenesis of idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive fibrotic lung disease with an appalling prognosis. The failure of anti-inflammatory therapies coupled with the observation that deranged epithelium overlies proliferative myofibroblasts to form the fibroblastic focus has lead to the emerging concept that IPF is a disease of deregulated epithelial-mesenchymal crosstalk. IPF is triggered by an as yet unidentified alveolar injury that leads to activation of transforming growth factor-β (TGF-β) and alveolar basement membrane disruption. In the presence of persisting injurious pathways, or disrupted repair pathways, activated TGF-β can lead to enhanced epithelial apoptosis and epithelial-to-mesenchymal transition (EMT) as well as fibroblast, and fibrocyte, transformation into myofibroblasts which are resistant to apoptosis. The resulting deposition of excess disrupted matrix by these myofibroblasts leads to the development of IPF.

Association of FcγRIIa R131H polymorphism with idiopathic pulmonary fibrosis severity and progression

Background

A significant genetic component has been described for idiopathic pulmonary fibrosis (IPF). The R131H (rs1801274) polymorphism of the IgG receptor FcγRIIa determines receptor affinity for IgG subclasses and is associated with several chronic inflammatory diseases. We investigated whether this polymorphism is associated with IPF susceptibility or progression.

Methods

In a case-control study, we compared the distribution of FcγRIIa R131H genotypes in 142 patients with IPF and in 218 controls using allele-specific PCR amplification.

Results

No differences in the frequency of FcγRIIa genotypes were evident between IPF patients and control subjects. However, significantly impaired pulmonary function at diagnosis was observed in HH compared to RR homozygotes, with evidence of more severe restriction (reduced forced vital capacity (FVC)) and lower diffusing capacity for carbon monoxide (DL_CO). Similarly, increased frequency of the H131 allele was observed in patients with severe disease (DL_CO < 40% predicted) (0.53 vs. 0.38; p = 0.03). Furthermore, the H131 allele was associated with progressive pulmonary fibrosis as determined by > 10% drop in FVC and/or > 15% fall in DL_CO at 12 months after baseline (0.48 vs. 0.33; p = 0.023).

Conclusions

These findings support an association between the FcγRIIa R131H polymorphism and IPF severity and progression, supporting the involvement of immunological mechanisms in IPF pathogenesis.

Extracellular matrix roles during cardiac repair

The cardiac extracellular matrix (ECM) provides a platform for cells to maintain structure and function, which in turn maintains tissue function. In response to injury, the ECM undergoes remodeling that involves synthesis, incorporation, and degradation of matrix proteins, with the net outcome determined by the balance of these processes. The major goals of this review are a) to serve as an initial resource for students and investigators new to the cardiac ECM remodeling field, and b) to highlight a few of the key exciting avenues and methodologies that have recently been explored. While we focus on cardiac injury and responses of the left ventricle (LV), the mechanisms reviewed here have pathways in common with other wound healing models.

Therapeutic effects of evasin-1, a chemokine binding protein, in bleomycin-induced pulmonary fibrosis

CC chemokines play an important role in the pathogenesis of idiopathic pulmonary fibrosis. Few studies have evaluated the efficacy of therapeutically targeting CC chemokines and their receptors during interstitial lung diseases. In the present study, the therapeutic effects of Evasin-1, a tick-derived chemokine-binding protein that has high affinity for CCL3/microphage inflammatory protein (MIP)-1α, was investigated in a murine model of bleomycin-induced lung fibrosis. CCL3/MIP-1α concentrations in lung homogenates increased significantly with time after bleomycin challenge, and this was accompanied by increased number of leukocytes and elevated levels of CCL2/monocyte chemoattractant protein (MCP)-1, CCL5/regulated upon activation, normal T cell expressed and secreted, TNF-α and transforming growth factor-β(1), and pulmonary fibrosis. Administration of evasin-1 on a preventive (from the day of bleomycin administration) or therapeutic (from Day 8 after bleomycin) schedule decreased number of leukocytes in the lung, reduced levels of TNF-α and transforming growth factor-β(1), and attenuated lung fibrosis. These protective effects were similar to those observed in CCL3/MIP-1α-deficient mice. In conclusion, targeting CCL3/MIP-1α by treatment with evasin-1 is beneficial in the context of bleomycin-induced lung injury, even when treatment is started after the fibrogenic insult. Mechanistically, evasin-1 treatment was associated with decreased recruitment of leukocytes and production of fibrogenic cytokines. Modulation of CCL3/MIP-1α function by evasin-1 could be useful for the treatment of idiopathic pulmonary fibrosis.

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.

A novel, orally active LPA(1) receptor antagonist inhibits lung fibrosis in the mouse bleomycin model

BACKGROUND AND PURPOSE

The aim of this study was to assess the potential of an antagonist selective for the lysophosphatidic acid receptor, LPA(1), in treating lung fibrosis We evaluated the in vitro and in vivo pharmacological properties of the high affinity, selective, oral LPA(1)-antagonist (4'-{4-[(R)-1-(2-chloro-phenyl)-ethoxycarbonylamino]-3-methyl-isoxazol-5-yl}-biphenyl-4-yl)-acetic acid (AM966).

EXPERIMENTAL APPROACH

The potency and selectivity of AM966 for LPA(1) receptors was determined in vitro by calcium flux and cell chemotaxis assays using recombinant and native cell cultures. The in vivo efficacy of AM966 to reduce tissue injury, vascular leakage, inflammation and fibrosis was assessed at several time points in the mouse bleomycin model.

KEY RESULTS

AM966 was a potent antagonist of LPA(1) receptors, with selectivity for this receptor over the other LPA receptors. In vitro, AM966 inhibited LPA-stimulated intracellular calcium release (IC(50)= 17 nM) from Chinese hamster ovary cells stably expressing human LPA(1) receptors and inhibited LPA-induced chemotaxis (IC(50)= 181 nM) of human IMR-90 lung fibroblasts expressing LPA(1) receptors. AM966 demonstrated a good pharmacokinetic profile following oral dosing in mice. In the mouse, AM966 reduced lung injury, vascular leakage, inflammation and fibrosis at multiple time points following intratracheal bleomycin instillation. AM966 also decreased lactate dehydrogenase activity and tissue inhibitor of metalloproteinase-1, transforming growth factor beta1, hyaluronan and matrix metalloproteinase-7, in bronchoalveolar lavage fluid.

CONCLUSIONS AND IMPLICATIONS

These findings demonstrate that AM966 is a potent, selective, orally bioavailable LPA(1) receptor antagonist that may be beneficial in treating lung injury and fibrosis, as well as other diseases that are characterized by pathological inflammation, oedema and fibrosis.

Effect of an immunotoxin to folate receptor beta on bleomycin-induced experimental pulmonary fibrosis

It has been suggested that alveolar and interstitial macrophages play a key role in the pathogenesis of idiopathic pulmonary fibrosis (IPF) by producing proinflammatory and/or fibrogenic cytokines. We showed that inflammatory macrophages expressed folate receptor beta (FRbeta) while resident macrophages in normal tissues expressed no or low levels of FRbeta. In the present study, we examined the distribution of FRbeta-expressing macrophages in the lungs of patients with usual idiopathic pulmonary fibrosis (UIP) and mice with bleomycin-induced pulmonary fibrosis (PF) and tested whether the depletion of FRbeta-expressing macrophages could suppress bleomycin-induced PF in mice. Immunostaining with anti-human or -mouse FRbeta monoclonal antibody (mAb) revealed that FRbeta-expressing macrophages were present predominantly in fibrotic areas of the lungs of patients with UIP and mice with bleomycin-induced PF. Intranasal administration of a recombinant immunotoxin, consisting of immunoglobulin heavy and light chain Fv portions of an anti-mouse FRbeta mAb and truncated Pseudomonas exotoxin A, increased survival significantly and reduced levels of total hydroxyproline and fibrosis in bleomycin-induced PF. In immunohistochemical analysis, decreased numbers of tumour necrosis factor-alpha-, chemokines CCL2- and CCL12-producing cells were observed in the immunotoxin-treated group. These findings suggest a pathogenic role of FRbeta-expressing macrophages in IPF. Thus, targeting FRbeta-expressing macrophages may be a promising treatment of IPF.

Requirement for inducible nitric oxide synthase in chronic allergen exposure-induced pulmonary fibrosis but not inflammation

The role of inducible NO synthase (iNOS) in allergic airway inflammation remains elusive. We tested the hypothesis that iNOS plays different roles during acute versus chronic airway inflammation. Acute and chronic mouse models of OVA-induced airway inflammation were used to conduct the study. We showed that iNOS deletion was associated with a reduction in eosinophilia, mucus hypersecretion, and IL-5 and IL-13 production upon the acute protocol. Such protection was completely abolished upon the chronic protocol. Interestingly, pulmonary fibrosis observed in wild-type mice under the chronic protocol was completely absent in iNOS(-/-) mice despite persistent IL-5 and IL-13 production, suggesting that these cytokines were insufficient for pulmonary fibrosis. Such protection was associated with reduced collagen synthesis and indirect but severe TGF-beta modulation as confirmed using primary lung smooth muscle cells. Although activation of matrix metalloproteinase-2/-9 exhibited little change, the large tissue inhibitor of metalloproteinase-2 (TIMP-2) increase detected in wild-type mice was absent in the iNOS(-/-) counterparts. The regulatory effect of iNOS on TIMP-2 may be mediated by peroxynitrite, as the latter reversed TIMP-2 expression in iNOS(-/-) lung smooth muscle cells and fibroblasts, suggesting that the iNOS-TIMP-2 link may explain the protective effect of iNOS-knockout against pulmonary fibrosis. Analysis of lung sections from chronically OVA-exposed iNOS(-/-) mice revealed evidence of residual but significant protein nitration, prevalent oxidative DNA damage, and poly(ADP-ribose) polymerase-1 activation. Such tissue damage, inflammatory cell recruitment, and mucus hypersecretion may be associated with substantial arginase expression and activity. The results in this study exemplify the complexity of the role of iNOS in asthma and the preservation of its potential as a therapeutic a target.

TGF-β: Titan of Lung Fibrogenesis

Pulmonary fibrosis is characterized by epithelial cell injury, accumulation of myofibroblasts, and excessive deposition of collagen and other extracellular matrix elements, leading to loss of pulmonary function. Studies in both humans and animal models strongly suggest that TGF-β1 plays a pivotal role in the pathogenesis of pulmonary fibrosis. This review will first give an overview of TGF-β signaling and the effects of its inhibition on lung fibrogenesis. This overview includes information on TGF-β signal transduction pathways, the importance of TGF-β in the accumulation of myofibroblasts, the role of TGF-β in epithelial injury and apoptosis, the role of TGF-β in extracellular matrix remodeling, and the effects of inhibiting TGF-β signaling in animal models of lung fibrosis. Subsequently this review will highlight recent advances in two areas of particular interest to our research group: (1) TGF-β and proteoglycans; (2) TGF-β and histone deacetylases. Although our understanding of the role of TGF-β and its mechanisms of action in lung fibrogenesis has increased dramatically in recent years, there is still much to be learned about this important molecule, especially how TGF-β function is modulated in vivo, and its complex interactions with other factors expressed during lung injury and repair. Research in these areas will help identify novel therapeutic targets for the treatment of pulmonary fibrosis that will hopefully improve the prognosis of this devastating illness.

Innate immune processes are sufficient for driving silicosis in mice

The lung is constantly exposed to potentially pathogenic particles and microorganisms. It has become evident recently that not only innate but also adaptive immune responses to particulates, such as SiO(2) entering the respiratory tract, are complex and dynamic events. Although the cellular mechanisms and anatomical consequences involved in the development of silicosis have been studied extensively, they still remain poorly understood. Based on their capacity for immune regulation, lymphocytes may play a key role in the respiratory response to environmental challenge by SiO(2). The objective of this study was to characterize the impact of SiO(2) exposure on respiratory immune processes, with particular emphasis on evaluating the importance of lymphocytes in the murine silicosis model. Therefore, lymphopenic mice, including NK-deficient, Rag1(-/-), or a combination (Rag1(-/-) NK-depleted), were used and demonstrated that SiO(2)-induced fibrosis and inflammation can occur independently of T, B, NK T, and NK cells. Studies in Rag1(-/-) mice suggest further that lymphocytes may participate in the regulation of SiO(2)-induced inflammation through modulation of the Nalp3 inflammasome. This observation may have clinical relevance in the treatment of inflammatory and fibrotic lung diseases that are refractory or respond suboptimally to current therapeutics.

Epithelial-mesenchymal transition: from molecular mechanisms, redox regulation to implications in human health and disease

Epithelial to mesenchymal transition (EMT) is a fundamental process, paradigmatic of the concept of cell plasticity, that leads epithelial cells to lose their polarization and specialized junctional structures, to undergo cytoskeleton reorganization, and to acquire morphological and functional features of mesenchymal-like cells. Although EMT has been originally described in embryonic development, where cell migration and tissue remodeling have a primary role in regulating morphogenesis in multicellular organisms, recent literature has provided evidence suggesting that the EMT process is a more general biological process that is also involved in several pathophysiological conditions, including cancer progression and organ fibrosis. This review offers first a comprehensive introduction to describe major relevant features of EMT, followed by sections dedicated on those signaling mechanisms that are known to regulate or affect the process, including the recently proposed role for oxidative stress and reactive oxygen species (ROS). Current literature data involving EMT in both physiological conditions (i.e., embryogenesis) and major human diseases are then critically analyzed, with a special final focus on the emerging role of hypoxia as a relevant independent condition able to trigger EMT.

Alternative activation of macrophages: mechanism and functions

The concept of an alternative pathway of macrophage activation has stimulated interest in its definition, mechanism, and functional significance in homeostasis and disease. We assess recent research in this field, argue for a restricted definition, and explore pathways by which the T helper 2 (Th2) cell cytokines interleukin-4 (IL-4) and IL-13 mediate their effects on macrophage cell biology, their biosynthesis, and responses to a normal and pathological microenvironment. The stage is now set to gain deeper insights into the role of alternatively activated macrophages in immunobiology.

Nonresolving inflammation

Nonresolving inflammation is a major driver of disease. Perpetuation of inflammation is an inherent risk because inflammation can damage tissue and necrosis can provoke inflammation. Nonetheless, multiple mechanisms normally ensure resolution. Cells like macrophages switch phenotypes, secreted molecules like reactive oxygen intermediates switch impact from pro- to anti-inflammatory, and additional mediators of resolution arise, including proteins, lipids, and gasses. Aside from persistence of initiating stimuli, nonresolution may result from deficiencies in these mechanisms when an inflammatory response begins either excessively or subnormally. This greatly complicates the development of anti-inflammatory therapies. The problem calls for conceptual, organizational, and statistical innovations.

Fibrocytes in health and disease

Fibrocytes are circulating mesenchymal progenitor cells that participate in tissue responses to injury and invasion. Accumulating knowledge from animal models regarding the differentiation, trafficking, and function of these cells implicates them in the development of diseases characterized by chronic inflammation and excessive collagen deposition. Recent data obtained from the clinical setting suggests that the enumeration of circulating fibrocytes may be a biomarker for disease progression in chronic lung diseases including asthma and pulmonary fibrosis. A greater understanding of the immunologic mediators that influence fibrocyte biology suggests new opportunities for therapeutic manipulation of these cells in fibrogenesis. This review integrates new developments in the cellular and molecular biology of fibrocytes with current concepts regarding the etiopathogenesis of fibrosing disorders.

Bleomycin and IL-1beta-mediated pulmonary fibrosis is IL-17A dependent

Idiopathic pulmonary fibrosis (IPF) is a destructive inflammatory disease with limited therapeutic options. To better understand the inflammatory responses that precede and concur with collagen deposition, we used three models of pulmonary fibrosis and identify a critical mechanistic role for IL-17A. After exposure to bleomycin (BLM), but not Schistosoma mansoni eggs, IL-17A produced by CD4⁺ and γδ⁺ T cells induced significant neutrophilia and pulmonary fibrosis. Studies conducted with C57BL/6 il17a^−/− mice confirmed an essential role for IL-17A. Mechanistically, using ifnγ^−/−, il10^−/−, il10^−/−il12p40^−/−, and il10^−/−il17a^−/− mice and TGF-β blockade, we demonstrate that IL-17A–driven fibrosis is suppressed by IL-10 and facilitated by IFN-γ and IL-12/23p40. BLM-induced IL-17A production was also TGF-β dependent, and recombinant IL-17A–mediated fibrosis required TGF-β, suggesting cooperative roles for IL-17A and TGF-β in the development of fibrosis. Finally, we show that fibrosis induced by IL-1β, which mimics BLM-induced fibrosis, is also highly dependent on IL-17A. IL-17A and IL-1β were also increased in the bronchoalveolar lavage fluid of patients with IPF. Together, these studies identify a critical role for IL-17A in fibrosis, illustrating the potential utility of targeting IL-17A in the treatment of drug and inflammation-induced fibrosis.

The role of interleukin-1beta and platelet-derived growth factor-AB in antifibrosis mediated by native human interferon alpha

BACKGROUND

Commercial preparations of native human interferon alpha (nHuIFN-alpha) contain several subtypes of interferon-alpha (IFN-alpha) and traces of other cytokines. Recently, we described its antifibrotic potential and showed nHuIFN-alpha to have a greater effect than that of recombinant human IFN-alpha (rHuIFN-alpha). We hypothesized that cooperation between different cytokines in the nHuIFN-alpha preparation is essential for this effect. Considerable concentrations of interleukin-1beta (IL-1beta) and platelet-derived growth factor AB (PDGF-AB) are present in the nHuIFN-alpha preparations.

METHODS

We tested the viability and the expression of procollagen type I messenger RNA (mRNA) in MRC5 fibroblasts treated with interleukin-1 beta (IL-1beta) and/or PDGF-AB, or the corresponding antibodies in combination with rHuIFN-alpha or nHuIFN-alpha.

RESULTS

We showed that neither IL-1beta nor PDGF-AB significantly affect the viability of MRC5 cells. Furthermore, cell viability was not affected when IL-1beta or PDGF-AB were applied along with rHuIFN-alpha, relative to the viability of cells treated with rHuIFN-alpha only. In contrast, both cytokines suppressed the synthesis of procollagen type I mRNA. When coadministered with rHuIFN-alpha, IL-1beta enhanced the suppression induced by rHuIFN-alpha. Conversely, PDGF-AB acted as an antagonist of rHuIFN-alpha and restored partially the synthesis of procollagen type I mRNA. Interestingly, the addition of IL-1beta to the PDGF-AB/rHuIFN-alpha mix not only abolished the antagonistic activity of PDGF-AB but also decreased the synthesis of procollagen type I mRNA beyond the level achieved by IL-1beta/rHuIFN-alpha. Therefore, IL-1beta was able to reverse the activity of PDGF-AB.

CONCLUSION

Our study suggests that IL-1beta is an important component of nHuIFN-alpha preparations, acting directly and indirectly to modulate the action of other components. This study provides insight into these complex cytokine networks, which is necessary for better and safer antifibrotic therapy.

Adenovirus-mediated gene transfer of hIGF-IB in mouse lungs induced prolonged inflammation but no fibroproliferation

Pulmonary fibrosis (PF), the end stage of a variety of fibroproliferative lung diseases, is characterized by excessive lung mesenchymal cell activation and extracellular matrix deposition. Most PF is induced after repetitive or chronic lung inflammation; however, a significant portion of PF occurs without apparent inflammation. The mechanisms of fibroproliferation are poorly understood. Studies have shown that cytokines regulating inflammation and tissue repair processes play essential roles in the development of PF. Insulin-like growth factor I (IGF-I) has been shown to stimulate lung mesenchymal cell proliferation and extracellular matrix synthesis in vitro and is significantly elevated in patients with PF. In this study, we investigated whether human IGF-IB (hIGF-IB) expression in the lungs induces PF in a C57BL/6 mouse model. Mice were subjected to adenoviral gene transfer, and the effects of hIGF-IB expression on the lungs were examined 3, 7, 14, 21, and 42 days after gene delivery. hIGF-IB expression induced significant and prolonged inflammatory cell infiltration into the lungs, with an early neutrophil infiltration followed by a late macrophage infiltration. No significant fibroblast or matrix accumulation could be detected in the lungs of these mice. No significant collagen accumulation could be detected in vivo, despite in vitro evidence that hIGF-IB induces collagen mRNA expression in fibroblasts. Therefore, IGF-IB alone is not sufficient to induce fibrosis, and it is possible that a coactivator is required to induce significant fibroproliferation in vivo.

Therapeutic efficacy of Cintredekin Besudotox (IL13-PE38QQR) in murine lung fibrosis is unaffected by immunity to Pseudomonas aeruginosa exotoxin A

BACKGROUND

We have previously explored a therapeutic strategy for specifically targeting the profibrotic activity of IL-13 during experimental pulmonary fibrosis using a fusion protein comprised of human IL-13 and a mutated form of Pseudomonas aeruginosa exotoxin A (IL13-PE) and observed that the intranasal delivery of IL13-PE reduced bleomycin-induced pulmonary fibrosis through its elimination of IL-13-responsive cells in the lung. The aim of the present study was to determine whether the presence of an immune response to P. aeruginosa and/or its exotoxin A (PE) would diminish the anti-fibrotic properties of IL13-PE.

METHODOLOGY/PRINCIPAL FINDINGS

Fourteen days after P. aeruginosa infection, C57BL/6 mice were injected with bleomycin via the intratracheal route. Other groups of mice received 4 doses of saline or IL13-PE by either intranasal or intraperitoneal application, and were challenged i.t. with bleomycin 28 days later. At day 21 after bleomycin, all mice received either saline vehicle or IL13-PE by the intranasal route and histopatological analyses of whole lung samples were performed at day 28 after bleomycin. Intrapulmonary P. aeruginosa infection promoted a neutralizing IgG2A and IgA antibody response in BALF and serum. Surprisingly, histological analysis showed that a prior P. aeruginosa infection attenuated the development of bleomycin-induced pulmonary fibrosis, which was modestly further attenuated by the intranasal administration of IL13-PE. Although prior intranasal administration of IL13-PE failed to elicit an antibody response, the systemic administration of IL13-PE induced a strong neutralizing antibody response. However, the prior systemic sensitization of mice with IL13-PE did not inhibit the anti-fibrotic effect of IL13-PE in fibrotic mice.

CONCLUSIONS

Thus, IL13-PE therapy in pulmonary fibrosis works regardless of the presence of a humoral immune response to Pseudomonas exotoxin A. Interestingly, a prior infection with P. aeruginosa markedly attenuated the pulmonary fibrotic response suggesting that the immune elicitation by this pathogen exerts anti-fibrotic effects.

Epithelial-mesenchymal transition in primary human bronchial epithelial cells is Smad-dependent and enhanced by fibronectin and TNF-alpha

Background

Defective epithelial repair, excess fibroblasts and myofibroblasts, collagen overproduction and fibrosis occur in a number of respiratory diseases such as asthma, chronic obstructive pulmonary disease (COPD) and pulmonary fibrosis. Pathological conversion of epithelial cells into fibroblasts (epithelial-mesenchymal transition, EMT) has been proposed as a mechanism for the increased fibroblast numbers and has been demonstrated to occur in lung alveolar epithelial cells. Whether other airway cell types also have the capability to undergo EMT has been less explored so far. A better understanding of the full extent of EMT in airways, and the underlying mechanisms, can provide important insights into airway disease pathology and enable the development of new therapies. The main aim of this study was to test whether primary human bronchial epithelial cells are able to undergo EMT in vitro and to investigate the effect of various profibrotic factors in the process.

Results

Our data demonstrate that primary human bronchial epithelial cells (HBECs) are able to undergo EMT in response to transforming growth factor-beta 1 (TGF-β1), as revealed by typical morphological alterations and EMT marker progression at the RNA level by real-time quantitative polymerase chain reaction and, at the protein level, by western blot. By using pharmacological inhibitors we show that this is a Smad-dependent mechanism and is independent of extracellular signal-related kinase pathway activation. Additional cytokines and growth factors such as tumour necrosis factor-alpha (TNF-α), interleukin-1 beta (IL1β) and connective tissue growth factor (CTGF) were also tested, alone or in combination with TGF-β1. TNF-α markedly enhances the effect of TGF-β1 on EMT, whereas IL1β shows only a very weak effect and CTGF has no significant effect. We have also found that cell-matrix contact, in particular to fibronectin, an ECM component upregulated in fibrotic lesions, potentiates EMT in both human alveolar epithelial cells and HBECs. Furthermore, we also show that the collagen discoidin domain receptor 1 (DDR1), generally expressed in epithelial cells, is downregulated during the EMT of bronchial epithelium whereas DDR2 is unaffected. Our results also suggest that bone morphogenetic protein-4 is likely to have a context dependent effect during the EMT of HBECs, being able to induce the expression of EMT markers and, at the same time, to inhibit TGF-β induced epithelial transdifferentiation.

Conclusions

The results presented in this study provide additional insights into EMT, a potentially very important mechanism in fibrogenesis. We show that, in addition to alveolar epithelial type II cells, primary HBECs are also able to undergo EMT in vitro upon TGF-β1 stimulation via a primarily Smad 2/3 dependent mechanism. The effect of TGF-β1 is potentiated on fibronectin matrix and in the presence of TNF-α, representing a millieu reminiscent of fibrotic lesions. Our results can contribute to a better understanding of lung fibrosis and to the development of new therapeutic approaches.

Natural killer cells in infection and inflammation of the lung

The lungs are a major site of entry of pathogens into the body and thus require rapid and effective innate responses to prevent pathogens establishing infection and to limit their spread. Additionally, the immune response in the lung must be tightly regulated such that pathogens are cleared, but immunopathology and chronic inflammation are prevented. In this review, I consider the role of natural killer (NK) cells in pulmonary infection and inflammation, specifically their contributions to influenza, tuberculosis, asthma and chronic obstructive pulmonary disease (COPD), which are major causes of morbidity and mortality world-wide. Despite evidence of the importance of NK cells in these diseases, there are still major gaps in our understanding of how their function is regulated in this unique tissue environment. Understanding how different beneficial and detrimental effector functions of NK cells are triggered will be crucial if NK cells are to be exploited therapeutically in respiratory disease.

Electrophilic peroxisome proliferator-activated receptor-gamma ligands have potent antifibrotic effects in human lung fibroblasts

Pulmonary fibrosis is a progressive scarring disease with no effective treatment. Transforming growth factor (TGF)-beta is up-regulated in fibrotic diseases, where it stimulates differentiation of fibroblasts to myofibroblasts and production of excess extracellular matrix. Peroxisome proliferator-activated receptor (PPAR) gamma is a transcription factor that regulates adipogenesis, insulin sensitization, and inflammation. We report here that a novel PPARgamma ligand, 2-cyano-3,12-dioxoolean-1,9-dien-28-oic acid (CDDO), is a potent inhibitor of TGF-beta-stimulated differentiation of human lung fibroblasts to myofibroblasts, and suppresses up-regulation of alpha-smooth muscle actin, fibronectin, collagen, and the novel myofibroblast marker, calponin. The inhibitory concentration causing a 50% decrease in aSMA for CDDO was 20-fold lower than the endogenous PPARgamma ligand, 15-deoxy-Delta(12,14)-prostaglandin J(2) (15 d-PGJ(2)), and 400-fold lower than the synthetic ligand, rosiglitazone. Pharmacologic and genetic approaches were used to demonstrate that CDDO mediates its activity via a PPARgamma-independent pathway. CDDO and 15 d-PGJ(2) contain an alpha/beta unsaturated ketone, which acts as an electrophilic center that can form covalent bonds with cellular proteins. Prostaglandin A(1) and diphenyl diselenide, both strong electrophiles, also inhibit myofibroblast differentiation, but a structural analog of 15 d-PGJ(2) lacking the electrophilic center is much less potent. CDDO does not alter TGF-beta-induced Smad or AP-1 signaling, but does inhibit acetylation of CREB binding protein/p300, a critical coactivator in the transcriptional regulation of TGF-beta-responsive genes. Overall, these data indicate that certain PPARgamma ligands, and other small molecules with electrophilic centers, are potent inhibitors of critical TGF-beta-mediated profibrogenic activities through pathways independent of PPARgamma. As the inhibitory concentration causing a 50% decrease in aSMA for CDDO is 400-fold lower than that in rosiglitazone, the translational potential of CDDO for treatment of fibrotic diseases is high.

Protease-activated receptors and prostaglandins in inflammatory lung disease

Protease-activated receptors (PARs) are a novel family of G protein-coupled receptors. Signalling through PARs typically involves the cleavage of an extracellular region of the receptor by endogenous or exogenous proteases, which reveals a tethered ligand sequence capable of auto-activating the receptor. A considerable body of evidence has emerged over the past 20 years supporting a prominent role for PARs in a variety of human physiological and pathophysiological processes, and thus substantial attention has been directed towards developing drug-like molecules that activate or block PARs via non-proteolytic pathways. PARs are widely expressed within the respiratory tract, and their activation appears to exert significant modulatory influences on the level of bronchomotor tone, as well as on the inflammatory processes associated with a range of respiratory tract disorders. Nevertheless, there is debate as to whether the principal response to PAR activation is an augmentation or attenuation of airways inflammation. In this context, an important action of PAR activators may be to promote the generation and release of prostanoids, such as prostglandin E(2), which have well-established anti-inflammatory effects in the lung. In this review, we primarily focus on the relationship between PARs, prostaglandins and inflammatory processes in the lung, and highlight their potential role in selected respiratory tract disorders, including pulmonary fibrosis, asthma and chronic obstructive pulmonary disease.

New drugs for exacerbations of chronic obstructive pulmonary disease

Tobacco smoking is the dominant risk factor for chronic obstructive pulmonary disease (COPD), but viral and bacterial infections are the major causes of exacerbations in later stages of disease. Reactive oxygen species (ROS), pathogen-associated molecular patterns (PAMPs), and damage-associated molecular patterns (DAMPs) activate families of pattern recognition receptors (PRRs) that include the toll-like receptors (TLRs). This understanding has led to the hypothesis that COPD is an archetypal disease of innate immunity. COPD is characterised by abnormal response to injury, with altered barrier function of the respiratory tract, an acute phase reaction, and excessive activation of macrophages, neutrophils, and fibroblasts in the lung. The activated non-specific immune system then mediates the processes of inflammation and repair, fibrosis, and proteolysis. COPD is also associated with corticosteroid resistance, abnormal macrophage and T-cell populations in the airway, autoinflammation and autoimmunity, aberrant fibrosis, accelerated ageing, systemic and concomitant disease, and defective regeneration. Such concepts have been used to generate a range of molecular targets, and clinical trials are taking place to identify effective drugs for the prevention and treatment of COPD exacerbations.

Asbestosis: demonstration of distinctive interstitial fibroelastosis: a pilot study

Asbestosis has long been defined as a diffuse interstitial "fibrotic" process, in similarity to other chronic interstitial pulmonary diseases. To address the hypothesis (which was based on morphological nuances) that the interstitial connective tissue response in asbestosis may be fibroelastotic rather than fibrotic, a comparative characterization of the connective response in cases of asbestosis and other forms of interstitial lung disease was performed. Archival open lung biopsies or autopsy specimens of pulmonary diseases featuring interstitial connective tissue abnormalities (15 of asbestosis, 21 of organizing pneumonia, 15 usual interstitial pneumonitis/idiopathic pulmonary fibrosis [IPF], 9 organizing diffuse alveolar damage, 9 "nonspecific" interstitial pneumonitis, 4 sarcoidosis, 3 each of desquamative interstitial pneumonia and chronic amiodarone toxicity, 2 cryptogenic organizing pneumonias, and 1 each of chronic hypersensitivity pneumonitis and chronic eosinophilic pneumonitis [85 total]) were stained histochemically with hematoxylin and eosin, Perl's method, Gomori's trichrome procedure, and the Verhoeff-van Gieson technique. Representative subsets of the cases (n = 20) were also studied immunohistologically using an antibody to elastin. Fibroelastosis in each of the samples was assessed for the degree of response and its location using a 3-tiered scale. The degree of fibroelastosis in the 15 cases of asbestosis was variable, with the pattern being peribronchial and perivascular in all instances; at least 2 asbestos bodies were identified in fibroelastotic foci in each of the 15 cases as highlighted with Perl's stain. Forty-seven cases of nonasbestotic lung disease (71%) showed interstitial fibrosis with a variable (usually modest) amount of admixed elastic tissue; when present, elastic fibers were distributed in a diffuse interstitial pattern, with or without perivascular accentuation. All cases of IPF also showed areas of fibroelastosis, but those foci were confined to regions of overt "honeycomb" change. No asbestos bodies were seen in any disease except asbestosis, and a predominantly peribronchial pattern of fibroelastosis was not identified in any nonasbestotic interstitial lung disease in this study. The authors conclude that the types and patterns of pulmonary connective tissue response in interstitial lung diseases may provide additional diagnostic clues to the presence of asbestosis.

Bronchoalveoloar lavage fluid cytokines and chemokines as markers and predictors for the outcome of interstitial lung disease in systemic sclerosis patients

Introduction

Interstitial lung disease (ILD) is a frequent manifestation of systemic sclerosis (SSc), and cytokines can contribute to the disease pathology. The aim of the current study was to identify specific changes in cytokine levels that may serve as disease markers and possible targets for therapy.

Methods

Cytokines were measured with bioplex analysis in 38 bronchoalveolar fluids (BALFs) from 32 SSc patients (27 with alveolitis and 11 without alveolitis) and 26 control patients. In the case of SSc patients, cytokines were correlated with the respective bronchoalveolar lavage (BAL) cell differentiation, lung function, and thoracic HR-CT score. For 35 BALF samples derived from 29 SSc patients, follow-up investigations of clinical data, lung-function parameter, or thoracic HR-CT scans were available to evaluate the predictive capacity of BALF cytokines and chemokines.

Results

High IL-7 levels were characteristic of SSc-associated interstitial lung disease (ILD) and, in addition, when compared with ILD-negative SSc patients, ILD-positive SSc patients revealed higher IL-4, IL-6, IL-8, and CCL2 (MCP-1) BALF levels. High CCL2 and IL-8 BALF concentrations were associated with neutrophilic and mixed alveolitis. Cytokine levels of IL-4, IL-8, and CCL2 correlated negatively with lung-function parameters; CCL2 concentrations also correlated with HR-CT scores. High concentrations of several cytokines were associated with the progress of ILD and end-stage ILD. Univariate analyses revealed high IL-2 and tumor necrosis factor-alpha (TNF-α) levels as the best predictors for progressive disease, together with lung-function parameters, young age, and neutrophilic alveolitis. Multivariate analyses partially confirmed these results but did not sufficiently converge because of the limited number of patients.

Conclusions

The association of BALF cytokines with lung fibrosis and its progress suggests that cytokines contribute to the pathogenesis of ILD and hence could be regarded as potential therapeutic targets.