Early growth response gene 1-mediated apoptosis is essential for transforming growth factor beta1-induced pulmonary fibrosis

Pro-apoptotic Noxa is involved in ablative focal irradiation-induced lung injury

Although lung injury including fibrosis is a well‐documented side effect of lung irradiation, the mechanisms underlying its pathology are poorly understood. X‐rays are known to cause apoptosis in the alveolar epithelial cells of irradiated lungs, which results in fibrosis due to the proliferation and differentiation of fibroblasts and the deposition of collagen. Apoptosis and BH3‐only pro‐apoptotic proteins have been implicated in the pathogenesis of pulmonary fibrosis. Recently, we have established a clinically analogous experimental model that reflects focal high‐dose irradiation of the ipsilateral lung. The goal of this study was to elucidate the mechanism underlying radiation‐induced lung injury based on this model. A radiation dose of 90 Gy was focally delivered to the left lung of C57BL/6 mice for 14 days. About 9 days after irradiation, the mice began to show increased levels of the pro‐apoptotic protein Noxa in the irradiated lung alongside increased apoptosis and fibrosis. Suppression of Noxa expression by small interfering RNA protected cells from radiation‐induced cell death and decreased expression of fibrogenic markers. Furthermore, we showed that reactive oxygen species participate in Noxa‐mediated, radiation‐induced cell death. Taken together, our results show that Noxa is involved in X‐ray‐induced lung injury.

Plexin C1 deficiency permits synaptotagmin 7-mediated macrophage migration and enhances mammalian lung fibrosis

Pulmonary fibrosis is a progressive and often fatal condition that is believed to be partially orchestrated by macrophages. Mechanisms that control migration of these cells into and within the lung remain undefined. We evaluated the contributions of the semaphorin receptor, plexin C1 (PLXNC1), and the exocytic calcium sensor, synaptotagmin 7 (Syt7), in these processes. We evaluated the role of PLXNC1 in macrophage migration by using Boyden chambers and scratch tests, characterized its contribution to experimentally induced lung fibrosis in mice, and defined the mechanism for our observations. Our findings reveal that relative to control participants, patients with idiopathic pulmonary fibrosis demonstrate excessive monocyte migration and underexpression of PLXNC1 in the lungs and circulation, a finding that is recapitulated in the setting of scleroderma-related interstitial lung disease. Relative to wild type, PLXNC1^-/- mouse macrophages are excessively migratory, and PLXNC1^-/- mice show exacerbated collagen accumulation in response to either inhaled bleomycin or inducible lung targeted TGF-β1 overexpression. These findings are ameliorated by replacement of PLXNC1 on bone marrow-derived cells or by genetic deletion of Syt7. These data demonstrate the previously unrecognized observation that PLXNC1 deficiency permits Syt7-mediated macrophage migration and enhances mammalian lung fibrosis.-Peng, X., Moore, M., Mathur, A., Zhou, Y., Sun, H., Gan, Y., Herazo-Maya, J. D., Kaminski, N., Hu, X., Pan, H., Ryu, C., Osafo-Addo, A., Homer, R. J., Feghali-Bostwick, C., Fares, W. H., Gulati, M., Hu, B., Lee, C.-G., Elias, J. A., Herzog, E. L. Plexin C1 deficiency permits synaptotagmin 7-mediated macrophage migration and enhances mammalian lung fibrosis.

The vitronectin RGD motif regulates TGF-β-induced alveolar epithelial cell apoptosis

Transforming growth factor-β (TGF-β) is a critical driver of acute lung injury and fibrosis. Injury leads to activation of TGF-β, which regulates changes in the cellular and matrix makeup of the lung during the repair and fibrosis phase. TGF-β can also initiate alveolar epithelial cell (AEC) apoptosis. Injury leads to destruction of the laminin-rich basement membrane, which is replaced by a provisional matrix composed of arginine-glycine-aspartate (RGD) motif-containing plasma matrix proteins, including vitronectin and fibronectin. To determine the role of specific matrix proteins on TGF-β-induced apoptosis, we studied primary AECs cultured on different matrix conditions and utilized mice with deletion of vitronectin (Vtn(-/-)) or mice in which the vitronectin RGD motif is mutated to nonintegrin-binding arginine-glycine-glutamate (RGE) (Vtn(RGE/RGE)). We found that AECs cultured on fibronectin and vitronectin or in wild-type mouse serum are resistant to TGF-β-induced apoptosis. In contrast, AECs cultured on laminin or in serum from Vtn(-/-) or Vtn(RGE/RGE) mice undergo robust TGF-β-induced apoptosis. Plasminogen activator inhibitor-1 (PAI-1) sensitizes AECs to greater apoptosis by disrupting AEC engagement to vitronectin. Inhibition of integrin-associated signaling proteins augments AEC apoptosis. Mice with transgenic deletion of PAI-1 have less apoptosis after bleomycin, but deletion of vitronectin or disruption of the vitronectin RGD motif reverses this protection, suggesting that the proapoptotic function of PAI-1 is mediated through vitronectin inhibition. Collectively, these data suggest that integrin-matrix signaling is an important regulator of TGF-β-mediated AEC apoptosis and that PAI-1 functions as a natural regulator of this interaction.

Increased Expression of EGR-1 in Diabetic Human Adipose Tissue-Derived Mesenchymal Stem Cells Reduces Their Wound Healing Capacity

The prevalence of type 2 diabetes mellitus (T2DM), which leads to diabetic complications, has been increasing worldwide. The possible applications of T2DM-derived stem cells in cell therapy are limited because their characteristics are still not fully understood. In this study, we characterized adipose tissue-derived mesenchymal stem cells (AT-MSCs) from diabetic patients (dAT-MSCs) and found that insulin receptor substrate-1 (IRS-1) was highly phosphorylated at serine 636/639 in dAT-MSCs. Moreover, we found that early growth response factor-1 (EGR-1) and its target genes of PTEN and GGPS1 were highly expressed in dAT-MSCs in comparison to healthy donor-derived AT-MSCs (nAT-MSCs). We observed impaired wound healing after the injection of dAT-MSCs in the ischemic flap mouse model. The expressions of EGR-1 and its target genes were diminished by small hairpin RNA-targeted EGR-1 (shEGR-1) and treatment with a mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) inhibitor (PD98059). Importantly, dAT-MSCs with shEGR-1 were able to restore the wound healing ability in the mouse model. Interestingly, under hypoxic conditions, hypoxia-inducible factor-1α (HIF-1α) can bind to the EGR-1 promoter in dAT-MSCs, but not in nAT-MSCs. Together, these results demonstrate that the expression of EGR-1 was upregulated in dAT-MSCs through two pathways: the main regulatory pathway is the MAPK/ERK pathway, the other is mediated by HIF-1α through direct transcriptional activation at the promoter region of the EGR1 gene. Our study suggests that dAT-MSCs may contribute to microvascular damage and delay wound healing through the overexpression of EGR-1. Interrupting the expression of EGR-1 in dAT-MSCs may be a useful treatment for chronic wounds in diabetic patients.

Immunization against TGF-β1 reduces collagen deposition but increases sustained inflammation in a murine asthma model

Transforming growth factor (TGF)-β1 is involved in the processes of airway inflammation and remodeling; however, its reported roles in asthma pathogenesis are controversial. We sought both to investigate the effects of active immunization targeting TGF-β1 on allergen-induced airway inflammatory responses and to evaluate its possible application for asthma treatment. BALB/c mice were immunized with a virus-like-particle (VLP) vaccine presenting a TGF-β1 peptide. For the preventive intervention of acute allergic airway inflammation, immunization was conducted before sensitization and challenges with ovalbumin (OVA), and for the therapeutic treatment of chronic inflammatory responses, immunization was initiated after inflammatory responses were established. Preventive immunization with VLPs led to increased proinflammatory IL-4, IL-13, and IL-33 levels in the bronchoalveolar lavage fluids (BALF) with no significant effects on lung tissue inflammation and airway goblet cell hyperplasia. Therapeutic treatment showed that at 24 h after the fourth 2-day challenge with OVA following 2 intraperitoneal sensitizations, airway subepithelial collagen deposition was significantly ameliorated in vaccinated mice, whereas the lung histology and cytokine profile in the BALF were not changed. In contrast, after a 4-week recovery from the last OVA challenge, the vaccinated mice's collagen deposition remained reduced, but they sustained lung-tissue inflammation and goblet-cell hyperplasia; elevated IL-13, TNF, and IFN-γ levels in the BALF; and increased airway resistance, tissue resistance, and tissue elastance. In a conclusion, the role of TGF-β1 is complicated in allergic airway inflammatory responses. It is important to make a careful assessment in accordance with specific disease conditions when targeting TGF-β1 for a therapeutic purpose.

Self-assembled Micelle Interfering RNA for Effective and Safe Targeting of Dysregulated Genes in Pulmonary Fibrosis

The siRNA silencing approach has long been used as a method to regulate the expression of specific target genes in vitro and in vivo. However, the effectiveness of delivery and the nonspecific immune-stimulatory function of siRNA are the limiting factors for therapeutic applications of siRNAs. To overcome these limitations, we developed self-assembled micelle inhibitory RNA (SAMiRNA) nanoparticles made of individually biconjugated siRNAs with a hydrophilic polymer and lipid on their ends and characterized their stability, immune-stimulatory function, and in vivo silencing efficacy. SAMiRNAs form very stable nanoparticles with no significant degradation in size distribution and polydispersity index over 1 year. Overnight incubation of SAMiRNAs (3 μm) on murine peripheral blood mononuclear cells did not cause any significant elaboration of innate immune cytokines such as TNF-α, IL-12, or IL-6, whereas unmodified siRNAs or liposomes or liposome complexes significantly stimulated the expression of these cytokines. Last, the in vivo silencing efficacy of SAMiRNAs was evaluated by targeting amphiregulin and connective tissue growth factor in bleomycin or TGF-β transgenic animal models of pulmonary fibrosis. Intratracheal or intravenous delivery two or three times of amphiregulin or connective tissue growth factor SAMiRNAs significantly reduced the bleomycin- or TGF-β-stimulated collagen accumulation in the lung and substantially restored the lung function of TGF-β transgenic mice. This study demonstrates that SAMiRNA nanoparticle is a less toxic, stable siRNA silencing platform for efficient in vivo targeting of genes implicated in the pathogenesis of pulmonary fibrosis.

Targeting of Proteoglycan Synthesis Pathway: A New Strategy to Counteract Excessive Matrix Proteoglycan Deposition and Transforming Growth Factor-β1-Induced Fibrotic Phenotype in Lung Fibroblasts

Stimulation of proteoglycan (PG) synthesis and deposition plays an important role in the pathophysiology of fibrosis and is an early and dominant feature of pulmonary fibrosis. Transforming growth factor-β1 (TGF-β1) is a major cytokine associated with fibrosis that induces excessive synthesis of matrix proteins, particularly PGs. Owing to the importance of PGs in matrix assembly and in mediating cytokine and growth factor signaling, a strategy based on the inhibition of PG synthesis may prevent excessive matrix PG deposition and attenuates profibrotic effects of TGF-β1 in lung fibroblasts. Here, we showed that 4-MU4-deoxy-β-D-xylopyranoside, a competitive inhibitor of β4-galactosyltransferase7, inhibited PG synthesis and secretion in a dose-dependent manner by decreasing the level of both chondroitin/dermatan- and heparin-sulfate PG in primary lung fibroblasts. Importantly, 4-MU4-deoxy-xyloside was able to counteract TGF-β1-induced synthesis of PGs, activation of fibroblast proliferation and fibroblast-myofibroblast differentiation. Mechanistically, 4-MU4-deoxy-xyloside treatment inhibited TGF-β1-induced activation of canonical Smads2/3 signaling pathway in lung primary fibroblasts. The knockdown of β4-galactosyltransferase7 mimicked 4-MU4-deoxy-xyloside effects, indicating selective inhibition of β4-galactosyltransferase7 by this compound. Collectively, this study reveals the anti-fibrotic activity of 4-MU4-deoxy-xyloside and indicates that inhibition of PG synthesis represents a novel strategy for the treatment of lung fibrosis.

Camel Milk: Potential Utility as an Adjunctive Therapy to Peg-IFN/RBV in HCV-4 Infected Patients in Egypt

The present prospective study aims to investigate the potential therapeutic effect and the underlying mechanisms of drinking camel milk for 60 days as an adjunctive therapy to the standard treatment PEG/RBV. Twenty-five hepatitis C virus (HCV)-infected Egyptian patients, with mild to moderate parenchymal affection to mild cirrhosis were enrolled in this study after proper history taking and clinical examination. Their biomarkers were evaluated before and after the addition of camel milk. The improving effect of camel milk was reflected on the marked inhibition of the serum levels of the proinflammatory markers, viz., tumor necrosis factor-α, monocyte chemotactic protein-1, hyaluronic acid, and TGF-β1, besides PCR, AST, ALT, GGT, bilirubin, prothrombin time, INR, and alpha-fetoprotein. In addition, camel milk elevated significantly (P < 0.001) the serum levels of albumin, the antiapoptotic protein BCL-2, the total antioxidant capacity, interleukin-10, and vitamin D. In conclusion, our study revealed a regulatory function of camel milk on multiple parameters of inflammatory mediators, immunomodulators, antiapoptosis, and antioxidants, giving insight into the potential therapeutic benefit underlying the anti-HCV actions of camel milk. The limitations of the current study include the small sample size recruited and the failure to test it on cohorts with severe stages of hepatitis; like Child-Pugh stage C, and hepatocellular carcinoma.

Reciprocal regulation of TGF-β and reactive oxygen species: A perverse cycle for fibrosis

Transforming growth factor beta (TGF-β) is the most potent pro-fibrogenic cytokine and its expression is increased in almost all of fibrotic diseases. Although signaling through Smad pathway is believed to play a central role in TGF-β's fibrogenesis, emerging evidence indicates that reactive oxygen species (ROS) modulate TGF-β's signaling through different pathways including Smad pathway. TGF-β1 increases ROS production and suppresses antioxidant enzymes, leading to a redox imbalance. ROS, in turn, induce/activate TGF-β1 and mediate many of TGF-β's fibrogenic effects, forming a vicious cycle (see graphic flow chart on the right). Here, we review the current knowledge on the feed-forward mechanisms between TGF-β1 and ROS in the development of fibrosis. Therapeutics targeting TGF-β-induced and ROS-dependent cellular signaling represents a novel approach in the treatment of fibrotic disorders.

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TGF-β1 is the most potent ubiquitous profibrogenic cytokine.

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TGF- β 1 induces redox imbalance by ↑ ROS production and ↓ anti-oxidant defense system

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Redox imbalance, in turn, activates latent TGF-β1 and induces TGF-β1 expression.

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Redox imbalance also mediates many of TGF-β1’s profibrogenic effects

Translational models of lung disease

The 2nd Cross Company Respiratory Symposium (CCRS), held in Horsham, U.K. in 2012, brought together representatives from across the pharmaceutical industry with expert academics, in the common interest of improving the design and translational predictiveness of in vivo models of respiratory disease. Organized by the respiratory representatives of the European Federation of Pharmaceutical Industries and Federations (EFPIA) group of companies involved in the EU-funded project (U-BIOPRED), the aim of the symposium was to identify state-of-the-art improvements in the utility and design of models of respiratory disease, with a view to improving their translational potential and reducing wasteful animal usage. The respiratory research and development community is responding to the challenge of improving translation in several ways: greater collaboration and open sharing of data, careful selection of the species, complexity and chronicity of the models, improved practices in preclinical research, continued refinement in models of respiratory diseases and their sub-types, greater understanding of the biology underlying human respiratory diseases and their sub-types, and finally greater use of human (and especially disease-relevant) cells, tissues and explants. The present review highlights these initiatives, combining lessons from the symposium and papers published in Clinical Science arising from the symposium, with critiques of the models currently used in the settings of asthma, idiopathic pulmonary fibrosis and COPD. The ultimate hope is that this will contribute to a more rational, efficient and sustainable development of a range of new treatments for respiratory diseases that continue to cause substantial morbidity and mortality across the world.

Chitinase 3-like-1 and its receptors in Hermansky-Pudlak syndrome-associated lung disease

Hermansky-Pudlak syndrome (HPS) comprises a group of inherited disorders caused by mutations that alter the function of lysosome-related organelles. Pulmonary fibrosis is the major cause of morbidity and mortality in patients with subtypes HPS-1 and HPS-4, which both result from defects in biogenesis of lysosome-related organelle complex 3 (BLOC-3). The prototypic chitinase-like protein chitinase 3-like-1 (CHI3L1) plays a protective role in the lung by ameliorating cell death and stimulating fibroproliferative repair. Here, we demonstrated that circulating CHI3L1 levels are higher in HPS patients with pulmonary fibrosis compared with those who remain fibrosis free, and that these levels associate with disease severity. Using murine HPS models, we also determined that these animals have a defect in the ability of CHI3L1 to inhibit epithelial apoptosis but exhibit exaggerated CHI3L1-driven fibroproliferation, which together promote HPS fibrosis. These divergent responses resulted from differences in the trafficking and effector functions of two CHI3L1 receptors. Specifically, the enhanced sensitivity to apoptosis was due to abnormal localization of IL-13Rα2 as a consequence of dysfunctional BLOC-3-dependent membrane trafficking. In contrast, the fibrosis was due to interactions between CHI3L1 and the receptor CRTH2, which trafficked normally in BLOC-3 mutant HPS. These data demonstrate that CHI3L1-dependent pathways exacerbate pulmonary fibrosis and suggest CHI3L1 as a potential biomarker for pulmonary fibrosis progression and severity in HPS.

Conditional overexpression of TGFβ1 promotes pulmonary inflammation, apoptosis and mortality via TGFβR2 in the developing mouse lung

Background

Earlier studies have reported that transforming growth factor beta 1(TGFβ1) is a critical mediator of hyperoxia-induced acute lung injury (HALI) in developing lungs, leading to impaired alveolarization and a pulmonary phenotype of bronchopulmonary dysplasia (BPD). However, the mechanisms responsible for the TGFβ1-induced inflammatory signals that lead to cell death and abnormal alveolarization are poorly understood. We hypothesized that TGFβ1 signaling via TGFβR2 is necessary for the pathogenesis of the BPD pulmonary phenotype resulting from HALI.

Methods

We utilized lung epithelial cell-specific TGFβ1 overexpressing transgenic and TGFβR2 null mutant mice to evaluate the effects on neonatal mortality as well as pulmonary inflammation and apoptosis in developing lungs. Lung morphometry was performed to determine the impaired alveolarization and multicolor flow cytometry studies were performed to detect inflammatory macrophages and monocytes in lungs. Apoptotic cell death was measured with TUNEL assay, immunohistochemistry and western blotting and protein expression of angiogenic mediators were also analyzed.

Results

Our data reveals that increased TGFβ1 expression in newborn mice lungs leads to increased mortality, macrophage and immature monocyte infiltration, apoptotic cell death specifically in Type II alveolar epithelial cells (AECs), impaired alveolarization, and dysregulated angiogenic molecular markers.

Conclusions

Our study has demonstrated the potential role of inhibition of TGFβ1 signaling via TGFβR2 for improved survival, reduced inflammation and apoptosis that may provide insights for the development of potential therapeutic strategies targeted against HALI and BPD.

Ameliorative effect of N-acetyl cysteine on alpha-cypermethrin-induced pulmonary toxicity in male rats

Alpha-cypermethrin (α-CYP) is one of the most widely used insecticides. It may become an air pollutant and adversely affect the health. The present study was designed to determine whether treatment with N-acetyl cysteine (NAC), a well-known antioxidant, can be useful for the management of the deleterious effects of α-CYP on lung tissues. For this purpose, thirty two male rats were divided into four different groups (eight rats for each). Group (I) gavaged with corn oil (control group), group (II) gavaged daily with NAC (150 mg kg(-1) body weight), group (III) gavaged with α-CYP (14.5 mg kg(-1) body weight/day, dissolved in corn oil), group (IV) gavaged with NAC then with α-CYP 2 h later for 12 weeks. α-CYP significantly increased serum lactate dehydrogenase (LDH) and pulmonary malondialdehyde (MDA) levels, while decreased the activities of catalase (CAT) and superoxide dismutase (SOD) as well as reduced glutathione (GSH) content in lung. It also provoked higher levels of serum nitric oxide (NO), lung interleukin-1 beta (IL-1β), tumor necrosis factor-alpha (TNF-α), hydroxyproline (Hyp) as well as heme oxygenase-1 (HO-1), inducible nitric oxide synthase (iNOS) and nuclear factor-kappa B (NF-К B) gene expression in lung tissues. Histopathological alterations in lung with congestion, cellular infiltration, necrotic changes and thickening of inter-alveolar septa were observed following α-CYP administration. NAC reduced the adverse effects of α-CYP on lung tissues and improved the histological architecture of lung since it showed antioxidant, anti-inflammatory and antifibrotic effects on lung tissues. Our results indicate that NAC exerts a potent protective effect against α-CYP-induced oxidative damage and inflammation in lung tissues.

Insights into potential pathogenesis mechanisms associated with Campylobacter jejuni-induced abortion in ewes

Background

Campylobacter jejuni is commonly found in the gastrointestinal tract of many food-animals including sheep without causing visible clinical symptoms of disease. However, C. jejuni has been implicated in ovine abortion cases worldwide. Specifically, in the USA, the C. jejuni sheep abortion (SA) clone has been increasingly associated with sheep abortion. In vivo studies in sheep (the natural host) are needed to better characterize the virulence potential and pathogenesis of this clone.

Results

Pregnant ewes intravenously (IV) or orally inoculated with ovine or bovine abortion-associated C. jejuni SA clones exhibited partial or complete uterine prolapse with retained placenta, and abortion or stillbirth, whereas delivery of healthy lambs occurred in pregnant ewes inoculated with C. jejuni 81–176 or in the uninfected group. In sheep inoculated with the SA clone, histopathological lesions including suppurative necrotizing placentitis and/or endometritis coincided with: 1) increased apoptotic death of trophoblasts, 2) increased expression of the host genes (e.g. genes encoding interleukin IL-6 and IL-15) related to cellular necrosis and pro-inflammatory responses in uterus, and 3) decreased expression of the genes encoding GATA binding protein 6, chordin, and insulin-like 3 (INSL3) that account for embryonic development in uterus. Immunohistochemistry revealed localization of bacterial antigens in trophoblasts lining the chorioallantoic membrane of ewes inoculated with the C. jejuni SA clone.

Conclusions

The results showed that C. jejuni SA clones are capable of causing abortion or stillbirth in experimentally infected sheep. Furthermore, down- or up-regulation of specific genes in the uterus of infected pregnant ewes might implicate host genes in facilitating the disease progression. Since the C. jejuni SA strains share genotypic similarities with clones that have been isolated from human clinical cases of gastroenteritis, these strains might represent a potential public health risk.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-014-0274-8) contains supplementary material, which is available to authorized users.

Indications for distinct pathogenic mechanisms of asbestos and silica through gene expression profiling of the response of lung epithelial cells

Occupational and environmental exposures to airborne asbestos and silica are associated with the development of lung fibrosis in the forms of asbestosis and silicosis, respectively. However, both diseases display distinct pathologic presentations, likely associated with differences in gene expression induced by different mineral structures, composition and bio-persistent properties. We hypothesized that effects of mineral exposure in the airway epithelium may dictate deviating molecular events that may explain the different pathologies of asbestosis versus silicosis. Using robust gene expression-profiling in conjunction with in-depth pathway analysis, we assessed early (24 h) alterations in gene expression associated with crocidolite asbestos or cristobalite silica exposures in primary human bronchial epithelial cells (NHBEs). Observations were confirmed in an immortalized line (BEAS-2B) by QRT-PCR and protein assays. Utilization of overall gene expression, unsupervised hierarchical cluster analysis and integrated pathway analysis revealed gene alterations that were common to both minerals or unique to either mineral. Our findings reveal that both minerals had potent effects on genes governing cell adhesion/migration, inflammation, and cellular stress, key features of fibrosis. Asbestos exposure was most specifically associated with aberrant cell proliferation and carcinogenesis, whereas silica exposure was highly associated with additional inflammatory responses, as well as pattern recognition, and fibrogenesis. These findings illustrate the use of gene-profiling as a means to determine early molecular events that may dictate pathological processes induced by exogenous cellular insults. In addition, it is a useful approach for predicting the pathogenicity of potentially harmful materials.

Integrins: therapeutic targets in airway hyperresponsiveness and remodelling?

Integrins are a group of transmembrane heterodimeric proteins that mediate cell-cell and cell-extracellular matrix (ECM) interactions. Integrins have been under intense investigation for their role in inflammation in asthma. Clinical trials investigating integrin antagonists, however, have shown that these compounds are relatively ineffective. Airway remodelling is another pathological feature of asthma that is thought to make an important contribution to airway hyperresponsiveness (AHR) and lung function decline. Recent studies have identified integrins as important players in this process, with a particular role for β1 and αv integrins. Here we review the role of these integrins in airway remodelling and hyperresponsiveness in obstructive airway disease and their potential as pharmacological targets for future treatment.

Danger-associated molecular patterns and danger signals in idiopathic pulmonary fibrosis

The chronic debilitating lung disease, idiopathic pulmonary fibrosis (IPF), is characterized by a progressive decline in lung function, with a median mortality rate of 2-3 years after diagnosis. IPF is a disease of unknown cause and progression, and multiple pathways have been demonstrated to be activated in the lungs of these patients. A recent genome-wide association study of more than 1,000 patients with IPF identified genes linked to host defense, cell-cell adhesion, and DNA repair being altered due to fibrosis (Fingerlin, et al. Nat Genet 2013;45:613-620). Further emerging data suggest that the respiratory system may not be a truly sterile environment, and it exhibits an altered microbiome during fibrotic disease (Molyneaux and Maher. Eur Respir Rev 2013;22:376-381). These altered host defense mechanisms might explain the increased susceptibility of patients with IPF to microbial- and viral-induced exacerbations. Moreover, chronic epithelial injury and apoptosis are key features in IPF, which might be mediated, in part, by both pathogen-associated (PA) and danger-associated molecular patterns (MPs). Emerging data indicate that both PAMPs and danger-associated MPs contribute to apoptosis, but not necessarily in a manner that allows for the removal of dying cells, without further exacerbating inflammation. In contrast, both types of MPs drive cellular necrosis, leading to an exacerbation of lung injury and/or infection as the debris promotes a proinflammatory response. Thus, this Review focuses on the impact of MPs resulting from infection-driven apoptosis and necrosis during chronic fibrotic lung disease.

Chitinase 3-like 1 suppresses injury and promotes fibroproliferative responses in Mammalian lung fibrosis

Epithelial injury, alternative macrophage accumulation, and fibroproliferation coexist in the lungs of patients with idiopathic pulmonary fibrosis (IPF). Chitinase 3-like 1 (CHI3L1) is a prototypic chitinase-like protein that has been retained over species and evolutionary time. However, the regulation of CHI3L1 in IPF and its ability to regulate injury and/or fibroproliferative repair have not been fully defined. We demonstrated that CHI3L1 levels were elevated in patients with IPF. High levels of CHI3L1 are associated with progression--as defined by lung transplantation or death--and with scavenger receptor-expressing circulating monocytes in an ambulatory IPF population. In preterminal acute exacerbations of IPF, CHI3L1 levels were reduced and associated with increased levels of apoptosis. We also demonstrated that in bleomycin-treated mice, CHI3L1 expression was acutely and transiently decreased during the injury phase and returned toward and eventually exceeded baseline levels during the fibrotic phase. In this model, CHI3L1 played a protective role in injury by ameliorating inflammation and cell death, and a profibrotic role in the repair phase by augmenting alternative macrophage activation, fibroblast proliferation, and matrix deposition. Using three-dimensional culture system of a human fibroblast cell line, we found that CHI3L1 is sufficient to induce low grade myofibroblast transformation. In combination, these studies demonstrate that CHI3L1 is stimulated in IPF, where it represents an attempt to diminish injury and induce repair. They also demonstrate that high levels of CHI3L1 are associated with disease progression in ambulatory patients and that a failure of the CHI3L1 antiapoptotic response might contribute to preterminal disease exacerbations.

Systems biology approaches to understanding Epithelial Mesenchymal Transition (EMT) in mucosal remodeling and signaling in asthma

A pathological hallmark of asthma is chronic injury and repair, producing dysfunction of the epithelial barrier function. In this setting, increased oxidative stress, growth factor- and cytokine stimulation, together with extracellular matrix contact produces transcriptional reprogramming of the epithelial cell. This process results in epithelial-mesenchymal transition (EMT), a cellular state associated with loss of epithelial polarity, expression of mesenchymal markers, enhanced mobility and extracellular matrix remodeling. As a result, the cellular biology of the EMT state produces characteristic changes seen in severe, refractory asthma: myofibroblast expansion, epithelial trans-differentiation and subepithelial fibrosis. EMT also induces profound changes in epithelial responsiveness that affects innate immune signaling that may have impact on the adaptive immune response and effectiveness of glucocorticoid therapy in severe asthma. We discuss how this complex phenotype is beginning to be understood using systems biology-level approaches through perturbations coupled with high throughput profiling and computational modeling. Understanding the distinct changes induced by EMT at the systems level may provide translational strategies to reverse the altered signaling and physiology of refractory asthma.

CD4+CD25+FoxP3+ Regulatory Tregs inhibit fibrocyte recruitment and fibrosis via suppression of FGF-9 production in the TGF-β1 exposed murine lung

Pulmonary fibrosis is a difficult to treat, often fatal disease whose pathogenesis involves dysregulated TGF-β1 signaling. CD4+CD25+FoxP3+ Regulatory T cells (“Tregs”) exert important effects on host tolerance and arise from naïve CD4+ lymphocytes in response to TGF-β1. However, the precise contribution of Tregs to experimentally induced murine lung fibrosis remains unclear. We sought to better understand the role of Tregs in this context. Using a model of fibrosis caused by lung specific, doxycycline inducible overexpression of the bioactive form of the human TGF-β1 gene we find that Tregs accumulate in the lung parenchyma within 5 days of transgene activation and that this enhancement persists to at least 14 days. Anti-CD25 Antibody mediated depletion of Tregs causes increased accumulation of soluble collagen and of intrapulmonary CD45+Col Iα1 fibrocytes. These effects are accompanied by enhanced local concentrations of the classical inflammatory mediators CD40L, TNF-α, and IL-1α, along with the neuroimmune molecule fibroblast growth factor 9 (FGF-9, also known as “glial activating factor”). FGF-9 expression localizes to parenchymal cells and alveolar macrophages in this model and antibody mediated neutralization of FGF-9 results in attenuated detection of intrapulmonary collagen and fibrocytes without affecting Treg quantities. These data indicate that CD4+CD25+FoxP3+ Tregs attenuate TGF-β1 induced lung fibrosis and fibrocyte accumulation in part via suppression of FGF-9.

Egr-1 mediates chronic hypoxia-induced renal interstitial fibrosis via the PKC/ERK pathway

BACKGROUND

Chronic hypoxia-induced epithelial-to-mesenchymal transition (EMT) is a crucial process in renal fibrogenesis. Egr-1, as a transcription factor, has been proven to be important in promoting EMT. However, whether it functions in hypoxia-induced renal tubular EMT has not been fully elucidated.

METHODS

Egr-1 were detected at mRNA and protein levels by qPCR and Western blot analysis respectively after renal epithelial cells were subjected to hypoxia treatment. Meanwhile, EMT phenotype was also observed through identification of relevant EMT-specific markers. siRNA was used to knock down Egr-1 expression and subsequent changes were observed. Specific PKC and MAPK/ERK inhibitors were employed to determine the molecular signaling pathway involved in Egr-1-mediated EMT phenotype. In vivo assays using rat remnant kidney model were used to validate the in vitro results. Furthermore, Egr-1 expression was examined in the samples of CKD patients with the clinical relevance revealed.

RESULTS

Hypoxia treatment enhanced the mRNA and protein levels of Egr-1 in HK-2 cells, which was accompanied by a reduced expression of the epithelial marker E-cadherin and an enhanced expression of the mesenchymal marker Fsp-1. Downregulation of Egr-1 with siRNA reversed hypoxia-induced EMT. Using the specific inhibitors to protein kinase C (calphostin C) or MAPK/ERK (PD98059), we identified that hypoxia induced Egr-1 expression through the PKC/ERK pathway. In addition, the upregulation of Egr-1 raised endogenous Snail levels, and the downregulation of Snail inhibited Egr-1-mediated EMT in HK-2 cells. Through in vivo assays using rat remnant kidney and CKD patients' kidney tissues, we found that Egr-1 and Snail were overexpressed in tubular epithelial cells with EMT.

CONCLUSION

Egr-1 may be an important regulator of the development of renal tubular EMT induced by hypoxia through the PKC/ERK pathway and the activation of Snail. Targeting Egr-1 expression or activity might be a novel therapeutic strategy to control renal fibrosis.

Modifiers of TGF-β1 effector function as novel therapeutic targets of pulmonary fibrosis

Pulmonary fibrosis is a fatal progressive disease with no effective therapy. Transforming growth factor (TGF)-β1 has long been regarded as a central mediator of tissue fibrosis that involves multiple organs including skin, liver, kidney, and lung. Thus, TGF-β1 and its signaling pathways have been attractive therapeutic targets for the development of antifibrotic drugs. However, the essential biological functions of TGF-β1 in maintaining normal immune and cellular homeostasis significantly limit the effectiveness of TGF-β1-directed therapeutic approaches. Thus, targeting downstream mediators or signaling molecules of TGF-β1 could be an alternative approach that selectively inhibits TGF-β1-stimulated fibrotic tissue response while preserving major physiological function of TGF-β1. Recent studies from our laboratory revealed that TGF-β1 crosstalk with epidermal growth factor receptor (EGFR) signaling by induction of amphiregulin, a ligand of EGFR, plays a critical role in the development or progression of pulmonary fibrosis. In addition, chitotriosidase, a true chitinase in humans, has been identified to have modulating capacity of TGF-β1 signaling as a new biomarker and therapeutic target of scleroderma-associated pulmonary fibrosis. These newly identified modifiers of TGF-β1 effector function significantly enhance the effectiveness and flexibility in targeting pulmonary fibrosis in which TGF-β1 plays a significant role.

Matrix biology of idiopathic pulmonary fibrosis: a workshop report of the national heart, lung, and blood institute

A hallmark of idiopathic pulmonary fibrosis (IPF) is excessive and disordered deposition of extracellular matrix. Although the lung extracellular matrix normally plays an essential role in development and maintenance of lung tissue through reciprocal interactions with resident cells, the disordered matrix in the diseased lung is increasingly recognized as an active and important contributor to IPF pathogenesis. This working group summary from a recently conducted National Heart, Lung, and Blood Institute strategic planning workshop for IPF research highlights recent advances, challenges, and opportunities in the study of matrix biology in IPF. Particular attention is given to the composition and mechanical properties of the matrix in normal and diseased lungs, and the biochemical and biomechanical influences exerted by pathological matrix. Recently developed model systems are also summarized as key tools for advancing our understanding of matrix biology in IPF. Emerging approaches to therapeutically target the matrix in preclinical and clinical settings are discussed, as are important concepts, such as alterations of the matrix with aging and the potential for the resolution of fibrosis. Specific recommendations for future studies in matrix biology of IPF are also proposed.

Impact of S-Adenosylmethionine Decarboxylase 1 on Pulmonary Vascular Remodeling

Background—

Pulmonary hypertension (PH) is a life-threatening disease characterized by vascular remodeling and increased pulmonary vascular resistance. Chronic alveolar hypoxia in animals is often used to decipher pathways being regulated in PH. Here, we aimed to investigate whether chronic hypoxia–induced PH in mice can be reversed by reoxygenation and whether possible regression can be used to identify pathways activated during the reversal and development of PH by genome-wide screening.

Methods and Results—

Mice exposed to chronic hypoxia (21 days, 10% O 2 ) were reoxygenated for up to 42 days. Full reversal of PH during reoxygenation was evident by normalized right ventricular pressure, right heart hypertrophy, and muscularization of small pulmonary vessels. Microarray analysis from these mice revealed s-adenosylmethionine decarboxylase 1 (AMD-1) as one of the most downregulated genes. In situ hybridization localized AMD-1 in pulmonary vessels. AMD-1 silencing decreased the proliferation of pulmonary arterial smooth muscle cells and diminished phospholipase Cγ1 phosphorylation. Compared with the respective controls, AMD-1 depletion by heterozygous in vivo knockout or pharmacological inhibition attenuated PH during chronic hypoxia. A detailed molecular approach including promoter analysis showed that AMD-1 could be regulated by early growth response 1, transcription factor, as a consequence of epidermal growth factor stimulation. Key findings from the animal model were confirmed in human idiopathic pulmonary arterial hypertension.

Conclusions—

Our study indicates that genome-wide screening in mice from a PH model in which full reversal of PH occurs can be useful to identify potential key candidates for the reversal and development of PH. Targeting AMD-1 may represent a promising strategy for PH therapy.

Network and matrix analysis of the respiratory disease interactome

BACKGROUND

Although respiratory diseases exhibit in a wide array of clinical manifestations, certain respiratory diseases may share related genetic mechanisms or may be influenced by similar chemical stimuli. Here we explore and infer relationships among genes, diseases, and chemicals using network and matrix based clustering methods.

RESULTS

In order to better understand and elucidate these shared genetic mechanisms and chemical relationships we analyzed a comprehensive collection of gene, disease, and chemical relationships pertinent to respiratory disease, using network and matrix based analysis approaches. Our methods enabled us to analyze relationships and make biological inferences among over 200 different respiratory and related diseases, involving thousands of gene-chemical-disease relationships.

CONCLUSIONS

The resulting networks provided insight into shared mechanisms of respiratory disease and in some cases suggest novel targets or repurposed drug strategies.

Future directions in idiopathic pulmonary fibrosis research. An NHLBI workshop report

The median survival of patients with idiopathic pulmonary fibrosis (IPF) continues to be approximately 3 years from the time of diagnosis, underscoring the lack of effective medical therapies for this disease. In the United States alone, approximately 40,000 patients die of this disease annually. In November 2012, the NHLBI held a workshop aimed at coordinating research efforts and accelerating the development of IPF therapies. Basic, translational, and clinical researchers gathered with representatives from the NHLBI, patient advocacy groups, pharmaceutical companies, and the U.S. Food and Drug Administration to review the current state of IPF research and identify priority areas, opportunities for collaborations, and directions for future research. The workshop was organized into groups that were tasked with assessing and making recommendations to promote progress in one of the following six critical areas of research: (1) biology of alveolar epithelial injury and aberrant repair; (2) role of extracellular matrix; (3) preclinical modeling; (4) role of inflammation and immunity; (5) genetic, epigenetic, and environmental determinants; (6) translation of discoveries into diagnostics and therapeutics. The workshop recommendations provide a basis for directing future research and strategic planning by scientific, professional, and patient communities and the NHLBI.

Absence of c-Jun NH2-terminal kinase 1 protects against house dust mite-induced pulmonary remodeling but not airway hyperresponsiveness and inflammation

Chronic allergic asthma leads to airway remodeling and subepithelial fibrosis via mechanisms not fully understood. Airway remodeling is amplified by profibrotic mediators, such as transforming growth factor-β1 (TGF-β1), which plays a cardinal role in various models of fibrosis. We recently have identified a critical role for c-Jun-NH2-terminal-kinase (JNK) 1 in augmenting the profibrotic effects of TGF-β1, linked to epithelial-to-mesenchymal transition of airway epithelial cells. To examine the role of JNK1 in house dust mite (HDM)-induced airway remodeling, we induced allergic airway inflammation in wild-type (WT) and JNK1-/- mice by intranasal administration of HDM extract. WT and JNK1-/- mice were sensitized with intranasal aspirations of HDM extract for 15 days over 3 wk. HDM caused similar increases in airway hyperresponsiveness, mucus metaplasia, and airway inflammation in WT and JNK1-/- mice. In addition, the profibrotic cytokine TGF-β1 and phosphorylation of Smad3 were equally increased in WT and JNK1-/- mice. In contrast, increases in collagen content in lung tissue induced by HDM were significantly attenuated in JNK1-/- mice compared with WT controls. Furthermore HDM-induced increases of α-smooth muscle actin (α-SMA) protein and mRNA expression as well as the mesenchymal markers high-mobility group AT-hook 2 and collagen1A1 in WT mice were attenuated in JNK1-/- mice. The let-7 family of microRNAs has previously been linked to fibrosis. HDM exposure in WT mice and primary lung epithelial cells resulted in striking decreases in let-7g miRNA that were not observed in mice or primary lung epithelial cells lacking JNK1-/- mice. Overexpression of let-7g in lung epithelial cells reversed the HDM-induced increases in α-SMA. Collectively, these findings demonstrate an important requirement for JNK1 in promoting HDM-induced fibrotic airway remodeling.

TGF-β1 as a therapeutic target for pulmonary fibrosis and COPD

TGF-β1 is a multifunctional molecule that is expressed in an exaggerated fashion during injury, inflammation and repair. Its expression is dysregulated in lung tissues from patients with pulmonary fibrosis and chronic obstructive pulmonary disease. In animal models, introduction of TGF-β1 expression in the lung causes prominent tissue fibrosis and alveolar destruction. On the other hand, the exaggerated production of TGF-β1, an inability to activate TGF-β1 or a block in TGF-β1 signaling have all been associated with the development of emphysematous pulmonary lesions. A number of studies have demonstrated that TGF-β1 is a major player in the pathogenesis of pulmonary fibrosis and emphysema. In this review, we discuss how TGF-β1 expression is regulated and mechanistically related to the development of tissue fibrosis and emphysema in experimental animal models and humans. We further highlight potential therapeutic options that control TGF-β1-associated genes or signals to restore extracellular matrix homeostasis in which TGF-β1 plays a central role.

Leukotriene C4 aggravates bleomycin-induced pulmonary fibrosis in mice

BACKGROUND AND OBJECTIVE

Synthesis of cysteinyl leukotrienes (cys-LT) is thought to cause inflammatory disorders such as bronchial asthma and allergic rhinitis. Recent reports have suggested that leukotriene C4 (LTC4 ) is an important regulator of pulmonary fibrosis. This study examined the effect of LTC4 in LTC4 synthase-overexpressed transgenic mice with bleomycin-induced pulmonary fibrosis. The function of lung-derived fibroblasts from transgenic mice was also investigated.

METHODS

Bleomycin was administrated to transgenic mice and wild-type (WT) mice by intratracheal instillation. Concentrations of interleukin (IL)-4 and -13, interferon-γ, and transforming growth factor (TGF)-β1 in bronchoalveolar lavage fluid were measured 1, 3, 7 and 14 days after the administration of bleomycin. Lung tissue was examined histopathologically on day 14. In addition, lung-derived fibroblasts from transgenic and WT mice were cultured for 7 days. Expression of TGF-β1 mRNA was measured by real-time polymerase chain reaction.

RESULTS

Both the pathological scores for pulmonary fibrosis (3.8 ± 0.4 vs 2.0 ± 0.1, P < 0.05) and the levels of IL-4 (12.1 ± 2.3 vs <7.8 pg/mL, P < 0.05), IL-13 (26.5 ± 5.2 vs <7.8 pg/mL, P < 0.01) and TGF-β1 (211.1 ± 30.2 vs 21.3 ± 1.2 pg/mL, P < 0.01) on day 14 were significantly greater in transgenic than in WT mice. Furthermore, the reduction of LTC4 by pranlukast hydrate, a cys-LT1 receptor antagonist, in fibroblasts from transgenic significantly (P < 0.05) decreased the expression of TGF-β1 mRNA (by ∼50%) compared with those from WT mice.

CONCLUSIONS

Overexpression of LTC4 , amplifies bleomycin-induced pulmonary fibrosis in mice. Our findings suggest a role for LTC4 in lung fibrosis.

Syndecan-2 exerts antifibrotic effects by promoting caveolin-1-mediated transforming growth factor-β receptor I internalization and inhibiting transforming growth factor-β1 signaling

RATIONALE

Alveolar transforming growth factor (TGF)-β1 signaling and expression of TGF-β1 target genes are increased in patients with idiopathic pulmonary fibrosis (IPF) and in animal models of pulmonary fibrosis. Internalization and degradation of TGF-β receptor TβRI inhibits TGF-β signaling and could attenuate development of experimental lung fibrosis.

OBJECTIVES

To demonstrate that after experimental lung injury, human syndecan-2 confers antifibrotic effects by inhibiting TGF-β1 signaling in alveolar epithelial cells.

METHODS

Microarray assays were performed to identify genes differentially expressed in alveolar macrophages of patients with IPF versus control subjects. Transgenic mice that constitutively overexpress human syndecan-2 in macrophages were developed to test the antifibrotic properties of syndecan-2. In vitro assays were performed to determine syndecan-2-dependent changes in epithelial cell TGF-β1 signaling, TGF-β1, and TβRI internalization and apoptosis. Wild-type mice were treated with recombinant human syndecan-2 during the fibrotic phase of bleomycin-induced lung injury.

MEASUREMENTS AND MAIN RESULTS

We observed significant increases in alveolar macrophage syndecan-2 levels in patients with IPF. Macrophage-specific overexpression of human syndecan-2 in transgenic mice conferred antifibrotic effects after lung injury by inhibiting TGF-β1 signaling and downstream expression of TGF-β1 target genes, reducing extracellular matrix production and alveolar epithelial cell apoptosis. In vitro, syndecan-2 promoted caveolin-1-dependent internalization of TGF-β1 and TβRI in alveolar epithelial cells, which inhibited TGF-β1 signaling and epithelial cell apoptosis. Therapeutic administration of human syndecan-2 abrogated lung fibrosis in mice.

CONCLUSIONS

Alveolar macrophage syndecan-2 exerts antifibrotic effects by promoting caveolin-1-dependent TGF-β1 and TβRI internalization and inhibiting TGF-β1 signaling in alveolar epithelial cells. Hence, molecules that facilitate TβRI degradation via endocytosis represent potential therapies for pulmonary fibrosis.

Decreased c-Abl activity in PC-3 and LNCaP prostate cancer cells overexpressing the early growth response-1 protein

Early growth response-1 (Egr-1) and the non-receptor protein tyrosine kinase (c-Abl) are 2 response genes that can act as regulators of cell growth and apoptosis in response to stress. Both Egr-1 and c-Abl regulate cell proliferation and survival in different types of cancer cells. To study the effect of overexpression of EGR-1 on the activity of c-Abl in prostate cancer cells, human PC-3 and LNCaP cells were transfected with a control vector or a vector containing the murine Egr-1 cDNA and assessed for the expression of the c-Abl gene. Cells overexpressing Egr-1 were studied with respect to apoptosis (Annexin V)/DEVDase activity, Egr-1/c-Abl activation (western blotting) and cell proliferation (MTT assay). The cells were exposed to tumor necrosis factor α (TNF-α), a known inductor of Egr-1, to c-Abl inhibitor STI-571 and to small interfering RNA (siRNA)-Egr-1, respectively. The results from our studies strongly suggest that overexpression of Egr-1 decreased c-Abl activity independent of endogenous Egr-1 inhibition by siRNA-Egr-1.

Growth factors and cytokines in acute lung injury

Cytokines and growth factors play an integral role in the maintenance of immune homeostasis, the generation of protective immunity, and lung reparative processes. However, the dysregulated expression of cytokines and growth factors in response to infectious or noxious insults can initiate and perpetuate deleterious lung inflammation and fibroproliferation. In this article, we will comprehensively review the contribution of individual cytokines and growth factors and cytokine networks to key pathophysiological events in human and experimental acute lung injury (ALI), including inflammatory cell recruitment and activation, alveolar epithelial injury and repair, angiogenesis, and matrix deposition and remodeling. The application of cytokines/growth factors as prognostic indicators and therapeutic targets in human ALI is explored.

Animal models of fibrotic lung disease

Interstitial lung fibrosis can develop as a consequence of occupational or medical exposure, as a result of genetic defects, and after trauma or acute lung injury leading to fibroproliferative acute respiratory distress syndrome, or it can develop in an idiopathic manner. The pathogenesis of each form of lung fibrosis remains poorly understood. They each result in a progressive loss of lung function with increasing dyspnea, and most forms ultimately result in mortality. To better understand the pathogenesis of lung fibrotic disorders, multiple animal models have been developed. This review summarizes the common and emerging models of lung fibrosis to highlight their usefulness in understanding the cell-cell and soluble mediator interactions that drive fibrotic responses. Recent advances have allowed for the development of models to study targeted injuries of Type II alveolar epithelial cells, fibroblastic autonomous effects, and targeted genetic defects. Repetitive dosing in some models has more closely mimicked the pathology of human fibrotic lung disease. We also have a much better understanding of the fact that the aged lung has increased susceptibility to fibrosis. Each of the models reviewed in this report offers a powerful tool for studying some aspect of fibrotic lung disease.

Molecular basis of organ fibrosis: potential therapeutic approaches

Fibrosis, a non-physiological wound healing in multiple organs, is associated with end-stage pathological symptoms of a wide variety of vascular injury and inflammation related diseases. In response to chemical, immunological and physical insults, the body's defense system and matrix synthetic machinery respond to healing the wound and maintain tissue homeostasis. However, uncontrolled wound healing leads to scarring or fibrosis, a pathological condition characterized by excessive synthesis and accumulation of extracellular matrix proteins, loss of tissue homeostasis and organ failure. Understanding the actual cause of pathological wound healing and identification of igniter(s) of fibrogenesis would be helpful to design novel therapeutic approaches to control pathological wound healing and to prevent fibrosis related morbidity and mortality. In this article, we review the significance of a few key cytokines (TGF-β, IFN-γ, IL-10) transcriptional activators (Sp1, Egr-1, Smad3), repressors (Smad7, Fli-1, PPAR-γ, p53, Klotho) and epigenetic modulators (acetyltransferase, methyltransferases, deacetylases, microRNAs) involved in major matrix protein collagen synthesis under pathological stage of wound healing, and the potentiality of these regulators as therapeutic targets for fibrosis treatment. The significance of endothelial to mesenchymal transition (EndMT) and senescence, two newly emerged fields in fibrosis research, has also been discussed.

Cross-talk between transforming growth factor-β₁ and muscarinic M₂ receptors augments airway smooth muscle proliferation

Transforming growth factor-β₁ (TGF-β₁) is a central mediator in tissue remodeling processes, including fibrosis and airway smooth muscle (ASM) hyperplasia, as observed in asthma. The mechanisms underlying this response, however, remain unclear because TGF-β₁ exerts only weak mitogenic effects on ASM cells. In this study, we hypothesized that the mitogenic effect of TGF-β₁ on ASM is indirect and requires prolonged exposure to allow for extracellular matrix (ECM) deposition. To address this hypothesis, we investigated the effects of acute and prolonged treatment with TGF-β₁, alone and in combination with the muscarinic receptor agonist methacholine, on human ASM cell proliferation. Acutely, TGF-β₁ exerted no mitogenic effect. However, prolonged treatment (for 7 d) with TGF-β₁ increased ASM cell proliferation and potentiated the platelet-derived growth factor-induced mitogenic response. Muscarinic receptor stimulation with methacholine synergistically enhanced the effect of TGF-β₁. Interestingly, the integrin-blocking peptide Arg-Gly-Asp-Ser, as well as integrin α5β1 function-blocking antibodies, inhibited the effects of TGF-β₁ and its combination with methacholine on cell proliferation. Accordingly, prolonged treatment with TGF-β₁ increased fibronectin expression, which was also synergistically enhanced by methacholine. The synergistic effects of methacholine on TGF-β₁-induced proliferation were reduced by the long-acting muscarinic receptor antagonist tiotropium and the M₂ receptor subtype-selective antagonist gallamine, but not the M₃-selective antagonist DAU5884. In line with these findings, the irreversible Gi protein inhibitor pertussis toxin also prevented the potentiation of TGF-β₁-induced proliferation by methacholine. We conclude that prolonged exposure to TGF-β₁ enhances ASM cell proliferation, which is mediated by extracellular matrix-integrin interactions, and which can be enhanced by muscarinic M₂ receptor stimulation.

Rapamycin regulates connective tissue growth factor expression of lung epithelial cells via phosphoinositide 3-kinase

The pathogenesis of idiopathic pulmonary fibrosis (IPF) remains largely unknown. It is believed that IPF is mainly driven by activated alveolar epithelial cells that have a compromised migration capacity, and that also produce substances (such as connective tissue growth factor, CTGF) that contribute to fibroblast activation and matrix protein accumulation. Because the mechanisms regulating these processes are unclear, the aim of this study was to determine the role of rapamycin in regulating epithelial cell migration and CTGF expression. Transformed epithelial cell line A549 and normal human pulmonary alveolar or bronchial epithelial cells were cultured in regular medium or medium containing rapamycin. Real time reverse transcriptase polymerase chain reaction was employed to determine CTGF mRNA expression. Western blotting and an enzyme-linked immunosorbent assay were used for detecting CTGF protein. Wound healing and migration assays were used to determine the cell migration potential. Transforming growth factor (TGF)-β type I receptor (TβRI) inhibitor, SB431542 and phosphoinositide 3-kinase (PI3K) inhibitor, LY294002 were used to determine rapamycin's mechanism of action. It was found that treatment of A549 and normal human alveolar or bronchial epithelial cells with rapamycin significantly promoted basal or TGF-β1 induced CTGF expression. LY294002, not SB431542 attenuated the promotional effect of rapamycin on CTGF expression. Cell mobility was not affected by rapamycin in wound healing and migration assays. These data suggest rapamycin has a profibrotic effect in vitro and underscore the potential of combined therapeutic approach with PI3K and mammalian target of rapamycin inhibitors for the treatment of animal or human lung fibrosis.

Hepatocyte growth factor is an attractive target for the treatment of pulmonary fibrosis

INTRODUCTION

Pulmonary fibrosis (PF) is a progressive fatal disorder and is characterized by alveolar epithelial injury, myofibroblast proliferation, and extracellular matrix remodeling, resulting in irreversible distortion of lung's architecture. Available therapies are associated with side effects and show restricted efficacy. Therefore, there is an urgent need to find a therapeutic solution to PF. Therapeutic strategies interfering myofibroblast expansion, apoptosis of epithelial and endothelial cells might be beneficial for treatment of PF. Hepatocyte growth factor (HGF), a pleiotropic growth factor, plays an important role in lung development, inflammation, repair, and regeneration. In animal model of PF, administration of recombinant HGF protein or ectopic HGF expression ameliorates fibrosis.

AREAS COVERED

The focus of this review is to highlight HGF as a promising therapeutic approach for the treatment of PF. The review discusses the currently available treatment option for PF as well as highlights the possible beneficial effect of HGF as a drug target.

EXPERT OPINION

HGF with its anti-fibrotic effect provides a promising new therapeutic approach by protecting lung from fibrotic remodeling and also promoting normal regeneration of lung. The development of HGF mimetics may provide a potential attractive therapy for treatment of this devastating and complex disease.

Activation of Egr-1 in human lung epithelial cells exposed to silica through MAPKs signaling pathways

The alveolar type II epithelial cell, regarded historically as a key target cell in initial injury by silica, now appears to be important in both defense from lung damage as well as elaboration of chemokines and cytokines. The molecular basis for silica-induced epithelial cell injury is poorly understood. In this study we explored the activation of nuclear factor Egr-1 and related signal pathway. Human II alveolar epithelial line A549 cells were exposed to silica for indicated time to assay the expression and activation of Egr-1 and upstream MAPKs. Immunofluorescence, western-blot techniques, RT-PCR, Electrophoretic mobility shift assay (EMSA), transient transfection assay, kinase inhibitor experiments were performed. It was found that the expression of Egr-1 at mRNA and protein level was significantly increased in A549 cells after administration with silica and the activity of Egr-1 peaked by silica treatment for 60 minutes. Furthermore, phosphorylated-ERK1/2, P38 MAPKs (the upstream kinase of Egr-1) ballooned during 15-30minutes, 30-60minutes respectively after silica exposure in A549 cells. By administration of ERK1/2, P38 inhibitor, the expression and transcription of Egr-1 were both markedly decreased. But PKC inhibitor did not prevent the increase of Egr-1. These results indicated Egr-1 played a critical role in silica-induced pulmonary fibrosis in an ERK1/2, P38 MAPKs-dependent manner, which suggests Egr-1 is an essential regulator in silicosis, and underlines a new molecular mechanism for fibrosis induced by silica.

Fibrosis of two: Epithelial cell-fibroblast interactions in pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is characterized by the progressive and ultimately fatal accumulation of fibroblasts and extracellular matrix in the lung that distorts its architecture and compromises its function. IPF is now thought to result from wound-healing processes that, although initiated to protect the host from injurious environmental stimuli, lead to pathological fibrosis due to these processes becoming aberrant or over-exuberant. Although the environmental stimuli that trigger IPF remain to be identified, recent evidence suggests that they initially injure the alveolar epithelium. Repetitive cycles of epithelial injury and resultant alveolar epithelial cell death provoke the migration, proliferation, activation and myofibroblast differentiation of fibroblasts, causing the accumulation of these cells and the extracellular matrix that they synthesize. In turn, these activated fibroblasts induce further alveolar epithelial cell injury and death, thereby creating a vicious cycle of pro-fibrotic epithelial cell-fibroblast interactions. Though other cell types certainly make important contributions, we focus here on the "pas de deux" (steps of two), or perhaps more appropriate to IPF pathogenesis, the "folie à deux" (madness of two) of epithelial cells and fibroblasts that drives the progression of pulmonary fibrosis. We describe the signaling molecules that mediate the interactions of these cell types in their "fibrosis of two", including transforming growth factor-β, connective tissue growth factor, sonic hedgehog, prostaglandin E2, angiotensin II and reactive oxygen species. This article is part of a Special Issue entitled: Fibrosis: Translation of basic research to human disease.

Global gene expression profiling in PAI-1 knockout murine heart and kidney: molecular basis of cardiac-selective fibrosis

Fibrosis is defined as an abnormal matrix remodeling due to excessive synthesis and accumulation of extracellular matrix proteins in tissues during wound healing or in response to chemical, mechanical and immunological stresses. At present, there is no effective therapy for organ fibrosis. Previous studies demonstrated that aged plasminogen activator inhibitor-1 (PAI-1) knockout mice develop spontaneously cardiac-selective fibrosis without affecting any other organs. We hypothesized that differential expressions of profibrotic and antifibrotic genes in PAI-1 knockout hearts and unaffected organs lead to cardiac selective fibrosis. In order to address this prediction, we have used a genome-wide gene expression profiling of transcripts derived from aged PAI-1 knockout hearts and kidneys. The variations of global gene expression profiling were compared within four groups: wildtype heart vs. knockout heart; wildtype kidney vs. knockout kidney; knockout heart vs. knockout kidney and wildtype heart vs. wildtype kidney. Analysis of illumina-based microarray data revealed that several genes involved in different biological processes such as immune system processing, response to stress, cytokine signaling, cell proliferation, adhesion, migration, matrix organization and transcriptional regulation were affected in hearts and kidneys by the absence of PAI-1, a potent inhibitor of urokinase and tissue-type plasminogen activator. Importantly, the expressions of a number of genes, involved in profibrotic pathways including Ankrd1, Pi16, Egr1, Scx, Timp1, Timp2, Klf6, Loxl1 and Klotho, were deregulated in PAI-1 knockout hearts compared to wildtype hearts and PAI-1 knockout kidneys. While the levels of Ankrd1, Pi16 and Timp1 proteins were elevated during EndMT, the level of Timp4 protein was decreased. To our knowledge, this is the first comprehensive report on the influence of PAI-1 on global gene expression profiling in the heart and kidney and its implication in fibrogenesis and several other biological processes. The significance of these observations in the light of heart-specific profibrotic signaling and fibrogenesis are discussed.

Interleukin-13 induces collagen type-1 expression through matrix metalloproteinase-2 and transforming growth factor-β1 in airway fibroblasts in asthma

Airway remodelling is a feature of asthma that contributes to loss of lung function. One of the central components of airway remodelling is subepithelial fibrosis. Interleukin (IL)-13 is a key T-helper 2 cytokine and is believed to be the central mediator of allergic asthma including remodelling, but the mechanism driving the latter has not been elucidated in human asthma. We hypothesised that IL-13 stimulates collagen type-1 production by the airway fibroblast in a matrix metalloproteinase (MMP)- and transforming growth factor (TGF)-β1-dependent manner in human asthma as compared to healthy controls. Fibroblasts were cultured from endobronchial biopsies in 14 subjects with mild asthma and 13 normal controls that underwent bronchoscopy. Airway fibroblasts were treated with various mediators including IL-13 and specific MMP-inhibitors. IL-13 significantly stimulated collagen type-1 production in asthma compared to normal controls. Inhibitors of MMP-2 significantly attenuated collagen production in asthma but had no effect in normal controls. IL-13 significantly increased total and active forms of TGF-β1, and this activation was blocked using an MMP-2 inhibitor. IL-13 activated endogenous MMP-2 in asthma patients as compared to normal controls. In an ex vivo model, IL-13 potentiates airway remodelling through a mechanism involving TGF-β1 and MMP-2. These effects provide insights into the mechanism involved in IL-13-directed airway remodelling in asthma.

Molecular basis of asbestos-induced lung disease

Asbestos causes asbestosis and malignancies by molecular mechanisms that are not fully understood. The modes of action underlying asbestosis, lung cancer, and mesothelioma appear to differ depending on the fiber type, lung clearance, and genetics. After reviewing the key pathologic changes following asbestos exposure, we examine recently identified pathogenic pathways, with a focus on oxidative stress. Alveolar epithelial cell apoptosis, which is an important early event in asbestosis, is mediated by mitochondria- and p53-regulated death pathways and may be modulated by the endoplasmic reticulum. We review mitochondrial DNA (mtDNA)-damage and -repair mechanisms, focusing on 8-oxoguanine DNA glycosylase, as well as cross talk between reactive oxygen species production, mtDNA damage, p53, OGG1, and mitochondrial aconitase. These new insights into the molecular basis of asbestos-induced lung diseases may foster the development of novel therapeutic targets for managing degenerative diseases (e.g., asbestosis and idiopathic pulmonary fibrosis), tumors, and aging, for which effective management is lacking.

Potential of targeting TGF-β for organ transplant patients

TGF-β was originally considered as an immunoregulatory cytokine, but accumulating data demonstrate that it also plays a critical role in development of effector immunity. Since TGF- β has a potent ability to alter immune responses, modulation of the TGF-β pathway for treatment of transplantation patients could be effective if carried out in a target selective manner. This review will focus on the role of TGF-β in T cell differentiation and discuss the prospect of TGF-β as the therapeutic target of lung transplantation acceptance.

Interstitial lung disease: is interstitial lung disease the same as scleroderma lung disease?

PURPOSE OF REVIEW

Pulmonary fibrosis is a devastating disease that affects millions of people worldwide. Among the most common forms of lung fibrosis are idiopathic pulmonary fibrosis (IPF) and scleroderma-related interstitial lung disease (SSc-ILD). Despite a wealth of literature regarding each of these diseases, studies that directly compare IPF and SSc-ILD are rare.

RECENT FINDINGS

This review compares the salient features of IPF and SSc-ILD. Clinical presentation and demographics will be presented, along with the newly released radiographic and pathologic criteria for IPF. Evolving concepts of pathogenesis including the role of structural cell injury, the pathogenic role of macrophages and lymphocytes, and the origin of fibroblasts are described. We conclude with new developments in the search for predictive biomarkers of disease progression, such as markers of epithelial injury, lymphocyte subsets, and circulating fibrocytes, will be presented. We conclude with a discussion of the results of recent clinical trials.

SUMMARY

It is found that despite differences in clinical presentation and response to treatment, similarities are noted in proposed pathogenesis and putative biomarkers. It is hoped that this information will lead to studies aimed at understanding the factors driving these difficult to treat and often deadly diseases.

Influence of age on wound healing and fibrosis

The incidence and severity of fibrotic lung diseases increase with age, but very little is known about how age-related changes affect the mechanisms that underlie disease emergence and progression. Normal ageing includes accumulation of DNA mutations, oxidative and cell stresses, mitochondria dysfunction, increased susceptibility to apoptosis, telomere length dysfunction and differential gene expression as a consequence of epigenetic changes and miR regulation. These inevitable ageing-related phenomena may cause dysfunction and impaired repair capacity of lung epithelial cells, fibroblasts and MSCs. As a consequence, the composition of the extracellular matrix changes and the dynamic interaction between cells and their environment is damaged, resulting ultimately in predisposition for several diseases. This review summarizes what is known about age-related molecular changes that are implicated in the pathobiology of lung fibrosis in lung tissue.

Activin, neutrophils, and inflammation: just coincidence?

During the 26 years that have elapsed since its discovery, activin-A, a member of the transforming growth factor β super-family originally discovered from its capacity to stimulate follicle-stimulating hormone production by cultured pituitary gonadotropes, has been established as a key regulator of various fundamental biological processes, such as development, homeostasis, inflammation, and tissue remodeling. Deregulated expression of activin-A has been observed in several human diseases characterized by an immuno-inflammatory and/or tissue remodeling component in their pathophysiology. Various cell types have been recognized as sources of activin-A, and plentiful, occasionally contradicting, functions have been described mainly by in vitro studies. Not surprisingly, both harmful and protective roles have been postulated for activin-A in the context of several disorders. Recent findings have further expanded the functional repertoire of this molecule demonstrating that its ectopic overexpression in mouse airways can cause pathology that simulates faithfully human acute respiratory distress syndrome, a disorder characterized by strong involvement of neutrophils. This finding when considered together with the recent discovery that neutrophils constitute an important source of activin-A in vivo and earlier observations of upregulated activin-A expression in diseases characterized by strong activation of neutrophils may collectively imply a more intimate link between activin-A expression and neutrophil reactivity. In this review, we provide an outline of the functional repertoire of activin-A and suggest that this growth factor functions as a guardian of homeostasis, a modulator of immunity and an orchestrator of tissue repair activities. In this context, a relationship between activin-A and neutrophils may be anything but coincidental.