Indomethacin suppresses the anti-proliferative effects of transforming growth factor-beta isoforms on fibroblast cell cultures

Prostaglandin E2 (PGE2) and Roflumilast Involvement in IPF Progression

The ECM propagates processes in idiopathic pulmonary fibrosis (IPF), leading to progressive lung scarring. We established an IPF-conditioned matrix (IPF-CM) system as a platform for testing drug candidates. Here, we tested the involvement of a PGE2 and PDE4 inhibitor, Roflumilast, in the IPF-CM system. Primary normal/IPF tissue-derived human lung fibroblasts (N/IPF-HLFs) were cultured on Matrigel and then removed to create the IPF-CM. N-HLFs were exposed to the IPF-CM/N-CM with/without PGE2 (1 nM) and Roflumilast (1 µM) for 24 h. The effect of the IPF-CM on cell phenotype and pro-fibrotic gene expression was tested. In addition, electronic records of 107 patients with up to 15-year follow-up were retrospectively reviewed. Patients were defined as slow/rapid progressors using forced vital capacity (FVC) annual decline. Medication exposure was examined. N-HLFs cultured on IPF-CM were arranged in large aggregates as a result of increased proliferation, migration and differentiation. A PGE2 and Roflumilast combination blocked the large aggregate formation induced by the IPF-CM (p < 0.001) as well as cell migration, proliferation, and pro-fibrotic gene expression. A review of patient records showed that significantly more slow-progressing patients were exposed to NSAIDs (p = 0.003). PGE2/PDE4 signaling may be involved in IPF progression. These findings should be further studied.

Development of Adaptive Immunity and Its Role in Lung Remodeling

Asthma is characterized by airflow limitations resulting from bronchial closure, which can be either reversible or fixed due to changes in airway tissue composition and structure, also known as remodeling. Airway remodeling is defined as increased presence of mucins-producing epithelial cells, increased thickness of airway smooth muscle cells, angiogenesis, increased number and activation state of fibroblasts, and extracellular matrix (ECM) deposition. Airway inflammation is believed to be the main cause of the development of airway remodeling in asthma. In this chapter, we will review the development of the adaptive immune response and the impact of its mediators and cells on the elements defining airway remodeling in asthma.

Modulation of COX-2 and NADPH oxidase-4 by alpha-lipoic acid ameliorates busulfan-induced pulmonary injury in rats

Aims

This study aimed to explore the potential protective effect of α-lipoic acid on busulfan-induced pulmonary fibrosis in rats.

Main methods

Eighteen adult male rats were divided into 3 groups; control, busulfan, and busulfan plus α-lipoic acid groups. Lung index ratio, serum level of proinflammatory cytokine were assessed. The activities of antioxidant enzymes and lipid peroxidation products were estimated in the lung tissues in addition to the histopathological analyses. The deposition of the collagen in the lung tissues was evaluated by Sirius red staining. The expressions of α-smooth muscle actin (α-SMA), TNF-α, and Caspase 3 were determined immunohistochemically. The pulmonary expression of COX-2 and NOX-4 mRNA was assessed using qRT-PCR.

Key findings

Administration of ALA significantly protect the lung against BUS-induced pulmonary fibrosis, besides the upregulation of antioxidants, and downregulation of pro-inflammatory cytokines. Also, it reduced collagen deposition that associated with a decreased expression of α-SMA, TNF-α, and Caspase 3 in the lung tissues. Moreover, ALA significantly upregulated the expression of COX-2 concomitant with the downregulation of elevated NOX-4.

Significance

ALA attenuates the lung cytotoxicity of busulfan through its anti-inflammatory, anti-apoptotic, and antifibrotic effects that may be mediated by upregulation of COX-2 and downregulation of NOX-4.

Adipose-derived stem cells inhibit dermal fibroblast growth and induce apoptosis in keloids through the arachidonic acid-derived cyclooxygenase-2/prostaglandin E2 cascade by paracrine

Background

The clinical features of keloids consist of aberrant proliferation, secretion, differentiation and apoptosis of keloid dermis-derived fibroblasts (KFBs). Notably, the apoptosis rate of KFBs is lower than the proliferation rate. Though the anti-fibrotic effect of adipose-derived stem cells (ADSCs) on keloids has become a hot topic of research, the exact anti-fibrotic mechanism of the paracrine effect remains unclear. This study aimed to find out how the conditioned medium of ADSCs (ADSC-CM) exerts an anti-fibrotic effect in KFBs.

Methods

KFBs and ADSCs were extracted and cultured. Then, ADSC-CM was prepared. Whether ADSC-CM could inhibit KFB growth and induce apoptosis was verified by the use of a cell counting kit-8, an 5-Ethynyl-2-deoxyuridine (Edu) kit and flow cytometry. The expressions of cyclooxygenase-1 (COX-1), COX-2, caspase 3 and B-cell lymphoma-2 (Bcl-2) in ADSC-CM-cultured KFBs were tested by real-time PCR and western blotting. To clarify the role of COX-2 in ADSC-CM-induced KFB apoptosis, a specific COX-2 inhibitor, celecoxib, was applied to KFBs cultured in ADSC-CM. Moreover, we tested the production of arachidonic acid (AA) and prostaglandin E2 (PGE2) by ELISA. Then, we established a keloid transplantation model in a nude mouse to validate the therapeutic effect in vivo.

Results

The proliferation ability of KFBs cultured in ADSC-CM was found to be weakened and apoptosis was significantly increased. Caspase 3 expression was significantly upregulated and Bcl-2 was downregulated in ADSC-CM-cultured KFBs. Furthermore, ADSC-CM strikingly elevated COX-2 mRNA and protein expressions, but COX-1 expression was unaltered. COX-2 inhibitors reduced ADSC-CM-induced apoptosis. Additionally, COX-2 inhibition blocked the elevation of caspase 3 and reversed the decrease in Bcl-2 expression. ADSC-CM increased PGE2 levels by 1.5-fold and this effect was restrained by COX-2 inhibition. In the nude mouse model, expressions of AA, COX-2 and PGE2 were higher in the translated keloid tissues after ADSC-CM injection than in the controls.

Conclusions

We showed activation of the COX-2/PGE2 cascade in KFBs in response to ADSC-CM. By employing a specific COX-2 inhibitor, COX-2/PGE2 cascade activation played a crucial role in mediating the ADSC-CM-induced KFB apoptosis and anti-proliferation effects.

DNA Methylation in Pulmonary Fibrosis

DNA methylations, including global methylation pattern and specific gene methylation, are associated with pathogenesis and progress of pulmonary fibrosis. This chapter illustrates alteration of DNA methylation in pulmonary fibrosis as a predictive or prognostic factor. Treatment with the DNA methylation inhibitors will be an emerging anti-fibrosis therapy, although we are still in the pre-clinical stage of using epigenetic markers as potential targets for biomarkers and therapeutic interventions.

Allergen-induced asthma, chronic rhinosinusitis and transforming growth factor-β superfamily signaling: mechanisms and functional consequences

Introduction: Often co-associated, asthma and chronic rhinosinusitis (CRS) are complex heterogeneous disease syndromes. Severity in both is related to tissue inflammation and abnormal repair (termed remodeling). Understanding signaling factors that can modulate, integrate the activation, and regulation of such key processes together is increasingly important. The transforming growth factor (TGF)-β superfamily of ligands comprise a versatile system of immunomodulatory molecules that are gaining recognition as having an essential function in the immunopathogenesis of asthma. Early data suggest an important role in CRS as well. Abnormal or dysregulated signaling may contribute to disease pathogenesis and severity.Areas covered: The essential biology of this complex family of growth factors in relation to the excess inflammation and remodeling that occurs in allergic asthma and CRS is reviewed. The need to understand the integration of signaling pathways together is highlighted. Studies in human airway tissue are evaluated and only selected key animal models relevant to human disease discussed given the highly context-dependent signaling and function of these ligands.Expert opinion: Abnormal or dysregulated TGF-β superfamily signaling may be central to the excess inflammation and tissue remodeling in asthma, and possibly CRS. Therefore, the TGF-β superfamily signaling pathways represent an emerging and attractive therapeutic target.

TGF-β1 Signaling and Tissue Fibrosis

Activation of TGF-β1 initiates a program of temporary collagen accumulation important to wound repair in many organs. However, the outcome of temporary extracellular matrix strengthening all too frequently morphs into progressive fibrosis, contributing to morbidity and mortality worldwide. To avoid this maladaptive outcome, TGF-β1 signaling is regulated at numerous levels and intimately connected to feedback signals that limit accumulation. Here, we examine the current understanding of the core functions of TGF-β1 in promoting collagen accumulation, parallel pathways that promote physiological repair, and pathological triggers that tip the balance toward progressive fibrosis. Implicit in better understanding of these processes is the identification of therapeutic opportunities that will need to be further advanced to limit or reverse organ fibrosis.

Safer approaches to therapeutic modulation of TGF-β signaling for respiratory disease

The transforming growth factor (TGF)-β cytokines play a central role in development and progression of chronic respiratory diseases. TGF-β overexpression in chronic inflammation, remodeling, fibrotic process and susceptibility to viral infection is established in the most prevalent chronic respiratory diseases including asthma, COPD, lung cancer and idiopathic pulmonary fibrosis. Despite the overwhelming burden of respiratory diseases in the world, new pharmacological therapies have been limited in impact. Although TGF-β inhibition as a therapeutic strategy carries great expectations, the constraints in avoiding compromising the beneficial pleiotropic effects of TGF-β, including the anti-proliferative and immune suppressive effects, have limited the development of effective pharmacological modulators. In this review, we focus on the pathways subserving deleterious and beneficial TGF-β effects to identify strategies for selective modulation of more distal signaling pathways that may result in agents with improved safety/efficacy profiles. Adverse effects of TGF-β inhibitors in respiratory clinical trials are comprehensively reviewed, including those of the marketed TGF-β modulators, pirfenidone and nintedanib. Precise modulation of TGF-β signaling may result in new safer therapies for chronic respiratory diseases.

Pulmonary fibrosis in vivo displays increased p21 expression reduced by 5-HT2B receptor antagonists in vitro - a potential pathway affecting proliferation

Serotonin (5-hydroxytryptamine) has repeatedly been associated with the development of fibrotic disorders such as pulmonary fibrosis. By blocking the binding of 5-HT to 5-HT_2B receptors with receptor antagonists, several pro-fibrotic mechanisms can be inhibited. Bleomycin-induced pulmonary fibrosis is a model used to evaluate pathological mechanisms and pharmacological interventions. Previously we have shown attenuated fibrosis in systemic bleomycin-treated mice following treatment with two 5-HT_2B receptor antagonists (EXT5 and EXT9). Our aim is to further identify cellular effects and signaling pathways associated with the anti-fibrotic effects of EXT5/9. Gene expressions in lung tissues from systemic bleomycin-treated mice were examined, revealing significant increased expression of Cdkn1α (a gene coding for p21), particularly in distal regions of the lung. In vitro studies in human lung fibroblasts revealed increased levels of p21 (p = 0.0032) and pAkt (p = 0.12) following treatment with 5-HT (10 µM). The induction of p21 and pAkt appears to be regulated by 5-HT_2B receptors, with diminished protein levels following EXT9-treatment (p21 p = 0.0024, pAkt p = 0.15). Additionally, 5-HT induced fibroblast proliferation, an event significantly reduced by EXT5 (10 µM) and EXT9 (10 µM). In conclusion, our results suggest that 5-HT_2B receptor antagonism attenuates pulmonary fibrosis in part by anti-proliferative effects, associated with inhibited pAkt/p21 signaling pathway.

Diverse functions of clusterin promote and protect against the development of pulmonary fibrosis

Pulmonary fibrosis is a progressive scarring disorder of the lung with dismal prognosis and no curative therapy. Clusterin, an extracellular chaperone and regulator of cell functions, is reduced in bronchoalveolar lavage fluid of patients with pulmonary fibrosis. However, its distribution and role in normal and fibrotic human lung are incompletely characterized. Immunohistochemical localization of clusterin revealed strong staining associated with fibroblasts in control lung and morphologically normal areas of fibrotic lung but weak or undetectable staining in fibrotic regions and particularly fibroblastic foci. Clusterin also co-localized with elastin in vessel walls and additionally with amorphous elastin deposits in fibrotic lung. Analysis of primary lung fibroblast isolates in vitro confirmed the down-regulation of clusterin expression in fibrotic compared with control lung fibroblasts and further demonstrated that TGF-β1 is capable of down-regulating fibroblast clusterin expression. shRNA-mediated down-regulation of clusterin did not affect TGF-β1-induced fibroblast-myofibroblast differentiation but inhibited fibroblast proliferative responses and sensitized to apoptosis. Down-regulation of clusterin in fibrotic lung fibroblasts at least partly due to increased TGF-β1 may therefore represent an appropriate but insufficient response to limit fibroproliferation. Reduced expression of clusterin in the lung may also limit its extracellular chaperoning activity contributing to dysregulated deposition of extracellular matrix proteins.

Biphasic response as a mechanism against mutant takeover in tissue homeostasis circuits

Tissues use feedback circuits in which cells send signals to each other to control their growth and survival. We show that such feedback circuits are inherently unstable to mutants that misread the signal level: Mutants have a growth advantage to take over the tissue, and cannot be eliminated by known cell-intrinsic mechanisms. To resolve this, we propose that tissues have biphasic responses in and the signal is toxic at both high and low levels, such as glucotoxicity of beta cells, excitotoxicity in neurons, and toxicity of growth factors to T cells. This gives most of these mutants a frequency-dependent selective disadvantage, which leads to their elimination. However, the biphasic mechanisms create a new unstable fixed point in the feedback circuit beyond which runaway processes can occur, leading to risk of diseases such as diabetes and neurodegenerative disease. Hence, glucotoxicity, which is a dangerous cause of diabetes, may have a protective anti-mutant effect. Biphasic responses in tissues may provide an evolutionary stable strategy that avoids invasion by commonly occurring mutants, but at the same time cause vulnerability to disease.

Pulmonary Hypertension Associated with Idiopathic Pulmonary Fibrosis: Current and Future Perspectives

Pulmonary hypertension (PH) is commonly present in patients with chronic lung diseases such as Chronic Obstructive Pulmonary Disease (COPD) or Idiopathic Pulmonary Fibrosis (IPF) where it is classified as Group III PH by the World Health Organization (WHO). PH has been identified to be present in as much as 40% of patients with COPD or IPF and it is considered as one of the principal predictors of mortality in patients with COPD or IPF. However, despite the prevalence and fatal consequences of PH in the setting of chronic lung diseases, there are limited therapies available for patients with Group III PH, with lung transplantation remaining as the most viable option. This highlights our need to enhance our understanding of the molecular mechanisms that lead to the development of Group III PH. In this review we have chosen to focus on the current understating of PH in IPF, we will revisit the main mediators that have been shown to play a role in the development of the disease. We will also discuss the experimental models available to study PH associated with lung fibrosis and address the role of the right ventricle in IPF. Finally we will summarize the current available treatment options for Group III PH outside of lung transplantation.

Prostaglandin E2-Dependent Phosphorylation of RAS Inhibition 1 (RIN1) at Ser 291 and 292 Inhibits Transforming Growth Factor-β-Induced RAS Activation Pathway in Human Synovial Fibroblasts: Role in Cell Migration

Prostaglandin E2 (PGE2 )-stimulated G-protein-coupled receptor (GPCR) activation inhibits pro-fibrotic TGFβ-dependent stimulation of human fibroblast to myofibroblast transition (FMT), though the precise molecular mechanisms are not fully understood. In the present study, we describe the PGE2 -dependent suppression and reversal of TGFβ-induced events such as α-sma expression, stress fiber formation, and Ras/Raf/ERK/MAPK pathway-dependent activation of myofibroblast migration. In order to elucidate post-ligand-receptor signaling pathways, we identified a predominant PKA phosphorylation motif profile in human primary fibroblasts after treatment with exogenous PGE2 (EC50 30 nM, Vmax 100 nM), mimicked by the adenyl cyclase activator forskolin (EC50 5 μM, Vmax 10 μM). We used a global phosphoproteomic approach to identify a 2.5-fold difference in PGE2 -induced phosphorylation of proteins containing the PKA motif. Deducing the signaling pathway of our migration data, we identified Ras inhibitor 1 (RIN1) as a substrate, whereby PGE2 induced its phosphorylation at Ser291 and at Ser292 by a 5.4- and 4.8-fold increase, respectively. In a series of transient and stable over expression studies in HEK293T and HeLa cells using wild-type (wt) and mutant RIN1 (Ser291/292Ala) or Ras constructs and siRNA knock-down experiments, we showed that PGE2 -dependent phosphorylation of RIN1 resulted in the abrogation of TGFβ-induced Ras/Raf signaling activation and subsequent downstream blockade of cellular migration, emphasizing the importance of such phosphosites in PGE2 suppression of wound closure. Overexpression experiments in tandem with pull-down assays indicated that specific Ser291/292 phosphorylation of RIN1 favored binding to activated Ras. In principal, understanding PGE2 -GPCR activated signaling pathways mitigating TGFβ-induced fibrosis may lead to more evidence-based treatments against the disease. J. Cell. Physiol. 232: 202-215, 2017. © 2016 Wiley Periodicals, Inc.

Normal Human Lung Epithelial Cells Inhibit Transforming Growth Factor-β Induced Myofibroblast Differentiation via Prostaglandin E2

Introduction

Idiopathic pulmonary fibrosis (IPF) is a chronic progressive disease with very few effective treatments. The key effector cells in fibrosis are believed to be fibroblasts, which differentiate to a contractile myofibroblast phenotype with enhanced capacity to proliferate and produce extracellular matrix. The role of the lung epithelium in fibrosis is unclear. While there is evidence that the epithelium is disrupted in IPF, it is not known whether this is a cause or a result of the fibroblast pathology. We hypothesized that healthy epithelial cells are required to maintain normal lung homeostasis and can inhibit the activation and differentiation of lung fibroblasts to the myofibroblast phenotype. To investigate this hypothesis, we employed a novel co-culture model with primary human lung epithelial cells and fibroblasts to investigate whether epithelial cells inhibit myofibroblast differentiation.

Measurements and Main Results

In the presence of transforming growth factor (TGF)-β, fibroblasts co-cultured with epithelial cells expressed significantly less α-smooth muscle actin and collagen and showed marked reduction in cell migration, collagen gel contraction, and cell proliferation compared to fibroblasts grown without epithelial cells. Epithelial cells from non-matching tissue origins were capable of inhibiting TGF-β induced myofibroblast differentiation in lung, keloid and Graves’ orbital fibroblasts. TGF-β promoted production of prostaglandin (PG) E₂ in lung epithelial cells, and a PGE₂ neutralizing antibody blocked the protective effect of epithelial cell co-culture.

Conclusions

We provide the first direct experimental evidence that lung epithelial cells inhibit TGF-β induced myofibroblast differentiation and pro-fibrotic phenotypes in fibroblasts. This effect is not restricted by tissue origin, and is mediated, at least in part, by PGE₂. Our data support the hypothesis that the epithelium plays a crucial role in maintaining lung homeostasis, and that damaged and/ or dysfunctional epithelium contributes to the development of fibrosis.

New treatment and markers of prognosis for idiopathic pulmonary fibrosis: lessons learned from translational research

Idiopathic pulmonary fibrosis (IPF) is a chronic progressive interstitial lung disease with increasing prevalence, high mortality rates and poor treatment options. The diagnostic process is complex and often requires an interdisciplinary approach between different specialists. Information gained over the past 10 years of intense research resulted in improved diagnostic algorithms, a better understanding of the underlying pathogenesis and the development of new therapeutic options. Specifically, the change from the traditional concept that viewed IPF as a chronic inflammatory disorder to the current belief that is primarily resulting from aberrant wound healing enabled the identification of novel treatment targets. This increased the clinical trial activity dramatically and resulted in the approval of the first IPF-specific therapy in many countries. Still, the natural history and intrinsic behavior of IPF are very difficult to predict. There is an urgent need for new therapies and also for development and validation of prognostic markers that predict disease progression, survival and also response to antifibrotic drugs. This review provides an up to date summary of the most relevant clinical trials, novel therapeutic drug targets and outlines a spectrum of potential prognostic biomarkers for IPF.

Fibroblasts in fibrosis: novel roles and mediators

Fibroblasts are the most common cell type of the connective tissues found throughout the body and the principal source of the extensive extracellular matrix (ECM) characteristic of these tissues. They are also the central mediators of the pathological fibrotic accumulation of ECM and the cellular proliferation and differentiation that occurs in response to prolonged tissue injury and chronic inflammation. The transformation of the fibroblast cell lineage involves classical developmental signaling programs and includes a surprisingly diverse range of precursor cell types—most notably, myofibroblasts that are the apex of the fibrotic phenotype. Myofibroblasts display exaggerated ECM production; constitutively secrete and are hypersensitive to chemical signals such as cytokines, chemokines, and growth factors; and are endowed with a contractile apparatus allowing them to manipulate the ECM fibers physically to close open wounds. In addition to ECM production, fibroblasts have multiple concomitant biological roles, such as in wound healing, inflammation, and angiogenesis, which are each interwoven with the process of fibrosis. We now recognize many common fibroblast-related features across various physiological and pathological protracted processes. Indeed, a new appreciation has emerged for the role of non-cancerous fibroblast interactions with tumors in cancer progression. Although the predominant current clinical treatments of fibrosis involve non-specific immunosuppressive and anti-proliferative drugs, a variety of potential therapies under investigation specifically target fibroblast biology.

Immunosuppression in acutely decompensated cirrhosis is mediated by prostaglandin E2

Liver disease is one of the leading causes of death worldwide. Patients with cirrhosis display an increased predisposition to and mortality from infection due to multimodal defects in the innate immune system; however, the causative mechanism has remained elusive. We present evidence that the cyclooxygenase (COX)-derived eicosanoid prostaglandin E2 (PGE2) drives cirrhosis-associated immunosuppression. We observed elevated circulating concentrations (more than seven times as high as in healthy volunteers) of PGE2 in patients with acute decompensation of cirrhosis. Plasma from these and patients with end-stage liver disease (ESLD) suppressed macrophage proinflammatory cytokine secretion and bacterial killing in vitro in a PGE2-dependent manner via the prostanoid type E receptor-2 (EP2), effects not seen with plasma from patients with stable cirrhosis (Child-Pugh score grade A). Albumin, which reduces PGE2 bioavailability, was decreased in the serum of patients with acute decompensation or ESLD (<30 mg/dl) and appears to have a role in modulating PGE2-mediated immune dysfunction. In vivo administration of human albumin solution to these patients significantly improved the plasma-induced impairment of macrophage proinflammatory cytokine production in vitro. Two mouse models of liver injury (bile duct ligation and carbon tetrachloride) also exhibited elevated PGE2, reduced circulating albumin concentrations and EP2-mediated immunosuppression. Treatment with COX inhibitors or albumin restored immune competence and survival following infection with group B Streptococcus. Taken together, human albumin solution infusions may be used to reduce circulating PGE2 levels, attenuating immune suppression and reducing the risk of infection in patients with acutely decompensated cirrhosis or ESLD.

Airway remodelling in asthma: role for mechanical forces

Asthma is a chronic airway inflammatory disease with functional and structural changes, leading to bronchial hyperresponsiveness and airflow obstruction. Airway structural changes or airway remodelling consist of epithelial injury, goblet cell hyperplasia, subepithelial layer thickening, airway smooth muscle hyperplasia and angiogenesis. These changes were previously considered as a consequence of chronic airway inflammation. Even though inhaled corticosteroids can suppress airway inflammation, the natural history of asthma is still unaltered after inhaled corticosteroid treatment. As such there is increasing evidence for the role of mechanical forces within the asthmatic airway contributing to airway structural changes.

Coordinated induction of cyclooxygenase-2/prostaglandin E2 and hepatocyte growth factor by apoptotic cells prevents lung fibrosis

Apoptotic cell instillation after bleomycin induces persistent HGF production and protects from pulmonary fibrosis, but the underlying mechanism remains unclear. We investigated immediate and prolonged effects of in vivo instillation of apoptotic cells into bleomycin-stimulated mouse lungs (2 days old) on COX-2 expression in lung tissue and alveolar macrophages and PGE2 production in BALF. Furthermore, functional interaction between these molecules and HGF, following apoptotic cell instillation in a bleomycin-induced lung fibrosis model, was assessed. Apoptotic cell instillation results in enhanced immediate and prolonged expression of COX-2 and PGE2 when compared with those from bleomycin-only-treated mice. Coadministration of the COX-2-selective inhibitor NS398 or the selective PGE2R EP2 inhibitor AH6809 inhibited the increase in HGF production. Inhibition of HGF signaling using PHA-665752 inhibited increases in COX-2 and PGE2. Long-term inhibition of COX-2, PGE2, or HGF reversed the reduction of TGF-β, apoptotic and MPO activities, protein levels, and hydroxyproline contents. Up-regulation of COX-2/PGE2 and HGF through a positive-feedback loop may be an important mechanism whereby apoptotic cell instillation exerts the net results of anti-inflammatory, antiapoptotic, and antifibrotic action.

The transcription factor Snail expressed in cutaneous squamous cell carcinoma induces epithelial-mesenchymal transition and down-regulates COX-2

Cutaneous spindle cell squamous cell carcinoma (SCC) is a rare, but highly malignant variant of SCC. The presence of spindle-shaped cells with a sarcomatous appearance, which are derived from squamous cells, suggests that these cells are produced as a result of epithelial-mesenchymal transition (EMT). EMT is a complex process in which epithelial cells lose their polarity and cell-cell contacts, while also acquiring increased motility and invasiveness. Snail regulates EMT by binding to proximal E-boxes in the promoter region of E-cadherin and repressing its transcription. When examining the expression of EMT markers and Snail in spindle cell SCCs, we found that cyclooxygenase-2 (COX-2) expression was down-regulated. Since it has been shown that COX-2 is constitutively overexpressed in a variety of malignancies, including colon, gastric, and lung carcinomas, the down-regulation of COX-2 expression was unexpected. The presence of E-box-like sequences in the promoter region of COX-2 prompted us to perform a more detailed analysis. We introduced a Snail expression vector into keratinocyte-derived cell lines (HaKaT, HSC5, and A431 cells), and isolated stable transfectants. We determined that COX-2 expression was down-regulated in cells expressing Snail. Consistent with these observations, reporter assays revealed that COX-2 promoter activity was repressed upon Snail overexpression. Thus Snail down-regulates COX-2 in these cells.

Idiopathic pulmonary fibrosis: an altered fibroblast proliferation linked to cancer biology

The fibrotic process that characterizes idiopathic pulmonary fibrosis (IPF) is commonly considered the result of a recurrent injury to the alveolar epithelium followed by an uncontrolled proliferation of fibroblasts. However, based on considerable scientific evidence, it has been recently hypothesized that IPF might be considered a neoproliferative disorder of the lung because this disease exhibits several pathogenic features similar to cancer. Indeed, epigenetic and genetic abnormalities, altered cell-to-cell communications, uncontrolled proliferation, and abnormal activation of specific signal transduction pathways are biological hallmarks that characterize the pathogenesis of IPF and cancer. IPF remains a disease marked by a survival of 3 years, and little therapeutic progress has been made in the last few years, underlining the urgent need to improve research and to change our approach to the comprehension of this disease. The concept of IPF as a cancer-like disease may be helpful in identifying new pathogenic mechanisms that can be borrowed from cancer biology, potentially leading to different and more effective therapeutic approaches. Such vision will hopefully increase the awareness of this disease among the public and the scientific community.

Sarcoidosis and interstitial pulmonary fibrosis; two distinct disorders or two ends of the same spectrum

PURPOSE OF REVIEW

Pulmonary fibrosis is a reparative response characterized by accumulation of extracellular matrix in the lung parenchyma that may be observed in end-stage sarcoidosis. This article will discuss the recent advancements in the understanding of the pathogenesis of pulmonary fibrosis in sarcoidosis in comparison with idiopathic pulmonary fibrosis (IPF)/usual interstitial pneumonia (UIP).

RECENT FINDINGS

A recent study examined clinical, radiographic, and histopathologic findings of end-stage sarcoidosis patients with lung fibrosis who underwent lung transplantation. The authors found many of the patients to have moderate-to-severe interstitial pneumonitis in some cases with UIP considered to be atypical of end-stage sarcoidosis. Furthermore, these patients had diagnosis of sarcoidosis for a shorter time prior to transplant compared with individuals without interstitial pneumonitis (mean 4.8 years vs. 23.3 years). Another study found a promoter polymorphism in prostaglandin-endoperoxide synthase 2 (PTGS2), -765G>C, to be associated with susceptibility and increased risk for pulmonary fibrosis in sarcoidosis in the white population compared with healthy controls. An altered Sp1/Sp3 binding to the -765 region has been proposed as a possible mechanism for reduced PTGS2 expression.

SUMMARY

A subset of patients with sarcoidosis that progresses to pulmonary fibrosis may share some similar mechanistic and morphologic aberrations with IPF/UIP. Future studies are needed to examine the significance of chronic interstitial pneumonitits and UIP pattern in fibrotic sarcoidosis as a potential marker for progressive disease, and the roles of PTGS2 polymorphism in various ethnic groups and Sp1/Sp3 binding in other fibrotic lung diseases.

Idiopathic pulmonary fibrosis: pathobiology of novel approaches to treatment

Idiopathic pulmonary fibrosis (IPF) is a progressive disease of unknown cause that conveys a dismal prognosis. In the United States there are currently no licensed therapies for treatment of IPF. The development of effective IPF clinical trials networks across the United States and Europe, however, has led to key developments in the treatment of IPF. Advances in understanding of the pathogenetic processes involved in the development of pulmonary fibrosis have led to novel therapeutic targets. These developments offer hope that there may, in the near future, be therapeutic options available for treatment of this devastating disease.

TIEG1-null tenocytes display age-dependent differences in their gene expression, adhesion, spreading and proliferation properties

The remodeling of extracellular matrix is a crucial mechanism in tendon development and the proliferation of fibroblasts is a key factor in this process. The purpose of this study was to further elucidate the role of TIEG1 in mediating important tenocyte properties throughout the aging process. Wildtype and TIEG1 knockout tenocytes adhesion, spreading and proliferation were characterized on different substrates (fibronectin, collagen type I, gelatin and laminin) and the expression levels of various genes known to be involved with tendon development were analyzed by RT-PCR. The experiments revealed age-dependent and substrate-dependent properties for both wildtype and TIEG1 knockout tenocytes. Taken together, our results indicate an important role for TIEG1 in regulating tenocytes adhesion, spreading, and proliferation throughout the aging process. Understanding the basic mechanisms of TIEG1 in tenocytes may provide valuable information for treating multiple tendon disorders.

Prostaglandin E2 and the pathogenesis of pulmonary fibrosis

Prostaglandin (PG)E(2) is a bioactive eicosanoid that regulates many biologically important processes in part due to its ability to signal through four distinct G-protein-coupled receptors with differential signaling activity and unique expression patterns in different cell types. Although PGE(2) has been linked to malignancy in many organs, it is believed to play a beneficial role in the setting of fibrotic lung disease. This is in part due to the ability of PGE(2) to limit many of the pathobiologic features of lung fibroblasts and myofibroblasts, including the ability of PGE(2) to limit fibroblast proliferation, migration, collagen secretion, and, as originally reported in the Journal by us in 2003, the ability to limit transforming growth factor (TGF)-β-induced myofibroblast differentiation. In the setting of lung fibrosis, PGE(2) production and signaling is often diminished. In the last 8 years, significant advances have been made to better understand the dysregulation of PGE(2) production and signaling in the setting of lung fibrosis. We also have a clearer picture of how PGE(2) inhibits myofibroblast differentiation and the receptor signaling pathways that can influence fibroblast proliferation. This review highlights these recent advances and offers new insights into the potential ways that PGE(2) and its downstream signals can be regulated for therapeutic benefit in a disease that has no validated treatment options.

Hormesis provides a generalized quantitative estimate of biological plasticity

Phenotypic plasticity represents an environmentally-based change in an organism's observable properties. Since biological plasticity is a fundamental adaptive feature, it has been extensively assessed with respect to its quantitative features and genetic foundations, especially within an ecological evolutionary framework. Toxicological investigations on the dose-response continuum (i.e., very broad dose range) that include documented evidence of the hormetic dose response zone (i.e., responses to doses below the toxicological threshold) can be employed to provide a quantitative estimate of phenotypic plasticity. The low dose hormetic stimulation is an adaptive response that reflects an environmentally-induced altered phenotype and provides a quantitative estimate of biological plasticity. Analysis of nearly 8,000 dose responses within the hormesis database indicates that quantitative features of phenotypic plasticity are highly generalizable, being independent of biological model, endpoint measured and chemical/physical stress inducing agent. The magnitude of phenotype changes indicative of plasticity is modest with maximum responses typically being approximately 30-60% greater than control values. The present findings provide the first quantitative estimates of biological plasticity and its capacity for generalization. Summary This article provides the first quantitative estimate of biological plasticity that may be generalized across plant, microbial, animal systems, and across all levels of biological organization. The quantitative features of plasticity are described by the hormesis dose response model. These findings have important biological, biomedical and evolutionary implications.

TGFβ1 induces IL-6 and inhibits IL-8 release in human bronchial epithelial cells: the role of Smad2/3

Human bronchial epithelial (HBE) cells contribute to asthmatic airway inflammation by secreting cytokines, chemokines, and growth factors, including interleukin (IL)-6, IL-8 and transforming growth factor (TGF) β1, all of which are elevated in asthmatic airways. This study examines the signaling pathways leading to TGFβ1 induced IL-6 and IL-8 in primary HBE cells from asthmatic and non-asthmatic volunteers. HBE cells were stimulated with TGFβ1 in the presence or absence of signaling inhibitors. IL-6 and IL-8 protein and mRNA were measured by ELISA and real-time PCR respectively, and cell signaling kinases by Western blot. TGFβ1 increased IL-6, but inhibited IL-8 production in both asthmatic and non-asthmatic cells; however, TGF induced significantly more IL-6 in asthmatic cells. Inhibition of JNK MAP kinase partially reduced TGFβ1 induced IL-6 in both cell groups. TGFβ1 induced Smad2 phosphorylation, and blockade of Smad2/3 prevented both the TGFβ1 modulated IL-6 increase and the decrease in IL-8 production in asthmatic and non-asthmatic cells. Inhibition of Smad2/3 also increased basal IL-8 release in asthmatic cells but not in non-asthmatic cells. Using CHIP assays we demonstrated that activated Smad2 bound to the IL-6, but not the IL-8 promoter region. We conclude that the Smad2/3 pathway is the predominant TGFβ1 signaling pathway in HBE cells, and this is altered in asthmatic bronchial epithelial cells. Understanding the mechanism of aberrant pro-inflammatory cytokine production in asthmatic airways will allow the development of alternative ways to control airway inflammation.

Hormetic electric field theory of pattern formation

The hormetic morphogen theory of curvature (Fosslien 2009) proposes that hormetic morphogen concentration gradients modulate the synthesis of adenosine triphosphate (ATP) by cells along the gradients (field cells) and thus regulate their proliferation and induce curvature such as vascular wall curvature; however, it is unclear whether such morphogen gradients can also determine the histological pattern of the walls. Here, I propose that the ATP gradients modulate export of H(+) by vacuolar H(+)-ATPase (V-ATPase) located on the surface of field cells and generate extracellular ion concentration gradients, ion currents and electrical fields along the paths of morphogen gradients. In vitro, electrical fields can induce directional migration and elongation of vascular cells and align the cells with their long axis perpendicular to electrical field vectors (Bai et al. 2004). I suggest that likewise, in vivo vascular transmural electrical fields induced by hormetic morphogen concentration gradients can modulate cell shape i.e. cell elongation and cell curvature, and determine cell orientation. Moreover, I suggest that the electrical fields can modulate bidirectional cell migration and cell sorting via dynamic hormetic galvanotaxis analogous to in vitro isoelectric focusing in proton gradients, thus, hormetic morphogen gradients can determine the curvature of vessel walls and their histological patterns.

Role of myofibroblasts in vascular remodelling: focus on restenosis and aneurysm

Myofibroblasts (MFs) are contractile cells deriving from a multiplicity of resident cells and/or circulating progenitors that are known to play a key role in wound healing. They were first discovered and analysed in the early 1970s in granulation tissue. Since their first identification, the role of MF and their mechanisms of differentiation have been highlighted in a number of diseases, including organ fibrosis and tumours, with particular attention devoted to the liver, kidney, and pulmonary fibrosis. The aim of this review is to summarize the current evidence for the role played by MFs in two frequent vascular diseases related to the remodelling of the vascular wall: the different forms of arterial restenosis and the most common forms of thoracic aortic aneurysm. The in-depth knowledge of the molecular pathways involved in MF differentiation, contraction, and survival/apoptosis could contribute to the identification of novel therapeutic strategies for anti-fibrotic and anti-remodelling therapy of vascular diseases in which these cells are involved.

Diminished prostaglandin E2 contributes to the apoptosis paradox in idiopathic pulmonary fibrosis

RATIONALE

Patients with idiopathic pulmonary fibrosis (IPF), a progressive disease with a dismal prognosis, exhibit an unexplained disparity of increased alveolar epithelial cell (AEC) apoptosis but reduced fibroblast apoptosis.

OBJECTIVES

To examine whether the failure of patients with IPF to up-regulate cyclooxygenase (COX)-2, and thus the antifibrotic mediator prostaglandin (PG)E(2), accounts for this imbalance.

METHODS

Fibroblasts and primary type II AECs were isolated from control and fibrotic human lung tissue. The effects of COX-2 inhibition and exogenous PGE(2) on fibroblast and AEC sensitivity to Fas ligand (FasL)-induced apoptosis were assessed.

MEASUREMENTS AND MAIN RESULTS

IPF lung fibroblasts are resistant to FasL-induced apoptosis compared with control lung fibroblasts. Inhibition of COX-2 in control lung fibroblasts resulted in an apoptosis-resistant phenotype. Administration of PGE(2) almost doubled the rate of FasL-induced apoptosis in fibrotic lung fibroblasts compared with FasL alone. Conversely, in primary fibrotic lung type II AECs, PGE(2) protected against FasL-induced apoptosis. In human control and, to a greater extent, fibrotic lung fibroblasts, PGE(2) inhibits the phosphorylation of Akt, suggesting that regulation of this prosurvival protein kinase is an important mechanism by which PGE(2) modulates cellular apoptotic responses.

CONCLUSIONS

The observation that PGE(2) deficiency results in increased AEC but reduced fibroblast sensitivity to apoptosis provides a novel pathogenic insight into the mechanisms driving persistent fibroproliferation in IPF.

Opposing roles of leukotrienes and prostaglandins in fibrotic lung disease

Lung fibrosis is a devastating disease that involves a variable degree of inflammation, alveolar epithelial injury, fibroblast hyperplasia and the deposition of extracellular matrix. Standard therapies that consist of corticosteroids and immunosuppressive agents offer little benefit and most patients experience a progressive deterioration in lung function which is ultimately fatal within 2-5 years of diagnosis. New pathogenetic insights and therapeutic approaches are badly needed. Eicosanoids are lipid mediators derived from arachidonic acid metabolism, the best studied of which are prostaglandins and leukotrienes. Although these mediators are primarily known for their roles in asthma, pain, fever and vascular responses, they also exert relevant effects on immune and inflammatory cells as well as structural cells such as epithelial cells and fibroblasts - cell types which participate in fibrogenesis. In general, leukotrienes promote while prostaglandin E(2) opposes fibrogenic responses. Lung fibrosis is associated with increased production of leukotrienes and decreased production of prostaglandin E(2). Furthermore, responses to prostaglandin E(2) are altered in fibrotic conditions. This review highlights the role of this leukotriene/prostaglandin imbalance in the evolution of fibrotic lung disease, offers insights into the mechanisms that underlie the dysregulated responses and discusses approaches for therapeutic targeting of eicosanoids in these conditions.

The antifibrotic effects of plasminogen activation occur via prostaglandin E2 synthesis in humans and mice

Plasminogen activation to plasmin protects from lung fibrosis, but the mechanism underlying this antifibrotic effect remains unclear. We found that mice lacking plasminogen activation inhibitor-1 (PAI-1), which are protected from bleomycin-induced pulmonary fibrosis, exhibit lung overproduction of the antifibrotic lipid mediator prostaglandin E2 (PGE2). Plasminogen activation upregulated PGE2 synthesis in alveolar epithelial cells, lung fibroblasts, and lung fibrocytes from saline- and bleomycin-treated mice, as well as in normal fetal and adult primary human lung fibroblasts. This response was exaggerated in cells from Pai1-/- mice. Although enhanced PGE2 formation required the generation of plasmin, it was independent of proteinase-activated receptor 1 (PAR-1) and instead reflected proteolytic activation and release of HGF with subsequent induction of COX-2. That the HGF/COX-2/PGE2 axis mediates in vivo protection from fibrosis in Pai1-/- mice was demonstrated by experiments showing that a selective inhibitor of the HGF receptor c-Met increased lung collagen to WT levels while reducing COX-2 protein and PGE2 levels. Of clinical interest, fibroblasts from patients with idiopathic pulmonary fibrosis were found to be defective in their ability to induce COX-2 and, therefore, unable to upregulate PGE2 synthesis in response to plasmin or HGF. These studies demonstrate crosstalk between plasminogen activation and PGE2 generation in the lung and provide a mechanism for the well-known antifibrotic actions of the fibrinolytic pathway.

The preclinical pharmacology of roflumilast--a selective, oral phosphodiesterase 4 inhibitor in development for chronic obstructive pulmonary disease

After more than two decades of research into phosphodiesterase 4 (PDE4) inhibitors, roflumilast (3-cyclopropylmethoxy-4-difluoromethoxy-N-[3,5-di-chloropyrid-4-yl]-benzamide) may become the first agent in this class to be approved for patient treatment worldwide. Within the PDE family of 11 known isoenzymes, roflumilast is selective for PDE4, showing balanced selectivity for subtypes A-D, and is of high subnanomolar potency. The active principle of roflumilast in man is its dichloropyridyl N-oxide metabolite, which has similar potency as a PDE4 inhibitor as the parent compound. The long half-life and high potency of this metabolite allows for once-daily, oral administration of a single, 500-microg tablet of roflumilast. The molecular mode of action of roflumilast--PDE4 inhibition and subsequent enhancement of cAMP levels--is well established. To further understand its functional mode of action in chronic obstructive pulmonary disease (COPD), for which roflumilast is being developed, a series of in vitro and in vivo preclinical studies has been performed. COPD is a progressive, devastating condition of the lung associated with an abnormal inflammatory response to noxious particles and gases, particularly tobacco smoke. In addition, according to the Global Initiative for Chronic Obstructive Lung Disease (GOLD), significant extrapulmonary effects, including comorbidities, may add to the severity of the disease in individual patients, and which may be addressed preferentially by orally administered remedies. COPD shows an increasing prevalence and mortality, and its treatment remains a high, unmet medical need. In vivo, roflumilast mitigates key COPD-related disease mechanisms such as tobacco smoke-induced lung inflammation, mucociliary malfunction, lung fibrotic and emphysematous remodelling, oxidative stress, pulmonary vascular remodelling and pulmonary hypertension. In vitro, roflumilast N-oxide has been demonstrated to affect the functions of many cell types, including neutrophils, monocytes/macrophages, CD4+ and CD8+ T-cells, endothelial cells, epithelial cells, smooth muscle cells and fibroblasts. These cellular effects are thought to be responsible for the beneficial effects of roflumilast on the disease mechanisms of COPD, which translate into reduced exacerbations and improved lung function. As a multicomponent disease, COPD requires a broad therapeutic approach that might be achieved by PDE4 inhibition. However, as a PDE4 inhibitor, roflumilast is not a direct bronchodilator. In summary, roflumilast may be the first-in-class PDE4 inhibitor for COPD therapy. In addition to being a non-steroid, anti-inflammatory drug designed to target pulmonary inflammation, the preclinical pharmacology described in this review points to a broad functional mode of action of roflumilast that putatively addresses additional COPD mechanisms. This enables roflumilast to offer effective, oral maintenance treatment for COPD, with an acceptable tolerability profile and the potential to favourably affect the extrapulmonary effects of the disease.

The hormetic morphogen theory of curvature and the morphogenesis and pathology of tubular and other curved structures

In vitro, morphogens such as transforming growth factor (TGF)-beta can up-and down-regulate cell growth at low and high concentrations respectively, i.e. they behave like hormetic agents. The hormetic morphogen theory of curvature proposes that in vivo tissue gradients of such morphogens secreted by source cells determine the fate of cells within their gradient fields (field cells) and that morphogen-induced amplitude modulation of field cell mitochondrial adenosine triphosphate (ATP) generation controls field cell growth along the morphogen gradients: At the high concentration end of gradients, field cell ATP generation and field cell growth is reduced. With declining concentrations along the rest of the gradients field cell ATP and growth is progressively less reduced until an equidyne point is reached, beyond which ATP generation and growth gradually increases. Thus, the differential growth rates along the gradients curve the tissue. Apoptosis at very high morphogen concentrations enables lumen and cavity formation of tubular, spherical, cystic, domed, and other curved biological structures. The morphogen concentration, the gradient slope and the hormesis responses of field cells determine the curvature of such structures during developmental morphogenesis, tissue remodeling and repair of injury. Aberrant hormetic morphogen signaling is associated with developmental abnormalities, vascular diseases, and tumor formation.

PDE4 inhibitors roflumilast and rolipram augment PGE2 inhibition of TGF-{beta}1-stimulated fibroblasts

Fibrotic diseases are characterized by the accumulation of extracellular matrix together with distortion and disruption of tissue architecture. Phosphodiesterase (PDE)4 inhibitors, by preventing the breakdown of cAMP, can inhibit fibroblast functions and may be able to mitigate tissue remodeling. Transforming growth factor (TGF)-beta1, a mediator of fibrosis, can potentially modulate cAMP by altering PGE(2) metabolism. The present study assessed whether PDE4 inhibitors functionally antagonize the profibrotic activity of fibroblasts stimulated by TGF-beta1. The PDE4 inhibitors roflumilast and rolipram both inhibited fibroblast-mediated contraction of three-dimensional collagen gels and fibroblast chemotaxis toward fibronectin in the widely studied human fetal lung fibroblast strain HFL-1 and several strains of fibroblasts from adult human lung. Roflumilast was approximately 10-fold more potent than rolipram. There was a trend for PDE4 inhibitors to inhibit more in the presence of TGF-beta1 (0.05 < P < 0.08). The effect of the PDE4 inhibitors was mediated through cAMP-stimulated protein kinase A (PKA), although a PKA-independent effect on gel contraction was also observed. The effect of PDE4 inhibitors depended on fibroblast production of PGE(2) and TGF-beta1-induced PGE(2) production. PDE4 inhibitors together with TGF-beta1 resulted in augmented PGE(2) production together with increased expression of COX mRNA and protein. The present study supports the concept that PDE4 inhibitors may attenuate fibroblast activities that can lead to fibrosis and that PDE4 inhibitors may be particularly effective in the presence of TGF-beta1-induced fibroblast stimulation.

Escape from the matrix: multiple mechanisms for fibroblast activation in pulmonary fibrosis

Lung fibrosis is a recognized feature of many chronic lung diseases and is central to the pathogenesis of idiopathic pulmonary fibrosis, a disease that carries a prognosis worse than many cancers. Current research into this condition is defining the key pathways of activation either in resident fibroblasts, matrix-producing cells derived from circulating fibrocytes, or epithelial cells that appear to transdifferentiate to fibroblast-like cells. The downstream signaling pathways are also being delineated as well as the gene interactions leading to altered cell phenotype. These studies have led to an appreciation that multiple pathways, including inflammatory and coagulation cascades, are involved in the pathogenesis of idiopathic pulmonary fibrosis. As these facts come to light, we are exploring promising new approaches to treat fibroses and halt the inexorable progression that is a feature of these disorders. This article reviews these findings and our current concepts of the key molecular events leading to tissue damage and excessive matrix deposition in lung fibrosis. It also highlights the need for new studies to delineate alternative pathogenetic mechanisms and integrate these pathways so we have a framework to better understand their importance in individual patients.

The essential role for c-Ski in mediating TGF-beta1-induced bi-directional effects on skin fibroblast proliferation through a feedback loop

The bi-directional regulation of TGF-beta1 (transforming growth factor-beta1) on fibroblast proliferation with stimulation at low concentration, but inhibition at high concentration, has important significance during tissue repair. The mechanism has not been defined. c-Ski is a major co-repressor of TGF-beta1/Smad3 signalling; however, the exact role of c-Ski in the bi-directional regulation of fibroblast proliferation remains to be determined. In the present study, we established a dose-effect relationship of bi-directional regulation of TGF-beta1-mediated proliferation in rat skin fibroblasts, and found that c-Ski overexpression promoted fibroblast proliferation by inhibiting Smad3 activity. Importantly, c-Ski expression was decreased at the high concentration of TGF-beta1, but increased at the low concentration of TGF-beta1. This dose-dependent change in TGF-beta1 action did not affect Smad3 phosphorylation or nuclear translocation, but altered Smad3 DNA-binding activity, transcriptional activity and expression of the downstream gene p21 that both increased at the high concentration and decreased at the low concentration. Furthermore, c-Ski overexpression exerted synergistic stimulation with TGF-beta1 at the low concentration, but reversed the inhibitory effect of TGF-beta1 at high concentrations, while knockdown of c-Ski by RNA interference abrogated bi-directional role of TGF-beta1 on fibroblast proliferation. Thus our data reveal a new mechanism for this bi-directional regulation, i.e. c-Ski expression change induced by low or high TGF-beta1 concentration in turn determines the promoting or inhibiting effects of TGF-beta1 on fibroblast proliferation, and suggests an important role of c-Ski that modulates the local availability of TGF-beta1 within the wound repair microenvironment.

Interaction between macrophages, TGF-beta1, and the COX-2 pathway during the inflammatory phase of skeletal muscle healing after injury

Inflammation, an important phase of skeletal muscle healing, largely involves macrophages, TGF-beta1, and the COX-2 pathway. To improve our understanding of how these molecules interact during all phases of muscle healing, we examined their roles in muscle cells in vitro and in vivo. Initially, we found that depletion of macrophages in muscle tissue led to reduced muscle regeneration. Macrophages may influence healing by inducing the production of TGF-beta1 and PGE2 in different muscle cell types. We then found that the addition of TGF-beta1 induced PGE2 production in muscle cells, an effect probably mediated by COX-2 enzyme. It was also found that TGF-beta1 enhanced macrophage infiltration in wild-type mice after muscle injury. However, this effect was not observed in COX-2(-/-) mice, suggesting that the effect of TGF-beta1 on macrophage infiltration is mediated by the COX-2 pathway. Furthermore, we found that PGE2 can inhibit the expression of TGF-beta1. PGE2 and TGF-beta1 may be involved in a negative feedback loop balancing the level of fibrosis formation during skeletal muscle healing. In conclusion, our results suggest a complex regulatory mechanism of skeletal muscle healing. Macrophages, TGF-beta1, and the COX-2 pathway products may regulate one another's levels and have profound influence on the whole muscle healing process.

Regulation of matrix turnover: fibroblasts, forces, factors and fibrosis

Fibroblasts are multifunctional cells that are responsible for matrix homoeostasis, continuously synthesizing and degrading a diverse group of extracellular molecules and their receptors. Rates of turnover of matrix molecules and the proteases that degrade them are normally under the control of diverse chemical and mechanical cues, with cytokines, growth factors, proteases, lipid mediators and mechanical forces playing roles. The maintenance of this homoeostasis is vital to the preservation of normal tissue function and is clearly lost in chronic diseases of the joints, skin and internal organs where destruction and excessive deposition is seen. Current research is focusing on defining the key pathways of activation either in resident fibroblasts, matrix-producing cells derived from circulating fibrocytes, or from transdifferentiation of resident cells. The common downstream signalling pathways are also being defined, as well as the gene interactions leading to altered cell phenotype. The present article reviews these findings and our current concepts of the key molecular events leading to tissue damage and excessive matrix deposition in tissue fibrosis. These studies are leading to an appreciation of the complexity of events with multiple pathways involved, but, as the facts emerge, we are finding promising new ways to treat fibrosis and halt the inexorable progression that is a feature of so many fibrotic and remodelling disorders.

Functional Prostaglandin-Endoperoxide Synthase 2 Polymorphism Predicts Poor Outcome in Sarcoidosis

RATIONALE

The majority of patients with sarcoidosis resolve their condition; however 5-10% of patients with sarcoidosis develop pulmonary fibrosis with poor prognosis. Prostaglandin-endoperoxide synthase 2 (PTGS2) is a key regulatory enzyme in the synthesis of the antifibrotic agent prostaglandin E(2) and is reduced in sarcoidosis lung. A promoter polymorphism in PTGS2, -765G>C, is reported to reduce its expression.

OBJECTIVES

To investigate if -765G>C is associated with susceptibility to, and poorer outcome within, sarcoidosis and to examine a possible mechanism by which -765G>C reduces PTGS2 expression.

METHODS

We used a case-control design study and genotyped -765G>C in a white British population of 198 patients with sarcoidosis and 166 control subjects. Patients with sarcoidosis were classified before genotyping as having persistent or nonpersistent disease using clinical criteria that included chest radiography staging, need for treatment, lung function, and longitudinal follow-up. Electrophoretic mobility shift assays were used to identify changes in transcription factor binding caused by the -765G>C polymorphism.

RESULTS

Carriage of the -765C allele was strongly associated with susceptibility to sarcoidosis (odds ratio, 2.50; 95% confidence interval, 1.51-4.13; p=0.006) and, within this disease, with poorer outcome (odds ratio, 3.11; 95% confidence interval, 1.35-7.13; p=0.008). The association with sarcoidosis was replicated in a second Austrian population. Electrophoretic mobility shift assays revealed that the -765C allele causes a loss of Sp1/Sp3 transcription factor binding and an increase in Egr-1 binding to the region.

CONCLUSION

Our data suggest that the -765G>C polymorphism identifies individuals who are susceptible to sarcoidosis and, more importantly, at risk of pulmonary fibrotic disease. An altered Sp1/Sp3 binding to the -765 region may contribute to the mechanism by which -765G>C reduces PTGS2 expression.

Prostaglandin E2 is a potent inhibitor of epithelial-to-mesenchymal transition: interaction with hepatocyte growth factor

Epithelial-to-mesenchymal transition (EMT) has emerged as a critical event in the pathogenesis of tubulointerstitial fibrosis. EMT is typically induced by transforming growth factor-beta1 (TGF-beta1) and inhibited by hepatocyte growth factor (HGF). The present study was undertaken to evaluate the potential role of cyclooxygenase (COX)-2-derived PGE2 in regulation of EMT in cultured Madin-Darby canine kidney (MDCK) cells, in the setting of HGF treatment. Exposure to 50 ng/ml HGF significantly induced COX-2 protein expression and PGE2 release, whereas other growth factors, including epidermal growth factor, the insulin-like growth factor I protein, platelet-derived growth factor-BB, and TGF-beta1, had no effects on COX-2 expression or PGE2 release. COX-2 induction by HGF was preceded by activation of ERK1/2, and an ERK1/2-specific inhibitor, U-0126 (10 microM), completely abolished HGF-induced COX-2 expression. Exposure of MDCK cells to 10 ng/ml TGF-beta1 for 72 h induced EMT as evidenced by conversion to the spindle-like morphology, loss of E-cadherin, and activation of alpha-smooth muscle actin. In contrast, treatment with 1 microM PGE2 completely blocked EMT, associated with a significant elevation of intracellular cAMP and complete blockade of TGF-beta1-induced oxidant production. cAMP-elevating agents, including 8-Br-cAMP, forskolin, and IBMX, inhibited EMT and associated oxidative stress induced by TGF-beta1, but inhibition of cAMP pathway with Rp-cAMP, the cAMP analog, and H89, the protein kinase A (PKA) inhibitor, did not block the effect of PGE2. The effect of HGF on EMT was inhibited by approximately 50% in the presence of a COX-2 inhibitor SC-58635 (10 microM). Therefore, our data suggest that PGE2 inhibits EMT via inhibition of oxidant production and COX-2-derived PGE2 partially accounts for the antifibrotic effect of HGF.

Involvement of cyclooxygenase-2 and prostaglandins in the molecular pathogenesis of inflammatory lung diseases

Inducible cyclooxygenase (COX-2) and its metabolites have diverse and potent biological actions that are important for both physiological and disease states of lung. The wide variety of prostaglandin (PG) products are influenced by the level of cellular activation, the exact nature of the stimulus, and the specific cell type involved in their production. In turn, the anti- and proinflammatory response of PG is mediated by a blend of specific surface and intracellular receptors that mediate diverse cellular events. The complexity of this system is being at least partially resolved by the generation of specific molecular biological research tools that include cloning and characterization of the enzymes distal to COX-2 and the corresponding receptors to the final cellular products of arachidonic metabolism. The most informative of these approaches have employed genetically modified animals and specific receptor antagonists to determine the exact role of specific COX-2-derived metabolites on specific cell types of the lung in the context of inflammatory models. These data have suggested a number of cell-specific, pathway-specific, and receptor-specific approaches that could lead to effective therapeutic interventions for most inflammatory lung diseases.

Transforming growth factor beta regulates cyclooxygenase-2 in glomerular mesangial cells

This study examines the hypothesis that transforming growth factor beta (TGFbeta) regulates cyclooxygenase-2 (COX-2) and induces prostaglandin E synthase (mPGES-1) in rat mesangial cells. COX-2 expression was determined by Northern blot analysis after treatment with either TGFbeta1 or the selective COX-2 inhibitor, NS398. mPGES-1 expression was determined by real-time polymerase chain reaction. The effect of TGFbeta1 on COX-2 gene transcription was assessed using a luciferase reporter assay, and mRNA stability was also determined. To determine whether TGFbeta1 activates elements of the COX-2 promoter, we performed gel shift analyses to examine activation of activator protein-1 (AP-1) and nuclear factor kappaB (NF-kappaB). Prostaglandin E(2) (PGE(2)) and thromboxane B2 (TxB2) production was assayed by enzyme immunoassay. Finally, the pathophysiological relevance of COX-2 inhibition on the downstream effects of TGFbeta was assessed by examining collagen type I mRNA and net collagen production. COX-2 mRNA and mPGES-1 were induced after treatment with TGFbeta1 for 4 h, and this rise was accompanied by a three-fold increase in PGE(2) production that could be antagonized by selective inhibition of COX-2 with NS398. TGFbeta1 increased transcription by approximately 50% and activated both AP-1 and NF-kappaB. These effects were antagonized by co-treatment with NS398. Treatment with TGFbeta1 also doubled the half-life of COX-2 mRNA. Neither collagen type I mRNA nor net collagen production were altered by co-treatment with NS398. In conclusion, these results indicate that TGFbeta stimulates COX-2 and mPGES-1, with additional effects on transcription and stability of COX-2 mRNA.

COX-2-derived prostacyclin protects against bleomycin-induced pulmonary fibrosis

Prostacyclin is one of a number of lipid mediators elaborated from the metabolism of arachidonic acid by the cyclooxygenase (COX) enzymes. This prostanoid is a potent inhibitor of platelet aggregation, and its production by endothelial cells and protective role in the vasculature are well established. In contrast, much less is known regarding the function of this prostanoid in other disease processes. We show here that COX-2-dependent production of prostacyclin plays an important role in the development of fibrotic lung disease, limiting both the development of fibrosis and the consequential alterations in lung mechanics. In stark contrast, loss of prostaglandin E(2) synthesis and signaling through the G(s)-coupled EP2 and EP4 receptors had no effect on the development of disease. These findings suggest that prostacyclin analogs will protect against bleomycin-induced pulmonary fibrosis in COX-2(-/-) mice. If such protection is observed, investigation of these agents as a novel therapeutic approach to pulmonary fibrosis in humans may be warranted.

The contribution of transforming growth factor-beta and epidermal growth factor signalling to airway remodelling in chronic asthma

Asthma is increasing in prevalence in the developing world, affecting approximately 10% of the world's population. It is characterised by chronic lung inflammation and airway remodelling associated with wheezing, shortness of breath, acute bronchial hyperresponsiveness to a variety of innocuous stimuli and a more rapid decline in lung function over time. Airway remodelling, involving proliferation and differentiation of mesenchymal cells, particularly myofibroblasts and smooth muscle cells, is generally refractory to corticosteroids and makes a major contribution to disease chronicity. Transforming growth factor-beta is a potent profibrogenic factor whose expression is increased in the asthmatic airways and is a prime candidate for the initiation and persistence of airway remodelling in asthma. This review highlights the role of transforming growth factor-beta in the asthmatic lung, incorporating biosynthesis, signalling pathways and functional outcome. In vivo, however, it is the balance between transforming growth factor-beta and other growth factors, such as epidermal growth factor, which will determine the extent of fibrosis in the airways. A fuller comprehension of the actions of transforming growth factor-beta, and its interaction with other signalling pathways, such as the epidermal growth factor receptor signalling cascade, may enable development of therapies that control airway remodelling where there is an unmet clinical need.

Eicosanoids: mediators and therapeutic targets in fibrotic lung disease

Fibrosis is a common end-stage sequella of a number of acute and chronic lung diseases. Current concepts of pathogenesis implicate dysregulated interactions between epithelial cells and mesenchymal cells. Although investigative efforts have documented important roles for cytokines and growth factors in the pathogenesis of fibrotic lung diseases, these observations have not as yet been translated into efficacious therapies, and there is a pressing need for new pathogenetic insights and therapeutic approaches for these devastating disorders. Eicosanoids are lipid mediators derived from arachidonic acid, the most studied of which are the prostaglandins and leukotrienes. Although they are primarily known for their roles in asthma, pain, fever and vascular responses, present evidence indicates that eicosanoids exert relevant effects on immune/inflammatory, as well as structural, cells pertinent to fibrogenesis. In general, leukotrienes promote, whereas prostaglandin E(2) opposes, fibrogenic responses. An imbalance of eicosanoids also exists in pulmonary fibrosis, which favours the production of leukotrienes over prostaglandin E(2). This review highlights the role of this imbalance in the evolution of fibrotic lung disease, discusses the mechanisms by which it may arise and considers approaches for therapeutic targeting of eicosanoids in these conditions.

[Drug treatments for idiopathic pulmonary fibrosis]

Idiopathic pulmonary fibrosis is a disease of unknown cause characterized by cough, progressive dyspnea, restrictive respiratory disorder, a typical honeycomb aspect on the high-resolution CT-scan, and usual interstitial pneumonia at histological examination of the lung biopsy. Most patients die 3 to 8 years after diagnosis. Current treatment is based on a combination of corticosteroids and immunosuppressants, but the efficacy of treatment remains a matter of debate. New therapeutics currently under evaluation in controlled clinical trials include interferon-gamma, pirfenidone, N-acetylcysteine, etanercept (anti-TNFalpha), bosentan (endothelin receptor antagonist), imatinib (tyrosine-kinases inhibitor of the PDGF receptor), etc. At the same time, new compounds showing efficacy in experimental models of fibrosis and the development of new pathophysiological concepts open new perspectives both in terms of concept and clinical practice.