Idiopathic Pulmonary Fibrosis

Toll-Like Receptor 9 Aggravates Pulmonary Fibrosis by Promoting NLRP3-Mediated Pyroptosis of Alveolar Epithelial Cells

The apoptosis-prone property of alveolar epithelial cells plays a crucial role in pulmonary fibrosis(PF), but the role of pyroptosis in it is still unclear. Toll-like receptor 9(TLR9) has been reported to play a vital role in the pathogenesis of many diseases. However, the effect of TLR9 on alveolar epithelial cells in PF has not been fully elucidated. Gene expression microarray related to Idiopathic pulmonary fibrosis(IPF) was obtained from the Gene Expression Omnibus(GEO) database. In the mouse model of bleomycin-induced PF, adeno-associated virus(AAV6) was used to interfere with TLR9 to construct TLR9 knockdown mice to study the role of TLR9 in PF, and the specific mechanism was studied by intratracheal instillation of NLR family pyrin domain containing 3(NLRP3) activator. In vitro experiments were performed using A549 cells. Bleomycin-induced pyroptosis in the lung tissue of PF mice increased, and TLR9 protein levels also increased, especially in alveolar epithelial cells. The levels of fibrosis and pyroptosis in lung tissue of TLR9 knockdown mice were improved. We found that TLR9 can bind to the NLRP3, thereby increasing the activation of the NLRP3/caspase-1 inflammasome pathway. When we use the NLRP3 activator, the levels of fibrosis and pyroptosis in lung tissue of TLR9 knockout mice can be counteracted. Pyroptosis of alveolar epithelial cells plays a vital role in PF, and TLR9 can promote NLRP3-mediated pyroptosis of alveolar epithelial cells to aggravate the progression of PF and may become a feasible target for the prevention and treatment of PF.

Induced pluripotent stem cell-derived mesenchymal stem cells reverse bleomycin-induced pulmonary fibrosis and related lung stiffness

Idiopathic pulmonary fibrosis (IPF) is characterised by lung scarring and stiffening, for which there is no effective cure. Based on the immunomodulatory and anti-fibrotic effects of induced pluripotent stem cell (iPSC) and mesenchymoangioblast-derived mesenchymal stem cells (iPSCs-MSCs), this study evaluated the therapeutic effects of iPSCs-MSCs in a bleomycin (BLM)-induced model of pulmonary fibrosis. Adult male C57BL/6 mice received a double administration of BLM (0.15 mg/day) 7-days apart and were then maintained for a further 28-days (until day-35), whilst control mice were administered saline 7-days apart and maintained for the same time-period. Sub-groups of BLM-injured mice were intravenously-injected with 1×106 iPSC-MSCs on day-21 alone or on day-21 and day-28 and left until day-35 post-injury. Measures of lung inflammation, fibrosis and compliance were then evaluated. BLM-injured mice presented with lung inflammation characterised by increased immune cell infiltration and increased pro-inflammatory cytokine expression, epithelial damage, lung transforming growth factor (TGF)-β1 activity, myofibroblast differentiation, interstitial collagen fibre deposition and topology (fibrosis), in conjunction with reduced matrix metalloproteinase (MMP)-to-tissue inhibitor of metalloproteinase (TIMP) ratios and dynamic lung compliance. All these measures were ameliorated by a single or once-weekly intravenous-administration of iPSC-MSCs, with the latter reducing dendritic cell infiltration and lung epithelial damage, whilst promoting anti-inflammatory interleukin (IL)-10 levels to a greater extent. Proteomic profiling of the conditioned media of cultured iPSC-MSCs that were stimulated with TNF-α and IFN-γ, revealed that these stem cells secreted protein levels of immunosuppressive factors that contributed to the anti-fibrotic and therapeutic potential of iPSCs-MSCs as a novel treatment option for IPF.

p53 and Myofibroblast Apoptosis in Organ Fibrosis

Organ fibrosis represents a dysregulated, maladaptive wound repair response that results in progressive disruption of normal tissue architecture leading to detrimental deterioration in physiological function, and significant morbidity/mortality. Fibrosis is thought to contribute to nearly 50% of all deaths in the Western world with current treatment modalities effective in slowing disease progression but not effective in restoring organ function or reversing fibrotic changes. When physiological wound repair is complete, myofibroblasts are programmed to undergo cell death and self-clearance, however, in fibrosis there is a characteristic absence of myofibroblast apoptosis. It has been shown that in fibrosis, myofibroblasts adopt an apoptotic-resistant, highly proliferative phenotype leading to persistent myofibroblast activation and perpetuation of the fibrotic disease process. Recently, this pathological adaptation has been linked to dysregulated expression of tumour suppressor gene p53. In this review, we discuss p53 dysregulation and apoptotic failure in myofibroblasts and demonstrate its consistent link to fibrotic disease development in all types of organ fibrosis. An enhanced understanding of the role of p53 dysregulation and myofibroblast apoptosis may aid in future novel therapeutic and/or diagnostic strategies in organ fibrosis.

The Challenge of Long-Term Cultivation of Human Precision-Cut Lung Slices

Human precision-cut lung slices (PCLS) have proven to be an invaluable tool for numerous toxicologic, pharmacologic, and immunologic studies. Although a cultivation period of <1 week is sufficient for most studies, modeling of complex disease mechanisms and investigating effects of long-term exposure to certain substances require cultivation periods that are much longer. So far, data regarding tissue integrity of long-term cultivated PCLS are incomplete. More than 1500 human PCLS from 16 different donors were cultivated under standardized, serum-free conditions for up to 28 days and the viability, tissue integrity, and the transcriptome was assessed in great detail. Even though viability of PCLS was well preserved during long-term cultivation, a continuous loss of cells was observed. Although the bronchial epithelium was well preserved throughout cultivation, the alveolar integrity was preserved for about 2 weeks, and the vasculatory system experienced significant loss of integrity within the first week. Furthermore, ciliary beat in the small airways gradually decreased after 1 week. Interestingly, keratinizing squamous metaplasia of the alveolar epithelium with significantly increasing manifestation were found over time. Transcriptome analysis revealed a significantly increased immune response and significantly decreased metabolic activity within the first 24 hours after PCLS generation. Overall, this study provides a comprehensive overview of histomorphologic and pathologic changes during long-term cultivation of PCLS.

Pulmonary fibrosis in Fra-2 transgenic mice is associated with decreased numbers of alveolar macrophages and increased susceptibility to pneumococcal pneumonia

Idiopathic pulmonary fibrosis (IPF) is a deadly condition characterized by progressive respiratory dysfunction. Exacerbations due to airway infections are believed to promote disease progression, and presence of Streptococcus in the lung microbiome has been associated with the progression of IPF and mortality. The aim of this study was to analyze the effect of lung fibrosis on susceptibility to pneumococcal pneumonia and bacteremia. The effects of subclinical (low dose) infection with Streptococcus pneumoniae were studied in a well characterized fos-related antigen-2 (Fra-2) transgenic (TG) mouse model of spontaneous, progressive pulmonary fibrosis. Forty-eight hours after transnasal infection with S. pneumoniae, bacterial load was assessed in lung tissue, bronchoalveolar lavage (BAL), blood, and spleen. Leukocyte subsets and cytokine levels were analyzed in BAL and blood. Lung compliance and arterial blood gases were assessed. In contrast to wildtype mice, low dose lung infection with S. pneumoniae in Fra-2 TG mice resulted in substantial pneumonia including weight loss, increased lung bacterial load, and bacteremia. BAL alveolar macrophages were reduced in Fra-2 TG mice compared to the corresponding WT mice. Proinflammatory cytokines and chemokines (IL-1β, IL-6, TNF-α, and CXCL1) were elevated upon infection in BAL supernatant and plasma of Fra-2 TG mice. Lung compliance was decreased in Fra-2 TG mice following low dose infection with S. pneumoniae. Pulmonary fibrosis increases susceptibility to pneumococcal pneumonia and bacteremia possibly via impaired alveolar bacterial clearance.

Regorafenib-Attenuated, Bleomycin-Induced Pulmonary Fibrosis by Inhibiting the TGF-β1 Signaling Pathway

Idiopathic pulmonary fibrosis (IPF) is a fatal and age-related pulmonary disease. Nintedanib is a receptor tyrosine kinase inhibitor, and one of the only two listed drugs against IPF. Regorafenib is a novel, orally active, multi-kinase inhibitor that has similar targets to nintedanib and is applied to treat colorectal cancer and gastrointestinal stromal tumors in patients. In this study, we first identified that regorafenib could alleviate bleomycin-induced pulmonary fibrosis in mice. The in vivo experiments indicated that regorafenib suppresses collagen accumulation and myofibroblast activation. Further in vitro mechanism studies showed that regorafenib inhibits the activation and migration of myofibroblasts and extracellular matrix production, mainly through suppressing the transforming growth factor (TGF)-β1/Smad and non-Smad signaling pathways. In vitro studies have also indicated that regorafenib could augment autophagy in myofibroblasts by suppressing TGF-β1/mTOR (mechanistic target of rapamycin) signaling, and could promote apoptosis in myofibroblasts. In conclusion, regorafenib attenuates bleomycin-induced pulmonary fibrosis by suppressing the TGF-β1 signaling pathway.

Plumbagin Suppresses Pulmonary Fibrosis via Inhibition of p300 Histone Acetyltransferase Activity

Idiopathic pulmonary fibrosis (IPF) is a chronic fibrosing interstitial lung disease with a poor prognosis similar to that of malignancy. The causes of IPF are not clearly known, and there is no effective therapy to date. In this study, the natural compound plumbagin, which was isolated from Plumbago rosea root extract, was screened for p300 inhibitory activity. Plumbagin specifically inhibited the activity of p300 toward histone acetyltransferases. Plumbagin treatment significantly suppressed transforming growth factor-β-induced profibrotic target-gene expression and proliferation of fibroblast cell lines. Moreover, plumbagin significantly inhibited bleomycin-induced pulmonary fibrosis in mice. Taken together, these data demonstrate the inhibitory effects of plumbagin on lung fibrosis and its promise as a therapeutic agent for IPF.

Oxidative Stress in Pulmonary Fibrosis

Oxidative stress has been linked to various disease states as well as physiological aging. The lungs are uniquely exposed to a highly oxidizing environment and have evolved several mechanisms to attenuate oxidative stress. Idiopathic pulmonary fibrosis (IPF) is a progressive age-related disorder that leads to architectural remodeling, impaired gas exchange, respiratory failure, and death. In this article, we discuss cellular sources of oxidant production, and antioxidant defenses, both enzymatic and nonenzymatic. We outline the current understanding of the pathogenesis of IPF and how oxidative stress contributes to fibrosis. Further, we link oxidative stress to the biology of aging that involves DNA damage responses, loss of proteostasis, and mitochondrial dysfunction. We discuss the recent findings on the role of reactive oxygen species (ROS) in specific fibrotic processes such as macrophage polarization and immunosenescence, alveolar epithelial cell apoptosis and senescence, myofibroblast differentiation and senescence, and alterations in the acellular extracellular matrix. Finally, we provide an overview of the current preclinical studies and clinical trials targeting oxidative stress in fibrosis and potential new strategies for future therapeutic interventions. © 2020 American Physiological Society. Compr Physiol 10:509-547, 2020.

Inactivation of nuclear histone deacetylases by EP300 disrupts the MiCEE complex in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive, and highly lethal lung disease with unknown etiology and poor prognosis. IPF patients die within 2 years after diagnosis mostly due to respiratory failure. Current treatments against IPF aim to ameliorate patient symptoms and to delay disease progression. Unfortunately, therapies targeting the causes of or reverting IPF have not yet been developed. Here we show that reduced levels of miRNA lethal 7d (MIRLET7D) in IPF compromise epigenetic gene silencing mediated by the ribonucleoprotein complex MiCEE. In addition, we find that hyperactive EP300 reduces nuclear HDAC activity and interferes with MiCEE function in IPF. Remarkably, EP300 inhibition reduces fibrotic hallmarks of in vitro (patient-derived primary fibroblast), in vivo (bleomycin mouse model), and ex vivo (precision-cut lung slices, PCLS) IPF models. Our work provides the molecular basis for therapies against IPF using EP300 inhibition.

Idiopathic pulmonary fibrosis (IPF) is a lethal disease with insufficient treatment strategies. Here the authors show that reduction of the microRNA MIRLET7D and hyperactivation of EP300 contribute to impaired epigenetic silencing by the MiCEE complex in pulmonary fibroblasts of IPF patients, and demonstrate the benefit of inhibiting EP300 for the treatment of IPF.

Application of Isobaric Tags for Relative and Absolute Quantification (iTRAQ) Coupled with Two-Dimensional Liquid Chromatography/Tandem Mass Spectrometry in Quantitative Proteomic Analysis for Discovery of Serum Biomarkers for Idiopathic Pulmonary Fibrosis

Background

The present study was performed to explore the presence of informative protein biomarkers of human serum proteome in idiopathic pulmonary fibrosis (IPF).

Material/Methods

Serum samples were profiled using iTRAQ coupled with two-dimensional liquid chromatography/tandem mass spectrometry (2D-LC-MS/MS) technique, and ELISA was used to validate candidate biomarkers.

Results

A total of 394 proteins were identified and 97 proteins were associated with IPF. Four biomarker candidates generated from iTRAQ experiments – CRP, fibrinogen-α chain, haptoglobin, and kininogen-1 – were successfully verified using ELISA.

Conclusions

The present study demonstrates that levels of CRP and fibrinogen-α are higher and levels of haptoglobin and kininogen-1 are lower in patients with IPF compared to levels in healthy controls. We found they are useful candidate biomarkers for IPF.

Lysocardiolipin acyltransferase regulates TGF-β mediated lung fibroblast differentiation

Lysocardiolipin acyltransferase (LYCAT), a cardiolipin remodeling enzyme, plays a key role in mitochondrial function and vascular development. We previously reported that reduced LYCAT mRNA levels in peripheral blood mononuclear cells correlated with poor pulmonary function outcomes and decreased survival in IPF patients. Further LYCAT overexpression reduced lung fibrosis, and LYCAT knockdown accentuated experimental pulmonary fibrosis. NADPH Oxidase 4 (NOX4) expression and oxidative stress are known to contribute to lung fibroblast differentiation and progression of fibrosis. In this study, we investigated the role of LYCAT in TGF-β mediated differentiation of human lung fibroblasts to myofibroblasts, and whether this occurred through mitochondrial superoxide and NOX4 mediated hydrogen peroxide (H₂O₂) generation. Our data indicated that LYCAT expression was up-regulated in primary lung fibroblasts isolated from IPF patients and bleomycin-challenged mice, compared to controls. In vitro, siRNA-mediated SMAD3 depletion inhibited TGF-β stimulated LYCAT expression in human lung fibroblasts. ChIP immunoprecipitation assay revealed TGF-β stimulated SMAD2/3 binding to the endogenous LYCAT promoter, and mutation of the SMAD2/3 binding sites (-179/-183 and -540/-544) reduced TGF-β-stimulated LYCAT promoter activity. Overexpression of LYCAT attenuated TGF-β-induced mitochondrial and intracellular oxidative stress, NOX4 expression and differentiation of human lung fibroblasts. Further, pretreatment with Mito-TEMPO, a mitochondrial superoxide scavenger, blocked TGF-β-induced mitochondrial superoxide_, NOX4 expression and differentiation of human lung fibroblasts. Treatment of human lung fibroblast with NOX1/NOX4 inhibitor, GKT137831, also attenuated TGF-β induced fibroblast differentiation and mitochondrial oxidative stress. Collectively, these results suggest that LYCAT is a negative regulator of TGF-β-induced lung fibroblast differentiation by modulation of mitochondrial superoxide and NOX4 dependent H₂O₂ generation, and this may serve as a potential therapeutic target for human lung fibrosis.

iTRAQ-Based Proteomics Reveals Novel Biomarkers for Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a gradual lung disease with a survival of less than 5 years post-diagnosis for most patients. Poor molecular description of IPF has led to unsatisfactory interpretation of the pathogenesis of this disease, resulting in the lack of successful treatments. The objective of this study was to discover novel noninvasive biomarkers for the diagnosis of IPF. We employed a coupled isobaric tag for relative and absolute quantitation (iTRAQ)-liquid chromatography–tandem mass spectrometry (LC–MS/MS) approach to examine protein expression in patients with IPF. A total of 97 differentially expressed proteins (38 upregulated proteins and 59 downregulated proteins) were identified in the serum of IPF patients. Using String software, a regulatory network containing 87 nodes and 244 edges was built, and the functional enrichment showed that differentially expressed proteins were predominantly involved in protein activation cascade, regulation of response to wounding and extracellular components. A set of three most significantly upregulated proteins (HBB, CRP and SERPINA1) and four most significantly downregulated proteins (APOA2, AHSG, KNG1 and AMBP) were selected for validation in an independent cohort of IPF and other lung diseases using ELISA test. The results confirmed the iTRAQ profiling results and AHSG, AMBP, CRP and KNG1 were found as specific IPF biomarkers. ROC analysis indicated the diagnosis potential of the validated biomarkers. The findings of this study will contribute in understanding the pathogenesis of IPF and facilitate the development of therapeutic targets.

Serum level of periostin can predict long-term outcome of idiopathic pulmonary fibrosis

BACKGROUND

KL-6 and surfactant proteins A and D are the only established serum biomarkers of idiopathic pulmonary fibrosis (IPF). We have previously shown that serum levels of periostin, a unique matricellular protein, are elevated and correlated with pulmonary function in patients with IPF. We sought to determine whether the serum periostin levels correlate with overall survival (OS) and time-to-event (TTE), as a parameter reflecting long-term outcome, and with the extent of abnormality on chest high-resolution computed tomography (HRCT) scores in patients with IPF.

METHODS

Twenty-nine patients with IPF were analyzed retrospectively. The mean observation period was 1035.2 ± 663.1 days (range, 112-1800 days). High-resolution computed tomography (HRCT) scores were calculated based on the extent of abnormality evidenced by HRCT. We evaluated if there were any correlations between the serum periostin levels and clinical parameters, including HRCT score, using Spearman's rank correlation coefficients and analyzed predictors of OS and TTE using the log-rank tests.

RESULTS

We showed that the serum periostin levels significantly correlated with the increase of honeycombing score on HRCT during a 6-month period. Log-rank tests showed that a higher serum periostin level was a predictor of a shortened OS and TTE. Greater extents of fibrotic lesions on HRCT scan were predictors of shortened OS and TTE.

CONCLUSIONS

In IPF patients, the serum periostin level may be a good predictive biomarker for an increase in the radiological fibrotic area and long-term outcome.

Epithelium-dependent profibrotic milieu in the pathogenesis of idiopathic pulmonary fibrosis: current status and future directions

BACKGROUND AND AIM

Idiopathic pulmonary fibrosis (IPF) is characterized by hyperplasia of type II alveolar epithelial cells, aggregation of activated (myo)fibroblasts and excessive deposition of extracellular matrix, which will ultimately lead to lung architecture destruction with no proven effective therapies. Despite a significant increase in our understanding on the etiology and pathogenesis of IPF, the real triggers that initiate epithelial cell injury and promote fibrosis evolution are still elusive. We wanted to discuss the evolution of hypothesis on IPF pathogenesis and to suggest some new directions which need to be further elucidated.

METHODS

We have done a literature search in PubMed database by using the term 'idiopathic pulmonary fibrosis' AND (pathogenesis OR inflammation OR wound healing OR apoptosis OR extracellular matrix OR animal model).

RESULTS

Inflammatory hypothesis had been the dominant idea for several decades which suggests that chronic inflammation drives the onset and advance of the fibrotic process. However, it is seriously challenged nowadays because lung tissues from IPF patients exhibit little inflammatory lesions. Also, anti-inflammation therapy failed to exert a beneficial effect to IPF patients. Furthermore, experimental lung fibrosis can be realized independent of inflammation. Today, modern paradigm suggests that IPF is mainly driven by the profibtic milieu formed by epithelial injury/ disability and dysregulated epithelial mesenchymal interaction.

CONCLUSIONS

Epithelium-dependent profibrotic milieu formation and mesenchymal activation is the current view on the pathogenesis of IPF. New evidence from more analogous animal models may emerge and shift our thinking to a new and more faithful concept in the future.

Polyhexamethyleneguanidine phosphate induces severe lung inflammation, fibrosis, and thymic atrophy

Polyhexamethyleneguanidine phosphate (PHMG-P) has been widely used as a disinfectant because of its strong bactericidal activity and low toxicity. However, in 2011, the Korea Centers for Disease Control and Prevention and the Ministry of Health and Welfare reported that a suspicious outbreak of pulmonary disease might have originated from humidifier disinfectants. The purpose of this study was to assess the toxicity of PHMG-P following direct exposure to the lung. PHMG-P (0.3, 0.9, or 1.5 mg/kg) was instilled into the lungs of mice. The levels of proinflammatory markers and fibrotic markers were quantified in lung tissues and flow cytometry was used to evaluate T cell distribution in the thymus. Administration of PHMG-P induced proinflammatory cytokines elevation and infiltration of immune cells into the lungs. Histopathological analysis revealed a dose-dependent exacerbation of both inflammation and pulmonary fibrosis on day 14. PHMG-P also decreased the total cell number and the CD4(+)/CD8(+) cell ratio in the thymus, with the histopathological examination indicating severe reduction of cortex and medulla. The mRNA levels of biomarkers associated with T cell development also decreased markedly. These findings suggest that exposure of lung tissue to PHMG-P leads to pulmonary inflammation and fibrosis as well as thymic atrophy.

Peptide-mediated inhibition of mitogen-activated protein kinase-activated protein kinase-2 ameliorates bleomycin-induced pulmonary fibrosis

Mitogen-activated protein kinase-activated protein kinase-2 (MAPKAPK2, or MK2), a serine/threonine kinase downstream of p38 mitogen-activated protein kinase, has been implicated in inflammation and fibrosis. Compared with pathologically normal lung tissue, significantly higher concentrations of activated MK2 are evident in lung biopsies of patients with idiopathic pulmonary fibrosis (IPF). Expression is localized to fibroblasts and epithelial cells. In the murine bleomycin model of pulmonary fibrosis, we observed robust, activated MK2 expression on Day 7 (prefibrotic stage) and Day 14 (postfibrotic stage). To determine the effects of MK2 inhibition during the postinflammatory/prefibrotic and postfibrotic stages, C57BL/6 mice received intratracheal bleomycin instillation (0.025 U; Day 0), followed by PBS or the MK2 inhibitor (MK2i; 37.5 μg/kg), administered via either local (nebulized) or systemic (intraperitoneal) routes. MK2i or PBS was dosed daily for 14 days subsequent to bleomycin injury, beginning on either Day 7 or Day 14. Regardless of mode of administration or stage of intervention, MK2i significantly abrogated collagen deposition, myofibroblast differentiation and activated MK2 expression. MK2i also decreased circulating TNF-α and IL-6 concentrations, and modulated the local mRNA expression of profibrotic cytokine il-1β, matrix-related genes col1a2, col3a1, and lox, and transforming growth factor-β family members, including smad3, serpine1 (pai1), and smad6/7. In vitro, MK2i dose-dependently attenuated total MK2, myofibroblast differentiation, the secretion of collagen Type I, fibronectin, and the activation of focal adhesion kinase, whereas activated MK2 was attenuated at optimal doses. The peptide-mediated inhibition of MK2 affects both inflammatory and fibrotic responses, and thus may offer a promising therapeutic target for IPF.

X-linked inhibitor of apoptosis regulates lung fibroblast resistance to Fas-mediated apoptosis

The accumulation of apoptosis-resistant fibroblasts within fibroblastic foci is a characteristic feature of idiopathic pulmonary fibrosis (IPF), but the mechanisms underlying apoptosis resistance remain unclear. A role for the inhibitor of apoptosis (IAP) protein family member X-linked inhibitor of apoptosis (XIAP) has been suggested by prior studies showing that (1) XIAP is localized to fibroblastic foci in IPF tissue and (2) prostaglandin E₂ suppresses XIAP expression while increasing fibroblast susceptibility to apoptosis. Based on these observations, we hypothesized that XIAP would be regulated by the profibrotic mediators transforming growth factor (TGF)β-1 and endothelin (ET)-1 and that increased XIAP would contribute to apoptosis resistance in IPF fibroblasts. To address these hypotheses, we examined XIAP expression in normal and IPF fibroblasts at baseline and in normal fibroblasts after treatment with TGF-β1 or ET-1. The role of XIAP in the regulation of fibroblast susceptibility to Fas-mediated apoptosis was examined using functional XIAP antagonists and siRNA silencing. In concordance with prior reports, fibroblasts from IPF lung tissue had increased resistance to apoptosis compared with normal lung fibroblasts. Compared with normal fibroblasts, IPF fibroblasts had significantly but heterogeneously increased basal XIAP expression. Additionally, TGF-β1 and ET-1 induced XIAP protein expression in normal fibroblasts. Inhibition or silencing of XIAP enhanced the sensitivity of lung fibroblasts to Fas-mediated apoptosis without causing apoptosis in the absence of Fas activation. Collectively, these findings support a mechanistic role for XIAP in the apoptosis-resistant phenotype of IPF fibroblasts.

FoxO3a (Forkhead Box O3a) deficiency protects Idiopathic Pulmonary Fibrosis (IPF) fibroblasts from type I polymerized collagen matrix-induced apoptosis via caveolin-1 (cav-1) and Fas

Idiopathic Pulmonary Fibrosis is a lethal fibrotic disease characterized by the unrelenting proliferation and persistence of fibroblasts in a type I collagen-rich matrix that result in an expanding reticular network of fibrotic tissue. However, the underlying mechanism responsible for the persistence of myofibroblasts in IPF remains unclear. During normal tissue repair, unwanted fibroblasts are eliminated during collagen-matrix contraction by a mechanism whereby high PTEN activity suppresses Akt. We have previously found that FoxO3a, a transcriptional activator of apoptosis-inducing proteins, is inactivated in IPF fibroblasts resulting from aberrantly high PI3K/Akt activity due to inappropriately low PTEN activity. Here we demonstrate that this low FoxO3a activity confers IPF fibroblasts with resistance to collagen-mediated apoptosis. We show that the mechanism by which low FoxO3a activity confers IPF fibroblasts with an apoptotic resistant phenotype involves suppression of Fas expression as a result of down regulation of cav-1 expression via a PTEN/Akt-dependent pathway. We demonstrate that PTEN over-expression or Akt inhibition increases FoxO3a expression in IPF fibroblasts, resulting in up-regulation of caveolin-1. We show that FoxO3a binds to the cav-1 promoter region and ectopic expression of FoxO3a transcriptionally increases cav-1 mRNA and protein expression. In turn, we show that overexpression of caveolin-1 increases Fas levels and caspase-3/7 activity and promotes IPF fibroblast apoptosis on polymerized type I collagen. We have found that the expression of caveolin-1, Fas and cleaved caspase-3 proteins in fibroblasts within the fibroblastic foci of IPF patient specimens is low. Our data indicate that the pathologically altered PTEN/Akt axis inactivates FoxO3a down-regulating cav-1 and Fas expression. This confers IPF fibroblasts with an apoptosis-resistant phenotype and may be responsible for IPF progression.

Increased survivin expression contributes to apoptosis-resistance in IPF fibroblasts

Fibroblasts perform critical functions during the normal host response to tissue injury, but the inappropriate accumulation and persistent activation of these cells results in the development of tissue fibrosis. The mechanisms accounting for the aberrant accumulation of fibroblasts during fibrotic repair are poorly understood, although evidence supports a role for fibroblast resistance to apoptosis as a contributing factor. We have shown that TGF-β1 and endothelin-1 (ET-1), soluble mediators implicated in fibrogenesis, promote fibroblast resistance to apoptosis. Moreover, we recently found that ET-1 induced apoptosis resistance in normal lung fibroblasts through the upregulation of survivin, a member of the Inhibitor of Apoptosis (IAP) protein family. In the current study, we sought to determine the role of survivin in the apoptosis resistance of primary fibroblasts isolated from the lungs of patients with Idiopathic Pulmonary Fibrosis (IPF), a fibrotic lung disease of unclear etiology for which there is no definitive therapy. First, we examined survivin expression in lung tissue from patients with IPF and found that there is robust expression in the fibroblasts residing within fibroblastic foci (the "active" lesions in IPF which correlate with mortality). Next, we show that survivin expression is increased in fibroblasts isolated from IPF lung tissue compared to cells from normal lung tissue. Consistent with a role in fibrogenesis, we demonstrate that TGF-β1 increases survivin expression in normal lung fibroblasts. Finally, we show that inhibition of survivin enhances susceptibility of a subset of IPF fibroblasts to apoptosis. Collectively, these findings suggest that increased survivin expression represents one mechanism contributing an apoptosis-resistant phenotype in IPF fibroblasts.

A novel single-chain Fv antibody for connective tissue growth factor against the differentiation of fibroblast into myofibroblast

This study was aimed to investigate the effect of a single-chain fragment variable antibody of connective tissue growth factor (anti-CTGF scFv) against the differentiation of fibroblast into myofibroblast. The scFv antibody was firstly expressed in Escherichia coli cells and was then purified by affinity chromatography. The yield scFv protein reached a purity over 95% after purification. Immunoreactivity assay demonstrated that scFv possessed a special affinity toward CTGF. RT-PCR, western blot, and immunofluorescence experiments showed that increased expression of α-smooth muscle actin induced by TGF-β1 could be suppressed by this scFv antibody through inhibiting the phosphorylation of Akt.

Survivin expression induced by endothelin-1 promotes myofibroblast resistance to apoptosis

Fibrosis of the lungs and other organs is characterized by the accumulation of myofibroblasts, effectors of wound-repair that are responsible for the deposition and organization of new extracellular matrix (ECM) in response to tissue injury. During the resolution phase of normal wound repair, myofibroblast apoptosis limits the continued deposition of ECM. Mounting evidence suggests that myofibroblasts from fibrotic wounds acquire resistance to apoptosis, but the mechanisms regulating this resistance have not been fully elucidated. Endothelin-1 (ET-1), a soluble peptide strongly associated with fibrogenesis, decreases myofibroblast susceptibility to apoptosis through activation of phosphatidylinositol 3'-OH kinase (PI3K)/AKT. Focal adhesion kinase (FAK) also promotes myofibroblast resistance to apoptosis through PI3K/AKT-dependent and -independent mechanisms, although the role of FAK in ET-1 mediated resistance to apoptosis has not been explored. The goal of this study was to investigate whether FAK contributes to ET-1 mediated myofibroblast resistance to apoptosis and to examine potential mechanisms downstream of FAK and PI3K/AKT by which ET-1 regulates myofibroblast survival. Here, we show that ET-1 regulates myofibroblast survival by Rho/ROCK-dependent activation of FAK. The anti-apoptotic actions of FAK are, in turn, dependent on activation of PI3K/AKT and the subsequent increased expression of Survivin, a member of the inhibitor of apoptosis protein (IAP) family. Collectively, these studies define a novel mechanism by which ET-1 promotes myofibroblast resistance to apoptosis through upregulation of Survivin.

Reversible pulmonary toxicity due to lenalidomide

Lenalidomide is a derivative of thalidomide and is FDA-approved for the treatment of myelodysplastic syndrome and, in combination with dexamethasone, for the treatment of relapsed multiple myeloma. Pulmonary toxicity with thalidomide is a recognized potential complication; however, there have only been two case reports in the literature of lenalidomide-associated pulmonary toxicity. In this case, we describe a patient who developed profound dyspnea, decreased exercisetolerance, and new ground-glass opacities with reticulation, consistent with a nonspecific interstitial pneumonia pattern. Clinical suspicion for pulmonary drug toxicity was high and lenalidomide was discontinued. Within 2 weeks of stopping lenalidomide, the patient had significant improvement in dyspnea and interstitial changes on CT were resolving. After 8 weeks, there was complete resolution of symptoms. Lenalidomide-induced pulmonary toxicity is significantly debilitating but, to date, it appears to be reversible with discontinuation of the medication.

Panax notoginseng Attenuates Bleomycin-Induced Pulmonary Fibrosis in Mice

Panax notoginseng (PN) is a traditional Chinese herb experimentally proven to have anti-inflammatory effects, and it is used clinically for the treatment of atherosclerosis, cerebral infarction, and cerebral ischemia. This study aimed to determine the anti-inflammatory effects of PN against bleomycin-induced pulmonary fibrosis in mice. First, in an in vitro study, culture media containing lipopolysaccharide (LPS) was used to stimulate macrophage cells (RAW 264.7 cell line). TNF-α and IL-6 levels were then determined before and after treatment with PN extract. In an animal model (C57BL/6 mice), a single dose of PN (0.5 mg/kg) was administered orally on Day 2 or Day 7 postbleomycin treatment. The results showed that TNF-α and IL-6 levels increased in the culture media of LPS-stimulated macrophage cells, and this effect was significantly inhibited in a concentration-dependent manner by PN extract. Histopathologic examination revealed that PN administered on Day 7 postbleomycin treatment significantly decreased inflammatory cell infiltrates, fibrosis scores, and TNF-α, TGF-β, IL-1β, and IL-6 levels in bronchoalveolar lavage fluid when compared with PN given on Day 2 postbleomycin treatment. These results suggest that PN administered in the early fibrotic stage can attenuate pulmonary fibrosis in an animal model of idiopathic pulmonary fibrosis.

Phosphodiesterase 6 subunits are expressed and altered in idiopathic pulmonary fibrosis

Background

Idiopathic Pulmonary Fibrosis (IPF) is an unresolved clinical issue. Phosphodiesterases (PDEs) are known therapeutic targets for various proliferative lung diseases. Lung PDE6 expression and function has received little or no attention. The present study aimed to characterize (i) PDE6 subunits expression in human lung, (ii) PDE6 subunits expression and alteration in IPF and (iii) functionality of the specific PDE6D subunit in alveolar epithelial cells (AECs).

Methodology/Principal Findings

PDE6 subunits expression in transplant donor (n = 6) and IPF (n = 6) lungs was demonstrated by real-time quantitative (q)RT-PCR and immunoblotting analysis. PDE6D mRNA and protein levels and PDE6G/H protein levels were significantly down-regulated in the IPF lungs. Immunohistochemical analysis showed alveolar epithelial localization of the PDE6 subunits. This was confirmed by qRT-PCR from human primary alveolar type (AT)II cells, demonstrating the down-regulation pattern of PDE6D in IPF-derived ATII cells. In vitro, PDE6D protein depletion was provoked by transforming growth factor (TGF)-β1 in A549 AECs. PDE6D siRNA-mediated knockdown and an ectopic expression of PDE6D modified the proliferation rate of A549 AECs. These effects were mediated by increased intracellular cGMP levels and decreased ERK phosphorylation.

Conclusions/Significance

Collectively, we report previously unrecognized PDE6 expression in human lungs, significant alterations of the PDE6D and PDE6G/H subunits in IPF lungs and characterize the functional role of PDE6D in AEC proliferation.

IPF: new insight on pathogenesis and treatment

Recent years have seen a robust influx of exciting new observations regarding the mechanisms that regulate the initiation and progression of pulmonary fibrosis but the pathogenesis remains poorly understood. The search for an alternative hypothesis to unremitting, chronic inflammation as the primary explanation for the pathophysiology of idiopathic pulmonary fibrosis (IPF) derives, in part, from the lack of therapeutic efficacy of high-dose immunosuppressive therapy in patients with IPF. The inflammatory hypothesis of IPF has since been challenged by the epithelial injury hypothesis, in which fibrosis is believed to result from epithelial injury, activation, and/or apoptosis with abnormal wound healing. This hypothesis suggests that recurrent unknown injury to distal pulmonary parenchyma causes repeated epithelial injury and apoptosis. The resultant loss of alveolar epithelium exposes the underlying basement membrane to oxidative damage and degradation. Emerging concepts suggest that IPF is the result of epithelial-mesenchymal interaction. The initiation of this fibrotic response may depend upon genetic factors and environmental triggers; the role of Th1 or Th2 cell-derived cytokines may also be important. This process appears to be unique to usual interstitial pneumonia/IPF. It is clear that IPF is a heterogeneous disease with variations in pathology, high-resolution computed tomography findings, and patterns of progression. Idiopathic pulmonary fibrosis is a complex disorder, and no unifying hypothesis has been identified at present that explains all the abnormalities.

Modulation of TGFbeta1-dependent myofibroblast differentiation by hyaluronan

Myofibroblasts are contractile cells that are characterized by the expression of alpha-smooth muscle actin and mediate the closure of wounds and the formation of collagen-rich scars. Their presence in organs such as lungs, liver, and kidney has long been established as a marker of progressive fibrosis. The transforming growth factor beta(1)-driven differentiation of fibroblasts is a major source of myofibroblasts, and recent data have shown that hyaluronan is a major modulator of this process. This study examines this differentiation mechanism in more detail. Transforming growth factor beta(1)-dependent differentiation to the myofibroblastic phenotype was antagonized by the inhibition of hyaluronan synthesis, confirming that hyaluronan was necessary for differentiation. This response, however, was not reproduced by simply adding hyaluronan to fibroblasts, as the results implicated hyaladherins, as well as the macromolecular assembly of de novo hyaluronan, as essential in this process. We previously suggested that there is a relocalization of lipid-raft components during myofibroblastic differentiation. The present study demonstrates that the hyaluronan receptor CD44, the hyaluronidase HYAL 2, and the transforming growth factor beta(1)-receptor ALK5 all relocalized from raft to non-raft locations, which was reversed by the addition of exogenous hyaluronan. These data highlight a role for endogenous hyaluronan in the mediation of myofibroblastic differentiation. While hyaluronan synthesis was both essential and necessary for differentiation, exogenously provided hyaluronan antagonized differentiation, underscoring a pathological role for hyaluronan in such cell fate processes.

Mesenchymal cell fate and phenotypes in the pathogenesis of emphysema

Emphysema is characterized by the destruction of alveolar parenchymal tissue and the concordant loss of lung epithelial cells, endothelial cells, and interstitial mesenchymal cells. Key features in the pathobiology of emphysema include inflammation, alveolar epithelial cell injury/apoptosis, and excessive activation of extracellular matrix (ECM) proteases. Mesenchymal cells are versatile connective tissue cells that are critical effectors of wound-repair. The excessive loss of connective tissue and the destruction of alveolar septae in emphysema suggest that the mesenchymal cell reparative response to epithelial injury is impaired. Yet, the mechanisms regulating mesenchymal cell (dys)function in emphysema remain poorly understood. We propose that mesenchymal cell fate, modulated by transforming growth factor beta-1 (TGF-beta1) and the balance of ECM proteases and antiproteases, is a critical determinant of the emphysema phenotype. We examine emphysema in the context of wound-repair responses, with a focus on the regulation of mesenchymal cell fate and phenotype. We discuss the emerging evidence supporting that genetic factors, inflammation and environmental factors, including cigarette smoke itself, collectively impair mesenchymal cell survival and function, thus contributing to the pathogenesis of emphysema.

Lung alveolar epithelium and interstitial lung disease

Interstitial lung diseases (ILDs) comprise a group of lung disorders characterized by various levels of inflammation and fibrosis. The current understanding of the mechanisms underlying the development and progression of ILD strongly suggests a central role of the alveolar epithelium. Following injury, alveolar epithelial cells (AECs) may actively participate in the restoration of a normal alveolar architecture through a coordinated process of re-epithelialization, or in the development of fibrosis through a process known as epithelial-mesenchymal transition (EMT). Complex networks orchestrate EMT leading to changes in cell architecture and behaviour, loss of epithelial characteristics and gain of mesenchymal properties. In the lung, AECs themselves may serve as a source of fibroblasts and myofibroblasts by acquiring a mesenchymal phenotype. This review covers recent knowledge on the role of alveolar epithelium in the pathogenesis of ILD. The mechanisms underlying disease progression are discussed, with a main focus on the apoptotic pathway, the endoplasmic reticulum stress response and the developmental pathway.

Endothelin-1 and transforming growth factor-beta1 independently induce fibroblast resistance to apoptosis via AKT activation

Myofibroblast apoptosis is critical for the normal resolution of wound repair responses, and impaired myofibroblast apoptosis is associated with tissue fibrosis. Lung expression of endothelin (ET)-1, a soluble peptide implicated in fibrogenesis, is increased in murine models of pulmonary fibrosis and in the lungs of humans with pulmonary fibrosis. Mechanistically, ET-1 has been shown to induce fibroblast proliferation, differentiation, contraction, and collagen synthesis. In this study, we examined the role ET-1 in the regulation of lung fibroblast survival and apoptosis. ET-1 rapidly activates the prosurvival phosphatidylinositol 3'-OH kinase (PI3K)/AKT signaling pathway in normal and fibrotic human lung fibroblasts. ET-1-induced activation of PI3K/AKT is dependent on p38 mitogen-activated protein kinase (MAPK), but not extracellular signal-regulated kinase (ERK) 1/2, JNK, or transforming growth factor (TGF)-beta1. Activation of the PI3K/AKT pathway by ET-1 inhibits fibroblast apoptosis, and this inhibition is reversed by blockade of p38 MAPK or PI3K. TGF-beta1 has been shown to attenuate myofibroblast apoptosis through the p38 MAPK-dependent secretion of a soluble factor, which activates PI3K/AKT. In this study, we show that, although TGF-beta1 induces fibroblast synthesis and secretion of ET-1, TGF-beta1 activation of PI3K/AKT is not dependent on ET-1. We conclude that ET-1 and TGF-beta1 independently promote fibroblast resistance to apoptosis through signaling pathways involving p38 MAPK and PI3K/AKT. These findings suggest the potential for novel therapies targeting the convergence of prosurvival signaling pathways activated by these two profibrotic mediators.

Targeting the endothelin pathway in the idiopathic pulmonary fibrosis: the role of bosentan

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is a rapidly lethal disease characterized by anarchic, progressive fibrosis. Pulmonary fibrosis is the result of interactions between many effector cells and cytokines and better understanding of this can help with identification of novel therapeutic targets.

OBJECTIVE

To evaluate the role of the endothelin-1 (ET-1) pathway in IPF pathogenesis and the effects of therapeutic targeting with bosentan, an ET-1 antagonist.

METHODS

Data on ET-1's pathogenic involvement in IPF and the preclinical and clinical data on bosentan in this context are discussed and analyzed. A parallel overview of existing and upcoming therapies for IPF is presented.

CONCLUSIONS

Bosentan is a promising antifibrotic therapy for IPF and clinical data on its long-term efficacy support its use.

Potential of imatinib mesylate as a novel treatment for pulmonary fibrosis

Pulmonary fibrosis is a disease characterized by progressive scarring of the lungs, with idiopathic pulmonary fibrosis (IPF) being the most aggressive form. The diagnosis of IPF is made after other conditions are excluded and is based on a characteristic clinical presentation, radiographic features and, sometimes, pathologic specimen. Existing IPF drug regimens, including corticosteroids and cytotoxic medications, are generally ineffective. To date, only lung transplantation has been shown to improve mortality in carefully selected patients. Multiple therapeutic agents have been investigated but none have proven to be successful. Novel drugs are constantly being sought in an attempt to find a therapy that halts or reverses this disease. Imatinib mesylate is used for chronic myelogenous leukemia and gastrointestinal stromal tumors. It also has antifibrotic properties, as demonstrated in several studies using mouse models of pulmonary fibrosis. Currently, trials are underway to investigate its efficacy in human subjects with IPF.