Interstitial lung disease (ILD) with pulmonary fibrosis is an important manifestation in systemic sclerosis (SSc, scleroderma) where it portends a poor prognosis. However, biomarkers that predict the development and or severity of SSc-ILD have not been validated, and the pathogenetic mechanisms that engender this pulmonary response are poorly understood. In this study, we demonstrate in two different patient cohorts that the levels of chitotriosidase (Chit1) bioactivity and protein are significantly increased in the circulation and lungs of SSc patients compared with demographically matched controls. We also demonstrate that, compared with patients without lung involvement, patients with ILD show high levels of circulating Chit1 activity that correlate with disease severity. Murine modeling shows that in comparison with wild-type mice, bleomycin-induced pulmonary fibrosis was significantly reduced in Chit1−/− mice and significantly enhanced in lungs from Chit1 overexpressing transgenic animals. In vitro studies also demonstrated that Chit1 interacts with TGF-β1 to augment fibroblast TGF-β receptors 1 and 2 expression and TGF-β–induced Smad and MAPK/ERK activation. These studies indicate that Chit1 is potential biomarker for ILD in SSc and a therapeutic target in SSc-associated lung fibrosis and demonstrate that Chit1 augments TGF-β1 effects by increasing receptor expression and canonical and noncanonical TGF-β1 signaling.
Idiopathic pulmonary fibrosis is a common and invariably fatal disease with limited therapeutic options. Ca2+-activated KCa3.1 potassium channels play a key role in promoting TGFβ1 and bFGF-dependent profibrotic responses in human lung myofibroblasts (HLMFs). We hypothesised that KCa3.1 channel-dependent cell processes regulate HLMF αSMA expression via Smad2/3 signalling pathways.
In this study we have compared the phenotype of HLMFs derived from non-fibrotic healthy control lungs (NFC) with cells derived from IPF lungs. HLMFs grown in vitro were examined for αSMA expression by immunofluorescence (IF), RT-PCR and flow cytommetry. Basal Smad2/3 signalling was examined by RT-PCR, western blot and immunofluorescence. Two specific and distinct KCa3.1 blockers (TRAM-34 200 nM and ICA-17043 [Senicapoc] 100 nM) were used to determine their effects on HLMF differentiation and the Smad2/3 signalling pathways.
IPF-derived HLMFs demonstrated increased constitutive expression of both α-smooth muscle actin (αSMA) and actin stress fibres, indicative of greater myofibroblast differentiation. This was associated with increased constitutive Smad2/3 mRNA and protein expression, and increased Smad2/3 nuclear localisation. The increased Smad2/3 nuclear localisation was inhibited by removing extracellular Ca2+ or blocking KCa3.1 ion channels with selective KCa3.1 blockers (TRAM-34, ICA-17043). This was accompanied by de-differentiation of IPF-derived HLMFs towards a quiescent fibroblast phenotype as demonstrated by reduced αSMA expression and reduced actin stress fibre formation.
Taken together, these data suggest that Ca2+- and KCa3.1-dependent processes facilitate “constitutive” Smad2/3 signalling in IPF-derived fibroblasts, and thus promote fibroblast to myofibroblast differentiation. Importantly, inhibiting KCa3.1 channels reverses this process. Targeting KCa3.1 may therefore provide a novel and effective approach for the treatment of IPF and there is the potential for the rapid translation of KCa3.1-directed therapy to the clinic.
Idiopathic pulmonary fibrosis (IPF); Fibrosis; Lung; Myofibroblast; KCa3.1; Ion channel; Differentiation; Smad 2; Smad 3
We undertook this hypothesis-generating study to identify skin transcripts correlating with severity of interstitial lung disease (ILD) in systemic sclerosis (SSc).
Skin biopsy samples from 59 patients enrolled in the Genetics versus Environment in Scleroderma Outcome Study (GENISOS) cohort or an open-label imatinib study (baseline visit) were examined by global gene expression analysis using Illumina HT-12 arrays. Skin transcripts correlating with concomitantly obtained forced vital capacity (FVC) values and the modified Rodnan skin thickness score (MRSS) were identified by quantitative trait analysis. Also, immunofluorescence staining for selected transcripts was performed in affected skin and lung tissue. Plasma levels of CCL2, soluble SELP, and soluble P-selectin glycoprotein ligand 1 (sPSGL-1) were examined in all patients enrolled in the GENISOS cohort (n = 266).
Eighty-two skin transcripts correlated significantly with FVC. This gene list distinguished patients with more severe ILD (FVC <70% predicted) in unsupervised hierarchical clustering analysis (P < 0.001). These genes included SELP, CCL2, and matrix metalloproteinase 3, which are involved in extravasation and adhesion of inflammatory cells. Among the FVC correlates, 8 genes (CCL2, HAPLN3, GPR4, ADCYAP1, WARS, CDC25B, PLP1, and STXBP6) also correlated with the MRSS. Immunofluorescence staining revealed that SELP and CCL2 were also overexpressed in affected skin and lung tissue from SSc patients compared to those from controls. Plasma levels of CCL2 and sPSGL-1 correlated with concomitantly obtained FVC values (r = −0.22, P = 0.001 and r = 0.17, P = 0.015, respectively). This relationship was independent of potential confounders (age, sex, ethnicity, smoking status, anti–topoisomerase I positivity, treatment with immunosuppressive agents, MRSS, disease type, and disease duration).
A limited number of skin transcripts including genes involved in extravasation and adhesion of inflammatory cells correlate with severity of ILD.
In addition to its expression in stem cells and many cancers, telomerase activity is transiently induced in murine bleomycin (BLM)–induced pulmonary fibrosis with increased levels of telomerase transcriptase (TERT) expression, which is essential for fibrosis. To extend these observations to human chronic fibrotic lung disease, we investigated the expression of telomerase activity in lung fibroblasts from patients with interstitial lung diseases (ILDs), including idiopathic pulmonary fibrosis (IPF). The results showed that telomerase activity was induced in more than 66% of IPF lung fibroblast samples, in comparison with less than 29% from control samples, some of which were obtained from lung cancer resections. Less than 4% of the human IPF lung fibroblast samples exhibited shortened telomeres, whereas less than 6% of peripheral blood leukocyte samples from patients with IPF or hypersensitivity pneumonitis demonstrated shortened telomeres. Moreover, shortened telomeres in late-generation telomerase RNA component knockout mice did not exert a significant effect on BLM-induced pulmonary fibrosis. In contrast, TERT knockout mice exhibited deficient fibrosis that was independent of telomere length. Finally, TERT expression was up-regulated by a histone deacetylase inhibitor, while the induction of TERT in lung fibroblasts was associated with the binding of acetylated histone H3K9 to the TERT promoter region. These findings indicate that significant telomerase induction was evident in fibroblasts from fibrotic murine lungs and a majority of IPF lung samples, whereas telomere shortening was not a common finding in the human blood and lung fibroblast samples. Notably, the animal studies indicated that the pathogenesis of pulmonary fibrosis was independent of telomere length.
fibrosis; telomere; telomerase
Selective silencing of the cyclooxygenase-2 (COX-2) gene with the loss of the antifibrotic mediator prostaglandin E2 contributes to the fibrotic process in idiopathic pulmonary fibrosis (IPF). This study explored the role of G9a- and enhancer of zeste homolog 2 (EZH2)-mediated methylation of histone H3 lysine 9 (H3K9me3) and histone H3 lysine 27 (H3K27me3) in COX-2 silencing in IPF. Chromatin immunoprecipitation (ChIP) and re-ChIP assays demonstrated marked increases in H3K9me3, H3K27me3, and DNA methylation, together with their respective modifying enzymes G9a, EZH2, and DNA methyltransferases (Dnmts) and respective binding proteins heterochromatin protein 1 (HP1), polycomb protein complex 1 (PRC1) and methyl CpG binding protein 2 (MeCP2), at the COX-2 promoter in lung fibroblasts from patients with IPF (F-IPFs) compared with fibroblasts from nonfibrotic lungs. HP1, EZH2, and MeCP2 in turn were associated with additional repressive chromatin modifiers in F-IPFs. G9a and EZH2 inhibitors and small interfering RNAs and the Dnmt1 inhibitor markedly reduced H3K9me3 (49−79%), H3K27me3 (44−81%), and DNA methylation (61−97%) at the COX-2 promoter. These reductions were correlated with increased histone H3 and H4 acetylation, resulting in COX-2 mRNA and protein reexpression in F-IPFs. Our results support a central role for G9a- and EZH2-mediated histone hypermethylation and a model of bidirectional, mutually reinforcing, and interdependent crosstalk between histone hypermethylation and DNA methylation in COX-2 epigenetic silencing in IPF.—Coward, W. R., Feghali-Bostwick, C. A., Jenkins, G., Knox, A. J., Pang, L. A central role for G9a and EZH2 in the epigenetic silencing of cyclooxygenase-2 in idiopathic pulmonary fibrosis.
histone hypermethylation; DNA methylation; histone deacetylation; antifibrotic gene; lung fibroblasts
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.
fibroblast; myofibroblast; fibrosis; scleroderma; idiopathic pulmonary fibrosis; extracellular matrix; endostatin
Idiopathic pulmonary fibrosis (IPF) is a complex disease in which a multitude of proteins and networks are disrupted. Interrogation of the transcriptome through RNA sequencing (RNA-Seq) enables the determination of genes whose differential expression is most significant in IPF, as well as the detection of alternative splicing events which are not easily observed with traditional microarray experiments. We sequenced messenger RNA from 8 IPF lung samples and 7 healthy controls on an Illumina HiSeq 2000, and found evidence for substantial differential gene expression and differential splicing. 873 genes were differentially expressed in IPF (FDR<5%), and 440 unique genes had significant differential splicing events in at least one exonic region (FDR<5%). We used qPCR to validate the differential exon usage in the second and third most significant exonic regions, in the genes COL6A3 (RNA-Seq adjusted pval = 7.18e-10) and POSTN (RNA-Seq adjusted pval = 2.06e-09), which encode the extracellular matrix proteins collagen alpha-3(VI) and periostin. The increased gene-level expression of periostin has been associated with IPF and its clinical progression, but its differential splicing has not been studied in the context of this disease. Our results suggest that alternative splicing of these and other genes may be involved in the pathogenesis of IPF. We have developed an interactive web application which allows users to explore the results of our RNA-Seq experiment, as well as those of two previously published microarray experiments, and we hope that this will serve as a resource for future investigations of gene regulation in IPF.
Systemic sclerosis (SSc) is characterized by excessive fibrosis of the skin and internal organs due to fibroblast proliferation and excessive production of extracellular matrix (ECM). We have shown that insulin-like growth factor binding protein (IGFBP)-5 plays an important role in the development of fibrosis in vitro, ex vivo, and in vivo. We identified a membrane-associated adaptor protein, downstream of tyrosine kinase/docking protein (DOK)5, as an IGFBP-5-regulated target gene using gene expression profiling of primary fibroblasts expressing IGFBP-5. DOK5 is a tyrosine kinase substrate associated with intracellular signaling. Our objective was to determine the role of DOK5 in the pathogenesis of SSc and specifically in IGFBP-5-induced fibrosis. DOK5 mRNA and protein levels were increased in vitro by endogenous and exogenous IGFBP-5 in primary human fibroblasts. DOK5 upregulation required activation of the mitogen-activated protein kinase (MAPK) signaling cascade. Further, IGFBP-5 triggered nuclear translocation of DOK5. DOK5 protein levels were also increased in vivo in mouse skin and lung by IGFBP-5. To determine the effect of DOK5 on fibrosis, DOK5 was expressed ex vivo in human skin in organ culture. Expression of DOK5 in human skin resulted in a significant increase in dermal thickness. Lastly, levels of DOK5 were compared in primary fibroblasts and lung tissues of patients with SSc and healthy donors. Both DOK5 mRNA and protein levels were significantly increased in fibroblasts and skin tissues of patients with SSc compared with those of healthy controls, as well as in lung tissues of SSc patients. Our findings suggest that IGFBP-5 induces its pro-fibrotic effects, at least in part, via DOK5. Furthermore, IGFBP-5 and DOK5 are both increased in SSc fibroblasts and tissues and may thus be acting in concert to promote fibrosis.
Rationale: Lymphocytes are increasingly associated with idiopathic pulmonary fibrosis (IPF). Semaphorin 7a (Sema 7a) participates in lymphocyte activation.
Objectives: To define the relationship between Sema 7a and lymphocytes in IPF.
Methods: We characterized the significance of Sema 7a+ lymphocytes in humans with IPF and in a mouse model of lung fibrosis caused by lung-targeted, transgenic overexpression of TGF-β1. We determined the site of Sema 7a expression in human and murine lungs and circulation and used adoptive transfer approaches to define the relevance of lymphocytes coexpressing Sema7a and the markers CD19, CD4, or CD4+CD25+FoxP3+ in TGF-β1–induced murine lung fibrosis.
Measurements and Main Results: Subjects with IPF show expression of Sema 7a on lung CD4+ cells and circulating CD4+ or CD19+ cells. Sema 7a expression is increased on CD4+ cells and CD4+CD25+FoxP3+ regulatory T cells, but not CD19+ cells, in subjects with progressive IPF. Sema 7a is expressed on lymphocytes expressing CD4 but not CD19 in the lungs and spleen of TGF-β1–transgenic mice. Sema 7a expressing bone marrow–derived cells induce lung fibrosis and alter the production of T-cell mediators, including IFN-γ, IL-4, IL-17A, and IL-10. These effects require CD4 but not CD19. In comparison to Sema 7a-CD4+CD25+FoxP3+ cells, Sema7a+CD4+CD25+FoxP3+ cells exhibit reduced expression of regulatory genes such as IL-10, and adoptive transfer of these cells induces fibrosis and remodeling in the TGF-β1–exposed murine lung.
Conclusions: Sema 7a+CD4+CD25+FoxP3+ regulatory T cells are associated with disease progression in subjects with IPF and induce fibrosis in the TGF-β1–exposed murine lung.
Semaphorin; lung; fibrosis; TGF-β1; regulatory T cells
Fibrosis is a major contributor to morbidity and mortality in systemic sclerosis (SSc). T cells are the predominant inflammatory infiltrate in affected tissues and are thought to produce cytokines that drive the synthesis of extracellular matrix proteins by fibroblasts, resulting in excessive fibrosis. We showed that aberrant IL-13 production by peripheral blood effector CD8+ T cells from SSc patients correlates with the extent of skin fibrosis. Here we investigate the role of IL-13 production by CD8+ T cells in dermal fibrosis, an early and specific manifestation of SSc.
Extracellular matrix production by normal dermal fibroblasts co-cultured with SSc CD8+ T-cell-supernatants was determined by quantitative PCR and Western blot. Skin-homing receptor expression and IL-13 production by peripheral blood SSc CD8+ T cells were measured by flow cytometry, whereas immunohistochemistry identified IL-13+ and CD8+ cells in sclerotic skin.
IL-13-producing circulating SSc CD8+ T cells express skin-homing receptors and induce a pro-fibrotic phenotype in normal dermal fibroblasts that is inhibited by an anti-IL-13 antibody. High numbers of CD8+ T cells and IL-13+ cells are found in the skin lesions of patients, particularly in the early inflammatory phase of the disease. Thus, IL-13-producing CD8+ T cells are directly involved in modulating dermal fibrosis in SSc.
We make an important mechanistic contribution to understanding the pathogenesis of dermal fibrosis in SSc by showing that CD8+ T cells homing to the skin early in the disease are associated with accumulation of IL-13 and may represent an important target for future therapeutic intervention.
Idiopathic pulmonary fibrosis (IPF) is a common, progressive and invariably lethal interstitial lung disease with no effective therapy. We hypothesised that KCa3.1 K+ channel-dependent cell processes contribute to IPF pathophysiology.
KCa3.1 expression in primary human lung myofibroblasts was examined using RT-PCR, western blot, immunofluorescence and patch-clamp electrophysiology. The role of KCa3.1 channels in myofibroblast proliferation, wound healing, collagen secretion and contraction was examined using two specific and distinct KCa3.1 blockers (TRAM-34 and ICA-17043 [Senicapoc]).
Both healthy non fibrotic control and IPF-derived human lung myofibroblasts expressed KCa3.1 channel mRNA and protein. KCa3.1 ion currents were elicited more frequently and were larger in IPF-derived myofibroblasts compared to controls. KCa3.1 currents were increased in myofibroblasts by TGFβ1 and basic FGF. KCa3.1 was expressed strongly in IPF tissue. KCa3.1 pharmacological blockade attenuated human myofibroblast proliferation, wound healing, collagen secretion and contractility in
vitro, and this was associated with inhibition of TGFβ1-dependent increases in intracellular free Ca2+.
KCa3.1 activity promotes pro-fibrotic human lung myofibroblast function. Blocking KCa3.1 may offer a novel approach to treating IPF with the potential for rapid translation to the clinic.
The purpose of this study was to evaluate the presence and levels of interferon-gamma inducible protein-10 (IP-10) in the plasma and skin of pediatric localized scleroderma (LS) patients compared to those of healthy pediatric controls and to determine if IP-10 levels correlate to clinical disease activity measures.
The presence of IP-10 in the plasma was analyzed using a Luminex panel in 69 pediatric patients with LS and compared to 71 healthy pediatric controls. Of these patients, five had available skin biopsy specimens with concurrent clinical and serological data during the active disease phase, which were used to analyze the presence and location of IP-10 in the skin by immunohistochemistry (IHC).
IP-10 levels were significantly elevated in the plasma of LS patients compared to that of healthy controls and correlated to clinical disease activity measures in LS. Immunohistochemistry staining of IP-10 was present in the dermal infiltrate of LS patients and was similar to that found in psoriasis skin specimens, the positive disease control.
Elevation of IP-10 levels in the plasma compared to those of healthy controls and the presence of IP-10 staining in the affected skin of LS patients indicates that IP-10 is a potential biomarker in LS. Furthermore, significant elevation of IP-10 in LS patients with active versus inactive disease and correlations between IP-10 levels and standardized disease outcome measures of activity in LS strongly suggest that IP-10 may be a biomarker for disease activity in LS.
Lung diseases such as chronic obstructive pulmonary disease (COPD), asthma, and lung infections are major causes of morbidity and mortality among HIV-infected patients even in the era of antiretroviral therapy (ART). Many of these diseases are strongly associated with smoking and smoking is more common among HIV-infected than uninfected people; however, HIV is an independent risk factor for chronic bronchitis, COPD, and asthma. The mechanism by which HIV promotes these diseases is unclear. Excessive airway mucus formation is a characteristic of these diseases and contributes to airway obstruction and lung infections. HIV gp120 plays a critical role in several HIV-related pathologies and we investigated whether HIV gp120 promoted airway mucus formation in normal human bronchial epithelial (NHBE) cells. We found that NHBE cells expressed the HIV-coreceptor CXCR4 but not CCR5 and produced mucus in response to CXCR4-tropic gp120. The gp120-induced mucus formation was blocked by the inhibitors of CXCR4, α7-nicotinic acetylcholine receptor (α7-nAChR), and γ-aminobutyric acid (GABA)AR but not the antagonists of CCR5 and epithelial growth factor receptor (EGFR). These results identify two distinct pathways (α7-nAChR-GABAAR and EGFR) for airway mucus formation and demonstrate for the first time that HIV-gp120 induces and regulates mucus formation in the airway epithelial cells through the CXCR4-α7-nAChR-GABAAR pathway. Interestingly, lung sections from HIV ± ART and simian immunodeficiency virus (SIV) ± ART have significantly more mucus and gp120-immunoreactivity than control lung sections from humans and macaques, respectively. Thus, even after ART, lungs from HIV-infected patients contain significant amounts of gp120 and mucus that may contribute to the higher incidence of obstructive pulmonary diseases in this population.
Systemic sclerosis (SSc) is more prevalent in women. Our goal is to determine the effects of 17β-estradiol (E2) on the development of fibrosis and to compare circulating levels of estrogens in SSc patients and healthy controls.
Using primary human dermal fibroblasts, we evaluated the effect of E2 on fibronectin (FN) expression with and without the estrogen receptor (ER) antagonist ICI 182,780, inhibitors of signaling, propyl-pyrazole-triol, an ERα specific ligand, and genistein, an ERβ selective ligand, to identify the signaling pathways mediating E2's effect. We confirmed the fibrotic effect of E2 in human skin using an ex vivo organ culture model. Lastly, we measured levels of E2 and estrone in serum samples from SSc patients with diffuse cutaneous involvement and healthy controls using mass spectrometry.
E2 increased expression of FN in dermal fibroblasts. ICI 182,780, inositol-1,4,5-triphosphate inhibitor, and p38 mitogen-activated protein kinase inhibitor blocked the effects of E2 on FN. Propyl-pyrazole-triol, but not genistein, significantly increased FN expression. Ex vivo, E2 induced fibrosis of human skin. The effects of E2 were abrogated by ICI 182,780. Circulating levels of E2 and estrone were significantly increased in sera of patients with diffuse cutaneous SSc.
Our findings implicate estrogens in the fibrotic process and may explain the preponderance of SSc in women. ICI 182,780 or other ER signaling antagonists may be effective agents for the treatment of fibrosis.
Tenascin (TN)-C is an extracellular matrix protein associated with injury and remodeling. Since Transforming Growth Factor (TGF)-β induces both TN-C and Insulin-Like Growth Factor Binding Protein (IGFBP)-3, we sought to determine the role of IGFBP-3 in mediating TGF-β’s effects on TN-C production and to assess the levels of TN-C in vivo in SSc-associated pulmonary fibrosis (PF).
Primary human lung fibroblasts were stimulated with TGF-β or IGFBP-3 in the presence or absence of specific siRNAs and chemical signaling cascade inhibitors. TN-C levels were examined in lung tissues of patients with Systemic Sclerosis (SSc)-associated pulmonary fibrosis using immunohistochemistry (IHC) and compared to those of normal donors. TN-C levels were quantified in serum from normal donors and patients with SSc with or without PF using ELISA.
IGFBP-3 mediated TGF-β induction of TN-C. Direct induction of TN-C by IGFBP-3 occurred in a p38K-dependent manner. TN-C levels were abundant in SSc lung tissues and localized to subepithelial layers of the distal airways. No TN-C was detectable around proximal airways. Patients with SSc-associated pulmonary fibrosis had significantly greater levels of circulating TN-C compared to patients without this complication. Longitudinal samples obtained from patients with SSc before and after the onset of PF showed increased levels post-PF.
IGFBP-3, which is overexpressed in fibrotic lungs, induces production of TN-C by subepithelial fibroblasts. The increased lung tissue levels of TN-C parallel levels detected in sera of patients with SSc and lung fibrosis, suggesting that TN-C may be a useful biomarker for SSc-PF.
Heightened production of collagen and other matrix proteins underlies the fibrotic phenotype of systemic sclerosis (SSc). Roscovitine is an inhibitor of cyclin-dependent kinases that promote cell cycling (CDK1, 2), neuronal development (CDK5) and control transcription (CDK7,9). In an in vivo glomerulonephritis model, roscovitine treatment decreased mesangial cell proliferation and matrix proteins . We investigated whether roscovitine could regulate fibrotic protein production directly rather than through cell cycling. Our investigations revealed that roscovitine coordinately inhibited the expression of collagen, fibronectin, and connective tissue growth factor (CTGF) in normal and SSc fibroblasts. This effect occurred on a transcriptional basis and did not result from roscovitine-mediated cell cycle inhibition. Roscovitine-mediated suppression of matrix proteins could not be reversed by the exogenous profibrotic cytokines TGF-β or IL-6. To our knowledge, we are the first to report that roscovitine modulates matrix protein transcription. Roscovitine may thus be a viable treatment option for SSc and other fibrosing diseases.
Pulmonary fibrosis is a disease that results in loss of normal lung architecture, but the signaling events that drive tissue destruction are incompletely understood. Wnt/β-catenin signaling is important in normal lung development, but whether abnormal signaling occurs in lung fibrosis due to systemic sclerosis and the consequences of β-catenin signaling toward the fibrogenic phenotype remain poorly defined. In this study, we show nuclear β-catenin accumulation in fibroblastic foci from lungs of patients with systemic sclerosis–associated advanced pulmonary fibrosis. Forced activation of β-catenin signaling in three independently derived sources of normal human lung fibroblasts promotes proliferation and migratory activities but is not sufficient to activate classic markers of fibroblast activation, such as TGF-β, type 1 collagen, α-smooth muscle actin, and connective tissue growth factor. These findings indicate that activation of β-catenin signaling in pulmonary fibroblasts may be a common feature of lung fibrosis, contributing to fibroproliferative and migratory activities associated with the disease.
Wnt/β-catenin signaling; scleroderma; fibrosis
Extracellular matrix deposition and tissue scarring characterize the process of fibrosis. Transforming growth factor beta (TGFβ) and Insulin-like growth factor binding protein-3 (IGFBP-3) have been implicated in the pathogenesis of fibrosis in various tissues by inducing mesenchymal cell proliferation and extracellular matrix deposition. We identified Syndecan-2 (SDC2) as a gene induced by TGFβ in an IGFBP-3-dependent manner. TGFβ induction of SDC2 mRNA and protein required IGFBP-3. IGFBP-3 independently induced production of SDC2 in primary fibroblasts. Using an ex-vivo model of human skin in organ culture expressing IGFBP-3, we demonstrate that IGFBP-3 induces SDC2 ex vivo in human tissue. We also identified Mitogen-activated protein kinase-interacting kinase (Mknk2) as a gene induced by IGFBP-3. IGFBP-3 triggered Mknk2 phosphorylation resulting in its activation. Mknk2 independently induced SDC2 in human skin. Since IGFBP-3 is over-expressed in fibrotic tissues, we examined SDC2 levels in skin and lung tissues of patients with systemic sclerosis (SSc) and lung tissues of patients with idiopathic pulmonary fibrosis (IPF). SDC2 levels were increased in fibrotic dermal and lung tissues of patients with SSc and in lung tissues of patients with IPF. This is the first report describing elevated levels of SDC2 in fibrosis. Increased SDC2 expression is due, at least in part, to the activity of two pro-fibrotic factors, TGFβ and IGFBP-3.
Fibrosis is a deregulated and ultimately defective form of tissue repair that underlies a large number of chronic human diseases, as well as obesity and aging. The pathogenesis of fibrosis involves multiple cell types and extracellular signals, of which transforming growth factor- β (TGF-β) is pre-eminent. The prevalence of fibrosis is rising worldwide, and to date no agents has shown clinical efficacy in the attenuating or reversing the process. Recent studies implicate the immediate-early response transcription factor Egr-1 in the pathogenesis of fibrosis. Egr-1 couples acute changes in the cellular environment to sustained alterations in gene expression, and mediates a broad spectrum of biological responses to injury and stress. In contrast to other ligand-activated transcription factors such as NF-κB, c-jun and Smad2/3 that undergo post-translational modification such as phosphorylation and nuclear translocation, Egr-1 activity is regulated via its biosynthesis. Aberrant Egr-1 expression or activity is implicated in cancer, inflammation, atherosclerosis, and ischemic injury and recent studies now indicate an important role for Egr-1 in TGF-β-dependent profibrotic responses. Fibrosis in various animal models and human diseases such as scleroderma (SSc) and idiopathic pulmonary fibrosis (IPF) is accompanied by aberrant Egr-1 expression. Moreover Egr-1 appears to be required for physiologic and pathological connective tissue remodeling, and Egr-1-null mice are protected from fibrosis. As a novel profibrotic mediator, Egr-1 thus appears to be a promising potential target for the development of anti-fibrotic therapies.
Egr-1; TGF-β; fibrosis; Scleroderma (systemic sclerosis); fibroblast
Our previous studies have demonstrated increased expression of insulin-like growth factor binding protein-5 (IGFBP-5) in fibrotic tissues and IGFBP-5 induction of extracellular matrix (ECM) components. The mechanism resulting in increased IGFBP-5 in the extracellular milieu of fibrotic fibroblasts is unknown. Since Caveolin-1 (Cav-1) has been implicated to play a role in membrane trafficking and signal transduction in tissue fibrosis, we examined the effect of Cav-1 on IGFBP-5 internalization, trafficking, and secretion. We demonstrated that IGFBP-5 localized to lipid rafts in human lung fibroblasts and bound Cav-1. Cav-1 was detected in the nucleus in IGFBP-5-expressing fibroblasts, within aggregates enriched with IGFBP-5, suggesting a coordinate trafficking of IGFBP-5 and Cav-1 from the plasma membrane to the nucleus. This trafficking was dependent on Cav-1 as fibroblasts from Cav-1 null mice had increased extracellular IGFBP-5, and as fibroblasts in which Cav-1 was silenced or lipid raft structure was disrupted through cholesterol depletion also had defective IGFBP-5 internalization. Restoration of Cav-1 function through administration of Cav-1 scaffolding peptide dramatically increased IGFBP-5 uptake. Finally, we demonstrated that IGFBP-5 in the ECM protects fibronectin from proteolytic degradation. Taken together, our findings identify a novel role for Cav-1 in the internalization and nuclear trafficking of IGFBP-5. Decreased Cav-1 expression in fibrotic diseases likely leads to increased deposition of IGFBP-5 in the ECM with subsequent reduction in ECM degradation, thus identifying a mechanism by which reduced Cav-1 and increased IGFBP-5 concomitantly contribute to the perpetuation of fibrosis.
Caveolin-1; insulin-like growth factor binding protein-5; fibrosis; extracellular matrix
Pulmonary complications in systemic sclerosis (SSc), including pulmonary fibrosis (PF) and pulmonary arterial hypertension (PAH), are the leading cause of mortality. We compared the molecular fingerprint of SSc lung tissues and matching primary lung fibroblasts to those of normal donors, and patients with idiopathic pulmonary fibrosis (IPF) and idiopathic pulmonary arterial hypertension (IPAH).
Lung tissues were obtained from 33 patients with SSc who underwent lung transplantation. Tissues and cells from a subgroup of SSc patients with predominantly PF or PAH were compared to those from normal donors, patients with IPF, or IPAH. Microarray data was analyzed using Efficiency Analysis for determination of optimal data processing methods. Real time PCR and immunohistochemistry were used to confirm differential levels of mRNA and protein, respectively.
We identified a consensus of 242 and 335 genes that were differentially expressed in lungs and primary fibroblasts, respectively. Enriched function groups in SSc-PF and IPF lungs included fibrosis, insulin-like growth factor signaling and caveolin-mediated endocytosis. Functional groups shared by SSc-PAH and IPAH lungs included antigen presentation, chemokine activity, and IL-17 signaling.
Using microarray analysis on carefully phenotyped SSc and comparator lung tissues, we demonstrated distinct molecular profiles in tissues and fibroblasts of patients with SSc-associated lung disease compared to idiopathic forms of lung disease. Unique molecular signatures were generated that are disease- (SSc) and phenotype- (PF vs PAH) specific. These signatures provide new insights into pathogenesis and potential therapeutic targets for SSc lung disease.
Rationale: Pulmonary hypertension (PH) is a progressive disease with unclear etiology. The significance of autophagy in PH remains unknown.
Objectives: To determine the mechanisms by which autophagic proteins regulate tissue responses during PH.
Methods: Lungs from patients with PH, lungs from mice exposed to chronic hypoxia, and human pulmonary vascular cells were examined for autophagy using electron microscopy and Western analysis. Mice deficient in microtubule-associated protein-1 light chain-3B (LC3B−/−), or early growth response-1 (Egr-1−/−), were evaluated for vascular morphology and hemodynamics.
Measurements and Main Results: Human PH lungs displayed elevated lipid-conjugated LC3B, and autophagosomes relative to normal lungs. These autophagic markers increased in hypoxic mice, and in human pulmonary vascular cells exposed to hypoxia. Egr-1, which regulates LC3B expression, was elevated in PH, and increased by hypoxia in vivo and in vitro. LC3B−/− or Egr-1−/−, but not Beclin 1+/−, mice displayed exaggerated PH during hypoxia. In vitro, LC3B knockdown increased reactive oxygen species production, hypoxia-inducible factor-1α stabilization, and hypoxic cell proliferation. LC3B and Egr-1 localized to caveolae, associated with caveolin-1, and trafficked to the cytosol during hypoxia.
Conclusions: The results demonstrate elevated LC3B in the lungs of humans with PH, and of mice with hypoxic PH. The increased susceptibility of LC3B−/− and Egr-1−/− mice to hypoxia-induced PH and increased hypoxic proliferation of LC3B knockdown cells suggest adaptive functions of these proteins during hypoxic vascular remodeling. The results suggest that autophagic protein LC3B exerts a protective function during the pathogenesis of PH, through the regulation of hypoxic cell proliferation.
autophagy; hypoxia; hypertension, pulmonary
Fibrosis involves an orchestrated cascade of events including activation of fibroblasts, increased production and deposition of extracellular matrix components, and differentiation of fibroblasts into myofibroblasts. Epithelial-mesenchymal cross-talk plays an important role in this process, and current hypotheses of organ fibrosis liken it to an aberrant wound healing response in which epithelial-mesenchymal transition (EMT) and cellular senescence may also contribute to disease pathogenesis. The fibrotic response is associated with altered expression of growth factors and cytokines, including increased levels of transforming growth factor-β1 (TGF-β1) and the more recent observation that increased levels of several insulin-like growth factor binding proteins (IGFBPs) are associated with a number of fibrotic conditions. IGFBPs have been implicated in virtually every cell type and process associated with the fibrotic response, making the IGFBPs attractive targets for the development of novel anti-fibrotic therapies. In this review, the current state of knowledge regarding the classical IGFBP family in organ fibrosis will be summarized and the clinical implications considered.
Extracellular matrix; fibrosis; IGFBP; senescence; systemic sclerosis; idiopathic pulmonary fibrosis.
Idiopathic pulmonary fibrosis (IPF) is a progressive and medically refractory lung disease with a grim prognosis. Although the etiology of IPF remains perplexing, abnormal adaptive immune responses are evident in many afflicted patients. We hypothesized that perturbations of human leukocyte antigen (HLA) allele frequencies, which are often seen among patients with immunologic diseases, may also be present in IPF patients.
HLA alleles were determined in subpopulations of IPF and normal subjects using molecular typing methods. HLA-DRB1*15 was over-represented in a discovery cohort of 79 Caucasian IPF subjects who had lung transplantations at the University of Pittsburgh (36.7%) compared to normal reference populations. These findings were prospectively replicated in a validation cohort of 196 additional IPF subjects from four other U.S. medical centers that included both ambulatory patients and lung transplantation recipients. High-resolution typing was used to further define specific HLA-DRB1*15 alleles. DRB1*1501 prevalence in IPF subjects was similar among the 143 ambulatory patients and 132 transplant recipients (31.5% and 34.8%, respectively, p = 0.55). The aggregate prevalence of DRB1*1501 in IPF patients was significantly greater than among 285 healthy controls (33.1% vs. 20.0%, respectively, OR 2.0; 95%CI 1.3–2.9, p = 0.0004). IPF patients with DRB1*1501 (n = 91) tended to have decreased diffusing capacities for carbon monoxide (DLCO) compared to the 184 disease subjects who lacked this allele (37.8±1.7% vs. 42.8±1.4%, p = 0.036).
DRB1*1501 is more prevalent among IPF patients than normal subjects, and may be associated with greater impairment of gas exchange. These data are novel evidence that immunogenetic processes can play a role in the susceptibility to and/or manifestations of IPF. Findings here of a disease association at the HLA-DR locus have broad pathogenic implications, illustrate a specific chromosomal area for incremental, targeted genomic study, and may identify a distinct clinical phenotype among patients with this enigmatic, morbid lung disease.