Paracrine SPARC signaling dysregulates alveolar epithelial barrier integrity and function in lung fibrosis.
ABSTRACT: Idiopathic pulmonary fibrosis (IPF) is a chronic scarring disease in which aging, environmental exposure(s) and genetic susceptibility have been implicated in disease pathogenesis, however, the causes and mechanisms of the progressive fibrotic cascade are still poorly understood. As epithelial–mesenchymal interactions are essential for normal wound healing, through human 2D and 3D in vitro studies, we tested the hypothesis that IPF fibroblasts (IPFFs) dysregulate alveolar epithelial homeostasis. Conditioned media from IPFFs exaggerated the wound-healing response of primary human Type II alveolar epithelial cells (AECs). Furthermore, AECs co-cultured with IPFFs exhibited irregular epithelialization compared with those co-cultured with control fibroblasts (NHLFs) or AECs alone, suggesting that epithelial homeostasis is dysregulated in IPF as a consequence of the abnormal secretory phenotype of IPFFs. Secretome analysis of IPFF conditioned media and functional studies identified the matricellular protein, SPARC, as a key mediator in the epithelial–mesenchymal paracrine signaling, with increased secretion of SPARC by IPFFs promoting persistent activation of alveolar epithelium via an integrin/focal adhesion/cellular-junction axis resulting in disruption of epithelial barrier integrity and increased macromolecular permeability. These findings suggest that in IPF fibroblast paracrine signaling promotes persistent alveolar epithelial activation, so preventing normal epithelial repair responses and restoration of tissue homeostasis. Furthermore, they identify SPARC-mediated paracrine signaling as a potential therapeutic target to promote the restoration of lung epithelial homoestasis in IPF patients.
Project description:The causes underlying the self-perpetuating nature of idiopathic pulmonary fibrosis (IPF), a progressive and usually lethal disease, remain unknown. We hypothesised that alveolar soluble annexin V contributes to lung fibrosis, based on the observation that human IPF bronchoalveolar lavage fluid (BALF) containing high annexin V levels promoted fibroblast involvement in alveolar epithelial wound healing that was reduced when annexin V was depleted from the BALF. Conditioned medium from annexin V-treated alveolar epithelial type 2 cells (AEC2), but not annexin V per se, induced proliferation of human fibroblasts and contained pro-fibrotic, IPF-associated proteins, as well as pro-inflammatory cytokines that were found to correlate tightly (r>0.95) with annexin V levels in human BALF. ErbB2 receptor tyrosine kinase in AECs was activated by annexin V, and blockade reduced the fibrotic potential of annexin V-treated AEC-conditioned medium. In vivo, aerosol delivery of annexin V to mouse lung induced inflammation, fibrosis and increased hydroxyproline, with activation of Wnt, transforming growth factor-?, mitogen-activated protein kinase and nuclear factor-?B signalling pathways, as seen in IPF. Chronically increased alveolar annexin V levels, as reflected in increased IPF BALF levels, may contribute to the progression of IPF by inducing the release of pro-fibrotic mediators.
Project description:Pathologic features of idiopathic pulmonary fibrosis (IPF) include genetic predisposition, activation of the unfolded protein response, telomere attrition, and cellular senescence. The mechanisms leading to alveolar epithelial cell (AEC) senescence are poorly understood. MicroRNAs (miRNAs) have been reported as regulators of cellular senescence. Senescence markers including p16, p21, p53, and senescence-associated ?-galactosidase (SA-?gal) activity were measured in type II AECs from IPF lungs and unused donor lungs. miRNAs were quantified in type II AECs using gene expression arrays and quantitative RT-PCR. Molecular markers of senescence (p16, p21, and p53) were elevated in IPF type II AECs. SA-?gal activity was detected in a greater percentage in type II AECs isolated from IPF patients (23.1%) compared to patients with other interstitial lung diseases (1.2%) or normal controls (0.8%). The relative levels of senescence-associated miRNAs miR-34a, miR-34b, and miR-34c, but not miR-20a, miR-29c, or miR-let-7f were significantly higher in type II AECs from IPF patients. Overexpression of miR-34a, miR-34b, or miR-34c in lung epithelial cells was associated with higher SA-?gal activity (27.8%, 35.1%, and 38.2%, respectively) relative to control treated cells (8.8%). Targets of miR-34 miRNAs, including E2F1, c-Myc, and cyclin E2, were lower in IPF type II AECs. These results show that markers of senescence are uniquely elevated in IPF type II AECs and suggest that the miR-34 family of miRNAs regulate senescence in IPF type II AECs.
Project description:Idiopathic pulmonary fibrosis (IPF) is the prototypic progressive fibrotic lung disease with a median survival of 2-4 years. Injury to and/or dysfunction of alveolar epithelium are strongly implicated in IPF disease initiation, but what factors determine why fibrosis progresses rather than normal tissue repair occurs remain poorly understood. We previously demonstrated that ZEB1-mediated epithelial-mesenchymal transition (EMT) in human alveolar epithelial type II (ATII) cells augments TGF-β-induced profibrogenic responses in underlying lung fibroblasts by paracrine signalling. Here we investigated bi-directional epithelial-mesenchymal crosstalk and its potential to drive fibrosis progression. RNA sequencing (RNA-seq) of lung fibroblasts exposed to conditioned media from ATII cells undergoing RAS-induced EMT identified many differentially expressed genes including those involved in cell migration and extracellular matrix (ECM) regulation. We confirmed that paracrine signalling between AS-activated ATII cells and fibroblasts augmented fibroblast recruitment and demonstrated that this involved a ZEB1-tissue plasminogen activator (tPA) axis. In a reciprocal fashion, paracrine signalling from TGF-β-activated lung fibroblasts or IPF fibroblasts induced RAS activation in ATII cells, at least partially via the secreted protein, SPARC. Together these data identify that aberrant bi-directional epithelial-mesenchymal crosstalk in IPF drives a chronic feedback loop that maintains a wound-healing phenotype and provides self-sustaining pro-fibrotic signals.
Project description:Endoplasmic Reticulum (ER) stress of alveolar epithelial cells (AECs) is recognized as a key event of cell dysfunction in pulmonary fibrosis (PF). However, the mechanisms leading to AECs ER stress and ensuing unfolded protein response (UPR) pathways in idiopathic PF (IPF) remain unclear. We hypothesized that alveolar hypoxic microenvironment would generate ER stress and AECs apoptosis through the hypoxia-inducible factor-1? (HIF-1?). Combining ex vivo, in vivo and in vitro experiments, we investigated the effects of hypoxia on the UPR pathways and ER stress-mediated apoptosis, and consecutively the mechanisms linking hypoxia, HIF-1?, UPR and apoptosis. HIF-1? and the pro-apoptotic ER stress marker C/EBP homologous protein (CHOP) were co-expressed in hyperplastic AECs from bleomycin-treated mice and IPF lungs, not in controls. Hypoxic exposure of rat lungs or primary rat AECs induced HIF-1?, CHOP and apoptosis markers expression. In primary AECs, hypoxia activated UPR pathways. Pharmacological ER stress inhibitors and pharmacological inhibition or silencing of HIF-1? both prevented hypoxia-induced upregulation of CHOP and apoptosis. Interestingly, overexpression of HIF-1? in normoxic AECs increased UPR pathways transcription factors activities, and CHOP expression. These results indicate that hypoxia and HIF-1? can trigger ER stress and CHOP-mediated apoptosis in AECs, suggesting their potential contribution to the development of IPF.
Project description:BACKGROUND: Idiopathic pulmonary fibrosis (IPF) is a poorly understood progressive disease characterized by the recurrent damage of alveolar epithelial cells as well as inappropriate expansion and activation of fibroblasts resulting in pronounced extracellular matrix (ECM) deposition. Although recent studies have indicated the involvement of secreted protein acidic and rich in cysteine (SPARC), a matricellular protein regulating ECM deposition, in the pathogenesis of fibrosis, factors regulating SPARC expression or roles of SPARC in fibrosis have not been fully elucidated. RESULTS: Among the profibrotic factors examined in cultured fibroblasts, we showed that SPARC expression was upregulated mainly by transforming growth factor (TGF)-?. We also showed that expression of SPARC in the lung was upregulated in the murine bleomycin-induced pulmonary fibrosis model, which was inhibited by TGF-? receptor I inhibitor. Knockdown of SPARC in fibroblasts using siRNA or treatment with the antioxidant N-acetylcysteine attenuated epithelial cell injury induced by TGF-?-activated fibroblasts in a coculture system. We also demonstrated that SPARC was required for hydrogen peroxide (H2O2) production in fibroblasts treated with TGF-?. Furthermore, TGF-? activated integrin-linked kinase (ILK), which was inhibited by SPARC siRNA. Knockdown of ILK attenuated extracellular H2O2 generation in TGF-?-stimulated fibroblasts. Our results indicated that SPARC is upregulated by TGF-? and is required for TGF-?-induced H2O2 production via activation of ILK, and this H2O2 production from fibroblasts is capable of causing epithelial cell injury. CONCLUSIONS: The results presented in this study suggest that SPARC plays a role in epithelial damage in the IPF lung via enhanced H2O2 production from fibroblasts activated by TGF-?. Therefore, SPARC inhibition may prevent epithelial injury in IPF lung and represent a potential therapeutic approach for IPF.
Project description:Tetraspanin 1(TSPAN1) as a clinically relevant gene target in cancer has been studied, but there is no direct in vivo or vitro evidence for pulmonary fibrosis (PF). Using reanalysing Gene Expression Omnibus data, here, we show for the first time that TSPAN1 was markedly down-regulated in lung tissue of patient with idiopathic PF (IPF) and verified the reduced protein expression of TSPAN1 in lung tissue samples of patient with IPF and bleomycin-induced PF mice. The expression of TSPAN1 was decreased and associated with transforming growth factor-?1 (TGF-?<sub>1</sub> )-induced molecular characteristics of epithelial-to-mesenchymal transition (EMT) in alveolar epithelial cells (AECs). Silencing TSPAN1 promoted cell migration, and the expression of alpha-smooth muscle actin, vimentin and E-cadherin in AECs with TGF-?<sub>1</sub> treatment, while exogenous TSPAN1 has the converse effects. Moreover, silencing TSPAN1 promotes the phosphorylation of Smad2/3 and stabilizes beta-catenin protein, however, overexpressed TSPAN1 impeded TGF-?<sub>1</sub> -induced activation of Smad2/3 and beta-catenin pathway in AECs. Together, our study implicates TSPAN1 as a key regulator in the process of EMT in AECs of IPF.
Project description:Current hypotheses suggest that aberrant wound healing has a critical role in the pathogenesis of idiopathic pulmonary fibrosis (IPF). In these hypotheses, continuous TGF-?1 secretion by alveolar epithelial cells (AECs) in abnormal wound healing has a critical role in promoting fibroblast differentiation into myofibroblasts. Mesenchymal stem cells (MSCs) home to the injury site and reduce fibrosis by secreting multifunctional antifibrotic humoral factors in IPF. In this study, we show that MSCs can correct the inadequate-communication between epithelial and mesenchymal cells through STC1 (Stanniocalcin-1) secretion in a bleomycin-induced IPF model. Inhalation of recombinant STC1 shows the same effects as the injection of MSCs. Using STC1 plasmid, it was possible to enhance the ability of MSCs to ameliorate the fibrosis. MSCs secrete large amounts of STC1 in response to TGF-?1 in comparison to AECs and fibroblasts. The antifibrotic effects of STC1 include reducing oxidative stress, endoplasmic reticulum (ER) stress, and TGF-?1 production in AECs. The STC1 effects can be controlled by blocking uncoupling protein 2 (UCP2) and the secretion is affected by the PI3/AKT/mTORC1 inhibitors. Our findings suggest that STC1 tends to correct the inappropriate epithelial-mesenchymal relationships and that STC1 plasmid transfected to MSCs or STC1 inhalation could become promising treatments for IPF.
Project description:BACKGROUND: Idiopathic pulmonary fibrosis (IPF) is a progressive disorder marked by relentless fibrosis and damage of the lung architecture. A growing body of evidence now suggests that IPF progresses as a result of aberrant epithelial-fibroblast crosstalk. Injured epithelia are a major source of growth factors such as PDGF which guide resident fibroblasts to injury sites. RESULTS: In this study, we utilized a novel co-culture system to investigate the effect of fibroblast phenotype on their response to epithelial injury. Fibroblasts from normal lungs (NHLF) responded to epithelial injury and populated the wound site forming a fibroblast plug/mechanical barrier which prevented epithelial wound closure. IPF fibroblasts were impaired in their response to epithelial injury. They also expressed reduced PDGFR? compared to NHLFs and were defective towards PDGF-AA mediated directional movement. Neutralization of PDGF-AA and pan-PDGF but not PDGF-BB reduced the injury response of NHLFs thereby preventing the formation of the mechanical barrier and promoting epithelial wound closure. Co-culture of epithelial cells with IPF fibroblasts led to marked increase in the levels of pro-fibrotic growth factors - bFGF and PDGF and significant depletion of anti-fibrotic HGF in the culture medium. Furthermore, IPF fibroblasts but not NHLFs induced a transient increase in mesenchymal marker expression in the wound lining epithelial cells. This was accompanied by increased migration and faster wound closure in co-cultures with IPF fibroblasts. CONCLUSIONS: Our data demonstrate that the IPF fibroblasts have an aberrant repair response to epithelial injury.
Project description:Telomeres are short in type II alveolar epithelial cells (AECs) of patients with idiopathic pulmonary fibrosis (IPF). Whether dysfunctional telomeres contribute directly to development of lung fibrosis remains unknown. The objective of this study was to investigate whether telomere dysfunction in type II AECs, mediated by deletion of the telomere shelterin protein TRF1, leads to pulmonary fibrosis in mice (SPC-Cre TRF1fl/fl mice). Deletion of TRF1 in type II AECs for 2 weeks increased ?H2AX DNA damage foci, but not histopathologic changes in the lung. Deletion of TRF1 in type II AECs for up to 9 months resulted in short telomeres and lung remodeling characterized by increased numbers of type II AECs, ?-smooth muscle actin+ mesenchymal cells, collagen deposition, and accumulation of senescence-associated ?-galactosidase+ lung epithelial cells. Deletion of TRF1 in collagen-expressing cells caused pulmonary edema, but not fibrosis. These results demonstrate that prolonged telomere dysfunction in type II AECs, but not collagen-expressing cells, leads to age-dependent lung remodeling and fibrosis. We conclude that telomere dysfunction in type II AECs is sufficient to cause lung fibrosis, and may be a dominant molecular defect causing IPF. SPC-Cre TRF1fl/fl mice will be useful for assessing cellular and molecular mechanisms of lung fibrosis mediated by telomere dysfunction.
Project description:Excessive extracellular matrix production by fibroblasts in response to tissue injury contributes to fibrotic diseases, such as idiopathic pulmonary fibrosis (IPF). Epithelial-mesenchymal transition, involving transition of alveolar epithelial cells (AECs) to pulmonary fibroblasts, appears to be an important contributory process to lung fibrosis. Although aberrant expression of microRNAs (miRs) is involved in a variety of pathophysiologic processes, the role of miRs in fibrotic lung diseases is less well understood. In the present study, we found that miR-200a, miR-200b, and miR-200c are significantly down-regulated in the lungs of mice with experimental lung fibrosis. Levels of miR-200a and miR-200c were reduced in the lungs of patients with IPF. miR-200 had greater expression in AECs than in lung fibroblasts, and AECs from mice with experimental pulmonary fibrosis had diminished expression of miR-200. We found that the miR-200 family members inhibit transforming growth factor-?1-induced epithelial-mesenchymal transition of AECs. miR-200 family members can reverse the fibrogenic activity of pulmonary fibroblasts from mice with experimental pulmonary fibrosis and from patients with IPF. Indeed, the introduction of miR-200c diminishes experimental pulmonary fibrosis in mice. Thus, the miR-200 family members participate importantly in fibrotic lung diseases and suggest that restoring miR-200 expression in the lungs may represent a novel therapeutic approach in treating pulmonary fibrotic diseases.