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Rationale: Extracellular vesicles (EVs) are small lipid vesicles, and EV-coupled microRNAs (miRNAs) are important modulators of biological processes. Fibrocytes are circulating bone marrow-derived cells that migrate into the injured lungs and contribute to fibrogenesis. The question of whether EV-coupled miRNAs derived from fibrocytes are able to regulate pulmonary fibrosis has not been addressed yet., Methods: Pulmonary fibrosis was induced in rats by intratracheal administration of an adenoviral gene vector encoding active transforming growth factor-β1 (TGF-β1) or control vector. Primary fibrocytes and fibroblasts were cultured from rat lungs and were sorted by anti-CD45 magnetic beads. Human circulating fibrocytes and fibrocytes in bronchoalveolar lavage fluid (BALF) were isolated by fibronectin-coated dishes. Fibrocytes were cultured on different stiffness plates or decellularised lung scaffolds. We also determined the effects of extracellular matrix (ECM) and recombinant TGF-β1 on the cellular and EV-coupled miRNA expression of fibrocytes., Results: The EVs of fibrocytes derived from fibrotic lungs significantly upregulated the expression of col1a1 of fibroblasts. Culturing on rigid plates or fibrotic decellularised lung scaffolds increased miR-21-5 p expression compared with soft plates or normal lung scaffolds. Dissolved ECM collected from fibrotic lungs and recombinant TGF-β1 increased miR-21-5 p expression on fibrocytes, and these effects were attenuated on soft plates. Fibrocytes from BALF collected from fibrotic interstitial pneumonia patients showed higher miR-21-5 p expression than those from other patients., Conclusions: Our results indicate that ECM contributes to fibrogenesis through biomechanical and biochemical effects on miRNA expression in fibrocytes., Competing Interests: Competing interests: MRJK reports grants and personal fees from the Canadian Institute for Health Research (PJT-162295), Roche, Boehringer Ingelheim, GSK, Gilead, Prometic, Alkermes, Actelion, Respivert and Synairgen., (© Author(s) (or their employer(s)) 2021. No commercial re-use. See rights and permissions. Published by BMJ.)

Purpose of Review: Pulmonary fibrosis is a chronic and progressive lung disease involving unclear pathological mechanisms. The present review presents and discusses the major and recent advances in our knowledge of the pathogenesis of lung fibrosis., Recent Findings: The past months have deepened our understanding on the cellular actors of fibrosis with a better characterization of the abnormal lung epithelial cells observed during lung fibrosis. Better insight has been gained into fibroblast biology and the role of immune cells during fibrosis. Mechanistically, senescence appears as a key driver of the fibrotic process. Extracellular vesicles have been discovered as participating in the impaired cellular cross-talk during fibrosis and deeper understanding has been made on developmental signaling in lung fibrosis., Summary: This review emphasizes the contribution of different cell types and mechanisms during pulmonary fibrosis, highlights new insights for identification of potential therapeutic strategies, and underlines where future research is needed to answer remaining open questions.

Background: The role of mast cells accumulating in idiopathic pulmonary fibrosis (IPF) lungs is unknown., Objectives: We investigated the effect of fibrotic extracellular matrix (ECM) on mast cells in experimental and human pulmonary fibrosis., Results: In IPF lungs, mast cell numbers were increased and correlated with disease severity (control vs 60%90% vs 60%90% vs FVC<60%, mean difference=-268.6, 95% CI of difference -441.0 to -96.17, p=0.0007). Plasma tryptase levels were increased in IPF and negatively correlated with FVC (control vs FVC<60%, mean difference=-17.12, 95% CI of difference -30.02 to -4.22, p=0.006: correlation curves R=-0.045, p=0.025). In a transforming growth factor (TGF)-β1-induced pulmonary fibrosis model, chymase-positive and tryptase-positive mast cells accumulated in fibrotic lung. Lung tissue was decellularised and reseeded with bone marrow or peritoneum-derived mast cells; cells on fibrotic ECM released more TGF-β1 compared with normal ECM (active TGF-β1: bone marrow-derived mast cell (BMMC)-DL vs BMMC-TGF-β1 p=0.0005, peritoneal mast cell (PMC)-DL vs PMC-TGF-β1 p=0.0003, total TGF-β1: BMMC-DL vs BMMC-TGF-β1 p=0.013, PMC-DL vs PMC-TGF-β1 p=0.001). Mechanical stretch of lungs caused mast cell degranulation; mast cell stabilisers inhibited degranulation (histamine: cont vs doxantrazole p=0.004, β-hexosaminidase: cont vs doxantrazole, mean difference=1.007, 95% CI of difference 0.2700 to 1.744, p=0.007) and TGF-β1 activation (pSmad2/Smad2: cont vs dox p=0.006). Cromoglycate attenuated pulmonary fibrosis in rats (collagen: phosphate-buffered saline (PBS) vs cromoglycate p=0.036, fibrotic area: PBS vs cromoglycate p=0.031)., Conclusion: This study suggests that mast cells may contribute to the progression of pulmonary fibrosis., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2019. No commercial re-use. See rights and permissions. Published by BMJ.)

Idiopathic pulmonary fibrosis (IPF) is a progressive disease with an unknown cause. Two drugs, nintedanib and pirfenidone, have been shown to slow, but not stop, disease progression. Pulmonary hypertension (PH) is a frequent complication in IPF patients and is associated with poor prognosis. Macitentan is a dual endothelin receptor antagonist that is approved for pulmonary arterial hypertension treatment. We hypothesised that using macitentan to treat animals with pulmonary fibrosis induced by adenoviral vector encoding biologically active transforming growth factor-β1 (AdTGF-β1) would improve the PH caused by chronic lung disease and would limit the progression of fibrosis.Rats (Sprague Dawley) which received AdTGF-β1 were treated by daily gavage of macitentan (100 mg·kg -1 ·day -1 ), pirfenidone (0.5% food admix) or a combination from day 14 to day 28. Pulmonary artery pressure (PAP) was measured before the rats were killed, and fibrosis was subsequently evaluated by morphometric measurements and hydroxyproline analysis.AdTGF-β1 induced pulmonary fibrosis associated with significant PH. Macitentan reduced the increase in PAP and both macitentan and pirfenidone stopped fibrosis progression from day 14 to day 28. Macitentan protected endothelial cells from myofibroblast differentiation and apoptosis whereas pirfenidone only protected against fibroblast-to-myofibroblast differentiation. Both drugs induced apoptosis of differentiated myofibroblasts in vitro and in vivo Our results demonstrate that dual endothelin receptor antagonism was effective in both PH and lung fibrosis whereas pirfenidone only affected fibrosis., Competing Interests: Conflict of interest: M. Iglarz is an employee of Actelion Pharmaceuticals Ltd, the manufacturer of macitentan. Conflict of interest: M. Kolb reports grants and personal fees from Roche, Boehringer Ingelheim, GSK, Gilead, Prometic and Alkermes, grants from Actelion, Respivert and Synairgen, and personal fees from AstraZeneca and Genoa, outside the submitted work., (Copyright ©ERS 2018.)

Idiopathic pulmonary fibrosis (IPF) is characterized by progressive fibroblast and myofibroblast proliferation, and extensive deposition of extracellular matrix (ECM). Fibroblast growth factor-1 (FGF-1) belongs to the FGF family and has been shown to inhibit fibroblast collagen production and differentiation into myofibroblasts, and revert epithelial-mesenchymal transition by inhibiting TGF-β1 signalling pathways. However, the precise role of FGF-1 in pulmonary fibrosis has not yet been elucidated. In this study, we explore the mechanisms underlying the anti-fibrogenic effect of FGF-1 in pulmonary fibrosis in vitro and in vivo by prolonged transient overexpression of FGF-1 (AdFGF-1) and TGF-β1 (AdTGF-β1) using adenoviral vectors. In vivo, FGF-1 overexpression markedly attenuated TGF-β1-induced pulmonary fibrosis in rat lungs when given both concomitantly, or delayed, by enhancing proliferation and hyperplasia of alveolar epithelial cells (AECs). AdFGF-1 also attenuated the TGF-β1 signalling pathway and induced FGFR1 expression in AECs. In vitro, AdFGF-1 prevented the increase in α-SMA and the decrease in E-cadherin induced by AdTGF-β1 in normal human lung fibroblasts, primary human pulmonary AECs, and A549 cells. Concomitantly, AdTGF-β1-induced Smad2 phosphorylation was significantly reduced by AdFGF-1 in both cell types. AdFGF-1 also attenuated the increase in TGFβR1 protein and mRNA levels in fibroblasts. In AECs, AdFGF-1 decreased TGFβR1 protein by favouring TGFβR1 degradation through the caveolin-1/proteasome pathway. Furthermore, FGFR1 expression was increased in AECs, whereas it was decreased in fibroblasts. In serum of IPF patients, FGF-1 levels were increased compared to controls. Interestingly, FGF-1 expression was restricted to areas of AEC hyperplasia, but not α-SMA-positive areas in IPF lung tissue. Our results demonstrate that FGF-1 may have preventative and therapeutic effects on TGF-β1-driven pulmonary fibrosis via inhibiting myofibroblast differentiation, inducing AEC proliferation, regulating TGF-β1 signalling by controlling TGFβR1 expression and degradation, and regulating FGFR1 expression. Thus, modulating FGF-1 signalling represents a potential therapy for the treatment of pulmonary fibrosis. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd., (Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.)

Endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) have been associated with fibrotic lung disease, although exactly how they modulate this process remains unclear. Here we investigated the role of GRP78, the main UPR regulator, in an experimental model of lung injury and fibrosis. Grp78(+/-) , Chop(-/-) and wild type C57BL6/J mice were exposed to bleomycin by oropharyngeal intubation and lungs were examined at days 7 and 21. We demonstrate here that Grp78(+/-) mice were strongly protected from bleomycin-induced fibrosis, as shown by immunohistochemical analysis, collagen content and lung function measurements. In the inflammatory phase of this model, a reduced number of lung macrophages associated with an increased number of TUNEL-positive cells were observed in Grp78(+/-) mice. Dual immunohistochemical and in situ hybridization experiments showed that the macrophage population from the protected Grp78(+/-) mice was also strongly positive for cleaved caspase-3 and Chop mRNA, respectively. In contrast, the administration of bleomycin to Chop(-/-) mice resulted in increased quasi-static elastance and extracellular matrix deposition associated with an increased number of parenchymal arginase-1-positive macrophages that were negative for cleaved caspase-3. The data presented indicate that the UPR is activated in fibrotic lung tissue and strongly localized to macrophages. GRP78- and CHOP-mediated macrophage apoptosis was found to protect against bleomycin-induced fibrosis. Overall, we demonstrate here that the fibrotic response to bleomycin is dependent on GRP78-mediated events and provides evidence that macrophage polarization and apoptosis may play a role in this process. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd., (Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.)

Rationale: Recent findings suggesting transforming growth factor (TGF)-β1 activation by mechanical stimuli in vitro raised the question of whether this phenomenon was relevant in vivo in the context of pulmonary fibrosis., Objectives: To explore the effect of mechanical stress on TGF-β1 activation and its signaling pathway in rat and human fibrotic lung tissue using a novel ex vivo model., Methods: Rat lung fibrosis was induced using transient gene expression of active TGF-β1. Lungs were harvested at Day 14 or 21 and submitted to various stimuli in a tissue bath equipped with a force transducer and servo-controlled arm., Measurements and Main Results: Fibrotic lung strips responded to tensile force by releasing active TGF-β1 from latent stores with subsequent increase in tissue phospho-Smad2/3. In contrast, measurable active TGF-β1 and phospho-Smad2/3 were not induced by mechanical stress in nonfibrotic lungs. Protease inhibition did not affect the release of active TGF-β1. A TGF-β1 receptor inhibitor, Rho-associated protein kinase inhibitor, and αv integrin inhibitor all attenuated mechanical stretch-induced phospho-Smad2/3 in fibrotic lung strips. Furthermore, the induction of phospho-Smad2/3 was enhanced in whole fibrotic rat lungs undergoing ventilation pressure challenge compared with control lungs. Last, tissue slices from human lung with usual interstitial pneumonia submitted to mechanical force showed an increase in TGF-β1 activation and induction of phospho-Smad2/3 in contrast with human nonfibrotic lungs., Conclusions: Mechanical tissue stretch contributes to the development of pulmonary fibrosis via mechanotransduced activation of TGF-β1 in rodent and human pulmonary fibrosis.

Idiopathic pulmonary fibrosis is a chronic, progressive and lethal disease of unknown etiology that ranks among the most frequent interstitial lung diseases. Idiopathic pulmonary fibrosis is characterized by dysregulated healing mechanisms that lead to the accumulation of large amounts of collagen in the lung tissue that disrupts the alveolar architecture. The two currently available treatments, nintedanib and pirfenidone, are only able to slow down the disease without being curative. We demonstrated in the past that HSPB5, a low molecular weight heat shock protein, was involved in the development of fibrosis and therefore was a potential therapeutic target. Here, we have explored whether NCI-41356, a chemical inhibitor of HSPB5, can limit the development of pulmonary fibrosis. In vivo, we used a mouse model in which fibrosis was induced by intratracheal injection of bleomycin. Mice were treated with NaCl or NCI-41356 (six times intravenously or three times intratracheally). Fibrosis was evaluated by collagen quantification, immunofluorescence and TGF-β gene expression. In vitro, we studied the specific role of NCI-41356 on the chaperone function of HSPB5 and the inhibitory properties of NCI-41356 on HSPB5 interaction with its partner SMAD4 during fibrosis. TGF-β1 signaling was evaluated by immunofluorescence and Western Blot in epithelial cells treated with TGF-β1 with or without NCI-41356. In vivo, NCI-41356 reduced the accumulation of collagen, the expression of TGF-β1 and pro-fibrotic markers (PAI-1, α-SMA). In vitro, NCI-41356 decreased the interaction between HSPB5 and SMAD4 and thus modulated the SMAD4 canonical nuclear translocation involved in TGF-β1 signaling, which may explain NCI-41356 anti-fibrotic properties. In this study, we determined that inhibition of HSPB5 by NCI-41356 could limit pulmonary fibrosis in mice by limiting the synthesis of collagen and pro-fibrotic markers. At the molecular level, this outcome may be explained by the effect of NCI-41356 inhibiting HSPB5/SMAD4 interaction, thus modulating SMAD4 and TGF-β1 signaling. Further investigations are needed to determine whether these results can be transposed to humans. [ABSTRACT FROM AUTHOR]

Purpose: Idiopathic pulmonary fibrosis (IPF) is a progressive disease with poor outcome and limited therapeutic options. Imaging of IPF is limited to high-resolution computed tomography (HRCT) which is often not sufficient for a definite diagnosis and has a limited impact on therapeutic decision and patient management. Hypoxia of the lung is a significant feature of IPF but its role on disease progression remains elusive. Thus, the aim of our study was to evaluate hypoxia imaging with [18F]FMISO as a predictive biomarker of disease progression and therapy efficacy in preclinical models of lung fibrosis in comparison with [18F]FDG. Methods: Eight-week-old C57/BL6 mice received an intratracheal administration of bleomycin (BLM) at day (D) 0 to initiate lung fibrosis. Mice received pirfenidone (300 mg/kg) or nintedanib (60 mg/kg) by daily gavage from D9 to D23. Mice underwent successive PET/CT imaging at several stages of the disease (baseline, D8/D9, D15/D16, D22/D23) with [18F]FDG and [18F]FMISO. Histological determination of the lung expression of HIF-1α and GLUT-1 was performed at D23. Results: We demonstrate that mean lung density on CT as well as [18F]FDG and [18F]FMISO uptakes are upregulated in established lung fibrosis (1.4-, 2.6- and 3.2-fold increase respectively). At early stages, lung areas with [18F]FMISO uptake are still appearing normal on CT scans and correspond to areas which will deteriorate towards fibrotic lesions at later timepoints. Nintedanib and pirfenidone dramatically and rapidly decreased mean lung density on CT as well as [18F]FDG and [18F]FMISO lung uptakes (pirfenidone: 1.2-, 2.9- and 2.6-fold decrease; nintedanib: 1.2-, 2.3- and 2.5-fold decrease respectively). Early [18F]FMISO lung uptake was correlated with aggressive disease progression and better nintedanib efficacy. Conclusion: [18F]FMISO PET imaging is a promising tool to early detect and monitor lung fibrosis progression and therapy efficacy. [ABSTRACT FROM AUTHOR]

Pulmonary fibrosis is a progressive lung disease characterized by myofibroblast accumulation and excessive extracellular matrix deposition. We sought to investigate the role of FKBP13 (13-kD FK506-binding protein), an endoplasmic reticulum-resident molecular chaperone, in various forms of pulmonary fibrosis. We first characterized the gene and protein expression of FKBP13 in lung biopsy specimens from 24 patients with idiopathic pulmonary fibrosis and 17 control subjects. FKBP13 expression was found to be elevated in the fibrotic regions of idiopathic pulmonary fibrosis lung tissues and correlated with declining forced vital capacity and dyspnea severity. FKBP13 expression was also increased in lung biopsy specimens of patientswith hypersensitivity pneumonitis, rheumatoid arthritis, and sarcoidosis-associated interstitial lung disease. We next evaluated the role of this protein using FKBP132/2mice in a bleomycin model of pulmonary fibrosis. Animals were assessed for lung function and histopathology at different stages of lung injury including the inflammatory (Day 7), fibrotic (Day 21), and resolution (Day 50) phases. FKBP132/2 mice showed increased infiltration of inflammatory cells and cytokines at Day 7, increased lung elastance and fibrosis at Day 21, and impaired resolution of fibrosis at Day 50. These changes were associated with an increased number of cells that stained positive for TUNEL and cleaved caspase 3 in the FKBP132/2 lungs, indicating a heightened cellular sensitivity to bleomycin. Our findings suggest that FKBP13 is a potential biomarker for severity of interstitial lung diseases and that it has a biologically relevant role in protecting mice against bleomycin-induced injury, inflammation, and fibrosis. [ABSTRACT FROM AUTHOR]

The editors comment on a study on the association of extracellular matrix (ECM) to the progression of lung fibrosis. They discuss the role of abnormal ECM properties in the progression of fibrosis and suggests the possible difference of the rate of disease progression or persistence between idiopathic pulmonary fibrosis (IPF) and systemic sclerosis (SSc)-related interstitial lung disease (ILD). They argue on the role of netrin-1 as mediator between mesenchymal cells and ECM.