Fibroblastic foci, covered with alveolar epithelia exhibiting epithelial-mesenchymal transition, destroy alveolar septa by disrupting blood flow in idiopathic pulmonary fibrosis

Progressive lung fibrosis: reprogramming a genetically vulnerable bronchoalveolar epithelium

Idiopathic pulmonary fibrosis (IPF) is etiologically complex, with well-documented genetic and nongenetic origins. In this Review, we speculate that the development of IPF requires two hits: the first establishes a vulnerable bronchoalveolar epithelium, and the second triggers mechanisms that reprogram distal epithelia to initiate and perpetuate a profibrotic phenotype. While vulnerability of the bronchoalveolar epithelia is most often driven by common or rare genetic variants, subsequent injury of the bronchoalveolar epithelia results in persistent changes in cell biology that disrupt tissue homeostasis and activate fibroblasts. The dynamic biology of IPF can best be contextualized etiologically and temporally, including stages of vulnerability, early disease, and persistent and progressive lung fibrosis. These dimensions of IPF highlight critical mechanisms that adversely disrupt epithelial function, activate fibroblasts, and lead to lung remodeling. Together with better recognition of early disease, this conceptual approach should lead to the development of novel therapeutics directed at the etiologic and temporal drivers of lung fibrosis that will ultimately transform the care of patients with IPF from palliative to curative.

The fibroblast activation protein alpha as a biomarker of pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a rare, chronic, and progressive interstitial lung disease with an average survival of approximately 3 years. The evolution of IPF is unpredictable, with some patients presenting a relatively stable condition with limited progression over time, whereas others deteriorate rapidly. In addition to IPF, other interstitial lung diseases can lead to pulmonary fibrosis, and up to a third have a progressive phenotype with the same prognosis as IPF. Clinical, biological, and radiological risk factors of progression were identified, but no specific biomarkers of fibrogenesis are currently available. A recent interest in the fibroblast activation protein alpha (FAPα) has emerged. FAPα is a transmembrane serine protease with extracellular activity. It can also be found in a soluble form, also named anti-plasmin cleaving enzyme (APCE). FAPα is specifically expressed by activated fibroblasts, and quinoline-based specific inhibitors (FAPI) were developed, allowing us to visualize its distribution in vivo by imaging techniques. In this review, we discuss the use of FAPα as a useful biomarker for the progression of lung fibrosis, by both its assessment in human fluids and/or its detection by imaging techniques and immunohistochemistry.

Mapping spatially resolved transcriptomes in human and mouse pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive lung disease with poor prognosis and limited treatment options. Efforts to identify effective treatments are thwarted by limited understanding of IPF pathogenesis and poor translatability of available preclinical models. Here we generated spatially resolved transcriptome maps of human IPF (n = 4) and bleomycin-induced mouse pulmonary fibrosis (n = 6) to address these limitations. We uncovered distinct fibrotic niches in the IPF lung, characterized by aberrant alveolar epithelial cells in a microenvironment dominated by transforming growth factor beta signaling alongside predicted regulators, such as TP53 and APOE. We also identified a clear divergence between the arrested alveolar regeneration in the IPF fibrotic niches and the active tissue repair in the acutely fibrotic mouse lung. Our study offers in-depth insights into the IPF transcriptional landscape and proposes alveolar regeneration as a promising therapeutic strategy for IPF.

Epigenetic Regulation of EMP/EMT-Dependent Fibrosis

Fibrosis represents a process characterized by excessive deposition of extracellular matrix (ECM) proteins. It often represents the evolution of pathological conditions, causes organ failure, and can, in extreme cases, compromise the functionality of organs to the point of causing death. In recent years, considerable efforts have been made to understand the molecular mechanisms underlying fibrotic evolution and to identify possible therapeutic strategies. Great interest has been aroused by the discovery of a molecular association between epithelial to mesenchymal plasticity (EMP), in particular epithelial to mesenchymal transition (EMT), and fibrogenesis, which has led to the identification of complex molecular mechanisms closely interconnected with each other, which could explain EMT-dependent fibrosis. However, the result remains unsatisfactory from a therapeutic point of view. In recent years, advances in epigenetics, based on chromatin remodeling through various histone modifications or through the intervention of non-coding RNAs (ncRNAs), have provided more information on the fibrotic process, and this could represent a promising path forward for the identification of innovative therapeutic strategies for organ fibrosis. In this review, we summarize current research on epigenetic mechanisms involved in organ fibrosis, with a focus on epigenetic regulation of EMP/EMT-dependent fibrosis.

Up-regulation by overexpression of c-MET in fibroblastic foci of usual interstitial pneumonia

Background

Usual interstitial pneumonia (UIP) is the radiologic and histologic hallmark of idiopathic pulmonary fibrosis (IPF) and the commonest histologic pattern of other progressive fibrosing interstitial lung diseases (e.g., fibrotic hypersensitivity pneumonia). Analogous to lung cancer, activation of epithelial-to-mesenchymal transition (EMT) is one of the main molecular pathways recently identified by transcriptomic studies in IPF. Fibroblastic foci (FF) are considered the active/trigger component of UIP pattern. The proto-oncogene C-MET is a key gene among molecules promoting EMT against which several inhibitors are currently available or promising in ongoing studies on lung cancer.

Methods

Twenty surgical cases of diffuse fibrosing interstitial lung diseases (fILD) with UIP pattern and FF-rich (17 IPF and 3 patients with fibrotic hypersensitivity pneumonia, fHP) were retrospectively selected. FF were manually microdissected and analysed for c-MET gene alterations (FISH amplification and gene hot-spot mutations Sanger sequencing) and tested with a c-MET companion diagnostic antibody (clone SP44 metmab) by immunohistochemistry.

Results

FF are characterized by upregulation of c-MET as shown by overexpression of the protein in 80% of cases, while no gene amplification by FISH or mutations were detected. C-MET upregulation of FF was observed either in IPF and fHP, with a tropism for the epithelial cell component only.

Conclusion

Upregulation of c-MET in FF of ILD with UIP pattern further confirms the key role of the proto-oncogene c-MET in its pathogenesis, possibly representing an interesting and easily-detectable molecular target for selective therapy using specific inhibitors in future clinical trials, similar to lung cancer. It is reasonable to speculate that molecular alterations in FF can also be detected in FF by transbronchial cryobiopsy.

In vitro co-culture studies and the crucial role of fibroblast-immune cell crosstalk in IPF pathogenesis

IPF is a fatal lung disease characterized by intensive remodeling of lung tissue leading to respiratory failure. The remodeling in IPF lungs is largely characterized by uncontrolled fibrosis. Fibroblasts and their contractile phenotype the myofibroblast are the main cell types responsible for typical wound healing responses, however in IPF, these responses are aberrant and result in the overactivation of fibroblasts which contributes to the inelasticity of the lung leading to a decrease in lung function. The specific mechanisms behind IPF pathogenesis have been elusive, but recently the innate and adaptive immunity have been implicated in the fibrotic processes of the disease. In connection with this, several in vitro co-culture models have been used to investigate the specific interactions occurring between fibroblasts and immune cells and how this contributes to the pathobiology of IPF. In this review, we discuss the in vitro models that have been used to examine the abnormal interactions between fibroblasts and cells of the innate and adaptive immune system, and how these contribute to the fibrotic processes in the lungs of IPF patients.

Lysyl oxidase like-2 in fibrosis and cardiovascular disease

Fibrosis is an important and essential reparative response to injury that, if left uncontrolled, results in the excessive synthesis, deposition, remodeling, and stiffening of the extracellular matrix, which is deleterious to organ function. Thus, the sustained activation of enzymes that catalyze matrix remodeling and cross linking is a fundamental step in the pathology of fibrotic diseases. Recent studies have implicated the amine oxidase lysyl oxidase like-2 (LOXL2) in this process and established significantly elevated expression of LOXL2 as a key component of profibrotic conditions in several organ systems. Understanding the relationship between LOXL2 and fibrosis as well as the mechanisms behind these relationships can offer significant insights for developing novel therapies. Here, we summarize the key findings that demonstrate the link between LOXL2 and fibrosis and inflammation, examine current therapeutics targeting LOXL2 for the treatment of fibrosis, and discuss future directions for experiments and biomedical engineering.

Wilms Tumor 1-Driven Fibroblast Activation and Subpleural Thickening in Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive fibrotic lung disease that is often fatal due to the formation of irreversible scar tissue in the distal areas of the lung. Although the pathological and radiological features of IPF lungs are well defined, the lack of insight into the fibrogenic role of fibroblasts that accumulate in distinct anatomical regions of the lungs is a critical knowledge gap. Fibrotic lesions have been shown to originate in the subpleural areas and extend into the lung parenchyma through processes of dysregulated fibroproliferation, migration, fibroblast-to-myofibroblast transformation, and extracellular matrix production. Identifying the molecular targets underlying subpleural thickening at the early and late stages of fibrosis could facilitate the development of new therapies to attenuate fibroblast activation and improve the survival of patients with IPF. Here, we discuss the key cellular and molecular events that contribute to (myo)fibroblast activation and subpleural thickening in IPF. In particular, we highlight the transcriptional programs involved in mesothelial to mesenchymal transformation and fibroblast dysfunction that can be targeted to alter the course of the progressive expansion of fibrotic lesions in the distal areas of IPF lungs.

A prognostic model based on clusters of molecules related to epithelial-mesenchymal transition for idiopathic pulmonary fibrosis

Background: Most patients with idiopathic pulmonary fibrosis (IPF) have poor prognosis; Effective predictive models for these patients are currently lacking. Epithelial-mesenchymal transition (EMT) often occurs during idiopathic pulmonary fibrosis development, and is closely related to multiple pathways and biological processes. It is thus necessary for clinicians to find prognostic biomarkers with high accuracy and specificity from the perspective of Epithelial-mesenchymal transition. Methods: Data were obtained from the Gene Expression Omnibus database. Using consensus clustering, patients were grouped based on Epithelial-mesenchymal transition-related genes. Next, functional enrichment analysis was performed on the results of consensus clustering using gene set variation analysis. The gene modules associated with Epithelial-mesenchymal transition were obtained through weighted gene co-expression network analysis. Prognosis-related genes were screened via least absolute shrinkage and selection operator (LASSO) regression analysis. The model was then evaluated and validated using survival analysis and time-dependent receiver operating characteristic (ROC) analysis. Results: A total of 239 Epithelial-mesenchymal transition-related genes were obtained from patients with idiopathic pulmonary fibrosis. Six genes with strong prognostic associations (C-X-C chemokine receptor type 7 [CXCR7], heparan sulfate-glucosamine 3-sulfotransferase 1 [HS3ST1], matrix metallopeptidase 25 [MMP25], murine retrovirus integration site 1 [MRVI1], transmembrane four L6 family member 1 [TM4SF1], and tyrosylprotein sulfotransferase 1 [TPST1]) were identified via least absolute shrinkage and selection operator and Cox regression analyses. A prognostic model was then constructed based on the selected genes. Survival analysis showed that patients with high-risk scores had worse prognosis based on the training set [hazard ratio (HR) = 7.31, p < .001] and validation set (HR = 2.85, p = .017). The time-dependent receiver operating characteristic analysis showed that the area under the curve (AUC) values in the training set were .872, .905, and .868 for 1-, 2-, and 3-year overall survival rates, respectively. Moreover, the area under the curve values in the validation set were .814, .814, and .808 for 1-, 2-, and 3-year overall survival rates, respectively. Conclusion: The independent prognostic model constructed from six Epithelial-mesenchymal transition-related genes provides bioinformatics guidance to identify additional prognostic markers for idiopathic pulmonary fibrosis in the future.

Hydrogen sulfide attenuates lung injury instigated by Bisphenol-A via suppressing inflammation and oxidative stress

The xenoestrogen bisphenol A (BPA), a commonly used industrial chemical, has been linked to endocrine disruption. The point of the study was to consider the effects of chronic BPA exposure on the respiratory system of adult female rats, and the potential mitigating benefits of Sodium hydrosulfide (NaHS), a donor of hydrogen sulfide (H₂S) administration. Detect biomarkers in Bronchoalveolar lavage fluid (BALF), including total protein content, Total cell counts, Neutrophils %, ICAM (intercellular adhesion molecule)-1 and TGF-β (Transforming growth factor beta). NaHS significantly reduced pro-inflammatory cytokines (IFN-β and MCAF,) also reduce (i.e. VCAM-1, VEGF, VIM, MMP-2, MMP-9), and reduced malondialdehyde and augmented activities of SOD and GSH-PX. Notably, H₂S induced a marked decrease in the expression levels of p-extracellular signal-regulated protein kinase (p-ERK), p-c-Jun N-terminal kinase (p-JNK), and p-p38, H₂S inhibits BPA-induced inflammation and injury in alveolar epithelial cells. These results suggest NaHS may prevent inflammation via the suppression of the ERK/JNK/ p-p38MAPK signaling pathway, Subsequent inhibition of inflammation, epithelial cell injury, and apoptosis may be providing insight into potential avenues for the treatment of lung injury.

Roles of NRF2 in Fibrotic Diseases: From Mechanisms to Therapeutic Approaches

Fibrosis is a persistent inflammatory response that causes scarring and tissue sclerosis by stimulating myofibroblasts to create significant quantities of extracellular matrix protein deposits in the tissue. Oxidative stress has also been linked to the development of fibrosis in several studies. The nuclear erythroid 2-related factor 2 (NRF2) transcription factor controls the expression of several detoxification and antioxidant genes. By binding to antioxidant response elements, NRF2 is activated by oxidative or electrophilic stress and promotes its target genes, resulting in a protective effect on cells. NRF2 is essential for cell survival under oxidative stress conditions. This review describes Kelch-like epichlorohydrin-associated protein 1 (KEAP1)/NRF2 signaling mechanisms and presents recent research advances regarding NRF2 and its involvement in primary fibrotic lesions such as pulmonary fibrosis, hepatic fibrosis, myocardial fibrosis, and renal fibrosis. The related antioxidant substances and drugs are described, along with the mechanisms by which KEAP1/NRF2 regulation positively affects the therapeutic response. Finally, the therapeutic prospects and potential value of NRF2 in fibrosis are summarized. Further studies on NRF2 may provide novel therapeutic approaches for fibrosis.

Bronchial epithelium epithelial-mesenchymal plasticity forms aberrant basaloid-like cells in vitro

Although epithelial-mesenchymal transition (EMT) is a common feature of fibrotic lung disease, its role in fibrogenesis is controversial. Recently, aberrant basaloid cells were identified in fibrotic lung tissue as a novel epithelial cell type displaying a partial EMT phenotype. The developmental origin of these cells remains unknown. To elucidate the role of EMT in the development of aberrant basaloid cells from the bronchial epithelium, we mapped EMT-induced transcriptional changes at the population and single-cell levels. Human bronchial epithelial cells grown as submerged or air-liquid interface (ALI) cultures with or without EMT induction were analyzed by bulk and single-cell RNA-Sequencing. Comparison of submerged and ALI cultures revealed differential expression of 8,247 protein coding (PC) and 1,621 long noncoding RNA (lncRNA) genes and revealed epithelial cell-type-specific lncRNAs. Similarly, EMT induction in ALI cultures resulted in robust transcriptional reprogramming of 6,020 PC and 907 lncRNA genes. Although there was no evidence for fibroblast/myofibroblast conversion following EMT induction, cells displayed a partial EMT gene signature and an aberrant basaloid-like cell phenotype. The substantial transcriptional differences between submerged and ALI cultures highlight that care must be taken when interpreting data from submerged cultures. This work supports that lung epithelial EMT does not generate fibroblasts/myofibroblasts and confirms ALI cultures provide a physiologically relevant system to study aberrant basaloid-like cells and mechanisms of EMT. We provide a catalog of PC and lncRNA genes and an interactive browser (https://bronc-epi-in-vitro.cells.ucsc.edu/) of single-cell RNA-Seq data for further exploration of potential roles in the lung epithelium in health and lung disease.

Significant accumulation of KRAS mutations in bronchiolar metaplasia‑associated honeycomb lesions of interstitial pneumonia

Interstitial pneumonia (IP) is a major risk factor for lung adenocarcinoma (LADC). IP-related LADC predominantly develops in the bronchiolar metaplasia lining in honeycomb lesions. Kirsten rat sarcoma virus (KRAS) is the most common oncogene mutated in IP-related LADC. The present study examined the metaplastic epithelia in honeycomb lesions for KRAS mutations using digital droplet polymerase chain reaction (ddPCR), a sensitive method used to detect infrequent mutations. Significantly higher KRAS mutation variant allele frequencies (VAFs) were detected in the metaplastic lung epithelia from 13 patients with IP compared with those in 46 non-lesioned lung samples from patients without IP (G12V, P=0.0004, G12C, P=0.0181, and G12A, P=0.0234; Mann Whitney U test). Multivariate analyses revealed that higher KRAS G12V (logistic regression model; P=0.0133, odds ratio=7.11) and G12C (P=0.0191, odds ratio=5.81) VAFs in patients with IP were independent of confounding variables, such as smoking and age. In patients with IP, metaplastic epithelia exhibited significantly higher KRAS G12V and G12C VAFs compared with the non-lesioned counterparts (paired t-test; G12V, P=0.0158, G12C, P=0.0465). These results suggested that IP could increase KRAS mutations and supported the hypothesis that bronchiolar metaplasia could be a precursor for IP-related LADC.

Epithelial-mesenchymal transition in organ fibrosis development: current understanding and treatment strategies

Organ fibrosis is a process in which cellular homeostasis is disrupted and extracellular matrix is excessively deposited. Fibrosis can lead to vital organ failure and there are no effective treatments yet. Although epithelial–mesenchymal transition (EMT) may be one of the key cellular mechanisms, the underlying mechanisms of fibrosis remain largely unknown. EMT is a cell phenotypic process in which epithelial cells lose their cell-to-cell adhesion and polarization, after which they acquire mesenchymal features such as infiltration and migration ability. Upon injurious stimulation in different organs, EMT can be triggered by multiple signaling pathways and is also regulated by epigenetic mechanisms. This narrative review summarizes the current understanding of the underlying mechanisms of EMT in fibrogenesis and discusses potential strategies for attenuating EMT to prevent and/or inhibit fibrosis. Despite better understanding the role of EMT in fibrosis development, targeting EMT and beyond in developing therapeutics to tackle fibrosis is challenging but likely feasible.

Iron-Dependent Mitochondrial Dysfunction Contributes to the Pathogenesis of Pulmonary Fibrosis

Although the pathogenesis of pulmonary fibrosis remains unclear, it is known to involve epithelial injury and epithelial-mesenchymal transformation (EMT) as a consequence of cigarette smoke (CS) exposure. Moreover, smoking deposits iron in the mitochondria of alveolar epithelial cells. Iron overload in mitochondria causes the Fenton reaction, leading to reactive oxygen species (ROS) production, and ROS leakage from the mitochondria induces cell injury and inflammation in the lungs. Nevertheless, the mechanisms underlying iron metabolism and pulmonary fibrosis are yet to be elucidated. In this study, we aimed to determine whether iron metabolism and mitochondrial dysfunction are involved in the pathogenesis of pulmonary fibrosis. We demonstrated that administration of the iron chelator deferoxamine (DFO) reduced CS-induced pulmonary epithelial cell death, mitochondrial ROS production, and mitochondrial DNA release. Notably, CS-induced cell death was reduced by the administration of an inhibitor targeting ferroptosis, a unique iron-dependent form of non-apoptotic cell death. Transforming growth factor-β-induced EMT of pulmonary epithelial cells was also reduced by DFO. The preservation of mitochondrial function reduced Transforming growth factor-β-induced EMT. Furthermore, transbronchial iron chelation ameliorated bleomycin-induced pulmonary fibrosis and leukocyte migration in a murine model. Our findings indicate that iron metabolism and mitochondrial dysfunction are involved in the pathogenesis of pulmonary fibrosis. Thus, they may be leveraged as new therapeutic targets for pulmonary fibrosis.

IL-22 inhibits bleomycin-induced pulmonary fibrosis in association with inhibition of IL-17A in mice

BACKGROUND

Interstitial lung disease, a common extra-articular complication of connective tissue disease, is characterized by progressive and irreversible pulmonary inflammation and fibrosis, which causes significant mortality. IL-22 shows a potential in regulating chronic inflammation and possibly plays an anti-fibrotic role by protecting epithelial cells. However, the detailed effects and underlying mechanisms are still unclear. In this study, we explored the impact of IL-22 on pulmonary fibrosis both in vivo and in vitro.

METHODS

To induce pulmonary fibrosis, wild-type mice and IL-22 knockout mice were intratracheally injected with bleomycin followed by treatments with recombinant IL-22 or IL-17A neutralizing antibody. We investigated the role of IL-22 on bleomycin-induced pulmonary fibrosis and the mechanism in the possible interaction between IL-22 and IL-17A. Fibrosis-related genes were detected using RT-qPCR, western blot, and immunofluorescence. Inflammatory and fibrotic changes were assessed based on histological features. We also used A549 human alveolar epithelial cells, NIH/3T3 mouse fibroblast cells, and primary mouse lung fibroblasts to study the impact of IL-22 on fibrosis in vitro.

RESULTS

IL-22 knockout mice showed aggravated pulmonary fibrosis compared with wild-type mice, and injection of recombinant IL-22 decreased the severe fibrotic manifestations in IL-22 knockout mice. In cell culture assays, IL-22 decreased protein levels of Collagen I in A549 cells, NIH/3T3 cells, and primary mouse lung fibroblasts. IL-22 also reduced the protein level of Collagen I in NIH/3T3 cells which were co-cultured with T cells. Mechanistically, IL-22 reduced the Th17 cell proportion and IL-17A mRNA level in lung tissues, and treatment with an IL-17A neutralizing antibody alleviated the severe pulmonary fibrosis in IL-22 knockout mice. The IL-17A neutralizing antibody also reduced Collagen I expression in NIH/3T3 cells in vitro. Knockdown of IL-17A with siRNAs or administration of IL-22 in NIH/3T3 cells and MLFs decreased expression of Collagen I, an effect blocked by concurrent use of recombinant IL-17A.

CONCLUSIONS

IL-22 mediated an anti-fibrogenesis effect in the bleomycin-induced pulmonary fibrosis model and this effect was associated with inhibition of IL-17A.

IL-23 amplifies the epithelial-mesenchymal transition of mechanically conditioned alveolar epithelial cells in rheumatoid arthritis-associated interstitial lung disease through mTOR/S6 signaling

Epithelial-mesenchymal transition (EMT) creates an environment facilitating fibrosis following alveolar epithelial cell injury. IL-23 has important roles in chronic autoimmune conditions like rheumatoid arthritis (RA), but its role in the interstitial lung disease that affects patients with RA is unclear. This study aimed to determine the profibrogenic role of IL-23 on somatic alveolar type I (ATI) epithelial cells. Primary ATI cells were isolated from rats and cultured on plastic dishes for 1-3 wk. After prolonged culture (≥14 days) on rigid culture dishes, primary ATI cells gradually acquired a mesenchymal phenotype, identified by decreased expression of caveolin-1, and reorganization of F-actin cytoskeleton, indicating the initiation of EMT by matrix stiffness. To determine how IL-23 promotes EMT in vitro, transitioning ATI cells, cultured on a stiff substrate for ≥14 days were stimulated with IL-23. The EMT phenotype was significantly enhanced by IL-23, which upregulated α-smooth muscle actin (α-SMA), collagen I/III protein, and decreased caveolin-1. Furthermore, IL-23 significantly promoted cell invasion, as well as apoptotic resistance on transitioning ATI cells. Mechanistically, IL-23-induced EMT was mammalian target of rapamycin/ribosomal protein S6 (mTOR/S6) signaling dependent and reversible by rapamycin. Transcriptional sequencing analysis of human lung fibrosis biopsy tissue revealed key roles for IL-23 in rheumatoid arthritis-associated interstitial lung disease (RA-ILD). This result was further validated by significantly upregulated IL-23 expression at the mRNA level in RA-ILD lung sections. Notably, transitioning ATI epithelial cells were abundantly detected in RA-ILD tissue. Taken together, these data support a role for IL-23 in the pathogenesis of RA lung fibrosis by promoting EMT in alveolar epithelial cells through mTOR/S6 signaling.

PD-L1 Expression in Patients with Idiopathic Pulmonary Fibrosis

Background: Idiopathic pulmonary fibrosis (IPF) is the most common and severe form within the group of idiopathic interstitial pneumonias. It is characterized by repetitive alveolar injury in genetically susceptible individuals and abnormal wound healing, leading to dysregulated bronchiolar proliferation and excessive deposition of extracellular matrix, causing complete architectural distortion and fibrosis. Epithelial-to-mesenchymal transition is considered an important pathogenic event, a phenomenon also observed in various malignant neoplasms, in which tumor cells express programmed death-ligand one (PD-L1). The aim of this study was to assess the presence of PD-L1 in patients with IPF and other interstitial lung diseases (ILDs). Method: Patients with a clinically and radiologically suspected idiopathic interstitial pneumonia or other ILDs undergoing transbronchial cryobiopsy to confirm the diagnosis at the Department of Respiratory Diseases and Allergy, Aarhus University Hospital, were included in this prospective observational study. Cellular membrane PD-L1 expression in epithelial cells was determined using the DAKO PD-L1 IHC 22C3 PharmDx Kit. Results: Membrane-bound PD-L1 (mPD-L1) was found in twelve (28%) of the forty-three patients with IPF and in five (9%) of the fifty-five patients with other ILDs (p = 0.015). When adjusting for age, gender and smoking status, the odds ratio of having IPF when expressing mPD-L1 in alveolar and/or bronchiolar epithelial cells was 4.3 (CI: 1.3–14.3). Conclusion: Expression of mPD-L1 in epithelial cells in the lung parenchymal zones was detected in a consistent subgroup of patients with IPF compared to other interstitial pneumonias. Larger studies are needed to explore the role of mPD-L1 in patients with IPF.

The Role of Interaction between Mitochondria and the Extracellular Matrix in the Development of Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a condition which affects mainly older adults, that suggests mitochondrial dysfunction and oxidative stress, which follow cells senescence, and might contribute to the disease onset. We have assumed pathogenesis associated with crosstalk between the extracellular matrix (ECM) and mitochondria, mainly based on mitochondrial equilibrium impairment consisting of (1) tyrosine kinases and serine-threonine kinase (TKs and ST-Ks) activation via cytokines, (2) mitochondrial electron transport chain dysfunction and in consequence electrons leak with lower ATP synthesis, (3) the activation of latent TGF-β via αVβ6 integrin, (4) tensions transduction via α2β1 integrin, (5) inefficient mitophagy, and (6) stress inhibited biogenesis. Mitochondria dysfunction influences ECM composition and vice versa. Damaged mitochondria release mitochondrial reactive oxygen species (mtROS) and the mitochondrial DNA (mtDNA) to the microenvironment. Therefore, airway epithelial cells (AECs) undergo transition and secrete cytokines. Described factors initiate an inflammatory process with immunological enhancement. In consequence, local fibroblasts exposed to harmful conditions transform into myofibroblasts, produce ECM, and induce progression of fibrosis. In our review, we summarize numerous aspects of mitochondrial pathobiology, which seem to be involved in the pathogenesis of lung fibrosis. In addition, an increasing body of evidence suggests considering crosstalk between the ECM and mitochondria in this context. Moreover, mitochondria and ECM seem to be important players in the antifibrotic treatment of IPF.

Cell tracing reveals the transdifferentiation fate of mouse lung epithelial cells during pulmonary fibrosis in vivo

Idiopathic pulmonary fibrosis (IPF) is a progressive and devastating interstitial lung disease. The origin of myofibroblasts is still to be elucidated and the existence of epithelial-mesenchymal transition (EMT) in IPF remains controversial. Hence, it is important to clarify the origin of fibroblasts by improving modeling and labeling methods and analyzing the differentiation pathway of alveolar epithelial cells (AEC) in pulmonary fibrosis with cell tracking technology. In the present study, adult transgenic mice with SPC-rtTA^+/-/tetO₇-CMV-Cre^+/-/mTmG^+/- were induced with doxycycline for 15 days. The gene knockout phenomenon occurred in type II AECs in the lung and the reporter gene cell membrane-localized enhanced green fluorescence protein (mEGFP) was expressed in the cell membrane. The expression of Cre recombinase and SPC was analyzed using immunohistochemical (IHC) staining to detect the labeling efficiency. A repetitive intraperitoneal bleomycin-induced pulmonary fibrosis model was established, and the mice were sacrificed on day 28. The co-localization of mEGFP and mesenchymal markers α-smooth muscle actin (α-SMA) and S100 calcium binding protein A4 (S100A4) were detected by multiple IHC staining. The results revealed that Cre was expressed in the airway and AECs in the lung tissue of adult transgenic mice with SPC-rtTA^+/-/tetO₇-CMV-Cre^+/-/mTmG^+/- induced by doxycycline; the labeling efficiency in the peripheral lung tissue was 63.27±7.51%. mEGFP was expressed on the membrane of type II AECs and their differentiated form of type I AECs. Expression of mEGFP was mainly observed in the fibrotic region in bleomycin-induced pulmonary fibrosis; 1.94±0.08% of α-SMA-positive cells were mEGFP-positive and 9.68±2.06% of S100A4-positive cells were mEGFP-positive in bleomycin-induced pulmonary fibrosis. In conclusion, the present results suggested that while EMT contributes to the pathogenesis of pulmonary fibrosis, it is not the major causative factor of this condition.

Regulation of the IGF1 signaling pathway is involved in idiopathic pulmonary fibrosis induced by alveolar epithelial cell senescence and core fucosylation

Idiopathic pulmonary fibrosis (IPF) mainly occurs in elderly people over the age of sixty. IPF pathogenesis is associated with alveolar epithelial cells (AECs) senescence. Activation of PI3K/AKT signaling induced by insulin-like growth factor 1 (IGF1) participates in AEC senescence and IPF by releasing CTGF, TGF-β1, and MMP9. Our previous study demonstrated that core fucosylation (CF) modification, catalyzed by a specific core fucosyltransferase (FUT8) can regulate the activation of multiple signaling pathways, and inhibiting CF can alleviate pulmonary fibrosis in mice induced by bleomycin. However, whether CF is involved in IGF1-mediated AEC senescence in IPF remains unclear. In this study, we found that the IGF1/PI3K/AKT signaling pathway was activated in IPF lung tissue. Meanwhile, CF was present in senescent AECs. We also showed that IGF1 could induce AECs senescence with enhanced CF in vivo and in vitro. Inhibiting CF alleviated AECs senescence and pulmonary fibrosis induced by IGF1. In addition, activation of IGF1/PI3K/AKT signaling depends on CF. In conclusion, this study confirmed that CF is an important target regulating the IGF1 signaling pathway in AEC senescence and IPF, which might be a candidate target to treat IPF in the future.

Adipose Stromal Cell-Secretome Counteracts Profibrotic Signals From IPF Lung Matrices

Introduction: Idiopathic pulmonary fibrosis (IPF) is a fibrotic lung disease characterized by excess deposition and altered structure of extracellular matrix (ECM) in the lungs. The fibrotic ECM is paramount in directing resident cells toward a profibrotic phenotype. Collagens, an important part of the fibrotic ECM, have been shown to be structurally different in IPF. To further understand the disease to develop better treatments, the signals from the ECM that drive fibrosis need to be identified. Adipose tissue-derived stromal cell conditioned medium (ASC-CM) has demonstrated antifibrotic effects in animal studies but has not been tested in human samples yet. In this study, the collagen structural integrity in (fibrotic) lung tissue, its interactions with fibroblasts and effects of ASC-CM treatment hereon were studied. Methods: Native and decellularized lung tissue from patients with IPF and controls were stained for denatured collagen using a collagen hybridizing peptide. Primary lung fibroblasts were seeded into decellularized matrices from IPF and control subjects and cultured for 7 days in the presence or absence of ASC-CM. Reseeded matrices were fixed, stained and analyzed for total tissue deposition and specific protein expression. Results: In both native and decellularized lung tissue, more denatured collagen was observed in IPF tissue compared to control tissue. Upon recellularization with fibroblasts, the presence of denatured collagen was equalized in IPF and control matrices, whereas total ECM was higher in IPF matrices than in the control. Treatment with ASC-CM resulted in less ECM deposition, but did not alter the levels of denatured collagen. Discussion: Our data showed that ASC-CM can inhibit fibrotic ECM-induced profibrotic behavior of fibroblasts. This process was independent of collagen structural integrity. Our findings open up new avenues for ASC-CM to be explored as treatment for IPF.

Identification and Validation of Potential Biomarkers and Pathways for Idiopathic Pulmonary Fibrosis by Comprehensive Bioinformatics Analysis

Objective

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive, irreversible, high-mortality lung disease, but its pathogenesis is still unclear. Our purpose was to explore potential genes and molecular mechanisms underlying IPF.

Methods

IPF-related data were obtained from the GSE99621 dataset. Differentially expressed genes (DEGs) were identified between IPF and controls. Their biological functions were analyzed. The relationships between DEGs and microRNAs (miRNAs) were predicted. DEGs and pathways were validated in a microarray dataset. A protein-protein interaction (PPI) network was constructed based on these common DEGs. Western blot was used to validate hub genes in IPF cell models by western blot.

Results

DEGs were identified for IPF than controls in the RNA-seq dataset. Functional enrichment analysis showed that these DEGs were mainly enriched in immune and inflammatory response, chemokine-mediated signaling pathway, cell adhesion, and other biological processes. In the miRNA-target network based on RNA-seq dataset, we found several miRNA targets among all DEGs, like RAB11FIP1, TGFBR3, and SPP1. We identified 304 upregulated genes and 282 downregulated genes in IPF compared to controls both in the microarray and RNA-seq datasets. These common DEGs were mainly involved in cell adhesion, extracellular matrix organization, oxidation-reduction process, and lung vasculature development. In the PPI network, 3 upregulated and 4 downregulated genes could be considered hub genes, which were confirmed in the IPF cell models.

Conclusion

Our study identified several IPF-related DEGs that could become potential biomarkers for IPF. Large-scale multicentric studies are eagerly needed to confirm the utility of these biomarkers.

Regulation of Cellular Senescence Is Independent from Profibrotic Fibroblast-Deposited ECM

Idiopathic pulmonary fibrosis (IPF) is a devastating lung disease with poor survival. Age is a major risk factor, and both alveolar epithelial cells and lung fibroblasts in this disease exhibit features of cellular senescence, a hallmark of ageing. Accumulation of fibrotic extracellular matrix (ECM) is a core feature of IPF and is likely to affect cell function. We hypothesize that aberrant ECM deposition augments fibroblast senescence, creating a perpetuating cycle favouring disease progression. In this study, primary lung fibroblasts were cultured on control and IPF-derived ECM from fibroblasts pretreated with or without profibrotic and prosenescent stimuli, and markers of senescence, fibrosis-associated gene expression and secretion of cytokines were measured. Untreated ECM derived from control or IPF fibroblasts had no effect on the main marker of senescence p16^Ink4a and p21^Waf1/Cip1. However, the expression of alpha smooth muscle actin (ACTA2) and proteoglycan decorin (DCN) increased in response to IPF-derived ECM. Production of the proinflammatory cytokines C-X-C Motif Chemokine Ligand 8 (CXCL8) by lung fibroblasts was upregulated in response to senescent and profibrotic-derived ECM. Finally, the profibrotic cytokines transforming growth factor β1 (TGF-β1) and connective tissue growth factor (CTGF) were upregulated in response to both senescent- and profibrotic-derived ECM. In summary, ECM deposited by IPF fibroblasts does not induce cellular senescence, while there is upregulation of proinflammatory and profibrotic cytokines and differentiation into a myofibroblast phenotype in response to senescent- and profibrotic-derived ECM, which may contribute to progression of fibrosis in IPF.

LncRNA-ATB regulates epithelial-mesenchymal transition progression in pulmonary fibrosis via sponging miR-29b-2-5p and miR-34c-3p

Dysregulation of non‐coding RNAs (ncRNAs) has been proved to play pivotal roles in epithelial‐mesenchymal transition (EMT) and fibrosis. We have previously demonstrated the crucial function of long non‐coding RNA (lncRNA) ATB in silica‐induced pulmonary fibrosis‐related EMT progression. However, the underlying molecular mechanism has not been fully elucidated. Here, we verified miR‐29b‐2‐5p and miR‐34c‐3p as two vital downstream targets of lncRNA‐ATB. As opposed to lncRNA‐ATB, a significant reduction of both miR‐29b‐2‐5p and miR‐34c‐3p was observed in lung epithelial cells treated with TGF‐β1 and a murine silicosis model. Overexpression miR‐29b‐2‐5p or miR‐34c‐3p inhibited EMT process and abrogated the pro‐fibrotic effects of lncRNA‐ATB in vitro. Further, the ectopic expression of miR‐29b‐2‐5p and miR‐34c‐3p with chemotherapy attenuated silica‐induced pulmonary fibrosis in vivo. Mechanistically, TGF‐β1‐induced lncRNA‐ATB accelerated EMT as a sponge of miR‐29b‐2‐5p and miR‐34c‐3p and shared miRNA response elements with MEKK2 and NOTCH2, thus relieving these two molecules from miRNA‐mediated translational repression. Interestingly, the co‐transfection of miR‐29b‐2‐5p and miR‐34c‐3p showed a synergistic suppression effect on EMT in vitro. Furthermore, the co‐expression of these two miRNAs by using adeno‐associated virus (AAV) better alleviated silica‐induced fibrogenesis than single miRNA. Approaches aiming at lncRNA‐ATB and its downstream effectors may represent new effective therapeutic strategies in pulmonary fibrosis.

Epithelial Barrier Dysfunction in Chronic Respiratory Diseases

Mucosal surfaces are lined by epithelial cells, which provide a complex and adaptive module that ensures first-line defense against external toxics, irritants, antigens, and pathogens. The underlying mechanisms of host protection encompass multiple physical, chemical, and immune pathways. In the lung, inhaled agents continually challenge the airway epithelial barrier, which is altered in chronic diseases such as chronic obstructive pulmonary disease, asthma, cystic fibrosis, or pulmonary fibrosis. In this review, we describe the epithelial barrier abnormalities that are observed in such disorders and summarize current knowledge on the mechanisms driving impaired barrier function, which could represent targets of future therapeutic approaches.

Tranilast Inhibits Pulmonary Fibrosis by Suppressing TGFβ/SMAD2 Pathway

Purpose

Idiopathic pulmonary fibrosis (IPF) is characterized by the accumulation of extracellular matrix (ECM) protein in the lungs. Transforming growth factor (TGF) β-induced ECM protein synthesis contributes to the development of IPF. Tranilast, an anti-allergy drug, suppresses TGFβ expression and inhibits interstitial renal fibrosis in animal models. However, the beneficial effects of tranilast or its mechanism as a therapy for pulmonary fibrosis have not been clarified.

Methods

We investigated the in vitro effect of tranilast on ECM production and TGFβ/SMAD2 pathway in TGFβ2-stimulated A549 human alveolar epithelial cells, using quantitative polymerase chain reaction, Western blotting, and immunofluorescence. In vitro observations were validated in the lungs of a murine pulmonary fibrosis model, which we developed by intravenous injection of bleomycin.

Results

Treatment with tranilast suppressed the expression of ECM proteins, such as fibronectin and type IV collagen, and attenuated SMAD2 phosphorylation in TGFβ2-stimulated A549 cells. In addition, based on a wound healing assay in these cells, tranilast significantly inhibited cell motility, with foci formation that comprised of ECM proteins. Histological analyses revealed that the administration of tranilast significantly attenuated lung fibrosis in mice. Furthermore, tranilast treatment significantly reduced levels of TGFβ, collagen, fibronectin, and phosphorylated SMAD2 in pulmonary fibrotic tissues in mice.

Conclusion

These findings suggest that tranilast inhibits pulmonary fibrosis by suppressing TGFβ/SMAD2-mediated ECM protein production, presenting tranilast as a promising and novel anti-fibrotic agent for the treatment of IPF.

A pre-investigational new drug study of lung spheroid cell therapy for treating pulmonary fibrosis

Idiopathic pulmonary fibrosis is a lethal interstitial lung disease with unknown etiology, no cure, and few treatment options. Herein, a therapy option is presented that makes use of a heterogeneous population of lung cells, including progenitor cells and supporting cells lines, cultured in adherent and suspension conditions, the latter of which induces spontaneous spheroid formation. Within these spheroids, progenitor marker expression is augmented. The cells, called lung spheroid cells, are isolated from fibrotic lungs, expanded, and delivered in single cell suspensions into rat models of pulmonary fibrosis via tail-vein injections. Two bleomycin-induced fibrotic rat models are used; a syngeneic Wistar-Kyoto rat model, treated with syngeneic cells, and a xenogeneic nude rat model, treated with human cells. The first objective was to study the differences in fibrotic progression in the two rat models after bleomycin injury. Nude rat fibrosis formed quickly and extended for 30 days with no self-resolution. Wistar-Kyoto rat fibrosis was more gradual and began to decrease in severity between days 14 and 30. The second goal was to find the minimum effective dose of cells that demonstrated safe and effective therapeutic value. The resultant minimum effective therapeutic dose, acquired from the nude rat model, was 3 × 10⁶ human cells. Histological analysis revealed no evidence of tumorigenicity, increased local immunological activity in the lungs, or an increase in liver enzyme production. These data demonstrate the safety and efficacy of lung spheroid cells in their application as therapeutic agents for pulmonary fibrosis, as well as their potential for clinical translation.

The CDR1as/miR-7/TGFBR2 Axis Modulates EMT in Silica-Induced Pulmonary Fibrosis

Silicosis is one of the typical forms of pneumoconiosis characterized by abnormal proliferation of fibroblasts and deposition of extracellular matrix. Recent findings have shown that microRNAs and circular RNAs (circRNAs) are implicated in many diseases. However, the function of noncoding RNAs in pulmonary fibrosis remain to be elucidated. Here, miR-7 was found significantly decreased in silica-treated pulmonary epithelial cells as well as in fibrotic lung tissues of mice. Elevated expression of miR-7 via agomir injection relieved lung fibrosis in vivo. Further molecular study showed that miR-7 played its role against pulmonary fibrosis by blocking epithelial-mesenchymal transition (EMT) progression of human bronchial epithelial cells and A549 cells. Notably, transforming growth factor beta receptor 2 (TGFBR2) was identified as a target gene of miR-7 with bioinformatics tools, which was verified by dual luciferase receptor gene assay in human bronchial epithelial cells and A549 cells. Silica induced elevation of TGFBR2 could be abolished by exogenous expression of miR-7. Furthermore, bioinformatics software indicated that circRNA CDR1as had several binding sites for miR-7. The inhibitory effects of miR-7 on EMT and its target TGFBR2 were suppressed by circRNA CDR1as, which contributed to pulmonary fibrosis. Our studies also revealed overexpressed miR-7 could repress fibrogenesis of lung fibroblasts induced by TGF-β1. Collectively, circRNA CDR1as stimulated by silica could sponge miR-7 to release TGFBR2, plays an important role during pulmonary fibrosis by promoting EMT process. These results indicated that the interaction between miR-7 and circRNA CDR1as may exert important functions and provide potential therapeutic targets in lung fibrotic diseases.

Gas6 Prevents Epithelial-Mesenchymal Transition in Alveolar Epithelial Cells via Production of PGE2, PGD2 and Their Receptors

The epithelial-mesenchymal transition (EMT) is important in organ fibrosis. We hypothesized that growth arrest-specific protein 6 (Gas6) and its underlying mechanisms play roles in the prevention of EMT in alveolar epithelial cells (ECs). In this study, to determine whether Gas6 prevents TGF-β1-induced EMT in LA-4 and primary alveolar type II ECs, real-time PCR and immunoblotting in cell lysates and ELISA in culture supernatants were performed. Migration and invasion assays were performed using Transwell chambers. Pretreatment of ECs with Gas6 inhibited TGF-β1-induced EMT based on cell morphology, changes in EMT marker expression, and induction of EMT-activating transcription factors. Gas6 enhanced the levels of cyclooxygenase-2 (COX-2)-derived prostaglandin E₂ (PGE₂) and PGD₂ as well as of their receptors. COX-2 inhibitors and antagonists of PGE₂ and PGD₂ receptors reversed the inhibition of TGF-β1-induced EMT, migration, and invasion by Gas6. Moreover, knockdown of Axl or Mer reversed the enhancement of PGE₂ and PGD₂ and suppression of EMT, migration and invasion by Gas6. Our data suggest Gas6-Axl or -Mer signalling events may reprogram ECs to resist EMT via the production of PGE₂, PGD₂, and their receptors.

Association of cell cycle arrest with anticancer drug-induced epithelial-mesenchymal transition in alveolar epithelial cells

Many drugs exert serious cytotoxic effects on pulmonary tissues. Although several reports have shown an association of epithelial-mesenchymal transition (EMT) with anticancer drug-induced lung injury, mechanisms of these effects are poorly understood. In the present study, we evaluated mechanisms of anticancer drug-induced EMT, with a focus on involvement of cell cycle arrest. We found that methotrexate (MTX) altered mRNA expression levels of many genes as determined by microarray analysis. Gene set enrichment analysis revealed that cell cycle arrest pathways may be associated with MTX-induced EMT. In addition, thymidine (THY) and nocodazole (NOC), which induce cell cycle arrest at S-phase and G2/M-phase, increased mRNA expression levels of α-smooth muscle actin (SMA), an EMT marker. Furthermore, α-SMA protein expression in cells arrested at S- and G2/M-phases by MTX and paclitaxel (PTX) was significantly higher than that in cells at G1. Notably, co-treatment of cells with THY or NOC and EMT-inducing anticancer drugs did not result in additional upregulation of α-SMA mRNA expression. These findings suggested that cell cycle arrest may be closely associated with anticancer drug-induced EMT in alveolar epithelial cells.

Bioengineered in Vitro Tissue Model of Fibroblast Activation for Modeling Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a complex disease of unknown etiology with no current curative treatment. Modeling pulmonary fibrotic (PF) tissue has the potential to improve our understanding of IPF disease progression and treatment. Rodent animal models do not replicate human fibroblastic foci (Hum-FF) pathology, and current iterations of in vitro model systems (e.g., collagen hydrogels, polyacrylamide hydrogels, and fibrosis-on-chip systems) are unable to replicate the three-dimensional (3D) complexity and biochemical composition of human PF tissue. Herein, we fabricated a 3D bioengineered pulmonary fibrotic (Eng-PF) tissue utilizing cell laden silk collagen type I dityrosine cross-linked hydrogels and Flexcell bioreactors. We show that silk collagen type I hydrogels have superior stability and mechanical tunability compared to other hydrogel systems. Using customized Flexcell bioreactors, we reproduced Hum-FF-like pathology with airway epithelial and microvascular endothelial cells. Eng-PF tissues can model myofibroblast differentiation and permit evaluation of antifibrotic drug treatments. Further, Eng-PF tissues could be used to model different facets of IPF disease, including epithelial injury with the addition of bleomycin and cellular recruitment by perfusion of cells through the hydrogel microchannel.

Epithelial⁻Mesenchymal Transition in the Pathogenesis of Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a serious disease of the lung, which leads to extensive parenchymal scarring and death from respiratory failure. The most accepted hypothesis for IPF pathogenesis relies on the inability of the alveolar epithelium to regenerate after injury. Alveolar epithelial cells become apoptotic and rare, fibroblasts/myofibroblasts accumulate and extracellular matrix (ECM) is deposited in response to the aberrant activation of several pathways that are physiologically implicated in alveologenesis and repair but also favor the creation of excessive fibrosis via different mechanisms, including epithelial⁻mesenchymal transition (EMT). EMT is a pathophysiological process in which epithelial cells lose part of their characteristics and markers, while gaining mesenchymal ones. A role for EMT in the pathogenesis of IPF has been widely hypothesized and indirectly demonstrated; however, precise definition of its mechanisms and relevance has been hindered by the lack of a reliable animal model and needs further studies. The overall available evidence conceptualizes EMT as an alternative cell and tissue normal regeneration, which could open the way to novel diagnostic and prognostic biomarkers, as well as to more effective treatment options.

Exercise training ameliorates bleomycin-induced epithelial mesenchymal transition and lung fibrosis through restoration of H2 S synthesis

AIMS

Clinical trials have shown the beneficial effects of exercise training against pulmonary fibrosis. This study aimed to investigate whether prophylactic intervention with exercise training attenuates lung fibrosis via modulating endogenous hydrogen sulphde (H₂ S) generation.

METHODS

First, ICR mice were allocated to Control, Bleomycin, Exercise, and Bleomycin + Exercise groups. Treadmill exercise began on day 1 and continued for 4 weeks. A single intratracheal dose of bleomycin (3 mg/kg) was administered on day 15. Second, ICR mice were allocated to Control, Bleomycin, H₂ S, and Bleomycin + H₂ S groups. H₂ S donor NaHS (28 μmol/kg) was intraperitoneally injected once daily for 2 weeks.

RESULTS

Bleomycin-treated mice exhibited increased levels of collagen deposition, hydroxyproline, collagen I, transforming growth factor (TGF)-β1, Smad2/Smad3/low-density lipoprotein receptor-related proteins (LRP-6)/glycogen synthase kinase-3β (GSK-3β) phosphorylation, and Smad4/β-catenin expression in lung tissues (P < 0.01), which was alleviated by exercise training (P < 0.01 except for Smad4 and phosphorylated GSK-3β: P < 0.05). Bleomycin-induced lung fibrosis was associated with increased α smooth muscle actin (α-SMA) and decreased E-cadherin expression (P < 0.01). Double immunofluorescence staining showed the co-localization of E-cadherin/α-SMA, indicating epithelial-mesenchymal transition (EMT) formation, which was ameliorated by exercise training. Moreover, exercise training restored bleomycin-induced downregulation of cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE) expression, as well as H₂ S generation in lung tissue (P < 0.01). NaHS treatment attenuated bleomycin-induced TGF-β1 production, activation of LRP-6/β-catenin signalling, EMT and lung fibrosis (P < 0.01 except for β-catenin: P < 0.05).

CONCLUSION

Exercise training restores bleomycin-induced downregulation of pulmonary CBS/CSE expression, thus contributing to the increased H₂ S generation and suppression of TGF-β1/Smad and LRP-6/β-catenin signalling pathways, EMT and lung fibrosis.

Characterization of distal airway stem-like cells expressing N-terminally truncated p63 and thyroid transcription factor-1 in the human lung

Distal airway stem cells (DASCs) in the mouse lung can differentiate into bronchioles and alveoli. However, it remains unclear whether the same stem cells exist in the human lung. Here, we found that human lung epithelial (HuL) cells, derived from normal, peripheral lung tissue, in monolayer, mostly express both the N-terminally truncated isoform of p63 (∆Np63), a marker for airway basal cells, and thyroid transcription factor-1 (TTF-1), a marker for alveolar epithelial cells, even though these two molecules are usually expressed in a mutually exclusive way. Three-dimensionally cultured HuL cells differentiated to form bronchiole-like and alveolus-like organoids. We also uncovered a few bronchiolar epithelial cells expressing both ∆Np63 and TTF-1 in the human lung, suggesting that these cells are the cells of origin for HuL cells. Taken together, ΔNp63⁺ TTF-1⁺ peripheral airway epithelial cells are possibly the human counterpart of mouse DASCs and may offer potential for future regenerative medicine.

PHF8 upregulation contributes to autophagic degradation of E-cadherin, epithelial-mesenchymal transition and metastasis in hepatocellular carcinoma

Background

Plant homeodomain finger protein 8 (PHF8) serves an activator of epithelial-mesenchymal transition (EMT) and is implicated in various tumors. However, little is known about PHF8 roles in hepatocellular carcinoma (HCC) and regulating E-cadherin expression.

Methods

PHF8 expression pattern was investigated by informatic analysis and verified by RT-qPCR and immunochemistry in HCC tissues and cell lines. CCK8, xenograft tumor model, transwell assay, and tandem mCherry-GFP-LC3 fusion protein assay were utilized to assess the effects of PHF8 on proliferation, metastasis and autophagy of HCC cells in vitro and in vivo. ChIP, immunoblot analysis, rescue experiments and inhibitor treatment were used to clarify the mechanism by which PHF8 facilitated EMT, metastasis and autophagy.

Results

PHF8 upregulation was quite prevalent in HCC tissues and closely correlated with worse overall survival and disease-relapse free survival. Furthermore, PHF8-knockdown dramatically suppressed cell growth, migration, invasion and autophagy, and the expression of SNAI1, VIM, N-cadherin and FIP200, and increased E-cadherin level, while PHF8-overexpression led to the opposite results. Additionally, FIP200 augmentation reversed the inhibited effects of PHF8-siliencing on tumor migration, invasion and autophagy. Mechanistically, PHF8 was involved in transcriptionally regulating the expression of SNAI1, VIM and FIP200, rather than N-cadherin and E-cadherin. Noticeably, E-cadherin degradation could be accelerated by PHF8-mediated FIP200-dependent autophagy, a crucial pathway complementary to transcriptional repression of E-cadherin by SNAI1 activation.

Conclusion

These findings suggested that PHF8 played an oncogenic role in facilitating FIP200-dependent autophagic degradation of E-cadherin, EMT and metastasis in HCC. PHF8 might be a promising target for prevention, treatment and prognostic prediction of HCC.

Electronic supplementary material

The online version of this article (10.1186/s13046-018-0890-4) contains supplementary material, which is available to authorized users.

Survivin knockdown induces senescence in TTF‑1-expressing, KRAS-mutant lung adenocarcinomas

Survivin plays a key role in regulating the cell cycle and apoptosis, and is highly expressed in the majority of malignant tumors. However, little is known about the roles of survivin in KRAS-mutant lung adenocarcinomas. In the present study, we examined 28 KRAS-mutant lung adenocarcinoma tissues and two KRAS-mutant lung adenocarcinoma cell lines, H358 and H441, in order to elucidate the potential of survivin as a therapeutic target. We found that 19 (68%) of the 28 KRAS-mutant lung adenocarcinomas were differentiated tumors expressing thyroid transcription factor-1 (TTF-1) and E-cadherin. Patients with tumors immunohistochemically positive for survivin (n=18) had poorer outcomes than those with survivin-negative tumors (n=10). In the H358 and H441 cells, which expressed TTF-1 and E-cadherin, survivin knockdown alone induced senescence, not apoptosis. However, in monolayer culture, the H358 cells and H441 cells in which survivin was silenced, underwent significant apoptosis following combined treatment with ABT-263, a Bcl-2 inhibitor, and trametinib, a MEK inhibitor. Importantly, the triple combination of survivin knockdown with ABT-263 and trametinib treatment, clearly induced cell death in a three-dimensional cell culture model and in an in vivo tumor xenograft model. We also observed that the growth of the H358 and H441 cells was slightly, yet significantly suppressed in vitro when TTF-1 was silenced. These findings collectively suggest that the triple combination of survivin knockdown with ABT-263 and trametinib treatment, may be a potential strategy for the treatment of KRAS-mutant lung adenocarcinoma. Furthermore, our findings indicate that the well-differentiated type of KRAS-mutant lung tumors depends, at least in part, on TTF-1 for growth.

Transmembrane protease, serine 4 (TMPRSS4) is upregulated in IPF lungs and increases the fibrotic response in bleomycin-induced lung injury

Idiopathic pulmonary fibrosis (IPF) is a chronic and progressive lung disease characterized by epithelial cell activation, expansion of the fibroblast population and excessive extracellular matrix accumulation. The mechanisms are incompletely understood but evidence indicates that the deregulation of several proteases contributes to its pathogenesis. Transmembrane protease serine 4 (TMPRSS4) is a novel type II transmembrane serine protease that may promote migration and facilitate epithelial to mesenchymal transition (EMT), two critical processes in the pathogenesis of IPF. Thus, we hypothesized that over-expression of TMPRSS4 in the lung could promote the initiation and/or progression of IPF. In this study we first evaluated the expression and localization of TMPRSS4 in IPF lungs by real time PCR, western blot and immunohistochemistry. Then we examined the lung fibrotic response in wild-type and TMPRSS4 deficient mice using the bleomycin-induced lung injury model. We found that this protease is upregulated in IPF lungs, where was primarily expressed by epithelial and mast cells. Paralleling the findings in vivo, TMPRSS4 was expressed by alveolar and bronchial epithelial cells in vitro and unexpectedly, provoked an increase of E-cadherin. No expression was observed in normal human or IPF lung fibroblasts. The lung fibrotic response evaluated at 28 days after bleomycin injury was markedly attenuated in the haplodeficient and deficient TMPRSS4 mice. By morphology, a significant reduction of the fibrotic index was observed in KO and heterozygous mice which was confirmed by measurement of collagen content (hydroxyproline: WT: 164±21.1 μg/lung versus TMPRSS4 haploinsufficient: 110.2±14.3 μg/lung and TMPRSS4 deficient mice: 114.1±24.2 μg/lung (p<0.01). As in IPF, TMPRSS4 was also expressed in epithelial and mast cells. These findings indicate that TMPRSS4 is upregulated in IPF lungs and that may have a profibrotic role.

The A2B Adenosine Receptor Modulates the Epithelial- Mesenchymal Transition through the Balance of cAMP/PKA and MAPK/ERK Pathway Activation in Human Epithelial Lung Cells

The epithelial-mesenchymal transition (EMT) is a complex process in which cell phenotype switches from the epithelial to mesenchymal one. The deregulations of this process have been related with the occurrence of different diseases such as lung cancer and fibrosis. In the last decade, several efforts have been devoted in understanding the mechanisms that trigger and sustain this transition process. Adenosine is a purinergic signaling molecule that has been involved in the onset and progression of chronic lung diseases and cancer through the A_2B adenosine receptor subtype activation, too. However, the relationship between A_2BAR and EMT has not been investigated, yet. Herein, the A_2BAR characterization was carried out in human epithelial lung cells. Moreover, the effects of receptor activation on EMT were investigated in the absence and presence of transforming growth factor-beta (TGF-β1), which has been known to promote the transition. The A_2BAR activation alone decreased and increased the expression of epithelial markers (E-cadherin) and the mesenchymal one (Vimentin, N-cadherin), respectively, nevertheless a complete EMT was not observed. Surprisingly, the receptor activation counteracted the EMT induced by TGF-β1. Several intracellular pathways regulate the EMT: high levels of cAMP and ERK1/2 phosphorylation has been demonstrated to counteract and promote the transition, respectively. The A_2BAR stimulation was able to modulated these two pathways, cAMP/PKA and MAPK/ERK, shifting the fine balance toward activation or inhibition of EMT. In fact, using a selective PKA inhibitor, which blocks the cAMP pathway, the A_2BAR-mediated EMT promotion were exacerbated, and conversely the selective inhibition of MAPK/ERK counteracted the receptor-induced transition. These results highlighted the A_2BAR as one of the receptors involved in the modulation of EMT process. Nevertheless, its activation is not enough to trigger a complete transition, its ability to affect different intracellular pathways could represent a mechanism at the basis of EMT maintenance/inhibition based on the extracellular microenvironment. Despite further investigations are needed, herein for the first time the A_2BAR has been related to the EMT process, and therefore to the different EMT-related pathologies.

Epithelial contribution to the profibrotic stiff microenvironment and myofibroblast population in lung fibrosis

The contribution of epithelial-to-mesenchymal transition (EMT) to the profibrotic stiff microenvironment and myofibroblast accumulation in pulmonary fibrosis remains unclear. We examined EMT-competent lung epithelial cells and lung fibroblasts from control (fibrosis-free) donors or patients with idiopathic pulmonary fibrosis (IPF), which is a very aggressive fibrotic disorder. Cells were cultured on profibrotic conditions including stiff substrata and TGF-β1, and analyzed in terms of morphology, stiffness, and expression of EMT/myofibroblast markers and fibrillar collagens. All fibroblasts acquired a robust myofibroblast phenotype on TGF-β1 stimulation. Yet IPF myofibroblasts exhibited higher stiffness and expression of fibrillar collagens than control fibroblasts, concomitantly with enhanced FAKY397 activity. FAK inhibition was sufficient to decrease fibroblast stiffness and collagen expression, supporting that FAKY397 hyperactivation may underlie the aberrant mechanobiology of IPF fibroblasts. In contrast, cells undergoing EMT failed to reach the values exhibited by IPF myofibroblasts in all parameters examined. Likewise, EMT could be distinguished from nonactivated control fibroblasts, suggesting that EMT does not elicit myofibroblast precursors either. Our data suggest that EMT does not contribute directly to the myofibroblast population, and may contribute to the stiff fibrotic microenvironment through their own stiffness but not their collagen expression. Our results also support that targeting FAKY397 may rescue normal mechanobiology in IPF.

Long non-coding RNA-ATB promotes EMT during silica-induced pulmonary fibrosis by competitively binding miR-200c

Long non-coding RNAs (lncRNAs) are important signal transduction regulators that act by various patterns. However, little is known about the molecular mechanisms of lncRNA related pathways in occupational lung fibrosis. Our previous study found that epithelial-mesenchymal transition (EMT) was one of the key events in silica-induced pulmonary fibrosis. This study showed that the lncRNA-ATB promoted EMT by acting as a miR-200c sponge. miR-200c was identified by miRNA array as a potential target of lncRNA-ATB and verified by dual luciferase reporter gene together with RNA pull-down assays. Moreover, our findings demonstrated that lncRNA-ATB is abundantly expressed during EMT of lung epithelial cells, which contributes to decreased levels of miR-200c. miR-200c targeted ZEB1 to relief silicosis by blocking EMT in vivo and in vitro. The results also suggested M2 macrophages secreted transforming growth factor-β1 (TGF-β1) to induce EMT process by activating lncRNA-ATB in epithelial cells. Collectively, silica-stimulated macrophages secreted TGF-β1 to induce lncRNA-ATB in epithelia cells, promoting EMT by binding with miR-200c and releasing ZEB1. These observations provide further understanding of the regulatory network of silica-induced pulmonary fibrosis and identify new therapeutic targets hopefully.

Posttranscriptional control of airway inflammation

Acute inflammation in the lungs is a vital protective response, efficiently and swiftly eliminating inciters of tissue injury. However, in respiratory diseases characterized by chronic inflammation, such as chronic obstructive pulmonary disease and asthma, enhanced expression of inflammatory mediators leads to tissue damage and impaired lung function. Although transcription is an essential first step in the induction of proinflammatory genes, tight regulation of inflammation requires more rapid, flexible responses. Increasing evidence shows that such responses are achieved by posttranscriptional mechanisms directly affecting mRNA stability and translation initiation. RNA-binding proteins, microRNAs, and long noncoding RNAs interact with messenger RNA and each other to impact the stability and/or translation of mRNAs implicated in lung inflammation. Recent research has shown that these biological processes play a central role in the pathogenesis of several important pulmonary conditions. This review will highlight several posttranscriptional control mechanisms that influence lung inflammation and the known associations of derangements in these mechanisms with common respiratory diseases. WIREs RNA 2018, 9:e1455. doi: 10.1002/wrna.1455 This article is categorized under: RNA in Disease and Development > RNA in Disease RNA Structure and Dynamics > Influence of RNA Structure in Biological Systems RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications RNA Turnover and Surveillance > Regulation of RNA Stability.

Biopsy in idiopathic pulmonary fibrosis: back to the future

INTRODUCTION

Idiopathic Pulmonary Fibrosis (IPF) is a relentlessly progressive, fibrosing interstitial pneumonia characterized by a radiologic and/or histologic pattern of usual interstitial pneumonia (UIP). The availability of two effective anti-fibrotic drugs in IPF has encouraged the identification and treatment of patients in early stages in order to maximize clinical benefit. The ability of high-resolution computed tomography (HRCT) to identify a 'definite' UIP pattern is suboptimal, particularly in the absence of honeycombing. Therefore, radiologic criteria for UIP are currently being redefined. Histology represents the major source of information to define a UIP pattern. Novel and less invasive approaches (particularly cryobiopsy) to sample interstitial lung diseases have demonstrated high sensitivity and specificity. In parallel, researchers are focusing on molecular mechanisms underlying IPF with the aim to identify more specific druggable targets. Lung tissue is therefore essential for diagnostic, pathogenetic and therapeutic purposes. Areas covered: We identified and critically reviewed the most relevant recent literature related to the limitations of current radiologic criteria, new lung sampling procedures, and molecular pathways in support of the need of lung tissue to better understand IPF. Expert commentary: The development of truly effective treatments for IPF requires the identification of key pathogenetic molecules and pathways. To this end, the availability of lung tissue is vital.

Angiotensin-converting enzyme 2 is a potential therapeutic target for EGFR-mutant lung adenocarcinoma

EGFR-mutant lung adenocarcinomas contain a subpopulation of cells that have undergone epithelial-to-mesenchymal transition and can grow independently of EGFR. To kill these cancer cells, we need a novel therapeutic approach other than EGFR inhibitors. If a molecule is specifically expressed on the cell surface of such EGFR-independent EGFR-mutant cancer cells, it can be a therapeutic target. We found that a mesenchymal EGFR-independent subline derived from HCC827 cells, an EGFR-mutant lung adenocarcinoma cell line, expressed angiotensin-converting enzyme 2 (ACE2) to a greater extent than its parental cells. ACE2 was also expressed at least partially in most of the primary EGFR-mutant lung adenocarcinomas examined, and the ACE2 expression level in the cancer cells was much higher than that in normal lung epithelial cells. In addition, we developed an anti-ACE2 mouse monoclonal antibody (mAb), termed H8R64, that was internalized by ACE2-expressing cells. If an antibody-drug conjugate consisting of a humanized mAb based on H8R64 and a potent anticancer drug were produced, it could be effective for the treatment of EGFR-mutant lung adenocarcinomas.

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A mesenchymal EGFR-mutant lung adenocarcinoma cell line expresses ACE2.

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EGFR-mutant lung adenocarcinoma tissues contain cancer cells that express ACE2.

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We developed an anti-ACE2 antibody that is internalized by ACE2-positive cells.

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ACE2 is a potential therapeutic target for EGFR-mutant lung cancer.