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

Modeling the profibrotic microenvironment in vitro: Model validation

Establishing the molecular and cellular mechanisms of fibrosis requires the development of validated and reproducible models. The complexity of in vivo models challenges the monitoring of an individual cell fate, in some cases making it impossible. However, the set of factors affecting cells in vitro culture systems differ significantly from in vivo conditions, insufficiently reproducing living systems. Thus, to model profibrotic conditions in vitro, usually the key profibrotic factor, transforming growth factor beta (TGFβ-1) is used as a single factor. TGFβ-1 stimulates the differentiation of fibroblasts into myofibroblasts, the main effector cells promoting the development and progression of fibrosis. However, except for soluble factors, the rigidity and composition of the extracellular matrix (ECM) play a critical role in the differentiation process. To develop the model of more complex profibrotic microenvironment in vitro, we used a combination of factors: decellularized ECM synthesized by human dermal fibroblasts in the presence of ascorbic acid if cultured as cell sheets and recombinant TGFβ-1 as a supplement. When culturing human mesenchymal stromal cells derived from adipose tissue (MSCs) under described conditions, we observed differentiation of MSCs into myofibroblasts due to increased number of cells with stress fibrils with alpha-smooth muscle actin (αSMA), and increased expression of myofibroblast marker genes such as collagen I, EDA-fibronectin and αSMA. Importantly, secretome of MSCs changed in these profibrotic microenvironment: the secretion of the profibrotic proteins SPARC and fibulin-2 increased, while the secretion of the antifibrotic hepatocyte growth factor (HGF) decreased. Analysis of transciptomic pattern of regulatory microRNAs in MSCs revealed 49 miRNAs with increased expression and 3 miRNAs with decreased expression under profibrotic stimuli. Bioinformatics analysis confirmed that at least 184 gene targets of the differently expressed miRNAs genes were associated with fibrosis. To further validate the developed model of profibrotic microenvironment, we cultured human dermal fibroblasts in these conditions and observed increased expression of fibroblast activation protein (FAPa) after 12 h of cultivation as well as increased level of αSMA and higher number of αSMA + stress fibrils after 72 h. The data obtained allow us to conclude that the conditions formed by the combination of profibrotic ECM and TGFβ-1 provide a complex profibrotic microenvironment in vitro. Thus, this model can be applicable in studying the mechanism of fibrosis development, as well as for the development of antifibrotic therapy.

Spatial regulation of substrate adhesion directs fibroblast morphotype and phenotype

The switching of the fibroblast phenotype to myofibroblast is a hallmark of a wide variety of tissue pathologies. This phenotypical switch is known to be influenced not only by humoral factors such as TGF-β, but also by mechanical and physical cues in the cellular environment, and is accompanied by distinctive changes in cell morphology. However, the causative link between these cues, the concomitant morphological changes, and the resulting phenotypic switch remain elusive. Here, we use protein micropatterning to spatially control dermal fibroblast adhesion without invoking exogenous mechanical changes and demonstrate that varying the spatial configuration of focal adhesions (FAs) is sufficient to direct fibroblast phenotype. We further developed an automated morphometry analysis pipeline, which revealed FA eccentricity as the primary determinant of cell-state positioning along the spectrum of fibroblast phenotype. Moreover, linear fibronectin patterns that constrain the FAs were found to promote a further phenotype transition, characterized by dispersed expression of alpha-smooth muscle actin, pointing to an interesting possibility of controlling fibroblast phenotype beyond the canonical fibroblast-myofibroblast axis. Together, our study reveals that the spatial configuration of adhesion to the cellular microenvironment is a key factor governing fibroblast morphotype and phenotype, shedding new light on fibroblast phenotype regulation.

Advanced 3D In Vitro Lung Fibrosis Models: Contemporary Status, Clinical Uptake, and Prospective Outlooks

Fibrosis has been characterized as a global health problem and ranks as one of the primary causes of organ dysfunction. Currently, there is no cure for pulmonary fibrosis, and limited therapeutic options are available due to an inadequate understanding of the disease pathogenesis. The absence of advanced in vitro models replicating dynamic temporal changes observed in the tissue with the progression of the disease is a significant impediment in the development of novel antifibrotic treatments, which has motivated research on tissue-mimetic three-dimensional (3D) models. In this review, we summarize emerging trends in preparing advanced lung models to recapitulate biochemical and biomechanical processes associated with lung fibrogenesis. We begin by describing the importance of in vivo studies and highlighting the often poor correlation between preclinical research and clinical outcomes and the limitations of conventional cell culture in accurately simulating the 3D tissue microenvironment. Rapid advancement in biomaterials, biofabrication, biomicrofluidics, and related bioengineering techniques are enabling the preparation of in vitro models to reproduce the epithelium structure and operate as reliable drug screening strategies for precise prediction. Improving and understanding these model systems is necessary to find the cross-talks between growing cells and the stage at which myofibroblasts differentiate. These advanced models allow us to utilize the knowledge and identify, characterize, and hand pick medicines beneficial to the human community. The challenges of the current approaches, along with the opportunities for further research with potential for translation in this field, are presented toward developing novel treatments for pulmonary fibrosis.

Multi-scale simulations of pulmonary airflow based on a coupled 3D-1D-0D model

Pulmonary airflow simulation is a valuable tool for studying respiratory function and disease. However, the respiratory system is a complex multiscale system that involves various physical and biological processes across different spatial and temporal scales. In this study, we propose a 3D-1D-0D multiscale method for simulating pulmonary airflow, which integrates different levels of detail and complexity of the respiratory system. The method consists of three components: a 3D computational fluid dynamics model for the airflow in the trachea and bronchus, a 1D pipe model for the airflow in the terminal bronchioles, and a 0D biphasic mixture model for the airflow in the respiratory bronchioles and alveoli coupled with the lung deformation. The coupling between the different components is achieved by satisfying the mass and momentum conservation law and the pressure continuity condition at the interfaces. We demonstrate the validity and applicability of our method by comparing the results with data of previous models. We also investigate the reduction in inhaled air volume due to the pulmonary fibrosis using the developed multiscale model. Our method provides a comprehensive and realistic framework for simulating pulmonary airflow and can potentially facilitate the diagnosis and treatment of respiratory diseases.

Catch your breath: The protective role of the angiotensin AT2 receptor for the treatment of idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive interstitial lung disease whereby excessive deposition of extracellular matrix proteins (ECM) ultimately leads to respiratory failure. While there have been advances in pharmacotherapies for pulmonary fibrosis, IPF remains an incurable and irreversible disease. There remains an unmet clinical need for treatments that reverse fibrosis, or at the very least have a more tolerable side effect profile than currently available treatments. Transforming growth factor β1(TGFβ1) is considered the main driver of fibrosis in IPF. However, as our understanding of the role of the pulmonary renin-angiotensin system (PRAS) in the pathogenesis of IPF increases, it is becoming clear that targeting angiotensin receptors represents a potential novel treatment strategy for IPF - in particular, via activation of the anti-fibrotic angiotensin type 2 receptor (AT2R). This review describes the current understanding of the pathophysiology of IPF and the mediators implicated in its pathogenesis; focusing on TGFβ1, angiotensin II and related peptides in the PRAS and their contribution to fibrotic processes in the lung. Preclinical and clinical assessment of currently available AT2R agonists and the development of novel, highly selective ligands for this receptor will also be described, with a focus on compound 21, currently in clinical trials for IPF. Collectively, this review provides evidence of the potential of AT2R as a novel therapeutic target for IPF.

Niclosamide-loaded nanoparticles (Ncl-NPs) reverse pulmonary fibrosis in vivo and in vitro

INTRODUCTION

Idiopathic pulmonary fibrosis (IPF), a life-threatening interstitial lung disease, is characterized by excessive activation and proliferation of fibroblasts and epithelial-mesenchymal transition (EMT) of alveolar epithelial cells (AEC) accompanied by a large amount of extracellular matrix aggregation. There are no therapies to reverse pulmonary fibrosis, and nintedanib and pirfenidone could only slow down the decline of lung function of IPF patients and delay their survival time. Niclosamide (Ncl) is an antihelminthic drug approved by FDA, which has been reported to have pleiotropic pharmacological activities in recent years, but it's almost complete insolubility in water limits its clinical application.

OBJECTIVES

To improve the water solubility of Ncl, explore its ability to reverse BLM-induced pulmonary fibrosis and its specific mechanism of action.

METHODS

The Niclosamide-loaded nanoparticles (Ncl-NPs) were formed by emulsification solvent evaporation method. A mouse model induced by bleomycin (BLM) was established to evaluate its effects and mechanisms of inhibiting and reversing fibrosis in vivo. The cell models treated by transforming growth factor-β1 (TGF-β1) were used to examine the mechanism of Ncl-NPs inhibiting fibrosis in vitro. Flow cytometry, IHC, IL-4-induced macrophage model and co-culture system were used to assess the effect of Ncl-NPs on M2 polarization of macrophages.

RESULTS

The Ncl-NPs improved the poor water solubility of Ncl. The lower dose of Ncl-NPs (2.5 mg/kg) showed the same effect of reversing established pulmonary fibrosis as free Ncl (5 mg/kg). Mechanistic studies revealed that Ncl-NPs blocked TGF-β/Smad and signaling transducer and activator of transcription 3 (Stat3) signaling pathways and inhibited the M2 polarization of macrophages. Additionally, H&E staining of the tissues initially showed the safety of Ncl-NPs.

CONCLUSION

These results indicate Ncl-NPs may serve as a new idea for the treatment of pulmonary fibrosis.

Cell-Specific Response of NSIP- and IPF-Derived Fibroblasts to the Modification of the Elasticity, Biological Properties, and 3D Architecture of the Substrate

The fibrotic fibroblasts derived from idiopathic pulmonary fibrosis (IPF) and nonspecific interstitial pneumonia (NSIP) are surrounded by specific environments, characterized by increased stiffness, aberrant extracellular matrix (ECM) composition, and altered lung architecture. The presented research was aimed at investigating the effect of biological, physical, and topographical modification of the substrate on the properties of IPF- and NSIP-derived fibroblasts, and searching for the parameters enabling their identification. Soft and stiff polydimethylsiloxane (PDMS) was chosen for the basic substrates, the properties of which were subsequently tuned. To obtain the biological modification of the substrates, they were covered with ECM proteins, laminin, fibronectin, and collagen. The substrates that mimicked the 3D structure of the lungs were prepared using two approaches, resulting in porous structures that resemble natural lung architecture and honeycomb patterns, typical of IPF tissue. The growth of cells on soft and stiff PDMS covered with proteins, traced using fluorescence microscopy, confirmed an altered behavior of healthy and IPF- and NSIP-derived fibroblasts in response to the modified substrate properties, enabling their identification. In turn, differences in the mechanical properties of healthy and fibrotic fibroblasts, determined using atomic force microscopy working in force spectroscopy mode, as well as their growth on 3D-patterned substrates were not sufficient to discriminate between cell lines.

Matrix Adhesiveness Regulates Myofibroblast Differentiation from Vocal Fold Fibroblasts in a Bio-orthogonally Cross-linked Hydrogel

Repeated mechanical and chemical insults cause an irreversible alteration of extracellular matrix (ECM) composition and properties, giving rise to vocal fold scarring that is refractory to treatment. Although it is well known that fibroblast activation to myofibroblast is the key to the development of the pathology, the lack of a physiologically relevant in vitro model of vocal folds impedes mechanistic investigations on how ECM cues promote myofibroblast differentiation. Herein, we describe a bio-orthogonally cross-linked hydrogel platform that recapitulates the alteration of matrix adhesiveness due to enhanced fibronectin deposition when vocal fold wound healing is initiated. The synthetic ECM (sECM) was established via the cycloaddition reaction of tetrazine (Tz) with slow (norbornene, Nb)- and fast (trans-cyclooctene, TCO)-reacting dienophiles. The relatively slow Tz-Nb ligation allowed the establishment of the covalent hydrogel network for 3D cell encapsulation, while the rapid and efficient Tz-TCO reaction enabled precise conjugation of the cell-adhesive RGDSP peptide in the hydrogel network. To mimic the dynamic changes of ECM composition during wound healing, RGDSP was conjugated to cell-laden hydrogel constructs via a diffusion-controlled bioorthognal ligation method 3 days post encapsulation. At a low RGDSP concentration (0.2 mM), fibroblasts residing in the hydrogel remained quiescent when maintained in transforming growth factor beta 1 (TGF-β1)-conditioned media. However, at a high concentration (2 mM), RGDSP potentiated TGF-β1-induced myofibroblast differentiation, as evidenced by the formation of an actin cytoskeleton network, including F-actin and alpha-smooth muscle actin. The RGDSP-driven fibroblast activation to myofibroblast was accompanied with an increase in the expression of wound healing-related genes, the secretion of profibrotic cytokines, and matrix contraction required for tissue remodeling. This work represents the first step toward the establishment of a 3D hydrogel-based cellular model for studying myofibroblast differentiation in a defined niche associated with vocal fold scarring.

Progression to lung fibrosis in severe COVID-19 patients: A morphological and transcriptomic study in postmortem samples

The development of lung fibrosis is a major concern in patients recovered from severe COVID-19 pneumonia. This study aimed to document the evolution of diffuse alveolar damage (DAD) to the fibrosing pattern and define the transcriptional programs involved. Morphological, immunohistochemical and transcriptional analysis were performed in lung samples obtained from autopsy of 33 severe COVID-19 patients (median illness duration: 36 days). Normal lung and idiopathic pulmonary fibrosis (IPF) were used for comparison. Twenty-seven patients with DAD and disease evolution of more than 2 weeks had fibrosis. Pathways and genes related with collagen biosynthesis and extracellular matrix (ECM) biosynthesis and degradation, myofibroblastic differentiation and epithelial to mesenchymal transition (EMT) were overexpressed in COVID-19. This pattern had similarities with that observed in IPF. By immunohistochemistry, pathological fibroblasts (pFBs), with CTHRC1 and SPARC expression, increased in areas of proliferative DAD and decreased in areas of mature fibrosis. Immunohistochemical analysis demonstrated constitutive expression of cadherin-11 in normal epithelial cells and a similar pattern of cadherin and catenin expression in epithelial cells from both normal and COVID-19 samples. Transcriptomic analysis revealed downregulation of the Hippo pathway, concordant with the observation of YAP overexpression in hyperplastic alveolar epithelial cells. Progression to fibrosis in severe COVID-19 is associated with overexpression of fibrogenic pathways and increased in CTHRC1- and SPARC-positive pFBs. Whereas the Hippo pathway seemed to be implicated in the response to epithelial cell damage, EMT was not a major process implicated in COVID-19 mediated lung fibrosis.

Modified hyaluronic acid-collagen matrices trigger efficient gene transfer and prohealing behavior in fibroblasts for improved wound repair

Growth factor therapy has demonstrated great promise for chronic wound repair, but controlling growth factor activity and cell phenotype over desired time frames remains a critical challenge. In this study, we developed a gene-activated hyaluronic acid-collagen matrix (GAHCM) comprising DNA/polyethylenimine (PEI) polyplexes retained on hyaluronic acid (HA)-collagen hydrogels using collagen mimetic peptides (CMPs). We hypothesized that manipulating both the number of CMP-collagen tethers and the ECM composition would provide a powerful strategy to control growth factor gene transfer kinetics while regulating cell behavior, resulting in enhanced growth factor activity for wound repair. We observed that polyplexes with 50% CMP-modified PEI (50 CP) showed enhanced retention of polyplexes in HCM hydrogels by 2.7-fold as compared to non-CMP modified polyplexes. Moreover, the incorporation of HA in the hydrogel promoted a significant increase in gene transfection efficiency based upon analysis of Gaussia luciferase (GLuc) reporter gene expression, and gene expression could be attenuated by blocking HA-CD44 signaling. Furthermore, when fibroblasts were exposed to vascular endothelial growth factor-A (VEGF-A)-GAHCM, the 50 CP matrix facilitated sustained VEGF-A production for up to 7 days, with maximal expression at day 5. Application of these VEGF-A-50 CP samples stimulated prolonged pro-healing responses, including the TGF-β1-induced myofibroblast-like phenotypes and enhanced closure of murine splinted wounds. Overall, these findings demonstrate the use of ECM-based materials to stimulate efficient gene transfer and regulate cellular phenotype, resulting in improved control of growth factor activity for wound repair. GAHCM have significant potential to overcome key challenges in growth factor therapy for regenerative medicine. STATEMENT OF SIGNIFICANCE: Despite great promise for growth factor therapies in wound treatment, controlling growth factor activity and providing a microenvironment for cells that maximizes growth factor signaling have continued to limit the success of existing formulations. Our GAHCM strategy, combining CMP gene delivery and hyaluronic acid-collagen matrix, enabled enhanced wound healing efficacy via the combination of controlled and localized growth factor expression and matrix-mediated regulation of cell behavior. Incorporation of CMPs and HA in the same matrix synergistically enhanced VEGF activity as compared with simpler matrices. Accordingly, GAHCM will advance our ability to leverage growth factor signaling for wound healing, resulting in new long-term treatments for recalcitrant wounds.

Matrix Metalloproteinases and Their Inhibitors in Pulmonary Fibrosis: EMMPRIN/CD147 Comes into Play

Pulmonary fibrosis (PF) is characterized by aberrant extracellular matrix (ECM) deposition, activation of fibroblasts to myofibroblasts and parenchymal disorganization, which have an impact on the biomechanical traits of the lung. In this context, the balance between matrix metalloproteinases (MMPs) and their tissue inhibitors of metalloproteinases (TIMPs) is lost. Interestingly, several MMPs are overexpressed during PF and exhibit a clear profibrotic role (MMP-2, -3, -8, -11, -12 and -28), but a few are antifibrotic (MMP-19), have both profibrotic and antifibrotic capacity (MMP7), or execute an unclear (MMP-1, -9, -10, -13, -14) or unknown function. TIMPs are also overexpressed in PF; hence, the modulation and function of MMPs and TIMP are more complex than expected. EMMPRIN/CD147 (also known as basigin) is a transmembrane glycoprotein from the immunoglobulin superfamily (IgSF) that was first described to induce MMP activity in fibroblasts. It also interacts with other molecules to execute non-related MMP aactions well-described in cancer progression, migration, and invasion. Emerging evidence strongly suggests that CD147 plays a key role in PF not only by MMP induction but also by stimulating fibroblast myofibroblast transition. In this review, we study the structure and function of MMPs, TIMPs and CD147 in PF and their complex crosstalk between them.

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.

Collagen 3D matrices as a model for the study of cell behavior in pulmonary fibrosis

Purpose: Idiopathic pulmonary fibrosis (IPF) is a complex progressive chronic lung disease where epithelial to mesenchymal interaction, extracellular matrix (ECM) contact, and pro-fibrotic cytokines dynamics take part in the development of the disease. The study of IPF in the widespread in vitro two-dimensional (2 D) culture fails to explain the interaction of cells with the changing environment that occurs in fibrotic lung tissue. A three-dimensional (3 D) co-culture model might shed light on the pathogenesis of IPF by mimicking the fibrotic environment. Materials and Methods: Fibroblasts from nine IPF were isolated and embedded in collagen matrices with the alveolar epithelial human cell line (A549) on the top. Cells were also cultured in 2 D with and without TGF-β1 as a conventional model to compare with. Both types of cells were isolated separately. Protein and gene expression of the main fibrotic markers were measured by qPCR, Western blot, and ELISA. Results: IPF fibroblasts to myofibroblasts differentiation was observed in the 3 D model and in cells stimulated with TGF-β1. In addition, ECM-related genes were highly up-regulated in the 3 D collagen matrix. A549 co-cultured 3 D with IPF fibroblasts showed EMT activation, with down-regulation of E-cadherin (CDH1). However, other pro-fibrotic genes as VIM, TGFB1, and MMP7 were up-regulated in A549 co-cultured 3 D with fibroblasts. Conclusions: 3 D-collagen matrices might induce fibroblasts' fibrotic phenotype as in the classic TGF-β1 model, by up-regulating genes associated with matrix production. In addition, IPF lung fibroblasts seem to exert a pro-fibrotic influence in A549 cells when they are co-cultured. These results suggest that an improved 3 D co-culture model might serve as an important tool to study the fibrotic process and its regulation.

Emerging Roles of Airway Epithelial Cells in Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a fatal disease with incompletely understood aetiology and limited treatment options. Traditionally, IPF was believed to be mainly caused by repetitive injuries to the alveolar epithelium. Several recent lines of evidence, however, suggest that IPF equally involves an aberrant airway epithelial response, which contributes significantly to disease development and progression. In this review, based on recent clinical, high-resolution imaging, genetic, and single-cell RNA sequencing data, we summarize alterations in airway structure, function, and cell type composition in IPF. We furthermore give a comprehensive overview on the genetic and mechanistic evidence pointing towards an essential role of airway epithelial cells in IPF pathogenesis and describe potentially implicated aberrant epithelial signalling pathways and regulation mechanisms in this context. The collected evidence argues for the investigation of possible therapeutic avenues targeting these processes, which thus represent important future directions of research.

Discrimination between NSIP- and IPF-Derived Fibroblasts Based on Multi-Parameter Characterization of Their Growth, Morphology and Physic-Chemical Properties

Background: The aim of the research presented here was to find a set of parameters enabling discrimination between three types of fibroblasts, i.e., healthy ones and those derived from two disorders mimicking each other: idiopathic pulmonary fibrosis (IPF), and nonspecific interstitial pneumonia (NSIP). Methods: The morphology and growth of cells were traced using fluorescence microscopy and analyzed quantitatively using cell proliferation and substrate cytotoxicity indices. The viability of cells was recorded using MTS assays, and their stiffness was examined using atomic force microscopy (AFM) working in force spectroscopy (FS) mode. To enhance any possible difference in the examined parameters, experiments were performed with cells cultured on substrates of different elasticities. Moreover, the chemical composition of cells was determined using time-of-flight secondary ion mass spectrometry (ToF-SIMS), combined with sophisticated analytical tools, i.e., Multivariate Curve Resolution (MCR) and Principal Component Analysis (PCA). Results: The obtained results demonstrate that discrimination between cell lines derived from healthy and diseased patients is possible based on the analysis of the growth of cells, as well as their physical and chemical properties. In turn, the comparative analysis of the cellular response to altered stiffness of the substrates enables the identification of each cell line, including distinguishing between IPF- and NSIP-derived fibroblasts.

Metformin Attenuates Silica-Induced Pulmonary Fibrosis by Activating Autophagy via the AMPK-mTOR Signaling Pathway

Long-term exposure to crystalline silica particles leads to silicosis characterized by persistent inflammation and progressive fibrosis in the lung. So far, there is no specific treatment to cure the disease other than supportive care. In this study, we examined the effects of metformin, a prescribed drug for type || diabetes on silicosis and explored the possible mechanisms in an established rat silicosis model in vivo, and an in vitro co-cultured model containing human macrophages cells (THP-1) and human bronchial epithelial cells (HBEC). Our results showed that metformin significantly alleviated the inflammation and fibrosis of lung tissues of rats exposed to silica particles. Metformin significantly reduced silica particle-induced inflammatory cytokines including transforming growth factor-β1 (TGF-β1), tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) in rat lung tissue and HBEC culture supernatant. The protein levels of Vimentin and α-smooth muscle actin (α-SMA) were significantly decreased by metfomin while expression level of E-cadherin (E-Cad) increased. Besides, metformin increased the expression levels of phosphorylated adenosine 5′-monophosphate (AMP)-activated protein kinase (p-AMPK), microtubule-associated protein (MAP) light chain 3B (LC3B) and Beclin1 proteins, and reduced levels of phosphorylated mammalian target of rapamycin (p-mTOR) and p62 proteins in vivo and in vitro. These results suggest that metformin could inhibit silica-induced pulmonary fibrosis by activating autophagy through the AMPK-mTOR pathway.

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.

A Model for Studying the Biomechanical Effects of Varying Ratios of Collagen Types I and III on Cardiomyocytes

PURPOSE

To develop a novel model composed solely of Col I and Col III with the lower and upper limits set to include the ratios of Col I and Col III at 3:1 and 9:1 in which the structural and mechanical behavior of the resident CM can be studied. Further, the progression of fibrosis due to change in ratios of Col I:Col III was tested.

METHODS

Collagen gels with varying Col I:Col III ratios to represent a healthy (3:1) and diseased myocardial tissue were prepared by manually casting them in wells. Absorbance assay was performed to confirm the gelation of the gels. Rheometric analysis was performed on each of the collagen gels prepared to determine the varying stiffnesses and rheological parameters of the gels made with varying ratios of Col I:Col III. Second Harmonic Generation (SHG) was performed to observe the 3D characterization of the collagen samples. Scanning Electron microscopy was used for acquiring cross sectional images of the lyophilized collagen gels. AC16 CM (human) cell lines were cultured in the prepared gels to study cell morphology and behavior as a result of the varying collagen ratios. Cellular proliferation was studied by performing a Cell Trace Violet Assay and the applied force on each cell was measured by means of Finite Element Analysis (FEA) on CM from each sample.

RESULTS

Second harmonic generation microscopy used to image Col I, displayed a decrease in acquired image intensity with an increase in the non-second harmonic Col III in 3:1 gels. SEM showed a fiber-rich structure in the 3:1 gels with well-distributed pores unlike the 9:1 gels or the 1:0 controls. Rheological analysis showed a decrease in substrate stiffness with an increase of Col III, in comparison with other cases. CM cultured within 3:1 gels exhibited an elongated rod-like morphology with an average end-to-end length of 86 ± 28.8 µm characteristic of healthy CM, accompanied by higher cell growth in comparison with other cases. Finite element analysis used to estimate the forces exerted on CM cultured in the 3:1 gels, showed that the forces were well dispersed, and not concentrated within the center of cells, in comparison with other cases.

CONCLUSION

This study model can be adopted to simulate various biomechanical environments in which cells crosstalk with the Collagen-matrix in diseased pathologies to generate insights on strategies for prevention of fibrosis.

Scutellarin ameliorates pulmonary fibrosis through inhibiting NF-κB/NLRP3-mediated epithelial-mesenchymal transition and inflammation

Idiopathic pulmonary fibrosis (IPF) is featured with inflammation and extensive lung remodeling caused by overloaded deposition of extracellular matrix. Scutellarin is the major effective ingredient of breviscapine and its anti-inflammation efficacy has been reported before. Nevertheless, the impact of scutellarin on IPF and the downstream molecular mechanism remain unclear. In this study, scutellarin suppressed BLM-induced inflammation via NF-κB/NLRP3 pathway both in vivo and in vitro. BLM significantly elevated p-p65/p65 ratio, IκBα degradation, and levels of NLRP3, caspase-1, caspase-11, ASC, GSDMD^Nterm, IL-1β, and IL-18, while scutellarin reversed the above alterations except for that of caspase-11. Scutellarin inhibited BLM-induced epithelial-mesenchymal transition (EMT) process in vivo and in vitro. The expression levels of EMT-related markers, including fibronectin, vimentin, N-cadherin, matrix metalloproteinase 2 (MMP-2) and MMP-9, were increased in BLM group, and suppressed by scutellarin. The expression level of E-cadherin showed the opposite changes. However, overexpression of NLRP3 eliminated the anti-inflammation and anti-EMT functions of scutellarin in vitro. In conclusion, scutellarin suppressed inflammation and EMT in BLM-induced pulmonary fibrosis through NF-κB/NLRP3 signaling.

Interleukin-1β Modulation of the Mechanobiology of Primary Human Pulmonary Fibroblasts: Potential Implications in Lung Repair

Pro-inflammatory cytokines like interleukin-1β (IL-1β) are upregulated during early responses to tissue damage and are expected to transiently compromise the mechanical microenvironment. Fibroblasts are key regulators of tissue mechanics in the lungs and other organs. However, the effects of IL-1β on fibroblast mechanics and functions remain unclear. Here we treated human pulmonary fibroblasts from control donors with IL-1β and used Atomic Force Microscopy to unveil that IL-1β significantly reduces the stiffness of fibroblasts concomitantly with a downregulation of filamentous actin (F-actin) and alpha-smooth muscle (α-SMA). Likewise, COL1A1 mRNA was reduced, whereas that of collagenases MMP1 and MMP2 were upregulated, favoring a reduction of type-I collagen. These mechanobiology changes were functionally associated with reduced proliferation and enhanced migration upon IL-1β stimulation, which could facilitate lung repair by drawing fibroblasts to sites of tissue damage. Our observations reveal that IL-1β may reduce local tissue rigidity by acting both intracellularly and extracellularly through the downregulation of fibroblast contractility and type I collagen deposition, respectively. These IL-1β-dependent mechanical effects may enhance lung repair further by locally increasing pulmonary tissue compliance to preserve normal lung distension and function. Moreover, our results support that IL-1β provides innate anti-fibrotic protection that may be relevant during the early stages of lung repair.

Effect of tuned elasticity and chemical modification of substrate on fibrotic and healthy lung fibroblasts

Response to substrate elasticity, dependent on mechanical properties of cells, differs for lung fibroblast derived from idiopathic pulmonary fibrosis (IPF) and the healthy ones. These altered interactions might potentially act as a 'biomarker' for easy and reliable IPF diagnosis. In this work, systematic studies on the effect of polydimethylsiloxane (PDMS) substrate elasticity, tuned stepwise from 600 kPa to 1.5 MPa on the growth of IPF-derived (LL97A) and healthy (LL24) lung fibroblasts were reported. Additionally, impact of substrate chemistry on both cell lines was studied for fibroblasts cultured on glass substrates modified with three organosilanes - 3-aminopropyltriethoxysilane (APTES), 3-mercaptopropyltriethoxysilane (MPTES) and 3-glycidyloxypropyl trimethoxysilane (GOPS), with different end groups. Finally, the effect of the simultaneous modification of mechanical and chemical properties on the cellular behavior was studied for fibroblast cultured on PDMS substrates covered with silanes. The growth of cells was traced using fluorescence microscopy and analyzed quantitatively by nucleus-cytoplasm ratio, indicating strong, cell-dependent impact of substrate elasticity dominating over effect of chemical modification.

Liver epithelial focal adhesion kinase modulates fibrogenesis and hedgehog signaling

Focal adhesion kinase (FAK) is an important mediator of extracellular matrix-integrin mechano-signal transduction that regulates cell motility, survival, and proliferation. As such, FAK is being investigated as a potential therapeutic target for malignant and fibrotic diseases, and numerous clinical trials of FAK inhibitors are underway. The function of FAK in nonmalignant, nonmotile epithelial cells is not well understood. We previously showed that hepatocytes demonstrated activated FAK near stiff collagen tracts in fibrotic livers. In this study, we examined the role of liver epithelial FAK by inducing fibrotic liver disease in mice with liver epithelial FAK deficiency. We found that mice that lacked FAK in liver epithelial cells developed more severe liver injury and worse fibrosis as compared with controls. Increased fibrosis in liver epithelial FAK-deficient mice was linked to the activation of several profibrotic pathways, including the hedgehog/smoothened pathway. FAK-deficient hepatocytes produced increased Indian hedgehog in a manner dependent on matrix stiffness. Furthermore, expression of the hedgehog receptor, smoothened, was increased in macrophages and biliary cells of hepatocyte-specific FAK-deficient fibrotic livers. These results indicate that liver epithelial FAK has important regulatory roles in the response to liver injury and progression of fibrosis.

Effect of Substrate Stiffness on Physicochemical Properties of Normal and Fibrotic Lung Fibroblasts

The presented research aims to verify whether physicochemical properties of lung fibroblasts, modified by substrate stiffness, can be used to discriminate between normal and fibrotic cells from idiopathic pulmonary fibrosis (IPF). The impact of polydimethylsiloxane (PDMS) substrate stiffness on the physicochemical properties of normal (LL24) and IPF-derived lung fibroblasts (LL97A) was examined in detail. The growth and elasticity of cells were assessed using fluorescence microscopy and atomic force microscopy working in force spectroscopy mode, respectively. The number of fibroblasts, as well as their shape and the arrangement, strongly depends on the mechanical properties of the substrate. Moreover, normal fibroblasts remain more rigid as compared to their fibrotic counterparts, which may indicate the impairments of IPF-derived fibroblasts induced by the fibrosis process. The chemical properties of normal and IPF-derived lung fibroblasts inspected using time-of-flight secondary ion mass spectrometry, and analyzed complexly with principal component analysis (PCA), show a significant difference in the distribution of cholesterol and phospholipids. Based on the observed distinctions between healthy and fibrotic cells, the mechanical properties of cells may serve as prospective diagnostic biomarkers enabling fast and reliable identification of idiopathic pulmonary fibrosis (IPF).

The extracellular matrix and mechanotransduction in pulmonary fibrosis

Pulmonary fibrosis is characterised by excessive scarring in the lung which leads to compromised lung function, serious breathing problems and in some diseases, death. It includes several lung disorders with idiopathic pulmonary fibrosis (IPF) the most common and most severe. Pulmonary fibrosis is considered to be perpetuated by aberrant wound healing which leads to fibroblast accumulation, differentiation and activation, and deposition of excessive amounts of extracellular matrix (ECM) components, in particular, collagen. Recent studies have identified the importance of changes in the composition and structure of lung ECM during the development of pulmonary fibrosis and the interaction between ECM and lung cells. There is strong evidence that increased matrix stiffness induces changes in cell function including proliferation, migration, differentiation and activation. Understanding how changes in the ECM microenvironment influence cell behaviour during fibrogenesis, and the mechanisms regulating these changes, will provide insight for developing new treatments.

Epigenetic SMAD3 Repression in Tumor-Associated Fibroblasts Impairs Fibrosis and Response to the Antifibrotic Drug Nintedanib in Lung Squamous Cell Carcinoma

The tumor-promoting fibrotic stroma rich in tumor-associated fibroblasts (TAF) is drawing increased therapeutic attention. Intriguingly, a trial with the antifibrotic drug nintedanib in non-small cell lung cancer reported clinical benefits in adenocarcinoma (ADC) but not squamous cell carcinoma (SCC), even though the stroma is fibrotic in both histotypes. Likewise, we reported that nintedanib inhibited the tumor-promoting fibrotic phenotype of TAFs selectively in ADC. Here we show that tumor fibrosis is actually higher in ADC-TAFs than SCC-TAFs in vitro and patient samples. Mechanistically, the reduced fibrosis and nintedanib response of SCC-TAFs was associated with increased promoter methylation of the profibrotic TGFβ transcription factor SMAD3 compared with ADC-TAFs, which elicited a compensatory increase in TGFβ1/SMAD2 activation. Consistently, forcing global DNA demethylation of SCC-TAFs with 5-AZA rescued TGFβ1/SMAD3 activation, whereas genetic downregulation of SMAD3 in ADC-TAFs and control fibroblasts increased TGFβ1/SMAD2 activation, and reduced their fibrotic phenotype and antitumor responses to nintedanib in vitro and in vivo. Our results also support that smoking and/or the anatomic location of SCC in the proximal airways, which are more exposed to cigarette smoke particles, may prime SCC-TAFs to stronger SMAD3 epigenetic repression, because cigarette smoke condensate selectively increased SMAD3 promoter methylation. Our results unveil that the histotype-specific regulation of tumor fibrosis in lung cancer is mediated through differential SMAD3 promoter methylation in TAFs and provide new mechanistic insights on the selective poor response of SCC-TAFs to nintedanib. Moreover, our findings support that patients with ADC may be more responsive to antifibrotic drugs targeting their stromal TGFβ1/SMAD3 activation. SIGNIFICANCE: This study implicates the selective epigenetic repression of SMAD3 in SCC-TAFs in the clinical failure of nintedanib in SCC and supports that patients with ADC may benefit from antifibrotic drugs targeting stromal TGFβ1/SMAD3.

Stromal markers of activated tumor associated fibroblasts predict poor survival and are associated with necrosis in non-small cell lung cancer

OBJECTIVES

Tumor associated fibroblasts (TAFs) are essential contributors of the progression of non-small cell lung cancer (NSCLC). Most lung TAFs exhibit an activated phenotype characterized by the expression of α-SMA and fibrillar collagens. However, the prognostic value of these activation markers in NSCLC remains unclear.

MATERIAL AND METHODS

We conducted a quantitative image analysis of α-SMA immunostaining and picrosirius red staining of fibrillar collagens imaged by bright-field and polarized microscopy, respectively, using tissue microarrays with samples from 220 surgical patients, which elicited a percentage of positive staining area for each marker and patient.

RESULTS

Kaplan-Meier curves showed that all TAF activation markers were significantly associated with poor survival, and their prognostic value was independent of TNM staging as revealed by multivariate analysis, which elicited an adjusted increased risk of death after 3 years of 129% and 94% for fibrillar collagens imaged with bright-field (p = 0.004) and polarized light (p = 0.003), respectively, and of 89% for α-SMA (p = 0.009). We also found a significant association between all TAF activation markers and tumor necrosis, which is often indicative of hypoxia, supporting a pathologic link between tumor desmoplasia and necrosis/hypoxia.

CONCLUSIONS

Our findings identify patients with large histologic coverage of fibrillar collagens and α-SMA + TAFs to be at higher risk of recurrence and death, supporting that they could be considered for adjuvant therapy.

Abrogation of myofibroblast activities in metastasis and fibrosis by methyltransferase inhibition

Myofibroblasts are a population of highly contractile fibroblasts that express and require the activity of the transcription factor Snail1. Cancer-associated fibroblasts (CAFs) correlate with low survival of cancer patients when present in the stroma of primary tumors. Remarkably, the presence of myofibroblastic CAFs (which express Snail1) creates mechanical properties in the tumor microenvironment that support metastasis. However, therapeutic blockage of fibroblast activity in patients with cancer is a double-edged sword, as normal fibroblast activities often restrict tumor cell invasion. We used fibroblasts depleted of Snail1 or protein arginine methyltransferases 1 and 4 (PRMT1/-4) to identify specific epigenetic modifications induced by TGFβ/Snail1. Furthermore, we analyzed the in vivo efficiency of methyltransferase inhibitors using mouse models of wound healing and metastasis, as well as fibroblasts isolated from patients with idiopathic pulmonary fibrosis (IPF). Mechanistically, TGFβ-induced Snail1 promotes the epigenetic mark of asymmetrically dimethylated arginine. Critically, we found that inhibitors of methyltransferases prevent myofibroblast activity (but not regular fibroblast activity) in the extracellular matrix, both in cell culture and in vivo. In a mouse breast cancer model, the inhibitor sinefungin reduces both the myofibroblast activity in the tumor stroma and the metastatic burden in the lung. Two distinct inhibitors effectively blocked the exacerbated myofibroblast activity of patient-derived IPF fibroblasts. Our data reveal epigenetic regulation of myofibroblast transdifferentiation in both wound healing and in disease (fibrosis and breast cancer). Thus, methyltransferase inhibitors are good candidates as therapeutic reagents for these diseases.

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.

Combined Activation of Guanylate Cyclase and Cyclic AMP in Lung Fibroblasts as a Novel Therapeutic Concept for Lung Fibrosis

Remodelling of the peripheral lung tissue and fibrotic foci are the main pathologies of idiopathic pulmonary fibrosis (IPF), a disease that is difficult to treat. TGF-β activation of peripheral lung fibroblasts is indicated as the major cause of tissue remodelling in IPF and is resulting in fibroblast hyperplasia and deposition of extracellular matrix. Soluble guanylate cyclase (sGC) stimulators combined with cyclic AMP (cAMP) activators have been reported to reduce proliferation and matrix deposition in other conditions than IPF. Therefore, this drug combination may present a novel therapeutic concept for IPF. This study investigated the effect of BAY 41-2272 and forskolin on remodelling parameters in primary human lung fibroblasts. The study determined TGF-β induced proliferation by direct cell counts after 3 days; and deposition of collagen type-I, type III, and fibronectin. BAY 41-2272 significantly reduced TGF-β induced fibroblast proliferation, but did not reduce viability. This inhibitory effect was further supported by forskolin. Both BAY 41-2272 and forskolin alone reduced TGF-β induced collagen and fibronectin de novo synthesis as well as deposition. This effect was significantly stronger when the two compounds were combined. Furthermore, the TGF-β induced expression of fibrilar α-smooth muscle actin was reduced by BAY 41-2272 and this effect was strengthened by forskolin. In addition, BAY 41-2272 and forskolin reduced TGF-β induced β-catenin. All effects of BAY 41-2272 were concentration dependent. The findings suggest that BAY 41-2272 in combination with cAMP stimulation may present a novel therapeutic strategy to reduce tissue remodelling in IPF.

Matrix Stiffness: the Conductor of Organ Fibrosis

PURPOSE OF REVIEW

Organ fibrosis is a lethal component of scleroderma. The hallmark of scleroderma fibrosis is extensive extracellular matrix (ECM) deposition by activated myofibroblasts, specialized hyper-contractile cells that promote ECM remodeling and matrix stiffening. The purpose of this review is to discuss novel mechanistic insight into myofibroblast activation in scleroderma.

RECENT FINDINGS

Matrix stiffness, traditionally viewed as an end point of organ fibrosis, is now recognized as a critical regulator of tissue fibrogenesis that hijacks the normal physiologic wound-healing program to promote organ fibrosis. Here, we discuss how matrix stiffness orchestrates fibrosis by controlling three fundamental pro-fibrotic mechanisms: (a) mechanoactivation of myofibroblasts, (b) integrin-mediated latent transforming growth factor beta 1 (TGF-β1) activation, and (c) activation of non-canonical TGF-β1 signaling pathways. We also summarize novel therapeutic targets for anti-fibrotic therapy based on the mechanobiology of scleroderma. Future research on mechanobiology of scleroderma may lead to important clinical applications such as improved diagnosis and treatment of patients with scleroderma and other fibrotic-related diseases.

Dysregulated Collagen Homeostasis by Matrix Stiffening and TGF-β1 in Fibroblasts from Idiopathic Pulmonary Fibrosis Patients: Role of FAK/Akt

Idiopathic pulmonary fibrosis (IPF) is an aggressive disease in which normal lung parenchyma is replaced by a stiff dysfunctional scar rich in activated fibroblasts and collagen-I. We examined how the mechanochemical pro-fibrotic microenvironment provided by matrix stiffening and TGF-β1 cooperates in the transcriptional control of collagen homeostasis in normal and fibrotic conditions. For this purpose we cultured fibroblasts from IPF patients or control donors on hydrogels with tunable elasticity, including 3D collagen-I gels and 2D polyacrylamide (PAA) gels. We found that TGF-β1 consistently increased COL1A1 while decreasing MMP1 mRNA levels in hydrogels exhibiting pre-fibrotic or fibrotic-like rigidities concomitantly with an enhanced activation of the FAK/Akt pathway, whereas FAK depletion was sufficient to abrogate these effects. We also demonstrate a synergy between matrix stiffening and TGF-β1 that was positive for COL1A1 and negative for MMP1. Remarkably, the COL1A1 expression upregulation elicited by TGF-β1 alone or synergistically with matrix stiffening were higher in IPF-fibroblasts compared to control fibroblasts in association with larger FAK and Akt activities in the former cells. These findings provide new insights on how matrix stiffening and TGF-β1 cooperate to elicit excessive collagen-I deposition in IPF, and support a major role of the FAK/Akt pathway in this cooperation.