Fibroblast growth factor 2 is required for epithelial recovery, but not for pulmonary fibrosis, in response to bleomycin

Beneficial and Detrimental Effects of Cytokines during Influenza and COVID-19

Cytokines are signaling molecules that play a role in myriad processes, including those occurring during diseases and homeostasis. Their homeostatic function begins during embryogenesis and persists throughout life, including appropriate signaling for the cell and organism death. During viral infections, antiviral cytokines such as interferons and inflammatory cytokines are upregulated. Despite the well-known benefits of these cytokines, their levels often correlate with disease severity, linking them to unfavorable outcomes. In this review, we discuss both the beneficial and pathological functions of cytokines and the potential challenges in separating these two roles. Further, we discuss challenges in targeting these cytokines during disease and propose a new method for quantifying the cytokine effect to limit the pathological consequences while preserving their beneficial effects.

T3 Intratracheal Therapy Alleviates Pulmonary Pathology in an Elastase-Induced Emphysema-Dominant COPD Mouse Model

Chronic obstructive pulmonary disease (COPD) is a complex pulmonary condition characterized by bronchitis, emphysema, and mucus stasis. Due to the variability in symptoms among patients, traditional approaches to treating COPD as a singular disease are limited. This led us to focus on phenotype/endotype classifications. In this study, we explore the potential therapeutic role of thyroid hormone (T3) by using mouse models: emphysema-dominant elastase-induced COPD and airway-dominant C57BL/6-βENaC-Tg to represent different types of the disease. Here, we showed that intratracheal T3 treatment (40, 80 μg/kg, i.t., every other day) resulted in significant improvements regarding emphysema and the enhancement of respiratory function in the elastase-induced COPD model. T3-dependent improvement is likely linked to the up-regulation of Ppargc1a, a master regulator of mitochondrial biogenesis, and Gclm, a factor associated with oxidative stress. Conversely, neither short- nor long-term T3 treatments improved COPD pathology in the C57BL/6-βENaC-Tg mice. Because the up-regulation of extrathyroidal T3-producing enzyme Dio2, which is also considered a marker of T3 requirement, was specifically observed in elastase-induced COPD lungs, these results demonstrate that exogenous T3 supplementation may have therapeutic potential for acute but not chronic COPD exacerbation. Moreover, this study highlights the relevance of considering not only COPD phenotypes but also COPD endotypes (expression levels of Ppargc1a and/or Dio2) in the research and development of better treatment approaches for COPD.

PTD-FGF2 Attenuates Elastase Induced Emphysema in Mice and Alveolar Epithelial Cell Injury

Aberrant communication in alveolar epithelium is a major feature of inflammatory response for the airway remodeling leading to chronic obstructive pulmonary disease (COPD). In this study, we investigated the effect of protein transduction domains (PTD) conjugated Basic Fibroblast Growth Factor (FGF2) (PTD-FGF2) in response to cigarette smoke extract (CSE) in MLE-12 cells and porcine pancreatic elastase (PPE)-induced emphysematous mice. When PPE-induced mice were intraperitoneally treated with 0.1-0.5 mg/kg PTD-FGF2 or FGF2, the linear intercept, infiltration of inflammatory cells into alveoli and pro-inflammatory cytokines were significantly decreased. In western blot analysis, phosphorylated protein levels of c-Jun N-terminal Kinase 1/2 (JNK1/2), extracellular signal-regulated kinase (ERK1/2) and p38 mitogen-activated protein kinases (MAPK) were decreased in PPE-induced mice treated PTD-FGF2. In MLE-12 cells, PTD-FGF2 treatment decreased reactive oxygen species (ROS) production and further decreased Interleukin-6 (IL-6) and IL-1b cytokines in response to CSE. In addition, phosphorylated protein levels of ERK1/2, JNK1/2 and p38 MAPK were reduced. We next determined microRNA expression in the isolated exosomes of MLE-12 cells. In reverse transcription-polymerase chain reaction (RT-PCR) analysis, level of let-7c miRNA was significantly increased while levels of miR-9 and miR-155 were decreased in response to CSE. These data suggest that PTD-FGF2 treatment plays a protective role in regulation of let-7c, miR-9 and miR-155 miRNA expressions and MAPK signaling pathways in CSE-induced MLE-12 cells and PPE-induced emphysematous mice.

Fibroblast growth factor 2

Fibroblast Growth Factor 2 (FGF2), also known as basic fibroblast growth factor, is a potent stimulator of growth and differentiation in multiple tissues. Its discovery traces back over 50 years ago when it was first isolated from bovine pituitary extracts due to its ability to stimulate fibroblast proliferation. Subsequent studies investigating the genomic structure of FGF2 identified multiple protein isoforms, categorized as the low molecular weight and high molecular weight FGF2. These isoforms arise from alternative translation initiation events and exhibit unique molecular and cellular functions. In this concise review, we aim to provide an overview of what is currently known about the structure, expression, and functions of the FGF2 isoforms within the contexts of development, homeostasis, and disease.

Fibroblast growth factor 2 acts as an upstream regulator of inhibition of pulmonary fibroblast activation

Fibroblast growth factor (FGF) signaling plays a crucial role in lung development and repair. Fibroblast growth factor 2 (FGF2) can inhibit fibrotic gene expression and suppress the differentiation of pulmonary fibroblasts (PFs) into myofibroblasts in vitro, suggesting that FGF2 is a potential target for inhibiting pulmonary fibrosis. To gain deeper insights into the molecular mechanism underlying FGF2-mediated regulation of PFs, we performed mRNA sequencing analysis to systematically and globally uncover the regulated genes and biological functions of FGF2 in PFs. Gene Ontology analysis revealed that the differentially expressed genes regulated by FGF2 were enriched in multiple cellular functions including extracellular matrix (ECM) organization, cytoskeleton formation, β-catenin-independent Wnt signaling pathway, supramolecular fiber organization, epithelial cell proliferation, and cell adhesion. Gene Set Enrichment Analysis and cellular experiments confirmed that FGF2 can suppress ECM and actin filament organization and increase PFs proliferation. Taken together, these findings indicate that FGF2 acts as an upstream regulator of the inhibition of PFs activation and may play a regulatory role in pulmonary fibrosis.

Rhinovirus induces airway remodeling: what are the physiological consequences?

BACKGROUND

Rhinovirus infections commonly evoke asthma exacerbations in children and adults. Recurrent asthma exacerbations are associated with injury-repair responses in the airways that collectively contribute to airway remodeling. The physiological consequences of airway remodeling can manifest as irreversible airway obstruction and diminished responsiveness to bronchodilators. Structural cells of the airway, including epithelial cells, smooth muscle, fibroblasts, myofibroblasts, and adjacent lung vascular endothelial cells represent an understudied and emerging source of cellular and extracellular soluble mediators and matrix components that contribute to airway remodeling in a rhinovirus-evoked inflammatory environment.

MAIN BODY

While mechanistic pathways associated with rhinovirus-induced airway remodeling are still not fully characterized, infected airway epithelial cells robustly produce type 2 cytokines and chemokines, as well as pro-angiogenic and fibroblast activating factors that act in a paracrine manner on neighboring airway cells to stimulate remodeling responses. Morphological transformation of structural cells in response to rhinovirus promotes remodeling phenotypes including induction of mucus hypersecretion, epithelial-to-mesenchymal transition, and fibroblast-to-myofibroblast transdifferentiation. Rhinovirus exposure elicits airway hyperresponsiveness contributing to irreversible airway obstruction. This obstruction can occur as a consequence of sub-epithelial thickening mediated by smooth muscle migration and myofibroblast activity, or through independent mechanisms mediated by modulation of the β2 agonist receptor activation and its responsiveness to bronchodilators. Differential cellular responses emerge in response to rhinovirus infection that predispose asthmatic individuals to persistent signatures of airway remodeling, including exaggerated type 2 inflammation, enhanced extracellular matrix deposition, and robust production of pro-angiogenic mediators.

CONCLUSIONS

Few therapies address symptoms of rhinovirus-induced airway remodeling, though understanding the contribution of structural cells to these processes may elucidate future translational targets to alleviate symptoms of rhinovirus-induced exacerbations.

Pharmacotherapy and pulmonary fibrosis risk after SARS-CoV-2 infection: a prospective nationwide cohort study in the United States

Background

Pulmonary fibrosis is characterized by lung parenchymal destruction and can increase morbidity and mortality. Pulmonary fibrosis commonly occurs following hospitalization for SARS-CoV-2 infection. As there are medications that modify pulmonary fibrosis risk, we investigated whether distinct pharmacotherapies (amiodarone, cancer chemotherapy, corticosteroids, and rituximab) are associated with differences in post-COVID-19 pulmonary fibrosis incidence.

Methods

We used the National COVID-19 Cohort Collaboration (N3C) Data Enclave, which aggregates and harmonizes COVID-19 data across the United States, to assess pulmonary fibrosis incidence documented at least 60 days after COVID-19 diagnosis among adults hospitalized between January 1st, 2020 and July 6th, 2022 without pre-existing pulmonary fibrosis. We used propensity scores to match pre-COVID-19 drug-exposed and unexposed cohorts (1:1) based on covariates with known influence on pulmonary fibrosis incidence, and estimated the association of drug exposure with risk for post-COVID-19 pulmonary fibrosis. Sensitivity analyses considered pulmonary fibrosis incidence documented at least 30- or 90-days post-hospitalization and pulmonary fibrosis incidence in the COVID-19-negative N3C population.

Findings

Among 5,923,394 patients with COVID-19, we analyzed 452,951 hospitalized adults, among whom pulmonary fibrosis incidence was 1.1 per 100-person-years. 277,984 hospitalized adults with COVID-19 were included in our primary analysis, among whom all drug exposed cohorts were well-matched to unexposed cohorts (standardized mean differences <0.1). The post-COVID-19 pulmonary fibrosis incidence rate ratio (IRR) was 2.5 (95% CI 1.2-5.1, P = 0.01) for rituximab, 1.6 (95% CI 1.3-2.0, P < 0.0001) for chemotherapy, and 1.2 (95% CI 1.0-1.3, P = 0.02) for corticosteroids. Amiodarone exposure had no significant association with post-COVID-19 pulmonary fibrosis (IRR = 0.8, 95% CI 0.6-1.1, P = 0.24). In sensitivity analyses, pre-COVID-19 corticosteroid use was not consistently associated with post-COVID-19 pulmonary fibrosis. In the COVID-19 negative hospitalized population (n = 1,240,461), pulmonary fibrosis incidence was lower overall (0.6 per 100-person-years) and for patients exposed to all four drugs.

Interpretation

Recent rituximab or cancer chemotherapy before COVID-19 infection in hospitalized patients is associated with increased risk for post-COVID-19 pulmonary fibrosis.

Funding

The analyses described in this publication were conducted with data or tools accessed through the NCATS N3C Data Enclave https://covid.cd2h.org and N3C Attribution & Publication Policy v1.2-2020-08-25b supported by NIHK23HL146942, NIHK08HL150291, NIHK23HL148387, NIHUL1TR002389, NCATSU24 TR002306, and a SECURED grant from the Walder Foundation/Center for Healthcare Delivery Science and Innovation, University of Chicago. WFP received a grant from the Greenwall Foundation. This research was possible because of the patients whose information is included within the data and the organizations (https://ncats.nih.gov/n3c/resources/data-contribution/data-transfer-agreement-signatories) and scientists who have contributed to the on-going development of this community resource (https://doi.org/10.1093/jamia/ocaa196).

The early and late intervention effects of collagen-binding FGF2 on elastase-induced lung injury

INTRODUCTION

Chronic obstructive pulmonary disease (COPD) has high morbidity and mortality, with no effective treatment at present. Emphysema, a major component of COPD, is a leading cause of human death worldwide. Fibroblast growth factor 2 (FGF2) is implicated in the pathogenesis of pulmonary emphysema and may play an important role in the lung repair process after injury, but concerns remain with respect to its effectiveness.

OBJECTIVE

In the present work, we sought to determine how the timing (early and late intervention) of sustained-release FGF2 system administration impacted its effectiveness on a porcine pancreatic elastase (PPE)-induced lung injury mouse model.

METHODS

To examine the early intervention efficiency of collagen-binding FGF2 (CBD-FGF2), mice received intratracheally nebulized CBD-FGF2 with concurrent intratracheal injection of PPE. To explore the late intervention effect, CBD-FGF2 was intratracheally aerosolized after PPE administration, and lungs were collected after CBD-FGF2 treatment for subsequent analysis.

RESULT

In response to PPE, mice had significantly increased alveolar diameter, collagen deposition and expression of inflammatory factors and decreased lung function indices and expression of alveolar epithelium markers. Our results indicate that CBD-FGF2 administration was able to prevent and repair elastase-induced lung injury partly through the suppression of the inflammatory response and recovery of the alveolar epithelium. The early use of CBD-FGF2 for the prevention of PPE-induced emphysema showed better results than late therapeutic administration against established emphysema.

CONCLUSION

These data provide insight regarding the prospective role of a drug-based option (CBD-FGF2) for preventing and curing emphysema.

Pulmonary Fibrosis as a Result of Acute Lung Inflammation: Molecular Mechanisms, Relevant In Vivo Models, Prognostic and Therapeutic Approaches

Pulmonary fibrosis is a chronic progressive lung disease that steadily leads to lung architecture disruption and respiratory failure. The development of pulmonary fibrosis is mostly the result of previous acute lung inflammation, caused by a wide variety of etiological factors, not resolved over time and causing the deposition of fibrotic tissue in the lungs. Despite a long history of study and good coverage of the problem in the scientific literature, the effective therapeutic approaches for pulmonary fibrosis treatment are currently lacking. Thus, the study of the molecular mechanisms underlying the transition from acute lung inflammation to pulmonary fibrosis, and the search for new molecular markers and promising therapeutic targets to prevent pulmonary fibrosis development, remain highly relevant tasks. This review focuses on the etiology, pathogenesis, morphological characteristics and outcomes of acute lung inflammation as a precursor of pulmonary fibrosis; the pathomorphological changes in the lungs during fibrosis development; the known molecular mechanisms and key players of the signaling pathways mediating acute lung inflammation and pulmonary fibrosis, as well as the characteristics of the most common in vivo models of these processes. Moreover, the prognostic markers of acute lung injury severity and pulmonary fibrosis development as well as approved and potential therapeutic approaches suppressing the transition from acute lung inflammation to fibrosis are discussed.

FGF2 isoforms play distinct roles in tubular epithelial-to-mesenchymal transition in diabetic nephropathy

INTRODUCTION

The role of different isoforms of Fibroblast growth factor-2 (FGF2) in tubular epithelial-to-mesenchymal transition (EMT) in diabetic nephropathy remains unknown. We aimed to evaluate the role of FGF2 isoforms in the pathogenesis of EMT.

MATERIALS AND METHODS

Western blot and immunofluorescence were used to assess the expression of FGF2 isoforms in db/db mice and high glucose-stimulated HK2 cells. The effects of specific FGF2 isoforms on EMT were explored via overexpression or knockdown of the corresponding isoform in HK2 cells cultivated in high glucose.

RESULTS

Expression of low molecular weight (LMW) FGF2 was up-regulated while high molecular weight (HMW) FGF2 was down-regulated in the kidney of db/db mice and HK2 cells cultured in high glucose that underwent EMT. Overexpression of the LMW FGF2 enhanced EMT changes, while overexpression of the HMW FGF2 attenuated EMT. Knockdown of HMW FGF2 in HK2 cells promoted the EMT process.

CONCLUSIONS

The expression and function of LMW and HMW FGF2 differed in the process of EMT in tubular cells. LMW FGF2 contributed to EMT, while HMW FGF2 played a protective role in the EMT process.

Functions of exogenous FGF signals in regulation of fibroblast to myofibroblast differentiation and extracellular matrix protein expression

Fibroblasts are widely distributed cells found in most tissues and upon tissue injury, they are able to differentiate into myofibroblasts, which express abundant extracellular matrix (ECM) proteins. Overexpression and unordered organization of ECM proteins cause tissue fibrosis in damaged tissue. Fibroblast growth factor (FGF) family proteins are well known to promote angiogenesis and tissue repair, but their activities in fibroblast differentiation and fibrosis have not been systematically reviewed. Here we summarize the effects of FGFs in fibroblast to myofibroblast differentiation and ECM protein expression and discuss the underlying potential regulatory mechanisms, to provide a basis for the clinical application of recombinant FGF protein drugs in treatment of tissue damage.

Bone Marrow Derived Mesenchymal Stromal Cells Promote Vascularization and Ciliation in Airway Mucosa Tri-Culture Models in Vitro

Patients suffering from irresectable tracheal stenosis often face limited treatment options associated with low quality of life. To date, an optimal tracheal replacement strategy does not exist. A tissue-engineered tracheal substitute promises to overcome limitations such as implant vascularization, functional mucociliary clearance and mechanical stability. In order to advance a tracheal mucosa model recently developed by our group, we examined different supporting cell types in fibrin-based tri-culture with primary human umbilical vein endothelial cells (HUVEC) and primary human respiratory epithelial cells (HRE). Bone marrow-derived mesenchymal stromal cells (BM-MSC), adipose-derived mesenchymal stromal cells (ASC) and human nasal fibroblasts (HNF) were compared regarding their ability to promote mucociliary differentiation and vascularization in vitro. Three-dimensional co-cultures of the supporting cell types with either HRE or HUVEC were used as controls. Mucociliary differentiation and formation of vascular-like structures were analyzed by scanning electron microscopy (SEM), periodic acid Schiff’s reaction (PAS reaction), two-photon laser scanning microscopy (TPLSM) and immunohistochemistry. Cytokine levels of vascular endothelial growth factor (VEGF), epidermal growth factor (EGF), interleukin-6 (IL6), interleukin-8 (IL8), angiopoietin 1, angiopoietin 2, fibroblast growth factor basic (FGF-b) and placenta growth factor (PIGF) in media supernatant were investigated using LEGENDplex™ bead-based immunoassay. Epithelial morphology of tri-cultures with BM-MSC most closely resembled native respiratory epithelium with respect to ciliation, mucus production as well as expression and localization of epithelial cell markers pan-cytokeratin, claudin-1, α-tubulin and mucin5AC. This was followed by tri-cultures with HNF, while ASC-supported tri-cultures lacked mucociliary differentiation. For all supporting cell types, a reduced ciliation was observed in tri-cultures compared to the corresponding co-cultures. Although formation of vascular-like structures was confirmed in all cultures, vascular networks in BM-MSC-tri-cultures were found to be more branched and extended. Concentrations of pro-angiogenic and inflammatory cytokines, in particular VEGF and angiopoietin 2, revealed to be reduced in tri-cultures compared to co-cultures. With these results, our study provides an important step towards a vascularized and ciliated tissue-engineered tracheal replacement. Additionally, our tri-culture model may in the future contribute to an improved understanding of cell-cell interactions in diseases associated with impaired mucosal function.

Fibroblast growth factor-9 expression in airway epithelial cells amplifies the type I interferon response and alters influenza A virus pathogenesis

Influenza A virus (IAV) preferentially infects conducting airway and alveolar epithelial cells in the lung. The outcome of these infections is impacted by the host response, including the production of various cytokines, chemokines, and growth factors. Fibroblast growth factor-9 (FGF9) is required for lung development, can display antiviral activity in vitro, and is upregulated in asymptomatic patients during early IAV infection. We therefore hypothesized that FGF9 would protect the lungs from respiratory virus infection and evaluated IAV pathogenesis in mice that overexpress FGF9 in club cells in the conducting airway epithelium (FGF9-OE mice). However, we found that FGF9-OE mice were highly susceptible to IAV and Sendai virus infection compared to control mice. FGF9-OE mice displayed elevated and persistent viral loads, increased expression of cytokines and chemokines, and increased numbers of infiltrating immune cells as early as 1 day post-infection (dpi). Gene expression analysis showed an elevated type I interferon (IFN) signature in the conducting airway epithelium and analysis of IAV tropism uncovered a dramatic shift in infection from the conducting airway epithelium to the alveolar epithelium in FGF9-OE lungs. These results demonstrate that FGF9 signaling primes the conducting airway epithelium to rapidly induce a localized IFN and proinflammatory cytokine response during viral infection. Although this response protects the airway epithelial cells from IAV infection, it allows for early and enhanced infection of the alveolar epithelium, ultimately leading to increased morbidity and mortality. Our study illuminates a novel role for FGF9 in regulating respiratory virus infection and pathogenesis.

Influenza viruses are respiratory viruses that cause significant morbidity and mortality worldwide. In the lungs, influenza A virus primarily infects epithelial cells that line the conducting airways and alveoli. Fibroblast growth factor-9 (FGF9) is a growth factor that has been shown to have antiviral activity and is upregulated during early IAV infection in asymptomatic patients, leading us to hypothesize that FGF9 would protect the lung epithelium from IAV infection. However, mice that express and secrete FGF9 from club cells in the conducting airway had more severe respiratory virus infection and a hyperactive inflammatory immune response as early as 1 day post-infection. Analysis of the FGF9-expressing airway epithelial cells found an elevated antiviral and inflammatory interferon signature, which protected these cells from severe IAV infection. However, heightened infection of alveolar cells resulted in excessive inflammation in the alveoli, resulting in more severe disease and death. Our study identifies a novel antiviral and inflammatory role for FGFs in the lung airway epithelium and confirms that early and robust IAV infection of alveolar cells results in more severe disease.

Novel drug delivery systems and disease models for pulmonary fibrosis

Pulmonary fibrosis (PF) is a serious and progressive lung disease which is possibly life-threatening. It causes lung scarring and affects lung functions including epithelial cell injury, massive recruitment of immune cells and abnormal accumulation of extracellular matrix (ECM). There is currently no cure for PF. Treatment for PF is aimed at slowing the course of the disease and relieving symptoms. Pirfenidone (PFD) and nintedanib (NDNB) are currently the only two FDA-approved oral medicines to slow down the progress of idiopathic pulmonary fibrosis, a specific type of PF. Novel drug delivery systems and therapies have been developed to improve the prognosis of the disease, as well as reduce or minimize the toxicities during drug treatment. The drug delivery routes for these therapies are various including oral, intravenous, nasal, inhalant, intratracheal and transdermal; although this is dependent on specific treatment mechanisms. In addition, researchers have also expanded current animal models that could not fully restore the clinicopathology, and developed a series of in vitro models such as organoids to study the pathogenesis and treatment of PF. This review describes recent advances on pathogenesis exploration, classifies and specifies the progress of drug delivery systems by their delivery routes, as well as an overview on the in vitro and in vivo models for PF research.

Anti-fibrotic effects of pharmacologic FGF-2: a review of recent literature

Fibrosis is a process of pathological tissue repair that replaces damaged, formerly functional tissue with a non-functional, collagen-rich scar. Complications of fibrotic pathologies, which can arise in numerous organs and from numerous conditions, result in nearly half of deaths in the developed world. Despite this, therapies that target fibrosis at its mechanistic roots are still notably lacking. The ubiquity of the occurrence of fibrosis in myriad organs emphasizes the fact that there are shared mechanisms underlying fibrotic conditions, which may serve as common therapeutic targets for multiple fibrotic diseases of varied organs. Thus, study of the basic science of fibrosis and of anti-fibrotic modalities is critical to therapeutic development and may have potential to translate across organs and disease states. Fibroblast growth factor 2 (FGF-2) is a broadly studied member of the fibroblast growth factors, a family of multipotent cytokines implicated in diverse cellular and tissue processes, which has previously been recognized for its anti-fibrotic potential. However, the mechanisms underlying this potential are not fully understood, nor is the potential for its use to ameliorate fibrosis in diverse pathologies and tissues. Presented here is a review of recent literature that sheds further light on these questions, with the hopes of inspiring further research into the mechanisms underlying the anti-fibrotic activities of FGF-2, as well as the disease conditions for which pharmacologic FGF-2 might be a useful option in the future.

Bronchoalveolar-Lavage-Derived Fibroblast Cell Line (B-LSDM7) as a New Protocol for Investigating the Mechanisms of Idiopathic Pulmonary Fibrosis

Background: The use of BAL to study ILDs has improved our understanding of IPF pathogenesis. BAL fluid is routinely collected and can be considered a clinical and research tool. The procedure is well tolerated and minimally invasive. No specific cell lines from BAL or immortalized cell lines from IPF patients are available commercially. A method to quickly isolate and characterize fibroblasts from BAL is an unmet research need. Materials and methods: Here we describe a new protocol by which we isolated a cell line from IPF. The cell line was expanded in vitro and characterized phenotypically, morphologically and functionally. Results: This culture showed highly filamentous cells with an evident central nucleus. From the phenotypic point of view, this cell line displays fibroblast/myofibroblast-like features including expression of alpha-SMA, vimentin, collagen type-1 and fibronectin. The results showed high expression of ROS in these cells. Oxidative stress invariably promotes extracellular matrix expression in lung diseases directly or through over-production of pro-fibrotic growth factors. Conclusions: Our protocol makes it possible to obtain fibroblasts BAL that is a routine non-invasive method that offers the possibility of having a large sample of patients. Standardized culture methods are important for a reliable model for testing molecules and eventual novel development therapeutic targets.

Steroid-induced fibroblast growth factors drive an epithelial-mesenchymal inflammatory axis in severe asthma

Asthma and inflammatory airway diseases restrict airflow in the lung, compromising gas exchange and lung function. Inhaled corticosteroids (ICSs) can reduce inflammation, control symptoms, and improve lung function; however, a growing number of patients with severe asthma do not benefit from ICS. Using bronchial airway epithelial brushings from patients with severe asthma or primary human cells, we delineated a corticosteroid-driven fibroblast growth factor (FGF)-dependent inflammatory axis, with FGF-responsive fibroblasts promoting downstream granulocyte colony-stimulating factor (G-CSF) production, hyaluronan secretion, and neutrophilic inflammation. Allergen challenge studies in mice demonstrate that the ICS, fluticasone propionate, inhibited type 2-driven eosinophilia but induced a concomitant increase in FGFs, G-CSF, hyaluronan, and neutrophil infiltration. We developed a model of steroid-induced neutrophilic inflammation mediated, in part, by induction of an FGF-dependent epithelial-mesenchymal axis, which may explain why some individuals do not benefit from ICS. In further proof-of-concept experiments, we found that combination therapy with pan-FGF receptor inhibitors and corticosteroids prevented both eosinophilic and steroid-induced neutrophilic inflammation. Together, these results establish FGFs as therapeutic targets for severe asthma patients who do not benefit from ICS.

Roles of the fibroblast growth factor signal transduction system in tissue injury repair

Following injury, tissue autonomously initiates a complex repair process, resulting in either partial recovery or regeneration of tissue architecture and function in most organisms. Both the repair and regeneration processes are highly coordinated by a hierarchy of interplay among signal transduction pathways initiated by different growth factors, cytokines and other signaling molecules under normal conditions. However, under chronic traumatic or pathological conditions, the reparative or regenerative process of most tissues in different organs can lose control to different extents, leading to random, incomplete or even flawed cell and tissue reconstitution and thus often partial restoration of the original structure and function, accompanied by the development of fibrosis, scarring or even pathogenesis that could cause organ failure and death of the organism. Ample evidence suggests that the various combinatorial fibroblast growth factor (FGF) and receptor signal transduction systems play prominent roles in injury repair and the remodeling of adult tissues in addition to embryonic development and regulation of metabolic homeostasis. In this review, we attempt to provide a brief update on our current understanding of the roles, the underlying mechanisms and clinical application of FGFs in tissue injury repair.

The Role of Fibroblast Growth Factor (FGF) Signaling in Tissue Repair and Regeneration

Fibroblast growth factors (FGFs) are a large family of secretory molecules that act through tyrosine kinase receptors known as FGF receptors. They play crucial roles in a wide variety of cellular functions, including cell proliferation, survival, metabolism, morphogenesis, and differentiation, as well as in tissue repair and regeneration. The signaling pathways regulated by FGFs include RAS/mitogen-activated protein kinase (MAPK), phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K)–protein kinase B (AKT), phospholipase C gamma (PLCγ), and signal transducer and activator of transcription (STAT). To date, 22 FGFs have been discovered, involved in different functions in the body. Several FGFs directly or indirectly interfere with repair during tissue regeneration, in addition to their critical functions in the maintenance of pluripotency and dedifferentiation of stem cells. In this review, we summarize the roles of FGFs in diverse cellular processes and shed light on the importance of FGF signaling in mechanisms of tissue repair and regeneration.

Lung epithelial and endothelial damage, loss of tissue repair, inhibition of fibrinolysis, and cellular senescence in fatal COVID-19

Coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is characterized by respiratory distress, multiorgan dysfunction, and, in some cases, death. The pathological mechanisms underlying COVID-19 respiratory distress and the interplay with aggravating risk factors have not been fully defined. Lung autopsy samples from 18 patients with fatal COVID-19, with symptom onset-to-death times ranging from 3 to 47 days, and antemortem plasma samples from 6 of these cases were evaluated using deep sequencing of SARS-CoV-2 RNA, multiplex plasma protein measurements, and pulmonary gene expression and imaging analyses. Prominent histopathological features in this case series included progressive diffuse alveolar damage with excessive thrombosis and late-onset pulmonary tissue and vascular remodeling. Acute damage at the alveolar-capillary barrier was characterized by the loss of surfactant protein expression with injury to alveolar epithelial cells, endothelial cells, respiratory epithelial basal cells, and defective tissue repair processes. Other key findings included impaired clot fibrinolysis with increased concentrations of plasma and lung plasminogen activator inhibitor-1 and modulation of cellular senescence markers, including p21 and sirtuin-1, in both lung epithelial and endothelial cells. Together, these findings further define the molecular pathological features underlying the pulmonary response to SARS-CoV-2 infection and provide important insights into signaling pathways that may be amenable to therapeutic intervention.

Cellular Mechanisms of FGF-Stimulated Tissue Repair

Growth factors belonging to the FGF family play important roles in tissue and organ repair after trauma. In this review, I discuss the regulation by FGFs of the aspects of cellular behavior important for reparative processes. In particular, I focus on the FGF-dependent regulation of cell proliferation, cell stemness, de-differentiation, inflammation, angiogenesis, cell senescence, cell death, and the production of proteases. In addition, I review the available literature on the enhancement of FGF expression and secretion in damaged tissues resulting in the increased FGF supply required for tissue repair.

Myofibroblast dedifferentiation proceeds via distinct transcriptomic and phenotypic transitions

Myofibroblasts are the major cellular source of collagen, and their accumulation - via differentiation from fibroblasts and resistance to apoptosis - is a hallmark of tissue fibrosis. Clearance of myofibroblasts by dedifferentiation and restoration of apoptosis sensitivity has the potential to reverse fibrosis. Prostaglandin E2 (PGE2) and mitogens such as FGF2 have each been shown to dedifferentiate myofibroblasts, but - to our knowledge - the resultant cellular phenotypes have neither been comprehensively characterized or compared. Here, we show that PGE2 elicited dedifferentiation of human lung myofibroblasts via cAMP/PKA, while FGF2 utilized MEK/ERK. The 2 mediators yielded transitional cells with distinct transcriptomes, with FGF2 promoting but PGE2 inhibiting proliferation and survival. The gene expression pattern in fibroblasts isolated from the lungs of mice undergoing resolution of experimental fibrosis resembled that of myofibroblasts treated with PGE2 in vitro. We conclude that myofibroblast dedifferentiation can proceed via distinct programs exemplified by treatment with PGE2 and FGF2, with dedifferentiation occurring in vivo most closely resembling the former.

Dysregulated Host Responses Underlie 2009 Pandemic Influenza-Methicillin Resistant Staphylococcus aureus Coinfection Pathogenesis at the Alveolar-Capillary Barrier

Influenza viruses are a continual public health concern resulting in 3-5 million severe infections annually despite intense vaccination campaigns and messaging. Secondary bacterial infections, including Staphylococcus aureus, result in increased morbidity and mortality during seasonal epidemics and pandemics. While coinfections can result in deleterious pathologic consequences, including alveolar-capillary barrier disruption, the underlying mechanisms are poorly understood. We have characterized host- and pathogen-centric mechanisms contributing to influenza-bacterial coinfections in a primary cell coculture model of the alveolar-capillary barrier. Using 2009 pandemic influenza (pH1N1) and methicillin-resistant S. aureus (MRSA), we demonstrate that coinfection resulted in dysregulated barrier function. Preinfection with pH1N1 resulted in modulation of adhesion- and invasion-associated MRSA virulence factors during lag phase bacterial replication. Host response modulation in coinfected alveolar epithelial cells were primarily related to TLR- and inflammatory response-mediated cell signaling events. While less extensive in cocultured endothelial cells, coinfection resulted in changes to cellular stress response- and TLR-related signaling events. Analysis of cytokine expression suggested that cytokine secretion might play an important role in coinfection pathogenesis. Taken together, we demonstrate that coinfection pathogenesis is related to complex host- and pathogen-mediated events impacting both epithelial and endothelial cell regulation at the alveolar-capillary barrier.

Fibroblast Growth Factor 2 Augments Transforming Growth Factor Beta 1 Induced Epithelial-mesenchymal Transition in Lung Cell Culture Model

Impaired lung epithelial cell regeneration following injury may contribute to the development of pulmonary fibrosis. Epithelial-mesenchymal transition (EMT) is a critical event in embryonic development, wound healing following injury, and even cancer progression. Previous studies have shown that the combination of transforming growth factor beta-1 (TGFβ1) and fibroblast growth factor 2 (FGF2) induces EMT during cancer metastasis. However, this synergy remains to be elucidated in inducing EMT associated with wound healing after injury. We set out this study to determine the effect of fibroblast growth factor 2 (FGF2) on TGFβ1-induced EMT in the human lung epithelium. BEAS-2B and A549 cells were treated with TGFβ1, FGF2, or both. EMT phenotype was investigated morphologically and by measuring mRNA expression levels; using quantitative real-time PCR. E-cadherin expression was assayed by western blot and immunofluorescence staining. Cell migration was confirmed using a wound-healing assay. TGFβ1 induced a morphological change and a significant increase in cell migration of BEAS-2B cells. TGFβ1 significantly reduced E-cadherin (CDH1) mRNA expression and markedly induced expression of N-cadherin (CDH2), tenascin C (TNC), fibronectin (FN), actin alpha 2 (ACTA2), and collagen I (COL1A1). While FGF2 alone did not significantly alter EMT gene expression, it enhanced TGFβ1-induced suppression of CDH1 and upregulation of ACTA2, but not TNC, FN, and CDH2. FGF2 significantly inhibited TGFβ1-induced COL1A1 expression. Furthermore, FGF2 maintained TGFβ1-induced morphologic changes and increased the migration of TGFβ1-treated cells. This study suggests a synergistic effect between TGFβ1 and FGF2 in inducing EMT in lung epithelial cells, which may play an important role in wound healing and tissue repair after injury.

FGFR2 Is Required for AEC2 Homeostasis and Survival after Bleomycin-induced Lung Injury

Alveolar epithelial cell (AEC) injury is central to the pathogenesis of pulmonary fibrosis. Epithelial FGF (fibroblast growth factor) signaling is essential for recovery from hyperoxia- and influenza-induced lung injury, and treatment with FGFs is protective in experimental lung injury. The cell types involved in the protective effect of FGFs are not known. We hypothesized that FGF signaling in type II AECs (AEC2s) is critical in bleomycin-induced lung injury and fibrosis. To test this hypothesis, we generated mice with tamoxifen-inducible deletion of FGFR1-3 (fibroblast growth factor receptors 1, 2, and 3) in surfactant protein C-positive (SPC⁺) AEC2s (SPC triple conditional knockout [SPC-TCKO]). In the absence of injury, SPC-TCKO mice had fewer AEC2s, decreased Sftpc (surfactant protein C gene) expression, increased alveolar diameter, and increased collagen deposition. After intratracheal bleomycin administration, SPC-TCKO mice had increased mortality, lung edema, and BAL total protein, and flow cytometry and immunofluorescence revealed a loss of AEC2s. To reduce mortality of SPC-TCKO mice to less than 50%, a 25-fold dose reduction of bleomycin was required. Surviving bleomycin-injured SPC-TCKO mice had increased collagen deposition, fibrosis, and ACTA2 expression and decreased epithelial gene expression. Inducible inactivation of individual Fgfr2 or Fgfr3 revealed that Fgfr2, but not Fgfr3, was responsible for the increased mortality and lung injury after bleomycin administration. In conclusion, AEC2-specific FGFR2 is critical for survival in response to bleomycin-induced lung injury. These data also suggest that a population of SPC⁺ AEC2s require FGFR2 signaling for maintenance in the adult lung. Preventing epithelial FGFR inhibition and/or activating FGFRs in alveolar epithelium may therefore represent a novel approach to treating lung injury and reducing fibrosis.

Choosing the Right Differentiation Medium to Develop Mucociliary Phenotype of Primary Nasal Epithelial Cells In Vitro

In vitro differentiation of airway epithelium is of interest for respiratory tissue engineering and studying airway diseases. Both applications benefit from the use of primary cells to maintain a mucociliated phenotype and thus physiological functionality. Complex differentiation procedures often lack standardization and reproducibility. To alleviate these shortfalls, we compared differentiation behavior of human nasal epithelial cells in four differentiation media. Cells were differentiated at the air-liquid interface (ALI) on collagen-coated inserts. Mucociliary differentiation status after five weeks was analyzed by electron microscopy, histology and immunohistochemistry. The amount of ciliation was estimated and growth factor concentrations were evaluated using ELISA. We found that retinoic-acid-supplemented mixture of DMEM and Airway Epithelial Cell Growth Medium gave most promising results to obtain ciliated and mucus producing nasal epithelium in vitro. We discovered the balance between retinoic acid (RA), vascular endothelial growth factor (VEGF), epidermal growth factor (EGF) and fibroblast growth factor β (FGF-β) to be relevant for differentiation. We could show that low VEGF, EGF and FGF-β concentrations in medium correspond to absent ciliation in specific donors. Therefore, our results may in future facilitate donor selection and non-invasive monitoring of ALI cultures and by this contribute to improved standardization of epithelial in vitro culture.

FGF2, an Immunomodulatory Factor in Asthma and Chronic Obstructive Pulmonary Disease (COPD)

The fibroblast growth factor 2 (FGF2) is a potent mitogenic factor belonging to the FGF family. It plays a role in airway remodeling associated with chronic inflammatory airway diseases, including asthma and chronic obstructive pulmonary disease (COPD). Recently, research interest has been raised in the immunomodulatory function of FGF2 in asthma and COPD, through its involvement in not only the regulation of inflammatory cells but also its participation as a mediator between immune cells and airway structural cells. Herein, this review provides the current knowledge on the biology of FGF2, its expression pattern in asthma and COPD patients, and its role as an immunomodulatory factor. The potential that FGF2 is involved in regulating inflammation indicates that FGF2 could be a therapeutic target for chronic inflammatory diseases.

The Tyrosine Kinase Inhibitor TAS-115 Attenuates Bleomycin-induced Lung Fibrosis in Mice

The signaling pathways of growth factors, including platelet-derived growth factor, can be considered specific targets for overcoming the poor prognosis of idiopathic pulmonary fibrosis. Nintedanib, the recently approved multiple kinase inhibitor, has shown promising antifibrotic effects in patients with idiopathic pulmonary fibrosis; however, its efficacy is still limited, and in some cases, treatment discontinuation is necessary owing to toxicities such as gastrointestinal disorders. Therefore, more effective agents with less toxicity are still needed. TAS-115 is a novel multiple tyrosine kinase inhibitor that preferably targets platelet-derived growth factor receptor (PDGFR), vascular endothelial growth factor receptor, and c-FMS in addition to other molecules. In this study, we evaluated the antifibrotic effect of TAS-115 on pulmonary fibrosis in vitro and in vivo. TAS-115 inhibited the phosphorylation of PDGFR on human lung fibroblast cell line MRC-5 cells and suppressed their platelet-derived growth factor-induced proliferation and migration. Furthermore, TAS-115 inhibited the phosphorylation of c-FMS, a receptor of macrophage colony-stimulating factor, in murine bone marrow-derived macrophages and decreased the production of CCL2, another key molecule for inducing pulmonary fibrosis, under the stimulation of macrophage colony-stimulating factor. Importantly, the inhibitory effects of TAS-115 on both PDGFR and c-FMS were 3- to 10-fold higher than those of nintedanib. In a mouse model of bleomycin-induced pulmonary fibrosis, TAS-115 significantly inhibited the development of pulmonary fibrosis and the collagen deposition in bleomycin-treated lungs. These data suggest that strong inhibition of PDGFR and c-FMS by TAS-115 may be a promising strategy for overcoming the intractable pathogenesis of pulmonary fibrosis.

Function of fibroblast growth factor 2 in gastric cancer occurrence and prognosis

The present study aimed to explore the role of fibroblast growth factor 2 (FGF2) in the development and prognosis of gastric cancer (GC). The relationship between FGF2 mRNA expression levels and the clinical characteristics of GC was investigated using microarray data from four GC cohorts involving 726 patients obtained from the Gene Expression Omnibus. The results of the present study indicated that FGF2 expression levels were an independent factor affecting the prognosis of GC. The primary functions of FGF2 were related to cell adhesion and angiogenesis, and patients with high levels of FGF2 expression had poorer TNM staging and prognosis; these differences were statistically significant. In terms of immune infiltration, a higher extent of M2 macrophage intrusion was observed in patients with higher levels of FGF2. However, the degree of infiltration by dendritic and CD4⁺ T cells was lower, and this difference was statistically significant. Multivariate Cox proportional hazards model analysis revealed that age, TNM staging and FGF2 expression levels were independent prognostic factors for GC. In summary, FGF2 expression was demonstrated to be an independent prognostic factor in GC, and higher levels of FGF2 may promote the progression of this malignancy.

Angiogenic signaling in the lungs of a metabolically suppressed hibernating mammal (Ictidomys tridecemlineatus)

To conserve energy in times of limited resource availability, particularly during cold winters, hibernators suppress even the most basic of physiologic processes. Breathing rates decrease from 40 breaths/minute to less than 1 breath/min as they decrease body temperature from 37 °C to ambient. Nevertheless, after months of hibernation, these incredible mammals emerge from torpor unscathed. This study was conducted to better understand the protective and possibly anti-inflammatory adaptations that hibernator lungs may use to prevent damage associated with entering and emerging from natural torpor. We postulated that the differential protein expression of soluble protein receptors (decoy receptors that sequester soluble ligands to inhibit signal transduction) would help identify inhibited inflammatory signaling pathways in metabolically suppressed lungs. Instead, the only two soluble receptors that responded to torpor were sVEGFR1 and sVEGFR2, two receptors whose full-length forms are bound by VEGF-A to regulate endothelial cell function and angiogenesis. Decreased sVEGFR1/2 correlated with increased total VEGFR2 protein levels. Maintained or increased levels of key γ-secretase subunits suggested that decreased sVEGFR1/2 protein levels were not due to decreased levels of intramembrane cleavage complex subunits. VEGF-A protein levels did not change, suggesting that hibernators may regulate VEGFR1/2 signaling at the level of the receptor instead of increasing relative ligand abundance. A panel of angiogenic factors used to identify biomarkers of angiogenesis showed a decrease in FGF-1 and an increase in BMP-9. Torpid lungs may use VEGF and BMP-9 signaling to balance angiogenesis and vascular stability, possibly through the activation of SMAD signaling for adaptive tissue remodeling.

Distinct profile of inflammatory and remodelling biomarkers in sputum of severe asthmatic patients with or without persistent airway obstruction

BACKGROUND

Both inflammatory and remodelling processes are associated with irreversible airway obstruction observed in severe asthma. Our aim was to characterize a group of severe asthmatic patients with or without persistent airway obstruction in relation to specific sputum inflammatory and remodelling biomarkers.

METHODS

Forty-five patients under regular high-dose inhaled corticosteroid/ß-2agonist treatment were studied, after a follow-up period of at least 2 years, with a minimum of 4 visits. Periostin, TGF-ß, RANTES, IL-8, GM-CSF, FGF-2, and cell counts were measured in induced sputum. Serum periostin was also measured.

RESULTS

Sputum induction was successfully performed in all but 5 patients. There were no significant differences in demographic and clinical data between patients with non-persistent obstruction (NO: FEV1/VC>88%pred.) and those with persistent obstruction (O: a not completely reversible obstruction with FEV1/VC<88%pred. at each visit before the study visit). Patients with persistent obstruction had significantly higher sputum periostin and TGF-ß concentrations than NO patients and a trend of higher serum periostin levels. GM-CSF and FGF-2 were significantly increased in NO compared to O patients. No differences between groups were found for RANTES, IL-8 and differential cell counts. Sputum periostin inversely correlated with functional parameters (prebronch. FEV1: rho = -0.36, p < 0.05; postbronch. FEV1: rho = -0.33, p = 0.05). Patients with high sputum periostin concentration (>103.3 pg/ml: median value) showed an absolute number of sputum eosinophils significantly higher than patients with low sputum periostin; this behavior was unobserved when serum periostin was considered.

CONCLUSIONS

Only periostin and TGF-ß identified a subgroup of severe asthmatic patients with persistent airway obstruction. Sputum periostin was also inversely associated with FEV1 and proved to be a more sensitive biomarker than serum periostin to identify severe asthmatics with higher sputum eosinophilia.

Basic fibroblast growth factor protects against influenza A virus-induced acute lung injury by recruiting neutrophils

Influenza virus (IAV) infection is a major cause of severe respiratory illness that affects almost every country in the world. IAV infections result in respiratory illness and even acute lung injury and death, but the underlying mechanisms responsible for IAV pathogenesis have not yet been fully elucidated. In this study, the basic fibroblast growth factor 2 (FGF2) level was markedly increased in H1N1 virus-infected humans and mice. FGF2, which is predominately derived from epithelial cells, recruits and activates neutrophils via the FGFR2-PI3K-AKT-NFκB signaling pathway. FGF2 depletion or knockout exacerbated influenza-associated disease by impairing neutrophil recruitment and activation. More importantly, administration of the recombinant FGF2 protein significantly alleviated the severity of IAV-induced lung injury and promoted the survival of IAV-infected mice. Based on the results from experiments in which neutrophils were depleted and adoptively transferred, FGF2 protected mice against IAV infection by recruiting neutrophils. Thus, FGF2 plays a critical role in preventing IAV-induced lung injury, and FGF2 is a promising potential therapeutic target during IAV infection.

Effect of FGF/FGFR pathway blocking on lung adenocarcinoma and its cancer-associated fibroblasts

Cancer-associated fibroblasts (CAFs) are known to promote tumourigenesis through various mechanisms. Fibroblast growth factor (FGF)/FGF receptor (FGFR)-dependent lung cancers have been described. We have developed a mouse model of lung adenocarcinoma that was constructed through the induction of Fgf9 overexpression in type 2 alveolar cells. The expression of Fgf9 in adult lungs resulted in the rapid development of multiple adenocarcinoma-like tumour nodules. Here, we have characterised the contribution of CAFs and the Fgf/Fgfr signalling pathway in maintaining the lung tumours initiated by Fgf9 overexpression. We found that CAF-secreted Fgf2 contributes to tumour cell growth. CAFs overexpressed Tgfb, Mmp7, Fgf9, and Fgf2; synthesised more collagen, and secreted inflammatory cell-recruiting cytokines. CAFs also enhanced the conversion of tumour-associated macrophages (TAMs) to the tumour-supportive M2 phenotype but did not influence angiogenesis. In vivo inhibition of Fgfrs during early lung tumour development resulted in significantly smaller and fewer tumour nodules, whereas inhibition in established lung tumours caused a significant reduction in tumour size and number. Fgfr inhibition also influenced tumour stromal cells, as it significantly abolished TAM recruitment and reduced tumour vascularity. However, the withdrawal of the inhibitor caused a significant recurrence/regrowth of Fgf/Fgfr-independent lung tumours. These recurrent tumours did not possess a higher proliferative or propagative potential. Our results provide evidence that fibroblasts associated with the Fgf9-induced lung adenocarcinoma provide multiple means of support to the tumour. Although the Fgfr blocker significantly suppressed the tumour and its stromal cells, it was not sufficient to completely eliminate the tumour, probably due to the emergence of alternative (resistance/maintenance) mechanism(s). This model represents an excellent tool to further study the complex interactions between CAFs, their related chemokines, and the progression of lung adenocarcinoma; it also provides further evidence to support the need for a combinatorial strategy to treat lung cancer. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

The therapeutic effects of bone marrow-derived mesenchymal stromal cells in the acute lung injury induced by sulfur mustard

Background

Sulfur mustard (SM) is a notorious chemical warfare agent that can cause severe acute lung injury (ALI), in addition to other lesions. Currently, effective medical countermeasures for SM are lacking. Bone marrow-derived mesenchymal stromal cells (BMSCs) possess self-renewal and multipotent differentiation capacity. BMSCs can also migrate to inflammation and injury sites and exert anti-inflammatory and tissue repair functions. Here, we report the curative effect of BMSCs on SM-induced ALI in a mouse model.

Methods

Mice BMSCs were injected into mice via the tail vein 24 h after SM exposure. The distribution of BMSCs in mice was detected by fluorescence imaging. The therapeutic potential of BMSCs was evaluated by the calculating survival rate. The effects of BMSCs on lung tissue injury and repair assessment were examined by staining with H&E and measuring the lung wet/dry weight ratio, BALF protein level, and respiratory function. The effects of BMSCs on the infiltration and phenotypic alteration of inflammatory cells were analyzed by immunohistochemistry and flow cytometry. The levels of chemokines and inflammatory cytokines were examined using the Luminex Performance Assay and ELISA. RNA interference, western blotting, and ELISA were applied to explore the role of the TLR4 signaling pathway in the anti-inflammatory effects of BMSCs. The extent of tissue repair was analyzed by ELISA, western blotting, and immunohistochemistry.

Results

Fluorescence imaging indicated that the lung is the major target organ of BMSCs after injection. The injection of BMSCs significantly improved the survival rate (p < 0.05), respiratory function, and related lung damage indexes (wet/dry weight ratio, total proteins in BALF, etc.) in mice. BMSC administration also reduced the level of pro-inflammatory cytokines, chemokines, and inflammatory cell infiltration, as well as affected the balances of M1/M2 and Th17/Treg. Furthermore, solid evidence regarding the effects of BMSCs on the increased secretion of various growth factors, the differentiation of alveolar epithelial cells, and the enhancement of cell barrier functions was also observed.

Conclusion

BMSCs displayed protective effects against SM-induced ALI by alleviating inflammation and promoting tissue repair. The present study provides a strong experimental basis in a mouse model and suggests possible application for future cell therapy.

Electronic supplementary material

The online version of this article (10.1186/s13287-019-1189-x) contains supplementary material, which is available to authorized users.

Blockade of platelet-derived growth factor receptor-β, not receptor-α ameliorates bleomycin-induced pulmonary fibrosis in mice

Platelet-derived growth factor (PDGF) has been implicated in the pathogenesis of pulmonary fibrosis. Nintedanib, a multi-kinase inhibitor that targets several tyrosine kinases, including PDGF receptor (PDGFR), was recently approved as an anti-fibrotic agent to reduce the deterioration of FVC in patients with idiopathic pulmonary fibrosis (IPF). However, the effects of PDGFR-α or -β on pulmonary fibrosis remain unclear. In an attempt to clarify their effects, we herein used blocking antibodies specific for PDGFR-α (APA5) and -β (APB5) in a bleomycin (BLM)-induced pulmonary fibrosis mouse model. The effects of these treatments on the growth of lung fibroblasts were examined using the ³H-thymidine incorporation assay in vitro. The anti-fibrotic effects of these antibodies were investigated with the Ashcroft score and collagen content of lungs treated with BLM. Their effects on inflammatory cells in the lungs were also analyzed using bronchoalveolar lavage fluid. We investigated damage to epithelial cells and the proliferation of fibroblasts in the lungs. APA5 and APB5 inhibited the phosphorylation of PDGFR-α and -β as well as the proliferation of lung fibroblasts induced by PDGF-AA and BB. The administration of APB5, but not APA5 effectively inhibited BLM-induced pulmonary fibrosis in mice. Apoptosis and the proliferation of epithelial cells and fibroblasts were significantly decreased by the treatment with APB5, but not by APA5. The late treatment with APB5 also ameliorated fibrosis in lungs treated with BLM. These results suggest that PDGFR-α and -β exert different effects on BLM-induced pulmonary fibrosis in mice. A specific approach using the blocking antibody for PDGFR-β may be useful for the treatment of pulmonary fibrosis.

Mesenchymal-Epithelial Interactome Analysis Reveals Essential Factors Required for Fibroblast-Free Alveolosphere Formation

Lung epithelial cells and fibroblasts are key cell populations in lung development. Fibroblasts support type 2 alveolar epithelial cells (AEC2) in the developing and mature lung. However, fibroblast-AEC2 interactions have not been clearly described. We addressed this in the present study by time course serial analysis of gene expression sequencing (SAGE-seq) of epithelial cells and fibroblasts of developing and mature murine lungs. We identified lung fibroblast-epithelial interactions that potentially regulate alveologenesis and are mediated by fibroblast-expressed ligands and epithelial cell surface receptors. In the epithelial-fibroblast co-culture alveolosphere formation assay, single intervention against fibroblast-expressed ligand or associated signaling cascades promoted or inhibited alveolosphere growth. Adding the ligand-associated molecules fibroblast growth factor 7 and Notch ligand and inhibitors of bone morphogenetic protein 4, transforming growth factor β, and glycogen synthase kinase-3β to the culture medium enabled fibroblast-free alveolosphere formation. The results revealed the essential factors regulating fibroblast-AEC2 interactions.

A murine model of acute lung injury identifies growth factors to promote tissue repair and their biomarkers

Type II alveolar epithelial cells (AEC2s) play a crucial role in the regeneration of type I AECs after acute lung injury. The mechanisms underlying the regeneration of AEC2s are not fully understood. To address this issue, here, we investigated a murine model of acute lung injury using mice expressing human Diphtheria Toxin Receptor (DTR) under the control of Lysozyme M promoter (LysM-DTR). DT injection induced the depletion of AEC2s, alveolar macrophages, and bone marrow (BM)-derived myeloid cells in LysM-DTR mice, and the mice died within 6 days after DT injection. Apoptotic AEC2s and bronchiolar epithelial cells appeared at 24 hr, whereas Ki67-positive proliferating cells appeared in the alveoli and bronchioles in the lung of LysM-DTR mice at 72-96 hr after DT injection. Transfer of wild-type BM cells into LysM-DTR mice accelerated the regeneration of AEC2s along with the up-regulation of several growth factors. Moreover, several metabolites were significantly decreased in the sera of LysM-DTR mice compared with WT mice after DT injection, suggesting that these metabolites might be biomarkers to predict AEC2s injury. Together, LysM-DTR mice might be useful to identify growth factors to promote lung repair and the metabolites to predict the severity of lung injury.

FGF-2 inhibits contractile properties of valvular interstitial cell myofibroblasts encapsulated in 3D MMP-degradable hydrogels

Valvular interstitial cells (VICs) are responsible for the maintenance of the extracellular matrix in heart valve leaflets and, in response to injury, activate from a quiescent fibroblast to a wound healing myofibroblast phenotype. Under normal conditions, myofibroblast activation is transient, but the chronic presence of activated VICs can lead to valve diseases, such as fibrotic aortic valve stenosis, for which non-surgical treatments remain elusive. We monitored the porcine VIC response to exogenously delivered fibroblast growth factor 2 (FGF-2; 100 ng/ml), transforming growth factor beta 1 (TGF-β1; 5 ng/ml), or a combination of the two while cultured within 3D matrix metalloproteinase (MMP)-degradable 8-arm 40 kDa poly(ethylene glycol) hydrogels that mimic aspects of the aortic valve. Here, we aimed to investigate VIC myofibroblast activation and subsequent contraction or the reparative wound healing response. To this end, VIC morphology, proliferation, gene expression related to the myofibroblast phenotype [alpha smooth muscle actin (α-SMA) and connective tissue growth factor (CTGF)] and matrix remodeling [collagens (COL1A1 and COL3) and MMP1], and contraction assays were used to quantify the cell response. Treatment with FGF-2 resulted in increased cellular proliferation while reducing the myofibroblast phenotype, as seen by decreased expression of CTGF and α-SMA, and reduced contraction relative to untreated control, suggesting that FGF-2 encourages a reparative phenotype, even in the presence of TGF-β1. TGF-β1 treatment predictably led to an increased proportion of VICs exhibiting the myofibroblast phenotype, indicated by the presence of α-SMA, increased gene expression indicative of matrix remodeling, and bulk contraction of the hydrogels. Functional contraction assays and biomechanical analyses were performed on VIC encapsulated hydrogels and porcine aortic valve tissue explants to validate these findings.

Fibroblast growth factor 2 decreases bleomycin-induced pulmonary fibrosis and inhibits fibroblast collagen production and myofibroblast differentiation

Fibroblast growth factor (FGF) signaling has been implicated in the pathogenesis of pulmonary fibrosis. Mice lacking FGF2 have increased mortality and impaired epithelial recovery after bleomycin exposure, supporting a protective or reparative function following lung injury. To determine whether FGF2 overexpression reduces bleomycin-induced injury, we developed an inducible genetic system to express FGF2 in type II pneumocytes. Double-transgenic (DTG) mice with doxycycline-inducible overexpression of human FGF2 (SPC-rtTA;TRE-hFGF2) or single-transgenic controls were administered intratracheal bleomycin and fed doxycycline chow, starting at either day 0 or day 7. In addition, wild-type mice received intratracheal or intravenous recombinant FGF2, starting at the time of bleomycin treatment. Compared to controls, doxycycline-induced DTG mice had decreased pulmonary fibrosis 21 days after bleomycin, as assessed by gene expression and histology. This beneficial effect was seen when FGF2 overexpression was induced at day 0 or day 7 after bleomycin. FGF2 overexpression did not alter epithelial gene expression, bronchoalveolar lavage cellularity or total protein. In vitro studies using primary mouse and human lung fibroblasts showed that FGF2 strongly inhibited baseline and TGFβ1-induced expression of alpha smooth muscle actin (αSMA), collagen, and connective tissue growth factor. While FGF2 did not suppress phosphorylation of Smad2 or Smad-dependent gene expression, FGF2 inhibited TGFβ1-induced stress fiber formation and serum response factor-dependent gene expression. FGF2 inhibition of stress fiber formation and αSMA requires FGF receptor 1 (FGFR1) and downstream MEK/ERK, but not AKT signaling. In summary, overexpression of FGF2 protects against bleomycin-induced pulmonary fibrosis in vivo and reverses TGFβ1-induced collagen and αSMA expression and stress fiber formation in lung fibroblasts in vitro, without affecting either inflammation or epithelial gene expression. Our results suggest that in the lung, FGF2 is antifibrotic in part through decreased collagen expression and fibroblast to myofibroblast differentiation. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Developmental pathways in the pathogenesis of lung fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive and terminal lung disease with no known cure. IPF is a disease of aging, with median age of diagnosis over 65 years. Median survival is between 3 and 5 years after diagnosis. IPF is characterized primarily by excessive deposition of extracellular matrix (ECM) proteins by activated lung fibroblasts and myofibroblasts, resulting in reduced gas exchange and impaired pulmonary function. Growing evidence supports the concept of a pro-fibrotic environment orchestrated by underlying factors such as genetic predisposition, chronic injury and aging, oxidative stress, and impaired regenerative responses may account for disease development and persistence. Currently, two FDA approved drugs have limited efficacy in the treatment of IPF. Many of the genes and gene networks associated with lung development are induced or activated in IPF. In this review, we analyze current knowledge in the field, gained from both basic and clinical research, to provide new insights into the disease process, and potential approaches to treatment of pulmonary fibrosis.

Idiopathic pulmonary fibrosis (IPF) signaling pathways and protective roles of melatonin

Idiopathic pulmonary fibrosis (IPF) is characterized by the progressive loss of lung function due to tissue scarring. A variety of pro-inflammatory and pro-fibrogenic factors including interleukin‑17A, transforming growth factor β, Wnt/β‑catenin, vascular endothelial growth factor, platelet-derived growth factor, fibroblast growth factors, endotelin‑1, renin angiotensin system and impaired caveolin‑1 function are involved in the IPF pathogenesis. Current therapies for IPF have some limitations and this highlights the need for effective therapeutic agents to treat this fatal disease. Melatonin and its metabolites are broad-spectrum antioxidants that not only remove reactive oxygen and nitrogen species by radical scavenging but also up-regulate the expression and activity of endogenous antioxidants. Via these actions, melatonin and its metabolites modulate a variety of molecular pathways in different pathophysiological conditions. Herein, we review the signaling pathways involved in the pathophysiology of IPF and the potentially protective effects of melatonin on these pathways.

Fibroblast growth factors: key players in regeneration and tissue repair

Tissue injury initiates a complex repair process, which in some organisms can lead to the complete regeneration of a tissue. In mammals, however, the repair of most organs is imperfect and results in scar formation. Both regeneration and repair are orchestrated by a highly coordinated interplay of different growth factors and cytokines. Among the key players are the fibroblast growth factors (FGFs), which control the migration, proliferation, differentiation and survival of different cell types. In addition, FGFs influence the expression of other factors involved in the regenerative response. Here, we summarize current knowledge on the roles of endogenous FGFs in regeneration and repair in different organisms and in different tissues and organs. Gaining a better understanding of these FGF activities is important for appropriate modulation of FGF signaling after injury to prevent impaired healing and to promote organ regeneration in humans.

Densification of Type I Collagen Matrices as a Model for Cardiac Fibrosis

Cardiac fibrosis is a disease state characterized by excessive collagenous matrix accumulation within the myocardium that can lead to ventricular dilation and systolic failure. Current treatment options are severely lacking due in part to the poor understanding of the complexity of molecular pathways involved in cardiac fibrosis. To close this gap, in vitro model systems that recapitulate the defining features of the fibrotic cellular environment are in need. Type I collagen, a major cardiac extracellular matrix protein and the defining component of fibrotic depositions, is an attractive choice for a fibrosis model, but demonstrates poor mechanical strength due to solubility limits. However, plastic compression of collagen matrices is shown to significantly increase its mechanical properties. Here, confined compression of oligomeric, type I collagen matrices is utilized to resemble defining hallmarks seen in fibrotic tissue such as increased collagen content, fibril thickness, and bulk compressive modulus. Cardiomyocytes seeded on compressed matrices show a strong beating abrogation as observed in cardiac fibrosis. Gene expression analysis of selected fibrosis markers indicates fibrotic activation and cardiomyocyte maturation with regard to the existing literature. With these results, a promising first step toward a facile heart-on-chip model is presented to study cardiac fibrosis.

Friends Turned Foes: Angiogenic Growth Factors beyond Angiogenesis

Angiogenesis, the formation of new blood vessels from pre-existing ones is a biological process that ensures an adequate blood flow is maintained to provide the cells with a sufficient supply of nutrients and oxygen within the body. Numerous soluble growth factors and inhibitors, cytokines, proteases as well as extracellular matrix proteins and adhesion molecules stringently regulate the multi-factorial process of angiogenesis. The properties and interactions of key angiogenic molecules such as vascular endothelial growth factors (VEGFs), fibroblast growth factors (FGFs) and angiopoietins have been investigated in great detail with respect to their molecular impact on angiogenesis. Since the discovery of angiogenic growth factors, much research has been focused on their biological actions and their potential use as therapeutic targets for angiogenic or anti-angiogenic strategies in a context-dependent manner depending on the pathologies. It is generally accepted that these factors play an indispensable role in angiogenesis. However, it is becoming increasingly evident that this is not their only role and it is likely that the angiogenic factors have important functions in a wider range of biological and pathological processes. The additional roles played by these molecules in numerous pathologies and biological processes beyond angiogenesis are discussed in this review.

Pluripotent stem cell differentiation reveals distinct developmental pathways regulating lung- versus thyroid-lineage specification

The in vitro-directed differentiation of pluripotent stem cells (PSCs) through stimulation of developmental signaling pathways can generate mature somatic cell types for basic laboratory studies or regenerative therapies. However, there has been significant uncertainty regarding a method to separately derive lung versus thyroid epithelial lineages, as these two cell types each originate from Nkx2-1⁺ foregut progenitors and the minimal pathways claimed to regulate their distinct lineage specification in vivo or in vitro have varied in previous reports. Here, we employ PSCs to identify the key minimal signaling pathways (Wnt+BMP versus BMP+FGF) that regulate distinct lung- versus thyroid-lineage specification, respectively, from foregut endoderm. In contrast to most previous reports, these minimal pathways appear to be evolutionarily conserved between mice and humans, and FGF signaling, although required for thyroid specification, unexpectedly appears to be dispensable for lung specification. Once specified, distinct Nkx2-1⁺ lung or thyroid progenitor pools can now be independently derived for functional 3D culture maturation, basic developmental studies or future regenerative therapies.

Fibroblast growth factor 2 (FGF2) regulates cytoglobin expression and activation of human hepatic stellate cells via JNK signaling

Cytoglobin (CYGB) belongs to the mammalian globin family and is exclusively expressed in hepatic stellate cells (HSCs) in the liver. In addition to its gas-binding ability, CYGB is relevant to hepatic inflammation, fibrosis, and cancer because of its anti-oxidative properties; however, the regulation of CYGB gene expression remains unknown. Here, we sought to identify factors that induce CYGB expression in HSCs and to clarify the molecular mechanism involved. We used the human HSC cell line HHSteC and primary human HSCs isolated from intact human liver tissues. In HHSteC cells, treatment with a culture supplement solution that included fibroblast growth factor 2 (FGF2) increased CYGB expression with concomitant and time-dependent α-smooth muscle actin (αSMA) down-regulation. We found that FGF2 is a key factor in inducing the alteration in both CYGB and αSMA expression in HHSteCs and primary HSCs and that FGF2 triggered the rapid phosphorylation of both c-Jun N-terminal kinase (JNK) and c-JUN. Both the JNK inhibitor PS600125 and transfection of c-JUN-targeting siRNA abrogated FGF2-mediated CYGB induction, and conversely, c-JUN overexpression induced CYGB and reduced αSMA expression. Chromatin immunoprecipitation analyses revealed that upon FGF2 stimulation, phospho-c-JUN bound to its consensus motif (5'-TGA(C/G)TCA), located -218 to -222 bases from the transcription initiation site in the CYGB promoter. Of note, in bile duct-ligated mice, FGF2 administration ameliorated liver fibrosis and significantly reduced HSC activation. In conclusion, FGF2 triggers CYGB gene expression and deactivation of myofibroblastic human HSCs, indicating that FGF2 has therapeutic potential for managing liver fibrosis.

Fibroblast Growth Factor Signaling Mediates Pulmonary Endothelial Glycocalyx Reconstitution

The endothelial glycocalyx is a heparan sulfate (HS)-rich endovascular structure critical to endothelial function. Accordingly, endothelial glycocalyx degradation during sepsis contributes to tissue edema and organ injury. We determined the endogenous mechanisms governing pulmonary endothelial glycocalyx reconstitution, and if these reparative mechanisms are impaired during sepsis. We performed intravital microscopy of wild-type and transgenic mice to determine the rapidity of pulmonary endothelial glycocalyx reconstitution after nonseptic (heparinase-III mediated) or septic (cecal ligation and puncture mediated) endothelial glycocalyx degradation. We used mass spectrometry, surface plasmon resonance, and in vitro studies of human and mouse samples to determine the structure of HS fragments released during glycocalyx degradation and their impact on fibroblast growth factor receptor (FGFR) 1 signaling, a mediator of endothelial repair. Homeostatic pulmonary endothelial glycocalyx reconstitution occurred rapidly after nonseptic degradation and was associated with induction of the HS biosynthetic enzyme, exostosin (EXT)-1. In contrast, sepsis was characterized by loss of pulmonary EXT1 expression and delayed glycocalyx reconstitution. Rapid glycocalyx recovery after nonseptic degradation was dependent upon induction of FGFR1 expression and was augmented by FGF-promoting effects of circulating HS fragments released during glycocalyx degradation. Although sepsis-released HS fragments maintained this ability to activate FGFR1, sepsis was associated with the downstream absence of reparative pulmonary endothelial FGFR1 induction. Sepsis may cause vascular injury not only via glycocalyx degradation, but also by impairing FGFR1/EXT1-mediated glycocalyx reconstitution.