Lung Pericytes and Resident Fibroblasts: Busy Multitaskers

The fate and role of the pericytes in myocardial diseases

The adult mammalian heart contains a large population of pericytes that play important roles in homeostasis and disease. In the normal heart, pericytes regulate microvascular permeability and flow. Myocardial diseases are associated with marked alterations in pericyte phenotype and function. This review manuscript discusses the role of pericytes in cardiac homeostasis and disease. Following myocardial infarction (MI), cardiac pericytes participate in all phases of cardiac repair. During the inflammatory phase, pericytes may secrete cytokines and chemokines and may regulate leukocyte trafficking, through formation of intercellular gaps that serve as exit points for inflammatory cells. Moreover, pericyte contraction induces microvascular constriction, contributing to the pathogenesis of 'no-reflow' in ischemia and reperfusion. During the proliferative phase, pericytes are activated by growth factors, such as transforming growth factor (TGF)-β and contribute to fibrosis, predominantly through secretion of fibrogenic mediators. A fraction of pericytes acquires fibroblast identity but contributes only to a small percentage of infarct fibroblasts and myofibroblasts. As the scar matures, pericytes form a coat around infarct neovessels, promoting stabilization of the vasculature. Pericytes may also be involved in the pathogenesis of chronic heart failure, by regulating inflammation, fibrosis, angiogenesis and myocardial perfusion. Pericytes are also important targets of viral infections (such as SARS-CoV2) and may be implicated in the pathogenesis of cardiac complications of COVID19. Considering their role in myocardial inflammation, fibrosis and angiogenesis, pericytes may be promising therapeutic targets in myocardial disease.

miR-126a-5p inhibits H1N1-induced inflammation and matrix protease secretion in lung fibroblasts by targeting ADAMTS-4

Upregulation of ADAMTS-4 has been reported to have an important role in lung injury, and ADAMTS-4 expression is regulated by miR-126a-5p in abdominal aortic aneurysms. The aim of this study was to investigate whether miR-126a-5p/ADAMTS-4 plays a role in influenza-virus-induced lung injury. Lung fibroblasts were infected with H1N1 influenza virus to detect changes in miR-126a-5p and ADAMTS-4 expression, and cell viability was measured by CCK-8 assay. Inflammatory factors and matrix protease levels were examined using ELISA kits, and cell apoptosis was assessed by measuring the levels of apoptosis-related proteins. A dual luciferase assay was used to verify the regulatory relationship between miR-126a-5p and ADAMTS-4. H1N1 influenza virus reduced fibroblast viability, inhibited miR-126a-5p expression, and promoted ADAMTS-4 expression. Overexpression of miR-126a-5p attenuated the cellular inflammatory response, apoptosis, matrix protease secretion, and virus replication. Luciferase reporter assays revealed that miR-126a-5p inhibited ADAMTS-4 expression by targeting ADAMTS-4 mRNA. Further experiments showed that overexpression of ADAMTS-4 significantly reversed the inhibitory effects of miR-126a-5p on fibroblast inflammation, apoptosis, matrix protease secretion, and virus replication. Upregulation of miR-126a-5p inhibits H1N1-induced apoptosis, inflammatory factors, and matrix protease secretion, as well as virus replication in lung fibroblasts.

Modulating in vitro lung fibroblast activation via senolysis of senescent human alveolar epithelial cells

Idiopathic pulmonary fibrosis (IPF) is an age-related disease with poor prognosis and limited therapeutic options. Activation of lung fibroblasts and differentiation to myofibroblasts are the principal effectors of disease pathology, but damage and senescence of alveolar epithelial cells, specifically type II (ATII) cells, has recently been identified as a potential trigger event for the progressive disease cycle. Targeting ATII senescence and the senescence-associated secretory phenotype (SASP) is an attractive therapeutic strategy; however, translatable primary human cell models that enable mechanistic studies and drug development are lacking. Here, we describe a novel system of conditioned medium (CM) transfer from bleomycin-induced senescent primary alveolar epithelial cells (AEC) onto normal human lung fibroblasts (NHLF) that demonstrates an enhanced fibrotic transcriptional and secretory phenotype compared to non-senescent AEC CM treatment or direct bleomycin damage of the NHLFs. In this system, the bleomycin-treated AECs exhibit classical hallmarks of cellular senescence, including SASP and a gene expression profile that resembles aberrant epithelial cells of the IPF lung. Fibroblast activation by CM transfer is attenuated by pre-treatment of senescent AECs with the senolytic Navitoclax and AD80, but not with the standard of care agent Nintedanib or senomorphic JAK-targeting drugs (e.g., ABT-317, ruxolitinib). This model provides a relevant human system for profiling novel senescence-targeting therapeutics for IPF drug development.

Identification of a myofibroblast differentiation program during neonatal lung development

Alveologenesis is the final stage of lung development in which the internal surface area of the lung is increased to facilitate efficient gas exchange in the mature organism. The first phase of alveologenesis involves the formation of septal ridges (secondary septae) and the second phase involves thinning of the alveolar septa. Within secondary septa, mesenchymal cells include a transient population of alveolar myofibroblasts (MyoFBs) and a stable but poorly described population of lipid-rich cells that have been referred to as lipofibroblasts or matrix fibroblasts (MatFBs). Using a unique Fgf18CreER lineage trace mouse line, cell sorting, single-cell RNA sequencing and primary cell culture, we have identified multiple subtypes of mesenchymal cells in the neonatal lung, including an immature progenitor cell that gives rise to mature MyoFB. We also show that the endogenous and targeted ROSA26 locus serves as a sensitive reporter for MyoFB maturation. These studies identify a MyoFB differentiation program that is distinct from other mesenchymal cell types and increases the known repertoire of mesenchymal cell types in the neonatal lung.

The CLCF1-CNTFR axis drives an immunosuppressive tumor microenvironment and blockade enhances the effects of established cancer therapies

Tumors comprise a complex ecosystem consisting of many cell types that communicate through secreted factors. Targeting these intercellular signaling networks remains an important challenge in cancer research. Cardiotrophin-like cytokine factor 1 (CLCF1) is an interleukin-6 (IL-6) family member secreted by cancer-associated fibroblasts (CAFs) that binds to ciliary neurotrophic factor receptor (CNTFR), promoting tumor growth in lung and liver cancer1,2. A high-affinity soluble receptor (eCNTFR-Fc) that sequesters CLCF1 has anti-oncogenic effects3. However, the role of CLCF1 in mediating cell-cell interactions in cancer has remained unclear. We demonstrate that eCNTFR-Fc has widespread effects on both tumor cells and the tumor microenvironment and can sensitize cancer cells to KRAS inhibitors or immune checkpoint blockade. After three weeks of treatment with eCNTFR-Fc, there is a shift from an immunosuppressive to an immunostimulatory macrophage phenotype as well as an increase in activated T, NKT, and NK cells. Combination of eCNTFR-Fc and αPD1 was significantly more effective than single-agent therapy in a syngeneic allograft model, and eCNTFR-Fc sensitizes tumor cells to αPD1 in a non-responsive GEM model of lung adenocarcinoma. These data suggest that combining eCNTFR-Fc with KRAS inhibition or with αPD1 is a novel therapeutic strategy for lung cancer and potentially other cancers in which these therapies have been used but to date with only modest effect. Overall, we demonstrate the potential of cancer therapies that target cytokines to alter the immune microenvironment.

Cytokine, chemokine alterations and immune cell infiltration in Radiation-induced lung injury: Implications for prevention and management

Radiation therapy is one of the primary treatments for thoracic malignancies, with radiation-induced lung injury (RILI) emerging as its most prevalent complication. RILI encompasses early-stage radiation pneumonitis (RP) and the subsequent development of radiation pulmonary fibrosis (RPF). During radiation treatment, not only are tumor cells targeted, but normal tissue cells, including alveolar epithelial cells and vascular endothelial cells, also sustain damage. Within the lungs, ionizing radiation boosts the intracellular levels of reactive oxygen species across various cell types. This elevation precipitates the release of cytokines and chemokines, coupled with the infiltration of inflammatory cells, culminating in the onset of RP. This pulmonary inflammatory response can persist, spanning a duration from several months to years, ultimately progressing to RPF. This review aims to explore the alterations in cytokine and chemokine release and the influx of immune cells post-ionizing radiation exposure in the lungs, offering insights for the prevention and management of RILI.

An agent-based modeling approach for lung fibrosis in response to COVID-19

The severity of the COVID-19 pandemic has created an emerging need to investigate the long-term effects of infection on patients. Many individuals are at risk of suffering pulmonary fibrosis due to the pathogenesis of lung injury and impairment in the healing mechanism. Fibroblasts are the central mediators of extracellular matrix (ECM) deposition during tissue regeneration, regulated by anti-inflammatory cytokines including transforming growth factor beta (TGF-β). The TGF-β-dependent accumulation of fibroblasts at the damaged site and excess fibrillar collagen deposition lead to fibrosis. We developed an open-source, multiscale tissue simulator to investigate the role of TGF-β sources in the progression of lung fibrosis after SARS-CoV-2 exposure, intracellular viral replication, infection of epithelial cells, and host immune response. Using the model, we predicted the dynamics of fibroblasts, TGF-β, and collagen deposition for 15 days post-infection in virtual lung tissue. Our results showed variation in collagen area fractions between 2% and 40% depending on the spatial behavior of the sources (stationary or mobile), the rate of activation of TGF-β, and the duration of TGF-β sources. We identified M2 macrophages as primary contributors to higher collagen area fraction. Our simulation results also predicted fibrotic outcomes even with lower collagen area fraction when spatially-localized latent TGF-β sources were active for longer times. We validated our model by comparing simulated dynamics for TGF-β, collagen area fraction, and macrophage cell population with independent experimental data from mouse models. Our results showed that partial removal of TGF-β sources changed the fibrotic patterns; in the presence of persistent TGF-β sources, partial removal of TGF-β from the ECM significantly increased collagen area fraction due to maintenance of chemotactic gradients driving fibroblast movement. The computational findings are consistent with independent experimental and clinical observations of collagen area fractions and cell population dynamics not used in developing the model. These critical insights into the activity of TGF-β sources may find applications in the current clinical trials targeting TGF-β for the resolution of lung fibrosis.

p38 MAPK signaling in chronic obstructive pulmonary disease pathogenesis and inhibitor therapeutics

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is characterized by persistent respiratory symptoms and airflow limitation due to airway and/or alveolar remodeling. Although the abnormalities are primarily prompted by chronic exposure to inhaled irritants, maladjusted and self-reinforcing immune responses are significant contributors to the development and progression of the disease. The p38 isoforms are regarded as pivotal hub proteins that regulate immune and inflammatory responses in both healthy and disease states. As a result, their inhibition has been the subject of numerous recent studies exploring their therapeutic potential in COPD.

MAIN BODY

We performed a systematic search based on the PRISMA guidelines to find relevant studies about P38 signaling in COPD patients. We searched the PubMed and Google Scholar databases and used "P38" AND "COPD" Mesh Terms. We applied the following inclusion criteria: (1) human, animal, ex vivo and in vitro studies; (2) original research articles; (3) published in English; and (4) focused on P38 signaling in COPD pathogenesis, progression, or treatment. We screened the titles and abstracts of the retrieved studies and assessed the full texts of the eligible studies for quality and relevance. We extracted the following data from each study: authors, year, country, sample size, study design, cell type, intervention, outcome, and main findings. We classified the studies according to the role of different cells and treatments in P38 signaling in COPD.

CONCLUSION

While targeting p38 MAPK has demonstrated some therapeutic potential in COPD, its efficacy is limited. Nevertheless, combining p38 MAPK inhibitors with other anti-inflammatory steroids appears to be a promising treatment choice. Clinical trials testing various p38 MAPK inhibitors have produced mixed results, with some showing improvement in lung function and reduction in exacerbations in COPD patients. Despite these mixed results, research on p38 MAPK inhibitors is still a major area of study to develop new and more effective therapies for COPD. As our understanding of COPD evolves, we may gain a better understanding of how to utilize p38 MAPK inhibitors to treat this disease. Video Abstract.

Radiotracers for Imaging of Fibrosis: Advances during the Last Two Decades and Future Directions

Fibrosis accompanies various pathologies, and there is thus an unmet medical need for non-invasive, sensitive, and quantitative methods for the assessment of fibrotic processes. Currently, needle biopsy with subsequent histological analysis is routinely used for the diagnosis along with morphological imaging techniques, such as computed tomography (CT), magnetic resonance imaging (MRI), and ultrasound (US). However, none of these imaging techniques are sufficiently sensitive and accurate to detect minor changes in fibrosis. More importantly, they do not provide information on fibrotic activity on the molecular level, which is critical for fundamental understanding of the underlying biology and disease course. Molecular imaging technology using positron emission tomography (PET) offers the possibility of imaging not only physiological real-time activity, but also high-sensitivity and accurate quantification. This diagnostic tool is well established in oncology and has exhibited exponential development during the last two decades. However, PET diagnostics has only recently been widely applied in the area of fibrosis. This review presents the progress of development of radiopharmaceuticals for non-invasive detection of fibrotic processes, including the fibrotic scar itself, the deposition of new fibrotic components (fibrogenesis), or the degradation of existing fibrosis (fibrolysis).

Sphingosine-1-Phosphate as Lung and Cardiac Vasculature Protecting Agent in SARS-CoV-2 Infection

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) may cause severe respiratory illness with high mortality. SARS-CoV-2 infection results in a massive inflammatory cell infiltration into the infected lungs accompanied by excessive pro-inflammatory cytokine production. The lung histology of dead patients shows that some areas are severely emphysematous, with enormously dilated blood vessels and micro-thromboses. The inappropriate inflammatory response damaging the pulmonary interstitial arteriolar walls suggests that the respiratory distress may come in a large part from lung vasculature injuries. It has been recently observed that low plasmatic sphingosine-1-phosphate (S1P) is a marker of a worse prognosis of clinical outcome in severe coronavirus disease (COVID) patients. S1P is an angiogenic molecule displaying anti-inflammatory and anti-apoptotic properties, that promote intercellular interactions between endothelial cells and pericytes resulting in the stabilization of arteries and capillaries. In this context, it can be hypothesized that the benefit of a normal S1P level is due to its protective effect on lung vasculature functionality. This paper provides evidence supporting this concept, opening the way for the design of a pharmacological approach involving the use of an S1P lyase inhibitor to increase the S1P level that in turn will rescue the lung vasculature functionality.

Cellular mechanisms in the pathogenesis of interstitial lung diseases

The interstitial lung diseases (ILDs) are a large, heterogeneous group of several hundred generally rare pulmonary pathologies, which show injury, inflammation and/or scarring in the lung. Although the aetiology of these disorders remains largely unknown, various cellular mechanisms have an important role in pathogenesis of fibrosis on the background of occupational, environmental and genetic factors. We have tried to provide new insights into the interactions and cellular contributions, analysing the roles of various cells in the pathogenesis of idiopathic pulmonary fibrosis.

S100 proteins in cardiovascular diseases

Cardiovascular diseases have become a serious threat to human health and life worldwide and have the highest fatality rate. Therefore, the prevention and treatment of cardiovascular diseases have become a focus for public health experts. The expression of S100 proteins is cell- and tissue-specific; they are implicated in cardiovascular, neurodegenerative, and inflammatory diseases and cancer. This review article discusses the progress in the research on the role of S100 protein family members in cardiovascular diseases. Understanding the mechanisms by which these proteins exert their biological function may provide novel concepts for preventing, treating, and predicting cardiovascular diseases.

Stretch regulates alveologenesis and homeostasis via mesenchymal Gαq/11-mediated TGFβ2 activation

Alveolar development and repair require tight spatiotemporal regulation of numerous signalling pathways that are influenced by chemical and mechanical stimuli. Mesenchymal cells play key roles in numerous developmental processes. Transforming growth factor-β (TGFβ) is essential for alveologenesis and lung repair, and the G protein α subunits Gαq and Gα11 (Gαq/11) transmit mechanical and chemical signals to activate TGFβ in epithelial cells. To understand the role of mesenchymal Gαq/11 in lung development, we generated constitutive (Pdgfrb-Cre+/-;Gnaqfl/fl;Gna11-/-) and inducible (Pdgfrb-Cre/ERT2+/-;Gnaqfl/fl;Gna11-/-) mesenchymal Gαq/11 deleted mice. Mice with constitutive Gαq/11 gene deletion exhibited abnormal alveolar development, with suppressed myofibroblast differentiation, altered mesenchymal cell synthetic function, and reduced lung TGFβ2 deposition, as well as kidney abnormalities. Tamoxifen-induced mesenchymal Gαq/11 gene deletion in adult mice resulted in emphysema associated with reduced TGFβ2 and elastin deposition. Cyclical mechanical stretch-induced TGFβ activation required Gαq/11 signalling and serine protease activity, but was independent of integrins, suggesting an isoform-specific role for TGFβ2 in this model. These data highlight a previously undescribed mechanism of cyclical stretch-induced Gαq/11-dependent TGFβ2 signalling in mesenchymal cells, which is imperative for normal alveologenesis and maintenance of lung homeostasis.

Mesenchymal cells in the Lung: Evolving concepts and their role in fibrosis

Mesenchymal cells in the lung are crucial during development, but also contribute to the pathogenesis of fibrotic disorders, including idiopathic pulmonary fibrosis (IPF), the most common and deadly form of fibrotic interstitial lung diseases. Originally thought to behave as supporting cells for the lung epithelium and endothelium with a singular function of producing basement membrane, mesenchymal cells encompass a variety of cell types, including resident fibroblasts, lipofibroblasts, myofibroblasts, smooth muscle cells, and pericytes, which all occupy different anatomic locations and exhibit diverse homeostatic functions in the lung. During injury, each of these subtypes demonstrate remarkable plasticity and undergo varying capacity to proliferate and differentiate into activated myofibroblasts. Therefore, these cells secrete high levels of extracellular matrix (ECM) proteins and inflammatory cytokines, which contribute to tissue repair, or in pathologic situations, scarring and fibrosis. Whereas epithelial damage is considered the initial trigger that leads to lung injury, lung mesenchymal cells are recognized as the ultimate effector of fibrosis and attempts to better understand the different functions and actions of each mesenchymal cell subtype will lead to a better understanding of why fibrosis develops and how to better target it for future therapy. This review summarizes current findings related to various lung mesenchymal cells as well as signaling pathways, and their contribution to the pathogenesis of pulmonary fibrosis.

Pericytes: The lung-forgotten cell type

Pericytes are a heterogeneous population of mesenchymal cells located on the abluminal surface of microvessels, where they provide structural and biochemical support. Pericytes have been implicated in numerous lung diseases including pulmonary arterial hypertension (PAH) and allergic asthma due to their ability to differentiate into scar-forming myofibroblasts, leading to collagen deposition and matrix remodelling and thus driving tissue fibrosis. Pericyte-extracellular matrix interactions as well as other biochemical cues play crucial roles in these processes. In this review, we give an overview of lung pericytes, the key pro-fibrotic mediators they interact with, and detail recent advances in preclinical studies on how pericytes are disrupted and contribute to lung diseases including PAH, allergic asthma, and chronic obstructive pulmonary disease (COPD). Several recent studies using mouse models of PAH have demonstrated that pericytes contribute to these pathological events; efforts are currently underway to mitigate pericyte dysfunction in PAH by targeting the TGF-β, CXCR7, and CXCR4 signalling pathways. In allergic asthma, the dissociation of pericytes from the endothelium of blood vessels and their migration towards inflamed areas of the airway contribute to the characteristic airway remodelling observed in allergic asthma. Although several factors have been suggested to influence this migration such as TGF-β, IL-4, IL-13, and periostin, recent evidence points to the CXCL12/CXCR4 pathway as a potential therapeutic target. Pericytes might also play an essential role in lung dysfunction in response to ageing, as they are responsive to environmental risk factors such as cigarette smoke and air pollutants, which are the main drivers of COPD. However, there is currently no direct evidence delineating the contribution of pericytes to COPD pathology. Although there is a lack of human clinical data, the recent available evidence derived from in vitro and animal-based models shows that pericytes play important roles in the initiation and maintenance of chronic lung diseases and are amenable to pharmacological interventions. Therefore, further studies in this field are required to elucidate if targeting pericytes can treat lung diseases.

Therapeutic strategies targeting pro-fibrotic macrophages in interstitial lung disease

Idiopathic pulmonary fibrosis (IPF) is the representative phenotype of interstitial lung disease where severe scarring develops in the lung interstitium. Although antifibrotic treatments are available and have been shown to slow the progression of IPF, improved therapeutic options are still needed. Recent data indicate that macrophages play essential pro-fibrotic roles in the pathogenesis of pulmonary fibrosis. Historically, macrophages have been classified into two functional subtypes, "M1" and "M2," and it is well described that "M2" or "alternatively activated" macrophages contribute to fibrosis via the production of fibrotic mediators, such as TGF-β, CTGF, and CCL18. However, highly plastic macrophages may possess distinct functions and phenotypes in the fibrotic lung environment. Thus, M2-like macrophages in vitro and pro-fibrotic macrophages in vivo are not completely identical cell populations. Recent developments in transcriptome analysis, including single-cell RNA sequencing, have attempted to depict more detailed phenotypic characteristics of pro-fibrotic macrophages. This review will outline the role and characterization of pro-fibrotic macrophages in fibrotic lung diseases and discuss the possibility of treating lung fibrosis by preventing or reprogramming the polarity of macrophages. We also utilized a systematic approach to review the literature and identify novel and promising therapeutic agents that follow this treatment strategy.

The underappreciated role of resident epithelial cell populations in metastatic progression: contributions of the lung alveolar epithelium

Metastatic cancer is difficult to treat and is responsible for the majority of cancer-related deaths. After cancer cells initiate metastasis and successfully seed a distant site, resident cells in the tissue play a key role in determining how metastatic progression develops. The lung is the second most frequent site of metastatic spread, and the primary site of metastasis within the lung is alveoli. The most abundant cell type in the alveolar niche is the epithelium. This review will examine the potential contributions of the alveolar epithelium to metastatic progression. It will also provide insight into other ways in which alveolar epithelial cells, acting as immune sentinels within the lung, may influence metastatic progression through their various interactions with cells in the surrounding microenvironment.

The Role of Mesothelin in Activation of Portal Fibroblasts in Cholestatic Liver Injury

Fibrosis is a common consequence of abnormal wound healing, which is characterized by infiltration of myofibroblasts and formation of fibrous scar. In liver fibrosis, activated Hepatic Stellate Cells (aHSCs) and activated Portal Fibroblasts (aPFs) are the major contributors to the origin of hepatic myofibroblasts. aPFs are significantly involved in the pathogenesis of cholestatic fibrosis, suggesting that aPFs may be a primary target for anti-fibrotic therapy in cholestatic injury. aPFs are distinguishable from aHSCs by specific markers including mesothelin (Msln), Mucin 16 (Muc16), and Thymus cell antigen 1 (Thy1, CD90) as well as fibulin 2, elastin, Gremlin 1, ecto-ATPase nucleoside triphosphate diphosphohydrolase 2. Msln plays a critical role in activation of PFs, via formation of Msln-Muc16-Thy1 complex that regulates TGFβ1/TGFβRI-mediated fibrogenic signaling. The opposing pro- and anti-fibrogenic effects of Msln and Thy1 are key components of the TGFβ1-induced activation pathway in aPFs. In addition, aPFs and activated lung and kidney fibroblasts share similarities across different organs with expression of common markers and activation cascade including Msln-Thy1 interaction. Here, we summarize the potential function of Msln in activation of PFs and development of cholestatic fibrosis, offering a novel perspective for anti-fibrotic therapy targeting Msln.

Anti-Fibrotic Effect of SDF-1β Overexpression in Bleomycin-Injured Rat Lung

Rational: Idiopathic pulmonary fibrosis (IPF) is a progressive interstitial lung disease and is associated with high mortality due to a lack of effective treatment. Excessive deposition of the extracellular matrix by activated myofibroblasts in the alveolar space leads to scar formation that hinders gas exchange. Therefore, selectively removing activated myofibroblasts with the aim to repair and remodel fibrotic lungs is a promising approach. Stromal-derived growth factor (SDF-1) is known to stimulate cellular signals which attract stem cells to the site of injury for tissue repair and remodeling. Here, we investigate the effect of overexpression of SDF-1β on lung structure using the bleomycin-injured rat lung model. Methods: Intratracheal administration of bleomycin was performed in adult male rats (F344). Seven days later, in vivo electroporation-mediated gene transfer of either SDF-1β or the empty vector was performed. Animals were sacrificed seven days after gene transfer and histology, design-based stereology, flow cytometry, and collagen measurement were performed on the tissue collected. For in vitro experiments, lung fibroblasts obtained from IPF patients were used. Results: Seven days after SDF-1β gene transfer to bleomycin-injured rat lungs, reduced total collagen, reduced collagen fibrils, improved histology and induced apoptosis of myofibroblasts were observed. Furthermore, it was revealed that TNF-α mediates SDF-1β-induced apoptosis of myofibroblasts; moreover, SDF-1β overexpression increased alveolar epithelial cell numbers and proliferation in vivo and also induced their migration in vitro. Conclusions: Our study demonstrates a new antifibrotic mechanism of SDF-1β overexpression and suggests SDF-1β as a potential new approach for the treatment of lung fibrosis.

GREM1/PPP2R3A expression in heterogeneous fibroblasts initiates pulmonary fibrosis

Background

Fibroblasts have important roles in the synthesis and remodeling of extracellular matrix (ECM) proteins during pulmonary fibrosis. However, the spatiotemporal distribution of heterogeneous fibroblasts during disease progression remains unknown.

Results

In the current study, silica was used to generate a mouse model of pathological changes in the lung, and single-cell sequencing, spatial transcriptome sequencing and an analysis of markers of cell subtypes were performed to identify fibroblast subtypes. A group of heterogeneous fibroblasts that play an important role at the early pathological stage were identified, characterized based on the expression of inflammatory and proliferation genes (termed inflammatory-proliferative fibroblasts) and found to be concentrated in the lesion area. The expression of GREM1/protein phosphatase 2 regulatory subunit B''alpha (PPP2R3A) in inflammatory-proliferative fibroblasts was found to initiate early pulmonary pathological changes by increasing the viability, proliferation and migration of cells.

Conclusions

Inflammatory-proliferative fibroblasts play a key role in the early pathological changes that occur in silicosis, and during this process, GREM1 is the driving factor that targets PPP2R3A and initiates the inflammatory response, which is followed by irreversible fibrosis induced by SiO₂. The GREM1/PPP2R3A pathway may be a potential target in the early treatment of silicosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-022-00860-0.

Intratracheally administered LNA gapmer antisense oligonucleotides induce robust gene silencing in mouse lung fibroblasts

The lung is a complex organ with various cell types having distinct roles. Antisense oligonucleotides (ASOs) have been studied in the lung, but it has been challenging to determine their effectiveness in each cell type due to the lack of appropriate analytical methods. We employed three distinct approaches to study silencing efficacy within different cell types. First, we used lineage markers to identify cell types in flow cytometry, and simultaneously measured ASO-induced silencing of cell-surface proteins CD47 or CD98. Second, we applied single-cell RNA sequencing (scRNA-seq) to measure silencing efficacy in distinct cell types; to the best of our knowledge, this is the first time scRNA-seq has been applied to measure the efficacy of oligonucleotide therapeutics. In both approaches, fibroblasts were the most susceptible to locally delivered ASOs, with significant silencing also in endothelial cells. Third, we confirmed that the robust silencing in fibroblasts is broadly applicable by silencing two targets expressed mainly in fibroblasts, Mfap4 and Adam33. Across independent approaches, we demonstrate that intratracheally administered LNA gapmer ASOs robustly induce gene silencing in lung fibroblasts. ASO-induced gene silencing in fibroblasts was durable, lasting 4-8 weeks after a single dose. Thus, lung fibroblasts are well aligned with ASOs as therapeutics.

Ogerin mediated inhibition of TGF-β(1) induced myofibroblast differentiation is potentiated by acidic pH

Transforming growth factor beta (TGF-β) induced myofibroblast differentiation is central to the pathological scarring observed in Idiopathic Pulmonary Fibrosis (IPF) and other fibrotic diseases. Our lab has recently identified expression of GPR68 (Ovarian Cancer Gene Receptor 1, OGR1), a pH sensing G-protein coupled receptor, as a negative regulator of TGF-β induced profibrotic effects in primary human lung fibroblasts (PHLFs). We therefore hypothesized that small molecule activators of GPR68 would inhibit myofibroblast differentiation. Ogerin is a positive allosteric modulator (PAM) of GPR68, inducing a leftward shift of the dose response curve to proton induced signaling. Using PHLFs derived from patients with both non-fibrotic and IPF diagnoses, we show that Ogerin inhibits, and partially reverses TGF-β induced myofibroblast differentiation in a dose dependent manner. This occurs at the transcriptional level without inhibition of canonical TGF-β induced SMAD signaling. Ogerin induces PKA dependent CREB phosphorylation, a marker of Gαs pathway activation. The ability of Ogerin to inhibit both basal and TGF-β induced collagen gene transcription, and induction of Gαs signaling is enhanced at an acidic pH (pH 6.8). Similar findings were also found using fibroblasts derived from dermal, intestinal, and orbital tissue. The biological role of GPR68 in different tissues, cell types, and disease states is an evolving and emerging field. This work adds to the understanding of Gαs coupled GPCRs in fibrotic lung disease, the ability to harness the pH sensing properties of GPR68, and conserved mechanisms of fibrosis across different organ systems.

Lymphocytic Airway Inflammation in Lung Allografts

Lung transplant remains a key therapeutic option for patients with end stage lung disease but short- and long-term survival lag other solid organ transplants. Early ischemia-reperfusion injury in the form of primary graft dysfunction (PGD) and acute cellular rejection are risk factors for chronic lung allograft dysfunction (CLAD), a syndrome of airway and parenchymal fibrosis that is the major barrier to long term survival. An increasing body of research suggests lymphocytic airway inflammation plays a significant role in these important clinical syndromes. Cytotoxic T cells are observed in airway rejection, and transcriptional analysis of airways reveal common cytotoxic gene patterns across solid organ transplant rejection. Natural killer (NK) cells have also been implicated in the early allograft damage response to PGD, acute rejection, cytomegalovirus, and CLAD. This review will examine the roles of lymphocytic airway inflammation across the lifespan of the allograft, including: 1) The contribution of innate lymphocytes to PGD and the impact of PGD on the adaptive immune response. 2) Acute cellular rejection pathologies and the limitations in identifying airway inflammation by transbronchial biopsy. 3) Potentiators of airway inflammation and heterologous immunity, such as respiratory infections, aspiration, and the airway microbiome. 4) Airway contributions to CLAD pathogenesis, including epithelial to mesenchymal transition (EMT), club cell loss, and the evolution from constrictive bronchiolitis to parenchymal fibrosis. 5) Protective mechanisms of fibrosis involving regulatory T cells. In summary, this review will examine our current understanding of the complex interplay between the transplanted airway epithelium, lymphocytic airway infiltration, and rejection pathologies.

Targeting fibrosis, mechanisms and cilinical trials

Fibrosis is characterized by the excessive extracellular matrix deposition due to dysregulated wound and connective tissue repair response. Multiple organs can develop fibrosis, including the liver, kidney, heart, and lung. Fibrosis such as liver cirrhosis, idiopathic pulmonary fibrosis, and cystic fibrosis caused substantial disease burden. Persistent abnormal activation of myofibroblasts mediated by various signals, such as transforming growth factor, platelet-derived growth factor, and fibroblast growh factor, has been recongized as a major event in the occurrence and progression of fibrosis. Although the mechanisms driving organ-specific fibrosis have not been fully elucidated, drugs targeting these identified aberrant signals have achieved potent anti-fibrotic efficacy in clinical trials. In this review, we briefly introduce the aetiology and epidemiology of several fibrosis diseases, including liver fibrosis, kidney fibrosis, cardiac fibrosis, and pulmonary fibrosis. Then, we summarise the abnormal cells (epithelial cells, endothelial cells, immune cells, and fibroblasts) and their interactions in fibrosis. In addition, we also focus on the aberrant signaling pathways and therapeutic targets that regulate myofibroblast activation, extracellular matrix cross-linking, metabolism, and inflammation in fibrosis. Finally, we discuss the anti-fibrotic drugs based on their targets and clinical trials. This review provides reference for further research on fibrosis mechanism, drug development, and clinical trials.

In vitro and vivo study of tranilast protects from acute respiratory distress syndrome and early pulmonary fibrosis induced by smoke inhalation

BACKGROUND

Tranilast (N-[3＇,4＇-dimethoxycinnamoyl]-anthranilic acid) is an analog of a tryptophan metabolite. It was identified with anti-inflammatory and antifibrotic activities, and used in the treatment of a variety of diseases, such as anti - allergy, bronchial asthma, and hypertrophic scars. As a drug with few adverse reactions, tranilast has attracted great attention, but its application is limited due to the uncertainty of dosages and mechanisms. In this study, the protection effects of different doses of tranilast on smoke inhalation mediated lung injury on rats, and on the damage of three kinds of lung cells in vitro were investigated.

METHOD

In vivo, Sprague-Dawley rats were randomly divided into sham group, smoke group (rats were exposed to pine sawdust smoke three times, each time for 5 min), different doses of tranilast treatment group (doses were 100 mg/kg, 200 mg/kg and 300 mg/kg, ip.) and placebo group. After 1, 3 and 7 days, pulmonary function, pathologic injury by HE staining, cytokines and oxidative stress level by kits were determined. At 7days, lung fibrosis was assessed by Masson's trichrome staining and the level of hydroxyproline (HYP). In vitro, three kinds of lung cells from normal rats were isolated: type II alveolar epithelial cells (AT-II), pulmonary microvascular endothelial cells (PMVECs) and pulmonary fibroblasts (PFs). To investigate the potential effects of tranilast on cell proliferation, cell cycle and cytokine production of three kinds of lung cells exposed to smoke.

RESULTS

Compared with smoke group and placebo group, tranilast treatment significantly reduced histopathological changes (such as pulmonary hemorrhage, edema and inflammatory cell infiltration, etc.), significantly reduced histopathological score (p < 0.05), increased arterial oxygen partial pressure, and decreased the levels of IL-1β, TNF-α, TGF-β1 (p < 0.05), oxidative stress and the expression of nuclear transcription factor κB (NF-κB) smoke exposed rats (p < 0.01). In particular, the effect of 200 mg/kg dose was more prominent. In vitro, smoke induced AT-II and PMVECs apoptosis, improved PFs proliferation (p < 0.01), activity of SOD and decreased the content of MDA (p < 0.01). However, tranilast seems to be turning this trend well. The inflammatory factor IL-11β, TNF-α and TGF-β1, and the expression of NF-κB were significantly lower in the tranilast treatment than in the smoke group (p < 0.01).

CONCLUSION

This study indicates that tranilast had a protective effect on acute respiratory distress syndrome and early pulmonary fibrosis of rats in vivo. In addition, tranilast promotes proliferation of AT-II and PMVECs but inhibits PFs proliferation, down-regulates secretion of inflammatory cytokines and alleviates oxidative stress of AT-II, PMVECs and PFs after smoke stimuli in vitro.

Central Nervous System Pericytes Contribute to Health and Disease

Successful neuroprotection is only possible with contemporary microvascular protection. The prevention of disease-induced vascular modifications that accelerate brain damage remains largely elusive. An improved understanding of pericyte (PC) signalling could provide important insight into the function of the neurovascular unit (NVU), and into the injury-provoked responses that modify cell–cell interactions and crosstalk. Due to sharing the same basement membrane with endothelial cells, PCs have a crucial role in the control of endothelial, astrocyte, and oligodendrocyte precursor functions and hence blood–brain barrier stability. Both cerebrovascular and neurodegenerative diseases impair oxygen delivery and functionally impair the NVU. In this review, the role of PCs in central nervous system health and disease is discussed, considering their origin, multipotency, functions and also dysfunction, focusing on new possible avenues to modulate neuroprotection. Dysfunctional PC signalling could also be considered as a potential biomarker of NVU pathology, allowing us to individualize therapeutic interventions, monitor responses, or predict outcomes.

Validation of Specific and Reliable Genetic Tools to Identify, Label, and Target Cardiac Pericytes in Mice

Background In the myocardium, pericytes are often confused with other interstitial cell types, such as fibroblasts. The lack of well-characterized and specific tools for identification, lineage tracing, and conditional targeting of myocardial pericytes has hampered studies on their role in heart disease. In the current study, we characterize and validate specific and reliable strategies for labeling and targeting of cardiac pericytes. Methods and Results Using the neuron-glial antigen 2 (NG2)DsRed reporter line, we identified a large population of NG2+ periendothelial cells in mouse atria, ventricles, and valves. To examine possible overlap of NG2+ mural cells with fibroblasts, we generated NG2DsRed; platelet-derived growth factor receptor (PDGFR) αEGFP pericyte/fibroblast dual reporter mice. Myocardial NG2+ pericytes and PDGFRα+ fibroblasts were identified as nonoverlapping cellular populations with distinct transcriptional signatures. PDGFRα+ fibroblasts expressed high levels of fibrillar collagens, matrix metalloproteinases, tissue inhibitor of metalloproteinases, and genes encoding matricellular proteins, whereas NG2+ pericytes expressed high levels of Pdgfrb, Adamts1, and Vtn. To validate the specificity of pericyte Cre drivers, we crossed these lines with PDGFRαEGFP fibroblast reporter mice. The constitutive NG2Cre driver did not specifically track mural cells, labeling many cardiomyocytes. However, the inducible NG2CreER driver specifically traced vascular mural cells in the ventricle and in the aorta, without significant labeling of PDGFRα+ fibroblasts. In contrast, the inducible PDGFRβCreER line labeled not only mural cells but also the majority of cardiac and aortic fibroblasts. Conclusions Fibroblasts and pericytes are topographically and transcriptomically distinct populations of cardiac interstitial cells. The inducible NG2CreER driver optimally targets cardiac pericytes; in contrast, the inducible PDGFRβCreER line lacks specificity.

Thorny ground, rocky soil: Tissue-specific mechanisms of tumor dormancy and relapse

Disseminated tumor cells (DTCs) spread systemically yet distinct patterns of metastasis indicate a range of tissue susceptibility to metastatic colonization. Distinctions between permissive and suppressive tissues are still being elucidated at cellular and molecular levels. Although there is a growing appreciation for the role of the microenvironment in regulating metastatic success, we have a limited understanding of how diverse tissues regulate DTC dormancy, the state of reversible quiescence and subsequent awakening thought to contribute to delayed relapse. Several themes of microenvironmental regulation of dormancy are beginning to emerge, including vascular association, co-option of pre-existing niches, metabolic adaptation, and immune evasion, with tissue-specific nuances. Conversely, DTC awakening is often associated with injury or inflammation-induced activation of the stroma, promoting a proliferative environment with DTCs following suit. We review what is known about tissue-specific regulation of tumor dormancy on a tissue-by-tissue basis, profiling major metastatic organs including the bone, lung, brain, liver, and lymph node. An aerial view of the barriers to metastatic growth may reveal common targets and dependencies to inform the therapeutic prevention of relapse.

Extracellular Matrix: Surface Proteoglycans

Cell surface proteoglycans, such as syndecans and glypicans, regulate molecular interactions that mediate cell adhesion, migration, proliferation, and differentiation. Through these activities, surface proteoglycans modulate critical biological processes of development, inflammation, infection, tissue repair, and cancer metastasis. Proteoglycans are unique glycoproteins comprised of one or several glycosaminoglycans attached covalently to core proteins. Glycosaminoglycans mediate the majority of ligand-binding functions of proteoglycans. Accumulating evidence indicates that surface proteoglycans regulate the onset, progression, and outcome of lung diseases, including lung injury, infection, fibrosis, and cancer. This article will review key features of surface proteoglycan biology in lung health and disease.

Advanced In Vitro Lung Models for Drug and Toxicity Screening: The Promising Role of Induced Pluripotent Stem Cells

The substantial socioeconomic burden of lung diseases, recently highlighted by the disastrous impact of the coronavirus disease 2019 (COVID-19) pandemic, accentuates the need for interventive treatments capable of decelerating disease progression, limiting organ damage, and contributing to a functional tissue recovery. However, this is hampered by the lack of accurate human lung research models, which currently fail to reproduce the human pulmonary architecture and biochemical environment. Induced pluripotent stem cells (iPSCs) and organ-on-chip (OOC) technologies possess suitable characteristics for the generation of physiologically relevant in vitro lung models, allowing for developmental studies, disease modeling, and toxicological screening. Importantly, these platforms represent potential alternatives for animal testing, according to the 3Rs (replace, reduce, refine) principle, and hold promise for the identification and approval of new chemicals under the European REACH (registration, evaluation, authorization and restriction of chemicals) framework. As such, this review aims to summarize recent progress made in human iPSC- and OOC-based in vitro lung models. A general overview of the present applications of in vitro lung models is presented, followed by a summary of currently used protocols to generate different lung cell types from iPSCs. Lastly, recently developed iPSC-based lung models are discussed.

Cyclo-VEGI inhibits bronchial artery remodeling in a murine model of chronic asthma

Purpose/Aim: In the context of asthma, airway bronchial remodeling and angiogenesis in the bronchial mucosa are well established. Cyclopeptidic-vascular endothelial growth inhibitor (cyclo-VEGI) is an inhibitor of the vascular endothelial growth factor (VEGF) receptor that increases the proliferation of endothelial cells and the formation of new vessels. However, changes in the bronchial arteries of patients with asthma have not been clearly elucidated. We investigated whether structural changes occurred in bronchial arteries, as well as the effects of cyclo-VEGI in a mouse model of chronic asthma (in vivo) and human fibroblasts (in vitro). Materials and Methods: A validated mouse model of allergic airway inflammation with ovalbumin (OVA) as the causative allergen was used for the study. Mice were treated with cyclo-VEGI or fluticasone during OVA challenge. In vitro experiments were conducted to determine whether fibroblasts proliferated following elastin exposure and the effects of cyclo-VEGI on them. Results: OVA sensitization and challenge led to greater perivascular smooth muscle area, more elastic fibers, and elevated expression of vascular cell adhesion molecule (VCAM)-1 antigen. These phenomena indicated changes to bronchial arteries. Cyclo-VEGI and fluticasone treatment both inhibited airway hyper-responsiveness and inflammation. Cyclo-VEGI-treated mice exhibited decreased perivascular smooth muscle area, elastin fibers, and VCAM-1 expression. Fluticasone-treated mice exhibited reductions in perivascular smooth muscle but not in perivascular elastin or VCAM-1 expression. In vitro, fibroblast proliferation was enhanced by elastin treatment, which was inhibited by cyclo-VEGI treatment. Eotaxin expression was elevated in elastin-treated fibroblasts and decreased with cyclo-VEGI treatment. Conclusions: Vascular remodeling occurred in our mouse model of chronic asthma. Cyclo-VEGI could reduce airway inflammation and hyper-responsiveness by inhibiting VCAM-1 expression and elastin deposition around the bronchial arteries.

Extracellular Vesicles and Alveolar Epithelial-Capillary Barrier Disruption in Acute Respiratory Distress Syndrome: Pathophysiological Role and Therapeutic Potential

Extracellular vesicles (EVs) mediate intercellular communication by transferring genetic material, proteins and organelles between different cells types in both health and disease. Recent evidence suggests that these vesicles, more than simply diagnostic markers, are key mediators of the pathophysiology of acute respiratory distress syndrome (ARDS) and other lung diseases. In this review, we will discuss the contribution of EVs released by pulmonary structural cells (alveolar epithelial and endothelial cells) and immune cells in these diseases, with particular attention to their ability to modulate inflammation and alveolar-capillary barrier disruption, a hallmark of ARDS. EVs also offer a unique opportunity to develop new therapeutics for the treatment of ARDS. Evidences supporting the ability of stem cell-derived EVs to attenuate the lung injury and ongoing strategies to improve their therapeutic potential are also discussed.

Roles of Mesenchymal Cells in the Lung: From Lung Development to Chronic Obstructive Pulmonary Disease

Mesenchymal cells are an essential cell type because of their role in tissue support, their multilineage differentiation capacities and their potential clinical applications. They play a crucial role during lung development by interacting with airway epithelium, and also during lung regeneration and remodeling after injury. However, much less is known about their function in lung disease. In this review, we discuss the origins of mesenchymal cells during lung development, their crosstalk with the epithelium, and their role in lung diseases, particularly in chronic obstructive pulmonary disease.

Molecular Mechanisms and Cellular Contribution from Lung Fibrosis to Lung Cancer Development

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive, fibrosing interstitial lung disease (ILD) of unknown aetiology, with a median survival of 2–4 years from the time of diagnosis. Although IPF has unknown aetiology by definition, there have been identified several risks factors increasing the probability of the onset and progression of the disease in IPF patients such as cigarette smoking and environmental risk factors associated with domestic and occupational exposure. Among them, cigarette smoking together with concomitant emphysema might predispose IPF patients to lung cancer (LC), mostly to non-small cell lung cancer (NSCLC), increasing the risk of lung cancer development. To this purpose, IPF and LC share several cellular and molecular processes driving the progression of both pathologies such as fibroblast transition proliferation and activation, endoplasmic reticulum stress, oxidative stress, and many genetic and epigenetic markers that predispose IPF patients to LC development. Nintedanib, a tyrosine–kinase inhibitor, was firstly developed as an anticancer drug and then recognized as an anti-fibrotic agent based on the common target molecular pathway. In this review our aim is to describe the updated studies on common cellular and molecular mechanisms between IPF and lung cancer, knowledge of which might help to find novel therapeutic targets for this disease combination.

Interrelation Between Fibroblasts and T Cells in Fibrosing Interstitial Lung Diseases

Interstitial lung diseases (ILDs) are a heterogeneous group of diseases characterized by varying degrees of inflammation and fibrosis of the pulmonary interstitium. The interrelations between multiple immune cells and stromal cells participate in the pathogenesis of ILDs. While fibroblasts contribute to the development of ILDs through secreting extracellular matrix and proinflammatory cytokines upon activation, T cells are major mediators of adaptive immunity, as well as inflammation and autoimmune tissue destruction in the lung of ILDs patients. Fibroblasts play important roles in modulating T cell recruitment, differentiation and function and conversely, T cells can balance fibrotic sequelae with protective immunity in the lung. A more precise understanding of the interrelation between fibroblasts and T cells will enable a better future therapeutic design by targeting this interrelationship. Here we highlight recent work on the interactions between fibroblasts and T cells in ILDs, and consider the implications of these interactions in the future development of therapies for ILDs.

Fibrotic Idiopathic Interstitial Lung Disease: The Molecular and Cellular Key Players

Interstitial lung diseases (ILDs) that are known as diffuse parenchymal lung diseases (DPLDs) lead to the damage of alveolar epithelium and lung parenchyma, culminating in inflammation and widespread fibrosis. ILDs that account for more than 200 different pathologies can be divided into two groups: ILDs that have a known cause and those where the cause is unknown, classified as idiopathic interstitial pneumonia (IIP). IIPs include idiopathic pulmonary fibrosis (IPF), non-specific interstitial pneumonia (NSIP), cryptogenic organizing pneumonia (COP) known also as bronchiolitis obliterans organizing pneumonia (BOOP), acute interstitial pneumonia (AIP), desquamative interstitial pneumonia (DIP), respiratory bronchiolitis-associated interstitial lung disease (RB-ILD), and lymphocytic interstitial pneumonia (LIP). In this review, our aim is to describe the pathogenic mechanisms that lead to the onset and progression of the different IIPs, starting from IPF as the most studied, in order to find both the common and standalone molecular and cellular key players among them. Finally, a deeper molecular and cellular characterization of different interstitial lung diseases without a known cause would contribute to giving a more accurate diagnosis to the patients, which would translate to a more effective treatment decision.

The bright side of fibroblasts: molecular signature and regenerative cues in major organs

Fibrosis is a pathologic process characterized by the replacement of parenchymal tissue by large amounts of extracellular matrix, which may lead to organ dysfunction and even death. Fibroblasts are classically associated to fibrosis and tissue repair, and seldom to regeneration. However, accumulating evidence supports a pro-regenerative role of fibroblasts in different organs. While some organs rely on fibroblasts for maintaining stem cell niches, others depend on fibroblast activity, particularly on secreted molecules that promote cell adhesion, migration, and proliferation, to guide the regenerative process. Herein we provide an up-to-date overview of fibroblast-derived regenerative signaling across different organs and discuss how this capacity may become compromised with aging. We further introduce a new paradigm for regenerative therapies based on reverting adult fibroblasts to a fetal/neonatal-like phenotype.

Digital Imaging Analysis Reveals Reduced Alveolar α-Smooth Muscle Actin Expression in Severe Asthma

Expansion of α-smooth muscle actin (α-SMA)-expressing airway smooth muscle of the large airways in asthma is well-studied. However, the contribution of α-SMA-expressing cells in the more distal alveolated parenchyma, including pericytes and myofibroblasts within the alveolar septum, to asthma pathophysiology remains relatively unexplored. The objective of this study was to evaluate α-SMA expression in the alveolated parenchyma of individuals with severe asthma (SA), compared with healthy controls or individuals with chronic obstructive pulmonary disease. Using quantitative digital image analysis and video-assisted thoracoscopic surgery lung biopsies, we show that alveolated parenchyma α-SMA expression is markedly reduced in SA in comparison to healthy controls (mean %positive pixels: 12% vs. 23%, P=0.005). Chronic obstructive pulmonary disease cases showed a similar, but trending, decrease in α-SMA positivity compared with controls (mean %positivity: 17% vs. 23%, P=0.107), which may suggest loss of α-SMA expression is a commonality of obstructive lung diseases. The SA group had similar staining for ETS-related gene protein, a specific endothelial marker, comparatively to controls (mean %positive nuclei: 34% vs. 42%, P=0.218), which suggests intact capillary endothelium and likely intact capillary-associated, α-SMA-positive pericytes. These findings suggest that the loss of α-SMA expression in SA may be because of changes in myofibroblast α-SMA expression or cell number. Further study is necessary to fully evaluate possible mechanisms and consequences of this phenomenon.

Triple negative breast cancer and non-small cell lung cancer: Clinical challenges and nano-formulation approaches

Triple negative breast cancer (TNBC) and non-small cell lung cancer (NSCLC) are amongst the most aggressive forms of solid tumors. TNBC is highlighted by absence of genetic components of progesterone receptor, HER2/neu and estrogen receptor in breast cancer. NSCLC is characterized by integration of malignant carcinoma into respiratory system. Both cancers are associated with poor median and overall survival rates with low progression free survival with high incidences of relapse. These cancers are characterized by tumor heterogeneity, genetic mutations, generation of cancer-stem cells, immune-resistance and chemoresistance. Further, these neoplasms have been reported for tumor cross-talk into second primary cancers for each other. Current chemotherapeutic regimens include usage of multiple agents in tandem to affect tumor cells through multiple mechanisms with various such combinations being clinically tested. However, lack of controlled delivery and effective temporospatial presence of chemotherapeutics has resulted in suboptimal therapeutic response. Consequently, passive targeted albumin bound paclitaxel and PEGylated liposomal doxorubicin have been clinically used and tested with newer drugs for improved therapeutic efficacy in these cancers. Active targeting of nanocarriers against surface overexpressed proteins in both neoplasms have been explored. However, use of single agent nanoparticulate formulations against both cancers have failed to elicit desired outcomes. This review aims to identify clinical unmet need in these cancers while establishing a correlation with tested nano-formulation approaches and issues with preclinical to clinical translation. Lipid and polymer-based drug-drug and drug-gene combinatorial nanocarriers delivering multiple chemotherapeutics simultaneously to desired site of action have been detailed. Finally, emerging opportunities such as pharmacological targets (immune check point and epigentic modulators) as well as gene-based modulation (siRNA/CRISPR/Cas9) and the nano-formulation challenges for effective treatment of both cancers have been explored.

Immunotherapy-based targeting of MSLN+ activated portal fibroblasts is a strategy for treatment of cholestatic liver fibrosis

We investigated the role of mesothelin (Msln) and thymocyte differentiation antigen 1 (Thy1) in the activation of fibroblasts across multiple organs and demonstrated that Msln^-/- mice are protected from cholestatic fibrosis caused by Mdr2 (multidrug resistance gene 2) deficiency, bleomycin-induced lung fibrosis, and UUO (unilateral urinary obstruction)-induced kidney fibrosis. On the contrary, Thy1^-/- mice are more susceptible to fibrosis, suggesting that a Msln-Thy1 signaling complex is critical for tissue fibroblast activation. A similar mechanism was observed in human activated portal fibroblasts (aPFs). Targeting of human MSLN⁺ aPFs with two anti-MSLN immunotoxins killed fibroblasts engineered to express human mesothelin and reduced collagen deposition in livers of bile duct ligation (BDL)-injured mice. We provide evidence that antimesothelin-based therapy may be a strategy for treatment of parenchymal organ fibrosis.

Dissecting the Role of Mesenchymal Stem Cells in Idiopathic Pulmonary Fibrosis: Cause or Solution

Idiopathic pulmonary fibrosis (IPF) is one of the most aggressive forms of idiopathic interstitial pneumonias, characterized by chronic and progressive fibrosis subverting the lung's architecture, pulmonary functional decline, progressive respiratory failure, and high mortality (median survival 3 years after diagnosis). Among the mechanisms associated with disease onset and progression, it has been hypothesized that IPF lungs might be affected either by a regenerative deficit of the alveolar epithelium or by a dysregulation of repair mechanisms in response to alveolar and vascular damage. This latter might be related to the progressive dysfunction and exhaustion of the resident stem cells together with a process of cellular and tissue senescence. The role of endogenous mesenchymal stromal/stem cells (MSCs) resident in the lung in the homeostasis of these mechanisms is still a matter of debate. Although endogenous MSCs may play a critical role in lung repair, they are also involved in cellular senescence and tissue ageing processes with loss of lung regenerative potential. In addition, MSCs have immunomodulatory properties and can secrete anti-fibrotic factors. Thus, MSCs obtained from other sources administered systemically or directly into the lung have been investigated for lung epithelial repair and have been explored as a potential therapy for the treatment of lung diseases including IPF. Given these multiple potential roles of MSCs, this review aims both at elucidating the role of resident lung MSCs in IPF pathogenesis and the role of administered MSCs from other sources for potential IPF therapies.

Living on the Edge of the CNS: Meninges Cell Diversity in Health and Disease

The meninges are the fibrous covering of the central nervous system (CNS) which contain vastly heterogeneous cell types within its three layers (dura, arachnoid, and pia). The dural compartment of the meninges, closest to the skull, is predominantly composed of fibroblasts, but also includes fenestrated blood vasculature, an elaborate lymphatic system, as well as immune cells which are distinct from the CNS. Segregating the outer and inner meningeal compartments is the epithelial-like arachnoid barrier cells, connected by tight and adherens junctions, which regulate the movement of pathogens, molecules, and cells into and out of the cerebral spinal fluid (CSF) and brain parenchyma. Most proximate to the brain is the collagen and basement membrane-rich pia matter that abuts the glial limitans and has recently be shown to have regional heterogeneity within the developing mouse brain. While the meninges were historically seen as a purely structural support for the CNS and protection from trauma, the emerging view of the meninges is as an essential interface between the CNS and the periphery, critical to brain development, required for brain homeostasis, and involved in a variety of diseases. In this review, we will summarize what is known regarding the development, specification, and maturation of the meninges during homeostatic conditions and discuss the rapidly emerging evidence that specific meningeal cell compartments play differential and important roles in the pathophysiology of a myriad of diseases including: multiple sclerosis, dementia, stroke, viral/bacterial meningitis, traumatic brain injury, and cancer. We will conclude with a list of major questions and mechanisms that remain unknown, the study of which represent new, future directions for the field of meninges biology.

Antibody-mediated depletion of CCR10+EphA3+ cells ameliorates fibrosis in IPF

Idiopathic pulmonary fibrosis (IPF) is characterized by aberrant repair that diminishes lung function via mechanisms that remain poorly understood. CC chemokine receptor (CCR10) and its ligand CCL28 were both elevated in IPF compared with normal donors. CCR10 was highly expressed by various cells from IPF lungs, most notably stage-specific embryonic antigen-4-positive mesenchymal progenitor cells (MPCs). In vitro, CCL28 promoted the proliferation of CCR10+ MPCs while CRISPR/Cas9-mediated targeting of CCR10 resulted in the death of MPCs. Following the intravenous injection of various cells from IPF lungs into immunodeficient (NOD/SCID-γ, NSG) mice, human CCR10+ cells initiated and maintained fibrosis in NSG mice. Eph receptor A3 (EphA3) was among the highest expressed receptor tyrosine kinases detected on IPF CCR10+ cells. Ifabotuzumab-targeted killing of EphA3+ cells significantly reduced the numbers of CCR10+ cells and ameliorated pulmonary fibrosis in humanized NSG mice. Thus, human CCR10+ cells promote pulmonary fibrosis, and EphA3 mAb-directed elimination of these cells inhibits lung fibrosis.

Distinct Fibroblast Lineages Give Rise to NG2+ Pericyte Populations in Mouse Skin Development and Repair

We have examined the developmental origins of Ng2+ perivascular cell populations that adhere to the basement membrane of blood vessels, and their contribution to wound healing. Neural/glial antigen 2 (Ng2) labeled most perivascular cells (70-80%) in developing and adult mouse back skin, a higher proportion than expressed by other pericyte markers Tbx18, Nestin and Pdgfrβ. In adult mouse back skin Ng2+ perivascular cells could be categorized into 4 populations based on whether they expressed Pdgfrα and Pdgfrβ individually or in combination or were Pdgfr-negative. Lineage tracing demonstrated that although Ng2+ cells in embryonic and neonatal back skin contributed to multiple cell types they did not give rise to interfollicular fibroblasts within the dermis. Lineage tracing of distinct fibroblast populations during skin development showed that papillary fibroblasts (Lrig1+) gave rise to Ng2+ perivascular cells in the upper dermis, whilst Ng2+ perivascular cells in the lower dermis were primarily derived from reticular Dlk1+ fibroblasts. Following wounding of adult skin, Ng2+ dermal cells only give rise to Ng2+ blood vessel associated cells and did not contribute to other fibroblast lineages. The relative abundance of Ng2+ Pdgfrβ+ perivascular populations was comparable in wounded and non-wounded skin, indicating that perivascular heterogeneity was maintained during full thickness skin repair. In the wound bed Ng2+ perivascular populations were primarily derived from Lrig1+ papillary or Dlk1+ reticular fibroblast lineages, according to the location of the regenerating blood vessels. We conclude that Ng2+ perivascular cells represent a heterogeneous lineage restricted population that is primarily recruited from the papillary or reticular fibroblast lineages during tissue regeneration.

Progenitor/Stem Cells in Vascular Remodeling during Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is characterized by an important occlusive vascular remodeling with the production of new endothelial cells, smooth muscle cells, myofibroblasts, and fibroblasts. Identifying the cellular processes leading to vascular proliferation and dysfunction is a major goal in order to decipher the mechanisms leading to PAH development. In addition to in situ proliferation of vascular cells, studies from the past 20 years have unveiled the role of circulating and resident vascular in pulmonary vascular remodeling. This review aims at summarizing the current knowledge on the different progenitor and stem cells that have been shown to participate in pulmonary vascular lesions and on the pathways regulating their recruitment during PAH. Finally, this review also addresses the therapeutic potential of circulating endothelial progenitor cells and mesenchymal stem cells.

Cell-specific drug targeting in the lung

Non-targeted drug delivery systems have several limitations including the decreased bioavailability of the drug, poor stability and rapid clearance in addition to off-target distribution. Cell-specific targeted delivery approaches promise to overcome some of these limitations and enhance therapeutic selectivity. In this review, we aim to discuss cell-specific targeted approachesin the lung at the biochemical and molecular levels. These approaches include;a) directly administered small molecule drugs with intracellular action; b) targeted biologics and synthetic hybrids with extracellular action; c) site activateddrugs; and d) delivery systems.We discuss the pharmaceutical and biochemical parameters that govern the fate of drug molecules at delivery sites while presenting an overview of relevant literature surrounding this area of research and current advancements.

Single cell transcriptomic analysis of murine lung development on hyperoxia-induced damage

During late lung development, alveolar and microvascular development is finalized to enable sufficient gas exchange. Impaired late lung development manifests as bronchopulmonary dysplasia (BPD) in preterm infants. Single-cell RNA sequencing (scRNA-seq) allows for assessment of complex cellular dynamics during biological processes, such as development. Here, we use MULTI-seq to generate scRNA-seq profiles of over 66,000 cells from 36 mice during normal or impaired lung development secondary to hyperoxia with validation of some of the findings in lungs from BPD patients. We observe dynamic populations of cells, including several rare cell types and putative progenitors. Hyperoxia exposure, which mimics the BPD phenotype, alters the composition of all cellular compartments, particularly alveolar epithelium, stromal fibroblasts, capillary endothelium and macrophage populations. Pathway analysis and predicted dynamic cellular crosstalk suggest inflammatory signaling as the main driver of hyperoxia-induced changes. Our data provides a single-cell view of cellular changes associated with late lung development in health and disease.

Extracellular matrix remodeling associated with bleomycin-induced lung injury supports pericyte-to-myofibroblast transition

Of the many origins of pulmonary myofibroblasts, microvascular pericytes are a known source. Prior literature has established the ability of pericytes to transition into myofibroblasts, but provide limited insight into molecular cues that drive this process during lung injury repair and fibrosis. Fibronectin and RGD-binding integrins have long been considered pro-fibrotic factors in myofibroblast biology, and here we test the hypothesis that these known myofibroblast cues coordinate pericyte-to-myofibroblast transitions. Specifically, we hypothesized that αvβ3 integrin engagement on fibronectin induces pericyte transition into myofibroblastic phenotypes in the murine bleomycin lung injury model. Myosin Heavy Chain 11 (Myh11)-CreERT2 lineage tracing in transgenic mice allows identification of cells of pericyte origin and provides a robust tool for isolating pericytes from tissues for further evaluation. We used this murine model to track and characterize pericyte behaviors during tissue repair. The majority of Myh11 lineage-positive cells are positive for the pericyte surface markers, PDGFRβ (55%) and CD146 (69%), and display typical pericyte morphology with spatial apposition to microvascular networks. After intratracheal bleomycin treatment of mice, Myh11 lineage-positive cells showed significantly increased contractile and secretory markers, as well as αv integrin expression. According to RNASeq measurements, many disease and tissue-remodeling genesets were upregulated in Myh11 lineage-positive cells in response to bleomycin-induced lung injury. In vitro, blocking αvβ3 binding through cycloRGDfK prevented expression of the myofibroblastic marker αSMA relative to controls. In response to RGD-containing provisional matrix proteins present in lung injury, pericytes may alter their integrin profile.

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Pericyte lineage model enables study of transdifferentiating pericytes.

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High dimensional flow cytometry used to characterize pulmonary stromal cells

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Pulmonary pericytes express matrix-remodeling genes and proteins in lung injury.

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Myofibroblasts derived from pericytes have active αvβ3 integrin.

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In vitro assay reveals necessity of RGD for pericyte transdifferentiation.

Insights Into Development and Progression of Idiopathic Pulmonary Fibrosis From Single Cell RNA Studies

Idiopathic pulmonary fibrosis (IPF) is a progressive and fatal lung disease with limited therapeutic options. The current model suggests that chronic or repetitive "micro-injuries" of the alveolar epithelium lead to activation and proliferation of fibroblasts and excessive extracellular matrix (ECM) deposition. Disruption of alveolar type II (ATII) epithelial cell homeostasis and the characteristics of mesenchymal cell populations in IPF have received particular attention in recent years. Emerging data from single cell RNA sequencing (scRNAseq) analysis shed novel light on alterations in ATII cell progenitor dysfunction and the diversity of mesenchymal cells within the fibrotic lung. Within this minireview, we summarize the data from most recent human scRNAseq studies. We aim to collate the current knowledge on cellular plasticity and heterogeneity in the development and progression of IPF, effects of drug treatment on transcriptional changes. Finally, we provide a brief outlook on future challenges and promises for large scale sequencing studies in the development of novel therapeutics for IPF.

Loss of Fas signaling in fibroblasts impairs homeostatic fibrosis resolution and promotes persistent pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive, irreversible fibrotic disease of the distal lung alveoli that culminates in respiratory failure and reduced lifespan. Unlike normal lung repair in response to injury, IPF is associated with the accumulation and persistence of fibroblasts and myofibroblasts, as well as continued production of collagen and other extracellular matrix (ECM) components. Prior in vitro studies have led to the hypothesis that the development of resistance to Fas-induced apoptosis by lung fibroblasts and myofibroblasts contributes to their accumulation in the distal lung tissues of IPF patients. Here, we test this hypothesis in vivo in the resolving model of bleomycin-induced pulmonary fibrosis in mice. Using genetic loss-of-function approaches to inhibit Fas signaling in fibroblasts, potentially novel flow cytometry strategies to quantify lung fibroblast subsets, and transcriptional profiling of lung fibroblasts by bulk and single cell RNA sequencing, we show that Fas is necessary for lung fibroblast apoptosis during homeostatic resolution of bleomycin-induced pulmonary fibrosis in vivo. Furthermore, we show that loss of Fas signaling leads to the persistence and continued profibrotic functions of lung fibroblasts. Our studies provide insights into the mechanisms that contribute to fibroblast survival, persistence, and continued ECM deposition in the context of IPF and how failure to undergo Fas-induced apoptosis impairs fibrosis resolution.