Activation of alveolar macrophages via the alternative pathway in herpesvirus-induced lung fibrosis

Liposomal sodium clodronate mitigates radiation-induced lung injury through macrophage depletion

Radiation-induced lung injury (RILI) is a severe complication arising from thoracic tumor radiotherapy, which constrains the possibility of increasing radiation dosage. Current RILI therapies provide only limited relief and may result in undesirable side effects. Therefore, there is an urgent demand for effective and low-toxicity treatments for RILI. Macrophages play a pivotal role in RILI, promoting inflammation in the initial stages and facilitating fibrosis in the later stages. Sodium clodronate, a bisphosphonate, can induce macrophage apoptosis when encapsulated in liposomes. In this study, we explored the potential of liposomal sodium clodronate (LC) as a specific agent for depleting macrophages to alleviate acute RILI. We assessed the impact of LC on macrophage consumption both in vitro and in vivo. In a mouse model of acute RILI, LC treatment group led to a reduction in alveolar macrophage counts, mitigated lung injury severity, and lowered levels of pro-inflammatory cytokines in both plasma and bronchoalveolar lavage fluid. Additionally, we further elucidated the specific effects and mechanism of LC on macrophages in vitro. Alveolar macrophages MHS cells were subjected to varying concentrations of LC (0, 50, 100, 200 μg/ml), and the results demonstrated its dose-dependent inhibition of cell proliferation and induction of apoptosis. Moreover, LC decreased the secretion of pro-inflammatory cytokines, including IL-1β, IL-6, and TNF-α. Conditioned media from LC-treated macrophages protected alveolar epithelial cells MLE-12 from radiation-induced damage, as demonstrated by reduced apoptosis and DNA damage. These findings imply that LC-mediated macrophage depletion may present a promising therapeutic strategy for alleviating radiation-induced lung injury.

Increase in venous thromboembolism in SARS-CoV-2 infected lung tissue: proteome analysis of lung parenchyma, isolated endothelium, and thrombi

AIMS

COVID-19 pneumonia is characterized by an increased rate of deep venous thrombosis and pulmonary embolism. To better understand the pathophysiology behind thrombosis in COVID-19, we performed proteomics analysis on SARS-CoV-2 infected lung tissue.

METHODS

Liquid chromatography mass spectrometry was performed on SARS-CoV-2 infected postmortem lung tissue samples. Five protein profiling analyses were performed: whole slide lung parenchyma analysis, followed by analysis of isolated thrombi and endothelium, both stratified by disease (COVID-19 versus influenza) and thrombus morphology (embolism versus in situ). Influenza autopsy cases with pulmonary thrombi were used as controls.

RESULTS

Compared to influenza controls, both analyses of COVID-19 whole-tissue and isolated endothelium showed upregulation of proteins and pathways related to liver metabolism including urea cycle activation, with arginase being among the top upregulated proteins in COVID-19 lung tissue. Analysis of isolated COVID-19 thrombi showed significant downregulation of pathways related to platelet activation compared to influenza thrombi. Analysis of isolated thrombi based on histomorphology shows that in situ thrombi have significant upregulation of coronavirus pathogenesis proteins.

CONCLUSIONS

The decrease in platelet activation pathways in severe COVID-19 thrombi suggests a relative increase in venous thromboembolism, as thrombi from venous origin tend to contain fewer platelets than arterial thrombi. Based on histomorphology, in situ thrombi show upregulation of various proteins related to SARS-CoV-2 pathogenesis compared to thromboemboli, which may indicate increased in situ pulmonary thrombosis in COVID-19. Therefore, this study supports the increase of venous thromboembolism without undercutting the involvement of in situ thrombosis in severe COVID-19.

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.

Identification and functional prediction of long non-coding RNA and mRNA related to connective tissue disease-associated interstitial lung diseases

Objective

Recently, the role of long non-coding RNA (lncRNA) in rheumatic immune diseases has attracted widespread attention. However, knowledge of lncRNA in connective tissue disease-associated interstitial lung disease (CTD-ILD) is limited. This study explored the expression profile and possible mechanisms of lncRNA and mRNA in peripheral blood mononuclear cells (PBMCs) of CTD-ILD patients, especially systemic sclerosis (SSc)-ILD and rheumatoid arthritis (RA)-ILD.

Methods

LncRNA microarray analysis identified 240 diferentially expressed lncRNAs and 218 diferentially expressed mRNA in the CTD-ILD group and the connective tissue disease without associated interstitial lung disease (CTD-NILD) group. The bioinformatics analysis of diferential genes has identified several important biological processes and signal pathways, including nuclear factor kappa B (NF-kappa B) signaling pathway, interleukin 17 (IL-17) signaling pathway, B cell receptor signaling pathway. Relative expression levels of five diferentially expressed lncRNAs and one mRNA in 120 SSc and RA patients with or without ILD were detected by quantitative reverse-transcription (PCR).

Results

The ENST00000604692 expression level was significantly higher in the ILD than the without interstitial lung disease (NILD) group; T311354 and arginase-1 were significantly higher in SSc than RA group.

Conclusion

These data suggest that the specific profile of lncRNA in PBMCs of CTD-ILD patients and the potential signal pathways related to the pathogenesis of CTD-ILD, which may provide newfound insights for the diagnosis and treatment of CTD-ILD patients.

Mechanisms and Effects of Macrophage Polarization and Its Specifics in Pulmonary Environment

Macrophages are a specific group of cells found in all body tissues. They have specific characteristics in each of the tissues that correspond to the functional needs of the specific environment. These cells are involved in a wide range of processes, both pro-inflammatory and anti-inflammatory ("wound healing"). This is due to their specific capacity for so-called polarization, a phenotypic change that is, moreover, partially reversible compared to other differentiated cells of the human body. This promises a wide range of possibilities for its influence and thus therapeutic use. In this article, we therefore review the mechanisms that cause polarization, the basic classification of polarized macrophages, their characteristic markers and the effects that accompany these phenotypic changes. Since the study of pulmonary (and among them mainly alveolar) macrophages is currently the focus of scientific interest of many researchers and these macrophages are found in very specific environments, given mainly by the extremely high partial pressure of oxygen compared to other locations, which specifically affects their behavior, we will focus our review on this group.

Dysregulation of metabolic pathways in pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic progressive disorder of unknown origin and the most common interstitial lung disease. It progresses with the recruitment of fibroblasts and myofibroblasts that contribute to the accumulation of extracellular matrix (ECM) proteins, leading to the loss of compliance and alveolar integrity, compromising the gas exchange capacity of the lung. Moreover, while there are therapeutics available, they do not offer a cure. Thus, there is a pressing need to identify better therapeutic targets. With the advent of transcriptomics, proteomics, and metabolomics, the cellular mechanisms underlying disease progression are better understood. Metabolic homeostasis is one such factor and its dysregulation has been shown to impact the outcome of IPF. Several metabolic pathways involved in the metabolism of lipids, protein and carbohydrates have been implicated in IPF. While metabolites are crucial for the generation of energy, it is now appreciated that metabolites have several non-metabolic roles in regulating cellular processes such as proliferation, signaling, and death among several other functions. Through this review, we succinctly elucidate the role of several metabolic pathways in IPF. Moreover, we also discuss potential therapeutics which target metabolism or metabolic pathways.

Ythdf2 promotes pulmonary hypertension by suppressing Hmox1-dependent anti-inflammatory and antioxidant function in alveolar macrophages

Pulmonary hypertension (PH) is a devastating disease characterized by irreversible pulmonary vascular remodeling (PVR) that causes right ventricular failure and death. The early alternative activation of macrophages is a critical event in the development of PVR and PH, but the underlying mechanisms remain elusive. Previously we have shown that N⁶-methyladenosine (m⁶A) modifications of RNA contribute to phenotypic switching of pulmonary artery smooth muscle cells and PH. In the current study, we identify Ythdf2, an m⁶A reader, as an important regulator of pulmonary inflammation and redox regulation in PH. In a mouse model of PH, the protein expression of Ythdf2 was increased in alveolar macrophages (AMs) during the early stages of hypoxia. Mice with a myeloid specific knockout of Ythdf2 (Ythdf2^{Lyz2 Cre}) were protected from PH with attenuated right ventricular hypertrophy and PVR compared to control mice and this was accompanied by decreased macrophage polarization and oxidative stress. In the absence of Ythdf2, heme oxygenase 1 (Hmox1) mRNA and protein expression were significantly elevated in hypoxic AMs. Mechanistically, Ythdf2 promoted the degradation of Hmox1 mRNA in a m⁶A dependent manner. Furthermore, an inhibitor of Hmox1 promoted macrophage alternative activation, and reversed the protection from PH seen in Ythdf2^{Lyz2 Cre} mice under hypoxic exposure. Together, our data reveal a novel mechanism linking m⁶A RNA modification with changes in macrophage phenotype, inflammation and oxidative stress in PH, and identify Hmox1 as a downstream target of Ythdf2, suggesting that Ythdf2 may be a therapeutic target in PH.

Adverse pulmonary effects after oral exposure to copper, manganese and mercury, alone and in mixtures, in a Spraque-Dawley rat model

The rise in respiratory disease has been attributed to an increase in environmental pollution. Heavy metals contribute to environmental contamination via air, water, soil and food. The effects of atmospheric exposure to heavy metals on pulmonary structure and function have been researched, but the effects through drinking water have been neglected. The aim of this study was to investigate the potential in vivo alterations in the pulmonary tissue of male Sprague-Dawley rats after a 28-day oral exposure to copper (Cu), manganese (Mn) and mercury (Hg), alone and in mixtures, at 100 times the World Health Organization's (WHO) safety limit for each heavy metal in drinking water. Forty-eight male Sprague-Dawley rats were randomly divided into eight groups (n = 6): control, Cu, Mn, Hg, Cu + Mn, Cu + Hg, Mn + Hg and Cu, Mn + Hg. The morphology of lung tissue and the bronchioles were evaluated using light- and transmission electron microscopy. For all exposed groups, morphological changes included thickened inter- and intra-alveolar spaces, stratified epithelium, disrupted smooth muscle and early fibrosis and desquamation of the epithelia of the bronchioles to varying degrees. In all exposed groups, ultrastructurally, an increase in disarranged collagen and elastin fibers, nuclear membrane detachment, chromatin condensation, indistinct nucleoli and an increase in collagen fiber disarrangement was observed. This study has identified that oral exposure to Cu, Mn and Hg and as part of mixtures caused pathogenesis due to inflammation, cellular damage and fibrosis with Mn + Hg being the most potent heavy metal group.

Integrated proteomics and metabolomics reveal variations in pulmonary fibrosis development and the potential therapeutic effect of Shuangshen Pingfei formula

ETHNOPHARMACOLOGICAL RELEVANCE

Shuangshen Pingfei formula (SSPF), a Chinese medicine prescription, has been prescribed to alleviate PF. However, little is known about the molecular mechanism underlying PF progression and the regulatory mechanism in SSPF.

AIMS OF THE STUDY

To discriminate the molecular alterations underlying the development of pulmonary fibrosis (PF) and reveal the regulatory mechanism of Shuangshen Pingfei formula (SSPF).

MATERIALS AND METHODS

An integrated analysis of a time-course pathology combined with proteomics and metabolomics was performed to investigate changes in body weight, survival rate, lung coefficient, histopathology, proteins, and metabolites of lung tissues at different time points upon bleomycin (BLM) exposure and SSPF treatment.

RESULTS

The results showed that PF progression was characterized by gradually aggravated fibrosis accompanied by inflammation with extended exposure (7, 14, and 21 days). SSPF significantly attenuated lung fibrosis, as evidenced by increased weight, and reduced lung coefficients and fibrosis scores. Moreover, 368 common differentially expressed proteins (DEPs) were identified, and 102 DEPs were continuously and monotonically upregulated via proteomics among the three BLM treatments. The DEPs were principally involved in extracellular matrix (ECM) remodeling and arginine and proline (AP) metabolic reprogramming. Additionally, metabolomics analyses revealed that BLM exposure mainly affected six metabolism pathways, including 34 differentially regulated metabolites (DRMs). Furthermore, correlation analysis found that several DEPs and DRMs, including L-ornithine, S-adenosyl-L-methionine, ARG, and AOC1, were associated with arginine and proline metabolism, and 8,9-EET, 8,9-DHET, CYP2B, etc., were involved in arachidonic acid (AA) metabolism, suggesting that these two pathways play a critical role in the development of fibrosis. After SSPF treatment, the related protein expression and metabolic disorders were regulated, implying that SSPF provides potential solutions to target these pathways for benefit in the treatment of PF.

CONCLUSION

Our data suggest that ECM remodeling, and metabolic reprogramming of AP and AA are distinctive features of PF development. Simultaneously, we confirmed that SSPF could effectively regulate metabolic disorders, indicating its potential clinical application for PF therapy. Our findings using multiple approaches provide a molecular-scale perspective on the mechanisms of PF progression and the amelioration of SSPF.

CC Chemokines in Idiopathic Pulmonary Fibrosis: Pathogenic Role and Therapeutic Potential

Idiopathic pulmonary fibrosis (IPF), characterized by progressive worsening of dyspnea and irreversible decline in lung function, is a chronic and progressive respiratory disease with a poor prognosis. Chronic or repeated lung injury results in inflammation and an excessive injury-repairing response that drives the development of IPF. A number of studies have shown that the development and progression of IPF are associated with dysregulated expression of several chemokines and chemokine receptors, several of which have been used as predictors of IPF outcome. Chemokines of the CC family play significant roles in exacerbating IPF progression by immune cell attraction or fibroblast activation. Modulating levels of detrimental CC chemokines and interrupting the corresponding transduction axis by neutralizing antibodies or antagonists are potential treatment options for IPF. Here, we review the roles of different CC chemokines in the pathogenesis of IPF, and their potential use as biomarkers or therapeutic targets.

Immune Mechanisms of Pulmonary Fibrosis with Bleomycin

Fibrosis and structural remodeling of the lung tissue can significantly impair lung function, often with fatal consequences. The etiology of pulmonary fibrosis (PF) is diverse and includes different triggers such as allergens, chemicals, radiation, and environmental particles. However, the cause of idiopathic PF (IPF), one of the most common forms of PF, remains unknown. Experimental models have been developed to study the mechanisms of PF, and the murine bleomycin (BLM) model has received the most attention. Epithelial injury, inflammation, epithelial-mesenchymal transition (EMT), myofibroblast activation, and repeated tissue injury are important initiators of fibrosis. In this review, we examined the common mechanisms of lung wound-healing responses after BLM-induced lung injury as well as the pathogenesis of the most common PF. A three-stage model of wound repair involving injury, inflammation, and repair is outlined. Dysregulation of one or more of these three phases has been reported in many cases of PF. We reviewed the literature investigating PF pathogenesis, and the role of cytokines, chemokines, growth factors, and matrix feeding in an animal model of BLM-induced PF.

The Role of Macrophages and Alveolar Epithelial Cells in the Development of ARDS

Acute lung injury (ALI) usually causes acute respiratory distress syndrome (ARDS), or even death in critical ill patients. Immune cell infiltration in inflamed lungs is an important hallmark of ARDS. Macrophages are a type of immune cell that participate in the entire pathogenic trajectory of ARDS and most prominently via their interactions with lung alveolar epithelial cells (AECs). In the early stage of ARDS, classically activated macrophages secrete pro-inflammatory cytokines to clearance of the pathogens which may damage alveolar AECs cell structure and result in cell death. Paradoxically, in late stage of ARDS, anti-inflammatory cytokines secreted by alternatively activated macrophages dampen the inflammation response and promote epithelial regeneration and alveolar structure remodeling. In this review, we discuss the important role of macrophages and AECs in the progression of ARDS.

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.

Plasticity towards Rigidity: A Macrophage Conundrum in Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive, chronic, and ultimately fatal diffuse parenchymal lung disease. The molecular mechanisms of fibrosis in IPF patients are not fully understood and there is a lack of effective treatments. For decades, different types of drugs such as immunosuppressants and antioxidants have been tested, usually with unsuccessful results. Although two antifibrotic drugs (Nintedanib and Pirfenidone) are approved and used for the treatment of IPF, side effects are common, and they only slow down disease progression without improving patients’ survival. Macrophages are central to lung homeostasis, wound healing, and injury. Depending on the stimulus in the microenvironment, macrophages may contribute to fibrosis, but also, they may play a role in the amelioration of fibrosis. In this review, we explore the role of macrophages in IPF in relation to the fibrotic processes, epithelial–mesenchymal transition (EMT), and their crosstalk with resident and recruited cells and we emphasized the importance of macrophages in finding new treatments.

The journey of SARS-CoV-2 in human hosts: a review of immune responses, immunosuppression, and their consequences

Coronavirus disease 2019 (COVID-19) is a highly infectious viral disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Laboratory findings from a significant number of patients with COVID-19 indicate the occurrence of leukocytopenia, specifically lymphocytopenia. Moreover, infected patients can experience contrasting outcomes depending on lymphocytopenia status. Patients with resolved lymphocytopenia are more likely to recover, whereas critically ill patients with signs of unresolved lymphocytopenia develop severe complications, sometimes culminating in death. Why immunodepression manifests in patients with COVID-19 remains unclear. Therefore, the evaluation of clinical symptoms and laboratory findings from infected patients is critical for understanding the disease course and its consequences. In this review, we take a logical approach to unravel the reasons for immunodepression in patients with COVID-19. Following the footprints of the virus within host tissues, from entry to exit, we extrapolate the mechanisms underlying the phenomenon of immunodepression.

Targeting monocytes/macrophages in fibrosis and cancer diseases: Therapeutic approaches

Over almost 140 years since their identification, the knowledge about macrophages has unbelievably evolved. The 'big eaters' from being thought of as simple phagocytic cells have been recognized as master regulators in immunity, homeostasis, healing/repair and organ development. Long considered to originate exclusively from bone marrow-derived circulating monocytes, macrophages have been also demonstrated to be the first immune cells colonizing tissues in the developing embryo and persisting in adult life by self-renewal, as long-lived tissue resident macrophages. Therefore, heterogeneous populations of macrophages with different ontogeny and functions co-exist in tissues. Macrophages act as sentinels of homeostasis and are intrinsically programmed to lead the wound healing and repair processes that occur after injury. However, in certain pathological circumstances macrophages get dysfunctional, and impaired or aberrant macrophage activities become key features of diseases. For instance, in both fibrosis and cancer, that have been defined 'wounds that do not heal', dysfunctional monocyte-derived macrophages overall play a key detrimental role. On the other hand, due to their plasticity these cells can be 're-educated' and exert anti-fibrotic and anti-cancer functions. Therefore macrophages represent an important therapeutic target in both fibrosis and cancer diseases. The current review will illustrate new insights into the role of monocytes/macrophages in these devastating diseases and summarize new therapeutic strategies and applications of macrophage-targeted drug development in their clinical setting.

Long Noncoding RNA FENDRR Inhibits Lung Fibroblast Proliferation via a Reduction of β-Catenin

Idiopathic Pulmonary Fibrosis (IPF) is a chronic, progressive, and usually lethal lung disease and it has been widely accepted that fibroblast proliferation is one of the key characteristics of IPF. Long noncoding RNAs (lncRNAs) play vital roles in the pathogenesis of many diseases. In this study, we investigated the role of lncRNA FENDRR on fibroblast proliferation. Human lung fibroblasts stably overexpressing FENDRR showed a reduced cell proliferation compared to those expressing the control vector. On the other hand, FENDRR silencing increased fibroblast proliferation. FENDRR bound serine-arginine rich splicing factor 9 (SRSF9) and inhibited the phosphorylation of p70 ribosomal S6 kinase 1 (PS6K), a downstream protein of the mammalian target of rapamycin (mTOR) signaling. Silencing SRSF9 reduced fibroblast proliferation. FENDRR reduced β-catenin protein, but not mRNA levels. The reduction of β-catenin protein levels in lung fibroblasts by gene silencing or chemical inhibitor decreased fibroblast proliferation. Adenovirus-mediated FENDRR transfer to the lungs of mice reduced asbestos-induced fibrotic lesions and collagen deposition. RNA sequencing of lung tissues identified 7 cell proliferation-related genes that were up-regulated by asbestos but reversed by FENDRR. In conclusion, FENDRR inhibits fibroblast proliferation and functions as an anti-fibrotic lncRNA.

Hydrogen regulates the M1/M2 polarization of alveolar macrophages in a rat model of chronic obstructive pulmonary disease

OBJECTIVE

Chronic obstructive pulmonary disease (COPD) is a respiratory disease with high morbidity and mortality worldwide, so far there is no ideal treatment method. Previous studies have shown that hydrogen (H₂) is involved in the treatment of COPD as an antioxidant. In this study, the effect of H₂ on M1/M2 polarization of alveolar macrophages in COPD rats was observed, and its anti-inflammatory mechanism was further elucidated. Methods: Twenty-four Sprague-Dawley rats were randomly divided into three groups including the control, COPD and H₂ group. A rat model of COPD was established by cigarette exposure combined with lipopolysaccharide (LPS) induction. H₂ therapy was administered 2 hours per day for 14 days. Lung function and pathology were assessed. The levels of interleukin (IL)-6, tumor necrosis factor (TNF)-α, transforming growth factor (TGF)-β1 and IL-10 in bronchoalveolar lavage fluid (BALF) and lung tissue were measured by enzyme-linked immunosorbent assay. The mRNA, protein expression and immunoreactivity of inducible nitric oxide synthase (iNOS) and arginase (Arg)-1 in lung were observed by quantitative real-time PCR, western blot and immunohistochemistry. Results: Compared with the control rats, there were a significant decline in lung function, a marked inflammatory infiltration and pulmonary parenchymal remodeling and the increases of IL-6, TNF-α and TGF-β1 levels in BALF and lung tissue, but a lower expression of IL-10 in COPD rats. The iNOS mRNA and protein expression, as well as its optical density (OD), were increased significantly in lung tissue, while those of Arg-1 decreased significantly. H₂ treatment improved the lung function and the parenchymal inflammation, reversed the increased levels of IL-6, TNF-α and TGF-β1, and the lower IL-10. Meanwhile, H₂ also down-regulated the expression of iNOS, but up-regulated expression of Arg-1 in lung tissue. Conclusion: H₂ reduces inflammation in the lung of COPD, which may be related to its inhibition of M1 type polarization and activation of M2 type polarization of alveolar macrophage.

The Role of Macrophages in the Pathogenesis of SARS-CoV-2-Associated Acute Respiratory Distress Syndrome

Macrophages are cells that mediate both innate and adaptive immunity reactions, playing a major role in both physiological and pathological processes. Systemic SARS-CoV-2-associated complications include acute respiratory distress syndrome (ARDS), disseminated intravascular coagulation syndrome, edema, and pneumonia. These are predominantly effects of massive macrophage activation that collectively can be defined as macrophage activation syndrome. In this review we focus on the role of macrophages in COVID-19, as pathogenesis of the new coronavirus infection, especially in cases complicated by ARDS, largely depends on macrophage phenotypes and functionalities. We describe participation of monocytes, monocyte-derived and resident lung macrophages in SARS-CoV-2-associated ARDS and discuss possible utility of cell therapies for its treatment, notably the use of reprogrammed macrophages with stable pro- or anti-inflammatory phenotypes.

Cellular metabolomics of pulmonary fibrosis, from amino acids to lipids

Idiopathic pulmonary fibrosis (IPF) is a chronic and progressive lung disease of unknown etiology with limited treatment options. It is characterized by repetitive injury to alveolar epithelial cells and aberrant activation of numerous signaling pathways. Recent evidence suggests that metabolic reprogramming, metabolic dysregulation, and mitochondria dysfunction are distinctive features of the IPF lungs. Through numerous mechanisms, metabolomic abnormalities in alveolar epithelial cells, myofibroblast, macrophages, and fibroblasts contribute to the abnormal collagen synthesis and dysregulated airway remodeling described in lung fibrosis. This review summarizes the metabolomic changes in amino acids, lipids, glucose, and heme seen in IPF lungs. Simultaneously, we provide new insights into potential therapeutic strategies by targeting a variety of metabolites.

The Role of Macrophages in the Development of Acute and Chronic Inflammatory Lung Diseases

Macrophages play an important role in the innate and adaptive immune responses of organ systems, including the lungs, to particles and pathogens. Cumulative results show that macrophages contribute to the development and progression of acute or chronic inflammatory responses through the secretion of inflammatory cytokines/chemokines and the activation of transcription factors in the pathogenesis of inflammatory lung diseases, such as acute lung injury (ALI), acute respiratory distress syndrome (ARDS), ARDS related to COVID-19 (coronavirus disease 2019, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)), allergic asthma, chronic obstructive pulmonary disease (COPD), and idiopathic pulmonary fibrosis (IPF). This review summarizes the functions of macrophages and their associated underlying mechanisms in the development of ALI, ARDS, COVID-19-related ARDS, allergic asthma, COPD, and IPF and briefly introduces the acute and chronic experimental animal models. Thus, this review suggests an effective therapeutic approach that focuses on the regulation of macrophage function in the context of inflammatory lung diseases.

Exposure to particulate matter upregulates ACE2 and TMPRSS2 expression in the murine lung

Coronavirus disease (COVID-19) is currently a serious global issue. Epidemiological studies have identified air pollutants, including particulate matter (PM), as a risk factor for COVID-19 infection and severity of illness, in addition to numerous factors such as pre-existing conditions, aging and smoking. However, the mechanisms by which air pollution is involved in the manifestation and/or progression of COVID-19 is still unknown. In this study, we used a mouse model exposed to crude PM, collected by the cyclone method, to evaluate the pulmonary expression of angiotensin-converting enzyme 2 (ACE2) and transmembrane protease serine type 2 (TMPRSS2), the two molecules required for the entry of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) into host cells. Multiplex immunohistochemical analysis revealed that exposure to PM increased the expression of these two molecules at the same site. Furthermore, image cytometry analysis revealed increased expression of these proteins, particularly, in the alveolar type 2 cells and macrophages, which are potential targets for SARS-CoV-2. Our findings provide an experimental evidence that exposure to PM may adversely affect the manifestation and progression of COVID-19, mediated by the impact of SARS-CoV-2 on the site of entry. The study results suggest that examining these effects might help to advance our understanding of COVID-19 and aid the development of appropriate social interventions.

Therapeutic targets in lung tissue remodelling and fibrosis

Structural changes involving tissue remodelling and fibrosis are major features of many pulmonary diseases, including asthma, chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis (IPF). Abnormal deposition of extracellular matrix (ECM) proteins is a key factor in the development of tissue remodelling that results in symptoms and impaired lung function in these diseases. Tissue remodelling in the lungs is complex and differs between compartments. Some pathways are common but tissue remodelling around the airways and in the parenchyma have different morphologies. Hence it is critical to evaluate both common fibrotic pathways and those that are specific to different compartments; thereby expanding the understanding of the pathogenesis of fibrosis and remodelling in the airways and parenchyma in asthma, COPD and IPF with a view to developing therapeutic strategies for each. Here we review the current understanding of remodelling features and underlying mechanisms in these major respiratory diseases. The differences and similarities of remodelling are used to highlight potential common therapeutic targets and strategies. One central pathway in remodelling processes involves transforming growth factor (TGF)-β induced fibroblast activation and myofibroblast differentiation that increases ECM production. The current treatments and clinical trials targeting remodelling are described, as well as potential future directions. These endeavours are indicative of the renewed effort and optimism for drug discovery targeting tissue remodelling and fibrosis.

High-Expressed Macrophage Scavenger Receptor 1 Predicts Severity Clinical Outcome in Transplant Patient in Idiopathic Pulmonary Fibrosis Disease

Background

Lung transplantation has been performed worldwide and admitted as an effective treatment for patients with various end-stage lung diseases. However, limit reliable clinical indicators exist to identify patients at high risk for allograft failure in lung transplant recipients. The recent advances in the knowledge of immunological aspects of the pulmonary diseases, for that innate macrophage activation, are induced by pathogen or pathogen-derived molecules and widely accepted as the critical evidence among the pathogenesis of lung inflammation and fibrosis. This study was aimed at evaluating the clinical significance of CD86- and macrophage scavenger receptor 1- (MSR1-) positive cells during the development of idiopathic pulmonary fibrosis (IPF) and pulmonary arterial hypertension (PAH), and their potential roles in the prediction of the outcomes after lung transplantation were examined.

Methods

Tissues from lung transplantation for 37 IPF and 15 PAH patients from the Department of Cardiothoracic Surgery in Wuxi People's Hospital from December 2015 to December 2016 were analyzed by immunohistochemistry (IHC) for detecting the expression and CD86 and MSR1 and correlated with clinical events after lung transplantation.

Results

IHC results showed that the expression of MSR1, IL-13, and arginase-1 (Arg1) but not CD86 in the lung section of IPF patients was dramatically enhanced when compared with that of PAH patients. The expression of MSR1, IL-13, and Arg1 but not CD86 in the lung from IPF patients with smoking was significantly increased when compared with that from nonsmoking subjects. In addition, the expression of MSR1-positive cells in IPF subjects with Klebsiella pneumoniae infection was dramatically enhanced than that in noninfection subjects. MSR1-positive macrophages were negatively associated with FEV1 and with FVC but not associated with TLC and with TL_CO. However, CD86-positive macrophages were not significantly associated with the above lung function-related factors. Furthermore, MSR1 had a higher area under the ROC curve (AUC) than CD86 for IPF diagnosis. Survival analysis indicated that high levels of MSR1-positive macrophages had a worse prognostic effect for IPF patients with lung transplantation.

Conclusion

Our study indicates the clinical significance of Klebsiella pneumoniae infection-related MSR1-positive cells in IPF progression, and it could be a prognostic marker in IPF after the lung transplant; development strategies to reduce the expression of MSR1-positive macrophages in IPF may be beneficial for the lung transplant.

Alveolar epithelial cell-derived Sonic hedgehog promotes pulmonary fibrosis through OPN-dependent alternative macrophage activation

The alternative activation of macrophages in the lungs has been considered as a major factor promoting pulmonary fibrogenesis; however, the mechanisms underlying this phenomenon are still elusive. In this study, we investigated the interaction between macrophages and fibrosis-associated alveolar epithelial cells using a bleomycin-induced mouse pulmonary fibrosis model and a coculture system. We demonstrated that fibrosis-promoting macrophages are spatially proximate to alveolar type II (ATII) cells, permissive for paracrine-induced macrophage polarization. Importantly, we revealed that fibrosis-associated ATII cells secrete Sonic hedgehog (Shh), a hedgehog pathway ligand, and that ATII cell-derived Shh promotes the development of pulmonary fibrosis by osteopontin (OPN)-mediated macrophage alternative activation. Mechanistically, Shh promotes the secretion of OPN in macrophages via Shh/Gli signaling cascade. The secreted OPN acts on the surrounding macrophages in an autocrine or paracrine manner and induces macrophage alternative activation through activating the JAK2/STAT3 signaling pathway. Tissue samples from idiopathic pulmonary fibrosis patients confirmed the increased expression of Shh and OPN in ATII cells and macrophages, respectively. Together, our study illustrated an alveolar epithelium-dependent mechanism for macrophage M2 polarization and pulmonary fibrogenesis and suggested that targeting Shh may offer a selective and efficient therapeutic strategy for the development and progression of pulmonary fibrosis.

Integrative Analysis of Transcriptome-Wide Association Study and mRNA Expression Profiles Identifies Candidate Genes Associated With Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a type of scarring lung disease characterized by a chronic, progressive, and irreversible decline in lung function. The genetic basis of IPF remains elusive. A transcriptome-wide association study (TWAS) of IPF was performed by FUSION using gene expression weights of three tissues combined with a large-scale genome-wide association study (GWAS) dataset, totally involving 2,668 IPF cases and 8,591 controls. Significant genes identified by TWAS were then subjected to gene ontology (GO) and pathway enrichment analysis. The overlapped GO terms and pathways between enrichment analysis of TWAS significant genes and differentially expressed genes (DEGs) from the genome-wide mRNA expression profiling of IPF were also identified. For TWAS significant genes, protein–protein interaction (PPI) network and clustering modules analyses were further conducted using STRING and Cytoscape. Overall, TWAS identified a group of candidate genes for IPF under the Bonferroni corrected P value threshold (0.05/14929 = 3.35 × 10^–6), such as DSP (P_TWAS = 1.35 × 10^–29 for lung tissue), MUC5B (P_TWAS = 1.09 × 10^–28 for lung tissue), and TOLLIP (P_TWAS = 1.41 × 10^–15 for whole blood). Pathway enrichment analysis identified multiple candidate pathways, such as herpes simplex infection (P value = 7.93 × 10^–5) and antigen processing and presentation (P value = 6.55 × 10^–5). 38 common GO terms and 8 KEGG pathways shared by enrichment analysis of TWAS significant genes and DEGs were identified. In the PPI network, 14 genes (DYNLL1, DYNC1LI1, DYNLL2, HLA-DRB5, HLA-DPB1, HLA-DQB2, HLA-DQA2, HLA-DQB1, HLA-DRB1, POLR2L, CENPP, CENPK, NUP133, and NUP107) were simultaneously detected by hub gene and module analysis. In conclusion, through integrative analysis of TWAS and mRNA expression profiles, we identified multiple novel candidate genes, GO terms and pathways for IPF, which contributes to the understanding of the genetic mechanism of IPF.

Immune response in SARS-CoV-2 infection: the role of interferons type I and type III

BACKGROUND

There is scarce information on the human immune response to the SARS-CoV-2 infection, and on the exacerbated inflammatory reaction observed in severe COVID-19 cases.

OBJECTIVE

To review the available evidence on the role of interferons type I and type III to SARS-CoV-2 infection.

METHODS

We reviewed the available published evidence on the role of immune response to SARS-CoV-2 infection as well as recent publications on characteristics and outcomes of COVID-19, and their relationship with interferons type I and type III.

RESULTS

The available data indicates that immune response plays an important role in controlling SARS-CoV-2 infection and the immune dysregulation can significantly modify the clinical outcomes of affected patients. In addition, the evidence suggests that IFN type I and III can play an important role in controlling viremia and modulating the immune response in COVID-19.

CONCLUSIONS

Due to their central role in immune response against SARS-CoV-2 infection, IFN type I and III could be considered for treatment of COVID-19.

Pathogenesis and treatment of idiopathic and rheumatoid arthritis-related interstitial pneumonia. The possible lesson from COVID-19 pneumonia

INTRODUCTION

Main clinical manifestations of SARS-CoV-2 infection are characterized by fever, dyspnea, and interstitial pneumonia, frequently evolving in acute respiratory distress syndrome (ARDS).

AREAS COVERED

Features of coronavirus disease 2019 (COVID-19) presents some common points with interstitial lung disease (ILD) both idiopathic and related to rheumatoid arthritis (RA), typically characterized by a chronic progression over time and possibly complicated by acute exacerbation (AE). The study of common pathogenetic mechanisms, such as the involvement of toll-like receptor 4, could contribute to the knowledge and treatment of idiopathic and RA-ILD. Moreover, hyperinflammation, mainly characterized by increase of effector T-cells and inflammatory cytokines, and activation of coagulation cascade, observed in COVID-19 related ARDS have been already shown in patients with AE of idiopathic and RA-ILD. A literature search was performed in PubMed, Embase, Scopus, and Web of Science, together with a manual search in COVID-resource centers of the main journals.

EXPERT OPINION

Despite the uncertainty about pathogenetic aspects about COVID-19- pneumonia, it could be a possible model for other forms of ILD and AE. The great amount of data from studies on COVID-19 could be helpful in proposing safe therapeutic approaches for RA-ILD, in understanding pathogenesis of usual interstitial pneumonia and to develop new therapeutic strategies for AE.

Conditioned medium from M2b macrophages modulates the proliferation, migration, and apoptosis of pulmonary artery smooth muscle cells by deregulating the PI3K/Akt/FoxO3a pathway

Background

Immunity and inflammation are considered to be central features of pulmonary artery hypertension (PAH), in which macrophages are one of the main components of inflammatory cell infiltration around the pulmonary artery. M2b macrophages, which are different from M1 and M2 macrophages, are believed to have immunomodulatory activities and produce little fibrosis. The purpose of this study was to explore the effect of M2b macrophages on pulmonary artery smooth muscle cells (PASMCs) derived from monocrotaline-induced PAH rats.

Methods

PASMCs were cultured in serum-free medium, the supernatant of M0 macrophages, or the supernatant of M2b macrophages for 24 hours. Then cell proliferation was assessed by cell counting kit-8 and cell migration ability was detected by wound healing and transwell assays. The apoptosis rate of cells was determined by TUNEL staining and annexin V-PE/7-ADD staining. Western blot was used to detect the expression of Bcl-2 family proteins, cleaved caspase-9 and PI3K/Akt/FoxO3a pathway. LY294002 (a specific inhibitor of PI3K) was used to investigate its effect on PASMCs and its relationship with M2b macrophages.

Results

Conditioned medium from M2b macrophages significantly inhibited the proliferation and migration of PASMCs compared with the control group and M0 macrophage group. Furthermore, conditioned medium from M2b macrophages promote PASMC apoptosis and increased the expression of pro-apoptotic proteins Bax and cleaved caspase-9, inhibited the expression of anti-apoptotic proteins Bcl-2 and Bcl-xl. Finally, conditioned medium from M2b macrophages inhibited the PI3K/Akt/FoxO3a pathway. Inhibition of PI3K/Akt/FoxO3a pathway also significantly inhibit the proliferation, migration, and apoptosis resistance of PASMCs.

Conclusion

Conditioned medium from M2b macrophages can inhibit the proliferation, migration, and apoptosis resistance of PASMCs, which may be at least partially by deregulating the PI3K/Akt/FoxO3a pathway.

Alveolar Dynamics and Beyond - The Importance of Surfactant Protein C and Cholesterol in Lung Homeostasis and Fibrosis

Surfactant protein C (SP-C) is an important player in enhancing the interfacial adsorption of lung surfactant lipid films to the alveolar air-liquid interface. Doing so, surface tension drops down enough to stabilize alveoli and the lung, reducing the work of breathing. In addition, it has been shown that SP-C counteracts the deleterious effect of high amounts of cholesterol in the surfactant lipid films. On its side, cholesterol is a well-known modulator of the biophysical properties of biological membranes and it has been proven that it activates the inflammasome pathways in the lung. Even though the molecular mechanism is not known, there are evidences suggesting that these two molecules may interplay with each other in order to keep the proper function of the lung. This review focuses in the role of SP-C and cholesterol in the development of lung fibrosis and the potential pathways in which impairment of both molecules leads to aberrant lung repair, and therefore impaired alveolar dynamics. From molecular to cellular mechanisms to evidences in animal models and human diseases. The evidences revised here highlight a potential SP-C/cholesterol axis as target for the treatment of lung fibrosis.

Origin and ontogeny of lung macrophages: from mice to humans

Macrophages are tissue-resident myeloid cells with essential roles in host defense, tissue repair, and organ homeostasis. The lung harbors a large number of macrophages that reside in alveoli. As a result of their strategic location, alveolar macrophages are critical sentinels of healthy lung function and barrier immunity. They phagocytose inhaled material and initiate protective immune responses to pathogens, while preventing excessive inflammatory responses and tissue damage. Apart from alveolar macrophages, other macrophage populations are found in the lung and recent single-cell RNA-sequencing studies indicate that lung macrophage heterogeneity is greater than previously appreciated. The cellular origin and development of mouse lung macrophages has been extensively studied, but little is known about the ontogeny of their human counterparts, despite the importance of macrophages for lung health. In this context, humanized mice (mice with a human immune system) can give new insights into the biology of human lung macrophages by allowing in vivo studies that are not possible in humans. In particular, we have created humanized mouse models that support the development of human lung macrophages in vivo. In this review, we will discuss the heterogeneity, development, and homeostasis of lung macrophages. Moreover, we will highlight the impact of age, the microbiota, and pathogen exposure on lung macrophage function. Altered macrophage function has been implicated in respiratory infections as well as in common allergic and inflammatory lung diseases. Therefore, understanding the functional heterogeneity and ontogeny of lung macrophages should help to develop future macrophage-based therapies for important lung diseases in humans.

Viral Infection Increases the Risk of Idiopathic Pulmonary Fibrosis: A Meta-Analysis

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive, fibrotic lung disease with a poor prognosis. Although many factors have been identified that possibly trigger or aggravate IPF, such as viral infection, the exact cause of IPF remains unclear. Until now, there has been no systematic review to assess the role of viral infection in IPF quantitatively.

OBJECTIVE

This meta-analysis aims to present a collective view on the relationship between viral infection and IPF.

METHODS

We searched studies reporting the effect of viral infection on IPF in the PubMed, Embase, Cochrane Library, Web of Science, and Wiley Online Library databases. We calculated ORs with 95% CIs to assess the risk of virus in IPF. We also estimated statistical heterogeneity by using I² and Cochran Q tests and publication bias by using the funnel plot, Begg test, Egger test, and trim-and-fill methods. Regression, sensitivity, and subgroup analyses were performed to assess the effects of confounding factors, such as sex and age.

RESULTS

We analyzed 20 case-control studies from 10 countries with 1,287 participants. The pooled OR of all viruses indicated that viral infection could increase the risk of IPF significantly (OR, 3.48; 95% CI, 1.61-7.52; P = .001), but not that of exacerbation of IPF (OR, 0.99; 95% CI, 0.47-2.12; P = .988). All analyzed viruses, including Epstein-Barr virus (EBV), cytomegalovirus (CMV), human herpesvirus 7 (HHV-7), and human herpesvirus 8 (HHV-8), were associated with a significant elevation in the risk of IPF, except human herpesvirus 6 (HHV-6).

CONCLUSIONS

The presence of persistent or chronic, but not acute, viral infections, including EBV, CMV, HHV-7, and HHV-8, significantly increases the risk of developing IPF, but not exacerbation of IPF. These findings imply that viral infection could be a potential risk factor for IPF.

Mesenchymal stromal cell exosomes prevent and revert experimental pulmonary fibrosis through modulation of monocyte phenotypes

Mesenchymal stromal/stem cell (MSC) therapy has shown promise in experimental models of idiopathic pulmonary fibrosis (IPF). The aim of this study was to test the therapeutic effects of extracellular vesicles produced by human BM MSCs (MEx) in a bleomycin-induced pulmonary fibrosis model and investigate mechanisms of action. Adult C57BL/6 mice were challenged with endotracheal instillation of bleomycin and treated with MEx concurrently, or for reversal models, at day 7 or 21. Experimental groups were assessed at day 7, 14, or 28. Bleomycin-challenged mice presented with severe septal thickening and prominent fibrosis, and this was effectively prevented or reversed by MEx treatment. MEx modulated lung macrophage phenotypes, shifting the proportions of lung proinflammatory/classical and nonclassical monocytes and alveolar macrophages toward the monocyte/macrophage profiles of control mice. A parallel immunomodulatory effect was demonstrated in the BM. Notably, transplantation of MEx-preconditioned BM-derived monocytes alleviated core features of pulmonary fibrosis and lung inflammation. Proteomic analysis revealed that MEx therapy promotes an immunoregulatory, antiinflammatory monocyte phenotype. We conclude that MEx prevent and revert core features of bleomycin-induced pulmonary fibrosis and that the beneficial actions of MEx may be mediated via systemic modulation of monocyte phenotypes.

Targeting Degradation of the Transcription Factor C/EBPβ Reduces Lung Fibrosis by Restoring Activity of the Ubiquitin-Editing Enzyme A20 in Macrophages

Although recent progress provides mechanistic insights into the pathogenesis of pulmonary fibrosis (PF), rare anti-PF therapeutics show definitive promise for treating this disease. Repeated lung epithelial injury results in injury-repairing response and inflammation, which drive the development of PF. Here, we report that chronic lung injury inactivated the ubiquitin-editing enzyme A20, causing progressive accumulation of the transcription factor C/EBPβ in alveolar macrophages (AMs) from PF patients and mice, which upregulated a number of immunosuppressive and profibrotic factors promoting PF development. In response to chronic lung injury, elevated glycogen synthase kinase-3β (GSK-3β) interacted with and phosphorylated A20 to suppress C/EBPβ degradation. Ectopic expression of A20 or pharmacological restoration of A20 activity by disturbing the A20-GSK-3β interaction accelerated C/EBPβ degradation and showed potent therapeutic efficacy against experimental PF. Our study indicates that a regulatory mechanism of the GSK-3β-A20-C/EBPβ axis in AMs may be a potential target for treating PF and fibroproliferative lung diseases.

Metabolomic study on bleomycin and polyhexamethylene guanidine phosphate-induced pulmonary fibrosis mice models

INTRODUCTION

Polyhexamethylene guanidine phosphate (PHMG) has been used as a disinfectant and biocide, and was known to be harmless and non-toxic. However, in 2011, PHMG used as a humidifier disinfectant was reported to be associated with lung diseases, such as, fibrosis in the toxicant studies on pulmonary fibrosis by PHMG. However, no metabolomics study has been performed in PHMG-induced mouse models of pulmonary fibrosis.

OBJECTIVES

We performed a metabolomic study to understand the biochemical events that occur in bleomycin (BLM)- and PHMG-induced mouse models of pulmonary fibrosis using gas chromatography-mass spectrometry (GC-MS), LC-tandem MS, and GC-tandem MS.

RESULTS

The levels of 61 metabolites of 30 amino acids, 13 organic acids, 12 fatty acids, 5 polyamines, and oxidized glutathione were determined in the pulmonary tissues of mice with BLM- and PHMG-induced pulmonary fibrosis and in normal controls. Principal component analysis and partial least squares discriminant analysis used to compare level of these 61 metabolites in pulmonary tissues. Levels of metabolites were significantly different in the BLM and PHMG groups as compared with the control group. In particular, the BLM- and PHMG-induced pulmonary fibrosis models showed elevated collagen synthesis and oxidative stress and metabolic disturbance of TCA related organic acids including fumaric acid by NADPH oxidase. In addition, polyamine metabolism showed severe alteration in the PHMG group than that of the BLM group.

CONCLUSION

This result suggests PHMG will be able to induce pulmonary fibrosis by arginine metabolism and NADPH oxidase signaling.

Baccatin III ameliorates bleomycin-induced pulmonary fibrosis via suppression of TGF-β1 production and TGF-β1-induced fibroblast differentiation

Idiopathic pulmonary fibrosis (IPF) is a progressive and generally lethal lung disease with a high mortality rate. Current therapeutic drugs exhibit limited efficacy but severe adverse effects. Paclitaxel has been identified to exert both anti-inflammatory and anti-fibrosis activity. Baccatin III (BAC), an important precursor of paclitaxel, has been identified as exhibiting immunomodulatory activity with decisively lower toxicity. However, its effects on pulmonary fibrosis remain unknown. In this study, the role of BAC in bleomycin (BLM)-induced pulmonary fibrosis and inflammation in mice was investigated in addition to elucidation of its mechanism of action. Our results demonstrated that administration of BAC in a dose-dependent manner reduced inflammatory infiltration, secretion of the pro-fibrotic mediator TGF-β1 and deposition of collagen and other components of the extracellular matrix (ECM), including alpha smooth muscle actin (α-SMA) and fibronectin. Administration of BAC to treat isolated macrophages stimulated with IL-13, known to activate macrophages, the principal source of TGF-β1, resulted in markedly reduced TGF-β1 expression from macrophages. The AKT/STAT6 signaling pathway was shown to be involved in this process. In addition, we have provided in vitro evidence that BAC inhibits TGF-β1-induced fibroblast differentiation via the Smad2/3 signaling pathway. Furthermore, intratracheal injection of rTGF-β1 significantly exacerbated the degree of fibrosis which was down-regulated by treatment with BAC. Taken together, our data suggest that BAC exerts a protective effect against lung fibrosis and may serve as a potential therapeutic strategy for IPF.

Therapeutic Role of Recombinant Human Soluble Thrombomodulin for Acute Exacerbation of Idiopathic Pulmonary Fibrosis

Acute exacerbation of idiopathic pulmonary fibrosis (AE-IPF) is an acute respiratory worsening of unidentifiable cause that sometimes develops during the clinical course of IPF. Although the incidence of AE-IPF is not high, prognosis is poor. The pathogenesis of AE-IPF is not well understood; however, evidence suggests that coagulation abnormalities and inflammation are involved. Thrombomodulin is a transmembranous glycoprotein found on the cell surface of vascular endothelial cells. Thrombomodulin combines with thrombin, regulates coagulation/fibrinolysis balance, and has a pivotal role in suppressing excess inflammation through its inhibition of high-mobility group box 1 protein and the complement system. Thus, thrombomodulin might be effective in the treatment of AE-IPF, and we and other groups found that recombinant human soluble thrombomodulin improved survival in patients with AE-IPF. This review summarizes the existing evidence and considers the therapeutic role of thrombomodulin in AE-IPF.

Flow cytometric analysis of the leukocyte landscape during bleomycin-induced lung injury and fibrosis in the rat

Bleomycin-induced lung injury and fibrosis is a well-described model to investigate lung inflammatory and remodeling mechanisms. Rat models are clinically relevant and are also widely used, but rat bronchoalveolar lavage (BAL) cells are not fully characterized with flow cytometry due to the limited availability of antibodies for this species. We optimized a comprehensive time-dependent flow cytometric analysis of cells after bleomycin challenge, confirming previous studies in other species and correlating them to histological staining, cytokine profiling, and collagen accumulation analysis in rat lungs. For this purpose, we describe a novel panel of rat surface markers and a strategy to identify and follow BAL cells over time. By combining surface markers in rat alveolar cells (CD45⁺), granulocytes and other myeloid cells, monocytes and macrophages can be identified by the expression of CD11b/c. Moreover, different activation states of macrophages (CD163⁺) can be observed: steady state (CD86^-MHC-II^low), activation during inflammation (CD86⁺,MHC-II^high), activation during remodeling (CD86⁺MHC-II^low), and a population of newly recruited monocytes (CD163^-α-granulocyte^-). Hydroxyproline measured as marker of collagen content in lung tissue showed positive correlation with the reparative phase (CD163^- cells and tissue inhibitor of metalloproteinases (TIMP) and IL-10 increase). In conclusion, after a very early granulocytic recruitment, inflammation in rat lungs is observed by activated macrophages, and high release of IL-6 and fibrotic remodeling is characterized by recovery of the macrophage population together with TIMP, IL-10, and IL-18 production. Recruited monocytes and a second peak of granulocytes appear in the transitioning phase, correlating with immunostaining of arginase-1 in the tissue, revealing the importance of events leading the changes from injury to aberrant repair.

Monocyte and Alveolar Macrophage Skewing Is Associated with the Development of Pulmonary Arterial Hypertension in a Primate Model of HIV Infection

We investigated the relationship of monocytes, alveolar, and tissue-resident macrophage populations and the development of pulmonary arterial hypertension (PAH) in a nonhuman primate model of HIV infection. A prospective study of simian immunodeficiency virus-associated pulmonary arterial hypertension (SIV-PAH) was done. Rhesus macaques (n = 21) were infected with SIV. Blood, bronchoalveolar lavage fluid (BALF), and lung tissue were analyzed for monocyte and macrophage phenotypes and inflammatory mediators. Serial right heart catheterizations were performed at three time points throughout the study to assess hemodynamic alterations and the development of PAH. All 21 animals showed similar courses of SIV infection with an increasing proinflammatory plasma environment. At 6 months postinfection (mpi), 11 of 21 animals developed SIV-PAH (mPAP ≤25 mmHg; right ventricular systolic pressure [RVSP] ≤36 mmHg). PAH+ animals had an increased frequency of proinflammatory, nonclassical monocytes (CD14dimCD16+) (p = .06) in the peripheral blood and CD14+CCR7-CD163-CD206+ macrophages (p = .04) in BALF compared with PAH- animals at 6 mpi. Increased frequencies of these monocyte and macrophage phenotypes correlated with elevated RVSP (p = .04; p = .03). In addition, PAH+ animals had greater frequencies of tissue resident inflammatory M1-like CD68+STAT1+ (p = .001) and M2a-like CD68+STAT3+ macrophages (p = .003) and a lower frequency of anti-inflammatory M2c-like CD68+STAT6+ macrophages (p = .003) as well as fewer interleukin (IL)-10+ cells (p = .01). The results suggest that HIV-PAH is associated with skewing of monocytes and alveolar macrophages toward a proinflammatory, profibrotic phenotype. Furthermore, PAH+ animals may have diminished capacity to downregulate exaggerated chronic inflammation, as indicated by lower levels of IL-10 in PAH+ animals, contributing to disease progression.

Radiation-induced lung injury: impact on macrophage dysregulation and lipid alteration - a review

Lung cancer continues to be the leading cause of cancer deaths and more than one million lung cancer patients will die every year worldwide. Radiotherapy (RT) plays an important role in lung cancer treatment, but the side effects of RT are pneumonitis and pulmonary fibrosis. RT-induced lung injury causes damage to alveolar-epithelial cells and vascular endothelial cells. Macrophages play an important role in the development of pulmonary fibrosis despite its role in immune response. These injury activated macrophages develop into classically activated M1 macrophage or alternative activated M2 macrophage. It secretes cytokines, interleukins, interferons, and nitric oxide. Several pro-inflammatory lipids and pro-apoptotic proteins cause lipotoxicity such as LDL, FC, DAG, and FFA. The overall findings in this review conclude the importance of macrophages in inducing toxic/inflammatory effects during RT of lung cancer, which is clinically vital to treat the radiation-induced fibrosis.

Ym1 induces RELMα and rescues IL-4Rα deficiency in lung repair during nematode infection

Ym1 and RELMα are established effector molecules closely synonymous with Th2-type inflammation and associated pathology. Here, we show that whilst largely dependent on IL-4Rα signaling during a type 2 response, Ym1 and RELMα also have IL-4Rα-independent expression patterns in the lung. Notably, we found that Ym1 has opposing effects on type 2 immunity during nematode infection depending on whether it is expressed at the time of innate or adaptive responses. During the lung migratory stage of Nippostrongylus brasiliensis, Ym1 promoted the subsequent reparative type 2 response but once that response was established, IL-4Rα-dependent Ym1 was important for limiting the magnitude of type 2 cytokine production from both CD4+ T cells and innate lymphoid cells in the lung. Importantly, our study demonstrates that delivery of Ym1 to IL-4Rα deficient animals drives RELMα production and overcomes lung repair deficits in mice deficient in type 2 immunity. Together, Ym1 and RELMα, exhibit time and dose-dependent interactions that determines the outcome of lung repair during nematode infection.

Insulin-Like Growth Factor-1 Signaling in Lung Development and Inflammatory Lung Diseases

Insulin-like growth factor-1 (IGF-1) was firstly identified as a hormone that mediates the biological effects of growth hormone. Accumulating data have indicated the role of IGF-1 signaling pathway in lung development and diseases such as congenital disorders, cancers, inflammation, and fibrosis. IGF-1 signaling modulates the development and differentiation of many types of lung cells, including airway basal cells, club cells, alveolar epithelial cells, and fibroblasts. IGF-1 signaling deficiency results in alveolar hyperplasia in humans and disrupted lung architecture in animal models. The components of IGF-1 signaling pathways are potentiated as biomarkers as they are dysregulated locally or systemically in lung diseases, whereas data may be inconsistent or even paradoxical among different studies. The usage of IGF-1-based therapeutic agents urges for more researches in developmental disorders and inflammatory lung diseases, as the majority of current data are collected from limited number of animal experiments and are generally less exuberant than those in lung cancer. Elucidation of these questions by further bench-to-bedside researches may provide us with rational clinical diagnostic approaches and agents concerning IGF-1 signaling in lung diseases.

S100a4 Is Secreted by Alternatively Activated Alveolar Macrophages and Promotes Activation of Lung Fibroblasts in Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a devastating interstitial lung disease, characterized by damage of lung epithelial cells, excessive deposition of extracellular matrix in the lung interstitium, and enhanced activation and proliferation of fibroblasts. S100a4, also termed FSP-1 (fibroblast-specific protein-1), was previously considered as a marker of fibroblasts but recent findings in renal and liver fibrosis indicated that M2 macrophages are an important cellular source of S100a4. Thus, we hypothesized that also in pulmonary fibrosis, M2 macrophages produce and secrete S100a4, and that secreted S100a4 induces the proliferation and activation of fibroblasts. To prove this hypothesis, we comprehensively characterized two established mouse models of lung fibrosis: infection of IFN-γR^−/− mice with MHV-68 and intratracheal application of bleomycin to C57BL/6 mice. We further provide in vitro data using primary macrophages and fibroblasts to investigate the mechanism by which S100A4 exerts its effects. Finally, we inhibit S100a4 in vivo in the bleomycin-induced lung fibrosis model by treatment with niclosamide. Our data suggest that S100a4 is produced and secreted by M2 polarized alveolar macrophages and enhances the proliferation and activation of lung fibroblasts. Inhibition of S100a4 might represent a potential therapeutic strategy for pulmonary fibrosis.

The Role of Macrophages in the Pathogenesis of ALI/ARDS

Despite development in the understanding of the pathogenesis of acute lung injury (ALI)/acute respiratory distress syndrome (ARDS), the underlying mechanism still needs to be elucidated. Apart from leukocytes and endothelial cells, macrophages are also essential for the process of the inflammatory response in ALI/ARDS. Notably, macrophages play a dual role of proinflammation and anti-inflammation based on the microenvironment in different pathological stages. In the acute phase of ALI/ARDS, resident alveolar macrophages, typically expressing the alternatively activated phenotype (M2), shift into the classically activated phenotype (M1) and release various potent proinflammatory mediators. In the later phase, the M1 phenotype of activated resident and recruited macrophages shifts back to the M2 phenotype for eliminating apoptotic cells and participating in fibrosis. In this review, we summarize the main subsets of macrophages and the associated signaling pathways in three different pathological phases of ALI/ARDS. According to the current literature, regulating the function of macrophages and monocytes might be a promising therapeutic strategy against ALI/ARDS.

Acute exacerbation of idiopathic pulmonary fibrosis: lessons learned from acute respiratory distress syndrome?

Idiopathic pulmonary fibrosis (IPF) is a fibrotic lung disease characterized by progressive loss of lung function and poor prognosis. The so-called acute exacerbation of IPF (AE-IPF) may lead to severe hypoxemia requiring mechanical ventilation in the intensive care unit (ICU). AE-IPF shares several pathophysiological features with acute respiratory distress syndrome (ARDS), a very severe condition commonly treated in this setting.A review of the literature has been conducted to underline similarities and differences in the management of patients with AE-IPF and ARDS.During AE-IPF, diffuse alveolar damage and massive loss of aeration occurs, similar to what is observed in patients with ARDS. Differently from ARDS, no studies have yet concluded on the optimal ventilatory strategy and management in AE-IPF patients admitted to the ICU. Notwithstanding, a protective ventilation strategy with low tidal volume and low driving pressure could be recommended similarly to ARDS. The beneficial effect of high levels of positive end-expiratory pressure and prone positioning has still to be elucidated in AE-IPF patients, as well as the precise role of other types of respiratory assistance (e.g., extracorporeal membrane oxygenation) or innovative therapies (e.g., polymyxin-B direct hemoperfusion). The use of systemic drugs such as steroids or immunosuppressive agents in AE-IPF is controversial and potentially associated with an increased risk of serious adverse reactions.Common pathophysiological abnormalities and similar clinical needs suggest translating to AE-IPF the lessons learned from the management of ARDS patients. Studies focused on specific therapeutic strategies during AE-IPF are warranted.

Acute Exacerbation in Interstitial Lung Disease

Acute exacerbation of idiopathic pulmonary fibrosis (AE-IPF) has been defined as an acute, clinically significant deterioration that develops within less than 1 month without obvious clinical cause like fluid overload, left heart failure, or pulmonary embolism. Pathophysiologically, damage of the alveoli is the predominant feature of AE-IPF which manifests histopathologically as diffuse alveolar damage and radiologically as diffuse, bilateral ground-glass opacification on high-resolution computed tomography. A growing body of literature now focuses on acute exacerbations of interstitial lung disease (AE-ILD) other than idiopathic pulmonary fibrosis. Based on a shared pathophysiology it is generally accepted that AE-ILD can affect all patients with interstitial lung disease (ILD) but apparently occurs more frequently in patients with an underlying usual interstitial pneumonia pattern. The etiology of AE-ILD is not fully understood, but there are distinct risk factors and triggers like infection, mechanical stress, and microaspiration. In general, AE-ILD has a poor prognosis and is associated with a high mortality within 6–12 months. Although there is a lack of evidence based data, in clinical practice, AE-ILD is often treated with a high dose corticosteroid therapy and antibiotics. This article aims to provide a summary of the clinical features, diagnosis, management, and prognosis of AE-ILD as well as an update on the current developments in the field.