Receptor for advanced glycation endproducts (RAGE) maintains pulmonary structure and regulates the response to cigarette smoke

Breathing new life into the study of COPD with genes identified from genome-wide association studies

COPD is a major cause of morbidity and mortality globally. While the significance of environmental exposures in disease pathogenesis is well established, the functional contribution of genetic factors has only in recent years drawn attention. Notably, many genes associated with COPD risk are also linked with lung function. Because reduced lung function precedes COPD onset, this association is consistent with the possibility that derangements leading to COPD could arise during lung development. In this review, we summarise the role of leading genes (HHIP, FAM13A, DSP, AGER and TGFB2) identified by genome-wide association studies in lung development and COPD. Because many COPD genome-wide association study genes are enriched in lung epithelial cells, we focus on the role of these genes in the lung epithelium in development, homeostasis and injury.

The RAGE Axis: A Relevant Inflammatory Hub in Human Diseases

In 1992, a transcendental report suggested that the receptor of advanced glycation end-products (RAGE) functions as a cell surface receptor for a wide and diverse group of compounds, commonly referred to as advanced glycation end-products (AGEs), resulting from the non-enzymatic glycation of lipids and proteins in response to hyperglycemia. The interaction of these compounds with RAGE represents an essential element in triggering the cellular response to proteins or lipids that become glycated. Although initially demonstrated for diabetes complications, a growing body of evidence clearly supports RAGE's role in human diseases. Moreover, the recognizing capacities of this receptor have been extended to a plethora of structurally diverse ligands. As a result, it has been acknowledged as a pattern recognition receptor (PRR) and functionally categorized as the RAGE axis. The ligation to RAGE leads the initiation of a complex signaling cascade and thus triggering crucial cellular events in the pathophysiology of many human diseases. In the present review, we intend to summarize basic features of the RAGE axis biology as well as its contribution to some relevant human diseases such as metabolic diseases, neurodegenerative, cardiovascular, autoimmune, and chronic airways diseases, and cancer as a result of exposure to AGEs, as well as many other ligands.

Mutual Regulation of Transcriptomes between Murine Pneumocytes and Fibroblasts Mediates Alveolar Regeneration in Air-Liquid Interface Cultures

Alveolar type 2 and club cells are part of the stem cell niche of the lung and their differentiation is required for pulmonary homeostasis and tissue regeneration. A disturbed crosstalk between fibroblasts and epithelial cells contributes to the loss of lung structure in chronic lung diseases. Therefore, it is important to understand how fibroblasts and lung epithelial cells interact during regeneration. Here, we analyzed the interaction of fibroblasts and the alveolar epithelium modeled in air-liquid interface cultures. Single-cell transcriptomics showed that cocultivation with fibroblasts leads to increased expression of type 2 markers in pneumocytes, activation of regulons associated with the maintenance of alveolar type 2 cells (e.g., Etv5), and transdifferentiation of club cells toward pneumocytes. This was accompanied by an intensified transepithelial barrier. Vice versa, the activation of NF-κB pathways and the CEBPB regulon and the expression of IL-6 and other differentiation factors (e.g., fibroblast growth factors) were increased in fibroblasts cocultured with epithelial cells. Recombinant IL-6 enhanced epithelial barrier formation. Therefore, in our coculture model, regulatory loops were identified by which lung epithelial cells mediate regeneration and differentiation of the alveolar epithelium in a cooperative manner with the mesenchymal compartment.

Akkermansia muciniphila attenuated lipopolysaccharide-induced acute lung injury by modulating the gut microbiota and SCFAs in mice

Gut microbiota are closely related to lipopolysaccharide (LPS)-induced acute lung injury (ALI). Akkermansia muciniphila (A. muciniphila) maintains the intestinal barrier function and regulates the balance of reduced glutathione/oxidized glutathione. However, it may be useful as a treatment strategy for LPS-induced lung injury. Our study aimed to explore whether A. muciniphila could improve lung injury by affecting the gut microbiota. The administration of A. muciniphila effectively attenuated lung injury tissue damage and significantly decreased the oxidative stress and inflammatory reaction induced by LPS, with lower levels of myeloperoxidase (MDA), enhanced superoxide dismutase (SOD) activity, decreased pro-inflammatory cytokine levels, and reduced macrophage and neutrophil infiltration. Moreover, A. muciniphila maintained the intestinal barrier function, reshaped the disordered microbial community, and promoted the secretion of short-chain fatty acids (SCFAs). A. muciniphila significantly downregulated the expression of TLR2, MyD88 and NF-kappa B (P < 0.05). Butyrate supplementation demonstrated a significant improvement in the inflammatory response (P < 0.05) and mitigation of histopathological damage in mice with ALI, thereby restoring the intestinal butyric acid concentration. In conclusion, our findings indicate that A. muciniphila inhibits the accumulation of inflammatory cytokines and attenuates the activation of the TLR2/Myd88/NF-κB pathway due to exerting anti-inflammatory effects through butyrate. This study provides an experimental foundation for the potential application of A. muciniphila and butyrate in the prevention and treatment of ALI.

Decreased Expression of Pulmonary Homeobox NKX2.1 and Surfactant Protein C in Developing Lungs That Over-Express Receptors for Advanced Glycation End-Products (RAGE)

Receptors for advanced glycation end-products (RAGE) are multi-ligand cell surface receptors of the immunoglobin superfamily prominently expressed by lung epithelium. Previous experiments demonstrated that over-expression of RAGE by murine alveolar epithelium throughout embryonic development causes neonatal lethality coincident with significant lung hypoplasia. In the current study, we evaluated the expression of NKX2.1 (also referred to as TTF-1), a homeodomain-containing transcription factor critical for branching morphogenesis, in mice that differentially expressed RAGE. We also contextualized NKX2.1 expression with the abundance of FoxA2, a winged double helix DNA binding protein that influences respiratory epithelial cell differentiation and surfactant protein expression. Conditional RAGE over-expression was induced in mouse lung throughout gestation (embryonic day E0-18.5), as well as during the critical saccular period of development (E15.5-18.5), and analyses were conducted at E18.5. Histology revealed markedly less lung parenchyma beginning in the canalicular stage of lung development and continuing throughout the saccular period. We discovered consistently decreased expression of both NKX2.1 and FoxA2 in lungs from transgenic (TG) mice compared to littermate controls. We also observed diminished surfactant protein C in TG mice, suggesting possible hindered differentiation and/or proliferation of alveolar epithelial cells under the genetic control of these two critical transcription factors. These results demonstrate that RAGE must be specifically regulated during lung formation. Perturbation of epithelial cell differentiation culminating in respiratory distress and perinatal lethality may coincide with elevated RAGE expression in the lung parenchyma.

The AGE-RAGE Axis and the Pathophysiology of Multimorbidity in COPD

Chronic obstructive pulmonary disease (COPD) is a disease of the airways and lungs due to an enhanced inflammatory response, commonly caused by cigarette smoking. Patients with COPD are often multimorbid, as they commonly suffer from multiple chronic (inflammatory) conditions. This intensifies the burden of individual diseases, negatively affects quality of life, and complicates disease management. COPD and comorbidities share genetic and lifestyle-related risk factors and pathobiological mechanisms, including chronic inflammation and oxidative stress. The receptor for advanced glycation end products (RAGE) is an important driver of chronic inflammation. Advanced glycation end products (AGEs) are RAGE ligands that accumulate due to aging, inflammation, oxidative stress, and carbohydrate metabolism. AGEs cause further inflammation and oxidative stress through RAGE, but also through RAGE-independent mechanisms. This review describes the complexity of RAGE signaling and the causes of AGE accumulation, followed by a comprehensive overview of alterations reported on AGEs and RAGE in COPD and in important co-morbidities. Furthermore, it describes the mechanisms by which AGEs and RAGE contribute to the pathophysiology of individual disease conditions and how they execute crosstalk between organ systems. A section on therapeutic strategies that target AGEs and RAGE and could alleviate patients from multimorbid conditions using single therapeutics concludes this review.

How does cigarette smoking affect airway remodeling in asthmatics?

Asthma is a prevalent chronic airway inflammatory disease involving multiple cells, and the prolonged course of the disease can cause airway remodeling, resulting in irreversible or partial irreversible airflow limitation and persistent airway hyperresponsiveness (AHR) in asthmatics. Therefore, we must ascertain the factors that affect the occurrence and development of airway remodeling in asthmatics. Smokers are not uncommon in asthmatics. However, there is no systematic description of how smoking promotes airway remodeling in asthmatics. This narrative review summarizes the effects of smoking on airway remodeling in asthmatics, and the progress of the methods for evaluating airway remodeling.

Role of RAGE and its ligand HMGB1 in the development of COPD

Smoking is a well-established risk factor for chronic obstructive pulmonary disease (COPD). Chronic lung inflammation continues even after smoking cessation and leads to COPD progression. To date, anti-inflammatory therapies are ineffective in improving pulmonary function and COPD symptoms, and new molecular targets are urgently needed to deal with this challenge. The receptor for advanced glycation end-products (RAGE) was shown to be relevant in COPD pathogenesis, since it is both a genetic determinant of low lung function and a determinant of COPD susceptibility. Moreover, RAGE is involved in the physiological response to cigarette smoke exposure. Since innate and acquired immunity plays an essential role in the development of chronic inflammation and emphysema in COPD, here we summarized the roles of RAGE and its ligand HMGB1 in COPD immunity.

Association of the RAGE/RAGE-ligand axis with interstitial lung disease and its acute exacerbation

The receptor for advanced glycation end product (RAGE) is a transmembrane receptor highly expressed in type 1 pneumocytes of healthy lungs. RAGE is considered to play a homeostatic role in the lung, as RAGE knockout mice develop lung fibrosis as they age. In contrast, RAGE can bind numerous ligands, including high-mobility group box 1 (HMGB1). These interactions initiate pro-inflammatory signaling associated with the pathogenesis of lung injury and interstitial lung disease (ILD), including idiopathic pulmonary fibrosis (IPF). ILD is a broad category of diffuse parenchymal lung disease characterized by various extents of lung fibrosis and inflammation, and IPF is a common and progressive ILD of unknown cause. The prognosis of patients with IPF is poor, and acute exacerbation of IPF (AE-IPF) is one of the main causes of death. Recent reports indicate that acute exacerbations can occur in other ILDs (AE-ILD). Notably, ILD is frequently observed in patients with lung cancer, and AE-ILD after surgical procedures or the initiation of chemotherapy for concomitant lung cancer are clinically important due to their association with increased mortality. In this review, we summarize the associations of RAGE/soluble RAGE (sRAGE)/RAGE ligands with the pathogenesis and clinical course of ILD, including IPF and AE-IPF. Additionally, the potential use of sRAGE and RAGE ligands as predictive markers of AE-IPF and cancer treatment-triggered AE-ILD is also discussed.

RAGE against the Machine: Can Increasing Our Understanding of RAGE Help Us to Battle SARS-CoV-2 Infection in Pregnancy?

The receptor of advanced glycation end products (RAGE) is a receptor that is thought to be a key driver of inflammation in pregnancy, SARS-CoV-2, and also in the comorbidities that are known to aggravate these afflictions. In addition to this, vulnerable populations are particularly susceptible to the negative health outcomes when these afflictions are experienced in concert. RAGE binds a number of ligands produced by tissue damage and cellular stress, and its activation triggers the proinflammatory transcription factor Nuclear Factor Kappa B (NF-κB), with the subsequent generation of key proinflammatory cytokines. While this is important for fetal membrane weakening, RAGE is also activated at the end of pregnancy in the uterus, placenta, and cervix. The comorbidities of hypertension, cardiovascular disease, diabetes, and obesity are known to lead to poor pregnancy outcomes, and particularly in populations such as Native Hawaiians and Pacific Islanders. They have also been linked to RAGE activation when individuals are infected with SARS-CoV-2. Therefore, we propose that increasing our understanding of this receptor system will help us to understand how these various afflictions converge, how forms of RAGE could be used as a biomarker, and if its manipulation could be used to develop future therapeutic targets to help those at risk.

Plasma sRAGE levels strongly associate with centrilobular emphysema assessed by HRCT scans

Background

There is a strong need for biomarkers to better characterize individuals with COPD and to take into account the heterogeneity of COPD. The blood protein sRAGE has been put forward as promising biomarker for COPD in general and emphysema in particular. Here, we measured plasma sRAGE levels using quantitative LC–MS and assessed whether the plasma sRAGE levels associate with (changes in) lung function, radiological emphysema parameters, and radiological subtypes of emphysema.

Methods

Three hundred and twenty-four COPD patients (mean FEV₁: 63%predicted) and 185 healthy controls from the COPDGene study were selected. Plasma sRAGE was measured by immunoprecipitation in 96-well plate methodology to enrich sRAGE, followed by targeted quantitative liquid chromatography-mass spectrometry. Spirometry and HRCT scans (inspiration and expiration) with a 5-year follow-up were used; both subjected to high quality control standards.

Results

Lower sRAGE values significantly associated with the presence of COPD, the severity of airflow obstruction, the severity of emphysema on HRCT, the heterogeneous distribution of emphysema, centrilobular emphysema, and 5-year progression of emphysema. However, sRAGE values did not associate with airway wall thickness or paraseptal emphysema.

Conclusions

Rather than being a general COPD biomarker, sRAGE is especially a promising biomarker for centrilobular emphysema. Follow-up studies should elucidate whether sRAGE can be used as a biomarker for other COPD phenotypes as well.

An Integrative Genomic Strategy Identifies sRAGE as a Causal and Protective Biomarker of Lung Function

BACKGROUND

There are few clinically useful circulating biomarkers of lung function and lung disease. We hypothesized that genome-wide association studies (GWAS) of circulating proteins in conjunction with GWAS of pulmonary traits represents a clinically relevant approach to identifying causal proteins and therapeutically useful insights into mechanisms related to lung function and disease.

STUDY QUESTION

Can an integrative genomic strategy using GWAS of plasma soluble receptor for advanced glycation end-products (sRAGE) levels in conjunction with GWAS of lung function traits identify putatively causal relations of sRAGE to lung function?

STUDY DESIGN AND METHODS

Plasma sRAGE levels were measured in 6,861 Framingham Heart Study participants and GWAS of sRAGE was conducted to identify protein quantitative trait loci (pQTL), including cis-pQTL variants at the sRAGE protein-coding gene locus (AGER). We integrated sRAGE pQTL variants with variants from GWAS of lung traits. Colocalization of sRAGE pQTL variants with lung trait GWAS variants was conducted, and Mendelian randomization was performed using sRAGE cis-pQTL variants to infer causality of sRAGE for pulmonary traits. Cross-sectional and longitudinal protein-trait association analyses were conducted for sRAGE in relation to lung traits.

RESULTS

Colocalization identified shared genetic signals for sRAGE with lung traits. Mendelian randomization analyses suggested protective causal relations of sRAGE to several pulmonary traits. Protein-trait association analyses demonstrated higher sRAGE levels to be cross-sectionally and longitudinally associated with preserved lung function.

INTERPRETATION

sRAGE is produced by type I alveolar cells, and it acts as a decoy receptor to block the inflammatory cascade. Our integrative genomics approach provides evidence for sRAGE as a causal and protective biomarker of lung function, and the pattern of associations is suggestive of a protective role of sRAGE against restrictive lung physiology. We speculate that targeting the AGER/sRAGE axis may be therapeutically beneficial for the treatment and prevention of inflammation-related lung disease.

Implication of RAGE Polymorphic Variants in COPD Complication and Anti-COPD Therapeutic Potential of sRAGE

Chronic obstructive pulmonary disease (COPD) is a slowly progressive and poorly reversible airway obstruction disease. It is caused either alone or in combination of emphysema, chronic bronchitis (CB), and small airways disease. COPD is thought to be a multi-factorial disorder in which genetic susceptibility, environmental factors and tobacco exposure could be doubly or simultaneously implicated. Available medicines against COPD include anti-inflammatory drugs, such as β2-agonists and anticholinergics, which efficiently reduce airflow limitation but are unable to avert disease progression and mortality. Advanced glycation end products (AGE) and their receptors i.e. receptor for advanced glycation end products (RAGE) are some molecules that have been implicated in the complication of COPD. Several RAGE single nucleotide polymorphic (SNP) variants are produced by the mammalian cells. Based on the ethnicity some SNPs aggravate the COPD severity. Mammalian cells produce several alternative RAGE splice variants including a soluble RAGE (sRAGE) and an endogenous soluble RAGE (esRAGE). Both of these act as decoy receptor and thus may help to arrest the COPD complications. Several lines of evidences indicate a decreased level of sRAGE in the COPD subjects. One of the new strategies to reduce COPD complication may be sRAGE therapeutic administration to the COPD subjects. This comprehensive discussion sheds light on the role of RAGE and its polymorphic variants in the COPD complication along with sRAGE therapeutic significance in the COPD prevention.

Reduced receptor for advanced glycation end products is associated with α-SMA expression in patients with idiopathic pulmonary fibrosis and mice

Background

Idiopathic pulmonary fibrosis (IPF) is a chronic and progressive interstitial lung disease. Despite alveolar epithelial cells is crucial role in lung, its contribution and the associated biomarker remain unknown in the pathogenesis of IPF. Recently, environmental factors including stone dust, silica and cigarette smoking were found as risk factors involved in IPF. Receptor for advanced glycation end products (RAGE) is a member of the immunoglobulin super family of cell surface receptors. It has been shown that interaction between RAGE and its ligands on immune cells mediates cellular migration and regulation of pro-inflammation. RAGE is highly expressed in the lung, in particular, alveolar epithelial cells. Therefore, we determined whether RAGE expression is associated with fibrosis-associated genes in patients with IPF and mice.

Results

When bleomycin (BLM) was intratracheally administered to C57BL/6 mice for 1, 2 weeks, macrophage and neutrophils were significantly increased. The fibrotic nodule formed and accumulation of collagen was determined after BLM injection in H&E- and Masson’s trichrome staining. Levels of elastin, Col1a1 and fibronectin were increased in quantitative real-time PCR and protein levels of α-SMA was increased in western blot analysis. In the lung tissues of 1 mg/kg BLM-induced mice, RAGE expression was gradually decreased in 1- and 2 weeks in immunohistochemistry and western blot analysis, and 3 mg/kg of BLM-induced mice exhibited decreased RAGE levels while α-SMA expression was increased. We next determined RAGE expression in the lungs of IPF patients using immunohistochemistry. As a result, RAGE expression was decreased, while α-SMA expression was increased compared with non-IPF subjects.

Conclusions

Our findings suggest that reduced RAGE was associated with increased fibrotic genes in BLM-induced mice and patients with IPF. Therefore, RAGE could be applied with a biomarker for prognosis and diagnosis in the pathogenesis of IPF.

Cigarette Smoke Condensate Exposure Induces Receptor for Advanced Glycation End-Products (RAGE)-Dependent Sterile Inflammation in Amniotic Epithelial Cells

Maternal smoking is a risk factor of preterm prelabor rupture of the fetal membranes (pPROM), which is responsible for 30% of preterm births worldwide. Cigarettes induce oxidative stress and inflammation, mechanisms both implicated in fetal membranes (FM) weakening. We hypothesized that the receptor for advanced glycation end-products (RAGE) and its ligands can result in cigarette-dependent inflammation. FM explants and amniotic epithelial cells (AECs) were treated with cigarette smoke condensate (CSC), combined or not with RAGE antagonist peptide (RAP), an inhibitor of RAGE. Cell suffering was evaluated by measuring lactate dehydrogenase (LDH) medium-release. Extracellular HMGB1 (a RAGE ligand) release by amnion and choriodecidua explants were checked by western blot. NF-κB pathway induction was determined by a luciferase gene reporter assay, and inflammation was evaluated by cytokine RT-qPCR and protein quantification. Gelatinase activity was assessed using a specific assay. CSC induced cell suffering and HMGB1 secretion only in the amnion, which is directly associated with a RAGE-dependent response. CSC also affected AECs by inducing inflammation (cytokine release and NFκB activation) and gelatinase activity through RAGE engagement, which was linked to an increase in extracellular matrix degradation. This RAGE dependent CSC-induced inflammation associated with an increase of gelatinase activity could explain a pathological FM weakening directly linked to pPROM.

Disulfide and Fully Reduced HMGB1 Induce Different Macrophage Polarization and Migration Patterns

Macrophage plasticity enables cells to obtain different functions over a broad proinflammatory and repairing spectrum. In different conditions, macrophages can be induced by high-mobility group box 1 (HMGB1), a nuclear DNA-binding protein that activates innate immunity, to polarize towards a pro- (M1) or anti-inflammatory (M2) phenotype. In this study, we investigated the phenotypes of murine bone-marrow-derived macrophages (BMDMs) induced by different HMGB1 redox isoforms in depth. Our results demonstrate that disulfide HMGB1 (dsHMGB1) induces a unique macrophage phenotype that secretes pro-inflammatory cytokines, rather than inducing metabolic changes leading to nitric oxide production. Fully reduced HMGB1 (frHMGB1) did not induce macrophage polarization. The migrating function of BMDMs was measured by scratch assay after the stimulation with dsHMGB1 and frHMGB1. Both dsHMGB1 and frHMGB1 induced cell migration. We found that dsHMGB1 mediates cytokine secretion and cellular motility, mainly through toll-like receptor 4 (TLR4). Importantly, our data shows that dsHMGB1 and frHMGB1 induce distinct BMDM polarization phenotypes, and that dsHMGB1 induces a unique phenotype differing from the classical proinflammatory macrophage phenotype.

Sesamin suppresses advanced glycation end products induced microglial reactivity using BV2 microglial cell line as a model

Neuroinflammation-mediated microglial reactivity is a major process, which explains the increased risk of Alzheimer's disease (AD) development in patients with Type 2 diabetes mellitus (T2DM). Advanced glycation end products (AGEs), formed by hyperglycemic condition in diabetes, is characterized as an intermediary of brain injury with diabetes through induction of microglial reactivity. Here, we explored the effect of AGEs on microglial reactivity using BV2 as a model. The NF-κB, p38 and JNK pathways were found to be important mechanism in AGEs-induced BV2 microglial reactivity. NF-κB inhibitor (BAY-11-7082), p38 inhibitor (SB203580) and JNK inhibitor (SP600125) exhibited the potential inhibition of AGEs-induced NO production. We also found that the sesamin, a major lignan found in sesame seed oils, exerts an anti-inflammatory effect under AGEs-induced microglial reactivity via suppressing the phosphorylation of NF-κB, p38 and JNK pathways. Moreover, sesamin also ameliorated AGEs-induced-receptor for advanced glycation end products (RAGE) expression. Taken together, sesamin may be a promising phytochemical compound to delay inflammatory progress by AGEs microglia function. Similarly, inhibition of AGEs-induced microglial reactivity might be potential therapeutic targets of neuroinflammation-based mechanisms in T2DM link progressive AD.

RAGE and TLR4 differentially regulate airway hyperresponsiveness: Implications for COPD

BACKGROUND

The receptor for advanced glycation end products (RAGE) and Toll-like receptor 4 (TLR4) is implicated in COPD. Although these receptors share common ligands and signalling pathways, it is not known whether they act in concert to drive pathological processes in COPD. We examined the impact of RAGE and/or TLR4 gene deficiency in a mouse model of COPD and also determined whether expression of these receptors correlates with airway neutrophilia and airway hyperresponsiveness (AHR) in COPD patients.

METHODS

We measured airway inflammation and AHR in wild-type, RAGE^-/- , TLR4^-/- and TLR4^-/- RAGE^-/- mice following acute exposure to cigarette smoke (CS). We also examined the impact of smoking status on AGER (encodes RAGE) and TLR4 bronchial gene expression in patients with and without COPD. Finally, we determined whether expression of these receptors correlates with airway neutrophilia and AHR in COPD patients.

RESULTS

RAGE^-/- mice were protected against CS-induced neutrophilia and AHR. In contrast, TLR4^-/- mice were not protected against CS-induced neutrophilia and had more severe CS-induced AHR. TLR4^-/- RAGE^-/- mice were not protected against CS-induced neutrophilia but were partially protected against CS-induced mediator release and AHR. Current smoking was associated with significantly lower AGER and TLR4 expression irrespective of COPD status, possibly reflecting negative feedback regulation. However, consistent with preclinical findings, AGER expression correlated with higher sputum neutrophil counts and more severe AHR in COPD patients. TLR4 expression did not correlate with neutrophilic inflammation or AHR.

CONCLUSIONS

Inhibition of RAGE but not TLR4 signalling may protect against airway neutrophilia and AHR in COPD.

IL-17C contributes to NTHi-induced inflammation and lung damage in experimental COPD and is present in sputum during acute exacerbations

Neutrophilic inflammation results in loss of lung function in chronic obstructive pulmonary disease (COPD). Gram-negative bacteria, such as nontypeable Haemophilus influenzae (NTHi), trigger acute exacerbations of COPD (AECOPD) and contribute to chronic lung inflammation. The pro-inflammatory cytokine interleukin-17C (IL-17C) is expressed by airway epithelial cells and regulates neutrophilic chemotaxis. Here, we explored the function of IL-17C in NTHi- and cigarette smoke (CS)-induced models of COPD. Neutrophilic inflammation and tissue destruction were decreased in lungs of IL-17C-deficient mice (Il-17c-/-) chronically exposed to NTHi. Numbers of pulmonary neutrophils were decreased in Il-17c-/- mice after acute exposure to the combination of NTHi and CS. However, Il-17c-/- mice were not protected from CS-induced lung inflammation. In a preliminary patient study, we show that IL-17C is present in sputum samples obtained during AECOPD and associates with disease severity. Concentrations of IL-17C were significantly increased during advanced COPD (GOLD III/IV) compared to moderate COPD (GOLD I/II). Concentrations of IL-17A and IL-17E did not associate with disease severity. Our data suggest that IL-17C promotes harmful pulmonary inflammation triggered by bacteria in COPD.

Immortalisation of primary human alveolar epithelial lung cells using a non-viral vector to study respiratory bioreactivity in vitro

To overcome the scarcity of primary human alveolar epithelial cells for lung research, and the limitations of current cell lines to recapitulate the phenotype, functional and molecular characteristics of the healthy human alveolar epithelium, we have developed a new method to immortalise primary human alveolar epithelial lung cells using a non-viral vector to transfect the telomerase catalytic subunit (hTERT) and the simian virus 40 large-tumour antigen (SV40). Twelve strains of immortalised cells (ICs) were generated and characterised using molecular, immunochemical and morphological techniques. Cell proliferation and sensitivity to polystyrene nanoparticles (PS) were evaluated. ICs expressed caveolin-1, podoplanin and receptor for advanced glycation end-products (RAGE), and most cells were negative for alkaline phosphatase staining, indicating characteristics of AT1-like cells. However, most strains also contained some cells that expressed pro-surfactant protein C, classically described to be expressed only by AT2 cells. Thus, the ICs mimic the cellular heterogeneity in the human alveolar epithelium. These ICs can be passaged, replicate rapidly and remain confluent beyond 15 days. ICs showed differential sensitivity to positive and negatively charged PS nanoparticles, illustrating their potential value as an in vitro model to study respiratory bioreactivity. These novel ICs offer a unique resource to study human alveolar epithelial biology.

The heterodimer S100A8/A9 is a potent therapeutic target for idiopathic pulmonary fibrosis

In patients with interstitial pneumonia, pulmonary fibrosis is an irreversible condition that can cause respiratory failure. Novel treatments for pulmonary fibrosis are necessary. Inflammation is thought to activate lung fibroblasts, resulting in pulmonary fibrosis. Of the known inflammatory molecules, we have focused on S100A8/A9 from the onset of inflammation to the subsequent progression of inflammation. Our findings confirmed the high expression of S100A8/A9 in specimens from patients with pulmonary fibrosis. An active role of S100A8/A9 was demonstrated not only in the proliferation of fibroblasts but also in the fibroblasts' differentiation to myofibroblasts (the active form of fibroblasts). S100A8/A9 also forced fibroblasts to upregulate the production of collagen. These effects were induced via the receptor of S100A8/A9, i.e., the receptor for advanced glycation end products (RAGE), on fibroblasts. The anti-S100A8/A9 neutralizing antibody inhibited the effects of S100A8/A9 on fibroblasts and suppressed the progression of fibrosis in bleomycin (BLM)-induced pulmonary fibrosis mouse model. Our findings strongly suggest a crucial role of S100A8/A9 in pulmonary fibrosis and the usefulness of S100A8/A9-targeting therapy for fibrosis interstitial pneumonia. HIGHLIGHTS: S100A8/A9 level is highly upregulated in the IPF patients' lungs as well as the blood. S100A8/A9 promotes not only the growth of fibroblasts but also differentiation to myofibroblasts. The cell surface RAGE acts as a crucial receptor to the extracellular S100A8/A9 in fibroblasts. The anti-S100A8/A9 antibody effectively suppresses the progression of IPF in a mouse model. In idiopathic pulmonary fibrosis (IPF), S100A8/A9, a heterodimer composed of S100A8 and S100A9 proteins, plays a crucial role in the onset of inflammation and the subsequent formation of a feed-forward inflammatory loop that promotes fibrosis. (1) The local, pronounced increase in S100A8/A9 in the injured inflammatory lung region-which is provided mainly by the activated neutrophils and macrophages-exerts strong inflammatory signals accompanied by dozens of inflammatory soluble factors including cytokines, chemokines, and growth factors that further act to produce and secrete S100A8/A9, eventually making a sustainable inflammatory circuit that supplies an indefinite presence of S100A8/A9 in the extracellular space with a mal-increased level. (2) The elevated S100A8/A9 compels fibroblasts to activate through receptor for advanced glycation end products (RAGE), one of the major S100A8/A9 receptors, resulting in the activation of NFκB, leading to fibroblast mal-events (e.g., elevated cell proliferation and transdifferentiation to myofibroblasts) that actively produce not only inflammatory cytokines but also collagen matrices. (3) Finally, the S100A8/A9-derived activation of lung fibroblasts under a chronic inflammation state leads to fibrosis events and constantly worsens fibrosis in the lung. Taken together, these findings suggest that the extracellular S100A8/A9 heterodimer protein is a novel mainstay soluble factor for IPF that exerts many functions as described above (1-3). Against this background, we herein applied the developed S100A8/A9 neutralizing antibody to prevent IPF. The IPF imitating lung fibrosis in an IPF mouse model was effectively blocked by treatment with the antibody, leading to enhanced survival. The developed S100A8/A9 antibody, as an innovative novel biologic, may help shed light on the difficulties encountered with IPF therapy in clinical settings.

The role of RAGE in host pathology and crosstalk between RAGE and TLR4 in innate immune signal transduction pathways

Although the innate immune receptor protein, Receptor for Advanced Glycation End products (RAGE), has been extensively studied, there has been renewed interest in RAGE for its potential role in sepsis, along with a host of other inflammatory diseases of chronic, noninfectious origin. In contrast to other innate immune receptors, for example, Toll-like receptors (TLRs), that recognize ligands derived from pathogenic organisms that are collectively known as "pathogen-associated molecular patterns" (PAMPs) or host-derived "damage-associated molecular patterns" (DAMPs), RAGE has been shown to recognize a broad collection of DAMPs exclusively. Historically, these DAMPs have been shown to be pro-inflammatory in nature. Early studies indicated that the adaptor molecule, MyD88, might be important for this change. More recent studies have explored further the mechanisms underlying this inflammatory change. Overall, the newer results have shown that there is extensive crosstalk between RAGE and TLRs. The three canonical RAGE ligands, Advanced Glycation End products (AGEs), HMGB1, and S100 proteins, have all been shown to activate both TLRs and RAGE to varying degrees in order to induce inflammation in in vitro models. As with any field that delves deeply into innate signaling, obstacles of reagent purity may be a cause of some of the discrepancies in the literature, and we have found that commercial antibodies that have been widely used exhibit a high degree of nonspecificity. Nonetheless, the weight of published evidence has led us to speculate that RAGE may be physically interacting with TLRs on the cell surface to elicit inflammation via MyD88-dependent signaling.

Multiomics of World Trade Center Particulate Matter-induced Persistent Airway Hyperreactivity. Role of Receptor for Advanced Glycation End Products

Pulmonary disease after World Trade Center particulate matter (WTC-PM) exposure is associated with dyslipidemia and the receptor for advanced glycation end products (RAGE); however, the mechanisms are not well understood. We used a murine model and a multiomics assessment to understand the role of RAGE in the pulmonary long-term effects of a single high-intensity exposure to WTC-PM. After 1 month, WTC-PM-exposed wild-type (WT) mice had airway hyperreactivity, whereas RAGE-deficient (Ager^-/-) mice were protected. PM-exposed WT mice also had histologic evidence of airspace disease, whereas Ager^-/- mice remained unchanged. Inflammatory mediators such as G-CSF (granulocyte colony-stimulating factor), IP-10 (IFN-γ-induced protein 10), and KC (keratinocyte chemoattractant) were differentially expressed after WTC-PM exposure. WTC-PM induced α-SMA, DIAPH1 (protein diaphanous homolog 1), RAGE, and significant lung collagen deposition in WT compared with Ager^-/- mice. Compared with WT mice with PM exposure, relative expression of phosphorylated to total CREB (cAMP response element-binding protein) and JNK (c-Jun N-terminal kinase) was significantly increased in the lung of PM-exposed Ager^-/- mice, whereas Akt (protein kinase B) was decreased. Random forests of the refined lung metabolomic profile classified subjects with 92% accuracy; principal component analysis captured 86.7% of the variance in three components and demonstrated prominent subpathway involvement, including known mediators of lung disease such as vitamin B₆ metabolites, sphingolipids, fatty acids, and phosphatidylcholines. Treatment with a partial RAGE antagonist, pioglitazone, yielded similar fold-change expression of metabolites (N₆-carboxymethyllysine, 1-methylnicotinamide, N¹+N⁸-acetylspermidine, and succinylcarnitine [C4-DC]) between WT and Ager^-/- mice exposed to WTC-PM. RAGE can mediate WTC-PM-induced airway hyperreactivity and warrants further investigation.

The IL-17 receptor IL-17RE mediates polyIC-induced exacerbation of experimental allergic asthma

BACKGROUND

The interleukin 17 receptor E (IL-17RE) is specific for the epithelial cytokine interleukin-17C (IL-17C). Asthma exacerbations are frequently caused by viral infections. Polyinosinic:polycytidylic acid (pIC) mimics viral infections through binding to pattern recognition receptors (e.g. TLR-3). We and others have shown that pIC induces the expression of IL-17C in airway epithelial cells. Using different mouse models, we aimed to investigate the function of IL-17RE in the development of experimental allergic asthma and acute exacerbation thereof.

METHODS

Wild-type (WT) and IL-17RE deficient (Il-17re-/-) mice were sensitized and challenged with OVA to induce allergic airway inflammation. pIC or PBS were applied intranasally when allergic airway inflammation had been established. Pulmonary expression of inflammatory mediators, numbers of inflammatory cells, and airway hyperresponsiveness (AHR) were analyzed.

RESULTS

Ablation of IL-17RE did not affect the development of OVA-induced allergic airway inflammation and AHR. pIC induced inflammation independent of IL-17RE in the absence of allergic airway inflammation. Treatment of mice with pIC exacerbated pulmonary inflammation in sensitized and OVA-challenged mice in an IL-17RE-dependent manner. The pIC-induced expression of cytokines (e.g. keratinocyte-derived chemokine (KC), granulocyte-colony stimulating factor (G-CSF)) and recruitment of neutrophils were decreased in Il-17re-/- mice. pIC-exacerbated AHR was partially decreased in Il-17re-/- mice.

CONCLUSIONS

Our results indicate that IL-17RE mediates virus-triggered exacerbations but does not have a function in the development of allergic lung disease.

Synergistic Effect of WTC-Particulate Matter and Lysophosphatidic Acid Exposure and the Role of RAGE: In-Vitro and Translational Assessment

World Trade Center particulate matter (WTC-PM)-exposed firefighters with metabolic syndrome (MetSyn) have a higher risk of WTC lung injury (WTC-LI). Since macrophages are crucial innate pulmonary mediators, we investigated WTC-PM/lysophosphatidic acid (LPA) co-exposure in macrophages. LPA, a low-density lipoprotein metabolite, is a ligand of the advanced glycation end-products receptor (AGER or RAGE). LPA and RAGE are biomarkers of WTC-LI. Human and murine macrophages were exposed to WTC-PM, and/or LPA, and compared to controls. Supernatants were assessed for cytokines/chemokines; cell lysate immunoblots were assessed for signaling intermediates after 24 h. To explore the translatability of our in-vitro findings, we assessed serum cytokines/chemokines and metabolites of symptomatic, never-smoking WTC-exposed firefighters. Agglomerative hierarchical clustering identified phenotypes of WTC-PM-induced inflammation. WTC-PM induced GM-CSF, IL-8, IL-10, and MCP-1 in THP-1-derived macrophages and induced IL-1α, IL-10, TNF-α, and NF-κB in RAW264.7 murine macrophage-like cells. Co-exposure induced synergistic elaboration of IL-10 and MCP-1 in THP-1-derived macrophages. Similarly, co-exposure synergistically induced IL-10 in murine macrophages. Synergistic effects were seen in the context of a downregulation of NF-κB, p-Akt, -STAT3, and -STAT5b. RAGE expression after co-exposure increased in murine macrophages compared to controls. In our integrated analysis, the human cytokine/chemokine biomarker profile of WTC-LI was associated with discriminatory metabolites (fatty acids, sphingolipids, and amino acids). LPA synergistically elaborated WTC-PM’s inflammatory effects in vitro and was partly RAGE-mediated. Further research will focus on the intersection of MetSyn/PM exposure.

Effects of PDE3 Inhibitor Olprinone on the Respiratory Parameters, Inflammation, and Apoptosis in an Experimental Model of Acute Respiratory Distress Syndrome

This study aimed to investigate whether a selective phosphodiesterase-3 (PDE3) inhibitor olprinone can positively influence the inflammation, apoptosis, and respiratory parameters in animals with acute respiratory distress syndrome (ARDS) model induced by repetitive saline lung lavage. Adult rabbits were divided into 3 groups: ARDS without therapy (ARDS), ARDS treated with olprinone i.v. (1 mg/kg; ARDS/PDE3), and healthy ventilated controls (Control), and were oxygen-ventilated for the following 4 h. Dynamic lung-thorax compliance (Cdyn), mean airway pressure (MAP), arterial oxygen saturation (SaO2), alveolar-arterial gradient (AAG), ratio between partial pressure of oxygen in arterial blood to a fraction of inspired oxygen (PaO2/FiO2), oxygenation index (OI), and ventilation efficiency index (VEI) were evaluated every hour. Post mortem, inflammatory and oxidative markers (interleukin (IL)-6, IL-1β, a receptor for advanced glycation end products (RAGE), IL-10, total antioxidant capacity (TAC), 3-nitrotyrosine (3NT), and malondialdehyde (MDA) and apoptosis (apoptotic index and caspase-3) were assessed in the lung tissue. Treatment with olprinone reduced the release of inflammatory mediators and markers of oxidative damage decreased apoptosis of epithelial cells and improved respiratory parameters. The results indicate a future potential of PDE3 inhibitors also in the therapy of ARDS.

HMGB1 participates in LPS‑induced acute lung injury by activating the AIM2 inflammasome in macrophages and inducing polarization of M1 macrophages via TLR2, TLR4, and RAGE/NF‑κB signaling pathways

High mobility group box 1 (HMGB1), a crucial proinflammatory cytokine, was reported to activate the absent in melanoma 2 (AIM2) inflammasome, which are both essential in acute lung injury (ALI). However, their interaction mechanism has remained elusive. Macrophages are known to express the AIM2 inflammasome and the main receptors [receptor for advanced glycation end products (RAGE), Toll‑like receptor 2/4 (TLR‑2/TLR‑4)] of HMGB1 to transmit intracellular signals. The present study aimed to indicate whether HMGB1 participates in the process of lipopolysaccharides (LPS)‑induced ALI through activating the AIM2 inflammasome in macrophages, as well as inducing polarization of M1 macrophages via TLR2, TLR4 and RAGE/ nuclear factor‑κB (NF‑κB) signaling pathways. In an in vivo mouse model of LPS‑induced ALI, anti‑HMGB1, recombinant (r)HMGB1, LPS from Rhodobacter sphaeroides (LPS‑RS, TLR2/4 antagonist) or FPS‑ZM1 (RAGE antagonist) were administrated. In in vitro studies, bone marrow‑derived macrophages from mice primed with LPS were stimulated with or without anti‑HMGB1, rHMGB1, LPS‑RS, or FPS‑ZM1. The findings revealed that anti‑HMGB1, LPS‑RS and FPS‑ZM1 significantly decreased infiltration of inflammatory cells, wet‑to‑dry ratio, myeloperoxidase activity in the lung, the levels of cytokines, as well as macrophages and neutrophil infiltration in the bronchoalveolar lavage fluid. However, rHMGB1 aggravated the inflammatory response in ALI. Mechanistically, anti‑HMGB1, LPS‑RS and FPS‑ZM1 attenuated activation of TLR2, TLR4, and RAGE/NF‑κB signaling pathways and expression of the AIM2 inflammasome in macrophages. However, rHMGB1 enhanced their expression levels and induced polarization of M1 macrophages. These results indicated that HMGB1 could participate in the pathogenesis of ALI by activating the AIM2 inflammasome in macrophages, as well as inducing polarization of M1 macrophages through TLR2, TLR4 and RAGE/NF‑κB signaling pathways.

Gene doubling increases glyoxalase 1 expression in RAGE knockout mice

BACKGROUND

The receptor for advanced glycation end-products (RAGE) is a multifunctional protein. Its function as pattern recognition receptor able to interact with various extracellular ligands is well described. Genetically modified mouse models, especially the RAGE knockout (RAGE-KO) mouse, identified the amplification of the immune response as an important function of RAGE. Pro-inflammatory ligands of RAGE are also methylglyoxal-derived advanced glycation end-products, which depend in their quantity, at least in part, on the activity of the methylglyoxal-detoxifying enzyme glyoxalase-1 (Glo1). Therefore, we studied the potential interaction of RAGE and Glo1 by use of RAGE-KO mice.

METHODS

Various tissues (lung, liver, kidney, heart, spleen, and brain) and blood cells from RAGE-KO and wildtype mice were analyzed for Glo1 expression and activity by biochemical assays and the Glo1 gene status by PCR techniques.

RESULTS

We identified an about two-fold up-regulation of Glo1 expression and activity in all tissues of RAGE-KO mice. This was result of a copy number variation of the Glo1 gene on mouse chromosome 17. In liver tissue and blood cells, the Glo1 expression and activity was additionally influenced by sex with higher values for male than female animals. As the genomic region containing Glo1 also contains the full-length sequence of another gene, namely Dnahc8, both genes were duplicated in RAGE-KO mice.

CONCLUSION

A genetic variance in RAGE-KO mice falsely suggests an interaction of RAGE and Glo1 function.

GENERAL SIGNIFICANCE

RAGE-independent up-regulation of Glo1 in RAGE-KO mice might be as another explanation for, at least some, effects attributed to RAGE before.

Inhalable Gene Delivery System Using a Cationic RAGE-Antagonist Peptide for Gene Delivery to Inflammatory Lung Cells

Acute lung injury (ALI) is a severe lung inflammatory disease. In ALI, the receptor for advanced glycation end-products (RAGE) is overexpressed in lung epithelial cells and involved in inflammatory reactions. A previous report showed that a RAGE-antagonist peptide (RAP), from high-mobility group box-1, bound to RAGE and reduced inflammatory reactions. RAP has high levels of positive amino acids, which suggests that RAP may form a complex with plasmid DNA (pDNA) by charge interactions. Because the charge density of RAP is lower than polyethylenimine (25 kDa, PEI25k), it may be able to avoid capture by the negatively charged mucus layer more easily and deliver pDNA into RAGE-positive lung cells of ALI animals by RAGE-mediated endocytosis. To prove this hypothesis, RAP was evaluated as a delivery carrier of adiponectin plasmid (pAPN) in lipopolysaccharide (LPS)-induced ALI animal models. In vitro transfection assays showed that RAP had lower transfection efficiency than PEI25k in L2 lung epithelial cells. However, in vivo administration to ALI animal models by inhalation showed that RAP had higher gene delivery efficiency than PEI25k. Particularly, due to a higher expression of RAGE in lung cells of ALI animals, the gene delivery efficiency of RAP was higher in ALI animals than that in normal animals. Delivery of the pAPN/RAP complex had anti-inflammatory effects, reducing pro-inflammatory cytokines. Hematoxylin and eosin staining confirmed that pAPN/RAP decreased inflammation in ALI models. Therefore, the results suggest that RAP may be useful as a carrier of pDNA into the lungs for ALI gene therapy.

Alternative Oxidase Attenuates Cigarette Smoke-induced Lung Dysfunction and Tissue Damage

Cigarette smoke (CS) exposure is the predominant risk factor for the development of chronic obstructive pulmonary disease (COPD) and the third leading cause of death worldwide. We aimed to elucidate whether mitochondrial respiratory inhibition and oxidative stress are triggers in its etiology. In different models of CS exposure, we investigated the effect on lung remodeling and cell signaling of restoring mitochondrial respiratory electron flow using alternative oxidase (AOX), which bypasses the cytochrome segment of the respiratory chain. AOX attenuated CS-induced lung tissue destruction and loss of function in mice exposed chronically to CS for 9 months. It preserved the cell viability of isolated mouse embryonic fibroblasts treated with CS condensate, limited the induction of apoptosis, and decreased the production of reactive oxygen species (ROS). In contrast, the early-phase inflammatory response induced by acute CS exposure of mouse lung, i.e., infiltration by macrophages and neutrophils and adverse signaling, was unaffected. The use of AOX allowed us to obtain novel pathomechanistic insights into CS-induced cell damage, mitochondrial ROS production, and lung remodeling. Our findings implicate mitochondrial respiratory inhibition as a key pathogenic mechanism of CS toxicity in the lung. We propose AOX as a novel tool to study CS-related lung remodeling and potentially to counteract CS-induced ROS production and cell damage.

AGER expression and alternative splicing in bronchial biopsies of smokers and never smokers

Cigarette smoking is one of the major risk factors for the development of chronic obstructive pulmonary disease (COPD). Evidence is accumulating that Receptor for Advanced Glycation-End products (RAGE)-signaling is a key pathway in the pathophysiology of COPD. To date, it is unknown how smoking affects RAGE expression. In the current study, we investigated the effect of smoking on AGER, the gene encoding RAGE, expression and on alternative splicing of AGER. To this end, we conducted RNA-Seq on bronchial biopsies for asymptomatic smokers (n = 36) and never smokers (n = 40). Total AGER gene expression was accessed using DESeq2, while alternative splicing was investigated by measuring the number of specific split reads spanning exon-exon junctions and the total split reads. One of the major isoforms of RAGE is endogenous soluble (es) RAGE, an anti-inflammatory decoy receptor, making up for approximately 10% of the total amount of soluble (s)RAGE. We found that smokers show decreased total gene expression of AGER in bronchial biopsies, while the relative abundance of the esRAGE isoform is increased. Furthermore, no difference in the serum levels of total sRAGE were observed between smokers and non-smokers. Our data indicates that smoking initiates a protective anti-inflammatory mechanism with decreased expression of the pro-inflammatory gene AGER and increased relative abundance of the anti-inflammatory isoform esRAGE.

The receptor for advanced glycation end-products (RAGE) is an important pattern recognition receptor (PRR) for inflammaging

The receptor for advanced glycation end-products (RAGE) was initially characterized and named for its ability to bind to advanced glycation end-products (AGEs) that form upon the irreversible and non-enzymatic interaction between nucleophiles, such as lysine, and carbonyl compounds, such as reducing sugars. The concentrations of AGEs are known to increase in conditions such as diabetes, as well as during ageing. However, it is now widely accepted that RAGE binds with numerous ligands, many of which can be defined as pathogen-associated molecular patterns (PAMPs) or damage-associated molecular patterns (DAMPs). The interaction between RAGE and its ligands mainly results in a pro-inflammatory response, and can lead to stress events often favouring mitochondrial dysfunction or cellular senescence. Thus, RAGE should be considered as a pattern recognition receptor (PRR), similar to those that regulate innate immunity. Innate immunity itself plays a central role in inflammaging, the chronic low-grade and sterile inflammation that increases with age and is a potentially important contributory factor in ageing. Consequently, and in addition to the age-related accumulation of PAMPs and DAMPs and increases in pro-inflammatory cytokines from senescent cells and damaged cells, PRRs are therefore important in inflammaging. We suggest here that, through its interconnection with immunity, senescence, mitochondrial dysfunction and inflammasome activation, RAGE is a key contributor to inflammaging and that the pro-longevity effects seen upon blocking RAGE, or upon its deletion, are thus the result of reduced inflammaging.

Receptor for advanced glycation end-products modulates lung development and lung sensitivity to hyperoxic injury in newborn mice

The receptor for advanced glycation end-products is mainly expressed in type I alveolar epithelial cells but its importance in lung development and response to neonatal hyperoxia is unclear. Therefore, our study aimed at the analysis of young wildtype and RAGE knockout mice which grew up under normoxic or hyperoxic air conditions for the first 14 days followed by a longer period of normoxic conditions. Lung histology, expression of lung-specific proteins, and respiratory mechanics were analyzed when the mice reached an age of 2 or 4 months. These analyses indicated less but larger and thicker alveoli in RAGE knockout mice, reverse differences in the mRNA and protein amount of pro-surfactant proteins (pro-SP-B, pro-SP-C) and aquaporin-5, and differences in the amount of elastin and CREB, a pro-survival transcription factor, as well as higher lung compliance. Despite this potential disadvantages, RAGE knockout lungs showed less long-term damages mediated by neonatal hyperoxia. In detail, the hyperoxia-mediated reduction in alveoli, enlargement of airspaces, fragmentation of elastic fibers, and increased lung compliance combined with reduced peak airflows was less pronounced in RAGE knockout mice. In conclusion, RAGE supports the alveolarization but makes the lung more susceptible to hyperoxic injury shortly after birth. Blocking RAGE function could still be a helpful tool in reducing hyperoxia-mediated lung pathologies during alveolarization.

RAGE is a Critical Mediator of Pulmonary Oxidative Stress, Alveolar Macrophage Activation and Emphysema in Response to Cigarette Smoke

The receptor for advanced glycation end products (RAGE), a cell membrane receptor, recognizes ligands produced by cigarette smoke (CS) and has been implicated in the pathogenesis of COPD. We demonstrate that deletion or pharmacologic inhibition of RAGE prevents development of CS-induced emphysema. To identify molecular pathways by which RAGE mediates smoking related lung injury we performed unbiased gene expression profiling of alveolar macrophages (AM) obtained from RAGE null and C57BL/6 WT mice exposed to CS for one week or four months. Pathway analysis of RNA expression identified a number of genes integral to the pathogenesis of COPD impacted by the absence of RAGE. Altered expression of antioxidant response genes and lung protein 4-HNE immunostaining suggest attenuated oxidative stress in the RAGE null mice despite comparable CS exposure and lung leukocyte burden as the WT mice. Reduced endoplasmic reticulum stress in response to CS exposure also was observed in the AM from RAGE null mice. These findings provide novel insight into the sources of oxidative stress, macrophage activation, and the pathogenesis of lung disease due to CS exposure.

Inhibition of RAGE Axis Signaling: A Pharmacological Challenge

The Receptor for Advanced Glycation End Products (RAGE) is an important cell surface receptor, which belongs to the IgG super family and is now considered as a pattern recognition receptor. Because of its relevance in many human clinical settings, it is now pursued as a very attractive therapeutic target. However, particular features of this receptor such as a wide repertoire of ligands with different binding domains, the existence of many RAGE variants as well as the presence of cytoplasmatic adaptors leading a diverse signaling, are important limitations in the search for successful pharmacological approaches to inhibit RAGE signaling. Therefore, the present review aimed to display the most promising approaches to inhibit RAGE signaling, and provide an up to date review of progress in this area.

Fine mapping of the major bleomycin-induced pulmonary fibrosis susceptibility locus in mice

Susceptibility to fibrotic lung disease differs among people and among inbred strains of mice exposed to bleomycin where C57BL/6J mice are susceptible and C3H/HeJ mice are spared fibrotic disease. Genetic mapping studies completed in offspring derived from these inbred strains revealed the inheritance of C57BL/6J alleles at loci, including the major locus on chromosome 17, called Blmpf1 bleomycin-induced pulmonary fibrosis 1, to be linked to pulmonary fibrosis in treated mice. In the present study, to reduce the interval of Blmpf1, we bred and phenotyped a panel of subcongenic mice with C3H/HeJ alleles in a C57BL/6J background. Subcongenic mice received bleomycin via osmotic minipump and the fibrosis phenotype was measured histologically. Inheritance of C3H/HeJ alleles from 34.31 to 35.02 Mb was revealed to spare bleomycin-induced pulmonary fibrosis of C57BL/6J mice. From database analysis, 40 protein coding genes have been mapped to this reduced Blmpf1 interval, 18 of which contain C57BL/6J:C3H/HeJ sequence polymorphisms predicted to affect protein structure or to confer allele-dependent expression, and by RT-PCR analysis of lung tissue, we show 6 of these genes to differ in expression between C57BL/6J and C3H/HeJ mice. Genes known to regulate T cell numbers and activation (Btnl family, Notch4) are among the limited list of potential causal variants leading to lung disease in this model and the bronchoalveolar lavage of protected subcongenic mice had fewer lymphocytes, post bleomycin, than did C57BL/6J mice. We conclude that Blmpf1genes contributing to the susceptibility to bleomycin-induced pulmonary fibrosis could alter the adaptive immune response of C57BL/6J mice.

Murine alveolar epithelial cells and their lentivirus-mediated immortalisation

In this study, we describe the isolation and immortalisation of primary murine alveolar epithelial cells (mAEpC), as well as their epithelial differentiation and barrier properties when grown on Transwell® inserts. Like human alveolar epithelial cells (hAEpC), mAEpC transdifferentiate in vitro from an alveolar type II (ATII) phenotype to an ATI-like phenotype and exhibit features of the air-blood barrier, such as the establishment of a thin monolayer with functional tight junctions (TJs). This is demonstrated by the expression of TJ proteins (ZO-1 and occludin) and the development of high transepithelial electrical resistance (TEER), peaking at 1800Ω ·cm². Transport across the air-blood barrier, for general toxicity assessments or preclinical drug development, is typically studied in mice. The aim of this work was the generation of novel immortalised murine lung cell lines, to help meet Three Rs requirements in experimental testing and research. To achieve this goal, we lentivirally transduced mAEpC of two different mouse strains with a library of 33 proliferation-promoting genes. With this immortalisation approach, we obtained two murine alveolar epithelial lentivirus-immortalised (mAELVi) cell lines. Both showed similar TJ protein localisation, but exhibited less prominent barrier properties (TEERmax ~250Ω·cm²) when compared to their primary counterparts. While mAEpC demonstrated their suitability for use in the assessment of paracellular transport rates, mAELVi cells could potentially replace mice for the prediction of acute inhalation toxicity during early ADMET studies.

What do polymorphisms tell us about the mechanisms of COPD?

COPD (chronic obstructive pulmonary disease) is characterized by irreversible lung airflow obstruction. Cigarette smoke is the major risk factor for COPD development. However, only a minority number of smokers develop COPD, and there are substantial variations in lung function among smokers, suggesting that genetic determinants in COPD susceptibility. During the past decade, genome-wide association studies and exome sequencing have been instrumental to identify the genetic determinants of complex traits, including COPD. Focused studies have revealed mechanisms by which genetic variants contribute to COPD and have led to novel insights in COPD pathogenesis. Through functional investigations of causal variants in COPD, from the proteinase-antiproteinase theory to emerging roles of developmental pathways (such as Hedgehog and Wnt pathways) in COPD, we have greatly expanded our understanding on this complex pulmonary disease. In this review, we critically review functional investigations on roles of genetic polymorphisms in COPD, and discuss future challenges and opportunities in discovering novel mechanisms of functional variants.