Promotion of cell adherence and spreading: a novel function of RAGE, the highly selective differentiation marker of human alveolar epithelial type I cells

The receptor for advanced glycation end-products enhances lung epithelial wound repair: An in vitro study

Re-epithelialization of the alveolar surface is a key process of lung alveolar epithelial barrier repair after acute lung injury. The receptor for advanced glycation end-products (RAGE) pathway plays key roles in lung homeostasis, and its involvement in wound repair has been already reported in human bronchial epithelial cells. However, its effects on lung alveolar epithelial repair after injury remain unknown. We investigated whether RAGE stimulation with its ligands high-mobility group box 1 protein (HMGB1) or advanced glycation end-products (AGEs), alone or associated with RAGE inhibition using RAGE antagonist peptide, affects in vitro wound healing in human alveolar epithelial A549 cells. We further asked whether these effects could be associated with changes in cell proliferation and migration. We found that treatment of A549 cells with HMGB1 or AGEs promotes RAGE-dependent wound healing after a scratch assay. In addition, both RAGE ligands increased cell proliferation in a RAGE-dependent manner. Treatment with HMGB1 increased migration of alveolar epithelial cells at 12 h, independently of RAGE, whereas AGEs stimulated migration as measured 48 h after injury in a RAGE-dependent manner. Taken together, these results suggest that RAGE pathway is involved in lung alveolar epithelial wound repair, possibly through enhanced cell migration and proliferation.

Xenobiotica-metabolizing enzymes in the lung of experimental animals, man and in human lung models

The xenobiotic metabolism in the lung, an organ of first entry of xenobiotics into the organism, is crucial for inhaled compounds entering this organ intentionally (e.g. drugs) and unintentionally (e.g. work place and environmental compounds). Additionally, local metabolism by enzymes preferentially or exclusively occurring in the lung is important for favorable or toxic effects of xenobiotics entering the organism also by routes other than by inhalation. The data collected in this review show that generally activities of cytochromes P450 are low in the lung of all investigated species and in vitro models. Other oxidoreductases may turn out to be more important, but are largely not investigated. Phase II enzymes are generally much higher with the exception of UGT glucuronosyltransferases which are generally very low. Insofar as data are available the xenobiotic metabolism in the lung of monkeys comes closed to that in the human lung; however, very few data are available for this comparison. Second best rate the mouse and rat lung, followed by the rabbit. Of the human in vitro model primary cells in culture, such as alveolar macrophages and alveolar type II cells as well as the A549 cell line appear quite acceptable. However, (1) this generalization represents a temporary oversimplification born from the lack of more comparable data; (2) the relative suitability of individual species/models is different for different enzymes; (3) when more data become available, the conclusions derived from these comparisons quite possibly may change.

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.

OCTN2-Mediated Acetyl-l-Carnitine Transport in Human Pulmonary Epithelial Cells In Vitro

The carnitine transporter OCTN2 is associated with asthma and other inflammatory diseases. The aims of this work were (i) to determine carnitine uptake into freshly isolated human alveolar type I (ATI)-like epithelial cells in primary culture, (ii) to compare the kinetics of carnitine uptake between respiratory epithelial in vitro cell models, and (iii) to establish whether any cell line was a suitable model for studies of carnitine transport at the air-blood barrier. Levels of time-dependent [³H]-acetyl-l-carnitine uptake were similar in ATI-like, NCl-H441, and Calu-3 epithelial cells, whereas uptake into A549 cells was ~5 times higher. Uptake inhibition was more pronounced by OCTN2 modulators, such as l-Carnitine and verapamil, in ATI-like primary epithelial cells compared to NCl-H441 and Calu-3 epithelial cells. Our findings suggest that OCTN2 is involved in the cellular uptake of acetyl-l-carnitine at the alveolar epithelium and that none of the tested cell lines are optimal surrogates for primary cells.

Autophagy is required for lung development and morphogenesis

Bronchopulmonary dysplasia (BPD) remains a major respiratory illness in extremely premature infants. The biological mechanisms leading to BPD are not fully understood, although an arrest in lung development has been implicated. The current study aimed to investigate the occurrence of autophagy in the developing mouse lung and its regulatory role in airway branching and terminal sacculi formation. We found 2 windows of epithelial autophagy activation in the developing mouse lung, both resulting from AMPK activation. Inhibition of AMPK-mediated autophagy led to reduced lung branching in vitro. Conditional deletion of beclin 1 (Becn1) in mouse lung epithelial cells (Becn1Epi-KO), either at early (E10.5) or late (E16.5) gestation, resulted in lethal respiratory distress at birth or shortly after. E10.5 Becn1Epi-KO lungs displayed reduced airway branching and sacculi formation accompanied by impaired vascularization, excessive epithelial cell death, reduced mesenchymal thinning of the interstitial walls, and delayed epithelial maturation. E16.5 Becn1Epi-KO lungs had reduced terminal air sac formation and vascularization and delayed distal epithelial differentiation, a pathology similar to that seen in infants with BPD. Taken together, our findings demonstrate that intrinsic autophagy is an important regulator of lung development and morphogenesis and may contribute to the BPD phenotype when impaired.

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.

Evaluation of the AGE/sRAGE Axis in Patients with Multiple Myeloma

Glycative stress influences tumor progression. The aim of the present study was to evaluate the advanced glycation end products/soluble receptor of advanced glycation end products (AGE/sRAGE) axis in patients with multiple myeloma (MM). Blood samples were taken from 19 patients affected by MM and from 16 sex-matched and age-matched healthy subjects. AGE and sRAGE axis were dosed in patients with MM and matched with controls. AGEs were measured by spectrofluorimetric methods. Blood samples for the determination of sRAGE were analyzed by ELISA. AGE levels were significantly reduced in patients with respect to controls. Instead, sRAGE was significantly elevated in patients affected by MM compared to healthy subjects. Moreover, we showed that there was a statistically significant difference in sRAGE according to the heavy and light chain. IgA lambda had significantly higher sRAGE values than IgA kappa, IgG kappa, and IgG Lambda MM patients. From our data emerges the role of the sRAGE/AGE axis in MM. Since AGE is a positive regulator of the activity of RAGE, circulating sRAGE concentrations may reflect RAGE expression and may be raised in parallel with serum AGE concentrations as a counter-system against AGE-caused tissue damage. Serum concentrations of AGE and sRAGE could therefore become potential therapeutic targets.

Effect of soluble cleavage products of important receptors/ligands on efferocytosis: Their role in inflammatory, autoimmune and cardiovascular disease

Efferocytosis, the clearance of apoptotic cells (ACs), is a physiologic, multifaceted and dynamic process and a fundamental mechanism for the preservation of tissue homeostasis by avoiding unwanted inflammation and autoimmune responses through special phagocytic receptors. Defective efferocytosis is associated with several disease states, including cardiovascular disease and impaired immune surveillance, as occurs in cancer and autoimmune disease. A major cause of defective efferocytosis is non-functionality of surface receptors on either the phagocytic cells or the ACs, such as TAM family tyrosine kinase, which turns to a soluble form by cleavage/shedding or alternative splicing. Recently, soluble forms have featured prominently as potential biomarkers, indicative of prognosis and enabling targeted therapy using several commonly employed drugs and inhibitors, such as bleomycin, dexamethasone, statins and some matrix metalloproteinase inhibitors such as TAPI-1 and BB3103. Importantly, to design drug carriers with enhanced circulatory durability, the adaptation of soluble forms of physiological receptors/ligands has been purported. Research has shown that soluble forms are more effective than antibody forms in enabling targeted treatment of certain conditions, such as autoimmune diseases. In this review, we sought to summarize the current knowledge of these soluble products, how they are generated, their interactions, roles, and their potential use as biomarkers in prognosis and treatment related to inflammatory, cardiovascular, and autoimmune diseases.

Danger signals in trauma

This review summarizes a short list of currently discussed trauma-induced danger-associated molecular patterns (DAMP). Due to the bivalent character and often pleiotropic effects of a DAMP, it is difficult to describe its "friend or foe" role in post-traumatic inflammation and regeneration, both systemically as well locally in tissues. DAMP can be used as biomarkers to indicate or monitor disease or injury severity, but also may serve as clinically applicable parameters for better indication and timing of surgery. Due to the inflammatory processes at the local tissue level or the systemic level, the precise role of DAMP is not always clear to define. While in vitro and experimental studies allow for the detection of these biomarkers at the different levels of an organism-cellular, tissue, circulation-this is not always easily transferable to the human setting. Increased knowledge exploring the dual role of DAMP after trauma, and concentrating on their nuclear functions, transcriptional targets, release mechanisms, cellular sources, multiple functions, their interactions and potential therapeutic targeting is warranted.

RAGE may act as a tumour suppressor to regulate lung cancer development

Although the correlation of the RAGE rs2070600 polymorphism and cancer risk has been confirmed, detailed studies with functional and experimental evaluations are lacking. In this study, we first aimed to examine whether this polymorphism is associated with cancer risk based on the latest published data, and consistent with previous meta-analyses, a significant association between the rs2070600 polymorphism and cancer risk was observed (A versus G: OR = 1.25; 95% CI = 1.12-1.40). In additional stratified analyses based on cancer type, rs2070600 was significantly associated with an increased risk of lung cancer (A versus G: OR = 1.20; 95% CI = 1.09-1.33). Moreover, TCGA database showed that the expression level of RAGE was significantly lower in lung cancer tumour tissues than in adjacent non-tumour tissues, which was validated in the GEO database. Additionally, eQTL analysis indicated that the rs2070600 polymorphism may modify the expression level of RAGE in lung squamous cell carcinoma tissues (P = 0.09). Finally, we performed functional experiments in lung cancer cells and preliminarily demonstrated that RAGE may act as a tumour suppressor in lung cancer development. These findings provide evidence that the variant A allele of rs2070600 may decrease the expression of the tumour suppressor gene RAGE, thereby increasing lung cancer risk.

Decreased soluble RAGE in neutrophilic asthma is correlated with disease severity and RAGE G82S variants

The advanced glycosylation end product-specific receptor (RAGE) has been demonstrated to be an important mediator of asthma pathogenesis. The soluble isoform of RAGE (sRAGE) acts as a 'decoy' to sequester RAGE ligands, and thus prevents their binding to the receptor. A number of reports have linked deficiency of sRAGE to the severity and outcomes of various human diseases, and association with RAGE G82S variants. However, whether sRAGE levels are increased or decreased in asthmatic patients is unclear. The aim of the present study was to determine plasma sRAGE levels in different asthma phenotypes and associations of plasma sRAGE levels with RAGE G82S variants. A total of 85 neutrophilic and 109 non‑neutrophilic newly diagnosed asthmatic patients, and 118 healthy controls, were recruited. Plasma sRAGE levels were measured by ELISA analysis. RAGE G82S genotypes were detected using the Sanger sequencing method. Plasma sRAGE levels were decreased in neutrophilic asthmatics (443.67±208.9 pg/ml) and increased in non‑neutrophilic asthmatics (677.63±300.75 pg/ml) compared with healthy controls (550.02±300.83 pg/ml) (P<0.001). Plasma sRAGE levels were positively correlated with FEV1% predicted (FEV1% Pre) (rp=0.258; P=0.023) in neutrophilic asthmatics. The frequency of G82S genotypes was significantly different between neutrophilic and non‑neutrophilic asthmatics (P=0.009). Neutrophilic asthmatics with genotypes A/G or A/A (389.83±150.37 and 264.59±161.74 pg/ml, respectively) had significantly decreased sRAGE levels compared with the G/G genotype (498.64±235.37 pg/ml) (P=0.022). Those with the A/G and A/A genotype (60.14±22.36%) displayed a trend toward lower FEV1% Pre compared with those with the G/G genotype (64.51±27.37%). No significant difference in sRAGE levels or an association with FEV1% Pre was observed between the different genotypes in non‑neutrophilic asthmatics. In conclusion, the results of the present study indicated that plasma sRAGE levels are altered in different asthma inflammatory phenotypes. Plasma sRAGE may be a biomarker of asthma severity and may be associated with G82S gene variants in neutrophilic asthmatics.

Glucagon-like peptide 1: A potential anti-inflammatory pathway in obesity-related asthma

Alterations in arginine metabolism and accelerated formation of advanced glycation end-products (AGEs), crucial mechanisms in obesity-related asthma, can be modulated by glucagon-like peptide 1 (GLP-1). l-arginine dysregulation in obesity promotes inflammation and bronchoconstriction. Prolonged hyperglycemia, dyslipidemia, and oxidative stress leads to production of AGEs, that bind to their receptor (RAGE) further potentiating inflammation. By binding to its widely distributed receptor, GLP-1 blunts the effects of RAGE activation and arginine dysregulation. The GLP-1 pathway, while comprehensively studied in the endocrine and cardiovascular literature, is under-recognized in pulmonary research. Insights into GLP-1 and the lung may lead to novel treatments for obesity-related asthma.

Potential contribution of alveolar epithelial type I cells to pulmonary fibrosis

Pulmonary fibrosis (PF) is characterized by inflammation and fibrosis of the interstitium and destruction of alveolar histoarchitecture ultimately leading to a fatal impairment of lung function. Different concepts describe either a dominant role of inflammatory pathways or a disturbed remodeling of resident cells of the lung parenchyma during fibrogenesis. Further, a combination of both the mechanisms has been postulated. The present review emphasizes the particular involvement of alveolar epithelial type I cells in all these processes, their contribution to innate immune/inflammatory functions and maintenance of proper alveolar barrier functions. Amongst the different inflammatory and repair events the purinergic receptor P2X7, an ATP-gated cationic channel that regulates not only apoptosis, necrosis, autophagy, and NLPR3 inflammosome activation, but also the turnover of diverse tight junction (TJ) and water channel proteins, seems to be essential for the stability of alveolar barrier integrity and for the interaction with protective factors during lung injury.

Alarmin S100A8 Activates Alveolar Epithelial Cells in the Context of Acute Lung Injury in a TLR4-Dependent Manner

Alveolar epithelial cells (AECs) are an essential part of the respiratory barrier in lungs for gas exchange and protection against pathogens. Damage to AECs occurs during lung injury and PAMPs/DAMPs have been shown to activate AECs. However, their interplay as well as the mechanism of AECs’ activation especially by the alarmin S100A8/A9 is unknown. Thus, our aim was to study the mechanism of activation of AECs (type I and type II) by S100A8 and/or lipopolysaccharide (LPS) and to understand the role of endogenous S100A8/A9 in neutrophil recruitment in the lung. For our studies, we modified a previous protocol for isolation and culturing of murine AECs. Next, we stimulated the cells with S100A8 and/or LPS and analyzed cytokine/chemokine release. We also analyzed the contribution of the known S100-receptors TLR4 and RAGE in AEC activation. In a murine model of lung injury, we investigated the role of S100A8/A9 in neutrophil recruitment to lungs. S100A8 activates type I and type II cells in a dose- and time-dependent manner which could be quantified by the release of IL-6, KC, and MCP-1. We here clearly demonstrate that AEC s are activated by S100A8 via a TLR4-dependent pathway. Surprisingly, RAGE, albeit mainly expressed in lung tissue, plays no role. Additionally, we show that S100A8/A9 is an essential factor for neutrophil recruitment to lungs. We, therefore, conclude that S100A8 promotes acute lung injury via Toll-like receptor 4-dependent activation of AECs.

AGER rs2070600 polymorphism elevates neutrophil-lymphocyte ratio and mortality in metastatic lung adenocarcinoma

Background

The receptor for advanced glycation end-product (RAGE) is a multi-ligand receptor involved in inflammation. In the gene encoding RAGE (AGER), there are three well-known polymorphisms; rs2070600, rs1800624, and rs1800625, which potentially increase the risk of lung cancer. Remarkably, AGER rs2070600 polymorphism, which increases ligand-binding affinity, is a potential prognostic factor in non-small cell lung cancer, but the underlying mechanism is unclear. The neutrophil-lymphocyte ratio (NLR) reflects tumor-associated systemic inflammatory conditions; high ratios are associated with poor prognosis in multiple cancers. Additionally, some humoral factors via RAGE-signaling are associated with elevated NLR in cancer patients.

Objectives

Associations of AGER polymorphisms with disease susceptibility, prognosis, and NLR were investigated in Japanese patients with lung adenocarcinoma.

Methods

We included 189 patients with lung adenocarcinoma, 96 of which had distant metastases, and 303 healthy controls. The correlation between AGER polymorphisms (rs2070600, rs1800624, rs1800625) and disease susceptibility and factors elevating the mortality and NLR in patients with metastases were evaluated.

Results

Only the minor allele of rs2070600 was associated with a higher NLR (β = 0.209, p = 0.043) and a poor prognosis (Hazard ratio = 2.06, 95% Confidence interval = 1.09-3.77, p = 0.028) in patients with metastatic disease, independently of background characteristics, including EGFR mutation status. All three polymorphisms were not associated with the risk of lung adenocarcinoma.

Conclusions

The AGER rs2070600 polymorphism was independently associated with systemic inflammation and poor prognosis in patients with metastatic lung adenocarcinoma.

Contribution of myo-inositol oxygenase in AGE:RAGE-mediated renal tubulointerstitial injury in the context of diabetic nephropathy

Advanced glycation end products (AGEs) play a role in pathogenesis of diabetic nephropathy (DN). Myo-inositol oxygenase (MIOX) has been implicated in tubulointerstitial injury in the context of DN. We investigated the effect of AGEs on MIOX expression and delineated mechanisms that lead to tubulointerstitial injury. The status of MIOX, RAGE, and relevant cellular signaling pathways activated following AGE:RAGE interaction was examined in tubular cells and kidneys of AGE-BSA-treated mice. A solid-phase assay revealed an enhanced binding of RAGE with AGE-BSA, AGE-laminin, and AGE-collagen IV. The cells treated with AGE-BSA had increased MIOX activity/expression and promoter activity. This was associated with activation of various signaling kinases of phosphatidylinositol 3-kinase (PI3K)-AKT pathway and increased expression of NF-κB, transforming growth factor (TGF)-β, and fibronectin, which was negated with the treatment of MIOX/RAGE- small interfering (si) RNA. Concomitant with MIOX upregulation, there was an increased generation of reactive oxygen species (ROS), which could be abrogated with MIOX/RAGE- siRNA treatment. The kidneys of mice treated with AGE-BSA had significantly high urinary A/C ratio, upregulation of MIOX, RAGE and NF-κB, along with influx of monocytes into the tubulointerstitium, increased the expression of MCP-1, IL-6, and fibronectin and increased the generation of ROS. Such perturbations were abrogated with the concomitant treatment of inhibitors MIOX or RAGE (d-glucarate and FPS-ZM1). These studies support a role of AGE:RAGE interaction in the activation of PI3K-AKT pathway and upregulation of MIOX, with excessive generation of ROS, increased expression of NF-κB, inflammatory cytokines, TGF-β, and fibronectin. Collectively, these observations highlight the relevance of the biology of MIOX in the contribution toward tubulointerstitial injury in DN.

Receptor for advanced glycation end-products and World Trade Center particulate induced lung function loss: A case-cohort study and murine model of acute particulate exposure

World Trade Center-particulate matter(WTC-PM) exposure and metabolic-risk are associated with WTC-Lung Injury(WTC-LI). The receptor for advanced glycation end-products (RAGE) is most highly expressed in the lung, mediates metabolic risk, and single-nucleotide polymorphisms at the AGER-locus predict forced expiratory volume(FEV). Our objectives were to test the hypotheses that RAGE is a biomarker of WTC-LI in the FDNY-cohort and that loss of RAGE in a murine model would protect against acute PM-induced lung disease. We know from previous work that early intense exposure at the time of the WTC collapse was most predictive of WTC-LI therefore we utilized a murine model of intense acute PM-exposure to determine if loss of RAGE is protective and to identify signaling/cytokine intermediates. This study builds on a continuing effort to identify serum biomarkers that predict the development of WTC-LI. A case-cohort design was used to analyze a focused cohort of male never-smokers with normal pre-9/11 lung function. Odds of developing WTC-LI increased by 1.2, 1.8 and 1.0 in firefighters with soluble RAGE (sRAGE)≥97pg/mL, CRP≥2.4mg/L, and MMP-9≤397ng/mL, respectively, assessed in a multivariate logistic regression model (ROCAUC of 0.72). Wild type(WT) and RAGE-deficient(Ager-/-) mice were exposed to PM or PBS-control by oropharyngeal aspiration. Lung function, airway hyperreactivity, bronchoalveolar lavage, histology, transcription factors and plasma/BAL cytokines were quantified. WT-PM mice had decreased FEV and compliance, and increased airway resistance and methacholine reactivity after 24-hours. Decreased IFN-γ and increased LPA were observed in WT-PM mice; similar findings have been reported for firefighters who eventually develop WTC-LI. In the murine model, lack of RAGE was protective from loss of lung function and airway hyperreactivity and was associated with modulation of MAP kinases. We conclude that in a multivariate adjusted model increased sRAGE is associated with WTC-LI. In our murine model, absence of RAGE mitigated acute deleterious effects of PM and may be a biologically plausible mediator of PM-related lung disease.

Effect of long-term maternal smoking on the offspring's lung health

Maternal smoking during pregnancy contributes to long-term health problems in offspring, especially respiratory disorders that can manifest in either childhood or adulthood. Receptors for advanced glycation end products (RAGE) are multiligand receptors abundantly localized in the lung, capable of responding to by-products of reactive oxygen species and proinflammatory responses. RAGE signaling is a key regulator of inflammation in cigarette smoking-related pulmonary diseases. However, the impact of maternal cigarette smoke exposure on lung RAGE signaling in the offspring is unclear. This study aims to investigate the effect of maternal cigarette smoke exposure (SE), as well as mitochondria-targeted antioxidant [mitoquinone mesylate (MitoQ)] treatment, during pregnancy on the RAGE-mediated signaling pathway in the lung of male offspring. Female Balb/c mice (8 wk) were divided into a sham group (exposed to air), an SE group (exposed to cigarette smoke), and an SE + MQ group (exposed to cigarette smoke with MitoQ supplement from mating). The lungs from male offspring were collected at 13 wk. RAGE and its downstream signaling, including nuclear factor-κB and mitogen-activated protein kinase family consisting of extracellular signal-regulated kinase 1, ERK2, c-JUN NH2-terminal kinase (JNK), and phosphorylated JNK, in the lung were significantly increased in the SE offspring. Mitochondrial antioxidant manganese superoxide dismutase was reduced, whereas IL-1β and oxidative stress response nuclear factor (erythroid-derived 2)-like 2 were significantly increased in the SE offspring. Maternal MitoQ treatment normalized RAGE, IL-1β, and Nrf-2 levels in the SE + MQ offspring. Maternal SE increased RAGE and its signaling elements associated with increased oxidative stress and inflammatory cytokines in offspring lungs, whereas maternal MitoQ treatment can partially normalize these changes.

Maillard reaction in food allergy: Pros and cons

Food allergens have a notable potential to induce various health concerns in susceptible individuals. The majority of allergenic foods are usually subjected to thermal processing prior to their consumption. However, during thermal processing and long storage of foods, Maillard reaction (MR) often takes place. The MR is a non-enzymatic glycation reaction between the carbonyl group of reducing sugars and compounds having free amino groups. MR may sometimes be beneficial by damaging epitope of allergens and reducing allergenic potential, while exacerbation in allergic reactions may also occur due to changes in the motifs of epitopes or neoallergen generation. Apart from these modulations, non-enzymatic glycation can also modify the food protein(s) with various type of advance glycation end products (AGEs) such as Nϵ-(carboxymethyl-)lysine (CML), pentosidine, pyrraline, and methylglyoxal-H1 derived from MR. These Maillard products may act as immunogen by inducing the activation and proliferation of various immune cells. Literature is available to understand pathogenesis of glycation in the context of various diseases but there is hardly any review that can provide a thorough insight on the impact of glycation in food allergy. Therefore, present review explores the pathogenesis with special reference to food allergy caused by non-enzymatic glycation as well as AGEs.

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

The receptor for advanced glycation endproducts (RAGE) is highly expressed in the lung but its physiological functions in this organ is still not completely understood. To determine the contribution of RAGE to physiological functions of the lung, we analyzed pulmonary mechanics and structure of wildtype and RAGE deficient (RAGE^-/-) mice. RAGE deficiency spontaneously resulted in a loss of lung structure shown by an increased mean chord length, increased respiratory system compliance, decreased respiratory system elastance and increased concentrations of serum protein albumin in bronchoalveolar lavage fluids. Pulmonary expression of RAGE was mainly localized on alveolar epithelial cells and alveolar macrophages. Primary murine alveolar epithelial cells isolated from RAGE^-/- mice revealed an altered differentiation and defective barrier formation under in vitro conditions. Stimulation of interferone-y (IFNy)-activated alveolar macrophages deficient for RAGE with Toll-like receptor (TLR) ligands resulted in significantly decreased release of proinflammatory cytokines and chemokines. Exposure to chronic cigarette smoke did not affect emphysema-like changes in lung parenchyma in RAGE^-/- mice. Acute cigarette smoke exposure revealed a modified inflammatory response in RAGE^-/- mice that was characterized by an influx of macrophages and a decreased keratinocyte-derived chemokine (KC) release. Our data suggest that RAGE regulates the differentiation of alveolar epithelial cells and impacts on the development and maintenance of pulmonary structure. In cigarette smoke-induced lung pathology, RAGE mediates inflammation that contributes to lung damage.

All the "RAGE" in lung disease: The receptor for advanced glycation endproducts (RAGE) is a major mediator of pulmonary inflammatory responses

The receptor for advanced glycation endproducts (RAGE) is a pro-inflammatory pattern recognition receptor (PRR) that has been implicated in the pathogenesis of numerous inflammatory diseases. It was discovered in 1992 on endothelial cells and was named for its ability to bind advanced glycation endproducts and promote vascular inflammation in the vessels of patients with diabetes. Further studies revealed that RAGE is most highly expressed in lung tissue and spurred numerous explorations into RAGE's role in the lung. These studies have found that RAGE is an important mediator in allergic airway inflammation (AAI) and asthma, pulmonary fibrosis, lung cancer, chronic obstructive pulmonary disease (COPD), acute lung injury, pneumonia, cystic fibrosis, and bronchopulmonary dysplasia. RAGE has not yet been targeted in the lungs of paediatric or adult clinical populations, but the development of new ways to inhibit RAGE is setting the stage for the emergence of novel therapeutic agents for patients suffering from these pulmonary conditions.

AGER gene polymorphisms and soluble receptor for advanced glycation end product in patients with idiopathic pulmonary fibrosis

BACKGROUND AND OBJECTIVE

The receptor for advanced glycation end product (RAGE) is a multiligand cell-surface receptor abundantly expressed in the lung. RAGE/ligand interaction has been postulated to participate in the pathogenesis of inflammatory diseases, while soluble RAGE (sRAGE) might act as a decoy receptor. A functional polymorphism rs2070600 in the gene coding RAGE (AGER) might modulate its receptor function. The aim of this study was to investigate the association of AGER polymorphisms and circulatory sRAGE with the development and progression of idiopathic pulmonary fibrosis (IPF).

METHODS

This study comprised 87 Japanese patients with IPF and 303 healthy controls. Seven tag polymorphisms in AGER were genotyped and their distributions were compared. We also measured serum sRAGE levels, and evaluated the correlations of sRAGE levels with AGER polymorphisms and the prognosis of the patients with IPF.

RESULTS

The frequency of AGER rs2070600 genotype with minor allele was significantly higher in patients with IPF (OR = 1.84, 95% CI = 1.08-3.10). Additionally, the carriage of the rs2070600 minor allele and the presence of IPF were independently associated with reduced serum levels of sRAGE. Moreover, reduced sRAGE (≤471.8 pg/mL) was related to acute exacerbation of IPF and was an independent predictor of 5-year survival in patients with the disease (hazard ratio (HR) = 7.956, 95% CI = 1.575-53.34).

CONCLUSION

These results suggest a possible association between a functional polymorphism in AGER and IPF disease susceptibility, and indicate a potential prognostic value of circulatory sRAGE.

Increased AGE-RAGE ratio in idiopathic pulmonary fibrosis

BACKGROUND

The abnormal epithelial-mesenchymal restorative capacity in idiopathic pulmonary fibrosis (IPF) has been recently associated with an accelerated aging process as a key point for the altered wound healing. The advanced glycation end-products (AGEs) are the consequence of non-enzymatic reactions between lipid and protein with several oxidants in the aging process. The receptor for AGEs (RAGEs) has been implicated in the lung fibrotic process and the alveolar homeostasis. However, this AGE-RAGE aging pathway has been under-explored in IPF.

METHODS

Lung samples from 16 IPF and 9 control patients were obtained through surgical lung biopsy. Differences in AGEs and RAGE expression between both groups were evaluated by RT-PCR, Western blot and immunohistochemistry. The effect of AGEs on cell viability of primary lung fibrotic fibroblasts and alveolar epithelial cells was assessed. Cell transformation of fibrotic fibroblasts cultured into glycated matrices was evaluated in different experimental conditions.

RESULTS

Our study demonstrates an increase of AGEs together with a decrease of RAGEs in IPF lungs, compared with control samples. Two specific AGEs involved in aging, pentosidine and Nε-Carboxymethyl lysine, were significantly increased in IPF samples. The immunohistochemistry identified higher staining of AGEs related to extracellular matrix (ECM) proteins and the apical surface of the alveolar epithelial cells (AECs) surrounding fibroblast foci in fibrotic lungs. On the other hand, RAGE location was present at the cell membrane of AECs in control lungs, while it was almost missing in pulmonary fibrotic tissue. In addition, in vitro cultures showed that the effect of AGEs on cell viability was different for AECs and fibrotic fibroblasts. AGEs decreased cell viability in AECs, even at low concentration, while fibroblast viability was less affected. Furthermore, fibroblast to myofibroblast transformation could be enhanced by ECM glycation.

CONCLUSIONS

All of these findings suggest a possible role of the increased ratio AGEs-RAGEs in IPF, which could be a relevant accelerating aging tissue reaction in the abnormal wound healing of the lung fibrotic process.

Levels of Soluble Receptor for Advanced Glycation End Products in Bronchoalveolar Lavage Fluid in Patients with Various Inflammatory Lung Diseases

Receptor for advanced glycation end products (RAGE) is a multiligand receptor of S100/calgranulins, high-mobility group box 1, and others, and it is associated with the pathogenesis of various inflammatory and circulatory diseases. The soluble form of RAGE (sRAGE) is a decoy receptor and competitively inhibits membrane-bound RAGE activation. In this study, we measured sRAGE levels in bronchoalveolar lavage fluid (BALF) of 78 patients, including 41 with interstitial pneumonia, 11 with sarcoidosis, 9 with respiratory infection, 7 with ARDS, 5 with lung cancer, and 5 with vasculitis. Among them, sRAGE was detectable in BALF of 73 patients (94%). In patients with ARDS and vasculitis, the sRAGE levels were significantly higher than in the control subjects and those with interstitial pneumonia. The sRAGE levels were positively correlated with total cell counts in BALF and serum levels of surfactant protein-D, lactate dehydrogenase, and C-reactive protein. There was an inverse correlation between PaO2/FIO2 ratio and sRAGE levels. These results indicate that sRAGE in BALF might be considered as a biomarker of lung inflammatory disorders, especially ARDS and vasculitis.

Regulation of Receptor for Advanced Glycation End Products (RAGE) Ectodomain Shedding and Its Role in Cell Function

The receptor for advanced glycation end products (RAGE) is a multiligand transmembrane receptor that can undergo proteolysis at the cell surface to release a soluble ectodomain. Here we observed that ectodomain shedding of RAGE is critical for its role in regulating signaling and cellular function. Ectodomain shedding of both human and mouse RAGE was dependent on ADAM10 activity and induced with chemical activators of shedding (ionomycin, phorbol 12-myristate 13-acetate, and 4-aminophenylmercuric acetate) and endogenous stimuli (serum and RAGE ligands). Ectopic expression of the splice variant of RAGE (RAGE splice variant 4), which is resistant to ectodomain shedding, inhibited RAGE ligand dependent cell signaling, actin cytoskeleton reorganization, cell spreading, and cell migration. We found that blockade of RAGE ligand signaling with soluble RAGE or inhibitors of MAPK or PI3K blocked RAGE-dependent cell migration but did not affect RAGE splice variant 4 cell migration. We finally demonstrated that RAGE function is dependent on secretase activity as ADAM10 and γ-secretase inhibitors blocked RAGE ligand-mediated cell migration. Together, our data suggest that proteolysis of RAGE is critical to mediate signaling and cell function and may therefore emerge as a novel therapeutic target for RAGE-dependent disease states.

Membrane mediated development of the vertebrate blood-gas-barrier

During embryonic lung development, establishment of the gas-exchanging units is guided by epithelial tubes lined by columnar cells. Ultimately, a thin blood-gas barrier (BGB) is established and forms the interface for efficient gas exchange. This thin BGB is achieved through processes, which entail lowering of tight junctions, stretching, and thinning in mammals. In birds the processes are termed peremerecytosis, if they involve cell squeezing and constriction, or secarecytosis, if they entail cutting cells to size. In peremerecytosis, cells constrict at a point below the protruding apical part, resulting in fusion of the opposing membranes and discharge of the aposome, or the cell may be squeezed by the more endowed cognate neighbors. Secarecytosis may entail formation of double membranes below the aposome, subsequent unzipping and discharge of the aposome, or vesicles form below the aposome, fuse in a bilateral manner, and release the aposome. These processes occur within limited developmental windows, and are mediated through cell membranes that appear to be of intracellular in origin. In addition, basement membranes (BM) play pivotal roles in differentiation of the epithelial and endothelial layers of the BGB. Laminins found in the BM are particularly important in the signaling pathways that result in formation of squamous pneumocytes and pulmonary capillaries, the two major components of the BGB. Some information exists on the contribution by BM to BGB formation, but little is known regarding the molecules that drive peremerecytosis, or even the origins and composition of the double and vesicular membranes involved in secarecytosis.

Pathophysiology of chronic rhinosinusitis, pharmaceutical therapy options

Research in immunology has brought great progress in knowledge of inflammatory processes in the last 2 decades, which also has an impact on the upper airways. Our understanding of the pathophysiology of chronic rhinosinusitis developed from a rather mechanistic point of view with a focus on narrow clefts and mucociliary clearance to the appreciation of a complex network of immunological pathways forming the basis of disease. We today differentiate various forms of inflammation, we start to understand complex immune-regulatory networks and the reasons for their failure, and have already developed innovative approaches for therapy for the most severely ill subjects. Due to this new knowledge in inflammation and remodeling processes within mucosal tissue, specifically on the key driving factors, new diagnostic tools and therapeutic approaches for chronic rhinosinusitis have developed; the differentiation of endotypes based on pathophysiological principles will be crucial for the use of innovative therapies, mostly humanized monoclonal antibodies. Several hundred of those antibodies are currently developed for various indications and will impact our specialty as well as pneumology to a great extent.

The HMGB1-RAGE Inflammatory Pathway: Implications for Brain Injury-Induced Pulmonary Dysfunction

SIGNIFICANCE

Deceased patients who have suffered severe traumatic brain injury (TBI) are the largest source of organs for lung transplantation. However, due to severely compromised pulmonary lung function, only one-third of these patients are eligible organ donors, with far fewer capable of donating lungs (∼ 20%). As a result of this organ scarcity, understanding and controlling the pulmonary pathophysiology of potential donors are key to improving the health and long-term success of transplanted lungs.

RECENT ADVANCES

Although the exact mechanism by which TBI produces pulmonary pathophysiology remains unclear, it may be related to the release of damage-associated molecular patterns (DAMPs) from the injured tissue. These heterogeneous, endogenous host molecules can be rapidly released from damaged or dying cells and mediate sterile inflammation following trauma. In this review, we highlight the interaction of the DAMP, high-mobility group box protein 1 (HMGB1) with the receptor for advanced glycation end-products (RAGE), and toll-like receptor 4 (TLR4).

CRITICAL ISSUES

Recently published studies are reviewed, implicating the release of HMGB1 as producing marked changes in pulmonary inflammation and physiology following trauma, followed by an overview of the experimental evidence demonstrating the benefits of blocking the HMGB1-RAGE axis.

FUTURE DIRECTIONS

Targeting the HMGB1 signaling axis may increase the number of lungs available for transplantation and improve long-term benefits for organ recipient patient outcomes.

Antifibrotic properties of receptor for advanced glycation end products in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive chronic interstitial lung disease with poor survival. Previous reports suggested the contributory effect of receptor for advanced glycation end products (RAGE) to the pathogenesis of IPF. But the findings are controversial. The present in vivo study with RAGE null mice, we further confirmed the evidence that lack of RAGE evolves worse bleomycin-induced pulmonary fibrosis compared with control mice. Moreover, RAGE null mice spontaneously developed similar pathogenesis of lung fibrosis via immunohistochemical staining. In addition, we investigated the negative roles of RAGE on epithelial-mesenchymal transition (EMT) indicated by elevated α-smooth muscle actin (α-SMA) and collagen-I (Col-I) deposition in A549 cell treated with transforming growth factor-β (TGF-β), all of which were blocked by sRAGE, a decoy receptor. Furthermore, interacting with the specific ligand as AGE, RAGE blocked TGF-β-induced activation of Smad2, ERK and JNK signals in A549 cells, which were also challenged by sRAGE administration. This present study confirmed an important role of RAGE in vivo and vitro models of pulmonary fibrosis and suggested the therapeutic possibility for pulmonary fibrosis via RAGE regulation.

Receptor for advanced glycation end products expressed on alveolar epithelial cells is the main target for hyperoxia-induced lung injury

BACKGROUND

Receptor for advanced glycation end products (RAGE) is abundantly expressed on alveolar epithelial cells (AECs) and participates in innate immune responses such as apoptosis and inflammation. However, it is unclear whether RAGE-mediated apoptosis of AECs is associated with hyperoxia-induced lung injury.

METHODS

We used wild-type and RAGE-knockout C57BL6/J mice in this study. In addition, we developed bone marrow chimeric mouse models expressing RAGE on hematopoietic or non-hematopoietic cells, including lung parenchymal cells, and compared survival ratios and changes in the permeability of the alveolar-capillary barrier after hyperoxia exposure. Further, we prepared single cell suspensions of lung cells and evaluated the apoptosis of AECs or microvascular endothelial cells (MVECs) by using a combination of antibodies and JC-1 dye. We also examined whether RAGE inhibition decreased hyperoxia-induced apoptosis of human lung epithelial cells in vitro.

RESULTS

After hyperoxia exposure, mice expressing RAGE on lung cells showed lower survival rate and increased alveolar-capillary permeability than mice expressing RAGE on hematopoietic cells. RAGE-expressing AECs showed significantly higher apoptosis than RAGE-knockout AECs after in vivo hyperoxia exposure. The level of hyperoxia-induced apoptosis was not different in MVECs. However, RAGE-null lung epithelial cells showed lower apoptosis than RAGE-expressing cells in vitro.

CONCLUSION

These results indicated that RAGE on AECs mainly contributed to hyperoxia-induced lung injury and alveolar-capillary barrier disruption.

Pulmonary receptor for advanced glycation end-products promotes asthma pathogenesis through IL-33 and accumulation of group 2 innate lymphoid cells

BACKGROUND

Single nucleotide polymorphisms in the human gene for the receptor for advanced glycation end-products (RAGE) are associated with an increased incidence of asthma. RAGE is highly expressed in the lung and has been reported to play a vital role in the pathogenesis of murine models of asthma/allergic airway inflammation (AAI) by promoting expression of the type 2 cytokines IL-5 and IL-13. IL-5 and IL-13 are prominently secreted by group 2 innate lymphoid cells (ILC2s), which are stimulated by the proallergic cytokine IL-33.

OBJECTIVE

We sought to test the hypothesis that pulmonary RAGE is necessary for allergen-induced ILC2 accumulation in the lung.

METHODS

AAI was induced in wild-type and RAGE knockout mice by using IL-33, house dust mite extract, or Alternaria alternata extract. RAGE's lung-specific role in type 2 responses was explored with bone marrow chimeras and induction of gastrointestinal type 2 immune responses.

RESULTS

RAGE was found to drive AAI by promoting IL-33 expression in response to allergen and by coordinating the inflammatory response downstream of IL-33. Absence of RAGE impedes pulmonary accumulation of ILC2s in models of AAI. Bone marrow chimera studies suggest that pulmonary parenchymal, but not hematopoietic, RAGE has a central role in promoting AAI. In contrast to the lung, the absence of RAGE does not affect IL-33-induced ILC2 influx in the spleen, type 2 cytokine production in the peritoneum, or mucus hypersecretion in the gastrointestinal tract.

CONCLUSIONS

For the first time, this study demonstrates that a parenchymal factor, RAGE, mediates lung-specific accumulation of ILC2s.

Organic cation transporter function in different in vitro models of human lung epithelium

Organic cation transporters (OCT) encoded by members of the solute carrier (SLC) 22 family of genes are involved in the disposition of physiological substrates and xenobiotics, including drugs used in the treatment of chronic obstructive lung diseases and asthma. The aim of this work was to identify continuously growing epithelial cell lines that closely mimic the organic cation transport of freshly isolated human alveolar type I-like epithelial cells (ATI) in primary culture, and which consequently, can be utilised as in vitro models for the study of organic cation transport at the air-blood barrier. OCT activity was investigated by measuring [(14)C]-tetraethylammonium (TEA) uptake into monolayers of Calu-3, NCI-H441 and A549 lung epithelial cell lines in comparison to ATI-like cell monolayers in primary culture. Levels of time-dependent TEA uptake were highest in A549 and ATI-like cells. In A549 cells, TEA uptake had a saturable and a non-saturable component with Km=528.5±373.1μM, Vmax=0.3±0.1nmol/min/mg protein and Kd=0.02μl/min/mg protein. TEA uptake into Calu-3 and NCI-H441 cells did not reach saturation within the concentration range studied. RNAi experiments in A549 cells confirmed that TEA uptake was mainly facilitated by OCT1 and OCT2. Co-incubation studies using pharmacological OCT modulators suggested that organic cation uptake pathways share several similarities between ATI-like primary cells and the NCI-H441 cell line, whereas more pronounced differences exist between primary cells and the A549 and Calu-3 cell lines.

Effects of RAGE Gene Polymorphisms on the Risk and Progression of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a common malignancy of the liver, whose heterogeneous incidence reflects genetic variations among individuals in the main risk factors. The receptor for advanced glycosylation endproducts (RAGE) is a multiligand receptor and known to be implicated in various pathogenic conditions, such as diabetes, inflammatory disorder, Alzheimer disease, and cancer. In this study, the impact of RAGE gene polymorphisms on the susceptibility to hepatocarcinogenesis was explored. Four single-nucleotide polymorphisms (SNPs), rs184003 (1704G > T), rs1800624 (-374T > A), rs1800625 (-429T > C), and rs2070600 (Gly82Ser), as well as 1 gene polymorphism of RAGE gene, a 63 bp deletion allele (-407 to -345) were analyzed between 300 cancer-free subjects and 265 HCC cases. We detected a significant association of rs1800625 with the increased risk of HCC (odds ratio [OR], 2.565; 95% confidence interval [CI], 1.492-4.409 and adjusted odds ratio [AOR], 2.568; 95% CI, 1.418-4.653). However, patients who possess at least 1 polymorphic allele of rs1800625 are less prone to develop late-stage (stage III/IV, OR, 0.502; 95% CI, 0.243-1.037; P = 0.059 and AOR, 0.461; 95% CI, 0.219-0.970; P = 0.041) and large-size tumors (OR, 0.398; 95% CI, 0.183-0.864; P = 0.017 and AOR, 0.351; 95% CI, 0.157-0.781; P = 0.010). Furthermore, individuals bearing specific haplotypes of 4 RAGE SNPs tested are more inclined to have HCC. In conclusion, our data suggest a correlation of RAGE gene polymorphism rs1800625 with the early stage of liver tumorigenesis and implicate its protective role in the progression of HCC.

Glycation of the high affinity NGF-receptor and RAGE leads to reduced ligand affinity

AGEs are posttranslational modifications generated by irreversible non-enzymatic crosslinking reactions between sugars and proteins - a reaction referred to as glycation. Glycation, a feature of ageing, can lead to non-degradable and less functional proteins and enzymes and can additionally induce inflammation and further pathophysiological processes such as neurodegeneration. In this study we investigated the influence of glycation on the high affinity NGF-receptor TrkA and the AGE-receptor RAGE. We quantified the binding affinity of the TrkA-receptor and RAGE to their ligands by surface plasmon resonance (SPR) and compared these to the binding affinity after glycation. At the same time, we established a glycation procedure using SPR. We found that glycation of TrkA reduced the affinity to NGF by a factor of three, which could be shown to lead to a reduction of NGF-dependent neurite outgrowth in PC12 cells. Glycation of RAGE reduced binding affinity of AGEs by 10-fold.

Emerging Targets for Therapeutic Development in Diabetes and Its Complications: The RAGE Signaling Pathway

Types 1 and 2 diabetes are on the rise worldwide. Although the treatment of hyperglycemia has benefited from recent advances, aggressive efforts to maintain euglycemia may be fraught with risk, especially in older subjects or in subjects vulnerable to hypoglycemic unawareness. Hence, strategies to prevent and treat the complications of hyperglycemia are essential. In this review we summarize recent updates on the biology of the receptor for advanced glycation endproducts (RAGE) in the pathogenesis of both micro- and macrovascular complications of diabetes, insights from the study of mouse models of obesity and diabetic complications, and from associative studies in human subjects. The study of the mechanisms and consequences of the interaction of the RAGE cytoplasmic domain with the formin, mDia1, in RAGE signal transduction, will be discussed. Lastly, we review the "state-of-the-art" on RAGE-directed therapeutics. Tackling RAGE/mDia1 may identify a novel class of therapeutics preventing diabetes and its complications.

Differential Regulation of Gene Expression of Alveolar Epithelial Cell Markers in Human Lung Adenocarcinoma-Derived A549 Clones

Stem cell therapy appears to be promising for restoring damaged or irreparable lung tissue. However, establishing a simple and reproducible protocol for preparing lung progenitor populations is difficult because the molecular basis for alveolar epithelial cell differentiation is not fully understood. We investigated an in vitro system to analyze the regulatory mechanisms of alveolus-specific gene expression using a human alveolar epithelial type II (ATII) cell line, A549. After cloning A549 subpopulations, each clone was classified into five groups according to cell morphology and marker gene expression. Two clones (B7 and H12) were further analyzed. Under serum-free culture conditions, surfactant protein C (SPC), an ATII marker, was upregulated in both H12 and B7. Aquaporin 5 (AQP5), an ATI marker, was upregulated in H12 and significantly induced in B7. When the RAS/MAPK pathway was inhibited, SPC and thyroid transcription factor-1 (TTF-1) expression levels were enhanced. After treatment with dexamethasone (DEX), 8-bromoadenosine 3′5′-cyclic monophosphate (8-Br-cAMP), 3-isobutyl-1-methylxanthine (IBMX), and keratinocyte growth factor (KGF), surfactant protein B and TTF-1 expression levels were enhanced. We found that A549-derived clones have plasticity in gene expression of alveolar epithelial differentiation markers and could be useful in studying ATII maintenance and differentiation.

Circulating HMGB1 and RAGE as Clinical Biomarkers in Malignant and Autoimmune Diseases

High molecular group box 1 (HMGB1) is a highly conserved member of the HMG-box-family; abundantly expressed in almost all human cells and released in apoptosis; necrosis or by activated immune cells. Once in the extracellular space, HMGB1 can act as a danger associated molecular pattern (DAMP), thus stimulating or inhibiting certain functions of the immune system; depending on the “combinatorial cocktail” of the surrounding milieu. HMGB1 exerts its various functions through binding to a multitude of membrane-bound receptors such as TLR-2; -4 and -9; IL-1 and RAGE (receptor for advanced glycation end products); partly complex-bound with intracellular fragments like nucleosomes. Soluble RAGE in the extracellular space, however, acts as a decoy receptor by binding to HMGB1 and inhibiting its effects. This review aims to outline today’s knowledge of structure, intra- and extracellular functions including mechanisms of release and finally the clinical relevance of HMGB1 and RAGE as clinical biomarkers in therapy monitoring, prediction and prognosis of malignant and autoimmune disease.

Role of receptor for advanced glycation end products in the complication and progression of various types of cancers

BACKGROUND

Receptor for advanced glycation end-products popularly known as RAGE is a cell surface immunoglobulin class of molecule, binds with multiple ligands and therefore considered as a multi-ligand receptor. Use of RAGE deficient mice (RAGE(-/-)) as well as established mouse models pertaining to inflammation-associated carcinogenesis such as that of chemically induced carcinogenesis and colitis associated cancer provides a direct genetic evidence for a likelihood novel role of RAGE in cancer, with respect to its ability to lead cancer cell proliferation and survival. Besides inflammation, interaction of RAGE with its various ligands enhances oxidative stress both in cancerous and noncancerous cells which further complicates the progression of cancers.

SCOPE OF REVIEW

Till date, no single review article has discussed the mechanism of RAGE dependent complication of cancers, particularly the role of RAGE in cancer cell proliferation, angiogenesis, survival and anti-apoptosis needs to be discussed.

MAJOR CONCLUSION

RAGE enhances the number of cancer cells by activating the cell cycle proteins (e.g., cyclin D1), anti-apoptotic proteins (e.g., BCl2), prosurvival (AKT) and autophagic proteins. Role of RAGE has also been detected in formation of new blood vessels (angiogenesis) in the cancer cells and activation of myeloid derived suppressor cells (MDSCs).

GENERAL SIGNIFICANCE

This review article describes the role of RAGE in the complication of various types of cancers and the possible usefulness of RAGE dependent therapy to confront cancers in a stronger magnitude.

The receptor for advanced glycation end products (RAGE) contributes to the progression of emphysema in mice

Several recent clinical studies have implied a role for the receptor for advanced glycation end products (RAGE) and its variants in chronic obstructive pulmonary disease (COPD). In this study we have defined a role for RAGE in the pathogenesis of emphysema in mice. RAGE deficient mice (RAGE-/-) exposed to chronic cigarette smoke were significantly protected from smoke induced emphysema as determined by airspace enlargement and had no significant reduction in lung tissue elastance when compared to their air exposed controls contrary to their wild type littermates. The progression of emphysema has been largely attributed to an increased inflammatory cell-mediated elastolysis. Acute cigarette smoke exposure in RAGE-/- mice revealed an impaired early recruitment of neutrophils, approximately a 6-fold decrease compared to wild type mice. Hence, impaired neutrophil recruitment with continued cigarette smoke exposure reduces elastolysis and consequent emphysema.

Receptor for advanced glycation end-products regulates lung fluid balance via protein kinase C-gp91(phox) signaling to epithelial sodium channels

The receptor for advanced glycation end-products (RAGE), a multiligand member of the Ig family, may play a crucial role in the regulation of lung fluid balance. We quantified soluble RAGE (sRAGE), a decoy isoform, and advanced glycation end-products (AGEs) from the bronchoalveolar lavage fluid of smokers and nonsmokers, and tested the hypothesis that AGEs regulate lung fluid balance through protein kinase C (PKC)-gp91(phox) signaling to the epithelial sodium channel (ENaC). Human bronchoalveolar lavage samples from smokers showed increased AGEs (9.02 ± 3.03 μg versus 2.48 ± 0.53 μg), lower sRAGE (1,205 ± 292 pg/ml versus 1,910 ± 263 pg/ml), and lower volume(s) of epithelial lining fluid (97 ± 14 ml versus 133 ± 17 ml). sRAGE levels did not predict ELF volumes in nonsmokers; however, in smokers, higher volumes of ELF were predicted with higher levels of sRAGE. Single-channel patch clamp analysis of rat alveolar epithelial type 1 cells showed that AGEs increased ENaC activity measured as the product of the number of channels (N) and the open probability (Po) (NPo) from 0.19 ± 0.08 to 0.83 ± 0.22 (P = 0.017) and the subsequent addition of 4-hydroxy-2, 2, 6, 6-tetramethylpiperidine-N-oxyl decreased ENaC NPo to 0.15 ± 0.07 (P = 0.01). In type 2 cells, human AGEs increased ENaC NPo from 0.12 ± 0.05 to 0.53 ± 0.16 (P = 0.025) and the addition of 4-hydroxy-2, 2, 6, 6-tetramethylpiperidine-N-oxyl decreased ENaC NPo to 0.10 ± 0.03 (P = 0.013). Using molecular and biochemical techniques, we observed that inhibition of RAGE and PKC activity attenuated AGE-induced activation of ENaC. AGEs induced phosphorylation of p47(phox) and increased gp91(phox)-dependent reactive oxygen species production, a response that was abrogated with RAGE or PKC inhibition. Finally, tracheal instillation of AGEs promoted clearance of lung fluid, whereas concomitant inhibition of RAGE, PKC, and gp91(phox) abrogated the response.

Effect of chronic hypoxia on RAGE and its soluble forms in lungs and plasma of mice

The receptor for advanced glycation end products (RAGE) is a multi-ligand receptor. Alternative splicing and enzymatic shedding produce soluble forms that protect against damage by ligands including Advanced Glycation End products (AGEs). A link between RAGE and oxygen levels is evident from studies showing RAGE-mediated injury following hyperoxia. The effect of hypoxia on pulmonary RAGE expression and circulating sRAGE levels is however unknown. Therefore mice were exposed to chronic hypoxia for 21 d and expression of RAGE, sheddases in lungs and circulating sRAGE were determined. In addition, accumulation of AGEs in lungs and expression of the AGE detoxifying enzyme GLO1 and receptors were evaluated. In lung tissue gene expression of total RAGE, variants 1 and 3 were elevated in mice exposed to hypoxia, whereas mRAGE and sRAGE protein levels were decreased. In the hypoxic group plasma sRAGE levels were enhanced. Although the levels of pro-ADAM10 were elevated in lungs of hypoxia exposed mice, the relative amount of the active form was decreased and gelatinase activity unaffected. In the lungs, the RAGE ligand HMGB1 was decreased and of the AGEs, only LW-1 was increased by chronic hypoxia. Gene expression of AGE receptors 2 and 3 was significantly upregulated. Chronic hypoxia is associated with downregulation of pulmonary RAGE protein levels, but a relative increase in sRAGE. These alterations might be part of the adaptive and protective response mechanism to chronic hypoxia and are not associated with AGE formation except for the fluorophore LW-1 which emerges as a novel marker of tissue hypoxia.