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

Adhesion of Mesenchymal Stem Cells to Glycated Collagen-Comparative Analysis of Dynamic and Static Conditions

Understanding mesenchymal stem cell (MSC) behavior on glycated collagen is crucial for advancing regenerative medicine and understanding pathological mechanisms in diseases such as diabetes, cancer, and aging. While previous research has demonstrated reduced MSC interaction with glycated collagen under static conditions due to disrupted integrin signaling, these studies did not accurately replicate the dynamic mechanical environment that MSCs encounter in vivo. Here we present a comprehensive investigation comparing adipose-derived MSC (ADMSC) behavior under both dynamic flow conditions and static adhesion, revealing unexpected temporal dynamics and challenging existing paradigms of cell-matrix interactions. Using a sophisticated microfluidic BioFlux system combined with traditional static adhesion assays, we examined ADMSC interactions with native collagen for 1-day glycated (GL1), and 5-day glycated (GL5) samples. Under flow conditions, MSCs demonstrated remarkably rapid attachment-within 3-5 min-contrasting sharply with the classical 2 h static incubation protocol. This rapid adhesion was particularly enhanced on 5-day glycated collagen, though subsequent testing revealed significantly weaker adhesion strength under shear stress compared to native collagen. Static conditions also showed a distinct pattern: increased ADMSC adhesion to glycated samples within the first 30 min, followed by a progressive decrease in adhesion and compromised cell spreading over longer periods. Atomic force microscopy (AFM) analysis revealed significant changes in collagen surface properties upon glycation. These included a substantial reduction in the negative surface charge (from ~800 to 600 mV), altered surface roughness patterns (Rrms varying from 3.0 ± 0.4 nm in native collagen to 7.70 ± 0.6 nm in GL5), and decreased elasticity (Young's modulus dropping from 34.8 ± 5.4 MPa to 2.07 ± 0.3 MPa in GL5). These physical alterations appear to facilitate rapid initial cell attachment while potentially compromising long-term stable adhesion through traditional integrin-mediated mechanisms. This study provides novel insights into the complex dynamics of MSC adhesion to glycated collagen, revealing previously unknown temporal patterns and challenging existing models of cell-matrix interactions. The findings suggest a need for revised approaches in tissue engineering and regenerative medicine, particularly in conditions where glycated collagen is prevalent.

Elucidating the causal associations and mechanisms between circulating immune cells and idiopathic pulmonary fibrosis: new insights from Mendelian randomization and transcriptomics

Background

Growing evidence indicates an association between circulating immune cell phenotypes and idiopathic pulmonary fibrosis (IPF). Although studies have attempted to elucidate the causal relationship between the two, further clarification of the specific mechanisms and causal linkages is warranted.

Objective

We aimed to conduct a two-sample Mendelian randomization (MR) analysis with transcriptomics data analysis to elucidate the causal relationship between circulating immune cells and IPF and to explore potential biomarkers.

Methods

We first explored the bidirectional causal association between IPF and immune cell phenotypes using two-sample MR analysis. Genome-wide association studies data for immune cell phenotype and IPF were obtained from publicly available databases. A standardized instrumental variable screening process was used to select single nucleotide polymorphisms (SNPs) for inclusion in the MR. Five methods represented by IVW were used to assess causal effects. Subsequently, SNP-nearest genes combined with the transcriptomics data of IPF were subjected to multiple bioinformatics analyses such as TIMER, WGCNA, functional enrichment analysis, protein-protein interaction analysis, and ROC to identify IPF biomarkers. Finally, the single-cell RNA sequencing (scRNA-seq) data was used to validate our findings by single-cell analysis.

Results

The MR study identified 27 immune cell phenotypes causally associated with IPF, of which 20 were associated with a decreased risk of developing IPF and 7 were associated with an increased risk. CTSB (AUC=0.98), IL10 (AUC=0.83), and AGER (AUC=0.87) were identified as promising biomarkers of IPF. Single cell analysis showed differences in CD14+ CD16+ monocytes, CD16+ monocytes and Granulocyte-monocyte progenito between the IPF group and the healthy control group. The three hub genes were highly expressed in three immune cell subsets of IPF patients. It underscores the potential feasibility of three genes as biomarkers.

Conclusions

Our study demonstrates the causal associations of specific immune cell phenotypes with IPF through genetic methods and identifies CTSB, IL10, and AGER as biomarkers of IPF through bioinformatics analysis. These findings provide guidance for future clinical and basic research.

Serum soluble isoform of receptor for advanced glycation end product is a predictive biomarker for acute exacerbation of idiopathic pulmonary fibrosis: a German and Japanese cohort study

BACKGROUND

The receptor for advanced glycation end product (RAGE) is a transmembrane receptor accelerating a pro-inflammatory signal. RAGE signalling is promoted by decreased soluble isoform of RAGE (sRAGE), which is a decoy receptor for RAGE ligands, and RAGE SNP rs2070600 minor allele. In Caucasian and Japanese cohorts, low circulatory sRAGE levels and presence of the minor allele are associated with poor survival of idiopathic pulmonary fibrosis (IPF) and increased disease susceptibility to interstitial lung disease, respectively. However, whether sRAGE and RAGE SNP rs2070600 are associated with acute exacerbation of IPF (AE-IPF) is unclear.

METHODS

This retrospective cohort study evaluated the association between the onset of AE-IPF and serum sRAGE levels in 69 German and 102 Japanese patients with IPF. The association of AE-IPF with RAGE SNP rs2070600 in 51 German and 84 Japanese patients, whose DNA samples were stored, was also investigated.

RESULTS

In each cohort, the incidence of AE-IPF was significantly and reproducibly higher in the patients with sRAGE < 467.1 pg/mL. In a pooled exploratory analysis, the incidence of AE-IPF was lowest in the patients with higher sRAGE levels and rs2070600 minor allele, although no significant difference in the incidence was observed between the patients with and without the rs2070600 minor allele.

CONCLUSIONS

Low sRAGE levels were associated with increased incidence of AE-IPF in two independent cohorts of different ethnicities. The combination of rs2070600 and sRAGE levels may stratify patients with IPF for the risk of AE.

Altered expression pattern of immune response-related genes and isoforms in hypersensitivity pneumonitis lung fibroblasts

Hypersensitivity pneumonitis (HP) is an immune-mediated inflammatory interstitial lung disease that may evolve to pulmonary fibrosis, a progressive disorder with a poor prognosis characterized by fibroblast activation and extracellular matrix accumulation. In HP lung fibroblasts, the gene expression of proteins involved in the interaction with the immune response, their isoforms, and how they influence their phenotype have yet to be elucidated. We analyzed the expression and splicing variants of 16 target genes involved in the interaction between HP fibroblasts and immune signaling and evaluated possible correlations with clinical data. The comparison of HP and control fibroblasts revealed distinct gene expression patterns. HP lung fibroblasts displayed an increased expression of IFI27 and PDFGRA and a downregulation of IL17RC and TGFBR3. IFI27 immunoreactive protein was markedly increased in HP lung tissues and normal fibroblasts treated with TGF-β. Furthermore, IFI27 overexpression in normal fibroblasts increased α-SMA and decreased cell number over time. The isoform analysis showed similar expression patterns for most genes, except for the AGER receptor with increased soluble variants relative to full-length AGER in HP fibroblasts. These findings indicate important differences in the expression of genes related to the immune response by HP fibroblasts, highlighting their unique characteristics and providing further insight into a possible profibrotic role of IFI27 in the disease.

New markers in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD), a global healthcare and socioeconomic burden, is a multifaceted respiratory disorder that results in substantial decline in health status and life quality. Acute exacerbations of the disease contribute significantly to increased morbidity and mortality. Consequently, the identification of reliable and effective biomarkers for rapid diagnosis, prediction, and prognosis of exacerbations is imperative. In addition, biomarkers play a crucial role in monitoring responses to therapeutic interventions and exploring innovative treatment strategies. Although established markers such as CRP, fibrinogen and neutrophil count are routinely used, a universal marker is lacking. Fortunately, an increasing number of studies based on next generation analytics have explored potential biomarkers in COPD. Here we review those advances and the need for standardized validation studies in the appropriate clinical setting.

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.

Breath of fresh air: Investigating the link between AGEs, sRAGE, and lung diseases

Advanced glycation end products (AGEs) are compounds formed via non-enzymatic reactions between reducing sugars and amino acids or proteins. AGEs can accumulate in various tissues and organs and have been implicated in the development and progression of various diseases, including lung diseases. The receptor of advanced glycation end products (RAGE) is a receptor that can bind to advanced AGEs and induce several cellular processes such as inflammation and oxidative stress. Several studies have shown that both AGEs and RAGE play a role in the pathogenesis of lung diseases, such as chronic obstructive pulmonary disease, asthma, idiopathic pulmonary fibrosis, cystic fibrosis, and acute lung injury. Moreover, the soluble form of the receptor for advanced glycation end products (sRAGE) has demonstrated its ability to function as a decoy receptor, possessing beneficial characteristics such as anti-inflammatory, antioxidant, and anti-fibrotic properties. These qualities make it an encouraging focus for therapeutic intervention in managing pulmonary disorders. This review highlights the current understanding of the roles of AGEs and (s)RAGE in pulmonary diseases and their potential as biomarkers and therapeutic targets for preventing and treating these pathologies.

The AGE-RAGE axis associates with chronic pulmonary diseases and smoking in the Rotterdam study

BACKGROUND

Chronic obstructive pulmonary disease (COPD) and asthma associate with high morbidity and mortality. High levels of advanced glycation end products (AGEs) were found in tissue and plasma of COPD patients but their role in COPD and asthma is unclear.

METHODS

In the Rotterdam Study (n = 2577), AGEs (by skin autofluorescence (SAF)), FEV1 and lung diffusing capacity (DLCOc and DLCOc /alveolar volume [VA]) were measured. Associations of SAF with asthma, COPD, GOLD stage, and lung function were analyzed using logistic and linear regression adjusted for covariates, followed by interaction and stratification analyses. sRAGE and EN-RAGE associations with COPD prevalence were analyzed by logistic regression.

RESULTS

SAF associated with COPD prevalence (OR = 1.299 [1.060, 1.591]) but not when adjusted for smoking (OR = 1.106 [0.89, 1.363]). SAF associated with FEV1% predicted (β=-3.384 [-4.877, -1.892]), DLCOc (β=-0.212 [-0.327, -0.097]) and GOLD stage (OR = 4.073, p = 0.001, stage 3&4 versus 1). Stratified, the association between SAF and FEV1%predicted was stronger in COPD (β=-6.362 [-9.055, -3.670]) than non-COPD (β=-1.712 [-3.306, -0.118]). Association of SAF with DLCOc and DLCOc/VA were confined to COPD (β=-0.550 [-0.909, -0.191]; β=-0.065 [-0.117, -0.014] respectively). SAF interacted with former smoking and COPD prevalence for associations with lung function. Lower sRAGE and higher EN-RAGE associated with COPD prevalence (OR = 0.575[0.354, 0.931]; OR = 1.778[1.142, 2.768], respectively).

CONCLUSIONS

Associations between SAF, lung function and COPD prevalence were strongly influenced by smoking. SAF associated with COPD severity and its association with lung function was more prominent within COPD. These results fuel further research into interrelations and causality between SAF, smoking and COPD.

TAKE-HOME MESSAGE

Skin AGEs associated with prevalence and severity of COPD and lung function in the general population with a stronger effect in COPD, calling for further research into interrelations and causality between SAF, smoking and COPD.

Predictive biomarkers of disease progression in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic interstitial disease that cannot be cured, and treatment options for IPF are very limited. Early diagnosis, close monitoring of disease progression, and timely treatment are therefore the best options for patients due to the irreversibility of IPF. Effective markers help doctors judge the development and prognosis of disease. Recent research on traditional biomarkers (KL-6, SP-D, MMP-7, TIMPs, CCL18) has provided novel ideas for predicting disease progression and prognosis. Some emerging biomarkers (HE4, GDF15, PRDX4, inflammatory cells, G-CSF) also provide more possibilities for disease prediction. In addition to markers in serum and bronchoalveolar lavage fluid (BALF), some improvements related to the GAP model and chest HRCT also show good predictive ability for disease prognosis.

Inflammatory Cytokine Elaboration Following Secondhand Smoke (SHS) Exposure Is Mediated in Part by RAGE Signaling

The receptor for advanced glycation end products (RAGE) is a key contributor to immune and inflammatory responses in myriad diseases. RAGE is a transmembrane pattern recognition receptor with a special interest in pulmonary anomalies due to its naturally abundant pulmonary expression. Our previous studies demonstrated an inflammatory role for RAGE following acute 30-day exposure to secondhand smoke (SHS), wherein immune cell diapedesis and cytokine/chemokine secretion were accentuated in part via RAGE signaling. However, the chronic inflammatory mechanisms associated with RAGE have yet to be fully elucidated. In this study, we address the impact of long-term SHS exposure on RAGE signaling. RAGE knockout (RKO) and wild-type (WT) mice were exposed to SHS using a nose-only delivery system (Scireq Scientific, Montreal, Canada) for six months. SHS-exposed animals were compared to mice exposed to room air (RA) only. Immunoblotting was used to assess the phospho-AKT and phospho-ERK activation data, and colorimetric high-throughput assays were used to measure NF-kB. Ras activation was measured via ELISAs. Bronchoalveolar lavage fluid (BALF) cellularity was quantified, and a mouse cytokine antibody array was used to screen the secreted cytokines. The phospho-AKT level was decreased, while those of phospho-ERK, NF-kB, and Ras were elevated in both groups of SHS-exposed mice, with the RKO + SHS-exposed mice demonstrating significantly decreased levels of each intermediate compared to those of the WT + SHS-exposed mice. The BALF contained increased levels of diverse pro-inflammatory cytokines in the SHS-exposed WT mice, and diminished secretion was detected in the SHS-exposed RKO mice. These results validate the role for RAGE in the mediation of chronic pulmonary inflammatory responses and suggest ERK signaling as a likely pathway that perpetuates RAGE-dependent inflammation. Additional characterization of RAGE-mediated pulmonary responses to prolonged exposure will provide a valuable insight into the cellular mechanisms of lung diseases such as chronic obstructive pulmonary disease.

Non-apoptotic programmed cell deaths in diabetic pulmonary dysfunction: the new side of advanced glycation end products

Diabetes mellitus (DM) is a chronic metabolic disorder that affects multiple organs and systems, including the pulmonary system. Pulmonary dysfunction in DM patients has been observed and studied for years, but the underlying mechanisms have not been fully understood. In addition to traditional mechanisms such as the production and accumulation of advanced glycation end products (AGEs), angiopathy, tissue glycation, oxidative stress, and systemic inflammation, recent studies have focused on programmed cell deaths (PCDs), especially the non-apoptotic ones, in diabetic pulmonary dysfunction. Non-apoptotic PCDs (NAPCDs) including autophagic cell death, necroptosis, pyroptosis, ferroptosis, and copper-induced cell death have been found to have certain correlations with diabetes and relevant complications. The AGE-AGE receptor (RAGE) axis not only plays an important role in the traditional pathogenesis of diabetes lung disease but also plays an important role in non-apoptotic cell death. In this review, we summarize novel studies about the roles of non-apoptotic PCDs in diabetic pulmonary dysfunction and focus on their interactions with the AGE-RAGE axis.

Human intestine and placenta exhibit tissue-specific expression of RAGE isoforms

The receptor for advanced glycation end products (RAGE) is encoded by AGER, a gene that is subjected to tissue-specific alternative splicing. Splice variants of RAGE in intestine and placenta are unknown and contradictory data concerning RAGE protein expression in these tissues have been published. As a basis for future functional studies, we examined RAGE expression in small intestine, colon and placentas. PCR cloning revealed that full-length RAGE is the only RAGE transcript isoform expressed in placenta. In the small intestine, the major transcript isoform detected was RAGE_v1 encoding the C-terminally truncated soluble receptor. In the colon, both full-length RAGE as well as several splice variants were identified. Four antibodies were used to study protein expression by immunoblotting and were carefully validated. Appropriate controls were essential to avoid misinterpretation of bands caused by non-specific reactivity of antibodies. Only one of four antibodies tested detected full-length RAGE in placenta, whereas no RAGE-specific band was detected in intestinal tissues despite loading >30-fold more intestinal tissue than the positive control, human lung. RAGE expression levels in the placenta were 100-fold lower compared with human lung when analyzed by ELISA, and no significant differences in RAGE expression were detected between healthy placentas and placentas from women with preeclampsia, gestational diabetes mellitus, or fetal growth restriction. We conclude that healthy placental chorionic tissue expresses low levels of full-length RAGE, whereas expression of the tissue-specific intestinal isoforms is below the limit of detection. Low RAGE expression levels in combination with a lack of antibody validation may explain the conflicting published results on RAGE protein expression in intestine and placenta.

Inflammation and coagulation abnormalities via the activation of the HMGB1‑RAGE/NF‑κB and F2/Rho pathways in lung injury induced by acute hypoxia

High‑altitude acute hypoxia is commonly associated with respiratory cardiovascular diseases. The inability to adapt to acute hypoxia may lead to cardiovascular dysfunction, lung injury and even death. Therefore, understanding the molecular basis of the adaptation to high‑altitude acute hypoxia may reveal novel therapeutic approaches with which to counteract the detrimental consequences of hypoxia. In the present study, a high‑altitude environment was simulated in a rat model in order to investigate the role of the high mobility group protein‑1 (HMGB1)/receptor for advanced glycation end products (RAGE)/NF‑κB and F2/Rho signaling pathways in lung injury induced by acute hypoxia. It was found that acute hypoxia caused inflammation through the HMGB1/RAGE/NF‑κB pathway and coagulation dysfunction through the F2/Rho pathway, both of which may be key processes in acute hypoxia‑induced lung injury. The present study provides new insight into the molecular basis of lung injury induced by acute hypoxia. The simultaneous activation of the HMGB1/RAGE/NF‑κB and F2/Rho signaling pathways plays a critical role in hypoxia‑induced inflammatory responses and coagulation abnormalities, and provides a theoretical basis for the development of potential therapeutic strategies.

Prospective epigenome and transcriptome analyses of cord and peripheral blood from preterm infants at risk of bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is a prevalent chronic lung disease of prematurity with limited treatment options. To uncover biomarkers of BPD risk, this study investigated epigenetic and transcriptomic signatures of prematurity at birth and during the neonatal period at day 14 and 28. Peripheral blood DNAs from preterm infants were applied to methylation arrays and cell-type composition was estimated by deconvolution. Covariate-adjusted robust linear regression elucidated BPD- and prolonged oxygen (≥ 14 days) exposure-associated CpGs. RNAs from cord and peripheral blood were sequenced, and differentially expressed genes (DEGs) for BPD or oxygen exposure were determined. Estimated neutrophil-lymphocyte ratios in peripheral blood at day 14 in BPD infants were significantly higher than nonBPD infants, suggesting an heightened inflammatory response in developing BPD. BPD-DEGs in cord blood indicated lymphopoiesis inhibition, altered Th1/Th2 responses, DNA damage, and organ degeneration. On day 14, BPD-associated CpGs were highly enriched in neutrophil activation, infection, and CD4 + T cell quantity, and BPD-DEGs were involved in DNA damage, cellular senescence, T cell homeostasis, and hyper-cytokinesis. On day 28, BPD-associated CpGs along with BPD-DEGs were enriched for phagocytosis, neurological disorder, and nucleotide metabolism. Oxygen supplementation markedly downregulated mitochondrial biogenesis genes and altered CpGs annotated to developmental genes. Prematurity-altered DNA methylation could cause abnormal lymphopoiesis, cellular assembly and cell cycle progression to increase BPD risk. Similar pathways between epigenome and transcriptome networks suggest coordination of the two in dysregulating leukopoiesis, adaptive immunity, and innate immunity. The results provide molecular insights into biomarkers for early detection and prevention of BPD.

RAGE inhibitor TTP488 (Azeliragon) suppresses metastasis in triple-negative breast cancer

Triple-negative breast cancer (TNBC) is a highly aggressive and metastatic cancer subtype, which is generally untreatable once it metastasizes. We hypothesized that interfering with the Receptor for Advanced Glycation End-products (RAGE) signaling with the small molecule RAGE inhibitors (TTP488/Azeliragon and FPS-ZM1) would impair TNBC metastasis and impair fundamental mechanisms underlying tumor progression and metastasis. Both TTP488 and FPS-ZM1 impaired spontaneous and experimental metastasis of TNBC models, with TTP488 reducing metastasis to a greater degree than FPS-ZM1. Transcriptomic analysis of primary xenograft tumor and metastatic tissue revealed high concordance in gene and protein changes with both drugs, with TTP488 showing greater potency against metastatic driver pathways. Phenotypic validation of transcriptomic analysis by functional cell assays revealed that RAGE inhibition impaired TNBC cell adhesion to multiple extracellular matrix proteins (including collagens, laminins, and fibronectin), migration, and invasion. Neither RAGE inhibitor impaired cellular viability, proliferation, or cell cycle in vitro. Proteomic analysis of serum from tumor-bearing mice revealed RAGE inhibition affected metastatic driver mechanisms, including multiple cytokines and growth factors. Further mechanistic studies by phospho-proteomic analysis of tumors revealed RAGE inhibition led to decreased signaling through critical BC metastatic driver mechanisms, including Pyk2, STAT3, and Akt. These results show that TTP488 impairs metastasis of TNBC and further clarifies the signaling and cellular mechanisms through which RAGE mediates metastasis. Importantly, as TTP488 displays a favorable safety profile in human studies, our study provides the rationale for evaluating TTP488 in clinical trials to treat or prevent metastatic TNBC.

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.

RAGE pathways play an important role in regulation of organ fibrosis

Organ fibrosis is a pathological process of fibroblast activation and excessive deposition of extracellular matrix after persistent tissue injury and therefore is a common endpoint of many organ pathologies. Multiple cellular types and soluble mediators, including chemokines, cytokines and non-peptidic factors, are implicated in fibrogenesis and the remodeling of tissue architecture. The molecular basis of the fibrotic process is complex and consists of closely intertwined signaling networks. Research has strived for a better understanding of these pathological mechanisms to potentially reveal novel therapeutic targets for fibrotic diseases. In light of new knowledge, the receptor for advanced glycation end products (RAGE) emerged as an important candidate for the regulation of a wide variety of cellular functions related to fibrosis, including inflammation, cell proliferation, apoptosis, and angiogenesis. RAGE is a pattern recognition receptor that binds a broad range of ligands such as advanced glycation end products, high mobility group box-1, S-100 calcium-binding protein and amyloid beta protein. Although the link between RAGE and fibrosis has been established, the exact mechanisms need be investigated in further studies. The aim of this review is to collect all available information about the intricate function of RAGE and its signaling cascades in the pathogenesis of fibrotic diseases within different organs. In addition, to the major ligands and signaling pathways, we discuss potential strategies for targeting RAGE in fibrosis. We emphasize the functional links between RAGE, inflammation and fibrosis that may guide further studies and the development of improved therapeutic drugs.

Diagnosis of Fibrotic Hypersensitivity Pneumonitis: Is There a Role for Biomarkers?

Hypersensitivity pneumonitis is a complex interstitial lung syndrome and is associated with significant morbimortality, particularly for fibrotic disease. This condition is characterized by sensitization to a specific antigen, whose early identification is associated with improved outcomes. Biomarkers measure objectively biologic processes and may support clinical decisions. These tools evolved to play a crucial role in the diagnosis and management of a wide range of human diseases. This is not the case, however, with hypersensitivity pneumonitis, where there is still great room for research in the path to find consensual diagnostic biomarkers. Gaps in the current evidence include lack of validation, validation against healthy controls alone, small sampling and heterogeneity in diagnostic and classification criteria. Furthermore, discriminatory accuracy is currently limited by overlapping mechanisms of inflammation, damage and fibrogenesis between ILDs. Still, biomarkers such as BAL lymphocyte counts and specific serum IgGs made their way into clinical guidelines, while others including KL-6, SP-D, YKL-40 and apolipoproteins have shown promising results in leading centers and have potential to translate into daily practice. As research proceeds, it is expected that the emergence of novel categories of biomarkers will offer new and thriving tools that could complement those currently available.

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

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

RAGE-Dependent Effect of Exogenous Methylglyoxal Intake on Lung Biomechanics in Mice

Methylglyoxal (MG) is a known highly reactive dicarbonyl and precursor to free radicals and advanced glycation end-products (AGEs). It is discussed to be involved in tissue aging and in the pathogenesis of different degenerative diseases. The effect of long-term oral administration of MG, simulating dietary MG intake, on the lung biomechanics of wild type (WT) and receptor for advanced glycation end-products knockout (RAGE-KO) mice was studied using an ex vivo ventilation system starting at the age of 6 months and after feeding for 6 and 12 months with MG. Our results showed that MG was taken up in the circulation and efficiently excreted with urine. The amount of free urinary MG measured after 12 months of feeding was lowered. After 12 months feeding, a significant airway resistance increase accompanied by a decrease of the maximal inspiratory airflow was observed in WT animals. No effect of MG in lung function of RAGE-KO mice could be detected. Despite the evidence that MG entered the systemic circulation, no MG-derived AGE accumulation was detected in the lung lysates in dependency on MG-feeding. Our data indicate that the short-term feeding of MG has little effect in vivo. Only after long-term treatment was MG secretion reduced, leading to tissue impairment.

Low Level of Advanced Glycation End Products in Serum of Patients with Allergic Rhinitis and Chronic Epstein-Barr Virus Infection at Different Stages of Virus Persistence

Advanced glycation end products (AGEs) are formed in a nonenzymatic reaction of the reducing sugars with amino groups of proteins, lipids, and nucleic acids of different tissues and body fluids. A relatively small number of studies have been conducted on the role of AGEs in allergic inflammation. In this study, patients with allergic rhinitis (AR) were examined for the presence of Epstein-Barr virus and the content of fluorescent and nonfluorescent AGEs. We have also determined the level of a unique epitope (AGE10) which was recently identified in human serum using monoclonal antibodies against synthetic melibiose-derived AGE (MAGE). The levels of AGE10 determined with an immunoenzymatic method revealed no significant difference in the patients' blood with intermittent AR and chronic EBV persistence in the active and latent phases. It has been shown that there is a statistically significantly smaller amount of AGEs and pentosidine in groups of patients, both with and without viremia, than in healthy subjects. In turn, higher levels of immune complexes than of AGE10 were detected in the groups of patients, in contrast to the control group, which had lower levels of complexes than AGE10 concentration. In patients with active infection, there is even more complexes than of noncomplexed AGE10 antigen. The lower level of AGE in allergic rhinitis patient sera may also be due, besides complexes, to allergic inflammation continuously activating the cells, which effectively remove glycation products from the body.

Effects of RAGE Deletion on the Cardiac Transcriptome during Aging

Cardiac aging is characterized by increased cardiomyocyte hypertrophy, myocardial stiffness, and fibrosis, which enhance cardiovascular risk. The receptor for advanced glycation end-products (RAGE) is involved in several age-related diseases. RAGE knockout (Rage−/−) mice show an acceleration of cardiac dimension changes and interstitial fibrosis with aging. This study identifies the age-associated cardiac gene expression signature induced by RAGE deletion. We analyzed the left ventricle transcriptome of 2.5-(Young), 12-(Middle age, MA), and 21-(Old) months-old female Rage−/− and C57BL/6N (WT) mice. By comparing Young, MA, and Old Rage−/− versus age-matched WT mice, we identified 122, 192, and 12 differently expressed genes, respectively. Functional inference analysis showed that RAGE deletion is associated with: (i) down-regulation of genes involved in antigen processing and presentation of exogenous antigen, adaptive immune response, and cellular responses to interferon beta and gamma in Young animals; (ii) up-regulation of genes related to fatty acid oxidation, cardiac structure remodeling and cellular response to hypoxia in MA mice; (iii) up-regulation of few genes belonging to complement activation and triglyceride biosynthetic process in Old animals. Our findings show that the age-dependent cardiac phenotype of Rage−/− mice is associated with alterations of genes related to adaptive immunity and cardiac stress pathways.

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.

Epigenome-wide association study of bronchopulmonary dysplasia in preterm infants: results from the discovery-BPD program

BACKGROUND

Bronchopulmonary dysplasia (BPD) is a lung disease in premature infants caused by therapeutic oxygen supplemental and characterized by impaired pulmonary development which persists into later life. While advances in neonatal care have improved survival rates of premature infants, cases of BPD have been increasing with limited therapeutic options for prevention and treatment. This study was designed to explore the relationship between gestational age (GA), birth weight, and estimated blood cell-type composition in premature infants and to elucidate early epigenetic biomarkers associated with BPD.

METHODS

Cord blood DNA from preterm neonates that went on to develop BPD (n = 14) or not (non-BPD, n = 93) was applied to Illumina 450 K methylation arrays. Blood cell-type compositions were estimated using DNA methylation profiles. Multivariable robust regression analysis elucidated CpGs associated with BPD risk. cDNA microarray analysis of cord blood RNA identified differentially expressed genes in neonates who later developed BPD.

RESULTS

The development of BPD and the need for oxygen supplementation were strongly associated with GA (BPD, p < 1.0E-04; O2 supplementation, p < 1.0E-09) and birth weight (BPD, p < 1.0E-02; O2 supplementation, p < 1.0E-07). The estimated nucleated red blood cell (NRBC) percent was negatively associated with birth weight and GA, positively associated with hypomethylation of the tobacco smoke exposure biomarker cg05575921, and high-NRBC blood samples displayed a hypomethylation profile. Epigenome-wide association study (EWAS) identified 38 (Bonferroni) and 275 (false discovery rate 1%) differentially methylated CpGs associated with BPD. BPD-associated CpGs in cord blood were enriched for lung maturation and hematopoiesis pathways. Stochastic epigenetic mutation burden at birth was significantly elevated among those who developed BPD (adjusted p = 0.02). Transcriptome changes in cord blood cells reflected cell cycle, development, and pulmonary disorder events in BPD.

CONCLUSIONS

While results must be interpreted with caution because of the small size of this study, NRBC content strongly impacted DNA methylation profiles in preterm cord blood and EWAS analysis revealed potential insights into biological pathways involved in BPD pathogenesis.

Comprehensive epigenomic profiling of human alveolar epithelial differentiation identifies key epigenetic states and transcription factor co-regulatory networks for maintenance of distal lung identity

BACKGROUND

Disruption of alveolar epithelial cell (AEC) differentiation is implicated in distal lung diseases such as chronic obstructive pulmonary disease, idiopathic pulmonary fibrosis, and lung adenocarcinoma that impact morbidity and mortality worldwide. Elucidating underlying disease pathogenesis requires a mechanistic molecular understanding of AEC differentiation. Previous studies have focused on changes of individual transcription factors, and to date no study has comprehensively characterized the dynamic, global epigenomic alterations that facilitate this critical differentiation process in humans.

RESULTS

We comprehensively profiled the epigenomic states of human AECs during type 2 to type 1-like cell differentiation, including the methylome and chromatin functional domains, and integrated this with transcriptome-wide RNA expression data. Enhancer regions were drastically altered during AEC differentiation. Transcription factor binding analysis within enhancer regions revealed diverse interactive networks with enrichment for many transcription factors, including NKX2-1 and FOXA family members, as well as transcription factors with less well characterized roles in AEC differentiation, such as members of the MEF2, TEAD, and AP1 families. Additionally, associations among transcription factors changed during differentiation, implicating a complex network of heterotrimeric complex switching in driving differentiation. Integration of AEC enhancer states with the catalog of enhancer elements in the Roadmap Epigenomics Mapping Consortium and Encyclopedia of DNA Elements (ENCODE) revealed that AECs have similar epigenomic structures to other profiled epithelial cell types, including human mammary epithelial cells (HMECs), with NKX2-1 serving as a distinguishing feature of distal lung differentiation.

CONCLUSIONS

Enhancer regions are hotspots of epigenomic alteration that regulate AEC differentiation. Furthermore, the differentiation process is regulated by dynamic networks of transcription factors acting in concert, rather than individually. These findings provide a roadmap for understanding the relationship between disruption of the epigenetic state during AEC differentiation and development of lung diseases that may be therapeutically amenable.

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.

In vitro and ex vivo models in inhalation biopharmaceutical research - advances, challenges and future perspectives

Oral inhalation results in pulmonary drug targeting and thereby reduces systemic side effects, making it the preferred means of drug delivery for the treatment of respiratory disorders such as asthma, chronic obstructive pulmonary disease or cystic fibrosis. In addition, the high alveolar surface area, relatively low enzymatic activity and rich blood supply of the distal airspaces offer a promising pathway to the systemic circulation. This is particularly advantageous when a rapid onset of pharmacological action is desired or when the drug is suffering from stability issues or poor biopharmaceutical performance following oral administration. Several cell and tissue-based in vitro and ex vivo models have been developed over the years, with the intention to realistically mimic pulmonary biological barriers. It is the aim of this review to critically discuss the available models regarding their advantages and limitations and to elaborate further which biopharmaceutical questions can and cannot be answered using the existing models.

YAP regulates alveolar epithelial cell differentiation and AGER via NFIB/KLF5/NKX2-1

Ventilation is dependent upon pulmonary alveoli lined by two major epithelial cell types, alveolar type-1 (AT1) and 2 (AT2) cells. AT1 cells mediate gas exchange while AT2 cells synthesize and secrete pulmonary surfactants and serve as progenitor cells which repair the alveoli. We developed transgenic mice in which YAP was activated or deleted to determine its roles in alveolar epithelial cell differentiation. Postnatal YAP activation increased epithelial cell proliferation, increased AT1 cell numbers, and caused indeterminate differentiation of subsets of alveolar cells expressing atypical genes normally restricted to airway epithelial cells. YAP deletion increased expression of genes associated with mature AT2 cells. YAP activation enhanced DNA accessibility in promoters of transcription factors and motif enrichment analysis predicted target genes associated with alveolar cell differentiation. YAP participated with KLF5, NFIB, and NKX2-1 to regulate AGER. YAP plays a central role in a transcriptional network that regulates alveolar epithelial differentiation.

HMGA1, Moonlighting Protein Function, and Cellular Real Estate: Location, Location, Location!

The gene encoding the High Mobility Group A1 (HMGA1) chromatin remodeling protein is upregulated in diverse cancers where high levels portend adverse clinical outcomes. Until recently, HMGA1 was assumed to be a nuclear protein exerting its role in cancer by transcriptionally modulating gene expression and downstream signaling pathways. However, the discovery of an extracellular HMGA1-RAGE autocrine loop in invasive triple-negative breast cancer (TNBC) cell lines implicates HMGA1 as a "moonlighting protein" with different functions depending upon cellular location. Here, we review the role of HMGA1, not only as a chromatin regulator in cancer and stem cells, but also as a potential secreted factor that drives tumor progression. Prior work found that HMGA1 is secreted from TNBC cell lines where it signals through the receptor for advanced glycation end products (RAGE) to foster phenotypes involved in tumor invasion and metastatic progression. Studies in primary TNBC tumors also suggest that HMGA1 secretion associates with distant metastasis in TNBC. Given the therapeutic potential to target extracellular proteins, further work to confirm this role in other contexts is warranted. Indeed, crosstalk between nuclear and secreted HMGA1 could change our understanding of tumor development and reveal novel therapeutic opportunities relevant to diverse human cancers overexpressing HMGA1.

The perplexing role of RAGE in pulmonary fibrosis: causality or casualty?

Idiopathic pulmonary fibrosis (IPF) is a progressive and fatal lung disease in which most patients die within 3 years of diagnosis. With an unknown etiology, IPF results in progressive fibrosis of the lung parenchyma, diminishing normal lung function, which results in respiratory failure, and eventually, death. While few therapies are available to reduce disease progression, patients continue to advance toward respiratory failure, leaving lung transplantation the only viable option for survival. As incidence and mortality rates steadily increase, the need for novel therapeutics is imperative. The receptor for advanced glycation endproducts (RAGE) is most highly expressed in the lungs and plays a significant role in a number of chronic lung diseases. RAGE has long been linked to IPF; however, confounding data from both human and experimental studies have left an incomplete and perplexing story. This review examines the present understanding of the role of RAGE in human and experimental models of IPF, drawing parallels to recent advances in RAGE biology. Moreover, this review discusses the role of RAGE in lung injury response, type 2 immunity, and cellular senescence, and how such mechanisms may relate to RAGE as both a biomarker of disease progression and potential therapeutic target in IPF.The reviews of this paper are available via the supplemental material section.

Intravenous Delivery of Lung-Targeted Nanofibers for Pulmonary Hypertension in Mice

Pulmonary hypertension is a highly morbid disease with no cure. Available treatments are limited by systemic adverse effects due to non-specific biodistribution. Self-assembled peptide amphiphile (PA) nanofibers are biocompatible nanomaterials that can be modified to recognize specific biological markers to provide targeted drug delivery and reduce off-target toxicity. Here, PA nanofibers that target the angiotensin I-converting enzyme and the receptor for advanced glycation end-products (RAGE) are developed, as both proteins are overexpressed in the lung with pulmonary hypertension. It is demonstrated that intravenous delivery of RAGE-targeted nanofibers containing the targeting epitope LVFFAED (LVFF) significantly accumulated within the lung in a chronic hypoxia-induced pulmonary hypertension mouse model. Using 3D light sheet fluorescence microscopy, it is shown that LVFF nanofiber localization is specific to the diseased pulmonary tissue with immunofluorescence analysis demonstrating colocalization of the targeted nanofiber to RAGE in the hypoxic lung. Furthermore, biodistribution studies show that significantly more LVFF nanofibers localized to the lung compared to major off-target organs. Targeted nanofibers are retained within the pulmonary tissue for 24 h after injection. Collectively, these data demonstrate the potential of a RAGE-targeted nanomaterial as a drug delivery platform to treat pulmonary hypertension.

Short Duration Alagebrium Chloride Therapy Prediabetes Does Not Inhibit Progression to Autoimmune Diabetes in an Experimental Model

Mechanisms by which advanced glycation end products (AGEs) contribute to type 1 diabetes (T1D) pathogenesis are poorly understood. Since life-long pharmacotherapy with alagebrium chloride (ALT) slows progression to experimental T1D, we hypothesized that acute ALT therapy delivered prediabetes, may be effective. However, in female, non-obese diabetic (NODShiLt) mice, ALT administered prediabetes (day 50-100) did not protect against experimental T1D. ALT did not decrease circulating AGEs or their precursors. Despite this, pancreatic β-cell function was improved, and insulitis and pancreatic CD45.1+ cell infiltration was reduced. Lymphoid tissues were unaffected. ALT pre-treatment, prior to transfer of primed GC98 CD8+ T cell receptor transgenic T cells, reduced blood glucose concentrations and delayed diabetes, suggesting islet effects rather than immune modulation by ALT. Indeed, ALT did not reduce interferon-γ production by leukocytes from ovalbumin-pre-immunised NODShiLt mice and NODscid recipients given diabetogenic ALT treated NOD splenocytes were not protected against T1D. To elucidate β-cell effects, NOD-derived MIN6N8 β-cell major histocompatibility complex (MHC) Class Ia surface antigens were examined using immunopeptidomics. Overall, no major changes in the immunopeptidome were observed during the various treatments with all peptides exhibiting allele specific consensus binding motifs. As expected, longer MHC Class Ia peptides were captured bound to H-2Db than H-2Kb under all conditions. Moreover, more 10-12 mer peptides were isolated from H-2Db after AGE modified bovine serum albumin (AGE-BSA) treatment, compared with bovine serum albumin (BSA) or AGE-BSA+ALT treatment. Proteomics of MIN6N8 cells showed enrichment of processes associated with catabolism, the immune system, cell cycling and presynaptic endocytosis with AGE-BSA compared with BSA treatments. These data show that short-term ALT intervention, given prediabetes, does not arrest experimental T1D but transiently impacts β-cell function.

Soluble Receptor for Advanced Glycation End-products regulates age-associated Cardiac Fibrosis

Myocardial aging increases the cardiovascular risk in the elderly. The Receptor for Advanced Glycation End-products (RAGE) is involved in age-related disorders. The soluble isoform (sRAGE) acts as a scavenger blocking the membrane-bound receptor activation. This study aims at investigating RAGE contribution to age-related cardiac remodeling. We analyzed the cardiac function of three different age groups of female Rage-/- and C57BL/6N (WT) mice: 2.5- (Young), 12- (Middle-age, MA) and 21-months (Old) old. While aging, Rage-/- mice displayed an increase in left ventricle (LV) dimensions compared to age-matched WT animals, with the main differences observed in the MA groups. Rage-/- mice showed higher fibrosis and a larger number of α-Smooth Muscle Actin (SMA)+ cells with age, along with increased expression of pro-fibrotic Transforming Growth Factor (TGF)-β1 pathway components. RAGE isoforms were undetectable in LV of WT mice, nevertheless, circulating sRAGE declined with aging and inversely associated with LV diastolic dimensions. Human cardiac fibroblasts stimulated with sRAGE exhibited a reduction in proliferation, pro-fibrotic proteins and TGF-beta Receptor 1 (TGFbR1) expression and Smad2-3 activation. Finally, sRAGE administration to MA WT animals reduced cardiac fibrosis. Hence, our work shows that RAGE associates with age-dependent myocardial changes and indicates sRAGE as an inhibitor of cardiac fibroblasts differentiation and age-dependent cardiac fibrosis.

Collagen Biosynthesis, Processing, and Maturation in Lung Ageing

In addition to providing a macromolecular scaffold, the extracellular matrix (ECM) is a critical regulator of cell function by virtue of specific physical, biochemical, and mechanical properties. Collagen is the main ECM component and hence plays an essential role in the pathogenesis and progression of chronic lung disease. It is well-established that many chronic lung diseases, e.g., chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis (IPF) primarily manifest in the elderly, suggesting increased susceptibility of the aged lung or accumulated alterations in lung structure over time that favour disease. Here, we review the main steps of collagen biosynthesis, processing, and turnover and summarise what is currently known about alterations upon lung ageing, including changes in collagen composition, modification, and crosslinking. Recent proteomic data on mouse lung ageing indicates that, while the ER-resident machinery of collagen biosynthesis, modification and triple helix formation appears largely unchanged, there are specific changes in levels of type IV and type VI as well as the two fibril-associated collagens with interrupted triple helices (FACIT), namely type XIV and type XVI collagens. In addition, levels of the extracellular collagen crosslinking enzyme lysyl oxidase are decreased, indicating less enzymatically mediated collagen crosslinking upon ageing. The latter contrasts with the ageing-associated increase in collagen crosslinking by advanced glycation endproducts (AGEs), a result of spontaneous reactions of protein amino groups with reactive carbonyls, e.g., from monosaccharides or reactive dicarbonyls like methylglyoxal. Given the slow turnover of extracellular collagen such modifications accumulate even more in ageing tissues. In summary, the collective evidence points mainly toward age-induced alterations in collagen composition and drastic changes in the molecular nature of collagen crosslinks. Future work addressing the consequences of these changes may provide important clues for prevention of lung disease and for lung bioengineering and ultimately pave the way to novel targeted approaches in lung regenerative medicine.

Targeting RAGE to prevent SARS-CoV-2-mediated multiple organ failure: Hypotheses and perspectives

A novel infectious disease (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), was detected in December 2019 and declared as a global pandemic by the World Health. Approximately 15% of patients with COVID-19 progress to severe pneumonia and eventually develop acute respiratory distress syndrome (ARDS), septic shock and/or multiple organ failure with high morbidity and mortality. Evidence points towards a determinant pathogenic role of members of the renin-angiotensin system (RAS) in mediating the susceptibility, infection, inflammatory response and parenchymal injury in lungs and other organs of COVID-19 patients. The receptor for advanced glycation end-products (RAGE), a member of the immunoglobulin superfamily, has important roles in pulmonary pathological states, including fibrosis, pneumonia and ARDS. RAGE overexpression/hyperactivation is essential to the deleterious effects of RAS in several pathological processes, including hypertension, chronic kidney and cardiovascular diseases, and diabetes, all of which are major comorbidities of SARS-CoV-2 infection. We propose RAGE as an additional molecular target in COVID-19 patients for ameliorating the multi-organ pathology induced by the virus and improving survival, also in the perspective of future infections by other coronaviruses.

The axis of the receptor for advanced glycation endproducts in asthma and allergic airway disease

Asthma is a generalized term that describes a scope of distinct pathologic phenotypes of variable severity, which share a common complication of reversible airflow obstruction. Asthma is estimated to affect almost 400 million people worldwide, and nearly ten percent of asthmatics have what is considered "severe" disease. The majority of moderate to severe asthmatics present with a "type 2-high" (T2-hi) phenotypic signature, which pathologically is driven by the type 2 cytokines Interleukin-(IL)-4, IL-5, and IL-13. However, "type 2-low" (T2-lo) phenotypic signatures are often associated with more severe, steroid-refractory neutrophilic asthma. A wide range of clinical and experimental studies have found that the receptor for advanced glycation endproducts (RAGE) plays a significant role in the pathogenesis of asthma and allergic airway disease (AAD). Current experimental data indicates that RAGE is a critical mediator of the type 2 inflammatory reactions which drive the development of T2-hi AAD. However, clinical studies demonstrate that increased RAGE ligands and signaling strongly correlate with asthma severity, especially in severe neutrophilic asthma. This review presents an overview of the current understandings of RAGE in asthma pathogenesis, its role as a biomarker of disease, and future implications for mechanistic studies, and potential therapeutic intervention strategies.

Development of novel nanofibers targeted to smoke-injured lungs

Smoke inhalation injury is associated with significant mortality and current therapies remain supportive. The purpose of our study was to identify proteins upregulated in the lung after smoke inhalation injury and develop peptide amphiphile nanofibers that target these proteins. We hypothesize that nanofibers targeted to angiotensin-converting enzyme or receptor for advanced glycation end products will localize to smoke-injured lungs.

METHODS

Five targeting sequences were incorporated into peptide amphiphile monomers methodically to optimize nanofiber formation. Nanofiber formation was assessed by conventional transmission electron microscopy. Rats received 8 min of wood smoke. Levels of angiotensin-converting enzyme and receptor for advanced glycation end products were evaluated by immunofluorescence. Rats received the targeted nanofiber 23 h after injury via tail vein injection. Nanofiber localization was determined by fluorescence quantification.

RESULTS

Peptide amphiphile purity (>95%) and nanofiber formation were confirmed. Target proteins were increased in smoke inhalation versus sham (p < 0.001). After smoke inhalation and injection of targeted nanofibers, we found a 10-fold increase in angiotensin-converting enzyme-targeted nanofiber localization to lung (p < 0.001) versus sham with minimal localization of non-targeted nanofiber (p < 0.001).

CONCLUSIONS

We synthesized, characterized, and evaluated systemically delivered targeted nanofibers that localized to the site of smoke inhalation injury in vivo. Angiotensin-converting enzyme-targeted nanofibers serve as the foundation for developing a novel nanotherapeutic that treats smoke inhalation lung injury.

Glycated Albumin Triggers an Inflammatory Response in the Human Airway Epithelium and Causes an Increase in Ciliary Beat Frequency

The role of inflammation in airway epithelial cells and its regulation are important in several respiratory diseases. When disease is present, the barrier between the pulmonary circulation and the airway epithelium is damaged, allowing serum proteins to enter the airways. We identified that human glycated albumin (GA) is a molecule in human serum that triggers an inflammatory response in human airway epithelial cultures. We observed that single-donor human serum induced IL-8 secretion from primary human airway epithelial cells and from a cystic fibrosis airway cell line (CF1-16) in a dose-dependent manner. IL-8 secretion from airway epithelial cells was time dependent and rapidly increased in the first 4 h of incubation. Stimulation with GA promoted epithelial cells to secrete IL-8, and this increase was blocked by the anti-GA antibody. The IL-8 secretion induced by serum GA was 10–50-fold more potent than TNF_α or LPS stimulation. GA also has a functional effect on airway epithelial cells in vitro, increasing ciliary beat frequency. Our results demonstrate that the serum molecule GA is pro-inflammatory and triggers host defense responses including increases in IL-8 secretion and ciliary beat frequency in the human airway epithelium. Although the binding site of GA has not yet been described, it is possible that GA could bind to the receptor for advanced glycated end products (RAGE), known to be expressed in the airway epithelium; however, further experiments are needed to identify the mechanism involved. We highlight a possible role for GA in airway inflammation.

Regulatory mechanisms of neutrophil migration from the circulation to the airspace

The neutrophil, a short-lived effector leukocyte of the innate immune system best known for its proteases and other degradative cargo, has unique, reciprocal physiological interactions with the lung. During health, large numbers of ‘marginated’ neutrophils reside within the pulmonary vasculature, where they patrol the endothelial surface for pathogens and complete their life cycle. Upon respiratory infection, rapid and sustained recruitment of neutrophils through the endothelial barrier, across the extravascular pulmonary interstitium, and again through the respiratory epithelium into the airspace lumen, is required for pathogen killing. Overexuberant neutrophil trafficking to the lung, however, causes bystander tissue injury and underlies several acute and chronic lung diseases. Due in part to the unique architecture of the lung’s capillary network, the neutrophil follows a microanatomic passage into the distal airspace unlike that observed in other end-organs that it infiltrates. Several of the regulatory mechanisms underlying the stepwise recruitment of circulating neutrophils to the infected lung have been defined over the past few decades; however, fundamental questions remain. In this article, we provide an updated review and perspective on emerging roles for the neutrophil in lung biology, on the molecular mechanisms that control the trafficking of neutrophils to the lung, and on past and ongoing efforts to design therapeutics to intervene upon pulmonary neutrophilia in lung disease.

Advanced glycation end products and their adverse effects: The role of autophagy

The critical roles played by advanced glycation endproducts (AGEs) accumulation in diabetes and diabetic complications have gained intense recognition. AGEs interfere with the normal functioning of almost every organ with multiple actions like apoptosis, inflammation, protein dysfunction, mitochondrial dysfunction, and oxidative stress. However, the development of a potential treatment strategy is yet to be established. Autophagy is an evolutionarily conserved cellular process that maintains cellular homeostasis with the degradation and recycling systems. AGEs can activate autophagy signaling, which could be targeted as a therapeutic strategy against AGEs induced problems. In this review, we have provided an overview of the adverse effects of AGEs, and we put forth the notion that autophagy could be a promising targetable strategy against AGEs.

Biomarker Potential of the Soluble Receptor for Advanced Glycation End Products to Predict Bronchopulmonary Dysplasia in Premature Newborns

Bronchopulmonary dysplasia (BPD) is a common cause of pulmonary disease in preterm infants. The soluble receptor for advanced glycation end products (sRAGE) is implicated in the development of various pulmonary diseases. The objectives of the current study were to investigate perinatal factors associated with serum sRAGE levels at birth and to establish whether serum sRAGE could be a biomarker for BPD. This retrospective single-center study was conducted at Fukushima Medical University Hospital's Department of Pediatrics Neonatal Intensive Care Unit from April 2014 to September 2020. Mechanically ventilated or oxygenated neonates born at <32 weeks gestational age and healthy control neonates were included in this study. Serum sRAGE levels in cord blood were measured using an enzyme-linked immunosorbent assay. Eighty-four preterm infants born at <32 weeks and 40 healthy infants were identified. The 84 born at <32 weeks were categorized as BPD (n = 34) or non-BPD (n = 50) neonates. The median gestational age (GA) and birthweight (BW) were significantly lower in BPD vs. non-BPD neonates (24.4 vs. 27.6 weeks, P < 0.001, 634 vs. 952 g, P < 0.001, respectively). Serum sRAGE at birth in all 124 preterm and term infants significantly correlated with BW (r = 0.417, P < 0.0001) and GA (r = 0.415, P < 0.0001). Among those born at <32 weeks, median serum sRAGE levels at birth were significantly lower in infants with BPD than without (1,726 vs. 2,797 pg/mL, P = 0.0005). Receiver operating characteristic analysis for sRAGE levels at birth in infants with and without BPD revealed that the area under the curve was 0.724 (95% confidence interval 0.714-0.834, P = 0.001). However, serum RAGE levels were not associated with severity of BPD. Serum sRAGE levels at birth were significantly correlated with BW and GA. Furthermore, serum sRAGE levels at birth could serve as a biomarker for predicting BPD, but not its severity.

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.

Serum soluble receptor for advanced glycation end-products (sRAGE) in infants with bronchiolitis: Associations with acute severity and recurrent wheeze

BACKGROUND

Although bronchiolitis contributes to substantial acute (e.g., intensive care use) and chronic (e.g., recurrent wheeze and infections) morbidities in young children, the pathobiology remains uncertain. We examined relations of serum soluble receptor for advanced glycation end-products (sRAGE) with acute and chronic morbidities of bronchiolitis and whether the effect of serum sRAGE on development of recurrent wheeze is mediated through acute severity.

METHODS

A multi-center, multi-year, prospective cohort study of infants hospitalized for bronchiolitis was analyzed. We measured serum sRAGE level at acute hospitalization and examined its association with intensive care use (use of mechanical ventilation and/or admission to intensive care unit) and development of recurrent wheeze by age 3 years. We performed causal mediation analysis to estimate indirect (mediation) and direct effects of sRAGE on recurrent wheeze.

RESULTS

In 886 infants with bronchiolitis, median age was 2.9 months. Overall, 15% underwent intensive care and 32% developed recurrent wheeze by age 3 years. In the multivariable model adjusting for 11 confounders, higher presenting sRAGE level was associated with significantly lower risk of intensive care use (OR for each one-log increment, 0.39; 95%CI 0.16-0.91; P=0.03) and significantly lower rate of recurrent wheeze (HR 0.58; 95%CI 0.36-0.94; P=0.03). In mediation analysis, the direct effect was significant (HR 0.60; 95%CI 0.37-0.97; P=0.04) while the indirect effect was not (P=0.30).

CONCLUSIONS

Serum sRAGE levels were inversely associated with acute and chronic morbidities of bronchiolitis. Effect of sRAGE on development of recurrent wheeze is potentially driven through pathways other than acute severity of bronchiolitis.

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.

Tobacco Smoke and Inhaled Drugs Alter Expression and Activity of Multidrug Resistance-Associated Protein-1 (MRP1) in Human Distal Lung Epithelial Cells in vitro

Multidrug resistance-associated protein-1 (MRP1/ABCC1) is highly expressed in human lung tissues. Recent studies suggest that it significantly affects the pulmonary disposition of its substrates, both after pulmonary and systemic administration. To better understand the molecular mechanisms involved, we studied the expression, subcellular localization and activity of MRP1 in freshly isolated human alveolar epithelial type 2 (AT2) and type 1-like (AT1-like) cells in primary culture, and in the NCI-H441 cell line. Moreover, the effect of cigarette smoke extract (CSE) and a series of inhaled drugs on MRP1 abundance and activity was investigated in vitro. MRP1 expression levels were measured by q-PCR and immunoblot in AT2 and AT1-like cells from different donors and in several passages of the NCI-H441 cell line. The subcellular localization of the transporter was studied by confocal laser scanning microscopy and cell surface protein biotinylation. MRP1 activity was assessed by bidirectional transport and efflux experiments using the MRP1 substrate, 5(6)-carboxyfluorescein [CF; formed intracellularly from 5(6)-carboxyfluorescein-diacetate (CFDA)] in AT1-like and NCI-H441 cell monolayers. Furthermore, the effect of CSE as well as several bronchodilators and inhaled corticosteroids on MRP1 abundance and CF efflux was investigated. MRP1 protein abundance increased upon differentiation from AT2 to AT1-like phenotype, however, ABCC1 gene levels remained unchanged. MRP1 abundance in NCI-H441 cells were comparable to those found in AT1-like cells. The transporter was detected primarily in basolateral membranes of both cell types which was consistent with net basolateral efflux of CF. Likewise, bidirectional transport studies showed net apical-to-basolateral transport of CF which was sensitive to the MRP1 inhibitor MK-571. Budesonide, beclomethasone dipropionate, salbutamol sulfate, and CSE decreased CF efflux in a concentration-dependent manner. Interestingly, CSE increased MRP1 abundance, whereas budesonide, beclomethasone dipropionate, salbutamol sulfate did not have such effect. CSE and inhaled drugs can reduce MRP1 activity in vitro, which implies the transporter being a potential drug target in the treatment of chronic obstructive pulmonary disease (COPD). Moreover, MRP1 expression level, localization and activity were comparable in human AT1-like and NCI-H441 cells. Therefore, the cell line can be a useful alternative in vitro model to study MRP1 in distal lung epithelium.

Progress of RAGE Molecular Imaging in Alzheimer's Disease

Alzheimer’s disease (AD) is a progressive neurodegenerative disease characterized by senile plaques (SPs), which are caused by amyloid beta (Aβ) deposition and neurofibrillary tangles (NFTs) of abnormal hyperphosphorylated tau protein. The receptor for advanced glycation end products (RAGE) binds to advanced glycation end products deposited during vascular dysfunction. Alzheimer’s disease may occur when RAGE binds to Aβ and releases reactive oxygen species, further exacerbating Aβ deposition and eventually leading to SPs and NFTs. As it is involved in early AD, RAGE may be considered as a more potent biomarker than Aβ. Positron emission tomography provides valuable information regarding the underlying pathological processes of AD many years before the appearance of clinical symptoms. Thus, to further reveal the role of RAGE in AD pathology and for early diagnosis of AD, a tracer that targets RAGE is needed. In this review, we first describe the early diagnosis of AD and then summarize the interaction between RAGE and Aβ and Tau that is required to induce AD pathology, and finally focus on RAGE-targeting probes, highlighting the potential of RAGE to be used as an effective target. The development of RAGE probes is expected to aid in AD diagnosis and treatment.

Prothrombin is a binding partner of the human receptor of advanced glycation end products

The receptor for advanced glycation end products (RAGE) plays a key role in mammal physiology and in the etiology and progression of inflammatory and oxidative stress-based diseases. In adults, RAGE expression is normally high only in the lung where the protein concentrates in the basal membrane of alveolar Type I epithelial cells. In diseases, RAGE levels increase in the affected tissues and sustain chronic inflammation. RAGE exists as a membrane glycoprotein with an ectodomain, a transmembrane helix, and a short carboxyl-terminal tail, or as a soluble ectodomain that acts as a decoy receptor (sRAGE). VC1 domain is responsible for binding to the majority of RAGE ligands including advanced glycation end products (AGEs), S100 proteins, and HMGB1. To ascertain whether other ligands exist, we analyzed by MS the material pulled down by VC1 from human plasma. Twenty of 295 identified proteins were selected and associated to coagulation and complement processes and to extracellular matrix. Four of them contained a γ-carboxyl glutamic acid (Gla) domain, a calcium-binding module, and prothrombin (PT) was the most abundant. Using MicroScale thermophoresis, we quantified the interaction of PT with VC1 and sRAGE in the absence or presence of calcium that acted as a competitor. PT devoid of the Gla domain (PT des-Gla) did not bind to sRAGE, providing further evidence that the Gla domain is critical for the interaction. Finally, the presence of VC1 delayed plasma clotting in a dose-dependent manner. We propose that RAGE is involved in modulating blood coagulation presumably in conditions of lung injury.

Reduced endogenous secretory RAGE in blood and bronchoalveolar lavage fluid is associated with poor prognosis in idiopathic pulmonary fibrosis

Background

The endogenous secretory receptor for advanced glycation end products (esRAGE) is a soluble isoform produced by alternative splicing of the RAGE gene. The isoform has anti-inflammatory properties due to its inhibition of the RAGE/ligand interaction and is reduced in the lung tissue of patients with idiopathic pulmonary fibrosis (IPF). This study aimed to investigate the association of esRAGE serum and bronchoalveolar lavage fluid (BALF) levels with progression of IPF.

Methods

This study included 79 IPF patients and 90 healthy controls. IPF and control serum esRAGE levels were compared, and the correlation between serum and BALF esRAGE levels was analyzed in 57 IPF patient samples. We also investigated the relationship of esRAGE serum and BALF levels with prognoses and lung function parameters in patients with IPF.

Results

Serum esRAGE levels in IPF patients were significantly lower than those in healthy controls (162.0 ± 102.4 ng/ml and 200.7 ± 107.3 ng/ml, p = 0.009), although the baseline characteristics of age and smoking history were not matched. Serum levels of esRAGE were correlated with BALF esRAGE levels (r_s = 0.317). The BALF esRAGE levels were also correlated with diffusion capacity for carbon monoxide (r_s = 0.406). A Kaplan-Meier curve analysis and univariate/multivariate Cox hazard proportion analysis revealed that lower levels of esRAGE in blood and BALF were significantly associated with poorer prognoses in patients with IPF.

Conclusions

Decreased esRAGE levels in BALF and blood were associated with poor prognoses in patients with IPF. These results suggest that esRAGE could be related to the pathophysiology of IPF and serum esRAGE could be a potential prognostic marker of IPF.

Modulation of soluble receptor for advanced glycation end-products (RAGE) isoforms and their ligands in healthy aging

The receptor for advanced glycation end-products (RAGE) recognizes several ligands involved in inflammatory diseases. Two circulating soluble isoforms exist: esRAGE derived from alternative splicing and cRAGE generated by the membrane-bound RAGE (FL-RAGE) proteolysis. Together, esRAGE and cRAGE constitute sRAGE and function as decoy receptors preventing FL-RAGE/ligands binding.

We determined serum concentration of both, esRAGE and cRAGE, and their ligands AGEs, HMGB1 and S100A8/A9 in a healthy population of 169 subjects aged 20-90 years. cRAGE showed a negative (r=-0.375, P<0.0001) while AGEs (r=0.160, P=0.0384) and S100A8/A9 (r=0.207, P=0.0091) a positive correlation with age. esRAGE did not change during aging and inversely correlated with Hemoglobin, ALT, insulin, HOMA index, Waist-Hip ratio (W/H), Waist Circumference (WC) and positively with AGEs. cRAGE exhibited also an inverse correlation with WC, W/H, PAI-1, HMGB1, AGEs and S100A8/A9. Age, W/H, HMGB1, S100A8/A9 and AGEs are independent predictors of cRAGE, whereas W/H and AGEs associate with esRAGE. Treatment of cells with glycated albumin reduced cRAGE production and upregulated FL-RAGE.

These results indicate that in a healthy population cRAGE is a biomarker of aging while esRAGE represents a more reliable marker of obesity and insulin resistance. Hence, sRAGE isoforms levels could be differentially associated with age-related diseases risk factors.