Osteopontin is increased in cystic fibrosis and can skew the functional balance between ELR-positive and ELR-negative CXC-chemokines

Mesenchymal stromal cells reduce inflammation and improve lung function in a mouse model of cystic fibrosis lung disease

Mesenchymal stromal cells (MSCs) are multipotent adult stem cells which possess immunomodulatory and repair capabilities. In this study, we investigated whether MSC therapy could modulate inflammation and lung damage in the lungs of Scnn1b-transgenic mice overexpressing the β-subunit of the epithelial sodium channel (β-ENaC), a model with features of Cystic Fibrosis lung disease. Human bone marrow derived MSC cells were intravenously delivered to mice, prior to collection of bronchoalveolar lavage (BALF) and tissue. BALF analysis revealed a significant reduction in inflammatory cells after MSC administration, with both monocytic cells and neutrophils significantly reduced. Pro-inflammatory cytokines keratinocyte-derived chemokine (KC) and osteopontin were also significantly reduced. Histological tissue analysis revealed a reduction in emphysema in Scnn1b-TG mice treated with MSCs and consistent with these findings, improvements in lung function after MSC therapy were observed. Furthermore, MSCs enhanced Ki67 staining in alveolar cells, which may indicate regeneration of the destroyed parenchyma. Mechanistically, restoration of peroxisome proliferator-activated receptor-γ (PPARγ) expression and its transcriptional program were identified after MSC treatment. Our data demonstrate that MSC therapy can reduce inflammation, damage, and lung function decline in the chronically inflamed lung of Scnn1b-Tg mice, suggesting that MSCs may provide an effective tool in the treatment of muco-obstructive diseases such as cystic fibrosis.

Interorgan communication networks in the kidney-lung axis

The homeostasis and health of an organism depend on the coordinated interaction of specialized organs, which is regulated by interorgan communication networks of circulating soluble molecules and neuronal connections. Many diseases that seemingly affect one primary organ are really multiorgan diseases, with substantial secondary remote organ complications that underlie a large part of their morbidity and mortality. Acute kidney injury (AKI) frequently occurs in critically ill patients with multiorgan failure and is associated with high mortality, particularly when it occurs together with respiratory failure. Inflammatory lung lesions in patients with kidney failure that could be distinguished from pulmonary oedema due to volume overload were first reported in the 1930s, but have been largely overlooked in clinical settings. A series of studies over the past two decades have elucidated acute and chronic kidney-lung and lung-kidney interorgan communication networks involving various circulating inflammatory cytokines and chemokines, metabolites, uraemic toxins, immune cells and neuro-immune pathways. Further investigations are warranted to understand these clinical entities of high morbidity and mortality, and to develop effective treatments.

Tartrate resistant acid phosphatase 5 (TRAP5) mediates immune cell recruitment in a murine model of pulmonary bacterial infection

Introduction

During airway infection, upregulation of proinflammatory cytokines and subsequent immune cell recruitment is essential to mitigate bacterial infection. Conversely, during prolonged and non-resolving airway inflammation, neutrophils contribute to tissue damage and remodeling. This occurs during diseases including cystic fibrosis (CF) and COPD where bacterial pathogens, not least Pseudomonas aeruginosa, contribute to disease progression through long-lasting infections. Tartrate-resistant acid phosphatase (TRAP) 5 is a metalloenzyme expressed by alveolar macrophages and one of its target substrates is the phosphoglycoprotein osteopontin (OPN).

Methods

We used a knockout mouse strain (Trap5-/-) and BALB/c-Tg (Rela-luc)31Xen mice paired with siRNA administration or functional protein add-back to elucidate the role of Trap5 during bacterial infection. In a series of experiments, Trap5-/- and wild-type control mice received intratracheal administration of P.aerugniosa (Xen41) or LPS, with mice monitored using intravital imaging (IVIS). In addition, multiplex cytokine immunoassays, flow cytometry, multispectral analyses, histological staining were performed.

Results

In this study, we found that Trap5-/- mice had impaired clearance of P. aeruginosa airway infection and reduced recruitment of immune cells (i.e. neutrophils and inflammatory macrophages). Trap5 knockdown using siRNA resulted in a decreased activation of the proinflammatory transcription factor NF-κB in reporter mice and a subsequent decrease of proinflammatory gene expression. Add-back experiments of enzymatically active TRAP5 to Trap5-/- mice restored immune cell recruitment and bacterial killing. In human CF lung tissue, TRAP5 of alveolar macrophages was detected in proximity to OPN to a higher degree than in normal lung tissue, indicating possible interactions.

Discussion

Taken together, the findings of this study suggest a key role for TRAP5 in modulating airway inflammation. This could have bearing in diseases such as CF and COPD where excessive neutrophilic inflammation could be targeted by pharmacological inhibitors of TRAP5.

Identification of kidney injury released circulating osteopontin as causal agent of respiratory failure

Tissue injury can drive secondary organ injury; however, mechanisms and mediators are not well understood. To identify interorgan cross-talk mediators, we used acute kidney injury (AKI)-induced acute lung injury (ALI) as a clinically important example. Using kidney and lung single-cell RNA sequencing after AKI in mice followed by ligand-receptor pairing analysis across organs, kidney ligands to lung receptors, we identify kidney-released circulating osteopontin (OPN) as a novel AKI-ALI mediator. OPN release from kidney tubule cells triggered lung endothelial leakage, inflammation, and respiratory failure. Pharmacological or genetic OPN inhibition prevented AKI-ALI. Transplantation of ischemic wt kidneys caused AKI-ALI, but not of ischemic OPN-global knockout kidneys, identifying kidney-released OPN as necessary interorgan signal to cause AKI-ALI. We show that OPN serum levels are elevated in patients with AKI and correlate with kidney injury. Our results demonstrate feasibility of using ligand-receptor analysis across organs to identify interorgan cross-talk mediators and may have important therapeutic implications in human AKI-ALI and multiorgan failure.

Interorgan crosstalk mechanisms in disease: the case of acute kidney injury-induced remote lung injury

Homeostasis and health of multicellular organisms with multiple organs depends on interorgan communication. Tissue injury in one organ disturbs this homeostasis and can lead to disease in multiple organs, or multiorgan failure. Many routes of interorgan crosstalk during homeostasis are relatively well known, but interorgan crosstalk in disease still lacks understanding. In particular, how tissue injury in one organ can drive injury at remote sites and trigger multiorgan failure with high mortality is poorly understood. As examples, acute kidney injury can trigger acute lung injury and cardiovascular dysfunction; pneumonia, sepsis or liver failure conversely can cause kidney failure; lung transplantation very frequently triggers acute kidney injury. Mechanistically, interorgan crosstalk after tissue injury could involve soluble mediators and their target receptors, cellular mediators, in particular immune cells, as well as newly identified neuro-immune connections. In this review, I will focus the discussion of deleterious interorgan crosstalk and its mechanistic concepts on one example, acute kidney injury-induced remote lung injury.

Anti-virulence Bispecific Monoclonal Antibody Mediated Protection Against Pseudomonas aeruginosa Ventilator-Associated Pneumonia in a Rabbit Model

Ventilator-associated pneumonia is an important clinical manifestation of the nosocomial pathogen Pseudomonas aeruginosa. We characterized the correlates of protection of MEDI3902, a bispecific human IgG1 mAb that targets the P. aeruginosa type-3-secretion PcrV protein and the Psl exopolysaccharide, in a rabbit model of ventilator-associated pneumonia using lung-protective, low-tidal volume mechanical ventilation. Rabbits infused with MEDI3902 prophylactically were protected, whereas those pretreated with irrelevant isotype-control IgG (c-IgG) succumbed between 12 and 44 hours post infection [100% (8/8) vs. 0% (8/8) survival, P<0.01 by log-rank test]. Lungs from rabbits pretreated with c-IgG, but not those with MEDI3902, had bilateral, multifocal areas of marked necrosis, hemorrhage, neutrophilic inflammatory infiltrate, diffuse fibrinous edema in alveolar spaces. All rabbits pretreated with c-IgG developed worsening bacteremia that peaked at the time of death, whereas only 38% (3/8) rabbits pretreated with MEDI3902 developed such high-grade bacteremia (two-sided Fisher's exact test, P=0.026). Biomarkers associated with acute respiratory distress syndrome were evaluated longitudinally in blood samples collected every 2-4 hours to assess systemic pathophysiological changes in rabbits pretreated with MEDI3902 or c-IgG. Biomarkers were sharply increased or decreased in rabbits pretreated with c-IgG, but not those pretreated with MEDI3902, including ratio of arterial oxygen partial pressure to fractional inspired oxygen PaO₂/FiO₂ <300, hypercapnia or hypocapnia, severe lactic acidosis, leukopenia and neutropenia. Cytokines and chemokines associated with ARDS were significantly downregulated in lungs from rabbits pretreated with MEDI3902 compared with c-IgG. These results suggest that MEDI3902 prophylaxis could have potential clinical utility for decreasing severity of P. aeruginosa ventilator-associated pneumonia.

Osteopontin Expression in Small Airway Epithelium in Copd is Dependent on Differentiation and Confined to Subsets of Cells

Osteopontin (OPN) plays a role in inflammation via recruitment of neutrophils and tissue remodeling. In this study, we investigated the distribution of OPN-expressing cells in the airway epithelium of normal lung tissue and that from patients with chronic obstructive pulmonary disease (COPD). OPN was detected on the epithelial cell surface of small airways and in scattered cells within the epithelial cell layer. Staining revealed higher OPN concentrations in tissue showing moderate to severe COPD compared to that in controls. In addition, OPN expression was confined to goblet and club cells, and was absent from ciliated and basal cells as detected via immunohistochemistry. However, OPN expression was up-regulated in submerged basal cells cultures exposed to cigarette smoke (CS) extract. Cell fractioning of air-liquid interface cultures revealed increased OPN production from basal compartment cells compared to that in luminal fraction cells. Furthermore, both constitutive and CS-induced expression of OPN decreased during differentiation. In contrast, cultures stimulated with interleukin (IL)-13 to promote goblet cell hyperplasia showed increased OPN production in response to CS exposure. These results indicate that the cellular composition of the airway epithelium plays an important role in OPN expression and that these levels may reflect disease endotypes in COPD.

Osteopontin as a Link between Inflammation and Cancer: The Thorax in the Spotlight

The glycoprotein osteopontin (OPN) possesses multiple functions in health and disease. To this end, osteopontin has beneficial roles in wound healing, bone homeostasis, and extracellular matrix (ECM) function. On the contrary, osteopontin can be deleterious for the human body during disease. Indeed, osteopontin is a cardinal mediator of tumor-associated inflammation and facilitates metastasis. The purpose of this review is to highlight the importance of osteopontin in malignant processes, focusing on lung and pleural tumors as examples.

Osteopontin protects against lung injury caused by extracellular histones

Extracellular histones are present in the airways because of cell death occurring during inflammation. They promote inflammation and cause tissue damage due to their cationic nature. The anionic phosphoglycoprotein osteopontin (OPN) is expressed at high levels during airway inflammation and has been ascribed both pro- and anti-inflammatory roles. In this study, it was hypothesized that OPN may neutralize the harmful activities of extracellular histones at the airway mucosal surface. In a model of histone-induced acute lung injury, OPN^-/- mice showed increased inflammation and tissue injury, and succumbed within 24 h, whereas wild-type mice showed lower degrees of inflammation and no mortality. In lipopolysaccharide-induced acute lung injury, wild-type mice showed less inflammation and tissue injury than OPN^-/- mice. In bronchoalveolar lavage fluid from ARDS patients, high levels of OPN and also histone-OPN complexes were detected. In addition, OPN bound to histones with high affinity in vitro, resulting in less cytotoxicity and reduced formation of tissue-damaging neutrophil extracellular traps (NETs). The interaction between OPN and histones was dependent on posttranslational modification of OPN, i.e., phosphorylation. The findings demonstrate a novel role for OPN, modulating the pro-inflammatory and cytotoxic properties of free histones.

Plasma Surfactant Protein-D, Matrix Metalloproteinase-7, and Osteopontin Index Distinguishes Idiopathic Pulmonary Fibrosis from Other Idiopathic Interstitial Pneumonias

RATIONALE

Idiopathic pulmonary fibrosis (IPF) is a progressive, fatal interstitial lung disease (ILD) characterized by abnormal extracellular matrix (ECM) remodeling. We hypothesized that ECM remodeling might result in a plasma profile of proteins specific for IPF that could distinguish patients with IPF from other idiopathic ILDs.

OBJECTIVES

To identify biomarkers that might assist in distinguishing IPF from non-IPF ILD.

METHODS

We developed a panel of 35 ECM, ECM-related, and lung-specific analytes measured in plasma from 86 patients with IPF (derivation cohort) and in 63 patients with IPF (validation cohort). Comparison groups included patients with rheumatoid arthritis-associated ILD (RA-ILD; n = 33), patients with alternative idiopathic ILDs (a-ILD; n = 41), and healthy control subjects (n = 127). Univariable and multivariable logistic regression models identified biomarkers that differentiated patients with IPF from those with a-ILD. Both continuous and diagnostic threshold versions of biomarkers were considered; thresholds were chosen to maximize summed diagnostic sensitivity and specificity in univariate receiver-operating characteristic curve analysis. A diagnostic score was created from the most promising analytes.

MEASUREMENTS AND MAIN RESULTS

Plasma surfactant protein (SP)-D > 31 ng/ml, matrix metalloproteinase (MMP)-7 > 1.75 ng/ml, and osteopontin > 6 ng/ml each significantly distinguished patients with IPF from patients with a-ILD, both individually and in a combined index. The odds ratio for IPF when at least one analyte in the index exceeded the threshold was 4.4 (95% confidence interval, 2.0-9.7; P = 0.0003). When at least two analytes were elevated, the odds ratio for IPF increased to 5.0 (95% confidence interval, 2.2-11.5; P = 0.0002).

CONCLUSIONS

A biomarker index of SP-D, MMP-7, and osteopontin enhanced diagnostic accuracy in patients with IPF compared with those with non-IPF ILD. Our data suggest that this biomarker index may improve diagnostic confidence in IPF.

Osteopontin That Is Elevated in the Airways during COPD Impairs the Antibacterial Activity of Common Innate Antibiotics

Bacterial infections of the respiratory tract contribute to exacerbations and disease progression in chronic obstructive pulmonary disease (COPD). There is also an increased risk of invasive pneumococcal disease in COPD. The underlying mechanisms are not fully understood but include impaired mucociliary clearance and structural remodeling of the airways. In addition, antimicrobial proteins that are constitutively expressed or induced during inflammatory conditions are an important part of the airway innate host defense. In the present study, we show that osteopontin (OPN), a multifunctional glycoprotein that is highly upregulated in the airways of COPD patients co-localizes with several antimicrobial proteins expressed in the airways. In vitro, OPN bound lactoferrin, secretory leukocyte peptidase inhibitor (SLPI), midkine, human beta defensin-3 (hBD-3), and thymic stromal lymphopoietin (TSLP) but showed low or no affinity for lysozyme and LL-37. Binding of OPN impaired the antibacterial activity against the important bacterial pathogens Streptococcus pneumoniae and Pseudomonas aeruginosa. Interestingly, OPN reduced lysozyme-induced killing of S. pneumoniae, a finding that could be explained by binding of OPN to the bacterial surface, thereby shielding the bacteria. A fragment of OPN generated by elastase of P. aeruginosa retained some inhibitory effect. Some antimicrobial proteins have additional functions. However, the muramidase-activity of lysozyme and the protease inhibitory function of SLPI were not affected by OPN. Taken together, OPN can contribute to the impairment of innate host defense by interfering with the function of antimicrobial proteins, thus increasing the vulnerability to acquire infections during COPD.

Osteopontin binds and modulates functions of eosinophil-recruiting chemokines

BACKGROUND

Allergic asthma is characterized by eosinophilic inflammation and airway obstruction. There is also an increased risk of pulmonary infection caused by Streptococcus pneumoniae, in particular during severe asthma where high levels of the glycoprotein, osteopontin (OPN), are present in the airways. Eosinophils can be recruited by chemokines activating the receptor CCR3 including eotaxin-1/CCL11, eotaxin-2/CCL24, eotaxin-3/CCL26, RANTES/CCL5, and MEC/CCL28. In addition to inducing chemotaxis, several of these molecules have defensin-like antibacterial properties. This study set out to elucidate the functional consequences of OPN binding to eosinophil-recruiting chemokines.

METHODS

Antibacterial activities of the chemokines were investigated using viable count assays and electron microscopy. Binding studies were performed by means of surface plasmon resonance. The potential interference of OPN with antibacterial, receptor-activating, and lipopolysaccharide-neutralizing abilities of these chemokines was investigated.

RESULTS

We found that OPN bound all eosinophil-recruiting chemokines with high affinity except for CCL5. The eosinophil-recruiting chemokines all displayed bactericidal activity against S. pneumoniae, but only CCL26 and CCL28 retained high antibacterial activity in the presence of sodium chloride at physiologic concentrations. Preincubation of the chemokines with OPN strongly inhibited their antibacterial activity against S. pneumoniae but did not affect their ability to activate CCR3. All chemokines investigated showed LPS-neutralizing activity that was impaired by OPN only in the case of CCL24.

CONCLUSIONS

The data suggest that OPN may impair host defense activities of the chemokines without affecting their eosinophil-recruiting properties. This could be one mechanism explaining the increased vulnerability to acquire pneumococcal infection in parallel with sustained allergic inflammation in asthma.