Integrins in pulmonary inflammatory diseases

Immune cell ratio and coagulation markers in assessing prognosis of asthma: a cross-sectional study from Saudi Arabia

Asthma affects a significant number of individuals in Saudi Arabia, with increasing prevalence worldwide, leading to a considerable impact on their quality of life and frequent hospitalizations. In this study, we aimed to explore the relationship between the immune cell ratio and coagulation markers, specifically to identify the occurrence of coagulation abnormalities associated with asthma. To achieve this, we assessed asthma history and severity using a questionnaire while analyzing coagulation biomarkers through venous blood samples. The biomarkers examined included d-dimer, prothrombin time (PT), partial thromboplastin time (PTT), and the international normalized ratio (INR). In addition, we evaluated various hematological parameters such as blood cell counts and hemoglobin (HGB) levels. Our findings revealed compelling evidence, showing significantly elevated levels of d-dimer and the eosinophil-to-neutrophil (ENR) ratio in asthma cases compared to the controls. Moreover, we observed a positive correlation between d-dimer levels and the ENR, with each unit increase in d-dimer associated with a 0.0006 increase in the ENR among asthma cases. These results highlight the potential of assessing ENR and d-dimer levels as predictive indicators for disease prognosis and the development of coagulation abnormalities in individuals with asthma. By shedding light on the relationship between immune cell ratios and coagulation markers in the context of asthma, our study contributes to a better understanding of disease progression and the associated complications. These insights can potentially lead to improved management strategies and better outcomes for asthma patients.

Co-Expression Analysis of Airway Epithelial Transcriptome in Asthma Patients with Eosinophilic vs. Non-Eosinophilic Airway Infiltration

Asthma heterogeneity complicates the search for targeted treatment against airway inflammation and remodeling. We sought to investigate relations between eosinophilic inflammation, a phenotypic feature frequent in severe asthma, bronchial epithelial transcriptome, and functional and structural measures of airway remodeling. We compared epithelial gene expression, spirometry, airway cross-sectional geometry (computed tomography), reticular basement membrane thickness (histology), and blood and bronchoalveolar lavage (BAL) cytokines of n = 40 moderate to severe eosinophilic (EA) and non-eosinophilic asthma (NEA) patients distinguished by BAL eosinophilia. EA patients showed a similar extent of airway remodeling as NEA but had an increased expression of genes involved in the immune response and inflammation (e.g., KIR3DS1), reactive oxygen species generation (GYS2, ATPIF1), cell activation and proliferation (ANK3), cargo transporting (RAB4B, CPLX2), and tissue remodeling (FBLN1, SOX14, GSN), and a lower expression of genes involved in epithelial integrity (e.g., GJB1) and histone acetylation (SIN3A). Genes co-expressed in EA were involved in antiviral responses (e.g., ATP1B1), cell migration (EPS8L1, STOML3), cell adhesion (RAPH1), epithelial-mesenchymal transition (ASB3), and airway hyperreactivity and remodeling (FBN3, RECK), and several were linked to asthma in genome- (e.g., MRPL14, ASB3) or epigenome-wide association studies (CLC, GPI, SSCRB4, STRN4). Signaling pathways inferred from the co-expression pattern were associated with airway remodeling (e.g., TGF-β/Smad2/3, E2F/Rb, and Wnt/β-catenin).

SARS-CoV-2 Spike Protein Unlikely to Bind to Integrins via the Arg-Gly-Asp (RGD) Motif of the Receptor Binding Domain: Evidence From Structural Analysis and Microscale Accelerated Molecular Dynamics

The Receptor Binding Domain (RBD) of SARS-CoV-2 virus harbors a sequence of Arg-Gly-Asp tripeptide named RGD motif, which has also been identified in extracellular matrix proteins that bind integrins as well as other disintegrins and viruses. Accordingly, integrins have been proposed as host receptors for SARS-CoV-2. However, given that the microenvironment of the RGD motif imposes a structural hindrance to the protein-protein association, the validity of this hypothesis is still uncertain. Here, we used normal mode analysis, accelerated molecular dynamics microscale simulation, and protein-protein docking to investigate the putative role of RGD motif of SARS-CoV-2 RBD for interacting with integrins. We found, that neither RGD motif nor its microenvironment showed any significant conformational shift in the RBD structure. Highly populated clusters of RBD showed no capability to interact with the RGD binding site in integrins. The free energy landscape revealed that the RGD conformation within RBD could not acquire an optimal geometry to allow the interaction with integrins. In light of these results, and in the event where integrins are confirmed to be host receptors for SARS-CoV-2, we suggest a possible involvement of other residues to stabilize the interaction.

Specific Features of the Coagulopathy Signature in Severe COVID-19 Pneumonia

Rationale: COVID-19 displays distinct characteristics that suggest a unique pathogenesis. The objective of this study was to compare biomarkers of coagulopathy and outcomes in COVID-19 and non-COVID-19 patients with severe pneumonia. Methods: Thirty-six non-COVID-19 and 27 COVID-19 non-immunocompromised patients with severe pneumonia were prospectively enrolled, most requiring intensive care. Clinical and biological characteristics (including plasma biomarkers of coagulopathy) were compared. Results: At similar baseline severity, COVID-19 patients required mechanical ventilation (MV) for significantly longer than non-COVID-19 patients (p = 0.0049) and more frequently developed venous thrombotic complications (p = 0.031). COVID-19 patients had significantly higher plasma concentrations of soluble VCAM1 (sVCAM1) (5,739 ± 3,293 vs. 3,700 ± 2,124 ng/ml; p = 0.009), but lower levels of D-dimers, vWF-A2, sICAM1, sTREM1, VEGF, and P-selectin, compared to non-COVID-19 patients. Principal component analysis identified two main patterns, with a clear distinction between non-COVID-19 and COVID-19 patients. Multivariable regression analysis confirmed that sVCAM1 rising levels were independently associated with a longer duration of MV. Finally, we identified close correlations between sVCAM1 and some features of COVID-19 immune dysregulation (ie. CXCL10, GM-CSF, and IL-10). Conclusion: We identified specific features of the coagulopathy signature in severe COVID-19 patients, with higher plasma sVCAM1 levels, that were independently associated with the longer duration of mechanical ventilation. Clinical Trial Registration:ClinicalTrials.gov, identifier: NCT03505281.

Interactions via α2β1 Cell Integrin May Protect against the Progression of Airway Structural Changes in Asthma

Increased airway wall thickness and remodeling of bronchial mucosa are characteristic of asthma and may arise from altered integrin signaling on airway cells. Here, we analyzed the expression of β₁-subfamily integrins on blood and airway cells (flow cytometry), inflammatory biomarkers in serum and bronchoalveolar lavage, reticular basement membrane (RBM) thickness and collagen deposits in the mucosa (histology), and airway geometry (CT-imaging) in 92 asthma patients (persistent airflow limitation subtype: n = 47) and 36 controls. Persistent airflow limitation was associated with type-2 inflammation, elevated soluble α₂ integrin chain, and changes in the bronchial wall geometry. Both subtypes of asthma showed thicker RBM than control, but collagen deposition and epithelial α₁ and α₂ integrins staining were similar. Type-I collagen accumulation and RBM thickness were inversely related to the epithelial expression of the α₂ integrin chain. Expression of α₂β₁ integrin on T-cells and eosinophils was not altered in asthma. Collagen I deposits were, however, more abundant in patients with lower α₂β₁ integrin on blood and airway CD8⁺ T-cells. Thicker airway walls in CT were associated with lower α₂ integrin chain on blood CD4⁺ T-cells and airway eosinophils. Our data suggest that α₂β₁ integrin on inflammatory and epithelial cells may protect against airway remodeling advancement in asthma.

Effect of omalizumab on bronchoalveolar lavage matrix metalloproteinases in severe allergic asthma

INTRODUCTION

Airway inflammation in asthma is accompanied by reconstruction of the bronchial wall extracellular matrix that most likely occurs with a contribution of matrix metalloproteinases (MMPs). Recently we have reported that omalizumab may decrease reticular basement membrane (RBM) thickness together with fibronectin deposits in asthmatic airways, although mechanisms involved are unknown.

OBJECTIVE

In the present study, we have investigated the impact of omalizumab on MMPs concentrations in bronchoalveolar lavage fluid (BAL) of asthmatic subjects in relation to airway remodeling changes in histology.

PATIENTS AND METHODS

The study group consisted of 13 severe allergic asthmatics treated with omalizumab for at least 12 months. In each subject, clinical and laboratory parameters, bronchoscopy with BAL, and endobronchial biopsy were evaluated before and after the biologic therapy. RBM thickness, fibronectin, and collagen deposits in bronchial mucosa specimens were analyzed in histology. The investigations also included BAL cytology and BAL concentrations of MMP-2, -3, and -9.

RESULTS

Omalizumab was related to a decrease in all measured MMPs in BAL (p < 0.001, each), although such declines were not observed in each patient. The depletions were associated with a lower asthma exacerbation rate and better asthma control. Interestingly, patients who showed a decline in at least one MMP (n = 10, 77%) were characterized by a higher decrease in the RBM thickness (-1.61 [-2.02 to -0.6] vs. -0.06 [-0.09 to +3.3], p = 0.03). Likewise, individuals with lower concentrations of MMP-9 after omalizumab (n = 7, 58%) had a greater reduction in the RBM layer as compared to those with steady MMP-9 levels (-1.8 [-2.4 to -1.14] vs. -0.13 [-0.6 to -0.06] μm, p = 0.03). Moreover, the latter group also had unfavorable higher collagen I accumulation after biologic (42 [20 to 55] vs. 0 [-10 to 20]%, respectively, p = 0.03). Higher concentrations of MMPs in BAL at baseline were related to the lower systemic steroid dose and better omalizumab response concerning the decline in RBM thickness.

CONCLUSION

Our data suggest that omalizumab therapy is associated with decreased BAL MMPs concentration in the subgroup of asthma patients. The decline was linked with a reduction in the RBM thickness what might play a beneficial role in airway remodeling.

Reticular Basement Membrane Thickness Is Associated with Growth- and Fibrosis-Promoting Airway Transcriptome Profile-Study in Asthma Patients

Airway remodeling in asthma is characterized by reticular basement membrane (RBM) thickening, likely related to epithelial structural and functional changes. Gene expression profiling of the airway epithelium might identify genes involved in bronchial structural alterations. We analyzed bronchial wall geometry (computed tomography (CT)), RBM thickness (histology), and the bronchial epithelium transcriptome profile (gene expression array) in moderate to severe persistent (n = 21) vs. no persistent (n = 19) airflow limitation asthmatics. RBM thickness was similar in the two studied subgroups. Among the genes associated with increased RBM thickness, the most essential were those engaged in cell activation, proliferation, and growth (e.g., CDK20, TACC2, ORC5, and NEK5) and inhibiting apoptosis (e.g., higher mRNA expression of RFN34, BIRC3, NAA16, and lower of RNF13, MRPL37, CACNA1G). Additionally, RBM thickness correlated with the expression of genes encoding extracellular matrix (ECM) components (LAMA3, USH2A), involved in ECM remodeling (LTBP1), neovascularization (FGD5, HPRT1), nerve functioning (TPH1, PCDHGC4), oxidative stress adaptation (RIT1, HSP90AB1), epigenetic modifications (OLMALINC, DNMT3A), and the innate immune response (STAP1, OAS2). Cluster analysis revealed that genes linked with RBM thickness were also related to thicker bronchial walls in CT. Our study suggests that the pro-fibrotic profile in the airway epithelial cell transcriptome is associated with a thicker RBM, and thus, may contribute to asthma airway remodeling.

Mechanisms of Wheat Allergenicity in Mice: Comparison of Adjuvant-Free vs. Alum-Adjuvant Models

Wheat protein is considered a major type of food allergen in many countries including the USA. The mechanisms of allergenicity of wheat proteins are not well understood at present. Both adjuvant-based and adjuvant-free mouse models are reported for this food allergy. However, it is unclear whether the mechanisms underlying wheat allergenicity in these two types of models are similar or different. Therefore, we compared the molecular mechanisms in a novel adjuvant-free (AF) model vs. a conventional alum-adjuvant (AA) model of wheat allergy using salt-soluble wheat protein (SSWP). In the AF model, Balb/cJ mice were sensitized with SSWP via skin exposure. In the AA model, mice were sensitized by an intraperitoneal injection of SSWP with alum. In both models, allergic reactions were elicited using an identical protocol. Robust IgE as well as mucosal mast cell protein-1 responses were elicited similarly in both models. However, an analysis of the spleen immune markers identified strikingly different molecular activation patterns in these two models. Furthermore, a number of immune markers associated with intrinsic allergenicity were also identified in both models. Since the AF model uses skin exposure without an adjuvant, the mechanisms in the AF model may more closely simulate the human wheat allergenicity mechanisms from skin exposure in occupational settings such as in the baking industry.

The relationship of airway structural changes to blood and bronchoalveolar lavage biomarkers, and lung function abnormalities in asthma

BACKGROUND

Airway structural changes are important in asthma pathology and require further investigations.

OBJECTIVE

We sought to evaluate which computed tomography (CT) indices, bronchial histological traits, or blood and bronchoalveolar lavage (BAL) biomarkers correlate best with lung function abnormalities in asthma.

METHODS

In 105 white adult asthmatics (53 with a component of fixed airflow obstruction), we determined airway cross-sectional geometry of two proximal (the right upper lobe apical segmental and the left apicoposterior) and two distal (the right and the left basal posterior) bronchi, quantified the low-attenuation lung area (LAA%), and analysed clusters based on airway CT-metrics. We also performed bronchofiberoscopy with BAL and endobronchial biopsy, assessed blood and BAL biomarkers, including interleukin (IL)-4, IL-5, IL-6, IL-10, IL-12p70, IL-17A, IL-23, interferon (INF)γ and periostin, together with circulating a disintegrin and metalloproteinase domain-containing protein (ADAM)33, and investigated interplays between analysed variables.

RESULTS

Patients with fixed airflow limitation were characterized by lower lumen area and increased wall area and wall thickness ratios in distal airways, accompanied by raised LAA%. They had also higher blood neutrophilia, blood and BAL eosinophilia, increased circulating fibrinogen, periostin, and ADAM33. Blood neutrophilia, serum high density lipoproteins, thyroid-stimulating hormone, and shortened activated partial thromboplastin time were determinants of thicker reticular basement membrane (RBM). BAL eosinophilia was the only positive predictor of collagen I accumulation. Surprisingly, we observed a negative correlation between RBM thickening and collagen I deposit. Cluster analysis based on CT-metrics of the right lower lobe basal posterior bronchus revealed three well-separated clusters similar in age, asthma duration, and BMI, but different in RBM thickness, collagen I accumulation, and inflammatory markers.

CONCLUSIONS AND CLINICAL RELEVANCE

Airway remodelling traits are mainly related to the Th₂ profile, higher circulating ADAM33, and blood neutrophilia. Lung function abnormalities and RBM thickening correlate better with CT-metrics of distal than proximal airways.

Omalizumab may decrease the thickness of the reticular basement membrane and fibronectin deposit in the bronchial mucosa of severe allergic asthmatics

Introduction: Immunoglobulin E is an important modulator of the inflammatory reaction in allergic asthma. It also contributes to airway remodeling in the course of the disease. The authors evaluated airway structural changes in severe allergic asthma during the omalizumab therapy. Patients and methods: The study included 13 patients with severe allergic asthma treated with omalizumab for at least one year. In each patient clinical, laboratory, and spirometry parameters were evaluated before and after the treatment. In addition, bronchoscopy with bronchial mucosa biopsy and bronchoalveolar lavage was performed. The basal lamina thickness, inflammatory cell infiltration, fibronectin, as well as type I and III collagen accumulation were assessed in bronchial mucosa specimens, together with the assessment of bronchoalveolar lavage cellularity. Results: The omalizumab therapy led to a decrease in the basal lamina thickness (p = 0.002), and to a reduction in fibronectin (p = 0.02), but not collagen deposits in the bronchial mucosa. The decrease in fibronectin accumulation was associated with an improvement in asthma control and quality of life (p = 0.01, both), and a diminished dose of systemic corticosteroids (p = 0.001). It was also associated with a tendency towards reduction of the eosinophil count in the peripheral blood, bronchoalveolar lavage fluid, and bronchial mucosa specimens. Conclusion: Our study has shown that omalizumab, effective in the treatment of severe allergic asthma, may also decrease unfavorable structural airway changes in allergic asthmatics, at least with respect to the fibronectin deposit and an increased thickness of the basal lamina. However, more extensive observational studies are needed to verify the above hypothesis.

Increased blood levels of cellular fibronectin in asthma: Relation to the asthma severity, inflammation, and prothrombotic blood alterations

BACKGROUND

Recently, we have reported that asthma is characterized by prothrombotic blood alterations, which were related to the low-grade inflammatory state. Inflammation, however, may also lead to vascular dysfunction. The aim of this study was to evaluate plasma levels of cellular fibronectin (cFN), a marker of vascular injury in asthmatics, and to analyze their impact on described previously prothrombotic blood alterations.

METHODS

In a cross-sectional study, we investigated 164 adult stable asthmatics and 72 matched controls. Plasma cFN was measured using an ELISA. Its relations to inflammation, thrombin generation, fibrinolytic capacity, expressed as clot lysis time (CLT), and platelet markers were evaluated.

RESULTS

Asthma was associated with 50.1% higher plasma cFN levels as compared with controls (p < 0.001, after adjustment for potential confounders). There was a positive association of cFN with asthma severity and inverse with the FEV₁/VC index (β = 0.2 [95%CI:0.13-0.28] and β = -0.15 [95%CI: -0.23 to -0.07], respectively). In asthmatics cFN positively correlated with high-sensitivity C-reactive protein (β = 0.24 [95%CI:0.16-0.32]), fibrinogen (β = 0.13 [95%CI:0.04-0.21]), interleukin-6 (β = 0.23 [95%CI:0.15-0.3]), platelet factor 4 (β = 0.14 [95%CI:0.06-0.21]), plasminogen (β = 0.11 [95%CI:0.04-0.19]) and CLT (β = 0.35 [95%CI:0.28-0.42]). In both groups cFN was related to the endogenous thrombin potential (ETP) (β = 0.51 [95%CI:0.44-0.57], and β = 0.17 [95%CI:0.07-0.27], respectively). Multiple regression models showed that cFN was the most potent independent predictor of both ETP and CLT in asthmatics.

CONCLUSION

Presented study is the first to show increased plasma cellular fibronectin in asthma, which is associated with disease severity, inflammation, and prothrombotic blood alterations. This novel observation suggests a previously unknown modulator of prothrombotic plasma properties in asthmatics.

Redox regulation of the actin cytoskeleton and its role in the vascular system

The actin cytoskeleton is critical for form and function of vascular cells, serving mechanical, organizational and signaling roles. Because many cytoskeletal proteins are sensitive to reactive oxygen species, redox regulation has emerged as a pivotal modulator of the actin cytoskeleton and its associated proteins. Here, we summarize work implicating oxidants in altering actin cytoskeletal proteins and focus on how these alterations affect cell migration, proliferation and contraction of vascular cells. Finally, we discuss the role of oxidative modification of the actin cytoskeleton in vivo and highlight its importance for vascular diseases.

Deletion of Nlrp3 Augments Survival during Polymicrobial Sepsis by Decreasing Autophagy and Enhancing Phagocytosis

NLRP3 inflammasome is a critical player in innate immunity. Neutrophil recruitment to tissues and effective neutrophil function are critical innate immune mechanisms for bacterial clearance. However, the role of NLRP3 in neutrophil-dependent bacterial clearance in polymicrobial sepsis is unclear. In this study, we evaluated the role of NLRP3 in polymicrobial sepsis induced by cecal ligation and puncture (CLP). Our results showed protection from death in NLRP3-deficient (Nlrp3^-/-) and NLRP3 inhibitor-treated wild-type (C57BL/6) mice. Nlrp3^-/- and NLRP3 inhibitor-treated mice displayed lower bacterial load but no impairment in neutrophil recruitment to peritoneum. However, neutrophil depletion abrogated protection from death in Nlrp3^-/- mice in response to CLP. Intriguingly, following CLP, Nlrp3^-/- peritoneal cells (primarily neutrophils) demonstrate decreased autophagy, augmented phagocytosis, and enhanced scavenger receptor (macrophage receptor with collagenous structure) and mannose-binding leptin expression. These findings enhance our understanding of the critical role of NLRP3 in modulating autophagy and phagocytosis in neutrophils and suggest that therapies should be targeted to modulate autophagy and phagocytosis in neutrophils to control bacterial burden in tissues during CLP-induced polymicrobial sepsis.

Integrins as Therapeutic Targets for Respiratory Diseases

Integrins are a large family of transmembrane heterodimeric proteins that constitute the main receptors for extracellular matrix components. Integrins were initially thought to be primarily involved in the maintenance of cell adhesion and tissue integrity. However, it is now appreciated that integrins play important roles in many other biological processes such as cell survival, proliferation, differentiation, migration, cell shape and polarity. Lung cells express numerous combinations and permutations of integrin heterodimers. The complexity and diversity of different integrin heterodimers being implicated in different lung diseases present a major challenge for drug development. Here we provide a comprehensive overview of the current knowledge of integrins from studies in cell culture to integrin knockout mouse models and provide an update of results from clinical trials for which integrins are therapeutic targets with a focus on respiratory diseases (asthma, emphysema, pneumonia, lung cancer, pulmonary fibrosis and sarcoidosis).

Lung extracellular matrix and redox regulation

Pulmonary fibrosis affects millions worldwide and, even though there has been a significant investment in understanding the processes involved in wound healing and maladaptive repair, a complete understanding of the mechanisms responsible for lung fibrogenesis eludes us, and interventions capable of reversing or halting disease progression are not available. Pulmonary fibrosis is characterized by the excessive expression and uncontrolled deposition of extracellular matrix (ECM) proteins resulting in erosion of the tissue structure. Initially considered an 'end-stage' process elicited after injury, these events are now considered pathogenic and are believed to contribute to the course of the disease. By interacting with integrins capable of signal transduction and by influencing tissue mechanics, ECM proteins modulate processes ranging from cell adhesion and migration to differentiation and growth factor expression. In doing so, ECM proteins help orchestrate complex developmental processes and maintain tissue homeostasis. However, poorly controlled deposition of ECM proteins promotes inflammation, fibroproliferation, and aberrant differentiation of cells, and has been implicated in the pathogenesis of pulmonary fibrosis, atherosclerosis and cancer. Considering their vital functions, ECM proteins are the target of investigation, and oxidation-reduction (redox) reactions have emerged as important regulators of the ECM. Oxidative stress invariably accompanies lung disease and promotes ECM expression directly or through the overproduction of pro-fibrotic growth factors, while affecting integrin binding and activation. In vitro and in vivo investigations point to redox reactions as targets for intervention in pulmonary fibrosis and related disorders, but studies in humans have been disappointing probably due to the narrow impact of the interventions tested, and our poor understanding of the factors that regulate these complex reactions. This review is not meant to provide a comprehensive review of this field, but rather to highlight what has been learned and to raise interest in this area in need of much attention.

Human eosinophil transmigration

In this chapter we describe an optimized eosinophil transmigration assay. Transmigration of purified human peripheral blood eosinophils can be studied using special insert with membrane coated with extracellular matrix components or membrane covered with cells growing as a confluent monolayer, such as vascular endothelial cells of any origin or airway epithelial cells. In our opinion, eosinophil transmigration assay performed through monolayer of human microvascular endothelial cells of lung origin is a suitable tool to estimate the full migratory potential of eosinophils in studies on the pathology of asthma or other respiratory diseases, where eosinophils play important effector functions. This experimental system is easy to perform, simple for optimization, and comparable to in vivo processes occurring during eosinophil migration to the inflammatory sites in lungs.

Integrins: therapeutic targets in airway hyperresponsiveness and remodelling?

Integrins are a group of transmembrane heterodimeric proteins that mediate cell-cell and cell-extracellular matrix (ECM) interactions. Integrins have been under intense investigation for their role in inflammation in asthma. Clinical trials investigating integrin antagonists, however, have shown that these compounds are relatively ineffective. Airway remodelling is another pathological feature of asthma that is thought to make an important contribution to airway hyperresponsiveness (AHR) and lung function decline. Recent studies have identified integrins as important players in this process, with a particular role for β1 and αv integrins. Here we review the role of these integrins in airway remodelling and hyperresponsiveness in obstructive airway disease and their potential as pharmacological targets for future treatment.

Monocyte chemoattractant protein 1 regulates pulmonary host defense via neutrophil recruitment during Escherichia coli infection

Neutrophil accumulation is a critical event to clear bacteria. Since uncontrolled neutrophil recruitment can cause severe lung damage, understanding neutrophil trafficking mechanisms is important to attenuate neutrophil-mediated damage. While monocyte chemoattractant protein 1 (MCP-1) is known to be a monocyte chemoattractant, its role in pulmonary neutrophil-mediated host defense against Gram-negative bacterial infection is not understood. We hypothesized that MCP-1/chemokine (C-C motif) ligand 2 is important for neutrophil-mediated host defense. Reduced bacterial clearance in the lungs was observed in MCP-1(-/-) mice following Escherichia coli infection. Neutrophil influx, along with cytokines/chemokines, leukotriene B(4) (LTB(4)), and vascular cell adhesion molecule 1 levels in the lungs, was reduced in MCP-1(-/-) mice after infection. E. coli-induced activation of NF-κB and mitogen-activated protein kinases in the lung was also reduced in MCP-1(-/-) mice. Administration of intratracheal recombinant MCP-1 (rMCP-1) to MCP-1(-/-) mice induced pulmonary neutrophil influx and cytokine/chemokine responses in the presence or absence of E. coli infection. Our in vitro migration experiment demonstrates MCP-1-mediated neutrophil chemotaxis. Notably, chemokine receptor 2 is expressed on lung and blood neutrophils, which are increased upon E. coli infection. Furthermore, our findings show that neutrophil depletion impairs E. coli clearance and that exogenous rMCP-1 after infection improves bacterial clearance in the lungs. Overall, these new findings demonstrate that E. coli-induced MCP-1 causes neutrophil recruitment directly via chemotaxis as well as indirectly via modulation of keratinocyte cell-derived chemokine, macrophage inflammatory protein 2, and LTB(4).

Involvement of cholangiocyte proliferation in biliary fibrosis

Cholangiocytes are the epithelial cells that line the biliary tree. In the adult liver, they are a mitotically dormant cell population, unless ductular reaction is triggered by injury. The ability of cholangiocytes to proliferate is important in many different human pathological liver conditions that target this cell type, which are termed cholangiopathies (i.e. primary biliary cirrhosis, primary sclerosing cholangitis and biliary atresia). In our article, we provide background information on the morphological and functional heterogeneity of cholangiocytes, summarize what is currently known about their proliferative processes, and briefly describe the diseases that target these cells. In addition, we address recent findings that suggest cholangiocyte involvement in epithelial-to-mesenchymal transformation and liver fibrosis, and propose directions for future studies.

The integrin-blocking peptide RGDS inhibits airway smooth muscle remodeling in a guinea pig model of allergic asthma

RATIONALE

Airway remodeling, including increased airway smooth muscle (ASM) mass and contractility, contributes to airway hyperresponsiveness in asthma. The mechanisms driving these changes are, however, incompletely understood. Recently, an important role for extracellular matrix proteins in regulating ASM proliferation and contractility has been found, suggesting that matrix proteins and their integrins actively modulate airway remodeling.

OBJECTIVES

To investigate the role of RGD (Arg-Gly-Asp)-binding integrins in airway remodeling in an animal model of allergic asthma.

METHODS

Using a guinea pig model of allergic asthma, the effects of topical application of the integrin-blocking peptide RGDS (Arg-Gly-Asp-Ser) and its negative control GRADSP (Gly-Arg-Ala-Asp-Ser-Pro) were assessed on markers of ASM remodeling, fibrosis, and inflammation induced by repeated allergen challenge. In addition, effects of these peptides on human ASM proliferation and maturation were investigated in vitro.

MEASUREMENTS AND MAIN RESULTS

RGDS attenuated allergen-induced ASM hyperplasia and hypercontractility as well as increased pulmonary expression of smooth muscle myosin heavy chain and the proliferative marker proliferating cell nuclear antigen (PCNA). No effects were observed for GRADSP. The RGDS effects were ASM selective, as allergen-induced eosinophil and neutrophil infiltration as well as fibrosis were unaffected. In cultured human ASM cells, we demonstrated that proliferation induced by collagen I, fibronectin, serum, and platelet-derived growth factor requires signaling via RGD-binding integrins, particularly of the alpha(5)beta(1) subtype. In addition, RGDS inhibited smooth muscle alpha-actin accumulation in serum-deprived ASM cells.

CONCLUSIONS

This is the first study indicating that integrins modulate ASM remodeling in an animal model of allergic asthma, which can be inhibited by a small peptide containing the RGD motif.

Both TRIF- and MyD88-dependent signaling contribute to host defense against pulmonary Klebsiella infection

Klebsiella pneumoniae causes extensive lung damage. TLR signaling involves adaptors TRIF and MyD88. However, the relative contribution of TRIF and MyD88 signaling in host defense against pulmonary K. pneumoniae infection has not been elucidated. Therefore, we investigated the role of TRIF and MyD88 in K. pneumoniae pneumonia. TRIF(-/-) mice infected with K. pneumoniae showed impaired survival and reduced bacterial clearance, neutrophil influx, histopathologic evidence of inflammation, and TNF-alpha, IL-6, KC, MIP-2, but not LIX, expression in the lungs. In addition, K. pneumoniae-induced late NF-kappaB activation and phosphorylation of MAPKs was attenuated in the lungs of TRIF(-/-) mice. However, MyD88(-/-) mice infected with K. pneumoniae showed a much more remarkable phenotype, including impaired survival and reduced bacterial clearance, histopathology, and TNF-alpha, IL-6, KC, MIP-2, and LIX expression with almost no neutrophil influx in the lungs. In MyD88(-/-) mice, K. pneumoniae-induced early NF-kappaB and MAPK activation in the lungs was also reduced. Furthermore, the role of MyD88 is dominant over TRIF because TRIF/MyD88 double knockout mice displayed a more pronounced phenotype than TRIF(-/-) mice. Moreover, human alveolar macrophages pretreated with MyD88 blocking peptide showed attenuated TNF-alpha, IL-6, and IL-8 expression. Also, C57BL/6 mice pretreated with MyD88 blocking peptide exhibited attenuation in K. pneumoniae-induced neutrophil influx and enhanced bacterial burden in the lungs and dissemination. Overall, this investigation provides new insights into the TRIF and MyD88 signaling triggered by pulmonary K. pneumoniae infection in the lungs and demonstrate the therapeutic potential of MyD88 in reducing excessive neutrophil influx in human disease during Gram-negative bacterial pneumonia.

Myeloid differentiation protein-2-dependent and -independent neutrophil accumulation during Escherichia coli pneumonia

Bacterial pneumonia remains a serious disease. Pattern recognition receptors play an integral role in neutrophil accumulation during pneumonia. Although myeloid differentiation protein (MD)-2 has been recognized as a key molecule for LPS signaling, the role of MD-2 in neutrophil accumulation in the lung during bacterial infection has not been explored. Here, we investigate the role of MD-2 in Escherichia coli LPS-induced lung inflammation and E. coli-induced pneumonia. LPS-induced CD14-independent neutrophil accumulation was abolished in CD14/MD-2(-/-) mice. MD-2(-/-) mice challenged with LPS displayed attenuated neutrophil influx, NF-kappaB activation, cytokine/chemokine expression, and lung histopathology. MD-2(-/-) mice transplanted with MD-2(+/+) bone marrow demonstrated decreased neutrophil influx and cytokine/chemokine expression in the lungs when challenged by LPS. MD-2(-/-) mice infected with E. coli demonstrated reduced neutrophil influx and cytokine/chemokine expression in the lungs, whereas heat-killed E. coli did not induce either neutrophil accumulation or cytokine/chemokine expression in MD-2(-/-) mice infected with E. coli. Furthermore, MD-2(-/-) mice displayed increased bacterial burden in the lungs and enhanced bacterial dissemination. Toll-like receptor (TLR)-5(-/-) mice infected with E. coli exhibited attenuated neutrophil accumulation, whereas MD-2/TLR5(-/-) mice inoculated with E. coli showed further attenuated neutrophil influx and impaired bacterial clearance. Taken together, these new findings demonstrate: (1) the important role of MD-2 in the CD14-independent LPS-mediated cascade of neutrophil influx; (2) the relative importance of bone marrow- and non-bone marrow cell-derived MD-2 in LPS-induced inflammation; and (3) the essential role of MD-2-dependent and MD-2-independent (TLR5) signaling in E. coli-induced neutrophil accumulation and pulmonary host defense.

Increased expression of collagen receptors: alpha1beta1 and alpha2beta1 integrins on blood eosinophils in bronchial asthma

BACKGROUND

Eosinophils are one of the major effector cells in bronchial asthma. Their infiltration of airways correlates with the asthma severity. Recruitment and activation of eosinophils are partially mediated by integrins alpha4beta1 and alpha4beta7. Collagens type I and IV constitute important components of extracellular matrix and vascular basement membrane, respectively. Therefore, collagen-binding integrins (alpha1beta1 and alpha2beta1) may also play a role in eosinophil lung infiltration.

OBJECTIVE

To evaluate the possible presence of alpha1beta1 and alpha2beta1 integrins on peripheral blood eosinophils from asthmatic subjects.

METHODS

Collagen receptors were studied on eosinophils separated by immunomagnetic CD16-negative method from healthy donors (n=13) and patients with moderate persistent atopic bronchial asthma (n=15). Surface receptor identification was performed by flow cytometry and cell adhesion assay.

RESULTS

Eosinophils isolated from the patients showed increased expression of both alpha1beta1 and alpha2beta1 integrins as compared with healthy controls. Moreover, adhesive function of eosinophils to collagen type IV was inhibited by snake venom disintegrins: viperistatin and obtustatin. These disintegrins contain KTS active motif and are specific inhibitors of alpha1beta1 integrin.

CONCLUSION

We demonstrated for the first time that collagen receptors: alpha1beta1 and alpha2beta1 integrins are overexpressed on the surface of peripheral blood eosinophils of asthmatic subjects. Further studies may reveal potential application of KTS-disintegrins or their structural analogs for therapy of bronchial asthma.

The regulatory role of TGF-beta in airway remodeling in asthma

Both structural and inflammatory cells are capable of secreting transforming growth factor (TGF)-beta and expressing TGF-beta receptors. TGF-beta can induce multiple cellular responses including differentiation, apoptosis, survival and proliferation, and has been implicated in the development of several pathogenic conditions including cancer and asthma. Elevated levels of TGF-beta have been reported in the asthmatic airway. TGF-beta binds to its receptor complex and activates multiple pathways involving proteins such as Sma and Mad homologues, phosphatidylinositol-3 kinase and the mitogen-activated protein kinases, leading to the transcription of several genes. Cell type, cellular condition, and microenvironment, all play a role in determining which pathway is activated, which, in turn, is an indication of which gene is to be transcribed. TGF-beta has been shown to induce apoptosis in airway epithelial cells. A possible role for TGF-beta in the regulation of epithelial cell adhesion properties has also been reported. Enhancement of goblet cell proliferation by TGF-beta suggests a role in mucus hyper-secretion. Elevated levels of TGF-beta correlate with subepithelial fibrosis. TGF-beta induces proliferation of fibroblast cells and their differentiation into myofibroblasts and extracellular matrix (ECM) protein synthesis during the development of subepithelial fibrosis. TGF-beta also induces proliferation and survival of and ECM secretion in airway smooth muscle cells (ASMCs), suggesting a possible cause of increased thickness of airway tissues. TGF-beta also induces the production and release of vascular endothelial cell growth factor and plasminogen activator inhibitor, contributing to the vascular remodeling in the asthmatic airway. Blocking TGF-beta activity inhibits epithelial shedding, mucus hyper-secretion, angiogenesis, ASMC hypertrophy and hyperplasia in an asthmatic mouse model. Reduction of TGF-beta production and control of TGF-beta effects would be beneficial in the development of therapeutic intervention for airway remodeling in chronic asthma.

Toll/IL-1R Domain-Containing Adaptor Protein (TIRAP) Is a Critical Mediator of Antibacterial Defense in the Lung against Klebsiella pneumoniae but Not Pseudomonas aeruginosa

Bacterial pneumonia is a leading cause of mortality and is associated with extensive neutrophil accumulation. Major pathogens associated with this disease include nonflagellated Klebsiella pneumoniae (Kp) and flagellated Pseudomonas aeruginosa (Pa). TLRs are essential for innate immune defense. TIRAP (Toll/IL-1R domain-containing adaptor protein) is an adaptor in TLR1, TLR2, TLR4, and TLR6 signaling, whereas MyD88 is an adaptor for all TLRs. However, the importance of TIRAP in pulmonary defense against Kp or Pa has not been examined. To demonstrate the role of TIRAP, TIRAP-deficient and wild-type littermates were intratracheally inoculated with Kp or Pa. We found that TIRAP(-/-) mice had substantial mortality, higher bacterial burden in the lungs, and enhanced dissemination following Kp challenge. Furthermore, Kp-induced neutrophil sequestration, histopathology, and MIP-2, TNF-alpha, IL-6, and LIX (lipopolysaccharide-induced CXC chemokine) production were attenuated in the lungs of TIRAP(-/-) mice. In contrast, TIRAP is not required for Pa-induced mortality, pulmonary bacterial burden, bacterial dissemination, neutrophil accumulation, or histopathology, yet it is necessary for MIP-2, TNF-alpha, and IL-6 production, but not LIX production. However, both Kp- and Pa-induced neutrophil influxes are MyD88 dependent. To determine the mechanisms associated with Pa-induced neutrophil accumulation, we inoculated mice with a flagellin C mutant of Pa (PaDeltafliC) or purified flagellin, a TLR5 agonist. PaDeltafliC-induced neutrophil sequestration and LIX expression are dependent on TIRAP, whereas flagellin-induced neutrophil influx and LIX expression are independent of TIRAP. These novel findings illustrate a pathogen-specific role for TIRAP in pulmonary defense and suggest that TLR5 plays an essential role for Pa-induced neutrophil influx via LIX production.

Grafting aminocyclopentane carboxylic acids onto the RGD tripeptide sequence generates low nanomolar alphaVbeta3/alphaVbeta5 integrin dual binders

Eleven gamma-aminocyclopentane carboxylic acid (Acpca) platforms, including four dihydroxy representatives (19-22), three hydroxy analogues (34-36), and four deoxy derivatives (30-33), were prepared in a chiral nonracemic format. These simple units were then grafted onto an Arg-Gly-Asp (RGD) tripeptide framework by a mixed solid phase/solution protocol delivering an ensemble of 11 macrocyclic analogues of type cyclo-[-Arg-Gly-Asp-Acpca-], 1-11. The individual compounds were evaluated for their binding affinity toward the alphaVbeta3 and alphaVbeta5 integrin receptors. The analogue 10 exhibited a very interesting activity profile (IC50/alphaVbeta3= 1.5 nM; IC50/alphaVbeta5= 0.59 nM), comparable to that of reference compounds EMD121974 and ST1646. Closely related congeners 6, 8, and 9 also proved to be excellent dual binders with activity levels in the low nanomolar range. The three-dimensional (3D) NMR solution structures were determined, and docking studies to X-ray crystal structure of the extracellular segment of integrin alphaVbeta3 in complex with the reference compound EMD121974 were performed on selected analogues to elucidate the interplay between structure and function in these systems and to evidence the subtle bases for receptorial recognition. The results prove that the principle of isosteric dipeptide replacement for peptidomimetics design and synthesis can be violated, without detriment to the development of highly effective integrin binders.

Toll-IL-1 Receptor Domain-Containing Adaptor Protein Is Critical for Early Lung Immune Responses against Escherichia coli Lipopolysaccharide and Viable Escherichia coli

Pulmonary bacterial diseases are a leading cause of mortality in the U.S. Innate immune response is vital for bacterial clearance from the lung, and TLRs play a critical role in this process. Toll-IL-1R domain-containing adaptor protein (TIRAP) is a key molecule in the TLR4 and 2 signaling. Despite its potential importance, the role of TIRAP-mediated signaling in lung responses has not been examined. Our goals were to determine the role of TIRAP-dependent signaling in the induction of lung innate immune responses against Escherichia coli LPS and viable E. coli, and in lung defense against E. coli in mice. LPS-induced neutrophil sequestration; NF-kappaB translocation; keratinocyte cell-derived chemokine, MIP-2, TNF-alpha, and IL-6 expression; histopathology; and VCAM-1 and ICAM-1 expression were abolished in the lungs of TIRAP-/- mice. A cell-permeable TIRAP blocking peptide attenuated LPS-induced lung responses. Furthermore, immune responses in the lungs of TIRAP-/- mice were attenuated against E. coli compared with TIRAP+/+ mice. TIRAP-/- mice also had early mortality, higher bacterial burden in the lungs, and more bacterial dissemination following E. coli inoculation. Moreover, we used human alveolar macrophages to examine the role of TIRAP signaling in the human system. The TIRAP blocking peptide abolished LPS-induced TNF-alpha, IL-6, and IL-8 expression in alveolar macrophages, whereas it attenuated E. coli-induced expression of these cytokines and chemokines. Taken together, this is the first study illustrating the crucial role of TIRAP in the generation of an effective early immune response against E. coli LPS and viable E. coli, and in lung defense against a bacterial pathogen.