Polarized secretion of fibrinogen by lung epithelial cells

Repair and regeneration of the alveolar epithelium in lung injury

Considerable progress has been made in understanding the function of alveolar epithelial cells in a quiescent state and regeneration mechanism after lung injury. Lung injury occurs commonly from severe viral and bacterial infections, inhalation lung injury, and indirect injury sepsis. A series of pathological mechanisms caused by excessive injury, such as apoptosis, autophagy, senescence, and ferroptosis, have been studied. Recovery from lung injury requires the integrity of the alveolar epithelial cell barrier and the realization of gas exchange function. Regeneration mechanisms include the participation of epithelial progenitor cells and various niche cells involving several signaling pathways and proteins. While alveoli are damaged, alveolar type II (AT2) cells proliferate and differentiate into alveolar type I (AT1) cells to repair the damaged alveolar epithelial layer. Alveolar epithelial cells are surrounded by various cells, such as fibroblasts, endothelial cells, and various immune cells, which affect the proliferation and differentiation of AT2 cells through paracrine during alveolar regeneration. Besides, airway epithelial cells also contribute to the repair and regeneration process of alveolar epithelium. In this review, we mainly discuss the participation of epithelial progenitor cells and various niche cells involving several signaling pathways and transcription factors.

Fibrinogen on extracellular vesicles derived from polyhexamethylene guanidine phosphate-exposed mice induces inflammatory effects via integrin β

Polyhexamethylene guanidine phosphate (PHMG-p), used as a humidifier disinfectant, causes interstitial lung disease, obliterative bronchiolitis, and lung fibrosis; however, little is known about its effect on intercellular interactions. Extracellular vesicles (EVs), which carry diverse compounds including proteins, RNA, and DNA to mediate cell-to-cell communication through their paracrine effects, have been highlighted as novel factors in lung fibrogenesis. This study aimed to identify the effect of proteins on small EVs (sEVs) from bronchoalveolar lavage fluid (BALF) of the recipient cells after PHMG-p exposure. A week after intratracheal administration of PHMG-p, sEVs were isolated from BALF of tissue showing overexpressed inflammatory and fibrosis markers. To investigate the role of sEVs in inflammation, naïve macrophages were cultured with sEVs, which induced their activation. To identify sEV proteins that are associated with these responses, proteomics analysis was performed. In the gene ontology analysis, coagulation, fibrinolysis, and hemostasis were associated with the upregulated proteins in sEVs. The highest increase was observed in fibrinogen levels, which was also related to those gene ontologies. We validated role of exosomal fibrinogen in inflammation using recombinant fibrinogen and an inhibitor of the integrin, which is the binding receptor for fibrinogen. Overall, we elucidated that increased fibrinogen levels in the early sEVs-PHMG activated inflammatory response during early fibrosis. These results suggest that sEVs from the BALF of PHMG-p-exposed mice could aggravate fibrogenesis by activating naïve macrophages via various proteins in the sEVs, Furthermore, this finding will be broadening the spectrum of communicating mediators.

Characterization of a flexible AAV-DTR/DT mouse model of acute epithelial lung injury

Animal models are important to mimic certain pathways or biological aspects of human pathologies including acute and chronic pulmonary diseases. We developed a novel and flexible mouse model of acute epithelial lung injury based on adeno-associated virus (AAV) variant 6.2 mediated expression of the human diphtheria toxin receptor (DTR). Following intratracheal administration of diphtheria toxin (DT), a cell-specific death of bronchial and alveolar epithelial cells can be observed. In contrast to other lung injury models, the here described mouse model provides the possibility of targeted injury using specific tropisms of AAV vectors or cell type specific promotors to drive the human DTR expression. Also, generation of cell specific mouse lines is not required. Detailed characterization of the AAV-DTR/DT mouse model including titration of viral genome (vg) load and administered DT amount revealed increasing cell numbers in bronchoalveolar lavage (BAL; macrophages, neutrophils, and unspecified cells) and elevation of degenerated cells and infiltrated leukocytes in lung tissue, dependent of vg load and DT dose. Cytokine levels in BAL fluid showed different patterns with higher vg load, e.g. IFNγ, TNFα, and IP10 increasing and IL-5 and IL-6 decreasing, while lung function was not affected. Additionally, laser-capture microdissection (LCM)-based proteomics of bronchial epithelium and alveolar tissue revealed upregulated immune and inflammatory response in all regions and extracellular matrix deposition in infiltrated alveoli. Overall, our novel AAV-DTR/DT model allows investigation of repair mechanisms following epithelial injury and resembles specific mechanistic aspects of acute and chronic pulmonary diseases.

Fibrin(ogen) Is Constitutively Expressed by Differentiated Intestinal Epithelial Cells and Mediates Wound Healing

Fibrinogen is a large molecule synthesized in the liver and released in the blood. Circulating levels of fibrinogen are upregulated after bleeding or clotting events and support wound healing. In the context of an injury, thrombin activation drives conversion of fibrinogen to fibrin. Fibrin deposition contains tissue damage, stops blood loss, and prevents microbial infection. In most circumstances, fibrin needs to be removed to allow the resolution of inflammation and tissue repair, whereas failure of this may lead to the development of various disorders. However, the contribution of fibrinogen to tissue inflammation and repair is likely to be context-dependent. In this study, the concept that fibrin needs to be removed to allow tissue repair and to reduce inflammation is challenged by our observations that, in the intestine, fibrinogen is constitutively produced by a subset of intestinal epithelial cells and deposited at the basement membrane as fibrin where it serves as a substrate for wound healing under physiological conditions such as epithelial shedding at the tip of the small intestinal villus and surface epithelium of the colon as well as under pathological conditions that require rapid epithelial repair. The functional integrity of the intestine is ensured by the constant renewal of its simple epithelium. Superficial denuding of the epithelial cell layer occurs regularly and is rapidly corrected by a process called restitution that can be influenced by various soluble and insoluble factors. Epithelial cell interaction with the extracellular matrix greatly influences the healing process by acting on cell morphology, adhesion, and migration. The functional contribution of a fibrin(ogen) matrix in the intestine was studied under physiological and pathological contexts. Our results (immunofluorescence, immunoelectron microscopy, and quantitative PCR) show that fibrin(ogen) is a novel component of the basement membrane associated with the differentiated epithelial cell population in both the small intestine and colon. Fibrin(ogen) alone is a weak ligand for epithelial cells and behaves as an anti-adhesive molecule in the presence of type I collagen. Furthermore, the presence of fibrin(ogen) significantly shortens the time required to achieve closure of wounded epithelial cell monolayers and co-cultures in a PI3K-dependent manner. In human specimens with Crohn’s disease, we observed a major accumulation of fibrin(ogen) throughout the tissue and at denuded sites. In mice in which fibrin formation was inhibited with dabigatran treatment, dextran sulfate sodium administration provoked a significant increase in the disease activity index and pathological features such as mucosal ulceration and crypt abscess formation. Taken together, these results suggest that fibrin(ogen) contributes to epithelial healing under both normal and pathological conditions.

Are elevated plasma fibrinogen associated with lung function? An 8-year follow-up of the ELSA study

Background

Fibrinogen is an important biomarker of inflammation, but findings from longitudinal studies that correlated fibrinogen with lung function in older adults are inconsistent.

Aim

To investigate the relationship between fibrinogen plasma levels and lung function impairment later in life.

Methods

Longitudinal analysis of 2,150 participants of the English Longitudinal Study of Ageing (ELSA) aged 50 years and older. Associations between changes in plasma fibrinogen between waves 2 (2004–05) and 4 (2008–09) and lung function in wave 6 (2012–13) were performed using multiple linear regression adjusted by potential confounders.

Results

Regarding the fibrinogen profile, 18.5% of the participants presented higher levels in both waves. In the adjusted models, the maintenance of high fibrinogen levels was associated with a significant reduction of lung function only for men. FEV₁ showed a reduction of 0.17L, FVC of 0.22L, and the percentages predicted were 5.16% for FEV₁ and 6.21% for FVC compared to those that maintained normal levels of fibrinogen.

Discussion

To the best of our knowledge, this was the first study investigating the relationship between changes in fibrinogen levels over a long follow-up period and lung function in older adults without pre-existing chronic diseases. ELSA has information on critical demographic and clinical parameters, which allowed to adjust for potential confounding factors.

Conclusion

It was found that the persistence of high levels of plasma fibrinogen in older English men, but not women, is associated with lung function decline. Therefore, plasma fibrinogen showed to be an important biomarker of pulmonary dysfunction in this population.

Construction of functional biliary epithelial branched networks with predefined geometry using digital light stereolithography

Cholangiocytes, biliary epithelial cells, are known to spontaneously self-organize into spherical cysts with a central lumen. In this work, we explore a promising biocompatible stereolithographic approach to encapsulate cholangiocytes into geometrically controlled 3D hydrogel structures to guide them towards the formation of branched tubular networks. We demonstrate that within the appropriate mix of hydrogels, normal rat cholangiocytes can proliferate, migrate, and organize into branched tubular structures with walls consisting of a cell monolayer, transport fluorescent dyes into the luminal space, and show markers of epithelial maturation such as primary cilia and continuous tight junctions. The resulting structures have dimensions typically found in the intralobular and intrahepatic biliary tree and are stable for weeks, without any requirement of bulk supporting material, thereby offering total access to the external side of these biliary epithelial constructs.

SARS-CoV-2 suppresses anticoagulant and fibrinolytic gene expression in the lung

Extensive fibrin deposition in the lungs and altered levels of circulating blood coagulation proteins in COVID-19 patients imply local derangement of pathways that limit fibrin formation and/or promote its clearance. We examined transcriptional profiles of bronchoalveolar lavage fluid (BALF) samples to identify molecular mechanisms underlying these coagulopathies. mRNA levels for regulators of the kallikrein-kinin (C1-inhibitor), coagulation (thrombomodulin, endothelial protein C receptor), and fibrinolytic (urokinase and urokinase receptor) pathways were significantly reduced in COVID-19 patients. While transcripts for several coagulation proteins were increased, those encoding tissue factor, the protein that initiates coagulation and whose expression is frequently increased in inflammatory disorders, were not increased in BALF from COVID-19 patients. Our analysis implicates enhanced propagation of coagulation and decreased fibrinolysis as drivers of the coagulopathy in the lungs of COVID-19 patients.

Serum fibrinogen as a diagnostic and prognostic biomarker for pancreatic ductal adenocarcinoma

BACKGROUND/OBJECTIVES

Early diagnosis of pancreatic ductal adenocarcinoma (PDAC) is important as PDAC can lead to mortality; however, no specific biomarker has been identified for its early diagnosis. We previously identified fibrinogen α chain as a promising biomarker for differentiating between patients with and without PDAC using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Here, we aimed to validate the clinical usefulness of serum fibrinogen as a biomarker for PDAC.

METHODS

From 2009 to 2011, blood samples of 67 PDAC patients and 43 healthy adults (controls) were prospectively collected. Serum fibrinogen levels and their clinical significances were evaluated.

RESULTS

Mean fibrinogen levels were significantly higher in the PDAC group than in the control group (3.08 ± 0.565 vs. 2.54 ± 0.249 log₁₀ ng/mL, P < 0.001). In the receiver operating characteristic analysis, overall sensitivity, and specificity of serum fibrinogen levels for differentiating PDAC patients from control patients were 67.4% and 83.6%, respectively, with a 427-ng/mL cutoff value. Serum fibrinogen levels were significantly higher in PDAC patients with distant metastasis than in those without distant metastasis (3.38 ± 0.581 vs. 2.93 ± 0.499 log₁₀ ng/mL, P = 0.002). Median overall survival was significantly longer in PDAC patients with low fibrinogen levels (<1000 ng/mL) than in those with high fibrinogen levels (≥1000 ng/mL) [489 days (95% confidence interval, 248.1-729.9) vs. 172 days (58.4-285.6) (P = 0.008)]. Although serum fibrinogen levels were poorly correlated with carbohydrate antigen 19-9 levels, these two biomarkers together predicted survival better.

CONCLUSIONS

Serum fibrinogen levels may be a useful biomarker for diagnosing and predicting PDAC prognosis.

Pulmonary Innate Immune Response Determines the Outcome of Inflammation During Pneumonia and Sepsis-Associated Acute Lung Injury

The lung is a primary organ for gas exchange in mammals that represents the largest epithelial surface in direct contact with the external environment. It also serves as a crucial immune organ, which harbors both innate and adaptive immune cells to induce a potent immune response. Due to its direct contact with the outer environment, the lung serves as a primary target organ for many airborne pathogens, toxicants (aerosols), and allergens causing pneumonia, acute respiratory distress syndrome (ARDS), and acute lung injury or inflammation (ALI). The current review describes the immunological mechanisms responsible for bacterial pneumonia and sepsis-induced ALI. It highlights the immunological differences for the severity of bacterial sepsis-induced ALI as compared to the pneumonia-associated ALI. The immune-based differences between the Gram-positive and Gram-negative bacteria-induced pneumonia show different mechanisms to induce ALI. The role of pulmonary epithelial cells (PECs), alveolar macrophages (AMs), innate lymphoid cells (ILCs), and different pattern-recognition receptors (PRRs, including Toll-like receptors (TLRs) and inflammasome proteins) in neutrophil infiltration and ALI induction have been described during pneumonia and sepsis-induced ALI. Also, the resolution of inflammation is frequently observed during ALI associated with pneumonia, whereas sepsis-associated ALI lacks it. Hence, the review mainly describes the different immune mechanisms responsible for pneumonia and sepsis-induced ALI. The differences in immune response depending on the causal pathogen (Gram-positive or Gram-negative bacteria) associated pneumonia or sepsis-induced ALI should be taken in mind specific immune-based therapeutics.

Alveolar lipids in pulmonary disease. A review

Lung lipid metabolism participates both in infant and adult pulmonary disease. The lung is composed by multiple cell types with specialized functions and coordinately acting to meet specific physiologic requirements. The alveoli are the niche of the most active lipid metabolic cell in the lung, the type 2 cell (T2C). T2C synthesize surfactant lipids that are an absolute requirement for respiration, including dipalmitoylphosphatidylcholine. After its synthesis and secretion into the alveoli, surfactant is recycled by the T2C or degraded by the alveolar macrophages (AM). Surfactant biosynthesis and recycling is tightly regulated, and dysregulation of this pathway occurs in many pulmonary disease processes. Alveolar lipids can participate in the development of pulmonary disease from their extracellular location in the lumen of the alveoli, and from their intracellular location in T2C or AM. External insults like smoke and pollution can disturb surfactant homeostasis and result in either surfactant insufficiency or accumulation. But disruption of surfactant homeostasis is also observed in many chronic adult diseases, including chronic obstructive pulmonary disease (COPD), and others. Sustained damage to the T2C is one of the postulated causes of idiopathic pulmonary fibrosis (IPF), and surfactant homeostasis is disrupted during fibrotic conditions. Similarly, surfactant homeostasis is impacted during acute respiratory distress syndrome (ARDS) and infections. Bioactive lipids like eicosanoids and sphingolipids also participate in chronic lung disease and in respiratory infections. We review the most recent knowledge on alveolar lipids and their essential metabolic and signaling functions during homeostasis and during some of the most commonly observed pulmonary diseases.

Cellular and Molecular Events in the Airway Epithelium Defining the Interaction Between House Dust Mite Group 1 Allergens and Innate Defences

Serodominant group 1 allergens of house dust mites (HDMs) are cysteine protease digestive enzymes. By increasing the detection of any allergen by dendritic antigen presenting cells, upregulating inflammatory signalling molecules, and activating cells crucial to the transition from innate to acquired immune responses, the proteolytic activity of these HDM allergens also underlies their behaviour as inhalant allergens. The significance of this property is underlined by the attenuation of allergic responses to HDMs by novel inhibitors in experimental models. The group 1 HDM allergens act as prothrombinases, enabling them to operate the canonical stimulation of protease activated receptors 1 and 4. This leads to the ligation of Toll-like receptor 4, which is an indispensable component in HDM allergy development, and reactive oxidant-regulated gene expression. Intermediate steps involve epidermal growth factor receptor ligation, activation of a disintegrin and metalloproteases, and the opening of pannexons. Elements of this transduction pathway are shared with downstream signalling from biosensors which bind viral RNA, suggesting a mechanistic linkage between allergens and respiratory viruses in disease exacerbations. This review describes recent progress in the characterisation of an arterial route which links innate responses to inhaled allergens to events underpinning the progression of allergy to unrelated allergens.

Allergen Delivery Inhibitors: A Rationale for Targeting Sentinel Innate Immune Signaling of Group 1 House Dust Mite Allergens through Structure-Based Protease Inhibitor Design

Diverse evidence from epidemiologic surveys and investigations into the molecular basis of allergenicity have revealed that a small cadre of "initiator" allergens promote the development of allergic diseases, such as asthma, allergic rhinitis, and atopic dermatitis. Pre-eminent among these initiators are the group 1 allergens from house dust mites (HDM). In mites, group 1 allergens function as cysteine peptidase digestive enzymes to which humans are exposed by inhalation of HDM fecal pellets. Their protease nature confers the ability to activate high gain signaling mechanisms which promote innate immune responses, leading to the persistence of allergic sensitization. An important feature of this process is that the initiator drives responses both to itself and to unrelated allergens lacking these properties through a process of collateral priming. The clinical significance of group 1 HDM allergens in disease, their serodominance as allergens, and their IgE-independent bioactivities in innate immunity make these allergens interesting therapeutic targets in the design of new small-molecule interventions in allergic disease. The attraction of this new approach is that it offers a powerful, root-cause-level intervention from which beneficial effects can be anticipated by interference in a wide range of effector pathways associated with these complex diseases. This review addresses the general background to HDM allergens and the validation of group 1 as putative targets. We then discuss structure-based drug design of the first-in-class representatives of allergen delivery inhibitors aimed at neutralizing the proteolytic effects of HDM group 1 allergens, which are essential to the development and maintenance of allergic diseases.

Streptococcus agalactiae Non-Pilus, Cell Wall-Anchored Proteins: Involvement in Colonization and Pathogenesis and Potential as Vaccine Candidates

Group B Streptococcus (GBS) remains an important etiological agent of several infectious diseases including neonatal septicemia, pneumonia, meningitis, and orthopedic device infections. This pathogenicity is due to a variety of virulence factors expressed by Streptococcus agalactiae. Single virulence factors are not sufficient to provoke a streptococcal infection, which is instead promoted by the coordinated activity of several pathogenicity factors. Such determinants, mostly cell wall-associated and secreted proteins, include adhesins that mediate binding of the pathogen to host extracellular matrix/plasma ligands and cell surfaces, proteins that cooperate in the invasion of and survival within host cells and factors that neutralize phagocytosis and/or modulate the immune response. The genome-based approaches and bioinformatics tools and the extensive use of biophysical and biochemical methods and animal model studies have provided a great wealth of information on the molecular structure and function of these virulence factors. In fact, a number of new GBS surface-exposed or secreted proteins have been identified (GBS immunogenic bacterial adhesion protein, leucine-rich repeat of GBS, serine-rich repeat proteins), the three-dimensional structures of known streptococcal proteins (αC protein, C5a peptidase) have been solved and an understanding of the pathogenetic role of "old" and new determinants has been better defined in recent years. Herein, we provide an update of our current understanding of the major surface cell wall-anchored proteins from GBS, with emphasis on their biochemical and structural properties and the pathogenetic roles they may have in the onset and progression of host infection. We also focus on the antigenic profile of these compounds and discuss them as targets for therapeutic intervention.

Pathways of airway oxidant formation by house dust mite allergens and viral RNA converge through myosin motors, pannexons and Toll-like receptor 4

Introduction

Intracellular reactive oxidant species (ROS) are generated in human airway epithelial cells by the prothrombinase action of Group 1 house dust mite (HDM) allergens and by ligation of viral RNA sensor Toll‐like receptors (TLRs). We explored signaling convergence between HDM allergens and TLRs in ROS generation because epithelial cells form the primary barrier against inhaled substances and dictate host responses to allergens and viruses.

Methods

ROS formation by Calu‐3 human airway cells was studied by measuring dihydrorhodamine 123 oxidation after activation by polyinosinic:polycytidylic acid (to activate TLR3), CL097 (to activate TLR7), a natural mixture of HDM allergens, or BzATP.

Results

TLR4 activation was identified as an indispensable response element for all stimuli, operating downstream from myosin motor activation, pannexon gating for ATP release and the endogenous activation of prothrombin. Exogenous prothrombin activation by HDM allergens was prevented by SGUL 1733, a novel inhibitor of the proteolytic activity of Group 1 HDM allergens, which thus prevented TLR4 from being activated at source.

Conclusions

Our data identify for the first time that endogenously‐generated prothrombin and TLR4 form a shared effector mechanism essential to intracellular ROS generation activated by a group 1 HDM allergen (itself a prothrombinase) or by ligation of viral RNA‐sensing TLRs. These stimuli operate a confluent signaling pathway in which myosin motors, gating of pannexons, and ADAM 10 lead to prothrombin‐dependent activation of TLR4 with a recycling activation of pannexons.

Putative salivary protein biomarkers for the diagnosis of oral lichen planus: a case-control study

BACKGROUND

Salivary protein biomarkers for screening and diagnosis of oral lichen planus (OLP) are not well-defined. The objective of this study was to identify putative protein biomarkers for OLP using proteomic approaches.

METHODS

Pooled unstimulated whole saliva was collected from five OLP patients and five healthy control participants. Saliva samples were then subjected to two-dimensional gel electrophoresis, followed by mass spectrometry to identify putative protein biomarkers. Subsequently, a subset of these putative biomarkers were validated in 24 OLP patients and 24 age-matched healthy control subjects, using an enzyme-linked immunosorbent assay (ELISA). Immunoblotting analyses were then performed in 3 pairs of age- and sex-matched OLP patients and healthy controls to confirm results from the ELISA study.

RESULTS

Thirty-one protein spots were identified, corresponding to 20 unique proteins. Notably, fibrinogen fragment D and complement component C3c exhibited increased expression in OLP patients, while cystatin SA exhibited decreased expression in OLP patients, compared with healthy control subjects. ELISA analyses indicated increased expression of fibrinogen fragment D and complement component C3c, and decreased expression of cystatin SA, in the saliva of OLP patients. Statistical differences in the expression of salivary complement C3c were observed between OLP patients and healthy control subjects. Immunoblotting analyses confirmed the results of our ELISA study.

CONCLUSION

Complement C3c, fibrinogen fragment D and cystatin SA may serve as salivary biomarkers for screening and/or diagnosis of OLP.

TREK-1 Regulates Cytokine Secretion from Cultured Human Alveolar Epithelial Cells Independently of Cytoskeletal Rearrangements

Background

TREK-1 deficient alveolar epithelial cells (AECs) secrete less IL-6, more MCP-1, and contain less F-actin. Whether these alterations in cytokine secretion and F-actin content are related remains unknown. We now hypothesized that cytokine secretion from TREK-1-deficient AECs was regulated by cytoskeletal rearrangements.

Methods

We determined F-actin and α-tubulin contents of control, TREK-1-deficient and TREK-1-overexpressing human A549 cells by confocal microscopy and western blotting, and measured IL-6 and MCP-1 levels using real-time PCR and ELISA.

Results

Cytochalasin D decreased the F-actin content of control cells. Jasplakinolide increased the F-actin content of TREK-1 deficient cells, similar to the effect of TREK-1 overexpression in control cells. Treatment of control and TREK-1 deficient cells with TNF-α, a strong stimulus for IL-6 and MCP-1 secretion, had no effect on F-actin structures. The combination of TNF-α+cytochalasin D or TNF-α+jasplakinolide had no additional effect on the F-actin content or architecture when compared to cytochalasin D or jasplakinolide alone. Although TREK-1 deficient AECs contained less F-actin at baseline, quantified biochemically, they contained more α-tubulin. Exposure to nocodazole disrupted α-tubulin filaments in control and TREK-1 deficient cells, but left the overall amount of α-tubulin unchanged. Although TNF-α had no effect on the F-actin or α-tubulin contents, it increased IL-6 and MCP-1 production and secretion from control and TREK-1 deficient cells. IL-6 and MCP-1 secretions from control and TREK-1 deficient cells after TNF-α+jasplakinolide or TNF-α+nocodazole treatment was similar to the effect of TNF-α alone. Interestingly, cytochalasin D decreased TNF-α-induced IL-6 but not MCP-1 secretion from control but not TREK-1 deficient cells.

Conclusion

Although cytochalasin D, jasplakinolide and nocodazole altered the F-actin and α-tubulin structures of control and TREK-1 deficient AEC, the changes in cytokine secretion from TREK-1 deficient cells cannot be explained by cytoskeletal rearrangements in these cells.

Transcriptional profile of Mycobacterium tuberculosis replicating in type II alveolar epithelial cells

Mycobacterium tuberculosis (M. tb) infection is initiated by the few bacilli inhaled into the alveolus. Studies in lungs of aerosol-infected mice provided evidence for extensive replication of M. tb in non-migrating, non-antigen-presenting cells in the alveoli during the first 2-3 weeks post-infection. Alveoli are lined by type II and type I alveolar epithelial cells (AEC) which outnumber alveolar macrophages by several hundred-fold. M. tb DNA and viable M. tb have been demonstrated in AEC and other non-macrophage cells of the kidney, liver, and spleen in autopsied tissues from latently-infected subjects from TB-endemic regions indicating systemic bacterial dissemination during primary infection. M. tb have also been demonstrated to replicate rapidly in A549 cells (type II AEC line) and acquire increased invasiveness for endothelial cells. Together, these results suggest that AEC could provide an important niche for bacterial expansion and development of a phenotype that promotes dissemination during primary infection. In the current studies, we have compared the transcriptional profile of M. tb replicating intracellularly in A549 cells to that of M. tb replicating in laboratory broth, by microarray analysis. Genes significantly upregulated during intracellular residence were consistent with an active, replicative, metabolic, and aerobic state, as were genes for tryptophan synthesis and for increased virulence (ESAT-6, and ESAT-6-like genes, esxH, esxJ, esxK, esxP, and esxW). In contrast, significant downregulation of the DevR (DosR) regulon and several hypoxia-induced genes was observed. Stress response genes were either not differentially expressed or were downregulated with the exception of the heat shock response and those induced by low pH. The intra-type II AEC M. tb transcriptome strongly suggests that AEC could provide a safe haven in which M. tb can expand dramatically and disseminate from the lung prior to the elicitation of adaptive immune responses.

Comparative proteomic analysis of lung tissue from guinea pigs with leptospiral pulmonary haemorrhage syndrome (LPHS) reveals a decrease in abundance of host proteins involved in cytoskeletal and cellular organization

Leptospiral pulmonary haemorrhage syndrome (LPHS) is a particularly severe form of leptospirosis. LPHS is increasingly recognized in both humans and animals and is characterized by rapidly progressive intra-alveolar haemorrhage leading to high mortality. The pathogenic mechanisms of LPHS are poorly understood which hampers the application of effective treatment regimes. In this study a 2-D guinea pig proteome lung map was created and used to investigate the pathogenic mechanisms of LPHS. Comparison of lung proteomes from infected and non-infected guinea pigs via differential in-gel electrophoresis revealed highly significant differences in abundance of proteins contained in 130 spots. Acute phase proteins were the largest functional group amongst proteins with increased abundance in LPHS lung tissue, and likely reflect a local and/or systemic host response to infection. The observed decrease in abundance of proteins involved in cytoskeletal and cellular organization in LPHS lung tissue further suggests that infection with pathogenic Leptospira induces changes in the abundance of host proteins involved in cellular architecture and adhesion contributing to the dramatically increased alveolar septal wall permeability seen in LPHS.

BIOLOGICAL SIGNIFICANCE

The recent completion of the complete genome sequence of the guinea pig (Cavia porcellus) provides innovative opportunities to apply proteomic technologies to an important animal model of disease. In this study, the comparative proteomic analysis of lung tissue from experimentally infected guinea pigs with leptospiral pulmonary haemorrhage syndrome (LPHS) revealed a decrease in abundance of proteins involved in cellular architecture and adhesion, suggesting that loss or down-regulation of cytoskeletal and adhesion molecules plays an important role in the pathogenesis of LPHS. A publically available guinea pig lung proteome map was constructed to facilitate future pulmonary proteomics in this species.

FbsC, a novel fibrinogen-binding protein, promotes Streptococcus agalactiae-host cell interactions

Streptococcus agalactiae (group B Streptococcus or GBS) is a common cause of invasive infections in newborn infants and adults. The ability of GBS to bind human fibrinogen is of crucial importance in promoting colonization and invasion of host barriers. We characterized here a novel fibrinogen-binding protein of GBS, designated FbsC (Gbs0791), which is encoded by the prototype GBS strain NEM316. FbsC, which bears two bacterial immunoglobulin-like tandem repeat domains and a C-terminal cell wall-anchoring motif (LPXTG), was found to be covalently linked to the cell wall by the housekeeping sortase A. Studies using recombinant FbsC indicated that it binds fibrinogen in a dose-dependent and saturable manner, and with moderate affinity. Expression of FbsC was detected in all clinical GBS isolates, except those belonging to the hypervirulent lineage ST17. Deletion of fbsC decreases NEM316 abilities to adhere to and invade human epithelial and endothelial cells, and to form biofilm in vitro. Notably, bacterial adhesion to fibrinogen and fibrinogen binding to bacterial cells were abolished following fbsC deletion in NEM316. Moreover, the virulence of the fbsC deletion mutant and its ability to colonize the brain were impaired in murine models of infection. Finally, immunization with recombinant FbsC significantly protected mice from lethal GBS challenge. In conclusion, FbsC is a novel fibrinogen-binding protein expressed by most GBS isolates that functions as a virulence factor by promoting invasion of epithelial and endothelial barriers. In addition, the protein has significant immunoprotective activity and may be a useful component of an anti-GBS vaccine.

Cleavage of fibrinogen by proteinases elicits allergic responses through Toll-like receptor 4

Proteinases and the innate immune receptor Toll-like receptor 4 (TLR4) are essential for expression of allergic inflammation and diseases such as asthma. A mechanism that links these inflammatory mediators is essential for explaining the fundamental basis of allergic disease but has been elusive. Here, we demonstrate that TLR4 is activated by airway proteinase activity to initiate both allergic airway disease and antifungal immunity. These outcomes were induced by proteinase cleavage of the clotting protein fibrinogen, yielding fibrinogen cleavage products that acted as TLR4 ligands on airway epithelial cells and macrophages. Thus, allergic airway inflammation represents an antifungal defensive strategy that is driven by fibrinogen cleavage and TLR4 activation. These findings clarify the molecular basis of allergic disease and suggest new therapeutic strategies.

Serum fibrinogen is an independent prognostic factor in operable nonsmall cell lung cancer

Serum fibrinogen converted to insoluble fibrin by activated thrombin, plays an important role in the coagulation system. Increased fibrinogen considerably influences cancer cell growth, progression and metastasis. In nonsmall cell lung cancer (NSCLC), however, the association between serum fibrinogen concentration and prognosis has not been fully examined. We enlisted 567 operable NSCLC patients in our study. Preoperative serum fibrinogen was measured by the Clauss method. The association of serum fibrinogen concentration with clinical pathological factors and patient outcome was evaluated. Survival analysis indicated that serum fibrinogen was an independent prognostic factor in operable NSCLC. Patients with hyperfibrinogenemia had an elevated risk of disease progression and death compared to patients with normal fibrinogen levels. The hazard ratio was 1.49 (95% confidence interval [CI] 1.07-2.05) for disease progression and 1.64 (95% CI 1.06-2.53) for death. The trend linking increasing fibrinogen levels with risk was also statistically significant for both outcomes (p < 0.05). These analyses were adjusted for patient age, sex, smoking behavior, disease stage, tumor grade and histology. Kaplan-Meier survival curves showed similar results. Preoperative serum fibrinogen is a novel independent prognostic biomarker in operable NSCLC.

Comparison of particle-exposure triggered pulmonary and systemic inflammation in mice fed with three different diets

BACKGROUND

Obesity can be linked to disease risks such as diabetes and cardiovascular disorders, but recently, the adipose tissue (AT) macrophage also emerges as actively participating in inflammation and immune function, producing pro- and anti-inflammatory factors. Connections between the AT and chronic lung diseases, like emphysema and asthma and a protective role of adipocyte-derived proteins against acute lung injury were suggested.In this study we addressed the question, whether a diet challenge increases the inflammatory response in the alveolar and the blood compartment in response to carbon nanoparticles (CNP), as a surrogate for ambient/urban particulate air pollutants.

METHODS

Mice were fed a high caloric carbohydrate-rich (CA) or a fat-rich (HF) diet for six weeks and were compared to mice kept on a purified low fat (LF) diet, respectively. Bronchoalveolar lavage (BAL) and blood samples were taken 24 h after intratracheal CNP instillation and checked for cellular and molecular markers of inflammation.

RESULTS AND DISCUSSION

The high caloric diets resulted in distinct effects when compared with LF mice, respectively: CA resulted in increased body and fat mass without affecting blood cellular immunity. Conversely, HF activated the blood system, increasing lymphocyte and neutrophil counts, and resulted in slightly increased body fat content. In contrast to higher pro-inflammatory BAL Leptin in CA and HF mice, on a cellular level, both diets did not lead to an increased pro-inflammatory basal status in the alveolar compartment per se, nor did result in differences in the particle-triggered response. However both diets resulted in a disturbance of the alveolar capillary barrier as indicated by enhanced BAL protein and lactate-dehydrogenase concentrations. Systemically, reduced serum Adiponectin in HF mice might be related to the observed white blood cell increase.

CONCLUSION

The increase in BAL pro-inflammatory factors in high caloric groups and reductions in serum concentrations of anti-inflammatory factors in HF mice, clearly show diet-specific effects, pointing towards augmented systemic inflammatory conditions. Our data suggest that extended feeding periods, leading to manifest obesity, are necessary to generate an increased susceptibility to particle-induced lung inflammation; although the diet-challenge already was efficient in driving pro-inflammatory systemic events.

Host Defense and the Airway Epithelium: Frontline Responses That Protect against Bacterial Invasion and Pneumonia

Airway epithelial cells are the first line of defense against invading microbes, and they protect themselves through the production of carbohydrate and protein matrices concentrated with antimicrobial products. In addition, they act as sentinels, expressing pattern recognition receptors that become activated upon sensing bacterial products and stimulate downstream recruitment and activation of immune cells which clear invading microbes. Bacterial pathogens that successfully colonize the lungs must resist these mechanisms or inhibit their production, penetrate the epithelial barrier, and be prepared to resist a barrage of inflammation. Despite the enormous task at hand, relatively few virulence factors coordinate the battle with the epithelium while simultaneously providing resistance to inflammatory cells and causing injury to the lung. Here we review mechanisms whereby airway epithelial cells recognize pathogens and activate a program of antibacterial pathways to prevent colonization of the lung, along with a few examples of how bacteria disrupt these responses to cause pneumonia.

Pathway focused protein profiling indicates differential function for IL-1B, -18 and VEGF during initiation and resolution of lung inflammation evoked by carbon nanoparticle exposure in mice

Background

Carbonaceous nanoparticles possess an emerging source of human exposure due to the massive release of combustion products and the ongoing revolution in nanotechnology. Pulmonary inflammation caused by deposited nanoparticles is central for their adverse health effects. Epidemiological studies suggest that individuals with favourable lung physiology are at lower risk for particulate matter associated respiratory diseases probably due to efficient control of inflammation and repair process. Therefore we selected a mouse strain C3H/HeJ (C3) with robust lung physiology and exposed it to moderately toxic carbon nanoparticles (CNP) to study the elicited pulmonary inflammation and its resolution.

Methods

5 μg, 20 μg and 50 μg CNP were intratracheally (i.t.) instilled in C3 mice to identify the optimal dose for subsequent time course studies. Pulmonary inflammation was assessed using histology, bronchoalveolar lavage (BAL) analysis and by a panel of 62 protein markers.

Results

1 day after instillation of CNP, C3 mice exhibited a typical dose response, with the lowest dose (5 μg) representing the 'no effect level' as reflected by polymorphonuclear leucocyte (PMN), and BAL/lung concentrations of pro-inflammatory proteins. Histological analysis and BAL-protein concentration did not reveal any evidence of tissue injury in 20 μg CNP instilled animals. Accordingly time course assessment of the inflammatory response was performed after 3 and 7 days with this dose (20 μg). Compared to day 1, BAL PMN counts were significantly decreased at day 3 and completely returned to normal by day 7. We have identified protein markers related to the acute response and also to the time dependent response in lung and BAL. After complete resolution of PMN influx on day 7, we detected elevated concentrations of 20 markers that included IL1B, IL18, FGF2, EDN1, and VEGF in lung and/or BAL. Biological pathway analysis revealed these factors to be involved in a closely regulated molecular cascade with IL1B/IL18 as upstream and FGF2/EDN1/VEGF as downstream molecules.

Conclusion

Considering the role of VEGF, FGF2 and EDN1 in lung development and morphogenesis together with the lack of any evident tissue damage we suggest a protective/homeostatic machinery to be associated in lungs of stable organisms to counter the CNP challenge as a precautionary measure.

The VE-cadherin binding domain of fibrinogen induces endothelial barrier permeability and enhances transendothelial migration of malignant breast epithelial cells

Fibrin deposition and exudation of plasma fibrinogen (Fg) have long been recognized as hallmarks of inflammation, cardiovascular disease and neoplasia. The Fg-beta(15-42) domain binds to the endothelial cell adhesion molecule, VE-cadherin, promoting endothelial cell proliferation, angiogenesis and leukocyte diapedesis. Furthermore, spontaneous blood-borne and lymphatic metastasis of some types of tumor emboli requires plasma fibrin(ogen); however, the molecular mechanisms by which this occurs are poorly understood. We sought to determine whether Fg-beta(15-42) and VE-cadherin binding interactions promote endothelial barrier permeability and breast cancer cell transendothelial migration (TEM) using transwell insert culture systems. Synthetic peptides containing/missing residues beta(15-17) critical for Fg-beta(15-42) binding to VE-cadherin, and antibodies that bind to Fg-beta(15-21) (T2G1) and VE-cadherin (BV9) were used to induce or inhibit Fg-mediated permeability and TEM. Fg induced dose-dependent permeability of human umbilical vein and microvascular endothelial but not epithelial cell barriers. Maximal Fg-induced endothelial permeability required Fg-beta(15-42) and VE-cadherin-binding interactions involving Fg-beta(15-17). Fg-induced TEM of malignant MDA-MB-231 and MCF-7 breast cancer cells also required Fg-beta(15-42) and VE-cadherin binding; however, such TEM was independent of E-cadherin or estrogen receptor expression. In contrast, Fg did not induce TEM of nonmalignant MCF-10A breast epithelial cells. Fg-induced endothelial permeability was retained in the presence of MDA-MB-231 but inhibited in the presence of MCF-10A cells. It is intriguing to speculate that loss of Fg-beta(15-42) binding by premalignant breast epithelial cells serves as a molecular switch to induce a highly aggressive, metastatic breast cancer phenotype. Hence, Fg-beta(15-42) represents a potential molecular target for therapeutic intervention of breast cancer metastasis.

RAPID PULMONARY EXPRESSION OF ACUTE-PHASE REACTANTS AFTER LOCAL LIPOPOLYSACCHARIDE EXPOSURE IN MICE IS FOLLOWED BY AN INTERLEUKIN-6 MEDIATED SYSTEMIC ACUTE-PHASE RESPONSE

This study investigated local and systemic innate immune responses in lipopolysaccharide (LPS)-induced lung inflammation in mice. Intratracheal LPS exposure resulted in increased pulmonary mRNA expression for acute-phase reactants (APRs) alpha(1)-antitrypsin (alpha(1)-AT), alpha(1)-acid glycoprotein (AGP), and LPS-binding protein (LBP) from 4 hours post exposure. Although pulmonary serum amyloid P component (SAP) mRNA was not increased, systemic levels of SAP, AGP, and LBP were elevated from 24 hours post exposure. Systemic APRs increase was associated with hepatic mRNA expression. As in vivo neutralization of interleukin (IL)-6, but not tumor necrosis factor (TNF)-alpha, fully ablated hepatic APR mRNA expression, IL-6 may act as signaling molecule between lung and liver. In conclusion, pulmonary LPS exposure induced rapid APR expression in lung, which precedes IL-6-mediated systemic elevation of APRs associated with hepatic APRs expression.

Electrospun fibrinogen: Feasibility as a tissue engineering scaffold in a rat cell culture model

Fibrinogen has a well-established tissue engineering track record because of its ability to induce improved cellular interaction and scaffold remodeling compared to synthetic scaffolds. While the feasibility of electrospinning fibrinogen scaffolds of submicron diameter fibers and their mechanical properties have been demonstrated, in vitro cellular interaction has not yet been evaluated. The goal of this study was to demonstrate, based on cellular interaction and scaffold remodeling, that electrospun fibrinogen can be used successfully as a tissue engineering scaffold. Electrospun fibrinogen scaffolds were disinfected, seeded with neonatal rat cardiac fibroblasts, and cultured for 2, 7, and 14 days. Cultures were treated to regulate scaffold degradation by either supplementing serum-containing media with aprotinin or crosslinking the scaffolds with glutaraldehyde vapor. Biocompatibility was assessed through a WST-1 cell proliferation assay. Postculture scaffolds were evaluated by scanning electron microscopy and histology. Cell culture demonstrated that fibroblasts readily migrate into and remodel electrospun fibrinogen scaffolds with deposition of native collagen. Supplementation of culture media with different concentrations of aprotinin-modulated scaffold degradation in a predictable fashion, but glutaraldehyde vapor fixation was less reliable. Based on the observed cellular interactions, there is tremendous potential for electrospun fibrinogen as a tissue engineering scaffold.

Cytoskeletal architecture differentially controls post-transcriptional processing of IL-6 and IL-8 mRNA in airway epithelial-like cells

Airway epithelial cells are critically dependent on an intact cytoskeleton for innate defense functions. There are various pathophysiological conditions that affect the cytoskeletal architecture. We studied the effect of cytoskeletal distortion in polarized airway epithelial-like NCI-H292 cells on inflammatory gene expression, exemplified by interleukin(IL)-6 and IL-8. Disruption of microtubule structure with vinblastin and of actin with cytochalasin D did not affect TNF-alpha-induced IL-6 and IL-8 gene transcription but stabilized IL-8 and IL-6 mRNA. In line with previous studies, IL-8 mRNA stabilization was paralleled by hyperresponsive IL-8 production, but surprisingly, IL-6 production was reduced despite IL-6 mRNA stabilization. Polysome profiling revealed that, in cells with a disrupted cytoskeleton, translational efficiency of IL-6 mRNA was reduced, whereas that of IL-8 mRNA remained unaffected. Our findings indicate that distortion of the cytoskeleton in airway epithelial cells differentially affects both degradation and translation of IL-6 and IL-8 mRNA, modifying inflammatory gene expression and thus their innate defense function.

Cell Type-specific Differential Induction of the Human γ-Fibrinogen Promoter by Interleukin-6

During an acute phase response, interleukin-6 (IL-6) and glucocorticoids up-regulate expression of the three fibrinogen (FBG) genes (fga, fgb, and fgg) in liver and lung epithelium; however, little constitutive lung expression occurs. Recently, we showed that the magnitude of Stat3 binding to three IL-6 motifs on the human gammaFBG promoter correlates negatively with their functional activity in hepatocytes, although these cis-elements are critical for promoter activity. We determined the role of IL-6-receptor-gp130-Stat3 signaling in IL-6 activation of the gammaFBG promoter in liver and lung epithelial cells. Although IL-6 induced gammaFBG promoter activity approximately 30-fold in HepG2 cells, it was increased only 2-fold in lung A549 cells. Equivalent production of gp130 was demonstrated in both cell types by Western blotting; however, lower production of both IL-6-receptor and Stat3 explains, in part, reduced activity of the gammaFBG promoter in lung cells. Dexamethasone potentiated IL-6 induction of the gammaFBG promoter 2.3-fold in both HepG2 and A549 cells for a combined increase in promoter activity of 70-fold or 4.5-fold, respectively. Dexamethasone potentiation is likely due to the induction of IL-6-receptor expression as well as prolonged intensity and duration of Stat3 activation. By circumventing IL-6-receptor-gp130-coupled signaling with ectopic expression of the granulocyte colony-stimulating factor receptor (GCSFR)-gp130(133) chimeric receptor, overexpression of Stat3 induced gammaFBG promoter activity 30-fold in A549 cells. Together, the data suggest tissue-specific differences in IL-6-receptor-gp130-coupled signaling, thereby limiting the extent of Stat3 activation and gammaFBG expression during lung inflammation.

Polarized entry and release of Junin virus, a New World arenavirus

Junin virus (JUNV), the causative agent of Argentine haemorrhagic fever, is a human pathogen that naturally enters the body through the epithelial cells of the respiratory and digestive tracts. The interaction of JUNV with two types of polarized epithelial cultures, Vero C1008 and A549, was investigated. Radioactive virus-binding assays showed that JUNV infects polarized lines preferentially through the apical surface. High-level expression of viral nucleoprotein was detected in polarized cell lines infected through the apical domain. Virus production from apical media was about 100-fold higher than that found into the basolateral medium. Confocal-immunofluorescence analysis revealed high-level expression of glycoprotein at the apical-membrane surface. Disruption of the microtubule network by colchicine impaired JUNV vectorial release. This is the first study to analyse the interaction between a member of the virus family Arenaviridae and polarized epithelial cells, showing preferential entry and release from the apical plasma membrane.

Fibrin(ogen)-alpha M beta 2 interactions regulate leukocyte function and innate immunity in vivo

In addition to its well-characterized role in hemostasis, fibrin(ogen) has been proposed to be a central regulator of the inflammatory response. Multiple in vitro studies have demonstrated that this hemostatic factor can alter leukocyte function, including cell adhesion, migration, cytokine and chemokine expression, degranulation, and other specialized processes. One important link between fibrin(ogen) and leukocyte biology appears to be the integrin receptor alpha(M)beta(2)/Mac-1, which binds to immobilized fibrin(ogen) and regulates leukocyte activities. Although it is well established that fibrin(ogen) is a ligand for alpha(M)beta(2), the precise molecular determinants that govern this interaction are only now becoming clear. A novel line of mice expressing a mutant form of fibrinogen (Fib gamma(390-396A)) has revealed that gamma chain residues 390-396 are important for the high-affinity engagement of fibrinogen by alpha(M)beta(2) and leukocyte function in vivo. Fibrinogen gamma(390-396A) failed to support alpha(M)beta(2)-mediated adhesion of primary neutrophils, monocytes, and macrophages, and mice expressing this fibrinogen variant were found to exhibit a major defect in the host inflammatory response following acute challenges. Most notably, Fib gamma(390-396A) mice display a profound impediment in Staphylococcus aureus elimination by leukocytes following intraperitoneal inoculation. These findings have positively established the physiological importance of fibrin(ogen) as a ligand for alpha(M)beta(2) and illustrate that the fibrin(ogen) gamma chain residues 390-396 constitute a critical feature of the alpha(M)beta(2) binding motif. Finally, the Fib gamma(390-396A) mice represent a valuable system for better defining the contribution of fibrin(ogen) to the inflammatory response in the absence of any confounding alteration in clotting function.

The fibrinogen receptor FbsA promotes adherence of Streptococcus agalactiae to human epithelial cells

Streptococcus agalactiae is a major cause of bacterial pneumonia, sepsis, and meningitis in human neonates. During the course of infection, S. agalactiae adheres to a variety of epithelial cells but the underlying mechanisms are only poorly understood. The present report demonstrates the importance of the fibrinogen receptor FbsA for the streptococcal adherence and invasion of epithelial cells. Deletion of the fbsA gene in various S. agalactiae strains substantially reduced their binding of soluble fibrinogen and their adherence to and invasion of epithelial cells, indicating a role of FbsA in these different processes. The adherence and invasiveness of an fbsA deletion mutant were partially restored by reintroducing the fbsA gene on an expression vector. Heterologous expression of fbsA in Lactococcus lactis enabled this bacterium to adhere to but not to invade epithelial cells, suggesting that FbsA is a streptococcal adhesin. Flow cytometry experiments revealed a dose-dependent binding of FbsA to the surface of epithelial cells. Furthermore, tissue culture experiments exhibited an intimate contact of FbsA-coated latex beads with the surfaces of human epithelial cells. Finally, host cell adherence and invasion were significantly blocked in competition experiments with either purified FbsA protein or a monoclonal antibody directed against the fibrinogen-binding epitope of FbsA. Taken together, our studies demonstrate that FbsA promotes the adherence of S. agalactiae to epithelial cells but that FbsA does not mediate the bacterial invasion into host cells. Our results also indicate that fibrinogen-binding epitopes within FbsA are involved in the adherence of S. agalactiae to epithelial cells.

The novel fibrinogen-binding protein FbsB promotes Streptococcus agalactiae invasion into epithelial cells

Streptococcus agalactiae is a major cause of bacterial sepsis and meningitis in human newborns. The interaction of S. agalactiae with host proteins and the entry into host cells thereby represent important virulence traits of these bacteria. The present report describes the identification of the fbsB gene, encoding a novel fibrinogen-binding protein that plays a crucial role in the invasion of S. agalactiae into human cells. In Western blots and enzyme-linked immunosorbent assay (ELISA) experiments, the FbsB protein was demonstrated to interact with soluble and immobilized fibrinogen. Binding studies showed the N-terminal 388 residues of FbsB and the Aalpha-subunit of human fibrinogen to recognize each other. By reverse transcription (RT)-PCR, the fbsB gene was shown to be cotranscribed with the gbs0851 gene in S. agalactiae. Deletion of the fbsB gene in the genome of S. agalactiae did not influence the binding of the bacteria to fibrinogen, suggesting that FbsB does not participate in the attachment of S. agalactiae to fibrinogen. In tissue culture experiments, however, the fbsB deletion mutant was severely impaired in its invasion into lung epithelial cells. Bacterial invasion could be reestablished by introducing the fbsB gene on a shuttle plasmid into the fbsB deletion mutant. Furthermore, treatment of lung epithelial cells with FbsB fusion protein blocked S. agalactiae invasion of epithelial cells in a dose-dependent fashion. These results suggest an important role of the FbsB protein in the overall process of host cell entry by S. agalactiae.

Matrix-fibrinogen enhances wound closure by increasing both cell proliferation and migration

Fibrinogen (FBG) assembles into matrix fibrils of fibroblasts, lung and mammary epithelial cells, but not endothelial cells. Furthermore, cryptic beta15-21 residues are exposed in FBG fibrils with no evidence of thrombin or plasmin proteolysis. Herein, the effects of FBG on migration and proliferation of wounded dermal fibroblasts were investigated. FBG preassembled into matrix prior to scrape-wounding induced 3H-thymidine incorporation 8-fold and shortened the time to wound closure 1.6-fold +/- 0.1-fold. FBG added immediately after wounding did not enhance either response. Fibroblast growth factor-2/platelet-derived growth factor (FGF-2/PDGF) stimulated cell proliferation 2.2-fold for FGF-2 and 3.2-fold for PDGF and wound closure 1.5-fold +/- 0.1-fold in the absence of matrix-FBG. Surprisingly, exogenous growth factors had negligible effect on wound closure and cell proliferation already enhanced by matrix-FBG. Matrix-FBG-enhanced wound closure required active assembly of an FBG-fibronectin matrix, engagement of alphavbeta3, and FBG Aalpha-RGDS572-575 integrin recognition sites; Aalpha-RGDF95-98 sites were not sufficient for matrix-FBG assembly, enhanced wound closure, or cell proliferation. Although Bbeta1-42 was not necessary for matrix assembly, it was required for matrix-FBG-enhanced cell migration. These data indicate that FBG serves as an important matrix constituent in the absence of fibrin formation to enhance wound repair and implicate Bbeta1-42 as a physiologic inducer of signal transduction to promote an intermediate state of cell adhesion and a migratory cell phenotype.

Functional analysis of interleukin 6 response elements (IL-6REs) on the human gamma-fibrinogen promoter: binding of hepatic Stat3 correlates negatively with transactivation potential of type II IL-6REs

Several families of transcription factors play important roles in modulating liver-specific gene expression during an acute phase response (APR). Stat3/APR factor is the main transactivator of gene expression by the interleukin (IL)-6 family of cytokines signaling through gp130. During an APR, fibrinogen (FBG) genes are coordinately up-regulated by IL-6 and glucocorticoids. Except for rat gammaFBG, attempts to demonstrate direct binding of IL-6-activated Stat3 to FBG CTGGGAA promoter elements have not been successful. Herein we show the presence of three functional type II IL-6 response elements (IL-6REs) on the human gammaFBG promoter and that the magnitude of Stat3 binding to these elements correlates negatively with their functional activity in reporter gene assays. Stat3-specific binding to gammaFBG IL-6REs was confirmed by cross-competition with alpha2-macroglobulin IL-6RE and specific interactions with anti-Stat3 in electrophoretic mobility shift assays. All type II IL-6REs contributed to full promoter activity; however, transactivation from Site II at -306 to -301 was strongest. In contrast to a previous report, IL-6 failed to induce activation of serum amyloid A-activating factor-1/c-Myc-associated zinc finger protein (SAF-1/MAZ), and mutation of the SAF-1RE had little effect on IL-6 induction of gammaFBG promoter activity. In the absence of a functional glucocorticoid receptor response element, dexamethasone potentiated IL-6-induced gammaFBG promoter activity 2-fold, requiring promoter-proximal Site I and Site II; the promoter-distal Site III had no effect on dexamethasone potentiation of IL-6-induced promoter activity. Notably the propensity for Stat3 binding to human gammaFBG IL-6REs was low compared with Stat3 binding to the alpha2-macroglobulin IL-6RE. Together these data suggest that Stat3 transactivation via IL-6REs on FBG promoters likely involves participation of additional transcription factors and/or coactivators to achieve optimal coordinated up-regulation during an APR.

Apical, but not basolateral, endotoxin preincubation protects alveolar epithelial cells against hydrogen peroxide-induced loss of barrier function: the role of nitric oxide synthesis

The influence of LPS preincubation on hydrogen peroxide (H(2)O(2))-induced loss of epithelial barrier function was investigated in rat alveolar epithelial type II cells (ATII). Both apical and basolateral H(2)O(2) administration caused a manyfold increase in transepithelial [(3)H]mannitol passage. Apical but not basolateral preincubation of ATII with LPS did not influence control barrier properties but fully abrogated the H(2)O(2)-induced leakage response. The effect of apical LPS was CD14 dependent and was accompanied by a strong up-regulation of NO synthase II mRNA and protein and NO release. Inhibition of NO by N(G)-monomethyl-L-arginine suppressed the LPS effect, whereas it was reproduced by exogenous application of gaseous NO or NO donor agents. Manipulation of the glutathione homeostasis (buthionine-(S,R)-sulfoximine) and the cGMP pathway (1H-(1,2,4)oxadiazolo[4,3-alpha]quinoxaline-1-one; zaprinast) did not interfere with the protective effect of LPS. Superoxide (O*(-)(2)) generation by ATII cells was reduced by exogenous NO and LPS preincubation. O*(-)(2) scavenging with exogenous superoxide dismutase, the intracellular superoxide dismutase analog Mn(III)tetrakis(4-benzoic acid) porphyrin, and the superoxide scavenger nitroblue tetrazolium and, in particular, hydroxyl radical scavenging with hydroxyl radical scavenger 1,3-dimethyl-thiourea inhibited the H(2)O(2)-induced epithelial leakage response. In conclusion, apical but not basolateral LPS preincubation of ATII cells provides strong protection against H(2)O(2)-induced transepithelial leakage, attributable to an up-regulation of epithelial NO synthesis. It is suggested that the LPS-induced NO formation is effective via interaction with reactive oxygen species, including superoxide and hydroxyl radicals. The polarized epithelial response to LPS may be part of the lung innate immune system, activated by inhaled endotoxin or under conditions of pneumonia.

Extracellular glutathione peroxidase is secreted basolaterally by human renal proximal tubule cells

Extracellular glutathione peroxidase (eGPx) is a secreted selenoenzyme with GPx activity. eGPx protein and activity are found in blood plasma and other extracellular fluids. eGPx in plasma is predominantly derived from the proximal tubules of kidneys in humans. Two types of human proximal tubule cells were cultured on semipermeable polycarbonate membranes to determine whether these cells secrete eGPx in a polarized direction. Immortalized human proximal tubule HK-2 cells and primary human proximal tubule cells formed confluent monolayers when cultured on these membrane inserts in culture dishes, as evidenced by transepithelial resistance. Both cell lines also constituted a barrier to diffusion of a fluoresceinated dextran of 75 kDa, a size similar to eGPx homotetramers. In both cell lines, 6- to 12-fold more 35S-methionine-labeled eGPx was immunoprecipitated from the basolateral media than from the apical media, indicating basolateral secretion of eGPx. eGPx was immunolocalized to the extracellular fluid at the basolateral surface of proximal tubules in human kidney. These data support the conclusion that eGPx is secreted through the basolateral membrane of human kidney proximal tubule cells into the extracellular fluid of the kidney, and from there enters blood plasma.

The incorporation of fibrinogen into extracellular matrix is dependent on active assembly of a fibronectin matrix

Fibrinogen is a soluble protein produced by hepatocytes and secreted into plasma, where it functions in hemostasis. During inflammation, the hepatic synthesis of fibrinogen is induced 2-10 fold. Recent studies demonstrate that after an inflammatory stimulus, fibrinogen gene expression and protein production is upregulated in lung epithelial cells, where it is secreted basolaterally and consequently deposited into the extracellular matrix in fibrils that extensively colocalize with fibronectin fibrils. In this study, we show that the deposition of fibrinogen into the matrix of fibroblasts occurred rapidly and in a Rho-dependent manner in response to serum or lysophosphatidic acid; RhoA GTPase signaling is also required for fibronectin matrix assembly. Using mouse embryonic fibronectin-null cells, we show that incorporation of exogenous fibrinogen into matrix fibrils occurred only in the presence of exogenous fibronectin, which is also assembled into matrix fibrils. Furthermore, treatment of fibroblasts and fibronectin-null cells with an antibody that inhibits fibronectin matrix assembly impaired incorporation of fibrinogen into matrix fibrils. Collectively, these data suggest that incorporation of fibrinogen into the extracellular matrix requires active fibronectin polymer elongation into matrix fibrils. From these data, we hypothesize that fibrinogen deposition rapidly changes the topology of the extracellular matrix to provide a surface for cell migration and matrix remodeling during tissue repair.

Plasminogen-binding activity of enolase in the opportunistic pathogen Pneumocystis carinii

The glycolytic enzyme enolase is one of the most abundant proteins expressed in fungi and has been shown to be an immunodominant cell-wall-associated antigen of the pathogenic fungus, Candida albicans. Enolase has also been found on the surface of some mammalian cells where it functions as a plasminogen-binding motif and facilitator of plasminogen activation to plasmin. To investigate the immunogenicity of enolase in the opportunistic pathogen, Pneumocystis carinii, the genomic and complementary DNA (cDNA) enolase were cloned and characterized. The predicted protein comprises 433 amino-acid residues and shows extensive homology to other fungal enolases, including those of C. albicans (76%), Aspergillus oryzae (79%) and Saccharomyces cerevisiae (77%). The purified recombinant P. carinii enolase was immunogenic, and may be an important antigen and indicator of P. carinii infection. The active site and conformation metal ion-binding site residues necessary for dimerization and enzyme function are conserved in the predicted P. carinii enolase protein. Enolase of P. carinii is unique among the fungal enolases in that it possesses a catalytic carboxyl-terminal lysyl residue that was necessary and sufficient for the plasminogen-binding activity of the enolase of P. carinii. The activity of the plasminogen binding suggests its involvement in the local regulation of fibrinolysis within the alveolar space.

Fibrinogen modulates gene expression in wounded fibroblasts

Fibrinogen (FBG) has long been regarded as serving essentially a hemostatic role by its conversion from a soluble, plasma protein to an insoluble fibrin gel. However, several extrahepatic sites of FBG biosynthesis have been identified. Indeed, we have demonstrated that both lung epithelial cell derived and plasma FBG assemble into the extracellular matrix (ECM) of epithelial cells and fibroblasts. In this report, we determined that FBG assembly into the ECM is a cell dependent step that occurs in the absence of de novo protein synthesis. Using an in vitro model of wound repair, we examined the role of FBG in modulating gene expression. Data collected from cDNA array analysis indicated that FBG downregulates steady state levels of fibronectin mRNA, whereas cyclin D1 mRNA levels were upregulated in fibroblasts. Taken together, these data suggest that FBG may function independently of hemostasis in cellular adhesive interactions to modulate cellular signaling processes during wound repair.

Tumors and fibrinogen. The role of fibrinogen as an extracellular matrix protein

The progression of a tumor from benign and localized to invasive and metastatic growth is the major cause of poor clinical outcome in cancer patients. Much like in a healing wound, the deposition of fibrin(ogen), along with other adhesive glycoproteins, into the extracellular matrix (ECM) serves as a scaffold to support binding of growth factors and to promote the cellular responses of adhesion, proliferation, and migration during angiogenesis and tumor cell growth. Inappropriate synthesis and deposition of ECM constituents is linked to altered regulation of cell proliferation, leading to tumor cell growth and malignant transformation. Fibrin deposition occurs within the stroma of a majority of tumor types. In contrast, abundant FBG, not fibrin, is present within the stroma of breast cancers. It is thought to originate from exudation of plasma FBG and subsequent deposition into the tumor stroma and not endogenous synthesis and secretion of FBG by breast tumor cells. However, we show that MCF-7 human breast cancer cells synthesize and secrete FBG polypeptides, suggesting that the origin of FBG in the stroma of breast carcinoma may be due to endogenous synthesis and deposition. Moreover, FBG assembles into ECM as conformationally altered FBG, not as fibrin. Studies in our laboratory demonstrate that FBG alters the ability of breast cancer cells to migrate. Together, the results of studies from our laboratory, as well as the laboratories of others, indicate that the presence of fibrin(ogen) within the tumor stroma likely affects the progression of tumor cell growth and metastasis. This review focuses on FBG within tumors and its relationship with other tumor constituents, ultimately focusing on the role of FBG in breast cancer.

Integrin alphavbeta3-mediated endocytosis of immobilized fibrinogen by A549 lung alveolar epithelial cells

Fibrinogen (FBG), together with its polymerized form fibrin, modulates cellular responses during wound repair and tissue remodeling. Thus, we sought to determine whether A549 lung epithelial type II-like cells would endocytose insoluble, surface-bound FBG as a potential mechanism of alveolar matrix remodeling. Surface-bound FBG was endocytosed into either lysosomes or late endosomes by A549 cells through arg-gly-asp-dependent binding to alphavbeta3 but not alpha5beta1 integrin receptors. Soluble FBG added to confluent monolayers of A549 cells was not endocytosed. Unlike the uptake of the extracellular matrix glycoproteins vitronectin and thrombospondin by other cell types, endocytosis of FBG by A549 cells was neither inhibited by heparin nor dependent on binding to cell-surface heparan sulfate proteoglycans. FBG did not colocalize with endocytosed transferrin, whereas dextran showed partial colocalization with FBG in endocytic vesicles, suggesting nonclathrin-mediated endocytosis. Inhibition of actin filament polymerization blocked endocytosis of both dextran and FBG but not transferrin, providing further support that FBG is endocytosed via a nonclathrin pathway. Disruption of actin polymerization inhibited integrin-mediated cell spreading, which contributed to an overall reduction in FBG clearance that was most likely due to reduced cell migration and associated pericellular proteolysis. Trasylol inhibition of extracellular plasmin activity did not inhibit endocytosis of FBG. The endocytosed FBG was degraded to trichloroacetic acid-soluble fragments that showed an electrophoretic pattern distinctly different from plasmin-degraded FBG. Together, these results suggest that endocytosis of matrix-associated FBG by alveolar epithelial cells may be involved in the processes of alveolar tissue repair and matrix remodeling.

Alveolar epithelial type II cell: defender of the alveolus revisited

In 1977, Mason and Williams developed the concept of the alveolar epithelial type II (AE2) cell as a defender of the alveolus. It is well known that AE2 cells synthesise, secrete, and recycle all components of the surfactant that regulates alveolar surface tension in mammalian lungs. AE2 cells influence extracellular surfactant transformation by regulating, for example, pH and [Ca2+] of the hypophase. AE2 cells play various roles in alveolar fluid balance, coagulation/fibrinolysis, and host defence. AE2 cells proliferate, differentiate into AE1 cells, and remove apoptotic AE2 cells by phagocytosis, thus contributing to epithelial repair. AE2 cells may act as immunoregulatory cells. AE2 cells interact with resident and mobile cells, either directly by membrane contact or indirectly via cytokines/growth factors and their receptors, thus representing an integrative unit within the alveolus. Although most data support the concept, the controversy about the character of hyperplastic AE2 cells, reported to synthesise profibrotic factors, proscribes drawing a definite conclusion today.

Cell type-specific regulation of fibrinogen expression in lung epithelial cells by dexamethasone and interleukin-1beta

Our recent studies demonstrating the expression of fibrinogen (FBG) by an alveolar type II cell line stimulated with proinflammatory mediators and also in the inflamed pulmonary epithelium of animals with Pneumocystis carinii pneumonia suggest that extrahepatic FBG participates in the local acute phase response (APR) to infection and subsequent wound repair. However, the mechanisms that regulate extrahepatic FBG expression are poorly understood. This study compares the regulation of hepatic and pulmonary FBG expression by mediators of the APR, interleukin (IL)-6, IL-1beta, and dexamethasone (DEX), a synthetic glucocorticoid. Northern blotting and metabolic labeling studies revealed that IL-6 with or without DEX upregulates gammaFBG messenger RNA and protein, whereas IL-1beta inhibits gammaFBG expression in human lung (A549) and liver (HepG2) epithelial cells. In contrast, the addition of DEX relieved the IL-1beta-mediated inhibition of FBG expression in lung epithelial cells only; this response is termed "DEX rescue." Studies with cycloheximide indicate that only DEX rescue required de novo protein synthesis. Nuclear run-on analysis revealed no increase in gammaFBG transcription by DEX treatment. Although DEX treatment alone increased the stability of gammaFBG transcripts in lung cells, this effect was not observed in the presence of IL-1beta. Together, these results suggest that pre-existing transcription factors mediate the effects of IL-6 with or without DEX, DEX, and IL-1beta on gammaFBG gene expression in lung and liver cells. Also, the data suggest that DEX induces new protein synthesis of an inhibitor of IL-1beta signal transduction to effectively "rescue" FBG production in lung but not liver epithelial cells. This cell type-specific stimulation of FBG production by glucocorticoids to overcome IL-1beta inhibition may promote pulmonary wound repair mechanisms.