Deficiency in neutrophil elastase does not impair neutrophil recruitment to inflamed sites

CRISPR-Cas9n-mediated ELANE promoter editing for gene therapy of severe congenital neutropenia

Severe congenital neutropenia (CN) is an inherited pre-leukemia bone marrow failure syndrome commonly caused by autosomal-dominant ELANE mutations (ELANE-CN). ELANE-CN patients are treated with daily injections of recombinant human granulocyte colony-stimulating factor (rhG-CSF). However, some patients do not respond to rhG-CSF, and approximately 15% of ELANE-CN patients develop myelodysplasia or acute myeloid leukemia. Here, we report the development of a curative therapy for ELANE-CN through inhibition of ELANE mRNA expression by introducing two single-strand DNA breaks at the opposing DNA strands of the ELANE promoter TATA box using CRISPR-Cas9D10A nickases-termed MILESTONE. This editing effectively restored defective neutrophil differentiation of ELANE-CN CD34+ hematopoietic stem and progenitor cells (HSPCs) in vitro and in vivo, without affecting the functions of the edited neutrophils. CRISPResso analysis of the edited ELANE-CN CD34+ HSPCs revealed on-target efficiencies of over 90%. Simultaneously, GUIDE-seq, CAST-Seq, and rhAmpSeq indicated a safe off-target profile with no off-target sites or chromosomal translocations. Taken together, ex vivo gene editing of ELANE-CN HSPCs using MILESTONE in the setting of autologous stem cell transplantation could be a universal, safe, and efficient gene therapy approach for ELANE-CN patients.

A comprehensive overview of investigational elastase inhibitors for the treatment of acute respiratory distress syndrome

INTRODUCTION

Excessive activity of neutrophil elastase (NE), the main enzyme present in azurophil granules in the neutrophil cytoplasm, may cause tissue injury and remodeling in various lung diseases, including acute lung injury (ALI)/acute respiratory distress syndrome (ARDS), in which it is crucial to the immune response and inflammatory process. Consequently, NE is a possible target for therapeutic intervention in ALI/ARDS.

AREAS COVERED

The protective effects of several NE inhibitors in attenuating ALI/ARDS in several models of lung injury are described. Some of these NE inhibitors are currently in clinical development, but only sivelestat has been evaluated as a treatment for ALI/ARDS.

EXPERT OPINION

Preclinical research has produced encouraging information about using NE inhibitors. Nevertheless, only sivelestat has been approved for this clinical indication, and only in Japan and South Korea because of the conflicting results of clinical trials and likely also because of the potential adverse events. Identifying subsets of patients with ARDS most likely to benefit from NE inhibitor treatment, such as the hyperinflammatory phenotype, and using a more advanced generation of NE inhibitors than sivelestat could enable better clinical results than those obtained with elastase inhibitors.

CLEC5A is critical in Pseudomonas aeruginosa-induced acute lung injury

Pseudomonas aeruginosa is one of the most common nosocomial infections worldwide, and it frequently causes ventilator-associated acute pneumonia in immunocompromised patients. Abundant neutrophil extracellular traps (NETs) contribute to acute lung injury, thereby aggravating ventilator-induced lung damage. While pattern recognition receptors (PRRs) TLR4 and TLR5 are required for host defense against P. aeruginosa invasion, the PRR responsible for P. aeruginosa–induced NET formation, proinflammatory cytokine release, and acute lung injury remains unclear. We found that myeloid C-type lectin domain family 5 member A (CLEC5A) interacts with LPS of P. aeruginosa and is responsible for P. aeruginosa–induced NET formation and lung inflammation. P. aeruginosa activates CLEC5A to induce caspase-1–dependent NET formation, but it neither causes gasdermin D (GSDMD) cleavage nor contributes to P. aeruginosa–induced neutrophil death. Blockade of CLEC5A attenuates P. aeruginosa–induced NETosis and lung injury, and simultaneous administration of anti-CLEC5A mAb with ciprofloxacin increases survival rate and decreases collagen deposition in the lungs of mice challenged with a lethal dose of P. aeruginosa. Thus, CLEC5A is a promising therapeutic target to reduce ventilator-associated lung injury and fibrosis in P. aeruginosa–induced pneumonia.

Doxorubicin-induced cardiotoxicity is mediated by neutrophils through release of neutrophil elastase

The mechanisms by which Doxorubicin (Dox) causes acute and late cardiotoxicity are not completely understood. One understudied area is the innate immune response, and in particular the role of neutrophils in Dox-induced cardiotoxicity. Here, using echocardiography, flow cytometry and immunofluorescence staining, we demonstrated increased infiltration of neutrophils that correlated with decreased heart function, disruption of vascular structures and increased collagen deposition in the heart after Dox treatment. Depleting neutrophils protected the heart from Dox-induced cardiotoxicity and changes in vascular structure. Furthermore, our data using neutrophil elastase (NE) knock-out mice and the NE inhibitor AZD9668 suggest that neutrophils cause this damage by releasing NE and that inhibiting NE can prevent Dox-induced cardiotoxicity. This work shows the role of neutrophils and NE in Doxorubicin-induced cardiotoxicity for the first time and suggests a new possible therapeutic intervention.

Magnetic Resonance Imaging of Protease-Mediated Lung Tissue Inflammation and Injury

Pulmonary inflammation usually involves strong neutrophil recruitment with a marked release of proteases such as neutrophil elastase (NE). Noninvasive in vivo assessment of unregulated elastase activity in the lungs would provide a valuable diagnostic tool. Here, it is proposed to use Overhauser-enhanced magnetic resonance imaging (OMRI) in mice where inflammation was induced by the instillation of lipopolysaccharide (LPS). OMRI contrast in the lungs was generated by a dedicated NE free radical substrate. The free radical decayed more rapidly in LPS-treated mouse lungs than in control mice, indicating the occurrence of increased proteolysis under inflammation. Preclinical detection of abnormal proteolysis opens the way for new diagnosis modality and antiprotease testing in vivo.

Use of a biopolymer delivery system to investigate the influence of interleukin-4 on recruitment of neutrophils in equids

OBJECTIVE

To use a biopolymer delivery system to investigate the ability of interleukin (IL)-4 to recruit neutrophils into subcutaneous tissues of equids.

ANIMALS

16 horses and 2 ponies.

PROCEDURES

Animals were assigned to 3 experiments (6/experiment). Effects of recombinant equine (Req) IL-4 (100, 250, or 500 ng/site) versus a positive control (ReqIL-8; 100 ng, 250 ng, or 1 μg/site) and a negative control (Dulbecco PBSS or culture medium) on neutrophil chemotaxis were assessed after SC injection into the neck with an injectable biopolymer used as the vehicle. Tissue samples including the biopolymer plug were collected by biopsy at various time points from 3 hours to 7 days after injection. Neutrophil infiltration was evaluated by histologic scoring (experiments 1, 2, and 3) or flow cytometry (experiment 3).

RESULTS

Histologic neutrophil infiltration scores did not differ significantly among treatments at most evaluated time points. On flow cytometric analysis, log-transformed neutrophil counts in biopsy specimens were significantly greater for the ReqIL-8 treatment (1 μg/site) than the negative control treatment at 3 but not 6 hours after injection; results did not differ between ReqIL-4 and control treatments at either time point. Negative control treatments induced an inflammatory response in most equids in all experiments.

CONCLUSIONS AND CLINICAL RELEVANCE

Flow cytometry was a more reliable method to estimate neutrophil migration than histologic score analysis. The ReqIL-4 treatment did not induce a detectable neutrophil response, compared with the negative control treatment in this study. Evidence of inflammation in negative control samples suggested the biopolymer is not a suitable vehicle for use in equids.

Src family kinase-mediated vesicle trafficking is critical for neutrophil basement membrane penetration

Leukocyte recruitment into inflamed tissue is highly dependent on the activation and binding of integrins to their respective ligands, followed by the induction of various signaling events within the cell referred to as outside-in signaling. Src family kinases (SFK) are the central players in the outside-in signaling process, assigning them a critical role for proper immune cell function. Our study investigated the role of SFK on neutrophil recruitment in vivo using Hck^−/- Fgr^−/- Lyn^−/- mice, which lack SFK expressed in neutrophils. We show that loss of SFK strongly reduces neutrophil adhesion and post-arrest modifications in a shear force dependent manner. Additionally, we found that in the absence of SFK, neutrophils display impaired Rab27a-dependent surface mobilization of neutrophil elastase, VLA3 and VLA6 containing vesicles. This results in a defect in neutrophil vascular basement membrane penetration and thus strongly impaired extravasation. Taken together, we demonstrate that SFK play a role in neutrophil post-arrest modifications and extravasation during acute inflammation. These findings may support the current efforts to use SFK-inhibitors in inflammatory diseases with unwanted neutrophil recruitment.

The Neutrophilic Response to Pseudomonas Damages the Airway Barrier, Promoting Infection by Klebsiella pneumoniae

Pseudomonas aeruginosa and Klebsiella pneumoniae are two common gram-negative pathogens that are associated with bacterial pneumonia and can often be isolated from the same patient. We used a mixed-pathogen pneumonia infection model in which mice were infected with sublethal concentrations of P. aeruginosa and K. pneumoniae, resulting in significant lethality, outgrowth of both bacteria in the lung, and systemic dissemination of K. pneumoniae. Inflammation, induced by P. aeruginosa activation of Toll-like receptor 5, results in prolonged neutrophil recruitment to the lung and increased levels of neutrophil elastase in the airway, resulting in lung damage and epithelial barrier dysfunction. Live P. aeruginosa was not required to potentiate K. pneumoniae infection, and flagellin alone was sufficient to induce lethality when delivered along with Klebsiella. Prophylaxis with an anti-Toll-like receptor 5 antibody or Sivelestat, a neutrophil elastase inhibitor, reduced neutrophil influx, inflammation, and mortality. Furthermore, pathogen-specific monoclonal antibodies targeting P. aeruginosa or K. pneumoniae prevented the outgrowth of both bacteria and reduced host inflammation and lethality. These findings suggest that coinfection with P. aeruginosa may enable the outgrowth and dissemination of K. pneumoniae, and that a pathogen- or host-specific prophylactic approach targeting P. aeruginosa may prevent or limit the severity of such infections by reducing neutrophil-induced lung damage.

CRISPR/Cas9-mediated ELANE knockout enables neutrophilic maturation of primary hematopoietic stem and progenitor cells and induced pluripotent stem cells of severe congenital neutropenia patients

A Autosomal-dominant ELANE mutations are the most common cause of severe congenital neutropenia. Although the majority of congenital neutropenia patients respond to daily granulocyte colony stimulating factor, approximately 15 % do not respond to this cytokine at doses up to 50 μg/kg/day and approximately 15 % of patients will develop myelodysplasia or acute myeloid leukemia. “Maturation arrest,” the failure of the marrow myeloid progenitors to form mature neutrophils, is a consistent feature of ELANE associated congenital neutropenia. As mutant neutrophil elastase is the cause of this abnormality, we hypothesized that ELANE associated neutropenia could be treated and “maturation arrest” corrected by a CRISPR/Cas9-sgRNA ribonucleoprotein mediated ELANE knockout. To examine this hypothesis, we used induced pluripotent stem cells from two congenital neutropenia patients and primary hematopoietic stem and progenitor cells from four congenital neutropenia patients harboring ELANE mutations as well as HL60 cells expressing mutant ELANE. We observed that granulocytic differentiation of ELANE knockout induced pluripotent stem cells and primary hematopoietic stem and progenitor cells were comparable to healthy individuals. Phagocytic functions, ROS production, and chemotaxis of the ELANE KO (knockout) neutrophils were also normal. Knockdown of ELANE in the mutant ELANE expressing HL60 cells also allowed full maturation and formation of abundant neutrophils. These observations suggest that ex vivo CRISPR/Cas9 RNP based ELANE knockout of patients’ primary hematopoietic stem and progenitor cells followed by autologous transplantation may be an alternative therapy for congenital neutropenia.

Neutrophil elastase plays a non-redundant role in remodeling the venular basement membrane and neutrophil diapedesis post-ischemia/reperfusion injury

Ischemia/reperfusion (I/R) injury is a severe inflammatory insult associated with numerous pathologies, such as myocardial infarction, stroke and acute kidney injury. I/R injury is characterized by a rapid influx of activated neutrophils secreting toxic free radical species and degrading enzymes that can irreversibly damage the tissue, thus impairing organ functions. Significant efforts have been invested in identifying therapeutic targets to suppress neutrophil recruitment and activation post‐I/R injury. In this context, pharmacological targeting of neutrophil elastase (NE) has shown promising anti‐inflammatory efficacy in a number of experimental and clinical settings of I/R injury and is considered a plausible clinical strategy for organ care. However, the mechanisms of action of NE, and hence its inhibitors, in this process are not fully understood. Here we conducted a comprehensive analysis of the impact of NE genetic deletion on neutrophil infiltration in four murine models of I/R injury as induced in the heart, kidneys, intestine and cremaster muscle. In all models, neutrophil migration into ischemic regions was significantly suppressed in NE^−/− mice as compared with wild‐type controls. Analysis of inflamed cremaster muscle and mesenteric microvessels by intravital and confocal microscopy revealed a selective entrapment of neutrophils within venular walls, most notably at the level of the venular basement membrane (BM) following NE deletion/pharmacological blockade. This effect was associated with the suppression of NE‐mediated remodeling of the low matrix protein expressing regions within the venular BM used by transmigrating neutrophils as exit portals. Furthermore, whilst NE deficiency led to reduced neutrophil activation and vascular leakage, levels of monocytes and prohealing M2 macrophages were reduced in tissues of NE^−/− mice subjected to I/R. Collectively our results identify a vital and non‐redundant role for NE in supporting neutrophil breaching of the venular BM post‐I/R injury but also suggest a protective role for NE in promoting tissue repair. © 2019 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Granulomatous lung inflammation is nanoparticle type-dependent

BACKGROUND

Nanoparticles are increasingly suspected as a strong etiologic factor of granuloma formation.

AIM OF THE STUDY

The aim of our study was to compare lung inflammatory response and histology changes following exposure of mice to two widely used nanoparticles: carbon nanotubes (MWCNT) and cadmium-based nanoparticles (QDOT705) in an attempt to better our understanding of granulomatous inflammation.

MATERIALS AND METHODS

Various groups of mice were included: control mice and mice that were intranasally instilled with QDOT or MWCNT. At defined time points post-challenge, bronchoalveolar lavages (BALs) and lung tissues were collected to study inflammatory and histologic changes.

RESULTS

Analyses of lung BAL fluids and tissues of nanoparticles-challenged mice in comparison to controls found: (1) increased cellularity in BALs, (2) increase of total protein concentration, LDH activity and proteolytic activity in BALs; (3) patchy granulomas, (4) macrophages, CD3 ± T, Treg and B cell infiltration in granulomatous areas; and (5) altered regulation of key inflammatory mediators and receptors. Importantly, these changes were nanoparticle type-dependent.

CONCLUSION

Our work enhances understanding of nanoparticles-induced lung inflammatory and histological changes that result in granuloma formation. We provide compelling evidence that not only exposure to nanoparticles leads to granulomatous lung inflammation, but the severity of this latter is nanostructure type-dependent. Of importance, while nanotechnology has the potential to revolutionize various fields including medicine, nanoparticles form the potential for an entirely new lung health risk that it is necessary to take seriously into consideration by setting up and/or reinforcing adequate safety measures.

Neutrophil elastase cleaves epithelial cadherin in acutely injured lung epithelium

Background

In acutely injured lungs, massively recruited polymorphonuclear neutrophils (PMNs) secrete abnormally neutrophil elastase (NE). Active NE creates a localized proteolytic environment where various host molecules are degraded leading to impairment of tissue homeostasis. Among the hallmarks of neutrophil-rich pathologies is a disrupted epithelium characterized by the loss of cell-cell adhesion and integrity. Epithelial-cadherin (E-cad) represents one of the most important intercellular junction proteins. E-cad exhibits various functions including its role in maintenance of tissue integrity. While much interest has focused on the expression and role of E-cad in different physio- and physiopathological states, proteolytic degradation of this structural molecule and ensuing potential consequences on host lung tissue injury are not completely understood.

Methods

NE capacity to cleave E-cad was determined in cell-free and lung epithelial cell culture systems. The impact of such cleavage on epithelial monolayer integrity was then investigated. Using mice deficient in NE in a clinically relevant experimental model of acute pneumonia, we examined whether degraded E-cad is associated with lung inflammation and injury and whether NE contributes to E-cad cleavage. Finally, we checked for the presence of both degraded E-cad and NE in bronchoalveolar lavage samples obtained from patients with exacerbated COPD, a clinical manifestation characterised by a neutrophilic inflammatory response.

Results

We show that NE is capable of degrading E-cad in vitro and in cultured cells. NE-mediated degradation of E-cad was accompanied with loss of epithelial monolayer integrity. Our in vivo findings provide evidence that NE contributes to E-cad cleavage that is concomitant with lung inflammation and injury. Importantly, we observed that the presence of degraded E-cad coincided with the detection of NE in diseased human lungs.

Conclusions

Active NE has the capacity to cleave E-cad and interfere with its cell-cell adhesion function. These data suggest a mechanism by which unchecked NE participates potentially to the pathogenesis of neutrophil-rich lung inflammatory and tissue-destructive diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/s12931-016-0449-x) contains supplementary material, which is available to authorized users.

Neutrophils rapidly transit inflamed lymphatic vessel endothelium via integrin-dependent proteolysis and lipoxin-induced junctional retraction

Neutrophils are the first leukocyte population to be recruited from the circulation following tissue injury or infection, where they play key roles in host defense. However, recent evidence indicates recruited neutrophils can also enter lymph and shape adaptive immune responses downstream in draining lymph nodes. At present, the cellular mechanisms regulating neutrophil entry to lymphatic vessels and migration to lymph nodes are largely unknown. Here, we have investigated these events in an in vivo mouse Mycobacterium bovis bacillus Calmette-Guérin vaccination model, ex vivo mouse dermal explants, and in vitro Transwell system comprising monolayers of primary human dermal lymphatic endothelial cells. We demonstrate that neutrophils are reliant on endothelial activation for adhesion, initially via E-selectin and subsequently, by integrin-mediated binding to ICAM-1 and VCAM-1, combined with CXCL8-dependent chemotaxis. Moreover, we reveal that integrin-mediated neutrophil adhesion plays a pivotal role in subsequent transmigration by focusing the action of matrix metalloproteinases and the 15-lipoxygenase-1-derived chemorepellent 12(S)-hydroxyeicosatetraenoic acid at neutrophil:endothelial contact sites to induce transient endothelial junctional retraction and rapid, selective neutrophil trafficking. These findings reveal an unexpectedly intimate collaboration between neutrophils and the lymphatic vessel endothelium, in which these phagocytic leukocytes act as pathfinders for their own transit during inflammation.

Neutrophil elastase mediates acute pathogenesis and is a determinant of long-term behavioral recovery after traumatic injury to the immature brain

While neutrophil elastase (NE), released by activated neutrophils, is a key mediator of secondary pathogenesis in adult models of brain ischemia and spinal cord injury, no studies to date have examined this protease in the context of the injured immature brain, where there is notable vulnerability resulting from inadequate antioxidant reserves and prolonged exposure to infiltrating neutrophils. We thus reasoned that NE may be a key determinant of secondary pathogenesis, and as such, adversely influence long-term neurological recovery. To address this hypothesis, wild-type (WT) and NE knockout (KO) mice were subjected to a controlled cortical impact at post-natal day 21, approximating a toddler-aged child. To determine if NE is required for neutrophil infiltration into the injured brain, and whether this protease contributes to vasogenic edema, we quantified neutrophil numbers and measured water content in the brains of each of these genotypes. While leukocyte trafficking was indistinguishable between genotypes, vasogenic edema was markedly attenuated in the NE KO. To determine if early pathogenesis is dependent on NE, indices of cell death (TUNEL and activated caspase-3) were quantified across genotypes. NE KO mice showed a reduction in these markers of cell death in the injured hippocampus, which corresponded to greater preservation of neuronal integrity as well as reduced expression of heme oxygenase-1, a marker of oxidative stress. WT mice, treated with a competitive inhibitor of NE at 2, 6 and 12h post-injury, likewise showed a reduction in cell death and oxidative stress compared to vehicle-treated controls. We next examined the long-term behavioral and structural consequences of NE deficiency. NE KO mice showed an improvement in long-term spatial memory retention and amelioration of injury-induced hyperactivity. However, volumetric and stereological analyses found comparable tissue loss in the injured cortex and hippocampus independent of genotype. Further, WT mice treated acutely with the NE inhibitor showed no long-term behavioral or structural improvements. Together, these findings validate the central role of NE in both acute pathogenesis and chronic functional recovery, and support future exploration of the therapeutic window, taking into account the prolonged period of neutrophil trafficking into the injured immature brain.

Neutrophil elastase causes tissue damage that decreases host tolerance to lung infection with burkholderia species

Two distinct defense strategies can protect the host from infection: resistance is the ability to destroy the infectious agent, and tolerance is the ability to withstand infection by minimizing the negative impact it has on the host's health without directly affecting pathogen burden. Burkholderia pseudomallei is a Gram-negative bacterium that infects macrophages and causes melioidosis. We have recently shown that inflammasome-triggered pyroptosis and IL-18 are equally important for resistance to B. pseudomallei, whereas IL-1β is deleterious. Here we show that the detrimental role of IL-1β during infection with B. pseudomallei (and closely related B. thailandensis) is due to excessive recruitment of neutrophils to the lung and consequent tissue damage. Mice deficient in the potentially damaging enzyme neutrophil elastase were less susceptible than the wild type C57BL/6J mice to infection, although the bacterial burdens in organs and the extent of inflammation were comparable between C57BL/6J and elastase-deficient mice. In contrast, lung tissue damage and vascular leakage were drastically reduced in elastase-deficient mice compared to controls. Bradykinin levels were higher in C57BL/6 than in elastase-deficient mice; administration of a bradykinin antagonist protected mice from infection, suggesting that increased vascular permeability mediated by bradykinin is one of the mechanisms through which elastase decreases host tolerance to melioidosis. Collectively, these results demonstrate that absence of neutrophil elastase increases host tolerance, rather than resistance, to infection by minimizing host tissue damage.

ADAM9 is a novel product of polymorphonuclear neutrophils: regulation of expression and contributions to extracellular matrix protein degradation during acute lung injury

A disintegrin and a metalloproteinase domain (ADAM) 9 is known to be expressed by monocytes and macrophages. In this study, we report that ADAM9 is also a product of human and murine polymorphonuclear neutrophils (PMNs). ADAM9 is not synthesized de novo by circulating PMNs. Rather, ADAM9 protein is stored in the gelatinase and specific granules and the secretory vesicles of human PMNs. Unstimulated PMNs express minimal quantities of surface ADAM9, but activation of PMNs with degranulating agonists rapidly (within 15 min) increases PMN surface ADAM9 levels. Human PMNs produce small quantities of soluble forms of ADAM9. Surprisingly, ADAM9 degrades several extracellular matrix (ECM) proteins, including fibronectin, entactin, laminin, and insoluble elastin, as potently as matrix metalloproteinase-9. However, ADAM9 does not degrade types I, III, or IV collagen or denatured collagens in vitro. To determine whether Adam9 regulates PMN recruitment or ECM protein turnover during inflammatory responses, we compared wild-type and Adam9(-/-) mice in bacterial LPS- and bleomycin-mediated acute lung injury (ALI). Adam9 lung levels increase 10-fold during LPS-mediated ALI in wild-type mice (due to increases in leukocyte-derived Adam9), but Adam9 does not regulate lung PMN (or macrophage) counts during ALI. Adam9 increases mortality, promotes lung injury, reduces lung compliance, and increases degradation of lung elastin during LPS- and/or bleomycin-mediated ALI. Adam9 does not regulate collagen accumulation in the bleomycin-treated lung. Thus, ADAM9 is expressed in an inducible fashion on PMN surfaces where it degrades some ECM proteins, and it promotes alveolar-capillary barrier injury during ALI in mice.

Lack of neutrophil elastase reduces inflammation, mucus hypersecretion, and emphysema, but not mucus obstruction, in mice with cystic fibrosis-like lung disease

RATIONALE

Recent evidence from clinical studies suggests that neutrophil elastase (NE) released in neutrophilic airway inflammation is a key risk factor for the onset and progression of lung disease in young children with cystic fibrosis (CF). However, the role of NE in the complex in vivo pathogenesis of CF lung disease remains poorly understood.

OBJECTIVES

To elucidate the role of NE in the development of key features of CF lung disease including airway inflammation, mucus hypersecretion, goblet cell metaplasia, bacterial infection, and structural lung damage in vivo.

METHODS

We used the Scnn1b-Tg mouse as a model of CF lung disease and determined effects of genetic deletion of NE (NE(-/-)) on the pulmonary phenotype. Furthermore, we used novel Foerster resonance energy transfer (FRET)-based NE reporter assays to assess NE activity in bronchoalveolar lavage from Scnn1b-Tg mice and sputum from patients with CF.

MEASUREMENTS AND MAIN RESULTS

Lack of NE significantly reduced airway neutrophilia, elevated mucin expression, goblet cell metaplasia, and distal airspace enlargement, but had no effect on airway mucus plugging, bacterial infection, or pulmonary mortality in Scnn1b-Tg mice. By using FRET reporters, we show that NE activity was elevated on the surface of airway neutrophils from Scnn1b-Tg mice and patients with CF.

CONCLUSIONS

Our results suggest that NE plays an important role in the in vivo pathogenesis and may serve as a therapeutic target for inflammation, mucus hypersecretion, and structural lung damage and indicate that additional rehydration strategies may be required for effective treatment of airway mucus obstruction in CF.

The mercurial nature of neutrophils: still an enigma in ARDS?

The acute respiratory distress syndrome (ARDS) is a life-threatening lung condition resulting from direct and indirect insults to the lung. It is characterized by disruption of the endothelial-epithelial barrier, alveolar damage, pulmonary edema, and respiratory failure. A key feature of ARDS is the accumulation of neutrophils in the lung microvasculature, interstitium, and alveolar space. Despite a clear association between neutrophil influx into the lung and disease severity, there is some debate as to whether neutrophils directly contribute to disease pathogenesis. The primary function of neutrophils is to provide immediate host defense against pathogenic microorganisms. Neutrophils release numerous antimicrobial factors such as reactive oxygen species, proteinases, and neutrophil extracellular traps. However, these factors are also toxic to host cells and can result in bystander tissue damage. The excessive accumulation of neutrophils in ARDS may therefore contribute to disease progression. Central to neutrophil recruitment is the release of chemokines, including the archetypal neutrophil chemoattractant IL-8, from resident pulmonary cells. However, the chemokine network in the inflamed lung is complex and may involve several other chemokines, including CXCL10, CCL2, and CCL7. This review will therefore focus on the experimental and clinical evidence supporting neutrophils as key players in ARDS and the chemokines involved in recruiting them into the lung.

Neutrophil elastase modulates cytokine expression: contribution to host defense against Pseudomonas aeruginosa-induced pneumonia

There is accumulating evidence that following bacterial infection, the massive recruitment and activation of the phagocytes, neutrophils, is accompanied with the extracellular release of active neutrophil elastase (NE), a potent serine protease. Using NE-deficient mice in a clinically relevant model of Pseudomonas aeruginosa-induced pneumonia, we provide compelling in vivo evidence that the absence of NE was associated with decreased protein and transcript levels of the proinflammatory cytokines TNF-α, MIP-2, and IL-6 in the lungs, coinciding with increased mortality of mutant mice to infection. The implication of NE in the induction of cytokine expression involved at least in part Toll-like receptor 4 (TLR-4). These findings were further confirmed following exposure of cultured macrophages to purified NE. Together, our data suggest strongly for the first time that NE not only plays a direct antibacterial role as it has been previously reported, but released active enzyme can also modulate cytokine expression, which contributes to host protection against P. aeruginosa. In light of our findings, the long held view that considers NE as a prime suspect in P. aeruginosa-associated diseases will need to be carefully reassessed. Also, therapeutic strategies aiming at NE inhibition should take into account the physiologic roles of the enzyme.

Anti-inflammatory effects of DX-890, a human neutrophil elastase inhibitor

BACKGROUND

Neutrophil elastase (NE)-mediated inflammation contributes to lung damage in cystic fibrosis (CF). We investigated if DX-890, a small-protein NE inhibitor, could reduce neutrophil trans-epithelial migration and reduce activity released from neutrophils and NE-induced cytokine expression in airway epithelial cells.

METHODS

Activated blood neutrophils (CF and healthy) treated ±DX-890 were assayed for NE activity. Transmigration of calcein-labeled neutrophils was studied using a 16HBE14o(-) epithelial monolayer. IL-8 release from primary nasal epithelial monolayers (CF and healthy) was measured after treatment ±DX-890 and NE or CF sputum.

RESULTS

DX-890 reduced NE activity from neutrophils (CF and healthy) and reduced neutrophil transmigration. DX-890 pre-treatment reduced IL-8 release from epithelial cells of healthy or CF subjects after stimulation with NE and CF sputum sol. All improvements with DX-890 were statistically significant (p<0.05).

CONCLUSIONS

DX-890 reduces NE-mediated transmigration and inflammation. NE inhibition could be useful in managing neutrophilic airway inflammation in CF.

Cleavage of the CD11b extracellular domain by the leukocyte serprocidins is critical for neutrophil detachment during chemotaxis

The β(2)-integrin CD11b/CD18 mediates the firm adhesion of neutrophils (PMNs) to epithelial monolayers, a key step in PMN transepithelial migration. To complete the transmigration process, adherent PMNs must detach from epithelial monolayer surfaces to move forward. The mechanism that governs the detachment of adherent PMNs, however, is not clear. Here, we present evidence that cleavage of the CD11b extracellular domain containing the ligand-binding I-domain by 3 structural and functional related serine proteases (elastase, proteinase-3 and cathepsin G) serves as a novel mechanism for PMN detachment after the initial cell adhesion. Kinetic studies showed that the cleavage of CD11b is positively correlated with PMN detachment and subsequent transmigration. Moreover, the results demonstrated that elastase, proteinase-3 and cathepsin G all cleaved the purified, functionally active form of CD11b in a pattern similar to the CD11b shedding that occurs during PMN transmigration. Their cleavage sites on purified CD11b were located at (761)Thr-Ala(762) (elastase/proteinase-3) and (760)Phe-Thr(761) (cathepsin G), respectively. CD11b cleavage and PMN detachment and chemotaxis, were impaired in elastase/cathepsin G-deficient Beige mice; this defect could be restored by the addition of extracellular elastase. By illustrating CD11b shedding by elastase, proteinase-3 and cathepsin G as a novel mechanism for PMN detachment, our study provides novel therapeutic targets for controlling inflammation.

Neutrophil elastase and myeloperoxidase regulate the formation of neutrophil extracellular traps

Neutrophil elastase escapes azurophilic granules, translocates to the nucleus, and degrades histones to promote chromatin decondensation necessary for NET formation.

Neutrophils release decondensed chromatin termed neutrophil extracellular traps (NETs) to trap and kill pathogens extracellularly. Reactive oxygen species are required to initiate NET formation but the downstream molecular mechanism is unknown. We show that upon activation, neutrophil elastase (NE) escapes from azurophilic granules and translocates to the nucleus, where it partially degrades specific histones, promoting chromatin decondensation. Subsequently, myeloperoxidase synergizes with NE in driving chromatin decondensation independent of its enzymatic activity. Accordingly, NE knockout mice do not form NETs in a pulmonary model of Klebsiella pneumoniae infection, which suggests that this defect may contribute to the immune deficiency of these mice. This mechanism provides for a novel function for serine proteases and highly charged granular proteins in the regulation of chromatin density, and reveals that the oxidative burst induces a selective release of granular proteins into the cytoplasm through an unknown mechanism.

Contribution of neutrophils to acute lung injury

Treatment of acute lung injury (ALI) and its most severe form, acute respiratory distress syndrome (ARDS), remain unsolved problems of intensive care medicine. ALI/ARDS are characterized by lung edema due to increased permeability of the alveolar-capillary barrier and subsequent impairment of arterial oxygenation. Lung edema, endothelial and epithelial injury are accompanied by an influx of neutrophils into the interstitium and broncheoalveolar space. Hence, activation and recruitment of neutrophils are regarded to play a key role in progression of ALI/ARDS. Neutrophils are the first cells to be recruited to the site of inflammation and have a potent antimicrobial armour that includes oxidants, proteinases and cationic peptides. Under pathological circumstances, however, unregulated release of these microbicidal compounds into the extracellular space paradoxically can damage host tissues. This review focuses on the mechanisms of neutrophil recruitment into the lung and on the contribution of neutrophils to tissue damage in ALI.

Tailor-made inflammation: how neutrophil serine proteases modulate the inflammatory response

Neutrophil granulocytes are important mediators of innate immunity, but also participate in the pathogenesis of (auto)inflammatory diseases. Neutrophils express a specific set of proteolytic enzymes, the neutrophil serine proteases (NSPs), which are stored in cytoplasmic granules and can be secreted into the extra- and pericellular space upon cellular activation. These NSPs, namely cathepsin G (CG), neutrophil elastase (NE), and proteinase 3 (PR3), have early been implicated in bacterial defense. However, NSPs also regulate the inflammatory response by specifically altering the function of cytokines and chemokines. For instance, PR3 and NE both inactivate the anti-inflammatory mediator progranulin, which may play a role in chronic inflammation. Here, we provide a concise update on NSPs as modulators of inflammation and discuss the biological and pathological significance of this novel function of NSPs. Mounting evidence support an important proinflammatory function for PR3, which may have been underestimated in the past.

Myeloperoxidase-dependent inactivation of surfactant protein D in vitro and in vivo

Surfactant protein D (SP-D) plays diverse and important roles in innate immunity and pulmonary homeostasis. Neutrophils and myeloperoxidase (MPO) colocalized with SP-D in a murine bacterial pneumonia model of acute inflammation, suggesting that MPO-derived reactive species might alter the function of SP-D. Exposure of SP-D to the complete MPO-H(2)O(2)-halide system caused loss of SP-D-dependent aggregating activity. Hypochlorous acid (HOCl), the major oxidant generated by MPO, caused a similar loss of aggregating activity, which was accompanied by the generation of abnormal disulfide-cross-linked oligomers. A full-length SP-D mutant lacking N-terminal cysteine residues and truncation mutants lacking the N-terminal domains were resistant to the oxidant-induced alterations in disulfide bonding. Mass spectroscopy of HOCl-treated human SP-D demonstrated several modifications, but none involved key ligand binding residues. There was detectable oxidation of cysteine 15, but no HOCl-induced cysteine modifications were observed in the C-terminal lectin domain. Together, the findings localize abnormal disulfide cross-links to the N-terminal domain. MPO-deficient mice showed decreased cross-linking of SP-D and increased SP-D-dependent aggregating activity in the pneumonia model. Thus, MPO-derived oxidants can lead to modifications of SP-D structure with associated alterations in its characteristic aggregating activity.

Matrix metalloproteinase-8 inactivates macrophage inflammatory protein-1 alpha to reduce acute lung inflammation and injury in mice

To determine the role of matrix metalloproteinase-8 (MMP-8) in acute lung injury (ALI), we delivered LPS or bleomycin by the intratracheal route to MMP-8(-/-) mice versus wild-type (WT) mice or subjected the mice to hyperoxia (95% O(2)) and measured lung inflammation and injury at intervals. MMP-8(-/-) mice with ALI had greater increases in lung polymorphonuclear neutrophils (PMNs) and macrophage counts, measures of alveolar capillary barrier injury, lung elastance, and mortality than WT mice with ALI. Bronchoalveolar lavage fluid (BALF) from LPS-treated MMP-8(-/-) mice had more MIP-1alpha than BALF from LPS-treated WT mice, but similar levels of other pro- and anti-inflammatory mediators. MIP-1alpha(-/-) mice with ALI had less acute lung inflammation and injury than WT mice with ALI, confirming that MIP-1alpha promotes acute lung inflammation and injury in mice. Genetically deleting MIP-1alpha in MMP-8(-/-) mice reduced the increased lung inflammation and injury and mortality in MMP-8(-/-) mice with ALI. Soluble MMP-8 cleaved and inactivated MIP-1alpha in vitro, but membrane-bound MMP-8 on activated PMNs had greater MIP-1alpha-degrading activity than soluble MMP-8. High levels of membrane-bound MMP-8 were detected on lung PMNs from LPS-treated WT mice, but soluble, active MMP-8 was not detected in BALF samples. Thus, MMP-8 has novel roles in restraining lung inflammation and in limiting alveolar capillary barrier injury during ALI in mice by inactivating MIP-1alpha. In addition, membrane-bound MMP-8 on activated lung PMNs is likely to be the key bioactive form of the enzyme that limits lung inflammation and alveolar capillary barrier injury during ALI.

Structural characterization of mouse neutrophil serine proteases and identification of their substrate specificities: relevance to mouse models of human inflammatory diseases

It is widely accepted that neutrophil serine proteases (NSPs) play a critical role in neutrophil-associated lung inflammatory and tissue-destructive diseases. To investigate NSP pathogenic role(s), various mouse experimental models have been developed that mimic acutely or chronically injured human lungs. We and others are using mouse exposure to cigarette smoke as a model for chronic obstructive pulmonary disease with or without exacerbation. However, the relative contribution of NSPs to lung disease processes as well as their underlying mechanisms remains still poorly understood. And the lack of purified mouse NSPs and their specific substrates have hampered advances in these studies. In this work, we compared mouse and human NSPs and generated three-dimensional models of murine NSPs based on three-dimensional structures of their human homologs. Analyses of these models provided compelling evidence that peptide substrate specificities of human and mouse NSPs are different despite their conserved cleft and close structural resemblance. These studies allowed us to synthesize for the first time novel sensitive fluorescence resonance energy transfer substrates for individual mouse NSPs. Our findings and the newly identified substrates should better our understanding about the role of NSPs in the pathogenesis of cigarette-associated chronic obstructive pulmonary disease as well as other neutrophils-associated inflammatory diseases.

Delineating protease functions during cancer development

Much progress has been made in understanding how matrix remodeling proteases, including metalloproteinases, serine proteases, and cysteine cathepsins, functionally contribute to cancer development. In addition to modulating extracellular matrix metabolism, proteases provide a significant protumor advantage to developing neoplasms through their ability to modulate bioavailability of growth and proangiogenic factors, regulation of bioactive chemokines and cytokines, and processing of cell-cell and cell-matrix adhesion molecules. Although some proteases directly regulate these events, it is now evident that some proteases indirectly contribute to cancer development by regulating posttranslational activation of latent zymogens that then directly impart regulatory information. Thus, many proteases act in a cascade-like manner and exert their functionality as part of a proteolytic pathway rather than simply functioning individually. Delineating the cascade of enzymatic activities contributing to overall proteolysis during carcinogenesis may identify rate-limiting steps or pathways that can be targeted with anti-cancer therapeutics. This chapter highlights recent insights into the complexity of roles played by pericellular and intracellular proteases by examining mechanistic studies as well as the roles of individual protease gene functions in various organ-specific mouse models of cancer development, with an emphasis on intersecting proteolytic activities that amplify programming of tissues to foster neoplastic development.

Transepithelial migration of neutrophils: mechanisms and implications for acute lung injury

The primary function of neutrophils in host defense is to contain and eradicate invading microbial pathogens. This is achieved through a series of swift and highly coordinated responses culminating in ingestion (phagocytosis) and killing of invading microbes. While these tasks are usually performed without injury to host tissues, in pathologic circumstances such as sepsis, potent antimicrobial compounds can be released extracellularly, inducing a spectrum of responses in host cells ranging from activation to injury and death. In the lung, such inflammatory damage is believed to contribute to the pathogenesis of diverse lung diseases, including acute lung injury and the acute respiratory distress syndrome, chronic obstructive lung disease, and cystic fibrosis. In these disorders, epithelial cells are targets of leukocyte-derived antimicrobial products, including proteinases and oxidants. Herein, we review the mechanisms involved in the physiologic process of neutrophil transepithelial migration, including the role of specific adhesion molecules on the leukocyte and epithelial cells. We examine the responses of the epithelial cells to the itinerant leukocytes and their cytotoxic products and the consequences of this for lung injury and repair. This paradigm has important clinical implications because of the potential for selective blockade of these pathways to prevent or attenuate lung injury.

Neutrophil elastase mediates innate host protection against Pseudomonas aeruginosa

According to the widely accepted view, neutrophil elastase (NE), a neutrophil-specific serine protease, is a major contributor to Pseudomonas aeruginosa infection-associated host tissue inflammation and damage, which in severe cases can lead to death. Herein, we provide for the first time compelling evidence that the host rather employs NE to protect itself against P. aeruginosa infection. Using a clinically relevant model of pneumonia, targeted deficiency in NE increased the susceptibility of mice to P. aeruginosa. We found that NE was required for maximal intracellular killing of P. aeruginosa by neutrophils. In investigating the mechanism of NE-mediated killing of P. aeruginosa, we found that NE degraded the major outer membrane protein F, a protein with important functions, including porin activity, maintenance of structural integrity, and sensing of host immune system activation. Consistent with this, the use of an isogenic mutant deficient in outer membrane protein F negated the role of NE in host defense against P. aeruginosa infection.

Neutrophil elastase activity compensates for a genetic lack of matrix metalloproteinase-9 (MMP-9) in leukocyte infiltration in a model of experimental peritonitis

Extracellular proteolysis of basement membranes and matrix is required for leukocyte diapedesis and migration to the inflammatory focus. Neutrophil elastase (NE) and matrix metalloproteinases (MMPs) are among the enzymes involved in these processes, as shown in mice genetically deprived of such enzymes. However, studies with MMP-9(-/-) mice revealed that albeit neutrophil influx is impaired initially in these animals versus controls, neutrophilia is subsequently augmented during later stages of zymosan peritonitis. MMP-9 as a MMP and NE as a serine protease belong to different enzyme classes. As MMP-9 and NE are produced by neutrophils and have similar biological effects on matrix remodeling, it was evaluated whether enhanced NE activity might compensate for the lack of MMP-9. In genetically uncompromised mice, two waves of NE expression and activity during zymosan peritonitis were observed in inflammatory neutrophils and macrophages at the time of influx of the respective cell populations into the peritoneum. Additionally, NE expression was associated with the activity of resident peritoneal mast cells and macrophages, as their depletion reduced NE activity. Most importantly, the NE mRNA and protein expression and activity were enhanced significantly in MMP-9(-/-) mice during late stages of zymosan peritonitis. In addition, the application of a selective NE inhibitor restrained enhanced neutrophil accumulation significantly. In conclusion, during acute peritoneal inflammation, NE expression and activity increase gradually, facilitating leukocyte influx. Moreover, increased NE activity might compensate for a genetic lack of MMP-9 (as detected in MMP-9(-/-) mice), resulting in delayed accumulation of neutrophils during late zymosan peritonitis.

Advances in neutrophil biology: clinical implications

Many lung diseases are characterized by neutrophil-dominated inflammation; therefore, an understanding of neutrophil function is of considerable importance to respiratory physicians. This review will focus on recent advances in our understanding of how neutrophils are produced, how these cells leave the circulation, the molecular events regulating neutrophil activation and, ultimately, how these cells die and are removed. The neutrophil is now recognized as a highly versatile and sophisticated cell with significant synthetic capacity and an important role in linking the innate and adaptive arms of the immune response. One of the key challenges in conditions such as COPD, bronchiectasis, cystic fibrosis, and certain forms of asthma is how to manipulate neutrophil function in a way that does not compromise antibacterial and antifungal capacity. The possession by neutrophils of a unique repertoire of surface receptors and signaling proteins may make such targeted therapy possible.

Proteinase 3 and neutrophil elastase enhance inflammation in mice by inactivating antiinflammatory progranulin

Neutrophil granulocytes form the body's first line of antibacterial defense, but they also contribute to tissue injury and noninfectious, chronic inflammation. Proteinase 3 (PR3) and neutrophil elastase (NE) are 2 abundant neutrophil serine proteases implicated in antimicrobial defense with overlapping and potentially redundant substrate specificity. Here, we unraveled a cooperative role for PR3 and NE in neutrophil activation and noninfectious inflammation in vivo, which we believe to be novel. Mice lacking both PR3 and NE demonstrated strongly diminished immune complex-mediated (IC-mediated) neutrophil infiltration in vivo as well as reduced activation of isolated neutrophils by ICs in vitro. In contrast, in mice lacking just NE, neutrophil recruitment to ICs was only marginally impaired. The defects in mice lacking both PR3 and NE were directly linked to the accumulation of antiinflammatory progranulin (PGRN). Both PR3 and NE cleaved PGRN in vitro and during neutrophil activation and inflammation in vivo. Local administration of recombinant PGRN potently inhibited neutrophilic inflammation in vivo, demonstrating that PGRN represents a crucial inflammation-suppressing mediator. We conclude that PR3 and NE enhance neutrophil-dependent inflammation by eliminating the local antiinflammatory activity of PGRN. Our results support the use of serine protease inhibitors as antiinflammatory agents.

Activation of the epidermal growth factor receptor (EGFR) by a novel metalloprotease pathway

Neutrophil Elastase (NE) is a pro-inflammatory protease present at higher than normal levels in the lung during inflammatory disease. NE regulates IL-8 production from airway epithelial cells and can activate both EGFR and TLR4. TACE/ADAM17 has been reported to trans-activate EGFR in response to NE. Here, using 16HBE14o-human bronchial epithelial cells we demonstrate a new mechanism by which NE regulates both of these events. A high molecular weight soluble metalloprotease activity detectable only in supernatants from NE-treated cells by gelatin and casein zymography was confirmed to be meprin alpha by Western immunoblotting. In vitro studies demonstrated the ability of NE to activate meprin alpha, which in turn could release soluble TGFalpha and induce IL-8 production from 16HBE14o- cells. These effects were abrogated by actinonin, a specific meprin inhibitor. NE-induced IL-8 expression was also inhibited by meprin alpha siRNA. Immunoprecipitation studies detected EGFR/TLR4 complexes in NE-stimulated cells overexpressing these receptors. Confocal studies confirmed colocalization of EGFR and TLR4 in 16HBE14o- cells stimulated with meprin alpha. NFkappaB was also activated via MyD88 in these cells by meprin alpha. In bronchoalveolar lavage fluid from NE knock-out mice infected intra-tracheally with Pseudomonas aeruginosa meprin alpha was significantly decreased compared with control mice, and was significantly increased and correlated with NE activity, in bronchoalveolar lavage fluid from individuals with cystic fibrosis but not healthy controls. The data describe a previously unidentified lung metalloprotease meprin alpha, and its role in NE-induced EGFR and TLR4 activation and IL-8 production.

Neutrophil elastase cleaves laminin-332 (laminin-5) generating peptides that are chemotactic for neutrophils

Proteolytic processing of laminin-332 by matrix metalloproteinase (MMP)-2 and MMP-14 has been shown to yield fragments that are promigratory for epithelial cells. During acute and chronic inflammation, proteases are elaborated by neutrophils and macrophages that can degrade basement membranes. We investigated the susceptibility of laminin-332 to degradation by the following neutrophil and macrophage proteases: neutrophil elastase (NE), cathepsin G, proteinase-3, and MMPs-2, -8, -9, and -12. Protease-specific differences were seen in the capacity to cleave the individual chains of laminin-332. NE and MMP-12 showed the greatest activity toward the gamma2 chain, generating a fragment similar in size to the gamma2x fragment generated by MMP-2. The digestion pattern of laminin-332 by degranulated neutrophils was nearly identical to that generated with NE alone. Digestion by supernatants of degranulated neutrophils was blocked by an inhibitor of NE, and NE-deficient neutrophils were essentially unable to digest laminin-332, suggesting that NE is the major neutrophil-derived protease that degrades laminin-332. In vivo, laminin gamma2 fragments were found in the bronchoalveolar lavage fluid of wild-type mice treated with lipopolysaccharide, whereas that obtained from NE-deficient mice showed a different cleavage pattern. In addition, NE cleaved a synthetic peptide derived from the region of human laminin gamma2 containing the MMP-2 cleavage site, suggesting that NE may generate laminin-332 fragments that are also promigratory. Both laminin-332 fragments generated by NE digestion and NE-digested laminin gamma2 peptide were found to be chemotactic for neutrophils. Collectively, these data suggest that degradation of laminin-332 by NE generates fragments with important biological activities.

Neutrophil elastase is needed for neutrophil emigration into lungs in ventilator-induced lung injury

Mechanical ventilation, often required to maintain normal gas exchange in critically ill patients, may itself cause lung injury. Lung-protective ventilatory strategies with low tidal volume have been a major success in the management of acute respiratory distress syndrome (ARDS). Volutrauma causes mechanical injury and induces an acute inflammatory response. Our objective was to determine whether neutrophil elastase (NE), a potent proteolytic enzyme in neutrophils, would contribute to ventilator-induced lung injury. NE-deficient (NE-/-) and wild-type mice were mechanically ventilated at set tidal volumes (10, 20, and 30 ml/kg) with 0 cm H2O of positive end-expiratory pressure for 3 hours. Lung physiology and markers of lung injury were measured. Neutrophils from wild-type and NE-/- mice were also used for in vitro studies of neutrophil migration, intercellular adhesion molecule (ICAM)-1 cleavage, and endothelial cell injury. Surprisingly, in the absence of NE, mice were not protected, but developed worse ventilator-induced lung injury despite having lower numbers of neutrophils in alveolar spaces. The possible explanation for this finding is that NE cleaves ICAM-1, allowing neutrophils to egress from the endothelium. In the absence of NE, impaired neutrophil egression and prolonged contact between neutrophils and endothelial cells leads to tissue injury and increased permeability. NE is required for neutrophil egression from the vasculature into the alveolar space, and interfering with this process leads to neutrophil-related endothelial cell injury.

Leukocyte cell surface proteinases: regulation of expression, functions, and mechanisms of surface localization

A number of proteinases are expressed on the surface of leukocytes including members of the serine, metallo-, and cysteine proteinase superfamilies. Some proteinases are anchored to the plasma membrane of leukocytes by a transmembrane domain or a glycosyl phosphatidyl inositol (GPI) anchor. Other proteinases bind with high affinity to classical receptors, or with lower affinity to integrins, proteoglycans, or other leukocyte surface molecules. Leukocyte surface levels of proteinases are regulated by: (1) cytokines, chemokines, bacterial products, and growth factors which stimulate synthesis and/or release of proteinases by cells; (2) the availability of surface binding sites for proteinases; and/or (3) internalization or shedding of surface-bound proteinases. The binding of proteinases to leukocyte surfaces serves many functions including: (1) concentrating the activity of proteinases to the immediate pericellular environment; (2) facilitating pro-enzyme activation; (3) increasing proteinase stability and retention in the extracellular space; (4) regulating leukocyte function by proteinases signaling through cell surface binding sites or other surface proteins; and (5) protecting proteinases from inhibition by extracellular proteinase inhibitors. There is strong evidence that membrane-associated proteinases on leukocytes play critical roles in wound healing, inflammation, extracellular matrix remodeling, fibrinolysis, and coagulation. This review will outline the biology of membrane-associated proteinases expressed by leukocytes and their roles in physiologic and pathologic processes.

Neutrophil serine proteases fine-tune the inflammatory response

Neutrophil serine proteases are granule-associated enzymes known mainly for their function in the intracellular killing of pathogens. Their extracellular release upon neutrophil activation is traditionally regarded as the primary reason for tissue damage at the sites of inflammation. However, studies over the past several years indicate that neutrophil serine proteases may also be key regulators of the inflammatory response. Neutrophil serine proteases specifically process and release chemokines, cytokines, and growth factors, thus modulating their biological activity. In addition, neutrophil serine proteases activate and shed specific cell surface receptors, which can ultimately prolong or terminate cytokine-induced responses. Moreover, it has been proposed that these proteases can impact cell viability through their caspase-like activity and initiate the adaptive immune response by directly activating lymphocytes. In summary, these studies point to neutrophil serine proteases as versatile mediators that fine-tune the local immune response and identify them as potential targets for therapeutic interventions.

Acute inflammation decreases the expression of connexin 40 in mouse lung

Transmigration of neutrophil polymorphonuclear leukocytes through the microvascular endothelium is a cardinal event of acute inflammation. In vitro, this process can be restricted by gap junctional intercellular communication, but whether it also occurs in vivo is unknown. Connexin 40 (Cx40) is a gap junctional protein abundantly present in the lung, notably in vascular endothelium. We hypothesized that acute lung inflammation would be aggravated in knockout mice genetically deficient in Cx40. This hypothesis was tested in two different models: 1) intranasal instillation of LPS at either supramaximal (50 microg/mouse) or inframaximal dose (0.01 microg/mouse) and 2) pulmonary inflammation as a distant consequence of an abdominal infection caused by cecal ligation and perforation. Pulmonary transmigration of neutrophils was assessed by counting these cells in bronchoalveolar lavage fluid (LPS model) or with the myeloperoxidase assay in homogenates of blood-free tissue (cecal ligation and perforation model). Pulmonary content in Cx40 and Cx43 was evaluated with immunoblots. In wild-type mice, there was a time-dependent decrease of Cx40 expression in both models. The time points for studies with the knockout mice were chosen in such a manner that inflammation was clearly present and Cx40 still largely expressed in wild-type animals. In either model, the development of lung inflammation did not differ between wild-type and Cx40-deficient mice. In conclusion, the pulmonary expression of the Cx40 protein is progressively and markedly decreased in two different murine models of acute lung inflammation, but there is no causal relationship between this process and the pulmonary transmigration of neutrophils.

Neutrophil elastase inhibitor (sivelestat) attenuates subsequent ventilator-induced lung injury in mice

Mechanical ventilation can paradoxically cause acute lung injury, which is termed ventilator-induced lung injury. Neutrophil recruitment and neutrophil elastase release play a central role in the pathogenesis of ventilator-induced lung injury including cell damage, extracellular matrix degradation and alveolar-capillary hyperpermeability. We therefore speculated that neutrophil elastase inhibition ameliorates ventilator-induced lung injury. Anesthetized C57/BL6 mice received mechanical ventilation with a high tidal volume (V(T); 20 ml/kg) for 4 h. The neutrophil elastase inhibitor (sivelestat, 100 mg/kg) or saline was given intraperitoneally (i.p.) 30 min before ventilation. Sivelestat completely inhibited both neutrophil elastase and myeloperoxidase activities that were increased by ventilation, and attenuated the histopathological degree of lung damage, neutrophil accumulation and lung water content, as well as the concentration of macrophage inflammatory protein (MIP)-2, interleukin (IL)-6 and tumor necrosis factor (TNF)-alpha in bronchoalveolar lavage fluid and serum. Moreover, mechanical ventilation increased the phosphorylation of c-Jun NH2-terminal kinase (JNK) and the expression of early growth response gene-1 (Egr-1) mRNA, and these increases were also recovered by sivelestat. The terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling (TUNEL) staining revealed apoptotic cells mainly in alveolar epithelial cells and their numbers corresponded to histological damage. These data suggested that sivelestat could protect against ventilator-induced lung injury by suppressing apoptotic responses through mechanical stress-induced cell signaling in addition to inhibiting neutrophil chemotaxis.

Role of neutrophil elastase in LTB4-induced neutrophil transmigration in vivo assessed with a specific inhibitor and neutrophil elastase deficient mice

BACKGROUND AND PURPOSE

The serine protease neutrophil elastase (NE) appears to regulate inflammatory responses at multiple levels but its role in leukocyte transmigration in vivo remains unclear. The present study aimed to address this issue by using both an NE inhibitor (ONO-5046) and NE deficient (NE(-/-)) mice.

EXPERIMENTAL APPROACH

A number of inflammatory mediators (LTB(4), KC and PAF) were investigated in vitro for their ability to stimulate the release and the surface expression of NE by neutrophils. In addition, the role of NE in leukocyte migration elicited by topical LTB(4) was investigated in vivo in mouse cremasteric venules as observed by intravital microscopy.

KEY RESULTS

Amongst the mediators tested in vitro, LTB(4) was found to be a highly potent and efficacious inducer of NE cell surface expression on murine neutrophils. Furthermore, in wild-type mice (WT), LTB(4)-induced leukocyte transmigration was reduced by intravenous ONO-5046 (66% inhibition), an effect that appeared to occur at the level of the perivascular basement membrane. Interestingly, LTB(4)-induced responses were normal in NE(-/-) mice and, while ONO-5046 had no inhibitory effect in these animals, the broad-spectrum serine protease inhibitor aprotinin suppressed leukocyte transmigration in both WT and NE(-/-) mice.

CONCLUSIONS AND IMPLICATIONS

The findings demonstrate the potent ability of LTB(4) to induce cell-surface expression of NE and provide evidence for the involvement of NE in LTB(4)-induced neutrophil transmigration in vivo. The results also suggest the existence of compensatory mechanisms in NE(-/-) mice, highlighting the added value of investigating pharmacological blockers in parallel with genetic deletion.

Neutrophil Elastase Up-Regulates Cathepsin B and Matrix Metalloprotease-2 Expression

Neutrophil elastase (NE) activity is increased in many diseases. Other families of proteases, including cathepsins and matrix metalloproteases (MMPs), are also present at elevated levels in similar disease conditions. We postulated that NE could induce expression of cathepsins and MMPs in human macrophages. NE exposure resulted in macrophages, producing significantly greater amounts of cathepsin B and latent and active MMP-2. Cathepsin B and MMP-2 activities were decreased in Pseudomonas-infected NE knockout mice compared with wild-type littermates. We also demonstrate that NE can activate NF-kappaB in macrophages, and inhibition of NF-kappaB resulted in a reduction of NE-induced cathepsin B and MMP-2. Also, inhibition of TLR-4 or transfection of macrophages with dominant-negative IL-1R-associated kinase-1 resulted in a reduction of NE-induced cathepsin B and MMP-2. This study describes for the first time a novel hierarchy among proteases whereby a serine protease up-regulates expression of MMPs and cathepsins. This has important implications for therapeutic intervention in protease-mediated diseases.