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

Neutrophil-derived serine proteases in immune complex-mediated diseases

Neutrophil-derived serine proteases play an important role in fighting infections. However, emerging data suggest that these proteases also regulate noninfectious inflammatory responses. Loss-of-function mutations in serine proteases have provided critical insights into the significance of these serine proteases in initiating and amplifying immune complex-mediated diseases.

Human neutrophil elastase inhibitors in innate and adaptive immunity

Recent evidence shows that human neutrophil elastase inhibitors can be synthesized locally at mucosal sites. In addition to efficiently targeting bacterial and host enzymes, they can be released in the interstitium and in the lumen of mucosa, where they have been shown to have antimicrobial activities, and to activate innate immune responses. This review will address more particularly the pleiotropic functions of low-molecular-mass neutrophil elastase inhibitors [SLPI (secretory leucocyte proteinase inhibitor) and elafin] and, more specifically, their role in the development of the adaptive immune response.

Increased local levels of granulocyte colony-stimulating factor are associated with the beneficial effect of pre-elafin (SKALP/trappin-2/WAP3) in experimental emphysema

Few therapeutic options are offered to treat inflammation and alveolar wall destruction in emphysema. The effect of recombinant human pre-elafin, an elastase inhibitor, was evaluated in porcine pancreatic elastase (PPE)-induced emphysema in C57BL/6 mice. In a first protocol, mice received a single instillation of pre-elafin (17.5 pmol/mouse) at 1 h post-PPE and were sacrificed up to 72 h post-PPE. A single instillation of pre-elafin significantly reduced PPE-induced neutrophil accumulation in lungs, as assessed by bronchoalveolar lavage (BAL), by 51%, 71% and 67% at 24, 48 and 72 h, respectively. In a second protocol, mice also received a single dose of PPE, but pre-elafin three times a week for 2 weeks. After 2 weeks, pre-elafin significantly reduced the PPE-induced increase in BAL macrophage numbers, airspace dimensions and lung hysteresivity by 74%, 62% and 52%, respectively. Since G-CSF was previously shown to reduce emphysematous changes in mice, the BAL levels of this mediator were measured 6 h post-PPE in animals treated as described in the first protocol. Pre-elafin significantly increased G-CSF levels in PPE-exposed mice compared to sham- and PPE only-exposed animals. This suggests that the beneficial effects of pre-elafin could be mediated, at least in part, by its ability to increase G-CSF levels in the lung.

Serine protease cathepsin G regulates adhesion-dependent neutrophil effector functions by modulating integrin clustering

The polymorphonuclear leukocyte (PMN)-derived serine proteases play a key role in immune complex (IC)-mediated inflammation. However, the mechanisms by which these proteases regulate inflammatory response remain largely undefined. Here, we show that IC-activated cathepsin G- and neutrophil elastase-deficient (CG/NE) PMNs adhered normally to IC-coated surfaces but did not undergo CD11b clustering and failed to initiate cytoskeletal reorganization and cell spreading. As a result, CG/NE-deficient PMNs exhibited severe defects in MIP-2 secretion and reactive oxygen intermediates production. Exogenously added CG, but not proteolytically inactive CG, was sufficient to restore these defects. These findings identify an important role for CG in integrin-dependent PMN effector functions that are separate from and downstream of integrin-dependent adhesion.

The fibrinolytic system and thrombotic tendency

The deposition of the insoluble protein matrix, fibrin is temporary. The mainly known mechanism of proteolytic removal is orchestrated by a cascade type of proteolytic process involving ultimately the formation from plasminogen of the active degradation enzyme plasmin. The occurrence of plasminogen deficiency without a massive deposition of fibrin and thrombotic events indicates the occurrence of alternate routes of fibrin degradation. In the literature, data have been reported about the direct fibrinolytic activity of various other enzymes including leucocytal elastase and cathepsin G and three metalloproteinases (MMP-3,MMP-7, MT1-MMP). The importance of each of these pathways and the possible differences in importance in various diseases, in acute situations and at different locations in the circulation, in tissues and organs is not known in detail. It is suggested that multiple combined knock-outs be created to evaluate the situation for various well-defined phenotypes. It is concluded that fibrin removal is an important biological process with various buffering mechanisms and only combinations of abnormalities in the various mechanisms and special situations will lead to fibrin accumulation and thrombotic events.

A chemotactic peptide from laminin alpha 5 functions as a regulator of inflammatory immune responses via TNF alpha-mediated signaling

Tissue injury triggers inflammatory responses that may result in release of degradation products or exposure of cryptic domains of extracellular matrix components. Previously, we have shown that a cryptic peptide (AQARSAASKVKVSMKF) in the alpha-chain of laminin-10 (alpha5beta1gamma1), a prominent basement membrane component, is chemotactic for both neutrophils (PMNs) and macrophages (Mphis) and induces matrix metalloproteinase-9 (MMP-9) production. To determine whether AQARSAASKVKVSMKF has additional effects on inflammatory cells, we performed microarray analysis of RNA from RAW264.7 Mphis stimulated with AQARSAASKVKVSMKF. Several cytokines and cytokine receptors were increased >3-fold in response to the laminin alpha5 peptide. Among these were TNF-alpha and one of its receptors, the p75 TNFR (TNFR-II), increasing 3.5- and 5.7-fold, respectively. However, the peptide had no effect on p55 TNFR (TNFR-I) expression. Corroborating the microarray data, the protein levels of TNF-alpha and TNFR-II were increased following stimulation of RAW264.7 cells with AQARSAASKVKVSMKF. In addition, we determined that the production of TNF-alpha and TNFR-II in response to AQARSAASKVKVSMKF preceded the production of MMP-9. Furthermore, using primary Mphis from mice deficient in TNFR-I, TNFR-II, or both TNF-alpha receptors (TNFRs), we determined that AQARSAASKVKVSMKF induces MMP-9 expression by Mphis through a pathway triggered by TNFR-II. However, TNF-alpha signaling is not required for AQARSAASKVKVSMKF-induced PMN release of MMP-9 or PMN emigration. These data suggest that interactions of inflammatory cells with basement membrane components may orchestrate immune responses by inducing expression of cytokines, recruitment of inflammatory cells, and release of proteinases.

Myeloperoxidase plays critical roles in killing Klebsiella pneumoniae and inactivating neutrophil elastase: effects on host defense

Activated neutrophils use myeloperoxidase (MPO) to generate an array of potent toxic oxidants. In the current studies we used genetically altered mice deficient in MPO to investigate the role of the enzyme in host defense against the Gram-negative bacterium Klebsiella pneumoniae, an important human pathogen. For comparison, we used mice deficient in the antimicrobial molecule, neutrophil elastase (NE). When challenged i.p., mice deficient in either MPO or NE were markedly more susceptible to bacterial infection and death. In vitro studies suggested that MPO impairs the morphology of bacteria in a distinctive way. Of importance, our in vitro studies found that MPO mediated oxidative inactivation of NE, an enzyme that has been widely implicated in the pathogenesis of various tissue-destructive diseases. This pathway of oxidative inactivation may be physiologically relevant, because activated neutrophils isolated from MPO-deficient mice exhibited increased elastase activity. Our observations provide strong evidence that MPO, like NE, is a key player in the killing of K. pneumoniae bacteria. They also suggest that MPO may modulate NE to protect the host from the tissue-degrading activity of this proteinase.

A novel, potent dual inhibitor of the leukocyte proteases cathepsin G and chymase: molecular mechanisms and anti-inflammatory activity in vivo

Certain leukocytes release serine proteases that sustain inflammatory processes and cause disease conditions, such as asthma and chronic obstructive pulmonary disease. We identified beta-ketophosphonate 1 (JNJ-10311795; RWJ-355871) as a novel, potent dual inhibitor of neutrophil cathepsin G (K(i) = 38 nm) and mast cell chymase (K(i) = 2.3 nm). The x-ray crystal structures of 1 complexed with human cathepsin G (1.85 A) and human chymase (1.90 A) reveal the molecular basis of the dual inhibition. Ligand 1 occupies the S(1) and S(2) subsites of cathepsin G and chymase similarly, with the 2-naphthyl in S(1), the 1-naphthyl in S(2), and the phosphonate group in a complex network of hydrogen bonds. Surprisingly, however, the carboxamido-N-(naphthalene-2-carboxyl)piperidine group is found to bind in two distinct conformations. In cathepsin G, this group occupies the hydrophobic S(3)/S(4) subsites, whereas in chymase, it does not; rather, it folds onto the 1-naphthyl group of the inhibitor itself. Compound 1 exhibited noteworthy anti-inflammatory activity in rats for glycogen-induced peritonitis and lipopolysaccharide-induced airway inflammation. In addition to a marked reduction in neutrophil influx, 1 reversed increases in inflammatory mediators interleukin-1alpha, interleukin-1beta, tissue necrosis factor-alpha, and monocyte chemotactic protein-1 in the glycogen model and reversed increases in airway nitric oxide levels in the lipopolysaccharide model. These findings demonstrate that it is possible to inhibit both cathepsin G and chymase with a single molecule and suggest an exciting opportunity in the treatment of asthma and chronic obstructive pulmonary disease.

Neutrophil Serine Proteinases Inactivate Surfactant Protein D by Cleaving within a Conserved Subregion of the Carbohydrate Recognition Domain

Surfactant protein D (SP-D) plays important roles in innate immunity including the defense against bacteria, fungi, and respiratory viruses. Because SP-D specifically interacts with neutrophils that infiltrate the lung in response to acute inflammation and infection, we examined the hypothesis that the neutrophil-derived serine proteinases (NSPs): neutrophil elastase, proteinase-3, and cathepsin G degrade SP-D. All three human NSPs specifically cleaved recombinant rat and natural human SP-D dodecamers in a time- and dose-dependent manner, which was reciprocally dependent on calcium concentration. The NSPs generated similar, relatively stable, disulfide cross-linked immunoreactive fragments of approximately 35 kDa (reduced), and sequencing of a major catheptic fragment definitively localized the major sites of cleavage to a highly conserved subregion of the carbohydrate recognition domain. Cleavage markedly reduced the ability of SP-D to promote bacterial aggregation and to bind to yeast mannan in vitro. Incubation of SP-D with isolated murine neutrophils led to the generation of similar fragments, and cleavage was inhibited with synthetic and natural serine proteinase inhibitors. In addition, neutrophils genetically deficient in neutrophil elastase and/or cathepsin G were impaired in their ability to degrade SP-D. Using a mouse model of acute bacterial pneumonia, we observed the accumulation of SP-D at sites of neutrophil infiltration coinciding with the appearance of approximately 35-kDa SP-D fragments in bronchoalveolar lavage fluids. Together, our data suggest that neutrophil-derived serine proteinases cleave SP-D at sites of inflammation with potential deleterious effects on its biological functions.