Normal Neutrophil Function in Cathepsin G-Deficient Mice

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.

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.

Granzyme B and the Downstream Granzymes C and/or F Are Important for Cytotoxic Lymphocyte Functions

Although the functions of granzyme A (GzmA) and GzmB are well-defined, a number of orphan granzymes of unknown function are also expressed in cytotoxic lymphocytes. Previously, we showed that a targeted loss-of-function mutation for GzmB was associated with reduced expression of several downstream orphan granzyme genes in the lymphokine-activated killer cell compartment. To determine whether this was caused by the retained phosphoglycerate kinase I gene promoter (PGK-neo) cassette in the GzmB gene, we retargeted the GzmB gene with a LoxP-flanked PGK-neo cassette, then removed the cassette in embryonic stem cells by transiently expressing Cre recombinase. Mice homozygous for the GzmB null mutation containing the PGK-neo cassette (GzmB-/-/+PGK-neo) displayed reduced expression of the closely linked GzmC and F genes in their MLR-derived CTLs and lymphokine-activated killer cells; removal of the PGK-neo cassette (GzmB-/-/DeltaPGK-neo) restored the expression of both genes. Cytotoxic lymphocytes derived from mice with the retained PGK-neo cassette (GzmB-/-/+PGK-neo) had a more severe cytotoxic defect than those deficient for GzmB only (GzmB-/-/DeltaPGK-neo). Similarly, GzmB-/-/+PGK-neo mice displayed a defect in the allogeneic clearance of P815 tumor cells, whereas GzmB-/-/DeltaPGK-neo mice did not. These results suggest that the retained PGK-neo cassette in the GzmB gene causes a knockdown of GzmC and F expression, and also suggest that these granzymes are relevant for the function of cytotoxic lymphocytes in vitro and in vivo.

Myeloperoxidase: friend and foe

Neutrophilic polymorphonuclear leukocytes (neutrophils) are highly specialized for their primary function, the phagocytosis and destruction of microorganisms. When coated with opsonins (generally complement and/or antibody), microorganisms bind to specific receptors on the surface of the phagocyte and invagination of the cell membrane occurs with the incorporation of the microorganism into an intracellular phagosome. There follows a burst of oxygen consumption, and much, if not all, of the extra oxygen consumed is converted to highly reactive oxygen species. In addition, the cytoplasmic granules discharge their contents into the phagosome, and death of the ingested microorganism soon follows. Among the antimicrobial systems formed in the phagosome is one consisting of myeloperoxidase (MPO), released into the phagosome during the degranulation process, hydrogen peroxide (H2O2), formed by the respiratory burst and a halide, particularly chloride. The initial product of the MPO-H2O2-chloride system is hypochlorous acid, and subsequent formation of chlorine, chloramines, hydroxyl radicals, singlet oxygen, and ozone has been proposed. These same toxic agents can be released to the outside of the cell, where they may attack normal tissue and thus contribute to the pathogenesis of disease. This review will consider the potential sources of H2O2 for the MPO-H2O2-halide system; the toxic products of the MPO system; the evidence for MPO involvement in the microbicidal activity of neutrophils; the involvement of MPO-independent antimicrobial systems; and the role of the MPO system in tissue injury. It is concluded that the MPO system plays an important role in the microbicidal activity of phagocytes.

Neutrophil elastase is important for PML-retinoic acid receptor alpha activities in early myeloid cells

Expression of the PML-retinoic acid receptor alpha (PML-RARalpha) fusion protein is the initiating genetic event for acute promyelocytic leukemia (APL), but the molecular mechanisms responsible for disease initiation are not yet clear. Several observations have suggested that early myeloid cells are uniquely susceptible to transformation by PML-RARalpha. Recently, we have shown that the early myeloid-specific protease neutrophil elastase is important for APL development in the mouse. To better understand the role of neutrophil elastase for the pathogenesis of APL, we examined the consequences of PML-RARalpha expression in early myeloid cells with or without neutrophil elastase. We found that high-level PML-RARalpha expression was associated with cellular toxicity that was dependent on the expression of neutrophil elastase; a mutant form of PML-RARalpha that resisted neutrophil elastase cleavage was not toxic. When PML-RARalpha was expressed at very low levels in the early myeloid cells of mice, it induced myeloid expansion and delayed myeloid maturation; neutrophil elastase was also required for these activities. The activities of PML-RARalpha in early myeloid cells are therefore strongly influenced by the presence of neutrophil elastase. To assure physiologic relevance, PML-RARalpha functions should be evaluated in neutrophil elastase-expressing early myeloid cells.

Neither neutrophils nor reactive oxygen species contribute to tissue damage during Pneumocystis pneumonia in mice

Neutrophils are implicated in the damage of lung tissue in many disease states, including infectious diseases and environmental insults. These effects may be due to oxidative or nonoxidative functions of the neutrophil or both. We examined the role of neutrophils in pulmonary damage during infection with the opportunistic fungal pathogen Pneumocystis sp. in four mouse models of neutrophil dysfunction. These were (i) a knockout of the gp91(phox) component of NADPH oxidase, in which reactive oxygen species (ROS) production is greatly reduced; (ii) a double knockout of gp91(phox) and inducible nitric oxide synthase, in which ROS and nitric oxide production is greatly decreased; (iii) a knockout of the chemokine receptor CXCR2, in which accumulation of intra-alveolar neutrophils is severely diminished; and (iv) antibody depletion of circulating neutrophils in wild-type mice with the monoclonal antibody RB6. Surprisingly, in each case, indicators of pulmonary damage (respiratory rates, arterial oxygen partial pressures, and intra-alveolar albumin concentrations) were the same in knockout mice and comparable wild-type mice. Therefore, whereas neutrophils are a valid correlative marker of lung damage during Pneumocystis infection, neither neutrophils nor ROS appear to be the causative agent of tissue damage. We also show that there is no difference in Pneumocystis burdens between wild-type and knockout mice, which supports the idea that neutrophils do not have a major role in the clearance of this organism.

Antimicrobial reactive oxygen and nitrogen species: concepts and controversies

Phagocyte-derived reactive oxygen and nitrogen species are of crucial importance for host resistance to microbial pathogens. Decades of research have provided a detailed understanding of the regulation, generation and actions of these molecular mediators, as well as their roles in resisting infection. However, differences of opinion remain with regard to their host specificity, cell biology, sources and interactions with one another or with myeloperoxidase and granule proteases. More than a century after Metchnikoff first described phagocytosis, and more than four decades after the discovery of the burst of oxygen consumption that is associated with microbial killing, the seemingly elementary question of how phagocytes inhibit, kill and degrade microorganisms remains controversial. This review updates the reader on these concepts and the topical questions in the field.

Characterization of hematopoietic progenitor mobilization in protease-deficient mice

Recent evidence suggests that protease release by neutrophils in the bone marrow may contribute to hematopoietic progenitor cell (HPC) mobilization. Matrix metalloproteinase-9 (MMP-9), neutrophil elastase (NE), and cathepsin G (CG) accumulate in the bone marrow during granulocyte colony-stimulating factor (G-CSF) treatment, where they are thought to degrade key substrates including vascular cell adhesion molecule-1 (VCAM-1) and CXCL12. To test this hypothesis, HPC mobilization was characterized in transgenic mice deficient in one or more hematopoietic proteases. Surprisingly, HPC mobilization by G-CSF was normal in MMP-9–deficient mice, NE × CG-deficient mice, or mice lacking dipeptidyl peptidase I, an enzyme required for the functional activation of many hematopoietic serine proteases. Moreover, combined inhibition of neutrophil serine proteases and metalloproteinases had no significant effect on HPC mobilization. VCAM-1 expression on bone marrow stromal cells decreased during G-CSF treatment of wild-type mice but not NE × CG-deficient mice, indicating that VCAM-1 cleavage is not required for efficient HPC mobilization. G-CSF induced a significant decrease in CXCL12α protein expression in the bone marrow of Ne × CG-deficient mice, indicating that these proteases are not required to down-regulate CXCL12 expression. Collectively, these data suggest a complex model in which both protease-dependent and -independent pathways may contribute to HPC mobilization.

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.

Neutrophil serine proteinases cleave bacterial flagellin, abrogating its host response-inducing activity

After bacterial infection, neutrophils dominate the cellular infiltrate. Their main function is assumed to be killing invading pathogens and resolving the inflammation they cause. Activated neutrophils are also known to release a variety of molecules, including the neutrophil serine proteinases, extracellularly. The release of these proteinases during inflammation creates a proteolytic environment where degradation of different molecules modulates the inflammatory response. Flagellin, the structural component of flagella on many bacterial species, is a virulence factor with a strong proinflammatory activity on epithelial cells and other cell types. In this study we show that both human and mouse neutrophil serine proteinases cleave flagellin from Pseudomonas aeruginosa and other bacterial species. More important, cleavage of P. aeruginosa flagellin by the neutrophil serine proteinases neutrophil elastase and cathepsin G resulted in loss of the biological activity of this virulence factor, as evidenced by the lack of innate host defense gene expression in human epithelial cells. The finding that flagellin is susceptible to cleavage by neutrophil serine proteinases suggests a novel role for these enzymes in the inflammatory response to infection. Not only can these enzymes kill bacteria, but they also degrade their virulence factors to halt the inflammatory response they trigger.

Neutrophil elastase cleaves PML-RARalpha and is important for the development of acute promyelocytic leukemia in mice

The fusion protein PML-RARalpha, generated by the t(15;17)(q22;q11.2) translocation associated with acute promyelocytic leukemia (APL), initiates APL when expressed in the early myeloid compartment of transgenic mice. PML-RARalpha is cleaved in several positions by a neutral serine protease in a human myeloid cell line; purification revealed that the protease is neutrophil elastase (NE). Immunofluorescence localization studies suggested that the cleavage of PML-RARalpha must occur within the cell, and perhaps, within the nucleus. The functional importance of NE for APL development was assessed in NE deficient mice. Greater than 90% of bone marrow PML-RARalpha cleaving activity was lost in the absence of NE, and NE (but not Cathepsin G) deficient animals were protected from APL development. Primary mouse and human APL cells also contain NE-dependent PML-RARalpha cleaving activity. Since NE is maximally produced in promyelocytes, this protease may play a role in APL pathogenesis by facilitating the leukemogenic potential of PML-RARalpha.

Synergism of gamma interferon and interleukin-5 in the control of murine filariasis

There has been a prevailing perception that Th1 and Th2 immune responses induce antagonistic immune effector mechanisms during an infection. We investigated the role of the Th1 cytokine gamma interferon (IFN-gamma) and the Th2 cytokine interleukin-5 (IL-5) in murine filariasis infections with the rodent filarial nematode Litomosoides sigmodontis with regard to immune responses to the parasite. Earlier data showed an important role for IL-5 and IFN-gamma in effective immune responses to filarial infection. Therefore, in this study it was asked whether IL-5 and IFN-gamma act synergistically or antagonistically. Indeed, IL-5 as well as IFN-gamma knockout (KO) mice show a higher worm load than the wild-type controls. IFN-gamma/IL-5 double-KO mice had a significantly higher worm load than any of the single-KO mice, suggesting a synergism between IFN-gamma and IL-5 in controlling worm infection. Neutrophils are known to play an important role for the containment and encapsulation process of the worms. In infected IFN-gamma KO, IL-5 KO, and IFN-gamma/IL-5 double-KO mice, neutrophils were significantly reduced in chemotactic activity levels compared to controls. In addition, the level of phagocytosis activity of neutrophils from IFN-gamma/IL-5 double-KO mice was further decreased in comparison to that of the single-KO mice. Levels of tumor necrosis factor alpha, which is an important factor for neutrophil activation, were found to be reduced in macrophages from KO mice. In conclusion, these results argue for immune effector mechanisms in murine filarial infection that are dependent on both IFN-gamma and IL-5. Synergistic effects of the two cytokines may be mediated, at least in part, by neutrophils for the control of adult worms.

Neutrophil elastase contributes to cigarette smoke-induced emphysema in mice

To address the role of neutrophil elastase in pulmonary emphysema, neutrophil elastase-deficient mice and wild-type littermate controls were exposed to long-term cigarette smoke. Compared to wild-type littermates, mice that were deficient in neutrophil elastase were significantly protected (59%) from the development of emphysema. Previously, we demonstrated complete protection from emphysema in the absence of macrophage elastase. Further analysis revealed several interactions between these two elastases. Each elastase inactivated the endogenous inhibitor of the other, with neutrophil elastase degrading tissue inhibitor of metalloproteinase-1, and macrophage elastase degrading alpha-1-antitrypsin. Cigarette smoke-induced recruitment of both neutrophils and monocytes was impaired in the absence of neutrophil elastase. Moreover, there was less macrophage elastase activity secondary to decreased macrophage accumulation in neutrophil elastase-deficient mice. This study demonstrates a direct role for neutrophil elastase in emphysema and highlights the interdependence of the proteinases and inflammatory cells that mediate lung destruction in response to cigarette smoke.

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

To reach the sites of inflammation, neutrophils traverse the endothelium, its underlying basement membrane, and other barriers depending on the localization of the insulting agent. Whether neutrophil elastase (NE) plays a role in neutrophil recruitment to inflamed sites is still debatable. By exploiting mice deficient in NE (NE(-/-)), we sought to address this dilemma. We recruited neutrophils to the lungs or the peritoneum of wild-type (WT) or NE(-/-) mice by intranasal or intraperitoneal challenge with Pseudomonas aeruginosa or its lipopolysaccharide. At designated times post-inoculation (0, 4, 24, and 48 h), groups of mice were killed to assess changes in leukocyte counts and inflammatory responses. NE(-/-) and WT mice had normal circulating leukocyte numbers including neutrophils and changes in the hemograms in the setting of acute inflammation were indistinguishable. Analyses of lung tissues or fluids from the lungs and peritoneum found that regardless of the inflammatory model, the leukocyte counts including neutrophils and the inflammatory response were similar in NE(-/-) and WT mice at all time points. In vitro, neutrophils isolated from the lungs or the peritoneum of NE(-/-) and WT mice had comparable chemotactic and respiratory-burst functions and migrated normally through Matrigel in response to various stimuli. Interestingly, preincubation of human peripheral blood neutrophils with NE physiologic inhibitors did not alter the migration of the cells through Matrigel. In sum, our findings present the first in vivo description that the absence of NE does not impair neutrophil recruitment to inflamed sites and that NE is not required for basement membrane transmigration of neutrophils.

Monoclonal LYM-1 antibody-dependent cytolysis by human neutrophils exposed to GM-CSF: auto-regulation of target cell attack by cathepsin G

Murine monoclonal antibody (mAb) Lym-1 is an immunoglobulin G2a specific for certain human leukocyte antigen-DR variants expressed on the surface of malignant B cells. It has been proposed for serotherapy in patients with B lymphomas. We have previously shown that mAb Lym-1 synergizes with granulocyte macrophage-colony stimulating factor to promote Raji B-lymphoid cell lysis by human neutrophils via the intervention of neutrophil Fc receptors type II and D-mannose-inhibitable interactions between CD11b-CD18 integrins and CD66b glycoproteins. Here, we provide evidence that the process is oxygen-independent by inference related to the release of primary granules and is regulated by cathepsin G activity. The lysis was indeed reproduced by replacing normal neutrophils with cells from three patients suffering from chronic granulomatous disease, i.e., neutrophils genetically incapable of generating oxidants. Moreover, the lysis was inhibited by the serine protease inhibitor 3,4-dichloroisocoumarin and by Z-glycyl-leucyl-phenyl-chloromethyl ketone (Z-Gly-Leu-Phe-CMK), which blocks cathepsin G. Conversely, the lysis was unaffected by N-methoxysuccinyl-alanyl-alanyl-prolyl-alanyl-CMK (MeOSuc-Ala-Ala-Pro-Ala-CMK; elastase inhibitor) and MeOSuc-Ala-Ala-Pro-valine (Val)-CMK, which inhibits elastase and proteinase 3. The ability of neutrophils, engaged in cytolysis, to release cathepsin G was proved by detecting this enzymatic activity spectrophotometrically and immunocytochemically. Moreover, inhibition of cathepsin G activity by concentrations of Z-Gly-Leu-Phe-CMK, incapable of affecting elastase activity, was found to reduce the release of elastase and myeloperoxidase from neutrophils under conditions similar to those used for cytolytic assays. These findings suggest that neutrophils auto-regulate their lytic efficiency by controlling the exocytosis of primary granules via their cathepsin G activity.

The orphan granzymes of humans and mice

The granzyme/perforin pathway is a central pathway for lymphocyte-mediated killing in both the innate and adaptive immune systems. This pathway is important in a variety of host defenses, including viral clearance and tumor cell killing, and its dysregulation results in several human and rodent diseases. To date, the majority of reports in this field have concentrated on the functions of granzymes A and B. Recent reports, however, suggest that the non-A/non-B 'orphan' granzymes found in both humans and mice are potentially significant. Although the functions of these orphan granzymes have yet to be fully established, initial data suggests their importance in both immune and nonimmune cells.

High-penetrance mouse model of acute promyelocytic leukemia with very low levels of PML-RARalpha expression

Transgenic mice expressing PML-RARalpha in early myeloid cells under control of human cathepsin G regulatory sequences all develop a myeloproliferative syndrome, but only 15% to 20% develop acute promyelocytic leukemia (APL) after a latent period of 6 to 14 months. However, this transgene is expressed at very low levels in the bone marrow cells of transgenic mice. Because the transgene includes only 6 kb of regulatory sequences from the human cathepsin G locus, we hypothesized that sequences required for high-level expression of the transgene might be located elsewhere in the cathepsin G locus and that a knock-in model might yield much higher expression levels and higher penetrance of disease. We, therefore, targeted a human PML-RARalpha cDNA to the 5' untranslated region of the murine cathepsin G gene, using homologous recombination in embryonic stem cells. This model produced a high-penetrance APL phenotype, with more than 90% of knock-in mice developing APL between 6 and 16 months of age. The latent period and phenotype of APL (including a low frequency of an interstitial deletion of chromosome 2) was similar to that of the previous transgenic model. Remarkably, however, the expression level of PML-RARalpha in bone marrow cells or APL cells was less than 3% of that measured in the low-penetrance transgenic model. Although the explanation for this result is not yet clear, one hypothesis suggests that very low levels of PML-RARalpha expression in early myeloid cells may be optimal for the development of APL in mice.

Defect in neutrophil killing and increased susceptibility to infection with nonpathogenic gram-positive bacteria in peptidoglycan recognition protein-S (PGRP-S)-deficient mice

Insect peptidoglycan recognition protein-S (PGRP-S), a member of a family of innate immunity pattern recognition molecules conserved from insects to mammals, recognizes bacterial cell wall peptidoglycan and activates 2 antimicrobial defense systems, prophenoloxidase cascade and antimicrobial peptides through Toll receptor. We show that mouse PGRP-S is present in neutrophil tertiary granules and that PGRP-S-deficient (PGRP-S-/-) mice have increased susceptibility to intraperitoneal infection with gram-positive bacteria of low pathogenicity but not with more pathogenic gram-positive or gram-negative bacteria. PGRP-S-/- mice have normal inflammatory responses and production of tumor necrosis factor alpha (TNF-alpha) and interleukin 6 (IL-6). Neutrophils from PGRP-S-/- mice have normal phagocytic uptake of bacteria but are defective in intracellular killing and digestion of relatively nonpathogenic gram-positive bacteria. Therefore, mammalian PGRP-S functions in intracellular killing of bacteria. Thus, only bacterial recognition by PGRP-S, but not its effector function, is conserved from insects to mammals.

Proteinases and their inhibitors in the immune system

The most important roles of proteinases in the immune system are found in apoptosis and major histocompatibility complex (MHC) class II-mediated antigen presentation. A variety of cysteine proteinases, serine proteinases, and aspartic proteinases as well as their inhibitors are involved in the regulation of apoptosis in neutrophils, monocytes, and dendritic cells, in selection of specific B and T lymphocytes, and in killing of target cells by cytotoxic T cells and natural killer cells. In antigen presentation, endocytosed antigens are digested into antigenic peptides by both aspartic and cysteine proteinases. In parallel, MHC class II molecules are processed by aspartic and cysteine proteinases to degrade the invariant chain that occupies the peptide-binding site. Proteinase activity in these processes is highly regulated, particularly by posttranslational activation and the balance between active proteinases and specific endogenous inhibitors such as cystatins, thyropins, and serpins. This article discusses the regulation of proteolytic processes in apoptosis and antigen presentation in immune cells and the consequences of therapeutic interference in the balance of proteinases and their inhibitors.

Towards the understanding of the local hematopoietic bone marrow renin-angiotensin system

The classical view of the renin-angiotensin system (RAS) as a circulating endocrine system has evolved to organ- and tissue-based systems that perform paracrine/autocrine functions. Angiotensin II (Ang II), the dominant effector peptide of the RAS, regulates cellular growth in a wide variety of tissues in (patho)biological states. In 1996, we hypothesized that there exists a locally active RAS in the bone marrow affecting the growth, production, proliferation and differentiation of hematopoietic cells. Evidences supporting this hypothesis are growing. Ang II, through interacting with Ang II type 1 (AT1) receptor stimulates erythroid differentiation. This stimulatory effect of Ang II on erythropoiesis was completely abolished by a specific AT1 receptor antagonist, losartan. AT1a receptors are present on human CD34(+) hematopoietic stem cells. Ang II increases hematopoietic progenitor cell proliferation and this effect was also blocked by losartan. Angiotensin-converting enzyme (ACE) is involved in enhancing the recruitment of primitive stem cells into S-phase in hematopoietic bone marrow by degrading tetrapeptide AcSDKP. ACE inhibitors modified the circulating hematopoietic progenitors in healthy subjects. RAS may also affect pathological/neoplastic hematopoiesis. Renin has been isolated from leukemic blast cells. Higher bone marrow ACE levels in acute leukemic patients suggested that ACE is produced at higher quantities in the leukemic bone marrow. In this review, the 'State of the Art' of the local bone marrow RAS is summarized. A local RAS in the bone marrow can mediate, in an autocrine/paracrine fashion, some of the principal steps of hematopoietic cell production. To show a causal link between the components of RAS and the other regulatory hematopoietic growth factors is not only an academic curiosity. Elucidation of such a local bone marrow system may offer novel therapeutic approaches in pathologic/neoplastic conditions.

Mice expressing a neutrophil elastase mutation derived from patients with severe congenital neutropenia have normal granulopoiesis

Severe congenital neutropenia (SCN) is a syndrome characterized by an isolated block in granulocytic differentiation and an increased risk of developing acute myeloid leukemia (AML). Recent studies have demonstrated that the majority of patients with SCN and cyclic neutropenia, a related disorder characterized by periodic oscillations in the number of circulating neutrophils, have heterozygous germline mutations in the ELA2 gene encoding neutrophil elastase (NE). To test the hypothesis that these mutations are causative for SCN, we generated transgenic mice carrying a targeted mutation of their Ela2 gene ("V72M") reproducing a mutation found in 2 unrelated patients with SCN, one of whom developed AML. Expression of mutant NE mRNA and enzymatically active protein was confirmed. Mice heterozygous and homozygous for the V72M allele have normal numbers of circulating neutrophils, and no accumulation of myeloid precursors in the bone marrow was observed. Serial blood analysis found no evidence of cycling in any of the major hematopoietic lineages. Rates of apoptosis following cytokine deprivation were similar in wild-type and mutant neutrophils, as were the frequency and cytokine responsiveness of myeloid progenitors. The stress granulopoiesis response, as measured by neutrophil recovery after cyclophosphamide-induced myelosuppression, was normal. To define the leukemogenic potential of V72M NE, a tumor watch was established. To date, no cases of leukemia have been detected. Collectively, these data suggest that expression of V72M NE is not sufficient to induce an SCN phenotype or leukemia in mice.

Neutrophil elastase-mediated killing of bacteria: lessons from targeted mutagenesis

Engineering of mice deficient in neutrophil elastase (NE) has allowed us to demonstrate the role of this protease in host defense against bacteria and to begin to understand its killing mechanism. Strategies to inhibit NE because of its involvement in tissue-destructive diseases should be reconsidered, while preserving its beneficial properties.

Nonpeptide inhibitors of cathepsin G: optimization of a novel beta-ketophosphonic acid lead by structure-based drug design

The serine protease cathepsin G (EC 3.4.21.20; Cat G), which is stored in the azurophilic granules of neutrophils (polymorphonuclear leukocytes) and released on degranulation, has been implicated in various pathological conditions associated with inflammation. By employing high-throughput screening, we identified beta-ketophosphonic acid 1 as a moderate inhibitor of Cat G (IC(50) = 4.1 microM). We were fortunate to obtain a cocrystal of 1 with Cat G and solve its structure by X-ray crystallography (3.5 A). Structural details from the X-ray analysis of 1.Cat G served as a platform for optimization of this lead compound by structure-based drug design. With the aid of molecular modeling, substituents were attached to the 3-position of the 2-naphthyl ring of 1, which occupies the S1 pocket of Cat G, to provide an extension into the hydrophobic S3 region. Thus, we arrived at analogue 7 with an 80-fold potency improvement over 1 (IC(50) = 53 nM). From these results, it is evident that the beta-ketophosphonic acid unit can form the basis for a novel class of serine protease inhibitors.

Use of genetically engineered mice in drug discovery and development: wielding Occam's razor to prune the product portfolio

Genetically engineered mice (GEMs) that either overexpress (transgenic) or lack (gene-targeted, or "knock-out") genes are used increasingly in industry to investigate molecular mechanisms of disease, to evaluate innovative therapeutic targets, and to screen agents for efficacy and/or toxicity. High throughput GEM construction in drug discovery and development (DDD) serves two main purposes: to test whether a given gene participates in a disease condition, or to determine the function(s) of a protein that is encoded by an expressed sequence tag (EST, an mRNA fragment for a previously uncharacterized protein). In some instances, phenotypes induced by such novel GEMs also may yield clues regarding potential target organs and toxic effects of potential therapeutic molecules. The battery of tests used in phenotypic analysis of GEMs varies between companies, but the goal is to define one or more easily measured endpoints that can be used to monitor the disease course--especially during in vivo treatment with novel drug candidates. In many DDD projects, overt phenotypes are subtle or absent even in GEMs in which high-level expression or total ablation of an engineered gene can be confirmed. This outcome presents a major quandary for biotechnology and pharmaceutical firms: given the significant expense and labor required to generate GEMs, what should be done with "negative" constructs? The 14th century philosophical principle known as Occam's razor-that the simplest explanation for a phenomenon is likely the truth-provides a reasonable basis for pruning potential therapeutic molecules and targets. In the context of DDD, Occam's razor may be construed to mean that correctly engineered GEMs lacking obvious functional or structural phenotypes have none because the affected gene is not uniquely essential to normal homeostasis or disease progression. Thus, a "negative" GEM construct suggests that the gene under investigation encodes a ligand or target molecule without significant therapeutic potential. This interpretation indicates that, at least in a market-driven industrial setting, such "negative" projects should be pruned aggressively so that resources may be redirected to more promising DDD ventures.

Release and degradation of angiotensin I and angiotensin II from angiotensinogen by neutrophil serine proteinases

Cathepsin G, elastase, and proteinase 3 are serine proteinases released by activated neutrophils. Cathepsin G can cleave angiotensinogen to release angiotensin II, but this activity has not been previously reported for elastase or proteinase 3. In this study we show that elastase and proteinase 3 can release angiotensin I from angiotensinogen and release angiotensin II from angiotensin I and angiotensinogen. The relative order of potency in releasing angiotensin II by the three proteinases at equivalent concentrations is cathepsin G > elastase > proteinase 3. When all three proteinases are used together, the release of angiotensin II is greater than the sum of the release when each proteinase is used individually. Cathepsin G and elastase can also degrade angiotensin II, reactions which might be important in regulating the activity of angiotensin II. The release and degradation of angiotensin II by the neutrophil proteinases are reactions which could play a role in the local inflammatory response and wound healing.

Endothelium-dependent relaxation induced by cathepsin G in porcine pulmonary arteries

Serine proteinases elicit profound cellular effects in various tissues mediated by activation of proteinase-activated receptors (PAR). In the present study, we investigated the vascular effects of cathepsin G, a serine proteinase that is present in the azurophil granules of leukocytes and is known to activate several cells that express PARs. In prostaglandin F2alpha (3 microM)-precontracted rings from porcine pulmonary arteries with intact endothelium, cathepsin G caused concentration-dependent relaxant responses (pEC(50)=9.64+/-0.12). The endothelium-dependent relaxant effect of cathepsin G could also be demonstrated in porcine coronary arteries (pEC(50)=9.23+/-0.07). In pulmonary arteries the cathepsin G-induced relaxation was inhibited after blockade of nitric oxide synthesis by L-NAME (200 microM) and was absent in endothelium-denuded vessels. Bradykinin- and cathepsin G-induced relaxant effects were associated with a 5.7 fold and 2.4 fold increase in the concentration of cyclic GMP, respectively. Compared with thrombin and trypsin, which also produced an endothelium-dependent relaxation in pulmonary arteries, cathepsin G was 2.5 and four times more potent, respectively. Cathepsin G caused only small homologous desensitization. In cathepsin G-challenged vessels, thrombin was still able to elicit a relaxant effect. The effects of cathepsin G were blocked by soybean trypsin inhibitor (IC(50)=0.043 microg ml(-1)), suggesting that proteolytic activity is essential for induction of relaxation. Recombinant acetyl-eglin C proved to be a potent inhibitor (IC(50)=0.14 microg ml(-1)) of the cathepsin G effect, whereas neither indomethacin (3 microM) nor the thrombin inhibitor hirudin (5 ATU ml(-1)) elicited any inhibitory activity. Due to their polyanionic structure defibrotide (IC(50)=0.11 microg ml(-1)), heparin (IC(50)=0.48 microg ml(-1)) and suramin (IC(50)=1.85 microg ml(-1)) diminished significantly the relaxation in response to the basic protein cathepsin G. In conclusion, like thrombin and trypsin, cathepsin G is able to induce endothelium-dependent vascular relaxation. It can be released from activated leukocytes at sites of vascular injury and inflammation and, therefore, sufficiently high concentrations might be reached locally in the vascular space to induce vasodilatation.

Interleukin-4 is essential for the control of microfilariae in murine infection with the filaria Litomosoides sigmodontis

Litomosoides sigmodontis is the only filaria which develops from infective larvae into microfilaria-producing adults in immunocompetent laboratory mice. In this study we report that interleukin-4 knockout (IL-4 KO) mice have an up to 100-fold-higher and a significantly prolonged microfilaremia compared to wild-type BALB/c mice, as well as 20 times more microfilariae in the thoracic cavity, the site of infection. While worm development and adult worm persistence were equivalent in IL-4 KO and wild-type mice, the fertility and length of adult female worms in IL-4 KO mice was clearly enhanced. The high susceptibility to microfilariae in IL-4 KO mice required the presence of adult worms in a full infection cycle since microfilariae loads did not differ much between IL-4 KO and wild-type mice when purified microfilariae were injected into mice. In addition, we found that eosinophilia was diminished and immunoglobulin E (IgE) was absent in IL-4 KO mice. IgE, however, does not seem to be the essential factor for microfilarial containment since microfilaremia was not elevated in B-cell KO mice. In conclusion, IL-4 is shown for the first time to be essential for the control of microfilarial loads but not of adult worm loads in a fully permissive murine filarial infection. IL-4 dependent effector pathways seem to operate on adult worms rather than directly on microfilariae.

Lack of interferon-γ confers impaired neutrophil granulocyte function and imparts prolonged survival of adult filarial worms in murine filariasis

We investigated the role of IFN-gamma in host defense during murine filariasis. Using the fully permissive infection of BALB/c mice with the rodent filaria Litomosoides sigmodontis, we show that interferon (IFN)-gamma is essential for encapsulation of adult filarial worms in inflammatory nodules and for normal worm clearance. IFN-gamma knockout (KO) mice had only one third of the nodules of wild-type mice but displayed a more than twofold increase in worm burden and increased microfilaremia. Neutrophil granulocytes, but not macrophages or eosinophils, appear to directly control worm load and nodule formation. Neutrophils, which we showed earlier to be essential for the encapsulation process in the thoracic cavity, where the worms reside, were diminished at this location in IFN-gamma KO compared to wild-type mice; they also displayed strongly reduced chemotactic and phagocytic activity compared to neutrophils of controls. This argues for a distinct defect in neutrophil activation accounting for the low formation of inflammatory nodules. Tumor necrosis factor-alpha, a major neutrophil-activating cytokine expressed by macrophages in the thoracic cavity around the worms, was highly induced in wild-type but absent in KO mice. Diminished activation of neutrophils seems to be a general hallmark of IFN-gamma KO mice, since neutrophils from uninfected KO mice also showed a reduction in chemotactic and phagocytic activity when induced by casein. In conclusion, these data are the first to define an IFN-gamma-dependent immune effector mechanism in murine filarial infection, i.e. neutrophil-mediated control of the adult worm load.

Inhibition of neutrophil elastase prevents cathelicidin activation and impairs clearance of bacteria from wounds

The host defense roles of neutrophil elastase in a porcine skin wound chamber model were explored. Analysis of wound fluid by acid-urea polyacrylamide gel electrophoresis, Western blot, and bacterial overlay confirmed that the neutrophil-derived protegrins constituted the major stable antimicrobial polypeptide in the wound fluid. The application to the wound of 0.10 and 0.25 mM N-methoxysuccinyl-alanine-alanine-proline-valine (AAPV) chloromethyl ketone, a specific neutrophil elastase inhibitor (NEI), blocked the proteolytic activation of protegrins and diminished the associated antimicrobial activity as detected by radial diffusion assay against Staphylococcus epidermidis, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Candida albicans or by bacterial gel overlay against S epidermidis and E coli. The application of the related cathepsin G inhibitor (CGI), benzyloxycarbonyl-glycine-leucine-phenylalanine (ZGLF) chloromethyl ketone, had no effect. In wound chambers that received 10(6) colony-forming unit (CFU)/mL of S epidermidis, the presence of NEI significantly decreased the 24-hour clearance of bacteria from the wound compared to wounds treated with CGI or solvent only. Neither inhibitor, at 0.10 or 0.25 mM concentration, affected leukocyte accumulation or degranulation in the wound chambers. The in vitro microbicidal decrement due to NEI was restored by an amount of the specific protegrin (PG-1), which was equivalent to the measured difference of protegrin between control and inhibited chambers. Administration of 1 microg/mL exogenous PG-1 4 hours after chamber preparation was sufficient to normalize in vivo antimicrobial activity. Although pharmacologic NEIs are promising candidates as anti-inflammatory drugs, they may impair host defense in part by inhibiting the activation of cathelicidins by neutrophil elastase.

Independent influence of strain difference and mi transcription factor on the expression of mouse mast cell chymases

Expression of mouse mast cell protease (mMCP) genes was examined with particular attention to the transactivation effect of mi transcription factor (MITF) and the expression differences between C57BL/6 (B6) and WB strains. We had reported the enhancing effect of MITF on the expression of mMCP-4, -5, and -6 genes in cultured mast cells (CMCs) of B6 strain, and in the present study we demonstrated the enhancing effect on the expression of mMCP-2 and -9 genes as well. The enhancing effect of MITF on the expression of mMCP-2, -4, -5, -6, and -9 genes was also detected in CMCs of the WB strain. The regulation of mMCP-2, -4, and -9 genes was localized to a specific promoter element (CANNTG) which was recognized and bound by MITF and which was conserved between the B6 and WB strains. On the other hand, the expression of mMCP-2, -4, and -9 genes was smaller in CMCs of the B6 strain when compared to their expression in CMCs of the WB strain. Although mMCP-5 is a chymase as mMCP-2, -4, and -9, and genes encoding all of the chymases are located on chromosome 14, the mMCP-5 gene was regulated in a manner distinct from mMCP-2, -4, and -9 genes.

Degradation of outer membrane protein A in Escherichia coli killing by neutrophil elastase

In determining the mechanism of neutrophil elastase (NE)-mediated killing of Escherichia coli, we found that NE degraded outer membrane protein A (OmpA), localized on the surface of Gram-negative bacteria. NE killed wild-type, but not OmpA-deficient, E. coli. Also, whereas NE-deficient mice had impaired survival in response to E. coli sepsis, as compared to wild-type mice, the presence or absence of NE had no influence on survival in response to sepsis that had been induced with OmpA-deficient E. coli. These findings define a mechanism of nonoxidative bacterial killing by NE and point to OmpA as a bacterial target in host defense.