Natural disruption of the mouse mast cell protease 7 gene in the C57BL/6 mouse

Protective role of protease-activated receptor-2 in anaphylaxis model mice

Anaphylaxis is a severe life-threatening hypersensitivity reaction induced by mast cell degranulation. Among the various mediators of mast cells, little is known about the role of tryptase. Therefore, we aimed to elucidate the role of protease-activating receptor-2 (PAR-2), a receptor activated by tryptase, in murine anaphylactic models using PAR-2-deficient mice and newly generated tryptase-deficient mice. Anaphylaxis was induced by IgE-dependent and IgE-independent mast cell degranulation in mice. PAR-2 deficiency exacerbated the decrease in body temperature and hypotension during anaphylaxis; however, the number of skin mast cells, degree of mast cell degranulation, and systemic and local vascular hyperpermeability were comparable in PAR-2 knockout and wild-type mice. Nitric oxide, which is produced by endothelial nitric oxide synthase (eNOS), is an indispensable vasodilator in anaphylaxis. In the lungs of anaphylactic mice, PAR-2 deficiency promoted eNOS expression and phosphorylation, suggesting a protective effect of PAR-2 against anaphylaxis by downregulating eNOS activation and expression. Based on the hypothesis that the ligand for PAR-2 in anaphylaxis is mast cell tryptase, tryptase-deficient mice were generated using CRISPR-Cas9. In wild-type mice, the PAR-2 antagonist exacerbated the body temperature drop due to anaphylaxis; however, the effect of the PAR-2 antagonist was abolished in tryptase-deficient mice. These results suggest that tryptase is a possible ligand of PAR-2 in anaphylaxis and that the tryptase/PAR-2 pathway attenuates the anaphylactic response in mice.

Disruption of the mast cell carboxypeptidase A3 gene does not attenuate airway inflammation and hyperresponsiveness in two mouse models of asthma

Mast cells are effector cells known to contribute to allergic airway disease. When activated, mast cells release a broad spectrum of inflammatory mediators, including the mast cell-specific protease carboxypeptidase A3 (CPA3). The expression of CPA3 in the airway epithelium and lumen of asthma patients has been associated with a Th2-driven airway inflammation. However, the role of CPA3 in asthma is unclear and therefore, the aim of this study was to investigate the impact of CPA3 for the development and severity of allergic airway inflammation using knockout mice with a deletion in the Cpa3 gene. We used the ovalbumin (OVA)- and house-dust mite (HDM) induced murine asthma models, and monitored development of allergic airway inflammation. In the OVA model, mice were sensitized with OVA intraperitoneally at seven time points and challenged intranasally (i.n.) with OVA three times. HDM-treated mice were challenged i.n. twice weekly for three weeks. Both asthma protocols resulted in elevated airway hyperresponsiveness, increased number of eosinophils in bronchoalveolar lavage fluid, increased peribronchial mast cell degranulation, goblet cell hyperplasia, thickening of airway smooth muscle layer, increased expression of IL-33 and increased production of allergen-specific IgE in allergen-exposed mice as compared to mocktreated mice. However, increased number of peribronchial mast cells was only seen in the HDM asthma model. The asthma-like responses in Cpa3-/- mice were similar as in wild type mice, regardless of the asthma protocol used. Our results demonstrated that the absence of a functional Cpa3 gene had no effect on several symptoms of asthma in two different mouse models. This suggest that CPA3 is dispensable for development of allergic airway inflammation in acute models of asthma in mice.

Differential protease content of mast cells and the processing of IL-33 in Alternaria alternata induced allergic airway inflammation in mice

Background

Recent in vitro studies strongly implicated mast cell-derived proteases as regulators of IL-33 activity by enzymatic cleavage in its central domain. A better understanding of the role of mast cell proteases on IL-33 activity in vivo is needed. We aimed to compare the expression of mast cell proteases in C57BL/6 and BALB/c mice, their role in the cleavage of IL-33 cytokine, and their contribution to allergic airway inflammation.

Results

In vitro, full-length IL-33 protein was efficiently degraded by mast cell supernatants of BALB/c mice in contrast to the mast cell supernatants from C57BL/6 mice. RNAseq analysis indicated major differences in the gene expression profiles of bone marrow-derived mast cells from C57BL/6 and BALB/c mice. In Alternaria alternata (Alt) - treated C57BL/6 mice the full-length form of IL-33 was mainly present, while in BALB/c mice, the processed shorter form of IL-33 was more prominent. The observed cleavage pattern of IL-33 was associated with a nearly complete lack of mast cells and their proteases in the lungs of C57BL/6 mice. While most inflammatory cells were similarly increased in Alt-treated C57BL/6 and BALB/c mice, C57BL/6 mice had significantly more eosinophils in the bronchoalveolar lavage fluid and IL-5 protein levels in their lungs than BALB/c mice.

Conclusion

Our study demonstrates that lung mast cells differ in number and protease content between the two tested mouse strains and could affect the processing of IL-33 and inflammatory outcome of Alt -induced airway inflammation. We suggest that mast cells and their proteases play a regulatory role in IL-33-induced lung inflammation by limiting its proinflammatory effect via the IL-33/ST2 signaling pathway.

mMCP7, a Mouse Ortholog of δ Tryptase, Mediates Pelvic Tactile Allodynia in a Model of Chronic Pelvic Pain

Chronic prostatitis/Chronic pelvic pain syndrome (CP/CPPS) is a condition that affects a large number of men and has unknown etiology. We have previously demonstrated the presence of elevated levels of mast cell tryptase in expressed prostatic secretions (EPS) of CP/CPPS patients. In a murine model of CP/CPPS, we showed tryptase and its cognate receptor PAR2 as critical to the development of pelvic pain and lower urinary tract symptoms. Here, we extend these observations to demonstrate that an isoform of tryptase called delta (δ)-tryptase, is elevated in the EPS of patients with CP/CPPS and is correlated with pelvic pain symptoms. Using an Escherichia coli (CP1) -induced murine model of CP/CPPS, we demonstrated a differential response in C57BL/6J and NOD/ShiLtJ mice, with C57BL6/J mice being resistant to an increase in pelvic tactile allodynia, despite having equivalent levels of activated mast cells in the prostate. Activated tryptase+ve mast cells were observed to be in closer apposition to PGP9.5+ve nerve fibers in the prostate stroma of NOD/ShiLtJ in comparison to C57BL/6J mice. The mouse ortholog of δ-tryptase, mouse mast cell protease 7 (mMCP7) has been reported to be unexpressed in C57BL/6J mice. We confirmed the absence of mMCP7 in the prostates of C57BL/6J and its presence in NOD/ShiLtJ mice. To evaluate a role for mMCP7 in the differential allodynia responses, we performed direct intra-urethral instillations of mMCP7 and the beta (β)-tryptase isoform ortholog, mMCP6 in the CP1-infection model. mMCP7, but not mMCP6 was able to induce an acute pelvic allodynia response in C57BL/6J mice. In-vitro studies with mMCP7 on cultured mast cells as well as dissociated primary neurons demonstrated the ability to induce differential activation of pain and inflammation associated molecules compared to mMCP6. We conclude that mMCP7, and possibility its human ortholog δ-tryptase, may play an important role in mediating the development of pelvic tactile allodynia in the mouse model of pelvic pain and in patients with CP/CPPS.

Mouse Tryptase Gene Expression is Coordinately Regulated by GATA1 and GATA2 in Bone Marrow-Derived Mast Cells

Mast cell tryptases have crucial roles in allergic and inflammatory diseases. The mouse tryptase genes represent a cluster of loci on chromosome 16p3.3. While their functional studies have been extensively performed, transcriptional regulation of tryptase genes is poorly understood. In this study, we examined the molecular basis of the tryptase gene expression in bone marrow-derived mast cells (BMMCs) of C57BL/6 mice and in MEDMC-BRC6 mast cells. The expression of the Tpsb2 and Tpsg1 genes, which reside at the 3′-end of the tryptase locus, is significantly decreased by the reduction of the GATA transcription factors GATA1 or GATA2. Chromatin immunoprecipitation assays have shown that the GATA factors bind at multiple regions within the locus, including 1.0 and 72.8 kb upstream of the Tpsb2 gene, and that GATA1 and GATA2 facilitate each other’s DNA binding activity to these regions. Deletion of the −72.8 kb region by genome editing significantly reduced the Tpsb2 and Tpsg1 mRNA levels in MEDMC-BRC6 cells. Furthermore, binding of CTCF and the cohesin subunit Rad21 was found upstream of the −72.8 kb region and was significantly reduced in the absence of GATA1. These results suggest that mouse tryptase gene expression is coordinately regulated by GATA1 and GATA2 in BMMCs.

Regulation of the pleiotropic effects of tissue-resident mast cells

Mast cells (MCs), which are best known for their detrimental role in patients with allergic diseases, act in a diverse array of physiologic and pathologic functions made possible by the plurality of MC types. Their various developmental avenues and distinct sensitivity to (micro-) environmental conditions convey extensive heterogeneity, resulting in diverse functions. We briefly summarize this heterogeneity, elaborate on molecular determinants that allow MCs to communicate with their environment to fulfill their tasks, discuss the protease repertoire stored in secretory lysosomes, and consider different aspects of MC signaling. Furthermore, we describe key MC governance mechanisms (ie, the high-affinity receptor for IgE [FcεRI]), the stem cell factor receptor KIT, the IL-4 system, and both Ca²⁺- and phosphatase-dependent mechanisms. Finally, we focus on distinct physiologic functions, such as chemotaxis, phagocytosis, host defense, and the regulation of MC functions at the mucosal barriers of the lung, gastrointestinal tract, and skin. A deeper knowledge of the pleiotropic functions of MC mediators, as well as the molecular processes of MC regulation and communication, should enable us to promote beneficial MC traits in physiology and suppress detrimental MC functions in patients with disease.

Immune Characterization of Bone Marrow-Derived Models of Mucosal and Connective Tissue Mast Cells

Purpose

It is well appreciated that mast cells (MCs) demonstrate tissue-specific imprinting, with different biochemical and functional properties between connective tissue MCs (CTMCs) and mucosal MCs (MMCs). Although in vitro systems have been developed to model these different subsets, there has been limited investigation into the functional characteristics of the 2 major MC subsets. Here, we report the immunologic characterization of 2 MCs subsets developed in vitro from bone marrow progenitors modeling MMCs and CTMCs.

Methods

We grew bone marrow for 4 weeks in the presence of transforming growth factor (TGF)-β, interleukin (IL)-9, IL-3, and stem cell factor (SCF) to generate MMCs, and IL-4, IL-3, and SCF to generate CTMCs.

Results

CTMCs and MMCs differed in growth rate and protease content, but their immune characteristics were remarkably similar. Both subsets responded to immunoglobulin E (IgE)-mediated activation with signaling, degranulation, and inflammatory cytokine release, although differences between subsets were noted in IL-10. CTMCs and MMCs showed a similar toll-like receptor (TLR) expression profile, dominated by expression of TLR4, TLR6, or both subsets were responsive to lipopolysaccharide (LPS), but not poly(I:C). CTMCs and MMCs express receptors for IL-33 and thymic stromal lymphopoietin (TSLP), and respond to these cytokines alone or with modified activation in response to IgE cross-linking.

Conclusions

The results of this paper show the immunologic characterization of bone marrow-derived MMCs and CTMCs, providing useful protocols for in vitro modeling of MC subsets.

Mast cell hyperactivity underpins the development of oxygen-induced retinopathy

Mast cells are classically thought to play an important role in protection against helminth infections and in the induction of allergic diseases; however, recent studies indicate that these cells also contribute to neovascularization, which is critical for tissue remodeling, chronic inflammation, and carcinogenesis. Here, we demonstrate that mast cells are essential for sprouting angiogenesis in a murine model of oxygen-induced retinopathy (OIR). Although mouse strains lacking mast cells did not exhibit retinal neovascularization following hypoxia, these mice developed OIR following infusion of mast cells or after injection of mast cell tryptase (MCT). Relative hypoxia stimulated mast cell degranulation via transient receptor potential ankyrin 1. Subsequent surges in MCT stimulated retinal endothelial cells to produce monocyte chemotactic protein-1 (MCP1) and angiogenic factors, leading to sprouting angiogenesis. Mast cell stabilizers as well as specific tryptase and MCP1 inhibitors prevented the development of OIR in WT mice. Preterm infants with early retinopathy of prematurity had markedly higher plasma MCT levels than age-matched infants without disease, suggesting mast cells contribute to human disease. Together, these results suggest therapies that suppress mast cell activity should be further explored as a potential option for preventing eye diseases and subsequent blindness induced by neovascularization.

Role of interleukin-18 in the pathophysiology of allergic diseases

Interleukin (IL)-18 is an IL-1 family cytokine expressed by macrophages, dendritic cells, epithelial cells, and keratinocytes and is implicated in various aspects of both the innate and adaptive immune systems. IL-18 signals similar to IL-1β intracellularly to activate gene transcription. Since its discovery, IL-18 has been demonstrated to play a key role in pathogen defense from helminths and some bacteria. Recently however, evidence has accumulated that IL-18 expression is increased in many presentations of allergic disease. A pathologic role for IL-18 includes stimulating mast cell and basophil degranulation, recruiting granulocytes to sites of inflammation, increasing cytotoxic activity of natural killer (NK) and NK-T cells, inducing Immunoglobulin (Ig)E production and isotype switching, and affecting a broad range of T cells to promote a type II helper T cell (Th2) response. Evidence and importance of these effects are presented, including novel results from our lab implicating IL-18 in the direct expansion of mast cells, basophils, and other myeloid-lineage cells from bone-marrow precursors. The development of urticaria, asthma, dermatitis, rhinitis, and eosinophilic disorders all have demonstrated correlations to increased IL-18 levels either in the tissue or systemically. IL-18 represents a novel site of immune regulation in not only allergic conditions, but also autoimmune diseases and other instances of aberrant immune functioning. Diagrammatic summarized abstract for readers convinance is presented in Fig. 1.

Mast cell proteases as pharmacological targets

Mast cells are rich in proteases, which are the major proteins of intracellular granules and are released with histamine and heparin by activated cells. Most of these proteases are active in the granule as well as outside of the mast cell when secreted, and can cleave targets near degranulating mast cells and in adjoining tissue compartments. Some proteases released from mast cells reach the bloodstream and may have far-reaching actions. In terms of relative amounts, the major mast cell proteases include the tryptases, chymases, cathepsin G, carboxypeptidase A3, dipeptidylpeptidase I/cathepsin C, and cathepsins L and S. Some mast cells also produce granzyme B, plasminogen activators, and matrix metalloproteinases. Tryptases and chymases are almost entirely mast cell-specific, whereas other proteases, such as cathepsins G, C, and L are expressed by a variety of inflammatory cells. Carboxypeptidase A3 expression is a property shared by basophils and mast cells. Other proteases, such as mastins, are largely basophil-specific, although human basophils are protease-deficient compared with their murine counterparts. The major classes of mast cell proteases have been targeted for development of therapeutic inhibitors. Also, a human β-tryptase has been proposed as a potential drug itself, to inactivate of snake venins. Diseases linked to mast cell proteases include allergic diseases, such as asthma, eczema, and anaphylaxis, but also include non-allergic diseases such as inflammatory bowel disease, autoimmune arthritis, atherosclerosis, aortic aneurysms, hypertension, myocardial infarction, heart failure, pulmonary hypertension and scarring diseases of lungs and other organs. In some cases, studies performed in mouse models suggest protective or homeostatic roles for specific proteases (or groups of proteases) in infections by bacteria, worms and other parasites, and even in allergic inflammation. At the same time, a clearer picture has emerged of differences in the properties and patterns of expression of proteases expressed in human mast cell subsets, and in humans versus other mammals. These considerations are influencing prioritization of specific protease targets for therapeutic inhibition, as well as options of pre-clinical models, disease indications, and choice of topical versus systemic routes of inhibitor administration.

Potential effector and immunoregulatory functions of mast cells in mucosal immunity

Mast cells (MCs) are cells of hematopoietic origin that normally reside in mucosal tissues, often near epithelial cells, glands, smooth muscle cells, and nerves. Best known for their contributions to pathology during IgE-associated disorders such as food allergy, asthma, and anaphylaxis, MCs are also thought to mediate IgE-associated effector functions during certain parasite infections. However, various MC populations also can be activated to express functional programs--such as secreting preformed and/or newly synthesized biologically active products--in response to encounters with products derived from diverse pathogens, other host cells (including leukocytes and structural cells), damaged tissue, or the activation of the complement or coagulation systems, as well as by signals derived from the external environment (including animal toxins, plant products, and physical agents). In this review, we will discuss evidence suggesting that MCs can perform diverse effector and immunoregulatory roles that contribute to homeostasis or pathology in mucosal tissues.

Approaches for analyzing the roles of mast cells and their proteases in vivo

The roles of mast cells in health and disease remain incompletely understood. While the evidence that mast cells are critical effector cells in IgE-dependent anaphylaxis and other acute IgE-mediated allergic reactions seems unassailable, studies employing various mice deficient in mast cells or mast cell-associated proteases have yielded divergent conclusions about the roles of mast cells or their proteases in certain other immunological responses. Such "controversial" results call into question the relative utility of various older versus newer approaches to ascertain the roles of mast cells and mast cell proteases in vivo. This review discusses how both older and more recent mouse models have been used to investigate the functions of mast cells and their proteases in health and disease. We particularly focus on settings in which divergent conclusions about the importance of mast cells and their proteases have been supported by studies that employed different models of mast cell or mast cell protease deficiency. We think that two major conclusions can be drawn from such findings: (1) no matter which models of mast cell or mast cell protease deficiency one employs, the conclusions drawn from the experiments always should take into account the potential limitations of the models (particularly abnormalities affecting cell types other than mast cells) and (2) even when analyzing a biological response using a single model of mast cell or mast cell protease deficiency, details of experimental design are critical in efforts to define those conditions under which important contributions of mast cells or their proteases can be identified.

Importance of mast cell Prss31/transmembrane tryptase/tryptase-γ in lung function and experimental chronic obstructive pulmonary disease and colitis

Protease serine member S31 (Prss31)/transmembrane tryptase/tryptase-γ is a mast cell (MC)-restricted protease of unknown function that is retained on the outer leaflet of the plasma membrane when MCs are activated. We determined the nucleotide sequences of the Prss31 gene in different mouse strains and then used a Cre/loxP homologous recombination approach to create a novel Prss31(-/-) C57BL/6 mouse line. The resulting animals exhibited no obvious developmental abnormality, contained normal numbers of granulated MCs in their tissues, and did not compensate for their loss of the membrane tryptase by increasing their expression of other granule proteases. When Prss31-null MCs were activated with a calcium ionophore or by their high affinity IgE receptors, they degranulated in a pattern similar to that of WT MCs. Prss31-null mice had increased baseline airway reactivity to methacholine but markedly reduced experimental chronic obstructive pulmonary disease and colitis, thereby indicating both beneficial and adverse functional roles for the tryptase. In a cigarette smoke-induced model of chronic obstructive pulmonary disease, WT mice had more pulmonary macrophages, higher histopathology scores, and more fibrosis in their small airways than similarly treated Prss31-null mice. In a dextran sodium sulfate-induced acute colitis model, WT mice lost more weight, had higher histopathology scores, and contained more Cxcl-2 and IL-6 mRNA in their colons than similarly treated Prss31-null mice. The accumulated data raise the possibility that inhibitors of this membrane tryptase may provide additional therapeutic benefit in the treatment of humans with these MC-dependent inflammatory diseases.

Mast cell-restricted tetramer-forming tryptases and their beneficial roles in hemostasis and blood coagulation

Tetramer-forming tryptase (hTryptase-β) was recently discovered to have a prominent role in preventing the internal accumulation of life-threatening fibrin deposits and fibrin-platelet clots. The anticoagulant activity of hTryptase-β is an explanation for the presence of hemorrhagic disorders in some patients with anaphylaxis or mastocytosis. The fragments of hFibrinogen formed by the proteolysis of this prominent protein by hTryptase-β could be used as biomarkers in the blood and/or urine for the identification and monitoring of patients with mast cell-dependent disorders. Recombinant hTryptase-β has potential to be used in clinical settings where it is desirable to inhibit blood coagulation.

Targeting mast cells in inflammatory diseases

Although mast cells have long been known to play a critical role in anaphylaxis and other allergic diseases, they also participate in some innate immune responses and may even have some protective functions. Data from the study of mast cell-deficient mice have facilitated our understanding of some of the molecular mechanisms driving mast cell functions during both innate and adaptive immune responses. This review presents an overview of the biology of mast cells and their potential involvement in various inflammatory diseases. We then discuss some of the current pharmacological approaches used to target mast cells and their products in several diseases associated with mast cell activation.

Relationship between numerous mast cells and early follicular development in neonatal MRL/MpJ mouse ovaries

In the neonatal mouse ovary, clusters of oocytes called nests break into smaller cysts and subsequently form individual follicles. During this period, we found numerous mast cells in the ovary of MRL/MpJ mice and investigated their appearance and morphology with follicular development. The ovarian mast cells, which were already present at postnatal day 0, tended to localize adjacent to the surface epithelium. Among 11 different mouse strains, MRL/MpJ mice possessed the greatest number of ovarian mast cells. Ovarian mast cells were also found in DBA/1, BALB/c, NZW, and DBA/2 mice but rarely in C57BL/6, NZB, AKR, C3H/He, CBA, and ICR mice. The ovarian mast cells expressed connective tissue mast cell markers, although mast cells around the surface epithelium also expressed a mucosal mast cell marker in MRL/MpJ mice. Some ovarian mast cells migrated into the oocyte nests and directly contacted the compressed and degenerated oocytes. In MRL/MpJ mice, the number of oocytes in the nest was significantly lower than in the other strains, and the number of oocytes showed a positive correlation with the number of ovarian mast cells. The gene expression of a mast cell marker also correlated with the expression of an oocyte nest marker, suggesting a link between the appearance of ovarian ? 4mast cells and early follicular development. Furthermore, the expression of follicle developmental markers was significantly higher in MRL/MpJ mice than in C57BL/6 mice. These results indicate that the appearance of ovarian mast cells is a unique phenotype of neonatal MRL/MpJ mice, and that ovarian mast cells participate in early follicular development, especially nest breakdown.

A new short-term mouse model of chronic obstructive pulmonary disease identifies a role for mast cell tryptase in pathogenesis

BACKGROUND

Cigarette smoke-induced chronic obstructive pulmonary disease (COPD) is a life-threatening inflammatory disorder of the lung. The development of effective therapies for COPD has been hampered by the lack of an animal model that mimics the human disease in a short timeframe.

OBJECTIVES

We sought to create an early-onset mouse model of cigarette smoke-induced COPD that develops the hallmark features of the human condition in a short time-frame. We also sought to use this model to better understand pathogenesis and the roles of macrophages and mast cells (MCs) in patients with COPD.

METHODS

Tightly controlled amounts of cigarette smoke were delivered to the airways of mice, and the development of the pathologic features of COPD was assessed. The roles of macrophages and MC tryptase in pathogenesis were evaluated by using depletion and in vitro studies and MC protease 6-deficient mice.

RESULTS

After just 8 weeks of smoke exposure, wild-type mice had chronic inflammation, mucus hypersecretion, airway remodeling, emphysema, and reduced lung function. These characteristic features of COPD were glucocorticoid resistant and did not spontaneously resolve. Systemic effects on skeletal muscle and the heart and increased susceptibility to respiratory tract infections also were observed. Macrophages and tryptase-expressing MCs were required for the development of COPD. Recombinant MC tryptase induced proinflammatory responses from cultured macrophages.

CONCLUSION

A short-term mouse model of cigarette smoke-induced COPD was developed in which the characteristic features of the disease were induced more rapidly than in existing models. The model can be used to better understand COPD pathogenesis, and we show a requirement for macrophages and tryptase-expressing MCs.

Heparan sulfate 6-O-sulfotransferase isoform-dependent regulatory effects of heparin on the activities of various proteases in mast cells and the biosynthesis of 6-O-sulfated heparin

Heparan sulfate 6-O-sulfotransferase (HS6ST) is an enzyme involved in heparan sulfate (HS) biosynthesis that transfers a sulfate residue to position 6 of the GlcNAc/GlcNSO(3) residues of HS, and it consists of three isoforms. Heparin, the highly sulfated form of HS, resides in connective tissue mast cells and is involved in the storage of mast cell proteases (MCPs). However, it is not well understood which isoform(s) of HS6ST participates in 6-O-sulfation of heparin and how the 6-O-sulfate residues in heparin affect MCPs. To investigate these issues, we prepared fetal skin-derived mast cells (FSMCs) from wild type (WT) and HS6ST-deficient mice (HS6ST-1(-/-), HS6ST-2(-/-), and HS6ST-1(-/-)/HS6ST-2(-/-)) and determined the structure of heparin, the protease activity, and the mRNA expression of each MCP in cultured FSMCs. The activities of tryptase and carboxypeptidase-A were decreased in HS6ST-2(-/-)-FSMCs in which 6-O-sulfation of heparin was decreased at 50% of WT-FSMCs and almost lost in HS6ST-1(-/-)/HS6ST-2(-/-)-FSMCs, which lacked the 6-O-sulfation in heparin nearly completely. In contrast, chymase activity was retained even in HS6ST-1(-/-)/HS6ST-2(-/-)-FSMCs. Each MCP mRNA was not decreased in any of the mutant FSMCs. Western blot analysis showed that tryptase (mMCP-6) was almost absent from HS6ST-1(-/-)/HS6ST-2(-/-)-FSMCs indicating degradation/secretion of the enzyme protein. These observations suggest that both HS6ST-1 and HS6ST-2 are involved in 6-O-sulfation of heparin and that the proper packaging and storage of tryptase, carboxypeptidase-A, and chymase may be regulated differently by the 6-O-sulfate residues in heparin. It is thus likely that 6-O-sulfation of heparin plays important roles in regulating MCP functions.

New models for analyzing mast cell functions in vivo

In addition to their well-accepted role as critical effector cells in anaphylaxis and other acute IgE-mediated allergic reactions, mast cells (MCs) have been implicated in a wide variety of processes that contribute to disease or help to maintain health. Although some of these roles were first suggested by analyses of MC products or functions in vitro, it is critical to determine whether, and under which circumstances, such potential roles actually can be performed by MCs in vivo. This review discusses recent advances in the development and analysis of mouse models to investigate the roles of MCs and MC-associated products during biological responses in vivo, and comments on some of the similarities and differences in the results obtained with these newer versus older models of MC deficiency.

Mast cell restricted mouse and human tryptase·heparin complexes hinder thrombin-induced coagulation of plasma and the generation of fibrin by proteolytically destroying fibrinogen

The mouse and human TPSB2 and TPSAB1 genes encode tetramer-forming tryptases stored in the secretory granules of mast cells (MCs) ionically bound to heparin-containing serglycin proteoglycans. In mice these genes encode mouse MC protease-6 (mMCP-6) and mMCP-7. The corresponding human genes encode a family of serine proteases that collectively are called hTryptase-β. We previously showed that the α chain of fibrinogen is a preferred substrate of mMCP-7. We now show that this plasma protein also is highly susceptible to degradation by hTryptase-β· and mMCP-6·heparin complexes and that Lys(575) is a preferred cleavage site in the protein α chain. Because cutaneous mouse MCs store substantial amounts of mMCP-6·heparin complexes in their secretory granules, the passive cutaneous anaphylaxis reaction was induced in the skin of mMCP-6(+)/mMCP-7(-) and mMCP-6(-)/mMCP-7(-) C57BL/6 mice. In support of the in vitro data, fibrin deposits were markedly increased in the skin of the double-deficient mice 6 h after IgE-sensitized animals were given the relevant antigen. Fibrinogen is a major constituent of the edema fluid that accumulates in tissues when MCs degranulate. Our discovery that mouse and human tetramer-forming tryptases destroy fibrinogen before this circulating protein can be converted to fibrin changes the paradigm of how MCs hinder fibrin deposition and blood coagulation internally. Because of the adverse consequences of fibrin deposits in tissues, our data explain why mice and humans lack a circulating protease inhibitor that rapidly inactivates MC tryptases and why mammals have two genes that encode tetramer-forming serine proteases that preferentially degrade fibrinogen.

Essential role for mast cell tryptase in acute experimental colitis

Patients with inflammatory bowel disease (IBD) have increased numbers of human tryptase-β (hTryptase-β)-positive mast cells (MCs) in the gastrointestinal tract. The amino acid sequence of mouse mast cell protease (mMCP)-6 is most similar to that of hTryptase-β. We therefore hypothesized that this mMCP, or the related tryptase mMCP-7, might have a prominent proinflammatory role in experimental colitis. The dextran sodium sulfate (DSS) and trinitrobenzene sulfonic acid (TNBS) colitis models were used to evaluate the differences between C57BL/6 (B6) mouse lines that differ in their expression of mMCP-6 and mMCP-7 with regard to weight loss, colon histopathology, and endoscopy scores. Microarray analyses were performed, and confirmatory real-time PCR, ELISA, and/or immunohistochemical analyses were carried out on a number of differentially expressed cytokines, chemokines, and matrix metalloproteinases (MMPs). The mMCP-6-null mice that had been exposed to DSS had significantly less weight loss as well as significantly lower pathology and endoscopy scores than similarly treated mMCP-6-expressing mice. This difference in colitis severity was confirmed endoscopically in the TNBS-treated mice. Evaluation of the distal colon segments revealed that numerous proinflammatory cytokines, chemokines that preferentially attract neutrophils, and MMPs that participate in the remodeling of the ECM were all markedly increased in the colons of DSS-treated WT mice relative to untreated WT mice and DSS-treated mMCP-6-null mice. Collectively, our data show that mMCP-6 (but not mMCP-7) is an essential MC-restricted mediator in chemically induced colitis and that this tryptase acts upstream of many of the factors implicated in IBD.

The inflammatory response after an epidermal burn depends on the activities of mouse mast cell proteases 4 and 5

A second-degree epidermal scald burn in mice elicits an inflammatory response mediated by natural IgM directed to nonmuscle myosin with complement activation that results in ulceration and scarring. We find that such burn injury is associated with early mast cell (MC) degranulation and is absent in WBB6F1-Kit(W)/Kit(Wv) mice, which lack MCs in a context of other defects due to a mutation of the Kit receptor. To address further an MC role, we used transgenic strains with normal lineage development and a deficiency in a specific secretory granule component. Mouse strains lacking the MC-restricted chymase, mouse MC protease (mMCP)-4, or elastase, mMCP-5, show decreased injury after a second-degree scald burn, whereas mice lacking the MC-restricted tryptases, mMCP-6 and mMCP-7, or MC-specific carboxypeptidase A3 activity are not protected. Histologic sections showed some disruption of the epidermis at the scald site in the protected strains suggesting the possibility of topical reconstitution of full injury. Topical application of recombinant mMCP-5 or human neutrophil elastase to the scalded area increases epidermal injury with subsequent ulceration and scarring, both clinically and morphologically, in mMCP-5-deficient mice. Restoration of injury requires that topical administration of recombinant mMCP-5 occurs within the first hour postburn. Importantly, topical application of human MC chymase restores burn injury to scalded mMCP-4-deficient mice but not to mMCP-5-deficient mice revealing nonredundant actions for these two MC proteases in a model of innate inflammatory injury with remodeling.

Protease inhibitors in respiratory disease: focus on asthma and chronic obstructive pulmonary disease

Respiratory diseases, such as asthma and chronic obstructive pulmonary disease (COPD), are a major health burden on society and current treatment modalities for these diseases have not significantly changed over the past 40 years. The only major pharmacological advancement for the treatment of these diseases has been to increase the duration of action of bronchodilators (asthma: salmeterol; COPD: tiotropium bromide) and glucocorticosteroids (asthma: fluticasone propionate) and, increasingly, to formulate these agents in the same delivery device. Despite our increasing understanding of the cell and molecular biology of these diseases, the development of novel treatments remains beyond the reach of the scientific community. Proteases are a family of proteins with diverse biological activity, which are found in abundance within the airways of asthma and COPD, and have been implicated in the pathogenesis of these diseases. The targeting of proteases, including mast cell tryptase, neutrophil elastase and matrix metalloprotease with low-molecular-weight inhibitors, has highlighted the potential role of these enzymes in mediating certain aspects of the disease process in preclinical studies. Several challenges remain regarding the development of protease inhibitors, including the synthesis of highly potent and specific inhibitors, and target validation in man.

Synovial fibroblasts promote the expression and granule accumulation of tryptase via interleukin-33 and its receptor ST-2 (IL1RL1)

A characteristic feature of tissue resident human mast cells (MCs) is their hTryptase-beta-rich cytoplasmic granules. Mouse MC protease-6 (mMCP-6) is the ortholog of hTryptase-beta, and we have shown that this tetramer-forming tryptase has beneficial roles in innate immunity but adverse roles in inflammatory disorders like experimental arthritis. Because the key tissue factors that control tryptase expression in MCs have not been identified, we investigated the mechanisms by which fibroblasts mediate the expression and granule accumulation of mMCP-6. Immature mouse bone marrow-derived MCs (mBMMCs) co-cultured with fibroblast-like synoviocytes (FLS) or mouse 3T3 fibroblasts markedly increased their levels of mMCP-6. This effect was caused by an undefined soluble factor whose levels could be increased by exposing FLS to tumor necrosis factor-alpha or interleukin (IL)-1beta. Gene expression profiling of mBMMCs and FLS for receptor.ligand pairs of potential relevance raised the possibility that IL-33 was a sought after fibroblast-derived factor that promotes tryptase expression and granule maturation via its receptor IL1RL1/ST2. MCs lacking IL1RL1 exhibited defective fibroblast-driven tryptase accumulation, whereas recombinant IL-33 induced mMCP-6 mRNA and protein accumulation in wild-type mBMMCs. In agreement with these data, synovial MCs from IL1RL1-null mice exhibited a marked reduction in mMCP-6 expression. IL-33 is the first factor shown to modulate tryptase expression in MCs at the mRNA and protein levels. We therefore have identified a novel pathway by which mesenchymal cells exposed to inflammatory cytokines modulate the phenotype of local MCs to shape their immune responses.

Mast cell proteases: multifaceted regulators of inflammatory disease

Mast cells (MCs) are currently receiving increased attention among the scientific community, largely because of the recent identification of crucial functions for MCs in a variety of disorders. However, it is in many cases not clear exactly how MCs contribute in the respective settings. MCs express extraordinarily high levels of a number of proteases of chymase, tryptase, and carboxypeptidase A type, and these are stored in high amounts as active enzymes in the MC secretory granules. Hence, MC degranulation leads to the massive release of fully active MC proteases, which probably have a major impact on any condition in which MC degranulation occurs. Indeed, the recent generation and evaluation of mouse strains lacking individual MC proteases have indicated crucial contributions of these to a number of different disorders. MC proteases may thus account for many of the effects ascribed to MCs and are currently emerging as promising candidates for treatment of MC-driven disease. In this review, we discuss these findings.

Mast cells contribute to autoimmune inflammatory arthritis via their tryptase/heparin complexes

Although mast cells (MCs) often are abundant in the synovial tissues of patients with rheumatoid arthritis, the contribution of MCs to joint inflammation and cartilage loss remains poorly understood. MC-restricted tryptase/heparin complexes have proinflammatory activity, and significant amounts of human tryptase beta (hTryptase-beta) are present in rheumatoid arthritis synovial fluid. Mouse MC protease-6 (mMCP-6) is the ortholog of hTryptase-beta, and this serine protease is abundant in the synovium of arthritic mice. We now report that C57BL/6 (B6) mice lacking their tryptase/heparin complexes have attenuated arthritic responses, with mMCP-6 as the dominant tryptase responsible for augmenting neutrophil infiltration in the K/BxN mouse serum-transfer arthritis model. While inflammation in this experimental arthritis model was not dependent on protease-activated receptor-2, it was dependent on the chemokine receptor CXCR2. In support of the latter data, exposure of synovial fibroblasts to hTryptase-beta/heparin or mMCP-6/heparin complexes resulted in expression of the neutrophil chemotactic factors CXCL1/KC, CXCL5/LIX, and CXCL8/IL-8. Our proteomics, histochemistry, and immunohistochemistry data also revealed substantial loss of cartilage-derived aggrecan proteoglycans in the arthritic joints of wild-type B6 mice but not mMCP-6-null B6 mice. These observations demonstrate the functional contribution of MC-restricted tryptase/heparin complexes in the K/BxN mouse arthritis model and connect our mouse findings with rheumatoid arthritis pathophysiology.

Alternate mRNA splicing in multiple human tryptase genes is predicted to regulate tetramer formation

Tryptases are serine proteases that are thought to be uniquely and proteolytically active as tetramers. Crystallographic studies reveal that the active tetramer is a flat ring structure composed of four monomers, with their active sites arranged around a narrow central pore. This model explains why many of the preferred substrates of tryptase are short peptides; however, it does not explain how tryptase cleaves large protein substrates such as fibronectin, although a number of studies have reported in vitro mechanisms for generating active monomers that could digest larger substrates. Here we suggest that alternate mRNA splicing of human tryptase genes generates active tryptase monomers (or dimers). We have identified a conserved pattern of alternate splicing in four tryptase alleles (alphaII, betaI, betaIII, and deltaI), representing three distinct tryptase gene loci. When compared with their full-length counterparts, the splice variants use an alternate acceptor site within exon 4. This results in the deletion of 27 nucleotides within the central coding sequence and 9 amino acids from the translated protein product. Although modeling suggests that the deletion can be easily accommodated by the enzymes structurally, it is predicted to alter the specificity by enlarging the S1' or S2' binding pocket and results in the complete loss of the "47 loop," reported to be critical for the formation of tetramers. Although active monomers can be generated in vitro using a range of artificial conditions, we suggest that alternate splicing is the in vivo mechanism used to generate active tryptase that can cleave large protein substrates.

The mouse mast cell-restricted tetramer-forming tryptases mouse mast cell protease 6 and mouse mast cell protease 7 are critical mediators in inflammatory arthritis

OBJECTIVE

Increased numbers of mast cells (MCs) that express beta tryptases bound to heparin have been detected in the synovium of patients with rheumatoid arthritis (RA). The corresponding tryptases in mice are mouse MC protease 6 (mMCP-6) and mMCP-7. Although MCs have been implicated in RA and some animal models of arthritis, no direct evidence for a MC-restricted tryptase in the pathogenesis of inflammatory arthritis has been shown. We created transgenic mice that lack heparin and different combinations of mMCP-6 and mMCP-7, to evaluate the roles of MC-restricted tryptase-heparin complexes in an experimental model of arthritis.

METHODS

The methylated bovine serum albumin/interleukin-1beta (mBSA/IL-1beta) experimental protocol was used to induce inflammatory monarthritis in different mouse strains. Mice were killed at the time of peak disease on day 7, and histochemical methods were used to assess joint pathology.

RESULTS

Arthritis was induced in the knee joints of mBSA/IL-1beta-treated mMCP-6(+)/mMCP-7(-) and mMCP-6(-)/mMCP-7(+) C57BL/6 mice, and numerous activated MCs that had exocytosed the contents of their secretory granules were observed in the diseased mice. In contrast, arthritis was markedly reduced in heparin-deficient mice and in mMCP-6(-)/mMCP-7(-) C57BL/6 mice.

CONCLUSION

MC-derived tryptase-heparin complexes play important roles in mBSA/IL-1beta-induced arthritis. Because mMCP-6 and mMCP-7 can compensate for each other in this disease model, the elimination of both tryptases is necessary to reveal the prominent roles of these serine proteases in joint inflammation and destruction. Our data suggest that the inhibition of MC-restricted tryptases could have therapeutic potential in the treatment of RA.

L-arginine metabolism and its impact on host immunity against Leishmania infection

Leishmaniasis is a vector-borne disease found in many countries worldwide. The causative agent of the disease, Leishmania spp., lives as an obligate intracellular parasite within mammalian hosts. Since tissue macrophages are major target cells for parasite replication, the outcome of infection depends largely on the activation status of these cells. L-arginine is a crucial amino acid required for both nitric oxide (NO)-mediated parasite killing and polyamine-mediated parasite replication. This review highlights the significance of L-arginine as a factor determining the outcomes of Leishmania infection in vitro and its influences on host immune responses in vivo. Various therapeutic approaches targeting L-arginine metabolic pathways during infections with Leishmania are also discussed.

Mouse mast cell tryptase mMCP-6 is a critical link between adaptive and innate immunity in the chronic phase of Trichinella spiralis infection

Although the innate immune function of mast cells in the acute phase of parasitic and bacterial infections is well established, their participation in chronic immune responses to indolent infection remains incompletely understood. In parasitic infection with Trichinella spiralis, the immune response incorporates both lymphocyte and mast cell-dependent effector functions for pathogen eradication. Among the mechanistic insights still unresolved in the reaction to T. spiralis are the means by which mast cells respond to parasites and the mast cell effector functions that contribute to the immunologic response to this pathogen. We hypothesized that mast cell elaboration of tryptase may comprise an important effector component in this response. Indeed, we find that mice deficient in the tryptase mouse mast cell protease-6 (mMCP-6) display a significant difference in their response to T. spiralis larvae in chronically infected skeletal muscle tissue. Mechanistically, this is associated with a profound inability to recruit eosinophils to larvae in mMCP-6-deficient mice. Analysis of IgE-deficient mice demonstrates an identical defect in eosinophil recruitment. These findings establish that mast cell secretion of the tryptase mMCP-6, a function directed by the activity of the adaptive immune system, contributes to eosinophil recruitment to the site of larval infection, thereby comprising an integral link in the chronic immune response to parasitic infection.

Doing What I Like

I have spent my entire professional life at Harvard Medical School, beginning as a medical student. I have enjoyed each day of a diverse career in four medical subspecialties while following the same triad of preclinical areas of investigation—cysteinyl leukotrienes, mast cells, and complement—with occasional translational opportunities. I did not envision a career with a predominant preclinical component. Such a path simply evolved because I chose instinctively at multiple junctures to follow what proved to be propitious opportunities. My commentary notes some of the highlights for each area of interest and the mentors, collaborators, and trainees whose counsel has been immensely important at particular intervals or over an extended period.

Protease-proteoglycan complexes of mouse and human mast cells and importance of their beta-tryptase-heparin complexes in inflammation and innate immunity

Approximately 50% of the weight of a mature mast cell (MC) consists of varied neutral proteases stored in the cell's secretory granules ionically bound to serglycin proteoglycans that contain heparin and/or chondroitin sulfate E/diB chains. Mouse MCs express the exopeptidase carboxypeptidase A3 and at least 15 serine proteases [designated as mouse MC protease (mMCP) 1-11, transmembrane tryptase/tryptase gamma/protease serine member S (Prss) 31, cathepsin G, granzyme B, and neuropsin/Prss19]. mMCP-6, mMCP-7, mMCP-11/Prss34, and Prss31 are the four members of the chromosome 17A3.3 family of tryptases that are preferentially expressed in MCs. One of the challenges ahead is to understand why MCs express so many different protease-proteoglycan macromolecular complexes. MC-like cells that contain tryptase-heparin complexes in their secretory granules have been identified in the Ciona intestinalis and Styela plicata urochordates that appeared approximately 500 million years ago. Because sea squirts lack B cells and T cells, it is likely that MCs and their tryptase-proteoglycan granule mediators initially appeared in lower organisms as part of their innate immune system. The conservation of MCs throughout evolution suggests that some of these protease-proteoglycan complexes are essential to our survival. In support of this conclusion, no human has been identified that lacks MCs. Moreover, transgenic mice lacking the beta-tryptase mMCP-6 are unable to combat a Klebsiella pneumoniae infection effectively. Here we summarize the nature and function of some of the tryptase-serglycin proteoglycan complexes found in mouse and human MCs.

The Mast Cell-restricted Tryptase mMCP-6 Has a Critical Immunoprotective Role in Bacterial Infections

Although it has been shown that mast cell-deficient mice have diminished innate immune responses against bacteria, the most important immunoprotective factors secreted from activated mast cells have not been identified. Mouse mast cell protease 6 is a tetramer-forming tryptase. This serine protease is abundant in the secretory granules and is exocytosed upon bacterial challenge. Here we have described the generation of a mast cell protease-6-null mouse. Our discovery that mice lacking this neutral protease cannot efficiently clear Klebsiella pneumoniae from their peritoneal cavities reveals an essential role for this serine protease, and presumably its human ortholog, in innate immunity.

Mast cell-restricted tryptases: structure and function in inflammation and pathogen defense

Mast cells (MCs) are highly specialized immune cells present in mammals and in lower organisms that predate the development of adaptive immunity. The strong evolutionary pressure to retain MCs for >500 million years suggests critical roles for these cells in our survival. In support of this conclusion, no human has been identified to date that lacks MCs, despite the adverse roles of MCs in systemic anaphylaxis and varied inflammatory disorders. MCs express numerous lineage-restricted neutral proteases, and four members of the chromosome 17A3.3 family of tryptases are preferentially expressed in mouse MCs. The anatomical location of MCs at host-environment interfaces has raised the possibility that some of these enzymes are evolutionally conserved because they are needed for combating infectious organisms. Here we review recent insights into the structure and function of MC tryptases in inflammation and host defense against bacteria and other infectious organisms.

Serglycin proteoglycan is required for secretory granule integrity in mucosal mast cells

SG (serglycin) PGs (proteoglycans) are strongly implicated in the assembly of MC (mast cell) granules. However, this notion has mainly been on the basis of studies of MCs of the connective tissue subtype, whereas the role of SG PG in mucosal MCs has not been explored. In the present study, we have addressed the latter issue by using mice with an inactivated SG gene. Bone marrow cells were differentiated in vitro into the mucosal MC phenotype, expressing the markers mMCP (mouse MC protease) -1 and -2. Biosynthetic labelling experiments performed on these cells revealed an approximately 80% reduction of 35SO4(2-) incorporation into PGs recovered from SG-/- cells as compared with SG+/+ counterparts, indicating that SG is the dominating cell-associated PG of mucosal MCs. Moreover, the absence of SG led to defective metachromatic staining of mucosal MCs, both in vivo and in the in vitro-derived mucosal MCs. Ultrastructural analysis showed that granules were present in similar numbers in SG+/+ and SG-/- cells, but that their morphology was markedly affected by the absence of SG, e.g. with electron-dense core formation only seen in SG+/+ granules. Analysis of the MC-specific proteases showed that mMCP-1 and mMCP-7 were completely independent of SG for storage, whereas mMCP-2 showed a partial dependence. In contrast, mMCP-4 and -6, and carboxypeptidase A were strongly dependent on SG for storage. Together, our data indicate that SG PG is of crucial importance for assembly of mature mucosal MC granules, but that the specific dependence on SG for storage varies between individual granule constituents.

Biology of mast cell tryptase. An inflammatory mediator

In 1960, a trypsin-like activity was found in mast cells [Glenner GG & Cohen LA (1960) Nature 185, 846-847] and this activity is now commonly referred to as 'tryptase'. Over the years, much knowledge about mast cell tryptase has been gathered, and a recent (18 January 2006) PubMed search for the keywords 'tryptase + mast cell*' retrieved 1661 articles. However, still very little is known about its true biological function. For example, the true physiological substrate(s) for mast cell tryptase has not been identified, and the potential role of tryptase in mast cell-related disease is not understood. Mast cell tryptase has several unique features, with perhaps the most remarkable being its organization into a tetrameric state with all of the active sites oriented towards a narrow central pore and its consequent complete resistance towards endogenous macromolecular protease inhibitors. Much effort has been invested to elucidate these properties of tryptase. In this review we summarize the current knowledge of mast cell tryptase, including novel insights into its possible biological functions and mechanisms of regulation.

The metabolic coupling of arginine metabolism to nitric oxide generation by astrocytes

Arginine, the only known precursor of nitric oxide, enters the brain parenchyma from the blood through the endothelial cells or from the cerebral spinal fluid through the ependymal cells. Astrocytes, whose processes abut the endothelium and ependymum, take up arginine through cationic amino acid transporters and release arginine through this transport system to the synapses that astrocytes shield. Some of these synapses are excitatory, and liberate glutamate into the synaptic cleft. Glutamate induces arginine release from astrocytes, making it available to the neuron. Neurons can take up arginine to be used in nitric oxide-mediated processes, such as neurotransmission. Thus, neural and nonneural cells act in concert to affect neuron physiology in an elegantly integrated system. This review focuses on the components of the interaction between astrocytes and neurons in nitric oxide biology.

Platonin attenuates LPS-induced CAT-2 and CAT-2B induction in stimulated murine macrophages

BACKGROUND

Platonin, a cyanine photosensitizing dye, is a potent immunomodulator that suppresses acute inflammation. Platonin not only inhibits interleukin (IL)-1beta, IL-6, and tumor necrosis factor (TNF)-alpha production but also improves circulatory failure in septic rats. In addition, platonin reduces plasma nitric oxide (NO) formation during sepsis. However, the effects of platonin on inducible NO synthase (iNOS) and cationic amino-acid transporter (including CAT-2, CAT-2 A, and CAT-2B) expressions during sepsis remain uninvestigated.

METHODS

Five groups of confluent murine macrophages (RAW264.7 cells) were randomly allocated to receive a 1-h pretreatment of one of five doses of platonin (0.1 microM, 1 microM, 10 microM, 100 microM, or 1000 microM) followed by lipopolysaccharide (LPS; 100 ng ml(-1)). For negative, positive, and platonin control, three other groups of cell cultures were randomly allocated to receive phosphate-buffered saline, LPS, or platonin (1000 microM). The cultures were harvested after exposing them to LPS for 18 h or a comparable duration in those groups without LPS. NO production, L-arginine transport, and expression of the relevant enzymes were then evaluated.

RESULTS

Platonin significantly attenuated LPS-induced up-regulation of iNOS expression and NO production in stimulated murine macrophages in a dose-dependent manner. Platonin also significantly inhibited up-regulation of CAT-2 and CAT-2B expression as well as L-arginine transport in LPS-stimulated murine macrophages in a dose-dependent manner. In contrast, CAT-2 A expression in murine macrophages was not affected by LPS and/or platonin.

CONCLUSIONS

Platonin attenuates NO production and L-arginine transport in LPS-stimulated murine macrophages possibly through inhibiting iNOS, CAT-2, and CAT-2B expression.

Targeting cytosolic phospholipase A2 by arachidonyl trifluoromethyl ketone prevents chronic inflammation in mice

Cytosolic phospholipase A(2) (cPLA(2)) plays a pivotal role in inflammation by catalyzing the release of arachidonic acid, a substrate for lipoxygenase and cyclooxygenase enzymes, from membrane phospholipids. In the present study we examined the role of cPLA(2) in inflammatory responses through the use of a specific inhibitor of the enzyme, cPLA(2), arachidonyl trifluoromethyl ketone (AACOCF3). Interestingly, we observed that AACOCF3 is an inhibitor of chronic but not acute inflammatory responses. Specifically, AACOCF3 inhibited phorbol 12-myristate 13-acetate (PMA)-induced chronic ear edema in mice. Additionally, oral treatment of ovalbumin-sensitized/ovalbumin-challenged BALB/c mice with 20 mg/kg AACOCF3 prevented the development of airway hyper-responsiveness in a model of asthma. Furthermore, AACOCF3 decreased cellular recruitment in the airway lumen and airway inflammation after the ovalbumin challenge. Taken together, these results suggest that a potent and specific chemical inhibitor of cPLA(2) may be useful for the treatment of chronic inflammatory diseases including rheumatoid arthritis, inflammatory bowel disease, psoriasis, and asthma.

Mast cell protease 5 mediates ischemia-reperfusion injury of mouse skeletal muscle

Ischemia with subsequent reperfusion (IR) injury is a significant clinical problem that occurs after physical and surgical trauma, myocardial infarction, and organ transplantation. IR injury of mouse skeletal muscle depends on the presence of both natural IgM and an intact C pathway. Disruption of the skeletal muscle architecture and permeability also requires mast cell (MC) participation, as revealed by the fact that IR injury is markedly reduced in c-kit defective, MC-deficient mouse strains. In this study, we sought to identify the pathobiologic MC products expressed in IR injury using transgenic mouse strains with normal MC development, except for the lack of a particular MC-derived mediator. Histologic analysis of skeletal muscle from BALB/c and C57BL/6 mice revealed a strong positive correlation (R(2) = 0.85) between the extent of IR injury and the level of MC degranulation. Linkage between C activation and MC degranulation was demonstrated in mice lacking C4, in which only limited MC degranulation and muscle injury were apparent. No reduction in injury was observed in transgenic mice lacking leukotriene C(4) synthase, hemopoietic PGD(2) synthase, N-deacetylase/N-sulfotransferase-2 (enzyme involved in heparin biosynthesis), or mouse MC protease (mMCP) 1. In contrast, muscle injury was significantly attenuated in mMCP-5-null mice. The MCs that reside in skeletal muscle contain abundant amounts of mMCP-5 which is the serine protease that is most similar in sequence to human MC chymase. We now report a cytotoxic activity associated with a MC-specific protease and demonstrate that mMCP-5 is critical for irreversible IR injury of skeletal muscle.

NF-kappaB inhibitors stabilize the mRNA of high-affinity type-2 cationic amino acid transporter in LPS-stimulated rat liver

BACKGROUND

Induction of inducible nitric oxide synthase (iNOS) results in nitric oxide (NO) overproduction during endotoxemia. Cellular uptake of L-arginine, modulated by the isozymes of type-2 cationic amino acid transporters (CAT), including CAT-2, CAT-2A and CAT-2B, has been reported to be a crucial factor in the regulation of iNOS activity. We sought to elucidate the expression of CAT-2 isozymes and the role of nuclear factor-kappaB (NF-kappaB) in this expression in lipopolysaccharide (LPS)-treated rat liver.

METHODS

Adult male Sprague-Dawley rats were randomly given intravenous (i.v.) injections of normal saline (N/S), LPS, LPS preceded by an NF-kappaB inhibitor (PDTC, dexamethasone or salicylate) or an NF-kappaB inhibitor alone. After injection, rats were sacrificed at different times and enzyme expression and liver injury were examined. Hepatic and systemic NO production were also measured.

RESULTS

CAT-2, CAT-2A and CAT-2B were constitutively expressed in un-stimulated rat liver. LPS stimulation not only significantly increased iNOS mRNA and NO concentrations but also decreased the mRNA concentrations of CAT-2 and CAT-2B, but not CAT-2A, in a time-dependent manner. LPS-induced hepatic and systemic NO overproduction was associated with hepatocellular injury. Pre-treatment with NF-kappaB inhibitors significantly attenuated LPS-induced iNOS induction as well as CAT-2/CAT-2B mRNA destabilization, which was associated with significant inhibition of NO biosynthesis and less liver injury.

CONCLUSION

NF-kappaB inhibitors stabilize CAT-2 and CAT-2B mRNA in LPS-stimulated rat liver. The hepatic CAT-2/CAT-2B pathway may be a constitutive part of cytoprotective mechanisms against sepsis.

NF-kappaB involvement in the induction of high affinity CAT-2 in lipopolysaccharide-stimulated rat lungs

BACKGROUND

Endotoxemia stimulates nitric oxide (NO) biosynthesis through induction of inducible NO synthase (iNOS). Cellular uptake of L-arginine, the sole substrate for iNOS, is an important mechanism regulating NO biosynthesis by iNOS. The isozymes of type-2 cationic amino acid transporters, including CAT-2, CAT-2A, and CAT-2B, constitute the most important pathways responsible for trans-membrane L-arginine transportation. Therefore, regulation of CAT-2 isozymes expression may constitute one of the downstream regulatory pathways that control iNOS activity. We investigated the time course of enzyme induction and the role of nuclear factor-kappaB (NF-kappaB) in CAT-2 isozymes expression in lipopolysaccharide-(LPS) treated rat lungs.

METHODS

Adult male Sprague-Dawley rats were randomly given intravenous injections of normal saline (N/S), LPS, LPS plus NF-kappaB inhibitor pre-treatment (PDTC, dexamethasone, or salicylate), or an NF-kappaB inhibitor alone. The rats were sacrificed at different times after injection and enzyme expression and lung injury were examined. Pulmonary and systemic NO production were also measured.

RESULTS

LPS co-induced iNOS, CAT-2, and CAT-2B but not CAT-2A expression in the lungs. Furthermore, NF-kappaB actively participated in LPS-induction of iNOS, CAT-2, and CAT-2B. LPS induced pulmonary and systemic NO overproduction and resulted in lung injuries. Attenuation of LPS-induced iNOS, CAT-2, and CAT-2B induction significantly inhibited NO biosynthesis and lessened lung injury.

CONCLUSION

NF-kappaB actively participates in the induction of CAT-2 and CAT-2B in intact animals. Our data further support the idea that CAT-2 and CAT-2B are crucial in regulating iNOS activity.

Renal transcription of high-affinity type-2 cationic amino acid transporter is up-regulated in LPS-stimulated rodents

OBJECTIVE

Sepsis stimulates renal nitric oxide (NO) biosynthesis through up-regulation of inducible NO synthase (iNOS) expression. Type-2 cationic amino acid transporter (CAT-2) mediation of trans-membrane L-arginine (L-Arg) transportation has been identified as one of the crucial regulatory mechanisms involved in the formation of NO by iNOS. We had previously shown that CAT-2B, a high-affinity alternative-spliced transcript of the CAT-2, is involved in induced NO biosynthesis by iNOS (Nitric Oxide, 2002). In this present study, we sought to assess the effects of sepsis on the expression of CAT-2B in lipopolysaccharide (LPS)-stimulated rat kidney.

METHODS

Forty rats were randomized to either a normal saline (N/S)-treated group or a LPS-treated group. Renal NO production was determined using chemiluminescence. Semi-quantitative RT-PCR was used to determine the mRNA concentrations of iNOS and L-Arg transporters (CAT-1, CAT-2 and CAT-2B) in kidney.

RESULTS

Lipopolysaccharide-coinduced iNOS, CAT-2 and CAT-2B mRNA expression in kidney and caused renal NO overproduction. A significant linear regression relationship was defined between renal NO concentrations and iNOS, CAT-2 and CAT-2B, respectively. On the contrary, CAT-1 expression was not affected by LPS-stimulation.

CONCLUSIONS

We provide the first evidence to illustrate that sepsis/septic shock induces the transcription of high-affinity CAT-2B in renal tissues. Transcription of iNOS, CAT-2 and CAT-2B correlates well with renal NO biosynthesis. Regulation of L-Arg uptake by modulating the expression regulation of induced CAT-2 and CAT-2B might be a potential target for therapies against renal pathologic conditions related to NO overproduction.

Generation of a large number of connective tissue type mast cells by culture of murine fetal skin cells

We describe a novel culture system for generating large numbers of murine skin-associated mast cells and distinguish their characteristics from bone marrow-derived cultured mast cells. Culture of day 16 fetal skin single cell suspensions in the presence of interleukin-3 and stem cell factor allowed expansion and maturation of mast cells in the presence of stromal cells. The average yield of mast cells after 2 wk was 7.3 million cells per fetus at a purity of 96%. These fetal skin-derived cultured mast cells increased their histamine content in a time-dependent manner to 3.6 pg per cell after 2 wk and 6.7 pg per cell after 4 wk. Phenotypic analyses revealed much greater expression of CD49b and CD81 and lesser expression of CD77 and CD102 on fetal skin-derived cultured mast cells as compared with bone marrow-derived cultured mast cells. These findings suggest a close similarity between fetal skin-derived cultured mast cells and freshly isolated cutaneous mast cells. Connective tissue mast cell characteristics of fetal skin-derived cultured mast cells were evidenced by: (1) their greater histamine content than bone marrow-derived cultured mast cells; (2) the presence of heparin; and (3) their degranulation in response to compound 48/80 and substance P. Importantly, fetal skin-derived cultured mast cells secreted greater amounts of interleukin-13 but much less MIP-1beta and interleukin-6 than bone marrow-derived cultured mast cells in response to ionomycin. Thus fetal skin-derived cultured mast cells have many characteristics distinct from bone marrow-derived cultured mast cells and can be used as a model of cutaneous mast cells to discern their functions.

Suppressor of cytokine signaling 1 regulates an endogenous inhibitor of a mast cell protease

Suppressor of cytokine signaling 1 (SOCS1) is a negative regulator of c-Kit and interleukin-3 (IL-3) receptor signaling. We examined the role of SOCS1 in regulating IL-3-induced cell growth of primary bone marrow-derived mast cells (BMMCs) from SOCS1-/- mice. Instead of showing increased proliferation, SOCS1-deficient BMMCs responded poorly to IL-3 and stem cell factor. SOCS1-/- BMMCs showed increased apoptosis and defective cell cycle entry. We show that the growth retardation of SOCS1-/- BMMCs was due to a cell intrinsic defect. Protein tyrosine phosphorylation following IL-3 stimulation was markedly diminished in SOCS1-/- BMMCs. Intriguingly, JAK2 and STAT5 proteins were selectively diminished in SOCS1-/- BMMCs, which also showed lower molecular mass products of p85 and Vav suggesting proteolytic degradation. Incubation of the SOCS1-/- BMMC lysate with STAT5, p85, and Vav immunoprecipitated from SOCS1+/+ cells directly demonstrated the dysregulated proteolytic activity in SOCS1-/- BMMCs. The proteolytic activity in SOCS1-/- BMMCs was selectively inhibited by phenylmethylsulfonyl fluoride and soybean trypsin inhibitor, suggesting that the protease regulated by SOCS1 is a tryptase. The dysregulated tryptase in SOCS1-/- BMMCs is unlikely to be mMCP6 or mMCP7, because the enzyme activity was not inhibited by Polybrene but was inhibited by normal mouse plasma. SOCS1+/+ BMMC lysate inhibited the proteolytic activity present in SOCS1-/- BMMC lysate, indicating that SOCS1-/- BMMCs lack an endogenous protease inhibitor. These results show that SOCS1 is required for the expression and/or stability of an endogenous protease inhibitor, which protects mast cells from their own proteolytic enzymes.

Mast cells in airway hyporesponsive C3H/HeJ mice express a unique isoform of the signaling protein Ras guanine nucleotide releasing protein 4 that is unresponsive to diacylglycerol and phorbol esters

cDNAs were recently isolated from BALB/c mouse mast cells (MCs) that encode the new signaling protein mouse Ras guanine nucleotide releasing protein 4 (mRasGRP4). The present study evaluates the expression pattern and biological activity of mRasGRP4 in a variety of mouse strains. As assessed immunohistochemically and by RNA analysis, mRasGRP4 is not coordinately expressed with any of its family members. Normally, mRasGRP4 is an MC-restricted protein in tissues, and kinetic studies revealed that mRasGRP4 is expressed relatively early in developing MCs. The expression of mRasGRP4 in the fetus before granulated MCs become abundant supports the conclusion that RasGRP4 participates in MC-specific differentiation pathways. Functional studies conducted with recombinant material revealed that mRasGRP4 is a cation-dependent, diacylglycerol (DAG)-regulated, guanine nucleotide exchange factor. Immunoelectron microscopic studies revealed that mRasGRP4 resides in either the cytosol or inner leaflet of the plasma membrane of the MC, implying that DAG controls the intracellular movement of this signaling protein in c-kit-stimulated MCs. The mRasGRP4 gene resides on chromosome 7B1 within a site that is prominently linked to baseline airway reactivity in backcrossed C3H/HeJ and A/J mice. A truncated isoform of mRasGRP4 that lacks its DAG-regulatory domain was isolated from C3H/HeJ mouse MCs. Sequence analysis showed that this isoform is the result of defective splicing of the precursor transcript. MCs play a central role in allergic inflammation. The discovery of a novel isoform of mRasGRP4 in hyporesponsive mice suggests that airway reactivity is influenced by RasGRP4-dependent signaling events in pulmonary MCs.

Regulation of enzymes of the urea cycle and arginine metabolism

The urea cycle is comprised of five enzymes but also requires other enzymes and mitochondrial amino acid transporters to function fully. The complete urea cycle is expressed in liver and to a small degree also in enterocytes. However, highly regulated expression of several enzymes present in the urea cycle occurs also in many other tissues, where these enzymes are involved in synthesis of nitric oxide, polyamines, proline and glutamate. Glucagon, insulin, and glucocorticoids are major regulators of the expression of urea cycle enzymes in liver. In contrast, the "urea cycle" enzymes in nonhepatic cells are regulated by a wide range of pro- and antiinflammatory cytokines and other agents. Regulation of these enzymes is largely transcriptional in virtually all cell types. This review emphasizes recent information regarding roles and regulation of urea cycle and arginine metabolic enzymes in liver and other cell types.

Rac2, a hematopoiesis-specific Rho GTPase, specifically regulates mast cell protease gene expression in bone marrow-derived mast cells

Rho family GTPases activate intracellular kinase cascades to modulate transcription of multiple genes. Previous studies have examined the roles of the ubiquitously expressed Rho GTPase, Rac1, in regulation of gene expression in cell lines and implicated NF-kappaB, serum response factor, and kinase signaling pathways in this regulation. To understand the role of the closely related but hematopoiesis-specific Rho GTPase, Rac2, in regulation of gene transcription, we compared the gene expression profiles between wild-type and Rac2(-/-) bone marrow-derived mast cells. Our data demonstrate remarkable specificity in the regulation of gene expression by Rac2 versus Rac1. Microarray analysis demonstrated that expression of 38 known genes was significantly altered in Rac2(-/-) mast cells after cytokine stimulation compared with those in wild-type cells. Of these, the expression of the mouse mast cell protease 7 (MMCP-7) gene in wild-type cells was highly induced at the transcriptional level after stimulation with stem cell factor (SCF). In spite of compensatorily increased expression of Rac1 in Rac2-deficient cells, SCF-induced MMCP-7 transcription did not occur. Surprisingly, the loss of MMCP-7 induction was not due to decreased activation of NF-kappaB, a transcription factor postulated to lie downstream of Rac1 and known to play a critical role in hematopoietic cell differentiation and proliferation. However, the activities of c-Jun N-terminal kinases (JNKs) were markedly decreased in Rac2(-/-) mast cells. Our results suggest that cytokine-stimulated activation of MMCP-7 gene transcription is selectively regulated by a Rac2-dependent JNK signaling pathway in primary mast cells and imply a remarkable specificity in the regulation of transcriptional activity by these two highly related Rho GTPases.

RasGRP4, a new mast cell-restricted Ras guanine nucleotide-releasing protein with calcium- and diacylglycerol-binding motifs. Identification of defective variants of this signaling protein in asthma, mastocytosis, and mast cell leukemia patients and demonstration of the importance of RasGRP4 in mast cell development and function

A cDNA was isolated from interleukin 3-developed, mouse bone marrow-derived mast cells (MCs) that contained an insert (designated mRasGRP4) that had not been identified in any species at the gene, mRNA, or protein level. By using a homology-based cloning approach, the approximately 2.6-kb hRasGRP4 transcript was also isolated from the mononuclear progenitors residing in the peripheral blood of normal individuals. This transcript information was then used to locate the RasGRP4 gene in the mouse and human genomes, to deduce its exon/intron organization, and then to identify 10 single nucleotide polymorphisms in the human gene that result in 5 amino acid differences. The >15-kb hRasGRP4 gene consists of 18 exons and resides on a region of chromosome 19q13.1 that had not been sequenced by the Human Genome Project. Human and mouse MCs and their progenitors selectively express RasGRP4, and this new intracellular protein contains all of the domains present in the RasGRP family of guanine nucleotide exchange factors even though it is <50% identical to its closest homolog. Recombinant RasGRP4 can activate H-Ras in a cation-dependent manner. Transfection experiments also suggest that RasGRP4 is a diacylglycerol/phorbol ester receptor. Transcript analysis of an asthma patient, a mastocytosis patient, and the HMC-1 cell line derived from a MC leukemia patient revealed the presence of substantial amounts of non-functional forms of hRasGRP4 due to an inability to remove intron 5 in the precursor transcript. Because only abnormal forms of hRasGRP4 were identified in the HMC-1 cell line, this immature MC progenitor was used to address the function of RasGRP4 in MCs. HMC-1 leukemia cells differentiated and underwent granule maturation when induced to express a normal form of RasGRP4. Thus, RasGRP4 plays an important role in the final stages of MC development.