Enzymes of the mast cell granule

Association between SNP rs1800875, serum chymase and immunoglobulin E levels in patients with coronary heart disease

OBJECTIVE

The gene for mast cell chymase (CMA1) is an ideal candidate for investigating the genetic predisposition to coronary heart disease (CHD), as activated mast cells have been found to be present in a greater proportion in the shoulder region of atheroma than in normal coronary intimae. Previous studies have indicated that CMA1 promoter polymorphism rs1800875 may be involved in regulating immunoglobulin E (IgE) levels in patients with eczema, and it is associated with the progression of immunoglobulin A nephropathy.

METHODS

The association between single nucleotide polymorphism (SNP) rs1800875, serum chymase, and serum IgE levels was examined in 175 CHD subjects and 95 non-CHD subjects.

RESULTS

Statistical analysis indicated no significant difference in allele frequency between CHD and non-CHD. However, a significant association was found between CMA1 genotypes and total IgE levels in CHD subjects. Meanwhile, crossover analysis revealed that, in GG homozygotes, CHD risk was nearly six times higher in those with IgE (U/ml) level <2.58 (natural logarithm conversion), while no association was found with chymase level.

CONCLUSIONS

Polymorphism rs1800875 of CMA1 may be associated with serum IgE level in CHD subjects, but not with chymase level in both groups. In GG homozygotes, high IgE level is a protective factor against coronary disease.

Inhibitory effects of costunolide isolated from Laurus nobilis on IgE-induced degranulation of mast cell-like RBL-2H3 cells and the growth of Y16 pro-B cells

This study investigated the inhibitory effects of costunolide isolated from the leaves of Laurus nobilis L. (Lauraceae) on basophil-mediated allergic reactions and interleukin (IL)-5-mediated B cell growth. The effects of costunolide on β-hexosaminidase (a key parameter of degranulation) release and IL-4 expression in rat basophilic leukemia (RBL-2H3) cells were determined by measuring β-hexosaminidase activity and by semi-quantitative RT-PCR, respectively. The effects of costunolide on Y16 pro-B cell viability and growth were determined by 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyltetrazolium bromide (MTT) assay. Costunolide was found significantly to inhibit β-hexosaminidase activity (p < 0.01) and IL-4 transcription in RBL-2H3 cells in a dose-dependent manner. Its 50% inhibitory concentration (IC50 ) was 34 µM, while that of the positive control, ketotifen, was 24 µM (IL-4 mRNA transcription). Moreover, costunolide dose-dependently suppressed pro-B cell growth in IL-5-stimulated Y16 cells. These results provide evidence that costunolide stabilizes mast cells by inhibiting IgE-mediated degranulation and inhibits IL-5-stimulated B cell growth.

Pharmacokinetic/pharmacodynamic analyses of chymase inhibitor SUN13834 in NC/Nga mice and prediction of effective dosage for atopic dermatitis patients

A chymase inhibitor SUN13834 has been shown to improve skin condition in animal models for atopic dermatitis. In the present study, effective dosages of SUN13834 for atopic dermatitis patients were predicted by pharmacokinetic/pharmacodynamic (PK/PD) analyses of SUN13834 in NC/Nga mice, which spontaneously develop atopic dermatitis-like skin lesions. For the PK/PD analyses, we utilized the minimum effective plasma concentration of unbound SUN13834 in late-phase reaction of trinitrochlorobenzene (TNCB)-induced biphasic dermatitis in mice, based on the assumption that the minimum effective plasma concentrations are the same among the two animal models. In late-phase reaction of biphasic dermatitis, SUN13834 was most effective when its plasma concentration was highest at the elicitation, and the minimum effective plasma concentration of unbound SUN13834 at the elicitation was calculated to be 0.13-0.2 ng/mL. Oral administration of SUN13834 improved dermatitis in NC/Nga mice at 15 mg/kg (twice a day; bid) and 30 mg/kg (once a day; qd), but not at 60 mg/kg (every other day; eod). At the three dosages, the duration times over the plasma level of 0.13-0.2 ng/mL were 16.1-20.3, 10.7-12.2 and 7.8-8.8h, respectively, suggesting an importance of maintenance of the minimum effective plasma concentration for at least about 10-12h. The clinical effective dosage predicted in this paper is also discussed in relation to a recently conducted Phase 2a study.

Biological implications of preformed mast cell mediators

Mast cells store an impressive array of preformed compounds (mediators) in their secretory granules. When mast cells degranulate, these are released and have a profound impact on any condition in which mast cell degranulation occurs. The preformed mast cell mediators include well-known substances such as histamine, proteoglycans, proteases, and preformed cytokines, as well as several recently identified compounds. Mast cells have recently been implicated in a large number of novel pathological settings in addition to their well-established contribution to allergic reactions, and there is consequently a large current interest in the molecular mechanisms by which mast cells act in the context of a given condition. In many cases, preformed mast cell mediators have been shown to account for functions ascribed to mast cells, and these compounds are hence emerging as major players in numerous pathologies. In this review we summarize the current knowledge of preformed mast cell mediators.

Mast cells generated from patients with atopic eczema have enhanced levels of granule mediators and an impaired Dectin-1 expression

BACKGROUND

The disrupted skin barrier of patients with atopic eczema (AE) might facilitate contact between mast cells (MCs) in the skin and environmental triggers of the disease. One such trigger is the skin-colonizing yeast Malassezia sympodialis (M. sympodialis). In this study, we investigated the interaction of MC with M. sympodialis.

METHODS

Mast cells were generated from peripheral blood CD34(+) progenitor cells of healthy controls (HC) and M. sympodialis-sensitized AE patients. Biopsy specimens were taken from HC and lesional AE skin for immunohistological stainings.

RESULTS

The progenitor-derived MCs expressed the macrophage-inducible C-type lectin receptor Mincle, and exposure of these cells to M. sympodialis induced up-regulation of the mRNA expression of Mincle. Furthermore, we demonstrate that, when compared to HC, the progenitor-derived MCs from AE patients (i) contain more intrinsic granule mediators such as histamine, (ii) exhibit enhanced IL-6 release in response to M. sympodialis exposure, and (iii) have an impaired up-regulation of the fungal recognition receptor Dectin-1. In addition, analysis of skin sections from HC and AE patients revealed MCs as the predominant Dectin-1-expressing cell type in the skin.

CONCLUSION

Our data indicate that progenitor-derived MCs from AE patients differ from those from HC. Further investigations with skin-derived MCs are necessary to confirm the observed differences which could provide new insights into the pathogenic mechanisms underlying AE.

The specific chymase inhibitor TY-51469 suppresses the accumulation of neutrophils in the lung and reduces silica-induced pulmonary fibrosis in mice

Chymase is a chymotrypsin-like serine protease that is present in mast cells. Its activities include various effects associated with inflammatory responses. But little is known about the effects of chymase in pulmonary fibrosis. The mouse silicosis model was induced by intratracheal injection of 10 mg silica. The Ashcroft pathological score and the hydroxyproline content of lungs were measured to evaluate the effect of a chymase inhibitor, 2-[4-(5-fluoro-3-methylbenzo[b]thiophen-2-yl)sulfonamido-3-methanesulfonylphenyl] thiazole-4-carboxylic acid (TY-51469). The cellular composition and cytokine levels in bronchoalveolar lavage fluid (BALF) were also examined. Following TY-51469 treatment, the lung fibrosis score and hydroxyproline level were significantly reduced, and the number of neutrophils and the levels of macrophage inflammatory protein-2, monocyte chemoattractant protein-1, and transforming growth factor-β₁ in BALF were reduced on day 21. The administration of TY-51469 at an early stage showed a greater reduction of fibrosis compared to administration at a later stage. The neutrophil number in BALF in mice treated with TY-51469 both at an early stage and late stage was significantly reduced. The level of mouse mast cell proteinase-4 mRNA increased with time in silica-induced fibrosing lung tissue. These results show that the chymase inhibitor TY51469 suppresses the migration of neutrophils, which results in the suppression of lung fibrosis.

Protein trafficking in immune cells

The majority of cells of the immune system are specialized secretory cells, whose function depends on regulated exocytosis. The latter is mediated by vesicular transport involving the sorting of specialized cargo into the secretory granules (SGs), thereby generating the transport vesicles; their transport along the microtubules and eventually their signal-dependent fusion with the plasma membrane. Each of these steps is tightly controlled by mechanisms, which involve the participation of specific sorting signals on the cargo proteins and their recognition by cognate adaptor proteins, posttranslational modifications of the cargo proteins and multiple GTPases and SNARE proteins. In some of the cells (i.e. mast cells, T killer cells) an intimate connection exists between the secretory system and the endocytic one, whereby the SGs are lysosome related organelles (LROs) also referred to as secretory lysosomes. Herein, we discuss these mechanisms in health and disease states.

TLR2/MyD88-dependent and -independent activation of mast cell IgE responses by the skin commensal yeast Malassezia sympodialis

Atopic eczema (AE) is a chronic inflammatory skin disease. Approximately 50% of adult AE patients have allergen-specific IgE reactivity to the skin commensal yeast Malassezia spp. Due to the ruptured skin barrier in AE, it is likely that Malassezia can come into contact with mast cells, which are known to be involved in AE. We therefore hypothesized that Malassezia spp. can activate mast cells. Bone marrow-derived mast cells (BMMCs) were generated from wild type, TLR2, TLR4, and MyD88 gene-deleted mice and cocultured with Malassezia sympodialis extract. We recorded that M. sympodialis induced release of cysteinyl leukotrienes in a dose-dependent manner in nonsensitized and IgE-anti-trinitrophenyl-sensitized BMMCs, respectively, with three times higher levels in the latter type of cells. IgE-sensitized BMMCs also responded by degranulation as assessed by release of beta-hexosaminidase, increased MCP-1 production through a MyD88-independent pathway, and activated phosphorylation of the MAPK ERK1/2. Furthermore, M. sympodialis enhanced the degranulation of IgE receptor cross-linked wild-type BMMCs and altered the IL-6 release dose-dependently. This degranulation was independent of TLR2, TLR4, and MyD88, whereas the IL-6 production was dependent on the TLR2/MyD88 pathway and MAPK signaling. In conclusion, M. sympodialis extract can activate nonsensitized and IgE-sensitized mast cells to release inflammatory mediators, to enhance the IgE-mediated degranulation of mast cells, and to modulate MAPK activation and by signaling through the TLR2/MyD88 pathway to modify the IL-6 production of IgE receptor cross-linked mast cells. Collectively, these findings indicate that M. sympodialis can activate mast cells and might thus exacerbate the inflammatory response in AE.

Anetodermic mastocytosis: response to PUVA therapy

Mastocytosis is a group of disorders characterized by the accumulation of mast cells in different tissues and organs. The skin is the most frequently involved organ (90% of cases) where mastocytosis may show a heterogenic clinical expression. Anetodermic lesions are an unusual clinical presentation of mastocytosis. We report a case of anetodermic mastocytosis in a 26-year-old man, with sparse lesions and a benign course. PUVA therapy obtained excellent results in this case. Darier's sign should be investigated in patients with anetodermic lesions of unclear origin in order to exclude cutaneous mastocytosis.

Granzyme B is expressed in mouse mast cells in vivo and in vitro and causes delayed cell death independent of perforin

Mast cells respond to pathogens and allergens by secreting a vast array of preformed and newly synthesized mediators, including enzymes, vasoactive amines, lipid mediators, cytokines and chemokines, thereby affecting innate and adaptive immune responses and pathogenesis. Here, we present evidence that skin-, but not lung-associated primary mast cells as well as in vitro-differentiated bone marrow-derived mast cells (BMMC) express granzyme (gzm) B, but not gzmA or perforin (perf). GzmB is associated with cytoplasmic granules of BMMC and secreted after Fcepsilon-receptor-mediated activation. BMMC from wild type but not gzmB-deficient mice cause cell death in susceptible adherent target cells, indicating that the perf-independent cytotoxicity of BMMC is executed by gzmB. Furthermore, gzmB induces a disorganization of endothelial cell-cell contacts. The data suggest that activated mast cells contribute, via secreted gzmB, to cell death, increased vascular permeability, leukocyte extravasation and subsequent inflammatory processes in affected tissues.

The mast cell: where endocytosis and regulated exocytosis meet

We have investigated whether Ca(2+)-binding proteins, which have been implicated in the control of neurons and neuroendocrine secretion, play a role in controlling mast cell function. These studies have identified synaptotagmins (Syts) II, III, and IX as well as neuronal Ca(2+) sensor 1 (NCS-1) as important regulators of mast cell function. Strikingly, we find that these Ca(2+)-binding proteins contribute to mast cell function by regulating specific endocytic pathways. Syt II, the most abundant Syt homologue in mast cells, resides in an amine-free lysosomal compartment. Studying the function of Syt II-knocked down rat basophilic leukemia cells has shown a dual function of this homologue. Syt II is required for the downregulation of protein kinase Calpha, but it negatively regulates lysosomal exocytosis. Syt III, the next most abundant homologue, localizes to early endosomes and is required for the formation of the endocytic recycling compartment (ERC). Syt IX and NCS-1 localize to the ERC and regulate ERC export, NCS-1 by activating phosphatidylinositol 4-kinase beta. Finally, we show that recycling through the ERC is needed for secretory granule protein sorting as well as for the activation of the mitogen-activated protein kinases, extracellular signal-regulated kinase 1 and 2. Accordingly, NCS-1 stimulates Fc epsilon RI-triggered exocytosis and release of arachidonic acid metabolites.

Mast Cell Proteases

Mast cells (MCs) are traditionally thought of as a nuisance for its host, for example, by causing many of the symptoms associated with allergic reactions. In addition, recent research has put focus on MCs for displaying harmful effects during various autoimmune disorders. On the other hand, MCs can also be beneficial for its host, for example, by contributing to the defense against insults such as bacteria, parasites, and snake venom toxins. When the MC is challenged by an external stimulus, it may respond by degranulation. In this process, a number of powerful preformed inflammatory "mediators" are released, including cytokines, histamine, serglycin proteoglycans, and several MC-specific proteases: chymases, tryptases, and carboxypeptidase A. Although the exact effector mechanism(s) by which MCs carry out their either beneficial or harmful effects in vivo are in large parts unknown, it is reasonable to assume that these mediators may contribute in profound ways. Among the various MC mediators, the exact biological function of the MC proteases has for a long time been relatively obscure. However, recent progress involving successful genetic targeting of several MC protease genes has generated powerful tools, which will enable us to unravel the role of the MC proteases both in normal physiology as well as in pathological settings. This chapter summarizes the current knowledge of the biology of the MC proteases.

Synaptotagmin (Syt) IX is an essential determinant for protein sorting to secretory granules in mast cells

The secretory granules (SGs) of secretory cells of the hematopoietic lineage, such as the mast cells, are lysosome-related organelles whose membrane proteins travel through the plasma membrane and the endocytic system. Therefore, a mechanism must exist to prevent proteins destined to recycling or to the trans-Golgi network (TGN) from reaching the SGs. We now show that synaptotagmin (Syt) IX, a Syt homologue that is required for recycling from the endocytic recycling compartment (ERC) in rat basophilic leukemia (RBL-2H3) cultured mast cells, is involved in segregating recycling proteins from the SGs. By using as a marker the recycling protein TGN38, which cycles between the TGN, plasma membrane, and the ERC, we show that knock-down of Syt IX results in mistargeting of HA-tagged TGN38 to the SGs. We further demonstrate that Syt IX binds directly the small GTPase ARF1 and associates with the clathrin adaptor complex AP-1. These results therefore implicate Syt IX as an essential factor for the correct sorting of SGs proteins. Moreover, they place Syt IX as part of the machinery that is involved in the formation of transport carriers that mediate SGs protein sorting.

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.

Efficient sorting of TNF-alpha to rodent mast cell granules is dependent on N-linked glycosylation

Mast cells play an important role at the early stages of immunological response to bacterial infections and parasite infestations. One of the major mast cell proinflammatory mediators is TNF-alpha. Mast cells are considered the only cells capable of storing TNF-alpha in cytoplasmic granules and rapidly releasing it upon activation. To determine what pathway is utilized to direct TNF-alpha to cytoplasmic granules and what motifs are responsible for the sorting process, we constructed a fusion protein covering the full sequence of TNF-alpha, N-terminally fused to enhanced green fluorescent protein (EGFP). In rodent mast cells, such protein was sorted to secretory granules, and this process was inhibited by both brefeldin A and monensin. Considering the relationship between lysosomes and secretory granules and following TNF-alpha sequence analysis, it was determined whether TNF-alpha is sorted through the mannose-6-phosphate receptor (MPR)-dependent pathway. We observed that ammonium chloride and tunicamycin blocked TNF-alpha-EGFP fusion protein delivery to secretory granules. In situ mutagenesis experiments confirmed the necessity of N-linked glycosylation for efficient sorting of TNF-alpha into rodent mast cell granules. In this work we established that TNF-alpha travels from the ER to mast cell granules via a brefeldin A- and monensin-sensitive route, utilizing the MPR-dependent pathway, although this dependency does not seem to be absolute.

Effect of chymase on intraocular pressure in rabbits

Chymase is a chymotrypsin-like serine protease that is stored exclusively in the secretory granules of mast cells and converts big endothelins to endothelin-1 (1-31). The aim of this study was to evaluate the effect of chymase on intraocular pressure in rabbits. Chymase injection (3 and 10 mU) resulted in a trend toward increased intraocular pressure and a significant increase in intraocular pressure at a dose of 10 mU compared with the control. A specific chymase inhibitor, Suc-Val-Pro-Phe(P)(OPh)(2), attenuated the ocular hypertension induced by chymase. Endothelin-1 (1-31) also caused ocular hypertension, which was inhibited by a selective endothelin ET(A) receptor antagonist, cyclo(D-Asp-Pro-D-Val-Leu-D-Trp) (BQ-123). Moreover, chymase-induced ocular hypertension was inhibited by BQ-123. These results suggest that chymase influences the regulation of intraocular pressure, and it is likely that the formation of endothelin-1 (1-31) and subsequent activation of endothelin ET(A) receptors are involved in the development of ocular hypertension induced by chymase.

Effects of clarithromycin on inflammatory cell mediator release and survival

BACKGROUND

Clarithromycin exhibits anti-inflammatory as well as antimicrobial activity, leading to decreased symptoms of asthma and chronic sinusitis. The mode of anti-inflammatory effects of clarithromycin on inflammatory cells is not well understood. We hypothesized that clarithromycin inhibits inflammatory cell mediator release and survival.

METHODS

We investigated the effects of this drug on survival and mediator release from mast cells, eosinophils and neutrophils.

RESULTS

Human eosinophil and neutrophil respiratory burst was inhibited by up to 54% after 1-2 h pretreatment with 100 microg/ml clarithromycin. Similar doses of erythromycin did not affect respiratory burst responses in these cells. Clarithromycin at doses of up to 100 microg/ml had no effect on granule-derived mediators released from mast cells and neutrophils. However, we found that clarithromycin (100 microg/ml) induced cell death in mast cells and eosinophils after 16-48 h incubation.

CONCLUSION

Clarithromycin inhibited inflammatory cell mediator release and survival, which may enhance its ability to reduce the symptoms of chronic sinusitis and asthma.

A protease activated receptor-2 (PAR-2) activating peptide, tc-LIGRLO-NH2, induces protease release from mast cells: role in TNF degradation

Background

Mast cell (MC)-derived serine proteases have been implicated in a variety of inflammatory processes. We have previously shown that rat peritoneal MC (PMC) express mRNA for protease activated receptor 2 (PAR-2), a G-coupled receptor activated by trypsin-like proteases. Recent evidence also suggests that MC-induced inflammation can be mediated through PAR. Therefore, we hypothesized that specific PAR-2 agonist peptides (PAR-2ap) induce protease release from PMC.

Results

Western blot analysis of PMC supernatants revealed that a PAR-2ap, tc-LIGRLO (10 μM), stimulated the release of rat MC protease (RMCP)-1, RMCP-5 and carboxypeptidase-A. The release was evident by 20 min but further increased up to 8 h. To study the biological effects of protease release we tested supernatants from tc-LIGRLO, tc-OLRGIL (inactive control peptide) and antigen-activated PMC for proteolytic activity by seeding with TNF (150 pg/ml), incubating for 8 h at 37°C, and measuring TNF remaining in the supernatants. Supernatants from tc-LIGRLO-stimulated PMC degraded 44 % of seeded TNF (n = 5). Moreover, this TNF proteolysis was dependent on the concentration of tc-LIGRLO used to stimulate PMC, and was significantly inhibited (94 %) by soybean trypsin inhibitor. Antigen and tc-OLRGIL induced no significant release of such proteolytic activity.

Conclusions

These data indicate that a PAR-2ap induces the release of proteases from mast cells, which may degrade extracellular cytokines and other substrates thus modulating the inflammatory response.

Involvement of mast cell chymase in bleomycin-induced pulmonary fibrosis in mice

The possible role of mast cell chymase in organ fibrosis was examined using a bleomycin-induced pulmonary fibrosis model in mice. Intratracheal injection of bleomycin to mice significantly increased not only hydroxyproline content but also chymase activity in the lung. Administration of a chymase inhibitor SUN C8077 (7-chloro-3-(3-amynophenyl) quinazoline-2, 4-dione methanesulfonate) dose-dependently reversed the bleomycin-induced increase in hydroxyproline content as well as chymase activity in the lung. Human chymase digested latent transforming growth factor-beta1 (TGF-beta1) to form mature TGF-beta1 in vitro, which was inhibited by SUN C8077. Human chymase, on the other hand, failed to stimulate DNA synthesis of human lung fibroblasts CCD-8Lu and LL97A. Taken together, it is suggested that mast cell chymase might participate in the pathogenesis of pulmonary fibrosis, and that the chymase-induced fibrosis might be mediated at least in part by TGF-beta1. Chymase inhibitor may be promising for treatment of pulmonary fibrosis in humans.

Mouse mast cell protease-1 cleaves angiotensin I to form angiotensin II

The ability to convert angiotensin (Ang) I to Ang II was compared between human alpha-chymase and two mouse beta-chymases, mouse mast cell protease (mMCP)-1 and mMCP-4. Human chymase hydrolyzed Ang I to produce Ang II without further degradation. mMCP-1 similarly generated Ang II from Ang I in a time-dependent manner and the formation of the fragment other than Ang II was marginal. In contrast, mMCP-4 hydrolyzed Ang I at two sites, Tyr(4)-Ile(5) and Phe(8)-His(9), with Ang II formation being tentative. Consistently, mMCP-4 but not human chymase hydrolyzed Ang II and mMCP-1 showed little hydrolytic activity against Ang II. These data suggest that not only human chymase but also mMCP-1 might possess a physiological role in Ang II formation. Our findings also imply that the Ang-converting activity of chymase may not be related to the categorization of chymase into alpha- or beta-type based on their primary structure.

Proteinase-activated receptor (PAR)-1 and -2 agonists induce mediator release from mast cells by pathways distinct from PAR-1 and PAR-2

Because thrombin-induced inflammation is partially mast cell-dependent and involves proteinase-activated receptors (PARs), we hypothesized that mast cells express PAR and can be stimulated with PAR-activating peptides (PAR-AP). We demonstrated that rat peritoneal mast cells expressed PAR-1 and PAR-2 mRNA, and that PAR-2AP (tc-LIGRLO-NH(2), 1 microm) induced 64.2 +/- 4.4% specific beta-hexosaminidase release from peritoneal mast cells, whereas another PAR-2AP (SLIGRL-NH(2), 10 microM), trypsin (40 U/ml), and mast cell tryptase (1.5 microg/ml) did not. PAR-1AP (ApfFRChaCitY-NH(2), 10 microM) (Cit) induced 11.7 +/- 3.7% specific beta-hexosaminidase release, whereas another PAR-1AP (TFLLR-NH(2), 40 microM) and human thrombin (10 U/ml) did not. PAR-AP, tc-LIGRLO-NH(2), and Cit increased the free intracellular Ca(2+) concentration, whereas trypsin, tryptase, thrombin, and other PAR-APs did not. Desensitization of Ca(2+) flux with different agonists suggests that although tc-LIGRLO-NH(2), Cit, and compound 48/80 have similar mechanisms of action, tc-LIGRLO-NH(2) also activates mast cells by a mechanism distinct from that of 48/80. Using benzalkonium chloride, which antagonizes the actions of 48/80 by competing for the same G(i) protein, we determined that benzalkonium chloride suppressed tc-LIGRLO-NH(2)-mediated (0.1 microM) beta-hexosaminidase release by 62%. Moreover, removal of sialic acid from peritoneal mast cells, using neuraminidase (2 U/ml), inhibited Cit- (10 microM, 52%) and tc-LIGRLO-NH(2) (0.5 microM, 29%)-mediated beta-hexosaminidase release. Thus, tc-LIGRLO-NH(2) and Cit have at least partially similar mechanisms of action as 48/80. PAR-AP may therefore activate mast cells via multiple mechanisms that are distinct from those of classical PAR-1 and PAR-2. The responsiveness of mast cells to PAR-AP via a non-PAR-1/non-PAR-2 mechanism complicates the interpretation of in vivo studies using these peptides.

Chymase participates in chronic dermatitis by inducing eosinophil infiltration

An epicutaneous application of 2,4-dinitrofluorobenzene (DNFB) to a mouse ear caused a transient skin swelling, and the repetition of the challenge enlarged the contact dermatitis. The repeated challenge with DNFB also induced eosinophil infiltration on the application site. Administration of a chymase inhibitor significantly inhibited the ear swelling as well as eosinophil accumulation. An intradermal injection of human chymase to the mouse ear also elicited transient skin swelling and eosinophil infiltration, both of which were augmented in proportion to the number of injections. Human serum albumin and heat-inactivated chymase failed to induce such skin reactions, suggesting the participation of proteolytic activity of the enzyme. In addition, chymase stimulated eosinophil migration in vitro in a concentration-dependent manner. Taken together, these observations suggest that mast cell chymase may contribute to development of the DNFB-induced dermatitis, probably by promoting eosinophil infiltration. It is therefore possible that chymase plays a role in pathogenesis of chronic dermatitis such as atopic dermatitis.

Human mast cells release metalloproteinase-9 on contact with activated T cells: juxtacrine regulation by TNF-alpha

Mast cells, essential effector cells in allergic inflammation, have been found to be activated in T cell-mediated inflammatory processes in accordance with their residence in close physical proximity to T cells. We have recently reported that mast cells release granule-associated mediators and TNF-alpha upon direct contact with activated T cells. This data suggested an unrecognized activation pathway, where mast cells may be activated during T cell-mediated inflammation. Herein, we show that this cell-cell contact results in the release of matrix metalloproteinase (MMP)-9 and the MMP inhibitor tissue inhibitor of metalloproteinase 1 from HMC-1 human mast cells or from mature peripheral blood-derived human mast cells. The expression and release of these mediators, as well as of beta-hexosaminidase and several cytokines, were also induced when mast cells were incubated with cell membranes isolated from activated, but not resting, T cells. Subcellular fractionation revealed that the mature form of MMP-9 cofractionated with histamine and tryptase, indicating its localization within the secretory granules. MMP-9 release was first detected at 6 h and peaked at 22 h of incubation with activated T cell membranes, while TNF-alpha release peaked after only 6 h. Anti-TNF-alpha mAb inhibited the T cell membrane-induced MMP-9 release, indicating a possible autocrine regulation of MMP release by mast cell TNF-alpha. This cascade of events, whereby mast cells are activated by T cells to release cytokines and MMP-9, which are known to be essential for leukocyte extravasation and recruitment to affected sites, points to an important immunoregulatory function of mast cells within the context of T cell-mediated inflammatory processes.

Mechanical fluid flow enhances high-affinity-IgE-receptor-mediated secretion by mast cells adherent to fibronectin

We demonstrated the effect of interaction between mechanical fluid flow and the extracellular matrix on high-affinity-IgE-receptor (FcepsilonRI)-mediated secretion by mast cells (cell line MC/9). Mechanical fluid flow did not affect secretion by the cells in the absence of exogenou agonists. Mechanical fluid flow did not affect secretion by cells adherent tofibronectin in the absence of exogenous agonists, but it did enhance FcepsilonRI-mediated secretion by cells adherent tofibronectin. These finding indicate that fluid-flow-induced enhancement of secretion by mast cells requires both exogenous agonists and interaction between integrins and the extracellular matrix. The present study is thefirst to demonstrate that mechanical fluid flow enhances FcepsilonRI-mediated secretion by a mast cell line adherent tofibronectin.

Chymase-dependent angiotensin II formation in the saphenous vein versus the internal thoracic artery

OBJECTIVES

The great saphenous vein graft is known to be less patent than the internal thoracic artery graft. Recently, we reported that chymase-dependent angiotensin II formation plays an important role in the development of intimal hyperplasia in dog grafted veins. In this study we investigated the levels of angiotensin II-forming enzymes, angiotensin-converting enzyme, and chymase in human saphenous veins and internal thoracic arteries.

METHODS

The saphenous vein and internal thoracic artery specimens were obtained from coronary artery bypass grafts of patients during surgical procedures (saphenous vein, n = 16; internal thoracic artery, n = 16). Activities of angiotensin-converting enzyme and chymase were determined by using the extract from the saphenous vein or internal thoracic artery. Sections of the saphenous vein or internal thoracic artery were stained with van Gieson's elastin stain and were immunostained with anti-human chymase antibody.

RESULTS

The activities of angiotensin-converting enzyme in the saphenous vein and internal thoracic artery were 0.34 +/- 0.12 and 0.32 +/- 0.17 mU/mg protein, respectively, and the difference was not significant. The chymase activity in the saphenous vein was significantly higher than that in the internal thoracic artery (saphenous vein, 10.1 +/- 0.81 mU/mg protein; internal thoracic artery, 6.21 +/- 1.86 mU/mg protein). Chymase-positive cells in the saphenous vein were located in both the media and adventitia, and those in the internal thoracic artery were located only in the adventitia. The number of chymase-positive cells in the saphenous vein was about 2.6 times that in the internal thoracic artery.

CONCLUSION

The chymase activity, but not the angiotensin-converting enzyme activity, was significantly higher in the saphenous vein, suggesting that the high levels of chymase activity may be related to the poorer performance of the saphenous vein for use as a bypass conduit.

Electron microscopy of mast cells in the venous wall of canine liver

Although many mast cells locate under the endothelial layer along the sublobular veins in canine liver, the cell function remains to be fully defined. To establish the nature of the canine mast cell, the mast cells were examined by electron microscopy. A few monocytes contacted with luminal surface of endothelial cells under which mast cells situated. To confirm the chemotaxis of monocyte by hepatic mast cells, the hepatic venous vessels were treated with a histamine releaser (compound 48/80). The monocytes invaded into the subendothelial layer and extended their pseudopodium to the degranulated mast cells. It presumes that some mediators within the mast cell granules might act as a chemotactic substance to the monocyte. On the contrary, mast cells were migrating from subendothelial layer to venous lumen under normal condition. The migrating mast cell showed strong acid phosphatase reaction in their granules. It suggests that the granules of migrating mast cell became visible to acid phosphatase activity by a physical force such as contact stimulation, and that a part of mast cells remigrate from the venous wall to other places by the blood flow. Furthermore, hepatic mast cells were revealed to contain both endothelin-1 and histamine in their granules by immunocytochemistry. As these substances have an activity of stronger venous constriction, it seems that the mast cells play an important role in the blood flow regulation of the canine liver, mast cell, monocyte.

The lysosomal protease cathepsin D is efficiently sorted to and secreted from regulated secretory compartments in the rat basophilic/mast cell line RBL

Basophils and mast cells contain a peculiar class of inflammatory granules that discharge their content upon antigen-mediated crosslinking of IgE-membrane receptors. The pathways for granule biogenesis and exocytosis in these cells are still largely obscure. In this study we employed the rat basophilic leukemia (RBL)/mast cell line to verify the hypothesis that inflammatory granules share common bioactive molecules and functional properties with lysosomes. We demonstrate that inflammatory granules, as identified by the monoclonal 5G10 antibody (which recognises an integral membrane protein) or by Toluidine Blue staining, have an intralumenal acidic pH, possess lysosomal enzymes and are accessible by fluid-phase and membrane endocytosis markers. In addition, we studied the targeting, subcellular localisation and regulated secretion of the lysosomal aspartic protease cathepsin D (CD) as affected by IgE receptor stimulation in order to obtain information on the pathways for granule biogenesis and exocytosis. Stimulation with DNP-BSA of specific IgE-primed RBL cells led to a prompt release of processed forms of CD, along with other mature lysosomal hydrolases. This release could be prevented by addition of EGTA, indicating that it was dependent on extracellular calcium influx. Antigen stimulation also induced exocytosis of immature CD forms accumulated by ammonium chloride, suggesting the existence of an intermediate station in the pathway for granule biogenesis still sensitive to regulated exocytosis. The targeting of molecules to secretory granules may occur via either a mannose-6-phosphate-dependent or mannose-6-phosphate-independent pathway. We conclude that endosomes and lysosomes in basophils/mast cells can act as regulated secretory granules or actually identify with them.

Synaptotagmin II negatively regulates Ca2+-triggered exocytosis of lysosomes in mast cells

Synaptotagmins (Syts) I and II are believed to act as Ca2+ sensors in the control of neurotransmission. Here we demonstrate that mast cells express Syt II in their lysosomal fraction. We further show that activation of mast cells by either aggregation of FcepsilonRI or by Ca2+ ionophores results in exocytosis of lysosomes, in addition to the well documented exocytosis of their secretory granules. Syt II directly regulates lysosomal exocytosis, whereby overexpression of Syt II inhibited Ca2+-triggered release of the lysosomal processed form of cathepsin D, whereas suppression of Syt II expression markedly potentiated this release. These findings provide evidence for a novel function of Syt II in negatively regulating Ca2+-triggered exocytosis of lysosomes, and suggest that Syt II-regulated secretion from lysosomes may play an important role in mast cell biology.

Accumulation of major histocompatibility complex class II molecules in mast cell secretory granules and their release upon degranulation

To investigate the relationship between major histocompatibility complex (MHC) class II compartments, secretory granules, and secretory lysosomes, we analyzed the localization and fate of MHC class II molecules in mast cells. In bone marrow-derived mast cells, the bulk of MHC class II molecules is contained in two distinct compartments, with features of both lysosomal compartments and secretory granules defined by their protein content and their accessibility to endocytic tracers. Type I granules display internal membrane vesicles and are accessed by exogenous molecules after a time lag of 20 min; type II granules are reached by the endocytic tracer later and possess a serotonin-rich electron-dense core surrounded by a multivesicular domain. In these type I and type II granules, MHC class II molecules, mannose-6-phosphate receptors and lysosomal membrane proteins (lamp1 and lamp2) localize to small intralumenal vesicles. These 60-80-nm vesicles are released along with inflammatory mediators during mast cell degranulation triggered by IgE-antigen complexes. These observations emphasize the intimate connection between the endocytic and secretory pathways in cells of the hematopoietic lineage which allows regulated secretion of the contents of secretory lysosomes, including membrane proteins associated with small vesicles.

Mid-dermal elastolysis: an ultrastructural and biochemical study

Mid-dermal elastolysis (MDE) is a particular elastic tissue disorder in which selective loss of elastic fibres occurs in the mid-dermis. It is clinically characterized by the appearance of fine wrinkling of the epidermis and perifollicular protrusion which gives the skin an aged appearance. It is sometimes associated with an inflammatory event such as urticaria while other cases are regarded as idiopathic. The pathogenesis of MDE is still obscure. Some authors have underlined the role of macrophage activation and others have imputed UV radiation. We report here a typical case of MDE arising after several attacks of solar urticaria. Electron microscopic and biochemical studies were carried out. Ultrastructural examination showed active elastophagocytosis by macrophages and mast cells, often degranulated, near phagocytosing cells. Biochemical studies demonstrated that fibroblasts derived from lesional skin of the MDE patient produced high levels of elastase and cathepsin G compared with fibroblasts from a healthy sex- and age-matched control. Phagocytosis of morphologically normal elastic tissue is a noticeable characteristic feature of MDE. In our case mast-cell activation and the abnormal synthesis and/or release of fibroblast elastolytic enzymes seemed to play a role in the pathogenesis of the MDE.

Effect of salbutamol, fenoterol, and sodium cromoglycate on the release of heparin from sensitized human lung fragments challenged with Dermatophagoides pteronyssinus allergen

Heparin from degranulating mast cells influences a wide range of cellular and humoral reactions associated with allergic inflammation and asthma. Agents that inhibit mast cell degranulation may therefore compromise the moderating effects of heparin in the tissues and result in worsening inflammation and other associated pathology. This study measures heparin release from allergen-challenged human lung tissue and compares the effect of the mast cell stabilizing beta 2-agonists, salbutamol and fenoterol, and a non-beta 2-agonist, sodium cromoglycate, on the release of heparin. Pieces of lung tissue 2 to 3 mm3 were sensitized with high titer Dermatoaphagoides pteronyssinus-specific IgE serum and challenged with D. pteronyssinus allergen, with and without prior addition of salbutamol, fenoterol, or sodium cromoglycate. Dextran sulfate was added to the mixture to prevent the binding of heparin to tissue proteins. Heparin was released together with histamine after challenge. The mean and 95% confidence interval of prechallenge and postchallenge heparin concentrations in the lung tissue filtrates were 0.10 IU/ml (0.07, 0.12) and 0.24 IU/ml (0.17, 0.30), respectively (P < 0.001). Addition of the beta 2-agonists produced a mean inhibition of released heparin of 71% (50, 92), and 73% (55, 91), respectively. Sodium cromoglycate gave a 35% (20, 51) inhibition that was significantly less than that produced by the beta 2-agonists (P < 0.01). The beta 2-agonists salbutamol and fenoterol strongly inhibited heparin release from mast cells. The therapeutic use of mast cell stabilizing agents may therefore be potentially detrimental to the control of allergic inflammation and other associated pathologies.

Proteoglycans in haemopoietic cells

Proteoglycans are produced by all types of haemopoietic cells including mature cells and the undifferentiated stem cells. The proteinase-resistant secretory granule proteoglycan (serglycin; Ref. 14), is the most prevalent and best characterised of these proteoglycans. Although its complete pattern of distribution in the haemopoietic system is unknown, serglycin has been identified in the mast cells, basophils and NK cells, in which secretion is regulated, and in HL-60 cells and a monocytoid cell line (Kolset, S.O., unpublished data) in which secretion is constitutive. Proteinase-resistant proteoglycans have been detected in human T-lymphocytes and murine stem cells (FDCP-mix) and the core proteins may be closely related to serglycin. A variety of glycosaminoglycan chains are assembled on the serglycin protein and it is likely that this class of proteoglycan can carry out a wide variety of functions in haemopoietic cells including the regulation of immune responses, inflammatory reactions and blood coagulation. There is strong evidence that in mast cells, NK cells and platelets, the proteoglycans are complexed to basic proteins (including enzymes and cytolytic agents) and amines in secretory granules and such complexes may dissociate following secretion from the cell. The stability of the complexes may be regulated by the ambient pH which may be acidic in the granules and neutral or above in the external medium. However, proteinase-proteoglycan complexes in mast cell granules seem to remain stable after secretion and it has been proposed that the proteoglycan regulates activity of proteinases released into the pericellular domain. The functions of proteoglycans which are constitutively secreted from cells are less clear. If cells have no requirement for storage of basic proteins why do they utilise the same design of proteoglycan as cells which accumulate secretory material prior to regulated release? We should stress that the so-called constitutive secretory pathway has been identified in haemopoietic cells in culture, which are usually maintained and grown in the presence of mitogenic factors (e.g., IL-2, IL-3). the cells are therefore activated and it has not been established that continuous proteoglycan secretion occurs in quiescent cells circulating in the peripheral blood. It is possible that lymphocytes, monocytes and macrophages, in which the constitutive secretion pathway operates in vitro, may store proteoglycan in vivo unless stimulated by mitogens or other activating agents.(ABSTRACT TRUNCATED AT 400 WORDS)

Structure of human neutrophil elastase in complex with a peptide chloromethyl ketone inhibitor at 1.84-A resolution

Human neutrophil elastase (HNE) has been implicated as a major contributor to tissue destruction in various disease states, including emphysema. The structure of HNE, at neutral pH, in complex with methoxysuccinyl-Ala-Ala-Pro-Ala chloromethyl ketone (MSACK), has been solved and refined to an R factor of 16.4% at 1.84-A resolution. Results are consistent with the currently accepted mechanism of peptide chloromethyl ketone inhibition of serine proteases, in that MSACK cross-links the catalytic residues His-57 and Ser-195. The structure of the HNE-MSACK complex is compared with that of porcine pancreatic elastase in complex with L-647,957, a beta-lactam inhibitor of both elastases. The distribution of positively charged residues on HNE is highly asymmetric and may play a role in its specific association with the underlying negatively charged proteoglycan matrix of the neutrophil granules in which the enzyme is stored.

Biological functions of serine proteases in mast cells in allergic inflammation

Serine proteases in mast cell granules, such as chymase, atypical chymase, and tryptase, which are major proteins in the granules, may play important roles in the process of immunoglobulin E (IgE)-mediated degranulation and in pathobiological alterations in tissues. Indeed, inhibitors of chymase, substrate analogs, and antichymase F(ab')2, but not inhibitors of tryptase, markedly inhibited histamine release induced by IgE-receptor bridging but not that induced by Ca ionophore. In contrast, inhibitors of metalloprotease inhibited histamine release induced not only by IgE-receptor bridging but also by Ca ionophore. These results suggest that chymase and metalloprotease are involved at different steps in the process of degranulation. The extents of inhibition of histamine release were closely correlated with the amounts of the inhibitors of chymase accumulated in the granules. After degranulation, the released proteases may in part contribute to pathobiological alterations in allergic disorders through generations of C3a anaphylatoxin and thrombin by human and rat tryptase, respectively, and those of angiotensin II and a chemotactic factor of neutrophils by human and rat chymase, respectively. Moreover, chymase and atypical chymase from rat were shown to destroy type IV collagen, and human tryptase was found to hydrolyze various plasma proteins, such as fibrinogen and high-molecular-weight kininogen. The biological activities of tryptase and chymase from rat may be regulated by their dissociation from and association with trypstatin, an endogenous inhibitor of these proteases.

Plasminogen activator release from cultured murine mast cells

Mast cells from the Furth murine mastocytoma tumour line were found to contain significant levels of plasminogen activator (PA). Cultured cells released PA activity into the culture medium in parallel with the release of histamine, and both were proportionately increased following exposure to degranulating agents. Pretreatment of the mast cells with cycloheximide did not alter their total PA content or their ability to release PA. These studies suggest that PA is a prestored granule constituent. The ability of PA to generate plasmin from plasminogen suggests an important role for mast cell PA in fibrinolysis and tissue degradation, observations that have been associated with mast cell degranulation and infiltration in vivo.

REV 2871 (CHBZ): a potent antiallergic agent with a novel mechanism of action. II. Studies on the mechanism of action

REV 2871 (CHBZ) was taken up by rat mast cells and human leukocytes in a specific and saturable manner. The compound can be hydrolyzed by a granule-associated enzyme in the mast cell to an ionic metabolite (REV 3579) whose in vitro profile is identical to that of disodium cromoglycate (DSCG). REV 3579, although achieving millimolar concentrations inside cells incubated with CHBZ, was not itself taken up by rat mast cells or human leukocytes. The unusual in vitro activity of CHBZ is postulated to arise from the fact that it is a prodrug for delivering a DSCG-like drug to the interior of a secretory cell. The internalized drug apparently exerts a more general and longer-lived inhibition of the secretory process than it can by acting on exterior membrane receptors. CHBZ thus represents a novel drug for studying anaphylactic responses in vitro.

Effect of proteases on the beta-thromboglobulin radioimmunoassay

Rat peritoneal mast cells and mast cell granules were evaluated by radioimmunoassay for the presence of beta-thromboglobulin and platelet factor 4. The initial assays indicated that a beta-thromboglobulin cross reacting material was released from mast cells by compound 48/80 in a similar dose-dependent manner as histamine release. The material was also found to be associated with purified granules. However, the use of protease inhibitors in the buffers completely abolished the positive assays. Further evaluation of the effects of various proteases on the beta-thromboglobulin assay indicated that elastase would also generate a false positive assay which could then be neutralized by the use of alpha 1-antitrypsin as a protease inhibitor. There was no protease effect on the platelet factor 4 radioimmunoassay which always showed no detectable amounts with mast cells, granules or proteases. These results clearly indicate the artifactual positive assays which can arise when using certain radioimmunoassay tests in the presence of cell proteases. The use of protease inhibitors is a necessary control when applying a radioimmunoassay to a system with potentially active proteases.

The isolation and characterization of globule leucocytes: their derivation from mucosal mast cells in parasitized sheep

Ovine mucosal mast cells and globule leucocytes have been isolated from the abomasum of normal sheep, and from animals challenged with Ostertagia circumcincta. The ultrastructural, morphological and histochemical properties of these cells have been investigated. The granules of ovine mucosal immunoglobulin and a serine esterase. These cells also possess surface immunoglobulin. Cells morphologically intermediate between mucosal mast cells and bulin. Cells morphologically intermediate between mucosal mast cells and globule leucocytes have similar granule and surface properties. These observations, together with quantitative data, indicate that alterations in the granule structure of mucosal mast cells as a consequence of prolonged antigenic challenge give rise to mast cells in the epithelium which, in the past, have been commonly recognized as globule leucocytes.

Mast cells at sites of cartilage erosion in the rheumatoid joint

Cartilage-pannus junctions of the rheumatoid lesion have been examined by histochemical and ultrastructural techniques in an attempt to identify the cells responsible for cartilage degradation. Mast cells have been identified at sites of cartilage erosion in 3 specimens of rheumatoid joint. It is known that mast cells participate in immunological reactions, produce the vasoactive and proteinase-modulating agents histamine and heparin as well as their own degradative proteinases. The close association of mast cells with sites of cartilage erosion suggests they may play an important role in the pathophysiology of joint destruction in rheumatoid arthritis.

Melanin: the organizing molecule

The hypothesis is advanced that (neuro)melanin (in conjunction with other pigment molecules such as the isopentenoids) functions as the major organizational molecule in living systems. Melanin is depicted as an organizational "trigger" capable of using established properties such as photon-(electron)-phonon conversions, free radical-redox mechanisms, ion exchange mechanisms, and semiconductive switching capabilities to direct energy to strategic molecular systems and sensitive hierarchies of protein enzyme cascades. Melanin is held capable of regulating a wide range of molecular interactions and metabolic processes primarily through its effective control of diverse covalent modifications. To support the hypothesis, established and proposed properties of melanin are reviewed (including the possibility that (neuro)melanin is capable of self-synthesis). Two "melanocentric systems"--key molecular systems in which melanin plays a central if not controlling role--are examined: 1) the melanin-purine-pteridine (covalent modification) system and 2) the APUD (or diffuse neuroendocrine) system. Melanin's role in embryological organization and tissue repair/regeneration via sustained or direct current is considered in addition to its possible control of the major homeostatic regulatory systems--autonomic, neuroendocrine, and immunological.

Histamine synthesis in intact and disrupted rat mast cells

Histamine production by purified intact rat peritoneal mast cells, as measured by formation of [beta-3H]histamine from [beta-3H]L-histidine or by release of 14CO2 from 14C-carboxyl-labeled histidine, was ten to thirty times greater than that of disrupted cells of soluble extracts of these cells. Loss of activity was evident whether cells were disrupted by sonification, freezing and thawing, or lysis, both in the absence and presence of inhibitors of proteolytic enzymes and agents known to preserve enzyme responsible for histamine formation in both the intact cells and cell extracts. In the presence of subsaturating concentrations of histidine, various histidine analogs and glutamine inhibited histidine data indicate that, at physiological concentrations of histidine, blockade of histidine transport (through system N) may limit histamine synthesis in the intact cell and that measurement of histidine decarboxylase activity in tissue homogenates or cell extracts may not reflect actual histidine decarboxylase activity in vivo.