Mast Cell-specific Proteases Research Articles

Neoadjuvant chemotherapy induces phenotypic mast cell changes in high grade serous ovarian cancer

BackgroundHigh grade serous ovarian cancer (HGSOC) is the most lethal gynecologic malignancy in which patients have still yet to respond meaningfully to clinically available immunotherapies. Hence, novel immune targets are urgently needed. Our past work has identified that mast cells are significantly upregulated at the mRNA level in HGSOC patient tumors following neoadjuvant chemotherapy (NACT) exposure. Therefore, in this current investigation we sought to characterize intratumoral mast cell phenotypic changes as a result of NACT exposure and determine how these adaptations are associated with patient clinical outcomes.MethodsHematologic immunohistochemistry was employed to determine mast cell levels in 36 matched pre- and post-NACT HGSOC patient tumors. Fluorescent Immunohistochemistry was utilized to identify Tryptase+(carboxypeptidase A3 (CPA3) + mast cells as well as histamine levels in 29 and 20, respectively, matched pre- and post-NACT HGSOC patient tumors. Finally, human immortalized mast cells, LUVA were stimulated with carboplatin and paclitaxel and genomic changes were analyzed by quantitative PCR.ResultsHematologic labeled intratumoral mast cells were significantly upregulated in the intraepithelial and stromal regions of the tumor, post-NACT. Lower levels of pre-NACT mast cells were significantly associated with an improved progression-free survival (PFS). Histamine, a marker of mast cell degranulation was similarly upregulated in post-NACT exposed tumors. Through the characterization of mast cell specific proteases Tryptase and CPA3, it was found that Tryptase+/ CPA3 + mast cells were significantly upregulated both in the intraepithelial and stromal compartments of the tumor, while Tryptase + cells were significantly upregulated in the stromal regions of the tumor. Lower post-NACT treated levels with Tryptase+/ CPA3 + cells were significantly associated with improved overall survival (OS) and PFS while higher Tryptase + mast cells were associated with improved OS. Finally, following chemotherapy exposure mast cell activating factors AREG and CCL2 were significantly upregulated while TGFB1, an inhibitor of mast cell activation was downregulated in LUVA cells.ConclusionsEnhanced mast cell numbers, as well as activation and degranulation are a consequence of NACT exposure. Post-NACT mast cells displayed differing associations with survival outcomes that was dependent upon granule classification. Ultimately, mast cells represent a clinically relevant putative HGSOC immune target.

Short-term high fat feeding induces inflammatory responses of tuft cells and mucosal barrier cells in the murine stomach.

Feeding mice with a high fat diet (HFD) induces inflammation and results in changes of gene expression and cellular composition in various tissues throughout the body, including the gastrointestinal tract. In the stomach, tuft cells expressing the receptor GPR120 are capable of sensing saturated long chain fatty acids (LCFAs) and thus may be involved in initiating mechanisms of mucosal inflammation. In this study, we assessed which cell types may additionally be affected by high fat feeding and which candidate molecular mediators might contribute to mucosa-protective immune responses. A high fat dietary intervention for 3 weeks caused an expansion of tuft cells that was accompanied by a higher frequency of mucosal mast cells and surface mucous cells which are a known source of the insult-associated cytokine interleukin 33 (IL-33). Our data demonstrate that both brush and mucosal mast cells comprise the enzyme ALOX5 and its activating protein FLAP and thus have the capacity for synthesizing leukotriene (LT). In HFD mice, several tuft cells showed a perinuclear colocalization of ALOX5 with FLAP which is indicative of an active LT synthesis. Monitoring changes in the expression of genes encoding elements of LT synthesis and signaling revealed that transcript levels of the leukotriene C4 synthase, LTC4S, catalyzing the first step in the biosynthesis of cysteinyl (cys) LTs, and the cysLT receptors, cysLTR2 and cysLTR3, were upregulated in mice on HFD. These mice also showed an increased expression level of IL-33 receptors, the membrane-bound ST2L and soluble isoform sST2, as well as the mast cell-specific protease MCPT1. Based on these findings it is conceivable that upon sensing saturated LCFAs tuft cells may elicit inflammatory responses which result in the production of cysLTs and activation of surface mucous cells as well as mucosal mast cells regulating gastric mucosal function and integrity.

IL-33 induces granzyme C expression in murine mast cells via an MSK1/2-CREB-dependent pathway.

Granzymes comprise a group of proteases involved in the killing of infected or cancerous cells by the immune system. Although best studied in T cells and natural killer (NK) cells, they are also expressed in some innate immune cells. Granzymes B and C are encoded in the mouse chymase locus that also encodes a number of mast cell-specific proteases. In line with this, mast cells can express granzyme B, although how this is regulated and their ability to express other granzymes is less well studied. We therefore examined how IL-33, a cytokine able to activate mast cells but not induce degranulation, regulated granzyme B and C levels in mast cells. Granzyme C, but not B, mRNA was strongly up-regulated in bone marrow-derived mast cells following IL-33 stimulation and there was a corresponding increase in granzyme C protein. These increases in both granzyme C mRNA and protein were blocked by a combination of the p38α/β MAPK inhibitor VX745 and the MEK1/2 inhibitor PD184352, which blocks the activation of ERK1/2. ERK1/2 and p38α activate the downstream kinases, mitogen and stress-activated kinases (MSK) 1 and 2, and IL-33 stimulated the phosphorylation of MSK1 and its substrate CREB in an ERK1/2 and p38-dependent manner. The promoter for granzyme C contains a potential CREB-binding site. Bone marrow-derived mast cells from either MSK1/2 double knockout or CREB Ser133Ala knockin mice were unable to up-regulate granzyme C. Together these results indicate that IL-33-induced granzyme C expression in mast cells is regulated by an MSK1/2-CREB-dependent pathway.

Heparin is required for the formation of granules in connective tissue mast cells.

Mast cells are innate immune cells strategically positioned around blood vessels near body surfaces. Their primary weapons are bioactive amines, mast cell-specific proteases, and cytokines stored in preformed granules. Mast cells granules constituents are packaged efficiently with the help of the highly negatively charged Heparan sulfate-derivative, Heparin. Heparin is one of the most widely used drugs to treat coagulation disorders, yet, it is not found in the circulation at a steady state, casting doubt that the prevention of blood clotting is its physiological function. Early studies using Ndst2 -/- mice have shown that Heparin is essential for mast cells granules formation. However, these mice could still produce less sulfated Heparan sulfate that could potentially replace Heparin. Here, we have created and validated a novel genetic model for Heparin deficiency, specifically in connective tissue mast cells, to address the physiological role of this molecule. Using this model, we have demonstrated that Heparin is required for mast cell granules formation; without it, mast cells are reduced in the peritoneal cavity and the skin. The absence of Heparin impaired the response to passive cutaneous anaphylaxis but, surprisingly, enhanced ear swelling in an irritant dermatitis model and reduced the lesion size and bacterial burden in a Staphylococcus aureus necrotizing dermatitis model. The altered function of Heparin-deficient mast cells in the latter two models was not mediated through enhanced Histamine or TNFα release. However, the Mrgprb2 receptor was up-regulated in knock-out mast cells, potentially explaining the enhanced response of mutant mice to irritant and necrotizing dermatitis. Altogether our results expand our current understanding of the physiological role of Heparin and provide unique tools to further dissect its importance.

Mast cell infiltration of the choroid and protease release are early events in age-related macular degeneration associated with genetic risk at both chromosomes 1q32 and 10q26.

Age-related macular degeneration (AMD) is a leading cause of visual loss. It has a strong genetic basis, and common haplotypes on chromosome (Chr) 1 (CFH Y402H variant) and on Chr10 (near HTRA1/ARMS2) contribute the most risk. Little is known about the early molecular and cellular processes in AMD, and we hypothesized that analyzing submacular tissue from older donors with genetic risk but without clinical features of AMD would provide biological insights. Therefore, we used mass spectrometry–based quantitative proteomics to compare the proteins in human submacular stromal tissue punches from donors who were homozygous for high-risk alleles at either Chr1 or Chr10 with those from donors who had protective haplotypes at these loci, all without clinical features of AMD. Additional comparisons were made with tissue from donors who were homozygous for high-risk Chr1 alleles and had early AMD. The Chr1 and Chr10 risk groups shared common changes compared with the low-risk group, particularly increased levels of mast cell–specific proteases, including tryptase, chymase, and carboxypeptidase A3. Histological analyses of submacular tissue from donors with genetic risk of AMD but without clinical features of AMD and from donors with Chr1 risk and AMD demonstrated increased mast cells, particularly the tryptase-positive/chymase-negative cells variety, along with increased levels of denatured collagen compared with tissue from low–genetic risk donors. We conclude that increased mast cell infiltration of the inner choroid, degranulation, and subsequent extracellular matrix remodeling are early events in AMD pathogenesis and represent a unifying mechanistic link between Chr1- and Chr10-mediated AMD.

Aedes albopictus salivary proteins adenosine deaminase and 34k2 interact with human mast cell specific proteases tryptase and chymase

ABSTRACT When mosquitoes probe to feed blood, they inoculate a mixture of salivary molecules into vertebrate hosts’ skin causing acute inflammatory reactions where mast cell-derived mediators are involved. Mosquito saliva contains many proteins with largely unknown biological functions. Here, two Aedes albopictus salivary proteins – adenosine deaminase (alADA) and al34k2 – were investigated for their immunological impact on mast cells and two mast cell-specific proteases, the tryptase and the chymase. Mouse bone marrow-derived mast cells were challenged with increased concentrations of recombinant alADA or al34k2 for 1, 3, and 6 h, and to measure mast cell activation, the activity levels of β-hexosaminidase and tryptase and secretion of IL-6 were evaluated. In addition, a direct interaction between alADA or al34k2 with tryptase or chymase was investigated. Results show that bone marrow-derived mast cells challenged with 10 μg/ml of alADA secreted significant levels of β-hexosaminidase, tryptase, and IL-6. Furthermore, both al34k2 and alADA are cut by human tryptase and chymase. Interestingly, al34k2 dose-dependently enhance enzymatic activity of both tryptase and chymase. In contrast, while alADA enhances the enzymatic activity of tryptase, chymase activity was inhibited. Our finding suggests that alADA and al34k2 via interaction with mast cell-specific proteases tryptase and chymase modulate mast cell-driven immune response in the local skin microenvironment. alADA- and al34k2-mediated modulation of tryptase and chymase may also recruit more inflammatory cells and induce vascular leakage, which may contribute to the inflammatory responses at the mosquito bite site.

Carboxypeptidase A3 expression in canine mast cell tumors and tissue-resident mast cells.

Mast cell tumors (MCTs) are one of the most common cutaneous malignancies in dogs. Previous studies have reported expression of mast cell–specific proteases chymase and tryptase in canine cutaneous MCTs and in connective tissue and mucosal mast cells. In humans and rodents, mast cells express an additional specific protease, carboxypeptidase A3 (CPA3). In this article, we describe CPA3 immunoreactivity in connective tissue, visceral, mucosal, and neoplastic mast cells in dogs. Positive immunolabeling for CPA3 was observed in nonneoplastic mast cells in 20/20 formalin-fixed paraffin-embedded normal tissues (skin, liver, spleen, intestine), and in 63/63 MCTs irrespective of their histological grade. CPA3 protein expression was comparable to that of c-kit in both the nonneoplastic and neoplastic mast cells. Three distinct labeling patterns (membranous, diffuse, and focal cytoplasmic) were observed for CPA3 in MCTs. The focal cytoplasmic labeling pattern was associated with high-grade MCTs staged with the Kiupel 2-tier grading criteria. We propose CPA3 as a novel immunohistochemical marker for canine mast cells in health and disease.

The Chymase Mouse Mast Cell Protease-4 Regulates Intestinal Cytokine Expression in Mature Adult Mice Infected with Giardiaintestinalis.

Mast cells have been shown to affect the control of infections with the protozoan parasite Giardia intestinalis. Recently, we demonstrated that Giardia excretory-secretory proteins inhibited the activity of the connective tissue mast cell-specific protease chymase. To study the potential role of the chymase mouse mast cell protease (mMCP)-4 during infections with Giardia, mMCP-4+/+ and mMCP-4−/− littermate mice were gavage-infected with G. intestinalis trophozoites of the human assemblage B isolate GS. No significant changes in weight gain was observed in infected young (≈10 weeks old) mMCP-4−/− and mMCP-4+/+ littermate mice. In contrast, infections of mature adult mice (>18 weeks old) caused significant weight loss as compared to uninfected control mice. We detected a more rapid weight loss in mMCP-4−/− mice as compared to littermate mMCP-4+/+ mice. Submucosal mast cell and granulocyte counts in jejunum increased in the infected adult mMCP-4−/− and mMCP-4+/+ mice. This increase was correlated with an augmented intestinal trypsin-like and chymotrypsin-like activity, but the myeloperoxidase activity was constant. Infected mice showed a significantly lower intestinal neutrophil elastase (NE) activity, and in vitro, soluble Giardia proteins inhibited human recombinant NE. Serum levels of IL-6 were significantly increased eight and 13 days post infection (dpi), while intestinal IL-6 levels showed a trend to significant increase 8 dpi. Strikingly, the lack of mMCP-4 resulted in significantly less intestinal transcriptional upregulation of IL-6, TNF-α, IL-25, CXCL2, IL-2, IL-4, IL-5, and IL-10 in the Giardia-infected mature adult mice, suggesting that chymase may play a regulatory role in intestinal cytokine responses.

Cooperative Regulation of the Mucosal Mast Cell-Specific Protease Genes Mcpt1 and Mcpt2 by GATA and Smad Transcription Factors.

Mouse mast cell proteases (mMCP)-1 and -2 are specifically expressed in mucosal mast cells (MCs). However, the transcriptional regulation mechanism of the Mcpt1 and Mcpt2 genes induced in mucosal MCs is largely unknown. In the current study, we found that TGF-β stimulation drastically induced upregulation of Mcpt1 and Mcpt2 mRNA in mouse bone marrow-derived MCs (BMMCs). TGF-β-induced expression of Mcpt1 and Mcpt2 was markedly suppressed by transfection with small interfering RNA targeting Smad2 or Smad4 and moderately reduced by Smad3 small interfering RNA. We next examined the roles of the hematopoietic cell-specific transcription factors GATA1 and GATA2 in the expression of Mcpt1 and Mcpt2 and demonstrated that knockdown of GATA1 and GATA2 reduced the mRNA levels of Mcpt1 and Mcpt2 in BMMCs. The recruitment of GATA2 and acetylation of histone H4 of the highly conserved GATA-Smad motifs, which were localized in the distal regions of the Mcpt1 and Mcpt2 genes, were markedly increased by TGF-β stimulation, whereas the level of GATA2 binding to the proximal GATA motif was not affected by TGF-β. A reporter assay showed that TGF-β stimulation upregulated GATA2-mediated transactivation activity in a GATA-Smad motif-dependent manner. We also observed that GATA2 and Smad4 interacted in TGF-β-stimulated BMMCs via immunoprecipitation and Western blotting analysis. Taken together, these results demonstrate that TGF-β induced mMCP-1 and -2 expression by accelerating the recruitment of GATA2 to the proximal regions of the Mcpt1 and Mcpt2 genes in mucosal MCs.

Computational identification of natural product leads that inhibit mast cell chymase: an exclusive plausible treatment for Japanese encephalitis

A recent research has identified chymase, a mast cell-specific protease as an exclusive novel therapeutic target to prevent Japanese encephalitis virus (JEV) induced encephalitis. Interestingly, JEV activates mast cell specific chymase during its penetration through blood brain barrier (BBB) which eventually guide to viral encephalitis. Hence, in this study, natural chemical entities (NCE) from multiple databases (MPD3, TIPDB and MTDP) were virtually screened for their binding affinity as chymase inhibitors, a promising negotiator for prolong survival against JEV tempted encephalitis. Merged computational programs, Maestro software, QikProp, ProTox and Gromacs were applied to screen the NCEs against target receptor (PDB: 4KP0). Three hits (C00008437, C00014417 and 8141903) were identified after employing a series of sieves such as High Throughput Virtual Screening (HTVS), Standard precision (SP) and Xtra precision (XP) molecular docking simulations followed by desired pharmacokinetic-toxicity profile predictions and molecular dynamics (MD) examinations. Maestro simulations resulted in best three binding energy scores as −11.992 kcal/mol (first ranked; C00008437), −11.673 kcal/mol (second ranked; C00014417) and −11.456 kcal/mol (third ranked; 8141903), respectively. The top three hits revealed an ideal range of pharmacokinetic and toxicity descriptors values. In addition, MD simulations enabled us to confirm top hits higher selectivity toward chymase receptor. In conclusion, this might potentially represent remarkable novel classes with an effective chymase mediated treatment to combat JEV induced encephalitis, which need to justify with further detail studies.

Giardia excretory-secretory proteins modulate the enzymatic activities of mast cell chymase and tryptase

BackgroundMast cells are involved in the host immune response controlling infection with the non-invasive intestinal protozoan parasite Giardia intestinalis. Experimental infections in rodents with G. intestinalis showed increased intestinal expression of mucosal and connective mast cell specific proteases suggesting that both mucosal and connective tissue mast cells are recruited and activated during infection. During infection Giardia excretory-secretory proteins (ESPs) with immunomodulatory capacity are released. However, studies investigating potential interactions between Giardia ESPs and the connective tissue mast cell specific serine proteases, i.e. human chymase and mouse mast cell protease (mMCP)-4 and, human and mouse tryptase (mMCP-6) remain scarce. ResultsWe first investigated if soluble Giardia proteins (sGPs), which over-lap extensively in protein content with ESP fractions, from the isolates GS, WB and H3, could induce mast cell activation. sGPs induced a minor activation of bone marrow derived mucosal-like mast cells, as indicated by increased IL-6 secretion and no degranulation. Furthermore, sGPs were highly resistant to degradation by human tryptase while human chymase degraded a 65 kDa sGP and, wild-type mouse ear tissue extracts degraded several protein bands in the 10 to 75 kDa range. In striking contrast, sGPs and ESPs were found to increase the enzymatic activity of human and mouse tryptase and to reduce the activity of human and mouse chymase. ConclusionOur finding suggests that Giardia ssp. via enhancement or reduction of mast cell protease activity may modulate mast cell-driven intestinal immune responses. ESP-mediated modulation of the mast cell specific proteases may also increase degradation of tight junctions, which may be beneficial for Giardia ssp. during infection.

Mast Cells: Key Contributors to Cardiac Fibrosis.

Historically, increased numbers of mast cells have been associated with fibrosis in numerous cardiac pathologies, implicating mast cells in the development of cardiac fibrosis. Subsequently, several approaches have been utilised to demonstrate a causal role for mast cells in animal models of cardiac fibrosis including mast cell stabilising compounds, rodents deficient in mast cells, and inhibition of the actions of mast cell-specific proteases such as chymase and tryptase. Whilst most evidence supports a pro-fibrotic role for mast cells, there is evidence that in some settings these cells can oppose fibrosis. A major gap in our current understanding of cardiac mast cell function is identification of the stimuli that activate these cells causing them to promote a pro-fibrotic environment. This review will present the evidence linking mast cells to cardiac fibrosis, as well as discuss the major questions that remain in understanding how mast cells contribute to cardiac fibrosis.

Abstract A64: Mast cell expressed FcεR beta subunit (MS4A2) is prognostic in lung adenocarcinoma

Abstract Background: The context of immune cell infiltrates within the tumor is associated with cancer prognosis. The type of immune cells and their activation state can provide mediators that either promote or inhibit tumor growth. A growing body of evidence suggest the presence of innate immune cells play a role in shaping early tumor growth. In attempts to gain insight into the immune networks that regulate tumorigenesis, we used genome wide expression datasets of patients with resected early stage non-small cell lung cancer (NSCLC) to identify immune-related genes associated with patient survival. Methods: Gene expression analysis was conducted on microarray datasets from 128 early-stage NSCLC adenocarcinoma resected tumor samples. Limiting analysis to immune-related genes, we identified a minimum gene set that is prognostic for lung adenocarcinoma and validated the gene signature in additional published microarray NSCLC datasets. Using pathway analysis and immunohistochemistry (IHC), we identified a role for mast cell-expressed IgE receptor beta subunit, MS4A2, in lung adenocarcinoma progression. Results: From an immune-related gene list, we identified a minimal gene signature that was able to separate patients into high or low-risk survival groups. This gene signature was shown to be prognostic for NSCLC adenocarcinoma in nine validation datasets (n=1264, hazard ratio 2.07, 95% confidence interval 1.69-2.53, p<0.0001). Pathway analysis of differentially expressed genes within high or low-risk survival subgroups reveals gene ontologies and immune signatures that are enriched for IgE receptor signaling and mast cells in patients with favourable prognosis. Univariate analysis shows that the IgE receptor complex genes, as well as mast cell specific protease, mast cell carboxypeptidase A, are highly prognostic for survival. We are currently using IHC of matched patient samples to validate receptor localization. Conclusion: By limiting gene expression analysis to immune-related genes, we identified a minimal gene set that indicate an important role for IgE receptor signaling and mast cells in favourable lung cancer prognosis. Our data highlights the importance of innate immune cells in shaping lung cancer development. Citation Format: Dalam Ly, Chang-Qi Zhu, Michael Cabanero, Ming-Sound Tsao, Li Zhang. Mast cell expressed FcεR beta subunit (MS4A2) is prognostic in lung adenocarcinoma. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2016 Oct 20-23; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2017;5(3 Suppl):Abstract nr A64.

The combined action of mast cell chymase, tryptase and carboxypeptidase A3 protects against melanoma colonization of the lung.

Mast cell secretory granules are densely packed with various bioactive mediators including proteases of chymase, tryptase and CPA3 type. Previous studies have indicated that mast cells can affect the outcome of melanoma but the contribution of the mast cell granule proteases to such effects has not been clear. Here we addressed this issue by assessing mice lacking either the chymase Mcpt4, the tryptase Mcpt6 or carboxypeptidase A3 (Cpa3), as well as mice simultaneously lacking all three proteases, in a model of melanoma dissemination from blood to the lung. Although mice with individual deficiency in the respective proteases did not differ significantly from wildtype mice in the extent of melanoma colonization, mice with multiple protease deficiency (Mcpt4/Mcpt6/Cpa3-deficient) exhibited a higher extent of melanoma colonization in lungs as compared to wildtype animals. This was supported by higher expression of melanoma-specific genes in lungs of Mcpt4/Mcpt6/CPA3-deficient vs. wildtype mice. Cytokine profiling showed that the levels of CXCL16, a chemokine with effects on T cell populations and NKT cells, were significantly lower in lungs of Mcpt4/Mcpt6/Cpa3-deficient animals vs. controls, suggesting that multiple mast cell protease deficiency might affect T cell or NKT cell populations. In line with this, we found that the Mcpt4/Mcpt6/Cpa3-deficiency was associated with a reduction in cells expressing CD1d, a MHC class 1-like molecule that is crucial for presenting antigen to invariant NKT (iNKT) cells. Together, these findings indicate a protective role of mast cell-specific proteases in melanoma dissemination, and suggest that this effect involves a CXCL16/CD1d/NKT cell axis.

Mast Cell Degranulation Is Accompanied by the Release of a Selective Subset of Extracellular Vesicles That Contain Mast Cell-Specific Proteases.

Mast cells (MC) are well known for their effector role in allergic disorders; moreover, they are associated with diverse modulatory effects in innate and adaptive immunity. It is largely unclear how MC exert these modulating functions. In this article, we show that IgE-mediated MC degranulation leads to a rapid release of high quantities of extracellular vesicles (EV), comparable to the release of preformed mediators. EV are submicron structures composed of lipid bilayers, proteins, and nucleic acids that are released by cells in a regulated fashion and are involved in intercellular communication. Primary murine mucosal-type MC and connective tissue-type MC released phenotypically different EV populations depending on the stimulus they received. Although unstimulated MC constitutively released CD9+ EV, degranulation was accompanied by the release of CD63+ EV, which correlated with release of the soluble mediator β-hexosaminidase. This CD63+ EV subset was smaller and exhibited a higher buoyant density and distinct phospholipid composition compared with CD9+ EV. Marked differences were observed for phosphatidylinositol, phosphatidic acid, and bis(monoacylglycero)phosphate species. Strikingly, proteomic analysis of CD63+ EV from connective tissue-type MC unveiled an abundance of MC-specific proteases. With regard to carboxypeptidase A3, it was confirmed that the enzyme was EV associated and biologically active. Our data demonstrate that, depending on their activation status, MC release distinct EV subsets that differ in composition and protease activity and are indicative of differential immunological functions. Concerning the strategic tissue distribution of MC and the presence of degranulated MC in various (allergic) disorders, MC-derived EV should be considered potentially important immune regulators.

Wnt-β-Catenin Signaling Promotes the Maturation of Mast Cells.

Mast cells play an important role in the pathogenesis of allergic diseases. Immature mast cells migrate into peripheral tissues from the bone marrow and undergo complete maturation. Interestingly, mast cells have characteristics similar to hematopoietic stem cells (HSCs), such as self-renewal and c-kit expression. In HSCs, Wnt signaling is involved in their maintenance and differentiation. On the other hand, the relation between Wnt signaling and mast cell differentiation is poorly understood. To study whether Wnt signals play a role in the maturation of mast cells, we studied the effect of Wnt proteins on mast cell maturation of bone marrow-derived mast cells (BMMCs). The expression levels of CD81 protein and histidine decarboxylase mRNA and activity of mast cell-specific protease were all elevated in BMMCs treated with Wnt5a. In addition, Wnt5a induced the expression of Axin2 and TCF mRNA in BMMCs. These results showed that Wnt5a could promote the maturation of mast cells via the canonical Wnt signaling pathway and provide important insights into the molecular mechanisms underlying the differentiation of mast cells.

Distinguishing Mast Cell Progenitors from Mature Mast Cells in Mice.

Mast cells originate from the bone marrow and develop into c-kit+ FcɛRI+ cells. Both mast cell progenitors (MCp) and mature mast cells express these cell surface markers, and ways validated to distinguish between the two maturation forms with flow cytometry have been lacking. Here, we show that primary peritoneal MCp from naïve mice expressed high levels of integrin β7 and had a low side scatter (SSC) light profile; whereas mature mast cells expressed lower levels of integrin β7 and had a high SSC light profile. The maturation statuses of the cells were confirmed using three main strategies: (1) MCp, but not mature mast cells, were shown to be depleted by sublethal whole-body γ-irradiation. (2) The MCp were small and immature in terms of granule formation, whereas the mature mast cells were larger and had fully developed metachromatic granules. (3) The MCp had fewer transcripts of mast cell-specific proteases and the enzyme responsible for sulfation of heparin than mature mast cells. Moreover, isolated peritoneal MCp gave rise to mast cells when cultured in vitro. To summarize, we have defined MCp and mature mast cells in naïve mice by flow cytometry. Using this strategy, mast cell maturation can be studied in vivo.

The Role of Mast Cell Specific Chymases and Tryptases in Tumor Angiogenesis.

An association between mast cells and tumor angiogenesis is known to exist, but the exact role that mast cells play in this process is still unclear. It is thought that the mediators released by mast cells are important in neovascularization. However, it is not known how individual mediators are involved in this process. The major constituents of mast cell secretory granules are the mast cell specific proteases chymase, tryptase, and carboxypeptidase A3. Several previous studies aimed to understand the way in which specific mast cell granule constituents act to induce tumor angiogenesis. A body of evidence indicates that mast cell proteases are the pivotal players in inducing tumor angiogenesis. In this review, the likely mechanisms by which tryptase and chymase can act directly or indirectly to induce tumor angiogenesis are discussed. Finally, information presented here in this review indicates that mast cell proteases significantly influence angiogenesis thus affecting tumor growth and progression. This also suggests that these proteases could serve as novel therapeutic targets for the treatment of various types of cancer.

Cinnamaldehyde is the main mediator of cinnamon extract in mast cell inhibition.

In terms of their involvement in allergic and inflammatory conditions, mast cells (MC) can be promising targets for medical agents in therapy. Because of their good compliance and effectiveness, phytochemicals are of great interest as new therapeutic tools in form of nutraceuticals. We found recently that cinnamon extract (CE) inhibits mast cell activation. Here, we analysed the effects of a major compound of CE, cinnamaldehyde (CA), on mast cell activation. Release of prestored and de novo synthesised mediators as well as expression of pro-inflammatory cytokines and mast cell-specific proteases were analysed in RBL-2H3 cells or in human mast cells isolated from intestinal tissue (hiMC) treated with CA prior to stimulation by FcεRI crosslinking or IONO/PMA. The results were compared with the corresponding effects of CE. Following treatment with CA, release of β-hexosaminidase in IgE-dependent or IgE-independent activated RBL-2H3 cells was down-regulated in a dose-dependent manner to about 10%. In hiMC, release of β-hexosaminidase was also significantly reduced, and release of LTC4 and CXCL8 was almost completely inhibited by CA. Moreover, IgE-mediated expression of CXCL8, CCL2, CCL3 and CCL4 in hiMC was significantly down-regulated by CA. With the exception of the expression of the mast cell proteases tryptase and chymase, the inhibitory effects of CA were very similar to the effects shown for CE treatment. The reducing effect of CA on mast cell mediators-seen for long- and for short-term incubations-could be related to particular signalling pathways as CA caused a down-regulation in ERK as well as PLCγ1 phosphorylation. CA decreases release and expression of pro-inflammatory mast cell mediators. This inhibitory action is similar to the effects observed for CE indicating CA as the main active compound in CE leading to its anti-allergic properties.

Granzyme H Is a Novel Protease Expressed by Human Mast Cells

Background: Many of the functions attributed to mast cells depend on the various pro-inflammatory mediators that are secreted upon mast cell activation. These include a panel of mast cell-specific proteases. In addition, recent studies have indicated that murine mast cells also express granzyme D, a protease previously thought to be confined to cytotoxic lymphocytes. Here, we address the human relevance of the latter findings by investigating whether human mast cells express granzyme H, the granzyme that may represent the functional counterpart to murine granzyme D. Methods: Cord blood-derived mast cells, LAD2 cells and skin mast cells in situ were evaluated for their expression of granzymes using quantitative PCR, Western blot analysis and immunostaining. Mast cells were activated by either calcium ionophore stimulation or IgE receptor cross-linking. Results: Cord blood-derived mast cells and LAD2 cells were shown to express granzyme H and B mRNA, while granzyme A, K and M expression was undetectable. Mast cell activation by either calcium ionophore or IgE receptor cross-linking caused down-regulated expression of granzyme H. In contrast, granzyme B expression was up-regulated by the same stimuli. Granzyme H expression was also confirmed at the protein level, as shown by both Western blot analysis and confocal microscopy. Further, we show that granzyme H is expressed by human skin mast cells in situ. Conclusions: The present findings implicate granzyme H as a novel protease expressed by human mast cells and support earlier findings obtained in natural killer cells suggesting that granzymes B and H are reciprocally regulated.