Histamine synthesis is required for granule maturation in murine mast cells

Crosstalk between Regnase-1 and -3 shapes mast cell survival and cytokine expression

Post-transcriptional regulation of immune-related transcripts by RNA-binding proteins (RBPs) impacts immune cell responses, including mast cell functionality. Despite their importance in immune regulation, the functional role of most RBPs remains to be understood. By manipulating the expression of specific RBPs in murine mast cells, coupled with mass spectrometry and transcriptomic analyses, we found that the Regnase family of proteins acts as a potent regulator of mast cell physiology. Specifically, Regnase-1 is required to maintain basic cell proliferation and survival, whereas both Regnase-1 and -3 cooperatively regulate the expression of inflammatory transcripts upon activation, with Tnf being a primary target in both human and mouse cells. Furthermore, Regnase-3 directly interacts with Regnase-1 in mast cells and is necessary to restrain Regnase-1 expression through the destabilization of its transcript. Overall, our study identifies protein interactors of endogenously expressed Regnase factors, characterizes the regulatory interplay between Regnase family members in mast cells, and establishes their role in the control of mast cell homeostasis and inflammatory responses.

Recruitment or activation of mast cells in the liver aggravates the accumulation of fibrosis in carbon tetrachloride-induced liver injury

Liver diseases caused by viral infections, alcoholism, drugs, or chemical poisons are a significant health problem: Liver diseases are a leading contributor to mortality, with approximately 2 million deaths per year worldwide. Liver fibrosis, as a common liver disease characterized by excessive collagen deposition, is associated with high morbidity and mortality, and there is no effective treatment. Numerous studies have shown that the accumulation of mast cells (MCs) in the liver is closely associated with liver injury caused by a variety of factors. This study investigated the relationship between MCs and carbon tetrachloride (CCl4)-induced liver fibrosis in rats and the effects of the MC stabilizers sodium cromoglycate (SGC) and ketotifen (KET) on CCl4-induced liver fibrosis. The results showed that MCs were recruited or activated during CCl4-induced liver fibrosis. Coadministration of SCG or KET alleviated the liver fibrosis by decreasing SCF/c-kit expression, inhibiting the TGF-β1/Smad2/3 pathway, depressing the HIF-1a/VEGF pathway, activating Nrf2/HO-1 pathway, and increasing the hepatic levels of GSH, GSH-Px, and GR, thereby reducing hepatic oxidative stress. Collectively, recruitment or activation of MCs is linked to liver fibrosis and the stabilization of MCs may provide a new approach to the prevention of liver fibrosis.

Diterpenoid WT-29 isolated from Wedelia exerted anti-inflammatory and anti-allergic activities

ETHNOPHARMACOLOGICAL RELEVANCE

Wedelia (Sphagneticola trilobata) is a traditional anti-inflammatory herb native to tropical America. It is commonly used to treat some inflammatory related diseases clinically, such as pertussis, pharyngitis, etc. However, its specific anti-inflammatory mechanism is still unclear.

AIM OF THE STUDY

WT-29 (3α-angeloyloxy-9β-hydroxyent-kaura-16-en-19-oic acid) is a main bioactive diterpenoid isolated and purified from Wedelia. This study aims to explore the potential anti-inflammatory and anti-allergic properties of WT-29 on RAW264.7 cells stimulated with LPS and P815 cells induced by C48/80, as well as investigating their underlying molecular mechanisms.

METHODS

The anti-inflammatory mechanism of WT-29 was analyzed and predicted using network pharmacology, and then verified through experiments. The Griess reagent assay was employed to evaluate the impact of WT-29 on the generation of nitric oxide (NO) in RAW264.7 cells induced by LPS, the expression of various inflammatory cytokines and the release of histamine in cells were measured through qRT-PCR and ELISA techniques. The impact of WT-29 on the translocation of the NF-κB p65 protein to the nucleus was assessed through immunofluorescence staining. Western blot technique was utilized to investigate protein expression in inflammation, allergy, and autophagy pathways.

RESULTS

The study found that WT-29 can reduce the secretion of inflammatory factors (NO, iNOS, COX-2, IL-6, IL-1β and TNF-α), inhibit NF-κB activation and MAPK family phosphorylation, and induce autophagy in RAW264.7 cells stimulated with LPS. In addition, it demonstrated that WT-29 could inhibit histamine release and degranulation, as well as inhibit the MAPK family in C48/80-induced P815 cells.

CONCLUSION

WT-29 isolated from Wedelia exerts anti-inflammatory and anti-allergic effects mainly through NF-κB, Nrf2/Keap-1, MAPK pathways and regulating of autophagy, suggesting that it might be a potential anti-inflammatory and anti-allergic agent and could be used as medicine or health benefit product.

Stabilizing histamine release in gut mast cells mitigates peripheral and central inflammation after stroke

Stroke is the most common cause of long-term disability and places a high economic burden on the global healthcare system. Functional outcomes from stroke are largely determined by the extent of ischemic injury, however, there is growing recognition that systemic inflammatory responses also contribute to outcomes. Mast cells (MCs) rapidly respond to injury and release histamine (HA), a pro-inflammatory neurotransmitter that enhances inflammation. The gut serves as a major reservoir of HA. We hypothesized that cromolyn, a mast cell stabilizer that prevents the release of inflammatory mediators, would decrease peripheral and central inflammation, reduce MC trafficking to the brain, and improve stroke outcomes. We used the transient middle cerebral artery occlusion (MCAO) model of ischemic stroke in aged (18 mo) male mice to investigate the role of MC in neuroinflammation post-stroke. After MCAO we treated mice with 25 mg/kg body weight of cromolyn (MC stabilizer) by oral gavage. Cromolyn was administered at 3 h, 10 h, 24 h and every 24 h for 3 days post-stroke. Three control groups were used. One group underwent a sham surgery and was treated with cromolyn, one received sham surgery with PBS vehicle and the third underwent MCAO with PBS vehicle. Mice were euthanized at 24 h and 3 days post-stroke. Cromolyn administration significantly reduced MC numbers in the brain at both 24 h and 3 days post-stroke. Infarct volume was not significantly different between groups, however improved functional outcomes were seen at 3 days post-stroke in mice that received cromolyn. Treatment with cromolyn reduced plasma histamine and IL-6 levels in both the 24-h and 3-day cohorts. Gut MCs numbers were significantly reduced after cromolyn treatment at 24 h and 3 days after stroke. To determine if MC trafficking from the gut to the brain occurred after injury, GFP+MCs were adoptively transferred to c-kit-/- MC knock-out animals prior to MCAO. 24 h after stroke, elevated MC recruitment was seen in the ischemic brain. Preventing MC histamine release by cromolyn improved gut barrier integrity and an improvement in stroke-induced dysbiosis was seen with treatment. Our results show that preventing MC histamine release possesses prevents post-stroke neuroinflammation and improves neurological and functional outcomes.

IRF3 Activation in Mast Cells Promotes FcεRI-Mediated Allergic Inflammation

(1) Background: This study aims to elucidate a novel non-transcriptional action of IRF3 in addition to its role as a transcription factor in mast cell activation and associated allergic inflammation; (2) Methods: For in vitro experiments, mouse bone-marrow-derived mast cells (mBMMCs) and a rat basophilic leukemia cell line (RBL-2H3) were used for investigating the underlying mechanism of IRF3 in mast-cell-mediated allergic inflammation. For in vivo experiments, wild-type and Irf3 knockout mice were used for evaluating IgE-mediated local and systemic anaphylaxis; (3) Results: Passive cutaneous anaphylaxis (PCA)-induced tissues showed highly increased IRF3 activity. In addition, the activation of IRF3 was observed in DNP-HSA-treated mast cells. Phosphorylated IRF3 by DNP-HSA was spatially co-localized with tryptase according to the mast cell activation process, and FcεRI-mediated signaling pathways directly regulated that activity. The alteration of IRF3 affected the production of granule contents in the mast cells and the anaphylaxis responses, including PCA- and ovalbumin-induced active systemic anaphylaxis. Furthermore, IRF3 influenced the post-translational processing of histidine decarboxylase (HDC), which is required for granule maturation; and (4) Conclusion: Through this study, we demonstrated the novel function of IRF3 as an important factor inducing mast cell activation and as an upstream molecule for HDC activity.

Role of Marine Bacterial Contaminants in Histamine Formation in Seafood Products: A Review

Histamine is a toxic biogenic amine commonly found in seafood products or their derivatives. This metabolite is produced by histamine-producing bacteria (HPB) such as Proteus vulgaris, P. mirabilis, Enterobacter aerogenes, E. cloacae, Serratia fonticola, S. liquefaciens, Citrobacter freundii, C. braakii, Clostridium spp., Raoultella planticola, R. ornithinolytica, Vibrio alginolyticus, V. parahaemolyticus, V. olivaceus, Acinetobacter lowffi, Plesiomonas shigelloides, Pseudomonas putida, P. fluorescens, Aeromonas spp., Photobacterium damselae, P. phosphoreum, P. leiognathi, P. iliopiscarium, P. kishitanii, and P. aquimaris. In this review, the role of these bacteria in histamine production in fish and seafood products with consequences for human food poisoning following consumption are discussed. In addition, methods to control their activity in countering histamine production are proposed.

Carboxypeptidase A3 in the structure of the protease phenotype of mast cells: cytophysiological aspects

Carboxypeptidase A3 (CPA3) is a specific protease of mast cells (MC) with variable expression and appears to be one of the preformed components of the secretome. CPA3 is involved in regulation of the state of a specifi tissue microenvironment and components of the integrative-buffer metabolic environment in adaptive and pathological processes; it affects implementation of the innate immunity, mechanisms of angiogenesis, processes of the extracellular matrix remodeling, etc. CPA3 identification using protocols of multiplex immunohistochemistry allows specifying details of the organ-specific mast cell population features, including the protease phenotype, mechanisms of biogenesis with cytoand histotopographic criteria, and features of secretory pathways. Numerous biological effects of CPA3, including participation in the regulation of the pulmonary parenchyma and systemic blood flow, in biogenesis and remodeling of the fibrous component of the extracellular matrix, in epigenetic reprogramming, determine the importance of fundamental investigation of the physiological activity of protease and its involvement in the implementation of pathological processes. Further studies will contribute to the detection of the translational value of the mast cell CPA3 expression features as a prognostic factor and a promising molecular target for treatment of socially significant diseases.

Carboxypeptidase A3 in the structure of the protease phenotype of mast cells: cytophysiological aspects

Carboxypeptidase A3 (CPA3) is a specific protease of mast cells (MC) with variable expression and appears to be one of the preformed components of the secretome. CPA3 is involved in regulation of the state of a specifi tissue microenvironment and components of the integrative-buffer metabolic environment in adaptive and pathological processes; it affects implementation of the innate immunity, mechanisms of angiogenesis, processes of the extracellular matrix remodeling, etc. CPA3 identification using protocols of multiplex immunohistochemistry allows specifying details of the organ-specific mast cell population features, including the protease phenotype, mechanisms of biogenesis with cyto- and histotopographic criteria, and features of secretory pathways. Numerous biological effects of CPA3, including participation in the regulation of the pulmonary parenchyma and systemic blood flow, in biogenesis and remodeling of the fibrous component of the extracellular matrix, in epigenetic reprogramming, determine the importance of fundamental investigation of the biological activity and regulation of pathological processes of CPA3. Further studies will contribute to the detection of the true value of the mast cell CPA3 expression features as a prognostic factor and a promising molecular target for treatment of socially significant diseases.

Carboxypeptidase A3—A Key Component of the Protease Phenotype of Mast Cells

Carboxypeptidase A3 (CPA3) is a specific mast cell (MC) protease with variable expression. This protease is one of the preformed components of the secretome. During maturation of granules, CPA3 becomes an active enzyme with a characteristic localization determining the features of the cytological and ultrastructural phenotype of MC. CPA3 takes part in the regulation of a specific tissue microenvironment, affecting the implementation of innate immunity, the mechanisms of angiogenesis, the processes of remodeling of the extracellular matrix, etc. Characterization of CPA3 expression in MC can be used to refine the MC classification, help in a prognosis, and increase the effectiveness of targeted therapy.

Roles of IgE and Histamine in Mast Cell Maturation

Mast cells are activated upon immunoglobulin E (IgE)-mediated antigen stimulation, and release a wide variety of mediators, including histamine to trigger inflammatory responses. The surface expression levels of Fcε receptor I (FcεRI), a high affinity receptor of IgE, were found to be positively regulated by IgE. IgE could protect murine cultured mast cells from apoptotic cell death induced by the deprivation of interleukin-3 and a certain kind of IgE could activate immature mast cells in the absence of antigens, leading to the release of pro-inflammatory cytokines and a transient increase in histamine synthesis. Histamine synthesis in mast cells was found to be required for the maturation of murine connective tissue-type mast cells, raising the possibility that IgE indirectly modulates local mast cell maturation. Although it remains controversial to what extent this concept of "monomeric IgE effects" could have relevance in the modulation of human mast cell functions, the therapeutic effects of anti-IgE antibodies might be accounted for in terms of the decreased serum IgE concentrations. Because drastic increases in serum IgE concentrations are often observed in patients with atopic dermatitis and chronic urticaria, a close investigation of the roles of IgE in mast cell maturation should contribute to development of novel therapeutic approaches for these inflammatory diseases.

Genetic Regulation of Tryptase Production and Clinical Impact: Hereditary Alpha Tryptasemia, Mastocytosis and Beyond

Tryptase is a serine protease that is predominantly produced by tissue mast cells (MCs) and stored in secretory granules together with other pre-formed mediators. MC activation, degranulation and mediator release contribute to various immunological processes, but also to several specific diseases, such as IgE-dependent allergies and clonal MC disorders. Biologically active tryptase tetramers primarily derive from the two genes TPSB2 (encoding β-tryptase) and TPSAB1 (encoding either α- or β-tryptase). Based on the most common gene copy numbers, three genotypes, 0α:4β, 1α:3β and 2α:2β, were defined as “canonical”. About 4–6% of the general population carry germline TPSAB1-α copy number gains (2α:3β, 3α:2β or more α-extra-copies), resulting in elevated basal serum tryptase levels. This condition has recently been termed hereditary alpha tryptasemia (HαT). Although many carriers of HαT appear to be asymptomatic, a number of more or less specific symptoms have been associated with HαT. Recent studies have revealed a significantly higher HαT prevalence in patients with systemic mastocytosis (SM) and an association with concomitant severe Hymenoptera venom-induced anaphylaxis. Moreover, HαT seems to be more common in idiopathic anaphylaxis and MC activation syndromes (MCAS). Therefore, TPSAB1 genotyping should be included in the diagnostic algorithm in patients with symptomatic SM, severe anaphylaxis or MCAS.

Neutrophil serine protease 4 is required for mast cell-dependent vascular leakage

Vascular leakage, or edema, is a serious complication of acute allergic reactions. Vascular leakage is triggered by the release of histamine and serotonin from granules within tissue-resident mast cells. Here, we show that expression of Neutrophil Serine Protease 4 (NSP4) during the early stages of mast cell development regulates mast cell-mediated vascular leakage. In myeloid precursors, the granulocyte-macrophage progenitors (GMPs), loss of NSP4 results in the decrease of cellular levels of histamine, serotonin and heparin/heparan sulfate. Mast cells that are derived from NSP4-deficient GMPs have abnormal secretory granule morphology and a sustained reduction in histamine and serotonin levels. Consequently, in passive cutaneous anaphylaxis and acute arthritis models, mast cell-mediated vascular leakage in the skin and joints is substantially reduced in NSP4-deficient mice. Our findings reveal that NSP4 is required for the proper storage of vasoactive amines in mast cell granules, which impacts mast cell-dependent vascular leakage in mouse models of immune complex-mediated diseases.

Mast cell activation markers for in vitro study

Mast cells (MCs) are well known for their role in allergic conditions. This cell can be activated by various types of secretagogues, ranging from a small chemical to a huge protein. Mast cell activation by secretagogues triggers the increase in intracellular calcium (iCa²⁺) concentration, granule trafficking, and exocytosis. Activated mast cells release their intra-granular pre-stored mediator or the newly synthesized mediator in the exocytosis process, in the form of degranulation or secretion. There are at least three types of exocytosis in mast cells, which are suggested to contribute to the release of different mediators, i.e.,, piecemeal, kiss-and-run, and compound exocytosis. The status of mast cells, i.e., activated or resting, is often determined by measuring the concentration of the released mediator such as histamine or β-hexosaminidase. This review summarizes several mast cell components that have been and are generally used as mast cell activation indicator, from the classical histamine and β-hexosaminidase measurement, to eicosanoid and granule trafficking observation. Basic principle of the component determination is also explained with their specified research application and purpose. The information will help to predict the experiment results with a certain study design.

Age-dependent involvement of gut mast cells and histamine in post-stroke inflammation

BACKGROUND

Risk of stroke-related morbidity and mortality increases significantly with age. Aging is associated with chronic, low-grade inflammation, which is thought to contribute to the poorer outcomes after stroke seen in the elderly. Histamine (HA) is a major molecular mediator of inflammation, and mast cells residing in the gut are a primary source of histamine.

METHODS

Stroke was induced in male C57BL/6 J mice at 3 months (young) and 20 months (aged) of age. Role of histamine after stroke was examined using young (Yg) and aged (Ag) mice; mice underwent MCAO surgery and were euthanized at 6 h, 24 h, and 7 days post-ischemia; sham mice received the same surgery but no MCAO. In this work, we evaluated whether worsened outcomes after experimental stroke in aged mice were associated with age-related changes in mast cells, histamine levels, and histamine receptor expression in the gut, brain, and plasma.

RESULTS

We found increased numbers of mast cells in the gut and the brain with aging. Using the middle cerebral artery occlusion (MCAO) model of ischemic stroke, we demonstrate that stroke leads to increased numbers of gut mast cells and gut histamine receptor expression levels. These gut-centric changes are associated with elevated levels of HA and other pro-inflammatory cytokines including IL-6, G-CSF, TNF-α, and IFN-γ in the peripheral circulation. Our data also shows that post-stroke gut inflammation led to a significant reduction of mucin-producing goblet cells and a loss of gut barrier integrity. Lastly, gut inflammation after stroke is associated with changes in the composition of the gut microbiota as early as 24-h post-stroke.

CONCLUSION

An important theme emerging from our results is that acute inflammatory events following ischemic insults in the brain persist longer in the aged mice when compared to younger animals. Taken together, our findings implicate mast cell activation and histamine signaling as a part of peripheral inflammatory response after ischemic stroke, which are profound in aged animals. Interfering with histamine signaling orally might provide translational value to improve stroke outcome.

Characterization of mast cell-derived rRNA-containing microvesicles and their inflammatory impact on endothelial cells

Tissue-resident mast cells (MCs) are well known for their role in inflammatory responses and allergic and anaphylactic reactions, but they also contribute to processes of arterial remodeling. Although ribosomes and cytosolic RNAs are located around secretory granules in mature MCs, their functional role in MC responses remains unexplored. Previous studies by our group characterized extracellular RNA (eRNA) as an inflammatory and pathogenetic factor in vitro and in vivo. In the present study, RNA-containing MCs and eRNA were located in close proximity to growing collateral arteries in vivo. In vitro, various agonists were found to induce the degranulation of MCs and the concomitant release of eRNA in association with microvesicles (MVs). The liberation of eRNA from MCs was abolished by MC stabilizers or by preventing the increase of intracellular Ca²⁺ in MCs. eRNA was found to be mainly contained inside MVs, as demonstrated by electron microscopy and immunocytochemistry. The exposure to and the uptake of MC-released MVs by cultured endothelial cells increased their expression of cytokines, such as monocyte chemoattractant protein or IL-6, in a dose- and time-dependent manner. These results indicate that RNA-containing MC-derived MVs are likely to be involved in inflammatory responses, relevant, for example, to processes of vascular remodeling.-Elsemüller, A.-K., Tomalla, V., Gärtner, U., Troidl, K., Jeratsch, S., Graumann, J., Baal, N., Hackstein, H., Lasch, M., Deindl, E., Preissner, K. T., Fischer, S. Characterization of mast cell-derived rRNA-containing microvesicles and their inflammatory impact on endothelial cells.

Lysosome biogenesis regulated by the amino-acid transporter SLC15A4 is critical for functional integrity of mast cells

Mast cells possess specialized lysosomes, so-called secretory granules, which play a key role not only in allergic responses but also in various immune disorders. The molecular mechanisms that control secretory-granule formation are not fully understood. Solute carrier family member 15A4 (SLC15A4) is a lysosome-resident amino-acid/oligopeptide transporter that is preferentially expressed in hematopoietic lineage cells. Here, we demonstrated that SLC15A4 is required for mast-cell secretory-granule homeostasis, and limits mast-cell functions and inflammatory responses by controlling the mTORC1-TFEB signaling axis. In mouse Slc15a4-/- mast cells, diminished mTORC1 activity increased the expression and nuclear translocation of TFEB, a transcription factor, which caused secretory granules to degranulate more potently. This alteration of TFEB function in mast cells strongly affected the FcεRI-mediated responses and IL-33-triggered inflammatory responses both in vitro and in vivo. Our results reveal a close relationship between SLC15A4 and secretory-granule biogenesis that is critical for the functional integrity of mast cells.

Expression of Histidine Decarboxylase and Its Roles in Inflammation

Histamine is a well-known mediator of inflammation that is released from mast cells and basophils. To date, many studies using histamine receptor antagonists have shown that histamine acts through four types of receptors: H1, H2, H3, and H4. Thus, histamine plays more roles in various diseases than had been predicted. However, our knowledge about histamine-producing cells and the molecular mechanisms underlying histamine production at inflammatory sites is still incomplete. The histamine producing enzyme, histidine decarboxylase (HDC), is commonly induced at inflammatory sites during the late and chronic phases of both allergic and non-allergic inflammation. Thus, histamine levels in tissues are maintained at effective concentrations for hours, enabling the regulation of various functions through the production of cytokines/chemokines/growth factors. Understanding the regulation of histamine production will allow the development of a new strategy of using histamine antagonists to treat inflammatory diseases.

Molecular Regulation of Histamine Synthesis

Histamine is a critical mediator of IgE/mast cell-mediated anaphylaxis, a neurotransmitter and a regulator of gastric acid secretion. Histamine is a monoamine synthesized from the amino acid histidine through a reaction catalyzed by the enzyme histidine decarboxylase (HDC), which removes carboxyl group from histidine. Despite the importance of histamine, transcriptional regulation of HDC gene expression in mammals is still poorly understood. In this review, we focus on discussing advances in the understanding of molecular regulation of mammalian histamine synthesis.

High-throughput screening system for dynamic monitoring of exocytotic vesicle trafficking in mast cells

Mast cells, in addition to endocrine cells and neurons, are typical secretory cells. Their function in allergic inflammation is to secrete inflammatory mediators from secretory vesicles. Intracellular synthesized inflammatory mediators are transported by vesicular monoamine transporters (VMATs) to vesicles where they are stored. After stimulation, the contents of the secretory vesicles are released via exocytosis. This study established a high throughput imaging screening system to monitor the functions of secretory vesicles in mast cells, including molecular uptake via VMAT2 and the exocytotic process, by using a novel fluorescent probe, FFN206, which was developed as a VMAT2 substrate. After loading with FFN206, the rapid uptake of FFN206 was observed and secretory vesicles in mouse bone marrow derived mast cells and a cultured mast cell line were clearly visualized. FFN206 uptake by secretory vesicles was time-dependent and was blocked by reserpine. Furthermore, exocytotic trafficking was monitored dynamically by real-time high-throughput fluorescence quantitation. In the present study, we verified the application of FFN206 for the monitoring of functional vesicles. This high-throughput screening system may benefit instinctive drug evaluation.

The transcription factors GATA2 and microphthalmia-associated transcription factor regulate Hdc gene expression in mast cells and are required for IgE/mast cell-mediated anaphylaxis

BACKGROUND

Histamine is a critical mediator of IgE/mast cell-mediated anaphylaxis. Histamine is synthesized by decarboxylating the amino acid histidine, a reaction catalyzed by the histidine decarboxylase (Hdc) gene-encoded enzyme HDC. However, regulation of the Hdc gene in mast cells is poorly understood.

OBJECTIVE

We sought to investigate the in vivo regulation of IgE/mast cell-mediated anaphylaxis by the transcription factors GATA2 and microphthalmia-associated transcription factor (MITF) and the mechanisms by which GATA2 and MITF regulate Hdc gene expression in mouse and human mast cells.

METHODS

Mice deficient in the transcription factors Gata2, aryl hydrocarbon receptor (Ahr), aryl hydrocarbon receptor repressor (Ahrr), or basic helix-loop-helix family member E40 (Bhlhe40) were assessed for anaphylactic reactions. Chromatin immunoprecipitation sequencing analysis identified putative Hdc enhancers. Luciferase reporter transcription assay confirmed enhancer activities of putative enhancers in the Hdc gene. The short hairpin RNA knockdown approach was used to determine the role of MITF in regulating mouse and human HDC gene expression.

RESULTS

Connective tissue mast cell-specific Gata2-deficient mice did not have IgE/mast cell-mediated anaphylaxis. GATA2 induced the expression of Mitf, Ahr, Ahrr, and Bhlhe40 in mast cells. MITF, but not AHR, AHRR, or BHLHE40, was required for anaphylaxis. MITF bound to an enhancer located 8.8 kb upstream of the transcription start site of the Hdc gene and directed enhancer activity. MITF overexpression largely restored Hdc gene expression in the Gata2-deficient mast cells. In the human mast cell line LAD2, MITF was required for the HDC gene expression and histamine synthesis.

CONCLUSION

The transcription factors GATA2 and MITF regulate Hdc gene expression in mast cells and are required for IgE/mast cell-mediated anaphylaxis.

Peroxisome proliferator-activated receptor γ agonist suppresses mast cell maturation and induces apoptosis

Peroxisome proliferator-activated receptor gamma (PPAR γ), is important in the immunoregulation of the allergic response. Mast cells are the most important inflammatory cells in immediate hypersensitivity and allergic diseases. However, there is limited information regarding the effects of PPAR γ on mast cell maturation. In the present study, mouse bone marrow-derived mast cells (BMMCs) were cultured in interleukin (IL)-3 and stem cell factor (SCF), in the presence or absence of the PPAR γ agonist, pioglitazone (PIO). The expression levels of the tyrosine kinase receptor CD117 and the high affinity IgE receptor FcεRI α, were assessed by flow cytometry, cell viability was assessed by Alamar-Blue assay and histamine release was determined by measuring the activity of β-hexosaminidase. IL-3 and SCF are required for the development of mast cells in vitro. PIO dose-dependently inhibited the expression of CD117 and FcεRI α, and the maturation of BMMCs. Treatment with PIO additionally inhibited the formation of granules and reduced the expression of β-hexosaminidase. In addition, reverse transcription-polymerase chain reaction analysis revealed that BMMCs treated with PIO expressed a lower level of mast cell protease (MCP)-6 mRNA and PIO treatment enhanced the level of PPAR γ mRNA. Furthermore, PIO induced mast cell progenitor apoptosis. PPAR γ agonists may maintain mast cell homeostasis by inhibiting maturation of their precursors. The inhibitory effects of PPAR γ agonists include suppression of the activation of mast cells and a decrease in mast cell function in the inflammatory response. Therefore, PPAR γ agonists may serve as effective anti-inflammatory reagents in the treatment of allergic reactions.

Role of mast cells in the induction of dry skin in a mouse model of rheumatoid arthritis

PURPOSE

Rheumatoid arthritis (RA) is known to induce dry skin as an extra-articular symptom. However, the mechanisms behind the induction are unclear. In this study, we utilized an arthritis mouse model to simulate RA to reveal the relationship between arthritis and dry skin.

MATERIALS AND METHODS

DBA/1JJmsSlc control mice (n = 5) and DBA/1JJmsSlc collagen-induced arthritis mouse model (arthritis mice; n = 5) were used. We measured transepidermal water loss (TEWL) and capacitance to reveal the effect of arthritis on skin barrier function. In addition, we measured the expression of biomarkers of skin barrier function.

RESULTS

We found that the hind limb volume of the arthritis mice was higher than that of the control mice. Our results showed that the arthritis mice had higher TEWL and lower capacitance when compared to the control mice. When compared to that of the control mice, the skin of the arthritis mice was thicker with more leukocyte infiltration. In the skin of arthritis mice, we observed lower expression of type I and IV collagens, but higher expression of matrix metalloproteinases (MMP)-1 and -9 when compared to that of the control mice. The levels of mast cells, histamine, substance P, and tryptase were higher in the arthritis mice than in the control mice. This study showed that the arthritis mice exhibited a disruption of skin barrier function (i.e. dry skin), which was improved following treatment with a mast cell inhibitor.

CONCLUSIONS

Our results on mast cells suggested that an improvement of dry skin is important for RA management.

Heterogeneity of mast cells and expression of Annexin A1 protein in a second degree burn model with silver sulfadiazine treatment

Mast cells (MCs) participate in all stages of skin healing and one of their mediators is the Annexin A1 protein (AnxA1), linked to inflammation, proliferation, migration and apoptosis processes, but not studied in thermal burns yet. Therefore, our objectives were to evaluate the behavior of MCs and AnxA1 in a second degree burn model, treated or not with silver sulfadiazine 1% (SDP 1%) and associated to macrophages quantification and cytokines dosages. MCs counts showed few cells in the early stages of repair but increased MCs in the final phases in the untreated group. The normal skin presented numerous tryptase-positive MCs that were reduced after burning in all analyzed periods. Differently, few chymase-positive MCs were observed in the early stages of healing, however, increased chymase-positive MCs were found at the final phase in the untreated group. MCs also showed high immunoreactivity for AnxA1 on day 3 in both groups. In the tissue there was a strong protein expression in the early stages of healing, but in the final phases only in the SDP treated animals. TNF-α, IL-1β, IL-6, IL-10 and MCP-1 levels and macrophages quantification were increased in inflammation and reepithelialization phases. Reduced IL-1β, IL-6 and IL-10 levels and numerous macrophages occurred in the treated animals during tissue repair. Our results indicate modulation in the profile of MCs and AnxA1expression during healing by the treatment with SDP 1%, pointing them as targets for therapeutic interventions on skin burns.

Sexual dimorphism in the mast cell transcriptome and the pathophysiological responses to immunological and psychological stress

Background

Biological sex plays a prominent role in the prevalence and severity of a number of important stress-related gastrointestinal and immune-related diseases including IBS and allergy/anaphylaxis. Despite the establishment of sex differences in these diseases, the underlying mechanisms contributing to sex differences remain poorly understood. The objective of this study was to define the role of biological sex on mast cells (MCs), an innate immune cell central to the pathophysiology of many GI and allergic disorders.

Methods

Twelve-week-old C57BL/6 male and female mice were exposed to immunological stress (2 h of IgE-mediated passive systemic anaphylaxis (PSA)) or psychological stress (1 h of restraint stress (RS)) and temperature, clinical scores, serum histamine, and intestinal permeability (for RS) were measured. Primary bone marrow-derived MCs (BMMCs) were harvested from male and female mice and analyzed for MC degranulation, signaling pathways, mediator content, and RNA transcriptome analysis.

Results

Sexually dimorphic responses were observed in both models of PSA and RS and in primary MCs. Compared with male mice, female mice exhibited increased clinical scores, hypothermia, and serum histamine levels in response to PSA and had greater intestinal permeability and serum histamine responses to RS. Primary BMMCs from female mice exhibited increased release of β-hexosaminidase, histamine, tryptase, and TNF-α upon stimulation with IgE/DNP and A23187. Increased mediator release in female BMMCs was not associated with increased upstream phospho-tyrosine signaling pathways or downstream Ca²⁺ mobilization. Instead, increased mediator release in female MCs was associated with markedly increased capacity for synthesis and storage of MC granule-associated immune mediators as determined by MC mediator content and RNA transcriptome analysis.

Conclusions

These results provide a new understanding of sexual dimorphic responses in MCs and have direct implications for stress-related diseases associated with a female predominance and MC hyperactivity including irritable bowel syndrome, allergy, and anaphylaxis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13293-016-0113-7) contains supplementary material, which is available to authorized users.

IL-17 producing mast cells promote the expansion of myeloid-derived suppressor cells in a mouse allergy model of colorectal cancer

Food allergy can influence the development of colorectal cancer, although the underlying mechanisms are unclear. While mast cells (MC) store and secrete histamine, immature myeloid cells (IMC) are the major site of histidine decarboxylase (HDC) expression, the enzyme responsible for histamine production. From our earlier work, we hypothesized that histamine is central to the association between allergy and colorectal carcinogenesis through its influence on the MC-MDSC axis. Here, we show that in wild type (WT) mice, ovalbumin (OVA) immunization elicits a typical T_H2 response. In contrast, in HDC−/− mice, the response to OVA allergy is skewed towards infiltration by IL-17 expressing MCs. This response is inhibited by histamine treatment. The HDC−/− allergic IL-17-expressing MCs promote MDSC proliferation and upregulation of Cox-2 and Arg-1. OVA allergy in HDC−/− mice increases the growth of colon tumor cells in both the MC38 tumor cell implantation model and the AOM/DSS carcinogenesis model. Taken together, our results show that histamine represses IL-17-expressing MCs and their subsequent activation of MDSCs, attenuating the risk of colorectal cancer in the setting of food allergy. Targeting the MC-MDSC axis may be useful for cancer prevention and treatment in patients, particularly in those with food allergy.

Skin disruption is associated with indomethacin-induced small intestinal injury in mice

One mechanism by which non-steroidal anti-inflammatory drugs (NSAIDs) cause intestinal injury is by inducing matrix metalloproteinases (MMPs) that degrade and remodel the extracellular matrix. In addition to the intestinal mucosa, MMPs are expressed in the skin and can be activated by mast cell-secreted tryptase. We therefore investigated whether intestinal injury resulting from treatment with the NSAID indomethacin induced MMPs in the skin of mice and caused an associated disruption of skin function. Hairless mice and mast cell-deficient mice were administered indomethacin, after which damage to the jejuna and skin was assessed with immunohistochemistry and Western blotting. The plasma concentration of inflammatory mediators was assessed to evaluate potential pathways for signalling skin disruption in response to intestinal injury. In hairless mice with intestinal injury, transepidermal water loss (TEWL) was higher and skin hydration was lower than in control mice. The expression levels of mast cells, tryptase, MMP-1 and MMP-9 were also increased, with concurrent degradation of types I and IV collagen. In contrast, no changes in skin TEWL or skin hydration were observed in mast cell-deficient mice with indomethacin-induced intestinal injury. In all mice evaluated, the plasma concentrations of IgE, IgA, histamine and TNF-α were increased in response to indomethacin treatment. Skin disruption was strongly associated with indomethacin-induced small intestinal injury, and the activation of mast cells and induction of tryptase, MMP-1 and MMP-9 are critical to this association.

Mast cell histamine-mediated transient inflammation following exposure to nickel promotes nickel allergy in mice

We previously reported that allergic responses to nickel (Ni) were minimal in mice deficient in the histamine-forming enzyme histidine decarboxylase (HDC-KO), suggesting an involvement of histamine in allergic responses to Ni. However, it remains unclear how histamine is involved in the process of Ni allergy. Here, we examined the role of histamine in Ni allergy using a murine model previously established by us. Mice were sensitized to Ni by intraperitoneal injection of a NiCl2 -lipopolysaccharide (LPS) mixture. Ten days later, allergic inflammation was elicited by challenging ear-pinnas intradermally with NiCl2 . Then, ear-swelling was measured. Pyrilamine (histamine H1-receptor antagonist) or cromoglicate (mast cell stabilizer) was intravenously injected 1 h before the sensitization or the challenge. In cell-transfer experiments, spleen cells from Ni-sensitized donor mice were intravenously transferred into non-sensitized recipient mice. In both sensitized and non-sensitized mice, 1 mm or more NiCl2 (injected into ear-pinnas) induced transient non-allergic inflammation (Ni-TI) with accompanying mast cell degranulation. LPS did not affect the magnitude of this Ni-TI. Pyrilamine and cromoglicate reduced either the Ni-TI or the ensuing allergic inflammation when administered before Ni-TI (at either the sensitization or elicitation step), but not if administered when the Ni-TI had subsided. Experiments on HDC-KO and H1-receptor-KO mice, and also cell-transfer experiments using these mice, demonstrated histamine's involvement in both the sensitization and elicitation steps. These results suggest that mast cell histamine-mediated Ni-TI promotes subsequent allergic inflammatory responses to Ni, raising the possibility that control of Ni-TI by drugs may be effective at preventing or reducing Ni allergy.

Phenotypic variability in human skin mast cells

Mast cells (MCs) are unique constituents of the human body. While inter-individual differences may influence the ways by which MCs operate in their skin habitat, they have not been surveyed in a comprehensive manner so far. We therefore set out to quantify skin MC variability in a large cohort of subjects. Pathophysiologically relevant key features were quantified and correlated: transcripts of c-kit, FcεRIα, FcεRIβ, FcεRIγ, histidine decarboxylase, tryptase, and chymase; surface expression of c-Kit, FcεRIα; activity of tryptase, and chymase; histamine content and release triggered by FcεRI and Ca(2+) ionophore. While there was substantial variability among subjects, it strongly depended on the feature under study (coefficient of variation 33-386%). Surface expression of FcεRI was positively associated with FcεRIα mRNA content, histamine content with HDC mRNA, and chymase activity with chymase mRNA. Also, MC signature genes were co-regulated in distinct patterns. Intriguingly, histamine levels were positively linked to tryptase and chymase activity, whereas tryptase and chymase activity appeared to be uncorrelated. FcεRI triggered histamine release was highly variable and was unrelated to FcεRI expression but unexpectedly tightly correlated with histamine release elicited by Ca(2+) ionophore. This most comprehensive and systematic work of its kind provides not only detailed insights into inter-individual variability in MCs, but also uncovers unexpected patterns of co-regulation among signature attributes of the lineage. Differences in MCs among humans may well underlie clinical responses in settings of allergic reactions and complex skin disorders alike.

The STAT5-GATA2 pathway is critical in basophil and mast cell differentiation and maintenance

Transcription factor GATA binding protein 2 (GATA2) plays critical roles in hematopoietic stem cell survival and proliferation, granulocyte-monocyte progenitor differentiation, and basophil and mast cell differentiation. However, precise roles of GATA2 in basophil and mast cell differentiation and maintenance have not been delineated. We have identified GATA2 as an essential transcription factor in differentiation of newly identified common basophil and mast cell progenitors into basophils and mast cells. We observed Gata2 haploinsufficiency for mast cell differentiation, but not for basophil differentiation. We examined the precise role of GATA2 in maintaining the expression of a wide range of genes that are important for performing basophil or mast cell functions. The effects of GATA2 on gene expression were broadly based. We demonstrated that GATA2 was required for maintaining Fcer1a mRNA and FcεRIα protein expression on both basophils and mast cells, as well as for maintaining Kit mRNA and c-Kit protein expression on mast cells. GATA2 was required for histamine synthesis and was also critical for Il4 mRNA expression in basophils and Il13 mRNA expression in mast cells. We demonstrate a STAT5-GATA2 connection, showing that the STAT5 transcription factor directly bound to the promoter and an intronic region of the Gata2 gene. Overexpression of the Gata2 gene was sufficient to direct basophil and mast cell differentiation in the absence of the Stat5 gene. Our study reveals that the STAT5-GATA2 pathway is critical for basophil and mast cell differentiation and maintenance.

Mast cell mediators: their differential release and the secretory pathways involved

Mast cells (MC) are widely distributed throughout the body and are common at mucosal surfaces, a major host-environment interface. MC are functionally and phenotypically heterogeneous depending on the microenvironment in which they mature. Although MC have been classically viewed as effector cells of IgE-mediated allergic diseases, they are also recognized as important in host defense, innate and acquired immunity, homeostatic responses, and immunoregulation. MC activation can induce release of pre-formed mediators such as histamine from their granules, as well as release of de novo synthesized lipid mediators, cytokines, and chemokines that play diverse roles, not only in allergic reactions but also in numerous physiological and pathophysiological responses. Indeed, MC release their mediators in a discriminating and chronological manner, depending upon the stimuli involved and their signaling cascades (e.g., IgE-mediated or Toll-like receptor-mediated). However, the precise mechanisms underlying differential mediator release in response to these stimuli are poorly known. This review summarizes our knowledge of MC mediators and will focus on what is known about the discriminatory release of these mediators dependent upon diverse stimuli, MC phenotypes, and species of origin, as well as on the intracellular synthesis, storage, and secretory processes involved.

Granule maturation in mast cells: histamine in control

Mast cells are derived from committed progenitors that originate in the BM. They mature into histochemically distinguishable, metachromatic mast cells containing numerous cytoplasmic secretory granules. Accumulating evidence demonstrates that mast cell granule maturation is very tightly regulated by many factors including different granule components such as proteoglycans. In this issue of the European Journal of Immunology, Nakazawa et al. [Eur. J. Immunol. 2014. 44: 204-214] highlight a role for mast cell derived histamine as another factor critical for mast cell maturation. Using histidine decarboxylase (HDC) deficient mice that are unable to make histamine, they show poorly formed secretory granules and decreased secretory granule protease expression in peritoneal mast cells. Co-culturing BM-derived mast cells with fibroblasts normally drives granule maturation, but HDC-deficient BM-derived mast cells fail to do so. Exogenously provided histamine partly restores granule differentiation as evidenced by increased tryptase and chymase activity, and this is histamine receptor type H4 -dependent. However, H4 -deficient mice have intact granule formation in peritoneal mast cells, suggesting that when HDC is functional, the intrinsic histamine production is sufficient for most granule maturation processes and H4 is dispensable. This study highlights the role of histamine in the regulation of mast cell maturation, although the cytosolic target remains unknown.