Bone marrow-derived mast cell differentiation is strongly reduced in histidine decarboxylase knockout, histamine-free mice

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.

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.

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.

Two-step differentiation of mast cells from induced pluripotent stem cells

Mast cells play important roles in the pathogenesis of allergic diseases. They are generally classified into 2 phenotypically distinct populations: connective tissue-type mast cells (CTMCs) and mucosal-type mast cells (MMCs). The number of mast cells that can be obtained from tissues is limited, making it difficult to study the function of mast cells. Here, we report the generation and characterization of CTMC-like mast cells derived from mouse induced pluripotent stem (iPS) cells. iPS cell-derived mast cells (iPSMCs) were generated by the OP9 coculture method or embryoid body formation method. The number of Safranin O-positive cells, expression levels of CD81 protein and histidine decarboxylase mRNA, and protease activities were elevated in the iPSMCs differentiated by both methods as compared with those in bone marrow-derived mast cells (BMMCs). Electron microscopic analysis revealed that iPSMCs contained more granules than BMMCs. Degranulation was induced in iPSMCs after stimulation with cationic secretagogues or vancomycin. In addition, iPSMCs had the ability to respond to stimulation with the IgE/antigen complex in vitro and in vivo. Moreover, when iPSMCs generated on OP9 cells were cocultured with Swiss 3T3 fibroblasts, protease activities as maturation index were more elevated, demonstrating that mature mast cells were differentiated from iPS cells. iPSMCs can be used as an in vitro model of CTMCs to investigate their functions.

Histamine deficiency promotes inflammation-associated carcinogenesis through reduced myeloid maturation and accumulation of CD11b+Ly6G+ immature myeloid cells

Histidine decarboxylase (HDC), the unique enzyme responsible for histamine generation, is highly expressed in myeloid cells but its function is poorly understood. Here, we show that Hdc knockout mice exhibit a markedly increased rate of colon and skin carcinogenesis. Using Hdc-EGFP BAC transgenic mice, we demonstrate that Hdc is expressed primarily in CD11b⁺Ly6G⁺ immature myeloid cells (IMCs) that are recruited early on in chemical carcinogenesis. Transplant of Hdc-deficient bone marrow to wildtype recipients results in increased CD11b⁺Ly6G⁺ cell mobilization and reproduces the cancer susceptibility phenotype. In addition, IMCs from Hdc knockout mice promote the growth of cancer xenografts and colon cancer cells downregulate Hdc expression through promoter hypermethylation and inhibits myeloid cell maturation. Exogenous histamine induces the differentiation of IMCs and suppresses their ability to support the growth of xenografts. These data indicate key roles for Hdc and histamine in myeloid cell differentiation, and CD11b⁺Ly6G⁺ IMCs in early cancer development.

Polyamines affect histamine synthesis during early stages of IL-3-induced bone marrow cell differentiation

Mast cells synthesize and store histamine, a key immunomodulatory mediator. Polyamines are essential for every living cell. Previously, we detected an antagonistic relationship between the metabolisms of these amines in established mast cell and basophilic cell lines. Here, we used the IL-3-driven mouse bone marrow-derived mast cell (BMMC) culture system to further investigate this antagonism in a mast cell model of deeper physiological significance. Polyamines and histamine levels followed opposite profiles along the bone marrow cell cultures leading to BMMCs. alpha-Difluoromethylornithine (DFMO)-induced polyamine depletion resulted in an upregulation of histidine decarboxylase (HDC, the histamine-synthesizing enzyme) expression and activity, accompanied by increased histamine levels, specifically during early stages of these cell cultures, where an active histamine synthesis process occurs. In contrast, DFMO did not induce any effect in either HDC activity or histamine levels of differentiated BMMCs or C57.1 mast cells, that exhibit a nearly inactive histamine synthesis rate. Sequence-specific DNA methylation analysis revealed that the DFMO-induced HDC mRNA upregulation observed in early bone marrow cell cultures is not attributable to a demethylation of the gene promoter caused by the pharmacological polyamine depletion. Taken together, the results support an inverse relationship between histamine and polyamine metabolisms during the bone marrow cell cultures leading to BMMCs and, moreover, suggest that the regulation of the histamine synthesis occurring during the early stages of these cultures depends on the concentrations of polyamines.

Activation of peroxisome proliferator-activated receptor gamma suppresses mast cell maturation involved in allergic diseases

BACKGROUND

Mast cells play a central role in allergic and inflammatory diseases. Several reports indicated role of peroxisome proliferator-activated receptor gamma (PPARgamma) on mast cell function. However, there is no report about the role of PPARgamma on differentiation of mast cells from the progenitors. In this study, we investigated the role of PPARgamma in regulating bone marrow-derived mast cell maturation and the therapeutic implications for mast cell-related diseases such as atopic or contact dermatitis.

METHODS

We used in vitro cell culture system for mast cell differentiation from bone marrow-progenitors using specific ligands and lentiviral-mediated short hairpin RNA of PPARgamma, and in vivo murine dermatitis models.

RESULTS

Activation of PPARgamma inhibited the maturation of bone marrow progenitors into connective tissue-type mast cells (CTMCs) through up-regulation of GATA-4 and GATA-6 resulting in a decrease in expression of histidine decarboxylase and mast cell histamine content. In comparison, the differentiation of bone marrow progenitors into CTMCs was significantly accelerated by the knockdown of PPARgamma expression by lentiviral-mediated short hairpin RNA. Peroxisome proliferator-activated receptor gamma ligand administration to mice inhibited the maturation of mast cells resulting in attenuation of atopic and contact dermatitis via diminishment of the number of mature mast cells.

CONCLUSION

Our results indicate that PPARgamma is one of master regulators on mast cell maturation and potentially useful for the therapy in various disorders involving mast cell activation.

Involvement of chemical mediators in nasal allergic responses of HDC-KO mice

The present study was undertaken to investigate the involvement of chemical mediators in nasal allergic responses using histidine decarboxylase knockout (HDC-KO) mice. An allergic rhinitis model was developed in HDC-KO and wild-type mice by the intraperitoneal injection of ovalbumin, aluminum hydroxide gel and pertussis toxin. Five days later, they were boosted by a subcutaneous injection of ovalbumin into the back. From day 18 after the first immunization to day 39, intranasal sensitization with ovalbumin was performed every day and the severity of allergic rhinitis was observed by measuring nasal allergic responses and total IgE levels. It was found that the intranasal administration of antigen caused a significant increase of nasal sneezing and rubbing from day 25 to day 39 both in sensitized HDC-KO and wild-type mice. In addition, a significant elevation of total IgE levels in serum was also found both in sensitized HDC-KO and wild-type mice from day 18 to day 39 after the first immunization. L-733,060, a tachykinin NK(1) receptor antagonist at a dose of 10 mg/kg (s.c.), resulted in the dose-dependent inhibition of nasal allergic responses induced by antigen in both HDC-KO and wild-type mice. In addition, both chlorpheniramine at doses of 3 and 10 mg/kg (p.o.) and BW A868C at doses of 0.3 and 1 mg/kg (i.v.) also showed a dose-related reduction of the nasal allergic responses induced by antigen in sensitized wild-type mice. On the other hand, they had no effects on the nasal signs induced by antigen in HDC-KO mice. From these results, it was revealed that substance P induces nasal allergic responses in the mouse model of chronic allergic rhinitis through the activation of tachykinin NK(1) receptors. Therefore, it can be concluded that not only histamine, but also substance P and prostaglandin D(2), participated in the nasal allergic responses induced by antigen in mice.

The CML-related oncoprotein BCR/ABL induces expression of histidine decarboxylase (HDC) and the synthesis of histamine in leukemic cells

Basophil numbers are typically elevated in chronic myeloid leukemia (CML) and increase during disease progression. Histamine is an essential mediator and marker of basophils and is highly up-regulated in CML. We examined the biochemical basis of histamine synthesis in CML cells. The CML-specific oncoprotein BCR/ABL was found to promote expression of histidine decarboxylase (HDC) and synthesis of histamine in Ba/F3 cells. Moreover, the BCR/ABL tyrosine kinase inhibitors imatinib (STI571) and nilotinib (AMN107) decreased histamine levels and HDC mRNA expression in BCR/ABL-transformed Ba/F3 cells, in the CML-derived basophil cell line KU812, and in primary CML cells. Synthesis of histamine was found to be restricted to the basophil compartment of the CML clone and to depend on signaling through the PI3-kinase pathway. CML cells also expressed histamine receptors (HRs), including HR-1, HR-2, HR-4, and histamine-binding CYP450 isoenzymes which also serve as targets of HR antagonists. The HR-1 antagonists loratadine and terfenadine, which bind to CYP450, were found to counteract proliferation of CML cells, whereas no growth inhibition was observed with the HR-1 antagonist fexofenadine which is not targeted or metabolized by CYP450. Moreover, DPPE, an inhibitor of histamine-binding CYP450 isoenzymes, produced growth inhibition in CML cells. Together, these data show that BCR/ABL promotes histamine production in CML cells and that certain HR-targeting drugs exert antileukemic effects on CML cells.

Histamine-cytokine connection in immunity and hematopoiesis

A number of recent studies have led to a reappraisal of the functional capacities of histamine in immunity and hematopoiesis. This change of perspective was provided by the following findings: (1) the evidence for multiple cellular sources of histamine, differing from mature basophils and mast cells by their ability to newly synthesize and liberate the mediator without prior storage, (2) the discovery of a novel histamine receptor (H4R), preferentially expressed on hematopoietic and immunocompetent cells, (3) the potential intracellular activity of histamine through cytochrome P450 and (4) the demonstration of a histamine-cytokine cross-talk. Indeed, cytokines not only modulate the degranulation process of histamine but also control its neosynthesis by the histamine-forming enzyme, histidine decarboxylase (HDC), at transcriptional and post-transcriptional levels. In turn, histamine intervenes in the intricate cytokine network, regulating cytokine production by immune cells through distinct receptors signaling distinct biological effects. This type of regulation is particularly relevant in the context of TH1/TH2 differentiation, autoimmunity and tumor immunotherapy.

The C-terminus of rat L-histidine decarboxylase specifically inhibits enzymic activity and disrupts pyridoxal phosphate-dependent interactions with L-histidine substrate analogues

Full-length rat HDC (L-histidine decarboxylase) translated in reticulocyte cell lysate reactions is inactive, whereas C-terminally truncated isoforms are capable of histamine biosynthesis. C-terminal processing of the approximately 74 kDa full-length protein occurs naturally in vivo, with the production of multiple truncated isoforms. The minimal C-terminal truncation required for the acquisition of catalytic competence has yet to be defined, however, and it remains unclear as to why truncation is needed. Here we show that approximately 74 kDa HDC monomers can form dimers, which is the conformation in which the enzyme is thought to be catalytically active. Nevertheless, the resulting dimer is unable to establish pyridoxal phosphate-dependent interactions with an L-histidine substrate analogue. Protein sequences localized to between amino acids 617 and 633 specifically mediate this inhibition. Removing this region or replacing the entire C-terminus with non-HDC protein sequences permitted interactions with the substrate analogue to be re-established. This corresponded exactly with the acquisition of catalytic competence, and the ability to decarboxylate natural L-histidine substrate. These studies suggested that the approximately 74 kDa full-length isoform is deficient in substrate binding, and demonstrated that C-terminally truncated isoforms with molecular masses between approximately 70 kDa and approximately 58 kDa have gradually increasing specific activities. The physiological relevance of our results is discussed in the context of differential expression of HDC isoforms in vivo.

High leptin level is accompanied with decreased long leptin receptor transcript in histamine deficient transgenic mice

Leptin is a multifunctional cytokine and hormone that primarily acts in the hypothalamus and plays a key role in regulation of food intake and energy expenditure. Leptin acts through its receptor (OBR), the product of db gene that activates the Jak/STAT pathway predominantly. To exert its functions, leptin interacts with histamine as well. Histamine is a downstream effector of leptin as its release, metabolism is enhanced by leptin and hypothalamic histamine reduces food intake. In a bi-directional regulatory loop histamine also influences leptin concentration by inhibiting its expression. In this study we demonstrate that histamine deficiency elevates serum leptin level and decreases full-length leptin receptor isoform with a slight increase of the short one and results in mild late onset obesity. These observation can help to elucidate further the bi-lateral interaction of leptin and histamine, and therefore provide useful data to understand the pathomechanism of obesity.

Partial protection against dextran sodium sulphate induced colitis in histamine-deficient, histidine decarboxylase knockout mice

OBJECTIVES

Chemically induced mucosal inflammation in animal models is a suitable tool for studying factors in the pathogenesis of inflammatory bowel disease. The aim of this study was to determine whether absence of histamine has an effect on the development of experimental colitis.

METHODS

Histamine-deficient, histidine decarboxylase (HDC) knockout Balb/c mice and genetically identical control animals with intact HDC were studied. Colitis was induced by the administration of 2% dextran sodium sulphate in drinking water. Mice were killed after 5 days and disease activity assessed by clinical, histologic, and immunohistologic parameters. Bacterial components of stool were examined.

RESULTS

Clinical disease activity was higher in the mice with intact HDC (disease activity index, 2.21) than in the histamine-deficient knock-out mice (1.88). Histologic findings were similar in the two groups. On day 5, the inflammation score of the HDC sufficient group was 5.25 (+/-1.055) and the crypt score was 5.00 (+/-1.128). The scores in the HDC knock-out group were 4.667 (+/- 0.707) and 4.667 (+/- 0.86), respectively. There was a significant difference in the number of interleukin (IL-10)-producing lymphocytes in colon mucosa. Large numbers of IL-10-positive lymphocytes were observed in wild type mice both those with DSS induced colitis and untreated controls. Only sporadic IL-10 positivity was found in histamine-deficient mice. Significant differences were found in the composition of the fecal bacterial flora between the two groups.

CONCLUSION

The reduced number of IL-10-positive lymphocytes in the intestinal mucosa of histamine-deficient, histidine decarboxylase knockout mice and the altered fecal bacterial flora in these animals suggest that histamine may play a role in the pathophysiology of inflammation in the colon of normal animals by upregulating local IL-10 production and stimulating a local shift to Th2 response.

Knock-out of the histidine decarboxylase gene modifies the repertoire of natural autoantibodies

Natural antibodies (NA) are antibodies produced in the absence of known immunization with specific antigens. NA are found in the blood of healthy humans and mice. Histamine influences many aspects of the immune response, including antibody production. However, the role of histamine in the generation of NA has not yet been studied. In this work, we used an ELISA assay to characterize the self-antigen binding repertoires of NA in wild type (WT) mice and in histidine decarboxylase knock-out (HDC-KO) mice, unable to synthesize histamine. We now report that HDC-KO and WT mice differed in the patterns of autoreactivity of their IgM and IgG NA. The NA in HDC-KO sera manifested a larger repertoire of IgM autoantibodies than did the WT sera. The self-antigens bound by IgM from HDC-KO mice included structural proteins, enzymes associated with cellular metabolism, double-stranded and single-stranded DNA, and tissue-specific antigens like insulin. There were relatively fewer differences in the NA repertoire of IgG autoantibodies of the mice: notably, the HDC-KO sera reacted with glutamic acid decarboxylase (GAD), an antigen associated with autoimmune diabetes. These results demonstrate that endogenous histamine can influence the self-reactivity of the NA repertoire.

IL-9 increases the expression of several cytokines in activated mast cells, while the IL-9-induced IL-9 production is inhibited in mast cells of histamine-free transgenic mice

Histamine and IL-9 are suspected to play an important role in the pathogenesis of asthmatic and allergic reactions. Mast cells store a large amount of histamine in their granules and are capable of producing different cytokines upon stimulation. In this study we show that mast cells stimulated by IL-9 and ionomycin or IL-9 and antigen-specific IgE/antigen express several cytokines at mRNA level, among them are IL-5, IL-4, IL-10, IL-9, IL-13, IL-1beta, IL-1Ra, IL-6 and MIF. Furthermore, both IL-9 and ionomycin are needed for the production of these cytokines in great quantities, which is mediated through the production of IL-1beta. Histamine-free mast cells respond by a markedly decreased IL-9 expression to this stimulation. Our results show that this IL-9-induced IL-9 production may result in a positive feedback loop in mast cells and the lack of histamine disturbs this loop, which may serve as an explanation for the reduced asthmatic symptoms, observed in histamine-free mice.

Histamine participates in the early phase of trabecular bone loss in ovariectomized rats

We have previously reported that cimetidine, a reference H2 receptor antagonist, attenuates the initial osteoclastic burst and subsequent trabecular bone loss induced by ovariectomy (ovx) in rats. This study was designed to determine whether these effects are specific to H2 antagonism. To this end, we compared the effects of two H2 receptor antagonists, cimetidine and famotidine. In addition, we analyzed the response of histamine-producing cells to these inhibitors. Seventy-two 90-day-old female Sprague-Dawley rats were ovariectomized or sham-operated, and received single daily intramuscular injections of cimetidine (125 mg/kg), famotidine (10 mg/kg), or vehicle. The animals were killed 14 days after surgery and their femurs were processed for histomorphometry. Trabecular bone volume was reduced by 30% in ovx rats and by 15% in cimetidine- and famotidine-treated rats. Architectural parameters were reduced by about 20% in ovx rats. Cimetidine and famotidine attenuated these consequences of ovx by about 50%. Trabecular connectivity was deteriorated by ovx, while cimetidine and famotidine attenuated this effect. Resorption parameters were increased by ovx, while cimetidine and famotidine prevented this increase. Kinetic bone formation parameters were increased by ovx, while cimetidine and famotidine had no influence. Neither cimetidine nor famotidine had any observable effect in sham-treated rats. Mast cell numbers increased by 250% in ovx rats and by only 40% in H2 antagonists-treated ovx rats. A resident histamine-positive, non-mast cell, population found in bone marrow was increased by 25% by ovx. Interestingly, cimetidine and famotidine reduced this population in both sham-operated and ovx rats, famotidine being more potent than cimetidine. These results show that H(2) receptor blockade partially prevents the consequences of castration on cancellous bone resorption in female rats, and strongly suggest that histamine participates in the mediator network regulating estrogen deficiency induced bone resorption. A large population of histamine-producing cells, which differ morphologically from mast cells and belong to an immature marrow population, may be a source of histamine in this model. The H(2) blockers targeted this population, and this effect appeared to explain the anti-resorptive action of the two drugs.

Histamine, part of the metabolome

Histamine, a decarboxylated amino acid with a molecular mass of 112 daltons reveals multicoloured functional activities. Its role in allergy and inflammation is abundantly characterized. Moreover histamine is one of the neuotransmitters, has a role in gastric acid production and in maintenance of blood-brain barrier. In the last decade, many data were collected suggesting an important function of histamine in events of immune response and also in both benign and malignant cell proliferation. Our group collected data on the relevance of histamine as an autocrine factor in human melanoma. The outcome of the action seems to be closely related to the local and actual balance of histamine receptors (H1R, H2R, H3R and H4R) on tumor cells. Recently, using a gene targeted mouse strain (lacking an enzyme, histidine decarboxylase, the only one responsible for histamine production) many phenotype of the histamine-free mice were demonstrated. Our data suggest, that histamine, as part of the poorly characterized metabolome of the mammalian cells plays significant role in many physiological and pathological processes.