Histidine decarboxylase deficiency inhibits NBP-induced extramedullary hematopoiesis by modifying bone marrow and spleen microenvironments.

Histidine decarboxylase (HDC), a histamine synthase, is expressed in various hematopoietic cells and is induced by hematopoietic cytokines such as granulocyte colony-stimulating factor (G-CSF). We previously showed that nitrogen-containing bisphosphonate (NBP)-treatment induces extramedullary hematopoiesis via G-CSF stimulation. However, the function of HDC in NBP-induced medullary and extramedullary hematopoiesis remains unclear. Here, we investigated changes in hematopoiesis in wild-type and HDC-deficient (HDC-KO) mice. NBP treatment did not induce anemia in wild-type or HDC-KO mice, but did produce a gradual increase in serum G-CSF levels in wild-type mice. NBP treatment also enhanced Hdc mRNA expression and erythropoiesis in the spleen and reduced erythropoiesis in bone marrow and the number of vascular adhesion molecule 1 (VCAM-1)-positive macrophages in wild-type mice, as well as increased the levels of hematopoietic progenitor cells and proliferating cells in the spleen and enhanced expression of bone morphogenetic protein 4 (Bmp4), CXC chemokine ligand 12 (Cxcl12), and hypoxia inducible factor 1 (Hif1) in the spleen. However, such changes were not observed in HDC-KO mice. These results suggest that histamine may affect hematopoietic microenvironments of the bone marrow and spleen by changing hematopoiesis-related factors in NBP-induced extramedullary hematopoiesis.

Acute Intestinal Inflammation Depletes/Recruits Histamine-Expressing Myeloid Cells From the Bone Marrow Leading to Exhaustion of MB-HSCs.

BACKGROUND & AIMS: Histidine decarboxylase (HDC), the histamine-synthesizing enzyme, is expressed in a subset of myeloid cells but also marks quiescent myeloid-biased hematopoietic stem cells (MB-HSCs) that are activated upon myeloid demand injury. However, the role of MB-HSCs in dextran sulfate sodium (DSS)-induced acute colitis has not been addressed. METHODS: We investigated HDC+ MB-HSCs and myeloid cells by flow cytometry in acute intestinal inflammation by treating HDC-green fluorescent protein (GFP) male mice with 5% DSS at various time points. HDC+ myeloid cells in the colon also were analyzed by flow cytometry and immunofluorescence staining. Knockout of the HDC gene by using HDC-/-; HDC-GFP and ablation of HDC+ myeloid cells by using HDC-GFP; HDC-tamoxifen-inducible recombinase Cre system; diphtheria toxin receptor (DTR) mice was performed. The role of H2-receptor signaling in acute colitis was addressed by treatment of DSS-treated mice with the H2 agonist dimaprit dihydrochloride. Kaplan-Meier survival analysis was performed to assess the effect on survival. RESULTS: In acute colitis, rapid activation and expansion of MB-HSC from bone marrow was evident early on, followed by a gradual depletion, resulting in profound HSC exhaustion, accompanied by infiltration of the colon by increased HDC+ myeloid cells. Knockout of the HDC gene and ablation of HDC+ myeloid cells enhance the early depletion of HDC+ MB-HSC, and treatment with H2-receptor agonist ameliorates the depletion of MB-HSCs and resulted in significantly increased survival of HDC-GFP mice with acute colitis. CONCLUSIONS: Exhaustion of bone marrow MB-HSCs contributes to the progression of DSS-induced acute colitis, and preservation of quiescence of MB-HSCs by the H2-receptor agonist significantly enhances survival, suggesting the potential for therapeutic utility.

Activation of the central histaminergic system is involved in hypoxia-induced stroke tolerance in adult mice.

We hypothesized that activation of the central histaminergic system is required for neuroprotection induced by hypoxic preconditioning. Wild-type (WT) and histidine decarboxylase knockout (HDC-KO) mice were preconditioned by 3 hours of hypoxia (8% O(2)) and, 48 hours later, subjected to 30 minutes of middle cerebral artery (MCA) occlusion, followed by 24 hours of reperfusion. Hypoxic preconditioning improved neurologic function and decreased infarct volume in WT or HDC-KO mice treated with histamine, but not in HDC-KO or WT mice treated with α-fluoromethylhistidine (α-FMH, an inhibitor of HDC). Laser-Doppler flowmetry analysis showed that hypoxic preconditioning ameliorated cerebral blood flow (CBF) in the periphery of the MCA territory during ischemia in WT mice but not in HDC-KO mice. Histamine decreased in the cortex of WT mice after 2, 3, and 4 hours of hypoxia, and HDC activity increased after 3 hours of hypoxia. Vascular endothelial growth factor (VEGF) mRNA and protein expressions showed a greater increase after hypoxia than those in HDC-KO or α-FMH-treated WT mice. In addition, the VEGF receptor-2 antagonist SU1498 prevented the protective effect of hypoxic preconditioning in infarct volume and reversed increased peripheral CBF in WT mice. Therefore, endogenous histamine is an essential mediator of hypoxic preconditioning. It may function by enhancing hypoxia-induced VEGF expression.

Enhanced goblet cell hyperplasia in HDC knockout mice with allergic airway inflammation.

BACKGROUND: Histamine is known to have immunoregulatory roles in allergic reactions through histamine receptor 1 (H1R), H2R, H3R and H4R. However, its role in goblet cell hyperplasia in the airways of asthma patients is yet to be clarified. OBJECTIVE: This study was designed to examine the role of histamine in goblet cell hyperplasia using histamine-deficient mice (Hdc-/- mice) with allergic airway inflammation. METHODS: Wild-type and Hdc-/- C57BL/6 mice were sensitized with ovalbumin (OVA). After a 2-week exposure to OVA, goblet cell hyperplasia was evaluated. Cell differentials and cytokines in BALF were analyzed. The mRNA levels of MUC5AC and Gob-5 gene were determined quantitatively. RESULTS: The number of eosinophils in BALF increased in both the sensitized wild-type mice and Hdc-/- mice with OVA inhalation. In addition, the numbers of alveolar macrophages and lymphocytes in BALF increased significantly in the sensitized Hdc-/- mice with OVA inhalation compared to the wild-type mice under the same conditions. The concentrations of Interleukin-4 (IL-4), IL-5, IL-13, Interferon-gamma (IFN-gamma), tumor necrosis factor-alpha (TNF-alpha) and IL-2 in the BALF all increased significantly in both groups compared to those exposed to saline. In particular, the concentration of TNF-alpha in the Hdc-/- mice exposed to OVA was significantly higher than that in the wild-type mice under the same conditions. The mRNA levels of Gob-5 and MUC5AC, and the ratio of the goblet cells in the airway epithelium significantly increased in Hdc-/- mice exposed to OVA compared to wild-type mice. CONCLUSIONS: These results suggested that histamine may play a regulatory role in goblet cell hyperplasia in allergic airway inflammation.

Progress in allergy signal research on mast cells: the role of histamine in immunological and cardiovascular disease and the transporting system of histamine in the cell.

Since its discovery in 1910, histamine has been regarded as one of the most important biogenic amines in the medical and biological fields. This article summarizes the information about the role of histamine in allergic situations, atherosclerosis, and autoimmune encephalomyelitis, especially focusing on our study with histidine decarboxylase gene knockout mouse. In the allergic bronchial asthma model, histamine positively controls eosinophilia but not bronchial hypersensitivity. Histamine is proved to be an important substance that controls body temperature and respiration in systemic anaphylaxis but its role in controlling blood pressure is minor. Histamine also plays a role in inducing atherosclerosis in the mouse model. We showed that experimental autoimmune encephalomyelitis (EAE) is significantly more severe in histamine-deficient mice with diffuse inflammatory infiltrates in the brain and cerebellum, including a prevalent granulocytic component. Histamine is mainly produced in mast cells and basophils in hematopoietic cells. We've shown that mast cells not only produce histamine, but also uptake it from the environmental medium and release it by allergic stimulants. The protein used for the plasma transport of histamine in basophils was identified as organic cation transporter (OCT3).

Elevated CREB activity in embryonic fibroblasts of gene-targeted histamine deficient mice.

OBJECTIVES: Histamine is a known inducer of cAMP-responsive element binding protein (CREB), which plays a key role in initiation of adipogenesis. Our present goal was to study how histamine deficiency impacts CREB signalling and adipogenesis. METHODS: We used a histidine-decarboxylase gene-targeted (HDC KO) mice model lacking endogenous histamine. We measured CREB activity and expression by EMSA, Western blot and real-time RT-PCR, as well as cAMP levels by ELISA in primary embryonic fibroblasts derived from WT and HDC KO mice. The ability of these cells to form adipocytes was also tested in preliminary experiments. RESULTS: We found that in the absence of the histamine, cells show higher constitutive CREB activity and greatly increased intracellular cAMP levels, as well as that in contrast to WT cells, HDC KO fibroblasts are more prone to differentiate into adipocytes. CONCLUSION: These data suggest a newly recognised inhibitory role for histamine in CREB activity and draws attention to the potential role of histamine in adipocyte differentiation.

Highly activated c-fos expression in specific brain regions (ependyma, circumventricular organs, choroid plexus) of histidine decarboxylase deficient mice in response to formalin-induced acute pain.

Activation of different brain regions for acute pain-related stress induced by a single subcutaneous injection of 4% formalin was investigated in histidine decarboxylase-deficient mice. Besides pain- and stress-related brain areas and the tuberomamillary neurons, strong Fos activation and c-fos mRNA expression were found in distinct brain regions and cell types, which have not been activated in wild type control mice. These structures include the circumventricular organs (organum vasculosum of the lamina terminalis, subfornical organ, area postrema), some of the ependymal cells along the wall of the ventricles, tanycytes in the third ventricle's ependyma and the median eminence, as well as in the epithelial cells of the choroid plexus in the lateral, third and fourth ventricles. All of these areas and cell types are known as compartments of the brain-blood-cerebrospinal fluid interface. The present observations provide strong evidence that an acute stressor, formalin-evoked painful stimulus elicits rapid alterations in the activity of neuroglial elements of histidine decarboxylase-deficient mice that are directly involved in the communication between the brain and the cerebrospinal fluid space.

The role of histamine in the intracellular survival of Mycobacterium bovis BCG.

The course and outcome of infection with mycobacteria are determined by a complex interplay between the immune system of the host and the survival mechanisms developed by the bacilli. Histamine plays an important role in various processes, including cell division, metabolism, and apoptosis, and it modulates innate and adaptive immune responses. In the present study we investigated the intracellular survival of Mycobacterium bovis BCG in murine bone-marrow macrophages isolated from wild-type (WT) and histidine-decarboxylase knock-out [HDC (-/-)] mice. Mycobacterial titers were significantly higher in the HDC (-/-) macrophages as compared with the WT cells. M. bovis BCG growth in WT macrophages could be enhanced by pyrilamine and cimetidine. Exogenously added histamine decreased the intracellular counts of M. bovis BCG in HDC (-/-) macrophages. Infection of activated macrophages with M. bovis BCG elicited apoptosis, but there was no significant difference between the WT and the HDC (-/-) cells. These bacilli induced comparable levels of tumor necrosis factor-alpha production in the WT and the HDC (-/-) macrophages. M. bovis BCG stimulated interleukin-18 (IL-18) production in the macrophages from WT mice, but not in the HDC (-/-) cells. Exogenously added IL-18 decreased the titers of intracellular mycobacteria in HDC (-/-) cells. In conclusion, these data implicate histamine in the intracellular survival of M. bovis BCG. The cellular control mechanisms restricting the growth of M. bovis BCG are complex and involve H1 and H2 receptor-mediated events. Histamine might be an important mediator of M. bovis BCG-induced IL-18 production, which in turn contributes to immune protection.

Role of macrophage-derived histamine in atherosclerosis-- chronic participation in the inflammatory response --.

The atherosclerotic intimal lesion contains endothelial cells, smooth muscle cells, monocytes/macrophages and T lymphocytes, which constitute a histamine-cytokine network that participates in chronic inflammatory responses. Monocytes/macrophages and T lymphocytes express the histamine-producing enzyme histidine decarboxylase (HDC), and specific histamine receptors (HHR), which are switched from HH2R to HHR1 during macrophage differentiation. Endothelial and smooth muscle cells also express HHR in response to histamine. The effects of histamine on these cells include a regulation of atherosclerosis-related events such as cell proliferation, expression of matrix metalloproteinase, adhesion molecules and cytokines. Furthermore, recent studies have indicated that histamine and the activation of its specific receptors modulate the Th1/Th2 balance in inflammatory lesions through the regulation of cytokine production from inflammatory cells. The histamine-cytokine network in the atherosclerotic intima could regulate inflammatory and immune responses, including Th1/Th2 balance, and contribute to atherogenesis.

[Physiological function mediated by histamine synthesis].

Histamine is involved in a variety of physiologic responses, such as inflammation, type I allergy, gastric acid secretion, and neurotransmission. Previous studies have focused on specific receptors for histamine and histamine release through degranulation, and the regulation of histamine synthesis and its physiologic roles remain to be clarified. We have studied histidine decarboxylase (HDC), the rate-limiting enzyme for mammalian histamine synthesis. Immunocytochemical approaches with an anti-HDC antibody revealed that histamine synthesis occurs in two distinct compartments of mast cells, cytosol and granules, and is regulated by the posttranslational processing of HDC. We also found that histamine synthesis in mast cells is markedly induced by IgE even in the absence of antigens, which may be relevant to enhanced responses of mast cells under allergic conditions. We then developed HDC-deficient mice by gene targeting to investigate the physiologic roles of histamine. We not only confirmed that histamine is essential for type I allergy and stimulates gastric acid secretion, but also found that histamine may regulate the proliferation and differentiation of mast cells. Furthermore, in HDC-deficient mice histamine produced by infiltrated neutrophils can suppress the production of antitumoral cytokines, such as interferon-gamma and tumor necrosis factor-alpha through H2 receptors in the tumor tissues. In this review, we describe recent topics in histamine research, including our results focusing on histamine synthesis and its physiologic roles.

Enhancement of neutrophil infiltration in histidine decarboxylase-deficient mice.

The roles of histamine in the anaphylactic increase in vascular permeability and leucocyte infiltration were analysed in an air pouch-type allergic inflammation model in histidine decarboxylase-deficient (HDC-/-) mice and wild-type mice. In the immunized wild-type mice, histamine content in the pouch fluid and vascular permeability in the anaphylaxis phase were increased by injection of the antigen solution into the air pouch. However, in the immunized HDC-/- mice, the antigen challenge did not increase histamine content in the pouch fluid and vascular permeability in the anaphylaxis phase. Number of leucocytes (more than 83% are neutrophils) in the pouch fluid 4-24 hr after the antigen challenge in the HDC-/- mice was significantly higher than that in the wild-type mice. Simultaneous injection of histamine with the antigen solution into the air pouch of the immunized HDC-/- mice reduced the antigen-induced leucocyte infiltration at 4 hr. Simultaneous injection of the H2 antagonist cimetidine but not the H1 antagonist pyrilamine with the antigen solution into the air pouch of the immunized wild-type mice further increased leucocyte infiltration at 4 hr. The levels of macrophage inflammatory protein-2 at 2 hr and of tumour necrosis factor-alpha at 4 hr in the pouch fluid of the HDC-/- mice were significantly higher than those of the wild-type mice. These findings indicate that histamine plays significant roles not only in the anaphylactic increase in vascular permeability via H1 receptors but also in the negative regulation of neutrophil infiltration via H2 receptors in allergic inflammation.

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

Mast cells are differentiated in vitro from bone marrow precursors. In this study the development of bone marrow-derived mast cells was examined from histidine decarboxylase deficient (HDC-/-) and wild-type mice in the presence of IL-3. The number of non-adherent, tryptase- and c-kit-positive mast cells in bone marrow-derived cultures of HDC(-/-) mice was decreased compared to that of wild-type (HDC+/+) animals, but within the tryptase- and c-kit-positive cells there was no difference in the expression intensity of both markers between the two groups. Furthermore, less serine proteases mMCP5, mMCP6 and FcepsilonRIalpha mRNA were detected in bone marrow-derived cell cultures originating from HDC-/- mice. Antigen-provoked degranulation through high-affinity FcepsilonI receptor was also lower in HDC-/- mice. The colony assays in semisolid medium yielded a significantly lower ratio of mixed colonies and higher proportion of macrophage colonies from HDC-/- mice-derived bone marrow compared to the wild-type. In the course of the differentiation of HDC-/- --derived mast cells exogenously added histamine is unable to substitute the endogenously missing histamine. Concordantly, alpha-fluoromethyl-histamine, the specific inhibitor of HDC, revealed only a marginal inhibition on the differentiation of tryptase-positive mast cells from wild-type mice. These findings suggest that the effect of histamine on the IL-3-dependent development of bone marrow-derived mast cell differentiation during the early period is crucial and irreplaceable.

[Regulation of histamine production in macrophages].

Stimulating cells of the mouse macrophage-like cell line RAW 264.7 with the Ca(2+)-ATPase inhibitor thapsigargin increased histamine production. Thapsigargin increased the levels of histidine decarboxylase (HDC) mRNA at 4 h and the expression of 74-kDa HDC protein at 8 h. PD98059, a specific inhibitor of MEK-1 which phosphorylates p44/p42 MAP kinase, strongly suppressed the thapsigargin-induced histamine production, the increase in HDC mRNA level and 74-kDa HDC protein expression. In contrast, SB203580, an inhibitor of p38 MAP kinase, showed only a partial inhibition of histamine production. TPA and LPS also induced histamine production in RAW 264.7 cells, and the histamine production induced by TPA or LPS was also inhibited by PD98059, but the effect of SB203580 was partial. The synthetic glucocorticoid dexamethasone inhibited thapsigargin-induced histamine production, 74-kDa HDC protein expression and the activation of p44/p42 MAP kinases. In conclusion, the increase in histamine production in macrophages stimulated with inflammatory stimulants is due to the increased expression of 74-kDa HDC, which is positively regulated by activated p44/p42 MAP kinases. Dexamethasone inhibits thapsigargin-induced HDC protein expression and histamine production by inhibiting the MAP kinase activation.

[Induction of histidine decarboxylase in inflammation and immune responses].

Histamine is a classical, but still interesting inflammatory mediator. Many people have long believed that histamine is derived from mast cells or basophils alone. However, the histamine-forming enzyme, histidine decarboxylase (HDC), is induced in a variety of tissues in response (i) to gram-positive and gram-negative bacterial components (lipopolysaccharides, peptidoglycan, and enterotoxin A) and (ii) to various cytokines (IL-1, IL-3, IL-12, IL-18, TNF, G-CSF, and GM-CSF). HDC is induced even in mast-cell-deficient mice. The histamine newly formed via the induction of HDC is released immediately and may be involved in a variety of immune responses. Reviewing our work and that of Schayer and Kahlson, the pioneers in this field, lead us to the conclusion that nowadays we need to understand that histamine can be produced via the induction of HDC by a mechanism coupled with the cytokine network. We call this histamine "neohistamine", to distinguish it from the classical histamine derived from mast cells or basophils. Neohistamine is involved in physiological reactions, inflammation, immune responses and a variety of diseases such as periodontitis, muscle fatigue (or temporomandibular disorders), stress- or drug-induced gastric ulcers, rheumatoid arthritis, complications in diabetes, hepatitis, allograft rejection, allergic reactions, tumor growth, and inflammatory side effects of aminobisphosphonates.