The Histamine H4 Receptor Participates in the Anti-Neuropathic Effect of the Adenosine A3 Receptor Agonist IB-MECA: Role of CD4+ T Cells

A₃ adenosine receptor (A₃AR) agonists have emerged as potent relievers of neuropathic pain by a T cell-mediated production of IL-10. The H₄ histamine receptor (H₄R), also implicated in pain modulation, is expressed on T cells playing a preeminent role in its activation and release of IL-10. To improve the therapeutic opportunities, this study aimed to verify the hypothesis of a possible cross-talk between A₃AR and H₄R in the resolution of neuropathic pain. In the mouse model of Chronic Constriction Injury (CCI), the acute intraperitoneal co-administration of the A₃AR agonist IB-MECA (0.5 mg/kg) and the H₄R agonist VUF 8430 (10 mg/kg), were additive in counteracting mechano-allodynia increasing IL-10 plasma levels. In H₄R^−/− mice, IB-MECA activity was reduced, lower pain relief and lower modulation of plasma IL-1β, TNF-α, IL-6 and IL-10 were shown. The complete anti-allodynia effect of IB-MECA in H₄R^−/− mice was restored after intravenous administration of CD4⁺ T cells obtained from naïve wild type mice. In conclusion, a role of the histaminergic system in the mechanism of A₃AR-mediated neuropathic pain relief was suggested highlighting the driving force evoked by CD4⁺ T cells throughout IL-10 up-regulation.

Identification of TSPAN4 as Novel Histamine H4 Receptor Interactor

The histamine H4 receptor (H4R) is a G protein-coupled receptor that is predominantly expressed on immune cells and considered to be an important drug target for various inflammatory disorders. Like most GPCRs, the H4R activates G proteins and recruits β-arrestins upon phosphorylation by GPCR kinases to induce cellular signaling in response to agonist stimulation. However, in the last decade, novel GPCR-interacting proteins have been identified that may regulate GPCR functioning. In this study, a split-ubiquitin membrane yeast two-hybrid assay was used to identify H4R interactors in a Jurkat T cell line cDNA library. Forty-three novel H4R interactors were identified, of which 17 have also been previously observed in MYTH screens to interact with other GPCR subtypes. The interaction of H4R with the tetraspanin TSPAN4 was confirmed in transfected cells using bioluminescence resonance energy transfer, bimolecular fluorescence complementation, and co-immunoprecipitation. Histamine stimulation reduced the interaction between H4R and TSPAN4, but TSPAN4 did not affect H4R-mediated G protein signaling. Nonetheless, the identification of novel GPCR interactors by MYTH is a starting point to further investigate the regulation of GPCR signaling.

Silencing of H4R inhibits the production of IL-1β through SAPK/JNK signaling in human mast cells

CONTEXT

Mast cell (MC) activation through H4R releases various inflammatory mediators which are associated with allergic asthma.

OBJECTIVES

To investigate the siRNA-mediated gene silencing effect of H4R on human mast cells (HMCs) functions and the activation of stress-activated protein kinases (SAPK)/jun amino-terminal kinases (JNK) signaling pathways for the release of ineterleukin-1β (IL-1β) in HMCs.

MATERIALS AND METHODS

H4R expression was analyzed by RT-PCR and western blotting in human mast cell line-1 (HMC-1) cells and H4RsiRNA transfected cells. The effect of H4RsiRNA and H4R-antagonist on H4R mediated MC functions such as intracellular Ca²⁺ release, degranulation, IL-6 and IL-1β release, and the activation SAPK/JNK signaling pathways were studied. HMC-1 cells were stimulated with 10 μM of histamine (His) and 4-methylhistamine (4-MH) and pretreated individually with H4R-antagonist JNJ7777120 (JNJ), histamine H1 receptor (H1R)-antagonist mepyramine, and signaling molecule inhibitors SP600125 (SP) and Bay117082.

RESULTS

We found that the HMC-1 cells expressed H4R and H4RsiRNA treatment down regulated the H4R expression in HMC-1 cells. Both His and 4-MH induced the intracellular Ca²⁺ release and degranulation whereas; H4R siRNA and JNJ inhibited the effect. Furthermore, the activation of H4R caused the phosphorylation of SAPK/JNK pathways. H4R gene silencing and pretreatment with SP and JNJ decreased His and 4-MH induced phosphorylation of SAPK/JNK. We found that the activation of H4R caused the release of IL-1β (124.22 pg/ml) and IL-6 (122.50 pg/ml) on HMC-1 cells. Whereas, SAPK/JNK inhibitor (68.36 pg/ml) inhibited the H4R mediated IL-1β release.

CONCLUSIONS

Taken together, the silencing of H4R inhibited the H4R mediated MC functions and SAPK/JNK phosphorylation. Furthermore, the H4R activation utilized SAPK/JNK signaling pathway for IL-1β release in HMC-1 cells.

Histamine therapeutic efficacy in metastatic melanoma: Role of histamine H4 receptor agonists and opportunity for combination with radiation

The aims of the work were to improve our knowledge of the role of H4R in melanoma proliferation and assess in vivo the therapeutic efficacy of histamine, clozapine and JNJ28610244, an H4R agonist, in a preclinical metastatic model of melanoma. Additionally, we aimed to investigate the combinatorial effect of histamine and gamma radiation on the radiobiological response of melanoma cells.Results indicate that 1205Lu metastatic melanoma cells express H4R and that histamine inhibits proliferation, in part through the stimulation of the H4R, and induces cell senescence and melanogenesis. Daily treatment with H4R agonists (1 mg/kg, sc) exhibited a significant in vivo antitumor effect and importantly, compounds reduced metastatic potential, particularly in the group treated with JNJ28610244, the H4R agonist with higher specificity. H4R is expressed in benign and malignant lesions of melanocytic lineage, highlighting the potential clinical use of histamine and H4R agonists. In addition, histamine increased radiosensitivity of melanoma cells in vitro and in vivo. We conclude that stimulation of H4R by specific ligands may represent a novel therapeutic strategy in those tumors that express this receptor. Furthermore, through increasing radiation-induced response, histamine could improve cancer radiotherapy for the treatment of melanoma.

Combined blockade of the histamine H1 and H4 receptor suppresses peanut-induced intestinal anaphylaxis by regulating dendritic cell function

BACKGROUND

Signaling through histamine receptors on dendritic cells (DCs) may be involved in the effector phase of peanut-induced intestinal anaphylaxis.

OBJECTIVES

The objective of this study was to determine the role of histamine H1 (H1R) and H4 receptors (H4R) in intestinal allergic responses in a model of peanut allergy.

METHODS

Balb/c mice were sensitized and challenged with peanut. During the challenge phase, mice were treated orally with the H1R antagonist, loratadine, and/or the H4R antagonist, JNJ7777120. Bone marrow-derived DCs (BMDCs) were adoptively transferred to nonsensitized WT mice. Symptoms, intestinal inflammation, and mesenteric lymph node and intestine mucosal DCs were assessed. Effects of the drugs on DC chemotaxis, calcium mobilization, and antigen-presenting cell function were measured.

RESULTS

Treatment with loratadine or JNJ7777120 individually partially suppressed the development of diarrhea and intestinal inflammation and decreased the numbers of DCs in the mesenteric lymph nodes and lamina propria. Combined treatment with both drugs prevented the development of diarrhea and intestinal inflammation. In vitro, the combination suppressed DC antigen-presenting cell function to T helper cells and DC calcium mobilization and chemotaxis to histamine.

CONCLUSION

Blockade of both H1R and H4R in the challenge phase had additive effects in preventing the intestinal consequences of peanut sensitization and challenge. These effects were mediated through the limitation of mesenteric lymph node and intestinal DC accumulation and function. Identification of this histamine H1R/H4R-DC-CD4⁺ T-cell axis provides new insights into the development of peanut-induced intestinal allergic responses and for prevention and treatment of peanut allergy.

Histamine induces proliferation in keratinocytes from patients with atopic dermatitis through the histamine 4 receptor

BACKGROUND

Epidermal hyperproliferation resulting in acanthosis is an important clinical observation in patients with atopic dermatitis, and its underlying mechanisms are not completely understood.

OBJECTIVE

Because increased levels of histamine are present in lesional skin, we investigated the effect of histamine, especially with regard to histamine 4 receptor (H4R) activation, on the proliferation of human and murine keratinocytes.

METHODS

The expression of H4R on human and murine keratinocytes was detected by using real-time PCR. Keratinocyte proliferation was evaluated by using different in vitro cell proliferation assays, scratch assays, and measurement of the epidermal thickness of murine skin.

RESULTS

We detected H4R mRNA on foreskin keratinocytes and on outer root sheath keratinocytes; H4R mRNA was more abundant in keratinocytes from patients with atopic dermatitis compared with those from nonatopic donors. Stimulation of foreskin keratinocytes, atopic dermatitis outer root sheath keratinocytes, and H4R-transfected HaCaT cells with histamine and H4R agonist resulted in an increase in proliferation, which was blocked with the H4R-specific antagonist JNJ7777120. Abdominal epidermis of H4R-deficient mice was significantly thinner, and the in vitro proliferation of keratinocytes derived from H4R-deficient mice was lower compared with that seen in control mice. Interestingly, we only detected H4R expression on murine keratinocytes after stimulation with LPS and peptidoglycan.

CONCLUSION

H4R is highly expressed on keratinocytes from patients with atopic dermatitis, and its stimulation induces keratinocyte proliferation. This might represent a mechanism that contributes to the epidermal hyperplasia observed in patients with atopic dermatitis.

Histamine receptor H4 regulates mast cell degranulation and IgE induced FcεRI upregulation in murine bone marrow-derived mast cells

There is increasing evidence that histamine regulates the immune system via histamine H4 receptors, therefore we sought to investigate the functions of the H4 receptor on mast cells. Mast cells were differentiated from murine bone marrow stem cells, and the expression of mast cell surface markers FcεRI and CD117 were measured using flow cytometry. Real-time qRT-PCR was used to determine the expression of mH4R; as a measure of antigen-dependent degranulation, β-hexosaminidase release assay was carried out using IgE sensitized mast cells. We determined that the expression kinetics of FcεRI and mH4R can be described with a function that has one maximum value in the time range of the culture's differentiation. Antigen-dependent degranulation of murine bone marrow-derived mast cells could be inhibited by a selective H4 antagonist/inverse agonist only when it was present during the IgE sensitization phase of degranulation. In addition, flow cytometric analysis revealed that the H4 antagonist/inverse agonist also inhibited IgE induced FcεRI upregulation. The inhibition percentage of H4 antagonist on IgE induced FcεRI upregulation was determined to be dependent upon the maturity of the mast cell cultures, and this time-dependency was consistent with the expression kinetics of both mH4R and FcεRI. These results imply that H4R has regulatory roles in FcεRI expression and FcεRI mediated functions in mast cells. In conclusion the present study shows that H4 receptors potentially play a role in IgE induced FcεRI upregulation and in the sensitization phase but not the effector phase of mast cell degranulation.