Expression Of Histamine H4 Receptor Research Articles

Expression of histamine H4 receptor in human epidermal tissues and attenuation of experimental pruritus using H4 receptor antagonist

Many medicines exist which can cause pruritus (itching) as "serious adverse events." Many severe pruritic conditions respond poorly to histamine H1 receptor antagonists; there is no generally accepted antipruritic treatment. Recently described histamine H4 receptors are expressed in haematopoietic cells and have been linked to the pathology of allergy and asthma. We previously reported their expression in human dermal fibroblasts; in this study we have investigated H4 receptor expression in human epidermal tissue and found it to be greater in keratinocytes in the epidermal upper layer than in the lower layer. We have also investigated the effect of histamine H4 receptor antagonists on histamine H1 receptor antagonist-resistant pruritus using a mouse model. Scratching behavior was induced by histamine (300 nmol) or substance P (100 nmol) injected intradermally into the rostral part of the back of each mouse. Fexofenadine, a histamine H1 receptor antagonist, reduced scratching induced by histamine but not by substance P, whereas JNJ7777120, a histamine H4 receptor antagonist, significantly reduced both histamine- and substance P-induced scratching. These results suggest that H4 receptor antagonists may be useful for treatment of H1 receptor antagonist-resistant pruritus.

Cloning and characterization of dominant negative splice variants of the human histamine H4 receptor

The H(4)R (histamine H(4) receptor) is the latest identified member of the histamine receptor subfamily of GPCRs (G-protein-coupled receptors) with potential functional implications in inflammatory diseases and cancer. The H(4)R is primarily expressed in eosinophils and mast cells and has the highest homology with the H(3)R. The occurrence of at least twenty different hH(3)R (human H(3)R) isoforms led us to investigate the possible existence of H(4)R splice variants. In the present paper, we report on the cloning of the first two alternatively spliced H(4)R isoforms from CD34+ cord blood-cell-derived eosinophils and mast cells. These H(4)R splice variants are localized predominantly intracellularly when expressed recombinantly in mammalian cells. We failed to detect any ligand binding, H(4)R-ligand induced signalling or constitutive activity for these H(4)R splice variants. However, when co-expressed with full-length H(4)R [H(4)R((390)) (H(4)R isoform of 390 amino acids)], the H(4)R splice variants have a dominant negative effect on the surface expression of H(4)R((390)). We detected H(4)R((390))-H(4)R splice variant hetero-oligomers by employing both biochemical (immunoprecipitation and cell-surface labelling) and biophysical [time-resolved FRET (fluorescence resonance energy transfer)] techniques. mRNAs encoding the H(4)R splice variants were detected in various cell types and expressed at similar levels to the full-length H(4)R((390)) mRNA in, for example, pre-monocytes. We conclude that the H(4)R splice variants described here have a dominant negative effect on H(4)R((390)) functionality, as they are able to retain H(4)R((390)) intracellularly and inactivate a population of H(4)R((390)), presumably via hetero-oligomerization.

Expression of histamine H4 receptor in human osteoarthritic synovial tissue

Osteoarthritis (OA) is a progressive non-infl ammatory disorder of the joints caused by gradual loss of cartilage and resulting in the development of bony spurt and cysts with the most common location being the knee [1]. Histamine (H) affects a variety of functions in the human body including joints. Mast cells present in the synovium are the major source of histamine [2]. They often increase in number at site of active cartilage erosion. Recently histamine has been implicated in the pathophysiological processes of OA and H receptors H1 and H2 as well as histamine decarboxylase expression were demonstrated immunohistochemically in OA chondrocytes [3]. This suggests that immuno/infl ammatory reactions are involved in the pathogenesis of OA. Histamine receptors are classifi ed into four subtypes, H1, H2, H3 and H4. The histamine H4 (HH4) receptor is a member of G-protein coupled receptors (GPCRs) and preferentially expressed on the cells of hematopoietic lineage (eosinophils, T cells, dendritic cells, basophils and mast cells) [4]. We have previously shown that the novel HH4 receptor is localized in synoviocytes found in infl amed tissue of patients with rheumatoid arthritis (RA) [5]. Here we report the studies of expression of HH4 receptor in various types of synovial cells of patients with OA.

Comparative study of histamine H4 receptor expression in human dermal fibroblasts

The histamine H4 receptor (H4R) is the newest receptor identified of four histamine receptors. Its expression in numerous immune and inflammatory organs has been implicated in relation to immune systems and allergic diseases. In the present study, we demonstrate the expression of H4R in human dermal fibroblasts and investigate changes in its expression level when stimulated by histamine, phorbol 12-myristate 13-acetate (PMA), lipopolysaccharides (LPS), dexamethasone and indomethacin. Histamine and PMA showed no effects on H4R expression. LPS and indomethacin up-regulated H4R mRNA expression, and 20 microM dexamethasone increased H4R protein levels. These results indicate a good prospective for this new receptor in the development of effective treatments of inflammatory diseases and pruritus or for the appropriate prevention of toxicities.

Histamine H4 receptor expression is elevated in human nasal polyp tissue

Altered histamine metabolism is thought to be involved in the pathomechanism of nasal polyposis characterized by local eosinophil infiltration. The present study was performed to determine whether histamine receptors play a role in the effect of histamine in nasal polyp tissue. The findings suggest that the expression of H1 and H4 receptors is elevated in polyp tissue (p=0.045; p<0.001), while the level of H2 and H3 receptors is not increased significantly. The elevation of H1 and H4 receptors' expression may indicate that the histamine related mechanisms are preferentially mediated through H1 and H4 histamine receptors in the polyp tissue. Simultaneously with increased H4 receptor expression, the concentration of eosinophil cationic protein (ECP) was increased significantly in polyp tissue (p=0.002). One may speculate that the H4 receptor mediated histamine effects have a role in eosinophil accumulation and activation in inflammatory diseases of the nasal and paranasal sinus mucosa, such as nasal polyposis.

Expression of Histamine H4 Receptor in Synovial Cells from Rheumatoid Arthritic Patients

The last of four histamine receptors (HRs), H4 receptor (H4R), was identified in the year 2000. Since that time, the H4R has been implicated in cellular mechanisms related to immune systems, inflammatory processes, and allergic reactions. We have previously reported the expression of H4R mRNA in rheumatoid arthritic (RA) synovial cell cultures by means of the RT-PCR method. The present study demonstrates the expression of H4R at the protein level in RA synovial cell cultures. We also identified that the receptor was expressed in two specific types of cell populations, fibroblast-like and macrophage-like cells from RA synovial tissues. In the culture system, the fifth generation of fibroblast-like synoviocytes showed as strong expression of H4R as in the primary culture. The results provide pragmatic evidence for H4R as a novel target in the development of pharmacotherapeutic agents for RA treatment. Furthermore, the culture system used here will be useful for future studies concerning basic molecular mechanisms underlying the pharmacology of H4R.

Histamine H4 Receptor Expression in Human Synovial Cells Obtained from Patients Suffering from Rheumatoid Arthritis

While histamine H4 receptor (H4R) has been implicated in immune system disturbances in different organ tissues, the presence and possible roles of H4R in synovial cells (SC) of rheumatoid arthritis (RA) patients has not previously been documented. This study conclusively evidences H4R expression in SC of RA patients by use of RT-PCR method. As RA consists mainly of immunological disturbances in SC of RA patients, this study's findings document a novel histamine action site, and opens potential new avenues to investigate mechanisms and to develop pharmacotherapeutic agents for the disease.