Increased expression of the histamine H4 receptor following differentiation and mediation of the H4 receptor on interleukin-8 mRNA expression in HaCaT keratinocytes

The involvement of keratinocytes in pruritus of chronic inflammatory dermatosis

Frequent itching and incessant scratching are commonly observed in various chronic inflammatory skin conditions, including atopic dermatitis and psoriasis. The persistent and prolonged nature of pruritus can worsen one's quality of life. Keratinocytes (KCs), the predominant cells of the epidermis, have been confirmed to interact with sensory neurons and immune cells and be involved in chronic skin inflammatory diseases associated with pruritus. Initially, KCs and sensory neurons form a unique synapse-like connection within the epidermis, serving as the structural foundation for their interaction. Additionally, several receptors, including toll-like receptors and protease-activated receptor 2, expressed on KCs, become activated in an inflammatory milieu. On the one hand, activated KCs are sources of pro-inflammatory cytokines and neurotrophic factors, such as adenosine triphosphate, thymic stromal lymphopoietin, and nerve growth factor, which directly or indirectly participate in stimulating sensory neurons, thereby contributing to the itch sensations. On the other hand, KCs also function as primary transducers alongside intraepidermal nerve endings, directly initiating pruritic responses. This review summarizes the current literature and highlights the critical role of KCs in the development and persistence of chronic itch in inflammatory skin disorders.

IL-8 (CXCL8) Correlations with Psychoneuroimmunological Processes and Neuropsychiatric Conditions

Interleukin-8 (IL-8/CXCL8), an essential CXC chemokine, significantly influences psychoneuroimmunological processes and affects neurological and psychiatric health. It exerts a profound effect on immune cell activation and brain function, suggesting potential roles in both neuroprotection and neuroinflammation. IL-8 production is stimulated by several factors, including reactive oxygen species (ROS) known to promote inflammation and disease progression. Additionally, CXCL8 gene polymorphisms can alter IL-8 production, leading to potential differences in disease susceptibility, progression, and severity across populations. IL-8 levels vary among neuropsychiatric conditions, demonstrating sensitivity to psychosocial stressors and disease severity. IL-8 can be detected in blood circulation, cerebrospinal fluid (CSF), and urine, making it a promising candidate for a broad-spectrum biomarker. This review highlights the need for further research on the diverse effects of IL-8 and the associated implications for personalized medicine. A thorough understanding of its complex role could lead to the development of more effective and personalized treatment strategies for neuropsychiatric conditions.

Effects of Cyclosporine A and Adalimumab on the expression profiles histaminergic system-associated genes and microRNAs regulating these genes in HaCaT cells

Previous studies have not completely elucidated the role of the histaminergic system in the pathogenesis of psoriasis. This study aimed to evaluate the effects of adalimumab and cyclosporine A on the expression of histaminergic system-related genes and miRNAs regulating these genes in bacterial lipopolysaccharide A (LPS)-stimulated human keratinocyte (HaCaT) cells. HaCaT cells were treated with 1 µg/mL LPS for 8 h, followed by treatment with 8 µg/mL adalimumab or 100 ng/mL cyclosporine A for 2, 8, or 24 h. Untreated cells served as controls. The cells were subjected to ribonucleic acid (RNA) extraction and microarray, quantitative real-time polymerase chain reaction, and enzyme-linked immunosorbent assay analyses. Statistical analysis was performed using the Statistica 13.0 PL (StatSoft, Cracow, Poland) and the Transcriptome Analysis Console programs (Affymetrix, Santa Clara, CA, USA) (p < 0.05). The differential expression of the following two miRNAs was not affected in LPS-stimulated cells upon treatment with cyclosporine A or adalimumab: hsa-miR-583 (downregulated expression), involved in the regulation of histamine receptor 1 - HRH1 (overexpression); has-miR-1275 (downregulated expression), involved in the regulation of histamine receptor 1 - HRH3 (overexpression) and Solute carrier family 22 member 3 - SLC23A2 (downregulated expression)). Adalimumab and cyclosporine A modulated the histaminergic system in HaCaT cells in vitro. However, further studies are needed to elucidate the underlying mechanisms.Abbreviations: (-) - downregulated in comparison to the control, (+) - overexpression in comparison to the control, ACTB - β-actine, ADA - Adenosine deaminase, ADCYAP1 - Adenylate Cyclase Activating Polypeptide 1, BMP - bone morphogenetic protein, bp - base pair, cAMP - adenosine 3' 5'-cyclic monophosphate, CBX7 - Chromobox protein homolog 7, cDNA - double-stranded complementary DNA, CSA - cyclosporine A DAG - diacylglycerol, DIAPH - Diaphanous related formin 1, DNMT - DNA methyltransferases, DRD2 - Dopamine receptor D2, EDN1 - Endothelin 1, EDNRA - Endothelin receptor type A, ELISA - Enzyme-linked immunosorbent assay, EZH2 - Enhancer of zeste homolog 2, FC - fold change, GABRB1 - Gamma-aminobutyric acid (GABA) A receptor, alpha 1, GABRB2 - Gamma-aminobutyric acid (GABA) A receptor, alpha 2, GABRB3 - Gamma-aminobutyric acid (GABA) A receptor, alpha 3, HaCaT - Human adult, low-calcium, high-temperature keratinocytes, HIS - Human Histamine, HLAs - human leukocyte antigens, HNMT - Histamine N-methyltransferase, HNMT - Histamine N-Methyltransferase, HRH1 - histamine receptor 1, HRH2 - histamine receptor 2, HRH3 - histamine receptor 3, HRH4 - histamine receptor 4, HTR6 - 5-Hydroxytryptamine Receptor 6, IGF1 - Insulin-like growth factor 1, IL10 -interleukin 10, IL12 -interleukin 12, IL6 - interleukin 6, IP3 - inositol 1,4,5-triphosphate, LPS - bacterial lipopolysaccharide A, LYN - LYN Proto-Oncogene, Src Family Tyrosine Kinase, MAPKs -mitogen-activated protein kinases, miRNA - micro RNA, MMP2 - matrix metalloproteinase-2, NHDF - Normal Human Dermal Fibroblasts, NHEK - Normal Human Epidermal Keratinocytes, OCT3 - organic cation transporter 3, PANTHER - Protein ANalysis THrough Evolutionary Relationships Classification, PBS - phosphate-buffered saline, PI3K-AKT - phosphatidylinositol 3-kinase-protein kinase B, PIP2 - phosphatidylinositol 4,5 bisphosphate, PMSF - phenylmethylsulfonyl fluoride, PSORS1- psoriasis susceptibility gene 1, qRT-PCR - quantitative Reverse Transcription Polymerase Chain Reaction, RNA - ribonucleic acid, RNAi - RNA interference, RTqPCR - Real-Time Quantitative Reverse Transcription Reaction, SLC223A2 - Solute carrier family 22 member 3, SNX -Sorting nexin, SOX9 - SRY-Box Transcription Factor 9, TGF-α - transforming growth factor α, TGF-β - transforming growth factor beta, TNF-α - tumor necrosis factor alpha, TP53 - tumor protein 5 z, VAMP2 - Vesicle associated membrane protein 2.

Quercetin inhibits histamine-induced calcium influx in human keratinocyte via histamine H4 receptors

Histamine is released from mast cells when tissues are inflamed or stimulated by allergens. Activation of histamine receptors and calcium influx via TRPV1 could be related to histamine-induced itch and skin inflammation. Quercetin is known to have anti-inflammatory and anti-itching effects. This study aims to understand whether quercetin can directly affect histamine-induced calcium influx in human keratinocyte. In it, we investigated quercetin, which acts on histamine-induced intracellular free calcium ([Ca2+]i) elevation in human keratinocyte. Changes in [Ca2+]i were measured using spectrofluorometry and confocal Imaging. We detected the expression of IL-8 after treatment of quercetin using qRT-PCR and evaluated its anti-itching effect in BALB/c mice. We also performed a docking study to estimate the binding affinity of quercetin to H4 receptors. We found that quercetin pretreatment decreased histamine-induced [Ca2+]i elevation in a concentration-dependent manner. The inhibitory effect of quercetin on histamine-induced [Ca2+]i elevation was blocked by JNJ7777120, a selective H4 antagonist, as well as by U73122, a PLC inhibitor, and by GF109203X, a PKC inhibitor. We also found that H4 agonist (4-methylhistamine)-induced [Ca2+]i elevation could be inhibited by quercetin. Moreover, the selective TRPV1 blocker capsazepine significantly suppressed the quercetin-mediated inhibition of histamine-induced [Ca2+]i elevation, whereas the TRPV4 blocker GSK2193874 had no effect. Last, quercetin decreased histamine and H4 agonist-induced IL-8 expression in keratinocyte and inhibited the scratching behavior-induced compound 48/80 in BALB/c mice. The molecular docking study also showed that quercetin exhibited high binding affinities with H4 receptors (autodock scores for H4 = -8.7 kcal/mol). These data suggest that quercetin could decrease histamine 4 receptor-induced calcium influx through the TRPV1 channel and could provide a molecular mechanism of quercetin in anti-itching, anti-inflammatory, and unpleasant sensations.

The role of the histamine H4 receptor in atopic dermatitis and psoriasis

Atopic dermatitis (AD) and psoriasis are common skin diseases with a high negative impact on patients' quality of life. Both diseases are mediated by a pro-inflammatory infiltrate consisting of several cell types, such as T-cells, antigen-presenting cells and granulocytes and display disturbed keratinocyte differentiation. Given the fact that histamine levels are also highly elevated in inflamed skin, it is likely that histamine plays a relevant role in disease pathology. However, antagonists blocking histamine H1 receptor or H2 receptors are largely ineffective in reducing chronic symptoms in AD and psoriasis. Over the last years, much research has been undertaken to shed light into the mode of action of the most recently discovered histamine H4 receptor. This research has shown that H4 receptor antagonists display antipruritic and anti-inflammatory effects not only in mouse models but also in first human clinical trials, and therefore, H4 receptors might present a novel therapeutic target. In this review, we summarize the effects of the H4 receptors on different cell types, mouse models and clinical studies in regard to AD and psoriasis respectively. LINKED ARTICLES: This article is part of a themed section on New Uses for 21st Century. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.3/issuetoc.

Preliminary study of histamine H4 receptor expressed on human CD4+ T cells and its immunomodulatory potency in the IL-17 pathway of psoriasis

BACKGROUND

Previous studies have shown the expression of histamine H₄ receptor (H4R) on CD4⁺ T cells, especially human CD4⁺ T_h2-polarized T cells.

OBJECTIVE

This study aimed to investigate the role of H4R on these effector T cells in psoriasis.

METHODS

We enrolled three patients each with active psoriasis, inactive psoriasis, scalp seborrheic dermatitis, and three normal controls, and compared the basal expression of H4R mRNA in their peripheral blood CD4⁺ T cells. Then, we identified H4R expression in dermal CD4⁺ T cells. Furthermore, we investigated H4R expression after stimulating separated peripheral blood CD4⁺ T cells with several inflammatory cytokines.

RESULTS

The results showed higher H4R expression in the active psoriasis group compared to the inactive psoriasis group. It was interesting that interleukin (IL)-23, which is a representative cytokine contributing to T_h17 cell differentiation, stimulated H4R expression significantly. After adding a selective H4R antagonist (JNJ-7777120) while the CD4⁺ T cells were polarized into T_h17 cells, we observed a tendency toward suppressed IL-17 secretion.

CONCLUSIONS

Histamine stimulation influences the IL-17 pathway in psoriasis via the fourth histamine receptor subtype, H4R, on CD4⁺ T cells. The immunomodulatory roles of H4R suggest its potency as a new therapeutic target for obstinate psoriasis.

Stimulation of the histamine 4 receptor upregulates thymic stromal lymphopoietin (TSLP) in human and murine keratinocytes

The cytokine thymic stromal lymphopoietin (TSLP) is involved in the development and the progression of allergic diseases. It is mainly released by epithelial cells at barriers such as skin and gut in response to danger signals. Overexpression of TSLP in keratinocytes (KC) can provoke the development of a type 2 inflammatory response. Additionally, TSLP directly acts on sensory neurons and thereby triggers itch. Since histamine is also increased in lesions of inflammatory skin diseases, the aim of this study was to investigate possible effects of histamine as well as different histamine receptor subtype agonists and antagonists on TSLP production in KC. We therefore stimulated human KC with histamine in the presence or absence of the known TSLP-inductor poly I:C and measured TSLP production at protein as well as mRNA level. Histamine alone did not induce TSLP production in human KC, but pre-incubation with histamine prior to challenge with poly I:C resulted in a significant increase of TSLP production compared to stimulation with poly I:C alone. Experiments with different histamine receptor agonists (H1R: 2-pyridylethylamine; H2R: amthamine; H2R/H4R: 4-methylhistamine (4MH)) revealed a dominant role for the H4R receptor, as 4-MH in combination with poly I:C displayed a significant increase of TSLP secretion, while the other agonists did not show any effect. The increase in TSLP production by 4MH was blocked with the H4R antagonist JNJ7777120. This effect was reproducible also in the murine KC cell line MSC. Taken together, our study indicates a new role for the H4 receptor in the regulation of TSLP in keratinocytes. Therefore, blocking of the H4R receptor in allergic diseases might be promising to alleviate inflammation and pruritus via TSLP.

[Expression and function of the histamine receptors in dermal and articular tissues]

Histamine was first identified in 1910 as a physiologically active amine. It is now recognized for its multiple regulatory activities in the digestive, neuronal, and immune systems, and new roles are still being elucidated. Histamine exerts its effects through four distinct receptor subtypes. The histamine H4 receptor was identified in 2000 and is the most recently identified of the four histamine receptors. It is expressed primarily in immune cells and is involved in physiologic functions related to inflammation and allergy. Recently, the H4 receptor was highlighted as a promising therapeutic target in atopic dermatitis, asthma, and chronic arthritis. In fact, some H4 receptor antagonists have reached clinical trials for the treatment of asthma, atopic dermatitis, and allergic rhinitis. Based on an initial assessment of its distribution, the H4 receptor has been referred to as the histamine receptor of the hematopoietic system. However, the H4 receptor has also been implicated in the regulation of other non-hematopoietic systems. Here, I review the expression and function of the identified histamine receptors, including the H4 receptor with a focus on articular and dermal tissues. In articular tissue, H4 receptor expression has been detected in synovial cells. Chondrocytes, a major cell source for cartilage tissue engineering, also express the H4 receptor. In skin, the H4 receptor is expressed in both the epidermis and dermis, with stronger receptor expression in the epidermis. Further understanding of the functions of H4 receptors in non-hematopoietic cells might lead to novel treatments for diseases with unmet medical needs.