The CysLT2R receptor mediates leukotriene C4-driven acute and chronic itch.

Acute and chronic itch are burdensome manifestations of skin pathologies including allergic skin diseases and atopic dermatitis, but the underlying molecular mechanisms are not well understood. Cysteinyl leukotrienes (CysLTs), comprising LTC4, LTD4, and LTE4, are produced by immune cells during type 2 inflammation. Here, we uncover a role for LTC4 and its signaling through the CysLT receptor 2 (CysLT2R) in itch. Cysltr2 transcript is highly expressed in dorsal root ganglia (DRG) neurons linked to itch in mice. We also detected CYSLTR2 in a broad population of human DRG neurons. Injection of leukotriene C4 (LTC4) or its nonhydrolyzable form NMLTC4, but neither LTD4 nor LTE4, induced dose-dependent itch but not pain behaviors in mice. LTC4-mediated itch differed in bout duration and kinetics from pruritogens histamine, compound 48/80, and chloroquine. NMLTC4-induced itch was abrogated in mice deficient for Cysltr2 or when deficiency was restricted to radioresistant cells. Itch was unaffected in mice deficient for Cysltr1, Trpv1, or mast cells (WSh mice). CysLT2R played a role in itch in the MC903 mouse model of chronic itch and dermatitis, but not in models of dry skin or compound 48/80- or Alternaria-induced itch. In MC903-treated mice, CysLT levels increased in skin over time, and Cysltr2-/- mice showed decreased itch in the chronic phase of inflammation. Collectively, our study reveals that LTC4 acts through CysLT2R as its physiological receptor to induce itch, and CysLT2R contributes to itch in a model of dermatitis. Therefore, targeting CysLT signaling may be a promising approach to treat inflammatory itch.

Chronic Itch of Unknown Origin Is Associated With an Enhanced Th2 Skin Immune Profile.

ABSTRACT: Chronic pruritus of unknown origin (CPUO) is described as chronic itch lasting longer than 6 weeks in the absence of a defined skin rash and any known causative disease process. A retrospective study was performed on biopsy samples from patients with CPUO and normal controls to compare the immune profiles of these patients with healthy individuals. We used dual CD3/T-bet and CD3/GATA3 immunohistochemical staining to assess for T-cells expressing Th1 versus Th2 transcription factors, respectively. Our data showed that CD3+ cells of patients with CPUO co-express significantly more GATA3 compared with normal controls. Meanwhile, the normal control skin showed a much more balanced T-bet/GATA3 ratio of co-expression. Our data suggest an enrichment of Th2 cells in CPUO skin by T cell/GATA3 co-staining, supporting that CPUO is increasingly considered a type 2/Th2 cell-associated disease. We thus speculate that type 2 cytokine blockade-based therapies may represent effective treatments for CPUO.

A basophil-neuronal axis promotes itch.

Itch is an evolutionarily conserved sensation that facilitates expulsion of pathogens and noxious stimuli from the skin. However, in organ failure, cancer, and chronic inflammatory disorders such as atopic dermatitis (AD), itch becomes chronic, intractable, and debilitating. In addition to chronic itch, patients often experience intense acute itch exacerbations. Recent discoveries have unearthed the neuroimmune circuitry of itch, leading to the development of anti-itch treatments. However, mechanisms underlying acute itch exacerbations remain overlooked. Herein, we identify that a large proportion of patients with AD harbor allergen-specific immunoglobulin E (IgE) and exhibit a propensity for acute itch flares. In mice, while allergen-provoked acute itch is mediated by the mast cell-histamine axis in steady state, AD-associated inflammation renders this pathway dispensable. Instead, a previously unrecognized basophil-leukotriene (LT) axis emerges as critical for acute itch flares. By probing fundamental itch mechanisms, our study highlights a basophil-neuronal circuit that may underlie a variety of neuroimmune processes.

Tick peptides evoke itch by activating MrgprC11/MRGPRX1 to sensitize TRPV1 in pruriceptors.

BACKGROUND: Tick bites severely threaten human health because they allow the transmission of many deadly pathogens, including viruses, bacteria, protozoa, and helminths. Pruritus is a leading symptom of tick bites, but its molecular and neural bases remain elusive. OBJECTIVES: This study sought to discover potent drugs and targets for the specific prevention and treatment of tick bite-induced pruritus and arthropod-related itch. METHODS: We used live-cell calcium imaging, patch-clamp recordings, and genetic ablation and evaluated mouse behavior to investigate the molecular and neural bases of tick bite-induced pruritus. RESULTS: We found that 2 tick salivary peptides, IP defensin 1 (IPDef1) and IR defensin 2 (IRDef2), induced itch in mice. IPDef1 was further revealed to have a stronger pruritogenic potential than IRDef2 and to induce pruritus in a histamine-independent manner. IPDef1 evoked itch by activating mouse MrgprC11 and human MRGPRX1 on dorsal root ganglion neurons. IPDef1-activated MrgprC11/X1 signaling sensitized downstream ion channel TRPV1 on dorsal root ganglion neurons. Moreover, IPDef1 also activated mouse MrgprB2 and its ortholog human MRGPRX2 selectively expressed on mast cells, inducing the release of inflammatory cytokines and driving acute inflammation in mice, although mast cell activation did not contribute to oxidated IPDef1-induced itch. CONCLUSIONS: Our study identifies tick salivary peptides as a new class of pruritogens that initiate itch through MrgprC11/X1-TRPV1 signaling in pruritoceptors. Our work will provide potential drug targets for the prevention and treatment of pruritus induced by the bites or stings of tick and maybe other arthropods.

Astrocytic STAT3 activation and chronic itch require IP3R1/TRPC-dependent Ca2+ signals in mice.

BACKGROUND: Chronic itch is a debilitating symptom of inflammatory skin diseases, but the underlying mechanism is poorly understood. We have recently demonstrated that astrocytes in the spinal dorsal horn become reactive in models of atopic and contact dermatitis via activation of the transcription factor signal transducer and activator of transcription 3 (STAT3) and critically contribute to chronic itch. In general, STAT3 is transiently activated; however, STAT3 activation in reactive astrocytes of chronic itch model mice persistently occurs via an unknown mechanism. OBJECTIVE: We aimed to determine the mechanisms of persistent activation of astrocytic STAT3 in chronic itch conditions. METHODS: To determine the factors that are required for persistent activation of astrocytic STAT3, Western blotting and calcium imaging with cultured astrocytes or spinal cord slices were performed. Thereafter, chronic itch model mice were used for genetic and behavioral experiments to confirm the role of the factors determined to mediate persistent STAT3 activation from in vitro and ex vivo experiments in chronic itch. RESULTS: IP3 receptor type 1 (IP3R1) knockdown in astrocytes suppressed IL-6-induced persistent STAT3 activation and expression of lipocalin-2 (LCN2), an astrocytic STAT3-dependent inflammatory factor that is required for chronic itch. IP3R1-dependent astrocytic Ca2+ responses involved Ca2+ influx through the cation channel transient receptor potential canonical (TRPC), which was required for persistent STAT3 activation evoked by IL-6. IL-6 expression was upregulated in dorsal root ganglion neurons in a mouse model of chronic itch. Dorsal root ganglion neuron-specific IL-6 knockdown, spinal astrocyte-specific IP3R1 knockdown, and pharmacologic spinal TRPC inhibition attenuated LCN2 expression and chronic itch. CONCLUSION: Our findings suggest that IP3R1/TRPC channel-mediated Ca2+ signals elicited by IL-6 in astrocytes are necessary for persistent STAT3 activation, LCN2 expression, and chronic itch, and they may also provide new targets for therapeutic intervention.

The polymorphisms of IL-6/STAT3 signaling pathway may contribute to cutaneous T-cell lymphomas susceptibility.

IL-6/STAT3 signaling pathway has been suggested to play a role in CTCL pathogenesis. Polymorphisms in STAT3 signaling pathway-related genes might be a risk factor for CTCL. However, the exact role of inherited gene polymorphisms of IL-6 and STAT3 in the pathogenesis of CTCL is still not fully understood. The aim was to examine whether IL-6 cytokine and polymorphisms of IL-6 and STAT3 gene are associated with CTCL susceptibility, stage of disease and pruritus intensity. We compared the IL-6 serum level and the frequency of selected single nucleotide polymorphisms of IL-6 and STAT3 in 106 CTCL and 198 control group using polymerase chain reaction with sequence-specific primers method and ELISA. We have found that serum IL-6 level in CTCL patients was significantly higher than in healthy controls (p < 0.05). We also demonstrated that two genotypes, CC of IL-6 and GG of STAT3, were overexpressed in CTCL patients compared to healthy controls, and that they increase the risk of malignancy development (OR = 1.8, p = 0.04 for IL-6 and OR 2.53, p = 0.0064 for STAT3). Moreover, the GG genotype of STAT3 polymorphism seems to be associated with lack of pruritus or mild pruritus in CTCL patients. Our results indicate that IL-6 is involved in pathogenesis of CTCL but not pruritus. Moreover, CC of IL-6 and GG genotype of STAT3 genes might be considered as the risk factor for development of CTCL.

Resolvin D3 controls mouse and human TRPV1-positive neurons and preclinical progression of psoriasis.

Rationale: Psoriasis is a chronic inflammatory disease caused by a complex interplay between the immune and nervous systems with recurrent scaly skin plaques, thickened stratum corneum, infiltration and activation of inflammatory cells, and itch. Despite an increasing availability of immune therapies, they often have adverse effects, high costs, and dissociated effects on inflammation and itch. Activation of sensory neurons innervating the skin and TRPV1 (transient receptor potential vanilloid 1) are emerging as critical components in the pathogenesis of psoriasis, but little is known about their endogenous inhibitors. Recent studies have demonstrated that resolvins, endogenous lipid mediators derived from omega-3 fatty acids, are potent inhibitors of TRP channels and may offer new therapies for psoriasis without known adverse effects. Methods: We used behavioral, electrophysiological and biochemical approaches to investigate the therapeutic effects of resolvin D3 (RvD3), a novel family member of resolvins, in a preclinical model of psoriasis consisting of repeated topical applications of imiquimod (IMQ) to murine skin, which provokes inflammatory lesions that resemble human psoriasis. Results: We report that RvD3 specifically reduced TRPV1-dependent acute pain and itch in mice. Mechanistically, RvD3 inhibited capsaicin-induced TRPV1 currents in dissociated dorsal root ganglion (DRG) neurons via the N-formyl peptide receptor 2 (i.e. ALX/FPR2), a G-protein coupled receptor. Single systemic administration of RvD3 (2.8 mg/kg) reversed itch after IMQ, and repeated administration largely prevented the development of both psoriasiform itch and skin inflammation with concomitant decreased in calcitonin gene-related peptide (CGRP) expression in DRG neurons. Accordingly, specific knockdown of CGRP in DRG was sufficient to prevent both psoriasiform itch and skin inflammation similar to the effects following RvD3 administration. Finally, we elevated the translational potential of this study by showing that RvD3 significantly inhibited capsaicin-induced TRPV1 activity and CGRP release in human DRG neurons. Conclusions: Our findings demonstrate a novel role for RvD3 in regulating TRPV1/CGRP in mouse and human DRG neurons and identify RvD3 and its neuronal pathways as novel therapeutic targets to treat psoriasis.

Ipilimumab plus nivolumab for patients with metastatic uveal melanoma: a multicenter, retrospective study.

BACKGROUND: Uveal melanoma (UM) is the most common intraocular malignancy in adults. In contrast to cutaneous melanoma (CM), there is no standard therapy, and the efficacy and safety of dual checkpoint blockade with nivolumab and ipilimumab is not well defined. METHODS: We conducted a retrospective analysis of patients with metastatic UM (mUM) who received treatment with ipilimumab plus nivolumab across 14 academic medical centers. Toxicity was graded using National Cancer Institute Common Terminology Criteria for Adverse Events V.5.0. Progression-free survival (PFS) and overall survival (OS) were calculated using Kaplan-Meier methodology. RESULTS: 89 eligible patients were identified. 45% had received prior therapy, which included liver directed therapy (29%), immunotherapy (21%), targeted therapy (10%) and radiation (16%). Patients received a median 3 cycles of ipilimumab plus nivolumab. The median follow-up time was 9.2 months. Overall response rate was 11.6%. One patient achieved complete response (1%), 9 patients had partial response (10%), 21 patients had stable disease (24%) and 55 patients had progressive disease (62%). Median OS from treatment initiation was 15 months and median PFS was 2.7 months. Overall, 82 (92%) of patients discontinued treatment, 34 due to toxicity and 27 due to progressive disease. Common immune-related adverse events were colitis/diarrhea (32%), fatigue (23%), rash (21%) and transaminitis (21%). CONCLUSIONS: Dual checkpoint inhibition yielded higher response rates than previous reports of single-agent immunotherapy in patients with mUM, but the efficacy is lower than in metastatic CM. The median OS of 15 months suggests that the rate of clinical benefit may be larger than the modest response rate.

Itch attenuates CD4 T-cell proliferation in mice by limiting WBP2 protein stability.

To mount an antipathogen response, CD4 T cells must undergo rapid cell proliferation; however, poorly controlled expansion can result in diseases such as autoimmunity. One important regulator of T-cell activity is the E3 ubiquitin ligase Itch. Itch deficient patients suffer from extensive autoinflammation. Similarly, Itch deficient mice exhibit inflammation characterized by high numbers of activated CD4 T cells. While the role of Itch in limiting CD4 T-cell cytokine production has been extensively studied, it is less clear whether and how Itch regulates proliferation of these cells. We determined that Itch deficient CD4 T cells are hyperproliferative in vitro and in vivo, due to increased S phase entry. Whole cell proteomics analysis of Itch deficient primary mouse CD4 T cells revealed increased abundance of the ß-catenin coactivator WW domain-binding protein 2 (WBP2). Furthermore, Itch deficient cells demonstrate increased WBP2 protein stability, and Itch and WBP2 interact in CD4 T cells. Knockdown of WBP2 in CD4 T cells caused reduced proliferation. Together, our data support that Itch attenuates CD4 T cell proliferation by promoting WBP2 degradation. This study identifies novel roles for Itch and WBP2 in regulating CD4 T cell proliferation, providing insight into how Itch may prevent inflammation.

Diagnosis and treatment of primary biliary cholangitis.

Primary biliary cholangitis is a cholestatic, chronic autoimmune liver disease with a wide individual variation in disease progression. The diagnosis is predominantly based on chronic elevation of alkaline phosphatase and the presence of anti-mitochondrial antibodies or other specific antinuclear antibodies (i.e. anti-gp210 and anti-sp100). Even in early-stage disease, health-related quality of life can be severely impaired by symptoms such as pruritus, fatigue, and sicca syndrome and metabolic bone disease should be assessed and treated. The prognosis of the disease is, however, largely determined by the development of cirrhosis and its complications. Ursodeoxycholic acid is associated with an improved prognosis and should be initiated and continued in all patients. Clinical outcome is related to the biochemical response to ursodeoxycholic acid, but the prognosis of those with an incomplete response is still better than those who remain untreated. Obeticholic acid was recently approved as second-line treatment and bezafibrate may serve as an adequate off-label alternative, particularly in patients with pruritus. Preliminary data suggest an additive effect of triple therapy with ursodeoxycholic acid, obeticholic acid, and bezafibrate, whereas other promising drugs are being evaluated in clinical trials.

PAR2 Mediates Itch via TRPV3 Signaling in Keratinocytes.

Animal studies have suggested that transient receptor potential ion channels and G-protein coupled receptors play important roles in itch transmission. TRPV3 gain-of-function mutations have been identified in patients with Olmsted syndrome, which is associated with severe pruritus. However, the mechanisms causing itch remain poorly understood. Here, we show that keratinocytes lacking TRPV3 impair the function of protease-activated receptor 2 (PAR2), resulting in reduced neuronal activation and scratching behavior in response to PAR2 agonists. Moreover, we show that TRPV3 and PAR2 were upregulated in skin biopsies from patients and mice with atopic dermatitis, whereas their inhibition attenuated scratching and inflammatory responses in mouse atopic dermatitis models. These results reveal a previously unrecognized link between TRPV3 and PAR2 in keratinocytes to convey itch information and suggest that a blockade of PAR2 or TRPV3 individually or both may serve as a potential approach for antipruritic therapy in atopic dermatitis.

Mechanisms of Itch in Stasis Dermatitis: Significant Role of IL-31 from Macrophages.

Stasis dermatitis (SD) is a common disease in the elderly population, with pruritus being one of the troublesome symptoms. However, there are few therapeutic modalities available for SD-associated itch because little is known about its pathophysiological mechanism. Therefore, we sought to investigate the mediators of itch in SD using an immunofluorescence study on patient lesions focusing on IL-31. Ex vivo stimulation studies using murine peritoneal macrophages were also used to elucidate the pathological mechanisms of the generation of IL-31. In SD lesions, dermal infiltrating IL-31(+) cells were increased in number compared with the healthy controls, and the majority of IL-31(+) cells were CD68(+) macrophages. The presence of itch in SD was significantly associated with the amount of CD68(+)/IL-31(+) macrophages and CD68(+)/CD163(+) M2 macrophages. The number of CD68(+)/IL-31(+) macrophages was correlated with the number of dermal C-C chemokine receptor type 4(+) T helper type 2 cells, IL-17(+) cells, basophils, substance P(+) cells, and dermal deposition of periostin and hemosiderin. Furthermore, murine peritoneal macrophages expressed an M2 marker arginase-1 and generated IL-31 when stimulated with a combination of substance P, periostin, and red blood cell lysate (representing hemosiderin). IL-31 from macrophages may play a role in itch in SD.

Sensitization of spinal itch transmission neurons in a mouse model of chronic itch requires an astrocytic factor.

BACKGROUND: Chronic itch is a highly debilitating symptom among patients with inflammatory skin diseases. Recent studies have revealed that gastrin-releasing peptide (GRP) and its receptor (gastrin-releasing peptide receptor [GRPR]) in the spinal dorsal horn (SDH) play a central role in itch transmission. OBJECTIVE: We aimed to investigate whether GRP-GRPR signaling is altered in SDH neurons in a mouse model of chronic itch and to determine the potential mechanisms underlying these alterations. METHODS: Patch-clamp recordings from enhanced green fluorescent protein (EGFP)-expressing (GRPR+) SDH neurons were used to examine GRP-GRPR signaling in spinal cord slices obtained from Grpr-EGFP mice. Immunohistochemical, genetic (gene expression and editing through adeno-associated virus vectors), and behavioral approaches were also used for in vivo experiments. RESULTS: We observed potentiation of GRP-evoked excitation in the GRPR+ SDH neurons of mice with contact dermatitis, without concomitant changes in GRPR expression. Interestingly, increases in excitation were attenuated by suppressing the reactive state of SDH astrocytes, which are known to be reactive in patients with chronic itch conditions. Furthermore, CRISPR-Cas9-mediated astrocyte-selective in vivo editing of a gene encoding lipocalin-2 (LCN2), an astrocytic factor implicated in chronic itch, suppressed increases in GRP-induced excitation of GRPR+ neurons, repetitive scratching, and skin damage in mice with contact dermatitis. Moreover, LCN2 potentiated GRP-induced excitation of GRPR+ neurons in normal mice. CONCLUSION: Our findings indicate that, under chronic itch conditions, the GRP-induced excitability of GRPR+ SDH neurons is enhanced through a non-cell-autonomous mechanism involving LCN2 derived from reactive astrocytes.

Nalbuphine, a kappa opioid receptor agonist and mu opioid receptor antagonist attenuates pruritus, decreases IL-31, and increases IL-10 in mice with contact dermatitis.

Chronic itch is one of the disturbing symptoms of inflammatory skin diseases. Kappa opioid receptor agonists are effective in suppressing scratching in mice against different pruritogens. Nalbuphine, a nonscheduled kappa opioid receptor agonist and mu opioid receptor antagonist, has been in clinical use for post-operative pain management since the 1980s and recently has been in clinical trials for chronic itch of prurigo nodularis (https://www.trevitherapeutics.com/nalbuphine). We studied whether nalbuphine is effective against chronic scratching induced by rostral neck application of 1-fluoro-2,4-dinitrobenzene (DNFB), an accepted mouse model of contact dermatitis to study pruritoceptive itch. Mice were treated once a week with either saline or nalbuphine 20 min before the third, fifth, seventh, and ninth sensitizations with DNFB and the number of scratching bouts was counted for 30 min. Skin samples from the neck of mice at week 4 were used to measure protein levels and mRNA expressions of chemokines and cytokines. Different sets of mice were used to study sedation and anhedonic-like behavior of nalbuphine. We found that: nalbuphine (a) antagonized scratching in a dose- and time-dependent manner without affecting locomotion, b) decreased IL-31, and increased anti-inflammatory IL-10, and c) induced more elevations in the levels of CCL2, CCL3, CCL12, CXCL1, CXCL2, CXCL9, CXCL10, IL-1ß, IL-16, TIMP-1, M-CSF, TREM-1 and M1-type macrophages compared to saline. Increases in chemokines and cytokines and M1 macrophages by nalbuphine suggest an inflammatory phase of healing in damaged skin due to scratching. Our data indicate that nalbuphine is an effective antipruritic in murine model of pruritoceptive itch.