TRPV4-ß-catenin axis is a novel therapeutic target for dry skin-induced chronic itch.

Dry skin induced chronic pruritus is an increasingly common and debilitating problem, especially in the elderly. Although keratinocytes play important roles in innate and adaptive immunity and keratinocyte proliferation is a key feature of dry skin induced chronic pruritus, the exact contribution of keratinocytes to the pathogenesis of dry skin induced chronic pruritus is poorly understood. In this study, we generated the acetone-ether-water induced dry skin model in mice and found that epidermal hyperplasia induced by this model is partly dependent on the ß-catenin signaling pathway. XAV939, an antagonist of ß-catenin signaling pathway, inhibited epidermal hyperplasia in dry skin model mice. Importantly, dry skin induced chronic pruritus also dramatically reduced in XAV939 treated mice. Moreover, acetone-ether-water treatment-induced epidermal hyperplasia and chronic itch were decreased in Trpv4-/- mice. In vitro, XAV939 inhibited hypo-osmotic stress induced proliferation of HaCaT cells, and hypo-osmotic stress induced proliferation of in HaCaT cells and primary cultured keratinocytes were also significantly reduced by blocking TRPV4 function. Finally, thymic stromal lymphopoietin release was examined both in vivo and in vitro, which was significantly inhibited by XAV939 treatment and Trpv4 deficiency, and anti-TSLP antibody treatment significantly decreased AEW-induced scratching behavior. Overall, our study revealed a unique ability of TRPV4 expressing keratinocytes in the skin, which critically mediated dry skin induced epidermal hyperplasia and chronic pruritus, thus provided novel insights into the development of therapies for chronic pruritus in the elderly.

Lysophosphatidic Acid Receptors LPAR5 and LPAR2 Inversely Control Hydroxychloroquine-Evoked Itch and Scratching in Mice.

Lysophosphatidic acids (LPAs) evoke nociception and itch in mice and humans. In this study, we assessed the signaling paths. Hydroxychloroquine was injected intradermally to evoke itch in mice, which evoked an increase of LPAs in the skin and in the thalamus, suggesting that peripheral and central LPA receptors (LPARs) were involved in HCQ-evoked pruriception. To unravel the signaling paths, we assessed the localization of candidate genes and itching behavior in knockout models addressing LPAR5, LPAR2, autotaxin/ENPP2 and the lysophospholipid phosphatases, as well as the plasticity-related genes Prg1/LPPR4 and Prg2/LPPR3. LacZ reporter studies and RNAscope revealed LPAR5 in neurons of the dorsal root ganglia (DRGs) and in skin keratinocytes, LPAR2 in cortical and thalamic neurons, and Prg1 in neuronal structures of the dorsal horn, thalamus and SSC. HCQ-evoked scratching behavior was reduced in sensory neuron-specific Advillin-LPAR5-/- mice (peripheral) but increased in LPAR2-/- and Prg1-/- mice (central), and it was not affected by deficiency of glial autotaxin (GFAP-ENPP2-/-) or Prg2 (PRG2-/-). Heat and mechanical nociception were not affected by any of the genotypes. The behavior suggested that HCQ-mediated itch involves the activation of peripheral LPAR5, which was supported by reduced itch upon treatment with an LPAR5 antagonist and autotaxin inhibitor. Further, HCQ-evoked calcium fluxes were reduced in primary sensory neurons of Advillin-LPAR5-/- mice. The results suggest that LPA-mediated itch is primarily mediated via peripheral LPAR5, suggesting that a topical LPAR5 blocker might suppress "non-histaminergic" itch.

Interleukin Profiling in Atopic Dermatitis and Chronic Nodular Prurigo.

The clinical manifestations of atopic dermatitis (AD) and chronic nodular prurigo (CNPG) include pruritus and eczema/lesions, posing significant challenges for patients. Th2 cells and ILC2, marked by cytokine production-particularly IL-4/13-are crucial therapeutic targets. Despite displaying a dose-dependent lack of pruritus induction post-injection, IL-13 acts through the IL-13Rα1 and IL-13Rα2 receptor system. Our study focused on investigating ex vivo skin biopsies in AD (n = 17), CNPG (n = 14) and healthy controls (HC; n = 10), examining the gene expression landscape of interleukins linked with pruritus (IL-13, IL-4, IL-31) and their corresponding receptors. Compared to HC, results revealed a significant upregulation of IL-4, IL-13, and IL-13RA1 in AD, whereas CNPG did not show increased IL13 expression. Notably, the decoy receptor IL-13RA2 displayed intriguing patterns, with AD showing a marked increase compared to both HC and CNPG. Positive correlations between receptor expression and itch intensity and hyperkinesis sensation underscore clinical relevance, potentially serving as biomarkers. The findings suggest a pivotal role of IL-4 and IL-13, along with IL-13RA1, in pruritus pathogenesis in both entities, while IL-13 upregulation in AD is countered by IL-13RA2. The comparable expression of IL-13RA2 to HC in CNPG suggests the absence of this regulatory mechanism, potentially worsening the disease and leading to prolonged scratching behavior. These insights illuminate the intricate interplay of interleukins and receptors in different pruritus phenotypes, laying the groundwork for understanding underlying mechanisms and offering avenues for therapeutic intervention.

Neural pathways that compel us to scratch an itch.

Itch is a unique sensory experience that is responded to by scratching. How pruritogens, which are mechanical and chemical stimuli with the potential to cause itch, engage specific pathways in the peripheral and central nervous system has been a topic of intense investigation over the last few years. Studies employing recently developed molecular, physiological, and behavioral techniques have delineated the dedicated mechanisms that transmit itch information to the brain. This review outlines the genetically defined and evolutionary conserved circuits for itch ranging from the skin-innervating peripheral neurons to the cortical neurons that drive scratching. Moreover, scratch suppression of itch is attributed to the concurrent activation of pain and itch pathways. Hence, we discuss the similarities between circuits driving pain and itch.

FGF13 enhances the function of TRPV1 by stabilizing microtubules and regulates acute and chronic itch.

Itching is an aversive somatosensation that triggers the desire to scratch. Transient receptor potential (TRP) channel proteins are key players in acute and chronic itch. However, whether the modulatory effect of fibroblast growth factor 13 (FGF13) on acute and chronic itch is associated with TRP channel proteins is unclear. Here, we demonstrated that conditional knockout of Fgf13 in dorsal root ganglion neurons induced significant impairment in scratching behaviors in response to acute histamine-dependent and chronic dry skin itch models. Furthermore, FGF13 selectively regulated the function of the TRPV1, but not the TRPA1 channel on Ca2+ imaging and electrophysiological recordings, as demonstrated by a significant reduction in neuronal excitability and current density induced by TRPV1 channel activation, whereas TRPA1 channel activation had no effect. Changes in channel currents were also verified in HEK cell lines. Subsequently, we observed that selective modulation of TRPV1 by FGF13 required its microtubule-stabilizing effect. Furthermore, in FGF13 knockout mice, only the overexpression of FGF13 with a tubulin-binding domain could rescue TRP channel function and the impaired itch behavior. Our findings reveal a novel mechanism by which FGF13 is involved in TRPV1-dependent itch transduction and provide valuable clues for alleviating pathological itch syndrome.

Immunologic Profiling of Immune-Related Cutaneous Adverse Events with Checkpoint Inhibitors Reveals Polarized Actionable Pathways.

PURPOSE: Immune-related cutaneous adverse events (ircAE) occur in ≥50% of patients treated with checkpoint inhibitors, but the underlying mechanisms for ircAEs are poorly understood. EXPERIMENTAL DESIGN: Phenotyping/biomarker analyses were conducted in 200 patients on checkpoint inhibitors [139 with ircAEs and 61 without (control group)] to characterize their clinical presentation and immunologic endotypes. Cytokines were evaluated in skin biopsies, skin tape strip extracts, and plasma using real-time PCR and Meso Scale Discovery multiplex cytokine assays. RESULTS: Eight ircAE phenotypes were identified: pruritus (26%), maculopapular rash (MPR; 21%), eczema (19%), lichenoid (11%), urticaria (8%), psoriasiform (6%), vitiligo (5%), and bullous dermatitis (4%). All phenotypes showed skin lymphocyte and eosinophil infiltrates. Skin biopsy PCR revealed the highest increase in IFNγ mRNA in patients with lichenoid (P < 0.0001) and psoriasiform dermatitis (P < 0.01) as compared with patients without ircAEs, whereas the highest IL13 mRNA levels were detected in patients with eczema (P < 0.0001, compared with control). IL17A mRNA was selectively increased in psoriasiform (P < 0.001), lichenoid (P < 0.0001), bullous dermatitis (P < 0.05), and MPR (P < 0.001) compared with control. Distinct cytokine profiles were confirmed in skin tape strip and plasma. Analysis determined increased skin/plasma IL4 cytokine in pruritus, skin IL13 in eczema, plasma IL5 and IL31 in eczema and urticaria, and mixed-cytokine pathways in MPR. Broad inhibition via corticosteroids or type 2 cytokine-targeted inhibition resulted in clinical benefit in these ircAEs. In contrast, significant skin upregulation of type 1/type 17 pathways was found in psoriasiform, lichenoid, bullous dermatitis, and type 1 activation in vitiligo. CONCLUSIONS: Distinct immunologic ircAE endotypes suggest actionable targets for precision medicine-based interventions.

Beyond the Surface: A Narrative Review Examining the Systemic Impacts of Recessive Dystrophic Epidermolysis Bullosa.

Recessive dystrophic epidermolysis bullosa (RDEB) is a rare genetic disease resulting from inadequate type VII collagen (C7). Although recurrent skin blisters and wounds are the most apparent disease features, the impact of C7 loss is not confined to the skin and mucous membranes. RDEB is a systemic disease marred by chronic inflammation, fibrotic changes, pain, itch, and anemia, significantly impacting QOL and survival. In this narrative review, we summarize these systemic features of RDEB and promising research avenues to address them.

The COL6A5-p.Glu2272* mutation induces chronic itch in mice.

Pruritus is a common irritating sensation that provokes the desire to scratch. Environmental and genetic factors contribute to the onset of pruritus. Moreover, itch can become a major burden when it becomes chronic. Interestingly, the rare Collagen VI alpha 5 (COL6A5) gene variant p.Glu2272* has been identified in two families and an independent patient with chronic neuropathic itch. These patients showed reduced COL6A5 expression in skin and normal skin morphology. However, little progress has been made until now toward understanding the relationships between this mutation and chronic itch. Therefore, we developed the first mouse model that recapitulates COL6A5-p.Glu2272* mutation using the CRISPR-Cas technology and characterized this new mouse model. The mutant mRNA, measured by RT-ddPCR, was expressed at normal levels in dorsal root ganglia and was decreased in skin. The functional exploration showed effects of the mutation with some sex dysmorphology. Mutant mice had increased skin permeability. Elevated spontaneous scratching and grooming was detected in male and female mutants, with increased anxiety-like behavior in female mutants. These results suggest that the COL6A5-p.Glu2272* mutation found in patients contributes to chronic itch and induces in mice additional behavioral changes. The COL6A5-p.Glu2272* mouse model could elucidate the pathophysiological mechanisms underlying COL6A5 role in itch and help identify potential new therapeutic targets.

Neuronal BST2: A Pruritic Mediator alongside Protease-Activated Receptor 2 in the IL-27-Driven Itch Pathway.

Chronic itch is a common and complex symptom often associated with skin diseases such as atopic dermatitis (AD). Although IL-27 is linked to AD, its role and clinical significance in itch remain undefined. We sought to investigate IL-27 function in itch using tissue-specific transgenic mice, various itch models, behavior scoring, RNA sequencing, and cytokine/kinase array. Our findings show that IL-27 receptors were overexpressed in human AD skin. Intradermal IL-27 injection failed to directly induce itch in mice but upregulated skin protease-activated receptor 2 (PAR2) transcripts, a key factor in itch and AD. IL-27 activated human keratinocytes, increasing PAR2 transcription and activity. Coinjection of SLIGRL (PAR2 agonist) and IL-27 in mice heightened PAR2-mediated itch. In addition, IL-27 boosted BST2 transcription in sensory neurons and keratinocytes. BST2 was upregulated in AD skin, and its injection in mice induced itch-like response. BST2 colocalized with sensory nerve branches in AD skin from both human and murine models. Sensory neurons released BST2, and mice with sensory neuron-specific BST2 knockout displayed reduced itch responses. Overall, this study provides evidence that skin IL-27/PAR2 and neuronal IL-27/BST2 axes are implicated in cutaneous inflammation and pruritus. The discovery of neuronal BST2 in pruritus shed light on BST2 in the itch cascade.

Molecular and cellular pruritus mechanisms in the host skin.

Pruritus, also known as itching, is a complex sensation that involves the activation of specific physiological and cellular receptors. The skin is innervated with sensory nerves as well as some receptors for various sensations, and its immune system has prominent neurological connections. Sensory neurons have a considerable impact on the sensation of itching. However, immune cells also play a role in this process, as they release pruritogens. Disruption of the dermal barrier activates an immune response, initiating a series of chemical, physical, and cellular reactions. These reactions involve various cell types, including keratinocytes, as well as immune cells involved in innate and adaptive immunity. Collective activation of these immune responses confers protection against potential pathogens. Thus, understanding the molecular and cellular mechanisms that contribute to pruritus in host skin is crucial for the advancement of effective treatment approaches. This review provides a comprehensive analysis of the present knowledge concerning the molecular and cellular mechanisms underlying itching signaling in the skin. Additionally, this review explored the integration of these mechanisms with the broader context of itch mediators and the expression of their receptors in the skin.

Influence of pathogenic filaggrin variants on dupilumab treatment in atopic dermatitis.

BACKGROUND: Pathogenic variants in filaggrin (FLG) are associated with an increased risk of atopic dermatitis (AD). OBJECTIVE: We evaluated the influence of FLG variants on the effectiveness of dupilumab treatment in AD. METHODS: This prospective observational study included adult AD patients treated with dupilumab from the BioDay registry. FLG was analyzed with single-molecule molecular inversion probe-targeted sequencing. Novel mutations were confirmed by Sanger sequencing. Eczema Area and Severity Index (EASI), Investigator Global Assessment (IGA), numeric rating scale (NRS) pruritus, Dermatology Quality of Life Index (DLQI), and Patient-Oriented Eczema Measure (POEM) were assessed at baseline and at weeks 16 and 52. The study was registered at ClinicalTrials.gov as NCT03549416. RESULTS: Genetic analysis of the 285 included patients showed biallelic pathogenic variants (FLG-/-) in 41 (14%), monoallelic pathogenic variants (FLG-/+) in 64 (23%), and wild-type alleles (FLG+/+) in 180 patients (63%). Three novel pathogenic variants were found. We observed no clinically relevant differences in EASI, IGA, NRS pruritus, DLQI, or total POEM scores for patients with and without pathogenic FLG variants at all time points. The FLG-/- group showed significantly higher POEM flaking and dryness scores at week 16 (P < .001 and P = .002, respectively) and week 52 (P < .001 and P = .016, respectively) compared to FLG+/+ as well as significant differences compared to FLG-/+, while differences in delta scores were nonsignificant. CONCLUSION: The effectiveness of dupilumab treatment in AD patients was not influenced by pathogenic FLG variants. However, patients with biallelic pathogenic FLG variants tended to have drier skin before and during dupilumab treatment compared to patients with monoallelic pathogenic variants or wild-type alleles.

Sensory neuronal STAT3 is critical for IL-31 receptor expression and inflammatory itch.

IL-31 receptor blockade suppresses pruritus of atopic dermatitis. However, cell-type-specific contributions of IL-31 receptor to itch, its expression mechanism, and the downstream signaling pathway to induce itch remain unknown. Here, using conditional knockout mice, we demonstrate that IL-31-induced itch requires sensory neuronal IL-31 receptor and STAT3. We find that IL-31 receptor expression is dependent on STAT3 in sensory neurons. In addition, pharmacological experiments suggest that STAT3 activation is important for the itch-inducing signaling downstream of the IL-31 receptor. A cutaneous IL-31 injection induces the nuclear accumulation of activated STAT3 first in sensory neurons that abundantly express IL-31 receptor and then in other itch-transmitting neurons. IL-31 enhances itch induced by various pruritogens including even chloroquine. Finally, pruritus associated with dermatitis is partially dependent on sensory neuronal IL-31 receptor and strongly on sensory neuronal STAT3. Thus, sensory neuronal STAT3 is essential for IL-31-induced itch and further contributes to IL-31-independent inflammatory itch.

Imiquimod-induced pruritus in female wild-type and knockin Wistar rats: underscoring behavioral scratching in a rat model for antipruritic treatments.

OBJECTIVES: Animal models of skin disease are used to evaluate therapeutics to alleviate disease. One common clinical dermatological complaint is pruritus (itch), but there is a lack of standardization in the characterization of pre-clinical models and scratching behavior, a key itch endpoint, is often neglected. One such model is the widely used imiquimod (IMQ) mouse model of psoriasis. However, it lacks characterized behavioral attributes like scratching, nor has widely expanded to other species like rats. Given these important attributes, this study was designed to broaden the characterization beyond the expected IMQ-induced psoriasis-like skin inflammatory skin changes and to validate the role of a potential therapeutic agent for pruritus in our genetic rat model. The study included female Wistar rats and genetically modified knockin (humanized proteinase-activated receptor 2 (F2RL1) female rats, with the widely used C57BL/6 J mice as a methodology control for typical IMQ dosing. RESULTS: We demonstrate that the IMQ model can be reproduced in rats, including their genetically modified derivatives, and how scratching can be used as a key behavioral endpoint. We systemically delivered an anti-PAR2 antibody (P24E1102) which reversed scratching bouts-validating this behavioral methodology and have shown its feasibility and value in identifying effective antipruritic drugs.

Descending dopaminergic pathway facilitates itch signal processing via activating spinal GRPR+ neurons.

A11 dopaminergic neurons regulate somatosensory transduction by projecting from the diencephalon to the spinal cord, but the function of this descending projection in itch remained elusive. Here, we report that dopaminergic projection neurons from the A11 nucleus to the spinal dorsal horn (dopaminergicA11-SDH ) are activated by pruritogens. Inhibition of these neurons alleviates itch-induced scratching behaviors. Furthermore, chemogenetic inhibition of spinal dopamine receptor D1-expressing (DRD1+ ) neurons decreases acute or chronic itch-induced scratching. Mechanistically, spinal DRD1+ neurons are excitatory and mostly co-localize with gastrin-releasing peptide (GRP), an endogenous neuropeptide for itch. In addition, DRD1+ neurons form synapses with GRP receptor-expressing (GRPR+ ) neurons and activate these neurons via AMPA receptor (AMPAR). Finally, spontaneous itch and enhanced acute itch induced by activating spinal DRD1+ neurons are relieved by antagonists against AMPAR and GRPR. Thus, the descending dopaminergic pathway facilitates spinal itch transmission via activating DRD1+ neurons and releasing glutamate and GRP, which directly augments GRPR signaling. Interruption of this descending pathway may be used to treat chronic itch.

Microglia-neuron interactions promote chronic itch via the NLRP3-IL-1ß-GRPR axis.

BACKGROUND: Spinal astrocytes contribute to chronic itch via sensitization of itch-specific neurons expressing gastrin-releasing peptide receptor (GRPR). However, whether microglia-neuron interactions contribute to itch remains unclear. In this study, we aimed to explore how microglia interact with GRPR+ neurons and promote chronic itch. METHODS: RNA sequencing, quantitative real-time PCR, western blot, immunohistochemistry, RNAscope ISH, pharmacologic and genetic approaches were performed to examine the roles of spinal NLRP3 (The NOD-like receptor family, pyrin-containing domain 3) inflammasome activation and IL-1ß-IL1R1 signaling in chronic itch. Grpr-eGFP and Grpr KO mice were used to investigate microglia-GRPR+ neuron interactions. RESULTS: We observed NLRP3 inflammasome activation and IL-1ß production in spinal microglia under chronic itch conditions. Blockade of microglial activation and the NLRP3/caspase-1/IL-1ß axis attenuated chronic itch and neuronal activation. Type 1 IL-1 receptor (IL-1R1) was expressed in GRPR+ neurons, which are essential for the development of chronic itch. Our studies also find that IL-1ß+ microglia are localized in close proximity to GRPR+ neurons. Consistently, intrathecal injection of IL1R1 antagonist or exogenous IL-1ß indicate that the IL-1ß-IL-1R1 signaling pathway enhanced the activation of GRPR+ neurons. Furthermore, our results demonstrate that the microglial NLRP3/caspase-1/IL-1ß axis contributes to several different chronic itches triggered by small molecules and protein allergens from the environment and drugs. CONCLUSION: Our findings reveal a previously unknown mechanism in which microglia enhances the activation of GRPR+ neurons through the NLRP3/caspase-1/IL-1ß/IL1R1 axis. These results will provide new insights into the pathophysiology of pruritus and novel therapeutic strategies for patients with chronic itch.

Native liver survival in bile salt export pump deficiency: results of a retrospective cohort study.

BACKGROUND: Bile salt export pump (ABCB11) deficiency [Progressive familial intrahepatic cholestasis (PFIC2)] is the most common genetic cause of PFIC and is associated with pruritus and progressive liver disease. Surgical biliary diversion or pharmacological [ileal bile acid transporter inhibitor (IBATi)] approaches can be used to block the recirculation of bile acids to the liver. There is a paucity of detailed data on the natural history and, in particular, the longitudinal evolution of bile acid levels to predict treatment response. Cross-sectional data from large international consortia suggested a maximum cutoff value of bile acids after the intervention to predict a successful outcome. METHODS: This retrospective, single-center, cohort study included all patients with confirmed biallelic pathogenic ABCB11 genotype PFIC2 treated at our institution with ≥2 years follow-up. The outcomes of interventions and predictors of long-term health were analyzed. RESULTS: Forty-eight cases were identified with PFIC2. Eighteen received partial external biliary diversion (PEBD) surgery, and 22 patients underwent liver transplantation. Two patients developed HCC and 2 died. Improved survival with native liver was closely associated with genotype, complete normalization of serum bile acids following PEBD, and alleviation of pruritus. Persistence of mild-to-moderate elevation of bile acids or a secondary rise following normalization was associated with liver disease progression and led to transplantation, suggesting that any prolonged elevation of bile acids worsens the chance of native liver survival. Higher-grade fibrosis at the time of PEBD was not associated with reduced long-term native liver survival. Patients with PFIC2 benefit from PEBD even at a stage of advanced fibrosis. CONCLUSION: Serum bile acid levels are an early predictor of treatment response and might serve as the gold standard in the evaluation of novel therapies including IBATi.

Interleukin-31 Receptor A Expression in the Dorsal Root Ganglion of Mice with Atopic Dermatitis.

Atopic dermatitis (AD) is a common skin disease caused by genetic and environmental factors. However, the mechanisms underlying AD development remain unclear. In this study, we examined the genetic factors contributing to the onset of itch-associated scratching in different strains of mice. Interleukin-31 (IL-31) induces severe scratching and dermatitis in mice. However, the site of action of IL-31 remains unclear. Cutaneous IL-31 and IL-31 receptor A (IL-31RA) mRNAs in the dorsal root ganglion (DRG) are expressed exclusively in the AD model, i.e., NC/Nga mice. Here we evaluated the effects of repeated administration of IL-31 on the scratching behavior in NC/Nga, BALB/c, and C57BL/6 mice. The results showed that repeated administration of IL-31 significantly increased itch-associated scratching (LLS) behavior in the three strains of mice. One hour after an intravenous IL-31 injection, BALB/c mice showed alloknesis-like behavior. Mite infestation and IL-31 administration triggered itchy skin, increased LLS counts and DRG neuronal IL-31RA expression, and eventually caused dermatitis. The dermatitis severity and LLS counts induced by mite infestation and IL-31 administration were in the order NC/Nga > BALB/c > C57BL/6. In conclusion, neuronal IL-31RA expression in the DRG was the most important genetic factor affecting the severity of LLS and dermatitis in mice.