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Introduction: Chronic itch is a central symptom of atopic dermatitis. Cutaneous afferent neurons express receptors interleukins (IL)-4, IL-13, and IL-33, which are type 2 cytokines that are elevated in atopic dermatitis. These neuronal cytokine receptors were found to be required in several murine models of itch. Prior exposure of neurons to either IL-4 or IL-33 increased their response to subsequent chemical pruritogens in mice but has not been previously examined in humans. The objective of the present study was to determine if type 2 cytokine stimulation sensitizes sensory neurons to future itch stimuli in a fully human ex vivo system. Methods: We measured calcium flux from human dorsal root ganglia cultures from cadaveric donors in response to pruritogens following transient exposure to type 2 cytokines. We also measured their effect on neuronal calcium flux and changes in gene expression by RNA sequencing. Results: Type 2 cytokines (IL-4, IL-13, and IL-33) were capable of sensitizing human dorsal root ganglia neurons to both histaminergic and nonhistaminergic itch stimuli. Sensitization was observed after only 2 h of pruritogen incubation. We observed rapid neuronal calcium flux in a small subset of neurons directly in response to IL-4 and to IL-13, which was dependent on the presence of extracellular calcium. IL-4 and IL-13 induced a common signature of upregulated genes after 24 h of exposure that was unique from IL-33 and non-type 2 inflammatory stimuli. Discussion: This study provides evidence of peripheral neuron sensitization by type 2 cytokines as well as broad transcriptomic effects in human sensory ganglia. These studies identify both unique and overlapping roles of these cytokines in sensory neurons.
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BACKGROUND: Chronic pruritus, or itch, is common and debilitating, but the neuroimmune mechanisms that drive chronic itch are only starting to be elucidated. Recent studies demonstrate that the IL-33 receptor (IL-33R) is expressed by sensory neurons. However, whether sensory neuron-restricted activity of IL-33 is necessary for chronic itch remains poorly understood. OBJECTIVES: We sought to determine if IL-33 signaling in sensory neurons is critical for the development of chronic itch in 2 divergent pruritic disease models. METHODS: Plasma levels of IL-33 were assessed in patients with atopic dermatitis (AD) and chronic pruritus of unknown origin (CPUO). Mice were generated to conditionally delete IL-33R from sensory neurons. The contribution of neuronal IL-33R signaling to chronic itch development was tested in mouse models that recapitulate key pathologic features of AD and CPUO, respectively. RESULTS: IL-33 was elevated in both AD and CPUO as well as their respective mouse models. While neuron-restricted IL-33R signaling was dispensable for itch in AD-like disease, it was required for the development of dry skin itch in a mouse model that mirrors key aspects of CPUO pathology. CONCLUSIONS: These data highlight how IL-33 may be a predominant mediator of itch in certain contexts, depending on the tissue microenvironment. Further, this study provides insight into future therapeutic strategies targeting the IL-33 pathway for chronic itch.
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Dermatitis Atópica , Interleucina-33 , Animales , Modelos Animales de Enfermedad , Humanos , Proteína 1 Similar al Receptor de Interleucina-1 , Interleucina-33/metabolismo , Ratones , Prurito , Células Receptoras Sensoriales/metabolismo , Transducción de Señal , PielRESUMEN
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.
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Basófilos/patología , Neuronas/patología , Prurito/patología , Enfermedad Aguda , Alérgenos/inmunología , Animales , Enfermedad Crónica , Dermatitis Atópica/inmunología , Dermatitis Atópica/patología , Modelos Animales de Enfermedad , Histamina/metabolismo , Humanos , Inmunoglobulina E/inmunología , Inflamación/patología , Leucotrienos/metabolismo , Mastocitos/inmunología , Ratones Endogámicos C57BL , Fenotipo , Prurito/inmunología , Canal Catiónico TRPA1/metabolismo , Canales Catiónicos TRPV/metabolismoRESUMEN
Recent studies suggest that mitochondria can be transferred between cells to support the survival of metabolically compromised cells. However, whether intercellular mitochondria transfer occurs in white adipose tissue (WAT) or regulates metabolic homeostasis in vivo remains unknown. We found that macrophages acquire mitochondria from neighboring adipocytes in vivo and that this process defines a transcriptionally distinct macrophage subpopulation. A genome-wide CRISPR-Cas9 knockout screen revealed that mitochondria uptake depends on heparan sulfates (HS). High-fat diet (HFD)-induced obese mice exhibit lower HS levels on WAT macrophages and decreased intercellular mitochondria transfer from adipocytes to macrophages. Deletion of the HS biosynthetic gene Ext1 in myeloid cells decreases mitochondria uptake by WAT macrophages, increases WAT mass, lowers energy expenditure, and exacerbates HFD-induced obesity in vivo. Collectively, this study suggests that adipocytes and macrophages employ intercellular mitochondria transfer as a mechanism of immunometabolic crosstalk that regulates metabolic homeostasis and is impaired in obesity.
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Tejido Adiposo Blanco/metabolismo , Homeostasis , Macrófagos/metabolismo , Mitocondrias/metabolismo , Obesidad/metabolismo , Animales , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Ratones TransgénicosRESUMEN
Atopic dermatitis (AD) is a widespread, chronic skin disease associated with aberrant allergic inflammation. Current treatments involve either broad or targeted immunosuppression strategies. However, enhancing the immune system to control disease remains untested. We demonstrate that patients with AD harbor a blood natural killer (NK) cell deficiency that both has diagnostic value and improves with therapy. Multidimensional protein and RNA profiling revealed subset-level changes associated with enhanced NK cell death. Murine NK cell deficiency was associated with enhanced type 2 inflammation in the skin, suggesting that NK cells play a critical immunoregulatory role in this context. On the basis of these findings, we used an NK cell-boosting interleukin-15 (IL-15) superagonist and observed marked improvement in AD-like disease in mice. These findings reveal a previously unrecognized application of IL-15 superagonism, currently in development for cancer immunotherapy, as an immunotherapeutic strategy for AD.
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Dermatitis Atópica , Deficiencia GATA2 , Animales , Dermatitis Atópica/terapia , Modelos Animales de Enfermedad , Humanos , Inmunoterapia , Células Asesinas Naturales , RatonesRESUMEN
Atopic dermatitis (AD) is a highly prevalent, itchy inflammatory skin disorder that is thought to arise from a combination of skin barrier defect and immune dysregulation. Kallikreins (KLK), a family of serine proteases with a diverse array of homeostatic functions, including skin desquamation and innate immunity, are hypothesized to contribute to AD pathogenesis. However, their precise role in AD has not been clearly defined. In this study, RNA sequencing analyses identified KLK7 as the most abundant and differentially expressed KLK in both human AD and murine AD-like skin. Further, in mice, Klk7 expression was localized to the epidermis in both steady state and inflammation. Unexpectedly, KLK7 was dispensable for the development of AD-associated skin inflammation. Instead, KLK7 was selectively required for AD-associated chronic itch. Even without the alleviation of skin inflammation, KLK7-deficient mice exhibited significantly attenuated scratching, compared with littermate controls, after AD-like disease induction. Collectively, our findings indicate that KLK7 promotes AD-associated itch independently from skin inflammation and reveal a previously unrecognized epidermal-neural mechanism of AD associated itch.
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Dermatitis Atópica/complicaciones , Epidermis/patología , Calicreínas/metabolismo , Prurito/patología , Adulto , Animales , Biopsia , Dermatitis Atópica/inmunología , Dermatitis Atópica/patología , Modelos Animales de Enfermedad , Epidermis/inmunología , Femenino , Humanos , Calicreínas/genética , Masculino , Ratones , Ratones Noqueados , Prurito/etiología , RNA-Seq , Regulación hacia ArribaRESUMEN
Although connections between the immune and nervous systems have long been recognized, the precise mechanisms that underlie this relationship are just starting to be elucidated. Advances in sensory biology have unveiled novel mechanisms by which inflammatory cytokines promote itch and pain sensations to coordinate host-protective behavioral responses. Conversely, new evidence has emphasized the importance of immune cell regulation by sensory neurons. By focusing on itch biology and how it has been informed by the more established field of pain research, we highlight recent interdisciplinary studies that demonstrate how novel neuroimmune interactions underlie a diversity of sensory, inflammatory, and infectious diseases.
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Neuroinmunomodulación , Percepción del Dolor , Prurito/inmunología , Células Receptoras Sensoriales/inmunología , Piel/inmunología , Animales , Humanos , Infecciones/inmunología , Infecciones/patología , Inflamación/inmunología , Inflamación/patología , Prurito/patología , Células Receptoras Sensoriales/patología , Piel/patologíaRESUMEN
Classical itch studies have focused on immunoglobulin E (IgE)-mediated mast cell activation and histamine release. Recently, members of the Mas-related G-protein-coupled receptor (Mrgpr) family have been identified as mast cell receptors, but their role in itch is unclear. Here, we report that mast cell activation via Mrgprb2 evoked non-histaminergic itch in mice independently of the IgE-Fc epsilon RI (FcεRI)-histamine axis. Compared with IgE-FcεRI stimulation, Mrgprb2 activation of mast cells was distinct in both released substances (histamine, serotonin, and tryptase) and the pattern of activated itch-sensory neurons. Mrgprb2 deficiency decreased itch in multiple preclinical models of allergic contact dermatitis (ACD), a pruritic inflammatory skin disorder, and both mast cell number and PAMP1-20 concentrations (agonist of the human Mrgprb2 homolog, MRGPRX2) were increased in human ACD skin. These findings suggest that this pathway may represent a therapeutic target for treating ACD and mast-cell-associated itch disorders in which antihistamines are ineffective.
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Mastocitos/inmunología , Proteínas del Tejido Nervioso/metabolismo , Prurito/patología , Receptores Acoplados a Proteínas G/metabolismo , Receptores de IgE/metabolismo , Receptores de Neuropéptido/metabolismo , Adolescente , Adulto , Anciano , Anciano de 80 o más Años , Animales , Femenino , Histamina/metabolismo , Antagonistas de los Receptores Histamínicos/uso terapéutico , Humanos , Inmunoglobulina E/inmunología , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Persona de Mediana Edad , Fragmentos de Péptidos/metabolismo , Receptores Acoplados a Proteínas G/genética , Serotonina/metabolismo , Piel/metabolismo , Triptasas/metabolismo , Adulto JovenRESUMEN
Relentless, repetitive itching and scratching is a debilitating feature of many chronic inflammatory skin disorders such as atopic dermatitis. While well known clinically, this itch-scratch cycle has historically lacked in-depth mechanistic understanding. However, recent advances at the interface of itch neurobiology and skin immunology have shed new light on this phenomenon. In this review, we highlight recent advances in our understanding of the neuroimmunology of chronic itch centered around three key points of entry into the itch-scratch cycle: the epithelial barrier, the immune system, and the peripheral nervous system. Furthermore, we explore novel neuro-epithelial-immune interactions that may represent promising therapeutic paradigms.
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Sistema Nervioso Periférico/inmunología , Prurito/inmunología , Animales , Humanos , Sistema Nervioso Periférico/patología , Prurito/patologíaRESUMEN
Peripheral nerve damage initiates a complex series of structural and cellular processes that culminate in chronic neuropathic pain. The recent success of a type 2 angiotensin II (Ang II) receptor (AT2R) antagonist in a phase II clinical trial for the treatment of postherpetic neuralgia suggests angiotensin signaling is involved in neuropathic pain. However, transcriptome analysis indicates a lack of AT2R gene (Agtr2) expression in human and rodent sensory ganglia, raising questions regarding the tissue/cell target underlying the analgesic effect of AT2R antagonism. We show that selective antagonism of AT2R attenuates neuropathic but not inflammatory mechanical and cold pain hypersensitivity behaviors in mice. Agtr2-expressing macrophages (MΦs) constitute the predominant immune cells that infiltrate the site of nerve injury. Interestingly, neuropathic mechanical and cold pain hypersensitivity can be attenuated by chemogenetic depletion of peripheral MΦs and AT2R-null hematopoietic cell transplantation. Our study identifies AT2R on peripheral MΦs as a critical trigger for pain sensitization at the site of nerve injury, and therefore proposes a translatable peripheral mechanism underlying chronic neuropathic pain.
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Dolor Crónico/metabolismo , Macrófagos/metabolismo , Neuralgia/metabolismo , Receptor de Angiotensina Tipo 2/metabolismo , Aloinjertos , Animales , Dolor Crónico/genética , Dolor Crónico/patología , Trasplante de Células Madre Hematopoyéticas , Macrófagos/patología , Ratones , Neuralgia/genética , Neuralgia/patología , Receptor de Angiotensina Tipo 2/genéticaRESUMEN
BACKGROUND: Chronic itch is a highly debilitating symptom that underlies many medical disorders with no universally effective treatments. Although unique neuronal signaling cascades in the sensory ganglia and spinal cord have been shown to critically promote the pathogenesis of chronic itch, the role of skin-associated cells remains poorly understood. OBJECTIVE: We sought to examine the cutaneous mechanisms underlying transient receptor potential vanilloid 4 (TRPV4)-mediated allergic and nonallergic chronic itch. METHODS: Expression of TRPV4 in chronic itch and healthy control skin preparations was examined by using real-time RT-PCR. Trpv4eGFP mice were used to study the expression and function of TRPV4 in the skin by means of immunofluorescence staining, flow cytometry, calcium imaging, and patch-clamp recordings. Genetic and pharmacologic approaches were used to examine the role and underlying mechanisms of TRPV4 in mouse models of dry skin-associated chronic itch and spontaneous scratching associated with squaric acid dibutylester-induced allergic contact dermatitis. RESULTS: TRPV4 is selectively expressed by dermal macrophages and epidermal keratinocytes in mice. Lineage-specific deletion of TRPV4 in macrophages and keratinocytes reduces allergic and nonallergic chronic itch in mice, respectively. Importantly, TRPV4 expression is significantly increased in skin biopsy specimens from patients with chronic idiopathic pruritus in comparison with skin from healthy control subjects. Moreover, TRPV4-dependent chronic itch requires 5-hydroxytryptamine (5-HT) signaling secondary to activation of distinct 5-HT receptors in mice with allergic and those with nonallergic chronic itch conditions. CONCLUSION: Our study reveals previously unrecognized mechanisms by which TRPV4-expressing epithelial and immune cells in the skin critically and dynamically mediate chronic itch and unravels novel targets for therapeutics in the setting of chronic itch.
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Dermatitis Alérgica por Contacto/inmunología , Dermis/inmunología , Regulación de la Expresión Génica/inmunología , Queratinocitos/inmunología , Macrófagos/inmunología , Prurito/inmunología , Canales Catiónicos TRPV/inmunología , Animales , Enfermedad Crónica , Dermatitis Alérgica por Contacto/genética , Dermatitis Alérgica por Contacto/patología , Dermis/patología , Femenino , Regulación de la Expresión Génica/genética , Humanos , Queratinocitos/patología , Macrófagos/patología , Masculino , Ratones , Ratones Noqueados , Prurito/genética , Prurito/patología , Canales Catiónicos TRPV/genéticaRESUMEN
Although both persistent itch and inflammation are commonly associated with allergic contact dermatitis (ACD), it is not known if they are mediated by shared or distinct signaling pathways. Here we show that both TRPA1 and TRPV1 channels are required for generating spontaneous scratching in a mouse model of ACD induced by squaric acid dibutylester (SADBE), a small molecule hapten, through directly promoting the excitability of pruriceptors. TRPV1 but not TRPA1 channels protect the skin inflammation, as genetic ablation of TRPV1 function or pharmacological ablation of TRPV1-positive sensory nerves promotes cutaneous inflammation in the SADBE-induced ACD. Our results demonstrate that persistent itch and inflammation are mediated by distinct cellular and molecular mechanisms in a mouse model of ACD. Identification of distinct roles of TRPA1 and TRPV1 in regulating itch and inflammation may provide new insights into the pathophysiology and treatment of chronic itch and inflammation in ACD patients.
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Dermatitis Alérgica por Contacto/inmunología , Prurito/inmunología , Piel/inmunología , Canal Catiónico TRPA1/inmunología , Canales Catiónicos TRPV/inmunología , Animales , Dermatitis Alérgica por Contacto/genética , Modelos Animales de Enfermedad , Femenino , Humanos , Masculino , Ratones , Ratones Endogámicos C57BL , Prurito/genética , Canal Catiónico TRPA1/genética , Canales Catiónicos TRPV/genéticaRESUMEN
Mammals have evolved neurophysiologic reflexes, such as coughing and scratching, to expel invading pathogens and noxious environmental stimuli. It is well established that these responses are also associated with chronic inflammatory diseases, including asthma and atopic dermatitis. However, the mechanisms by which inflammatory pathways promote sensations such as itch remain poorly understood. Here, we show that type 2 cytokines directly activate sensory neurons in both mice and humans. Further, we demonstrate that chronic itch is dependent on neuronal IL-4Rα and JAK1 signaling. We also observe that patients with recalcitrant chronic itch that failed other immunosuppressive therapies markedly improve when treated with JAK inhibitors. Thus, signaling mechanisms previously ascribed to the immune system may represent novel therapeutic targets within the nervous system. Collectively, this study reveals an evolutionarily conserved paradigm in which the sensory nervous system employs classical immune signaling pathways to influence mammalian behavior.
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Prurito/inmunología , Células Receptoras Sensoriales/inmunología , Células Receptoras Sensoriales/metabolismo , Transducción de Señal , Enfermedades de la Piel/inmunología , Animales , Ganglios Espinales , Humanos , Interleucina-13/inmunología , Interleucina-4/inmunología , Janus Quinasa 1/metabolismo , Ratones , Ratones Endogámicos C57BL , Prurito/metabolismo , Enfermedades de la Piel/patologíaAsunto(s)
Antiinfecciosos/farmacología , Prurito/inmunología , Receptor Toll-Like 4/inmunología , beta-Defensinas/farmacología , Animales , Ganglios Espinales , Células HEK293 , Humanos , Ratones Endogámicos C57BL , Ratones Transgénicos , Neuronas/fisiología , Receptores CCR2/genética , Receptores CCR2/inmunología , Receptores CCR6/genética , Receptores CCR6/inmunología , Transducción de Señal/efectos de los fármacos , Piel/inmunología , Canales Catiónicos TRPV/genética , Receptor Toll-Like 4/genéticaRESUMEN
The skin barrier is essential for host defense, but how the skin provides protection when the barrier is breached is not well understood. In this issue of Immunity, Gallo and colleagues report that keratinocytes integrate signals from antimicrobial peptides via MAVS signaling to amplify their antiviral immune response.
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Antiinfecciosos , Piel/inmunología , Péptidos Catiónicos Antimicrobianos/inmunología , Humanos , Inmunidad , Inmunidad Innata , Queratinocitos/inmunología , Transducción de SeñalRESUMEN
Mesenchymal stem cell (MSC) therapy is an emerging field of regenerative medicine; however, it is often unclear how these cells mediate repair. Here, we investigated the use of MSCs in the treatment of intestinal disease and modeled abnormal repair by creating focal wounds in the colonic mucosa of prostaglandin-deficient mice. These wounds developed into ulcers that infiltrated the outer intestinal wall. We determined that penetrating ulcer formation in this model resulted from increased hypoxia and smooth muscle wall necrosis. Prostaglandin I2 (PGI2) stimulated VEGF-dependent angiogenesis to prevent penetrating ulcers. Treatment of mucosally injured WT mice with a VEGFR inhibitor resulted in the development of penetrating ulcers, further demonstrating that VEGF is critical for mucosal repair. We next used this model to address the role of transplanted colonic MSCs (cMSCs) in intestinal repair. Compared with intravenously injected cMSCs, mucosally injected cMSCs more effectively prevented the development of penetrating ulcers, as they were more efficiently recruited to colonic wounds. Importantly, mucosally injected cMSCs stimulated angiogenesis in a VEGF-dependent manner. Together, our results reveal that penetrating ulcer formation results from a reduction of local angiogenesis and targeted injection of MSCs can optimize transplantation therapy. Moreover, local MSC injection has potential for treating diseases with features of abnormal angiogenesis and repair.