Intractable Itch Research Articles

The role of PAR2 in regulating MIF release in house dust mite-induced atopic dermatitis.

Atopic dermatitis (AD) is a chronic disease characterized by relapsed eczema and intractable itch, and is often triggered by house dust mites (HDM). PAR2 is a G-protein coupled receptor on keratinocytes and may be activated by HDM to affect AD processes. We first established a HDM-derived AD mouse model in wild-type (WT) and Par2-/- mice. Single cell RNA sequencing of the diseased skins found a stronger cellular communication between the ligand macrophage migration inhibitory factor (MIF) from keratinocytes and its receptors on antigen-presenting cells, suggesting the critical role of MIF in AD. HDM-WT mice showed severer skin lesions and pathological changes with stronger immunofluorescence MIF signals in skin sections than HDM-Par2-/- mice. Primary keratinocytes from WT mice stimulated with HDM or SLIGRL (PAR2 agonist) secreted more MIF in cultured medium and induced stronger immunofluorescence MIF signals than those from Par2-/- mice. The skin section of HDM-WT mice showed higher immunofluorescence signals of P115 (relating to MIF secretion) and KIF13B (possibly relating to intracellular trafficking of MIF) than that of HDM-Par2-/- mice. Acetylation of α-tubulin increased after stimulation by SLIGRL in WT keratinocytes but not in Par2-/- keratinocytes. HDM-WT mice treated with the MIF antagonist ISO-1 displayed improvement of AD-like presentations and lower expressions of IL-4, IL-13, TSLP and Arg1 (a biomarker of M2 macrophage) mRNAs. We conclude that MIF is an important cytokine and is significantly increased in the AD model. PAR2 affects AD changes by regulating the expression, intracellular trafficking, and secretion of MIF in epidermis.

Maralixibat (Livmarli)

CADTH recommends that Livmarli should be reimbursed by public drug plans for the treatment of cholestatic pruritus in patients with Alagille syndrome (ALGS) if certain conditions are met. Livmarli should only be covered to treat patients aged 12 months and older with a diagnosis of ALGS and who have impaired bile flow demonstrated by at least 1 of the following: elevated serum bile acids (sBAs), conjugated bilirubin, or gamma-glutamyl transferase; fat-soluble vitamin deficiency; and/or intractable itch. Patients must experience moderate to severe itch symptoms and must be currently or have been previously treated with systemic medication for itch. Livmarli should only be reimbursed if it is prescribed under the care of a specialist with experience in managing ALGS, if patients experience an improvement in their itching after using Livmarli for 6 months, and if the cost of Livmarli is reduced. Livmarli should be stopped if the patient receives a liver transplant or biliary diversion surgery.

Possible involvement of satellite glial cell–derived lipocalin-2 in dermatitis not itch-related behavior of atopic dermatitis model mice

Introduction: Atopic dermatitis (AD) is a chronic inflammatory skin disease with intractable itch. Dorsal root ganglion (DRG) plays an important role in signal transduction of itch. It has been reported that satellite glial cells (SGC) present around DRG neurons are involved in pain and itch through interactions with DRG neurons. However, it is unclear what factors in SGC are involved in inducing dermatitis and itch in DRG. In this study, we found that the expression of lipocalin-2 (LCN2) was increased in SGC of AD model NC/Nga mouse. Therefore, we also examined whether SGC-derived lipocalin-2 is involved in the induction of dermatitis and itch-related behavior in this model mice. Materials and methods: AD-like dermatitis was induced by the application of Dermatophagoides farinae body ointment to NC/Nga mice (AD-NC/Nga mice). Protein and gene expression in the DRG and spinal cord of AD-NC/Nga mice were examined. The effect of the LCN2 antibody on dermatitis pathology in AD-NC/Nga mice was confirmed. Results: LCN2 expression in DRG of AD-NC/Nga mice was higher than that of control NC/Nga mice. Immunohistochemical analysis revealed that LCN2 was expressed on SGC in DRG. Gene expression level of LCN2 in the DRG was significantly increased faster than in the spinal cord during the process of induction of AD-like dermatitis. LCN2 increased gene expression of MMP-9 in mouse DRG. Intrathecally administrated anti-LCN2 antibody twice a week for 3 weeks at the same time as induction of AD-like dermatitis reduced dermatitis score without inhibiting scratching behavior. Discussion: In conclusion, our data suggest that SGC-derived LCN2 is involved in the pathogenesis of dermatitis rather than itch-related behavior in AD-NC/Nga mice.

INDIVIDUAL ARTICLE: Prurigo Nodularis: Current Clinicopathologic Overview and Psychodermatological Perspectives.

Prurigo nodularis (PN) is a quintessential neurocutaneous condition characterized by neural sensitization and intractable itch leading to intense scratching. This causes the formation of nodules with epidermal thickening and further release of pro-inflammatory mediators that recruit immune cells and increase dermal nerve proliferation and hypertrophy perpetuating the itch-scratch cycle. Those with PN have a significant quality-of-life (QoL) burden due to itch, anxiety, and sleep disturbance. In addition, PN exhibits psychiatric comorbidities that affect mental wellbeing such as depression, mood disorders, and substance abuse. This paper serves as an overview of the clinicopathologic aspects of PN, the burden of PN on QoL, and the psychodermatological aspects of the disease state.  J Drugs Dermatol. 2023;22:12(Suppl 2):s6-11.

Potential antipruritic neuronal targets of nalfurafine in the murine spinal dorsal horn

Introduction: Itch is an unpleasant sensation that evokes a scratching behavior which often damages the skin. Nalfurafine is a kappa opioid receptor (KOR) agonist known as an effective drug used to control the intractable itch. Mechanistically, the spinal cord is a target of nalfurafine, however, little is known about the specific sites important to the antipruritic effects of nalfurafine. Therefore, the aim of this study was an investigation to uncover the sites of action of nalfurafine in the spinal neuronal pathway of itch. Materials and Methods: To reveal the antipruritic action of nalfurafine in the murine spinal dorsal horn, we conducted in vivo electrophysiology, behavioral experiments, and high-sensitive in situ hybridization (ISH) using normal C57BL/6J mice. Results: Behavioral analyses indicated that intrathecal injection of nalfurafine reduced, but not entirely eliminated the gastrin-releasing peptide (GRP)-evoked scratching bouts. In vivo electrophysiological recordings revealed that nalfurafine administration suppressed chloroquine (CQ)-responsive dorsal horn neurons in 15.8% (3/19) of mice. In fact, only 1 of 3 nalfurafine-suppressed mice responded to GRP. ISH in 3 sections of the spinal cord showed that 24.8% (154/623) were double-positive for GRP and KOR and 13.6% (68/431) for GRP receptor (GRPR) and KOR in total KOR+ cells. Most KOR+ cells were negative for GRP and GRPR. Intrathecal injection of dynorphin-saporin did not change the number of scratching bouts caused by GRP. However, it reduced the number of scratching bouts evoked by intradermal injection of CQ. Discussion: In conclusion, our data suggest that nalfurafine targets both GRP+ KOR+ and GRPR+ KOR+ cells which are present in a 2:1 ratio and suppresses CQ-induced itch in the spinal dorsal horn. These findings suggest that GRP+ KOR- or GRPR+ KOR- cells may function as interneurons in the spinal neuronal pathway of itch.

360 TLR4 Plays An Important Role In Chronic Relapsing Pruritus Induced By Subcutaneous Capsaicin Injection In Neonatal Rats

Despite the high prevalence of chronic dermatitis and the accompanied intractable itch, therapeutics that specifically target itching have low efficacy. Although toll-like receptors (TLRs) are suggested to contribute to immune activation and neural sensitization, their roles in chronic itch in the skin remain elusive. Here, we show that the RBL-2H3 mast cell line expresses TLR4 and that treatment with a TLR4 antagonist opposes the LPS-dependent increase in mRNA levels of Th2 and innate cytokines.

Chronic Nodular Prurigo: An Update on the Pathogenesis and Treatment.

Chronic nodular prurigo (CNPG) is a recalcitrant chronic itchy disorder that affects the quality of life. It can be triggered by multiple etiologies, such as atopic dermatitis, diabetes, and chronic renal diseases. The mechanisms of CNPG are complicated and involved the interaction of the cutaneous, immune, and nervous systems. Diverse immune cells, including eosinophils, neutrophils, T cells, macrophages, and mast cells infiltrated the lesional skin of CNPG, which initiated the inflammatory cytokines and pruritogens release. In addition, the interaction between the immune cells and activated peripheral sensory nerve fibers by neurotransmitters caused neuroinflammation in the skin and intractable itch. This itch-scratch vicious cycle of CNPG results in disease exacerbation. CNPG is difficult to treat with traditional therapies. Recently, great advances have been made in the pathophysiology of both inflammation and pruritus transmission in CNPG. In this review, we summarize the updated mechanisms and novel therapies for CNPG.

518 Role Of TLR4 In chronic relapsing itch induced by subcutaneous capsaicin injection in neonatal rats

Despite the high prevalence of chronic dermatitis and the accompanied intractable itch, therapeutics that specifically target itching have low efficacy. Increasing evidence suggests that TLRs contribute to immune activation and neural sensitization; however, their roles in chronic itch remain elusive. Here, we show that the RBL-2H3 mast cell line expresses TLR4 and that treatment with a TLR4 antagonist opposes the LPS dependent increase in mRNA levels of Th2 and innate cytokines. The pathological role of TLR4 activation in itching was studied in neonate rats that developed chronic itch due to neuronal damage after receiving subcutaneous capsaicin injections.

Pathophysiological Role of TLR4 in Chronic Relapsing Itch Induced by Subcutaneous Capsaicin Injection in Neonatal Rats.

Despite the high prevalence of chronic dermatitis and the accompanied intractable itch, therapeutics that specifically target itching have low efficacy. Increasing evidence suggests that TLRs contribute to immune activation and neural sensitization; however, their roles in chronic itch remain elusive. Here, we show that the RBL-2H3 mast cell line expresses TLR4 and that treatment with a TLR4 antagonist opposes the LPS dependent increase in mRNA levels of Th2 and innate cytokines. The pathological role of TLR4 activation in itching was studied in neonate rats that developed chronic itch due to neuronal damage after receiving subcutaneous capsaicin injections. Treatment with a TLR4 antagonist protected these rats with chronic itch against scratching behavior and chronic dermatitis. TLR4 antagonist treatment also restored the density of cutaneous nerve fibers and inhibited the histopathological changes that are associated with mast cell activation after capsaicin injection. Additionally, the expression of IL-1β, IL-4, IL-5, IL-10, and IL-13 mRNA in the lesional skin decreased after TLR4 antagonist treatment. Based on these data, we propose that inhibiting TLR4 alleviated itch in a rat model of chronic relapsing itch, and the reduction in the itch was associated with TLR4 signaling in mast cells and nerve fibers.

Cluster Analysis of Circulating Plasma Biomarkers in Prurigo Nodularis Reveals a Distinct Systemic Inflammatory Signature in African Americans

Patients with prurigo nodularis (PN) suffer from intractable itch and dramatic reduction in QOL. Although there is significant clinical heterogeneity in the presentation of PN, disease endotypes remain unknown. We assayed circulating plasma cytokine concentrations in patients with PN (n= 20) along with matched healthy controls and utilized an unsupervised machine learning algorithm to identify disease endotypes. We found two distinct clusters of patients with PN with noninflammatory (cluster 1) and inflammatory (cluster 2) plasma profiles. Cluster 2 had more African Americans (82%, n= 9 vs. 33%, n= 3; P= 0.028), higher Worst Itch Numeric Rating Scale scores (9.5 ± 0.9 vs. 8.3 ± 1.2; P= 0.036), and lower QOL as reflected by higher Dermatology Life Quality Index scores (21.9 ± 6.4 vs. 13.0 ± 4.1; P= 0.015). In addition, cluster 1 had a higher rate of myelopathy (67%, n= 6 vs. 18%, n= 2; P= 0.028). Compared with cluster 1, cluster 2 had higher levels of IL-1α, IL-4, IL-5, IL-6, IL-10, IL-17A, IL-22, IL-25, and IFN-α. With population-level analysis, African American patients with PN had higher erythrocyte sedimentation rate, C-reactive protein, ferritin, and eosinophils and lower transferrin than Caucasian patients with PN. These findings indicate discrete clusters of patients with PN with plasma biomarker profiles corresponding to distinct demographic and clinical characteristics, potentially allowing for precision medicine approaches to treat PN.

Qol-P-01 - Interviews with patients and their spouses to capture personal descriptions of early treatment experience with mogamulizumab for mycosis fungoides (MF) and Sézary syndrome (SS)

<h3>Background:</h3> Mycosis fungoides (MF) and Sézary syndrome (SS) are rare and chronic non-Hodgkin lymphomas that present in skin and can progress to involve extracutaneous sites. For many patients, skin lesions are disfiguring with an intractable itch. Other symptoms can include difficulty regulating body temperature and sleep disturbance. Symptomatic MF and SS can have a negative impact on health-related quality of life (HRQL). Mogamulizumab is approved in Europe for the treatment of adult patients with MF or SS after at least one prior systemic therapy based on the efficacy and safety demonstrated in the phase 3 MAVORIC trial (NCT01728805). <h3>Objectives:</h3> To capture personal descriptions from patients and their spouses of the burden of MF and SS before starting mogamulizumab treatment and their early treatment experience. <h3>Methods:</h3> Five patients and three spouses were recruited at two hospital clinics in the UK. Following informed consent, 1:1 semi-structured, 60-minute telephone interviews were conducted. Participants were asked about their experience of symptoms and impact of their condition on domains of HRQL prior to starting treatment with mogamulizumab, and any changes during the first six months of treatment. Spouses were also asked about any impact on their role as a carer since mogamulizumab treatment was initiated. Interviews were transcribed, responses coded, and narrative summary provided. <h3>Findings:</h3> Prior to treatment with mogamulizumab, patients and their spouses reported moderate-to-severe problems with all skin-related symptoms and regulating their body temperature. The majority described fatigue and sleep problems, with spouses also reporting patients' moderate-to-severe problems with those symptoms. On starting mogamulizumab, both patients and their spouses described rapid improvement in itching, with gradual improvement in skin flaking, redness, and pain/discomfort. Similarly, body temperature regulation, fatigue and sleep quality gradually improved in the first six months of treatment. There was a wide distribution in the reported level of disease impact on HRQL domains prior to treatment with mogamulizumab including emotional well-being, ability to self-care, activities of daily living, social well-being, and family relationships. Symptom presentation on hands and feet was associated with greater impact on these QoL domains. For those with moderate-to-severe problems pre-treatment, patients and spouses described a meaningful reduction in the level of impairment, sometimes within the first few months of treatment. Spouses reported that their everyday life as a carer had positively changed since their partner had received treatment with mogamulizumab. <h3>Conclusion:</h3> Participants described multiple symptoms and the detrimental impact on their HRQL prior to treatment with mogamulizumab. There was a rapid improvement in itching with improvement in other symptoms and overall HRQL in the first six months of mogamulizumab treatment.

Dorsal root ganglion neurostimulation: a target for treatment for intractable neuropathic itch?

Intractable itch is a severe, relentless, and debilitating chronic itch that is not curable by any known means. Ordinary medical measures usually are not helpful for these patients who often suffer from neural hypersensitization. These patients have often exhausted numerous treatments and still suffer from intractable pruritus. As chronic pain and chronic pruritus share many similarities, the use of medical treatments that reduce neural sensitization in intractable chronic pain may similarly help intractable chronic itch. One of the fastest growing treatments for chronic pain management is spinal neuromodulation. To our knowledge, the use of these modalities has not been applied to chronic intractable itch. The dorsal root ganglion (DRG) has recently become a target for neuromodulation. Through this review, we evaluate the rationale behind the use of the DRG electrical stimulation modality for chronic pain and assess its potential utility for patients with chronic, intractable pruritus. Given the similarities between chronic pain and chronic pruritus and the success of DRG neurostimulation in chronic pain, it may prove worthwhile to explore the efficacy of the modality for specific conditions presenting with chronic intractable pruritus.

Qol-O-06 - Development of EORTC/CLTF questionnaire to assess HRQOL in primary cutaneous T-cell and B-cell lymphomas: phase I

<h3>Background:</h3> Health-related quality of life (HRQoL) in patients with cutaneous lymphoma (CL) is negatively impacted by a large burden of disease symptoms including intractable itch, pain, discomfort and socially stigmatising cosmetic disfigurement which may adversely affect patient self-esteem and interpersonal relationships. There is currently no cure for CL and as such, accurate determination of patient HRQoL is of paramount importance. To date, the impact of both skin disease and of a cancer diagnosis on patient HRQoL in CL is assessed using separate, non-CL-specific questionnaires. A composite HRQoL questionnaire addressing all aspects of the disease is lacking. <h3>Methods:</h3> The EORTC Quality of Life Group questionnaire development guidelines were followed. For phase I, semi-structured interviews were conducted in 15 patients with early-stage mycosis fungoides (IA–IIA), 30 patients with late-stage mycosis fungoides/Sézary syndrome (IIB–IVB) (15 patients <3 years and >3 years from diagnosis) and 15 patients with cutaneous B cell lymphoma. Collaborators communicated during the patient recruitment to ensure balanced patient selection with respect to age, gender, stage, duration of the disease, and number of (previous) treatments. <h3>Results:</h3> Patients were recruited in 5 countries (6 centres) across Europe. So far, 62 patients participated (target 60) from each of the following representative patient groups: early MF (stage IA–IIA), late MF (stage IIB–IVB) and cutaneous B cell lymphoma. Data from patient interviews and questionnaires is being analyzed using basic quantitative analyses, including generation of descriptive statistics (e.g., %missing data, means and standard deviations, floor and ceiling effects, etc.), prevalence (number of patients who experienced each complaint i.e. who scored 2, 3 or 4, divided by the total number of patients who completed that item, multiplied by 100), priority ratings (number of patients and professionals who have given priority ratings to each item) and range of responses for each item. The data from the debriefing questions will be reported both quantitatively and qualitatively (in narrative form). <h3>Conclusion:</h3> Once completed, phase I issues will be operationalised into items and any new items created in a style and format compatible with the EORTC quality of life group translation guidelines (phase II). The preliminary module will be pre-tested in phase III followed by large-scale international field-testing in phase IV. A comprehensive HRQoL questionnaire (module) for patients with CL is being developed to more accurately measure assessment of the impact of HRQoL in patients with skin lymphomas.

Central, but not peripheral, nervous system ERK2 is essential for itch signals in murine allergic skin inflammation.

Itch is a common cutaneous symptom in a variety of dermatological diseases, but detailed neuropathological mechanisms remain to be fully elucidated. This study aimed to assess in vivo ERK2 functions in the nervous system for itch responses. We generated conditional knockout mice deficient in ERK2 of the central nervous system (CNS) or peripheral nervous system (PNS), respectively, and assessed chemical and mechanical itch responses in vivo. Chemical itch responses to histamine, but not to BAM8-22, were alleviated in CNS Erk2-deficient mice. In contrast, both histamine- and BAM8-22-induced mechanical itch (alloknesis) were alleviated in CNS Erk2-deficient mice. Neither chemical itch nor mechanical itch induced by these pruritogens was affected by PNS ERK2 deficiency. Spontaneous scratching behaviors during acute and chronic contact hypersensitivity were impaired in CNS Erk2-deficient mice, but not PNS Erk2-deficient mice. In addition, CNS ERK2 deficiency attenuated mechanical itch responses during chronic contact hypersensitivity. Again, PNS Erk2-deficient mice showed comparable responses of mechanical itch to control mice. In addition, alleviated mechanical itch in CNS Erk2-deficient mice was observed in IgE-mediated prurigo-like allergic skin inflammation. Mechanical itch induced by IL-31 was also alleviated by CNS ERK2 deficiency. Phosphorylated ERK1/2 was detected in neurokinin B-expressing cells of the spinal dorsal horn of control mice; these cells accumulated during the induction of chronic contact hypersensitivity. Notably, phosphorylated ERK1/2 was also localized in spinal urocortin3-expressing neurons that are known to transmit mechanical itch. Spinal cord ERK2 could be a potential therapeutic target for intractable itch in pruritic skin diseases.

Intractable Itch in Atopic Dermatitis: Causes and Treatments.

Itch or pruritus is the hallmark of atopic dermatitis and is defined as an unpleasant sensation that evokes the desire to scratch. It is also believed that itch is a signal of danger from various environmental factors or physiological abnormalities. Because histamine is a well-known substance inducing itch, H1-antihistamines are the most frequently used drugs to treat pruritus. However, H1-antihistamines are not fully effective against intractable itch in patients with atopic dermatitis. Given that intractable itch is a clinical problem that markedly decreases quality of life, its treatment in atopic dermatitis is of high importance. Histamine-independent itch may be elicited by various pruritogens, including proteases, cytokines, neuropeptides, lipids, and opioids, and their cognate receptors, such as protease-activated receptors, cytokine receptors, Mas-related G protein-coupled receptors, opioid receptors, and transient receptor potential channels. In addition, cutaneous hyperinnervation is partly involved in itch sensitization in the periphery. It is believed that dry skin is a key feature of intractable itch in atopic dermatitis. Treatment of the underlying conditions that cause itch is necessary to improve the quality of life of patients with atopic dermatitis. This review describes current insights into the pathophysiology of itch and its treatment in atopic dermatitis.

Critical role of GRP receptor-expressing neurons in the spinal transmission of imiquimod-induced psoriatic itch.

AimAmple evidence indicates that gastrin‐releasing peptide receptor (GRPR)–expressing neurons play a critical role in the transmission of acute itch. However, the pathophysiology of spinal mechanisms underlying intractable itch such as psoriasis remains unclear. In this study, we aimed to determine whether itch‐responsive GRPR+ neurons contribute to the spinal transmission of imiquimod (IMQ)‐induced psoriatic itch.MethodsTo generate a psoriasis model, C57BL/6J mice received a daily topical application of 5% IMQ cream on their shaved back skin for 7‐10 consecutive days. GRP+ neurons were inhibited using Cre‐dependent expression of Gi‐designer receptors exclusively activated by designer drugs (DREADDs), while GRPR+ neurons were ablated by intrathecal administration of bombesin‐saporin.ResultsRepeated topical application of IMQ elicited psoriasis‐like dermatitis and scratching behaviors. The mRNA expression levels of GRP and GRPR were upregulated in the cervical spinal dorsal horn (SDH) on days 7 and 10 after IMQ application. Either chemogenetic silencing of GRP+ neurons by Gi‐DREADD or ablation of GRPR+ neurons significantly attenuated IMQ‐induced scratching behaviors.ConclusionThe GRP‐GRPR system might be enhanced in the SDH, and itch‐responsive GRPR+ neurons largely contribute to intractable itch in a mouse model of psoriasis.

Robust induction of neural crest cells to derive peripheral sensory neurons from human induced pluripotent stem cells

Because intractable itch reduces quality of life, understanding the fundamental mechanisms of itch is required to develop antipruritic treatments. Itch is mediated by peripheral sensory neurons, which originate from the neural crest (NC) during development. Itch-associated signaling molecules have been detected in genetically engineered animals and in cultures of peripheral neurons from dorsal root ganglia (DRG). Ethical difficulties collecting peripheral neurons from human DRG have limited analysis of itch in humans. This study describes a method of differentiating peripheral neurons from human induced pluripotent stem cells (hiPSCs) for physiological study of itch. This method resulted in the robust induction of p75 and HNK1 double-positive NC cells from hiPSCs. The expression of NC markers TFAP2A, SOX10 and SNAI1 increased during NC induction. The induction efficiency was nearly 90%, and human peripheral neurons expressing peripherin were efficiently differentiated from hiPSC-derived NC cells. Moreover, induced peripheral neurons expressed the sensory neuronal marker BRN3A and the itch-related receptors HRH1, MRGPRX1, IL31R and IL-4R. Calcium imaging analyses indicated that these peripheral neurons included sensory neurons responsive to itch-related stimuli such as histamine, BAM8-22, IL-31 and IL-4. These findings may enable detailed analyses of human DRG neurons and may result in new therapies for intractable itch.

Report of the 5 &lt;sup&gt;th&lt;/sup&gt; Academic Symposium “Aiming to Overcome Intractable Itch” in Juntendo University

Report of the 5 &lt;sup&gt;th&lt;/sup&gt; Academic Symposium “Aiming to Overcome Intractable Itch” in Juntendo University

Tissue-specific contributions of Tmem79 to atopic dermatitis and mast cell-mediated histaminergic itch

Atopic dermatitis (AD) is the most common skin disease in children. It is characterized by relapsing inflammation, skin-barrier defects, and intractable itch. However, the pathophysiology of itch in AD remains enigmatic. Here, we examine the contribution of Tmem79, an orphan transmembrane protein linked to AD in both mice and humans. We show that Tmem79 is expressed by both keratinocytes and sensory neurons, but that loss of keratinocytic Tmem79 is sufficient to elicit robust scratching. Tmem79-/- mice demonstrate an accumulation of dermal mast cells, which are diminished following chronic treatment with cyclooxygenase inhibitors and an EP3 receptor antagonist. In Tmem79-/- mice, mast cell degranulation produces histaminergic itch in a histamine receptor 1/histamine receptor 4 (H4R/H1R)-dependent manner that may involve activation of TRPV1- afferents. TMEM79 has limited sequence homology to a family of microsomal glutathione transferases and confers protection from cellular accumulation of damaging reactive species, and may thus play a role in regulating oxidative stress. In any case, mechanistic insights from this model suggest that therapeutics targeting PGE2 and/or H1R/H4R histaminergic signaling pathways may represent useful avenues to treat Tmem79-associated AD itch. Our findings suggest that individuals with mutations in Tmem79 develop AD due to the loss of protection from oxidative stress.

Advances in Immune Pathways and Pathogenesis of Atopic Dermatitis

Atopic dermatitis (AD) is a common chronic skin inflammatory disorder characterized by recurrent eczema accompanied by an intractable itch that leads to an impaired quality of life. This review aims to summarize the advances in immune pathways and pathogenesis of AD. We review and summarize the current literature characterizing immune pathways and pathogenesis of AD. The complex interplay among skin barrier deficiency, immunological derangement, microbiome dysbiosis especially Staphylococcus aureus predominance, and pruritus contribute to the development, progression, and chronicity of the disease. AD is a complex and multifactorial disease. The skin barrier, dysbiosis of the skin microbiome, immune dysregulation, and severe itch all play a part in the pathogenesis of AD. Based on this progress, better targeted therapies are now emerging.