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Itch, initiated by the activation of sensory neurons, is frequently associated with dermatological diseases. MrgprA3 sensory neurons have been identified as one of the major itch-sensing neuronal populations. Mounting evidence has demonstrated that peripheral pathological conditions induce physiological regulations of sensory neurons, which is critical for the maintenance of chronic itch sensation. However, the underlying molecular mechanisms are not clear. Here we performed RNA sequencing of genetically labeled MrgprA3 neurons under both naïve and allergic contact dermatitis conditions. Our results revealed the unique molecular signature of itch-sensing neurons and the distinct transcriptional profile changes that result in response to dermatitis. We found enrichment of nine Mrgpr family members and two histamine receptors in MrgprA3 neurons, suggesting that MrgprA3 neurons are a direct neuronal target for histamine and Mrgprs agonists. In addition, Ptpn6 and Pcdh12 were identified as highly selective markers of MrgprA3 neurons. We also discovered that MrgprA3 neurons respond to skin dermatitis in a way that is unique from other sensory neurons by regulating a combination of transcriptional factors, ion channels, and key molecules involved in synaptic transmission. These results significantly increase our knowledge of itch transmission and uncover potential targets for combating itch.
Learn More >Dupilumab is an anti-interleukin-4 receptor monoclonal antibody that was recently approved for the treatment of atopic dermatitis (AD). In this single-center retrospective study, clinical baseline data of 117 severe AD patients treated with dupilumab were collected. At baseline and at weeks 4 and 16, disease severity was assessed through the Eczema Area and Severity Index (EASI) and quality of life through the Dermatology Life Quality Index (DLQI) questionnaire, Patient-Oriented Eczema Measure (POEM), Hospital Anxiety and Depression Scale (HADS), Peak Pruritus Numerical Rating Scale (NRS-itch), and VAS-sleep. Response to dupilumab was defined as an improvement of ≥75% in EASI from baseline (EASI75). At multivariate analysis, AD onset before 18 years [OR, 2.9; 95% CI, 1.2-7.2; = 0.0207] and absence of hypereosinophilia [OR, 2.24; 95% CI, 1.03-4.86; = 0.0412] were identified as significant predictive parameters for response to dupilumab in terms of EASI75 at week 4 but not at week 16. Significant reductions in EASI, DLQI, POEM, HADS, NRS-itch, and VAS-sleep were found between week 4 versus baseline ( < 0.0001 for all) and week 16 versus baseline ( < 0.0001 for all). Early AD onset and absence of hypereosinophilia may be suggested as predictive markers of early response to dupilumab. We confirmed the efficacy and safety of this agent along with the improvement of life quality in severe AD patients.
Learn More >Gastrin-releasing peptide (GRP) functions as a neurotransmitter for non-histaminergic itch, but its site of action (sensory neurons vs spinal cord) remains controversial. To determine the role of GRP in sensory neurons, we generated a floxed Grp mouse line. We found that conditional knockout of Grp in sensory neurons results in attenuated non-histaminergic itch, without impairing histamine-induced itch. Using a Grp-Cre knock-in mouse line, we show that the upper epidermis of the skin is exclusively innervated by GRP fibers, whose activation via optogeneics and chemogenetics in the skin evokes itch- but not pain-related scratching or wiping behaviors. In contrast, intersectional genetic ablation of spinal Grp neurons does not affect itch nor pain transmission, demonstrating that spinal Grp neurons are dispensable for itch transmission. These data indicate that GRP is a neuropeptide in sensory neurons for non-histaminergic itch, and GRP sensory neurons are dedicated to itch transmission.
Learn More >Inflammatory bowel diseases are associated with complex shifts in microbiota composition. However, it remains unclear whether specific subsets of commensal bacteria induce inflammatory bowel diseases in genetically susceptible hosts. In this study, we found that deficiency of the E3 ligase Itch, which leads to spontaneous colitis and rectal prolapse, is associated with alteration of the gut microbiota. 16S rRNA sequencing showed expansion of colitogenic sp. in Itch mice. Treatment with broad-spectrum antibiotics substantially reduced colonic inflammation in Itch mice. Microbiota of Itch mice failed to induce spontaneous colitis upon transfer to Itch mice but aggravated chemically induced colitis. Furthermore, we found that , which is expanded in Itch mice, was sufficient to induce colon inflammation in Itch mice.
Learn More >Itch is an unpleasant feeling that triggers scratching behavior. Much progress has been made in identifying the mechanism of itch at the peripheral and spinal levels, however, itch circuits in the brain remain largely unexplored. We previously found that anterior cingulate cortex (ACC) to dorsal medial striatum (DMS) inputs modulated histamine-induced itch sensation, but how itch information was transmitted to ACC remained unclear. Here, we demonstrated that the anteromedial thalamic nucleus (AM) was activated during histaminergic itch, and there existed reciprocal neuronal projections between AM and ACC. Disconnection between AM and ACC resulted in a significant reduction of histaminergic, but not nonhistaminergic, itch-related scratching behavior. Optogenetic activation of AM-ACC, but not ACC-AM, projections evoked histaminergic itch sensation. Thus, our studies firstly reveal that AM is critical for histaminergic itch sensation and AM-ACC projections modulate histaminergic itch-induced scratching behavior.
Learn More >Psychological stress and ensuing modulation of the immune and nervous systems can have a significant impact on itch. Stress can exacerbate itch and vice versa, resulting in a vicious cycle that can greatly impair a patient's quality of life. This review summarizes the association between stress and itch, elucidates the mechanism by which these two phenomena influence one another, and explores treatment modalities that aim to reduce stress-induced itch.
Learn More >Gastrin-releasing peptide (GRP) receptor-expressing (GRPR) neurons have a central role in the spinal transmission of itch. Because their fundamental regulatory mechanisms are not yet understood, it is important to determine how such neurons are excited and integrate itch sensations. In this study, we investigated the mechanisms for the activation of itch-responsive GRPR neurons in the spinal dorsal horn (SDH). GRPR neurons expressed the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) containing the GluR2 subunit. In mice, peripherally elicited histaminergic and non-histaminergic itch was prevented by intrathecal (i.t.) administration of the AMPAR antagonist NBQX, which was consistent with the fact that firing of GRPR neurons in SDH under histaminergic and non-histaminergic itch was completely blocked by NBQX, but not by the GRPR antagonist RC-3095. Because GRP neurons in SDH contain glutamate, we investigated the role of GRP (GRP/Glu) neurons in regulating itch. Chemogenetic inhibition of GRP neurons suppressed both histaminergic and non-histaminergic itch without affecting the mechanical pain threshold. In nonhuman primates, i.t. administration of NBQX also attenuated peripherally elicited itch without affecting the thermal pain threshold. In a mouse model of diphenylcyclopropenone (DCP)-induced contact dermatitis, GRP, GRPR, and AMPAR subunits were upregulated in SDH. DCP-induced itch was prevented by either silencing GRP neurons or ablation of GRPR neurons. Altogether, these findings demonstrate that GRP and glutamate cooperatively regulate GRPR AMPAR neurons in SDH, mediating itch sensation. GRP-GRPR and the glutamate-AMPAR system may play pivotal roles in the spinal transmission of itch in rodents and nonhuman primates.
Learn More >Pruritus (itch) is a cardinal symptom in atopic dermatitis (AD).
Learn More >Itch is a highly prevalent and multi-dimensional symptom. We aimed to analyze the association between itch and mental health in dermatological patients. This multi-center study is observational cross-sectional conducted in dermatological clinics across 13 European countries. A total of 3530 patients and 1094 healthy controls were included. Patients were examined clinically. Outcome measures were itch (presence, chronicity and intensity), the Hospital Anxiety and Depression Scale, EQ5D-VAS, sociodemographics, suicidal ideation, stress (negative life events and economic difficulties). Ethical approval was obtained. Results showed significant association between the presence of itch in patients and clinical depression, suicidal ideation and economic difficulties (odds ratios respectively OR 1.53 (95% CI 1.15 to 2.02), OR 1.27 (95% CI 1.01 to 1.60), OR 1.24 (95% CI 1.10 to 1.50). The mean score of reported generic health status assessed by the EQ5D-VAS was 65.9 (SD=20.1) in patients with itch, compared to 74.7 (SD= 18.0) in patients without itch, p value < .001 and 74.9 (SD= 15.7) in controls with itch compared to 82.9 (SD= 15.6) in controls without itch, p value <.001. Itch contributes substantially to the psychological disease burden in dermatological patients and the management of patients should include access to multidisciplinary care.
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