Molecular signature of pruriceptive MrgprA3+ neurons

Yanyan Xing, Junyu Chen, Henry Hilley, Haley Steele, Jingjing Yang, Liang Han

Abstract

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.

Neuronal branching of sensory neurons is associated with BDNF-positive eosinophils in atopic dermatitis

Guseva D, Rüdrich U, Kotnik N, Gehring M, Patsinakidis N, Agelopoulos K, Ständer S, Homey B, Kapp A, Gibbs BF, Ponimaskin E, Raap U.

Abstract

BACKGROUND: Pruritus is a major symptom of atopic dermatitis (AD) and is transmitted by a subpopulation of non-myelinated C-type free nerve endings in the epidermis and upper dermis. Stimulation of these nerve terminals is affected by histamine, neurotrophins and physical factors. Eosinophils of patients with AD are a source of neurotrophins, including brain-derived neurotrophic factor (BDNF), levels of which correlate with disease severity.

OBJECTIVE: The purpose of this study was to determine the anatomical localization of eosinophils in the skin of patients with AD with regard to peripheral nerves and to investigate whether eosinophils induce sprouting and neurite outgrowth in murine sensory neurons.

RESULTS: Dermal axon density and the proximity of eosinophils to nerve fibres were significantly higher in AD patients vs NA. Both neuronal projections and eosinophils expressed BDNF. Furthermore, activated eosinophil supernatants induced BDNF-dependent mouse DRG neuron branching.

CONCLUSIONS AND CLINICAL RELEVANCE: Our results indicate that BDNF-positive eosinophils are also localized in close proximity with nerve fibres in AD, suggesting a functional relationship between BDNF-expressing eosinophils and neuronal projections. These observations suggest that eosinophils may have considerable impact on pruritus by supporting sensory nerve branching.

Calcium imaging of primary canine sensory neurons: Smalldiameter neurons responsive to pruritogens and algogens

Joy Rachel C. Ganchingco| Tomoki Fukuyama | Jeffrey A. Yoder | Wolfgang Bäumer

Abstract

Calcium imaging of primary canine sensory neurons: Smalldiameter neurons responsive to pruritogens and algogensAbstract Introduction: Rodent primary sensory neurons are commonly used for studying itch and pain neurophysiology, but translation from rodents to larger mammals and humans is not direct and requires further validation to make correlations. Methods: This study developed a primary canine sensory neuron culture from dorsal root ganglia (DRG) excised from cadaver dogs. Additionally, the canine DRG cell cultures developed were used for single‐cell ratiometric calcium imaging, with the activation of neurons to the following pruritogenic and algogenic substances: histamine, chloroquine, canine protease‐activated receptor 2 (PAR2) activating peptide (SLIGKT), compound 48/80, 5‐hydroxytryptamine receptor agonist (5‐HT), bovine adrenal medulla peptide (BAM8‐22), substance P, allyl isothiocyanate (AITC), and capsaicin. Results: This study demonstrates a simple dissection and rapid processing of DRG collected from canine cadavers used to create viable primary sensory neuron cultures to measure responses to pruritogens and algogens. Conclusion: Ratiometric calcium imaging demonstrated that small‐diameter canine sensory neurons can be activated by multiple stimuli, and a single neuron can react to both a pruritogenic stimulation and an algogenic stimulation.

K E Y W O R D S dorsal laminectomy dissection, dorsal root ganglia cell culture, fura‐2AM, ratiometric calcium imagingCalcium imaging of primary canine sensory neurons: Smalldiameter neurons responsive to pruritogens and algogens