Itch, initiated by the activation of sensory neurons, is associated frequently with dermatological diseases. MrgprA3 þ sensory neurons have been identified as one of the major itch-sensing neuronal populations. Mounting evidence has demonstrated that peripheral pathological conditions induce physiological regulation 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 þ 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 þ neurons, suggesting that MrgprA3 þ neurons are a direct neuronal target for histamine and Mrgpr agonists. In addition, PTPN6 and PCDH12 were identified as highly selective markers of MrgprA3 þ neurons. We also discovered that MrgprA3 þ 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.

Itch, initiated by the activation of sensory neurons, is frequently associated with dermatological or systemic diseases and significantly affects patient quality of life. 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 naï ve and allergic contact dermatitis condition.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 the main, direct neuronal target for histamine and Mrgprs agonists. In addition, Ptpn6 and Pcdh12 were identified as novel and 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 potentially novel targets for combating itch.

Diverse sensory neurons exhibit distinct neuronal morphologies with a variety of axon terminal arborizations used to subserve their functions. Due to its clinical significance, the molecular and cellular mechanisms of itch are being intensely studied. However, a complete analysis of itchsensing terminal arborization morphology is missing. Using a novel MrgprC11 CreERT2 transgenic mouse line, we labeled a small subset of itch-sensing neurons that express multiple itch-related molecules including MrgprA3, MrgprC11, histamine receptor H1, IL-31 receptor, 5-HT receptor 1F, natriuretic precursor peptide B, and neuromedin B. By combining sparse genetic labeling and whole-mount PLAP histochemistry, we found that itch-sensing skin arbors exhibit free endings with extensive axonal branching in the superficial epidermis and large receptive fields. These results revealed the unique morphological characteristics of itch-sensing neurons and provide novel insights into the basic mechanisms of itch transmission..

Itch arising from glabrous skin (palms and soles) has attracted limited attention within the field due to the lack of methodology. This is despite glabrous itch arising from many medical conditions such as plantar and palmar psoriasis, dyshidrosis, and cholestasis. Therefore, we developed a mouse glabrous skin behavioral assay to investigate the contribution of three previously identified pruriceptive neurons in glabrous skin itch. Our results show that MrgprA3+ and MrgprD+ neurons, although key mediators for hairy skin itch, do not play important roles in glabrous skin itch, demonstrating a mechanistic difference in itch sensation between hairy and glabrous skin. We found that MrgprC11+ neurons are the major mediators for glabrous skin itch. Activation of MrgprC11+ neurons induced glabrous skin itch, while ablation of MrgprC11+ neurons reduced both acute and chronic glabrous skin itch. Our study provides insights into the mechanisms of itch and opens up new avenues for future glabrous skin itch research.

Diverse sensory neurons exhibit distinct neuronal morphologies with a variety of axon terminal arborizations used to subserve their functions. Due to its clinical significance, the molecular and cellular mechanisms of itch are being intensely studied. However, a complete analysis of itchsensing terminal arborization morphology is missing. Using a novel MrgprC11 CreERT2 transgenic mouse line, we labeled a small subset of itch-sensing neurons that express multiple itch-related molecules including MrgprA3, MrgprC11, histamine receptor H1, IL-31 receptor, 5-HT receptor 1F, natriuretic precursor peptide B, and neuromedin B. By combining sparse genetic labeling and whole-mount PLAP histochemistry, we found that itch-sensing skin arbors exhibit free endings with extensive axonal branching in the superficial epidermis and large receptive fields. These results revealed the unique morphological characteristics of itch-sensing neurons and provide novel insights into the basic mechanisms of itch transmission.

No abstract

Dermal fibroblasts (dFBs) are an essential component of skin; they not only produce and organize the extracellular matrix of the dermis, but also are essential for wound healing, hair growth, fibrosis and defense against infection. Fibroblast heterogeneity has long been recognized in mouse and human skin, but the cellular hierarchy and mechanisms governing fibroblast heterogeneity are incompletely understood. Here, we used single-cell RNAsequencing to study how cellular heterogeneity of murine skin is turned at the transcriptional level during post-natal periods using single cells isolated from the skin of new born (P1), young (3 weeks) and adult (2 month) mice. Unbiased clustering of >10,000 single-cell transcriptomes revealed 29 distinct population of the skin. Within these clusters, Pdgfra clearly marked 13 dFB clusters, which were then re-clustered into 23 dFB clusters. Pseudotime analyses of these dFB clusters identified a Pdgfra + CD24 hi Thy1 lo Sca1 lo progenitor population that was highly abundant in neonatal skin early in life but declined in adulthood. Pseudotime analyses revealed that this progenitor population gave rise to several FB subtypes, including dermal papillary FBs, reticular FBs that produce high levels of type1 collagen, adipocytes that produce antimicrobial peptide Camp as well as the interstitial reticular FB that are enriched with inflammatory gene signature during post-natal development. The ability of this progenitor population to commit to collagen 1 producing reticular dFB and to differentiate into adipocytes was confirmed by primary dFB culture in vitro. Together, our study allows the reconstruction of gene expression programs during fibroblast development and provides insights into how fibroblasts develop heterogeneity from progenitors during adulthood.