Protease-Activated Receptor-2 Regulates Neuro-Epidermal Communication in Atopic Dermatitis

Timo Buhl, Akihiko Ikoma, Cordula Kempkes, Ferda Cevikbas, Mathias Sulk, Joerg Buddenkotte, Tasuku Akiyama, Debbie Crumrine, Eric Camerer, Earl Carstens, Michael P Schön, Peter Elias, Shaun R Coughlin, Martin Steinhoff

Background: Activation of protease-activated receptor-2 (PAR2) has been implicated in inflammation, pruritus, and skin barrier regulation, all characteristics of atopic dermatitis(AD), as well as Netherton syndrome which has similar characteristics. However, understanding the precise role of PAR2 on neuro-immune communication in AD has been hampered by the lack of appropriate animal models.
Methods: We used a recently established mouse model with epidermal overexpression of PAR2 (PAR2OE) and littermate WT mice to study the impact of increased PAR2 expression in epidermal cells on spontaneous and house dust mite (HDM)-induced skin inflammation, itch, and barrier dysfunction in AD, in vivo and ex vivo.
Results: PAR2OE newborns displayed no overt abnormalities, but spontaneously developed dry skin, severe pruritus, and eczema. Dermatological, neurophysiological, and immunological analyses revealed the hallmarks of AD-like skin disease. Skin barrier defects were observed before onset of skin lesions. Application of HDM onto PAR2OE mice triggered pruritus and the skin phenotype. PAR2OE mice displayed an increased density of nerve fibers, increased nerve growth factor and endothelin-1 expression levels, alloknesis, enhanced scratching (hyperknesis), and responses of dorsal root ganglion
cells to non-histaminergic pruritogens.

Conclusion: PAR2 in keratinocytes, activated by exogenous and endogenous proteases, is sufficient to drive barrier dysfunction, inflammation, and pruritus and sensitize skin to the effects of HDM in a mouse model that mimics human AD. PAR2 signaling in keratinocytes appears to be sufficient to drive several levels of neuro-epidermal communication, another feature of human AD.

Inhibition of mite-induced dermatitis, pruritus, and nerve sprouting in mice by the endothelin receptor antagonist bosentan

Makiko Kido-Nakahara1, Bing Wang, Fumitaka Ohno, Gaku Tsuji, Dugarmaa Ulzii, Masaki Takemura, Masutaka Furue, Takeshi Nakahara

Abstract

Background: Endothelin-1 (EDN1) can evoke histamine-independent pruritus in mammals and is
upregulated in the lesional epidermis of atopic dermatitis (AD). EDN1 increases the production of
interleukin 25 (IL-25) from keratinocytes to accelerate T helper type 2 immune deviation. Plasma EDN1
levels are positively correlated with the clinical severity and itch intensity of AD. Therefore, we
hypothesized that the inhibition of EDN1 might be useful for treating atopic inflammation and itch and
investigated the effects of the topical application of the EDN1 receptor antagonist bosentan on the skin
inflammation and itch in a murine AD model.
Methods: We analyzed the mite-induced AD-like NC/Nga murine model, which was topically applied with
bosentan or ethanol control every day for 3 weeks. We also subjected in vitro primary sensory neuron
culture systems to nerve elongation and branching assays after EDN1 stimulation.
Results: Topical application of bosentan significantly attenuated the development of mite-induced AD-like
skin inflammation, dermatitis scores, ear thickness, scratching bouts, and serum level of thymus and
activation‐regulated chemokine in NC/Nga mice. Bosentan application also significantly reduced the gene
expression of Il13, Il17, and Ifng in the treated lesions. Histologically, the number of infiltrated dermal
cells, the epidermal EDN1 expression, and the number of intraepidermal nerve fibers were significantly
inhibited upon bosentan application. While EDN1 significantly elongated the neurites of dorsal root
ganglion cells in a dose- and time-dependent manner, bosentan treatment attenuated this.
Conclusions: EDN1 plays a significant role in mite-induced inflammation and itch. Topical bosentan is a
potential protective candidate for AD.

Baicalin induces Mrgprb2-dependent pseudo-allergy in mice 

Jue Wanga, Yongjing Zhanga, Delu Chea, Yingnan Zenga, Yuanyuan Wub, Qiaohong Qinc, Nan Wanga,*

a School of Pharmacy, Xi’an Jiaotong University, Xi’an, 710061, China
b Department of Respiratory and Critical Care Medicine, The Second Affiliated Hospital of Xi’an Jiaotong University, Xi’an, 710061, China  c Institute of Basic and Translational Medicine, Xi’an Medical University, Xi’an, 710021, China

Baicalin, a component of traditional Chinese medicine, is one of the main compounds present in Scutellaria baicalensis Georgi. Pseudo-allergy induced by the injection of these medicines is a frequent adverse drug reaction. Therefore, elucidation of the anaphylactoid reaction of baicalin and its underlying mechanisms are important. Mast cells are primary effectors of allergic reactions, including pseudo-allergy. Studies have shown that Mrgprx2 in human mast cells is a specific receptor that is crucial for pseudo-allergic drug reactions, Mrgprb3 is the rat ortholog of human Mrgprx2, which in mice is designated as Mrgprb2. Here, we aimed to investigate baicalin- induced pseudo-allergy and the association of Mrgprb3 and Mrgprb2 with this effect. We examined the aller- genic effect of baicalin on RBL-2H3 cells and Mrgprb3-knockdown RBL-2H3 cells. Mrgprb2-expressing HEK293 cells and Mrgprb2-knockout mice were used to evaluate the role of Mrgprb2 in baicalin-induced allergy. Baicalin was found to dose-dependently induce pseudo-allergy both in vitro and in vivo. RBL-2H3 cells were activated by baicalin, whereas in Mrgprb3-knockout RBL-2H3 cells, baicalin showed a negligible effect on cell activation. Furthermore, baicalin activated the Mrgprb2-expressing HEK293 cells. Our data showed that baicalin did not induce allergy in Mpgprb2-knockout mice. We conclude that baicalin induces pseudo-allergy via Mrgprb2 in mice.

Keywords:Baicalin Pseudo-allergy Mrgprb2 Mrgprb3 Degranulation

Exploration of sensory and spinal neurons expressing gastrin-releasing peptide in itch and pain related behaviors

Devin M Barry ^1 2, Xue-Ting Liu ^1 2 3, Benlong Liu ^1 2, Xian-Yu Liu ^1 2, Fang Gao ^1 2, Xiansi Zeng ^1 2 4, Juan Liu ^1 2, Qianyi Yang ^1 2, Steven Wilhelm ^1 2, Jun Yin ^1 2, Ailin Tao ^1 3, Zhou-Feng Chen ^5 6 7 

Abstract

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.