Neuronal pentraxin 2 in peripheral sensory neurons drives chronic itch through potentiation of the interleukin-31/interleukin-31 receptor pathway in atopic dermatitis

Xue-Qiang Bai ^{a b 1}, Bing-Xin Wu ^{a 1}, Ji-An Wang ^{c 1}, Cheng He ^a, Yong-Liang Shen ^d, Xiao Wei ^a, Yu-Qi Zhang ^a, Xue-Wen Chen ^c, Rong Sun ^a, Qun-Feng Gui ^d, Juan Wang ^a,  Zhi-Jun Zhang ^{a e}

Keywords
Pruritus; NPTX2; Interleukin-31; Trigeminal ganglion; Atopic dermatitis

Abstract

Atopic dermatitis (AD) is one of the most prevalent chronic inflammatory skin conditions, primarily characterized by intense itching that leads to scratching and presents a challenging clinical issue with incompletely understood mechanisms. Neuronal pentraxin 2 (NPTX2) is associated with neurodevelopment, synaptic plasticity, and neuroinflammation in the central nervous system. In this study, we aimed to thoroughly investigate the peripheral role of NPTX2 in mediating chronic itch in AD. Real-time polymerase chain reaction (PCR), immunohistochemistry, ELISA assays, western blot, and small interfering RNA (siRNA) intervention were performed to explore the peripheral role of NPTX2 in an AD model. We demonstrated that NPTX2 was selectively upregulated in small- and medium-sized trigeminal ganglion (TG) neurons in the MC903-induced AD model, and was transported to peripheral nerve terminals. Importantly, protein expression of NPTX2 was significantly elevated in the skin nerves of patients with AD. Notably, NPTX2 administration alone, intradermally, provoked moderate scratching behavior in mice. However, Nptx2 and neuronal pentraxin receptor (NPTXR) siRNA intra-TG injection significantly attenuated scratching behaviors in AD mice. Critically, NPTXR, its cognate receptor, was specifically localized to pruriceptive calcitonin gene–related peptide-positive neurons (CGRP⁺) and isolectin B4 (IB4⁺) neuronal subsets. Mechanistically, NPTX2 synergizes with interleukin-31 (IL-31), a well-known pruritic cytokine in AD, to potentiate phosphorylated-extracellular signal-regulated kinase (p-ERK) signaling in primary sensory neurons. PD98059, the inhibitor of p-ERK, significantly alleviated the scratching induced by the combination of NPTX2 and IL-31. Additionally, PD98059 also significantly reduced the upregulation and release of NPTX2 caused by IL-31 stimulation. Our results offer a new understanding of the molecular mechanisms underlying chronic pruritus in the MC903-induced AD model, highlighting NPTX2-dependent signaling as a key therapeutic strategy for refractory itch disorders.

https://doi.org/10.1016/j.intimp.2026.116223

Therapeutic effect of an MRGPRX2/MRGPRB2 antagonist on LL-37-induced rosacea-like inflammation in mice

Billy Kwok Chong Chow ^# 1 2 3, Ye Gi Choi ^# 4, Trevor K Wong ^# 4 5, Shaik Abdullah Nawabjan ⁶, Kesang Li ⁷, Mukesh Kumar ⁸

• ¹Ningbo No.2 Hospital, Ningbo, Zhejiang, China. bkcc@hku.hk.
• ²Guoke Ningbo Life Science and Health Industry Research Institute, Ningbo, Zhejiang, China. bkcc@hku.hk.
• ³School of Biological Sciences, The University of Hong Kong, Pok Fu Lam Road, Pok Fu Lam, Hong Kong, China. bkcc@hku.hk.
• ⁴School of Biological Sciences, The University of Hong Kong, Pok Fu Lam Road, Pok Fu Lam, Hong Kong, China.
• ⁵Faculty of Health Sciences, McMaster University, Hamilton, ON, L8S 4L8, Canada.
• ⁶School of Biological Sciences, The University of Hong Kong, Pok Fu Lam Road, Pok Fu Lam, Hong Kong, China. shaik@connect.hku.hk.
• ⁷Ningbo No.2 Hospital, Ningbo, Zhejiang, China.
• ⁸School of Biological Sciences, The University of Hong Kong, Pok Fu Lam Road, Pok Fu Lam, Hong Kong, China. mkumar@connect.hku.hk.

^#Contributed equally.

https://doi.org/10.1007/s00011-025-02144-y

Abstract

Introduction

Rosacea is a chronic inflammatory skin disorder characterized by symptoms like itching, redness, and impaired skin barrier function. Mast cell activation plays a crucial role in its pathogenesis. Recent evidence shows higher expression of mast cell receptor MRGPRX2/MRGPRB2 in rosacea patients’ skin tissues and its potential as a novel drug target. We evaluated the therapeutic effect of a novel small-molecule MRGPRX2/MRGPRB2 antagonist in a mouse model of rosacea and itch.

Methods

The therapeutic effects of GE1111 were evaluated in vivo on wildtype and MRGPRB2 knock-out mice with LL-37-induced rosacea. Serum MCP-1 level and histochemistry measured inflammation and mast cell degranulation in skin tissue. Functional in vitro cell culture assays were developed using MRGPRX2/MRGPRB2 agonist LL-37, mast cells, keratinocytes, and macrophage cell lines.

Results

LL-37-treated mice showed redness, increased serum MCP-1, and epidermal thickness of skin tissue, while these changes were absent in LL-37-treated MRGPRB2 knock-out mice. Treatment with GE1111 reduced rosacea symptoms, epidermal thickness, and serum MCP-1 levels. GE1111 protected tight junction protein expression and reduced mast cell degranulation and inflammatory cytokine gene and protein expression in skin lesions. GE1111 treatment reduced the number and duration of itch in the compound 48/80 induced itch model. In vitro evidence showed GE1111’s mechanism by inhibiting inflammatory interaction of mast cells with keratinocytes and macrophages.

Conclusion

GE1111 showed promising therapeutic effects in rosacea via targeting interactions between mast cells, keratinocytes, and macrophages and inhibiting inflammatory cytokines. These findings open possibilities for developing MRGPRX2/MRGPRB2 antagonists as novel treatments for rosacea.

Caffeine acts as an agonist of Siglec-6, inhibits MRGPRX2-triggered mast cell degranulation and anaphylactoid reactions

https://doi.org/10.1155/mi/9580121

Abstract

Background: Mast cells (MCs) are effectors of anaphylactoid reactions. Mas-related G-protein-coupled receptor X2 (MRGPRX2) receptor mediates the direct activation of MCs in anaphylactoid disease. Siglec-6 negatively regulates MC activation and is a promising target in the development of antianaphylactoid reaction drugs. While caffeine exhibits an inhibitory effect against anaphylactic shock, the molecular mechanisms underlying these activities remain unknown.

Objectives: Our objective was to investigate the inhibitory effect of caffeine and its underlying molecular mechanism in MRPGRX2-induced MC activation and anaphylactoid reactions.

Methods: Local and systemic anaphylactoid reactions in mice and in vitro MC activation experiments were conducted to investigate the effects of caffeine on anaphylactoid reactions. Molecular docking and surface plasmon resonance (SPR) experiments were used to predict and verify the molecular target of caffeine activity. siRNA silencing and western blot analyses were utilized to investigate the molecular mechanisms underlying caffeine activity.

Results: Caffeine inhibited local and systemic anaphylactoid reactions in mice and attenuated MRGPRX2-induced MC activation. Release of β-hexosaminidase, histamine, and Ca²⁺ in siRNA-Siglec-6-laboratory allergic disease 2 (LAD2) cells was significantly higher than in NC-LAD2 cells. The binding affinity between caffeine and Siglec-6 protein is with a calculated K_D of 1.76 × 10⁻⁷ mol/L. Caffeine increased Siglec-6 expression, phosphorylation of SHP-1, and dephosphorylation of PLC-γ1, IP3R, and ERK1/2 in the MRGPRX2 signaling pathway. Western blot demonstrated that phosphorylated SHP-1 (p-SHP-1) protein levels showed no increase, and MRGPRX2, phosphorylated PLCγ1 (p-PLCγ1), and phosphorylated ERK1/2 (p-ERK1/2) were abolished with caffeine treatment in Siglec-6-knockdown cells than in NC-knockdown cells. Caffeine suppressed the m-3M3FBS-induced upregulation of p-PLCγ1 and p-ERK1/2 levels.

Conclusions: We have demonstrated that caffeine is an agonist of Siglec-6 and that subsequent activation of the ITIM motif of Siglec-6 phosphorylates SHP-1. This arrests MRGPRX2/PLC-γ1/IP3R signal transduction, thereby attenuating anaphylactoid reactions, including anaphylactic shock.

Involvement of α-Melanocyte–Stimulating Hormone–Thromboxane A₂ System on Itching in Atopic Dermatitis

Tsugunobu Andoh ^∗, Chihiro Akasaka ^∗, Kyoko Shimizu ^†, Jung-Bum Lee ^‡, Yoko Yoshihisa ^†, Tadamichi Shimizu ^†

^∗Department of Applied Pharmacology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan

^†Department of Dermatology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan

^‡Laboratory of Medicinal Bio-resources, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan

https://doi.org/10.1016/j.ajpath.2019.05.017

α-Melanocyte–stimulating hormone (α-MSH) is an endogenous peptide hormone involved in cutaneous pigmentation in atopic dermatitis (AD) with severe itching. α-MSH elicits itch-related responses in mice. We, therefore, investigated whether α-MSH was involved in itching in AD. In the skin of AD patients and mice with atopy-like dermatitis, α-MSH and the prohormone convertase 2, which is the key processing enzyme for the production of α-MSH, were distributed mainly in keratinocytes. In the skin of mice with dermatitis, melanocortin receptors (MC1R and MC5R) were expressed at the mRNA level and were distributed in the dermis. In the dorsal root ganglion of mice with dermatitis, mRNAs encoding MC1R, MC3R, and MC5R were also expressed. MC1R antagonist agouti-signaling protein inhibited spontaneous scratching in mice with dermatitis. In healthy mice, intradermal α-MSH elicited itch-associated responses, which were inhibited by thromboxane (TX) A₂ receptor antagonist ONO-3708. In mouse keratinocytes, α-MSH increased the production of TXA₂, which was inhibited by adenylyl cyclase inhibitor SQ-22536 and Ca²⁺chelatorEGTA. In mouse keratinocytes treated with siRNA for MC1R and/or MC5R, α-MSH–induced TXA₂ production was decreased. α-MSH increased intracellular Ca²⁺ ion concentration in dorsal root ganglion neurons and keratinocytes. These results suggest that α-MSH is involved in itching during AD and may elicit itching through the direct action of primary afferents and TXA₂ production by keratinocytes.

Mast Cells Initiate Type 2 Inflammation through Tryptase Released by MRGPRX2/MRGPRB2 Activation in Atopic Dermatitis

https://doi.org/10.1016/j.jid.2023.06.201

Tao Jia ¹³, Delu Che ¹²³, Yi Zheng ¹, Huan Zhang ¹, Yaxiang Li ¹, Tong Zhou ¹, Bin Peng ¹, Xueshan Du ¹, Longfei Zhu ¹, Jingang An ¹, Songmei Geng ¹

¹Department of Dermatology, Northwest Hospital, The Second Hospital Affiliated to Xi’an Jiaotong University, Xi’an, China

²Center for Dermatology Disease, Precision Medical Institute, Xi’an, China

Keywords

AD: Atopic Dermatitis, ADI: Atopic Dermatitis Index, MC: Mast Cell, TSLP: Thymic Stromal Lymphopoietin