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