Endosomal MrGPRX1 signaling sensitizes TRPV1 to enhance itch

Paz Duran1,2,3, Jeffri S. Retamal2,4, Marcella de Amorim Ferreira1,2,3, Kai Trevett1,3, Evan Chen1,3 and Dane D. Jensen1,2,3*
1Department of Molecular Pathobiology, College of Dentistry, New York University, New York, NY,
United States, 2Translational Research Center, College of Dentistry, New York University, New York, NY,
United States, 3NYU Pain Research Center, College of Dentistry, New York University, New York, NY,
United States, 4Department of Chemistry and Biology, University of Santiago Chile, Santiago, Chile

G protein-coupled receptors (GPCRs) and TRPV (transient receptor potential
vanilloid) channels are crucial for signal transduction in physiological
processes, including neurotransmission, pain, and itch. Downstream effectors
of GPCR signaling can directly stimulate TRPV channels or enhance their
sensitivity to stimuli, a process known as TRPV sensitization. Traditionally,
GPCRs are activated at the cell surface by extracellular agonists, triggering
signaling cascades. Recent evidence suggests GPCRs continue to signal
from intracellular organelles. The human Mas-related G-protein coupled
receptor X1 (MrGPRX1) is a GPCR expressed in primary sensory neurons
involved in nociception and pruritus. Recent studies demonstrated how
intracellular GPCR signaling regulates neuronal activity. However, there is no
evidence characterizing MrGPRX1 trafficking or intracellular signaling. Herein,
we characterized MrGPRX1 signaling within the endosomal network and its role
in sensitizing TRPV1 channels to enhance itch signaling. Utilizing subcellular
targeted biosensors, we demonstrated MrGPRX1 can traffic and signal from
endosomes. Immunofluorescence analysis showed that MrGPRX1 internalizes
following BAM8-22 stimulation. BRET assays revealed that MrGPRX1 activation
induces Gαq and β-arrestin-1 recruitment to the plasma membrane and
early endosomes. Inhibition of dynamin or clathrin blocked BAM8-22-induced
MrGPRX1 endocytosis and decreased nuclear extracellular signal-regulated
kinase (ERK) signaling. Calcium signaling confirmed that MrGPRX1-mediated
TRPV1 sensitization is mediated by protein kinase C and ERK activation.
Our findings reveal a novel role for MrGPRX1 endosomal signaling in TRPV1
sensitization. Understanding the mechanisms of MrGPRX1 signaling offers
valuable insights into differentiating between pain and itch pathways, aiding in
the development of targeted therapies for chronic pain and persistent itch.

KEYWORDS
endosome, intracellular signaling, MrGPRs, signal transduction, transient receptor
potential channels (TRP Channels)

Fibroblast MrgprX2/B2 signaling drives hypertrophic
scar fibrosis

Hypertrophic scarring (HTS) represents a common clinical challenge characterized by excessive fibroblast
activation and tissue fibrosis. However, the upstream signals driving pathological fibroblast proliferation
remain poorly understood. Here, we identify the G protein-coupled receptor MrgprX2 (human)/MrgprB2
(mouse), traditionally restricted to mast cells, as an inducible pro-fibrotic receptor in dermal fibroblasts dur
ing HTS progression. MrgprX2 is markedly upregulated in dermal fibroblasts from HTS, and pharmacological
inhibition of MrgprX2 significantly reduces fibrosis in humanized skin organoid models. In mouse studies, the
endogenous peptide LL37 emerged as an MrgprX2/B2 activator in fibroblasts, triggering calcium influx,
transforming growth factor β1 (TGF-β1) secretion, and proliferation. Genetic ablation of MrgprB2 in fibro
blasts significantly reduced fibrosis in vivo, establishing the LL37-MrgprX2/B2-TGF-β1 axis as a key mediator
of fibroblast activation and fibrotic remodeling. Together, our findings position MrgprX2/B2 as a critical mo
lecular link between tissue injury-associated signals and fibrotic pathology, offering a promising therapeutic
target for fibroblast-driven fibrosis in HTS.

A B S T R A C T
Biosensors inspired by biological sensory systems are valuable tools for detecting physiological and environmental
stimuli with high degrees of specificity and sensitivity. An itch irritant biosensor to detect environmental
changes or pruritogenic substances in human blood or tissues highly associated with inflammation and prevalent
conditions like atopic dermatitis (AD) has not been developed. To address this gap, we developed a novel bioelectronic
sensor by integrating the human itch receptor Mas-related G-protein-coupled receptor X2 (MRGPRX2)
with a graphene field-effect transistor (GFET). This MRGPRX2–GFET biosensor covalently immobilizes functional
receptors, enabling direct conversion of ligand-binding events into quantifiable electrical signals. We
demonstrate that the sensor can detect known MRGPRX2 agonists with exceptional sensitivity and specificity,
achieving a detection limit for SP at approximately 7 pM. Molecular dynamics (MD) simulations and mutational
effects reveal that ligand binding induces cytoplasmic conformational rearrangements in MRGPRX2, strengthening
receptor–graphene coupling and providing a mechanistic basis for signal transduction. Importantly, the
biosensor effectively distinguishes plasma samples from AD patients and healthy controls by capturing different
electrical signal responses. In our study, we establish a versatile platform for diagnosing and subtyping chronic itch disorders and offer a generalizable strategy for developing membrane receptor-based multiplexed “itch- print” biosensors.

Platelets Orchestrate a Neuroimmune Axis Driving Cutaneous Inflammation and Itch

Ximin Hu1,2,3, Fujun Wang1,4, Ting Wang2, Yifei Liu2, Lei Zhang2,
Libei Liu2,3, Liang Cao5, Shaofeng Pu6, Ronghua Yang1, and Jing Feng2,7*
1Department of Burn and Plastic Surgery, School of Medicine, the Second Affiliated Hospital of South
China University of Technology (Guangzhou First People’s Hospital), Guangzhou 510180, China. 2State
Key Laboratory of Chemical Biology, Shanghai Institute of Materia Medica, Shanghai 200000, China.
3Department of Dermatology, Xiangya Hospital, Central South University, Changsha, Hunan 410000,
China. 4School of Basic Medicine, Qiqihar Medical University, Qiqihar, Heilongjiang 161006, China.
5Department of Chinese Medicine, The Second Affiliated Hospital of Air Force Medical University, Xi’an,
Shaanxi 710038, China. 6Department of Pain Management, Shanghai Jiao Tong University Affiliated
Sixth People’s Hospital, 200000, Shanghai, China. 7University of Chinese Academy of Sciences, Beijing
100000, China.
*Address correspondence to: shaofpu@sjtu.edu.cn (S.P.); eyyangronghua@scut.edu.cn (R.Y.); fengjing@
simm.ac.cn (J.F.)

Platelets are traditionally recognized for their roles in hemostasis, but their involvement as active immune
modulators in cutaneous neuroimmune signaling remains poorly understood. In this study, we integrated
multi-modal genetic and pharmacological strategies to investigate the functional contribution of platelets
to skin inflammation and chronic itch. Optogenetic activation of platelets was sufficient to elicit localized
skin inflammation, erythema, and robust pruritus, with transcriptomic profiling of lesions showing strong
concordance with the clinical signatures of atopic dermatitis (AD). In experimental AD models, platelet
depletion markedly reduced scratching behavior, inflammatory cell infiltration, and C-fiber excitability,
whereas platelet activation exacerbated these phenotypes. Mechanistically, activated platelets release
serotonin [5-hydroxytryptamine (5-HT)], which compromises vascular integrity and facilitates platelet
extravasation into the dermis. This “neuroimmune hub” promotes macrophage recruitment and sensitizes
TRPV1+ pruriceptors. Transcriptomic analysis revealed that platelet-derived 5-HT drives these processes
via HTR2B and HTR7 signaling. Specifically, genetic ablation of HTR2B in TRPV1+ neurons selectively
impaired itch transmission. Furthermore, re-analysis of clinical datasets confirmed the enrichment of
HTR2B and HTR7 in skin macrophage populations during inflammation. Systemic administration of
HTR antagonists or the anti-platelet agent clopidogrel markedly attenuated both inflammation and
pruritus across multiple models. Our findings identify the platelet–immune–neuron axis as a key driver
of cutaneous dysfunction and a promising therapeutic target for chronic inflammatory skin disorders.

Chi3l1 Knockout Mitigates Chronic Itch and Cutaneous Inflammation in Mice

Sam Kahler1, Brigid Betz-Stablein1, Fabian Lee1, Joachim Torrano1, Monika Janda2, Clare Primiero1, H, Peter Soyer1 and Dilki Jayasinghe

CHI3L1, also known as YKL-40, is a 40- kDa glycoprotein that is overexpressed
in patients with atopic dermatitis (AD) and is induced by various proinflammatory
cytokines. This protein interacts with multiple receptors (He et al,
2013; Lee et al, 2016), and its serum levels corelate with the severity of AD in
humans. CHI3L1 regulates T helper type 2 cytokines and modulates IgE release
(Curtiss et al, 2023; Lee et al, 2022). Antibody therapy targeting CHI3L1 has
been shown to improve skin inflammation in AD in mice (Lee et al, 2022; Yu
et al, 2024). CHI3L1 also activates IL- 13Ra2 (Kwak et al, 2019). Although IL-
13Ra2 was traditionally considered as a decoy receptor, our studies have
revealed its crucial role in AD associated itch, with increased expression
observed in patients with AD (Xiao et al, 2021). Despite these findings, the
role of CHI3L1 in chronic itch sensation remains largely unexplored. This study
aims to elucidate the role of CHI3L1 in itch by investigating its interactions with
IL-13Ra2 and IL-31 receptor, which are key itch receptors (Meng et al, 2018). In
addition, our study explored the function and the effects of CHI3L1 gene
knockout (KO) on itch generation and related signaling pathways.

From skin to spinal Cord: How IL-17a Drives psoriatic chronic itch

Xin Liu a,1 , Jian Jiang b,1, Shiying Lin b,1, Wenqiang Ge c, Qingxiao Tao b, Suwen Liu b, Ouyang Zhanmu c, Yang Yang c, Bao Chai d,e, Jingyu Zhang a, Man Li c,*, Hongxiang Chen a,f,**

Highlights

• •IL-17a directly provokes psoriatic itch by activating IL17ra on sensory neurons.
• •Spinal IL-6-astrocyte-IL-1β axis acts as a central itch amplifier in psoriasis.
• •A novel IL-17a-driven neuro-immune circuit connects skin to spinal cord.

Abstract

Interleukin-17a (IL-17a) has been established as a master regulator of inflammatory cascades in psoriasis pathogenesis. Monoclonal antibodies targeting IL-17a have demonstrated significant efficacy in relieving psoriasis-related symptoms, including the rapid alleviation of chronic itching. However, whether IL-17a is involved in chronic psoriatic pruritus and the specific mechanisms of its action remain poorly understood. In this study, we demonstrate that IL-17a significantly exacerbates chronic itch in a murine model of psoriasis. Mechanistically, IL-17a upregulation in psoriatic skin tissues activated the IL-17a receptor (IL-17Ra) in sensory neurons, subsequently promoting the expression of IL-6 in dorsal root ganglion (DRG) neurons. This neuron-derived IL-6 is transported via sensory nerve fibers to the spinal dorsal horn (SDH), where it triggers astrocyte activation and subsequent IL-1β secretion to potentiates chronic itch signaling in psoriasis. Our findings uncover a neuroimmune circuit in which IL-17a-IL-17Ra signaling on sensory neurons mediates the propagation of pruritic signals from peripheral skin to the central nervous system, with spinal IL-6-astrocyte-IL-1β axis serving as an amplifier of psoriatic pruritus.

Keywords

Astrocyte; Chronic itch; IL-17a; Psoriasis; Sensory neuron; Spinal cord

Subnanomolar MAS-related G protein-coupled receptor-X2/B2 antagonists with efficacy in human mast cells and disease models

Ghazl Al Hamwi¹, Mohamad Wessam Alnouri¹, Sven Verdonck ², Piotr Leonczak ², Shaswati Chaki ³, Stefan Frischbutter ^4,5,
Pavel Kolkhir^4,5, Michaela Matthey⁶, Constantin Kopp¹, Marek Bednarski⁷, Yvonne K. Riedel¹, Daniel Marx¹, Sophie Clemens¹,
Vigneshwaran Namasivayam ¹, Susanne Gattner¹, Dominik Thimm¹, Katharina Sylvester¹, Katharina Wolf^8,9, Andreas E. Kremer ^8,10,
Steven De Jonghe ², Daniela Wenzel^6,11, Magdalena Kotańska⁷, Hydar Ali ³, Piet Herdewijn² and Christa E. Müller ^1✉

¹PharmaCenter Bonn, Pharmaceutical Institute, Pharmaceutical & Medicinal Chemistry, University of Bonn, An der Immenburg 4, 53121 Bonn, Germany; ²Medicinal Chemistry,
Rega Institute for Medical Research, KU Leuven, Herestraat 49-box 1041, 3000 Leuven, Belgium; ³Department of Basic & Translational Sciences, School of Dental Medicine,
University of Pennsylvania, Philadelphia, PA 19104, USA; ⁴Institute of Allergology, Charité—Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and
Humboldt-Universität zu Berlin, 12203 Berlin, Germany; ⁵Fraunhofer Institute for Translational Medicine and Pharmacology ITMP, Immunology and Allergology, 12203 Berlin,
Germany; ⁶Department of Systems Physiology, Institute of Physiology, Medical Faculty, Ruhr University of Bochum, 44801 Bochum, Germany; ⁷Department of Pharmacological
Screening, Jagiellonian University, Medical College, Medyczna 9, 30-688 Krakow, Poland; ⁸Department of Medicine 1, University Hospital Erlangen and Friedrich-Alexander-
University Erlangen-Nürnberg, Nürnberg, Germany; ⁹Helmholtz Institute for Translational Oncology, Mainz (HI-TRON Mainz)—A Helmholtz Institute of the DKFZ, Mainz, Germany;
¹⁰Department of Gastroenterology and Hepatology, University Hospital Zürich, University of Zürich, Zürich, Switzerland and ¹¹Institute of Physiology I, Life & Brain Center, Medical
Faculty, University of Bonn, 53127 Bonn, Germany
Correspondence: Christa E Müller (christa.mueller@uni-bonn.de)
These authors contributed equally: Ghazl Al Hamwi, Mohamad Wessam Alnouri, Sven Verdonck

Received: 14 August 2024 Revised: 24 February 2025 Accepted: 18 March 2025

Published online: 21 April 2025

Abstract

The MAS-related G protein-coupled receptor-X2 (MRGPRX2), an orphan receptor expressed on mast cells (MCs), is upregulated upon inflammation and induces hypersensitivity and inflammatory diseases. In contrast to the large number of MRGPRX2 agonists, only a few antagonists have been described, and no optimization has been reported to improve potency, selectivity, and drug-like properties. Antagonists with ancillary inhibition of the putative mouse ortholog MRGPRB2 have not been described. Here, we present a multi-disciplinary approach involving chemistry, biology, and computational science, resulting in the development of a small-molecule MRGPRX2 antagonist (PSB-172656, 3-ethyl-7,8-difluoro-2-isopropylbenzo[4,5]imidazo [1,2-a] pyrimidin-4(1H)-one) based on a fragment screening hit. The compound exhibits metabolic stability, low cytotoxicity, and competitive blockade of MRGPRX2 activation induced by a diverse range of agonists. It displays subnanomolar potency in Ca²⁺ mobilization assays (K_i value 0.142 nM) and was found to block MRGPRX2-mediated Gα_q and Gα_i1 dissociation, in addition to β-arrestin-2 recruitment. PSB-172656 is selective for MRGPRX2 versus all other MRGPRX subtypes. Its effect on MCs was confirmed in cell lines, including rat basophilic leukemia cells (RBL-2H3) recombinantly expressing human MRGPRX2, human Laboratory of Allergic Diseases 2 (LAD2) MCs, and native human skin MCs. PSB-172656 was found to additionally block the putative mouse ortholog of MRGPRX2, MRGPRB2, as determined in Ca²⁺ mobilization assays (K_i 0.302 nM), and to prevent mouse tracheal contractions, local allergic reactions, and systemic anaphylactic symptoms. PSB-172656 constitutes a unique pharmacological tool and has the potential to be developed as a drug for mast cell-mediated hypersensitivity reactions and chronic inflammatory diseases, addressing a huge unmet medical need.

Signal Transduction and Targeted Therapy volume 10, Article number: 128 (2025)

https://doi.org/10.1038/s41392-025-02209-8

A specialized population of hair afferents dedicated to transmitting mechanical itch

Neuron  2026 Jun 4:S0896-6273(26)00409-5. doi: 10.1016/j.neuron.2026.05.017.

Mahar Fatima,1,9 Hankyu Lee,1,9 Hwayeon Cha,1,9 Chia Chun Hor,1 Feng Wang,2 Jingyi Liu,1 Jonathan Damblon,2 Wenwen Zhang,3 Katie Qu,1 Yumena Nagai,1 Abbey Dinh,1 Ziyan Wu,1 Ranveer Ajimal,1 Ailin Emily Xiong,1 Madeleine Chai,1 Alyssa Asmar,1 Wei Cai,3,6 Xiaowei Zhou,1 Anuraag Balaji,4 Haili Pan,1,7 Lorraine Horwitz,1 Lam C. Tsoi,4 Hongzhen Hu,5 X. Z. Shawn Xu,3,8 Yves De Koninck,2 and Bo Duan1,10,

*Correspondence: bduan@umich.edu

SUMMARY
Hairs serve as sensory structures that are crucial for perceiving environmental cues through interactions with
sensory endings. Depigmented and demedullated atypical hairs exhibit a limited distribution on mammalian
skin and have not been extensively studied. In this study, we identify a specific type of hair, termed vellus-like
hairs (VLHs), which are enriched in the postauricular region and on the hindpaws of mice. These hairs are
innervated by Aβ low-threshold mechanoreceptors (LTMRs) that co-express Toll-like receptor 5 and Calbindin1
(TLR5Calb1). Genetic ablation or silencing of these hair afferents eliminated mechanical itch generated by
gentle VLH stroking or indentation under both physiological and pathological conditions. Conversely, optogenetic
activation of TLR5Calb1 hair afferents evoked itch behaviors. Mechanosensitive Piezo2 channels in
TLR5Calb1 Aβ-LTMRs function as key mechanotransducers for mechanical itch signaling. Our study sheds
light on the previously poorly understood somatosensory physiology of unique hairs, emphasizing the significant
role of TLR5Calb1 Aβ-LTMRs in itch transmission.

https://doi.org/10.1016/j.neuron.2026.05.017

2026.07.03

Abstract

Chronic itch, particularly in cholestatic and uremic conditions, poses
a notable clinical burden, yet treatment options remain inadequate.
MRGPRX4 (hX4), a bile-acid-sensing G-protein-coupled receptor
predominantly expressed in human sensory neurons, has emerged
as a critical mediator of cholestatic pruritus. Here we identified and
characterized HEP-50768, a potent and selective small-molecule inverse
agonist of hX4 through high-throughput screening and structure–activity
optimization. Structural elucidation through cryo-electron microscopy of
the hX4–inverse agonist complex structure revealed the unique binding
mode and inhibitory mechanism of HEP-50768. In hX4-humanized rats,
HEP-50768 robustly suppressed bile-acid-induced pruritic behaviors.
Comprehensive preclinical absorption, distribution, metabolism, excretion
and safety profiling was performed in both rats and monkeys, and these
findings establish HEP-50768 as a promising therapeutic candidate for
chronic itch, supporting its advancement to clinical evaluation.

Itch receptor MRGPRX4 interacts with the receptoractivity–modifying proteins

Ilana B. Kotliar1,2,‡ , Emilie Ceraudo1,‡ , Kevin Kemelmakher-Liben1 , Deena A. Oren3 , Emily Lorenzen1 ,
Tea Dodig-Crnkovic4 , Mizuho Horioka-Duplix1 , Thomas Huber1 , Jochen M. Schwenk4 , and
Thomas P. Sakmar1,5,*

Cholestatic itch is a severe and debilitating symptom in liver
diseases with limited treatment options. The class A G proteincoupled
receptor (GPCR) Mas-related GPCR subtype X4
(MRGPRX4) has been identified as a receptor for bile acids,
which are potential cholestatic pruritogens. An increasing
number of GPCRs have been shown to interact with receptor
activity–modifying proteins (RAMPs), which can modulate
different aspects of GPCR biology. Using a combination of
multiplexed immunoassay and proximity ligation assay, we
show that MRGPRX4 interacts with RAMPs. The interaction of
MRGPRX4 with RAMP2, but not RAMP1 or 3, causes attenuation
of basal and agonist-dependent signaling, which correlates
with a decrease of MRGPRX4 cell surface expression as
measured using a quantitative NanoBRET pulse-chase assay.
Finally, we use AlphaFold Multimer to predict the structure of
the MRGPRX4–RAMP2 complex. The discovery that RAMP2
regulates MRGPRX4 may have direct implications for future
drug development for cholestatic itch.