Palmitic acid aggravates atopic dermatitis by regulating SGK1/NEDD4L-involved cutaneous neuroimmune inflammation throughdriving TRPV1 and MRGPRB2 S-palmitoylation

Abstract

Objective To determine how cutaneous palmitic acid (PA) modulates transient receptor potential vanilloid-1(TRPV1) in
nociceptor and dorsal-root-ganglions (DRGs), and Mas-related G protein-coupled receptor B2 (MRGPRB2) in mast cells
(MCs), and to investigate their associations with serum- and glucocorticoid-regulated kinase-1 (SGK1)/neural precursor cell
expressed developmentally down regulated 4-like (NEDD4L) in atopic dermatitis (AD).
Methods AD was induced in mice with nedd4l or sgk1 conditional knock-out(cKO) in nociceptor, mrgprb2, nedd4l, or sgk1
cKO in MCs. Intradermal PA, substance P(SP), or pan-palmitoylation inhibitor 2BP was administered. Isolated DRGs and
mouse bone-marrow-derived-MCs (mBMMCs) were used.
Results Cutaneous PA levels were increased in AD mice.PA intradermal injection promoted a TRPV1+ nociceptor-SP-MCs
MRGPRB2-tryptase-AD axis. nedd4l cKO in nociceptor up-regulated cutaneous SP expression, which was further enhanced
by PA. sgk1 cKO in nociceptor slightly reduced SP levels, which were further decreased by PA or 2BP. SP levels in mice with
nedd4l or sgk1 cKO in MCs were increased by PA. In DRGs, supernatants from MC903-treated keratinocytes induced SGK1
and NEDD4L phosphorylation, TRPV1 S-palmitoylation, and SP production, all of which were up-regulated by PA; total and
S-palmitoylated TRPV1 levels and SP production were increased following nedd4l knockdown, whereas they were slightly
reduced following sgk1 knockdown and further decreased by PA. SP induced weak phosphorylation of SGK1 and NEDD4L
in MCs. SP induced MRGPRB2 S-palmitoylation and tryptase release in wild-type, nedd4l or sgk1 knock-out MCs, and these
effects were enhanced by PA; 2BP caused MRGPRB2 reduction in wild-type and sgk1 knock-out MCs.
Conclusions The increased cutaneous PA exacerbates AD by promoting TRPV1 S-palmitoylation and SP production in nociceptor,
followed by MRGPRB2 S-palmitoylation and tryptase release in MCs. S-palmitoylation promotes TRPV1 whereas
inhibits MRGPRB2 reduction via lysosome when NEDD4L and its upstream SGK1 are not phosphorylated.

Keywords

S-palmitoylation · Palmitic acid · Atopic dermatitis · TRPV1 · MRGPRB2 · NEDD4L

Mast cell–expressed Mrgprb2/MRGPRX2
mediates gout pain and inflammation via
a neuroimmune axis

Dongyee Kim

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

Processing of pain and itch information by modality-specific neurons within the anterior cingulate cortex in mice

Hyoung-Gon Ko^1,2,  Hyunsu Jung^#3,4,  Seunghyo Han^#5,  Dong Il Choi^#4,  Chiwoo Lee^#4,  Ja Eun Choi⁴,  Jihae Oh⁴,  Chuljung Kwak³,  Dae Hee Han³,  Jun-Nyeong Kim⁵,  Sanghyun Ye⁴,  Jiah Lee⁴,  Jaehyun Lee⁴,  Kyungmin Lee⁶,  Jae-Hyung Lee⁷,  Min Zhuo^8,9 &  Bong-Kiun Kaang^10,11

¹Department of Anatomy and Neurobiology, School of Dentistry, Brain Science and Engineering Institute, Kyungpook National University, 2177 Dalgubeol-daero, Daegu, South Korea. hgko@khu.ac.kr.²Department of Oral Anatomy and Developmental Biology, Kyung Hee University College of Dentistry, Seoul, South Korea. hgko@khu.ac.kr.³Center for Cognition and Sociality, Institute for Basic Science (IBS), Daejeon, 34126, South Korea.⁴Department of Biological Sciences, College of Natural Sciences, Seoul National University, 1 Gwanangno, Seoul, South Korea.⁵Department of Anatomy and Neurobiology, School of Dentistry, Brain Science and Engineering Institute, Kyungpook National University, 2177 Dalgubeol-daero, Daegu, South Korea.⁶Laboratory for Behavioral Neural Circuitry and Physiology, Department of Anatomy, Brain Science and Engineering Institute, School of Medicine, Kyungpook National University, 680 Gukchaebosang-ro, Daegu, South Korea.⁷Department of Oral Microbiology, College of Dentistry, Kyung Hee University, 26 Kyungheedae-ro, Seoul, South Korea.⁸Department of Physiology, Faculty of Medicine, University of Toronto, 1 King’s College Circle, Toronto, Ontario, Canada.⁹International Institute for Brain Research, Qingdao International Academician Park, Qingdao, China.¹⁰Center for Cognition and Sociality, Institute for Basic Science (IBS), Daejeon, 34126, South Korea. kaang@ibs.re.kr.¹¹Department of Biological Sciences, College of Natural Sciences, Seoul National University, 1 Gwanangno, Seoul, South Korea. kaang@ibs.re.kr.^#Contributed equally.

• PMID: 40038260
• PMCID: PMC11880300
• DOI: 10.1038/s41467-025-57041-z

Abstract

Pain and itch are aversive sensations with distinct qualities, processed in overlapping pathways and brain regions, including the anterior cingulate cortex (ACC), which is critical for their affective dimensions. However, the cellular mechanisms underlying their processing in the ACC remain unclear. Here, we identify modality-specific neuronal populations in layer II/III of the ACC in mice involved in pain and itch processing. Using a synapse labeling tool, we show that pain- and itch-related neurons selectively receive synaptic inputs from mediodorsal thalamic neurons activated by pain and itch stimuli, respectively. Chemogenetic inhibition of these neurons reduced pruriception or nociception without affecting the opposite modality. Conversely, activation of these neurons did not enhance stimulus-specific responses but commonly increased freezing-like behavior. These findings reveal that the processing of itch and pain information in the ACC involves activity-dependent and modality-specific neuronal populations, and that pain and itch are processed by functionally distinct ACC neuronal subsets.

Tmem45b modulates itch via endoplasmic reticulum calcium regulation

Sa-shuang Wang1,2,3†, Chen Liang3†, Ruo-lin Wang3, Ze-lin Sun3, Peng-yu Ren3, Bin Wu3, Juan-juan Sun3, Li Fu4, Li-zu Xiao1,Wu-ping Sun1* and Chang-lin Li3,5*

1Department of Pain Medicine and Shenzhen Municipal Key Laboratory for Pain Medicine, Shenzhen Nanshan People’s Hospital, and the 6th Affiliated Hospital of Shenzhen University Medical School,Shenzhen, China

 2Guangdong Key Laboratory for Biomedical Measurements and Ultrasound Imaging, National-Regional Key Technology Engineering Laboratory for Medical Ultrasound, School of Biomedical Engineering, Shenzhen University Medical School, Shenzhen, China

3Guangdong Institute of Intelligence Science and Technology, Zhuhai, Guangdong, China

4Guangdong Key Laboratory for Genome Stability and Disease Prevention, Department of Pharmacology and Shenzhen International Cancer Center, Shenzhen University Medical School, Shenzhen University, Shenzhen, Guangdong, China

5Institute of Medical Research, Northwestern Polytechnical University, Xi’an, China

Objective: This study aimed to investigate the role of Tmem45b, a gene expressed in itch-associated Dorsal root ganglion (DRG) neurons, in the regulation of itch sensation.

Methods: The expression of Tmem45b was examined in DRG neurons. These neurons included Nppb-, Mrgpra3-, and Mrgprd-positive subtypes, which are known to mediate itch. Behavioral response to various pruritogens including β-alanine, chloroquine, histamine, serotonin, and N-met-LTC4 were assessed on Mrgprd-cre::Tmem45bflox/flox conditional knockout (cKO) mice. Chronic itch was evaluated using both atopic dermatitis-like and dry skin-like mouse models. To investigate intracellular calcium dynamics, calcium imaging was performed on dissociated DRG neurons. Additionally, bulk RNA-seq was conducted on DRG from Tmem45b cKO mice to assess transcriptomic changes. Serca1 expression and the calcium storage capacity of the endoplasmic reticulum (ER) were analyzed following Tmem45b deletion.

Results: Tmem45b was found to be expressed in itch-associated DRG neurons. In Tmem45b cKO mice, scratching behavior was reduced in response to β-alanine but increased in response to chloroquine. Notably, chronic itch was alleviated in Tmem45b-deficient mice. Calcium imaging revealed that Tmem45b cKO impaired calcium responses to β-alanine and allyl isothiocyanate, but not to chloroquine. Mechanistically, Tmem45b deficiency led to a significant downregulation of Serca1, reducing ER calcium storage capacity. Pharmacological inhibition of Serca1 in DRG neurons similarly suppressed intracellular calcium release in response to β-alanine and chloroquine.

Conclusion: Tmem45b plays a critical role in nonhistaminergic itch by regulating ER calcium homeostasis through Serca1. Its deficiency reduces itch behavior and impairs calcium signaling in DRG neurons, suggesting that Tmem45b is a potential therapeutic target for chronic itch.

KEYWORDS : DRG-dorsal root ganglion, itch (pruritus), calcium, endoplasmic reticulum, TMEM45B

Guangdong, China, 5Institute of Medical Research, Northwestern Polytechnical University, Xi’an, China

The Role of MRGPRX1 in the Melanogenesis of Human Primary Epidermal Melanocytes

MRGPRX1 (mas-related G protein-coupled receptor X1) is an orphan receptor, and its function in the skin cells remains unclear. In this study, we demonstrated MRGPRX1 expression in skin cells, including melanocytes. We also found that MRGPRX1 knockdown using short hairpin RNA increased melanin content, cellular tyrosinase activity, and the expression of melanogenic proteins, including tyrosinase, tyrosinase-related protein 2, and MITF in human epidermal melanocytes. In addition, MRGPRX1 knockdown increased CRE-binding protein and p38 phosphorylation and decreased p44/42 phosphorylation. Furthermore, we demonstrated that chloroquine acts as an MRGPRX1 agonist. Specifically, in silico docking simulation showed that chloroquine binds to MRGPRX1. Chloroquine treatment increased MRGPRX1 expression, activation, and intracellular calcium influx. Unlike MRGPRX1 knockdown, chloroquine treatment had antimelanogenic effects on melanin content, tyrosinase activity, melanogenic genes, and MAPKs. Furthermore, whereas chloroquine treatment increased calcium influx through TRPV1 and TRPA1, TRPA1 operated upstream of CRE-binding protein and p38 and activated them through calcium influx. We also found that tert-butyl hydroperoxide and UVA irradiation increased MRGPRX1 expression, suggesting that environmental factors affect MRGPRX1-mediated signaling. Collectively, these findings indicate that MRGPRX1-mediated signaling contributes to melanogenesis sup-
pression, and chloroquine is a possible MRGPRX1 protein agonistic ligand, suggesting that MRGPRX1 could be a therapeutic target for pigmentary disorders.
Keywords: Chloroquine, CREB/p38 MAPK signaling, Melanogenesis, MRGPRX1, Pigmentation

DongYee Kim

An orally bioavailable MrgprX1-positive allosteric
modulator alleviates certain neuropathic pain–related
behaviors in humanized mice

The human Mas- related G protein–coupled receptor X1 (MrgprX1) represents a promising nonopioid analgesic tar
get because of its selective expression in primary nociceptive sensory neurons. Positive allosteric modulators (PAMs)
promote receptor signaling, depending on the availability of endogenous ligands, offering physiological selectivity
over orthosteric agonists. We developed an orally bioavailable MrgprX1 PAM, 6- tert- butyl- 5- (4- chlorophenyl)- 4- (2-
f
luoro- 6- (trifluoromethoxy)phenoxy)thieno[2,3- d]pyrimidine (BCFTP). BCFTP selectively potentiated the functional
response of MrgprX1 in HEK293 cells, was metabolically stable, and demonstrated a favorable in vitro safety profile.
BCFTP was orally bioavailable and distributed into the spinal cords of wild- type mice. BAM22, an endogenous ligand
for MrgprX1, was up- regulated in the spinal cord after nerve injury in both wild- type and humanized MrgprX1 mice
and was expressed in peptidergic and nonpeptidergic dorsal root ganglion neurons. Oral administration of BCFTP
dose- dependently inhibited heat hyperalgesia and spontaneous pain- like behavior but not mechanical hypersensi
tivity after sciatic chronic constrictive injury (CCI) in MrgprX1 mice. BCFTP did not have analgesic effects in Mrgpr
cluster knockout (Mrgpr−/−) mice, indicating that the analgesic effects in MrgprX1 mice were MrgprX1 dependent.
BCFTP enhanced BAM8- 22–induced, MrgprX1- mediated reduction of C- fiber eEPSC amplitudes in spinal lamina II
neurons, indicating inhibition of spinal nociceptive synaptic transmission. BCFTP did not induce tolerance or side
effects, such as itch, sedation, and motor incoordination, and had no rewarding properties. The mRNAs encoding
MrgprX1 and μ- opioid receptors were colocalized in human DRG neurons, and BCFTP synergistically enhanced mor
phine analgesia in CCI MrgprX1 mice. Our research suggests an approach for developing safer, orally bioavailable
MrgprX1 PAM as a nonopioid therapy for neuropathic pain.

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.

Tick peptides evoke itch by activating MrgprC11/MRGPRX1 to sensitize TRPV1 in pruriceptors

Xueke Li MSc ^a∗, Haifeng Yang MSc ^a∗, Yuewen Han MSc ^a, Shijin Yin PhD ^b, Bingzheng Shen PhD ^a, Yingliang Wu PhD ^a, Wenxin Li PhD ^a, Zhijian Cao PhD ^a c d

^aState Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, China ^bSchool of Pharmaceutical Sciences, South-Central University for Nationalities, Wuhan, China ^cBio-drug Research Center, Wuhan University, Wuhan, China ^dHubei Province Engineering and Technology Research, Center for Fluorinated Pharmaceuticals, Wuhan University, Wuhan, China

Received 4 May 2020, Revised 21 November 2020, Accepted 2 December 2020, Available online 22 December 2020, Version of Record 3 June 2021.

https://doi.org/10.1016/j.jaci.2020.12.626

Background

Tick bites severely threaten human health because they allow the transmission of many deadly pathogens, including viruses, bacteria, protozoa, and helminths. Pruritus is a leading symptom of tick bites, but its molecular and neural bases remain elusive.

Objectives

This study sought to discover potent drugs and targets for the specific prevention and treatment of tick bite–induced pruritus and arthropod-related itch.

Methods

We used live-cell calcium imaging, patch-clamp recordings, and genetic ablation and evaluated mouse behavior to investigate the molecular and neural bases of tick bite–induced pruritus.

Results

We found that 2 tick salivary peptides, IP defensin 1 (IPDef1) and IR defensin 2 (IRDef2), induced itch in mice. IPDef1 was further revealed to have a stronger pruritogenic potential than IRDef2 and to induce pruritus in a histamine-independent manner. IPDef1 evoked itch by activating mouse MrgprC11 and human MRGPRX1 on dorsal root ganglion neurons. IPDef1-activated MrgprC11/X1 signaling sensitized downstream ion channel TRPV1 on dorsal root ganglion neurons. Moreover, IPDef1 also activated mouse MrgprB2 and its ortholog human MRGPRX2 selectively expressed on mast cells, inducing the release of inflammatory cytokines and driving acute inflammation in mice, although mast cell activation did not contribute to oxidated IPDef1–induced itch.

Conclusions

Our study identifies tick salivary peptides as a new class of pruritogens that initiate itch through MrgprC11/X1-TRPV1 signaling in pruritoceptors. Our work will provide potential drug targets for the prevention and treatment of pruritus induced by the bites or stings of tick and maybe other arthropods.

Keratinocyte–TRPV1 sensory neuron interactions in a genetically controllable mouse model of chronic neuropathic itch

Andrew J. Crowther https://orcid.org/0000-0001-9269-6188, Sakeen W. Kashem, Madison E. Jewell https://orcid.org/0009-0004-8337-1583, +8 , and Allan I. Basbaum https://orcid.org/0000-0002-1710-6333 allan.basbaum@ucsf.eduAuthors Info & Affiliations

Edited by Peter Strick, University of Pittsburgh Brain Institute, Pittsburgh, PA; received June 13, 2024; accepted May 5, 2025

June 11, 2025, 122 (24) e2411724122, https://doi.org/10.1073/pnas.2411724122

Abstract

Our understanding of neural circuits that respond to skin dysfunction, triggering itch, and pathophysiological scratching remains incomplete. Here, we describe a profound chronic itch phenotype in transgenic mice expressing the tetracycline transactivator (tTA) gene within the Phox2a lineage. Phox2a; tTA mice exhibit intense, localized scratching and regional skin lesions, controllable by the tTA inhibitor, doxycycline. As gabapentin and the kappa opioid receptor agonist, nalfurafine, but not morphine, significantly reduce scratching, this phenotype has a pharmacological profile of neuropathic pruritus. Importantly, the Phox2a; tTA expression occurs in a spatially restricted population of skin keratinocytes that overlaps precisely with the skin area that is scratched. Localized G_i-DREADD-mediated inactivation of these Phox2a-keratinocytes completely reverses the skin lesions, while inducible tTA activation of keratinocytes initiates the condition. Notably, ablation of TRPV1-expressing primary afferent neurons also reduces scratching and skin lesions, but this occurs slowly, over a course of two months. In contrast denervation induced loss of all cutaneous input rapidly blocks scratching. These findings identify the cellular, molecular, and topographic basis of a robust and chronic sensory neuron–dependent and gabapentin-responsive neuropathic itch that is initiated by genetic factors within keratinocytes.