Topical Application of a PDE4 InhibitorAmeliorates Atopic Dermatitis throughInhibition of Basophil IL-4 Production
Abstract
Phosphodiesterase 4 inhibitors have been approved for the treatment of atopic dermatitis. However, the cellular and molecular mechanisms underlying their therapeutic effect remain to be fully elucidated. In this study, we addressed this unsolved issue by analyzing the action of difamilast, a novel phosphodiesterase 4 inhibitor, on an oxazolone-induced skin allergic inflammation commonly used as a mouse model of atopic dermatitis. Topical application of difamilast ameliorated skin inflammation in association with reduced IL-4 expression even when the treatment commenced 4 days after the initiation of oxazolone challenge, showing its therapeutic effect on atopic dermatitis. IL-4edeficient mice displayed milder skin inflammation than did wild-type mice, and the difamilast treatment had little or no further therapeutic effect. This was also the case in mice depleted of basophils, predominant producers of IL-4 in the skin lesion, suggesting that difamilast may act on basophils. Notably, basophils accumulating in the skin lesion showed highly upregulated expression of Pde4b encoding the B subtype of the phosphodiesterase 4 family. Difamilast suppressed IL-4 production from basophils activated in vitro, at least in part, through inhibition of ERK phosphorylation. Taken together, difamilast appeared to ameliorate atopic dermatitis inflammation through the suppression of basophil IL-4 production in the skin lesion.
Neuropeptide Y neurons mediate opioid-induced itch by disinhibiting GRP-GRPR microcircuits in the spinal cord
Abstract
Itch is a common side effect of opioid analgesics. The specific neurons mediating opioid-induced itch are still debated, and the mechanistic neuronal circuits remain elusive. Here, we show that the μ-opioid receptors (MOR) onneuropeptide Y (NPY)+inhibitory interneurons mediate opioid-induced itch at the spinal cord level in mice. The MOR gene Oprm1 is expressed in NPY+ neurons in the spinal dorsal horn, and specific deletion of Oprm1 in NPY+ interneurons abolishes intrathecal morphine-induced itch. Furthermore, gastrin releasing peptide (GRP)+ neurons are the direct downstream targets of NPY+ neurons. Mechanistically, morphine inhibits the neuronal excitability of NPY+ interneurons and reduces inhibitory synaptic inputs on GRP+ neurons, causing disinhibition of GRP+ neurons and further activation of gastrin releasing peptide receptor (GRPR)+ neurons. The NPY/neuropeptide Y receptor 1(NPY1R) system is essential for regulating GRP+neurons in opioid-induced itch. These findings reveal that intrathecal opioids act on MOR on NPY+ inhibitory neurons in the spinal dorsal horn, which subsequently disinhibit GRP-GRPR microcircuits, triggering the itch response.
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 KD 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.
“Note: Please use the DOI link to access the full article. Unfortunately, due to the file size, I am unable to upload the PDF. I apologize for the inconvenience, and thank you for your understanding.”
A mast cell receptor mediates post-stroke brain inflammation via a dural-brain axis
1The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA 2Department of Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA 3Johns Hopkins Asthma and Allergy Center, Baltimore, MD 21224, USA 4Department of Neurosurgery, The Ohio State University College of Medicine, Columbus, OH 43210, USA 5Department of Neurology, The University of Texas Health Science Center Houston, McGovern Medical School, Houston, TX 77030, USA 6Department of Anesthesiology and Critical Care Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA 7Department of Dermatology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA 8Howard Hughes Medical Institute, Chevy Chase, MD 20815, USA 9 These authors contributed equally 10Lead contact
Publication History: Received December 20, 2024; Revised May 2, 2025; Accepted June 30, 2025; Published online July 24, 2025
Mrgprb2/MRGPRX2 is a key receptor that activates meningeal mast cells after stroke
Mrgprb2 regulates skull bone marrow neutrophil recruitment into the brain post-stroke
Mast cell proteases cleave semaphorin, mediating neutrophil infiltration into the brain
Inhibiting Mrgprb2 alleviates post-stroke brain inflammation and improves survival
Summary
The immune environment surrounding the brain plays a fundamental role in monitoring signs of injury. Insults, including ischemic stroke, can disrupt this balance and incite an exaggerated inflammatory response, yet the underlying mechanism remains unclear. Here, we show that the mast-cell-specific receptor Mrgprb2 regulates post-stroke brain inflammation from the meninges. Mrgprb2 causes meningeal mast cell degranulation after stroke, releasing immune mediators. This process recruits skull bone marrow neutrophils into the dura and further promotes neutrophil migration from the dura into the brain by cleaving the chemorepellent semaphorin 3a. We demonstrate that the human ortholog, MRGPRX2, is expressed in human meningeal mast cells and is activated by upregulation of the neuropeptide substance P following stroke. Pharmacologically inhibiting Mrgprb2 reduces post-stroke inflammation and improves neurological outcomes in mice, providing a druggable target. Collectively, our study identifies Mrgprb2 as a critical meningeal gatekeeper for immune migration from skull bone marrow reservoirs into the brain.
Estrogen alleviates acute and chronic itch in mice
DOI: 10.3892/etm.2023.11954
Abstract. Itching is associated with various skin diseases,including atopic dermatitis and allergic dermatitis, and leadsto repeated scratching behavior and unpleasant sensation.Although clinical and laboratory research data have shown that estrogen is involved in regulating itch, the molecular and cellular basis of estrogen in itch sensation remains elusive.In the present study, it was found that estrogen‑treated mice exhibited reduced scratching bouts when challenged with histamine, chloroquine, the proteinase‑activated receptor‑2 activating peptide SLIGRL‑NH2 (SLIGRL), compound48/80, and 5‑hydroxytryptamine when compared with mice in the placebo group. Moreover, estrogen also suppressed scratching bouts in the mouse model of chronic itch induced by acetone‑ether‑water treatment. Notably, consistent with the behavioral tests, the present RNA‑seq analysis showed that estrogen treatment caused significantly reduced expression levels of itch‑related molecules such as Mas‑related G‑protein coupled receptor member A3, neuromedin B and natriuretic polypeptide b. In addition, estradiol attenuated histamine‑induced and chloroquine‑induced calcium influx in dorsal root ganglion neurons. Collectively, the data of the present study suggested that estrogen modulates the expression of itch‑related molecules and suppresses both acute and chronic itch in mice.
Decreased Responsiveness to Chemical Itch in Old Mice
Qiaofeng Zhao, Mitsutoshi Tominaga, Yayoi Kamata, Sumika Toyama, Kotaro Honda, Hang Ma, Eriko Komiya, and Kenji Takamori.
Abstract: Aging is associated with altered itch perception, potentially due to changes in neuronal function and pruriceptive signaling. The underlying mechanisms, however, remain unclear. We investigated age-related differences in itch sensitivity at behavioral, cellular, and molecular levels. Young and old mice were intradermally injected with various pruritogens, including small molecules (histamine, chloroquine, and serotonin). Additionally, immunofluorescence staining was performed to analyze the expression of TRPV1 and Cav3.2. Old mice exhibited reduced scratching behavior following injections, and their neuronal responses to histamine and chloroquine were diminished. Although all treated groups showed increased mechanical alloknesis, the effect was less pronounced in old animals. The expression of TRPV1 and Cav3.2 was also reduced in dorsal root ganglia neurons of old mice. These findings suggest that aging impairs both functional responsiveness and molecular signaling in sensory neurons, contributing to reduced chemical itch sensitivity in aged individuals.
Ting Yi ab1, Mengping Lou a1, Xinyi Gao a, Liyuan Bao a, Heting Yan a, Teng Lin a, Yayue Yang a, Tianchi Gao a, Chenghao Wang a, Jianyu Zhu a, Yanqing Wang ab, Wenli Mi a
aDepartment of Integrative Medicine and Neurobiology, School of Basic Medical Science, Institutes of Integrative Medicine, Shanghai Key Laboratory of Acupuncture Mechanism and Acupoint Function, State Key Laboratory of Medical Neurobiology and MOE Frontiers Center for Brain Science, Institutes of Brain Science, Shanghai Medical College, Fudan University, Shanghai, 200032, China
bChinese Medicine Research Institute, Guangdong Pharmaceutical University, Guangzhou, 510006, China
Received 3 July 2024, Revised 1 February 2025, Accepted 5 February 2025, Available online 6 February 2025, Version of Record 11 February 2025.
Abstract
Itch (pruritus), a maladaptive and debilitating cutaneous symptom, is commonly associated with many skin conditions; however, the available therapies with sufficient efficacy are lacking. The role of astrocytes in the rostral ventromedial medulla (RVM), a crucial brain region in the descending pain modulation system, in chronic itch remains uncertain. In this study, we examined the chronic itch behavior and itch-related anxiety behavior in the diphenylcyclopripenone (DCP)-induced contact dermatitis mice, and also observed the activation of astrocytes in the RVM in the DCP mice. Reducing calcium signaling in astrocytes through global IP3R2 gene knockout, conditional astroglial IP3R2 gene knockout in the RVM, or microinjection of AAV-GfaABC1D-hPMCA2 w/b into the RVM, exhibited an anti-pruritic effect on the chronic itch. These findings suggest that RVM astrocytes play a role in regulating chronic itch, and interventions targeting astrocytic activation may offer potential relief for chronic itch.
Dithranol is one of the most effective topical medications for treating plaque psoriasis. However, its clinical use is limited by irritative adverse reactions to the skin, such as oedema, erythema, and pruritus, caused by poorly understood mechanisms. Because TRPV1 activation mediates skin irritation caused by several drugs, we conducted blind and randomised experiments in male and female C57BL/6 mice to elucidate the role of TRPV1 in dithranol-induced irritation. Dithranol (0.01%–0.5%) or vehicle was applied topically to the right ear of the animals. Oedema, erythema, and pruritus were monitored from 2 h to 6 days after application. Treatment with 0.5% dithranol caused oedema and erythema, but not pruritus, starting at 6 h, reaching its highest point at 1 day, and persisting up to 6 days after treatment, mainly in male mice. The 0.1% dose induced erythema but not oedema. Interestingly, topical application of 1% capsaicin was shown to defunctionalise TRPV1-positive fibres and did not influence early irritation caused by dithranol (2 h–2 days). However, it increased the late phase of irritation (5–6 days). Similarly, salicylate did not reduce the early irritation caused by dithranol but also increased the late phase. Antagonism by SB366791 and 4-tert-butylcyclohexanol did not alter skin irritation. Our results suggest that, contrary to our initial hypothesis, TRPV1 appears to act protectively against skin irritation caused by dithranol, particularly in the late stage.
Investigation of the participation of the TRPV1 receptor in the irritant effectof dithranol in mice
Ana Merian da Silva, Marcella de Amorim Ferreira, Roberta Giusti Schran, Debora Denardin Lückemeyer, Arthur Silveira Prudente, Juliano Ferreira
Abstract
Dithranol is one of the most effective topical medications for treating plaque psoriasis. However, its clinical use is limited by irritative adverse reactions to the skin, such as oedema, erythema, and pruritus, caused by poorly understood mechanisms. Because TRPV1 activation mediates skin irritation caused by several drugs, we conducted blind and randomised experiments in male and female C57BL/6 mice to elucidate the role of TRPV1 in dithranol-induced irritation. Dithranol (0.01%–0.5%) or vehicle was applied topically to the right ear of the animals. Oedema, erythema, and pruritus were monitored from 2 h to 6 days after application. Treatment with 0.5% dithranol caused oedema and erythema, but not pruritus, starting at 6 h, reaching its highest point at 1 day, and persisting up to 6 days after treatment, mainly in male mice. The 0.1% dose induced erythema but not oedema. Interestingly, topical application of 1% capsaicin was shown to defunctionalise TRPV1-positive fibres and did not influence early irritation caused by dithranol (2 h–2 days). However, it increased the late phase of irritation (5–6 days). Similarly, salicylate did not reduce the early irritation caused by dithranol but also increased the late phase. Antagonism by SB366791 and 4-tert-butylcyclohexanol did not alter skin irritation. Our results suggest that, contrary to our initial hypothesis, TRPV1 appears to act protectively against skin irritation caused by dithranol, particularly in the late stage.
