The Role of Transient Receptor Potential A1 and G Protein-Coupled Receptor 39 in Zinc-Mediated Acute and Chronic Itch in Mice

Yue Hu^1†, Qing-Yue Fu^1†, Dan-Ni Fu^1†, Xue-Long Wang^2†, Zhi-Hong Wang¹, Jiang-Tao Zhang³, Wen-Jing Xu³, Guo-Kun Zhou³, Li-Hua Chen^4* and Tong Liu^3,5,6*

• ¹Jiangsu Key Laboratory of Neuropsychiatric Diseases and Institute of Neuroscience, Soochow University, Suzhou, China
• ²Department of Thoracic Surgery, Capital Medical University Electric Power Teaching Hospital Beijing, Beijing, China
• ³Institute of Pain Medicine and Special Environmental Medicine, Nantong University, Nantong, China
• ⁴Department of Nutrition and Food Hygiene, School of Public Health, Nantong University, Nantong, China
• ⁵College of Life Sciences, Yanan University, Yan’an, China
• ⁶Suzhou Key Laboratory of Intelligent Medicine and Equipment, Soochow University, Suzhou, China

Itching is a common symptom of many skin or systemic diseases and has a negative impact on the quality of life. Zinc, one of the most important trace elements in an organism, plays an important role in the regulation of pain. Whether and how zinc regulates itching is largely unclear. Herein, we explored the role of Zn²⁺ in the regulation of acute and chronic itch in mice. It is found that intradermal injection (i.d.) of Zn²⁺ dose-dependently induced acute itch and transient receptor potential A1 (TRPA1) participated in Zn²⁺-induced acute itch in mice. Moreover, the pharmacological analysis showed the involvement of histamine, mast cells, opioid receptors, and capsaicin-sensitive C-fibers in Zn²⁺-induced acute itch in mice. Systemic administration of Zn²⁺ chelators, such as N,N,N′,N′-Tetrakis(2-pyridylmethyl)ethylenediamine (TPEN), pyrithione, and clioquinol were able to attenuate both acute itch and dry skin-induced chronic itch in mice. Quantitative polymerase chain reaction (Q-PCR) analysis showed that the messenger RNA (mRNA) expression levels of zinc transporters (ZIPs and ZnTs) significantly changed in the dorsal root ganglia (DRG) under dry skin-induced chronic itch condition in mice. Activation of extracellular signal-regulated kinase (ERK) pathway was induced in the DRG and skin by the administration of zinc or under dry skin condition, which was inhibited by systemic administration of Zn²⁺ chelators. Finally, we found that the expression of GPR39 (a zinc-sensing GPCR) was significantly upregulated in the dry skin mice model and involved in the pathogenesis of chronic itch. Together, these results indicated that the TRPA1/GPR39/ERK axis mediated the zinc-induced itch and, thus, targeting zinc signaling may be a promising strategy for anti-itch therapy.

Keywords: GPR39; Itch; TRPA1; Zn2+; p-ERK.

Sensory neuron expressed TRPC3 mediates acute and chronic itch.

Yan Liu , Yutong Liu , Nathachit Limjunyawong , Claire Narang , Hanna Jamaldeen, Shimeng Yu , Shivanie Patiram , Hong Nie , Michael J. Caterina , Xinzhong Dong , Lintao Qu

Abstract

Chronic pruritus is a prominent symptom of allergic contact dermatitis(ACD) and represent a huge unmet health problem. However, its underlying cellular and molecular mechanisms remain largely unexplored. TRPC3 is highly expressed in primary sensory neurons and has been implicated in peripheral sensitization induced by proinflammatory mediators. Yet, the role of TRPC3 in acute and chronic itch is still not well defined. Here, we show that, among mouse trigeminal ganglion (TG) neurons, Trpc3 mRNA is predominantly expressed in nonpeptidergic small diameter TG neurons of mice. Moreover, Trpc3 mRNA signal was present in the majority of presumptively itch sensing neurons. TRPC3 agonism induced TG neuronal activation and acute nonhistaminergic itch- and pain-like behaviors in naïve mice. In addition, genetic deletion of Trpc3 attenuated acute itch evoked by certain common nonhistaminergic pruritogens, including endothelin-1 and SLIGRL-NH2. In a murine model of contact hypersensitivity (CHS), Trpc3 mRNA expression level and function were upregulated in the TG following CHS. Pharmacological inhibition and global knockout of Trpc3 significantly alleviated spontaneous scratching behaviors without affecting concurrent cutaneous inflammation in the CHS model. Furthermore, conditional deletion of Trpc3 in primary sensory neurons but not in keratinocytes produced similar antipruritic effects in this model. These findings suggest that TRPC3 expressed in primary sensory neurons may contribute to acute and chronic itch via a histamine independent mechanism and that targeting neuronal TRPC3 might benefit the treatment of chronic itch associated with ACD and other inflammatory skin disorders.

Keywords: TRPC3, itch, pain, primary sensory neurons, dermatitis

Neuronal pentraxin 2 is required for facilitating excitatory synaptic inputs onto spinal neurons involved in pruriceptive transmission in a model of chronic itch

Kensho Kanehisa, Keisuke Koga, Sho Maejima, Yuto Shiraishi, Konatsu Asai, Miho Shiratori-Hayashi, Mei-Fang Xiao, Hirotaka Sakamoto, Paul F. Worley & Makoto Tsuda

Abstract

An excitatory neuron subset in the spinal dorsal horn (SDH) that expresses gastrin-releasing peptide receptors (GRPR) is critical for pruriceptive transmission. Here, we show that glutamatergic excitatory inputs onto GRPR⁺ neurons are facilitated in mouse models of chronic itch. In these models, neuronal pentraxin 2 (NPTX2), an activity-dependent immediate early gene product, is upregulated in the dorsal root ganglion (DRG) neurons. Electron microscopy reveals that NPTX2 is present at presynaptic terminals connected onto postsynaptic GRPR⁺ neurons. NPTX2-knockout prevents the facilitation of synaptic inputs to GRPR⁺ neurons, and repetitive scratching behavior. DRG-specific NPTX2 expression rescues the impaired behavioral phenotype in NPTX2-knockout mice. Moreover, ectopic expression of a dominant-negative form of NPTX2 in DRG neurons reduces chronic itch-like behavior in mice. Our findings indicate that the upregulation of NPTX2 expression in DRG neurons contributes to the facilitation of glutamatergic inputs onto GRPR⁺ neurons under chronic itch-like conditions, providing a potential therapeutic target.

Presenter: Lee Ki Baek

Molecular and neural basis of pleasant touch sensation

Benlong Liu, Lina Qiao, Kun Liu1, Juan Liu, Tyler J. Piccinni-Ash, Zhou-Feng Chen

DOI: 10.1126/science.abn2479

Abstract

Pleasant touch provides emotional and psychological support that helps mitigate social isolation and stress. However, the underlying mechanisms remain poorly understood. Using a pleasant touch-conditioned place preference (PT-CPP) test, we show that genetic ablation of spinal excitatory interneurons expressing prokineticin receptor 2 (PROKR2), or its ligand PROK2 in sensory neurons, abolishes PT-CPP without impairing pain and itch behaviors in mice. Mutant mice display profound impairments in stress response and prosocial behaviors. Moreover, PROKR2 neurons respond most vigorously to gentle stroking and encode reward value. Collectively, we identify PROK2 as a long-sought neuropeptide that encodes and transmits pleasant touch to spinal PROKR2 neurons. These findings may have important implications for elucidating mechanisms by which pleasant touch deprivation contributes to social avoidance behavior and mental disorders.

Presenter: Hyein Kim

The role of PTEN in primary sensory neurons in processing itch and thermal information in mice

Published in :- Cell reports ; I.F.:- 9.423

Abstract

PTEN is known as a tumor suppressor and plays essential roles in brain development. Here, we report that PTEN in primary sensory neurons is involved in processing itch and thermal information in adult mice. Dele- tion of PTEN in the dorsal root ganglia (DRG) is achieved in adult Drg11-CreER: PTENflox/flox (PTEN CKO) mice with oral administration of tamoxifen, and CKO mice develop pathological itch and elevated itch responses on exposure to various pruritogens. PTEN deletion leads to ectopic expression of TRPV1 and MrgprA3 in IB4+ non-peptidergic DRG neurons, and the TRPV1 is responsive to capsaicin. Importantly, the elevated itch re- sponses are no longer present in Drg11-CreER: PTENflox/flox: TRPV1flox/flox (PTEN: TRPV1 dCKO) mice. In addi- tion, thermal stimulation is enhanced in PTEN CKO mice but blunted in dCKO mice. PTEN-involved regulation of itch-related gene expression in DRG neurons provides insights for understanding molecular mechanism of itch and thermal sensation at the spinal level.

Lysophosphatidic acid activates nociceptors and causes pain or itch depending on the application mode in human skin

Miriam M Düll , Martina Stengel , Vivien Ries , Marion Strupf , Peter W Reeh , Andreas E Kremer , Barbara Namer 

Abstract

Lysophosphatidic acid (LPA) is involved in the pathophysiology of cholestatic pruritus and neuropathic pain. Slowly conducting peripheral afferent C-nerve fibers are crucial in the sensations of itch and pain. In animal studies, specialized neurons (“pruriceptors”) have been described, expressing specific receptors, eg, from the Mas-related G-protein-coupled receptor family. Human nerve fibers involved in pain signaling (“nociceptors”) can elicit itch if activated by focalized stimuli such as cowhage spicules. In this study, we scrutinized the effects of LPA in humans by 2 different application modes on the level of psychophysics and single nerve fiber recordings (microneurography). In healthy human subjects, intracutaneous LPA microinjections elicited burning pain, whereas LPA application through inactivated cowhage spicules evoked a moderate itch sensation. Lysophosphatidic acid microinjections induced heat hyperalgesia and hypersensitivity to higher electrical stimulus frequencies. Pharmacological blockade of transient receptor potential channel A1 or transient receptor potential channel vanilloid 1 reduced heat hyperalgesia, but not acute chemical pain. Microneurography revealed an application mode-dependent differential activation of mechanosensitive (CM) and mechanoinsensitive C (CMi) fibers. Lysophosphatidic acid microinjections activated a greater proportion of CMi fibers and more strongly than CM fibers; spicule application of LPA activated CM and CMi fibers to a similar extent but excited CM fibers more and CMi fibers less intensely than microinjections. In conclusion, we show for the first time in humans that LPA can cause pain as well as itch dependent on the mode of application and activates afferent human C fibers. Itch may arise from focal activation of few nerve fibers with distinct spatial contrast to unexcited surrounding afferents and a specific combination of activated fiber subclasses might contribute.

Keywords: Lysophosphatidic acid, C- fibers, Microneurography, Psychophysics, TRPV1, TRPA1, Itch, Neuropathic pain, Cholestatic pruritus

Mast cells instruct keratinocytes to produce thymic stromal lymphopoietin: Relevance of the tryptase/protease-activated receptor 2 axis

Davender Redhu, PhD,a Kristin Franke, PhD,a Marina Aparicio-Soto, PhD,a Vandana Kumari, PhD,a Kristijan Pazur, PhD,a Anja Illerhaus, PhD,b Karin Hartmann, MD,c,d Margitta Worm, MD,a and Magda Babina, PhDa Berlin and Cologne, Germany; and Basel, Switzerland

Background: Thymic stromal lymphopoietin (TSLP) promotes TH2 inflammation and is deeply intertwined with inflammatory dermatoses like atopic dermatitis. The mechanisms regulating TSLP are poorly defined.

Objective: We investigated whether and by what mechanisms mast cells (MCs) foster TSLP responses in the cutaneous environment.
Methods: Ex vivo and in vivo skin MC degranulation was induced by compound 48/80 in wild-type protease-activated receptor 2 (PAR-2)- and MC-deficient mice in the presence or absence of neutralizing antibodies, antagonists, or exogenous mouse MC protease 6 (mMCP6). Primary human keratinocytes and murine skin explants were stimulated with lysates/supernatants of human skin MCs, purified tryptase, or MC lysate diminished of tryptase. Chymase and histamine were also used. TSLP was quantified by ELISA, real-time quantitative PCR, and immunofluorescence staining.
Results: Mas-related G protein–coupled receptor X2 (Mrgprb2) activation elicited TSLP in intact skin, mainly in the epidermis. Responses were strictly MC dependent and relied on PAR-2. Complementarily, TSLP was elicited by tryptase in murine skin explants. Exogenous mMCP6 could fully restore responsiveness in MC-deficient murine skin explants. Conversely, PAR-2 knockout mice were unresponsive to mMCP6 while displaying increased responsiveness to other inflammatory pathways, such as IL-1a. Indeed, IL-1a acted in concert with tryptase. In primary human keratinocytes, MC-elicited TSLP generation was likewise abolished by tryptase inhibition or elimination. Chymase and histamine did not affect TSLP production, but histamine triggered IL-6, IL- 8, and stem cell factor.
Conclusion: MCs communicate with kerationocytes more broadly than hitherto suspected. The tryptase/PAR-2 axis is a crucial component of this cross talk, underlying MC-dependent stimulation of TSLP in neighboring kerationocytes. Interference specifically with MC tryptase may offer a treatment option for disorders initiated or perpetuated by aberrant TSLP, such as atopic dermatitis. (J Allergy Clin Immunol 2022;nnn:nnn-nnn.)

Key words: Atopic dermatitis, interleukin 1, keratinocytes, mast cells, PAR-2, TSLP, tryptase

Slick Potassium Channels Control Pain and Itch in Distinct Populations of Sensory and Spinal Neurons in Mice

Published in :- Journal of Anesthesiology, I.F.- 7.89

Abstract

Background: Slick, a sodium-activated potassium channel, has been recently identified in somatosensory pathways, but its functional role is poorly understood. The authors of this study hypothesized that Slick is involved in processing sensations of pain and itch.

Methods: Immunostaining, in situ hybridization, Western blot, and real-time quantitative reverse transcription polymerase chain reaction were used to investigate the expression of Slick in dorsal root ganglia and the spinal cord. Mice lacking Slick globally (Slick–/–) or conditionally in neurons of the spinal dorsal horn (Lbx1-Slick–/–) were assessed in behavioral models.

Results: The authors found Slick to be enriched in nociceptive Aδ-fibers and in populations of interneurons in the spinal dorsal horn. Slick–/– mice, but not Lbx1-Slick–/– mice, showed enhanced responses to noxious heat in the hot plate and tail-immersion tests. Both Slick–/– and Lbx1-Slick–/– mice demonstrated prolonged paw licking after capsaicin injection (mean ± SD, 45.6±30.1s [95% CI, 19.8 to 71.4]; and 13.1±16.1s [95% CI, 1.8 to 28.0]; P = 0.006 [Slick–/– {n = 8} and wild-type {n = 7}, respectively]), which was paralleled by increased phosphorylation of the neuronal activity marker extracellular signal–regulated kinase in the spinal cord. In the spi- nal dorsal horn, Slick is colocalized with somatostatin receptor 2 (SSTR2), and intrathecal preadministration of the SSTR2 antagonist CYN-154806 pre- vented increased capsaicin-induced licking in Slick–/– and Lbx1-Slick–/– mice. Moreover, scratching after intrathecal delivery of the somatostatin analog octreotide was considerably reduced in Slick–/– and Lbx1-Slick–/– mice (Slick–/– [n = 8]: 6.1 ± 6.7 bouts [95% CI, 0.6 to 11.7]; wild-type [n =8]: 47.4 ± 51.1 bouts [95% CI, 4.8 to 90.2]; P = 0.039).

Conclusions: Slick expressed in a subset of sensory neurons modulates heat-induced pain, while Slick expressed in spinal cord interneurons inhibits capsaicin-induced pain but facilitates somatostatin-induced itch.

A novel sphingosylphosphorylcholine and sphingosine-1-phosphate receptor 1 antagonist, KRO-105714, for alleviating atopic dermatitis

Sae-Bom Yoon ^# 1, Chang Hoon Lee ^# 1, Hyun Young Kim ¹, Daeyoung Jeong ¹, Moon Kook Jeon ¹, Sun-A Cho ², Kwangmi Kim ³, Taeho Lee ⁴, Jung Yoon Yang ¹, Young-Dae Gong ⁵, Heeyeong Cho ^1 6

PMID: 32514255, DOI: 10.1186/s12950-020-00244-6

Abstract

Background: Atopic dermatitis (eczema) is a type of inflammation of the skin, which presents with itchy, red, swollen, and cracked skin. The high global incidence of atopic dermatitis makes it one of the major skin diseases threatening public health. Sphingosylphosphorylcholine (SPC) and sphingosine-1-phosphate (S1P) act as pro-inflammatory mediators, as an angiogenesis factor and a mitogen in skin fibroblasts, respectively, both of which are important biological responses to atopic dermatitis. The SPC level is known to be elevated in atopic dermatitis, resulting from abnormal expression of sphingomyelin (SM) deacylase, accompanied by a deficiency in ceramide. Also, S1P and its receptor, sphingosine-1-phosphate receptor 1 (S1P1) are important targets in treating atopic dermatitis.

Results: In this study, we found a novel antagonist of SPC and S1P1, KRO-105714, by screening 10,000 compounds. To screen the compounds, we used an SPC-induced cell proliferation assay based on a high-throughput screening (HTS) system and a human S1P1 protein-based [³⁵S]-GTPγS binding assay. In addition, we confirmed the inhibitory effects of KRO-105714 on atopic dermatitis through related cell-based assays, including a tube formation assay, a cell migration assay, and an ELISA assay on inflammatory cytokines. Finally, we confirmed that KRO-105714 alleviates atopic dermatitis symptoms in a series of mouse models.

Conclusions: Taken together, our data suggest that SPC and S1P1 antagonist KRO-105714 has the potential to alleviate atopic dermatitis.

Keywords: Antagonist; Anti-inflammatory; Atopic dermatitis; High-throughput screening; Sphingosine-1-phosphate receptor 1; Sphingosylphosphorylcholine.

Presenter: Song Da-Eun

J Invest Dermatol. 2022 Mar;142(3 Pt A):594-602. doi: 10.1016/j.jid.2021.07.178.Epub 2021 Sep 1.

Specific β-Defensins Stimulate Pruritus through Activation of Sensory Neurons

Pang-Yen Tseng ¹, Mark A Hoon ²

• PMID: 34480893
• DOI: 10.1016/j.jid.2021.07.178

Abstract

Pruritus is a common symptom of dermatological disorders and has a major negative impact on QOL. Previously, it was suggested that human β-defensin peptides elicit itch through the activation of mast cells. In this study, we investigated in more detail the mechanisms by which β-defensins induce itch by defining the receptors activated by these peptides in humans and mice, by establishing their action in vivo, and by examining their expression in inflammatory dermal diseases. We found that elevated expression of DEFB103 is highly correlated with skin lesions in psoriasis and atopic dermatitis. We showed that the peptide encoded by this gene and related genes activate Mas-related G protein-coupled receptors with different potencies that are related to their charge density. Furthermore, we establish that although these peptides can activate mast cells, they also activate sensory neurons, with the former cells being dispensable for itch reactions in mice. Together, our studies highlight that specific β-defensins are likely endogenous pruritogens that can directly stimulate sensory neurons.

Presenter: Lee Gi-Baek