Pain-sensing TRPA1 channel resolved
nature14383
The TRPA1 ion channel activates pain pathways in response to noxious compounds. The structure of TRPA1 has now been solved, providing insight into how it functions.Pain-sensing TRPA1 channel resolved
Journal Club 2015.4.24 Read More »
Structure of the TRPA1 ion channel suggests regulatory mechanisms
Candice E. Paulsen1*, Jean-Paul Armache2*, Yuan Gao1,2, Yifan Cheng2 & David Julius1
doi:10.1038/nature14367 nature14367
The TRPA1 ion channel (also known as the wasabi receptor) is a detector of noxious chemical agents encountered in our environment or produced endogenously during tissue injury or drug metabolism. These include a broad class of electrophiles that activate the channel through covalent protein modification. TRPA1 antagonists hold potential for treating neurogenic inflammatory conditions provoked or exacerbated by irritant exposure. Despite compelling reasons to understand TRPA1 function, structural mechanisms underlying channel regulation remain obscure. Here we use single-particle electron cryo- microscopy to determine the structure of full-length human TRPA1 to 4 A ̊ resolution in the presence of pharmacophores, including a potent antagonist. Several unexpected features are revealed, including an extensive coiled-coil assembly domain stabilized by polyphosphate co-factors and a highly integrated nexus that converges on an unpredicted transient receptor potential (TRP)-like allosteric domain. These findings provide new insights into the mechanisms of TRPA1 regulation, and establish a blueprint for structure-based design of analgesic and anti-inflammatory agents.
Journal Club 2015.4.17 Read More »
5-HT3 receptors antagonists reduce serotonin-induced scratching in mice
Running title: 5-HT3 receptors mediate serotonin-induced scratching
Sattar Ostadhadi a,b, Nastaran Kordjazy a,b, Arya Haj-Mirzaian a,b, Parvin Mansouri c, Ahmad Reza Dehpour a,b*
a Experimental Medicine Research Center, Tehran University of Medical Sciences, Tehran, Iran
b Department of Pharmacology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran
c Skin and Stem cell Research Center, Tehran University of Medical Sciences, Tehran, Iran
* Corresponding author:
Prof. Ahmad Reza Dehpour, PharmD, PhD, Department of Pharmacology, School of Medicine, Tehran University of Medical Sciences, P.O. Box 13145-784, Tehran, Iran. Tel: +98 21 88973652, fax: + 98 21 66402569, e-mail: dehpoura@sina.tums.ac.ir
ABSTRACT
Serotonin (5-hydroxytryptamine, 5-HT) acts as a pruritogen in humans and animals, but the mechanisms of action through that serotonin induces itch-response have not been extensively discovered. In our study, we attempted to investigate the role of 5-HT3 receptors in scratching behavior due to intradermal serotonin injection. Intradermal injection of serotonin (14.1–235 nmol/site) into the nape of the neck of mice was performed to elicit itch. Scratching behavior was evaluated by measuring the number of bouts during 60 minutes after injection. We evaluated the effect of intraperitoneal pretreatment with ondansetron and tropisetron (0.1, 0.3, and 1 mg/kg) on itch induced by serotonin. Also, intradermal ondansetron and tropisetron at doses 50, 100, and 200 nmol/site were concurrently administrated with serotonin. Serotonin produced a significant enhancement in scratching at dose 141 nmol/site. Concurrent administration of ondansetron (50, 100, and 200 nmol/site) and tropisetron (100 and 200 nmol/site) with serotonin reduced scratching activity compared to the animals that only received serotonin. Also, pretreatment with intraperitoneal ondansetron and tropisetron (0.3 and 1 mg/kg) 30 min before serotonin attenuated the itch response. We showed that the scratching induced by intradermal serotonin is mediated by 5-HT3 receptors subtype. It can be concluded that 5-HT3 may play a role in mediating serotonin-associated itch responses, and we introduce 5-HT3 receptors as possible targets for antipruritic agents.
Key words: Scratching; Serotonin (5-HT); 5-HT3 antagonists; Mice
journal club 2015-03-06 Read More »
Protein kinase Cdelta mediates histamine-evoked itch and responses in pruriceptors
Molecular Pain 2015, 11:1 doi:10.1186/1744-8069-11-1
Manouela V Valtcheva (valtchevam@wusm.wustl.edu) Steve Davidson (sdavidson@wustl.edu) Chengshui Zhao (zhaoc@anest.wustl.edu) Michael Leitges (michael.leitges@biotek.uio.no) Robert W Gereau IV (gereaur@wustl.edu)
Abstract Background
Itch-producing compounds stimulate receptors expressed on small diameter fibers that innervate the skin. Many of the currently known pruritogen receptors are Gq-Protein Coupled Receptors (GqPCR), which activate Protein Kinase C (PKC). Specific isoforms of PKC have been previously shown to perform selective functions; however, the roles of PKC isoforms in regulating itch remain unclear. In this study, we investigated the novel PKC isoform PKCδ as an intracellular modulator of itch signaling in response to histamine and the non- histaminergic pruritogens chloroquine and β-alanine.
Results
Behavioral experiments indicate that PKCδ knock-out (KO) mice have a 40% reduction in histamine-induced scratching when compared to their wild type littermates. On the other hand, there were no differences between the two groups in scratching induced by the MRGPR agonists chloroquine or β-alanine. PKCδ was present in small diameter dorsal root ganglion (DRG) neurons. Of PKCδ-expressing neurons, 55% also stained for the non-peptidergic marker IB4, while a smaller percentage (15%) expressed the peptidergic marker CGRP. Twenty-nine percent of PKCδ-expressing neurons also expressed TRPV1. Calcium imaging studies of acutely dissociated DRG neurons from PKCδ-KO mice show a 40% reduction in the total number of neurons responsive to histamine. In contrast, there was no difference in the number of capsaicin-responsive neurons between KO and WT animals. Acute pharmacological inhibition of PKCδ with an isoform-specific peptide inhibitor (δV1-1) also significantly reduced the number of histamine-responsive sensory neurons.
Conclusions
Our findings indicate that PKCδ plays a role in mediating histamine-induced itch, but may be dispensable for chloroquine- and β-alanine-induced itch.
journal club 2015.01.23. Read More »
A natural dye, Niram improves atopic dermatitis through down-regulation of TSLP
Na-Ra Hana, Jin-Young Parkb, Jae-Bum Jangb, Hyun-Ja Jeongc,∗, Hyung-Min Kima,∗∗
a Department of Pharmacology, College of Korean Medicine, Kyung Hee University, 1 Hoegi-dong, Dongdaemun-gu, Seoul 130-701, Republic of Korea
b Regional Innovation Center and Inflammatory Disease Research Center, Hoseo University, 165, Sechul-ri, Baebang-myun, Asan, Chungnam 336-795, Republic of Korea
c Department of Food Technology, Biochip Research Center, and Inflammatory Disease Research Center, Hoseo University, 165, Sechul-ri, Baebang-myun, Asan, Chungnam 336-795,Republic of Korea
abstract
Naju Jjok (Polygonum tinctorium Lour.) has been known to treat skin diseases in traditional Korean medicine. A natural textile dye, Niram made from Naju Jjok has traditionally been used to dye clothes. Thymic stromal lymphopoietin (TSLP) plays an important role in the development of atopic dermatitis (AD). Thus, we investigated that Niram might amelio- rate AD through regulation of TSLP. Niram significantly inhibited the levels of TSLP through blockade of caspase-1/receptor-interacting protein 2 pathway in stimulated mast cells. Fur- ther, Niram ameliorated clinical symptoms in AD mouse. Niram significantly inhibited the infiltration of inflammatory cells in lesional skin. The levels of TSLP, caspase-1, IL-4, and IL-6 were inhibited in lesional skin applied topically with Niram. Niram significantly inhibited the serum levels of IgE and histamine in AD mouse. Finally, Niram significantly inhibited the levels of TSLP in polyriboinosinic polyribocytidylic acid-stimulated human keratinocyte HaCaT cells. These results establish Niram as a functional dye embracing the aspects of not only a traditional use but also a pharmacological effect.
© 2014 Elsevier B.V. All rights reserved.
Keywords : Niram, TSLP, Caspase-1, Mast cell, Atopic dermatitis, NC/Nga mice
journal club – 2014.12.15. Read More »
Propofol-induced pain sensation involves multiple mechanisms in sensory neurons
Rei Nishimoto & Makiko Kashio & Makoto Tominaga
Received: 18 June 2014 / Revised: 22 September 2014 / Accepted: 25 September 2014 # Springer-Verlag Berlin Heidelberg 2014
Abstract Propofol, a commonly used intravenous anesthetic agent, is known to at times cause pain sensation upon injection in humans. However, the molecular mechanisms underlying this effect are not fully understood. Although propofol was reported to activate human transient receptor potential ankyrin 1 (TRPA1) in this regard, its action on human TRP vanilloid 1 (TRPV1), another nociceptive receptor, is unknown. Further- more, whether propofol activates TRPV1 in rodents is con- troversial. Here, we show that propofol activates human and mouse TRPA1. In contrast, we did not observe propofol- evoked human TRPV1 activation, while the ability of propofol to activate mouse TRPV1 was very small. We also found that propofol caused increases in intracellular Ca2+ concentrations in a considerable portion of dorsal root gangli- on (DRG) cells from mice lacking both TRPV1 and TRPA1, indicating the existence of TRPV1- and TRPA1-independent mechanisms for propofol action. In addition, propofol pro- duced action potential generation in a type A γ-amino butyric acid (GABAA) receptor-dependent manner. Finally, we found that both T-type and L-type Ca2+ channels are activated downstream of GABAA receptor activation by propofol. Thus, we conclude that propofol may cause pain sensation through multiple mechanisms involving not only TRPV1 and TRPA1 but also voltage-gated channels downstream of GABAA receptor activation.
Keywords Propofol . TRPV1 . TRPA1 . Voltage-gated Ca2+ channel . GABAA receptor
journal club – 14.10.27. Read More »
Extracellular MicroRNAs Activate Nociceptor Neurons to Elicit Pain via TLR7 and TRPA1
Chul-Kyu Park,1,2 Zhen-Zhong Xu,1,2 Temugin Berta,1,2 Qingjian Han,1 Gang Chen,1 Xing-Jun Liu,1 and Ru-Rong Ji1,* 1Pain Signaling and Plasticity Laboratory, Departments of Anesthesiology and Neurobiology, Duke University Medical Center, Durham, NC 27710, USA
2Co-first authors
*Correspondence: ru-rong.ji@duke.edu http://dx.doi.org/10.1016/j.neuron.2014.02.011 Extracellular MicroRNAs Activate Nociceptor neurins to elicit pain via TLR7 and TRPV1
Intracellular microRNAs (miRNAs) are key regulators of gene expression. The role of extracellular miRNAs in neuronal activation and sensory behaviors are unknown. Here we report an unconventional role of extracellular miRNAs for rapid excitation of nocicep- tor neurons via toll-like receptor-7 (TLR7) and its coupling to TRPA1 ion channel. miRNA-let-7b induces rapid inward currents and action potentials in dorsal root ganglion (DRG) neurons. These re- sponses require the GUUGUGU motif, only occur in neurons coexpressing TLR7 and TRPA1, and are abolished in mice lacking Tlr7 or Trpa1. Furthermore, let-7b induces TLR7/TRPA1-dependent single-chan- nel activities in DRG neurons and HEK293 cells over- expressing TLR7/TRPA1. Intraplantar injection of let-7b elicits rapid spontaneous pain via TLR7 and TRPA1. Finally, let-7b can be released from DRG neurons by neuronal activation, and let-7b inhibitor reduces formalin-induced TRPA1 currents and spon- taneous pain. Thus, secreted extracellular miRNAs may serve as novel pain mediators via activating TLR7/TRPA1 in nociceptor neurons.
journal club 20-10-2014 Read More »
The Bile Acid Receptor TGR5 Activates the TRPA1 Channel to Induce Itch in Mice Short Title: Bile Acid Evoked Itch
The Bile Acid Receptor TGR5 Activates the TRPA1 Channel to Induce Itch in Mice
TinaMarie Lieu, Gihan Jayaweera, Peishen Zhao, Daniel P. Poole, Dane Jensen, Megan Grace, Peter McIntyre, Romke Bron, Yvette M. Wilson, Matteus Krappitz, Silke Haerteis, Christoph Korbmacher, Martin S. Steinhoff, Romina Nassini, Serena Materazzi, Pierangelo Geppetti, Carlos U. Corvera, Nigel W. Bunnett
Abstract
Background & Aims: Patients with cholestatic disease have increased systemic concentrations of bile acids (BAs) and profound pruritus. The G protein-coupled BA receptor 1 TGR5 (encoded by GPBAR1) is expressed by primary sensory neurons; its activation induces neuronal hyperexcitability and scratching, by unknown mechanisms. We investigated whether the transient receptor potential ankyrin 1 (TRPA1) is involved in BA-evoked, TGR5-dependent pruritus in mice.
Methods: Co-expression of TGR5 and TRPA1 in cutaneous afferent neurons isolated from mice
was analyzed by immunofluorescence, in situ hybridization, and single-cell PCR. TGR5-induced
activation of TRPA1 was studied in in HEK293 cells, Xenopus laevis oocytes, and primary 2+
sensory neurons by measuring Ca signals. The contribution of TRPA1 to TGR5-induced release of pruritogenic neuropeptides, activation of spinal neurons, and scratching behavior were studied using TRPA1 antagonists or Trpa1–/– mice.
Results: TGR5 and TRPA1 protein and mRNA were expressed by cutaneous afferent neurons. In
HEK cells, oocytes, and neurons co-expressing TGR5 and TRPA1, BAs caused TGR5-dependent
activation and sensitization of TRPA1 by mechanisms that required Gβγ, protein kinase C and 2+
Ca . Antagonists or deletion of TRPA1 prevented BA-stimulated release of the pruritogenic neuropeptides gastrin-releasing peptide and atrial natriuretic peptide B in the spinal cord. Disruption of Trpa1 in mice blocked BA-induced expression of Fos in spinal neurons and prevented BA-stimulated scratching. Spontaneous scratching was exacerbated in transgenic mice that overexpressed TRG5. Administration of a TRPA1 antagonist or the BA sequestrant colestipol, which lowered circulating levels of BAs, prevented exacerbated spontaneous scratching in TGR5 overexpressing mice.
Conclusions: BAs induce pruritus in mice by co-activation of TGR5 and TRPA1. Antagonists of TGR5 and TRPA1, or inhibitors of the signaling mechanism by which TGR5 activates TRPA1, might be developed for treatment of cholestatic pruritus.
KEYWORDS: liver, mouse model, itching, signal transduction
Journal Club 2014. 09. 29. Read More »
Activation of TRPV1 mediates thymic stromal lymphopoietin release via the Ca2+/NFAT pathway in airway epithelial cells
Xinying Jia a, Hong Zhang a, Xu Cao b,⇑, Yuxin Yin a, Bo Zhang a,⇑ a Department of Pathology, Peking University Health Science Center, 100191 Beijing, China
b Department of Neurology, Peking University Health Science Center, 100191 Beijing, China
1-s2.0-S0014579314004773-main-2 S0014579314004773-fx1.jpg
1-s2.0-S0014579314004773-main-2
Abstract
The airway epithelium is exposed to a range of irritants in the environment that are known to trig- ger inflammatory response such as asthma. Transient receptor potential vanilloid 1 (TRPV1) is a Ca2+-permeable cation channel critical for detecting noxious stimuli by sensory neurons. Recently increasing evidence suggests TRPV1 is also crucially involved in the pathophysiology of asthma on airway epithelium in human. Here we report that in airway epithelial cells TRPV1 activation potently induces allergic cytokine thymic stromal lymphopoietin (TSLP) release. TSLP induction by protease-activated receptor (PAR)-2 activation is also partially mediated by TRPV1 channels.
Ó 2014 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.
Journal club 2014.07.25. Read More »
Ligand determinants of fatty acid activation of the pronociceptive ion channel TRPA1
William John Redmond1, Liuqiong Gu2, Maxime Camo1, Peter McIntyre2,3 and Mark Connor1
Victoria, Australia
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ABSTRACT |
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Background and purpose. Arachidonic acid (AA) and its derivatives are important modulators of cellular signalling. The transient receptor potential cation channel subfamily A, member 1 (TRPA1) is a cation channel with important functions in mediating cellular responses to noxious stimuli and inflammation. There is limited information about the interactions between AA itself and TRPA1, so we investigated the effects of AA and key ethanolamide and amino acid/neurotransmitter deriva- tives of AA on hTRPA1. Experimental approach. HEK 293 cells expressing hTRPA1 were studied by mea- suring changes in intracellular calcium ([Ca]i) with a fluorescent dye and by stan- dard whole cell patch clamp recordings. (300 μM) increased fluorescence by 430% (EC50, 11 μM). Anandamide (230%) and N -arachidonoyl tyrosine (170%) substantially activated hTRPA1 at 30 μM, how- ever, N -arachidonoyl conjugates of glycine and taurine were less effective while |
Journal club 2014-06-27 Read More »
