Journal club 2013-02-01

A Heat-Sensitive TRP Channel Expressed in Keratinocytes

Andrea M. Peier,1 Alison J. Reeve,2 David A. Andersson,2 Aziz Moqrich,3 Taryn J. Earley,3 Anne C. Hergarden,1 Gina M. Story,3 Sian Colley,2 John B. Hogenesch,1 Peter McIntyre,2 Stuart Bevan,2 Ardem Patapoutian1,3*

1073140s

Science-2002-Peier-2046-9

Mechanical and thermal cues stimulate a specialized group of sensory neurons that terminate in the skin. Three members of the transient receptor potential (TRP) family of channels are expressed in subsets of these neurons and are activated at distinct physiological temperatures. Here, we describe the cloning and characterization of a novel thermosensitive TRP channel. TRPV3 has a unique threshold: It is activated at innocuous (warm) temperatures and shows an increased response at noxious temperatures. TRPV3 is specifically expressed in keratinocytes; hence, skin cells are capable of detecting heat via molecules similar to those in heat-sensing neurons.

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Journal club 2013-01-25

1744-8069-8-75

Mol Pain. 2012 Sep 27;8:75. doi: 10.1186/1744-8069-8-75.

Prostaglandin metabolite induces inhibition of TRPA1 and channel-dependent nociception.

Source

Department of Anesthesiology, Washington University Pain Center, St, Louis, MO 63110, USA. storyg@wustl.edu.

ABSTRACT:

BACKGROUND:

The Transient Receptor Potential (TRP) ion channel TRPA1 is a key player in pain pathways. Irritant chemicals activate ion channel TRPA1 via covalent modification of N-terminal cysteines. We and others have shown that 15-Deoxy-Δ12, 14-prostaglandin J2 (15d-PGJ2) similarly activates TRPA1 and causes channel-dependent nociception. Paradoxically, 15d-PGJ2 can also be anti-nociceptive in several pain models. Here we hypothesized that activation and subsequent desensitization of TRPA1 in dorsal root ganglion (DRG) neurons underlies the anti-nociceptive property of 15d-PGJ2. To investigate this, we utilized a battery of behavioral assays and intracellular Ca2+ imaging in DRG neurons to test if pre-treatment with 15d-PGJ2 inhibited TRPA1 to subsequent stimulation.

RESULTS:

Intraplantar pre-injection of 15d-PGJ2, in contrast to mustard oil (AITC), attenuated acute nocifensive responses to subsequent injections of 15d-PGJ2 and AITC, but not capsaicin (CAP). Intraplantar 15d-PGJ2-administered after the induction of inflammation-reduced mechanical hypersensitivity in the Complete Freund’s Adjuvant (CFA) model for up to 2 h post-injection. The 15d-PGJ2-mediated reduction in mechanical hypersensitivity is dependent on TRPA1, as this effect was absent in TRPA1 knockout mice. Ca2+ imaging studies of DRG neurons demonstrated that 15d-PGJ2 pre-exposure reduced the magnitude and number of neuronal responses to AITC, but not CAP. AITC responses were not reduced when neurons were pre-exposed to 15d-PGJ2 combined with HC-030031 (TRPA1 antagonist), demonstrating that inhibitory effects of 15d-PGJ2 depend on TRPA1 activation. Single daily doses of 15d-PGJ2, administered during the course of 4 days in the CFA model, effectively reversed mechanical hypersensitivity without apparent tolerance or toxicity.

CONCLUSIONS:

Taken together, our data support the hypothesis that 15d-PGJ2 induces activation followed by persistent inhibition of TRPA1 channels in DRG sensory neurons in vitro and in vivo. Moreover, we demonstrate novel evidence that 15d-PGJ2 is analgesic in mouse models of pain via a TRPA1-dependent mechanism. Collectively, our studies support that TRPA1 agonists may be useful as pain therapeutics.

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Journal club 2013-01-14

Mechanisms of Itch Evoked by ß-Alanine

Dong

Qin Liu,1,2 Parul Sikand,3 Chao Ma,3 Zongxiang Tang,1,2 Liang Han,1 Zhe Li,1 Shuohao Sun,1 Robert H. LaMotte,3
and Xinzhong Dong1,2
1The Solomon H. Snyder Department of Neuroscience, Center for Sensory Biology, and 2Howard Hughes Medical Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, and 3Department of Anesthesiology, Yale University School of Medicine, New Haven, Connecticut 06520

ß-alanine, a popular supplement for muscle building, induces itch and tingling after consumption, but the underlying molecular and neural mechanisms are obscure. Here we show that, in mice,

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Journal club 2012-12-27

10.1177_0022034511412074

J Dent Res. 2011 Sep;90(9):1098-102. doi: 10.1177/0022034511412074. Epub 2011 Jun 10.

Cold suppresses agonist-induced activation of TRPV1.

Source

Department of Neural and Pain Sciences, University of Maryland Dental School, Program in Neuroscience, 650 W. Baltimore Street, Baltimore, MD 21201, USA. mchung@umaryland.edu

Abstract

Cold therapy is frequently used to reduce pain and edema following acute injury or surgery such as tooth extraction. However, the neurobiological mechanisms of cold therapy are not completely understood. Transient receptor potential vanilloid 1 (TRPV1) is a capsaicin- and heat-gated nociceptive ion channel implicated in thermosensation and pathological pain under conditions of inflammation or injury. Although capsaicin-induced nociception, neuropeptide release, and ionic currents are suppressed by cold, it is not known if cold suppresses agonist-induced activation of recombinant TRPV1. We demonstrate that cold strongly suppressed the activation of recombinant TRPV1 by multiple agonists and capsaicin-evoked currents in trigeminal ganglia neurons under normal and phosphorylated conditions. Cold-induced suppression was partially impaired in a TRPV1 mutant that lacked heat-mediated activation and potentiation. These results suggest that cold-induced suppression of TRPV1 may share a common molecular basis with heat-induced potentiation, and that allosteric inhibition may contribute, in part, to the cold-induced suppression. We also show that combination of cold and a specific antagonist of TRPV1 can produce an additive suppression. Our results provide a mechanistic basis for cold therapy and may enhance anti-nociceptive approaches that target TRPV1 for managing pain under inflammation and tissue injury, including that from tooth extraction.

PMID:
21666106
[PubMed – indexed for MEDLINE]
PMCID:
PMC3169882

Free PMC Article

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Journal club 2012-12-07

TRPA1 underlies a sensing mechanism for O2

nchembio.640 , nchembio.640-S1

nobuaki takahashi1–3, tomoyuki Kuwaki4, shigeki Kiyonaka1,2,5, tomohiro numata1,2, daisuke Kozai1,2, Yusuke Mizuno1,2, shinichiro Yamamoto1,2, shinji naito6, ellen Knevels7,8, peter Carmeliet7,8, toru Oga9, shuji Kaneko10, seiji suga1, toshiki nokami1, Jun-ichi Yoshida1 & Yasuo Mori1,2,5*

Oxygen (O2) is a prerequisite for cellular respiration in aerobic organisms but also elicits toxicity. To understand how animals cope with the ambivalent physiological nature of O2, it is critical to elucidate the molecular mechanisms responsible for O2 sens- ing. Here our systematic evaluation of transient receptor potential (TRP) cation channels using reactive disulfides with differ- ent redox potentials reveals the capability of TRPA1 to sense O2. O2 sensing is based upon disparate processes: whereas prolyl hydroxylases (PHDs) exert O2-dependent inhibition on TRPA1 activity in normoxia, direct O2 action overrides the inhibition via the prominent sensitivity of TRPA1 to cysteine-mediated oxidation in hyperoxia. Unexpectedly, TRPA1 is activated through relief from the same PHD-mediated inhibition in hypoxia. In mice, disruption of the Trpa1 gene abolishes hyperoxia- and hypoxia-induced cationic currents in vagal and sensory neurons and thereby impedes enhancement of in vivo vagal discharges induced by hyperoxia and hypoxia. The results suggest a new O2-sensing mechanism mediated by TRPA1.

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Journal club 2012-11-30

1-s2.0-S0304395910003246-main

Pain. 2010 Aug;150(2):340-50. Epub 2010 Jun 12.

TRPM8, but not TRPA1, is required for neural and behavioral responses to acute noxious cold temperatures and cold-mimetics in vivo.

Source

Neuroscience Graduate Program, Department of Biological Sciences, University of Southern California, Los Angeles, CA 90089, USA.

Abstract

Somatosensory neurons detect environmental stimuli, converting external cues into neural activity that is relayed first to second-order neurons in the spinal cord. The detection of cold is proposed to be mediated by the ion channels TRPM8 and TRPA1. However, there is significant debate regarding the role of each channel in cold-evoked pain, complicating their potential as drug targets for conditions such as cold allodynia and hyperalgesia. To address this debate, we generated mice lacking functional copies of both channels and examined behaviors and neural activity in response to painful cold and noxious cooling compounds. Whereas normal mice display a robust preference for warmth over cold, both TRPM8-null (TRPM8(-/-)) and TRPM8/TRPA1 double-knockout mice (DKO) display no preference until temperatures reach the extreme noxious range. Additionally, in contrast to wildtype mice that avoid touching cold surfaces, mice lacking TRPM8 channels display no such avoidance and explore noxious cold surfaces, even at 5 degrees C. Furthermore, nocifensive behaviors to the cold-mimetic icilin are absent in TRPM8(-/-) and DKO mice, but are retained in TRPA1-nulls (TRPA1(-/-)). Finally, neural activity, measured by expression of the immediate-early gene c-fos, evoked by hindpaw stimulation with noxious cold, menthol, or icilin is reduced in TRPM8(-/-) and DKO mice, but not in TRPA1(-/-) animals. Thus our results show that noxious cold signaling is exclusive to TRPM8, mediating neural and behavioral responses to cold and cold-mimetics, and that TRPA1 is not required for acute cold pain in mammals.

Copyright (c) 2010 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.

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Journal club 2012-11-09

Piezo1 and Piezo2 Are Essential Components of Distinct Mechanically Activated Cation Channels

Coste-SOM
Filename : coste-som.pdf (10 MB)
Caption :
sci
Filename : sci.pdf (1 MB)
Caption :

Bertrand Coste,1 Jayanti Mathur,2 Manuela Schmidt,1 Taryn J. Earley,1 Sanjeev Ranade,1 Matt J. Petrus,2 Adrienne E. Dubin,1 Ardem Patapoutian1,2*

Mechanical stimuli drive many physiological processes, including touch and pain sensation, hearing, and blood pressure regulation. Mechanically activated (MA) cation channel activities have been recorded in many cells, but the responsible molecules have not been identified.
We characterized a rapidly adapting MA current in a mouse neuroblastoma cell line. Expression profiling and RNA interference knockdown of candidate genes identified Piezo1 (Fam38A) to be required for MA currents in these cells. Piezo1 and related Piezo2 (Fam38B) are vertebrate multipass transmembrane proteins with homologs in invertebrates, plants, and protozoa. Overexpression of mouse Piezo1 or Piezo2 induced two kinetically distinct MA currents. Piezos are expressed in several tissues, and knockdown of Piezo2 in dorsal root ganglia neurons specifically reduced rapidly adapting MA currents. We propose that Piezos are components of MA cation channels.

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Journal club 2012-11-09

TRPA1 contributes to specific mechanically activated currents and sensory neuron mechanical hypersensitivity

Stuart M. Brierley1,2,3, Joel Castro1,2, Andrea M. Harrington1,2, Patrick A. Hughes1,2, Amanda J. Page1,2,3, Grigori Y. Rychkov3 and L. Ashley Blackshaw1,2,3

1Nerve-Gut Research Laboratory, Department of Gastroenterology and Hepatology, Hanson Institute, Royal Adelaide Hospital, Adelaide, South Australia, Australia 5000
Disciplines of 2Medicine and 3Physiology, Faculty of Heath Sciences, University of Adelaide, Adelaide, South Australia, Australia 5000

 tjp0589-3575

Abstract
The mechanosensory role of TRPA1 and its contribution to mechanical hypersensitivity in sensory neurons remains enigmatic. We elucidated this role by recording mechanically activated currents in conjunction with TRPA1 over- and under-expression and selective pharmacology. First, we established that TRPA1 transcript, protein and functional expression are more abundant in smaller-diameter neurons than larger-diameter neurons, allowing comparison of two different neuronal populations. Utilising whole cell patch clamping, we applied calibrated displacements to neurites of dorsal root ganglion (DRG) neurons in short-term culture and recorded mechanically activated currents termed intermediately (IAMCs), rapidly (RAMCs) or slowly adapting (SAMCs). Trpa1 deletion (–/–) significantly reduced maximum IAMC amplitude by 43% in small-diameter neurons compared with wild-type (+/+) neurons. All other mechanically activated currents in small- and large-diameter Trpa1−/− neurons were unaltered. Seventy-three per cent of Trpa1+/+ small-diameter neurons responding to the TRPA1 agonist allyl-isothiocyanate (AITC) displayed IAMCs to neurite displacement, which were significantly enhanced after AITC addition. The TRPA1 antagonist HC-030031 significantly decreased Trpa1+/+ IAMC amplitudes, but only in AITC responsive neurons. Using a trans- fection system we also showed TRPA1 over-expression in Trpa1+/+ small-diameter neurons increases IAMC amplitude, an effect reversed by HC-030031. Furthermore, TRPA1 introduction into Trpa1−/− small-diameter neurons restored IAMC amplitudes to Trpa1+/+ levels, which was subsequently reversed by HC-030031. In summary our data demonstrate TRPA1 makes a contribution to normal mechanosensation in a specific subset of DRG neurons. Furthermore, they also provide new evidence illustrating mechanisms by which sensitisation or over-expression of TRPA1 enhances nociceptor mechanosensitivity. Overall, these findings suggest TRPA1 has the capacity to tune neuronal mechanosensitivity depending on its degree of activation or expression.

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Journal club 2012-11-02

nihms225332

Enhanced scratching evoked by PAR-2 agonist and 5-HT but not histamine in a mouse model of chronic dry skin itch.

Source

Department of Neurobiology, Physiology and Behavior, University of California, Davis, CA 95616, USA.

Abstract

Chronic itch is a symptom of many skin conditions and systemic disease, and it has been hypothesized that the chronic itch may result from sensitization of itch-signaling pathways. We induced experimental chronic dry skin on the rostral back of mice, and observed a significant increase in spontaneous hindlimb scratches directed to the dry skin. Spontaneous scratching was significantly attenuated by a PAR-2 antibody and 5-HT2A receptor antagonist, indicating activation of these receptors by endogenous mediators released under dry skin conditions. We also observed a significant increase in the number of scratch bouts evoked by acute intradermal injections of a protease-activated receptor (PAR)-2 agonist and serotonin (5-HT), but not histamine. We additionally investigated if pruritogen-evoked activity of dorsal root ganglion (DRG) neurons is enhanced in this model. DRG cells from dry skin mice exhibited significantly larger responses to the PAR-2 agonist and 5-HT, but not histamine. Spontaneous scratching may reflect ongoing itch, and enhanced pruritogen-evoked scratching may represent hyperknesis (enhanced itch), both potentially due to sensitization of itch-signaling neurons. The correspondence between enhanced behavioral scratching and DRG cell responses suggest that peripheral pruriceptors that respond to proteases and 5-HT, but not histamine, may be sensitized in dry skin itch.

Copyright © 2010 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.

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Journal club 2012-10-26

TRPV1 is a novel target for omega-3 polyunsaturated fatty acids

tjp0578-0397

Jose ́ A. Matta, Rosa L. Miyares and Gerard P. Ahern

From the Department of Pharmacology, Georgetown University, Washington, DC 20007, USA

Omega-3 (n-3) fatty acids are essential for proper neuronal function, and they possess prominent analgesic properties, yet their underlying signalling mechanisms are unclear. Here we show that n-3 fatty acids interact directly with TRPV1, an ion channel expressed in nociceptive neurones and brain. These fatty acids activate TRPV1 in a phosphorylation-dependent manner, enhance responses to extracellular protons, and displace binding of the ultrapotent TRPV1 ligand [3 H]resiniferatoxin. In contrast to their agonistic properties, n-3 fatty acids competitively inhibit the responses of vanilloid agonists. These actions occur in mammalian cells in the physiological concentration range of 1–10 μM. Significantly, docosahexaenoic acid exhibits the greatest efficacy as an agonist, whereas eicosapentaenoic acid and linolenic acid are markedly more effective inhibitors. Similarly, eicosapentaenoic acid but not docosahexaenoic acid profoundly reduces capsaicin-evoked pain-related behaviour in mice. These effects are independent of alterations in membrane elasticity because the micelle-forming detergent Triton X-100 only minimally affects TRPV1 properties. Thus, n-3 fatty acids differentially regulate TRPV1 and this form of signalling may contribute to their biological effects. Further, these results suggest that dietary supplementation with selective n-3 fatty acids would be most beneficial for the treatment of pain.

(Resubmitted 28 September 2006; accepted 8 October 2006; first published online 12 October 2006)
Corresponding author G. P. Ahern: Department of Pharmacology, Georgetown University, MedDent SW401, 3900 Reservoir Rd, Washington, DC 20007, USA. Email: gpa3@georgetown.edu

 

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