Regulation of hepatic EAAT-2 glutamate transporter expression in human liver cholestasis.

Long-Term Activation of Group I Metabotropic Glutamate Receptors Increases Functional TRPV1- Expressing Neurons in Mouse Dorsal Root Ganglia

Takayoshi Masuoka1*, Makiko Kudo1, Junko Yoshida1, Takaharu Ishibashi1,2, Ikunobu Muramatsu1, Nobuo Kato3, Noriko Imaizumi1 and Matomo Nishio1
1 Department of Pharmacology, School of Medicine, Kanazawa Medical University, Uchinada, Japan, 2 Department
of Pharmacology, School of Nursing, Kanazawa Medical University, Uchinada, Japan, 3 Department of Physiology I, School of Medicine, Kanazawa Medical University, Uchinada, Japan

fncel-10-00079

Damaged tissues release glutamate and other chemical mediators for several hours. These chemical mediators contribute to modulation of pruritus and pain. Herein, we investigated the effects of long-term activation of excitatory glutamate receptors on functional expression of transient receptor potential vaniloid type 1 (TRPV1) in dorsal root ganglion (DRG) neurons and then on thermal pain behavior. In order to detect the TRPV1-mediated responses in cultured DRG neurons, we monitored intracellular calcium responses to capsaicin, a TRPV1 agonist, with Fura-2. Long-term (4 h) treatment with glutamate receptor agonists (glutamate, quisqualate or DHPG) increased the proportion of neurons responding to capsaicin through activation of metabotropic glutamate receptor mGluR1, and only partially through the activation of mGluR5; engagement of these receptors was evident in neurons responding to allylisothiocyanate (AITC), a transient receptor potential ankyrin type 1 (TRPA1) agonist. Increase in the proportion was suppressed by phospholipase C (PLC), protein kinase C, mitogen/extracellular signal-regulated kinase, p38 mitogen-activated protein kinase or transcription inhibitors. Whole-cell recording was performed to record TRPV1-mediated membrane current; TRPV1 current density significantly increased in the AITC-sensitive neurons after the quisqualate treatment. To elucidate the physiological significance of this phenomenon, a hot plate test was performed. Intraplantar injection of quisqualate or DHPG induced heat hyperalgesia that lasted for 4 h post injection. This chronic hyperalgesia was attenuated by treatment with either mGluR1 or mGluR5 antagonists. These results suggest that long-term activation of mGluR1/5 by peripherally released glutamate may increase the number of neurons expressing functional TRPV1 in DRG, which may be strongly associated with chronic hyperalgesia.
Keywords: metabotropic glutamate receptors, TRPV1, TRPA1, dorsal root ganglion, heat hyperalgesia

Molecular Basis of the Functional Differences between Soluble Human Versus Murine MD-2: Role of Val135 in Transfer of Lipopolysaccharide from CD14 to MD-2.

Impaired Itching Perception in Murine Models of Cholestasis Is Supported by Dysregulation of GPBAR1 Signaling
Sabrina Cipriani1☯, Barbara Renga2☯, Claudio D’Amore2, Michele Simonetti2, Antonio
Angelo De Tursi2, Adriana Carino2, Maria Chiara Monti3, Valentina Sepe4,
Angela Zampella4, Stefano Fiorucci2*
1 Department of Medicine University of Perugia, Perugia, Italy, 2 Department of Surgery and Biomedical
Sciences, University of Perugia, Perugia, Italy, 3 Department of Pharmacy, University of Salerno, Salerno,
Italy, 4 Department of Pharmacy, University of Naples “Federico II”, Naples, Italy

Abstract
Background & Aims
In cholestatic syndromes, body accumulation of bile acids is thought to cause itching. However,
the mechanisms supporting this effect remain elusive. Recently, GPBAR1 (TGR5) a
G-protein coupled receptor has been shown to mediate itching caused by intradermal
administration of DCA and LCA. 6α-ethyl-3α, 7α-dihydroxy-24-nor-5β-cholan-23-ol
(BAR502) is a non-bile acid dual ligand for FXR and GPBAR1.
Methods
Cholestasis was induced in wild type and GPBAR1-/- mice by administration of α-naphthylisothiocyanate (ANIT) or 17α-ethynylestradiol.
Results.
In naïve mice skin application of DCA, TLCA, 6-ECDCA, oleanolic and betulinic acid
induces a GPBAR1 dependent pruritogenic response that could be desensitized by re-challengingthe mice with the same GPBAR1 agonist. In wild type and GPBAR1-/- mice cholestasisinduced by ANIT fails to induce spontaneous itching and abrogates scratching
behavior caused by intradermal administration of DCA. In this model, co-treatment with
BAR502 increases survival, attenuates serum alkaline phosphatase levels and robustly
modulates the liver expression of canonical FXR target genes including OSTα, BSEP, SHP
and MDR1, without inducing pruritus. Betulinic acid, a selective GPBAR1 ligand, failed to
rescue wild type and GPBAR1-/- mice from ANIT cholestasis but did not induced itching. In
the 17α-ethynylestradiol model BAR502 attenuates cholestasis and reshapes bile acid pool
without inducing itching.

Impaired itching perception in murine models of cholestasis is supported by dysregulation of GPBAR1 signalling

Transient receptor potential vanilloid 4 ion channel functions as a pruriceptor in epidermal keratinocytes to evoke histaminergic itch

+ Author Affiliations

1. 
   
   Duke University, United States

Abstract

TRPV4 ion channels function in epidermal keratinocytes and in innervating sensory neurons, however, the contribution of the channel in either cell to neurosensory function remains to be elucidated. We recently reported TRPV4 as a critical component of the keratinocyte machinery that responds to UVB, and functions critically to convert the keratinocyte into a pain-generator cell after excess UVB exposure. One key mechanism in keratinocytes was increased expression and secretion of endothelin-1, which is also a known pruritogen. Here we address the question whether TRPV4 in skin keratinocytes functions in itch, as a particular form of forefront signaling in non-neural cells. Our results support this novel concept, based on attenuated scratching behavior in response to histaminergic (histamine, compound 48/80, endothelin-1), not non-histaminergic (chloroquine) pruritogens in Trpv4 keratinocyte-specific and inducible knockout mice. We demonstrate that keratinocytes rely on TRPV4 for calcium influx in response to histaminergic pruritogens. TRPV4 activation in keratinocytes evokes phosphorylation of MAP-kinase, ERK, for histaminergic pruritogens. This finding is relevant because we observed robust anti-pruritic effects with topical applications of selective inhibitors for TRPV4 and also for MEK, the kinase upstream of ERK, suggesting that calcium influx via TRPV4 in keratinocytes leads to ERK-phosphorylation, which in-turn rapidly converts the keratinocyte into an organismal itch-generator cell. In support of this concept we found that scratching behavior, evoked by direct intradermal activation of TRPV4, was critically dependent on TRPV4-expression in keratinocytes. Thus, TRPV4 functions as a pruriceptor-TRP in skin keratinocytes in histaminergic itch, a novel basic concept with translational-medical relevance.

TRPV4 in histaminergic itch