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
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Filename : the-bile-acid-receptor-tgr5-activates-the-trpa1-channel-to-induce-itch-in-mice.pdf (1 MB)
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