Transient Receptor Potential Ankyrin 1 Channel Localized to Non-Neuronal Airway Cells Promotes Non-Neurogenic Inflammation

Romina Nassini,Naila Svitacheva,Pamela Pedretti,Riccardo Patacchini,Fabrizio Facchinetti,Pierangelo Geppetti,Susan Stokesberry,Lorcan Mcgarvey,Charlott Brunmark,Serena Materazzi,Anna Rita Pisano,Nadia Moretto,Anders B Damholt,Chiara Carnini,Camilla Fusi,Arturo Roberto Viscomi,Agustin Guerrero-Hernandez

doi:10.1371/journal.pone.0042454

Abstract

BackgroundThe transient receptor potential ankyrin 1 (TRPA1) channel, localized to airway sensory nerves, has been proposed to mediate airway inflammation evoked by allergen and cigarette smoke (CS) in rodents, via a neurogenic mechanism. However the limited clinical evidence for the role of neurogenic inflammation in asthma or chronic obstructive pulmonary disease raises an alternative possibility that airway inflammation is promoted by non-neuronal TRPA1.Methodology/Principal FindingsBy using Real-Time PCR and calcium imaging, we found that cultured human airway cells, including fibroblasts, epithelial and smooth muscle cells express functional TRPA1 channels. By using immunohistochemistry, TRPA1 staining was observed in airway epithelial and smooth muscle cells in sections taken from human airways and lung, and from airways and lung of wild-type, but not TRPA1-deficient mice. In cultured human airway epithelial and smooth muscle cells and fibroblasts, acrolein and CS extract evoked IL-8 release, a response selectively reduced by TRPA1 antagonists. Capsaicin, agonist of the transient receptor potential vanilloid 1 (TRPV1), a channel co-expressed with TRPA1 by airway sensory nerves, and acrolein or CS (TRPA1 agonists), or the neuropeptide substance P (SP), which is released from sensory nerve terminals by capsaicin, acrolein or CS), produced neurogenic inflammation in mouse airways. However, only acrolein and CS, but not capsaicin or SP, released the keratinocyte chemoattractant (CXCL-1/KC, IL-8 analogue) in bronchoalveolar lavage (BAL) fluid of wild-type mice. This effect of TRPA1 agonists was attenuated by TRPA1 antagonism or in TRPA1-deficient mice, but not by pharmacological ablation of sensory nerves.ConclusionsOur results demonstrate that, although either TRPV1 or TRPA1 activation causes airway neurogenic inflammation, solely TRPA1 activation orchestrates an additional inflammatory response which is not neurogenic. This finding suggests that non-neuronal TRPA1 in the airways is functional and potentially capable of contributing to inflammatory airway diseases.

Highlights

A subset of primary sensory neurons expresses and releases the neuropeptides calcitonin gene-related peptide (CGRP) and tachykinins, substance P (SP) and neurokinin A (NKA), producing a series of inflammatory responses, collectively referred to as neurogenic inflammation [1]
As clinical trials in the last 20 years with NK1/NK2 receptor antagonists have shown little efficacy in asthma [23,24], and, with no reported therapeutic role so far reported by the use of NK1/NK2 receptor antagonists in chronic obstructive pulmonary diseases (COPD), it seems unlikely that SP/NKA released from sensory nerves are the sole and the major contributors of transient receptor potential ankyrin 1 (TRPA1)-mediated inflammation in the airways
To assess the expression of TRPA1 in different types of human airway/pulmonary cells, we performed Real-Time PCR on total mRNA isolated from human alveolar type II epithelium-like adherent cell line (A549), human small airway epithelial cells (SAEC), human embryonic lung fibroblasts (IMR90), normal human lung fibroblasts (NHLF), and human bronchial smooth muscle cells (HBSMC)

Summary

Introduction

A subset of primary sensory neurons expresses and releases the neuropeptides calcitonin gene-related peptide (CGRP) and tachykinins, substance P (SP) and neurokinin A (NKA), producing a series of inflammatory responses, collectively referred to as neurogenic inflammation [1]. It has been shown that activation of TRPA1, but not TRPV1, modulates airway inflammatory response in murine models of allergic asthma, reactive airways dysfunction syndrome (RADS) and COPD, induced by cigarette smoke [20], reactive acetaminophen metabolite [21] or allergen [22]. Such observations have advanced the hypothesis that airway sensory nerves via a neurogenic inflammatory mechanism mediate these clinical phenomena. The limited clinical evidence for the role of neurogenic inflammation in asthma or chronic obstructive pulmonary disease raises an alternative possibility that airway inflammation is promoted by non-neuronal TRPA1

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Discussion

Conclusion