Bitter Taste Receptors (TAS2Rs) in Human Lung Macrophages: Receptor Expression and Inhibitory Effects of TAS2R Agonists.

Stanislas Grassin-Delyle,Emmanuel Naline,Christophe Faisy,Charlotte Abrial,Louis-Jean Couderc,Hélène Salvator,Marion Brollo,Philippe Devillier,Nikola Mantov

doi:10.3389/fphys.2019.01267

Abstract

BackgroundBitter-taste receptors (TAS2Rs) are involved in airway relaxation but are also expressed in human blood leukocytes. We studied TAS2R expression and the effects of TAS2R agonists on the lipopolysaccharide (LPS)-induced cytokine release in human lung macrophages (LMs).MethodsLung macrophages were isolated from patients undergoing surgery for carcinoma. We used RT-qPCR to measure transcripts of 16 TAS2Rs (TAS2Rs 3/4/5/7/8/9/10/14/19/20/31/38/39/43/45 and 46) in unstimulated and LPS-stimulated (10 ng.mL–1) LMs. The macrophages were also incubated with TAS2R agonists for 24 h. Supernatant levels of the cytokines TNF-α, CCL3, CXCL8 and IL-10 were measured using ELISAs.ResultsThe transcripts of all 16 TAS2Rs were detected in macrophages. The addition of LPS led to an increase in the expression of most TAS2Rs, which was significant for TAS2R7 and 38. Although the promiscuous TAS2R agonists, quinine and denatonium, inhibited the LPS-induced release of TNF-α, CCL3 and CXCL8, diphenidol was inactive. Partially selective agonists (dapsone, colchicine, strychnine, and chloroquine) and selective agonists [erythromycin (TAS2R10), phenanthroline (TAS2R5), ofloxacin (TAS2R9), and carisoprodol (TAS2R14)] also suppressed the LPS-induced cytokine release. In contrast, two other agonists [sodium cromoglycate (TAS2R20) and saccharin (TAS2R31 and 43)] were inactive. TAS2R agonists suppressed IL-10 production – suggesting that this anti-inflammatory cytokine is not involved in the inhibition of cytokine production.ConclusionHuman LMs expressed TAS2Rs. Experiments with TAS2R agonists’ suggested the involvement of TAS2Rs 3, 4, 5, 9, 10, 14, 30, 39 and 40 in the inhibition of cytokine production. TAS2Rs may constitute new drug targets in inflammatory obstructive lung disease.

Highlights

Inflammatory lung diseases such as asthma and chronic obstructive pulmonary disease (COPD) are characterized by airway obstruction and airflow limitation
The TAS2R agonists chloroquine diphosphate, quinine hydrochloride dihydrate, saccharin sodium hydrate, denatonium benzoate, 1,10-phenanthroline hydrochloride monohydrate, ofloxacin, strychnine hemisulphate, erythromycin, dapsone, carisoprodol, and sodium cromoglycate were obtained from Sigma-Aldrich (Saint-Quentin Fallavier, France) and diphenidol hydrochloride was provided by TCI Europe (Zwijndrecht, Belgium)
Transcripts of genes coding for 15 bitter taste receptors were identified in all the preparations (n = 5 to 12), whereas TAS2R43 transcripts were found in lung macrophages (LMs) from 4 of 6 patients only

Summary

Introduction

Inflammatory lung diseases such as asthma and chronic obstructive pulmonary disease (COPD) are characterized by airway obstruction and airflow limitation. TAS2Rs are known to be expressed in the human bronchus (Deshpande et al, 2010; Grassin-Delyle et al, 2013), airway epithelial cells (Shah et al, 2009; Jaggupilli et al, 2017), mast cells (Ekoff et al, 2014) and blood leukocytes (Orsmark-Pietras et al, 2013; Malki et al, 2015). Blood leukocytes from children with severe asthma display elevated TAS2R expression levels and two TAS2R agonists inhibited the release of several pro-inflammatory cytokines and eicosanoids in whole blood from adults (Orsmark-Pietras et al, 2013). We studied TAS2R expression and the effects of TAS2R agonists on the lipopolysaccharide (LPS)-induced cytokine release in human lung macrophages (LMs)

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