Novel airway smooth muscle-mast cell interactions and a role for the TRPV4-ATP axis in non-atopic asthma.

Sara J Bonvini,Michael A Wortley,Eric Dubuis,John J Adcock,Mark A Birrell,Pauline Flajolet,Maria G Belvisi,Peter Bradding

doi:10.1183/13993003.01458-2019

Abstract

Mast cell–airway smooth muscle (ASM) interactions play a major role in the immunoglobulin (Ig)E- dependent bronchoconstriction seen in asthma but less is known about IgE-independent mechanisms of mast cell activation. Transient receptor potential cation channel, subfamily V, member 4 (TRPV4) activation causes contraction of human ASM via the release of cysteinyl leukotrienes (cysLTs) but the mechanism is unknown. The objective of the present study was to investigate a role for IgE-independent, mast cell–ASM interaction in TRPV4-induced bronchospasm.Bronchoconstriction was measured in anaesthetised guinea pigs and contraction of human and guinea-pig airway tissue assessed using isometric tension measurements. Increases in intracellular [Ca2+] were imaged using the Ca2+-sensitive dye FURA2, and time-lapse ptychography was utilised as a surrogate for contraction of ASM cells.The TRPV4 agonist GSK1016790A caused contraction in vivo in the guinea pig, and in human and guinea-pig tracheal tissue, which was inhibited by the TRPV4 antagonist GSK2193874. GSK1016790A increased [Ca2+]i and released ATP in human ASM cells without causing contraction. TRPV4 and ATP evoked contraction in isolated tracheal tissue but co-culture experiments indicated a requirement for human lung mast cells. Expression profiling and pharmacological studies demonstrated that mast cell activation was dependent upon ATP activating the P2X4 receptor. Trypsin was shown to evoke contraction of tracheal tissue via activation of PAR-2-TRPV4-ATP-cysLT axis indicating the potential disease relevance of this signalling pathway.TRPV4 activation increases [Ca2+]i and releases ATP from ASM cells triggering P2X4-dependent release of cysLTs from mast cells resulting in ASM contraction. This study delineates a novel mast cell–ASM interaction and TRPV4 as a driver of IgE-independent mast cell-dependent bronchospasm.

Highlights

Asthma is a chronic airway inflammatory disease characterised by airflow obstruction and symptoms, such as chest tightness, wheezing and cough [1, 2]
Contraction-specific as neither GSK2193874 (10 μM), montelukast (10 μM) nor 5BDBD (50 μM) had any effect on contraction induced by the common contractile stimuli histamine and ACh. In this series of experiments, we have demonstrated that activation of TRPV4 on human airway smooth muscle (ASM) induces the release of ATP which activates P2X4 receptors on human lung mast cells (HLMCs) in close proximity to the ASM, in turn inducing the release of cysteinyl leukotrienes (cysLTs) which causes cysLT1-dependent contraction of ASM
HLMC–ASM interactions are thought to play a fundamental role in the pathogenesis of atopic asthma due to the IgE-dependent release of bronchoconstrictor mediators and cytokines which contribute to the earlyand late-phase responses following allergen exposure

Summary

Introduction

Asthma is a chronic airway inflammatory disease characterised by airflow obstruction and symptoms, such as chest tightness, wheezing and cough [1, 2]. Most asthmatics with early onset disease are atopic and demonstrate an allergic inflammatory response. This is referred to as T2 asthma and is driven by CD4+ T-helper (Th) 2 lymphocytes, mast cells and possibly innate lymphoid cells (ILC2) which secrete interleukin (IL)-4, IL-5 and IL-13 leading to eosinophilic inflammation and production of immunoglobulin (Ig)E from B cells [3, 4]. Atopic asthma and the T2 inflammatory response are often suppressed in patients treated with inhaled corticosteroids (ICS) subgroups of patients with both atopic and non-atopic asthma have persistent symptoms despite high doses of ICS [5] and so novel approaches to treatment are required

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