Activation of TRPV4 triggers ATP release and mast cell dependent contraction of airway smooth muscle (ASM)

Abstract

Bronchoconstriction is a key feature of asthma but the disease drivers and signalling mechanisms involved are not fully understood. TRPV4 activation has been shown to trigger ATP release from various cell types (Baxter M.etal.Thorax:2014,0:1-10) and evoke bronchoconstriction via release of cysteinyl leukotrienes (cysLTs)(McAlexander M.etal.JPET,349:118-125). The aim of this study was to investigate the mechanism by which TRPV4 activation leads to cysLT release and ASM contraction. Initial data indicated that whilst a TRPV4 agonist triggered Ca2+ flux in cultured human ASM cells, it failed to cause contraction, unlike direct spasmogens such as ACh. However, contractile responses were observed when ASM cells were co-cultured with human lung mast cells (HLMCs) a known source of cysLTs. TRPV4 (mRNA) was not detected in HLMCs and so it was hypothesised that a secondary mediator was involved in the interaction between ASM and mast cells (i.e. ATP) and that contraction was caused via purinoceptor-induced cysLT release. Data revealed that TRPV4 agonists triggered ATP release from cultured ASM cells, ATP caused contraction of airway tissue and a non-selective P2X inhibitor, suramin, blocked ATP and TRPV4 induced contraction in an isolated tracheal preparation. RT-PCR and selective antagonists demonstrated that the contractile response to TRPV4 was dependent upon P2X4 receptor activation. These data suggest that TRPV4 activation causes release of ATP from ASM, triggering P2X4-dependent release of cysLTs from mast cells which results in airway contraction. This implicates TRPV4 as a key driver of bronchoconstriction and highlights it as a novel therapeutic target for airway disease.