Transient Receptor Potential Channels contribute to agonist induced-Ca2+ influx in human airway smooth muscle – a therapeutic target for asthma?

Asthma is a common, chronic, inflammatory condition affecting 5.4 million people in the UK. Up to 10% of people with asthma have shown resistance to treatment and are liable for approximately 50% of asthma healthcare spend, highlighting the urgent unmet clinical need for novel asthma therapies. Bronchoconstriction caused by airway smooth muscle contraction is a major factor limiting airflow obstruction in asthma. Calcium signalling plays a key role in cellular responses of airway smooth muscle cells, sustained by the recruitment of extracellular Ca2+ from plasmalemmal calcium channels to replace [Ca2+]i stores. Expression and function of Ca2+carrying plasmalemmal channels highlight a potential therapeutic target to attenuate bronchoconstriction providing an effective treatment strategy for asthma. The family of transient receptor potential (TRP) channels are cation channels, most TRP channels are Ca2+ permeable. In addition, several TRP channels in human airway smooth muscle cells (HASMs) have not yet been studied, nor have comparative, quantitative expression profiles for TRP family members been conducted in HASMs. The rationale for this project was to define the relative expression of Ca2+-carrying TRP channels in human airways smooth muscle (ASM), both ex vivo and in vitro, for healthy controls and asthmatic subjects. This will be followed by a functional analysis of selected TRP channels expressed in human ASM cells to elucidate their potential role in calcium signalling and in asthma airway hyperresponsiveness and bronchoconstriction. TRPA1, TRPM4, TRPM7, TRPV2, TRPV4, PKD1, PKD2, MCOLN1 showed high expression in vitro. TRPA1 was investigated as gene of interest due to the in vitro expression in HASMs (in addition to evidence from animal models and SNP data which suggests a role in asthma). TRPA1 displayed marked protein expression detected by flow cytometry. In functional studies, selective TRPA1 agonism reliably contributed to Ca2+ influx, however high concentrations of TRPA1 agonists demonstrated cytotoxic effects. Collagen contraction assays were inconclusive as to the role of TRPA1 in ASM contraction.