Characterisation of TRPA1 activation on sensory nerves

Transient Receptor Potential (TRP) A1 channels are expressed on airway sensory nerves and are linked to the initiation of respiratory symptoms and disease pathogenesis. TRPA1 is believed to be an oxidative stress (OS) sensor and is triggered by a range of stimuli e.g. acrolein, PGE2 and bradykinin (BK), hydrogen peroxide (HP), diesel exhaust particles (DEP), hyper-osmolarity (HO) and low temperature (10°C). The aim was to investigate the mechanisms involved in TRPA1 activation on airway sensory nerves and study the role played by OS. We assessed activation of guinea-pig (gp), mice (wild-type versus TRPA1 KO) and human vagus nerve. We used a selective TRPA1 antagonist and three different antioxidants: N-acetyl-L-cysteine (NAC, an extracellular oxidative stress scavenger), Glutathione (GSH, an intracellular anti-oxidant) and VAS2780 (NADPH oxidase inhibitor). The results showed that the TRPA1 antagonist abolished responses to acrolein, HP, DEP, and 10°C and were lost in the tissue from TRPA1 KO mice, whereas responses to PGE2, BK and HO were partially suppressed (approx. 50%). NAC and GSH inhibited acrolein, HP and DEP activation. Whereas, PGE2, BK and HO induced activation appeared to be dependent on NADPH oxidase. Stimulation with 10°C was not sensitive to the anti-oxidants. We have shown a number of different modalities activate TRPA1 on sensory nerves and they, with the exception of 10°C, are mediated via an oxidative stress response. Interestingly, it appears that a number of stimuli are dependent on NADPH oxidase activity to activate TRPA1. This highlights the range of disease relevant mechanisms by which TRPA1 can be activated and implies that modulating the channel is a promising target for future drug discovery.