TRPC6-dependent Ca ²⁺ signaling mediates airway inflammation in response to oxidative stress via ERK pathway

Abstract

Ozone (O ₃) plays an extremely important role in airway inflammation by generating reactive oxygen species (ROS) including hydrogen peroxide, then promoting redox actions and causing oxidative stress. Evidences indicate that TRPC6 (canonical transient receptor potential channel 6) is a redox-regulated Ca ²⁺ permeable nonselective cation channel, but its role in the setting of oxidative stress-related airway inflammation remains unknown. Here, we found that both TRPC6 ^−/− mice and mice pretreated with SAR7334, a potent TRPC6 inhibitor, were protected from O ₃-induced airway inflammatory responses. In vitro, both knockdown of TRPC6 expression with shRNA and TRPC6 blockage markedly attenuated the release of cytokines IL-6 and IL-8 induced by O ₃ or H ₂O ₂ in 16HBE cells (human bronchial epithelial cell line). Treatment with O ₃ or H ₂O ₂ enhanced TRPC6 protein expression in vivo and vitro. We also observed that TRPC6-dependent increase of intracellular Ca ²⁺ concentration ([Ca ²⁺] _i) was triggered by H ₂O ₂, which consisted of the release from intracellular calcium store and the influx of extracellular Ca ²⁺ and could be further strengthened by 6-h O ₃ exposure in both 16HBE cells and HBEpiCs (primary human bronchial epithelial cells). Moreover, we confirmed that the activation of MAPK signals (ERK1/2, p38, JNK) was required for the inflammatory response induced by O ₃ or H ₂O ₂ while only the phosphorylation of ERK pathway was diminished in the TRPC6-knockdown situation. These results demonstrate that oxidative stress regulates TRPC6-mediated Ca ²⁺ cascade, which leads to the activation of ERK pathway and inflammation and could become a potential target to treat oxidative stress-associated airway inflammatory diseases.